Molded body of polylactic acid resin foam

Abstract

Provided is a molded body of a polylactic acid resin foam, the molded body having excellent heat-insulating properties.　The molded body of a polylactic acid resin foam according to this embodiment is obtained by molding a polylactic acid resin foam sheet, the molded body having a thickness of at least 1.0 mm, a degree of crystallization of at least 20%, and an open cell percentage of no greater than 60%.

Description

Polylactic acid resin foam molding

[0001] The present invention relates to a foamed molded polylactic acid resin article.

[0002] Resin foams are lightweight, have excellent cushioning properties, and can be easily molded into a variety of shapes, making them popular raw materials for various molded products such as containers and packaging materials.

[0003] For example, containers obtained by thermoforming resin foams are widely used in convenience stores and the like as various food packaging containers such as trays, lunch boxes, rice bowls, cups, etc. Among these, there has been an increasing demand in recent years for so-called microwaveable containers, which are intended to heat pre-cooked foods such as pasta in a packaged state in a microwave oven.

[0004] On the other hand, resin foams and resin foam molded articles obtained by molding them are used in large quantities and then discarded in large quantities. This places a heavy burden on the environment and is a factor in various social problems, such as global warming, resource depletion, and waste disposal. Therefore, polylactic acid resin, which is biodegradable, has a small environmental impact, and can be produced relatively inexpensively, has attracted attention, and polylactic acid resin foam sheets and polylactic acid resin foam molded articles obtained from polylactic acid resin have been proposed (for example, Patent Document 1).

[0005] However, when a polylactic acid resin foam molded body made by molding a polylactic acid resin foam sheet is used as a container and cooked food such as pasta is packaged and heated in a microwave oven, the surface of the container becomes very hot, making it impossible to carry the container safely by hand.

[0006] Patent No. 6971947

[0007] An object of the present invention is to provide a foamed molded polylactic acid resin article having excellent heat insulation properties.

[0008] [1] A polylactic acid resin foam molded article according to an embodiment of the present invention is a polylactic acid resin foam molded article obtained by molding a polylactic acid resin foam sheet, and has a thickness of 1.0 mm or more, a crystallinity of 20% or more, and an open cell ratio of 60% or less. [2] In the polylactic acid resin foam molded article described in [1] above, the crystallization temperature may be 100°C or less. [3] In the polylactic acid resin foam molded article described in [1] or [2] above, the open cell ratio of the polylactic acid resin foam sheet may be 20% or less. [4] In the polylactic acid resin foam molded article described in any one of [1] to [3] above, the crystallinity of the polylactic acid resin foam sheet may be 5% or more. [5] In the polylactic acid resin foam molded article described in any one of [1] to [4] above, the thermal conductivity of the polylactic acid resin foam sheet at 23°C may be 0.038 W / m·k or less. [6] In the polylactic acid resin foam molded product according to any one of [1] to [5] above, the crystallization temperature of the polylactic acid resin foam sheet may be 100°C or lower. [7] In the polylactic acid resin foam molded product according to any one of [1] to [6] above, the weight average molecular weight (Mw) of the polylactic acid resin foam sheet may be 200,000 or higher. [8] In the polylactic acid resin foam molded product according to any one of [1] to [7] above, the polylactic acid resin foam sheet may have an MFR of 4.0 g / 10 min or lower. [9] In the polylactic acid resin foam molded product according to any one of [1] to [8] above, the polylactic acid resin foam sheet may have a gel fraction of 2.0 wt% or lower.

[10] In the polylactic acid resin foam molded product according to any one of [1] to [9] above, the polylactic acid resin foam sheet may have a melt tension of 10 cN or higher.

[0009] According to an embodiment of the present invention, a polylactic acid resin foam molded article having excellent heat insulation properties can be provided.

[0010] 1 is a schematic cross-sectional view of a polylactic acid resin foam molded body according to an embodiment of the present invention, which is a molded body produced by drawing (typically, a shallow-draw molded body or a deep-draw molded body). FIG. 2 is a schematic diagram showing the configuration of a manufacturing apparatus in a first step of embodiment A. FIG. 3 is a schematic diagram showing the configuration of a manufacturing apparatus in a second step of embodiment A. FIG. 4 is a schematic diagram showing the configuration of a manufacturing apparatus in embodiment B.

[0011] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0012] <<Polylactic Acid Resin Foam Molded Article>> A polylactic acid resin foam molded article according to an embodiment of the present invention is a polylactic acid resin foam molded article obtained by molding a polylactic acid resin foam sheet.

[0013] The polylactic acid resin foam molded articles according to the embodiments of the present invention can be used in various applications of conventional resin foam molded articles. Examples of such applications include food packaging containers such as trays, lunch boxes, bowls, and cups, as well as components such as handles that may be provided on such containers. Because the polylactic acid resin foam molded articles according to the embodiments of the present invention have excellent heat insulation properties, they can be suitably used as so-called microwaveable containers. The polylactic acid resin foam molded articles according to the embodiments of the present invention can also be used as various packaging materials, various cushioning materials, and the like.

[0014] The polylactic acid resin foam molded article according to the embodiment of the present invention may have any suitable shape, such as a bowl shape, a cup shape, a box shape, a tray shape, or any of a variety of other container shapes.

[0015] The polylactic acid resin foam molded body according to the embodiment of the present invention may be, for example, a molded body formed by drawing, and may be a shallow-drawn molded body having a drawing depth smaller than the diameter of the container, or a deep-drawn molded body having a drawing depth larger than the diameter of the container.

[0016] The polylactic acid resin foam molded article according to the embodiment of the present invention has a thickness of 1.0 mm or more, a crystallinity of 20% or more, and an open cell ratio of 60% or less. By satisfying all of these conditions, the polylactic acid resin foam molded article according to the embodiment of the present invention can exhibit the effects of the present invention.

[0017] As described above, the polylactic acid resin foam molded article according to an embodiment of the present invention typically has a thickness of 1.0 mm or more. In order to further demonstrate the effects of the present invention, the thickness is preferably 1.0 mm to 10 mm, more preferably 1.1 mm to 7 mm, even more preferably 1.2 mm to 5 mm, particularly preferably 1.3 mm to 3 mm, and most preferably 1.4 mm to 2.5 mm. If the thickness is too small and outside the above range, the polylactic acid resin foam molded article may not be able to fully demonstrate its heat insulating properties. If the thickness is too large and outside the above range, the appearance of the polylactic acid resin foam molded article may be impaired. The method for measuring the thickness will be described later.

[0018] The thickness of the polylactic acid resin foam molded article according to the embodiment of the present invention means the minimum thickness of the cross section of the polylactic acid resin foam molded article, excluding the flanges and protrusions. The method for measuring the thickness of the polylactic acid resin foam molded article will be described in detail later.

[0019] FIG. 1 is a schematic cross-sectional view of a polylactic acid resin foam molded article according to an embodiment of the present invention, which is a molded article formed by drawing (typically, a shallow-draw molded article or a deep-draw molded article). In FIG. 1 , polylactic acid resin foam molded article 1000 includes a main body including a bottom 110 and a side wall 120. As shown in FIG. 1 , polylactic acid resin foam molded article 1000 may include a flange 200 or a protrusion 300 that protrudes outward from the upper end of side wall 120. The cross-sectional shape of polylactic acid resin foam molded article 1000 is not limited to the shape shown in FIG. 1 . For example, bottom 110 or side wall 120 may have a curved structure. Furthermore, the shapes of flange 200 and protrusion 300 are not limited to those shown in FIG. 1 , and the positions of flange 200 and protrusion 300 are not limited to those shown in FIG. 1 . In FIG. 1, the thickness L of the polylactic acid resin foam molded body 1000 means the minimum value of the thickness of the part of the cross section of the polylactic acid resin foam molded body 1000, excluding the flange portion 200, from the main body portion 100, excluding the protrusion portion 300.

[0020] As described above, the polylactic acid resin foam molded article according to an embodiment of the present invention typically has a crystallinity of 20% or more, and in order to more effectively exhibit the effects of the present invention, it is preferably 20% to 50%, more preferably 22% to 50%, even more preferably 24% to 50%, particularly preferably 26% to 45%, and most preferably 28% to 45%. If the crystallinity is too low outside the above range, the heat resistance of the polylactic acid resin foam molded article may be impaired. If the crystallinity is too high outside the above range, the moldability may be impaired. A method for measuring the crystallinity will be described later.

[0021] As described above, the open cell ratio of the polylactic acid resin foam molded article according to an embodiment of the present invention is typically 60% or less. To maximize the effects of the present invention, the open cell ratio is preferably 10% to 60%, more preferably 15% to 60%, even more preferably 20% to 55%, even more preferably 25% to 55%, and particularly preferably 30% to 55%. If the open cell ratio is too high outside of this range, the insulating properties of the polylactic acid resin foam molded article may be impaired. If the open cell ratio is too low outside of this range, for example, the surface irregularities of the polylactic acid resin foam molded article may be reduced and flattened, reducing the surface area of ​​the molded article and, therefore, the contact area with microorganisms, which may result in reduced biodegradability. The method for measuring the open cell ratio will be described later.

[0022] The polylactic acid resin foam molded article according to the embodiment of the present invention preferably has a crystallization temperature of 100°C or less. If the crystallization temperature is too high outside the above range, the degree of crystallization may be too low, resulting in poor heat resistance. The method for measuring the crystallization temperature will be described later.

[0023] <<Production of Polylactic Acid Resin Foam Molded Article>> The polylactic acid foam molded article according to an embodiment of the present invention may be produced by any appropriate method as long as the effects of the present invention are not impaired. Typically, the polylactic acid foam molded article according to an embodiment of the present invention may be produced by preheating a polylactic acid resin foam sheet and thermoforming it using a mold.

[0024] Any suitable method can be used for preheating. For example, the polylactic acid resin foam sheet can be heated by any suitable heating means. Examples of such heating means include heaters such as electric heaters and infrared heaters.

[0025] Preheating can be carried out so that the surface temperature of the polylactic acid resin foam sheet is preferably in the range of 100°C to 140°C, more preferably in the range of 105°C to 135°C, even more preferably in the range of 110°C to 130°C, and particularly preferably in the range of 115°C to 125°C.

[0026] Preheating can be performed by heating for any appropriate time using a heating means set to any appropriate heating temperature. The heating temperature (temperature set by the heating means) is preferably 200°C to 800°C, more preferably 300°C to 700°C. The heating time is preferably 0.1 seconds to 60 seconds, more preferably 1 second to 30 seconds.

[0027] Preheating methods for producing a polylactic acid resin foam molded article according to an embodiment of the present invention include a method of heating for a short time at a higher heating temperature and a method of heating for a long time at a lower heating temperature. From the viewpoint of being able to appropriately provide a polylactic acid resin foam molded article according to an embodiment of the present invention, a method of heating for a long time at a lower heating temperature is preferred. For example, a method of heating at a temperature of less than 500°C for more than 5 seconds is preferred, a method of heating at a heating temperature of 300°C to 470°C for a heating time of more than 5 seconds but not more than 30 seconds is more preferred, a method of heating at a heating temperature of 350°C to 450°C for a heating time of more than 5 seconds but not more than 20 seconds is even more preferred, and a method of heating at a heating temperature of 370°C to 430°C for a heating time of more than 5 seconds but not more than 15 seconds is particularly preferred.

