JP7100996B2 - Heat-resistant styrene resin compositions, articles, foam sheets, and food packaging containers - Google Patents

Description

The present invention relates to a heat-resistant styrene-based resin composition having an excellent balance between heat resistance, toughness, and moldability, a molded product formed by using the heat-resistant styrene-based resin composition, and a foamed sheet.

Since styrene- (meth) acrylic acid-based copolymers are superior in heat resistance to general polystyrene, they are used as packaging materials for food containers, foam boards for heat insulating materials in houses, light diffusers for liquid crystal televisions, etc. It is widely used as a raw material for. In the field of packaging materials, styrene- (meth) acrylic acid-based copolymers are often used as food packaging containers for heating in microwave ovens, etc., but in recent years, in convenience stores, etc., the heating time has been shortened. High-output microwave ovens have become widespread in order to improve work efficiency, and higher heat resistance than before is required. Further, in order to save resources, it is required to reduce the weight of the molded product, and further, from the viewpoint of increasing the size of the container and designability due to the increase in the amount of contents, the mechanical strength such as brittleness and the moldability are improved. Resin is desired.

Since the styrene- (meth) acrylic acid-based copolymer has the disadvantage of being more brittle than general polystyrene, a rubbery component is added to the styrene- (meth) acrylic acid-based copolymer as a reinforcing material. How to do it is 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, and Patent Document 2 Discloses a styrene-based resin foam sheet composed of a styrene-methacrylic acid copolymer resin and a styrene-butadiene copolymer resin.

Further, as a method for improving brittleness and moldability without adding a rubbery component, Patent Document 3 mainly describes methyl methacrylate having a specific weight average molecular weight or more in a styrene- (meth) acrylic acid-based copolymer. A method of adding a resin as a component is disclosed.

Japanese Unexamined Patent Publication No. 2-58548 Japanese Unexamined Patent Publication No. 2000-136257 Japanese Unexamined Patent Publication No. 10-87929

However, the prior art described in the above document has room for improvement in the following points.
First, the techniques of Patent Documents 1 and 2 are insufficient to improve mechanical strength such as brittleness, and if a large amount of rubbery component is added to improve brittleness, there is a problem that heat resistance and rigidity are lowered. there were. In addition, in the secondary molding of the foamed sheet, molding defects such as cracks and naki may occur in the molded product.
Secondly, the technique of Patent Document 3 is improved in heat resistance and moldability as compared with the conventional technique, but the effect of improving brittleness is insufficient.
The present invention has been made in view of the above circumstances, and an object of the present invention is to achieve the above-mentioned problem of excellent balance between heat resistance, toughness, and moldability.

In view of the above problems, the present inventors have conducted diligent research, and found that a resin composition containing a styrene- (meth) acrylic acid copolymer (A) and an MBS resin (B) contains styrene- (meth). By setting the dispersed particle size of the MBS resin (B) dispersed in the sea phase of the meta) acrylic acid copolymer (A) within a specific range, heat resistance, toughness, and moldability that could not be achieved by conventional techniques can be achieved. We have found that a heat-resistant styrene-based resin composition having a balance can be obtained, and further, by using the heat-resistant styrene-based resin composition, a foamed sheet having an excellent balance of heat resistance, toughness, and moldability can be obtained. The invention was completed.

