Resin composition

Abstract

The present invention aims to provide a resin composition which is excellent in coloring property and mold release property during injection molding. According to the present invention, there is provided a resin composition which contains a copolymer (A) having styrene-based monomer units and cyano-based vinyl monomer units, and a mold release agent (B) selected from at least one kind of fatty alcohol having 16 or more carbon atoms, fatty acid, the content of the mold release agent (B) being 200 to 800 ppm, and the transmittance being 40% or more at an optical path length of 115 mm and a wavelength of 450 nm.

Description

Technical Field

[0001] This invention relates to a resin composition of a copolymer containing styrene-based monomer units and cyanide vinyl-based monomer units. Background Technology

[0002] Copolymers primarily composed of styrene-based and cyanovinyl-based monomer units are widely used due to their excellent transparency, chemical resistance, rigidity, and moldability. Furthermore, they are easily colored with dyes and are used in cosmetic containers and cold water containers (Patent Documents 1-4).

[0003] [Existing Technical Documents]

[0004] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 04-503083

[0006] [Patent Document 2] Japanese Patent Application Publication No. 08-301913

[0007] [Patent Document 3] Japanese Patent Application Publication No. 10-139965

[0008] [Patent Document 4] Japanese Patent Application Publication No. 2002-114822 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] The purpose of this invention is to provide a resin composition with excellent colorability and release properties during injection molding.

[0011] Solution for solving the problem

[0012] (1) A resin composition comprising a copolymer (A) having styrene monomer units and cyanide vinyl monomer units, and a release agent (B) selected from at least one type of aliphatic alcohols and fatty acids having 16 or more carbon atoms, wherein the content of the release agent (B) is 200 to 800 ppm and the transmittance is 40% or more at an optical path length of 115 mm and a wavelength of 450 nm.

[0013] (2) The resin composition of (1), wherein the content of the styrene monomer unit in 100% by mass of the copolymer (A) is 79-85% by mass, and the content of the vinyl cyanide monomer unit is 15-21% by mass.

[0014] (3) The resin composition described in (1) or (2) further contains an antioxidant (C).

[0015] The resin composition described in any one of (4)(1) to (3) is colored by dye.

[0016] Injection-molded articles of the resin compositions described in any one of (5)(1) to (4).

[0017] The effects of the invention

[0018] The resin composition of this invention exhibits very little discoloration due to degradation caused by high-temperature treatment during molding. Therefore, due to its excellent colorability, molded articles with clear hues can be obtained by coloring with dyes. Furthermore, in applications such as cosmetic containers and water coolers, the molded articles are mostly manufactured by injection molding, yet the release properties during injection molding are also excellent. Consequently, cracks are less likely to occur during demolding, enabling stable continuous molding. Detailed Implementation

[0019] <Terminology Explanation>

[0020] In this specification, references such as "A~B" refer to terms above A and below B.

[0021] The embodiments of the present invention will be described in detail below. The embodiments shown below can be combined with each other.

[0022] The resin composition of the present invention contains a copolymer (A) having styrene monomer units and cyanide vinyl monomer units, and a release agent (B) selected from at least one type of aliphatic alcohols and fatty acids having 16 or more carbon atoms.

[0023] The copolymer (A) is a copolymer having styrene monomer units and cyanide vinyl monomer units, such as a styrene-acrylonitrile copolymer.

[0024] The styrene monomer units include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, α-methylstyrene, α-methyl-p-methylstyrene, etc. Styrene is preferred. The styrene monomer units can be used alone or in combination of two or more. The copolymer (A) preferably contains 79-85% by mass of styrene monomer units per 100% by mass, more preferably 80-82% by mass. Specifically, the content of the styrene monomer units is, for example, 79, 80, 81, 82, 83, 84, or 85% by mass, or can be within any two of the exemplified values. If the content of the styrene monomer units is within this range, the resulting resin composition exhibits excellent chemical resistance and color balance. The styrene monomer unit values ​​are measured using 13C-NMR.

[0025] The cyanide vinyl monomer units include acrylonitrile, methacrylonitrile, ethyl acrylonitrile, fumaronitrile, etc. Acrylonitrile is preferred. The cyanide vinyl monomer units can be used alone or in combination of two or more.