[0028] After preheating, any suitable thermoforming method can be used for thermoforming using a mold, such as vacuum forming, pressure forming, vacuum pressure forming, plug assist forming, or matched mold forming, with matched mold forming being preferred.

[0029] The mold temperature during thermoforming is preferably 15°C to 100°C, more preferably 20°C to 80°C, even more preferably 25°C to 70°C, even more preferably 30°C to 60°C, particularly preferably 35°C to 55°C, and most preferably 35°C to 50°C, in order to properly provide a polylactic acid resin foam molded article according to an embodiment of the present invention. If the temperature is too low, the crystallinity of the polylactic acid resin foam molded article may decrease. If the temperature is too high, the polylactic acid resin foam molded article may be prone to shrinkage and foaming after release from the mold, resulting in a loss of surface smoothness, a dirty appearance, and possible impairment of printability.

[0030] The mold holding time during thermoforming (the time the mold is held during molding) is preferably 0.1 to 60 seconds, more preferably 1 to 30 seconds, even more preferably 3 to 30 seconds, and particularly preferably 5 to 20 seconds, in order to be able to appropriately provide a polylactic acid resin foam molded article according to an embodiment of the present invention.

[0031] In order to obtain a polylactic acid foam molded article according to an embodiment of the present invention, any appropriate step may be carried out, such as a step of releasing the polylactic acid foam molded article from the mold, in addition to the above-mentioned preheating and thermoforming.

[0032] <<Polylactic Acid Resin Foam Sheet>> A polylactic acid resin foam molded article according to an embodiment of the present invention is a polylactic acid resin foam molded article obtained by molding a polylactic acid resin foam sheet.

[0033] As the polylactic acid resin foam sheet that can be used to obtain the polylactic acid resin foam molded article according to the embodiment of the present invention, any appropriate polylactic acid resin foam sheet can be used as long as the effects of the present invention are not impaired. As such a polylactic acid resin foam sheet, a polylactic acid resin foam sheet according to the preferred embodiment described below can be used, as it can further exhibit the effects of the present invention.

[0034] The polylactic acid resin foam sheet according to a preferred embodiment has a thickness of preferably 1.0 mm to 10 mm, more preferably 1.2 mm to 7 mm, even more preferably 1.4 mm to 5 mm, particularly preferably 1.5 mm to 3 mm, and most preferably 1.5 mm to 2.5 mm. When the thickness of the polylactic acid resin foam sheet is within the above range, the effects of the present invention can be more effectively exhibited. The method for measuring the thickness will be described later.

[0035] The polylactic acid resin foam sheet according to a preferred embodiment has a basis weight of preferably 100 g / m 2 ~500g / m 2 and more preferably 200 g / m 2 ~450g / m 2 and more preferably 300 g / m 2 ~400g / m 2 When the basis weight of the polylactic acid resin foam sheet is within the above range, the effects of the present invention can be more effectively exhibited. The method for measuring the basis weight will be described later.

[0036] The polylactic acid resin foam sheet according to a preferred embodiment has an expansion ratio of preferably 4 to 20, more preferably 4 to 15, even more preferably 4 to 12, and particularly preferably 4 to 10. When the expansion ratio of the polylactic acid resin foam sheet is within the above range, the effects of the present invention can be more effectively exhibited. The method for measuring the expansion ratio will be described later.

[0037] In a preferred embodiment, the polylactic acid resin foam sheet has an open cell ratio of preferably 20% or less, more preferably 17% or less, even more preferably 15% or less, and particularly preferably 13% or less. The smaller the open cell ratio of the polylactic acid resin foam sheet, the better, and the lower limit is preferably 0% or more, and may be 3% or more, or even 5% or more. When the open cell ratio of the polylactic acid resin foam sheet is within the above range, the effects of the present invention can be more effectively exhibited, and, for example, the open cell ratio of the resulting polylactic acid resin foam molded product can be appropriately adjusted. If the open cell ratio of the polylactic acid resin foam sheet is too high outside the above range, the open cell ratio of the resulting polylactic acid resin foam molded product may be too high, which may result in poor thermal insulation of the polylactic acid resin foam molded product. The method for measuring the open cell ratio will be described later.

[0038] The polylactic acid resin foam sheet according to a preferred embodiment has a thermal conductivity at 23°C of preferably 0.038 w / m·k or less, more preferably 0.037 w / m·k or less. The lower the thermal conductivity of the polylactic acid resin foam sheet at 23°C, the better, and the lower limit is preferably 0 w / m·k or more. When the thermal conductivity of the polylactic acid resin foam sheet at 23°C is within the above range, the effects of the present invention can be more effectively exhibited. If the thermal conductivity of the polylactic acid resin foam sheet at 23°C is too high and outside the above range, the insulating properties of the resulting polylactic acid resin foam molded article may be poor. The method for measuring thermal conductivity at 23°C will be described later.

[0039] The polylactic acid resin foam sheet according to a preferred embodiment has a crystallinity of preferably 5% or more, more preferably 5% to 40%, even more preferably 5.2% to 30%, particularly preferably 5.4% to 25%, and most preferably 5.5% to 20%. When the crystallinity of the polylactic acid resin foam sheet is within the above range, the effects of the present invention can be more effectively achieved. If the crystallinity of the polylactic acid resin foam sheet is too low outside the above range, the heat resistance of the resulting polylactic acid resin foam molded article may be poor. If the crystallinity of the polylactic acid resin foam sheet is too high outside the above range, the moldability may be poor. The method for measuring the crystallinity will be described later.

[0040] The polylactic acid resin foam sheet according to a preferred embodiment has a crystallization temperature of preferably 100°C or less, more preferably 60°C or more but less than 100°C, and even more preferably 70°C to 99.5°C. When the crystallization temperature of the polylactic acid resin foam sheet is within the above range, the effects of the present invention can be more effectively achieved. If the crystallization temperature of the polylactic acid resin foam sheet is too high outside the above range, the crystallization degree of the resulting polylactic acid resin foam molded article may be too low, resulting in poor heat resistance. The method for measuring the crystallization temperature will be described later.

[0041] The polylactic acid resin foam sheet according to a preferred embodiment has a melting point of preferably 150°C to 180°C, more preferably 155°C to 175°C, and even more preferably 160°C to 175°C. When the melting point of the polylactic acid resin foam sheet is within the above range, the effects of the present invention can be more effectively exhibited. The method for measuring the melting point will be described later.

[0042] The polylactic acid resin foam sheet according to a preferred embodiment has a number average molecular weight (Mn) of preferably 10,000 or more, more preferably 10,000 to 200,000, even more preferably 30,000 to 150,000, particularly preferably 50,000 to 130,000, and most preferably 70,000 to 100,000. When the number average molecular weight (Mn) of the polylactic acid resin foam sheet falls within the above range, the effects of the present invention can be more effectively exhibited. The method for measuring the number average molecular weight (Mn) will be described later.

[0043] The polylactic acid resin foam sheet according to a preferred embodiment preferably has a weight-average molecular weight (Mw) of 200,000 or more, more preferably 200,000 to 1,000,000, even more preferably 200,000 to 500,000, particularly preferably 200,000 to 350,000, and most preferably 250,000 to 320,000. When the weight-average molecular weight (Mw) of the polylactic acid resin foam sheet falls within the above range, the effects of the present invention can be more effectively exhibited. The method for measuring the weight-average molecular weight (Mw) will be described later.

[0044] The polylactic acid resin foam sheet according to a preferred embodiment has a Z-average molecular weight (Mz) of preferably 300,000 or more, more preferably 300,000 to 1,000,000, even more preferably 500,000 to 1,000,000, particularly preferably 700,000 to 950,000, and most preferably 770,000 to 950,000. When the Z-average molecular weight (Mz) of the polylactic acid resin foam sheet is within the above range, the effects of the present invention can be more effectively exhibited. The method for measuring the Z-average molecular weight (Mz) will be described later.

[0045] The polylactic acid resin foam sheet according to a preferred embodiment has an MFR of preferably 4.0 g / 10 min or less, more preferably 3.9 g / 10 min or less, and even more preferably 3.8 g / 10 min or less. When the MFR of the polylactic acid resin foam sheet is within the above range, the effects of the present invention can be further exhibited. The method for measuring MFR will be described later.

[0046] The polylactic acid resin foam sheet according to a preferred embodiment has a gel fraction of preferably 2.0% by weight or less, more preferably 1.7% by weight or less, even more preferably 1.5% by weight or less, and particularly preferably 1.3% by weight or less. Since a high gel fraction in a polylactic acid resin foam sheet can deteriorate the sheet's appearance, the smaller the gel fraction, the better, with the lower limit preferably being 0% by weight or more. When the gel fraction of the polylactic acid resin foam sheet is within the above range, the effects of the present invention can be more effectively exhibited. The method for measuring the gel fraction will be described later.

[0047] The polylactic acid resin foam sheet according to a preferred embodiment has a melt tension of preferably 10 cN or more, more preferably 10 to 100 cN, even more preferably 10 to 80 cN, particularly preferably 15 to 60 cN, and most preferably 15 to 50 cN. When the melt tension of the polylactic acid resin foam sheet is within the above range, the effects of the present invention can be more effectively exhibited. The method for measuring the melt tension will be described later.

[0048] <<Production of Polylactic Acid Resin Foam Sheet>> The polylactic acid resin foam sheet that can be used to mold the polylactic acid resin foam molded article according to the embodiment of the present invention can be produced by any appropriate method as long as the effects of the present invention are not impaired. Such a polylactic acid resin foam sheet can be preferably produced by melt-kneading the polylactic acid resin (P) with a foaming agent in an extruder, followed by extrusion-foaming.

[0049] Preferred embodiments of the polylactic acid resin (P) include an embodiment containing a modified polylactic acid resin as a main component, and an embodiment containing an unmodified polylactic acid resin as a main component.

[0050] "Modified polylactic acid resin" refers to a polylactic acid resin that has been modified, typically a polylactic acid resin that has been modified as described in the first step of embodiment A below. "Unmodified polylactic acid resin" refers to a polylactic acid resin that has not been modified, typically a commonly available polylactic acid resin that has not been modified as described in the first step of embodiment A below.

[0051] Here, in this specification, "contained as a main component" means that the content ratio thereof is preferably more than 50% by weight, more preferably 70% by weight or more, even more preferably 90% by weight or more, particularly preferably 95% by weight or more, and most preferably substantially 100% by weight. Note that in this specification, "substantially 100% by weight" means that the presence of a trace amount (e.g., less than 1% by weight) of impurities that are unintentionally mixed in can be ignored.

