Extruded Foamed Sheet and Method for Producing Extruded Foamed Sheet

Abstract

To provide an extrusion foamed sheet which is excellent in environmental load reduction property and foaming property, and has good appearance, and a method for manufacturing the same.SOLUTION: An extrusion foamed sheet contains a mixed resin of a polystyrene-based resin, a polyphenylene ether-based resin and a polylactic acid-based resin as a base material resin, wherein a blending amount of the polylactic acid-based resin in the mixed resin is 10 mass% or more and 50 mass% or less (total of blending amounts of the polystyrene-based resin, the polyphenylene ether-based resin and the polylactic acid-based resin is 100 mass%), a Vicat softening temperature of the mixed resin is 110°C or higher and 150°C or lower, a value of a difference (Tm-Vst) between a melting point Tm [°C] of the polylactic acid-based resin and a Vicat softening temperature Vst[°C] of the mixed resin is more than 0°C and 40°C or less, apparent density of the extrusion foamed sheet is 50 kg / m3 or more and 300 kg / m3 or less, and a ratio of closed cells of the extrusion foamed sheet is 70% or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an extruded foam sheet and a method for manufacturing the same.

Background Art

[0002] Foam sheets such as resin extruded foam sheets are excellent in lightness, formability, etc., and are used in various applications. For example, a molded body obtained by thermoforming a polystyrene-based resin foam sheet is used in a wide range of applications such as food containers.

[0003] Regarding the resin constituting such a molded body, polylactic acid has attracted attention as a resin that contributes to reducing the environmental load. Polylactic acid can be polymerized from biomass-derived raw materials, is a carbon-neutral material, and is said to have excellent physical properties. Therefore, from the viewpoint of reducing the environmental load, Patent Document 1 has considered manufacturing a foam sheet using a mixed resin of a polystyrene-based resin and polylactic acid as a base resin.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the technology of Patent Document 1, there is room for improvement from the viewpoint of obtaining an extruded foam sheet having good foamability, appearance, and formability. In particular, there is room for improvement from the viewpoint of obtaining a foam sheet with less unevenness and streak patterns on the surface, such as when manufacturing a foam sheet by extrusion foaming.

[0006] An object of the present invention is to provide an extruded foam sheet excellent in environmental load reduction and foamability, having a good appearance and good formability, and a method for manufacturing the same.

Means for Solving the Problems

[0007] The gist of the present invention is the invention shown in the following (1) to (6).

[0008] (1) An extruded foam sheet having a mixed resin of a polystyrene-based resin, a polyphenylene ether-based resin, and a polylactic acid-based resin as a base resin, wherein the blending amount of the polylactic acid-based resin in the mixed resin is 10% by mass or more and 50% by mass or less (however, the total blending amount of the polystyrene-based resin, the polyphenylene ether-based resin, and the polylactic acid-based resin is 100% by mass), the Vicat softening temperature Vst [°C] of the mixed resin is 110°C or more and 150°C or less, and the difference (Tm - Vst) between the melting point Tm [°C] of the polylactic acid-based resin and the Vicat softening temperature Vst [°C] of the mixed resin is more than 0°C and 40°C or less, the apparent density of the extruded foam sheet is 50 kg / m 3 or more and 300 kg / m 3 or less, and the closed cell ratio of the extruded foam sheet is 70% or more, characterized by an extruded foam sheet. (2) The melting point Tm [°C] of the polylactic acid-based resin is 125°C or more and 160°C or less, the extruded foam sheet according to the above (1). (3) The Vicat softening temperature Vst [°C] of the mixed resin is 120°C or more and 140°C or less, the extruded foam sheet according to the above (1) or (2). (4) The closed cell ratio of the extruded foam sheet is 80% or more, the extruded foam sheet according to any one of the above (1) to (3). (5) A method for producing an extruded foam sheet, comprising a step of extruding and foaming a foamable molten resin containing a mixed resin of a polystyrene-based resin, a polyphenylene ether-based resin, and a polylactic acid-based resin and a physical foaming agent, The blending amount of the polylactic acid resin in the mixed resin is 10% by mass or more and 50% by mass or less (however, the total blending amount of the polystyrene resin, the polyphenylene ether resin, and the polylactic acid resin in the mixed resin is defined as 100% by mass). The Vicat softening temperature Vst [°C] of the mixed resin is 110°C or more and 150°C or less, and the difference (Tm - Vst) between the melting point Tm [°C] of the polylactic acid resin and the Vicat softening temperature Vst [°C] of the mixed resin is more than 0°C and 40°C or less, the apparent density of the extruded foam sheet is 50 kg / m 3 or more and 300 kg / m 3 or less, and the closed cell ratio of the extruded foam sheet is 70% or more. A method for producing an extruded foam sheet, characterized by the above. A method for producing an extruded foam sheet. (6) The polyphenylene ether resin is derived from a modified polyphenylene ether resin defined as a mixture obtained by kneading the polyphenylene ether resin and the polystyrene resin, and the glass transition temperature Tg [°C] of the modified polyphenylene ether resin is 110°C or more and 150°C or less. The method for producing an extruded foam sheet according to (5) above. [[Effect of the Invention]]

[0009] According to the present invention, it is possible to provide an extruded foam sheet excellent in environmental load reduction and foamability, and having good moldability and appearance, and a method for producing the same. [[Embodiments for Carrying Out the Invention]]

[0010] Embodiments of the present invention will be described below in the order of 1. First Embodiment (extruded foam sheet), 2. Second Embodiment (laminated sheet having an extruded foam sheet (foamed sheet with skin)), 3. Method for producing an extruded foam sheet, and 4. Application examples.

[0011] Note that the present invention is not limited to the embodiments described below and the like.

[0012] The extruded foamed sheet of the present invention is a sheet having a structure obtained by extruding and foaming a base resin.

[0013] [1 First Embodiment (Extruded Foamed Sheet)] [1-1 Configuration] The extruded foamed sheet according to the first embodiment of the present invention uses a resin containing a polystyrene-based resin, a polyphenylene ether-based resin, and a polylactic acid-based resin (hereinafter referred to as a mixed resin) as the base resin.

[0014] (Polystyrene-based Resin) The polystyrene-based resin is not particularly limited. For example, polystyrene (general-purpose polystyrene), rubber-modified polystyrene (impact-resistant polystyrene), styrene-α-methylstyrene copolymer, styrene-p-methylstyrene copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-maleic anhydride copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-acrylonitrile copolymer, etc. may be mentioned. Among these, polystyrene is preferable.

[0015] (Vicat Softening Temperature of Polystyrene-based Resin) Regarding the Vicat softening temperature of the polystyrene-based resin used for the extruded foamed sheet, from the viewpoint of obtaining an extruded foamed sheet with good moldability and appearance, etc., the Vicat softening temperature of the polystyrene-based resin is preferably 100°C or higher, more preferably 105°C or higher. From the viewpoint of the fluidity of the resin, etc., the Vicat softening temperature of the polystyrene-based resin is preferably approximately 120°C or lower, more preferably 110°C or lower.

[0016] (Measurement of Vicat Softening Temperature of Polystyrene-based Resin) The Vicat softening temperature of the polystyrene-based resin is determined by the A50 method of JIS K7206:2016.

[0017] (Polyphenylene ether resin) The polyphenylene ether resin refers to a polymer having at least a unit structure defined by an aromatic polyether compound in the main chain (referred to as a polymer having an aromatic polyether structure). For example, as the polyphenylene ether resin, a polymer having a main chain with a structure shown by the following general formula (Formula (A)) as a unit structure can be mentioned. The polymer having an aromatic polyether structure may have one type of unit structure or a plurality of types of unit structures. The degree of polymerization of the polymer having an aromatic polyether structure (the number of unit structures per molecule) is not particularly limited, and for example, numbers in the range of about 10 to about 5500 can be exemplified.

