Method for producing graft copolymer

Abstract

Provided is a method for producing a graft copolymer, the method including a grafting step in which a side chain comprising a polymer of ethylenically unsaturated monomers is introduced into a main chain comprising an ethylene-propylene-diene copolymer in an aqueous medium, wherein: the grafting step is implemented in a state in which the ethylene-propylene-diene copolymer is dispersed in the aqueous medium; the proportion of diene in all monomers constituting the ethylene-propylene-diene copolymer is 7-11 mass%; and the aqueous medium contains a water-soluble cellulose ether.

Description

Method for producing graft copolymer

[0001] The present invention relates to a method for producing a graft copolymer.

[0002] Ethylene-propylene-diene copolymers (hereinafter also referred to as "EPDM") are used in various applications as elastomers with excellent weather resistance and ozone resistance, and are also sometimes used as the base material for graft copolymers. For example, Patent Document 1 discloses a method for producing graft copolymers, characterized in that a specific block polyether compound is used as a dispersant in a method for graft copolymerizing a polymerizable monomer onto a shredded rubber-like polymer such as an ethylene-α-monoolefin copolymer rubber or an ethylene-α-monoolefin non-conjugated diene terpolymer rubber in an aqueous suspension.

[0003] Special Publication No. 62-010565

[0004] However, the present inventors have found that when a graft copolymer is produced using shredded EPDM as a raw material, particles in the suspension tend to adhere to each other, forming coarse particles, and that when an EPDM containing a high proportion of propylene or diene among all monomers is used, coarse particles tend to form, which interfere with the graft polymerization. Furthermore, the present inventors have found that, regardless of whether coarse particles are formed, when a graft copolymer obtained by a conventional method is mixed with another resin to improve the impact resistance, the resulting mixture does not have a sufficiently improved impact resistance.

[0005] Therefore, an object of the present invention is to provide a method for producing a graft copolymer having an EPDM main chain in an aqueous medium, in which the formation of coarse particles during production is sufficiently suppressed, and which can obtain a graft copolymer that can sufficiently improve the impact resistance of the mixture when mixed with other resins.

[0006] The present disclosure provides, for example, methods for producing graft copolymers described in the following [1] to [5].

[0007] [1] A method for producing a graft copolymer, comprising a grafting step of introducing, in an aqueous medium, side chains composed of a polymer of an ethylenically unsaturated monomer into a main chain composed of an ethylene-propylene-diene copolymer, wherein the grafting step is carried out in a state in which the ethylene-propylene-diene copolymer is dispersed in the aqueous medium, the proportion of diene in all monomers constituting the ethylene-propylene-diene copolymer is 7 to 11 mass %, and the aqueous medium contains a water-soluble cellulose ether.

[0008] In the production method [1], the formation of coarse particles is sufficiently suppressed. For example, even when an EPDM having a propylene content of 33 to 39% by mass and a diene content of 8% by mass among all monomers is used as a raw material, a graft copolymer can be produced without forming coarse particles (e.g., particles having a longest axis length of 20 mm or more) even if the EPDM has a high propylene or diene content among all monomers.

[0009] Furthermore, resins such as polymer blends and polymer alloys containing the above graft copolymers have high impact resistance. For example, a resin obtained by mixing ethylene-propylene-diene-graft-poly(styrene-co-acrylonitrile) as the graft copolymer with an acrylonitrile-styrene resin has a Charpy impact value of 45 kJ / m2, which is determined in the impact resistance evaluation described below. ２ The nomenclature of polymers is based on Mita et al. (2002), Polymer Nomenclature Handbook, Volume 51, and a graft copolymer is written as "polyA-graft-polyB" when polyA is the main chain and polyB is the side chain, and a copolymer is written as "poly(A-co-B)".

[0010] Furthermore, resins such as polymer blends and polymer alloys containing the graft copolymer produced by the above-mentioned production method are less likely to develop silver streaks during molding and have a good appearance.

