Resin composition and molded article

Abstract

Provided are: a resin composition that can be thinly molded and that is superior in terms of light blocking properties; and a molded body employing the resin composition. The present invention provides a resin composition: that contains carbon black and a dispersant at, in total, a proportion greater than 2.0 parts by mass and equal to or less than 10.0 parts by mass with respect to 100 parts by mass of a polyacetal resin; and in which the proportion of the carbon black with respect to the total quantity of the carbon black and the dispersant is greater than 60 mass% and less than 100 mass%, wherein the melt volume rate of the resin composition measured under the conditions of 190°C and a load of 2.16 kg-weight is greater than 50 cm3 / 10 min and less than 100 cm3 / 10 min.

Description

[Technical Field]

[0001] This invention relates to resin compositions and molded articles, and more particularly to resin compositions suitable for use in digital device components. [Background technology]

[0002] Polyacetal resin, an engineering plastic, possesses excellent mechanical properties, sliding characteristics, friction and wear characteristics, heat resistance, and moldability. For this reason, resin compositions containing polyacetal resin are widely used in various mechanical and electrical components for automobiles, office automation equipment, and other applications.

[0003] As an example of a resin composition using polyacetal resin, Patent Document 1 discloses a polyacetal resin composition in which carbon black (B) and a dispersant (C) are blended in a ratio greater than 4 parts by mass and less than or equal to 10 parts by mass per 100 parts by mass of polyacetal resin (A), and the proportion of carbon black in the total blended amount of carbon black (B) and the dispersant (C) is greater than 60% by mass and less than 100% by mass. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-014304 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, in recent years, various mechanical and electrical parts made of polyacetal resin have been required to be lightweight and have high light-shielding properties, depending on the application. To reduce weight, it is necessary to make the molded body thinner, but the thinner the molded body, the worse the light-shielding properties tend to be. Therefore, in order to ensure light-shielding properties in thin-walled molded bodies, it is conceivable to blend a carbon black dispersant together with carbon black. However, when the above additive is blended to ensure light-shielding properties, the fluidity is reduced, and thin-walled molding may become difficult. The present invention aims to solve the aforementioned problems and to provide a resin composition that allows for thin-wall molding and has excellent light-shielding properties, and a molded article using the resin composition. [Means for solving the problem]

