TWI605069B - Polylactic acid foaming molding material, foamed molded article and manufacturing method thereof - Google Patents

Description

Polylactic acid foam molding material, foamed molded article thereof, and production method

The present invention relates to a polymer, a finished product thereof, and a process for producing the same, and more particularly to a method for producing a polylactic acid foamed molding material, a polylactic acid foamed molded article, and a foamed molded article thereof.

Polylactic acid is made from starch of recycled materials and is environmentally friendly because of its biodegradability. Products made from polylactic acid can be disposed of as compost because they are biodegradable. Polystyrene foamed products are mostly used in food containers, cushioning materials, etc., but must be recycled or recycled because they are not biodegradable.

Patent Document 1 listed below discloses a polyhydric alcohol such as glycerin, tetramethylene alcohol or pentaerythritol, or a polyvalent carboxylic acid such as trimellitic acid or pyrophoric acid, which is added to substantially amorphous lactic acid. A method of producing a foamed molded article by crosslinking an isocyanate and increasing the molecular weight.

Since it is difficult to obtain a stable composition of a melt viscosity suitable for foam molding by polylactic acid, it is preferable to satisfy the conditions of the following formula in order to obtain a stable melt viscosity of the polylactic acid composition.

(0.5xn-100EM _i )M _c /10NM _i ≦W≦(0.5xn-100EM _i )M _c /NM _i )

(here E: the number of terminal carboxyl groups of polylactic acid (equivalent/gr)

x: amount of isocyanate compound added (% by weight)

n: number of functional groups of the isocyanate compound (equivalent/mole)

M _i : molecular weight of the isocyanate compound (gr)

W: addition amount (% by weight) of a polyhydric alcohol or a polyvalent carboxylic acid

N: number of functional groups of polyol or polycarboxylic acid (equivalent/mole)

M _c : molecular weight (gr) of the polyol or polycarboxylic acid)

Further, the amount of the polyisocyanate blended is preferably from 0.3 to 3% by weight, preferably from 0.7 to 2% by weight. When the polyisocyanate is insufficient, the molecular weight of the polylactic acid after the reaction is too small to form a foamed molded body having a low expansion ratio. On the other hand, when the polyisocyanate is excessive, it becomes gelled, and a foamed molded article which is not good can be obtained.

The foamed molded body is immersed in a foaming agent, transported in a pre-expanded bead shape, placed in a mold, and heated by steam to form a foam. As the foaming agent, hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, and hexane can be used; methyl chloride, dichloromethane, and dichlorodifluoro Halogenated hydrocarbons such as methane; ethers such as dimethyl ether and methyl ethyl ether are used as foaming agents, and alcohols, ketones, ethers, benzene, and toluene having a carbon number of 1 to 4 can be used as a foaming aid.

In the following Patent Document 2, it is described that a uniform nucleating agent is preferably formed in order to form a uniform foaming cell, and a nucleating agent to be used is, for example, talc, cerium, kaolin, zeolite, mica or alumina. Particles; carbonates or hydrogencarbonates; salts such as alkali metal salts of carboxylic acids are preferred.

Addition of glycerin, tetramethylene alcohol, and pentaerythritol described in Patent Document 1 below In the production method of a polyhydric carboxylic acid such as a polyhydric alcohol or trimellitic acid or pyroic acid, it is necessary to mix a polyisocyanate with a polylactic acid in the first stage, and to add a polyhydric alcohol or a polycarboxylic acid in the second stage. Mix the reaction. When the order of the reactions is reversed, or at the same time, the gelation occurs upon reaction. In the above production method, in order to add a reactive polyol or a polyvalent carboxylic acid in the second stage, it is necessary to have an additional equipment investment, and the manufacturing process is also long, which is economically disadvantageous. Moreover, since the amorphous polylactic acid is used, there is a major disadvantage that the heat-resistant property of the foamed molded article is insufficient.

Patent Document 1: Japanese Laid-Open Patent Publication No. 2000-169546. Patent Document 2: Japanese Patent Laid-Open Publication No. 2000-17039

An object of the present invention is to provide a method and an apparatus for producing a high-viscosity polylactic acid foam molding material which are suitable for high-rate foam molding, and a high-rate foamed molded article.

The polylactic acid foam molding material of the present invention is a polylactic acid (A), (B), and (C) having a composition ratio of three types of D and L bodies, and 100 parts by weight based on 100 parts by weight of the polylactic acid. A cross-linking agent having an epoxy group or a polyisocyanate group of 0.2 to 2.0 parts by weight, which does not contain polylactic acid having a polystyrene-equivalent molecular weight of 2,000,000 or more as measured by GPC, and the polylactic acid (A): B): The weight ratio of (C) is 25~50:25~50:25~50 [but (A)+(B)+(C)=100], which is based on JIS K7210 at 190 °C and pressure of 21.6kg. The measured MI value was 0.05 to 5.

Moreover, in the polylactic acid foam molding material having the above characteristics, the composition ratio (D/L) of the D body and the L body in the polylactic acid (A), (B), and (C) is In the above polylactic acid (A), D _A /L _A = 5 to 20/95 to 80 [but D _A + L _A = 100], and in the above polylactic acid (B), D _B / L _B = (D _A +3~D _A +10)/(L _A -3~L _A -10) [but D _B +L _B =100], in the above polylactic acid (C), D _C /L _C =(D _B + 3~D _B +10)/(L _B -3~L _B -10) [but D _C + L _C = 100] is a characteristic polylactic acid foam molding material.

Further, the present invention is a polylactic acid foam molding material characterized by containing 0.5 to 5 parts by weight of calcium carbonate or talc fine particles in the polylactic acid foam molding material having the above characteristics.

Further, the present invention further comprises a polylactic acid foam molding material having the above-described characteristics as a special foamed molded article, wherein the foamed molded article has a molded article in which pre-expanded beads are molded and foamed, and is not directly formed into beads. Extrusion molded foamed article.

Furthermore, in the foamed molded article having the above-described characteristics, the foamed molded article is held in a form of a hot water of 90 ° C, and the molded product (molded container) is a hot water poured at 90 ° C. After 3 minutes, the container shape was maintained without deformation, and it had excellent heat resistance.

The present invention is also a method for producing a polylactic acid foam molding material having a MI value of 0.05 to 5, which is measured at 190 ° C and a pressure of 21.6 kg of JIS K7210, characterized in that the manufacturing method comprises: Composed of D body and L body a product produced by a crosslinking reaction between 100 parts by weight of polylactic acid and 0.2 to 2.0 parts by weight of a crosslinking agent having an epoxy group or a polyisocyanate group, in the environment of a supercritical inert gas, physical property Or mechanically, the product is reduced in molecular weight and then combined to obtain crosslinked polylactic acid (A), (B) and (C) of three kinds of D and L bodies having different composition ratios. And, the cross-linked polylactic acid (A), (B) and (C) are 25~50:25~50:25~50 [but (A)+(B)+(C)=100] When the weight ratio is mixed, the polylactic acid having a polystyrene-equivalent molecular weight of 2 million or more measured by GPC obtained by melting the obtained mixture is physically or mechanically reduced in molecular weight in an environment of supercritical inert gas. The steps of combining.