That is, the present invention is as shown in the following (1) to (8).
(1) A styrene- (meth) acrylic acid copolymer (A), a copolymer having a butadiene-based rubber core phase and a methyl methacrylate monomer and a styrene-based monomer as main components in the shell phase. A heat-resistant styrene-based resin composition containing the MBS resin (B).
The MBS resin (B) is dispersed as an island phase in the sea phase composed of the copolymer (A), and the weight average circle of the rubber island phase of the MBS resin (B) obtained from the image observation of the electron micrograph. A heat-resistant styrene-based resin composition having an equivalent particle size of 120 nm or more and a number ratio of a circle-equivalent particle size of 100 nm or more of 40% or more.
(2) When the total amount of the copolymer (A) and the MBS resin (B) is 100% by mass, the content of the copolymer (A) is 70 to 99% by mass, and the MBS resin (2). The heat-resistant styrene resin composition according to (1) above, wherein the content of B) is 1 to 30% by mass.
(3) The content of the styrene-based monomer unit when the total amount of the styrene-based monomer unit and the (meth) acrylic acid monomer unit contained in the copolymer (A) is 100% by mass. The heat-resistant styrene resin composition according to (1) or (2) above, wherein the content is 80 to 99% by mass and the content of the (meth) acrylic acid monomer unit is 1 to 20% by mass.
(4) The heat-resistant styrene resin composition according to any one of (1) to (3) above, wherein the copolymer (A) has a weight average molecular weight (Mw) of 100,000 to 400,000.
(5) The heat-resistant styrene resin composition according to any one of (1) to (4) above, wherein the Vicat softening temperature is 110 ° C. or higher.
(6) A molded product obtained by molding the heat-resistant styrene resin composition according to any one of (1) to (5) above.
(7) A foamed sheet obtained by molding the heat-resistant styrene resin composition according to any one of (1) to (5) above.
(8) A food packaging container formed by molding the foam sheet according to (7) above.

Since the heat-resistant styrene resin composition of the present invention has an excellent balance between heat resistance, toughness, and moldability, it can be particularly suitably used as a food container for a microwave oven, and a food container with less cracking can be obtained. can.

Hereinafter, the present invention will be described in detail.

<Heat-resistant styrene resin composition>
The heat-resistant styrene-based resin composition of the present invention comprises a styrene- (meth) acrylic acid copolymer (A), a butadiene-based rubber as the core phase, and a methyl methacrylate monomer and a styrene-based monomer as the shell phase. Includes MBS resin (B), which is a copolymer containing styrene as a main component.

The heat-resistant styrene resin composition of the present invention has a content of the polymer (A) of 70 when the total amount of the copolymer (A) and the MBS resin (B) is 100% by mass. The content of the MBS resin (B) is preferably 1 to 30% by mass, and the content of the copolymer (A) is 75 to 97% by mass, and the MBS resin (B) is contained. ) Is more preferably 3 to 25% by mass, the polymer (A) is 80 to 95% by mass, and the MBS resin (B) is 5 to 20% by mass. % Is particularly preferable. When the content of the MBS resin (B) is less than 1% by mass, the effect of improving brittleness and moldability is small, and when the content of the MBS resin (B) exceeds 20% by mass, the fluidity is too low. , Moldability is reduced.

The melt mass flow rate (MFR) of the heat-resistant styrene resin composition of the present invention measured under the conditions of 200 ° C. and 49 N load is preferably 0.1 to 10 g / 10 minutes, preferably 0.2 to 5. It is more preferably 0 g / 10 minutes, and particularly preferably 0.3 to 3.0 g / 10 minutes. If the melt mass flow rate (MFR) is less than 0.1 g / 10 minutes, the productivity during extrusion molding may deteriorate, and if it exceeds 10 g / 10 minutes, the mechanical strength may decrease.

The Vicat softening temperature of the heat-resistant styrene 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. If the Vicat softening temperature is less than 110 ° C., the heat resistance of the molded product obtained from the heat-resistant styrene resin composition may be insufficient.

The melt tension (MT) of the heat-resistant styrene resin composition of the present invention measured at 200 ° C. is preferably 10 gf or more, and more preferably 15 gf or more. When the melt tension is less than 10 gf, the effect of improving the moldability is small.

