JP2008239728A - Method for producing polylactic acid foamed molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple method for producing a low-volatile content polylactic acid foamed molding excellent in dimensional stability under high-temperature high-humidity conditions and to provide a molding produced thereby. <P>SOLUTION: A low-volatile content polylactic acid foamed molding is produced by subjecting a polylactic acid foamed molding containing a hydrocarbon blowing agent to treatment with carbon dioxide. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a polylactic acid-based foamed molded article.

  As an alternative to expanded polystyrene and expanded polyolefin using a fossil resource as a raw material, Patent Document 1 proposes an expanded molded body using polylactic acid as a main raw material. This foamed molded article uses starch, which is a non-petroleum resource, as a starting material, and can be said to be very desirable from the viewpoint of recent petroleum circumstances and environmental conservation. The foamed molded article had mechanical properties and secondary processability equivalent to those of expanded polystyrene, and could be sufficiently used as a normal packing cushioning material. However, the foamed molded article of Patent Document 1 has a large amount of volatile components such as a foaming agent remaining, so that the volume changes significantly under high temperature and high humidity conditions, and cannot be used under severe conditions such as overseas export. was there.

  Regarding the technology for imparting heat resistance to a polylactic acid-based foamed molded article, in Patent Document 2, the content of the hydrocarbon-based foaming agent having 3 to 5 carbon atoms is less than 0.5 mol / kg (vs. resin). A technique is disclosed in which the volume expansion coefficient under high-temperature and high-humidity conditions (60 ° C. × 80% RH) can be reduced to 20% or less by producing a foamed molded article. Specifically, (1) the foaming ratio is low, but the method of reducing the content of the first foaming agent, (2) the method of reducing the residual foaming agent stepwise by repeating pre-foaming multiple times, (3) The foaming agent content in the molded body is less than 0.5 mol / kg (vs. resin) by applying or dipping a swelling agent such as alcohol on the foam and drying, etc., both of which take time As a result, the lowering of the foaming agent content in the molded product was 0.21 mol / kg (vs. resin).

As described above, there are several techniques for imparting heat resistance to the polylactic acid-based foamed molded article, but a simpler method is desired.
International Publication No. 99/21915 Pamphlet JP 2005-105097 A

  It is an object of the present invention to provide a simple method for producing a polylactic acid-based foamed molded article having excellent dimensional stability under high-temperature and high-humidity conditions and having a reduced volatile content, and a molded article related thereto.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have conducted a carbon dioxide treatment under specific conditions on a polylactic acid-based foamed molded article containing a hydrocarbon-based foaming agent. Foam with reduced volatile content, with a reduced volume content of hydrocarbon-based foaming agent in lactic acid-based foamed moldings and a significant improvement in volume change rate under high temperature and high humidity conditions (60 ° C x 80% RH) The present inventors have found that a molded body can be obtained and have completed the present invention.

  That is, the first of the present invention is a polylactic acid-based foamed molded article having a reduced volatile content, characterized by performing carbon dioxide treatment on a polylactic acid-based foamed molded article containing a hydrocarbon-based foaming agent. It relates to the manufacturing method. In a preferred embodiment, the carbon dioxide treatment is performed by exposing the polylactic acid-based foamed molded article to a carbon dioxide atmosphere having a pressure of 0.1 MPa or more and less than 2.0 MPa. The present invention also relates to a method for producing a polylactic acid-based foamed molded article. More preferably, the carbon dioxide treatment exposes the polylactic acid-based foamed molded article to a carbon dioxide atmosphere in a time of 0.5 minutes or more and less than 10 minutes, and the volatile content is reduced as described above A process for producing a polylactic acid-based foamed molded article, more preferably, the polylactic acid-based foamed molded article having a reduced volatile content as described above, wherein the hydrocarbon-based foaming agent is an aliphatic hydrocarbon having 3 to 6 carbon atoms. A production method, particularly preferably, a polylactic acid-based foamed molded article comprising a polylactic acid-based resin as a main component and gelling treatment of the polylactic acid-based resin as described above. The present invention relates to a method for producing a lactic acid-based foamed molded article.

