Polylactic acid resin foam sheet and method for producing sheet molded body

Abstract

Provided is a polylactic acid resin foam sheet which is suitable for efficiently producing a sheet molded body having excellent heat resistance, and which improves the efficiency of producing a sheet molded body having excellent heat resistance. The present invention provides a polylactic acid resin foam sheet comprising a polylactic acid resin composition containing a polylactic acid resin having crystallinity of 30% or less and a crystallization temperature of 105 DEG C or less as observed in heat flow differential scanning calorimetry at a heating rate of 5 DEG C / min, the polylactic acid resin foam sheet comprising a polylactic acid resin composition containing a polylactic acid resin having crystallinity.

Description

[0001] Cross-reference to related applications

[0002] The present invention claims the benefit of Japanese Patent Application No. 2023-052796, which is hereby incorporated by reference into the description of the present invention. Technical Field

[0003] The present invention relates to a polylactic acid resin foam sheet and a method for producing a sheet molded body using the polylactic acid resin foam sheet. Background Art

[0004] All along, the foamed article that is made of the resin combination of foamed state has been widely used.This foamed article is not only lightweight but also excellent in strength, and has excellent cushioning property and thermal insulation.As this foamed article, known foam sheet, foamed microbead and the molded body etc. that have used them to form.In addition, about resin foam sheet, known extrusion foam sheet that obtains by following method (extrusion foaming method), described method is: in forcing machine, the resin combination that will be used for foaming and whipping agent are carried out melt mixing, the melt mixing obtained is extruded into sheet and is made to foam from the sheet die (flat die, round die) that is installed on the forcing machine front end.

[0005] These extruded foam sheets can be used directly as cushioning sheets or formed into bags for packaging. They are also widely used as blanks for sheet-molded products such as food trays and cups. These sheet-molded products are produced through thermoforming methods such as matching molds and vacuum / compression molding.

[0006] However, in recent years, there has been a growing demand for solutions to the problem of landscape damage caused by illegally discarded packaging materials in mountainous areas, rivers, and coastal areas. Against this backdrop, research has been conducted on technologies for producing molded articles using polylactic acid resin, which is biodegradable in the natural environment, and on technologies for expanding the use of polylactic acid resin foam sheets into various applications.

[0007] Most existing polylactic acid resin foam sheets use easily foamed non-crystalline polylactic acid resin as a raw material. However, such polylactic acid resin foam sheets and sheet molded bodies made from such polylactic acid resin foam sheets are difficult to exert sufficiently good heat resistance. Due to this situation, the opportunities for utilizing crystalline polylactic acid resins have increased. Consequently, the opportunities for manufacturing polylactic acid resin foam sheets from resin compositions containing crystalline polylactic acid resins have also increased. In addition, for such polylactic acid resin foam sheets, those that have not been crystallized are easy to thermoform. Therefore, when manufacturing sheet molded bodies from polylactic acid resin foam sheets using crystalline polylactic acid resins, polylactic acid resin foam sheets produced in a state where crystallization is suppressed are used. In addition, when thermoforming is performed, the polylactic acid resin foam sheet is heated for a certain period of time to increase the degree of crystallinity (for example, refer to paragraphs 0059 to 0061 of the following patent document 1).

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent No. 5517280 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] When a polylactic acid resin foam sheet containing crystalline polylactic acid resin is used to manufacture a sheet molded body, a process called "heat setting" is provided, that is, the sheet is kept in a heated mold for a certain period of time during heat forming to increase the crystallinity. If a polylactic acid resin foam sheet with a sufficiently low crystallinity is used in order to exert the moldability, heat setting will take time, which will reduce the manufacturing efficiency of the sheet molded body. In view of the above problems, the purpose of the present invention is to provide a polylactic acid resin foam sheet suitable for efficiently manufacturing a sheet molded body with excellent heat resistance, thereby improving the manufacturing efficiency of the sheet molded body with excellent heat resistance.

[0013] Solutions for solving problems

[0014] In order to solve the above-mentioned problems, the present invention provides a polylactic acid resin foam sheet comprising a polylactic acid resin composition containing a crystalline polylactic acid resin.

[0015] The crystallinity of the polylactic acid resin foam sheet is less than 30%,

[0016] The crystallization temperature observed by heat flow differential scanning calorimetry analysis at a heating rate of 5°C / min was 105°C or lower.

[0017] In order to solve the above-mentioned problems, the present invention provides a method for producing a sheet molded body, wherein the method comprises thermoforming a resin foam sheet to produce the sheet molded body.

[0018] The resin foam sheet is a polylactic acid resin foam sheet, which is composed of a polylactic acid resin composition containing a crystalline polylactic acid resin.

[0019] The crystallinity of the resin foam sheet is 30% or less.

[0020] The crystallization temperature observed in heat flow differential scanning calorimetry analysis at a heating rate of 5°C / min was 105°C or lower.

[0021] The following steps are performed in the method for producing the sheet molded body:

[0022] a primary heating step of heating the polylactic acid resin foam sheet; and

[0023] In the secondary heating step, the polylactic acid resin foam sheet subjected to the primary heating step is sandwiched between heated molding dies to produce a sheet molded body, and the crystallinity of the sheet molded body is increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic front view showing an example of a sheet production apparatus for producing a polylactic acid resin foam sheet.

[0025] Figure 2 This is a schematic diagram showing a method for determining the half-crystallization time from a DSC curve.

[0026] Figure 3 It is a schematic perspective view showing a method for measuring the gel fraction. DETAILED DESCRIPTION

[0027] Hereinafter, the embodiments of the present invention will be described. Figure 1 The embodiment of the present invention will be described using the case of an extruded foam sheet obtained by the apparatus shown in FIG. The polylactic acid resin foam sheet of this embodiment can be suitably used to produce a sheet molded article by thermoforming. Examples of such thermoforming methods include vacuum forming, pressure forming, vacuum / pressure forming, matched mold forming, and press forming.

[0028] As the polylactic acid resin foam sheet of this embodiment, for example, Figure 1 The extruded foam sheet is produced using the sheet production apparatus 100 and the like shown in the example. Figure 1The sheet production apparatus 100 illustrated in the figure comprises a tandem extruder 10 and a circular die CD for discharging a polylactic acid resin composition melt-kneaded in the tandem extruder 10 in a cylindrical shape. The production apparatus further comprises a cooling device CL for air-cooling the polylactic acid resin foam sheet extruded in a cylindrical shape from the circular die CD, and a mandrel MD for expanding the diameter of the cylindrical polylactic acid resin foam sheet to form a cylindrical shape of a predetermined size.

[0029] The sheet manufacturing apparatus 100 includes: a cutting device for cutting the polylactic acid resin foam sheet 1 formed into a cylindrical shape having a predetermined diameter by the mandrel MD into two strip-shaped sheets; and a winding roller 22 for winding the cut polylactic acid resin foam sheet 1 after passing through a plurality of rollers 21 .

[0030] The extruder on the upstream side of the aforementioned tandem extruder 10 (hereinafter also referred to as the "first extruder 10a") is provided with: a hopper 11 for inputting a polylactic acid resin composition (hereinafter also referred to as the "resin composition") which is the raw material of the polylactic acid resin foam sheet; and a gas inlet part 12 for supplying a foaming agent such as hydrocarbons into the barrel.

[0031] In the sheet manufacturing device 100 of the present embodiment, an extruder (hereinafter also referred to as "second extruder 10b") is further provided on the downstream side of the first extruder 10a. In the second extruder 10b, the resin composition containing the foaming agent is melt-kneaded. The polylactic acid resin contained in the polylactic acid resin foam sheet has crystallinity. The polylactic acid resin is preferably modified by cross-linking or the like to exert excellent melt strength (melt tension). The modified polylactic acid resin (hereinafter also referred to as "modified polylactic acid resin") can be introduced from the hopper 11 with the modified material being implemented in advance. When manufacturing the polylactic acid resin foam sheet, the unmodified polylactic acid resin and the cross-linking agent can also be introduced into the extruder, and the polylactic acid resin can be modified in the extruder.

[0032] If the polylactic acid resin foam sheet is not cooled quickly, it will crystallize. The polylactic acid resin foam sheet of this embodiment is produced by using a cooling device CL and a mandrel MD to suppress the crystallization of the polylactic acid resin contained therein. The polylactic acid resin foam sheet containing fully crystallized polylactic acid resin is not easily deformed even when heated. Such a polylactic acid resin foam sheet is not easily deformed to the shape of the molding mold during thermoforming. In addition, such a polylactic acid resin foam sheet is stretched by a strong force during thermoforming. The sheet molded body obtained in this way is likely to shrink over time or when heat is applied. On the other hand, the polylactic acid resin foam sheet of this embodiment is produced in a manner such that the crystallinity is 30% or less. When the crystallinity of the polylactic acid resin foam sheet is low, the moldability when producing the sheet molded body becomes good. Therefore, the crystallinity of the polylactic acid resin foam sheet can be 25% or less, or 20% or less. By setting the crystallinity to 30% or less, it is possible to suppress excessive tensile load in the forming mold during thermoforming, and to suppress shrinkage of the obtained sheet molded article over time.

[0033] A polylactic acid resin foam sheet having a certain degree of crystallinity or higher is advantageous in imparting sufficient crystallinity for the sheet molded body to exhibit excellent heat resistance. The polylactic acid resin foam sheet may have a degree of crystallinity of 5% or higher, or 10% or higher.