[0018] [Chemical formula]

[0019] In the above formula (A), R1 to R3 represent an alkyl group having 1 to 4 carbon atoms (including those in which at least a part of hydrogen is substituted) or a halogen atom. It is preferable that R1 to R3 are each independently a methyl group or an ethyl group.

[0020] Examples of the polyphenylene ether resin include poly(2,6-dimethyl-1,4-phenylene) ether, poly(2,6-diethyl-1,4-phenylene) ether, poly(2,6-dipropyl-1,4-phenylene) ether, poly(2-methyl-6-ethyl-1,4-phenylene) ether, poly(2-methyl-6-propyl-1,4-phenylene) ether, and the like. In addition, examples of the polyphenylene ether resin include copolymers using 2,6-dialkylphenol and 2,3,6-trialkylphenol. The polyphenylene ether resin contained in the mixed resin may be a derivative of a polymer compound (a polymer having an aromatic polyether structure) that can be used as the above-mentioned polyphenylene ether resin. Furthermore, the polyphenylene ether resin may be a mixture of a plurality of types of the above-mentioned polymer compounds.

[0021] (Polylactic acid resin) The polylactic acid resin is defined as a polymer containing 50 mol% or more of lactic acid component units. The polylactic acid resin includes, for example, the polymers (including copolymers) shown in the following (1) to (5), and mixtures by combinations of (1) to (5), etc.

[0022] (1) Polymer of lactic acid (polymer), (2) Copolymer of lactic acid and other (other than lactic acid) aliphatic hydroxycarboxylic acids, (3) Copolymer of lactic acid, aliphatic polyhydric alcohol and aliphatic polybasic carboxylic acid, (4) Copolymer of lactic acid and aliphatic polybasic carboxylic acid, and (5) Copolymer of lactic acid and aliphatic polyhydric alcohol.

[0023] Specific examples of the above lactic acid include L-lactic acid, D-lactic acid, DL-lactic acid, or their cyclic dimers, L-lactide, D-lactide, DL-lactide, or mixtures thereof. Examples of other (other than lactic acid) aliphatic hydroxycarboxylic acids include tartaric acid, citric acid, etc. Examples of aliphatic polybasic carboxylic acids include butanetetracarboxylic acid, etc. Examples of aliphatic polyhydric alcohols include, for example, glycerin.

[0024] As the compounds (monomers) constituting the lactic acid component units, there are two types of optical isomers of the D-form and the L-form (hereinafter sometimes referred to as the D-form compound and the L-form compound, respectively) as described above. As the polylactic acid resin, those using only the L-form compound, only the D-form compound, or both the L-form compound and the D-form compound may be used.

[0025] As the polylactic acid resin, the polymer of lactic acid described in (1) above is preferable. Examples of the polymer of lactic acid include a homopolymer of L-lactic acid (PLLA), a homopolymer of D-lactic acid (PDLA), a copolymer of L-lactic acid and D-lactic acid, a mixture of PLLA and PDLA, etc. From the viewpoint of foamability, the polylactic acid resin is preferably a copolymer of L-lactic acid and D-lactic acid.

[0026] The method for producing the polylactic acid resin is not particularly limited. For example, the method for producing the polylactic acid resin includes a method of directly performing 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, etc.

[0027] (D-form content of the polylactic acid resin) The D-form content (mass%) of the polylactic acid resin is not particularly limited, but is preferably 0.5 mass% or more and 15 mass% or less. The lower the D-form content of the polylactic acid resin, the more the crystallinity of the polylactic acid resin improves, and the heat resistance tends to improve. On the other hand, the higher the D-form content of the polylactic acid resin, the lower the crystallinity of the polylactic acid resin (the non-crystallinity increases), and the foamability tends to be improved. When the D-form content (mass%) of the polylactic acid resin is within the above range, heat resistance and foamability can be balanced well. Further, from the viewpoint of further enhancing the impact resistance of the extrusion-foamed sheet, the D-form content of the polylactic acid resin is more preferably 2 mass% or more and 12 mass% or less, and even more preferably 3 mass% or more and 8 mass% or less.

[0028] Note that the D-form content (mass%) of the polylactic acid resin is the mass ratio (mass%) of the D-form compound to the total amount of the compounds constituting the lactic acid component unit in the polylactic acid resin.

[0029] (Melting point of the polylactic acid resin) The melting point Tm [°C] of the polylactic acid resin is preferably 165°C or lower. When the melting point of the polylactic acid resin is within this range, during the formation of the extrusion foamed sheet, the progress of solidification of the polylactic acid resin tends to be slow immediately after extrusion foaming, the elongation of the extrusion foamed sheet is excellent immediately after extrusion foaming, and it is easy to obtain a foamed sheet with good foamability and a high closed cell ratio. From this perspective, it is more preferable that the melting point of the polylactic acid resin is 160°C or lower. On the other hand, from the perspective of further enhancing the heat resistance of the extrusion foamed sheet, the melting point Tm [°C] of the polylactic acid resin is preferably 125°C or higher, and more preferably 150°C or higher.

[0030] (Measurement of the melting point of the polylactic acid resin) The melting point of the polylactic acid resin is determined based on JIS K7121:1987. Specifically, as the condition adjustment, “(2) After performing a certain heat treatment, when measuring the melting temperature” is adopted, and a DSC curve is obtained by heating the conditioned test piece from 30°C to 200°C at a heating rate of 10°C / min, and the peak temperature of the melting (endothermic) peak is taken as the melting point. In addition, when multiple melting peaks appear in the DSC curve, the peak temperature of the melting peak with the highest height is taken as the melting point.

[0031] (Tm-Vst) In the extrusion foamed sheet according to the present invention, the relationship between the melting point of the polylactic acid resin and the Vicat softening temperature of the mixed resin is as follows. That is, in the extrusion foamed sheet, the value of the difference (Tm-Vst) between the Vicat softening temperature (Vst [°C]) of the mixed resin and the melting point (Tm [°C]) of the polylactic acid resin is more than 0°C and 40°C or lower. By the way, generally, it is considered difficult to perform extrusion foaming on a resin containing a certain amount of polylactic acid (for example, the blending amount of the polylactic acid resin in the resin is 10% by mass or more, etc.). In this regard, by satisfying the range where the value of (Tm-Vst) is more than 0°C and 40°C or lower, even if the mixed resin contains polylactic acid, it becomes easy to perform extrusion foaming, and it becomes easy to obtain an extrusion foamed sheet with good appearance. From this perspective, the value of (Tm-Vst) is preferably 5°C or higher and 35°C or lower, and more preferably 10°C or higher and 30°C or lower.

[0032] (Vicat softening temperature of the blended resin) The Vicat softening temperature Vst [°C] of the blended resin is 110°C or higher and 150°C or lower, preferably 115°C or higher and 145°C or lower, and more preferably 120°C or higher and 140°C or lower. When the Vicat softening temperature Vst [°C] of the blended resin is within the above range, even if the blended resin contains polylactic acid, it becomes easy to perform extrusion foaming of the blended resin. The Vicat softening temperature Vst [°C] of the blended resin can be adjusted by adjusting the blending ratio of the polystyrene resin and the polyphenylene ether resin contained in the blended resin, or by adjusting the blending ratio of the three components of the polystyrene resin, the polyphenylene ether resin, and the polylactic acid resin. The Vicat softening temperature Vst [°C] of the blended resin is determined by the A50 method of JIS K7206:2016 in the same manner as described above for the Vicat softening temperature of the polystyrene resin.

[0033] (Blending ratio of the polylactic acid resin in the blended resin) The blending amount of the polylactic acid resin in the blended resin is 10% by mass or more and 50% by mass or less. However, the total blending amount of the polystyrene resin, the polyphenylene ether resin, and the polylactic acid resin is 100% by mass.