[0026] Other copolymerizable monomers for copolymer (A) may include (meth)acrylate monomers such as methyl methacrylate, acrylate monomers such as butyl acrylate and ethyl acrylate, (meth)acrylate monomers such as methacrylic acid, acrylate monomers such as acrylic acid, and N-substituted maleimide monomers such as N-phenylmaleimide. The copolymer (A) preferably contains 15-21% by mass of cyanide vinyl monomer units per 100% by mass, more preferably 18-20% by mass. Specifically, the content of cyanide vinyl monomer units is, for example, 15, 16, 17, 18, 19, 20, or 21% by mass, or may be within any two of the exemplified values. If the content of cyanide vinyl monomer units is within this range, the resulting resin composition exhibits excellent chemical resistance and color balance. The cyanide vinyl monomer unit is a value determined using 13C-NMR.

[0027] The copolymer (A) is a copolymer mainly composed of styrene-based monomer units and cyanide-based vinyl monomer units. Preferably, copolymer (A) is a copolymer substantially composed only of styrene-based monomer units and cyanide-based vinyl monomer units. The constituent units of copolymer (A) are preferably 79-85% by mass of styrene-based monomer units and 15-21% by mass of cyanide-based vinyl monomer units, more preferably 80-82% by mass of styrene-based monomer units and 18-20% by mass of cyanide-based vinyl monomer units. If the constituent units are within this range, the resulting resin composition exhibits excellent chemical resistance and color balance.

[0028] The copolymer (A) can be manufactured using known methods. For example, bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization can be employed. As for the operation of the reaction apparatus, continuous, batch, and semi-batch methods are all suitable. Considering quality factors such as color tone and productivity, bulk polymerization or solution polymerization is preferred, with continuous polymerization being the most preferred. Solvents used in bulk polymerization or solution polymerization include, for example, alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene; ketones such as acetone and methyl ethyl ketone; and aliphatic hydrocarbons such as hexane and cyclohexane.

[0029] In the bulk or solution polymerization of copolymer (A), polymerization initiators and chain transfer agents can be used, and the polymerization temperature is preferably in the range of 120–170°C. Examples of polymerization initiators include peroxyacetals such as 1,1-di(tert-butylperoxide)cyclohexane, 2,2-di(tert-butylperoxide)butane, 2,2-di(4,4-di-tert-butylperoxidecyclohexyl)propane, and 1,1-di(tert-pentylperoxide)cyclohexane; hydroperoxides such as cumene hydroperoxide and tert-butyl hydroperoxide; alkyl peroxides such as tert-butyl acetate peroxide and tert-pentyl benzoate peroxide; and tert-butyl peroxide, di-tert-butyl peroxide, di-tert-butyl peroxide, and di-tert-hexyl peroxide. Alkyl peroxides, peroxide esters such as tert-butyl peroxyacetate, tert-butyl peroxybenzoate, and tert-butyl peroxyisopropyl monocarbonate; peroxy carbonates such as tert-butyl peroxyisopropyl carbonate and polyether tetra(tert-butyl peroxycarbonate); N,N'-azobis(cyclohexane-1-onitrile), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylpentanonitrile), and N,N'-azobis[2-(hydroxymethyl)propionitrile], etc., may be used, either one or a combination of two or more. Chain transfer agents include, for example, n-octyl mercaptan, n-dodecyl mercaptan, tert-dodecyl mercaptan, α-methylstyrene dimer, ethyl mercaptoside, limonene, and terpinene.

[0030] The devolatilization method for removing unreacted monomers or volatile components such as solvents used in solution polymerization from the solution after copolymer (A) polymerization can employ known methods. For example, a vacuum devolatilization tank with a preheater or a devolatilization extruder with an exhaust port can be used. The resin temperature during devolatilization is preferably below 240°C, and when using a vacuum devolatilization tank with a preheater, the external temperature of the preheater is preferably below 280°C. The devolatilized molten copolymer (A) can be transferred to a granulation process, where it is extruded in a rope-like manner through a porous die and processed into granules using cold cutting, air hot cutting, or underwater hot cutting methods.