[0006] Based on the above-mentioned problems, the inventors conducted investigations and found that the above-mentioned problems can be solved by adjusting the MVR of the resin composition itself while adjusting the amounts of carbon black and dispersant used. Specifically, the above problem was solved by the following means. <1> Per 100 parts by mass of polyacetal resin, It contains carbon black and a dispersant in a total proportion of more than 2.0 parts by mass and 10.0 parts by mass or less. A resin composition in which the proportion of carbon black in the total amount of carbon black and dispersant is greater than 60% by mass and less than 100% by mass, The melt volume rate of the resin composition, measured at 190°C and under a load of 2.16 kgf, was 50 cm³. 3 / 10 minutes or more 100cm 3 A resin composition with a time of less than 10 minutes. <2> The melt volume rate of the aforementioned resin composition, measured at 190°C and under a load of 2.16 kgf, was 60 cm³. 3 / 10 minutes or more 100cm 3 / Less than 10 minutes <1> The resin composition described above. <3> The carbon black content is greater than 1.5 parts by mass and less than or equal to 9 parts by mass per 100 parts by mass of polyacetal resin. <1> or <2> The resin composition described above. <4> The carbon black content is greater than 1.5 parts by mass and less than or equal to 6 parts by mass per 100 parts by mass of polyacetal resin. <1> or <2> The resin composition described above. <5> The carbon black content is greater than 1.5 parts by mass and less than or equal to 4 parts by mass per 100 parts by mass of polyacetal resin. <1> or <2> The resin composition described above. <6> The dispersant comprises at least one selected from the group consisting of polyolefin wax, fatty acid, fatty acid amide, polyalkylene glycol, and silicone. <1> ~ <5> A resin composition as described in any one of the following. <7> The dispersant comprises at least two selected from the group consisting of polyolefin wax, fatty acids, fatty acid amides, polyalkylene glycols, and silicones. <1> ~ <5> A resin composition as described in any one of the following. <8> The dispersant comprises a fatty acid amide. <6> or <7> The resin composition described above. <9> The dispersant contains silicone. <6> ~ <8> A resin composition as described in any one of the following. <10> The dispersant comprises an aliphatic amide and a silicone. <7> The resin composition described above. <11> The amount of fatty acid amide in the dispersant is 40% by mass or less relative to the total amount of dispersant. <1> ~ <10> A resin composition as described in any one of the following. <12> The melt volume rate of the aforementioned polyacetal resin, measured at 190°C and under a load of 2.16 kgf, was 45 cm³. 3 / 10 minutes or more 100cm 3 / Less than 10 minutes <1> ~ <11> A resin composition as described in any one of the following. <13> This is for the aperture spring of a digital camera. <1> ~ <12> A resin composition as described in any one of the following. <14>The resin composition according to any one of <1> to <13>, wherein the total light transmittance measured according to JIS-K-7136 when the resin composition is molded to a thickness of 0.05 mm is 2% or less. <15>The resin composition according to any one of <1> to <13>, wherein the total light transmittance measured according to JIS-K-7136 when the resin composition is molded to a thickness of 0.05 mm is 1% or less. <16>A molded body formed from the resin composition according to any one of <1> to <15>. <17>The molded body according to <16>, wherein the molded body is a digital device part. <18>The molded body according to <16>, wherein the molded body is a diaphragm spring of a digital camera. <19>The molded body according to any one of <16> to <18>, wherein the thickness of the thinnest part of the molded body is 0.1 mm or less. <20>The molded body according to any one of <16> to <18>, wherein the thickness of the thinnest part of the molded body is 0.075 mm or less.

Advantages of the Invention

[0007] According to the present invention, it has become possible to provide a resin composition that enables thin-wall molding and has excellent light-shielding properties, and a molded body using the resin composition.

Modes for Carrying Out the Invention

[0008] Hereinafter, modes for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. Note that the following present embodiment is an exemplification for explaining the present invention, and the present invention is not limited to only the present embodiment. In this specification, "~" is used to mean including the numerical values described before and after it as lower and upper limits. In this specification, various physical property values and characteristic values are those at 23°C unless otherwise specified. When the standards shown in this specification differ depending on the year in terms of measurement methods and the like, they are based on the standards at the time of filing unless otherwise specified.

[0009] The resin composition of this embodiment contains carbon black and a dispersant in a total amount of more than 2.0 parts by mass and 10.0 parts by mass or less per 100 parts by mass of polyacetal resin, wherein the proportion of carbon black in the total amount of carbon black and dispersant is more than 60% by mass and less than 100% by mass, and the melt volume rate (hereinafter sometimes referred to as "MVR") of the resin composition measured at 190°C and a load of 2.16 kgf is 50 cm³. 3 / 10 minutes or more 100cm 3 / It is characterized by being less than 10 minutes long. This configuration makes it possible to provide a resin composition that allows for thin-wall molding and has excellent light-shielding properties.

[0010] <Polyacetal resin> The resin composition of this embodiment contains a polyacetal resin. By including the polyacetal resin, a molded article with excellent sliding properties can be obtained. The polyacetal resin used in this embodiment is a copolymer containing an oxymethylene group and an oxyalkylene group having two or more carbon atoms as constituent units.

[0011] Examples of oxyalkylene groups with two or more carbon atoms include oxyethylene groups, oxypropylene groups, and oxybutylene groups. Among these, the oxyethylene group is preferred because it more effectively suppresses the deterioration of the characteristics of the polyacetal resin.

