Polylactic acid resin foamed molding

Abstract

To provide a polylactic acid resin foamed molding that exhibits beautiful appearance.SOLUTION: A polylactic acid resin foamed molding according to an embodiment of the present invention is formed by molding a polylactic acid resin foamed sheet, the polylactic acid resin foamed molding having a surface roughness Sa of 30 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[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 the 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, attention has been focused on polylactic acid resin, which is biodegradable, has a small environmental impact, and can be produced relatively inexpensively, 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, conventional polylactic acid resin foam molded articles obtained by molding a polylactic acid resin foam sheet have the problem of poor appearance, such as noticeable surface irregularities. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6971947 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a foamed molded polylactic acid resin article having a beautiful appearance. [Means for solving the problem]

[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 surface roughness Sa of 35 μm or less. [2] The polylactic acid resin foam molded article according to the above item [1] may have an average cell diameter of 700 μm or less. [3] The polylactic acid resin foam molded article according to the above [1] or [2] may have a gel fraction of 4.5% by weight or less. [4] The polylactic acid resin foam molded article according to any one of the above items [1] to [3] may have an expansion ratio of 2 to 20 times. [5] The polylactic acid resin foam molded article according to any one of [1] to [4] above may be a food packaging container. [Effects of the Invention]

[0009] According to an embodiment of the present invention, a foam molded polylactic acid resin article with a beautiful appearance can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] 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). [Figure 2] FIG. 2 is a schematic diagram showing the configuration of a manufacturing apparatus in a first step of embodiment A. [Figure 3] FIG. 2 is a schematic diagram showing the configuration of a manufacturing apparatus in a second step of embodiment A. [Figure 4] FIG. 1 is a schematic diagram showing the configuration of a manufacturing apparatus in embodiment B. DETAILED DESCRIPTION OF THE INVENTION

[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 molding>> The polylactic acid resin foam molded article according to the 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. The polylactic acid resin foam molded articles according to the embodiments of the present invention have a beautiful appearance and are therefore suitable for use as food packaging 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 surface roughness Sa of the polylactic acid resin foam molded article according to the embodiment of the present invention is typically 35 μm or less, preferably 30 μm or less, more preferably 25 μm or less, particularly preferably 22 μm or less, and most preferably 20 μm or less. The smaller the surface roughness Sa of the polylactic acid resin foam molded article according to the embodiment of the present invention, the better, and the lower limit thereof is preferably 0 μm or more, for example, 1 μm or more. The polylactic acid resin foam molded article according to the embodiment of the present invention has a smaller surface roughness Sa than conventional polylactic acid resin foam molded articles. Therefore, the appearance of the polylactic acid resin foam molded article according to the embodiment of the present invention is significantly more beautiful than conventional polylactic acid resin foam molded articles. The method for measuring the surface roughness Sa will be described later.

[0017] In order to further exhibit the effects of the present invention, the polylactic acid resin foam molded article according to the embodiment of the present invention preferably has an average cell diameter of 700 μm or less, more preferably 600 μm or less, even more preferably 100 μm to 550 μm, particularly preferably 100 μm to 520 μm, and most preferably 100 μm to 500 μm. If the average cell diameter of the polylactic acid resin foam molded article according to the embodiment of the present invention is too large and outside the above range, the effects of the present invention may not be exhibited easily and the appearance may be deteriorated. If the average cell diameter of the polylactic acid resin foam molded article according to the embodiment of the present invention is too small and outside the above range, the cells may be easily broken, the open cell ratio may be high, and the appearance may be deteriorated. The method for measuring the average cell diameter will be described later.

[0018] In order to further enhance the effects of the present invention, the polylactic acid resin foam molded article according to the embodiment of the present invention preferably has a gel fraction of 4.5 wt% or less, more preferably 4.0 wt% or less, even more preferably 3.5 wt% or less, even more preferably 3.0 wt% or less, even more preferably 2.5 wt% or less, even more preferably 2.0 wt% or less, particularly preferably 1.5 wt% or less, and most preferably 1.0 wt% or less. The smaller the gel fraction of the polylactic acid resin foam molded article according to the embodiment of the present invention, the better, and the lower limit thereof is preferably 0 wt% or more. If the gel fraction of the polylactic acid resin foam molded article according to the embodiment of the present invention is too high, outside the above range, the effects of the present invention may not be fully achieved and the appearance may be poor. The method for measuring the gel fraction will be described later.

