JP2019194287A - Heat-resistant styrenic resin composition, molding, foam sheet, and food package - Google Patents

Abstract

To provide a heat-resistant styrenic resin composition that has excellent heat resistance, strength, and moldability in a balanced manner, and a molding and a foam sheet that are formed with the heat-resistant styrenic resin composition, resist cracking when processed into various shapes such as deep drawing, and can be suitably used particularly as a food container for microwave oven.SOLUTION: A heat-resistant styrenic resin composition has a styrene-(meth) acrylic acid copolymer (A), a polyphenylene ether resin (B) and a metal element (C).SELECTED DRAWING: None

Description

  The present invention relates to a heat-resistant styrenic resin composition having an excellent balance of heat resistance, strength, and moldability, a molded product formed using the heat-resistant styrenic resin composition, and a foamed sheet.

  Styrene- (meth) acrylic acid copolymer is superior in heat resistance compared to general polystyrene, so it can be used for packaging materials for food containers, foam boards for thermal insulation of houses, light diffusing plates for LCD TVs, etc. It is widely used as a raw material. In the field of packaging materials, styrene- (meth) acrylic acid-based copolymers are often used as food packaging containers for heating in a microwave oven or the like. High-power microwave ovens have become widespread in order to improve the efficiency of business operations, and higher heat resistance is required than before. In addition, in order to save resources, there is a demand for weight reduction of molded products. In addition, from the viewpoint of increasing the size of containers and increasing the design characteristics associated with the increase in contents, mechanical strength such as brittleness and moldability are improved. Resin is desired.

  Styrene- (meth) acrylic acid copolymer has a disadvantage that it is brittle compared to general polystyrene, so a rubber component is added as a reinforcing material to styrene- (meth) acrylic acid copolymer. A method has been proposed. For example, Patent Document 1 discloses a foamed sheet obtained by adding impact-resistant polystyrene (HIPS) or methyl methacrylate-butadiene-styrene copolymer resin (MBS) as a rubber component. Discloses a styrene resin foam sheet comprising a styrene-methacrylic acid copolymer resin and a styrene-butadiene copolymer resin.

  Moreover, as a method for achieving both heat resistance and toughness, Patent Document 3 discloses a copolymer resin of polyphenylene ether and an aromatic vinyl-acrylic acid monomer, and a blend resin of polystyrene. By combining a styrene-methacrylic acid copolymer having a specific composition and a polyphenylene ether and having a specific weight average molecular weight, attempts have been made to improve heat resistance, strength, and moldability.

JP-A-2-58548 JP 2000-136257 A JP 2012-140549 A JP 2014-205761 A

However, the prior art described in the above literature has room for improvement in the following points.
First, in the techniques of Patent Documents 1 and 2, in order to improve mechanical strength such as brittleness, it is necessary to add a relatively large amount of a rubber component, and there is a problem that heat resistance is lowered. Further, in secondary forming of an extruded sheet, it is difficult to maintain a melt tension that can withstand large deformations, and molding defects such as cracks and cracks may occur in the molded product.
Secondly, in the techniques of Patent Documents 3 to 4, although heat resistance and formability are improved as compared with the conventional techniques, improvement in brittleness is insufficient, and in particular, deep-drawn containers and complex shaped containers However, since further cracks may occur during product transportation or when fitted with food container lids, further improvements are required.
This invention is made | formed in view of the said situation, and it aims at achieving the subject that it is excellent in the balance of the heat resistance described above, intensity | strength, and a moldability.

  In light of the above-mentioned problems, the present inventors have conducted extensive research and have not been able to achieve the conventional technique by combining a styrene- (meth) acrylic acid copolymer, a polyphenylene ether, and a metal element. A heat-resistant styrenic resin composition having a balance of heat resistance, strength, and moldability is obtained, and further, by using the heat-resistant styrenic resin composition, a foam sheet having an excellent balance of heat resistance, strength, and moldability Has been found, and the present invention has been completed.