[0034] By containing 10% by mass or more of the polylactic acid resin, the blended resin can easily ensure a substantial effect of reducing the environmental load. By containing 50% by mass or less of the polylactic acid resin, the total of the polystyrene resin and the polyphenylene ether resin can be 50% by mass or more, and physical properties such as the moldability of the extrusion foamed sheet are likely to be improved. From the viewpoints of reducing the environmental load and improving the moldability, the blending amount of the polylactic acid resin in the blended resin is preferably 15% by mass or more and 45% by mass or less, and more preferably 20% by mass or more and 40% by mass or less.

[0035] (Blending ratio of the polystyrene resin and the polyphenylene ether resin in the blended resin) Regarding the blending ratio of the polystyrene-based resin and the polyphenylene ether-based resin in the mixed resin, it is preferably 5% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less for the polyphenylene-based resin. However, the total of the polystyrene-based resin and the polyphenylene ether-based resin is 100% by mass. By including the polystyrene-based resin and the polyphenylene ether-based resin in this range in the mixed resin, physical properties such as the moldability of the extrusion-foamed sheet are likely to be improved.

[0036] (Other additives) In the present invention, the base resin may contain other thermoplastic resins to such an extent that the intended object of the present invention is not inhibited. For example, examples of other thermoplastic resins include polyolefin-based resins. Examples of polyolefin-based resins include homopolymers of olefin-based monomers such as ethylene and propylene, or copolymers thereof, and copolymers having an olefin-based monomer as a main component and a vinyl monomer copolymerizable therewith. The content of other thermoplastic resins is preferably 20% by mass or less, preferably 10% by mass or less, and more preferably 5% by mass or less in the base resin. Further, from the viewpoint of enhancing the rigidity of the extrusion-foamed sheet, it is preferable that the base resin does not contain rubber-modified styrene.

[0037] The extrusion foamed sheet may contain various additives as required. The additives refer to other constituent components excluding polystyrene resins, polyphenylene ether resins, polylactic acid resins, and the foaming agents described below. Examples of the additives include antioxidants, stabilizers, inorganic fillers, colorants, deodorants, flame retardants, antistatic agents, cell regulators, ultraviolet absorbers, etc. The various specific substances listed as additives are not particularly limited and may be appropriately adopted according to the properties required for the extrusion foamed sheet. Regarding the specific substances, for example, titanium oxide, carbon, etc. may be mentioned as antioxidants. Examples of the stabilizer can include heat stabilizers. Examples of the colorant can include various pigments. Examples of the deodorant can include zeolite, silica, zirconium phosphate, etc. As the additives, one type or a plurality of types may be adopted.

[0038] The content of the additives is not particularly limited, but from the viewpoint of suppressing the influence on the moldability of the extrusion foamed sheet, it is preferably about 0.03% by mass or more and 25% by mass or less in terms of the mass ratio to the base resin.

[0039] (Thickness of the extrusion foamed sheet) The thickness of the extrusion foamed sheet is not particularly limited, but it is preferably about 0.5 mm or more and 15 mm or less. When the thickness of the extrusion foamed sheet is within this range, the extrusion foamed sheet can be suitably used for applications such as food containers, folding boxes such as lunch boxes, and display panels. The extrusion foamed sheet of the present invention can be suitably used as an extrusion foamed sheet for thermoforming, and from the viewpoint of being able to thermoform a container excellent in rigidity, heat insulation, and handleability, etc., the thickness of the extrusion foamed sheet is more preferably 0.5 mm or more and 3 mm or less.

[0040] (Method for measuring the thickness of the extrusion foamed sheet) The thickness (mm) of the extrusion foamed sheet can be determined as a value obtained by measuring the thickness at 10 equally spaced points over the width direction of the extrusion foamed sheet and calculating their arithmetic mean.

[0041] (Apparent density of the extruded foam sheet) The apparent density of the extruded foam sheet is 50 kg / m 3 or more and 300 kg / m 3 or less. If the apparent density of the extruded foam sheet is too small, the strength of a molded article such as a container obtained by thermoforming the extruded foam sheet may decrease. On the other hand, if the apparent density of the extruded foam sheet is too large, the heat insulation property and lightweight property of the above molded article may decrease. From these viewpoints, the apparent density of the extruded foam sheet is preferably 80 kg / m 3 or more and 180 kg / m 3 or less, and more preferably 100 kg / m 3 or more and 150 kg / m 3 or less. Note that the apparent density referred to here indicates the density over the entire thickness direction of the foam sheet, which is different from the apparent density of the foam sheet in the surface layer part described later.

[0042] (Method for measuring the apparent density of the extruded foam sheet) The apparent density of the extruded foam sheet can be specified as a value measured as follows, for example. First, a test piece measuring 25 mm in length and 25 mm in width 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-out test piece is measured. The measured mass is multiplied by 1600 and unit-converted to obtain the basis weight (g / m 2 ). Further, the value obtained by dividing the obtained basis weight (g / m 2 ) of the extruded foam sheet by the thickness (mm) of the extruded foam sheet is unit-converted to obtain the apparent density (kg / m 3 ) of the extruded foam sheet. The above measurement is performed at 10 equally spaced positions 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.

[0043] (Basis weight of the extruded foam sheet) The basis weight of the extruded foam sheet is preferably 100 g / m 2 to 400 g / m 2 , and more preferably 150 g / m 2 to 300 g / m 2When the basis weight is within this range, a container obtained by thermoforming an extruded foam sheet will be excellent in terms of the balance between rigidity and light weight.

[0044] (Method for Measuring the Basis Weight of an Extruded Foam Sheet) The basis weight of the extruded foam sheet can be specified as a value measured as follows. First, a test piece measuring 25 mm in length and 25 mm in width 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-out test piece is measured. The measured mass is multiplied by 1600 and unit conversion is performed to obtain the basis weight (g / m 2 ). The above measurement is performed at 10 equally spaced positions 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.

[0045] (Closed Cell Ratio of an Extruded Foam Sheet) The closed cell ratio of the extruded foam sheet is 70% or more, and preferably 75% or more. When the closed cell ratio of the extruded foam sheet is within this preferred range, the secondary foaming property of the extruded foam sheet during thermoforming of a molded body using the extruded foam sheet can be improved. In addition, the strength and the like of the molded body obtained by thermoforming the extruded foam sheet can be ensured. From this viewpoint, the closed cell ratio of the extruded foam sheet is preferably 80% or more.

[0046] (Method for Measuring the Closed Cell Ratio of an Extruded Foam Sheet) Randomly cut samples measuring 25 mm × 25 mm × sheet thickness (the thickness of the extruded foam sheet) are prepared from the extruded foam sheet. A plurality of cut samples are stacked so that the total thickness is closest to 20 mm (however, not exceeding 20 mm) to form a test piece. Next, according to Procedure C of ASTM-D2856-70, using an air comparison pycnometer model 930 or the like of Toshiba Beckman Co., Ltd., the true volume Vx of the test piece is measured, and the closed cell ratio S (%) is calculated by the following mathematical formula (Formula (1)). The above measurement is performed using 5 test pieces, and the arithmetic mean value thereof is taken as the closed cell ratio of the foam sheet.

[0047]

Number

[0048] 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 the bubbles in the independent bubble portion in the test piece, Va: The apparent volume (cm 3 ) of the test piece calculated from the outer dimensions of the test piece used for the measurement, W: The total mass (g) of all the cut samples used for the measurement, and ρ: The density (g / cm 3 ) of the resin constituting the foamed sheet, is as follows.