[0034] The polylactic acid resin foam sheet is preferably subjected to a heat setting process such as heating for a certain period of time to develop a higher degree of crystallinity than before heating. The polylactic acid resin foam sheet is preferably formed in a manner that can increase the degree of crystallinity by more than 5%, and more preferably formed in a manner that can increase the degree of crystallinity by more than 10%. The degree of crystallinity that the polylactic acid resin foam sheet can achieve is preferably more than 25%, more preferably more than 30%. The degree of crystallinity that the polylactic acid resin foam sheet can achieve is generally less than 60%. The degree of crystallinity that the polylactic acid resin foam sheet can achieve can be less than 50%.

[0035] The resin composition constituting the polylactic acid resin foam sheet of this embodiment preferably has a half-crystallization time of 30 minutes or less at 80°C. More preferably, the half-crystallization time is 25 minutes or less. Since the resin composition constituting the polylactic acid resin foam sheet has a half-crystallization time of 30 minutes or less, the crystallinity of the sheet can be increased in a shorter molding time during thermoforming, thereby imparting excellent heat resistance to the sheet.

[0036] (half crystallization time)

[0037] The crystallization half time can be measured as follows using a heat flow differential scanning calorimeter (heat flow DSC).

[0038] The sampling method and temperature conditions were as follows.

[0039] After filling an aluminum measuring container (manufactured by Hitachi High-Tech Corporation, product number: GAA-0065) with 5.5±0.5 mg of the sample without any gaps at the bottom, the container was covered with an aluminum lid (manufactured by Hitachi High-Tech Corporation, product number: GAA-0064). Then, using a differential scanning calorimeter (manufactured by Hitachi High-Tech Science Corporation, "NEXTADSC600"), the temperature was maintained at 30°C for 2 minutes at a nitrogen flow rate of 20 mL / min, and then the temperature was increased from 30°C to 210°C (first temperature increase) at the maximum capacity of the device and maintained for 10 minutes.

[0040] Then, the sample was taken out from the measuring device, left to stand at room temperature for 10 minutes, and then returned to the measuring device at 30°C.

[0041] Second heating: After heating to 70°C at the maximum capacity of the device, heat to 80°C at a rate of 20°C / min and maintain for 30 minutes.

[0042] Alumina was used as the standard substance in this case.

[0043] (DSC curve preparation method)

[0044] The heat flow was read every 0.2 seconds from the start of the second heating to the end of the holding time at the heating end temperature, and a DSC curve was prepared by plotting the time (minutes) on the horizontal axis and the heat flow (mW) on the vertical axis (see Figure 2 ). Figure 2 In the equation (5), the time from the start of measurement to the top of the exothermic peak (point x) is defined as the half-crystallization time.

[0045] The resin composition comprises a crystalline polylactic acid resin as a main component. The polylactic acid resin refers to a polymer containing 50 mol% or more of lactic acid component units. Examples of such polymers include:

[0046] (1) Polymers of lactic acid only,

[0047] (2) Copolymers of lactic acid and other aliphatic hydroxycarboxylic acids,

[0048] (3) Copolymers of lactic acid, aliphatic polyols and aliphatic polycarboxylic acids,

[0049] (4) Copolymers of lactic acid and aliphatic polycarboxylic acids,

[0050] (5) Copolymers of lactic acid and aliphatic polyols,

[0051] (6) A mixture or the like comprising any combination of the above (1) to (5).

[0052] Specific examples of the lactic acid include L-lactic acid, D-lactic acid, DL-lactic acid, or cyclic dimers thereof, namely, L-lactide, D-lactide, DL-lactide, or mixtures thereof.

[0053] Examples of the aliphatic polycarboxylic acid constituting the copolymer 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 be an acid anhydride.

[0054] Examples of the aliphatic polyol 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.

[0055] Examples of the aliphatic hydroxycarboxylic acid other than lactic acid constituting the copolymer include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, and 6-hydroxyhexanoic acid.

[0056] The polylactic acid resin contained in the resin composition may be only a crystalline polylactic acid resin, or may contain a crystalline polylactic acid resin and an amorphous polylactic acid resin.

[0057] The polylactic acid resin used may have a heat endotherm (ΔHendo) of 10 J / g or greater as determined by heat flow differential scanning calorimetry. The heat endotherm (ΔHendo) of the polylactic acid resin is preferably 20 J / g or greater, more preferably 30 J / g or greater. The upper limit of the heat endotherm (ΔHendo) of the polylactic acid resin is not particularly limited, but is generally 60 J / g.

[0058] In this embodiment, the crystalline polylactic acid resin refers to a crystalline polylactic acid resin having an endothermic value (ΔHendo) exceeding 2 J / g as determined by heat flow differential scanning calorimetry. The endothermic value (ΔHendo) of the crystalline polylactic acid resin is typically 20 to 65 J / g.

[0059] The polylactic acid resin contained in the resin composition preferably comprises a copolymer of the D-isomer and the L-isomer of lactic acid. The D-isomer ratio in this copolymer is preferably 0.5 mol% to 5 mol%. The melting point of the polylactic acid resin comprising this copolymer is preferably 130°C to 170°C. Such a polylactic acid resin exhibits excellent foaming properties, moldability, and heat resistance.

[0060] The polylactic acid resin foam sheet in this embodiment is preferably confirmed to have a crystallization temperature of 105°C or less in a heat flow differential scanning calorimetry measurement at a heating rate of 5°C / min. The crystallization temperature of the polylactic acid resin foam sheet is more preferably below 100°C, and further preferably below 98°C. Since the polylactic acid resin foam sheet has a crystallization temperature below a specified temperature, crystallization proceeds rapidly during thermoforming. Such a polylactic acid resin foam sheet has excellent moldability. In addition, in order to prevent an excessive increase in the degree of crystallization during preheating before thermoforming, the crystallization temperature is preferably visible in a range of 70°C or more, more preferably in a range of 75°C or more, and further preferably in a range of 80°C or more.

[0061] (melting point, crystallization temperature, crystallinity)

[0062] The melting point, crystallization temperature, and crystallinity of the polylactic acid resin, the polylactic acid resin foam sheet, and the sheet molded article can be determined as follows.

[0063] The melting point and crystallization temperature of the polylactic acid resin, the polylactic acid resin foam sheet, and the sheet molded article can be measured as follows using a heat-flux differential scanning calorimeter (heat-flux DSC).

[0064] The measurement was performed by the method described in JIS K7122: 1987, JIS K7122: 2012 “Methods for measuring transition heat of plastics” and JIS K7121: 1987, 2012 “Methods for measuring transition temperature of plastics”.

[0065] The sampling method and temperature conditions can be carried out as follows.

[0066] After filling an aluminum measuring container (manufactured by Hitachi High-Tech Corporation, product number: GAA-0065) with 5.5±0.5 mg of the sample without any gaps at the bottom, the container was covered with an aluminum lid (manufactured by Hitachi High-Tech Corporation, product number: GAA-0064). Then, using a differential scanning calorimeter (manufactured by Hitachi High-Tech Science Corporation, "NEXTADSC600"), the sample was heated / cooled according to the following steps at a nitrogen flow rate of 20 mL / min to obtain a DSC curve.

[0067] (Step 1) The temperature was raised from 30°C to 210°C (first temperature increase) and then maintained for 10 minutes.

[0068] (Step 2) Take out from the measuring device, let it stand at room temperature for 10 minutes, and then return it to the measuring device at 30°C (quench cooling).

[0069] (Step 3) Raise the temperature from 30°C to 210°C (second temperature increase).

[0070] It should be noted that all heating was performed at a rate of 5°C / min.

[0071] Alumina was used as a standard substance.

[0072] (Melting Point)

[0073] Using the analysis software attached to the apparatus, the peak top temperature of the melting peak observed during the second temperature increase was read as the melting temperature (melting point).

[0074] (Crystallization temperature)

[0075] The crystallization temperature is the peak top temperature of the exothermic peak observed during the second heating process as the (cold) crystallization temperature. It should be noted that when multiple exothermic peaks appear, the peak on the lower temperature side is read as the temperature.

[0076] (Crystallinity)

[0077] The degree of crystallinity is determined as follows: the difference between the endothermic heat (melting heat (J / g)) obtained from the area of the endothermic peak appearing during the crystalline melting observed in the first heating process and the crystallization heat (J / g) obtained from the area of the crystallization peak is divided by the theoretical melting heat (93 J / g) of complete crystallization of polylactic acid.

[0078] The heat of fusion and the heat of crystallization were calculated using the analysis software included with the device.

[0079] Specifically, the heat of fusion is calculated from the portion enclosed by a straight line connecting the point where the DSC curve deviates from the low-temperature baseline and the point where the DSC curve returns to the high-temperature baseline.

[0080] Heat of crystallization: The area of the portion enclosed by a straight line is calculated by connecting the point where the DSC curve deviates from the low-temperature baseline and the point where the DSC curve returns to the high-temperature baseline.

[0081] In addition, the crystallinity was calculated by the following formula.

[0082] Crystallinity (%) = [Heat of fusion (J / g) - Heat of crystallization (J / g)] / 93 (J / g) × 100 (%)

[0083] The resin composition may contain the polylactic acid resin at a ratio of 100% by mass, or may be a mixture of the polylactic acid resin and a thermoplastic resin other than the polylactic acid resin. The mixture may contain the polylactic acid resin at a ratio of 50% to less than 100% by mass, and the thermoplastic resin at a ratio of more than 0% to less than 50% by mass. In other words, the resin composition may contain a thermoplastic resin other than the polylactic acid resin at a ratio of 50% to less than 50% by mass.

