JP6494086B2 - Manufacturing method of thermoforming sheet - Google Patents

Description

  The present invention relates to a method for producing a thermoforming sheet. More specifically, a method for producing a sheet made of a polylactic acid resin composition that can be suitably used for molded articles such as packs and trays for daily necessities, cosmetics, home appliances, etc., and molding formed by molding a sheet obtained by the production method The present invention relates to a method for manufacturing a body.

  Currently, there are various plastic products around us, which are indispensable for people's lives. While the amount used is increasing year by year, the amount of plastic waste is also increasing. Most plastics are made from fossil fuels, and incineration of plastic waste increases the amount of carbon dioxide in the atmosphere, which is said to have an impact on global warming.

  As an effort to reduce the impact on global warming, plant-derived resins have attracted attention, and among them, biolactic acid polylactic acid has been actively researched and developed.

  A characteristic of polylactic acid is its high transparency, and it can be expected to be used as a packaging container that requires content visibility. However, polylactic acid also has a drawback of low heat resistance. The reason for this is that the glass transition temperature of polylactic acid is around 60 ° C., and above this temperature, the molded product is softened. As a method for improving this low heat resistance, crystallization can be mentioned. It is possible to improve the resin softening point to near the melting point by crystallization. However, polylactic acid has a very low crystallization rate, and many of the formed spherulites grow to a wavelength longer than the visible light wavelength, and the visible light is not scattered and travels straight.

  Therefore, the addition of a crystal nucleating agent is known as a method for solving the low crystallization rate of polylactic acid resin and the decrease in transparency due to crystallization. Inorganic crystal nucleating agents such as amide-based organic crystal nucleating agents and talc are well known, and the addition of these nucleating agents increases the number of crystal nuclei and shortens the internuclear distance. Becomes smaller. As a result, the crystallization speed is improved, the heat resistance is improved, and the formed spherulites are suppressed to a visible light wavelength or less, so that the transparency can be maintained.

  On the other hand, Patent Document 1 discloses that heat resistance is improved by applying heat treatment to a polylactic acid film within a temperature range from a temperature 30 ° C. lower than the glass transition temperature to a temperature 10 ° C. higher. ing.

  Patent Document 2 describes that in order to obtain a sheet having excellent thermoformability, the sheet is heat-treated in an apparatus used for sheet preparation for the purpose of controlling the phase difference of the sheet.

JP 2008-266369 A JP 2014-51646 A

  However, the heat treatment in Patent Document 1 is performed in order to impart heat resistance regardless of crystallization. Regarding the blending of the crystal nucleating agent, inorganic fillers, layered silicates, fatty acid salts, aliphatics are used. Although polyester is illustrated, only examples that are not used in the examples or that use talc are disclosed. Therefore, even if an attempt is made to obtain a crystalline thermoformed product using the film, there is a practical problem because it takes an enormous amount of time to crystallize. When an inorganic filler is used, transparency can be maintained by adding a small amount, but there is a practical problem because the crystallization rate is slow. In addition, the addition of a large amount causes the crystallization rate to be at a practical level but inhibits transparency.

  In addition, when the heat treatment in Patent Document 2 is prepared by, for example, extrusion molding, if the sheet surface temperature is high, stretching in the extrusion direction occurs at the time of winding, and thermoformability decreases due to slight stretching. (See [0106] of Patent Document 2), in the example, the heat treatment is performed by bringing the sheet surface temperature into contact with the cooling roll until the surface temperature reaches 20 to 40 ° C. Although the heat treatment time is as short as 0.1 to 50 seconds, the wound sheet eventually needs to be stored in a warehouse or the like until it is sold or molded. Depending on the storage conditions, the subsequent thermoformability may be deteriorated. Particularly, the thermoformability is greatly deteriorated by storage at a relatively high temperature (30 to 45 ° C.) such as storage in a summer warehouse. It was a challenge.

  Therefore, the present inventors examined the influence of storage at high temperature on the sheet, and surprisingly found that although the crystallization rate once decreased with storage time, it gradually recovered. Such a tendency is peculiar when a polylactic acid resin composition containing an amide organic crystal nucleating agent is used as a material, and suppresses fluctuations in the crystallization speed of a sheet made of the polylactic acid resin composition. Therefore, it is necessary to improve the thermal stability.

  The present invention provides a method for producing a thermoforming sheet comprising a polylactic acid resin composition having good thermoformability even after storage at a relatively high temperature in summer, and a sheet obtained by the production method. The present invention relates to a method for producing a molded article.

  As a result of intensive studies in view of such a situation, the present inventors have determined that a sheet of an amorphous or semi-crystalline state of a polylactic acid resin composition containing a polylactic acid resin and an amide organic crystal nucleating agent is a specific method. By storing for a set time and a specific temperature condition based on the numerical value obtained by the above, it suppresses the fluctuation of the specific crystallization rate based on the amide organic crystal nucleating agent, and even after storage at high temperature However, it was found that a thermoforming sheet exhibiting excellent transparency and excellent thermoformability when crystallized was obtained, and the present invention was completed.

That is, the present invention relates to [1] to [2].
[1] A method for producing a thermoforming sheet, comprising the following steps (1) and (2).
Step (1): Preparing an amorphous or semi-crystalline sheet of a polylactic acid resin composition containing a polylactic acid resin and an amide organic crystal nucleating agent Step (2): The sheet obtained in step (1) It is a step of storing at a temperature not higher than the glass transition temperature (Tg) of the polylactic acid resin composition, which is increased by storing the half crystallization time calculated by the following method (A) to 0.7 min or more. (A) Using a differential scanning calorimeter, the sample is heated from 25 ° C. to 90 ° C. at a rate of 500 ° C./min. Then, from the amount of heat measured when held at 90 ° C. for 10 minutes, the time required for 50% crystallization to proceed is calculated and set as the half crystallization time (minutes) [2] Next step (1 ) To (4).
Step (1): Preparing an amorphous or semi-crystalline sheet of a polylactic acid resin composition containing a polylactic acid resin and an amide organic crystal nucleating agent Step (2): The sheet obtained in step (1) It is a step of storing at a temperature not higher than the glass transition temperature (Tg) of the polylactic acid resin composition, which is increased by storing the half crystallization time calculated by the following method (A) to 0.7 min or more. (A) Using a differential scanning calorimeter, the sample is heated from 25 ° C. to 90 ° C. at a rate of 500 ° C./min. Then, from the amount of heat measured when held at 90 ° C. for 10 minutes, the time necessary for 50% crystallization to proceed is calculated and set as the semi-crystallization time (minutes): Step (3): Step (2) The sheet obtained in step 1) is made of glass of polylactic acid resin composition. Step (4) of heating in a temperature range not lower than the transition temperature (Tg) and lower than the melting point (Tm): Thermoforming the sheet obtained in the step (3) using a mold having a mold temperature of 60 to 140 ° C. Process

  The thermoforming sheet obtained by the production method of the present invention suppresses fluctuations in the crystallization rate, has a high crystallization rate even after storage at high temperature, and exhibits excellent transparency when crystallized. And since it is excellent in thermoformability, the molded object which has a favorable external appearance can be provided very easily. Moreover, since it is excellent in thermoformability even after high temperature storage, the thermoforming sheet obtained by the production method of the present invention has an excellent effect of excellent storage stability.