[0049] (Apparent density of the surface layer of the extruded foamed sheet) The apparent density (kg / m 3 ) of the surface layer of the extruded foamed sheet is defined as the apparent density of the portion from the surface of the extruded foamed sheet to a thickness of 200 μm in the thickness direction. The apparent density (kg / m 3 ) of the surface layer of the extruded foamed sheet is preferably 50 kg / m 3 or more and 450 kg / m 3 or less. From the viewpoint of obtaining an extruded foamed sheet with a smooth surface and excellent appearance, it is preferable that the apparent density of the surface layer of the extruded foamed sheet is higher than the above-described apparent density of the extruded foamed sheet. More preferably, the ratio of the apparent density of the surface layer of the extruded foamed sheet to the apparent density of the extruded foamed sheet is 1.1 or more, and even more preferably 1.2 or more. The upper limit of the ratio of the apparent density of the surface layer of the extruded foamed sheet to the apparent density of the extruded foamed sheet is preferably approximately 1.5. In addition, in order to set the apparent density of the surface layer of the extruded foamed sheet within a specific range, it is preferable to apply cooling air to the cylindrical foam immediately after extrusion from the annular die to cool it, thereby increasing the apparent density of the surface layer of the extruded foamed sheet and suppressing the growth of the bubbles in the surface layer of the polystyrene-based resin foam layer.

[0050] (Method for Measuring Apparent Density of Surface Layer Portion of Extruded Foamed Sheet) Slice a 200-μm portion from the surface of the extruded foamed sheet in the thickness direction, and obtain a test piece with the length (extrusion direction of the sheet) and width (width direction perpendicular to the extrusion direction of the sheet) aligned. Measure the mass and thickness of the test piece using a gauge or the like. By dividing the mass of the test piece by the volume of the test piece (width × length × thickness) and performing unit conversion to obtain the apparent density of the test piece, the apparent density of the surface layer portion of the extruded foamed sheet can be obtained.

[0051] [1-2 Actions and Effects] Thermoformed bodies of extruded foamed sheets using polystyrene-based resins are used in various fields such as containers for food storage. The thermoformed body can be obtained, for example, by shaping the extruded foamed sheet into a shape suitable for the application under heating conditions using a mold or the like. Such thermoformed bodies are often used for disposable applications and there are concerns about their impact on the natural environment. In addition, polystyrene-based resins are often manufactured using petroleum-based raw materials, and there are also concerns about their impact on petroleum resources. Therefore, it is considered to use a part or all of the resin used in the thermoformed body as a resin that can be synthesized from biodegradable resins or raw materials derived from biomass.

[0052] The extruded foamed sheet according to the first embodiment uses a mixed resin of a polystyrene-based resin, a polyphenylene ether-based resin, and a polylactic acid-based resin as the base resin. By using such a polylactic acid-based resin as part of the base resin of the extruded foamed sheet, it is possible to contribute to reducing the environmental load. For example, polylactic acid, which is an example of a polylactic acid-based resin, is a resin that can be synthesized from raw materials derived from biomass and is also a resin that is biodegradable in composting, thus contributing to reducing the environmental load.

[0053] When forming an extrusion foamed sheet using a resin containing a polylactic acid resin and a polystyrene resin as a base resin, there are concerns about the effects on the appearance such as unevenness and streak patterns on the surface of the extrusion foamed sheet, and the effects on thermoformability and the like when the extrusion foamed sheet is secondary formed. The cause is not clear, but as factors for such concerns, the low compatibility between the polystyrene resin and the polylactic acid resin, and the temperature assumed as the temperature at which the resin containing the polystyrene resin can foam (referred to as the first assumed temperature) and the temperature assumed as the temperature at which the resin can foam in a state where the polylactic acid resin is further added to the resin (the second assumed temperature) and the like can be considered. In this regard, in the extrusion foamed sheet of the present invention, by setting the value of the melting point Tm [°C] of the polylactic acid resin and the difference (Tm - Vst) between the melting point Tm [°C] of the polylactic acid resin and the Vicat softening temperature Vst [°C] of the mixed resin within a predetermined range, it can be expected that the difference between the first assumed temperature and the second assumed temperature can be kept within an appropriate range for performing extrusion foaming. Therefore, according to the present invention, it is considered that an extrusion foamed sheet excellent in foamability, moldability, and appearance can be obtained.

[0054] [2 Second Embodiment (Laminated Sheet Having an Extrusion Foamed Sheet (Foamed Sheet with Skin))] An epidermal layer may be provided on the extrusion foamed sheet described in the first embodiment. That is, the extrusion foamed sheet may be used as a laminated sheet in which an epidermal layer is laminated on the surface of the extrusion foamed sheet. The laminated sheet has an extrusion foamed sheet and an epidermal layer, and is a so-called foamed sheet with skin. Such a form of the laminated sheet is referred to as the second embodiment.

[0055] As the extrusion foamed sheet according to the second embodiment, the extrusion foamed sheet according to the first embodiment described above is used. Therefore, in the second embodiment, since the extrusion foamed sheet forming the laminated sheet has substantially the same configuration as the extrusion foamed sheet according to the first embodiment, the description thereof is omitted.

[0056] (Epidermal Layer) The structure of the skin layer is not particularly limited as long as it has a structure different from that of the extruded foam sheet. Examples of the skin layer include a resin layer in a non-foamed state (hereinafter sometimes simply referred to as a resin layer). By having a skin layer, the surface strength and designability of the extruded foam sheet can be improved.

[0057] The resin constituting the skin layer is not particularly limited, and may be the same resin as the mixed resin constituting the extruded foam sheet described in the first embodiment, or various resins constituting the mixed resin (for example, resins selected from polystyrene-based resins, polyphenylene ether-based resins, and polylactic acid-based resins) or combinations thereof.

[0058] More specifically, as the skin layer, for example, a film made of polystyrene resin, a film made of high-impact polystyrene resin, etc. can be used. From the viewpoints of thermoformability and adhesion to the extruded foam sheet, it is preferable to use a film made of polystyrene resin as the skin layer. Also, from the viewpoints of microwave heating applications and oil resistance, it is preferably to use a multilayer film of a polystyrene-based resin and a polyolefin-based resin or a polyolefin-based resin film as the skin layer. Examples of the polyolefin-based resin film include a film made of polyethylene resin, a film made of polypropylene-based resin, etc. When the skin layer is such a film, the film may be an unstretched film or a stretched film.

[0059] The thickness of the skin layer is not particularly limited, but is preferably 5 μm to 100 μm, more preferably 10 μm to 80 μm, and even more preferably 15 μm to 60 μm.

[0060] The method for forming the skin layer is not particularly limited. The skin layer may be formed together with the extruded foam sheet by a coextrusion method. In addition, for example, after the extruded foam sheet is formed, the resin layer forming the skin layer may be bonded under heating conditions (heat lamination method). In this way, a structure in which the skin layer is formed on the extruded foam sheet can be formed, and a laminated sheet can be obtained.

[0061] [Function and Effect of [2-2]] According to the laminated sheet according to the second embodiment, the same functions and effects as those described in the functions and effects of the first embodiment can be obtained.

[0062] As shown in the second embodiment, in the present invention, a configuration including an extruded foam sheet according to the first embodiment and a laminated sheet having a skin layer (foam sheet with skin) can be adopted.

[0063] [Manufacturing Method of Extruded Foam Sheet] The extruded foam sheet according to the present invention can be manufactured, for example, as follows.

[0064] [Contents of Manufacturing Method] (Preparation of Mixed Resin) Prepare a mixed resin by mixing a polystyrene-based resin, a polyphenylene ether-based resin, and a polylactic acid-based resin. As also shown in the description of the first embodiment, the mixed resin has a polylactic acid-based resin content of 10% by mass or more and 50% by mass or less. However, the total content of the polystyrene-based resin, the polyphenylene ether-based resin, and the polylactic acid-based resin in the mixed resin is 100% by mass. Further, the Vicat softening temperature of the mixed resin is 110°C or higher and 150°C or lower, and the value of the difference (Tm - Vst) between the Vicat softening temperature (Vst [°C]) of the mixed resin and the melting point (Tm [°C]) of the polylactic acid-based resin is more than 0°C and 40°C or lower.