In the heat-resistant styrene resin composition of the present invention, the MBS resin (B) is dispersed as an island phase in the sea phase composed of the copolymer (A), which can be obtained by observing an image of an electron micrograph. The weight average circle-equivalent particle size of the rubber island phase of the MBS resin (B) is 120 nm or more, and the number ratio of the circle-equivalent particle diameters of 100 nm or more is 40% or more. The particle size corresponding to the weight average circle of the rubber island phase of the MBS resin (B) is preferably 150 nm or more, and particularly preferably 200 nm or more. The number ratio of the particle size corresponding to a circle having a diameter of 100 nm or more is preferably 50% or more, and particularly preferably 60% or more. When the weight average circle-equivalent particle diameter and the number ratio of the circle-equivalent particle diameters of 100 nm or more are out of the above range, the brittleness improving effect of the present invention cannot be obtained.

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

Examples of the styrene-based monomer include substituted styrenes such as styrene, α-methylstyrene, o-, m-, and p-methylstyrene, and one or a mixture of two or more of these may be used, but styrene is preferable. Is.

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

Examples of the vinyl-based monomer copolymerizable with the styrene-based monomer and the (meth) acrylic acid monomer include methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, and methacryl. Acrylic monomers such as butyl acid acid, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, N-methylmaleimide, N-ethylmaleimide, N-butylmaleimide, N-octylmaleimide, N-isopropylmaleimide, N-phenylmaleimide , N-cyclohexyl maleimide and other maleimide-based monomers, maleic anhydride, itaconic anhydride, citraconic anhydride and other unsaturated carboxylic acid anhydrides, and one or more of these may be used in combination. 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. Further, as the solvent, 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 can be used. As a mode of the reactor, a continuous polymerization method in which a completely mixed reactor, a plug flow reactor, a loop reactor and the like are combined is preferably used.

The styrene- (meth) acrylic acid copolymer (A) of the present invention is a styrene-based monomer when the total amount of the styrene-based monomer unit and the (meth) acrylic acid monomer unit is 100% by mass. The content of the unit is preferably 80 to 99% by mass, the content of the (meth) acrylic acid monomer unit is preferably 1 to 20% by mass, and the content of the styrene-based monomer unit is 85 to 98. It is more preferably by mass% and the content of the (meth) acrylic acid monomer unit is 2 to 15% by mass, and the content of the styrene-based monomer unit is 87 to 96% by mass and (meth). ) It is particularly preferable that the content of the acrylic acid monomer unit is 4 to 13% by 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 is insufficient. When it exceeds 20% by mass, the moldability of the heat-resistant styrene resin composition and the obtained foamed sheet is lowered. The content of the (meth) acrylic acid monomer unit can be adjusted by adjusting the concentration of the (meth) acrylic acid monomer in the raw material liquid in the polymerization step.

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 120,000 to 350,000, and 150,000 to 30. It is particularly preferable that it is 10,000. If the Mw is less than 100,000, the strength is insufficient, and if the Mw exceeds 400,000, the fluidity decreases. Mw of the styrene- (meth) acrylic acid copolymer is the reaction temperature in the polymerization step, the residence time, the type and amount of the polymerization initiator, the type and amount of the chain transfer agent, and the type and amount of the solvent used in the polymerization. It can be adjusted by such as.

<MBS resin (B)>
The MBS resin (B) of the present invention has a so-called core-shell structure, which is a copolymer having a butadiene-based rubber core phase and a methyl methacrylate-based monomer and a styrene-based monomer as main components in the shell phase. It is a methyl-butadiene-styrene copolymer.

Examples of the butadiene rubber constituting the core phase include polybutadiene, styrene-butadiene rubber, acrylonitrile-butadiene copolymer rubber, and butadiene-acrylic copolymer rubber, and polybutadiene and styrene-butadiene copolymer are preferable. ..

Further, the shell phase is formed by grafting a copolymer containing a methyl methacrylate monomer and a styrene monomer as main components on the butadiene-based rubber, and all the monomer units of the copolymer to be grafted are formed. The total ratio of the methyl methacrylate monomer and the styrene monomer to the ratio is preferably 90% by mass or more, more preferably 92% by mass or more, and particularly preferably 94% by mass or more. Examples of the monomer unit other than the methyl methacrylate monomer and the styrene monomer include (meth) acrylic acid esters such as ethyl (meth) acrylate and butyl (meth) acrylate, from the viewpoint of improving fluidity. Therefore, butyl acrylate is preferable.

