JP2022156132A - Extrusion foam sheet and method for manufacturing extrusion foam sheet - Google Patents

Abstract

To provide an extrusion foam sheet which is excellent in environmental load reduction and foamability and has good appearance, and a method for manufacturing the same.SOLUTION: An extrusion foam sheet contains a mixed resin of a polystyrene-based resin and a polylactic acid-based resin as a base material resin, wherein the mixed resin contains 30 mass% or more and 95 mass% or less of the polystyrene-based resin and 5 mass% or more and 70 mass% or less of the polylactic acid-based resin (wherein, total of blending amounts of polystyrene-based resin and polylactic acid-based resin is 100 mass%), the polystyrene-based resin is a styrene-(meth)acrylic acid copolymer, a content of a (meth)acrylic acid component in the styrene-(meth)acrylic acid copolymer is 2 mass% or more and 10 mass% or less, and the extrusion foam sheet has apparent density of 50 kg/m3 or more and 200 kg/m3 or less and a closed cell ratio of 70% or more.SELECTED DRAWING: None

Description

The present invention relates to an extruded foam sheet and a method for producing an extruded foam sheet.

Resin foam sheets are excellent in lightness, moldability, rigidity, etc. For example, molded articles obtained by thermoforming polystyrene resin foam sheets are used in a wide range of applications such as food containers. There is concern that such molded articles, if discarded as plastic waste, may become a source of microplastics. Accordingly, there is a demand for a foamed sheet using a resin that reduces the burden on the environment. Polylactic acid is attracting attention as a resin that contributes to reducing the burden on the environment. Polylactic acid can be polymerized from raw materials derived from biomass, is a biodegradable plastic, and is said to have excellent physical properties.

In the field of extruded foam sheets, it is being studied to use a mixed resin of polystyrene resin and polylactic acid as a base resin. Patent Literature 1 discloses a foamed sheet having a predetermined expansion ratio and thickness using a resin composition containing polylactic acid, a polystyrene-based resin, and a compatibilizer as a raw material. Patent Document 2 discloses a foam having a predetermined density made of a polylactic acid-based resin composition containing a polylactic acid-based resin and a polystyrene-based resin, and specifically describes a foamed sheet. Further, Patent Document 3 discloses a foamed sheet having predetermined physical properties, which is obtained by foaming a styrene-based resin composition containing a styrene-based resin and a polylactic acid-based resin.

Japanese Patent Application Laid-Open No. 2006-328318 Japanese Unexamined Patent Application Publication No. 2010-77180 WO2020/54536

In the technique of Patent Document 1, there is room for improvement in terms of obtaining a foamed sheet with a high expansion ratio in order to improve lightness, and there is also room for improvement in terms of appearance, moldability, and heat resistance. The techniques of Patent Literatures 2 and 3 have room for improvement from the viewpoint of stably producing a foamed sheet with good appearance and the like, and there is also room for improvement from the viewpoint of rigidity. In addition, the techniques of Patent Documents 2 and 3 have room for improvement from the viewpoint of ensuring a wide range of molding conditions under which molded bodies such as containers can be molded.

An object of the present invention is to provide an extruded foam sheet that is excellent in environmental load reduction properties, foamability, good appearance, and high rigidity, and a method for producing the same.

The gist of the present invention is the disclosure shown in the following (1) to (7).

(1) A mixed resin of polystyrene resin and polylactic acid resin is used as the base resin,
An apparent density of 50 kg/m ³ or more and 200 kg/m ³ or less, and a closed cell ratio of 70% or more,
The mixed resin contains the polystyrene resin in a ratio of 30% by mass to 95% by mass and the polylactic acid resin in a ratio of 5% by mass to 70% by mass (however, the polystyrene resin and the The total amount of the polylactic acid resin is 100% by mass),
The polystyrene resin is a styrene-(meth)acrylic acid copolymer,
The content of the (meth)acrylic acid component in the styrene-(meth)acrylic acid copolymer is 2% by mass or more and 10% by mass or less,
Extruded foam sheet.
(2) The mixed resin contains a polystyrene resin in a ratio of 40% by mass to 80% by mass and a polylactic acid resin in a ratio of 20% by mass to 60% by mass (however, the polystyrene resin and the polylactic acid The total amount of the system resin compounded is 100% by mass),
The extruded foam sheet according to (1) above.
(3) The extruded foam sheet according to (1) or (2) above, wherein the polystyrene-based resin has a glass transition temperature of 110°C or higher and 125°C or lower.
(4) The extrusion foaming according to any one of (1) to (3) above, wherein the polystyrene resin has an MFR measured at a temperature of 200° C. and a load of 5 kg of 0.5 or more and 2.0 or less. sheet.
(5) The above (1) to (4), wherein the polylactic acid resin is a copolymer of L-lactic acid and D-lactic acid, and the content of D-lactic acid is 3% or more and 12% or less. The extruded foam sheet according to any one of .
(6) A polystyrene-based resin and a polylactic acid-based resin having a step of extruding an expandable molten resin obtained by kneading a mixed resin of a polystyrene-based resin and a polylactic acid-based resin and a physical blowing agent from an annular die and expanding the resin. A method for producing an extruded foam sheet using a mixed resin of
The mixed resin contains the polystyrene-based resin in a ratio of 30% by mass to 95% by mass and the polylactic acid-based resin in a ratio of 5% by mass to 70% by mass (however, the polystyrene-based resin and the The total amount of the polylactic acid-based resin is 100% by mass),
The polystyrene resin is a styrene-(meth)acrylic acid copolymer,
The content of the (meth)acrylic acid component in the styrene-(meth)acrylic acid copolymer is 2% by mass or more and 10% by mass or less,
The apparent density of the extruded foam sheet is 50 kg/m ³ or more and 200 kg/m ³ or less, and the closed cell rate is 70% or more,
A method for producing an extruded foam sheet.
(7) The physical blowing agent contains at least one selected from saturated hydrocarbons having 3 to 5 carbon atoms,
A method for producing an extruded foam sheet according to (6) above.

ADVANTAGE OF THE INVENTION According to this invention, the extruded foam sheet|seat which is excellent in environmental impact reduction property and foaming property, has a favorable appearance, and has high rigidity, and its manufacturing method can be provided.

Embodiments of the present invention will be described in the following order.
1 Extruded foam sheet 2 Manufacturing method of extruded foam sheet

It should be noted that the present invention is not limited to the embodiments and the like described below.

[1 Extruded foam sheet]
[1-1 Configuration]
The extruded foam sheet according to the present invention uses a mixed resin of polystyrene resin and polylactic acid-based resin as a base resin.