FIG. 1 is a diagram showing an example of a DSC curve used for calculation of the half crystallization time. FIG. 2 is a diagram showing an example of the transition of the half crystallization time of a composition containing an amide organic crystal nucleating agent. FIG. 3 is a view showing a mold used in the example.

  The method for producing a thermoforming sheet of the present invention comprises a step of preparing an amorphous or semi-crystalline sheet of a polylactic acid resin composition containing a polylactic acid resin and an amide organic crystal nucleating agent [step (1)], and , A manufacturing method comprising a step of storing the sheet obtained in the above step at a specific temperature [Step (2)], wherein the storage time is a time defined based on a numerical value calculated by a specific condition There is a big feature in a certain thing.

  In the present invention, from the viewpoint of suppressing fluctuations in the crystallization speed of the resulting thermoforming sheet, the sheet before being subjected to thermoforming is stored in advance at a temperature below the glass transition temperature (Tg) of the polylactic acid resin composition. However, the storage time is defined based on the semi-crystallization time of the sheet. Here, the semi-crystallization time, which is an index in the method of the present invention, will be described with reference to FIG. The half crystallization time is the time when half of the calorific value associated with the total crystallization is generated when an amorphous or semi-crystalline sheet is isothermally crystallized at 90 ° C., for example, the exotherm shown in FIG. The amount of heat occupying 50% of the peak area is defined as 0.272 minutes, which is the elapsed time observed. In the case of a composition containing an amide-based organic crystal nucleating agent, this half-crystallization time is 0.6 minutes or less immediately after the preparation of the composition. This shows a characteristic tendency of fluctuation of the crystallization rate, which becomes longer as time goes on, and then recovers (see FIG. 2). Therefore, in the present invention, the sheet is provided at the temperature exceeding the time until the half crystallization time increases by storing and becomes 0.7 minutes or more and then becomes 0.6 minutes or less. Thus, the amide organic crystal nucleating agent in the sheet was unstable before the treatment and the crystal nucleating agent ability was variable, and became stable and the fluctuation of the crystallization rate was suppressed. It is presumed that a thermoforming sheet having a high crystallization speed and excellent thermoformability even after storage at a high temperature can be obtained. Further, it is presumed that when the crystal nucleating agent used is an amide organic crystal nucleating agent, excellent transparency can be exhibited when crystallized.

<Step (1)>
Step (1) of the production method of the present invention is a step of preparing an amorphous or semi-crystalline sheet of a polylactic acid resin composition containing a polylactic acid resin and an amide organic crystal nucleating agent.

[Polylactic acid resin composition]
[Polylactic acid resin]
Examples of the polylactic acid-based resin include commercially available polylactic acid resins such as those manufactured by Nature Works: Nature Works PLA / 3001D, 4032D, 2500HP, and 3100HP, as well as polylactic acid resins synthesized from lactic acid and lactide. From the viewpoint of strength and transparency, a polylactic acid resin having an optical purity of 90% or more is preferable. For example, a polylactic acid resin (4032D, 2500HP, etc.) manufactured by Nature Works with a relatively high molecular weight and high optical purity is preferable.

  Moreover, in this invention, from the viewpoint of the intensity | strength and transparency of a polylactic acid resin composition, the stereo which consists of two types of polylactic acid obtained using the lactic acid component which has a different isomer as a main component as a polylactic acid-type resin. Complex polylactic acid resin may be used.

  The polylactic acid resin in the present invention may contain a biodegradable polyester resin other than the polylactic acid resin or a non-biodegradable resin such as polypropylene as a polymer alloy by blending with the polylactic acid resin. In the present specification, “biodegradable” means a property that can be decomposed into a low molecular weight compound by a microorganism in nature. Specifically, JIS K6953 (ISO 14855) “controlled aerobic composting conditions”. This means biodegradability based on the “Aerobic and Ultimate Biodegradation and Disintegration Test”.

  The content of the polylactic acid resin is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 90% by mass or more in the polylactic acid resin composition from the viewpoint of biodegradability.

[Organic crystal nucleating agent]
In the present invention, an amide organic crystal nucleating agent is used as the organic crystal nucleating agent.

  The amide organic crystal nucleating agent is not particularly limited as long as it is a compound having one or more amide bonds, and a compound having a hydroxyl group and / or an ester group in addition to the amide bond is preferably used. Such a compound is preferably one or two selected from fatty acid monoamides and fatty acid bisamides, and more preferably fatty acid bisamides, from the viewpoint of shortening the semicrystallization time of the thermoforming sheet.

  The number of carbon atoms of the fatty acid in the fatty acid monoamide or fatty acid bisamide is preferably 8 or more, more preferably 12 or more, still more preferably 16 or more, and preferably 24 or less, from the viewpoint of shortening the semicrystallization time of the thermoforming sheet. More preferably, it is 22 or less, More preferably, it is 20 or less. Moreover, the fatty acid in the fatty acid monoamide or fatty acid bisamide may have a hydroxyl group, and is preferably a fatty acid having a hydroxyl group from the viewpoint of shortening the semicrystallization time of the thermoforming sheet.

  Specific examples of the fatty acid monoamide include 12-hydroxystearic acid monoethanolamide.

  Specific examples of fatty acid bisamides include methylene bis 12-hydroxystearic acid amide, ethylene bis 12-hydroxystearic acid amide, hexamethylene bis 12-hydroxystearic acid amide, xylylene bis 12-hydroxystearic acid amide, and ethylene bisstearic acid. And acid amide, ethylenebisoleic acid amide, ethylenebislauric acid amide and the like.