[0011] [2] The production method according to [1], wherein the grafting step is carried out in a state in which the pulverized product of the ethylene-propylene-diene copolymer is dispersed in the aqueous medium.

[0012] In this case, the formation of coarse particles is further suppressed. In addition, since the pulverized ethylene-propylene-diene copolymer can be used, there is no need to strictly control the particle shape, which facilitates industrial use.

[0013] [3] The production method according to [1] or [2], wherein the proportion of propylene in all monomers constituting the ethylene-propylene-diene copolymer is 33 mass% or more.

[0014] In such a case, the resins such as polymer blends and polymer alloys containing the produced graft copolymers have higher impact resistance and low-temperature impact resistance. In particular, resins containing the graft copolymer and acrylonitrile-styrene resin have excellent impact resistance and low-temperature impact resistance, and resins containing the graft copolymer and polycarbonate resin have excellent low-temperature impact resistance.

[0015] [4] The method according to any one of [1] to [3], wherein the water-soluble cellulose ether is at least one selected from the group consisting of hydroxypropyl methylcellulose, hydroxybutyl methylcellulose, methylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methylcellulose, and carboxymethylcellulose.

[0016] Among the water-soluble cellulose ethers, the ones mentioned above are particularly effective in suppressing the formation of coarse particles.

[0017] [5] The method according to any one of [1] to [4], wherein the proportion of the water-soluble cellulose ether is 0.1 to 0.4 parts by mass per 100 parts by mass of the ethylene-propylene-diene copolymer.

[0018] In such a case, the formation of coarse particles is particularly suppressed, and bumping during pressure release after polymerization is suppressed.

[0019] According to the present invention, there can be provided a method for producing a graft copolymer having an EPDM main chain in an aqueous medium, in which the formation of coarse particles during production is sufficiently suppressed, and which can obtain a graft copolymer that can sufficiently improve the impact resistance of the mixture when mixed with other resins.

[0020] Hereinafter, embodiments of the present disclosure will be described in detail.

[0021] The method for producing a graft copolymer according to the present embodiment includes a grafting step of introducing, in an aqueous medium, side chains composed of a polymer of an ethylenically unsaturated monomer onto a main chain composed of an ethylene-propylene-diene copolymer. The grafting step is carried out while the ethylene-propylene-diene copolymer is dispersed in the aqueous medium. The proportion of diene in the total monomers constituting the ethylene-propylene-diene copolymer is 7 to 11% by mass, and the aqueous medium contains a water-soluble cellulose ether. While side chains other than the side chains composed of the polymer of the ethylenically unsaturated monomer may be introduced into the main chain, it is preferred that only side chains composed of a polymer of the ethylenically unsaturated monomer are introduced. One or more side chains composed of a polymer of an ethylenically unsaturated monomer are present per molecule of the ethylene-propylene-diene copolymer. When two or more side chains are present, the types and ratios of the monomers constituting the polymer of the ethylenically unsaturated monomer may be the same or different.

[0022] According to the above-described production method, the formation of coarse particles during the production of the graft copolymer is sufficiently suppressed. Here, "coarse particles" refer to particles formed by EPDM particles and / or graft copolymer particles adhering to one another. The length of the longest axis of the coarse particles may be, for example, 20 mm or more. "Sufficiently suppressing the formation of coarse particles" means that the number of coarse particles formed during the production of the graft copolymer is smaller than the number of coarse particles formed when the graft copolymer is produced by a similar method except that the aqueous medium contains a dispersant other than the water-soluble cellulose ether instead of the water-soluble cellulose ether. For example, when the number of the former coarse particles is 0.9 times or less compared to the number of the latter coarse particles, it can be said that the formation of coarse particles during the production of the graft copolymer is sufficiently suppressed. The number of the former coarse particles is preferably 0.7 times or less, 0.5 times or less, 0.3 times or less, or 0.1 times or less compared to the number of the latter coarse particles, and more preferably, the number of the former coarse particles is zero. The "dispersant other than the water-soluble cellulose ether" may be polyoxyethylene polyoxypropylene glycol.