[0065] (Supply of Mixed Resin) Using the above-described mixed resin containing the polystyrene resin, polyphenylene ether resin, and polylactic acid resin as the base resin, the base resin is supplied to an extruder. The extruder for obtaining an extruded foam sheet is not particularly limited, but generally, a tandem extruder in which a plurality of extruders (for example, a first extruder and a second extruder) are connected is used. Usually, in the first extruder, various resins serving as raw materials of the base resin are mixed, melted, and kneaded to form a foamable molten resin. In the second extruder, the foamable molten resin sent from the first extruder is adjusted to a predetermined temperature, and extrusion foaming is performed.

[0066] (Extrusion foaming) The base resin is heated, melted, and kneaded in the extruder. In addition, various additives such as a bubble regulator are supplied to the extruder as necessary. Further, a foaming agent is press-fitted into the extruder, and the base resin is further kneaded to form a foamable molten resin. The foamable molten resin is adjusted to the target resin temperature. Then, the foamable molten resin adjusted to a predetermined resin temperature is extruded under atmospheric pressure through an annular die (such as a circular die) to foam the foamable molten resin, thereby forming an extruded foam in a cylindrical shape. The cylindrical extruded foam (foamed cylindrical body) extruded from the annular die is cooled while being drawn along a mandrel (cooling cylinder) having a cooling function. The cylindrical extruded foam is slit with a cutter or the like and expanded into a flat shape to obtain an extruded foam sheet. The extruded foam sheet expanded into a flat shape is usually wound up with a winding roll or the like to be in a roll shape. The apparent density of the extruded foam sheet thus obtained may be set according to the functions required for the molded product obtained by secondary molding. However, the extruded foam sheet generally has an apparent density of about 50 kg / m 3 to 300 kg / m 3 or less. Also, as the extruded foam sheet, one having an independent bubble ratio of 70% or more can be obtained.

[0067] As the foaming agent, for example, aliphatic saturated hydrocarbons such as propane, butane, pentane, hexane, heptane, etc., halogenated hydrocarbons such as methyl chloride, ethyl chloride, methylene chloride, etc., ethers such as dimethyl ether, diethyl ether, methyl ethyl ether, etc., and physical foaming agents such as carbon dioxide, nitrogen, water, etc. can be used. Among these, from the viewpoint of making it easier to plasticize the mixed resin of the present invention and facilitating the production of the extruded foam sheet, and from the viewpoint of improving the thermoformability using the extruded foam sheet, as the foaming agent, it is preferable to use one or more selected from aliphatic saturated hydrocarbons having 3 to 5 carbon atoms, and it is more preferable to use normal butane, isobutane or a mixture thereof.

[0068] The addition amount of the foaming agent and the addition amount of the bubble regulator can be appropriately selected according to the type of the base resin, the type of the foaming agent, the type of the bubble regulator, and the density of each target foamed layer. Usually, based on 100 parts by mass of the base resin, the foaming agent is 0.5 to 10 parts by mass, and the bubble regulator is 0.1 to 3 parts by mass. Also, the resin temperature of the molten resin mixture during foaming can be appropriately selected according to the type of the base resin, the type of the foaming agent, the type of the bubble regulator, and the density of the target extruded foam sheet.

[0069] In the method for producing the above-mentioned extruded foam sheet, the annular die is used in consideration of the ease of application in subsequent processes such as thickness adjustment. Also, by extruding and foaming the foamable molten resin from the annular die, the resin is likely to be oriented, and the rigidity of the obtained extruded foam sheet can be increased.

[0070] In the description of the method for manufacturing the above-mentioned extruded foam sheet, an example in which the mixed resin is supplied to the extruder is used, but the method for manufacturing the extruded foam sheet is not limited to this. As long as various raw materials (such as polystyrene-based resin, polylactic acid-based resin, and polyphenylene ether-based resin, etc.) constituting the extruded foam sheet are heated, melted, and kneaded in the extruder, they may be supplied to the extruder in a mixed state of various raw materials, or they may be supplied to the extruder individually. In this case, regarding the supply order to the extruder, first, the polystyrene-based resin and the polyphenylene ether-based resin are supplied to the extruder, and after mixing (after melting) the polystyrene-based resin and the polyphenylene ether-based resin, the polylactic acid-based resin may be supplied to the extruder for further mixing. Also, a part of the polystyrene-based resin and the polyphenylene ether-based resin may be supplied to the extruder, and after mixing (after melting) the polystyrene-based resin and the polyphenylene ether-based resin, the polylactic acid-based resin and the remaining polystyrene-based resin may be supplied to the extruder for further mixing. Furthermore, a mixture obtained by kneading the polystyrene-based resin and the polyphenylene ether-based resin (this mixture is a so-called modified polyphenylene ether-based resin) may be prepared in advance, this mixture may be supplied to the extruder, and then the polylactic acid-based resin may be supplied to the extruder for further mixing of the polylactic acid-based resin with the mixture. In this case, the polyphenylene ether-based resin supplied to the extruder can be derived from the modified polyphenylene ether-based resin. Thus, it is preferable that the mixed resin is obtained by mixing the polylactic acid-based resin after mixing the polystyrene-based resin and the polyphenylene ether-based resin. Specifically, such a mixed resin can be obtained by supplying the polystyrene-based resin and the polyphenylene ether-based resin to the extruder, heating, melting, and kneading them to form a first kneaded product, and then supplying the polylactic acid-based resin to the extruder that formed the first kneaded product under the condition that the heating temperature is lower than the decomposition temperature of the polylactic acid-based resin, and melting and kneading it together with the first kneaded product. Incidentally, at this time, if the foaming agent is press-fitted into the extruder, a foamable molten resin is formed together with the formation of the mixed resin (i.e., the formation of the base resin).When preparing in advance a mixture obtained by kneading a polystyrene resin and a polyphenylene ether resin (so-called modified polyphenylene ether resin), it is preferable to prepare the modified polyphenylene ether resin so that its glass transition temperature Tg [°C] is 110°C or higher and 150°C or lower.

[0071] In the above-described method for producing an extruded foam sheet, the extruded foam sheet is formed into a sheet shape by splitting a cylindrical extruded foam. However, the method for producing the extruded foam sheet is not limited thereto. For example, a cylindrical extruded foam in a foamed state obtained by extruding a foamable molten resin from an extruder may be used as the extruded foam sheet by pressing it along a direction substantially perpendicular to the extrusion direction to fuse the inner surface of the extruded foam into one sheet.

[0072] [3-2 Action and Effect] According to the above-described method for producing an extruded foam sheet, the extruded foam sheet of the present invention can be easily produced. Further, in the method for producing an extruded foam sheet, when one or more physical foaming agents are selected from saturated hydrocarbons having 3 to 5 carbon atoms, the gas permeability is suppressed as compared with foaming agents such as carbon dioxide (it is easy to be retained in the extruded foam sheet), and the secondary foaming ratio during thermoforming can be increased, so that the thermoformability can be improved. Specifically, the range of forming conditions such as the heating temperature and heating time when thermoforming a container or the like can be widened. Further, even when the extruded foam sheet is stored for a long time after production, good thermoforming can be ensured.

[0073] In the above-described method for producing an extruded foam sheet, since the mixed resin is obtained by mixing a polystyrene resin and a polyphenylene ether resin and then mixing a polylactic acid resin, a state in which the polylactic acid resin is present more uniformly in the mixed resin can be formed, the mixing unevenness of the resin components contained in the base resin can be suppressed, and an extruded foam sheet excellent in appearance can be obtained.