[0012] In the above polyacetal resin, the proportion of the oxyalkylene group having 2 or more carbon atoms is preferably 0.3 to 6.0 mol% with respect to 100 mol% of the oxymethylene group. By setting it to 0.3 mol% or more, the polyacetal resin has more sufficient thermal stability. Further, by setting it to 6.0 mol% or less, the crystallinity of the polyacetal resin is further improved, and it is possible to sufficiently suppress a significant decrease in the strength of the resin composition or a decrease in creep fatigue characteristics. When the above proportion is within the range of 0.3 to 6.0 mol%, compared with the case where it is outside the above range, the thermal stability of the polyacetal resin is further improved, and the resin composition can produce a molded body having more excellent impact resistance. The above proportion is more preferably 0.5 to 5.5 mol%, further preferably 0.7 to 5.0 mol%, and still more preferably 1.0 to 4.5 mol%.

[0013] In order to produce the above polyacetal resin, trioxane is usually used as the main raw material. Further, in order to introduce an oxyalkylene group having 2 or more carbon atoms into the polyacetal resin, for example, a cyclic formal or a cyclic ether can be used. Specific examples of the cyclic formal include, for example, 1,3-dioxolane, 1,3-dioxane, 1,3-dioxepane, 1,3-dioxocane, 1,3,5-trioxepane, 1,3,6-trioxocane, etc., and specific examples of the cyclic ether include, for example, ethylene oxide, propylene oxide, and butylene oxide. In order to introduce an oxyethylene group into the polyacetal resin, for example, 1,3-dioxolane can be used, in order to introduce an oxypropylene group, 1,3-dioxane can be used, and in order to introduce an oxybutylene group, 1,3-dioxepane can be used.

[0014] The polyacetal resin used in the present embodiment preferably has a high MVR. Specifically, the MVR measured under the conditions of 190 ° C. and a load of 2.^{16} kg for the polyacetal resin used in the present embodiment is preferably more than 45 cm 3 / 10 minutes, more preferably 50 cm 3 / 10 minutes or more, and still more preferably 60 cm 3 / More preferably 10 minutes or more, 65cm 3 / More preferably 10 minutes or more, 70cm 3 It is even more preferable that the time is 10 minutes or more. Setting it above the lower limit tends to increase fluidity. The MVR of the polyacetal resin is 100 cm 3 / Preferably less than 10 minutes, 90cm 3 It is more preferable that it be 10 minutes or less, and 80cm 3 / More preferably it is 10 minutes or less, and 76cm 3 It is even more preferable that the time is 10 minutes or less. By keeping it below the upper limit, the thin-walled shape tends to be maintained more effectively. The MVR is measured according to the example described below.

[0015] The polyacetal resin content in the resin composition of this embodiment is preferably 90% by mass or more, more preferably 93% by mass or more, and even more preferably 95% by mass or more. Setting it above the lower limit tends to more effectively maintain the thin-walled shape. Furthermore, the polyacetal resin content is preferably 99% by mass or less in the resin composition. Setting it below the upper limit tends to achieve better light-shielding properties in thin-walled designs. The resin composition of this embodiment may contain only one type of polyacetal resin, or it may contain two or more types. When it contains two or more types, it is preferable that the total amount is within the above range.

[0016] <Carbon Black> The resin composition of this embodiment contains carbon black. By including carbon black, a molded article with excellent light-shielding properties can be obtained. Examples of carbon blacks that can be used in this embodiment include furnace black, acetylene black, channel black, and lamp black.

[0017] The average particle size of the carbon black is not particularly limited, but is preferably 5 nm or larger, more preferably 10 nm or larger, and even more preferably 15 nm or larger. Setting it above the lower limit tends to further improve the dispersibility of the carbon black. Furthermore, the average particle size of the carbon black is preferably 50 nm or smaller, more preferably 40 nm or smaller, even more preferably 30 nm or smaller, and even more preferably 25 nm or smaller. Setting it below the upper limit tends to further improve the light-shielding properties. Here, the average particle size refers to the average value of the particle sizes of multiple carbon black particles observed using a scanning electron microscope.