Moreover, in the method for producing a polylactic acid foam molding material having the above characteristics, the composition ratio of the D body to the L body in the crosslinked polylactic acid (A), (B), and (C) is (D/). L) is, in the above-mentioned crosslinked polylactic acid (A), D _A /L _A = 5 to 20/95 to 80 [but D _A + L _A = 100], in the above-mentioned crosslinked polylactic acid (B) D _B /L _B =(D _A +3~D _A +10)/(L _A -3~L _A -10) [but D _B +L _B =100], in the aforementioned crosslinked polylactic acid (C) It is a manufacturing method characterized by D _C /L _C =(D _B +3~D _B +10)/(L _B -3~L _B -10) [but D _C +L _C =100].

Further, the present invention is a method for producing a polylactic acid foam molding material having a MI value of 0.05 to 5, which is measured at 190 ° C and a pressure of 21.6 kg of JIS K7210, wherein the manufacturing method comprises: Preparing three kinds of polylactic acid (A), (B) and (C) having different composition ratios of D body and L body, and preparing the above polylactic acid (A), (B) and (C) a step of mixing at a weight ratio of 25 to 50:25 to 50:25 to 50 [but (A)+(B)+(C)=100], and 100 parts by weight of the polylactic acid mixture obtained by the foregoing steps Polylactic acid having a polystyrene-equivalent molecular weight of 2 million or more in a GPC measurement by a crosslinking reaction between 0.2 and 2.0 parts by weight of a crosslinking agent having an epoxy group or a polyisocyanate group, and the polylactic acid In the environment of supercritical inert gas, the step of recombination after physical or mechanical low molecularization.

Moreover, in the method for producing a polylactic acid foam molding material having the above characteristics, the composition ratio (D/L) of the D body and the L body in the polylactic acid (A), (B), and (C). Yes, in the above polylactic acid (A), D _A /L _A = 5 to 20/95 to 80 [but D _A + L _A = 100], and in the above polylactic acid (B), D _B / L _B = (D _A +3~D _A +10)/(L _A -3~L _A -10) [but D _B +L _B =100], in the above polylactic acid (C), D _C /L _C =( D _B +3~D _B +10)/(L _B -3~L _B -10) [but D _C +L _C =100] is a characteristic manufacturing method.

The present invention is also a method for producing a foamed molded article of a polylactic acid foam molding material having a MI value of 0.05 to 5, which is measured at 190 ° C and a pressure of 21.6 kg of JIS K7210, and is characterized in that it is manufactured. The method comprises: a product produced by a crosslinking reaction between 100 parts by weight of polylactic acid composed of a D body and an L body, and 0.2 to 2.0 parts by weight of a crosslinking agent having an epoxy group or a polyisocyanate group. a cross-linked polylactic acid (A) having a composition ratio of three kinds of D bodies and L bodies which are obtained by physically or mechanically lowering and then combining the products in a supercritical inert gas atmosphere. B) and (C) Cross-linking the polylactic acid preparation step, and the cross-linked polylactic acid (A), (B) and (C) are 25 to 50:25 to 50:25 to 50 [but (A) + (B) + (C The weight ratio of =100] is mixed, and the polystyrene-reduced polylactic acid having a polystyrene-equivalent molecular weight of 2 million or more, which is produced by melting the obtained mixture, is physically or mechanically in a supercritical inert gas atmosphere. After the polymolecularization is carried out, the polylactic acid foam molding material is combined, and the polylactic acid foam molding material is discharged at a temperature equal to or higher than the softening point and at a temperature of 110 ° C or lower to be foam-molded.

Moreover, in the method for producing a foamed molded article of the polylactic acid foam molding material having the above characteristics, the present invention is characterized in that 0.5 to 5 parts by weight of calcium carbonate or talc fine particles are added to 100 parts by weight of the mixture. Production method.

The present invention is also a method for producing a foamed molded article of a polylactic acid foam molding material having a MI value of 0.05 to 5, which is measured at 190 ° C and a pressure of 21.6 kg of JIS K7210, and is characterized in that it is manufactured. The method comprises: preparing three kinds of polylactic acid (A), (B) and (C) having different composition ratios of D body and L body, and the polylactic acid (A), (B) and (C) are 25~ a step of mixing 50:25 to 50:25 to 50 [but (A)+(B)+(C)=100] by weight ratio, and 100 parts by weight of the polylactic acid mixture obtained by the foregoing steps, and having Polylactic acid having a polystyrene-equivalent molecular weight of 2 million or more in GPC measurement by a GPC measurement of a crosslinking reaction between 0.2 to 2.0 parts by weight of an epoxy group or a polyisocyanate group crosslinking agent, and the polylactic acid is supercritical In an environment of an inert gas, a polylactic acid foam molding material is produced by being physically or mechanically low molecularly combined and then combined to form a polylactic acid foam molding material. The lactic acid foam molding material is discharged at a temperature equal to or higher than the softening point and at a temperature of 110 ° C or lower to form a foam molding.

Moreover, in the method for producing a foamed molded article of the polylactic acid foam molding material having the above characteristics, the present invention adds 0.5 to 5 parts by weight of calcium carbonate or talc fine particles to 100 parts by weight of the polylactic acid mixture. The manufacturing method of the feature.

The present invention is also a foam molded article characterized by a molded article produced by the method for producing a foamed molded article of the above polylactic acid foam molding material.

Further, the present invention is a foam molded article characterized by retaining a shape after injecting hot water at 90 ° C in the foam molded article having the above characteristics.

The effect of the present invention is that the polylactic acid foam molding material of the present invention has a gelation portion or a polylactic acid portion having a large molecular weight which is a cause of hindrance of high-rate foaming, and the foaming chamber film can be thinned. Moreover, the high-rate foamed molded article can be supplied inexpensively and stably. Moreover, the foamed molded article of the present invention which uses a polylactic acid foam molding material which is stable in a high melt-melting viscosity without adding a polyhydric alcohol or a polyvalent carboxylic acid is a foam molded article sheet and a container which are practically heat-resistant to water.

1‧‧‧ Henschel mixer

2‧‧‧Addition funnel

3‧‧‧Cylinder

4‧‧‧ screws

5‧‧‧Front gear pump

6‧‧‧Aperture or broken orifice

7‧‧‧vacuum pump

8‧‧‧Ventinel

9‧‧‧ rear gear pump

10‧‧‧water cutter

11‧‧‧Resin pressure gauge

12‧‧‧Rip pad

13‧‧‧Baffle

14‧‧‧Switching nozzle

15‧‧‧Mold injection hole

16‧‧‧ solenoid valve

17‧‧‧ side cylinder (air cylinder)

18‧‧‧Piston

19‧‧‧movable department

20‧‧‧ Hollow

21‧‧‧ Viscosity

22‧‧‧Decompression expansion or degassing and dehydration

23‧‧‧ Cooling should take over

24‧‧‧ gas injection holes

25‧‧‧The Ministry of Cooling

26‧‧‧Foam gas injection hole

27‧‧‧T-model

28‧‧‧ traction device

29‧‧‧Cooling roller

30‧‧‧Squeezed foamed tablets

Other features and effects of the present invention will be apparent from the following description of the embodiments of the present invention. FIG. 1 is a view showing a configuration of a preferred embodiment of the reaction extruder used in the manufacturing method of the present invention. Fig. 2 is a view showing an internal configuration of a preferred embodiment of a gear pump portion of the reaction extruder illustrated in Fig. 1; and Fig. 3 is a view showing a preferred embodiment of the orifice portion of the reaction extruder illustrated in Fig. 1. FIG. 4 is a view showing an internal configuration of a preferred embodiment of the orifice portion illustrated in FIG. 3, and showing that the separator and the slit plate are laminated to each other; and FIG. 5 is a view showing the PLA used in the manufacturing method of the present invention. FIG. 6 is a view showing a configuration of a preferred embodiment of the variable thickness constant temperature foaming mold used in the production method of the present invention; and FIG. 7 is a view showing a configuration of a preferred embodiment of the foam injection molding machine; A schematic diagram of a three-dimensional parallel structure (such as a spiral quaternary tetrahedral structure (Gyroid)) exhibited by polylactic acid having a different composition ratio of D body to L body; and FIG. 8 is a mechanically low molecular weight and mechanical In the case where the ground is broken and recombined, a more complicated example of the case of more complicated joining is shown; and Fig. 9 is a view showing a preferred configuration of the foamed sheet forming extruder used in the production method of the present invention.