[0084] When the resin composition contains a thermoplastic resin other than the polylactic acid resin, the proportion of the polylactic acid resin is preferably 60% by mass or more, more preferably 70% by mass or more. It should be noted that, as thermoplastic resins other than the polylactic acid resin, polyethylene resins, polypropylene resins, polystyrene resins, polyester resins, etc. can be listed. From the viewpoint of improving the impact resistance of the sheet molded body made of the polylactic acid resin foam sheet, the resin composition in this embodiment preferably includes a thermoplastic elastomer and an aliphatic polyester resin.

[0085] Examples of the thermoplastic elastomer include olefin elastomers, styrene elastomers, propionic acid elastomers, and ester elastomers. Of these, propionic acid elastomers, styrene elastomers, and ester elastomers are preferred due to their good compatibility with polylactic acid resins. Styrene elastomers are preferably acid-modified. Specifically, commercially available products such as METABLEN W-600A manufactured by MITSUBISHI RAYON CO., LTD., Tuftec MP10 manufactured by Asahi Kasei Corporation, and NOFALLOY TZ810 manufactured by NOF Corporation can be suitably used.

[0086] As the aforementioned aliphatic polyester resin, it can be a hydroxy acid polycondensate, a ring-opening polymer of lactone, and a polycondensate of a polyol component and a polycarboxylic acid component. As the hydroxy acid polycondensate, for example, polylactic acid, a polycondensate of hydroxybutyric acid, etc. can be listed. As the ring-opening polymer of lactone, for example, polycaprolactone, polypropiolactone, etc. can be listed. As the polycondensate of a polyol component and a polycarboxylic acid component, for example, polyethylene succinate, polybutylene succinate, polybutylene adipate, polybutylene succinate adipate, polybutylene adipate terephthalate, etc. can be listed. The aforementioned aliphatic polyester resin is preferably any of polybutylene succinate (PBS) or polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT) that has good compatibility with polylactic acid resin.

[0087] The polylactic acid resin is preferably suitable for extrusion foaming. It is known that in extrusion foaming, a foam sheet with a high expansion ratio can generally be obtained by using a resin with high melt strength. Generally, the melt strength of crystalline resins is relatively low. Therefore, when extrusion foaming is performed on a crystalline resin, the crystalline resin is crosslinked by chemical crosslinking, electron beam crosslinking, or the like to increase the melt strength of the resin composition. In addition, instead of crosslinking the crystalline resin, a method of increasing the melt strength of the resin composition by mixing a high molecular weight component is known.

[0088] The polylactic acid resin of the present embodiment preferably shows a specific characteristic value in the measurement of melt strength at 190°C. For example, the polylactic acid resin preferably shows a melt strength of 5 cN or more and 80 cN or less in the measurement at 190°C. The aforementioned melt strength of the polylactic acid resin may be 75 cN or less, 70 cN or less, or 65 cN or less. The aforementioned melt strength of the polylactic acid resin may be 8 cN or more, or 10 cN or more. By having the preferred melt strength as described above, the polylactic acid resin can suppress the occurrence of bubble breakage when the resin composition is foamed. Even if the polylactic acid resin foam sheet containing such a polylactic acid resin is foamed at a high foaming ratio, the continuous bubble rate is not likely to become high. Such a polylactic acid resin can be advantageous in producing a polylactic acid resin foam sheet with a good appearance.

[0089] In the present embodiment, the resin composition containing the polylactic acid resin described above also preferably exhibits the above-described melt strength.

[0090] The melt flow rate (MFR: temperature 190°C, nominal load 2.16 kg) of the polylactic acid resin of this embodiment is, for example, 0.1 g / 10 min or more and 15 g / 10 min or less. The melt flow rate of the resin composition may be 10 g / 10 min or less, 5 g / 10 min or less, 4 g / 10 min or less, or 3 g / 10 min or less.

[0091] In the present embodiment, the resin composition containing the polylactic acid resin described above also preferably exhibits the above-described melt flow rate.

[0092] The melt strength and melt flow rate of the polylactic acid resin can be measured by the following method.

[0093] Melt Strength

[0094] The melt strength can be measured using a capillary rheometer “Capillograph 1D” (furnace special specification) manufactured by Toyo Seiki Co., Ltd. or “Rheotens 71.97” manufactured by Goettfert.

[0095] The melt strength was measured under the following conditions.

[0096] The sample was vacuum-dried at 90°C for 4 hours or more in advance, placed in a nylon plastic bag for vacuum packaging, and vacuum-packed. The sample was then stored in a desiccator until the measurement.

[0097] Set the Rheotens 71.97 so that the distance from the die exit of the Capillograph 1D to the measuring section is 80 mm. (Note: If interference occurs and the Rheotens cannot be brought close to 80 mm while maintaining the original position, measures should be taken to avoid interference and set the Rheotens to the specified position.)

[0098] First, a sample was filled into a cylinder heated to a test temperature of 190° C., and then preheated for 5 minutes.

[0099] The measurement time was set to not more than 10 minutes including the preheating time after the cylinder was filled.

[0100] Next, a piston is inserted from the upper part of the cylinder to extrude the molten resin into a ribbon shape.

[0101] At this point, the piston descent speed (20 mm / min) was kept constant and the extruded ribbon was passed through the wheels of the Rheotens.

[0102] Then, the pulling speed was gradually increased and the melt strength of the sample was measured.

[0103] The melt strength of the sample was determined by averaging the maximum and minimum tension values immediately before the ribbon broke. If there was only one maximum point in the tension graph, that maximum value was considered the melt strength. Furthermore, when the ribbon thinned and the winding entered an idle state, that point was considered the breaking point, and the average of the maximum and minimum tension values immediately preceding it was used as the melt strength of the sample.

[0104] (Capillograph 1D measurement conditions)

[0105] Die: diameter 2.095mm, length 8mm, inflow angle 90 degrees (tapered)

[0106] Barrel diameter: 9.55mm

[0107] Piston speed: 20 mm / min

[0108] Measurement temperature: 190°C

[0109] (Rheotens measurement conditions)

[0110] Wheel spacing: upper 0.7mm, lower 1.0mm

[0111] Acceleration: 10 mm / s 2

[0112] Traction speed: initial velocity 6.92mm / s

[0113] Melt Flow Rate (MFR)

[0114] The melt flow rate (MFR) of the polylactic acid resin or the resin composition can be measured using a "Semi-automatic Melt Flow Indexer 2A" manufactured by Toyo Seiki Seisaku-sho, Ltd.

[0115] MFR is measured in accordance with JIS K7210-1:2014 "Plastics - Determination of Melt Flow Rate (MFR) and Melt Volume-Flow Rate (MVR) of Thermoplastics - Part 1," Method B, which states that the time it takes for a piston to move a specified distance is measured under the following measurement conditions.

[0116] The measurement sample was vacuum-dried at 90° C. for 4 hours or longer, placed in a nylon plastic bag for vacuum packaging, and vacuum-packed. The sample was then stored in a desiccator until immediately before measurement.

[0117] (Measurement conditions)

[0118] Sample: 3-8g

[0119] Warm-up time: 200 seconds

[0120] Load holding time: 30 seconds

[0121] Test temperature: 190℃

[0122] Test load: 21.18N

[0123] Piston movement distance (interval): 4mm

[0124] Number of trials: 3 times

[0125] The arithmetic mean of the measured values obtained in each test was defined as the MFR (g / 10 minutes) value.

[0126] The above-mentioned hot melt properties can be exhibited by giving the polylactic acid resin a bulky molecular structure. The mass average molecular weight (Mw) of the polylactic acid resin is preferably 100,000 to 1,000,000. The mass average molecular weight (Mw) of the polylactic acid resin is more preferably 150,000 or more, and even more preferably 200,000 or more. The mass average molecular weight (Mw) of the polylactic acid resin is more preferably 800,000 or less, even more preferably 600,000 or less, and particularly preferably 400,000 or less.

[0127] The ratio (Mw / Mn) of the mass average molecular weight (Mw) to the number average molecular weight (Mn) of the polylactic acid resin of this embodiment is preferably 2.5 or greater, more preferably 2.7 or greater, and particularly preferably 2.9 or greater. The ratio (Mw / Mn) of the polylactic acid resin is preferably 4.5 or less, more preferably 4.0 or less, and particularly preferably 3.5 or less.

[0128] The number average molecular weight (Mn) and mass average molecular weight (Mw) of the polylactic acid resin can be measured using gel permeation chromatography (GPC) and can be obtained as values converted to polystyrene (PS). Specifically, the average molecular weight of the polylactic acid resin can be obtained by the following procedure.

[0129] (Method for determining average molecular weight)

[0130] A 20 mg sample was dissolved in 6 mL of chloroform (immersion time: 6 ± 1.0 hours), filtered using a non-aqueous 0.45 μm syringe filter manufactured by Shimadzu GLC Ltd., and then measured using a chromatograph under the following measurement conditions. The mass average molecular weight of the sample was determined based on a pre-prepared standard polystyrene calibration curve.

[0131] <Device used>

[0132] Tosoh Corporation's "HLC-8320GPC EcoSEC" gel permeation chromatograph (with built-in RI detector and UV detector)

[0133] <GPC measurement conditions>

[0134] Sample side

[0135] Guard column = TSK guardcolumn HXL-H (6.0 mm x 4.0 cm) manufactured by Tosoh Corporation x 1

[0136] Measurement column = TSKgel GMHXL (7.8 mm I.D. × 30 cm) manufactured by Tosoh Corporation × 2 connected in series

[0137] Reference side = resistance tube (inner diameter 0.1mm×2m)×2 in series

[0138] Column temperature = 40°C

[0139] Mobile phase = chloroform

[0140] Mobile phase flow rate:

[0141] Reference side pump = 0.5 mL / min

[0142] Sample side pump = 1.0 mL / min

[0143] Detector = RI detector

[0144] Injection volume = 50 μL

[0145] Measurement time = 25 minutes

[0146] Sampling interval = 500 milliseconds

[0147] Standard polystyrene samples used for the calibration curve were "STANDARD SM-105" and "STANDARD SH-75" manufactured by Showa Denko K.K., having mass 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.