[0019] The polylactic acid resin foam molded article according to the embodiment of the present invention preferably has an expansion ratio of 2 to 20 times, more preferably 3 to 15 times, even more preferably 4 to 12 times, and particularly preferably 4 to 10 times, in order to more effectively exhibit the effects of the present invention.

[0020] The polylactic acid resin foam molded article according to the embodiment of the present invention preferably has a thickness of 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 of the polylactic acid resin foam molded article is too large outside the above range, the appearance of the polylactic acid resin foam molded article may be impaired. If the thickness of the polylactic acid resin foam molded article is too small outside the above range, for example, the heat insulating properties of the polylactic acid resin foam molded article may be reduced. The method for measuring the thickness will be described later.

[0021] 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.

[0022] FIG. 1 is a schematic cross-sectional view of a polylactic acid resin foam molded body according to an embodiment of the present invention, in which the body is a molded body formed by drawing (typically, a shallow-draw molded body or a deep-draw molded body). In FIG. 1, polylactic acid resin foam molded body 1000 has a main body including a bottom 110 and a side wall 120. As shown in FIG. 1, polylactic acid resin foam molded body 1000 may have flanges 200 and ridges 300 that protrude outward from the upper ends of side wall 120. The cross-sectional shape of polylactic acid resin foam molded body 1000 is not limited to the shape shown in FIG. 1; for example, bottom 110 and side wall 120 may have a curved structure. Furthermore, the shapes of flanges 200 and ridges 300 are not limited to those shown in FIG. 1, and the positions of flanges 200 and ridges 300 are not limited to those shown in FIG. 1. In Figure 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.

[0023] The polylactic acid resin foam molded article according to an embodiment of the present invention preferably has an open cell ratio of 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 of the polylactic acid resin foam molded article is too high outside the above range, for example, the heat insulating properties of the polylactic acid resin foam molded article may be impaired. If the open cell ratio of the polylactic acid resin foam molded article is too low outside the above 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 article and correspondingly reducing the contact area with microorganisms, which may result in reduced biodegradability. The method for measuring the open cell ratio will be described later.

[0024] <<<Manufacturing of foamed polylactic acid resin molded products>>> The polylactic acid 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. Typically, the polylactic acid foam molded article according to the embodiment of the present invention can be produced by preheating a polylactic acid resin foam sheet and thermoforming it using a mold.

[0025] 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.

[0026] Preheating can be carried out so that the surface temperature of the polylactic acid resin foam sheet is preferably within the range of 100°C to 140°C, more preferably within the range of 105°C to 135°C, even more preferably within the range of 110°C to 130°C, and particularly preferably within the range of 115°C to 125°C.

[0027] Preheating can be performed by heating for any suitable time using a heating means set to any suitable 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 to 60 seconds, more preferably 1 to 30 seconds.

[0028] 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 appropriately providing 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 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 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 more than 5 seconds but not more than 15 seconds is particularly preferred.

[0029] 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.

[0030] 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, so as to be able to appropriately 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.

[0031] 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 properly provide a polylactic acid resin foam molded article according to an embodiment of the present invention.

[0032] 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.

[0033] <<Polylactic acid resin foam sheet>> The polylactic acid resin foam molded article according to the embodiment of the present invention is a polylactic acid resin foam molded article obtained by molding a polylactic acid resin foam sheet.

[0034] 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.

[0035] 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 1.6 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.

[0036] 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 ~450g / m 2 and particularly preferably 350 g / m 2 ~450g / 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.

[0037] 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.

[0038] The polylactic acid resin foam sheet according to a preferred embodiment 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 article can be appropriately adjusted. When the open cell ratio of the polylactic acid resin foam sheet is too high outside the above range, the effects of the present invention may not be exhibited. The method for measuring the open cell ratio will be described later.

[0039] 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.