[0023] Furthermore, resins such as polymer blends and polymer alloys containing the graft copolymer produced by the above-mentioned production method have high impact resistance. For example, a resin obtained by mixing ethylene-propylene-diene-graft-poly(styrene-co-acrylonitrile) as the graft copolymer with an acrylonitrile-styrene resin has a Charpy impact value of 45 kJ / m, as determined by the impact resistance evaluation shown below. ２ The resin obtained by mixing the ethylene-propylene-diene-graft-poly(styrene-co-acrylonitrile) as the graft copolymer and the acrylonitrile-styrene resin may be specifically produced by the method described in the examples.

[0024] The impact resistance was evaluated by molding a test piece in accordance with ISO 294 using pelletized resin, measuring the notched Charpy impact value (kJ / m) of a 4 mm thick test piece in accordance with ISO 179. ２ ) is measured.

[0025] The diene as a monomer constituting the EPDM is preferably a non-conjugated diene. Examples of non-conjugated dienes include 5-ethylidene-2-norbornene, dicyclopentadiene, 1,4-hexadiene, 1,5-hexadiene, 2-methyl-1,5-hexadiene, 1,4-cycloheptadiene, and 1,5-cyclooctadiene, with 5-ethylidene-2-norbornene being preferred. One type of diene may be used alone, or two or more types may be used in combination.

[0026] The proportion of diene in all monomers constituting the EPDM is 7 to 11 mass%, more preferably 7.5 to 10 mass%, and even more preferably 7.5 to 9 mass%. By keeping the diene proportion at 11 mass% or less, the formation of coarse particles is further suppressed, and the resulting resin, such as a polymer blend or polymer alloy containing the graft copolymer, is less likely to develop silver streaks during molding. By keeping the diene proportion at 7 mass% or more, the impact resistance of the resulting resin, such as a polymer blend or polymer alloy containing the graft copolymer, can be further improved.

[0027] The proportion of propylene in all monomers constituting the EPDM is preferably 33% by mass or more, and in that case, it may be, for example, 33 to 60% by mass, 33 to 50% by mass, or 33 to 47% by mass. By increasing the propylene proportion within the above range, the impact resistance and low-temperature durability of the resin, such as a polymer blend or polymer alloy, containing the produced graft copolymer can be further improved.

[0028] The proportion of ethylene in all the monomers constituting the EPDM may be, for example, 40 to 70 mass %, 40 to 65 mass %, or 50 to 60 mass %.

[0029] The EPDM may be composed of monomer units consisting of diene, propylene, and ethylene, and may also contain other monomers as monomer units as long as the formation of coarse particles in the production of the graft copolymer is sufficiently suppressed. The proportion of the other monomers in the total monomers constituting the EPDM may be 0 to 5 mass %, or 0 to 3 mass %.

[0030] The Mooney viscosity (ML1+4, 125°C) of the EPDM is not particularly limited, but may be, for example, 50 to 80, preferably 55 to 75, more preferably 58 to 69, and even more preferably 62 to 69. When the Mooney viscosity (ML1+4, 125°C) is within the above range, the processability of the graft copolymer is excellent. The Mooney viscosity (ML1+4, 125°C) can be measured by a known method.

[0031] As the ethylene-propylene-diene copolymer, it is preferable to use a pulverized product of the copolymer. The length of the longest axis of the pulverized product may be, for example, 2 to 10 mm, preferably 2 to 7 mm, and more preferably 2 to 4 mm. When the length of the longest axis of the EPDM is short within the above-mentioned range, the formation of coarse particles is further suppressed.

[0032] The pulverized product of the ethylene-propylene-diene copolymer may be produced by pulverizing a mass of the ethylene-propylene-diene copolymer using, for example, a shredder, a hammer mill, a mixer mill, or the like, or a commercially available pulverized product of the ethylene-propylene-diene copolymer may be used.

[0033] The EPDM may be produced by a known method or may be commercially available.