[0018] In the resin composition of this embodiment, the carbon black content is preferably more than 1.5 parts by mass per 100 parts by mass of polyacetal resin. Setting it above the lower limit tends to further improve light shielding properties. Furthermore, the carbon black content is preferably 9 parts by mass or less, more preferably 6 parts by mass or less, even more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less per 100 parts by mass of polyacetal resin. Setting it below the upper limit tends to more effectively maintain the fluidity necessary for thin-wall molding. The resin composition of this embodiment may contain only one type of carbon black, or it may contain two or more types. When it contains two or more types, it is preferable that the total amount is within the above range.

[0019] <Dispersant> The resin composition of this embodiment includes a dispersant. By including a dispersant, the carbon black is dispersed more effectively, resulting in a molded article with superior light-shielding properties. The dispersant is not particularly limited as long as it can disperse carbon black in the polyacetal resin, but it preferably contains at least one selected from the group consisting of polyolefin wax, fatty acids, fatty acid amides, polyalkylene glycols, and silicones. One embodiment of the dispersant is that it contains a fatty acid amide. Another embodiment of the dispersant is that it contains silicone. Another embodiment of the dispersant is that it comprises an aliphatic amide and a silicone. By using the above-mentioned dispersant, the sliding properties of the molded article can be further improved. Furthermore, in this embodiment, a combination of at least two (preferably two to four, more preferably three) selected from the group consisting of polyolefin wax, fatty acids, fatty acid amides, polyalkylene glycol, and silicone is preferred. By using a combination of two or more, a molded article with even better sliding properties tends to be obtained. In the resin composition of this embodiment, it is preferable that the dispersant contains at least two selected from the group consisting of polyolefin wax, fatty acids, fatty acid amides, polyalkylene glycol, and silicone, and it is even more preferable to use a mixture of polyolefin wax, fatty acid amide, and silicone.

[0020] Examples of polyolefin waxes include polyethylene wax and polypropylene wax.

[0021] Examples of fatty acids include higher fatty acids such as stearic acid, oleic acid, octanoic acid, lauric acid, ricinoleic acid, and behenic acid.

[0022] Fatty acid amides are compounds obtained by the dehydration reaction of higher fatty acids and / or polybasic acids with diamines. Here, preferred higher fatty acids are saturated aliphatic monocarboxylic acids having 16 or more carbon atoms, for example, 16 to 30 carbon atoms, specifically palmitic acid, stearic acid, behenic acid, montanic acid, etc. Polybasic acids include dibasic or higher carboxylic acids, such as aliphatic dicarboxylic acids such as malonic acid, succinic acid, adipic acid, sebacic acid, pimelic acid, and azelaic acid, as well as aromatic dicarboxylic acids such as phthalic acid and terephthalic acid, and alicyclic dicarboxylic acids such as cyclohexyldicarboxylic acid and cyclohexylsuccinic acid. Examples of diamines include ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, hexamethylenediamine, metaxylylenediamine, tolylenediamine, paraxylylenediamine, phenylenediamine, and isophoronediamine. Specific examples of fatty acid amides include stearylamide, behenylamide, montanilamide, methylenebisstearylamide, and ethylenebisstearylamide.

[0023] Examples of polyalkylene glycols include polymethylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, polypentylene glycol, polyhexylene glycol, polyheptylene glycol, polyoctylene glycol, polynonylene glycol, and polydecylene glycol.

