Foam sheet, method for producing foam sheet, and molded product

Abstract

To provide a foamed sheet which is excellent in heat resistance, heat insulation property, strength, and biodegradability.SOLUTION: A foamed sheet is provided which is formed of a composition containing a polylactic resin, wherein the composition containing the polylactic resin contains at least a polylactic resin and inorganic particles, in the polylactic resin, any one of a D body of a lactic acid and an L body of the lactic acid that is a constituent monomer unit of the polylactic resin is 98 mol% or more in the polylactic resin, and a content of the polylactic resin to the total amount of organic matters in the foamed sheet is 98 mass% or more, the inorganic particles contain a lamellar silicate, a volume average particle diameter of the lamellar silicate is 10 μm or more and 200 μm or less, an aspect ratio of the lamellar silicate is 10 or more and 100 or less, and a content of the lamellar silicate in the foamed sheet is 2 mass% or less.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a foam sheet, a method for producing a foam sheet, and a molded article. [Background technology]

[0002] Plastics are widely distributed after being processed into various product shapes such as bags and containers. However, plastic products are difficult to decompose in nature, making their disposal after use a problem. In recent years, with growing environmental awareness, there has been active development of materials to replace non-biodegradable plastics, which are difficult to decompose in nature, with biodegradable bioplastics, which are easily decomposed in nature.

[0003] Among biodegradable biomass plastics, polylactic acid resin has attracted attention as an alternative to non-degradable plastics because its properties are similar to those of polystyrene, which is a plastic that has been conventionally used. One use form of polystyrene is expanded polystyrene, which is made by expanding polystyrene to provide functions such as light weight, cushioning properties, and heat insulation, and is widely used. Expanded polylactic acid, which uses polylactic acid resin, a biodegradable plastic, has also been proposed as an environmentally friendly alternative to such expanded polystyrene (see, for example, Patent Documents 1 to 4).

[0004] It is generally pointed out that polylactic acid resin has low heat resistance when used in food containers due to its low glass transition temperature (approximately 60°C). However, it has been confirmed that heat resistance can be improved by increasing the crystallinity of polylactic acid resin during the molding process (see Patent Documents 5 and 6). Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a foamed sheet that is excellent in heat resistance, heat insulation, strength, and biodegradability. [Means for solving the problem]

[0006] The foam sheet of the present invention, as a means for solving the above problems, is a foam sheet made of a composition containing a polylactic acid resin, wherein the composition containing the polylactic acid resin contains at least polylactic acid resin and inorganic particles, wherein the polylactic acid resin contains 98 mol % or more of either the D-form of lactic acid or the L-form of lactic acid, which are constituent monomer units of the polylactic acid resin, in the polylactic acid resin, the content of the polylactic acid resin relative to the total amount of organic matter in the foam sheet is 98 mass % or more, the inorganic particles contain a layered silicate, the volume average particle diameter of the layered silicate is 10 μm or more and 200 μm or less and the aspect ratio of the layered silicate is 10 or more and 100 or less, and the content of the layered silicate in the foam sheet is 2 mass % or less. [Effects of the Invention]

[0007] According to the present invention, a foamed sheet having excellent heat resistance, heat insulation, strength, and biodegradability can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram illustrating the shape of the outermost surface in the TD direction of the cross section of the foamed sheet of the present invention. [Figure 2] FIG. 2 is a schematic explanatory view showing an example of a continuous kneading apparatus used in the method for producing a foamed sheet of the present invention. [Figure 3] FIG. 3 is a schematic diagram showing an example of a tandem type continuous foamed sheet production apparatus used in the foamed sheet production method of the present invention. [Figure 4] FIG. 4 is a schematic explanatory view showing an example of a flow path in a die of an extruder used in the method for producing a foamed sheet of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] The foam sheet, the method for producing the foam sheet, the apparatus for producing the foam sheet, and the molded article of the present invention are described in detail below. The present invention is not limited to the following embodiments, and may be modified, added, modified, or deleted within the scope of what one skilled in the art can conceive. Any embodiment is within the scope of the present invention as long as it exhibits the functions and effects of the present invention.

[0010] (Foam sheet) The foam sheet of the present invention is a foam sheet made of a composition containing a polylactic acid resin (hereinafter sometimes referred to as a "polylactic acid resin composition"), wherein the composition containing the polylactic acid resin contains at least a polylactic acid resin and inorganic particles, wherein the polylactic acid resin contains 98 mol % or more of either a D-form of lactic acid or an L-form of lactic acid, which are constituent monomer units of the polylactic acid resin, in the polylactic acid resin, and the content of the polylactic acid resin relative to the total amount of organic matter in the foam sheet is 98 mass % or more, the inorganic particles contain a layered silicate, and the layered silicate has a volume average particle diameter of 10 μm or more and 200 μm or less and an aspect ratio of 10 or more and 100 or less, and the content of the layered silicate in the foam sheet is 2 mass % or less.

[0011] The present inventors have found that, in order to increase the productivity of biodegradable and heat-resistant molded articles, it is preferable to use a polylactic acid resin of high optical purity which has a fast crystallization rate. However, when an attempt is made to increase the expansion ratio of a foamed sheet in order to improve functions such as heat insulation and strength, that is, when an attempt is made to produce a foamed sheet of low bulk density, the high-optical purity polylactic acid resin has a high melting point and a fast crystallization rate, and therefore, when the foaming temperature is lowered, rapid crystallization occurs in the extrusion device, making it impossible to expect an improvement in the expansion ratio due to the foaming temperature, and stable operation tends to be difficult. Furthermore, even if a foamed sheet is obtained, when produced at a low temperature, the foamed sheet tends to undergo crystallization and have poor thermoformability.

[0012] In order to solve these problems, the present inventors have conducted extensive research and found that, by having the above-mentioned configuration, it is possible to provide a foamed sheet that is excellent in heat resistance, heat insulation, strength, and biodegradability, and is suitable as a material for food containers.

[0013] Since the foamed sheet of the present invention is made of a composition containing a polylactic acid resin, the foamed sheet of the present invention may also be referred to as a "polylactic acid foamed sheet," "expanded polylactic acid composition sheet," etc. As will be described in detail below, the foamed sheet of the present invention has good heat resistance and can be used, for example, as a heat-resistant food container. The foamed sheet of the present invention refers to a sheet-shaped product obtained by foaming a composition containing a polylactic acid resin.

[0014] [Physical properties of foam sheet] Since the foamed sheet is obtained by foaming the polylactic acid resin composition, the physical properties of the foamed sheet and the physical properties of the polylactic acid resin composition are synonymous with each other, except for the physical properties that characterize the thermal history and shape of the foamed sheet. As will be described in detail later, the physical properties that characterize the thermal history of the foamed sheet include cold crystallization enthalpy, and the physical properties that characterize the shape include bulk density, foam diameter, basis weight, Ra, and RSm.

[0015] -Bulk density- The bulk density of the foamed sheet is not particularly limited and can be appropriately selected depending on the purpose. 3 More than 0.156g / cm 3 Preferably, it is 0.063 g / cm or less. 3 More than 0.125g / cm 3 More preferably, it is 0.063 g / cm or less. 3 More than 0.096g / cm 3 It is more preferable that the bulk density of the foamed sheet is 0.063 g / cm or less. 3 More than 0.156g / cm 3 By using the following method, the foamed sheet contains many bubbles and exhibits high heat insulating properties. In addition, the thickness of the foamed sheet is increased, and the moment of inertia of the area is increased, resulting in high strength.

[0016] The bulk density of the foamed sheet can be adjusted by changing the expansion ratio during production of the foamed sheet, such as the expansion temperature, the amount of the foaming agent, the type of die, etc. Specifically, the expansion ratio can be increased by lowering the expansion temperature during production of the foamed sheet, increasing the amount of the foaming agent, or using a circular die, and thus the bulk density of the foamed sheet can be reduced.

[0017] The bulk density of the foamed sheet in the present invention is a value measured as follows. The foamed sheet is left to stand for 24 hours or more in an environment adjusted to a temperature of 23°C and a relative humidity of 50%, and a 50 mm x 50 mm test piece is cut out. The bulk density of the cut test piece is measured by a submerged weighing method using an automatic hydrometer (e.g., DSG-1 manufactured by Toyo Seiki Seisakusho, Ltd.). In the liquid weighing method, the mass (g) of the test piece of the foamed sheet in air is precisely weighed, and then the mass (g) of the test piece of the foamed sheet in water is precisely weighed, and the mass can be calculated using the following formula (1). Bulk density [g / cm 3 ] = density of water [g / cm 3 ] × mass of test piece in air [g] / (mass of test piece in air [g] - mass of test piece in liquid [g]) Equation (1)

[0018] - Foam diameter (median diameter) - The foam diameter of the foam sheet is not particularly limited and can be appropriately selected depending on the purpose, but the median diameter is preferably 200 μm to 800 μm, more preferably 400 μm to 800 μm, and even more preferably 500 μm to 650 μm. By setting the foam diameter (median diameter) of the foam sheet to 200 μm or more, it is possible to prevent the cell walls from becoming thin and reducing strength. Furthermore, by setting the foam diameter (median diameter) of the foam sheet to 800 μm or less, it is possible to prevent an increase in thermal conductivity and a decrease in heat insulation.

[0019] The method for measuring the foam diameter (median diameter) of the foamed sheet is not particularly limited and can be appropriately selected depending on the purpose. For example, the foam sheet is cut into a cross section using a sharp razor (e.g., a 76 razor manufactured by Nissin EM Co., Ltd.), and the cross section of the foam sheet is observed using a scanning electron microscope (SEM) (e.g., a 3D real surface view microscope VE-9800 manufactured by KEYENCE Corporation). The magnification is adjusted so that the number of bubbles in the observation area is several tens to several hundreds, so that an image suitable for the image analysis described below can be obtained (e.g., 50x for a foam diameter of approximately 100 μm). If necessary, multiple fields of view may be photographed, and the images may be joined together for image analysis. The obtained image is subjected to region segmentation using the watershed method (morphological segmentation) using, for example, image analysis software (e.g., the MorphoLibJ plug-in for ImageJ). In this case, the tolerance is adjusted for each image so that the segmentation is appropriate (e.g., 60). The region dividing lines are output as a binary image, and the distribution of bubble area is determined using the particle size analysis function of the image analysis software. In this case, bubbles adjacent to the edge of the image are excluded from the analysis. The cumulative distribution of the bubble area is created using a spreadsheet software or the like, the area where the cumulative distribution is 50% is determined, and the circle equivalent diameter of that area is calculated and used as the bubble diameter (median diameter).

[0020] -Basic weight- The basis weight of the foamed sheet is not particularly limited and can be appropriately selected depending on the application. When the foamed sheet is used as a food packaging container, the basis weight is preferably 100 g / m 2 More than 300g / m 2 Preferably less than 140 g / m 2 More than 280g / m 2 Less than 250 g / m is more preferable. 2 More than 280g / m 2 More preferably, the foam sheet has a basis weight of 100 g / m 2 More than 300g / m 2 If the thickness is less than or equal to 1000 μm, a foamed sheet that is both lightweight and strong tends to be obtained.

[0021] The method for measuring the basis weight of the foamed sheet in the present invention is not particularly limited, but for example, it can be measured as follows. The foamed sheet is left to stand for 24 hours or more in an environment adjusted to a temperature of 23°C and a relative humidity of 50%, and a 50 mm x 50 mm test piece is cut out. The mass of the test piece is measured using a balance. The basis weight can be calculated from the measured mass using the following formula (2). The basis weight of the foamed sheet is determined by measuring at least three points in the extrusion direction (MD) of the foamed sheet and in the direction perpendicular to the MD (TD), and the arithmetic average of these three points is used. Basis weight [g / m 2 ]=Measurement mass [g] / (0.05m×0.05m) ··· Formula (2)

[0022] In the present invention, the term "MD (machine direction)" refers to the direction in which the foam sheet is produced (extrusion direction), and the term "TD (transverse direction)" refers to the direction perpendicular to the MD direction. The TD direction of the foam sheet is synonymous with the width direction of the foam sheet.

[0023] -Top surface shape of foam sheet- As described above, the shape of at least one surface of the foam sheet in the TD direction, as viewed from a cross section in the thickness direction and TD direction of the foam sheet, significantly affects molding defects such as breakage during molding of the foam sheet. In particular, when the surface of the foam sheet has corrugated wrinkles, molding defects are likely to occur during molding of the foam sheet. In contrast, the surface of the foam sheet of the present invention has very few corrugated wrinkles.

[0024] --Ratio [Ra / RSm]-- The corrugated wrinkles on the surface of the foam sheet can be expressed as the ratio [Ra / RSm] of the arithmetic mean roughness Ra calculated in accordance with JIS B 0601:2013 (Geometric Product Specifications (GPS) - Surface Texture: Profile Method - Terms, Definitions and Surface Texture Parameters) to the mean length RSm of the roughness curve elements calculated in accordance with JIS B 0601:2013, for the shape of at least one surface of the foam sheet in the direction perpendicular to the extrusion direction (TD) of the foam sheet, as viewed from a cross section in the thickness direction of the foam sheet and in the direction perpendicular to the extrusion direction (TD) of the foam sheet.

[0025] The shape of at least one surface of the foamed sheet in the TD direction, as viewed from a cross section of the foamed sheet in the thickness direction and the TD direction, will be specifically described with reference to the drawings. FIG. 1 is a schematic diagram (perspective view) illustrating the TD shape of at least one surface of a foamed sheet of the present invention, as viewed from a cross section in the thickness direction and TD of the foamed sheet. In FIG. 1, the up-down direction indicates the thickness direction of the foamed sheet 200, the left-right direction indicates the TD direction of the foamed sheet 200, and the depth direction indicates the MD direction of the foamed sheet 200. The contour shape of one surface (outermost surface) 202 of the foamed sheet 200, as viewed from a cross section 201 in the thickness direction and TD of the foamed sheet 200, has corrugated wrinkles (wave-shaped irregularities, periodic wave-shaped undulations), as indicated by the bold line. Note that while one surface (outermost surface) 202 of the foamed sheet 200 has been described here, the other surface (outermost surface) of the foamed sheet 200 also has a similar shape.

[0026] Hereinafter, in this specification, the shape of at least one surface of the foamed sheet in the TD direction as viewed from a cross section of the foamed sheet in the thickness direction and TD direction may be referred to as "the shape of the outermost surface in the TD direction of the cross section of the foamed sheet."

[0027] Regarding the outermost surface shape in the TD direction of the cross section of the foam sheet, the ratio [Ra / RSm] of the arithmetic mean roughness Ra calculated in accordance with JIS B 0601:2013 to the average length RSm of roughness curve elements calculated in accordance with JIS B 0601:2013 is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.050 or less, more preferably 0.030 or less, and even more preferably 0.015 or less. A ratio [Ra / RSm] of 0.050 or less indicates that the outermost surface in the TD direction of the cross section of the foam sheet has very few corrugated wrinkles, which reduces the number of areas that can become the starting point of tears during molding of the foam sheet and suppresses molding defects.

[0028] --Arithmetic mean roughness Ra-- The arithmetic mean roughness Ra (hereinafter sometimes abbreviated as "arithmetic mean roughness Ra") of the outermost surface profile in the TD direction of the cross section of the foam sheet, calculated in accordance with JIS B 0601:2013, correlates with the magnitude of the corrugated wrinkles of the foam sheet. When the arithmetic mean roughness Ra is large, the corrugated wrinkles of the foam sheet are more pronounced, which tends to become the starting point for tearing when the foam sheet is molded, leading to molding defects.

[0029] The arithmetic mean roughness Ra is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.15 mm or less, more preferably 0.08 mm or less. By setting the arithmetic mean roughness Ra to 0.15 mm or less, molding defects during molding of the foamed sheet can be suppressed.

[0030] --Average length of roughness curve element RSm-- The average length RSm of roughness curve elements (hereinafter sometimes abbreviated as "average length RSm of roughness curve elements") calculated in accordance with JIS B 0601:2013 for the outermost surface shape in the TD direction of the cross section of the foam sheet indicates the period of corrugated wrinkles in the foam sheet. When the average length RSm of roughness curve elements is small, the period of corrugated wrinkles in the foam sheet is short, resulting in sharper unevenness, which is likely to become the starting point for tearing when the foam sheet is molded, leading to molding defects.

[0031] The average length RSm of the roughness curve elements is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 4.0 mm or more, more preferably 5.0 mm or more. By setting the average length RSm of the roughness curve elements to 4.0 mm or more, molding defects during molding of the foamed sheet can be suppressed.