(polystyrene resin)
A polystyrene resin is a styrene-(meth)acrylic acid copolymer. As used herein, the term "(meth)acrylic acid" indicates a concept that includes acrylic acid and methacrylic acid. Examples of styrene-(meth)acrylic acid copolymers include copolymers of styrene and acrylic acid and copolymers of styrene and methacrylic acid. Among them, the styrene-(meth)acrylic acid copolymer is preferably a copolymer of styrene and methacrylic acid. However, copolymers of styrene and acrylic acid are copolymerized with a small amount of methacrylic acid, and a small amount of methacrylic acid alkyl esters such as methyl methacrylate and butyl acrylate and/or acrylic acid alkyl esters as the third component. It may be copolymerized. Copolymers of styrene and methacrylic acid are obtained by further copolymerizing a small amount of acrylic acid, and by copolymerizing a small amount of methacrylic acid alkyl esters such as methyl methacrylate and butyl acrylate and/or acrylic acid alkyl esters as a third component. It may have been However, from the viewpoint of suppressing the influence of the third component, the content of copolymers other than styrene and (meth)acrylic acid in the styrene-(meth)acrylic acid copolymer is preferably 3% by mass or less. It is more preferably 1% by mass or less, and even more preferably 0% by mass.

(Content of (meth)acrylic acid component)
The content of the (meth)acrylic acid component in the styrene-(meth)acrylic acid copolymer is 2% by mass or more and 10% by mass or less. When the content of the (meth)acrylic acid component is less than 2% by mass (including 0% by mass), the glass transition temperature and Vicat softening temperature of the styrene-(meth)acrylic acid copolymer are low, and the extruded foam sheet There is a risk that the heat resistance of will be insufficient. Also, the appearance of the extruded foam sheet may deteriorate. From the above viewpoint, the content of the (meth)acrylic acid component in the styrene-(meth)acrylic acid copolymer is preferably 4% by mass or more, more preferably 6% by mass or more. On the other hand, if the content of the (meth)acrylic acid component exceeds 10% by mass, the rigidity of the extruded foam sheet may be insufficient. In addition, the closed cell ratio of the extruded foam sheet may be lowered, and physical properties such as rigidity and impact resistance, thermoformability, and the like may be impaired. Furthermore, during the production of the extruded foam sheet, the extrusion foaming is not stable, and there is a possibility that the productivity of the extruded foam sheet is lowered. From the above viewpoint, the content of the (meth)acrylic acid component in the styrene-(meth)acrylic acid copolymer is preferably 9% by mass or less. When a plurality of types of (meth)acrylic acid components to be copolymerized with styrene are used, the content of the (meth)acrylic acid components indicates the total of these multiple types of (meth)acrylic acid components.

(Vicat softening temperature of polystyrene resin)
The heat resistance of polystyrene resins can be evaluated by the Vicat softening point temperature. The Vicat softening temperature of the polystyrene resin used for the extruded foam sheet according to the present invention is preferably 108° C. or higher. When the Vicat softening temperature of the polystyrene-based resin is 108°C or higher, it becomes easy to obtain an extruded foam sheet having sufficient heat resistance. From the above point of view, the Vicat softening temperature of the polystyrene resin is more preferably 110° C. or higher, and even more preferably 115° C. or higher. The upper limit of the Vicat softening temperature of the polystyrene resin is preferably about 150° C., more preferably 130° C. or less, from the viewpoint of the fluidity of the resin.

(Measurement of Vicat softening temperature of polystyrene resin)
The Vicat softening temperature of a polystyrene resin is determined by the A50 method of JIS K7206:1999.

(Glass transition temperature of polystyrene resin)
It is preferable that the glass transition temperature Tg of the polystyrene resin is 110° C. or higher and 125° C. or lower. When the glass transition temperature of the polystyrene resin is within this range, the heat resistance of the extruded foam sheet can be easily ensured. In addition, in the production of extruded foam sheets using a mixed resin of polystyrene resin and polylactic acid as a base resin, the foaming temperature can be easily adjusted within a suitable range, and the resulting extruded foam sheets have good physical properties and appearance. easier. From the above viewpoint, the glass transition temperature Tg of the polystyrene resin is preferably 115° C. or higher and 123° C. or lower.

(Measurement of glass transition temperature of polystyrene resin)
The glass transition temperature (Tg) can be measured by heat flux differential scanning calorimetry (DSC) according to the method described in JIS K7121:1987 "Method for measuring transition temperature of plastics".

(MFR of polystyrene resin)
The MFR (melt flow rate) of the polystyrene resin measured at a temperature of 200 ° C. and a load of 5 kg is preferably 0.5 g / 10 minutes or more and 2.0 g / 10 minutes or less, 1.0 g / 10 minutes or more, It is more preferably 1.8 g/10 minutes or less. When the MFR is within this range, it is easy to suppress a decrease in the closed cell ratio of the extruded foam sheet, improve the thermoformability of the extruded foam sheet, and easily improve the mechanical strength and rigidity of the extruded foam sheet. becomes.

(Measurement of MFR of polystyrene resin)
The MFR of a polystyrene resin can be specified as a value measured under conditions of 200° C. and a load of 5 kg based on JIS K7210-1:2014.

(Polylactic acid resin)
A polylactic acid-based resin is defined as a polymer containing 50 mol % or more of lactic acid component units. Polylactic acid-based resins include, for example, the following polymers (1) to (5) (including copolymers), mixtures of any combination of (1) to (5), and the like.

(1) a polymer of lactic acid,
(2) copolymers of lactic acid and other (other than lactic acid) aliphatic hydroxycarboxylic acids;
(3) a copolymer of lactic acid, an aliphatic polyhydric alcohol and an aliphatic polycarboxylic acid;
(4) copolymers of lactic acid and aliphatic polycarboxylic acids; and (5) copolymers of lactic acid and aliphatic polyhydric alcohols.

Specific examples of the lactic acid include L-lactic acid, D-lactic acid, DL-lactic acid, L-lactide, D-lactide, DL-lactide which are cyclic dimers thereof, and mixtures thereof. Examples of other (other than lactic acid) aliphatic hydroxycarboxylic acids include tartaric acid and citric acid. Butane tetracarboxylic acid etc. can be illustrated as aliphatic polyhydric carboxylic acid. Examples of aliphatic polyhydric alcohols include glycerin.

The compound (monomer) constituting the lactic acid component unit includes two types of optical isomers, D- and L-isomers (hereinafter sometimes referred to as D-isomer compound and L-isomer compound, respectively), as described above. As the polylactic acid-based resin, any of L-compound only, D-compound only, and both L-compound and D-compound may be used.