[0024] Examples of silicones include silicone oils having properties of oil, rubber, and resin, silicone rubber, silicone resins, and silicone greases with added metal soaps. Specific examples of silicones include polydimethylsiloxane, organosiloxanes in which some of the methyl groups of polydimethylsiloxane are replaced with phenyl groups, organosiloxanes in which some of the methyl groups of polydimethylsiloxane are replaced with hydrogen or alkyl groups having 2 or more carbon atoms, organosiloxanes in which some of the methyl groups of polydimethylsiloxane are replaced with halogenated phenyl groups, organosiloxanes in which some of the methyl groups of polydimethylsiloxane are replaced with fluoroester groups, epoxy-modified organosiloxanes, amino-modified organosiloxanes, alcohol-modified organosiloxanes, alkylaralkyl organosiloxanes, and polyether-modified organosiloxanes.

[0025] The silicone preferably has a kinematic viscosity of 500,000 cSt or more at 25°C. By using a silicone with a kinematic viscosity of 500,000 cSt or more at 25°C, the appearance of the resulting molded article will be better and higher sliding properties can be maintained. There is no particular upper limit to the kinematic viscosity, but for example, it is preferably 2,000,000 cSt or less.

[0026] The dispersant content in the resin composition of this embodiment is preferably 0.5 parts by mass or more, more preferably 0.7 parts by mass or more, and even more preferably 0.8 parts by mass or more, per 100 parts by mass of polyacetal resin. Setting it above the lower limit tends to further improve the dispersibility of carbon black. Furthermore, the dispersant content is preferably 7.0 parts by mass or less, more preferably 6.0 parts by mass or less, even more preferably 4.0 parts by mass or less, and even more preferably 2.0 parts by mass or less, per 100 parts by mass of polyacetal resin. Setting it below the upper limit tends to effectively maintain the inherent strength of the polyacetal resin. The resin composition of this embodiment may contain only one type of dispersant, or it may contain two or more types. When it contains two or more types, it is preferable that the total amount is within the above range.

[0027] The total content of carbon black and dispersant in the resin composition of this embodiment is more than 2.0 parts by mass, preferably 2.5 parts by mass or more, and more preferably 2.8 parts by mass or more, per 100 parts by mass of polyacetal resin. Setting it above the lower limit tends to further improve light shielding properties. Furthermore, the total content of carbon black and dispersant is 10.0 parts by mass or less, preferably 8.0 parts by mass or less, more preferably 6.0 parts by mass or less, even more preferably 5.0 parts by mass or less, and even more preferably 4.0 parts by mass or less, per 100 parts by mass of polyacetal resin. Setting it below the upper limit allows the inherent strength of the polyacetal resin to be exhibited more effectively.

[0028] Furthermore, in the resin composition of this embodiment, the proportion of carbon black in the total amount of carbon black and dispersant is more than 60% by mass, preferably 61% by mass or more, and more preferably 62% by mass or more. Setting it above the lower limit tends to further improve light shielding properties. Also, the proportion of carbon black in the total amount of carbon black and dispersant is less than 100% by mass, preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less. Setting it below the upper limit tends to more effectively maintain the thin-walled shape while ensuring light shielding properties.

[0029] <Other ingredients> The resin composition of this embodiment may contain other components besides those listed above. Specifically, other components include inorganic fillers, heat stabilizers, antioxidants, weather stabilizers, light stabilizers, ultraviolet absorbers, crystal nucleating agents, antistatic agents, antibacterial agents, and the like. These can be used individually or in combination of two or more. Furthermore, the resin composition in this embodiment may be configured to be substantially free of inorganic fillers. "Substantially free" means that the inorganic filler content in the resin composition in this embodiment is less than 1% by mass of the resin composition. The resin composition of this embodiment is formulated so that the total amount of polyacetal resin, carbon black, dispersant, and other components added as needed is 100% by mass. Preferably, the total amount of polyacetal resin, carbon black, and dispersant accounts for 95 to 100% by mass of the resin composition, and more preferably 99 to 100% by mass.