[0031] From the viewpoint of the strength and moldability of the resin composition, the weight-average molecular weight of copolymer (A) is preferably 50,000 to 250,000, more preferably 150,000 to 200,000. The weight-average molecular weight of copolymer (A) is a polystyrene equivalent value measured by gel permeation chromatography (GPC) in THF solvent.

[0032] Device Name: SYSTEM-21Shodex (manufactured by Showa Denko Corporation)

[0033] Column: PL gelMIXED-B 3 in series

[0034] Temperature: 40℃

[0035] Detection: Differential Refractive Index

[0036] Solvent: Tetrahydrofuran

[0037] Concentration: 2% by mass

[0038] Standard curve: plotted using standard polystyrene (PS) (PL Corporation).

[0039] The mold release agent (B) is selected from at least one type of aliphatic alcohol and fatty acid. The aliphatic alcohol and fatty acid have 16 or more carbon atoms, preferably 16 to 22, and more preferably 16 to 18. Specifically, for example, 16, 17, 18, 19, 20, 21, or 22, or any two of the exemplified values. The mold release agent (B) is preferably an aliphatic alcohol, which exhibits excellent heat stability during injection molding.

[0040] Aliphatic alcohols with 16 or more carbon atoms include cetyl alcohol, heptadecanol, stearyl alcohol, etc., with stearyl alcohol being preferred. When the number of carbon atoms is less than 16, mold stains may occur during injection molding. Considering industrial availability, the number of carbon atoms is preferably 22 or less, and more preferably 20 or less.

[0041] Fatty acids with 16 or more carbon atoms include palmitic acid, stearic acid, and benzyl acid, with stearic acid being the preferred choice. When the number of carbon atoms is less than 16, mold stains may occur during injection molding. Considering industrial availability, the number of carbon atoms is preferably 22 or less, and more preferably 20 or less.

[0042] The content of mold release agent (B) in the resin composition is 200–800 ppm, preferably 300–700 ppm. Specifically, it is, for example, 200, 300, 400, 500, 600, 700, or 800 ppm, or any two of the exemplified values. When the content of mold release agent (B) is less than 200 ppm, the release properties during injection molding are poor; when it is greater than 800 ppm, it is difficult to disperse in the resin composition.

[0043] The resin composition preferably contains an antioxidant (C) for better color tone. The antioxidant is preferably a combination of hindered phenolic antioxidants and phosphorus-based antioxidants.

[0044] The content of antioxidant (C) in 100% by mass of the resin composition is preferably 0.05 to 0.5% by mass, more preferably 0.05 to 0.4% by mass, from the viewpoint of optimizing the color tone. Specifically, it is, for example, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.45 or 0.5% by mass, or it may be within any two of the exemplified values.

[0045] Hindered phenolic antioxidants are antioxidants whose basic skeleton contains phenolic hydroxyl groups. Examples of hindered phenolic antioxidants include octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, ethylene bis(oxyvinyl)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], 3,9-bis[2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane, pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 4,6-bis(octylthiomethyl)-o-cresol, 4,6-bis[(n-dodecylthio)methyl]-o-cresol, 2,4-di... Methyl-6-(1-methylpentadecanyl)phenol, tetra[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]methane, 4,4'-thiobis(6-tert-butyl-3-methylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 4,4'-butylenebis(3-methyl-6-tert-butylphenol), bis-[3,3-bis-(4'-hydroxy-3'-tert-butylphenyl)-butyric acid]-ethylene glycol ester, 3,3',3”,5,5',5”-hexa-tert-butyl-a,a'a”-(trimethylbenzene-2,4,6-trimethyl)tri-p-cresol, 2,6-di-tert-butyl-4-[4 [6-bis(octylthio)-1,3,5-triazine-2-ylamino]phenol, 2',3-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]propionylhydrazine, 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate, etc. Preferably, pentaerythritol tetratetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 4,4'-butylenebis(3-methyl- 6-tert-butylphenol), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 4,6-bis[(n-dodecylthio)methyl]-o-cresol, 2,6-di-tert-butyl-4-[4,6-bis(octylthio)-1,3,5-triazin-2-ylamino]phenol, 2',3-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]propionylhydrazine. More preferably, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane. Hindered phenolic antioxidants can be used alone or in combination of two or more.