  Of these, ethylene bis 12-hydroxystearic acid amide and ethylene bis stearic acid amide are preferable, and ethylene bis 12-hydroxystearic acid amide is more preferable from the viewpoint of shortening the semicrystallization time of the thermoforming sheet. It is.

  In the present invention, other known organic crystal nucleating agents other than the amide-based organic crystal nucleating agent can be used as long as the effects of the present invention are not impaired. Although it does not specifically limit as another organic crystal nucleating agent, The compound which has an ester group, a urea group, a thiourea group etc. is mentioned, For example, glycerol fatty acid ester is mentioned. The content of the amide-based organic crystal nucleating agent in the organic crystal nucleating agent is preferably 40% by mass or more, more preferably 60% by mass or more, and more preferably 80% by mass or more from the viewpoint of shortening the semicrystallization time of the thermoforming sheet. Is more preferable, and it is still more preferable that it is 100 mass%.

  The content of the organic crystal nucleating agent is 0.01 parts by mass with respect to 100 parts by mass of the polylactic acid-based resin from the viewpoint of shortening the semicrystallization time of the thermoforming sheet and thermoforming after storage at high temperature. The above is preferable, 0.1 part by mass or more is more preferable, 0.2 part by mass or more is more preferable, and 5 parts by mass or less is preferable from the viewpoint of thermoformability and transparency after storage at high temperature, and 1 part by mass The following is more preferable, and 0.7 mass part or less is still more preferable.

[Plasticizer]
In the present invention, a plasticizer can be further used in addition to the above components from the viewpoint of thermoformability and transparency after storage at high temperature.

  It does not specifically limit as a plasticizer used by this invention, The plasticizer used for general biodegradable resin is mentioned. Of these, compounds having two or more ester groups in the molecule are preferred from the viewpoints of thermoformability and transparency after storage at high temperatures. Examples of such compounds include esters of polyvalent carboxylic acids and monoalcohols or their (poly) oxyalkylene adducts, and esters of polyhydric alcohols or their (poly) oxyalkylene adducts.

  Specific examples include the plasticizers described in JP-A-4-335060, JP-A 2008-174718, and JP-A 2008-115372. Among these, from the viewpoint of thermoformability after storage at high temperature and transparency, preferably an ethylene oxide average adduct of 3 to 6 mol of acetic acid and glycerin (addition of 1 to 2 mol of ethylene oxide per hydroxyl group) Esters, esters of acetic acid and ethylene oxide with polyethylene glycol having an average addition mole number of 4 to 6, polyethylene glycol monomethyl ether with an average addition mole number of succinic acid and ethylene oxide of 2 to 3 (2 ethylene oxides per hydroxyl group) ~ 3 mol addition), ester of adipic acid and diethylene glycol monomethyl ether, ester of adipic acid and 1-butyl alcohol, ester of acetylcitric acid and 1-butyl alcohol, 1,3,6-hexanetricarboxylic acid Acid and diethylene glycol monomer One or more selected from the group consisting of esters with ethers, more preferably polyethylene glycol monomethyl ether having an average addition mole number of succinic acid and ethylene oxide of 2 to 3, ester of adipic acid and diethylene glycol monomethyl ether, acetyl One or more selected from the group consisting of an ester of an acid and 1-butyl alcohol is preferably used.

  The content of the plasticizer is preferably 0.01 parts by mass or more, more preferably 0.5 parts by mass or more, and more preferably 1 part by mass with respect to 100 parts by mass of the polylactic acid resin from the viewpoint of thermoformability and transparency. More preferably, 2 parts by mass or more are even more preferable, shortening the semicrystallization time of the thermoforming sheet, improving the glass transition temperature of the thermoforming sheet, transparency, and thermoformability after storage at high temperature In view of the above, it is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, still more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less.

[Hydrolysis inhibitor]
In the present invention, from the viewpoint of thermoformability, a carbodiimide compound can be used as a hydrolysis inhibitor in addition to the above components.

  Specific examples include a monocarbodiimide compound and a polycarbodiimide compound. These can be used alone or in combination of two or more.

  Examples of the polycarbodiimide compound include poly (4,4′-diphenylmethanecarbodiimide), poly (4,4′-dicyclohexylmethanecarbodiimide), poly (1,3,5-triisopropylbenzene) polycarbodiimide, poly (1,3,3). 5-triisopropylbenzene and 1,5-diisopropylbenzene) polycarbodiimide and the like, and monocarbodiimide compounds include di-isopropylcarbodiimide, di-octadecylcarbodiimide, N, N′-di-2,6-diisopropylphenylcarbodiimide Etc.

  The carbodiimide compounds may be used singly or in combination of two or more in order to satisfy the durability, impact resistance and thermoformability of the molded body made of the polylactic acid resin composition. Poly (4,4′-dicyclohexylmethane carbodiimide) is obtained from carbodilite LA-1 (manufactured by Nisshinbo Chemical Co., Ltd.), poly (1,3,5-triisopropylbenzene) polycarbodiimide and poly (1,3,5-tri (Isopropylbenzene and 1,5-diisopropylbenzene) polycarbodiimide is stavaxol P and stabaxol P-100 (manufactured by Rhein Chemie), N, N'-di-2,6-diisopropylphenylcarbodiimide is stavaxol I (Rhein Chemie) Can be purchased and used.

  The content of the hydrolysis inhibitor is preferably 0.01 parts by mass or more with respect to 100 parts by mass of the polylactic acid-based resin from the viewpoints of hydrolysis inhibition, thermoformability after high-temperature storage, and transparency. More than mass part is more preferable, 0.15 mass part or more is still more preferable, 5 mass parts or less are preferable from a viewpoint of transparency, 3 mass parts or less are more preferable, and 1 mass part or less are still more preferable.

  The polylactic acid resin composition in the present invention includes, as components other than the above, a lubricant, an inorganic crystal nucleating agent, a filler (inorganic filler, organic filler), a flame retardant, an antioxidant, an ultraviolet absorber, and an antistatic agent. An agent, an antifogging agent, a light stabilizer, a dispersant, a pigment, an antifungal agent, an antibacterial agent, a foaming agent and the like can be contained within a range not impairing the effects of the present invention. Similarly, other polymer materials and other resin compositions can be contained within a range that does not impair the effects of the present invention.