The rubber content contained in the MBS resin (B) of the present invention is preferably 60 to 98% by mass, more preferably 70 to 95% by mass, and particularly preferably 80 to 90% by mass. .. When the rubber content is less than 60% by mass, the reinforcing effect is small, and when the rubber content exceeds 98%, the sea phase made of the styrene- (meth) acrylic acid copolymer (A) and the MBS resin (B). ) Is not preferable because the compatibility with the rubber island phase is reduced.

<Manufacturing method of heat-resistant styrene resin composition>
Examples of the method for producing the heat-resistant styrene resin composition of the present invention include a method in which the styrene- (meth) acrylic acid copolymer (A) and the MBS resin (B) are collectively blended and melt-extruded. Examples thereof include a method in which a masterbatch containing the MBS resin (B) is prepared in advance, and later blended with the styrene- (meth) acrylic acid copolymer (A) and melt-extruded.

If necessary, another thermoplastic resin or rubber reinforcing material can be added to the heat-resistant styrene resin composition of the present invention as long as the effects of the present invention are not impaired.

Specific examples of the thermoplastic resin include polystyrene, impact resistant polystyrene (HIPS), syndiotactic polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, and methacrylate-methyl methacrylate-styrene copolymer. Combined, polystyrene resin such as butyl methacrylate-styrene copolymer, maleic anhydride-styrene copolymer, maleimide-styrene copolymer, α-methylstyrene-styrene copolymer, polypropylene, propylene-α-olefin copolymer weight Examples thereof include polymer resins such as coalesced and aliphatic polyester resins such as poly L-lactic acid, poly D-lactic acid, poly D, and L-lactic acid, and one or a combination of two or more thereof can be used.

Specific examples of the rubber reinforcing material include natural rubber, polybutadiene, polyisoprene, polyisobutylene, polychloroprene, polysulfide rubber, thiocol rubber, acrylic rubber, urethane rubber, silicone rubber, epichlorohydrin rubber, styrene-butadiene block copolymer, and the like. 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-based rubbers such as added styrene-isoprene block copolymers and hydrogenated styrene-isoprene-styrene block copolymers, as well as olefin-based rubbers such as ethylene propylene rubber, ethylene propylene diene rubber, and linear low-density polyethylene-based elastomers. Can be used in combination of one or more of these.

The heat-resistant styrene resin composition of the present invention contains, as additives, antioxidants such as phosphorus, phenol and amine, higher fatty acids such as stearic acid, and lubricants such as salts thereof and ethylene bisstearylamide. Add plasticizers such as liquid paraffin, polyethylene wax, microcrystallin wax, lubricants, inorganic fillers, ultraviolet absorbers, antistatic agents, flame retardants, colorants, pigments, deodorants, antifogging agents, etc. as necessary. be able to.

<Manufacturing method of foam sheet>

As a method for producing a foamed sheet of the present invention, a known extruded foamed sheet manufacturing method can be used. Specifically, two single-screw extruders and twin-screw extruders are arranged in series, and the foaming agent is melt-kneaded together with the foam nucleating agent in the first extruder and cooled by the second extruder. Examples thereof include 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 to foam under reduced pressure.

Examples of the foaming agent 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, and the like. Physical foaming agents such as halogenated hydrocarbons such as 1,1-difluoro-chloride and methylene chloride can be used. Further, a decomposable foaming agent such as azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate and citric acid, an inorganic gas such as carbon dioxide and nitrogen, and water can also be used. Although these foaming agents can be appropriately mixed and used, butane is often used industrially, and is a mixture of isobutane and normal butane from the viewpoint of foam extrudability, secondary moldability of foam sheet, and foaming agent. It is preferable to use butane. Since butane has a slow permeation rate with respect to polystyrene resin, it usually remains in the foamed sheet in an amount of about 1 to 3% by mass immediately after foam extrusion. Since this residual amount affects the secondary foam thickness and thermoforming property in the secondary molding, it is appropriately adjusted by providing a certain aging period.