That is, the present invention is as shown in the following (1) to (9).
(1) A heat-resistant styrene resin composition comprising a styrene- (meth) acrylic acid copolymer (A), a polyphenylene ether resin (B), and a metal element (C).
(2) The metal element (C) is added in an amount of 0.01 to 5 with respect to 100 parts by mass in total of 70 to 99 parts by mass of the copolymer (A) and 1 to 30 parts by mass of the polyphenylene ether resin (B). The heat-resistant styrenic resin composition according to (1), including part by mass.
(3) When the copolymer (A) has a total amount of styrene monomer units and (meth) acrylic acid monomer units of 100% by mass, the content of styrene monomer units is 80%. The heat-resistant styrene-based resin composition according to (1) or (2), wherein the content of the (meth) acrylic acid monomer unit is 1 to 20% by mass.
(4) The heat-resistant styrenic resin composition according to any one of (1) to (3), wherein the metal element (C) is an alkali metal and / or zinc.
(5) The heat-resistant styrenic resin composition according to any one of (1) to (4), wherein the Vicat softening temperature is 110 ° C. or higher.
(6) The heat resistant styrenic resin composition according to any one of (1) to (5), wherein the melt tension value (MT) measured at 220 ° C. is 10 to 150 gf.
(7) A molded product obtained from the heat-resistant styrene-based resin composition according to any one of (1) to (6).
(8) A foam sheet obtained from the heat-resistant styrenic resin composition according to any one of (1) to (6).
(9) A food packaging container using the foamed sheet according to (8).

  The heat-resistant styrenic resin composition of the present invention is excellent in the balance between heat resistance, strength, and moldability, and can be suitably used particularly as a food container for microwave ovens, when processed into various shapes such as deep drawing. In addition, a food container with less cracking can be obtained.

  Hereinafter, the present invention will be described in detail.

<Heat resistant styrene resin composition>
The heat-resistant styrene resin composition of the present invention contains a styrene- (meth) acrylic acid copolymer (A), a polyphenylene ether resin (B), and a metal element (C).

  In the heat-resistant styrene resin composition of the present invention, when the total amount of the copolymer (A) and the polyphenylene ether resin (B) is 100 parts by mass, the content of the copolymer (A) is 70 to 99 parts by mass, the content of the polyphenylene ether-based resin (B) is preferably 1 to 30 parts by mass, the content of the copolymer (A) is 80 to 98 parts by mass, The content of the polyphenylene ether resin (B) is more preferably 2 to 20 parts by mass. When the content of the polyphenylene ether resin (B) is less than 1 part by mass, improvement in brittleness and heat resistance may be insufficient, and the content of the polyphenylene ether resin (B) may be 30 parts by mass. When exceeding, since fluidity | liquidity falls, it is not preferable.

  The heat resistant styrenic resin composition of the present invention contains 0.01 to 5 of the metal element (C) with respect to a total of 100 parts by mass of the copolymer (A) and the polyphenylene ether resin (B). It is preferable to include part by mass, more preferably 0.02 to 3 parts by mass of the metal element (C), and particularly preferably 0.05 to 1 part by mass of the metal element (C). When the content of the metal element (C) is less than 0.01 parts by mass, the improvement of brittleness and formability may be insufficient, and the content of the metal element (C) exceeds 5 parts by mass. Since the fluidity is too low, the moldability is deteriorated.

  The melt mass flow rate (MFR) measured under the conditions of 200 ° C. and 49 N load of the heat-resistant styrenic resin composition of the present invention is preferably 0.01 to 10 g / 10 min, and 0.05 to 5. 0 g / 10 min is more preferable, and 0.1 to 3.0 g / 10 min is particularly preferable. When the melt mass flow rate (MFR) is less than 0.01 g / 10 minutes, productivity at the time of extrusion molding deteriorates, and when it exceeds 10 g / 10 minutes, the mechanical strength may decrease.

  The Vicat softening temperature of the heat-resistant styrenic resin composition of the present invention is preferably 110 ° C. or higher, more preferably 112 ° C. or higher, and particularly preferably 115 ° C. or higher. When the Vicat softening temperature is less than 110 ° C., the heat resistance of the molded product obtained from the heat-resistant styrenic resin composition may be insufficient.

  The melt tension (MT) measured at 220 ° C. of the heat-resistant styrenic resin composition of the present invention is preferably 10 to 150 gf, more preferably 12 to 100 gf, and particularly preferably 13 to 80 gf. . If the melt tension is less than 10 gf, the effect of improving the moldability may be small, and if the melt tension exceeds 150 gf, the moldability deteriorates, which is not preferable.

<Styrene- (meth) acrylic acid copolymer (A)>
The styrene- (meth) acrylic acid copolymer (A) of the present invention comprises a styrene monomer and a (meth) acrylic acid monomer as essential components, but other copolymerizable with these as required. Vinyl monomers can be copolymerized.

  Examples of the styrenic monomer include substituted styrenes such as styrene, α-methylstyrene, o-, m-, and p-methylstyrene. These may be one kind or a mixture of two or more kinds, but styrene is preferred. It is.