[0032] The outermost surface profile in the TD direction of the cross section of the foamed sheet in the present invention can be measured using a laser microscope, a three-dimensional measuring instrument, or the like, and the arithmetic mean roughness Ra and the average length RSm of the roughness curve elements can be calculated using software attached to the laser microscope or three-dimensional measuring instrument used to measure the outermost surface profile in the TD direction of the cross section of the foamed sheet. The measuring device and measuring conditions are not particularly limited, but examples thereof include the following measuring method.

[0033] First, to prepare a measurement sample, cut out a 5 cm x 5 cm square from the center of the foam sheet in the TD direction and fix the foam sheet to the stage of a laser microscope or three-dimensional measuring device using double-sided tape or the like so that it does not float.

[0034] The response waviness, which has a short period and a large difference in height in the outermost surface shape in the TD direction of the cross section of the foam sheet, particularly affects molding defects during molding of the foam sheet. On the other hand, long-period waviness in the outermost surface shape in the TD direction of the cross section of the foam sheet does not significantly affect molding defects during molding of the foam sheet. Therefore, it is preferable to measure the arithmetic mean roughness Ra and the average length RSm of the roughness curve elements while excluding the influence of large waviness. In the present invention, when the average length RSm of the roughness curve elements is evaluated and a value of 10 mm or more is measured, the waviness cutoff (λc) is set to 10 mm and measurement is performed.

[0035] In the present invention, the arithmetic mean roughness Ra and the average length of roughness curve elements RSm of the foamed sheet are values ​​calculated in accordance with JIS B 0601:2013, and specifically, the arithmetic mean roughness Ra and the average length of roughness curve elements RSm can be calculated by observing the outermost surface shape in the TD direction of the cross section of the foamed sheet using the following measuring device and measuring conditions, and using accompanying software. Note that in the present invention, the arithmetic mean roughness Ra and the average length of roughness curve elements RSm are calculated by cutting three or more measurement samples from the foamed sheet at different positions during the preparation of the measurement samples, and averaging the results of three or more measurements. [[Measurement equipment and conditions]] Equipment: 3D measuring device VR-3200 (Keyence) Magnification: 12x Measurement mode: Standard Measurement direction: both sides Measurement brightness adjustment: Auto (setting value: 80) Reference plane setting: Select and set the x and y directions of the screen

[0036] -Cold crystallization enthalpy- The cold crystallization enthalpy of the foamed sheet is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 20 J / g or more, more preferably 30 J / g or more. The cold crystallization enthalpy of the foamed sheet being 20 J / g or more and the recrystallization enthalpy of the foamed sheet being 20 J / g or more mean that the crystallization rate of the foamed sheet is fast but there is still sufficient room for crystallization.

[0037] In thermoforming, the foam sheet is stretched at a temperature equal to or higher than the glass transition temperature, and the elongation at break of the foam sheet tends to decrease as the crystallinity of the foam sheet increases. If the cold crystallization enthalpy of the foam sheet is 20 J / g or higher, problems such as the foam sheet not being able to stretch during thermoforming, causing breakage in the molded product, or the foam sheet being unable to conform to the mold, resulting in poor shaping, can be prevented. There is no particular upper limit to the cold crystallization enthalpy of the foam sheet, and it can be appropriately selected depending on the purpose, but it is generally 50 J / g or less.

[0038] The cold crystallization enthalpy of the foamed sheet can be adjusted to fall within the preferred range by appropriately setting the temperature of the entire foamed sheet manufacturing apparatus or by cooling the extruded foamed sheet. Although this depends on the concentration of the foaming agent in the foamed sheet and the composition containing the polylactic acid resin, the cold crystallization enthalpy of the foamed sheet tends to fall within the preferred range by setting the minimum temperature of the foamed sheet manufacturing apparatus within a range of −20°C below the melting point of the polylactic acid resin and rapidly cooling the extruded foamed sheet.

[0039] The cooling method for the foamed sheet is not particularly limited, and any known method can be used. For example, in the foamed sheet production method described below, a method in which a cylindrical foam extruded from a die is drawn along a cooled mandrel and cooled, or a method in which cooling air is blown onto the outer periphery of a cylindrical foam, can be mentioned.

[0040] In the present invention, the cold crystallization enthalpy of the foamed sheet can be determined by differential scanning calorimetry (DSC) measurement in accordance with JIS K 7122:2012 (Method for measuring heat of transition of plastics). Specifically, approximately 5 mg to 10 mg of the foamed sheet is flattened by pressing (applying a load of approximately 500 gf) for 1 to 3 seconds with a copper rod (approximately 20 mm in diameter, also heated to 65°C) on a hot plate heated to 65°C to prepare a sample. This flattening is performed to improve thermal contact between the sample and the sample pan and to accurately measure the cold crystallization enthalpy. This sample is measured using the following measuring device and under the following conditions and analyzed by the following analytical method. In the present invention, the cold crystallization enthalpy is calculated by the arithmetic average of the results obtained by performing the process from sample preparation to analysis five times. [[Measurement equipment and conditions]] Equipment: Q-2000 (TA Instruments) Temperature program: Scan from 10°C to 200°C at a heating rate of 10°C / min (1st heating). Analysis of cold crystallization enthalpy: The area of ​​the exothermic peak associated with crystallization observed during the first heating at 60 to 100°C is integrated to determine the cold crystallization enthalpy. The baseline for the integration is a straight line connecting the front and back of the exothermic peak.

[0041] -Cold crystallization temperature- The cold crystallization temperature of the foamed sheet is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 70° C. to 100° C., more preferably 75° C. to 85° C. A cold crystallization temperature of 70° C. or higher is advantageous in terms of moldability, and a cold crystallization temperature of 100° C. or lower is advantageous in terms of heat resistance. The cold crystallization temperature of the foamed sheet can be adjusted by the molar ratio of either the D-lactic acid or the L-lactic acid, which are constituent monomer units of the polylactic acid resin contained in the foamed sheet.

[0042] The cold crystallization temperature of the foamed sheet can be determined by differential scanning calorimetry (DSC) measurement in accordance with JIS K 7121:2012 (Method for measuring transition temperature of plastics). Specifically, a 5 mg to 10 mg sample cut out from the foamed sheet is placed in a container of a differential scanning calorimeter (e.g., Q-2000 manufactured by TA Instruments), and the temperature is increased from 10°C to 200°C at a heating rate of 10°C / min. At this time, the peak top temperature of the exothermic peak observed in a temperature range above the glass transition temperature can be measured as the cold crystallization temperature of the foamed sheet.

[0043] -Recrystallization enthalpy- In the present invention, the term "high crystallinity of the foamed sheet" means that the recrystallization enthalpy measured by DSC is 20 J / g or more. When the recrystallization enthalpy of the foamed sheet is 20 J / g or more, the shape of the foamed sheet can be fixed by crystallization on a mold during thermoforming, and heat resistance can be imparted to the molded product within a practical molding time, resulting in a foamed sheet with excellent thermoformability.

[0044] The upper limit of the recrystallization enthalpy of the foamed sheet is not particularly limited, but is generally 40 J / g to 50 J / g for the foamed sheet of the present invention. The recrystallization enthalpy of the foamed sheet can be adjusted by increasing the optical purity of the polylactic acid resin, adding a component that acts as a crystal nucleating agent (a method for promoting the generation of crystal nuclei), adding a component that acts as a crystallization accelerator (a method for promoting the growth of crystal nuclei), or using an epoxy-functional (meth)acrylic monomer and a styrene monomer (an epoxy-functional (meth)acrylic-styrene-based chain extender) as a chain extender (crosslinking agent). Among these, from the viewpoints of the recyclability, environmental friendliness, and cost of the foamed sheet without inhibiting the foamability of the polylactic acid resin composition, it is preferable to adjust the recrystallization enthalpy of the foamed sheet by combining the method of increasing the optical purity of the polylactic acid resin with the method of using the epoxy-functional (meth)acrylic-styrene-based chain extender.

[0045] On the other hand, in extrusion molding of such a polylactic acid resin composition with excellent crystallinity, it is essential to maintain the temperature from kneading to extrusion, excluding the material input area, at or above the melting point of the polylactic acid resin composition or at or above the recrystallization temperature of the polylactic acid resin composition. The recrystallization temperature of the polylactic acid resin composition cannot be generalized because it can vary depending on the thermal history, the composition of the polylactic acid resin composition, the degree of shear, etc., but in the present invention, it is preferable that the temperature from kneading to extrusion be at least 20°C below the melting point of the polylactic acid resin composition.

[0046] If the temperature from kneading to extrusion is set to 20°C or less than the melting point of the polylactic acid resin composition, the polylactic acid resin composition can be cooled to a viscosity suitable for foaming. However, the degree of supercooling (the difference between the melting point and the resin temperature) increases, which increases the risk of sudden crystallization in the apparatus, leading to shutdowns, and the resulting foam sheet tends to undergo further crystallization, resulting in poor thermoformability. If the temperature from kneading to extrusion is set to 20°C or more than the melting point of the polylactic acid resin composition, the risk of shutdowns due to crystallization can be reduced, and the resulting foam sheet tends to have a low degree of crystallization, resulting in a foam sheet with excellent thermoformability. The crystallinity of the foam sheet can be evaluated by the cold crystallization enthalpy of the foam sheet measured by DSC.

[0047] In the present invention, the recrystallization enthalpy of the foamed sheet can be determined by differential scanning calorimetry (DSC) measurement in accordance with JIS K 7122:2012 (Method for measuring heat of transition of plastics). The DSC apparatus is not particularly limited, but the measurement can be performed, for example, as follows. Specifically, approximately 5 mg to 10 mg of the foamed sheet is flattened by pressing (applying a load of approximately 500 gf) for 1 to 3 seconds with a copper rod (approximately 20 mm in diameter, also heated to 65°C) on a hot plate heated to 65°C to prepare a sample. This flattening is performed to improve thermal contact between the sample and the sample pan and to accurately measure the recrystallization enthalpy. This sample is measured using the following measuring device and under the following conditions and analyzed by the following analytical method. In the present invention, the recrystallization enthalpy is calculated by the arithmetic average of the results obtained by performing the process from sample preparation to analysis five times. [[Measurement equipment and conditions]] Equipment: Q-2000 (TA Instruments) Temperature program: Scan from 10°C to 200°C at a heating rate of 10°C / min (1st heating), hold at 200°C for 1 minute, then scan from 200°C to 25°C at a cooling rate of 10°C / min (1st cooling). Analysis of recrystallization enthalpy: The area of ​​the exothermic peak associated with crystallization observed in the first cooling is determined by integration, and this is taken as the recrystallization enthalpy. In the present invention, the position of the exothermic peak associated with crystallization is in the range of approximately 100°C to 130°C. The baseline for integration is a straight line connecting the front and back of the exothermic peak.

[0048] -Recrystallization temperature- The recrystallization temperature of the foamed sheet is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 120° C. to 150° C., more preferably 130° C. to 145° C. When the recrystallization temperature of the foamed sheet is 120° C. or higher, the crystallization rate of the polylactic acid resin is high, and crystallization progresses during the molding process, which is advantageous for heat resistance. When the recrystallization temperature is 150° C. or lower, crystallization does not progress too much during the production of the foamed sheet, making it less likely to break during molding, which is advantageous from the standpoint of moldability. The recrystallization temperature of the foamed sheet can be adjusted by the molar ratio of either the D-form of lactic acid or the L-form of lactic acid, which are constituent monomer units of the polylactic acid resin contained in the foamed sheet.

[0049] The recrystallization temperature of the foamed sheet can be determined by differential scanning calorimetry (DSC) measurement in accordance with JIS K 7121:2012 (Method for measuring transition temperature of plastics). Specifically, a 5 mg to 10 mg sample cut out from the foamed sheet is placed in a container of a differential scanning calorimeter (e.g., Q-2000 model manufactured by TA Instruments), heated from 10°C to 200°C at a heating rate of 10°C / min, maintained at that temperature for 10 minutes, and then cooled from 200°C to 10°C at a heating rate of 10°C / min. At this time, the peak top temperature of the exothermic peak can be measured as the recrystallization temperature of the foamed sheet.

[0050] -Melting point- The melting point of the foamed sheet can be determined by differential scanning calorimetry (DSC) measurement in accordance with JIS K 7121:2012 (Method for measuring transition temperature of plastics). Specifically, the melting point of the foamed sheet can be measured by DSC using, for example, a differential scanning calorimeter (e.g., Model Q-2000, manufactured by TA Instruments). A sample of 5 mg to 10 mg of the foamed sheet is placed in a container of the differential scanning calorimeter, and the temperature is increased at a rate of 10°C / min up to 200°C. The melting point of the foamed sheet is determined as the peak-top temperature (melting peak temperature, Tpm) of the endothermic peak associated with the melting of crystals observed above the glass transition temperature. When multiple endothermic peaks are observed above the glass transition temperature, the peak-top temperature of the peak with the largest area is determined as the melting point of the foamed sheet. The melting point of the foamed sheet is generally within the range of 160°C to 190°C.

[0051] -Glass transition temperature- The glass transition temperature of the foamed sheet can be determined by differential scanning calorimetry (DSC) measurement in accordance with JIS K 7121:2012 (Method for measuring the glass transition temperature of plastics). Specifically, the glass transition temperature of the foamed sheet can be measured by DSC using, for example, a differential scanning calorimeter (e.g., Model Q-2000, manufactured by TA Instruments). A sample of 5 mg to 10 mg cut out from the foamed sheet is placed in a container of the differential scanning calorimeter, and the temperature is increased from 10°C to 200°C at a rate of 10°C / min. The glass transition temperature in the present invention refers to the extrapolated glass transition onset temperature (Tig) described in JIS K 7121: 2012. The glass transition temperature of the foamed sheet is generally within the range of 55°C to 70°C.

[0052] -Weight average molecular weight (Mw)- The weight average molecular weight (Mw) of the foamed sheet is not particularly limited and can be appropriately selected depending on the purpose, but is preferably from 230,000 to 600,000, and more preferably from 250,000 to 400,000. When the weight average molecular weight (Mw) of the foamed sheet is from 230,000 to 600,000, the sheet has a melt viscosity suitable for foaming, which improves the foaming ratio and leads to improved heat insulating properties.

[0053] The weight average molecular weight (Mw) of the foam sheet can be measured by gel permeation chromatography (GPC). The weight-average molecular weight (Mw) is calculated using a calibration curve prepared using polystyrene samples with known weight-average molecular weights (e.g., A-500 (weight-average molecular weight 589), A-1000 (weight-average molecular weight 1,010), A-2500 (weight-average molecular weight 312), A-5000 (weight-average molecular weight 5,430), F-1 (weight-average molecular weight 9,490), F-2 (weight-average molecular weight 15,700), F-4 (weight-average molecular weight 37,200), F-10 (weight-average molecular weight 98,900), F-20 (weight-average molecular weight 189,000), F-40 (weight-average molecular weight 397,000), F-80 (weight-average molecular weight 707,000), and F-128 (weight-average molecular weight 1,110,000) manufactured by Tosoh Corporation).

[0054] The sample to be subjected to the GPC is prepared by mixing the foam sheet with chloroform to a foam sheet concentration of about 2 mg / mL, shaking the mixture for about half a day using a tabletop shaker (e.g., MSI-60 manufactured by AS ONE Corporation), confirming that the foam sheet has dissolved, and then filtering the mixture through a 0.45 μm membrane filter. Difficult-to-dissolve foam sheets can also be dissolved by heating at a temperature below the boiling point of chloroform. There are no particular limitations on the GPC measurement device or measurement conditions. The weight-average molecular weight (Mw) of the foam sheet can be measured by GPC measurement of the sample prepared in this manner, for example, under the following conditions. [[Measurement equipment and conditions]] Equipment: HLC-8320GPC (Tosoh Technosystems) Columns: TSKgel (registered trademark) guard column SuperHZ-L and TSKgel SuperHZM-M x 4 Detector: RI · Measurement temperature: 40℃ Mobile phase: chloroform Flow rate: 0.45 mL / min · Injection volume: 20μL

[0055] -Melt viscosity- The melt viscosity of the foamed sheet is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 10,000 Pa·s or more and 40,000 Pa·s or less. When the foamed sheet has a melt viscosity of 10,000 Pa·s or more, a sheet having a low bulk density and excellent heat insulating properties, strength, and surface properties tends to be obtained while maintaining a low degree of crystallinity. When the melt viscosity is 40,000 Pa·s or less, an increased load on the foaming device can be prevented, preventing a decrease in productivity.