[0074] [4 Application Examples] The extrusion foamed sheet shown in the first embodiment of the present invention and the laminated sheet shown in the second embodiment may be used as a sheet material as it is, or can be used as a raw material for various molded products. Examples of molded products using the extrusion foamed sheet include containers such as donburi containers, dishes, and cups. The molded product can be obtained by secondary molding of the extrusion foamed sheet or the laminated sheet. The method of secondary molding is not particularly limited, and examples thereof include vacuum molding, pressure air molding, vacuum pressure air molding, press molding, and injection molding.

[0075] Next, it will be described in more detail using examples.

Examples

[0076] (Preparation of Extruder and Resin) A tandem extruder connecting a first extruder and a second extruder was prepared, and a polystyrene-based resin, a polyphenylene ether-based resin, and a polylactic acid-based resin shown in Table 1 were prepared. However, the polyphenylene ether-based resin was prepared in a mixture state of the polystyrene-based resin and the polyphenylene ether-based resin.

[0077] Table 1 shows the contents of the prepared polylactic acid-based resin, polyphenylene ether-based resin, and polystyrene-based resin. PLA1, PLA2, PLA3, and PLA4 in Table 1 are polylactic acids with a D-form compound (all D-form lactic acid) content of 12% by mass, 4% by mass, 2.7% by mass, and 1% by mass, respectively. PLA1, PLA2, PLA3, and PLA4 were prepared with the trade names (grade names) LX975 manufactured by Total Corbion, LX175 manufactured by Total Corbion, REVODE110 manufactured by Zhejiang Hisun Biomaterials Co., Ltd., and L175 manufactured by Total Corbion, respectively.

[0078] In addition, the mPPE in Table 1 represents a mixture of a polystyrene-based resin and a polyphenylene ether-based resin. For mPPE, the content of the polyphenylene ether-based resin and the polystyrene-based resin is such that the content of the polyphenylene ether-based resin is 70% by mass and the content of the polystyrene-based resin is 30% by mass. However, the total of the polyphenylene ether-based resin and the polystyrene-based resin is 100% by mass. As mPPE, the product name (grade name) EFN4230 manufactured by SABIC was prepared. PS in Table 1 represents a polystyrene-based resin. As PS, the product name (grade name) GX154 manufactured by PS Japan was prepared.

[0079] Table 1 shows the glass transition temperature (Tg) of each resin, and the MFR of each resin of PLA1, PLA2, PLA3, PLA4 and PS is shown. Table 1 further shows the crystallization temperature and melting point (Tm) for each of the resins PLA1, PLA2, PLA3 and PLA4. Table 1 also shows the Vicat softening temperature (°C) of the polystyrene-based resin (PS) that constitutes the mixed resin as the base resin. The measurement methods for the glass transition temperature (°C) and MFR (g / 10 min (190 °C)), crystallization temperature (°C) and melting point (°C) of the resins shown in Table 1, and the measurement method for the Vicat softening temperature (°C) of the mixed resin are as follows, respectively.

[0080] (Measurement of the MFR of the resin) The MFR (g / 10 min (190 °C)) of the resins shown in Table 1 was determined based on JIS K7210-1:2014. As the measurement conditions, the conditions of 190 °C and a load of 2.16 kg were adopted.

[0081] (Glass transition temperature of the resin) The glass transition temperature (°C) of the resin shown in Table 1 was determined by performing heat flux differential scanning calorimetry in accordance with JIS K7121-1987. As the measuring device, a heat flux differential scanning calorimeter (Model: 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. As the state adjustment for determining the glass transition temperature of the resin, “When measuring the glass transition temperature after performing a certain heat treatment” described in “3. State adjustment of test pieces (3)” of JIS K7121-1987 was adopted. Resin pieces were placed in the container of the DSC device, heated and melted at a rate of 10 °C / min up to 200 °C, and immediately cooled at a rate of 10 °C / min to 0 °C for state adjustment, and the resulting specimens were used for testing.

[0082] (Melting point of polylactic acid resin) The melting point Tm (°C) of the polylactic acid resin was determined based on JIS K7121:1987. Specifically, “(2) When measuring the melting temperature after performing a certain heat treatment” was adopted as the state adjustment. A DSC curve was obtained by heating the state-adjusted test piece from 30 °C to 200 °C at a heating rate of 10 °C / min, and the peak temperature of the melting (endothermic) peak was taken as the melting point. As the measuring device, a heat flux differential scanning calorimeter (Model: DSC Q1000 manufactured by TA Instruments) was used.

[0083] (Crystallization temperature of polylactic acid resin) The crystallization temperature Tc (°C) of the polylactic acid resin was determined based on JIS K7121:1987. Specifically, “(2) When measuring the melting temperature after performing a certain heat treatment” was adopted as the state adjustment. A DSC curve was obtained by heating the state-adjusted test piece from 30 °C to 200 °C at a heating rate of 10 °C / min, and the peak temperature of the crystallization (exothermic) peak was taken as the crystallization temperature. As the measuring device, a heat flux differential scanning calorimeter (Model: DSC Q1000 manufactured by TA Instruments) was used.

[0084] (Measurement of Vicat softening temperature of the mixed resin) The Vicat softening temperature (°C) of the mixed resin (a mixture of each raw material resin such as polystyrene-based resin, polyphenylene ether-based resin, and polylactic acid-based resin) was determined in accordance with Method A50 of JIS K7206:2016. A kneaded product of the mixed resin melted and kneaded by an extruder with the same materials and compounding ratios as those shown in the examples and comparative examples respectively was pressurized to 5 MPa at 230 °C so that no bubbles were mixed in, and a test piece with a length of 20 mm × width of 20 mm × thickness of 4 mm was prepared and used for measurement without annealing treatment. As the measuring device, "HDT / VSPT test device MODEL TM-4123" manufactured by Ueshima Seisakusho Co., Ltd. was used.

[0085] [Table 1]

[0086] (Examples 1 to 9 and Comparative Example 5) The polystyrene-based resin, polyphenylene ether-based resin, and polylactic acid-based resin were supplied to the first extruder of a tandem extruder so as to achieve the blending ratio (blending ratio of the mixed resin) (mass %) of the raw material resins in the mixed resins shown in Tables 2 and 3, and further heated, melted, and kneaded in the first extruder. A mixture (modified polyphenylene ether-based resin) (sometimes referred to as mPPE2) obtained by kneading the polystyrene-based resin and the mPPE shown in Table 1 so that the mass ratio of the polystyrene-based resin to the polyphenylene ether-based resin (polystyrene-based resin: polyphenylene ether-based resin) was 65:35 was prepared in advance. The glass transition temperature of the mixture (mPPE2) was 131°C. The proportion of the polystyrene-based resin in mPPE2 was higher than that in the mPPE shown in Table 1. By appropriately combining this modified polyphenylene ether-based resin, the polystyrene-based resin, and the polylactic acid-based resin, the blending ratios of the raw material resins in the mixed resins shown in Tables 2 and 3 were realized. At this time, a mixed resin of the polystyrene-based resin, polyphenylene ether-based resin, and polylactic acid-based resin was formed, and this mixed resin was used as the base resin. Also, when forming the mixed resin, talc was also supplied to the first extruder. The above-described blending ratio is a value when the total of the mass ratios (mass %) of the polystyrene-based resin, polyphenylene ether-based resin, and polylactic acid-based resin is 100 mass%.

[0087] Next, a physical foaming agent was injected into the first extruder and further kneaded to form a kneaded product. The kneaded product was transferred to the second extruder, and the resin temperature (temperature of the kneaded product) was adjusted to form a resin melt for forming a foamed sheet. Then, the resin melt for forming a foamed sheet was extruded and foamed into the atmosphere at a discharge rate of 50 kg / hr at a predetermined foaming temperature from an annular die (the diameter of the annular die was 50 mm) to form a foamed cylindrical body. Further, while the foamed cylindrical body was being guided along the outer surface of a cooling cylinder (mandrel) having an outer diameter of 150 mm, the foamed cylindrical body was cut along the extrusion direction while being drawn at a draw ratio of 3 and a draw speed of 8 m / min to produce an extruded foamed sheet.