As the polylactic acid-based resin, (1) a polymer of lactic acid is preferable. Polymers of lactic acid include homopolymers of L-lactic acid (PLLA), homopolymers of D-lactic acid (PDLA), copolymers of L-lactic acid and D-lactic acid, mixtures of PLLA and PDLA, and the like. exemplified. From the viewpoint of foamability, the polylactic acid resin is preferably a copolymer of L-lactic acid and D-lactic acid.

The method for producing the polylactic acid-based resin is not particularly limited. For example, the method for producing a polylactic acid resin includes a method of direct dehydration polycondensation using lactic acid or a mixture of lactic acid and an aliphatic hydroxycarboxylic acid as a raw material, a ring-opening polymerization method of polymerizing a cyclic dimer (lactide) of lactic acid, and the like. can be mentioned.

(D body content of polylactic acid resin)
The D-isomer content (% by mass) of the polylactic acid resin is not particularly limited, but is preferably 0.5% by mass or more and 15% by mass or less. As the D-form content of the polylactic acid-based resin decreases, the crystallinity of the polylactic acid-based resin tends to improve and the heat resistance tends to improve. On the other hand, the higher the D-form content of the polylactic acid-based resin, the lower the crystallinity of the polylactic acid-based resin (increasing the amorphousness), which tends to make it easier to improve the foamability. When the D-form content (% by mass) of the polylactic acid-based resin is within the above range, both heat resistance and foamability can be achieved in a well-balanced manner. Further, from the viewpoint of further increasing the impact resistance of the extruded foam sheet, the D-isomer content of the polylactic acid resin is more preferably 3% by mass or more and 12% by mass or less, and more preferably 3% by mass or more and 8% by mass or less. is more preferred.

The D-form content (% by mass) of the polylactic acid-based resin is the mass ratio (% by mass) of the D-form compound to the total amount of compounds constituting the lactic acid component units in the polylactic acid-based resin.

(Melting point of polylactic acid resin)
The melting point of the polylactic acid resin is preferably 130°C or higher and 190°C or lower. When the melting point of the polylactic acid-based resin is within this range, the heat resistance and foamability of the extruded foam sheet can be easily ensured. From the above viewpoint, the melting point of the polylactic acid resin is preferably 145° C. or higher and 185° C. or lower.

(Measurement of melting point of polylactic acid resin)
The melting point of polylactic acid-based resin is determined based on JIS K7121:1987. Specifically, "(2) When measuring the melting temperature after performing a constant heat treatment" is adopted as the condition adjustment, and the condition-adjusted test piece is heated from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min. A DSC curve is obtained by heating to °C, and the apex temperature of the melting (endothermic) peak is taken as the melting point. When a plurality of melting peaks appear in the DSC curve, the apex temperature of the highest melting peak is taken as the melting point.

(Crystallization temperature of polylactic acid resin)
The crystallization temperature of the polylactic acid-based resin is preferably 100° C. or higher and 130° C. or lower. When the crystallization temperature of the polylactic acid-based resin is within this range, the heat resistance can be improved by, for example, providing a step of heating and crystallizing an extruded foam sheet or a container formed by thermoforming the extruded foam sheet. becomes easier. From the above viewpoint, the crystallization temperature of the polylactic acid-based resin is more preferably 100° C. or higher and 125° C. or lower, and further preferably 102° C. or higher and 118° C. or lower.

(Measurement of crystallization temperature of polylactic acid resin)
The crystallization temperature of polylactic acid resin is obtained based on JIS K7121:1987. Specifically, in the same manner as the measurement of the melting point of the polylactic acid-based resin, the condition adjustment is performed by adopting “(2) When measuring the melting temperature after performing a certain heat treatment” and adjusting the condition. A DSC curve is obtained by heating from 30° C. to 200° C. at a heating rate of 10° C./min. The apex temperature of the crystallization (exothermic) peak determined from the DSC curve is defined as the crystallization temperature. When two or more crystallization peaks appear, the apex temperature of the highest crystallization peak is taken as the crystallization temperature.

(MFR of polylactic acid resin)
From the viewpoint of foamability, the melt flow rate (MFR) of the polylactic acid resin is preferably 1.0 g/10 min or more and 8.0 g/10 min or less, more preferably 2.0 g/10 min or more and 5.0 g/10 min or more. 10 minutes or less.

(Measurement of MFR of polylactic acid resin)
The MFR of polylactic acid resin can be specified as a value measured under conditions of 190° C. and a load of 2.16 kg based on JIS K7210-1:2014.

(Blending ratio in mixed resin)
The mixed resin contains 30% by mass or more and 95% by mass or less of polystyrene resin and 5% by mass or more and 70% by mass or less of polylactic acid resin. However, the total amount of the polystyrene-based resin and the polylactic acid-based resin is 100% by mass.

When the mixed resin contains 5% by mass or more of the polylactic acid-based resin, it becomes easier to ensure the substantial effect of reducing the environmental load. When the mixed resin contains 30% by mass or more of the polystyrene-based resin, physical properties such as thermoformability and rigidity of the extruded foam sheet can be easily improved.

The mixed resin contains polystyrene-based resin in a ratio of 40% by mass to 80% by mass and polylactic acid-based resin in a ratio of 20% by mass to 60% by mass (however, the amount of polystyrene-based resin and polylactic acid-based resin blended total is 100% by mass). By including the polylactic acid resin in the mixed resin at a ratio of 20% by mass or more and 60% by mass or less, the heat moldability, heat resistance, rigidity, etc. It becomes possible to improve impact resistance, and it is possible to achieve both rigidity and impact resistance. From the above viewpoint, the mixed resin contains polystyrene resin at a ratio of 50% by mass to 70% by mass and polylactic acid resin at a ratio of 30% by mass to 50% by mass (however, polystyrene resin and polylactic acid resin is 100% by mass) is more preferable.

(other additives)
In the present invention, the base resin may contain other thermoplastic resins to the extent that the intended purpose of the present invention is not hindered. For example, other thermoplastic resins include styrene-( Examples include polystyrene-based resins other than meth)acrylic acid copolymers, polyolefin-based resins, polyphenylene ether-based resins, and the like. The content of other thermoplastic resins in the base resin is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. In addition, from the viewpoint of increasing the rigidity of the extruded foam sheet and more reliably expanding the range of thermoforming molding conditions, it is preferable that the base resin does not contain rubber-modified styrene.

Various additives such as antioxidants, heat stabilizers, inorganic fillers, colorants and the like can be added to the base resin as required.