[0148] The above-mentioned standard curve was classified into A (5620000, 1250000, 151000, 17000, 2900) and B (3120000, 442000, 53500, 7660, 1320) using standard polystyrene, and then A (2 mg, 3 mg, 4 mg, 4 mg, 4 mg) was weighed and dissolved in 30 mL of chloroform. B (3 mg, 4 mg, 4 mg, 4 mg, 4 mg) was also weighed and dissolved in 30 mL of chloroform.

[0149] The standard polystyrene calibration curve was obtained by preparing a calibration curve (cubic form) based on the retention times obtained by injecting 50 μL of each of the prepared A and B solutions and measuring them. The average molecular weight was calculated using this calibration curve.

[0150] A polylactic acid resin having such melting characteristics and molecular weight distribution can be obtained by modifying a commercially available polylactic acid resin. The aforementioned modification can be implemented, for example, by having a cross-linked structure or a long-chain branched structure in the molecular structure of the polylactic acid resin. In addition, the modification can be implemented by increasing the molecular weight of the polylactic acid resin. When increasing the molecular weight of the polylactic acid resin, a chain extender such as carbodiimide can be used. In addition, the modification based on the chain extender can be carried out using compounds such as oleic acid-based organic compounds, epoxy-based organic compounds, and isocyanate-based organic compounds that have one or more functional groups that can undergo condensation reactions with the hydroxyl groups and carboxyl groups present in the molecular structure of the polylactic acid resin. The aforementioned modification can be implemented by combining oleic acid-based organic compounds, epoxy-based organic compounds, isocyanate-based organic compounds, etc. with the polylactic acid resin through a reaction.

[0151] The modification of the polylactic acid resin based on crosslinking and long-chain branching can be carried out by, for example, a method in which the polylactic acid resins are reacted with each other using a free radical initiator. In the above-mentioned modification method, from the perspective of being able to suppress the presence of other components in the polylactic acid resin foam sheet, it is preferred to use a free radical initiator to react the polylactic acid resins with each other. It should be noted that when a free radical initiator with moderate reactivity is used to react the polylactic acid resins with each other in an extruder, the site where the polylactic acid resin is easily decomposed will be attacked by the free radicals generated by the free radical initiator. In addition, the site can become a crosslinking point (branching point) and thus stabilized. The polylactic acid resin increases its thermal stability by carrying out such a modification and is not prone to low molecular weight when passing through an extruder. As the above-mentioned free radical initiator used in the modification of the polylactic acid resin, for example, organic peroxides, azo compounds, halogen molecules, etc. can be listed. Among these, organic peroxides are preferred.

[0152] Examples of the organic peroxide used in the present embodiment include peroxyesters, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, peroxyketals, and ketone peroxides.

[0153] Examples of the peroxyester include tert-butyl peroxy-2-ethylhexyl carbonate, tert-hexyl peroxyisopropyl monocarbonate, tert-hexyl peroxybenzoate, tert-butyl peroxybenzoate, tert-butyl peroxylaurate, tert-butyl peroxy-3,5,5-trimethylhexanoate, tert-butyl peroxyacetate, 2,5-dimethyl-2,5-bis(benzoyl peroxide)hexane, and tert-butyl peroxyisopropyl monocarbonate.

[0154] Examples of the hydroperoxide include methane hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, and tert-butyl hydroperoxide.

[0155] Examples of the dialkyl peroxide include dicumyl peroxide, di-tert-butyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexyne.

[0156] Examples of the diacyl peroxide include dibenzoyl peroxide, di(4-methylbenzoyl)peroxide, and di(3-methylbenzoyl)peroxide.

[0157] Examples of the peroxydicarbonate include di(2-ethylhexyl) peroxydicarbonate and diisopropyl peroxydicarbonate.

[0158] Examples of the peroxyketal include 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane, 1,1-di-tert-butylperoxycyclohexane, 2,2-di(tert-butylperoxy)-butane, n-butyl 4,4-di(tert-butylperoxy)valerate, and 2,2-bis(4,4-di-tert-butylperoxycyclohexyl)propane.

[0159] Examples of the ketone peroxide include methyl ethyl ketone peroxide and acetylacetone peroxide.

[0160] When the polylactic acid resin is modified with the organic peroxide, there is a concern that components with excessively large molecular weight that form a gel during heat melting may be mixed in the modified polylactic acid resin, or that decomposition residues of the organic peroxide may generate odor.

[0161] The gel contained in the polylactic acid resin may cause the formation of coarse bubbles in the foaming layer or the formation of micro protrusions. The gel content (gel fraction) in the polylactic acid resin or resin composition is preferably 4% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less. It should be noted that when determining the gel content (gel fraction) for the polylactic acid resin or resin composition, the following formula can be used: Figure 3 The instrument shown is used and the result is obtained as follows.

[0162] <Gel content measurement method>

[0163] The pellets were used directly as samples.

[0164] Prepare about 0.5g of sample and accurately weigh the initial mass of the sample (m0(g)). In addition, prepare a 200-mesh metal mesh (wire diameter φ0.05mm) for filtering the solution containing the sample. Also accurately weigh the initial mass of the metal mesh (M0(g)). Place the weighed measurement sample in a 100mL beaker ( Figure 3 Symbol TB). Add 50 mL of chloroform as a solvent and a stirrer to the beaker and cover it with aluminum foil. Stir with a stirring rod for 2 hours to dissolve the test sample at room temperature. After 2 hours, remove the aluminum foil and filter the dissolved material in the beaker with a 200-mesh metal mesh. After filtration, dry the metal mesh naturally in a fume hood for 24 hours. After drying, cool it in a desiccator. After cooling, weigh the metal mesh (M1 (g)) with resin-insoluble matter attached, and calculate the gel fraction using the following formula.

[0165] Gel fraction (mass %) = m1 / m0×100

[0166] m0: initial mass of the sample

[0167] m1: mass of resin insoluble matter (M1-M0)

[0168] M0: Initial mass of the metal mesh

[0169] M1: Total mass of resin insoluble matter and metal mesh

[0170] From the perspective of being able to suppress the risk of gel formation and easily modifying the polylactic acid resin to a state suitable for foaming, the aforementioned organic peroxide is preferably a peroxyester. Furthermore, among the peroxyesters, the organic peroxide that can be used for modifying the polylactic acid resin is preferably a peroxycarbonate-based organic peroxide such as peroxymonocarbonate and peroxydicarbonate. In the present embodiment, among the peroxycarbonate-based organic peroxides that can be used for modifying the polylactic acid resin, a peroxymonocarbonate-based organic peroxide is preferably a peroxymonocarbonate-based organic peroxide, and particularly preferably tert-butyl peroxyisopropyl monocarbonate.

[0171] The above-mentioned organic peroxide also depends on its molecular weight, etc., and is usually used in a ratio of 0.1 mass part or more relative to 100 mass parts of the polylactic acid resin to be modified. The amount of the organic peroxide used is preferably 0.2 mass parts or more, and particularly preferably 0.3 mass parts or more. The amount of the organic peroxide used is preferably 2.0 mass parts or less, more preferably 1.5 mass parts or less, and particularly preferably 1.0 mass parts or less.

[0172] By using an organic peroxide in such a ratio to modify a polylactic acid resin, the modified polylactic acid resin can be made suitable for foaming. If the amount of the organic peroxide is set to 0.1 parts by mass or more, the modification effect on the polylactic acid resin can be more reliably exerted. Alternatively, if the amount of the organic peroxide is set to 2.0 parts by mass or less, the modified polylactic acid resin is less likely to contain gel.

[0173] The polylactic acid resin of this embodiment can have a gel fraction of, for example, 1.5% by mass or less by using multiple polylactic acid resins having different MFRs as starting materials. Even when using multiple polylactic acid resins having different MFRs as starting materials, the gel fraction can be set to 1.0% by mass or less, or even 0.8% by mass or less.

[0174] Examples of the components for foaming used when the polylactic acid resin is formed into an extruded foam sheet include a foaming agent and a cell regulator.

[0175] As the aforementioned foaming agent, a common foaming agent can be used, and a volatile foaming agent that becomes a gas at normal temperature (23°C) and normal pressure (1 atmosphere) and a decomposition-type foaming agent that generates a gas by thermal decomposition can be used. As the aforementioned volatile foaming agent, for example, an inert gas, an aliphatic hydrocarbon, an alicyclic hydrocarbon, etc. can be used. As the aforementioned inert gas, for example, carbon dioxide, nitrogen, etc. can be listed. As the aforementioned aliphatic hydrocarbon, for example, propane, n-butane, isobutane, n-pentane, isopentane, etc. can be listed. As the aforementioned aliphatic hydrocarbon, for example, cyclopentane, cyclohexane, etc. can be listed. In the present embodiment, n-butane and isobutane among the above can be particularly preferably used.

[0176] Examples of the decomposable foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, sodium hydrogen carbonate, and mixtures of organic acids such as citric acid or salts thereof with hydrogen carbonate.