The lactic acid 2 polymer of the ring-opening polymerization monomer of polylactic acid has a L body and a D body of a racemic body, and various polylactic acid having a D body and a L body composition are produced by the compounding ratio thereof. When the polylactic acid foam molding material of the present invention is produced, three types of crosslinked polylactic acid (A), (B), and (C) having different composition ratios of the D body and the L body are used, and the crosslinked polylactic acid is used. 100 parts by weight of a mixture of D-lactide and L-lactide, 0.5 parts by weight of tin octylate as a catalyst, and ring-opening polymerization to obtain a material having a number average molecular weight of 5,000 or more as a raw material, 100 parts by weight of the polylactic acid raw material, 0.2 to 2.0 parts by weight of a crosslinking agent having an epoxy group or a polyisocyanate group, and a molecular weight generated when melted is significantly large (the polystyrene-converted molecular weight measured by GPC is 2,000,000 or more). The polylactic acid is obtained by pulverizing the polylactic acid in a supercritical inert gas atmosphere by physically lowering the molecular weight or mechanically applying a shearing force. Then, a mixture of three types of crosslinked polylactic acid produced as described above is mixed at a specific weight ratio, and supplied to an injection molding machine or an extrusion molding machine in which a chipping orifice is provided, by melting. The polylactic acid having a significantly large molecular weight is physically or mechanically low-molecularized and then combined in a supercritical inert gas atmosphere to thereby produce the polylactic acid foam molding material of the present invention. The crosslinked polylactic acid (A), (B), and (C) used at this time have the following composition ratio (D/L) of the D body and the L body.

In the present invention, the composition ratio of the crosslinked polylactic acid (A) having the smallest ratio of the D body is D _A /L _A = 5 parts by weight to 20 parts by weight / 95 parts by weight to 80 parts by weight [but D _A + L _A = 100 parts by weight], the ratio of the D body in the crosslinked polylactic acid (B) is 3 to 10 parts by weight more than the ratio of the D body of the crosslinked polylactic acid (A) with respect to the above-mentioned crosslinked polylactic acid (A). The ratio of the L body is 3 to 10 parts by weight less than the ratio of the L body of the crosslinked polylactic acid (A). Further, the ratio of the D body in the crosslinked polylactic acid (C) is 3 to 10 parts by weight more than the ratio of the D body of the crosslinked polylactic acid (B). Conversely, the ratio of the L body is higher than that of the crosslinked polylactic acid (B). The ratio of the L body is 3 to 10 parts by weight. Specific examples of the composition ratio (weight ratio) of the D body and the L body in the three types of crosslinked polylactic acid (A), (B), and (C) include, for example, D _{A of the} crosslinked polylactic acid (A). L _A =7/93, cross-linked polylactic acid (B) D _B /L _B =10/90, cross-linked polylactic acid (C) D _C /L _C =13/87, cross-linked polylactic acid ( A) D _A / L _A = 10/90, cross-linked polylactic acid (B) D _B / L _B = 20/80, cross-linked polylactic acid (C) D _C / L _C = 30/70 , or cross-linked polylactic acid (A) D _A / L _A = 20/80, cross-linked polylactic acid (B) D _B / L _B = 30 / 70, cross-linked polylactic acid (C) D _C / L _C = 40/60, but not limited to these ratios.

Since polylactic acid is a condensation polymer, the molecular weight will vary depending on the equilibrium moisture content. Even high molecular weight polylactic acid, after moisture absorption, melts and causes a rapid decrease in molecular weight, and the average molecular weight decreases depending on the amount of water. In the present invention, as shown in Fig. 3, when the thickening portion 21, the orifice portion 6, and the reduced pressure expansion portion 22 are provided, when the moisture is excessive, the molecular weight of the polylactic acid due to remelting can be prevented from being reduced.

The polylactic acid used in the present invention may be either crystalline polylactic acid or amorphous polylactic acid. When the pre-expanded beads are immersed in the foaming agent, amorphous polylactic acid copolymerized with the D body and the L body is used. In the case of extrusion foam molding, crystalline polylactic acid is preferred because heat resistance is improved. The heat resistance of the composite polylactic acid in which the D body and the L body are mixed is further improved, which is preferable.

The number average molecular weight of the polylactic acid before crosslinking by the polyisocyanate is preferably 5,000 or more, preferably 20,000 or more, more preferably 100,000 or more. When the molecular weight of the polylactic acid is small, in order to obtain a high expansion ratio and a viscosity necessary for molding, the amount of the crosslinking agent such as polyisocyanate to be reacted is increased, which is economically disadvantageous.

The polylactic acid before crosslinking is dried by a standard method such as vacuum drying in advance to control the water content. The moisture content of the polylactic acid before crosslinking is preferably 500 ppm or less, and more preferably 100 ppm or less. More preferably, it is 50 ppm or less. The polyisocyanate reacts with water to produce carbon dioxide, which becomes inactive, so the efficiency of the polyisocyanate is deteriorated. When the moisture content of the polylactic acid before crosslinking is excessive, it is economically disadvantageous.

The polyisocyanate used in the present invention is a divalent or higher polyisocyanate, preferably an adduct containing a triisocyanate, a tetraisocyanate or a diisocyanate. When a polyisocyanate having a valence of 3 or more is used, the polylactic acid polymer chain is diverged, and the strength of the film is strengthened, and the expansion ratio can be increased.