[0056] The melt viscosity of the foamed sheet can be measured, for example, by weighing 1.5 g of the foamed sheet, drying it in a dryer at 80°C for 2 hours, and using the resulting sample as a flow tester under the following measurement conditions. [[Measurement equipment and conditions]] Equipment: CFT-100EX (Shimadzu Corporation) Test conditions: constant temperature method, test temperature: 190°C, test force: 40 kgf, preheating time: 180 seconds, die hole diameter: 1 mm, die length: 1 mm Analysis: Using the attached software CFT-EX, calculate the melt viscosity using the following calculation parameters. Calculation parameters: Confinement method, Calculation start position: 3.0 mm, Calculation end position: 7.0 mm, Sample density: 1 g / cm 3

[0057] A method for adjusting the melt viscosity of the foamed sheet to fall within the preferred range includes melt-kneading (reactive extrusion) a polylactic acid resin having the characteristics disclosed in the present invention with a chain extender (crosslinking agent) to obtain a polylactic acid resin composition. The melt viscosity of the foamed sheet varies greatly depending on the temperature from kneading to extrusion, but it is preferable to provide a section in the kneading section set at 200°C to 240°C, more preferably 220°C to 240°C.

[0058] <Composition containing polylactic acid resin> In the present invention, the term "composition containing a polylactic acid resin" refers to the composition before being foamed. The composition containing the polylactic acid resin preferably contains at least polylactic acid resin and inorganic particles, and further contains a chain extender (also called a "crosslinking agent"), and may further contain other components as necessary.

[0059] <<Polylactic acid resin>> Because polylactic acid resins are biodegradable by microorganisms, they have attracted attention as environmentally friendly polymeric materials with low environmental impact (see "Structure, Properties, and Biodegradability of Aliphatic Polyesters," Yoshio Inoue, Polymers, 2001, Vol. 50, No. 6, pp. 374-377). Examples of polylactic acid resins include copolymers of D-lactic acid (D-lactic acid) and L-lactic acid (L-lactic acid) (DL-lactic acid); homopolymers of either D-lactic acid or L-lactic acid; ring-opening polymers of one or more lactides selected from the group consisting of D-lactide (D-lactide), L-lactide (L-lactide), and DL-lactide. These may be used alone or in combination. The polylactic acid resin may be appropriately synthesized or commercially available.

[0060] The polylactic acid resin can be synthesized by known methods, such as a method in which lactide is produced from lactic acid as a raw material and the lactide is subjected to ring-opening polymerization using an initiator such as an alcohol, or a method in which lactic acid is directly subjected to dehydration condensation.

[0061] In the synthesis of the polylactic acid resin, in addition to the monomer, an initiator, a catalyst, an antioxidant, an end-capping agent, etc. may be included.

[0062] Examples of the initiator include water and alcohols having one or more active hydrogen groups. The alcohol having one or more active hydrogen groups is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include aliphatic alcohols, polyalkylene glycols, polyhydric alcohols, etc. These may be used alone or in combination of two or more.

[0063] The polyhydric alcohol is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include glycerin, trimethylolpropane, 1,4-cyclohexanedimethanol, neopentyl glycol, erythritol, etc. These may be used alone or in combination of two or more.

[0064] [Physical properties of polylactic acid resin] -Optical isomers- When a copolymer of D-lactic acid and L-lactic acid (DL-lactic acid) or a ring-opening polymer of one or more lactides selected from the group consisting of D-lactide, L-lactide, and DL-lactide is used as the polylactic acid resin, the crystallinity tends to increase and the melting point and crystallization rate tend to increase as the amount of the lesser optical isomer of the D- and L-forms decreases.On the other hand, the crystallinity tends to decrease and eventually become amorphous as the amount of the lesser optical isomer of the D- and L-forms increases.

[0065] In the present invention, since sufficient heat resistance must be imparted by crystallization accompanying bubble growth during foaming, the molar ratio of either the D- or L-lactic acid, which is a constituent monomer unit of the polylactic acid resin contained in the polylactic acid resin composition, is 98 mol% or more, preferably 99 mol% or more, in the polylactic acid resin. For this reason, the polylactic acid resin may be a polylactic acid resin composed solely of one of the optical isomers of the D- or L-lactic acid. If the polylactic acid resin contains less than 98 mol% of either the D- or L-lactic acid, which is a constituent monomer unit of the polylactic acid resin, the molded article obtained by molding a foamed sheet made of the polylactic acid resin composition will not exhibit good heat resistance. On the other hand, by increasing the content of either the D- or L-lactic acid, which is a constituent monomer unit of the polylactic acid resin, in the polylactic acid resin to 98 mol% or more, the crystallization rate is increased, resulting in over-crystallization during molding, improving the heat resistance of the molded article.

[0066] The ratio of either the D-lactic acid or the L-lactic acid, which are the constituent monomer units, can be confirmed by analysis using liquid chromatography using an optically active column. Specifically, the foam sheet was freeze-pulverized, and 200 mg of the foam sheet powder was placed in an Erlenmeyer flask. 30 mL of 1N aqueous sodium hydroxide solution was added. The Erlenmeyer flask was heated to 65°C while shaking to completely dissolve the polylactic acid resin in the foam sheet. The pH was then adjusted to 4-7 using 1N hydrochloric acid and diluted to a predetermined volume using a measuring flask to obtain a polylactic acid resin solution. The polylactic acid resin solution was then filtered through a 0.45 μm membrane filter and analyzed using a liquid chromatograph. Based on the resulting chart, the area ratio of the peaks derived from the D- and L-lactic acid is calculated, and the amounts of the D- and L-lactic acid are calculated as the abundance ratio. The arithmetic mean of the results obtained by performing the above procedure three times was used as the amounts of the D- and L-lactic acid comprising the polylactic acid resin in the foam sheet.

[0067] The measurement device and measurement conditions for the liquid chromatography are not particularly limited, but for example, the measurement can be performed using the following measurement device and measurement conditions. [[Measurement equipment and conditions]] HPLC device (liquid chromatograph): PU-2085Plus system (manufactured by JASCO Corporation) Column: Chromolith® coated with SUMICHIRAL OA-5000 (inner diameter 4.6 mm, length 250 mm) (Sumitomo Analysis Center, Ltd.) Column temperature: 25℃ Mobile phase: A mixture of 2 mM CuSO4 aqueous solution and 2-propanol (CuSO4 aqueous solution:2-propanol (volume ratio) = 95:5) Mobile phase flow rate: 1.0 mL / min Detector: UV254nm · Injection volume: 20μL

[0068] When the foamed sheet is subjected to the above-mentioned liquid chromatography analysis, if the area of ​​the larger peak derived from the D-lactic acid or L-lactic acid is 98% or more of the total area of ​​the peaks derived from the D-lactic acid and L-lactic acid, it can be said that either the D-lactic acid or L-lactic acid, which is a constituent monomer unit of the polylactic acid resin in the foamed sheet, accounts for 98 mol% or more of the polylactic acid resin.

[0069] In addition, in the obtained chart, the ratio of the area of ​​the larger peak from the D-lactic acid and the L-lactic acid to the total area of ​​the peaks from the D-lactic acid and the L-lactic acid is calculated and defined as an area ratio of 1. The proportion of the minor optical isomer of D-lactic acid and L-lactic acid in the structure of the polylactic acid resin can also be calculated using the following formula (3). (Proportion of the smaller optical isomer of D-lactic acid or L-lactic acid [mol %]) = 100 × (1 - area ratio 1) [mol %] Equation (3)

[0070] -Weight average molecular weight- The weight-average molecular weight (Mw) of the polylactic acid resin is not particularly limited and can be selected appropriately depending on the purpose. However, it is preferably 180,000 to 320,000, and more preferably 210,000 to 310,000. When the weight-average molecular weight (Mw) of the polylactic acid resin is 180,000 to 320,000, the viscosity of the polylactic acid resin composition can be controlled within a range appropriate for foaming, thereby suppressing cell coalescence and cell breakage during the production of the foamed sheet, and enabling the stable production of foamed sheets with excellent expansion ratios and surface properties. On the other hand, when the weight-average molecular weight (Mw) of the polylactic acid resin is 180,000 or less, the amount of chain extender required to adjust the viscosity of the polylactic acid resin composition to a range appropriate for foaming becomes large, or it tends to be difficult to adjust the viscosity to a range appropriate for foaming. Chain extenders are generally petroleum-derived compounds and are non-biodegradable, so it is desirable to minimize the amount added to reduce environmental impact. Furthermore, if the weight-average molecular weight (Mw) of the polylactic acid resin is 320,000 or more, the viscosity of the polylactic acid resin composition tends to change sharply depending on the amount of the chain extender added, which reduces the controllability of the viscosity of the polylactic acid resin composition and may make it difficult to stably produce the foamed sheet.

[0071] The weight average molecular weight (Mw) of the polylactic acid resin can be measured using GPC. The weight-average molecular weight (Mw) of the polylactic acid resin is calculated using a calibration curve prepared using polystyrene samples with known weight-average molecular weights (e.g., A-500 (weight-average molecular weight 589), A-1000 (weight-average molecular weight 1,010), A-2500 (weight-average molecular weight 312), A-5000 (weight-average molecular weight 5,430), F-1 (weight-average molecular weight 9,490), F-2 (weight-average molecular weight 15,700), F-4 (weight-average molecular weight 37,200), F-10 (weight-average molecular weight 98,900), F-20 (weight-average molecular weight 189,000), F-40 (weight-average molecular weight 397,000), F-80 (weight-average molecular weight 707,000), and F-128 (weight-average molecular weight 1,110,000) manufactured by Tosoh Corporation).

[0072] The sample to be subjected to GPC is prepared by mixing the polylactic acid resin and chloroform to a polylactic acid resin concentration of approximately 2 mg / mL, shaking the mixture for approximately half a day using a tabletop shaker (e.g., MSI-60 manufactured by AS ONE Corporation), confirming that the polylactic acid resin has dissolved, and then filtering the mixture through a 0.45 μm membrane filter to obtain a filtrate. Resistant polylactic acid resins can also be dissolved by heating at a temperature below the boiling point of chloroform. The sample thus prepared can be measured, for example, using the same measuring device and conditions as those used to measure the weight-average molecular weight (Mw) of the foamed sheet.

[0073] -Acid value- The acid value of the polylactic acid resin in the polylactic acid resin composition is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 5 mgKOH / g or less. When the acid value of the polylactic acid resin is 5 mgKOH / g or less, the viscosity of the polylactic acid resin composition can be easily adjusted to a range suitable for foaming, and further, decomposition of the polylactic acid resin during storage tends to be suppressed. The method for measuring the acid value of the polylactic acid resin is not particularly limited, but it can be determined by, for example, titration.

[0074] Specifically, approximately 1 g to 3 g of the polylactic acid resin is placed in an Erlenmeyer flask, 40 mL of dichloromethane is added, and the mixture is shaken at room temperature for approximately half a day. The resulting dichloromethane solution of polylactic acid resin is used as a sample for measurement. If the viscosity of the dichloromethane solution is high, the amount of polylactic acid resin is reduced or the amount of dichloromethane is appropriately increased to adjust the sample. Phenolphthalein is added to the sample as an indicator, and the sample and blank are titrated using a 0.01 N ethanol solution of potassium hydroxide, and the acid value is calculated using the following formula (4). Acid value [mgKOH / g] = (titration value [mL] - blank [mL]) × factor × 0.01 [N] × 56.1 [g / mol] / (mass of sample [g]) Equation (4)

[0075] -Water content- The water content of the polylactic acid resin is preferably reduced to 500 ppm or less before it is used to produce the polylactic acid resin composition or the foamed sheet. When the water content of the polylactic acid resin is 500 ppm or less, the viscosity of the polylactic acid resin composition tends to be adjusted to an appropriate level for foaming.

[0076] The method for measuring the water content of the polylactic acid resin is not particularly limited, and any known method can be used, such as Karl Fischer titration. The method for drying the polylactic acid resin is not particularly limited, and known methods can be used, such as methods using a hot air dryer or a vacuum dryer. The drying temperature is not particularly limited, but is preferably 60° C. to 80° C. The method for measuring the water content is not particularly limited, and for example, Karl Fischer titration or the like can be applied.

[0077] -Content- From the viewpoints of biodegradability and recyclability (facilitating recycling), the content of the polylactic acid resin in the polylactic acid resin composition is 98% by mass or more relative to the total amount of organic matter in the polylactic acid resin composition. Note that, since the foam sheet is made of the polylactic acid resin composition, the content of the polylactic acid resin relative to the total amount of organic matter in the polylactic acid resin composition is synonymous with the content of the polylactic acid resin relative to the total amount of organic matter in the foam sheet.

[0078] The organic substance in the polylactic acid resin composition is mainly the polylactic acid resin, but examples of organic substances other than the polylactic acid resin include organic nucleating agents as foam nucleating agents described below, chain extenders, etc. When an inorganic nucleating agent is used as the foam nucleating agent for the foam sheet, the inorganic nucleating agent does not fall under the category of the organic substance.

[0079] The content of the polylactic acid resin relative to the total amount of organic matter in the polylactic acid resin composition can be calculated from the mixing ratio (feed ratio) used when preparing the polylactic acid resin composition. If the mixing ratio is unknown, it may be determined by nuclear magnetic resonance analysis (NMR) as follows.

[0080] The solvent used in the nuclear magnetic resonance analysis is prepared by weighing out approximately 100 mg of 1,3,5-trimethoxybenzene standard (for quantitative NMR, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as an internal standard substance and dissolving it in deuterated chloroform (containing 0.3% by volume of tetramethylsilane (TMS)) in a 10 mL measuring flask.

[0081] To prepare a sample for nuclear magnetic resonance analysis, the polylactic acid resin composition or the foamed sheet is added to the solvent so that the concentration of the polylactic acid resin composition or the foamed sheet becomes 10 mg / mL, and the mixture is dissolved by shaking for about half a day using a tabletop shaker (e.g., MSI-60 manufactured by AS ONE Corporation). To minimize changes in sample concentration due to evaporation, the smallest possible container is selected. The sample prepared by the above method is sealed in a 5 mm diameter sample tube and subjected to NMR.

[0082] Using the sample, the following measurement apparatus and measurement conditions were used in accordance with JIS K0138:2018 (General rules for quantitative nuclear magnetic resonance spectroscopy (qNMR general rules)). 1 NMR measurement of H nuclei ( 1 H-NMR measurement). [[Measurement equipment and conditions]] · Nuclear magnetic resonance (NMR) device: JNM-ECX-500 FT-NMR (manufactured by JEOL Ltd.) Observed nucleus: 1H · Measurement temperature: 30℃ Spin:Off Digital resolution: 0.25Hz Observation range: -0.5 to 15 ppm Pulse angle: 90° Relaxation time: 60 seconds Number of scans: 16 (Two dummy scans are performed before the actual measurement) 13C decoupling: Yes

[0083] The obtained data is integrated with respect to the peaks of the chemical shifts shown below, and the integral ratio is calculated by the following formula (5). Integral 1 (derived from polylactic acid resin): 5.2 ppm Integral 2 (from internal standard): 6.1ppm Integral ratio = integral 1 / (integral 2 × sample mass) Equation (5)

[0084] A similar NMR measurement is performed on a polylactic acid resin of known purity using the same solvent as the sample, and the ratio of the integral ratio obtained from equation (5) for the polylactic acid resin of known purity to the integral ratio for the sample is calculated, and the content of the polylactic acid resin relative to the total amount of organic matter in the polylactic acid resin composition or the foam sheet is calculated using the following equation (6). Note that the steps from sample preparation to analysis are performed three times, and the arithmetic average of the resulting polylactic acid resin contents is used as the content of the polylactic acid resin relative to the total amount of organic matter in the polylactic acid resin composition or the foam sheet. Polylactic acid resin content [mass%] = 100 × purity of polylactic acid resin of known purity [mass%] × (integral ratio of sample) / (integral ratio of polylactic acid resin of known purity) Equation (6)

[0085] -Melting point- The melting point of the polylactic acid resin can be determined by differential scanning calorimetry (DSC) measurement in accordance with JIS K 7121:2012 (Method for measuring transition temperature of plastics). Specifically, the melting point of the polylactic acid resin can be measured by DSC using, for example, a differential scanning calorimeter (e.g., Q-2000 model, manufactured by TA Instruments). A sample of 5 mg to 10 mg of the polylactic acid resin is placed in a container of the differential scanning calorimeter, and the temperature is increased at a rate of 10°C / min up to 200°C. The melting point of the polylactic acid resin is determined as the peak-top temperature (melting peak temperature, Tpm) of the endothermic peak associated with the melting of crystals observed above the glass transition temperature. When multiple endothermic peaks are observed above the glass transition temperature, the peak-top temperature of the peak with the largest area is determined as the melting point of the polylactic acid resin. The melting point of the polylactic acid resin is generally within the range of 150°C to 190°C.