[0040] The polylactic acid resin foam sheet according to a preferred embodiment has a weight-average molecular weight (Mw) of preferably 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.

[0041] 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.

[0042] 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 more effectively exhibited. The method for measuring the MFR will be described later.

[0043] 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. The smaller the gel fraction of the polylactic acid resin foam sheet, the better, and the lower limit is preferably 0% by weight or more. A high gel fraction in a polylactic acid resin foam sheet can deteriorate the sheet's appearance, so as long as the gel fraction is within the above range, the effects of the present invention can be more effectively achieved. The method for measuring the gel fraction will be described later.

[0044] <<<Manufacturing of polylactic acid resin foam sheets>>> 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.

[0045] 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.

[0046] "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.

[0047] Here, in this specification, "contains as a main component" means that the content ratio 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 trace amounts (e.g., less than 1% by weight) of impurities that have been unintentionally mixed in can be ignored.

[0048] 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 the 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 the main component is melt-kneaded with a foaming agent in an extruder and extrusion-foamed to produce a polylactic acid resin foam sheet.

[0049] <Embodiment A (Two-Step Method)> 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 and extrusion-foaming the mixture.

[0050] 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.

[0051] 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.

[0052] 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 a 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 a main component may actually be the proportion of the modified polylactic acid resin contained as a main component, as described above.

[0053] <1st process> In the first step, a polylactic acid resin composition containing a polylactic acid resin and a modifier is melt-kneaded in an extruder to produce a modified polylactic acid resin. The polylactic acid resin used as the raw material in the first step herein preferably refers to an unmodified polylactic acid resin.

[0054] 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.

[0055] The lactic acid constituting the polylactic acid resin may be either the L- or D-form, or both the L- and D-forms. 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.

[0056] 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.

[0057] Examples of aliphatic polyhydric alcohols 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.

[0058] 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.

[0059] 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.

[0060] In the polylactic acid resin, the content of structural portions derived from lactic acid (L- and D-forms) in the molecule 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.

[0061] At least a part of the polylactic acid resin used as a raw material may be recycled.

[0062] 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.

[0063] The modifier may be used in a single type or in a combination of two or more types. The amount of 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.

[0064] 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 undergoing 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.

[0065] Examples of the radical initiator include organic peroxides, azo compounds, and halogen molecules, with organic peroxides being preferred.

[0066] Examples of organic peroxides include peroxyesters, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, peroxyketals, and ketone peroxides.

[0067] 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.

[0068] Examples of hydroperoxides include permethane hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, and t-butyl hydroperoxide.

[0069] 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.

[0070] Examples of diacyl peroxides include dibenzoyl peroxide, di(4-methylbenzoyl) peroxide, and di(3-methylbenzoyl) peroxide.

[0071] Examples of peroxydicarbonates include di(2-ethylhexyl) peroxydicarbonate and diisopropyl peroxydicarbonate.

[0072] 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.

[0073] Examples of ketone peroxides include methyl ethyl ketone peroxide and acetylacetone peroxide.

[0074] 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.

[0075] In one preferred embodiment, the organic peroxide is at least one selected from the group consisting of peroxyesters and dialkyl peroxides, because it can suppress the problems associated with modification using organic peroxides, easily modify polylactic acid resin to a state suitable for foaming, and provide a polylactic acid resin foam molded article that can better demonstrate 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.

[0076] 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 that they can 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.

[0077] The organic peroxides described above may be liquid or solid (powder), but are preferably liquid from the viewpoints of uniform reactivity in the extruder, ease of handling, and the like.

[0078] The amount of organic peroxide used depends on its molecular weight, etc., but in order to further demonstrate 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 per 100 parts by weight of polylactic acid resin.

[0079] 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.

[0080] Examples of chain extenders include Joncryl (registered trademark) ADR 4368 (manufactured by BASF), Joncryl (registered trademark) ADR 4468 (manufactured by BASF), Cardura (registered trademark) E10 (manufactured by Shell), and long-chain acrylates described in EP Application No. 08166596.0.

[0081] 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, per 100 parts by weight of polylactic acid resin, in order to further demonstrate the effects of the present invention.