  According to the production method of the present invention, it is possible to provide a simple production method of a polylactic acid-based foamed molded article having a reduced volatile content which is excellent in dimensional stability under high temperature and high humidity conditions, and a molded article related thereto. it can.

  Hereinafter, the present invention will be described in more detail. In the method for producing a polylactic acid-based foam molded article with a reduced volatile content according to the present invention, carbon dioxide treatment is performed on a polylactic acid-based foam molded article produced using a hydrocarbon-based foaming agent under specific conditions. It is characterized by that. In the polylactic acid-based foam molded article, the base resin is a polylactic acid-based resin, and the base resin may contain other resins in the polylactic acid-based resin as long as the effects of the present invention are not impaired. In addition, additives such as coloring pigments or dyes, flame retardants, antistatic agents, weathering agents, and end-capping agents may be added.

  The polylactic acid-based foamed molded product in the present invention is a foamed molded product in which the base resin is a polylactic acid-based resin. The polylactic acid-based resin is not particularly limited. However, since a resin having high crystallinity may be difficult to foam and mold due to crystallization, the isomer ratio of the lactic acid component is preferably 5% or more, more preferably The main component is 8% or more of polylactic acid. As long as the effects of the present invention are not impaired, other resins can be added to the polylactic acid resin to form a base resin. The whole base resin preferably contains 50% by weight or more of polylactic acid resin, more preferably 70% by weight or more, and still more preferably 90% by weight or more. Examples of the other resins include polyethylene resins, polypropylene resins, polystyrene resins, polyester resins, acrylic resins, vinyl resins, biodegradable aliphatic polyester resins, and the like, selected from these groups. At least one kind can be used. Examples of the biodegradable aliphatic polyester-based resin include biodegradable aliphatic polyester-based resins containing at least 35 mol% of aliphatic polyester component units. Condensates, ring-opening polymers of lactones such as polycaprolactone, polybutylene succinates, polybutylene adipates, polybutylene succinate adipates, poly (butylene adipates / terephthalates) and other aliphatic polyhydric alcohols and aliphatic carboxylic acids A polycondensate is mentioned, At least 1 sort (s) chosen from those groups can be used.

  The polylactic acid-based resin may be a copolymer in which a part of the monomer is replaced with an aliphatic hydroxycarboxylic acid, an aliphatic polyvalent carboxylic acid, an aliphatic polyhydric alcohol or the like that can be exchanged with lactic acid. It may be partially crosslinked with epoxidized flaxseed.

  Examples of the aliphatic hydroxycarboxylic acid include glycolic acid, hydroxybutyric acid, hydroxyvalic acid, hydroxycaproic acid, hydroxyheptanoic acid, and the like, and at least one selected from these groups is used. Examples of the aliphatic polyvalent carboxylic acid include succinic acid, adipic acid, suberic acid, sebacic acid, dodecanedicarboxylic acid, succinic anhydride, adipic anhydride, trimesic acid, propanetricarboxylic acid, pyromellitic anhydride, pyromellitic anhydride An acid etc. are mentioned, At least 1 sort (s) chosen from those groups is used. Examples of the aliphatic polyhydric alcohol include ethylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, decamethylene glycol, glycerin, trimethylolpropane, Examples include pentaerythritol, and at least one selected from the group is used.

  The melt viscosity of the polylactic acid resin is preferably a high molecular weight polylactic acid resin having a melt index (MI) value of 0.1 to 10 g / 10 min in accordance with JIS K 7210 (load 2.16 kg). . If the MI value is within this range, it tends to be easy to obtain a foamed molded article having excellent productivity and a high expansion ratio, and the object and effect of the present invention can be obtained effectively.