[0052] Hereinafter, we will explain embodiment A (sometimes referred to as a two-stage method) in which a polylactic acid resin (P) containing a modified polylactic acid resin as a main component is melt-kneaded with a foaming agent in an extruder and extrusion-foamed to produce a polylactic acid resin foam sheet, and embodiment B (sometimes referred to as a one-stage method) in which a polylactic acid resin (P) containing an unmodified polylactic acid resin as a main component is melt-kneaded with a foaming agent in an extruder and extrusion-foamed to produce a polylactic acid resin foam sheet.

[0053] <<Embodiment A (Two-Stage Process)>> In embodiment A, a polylactic acid resin foam sheet is produced by melt-kneading a polylactic acid resin (P) containing a modified polylactic acid resin as a main component with a foaming agent in an extruder, followed by extrusion-foaming.

[0054] The modified polylactic acid resin is preferably obtained by melt-kneading a polylactic acid resin composition containing a polylactic acid resin and a modifier in an extruder.

[0055] Therefore, embodiment A preferably includes a first step of melt-kneading a polylactic acid resin composition containing a polylactic acid resin and a modifier in an extruder to produce a polylactic acid resin containing a modified polylactic acid resin as a main component, and a subsequent second step of melt-kneading the polylactic acid resin containing the modified polylactic acid resin as a main component with a foaming agent in the extruder, followed by extrusion-foaming to produce a polylactic acid resin foam sheet.

[0056] For convenience, the following description will be given assuming that the content of the modified polylactic acid resin in the polylactic acid resin (P) containing the modified polylactic acid resin as the main component is substantially 100% by weight. In other words, in the following description, embodiment A includes a first step of melt-kneading a polylactic acid resin composition containing the polylactic acid resin and a modifier in an extruder to produce a modified polylactic acid resin, followed by a second step of melt-kneading the modified polylactic acid resin with a foaming agent in the extruder and extrusion-foaming to produce a polylactic acid resin foam sheet. However, of course, the content of the modified polylactic acid resin in the polylactic acid resin (P) containing the modified polylactic acid resin as the main component may actually be the proportion of the modified polylactic acid resin contained as the main component, as described above.

[0057] In the first step, a modified polylactic acid resin is produced by melt-kneading a polylactic acid resin composition containing a polylactic acid resin and a modifier in an extruder. The polylactic acid resin used as the raw material in the first step is preferably an unmodified polylactic acid resin.

[0058] The polylactic acid resin may be a homopolymer of lactic acid or a copolymer of lactic acid with other monomers, such as aliphatic hydroxycarboxylic acids other than lactic acid, aliphatic polyhydric alcohols, aliphatic polycarboxylic acids, and polyfunctional polysaccharides.

[0059] The lactic acid constituting the polylactic acid resin may be either the L-configuration or the D-configuration, or may be both the L-configuration and the D-configuration. That is, the polylactic acid resin, which is a homopolymer of lactic acid, may be any of poly(L-lactic acid) resin, poly(D-lactic acid) resin, and poly(DL-lactic acid) resin.

[0060] Examples of hydroxycarboxylic acids other than lactic acid include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, and 6-hydroxycaproic acid.

[0061] Examples of the aliphatic polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, neopentyl glycol, tetramethylene glycol, and 1,4-cyclohexanedimethanol.

[0062] Examples of the aliphatic polycarboxylic acid include oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, undecanedioic acid, and dodecanedioic acid. The aliphatic polycarboxylic acid may also be an acid anhydride.

[0063] Examples of polyfunctional polysaccharides include cellulose, cellulose nitrate, methyl cellulose, ethyl cellulose, celluloid, viscose rayon, regenerated cellulose, cellophane, cupra, cuprammonium rayon, cuprophane, Bemberg, hemicellulol, starch, acropectin, dextrin, dextran, glycogen, pectin, chitin, chitosan, gum arabic, guar gum, locust bean gum, and acacia gum.

[0064] The content of structural moieties derived from lactic acid (L- and D-forms) in the molecule of the polylactic acid resin is preferably 50% by weight or more, more preferably 60% by weight or more, even more preferably 70% by weight or more, particularly preferably 80% by weight or more, and most preferably 90% by weight or more.

[0065] At least a part of the polylactic acid resin used as a raw material may be recycled.

[0066] In the first step, a modifier is used to increase the molecular weight of the polylactic acid resin or to impart a crosslinked structure or a long-chain branched structure to the molecular structure of the polylactic acid resin, thereby producing a modified polylactic acid resin.

[0067] The amount of the modifier used is preferably 0.1 to 2.0 parts by weight, more preferably 0.2 to 1.5 parts by weight, and even more preferably 0.3 to 1.0 part by weight, relative to 100 parts by weight of the polylactic acid resin, in order to further exhibit the effects of the present invention.

[0068] A radical initiator can be used as the modifier. By using a radical initiator as a modifier, crosslinked structures and long-chain branched structures can be imparted to the molecular structure of the polylactic acid resin. In this case, polylactic acid resins are reacted with each other using a radical initiator. When polylactic acid resins are reacted with each other using a radical initiator with appropriate reactivity, for example, the decomposition starting points of the polylactic acid resin in the extruder are attacked by free radicals generated by the radical initiator, and these points become crosslinked points (branching points) and can be stabilized. By performing such modification, the thermal stability of the polylactic acid resin is increased, making it less susceptible to molecular weight degradation when passing through the extruder.

[0069] Examples of the radical initiator include organic peroxides, azo compounds, and halogen molecules, with organic peroxides being preferred.

[0070] Examples of organic peroxides include peroxyesters, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, peroxyketals, and ketone peroxides.

[0071] Examples of peroxyesters include t-butylperoxyisopropyl carbonate, t-butylperoxy-2-ethylhexyl carbonate, t-hexylperoxyisopropyl carbonate, t-butylperoxybenzoate, t-hexylperoxybenzoate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxylaurate, t-butylperoxyacetate, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane.

[0072] Examples of hydroperoxides include permethane hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, and t-butyl hydroperoxide.

[0073] Examples of dialkyl peroxides include α,α-bis(t-butylperoxy)diisopropylbenzene, dicumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3.

[0074] Examples of diacyl peroxides include dibenzoyl peroxide, di(4-methylbenzoyl) peroxide, and di(3-methylbenzoyl) peroxide.

[0075] Examples of peroxydicarbonates include di(2-ethylhexyl) peroxydicarbonate and diisopropyl peroxydicarbonate.

[0076] Examples of peroxyketals include 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, 1,1-di-t-butylperoxycyclohexane, 2,2-di(t-butylperoxy)-butane, n-butyl-4,4-di-(t-butylperoxy)valerate, and 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane.

[0077] Examples of ketone peroxides include methyl ethyl ketone peroxide and acetylacetone peroxide.

[0078] Modification with organic peroxides can cause undesirable problems, such as the risk of the modified polylactic acid resin being mixed with components with excessively large molecular weights that will gel when thermally melted, or the risk of odor problems due to decomposition residues of the organic peroxides, which may have a negative impact on the effectiveness of the present invention.

[0079] In one preferred embodiment, the organic peroxide is at least one selected from the group consisting of peroxyesters and dialkyl peroxides, from the viewpoints of being able to suppress the problems associated with modification by organic peroxides as described above, easily modifying polylactic acid resin to a state suitable for foaming, and providing a polylactic acid resin foam molded article that can better exhibit the effects of the present invention. In terms of being able to provide a polylactic acid resin foam molded article that can better exhibit the effects of the present invention, the peroxyester is more preferably a peroxycarbonate-based organic peroxide such as t-butylperoxyisopropyl carbonate, t-butylperoxy-2-ethylhexyl carbonate, or t-hexylperoxyisopropyl carbonate, and even more preferably t-butylperoxyisopropyl carbonate. The dialkyl peroxide is more preferably α,α-bis(t-butylperoxy)diisopropylbenzene.

[0080] The organic peroxides described above have a one-minute half-life temperature of preferably 140° C. to 190° C., more preferably 145° C. to 185° C., even more preferably 150° C. to 180° C., and particularly preferably 152° C. to 178° C., in order to provide a polylactic acid resin foam molded article that can further exhibit the effects of the present invention. In one preferred embodiment, the one-minute half-life temperature is preferably 140° C. to 180° C., more preferably 145° C. to 170° C., even more preferably 150° C. to 160° C., and particularly preferably 150° C. to 158° C.

[0081] The organic peroxide may be liquid or solid (powder), but is preferably liquid from the viewpoints of uniform reactivity in the extruder, ease of handling, etc.

[0082] The amount of organic peroxide used depends on the molecular weight, etc., but in terms of being able to further exhibit the effects of the present invention, it is preferably 0.1 to 2.0 parts by weight, more preferably 0.2 to 1.5 parts by weight, and even more preferably 0.3 to 1.0 part by weight, relative to 100 parts by weight of polylactic acid resin.

[0083] A chain extender may be used as the modifier. In the modification using a chain extender, a compound having one or more functional groups capable of undergoing a condensation reaction with a hydroxyl group or a carboxyl group present in the molecular structure of the polylactic acid resin, such as an acrylic organic compound, an epoxy organic compound, or an isocyanate organic compound, may be used.

[0084] Examples of chain extenders include Joncryl® ADR 4368 (manufactured by BASF), Joncryl® ADR 4468 (manufactured by BASF), Cardura® E10 (manufactured by Shell), and long-chain acrylates described in EP Application No. 08166596.0.

[0085] When a chain extender is used as the modifier, the amount of the chain extender used is preferably 0.1 to 2.0 parts by weight, more preferably 0.2 to 1.5 parts by weight, and even more preferably 0.3 to 1.0 part by weight, relative to 100 parts by weight of the polylactic acid resin, in order to further exhibit the effects of the present invention.

[0086] In the first step, the polylactic acid resin composition containing the polylactic acid resin and the modifier may contain any appropriate components other than the polylactic acid resin and the modifier, as long as the effects of the present invention are not impaired. The total content of the polylactic acid resin and the modifier in the polylactic acid resin composition containing the polylactic acid resin and the modifier is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, even more preferably 90% by weight to 100% by weight, and particularly preferably 95% by weight to 100% by weight.

[0087] In the first step, the polylactic acid resin composition containing the polylactic acid resin and the modifier may be prepared by pre-mixing the polylactic acid resin, the modifier, and other components as needed. Examples of such mixing methods include mixing methods using a mixer such as a tumbler, ribbon blender, V blender, Henschel mixer, or Redige mixer.

[0088] In the first step, a polylactic acid resin composition containing a polylactic acid resin and a modifier is melt-kneaded in an extruder.

[0089] As the extruder, any appropriate extruder can be used as long as the effects of the present invention are not impaired. In terms of being able to further exhibit the effects of the present invention, a twin-screw extruder is preferred.

[0090] The twin-screw extruder may be equipped with a strand die or a T-die. In this case, the extruded strand-shaped or sheet-shaped kneaded product may be cooled and cut into pellets using a pelletizer or the like.

[0091] The twin-screw extruder may be equipped with a pelletizing die (hot cut die), in which case the kneaded material is pelletized immediately after being extruded.

[0092] The temperature conditions for melt-kneading may vary depending on the size of extrusion, the discharge amount, etc., and any appropriate conditions may be adopted as long as the effects of the present invention are not impaired. For example, the temperature of the raw material feed section is preferably set to 100°C to 200°C.