[0082] 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.

[0083] 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.

[0084] In the first step, a polylactic acid resin composition containing a polylactic acid resin and a modifier is melt-kneaded in an extruder.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] The rotation speed of the extruder can vary depending on the size of the extrusion, the discharge amount, etc., and any appropriate condition can be adopted as long as the effects of the present invention are not impaired. Such a rotation speed is preferably, for example, 20 rpm to 800 rpm.

[0090] 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.

[0091] 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 just before being charged in the subsequent second step.

[0092] Step 1 can be carried out using any appropriate apparatus as long as the effects of the present invention are not impaired. In order to further enhance the effects of the present invention, Step 1 can be carried out using, for example, a production apparatus such as that shown in FIG.

[0093] As shown in FIG. 2, in the first step, typically, polylactic acid resin as raw material fed into a hopper 11 is melt-kneaded by a twin-screw extruder 30, the strand-shaped kneaded material 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] <Second process> 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 to produce a polylactic acid resin foam sheet.

[0098] The foaming agent may be of one kind or two or more kinds.

[0099] 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.

[0100] The volatile blowing agent is preferably an organic compound whose boiling point is equal to or lower than the softening point of the polylactic acid resin and which is gaseous or liquid 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.

[0101] 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.

[0102] 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 modified polylactic acid resin.

[0103] In the second step, the extruder may contain any appropriate other 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.

[0104] 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.

[0105] In the second step, a cell-cell control agent may be contained in the extruder as another component. The cell-cell control agent may be one type or two or more types. Examples of the cell-cell control agent 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 the 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 the partial esters of higher fatty acids and alcohols include stearic acid monoglyceride and stearic acid diglyceride.

[0106] 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.

[0107] 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.

[0108] In the second step, the modified polylactic acid resin, the cell control agent, and other components, if necessary, may be mixed in advance using a mixer such as a tumbler, ribbon blender, V blender, Henschel mixer, or Redige mixer.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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 enhance the effects of the present invention, the second step can be carried out using, for example, a production apparatus as shown in FIG.

[0113] 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 blowing agent into the cylinder. Downstream of the first extruder 10a, an extruder (hereinafter also referred to as "second extruder 10b") is provided for melt-kneading a polylactic acid resin composition containing a modified polylactic acid resin and a foaming agent.

[0114] 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.

[0115] 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 that of the downstream extruder 10b is preferably 5 rpm to 200 rpm.

[0116] A polylactic acid resin foam sheet is obtained by the second step described above.

[0117] <Embodiment B (One-Step Method)> 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, and extrusion-foamed to produce a polylactic acid resin foam sheet.

[0118] 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 of unmodified polylactic acid resin contained as a main component, as described above.

[0119] For the polylactic acid resin, the explanation in the <First Step> of <Embodiment A> above can be directly applied.

[0120] At least a part of the polylactic acid resin used as a raw material may be recycled.

[0121] 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 ideally 0% by weight.

[0122] 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.

[0123] With regard to the type of foaming agent, the explanation in the <Second Step> of the above-mentioned <Embodiment A> can be directly applied.

[0124] 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.

[0125] 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.

[0126] In embodiment B, the extruder preferably contains a modifier as another component, which 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.

[0127] With regard to the modifier, the explanation in the <First Step> of the above-mentioned <Embodiment A> can be directly applied.

[0128] In embodiment B, a foaming aid may be contained as another component in the extruder. Regarding the foaming aid, the explanation in the second step of embodiment A above can be applied as is.

[0129] In embodiment B, a cell control agent may be contained as another component in the extruder. Regarding the cell control agent, the explanation in the second step of embodiment A above can be applied as is.

[0130] 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.

[0131] In embodiment B, the polylactic acid resin, the modifier, the cell control agent, and optionally other components may be premixed. Examples of such mixing methods include mixing methods using a mixer such as a tumbler, a ribbon blender, a V blender, a Henschel mixer, or a Redige mixer.