[0086] -Glass transition temperature- The glass transition temperature of the polylactic acid resin can be determined by differential scanning calorimetry (DSC) measurement in accordance with JIS K 7121:2012 (Method for measuring the glass transition temperature of plastics). Specifically, the glass transition temperature of the polylactic acid resin can be measured by DSC using, for example, a differential scanning calorimeter (e.g., Q-2000 model, manufactured by TA Instruments). The measurement can be performed by placing 5 mg to 10 mg of a sample of the polylactic acid resin in a container of the differential scanning calorimeter and heating it from 10°C to 200°C at a heating rate of 10°C / min. The glass transition temperature in the present invention refers to the extrapolated glass transition onset temperature (Tig) described in JIS K 7121: 2012. The glass transition temperature of the polylactic acid resin is generally within the range of 55°C to 70°C.

[0087] -Melt viscosity- The melt viscosity of the polylactic acid resin is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 500 Pa s or more and 1,500 Pa s or less. When the melt viscosity of the polylactic acid resin is 500 Pa s or more and 1,500 Pa s or less, the viscosity of the polylactic acid resin composition can be easily adjusted to a viscosity suitable for foaming, the load on the foaming device can be reduced, productivity can be improved, and a foamed sheet with low bulk density and excellent surface properties can be obtained.

[0088] The melt viscosity of the polylactic acid resin can be measured, for example, by weighing 1.5 g of the polylactic acid resin, drying it in a dryer at 80° C. for 2 hours, and using the resultant as a sample, using a flow tester under the following measurement conditions. [[Measurement equipment and conditions]] Equipment: CFT-100EX (Shimadzu Corporation) Test conditions: constant temperature method, test temperature: 190°C, test force: 40 kgf, preheating time: 180 seconds, die hole diameter: 1 mm, die length: 1 mm Analysis: Using the attached software CFT-EX, calculate the melt viscosity using the following calculation parameters. Calculation parameters: Confinement method, Calculation start position: 3.0 mm, Calculation end position: 7.0 mm, Sample density: 1 g / cm 3

[0089] -Ratio of the melt viscosity of foam sheet to that of polylactic acid resin- The ratio of the melt viscosity of the foamed sheet to the melt viscosity of the polylactic acid resin is not particularly limited and can be appropriately selected depending on the purpose, but is preferably from 7 to 80. When the ratio of the melt viscosity of the foamed sheet to the melt viscosity of the polylactic acid resin is from 7 to 80, the load on the foaming device is reduced, resulting in excellent productivity, and a foamed sheet having a low bulk density and excellent heat insulating properties, strength, and surface properties can be obtained while maintaining a low degree of crystallinity.

[0090] The ratio of the melt viscosity of the foamed sheet to the melt viscosity of the polylactic acid resin is calculated by the following formula (7). Ratio of melt viscosity of foam sheet to melt viscosity of polylactic acid resin = Melt viscosity of foam sheet / Melt viscosity of polylactic acid resin Equation (7)

[0091] <<Inorganic particles>> The polylactic acid resin composition contains inorganic particles. The inorganic particles are suitably used as a foam nucleating agent and / or a cell adjusting agent. The inorganic particles in the present invention contain a layered silicate.

[0092] The layered silicate has a high aspect ratio and is effectively oriented in the bubble walls. Gas components cannot pass through without taking a detour through the oriented layered silicate (tortuous path effect), which increases the retention of gas components and improves the expansion ratio. As the expansion ratio increases, the amount of gas contained increases, improving the heat insulating properties. Furthermore, as the expansion ratio increases, the thickness of the foamed sheet increases, increasing the moment of inertia of area and improving the strength. Therefore, by increasing the expansion ratio of the foamed sheet, the heat insulating properties and strength can be improved while maintaining light weight.

[0093] -Volume average particle size (Mv)- The layered silicate has a volume average particle diameter (Mv) of 10 μm or more and 200 μm or less, preferably 15 μm or more and 200 μm or less. If the layered silicate has a volume average particle diameter (Mv) of less than 10 μm, the detour path becomes too short and the gas component cannot be sufficiently retained, resulting in an insufficient improvement in the expansion ratio. If the layered silicate has a volume average particle diameter (Mv) of more than 200 μm, the cell walls become brittle, leading to cell breakage, resulting in an insufficient improvement in the expansion ratio.

[0094] The volume average particle size (Mv) may be measured by measuring the layered silicate before charging, or may be measured by taking out the layered silicate from the foamed sheet by, for example, the following method. A sample of the foamed sheet is cut out, placed in a crucible, and burned in a muffle furnace (e.g., FP-310, manufactured by Yamato Scientific Co., Ltd.) at 600°C for 4 hours to burn off the organic components. The crucible is then cooled in a desiccator for 1 hour, and the resulting inorganic particles are used as a measurement sample. If two or more types of inorganic particles are contained, the layered silicate can be further separated by gravity separation. The method for measuring the volume average particle size (Mv) of the layered silicate is not particularly limited, and can be determined, for example, using the following measuring device and under the following measuring conditions. In the present invention, the volume average particle size (Mv) of the layered silicate is defined as the average particle size of the layered silicate. [[Measurement equipment and conditions]] Equipment: Microtrac MT3300EX (Microtrac Bell Co., Ltd.) Measurement conditions: Transmittance / Transmission, Refractive index / 1.53, Shape / Aspheric, Solvent / Air, Solvent refractive index / 1, Measurement time / 10s, Extension filter / Disabled, Distribution / Volume

[0095] -Aspect ratio- The aspect ratio of the layered silicate is from 10 to 100, preferably from 25 to 75. If the aspect ratio of the layered silicate is less than 10, the orientation will be poor and a sufficient tortuous effect will not be obtained, resulting in an insufficient effect in improving the expansion ratio of the foamed sheet. If the aspect ratio of the layered silicate is more than 100, the layered silicate will be pulverized when the polylactic acid resin composition and the layered silicate are kneaded, resulting in a small aspect ratio and an insufficient effect.

[0096] The aspect ratio of the layered silicate is calculated by the following formula (8). Aspect ratio = volume average particle size of layered silicate (Mv) / average thickness of layered silicate Equation (8) In the formula (8), the method for measuring the volume average particle diameter (Mv) of the layered silicate and the thickness of the layered silicate is not particularly limited. For example, the volume average particle diameter (Mv) can be determined by the above-mentioned measurement method, and the thickness can be determined by the following method.

[0097] The thickness of the layered silicate can be measured, for example, by SEM observation of the layered silicate using a scanning electron microscope (SEM) (e.g., 3D Real Surface View Microscope VE-9800, manufactured by KEYENCE Corporation). The magnification is adjusted so that the number of particles in the observation range is several tens to several hundreds. If necessary, multiple fields of view can be photographed, and the images can be linked and subjected to image analysis. From the captured images, particles whose thickness planes are parallel to the observation surface are selected, and their thicknesses are measured. The average value of 50 particles is calculated and used as the average thickness of the layered silicate.

[0098] The content of the layered silicate in the polylactic acid resin composition is 2% by mass or less, preferably 0.1% to 2% by mass, more preferably 0.5% to 2% by mass, and even more preferably 1.0% to 1.7% by mass, based on the total mass of the polylactic acid resin composition. If the content of the layered silicate exceeds 2% by mass, the layered silicate may destroy the cell walls, resulting in a decrease in the expansion ratio, embrittlement of the foam sheet, or an increase in the specific gravity of the polylactic acid resin composition, thereby compromising the lightweight properties of the foam sheet. On the other hand, if the content of the layered silicate is 0.1% to 2% by mass, it is possible to prevent a decrease in the expansion ratio due to destruction of the cell walls by the layered silicate, embrittlement of the foam sheet, and an increase in the specific gravity of the polylactic acid resin composition, thereby compromising the lightweight properties of the foam sheet.

[0099] The content of the layered silicate in the polylactic acid resin composition can be calculated from the mixing ratio (feed ratio) used to obtain the polylactic acid resin composition. If the mixing ratio of the layered silicate is unknown, it may be determined by measuring the ash content as follows.

[0100] The ash content can be measured as follows. A sample of the foamed sheet is cut out and weighed out (approximately 3 g) into a 100 mL crucible whose mass has been accurately measured to four decimal places using a precision balance, and the total mass of the crucible and the sample is accurately weighed. The crucible is placed in a muffle furnace (e.g., FP-310, manufactured by Yamato Scientific Co., Ltd.) and burned at 600°C for 4 hours to combust the organic components. The crucible is then cooled in a desiccator for 1 hour, and the crucible is again accurately weighed to measure the total mass of the crucible and ash. The ash content, i.e., the content of the inorganic particles, is calculated using the following formula (9). This measurement is performed twice, and the average value is calculated to determine the content of the inorganic particles. Inorganic particle content [mass%] = ash content [mass%] = (total mass of crucible and sample after combustion and cooling [g] - mass of crucible [g]) / (total mass of crucible and sample before combustion [g] - mass of crucible [g]) × 100 Equation (9)

[0101] Specific examples of the layered silicate include talc, pyrophyllite smectite, montmorillonite, beidellite, hectorite, saponite, vermiculite, lepidolite, illite, paragolite, and mica. These may be used alone or in combination of two or more. Among these, mica is preferred as the layered silicate, as it is easy to achieve the particle size and aspect ratio.

[0102] The layered silicate may be a natural product or a synthetic product. The method for producing the layered silicate synthesis product is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a melting method, an intercalation method, a hydrothermal method, etc. These layered silicates may be used alone, or two or more types of layered silicates differing in mineral type, origin, production method, particle size, etc. may be used in combination.

[0103] <<Other ingredients>> The other components in the polylactic acid resin composition are not particularly limited as long as they do not impair the effects of the present invention and can be appropriately selected depending on the purpose, and examples thereof include chain extenders (crosslinking agents), foam nucleating agents other than the layered silicates, resin components other than the polylactic acid resin, various additives, etc. These may be used alone or in combination of two or more.

[0104] -Chain extender (crosslinking agent)- The chain extender (crosslinking agent) is preferably contained in the polylactic acid resin composition to adjust the viscosity of the polylactic acid resin to a range suitable for foaming. The chain extender (crosslinking agent) also has the effect of improving the heat resistance and hydrolysis resistance of the polylactic acid resin composition and the foam sheet.

[0105] The chain extender (crosslinking agent) is not particularly limited and can be appropriately selected depending on the purpose, and can be, for example, a compound reactive with a hydroxyl group and / or a carboxylic acid group, a peroxide, etc. Among these, a compound reactive with a hydroxyl group and / or a carboxylic acid group of the polylactic acid resin is preferred from the viewpoint of not inhibiting or improving the crystallinity of the polylactic acid resin after reaction with the polylactic acid resin.

[0106] The compound reactive with the hydroxyl group and / or carboxylic acid group of the polylactic acid resin is not particularly limited and can be appropriately selected depending on the purpose, but a compound having an epoxy group, a compound having an isocyanate group, or a compound having a carbodiimide group is preferred. These may be used alone or in combination of two or more.

[0107] The compound reactive with the hydroxyl and / or carboxylic acid groups of the polylactic acid resin is preferably a compound having two or more reactive groups in its molecule, because it can introduce a branched structure into the polylactic acid resin, thereby efficiently improving the viscosity of the polylactic acid resin composition and reducing the release of unreacted chain extender (crosslinker). Compounds having two or more epoxy groups or two or more isocyanate groups in its molecule are more preferred. From the viewpoints of workability and safety, compounds having two or more epoxy groups in its molecule are even more preferred. From the viewpoints of reactivity, workability, and safety, epoxy-functional (meth)acrylic-styrene-based chain extenders having two or more epoxy groups in their molecule are particularly preferred. Among these, epoxy-functional (meth)acrylic-styrene-based chain extenders having two or more epoxy groups in their molecule are most preferred from the viewpoints of reactivity, workability, and safety.

[0108] --Compounds containing epoxy groups-- The compound having two or more epoxy groups in the molecule as the chain extender (crosslinking agent) is a compound obtained by copolymerizing a (meth)acrylic monomer having at least an epoxy group. The (meth)acrylic monomer having an epoxy group is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include monomers containing a 1,2-epoxy group such as glycidyl acrylate and glycidyl methacrylate. These may be used alone or in combination of two or more.

[0109] The compound having two or more epoxy groups in the molecule may further contain, as a copolymerization component, a (meth)acrylic monomer having no epoxy group in addition to the above-mentioned monomer. The (meth)acrylic monomer having no epoxy group is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, and cyclohexyl methacrylate. These may be used alone or in combination of two or more.

[0110] The compound having two or more epoxy groups in the molecule may further contain a monomer having a double bond group in addition to the (meth)acrylic monomer not having an epoxy group. The monomer having a double bond group is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include styrene monomer, α-methylstyrene monomer, vinyl acetate monomer, etc. These may be used alone or in combination of two or more. Examples of the styrene monomer include styrene, α-methylstyrene, etc.

[0111] The epoxy-functional (meth)acrylic-styrene chain extender having two or more epoxy groups in the molecule is a compound obtained by copolymerizing a (meth)acrylic monomer having at least an epoxy group with a styrene monomer.

[0112] The compound having an epoxy group may be synthesized as appropriate, or a commercially available product may be used. Examples of commercially available products of the compound having an epoxy group include, for example, trade names such as Marproof (registered trademark) G-01100 (manufactured by NOF Corporation), Marproof (registered trademark) G-0105SA (manufactured by NOF Corporation), Marproof (registered trademark) G-2050M (manufactured by NOF Corporation), Marproof (registered trademark) G-0130SP (manufactured by NOF Corporation), Marproof (registered trademark) G-0130SF (manufactured by NOF Corporation), Marproof (registered trademark) G-0250SP (manufactured by NOF Corporation), Marproof G-0250SF (manufactured by NOF Corporation), Metablen (registered trademark) P1901 (manufactured by Mitsui Chemicals Co., Ltd.), Joncy (registered trademark) ADR4368 (manufactured by BASF), Joncy (registered trademark) ADR4370 (manufactured by BASF), Joncy (registered trademark). Examples of such an adhesive include ADR4468 (manufactured by BASF), Bondfast (registered trademark) BF-2C (manufactured by Sumitomo Chemical Co., Ltd.), Bondfast (registered trademark) BF-E (manufactured by Sumitomo Chemical Co., Ltd.), Bondfast (registered trademark) BF-2B (manufactured by Sumitomo Chemical Co., Ltd.), Bondfast (registered trademark) BF-7B (manufactured by Sumitomo Chemical Co., Ltd.), Bondfast (registered trademark) BF-7M (manufactured by Sumitomo Chemical Co., Ltd.), CESA-Extend OMAN698493 (manufactured by Clariant), and ARUFON UG-4040 (manufactured by Toagosei Co., Ltd.). Among these, as commercially available products of the compound having an epoxy group, Marproof (registered trademark) G-0250SP (manufactured by NOF Corporation), Marproof (registered trademark) G-0250SF (manufactured by NOF Corporation), and Joncy (registered trademark) ADR4468 (manufactured by BASF) are preferred from the viewpoints of heat insulation, biodegradability, and prevention of molding defects, because they can achieve a high expansion ratio at a low addition concentration under conditions for producing a foamed sheet that is less likely to develop corrugated wrinkles in the foamed sheet.

[0113] The content of the epoxy group-containing compound is not particularly limited and can be selected appropriately depending on the purpose. However, it is preferably 0.2% by mass or more but less than 2.0% by mass, more preferably 0.5% by mass or more but less than 1.3% by mass, and even more preferably 0.7% by mass or more but less than 0.9% by mass, relative to the total amount of organic matter in the polylactic acid resin composition. When the content of the epoxy group-containing compound is 0.2% by mass or more but less than 2.0% by mass, relative to the total amount of organic matter in the polylactic acid resin composition, the epoxy group-containing compound is a non-biodegradable material. Therefore, by reducing the content as much as possible and increasing the content of the polylactic acid resin in the polylactic acid resin composition, biodegradability is improved. On the other hand, if the content of the epoxy group-containing compound is low, the melt viscosity during melt foaming is low, and the foaming ratio does not increase, which may result in poor thermal insulation. By setting the content of the epoxy group-containing compound to 0.2% by mass or more but less than 2.0% by mass relative to the total amount of organic matter in the polylactic acid resin composition, both biodegradability and thermal insulation properties can be achieved. Furthermore, when a compound having an epoxy group whose weight-average molecular weight (Mw) and epoxy equivalent are within an appropriate range is used as a chain extender (crosslinking agent), high heat insulation can be obtained even when the content of the compound having an epoxy group is small, which leads to improved biodegradability.