  In the present invention, it is preferable from the viewpoints of foamability and moldability that the polylactic acid resin, which is the base resin of the polylactic acid foam molded article, is subjected to gelation treatment. The gelation treatment can increase the viscosity of the polylactic acid resin to a viscosity range suitable for foaming. For this gelation treatment, various conventionally known methods, for example, a method of selecting and using at least one general crosslinking agent such as a polyisocyanate compound, a peroxide, an acid anhydride, and an epoxy compound, an electron Although a wire cross-linking method, a silane cross-linking method, and the like are included, among them, the method using a cross-linking agent is preferable.

  As the polyisocyanate compound, aromatic, alicyclic and aliphatic polyisocyanate compounds can be used. As the aromatic polyisocyanate, polyisocyanate compounds having a skeleton of tolylene, diphenylmethane, naphthylene and triphenylmethane. Is mentioned. Examples of the alicyclic polyisocyanate include polyisocyanate compounds having isophorone and diphenylmethane hydroxide as a skeleton, and examples of the aliphatic polyisocyanate include polyisocyanate compounds having hexamethylene and lysine as a skeleton.

  Examples of the peroxide include benzoyl peroxide, bis (butylperoxy) trimethylcyclohexane, bis (butylperoxy) cyclododecane, butylbis (butylperoxy) valerate, dicumyl peroxide, butylperoxybenzoate, and dibutyl peroxide. And organic oxides such as bis (butylperoxy) diisopropylbenzene, dimethyldi (butylperoxy) hexane, dimethyldi (butylperoxy) hexyne, and butylperoxycumene.

  Examples of the acid anhydride include trimellitic anhydride, pyromellitic anhydride, ethylene-maleic anhydride copolymer, methyl vinyl ether-maleic anhydride copolymer, styrene-maleic anhydride copolymer, and the like.

  Examples of the epoxy compound include glycidyl methacrylate-methyl methacrylate copolymer, glycidyl methacrylate-styrene copolymer, glycidyl methacrylate-styrene-butyl acrylate copolymer, polyethylene glycol diglycidyl ether, trimethylolpropane polyglycidyl ether, coconut fatty acid glycidyl. Examples thereof include various glycidyl ethers such as esters, epoxidized soybean oil, and epoxidized linseed oil, and various glycidyl esters.

  Of the cross-linking agents, polyisocyanate compounds are preferably used. The reason is that if a polyisocyanate compound is used, torque increase due to cross-linking thickening during kneading is small, and post-thickening due to urea bond, urethane bond, allophanate bond, etc. is possible by heating in the presence of moisture after kneading. Because it becomes. Among the polyisocyanate compounds, it is preferable to use a polyisocyanate compound having a tolylene or diphenylmethane skeleton, particularly a polyisocyanate of diphenylmethane, from the viewpoints of versatility, handleability, weather resistance, and the like. The addition amount of the crosslinking agent can be arbitrarily selected, but it is preferably 0.1 to 6.0 parts by weight, more preferably 0.00 parts by weight with respect to 100 parts by weight of the polylactic acid resin. It is 2 to 5.0 parts by weight, more preferably 0.5 to 4.0 parts by weight. When the addition amount is 0.1 to 6.0 parts by weight, the melt viscosity of the polylactic acid resin can be increased to a region suitable for foaming.

  The foaming agent of the present invention is not particularly limited and conventionally known ones can be used, and hydrocarbon-based foaming agents such as propane, isobutane, normal butane, isohexane, normal hexane, cyclobutane, cyclohexane, isopentane, normal pentane, cyclopentane, etc. And halogenated hydrocarbon blowing agents such as methyl chloride, methylene chloride and dichlorodifluoromethane, ether blowing agents such as dimethyl ether and methyl ethyl ether, and inorganic blowing agents such as nitrogen, carbon dioxide, argon and air. , At least one selected from these groups can be used. Among them, a hydrocarbon foaming agent having 3 to 6 carbon atoms is preferable from the viewpoint that the gas dissipation with respect to the polylactic acid resin is small, the foamable particles can be transported, and the desired foamability can be obtained.