(Thickness of extruded foam sheet)
Although the thickness of the extruded foam sheet of the present invention obtained using the base resin described above is not particularly limited, it is preferably approximately 0.5 mm or more and 15 mm or less. When the thickness of the extruded foam sheet is within this range, the extruded foam sheet can be suitably used for applications such as food containers, folding boxes such as lunch boxes, and display panels. The extruded foam sheet of the present invention can be suitably used as an extruded foam sheet for thermoforming, and the thickness of the extruded foam sheet is is more preferably 0.5 mm or more and 3 mm or less.

(Method for measuring thickness of extruded foam sheet)
The thickness (mm) of the extruded foam sheet can be determined as a value obtained by measuring the thickness of 10 equally spaced points across the width of the extruded foam sheet and averaging the measured values.

(Apparent density of extruded foam sheet)
The apparent density of the extruded foam sheet is 50 kg/m ³ or more and 200 kg/m ³ or less. If the apparent density of the extruded foam sheet is too low, the strength of molded articles such as containers obtained by thermoforming the extruded foam sheet may decrease. In addition, if the apparent density of the extruded foam sheet is too high, the heat insulating properties and lightness of the molded article may deteriorate. From these points of view, the apparent density of the extruded foam sheet is preferably 80 kg/m ³ or more and less than 180 kg/m ³ , more preferably 100 kg/m ³ or more and less than 150 kg/m ³ .

(Method for measuring apparent density of extruded foam sheet)
The apparent density of the extruded foam sheet can be specified, for example, as a value measured as follows. First, a test piece having a length of 25 mm and a width of 25 mm is cut out from the extruded foam sheet. The thickness of the test piece is the thickness of the extruded foam sheet. Next, the mass (g) of the cut test piece is measured. The basis weight (g/m ² ) is obtained by multiplying the measured mass by 1600 and converting the unit. Furthermore, the obtained basis weight (g/m ² ) of the extruded foam sheet is divided by the thickness (mm) of the extruded foam sheet, and the value is converted into units to obtain the apparent density (kg/m ³ ) of the extruded foam sheet. The above measurements are performed at 10 equally spaced points in the width direction of the extruded foam sheet, and the arithmetic mean value thereof is taken as the apparent density of the extruded foam sheet.

(Basis weight of extruded foam sheet)
The basis weight of the extruded foam sheet is preferably 100 g/m ² to 400 g/m ² , more preferably 150 g/m ² to 300 g/m ² . If the basis weight is within this range, the container obtained by thermoforming the extruded foam sheet will have an excellent balance between rigidity and lightness.

(Method for measuring basis weight of extruded foam sheet)
The basis weight of the extruded foam sheet can be specified, for example, as a value measured as follows. First, a test piece having a length of 25 mm and a width of 25 mm is cut out from the extruded foam sheet. The thickness of the test piece is the thickness of the extruded foam sheet. Next, the mass (g) of the cut test piece is measured. The basis weight (g/m ² ) is obtained by multiplying the measured mass by 1600 and converting the unit. The above measurements are performed at 10 equally spaced points in the width direction of the extruded foam sheet, and the arithmetic mean value thereof is taken as the basis weight of the extruded foam sheet.

(Closed cell ratio of extruded foam sheet)
The closed cell rate of the extruded foam sheet is 70% or more. When the closed cell content of the extruded foam sheet is within this range, the secondary foamability of the extruded foam sheet can be improved when thermoforming a molded article using the extruded foam sheet. In addition, the strength and the like of the molded product obtained by thermoforming the extruded foam sheet can be ensured. From this point of view, the closed cell rate of the extruded foam sheet is preferably 80% or more.

(Method for measuring closed cell content of extruded foam sheet)
Cut samples of 25 mm×25 mm×sheet thickness (thickness of extruded foam sheet) are randomly cut from the extruded foam sheet. A test piece is obtained by stacking a plurality of cut samples so that the total thickness of the sheet is closest to 20 mm (but does not exceed 20 mm). Next, according to the procedure C of ASTM-D2856-70, the true volume Vx of the test piece is measured using a comparative air specific gravity meter 930 of Toshiba Beckman Co., Ltd., and the closed cell ratio is calculated by the following formula (1). Calculate S (%). The above measurement is performed using 5 test pieces, and the arithmetic average value is taken as the closed cell content of the extruded foam sheet.

however,
Vx: The true volume (cm ³ ) of the test piece measured by the above method, which corresponds to the sum of the volume of the resin constituting the foamed sheet and the total volume of closed cells in the test piece.
Va: Apparent volume (cm ³ ) of the test piece calculated from the outer dimensions of the test piece used for measurement,
W: the total weight of the cut sample used for measurement (g), and ρ: the density of the resin constituting the foamed sheet (g/cm ³ ),
is.

(Content of butane in extruded foam sheet)
The extruded foam sheet of the present invention preferably contains butane. When the extruded foam sheet contains butane, the secondary foamability of the foam sheet is improved, and the range of molding conditions such as heating temperature and heating time when thermoforming a container or the like can be widened. In addition, good thermoforming can be ensured even when the extruded foam sheet is stored for a long period of time after production. From this point of view, the content of butane in the extruded foam sheet is preferably 1.0% by mass or more, more preferably 1.2% by mass or more, and further preferably 1.5% by mass or more. preferable. On the other hand, for example, from the viewpoint of suppressing delamination (delamination) between the film and the extruded foam sheet when the extruded foam sheet laminated with the film is heated, the butane content in the extruded foam sheet is 3.0% by mass or less. and more preferably 2.5% by mass or less.
As a method for adjusting the content of butane in the extruded foam sheet within the above range, in the method for producing the extruded foam sheet, the mixed resin is used as the base resin, and butane is used as a physical foaming agent. .
The content of butane in the extruded foam sheet means the content of butane in the extruded foam sheet after curing for 30 days in an indoor environment (23° C., relative humidity of 50%).

The content of butane in the extruded foam sheet is a value measured by an internal standard method using a gas chromatograph. Specifically, an appropriate amount of sample is cut out from an extruded foam sheet that has been aged for 30 days in a room environment, and the sample is placed in a sample bottle with a lid containing an amount of toluene and an internal standard that can completely dissolve the sample, and the lid is closed. After closing, the butane content can be determined by conducting a gas chromatograph analysis using a solution prepared by sufficiently stirring and dissolving the foaming agent of the extruded foam sheet in toluene as a measurement sample.