[0046] Phosphorus-based antioxidants are phosphites of trivalent phosphorus compounds. Examples of phosphorus-based antioxidants include 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butylphenyl[d,f][1,3,2]dioxaphosphatine, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5]undecane, bis(2,4-cumylphenyl)pentaerythritol diphosphite, 2,2'-methylenebis(4,6-di-tert-butyl-1-phenoxy)(2-ethylhexyloxy)phosphite, tri(2,4- Di-tert-butylphenyl) phosphite, bis[2,4-bis(1,1-dimethylethyl)-6-methylphenyl] ethyl phosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, cyclooctylpentanetetrayl bis(octadecyl phosphite), bis(nonylphenyl) pentaerythritol diphosphite, 4,4'-biphenylene diphosphate tetra(2,4-di-tert-butylphenyl), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, tetrakis(2,4-di-tert-butyl-5-methylphenyl)-4,4'-biphenyl diphosphite, etc. Preferably, tris(2,4-di-tert-butylphenyl) phosphite, 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butylphenyl[d,f][1,3,2]dioxaphosphatine, or bis(2,4-cumylphenyl)pentaerythritol diphosphite is preferred. More preferably, tris(2,4-di-tert-butylphenyl) phosphite is preferred. Phosphorus-based antioxidants can be used alone or in combination of two or more.

[0047] As a method for preparing a resin composition from copolymer (A), release agent (B), and antioxidant (C), known methods can be employed, but adding and mixing during the manufacture of copolymer (A) is preferred because it minimizes the thermal history of the copolymer. Release agent (B) is preferably added after the copolymer (A) has been devolatilized and before granulation, preferably using a static mixer or extruder. Antioxidant (C) has the effect of preventing discoloration and degradation of copolymer (A) due to the thermal history during devolatilization, and is therefore preferably added to the solution containing copolymer (A) before devolatilization.

[0048] The resin composition may contain plasticizers, UV absorbers, hindered amine stabilizers, antistatic agents, ethylene bis-stearamides, and other external lubricants, provided that transparency is not compromised.

[0049] The transmittance of the resin composition at a wavelength of 450 nm, measured at an optical path length of 115 mm, is 40% or more, preferably 50% or more. Specifically, for example, it is 40, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 60, 65, or 70%, or any two of the listed values. The measured value is obtained using a spectrophotometer on a plate-shaped molded article after end face grinding. If the transmittance at a wavelength of 450 nm is less than 40%, the resin composition will turn dark even when dyed. By setting the cyanide vinyl monomer units of the copolymer (A) within an appropriate range, and by appropriately combining the resin temperature adjustment during devolatilization, the addition of antioxidant (C), etc., the transmittance at a wavelength of 450 nm can reach 40% or more.

[0050] The resin composition is preferably colored by dyes. Dyes are assigned color indices based on their chemical structure, such as Disperse Violet 28, Solvent Blue 35, 83, 94, 97, 104, 105, Solvent Green 3, Solvent Red 52, Solvent Violet 13, 31, 33, 34, 36, etc.

[0051] Coloring with dyes can be done by known methods, either by coloring with an extruder or by adding coloring during the manufacturing process of the copolymer (A).

[0052] The resin composition can be molded into a molded body using known molding methods, but due to its excellent release properties, it is preferably used for injection molding. Furthermore, due to its excellent colorability, it can be used for molded bodies requiring a high-end feel, such as cosmetic containers.

[0053]

Example

[0054] The following describes the details with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0055] The release agent (B) and antioxidant (C) used in the examples and comparative examples are as follows.

[0056] <Mold Release Agent (B)>

[0057] (B-1) Stearyl alcohol (manufactured by Kao Corporation, KALKOL8098)

[0058] (B-2) Stearic acid (Manufactured by Kao Corporation, LUNACS-90)

[0059] (B-3) Docosanol (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0060] (B-4) Ethylene bis-stearamide (manufactured by Kao Corporation, KAO WAXEB-P)

[0061] (B-5) Myristyl alcohol (KALKOL4098 manufactured by Kao Corporation)

[0062] <Antioxidant (C)>

[0063] (C-1) Pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (manufactured by BASF Japan Co., Ltd. Irganox 1010)