In the present invention, the polyisocyanate used for the crosslinking reaction may be an isocyanate compound having two or more isocyanate groups in the molecule. As the polyisocyanate, for example, 1,6-hexamethylene diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (diisocyanate) 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate), 1,4-butylene diisocyanate 1,4-tetramethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexyldiisocyanate (2, 2,4-trimethylhexamethylene diisocyanate), dicyclohexylmethane-4,4'-diisocyanate, methylcyclohexyl-2,4-diisocyanate ), methylcyclohexyl-2,6-diisocyanate, xylylene diisocyanate, 1,3-bis(isocyanate)methylcyclohexane (1,3) -bis(isocyanate)methyl cyclohexan), tetramethyl xylylene diisocyanate, trans-cyclohexane-1,4-diisocyanate, lysine Aliphatic diisocyanate such as lysine diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene Alicyclic polyisocyanate such as hydrogenated xylylene diisocyanate, hydrogenated tetramethyl xylylene diisocyanate, cyclohexane diisocyanate, 2,4-stilbene diisocyanate (2,4-toluylene Diisocyanate), 2,6-toluylene diisocyanate, diphenylmethane-4,4'-isocyanate, 1,5'-cycloalkane Isocyanate (1,5'-naphthene diisocyanate), tolidine diisocyanate, diphenyl methyl methane, tetraalkyl diphenylmethane diisocyanate, 4, Aromatic diisocyanate such as 4'-4'-dibenzyl diisocyanate or 1,3-phenylene diisocyanate, lysine ester triisocyanate , triphenylmethane triisocyanate, 1,6,11-undecane triisocyanate, 1,8-isocyanate-4,4-isocyanate methyloctane (1) , 8-isocyanate-4,4-isocyanate methyl octane), 1,3,6-hexamethylene isocyanate, bicycloheptane triisocyanate, trimethylolpropane With 2,4-stilbene diisocyanate ( a diisocyanate such as an adduct of 2,4-toluylene diisocyanate), an adduct of diisocyanate such as trimethylolpropane and 1,6-hexamethylene diisocyanate, and glycerin, new a polyol such as pentaerythritol reacts with the above aliphatic and aromatic diisocyanate compound and the aforementioned triisocyanate compound The obtained denatured polyisocyanate compound or the like. These may be used alone or in combination of two or more. Further, in the present invention, an acrylic crosslinking agent having an epoxy group may be used instead of the above isocyanate.

By using a trivalent or higher polyisocyanate, the molecular chains of the polylactic acid are divided, and the strength of the foamed cell film is increased, which is preferable. This phenomenon is the same in the case where the polyethylene is thinned, and it is more suitable than the low-density polyethylene which has a difference in the polymer chain than the linear high-density polyethylene.

The blending amount of the polyisocyanate varies depending on the molecular weight of the polylactic acid before crosslinking. Further, it varies depending on the molecular weight distribution of polylactic acid. When the low molecular weight polylactic acid is increased, in order to obtain a melt viscosity suitable for foaming, it is necessary to add more compounding amount. The amount of the polyisocyanate to be added is preferably 0.2 to 2.0 parts by weight based on 100 parts by weight of the polylactic acid mixture before crosslinking. When the amount of the polyisocyanate blended is too small, the melt viscosity suitable for foaming cannot be obtained and the expansion ratio is reduced. Further, excessive gelation occurs and the expansion ratio is reduced.

However, when the pelletized polylactic acid and the liquid cross-linking agent are stirred and mixed, and the crosslinked PLA is produced by an extruder, a large molecular block is generated by mixing due to uneven dispersion. Assuming that the crosslinked PLA was processed into a film by an expander, it was found that a convex portion of a large molecular block was generated in a flat film, which hindered the subsequent process. As a physical solution, the more macromolecules, the more easily it is in the supercritical state of nitrogen or carbon dioxide, the faster it is to cut off part of the chain of the cross-linking part. Macromolecules have a tendency to slowly decrease in molecular weight. Further, when it is discharged from the nozzle to the pressure-free open space attracted by the vacuum pump in the super-flow state, it is instantaneously cross-linked with other molecular groups, and the molecular weight of the cross-linked PLA is more average than before. Further, by constituting the nozzle with a long slit (Fig. 4), the giant molecules are mechanically broken. In addition, in the extruder, the residence time required from the supercritical state to the passage of the slit is less than 2 minutes, and pure PLA is hardly lowered in molecular weight. Moreover, the volume of the gas that reaches the out of the slit (Fig. 4) is extremely compressed, and the heat contained in the gas is only slightly stored. When released into the open space without pressure, the gas will rapidly expand and degas, resulting in less heat loss. Adiabatic expansion. Further, the crosslinking reaction of the remaining unreacted portion in the time period until the cutting of the water cutter in the latter stage is completed.

The cross-linked portion which is broken at the orifice portion is joined in the non-pressure open space region (Fig. 3) which is attracted by the vent hole, or after the nozzle of the injection molding machine (Fig. 5). Further, the pressure after the nozzle at the time of injection molding is equivalent to the pressure inside the mold. In this recombination, for example, as shown in Fig. 8, the chance of combining into a complicated structure is increased, and the complicated combination thus created has an effect of increasing the viscosity. Further, the fragmentation in the orifice portion and the recombination in the pressureless open space are repeated two times or three times, for example, the combination is more complicated, but the actual application may be performed only once.

Then, when the polylactic acid foam molding material of the present invention is produced, the above three types of crosslinked polylactic acid (A), (B) and (C) are mixed to a weight ratio of 25 to 50:25 to 50:25 to 50. (The ratio of each polylactic acid is 50% by weight or less, and (A) + (B) + (C) = 100), polylactic acid having a polystyrene-equivalent molecular weight of 2 million or more measured by GPC during melting, is physically low in a supercritical nitrogen or carbon dioxide environment Molecularization, and mechanical shearing by applying shear force. Further, in the present invention, the three types of polylactic acid before crosslinking may be mixed to a weight ratio of 25 to 50:25 to 50:25 to 50 (the ratio of each polylactic acid is 50% by weight or less, and (A) +(B)+(C)=100), polyisocyanate is added to crosslink, and polylactic acid having a polystyrene-converted molecular weight of 2 million or more measured by GPC during melting is used in a supercritical nitrogen or carbon dioxide atmosphere. Physically low molecular weight, and mechanical shearing by applying shearing force. The polylactic acid foam molding material of the present invention has a MI value of 0.05 to 5 as measured by JIS K7210 at 190 ° C and a pressure of 21.6 kg.

When the above-mentioned three types of polylactic acid having a mixing ratio of the D body and the L body differs by 3% by weight or more, and the above-mentioned mixing ratio is blended and kneaded, the structure of the spiral quaternary tetrahedron shown in FIG. 7 is exhibited ( Gyroid) is a three-dimensional parallel structure of polylactic acid aggregates, and obtains a quasi-stable state in energy. If the quasi-stable structure is maintained, the viscosity of the melt is apparently higher than that of the individual composition. However, when the composition ratio of the D body/L body in each polylactic acid, the difference in the D body/L body composition ratio between the three types of polylactic acid, and the mixing ratio of the three types of polylactic acid do not satisfy the above conditions, A three-dimensional parallel structure such as a spiral quaternary tetrahedron structure is not exhibited, and the viscosity on the appearance is not increased.

In the polylactic acid foam molding material of the present invention, the composition of the D body/L body is used. Three types of polylactic acid (A), (B) and (C) with different ratios, and by using polylactic acid (A), (B) and (C) at 25~50:25~50:25~50 The compounding ratio shows a three-dimensional quasi-stable state, whereby the melt viscosity is about 10 times stronger than that of the single composition. In the present invention, the production of a significantly large polymer is suppressed by reducing the crosslinking agent, and the polymer is formed by the above-mentioned heterogeneous reaction with the epoxy group or the polyisocyanate group. In the environment of supercritical inert gas, it is mechanically pulverized and averaged by physical low molecular weight, and shearing force is applied, and the molecular weight of the significantly large polymer can be reduced and stable foaming can be obtained. Air chamber membrane.