The extruded foam sheet of the present invention can be laminated with a film on one or both sides thereof in order to improve oil resistance and the like. Examples of films include thermoplastic resin films such as polylactic acid resin films and polyolefin resin films, and so-called PO/PS dry laminate films in which a polyolefin resin film and a polystyrene resin film are previously bonded. . As a method for laminating the film, a known method such as thermal lamination can be used.

[1-2 Effect]
BACKGROUND ART Thermoformed extruded foam sheets using polystyrene resins are used in various fields such as food containers. Such thermoformed articles are often used for disposable purposes, and there are concerns about their impact on the natural environment. In addition, polystyrene resins are often produced using petroleum-based raw materials, and there is concern about the impact on petroleum resources. Therefore, some or all of the resins used in thermoformed articles are considered to be biodegradable resins or resins that can be synthesized from raw materials derived from biomass.

According to the extruded foam sheet of the present invention, a mixed resin of polystyrene resin and polylactic acid-based resin is used as the base resin. By using such a polylactic acid-based resin as a part of the base resin of the extruded foam sheet, it is possible to contribute to the reduction of the environmental load. For example, polylactic acid, which is an example of a polylactic acid-based resin system, is a resin that can be synthesized from biomass-derived raw materials, and is a resin that is biodegradable in composting, and thus contributes to reducing environmental impact.

When forming an extruded foam sheet using a mixed resin of a polystyrene-based resin and a polylactic acid-based resin, there is concern about the influence on the appearance, thermoformability, rigidity, etc. of the extruded foam sheet. In the extruded foamed sheet of the present invention, the polystyrene-based resin is a styrene-(meth)acrylic acid copolymer that satisfies the predetermined conditions, so that the extruded foamed sheet is excellent in heat resistance, appearance thermoformability, and rigidity. you can get a sheet.

In particular, the styrene-(meth)acrylic acid copolymer used in the polystyrene resin has a (meth)acrylic acid component content of 2% by mass or more, so compared to the styrene homopolymer, polylactic acid The compatibility with the system resin is improved, and an extruded foam sheet having an excellent appearance can be obtained. In addition, since the styrene-(meth)acrylic acid copolymer has a (meth)acrylic acid component content of 10% by mass or less, the extruded foam sheet can have a favorable closed cell content.

According to the extruded foam sheet of the present invention, the polystyrene-based resin is a styrene-(meth)acrylic acid copolymer that satisfies predetermined conditions, so that it is excellent in rigidity. In general, resin materials with high rigidity are said to tend to have lower impact resistance. In this regard, according to the extruded foam sheet of the present invention, the mixed resin contains a polystyrene resin in a ratio of 40% by mass to 80% by mass and a polylactic acid resin in a ratio of 20% by mass to 60% by mass (however, When the total amount of polystyrene-based resin and polylactic acid-based resin is 100% by mass), both rigidity and impact resistance can be improved as an extruded foam sheet, that is, excellent rigidity and impact resistance. It is possible to achieve compatibility between sexuality. In addition, from the viewpoint of ensuring consideration for environmental load and impact resistance, polystyrene resin with high impact resistance such as rubber-modified styrene is used as polystyrene resin, and polylactic acid resin is used in combination. It is also conceivable to obtain an extruded foam sheet as the base resin. However, in this case, the rigidity of the extruded foam sheet tends to be insufficient, and the retention of the foaming agent such as butane in the extruded foam sheet is low, so that the molding conditions for thermoforming containers and the like become narrow. There is a risk.

The mixed resin contains polystyrene resin at a ratio of 40% by mass to 80% by mass and polylactic acid resin at a ratio of 20% by mass to 60% by mass (however, the amount of polystyrene resin and polylactic acid resin mixed is Although the reason why the impact resistance is improved while ensuring the rigidity of the extruded foam sheet is not clear, it is considered as follows. Polylactic acid-based resins are known to be resins that are superior in impact resistance to styrene-(meth)acrylic acid copolymers. Further, in the present invention, the polystyrene resin is a styrene-(meth)acrylic acid copolymer that satisfies predetermined conditions. Therefore, it is considered that the predetermined polystyrene-based resin of the present invention has high compatibility with the polylactic acid-based resin in the mixed resin, and is likely to disperse more uniformly. Furthermore, even when the polylactic acid-based resin is contained in a relatively large amount, the closed cell rate of the extruded foam sheet is high. Therefore, when the blending ratio of the polystyrene-based resin and the polylactic acid-based resin in the mixed resin serving as the base resin satisfies a predetermined condition, the polystyrene-based resin contained in the mixed resin is a styrene-(meth)acrylic acid copolymer. Even when polymerization is used, it is believed that extruded foam sheets with excellent impact resistance are obtained. That is, according to the present invention, it is possible to obtain an extruded foam sheet that takes advantage of the excellent rigidity of the styrene-(meth)acrylic acid copolymer and the excellent impact resistance of the polylactic acid resin. Conceivable. In addition, in the process of manufacturing the extruded foam sheet, it is also conceivable that the reduction in rigidity of the extruded foam sheet can be suppressed by orientation of the mixed resin due to stretching during extrusion foaming.

In the specification of the present application, the rigidity of the extruded foam sheet is evaluated using, for example, the bending stress of the extruded foam sheet as an index. Maximum bending stress can be measured according to JIS K7171:2016. The impact resistance of the extruded foam sheet is evaluated, for example, using puncture impact strength as an index. Puncture impact strength can be measured according to JIS K7211-2.

[2 Manufacturing method of extruded foam sheet]
The extruded foam sheet according to the present invention can be produced, for example, as follows.

[2-1 Details of manufacturing method]
The above-described mixed resin containing the above-described polystyrene-based resin and the above-described polylactic acid-based resin is charged into an extruder. Regarding the blending ratio of the polystyrene resin and polylactic acid resin mixed resin, the polystyrene resin is 30% by mass or more and 95% by mass or less, and the polylactic acid resin is 5% by mass or more and 70% by mass or less (however, polystyrene The total amount of the polylactic acid resin and the polylactic acid resin is 100% by mass).

The base resin is heated, melted and kneaded within the extruder. Various additives such as a cell control agent are added to the extruder as necessary. Further, a physical foaming agent is injected into the extruder, and the base resin is further kneaded to form a foamable molten resin. The foamable molten resin is adjusted to a desired resin temperature. Then, the foamable molten resin adjusted to a predetermined resin temperature is extruded through an annular die under atmospheric pressure to foam the foamable molten resin, thereby forming an extruded foam sheet.