[0034] The ethylenically unsaturated monomer refers to a monomer having an ethylenically unsaturated bond (carbon-carbon double bond). The ethylenically unsaturated monomer is not particularly limited, and examples thereof include α-olefins such as propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-dodecene, 4-methyl-1-pentene, and 4-methyl-1-hexene; internal olefins such as 2-butene, 2-pentene, 3-hexene, 4-heptene, 5-octene, and 2-methyl-2-pentene; and bicyanides such as acrylonitrile, methacrylonitrile, ethacrylonitrile, and fumaronitrile. Examples of the ethylenically unsaturated monomer include vinyl monomers; aromatic vinyl monomers such as styrene, α-methylstyrene, paramethylstyrene, and bromostyrene; acrylate monomers such as methyl acrylate, ethyl acrylate, and propyl acrylate; and methacrylate monomers such as methyl methacrylate, ethyl methacrylate, and propyl methacrylate. Of these, aromatic vinyl monomers, vinyl cyanide monomers, and combinations thereof are preferred, and styrene, acrylonitrile, and combinations thereof are more preferred. One type of ethylenically unsaturated monomer may be used alone, or two or more types may be used in combination. The ethylenically unsaturated monomer may be one produced by a known method, or a commercially available product may be used.

[0035] The ratio of the ethylenically unsaturated monomer to 100 parts by mass of EPDM may be, for example, 40 to 180 parts by mass, or 80 to 140 parts by mass.

[0036] The aqueous medium is not particularly limited as long as it can suspend the EPDM and the ethylenically unsaturated monomer, and examples thereof include deionized water and distilled water.

[0037] The ratio of the aqueous medium to 100 parts by mass of EPDM may be, for example, 250 to 850 parts by mass, or 400 to 700 parts by mass.

[0038] The aqueous medium contains a water-soluble cellulose ether. The water-soluble cellulose ether refers to a cellulose obtained by substituting some of the hydrogen atoms of the hydroxyl groups of cellulose with methyl groups or the like to weaken the hydrogen bonds and make the cellulose water-soluble. When the aqueous medium contains a water-soluble cellulose ether, the formation of coarse particles can be suppressed. Examples of water-soluble cellulose ethers include hydroxypropyl methylcellulose, hydroxybutyl methylcellulose, methylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methylcellulose, and carboxymethylcellulose, with hydroxypropyl methylcellulose being preferred. One type of water-soluble cellulose ether may be used alone, or two or more types may be used in combination.

[0039] In hydroxypropyl methylcellulose, the average number of hydroxyl groups substituted with methoxy groups in the glucopyranose ring unit may be, for example, 0.5 to 2.5, or may be 1 to 2. The average number of moles of hydroxypropoxy groups attached to the glucopyranose ring unit in hydroxypropyl methylcellulose may be, for example, 0.05 to 0.4 mol, or may be 0.1 to 0.3 mol. The viscosity of a 2% by mass aqueous solution of hydroxypropyl methylcellulose at 20°C, measured according to the Japanese Pharmacopoeia, may be, for example, 25 to 400 mPa·S, or may be 50 to 200 mPa·S.

[0040] Commercially available water-soluble cellulose ethers may be used. For example, examples of hydroxypropyl methylcellulose include Metolose (registered trademark) 90SH, such as Metolose (registered trademark) 90SH-100 and Metolose (registered trademark) 90SH-400, Metolose (registered trademark) 65SH, and Metolose (registered trademark) 60SH.

[0041] The proportion of water-soluble cellulose ether in the aqueous medium relative to 100 parts by mass of EPDM is preferably 0.1 to 0.4 parts by mass, more preferably 0.1 to 0.34 parts by mass, and even more preferably 0.1 to 0.3 parts by mass. By increasing the proportion of water-soluble cellulose ether within the above-mentioned range, the generation of coarse particles is suppressed, and the occurrence of silver streaks during molding of the produced resin, such as a polymer blend or polymer alloy, containing the graft copolymer is less likely to occur. By decreasing the proportion of water-soluble cellulose ether within the above-mentioned range, bumping during depressurization after polymerization is suppressed.