[0093] The rotation speed of the extruder may vary depending on the size of the extrusion, the discharge rate, etc., and any appropriate condition may be adopted as long as the effects of the present invention are not impaired. For example, such a rotation speed is preferably 20 rpm to 800 rpm.

[0094] The modified polylactic acid resin obtained in the first step may be, for example, one that has been subjected to a drying step for drying. Typically, the modified polylactic acid resin obtained in the first step may be one that has been obtained by cooling a strand-like kneaded product extruded from a twin-screw extruder equipped with a strand die, cutting the resulting pellets with a pelletizer or the like, and then subjecting the pellets to a drying step for drying.

[0095] In the drying step, drying can be carried out using a dryer such as a dehumidifying dryer, a vacuum dryer, a hot air dryer, etc. The modified polylactic acid resin that has been thoroughly dried in such a dryer or the like may be directly charged into an extruder in the subsequent second step (without being exposed to a moist environment), or the modified polylactic acid resin that has been thoroughly dried in such a dryer or the like may be sealed in an aluminum bag or the like immediately after drying, and then opened and charged into the extruder in the subsequent second step.

[0096] The first step can be carried out using any appropriate apparatus as long as the effects of the present invention are not impaired. In order to further demonstrate the effects of the present invention, the first step can be carried out using, for example, a production apparatus as shown in FIG.

[0097] As shown in Figure 2, in the first step, typically, polylactic acid resin as a raw material fed into a hopper 11 is melt-kneaded by a twin-screw extruder 30, the strand-shaped kneaded product extruded from a strand die 3 is cooled by a cooling device 6, and then pelletized by a pelletizer 4 and dried by a drying device 5, and the resulting modified polylactic acid resin is supplied to the second step.

[0098] The modified polylactic acid resin obtained in the first step preferably has a moisture content of 0.30% by weight or less, more preferably 0.25% by weight or less, even more preferably 0.20% by weight or less, particularly preferably 0.17% by weight or less, and most preferably 0.15% by weight or less. The lower limit of the moisture content is preferably as low as possible, and is ideally 0% by weight.

[0099] The MFR (melt mass flow rate) of the modified polylactic acid resin obtained in the first step is preferably 0.2 g / 10 min to 20 g / 10 min, more preferably 0.5 g / 10 min to 10 g / 10 min, even more preferably 1.0 g / 10 min to 5.0 g / 10 min, particularly preferably 1.1 g / 10 min to 4.0 g / 10 min, and most preferably 1.2 g / 10 min to 3.0 g / 10 min.

[0100] The melt tension of the modified polylactic acid resin obtained in the first step is preferably 5 cN to 100 cN, more preferably 10 cN to 80 cN, even more preferably 20 cN to 70 cN, and particularly preferably 25 cN to 60 cN.

[0101] <Second Step> In the second step, the modified polylactic acid resin obtained in the first step is melt-kneaded with a foaming agent in an extruder, followed by extrusion foaming to produce a polylactic acid resin foam sheet.

[0102] The foaming agent may be one kind or two or more kinds.

[0103] Any appropriate foaming agent can be used as long as it does not impair the effects of the present invention. Examples of the foaming agent include volatile foaming agents that become gas at room temperature (23°C) and normal pressure (1 atmosphere) and decomposition type foaming agents that generate gas by thermal decomposition, and volatile foaming agents are preferred.

[0104] The volatile blowing agent is preferably an organic compound having a boiling point equal to or lower than the softening point of the polylactic acid resin and being in a gaseous or liquid state at normal pressure. Specific examples include aliphatic hydrocarbons such as propane, n-butane, isobutane, pentane (n-pentane, isopentane, neopentane), and n-hexane; alicyclic hydrocarbons such as cyclopentane and cyclopentadiene; ketones such as acetone and methyl ethyl ketone; alcohols such as methanol, ethanol, and isopropyl alcohol; low-boiling ether compounds such as dimethyl ether, diethyl ether, dipropyl ether, and methyl ethyl ether; and halogen-containing hydrocarbons such as trichloromonofluoromethane and dichlorodifluoromethane. Inorganic gases such as carbon dioxide, nitrogen, and ammonia may also be used as the volatile blowing agent. Among these, the volatile blowing agent is preferably at least one selected from n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, and cyclopentadiene, and more preferably at least one selected from n-butane, isobutane, n-pentane, and isopentane, in terms of being able to further exhibit the effects of the present invention.

[0105] Examples of decomposition type foaming agents include azodicarbonamide, dinitrosopentamethylenetetramine, sodium bicarbonate, or a mixture of an organic acid such as citric acid or its salt with a bicarbonate.

[0106] The amount of the foaming agent used can be appropriately set depending on the purpose. The amount of the foaming agent used is preferably 0.1 to 10.0 parts by weight, more preferably 0.3 to 7.0 parts by weight, even more preferably 0.5 to 5.0 parts by weight, and particularly preferably 0.8 to 3.0 parts by weight, based on 100 parts by weight of the modified polylactic acid resin.

[0107] In the second step, the extruder may contain any other appropriate components other than the modified polylactic acid resin and the foaming agent, as long as the effects of the present invention are not impaired. In the second step, the total content of the modified polylactic acid resin and the foaming agent in the extruder is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, even more preferably 90% by weight to 100% by weight, and particularly preferably 95% by weight to 100% by weight.

[0108] In the second step, the extruder may contain a foaming aid as another component. The foaming aid may be one kind or two or more kinds. Examples of the foaming aid include diisobutyl adipate, toluene, cyclohexane, ethylbenzene, liquid paraffin, and coconut oil.

[0109] In the second step, a cell-forming agent may be contained in the extruder as another component. The cell-forming agent may be one type only, or two or more types may be used. Examples of cell-forming agents include higher fatty acid amides, partial esters of higher fatty acids and alcohols, talc, calcium carbonate, mica, citric acid, sodium bicarbonate, polytetrafluoroethylene, aluminum hydroxide, and silica. Examples of higher fatty acid amides include fatty acid monoamides such as oleic acid amide, stearic acid amide, and hydroxystearic acid amide; and fatty acid bisamides such as methylene bisstearic acid amide and ethylene bisstearic acid amide. Examples of higher fatty acids in the partial esters of higher fatty acids and alcohols include fatty acids having 15 or more carbon atoms, such as palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, and behenic acid. Examples of partial esters of higher fatty acids and alcohols include stearic acid monoglyceride and stearic acid diglyceride.

[0110] The amount of the cell regulator used can be appropriately set depending on the purpose. The amount of the cell regulator used is preferably 10.0 parts by weight or less, more preferably 0.1 to 10.0 parts by weight, even more preferably 0.3 to 7.0 parts by weight, particularly preferably 0.5 to 5.0 parts by weight, and most preferably 0.8 to 3.0 parts by weight, based on 100 parts by weight of the modified polylactic acid resin.

[0111] Examples of other components other than those described above include other resins, pigments, radiant heat transfer suppressing components, crosslinking agents, plasticizers, stabilizers, fillers, lubricants, colorants, antioxidants, antistatic agents, spreading agents, weather resistance agents, flame retardants, ultraviolet absorbers, light stabilizers, antioxidants, anti-fogging agents, fragrances, and antibacterial agents.

[0112] In the second step, the modified polylactic acid resin, the cell control agent, and other components, if necessary, may be premixed using a mixer such as a tumbler, ribbon blender, V blender, Henschel mixer, or Redige mixer.

[0113] In the second step, the modified polylactic acid resin obtained in the first step is melt-kneaded with a foaming agent in an extruder and extrusion-foamed.

[0114] As the extruder, any appropriate extruder can be used as long as the effects of the present invention are not impaired. In terms of being able to further exhibit the effects of the present invention, a tandem extruder is preferably used as the extruder.

[0115] The tip of the tandem extruder may be equipped with any appropriate die so as to ultimately obtain a polylactic acid resin foam sheet, provided that the effects of the present invention are not impaired. Preferably, the tandem extruder may further be equipped with a cooling mandrel, a take-up roller for winding the polylactic acid resin foam sheet into a raw roll, and the like.

[0116] The second step can be carried out using any appropriate apparatus as long as the effects of the present invention are not impaired. In order to further demonstrate the effects of the present invention, the second step can be carried out using, for example, a production apparatus such as that shown in FIG.

[0117] The manufacturing apparatus illustrated in Figure 3 includes a tandem extruder 10 and a circular die CD that discharges the polylactic acid resin composition melt-kneaded in the tandem extruder 10 into a cylindrical shape. The manufacturing apparatus also includes a cooling device CL that air-cools the foamed sheet discharged into a cylindrical shape from the circular die CD, a mandrel MD that expands the cylindrical foamed sheet into a cylindrical shape of a predetermined size, a slitting device that slits the foamed sheet after passing through the mandrel MD to divide it into two sheets, and a take-up roller 22 that winds up the slit foamed sheet 1 after passing it through multiple rollers 21. An extruder upstream of the tandem extruder 10 (hereinafter also referred to as "first extruder 10a") includes a hopper 11 for introducing the modified polylactic acid resin, which is the raw material for the foamed sheet, and a gas inlet 12 for supplying a foaming agent into the cylinder. Downstream of the first extruder 10a, there is provided an extruder (hereinafter also referred to as "second extruder 10b") for melt-kneading a polylactic acid resin composition containing a modified polylactic acid resin and a foaming agent.

[0118] The temperature conditions for melt-kneading may vary depending on the size of extrusion, the discharge rate, etc., and any appropriate conditions may be adopted as long as the effects of the present invention are not impaired. For example, the temperature of the raw material feed section of the upstream extruder 10a is preferably set to 100°C to 200°C, more preferably 140°C to 200°C, the temperature after the upstream extruder 10a is preferably set to 120°C to 300°C, more preferably 140°C to 270°C, and the temperature of the downstream extruder 10b is preferably set to 100°C to 250°C, more preferably 120°C to 220°C.

[0119] The rotation speed of the extruder may vary depending on the size of the extrusion, the discharge rate, etc., and any appropriate condition may be adopted as long as the effects of the present invention are not impaired. For example, the rotation speed of the upstream extruder 10a is preferably 10 rpm to 300 rpm, and the rotation speed of the downstream extruder 10b is preferably 5 rpm to 200 rpm.

[0120] By the second step, a polylactic acid resin foam sheet is obtained.

[0121] <<Embodiment B (One-Step Process)>> In embodiment B, a polylactic acid resin (P) containing an unmodified polylactic acid resin as a main component is melt-kneaded with a foaming agent in an extruder, followed by extrusion-foaming to produce a polylactic acid resin foam sheet.

[0122] For convenience, the following description will be given assuming that the content of unmodified polylactic acid resin in polylactic acid resin (P) containing unmodified polylactic acid resin as a main component is substantially 100% by weight. That is, in the following description, embodiment B is assumed to be a polylactic acid resin foam sheet produced by melt-kneading polylactic acid resin (i.e., unmodified polylactic acid resin) with a foaming agent in an extruder and extrusion-foaming. However, of course, the content of unmodified polylactic acid resin in polylactic acid resin (P) containing unmodified polylactic acid resin as a main component may actually be the proportion contained as a main component, as described above.