  For example, a coloring pigment or dye such as black, gray, brown, blue, or green may be added to the base resin. If the colored base resin is used, colored foamed particles and foamed molded products can be obtained. Examples of the colorant include organic and inorganic pigments and dyes. As such pigments and dyes, various conventionally known pigments can be used. Moreover, as a bubble regulator, inorganic substances, such as talc, calcium carbonate, borax, zinc borate, aluminum hydroxide, calcium stearate, can be added in advance. When additives such as color pigments, dyes or inorganic substances are added to the base resin, the additives can be kneaded as they are into the polylactic acid resin as the base resin, but usually in consideration of dispersibility, etc. It is preferable to make a master batch of the additive and knead it with the base resin. Here, the master batch is prepared by mixing a desired additive with a polylactic acid resin. The addition amount of the color pigment or dye varies depending on the color of the color, but is usually preferably 0.001 to 5 parts by weight, and 0.02 to 3 parts by weight with respect to 100 parts by weight of the polylactic acid resin. More preferred. Other additives such as flame retardants, antistatic agents, weathering agents, and end-capping agents may be added to the polylactic acid resin as long as the effects of the present invention are not impaired.

  The method for producing a polylactic acid-based foamed molded article having a reduced volatile content of the present invention is not particularly limited. For example, first, polylactic acid-based foamable particles are prepared, and then the foamable particles are produced as follows. Is expanded to obtain polylactic acid-based expanded particles, and then molded in-mold to obtain a polylactic acid-based expanded molded body. Thereafter, the foamed molded product is treated with carbon dioxide to obtain a polylactic acid-based foamed molded product having a reduced volatile content.

<Process for producing polylactic acid-based foamed molded products>
As a method for producing the polylactic acid-based foam molded article used in the present invention, a conventionally known method can be employed (for example, International Publication No. WO 99/021915).

(Preparation of polylactic acid resin particles)
In the present invention, in order to preferably produce a polylactic acid-based foamed molded article, first, polylactic acid-based resin particles are prepared. These polylactic acid-based resin particles can be produced by a conventionally known method. For example, after polylactic acid-based resin and a crosslinking agent, and if necessary, other additives are melt-kneaded with an extruder, an underwater cutter or a strand cutter is used. It can be obtained by extrusion cutting. The weight per polylactic acid resin particle is preferably 0.05 to 10 mg, more preferably 0.1 to 4 mg. When the particle weight is in the above range, the productivity of the resin particles is good, and the filling property during in-mold molding tends to be good.

(Polylactic acid resin particles impregnated with foaming agent)
Next, the polylactic acid resin particles are impregnated with a foaming agent to obtain polylactic acid foamable particles. The method for impregnating the polylactic acid resin particles with the foaming agent is not particularly limited as long as sufficient pressure is applied in the presence of the foaming agent that provides the desired foamability. For example, it is possible to impregnate a resin particle with a foaming agent by placing an aqueous medium or a non-aqueous medium in an airtight container, adding resin particles and a foaming agent thereto, and stirring at an appropriate temperature and time. is there. In the case of impregnation with an aqueous medium, it is preferable to end the impregnation in a short time or a device that suppresses hydrolysis in consideration of the polyester resin composition that is susceptible to hydrolysis reaction.

  The impregnation amount of the foaming agent may be adjusted depending on the type of foaming agent and the desired foaming ratio. For example, in order to obtain foamed particles having a foaming ratio of 30 times or more, the base resin 100 constituting the foamable particles 4 parts by weight or more is preferable with respect to parts by weight.