[0177] Examples of the cell control agent include polytetrafluoroethylene, talc, aluminum hydroxide, and silicon dioxide. The decomposable foaming agent can be used in combination with a volatile foaming agent to adjust the foaming state and can also be used as a cell control agent.

[0178] Various additives can be added as needed in the resin combination that constitutes the aforementioned polylactic acid resin foam sheet. As this additive, resins, inorganic fillers and various medicaments other than the polylactic acid resin can be listed. As the aforementioned medicament, for example, crystallization nucleating agents, lubricants, antioxidants, antistatic agents, flame retardants, ultraviolet light absorbers, light stabilizers, colorants, antibacterial agents, etc. can be listed. It should be noted that the ratio of these additives in the resin combination is preferably below 25 mass parts relative to 100 mass parts of polylactic acid resin, more preferably below 15 mass parts.

[0179] The resin composition preferably contains a crystallization nucleating agent. The crystallization nucleating agent is preferably one that functions like a plasticizer and promotes the crystallization of polylactic acid. Such a crystallization nucleating agent can be a reaction product (A) of at least one of (A1) a polyol and a polyol dehydrated condensate, (A2) an alkylene oxide mainly composed of ethylene oxide, and (A3) a fatty acid having 12 to 24 carbon atoms.

[0180] Examples of the polyols in (A1) "polyols and polyol dehydrated condensates" include glycerin, erythritol, pentaerythritol, xylitol, sorbitol, mannitol, galactitol, and maltitol. These substances are also advantageous in imparting impact resistance to the polylactic acid resin foam sheet.

[0181] The term "alkylene oxide mainly composed of ethylene oxide" in (A2) above means that more than half of the alkylene oxide is ethylene oxide, and also includes the meaning that the alkylene oxide is entirely ethylene oxide. When a substance other than ethylene oxide is used in combination with ethylene oxide as the alkylene oxide, for example, propylene oxide, butylene oxide, methylpropylene oxide, etc. may be used in combination.

[0182] Examples of the (A3) "fatty acids having 12 to 24 carbon atoms" include saturated fatty acids such as dodecanoic acid (lauric acid), tetradecanoic acid (myristic acid), pentadecanoic acid (pentadecanoic acid), hexadecanoic acid (palmitic acid), heptadecanoic acid (margaric acid), octadecanoic acid (stearic acid), eicosanoic acid (arachidic acid), heneicosanoic acid (heneicosanoic acid), docosanoic acid (behenic acid), and tetracosanoic acid (lignoceric acid); and monounsaturated fatty acids such as myristoleic acid, palmitoleic acid, hexadecanoic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, eicosenoic acid, and erucic acid. Examples of the (A3) "fatty acids having 12 to 24 carbon atoms" include diunsaturated fatty acids such as linoleic acid, triunsaturated fatty acids such as linolenic acid, tetraunsaturated fatty acids, and pentaunsaturated fatty acids. (A3) "C 12-24 fatty acid" may be a mixture of a plurality of fatty acids such as coconut oil fatty acid. Preferred examples of (A3) "C 12-24 fatty acid" include dodecanoic acid (lauric acid) and octadecanoic acid (stearic acid).

[0183] In making the polylactic acid resin foam sheet bring into play excellent impact resistance, the content ratio of oxyethylene in the above-mentioned reaction product (A) is preferably more than 20 mass % and less than 95 mass %. The content ratio of oxyethylene in the above-mentioned reaction product (A) is more preferably more than 30 mass % and less than 95 mass %. In addition, the above-mentioned reaction product (A) can be a saturated ester that the hydroxyl groups of polyol and polyol dehydration condensate are all formed by fatty acid esterification, or can be a partial ester that a part of hydroxyl groups is esterified. In addition, in making the polylactic acid resin foam sheet bring into play excellent impact resistance, reaction product (A) preferably has the ester group of a specified number on average in the molecule. The average ester group number in the molecule of reaction product (A) is preferably more than 2 and is less than 9, more preferably more than 2.5 and is less than 6.

[0184] As the manufacturing method of the above-mentioned reaction product (A), for example, the following method can be listed: polyol and fatty acid are reacted under heating to carry out the esterification of polyol, and then ethylene oxide is added in an autoclave under heating to obtain the above-mentioned reaction product (A). In addition, the dehydrated condensation product of polyol can also be reacted with fatty acid for esterification, and then ethylene oxide is added in the same manner as the above-mentioned method. In addition, polyol and polyol dehydrated condensation product can also be reacted with fatty acid after ethylene oxide addition. In addition, there is also the following method, etc.: fatty acid ester is pre-synthesized from fatty acid and monohydric alcohol (methanol, ethanol) with short carbon number, the fatty acid ester is subjected to ester exchange reaction with polyol and polyol dehydrated condensation product, and ethylene oxide is added in the same manner as the above-mentioned method, thereby obtaining the above-mentioned reaction product (A). The above-mentioned reaction product (A) thus obtained can be used alone or in combination with two or more in the resin composition in the present embodiment.

[0185] As the crystal nucleating agent of this embodiment, for example, the "(B) fatty acid amide" shown below can be used instead of the "(A) reaction product" described above. As the crystal nucleating agent of this embodiment, one or more of the above-mentioned (A) reaction products and one or more of the (B) fatty acid amides can also be used in combination.

[0186] The fatty acid amide (B) is preferably at least one fatty acid amide selected from the group consisting of fatty acid monoamides, fatty acid bisamides, hydroxyl-containing fatty acid monoamides, and hydroxyl-containing fatty acid bisamides, and is preferably a fatty acid amide derived from a fatty acid having 8 to 24 carbon atoms. More preferably, the fatty acid amide (B) is a fatty acid bisamide such as N,N'-ethylenebisstearamide, or a hydroxyl-containing fatty acid bisamide such as N,N'-ethylenebis(12-hydroxystearamide) or N,N'-xylylenebis(12-hydroxystearamide). Fatty acid amides are effective in providing excellent moldability to the polylactic acid resin foam sheet. Fatty acid amides are also effective in providing excellent heat resistance and impact resistance to the sheet molded article.

[0187] In addition, as the above-mentioned crystal nucleating agents, hydrocarbons such as liquid paraffin, paraffin, and synthetic polyethylene wax; metal soaps such as zinc stearate, calcium stearate, and magnesium stearate; ethylene glycol, diethylene glycol, and polyethylene glycols having a structure formed by the condensation of three or more ethylene glycols; propylene glycol, dipropylene glycol, and polypropylene glycols having a structure formed by the condensation of three or more propylene glycols; 1,3-butanediol, 1,4-butanediol, and polybutylene glycols of their polymers; and polyols such as glycerol, diglycerol, and polyglycerols thereof.

[0188] It should be noted that the crystallization nucleating agents exemplified above, which function as plasticizers, sometimes cause a phenomenon known as "bleeding"—migration to the surface of the polylactic acid resin foam sheet and oozing out from the surface. In particular, fatty acid amides tend to ooze out of the polylactic acid resin foam sheet during thermoforming. Although this situation may generally be considered a problem, it can be advantageous in terms of producing moderate sliding between the molding die and improving the thickness uniformity of the sheet molded body. That is, if good sliding is not achieved between the molding die and the polylactic acid resin foam sheet, the polylactic acid resin foam sheet is locally stretched and thin-walled areas may be formed on the sheet molded body. On the other hand, such problems can be avoided by using fatty acid amides as crystallization nucleating agents. In addition, the tendency to ooze out means that the residual amount in the sheet molded body is reduced. Therefore, when the sheet molded body is subjected to unexpected heating, the occurrence of strain caused by further crystallization can be suppressed.

[0189] The crystallization nucleating agent can be used in a ratio of 0.5 parts by mass or more and 15 parts by mass or less relative to 100 parts by mass of the polylactic acid resin. The ratio of the crystallization nucleating agent can be 1 part by mass or more, or 1.5 parts by mass or more. The ratio of the crystallization nucleating agent can be 10 parts by mass or less, or 5 parts by mass or less relative to 100 parts by mass of the polylactic acid resin.

[0190] The polylactic acid resin foam sheet in this embodiment can be produced by implementing the following steps: a step of modifying the polylactic acid resin using a twin-screw extruder or the like (modification step); and a step of extruding and foaming the polylactic acid resin composition containing the modified polylactic acid resin through an extruder with a circular die head installed at the front end (extrusion foaming step).

[0191] In the aforementioned modification process, for example, the modified polylactic acid resin may be pelletized using a twin-screw extruder equipped with a pelletizing die (thermal cutting die). The twin-screw extruder used in the aforementioned modification process may be equipped with a drawing die or a T-die to produce strands or sheets from the modified polylactic acid resin in the aforementioned modification process. Subsequently, a separate process of cutting the strands or sheets and pelletizing the strands or sheets may be performed. Alternatively, as previously described, a tandem extruder may be used to perform the modification process and the extrusion foaming process continuously.

[0192] In the above-mentioned extrusion foaming process, the resin composition in the present embodiment will not be easily stretched, and the resin film defining the cells will not easily become too thin. That is, in the polylactic acid resin foam sheet of the present embodiment, when the aforementioned resin film comprising polylactic acid resin is stretched by the foaming force brought by the foaming agent, it will exert a resistance greater than a certain value. In addition, in the polylactic acid resin foam sheet of the present embodiment, it is easy to become a state in which the central portion of the resin film is thin and the peripheral portion is thick. Therefore, the polylactic acid resin foam sheet of the present embodiment forms a connected state in the three-dimensional space on the entire sheet through the thicker resin film, thereby exerting excellent mechanical properties.

