JP6271147B2 - Heat-resistant resin foam sheet and container - Google Patents

Description

  The present invention provides a heat-resistant resin foam sheet that is excellent in the balance between heat resistance, strength, and moldability, and that can be suitably used particularly as a food container for microwave ovens.

  Polystyrene resin foam sheets are lightweight, heat-insulating, and have a beautiful appearance, so they are processed into food trays, lunch boxes, instant noodle cups, etc., and are widely used in food packaging applications.

  On the other hand, with the recent spread of microwave ovens, prepared food containers and lunch boxes are often required to be compatible with microwave ovens, and these food containers are required to have high heat resistance.

  However, as is well known, a foamed container made of a polystyrene resin alone has insufficient heat resistance. Therefore, when the foamed container is heated in a microwave oven, significant thermal deformation occurs.

  As a method for improving the heat resistance of a polystyrene-based resin, Patent Document 1 discloses a foamed molded article using a styrene-methacrylic acid copolymer, but brittleness when the methacrylic acid ratio is increased becomes a problem. . As a method for improving brittleness, Patent Document 2 discloses a styrene-based resin foam sheet made of a styrene-methacrylic acid and a styrene-butadiene copolymer. Absent.

  Patent Document 3 discloses a method of using a blend resin of polystyrene and polyphenylene ether as a method for achieving both heat resistance and toughness, but is unsuitable for food applications because of the odor peculiar to polyphenylene ether. Further, as a method for improving odor, Patent Document 4 discloses a method containing zeolite or the like, but since a large amount of inorganic substances are present, a decrease in toughness and poor appearance of the foam are problematic.

  Furthermore, Patent Document 5 attempts to improve heat resistance, low temperature brittleness, compoundability and thermoformability by using a copolymer resin of polyphenylene ether and an aromatic vinyl-acrylic acid monomer and a blend resin of polystyrene. However, the strength and formability were not sufficient.

Japanese Patent Laid-Open No. 17-247888 JP 2000-136257 A Japanese Patent Laid-Open No. 3-157432 JP 2008-94919 A JP2012-140549A

  The present inventors have conducted extensive research to achieve the problem of excellent balance between heat resistance, strength, and moldability of the foamed sheet using the polystyrene-based resin described above. As a result, styrene having a specific composition is obtained. -A combination of methacrylic acid copolymer and polyphenylene ether, with a specific weight average molecular weight (Mw), found that a heat resistant resin foam sheet having an excellent balance of heat resistance, strength and moldability can be obtained. It was completed.

That is, this invention is a place shown to following (1)-(7).
(1) A styrene-methacrylic acid copolymer having a methacrylic acid content of 2 to 7% by mass, 97 to 15 parts by mass, 3 to 25 parts by mass of polyphenylene ether, and 0 to 60 parts by mass of polystyrene. A heat-resistant resin foam sheet having Mw) of 160,000 or more. However, the total amount of each resin component in the heat resistant resin is 100 parts by mass.
(2) The heat resistant resin foamed sheet according to (1), wherein the Z average molecular weight (Mz) / weight average molecular weight (Mw) is 1.6 or more.
(3) The heat resistant resin foam sheet according to (1) or (2), wherein the heat resistant resin contains 1 to 10 parts by mass of a rubber reinforcing material.
(4) The heat-resistant resin foam sheet according to (3), wherein the rubber reinforcing material is high impact polystyrene.
(5) The heat-resistant resin foam sheet according to (4), wherein the rubber content of the high-impact polystyrene is 6 to 12% by mass.
(6) The heat-resistant resin foam sheet according to the above (1) to (5), wherein a thermoplastic resin sheet or film is laminated on one side or both sides.
(7) A container formed by molding the heat-resistant resin foam sheet according to (1) to (6).

  Since the heat resistant resin foam sheet of the present invention is excellent in the balance between heat resistance, strength and moldability, it is possible to provide a food container having sufficient heat resistance and strength even when the foam sheet is reduced in weight. Moreover, since it can be processed into various shapes such as deep drawing, it can be used in a wide range of applications as a food container for microwave ovens.

  Hereinafter, the present invention will be described in detail.