[0114] The epoxy equivalent of the epoxy group-containing compound is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 170 to 350, more preferably 150 to 310, and even more preferably 250 to 310. The epoxy equivalent of the epoxy group-containing compound affects the distance between crosslink points of the reaction product of the polylactic acid resin and the epoxy group-containing compound. When the charge amount (mass) of the epoxy group-containing compound is the same as the charge amount (mass) of the polylactic acid resin, the smaller the epoxy equivalent of the epoxy group-containing compound, the greater the amount of epoxy groups per molecule of the epoxy group-containing compound, resulting in a shorter distance between crosslink points of the reaction product of the polylactic acid resin and the epoxy group-containing compound. On the other hand, the larger the epoxy equivalent of the epoxy group-containing compound, the smaller the amount of epoxy groups per molecule of the epoxy group-containing compound, resulting in a longer distance between crosslink points of the reaction product of the polylactic acid resin and the epoxy group-containing compound. If the distance between crosslinking points of the reaction product of the polylactic acid resin and the compound having an epoxy group is too short, excessive crosslinking occurs locally in the reaction product of the polylactic acid resin and the compound having an epoxy group, resulting in uneven melt viscosity and a low expansion ratio. If the distance between crosslinking points of the reaction product of the polylactic acid resin and the compound having an epoxy group is too long, the effect of improving melt viscosity is small, and the expansion ratio also does not increase. When the epoxy equivalent of the compound having an epoxy group is 170 or more and 350 or less, the viscosity of the polylactic acid resin composition tends to be efficiently adjusted to a range appropriate for foaming with a small amount of chain extender (crosslinking agent).

[0115] The method for measuring the epoxy equivalent of the compound having an epoxy group is not particularly limited, but it can be measured by titration in accordance with JIS K7236:2001 (method for determining the epoxy equivalent of an epoxy resin). Specifically, 10 mL of chloroform is added to 0.1 g to 0.3 g of the compound having an epoxy group, and the mixture is completely dissolved by stirring with a magnetic stirrer or the like. 20 mL of acetic acid and 10 mL of a chloroform solution of tetraethylammonium bromide (concentration: 0.25 g / mL) are added to prepare a sample. The epoxy equivalent of the sample thus prepared can be measured, for example, using the following measuring device and under the following measuring conditions. [[Measurement equipment and conditions]] Equipment: Automatic titrator COM-A-19 (manufactured by Hiranuma Co., Ltd.) Standard solution: 0.1 mol / L perchloric acid-acetic acid standard solution Electrode: Glass electrode GTRS10B Reference electrode GTPH1B (internal solution is saturated sodium perchlorate / acetic acid solution) Measurement mode: Inflection point detection Differential judgment value: 100mV / mL · Calculation formula: 1,000×S / ((A1-BL)×M×f) Here, S is the mass (g) of the compound having an epoxy group, A1 is the amount dropped at the inflection point (mL), BL is the result of the blank measurement (mL), M is the concentration of the standard solution (mol / L), and f is the factor of the standard solution. The blank measurement is performed twice, and the average value of the two measurements is used.

[0116] The weight-average molecular weight (Mw) of the epoxy group-containing compound is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 10,000 to 20,000, and more preferably 12,500 to 17,500. The weight-average molecular weight (Mw) of the epoxy group-containing compound affects the number of crosslinking points of the reaction product between the polylactic acid resin and the epoxy group-containing compound. The weight-average molecular weight (Mw) of the epoxy group-containing compound also affects the number of epoxy groups per molecule. When the number of epoxy groups per molecule is the same and the amount (mass) of the epoxy group-containing compound charged is the same as the amount (mass) of the polylactic acid resin charged, the smaller the weight-average molecular weight (Mw) of the epoxy group-containing compound, the smaller the number of crosslinking points of the reaction product between the polylactic acid resin and the epoxy group-containing compound. Meanwhile, the larger the weight-average molecular weight (Mw) of the epoxy group-containing compound, the larger the number of crosslinking points of the reaction product between the polylactic acid resin and the epoxy group-containing compound. The greater the number of crosslinking points in the reaction product of the polylactic acid resin and the epoxy group-containing compound, the more entangled the molecular chains of the reaction product of the polylactic acid resin and the epoxy group-containing compound become, resulting in a higher melt viscosity of the polylactic acid resin composition during melt foaming, a higher expansion ratio, and improved thermal insulation. However, if the weight-average molecular weight (Mw) of the epoxy group-containing compound is too large, the epoxy group-containing compound loses its fluidity at the reaction temperature, reducing the reactivity between the polylactic acid resin and the epoxy group-containing compound, resulting in a lower melt viscosity of the polylactic acid resin composition and a lower expansion ratio. As a result, by setting the weight-average molecular weight of the epoxy group-containing compound to between 10,000 and 20,000, the melt viscosity of the polylactic acid resin composition increases, increasing the expansion ratio and improving thermal insulation.

[0117] The weight average molecular weight (Mw) of the compound having an epoxy group can be measured using GPC. The weight-average molecular weight (Mw) of the compound having an epoxy group is calculated using a calibration curve prepared using polystyrene samples with known weight-average molecular weights (e.g., A-500 (weight-average molecular weight 589), A-1000 (weight-average molecular weight 1,010), A-2500 (weight-average molecular weight 312), A-5000 (weight-average molecular weight 5,430), F-1 (weight-average molecular weight 9,490), F-2 (weight-average molecular weight 15,700), F-4 (weight-average molecular weight 37,200), F-10 (weight-average molecular weight 98,900), F-20 (weight-average molecular weight 189,000), F-40 (weight-average molecular weight 397,000), F-80 (weight-average molecular weight 707,000), and F-128 (weight-average molecular weight 1,110,000) manufactured by Tosoh Corporation).

[0118] The sample to be subjected to the GPC is prepared by mixing the epoxy group-containing compound with chloroform so that the concentration of the epoxy group-containing compound is about 2 mg / mL, shaking the mixture for about half a day using a tabletop shaker (e.g., MSI-60 manufactured by AS ONE Corporation), confirming that the epoxy group-containing compound has dissolved, and then filtering the mixture through a 0.45 μm membrane filter. Difficult-to-dissolve compounds can also be dissolved by heating at a temperature below the boiling point of chloroform. The GPC measurement device and measurement conditions are not particularly limited, and the sample prepared in this manner can be measured, for example, using the same measurement device and measurement conditions as those used to measure the weight-average molecular weight (Mw) of the foamed sheet.

[0119] - Compounds containing an isocyanate group - The compound having two or more isocyanate groups in the molecule as the chain extender (crosslinking agent) is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include aliphatic diisocyanate compounds, alicyclic polyisocyanate compounds, aromatic diisocyanate compounds, triisocyanate compounds, modified polyisocyanate compounds, etc. These may be used alone or in combination of two or more.

[0120] Examples of the aliphatic diisocyanate compound include 1,6-hexamethylene diisocyanate, 3-isocyanatemethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate), 1,4-tetramethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, methylcyclohexyl-2,4-diisocyanate, methylcyclohexyl-2,6-diisocyanate, xylylene diisocyanate, 1,3-bis(isocyanate)methylcyclohexane, tetramethylxylylene diisocyanate, transcyclohexane-1,4-diisocyanate, and lysine diisocyanate.

[0121] Examples of the alicyclic polyisocyanate include isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tetramethylxylylene diisocyanate, and cyclohexane diisocyanate.

[0122] Examples of the aromatic diisocyanate include 2,4-toluylene diisocyanate, 2,6-toluylene diisocyanate, diphenylmethane-4,4′-isocyanate, 1,5′-naphthene diisocyanate, tolidine diisocyanate, diphenylmethylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 4,4′-dibenzyl diisocyanate, and 1,3-phenylene diisocyanate.

[0123] Examples of the triisocyanate compound include lysine ester triisocyanate, triphenylmethane triisocyanate, 1,6,11-undecane triisocyanate, 1,8-isocyanate-4,4-isocyanate methyloctane, 1,3,6-hexamethylene triisocyanate, bicycloheptane triisocyanate, an adduct of trimethylolpropane and 2,4-toluylene diisocyanate, and an adduct of trimethylolpropane and a diisocyanate such as 1,6-hexamethylene diisocyanate.

[0124] Examples of the modified polyisocyanate compound include compounds obtained by reacting a polyhydric alcohol such as glycerin or pentaerythritol with the aliphatic diisocyanate compound, the aromatic diisocyanate compound, and / or the triisocyanate compound.

[0125] The content of the chain extender (crosslinker) in the polylactic acid resin composition varies depending on the molecular weight and molecular weight distribution of the polylactic acid resin used. For example, when the weight-average molecular weight is small or when a large amount of low-molecular-weight polylactic acid resin is used, it tends to be necessary to add a larger amount of the chain extender (crosslinker) to adjust the viscosity of the polylactic acid resin composition to a level suitable for foaming. However, increasing the amount of the chain extender (crosslinker) added tends to result in poor biodegradability, and since the chain extender (crosslinker) is generally a petroleum-derived compound, it is undesirable from the perspective of contributing to a sustainable society.

[0126] The content of the chain extender other than the compound having an epoxy group in the polylactic acid resin composition is not particularly limited and can be selected appropriately depending on the purpose, but it is preferable that the total amount of the compound having an epoxy group and the chain extender other than the compound having an epoxy group is less than 2 mass% of the total amount of organic matter in the polylactic acid resin composition.

[0127] Other viscosity adjustment methods besides compounding the chain extender (crosslinking agent) include crosslinking the polylactic acid resin composition using electron beams or the like, and blending with another resin composition having high melt tension or a small amount of a high molecular weight component.

[0128] - Foam nucleating agents other than layered silicates - The polylactic acid resin composition may contain a foam nucleating agent other than the layered silicate as needed, as long as the physical properties of the foam sheet are not impaired. Examples of foam nucleating agents other than the layered silicate include inorganic nucleating agents and organic nucleating agents. These may be used alone or in combination of two or more.

[0129] --Inorganic nucleating agents other than layered silicates-- Inorganic nucleating agents other than the layered silicates can be added for the purposes of adjusting the foam diameter as a foam nucleating agent, improving the mechanical properties of the foam sheet as a reinforcing agent, improving the crystallization rate as a crystal nucleating agent, adjusting the appearance (color), etc. The inorganic nucleating agent other than the layered silicate can be used as the inorganic particles other than the layered silicate in the polylactic acid resin composition.

[0130] The foam nucleating agent other than the layered silicate is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include kaolin, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, sodium aluminosilicate, magnesium silicate, glass balloons, carbon black, zinc oxide, antimony trioxide, zeolite, hydrotalcite, metal fibers, metal whiskers, ceramic whiskers, potassium titanate, boron nitride, graphite, glass fibers, carbon fibers, etc. These may be used alone or in combination of two or more.

[0131] The average hydrophobicity and carbon content of the inorganic nucleating agent are not particularly limited and can be selected appropriately depending on the purpose. However, the average hydrophobicity is preferably 65% ​​by volume or more, and the carbon content is preferably 4% by mass or more. When the average hydrophobicity and carbon content of the inorganic nucleating agent are within the above-mentioned preferred ranges, when a non-polar blowing agent such as carbon dioxide or nitrogen is used, the hydrophobic inorganic particle surface acts favorably as a foam nucleation site, enabling efficient foam nucleation. Furthermore, the upper limits of the average hydrophobicity and carbon content of the inorganic nucleating agent are not particularly limited. However, the average hydrophobicity is preferably 68% by volume or less, and the carbon content is preferably 8.9% by mass or less. When the average hydrophobicity of the inorganic nucleating agent is within the above-mentioned preferred ranges, aggregation of inorganic particles tends to be suppressed. However, since the degree of aggregation is strongly dependent on the kneading conditions and kneading equipment used, the effects of the present invention are not limited to the above-mentioned preferred ranges. Furthermore, when the carbon content of the inorganic nucleating agent is within the above-mentioned preferred ranges, the amount of surface treatment agent-derived components released from the inorganic particles tends to be reduced.

[0132] According to classical nucleation theory, a smaller contact angle between the bubble nuclei and the inorganic particle surface reduces the activation energy for foam nucleation, resulting in smoother nucleation. Therefore, the hydrophobicity alone appears to be an important chemical property of the inorganic particle surface. However, the inventors' extensive research revealed that a high hydrophobicity alone of inorganic particles serving as the inorganic nucleating agent tends not to be effective as a foam nucleating agent. While the exact reason is unclear, they found that a significant effect as a foam nucleating agent can be achieved when the inorganic particles serving as the inorganic nucleating agent have an average hydrophobicity of 65% by volume or more and a carbon content of 4% by mass or more. It is believed that a carbon content of 4% by mass or more creates a certain volume on the surface of the inorganic particles that has a high affinity with the blowing agent. When the blowing agent concentration is low, as in the present invention, it is thought that the diffusion of the blowing agent becomes the rate-limiting factor for foam nucleation. It is believed that the blowing agent concentration is substantially higher in the certain volume of inorganic particle surfaces with a high affinity for the blowing agent than in other areas, which is advantageous for sourcing the blowing agent during foam nucleation.

[0133] The hydrophobicity of the inorganic particles is determined by the methanol wettability method (MW method). A larger value indicates a higher hydrophobicity, and a smaller value indicates a higher hydrophilicity. The hydrophobicity of the inorganic particles is calculated by the following formula (10), where the inorganic particles are added to V1 [mL] of pure water, methanol is added dropwise while stirring, and the amount of methanol required for the inorganic particles to be wetted and dispersed in the liquid is V2 [mL]. Hydrophobicity [volume %] = {V2 / (V1+V2)} × 100 Equation (10)

[0134] The degree of hydrophobicity in the present invention refers to a value obtained by the measurement method described below. Weigh 50 mg of inorganic particles into a 50 mL screw cap (Laboran screw cap vial 9-852-09, No. 7, Laborantec) and add 5 mL of pure water (V1 [mL]) to prepare the sample. Gently place a stirring bar (6 mm diameter, 20 mm length, oval) in the cap, and gently stir the cap with a magnetic stirrer (MX-1, Shibata Scientific Co., Ltd.) to avoid creating a vortex on the water surface. Cover the cap with perforated parafilm, and add methanol (special grade, >99.8%, Kanto Chemical Co., Ltd.) at a rate of 0.3 mL / min using a 25 mL burette (tolerance ±0.03 mL, AS ONE Corporation). Measure the amount of methanol (V2 [mL]) required for the inorganic particles to disperse in the liquid. Measurements were performed three times, and the hydrophobicity was calculated using Equation (10) above. The arithmetic mean value was used as the average hydrophobicity.

[0135] The carbon content of the inorganic particles can be measured in accordance with ISO 3262-20:2021 by the measurement method described below. The inorganic particles are completely combusted at 800°C, and then carbon dioxide in the combustion gas is detected and quantified using a thermal conductivity detector (TCD) gas chromatograph to calculate the carbon dioxide content.

[0136] --Organic foam nucleating agent-- Examples of the organic nucleating agent include naturally occurring polymers such as starch, cellulose nanofibers, cellulose fine particles, wood flour, soybean pulp, rice husks, and bran, as well as modified products thereof, glycerin compounds, sorbitol compounds, metal salts of benzoic acid and its compounds, metal salts of phosphate esters, and rosin compounds. These may be used alone or in combination of two or more.

[0137] The content of the foam nucleating agent other than the layer silicate in the polylactic acid resin composition is not particularly limited as long as it does not impair the effects of the present invention and can be appropriately selected depending on the purpose, but it is preferably less than 2 mass% relative to the total amount of organic matter in the polylactic acid resin composition. By having the content of the foam nucleating agent other than the layer silicate in the polylactic acid resin composition be less than 2 mass%, biodegradability and recyclability are improved.

[0138] -Resin components other than polylactic acid resin- The resin component other than the polylactic acid resin is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, styrene-butadiene resin, vinyl chloride resin, acrylic styrene resin, acrylic silicone resin, etc. These may be used alone or in combination of two or more.

[0139] The content of resin components other than the polylactic acid resin in the polylactic acid resin composition is not particularly limited as long as it does not impair the effects of the present invention and can be appropriately selected depending on the purpose, but it is preferably less than 2% by mass of the total amount of organic matter in the polylactic acid resin composition, which improves biodegradability and recyclability.

[0140] -Additives- The additives are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include heat stabilizers, antioxidants, plasticizers, lubricants, crystallization accelerators, thickeners, etc. These may be used alone or in combination of two or more.

[0141] The content of the other components in the polylactic acid resin composition is not particularly limited and can be appropriately selected depending on the purpose, but is preferably less than 2 mass% of the total amount of organic matter in the polylactic acid resin composition, which improves biodegradability and recyclability.