  The polylactic acid resin composition in the present invention can be prepared without particular limitation as long as it contains a polylactic acid resin and an amide organic crystal nucleating agent. For example, a known kneader such as a polylactic acid resin and an amide organic crystal nucleating agent, and further, if necessary, a raw material containing various additives, a closed kneader, a single or twin screw extruder, an open roll kneader, etc. And can be prepared by melt kneading. The raw materials can be subjected to melt kneading after being uniformly mixed in advance using a Henschel mixer, a super mixer, or the like. In order to promote the plasticity of the polylactic acid resin when preparing the polylactic acid resin composition, it may be melt-mixed in the presence of a supercritical gas, and after the melt-kneading, the melt-kneaded product is dried or dried according to a known method. It may be cooled.

  From the viewpoint of improving the moldability and deterioration prevention of the polylactic acid resin composition, the melt kneading temperature is not less than the melting point (Tm) of the polylactic acid resin, preferably not less than Tm ° C. and not more than Tm + 100 ° C., more The range is preferably Tm ° C. or higher and Tm + 50 ° C. or lower. Specifically, for example, it is preferably 170 ° C. or higher, preferably 240 ° C. or lower, more preferably 220 ° C. or lower. The melt-kneading time cannot be generally determined depending on the melt-kneading temperature and the type of the kneader, but is preferably 15 seconds or more and 900 seconds or less. In addition, in this specification, melting | fusing point (Tm) and glass transition temperature (Tg) can be calculated | required according to the method as described in the below-mentioned Example.

  The melting point (Tm) of the polylactic acid resin composition is preferably 140 ° C. or higher, more preferably 150 ° C. or higher, still more preferably 160 ° C. or higher, preferably 240 ° C. or lower, and 200 ° C. or lower from the viewpoint of thermoformability. More preferably, 180 degrees C or less is still more preferable.

  The glass transition temperature (Tg) of the polylactic acid resin composition is preferably 45 ° C or higher, more preferably 46 ° C or higher, still more preferably 47 ° C or higher, and preferably 65 ° C or lower, from the viewpoint of thermoformability. 62 ° C. or lower is more preferable, and 60 ° C. or lower is still more preferable.

[Preparation of amorphous or semi-crystalline sheet]
Next, an amorphous or semi-crystalline sheet is prepared using the obtained melt-kneaded material. Here, in the present specification, the amorphous state and the semi-crystalline state are an amorphous state where the relative crystallinity obtained by the following formula is less than 60%, a relative crystallinity of 60% or more, 80 The case where it is less than% is defined as a semi-crystalline state. Thus, an amorphous or semi-crystalline sheet means a sheet having a relative crystallinity of less than 80%.
Relative crystallinity (%) = {(ΔHm−ΔHcc) / ΔHm} × 100
Specifically, the relative crystallinity was raised from 25 ° C. to 200 ° C. at a rate of temperature increase of 15 ° C./min using a DSC apparatus (diamond DSC manufactured by PerkinElmer Co., Ltd.) at a rate of temperature increase of 15 ° C./min. After being held, the temperature was lowered from 200 ° C. to 25 ° C. at a temperature drop rate of −500 ° C./min, held at 25 ° C. for 1 minute, and further increased from 25 ° C. to 200 ° C. at a temperature rising rate of 15 ° C./min as 2ndRUN. The absolute value ΔHcc of the cold crystallization enthalpy of the polylactic acid resin observed at 1st RUN and the crystal melting enthalpy ΔHm observed at 2nd RUN can be used.

  The amorphous or semi-crystalline sheet in the present invention can be prepared by extrusion molding, injection molding, or press molding the polylactic acid resin composition.

  Specifically, in the extrusion molding, the polylactic acid resin composition filled in a heated extruder is melted and then extruded from a T die to obtain a sheet-like molded product (also referred to as a sheet molded product). be able to. The sheet molded product is immediately brought into contact with a cooling roll, cooled, and separated from the cooling roll, and then wound up with a winding roll, whereby an amorphous or semi-crystalline sheet can be obtained. When filling the extruder, the raw materials constituting the polylactic acid resin composition, for example, the raw materials containing polylactic acid resin and amide organic crystal nucleating agent, and further various additives as necessary, are filled as they are. Melt-kneading may be performed, and the melt-kneaded material may be filled in an extruder.

  The temperature of the extruder is preferably 170 ° C. or higher, preferably 240 ° C. or lower, more preferably 220 ° C. or lower, from the viewpoint of uniformly mixing the polylactic acid resin composition and preventing deterioration of the polylactic acid resin. is there. In the present invention, the temperature of the extruder means the barrel set temperature of the extruder. Further, the residence time in the extruder cannot be defined unconditionally because it depends on the thickness, width, and winding speed of the sheet, but is preferably about 30 seconds to several minutes from the viewpoint of avoiding deterioration due to heat.

  The temperature of the cooling roll is preferably set to be less than Tg of the polylactic acid resin composition from the viewpoint of obtaining a sheet in an amorphous state or a semi-crystalline state, specifically, preferably less than 40 ° C., and preferably 30 ° C. or less. More preferred.

  The time of contact with the cooling roll is not necessarily specified because it varies depending on the set temperature of the cooling roll, the number of cooling rolls, the extrusion speed, and the sheet winding speed, but an amorphous or semi-crystalline sheet is efficiently obtained. From the viewpoint, it is preferably 0.1 seconds or more, more preferably 0.5 seconds or more, still more preferably 0.8 seconds or more, preferably 50 seconds or less, more preferably 10 seconds or less, still more preferably 5 seconds or less. It is. Further, from the same viewpoint, the sheet winding speed is preferably 0.1 m / min or more, more preferably 0.5 m / min or more, still more preferably 1 m / min or more, preferably 50 m / min or less, more Preferably it is 30 m / min or less, More preferably, it is 20 m / min or less.

  When molding an amorphous or semi-crystalline sheet by injection molding, specifically, from the viewpoint of uniformly mixing the polylactic acid resin composition and preventing the deterioration of the polylactic acid resin, the polylactic acid resin composition is used. The cylinder temperature is preferably 180 ° C. or higher, preferably 220 ° C. or lower, more preferably 210 ° C. or lower, and filled into a mold having a desired shape and molded into a sheet shape. can do.

  When forming an amorphous or semi-crystalline sheet by press molding, specifically, the polylactic acid resin composition is surrounded by a frame having a desired sheet shape, preferably 170 ° C. or higher and 240 ° C. or lower, preferably 5 MPa or higher and 30 MPa or lower. It can be obtained by press molding under the following conditions. Further, after the pressing, the amorphous state or the semi-crystalline state can be maintained by pressing preferably at 0 ° C. or higher and 40 ° C. or lower and 0.1 MPa or higher and 20 MPa or lower.