  The styrene-methacrylic acid copolymer of the present invention can be obtained by copolymerizing a styrene monomer and a methacrylic acid monomer by heat or radical polymerization with a peroxide catalyst. The polymerization method is bulk polymerization, solution polymerization, suspension polymerization. For example, a known styrene polymerization method can be used. The content of methacrylic acid in the styrene-methacrylic acid copolymer is 2 to 7% by mass, preferably 3 to 6% by mass. When the content of methacrylic acid is less than 2% by mass, the effect of improving heat resistance cannot be obtained. Moreover, when content of methacrylic acid exceeds 7 mass%, since the intensity | strength and moldability of a heat resistant resin foam sheet become inadequate, it is unpreferable. Content of methacrylic acid can be adjusted with the methacrylic acid density | concentration of the raw material liquid in a superposition | polymerization process.

  The weight average molecular weight (Mw) of the styrene-methacrylic acid copolymer of the present invention is preferably 160,000 or more, more preferably 200,000 or more, and particularly preferably 220,000 or more. If Mw is less than 160,000, the strength and formability of the heat-resistant resin foam sheet will be insufficient. Mw of styrene-methacrylic acid copolymer is adjusted by reaction temperature, residence time, type and amount of polymerization initiator in polymerization process, type and amount of chain transfer agent, type and amount of solvent used during polymerization, etc. I can do it.

The polyphenylene ether of the present invention is produced by oxidative coupling of a phenol compound. The oxidative coupling reaction catalyst of polyphenylene ether is not particularly limited, but at least one heavy metal compound such as copper, manganese, cobalt and the like is used (US Pat. Nos. 4,042,056 and 3,306,874). No. 3,306,875, etc.).
Specific examples of phenol 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-t-butylphenol and the like can be mentioned. Two or more of the phenol compounds may be copolymerized, and two or more homopolymers or copolymers obtained may be used in combination. Among the above phenol compounds, 2,6-dimethylphenol is particularly preferable. Therefore, in the present invention, poly (2,6-dimethyl-1,4-phenylene) ether obtained by polymerizing this gives good results.
The molecular weight of the polyphenylene ether in the present invention is not particularly limited, but preferably has an intrinsic viscosity of 0.3 dl / g or more (at a temperature of 25 ° C. in a solvent chloroform). If it is less than 0.3 dl / g, the mechanical strength is inferior. The intrinsic viscosity is preferably 0.3 to 0.6 dl / g.

  The polystyrene of the present invention is a homopolymer of styrene and can be obtained by known methods such as radical polymerization and anionic polymerization. Although molecular weight is not specifically limited, It is preferable that a weight average molecular weight (Mw) is 200,000 or more.

  The heat resistant resin of the present invention is obtained by blending the styrene-methacrylic acid copolymer, polyphenylene ether, and polystyrene. These resins have relatively good compatibility. However, since the glass transition temperature difference between polyphenylene ether and other components is particularly large, dispersion tends to be insufficient, and in this case, the effects of the present invention may not be obtained. Therefore, it is desirable to melt and compound before introducing into the foaming extruder. As a method of melt compounding, there are a method of compounding all of styrene-methacrylic acid copolymer, polyphenylene ether and polystyrene, and a compound of styrene-methacrylic acid copolymer before compounding only polyphenylene ether and polystyrene and introducing them into a foaming extruder. And a method of dry blending in a pellet state.

  The heat resistant resin of the present invention contains 97 to 15 parts by mass of styrene-methacrylic acid copolymer in 100 parts by mass of the resin composition, more preferably 97 to 50 parts by mass, and still more preferably 97 to 75 parts by mass. It is. If the styrene-methacrylic acid copolymer exceeds 97 parts by mass, the effect of improving heat resistance may not be obtained, and if it is less than 15 parts by mass, the strength and moldability are insufficient.

  The heat resistant resin of the present invention contains 3 to 25 parts by mass of polyphenylene ether in 100 parts by mass of the resin composition, more preferably 3 to 15 parts by mass, and further preferably 3 to 9 parts by mass. When the polyphenylene ether is less than 3 parts by mass, the heat resistance is insufficient, and when it exceeds 25 parts by mass, the moldability is reduced and the odor is deteriorated, so a deodorant is required, resulting in the strength of the foam sheet. Decreases. As the polyphenylene ether, a polyphenylene ether called modified PPE and an alloy of other resins can be used. In that case, the content of the polyphenylene ether contained in the modified PPE is adjusted to the above range. .