[0088] The above talc was used as a foam regulator and was supplied to the first extruder at a ratio of 2 parts by mass based on a total of 100 parts by mass of the polystyrene-based resin and the polylactic acid-based resin. Further, as the physical foaming agent, butane (a mixed butane of 30% by mass of isobutane and 70% by mass of normal butane) was used and was injected into the first extruder so as to be 2.3 parts by mass based on a total of 100 parts by mass of the polystyrene-based resin and the polylactic acid-based resin.

[0089] (Comparative Examples 1 to 4, 6) During melt-kneading, without preparing a mixture (mPPE2) obtained by previously kneading a polystyrene-based resin and a polyphenylene ether resin in advance, mPPE, a polystyrene-based resin, and polylactic acid shown in Table 1 were supplied to the first extruder, and an extrusion foamed sheet was produced in the same manner as in Example 1 except that the blending ratio of the raw material resins in the mixed resin shown in Table 3 was realized.

[0090] For each of Examples 1 to 9 and Comparative Examples 1 to 6, the situation during the production of the extrusion foamed sheet was observed as follows, and the production stability was evaluated. Further, for each of Examples 1 to 9 and Comparative Examples 1 to 6, the obtained extrusion foamed sheet was cured for 1 week in an indoor environment (23°C, relative humidity 50%), and using the cured extrusion foamed sheet, the thickness, basis weight, foaming ratio, apparent density, width, average bubble diameter in the thickness direction, closed cell ratio, apparent density of the surface layer portion, and appearance (surface property) were evaluated as follows. The results are shown in Tables 2 and 3. In addition, Tables 2 and 3 also show the Vicat softening temperature Vst (°C) of the mixed resin which is the base resin used in each example and comparative example. The Vicat softening temperature Vst (°C) of the mixed resin is determined by the A50 method of JIS K7206:2016 as described above.

[0091] Further, for each of Examples 1 to 9 and Comparative Examples 1 to 6, a non-foamed resin sheet was produced by the following method using the base resin used during the production of the extrusion foamed sheet.

[0092] (Production of non-foamed resin sheet) An extruder with an output of 15 kg was prepared. For each of Examples 1 to 9 and Comparative Examples 1 to 6, each raw material resin such as a polystyrene-based resin, a polyphenylene ether-based resin, and a polylactic acid-based resin was supplied to this extruder so as to have the compounding ratios shown in Tables 2 and 3, and heated, melted, and kneaded to obtain a kneaded product. Then, the kneaded product was extruded from a slit die (slit width: 1 mm) to produce a non-foamed resin sheet (thickness: 1.5 mm). The obtained non-foamed resin sheet was evaluated for its appearance (surface property). The results are shown in Tables 2 and 3.

[0093] As shown in Tables 2 and 3, in Examples 1 to 9, the extruded foam sheet was excellent in surface property. Also, for both Examples 1 to 9 and Comparative Examples 1 to 6, since the appearance (surface property) of the non-foamed resin sheet was good, it was confirmed that the conditions for improving the surface property with the extruded foam sheet and the conditions for improving the surface property with the non-foamed resin sheet did not match.

[0094] (Thickness of the extruded foam sheet) The thickness of the extruded foam sheet was measured by the method described above.

[0095] (Grammage and apparent density of the extruded foam sheet) The apparent density of the extruded foam sheet was measured by the method described above. Specifically, test pieces with dimensions of 25 mm in length × 25 mm in width × the thickness of the extruded foam sheet were cut out from 10 equally spaced locations in the width direction of the extruded foam sheet, and their masses were measured. Next, the mass was multiplied by 1600 and unit conversion was performed to calculate the grammage. Further, the value obtained by dividing the calculated grammage of the extruded foam sheet by the thickness of the extruded foam sheet was unit-converted to calculate the apparent density of each test piece. Then, the arithmetic mean value of these was taken as the apparent density (D1) of the foam sheet.

[0096] (Width of the extruded foam sheet) The width of the extruded foam sheet was specified as follows. That is, ten positions were selected from different positions on the extruded foam sheet, and at each position, the distance from one end to the other end of the extruded foam sheet was measured in a direction approximately perpendicular to the extrusion direction. The values measured at each position were arithmetically averaged. This arithmetically averaged value was taken as the width of the extruded foam sheet.

[0097] (Average bubble diameter in the thickness direction) The average bubble diameter (μm) in the thickness direction of the extruded foam sheet was determined as follows. First, the extruded foam sheet was cut perpendicular to the extrusion direction, and magnified photographs of the cut surfaces (cross-sections perpendicular to the width direction) were taken at ten equally spaced positions in the width direction of the extruded foam sheet. Next, the length in the thickness direction (the direction perpendicular to the extrusion direction) of the extruded foam sheet was measured based on the magnified photograph of each cut surface. Next, a straight line was drawn in the thickness direction of the extruded foam sheet in each magnified photograph, and the total number of bubbles in the extruded foam sheet intersecting the straight line was counted, thereby obtaining the number of bubbles in the thickness direction of the extruded foam sheet. Next, for each of the ten positions, the bubble diameter in the thickness direction was calculated by dividing the number of bubbles in the thickness direction of the extruded foam sheet by the length in the thickness direction of the extruded foam sheet. Then, the arithmetic mean value of the bubble diameters in the thickness direction at each of the ten obtained positions was taken as the average bubble diameter (average bubble diameter in the thickness direction) of the extruded foam sheet.

[0098] (Closed cell ratio) Cut samples measuring 25 mm × 25 mm × sheet thickness (the thickness of the extruded foam sheet) were randomly cut from the extruded foam sheet. A plurality of cut samples were stacked so that the total sum of the sheet thicknesses was closest to 20 mm (however, not exceeding 20 mm) to form a test piece. Next, according to Procedure C of ASTM-D2856-70, using an air comparison pycnometer model 930 of Toshiba Beckman Co., Ltd., etc., the true volume Vx of the test piece was measured, and the closed cell ratio S (%) was calculated by the following mathematical formula (Formula (1)). The above measurement was performed using five test pieces, and the arithmetic mean value was taken as the closed cell ratio of the foam sheet.

[0099]

Equation

[0100] 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 the bubbles in the independent bubble portion within the test piece, Va: The apparent volume (cm 3 ) of the test piece calculated from the outer dimensions of the test piece used for the measurement, W: The total mass (g) of the cut samples used for the measurement, and ρ: The density (g / cm 3 ) of the resin constituting the foamed sheet, is as follows.

[0101] (Apparent density of the surface layer of the extruded foamed sheet) The apparent density of the surface layer of the extruded foamed sheet was specified as follows. A 200-μm-thick portion was sliced from the surface of the extruded foamed sheet in the thickness direction and trimmed into test pieces with a length (extrusion direction of the extruded foamed sheet) of 20 mm × width (width direction perpendicular to the extrusion direction of the extruded foamed sheet) of 5 mm. At the same time, the mass and thickness of the test pieces were measured with a gauge. The mass of the test piece was divided by the volume of the test piece (width × length × thickness), and the apparent density of the test piece was obtained through unit conversion. The above measurement was performed at 10 equally spaced locations in the width direction of the extruded foamed sheet, and the arithmetic mean value thereof was taken as the apparent density of the surface layer of the extruded foamed sheet.

[0102] (Evaluation of appearance (surface property)) Regarding the evaluation method of the quality of the appearance of the extruded foamed sheet, the surface of the extruded foamed sheet was visually observed, and based on the observation results, the appearance (surface property) of the extruded foamed sheet was evaluated according to the following criteria. In the observation, 20 test pieces with a length of 1 m in the extrusion direction (width and thickness are the values described in Tables 2 and 3) were randomly cut out from the extruded foamed sheet, and each test piece was observed.