The extruded foam sheet may be used in the form of an extruded sheet that is foamed by extruding a foamable molten resin from an extruder, or the extruded sheet is further laminated and fused to form a single sheet. may be used as extruded foam sheets. When the extruded sheet itself is used, it is easy to make the extruded foam sheet thin, and when the extruded sheets are laminated to form a single sheet, the extruded foam sheet is thick. It is easy to make things.

In addition, the reason why an annular die is used in the method for manufacturing the extruded foam sheet is that the easiness of application to post-processes such as adjustment of the thickness is taken into consideration. Further, by extruding the foamable molten resin from an annular die and foaming it, the resin is easily oriented, and the rigidity of the resulting extruded foam sheet can be increased.

Examples of blowing agents include aliphatic saturated hydrocarbons such as propane, butane, pentane, hexane, and heptane; halogenated hydrocarbons such as methyl chloride, ethyl chloride, and methylene chloride; dimethyl ether, diethyl ether, and methyl ethyl ether. Physical blowing agents such as ethers, carbon dioxide, nitrogen, and water can be used. Among these, from the viewpoint of facilitating the production of the extruded foam sheet because the mixed resin of the present invention can be more easily plasticized, and from the viewpoint of improving the thermoformability using the extruded foam sheet, , and saturated hydrocarbons having 3 to 5 carbon atoms are preferably used, and butane is more preferably used.

The addition amount of the foaming agent and the addition amount of the cell control agent can be appropriately selected according to the type of the base resin, the type of the foaming agent, the type of the cell control agent, and the desired density of each foamed layer. The foaming agent is 0.5 to 10 parts by mass, and the cell control agent is 0.1 to 3 parts by mass, with respect to 100 parts by mass of the material resin. Further, the resin temperature of the molten resin mixture during foaming can be appropriately selected according to the type of base resin, the type of foaming agent, the type of cell control agent, and the desired density of the extruded foam sheet.

In addition, in the above description of the production method, an example in which the mixed resin is put into an extruder is used, but the production method of the extruded foam sheet is not limited to this. If various raw materials (for example, polystyrene-based resin, polylactic acid-based resin, etc.) constituting the extruded foam sheet are heated, melted, and kneaded in the extruder, the various raw materials are mixed and put into the extruder. Alternatively, various raw materials may be individually charged into the extruder.

[2-2 Effects]
According to the method for producing an extruded foam sheet described above, the extruded foam sheet of the present invention can be easily produced. In addition, in the method for producing an extruded foam sheet, when one or more types selected from saturated hydrocarbons having 3 to 5 carbon atoms are used as the physical foaming agent, gas permeability is suppressed compared to foaming agents such as carbon dioxide. (it tends to remain in the extruded foam sheet), and the secondary expansion ratio during thermoforming can be increased, so that the thermoformability can be improved. Specifically, it is possible to widen the range of molding conditions such as heating temperature and heating time when thermoforming a container or the like. In addition, good thermoforming can be ensured even when the extruded foam sheet is stored for a long period of time after production.

Next, a more detailed description will be given using examples.

(Resin preparation)
A tandem extruder connecting the first extruder and the second extruder was prepared, and the polystyrene-based resin and the polylactic acid-based resin shown in Table 1 were prepared.

Table 1 shows the contents of the prepared polystyrene-based resin and polylactic acid-based resin. PLA1, PLA2, and PLA3 in Table 1 are polylactic acid having a D-form compound (all D-form lactic acid) content of 4% by mass, 1% by mass, and 12% by mass, respectively. PS1, PS2 and PS3 in Table 1 are all styrene-(meth)acrylic acid copolymers as polystyrene resins. Regarding the content of copolymer components other than styrene, PS1 has a methacrylic acid content of 8% by mass, PPS2 has a methacrylic acid content of 4% by mass, and PS3 has a content of methacrylic acid and methyl methacrylate components. The contents are respectively 14% by mass and 3% by mass (17% by mass in total). PS4 is a styrene homopolymer as a polystyrene resin. HIPS1 is rubber-modified polystyrene (a resin in which rubber particles containing polybutadiene are dispersed in polystyrene). The rubber (polybutadiene rubber) content in the rubber-modified polystyrene is 12% by mass.

Table 1 also shows the glass transition temperature (Tg) and MFR of each resin. Table 1 shows the Vicat softening temperature of the polystyrene resin. Table 1 shows the crystallization temperature (Tc) and melting point (Tm) of the polylactic acid resin. In addition, MFR (g / 10 min) and glass transition temperature (°C) of each resin shown in Table 1, Vicat softening temperature (°C) of polystyrene resin, crystallization temperature (°C) and melting point (°C) of polylactic acid resin The measurement methods of are as follows.

(Measurement of MFR of resin)
The MFR of the resin was obtained based on JIS K7210-1:2014. As the measurement conditions, a condition of 200° C. and a load of 5 kg was adopted for the polystyrene resin, and a condition of 190° C. and a load of 2.16 kg was adopted for the polylactic acid resin.

(Glass transition temperature of resin)
The glass transition temperature of the resin was determined by DSC measurement in accordance with JIS K7121:1987. As a measuring device, a heat flux differential scanning calorimeter (“Device name: DSC Q1000” manufactured by TA Instruments) was used. The heating rate in the DSC measurement was set at 10°C/min. The midpoint glass transition temperature of the DSC curve obtained by DSC measurement was taken as the glass transition temperature of the resin.

(Measurement of Vicat softening temperature of polystyrene resin)
The Vicat softening temperature of the polystyrene resin was obtained according to the A50 method of JIS K7206:1999.

(Melting point of polylactic acid resin)
The melting point Tm (°C) of the polylactic acid resin was obtained based on JIS K7121:1987. Specifically, "(2) When measuring the melting temperature after performing a constant heat treatment" is adopted as the condition adjustment, and the condition-adjusted test piece is heated from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min. A DSC curve was obtained by heating to °C, and the apex temperature of the melting (endothermic) peak was defined as the melting point. As a measuring device, a heat flux differential scanning calorimeter (“Device name: DSC Q1000” manufactured by TA Instruments) was used.

(Crystallization temperature of polylactic acid resin)
The crystallization temperature Tc (°C) of the polylactic acid-based resin was obtained based on JIS K7121:1987. Specifically, "(2) When measuring the melting temperature after performing a constant heat treatment" is adopted as the condition adjustment, and the condition-adjusted test piece is heated from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min. A DSC curve was obtained by heating to ° C., and the apex temperature of the crystallization (exothermic) peak was defined as the crystallization temperature. As a measuring device, a heat flux differential scanning calorimeter (“Device name: DSC Q1000” manufactured by TA Instruments) was used.