Since the isocyanate is highly reactive, it reacts with a low molecular weight polyol or a polycarboxylic acid to produce a gel. The reaction with the polymer is carried out by reacting with the terminal group, and if the amount of the isocyanate is not excessive, a gelled network structure is not formed. However, although a large network structure which does not melt is formed, it becomes a heterogeneous reaction and produces a polymer having a significantly large molecular weight. When a polymer having a polystyrene-converted molecular weight of 2 million or more measured by GPC is partially present, a stretching enthalpy of the foamed cell membrane is generated, which makes high-rate foaming difficult. It is preferably a composition of a polymer having a molecular weight of less than 1.5 million in terms of polystyrene.

Heat resistance is inversely proportional to the mobility of molecules. When the molecular weight is increased, the heat resistance is improved. The liquid paraffin is liquid at normal temperature, but the paraffin wax having a slightly increased molecular weight is solid at normal temperature. Further, the polyethylene having a large molecular weight has a melting point of about 130 ° C, and the melting point of the ultrahigh molecular weight polyethylene rises to 150 ° C.

In the method for producing a polylactic acid foam molding material of the present invention, after the polylactic acid is coupled with a polyisocyanate or an epoxy group to increase the molecular weight of the polylactic acid foam molding material, it is necessary to have a supercritical inert gas atmosphere. The step of lowering the molecular weight, or mechanically applying a large shearing force to pulverize the significantly large polylactic acid molecules. Without this step, the apparently large polylactic acid molecules locally inhibit the expansion of the foamed cell membrane, and the high-rate foamed molded article cannot be obtained.

Examples of the inert gas which does not react with the polylactic acid according to the present invention include nitrogen gas, carbon dioxide gas, helium gas, argon gas, methane gas, ethane gas, propane gas, butane gas, ethylene gas, and propylene gas. Among them, nitrogen gas or carbon dioxide which is easy to reach supercritical conditions and which is inexpensive and has no flammability is preferable, and these gases may be used in combination. The supercritical point of nitrogen is (-147 ° C, 3.39 MPa), the supercritical point of carbon dioxide is (31.1 ° C, 7.38 MPa), and the supercritical point of methane gas is (-83 ° C, 4.6 MPa). The supercritical point of ethane gas is (32.4 ° C, 4.88 MPa), the supercritical point of propane gas is (93.8 ° C, 4.25 MPa), and the supercritical point of butane gas is (152 ° C, 3.380 MPa). When the beads are produced, the inert gas is quantitatively supplied in an amount of 0.1 to 2% by weight based on the polylactic acid, but it is recovered and reused after separating the water. The processor system of the present invention only replenishes the amount actually lost by the inert gas. In the case of direct injection foam molding, an inert gas is excessively used as a foaming gas. However, when the hollow portion thickness variable temperature foaming mold of the present invention (see Fig. 6) is used, the foaming efficiency of the inert gas used for foaming is the same as that of the bead foaming, so the quantitative supply is relative to The polylactic acid is blended in an amount of 0.1 to 2% by weight.

Generally, the method of pressurizing the pressure above the supercritical point is, for example, a plunger pump, a gear pump, a screw, etc., and the temperature above the supercritical point is a buried heater or a coating. Heating device such as a heater.

The melting point of polylactic acid varies depending on the degree of copolymerization, but is about 170 ° C or less. In the present invention, the polyisocyanate or the epoxy group is reacted at a temperature higher than the melting point of the polylactic acid before crosslinking. In the present invention, the very warm liquid polyisocyanate is heated and melted, and is quantitatively added to the semi-melted polylactic acid by a plunger pump or the like to be reacted with the polylactic acid. When a high-viscosity reactant is mixed with a low-viscosity compound, a high-viscosity substance is mixed in a low-temperature and semi-melted state to be sufficiently dispersed in advance, and a more uniform reaction can be expected.

In the polylactic acid foam molding material of the present invention, other biodegradable polymers may be blended in a range in which the physical properties of the foamed molded article are not significantly deteriorated. Examples of other biodegradable polymers include polycaprolactam, polybutylene succinate, polyhydroxybutyrate, and poly(hydroxybutyrate). /(hydroxybutyrate/hydroxyhexanoate), (polylactic acid/polybutylene succinic acid) block copolymer, poly(caprolactone/butylene succinate) (poly(caprolactone/) Butylene succinate)), poly(butylene succinate/adipate), poly(butyl) Poly(butylene succinate/carbonate), poly(ethylene terephthalate/succinate), poly(ethylene terephthalate/succinate), poly(ethylene terephthalate/succinate) Poly(butylene adipate/terephthalate), poly(tetramethylene adipate/terephthalate), or the like.

In order to form a uniform and fine foaming chamber, a synthetic nucleating agent is preferred. Examples of the nucleating agent include inorganic particles such as talc, cerium, kaolin, zeolite, mica, and alumina; carbonic acid or hydrogencarbonate such as calcium carbonate; and alkali metal salts of carboxylic acid. Among them, calcium carbonate and talc are preferred because they are soft and can be produced at low cost. In the high-rate foaming, the film thickness of the foaming chamber is small, and the particle diameter of the nucleating agent is preferably 1 μm or less, preferably 0.5 μm or less. The amount of the nucleating agent is preferably 0.5 to 5% by weight, more preferably 0.5 to 2% by weight, based on the polylactic acid foam molding material. When the amount of the nucleating agent is too small, the size of the gas cell tends to become uneven, and when it is too large, it is difficult to obtain a high expansion ratio. The nucleating agent may be blended in the production of the crosslinked polylactic acid (A), (B), and (C), or may be blended in the polylactic acid foam molding material of the present invention at the time of foam molding.

In the present invention, the polylactic acid foam molding material of the present invention is side injected with a foaming inert gas such as nitrogen gas and foamed. In this case, in the case of foam molding under conditions of a high temperature or a high pressure of a foaming inert gas such as nitrogen or a supercritical point or a subcritical state, it is preferable to obtain a foamed molded article having a finer gas chamber. Examples of the foaming inert gas as the foaming inert gas include propane, n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, hexane, butane, and the like. Hydrocarbons; halogenated hydrocarbons such as methyl chloride, dichloromethane, and dichlorodifluoromethane; ethers such as dimethyl ether and methyl ethyl ether. Further, as the foaming aid, an alcohol having 1 to 4 carbon atoms, a ketone, an ether, benzene or toluene may be used. These blowing agents can also be used in combination.

In the above-mentioned molded article produced by using the polylactic acid foam molding material of the present invention, generally used, for example, a pigment, a flame retardant, and a deodorant can be used within a range that does not affect the biodegradability or the quality of the foamed molded article. Additives such as stabilizers, antibacterial agents, and fungicides. Further, in the present invention, the powder of the vegetable fiber, for example, paper powder or bamboo powder, is added in an amount of 0.2 to 2.0 parts by weight based on the crosslinked polylactic acid (A) + (B) + (C) = 100 parts by weight. Thereby, the enthalpy change immediately after forming can be remarkably improved without sacrificing other foaming characteristics; the enthalpy change due to humidity, temperature, thickness deviation pressure, etc.; The shape changes.