[0103] ◎(Extremely good): No unevenness or streak patterns were observed on the surface of all the sheets, and the surface was smooth. 〇 (Good): There was only a rare occurrence of a sheet in which at least one of unevenness and streaks was observed on the surface. × (Bad): At least one of unevenness and streaks was observed on the surface of almost all the sheets.

[0104] Here, the evaluation method for the appearance of the extruded foam sheet was described. However, the evaluation method and criteria for the appearance of the non-foamed sheet are the same as those for the evaluation method and criteria for the quality of the appearance of the extruded foam sheet. The above-described evaluation criteria were described using the same sheet language that is common to both the extruded foam sheet and the extruded foam sheet.

[0105] Furthermore, for each of Examples 1 to 9 and Comparative Examples 1 to 6, molded products were manufactured as follows using the foamed sheets (extruded foam sheets after curing) obtained by curing the obtained extruded foam sheets for 30 days in an indoor environment (23°C, relative humidity 50%). Then, the moldability of the extruded foam sheet and the appearance (surface property) of the molded product were evaluated. The results are shown in Tables 2 and 3. Also, the thickness (primary thickness) of the extruded foam sheet after curing was measured. Furthermore, a secondary foaming test was conducted using the extruded foam sheet after curing. The thickness after secondary foaming (secondary thickness) and the secondary foaming ratio were measured. The results are shown in accordance with the molded product columns in Tables 2 and 3.

[0106] (Manufacture of Molded Product) Using the extruded foam sheet after curing, 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 vacuum forming. The forming machine consists of a heating zone for heating the extruded foam sheet and a forming zone for forming, and heating heaters are provided above and below the extruded foam sheet in the heating zone. The extruded foam sheet was fixed to a frame having an opening of 600 mm square, the upper heater was adjusted to 290°C, the lower heater was adjusted to 290°C, and the extruded foam sheet was heated for 13.6 seconds. Then, the heated extruded foam sheet was sent to the forming zone, and a container having a circular opening with a diameter of φ202 mm, a depth of 38 mm, and a draw ratio of 0.19 was formed.

[0107] The above-mentioned match mold vacuum forming was carried out multiple times by changing the heating seconds from the above values. The time width obtained from the difference between the longest time and the shortest time among the heating seconds for which good molded products could be obtained was measured, and this time width was defined as the moldable time width.

[0108] (Formability) Based on the moldable time width, the formability of the extruded foam sheet was evaluated according to the following criteria. ◎(Extremely good): The width of the moldable time is 8 seconds or more. 〇(Good): The width of the moldable time is 3 seconds or more and less than 8 seconds. ×(Poor): The width of the moldable time was less than 3 seconds, or good molded products could not be obtained.

[0109] (Appearance of molded product (surface property)) More than 20 molded products were manufactured by the production of the above-mentioned molded products. Twenty were randomly selected from the obtained multiple molded products, and the surface of each molded product was visually observed. The appearance (surface property) of the molded product was evaluated according to the following criteria. ◎(Extremely good): Neither unevenness nor streak patterns were observed on the surface of all molded products. 〇(Good): Molded products in which at least one of unevenness and streak patterns was rarely observed on the surface of the molded product were only rarely observed. ×(Poor): At least one of unevenness and streak patterns was observed on the surface of almost all molded products.

[0110] (Primary thickness) The thickness of the extruded foam sheet after curing (primary thickness) was measured by the same method as the method for measuring the thickness of the extruded foam sheet described above.

[0111] (Secondary foaming test) A test piece of 200 mm × 200 mm was cut out from near the center in the width direction of the extruded foam sheet after curing (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 were both 200 mm), and the test piece was placed in an oven set at 160 °C (product number PERFECT OVEN PH-200, manufactured by Tabai Espec Corporation) and heated for 25 seconds. The test piece after heating was taken out of the oven.

[0112] (Secondary thickness) The thickness after secondary foaming (secondary thickness) of the extruded foam sheet after curing was measured as the thickness of the test piece after heating obtained in the above secondary foaming test. The thickness of the test piece after heating was measured by the same method as the method for measuring the thickness of the extruded foam sheet described above.

[0113] (Secondary foaming ratio) The cured foam sheet was placed in an oven at 160 °C and heated, and for the foam sheet after heating, the apparent density (D2) was measured by the same method as the method for measuring the apparent density (D1) of the extruded foam sheet. The secondary foaming ratio (times) was calculated by the following mathematical formula (Formula (2)).

[0114]

Number

[0115] As shown in Table 2 and Table 3, it was confirmed that in Examples 1 to 9, the moldability of the extruded foam sheet and the surface property of the molded product were excellent.

[0116]

Table 2

[0117]

Table 3

[0118] As described above, the first embodiment, the second embodiment, the manufacturing method, and the application example of the present invention have been specifically described, but these are merely examples, and various modifications based on the technical idea of the present invention are possible.

[0119] For example, the configurations, methods, steps, shapes, materials, numerical values, etc. mentioned above are merely examples, and different configurations, methods, steps, shapes, materials, numerical values, etc. may be used as necessary. Further, the configurations, methods, steps, shapes, materials, numerical values, etc. of the above-described embodiments, etc. can be combined with each other as long as the gist of the present invention is not deviated from.

Claims

1. An extruded foam sheet having a mixed resin of a polystyrene resin, a polyphenylene ether resin, and a polylactic acid resin as a base resin, wherein the blending amount of the polylactic acid resin in the mixed resin is 10% by mass or more and 50% by mass or less (however, the total blending amount of the polystyrene resin, the polyphenylene ether resin, and the polylactic acid resin in the mixed resin is 100% by mass), the Vicat softening temperature Vst [°C] of the mixed resin is 110°C or more and 150°C or less, and the difference (Tm - Vst) between the melting point Tm [°C] of the polylactic acid resin and the Vicat softening temperature Vst [°C] of the mixed resin exceeds 0°C and is 40°C or less, The apparent density of the extruded foam sheet is 50 kg / m ３ or more and 300 kg / m ３ or less, and and the closed cell ratio of the extruded foam sheet is 70% or more, characterized by an extruded foam sheet.

2. The melting point Tm [°C] of the polylactic acid resin is 125°C or more and 160°C or less, The extruded foam sheet according to Claim 1.

3. The Vicat softening temperature Vst [°C] of the mixed resin is 120°C or more and 140°C or less, The extruded foam sheet according to Claim 1 or 2.

4. The closed cell ratio of the extruded foam sheet is 80% or more, The extruded foam sheet according to any one of Claims 1 to 3.

5. A method for manufacturing an extruded foam sheet, comprising a step of extruding and foaming a foamable molten resin containing a mixed resin of a polystyrene resin, a polyphenylene ether resin, and a polylactic acid resin and a physical foaming agent, wherein the blending amount of the polylactic acid resin in the mixed resin is 10% by mass or more and 50% by mass or less (however, the total blending amount of the polystyrene resin, the polyphenylene ether resin, and the polylactic acid resin in the mixed resin is 100% by mass), the Vicat softening temperature Vst [°C] of the mixed resin is 110°C or more and 150°C or less, and the difference (Tm - Vst) between the melting point Tm [°C] of the polylactic acid resin and the Vicat softening temperature Vst [°C] of the mixed resin exceeds 0°C and is 40°C or less, The apparent density of the extruded foam sheet is 50 kg / m ３ or more and 300 kg / m ３ or less, and and the closed cell ratio of the extruded foam sheet is 70% or more, characterized by a method for manufacturing an extruded foam sheet.

6. The polyphenylene ether-based resin is derived from a modified polyphenylene ether-based resin defined as a mixture obtained by kneading the polyphenylene ether-based resin and the polystyrene-based resin, and the glass transition temperature Tg [°C] of the modified polyphenylene ether-based resin is 110°C or higher and 150°C or lower. The method for producing an extruded foam sheet according to claim 5.

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