[0193] For the polylactic acid resin foam sheet of this embodiment, even if bubbles break during foaming and holes appear on the resin film, the resin film surrounding the holes will not remain in its original state, but will shrink and thicken to form a form that effectively exerts strength. Therefore, even if there are continuous bubbles in a certain proportion, excellent strength can be exerted.

[0194] The apparent density of the polylactic acid resin foam sheet is preferably 63 kg / m 3 Above and 500kg / m 3 Below, more preferably 83kg / m 3 Above and 250kg / m 3 By making the apparent density of the polylactic acid resin foam sheet 63kg / m 3 As described above, the sheet molded article of the present embodiment has increased strength, and further, has the advantage that the thermoformability of the polylactic acid resin foam sheet is improved, resulting in a molded article that accurately reflects the mold shape.

[0195] By making the apparent density of the polylactic acid resin foam sheet 500 kg / m 3 Next, there is an advantage that the sheet molded article of the present embodiment has the advantage of being able to significantly exhibit characteristics of a foam such as lightness, heat insulation, and cushioning properties.

[0196] The thickness of the polylactic acid resin foam sheet is preferably 0.5 mm or more and 7 mm or less, more preferably 0.5 mm or more and 5 mm or less, and even more preferably 0.7 mm or more and 3 mm or less. By setting the thickness of the polylactic acid resin foam sheet to 0.5 mm or more, the sheet molded body of this embodiment has the advantage of high strength. Furthermore, by setting the thickness of the polylactic acid resin foam sheet to 7 mm or less, thermoformability is improved, resulting in less uneven thickness of the sheet molded body of this embodiment.

[0197] <Apparent density>

[0198] Apparent density of polylactic acid resin foam sheet (kg / m 3) can be calculated by using the mass of the polylactic acid resin foam sheet per unit area (mass per unit area: g / m 2 ) divided by the thickness (mm) of the polylactic acid resin foam sheet. The mass per unit area can be determined by taking the arithmetic average of the values obtained by measuring a plurality of samples cut out from the polylactic acid resin foam sheet. The mass per unit area of the polylactic acid resin foam sheet can be determined by cutting a measurement sample from the polylactic acid resin foam sheet with a size of 20 cm in the extrusion direction (MD) and a size of the entire width in the width direction (TD), and calculating the mass W (g) and area S (cm 2 ) can be obtained by the following formula.

[0199] Mass per unit area (g / m 2 )=W / S×10000

[0200] In addition, the apparent density can be obtained by the following calculation.

[0201] Apparent density (kg / m 3 ) = mass per unit area (g / m 2 )÷Thickness(mm)

[0202] <Thickness>

[0203] The thickness of the polylactic acid resin foam sheet can be determined from an enlarged photograph of a cross section of the polylactic acid resin foam sheet cut along a plane perpendicular to the polylactic acid resin foam sheet, for example, as an average value of a plurality of randomly selected locations (e.g., 20 locations).

[0204] The polylactic acid resin foam sheet preferably has a predetermined average bubble diameter. The average bubble diameter is preferably 0.1 mm or more and 1 mm or less, more preferably 0.1 mm or more and 0.8 mm or less, and further preferably 0.1 mm or more and 0.6 mm or less. By making the average bubble diameter of the polylactic acid resin foam sheet 0.1 mm or more, the continuous bubble rate tends to be low. As a result, it is possible to obtain an advantage such as a sheet molded body with a low apparent density. In addition, as a result, it is possible to obtain advantages such as good thermoformability of the polylactic acid resin foam sheet and ability to reduce uneven thickness of the sheet molded body. In addition, by making the average bubble diameter of the polylactic acid resin foam sheet 1 mm or less, the sheet molded body of this embodiment has good properties such as thermal insulation and cushioning. The average bubble diameter of the sheet molded body of this embodiment is preferably the same value as the average bubble diameter of the polylactic acid resin foam sheet.

[0205] (Average bubble diameter)

[0206] The average cell diameter can be measured according to the test method of ASTM D2842-69.

[0207] Specifically, the polylactic acid resin foam sheet was cut along the extrusion direction (MD) and the width direction (TD) perpendicular to the extrusion direction, and the center of each cut surface was magnified using a scanning electron microscope (S-3000N manufactured by Hitachi, Ltd.) and photographed twice at different locations.

[0208] Next, print the captured image onto A4 paper and draw three 60mm-long lines on the image. For sections cut along the MD direction, draw the lines parallel to the MD; for sections cut along the TD direction, draw the lines parallel to the TD. Additionally, draw lines in the thickness direction (VD) on one image each. Adjust the magnification of the electron microscope so that at least six bubbles are visible on the lines.

[0209] Then, based on the average number of bubbles in each direction on the six straight lines drawn in each direction, the average chord length (t) of the bubbles was calculated using the following formula, and the bubble diameter in each direction (MD, TD, VD) was calculated using the following formula based on the average chord length.

[0210] Average chord length t = 60 (mm) / (number of bubbles × photo magnification)

[0211] Bubble diameter D = t / 0.616 (mm)

[0212] It should be noted that when drawing a straight line, the line should be drawn so that it passes through the bubbles rather than making point contact. Furthermore, if some bubbles make point contact with the straight line, these bubbles are included in the bubble count. Furthermore, if the ends of the straight line do not pass through the bubbles but are located within them, the bubbles at the ends of the straight line are also included in the bubble count.

[0213] Then, the bubble diameter (D MD ) and the bubble diameter in TD (D TD ) and the bubble diameter (D VD ) is multiplied by the average value as the average cell diameter of the polylactic acid resin foam sheet. That is, the average cell diameter of the polylactic acid resin foam sheet is calculated using the following formula.

[0214] Average bubble diameter (mm) = (D MD ×D TD ×D VD ) 1 / 3

[0215] The open cell ratio of the aforementioned polylactic acid resin foam sheet is preferably 50% or less, more preferably 40% or less, and further preferably 30% or less. By setting the open cell ratio of the aforementioned polylactic acid resin foam sheet to 50% or less, there is an advantage that the mechanical strength of the polylactic acid resin foam sheet and the secondary foaming properties during thermoforming become particularly excellent. In addition, the sheet molded body manufactured from such a polylactic acid resin foam sheet has excellent mechanical strength and, furthermore, also excellent appearance aspects such as mold reproducibility. In this embodiment, the open cell ratio of the sheet molded body itself is also preferably the above-mentioned value. The aforementioned open cell ratio can be calculated as follows.

[0216] (Continuous bubble rate)

[0217] The interconnected cell ratio can be determined by the following method.

[0218] Cut out a number of sheet samples of 25 mm in length and 25 mm in width from the polylactic acid resin foam sheet. Overlap the cut samples without gaps to make test pieces with a thickness of 21 to 23 mm. Make 3 test pieces. The test pieces are conditioned for 16 hours under the environment of JIS K7100: 1999, standard 23 / 50, level 2, and the thickness (mm) is measured. The thickness can be measured using, for example, a "Digimatic caliper" manufactured by Mitutoyo Corporation. The thickness is measured to 1 / 100 mm, and the apparent volume (cm 3 ).

[0219] Next, the volume (cm2) of the test piece is measured under the above-mentioned environment using a dry automatic density meter (for example, "AccuPyc II 1340-100cc" manufactured by Shimadzu Corporation). 3 ).

[0220] The measurement conditions are as follows.

[0221] Using gas: nitrogen

[0222] Container: 35cc

[0223] Filling pressure: 0.005 psig

[0224] Pressure balance end rate: 0.005psig / minute

[0225] Number of repetitions: 1

[0226] Then, the open cell ratio (%) of each test piece was calculated using the following formula, and the average value was defined as the apparent density of the polylactic acid resin foam sheet.

[0227] Open cell ratio (%) = [(apparent volume - volume measured by dry automatic density meter) / apparent volume] × 100 (%)

[0228] Next, a method for producing the sheet molded body according to this embodiment will be described.

[0229] In the manufacturing method of the sheet molding of this embodiment, the following steps are implemented to form the sheet molding: a first heating step of heating the aforementioned polylactic acid resin foam sheet; and a second heating step of clamping the aforementioned polylactic acid resin foam sheet that has undergone the first heating step with a heated molding mold to manufacture the sheet molding and increase the crystallinity of the sheet molding.

[0230] In the primary heating step, the polylactic acid resin foam sheet can be heated by a known method such as a method of sandwiching the polylactic acid resin foam sheet with a heating plate or a method of heating the foam sheet with an electric heater. Furthermore, in the primary heating step of the method for producing a sheet molded article according to this embodiment, the polylactic acid resin foam sheet is heated to a surface temperature of preferably 60°C or higher, more preferably 70°C or higher, even more preferably 80°C or higher, and particularly preferably 90°C or higher. The heating in the primary heating step is preferably performed so that the surface temperature of the polylactic acid resin foam sheet is 130°C or lower, more preferably 120°C or lower.

[0231] In the method for manufacturing a sheet molded body of the present embodiment, by setting the surface temperature of the polylactic acid resin foam sheet in the aforementioned primary heating process to the above-mentioned temperature, the transferability of the molding die becomes good. In addition, if the primary heating process is performed at the above-mentioned temperature, the softening state of the polylactic acid resin foam sheet becomes good, and the polylactic acid resin foam sheet can be suppressed from breaking during molding. In addition, in the method for manufacturing a sheet molded body of the present embodiment, by setting the surface temperature of the polylactic acid resin foam sheet in the aforementioned primary heating process to preferably 130°C or less, more preferably 120°C or less, the surface state of the polylactic acid resin foam sheet becomes good. In addition, if the primary heating process is performed at such a temperature, moderate crystallization will occur at the stage of the primary heating process, the crystallinity of the formed sheet molded body will increase, and a sheet molded body with excellent heat resistance will be easily obtained.