[0142] The content of each component in the polylactic acid resin composition is synonymous with the content of each component in a foamed sheet made of the polylactic acid resin composition.

[0143] As described above, the present invention is characterized by molding a highly crystalline polylactic acid resin composition into a foam sheet while maintaining a low degree of crystallinity in order to obtain a foam sheet with excellent thermoformability. To achieve this characteristic, the temperature of the polylactic acid resin composition from kneading to extrusion must be maintained at a relatively high temperature of at least −20°C below the melting point of the polylactic acid resin composition. This means that it is difficult to adjust the viscosity of the polylactic acid resin composition to a range suitable for foaming by cooling it, as disclosed in prior art documents. Therefore, the polylactic acid resin composition of the present invention is characterized by having a high melt viscosity that allows the foaming agent to be maintained at a relatively high temperature of at least −20°C below the melting point of the polylactic acid resin composition.

[0144] The foamed sheet of the present invention may be used as it is, or may be molded into a molded article (product). The foamed sheet of the present invention is excellent in heat resistance, heat insulation, strength, and biodegradability, and is therefore suitable for use as food containers, tableware, etc. It is also suitable as a heat-resistant food container, but is not limited to such uses. The foamed sheet of the present invention may also be used as it is after printing, etc.

[0145] (Method of manufacturing foam sheet) The foamed sheet of the present invention is obtained by extrusion foaming the polylactic acid resin composition. The process for producing the foamed sheet of the present invention will be described in more detail below. The process for producing the foamed sheet of the present invention preferably includes at least a kneading step, an impregnation step, and a foaming step, and may further include other steps as necessary.

[0146] The extruder used for the extrusion foaming may be, for example, a single-screw extruder, a twin-screw extruder, or a tandem extruder that combines these. Among these, a tandem extruder is preferred from the viewpoint of efficiently melt-kneading the raw materials for the foamed sheet, such as the polylactic acid resin and inorganic particles, and, if necessary, the chain extender, the foam nucleating agent, the other components, and the foaming agent, and cooling the molten mixture to a predetermined temperature before extrusion. From the viewpoint of melt-kneading and cooling efficiency, a tandem extruder that combines a twin-screw extruder and a single-screw extruder is most preferred. Furthermore, a flow rate control mechanism, such as a gear pump, may be installed between the twin-screw extruder and the single-screw extruder or between the extruder and the die, if necessary.

[0147] When a foamed sheet having a low bulk density is to be obtained, it is preferable to produce the foamed sheet using a circular die, from the viewpoint of easing the corrugation. In this case, it is preferable to take up the tubular foam extruded from the circular die while passing it along a cooled mandrel, and further to rapidly cool it by blowing air onto the outer periphery. By performing such cooling, crystallization of the foamed sheet after extrusion can be suppressed, and a foamed sheet having excellent thermoformability can be obtained.

[0148] Furthermore, if necessary, a flow rate adjusting mechanism such as a gear pump may be installed between the twin-screw extruder and the single-screw extruder or between the extruder and the die.

[0149] <<Foaming agent>> The foamed sheet can be obtained by melt-kneading the polylactic acid resin composition with a foaming agent, followed by extrusion foaming. Known physical foaming agents can be used as the foaming agent. For example, physical blowing agents include hydrocarbons such as ethane, butane, pentane, hexane, heptane, ethylene, propylene, and petroleum ether; halogen-based blowing agents such as methyl chloride, monochlorotrifluoromethane, dichlorodifluoromethane, and dichlorotetrafluoroethane; air; carbon dioxide; and nitrogen.

[0150] In the present invention, carbon dioxide and nitrogen are preferred from the viewpoints of low environmental impact, high operational safety, and ease of handling, and carbon dioxide is more preferred than nitrogen from the viewpoint of solubility in the polylactic acid resin composition.

[0151] On the other hand, carbon dioxide is known to have a higher vapor pressure and a faster diffusion rate in a polylactic acid resin composition than hydrocarbon-based blowing agents. Therefore, when producing a foamed sheet using carbon dioxide as a blowing agent, at a high blowing agent concentration that results in a finely foamed state, foaming tends to occur rapidly, resulting in a streaky appearance called corrugation, surface roughness due to cell breakage, and a decrease in the expansion ratio.

[0152] When a tandem extruder is used, it is preferable to inject the foaming agent into the first-stage extruder. Injecting the foaming agent into the first-stage extruder can lengthen the time during which the foaming agent and the polylactic acid resin composition are in contact with each other, which tends to suppress problems such as partial coarsening of bubbles and pinholes caused by the expansion of undissolved foaming agent.

[0153] In the present invention, the amount of the foaming agent added is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 2 to 5 parts by mass, more preferably 2 to 4 parts by mass, per 100 parts by mass of the polylactic acid resin composition. When the amount of the foaming agent added is 2 parts by mass or more per 100 parts by mass of the polylactic acid resin composition, problems such as limited plasticization of the polylactic acid resin composition and an inability to achieve a high expansion ratio can be prevented. Furthermore, when the amount of the foaming agent added is 5 parts by mass or less per 100 parts by mass of the polylactic acid resin composition, poor surface properties due to rapid foaming can be prevented.

[0154] <Kneading process> The kneading step is a step of melting and kneading a mixture containing the polylactic acid resin, the inorganic particles, and, if necessary, the chain extender and other components to obtain a polylactic acid resin composition having a viscosity suitable for foaming. The kneading step preferably further includes a compressive fluid. The compressive fluid is blended to plasticize the polylactic acid resin composition and reduce the load on the equipment, and is preferably the same as the foaming agent from the viewpoint of omitting the subsequent impregnation step.

[0155] When the chain extender is added to the polylactic acid resin, the viscosity of the polylactic acid resin composition is adjusted in the kneading step by the reaction between the polylactic acid resin and the chain extender.

[0156] In the present invention, a compound having two or more epoxy groups in the molecule is preferably used as the chain extender, and therefore the temperature in the kneading step is preferably from the melting point of the polylactic acid resin composition to 240° C., more preferably from 220° C. to 240° C. When the temperature in the kneading step is from the melting point of the polylactic acid resin composition to 240° C., the viscosity of the polylactic acid resin composition can be effectively improved, and furthermore, elution of unreacted compound having two or more epoxy groups in the molecule can be reduced.

[0157] <Impregnation process> The impregnation step is a step in which a foaming agent is kneaded into the polylactic acid resin composition to obtain an expandable polylactic acid resin composition. The solubility (solubility and dissolution rate) of the foaming agent in the polylactic acid resin composition varies depending on the temperature and pressure of the impregnation step. The temperature and pressure of the impregnation step can be appropriately set while observing the state of the foam sheet. Generally, the solubility of the foaming agent in the polylactic acid resin composition can be increased by increasing the pressure and decreasing the temperature of the polylactic acid resin composition.

[0158] In the present invention, the term "expandable polylactic acid resin composition" refers to a composition in which the foaming agent is dissolved and / or dispersed in the polylactic acid resin composition, and is a composition in a state in which it foams when the pressure inside the extruder is released to atmospheric pressure in the foaming step described below.

[0159] The impregnation step is preferably carried out while slowly cooling the expandable polylactic acid resin composition. A tandem extruder combining a twin-screw extruder and a single-screw extruder is suitable for producing the foamed sheet of the present invention because it can dissolve the foaming agent while slowly cooling the polylactic acid resin composition using the single-screw extruder.

[0160] <Foaming process> The foaming step is a step of extruding and discharging the expandable polylactic acid resin composition obtained in the impregnation step through the flow path of the mold to obtain a foam, and preferably is a step of vaporizing and removing the compressive fluid as a foaming agent dissolved in the expandable polylactic acid resin composition obtained in the impregnation step, generating bubbles in the polylactic acid resin composition to foam it, and extruding the polylactic acid resin composition through the flow path of the mold to mold it. In the foaming step, foaming occurs using the pressure difference between the pressure inside the extruder and atmospheric pressure as a driving force.

[0161] The expandable polylactic acid resin composition is preferably adjusted to about 150°C to 170°C in the expansion step. Here, the temperature in the expansion step refers to the set temperature of the mold. By adjusting the temperature in the expansion step to this range, it is possible to adjust the viscosity of the expandable polylactic acid resin composition to a range suitable for expansion while suppressing crystallization.

[0162] If the mold is cooled to about 130°C, crystallization will proceed, which will tend to impair the thermoformability of the foamed sheet and cause the die to become clogged with crystals. By setting the temperature in the foaming step within the above range, the viscosity of the expandable polylactic acid composition can be adjusted to a range suitable for foaming while suppressing crystallization.

[0163] The kneading step and the impregnation step may be carried out simultaneously, or the kneading step alone may be carried out to obtain a polylactic acid resin composition, and then the impregnation step and the foaming step may be carried out to obtain a foam.

[0164] The non-foamable polylactic acid resin composition obtained by carrying out only the kneading step is sometimes called a masterbatch or simply a polylactic acid resin composition.

[0165] The mold is preferably provided at the outlet tip of the extruder serving as the foaming means. The mold is not particularly limited and can be appropriately selected depending on the purpose. For example, a circular die called a circular die (sometimes called a "round die"), a T-die, or the like can be used. Such a die can be connected to the tip of the extruder to extrude the expandable polylactic acid resin composition to obtain a foamed sheet. Among these, a circular die is preferred from the viewpoint of the bulk density of the foamed sheet.

[0166] The die preferably has a flow path therein, and includes a first flow path-forming member and a second flow path-forming member that form at least a cylindrical flow path. The expandable polylactic acid resin composition is passed through the flow path inside the mold having the first flow path-forming member and the second flow path-forming member, i.e., the region sandwiched between the flow path-forming surface of the first flow path-forming member and the flow path-forming surface of the second flow path-forming member, thereby foaming the polylactic acid resin composition and molding the polylactic acid resin composition.

[0167] The surface roughness parameter Rk (hereinafter sometimes abbreviated as "surface roughness parameter Rk") of at least one of the flow path forming surface of the first flow path forming member and the flow path forming surface of the second flow path forming member is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 1.0 μm to 6.3 μm, more preferably 2.0 μm to 5.0 μm. When the surface roughness parameter Rk is 1.0 μm to 6.3 μm and the polylactic acid resin composition contains the layered silicate, the oriented layered silicate further reduces friction between the expandable polylactic acid resin composition and at least one of the flow path forming surface of the first flow path forming member and the flow path forming surface of the second flow path forming member, and the density of the foamed sheet becomes more uniform, thereby further improving the strength of the foamed sheet. On the other hand, if the surface roughness parameter Rk is less than 1.0 μm, uneven density of the foamed sheet occurs due to slip-stick, and the low-density portions of the foamed sheet become brittle, which may reduce the strength of the foamed sheet. On the other hand, if the surface roughness parameter Rk is more than 6.3 μm, poor appearance may occur due to transfer of the mold shape.

[0168] The surface roughness parameter Rk is an index that represents the height of the entire cross-sectional shape of the surface, excluding extremely protruding peaks and valleys, and is a parameter based on JIS B0671-2:2002 (Geometric Product Specifications (GPS) - Surface Properties).

[0169] The surface roughness parameter Rk1 of the flow path forming surface of the first flow path forming member and the surface roughness parameter Rk2 of the flow path forming surface of the second flow path forming member may be the same as or different from each other, but it is preferable that both of the surface roughness parameter Rk1 and the surface roughness parameter Rk2 are 1.0 μm or more and 6.3 μm or less, and it is more preferable that the surface roughness parameter Rk1 and the surface roughness parameter Rk2 are the same numerical value.

[0170] There are no particular limitations on the method for measuring the surface roughness parameter Rk, and it can be measured using, for example, a portable roughness meter (for example, a shape analysis laser microscope VK-X250 manufactured by Keyence Corporation, or a small surface roughness measuring instrument SJ-210 manufactured by Mitutoyo Corporation). Specifically, it can be measured using a VK-X250 manufactured by Keyence Corporation under the following measurement conditions and under the conditions described in the image processing and measurement. Note that the measurement conditions and image processing and measurement are similar to those described below, and the method is not limited thereto as long as a correlation between instrument errors, if any, is understood in advance. [Measurement conditions] Measuring device: Keyence VK-X250 Brightness: Automatic setting Double scan (automatic) Measurement mode: Surface profile mode Resolution: 1024×768 High accuracy mode RPD: Not set Measurement height pitch: 0.1 μm Single field of view (no image merging) Uses a 20x objective lens [Image processing and measurement] · Plane correction: “Reference plane correction (all areas)” Curvature correction: "Surface waviness correction strength 3" · Binding point removal A total of 20 measurements were taken on vertical lines (the average value of 20 points was used for the line roughness, but this can also be used for parameters that define surface roughness) Roughness measurement: No cutoff for either λs or λc, end correction is performed Field of view during measurement: Approx. 536 μm in the measurement length direction, approx. 714 μm in the direction perpendicular to the measurement length

[0171] The method for forming the flow path forming surface of the first flow path forming member and the flow path forming surface of the second flow path forming member is not particularly limited and can be appropriately selected depending on the purpose. Examples of methods include, but are not limited to, sandblasting. Other methods include electrolysis, chemical etching, and machining using a lathe. In the case of air sandblasting, it is known that roughness can be controlled by controlling the application time, spray pressure, distance from the workpiece, processing angle, media shape, media material, etc. Sandblasting is affected by environmental factors such as the hardness of the outermost surface of the workpiece, the configuration of the application equipment, the degree of media deterioration, and the nozzle shape. However, since there is a relationship in which roughness increases as the spray pressure increases, for example, a desired roughness can be obtained by repeatedly making prototypes using test pieces made of the same material as the product.

[0172] The temperature of the mold, preferably the die, is preferably set to 150° C. or higher and 170° C. or lower. By setting the temperature of the mold within this range, the viscosity of the expandable polylactic acid resin composition can be adjusted to a range suitable for foaming while suppressing crystallization of the expandable polylactic acid resin composition.

[0173] Next, an example of an apparatus for carrying out the kneading step will be described with reference to the drawings, but the kneading step of the present invention is not limited to this. FIG. 2 is a schematic diagram showing a twin-screw extruder (continuous kneading apparatus) 100 as an example of a kneading means in the foam sheet manufacturing apparatus of the present invention. For example, the twin-screw extruder 100 has a screw diameter of 42 mm, and the ratio of the extruder length (L) to the screw diameter (D) [L / D] is 48. In this example, raw materials such as polylactic acid resin, inorganic particles, a foam nucleating agent, and a chain extender are supplied from a first supply section 1 and a second supply section 2 to a raw material mixing and melting section a, where they are mixed and melted. If the polylactic acid resin composition is composed of three or more components, the number of supply sections can be appropriately increased, or the components can be premixed with the polylactic acid resin and then supplied from the supply sections to the raw material mixing and melting section a.

[0174] The mixed and melted raw materials are supplied with compressible fluid from compressible fluid storage section 3 in compressible fluid supply section b. The mixture containing compressible fluid is then kneaded in kneading section c. Next, the compressible fluid F is removed from the mixture in compressible fluid removal section d, and the mixture is then pelletized in molding section e to become, for example, resin pellets P. In this manner, a polylactic acid resin composition (masterbatch) can be produced.

[0175] The compressive fluid may be cooled and liquefied before being supplied by a metering pump, and solid raw materials such as resin pellets and foam nucleating agents may be supplied by a metering feeder.

[0176] When the kneading step, the impregnation step, and the foaming step are carried out in a continuous manner, it is preferable to use a foaming agent as the compressive fluid, and the compressive fluid F is not removed in the compressive fluid removal section d.

[0177] Next, the steps performed in each part of the kneading device shown in FIG. 2 will be described.

[0178] -Raw material mixing and melting section a- In the raw material mixing and melting section a, resin pellets and components other than polylactic acid resin, which are added as needed, are mixed and heated. The heating temperature is set to a temperature higher than the melting point of the resin, and the mixture is brought to a state where it can be uniformly mixed with compressible fluid F in the next compressible fluid supply section b.

[0179] -Compressible fluid supply section b- In the compressible fluid supplying section b, compressible fluid F is supplied to the resin pellets that have been heated to a molten state, thereby plasticizing the molten resin.

[0180] -Kneading section c- In the kneading section c, components other than the polylactic acid resin are uniformly dispersed in the polylactic acid resin. The set temperature may be changed appropriately depending on the specifications of the reaction apparatus, the load conditions, etc., but is preferably from the melting point of the polylactic acid resin composition to 240°C.

[0181] Next, an example of a foamed sheet manufacturing apparatus (continuous foamed sheet manufacturing apparatus 110) for continuously carrying out the kneading and foaming is shown in FIG.