[0064] (C-2): Tris(2,4-di-tert-butylphenyl) phosphite (manufactured by ADEKA Co., Ltd., ADK STAB2112)

[0065] <Example 1>

[0066] The feed solution supplied to the 50L reaction tank was prepared as follows: 70 parts by mass of styrene, 15 parts by mass of acrylonitrile, 15 parts by mass of ethylbenzene, 0.02 parts by mass of tert-butylperoxyisopropyl carbonate as a polymerization initiator, and 0.01 parts by mass of n-dodecyl mercaptan as a chain transfer agent. After bubbling the feed solution with nitrogen, it was continuously supplied to the reaction tank at a rate of 10.8 L / h. The polymerization temperature was maintained at 145°C by continuously extracting the same amount of polymer solution as the feed solution, and the reaction tank was filled to 70 vol%. The polymer solution continuously extracted from the reaction tank was then supplemented with 0.5 ppm of Solvent Violet 13 as a dye, and antioxidants C-1 and C-2 were added according to the contents of Table 1. This solution was then fed into a vacuum devolatilization tank equipped with a preheater, where it was separated into unreacted styrene, acrylonitrile, ethylbenzene, etc. The temperature of the preheater was adjusted to bring the polymer temperature in the devolatilization tank to 235°C, and the pressure in the devolatilization tank to 1 kPa.

[0067] Molten polymer was extracted from the vacuum devourer using a gear pump. Release agent B-1 was mixed to the concentrations shown in Table 1 using a static mixer. The mixture was then extruded into strands, cooled with cooling water, and subsequently cut and granulated to obtain the resin composition. The copolymer had a weight-average molecular weight of 182,000.

[0068] <Example 2>

[0069] Except for changing the content of B-1, the resin composition was obtained in the same manner as in Example 1.

[0070] <Example 3>

[0071] The resin composition was obtained in the same manner as in Example 1, except that the addition of C-1 and C-2 was stopped.

[0072] <Example 4>

[0073] The resin composition was obtained in the same manner as in Example 1, except that B-1 was changed to B-2.

[0074] <Example 5>

[0075] The resin composition was obtained in the same manner as in Example 1, except that B-1 was changed to B-3.

[0076] <Example 6>

[0077] Except for changing the content of C-1, the resin composition was obtained in the same manner as in Example 1.

[0078] <Example 7>

[0079] Except for changing the content of C-2, the resin composition was obtained in the same manner as in Example 1.

[0080] <Example 8>

[0081] Except that the feed liquid supplied to the reaction vessel contained 65 parts by mass of styrene and 20 parts by mass of acrylonitrile, the resin composition was obtained in the same manner as in Example 1. The weight-average molecular weight of the copolymer was 176,000.

[0082] <Comparative Example 1>

[0083] The resin composition was obtained in the same manner as in Example 1, except that the addition of B-1, C-1, and C-2 was stopped.

[0084] <Comparative Example 2>

[0085] Except for changing B-1 to B-4 and changing the content, the resin composition was obtained in the same manner as in Example 1.

[0086] <Comparative Example 3>

[0087] Except for changing the content of B-1, the resin composition was obtained in the same manner as in Example 1.

[0088] <Comparative Example 4>

[0089] The result of changing the content of B-1 was that the dispersibility of B-1 deteriorated, the strands became disordered, and the resin composition could not be manufactured.

[0090] <Comparative Example 5>

[0091] The resin composition was obtained in the same manner as in Example 1, except that B-1 was changed to B-5.

[0092] <Comparative Example 6>

[0093] The resin composition was obtained in the same manner as in Example 8, except that the addition of C-1 and C-2 was stopped.

[0094] (Mel flow rate)

[0095] Melt flow rate was determined at 220°C with a 98N load based on JIS K7210.

[0096] (Vicat softening temperature)

[0097] The Vicat softening point was determined based on JIS K7206 using the 50 method (load 50N, heating rate 50℃ / hour) with a 10mm × 10mm test piece and a thickness of 4mm. It should be noted that the testing equipment used was the HDT & VSPT testing apparatus manufactured by Toyo Seiki Co., Ltd.