[0123] For the polylactic acid resin, the explanation in the <First Step> of <Embodiment A> above can be directly applied.

[0124] At least a part of the polylactic acid resin used as a raw material may be recycled.

[0125] In embodiment B, the moisture content of the polylactic acid resin as a raw material fed into the extruder is preferably 0.30% by weight or less, more preferably 0.25% by weight or less, even more preferably 0.20% by weight or less, particularly preferably 0.17% by weight or less, and most preferably 0.15% by weight or less. The lower limit of the moisture content is preferably as low as possible, and is ideally 0% by weight.

[0126] In embodiment B, the polylactic acid resin as a raw material to be fed into the extruder may be dried using a dryer such as a dehumidifying dryer, a vacuum dryer, a hot air dryer, etc., before being fed into the extruder. Furthermore, the polylactic acid resin that has been thoroughly dried using such a dryer or the like may be fed directly into the extruder (without being exposed to a moist environment), or the polylactic acid resin that has been thoroughly dried using such a dryer or the like may be sealed in an aluminum bag or the like immediately after drying, and the bag may be opened and fed into the extruder immediately before being fed.

[0127] The type of foaming agent can be directly referred to in the description of the second step in the above-mentioned embodiment A.

[0128] The amount of the foaming agent used can be appropriately set depending on the purpose, and is preferably 0.1 to 10.0 parts by weight, more preferably 0.3 to 7.0 parts by weight, even more preferably 0.5 to 5.0 parts by weight, and particularly preferably 0.8 to 3.0 parts by weight, based on 100 parts by weight of the polylactic acid resin.

[0129] In embodiment B, the extruder may contain any appropriate other components other than the polylactic acid resin and the foaming agent, as long as the effects of the present invention are not impaired. In embodiment B, the total content of the polylactic acid resin and the foaming agent in the extruder is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, even more preferably 90% by weight to 100% by weight, and particularly preferably 95% by weight to 100% by weight.

[0130] In embodiment B, the extruder preferably contains a modifier as another component. The modifier can increase the molecular weight of the polylactic acid resin and can provide a crosslinked structure or a long-chain branched structure in the molecular structure of the polylactic acid resin.

[0131] With regard to the modifier, the explanation in the first step of the above-mentioned <Embodiment A> can be directly applied.

[0132] In embodiment B, a foaming aid may be contained as another component in the extruder. Regarding the foaming aid, the description in the <Second Step> of the above-mentioned <Embodiment A> may be directly applied.

[0133] In embodiment B, a cell control agent may be contained as another component in the extruder. Regarding the cell control agent, the description in the second step of embodiment A above may be applied as is.

[0134] Examples of other components other than those described above include other resins, pigments, radiant heat transfer suppressing components, crosslinking agents, plasticizers, stabilizers, fillers, lubricants, colorants, antioxidants, antistatic agents, spreading agents, weather resistance agents, flame retardants, ultraviolet absorbers, light stabilizers, antioxidants, anti-fogging agents, fragrances, and antibacterial agents.

[0135] In embodiment B, the polylactic acid resin, the modifier, the cell control agent, and optionally other components may be premixed. Examples of such a mixing method include a mixing method using a mixer such as a tumbler, a ribbon blender, a V blender, a Henschel mixer, or a Redige mixer.

[0136] In embodiment B, the polylactic acid resin is melt-kneaded with a foaming agent in an extruder.

[0137] As the extruder, any appropriate extruder can be used as long as the effects of the present invention are not impaired. In terms of being able to further exhibit the effects of the present invention, a twin-screw extruder is preferred.

[0138] In embodiment B, the tip of the twin-screw extruder may be equipped with any appropriate die so as to ultimately obtain a polylactic acid resin foam sheet, as long as the effects of the present invention are not impaired. Preferably, the extruder may further be equipped with a cooling mandrel, a take-up roller for winding the polylactic acid resin foam sheet into a raw roll, and the like.

[0139] Embodiment B can be carried out using any appropriate apparatus as long as the effects of the present invention are not impaired. In order to further demonstrate the effects of the present invention, Embodiment B can be carried out using, for example, a manufacturing apparatus such as that shown in FIG.

[0140] The manufacturing apparatus illustrated in Figure 4 includes a twin-screw extruder 30 and a circular die CD that extrudes the polylactic acid resin composition melt-kneaded in the twin-screw extruder 30 into a cylindrical shape. The manufacturing apparatus also includes a cooling device CL that air-cools the foamed sheet extruded into a cylindrical shape from the circular die CD, a mandrel MD that expands the cylindrical foamed sheet into a cylindrical shape of a predetermined size, a slitting device that slits the foamed sheet after passing through the mandrel MD to divide it into two sheets, and a take-up roller 22 that winds up the slit foamed sheet 1 after passing it through multiple rollers 21. A hopper 11 is provided upstream of the twin-screw extruder 30 for introducing polylactic acid resin, which is a raw material for the foamed sheet. A gas inlet 12 is provided downstream of the twin-screw extruder 30 for supplying a blowing agent into the cylinder. When the extrusion foaming process is carried out using such an apparatus, the polylactic acid resin is modified and mixed with a foaming agent and the like in the twin-screw extruder 30, and a polylactic acid resin composition that serves as the raw material for the foamed sheet is prepared, and extrusion foaming is carried out through the circular die CD.

[0141] The temperature conditions for melt-kneading may vary depending on the size of extrusion, the discharge rate, etc., and any appropriate conditions may be adopted as long as the effects of the present invention are not impaired. For example, the temperature of the raw material feed section of the twin-screw extruder 30 is preferably set to 100°C to 200°C, more preferably 120°C to 200°C, and the temperature after the twin-screw extruder 30 is preferably set to 120°C to 300°C, more preferably 120°C to 250°C.

[0142] The rotation speed of the extruder may vary depending on the size of the extrusion, the discharge rate, etc., and any appropriate condition may be adopted as long as the effects of the present invention are not impaired. For example, the rotation speed of the twin-screw extruder 30 is preferably 20 rpm to 800 rpm.

[0143] According to the above-described embodiment B, a polylactic acid resin foam sheet can be obtained.

[0144] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring and evaluating each property are as follows.

[0145] <Measurement of Thickness of Polylactic Acid Resin Foam Sheet> The polylactic acid resin foam sheet (width: 650 mm) obtained in Production Example was divided into 8 equal intervals in the width direction (TD direction) excluding 20 mm at both ends, and 9 measurement points were used to measure the thickness at these 9 measurement points using a dial thickness gauge SM-112 (manufactured by Teclock). The arithmetic mean of the measured values ​​was taken as the thickness of the polylactic acid resin foam sheet.

[0146] <Measurement of basis weight of polylactic acid resin foam sheet> Six 10 cm x 10 cm pieces were cut out of the polylactic acid resin foam sheet obtained in the Production Example at equal intervals in the width direction (TD direction) except for 25 mm at both ends, and the weight (g) of each piece was measured to the nearest 0.001 g. The average weight (g) of each piece was used to calculate the basis weight of 1 m 2 The value converted into the weight per unit area is used as the basis weight (g / m) of the polylactic acid resin foam sheet. 2 ) Basis weight (g / m 2 ) = (average weight of the slices (g) / (10 (cm) x 10 (cm))) x 10000 (cm 2 / m 2 )

[0147] <Measurement of Expansion Ratio of Polylactic Acid Resin Foam Sheet> The expansion ratio of the polylactic acid resin foam sheet obtained in the Production Examples was determined by determining the apparent density (ρ1) of the polylactic acid resin foam sheet, determining the density (true density: ρ0) of the resin composition constituting the polylactic acid resin foam sheet, and dividing the true density (ρ0) by the apparent density (ρ1). Expansion ratio = true density (ρ0) (kg / m 3) / apparent density (ρ1) (kg / m 3 The density (apparent density) of the polylactic acid resin foam sheet can be determined by the method described in JIS-K7222:1999 "Foamed plastics and rubber - Measurement of apparent density", and specifically, it was determined by the following method. [Method for measuring density (apparent density)] A 100 cm 3 The above samples were cut without changing the original cell structure, and the samples were conditioned for 16 hours under a grade 2 environment, 23 / 50, of JIS K7100:1999. The dimensions and weight were then measured, and the density (apparent density) was calculated using the following formula: Apparent density (kg / m 3 ) = weight of sample (kg) / volume of sample (m 3 The dimensions of the samples were measured using a "DIGIMATIC" CD-15 type (manufactured by Mitutoyo Corporation). The density (true density) of the resin composition constituting the polylactic acid resin foam sheet was determined by measuring a sample made by heat pressing the polylactic acid resin foam sheet to make it non-foamed, based on the Archimedes method (a liquid weighing method in JIS-K8807:2012 "Methods for determining density and specific gravity of solids").

[0148] <Measurement of open cell ratio of polylactic acid resin foam sheet> A plurality of sheet samples measuring 25 mm in length and 25 mm in width were cut out from the polylactic acid resin foam sheet obtained in the Production Example, and the cut out samples were stacked together without leaving any gaps to form a measurement sample with a thickness of 20 mm. The outer dimensions of this measurement sample were measured to 1 / 100 mm using a "Digimatic Caliper" (manufactured by Mitutoyo Corporation), and the apparent volume (cm 3 Next, the volume (cm) of the measurement sample was measured under the following conditions using an "Accupyk II 1340-100cc" dry automatic density meter manufactured by Shimadzu Corporation. 3) was measured. The measurement conditions were as follows. Gas used: Nitrogen Container used: 35 cc Filling pressure: 0.005 psig End rate of pressure equilibrium: 0.005 psig / min Number of repetitions: 1 The open cell ratio (%) was calculated using these determined values ​​and the following formula, and the average value for five tests was calculated. The measurement was carried out in an environment conforming to JIS K7100-1999, Code 23 / 50, Class 2, after conditioning the measurement sample for 16 hours in the environment conforming to JIS K7100-1999, Code 23 / 50, Class 2. Open cell ratio (%) = [(apparent volume - volume measured with a dry automatic density meter) / apparent volume] x 100 (%)

[0149] <Measurement of Thermal Conductivity of Polylactic Acid Resin Foam Sheet> The thermal conductivity of the polylactic acid resin foam sheet obtained in the production examples was measured in accordance with JIS A 1412-2:1999 using an "HC-074 / 200 (AutoΛ)" thermal conductivity measuring device (manufactured by Eiko Seiki Co., Ltd.). The test specimens measured 200 mm long x 200 mm wide x 10-25 mm thick, with both surfaces of the polylactic acid resin foam sheet left intact. The test specimens were conditioned for 24 hours in a JIS K7100:1999, 23 / 50, Class 2 environment before use. Measurements were performed at an average temperature of 23°C (hot plate temperature 38°C, cold plate temperature 8°C) with a plate temperature difference of 30°C. The calibration reference value used was the NIST (National Institute of Standards and Technology) SRM1450B registered with the device.