  Examples of the (meth) acrylic acid monomer include acrylic acid and methacrylic acid, and a mixture thereof may be used. Among them, methacrylic acid is preferable because of ease of production.

  Examples of the vinyl monomer copolymerizable with the styrene monomer and the (meth) acrylic acid monomer include, for example, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, methacrylic acid. Acrylic monomers such as butyl acid, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, N-methylmaleimide, N-ethylmaleimide, N-butylmaleimide, N-octylmaleimide, N-isopropylmaleimide, N-phenylmaleimide , Maleimide monomers such as N-cyclohexylmaleimide, and unsaturated carboxylic acid anhydrides such as maleic anhydride, itaconic anhydride and citraconic anhydride. These may be used alone or in combination of two or more. it can.

  Examples of the polymerization method of the styrene- (meth) acrylic acid copolymer (A) of the present invention include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, and a suspension polymerization method. Examples of the solvent include alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane. As the type of the reactor, a continuous polymerization system in which a complete mixing type reactor, a plug flow reactor, a loop type reactor and the like are combined is preferably used.

  The styrene- (meth) acrylic acid copolymer (A) of the present invention has a styrene monomer when the total amount of styrene monomer units and (meth) acrylic acid monomer units is 100% by mass. The unit content is 80 to 99% by mass, the (meth) acrylic acid monomer unit content is preferably 1 to 20% by mass, and the styrene monomer unit content is 85 to 98%. More preferably, the content of the mass% and (meth) acrylic acid monomer units is 2 to 15 mass%. If the content of the (meth) acrylic acid monomer unit is less than 1% by mass, the heat resistance of the molded product obtained from the heat-resistant styrene resin composition becomes insufficient, and the content of the (meth) acrylic acid monomer unit When it exceeds 20 mass%, the moldability of a heat-resistant styrene-based resin composition or a foamed sheet obtained therefrom is lowered. Content of a (meth) acrylic acid monomer unit can be adjusted with the (meth) acrylic acid monomer density | concentration of the raw material liquid in a superposition | polymerization process.

  The weight average molecular weight (Mw) of the styrene- (meth) acrylic acid copolymer (A) of the present invention is preferably 100,000 to 400,000, more preferably 11 to 350,000, and more preferably 120,000 to 30. It is particularly preferable that the number is 10,000. If Mw is less than 100,000, the strength is insufficient, and if Mw exceeds 400,000, the fluidity decreases. Mw of the styrene- (meth) acrylic acid copolymer is the reaction temperature in the polymerization process, the residence time, the type and addition amount of the polymerization initiator, the type and addition amount of the chain transfer agent, and the type and amount of the solvent used during the polymerization. It can be adjusted by etc.

（式中、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^４は、それぞれ水素原子、ハロゲン原子、炭化水素基、置換炭化水素基であり、そのうち１個は必ず水素原子である。また、ｎは繰り返し単位である） <Polyphenylene ether resin (B)>
The polyphenylene ether resin (B) of the present invention is obtained by oxidative polymerization of at least one phenol compound with oxygen or an oxygen-containing gas using an oxidative coupling catalyst, and is represented by a repeating unit of the formula (1). It is a homopolymer or a copolymer. These may be one kind or a mixture of two or more kinds of resins.

(Wherein R ¹ , R ² , R ³ and R ⁴ are each a hydrogen atom, a halogen atom, a hydrocarbon group or a substituted hydrocarbon group, one of which is necessarily a hydrogen atom. Unit)

  Specific examples of the phenol compound include phenol, o-, m-, p-cresol, 2,6-, 2,5-, 2,4- or 3,5-dimethylphenol, 2-methyl-6-phenylphenol. 2,6-diphenylphenol, 2,6-diethylphenol, 2-methyl-6-ethylphenol, 2,3,5-, 2,3,6-, or 2,4,6-trimethylphenol, 3- Methyl-6-tert-butylphenol, thymol, 2-methyl-6-allylphenol, etc., among which 2,6-dimethylphenol, 2,6-diphenylphenol, 3-methyl-tert-butylphenol and 2,3 1,6-trimethylphenol is preferred.

  The oxidative coupling catalyst used for the polymerization of the polyphenylene ether-based resin (B) of the present invention is not particularly limited, but at least one heavy metal compound such as copper, manganese, cobalt and the like is used (US Pat. No. 4,042). No. 056, No. 3,306,874, No. 3,306,875, etc.).