[0182] The continuous foamed sheet manufacturing apparatus 110 may be a tandem extruder in which a kneading apparatus 10 and a single-screw extruder 20 are connected together. In the continuous foamed sheet manufacturing apparatus 110, for example, raw materials such as polylactic acid resin, inorganic particles, a foam nucleating agent, and a chain extender are supplied from a first supply unit 1 and a second supply unit 2 to a raw material mixing and melting unit a, where they are mixed and melted.

[0183] The mixed and melted raw materials are supplied with a compressible fluid as a foaming agent from a compressible fluid storage section 3 in a compressible fluid supply section b. The mixture containing the compressible fluid as a foaming agent is then kneaded in a kneading section c to form an expandable polylactic acid resin composition.

[0184] The expandable polylactic acid resin composition is fed to a temperature control section f, where it is adjusted to a temperature suitable for foaming and the foaming agent is further dissolved. The composition is then extruded through a die into the atmosphere, and the resulting cylindrical foam 4 is cooled by air cooling from the periphery while being placed on a cooling mandrel 5. A portion of the foam is then cut open with a rotary blade, flattened, and wound into a roll to obtain the foam sheet of the present invention.

[0185] In the present invention, the temperature in the kneading section c is from the melting point of the polylactic acid resin composition to 240° C., more preferably from 220° C. to 240° C. The temperature in the temperature adjusting section f is preferably at least 20° C. below the melting point of the polylactic acid resin composition.

[0186] 4, the mold at the outlet end of the single-screw extruder 20 has a first flow path-forming member 31 and a second flow path-forming member 32 that form at least a cylindrical flow path 30, and the expandable polylactic acid resin composition passes through the flow path 30 to be molded. At this time, since the surface roughness parameter Rk of at least one of the flow path-forming surface 31a of the first flow path-forming member 31 and the flow path-forming surface 32a of the second flow path-forming member 32 is 1.0 μm or more and 6.3 μm or less, the density of the foamed sheet becomes uniform, and a foamed sheet with improved strength is obtained.

[0187] In this example, the kneading step is performed by a kneading device 10, and the foaming step is performed by a single-screw extruder 20. However, the present invention is not limited to this configuration. For example, the areas where the kneading step and the foaming step are performed can be changed as appropriate.

[0188] (molded body) One embodiment of the molded article of the present invention contains the foamed sheet of the present invention. This may be a molded article made of the foamed sheet of the present invention, and may further contain other components as necessary. Another embodiment of the molded article of the present invention is obtained by thermoforming the foamed sheet of the present invention, and may further contain other components as necessary. The other components are not particularly limited as long as they are those commonly used in resin products, and can be appropriately selected depending on the purpose.

[0189] The thermoforming of the foamed sheet is not particularly limited, and for example, the foamed sheet may be subjected to a process of thermoforming using a mold to obtain a product. The method of thermoforming the foamed sheet using a mold is not particularly limited, and a conventionally known method for thermoplastic resins can be used, such as vacuum molding, pressure molding, vacuum / pressure molding, and press molding.

[0190] Examples of the molded body (also referred to as a manufactured product, consumer product, etc.) include daily necessities such as containers, bags, packaging containers, trays, tableware, cutlery, stationery, cushioning materials, etc. The concept of the molded body includes not only a roll of the foamed sheet as an intermediate for processing a molded body, and a single molded body, but also a part made of the molded body such as a tray handle, and a product equipped with a molded body such as a tray with a handle attached.

[0191] The form of the container can be selected without any particular limitation. For example, it may be a container without a lid, such as a tray, or a container in a form in which the opening is closed with a shrink film, a top seal, a fitting lid, etc. The container of the present invention also includes a container lid, and can be used as a container lid.

[0192] Examples of the bags include plastic bags, shopping bags, and garbage bags.

[0193] Examples of the stationery include clear files and badges.

[0194] The molded body can also be used for purposes other than the above-mentioned daily necessities, and can be widely used as, for example, sheets and packaging materials for industrial materials, daily necessities, agricultural products, food products, pharmaceutical products, cosmetics, etc.

[0195] The foamed sheet may be subjected to processing such as lamination or coating, if necessary. The processing may be performed before winding the foamed sheet during production, or after the foamed sheet has been wound up. The type of laminating film, coating agent, etc., and the processing method may be selected without particular limitation.

[0196] Such molded articles may not maintain the properties of the foamed sheet, but are within the scope of the present invention as long as the foamed sheet is used as a raw material.

[0197] <Molded body manufacturing method and molded body manufacturing device> The method for producing the molded body is not particularly limited and can be appropriately selected depending on the shape of the desired molded body, etc., but when producing a molded body by a thermal molding method, it is preferable to include a heating step and a thermal molding step, and further include other steps as necessary. The manufacturing apparatus for the molded body is not particularly limited and can be appropriately selected depending on the shape of the desired molded body, etc., but it is preferable that the apparatus has a heating means and a heat molding means, and further has other means as necessary. The method for manufacturing the molded body is preferably carried out by the molded body manufacturing apparatus.

[0198] <<Heating process and heating means>> The heating step is a step of heating and softening the foamed sheet before molding the foamed sheet of the present invention. The heating means is a means for heating and softening the foamed sheet before molding the foamed sheet of the present invention. The heating step is preferably carried out by the heating means.

[0199] In the heating step, the method for heating the foamed sheet is not particularly limited and can be appropriately selected depending on the purpose. For example, a method in which the heating means is disposed above and below the foamed sheet, or on either the upper surface or the lower surface of the foamed sheet, may be mentioned.

[0200] The heating means is not particularly limited and can be appropriately selected from known heating elements depending on the purpose, and examples thereof include an electric heater, a heating plate, and an IR (infrared) heater.

[0201] In the heating step, it is preferable to not proceed with crystallization of the polylactic acid resin before molding the foamed sheet, but to proceed with crystallization of the polylactic acid resin in the subsequent heat molding step, from the viewpoint of improving heat resistance. Therefore, the heating step is preferably a method that can heat the foamed sheet in a short time, and a method of heating the foamed sheet by arranging IR (infrared) heaters above and below the foamed sheet is particularly preferable.

[0202] The heating temperature of the foam sheet in the heating step is not particularly limited and can be appropriately selected depending on the purpose, but is preferably a temperature equal to or higher than the glass transition temperature of the polylactic acid resin, more preferably 60°C or higher, and even more preferably 80°C or higher. Furthermore, if the foam sheet is heated near the cold crystallization temperature of the polylactic acid resin, crystallization will proceed during the heating step. Therefore, the heating temperature of the foam sheet in the heating step is preferably a maximum of 110°C or lower. The lower and upper limits of the heating temperature can be appropriately combined, but the heating temperature of the foam sheet in the heating step is more preferably 60°C or higher and 100°C or lower, and particularly preferably 80°C or higher and 100°C or lower.

[0203] The heating time of the foamed sheet in the heating step is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 15 seconds or less, more preferably 10 seconds or less, and even more preferably 5 seconds or less, from the viewpoint of preventing excessive crystallization.

[0204] <<Heat molding process>> The heat-molding step is a step of molding the foamed sheet softened by the heating step using a mold, preferably a metal die, and is preferably a step of forming the foamed sheet into the shape of a container.

[0205] The molding method using the mold is not particularly limited, and any conventionally known thermoforming method for thermoplastic resins can be used, such as vacuum molding, pressure molding, vacuum-pressure molding, and matched mold molding. However, the matched mold molding method is particularly preferred from the viewpoint of promoting crystallization of the polylactic acid resin of the foamed sheet during the molding process and improving heat resistance.

[0206] The temperature of the mold in the heat molding step is not particularly limited and can be appropriately selected depending on the purpose. However, it is preferable to perform the heat molding step at a temperature close to the cold crystallization temperature of the polylactic acid resin so that the crystallization of the polylactic acid resin in the foamed sheet can proceed.

[0207] In the present invention, "near the cold crystallization temperature of the polylactic acid resin" means a temperature 20°C or lower than the cold crystallization temperature of the polylactic acid resin. Specifically, the temperature of the mold in the heat molding step is preferably 100°C or higher and 120°C or lower, and more preferably 100°C or higher and 110°C or lower. By maintaining the temperature of the mold in the heat molding step at a temperature near the cold crystallization temperature of the polylactic acid resin, a molded product with excellent heat resistance can be obtained.

[0208] The heat molding time in the heat molding step is not particularly limited and can be appropriately selected depending on the purpose, but it is preferable to ensure a time sufficient for the foamed sheet to crystallize, more preferably 5 seconds or more, and even more preferably 7 seconds or more. The upper limit of the heat molding time is not particularly limited, but is preferably 10 seconds or less from the viewpoint of heat resistance. The lower limit and upper limit of the heat molding time can be appropriately combined, and the heat molding time is preferably 5 seconds or more and 10 seconds or less, more preferably 7 seconds or more and 10 seconds or less.

[0209] <<Other processes and other means>> The other steps are not particularly limited and can be appropriately selected depending on the purpose. Examples of the other steps include a demolding step of removing the molded body from the mold, a step of punching the molded body from the foam sheet, and a step of cutting off excess portions of the foam sheet other than the molded body. [Example]

[0210] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the examples, "parts" means "parts by mass" and "%" means "% by mass" except in the evaluation criteria.

[0211] Example 1 <Preparation of foam sheet> -Raw material mixing and melting process- Using a tandem type continuous foam sheet forming apparatus 110 shown in FIG. 3, a polylactic acid resin composition comprising polylactic acid resin, inorganic particles, and a chain extender was supplied to the raw material mixing and melting section a of the kneading device 10 at a rate of 20 kg / hour in the following ratios: 97.7 parts polylactic acid resin (REVODE190, manufactured by HISUN Corporation), 1 part inorganic particles (M-400, manufactured by Repco Corporation), and 1.3 parts chain extender (Joncy (registered trademark) ADR4468, manufactured by BASF).

[0212] -Compressible fluid supply process and kneading / impregnation process- Next, carbon dioxide, a compressible fluid used as a foaming agent, was supplied to the compressible fluid supply section b of the kneading device 10 at 0.76 kg / hour (equivalent to 3.8 parts per 100 parts of the polylactic acid resin composition), and these were mixed, melted, and kneaded in the kneading section c, and supplied to the single-screw extruder 20.

[0213] -Foaming process- The polylactic acid resin composition was then cooled in the temperature control section f of the single-screw extruder 20 until the resin temperature reached 160°C, and extruded and foamed by discharging it into the atmosphere through a circular die attached to the tip of the single-screw extruder to vaporize the carbon dioxide. The circular die used had a slit diameter of 70 mm, a slit gap of 0.5 mm, and the surface roughness parameter Rk of the first flow path forming member and second flow path forming surface forming the flow path leading from the temperature control section f to the slit opening was 3.5 μm.

[0214] The first flow path forming member and the second flow path forming member were manufactured by processing S45C (manufactured by Misumi Corporation) by sandblasting (using alumina polishing media for blasting manufactured by Monotaro Corporation, processing angle approximately 45 degrees).

[0215] -Molding process- The obtained cylindrical foamed sheet was placed on a cooling mandrel 5 and forcedly cooled by blowing air onto the outer surface thereof, and the sheet was cut with a rotary blade cutter to obtain a flat sheet-like foam (hereinafter, sometimes referred to as the "foamed sheet" of Example 1).

[0216] In Example 1, the temperatures of the various parts were as follows: Mixing and melting section of the kneading equipment: 200℃ Compressible fluid supply section b of the kneading device: 240°C Mixing section c of the mixer: 240℃ Single-screw extruder temperature control section: Cooling from 180℃ to 160℃ Circular die: 160℃

[0217] In Example 1, the pressures at the various parts were as follows: Compressible fluid supply section b of the kneading device: 7MPa to 10MPa Mixing section c of the mixer: 8MPa to 20MPa Single screw extruder temperature control: 8MPa~35MPa

[0218] Examples 2 to 5 Foamed sheets of Examples 2 to 5 were obtained in the same manner as in Example 1, except that the blending amounts of polylactic acid resin and inorganic particles in Example 1 were changed to those shown in Table 1 below.

[0219] Example 6 A foamed sheet of Example 6 was obtained in the same manner as in Example 1, except that the type of inorganic particles used in Example 1 was changed from M-400 (manufactured by Repco Corporation) to M-200 (manufactured by Repco Corporation).

[0220] Example 7 A foamed sheet of Example 7 was obtained in the same manner as in Example 1, except that the type of inorganic particles used in Example 1 was changed from M-400 (manufactured by Repco Co., Ltd.) to J-31M (manufactured by Yamaguchi Mica Co., Ltd.).

[0221] Example 8 A foamed sheet of Example 8 was obtained in the same manner as in Example 1, except that the type of inorganic particles used in Example 1 was changed from M-400 (manufactured by Repco Co., Ltd.) to B-82 (manufactured by Yamaguchi Mica Co., Ltd.).

[0222] Examples 9 to 10 The foamed sheets of Examples 9 and 10 were obtained in the same manner as in Example 1, except that the type of inorganic particles in Example 1 was changed to two types: M-400 (manufactured by Repco Co., Ltd.) and AEROSIL (registered trademark) RY300 (manufactured by Nippon Aerosil Co., Ltd.), and the blending amounts of polylactic acid resin and inorganic particles were changed to the blending amounts shown in Table 2 below.

[0223] Examples 11 to 13 The foamed sheets of Examples 11 to 13 were obtained in the same manner as in Example 1, except that the surface roughness parameter Rk of the first flow path forming member and the second flow path forming surface was changed from 3.5 μm to the values ​​shown in Table 3 below.

[0224] (Comparative Example 1) A foamed sheet of Comparative Example 1 was obtained in the same manner as in Example 1, except that no inorganic particles were added.

[0225] (Comparative Example 2) A foamed sheet of Comparative Example 2 was obtained in the same manner as in Example 1, except that the blending amount of the inorganic particles in Example 1 was changed to the blending amount shown in Table 4 below.

[0226] (Comparative Example 3) A foamed sheet of Comparative Example 3 was obtained in the same manner as in Example 1, except that the type of inorganic particles used in Example 1 was changed from M-400 (manufactured by Repco Corporation) to M-XF (manufactured by Repco Corporation).

[0227] Comparative Example 4 A foamed sheet of Comparative Example 4 was obtained in the same manner as in Example 1, except that the type of inorganic particles used in Example 1 was changed from M-400 (manufactured by Repco Co., Ltd.) to D-1000 (Nano Ace series, manufactured by Nippon Talc Industries Co., Ltd.).

[0228] (Comparative Example 5) A foamed sheet of Comparative Example 5 was obtained in the same manner as in Example 1, except that the type of inorganic particles in Example 1 was changed from M-400 (manufactured by Repco Co., Ltd.) to AEROSIL (registered trademark) RY300 (manufactured by Nippon Aerosil Co., Ltd.).

[0229] (Comparative Example 6) A foamed sheet of Comparative Example 6 was obtained in the same manner as in Example 1, except that the type of polylactic acid resin in Example 1 was changed from REVODE190 (manufactured by HISUN) to REVODE110 (manufactured by HISUN) and the temperature of the circular die was changed from 150°C to 160°C.

[0230] (Comparative Example 7) A foamed sheet of Comparative Example 7 was obtained in the same manner as in Comparative Example 5, except that the surface roughness parameter Rk of the first flow path forming member and the second flow path forming surface was changed from 3.5 μm to 0.38 μm.

[0231] (Comparative Example 8) A foamed sheet of Comparative Example 8 was obtained in the same manner as in Example 1, except that instead of using only REVODE190 (manufactured by HISUN Co., Ltd.) as the resin component in the polylactic acid resin composition in Example 1, an acrylic resin (Metablen P-501, Mitsubishi Chemical Corporation) was used in addition to REVODE190 (manufactured by HISUN Co., Ltd.) and the blending amounts of each component were changed to the blending amounts shown in Table 5 below.

[0232] <Measurement of physical properties> The foam sheets of Examples 1 to 13 and Comparative Examples 1 to 8 were measured for the "molar ratio of D-lactic acid to L-lactic acid constituting the polylactic acid resin in the foam sheet," "content of polylactic acid resin relative to the total amount of organic matter in the foam sheet," "foam diameter (median diameter) of the foam sheet," and "bulk density of the foam sheet" by the following methods. The measurement results are shown in Tables 1 to 5 below.