[0150] <Measurement of MFR (Melt Mass Flow Rate) of Polylactic Acid Resin Foam Sheet> The MFR of the polylactic acid resin foam sheet obtained in the Production Examples was measured in accordance with JIS K 7210:1999. Specifically, it was measured by "b) Measuring the time it takes for a piston to move a predetermined distance" as described in Method B of JIS K 7210:1999. The MFR was measured using a Melt Flow Index Tester (Automatic) 120-SAS (manufactured by Yasuda Seiki Seisakusho Co., Ltd.). The samples were vacuum dried at 90°C for 5 hours and then sealed and stored in a desiccator until immediately before measurement. Measurement was performed three times, and the average value was used. The measurement conditions were as follows: Sample: 3g to 8g Preheating (1): 200 seconds Preheating (2): 30 seconds Test temperature: 190°C Test load: 21.18 N Piston movement distance (interval): 25mm

[0151] <Measurement of Molecular Weight of Polylactic Acid Resin Foam Sheet> The number-average molecular weight (Mn), weight-average molecular weight (Mw), and Z-average molecular weight (Mz) of the polylactic acid resin foam sheets obtained in the Production Examples were determined as follows. 20 mg of a sample to be measured for molecular weight was dissolved in 6 mL of chloroform (immersion time: 6 hours ± 1.0 hour (partially insoluble)), filtered through a non-aqueous 0.45 μm syringe filter (manufactured by Shimadzu GLC Corporation), and then measured using a chromatograph under the following measurement conditions. The average molecular weight of the sample was determined from a previously prepared standard polystyrene calibration curve. The instrument used was a gel permeation chromatograph "HLC-8320GPC EcoSEC" (with built-in RI detector and UV detector) (manufactured by Tosoh Corporation). [GPC measurement conditions] Guard column: TSK guard column HXL-H (6.0 mm x 4.0 cm) (manufactured by Tosoh Corporation) x 1 Measurement column: TSKgel GMHXL (7.8 mm I.D. x 30 cm) (manufactured by Tosoh Corporation) x 2 in series Reference side: Resistance tube (inner diameter 0.1 mm x 2 m) x 2 in series Column temperature: 40°C Mobile phase: chloroform Mobile phase flow rate of reference side pump: 0.5 mL / min Mobile phase flow rate of sample side pump: 1.0 mL / min Detector: RI detector Injection volume: 50 μL Measurement time: 25 min Sampling interval: 500 msec Standard polystyrene samples for the calibration curve were obtained under the product names "STANDARD SM-105" and "STANDARD SH-75" (all manufactured by Showa Denko K.K.) with weight average molecular weights of 5,620,000, 3,120,000, 1,250,000, 442,000, 151,000, 53,500, 17,000, 7,660, 2,900, and 1,320 were used. The standard polystyrene for the calibration curve was divided into groups A (5,620,000, 1,250,000, 151,000, 17,000, 2,900) and B (3,120,000, 442,000, 53,500, 7,660, 1,320), and then A was weighed out to (2 mg, 3 mg, 4 mg, 4 mg, 4 mg) and dissolved in 30 mL of chloroform, and B was weighed out to (3 mg, 4 mg, 4 mg, 4 mg, 4 mg) and dissolved in 30 mL of chloroform.A standard polystyrene calibration curve was obtained by injecting 50 μL of each prepared solution A and solution B, and creating a calibration curve (cubic equation) from the retention times obtained after measurement. The average molecular weight was calculated using this calibration curve.

[0152] <Measurement of Gel Fraction of Polylactic Acid Resin Foam Sheet> The gel fraction (wt %) of the polylactic acid resin foam sheet obtained in the production example was measured by the following method. Approximately 0.5 g of sample was prepared, and the initial weight (m0 (g)) of this sample was precisely weighed. A 200-mesh wire mesh (wire diameter 0.05 mm) was also prepared for filtering the solution in which the sample was dissolved. The initial weight (M0 (g)) of this wire mesh was also precisely weighed. The weighed sample was placed in a 100 mL beaker. 50 mL of chloroform as a solvent and a stir bar were added to the beaker, which was then covered with aluminum foil. The mixture was stirred with a stirrer for 2 hours to dissolve the sample at room temperature. After 2 hours, the aluminum foil was removed, and the solution in the beaker was filtered through the wire mesh. After filtration, the wire mesh was air-dried in a draft chamber for at least 12 hours. After air-drying, the wire mesh was further dried in a constant-temperature dryer at 120°C for 2 hours. The dried wire mesh was cooled in a desiccator. After cooling, the weight (M1 (g)) of the wire mesh to which the insoluble resin matter was attached was weighed, and the gel fraction was calculated using the following formula: Gel fraction (wt %) = (m1 (g) / m0 (g)) x 100, where m0 is the initial weight of the sample, m1 is the weight of the insoluble resin matter (M1 - M0), M0 is the initial weight of the wire mesh, and M1 is the weight of the wire mesh to which the insoluble resin matter was attached (total weight of the insoluble resin matter and the wire mesh).

[0153] <Measurement of Melt Tension (MT) of Polylactic Acid Resin Foam Sheet> The melt tension of the polylactic acid resin foam sheet obtained in the Production Examples was measured using a Capilograph 1D (manufactured by Toyo Seiki Seisaku-sho, Ltd.) and a Rheotens 71.97 (manufactured by Gottfert GmbH) as measuring devices. The measurement sample was vacuum-dried at 90°C for 5 hours or more, and after drying, was placed in a nylon plastic bag for vacuum packing, vacuum-packed, and stored in a desiccator until just before measurement. First, a measurement sample was filled into a 9.55 mm diameter barrel heated to a test temperature of 190°C, and then preheated for 5 minutes. The molten resin was then extruded into a string shape from a capillary die (diameter 2.095 mm, length 8 mm, inlet angle 90° (conical)) of the measurement device while maintaining a constant piston descending speed (20 mm / min). This string-like material was then passed through a wheel (wheel spacing: upper 0.6 mm to 0.8 mm, lower 1.0 mm) installed so that the distance from the outlet of the capillary die to the measurement section was 80 mm, and the take-up speed was set at an initial speed of 6.92 mm / s and an acceleration of 10 mm / s. 2 The Rheotensor was passed through the test piece while gradually increasing the tension, and the average of the maximum and minimum tension values ​​just before the point at which the string-like material broke was taken as the melt tension (MT) of the test sample. If interference occurred and the Rheotensor could not be brought within 80 mm, measures were taken to avoid interference and the Rheotensor was set at a predetermined location. If there was only one maximum point on the tension chart, that maximum value was taken as the melt tension, and if the string-like material became thinner and the take-up became idling, that point was taken as the break point, and the average of the maximum and minimum tension values ​​just before that point was taken as the melt tension of the test sample. [Measurement conditions for "Capilograph 1D"] Die: diameter 2.095 mm, length 8 mm, inlet angle 90 degrees (conical) Barrel diameter: 9.55 mm Piston speed: 20 mm / min Measurement temperature: 190°C [Measurement conditions for "Rheotens 71.97"] Wheel spacing: upper 0.6 mm to 0.8 mm, lower 1.0 mm Acceleration: 10 mm / s 2 Pull-up speed: initial speed 6.92 mm / s

[0154] <Measurement of Thickness of Polylactic Acid Resin Foam Molded Article> For the polylactic acid resin foam molded articles obtained in the Examples and Comparative Examples, if the articles were point-symmetrical when viewed in a planar direction, the thickness from end to end of a cross section obtained by cutting the articles along a plane passing through the center point and passing through a central axis forming a 90-degree angle with the planar direction was measured using a dial thickness gauge SM-112 (manufactured by Teclock). If the articles were not point-symmetrical when viewed in a planar direction, the thickness was measured by cutting the articles along a plane passing through the center point and passing through a central axis forming a 90-degree angle with the planar direction.

[0155] <Measurement of open cell ratio of polylactic acid resin foam molded article> A plurality of sheet-like samples measuring 25 mm long x 25 mm wide were cut out from the side wall portion (corresponding to the portion 120 in Figure 1) of the polylactic acid resin foam molded article obtained in the Examples and Comparative Examples, and the cut-out samples were stacked together without leaving any gaps to obtain a measurement sample with a thickness of approximately 20 mm. The outer dimensions of this measurement sample were measured to 1 / 100 mm using a "Digimatic Caliper" (manufactured by Mitutoyo Corporation), and the apparent volume (cm 3 ) was determined. If it is difficult to prepare a measurement sample having a thickness of about 20 mm as described above by cutting out a plurality of sheet-like samples of 25 mm length x 25 mm width from the side wall portion (corresponding to the portion 120 in Fig. 1) of the polylactic acid resin foam molded article, a sample having a volume of 12,500 mm 3 The molded body was cut out to a size equivalent to the open cell ratio (25 mm x 25 mm x 20 mm), and after measuring the open cell ratio, the apparent volume (cm ) of the measurement sample was measured according to the Archimedes method (a submerged weighing method in JIS-K8807:2012 "Method for measuring density and specific gravity of solids"). 3 Next, the volume (cm ) of the measurement sample is measured under the following conditions using an "AccuPyc II 1340-100cc" dry automatic density meter manufactured by Shimadzu Corporation. 3) was measured. The measurement conditions were as follows. Gas used: Nitrogen Container used: 35 cc Filling pressure: 0.005 psig End rate of pressure equilibrium: 0.005 psig / min Number of repetitions: 1 Note that if the open cell ratio is too high, the equilibrium pressure will not be reached within the adjustment time (1000 seconds) and measurement will be impossible, so in that case the measurement was deemed unacceptable. The open cell ratio (%) was calculated using these determined values ​​and the following formula, and the average value for five tests was obtained. Note that the measurement was performed in an environment of JIS K7100-1999, Symbol 23 / 50, Class 2, after conditioning the measurement sample for 16 hours in an environment of JIS K7100-1999, Symbol 23 / 50, Class 2. Open cell ratio (%) = [(Apparent volume - Volume measured with a dry automatic density meter) / Apparent volume] x 100 (%)