[0030] <Method for producing resin compositions> The method for producing the resin composition of this embodiment is not particularly limited and can be prepared by various conventional methods for preparing resin compositions. For example, (1) a method of mixing all the components constituting the resin composition, supplying it to an extruder and melt-kneading it to obtain a pelletized composition; (2) a method of supplying a portion of the components constituting the resin composition from the main feed port of an extruder and the remaining components from the side feed port and melt-kneading them to obtain a pelletized composition; (3) a method of preparing pellets with different compositions by extrusion or the like, and then mixing the pellets to adjust them to a predetermined composition; (4) a method of mixing a predetermined amount of blending components with polyacetal resin pellets or pulverized material, or coating the surface of polyacetal resin pellets or pulverized material with a predetermined amount of blending components to obtain a predetermined resin composition.

[0031] <Characteristics and physical properties of resin compositions> The resin composition of this embodiment has a high MVR. Specifically, the MVR of the resin composition measured at 190°C and a load of 2.16 kgf is 50 cm². 3 / Over 10 minutes, 55cm 3 / Preferably 10 minutes or more, 60cm 3 More preferably more than 10 minutes, 61cm 3 / More preferably 10 minutes or more, 62cm 3It is even more preferable that the interval be 10 minutes or longer. Setting it above the lower limit tends to further improve fluidity. The MVR is 100 cm 3 / Less than 10 minutes, 90cm 3 Preferably 10 minutes or less, 80cm 3 It is more preferable that the time is 10 minutes or less. By keeping it below the upper limit, the thin-walled shape tends to be maintained more effectively. The MVR is measured according to the example described below.

[0032] The resin composition of this embodiment preferably has excellent light-shielding properties. Specifically, the total light transmittance measured according to JIS-K-7136 when the resin composition is molded to a thickness of 0.05 mm is preferably 2% or less, more preferably 1.5% or less, and even more preferably 1% or less. The lower limit of the total light transmittance is preferably 0%. The total light transmittance is measured according to the description in the examples below.

[0033] <Applications of resin compositions and molded articles> This embodiment also includes molded articles formed from the resin composition of this embodiment. The molded articles in this embodiment have excellent light-shielding properties and can be thin-walled. The thickness of the thinnest part of the molded article in this embodiment can be 0.1 mm or less, and furthermore, it can be 0.075 mm or less. The lower limit of the thickness of the thinnest part is practically 0.01 mm or more, and may be 0.02 mm or more. The resin composition of this embodiment can be molded by known molding methods such as injection molding, extrusion molding, compression molding, blow molding, and vacuum molding.

[0034] The resin composition and molded articles of this embodiment can be suitably used in automotive parts, electrical and electronic components, precision machine parts, building materials and piping parts, daily necessities, cosmetic parts, medical device parts, etc., but are preferably used in digital device parts, and particularly preferably in aperture springs for digital cameras. [Examples]

[0035] The present invention will be described in more detail below with reference to examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate, as long as they do not depart 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 other reasons, measurements can be taken using other instruments with equivalent performance.

[0036] 1.Raw materials Polyacetal resin (A1): An oxymethylene copolymer obtained by copolymerizing trioxane and 1,3-dioxolane such that the proportion of oxyethylene groups is 1.4 mol% relative to 100 mol% of oxymethylene groups, with an MVR (190°C, 2.16 kgf) of 75 cm³. 3 Oxymethylene copolymer / 10 minutes Polyacetal resin (A2): An oxymethylene copolymer obtained by copolymerizing trioxane and 1,3-dioxolane such that the proportion of oxyethylene groups is 1.4 mol% relative to 100 mol% of oxymethylene groups, with an MVR (190°C, 2.16 kgf) of 45 cm³. 3 Oxymethylene copolymer / 10 minutes

[0037] Carbon Black (B): Furnace Black, product name "Raven PFEB", average particle size 21nm, manufactured by Colombian Carbon.