  Thus, an amorphous or semicrystalline sheet in step (1) is obtained. The thickness of the amorphous or semi-crystalline sheet is preferably 0.1 mm or more, more preferably 0.2 mm or more, preferably 1.5 mm or less, more preferably 1.2 mm or less, still more preferably 0.8 mm or less. Even more preferably, it is 0.5 mm or less.

  The amorphous or semi-crystalline sheet in step (1) preferably has a relative crystallinity obtained by the above formula of less than 80%, more preferably less than 60%, and even more preferably less than 55%. The lower limit is not particularly set, but may be 0% or more.

  The amorphous or semicrystalline sheet immediately after preparation obtained in step (1) is crystallized because the amide organic crystal nucleating agent is considered to have good interaction with the polylactic acid resin and excellent dispersibility in the resin. The speed is fast. Therefore, the semi-crystallization time calculated by the method (A) described later is not particularly set, but is preferably within 0.6 minutes, more preferably within 0.55 minutes, and even more preferably within 0.52 minutes. Further, if it contains a plasticizer that further improves the crystallization rate, it is preferably within 0.50 minutes, more preferably within 0.45 minutes, and even more preferably within 0.42 minutes.

<Step (2)>
In the step (2) of the production method of the present invention, the sheet obtained in the step (1) is a semi-crystal calculated by the following method (A) at a temperature not higher than the glass transition temperature (Tg) of the polylactic acid resin composition. It is a process of storing beyond the time until it becomes 0.6 minutes or less after increasing to 0.7 minutes or more by storing, and from the viewpoint of thermoformability, productivity and transparency Preferably, it is a step of storing for a time exceeding 0.55 minutes or less, more preferably 0.52 minutes or less, and further including a plasticizer for improving the crystallization rate, , 0.50 minutes or less, more preferably 0.45 minutes or less, and even more preferably 0.42 minutes or less. In addition, in this specification, the preservation | save of a process (2) includes storage, leaving, and mounting in addition to what is called preservation | save.
Method (A) Using a differential scanning calorimeter, about 10 mg of sample is heated from 25 ° C. to 90 ° C. at 500 ° C./min, and then 50% from the calorific value measured when held at 90 ° C. for 10 minutes. Calculate the time required for crystallization to proceed and use it as the semi-crystallization time (minutes)

  Specifically, for example, the sheet obtained in step (1) may be directly contacted with a heating roll or the like at the above temperature to perform direct processing. Further, indirect processing such as a method of passing through a heating furnace, a method of heating with infrared rays or the like, a method of storing in a thermo-hygrostat or a warehouse can also be performed. The sheet state when stored at the above temperature is particularly limited, such as a state where the sheet is wound by a winding roll, a state where sheets are stacked while being cut to a specific length after being cooled by a cooling roll. Not. Among these, in the case of a roll, a problem such as blocking does not occur even when the treatment is performed, and therefore, it is preferable.

  The temperature at the time of the treatment may be not more than the glass transition temperature (Tg) of the polylactic acid resin composition from the viewpoint of improving the formability of the thermoformed product without forming a crystal structure, and depends on the treatment time. Specifically, it is preferably 58 ° C. or lower, more preferably 55 ° C. or lower, still more preferably 50 ° C. or lower, even more preferably 45 ° C. or lower, even more preferably 40 ° C. or lower, more preferably 30 ° C. or higher, and 35 ° C. The above is more preferable.

  As the processing time, if the semi-crystallization time calculated by the method (A) increases by storing and becomes 0.7 minutes or more and then exceeds the time until 0.6 minutes or less, There is no particular limitation, and it can be set appropriately depending on the method of adding heat and the relative crystallinity, thickness, etc. of the sheet to be processed. For example, when storing in a warehouse that is about 10 ° C. lower than the glass transition temperature (Tg) of the polylactic acid resin composition, 12 hours or more is required from the viewpoint of improving the shapeability of the thermoformed product without forming a crystal structure. It is preferably 18 hours or longer, more preferably 24 hours or longer, and preferably 100 hours or shorter, and preferably 72 hours or shorter, from the viewpoint of influence on mechanical properties due to hydrolysis of polylactic acid.

  As the differential scanning calorimetry apparatus used in the method (A), any apparatus known in the art can be used without limitation. For example, DSC8500 manufactured by PerkinElmer Co., Ltd. can be used.

  Thus, a thermoforming sheet subjected to heat treatment for a specific time is obtained. Therefore, this invention also provides the sheet | seat for thermoforming obtained by the manufacturing method of this invention.

  The thickness of the thermoforming sheet obtained by the production method of the present invention is preferably 0.1 mm or more, more preferably 0.2 mm or more, preferably 1.5 mm or less, more preferably 1.2 mm or less, More preferably, it is 0.8 mm or less, More preferably, it is 0.5 mm or less.

  The relative crystallinity of the obtained thermoforming sheet is preferably less than 80%, more preferably less than 60%, and still more preferably less than 55%. The lower limit is not particularly set, but may be 0% or more. The variation in relative crystallinity due to the treatment in the step (2) is preferably ± 10% or less.

  The thermoforming sheet obtained by the production method of the present invention has no fluctuation in the crystallization rate, has a high crystallization rate even after storage at high temperature, and exhibits excellent transparency when crystallized. Since it is excellent in thermoformability and can be stably produced, a molded article having a good appearance can be provided very easily. For example, as packaging materials for daily necessities, cosmetics, home appliances, etc., they can be thermoformed into blister packs and trays, food containers such as lunch box lids, industrial trays used for transportation and protection of industrial parts, and the like.

  The reason why the sheet for thermoforming having the effects of the present invention can be obtained by the production method of the present invention is unknown, but the polylactic acid-based resin forms a metastable phase by adding the amount of heat based on the step (2). Thus, it is presumed that the amide organic crystal nucleating agent can be stabilized by suppressing the movement of molecules.

  The present invention also provides a thermoformed article formed by molding the thermoforming sheet of the present invention.

  The thermoformed body of the present invention is not particularly limited as long as it is obtained by thermoforming the thermoforming sheet obtained by the production method of the present invention, and the forming method is not particularly limited and can be performed according to a known method. For example, a sheet formed by vacuum forming or pressure forming the thermoforming sheet of the present invention can be mentioned.