  The heat resistant resin of the present invention contains 0 to 60 parts by mass of polystyrene in 100 parts by mass of the resin composition. By containing polystyrene, the dispersibility of the styrene-methacrylic acid copolymer and polyphenylene ether can be improved. However, if it exceeds 60 parts by mass, the strength and heat resistance are lowered, which is not preferable.

  The weight average molecular weight (Mw) of the heat resistant resin of the present invention is 160,000 or more, preferably 180,000 or more, and more preferably 200,000 or more. If Mw is less than 160,000, sufficient strength and formability cannot be obtained.

  The ratio (Mz / Mw) of the Z average molecular weight (Mz) and the weight average molecular weight (Mw) of the heat resistant resin of the present invention is preferably 1.6 or more. When Mz / Mw is less than 1.6, moldability is lowered.

  The heat resistant resin of the present invention preferably contains 1 to 10 parts by mass of a rubber reinforcing material in 100 parts by mass of the resin. The rubber reinforcing material is a rubbery polymer having styrene and butadiene as structural units, specifically, high impact polystyrene, styrene-butadiene copolymer, styrene-butadiene-styrene copolymer, styrene-ethylene- Examples include butylene-styrene copolymer and methyl methacrylate-butadiene-styrene copolymer. Among them, high impact polystyrene is preferable in terms of the balance between heat resistance and reinforcing effect. The rubber content of the high impact polystyrene is preferably 5 to 12% by mass, and more preferably 7 to 12% by mass.

  The heat-resistant resin of the present invention includes additives such as phosphorus-based, phenol-based, and amine-based stabilizers, higher fatty acids such as stearic acid, zinc stearate, calcium stearate, and magnesium stearate, and salts thereof and ethylene bisstearyl. Lubricants such as amides, plasticizers such as liquid paraffin, deodorizers such as zeolite, activated carbon and zirconium phosphate can be added.

  The heat-resistant resin of the present invention can be blended with punched scraps called skeletons generated when the foamed sheet is secondarily molded and recycled pellets thereof within a range not impairing the effects of the present invention.

  The Vicat softening temperature of the heat resistant resin of the present invention is preferably 110 to 130 ° C, more preferably 115 to 125 ° C. When the Vicat softening temperature is less than 110 ° C., the range-up deformation of the container obtained by thermoforming the heat-resistant resin foam sheet becomes insufficient. When Vicat softening temperature exceeds 130 degreeC, a moldability will fall.

  In order to increase the heat resistance, the heat resistant resin of the present invention includes a styrene-methyl methacrylate copolymer, a styrene-methacrylic acid-methyl methacrylate copolymer, a styrene-maleic anhydride copolymer, and a styrene-maleimide copolymer. Polystyrene resins such as polymers, polyolefin resins such as polypropylene and propylene-α-olefin copolymers, and aliphatic polyester resins such as poly L-lactic acid, poly D-lactic acid, poly D, and L-lactic acid. It can mix | blend in the range which does not impair the effect.

  The heat-resistant resin foam sheet of the present invention can be obtained by melt-extruding the heat-resistant resin together with a foaming agent, and a known method for producing an extruded foam 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 heat resistant 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.

  0.5-4.0 mm is preferable and, as for the thickness of the heat resistant resin foam sheet of this invention, 1.0-3.0 mm is more preferable. When the thickness of the heat resistant resin foam sheet is less than 0.5 mm, the strength and heat insulation of the container after the secondary molding are lowered. When the thickness of the heat-resistant resin foam sheet exceeds 4.0 mm, the temperature unevenness of the sheet tends to occur during the secondary molding, and the moldability deteriorates.

The density of heat-resistant resin foam sheet of the present invention is preferably 50~150kg / ^{m 3,} more preferably 60~130kg / ^{m 3.} When the density of the heat-resistant resin foam sheet is less than 50 kg / m ³ , the strength of the container after the secondary molding is lowered. When the density of the heat-resistant resin foam sheet exceeds 150 kg / m ³ , the container weight becomes heavy, which is not desirable from the viewpoint of weight reduction. 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 the heat resistant resin foam sheet of the present invention, the average cell diameter X in the thickness direction of the sheet is preferably 0.10 to 0.40 mm. If the average cell diameter X in the thickness direction of the sheet is less than 0.10 mm, the formability in the secondary molding is lowered. When the average cell diameter X in the thickness direction of the sheet exceeds 0.40 mm, the appearance of the foamed sheet deteriorates and the strength also decreases.