Examples of the effervescent nucleating agent include inorganic powders such as talc, calcium carbonate, and clay, which can be used alone or as a mixture. Among them, talc is most preferable because it has a large effect of reducing the bubble diameter and is inexpensive. The method of adding the foam nucleating agent is not particularly limited, and the foam nucleating agent may be added directly to the supply hole of the extruder, or may be added together with the resin. It is also possible to prepare a masterbatch using a styrene homopolymer, a styrene-methyl methacrylate copolymer or the like as a base material, and supply the masterbatch using the masterbatch. The amount of the foam nucleating agent added is usually 0.1 to 5% by mass. Further, the masterbatch may be pre-blended with a higher fatty acid or a metal salt of the higher fatty acid. Even if a lubricant such as ethylene bisstearylamide, a spreading agent such as liquid paraffin or silicone oil, other surfactants, an antistatic agent, an antioxidant, a plasticizer, a weathering agent, a pigment, etc. are contained. good.

The thickness of the foamed 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 is generally 5 to 500 kg / m ³ , preferably 50 to 400 kg / m ³ , and more preferably 60 to 300 kg / m ³ . If the density of the foamed sheet is less than 5 kg / m ³ , the strength of the container after the secondary molding is lowered. When the density of the foamed sheet exceeds 500 kg / m ³ , it is not desirable from the viewpoint of weight reduction and heat insulating property. The density D (kg / m ³ ) can be calculated by D = S / T from the basis weight S (g / m ² ) of the foamed sheet and the sheet thickness T (mm).

Further, in the foamed sheet of the present invention, a surface layer called a so-called skin layer, which has a lower density than the central portion in the thickness direction, can be provided 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 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 side or both sides thereof. The thermoplastic resins constituting the sheets and films include polystyrene-based resins such as polystyrene and high-impact polystyrene, polypropylene-based resins, polyester-based resins, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and ethylene-vinyl acetate. Examples thereof include a copolymer. The thickness of the sheet or film is not particularly limited, but is preferably 0.01 mm to 0.3 mm.

The foamed sheet of the present invention uses known thermoforming methods such as vacuum molding, pressure molding, matched molding, reverse draw molding, air slip molding, ridge molding, plug and ridge molding, plug assist molding, and plug assist reverse draw molding. It can be used to process containers of various shapes and sizes such as trays, lunch containers, bowl containers, cups, and box molds with lids.

The container obtained by molding the foamed sheet of the present invention is suitably used as a food container for a microwave oven because the container does not deform or swell even when cooked in a microwave oven with food in it. can.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

<Manufacturing 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 form a polymerization step.

1st reactor: Completely mixed reactor with stirring blade of 39 L volume 2nd reactor: Completely mixed reactor with stirring blade of 39 L volume 3rd reactor: Plug flow reactor with static mixer of 16 L volume

The conditions for each reactor were as follows.

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 formed in the flow direction.

The following materials were used as the raw material liquid.

10 parts by mass of ethylbenzene and 2,2 bis (4,5-t-butylperoxycyclohexyl) as a polymerization initiator with respect to 100 parts by mass of a monomer composition of 94.8% by mass of styrene and 5.2% by mass of methacrylic acid. 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 continuously charged to the second reactor set at 125 ° C. for polymerization. .. The polymerization conversion rate at the outlet of the second reactor was 65%. Further, the polymerization was allowed to proceed until the polymerization conversion rate reached 70% in the third reactor adjusted so as to have a temperature gradient of 125 to 130 ° C.
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, extruded into strands, cooled, and then cut into pellets. 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 Using the following raw material liquid, the supply speed of the raw material liquid was set to 12.0 kg / hr, and the temperature conditions of the 1 to 3 reactors were changed as follows. Other than that, it was the same as the production of S-1. The characteristics are shown in Table 1.