  In the impregnation of the foaming agent, an impregnation aid, a dispersing agent or the like may be used in order to obtain stable impregnation properties and foamability. As impregnation aids, proton solvents represented by alcohols such as methanol, ethanol and propanol, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, butyl acetate and normal propyl acetate, toluene, xylene and the like Examples include aprotic solvents such as aromatic hydrocarbons. When impregnated with an aqueous medium, it is preferable to use an aprotic solvent that does not promote hydrolysis of the polylactic acid resin.

  Examples of the dispersant include a cationic surfactant, an anionic surfactant, and a nonionic surfactant.

  When impregnated with an aqueous medium, monovalent metal salts such as sodium chloride, sodium sulfate, sodium carbonate, potassium chloride, potassium sulfate, and potassium carbonate, magnesium chloride for the purpose of suppressing water penetration into the resin Water-soluble salts such as divalent metal salts such as magnesium sulfate and trivalent metal salts such as aluminum sulfate are preferably added. The amount of water-soluble salts added for the purpose of suppressing the penetration of water into the resin is 5 parts by weight or more, more preferably 7.5 parts by weight or more with respect to 100 parts by weight of water.

  In the above, when obtaining polylactic acid-based expandable particles, an extruder can be used. In that case, a polylactic acid-based resin and a crosslinking agent, and if necessary, other additives are added to the extruder, and then the foaming agent. After kneading and melt-kneading, the kneaded product can be extruded, and the extruded kneaded product can be cut to obtain expandable particles.

(Foaming of polylactic acid-based expandable particles)
Next, the polylactic acid-based expandable particles obtained as described above are expanded to obtain polylactic acid-based expanded particles. As such a method, for example, a method (A) in which polylactic acid-based expandable particles are pre-foamed with steam, hot air, high frequency or the like using a pre-foaming machine for foamed polystyrene is the simplest method. As another method, the resin particles are dispersed in a dispersion medium in the presence of a foaming agent in a sealed container, and the contents are heated to soften the resin particles and impregnate the foaming agent in the particles. Next, one end of the container is opened, and while maintaining the internal pressure of the container at a pressure equal to or higher than the vapor pressure of the foaming agent, the particles and the dispersion medium are simultaneously released into an atmosphere at a lower pressure (usually under atmospheric pressure) than in the container to foam Foaming method (B), base resin, crosslinking agent, and other additives are melted with an extruder, kneaded with a foaming agent to form a foamable melt-kneaded product, and then extruded into a strand to foam, and after cooling There is a method (C) for producing expanded particles by cutting to an appropriate length or by cooling the strands to an appropriate length and then cooling. The method (A) is possible because the expandable particles can be transported. Is preferred

(In-mold molding)
A predetermined amount of the polylactic acid-based foamed particles obtained above is filled into a desired mold, heated under appropriate conditions with steam or the like to be secondarily foamed, and the foamed particles are fused together in the mold to form a polylactic acid-based A foamed molded product is obtained. In this in-mold molding, a conventional molding machine such as foamed polystyrene or foamed polyolefin can be used.

<Production process of polylactic acid-based foamed molded product with reduced volatile content>
The polylactic acid-based foamed molded product obtained above was subjected to the following carbon dioxide treatment to reduce the volatile content, thereby obtaining a polylactic acid-based foamed molded product having a desired volatile content reduced.

<CO2 treatment>
In this step, it is possible to obtain a polylactic acid-based foam molded article having a reduced volatile content by maintaining the polylactic acid-based foam molded article obtained above in a carbon dioxide atmosphere under a specific pressure for a certain period of time. it can. By performing the carbon dioxide treatment, the content of the hydrocarbon-based foaming agent in the polylactic acid-based foamed molded product is reduced, and as a result, volume expansion under high-temperature and high-humidity conditions can be suppressed.