[0232] In the secondary heating step, a pair of molds, each serving as a male mold and a female mold, can be suitably used as the molding mold. In the secondary heating step, the polylactic acid resin foam sheet, softened by heating in the primary heating step, is sandwiched between the heated male and female molds to form the sheet molded article. By maintaining this state for a predetermined period of time during the secondary heating step, the crystallinity of the sheet molded article can be increased over time.

[0233] The secondary heating process is carried out by adjusting the temperature of the forming mold to preferably 50°C or more, more preferably 60°C or more, and further preferably 70°C or more. The secondary heating process is carried out by adjusting the temperature of the forming mold to preferably 130°C or less, more preferably 120°C or less. By setting the temperature of the forming mold to 50°C or more in the secondary heating process, the advantage of easily increasing the crystallinity of the sheet molded body can be obtained. In addition, by setting the temperature of the forming mold to 50°C or more in the secondary heating process, the advantage of easily shortening the crystallization time and easily improving productivity can also be obtained. In addition, in the secondary heating process, by setting the heated forming mold to 130°C or less, the advantage of improving the surface condition of the sheet molded body can be obtained.

[0234] In the method for manufacturing the sheet molded body of the present embodiment, from the viewpoint of obtaining a polylactic acid resin foam sheet having a difference between heat absorption and heat generation within a preferred range, it is preferred to temperature-regulate the polylactic acid resin foam sheet obtained by the extrusion foaming method immediately after extrusion. The temperature regulation method can be, for example, a method of cooling by air, water, etc., or a method of heat preservation (heating) by heating air, hot water, etc. The sheet molded body formed by the method for manufacturing the sheet molded body of the present embodiment becomes a molded body with excellent heat resistance. The sheet molded body of the present embodiment has excellent heat resistance and can therefore be suitably used as food packaging containers such as lunch boxes, cup noodle containers, and microwave containers.

[0235] The above examples of the polylactic acid resin foam sheet, sheet molded article, and method for producing the same according to the present embodiment are merely limiting examples, and the present invention is not limited to the above examples, but can be implemented by adding appropriate modifications to the above examples.

[0236] As described above, this embodiment includes the following inventions. (1)

[0238] A polylactic acid resin foam sheet, comprising a polylactic acid resin composition containing a crystalline polylactic acid resin.

[0239] The crystallinity of the polylactic acid resin foam sheet is less than 30%,

[0240] The crystallization temperature observed by heat flow differential scanning calorimetry analysis at a heating rate of 5°C / min was 105°C or lower. (2)

[0242] The polylactic acid resin foam sheet according to (1), wherein the polylactic acid resin composition has a half-crystallization time at 80° C. of 30 minutes or less. (3)

[0244] The polylactic acid resin foam sheet according to (1) or (2), wherein the polylactic acid resin composition contains the polylactic acid resin, the polylactic acid resin is a copolymer obtained by copolymerizing the D-isomer and the L-isomer of lactic acid, the content of the D-isomer in the copolymer is from 0.5 mol% to 5 mol%, and the melting point of the copolymer is from 130°C to 170°C. (4)

[0246] The polylactic acid resin foam sheet according to any one of (1) to (3), wherein the apparent density is 63 kg / m 3 Above and 500kg / m 3 the following. (5)

[0248] The polylactic acid resin foam sheet according to any one of (1) to (4), wherein the thickness is 0.5 mm to 7 mm. (6)

[0250] The polylactic acid resin foam sheet according to any one of (1) to (5), wherein the open cell ratio is 50% or less. (7)

[0252] The polylactic acid resin foam sheet according to any one of (1) to (6), wherein the polylactic acid resin composition contains a modified polylactic acid resin as the polylactic acid resin, and the modified polylactic acid resin is a modified product based on an organic peroxide. (8)

[0254] The polylactic acid resin foam sheet according to any one of (1) to (7), wherein the polylactic acid resin composition contains a crystal nucleating agent. (9)

[0256] A method for producing a sheet molded body, the method comprising thermoforming a resin foam sheet to produce the sheet molded body.

[0257] The resin foam sheet is a polylactic acid resin foam sheet, which is composed of a polylactic acid resin composition containing a crystalline polylactic acid resin.

[0258] The crystallinity of the polylactic acid resin foam sheet is less than 30%,

[0259] The crystallization temperature observed in heat flow differential scanning calorimetry analysis at a heating rate of 5°C / min was 105°C or lower.

[0260] The following steps are performed in the method for producing the sheet molded body:

[0261] a primary heating step of heating the polylactic acid resin foam sheet; and

[0262] In the secondary heating step, the polylactic acid resin foam sheet subjected to the primary heating step is sandwiched between heated molding dies to produce a sheet molded body, and the crystallinity of the sheet molded body is increased. (10)

[0264] The method for producing a sheet molded body according to (9), wherein in the primary heating step,

[0265] The polylactic acid resin foam sheet is heated so that the surface temperature becomes 60° C. or higher and 130° C. or lower. (11)

[0267] The method for producing a sheet molded product according to (9) or (10), wherein the temperature of the molding die is adjusted to 50° C. or higher and 130° C. or lower in the secondary heating step.

[0268] According to the above invention, a polylactic acid resin foam sheet suitable for efficiently producing a sheet molded body having excellent heat resistance is provided, and the production efficiency of the sheet molded body having excellent heat resistance can be improved.

[0269] Example 1

[0270] Hereinafter, the present invention will be described in further detail with reference to Examples, but the present invention is not limited thereto.

[0271] (Reference Production Example 1)

[0272] (1) Preparation of modified polylactic acid resin

[0273] Polylactic acid resin (MFR = 10.0 g / 10 min, density = 1240 kg / m 3 ) 100 parts by mass of t-butyl peroxyisopropyl monocarbonate (1 minute half-life temperature T1: 158.8° C.) were stirred and mixed to obtain a mixture.

[0274] The obtained mixture was supplied to a twin-screw extruder having a diameter of 57 mm (L / D=31.5).

[0275] The set temperature of the feed section was set to 170°C, and the temperature thereafter was set to 230°C. The mixture was melt-kneaded in a twin-screw extruder at a rotation speed of 150 rpm, and the mixture was extruded in the form of strands at a discharge rate of 50 kg / hour from a die head having a diameter of 3 mm and 18 holes installed at the front end of the extruder.

[0276] Next, the extruded strand-shaped kneaded product was cooled by passing through a cooling water tank containing water at 30° C. and having a length of 2 m.

[0277] The cooled strands were cut into pieces using a pelletizer to obtain pellets of the modified polylactic acid resin.

[0278] (Reference Production Examples 2 to 5)

[0279] For Reference Production Examples 2 to 5, modified polylactic acid resins were prepared in the same manner as Reference Production Example 1 except that the type of polylactic acid resin and the amount of organic peroxide added (amount added (parts by mass) relative to 100 parts by mass of polylactic acid resin) were changed.

[0280] (Reference Examples 1 and 2)

[0281] Reference Examples 1 and 2 are commercially available polylactic acid resins, which are raw materials before the above-described reactions are carried out.

[0282] Table 1 shows the types of the polylactic acid resin and organic peroxide used in Reference Production Examples 1 to 5, the amount (parts by mass) of the organic peroxide added relative to 100 parts by mass of the polylactic acid resin, and the physical properties of the obtained polylactic acid resin.

[0283] [Table 1]

[0284]

[0285] Polylactic acid resin type a: MFR = 10.0 g / min, melt strength = 0.5 cN, D-phase content = 1.5-2.5 mol%, melting point = 165°C

[0286] Type b of polylactic acid resin: MFR = 4.0 g / min, melt strength = 2.0 cN, D-phase content = 3.5-4.5 mol%, melting point = 150°C

[0287] Polylactic acid resin type c: MFR = 15.0 g / min, melt strength = below the lower limit of measurement, D-body content = 1.5-2.5 mol%, melting point = 160°C

[0288] Polylactic acid resin type d: MFR = 7.5 g / min, melt strength = 3 cN, D-phase content = 4.7 mol%, melting point = 152°C

[0289] Type of organic peroxide X: tert-butyl isopropyl monocarbonate, 75% solution (solvent: isododecane)

[0290] (Production of Polylactic Acid Foam Sheet)

[0291] (Example 1)

[0292] 100 parts by mass of the polylactic acid resin obtained in Reference Production Example 1 and 1.0 part by mass of a cell regulator ("CROWN TALC" manufactured by Matsumura Sangyo Co., Ltd.) were dry-blended to prepare a mixture.

[0293] The mixture was supplied through a hopper to the first extruder (diameter φ50 mm) of a tandem extruder, where it was heated and melted. The tandem extruder comprised a first extruder (upstream side) having a diameter of φ50 mm and a second extruder (downstream side) having a diameter of φ65 mm.

[0294] Then, butane (isobutane / n-butane = 70 / 30) as a foaming agent was pressed into the first extruder and melt-mixed with the above mixture.

[0295] The molten mixture was then transferred to a second extruder with a diameter of 65 mm and uniformly cooled to a temperature suitable for extrusion foaming. It was then extruded and foamed from a circular die with a diameter of 70 mm at a discharge rate of 30 kg / hour to obtain a cylindrical foam.