  The molecular weight of the polyphenylene ether-based resin (B) of the present invention is not particularly limited, but preferably has an intrinsic viscosity of 0.30 dl / g or more (at a temperature of 25 ° C. in a solvent chloroform). If it is less than 0.30 dl / g, the mechanical strength may be inferior. The intrinsic viscosity is preferably 0.30 to 0.60 dl / g.

<Metal element (C)>
The metal element (C) of the present invention is selected from alkali metals such as lithium, sodium and potassium, alkaline earth metals such as magnesium and calcium, transition metals such as chromium, manganese, iron, cobalt and nickel, aluminum and zinc One or two or more of these may be combined, and among them, alkali metals and / or zinc are particularly preferable.

  About the kind and quantity of the metal element (C) of this invention, it can adjust easily by using the alkaline substance containing the said metal element as a neutralizing agent. Examples of the neutralizing agent include metal formate, acetate, oxide, hydroxide, methoxide, ethoxide, carbonate, bicarbonate, organic acid metal salt such as fatty acid metal salt, and carboxylate metal salt. And organic acid metal salt-containing polymers such as a polymer containing sulfonic acid metal salt and the like. The metal element (C) forms a metal salt with the carboxylic acid of the (meth) acrylic acid monomer unit of the styrene- (meth) acrylic acid copolymer (A), thereby greatly increasing toughness and melt tension. improves.

<Method for producing heat-resistant styrene-based resin composition>
As a method for producing the heat-resistant styrene resin composition of the present invention, a neutralizing agent containing the copolymer (A), the polyphenylene ether resin (B), and the metal element (C) is blended in a lump. , A method of melt extrusion, or a mixture obtained by previously extruding a neutralizer containing the copolymer (A) and the metal element (C), and then blending the polyphenylene ether resin (B) again and melting again. A method of extruding, a method in which the copolymer (A) and the polyphenylene ether-based resin (B) are melt-extruded in advance and a neutralizing agent containing the metal element (C) is blended later and melt-extruded again. Etc. Moreover, the resin composition obtained by the method of adding the neutralizing agent containing the said metal element (C) continuously in any of the superposition | polymerization process of the said copolymer (A), a devolatilization process, or an extrusion process. On the other hand, the polyphenylene ether-based resin (B) may be blended and melt-extruded later. The neutralizing agent may be added as a solid or an aqueous solution, but a method of adding it as an aqueous solution is preferable from the viewpoint of dispersibility and reactivity. Alternatively, a master batch containing the polyphenylene ether resin (B) and / or the metal element (C) may be prepared in advance and then blended with the copolymer (A).

  In the heat-resistant styrene-based resin composition of the present invention, if necessary, another thermoplastic resin or a rubber reinforcing material can be blended within a range that does not impair the effects of the present invention.

  Specific examples of the thermoplastic resin include polystyrene, high impact polystyrene (HIPS), syndiotactic polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, methacrylic acid-methyl methacrylate-styrene copolymer. Polystyrene resins such as polymers, butyl methacrylate-styrene copolymer, maleic anhydride-styrene copolymer, maleimide-styrene copolymer, α-methylstyrene-styrene copolymer, polypropylene, propylene-α-olefin copolymer Examples thereof include polyolefin resins such as coalescence, aliphatic polyester resins such as poly L-lactic acid, poly D-lactic acid, poly D, and L-lactic acid, and these can be used alone or in combination.

  Specific examples of rubber reinforcing materials include natural rubber, polybutadiene, polyisoprene, polyisobutylene, polychloroprene, polysulfide rubber, thiocol rubber, acrylic rubber, urethane rubber, silicone rubber, epichlorohydrin rubber, styrene-butadiene block copolymer, Styrene-butadiene-styrene copolymer, styrene-isoprene block copolymer, styrene-isoprene-styrene block copolymer, hydrogenated styrene-butadiene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, hydrogen Styrene rubber such as added styrene-isoprene block copolymer, hydrogenated styrene-isoprene-styrene block copolymer, methyl methacrylate-butadiene-styrene copolymer, and ethylene Pirengomu, ethylene propylene diene rubber, include olefin rubbers such as linear low-density polyethylene-based elastomer, may be used in combination one or two or more kinds.

  In the heat-resistant styrenic resin composition of the present invention, as additives, phosphorus-based, phenol-based, amine-based antioxidants, higher fatty acids such as stearic acid, and salts thereof, lubricants such as ethylenebisstearylamide, Add plasticizers such as liquid paraffin, polyethylene wax, microcrystalline wax, talc, inorganic filler, UV absorber, antistatic agent, flame retardant, colorant, pigment, deodorant, anti-fogging agent, etc. as necessary be able to.