<Raw material solution>
10 parts by mass of ethylbenzene and 2,2 bis (4,5-t-butylperoxycyclohexyl) 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. Raw material liquid mixed with 0.02 parts by mass of propane

<Conditions>
First reactor: [Reaction temperature] 128 ° C
Second reactor: [Reaction temperature] 138 ° C
Third reactor: [Reaction temperature] Adjusted so that a temperature gradient of 120 to 125 ° C is formed in the flow direction.

(3) Production of styrene-methacrylic acid copolymer S-3 Using the following raw material liquid, the supply speed of the raw material liquid was set to 12.0 kg / hr, and the temperature conditions of the 1 to 3 reactors were changed as follows. Other than that, it was the same as the production of S-1. The characteristics are shown in Table 1.

<Raw material solution>
15 parts by mass of ethylbenzene and 0.025 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 91.7% by mass of styrene and 8.3% by mass of methacrylic acid. , Raw material liquid mixed with 0.1 part by mass of α-methylstyrene dimer as a chain transfer agent

<Conditions>
First reactor: [Reaction temperature] 124 ° C
Second reactor: [Reaction temperature] 138 ° C
Third reactor: [Reaction temperature] Adjusted so that a temperature gradient of 125 to 138 ° C is formed in the flow direction.

<Examples 1 to 9, Comparative Examples 1 to 2>
The styrene-methacrylic acid copolymer (A) (S-1 to 3) produced by the above method, MBS resin (B), and high-impact polystyrene (C) are mixed in a mass% ratio shown in Table 2 with a Henshell mixer. The mixture was mixed and melt-compounded with a twin-screw extruder (KTX30α manufactured by Kobe Steel, Ltd.) set at 230 to 260 ° C. Table 2 shows the solid physical characteristics.

The following were used as the MBS resin (B) and high-impact polystyrene (C).
<MBS resin (B)>
MBS-1 Product name: "Kaneka B-564" Kaneka Corporation Rubber content 79%
MBS-2 Product name: "Kaneka M-511" Kaneka Corporation Rubber content 85%
MBS-3 Product name: "Metabrene C-223A" Mitsubishi Chemical Corporation Rubber content 75%
MBS-4 Product name: "Metabrene C-215A" Mitsubishi Chemical Corporation Rubber content 73%
<High Impact Polystyrene (C)>
Product name: "Toyo Styrol 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 a screw diameter of 40 mmφ and 50 mmφ to manufacture a foamed sheet. First, 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 is uniformly mixed with 100 parts by mass of the melt-compounded resin, and the screw diameter is 40 mmφ. Supplied to the extruder. Further, butane as a foaming agent was press-fitted 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.
After that, it is transferred to an extruder having a screw diameter of 50 mmφ via 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 has a lip opening of 0.6 mm. It was extruded from a circular die having a diameter of 40 mm at a discharge rate of 10 kg / hr, taken along with a cooled cylinder having a diameter of 152 mm, and cut with a cutter at one point at the lower part of the circumference to obtain a foamed sheet. The thickness of the obtained foamed sheet was 1.7 mm, and the density was 120 kg / m ³ . The characteristics are shown in Table 2.

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

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

The resin properties were evaluated by the following method.
(3) Particle size equivalent to weight circle, number ratio of particle size equivalent to circle The resin composition was cut into ultrathin sections of 80 nm, stained with osmium tetroxide, and transmitted with a transmission microscope (H-7500 manufactured by Hitachi High-Technologies). A photograph with a magnification of 15,000 times was taken using the image, and the rubber dispersed particles existing in an area of 100 μm ² were binarized using the image analysis software "A image-kun" manufactured by Asahi Kasei Engineering Co., Ltd. The diameter of a circle having the same area as the area of the obtained dispersed particles (circle equivalent particle diameter: Di) was obtained, and the weight average circle equivalent particle diameter (Dv) was obtained from the following formula. Furthermore, the number ratio of the particle size equivalent to a circle of 100 nm or more was obtained from the number of particle size equivalent to each circle obtained. In addition, regarding the aggregated rubber dispersed particles, the aggregated form was counted as one, but the aggregate having a particle size equivalent to a circle exceeding 500 nm was excluded.