[0038] Dispersant (C) Ethylene bisstearylamide (C1): Product name: "EB-FF", manufactured by Kao Corporation. Polyethylene wax (C2): Product name: "High Wax 720P", manufactured by Mitsui Chemicals, Inc. Silicone (C3): Kinematic viscosity at 25°C: 1 million cSt of silicone

[0039] 2. Examples 1-4, Comparative Examples 1-4 <Compound> Polyacetal resin (A), carbon black (B), and dispersant (C) were uniformly mixed using a Kawada Manufacturing Co., Ltd. Super Mixer in the proportions shown in Table 1. Then, the mixture was melt-kneaded using a twin-screw extruder (Ikegai Iron Works Co., Ltd. PCM-29, screw diameter 29 mm) under conditions of screw rotation speed of 120 rpm and cylinder setting temperature of 190°C, extruded into strands, and cut with a pelletizer to produce resin compositions (pellets).

[0040] <MVR of resins and resin compositions> Polyacetal resin and the MVR (unit: cm) of the resin composition (pellets) obtained above. 3 The MVR (Mass Volume Rating) was measured in accordance with ISO 1133 under conditions of 190°C and a load of 2.16 kgf. The MVR results for the resin composition (pellets) are shown in Table 1.

[0041] <Light blocking property (total light transmittance)> The resin composition (pellets) obtained above was dried at 80°C for 3 hours, and then pressed using a press machine to prepare a test sheet measuring 0.05 mm × 20 mm × 20 mm in thickness. The total light transmittance (unit: %) of the obtained test sheet was measured using a haze meter in accordance with JIS-K-7136. The results are shown in Table 1. The press used was the "Mini Test Press," manufactured by Toyo Seiki Co., Ltd. The haze meter used was the NDH4000, manufactured by Nippon Denshoku Co., Ltd.

[0042] <Liquidity> After drying the resin composition pellets at 80°C for 3 hours, they were injection molded using an injection molding machine (Sumitomo Heavy Industries, Ltd. "SE30DUZ") under conditions of cylinder temperature 195°C and mold temperature 80°C to form a flat plate measuring 145 mm x 13 mm x 0.3 mm thick, and the fluidity during this process was confirmed. A: It had excellent fluidity. B: It was at a practical level, but its liquidity was inferior to A. C: Liquidity was poor (not at a practical level).

[0043] <Appearance after heat treatment> After drying the resin composition pellets at 80°C for 3 hours, injection molding was performed using an injection molding machine (Shibaura Machine Co., Ltd. "EC100SX") under conditions of cylinder temperature 195°C and mold temperature 90°C to form a 100mm x 100mm x 2.0mm thick flat plate. The resulting flat plate was heat-treated at 80°C for 100 hours, and the appearance of the flat plate after heat treatment was observed. A: No foreign matter was found on the surface of the flat plate. B: A small amount of foreign matter was observed on the surface of the flat plate. C: A large amount of foreign matter was observed on the surface of the flat plate.

[0044] <Sliding properties> Cylindrical thrust test specimens were fabricated by injection molding at a cylinder temperature of 200°C and a mold temperature of 80°C. Measurements were taken using an Orientec thrust-type friction and wear testing machine at a temperature of 23°C and 50% humidity, with a surface pressure of 0.25 MPa and a linear velocity of 0.1 m / sec.

[0045] [Table 1]

[0046] In the table above, "(C) total amount" means the sum of (C1) to (C3) (unit: parts by mass). "(B) + (C) amount" means the sum of (B) and (C1) to (C3), that is, the sum of carbon black and dispersant (unit: parts by mass). Therefore, "{(B) / [(B)+(C)]}×100" represents the proportion of carbon black in the total amount of carbon black and dispersant (unit: mass%). As is clear from the above results, the molded articles obtained from the resin compositions of the present invention (Examples 1-4) were thin but exhibited excellent light-shielding properties. Furthermore, the resin compositions of the present invention also exhibited excellent fluidity and excellent moldability for thin-walled molded articles. On the other hand, when the carbon black and dispersant content did not meet the scope of the present invention (Comparative Example 1), the light-shielding properties were poor. Also, when the MVR of the resin composition did not meet the scope of the present invention, the fluidity was somewhat poor, and it was not fluid enough for use in thin-walled molded articles such as aperture springs in digital cameras (Comparative Example 2). Furthermore, when (B) / (B)+(C)×100 was 60% by mass or less, the total light transmittance was high (Comparative Example 3). When the carbon black content was high, the fluidity decreased (Comparative Example 4).