[0156] <Measurement of Melting Point, Crystallization Temperature, and Crystallinity of Polylactic Acid Resin Foam Sheet and Polylactic Acid Resin Foam Molded Product> The melting point, crystallization temperature, and crystallinity of the polylactic acid resin foam sheet and polylactic acid resin foam molded product were determined as follows using a heat flux differential scanning calorimeter (heat flux DSC) in accordance with the methods described in JIS K7122:1987, JIS K7122:2012 "Method for measuring heat of transition of plastics," and JIS K7121:1987, 2012 "Method for measuring transition temperature of plastics." The sample to be measured was packed into an aluminum measurement container (Hitachi High-Tech Science Corporation, product code: GAA-0065) so that 5.5±0.5 mg of the sample was tightly packed at the bottom, and then closed with an aluminum lid (Hitachi High-Tech Science Corporation, product code: GAA-0064). The sample was then heated and cooled using a differential scanning calorimeter (Hitachi High-Tech Science Corporation, "NEXTA DSC600") at a nitrogen gas flow rate of 20 mL / min, in the following steps to obtain a DSC curve: (Step 1) The sample was heated from 30°C to 210°C (first heating), and then held for 10 minutes. (Step 2) The sample was removed from the measurement device, allowed to stand at room temperature for 10 minutes, and then returned to the measurement device at 30°C (rapid cooling). (Step 3) The sample was heated from 30°C to 210°C (second heating). All heating was performed at a rate of 5°C / min. Alumina was used as the reference material. [Melting Point] Using the analysis software provided with the apparatus, the temperature at the top of the melting peak observed during the second heating process was read and used as the melting point (melting temperature). [Crystallization Temperature] The crystallization temperature was determined by reading the temperature at the top of the exothermic peak observed during the second heating process and using it as the (cold) crystallization temperature. If multiple exothermic peaks appeared, the temperature of the lower temperature peak was read. [Crystallization Degree] The crystallization degree was determined by dividing the difference between the endothermic amount (heat of fusion (J / g)) calculated from the area of ​​the endothermic peak appearing in the crystalline melting observed during the first heating process and the heat of crystallization (J / g) calculated from the area of ​​the crystallization peak by the theoretical heat of fusion of perfectly crystalline polylactic acid (93 J / g). The heat of fusion and heat of crystallization were calculated using the analysis software provided with the apparatus.Specifically, the heat of fusion was calculated from the area enclosed by the line connecting the point where the DSC curve departs from the low-temperature baseline and the point where the DSC curve returns to the high-temperature baseline, and the DSC curve. The heat of crystallization was calculated from the area enclosed by the line connecting the point where the DSC curve departs from the low-temperature baseline and the point where the DSC curve returns to the high-temperature baseline, and the DSC curve. The crystallinity was calculated using the following formula: Crystallinity (%) = [[heat of fusion (J / g) - heat of crystallization (J / g)] / 93 (J / g)] x 100 (%).

[0157] <Measurement of Average Cell Diameter of Polylactic Acid Resin Foam Molded Articles> The bottom surface (corresponding to the portion 110 in FIG. 1 ) of the polylactic acid resin foam molded articles obtained in the Examples and Comparative Examples was cut perpendicular to the bottom surface along an arbitrary direction A and a direction B perpendicular to the direction A. One of the cross sections to be observed was a cross section cut perpendicular to the bottom surface along the direction A (hereinafter referred to as "cross section A"). The other cross section to be observed was a cross section cut perpendicular to the bottom surface along the direction B (hereinafter referred to as "cross section B"). The cross sections were photographed at 20x magnification using a scanning electron microscope (SU1510, manufactured by Hitachi High-Technologies Corporation). The microscopic images were taken so that the desired magnification would be obtained when two images (four images total) were printed side by side on a single sheet of A4 paper in landscape orientation. Specifically, two microscopic images were taken for each of the cross sections cut along the A direction (A cross section) and the cross section cut along the B direction (B cross section), for a total of four fields of view. Two images of the A cross section (A direction x VD direction perpendicular to the A direction) (Image A1 and Image A2) and two images of the B cross section (B direction x VD direction perpendicular to the B direction) (Image B1 and Image B2) were printed on A4 paper in the order of upper left, upper right, lower left, and lower right, so that the four images were image A1, image A2, image B1, and image B2. Next, for each of images A1 and A2, three arbitrary straight lines each 60 mm long parallel to the A direction and three arbitrary straight lines each 60 mm long in the VD direction were drawn, and for each of images B1 and B2, three arbitrary straight lines each 60 mm long parallel to the B direction and three arbitrary straight lines each 60 mm long in the VD direction were drawn. In addition, we tried to avoid contact of bubbles only at the contact points of any given line as much as possible, and if bubbles did contact, these bubbles were also counted. The number of bubbles D present on all the above lines was arithmetically averaged to obtain the number of bubbles in each direction. The average chord length t of the bubbles in each direction was calculated from the image magnification at which the number of bubbles was counted and the number of bubbles obtained using the following formula.Average chord length t (μm) = 60,000 / (number of bubbles × image magnification) (Average chord length in A direction tA (μm) = 60,000 / (number of bubbles in A direction × image magnification)) (Average chord length in B direction tB (μm) = 60,000 / (number of bubbles in B direction × image magnification)) (Average chord length in VD directions tV (μm) = 60,000 / (number of bubbles in VD direction × image magnification)) The image magnification was calculated using the following formula by measuring the scale bar on the image to 1 / 100 mm using a Digimatic caliper (manufactured by Mitutoyo Corporation): Image magnification = measured value of scale bar (mm) / displayed value of scale bar (mm) The bubble diameter in each direction was calculated using the following formula. Average bubble diameter in the A direction dM (μm) = tA (μm) / 0.616 Average bubble diameter in the B direction dT (μm) = tB (μm) / 0.616 Average bubble diameter in the VD direction dV (μm) = tV (μm) / 0.616 Furthermore, the cube root of the product of these was taken as the average bubble diameter: Average bubble diameter d (μm) = (dA (μm) × dB (μm) × dV (μm)). 1 / 3

[0158] <Evaluation of Heat Insulation Properties of Polylactic Acid Resin Foam Molded Articles> 600 cc of boiling water was poured into the polylactic acid resin foam molded articles obtained in the Examples and Comparative Examples, and the surface temperature of the outer surface of the polylactic acid resin foam molded article was measured. The highest of the measured surface temperatures was taken as the evaluation temperature and evaluated according to the following criteria: ◯: Evaluation temperature is 60°C or lower. ×: Evaluation temperature is higher than 60°C. Note that cases where the container was deformed during measurement and measurement was not possible were also evaluated as ×.

[0159] [Production Example 1] Polylactic acid resin (trade name "FY602", manufactured by Anhui Fengyuan Fort Laiju Lactic Acid Co., Ltd., MFR = 16.0 g / 10 min, D-form ratio = 2.0 ± 0.5 mol%, melting point = 164.3°C, density = 1240 kg / m 3): 100 parts by weight, and 0.5 parts by weight of t-butylperoxyisopropyl monocarbonate (manufactured by Kayaku Nouryon, "Trigonox BPIC-75", 1-minute half-life temperature T1 = 158.8°C): were stirred and mixed in a ribbon blender to obtain a mixture. The obtained mixture was fed into a twin-screw extruder (L / D = 31.5) with a diameter of 57 mm. The temperature setting in the feed section was set to 170°C, the temperature thereafter to 200°C, and the rotation speed was set to 100 rpm. The mixture was melt-kneaded in the twin-screw extruder, and the kneaded product was extruded into strands at a discharge rate of 50 kg / hour from a die (diameter φ3 mm, number of holes 18) attached to the tip of the twin-screw extruder. The extruded strand-like kneaded product was then passed through a 2-m-long cooling water bath containing water at 30°C to cool it. The cooled strands were cut and pelletized using a pelletizer, and then dried in a dehumidifying dryer at a drying temperature of 60 ° C. In this way, a modified polylactic acid resin was obtained. 100 parts by weight of the obtained modified polylactic acid resin and 1.5 parts by weight of a cell regulator (manufactured by Matsumura Sangyo Co., Ltd., "Crown Talc") were dry-blended to prepare a mixture. In a tandem extruder equipped with a first extruder (upstream) with a diameter of φ50 mm and a second extruder (downstream) with a diameter of φ65 mm, the mixture was fed through a hopper to the first extruder with a diameter of φ50 mm and heated and melted at 220 ° C. Then, 1.2 parts by weight of butane (isobutane / normal butane = 35 wt% / 65 wt%) as a foaming agent was injected into the first extruder and melt-kneaded with the mixture to obtain a melt-kneaded product. The molten mixture was then transferred to a second extruder with a diameter of 65 mm and cooled to 170°C. It was then extruded through a circular die with a diameter of 70 mm at a discharge rate of 30 kg / hour to obtain a cylindrical foam. The resulting cylindrical foam was placed on a mandrel with a diameter of 206 mm, the interior of which was cooled with water at approximately 20°C, and cooled by blowing air onto its outer surface using an air ring larger than the diameter of the mandrel. The foam was then cut open at one point on the circumference with a cutter to obtain a strip-shaped polylactic acid resin foam sheet (1). The physical properties of the resulting polylactic acid resin foam sheet (1) are shown in Table 1.

[0160] [Production Example 2] Polylactic acid resin (trade name "FY602", manufactured by Anhui Fengyuan Fort Laiju Lactic Acid Co., Ltd., MFR = 16.0 g / 10 min, D-form ratio = 2.0 ± 0.5 mol%, melting point = 164.3°C, density = 1240 kg / m 3 100 parts by weight of polylactic acid resin (Nature Works LLC, "Biopolymer Ingeo 6202D", MFR = 11.2 g / 10 min, D-form ratio = 2.0 ± 0.5 mol%, melting point = 164.6, density = 1240 kg / m 3 A strip-shaped polylactic acid resin foam sheet (2) was produced in the same manner as in Production Example 1, except that 100 parts by weight of lactic acid resin foam (2) was used. The physical properties of the obtained polylactic acid resin foam sheet (2) are shown in Table 1.

[0161] [Production Example 3] Polylactic acid resin (trade name "FY602", manufactured by Anhui Fengyuan Fort Laiju Lactic Acid Co., Ltd., MFR = 16.0 g / 10 min, D-form ratio = 2.0 ± 0.5 mol%, melting point = 164.3°C, density = 1240 kg / m 3 100 parts by weight of polylactic acid resin (Nature Works LLC, "Biopolymer Ingeo 3100HP", MFR = 12.6 g / 10 min, D-form ratio = 0.4 mol%, melting point = 176.7, density = 1240 kg / m 3 A strip-shaped polylactic acid resin foam sheet (3) was produced in the same manner as in Production Example 1, except that 100 parts by weight of lactic acid resin foam (3) was used. The physical properties of the obtained polylactic acid resin foam sheet (3) are shown in Table 1.

[0162] [Production Example 4] Polylactic acid resin (trade name "FY602", manufactured by Anhui Fengyuan Fort Laiju Lactic Acid Co., Ltd., MFR = 16.0 g / 10 min, D-form ratio = 2.0 ± 0.5 mol%, melting point = 164.3°C, density = 1240 kg / m 3 100 parts by weight of a polylactic acid resin (manufactured by Anhui Fengyuan Fort Lai Ju Lactic Acid Co., Ltd., trade name "FY601", MFR = 12.9 g / 10 min, D-form ratio = 0.6 mol%, melting point = 172.7 ° C, density = 1240 kg / m 3A strip-shaped polylactic acid resin foam sheet (4) was produced in the same manner as in Production Example 1, except that 100 parts by weight of lactic acid resin foam (4) was used. The physical properties of the obtained polylactic acid resin foam sheet (4) are shown in Table 1.