(Examples 1 to 9 and Comparative Examples 1 to 6)
The types and compounding ratios (mass ratios) of polystyrene resins and polylactic acid resins shown in Tables 2 and 3, and talc (manufactured by Matsumura Sangyo Co., Ltd.) are supplied to the first extruder of the tandem extruder, and further the first It was heated, melted and kneaded in an extruder. After that, the physical blowing agent was injected into the first extruder and further kneaded to form a kneaded material. The kneaded material was transferred to the second extruder, and the resin temperature was adjusted to form a resin melt for forming a foamed sheet. Then, the resin melt for forming a foamed sheet is extruded into the atmosphere from an annular die (diameter of the annular die is 50 mm) at a foaming temperature shown in Tables 2 and 3 at a discharge rate of 50 kg/hr to form a foamed cylinder. body was formed. Furthermore, the foamed tubular body is cut open along the extrusion direction while being pulled along the outer surface of a cooling tube (mandrel) having an outer diameter of 150 mm, with a blow ratio of 3 and a take-up speed of 8 m/min. This produced an extruded foam sheet. The width of the extruded foam sheet was 480 mm.

The above talc was used as a cell control agent and supplied to the first extruder at a ratio of 2 parts by mass with respect to a total of 100 parts by mass of the polystyrene-based resin and the polylactic acid-based resin. In addition, the physical foaming agent is butane (mixed butane of 30% by mass of isobutane and 70% by mass of normal butane). It was press-fitted into the first extruder so that the compounding amount shown in Table 3 was obtained.

For each of Examples 1 to 9 and Comparative Examples 1 to 6, the production stability of the extruded foam sheets was evaluated by observing the production conditions as follows. Further, for each of Examples 1 to 9 and Comparative Examples 1 to 6, the obtained extruded foam sheet was cured in an indoor environment (23 ° C., relative humidity 50%) for 7 days, and the extruded foam sheet after curing was used. , measurement of thickness, basis weight, apparent density, closed cell ratio, puncture impact strength, maximum bending stress, and appearance evaluation were performed as follows. Tables 2 to 5 show the results. In Tables 4 and 5, puncture impact strength is simply referred to as impact strength for convenience of explanation.

As shown in Tables 2 to 5, Examples 1 to 9 were excellent in production stability. In addition, the extruded foam sheet was excellent in foamability, appearance and rigidity. It was also confirmed that the thermoformability and heat resistance were excellent. Moreover, in Examples 2 to 9, it was confirmed that the impact resistance could be improved while maintaining the rigidity of the extruded foam sheet.

(Evaluation of manufacturing stability)
The production stability of extruded foam sheets was evaluated according to the following criteria.
◯ (Good): The extruded foam sheet was hardly cut during the production of the extruded foam sheet, and the extruded foam sheet could be produced stably.
x (defective): The extruded foam sheet was likely to be cut during production of the extruded foam sheet, or the extruded foam sheet was cut immediately after extrusion.

(Thickness of extruded foam sheet)
The thickness of the extruded foam sheet was measured by the method described above.

(Basis Weight and Apparent Density of Extruded Foam Sheet)
The apparent density of the extruded foam sheet was measured by the method described above. Specifically, a test piece having dimensions of 25 mm long×25 mm wide×thickness of the extruded foam sheet was cut out from each of 10 equally spaced locations in the width direction of the extruded foam sheet, and the mass was measured. Next, the basis weight was calculated by multiplying the mass by 1600 and converting the unit. Furthermore, the value obtained by dividing the calculated basis weight of the extruded foam sheet by the thickness of the extruded foam sheet was converted into units, and the apparent density of each test piece was calculated. Then, the arithmetic average value thereof was taken as the apparent density (D1) of the foamed sheet.

(Closed cell rate)
The closed cell content of the extruded foam sheet was measured by the method described above.

(Evaluation of foamability)
The foamability of the extruded foam sheet was evaluated according to the following criteria.
○ (Good): The closed cell rate of the foam sheet is 70% or more × (Poor): The closed cell rate of the foam sheet is less than 70%

(Appearance evaluation)
The surface of the extruded foam sheet was visually observed, and the appearance of the extruded foam sheet was evaluated according to the following criteria.
◯ (Good): Almost no irregularities or streak patterns are observed on the surface of the foamed sheet.
x (defective): At least one of unevenness and streak pattern is observed on the surface of the foamed sheet.

(puncture impact strength)
The impact strength of extruded foam sheets was determined by puncture impact strength measurements. The puncture impact strength was measured according to JIS K7211-2, except that the test speed was set as follows. Specifically, in an environment of temperature 23° C. and humidity 50%, a test piece having a length of 60 mm and a width of 60 mm was cut out from the extruded foam sheet along the extrusion direction, and the measurement was performed using the following measuring device. . The strikers used in the measurements are as follows. Ten test pieces were measured, and the arithmetic mean value of each measured value was defined as the puncture impact strength (N) of the extruded foam sheet.

Measuring device: Tensilon, compression mode (load cell 10kN)
Striker: φ20, 10R iron hemispherical head (without lubricating oil)
Test speed: 500mm/min

(Evaluation of impact resistance)
The impact resistance of the extruded foam sheet was evaluated according to the following criteria.
◎ (extremely good): the puncture impact strength of the extruded foam sheet is 60 N or more ○ (good): the puncture impact strength of the extruded foam sheet is 20 N or more and less than 60 N × (poor): the puncture impact strength of the extruded foam sheet is 20 N Less than

(maximum bending stress)
The maximum bending stress of the extruded foam sheet was measured based on JIS K7171:2016. Specifically, in an environment of temperature 23° C. and humidity 50%, a test piece having a length of 80 mm and a width of 10 mm was cut out along the extrusion direction from the extruded foam sheet, and the measurement was performed under the following measurement conditions. . A total of 10 test pieces, 5 each on the front surface and the back surface of the extruded foam sheet, were measured, and the arithmetic mean value of each measured value was taken as the maximum bending stress (MPa) of the extruded foam sheet.

Measuring device: Tensilon, compression mode (load cell 1kN)
Indenter: R=5
Span: 50mm
Test speed: 10mm/min

(Rigidity evaluation)
The stiffness of the extruded foam sheet was evaluated according to the following criteria.
○ (good): the maximum bending stress of the extruded foam sheet is 7.0 MPa or more × (poor): the maximum bending stress of the extruded foam sheet is less than 7.0 MPa

Further, for each of Examples 1 to 9 and Comparative Examples 1 to 6, the extruded foam sheet obtained by curing the obtained foam sheet for 30 days in an indoor environment (23 ° C., relative humidity 50%) (hereinafter referred to as foam after curing for 30 days sheet) was used to measure the content of butane in the extruded foam sheet. Tables 4 and 5 show the results.