[0132] In embodiment B, the polylactic acid resin is melt-kneaded with a foaming agent in an extruder.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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, etc., in the twin-screw extruder 30 to prepare a polylactic acid resin composition that will be the raw material for the foamed sheet, and extrusion foaming is carried out through the circular die CD.

[0137] 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 that in the twin-screw extruder 30 is preferably set to 120°C to 300°C, more preferably 120°C to 250°C.

[0138] The rotation speed of the extruder can vary depending on the size of the extrusion, the discharge rate, etc., and any appropriate condition can 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.

[0139] According to the above-described embodiment B, a polylactic acid resin foam sheet is obtained. [Example]

[0140] 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.

[0141] <Measurement of the thickness of polylactic acid resin foam sheet> For the polylactic acid resin foam sheet (width: 650 mm) obtained in the manufacturing example, excluding 20 mm at both ends of the width direction (TD direction), 9 points were measured at equally spaced 8 intervals in the width direction, and the thickness was measured 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.

[0142] <Measurement of basis weight of polylactic acid resin foam sheet> Six 10 cm x 10 cm pieces were cut out at equal intervals in the width direction (TD) of the polylactic acid resin foam sheet obtained in the Production Example, excluding 25 mm from 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 as the 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) was decided. Basis weight (g / m 2 ) = (average weight of the sections (g) / (10(cm) x 10(cm))) x 10000(ccm 2 / m 2 )

[0143] <Measurement of foaming 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 calculating the apparent density (ρ1) of the polylactic acid resin foam sheet, calculating 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. [Density (apparent density) measurement method] Polylactic acid resin foam sheet, 100cm 3 The above samples were cut without changing the original cell structure, and the samples were conditioned for 16 hours in a JIS K7100:1999, 23 / 50, Class 2 environment. Thereafter, the dimensions and weight were measured, and the density (apparent density) was calculated using the following formula. Apparent density (kg / m 3 ) = sample weight (kg) / sample volume (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 of the polylactic acid resin foam sheet that had been made non-foamed by, for example, heat pressing, based on the Archimedes method (liquid weighing method in JIS-K8807:2012 "Methods for determining density and specific gravity of solids").

[0144] <Measurement of open cell ratio of polylactic acid resin foam sheet> From the polylactic acid resin foam sheet obtained in the Production Example, several sheet-like samples of 25 mm in length and 25 mm in width were cut out, and the cut samples were stacked without leaving any gaps to make a measurement sample of 20 mm in thickness. 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 sought. Next, using a dry automatic density meter "AccuPic II 1340-100cc" manufactured by Shimadzu Corporation, the volume (cm) of the measurement sample was measured under the following conditions. 3 The measurement conditions were as follows: Gas used: Nitrogen Container used: 35cc Filling pressure: 0.005 psig Pressure equilibrium end rate: 0.005 psig / min Repeat count: 1 time The open cell rate (%) was calculated using these determined values ​​and the following formula, and the average value for five test pieces was calculated. The measurement was carried out in a JIS K7100-1999, symbol 23 / 50, grade 2 environment after conditioning the measurement sample for 16 hours in the JIS K7100-1999, symbol 23 / 50, grade 2 environment. Open cell rate (%) = [(apparent volume - volume measured with dry automatic density meter) / apparent volume] x 100 (%)

[0145] <Measurement of MFR (Melt Mass Flow Rate) of Polylactic Acid Resin Foam Sheet> The MFR of the polylactic acid resin foam sheets 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 specified distance" as described in Method B of JIS K 7210:1999. The MFR was measured using a Melt Flow Index Tester (Automatic) 120-SAS (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. The measurement was performed three times, and the average value was used. The measurement conditions were as follows: Sample: 3g to 8g Preheat (1): 200 seconds Preheat (2): 30 seconds Test temperature: 190℃ Test load: 21.18N Piston travel distance (interval): 25mm

[0146] <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 the 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 (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 equipment used was a gel permeation chromatograph "HLC-8320GPC EcoSEC" (with built-in RI and UV detectors) (Tosoh Corporation). [GPC measurement conditions] Guard column: TSK guard column HXL-H (6.0 mm x 4.0 cm) (Tosoh Corporation) x 1 Measurement column: TSKgel GMHXL (7.8 mm I.D. x 30 cm) (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℃ Mobile phase: chloroform Reference pump mobile phase flow rate: 0.5 mL / min Mobile phase flow rate of sample pump: 1.0 mL / min Detector: RI detector Injection volume: 50μL Measurement time: 25 min Sampling pitch: 500 msec The standard polystyrene samples used for the calibration curve were "STANDARD SM-105" and "STANDARD SH-75" (both 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. The above-mentioned 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.