[0163] Production Example 5 A strip-shaped polylactic acid resin foam sheet (5) was produced in the same manner as in Production Example 1, except that 0.5 parts by weight of t-butylperoxy-3,5,5-trimethylhexanoate (manufactured by Kayaku Nouryon, "Trigonox 42S", 1-minute half-life temperature T1: 159°C) was used instead of 0.5 parts by weight of t-butylperoxyisopropyl monocarbonate (manufactured by Kayaku Nouryon, "Trigonox BPIC-75", 1-minute half-life temperature T1 = 158.8°C). The physical properties of the obtained polylactic acid resin foam sheet (5) are shown in Table 1.

[0164] [Production Example 6] Polylactic acid resin (trade name "FY602", manufactured by Anhui Fengyuan Fort Laiju Lactic Acid Co., Ltd., MFR = 16.0 g / 10 min, D-form ratio = 2.0 ± 0.5 mol%, melting point = 164.3°C, density = 1240 kg / m 3): 100 parts by weight, t-butylperoxyisopropyl monocarbonate ("Trigonox BPIC-75" manufactured by Kayaku Nouryon Co., Ltd., 1-minute half-life temperature T1 = 158.8°C): 0.2 parts by weight, epoxy group-containing acrylic-modified styrene resin ("Joncryl ADR 4468" manufactured by BASF Corporation): 0.5 parts by weight, and cell regulator ("Crown Talc" manufactured by Matsumura Sangyo Co., Ltd.): 1.5 parts by weight were stirred and mixed in a ribbon blender to obtain a mixture. In a tandem extruder equipped with a first extruder (upstream) with a diameter of φ50 mm and a second extruder (downstream) with a diameter of φ65 mm, the mixture was fed through a hopper to the first extruder with a diameter of φ50 mm and heated to melt at 220°C. Subsequently, 1.2 parts by weight of butane (isobutane / normal butane = 35 wt% / 65 wt%) as a foaming agent was pressure-fed into the first extruder and melt-kneaded with the above mixture to produce a melt-kneaded mixture. The melt-kneaded mixture was then transferred to a second extruder with a φ65 mm diameter and cooled to 170°C, after which it was extruded through a circular die with a φ70 mm diameter at a discharge rate of 30 kg / hour to produce a cylindrical foam. The resulting cylindrical foam was placed on a φ206 mm mandrel whose interior was cooled with water at approximately 20°C, and cooled and molded by blowing air onto its outer surface using an air ring larger than the diameter of the mandrel. The foam was then cut at one point on the circumference with a cutter to produce a strip-shaped polylactic acid resin foam sheet (6). The physical properties of the resulting polylactic acid resin foam sheet (6) are shown in Table 1.

[0165] Production Example 7 A strip-shaped polylactic acid resin foam sheet (7) was produced in the same manner as in Production Example 6, except that 0.2 parts by weight of α,α-bis(t-butylperoxy)diisopropylbenzene (NOF Corporation, "Perbutyl P," 1-minute half-life temperature T1: 175°C) was used instead of 0.2 parts by weight of t-butylperoxyisopropyl monocarbonate (Kayaku Nouryon Co., Ltd., "Trigonox BPIC-75," 1-minute half-life temperature T1 = 158.8°C). The physical properties of the obtained polylactic acid resin foam sheet (7) are shown in Table 1.

[0166] Production Example 8 A strip-shaped polylactic acid resin foam sheet (8) was produced in the same manner as in Production Example 6, except that 0.2 parts by weight of t-butylperoxy-3,5,5-trimethylhexanoate (manufactured by Kayaku Nouryon Co., Ltd., "Trigonox 42S", 1-minute half-life temperature T1: 159°C) was used instead of 0.2 parts by weight of t-butylperoxyisopropyl monocarbonate (manufactured by Kayaku Nouryon Co., Ltd., "Trigonox BPIC-75", 1-minute half-life temperature T1 = 158.8°C). The physical properties of the obtained polylactic acid resin foam sheet (8) are shown in Table 1.

[0167] Production Example 9 A strip-shaped polylactic acid resin foam sheet (9) was produced in the same manner as in Production Example 8, except that the amount of t-butylperoxy-3,5,5-trimethylhexanoate (manufactured by Kayaku Nouryon Co., Ltd., "Trigonox 42S," 1-minute half-life temperature T1: 159°C) was changed to 0.3 parts by weight. The physical properties of the obtained polylactic acid resin foam sheet (9) are shown in Table 1.

[0168] Example 1 A flat square foamed sheet (test piece) measuring 340 mm long x 340 mm wide was cut from the polylactic acid resin foamed sheet (1) obtained in Production Example 1. A small single-shot molding machine (manufactured by Wakisaka Engineering Co., Ltd., product name "FVS-500 Model") was used, and the heater temperature of the heating furnace was set to 400°C. The test piece was then introduced into the heating furnace of the small single-shot molding machine and preheated. The preheating time (t1) was 10 seconds, and the surface temperature of the foamed sheet after preheating was 119°C. The preheated foamed sheet (test piece) was immediately subjected to matched mold molding using a 60°C mold (opening diameter 160 mm, bottom diameter 103.5 mm, height 70 mm, drawing ratio 0.44) to produce a bowl-shaped polylactic acid resin foamed molded article (foam container) (1) with an opening at the top. The time the foamed sheet (test piece) was held between the molds (mold retention time (t2)) was 10 seconds. The physical properties of the obtained polylactic acid resin foam molded article (1) are shown in Table 2.

[0169] Example 2 A bowl-shaped polylactic acid resin foam molded product (foam container) (2) having an opening at the top was produced in the same manner as in Example 1, except that the time for which the foam sheet (test piece) was clamped in the mold (mold retention time (t2)) was changed to 13 seconds. The physical properties of the obtained polylactic acid resin foam molded product (2) are shown in Table 2.

[0170] Example 3 A bowl-shaped polylactic acid resin foam molded product (foam container) (3) having an opening at the top was produced in the same manner as in Example 1, except that the polylactic acid resin foam sheet (2) obtained in Production Example 2 was used instead of the polylactic acid resin foam sheet (1) obtained in Production Example 1. The physical properties of the obtained polylactic acid resin foam molded product (3) are shown in Table 2.

[0171] Example 4 A bowl-shaped polylactic acid resin foam molded product (foam container) (4) having an opening at the top was produced in the same manner as in Example 1, except that the polylactic acid resin foam sheet (3) obtained in Production Example 3 was used instead of the polylactic acid resin foam sheet (1) obtained in Production Example 1. The physical properties of the obtained polylactic acid resin foam molded product (4) are shown in Table 2.

[0172] Example 5 A bowl-shaped polylactic acid resin foam molded product (foam container) (5) having an opening at the top was produced in the same manner as in Example 1, except that the polylactic acid resin foam sheet (4) obtained in Production Example 4 was used instead of the polylactic acid resin foam sheet (1) obtained in Production Example 1. The physical properties of the obtained polylactic acid resin foam molded product (5) are shown in Table 2.

[0173] Comparative Example 1 A bowl-shaped polylactic acid resin foam molded product (foam container) (C1) having an opening at the top was produced in the same manner as in Example 1, except that the preheating time (t1) was changed to 5 seconds. The physical properties of the obtained polylactic acid resin foam molded product (C1) are shown in Table 2.

[0174] Comparative Example 2 A bowl-shaped polylactic acid resin foam molded product (foam container) (C2) having an opening at the top was produced in the same manner as in Example 3, except that the preheating time (t1) was set to 5 seconds. The physical properties of the obtained polylactic acid resin foam molded product (C2) are shown in Table 2.

[0175] Comparative Example 3 A bowl-shaped polylactic acid resin foam molded product (foam container) (C3) having an opening at the top was produced in the same manner as in Example 1, except that the polylactic acid resin foam sheet (5) obtained in Production Example 5 was used instead of the polylactic acid resin foam sheet (1) obtained in Production Example 1. The physical properties of the obtained polylactic acid resin foam molded product (C3) are shown in Table 2.

[0176] Example 6 A bowl-shaped polylactic acid resin foam molded product (foam container) (6) having an opening at the top was produced in the same manner as in Example 1, except that the polylactic acid resin foam sheet (6) obtained in Production Example 6 was used instead of the polylactic acid resin foam sheet (1) obtained in Production Example 1. The physical properties of the obtained polylactic acid resin foam molded product (6) are shown in Table 2.

[0177] Example 7 A bowl-shaped polylactic acid resin foam molded product (foam container) (7) having an opening at the top was produced in the same manner as in Example 1, except that the polylactic acid resin foam sheet (7) obtained in Production Example 7 was used instead of the polylactic acid resin foam sheet (1) obtained in Production Example 1. The physical properties of the obtained polylactic acid resin foam molded product (7) are shown in Table 2.

[0178] Comparative Example 4 A bowl-shaped polylactic acid resin foam molded product (foam container) (C4) having an opening at the top was produced in the same manner as in Example 1, except that the polylactic acid resin foam sheet (8) obtained in Production Example 8 was used instead of the polylactic acid resin foam sheet (1) obtained in Production Example 1. The physical properties of the obtained polylactic acid resin foam molded product (C4) are shown in Table 2.

[0179] Comparative Example 5 A bowl-shaped polylactic acid resin foam molded product (foam container) (C5) having an opening at the top was produced in the same manner as in Example 1, except that the polylactic acid resin foam sheet (9) obtained in Production Example 9 was used instead of the polylactic acid resin foam sheet (1) obtained in Production Example 1. The physical properties of the obtained polylactic acid resin foam molded product (C5) are shown in Table 2.

[0180]

[0181]

[0182] The polylactic acid resin foam obtained by the production method of the present invention has excellent heat insulation properties and can be suitably used, for example, as a microwaveable container. The polylactic acid resin foam molded article according to the embodiment of the present invention can also be used as other containers, various packaging materials, various cushioning materials, etc.

Claims

1. A polylactic acid resin foam molded product obtained by molding a polylactic acid resin foam sheet, having a thickness of 1.0 mm or more, a crystallinity of 20% or more, and an open cell rate of 60% or less.

2. The polylactic acid resin foam molded article according to claim 1, having a crystallization temperature of 100°C or lower.

3. The polylactic acid resin foam molded article according to claim 1, wherein the polylactic acid resin foam sheet has an open cell rate of 20% or less.

4. The polylactic acid resin foam molded article according to claim 1, wherein the polylactic acid resin foam sheet has a crystallinity of 5% or more.

5. The polylactic acid resin foam molded article according to claim 1, wherein the thermal conductivity of the polylactic acid resin foam sheet at 23°C is 0.038 W / m·k or less.

6. The polylactic acid resin foam molded article according to claim 1, wherein the crystallization temperature of the polylactic acid resin foam sheet is 100°C or lower.

7. The polylactic acid resin foam molded article according to claim 1, wherein the weight average molecular weight (Mw) of the polylactic acid resin foam sheet is 200,000 or more.

8. The polylactic acid resin foam molded article according to claim 1, wherein the polylactic acid resin foam sheet has an MFR of 4.0 g / 10 min or less.

9. The polylactic acid resin foam molded article according to claim 1, wherein the gel fraction of the polylactic acid resin foam sheet is 2.0% by weight or less.

10. The polylactic acid resin foam molded article according to claim 1, wherein the polylactic acid resin foam sheet has a melt tension of 10 cN or more.

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