(Content of butane in foam sheet)
The content of butane in the test piece was measured using a gas chromatograph (GC-4000 manufactured by GL Sciences Co., Ltd.) according to the above method for a test piece cut out in a size of about 1 g from the width direction central part of the extruded foam sheet after curing for 30 days. The amount was measured and taken as the content of butane in the foam sheet. The content of butane was the total content of isobutane and normal butane.

Furthermore, for each of Examples 1 to 9 and Comparative Examples 1 to 6, the obtained foam sheet was cured for 37 days in an indoor environment (23 ° C., relative humidity 50%). The extruded foam sheet was evaluated for thermoformability and heat resistance. Also, the secondary foaming ratio was measured. Tables 4 and 5 show the results.

(Thermoformability)
Using the foamed sheet after curing for 37 days, a molded product was obtained by match mold vacuum forming as shown below. A thermoforming machine (model number FKS-0631-10 manufactured by Asano Laboratory) was used for the vacuum forming. Under the conditions of a heater temperature of 290° C. and a heating time of 10 to 24 seconds, using a circular opening with a diameter of 202 mm and a dish-shaped mold with a height of 38 mm (expansion magnification of 1.28 times), The cured foam sheet was thermoformed. A dish-shaped molded article was thus obtained.

The above-mentioned match mold vacuum forming was performed several times by changing the heating time from the above value. The width of the time obtained from the difference between the longest time and the shortest time in the heating seconds for obtaining a good molded product was measured, and this time width was defined as the moldable time width.

Based on the moldable time span, the thermoformability of the extruded foam sheet was evaluated according to the following criteria.
◯ (Good): The width of the moldable time is 8 seconds or more.
x (defective): The width of the moldable time is less than 8 seconds, or a good molded product cannot be obtained.

(Secondary foaming ratio)
The foamed sheet after curing for 37 days is placed in an oven at 160°C and heated, and the apparent density (D2) of the heated foamed sheet is measured by the same method as the method for measuring the apparent density (D1) of the extruded foamed sheet. did. The secondary foaming ratio (times) was calculated by the following formula (2).

(Heat-resistant)
A test piece of 200 mm × 200 mm from near the center in the width direction of the extruded foam sheet after curing for 37 days (the length of the test piece before heating in the extrusion direction and the length of the test piece before heating in the width direction are both 200 mm) Cut out, the test piece was placed in an oven (PH-200 modified manufactured by Tabai Espec Co., Ltd.) set at 110° C. and heated for 30 seconds. The test piece after heating was taken out from the oven. After heating, the dimensions of the test piece in the extrusion direction and the width direction were measured to calculate the dimensional change rate before and after heating. Furthermore, the test piece after heating was visually observed to see if there was any change in appearance before and after heating (hereinafter referred to as observation of change in appearance).

Note that the dimensional change rate is a value obtained by the following formula (3), and is calculated for each of the extrusion direction and the width direction. Then, the arithmetic average value of the dimensional change rates obtained for the calculated extrusion direction and width direction is specified as the heating dimensional change rate (%) of the extruded foam sheet.

The heat resistance of the extruded foamed sheet after curing for 37 days was evaluated according to the following criteria based on the above calculated dimensional change rate (%) of the extruded foamed sheet upon heating and the results of appearance change observation.

◯ (Good): No significant change in appearance was observed, and the dimensional change rate upon heating was 10% (20 mm) or less.
x (defective): at least one of a marked change in appearance and a heat dimensional change rate exceeding 10% (20 mm) is satisfied.

The configurations, methods, processes, shapes, materials, numerical values, and the like described above are merely examples, and different configurations, methods, processes, shapes, materials, numerical values, and the like may be used as necessary. Also, the configurations, methods, steps, shapes, materials, numerical values, etc. shown above can be combined with each other without departing from the gist of the present invention.

Claims (7)

A mixed resin of polystyrene resin and polylactic acid resin is used as the base resin,
An apparent density of 50 kg/m ³ or more and 200 kg/m ³ or less, and a closed cell ratio of 70% or more,
The mixed resin contains the polystyrene resin in a ratio of 30% by mass to 95% by mass and the polylactic acid resin in a ratio of 5% by mass to 70% by mass (however, the polystyrene resin and the The total amount of the polylactic acid resin is 100% by mass),
The polystyrene resin is a styrene-(meth)acrylic acid copolymer,
The content of the (meth)acrylic acid component in the styrene-(meth)acrylic acid copolymer is 2% by mass or more and 10% by mass or less,
Extruded foam sheet.
The mixed resin contains the polystyrene resin in a ratio of 40% by mass to 80% by mass and the polylactic acid resin in a ratio of 20% by mass to 60% by mass (however, the polystyrene resin and the polylactic acid The total amount of the system resin compounded is 100% by mass),
The extruded foam sheet according to claim 1.
The polystyrene resin has a glass transition temperature of 110° C. or higher and 125° C. or lower.
The extruded foam sheet according to claim 1 or 2.
The MFR of the polystyrene resin measured at a temperature of 200° C. and a load of 5 kg is 0.5 g/10 minutes or more and 2.0 g/10 minutes or less.
The extruded foam sheet according to any one of claims 1-3.
The polylactic acid resin is a copolymer of L-lactic acid and D-lactic acid, and the content of D-lactic acid is 3% by mass or more and 12% by mass or less.
The extruded foam sheet according to any one of claims 1-4.
Based on a mixed resin of the polystyrene-based resin and the polylactic acid-based resin, which has a step of extruding and foaming an expandable molten resin obtained by kneading a polystyrene-based resin, a polylactic acid-based resin and a physical blowing agent from an annular die. A method for producing an extruded foam sheet as a material resin,
The mixed resin contains the polystyrene resin in a ratio of 30% by mass to 95% by mass and the polylactic acid resin in a ratio of 5% by mass to 70% by mass (however, the polystyrene resin and the The total amount of the polylactic acid resin is 100% by mass),
The polystyrene resin is a styrene-(meth)acrylic acid copolymer,
The content of the (meth)acrylic acid component in the styrene-(meth)acrylic acid copolymer is 2% by mass or more and 10% by mass or less,
The apparent density of the extruded foam sheet is 50 kg/m ³ or more and 200 kg/m ³ or less, and the closed cell rate is 70% or more,
A method for producing an extruded foam sheet.
The physical blowing agent contains at least one selected from saturated hydrocarbons having 3 to 5 carbon atoms,
A method for producing an extruded foam sheet according to claim 6.