Next, the functional configuration of each part in the preferred embodiment of the reaction extruder used in the production method of the present invention will be described. In the reaction extruder shown in Fig. 1, the measured polylactic acid (PLA) and the crosslinking agent were placed in a Henschel mixer, stirred and mixed, and supplied to a hopper 2. Then, the feeding funnel 2 is completely melted by the heated cylinder 3 and the screw 4, and the PLA reaches the front stage gear pump 5, and polylactic acid having a polystyrene-equivalent molecular weight of 2 million or more measured by GPC is produced. At this time, the PLA melt above the carrying capacity of the front gear pump 5 will slide in the screw 4. There will be no excess supply. Thereafter, a supercritical gas of a controlled flow rate is injected into the outlet of the front stage gear pump 5. The amount of inflow of the PLA melt into the region per unit time is controlled to be fixed by controlling the number of revolutions of the drive servo motor of the front gear pump 5. Next, the PLA melt is passed through the slit of the orifice portion 6 together with the super-flowing supercritical gas, and since the shearing force is applied thereto, the aforementioned polylactic acid having a molecular weight of 2 million or more is physically low molecular weight. At the same time, it is mechanically pulverized. Then, the polylactic acid which is physically low-molecularized and mechanically pulverized is discharged to the pressure-free open space of the vent hole 8 which sucks the separation gas by the vacuum pump 7, and reaches the inlet of the rear-stage gear pump 9 by the screw. Finally, it is difficult to ensure the pressure necessary to pass the PLA melt through the die of the water cutter 10 with only the screw, and for this purpose, the rear gear pump 9 is provided at this portion. The gas has been sucked by the vent hole 8 to be in a state close to a vacuum, and for the purpose of preventing leakage of the PLA melt, the number of revolutions of the rear stage gear pump 9 is set to be slightly larger than the actual amount of conveyance. The PLA melt through the mold is cooled by water while being cut by a cutter to form a solid pellet. Furthermore, the reaction extruder having the above configuration is not only used for producing crosslinked polylactic acid (A), (B) and (C) as raw materials, but also for crosslinking polylactic acid (A), (B). And the mixture of (C), the polylactic acid foam molded article of the present invention is produced.

When the pellets produced by the reaction extruder having the configuration shown in Fig. 1 were used for forming a test piece, the size was reduced by about 2%, and such a phenomenon was considered to be a fine and trace amount of gas remaining inside the pellet. In the reaction extruder of Fig. 1, the rear stage gear pump 9 is different from the front stage gear pump 5, and the rear stage gear pump 9 is not provided with a supercritical gas injection hole, but In this part, a supercritical gas can also be injected to produce a foamed material in which a gas is enclosed. The granular cross-linked polylactic acid PLA (A), PLA (B), and PLA (C) are basically produced separately, and it is confirmed that PLA (A), PLA (B), and PLA (C) before crosslinking are confirmed. In the case where it is produced by stirring with a Henschel mixer at the same time as the crosslinking agent, the chance of exhibiting a three-dimensional parallel structure is inferior.

The front-stage gear pump 5 and the rear-stage gear pump 9 in the reaction extruder having the configuration shown in Fig. 1 have an internal structure as shown in Fig. 2, and the flow rate of the PLA melt is adjusted by controlling the number of revolutions of the gear. In the present invention, a general and well-known gear pump that is commercially available can be used, but if the entire extruder is constructed by a screw 4, as shown in Fig. 2, the gear pump can be separated from the screw shaft and set. . Then, in order to make the passage of the PLA melt (indicated by a broken line) toward the gear pump side, the groove is not provided in the corresponding portion of the screw, and in the case where the external leakage corresponding method is necessary, it is preferable to adopt a structure in which the seal can be fitted. Further, a supercritical gas of a controlled flow rate is injected from a gas supply portion on the outlet side of the front stage gear pump 5, and a pressure of the PLA melt is measured by a resin pressure gauge 11.

Specific examples of the structural dimensions of the thickening portion 21 shown in Fig. 3 include a screw diameter of 50 mm and a tackifying degree of 100 mm, and two types of wires are combined in a groove shape 2R semicircle. One type of wire is 50mm and 8 pieces, and the other type of wire is 150mm and 8 pieces. The commonly known Dulmage screw has a shape called pineapple, in which one wire is disposed along the flow direction of the resin melt, and the other wire is in the opposite direction to the flow direction of the melt of the resin. Configuration, so there is a disadvantage of large heat in this part. here, In order to arrange the two kinds of wires together in the same direction as the flow direction of the resin melt, different wires are used, so that the same viscosity-increasing effect is obtained, but the degree of heat generation is small, and the resin melt due to heat generation is prevented. Deterioration.

The hole portion 6 in the reaction extruder having the configuration shown in Fig. 1 has an internal structure as shown in Fig. 3. The structure of the screw 4 of the hole portion 6 is the same as that of the front stage gear pump 5 and the rear stage gear pump 9. . A vent hole 8 is provided in the cylinder on the outlet side of the hole portion 6, and is formed as a pressureless open space by suction by the vacuum pump. The laminated structure of the rip pad 12 and the separator 13 disposed in the hole portion 6 is shown in Fig. 4 .

In Fig. 4, the structure of the holes shown in the hole portion 6 of Fig. 3 is exemplified, and a plurality of pieces (10 or more, preferably 20 to 40, preferably 12) of the rip plate 12 are alternately laminated. The separator 13 is configured. As a preferable size in the present invention, the separator 13 has a thickness of 1 mm and the slit pad 12 has a thickness of 0.2 mm. The slit provided in the slit plate 12 has a groove width of 2 mm and a slit length of 35 mm. In the laminated structure shown in Fig. 4, the PLA melt flows through the slit from the center portion in together with the supercritical gas, and moves to the outer peripheral portion and flows. In the present invention, in order to generate a large shearing force, a polylactic acid foam molding material in a supercritical or subcritical state, for example, as shown in Fig. 4, passes through a cracked hole portion composed of four slits extending in four directions at a high speed. .

Fig. 5 shows a configuration of a preferred embodiment of the PLA foam injection molding machine used in the production method of the present invention. In the present invention, the front end portion of a generally known injection molding machine can be constructed as shown in Fig. 5 . It is used as a PLA foam injection molding machine. Reference numeral 23 in Fig. 5 denotes a suitable cooling adaptor for cooling to 100 ° C or lower before injection into the mold, reference numeral 14 is a Shut-off nozzle, and reference numeral 15 is a mold injection port. The supercritical gas supplied to the inside of the cylinder barrel 3 is injected while the solenoid valve is opened at the timing of the squeeze cycle of the piston. At this time, it is preferable to provide a gas injection port of at least two places or more to produce a more uniform foam. The expansion ratio of the PLA resin is inversely proportional to the volume of the PLA melt injected into the mold. In one example of the pressure setting method of the supercritical gas, although a long injection time is required, in the case of trial injection, when the crucible at the time of cooling of the molded article becomes concave, the pressure is increased and the ridge becomes convex. Adjust the setting to reduce the pressure and fix it. As a method of shortening the injection time, the movable portion 19 mechanically controls the stroke of the piston 18 provided in the cylinder 17, and the supercritical gas is injected into the cylinder during the suction of the piston 18, and is discharged during the compression cycle of the piston 18. The method of PLA melt melting.

Fig. 6 shows a configuration of a preferred embodiment of a thickness variable temperature constant temperature foaming mold (molding mold for injection molding) used in the production method of the present invention, in which the hollow portion 20 is movable. In the first stage of the foam molding of the PLA resin, the thickness of the hollow portion 20 is injected into the molten polymer in a thin state (for example, 0.1 mm) (see FIG. 6A), and in the second stage, the polymerization is performed. The temperature of the material is reduced to an appropriate temperature below 100 ° C. After the polymer is cured, the hollow portion is expanded to a predetermined expansion ratio (for example, 20 times foaming at 2 mm, see FIG. 6 and FIG. B) for 30 seconds to 1 minute. Time, foaming above the softening point of the polymer, and cooling and fixing, thereby producing high expansion at the same time of forming The molded product of the ratio. In the injection molding cycle, during the cycle of foaming and cooling, the injection molding cycle is longer than the cycle in which only cooling is generally performed. In order to shorten the cycle time, a multi-foaming mold injection molding apparatus that takes out a plurality of molds and takes out a molded article is preferable.