[0042] The grafting step is carried out in a state in which the ethylene-propylene-diene copolymer is dispersed in an aqueous medium, but is preferably carried out in a state in which a pulverized product of the ethylene-propylene-diene copolymer is dispersed in an aqueous medium. In this case, the pulverized product of the ethylene-propylene-diene copolymer may be dispersed in the aqueous medium by stirring the aqueous medium.

[0043] A preferred method for introducing a side chain consisting of a polymer of an ethylenically unsaturated monomer into the main chain of EPDM is a reaction utilizing the unsaturated bond of the side chain derived from the diene (particularly a non-conjugated diene) of EPDM. For example, a method can be used in which EPDM and an ethylenically unsaturated monomer are brought into the presence of each other to generate radicals, thereby growing the polymer of the ethylenically unsaturated monomer as a side chain from the EPDM main chain. Alternatively, an ethylenically unsaturated monomer can be polymerized to produce an oligomer or polymer, which can then be brought into the presence of EPDM (optionally with an additional ethylenically unsaturated monomer), generating radicals to introduce a side chain consisting of the polymer of the ethylenically unsaturated monomer into the main chain of EPDM. Radical generation is typically achieved using a radical initiator, but radicals can also be generated without a radical initiator by energy beams such as electron beams. Another method involves introducing a functional group X into EPDM (or utilizing the unsaturated bond in the side chain) and reacting it with a polymer of an ethylenically unsaturated monomer into which a functional group Y reactive with the functional group X has been introduced. The functional group X and the functional group Y can be bonded together by a condensation reaction, an addition reaction, or other coupling reaction.

[0044] Introduction of a side chain consisting of a polymer of an ethylenically unsaturated monomer into a main chain consisting of an ethylene-propylene-diene copolymer can be carried out, for example, by suspension polymerization or emulsion polymerization of the ethylene-propylene-diene copolymer and the ethylenically unsaturated monomer. Suspension polymerization can be carried out by using an oil-soluble radical initiator in an aqueous medium, and emulsion polymerization can be carried out by using a water-soluble radical initiator in an aqueous medium.

[0045] Examples of oil-soluble radical initiators include tert-butyl peroxypivalate, tert-butylperoxy-2-ethylhexanoate, cumene hydroperoxide, benzoyl peroxide, tert-butyl hydroperoxide, acetyl peroxide, diisopropylbenzene hydroperoxide, and 1,1,3,3-tetramethylbutyl hydroperoxide. Preferred are tert-butyl peroxypivalate, tert-butylperoxy-2-ethylhexanoate, or a combination thereof. A combination of tert-butyl peroxypivalate and tert-butylperoxy-2-ethylhexanoate is preferred. One oil-soluble radical initiator may be used alone, or two or more may be used in combination. The oil-soluble radical initiator may be added in an amount of 0.5 to 4 parts by mass, or 1 to 3 parts by mass, per 100 parts by mass of EPDM.

[0046] Examples of the water-soluble radical initiator include lithium persulfate, potassium persulfate, sodium persulfate, and ammonium persulfate. One type of water-soluble radical initiator may be used alone, or two or more types may be used in combination. The water-soluble radical initiator may be added in an amount of 0.5 to 4 parts by mass, or 1 to 3 parts by mass, per 100 parts by mass of EPDM.

[0047] The suspension polymerization or emulsion polymerization may be carried out by further adding other components to the aqueous medium as necessary. Examples of other components include water-soluble metal salts such as magnesium sulfate, antioxidants such as octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, polymerization inhibitors such as 1,4-benzoquinone, chain transfer agents, surfactants, etc. The water-soluble metal salt may be added in an amount of 0.5 to 2 parts by mass per 100 parts by mass of EPDM. The antioxidant may be added in an amount of 0.1 to 1 part by mass per 100 parts by mass of EPDM. The polymerization inhibitor may be added in an amount of 0.02 to 0.2 parts by mass per 100 parts by mass of EPDM.