  As a condition for performing the carbon dioxide treatment on the polylactic acid-based foamed molded article, it is preferable to carry out for a short time under the necessary pressure condition. Specifically, the pressurizing condition with carbon dioxide is preferably 0.1 ≦ pressure (MPa) <2.0, more preferably 0.2 ≦ pressure (MPa) ≦ 1.0, and further preferably 0.3 ≦ pressure. (MPa) ≦ 1.0. The treatment time for applying carbon dioxide to the foamed molded article at a predetermined pressure depends on the temperature to be treated or the humidity held by the carbon dioxide, but preferably 0.5 ≦ treatment time (min) <10, more preferably 1. ≦ Processing time (min) <10, more preferably 3 ≦ Processing time (min) <10, and particularly preferably 3 ≦ Processing time (min) <5. The pressurizing condition with carbon dioxide is preferably less than 2.0 MPa because the cost including the equipment is increased when the pressure is 2.0 MPa or more. Further, the carbon dioxide application treatment time is sufficient in a short time, and considering the productivity advantage, it is preferably less than 10 minutes.

  The equipment for imparting carbon dioxide can be used regardless of its shape and size as long as the pressure resistance is guaranteed. After taking out the polylactic acid-based foamed molded product from the mold, the molded product may be put into another pressure-resistant container and subjected to carbon dioxide treatment, or the molding is completed using a pressure-resistant mold in in-mold molding. Later, carbon dioxide may be treated by enclosing carbon dioxide in a mold. The latter is preferable from the viewpoint of productivity.

  The polylactic acid-based foam molded article having a reduced volatile content obtained as described above is excellent in dimensional stability under high temperature and high humidity conditions. In the present invention, the residual volatile content in the low volatile polylactic acid-based foamed molded article is measured as follows. The carbon dioxide-treated foam molded product obtained above is sufficiently dried, and then left in an atmosphere at 150 ° C. for 30 minutes, and then the change in weight before and after standing is measured with respect to the original weight of the foam molded product. The value divided by the original weight of the foamed molded product is defined as the volatile content (%). The volatile matter is mostly a foaming agent, but contains a small amount of moisture.

  The polylactic acid-based foamed molded article having a reduced volatile content of the present invention can be used for various applications. For example, cushioning materials such as precision equipment, electrical appliances, electronic equipment, electronic parts, packaging materials such as foods, alcoholic beverages, chemicals, cosmetics such as display panels, mannequins, decorations, foods, mechanical parts, electronic parts, etc. It can be used for heat retaining materials such as returnable boxes, heat insulating materials, building materials, toys, ice cream, frozen foods, and the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples at all. The evaluation was performed by the following method. In the examples, “parts” and “%” are based on weight.

<Evaluation method>
(1) Foaming agent impregnation rate of expandable particles:
The impregnation rate was obtained from the weight of resin particles before and after impregnation by the following formula.
Impregnation rate (%) = 100 × (weight after impregnation−weight before impregnation) / weight before impregnation (2) Method for measuring expansion ratio of expanded particles:
The foamed particles are scraped off into a polyethylene cup having an internal volume of 2000 cm ³ , and the weight is measured. The weight of the foamed particles is determined by subtracting the weight of the cup. It calculated | required by the following formula from the weight and the apparent volume (2000 cm < ³ >) of the expanded particle.
Foaming ratio = apparent volume (2000 cm ³ ) / weight of foamed particles (3) volatile content of foam molded article:
The sufficiently dried foamed molded product was allowed to stand for 30 minutes in an atmosphere of 150 ° C., and the change in weight before and after the standing with respect to the original weight of the foamed molded product was measured to obtain the volatile content.
(4) Heat resistance (volume change rate under high temperature and high humidity conditions):
The foamed molded product is cut into 150 × 150 × 20 mm, treated under conditions of 60 ° C. × 80% RH for 24 hours, and the respective volumes are calculated from the measured values of length, width, and thickness before and after the processing, and molding before processing. The ratio of volume change to the body was calculated.