The physical characteristics were evaluated by the following method.
(4) Melt mass flow rate Obtained based on JIS K7210 under the conditions of 200 ° C. and 49N load.
(5) Vicat softening temperature A test piece was prepared using an injection molding machine, and the temperature was determined based on JIS K7206 under the condition of a 50 N load.
(6) Deflection temperature under load A test piece was prepared using an injection molding machine and determined under the condition of 1.8 MPa stress based on JIS K7191.
(7) Melt tension (MT)
Capillograph 1B type (manufactured by Toyo Seiki Co., Ltd.) is used, barrel temperature 200 ° C., barrel diameter 9.55 mm, capillary length: L = 10 mm, capillary diameter: D = 1 mm (L / D = 10), extrusion in the barrel. The resin is extruded at a speed of 10 mm / min, the load measuring unit is set 60 cm below the die, the strand-shaped resin flowing out of the capillary is set in the winder, and the winding wire speed is gradually increased from 4 m / min. And measure the load until the strand breaks. Since the load stabilizes at a constant value as the take-up wire speed is increased, the range in which the load is stable is averaged to obtain the melt tension value (MT).

The characteristics of the foamed sheet were evaluated by the following method.
(8) Sheet Impact Strength A film impact tester BU-302 (manufactured by Tester Sangyo Co., Ltd.) was used to measure the impact spherical surface R12.7 mm. The measurement was performed 20 times each on the front surface and the back surface of the foam sheet, and the average value of all was taken as the sheet impact strength.
(9) Formability A cup-shaped container having a diameter of 100 mm and a depth of 60 mm was thermoformed from the foam sheet using a single-shot molding machine. Keep the heater temperature constant at 280 ° C, change the heating time in 0.5 second increments, check the heating time width that does not cause holes or holes in the container, and if the moldable time width is 10 seconds or more, ◎, 8 The deep draw moldability was evaluated by ◯ in the case of ~ 10 seconds, Δ in the case of 5 to 8 seconds, and × in the case of 5 seconds or less.
(10) Container strength (cracking)
For the container obtained under the above moldable conditions, use a small tabletop tester Ez-test (manufactured by Shimadzu Corporation, model: Ez-SX), and use two plates at both ends of the container in the TD direction. In the sandwiched state, one end is compressed at a speed of 500 m / mm, and the one with no crack at the time of displacement of 30 mm is ◎, the one with crack only inside the foamed cross section is ○, and the one with cracked on the surface layer of the foamed cross section is cracked. The strength of the container was evaluated as Δ, and x for the entire cracking from the surface layer to the inside of the foamed cross section.
(11) Range-up resistance deformation The container obtained under the above moldable conditions is heated in a microwave oven with an output of 1500 W for 70 seconds, the surface condition is observed, and the container is not deformed or raised at all. The heat resistance was evaluated as ○ for a part of the container with slight deformation or ridges, △ for those with large deformations or ridges in the container, and × for those with a deformed or perforated container. ..

In the heat-resistant styrene resin composition of the example, the particle size equivalent to the weight average circle of the rubber island phase of the MBS resin (B) is larger than that of Comparative Examples 1 and 2, and the particle size corresponding to the circle is 100 nm or more. Since the number ratio is large, the strength and moldability are greatly improved while maintaining the heat resistance of the foamed sheet.