In the method for producing a polylactic acid foam molding material of the first aspect of the present invention, the injection molding machine (see FIG. 5) is provided with a chipping orifice portion, and a hollow portion thickness variable temperature foaming mold is used (see FIG. 6). Under the supercritical or subcritical conditions of the foaming gas, the polylactic acid having an excessive molecular weight of 2 million or more molecular weight is physically and mechanically pulverized by applying a shearing force, and crosslinked by polyisocyanate or epoxy group. A method of foaming a polylactic acid foam molding material having a MI value of 0.05 to 5, which is measured at 190 ° C and a pressure of 21.6 kg of JIS K7210, is produced by foaming at a temperature of 100 ° C or less and a softening point or higher.

The MI value in the present invention is measured under the conditions of a pore diameter of 2 mm, a pore length of 10 mm, a temperature of 190 ° C, and a pressure of 21.6 kg when the polylactic acid foam molding material is used; Under the conditions of a diameter of 1 mm, an orifice length of 10 mm, a temperature of 190 ° C, and a pressure of 21.6 kg, the weight g of the flow for 10 minutes or the weight g of 10 minutes was measured in accordance with JIS K7210. The expansion ratio was measured by cutting 1 ml of the foamed molded article, measuring the weight g1, and cutting out 1 ml of the polylactic acid foam molding material of the present invention, measuring the weight g2, and determining the quotient of dividing g2 by g1. The water content of the raw material polylactic acid or the like is measured by the Karl Fischer's method. The heat resistance of the foamed molded article is 80% of the depth of the hot water of 90° C., and is determined to be “good” when there is no deformation after 3 minutes. Similarly, after injecting boiling water for 3 minutes. Also determined without deformation "Excellent" is "bad" when it is found to be deformed after injecting hot water. The measurement of a significantly large polymer was measured by GPC to determine the molecular weight distribution in terms of PSt. The invention is further illustrated in the examples, but the invention is not limited to the inventions of the embodiments. Further, the above-mentioned reaction extruder or injection molding machine can also be used in the production of crosslinked polylactic acid (A), (B), (C) and (E) of the starting materials.

Three kinds of raw materials, polylactic acid, which are equivalent to the D body/L body ratio which are used for the main purpose of the present invention, are not listed, D/L=13/87, D/L=19/81, D/L=25/75. The three types of raw material polylactic acid were produced by the following methods (Production Examples 1 to 3). In Production Examples 1 to 3, commercially available L-lactide and D-lactide were recrystallized by ethyl acetate to be purified. The weight ratio of the purified D-lactide to the weight part of L-lactide is 100 in total, and 0.5 parts by weight of tin octylate as a catalyst is added to an autoclave having a stirrer, and the pressure is reduced. After degassing, ring-opening polymerization was carried out under a polymerization condition of 190 ° C for 1 hour in an N ₂ atmosphere. After completion of the reaction, the polymer was taken out from the autoclave in a dough form, quenched, and then cut with a rotary cutter to produce a polylactic acid pellet before crosslinking. The pellet was dried in a vacuum dryer at 80 ° C for 24 hours, and then placed in an aluminum foil bag sealed with nitrogen for storage. A polylactic acid as a raw material having a water content of 100 ppm or less is used.

(Manufacturing Machine 1) Extruder: Fig. 1 shows a schematic configuration of a preferred extruder for carrying out the present invention. It is provided with: Henschel mixer with nitrogen sealed, raw material supply and addition funnel 2, stable delivery of PLA melt and more to prevent supercritical gas For the purpose of countercurrent flow, the front gear pump 5 is injected from the nitrogen bottle, the nitrogen supply side plunger, and the accumulator tank for the purpose of stabilizing the gas pressure through the pressure reducing valve and the flow control valve. The holes are supplied with nitrogen. In the environment of supercritical inert gas, the hole portion 6 for mechanical pulverization is mechanically pulverized by applying a shearing force while being physically low molecular weight. Further, a supercritical state is maintained from the front stage gear pump 5 to the orifice portion 6. The oil diffusion vacuum pump symbol 7 and the reduced pressure nitrogen gas recovery unit are connected from the vent hole 8, and the recovered nitrogen gas is reused via the water separation device. From the orifice portion 6, particularly from the outlet opening of the split gasket (Fig. 4) to the inlet of the rear gear pump 9, there is a pressureless open interval that is attracted to the degassing and dehydration by the vacuum pump. In the pressureless open section, the recombination of the crosslinked portion of the PLA which is physically low molecularly and mechanically fragmented is rapidly performed. The PLA melt is pressurized to the mold of the water cutter 10 by the rear gear pump. The pellet of the polylactic acid foam molding material of the present invention obtained from the outlet of the water cutter is transferred to a dry addition funnel, and after a certain period of time, a processing system dried by a vacuum dryer is used.

(Production Example 1) Production of Starting Material A (Crosslinked Polylactic Acid Round Particles): Using an extruder described in the manufacturing machine 1, a polylactic acid raw material having a D/L ratio of 13/87 and a number average molecular weight of 100,000 was used. 100 parts by weight of an adduct of 1,6-extended hexyl diisocyanate and trimethylolpropane at room temperature, respectively, in an amount of 1.5 parts by weight, 1 part by weight, 0.5 parts by weight, and a talc fine powder having an average particle diameter of 0.4 μm. 1 part by weight was quantitatively supplied to the Henschel mixer for mixing, and was quantitatively supplied to the extruder from an addition funnel sealed with nitrogen, and The polylactic acid foam molding material is continuously quantitatively supplied with 0.2% by weight of nitrogen gas in the initial stage of the Gas injection hole, and the polylactic acid having a polystyrene-equivalent molecular weight of 2 million or more measured by GPC is physically used in a supercritical nitrogen atmosphere. The ground is low in molecular weight and mechanically pulverized by applying a shearing force to produce recombined round particles (A1), (A2), and (A3). The MI values of 21.6 kg were 1.1, 1.3, and 1.6, respectively.

(Production Example 2) Production of Starting Material B (Crosslinked Polylactic Acid Round Particles): 100 parts by weight of a polylactic acid raw material having a D/L = 19/81 and a number average molecular weight of 100,000 was produced in the same manner as in Production Example 1. The binder and talc are separately supplied and mixed to produce round pellets (B1), (B2), and (B3). The MI values of 21.6 kg were 1.0, 1.2, and 1.5, respectively.

(Production Example 3) Production of Starting Material C (Crosslinked Polylactic Acid Round Particles): 100 parts by weight of a polylactic acid raw material having a D/L ratio of 25/75 and a number average molecular weight of 100,000 was produced in the same manner as in Production Example 1. The binder and talc are separately supplied and mixed to produce round pellets (C1), (C2), and (C3). The MI values of 21.6 kg were 0.9, 1.1, and 1.4, respectively.