Example 1
First, 100 parts by weight of polylactic acid and a polyisocyanate compound (MR-200, manufactured by Nippon Polyurethane Co., Ltd.) having a D-form ratio of 10% and an MI value of 3.7 g / 10 min based on JIS K 7210 (load 2.16 kg) 3.0 parts by weight is melt-kneaded at a cylinder temperature of 185 ° C. using a twin screw extruder (Toshiba Machine, TEM35B), and about 1 mmφ (about 1.5 mg) bead-shaped polylactic acid using an underwater cutter System resin particles were obtained.

  With respect to 100 parts by weight of the obtained polylactic acid-based resin particles, 100 parts by weight of water, 12 parts by weight of deodorized butane (normal butane / isobutane weight ratio = 7/3) as a foaming agent, 10 parts by weight of sodium chloride as an impregnation aid, As a dispersant, 0.3 part by weight of polyoxyethylene oleyl ether was charged in a pressure vessel and held at 90 ° C. for 90 minutes. After sufficiently cooling, it was taken out and dried to obtain polylactic acid-based expandable particles. The impregnation rate of the obtained polylactic acid-based expandable particles was 5.7%.

  About 1.5 kg of the polylactic acid-based expandable particles were put into a pre-foaming machine (manufactured by Daisen Kogyo Co., Ltd., BHP-300) and held under steam at 90 ° C. for 40 to 60 seconds to obtain polylactic acid-based expanded particles. The obtained polylactic acid-based foamed particles were air-dried, and then the fused particles were separated using a sieve. The expansion ratio of the fractionated polylactic acid-based expanded particles was 35 times.

  After the separated polylactic acid-based foamed particles are aged for 24 hours or more, a 300 × 450 × 20 mm mold is placed on a foam molding machine (made by Daisen Kogyo, KR-57), and the foamed particles are compressed at 0%. Filled and treated with a steam pressure of 0.1 MPa for 10 to 20 seconds to perform in-mold molding to obtain a foam molded article.

  The obtained foamed molded article was put into a sealed container, and carbon dioxide treatment was performed by enclosing carbon dioxide in accordance with Table 1 and maintaining the pressure in the sealed container at 0.3 MPa for 3 minutes. Thereafter, the pressure in the container was released to obtain a polylactic acid-based foamed molded article having a reduced volatile content. The polylactic acid-based foamed molded article having a reduced volatile content was evaluated for the volatile content and heat resistance. The evaluation results are shown in Table 1.

(Comparative Example 1)
A foamed molded article was obtained in the same manner as in Example 1 except that the carbon dioxide treatment was not performed. At that time, the results of evaluating the volatile content and heat resistance of the foamed molded product are shown in Table 1.

(Comparative Example 2)
A foam molded article was obtained in the same manner as in Example 1 except that methanol treatment was performed instead of carbon dioxide treatment. In the methanol treatment, the foamed molded product was immersed in methanol for 10 seconds and air-dried at room temperature.

  From Example 1 and Comparative Example 1, it was found that by performing carbon dioxide treatment on the polylactic acid-based foamed molded article, the foaming agent content was reduced and the expansion at 60 ° C. × 80% RH was suppressed. Moreover, even in Comparative Example 2 based on JP-A-2005-105097, it was found that the foaming agent content was reduced by the methanol treatment and the expansion at 60 ° C. × 80% RH was suppressed. It was found that this method is advantageous because it has a low volatile content, good heat resistance, and is easy to handle.

(Example 2)
When producing a low volatile polylactic acid-based foam molded article, the same procedure as in Example 1 was performed except that the pressure in the sealed container after the carbon dioxide was sealed after the foam molded article was charged was changed to 0.1 MPa. Thus, a polylactic acid-based foamed molded article having a reduced volatile content was obtained. At that time, the results of evaluating the volatile content and heat resistance of the polylactic acid-based foamed molded product having a reduced volatile content are shown in Table 2.

(Example 3)
When producing a polylactic acid-based foamed molded product with a reduced volatile content, it was carried out except that the pressure inside the sealed container after enclosing the carbon dioxide after the foamed molded product was charged was changed to 0.5 MPa. A polylactic acid-based foamed molded article having a reduced volatile content was obtained in the same manner as in Example 1. At that time, the results of evaluating the foaming agent content and the heat resistance of the polylactic acid-based foamed molded article having a reduced volatile content are shown in Table 2.