[0147] <Measurement of Gel Fraction in Polylactic Acid Resin Foam Sheets and Polylactic Acid Resin Foam Molded Products> The gel fraction (% by weight) of the polylactic acid resin foam sheet obtained in the Production Examples was measured by the following method. Approximately 0.5 g of sample was prepared, and its initial weight (m0 (g)) was precisely weighed. A 200-mesh wire mesh (wire diameter 0.05 mm) was also prepared to filter the solution containing the sample. The initial weight (M0 (g)) of this wire mesh was also precisely weighed. The weighed sample to be measured was placed in a 100 mL beaker. 50 mL of chloroform as a solvent and a stir bar were placed in the beaker, which was then covered with aluminum foil. The mixture was stirred with a stirrer for 2 hours to dissolve the resin 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 at 120°C for 2 hours in a constant-temperature dryer. The dried wire mesh was cooled in a desiccator. After cooling, the weight (M1 (g)) of the wire mesh to which the resin insoluble matter had adhered was precisely weighed, and the gel fraction was calculated using the following formula: Gel fraction (wt%) = (m1 (g) / m0 (g)) × 100 m0: initial weight of the sample m1: Weight of insoluble resin (M1-M0) M0: Initial weight of the wire mesh M1: Weight of wire mesh with insoluble resin attached (total weight of insoluble resin and wire mesh)

[0148] <Measurement of surface roughness Sa of polylactic acid resin foam molding> A 10mm x 10mm sample was cut from the surface of the bottom surface (corresponding to part 110 in Figure 1) of the polylactic acid resin foam molded article obtained in the Examples and Comparative Examples. This sample was attached to a sample stage with double-sided tape. A Keyence VK-X1000 laser microscope was used to capture 3D images in basic measurement mode. A 5x objective lens was used for capture. The surface roughness Sa (sometimes referred to as "arithmetic mean height") was determined using the included software, "Multifile Analysis Application."

[0149] <Measurement of the thickness of polylactic acid resin foam molding> For the polylactic acid resin foam molded articles obtained in the Examples and Comparative Examples, if the articles were point-symmetrical when viewed from above, the thickness from end to end of the cross section obtained by cutting along a plane passing through the center point and 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 from above, the thickness from end to end of the cross section obtained by cutting along a plane passing through the center point and a central axis forming a 90-degree angle with the planar direction was measured. Note that if there were flanges or protrusions, these were excluded.