As a suitable aspect of the manufacturing method of the thermoformed body of this invention, the manufacturing method of the thermoformed body containing the following process (1)-(4) is mentioned.
Step (1): Preparing an amorphous or semi-crystalline sheet of a polylactic acid resin composition containing a polylactic acid resin and an amide organic crystal nucleating agent Step (2): The sheet obtained in step (1) It is a step of storing at a temperature not higher than the glass transition temperature (Tg) of the polylactic acid resin composition, and the storage time is increased by storing the semi-crystallization time calculated by the following method (A) to be 0.7. Step method of storing for more than 0.6 minutes or less until it becomes 0.6 minutes or less (A) Using a differential scanning calorimeter, about 10 mg of sample from 25 ° C. to 90 ° C. at 500 ° C./min Step (3) of calculating the time required for 50% crystallization to proceed from the amount of heat measured when the temperature is raised and then holding at 90 ° C. for 10 minutes, and setting it as a half crystallization time (minutes): The sheet obtained in step (2) is Step (4) of heating the lactic acid resin composition to a temperature range not lower than the glass transition temperature (Tg) and lower than the melting point (Tm): the sheet obtained in the step (3) has a mold temperature of 60 ° C. or higher and 140 ° C. or lower. Process of thermoforming using metal mold

  Steps (1) and (2) are the same as steps (1) and (2) in the above-described method for producing a thermoforming sheet of the present invention. Further, since it is necessary to soften the thermoforming sheet in an amorphous state by heating in the step (3), the sheet surface temperature is set to a glass transition temperature (Tg) or higher of the polylactic acid resin composition, a melting point ( Tm) is necessary. The heating temperature of the thermoforming sheet is preferably 50 ° C. or higher, more preferably 60 ° C. or higher, still more preferably 65 ° C. or higher, preferably 120 ° C. or lower, more preferably 100 ° C. or lower, still more preferably 90 ° C. or lower. It is.

  In step (4), thermoforming is performed using a mold having a desired shape. Specifically, for example, the thermoforming sheet heated in the step (3) is placed in a mold in a vacuum / pressure forming machine as it is, and the inside of the mold is heated to a predetermined temperature to be pressurized or not applied. By maintaining the pressure state, a molded body obtained by vacuum forming or pressure forming is obtained. The mold temperature is 60 ° C. or higher, preferably 70 ° C. or higher, more preferably 75 ° C. or higher, more preferably 80 ° C. or higher, from the viewpoint of improving the crystallization speed and workability of the polylactic acid resin composition. From the same viewpoint, it is 140 ° C. or lower, preferably 120 ° C. or lower, more preferably 115 ° C. or lower, and further preferably 110 ° C. or lower. From the viewpoint of improving the heat resistance and productivity of the thermoformed article made of the polylactic acid resin composition, the holding time in the mold is preferably 2 seconds or more and 60 seconds or less in a 90 ° C. mold, for example, 3 seconds. It is more preferably 30 seconds or less and more preferably 5 seconds or more and 20 seconds or less. In a mold at 100 ° C., 2 seconds or more and 60 seconds or less are preferable, 3 seconds or more and 30 seconds or less are more preferable, and 5 seconds or more and 20 seconds or less. The following is more preferable, and more preferably 5 seconds or longer and 15 seconds or shorter. Since the polylactic acid resin composition in the present invention has a high crystallization rate, a molded product having sufficient heat resistance can be obtained even with a short holding time as described above. The mold temperature referred to here is preferably the set temperature of the upper mold, and the set temperature of the lower mold may be the same as or different from the upper mold, The temperature is preferably lower, for example, 10 ° C. or higher and 30 ° C. or lower.

  The thermoformed article of the present invention thus obtained has excellent fitability, high crystallinity, excellent heat resistance and transparency because the thermoforming sheet of the present invention has good thermoformability. Is.

  The thickness of the thermoformed product of the present invention is not particularly limited, but from the viewpoint of obtaining a uniform formed product (secondary processed product), it is preferably 0.1 mm or more, more preferably 0.15 mm or more, still more preferably 0.00. It is 2 mm or more, preferably 1.5 mm or less, more preferably 1.2 mm or less, still more preferably 0.8 mm or less, and even more preferably 0.5 mm or less.

  The Haze value of the thermoformed article of the present invention is preferably 0.1% or more, more preferably 0.2% or more, still more preferably 0.3% or more from the viewpoint of heat resistance, and from the viewpoint of transparency. Preferably, it is 10.0% or less, more preferably 7.0% or less, and still more preferably 6.5% or less. In the present specification, the Haze value is an index of transparency, and can be measured by the method described in Examples described later.

  Further, the relative crystallinity of the thermoformed product of the present invention is preferably 80% or more, more preferably 85% or more, and still more preferably 88% or more. There is no particular upper limit.

  The thus obtained thermoformed article of the present invention is excellent in heat resistance because of its high crystallinity, and also because of its excellent transparency, bleed resistance, and strength. As packaging materials for cosmetics, home appliances, etc., it can be suitably used for blister packs and trays, food containers such as lunch box lids, and industrial trays used for transport and protection of industrial parts.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example. The parts in the examples are parts by mass unless otherwise specified. “Normal pressure” indicates 101.3 kPa, and “normal temperature” indicates 25 ° C.

[Melting point, glass transition temperature of polylactic acid resin composition]
Using the differential scanning calorimeter “DSC8500” (manufactured by PerkinElmer), the inflection point of 2ndRUN measured under the following measurement conditions is defined as the glass transition temperature (Tg). The peak top of the endothermic peak observed at around 160 ° C. is defined as the melting point (Tm).
Measurement conditions: Weigh about 10 mg of sample in a standard aluminum pan manufactured by PerkinElmer, set the prepared aluminum pan on DSC8500, raise the temperature from 25 ° C. to 200 ° C. at 15 ° C./min, and hold at 200 ° C. for 1 minute. (1stRUN). Then, after cooling from 200 ° C. to 25 ° C. at −500 ° C./min and holding at 25 ° C. for 1 minute, the temperature is raised from 25 ° C. to 200 ° C. at a rate of 15 ° C./min (2ndRUN).