[0233] <<Measurement of the molar ratio of D-lactic acid and L-lactic acid that make up the polylactic acid resin in foam sheets>> The foam sheets of Examples 1 to 13 and Comparative Examples 1 to 8 were freeze-pulverized, and 200 mg of the freeze-pulverized foam sheet powder was weighed out using a precision balance and placed in an Erlenmeyer flask. 30 mL of 1N aqueous sodium hydroxide solution was then added. The Erlenmeyer flask was then heated to 65°C with shaking to completely dissolve the polylactic acid resin. The pH was then adjusted to 7 using 1N hydrochloric acid, and the solution was diluted to a predetermined volume using a measuring flask to obtain a polylactic acid resin solution. The polylactic acid resin solution was then filtered through a 0.45 μm membrane filter and analyzed by liquid chromatography under the following measurement conditions. [[Measurement equipment and conditions]] HPLC device (liquid chromatograph): PU-2085Plus system (manufactured by JASCO Corporation) Column: Chromolith® coated with SUMICHIRAL OA-5000 (inner diameter 4.6 mm, length 250 mm) (Sumitomo Analysis Center, Ltd.) Column temperature: 25℃ Mobile phase: A mixture of 2 mM CuSO4 aqueous solution and 2-propanol (CuSO4 aqueous solution:2-propanol (volume ratio) = 95:5) Mobile phase flow rate: 1.0 mL / min Detector: UV254nm · Injection volume: 20μL

[0234] Based on the obtained chart, the peak area ratios of the D-lactic acid and the L-lactic acid were calculated from the peak areas of the D-lactic acid and the L-lactic acid, respectively, and the total area of ​​these peaks. The D-lactic acid amount ratio and the L-lactic acid amount ratio were calculated using these as the abundance ratios. The above procedure was performed three times, and the arithmetic mean of the results was used as the amount of the D-lactic acid and the amount of the L-lactic acid constituting the polylactic acid resin in the foamed sheet. The results are shown in Tables 1 to 5 below as "molar ratio (L-lactic acid:D-lactic acid)".

[0235] <<Measurement of the content of polylactic acid resin relative to the total amount of organic matter in a foam sheet>> The content of polylactic acid resin relative to the total amount of organic substances in the foamed sheets of Examples 1 to 13 and Comparative Examples 1 to 8 was measured by the following procedure.

[0236] -Preparation of solvent- The solvent used for the measurement was prepared by weighing out approximately 100 mg of 1,3,5-trimethoxybenzene standard (for quantitative NMR, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as an internal standard substance and dissolving it in deuterated chloroform (containing 0.3% by volume of tetramethylsilane (TMS)) in a 10 mL measuring flask.

[0237] -Sample preparation- The solvent was added to the foam sheets of Examples 1 to 13 and Comparative Examples 1 to 8 so that the concentration of the foam sheets was 10 mg / mL, and the foam sheets were dissolved by shaking for about half a day using a tabletop shaker (MSI-60, AS ONE Corporation). To minimize changes in sample concentration due to evaporation, the smallest possible container was selected. The samples prepared by the above method were sealed in sample tubes with a diameter of 5 mm and subjected to NMR.

[0238] -measurement- Using the following measuring equipment and conditions, in accordance with JIS K0138:2018 (General rules for quantitative nuclear magnetic resonance spectroscopy (qNMR general rules)), 1 NMR measurement of H nuclei ( 1 H-NMR measurements were performed. [[Measurement equipment and conditions]] · Nuclear magnetic resonance (NMR) device: JNM-ECX-500 FT-NMR (manufactured by JEOL Ltd.) Observed nucleus: 1H · Measurement temperature: 30℃ Spin:Off Digital resolution: 0.25Hz Observation range: -0.5 to 15 ppm Pulse angle: 90° Relaxation time: 60 seconds Number of scans: 16 (Two dummy scans are performed before the actual measurement) 13C decoupling: Yes

[0239] -analysis- The obtained data was integrated with respect to the peaks of the chemical shifts shown below, and the integral ratio was calculated by the following formula (5). Integral 1 (derived from polylactic acid resin): 5.2 ppm Integral 2 (from internal standard): 6.1ppm Integral ratio = integral 1 / (integral 2 × sample mass) Equation (5)

[0240] A similar NMR measurement was performed on a polylactic acid resin of known purity using the same solvent as the sample. The ratio of the integral ratio obtained from the formula (5) for the polylactic acid resin of known purity to the integral ratio for the sample was calculated, and the content of the polylactic acid resin relative to the total amount of organic matter in the foam sheet was calculated using the following formula (6). Polylactic acid resin content [mass%] = 100 × purity of polylactic acid resin of known purity [mass%] × (integral ratio of sample) / (integral ratio of polylactic acid resin of known purity) Equation (6)

[0241] The steps from sample preparation to analysis were repeated three times, and the arithmetic mean of the obtained polylactic acid resin contents was taken as the polylactic acid resin content relative to the total amount of organic matter in the foamed sheets of Examples 1 to 13 and Comparative Examples 1 to 8.

[0242] <<Measurement of foam diameter (median diameter) of foamed sheet>> The cross sections of the foam sheets of Examples 1 to 13 and Comparative Examples 1 to 8 were cut using a sharp razor (76 razor, manufactured by Nissin EM Co., Ltd.). The cross sections of the foam sheets were observed using a scanning electron microscope (SEM) (3D Real Surface View Microscope VE-9800, manufactured by KEYENCE Corporation) at a magnification of 20x to 50x. The obtained images were subjected to region segmentation using the watershed method (morphological segmentation) using the MorphoLibJ plugin of the image analysis software ImageJ (free software). The tolerance was adjusted for each image to ensure reasonable segmentation. The region division lines were output as binary images, and the bubble area distribution was calculated using the particle size analysis function of the image analysis software, excluding bubbles bordering the image edges from the analysis. The cumulative distribution of the bubble area was created using spreadsheet software (Excel, manufactured by Microsoft), and the area where the cumulative distribution reached 50% was determined. The circle-equivalent diameter of this area was calculated and used as the foam diameter (median diameter).

[0243] <<Measurement of bulk density of foam sheet>> The foamed sheets of Examples 1 to 13 and Comparative Examples 1 to 8 were allowed to stand for 24 hours or more in an environment controlled at a temperature of 23°C and a relative humidity of 50%, and 50 mm x 50 mm test pieces were cut out. The cut test pieces were subjected to a liquid weighing method using an automatic hydrometer (DSG-1, manufactured by Toyo Seiki Seisaku-sho, Ltd.) to determine their bulk densities. In the liquid weighing method, the mass (g) of the foamed sheet test piece in air was precisely weighed, and then the mass (g) of the foamed sheet test piece in water was precisely weighed, and the mass was calculated using the following formula (1): Bulk density [g / cm 3 ] = density of water [g / cm 3 ] × mass of test piece in air [g] / (mass of test piece in air [g] - mass of test piece in liquid [g]) Equation (1)

[0244] <Evaluation> The foamed sheets of Examples 1 to 13 and Comparative Examples 1 to 8 were evaluated for "heat resistance," "heat insulation," and "strength" by the following methods. The evaluation results are shown in Tables 1 to 5 below.

[0245] <<Heat resistance>> The foamed sheets of Examples 1 to 13 and Comparative Examples 1 to 8 were preheated and then molded into the shape of a cup yakisoba container (opening diameter 180 mm, bottom diameter 110 mm, depth 60 mm) in a match mold type heating die at 110°C for 30 seconds. Water at 25°C was poured into the opening of each of the foamed sheet molded bodies (cup yakisoba containers) of Examples 1 to 7 and Comparative Examples 1 to 7 up to the top of the opening, and the mass of the water poured into the molded body was measured. The value converted to volume using the density of water at 25°C was used as the "initial volume" of the molded body. Next, the molded foam sheets of Examples 1 to 13 and Comparative Examples 1 to 8 were heated at 120°C for 10 minutes, and then water at 25°C was poured into the opening up to the top. The mass of the water poured into the molded body was measured, and the value converted into volume using the density of water at 25°C was used as the "volume after heating" of the molded body. The volume change rate of the molded body before and after heating was calculated using the following formula (11), and this volume change rate was used as an index of the heat resistance of the molded body and evaluated based on the following evaluation criteria. The evaluation result was A, which was the best, and A or B was within the acceptable range. Volume change rate (%) = (initial volume - volume after heating) / initial volume × 100 Equation (11) -Heat resistance evaluation criteria- A: The volume change rate is less than 3% B: The volume change rate is 3% or more and less than 10% C: The volume change rate is 10% or more, or the original shape is no longer recognizable.

[0246] <<Thermal insulation>> Test pieces measuring 50 mm x 50 mm were cut out from the foam sheets of Examples 1 to 13 and Comparative Examples 1 to 8. The cut test pieces were placed on a hot plate heated to 100°C and allowed to stand for 3 minutes. After standing, a thermocouple was attached to the surface opposite the heated surface to measure the surface temperature of the foam sheet. The surface temperature of the foam sheet was used as an index of heat insulation and evaluated according to the following evaluation criteria. A was the best evaluation result, and A or B was within the acceptable range. -Insulation evaluation criteria- A: The surface temperature of the foam sheet is less than 45°C. B: The surface temperature of the foam sheet is 45°C or higher and less than 55°C. C: The surface temperature of the foam sheet is 55°C or higher and less than 65°C. D: The surface temperature of the foam sheet is 65°C or higher

[0247] <<Strength>> Strip-shaped test pieces were cut out from the foam sheets of Examples 1 to 13 and Comparative Examples 1 to 8. Test pieces measuring 25 mm wide and 80 mm long were cut out so that the width direction of the strip was the MD direction of the foam sheet. Using the cut out test pieces, the maximum point load (N) was measured under the following measurement conditions and by the following analysis method, and evaluated as an index of strength based on the following evaluation criteria. A was the best evaluation result, and A, B, or C were within the acceptable range. [[Measurement conditions]] Equipment: Precision universal testing machine Autograph (Shimadzu Corporation) Load cell: 50N Jig: 3-point bending jig · Distance between support points: 32mm Bending speed: 100mm / min Test piece width: Actual measurement (measured with a digital micrometer, calipers, etc.) Test end point: Manually stop after detecting the maximum peak [[Analysis method]] Read the maximum load (unit: N) Measurements are taken at different sampling locations, n=3 or more, and the average value is calculated. - Strength evaluation criteria - A: The maximum point load is 14N or more. B: The maximum point load is 12N or more and less than 14N C: The maximum point load is 10N or more and less than 12N D: Maximum point load is 8N or more but less than 10N E: Maximum point load is less than 8N

[0248] <<Biodegradable>> The biodegradability of the foamed sheets of Examples 1 to 13 and Comparative Examples 1 to 8 was evaluated by determining the degree of biodegradability in accordance with JIS K6953-2. The evaluation criteria were as follows. The acceptable range for the evaluation results was A or higher. An evaluation result of A is better, and A was set as the acceptable range. -Evaluation criteria- A: Biodegradability of 60% or more in 6 months B: Less than 60% biodegradation in 6 months [Table 1]

[0249] [Table 2]

[0250] [Table 3]

[0251] [Table 4]

[0252] [Table 5]

[0253] The present invention includes, for example, the following aspects. <1> A foamed sheet made of a composition containing a polylactic acid resin, the composition containing the polylactic acid resin contains at least a polylactic acid resin and inorganic particles, The polylactic acid resin contains 98 mol % or more of either D-lactic acid or L-lactic acid, which are constituent monomer units of the polylactic acid resin, in the polylactic acid resin; the content of the polylactic acid resin relative to the total amount of organic matter in the foam sheet is 98% by mass or more; the inorganic particles contain a layered silicate, the layered silicate has a volume average particle size of 10 μm or more and 200 μm or less, and an aspect ratio of 10 or more and 100 or less; The foamed sheet is characterized in that the content of the layered silicate in the foamed sheet is 2% by mass or less. <2> The layered silicate is mica. <1> 1. The foam sheet according to claim 1. <3> The content of the inorganic particles in the foamed sheet is 1.0% by mass or more and 1.7% by mass or less. <1> or <2> 1. The foam sheet according to claim 1. <4> The bulk density of the foam sheet is 0.063 g / cm 3 More than 0.156g / cm 3 The above-mentioned <1> from <3> 1. The foamed sheet according to claim 1, wherein the foamed sheet is a foamed sheet having a diameter of 100 mm or less. <5> The foamed sheet has a median foam diameter of 200 μm or more and 800 μm or less. <1> from <4> 1. The foamed sheet according to claim 1, wherein the foamed sheet is a foamed sheet having a diameter of 100 mm or less. <6> The aforementioned <1> from <5> A method for producing a foamed sheet according to any one of the above, a kneading step of kneading a polylactic acid resin and inorganic particles to obtain a polylactic acid resin composition; an impregnation step of kneading the polylactic acid resin composition with a foaming agent to obtain an expandable polylactic acid resin composition; a foaming step of extruding the expandable polylactic acid resin composition through a flow path in a mold and vaporizing the foaming agent to foam the polylactic acid resin composition; The method for producing a foamed sheet is characterized by comprising the steps of: <7> the mold has a first flow path forming member and a second flow path forming member that form at least a cylindrical flow path, a surface roughness parameter Rk of at least one of the flow path forming surface of the first flow path forming member and the flow path forming surface of the second flow path forming member is 1.0 μm or more and 6.3 μm or less; <6> 1. A method for producing the foamed sheet according to claim 1. <8> The aforementioned <1> from <5> The foamed sheet according to any one of the above items is subjected to thermoforming. <9> The aforementioned <1> from <5> A molded article characterized by containing the foamed sheet according to any one of the above items.

[0254] The aforementioned <1> from <5> The foamed sheet according to any one of the preceding claims. <6> or <7> and a method for producing the foamed sheet according to the above. <8> or <9> The molded body described in the above can solve the above-mentioned problems in the prior art and achieve the object of the present invention. [Explanation of symbols]

[0255] 1. First Supply Section 2. Second Supply Section 3 Compressible fluid reservoir 4 Cylindrical foam 5 Cooling mandrel 10 Kneading equipment 20 Single-screw extruder 30 Flow path 31 First flow path forming member 31a flow path forming surface of first flow path forming member 32 Second flow path forming member 32a: flow path forming surface of second flow path forming member 100 Twin-screw extrusion device (continuous kneading device) 110 Continuous foam sheet manufacturing equipment a Raw material mixing and melting section b Compressible fluid supply section c Mixing section d Compressible fluid removal section e Molding processing department f Temperature adjustment section F compressible fluid P pellets [Prior art documents] [Patent documents]

[0256] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-46019 [Patent Document 2] Patent No. 5207277 [Patent Document 3] Patent No. 5454137 [Patent Document 4] Japanese Patent Application Laid-Open No. 2006-328225 [Patent Document 5] Patent No. 4842745 [Patent Document 6] Patent Publication No. 2020-158608

Claims

1. A foamed sheet made of a composition containing a polylactic acid resin, the composition containing the polylactic acid resin contains at least a polylactic acid resin and inorganic particles, The polylactic acid resin contains 98 mol % or more of either D-lactic acid or L-lactic acid, which are constituent monomer units of the polylactic acid resin, in the polylactic acid resin; the content of the polylactic acid resin relative to the total amount of organic matter in the foamed sheet is 98% by mass or more; the inorganic particles contain a layered silicate, the layered silicate has a volume average particle size of 10 μm or more and 200 μm or less, and an aspect ratio of 10 or more and 100 or less; A foamed sheet, wherein the content of the layered silicate in the foamed sheet is 2% by mass or less.

2. 2. The foam sheet according to claim 1, wherein the layered silicate is mica.

3. 3. The foamed sheet according to claim 1, wherein the content of the layered silicate in the foamed sheet is 1.0% by mass or more and 1.7% by mass or less.

4. The bulk density of the foamed sheet is 0.063 g / cm ３ 0.156g / cm or more ３ 2. The foam sheet according to claim 1, wherein:

5. 2. The foamed sheet according to claim 1, wherein the foam diameter of the foamed sheet is 200 μm or more and 800 μm or less in terms of median diameter.

6. A method for producing the foamed sheet according to claim 1, a kneading step of kneading a polylactic acid resin and inorganic particles to obtain a polylactic acid resin composition; an impregnation step of kneading the polylactic acid resin composition with a foaming agent to obtain an expandable polylactic acid resin composition; a foaming step in which the foamable polylactic acid resin composition is extruded through a flow path of a mold to vaporize the foaming agent and foam the polylactic acid resin composition; A method for producing a foamed sheet, comprising:

7. the mold has a first flow path forming member and a second flow path forming member that form at least a cylindrical flow path, 7. The method for producing a foamed sheet according to claim 6, wherein a surface roughness parameter Rk of at least one of a flow path forming surface of the first flow path forming member and a flow path forming surface of the second flow path forming member is 1.0 μm or more and 6.3 μm or less.

8. A molded article obtained by thermoforming the foamed sheet according to claim 1.

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