<Method for producing foam sheet>

  As a method for producing the foamed sheet of the present invention, a known method for producing an extruded foamed sheet can be used. Specifically, two single-screw extruders and two-screw extruders are arranged in series, the foaming agent is melted and kneaded with the foam nucleating agent in the first extruder, and cooled by the second extruder. An example is a method in which the resin temperature is adjusted to 120 ° C. to 180 ° C. and then released into the atmosphere with a circular die and foamed under reduced pressure.

  Examples of blowing agents include aliphatic hydrocarbons such as propane, normal butane, isobutane, pentane and hexane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, 1,1-difluoroethane, Physical foaming agents such as halogenated hydrocarbons such as 1,1-difluoro-chloride and methylene chloride can be used. Also, decomposable foaming agents such as azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate and citric acid, inorganic gases such as carbon dioxide and nitrogen, and water can be used. These foaming agents can be used by appropriately mixing them, but industrially, butane is often used, and from the viewpoint of foaming extrudability, secondary formability of foamed sheets, and foaming agents, mixing consisting of isobutane and normal butane It is preferred to use butane. Since butane has a slow permeation rate with respect to the polystyrene-based resin, about 1 to 3% by mass usually remains in the foamed sheet immediately after foam extrusion. Since this remaining amount affects the secondary foam thickness and thermoformability in secondary molding, it is appropriately adjusted by providing a certain aging period.

  Examples of the foam nucleating agent include inorganic powders such as talc, calcium carbonate, and clay, and these can be used alone or as a mixture. Among them, talc is most preferable in that it has a large effect of reducing the bubble diameter and is inexpensive. The method for adding the foam nucleating agent is not particularly limited, and may be added directly to the supply hole of the extruder or may be added together with the resin. Moreover, the masterbatch which made the base material the homopolymer of styrene, a styrene-methyl methacrylate copolymer, etc. can also be created, and it can also supply using the masterbatch. The addition amount of the foam nucleating agent is usually 0.1 to 5% by mass. The master batch may contain a higher fatty acid or a metal salt of a higher fatty acid in advance. It may also contain lubricants such as ethylenebisstearylamide, spreading agents such as liquid paraffin and silicone oil, other surfactants, antistatic agents, antioxidants, plasticizers, weathering agents, pigments, etc. good.

The thickness of the foam sheet of the present invention is generally 0.1 to 100 mm, preferably 0.5 to 4 mm, and more preferably 1 to 3 mm. If the thickness of the foamed sheet is less than 0.1 mm, the strength and heat insulating properties of the container after the secondary molding are lowered. If the thickness of the foamed sheet exceeds 100 mm, temperature unevenness of the sheet is likely to occur during secondary molding, and the moldability may deteriorate.

The density of the foamed sheet of the present invention are generally 5~500kg / ^{m 3,} preferably ^{50~400kg / m 3, 60~300kg / m} 3 and more preferably. When the density of the foam sheet is less than 5 kg / m ³ , the strength of the container after the secondary molding is lowered. When the density of the foam sheet exceeds 500 kg / m ³ , it is not desirable from the viewpoints of weight reduction and heat insulation. The density D (kg / m ³ ) can be calculated as D = S / T from the basis weight S (g / m ² ) of the foamed sheet and the sheet thickness T (mm).

  In addition, the foamed sheet of the present invention can be provided with a surface layer called a skin layer having a lower density than the central portion in the thickness direction on the front and back surfaces of the sheet. By providing a skin layer, the strength of the sheet can be increased and the appearance is also beautifully finished. The skin layer can be adjusted by air cooling the surface of the foam sheet immediately after leaving the circular die.

  The foamed sheet of the present invention can be improved in properties such as moldability, strength, rigidity, and oil resistance by laminating a thermoplastic resin sheet or film on one or both sides. The thermoplastic resins constituting the sheet and film are polystyrene resins such as polystyrene and high impact polystyrene, polypropylene resins, polyester resins, high density polyethylene, low density polyethylene, linear low density polyethylene, ethylene-vinyl acetate. A copolymer etc. are mentioned. Although there is no restriction | limiting in particular in the thickness of a sheet | seat or a film, 0.01 mm-0.3 mm are preferable.

  The foamed sheet of the present invention is formed by a known thermoforming method such as vacuum forming, pressure forming, matched mold forming, reverse draw forming, air slip forming, ridge forming, plug and ridge forming, plug assist forming, plug assist reverse draw forming, etc. It can be used to process containers of various shapes and sizes, such as trays, lunch containers, bowl containers, cups, and box-types with lids.