Production Example 1 of Plasticizer (Diester Compound of Succinic Acid and Triethylene Glycol Monomethyl Ether)
A four-necked flask (with a stirrer, thermometer, dropping funnel, distillation tube and nitrogen blowing tube) was charged with 363 g (3.42 mol) of diethylene glycol and 6.6 g of a methanol solution containing 28% by weight sodium methoxide as a catalyst (sodium methoxide 0). 0.034 mol) was added, and methanol was distilled off while stirring at normal pressure and 120 ° C. for 0.5 hour. Thereafter, 1000 g (6.84 mol) of dimethyl succinate (manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise over 3 hours, and methanol produced by the reaction was distilled off at normal pressure and 120 ° C. Next, the mixture was cooled to 75 ° C., the pressure was gradually reduced from normal pressure to 6.7 kPa over 1.5 hours to distill off methanol, and the pressure was returned to normal pressure. Further, 28% by mass sodium methoxide as a catalyst was obtained. A methanol solution containing 5.8 g (sodium methoxide 0.030 mol) was added, and the pressure was gradually reduced from normal pressure to 2.9 kPa over 2 hours at 100 ° C. to distill methanol. Then, after cooling to 80 ° C., 18 g of KYOWARD 600S (manufactured by Kyowa Chemical Industry Co., Ltd.) was added and stirred at a pressure of 4.0 kPa and 80 ° C. for 1 hour, followed by filtration under reduced pressure. The filtrate was pressured at 0.3 kPa and the temperature was raised from 70 ° C. to 190 ° C. over 1 hour to distill off the remaining dimethyl succinate to obtain a room temperature yellow liquid. In addition, the usage-amount of the catalyst was 0.94 mol with respect to 100 mol of dicarboxylic acid ester.

<Step (1)>
As a polylactic acid resin composition, the composition raw materials shown in Tables 1 to 3 were melted and kneaded at a rotational speed of 90 r / min for 10 minutes using a twin screw extruder “HK-25D” (manufactured by PARKER) at a melt kneading temperature of 180 to 190. The mixture was melt-kneaded at 0 ° C., strand cut was performed, and polylactic acid resin composition pellets were obtained. The obtained pellets were dried at 70 ° C. under reduced pressure for 1 day, and the water content was adjusted to 500 ppm or less.

About the polylactic acid resin composition obtained above, an extrusion sheet molding machine “single-layer sheet molding apparatus, model: BNT-32” (Plastics Engineering Laboratory Co., Ltd.) equipped with a cooling roll and a heating roll was used. A sheet having a width of 40 cm was formed (thickness: 0.25 mm) under the following extrusion molding conditions. Note that the cylinder temperature and the die (outlet) temperature of the biaxial kneading section were measured using a contact thermometer.
<Extrusion conditions>
Cylinder temperature of biaxial kneading part: 200 ° C (actual measured value)
Die (outlet) temperature: 190 ° C (actual measured value)
Cooling roll temperature: 25 ° C

<Step (2)>
[Constant temperature and humidity machine]
The obtained sheet is wound around a paper core (made by Oka Packing Materials, inner diameter 76.2 mm, thickness 10 mm, length 300 mm) with a force of 2 kg, and then stored in a constant temperature and humidity machine (LHL-113 made by ESPEC). A heat treatment was performed. Regarding Examples 1 to 5 and Comparative Examples 1 to 8, the heat treatment temperature was 38 ° C. for 24 hours, and for Example 6 and Comparative Example 9, the heat treatment temperature was 48 ° C. for 24 hours. It was. The sheet thickness after the treatment was 0.25 mm. The results are shown in Tables 1 and 2.

In Table 3, an experiment corresponding to the example of Patent Document 2 described above was performed.
Specifically, heat treatment was performed by adjusting the temperature and winding speed of the cooling roll and heating roll in the extrusion sheet molding machine “BNT-32” used at the time of creating the sheet in the step (1). Evaluation was performed under the following conditions as the conditions for applying the most heat to the sheet.
<Extrusion conditions>
Cylinder temperature of biaxial kneading part: 200 ° C (actual measured value)
Die (outlet) temperature: 190 ° C (actual measured value)
Winding speed (take-up speed): 30m / min
Cooling roll temperature: 30 ° C
Heating roll temperature: 40 ° C

<Steps (3) and (4)>
Subsequently, the thermoforming sheet was attached to a guide using a single vacuum / pressure forming machine “FVS-500P WAKITEC” (manufactured by Wakisaka Manufacturing Co., Ltd.), and the thermoforming sheet was heated to 80 ° C. using a heater. Thereafter, the heated thermoforming sheet was vacuum-formed using upper and lower molds set to an upper mold of 100 ° C. and a lower mold of 25 ° C., and held in the mold for 5 seconds to obtain a molded body (thickness). 0.25 mm). The sheet surface temperature was measured by directly measuring the sheet surface temperature after heating with a surface thermometer. The mold (lid) used is shown in FIG. In addition, the sheet | seat prepared the thermoformed body about each before and after the preservation | save on the conditions shown in Tables 1-3.

  The characteristics of the obtained thermoforming sheet and thermoformed body were evaluated according to the following Test Examples 1 to 4. The results are shown in Tables 1-3. In addition, for Test Example 2, if there is storage in a thermo-hygrostat, it is once taken out and evaluated at the stage after storage for 4 hours, and then stored again and evaluated again when storage is completed. went. Moreover, in the sheet | seat for thermoforming of Examples 1-5 and Comparative Examples 6 and 8, the relationship between the time preserve | saved at 38 degree | times and a half crystallization time is shown in FIG.

Test Example 1 <Semi-crystallization time>
Using a differential scanning calorimeter “DSC8500” (manufactured by PerkinElmer), the amount of time required for 50% crystallization to proceed is calculated from the amount of heat measured under the following measurement conditions. Time (minutes). The shorter the half crystallization time, the better the crystallization speed.
Measurement conditions: About 10 mg of thermoforming sheet is weighed on a standard aluminum pan manufactured by PerkinElmer, set on DSC8500, heated from 25 ° C. to 90 ° C. at 500 ° C./min, and then held at 90 ° C. for 10 minutes.