[0098] (Transmittance at an optical path length of 115mm and a wavelength of 450nm)

[0099] Using an injection molding machine (J140AD-180H, manufactured by Nippon Steel Corporation), a sheet-like molded product measuring 127mm in length, 127mm in width, and 3mm in thickness, formed under conditions of cylinder temperature 240℃ and mold temperature 70℃, was cut and its end faces polished to prepare a test piece with an optical path length of 115mm. The transmittance at a wavelength of 450nm with an incident light size of 20×1.6mm and a divergence angle of 0° was measured using a V-670 UV-Vis spectrophotometer manufactured by Nippon Spectrophotometer Co., Ltd., with an optical path length of 115mm.

[0100] (Haze)

[0101] A mirror plate measuring 90 mm in length, 55 mm in width, and 2 mm in thickness, was formed using an injection molding machine (manufactured by Toshiba Machine Co., Ltd., IS-50EP). The haze was measured according to ASTM D1003 using a haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd., NDH-1001DP type) under molding conditions of cylinder temperature 240°C and mold temperature 60°C. Additionally, the b-value was measured according to JIS K7105 using a UV-Vis spectrophotometer (manufactured by Nippon Spectrophotometer Co., Ltd., V-670).

[0102] (Retention thermal stability)

[0103] Using an injection molding machine (manufactured by Toshiba Machine Co., Ltd., IS-50EP), a mirror plate measuring 90mm in length, 55mm in width, and 2mm in thickness was formed under molding conditions of 240℃ cylinder temperature and 60℃ mold temperature. After obtaining a qualified product, 10 molding cycles were performed, allowing the resin to remain in the cylinder for 10 minutes, followed by another 10 molding cycles. The maximum value of the hue after retention (b) minus the maximum value of the hue before retention (b) is taken as Δb. The larger Δb is, the more severe the discoloration caused by retention during molding.

[0104] (Demolding resistance)

[0105] A demolding resistance mold (box-shaped molded part dimensions: length 60mm, width 130mm, depth 45mm, thickness 2mm) equipped with a weighing sensor on the ejector pin was installed on an injection molding machine 100t (J100E-P) manufactured by Nippon Steel Corporation. Continuous molding was performed with a cylinder temperature of 230°C and a mold temperature of 40°C. The ejection force of the ejector pin during demolding was measured. Demolding performance was evaluated by the maximum demolding resistance value (N), with a smaller value indicating better demolding performance.

[0106] (Mold stains)

[0107] Using an injection molding machine (manufactured by Toshiba Machine Co., Ltd., IS-50EP), after 50 consecutive molding cycles under molding conditions of cylinder temperature 280°C and mold temperature 60°C, the appearance of the mold surface and the molded product is observed. Those without contamination are marked with 〇, and those with contamination are marked with ×.

[0108] (tone)

[0109] When inspecting the injection-molded product with the naked eye, a clear and bright blue is marked with ◎, a slightly grayish-blue is marked with ○, and a light grayish-blue is marked with ×.

[0110] Table 1

[0111]

[0112] As shown in Table 1, the resin composition of the examples exhibits low demolding resistance and excellent demolding properties. Furthermore, a clear and bright blue molded body is obtained due to its excellent color tone.

[0113] Industrial availability

[0114] The resin composition according to the present invention has excellent colorability, allowing for the acquisition of molded articles with clear color tones by dyeing. Furthermore, due to its excellent release properties during injection molding, cracks are less likely to occur during demolding, enabling stable continuous molding.

Claims

1. A resin composition, which is dyed and contains a copolymer (A) having styrene-based monomer units and cyanide vinyl-based monomer units, at least one mold release agent (B) selected from aliphatic alcohols having 16 or more carbon atoms and fatty acids, and an antioxidant (C). The antioxidant (C) is a combination of hindered phenolic antioxidants and phosphorus-based antioxidants. The content of the release agent (B) is 200~800ppm. With an optical path length of 115mm and a wavelength of 450nm, the transmittance is over 50%.

2. The resin composition according to claim 1, wherein, The copolymer (A) contains 79-85% by mass of the styrene monomer units and 15-21% by mass of the vinyl cyanide monomer units.

3. An injection-molded article, which is an injection-molded article of the resin composition according to claim 1 or claim 2.

Images