  The ratio of the average bubble diameter Y in the extrusion direction to the average bubble diameter X in the thickness direction (Y / X) and the ratio of the average bubble diameter Z in the width direction to the average bubble diameter X in the thickness direction (Z / X) are respectively It is preferable that it is 1.0-2.5. If Y / X and Z / X are less than 1.0, drawdown during secondary molding is increased, which is not desirable. Moreover, when Y / X and Z / X exceed 2.5, the flatness of the bubbles is large, and the strength of the foamed sheet may be reduced.

The average bubble diameter X in the thickness direction of the sheet, the average bubble diameter Y in the extrusion direction, and the average bubble diameter Z in the width direction are observed using a scanning electron microscope. Based on the average chord length described in ASTM D2842-06, the following formula can be used.
Average chord length = straight line length / number of bubbles Average bubble diameter = average chord length / 0.616

  In addition, the heat-resistant resin foam sheet of the present invention can be provided with a surface layer called a skin layer having a lower density than the central part 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 heat-resistant resin foam sheet of the present invention can be improved in formability, strength, and rigidity by laminating a thermoplastic resin sheet or film on one or both surfaces. 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. Examples thereof include a copolymer, and a polystyrene resin that can be laminated without using an adhesive layer and has good recyclability is preferable.

  Although there is no restriction | limiting in particular in the thickness of the thermoplastic resin sheet or film laminated | stacked above, 0.01 mm-0.3 mm are preferable. If the thickness of the sheet or film is thin, the effect of improving the physical properties is small, and if it is too thick, it is not desirable from the viewpoint of weight reduction.

  The heat-resistant resin foam sheet of the present invention is a known heat treatment such as vacuum molding, pressure molding, matched mold molding, reverse draw molding, air slip molding, ridge molding, plug and ridge molding, plug assist molding, plug assist reverse draw molding, etc. Using the molding method, it can be processed into various shapes and sizes of containers such as trays, lunch boxes, bowl containers, cups, and box-types with lids.

  The container obtained by molding the heat-resistant resin foam sheet of the present invention does not cause deformation or blistering of the container even when cooking in a microwave oven with food in it. It can be used suitably.

  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>
(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 135 ° C is applied in the flow direction.

  The following were used as the raw material liquid.

  10 parts by mass of ethylbenzene with respect to 100 parts by mass of the monomer composition of 97% by mass of styrene and 3% by mass of methacrylic acid, 0.025 of 2,2bis (4,4-t-butylperoxycyclohexyl) propane as a polymerization initiator Raw material liquid mixed with parts by mass

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 advanced in a third reactor adjusted so as to have a temperature gradient of 125 to 135 ° 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) Manufacture of styrene-methacrylic acid copolymer S-2 Except having used the following raw material liquids, it carried out similarly to manufacture of S-1. The characteristics are shown in Table 1.

<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 95.5% by mass of styrene and 4.5% by mass of methacrylic acid Raw material liquid mixed with 0.025 parts by mass of propane

(3) Production of Styrene-Methacrylic Acid Copolymer S-3 Except that the following raw material liquid was used and the temperature conditions of the first to third reactors were changed as follows, the production was the same as that 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 94.5% by mass of styrene and 5.5% by mass of methacrylic acid, 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.

(4) Production of Styrene-Methacrylic Acid Copolymer S-4 Except that the temperature conditions of the first to third reactors were changed as follows using the following raw material liquid, 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 93% by mass of styrene and 7% by mass of methacrylic acid, 0.02 of 2,2bis (4,4-t-butylperoxycyclohexyl) propane as a polymerization initiator Raw material liquid mixed with parts by mass

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

(5) Manufacture of styrene-methacrylic acid copolymer S-5 Except having used the following raw material liquids, it carried out similarly to manufacture of S-1. The characteristics are shown in Table 1.