Test Example 2 <Crystallinity>
About 10 mg of each of the thermoforming sheet and the thermoformed body, each was precisely weighed, sealed in an aluminum pan, and then using a differential scanning calorimetric analyzer “DSC8500” (manufactured by PerkinElmer) as 1stRUN at a heating rate of 15 ° C./min. After raising the temperature from 25 ° C. to 200 ° C. and holding at 200 ° C. for 1 minute, the temperature was lowered from 200 ° C. to 25 ° C. at a temperature drop rate of −500 ° C./minute, held at 25 ° C. for 1 minute, and further increased to 2ndRUN. The temperature was raised from 25 ° C. to 200 ° C. at a temperature rate of 15 ° C./min, and the absolute value ΔHc of the cold crystallization enthalpy of the polylactic acid resin observed at 1stRUN was obtained, and the crystal melting enthalpy ΔHm observed at 2ndRUN was obtained. From the value, the relative crystallinity (%) was determined by the following formula, and the crystallinity was evaluated. When the relative crystallinity is less than 60%, it is in an amorphous state, when it is 65% or more and less than 80%, it is in a semi-crystalline state, and when it is 80% or more, it is in a crystalline state.
Relative crystallinity (%) = {(ΔHm−ΔHc) / ΔHm} × 100

Test Example 3 <Transparency>
About the sheet | seat for thermoforming, and a thermoformed object, the haze value (%) was measured using the haze meter "HM-150 type" (made by Murakami Color Research Laboratory), and this was made into the parameter | index of transparency. A small Haze value indicates good transparency.

Test Example 4 <Thermoformability>
The shape and fit of the molded body were evaluated according to the following methods. In addition, a molded object standard is a lid | cover of the container (brand name Yugaku 90 Shino CPP Kasei Co., Ltd.) of a commercial item. If it is 3 or more by evaluation criteria, it is preferable that it is 4 or more.
Shape: The shape of the obtained molded body was visually compared with the shape of the molded body specimen molded with the mold (lid) of FIG. 1 and evaluated according to the following evaluation criteria.
Fitting property: It was fitted to a main body part (φ81 mm, height 51 mm, material made of low foamed PS containing PP) of a commercially available container (trade name: Yubumimi 90, Shino CPC Kasei Co., Ltd.) and evaluated according to the following evaluation criteria. Two or more are preferable, and three or more are more preferable.
〔Evaluation criteria〕
4: It is the same shape as a molded object standard, and can be fitted without applying a load.
3: It is the same shape as a molded object standard, and can be fitted by applying a load.
2: It has almost the same shape as the molded product, and can be barely fitted.
1: The shape is clearly different from the molded product or does not fit.

In addition, the raw material in Tables 1-3 is as follows.
[Polylactic acid resin]
4032D: Poly-L-lactic acid (optical purity 98.5%), manufactured by Nature Works [Plasticizer]
(MeEO ₃ ) ₂ SA: Diester compound ATBC produced in Production Example 1 of the plasticizer: Acetyltributyl citrate DAIFATTY-101 manufactured by Taoka Chemical Co., Ltd .: Daihachi Chemical Co., Ltd. [crystal nucleating agent]
Ethylene bis-12-hydroxystearic acid amide: SLIPAX H, Nippon Kasei Co., Ltd. Ethylene bis stearic acid amide: Kao wax EB-G, Kao Corporation Phenylphosphonic acid zinc salt: Eco Promote, Nissan Chemical Co., Ltd. Talc: MICROACE P -6, manufactured by Nippon Talc Co., Ltd. [hydrolysis inhibitor]
Carbodilite LA-1: Aliphatic polycarbodiimide compound, manufactured by Nisshinbo Chemical Co., Ltd.

From the results of Tables 1 to 3, the sheet for thermoforming obtained by the production method of the present invention is excellent in thermoforming even after storage at high temperature, and the obtained thermoformed body exhibits high crystallinity. And, it had good transparency and good appearance.
As is clear from FIG. 2, in the case of a nucleating agent other than an amide organic crystal nucleating agent, for example, zinc salt of phenylphosphonic acid or talc, a phenomenon occurs in which the semicrystallization time once increases with the storage period and then decreases. Absent. That is, it can be seen that the nucleating agent other than the amide organic crystal nucleating agent does not have the problem of the present application.

  Since the thermoforming sheet obtained by the production method of the present invention has high thermoformability, it can be suitably used for various applications such as food containers, packaging materials for household goods and household appliances, and trays for industrial parts. it can.

Claims (6)

The manufacturing method of the sheet | seat for thermoforming including following process (1) and (2).
Step (1): Preparing an amorphous or semi-crystalline sheet of a polylactic acid resin composition containing a polylactic acid resin and an amide organic crystal nucleating agent Step (2): The sheet obtained in step (1) It is a step of storing at a temperature not higher than the glass transition temperature (Tg) of the polylactic acid resin composition, which is increased by storing the half crystallization time calculated by the following method (A) to 0.7 min or more. (A) Using a differential scanning calorimeter, the sample is heated from 25 ° C. to 90 ° C. at a rate of 500 ° C./min. Then, from the amount of heat measured when held at 90 ° C. for 10 minutes, the time necessary for 50% crystallization to proceed is calculated and set as the half crystallization time (minutes). Step (2) Storage temperature in is 30 ° C. or higher 40 ° C. or less, the production method according to claim 1, wherein.
  The production method according to claim 1 or 2, wherein the content of the amide organic crystal nucleating agent is 0.01 to 5 parts by mass with respect to 100 parts by mass of the polylactic acid resin.   The production method according to any one of claims 1 to 3, wherein the amide organic crystal nucleating agent contains one or two selected from fatty acid monoamide and fatty acid bisamide.   The manufacturing method according to any one of claims 1 to 4, wherein the obtained thermoforming sheet has a thickness of 0.1 to 1.5 mm. A method for producing a thermoformed article comprising the following steps (1) to (4).
Step (1): Preparing an amorphous or semi-crystalline sheet of a polylactic acid resin composition containing a polylactic acid resin and an amide organic crystal nucleating agent Step (2): The sheet obtained in step (1) It is a step of storing at a temperature not higher than the glass transition temperature (Tg) of the polylactic acid resin composition, and increases by storing the half crystallization time calculated by the following method (A) to be 0.7 minutes or more. (A) Using a differential scanning calorimeter, the sample is heated from 25 ° C. to 90 ° C. at a rate of 500 ° C./min. Then, from the amount of heat measured when held at 90 ° C. for 10 minutes, the time necessary for 50% crystallization to proceed is calculated and set as the semi-crystallization time (minutes): Step (3): Step (2) ) Of the polylactic acid resin composition Step (4) of heating in a temperature range not lower than the glass transition temperature (Tg) and lower than the melting point (Tm): Heat the sheet obtained in the step (3) using a mold having a mold temperature of 60 to 140 ° C. Molding process

Images