  The container obtained by molding the foamed sheet of the present invention is suitable for use as a food container for microwave ovens because even when cooking with a microwave in a state where food is put, the container does not deform or swell. it can.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.

<Production of styrene-methacrylic acid copolymer (A)>
(1) Production of Styrene-Methacrylic Acid Copolymer S-1 The following first to third reactors were connected in series to constitute a polymerization step.

First reactor: 39 L capacity complete mixing reactor with stirring blades Second reactor: 39 L capacity mixing mixing reactor with stirring blades Third reactor: 16 L capacity plug flow reactor with static mixer

  The conditions of each reactor were as follows.

First reactor: [reaction temperature] 120 ° C
Second reactor: [reaction temperature] 128 ° C
Third reactor: [Reaction temperature] Adjusted so that a temperature gradient of 125 to 130 ° C is applied in the flow direction.

  The following were used as the raw material liquid.

  10 parts by mass of ethylbenzene and 2,2 bis (4,4-t-butylperoxycyclohexyl) as a polymerization initiator with respect to 100 parts by mass of the monomer composition of styrene 97.3% by mass and methacrylic acid 2.7% by mass Raw material liquid mixed with 0.025 parts by mass of propane

The raw material liquid was continuously supplied to the first reactor set at 120 ° C. at a supply rate of 12.0 kg / hr for polymerization, and then charged continuously into the second reactor set at 128 ° C. for polymerization. . The polymerization conversion rate at the outlet of the second reactor was 65%. Further, the polymerization was allowed to proceed in a third reactor adjusted to have a temperature gradient of 125 to 130 ° C. until the polymerization conversion reached 70%.
This polymerization solution was introduced into a vacuum devolatilization tank equipped with a preheater composed of two stages in series, and unreacted styrene and ethylbenzene were separated, then extruded into a strand, cooled, cut and pelletized. The temperature of the first stage preheater is set to 200 ° C., the pressure of the vacuum devolatilization tank is set to 66.7 kPa, the temperature of the second stage preheater is set to 240 ° C., and the pressure of the vacuum devolatilization tank is set. Was 0.9 kPa. The characteristics of the obtained styrene-methacrylic acid copolymer S-1 are shown in Table 1.

(2) Production of Styrene-Methacrylic Acid Copolymer S-2 Except that the temperature conditions of the first to third reactors were changed as follows using the following raw material liquids, the production was the same as the production of S-1. The characteristics are shown in Table 1.

<Raw material liquid>
10 parts by mass of ethylbenzene with respect to 100 parts by mass of the monomer composition of 94.8% by mass of styrene and 5.2% by mass of methacrylic acid, and 2,2bis (4,4-t-butylperoxycyclohexyl) as a polymerization initiator Raw material liquid mixed with 0.025 parts by mass of propane

<Conditions>
First reactor: [reaction temperature] 120 ° C
Second reactor: [reaction temperature] 125 ° C
Third reactor: [Reaction temperature] Adjusted so that a temperature gradient of 125 to 130 ° C is applied in the flow direction.

(3) Manufacture of styrene-methacrylic acid copolymer S-3 The following raw material liquid was used, and the same process as S-1 was performed except that the temperature conditions of the first to third reactors were changed as follows. The characteristics are shown in Table 1.

<Raw material liquid>
15 parts by mass of ethylbenzene and 0.030 parts by mass of 1,1-di (t-butylperoxy) cyclohexane as a polymerization initiator with respect to 100 parts by mass of a monomer composition of 93.0% by mass of styrene and 7.0% by mass of methacrylic acid , A raw material liquid in which 0.095 parts by mass of t-dodecyl mercaptan is mixed as a chain transfer agent

<Conditions>
First reactor: [reaction temperature] 128 ° C
Second reactor: [reaction temperature] 140 ° C
Third reactor: [Reaction temperature] Adjusted so that a temperature gradient of 120 to 125 ° C is formed in the flow direction.

<Examples 1-13, Comparative Examples 1-3>
Table 2 shows the styrene-methacrylic acid copolymer (A) (S-1 to 3) and polyphenylene ether (B) produced by the above method, the neutralizing agent containing the metal element (C), and the rubber reinforcing agent (D). To a twin screw extruder (manufactured by Toshiba Machine Co., TEM26-SS) set at a cylinder temperature of 180 to 250 ° C. at a feed rate of 20 kg / hr, Melt kneading was performed at a resin temperature of 270 ° C. In Comparative Example 1, no polyphenylene ether (B) was added, and in Comparative Examples 2 to 3, a neutralizing agent containing a metal element (C) was not added. The physical properties are shown in Tables 2-3. The content of the metal element (C) was quantified by inductively coupled plasma emission analysis (ICP-AES) after oxidative decomposition of the obtained resin composition.