[0150] <Measurement of the average cell diameter of polylactic acid resin foam molded products> The bottom surface (corresponding to the part 110 in FIG. 1) of the polylactic acid resin foam molded article obtained in the Examples and Comparative Examples was cut out perpendicular to the bottom surface along any direction A and direction B perpendicular to direction A. One of the cross sections to be observed was a cross section cut perpendicular to the bottom surface along direction A (hereinafter referred to as "cross section A"), and the other cross section to be observed was a cross section cut perpendicular to the bottom surface along direction B (hereinafter referred to as "cross section B"). The cross section was photographed at 20x magnification using a scanning electron microscope (SU1510, Hitachi High-Technologies Corporation). The microscope images were taken so that the desired magnification would be obtained when two images (a total of four images) were printed side by side on a single A4 sheet of 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) (Images A1 and A2) and two images of the B cross section (B direction x VD direction perpendicular to the B direction) (Images B1 and B2) were printed on A4 paper in the order of top left, top right, bottom left, and bottom right, as follows: Image A1, Image A2, Image B1, Image B2. Next, for each of images A1 and A2, three arbitrary straight lines 60 mm long parallel to the A direction and three arbitrary straight lines 60 mm long in the VD direction were drawn, and for each of images B1 and B2, three arbitrary straight lines 60 mm long parallel to the B direction and three arbitrary straight lines 60 mm long in the VD direction were drawn. Note that the arbitrary straight lines were drawn with care to avoid air bubbles touching only at their contact points, and if they did touch, these air bubbles were also counted. The number of bubbles present on all the above straight lines, D, was calculated as the arithmetic mean, which was used to calculate 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 this number of bubbles using the following formula. Average chord length t (μm) = 60000 / (number of bubbles x image magnification) (Average chord length in the A direction tA (μm) = 60,000 / (number of bubbles in the A direction × image magnification)) (Average chord length in B direction tB (μm) = 60,000 / (number of bubbles in B direction x image magnification)) (Average chord length in the VD direction tV (μm) = 60,000 / (number of bubbles in the VD direction × image magnification)) The image magnification was calculated by measuring the scale bar on the image to 1 / 100 mm using a Digimatic caliper (Mitutoyo Corporation) and using the following formula: Image magnification = Scale bar actual measurement value (mm) / Scale bar display value (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 B direction dT (μm) = tB (μm) / 0.616 Average bubble diameter in VD direction dV (μm) = tV (μm) / 0.616 Furthermore, the cube root of the product of these values ​​was taken as the average bubble diameter. Average bubble diameter d(μm)=(dA(μm)×dB(μm)×dV(μm)) 1 / 3

[0151] <Measurement of open cell ratio of polylactic acid resin foam molded body> A number of sheet-like samples measuring 25 mm long x 25 mm wide were cut out from the side wall (corresponding to the part 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 form 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 sought. If it is difficult to cut out multiple sheet samples of 25 mm length x 25 mm width from the side wall of the polylactic acid resin foam molded body (corresponding to the part 120 in Figure 1) to prepare a measurement sample with a thickness of approximately 20 mm as described above, a sample with 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 (JIS-K8807:2012 "Method for measuring density and specific gravity of solids"). 3 ) may be obtained. Next, using a dry automatic density meter "AccuPic II 1340-100cc" manufactured by Shimadzu Corporation, the volume (cm) of the measurement sample was measured under the following conditions. 3The measurement conditions were as follows: Gas used: Nitrogen Container used: 35cc Filling pressure: 0.005 psig Pressure equilibrium end rate: 0.005 psig / min Repeat count: 1 time If the open cell ratio is too high, the equilibrium pressure is not reached within the adjustment time (1000 seconds), making measurement impossible. In this case, measurement was deemed impossible. The open cell rate (%) was calculated using these determined values ​​and the following formula, and the average value for five test pieces was calculated. The measurement was carried out in a JIS K7100-1999, symbol 23 / 50, grade 2 environment after conditioning the measurement sample for 16 hours in the JIS K7100-1999, symbol 23 / 50, grade 2 environment. Open cell rate (%) = [(apparent volume - volume measured with dry automatic density meter) / apparent volume] x 100 (%)

[0152] <Evaluation of the appearance beauty of polylactic acid resin foam moldings> The surfaces of the polylactic acid resin foam molded articles obtained in the examples and comparative examples were visually observed, and the appearance was evaluated according to the following criteria. ◯: No irregularities or cracks in the cells were observed on the surface of the polylactic acid resin foam molded article, and the appearance was good. ×: A large number of irregularities and cracks in the cells were observed on the surface of the polylactic acid resin foam molded article, and the appearance was very poor.