[0048] The suspension polymerization or emulsion polymerization may be carried out, for example, by stirring an aqueous medium containing EPDM, an ethylenically unsaturated monomer, a water-soluble cellulose ether, and, if necessary, a radical initiator and other components, under high-temperature and high-pressure conditions in an atmosphere of an inert gas such as nitrogen. The high-temperature and high-pressure conditions include, for example, a pressure of 0.7 to 1.3 kg / cm based on atmospheric pressure. ３ The temperature may be 80 to 130°C. Polymerization may be allowed to proceed for 20 to 40 minutes under such high-temperature, high-pressure conditions. Furthermore, prior to suspension polymerization or emulsion polymerization, EPDM, a portion of the aqueous medium, and, if added, an inorganic salt may be stirred in advance. After completion of suspension polymerization or emulsion polymerization, the graft copolymer may be recovered, washed, and suspended by a known method.

[0049] Resins such as polymer blends and polymer alloys containing the graft copolymer produced by the production method according to this embodiment have excellent physical properties such as impact resistance. Examples of the resins such as polymer blends and polymer alloys include rubber-reinforced styrene resins such as rubber-reinforced polystyrene resin (HIPS resin), acrylonitrile-butadiene rubber-styrene polymer (ABS resin), acrylonitrile-acrylic rubber-styrene polymer (AAS resin), and methyl methacrylate-butadiene rubber-styrene resin (MBS resin), as raw materials; styrene polymer (PS resin), styrene-acrylonitrile copolymer (AS resin), α-methylstyrene-acrylonitrile copolymer (αMS-ACN resin), methyl methacrylate-styrene copolymer (MS resin), and methyl methacrylate-acrylonitrile-styrene copolymer. The resin may contain non-rubber-reinforced styrene resins such as copolymers of styrene and N-phenylmaleimide (MAS resin), styrene-N-phenylmaleimide copolymers (S-NPMI resin), and styrene-N-phenylmaleimide-acrylonitrile copolymers (S-A-NPMI resin); polycarbonate resins (PC resin); polyester resins such as polyethylene terephthalate resins (PET resin), polybutylene terephthalate resins (PBT resin), and polylactic acid resins (PLA resin); polyacetal resins; polyamide resins such as nylon resins; acrylic resins such as polymethyl methacrylate resins (PMMA resin); polyvinyl chloride resins; and polyether resins such as polyphenylene ether resins. Resins such as polymer blends and polymer alloys can be produced by known methods.

[0050] For example, in the method for producing a graft copolymer according to this embodiment, when the ethylenically unsaturated monomer contains styrene and acrylonitrile, it is possible to produce an ethylene-propylene-diene-graft-poly(styrene-co-acrylonitrile) (hereinafter also referred to as "AES resin") as the graft copolymer. A resin obtained by mixing the AES resin with an acrylonitrile-styrene resin can have excellent impact resistance. Furthermore, a resin obtained by mixing the AES resin with a polycarbonate resin has good physical properties.

[0051] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0052] [Production of Graft Copolymers (A-1) to (A-7)] (Preparation of Ethylene-Propylene-Diene Copolymers) Ethylene-propylene-diene copolymers (a-1) to (a-5) were prepared, with the proportions of ethylene, propylene, and diene in all monomers, the type of diene, and Mooney viscosity (ML1+4, 125°C) as shown in Table 1 below. In Table 1 below, "ENB" means 5-ethylidene-2-norbornene, and "DCPD" means dicyclopentadiene. Baled ethylene-propylene-diene copolymers (a-1) to (a-5) were passed through a crusher and crushed to a size of 8 mm or less, and used in the production of the following graft copolymers (A-1) to (A-7).