In addition, the following were used as polyphenylene ether (B) and rubber reinforcing agent (D).
<Polyphenylene ether (B)>
Product name: “IUPACE PX100L” Intrinsic viscosity 0.41 g / dl manufactured by Mitsubishi Engineering Plastics
<Rubber reinforcement (D)>
MBS (Methyl methacrylate-butadiene-styrene copolymer)
Product name: “METABBRENE C-223A” 75% rubber by Mitsubishi Chemical Corporation
HIPS (High Impact Polystyrene)
Product name: “Toyostyrene H848” manufactured by Toyo Styrene Co., Ltd., rubber content 10.0%, rubber particle diameter 1.9 μm

Next, the resin composition was supplied to a tandem extruder having screw diameters of 40 mmφ and 50 mmφ to produce a foam sheet. First, 100 parts by mass of the above melt-compounded resin was obtained by uniformly mixing 2.3 parts by mass of a talc masterbatch composed of 60% by mass of a styrene-methyl methacrylate copolymer and 40% by mass of talc with a screw diameter of 40 mmφ. Feeded to the extruder. Further, butane was injected as a foaming agent from the tip of the extruder at a ratio of 2.3 parts by mass with respect to 100 parts by mass of the resin, and melt mixed. At this time, the cylinder temperature was 230 to 270 ° C, the resin temperature was 235 to 250 ° C, and the pressure was 12 to 18 MPa.
Then, it is transferred to an extruder with a screw diameter of 50 mmφ through a connecting pipe set at 230 ° C., adjusted to a cylinder temperature of 160 to 200 ° C., a resin temperature of 160 to 170 ° C., and 15 to 17 MPa, and a lip opening of 0.6 mm, The foamed sheet was obtained by extruding from a circular die having a diameter of 40 mm at a discharge rate of 10 kg / hr, following a cooled cylinder having a diameter of 152 mm, and incising with a cutter at one lower point of the circumference. The thickness of the obtained foam sheet was 1.7 mm, and the density was 120 kg / m ³ . The characteristics are shown in Tables 2-3.

  Various physical properties and performance evaluation were performed by the following methods.

(1) Methacrylic acid content in styrene-methacrylic acid copolymer At room temperature, 0.5 g of the copolymer was weighed and dissolved in a mixed solution of toluene / ethanol = 8/2 (volume ratio), and then hydroxylated. Neutralization titration is performed with 1 mol of potassium / ethanol solution to detect the end point, and the content of methacrylic acid based on mass is calculated from the amount of potassium hydroxide ethanol solution used. In addition, it measured with the electrical potential difference automatic detection apparatus (Kyoto Electronics Industry Co., Ltd. make, AT-510).
(2) Molecular weight The weight average molecular weight (Mw), the Z average molecular weight (Mz), and the number average molecular weight (Mn) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Waters Alliance System 2695
Column: TSKgel-GMHXL (ID) x 300 mm (L) manufactured by Tosoh Corporation
Mobile phase: tetrahydrofuran 0.35 ml / min
Sample concentration: 0.2% by mass
Injection volume: 50 μL
Temperature: 40 ° C
Detector: Differential refractometer Alliance system 2414 manufactured by Waters
The molecular weight at each elution time was calculated from the elution curve of monodisperse polystyrene and calculated as the molecular weight in terms of polystyrene.

(3) Content of metal element 2.0 g of the resin composition was weighed and a mixed solution of sulfuric acid / nitric acid was added, followed by heating on a hot plate at 150 ° C. for oxidative decomposition. A volume of 50 mL of the solution after oxidative decomposition was fixed, diluted 20 times, and the content of the metal element was quantified by inductively coupled plasma atomic emission spectrometry (ICP-AES). In addition, Optima4300DV (made by Perkin Elmer) was used for the analytical instrument.