Claims

1. Per 100 parts by mass of polyacetal resin, It contains carbon black and a dispersant in a total proportion of more than 2.0 parts by mass and 10.0 parts by mass or less. A resin composition in which the proportion of carbon black in the total amount of carbon black and dispersant is greater than 60% by mass and less than 100% by mass, The melt volume rate of the resin composition, measured at 190°C and under a load of 2.16 kgf, was 50 cm³. ３ / 10 minutes or more 100cm ３ A resin composition with a time of less than 10 minutes.

2. The melt volume rate of the aforementioned resin composition, measured at 190°C and under a load of 2.16 kgf, was 60 cm³. ３ / 10 minutes or more 100cm ３ The resin composition according to claim 1, wherein the time is less than 10 minutes.

3. The resin composition according to claim 1 or 2, wherein the carbon black content is more than 1.5 parts by mass and 9 parts by mass or less per 100 parts by mass of polyacetal resin.

4. The resin composition according to claim 1 or 2, wherein the carbon black content is more than 1.5 parts by mass and 6 parts by mass or less per 100 parts by mass of polyacetal resin.

5. The resin composition according to claim 1 or 2, wherein the carbon black content is greater than 1.5 parts by mass and less than or equal to 4 parts by mass per 100 parts by mass of polyacetal resin.

6. The resin composition according to any one of claims 1 to 5, wherein the dispersant comprises at least one selected from the group consisting of polyolefin wax, fatty acid, fatty acid amide, polyalkylene glycol, and silicone.

7. The resin composition according to any one of claims 1 to 5, wherein the dispersant comprises at least two selected from the group consisting of polyolefin wax, fatty acids, fatty acid amides, polyalkylene glycols, and silicones.

8. The resin composition according to claim 6 or 7, wherein the dispersant comprises a fatty acid amide.

9. The resin composition according to any one of claims 6 to 8, wherein the dispersant comprises silicone.

10. The resin composition according to claim 7, wherein the dispersant comprises a fatty acid amide and a silicone.

11. The resin composition according to any one of claims 1 to 10, wherein the amount of fatty acid amide in the dispersant is 40% by mass or less relative to the total amount of dispersant.

12. The melt volume rate of the aforementioned polyacetal resin, measured at 190°C and under a load of 2.16 kgf, was 45 cm³. ３ / 10 minutes or more 100cm ３ A resin composition according to any one of claims 1 to 11, wherein the time is less than 10 minutes.

13. A resin composition according to any one of claims 1 to 12, for use in aperture springs of digital cameras.

14. The resin composition according to any one of claims 1 to 13, wherein the total light transmittance measured according to JIS-K-7136 when the resin composition is molded to a thickness of 0.05 mm is 2% or less.

15. The resin composition according to any one of claims 1 to 13, wherein the total light transmittance measured according to JIS-K-7136 when the resin composition is molded to a thickness of 0.05 mm is 1% or less.

16. A molded article formed from the resin composition according to any one of claims 1 to 15.

17. The molded body according to claim 16, wherein the molded body is a digital device component.

18. The molded body according to claim 16, wherein the molded body is an aperture spring for a digital camera.

19. The molded body according to any one of claims 16 to 18, wherein the thickness of the thinnest part of the molded body is 0.1 mm or less.

20. The molded body according to any one of claims 16 to 18, wherein the thickness of the thinnest part of the molded body is 0.075 mm or less.

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