<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 99.1% by mass of styrene and 0.9% by mass of methacrylic acid Raw material liquid mixed with 0.02 parts by mass of propane

<Examples 1-14, Comparative Examples 1-7>
The styrene-methacrylic acid copolymer (S-1 to 5) produced by the above method, polystyrene, polyphenylene ether, and rubber reinforcing material are mixed by a Henschel mixer at a mass part ratio shown in Tables 2 to 4, and 230 to 260. It melt-compounded with the twin-screw extruder (Kobe Steel Works make, KTX30 (alpha)) set to ° C. The solid physical properties are shown in Tables 2-4.

The following materials were used as polystyrene, polyphenylene ether, and rubber reinforcement.
<Polystyrene>
GPPS product name: “Toyostyrene HRM12” manufactured by Toyo Styrene Co., Ltd. Mw = 250,000, Mz / Mw = 2.04
<Polyphenylene ether>
Product name: “IUPACE PX100L” Intrinsic viscosity 0.41 g / dl manufactured by Mitsubishi Engineering Plastics
Product name: “IUPACE PX100F” Intrinsic viscosity 0.36 g / dl, manufactured by Mitsubishi Engineering Plastics
Product name: “Noryl EFN 4230-111” manufactured by Subic Innovative Plastics, Polyphenylene ether / polystyrene = 70/30
<Rubber reinforcement>
HIPS1 Product name: “Toyostyrene H848” manufactured by Toyo Styrene Co., Ltd., rubber content 10.0%, rubber particle diameter 1.9 μm
HIPS2 Product name: “Toyostyrene E640N” manufactured by Toyo Styrene Co., Ltd., rubber content 6.2%, rubber particle diameter 2.5 μm
SBS product name: “Tufprene 125” manufactured by Asahi Kasei Chemicals

Next, a foam sheet was produced with a tandem extruder having a screw diameter of 40 mmφ and 50 mmφ. 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 as a blowing agent was injected from the tip of the extruder at a ratio of 2.5 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.
Thereafter, it is transferred to an extruder having a screw diameter of 50 mmφ through a connecting pipe set at 230 ° C., adjusted to a cylinder temperature of 170 to 200 ° C., a resin temperature of 155 to 165 ° 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 characteristics of the foam sheet are shown in Tables 2 to 4.

  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: Shodex GPC-101 manufactured by Showa Denko
Column: Polymer Laboratories PLgel 10 μm MIXED-B, 300 × 7.5 mm
Mobile phase: tetrahydrofuran 1.0 ml / min
Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: differential refractometer The molecular weight at each elution time was calculated from the elution curve of monodisperse polystyrene, and was calculated as the molecular weight in terms of polystyrene.

The solid physical properties were evaluated by the following methods.
(3) Melt Mass Flow Rate A test piece was prepared using an injection molding machine, and was determined under the conditions of 200 ° C. and 49 N load based on JIS K7210.
(4) Vicat softening temperature A test piece was prepared using an injection molding machine, and determined under a condition of 49 N load based on JIS K7206.
(5) 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.
(6) Charpy impact strength A test piece was prepared using an injection molding machine and determined according to JIS K7111.