The physical properties were evaluated by the following methods.
(4) Melt Mass Flow Rate Determined under conditions of 200 ° C. and 49 N load based on JIS K7210.
(5) Vicat softening temperature A test piece was prepared using an injection molding machine, and obtained under conditions of 50 N load based on JIS K7206.
(6) Deflection temperature under load A test piece was prepared using an injection molding machine, and obtained under conditions of 1.8 MPa stress based on JIS K7191.
(7) Melt tension (MT)
Using Capillograph Type 1B (manufactured by Toyo Seiki Co., Ltd.), barrel temperature 220 ° C., barrel diameter 9.55 mm, capillary length: L = 10 mm, capillary diameter: D = 1 mm (L / D = 10), extrusion in barrel The resin is extruded at a speed of 10 mm / min, the load measuring part is set 60 cm below the die, the strand-shaped resin flowing out from the capillary is set in the winder, and the winding line speed is gradually increased from 4 m / min. The load until the strand breaks is measured. Since the load is stabilized at a constant value as the winding linear speed is increased, the range in which the load is stable is averaged to obtain a melt tension value (MT).

The characteristics of the foam sheet were evaluated by the following methods.
(8) Sheet impact strength Using a film impact tester BU-302 (manufactured by Tester Sangyo Co., Ltd.), measurement was performed on an impact spherical surface R12.7 mm. The measurement was performed 20 times for each of the front and back surfaces of the foam sheet, and the average value of all the sheets was used as the sheet impact strength.
(9) Formability A cup-shaped container having a diameter of 100 mm and a depth of 100 mm was thermoformed from a foam sheet using a single molding machine. When the heater temperature is kept constant at 280 ° C., the heating time is changed in 0.5 second increments, the heating time width in which the container is not perforated or cracked is confirmed, and the molding time width is 10 seconds or more. The deep drawability was evaluated by ◯ for 10 seconds, Δ for 5-8 seconds, and x for 5 seconds or less.
(10) Container strength (crack)
About the container obtained on the conditions which can be shape | molded above, using the small desktop testing machine Ez-test (The Shimadzu Corporation make, model: Ez-SX), the both ends of the mouth TD direction of a container with two boards In a sandwiched state, one end is compressed at a speed of 500 m / mm, ◎ if there is no crack at the time of displacement of 30 mm, ◯ if there is a crack only inside the foamed section, ○ cracked on the surface of the foamed section The container strength was evaluated with Δ for the case where the crack occurred, and x for the case where the entire crack occurred from the surface layer to the inside of the foamed cross section.
(11) Range-resistant deformation With respect to the container obtained under the above moldable conditions, it is heated for 70 seconds in a microwave oven with an output of 1500 W, the surface state is observed, and there is no deformation or bulging of the container at all. The heat resistance was evaluated with a circle indicating a slight deformation or bulge in a part of the container and a mark indicating a large deformation or bulge in the container as x.

  The heat-resistant styrene-based resin composition of the Examples is compared with the resin composition not containing the polyphenylene ether (B) of Comparative Example 1 and the resin composition not containing the metal element (C) of Comparative Examples 2 to 3, The strength and formability of the foam sheet have been greatly improved.

  Since the heat-resistant styrenic resin composition of the present invention has an excellent balance between heat resistance, strength, and moldability, extruded sheets prepared using the heat-resistant styrenic resin composition have various shapes such as deep drawn containers. It can be processed and used in a wide range of applications. In particular, when used as a food container for microwave ovens, it is possible to obtain a food container with less cracking, which reduces cracks during product transportation and when fitted with food container lids, resulting in food waste loss. It leads to reduction.

Claims (9)

  A heat-resistant styrene resin composition comprising a styrene- (meth) acrylic acid copolymer (A), a polyphenylene ether resin (B), and a metal element (C).   The metal element (C) is included in an amount of 0.01 to 5 parts by mass with respect to 100 parts by mass in total of 70 to 99 parts by mass of the copolymer (A) and 1 to 30 parts by mass of the polyphenylene ether resin (B). The heat-resistant styrenic resin composition according to claim 1.   When the copolymer (A) has a total amount of styrene monomer units and (meth) acrylic acid monomer units of 100% by mass, the content of styrene monomer units is 80 to 99% by mass. %, The heat-resistant styrene resin composition of Claim 1 or 2 whose content of a (meth) acrylic-acid monomer unit is 1-20 mass%.   The heat-resistant styrenic resin composition according to any one of claims 1 to 3, wherein the metal element (C) is an alkali metal and / or zinc.   The heat-resistant styrenic resin composition according to any one of claims 1 to 4, wherein the Vicat softening temperature is 110 ° C or higher.   The heat-resistant styrenic resin composition according to any one of claims 1 to 5, wherein a melt tension value (MT) measured at 220 ° C is 10 to 150 gf.   A molded article obtained from the heat-resistant styrenic resin composition according to any one of claims 1 to 6.   The foam sheet obtained from the heat-resistant styrene-type resin composition of any one of Claims 1-6.   A food packaging container comprising the foamed sheet according to claim 8.