Example 4
When producing a polylactic acid-based foamed molded product with a reduced volatile content, it was carried out except that the pressure inside the sealed container after the carbon dioxide was sealed after the foamed molded product was charged was changed to 1.0 MPa. A polylactic acid-based foamed molded article having a reduced volatile content was obtained in the same manner as in Example 1. At that time, the results of evaluating the foaming agent content and the heat resistance of the polylactic acid-based foamed molded article having a reduced volatile content are shown in Table 2.

  From Examples 1 to 4 and Comparative Example 1, when the carbon dioxide treatment was performed, when the closed container holding time was 3 minutes, the volatile content decreased even when the pressure in the container was 0.1 MPa, and 60 ° C. × 80% It was found that expansion at RH was suppressed.

(Example 5)
When producing a polylactic acid-based foamed molded product with a reduced volatile content, the time during which the pressure inside the sealed container is maintained at 0.3 MPa after the carbon dioxide is sealed after the foamed molded product is charged is 1 minute. A foamed molded article was obtained in the same manner as in Example 1 except that the above was changed. The results of evaluating the foaming agent content and heat resistance of the foamed molded product were as shown in Table 3.

(Example 6)
When producing a low volatile polylactic acid-based foamed molded article, except that the time for maintaining the pressure inside the sealed container at 0.3 MPa after charging the carbon dioxide after charging the foamed molded article was changed to 5 minutes. In the same manner as in Example 1, a polylactic acid-based foamed molded article having a reduced volatile content was obtained. At that time, the results of evaluating the volatile content and the heat resistance of the polylactic acid-based foamed molded product having a reduced volatile content are shown in Table 3.

(Example 7)
When producing a low volatile polylactic acid-based foamed molded article, except that the time for maintaining the pressure in the sealed container at 0.3 MPa after charging the carbon dioxide after the foamed molded article was charged was changed to 10 minutes. In the same manner as in Example 1, a polylactic acid-based foamed molded article having a reduced volatile content was obtained. At that time, the results of evaluating the volatile content and the heat resistance of the polylactic acid-based foamed molded product having a reduced volatile content are shown in Table 3.

  From Examples 1, 5 to 7 and Comparative Example 1, when the carbon dioxide treatment was performed, when the pressure in the sealed container was 0.3 MPa, the volatile content decreased even at a holding time of 1 minute, and 60 ° C. × 80 It was found that the expansion at% RH was suppressed.

Claims (5)

  A method for producing a polylactic acid-based foamed molded article having a reduced volatile content, characterized by subjecting a polylactic acid-based foamed molded article containing a hydrocarbon-based foaming agent to carbon dioxide treatment.   The lactic acid content-reduced polylactic acid according to claim 1, wherein the carbon dioxide treatment exposes the polylactic acid-based foamed molded article to a carbon dioxide atmosphere having a pressure of 0.1 MPa or more and less than 2.0 MPa. Method for manufacturing a foamed molded article.   The volatile matter content according to claim 1 or 2, wherein the carbon dioxide treatment exposes the polylactic acid-based foamed molded article to a carbon dioxide atmosphere for a time of 0.5 minutes or more and less than 10 minutes. A method for producing a polylactic acid-based foamed molded article.   The method for producing a polylactic acid-based foamed molded article having a reduced volatile content according to any one of claims 1 to 3, wherein the hydrocarbon-based foaming agent is an aliphatic hydrocarbon having 3 to 6 carbon atoms.   The polylactic acid-based foamed molded article is composed of a polylactic acid-based resin as a main component, and the polylactic acid-based resin is obtained by gelation treatment. The volatile content in any one of claims 1 to 4 is reduced. A method for producing a polylactic acid-based foamed molded article.