The characteristics of the foam sheet were evaluated by the following methods.
(7) Thickness Except for 20 mm at both ends of the foamed sheet, positions at intervals of 50 mm in width were used as measurement points. Using the dial thickness gauge Peacock model G (manufactured by Ozaki Mfg. Co., Ltd.) at this measurement point, measuring the thickness to the minimum unit of 0.01 mm while taking care not to deform the test piece, this average value is the thickness of the foam sheet. (Mm).
(8) Density A test piece having a length of 10 cm and a width of 10 cm was carefully cut out from the foamed sheet so that the cell structure of the material was not broken, and calculated from the weight and thickness of the test piece by the following formula.
Density (kg / m ³ ) = weight of test piece (g) / thickness of test piece (mm) × 100
(9) Average cell diameter The average cell diameter X in the thickness direction of the foam sheet, the average cell diameter Y in the extrusion direction, and the average cell diameter Z in the width direction are based on the average chord length measured by the test method of ASTM D2842-06. Calculated.
The average bubble diameter X in the thickness direction is an average chord length determined from a length of the straight line and the number of bubbles intersecting the straight line in a vertical section in the extrusion direction observed with a scanning electron microscope. X1 was determined and calculated from X1 / 0.616.
The average bubble diameter Y in the extrusion direction is obtained by dividing the vertical cross section in the extrusion direction observed with a scanning electron microscope into four equal parts in the thickness direction, and in each of the three line segments in the vicinity of the surface layer, the central part in the thickness direction, and the vicinity of the back surface. The average chord length Y1 is obtained from the length of the straight line and the number of bubbles intersecting the straight line, the average bubble diameter of each line segment is calculated from Y1 / 0.616, and the average bubble in the extrusion direction is calculated using these arithmetic average values. The diameter was Y.
The average bubble diameter Z in the extrusion direction is obtained by dividing the vertical cross section in the width direction observed with a scanning electron microscope into four equal parts in the thickness direction, and in each of the three line segments in the vicinity of the surface layer, the central portion in the thickness direction, and the vicinity of the back surface. The average chord length Z1 is obtained from the length of the straight line and the number of bubbles intersecting the straight line, the average bubble diameter of each line segment is calculated from Z1 / 0.616, and the average bubble in the extrusion direction is calculated using these arithmetic average values. The diameter was Z.
(10) Sheet impact strength Using a film impact tester (manufactured by Toyo Seiki Co., Ltd.), measurement was performed on the impact spherical surface 10R. 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.
(11) Thermoformability A deep-drawn bowl-shaped container having a diameter of 100 mm and a depth of 70 mm was thermoformed from a foam sheet using a single molding machine. Regarding the molding conditions, the heating time was kept constant at a heater temperature of 230 ° C., and the crack generation state of the container was observed. Out of 100 molded containers, the case where the number of containers in which cracks are observed is 0, ◎ if less than 5, ○ if 5 or less, and △ if 10 or more, × Deep drawability was evaluated.

The container characteristics were evaluated by the following method.
(12) Range-resistant deformation A square pasta container having a length of 195 mm, a width of 220 mm, and a depth of 34 mm was thermoformed from a foam sheet using a single molding machine. As for the molding conditions, the heater temperature was kept constant at 230 ° C., and the heating time during which surface roughness did not occur was appropriately adjusted. The obtained square pasta container is heated in a microwave oven with an output of 1500 W for 70 seconds, the surface state is observed, and the container is not deformed or raised at all. The heat resistance was evaluated with ○ as the case, × as the case where a large deformation or bulge was seen in the container, and × as the case where the shape of the container collapsed or a hole was generated.
(13) Container strength A 13.8 g stainless steel sphere was dropped on the bottom of the square pasta container, and the 50% fracture height at which the container cracked after 20 measurements was defined as the container strength. The measurement was performed at room temperature and in an environment of −40 ° C.

  The foamed sheets of the examples have greatly improved moldability and strength as compared with the comparative examples, and the container obtained by thermoforming the foamed sheet is excellent in range-up deformation resistance and container strength balance.

  Since the heat-resistant resin foam sheet of the present invention has an excellent balance between heat resistance, strength and moldability, it can be processed into various shapes such as deep drawing and can be suitably used as a food container for microwave ovens.

Claims (7)

It consists of 97 to 15 parts by mass of a styrene-methacrylic acid copolymer having a methacrylic acid content of 2 to 7% by mass, 3 to 15 parts by mass of polyphenylene ether, and 0 to 60 parts by mass of polystyrene, and has a weight average molecular weight (Mw). A heat-resistant resin foam sheet of 160,000 or more. However, the total amount of each resin component in the heat resistant resin is 100 parts by mass.   The heat-resistant resin foamed sheet according to claim 1, wherein Z average molecular weight (Mz) / weight average molecular weight (Mw) is 1.6 or more.   The heat resistant resin foam sheet according to claim 1 or 2, wherein the heat resistant resin contains 1 to 10 parts by mass of a rubber reinforcing material.   The heat-resistant resin foam sheet according to claim 3, wherein the rubber reinforcing material is high impact polystyrene.   The heat-resistant resin foam sheet according to claim 4, wherein the rubber content of the high impact polystyrene is 5 to 12% by mass.   The heat-resistant resin foam sheet according to claim 1, wherein a thermoplastic resin sheet or film is laminated on one side or both sides.   A container formed by molding the heat-resistant resin foam sheet according to claim 1.