[0053] Example 1 Production of Graft Copolymer (A-1) A 100 L pressure vessel was charged with 494 parts by mass of deionized water, 0.12 parts by mass of hydroxypropyl methylcellulose (trade name: Metrose (registered trademark) 90SH-100, manufactured by Shin-Etsu Chemical Co., Ltd.), 0.99 parts by mass of magnesium sulfate, and 100 parts by mass of ethylene-propylene-diene copolymer (a-1), and the atmosphere inside the vessel was replaced with nitrogen while stirring. Thereafter, a monomer mixture consisting of 78.2 parts by mass of styrene, 32.5 parts by mass of acrylonitrile, 1.77 parts by mass of tert-butyl peroxypivalate (B(PV)), 0.17 parts by mass of tert-butylperoxy-2-ethylhexanoate (trade name: Kayaester O, manufactured by Kayaku Nouryon Co., Ltd.), 0.074 parts by mass of 1,4-benzoquinone, and 0.40 parts by mass of octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (trade name: SONGNOX1076, manufactured by SONGWON Co., Ltd.), and 50 parts by mass of deionized water were charged, and the inside of the tank was pressurized to 0.1 kg / cm ３ The temperature inside the tank was raised to 90°C, and the reaction was continued for 30 minutes after reaching 90°C. During the 30-minute reaction, the temperature was raised to 120°C, and after the temperature was raised, the reaction was continued at 120°C. After completion of the reaction, the temperature inside the tank was cooled to 40°C, and the contents were recovered, washed, and dried to obtain a graft copolymer (A-1).

[0054] Example 2: Production of graft copolymer (A-2) Graft copolymer (A-2) was obtained in the same manner as in the production of graft copolymer A-1 above, except that ethylene-propylene-diene copolymer (a-2) was used instead of ethylene-propylene-diene copolymer (a-1) and the amount of hydroxypropyl methylcellulose added was changed to 0.38 parts by mass instead of 0.12 parts by mass.

[0055] Comparative Example 1: Production of Graft Copolymer (A-3) Graft copolymer (A-3) was obtained in the same manner as in the production of graft copolymer A-2 above, except that ethylene-propylene-diene copolymer (a-3) was used instead of ethylene-propylene-diene copolymer (a-2).

[0056] Comparative Example 2: Production of Graft Copolymer (A-4) Graft copolymer (A-4) was obtained in the same manner as in the production of graft copolymer A-1 above, except that 0.38 parts by mass of polyoxyethylene polyoxypropylene glycol (trade name: Pluronic (registered trademark) F-68, manufactured by ADEKA Corporation) was used instead of 0.12 parts by mass of hydroxypropyl methylcellulose.

[0057] (Comparative Example 3: Production of Graft Copolymer (A-5)) Graft copolymer (A-5) was obtained in the same manner as in the above (Production of Graft Copolymer A-2), except that polyoxyethylene polyoxypropylene glycol (trade name: Pluronic (registered trademark) F-68, manufactured by ADEKA Corporation) was used instead of hydroxypropyl methylcellulose.

[0058] (Comparative Example 4: Production of Graft Copolymer (A-6)) Graft copolymer (A-6) was obtained in the same manner as in the above (Production of Graft Copolymer A-2), except that ethylene-propylene-diene copolymer (a-4) was used instead of ethylene-propylene-diene copolymer (a-2).

[0059] (Comparative Example 5: Production of Graft Copolymer (A-7)) Graft copolymer (A-7) was obtained in the same manner as in the above (Production of Graft Copolymer A-2), except that ethylene-propylene-diene copolymer (a-5) was used instead of ethylene-propylene-diene copolymer (a-2).

[0060] [Evaluation of Adhesion State of Graft Copolymers (A-1) to (A-7)] 500 g samples were randomly collected from each of the produced graft copolymers (A-1) to (A-7). The length of the longest axis of the particles in the samples was confirmed and evaluated according to the following criteria. The results are shown in Table 1. In Table 1, "HPMC" represents hydroxypropyl methylcellulose, and "EO-PO block copolymer" represents polyoxyethylene polyoxypropylene glycol. ◯: No particles of 20 mm or more (coarse particles). ×: Particles of 20 mm or more (coarse particles) are present.