Since the heat-resistant styrene-based resin composition of the present invention has an excellent balance between heat resistance, strength, and moldability, the extruded sheet produced using the heat-resistant styrene-based resin composition can be formed into various shapes such as deep-drawn containers. It can be processed and can be used for a wide range of purposes. In particular, when used as a food container for a microwave oven, it is possible to obtain a food container with less cracking, so that cracking during product transportation and fitting with the food container lid material is reduced, resulting in food waste loss. It leads to reduction.

Claims (11)

Styrene- (meth) acrylic acid copolymer (A), MBS resin (MBS resin) in which the core phase is a butadiene rubber and the shell phase is a copolymer mainly composed of a methyl methacrylate monomer and a styrene monomer. A heat-resistant styrene-based resin composition containing B).
The MBS resin (B) is dispersed as an island phase in the sea phase composed of the copolymer (A), and the weight average circle of the rubber island phase of the MBS resin (B) obtained from the image observation of the electron micrograph. A heat-resistant styrene-based resin composition having an equivalent particle diameter of 120 nm or more and a number ratio of circle-equivalent particle diameters of 100 nm or more being 40% or more and 78% or less. Styrene- (meth) acrylic acid copolymer (A), MBS resin (MBS resin) in which the core phase is a butadiene rubber and the shell phase is a copolymer mainly composed of a methyl methacrylate monomer and a styrene monomer. A heat-resistant styrene-based resin composition containing B).
The MBS resin (B) is dispersed as an island phase in the sea phase composed of the copolymer (A), and the weight average circle of the rubber island phase of the MBS resin (B) obtained from the image observation of the electron micrograph. The equivalent particle size is 120 nm or more, and the number ratio of the equivalent particle size of a circle of 100 nm or more is 40% or more.
When the total amount of the copolymer (A) and the MBS resin (B) is 100% by mass, the content of the copolymer (A) is 70 to 99% by mass, and the MBS resin (B) has a content of 70 to 99% by mass. A heat-resistant styrene resin composition having a content of 5 to 30% by mass. Styrene- (meth) acrylic acid copolymer (A), MBS resin (MBS resin) in which the core phase is a butadiene rubber and the shell phase is a copolymer mainly composed of a methyl methacrylate monomer and a styrene monomer. A heat-resistant styrene-based resin composition containing B).
The MBS resin (B) is dispersed as an island phase in the sea phase composed of the copolymer (A), and the weight average circle of the rubber island phase of the MBS resin (B) obtained from the image observation of the electron micrograph. The equivalent particle size is 120 nm or more, and the number ratio of the equivalent particle size of a circle of 100 nm or more is 40% or more.
When the total amount of the styrene-based monomer unit and the (meth) acrylic acid monomer unit contained in the copolymer (A) is 100% by mass, the content of the styrene-based monomer unit is 91. A heat-resistant styrene resin composition having an amount of 7 to 99% by mass and a content of (meth) acrylic acid monomer unit of 1 to 8.3% by mass. The heat-resistant styrene resin composition according to any one of claims 1 to 3, wherein the copolymer (A) has a weight average molecular weight (Mw) of 100,000 to 400,000. The heat-resistant styrene resin composition according to any one of claims 1 to 4, wherein the copolymer (A) has a number average molecular weight (Mn) of 62,000 to 121,000. The invention according to any one of claims 1 to 5 , wherein the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the copolymer (A) is 2.60 to 2.90. Heat resistant styrene resin composition. The invention according to any one of claims 1 to 6 , wherein the ratio (Mz / Mw) of the Z average molecular weight (Mz) to the weight average molecular weight (Mw) of the copolymer (A) is 1.65 to 1.87. Heat resistant styrene resin composition. The heat-resistant styrene resin composition according to any one of claims 1 to 7 , wherein the Vicat softening temperature is 110 ° C. or higher. A molded product obtained by molding the heat-resistant styrene resin composition according to any one of claims 1 to 8 . A foamed sheet obtained by molding the heat-resistant styrene resin composition according to any one of claims 1 to 8 . A container for food packaging formed by molding the foam sheet according to claim 10 .