[0153] [Manufacturing Example 1] Polylactic acid resin (manufactured by Anhui Fengyuan Fort Lai Lactic Acid Co., Ltd., product name "FY602", MFR = 16.0 g / 10 min, D-isomer ratio = 2.0 ± 0.5 mol%, melting point = 164.3 °C, density = 1240 kg / m 3 ): 100 parts by weight and t-butylperoxyisopropyl monocarbonate (manufactured by Kayaku Nouryon Co., Ltd., "Trigonox BPIC-75", 1-minute half-life temperature T1 = 158.8°C): 0.5 parts by weight were stirred and mixed in a ribbon blender to obtain a mixture. The resulting mixture was fed into a twin-screw extruder (L / D=31.5) with a diameter of 57 mm. The temperature setting for the feed section was 170°C, and the temperature thereafter was 200°C. The mixture was melt-kneaded in the twin-screw extruder at a rotation speed of 100 rpm, and the kneaded material was extruded in the form of 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. Next, the extruded strand-like kneaded product was passed through a 2 m long cooling water tank containing water at 30°C to cool it. The cooled strands were cut into pellets 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 above mixture was supplied to the first extruder with a diameter of φ50 mm through a hopper and heated to melt at 220°C. Thereafter, 1.2 parts by weight of butane (isobutane / normal butane=35% by weight / 65% by weight) as a foaming agent was pressure-fed into the first extruder and melt-kneaded together with the above mixture to form 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, after which it was extruded and foamed through a circular die with a diameter of 70 mm at a discharge rate of 30 kg / hour to obtain a cylindrical foam. The obtained cylindrical foam was placed on a φ206 mm mandrel whose inside was cooled with water at about 20°C, and its outer surface was cooled and molded by blowing air onto it using an air ring larger than the diameter of the mandrel.Then, it was cut at one point on the circumference using 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.

[0154] [Manufacturing Example 2] A strip-shaped polylactic acid resin foam sheet (2) was produced in the same manner as in Production Example 1, except that the amount of the cell regulator (manufactured by Matsumura Sangyo Co., Ltd., "Crown Talc") was changed to 3.0 parts by weight. The physical properties of the resulting polylactic acid resin foam sheet (2) are shown in Table 1.

[0155] [Manufacturing Example 3] A strip-shaped polylactic acid resin foam sheet (3) was produced in the same manner as in Production Example 1, except that the amount of t-butylperoxyisopropyl monocarbonate was changed to 0.8 parts by weight and the amount of the cell regulator ("Crown Talc" manufactured by Matsumura Sangyo Co., Ltd.) was changed to 0.3 parts by weight. The physical properties of the resulting polylactic acid resin foam sheet (3) are shown in Table 1.

[0156] [Example 1] A flat square foam sheet (test piece) measuring 340 mm long x 340 mm wide was cut out from the polylactic acid resin foam sheet (1) obtained in Production Example 1. A small single-shot molding machine (manufactured by Wakisaka Engineering Co., Ltd., product name "FVS-500 type") was used, and the heater temperature of the heating furnace was set to 400°C. Next, the test piece was introduced into the heating furnace of a 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 (foamed container) (1) with an opening at the top. The time the foamed sheet (test piece) was held in the mold (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.

[0157] [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 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 article (2) are shown in Table 2.

[0158] [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 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. Table 2 shows the physical properties of the obtained polylactic acid resin foam molded article (C1).

[0159] [Table 1]

[0160] [Table 2] [Industrial Applicability]

[0161] The polylactic acid resin foam obtained by the production method of the present invention has a beautiful appearance and can be suitably used as a food packaging container. The polylactic acid resin foam molded article according to the embodiment of the present invention can also be used as various packaging materials, various cushioning materials, etc. [Explanation of symbols]

[0162] 1 foam sheet 3 strand die 4 Pelletizer 5 Drying equipment 6 Cooling device 10 Tandem Extruder 10a First extruder 10b Second extruder 11 Hopper 12 Gas inlet 21 Laura 22 Winding roller 30 Twin-screw extruder 1000 Polylactic acid resin foam molding 110 Bottom 120 Side wall 200 flange 300 Projection part L Thickness

Claims

1. A polylactic acid resin foam molded article obtained by molding a polylactic acid resin foam sheet, The surface roughness Sa is 35 μm or less. Polylactic acid resin foam molding.

2. 2. The polylactic acid resin foam molded article according to claim 1, wherein the average cell diameter is 700 μm or less.

3. 2. The polylactic acid resin foam molded article according to claim 1, which has a gel fraction of 4.5% by weight or less.

4. 2. The polylactic acid resin foam molded article according to claim 1, having an expansion ratio of 2 to 20 times.

5. 2. The polylactic acid resin foam molded article according to claim 1, which is a food packaging container.

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