[0296] The obtained cylindrical foam is pulled along a φ206mm core rod with cooling water at about 20°C inside, and the outer surface of the cylindrical foam is cooled and formed by blowing gas using an air ring with a diameter larger than the outer surface of the cylindrical foam. It is then cut with a tool at a point on the circumference to obtain a strip-shaped polylactic acid resin foam sheet.

[0297] (Example 2)

[0298] A polylactic acid resin foam sheet was obtained in the same manner as in Example 1 except that 10 parts by mass of a crystallization nucleating agent (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name "TRIBIO S-920MB") was added to 100 parts by mass of the polylactic acid resin.

[0299] (Example 3)

[0300] A polylactic acid resin foam sheet was obtained in the same manner as in Example 1 except that 2 parts by mass of a crystallization nucleating agent (manufactured by Ito Oil Manufacturing Co., Ltd., trade name "ITOHWAX J-530" (fatty acid amide)) was added to 100 parts by mass of the polylactic acid resin.

[0301] (Example 4)

[0302] A polylactic acid resin foam sheet was obtained in the same manner as in Example 3 except that the polylactic acid resin used was changed to the one obtained in Reference Production Example 2.

[0303] (Example 5)

[0304] A polylactic acid resin foam sheet was obtained in the same manner as in Example 3 except that the amount of the crystallization nucleating agent added was changed from 2 parts by mass to 3 parts by mass.

[0305] (Example 6)

[0306] A polylactic acid resin foam sheet was obtained in the same manner as in Example 1 except that 3 parts by mass of polyethylene glycol (PEG-4000P) was added as a crystal nucleating agent based on 100 parts by mass of the polylactic acid resin.

[0307] (Example 7)

[0308] A polylactic acid resin foam sheet was obtained in the same manner as in Example 1 except that "ITOHWAX J-530" and "PEG-4000P" were used in combination as crystal nucleating agents and the amount of each added was 3 parts by mass per 100 parts by mass of the polylactic acid resin (total 6 parts by mass).

[0309] (Example 8)

[0310] A polylactic acid resin foam sheet was obtained in the same manner as in Example 1 except that the polylactic acid resin used was changed to the one obtained in Reference Production Example 3.

[0311] (Example 9)

[0312] A polylactic acid resin foam sheet was obtained in the same manner as in Example 3 except that the polylactic acid resin used was changed to the one obtained in Reference Production Example 4.

[0313] (Comparative Example 1)

[0314] A polylactic acid resin foam sheet was obtained in the same manner as in Example 1 except that the trade names "ITOHWAX J-530" and "PEG-4000P" were used in combination as crystallization nucleating agents, the amount of "ITOHWAX J-530" added was 1 part by mass, and the amount of "PEG-4000P" added was 4 parts by mass relative to 100 parts by mass of the polylactic acid resin.

[0315] (Comparative Example 2)

[0316] A polylactic acid resin foam sheet was obtained in the same manner as in Example 1 except that the polylactic acid resin used was changed to the one obtained in Reference Production Example 4.

[0317] (Comparative Example 3)

[0318] A polylactic acid resin foam sheet was obtained in the same manner as in Example 1 except that the polylactic acid resin used was changed to that obtained in Reference Production Example 5.

[0319] (Comparative Examples 4 and 5)

[0320] The preparation of a polylactic acid resin foam sheet was attempted in the same manner as in Example 1 except that the polylactic acid resin used was that of Reference Example 1 (Comparative Example 4) and Reference Example 2 (Comparative Example 5). However, the melt strength of the resin was low, and a polylactic acid resin foam sheet could not be obtained in a good state.

[0321] <Molding>

[0322] A square test piece measuring 340 mm in length and 340 mm in width was cut from the polylactic acid resin foam sheet of each example using a single-station molding machine (manufactured by Tosei Sangyo Co., Ltd., trade name "FM-3A") with the average temperature of the upper heater of the single-station molding machine set to 300°C and the average temperature of the lower heater set to 300°C.

[0323] Next, the test pieces were introduced into a single-station molding machine and heated for 30 seconds. They were then thermoformed using a molding die maintained at 100°C. Five sheet molded articles (foamed containers) with an upper opening were produced for each example. It should be noted that the surface temperature of the polylactic acid resin foam sheet during the primary heating step under these conditions was approximately 120°C. The containers were in the shape of an inverted quadrangular pyramid with a square bottom, and the dimensions of each component are as follows.

[0324] Opening: 140mm x 150mm

[0325] Bottom: 110mm×110mm

[0326] Height: 60mm

[0327] The crystallinity and shrinkage rate during heating (hereinafter referred to as heating shrinkage rate) of each container obtained were measured. The shrinkage rate during heating was measured by the following method.

[0328] (Heating shrinkage)

[0329] The heat shrinkage ratio is measured using an air circulation oven, for example, a product name "MODEL PSL-2" manufactured by Tabai Espec Corp.

[0330] The heat shrinkage ratio was calculated as follows: each container was placed in an air circulation oven heated to 100° C., heated for 150 seconds, taken out of the oven, and the length of each side of the container was measured. The heat shrinkage ratio was calculated from the measured values.

[0331] The heat shrinkage rate of the container is the value obtained by dividing the difference between the length before heating and the length after heating by the length before heating and multiplying the result by 100. This value is calculated for each of the two sides of the container's opening.

[0332] Based on the calculated values, evaluation was performed based on the following evaluation criteria.

[0333] Evaluation Benchmarks

[0334] ○: Both sides are "within 5%."

[0335] △: One side is "within 5%" and the other side is "exceeding 5%".

[0336] ×: The value on both sides is "more than 5%".

[0337] In addition, the thickness, basis weight, expansion ratio, open cell ratio, average cell diameter, crystallinity, crystallization temperature, and crystallization half time of the polylactic acid resin foam sheets of Examples and Comparative Examples were measured.

[0338] The expansion ratio was measured by the following method. Other parameters were measured by the aforementioned methods.

[0339] (Foaming ratio)

[0340] Three 10×10 cm measurement samples were cut out from the polylactic acid resin foam sheet along the width direction (TD), and the thickness and mass of each sample were measured. The arithmetic mean of the density calculated from the mass and volume of each sample was taken as the apparent density of the polylactic acid resin foam sheet.

[0341] Then, the density of polylactic acid resin (1240kg / m 3 ) divided by the apparent density of the polylactic acid resin foam sheet is taken as the expansion ratio.

[0342] Foaming ratio = 1240 / apparent density of polylactic acid resin foam sheet (kg / m 3 )

[0343] The results are shown in Tables 2 and 3 below.

[0344] [Table 2]

[0345]

[0346] [Table 3]

[0347]

[0348] As can be seen from the above results, the present invention can provide a polylactic acid resin foam sheet suitable for efficiently producing a sheet molded body having excellent heat resistance.

[0349] Description of Reference Numerals

[0350] 1: Polylactic acid resin foam sheet, 100: Sheet manufacturing apparatus.

Claims

1. A polylactic acid resin foam sheet, comprising a polylactic acid resin composition containing a crystalline polylactic acid resin, The crystallinity of the polylactic acid resin foam sheet is less than 30%, The crystallization temperature observed by heat flow differential scanning calorimetry analysis at a heating rate of 5°C / min was 105°C or lower.

2. The polylactic acid resin foam sheet according to claim 1, wherein The polylactic acid resin composition has a half-crystallization time at 80° C. of less than 30 minutes.

3. The polylactic acid resin foam sheet according to claim 1 or 2, wherein The polylactic acid resin composition contains the polylactic acid resin, which is a copolymer obtained by copolymerizing the D-isomer and the L-isomer of lactic acid, the content of the D-isomer in the copolymer is greater than or equal to 0.5 mol% and less than or equal to 5 mol%, and the melting point of the copolymer is greater than or equal to 130°C and less than or equal to 170°C.

4. The polylactic acid resin foam sheet according to claim 1 or 2, having an apparent density of 63 kg / m 3 Above and 500kg / m 3 the following. The polylactic acid resin foam sheet according to claim 1 or 2, which has a thickness of 0.5 mm to 7 mm. 6 . The polylactic acid resin foam sheet according to claim 1 , wherein the open cell ratio is 50% or less.

7. The polylactic acid resin foam sheet according to claim 1 or 2, wherein The polylactic acid resin is a modified polylactic acid resin, and the modified polylactic acid resin is a modified product based on an organic peroxide.

8. The polylactic acid resin foam sheet according to claim 1 or 2, wherein The polylactic acid resin composition contains a crystallization nucleating agent.

9. A method for producing a sheet molded body, the method comprising thermoforming a resin foam sheet to produce a sheet molded body. The resin foam sheet is a polylactic acid resin foam sheet, which is composed of a polylactic acid resin composition containing a crystalline polylactic acid resin. The crystallinity of the resin foam sheet is less than 30%, The crystallization temperature observed in heat flow differential scanning calorimetry analysis at a heating rate of 5°C / min was 105°C or lower. The following steps are performed in the method for producing the sheet molded body: a primary heating step of heating the polylactic acid resin foam sheet; and In the secondary heating step, the polylactic acid resin foam sheet subjected to the primary heating step is sandwiched between heated molding dies to produce a sheet molded body, and the crystallinity of the sheet molded body is increased.

10. The method for producing a sheet molded body according to claim 9, wherein: In the primary heating step, the polylactic acid resin foam sheet is heated so that the surface temperature becomes 60° C. or higher and 130° C. or lower.

11. The method for producing a sheet molded body according to claim 9 or 10, wherein: In the secondary heating step, the temperature of the molding die is adjusted to 50° C. or higher and 130° C. or lower.

Images