[0061] As shown in Table 1, in the graft copolymers (A-1), (A-2), (A-6), and (A-7) in which the proportion of diene to all monomers was 11% by mass or less and hydroxypropyl methylcellulose was used, there were no particles (coarse particles) with a longest axis length of 20 mm or more. On the other hand, in the graft copolymer (A-3) in which the proportion of diene to all monomers was greater than 11% by mass, and in the graft copolymers (A-4) and (A-5) in which polyoxyethylene polyoxypropylene glycol was used instead of hydroxypropyl methylcellulose, particles with a longest axis length of 20 mm or more (coarse particles) were observed, and the state of fixation was poor. Therefore, the formation of coarse particles was sufficiently suppressed in the production of the graft copolymers of Examples 1 and 2 and Comparative Examples 4 and 5.

[0062] [Production of pellets for Charpy impact value evaluation] (Production of styrene-based hard resin (B)) A copolymer containing 75% by mass of styrene and 25% by mass of acrylonitrile based on all monomers was obtained by a known bulk polymerization method. The copolymer was dissolved in N,N-dimethylformamide to prepare a solution with a concentration of 0.4 g / 100 ml, and the reduced viscosity [IV] was calculated from the flow time measured at 30°C using a Cannon-Fenske viscometer. The reduced viscosity of the copolymer was found to be 0.6 dl / g.

[0063] (Production of pellets for Charpy impact value evaluation) 40% by mass of the graft copolymer (A-1), (A-2), (A-6) or (A-7) which was evaluated as "○" in the above [Evaluation of adhesion state of graft copolymers (A-1) to (A-7)], 60% by mass of the styrene-based hard resin (B) and 1% by mass of ethylene bisstearamide were mixed and then melt-kneaded in a φ26 mm twin-screw extruder set at a cylinder temperature of 230°C to produce pellets for evaluation.

[0064] (Evaluation of Charpy Impact Value) Using the evaluation pellets produced in the above (Production of pellets for Charpy impact value evaluation), various test pieces were molded in accordance with ISO 294, and impact resistance was measured. Impact resistance was measured in accordance with ISO 179, using a 4 mm thick test piece with a notched Charpy impact value (kJ / m ２ The results are shown in Table 1. In Table 1, "NC" means Charpy impact value.

[0065] As shown in Table 1, the Charpy impact values ​​of the graft copolymers (A-1) and (A-2), in which the proportion of diene in all monomers was 7 to 11 mass% and which contained hydroxypropyl methylcellulose, were 2.5 times or more higher than those of the graft copolymers (A-6) and (A-7), in which the proportion of diene in all monomers was less than 7 mass%. This demonstrates that the resins containing the graft copolymers of Examples 1 and 2 have high impact resistance.

[0066]

Claims

1. A method for producing a graft copolymer, comprising a grafting step of introducing, in an aqueous medium, side chains consisting of a polymer of an ethylenically unsaturated monomer onto a main chain consisting of an ethylene-propylene-diene copolymer, wherein the grafting step is carried out in a state in which the ethylene-propylene-diene copolymer is dispersed in the aqueous medium, the proportion of diene in all monomers constituting the ethylene-propylene-diene copolymer is 7 to 11% by mass, and the aqueous medium contains a water-soluble cellulose ether.

2. The manufacturing method according to claim 1, wherein the grafting step is carried out in a state where the pulverized ethylene-propylene-diene copolymer is dispersed in the aqueous medium.

3. The method of claim 1, wherein the proportion of propylene in all monomers constituting the ethylene-propylene-diene copolymer is 33% by mass or more.

4. The method of claim 1, wherein the water-soluble cellulose ether is at least one selected from the group consisting of hydroxypropyl methylcellulose, hydroxybutyl methylcellulose, methylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methylcellulose, and carboxymethyl cellulose.

5. The method of any one of claims 1 to 4, wherein the proportion of the water-soluble cellulose ether is 0.1 to 0.4 parts by mass per 100 parts by mass of the ethylene-propylene-diene copolymer.

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