(Production Example 4) Production of starting material E (crosslinked polylactic acid pellet): three were D/L = 13/87, D/L = 19/81, D/L = 25/75, and the number averaged Each of the polylactic acid raw materials having a molecular weight of 100,000 was 30 parts by weight, 33 parts by weight, and 37 parts by weight, respectively, in a total amount of 100 parts by weight, and was supplied and mixed with a crosslinking agent and talc in the same manner as in Production Example 1 to produce round particles (E1). , (E2), (E3). The MI values of 21.6 kg were 0.30, 0.42, and 0.54, respectively.

(Manufacturing Machine 2) Injection Molding Machine: It is generally known as shown in FIG. The apparatus for reforming the injection molding machine was equipped with a Henschel mixer in which nitrogen gas was sealed, and a raw material supply and supply funnel 2. The gas injection hole 24, the orifice portion 6, the cooling contact pipe 23, and the switching nozzle 14 are provided at the modified front end portion, and a configuration in which the switching nozzle is connected to the injection hole of the foaming mold is formed. The supply unit that uses the foaming gas is temporarily stored in the side cylinder (the gas cylinder) by the piston 18 that is interlocked with the movable part body of the injection molding machine from the nitrogen gas bottle via the pressure reducing valve. 17), in conjunction with the injection extrusion cycle from the gas injection hole to the PLA melt injection processing system.

(Example 1) Injection-foaming molding: 30 parts by weight of (B1), 33 parts by weight (B1) of cross-linked polylactic acid pellets (A1) produced in Production Examples 1 to 3, using an injection molding machine for manufacturing machine 2 37 parts by weight were quantitatively supplied to a Henschel mixer, stirred and mixed, and quantitatively supplied to an injection molding machine from an addition funnel sealed with nitrogen. Into the nitrogen supply side cylinder, 2% by weight of nitrogen gas is injected into the polylactic acid foam molding material, and the polylactic acid having a polystyrene equivalent molecular weight of 2 million or more measured by GPC at the time of melting is in a supercritical nitrogen atmosphere. The orifice portion having a thickness of 0.2 mm, a slit groove width of 2 mm, and a slit length of 35 mm as shown in Fig. 4 at 170 ° C was reduced in molecular weight and recombined, and pressed to maintain a temperature of 40 ° C in a 30 second stroke. The injection hole 15 of the box-shaped molding die having a thickness of 10 mm, a depth of 90 mm, and an outer dimension of 100 mm was produced by the injection-molded article T1 of the present invention having a different amount of the crosslinking agent. Similarly, T2 was produced by crosslinking polylactic acid round particles (A2), (B2), and (C2). Further, T3 was produced by cross-linking polylactic acid pellets (A3), (B3), and (C3) in the same manner.

The expansion ratio of T1, T2, and T3 is 22 times. Heat resistance is excellent. The MI values of T1, T2, and T3 measured at 190 ° C and a pressure of 21.6 kg were 0.21, 0.31, and 0.42, respectively. Further, by the GPC measurement of T1, T2, and T3, a significantly large high molecular weight substance having a molecular weight of 1.5 million or more in terms of polystyrene was not detected.

In order to compare with the results of the preceding items T1, T2, and T3, E1 was produced in the same manner as in Example 1 except that (E1) was used instead of (A1), (B1), and (C1). Similarly, (E2) is used instead of (A2), (B2), and (C2) to produce E2. Further, E3 was produced by substituting (E3) instead of (A3), (B3), and (C3). The expansion ratio of E1, E2, and E3 is 16 times. Heat resistance is excellent. The MI values of E1, E2, and E3 measured at 190 ° C and a pressure of 21.6 kg were 0.30, 0.42, and 0.54, respectively. Further, a significantly high molecular weight substance having a polystyrene-equivalent molecular weight of 1.5 million or more in GPC measurement of E1, E2, and E3 was not detected. Further, in Production Example 4, three types of polylactic acid were simultaneously introduced to produce starting materials E1, E2, and E3, and it was found that even if the raw materials were identical in composition, the performance was significantly inferior to that of T1, T2, and T3. This was investigated because the chances of showing a three-dimensional parallel structure were inferior.

(Comparative Example 1) Injection foam molding: For comparison, the slit plate of the orifice portion to which the low molecular weight and the shearing force were applied was taken out from the extruder of the manufacturing machine 1, and the other conditions were the same, but the resin pressure gauge showed The pressure is 0.6 MPa, and the corresponding cross-linked polylactic acid round particles (A1), (A2), (A3), (B1), (B2), (B3), (C1), and the like are produced under the condition that the nitrogen gas does not reach the supercritical state. (C2), (C3), and the orifice of the injection molding machine of the manufacturing machine 2, and the comparative product of the injection foamed products T1, T2, and T3 are produced, but each Each of them is less than 5 times the expansion ratio, and the local expansion ratio is not uniform. Since the expansion ratio does not rise to a predetermined value, it cannot be formed into a box shape. The significantly larger high molecular weight substance having a polystyrene-equivalent molecular weight of 2 million or more measured by GPC was measured to be 1% by weight or more. It is presumed that this is because the orifice portion 6 to which the shearing force is applied is removed, and the polylactic acid foam molding material having a large molecular weight is likely to hinder the elongation of the foaming cell membrane, and therefore, the expansion ratio cannot be increased.

(Example 2) Injection foam molding: T1, T2 corresponding to Example 1 was produced in the same manner as in Example 1 except that only 0.3 parts by weight of the talc fine powder in the steps of Production Examples 1 to 3 was changed. The foamed molded article of the present invention of T3. The MI value of the pressure molded article of the present invention of 21.6 kg was not changed to 0.4, 0.3, and 0.2, respectively, but the heat resistance was good.

(Comparative Example 2) Injection foam molding: an additive of 1,6-extended hexamethylene diisocyanate and trimethylolpropane was added without changing the parts by weight of the polylactic acid raw material and the talc fine powder in the steps of Production Examples 1 to 3. The amount of the compounding amount was changed to 0.1 part by weight, and the foamed molded article produced by the same procedure as that of T1 of Example 1 had a MI value of 6 at a pressure of 21.6 kg, and the viscosity was insufficient and the expansion ratio was low, so that it could not be molded into a box type. .

(Comparative Example 3) Injection foam molding: an additive of 1,6-extended hexamethylene diisocyanate and trimethylolpropane was added without changing the parts by weight of the polylactic acid raw material and the talc fine powder in the steps of Production Examples 1 to 3. The amount of the compounding amount was changed to 3 parts by weight, and the foamed molded article produced by the same procedure as that of T1 of Example 1 had a MI of 0.003 kg and a viscosity of 0.003, and the viscosity was too high and the expansion ratio was low, so that it could not be molded into a box type. .

(Example 3) Injection-foaming molding: 40 parts by weight of (B1) 30 parts by weight of (B1) cross-linked polylactic acid pellets (A1) produced in Production Examples 1 to 3, using an injection molding machine for manufacturing machine 2, (C1) 30 parts by weight was quantitatively supplied to a Henschel mixer, stirred and mixed, and quantitatively supplied to an injection molding machine from an addition funnel sealed with nitrogen. A mixed gas having a capacity ratio of nitrogen gas to methanol of 2% by weight with respect to the polylactic acid foaming molding material is injected from a nitrogen supply side cylinder, and the polystyrene-converted molecular weight measured by GPC at the time of melting is 2 million. The above polylactic acid was injected into the orifice portion shown in Fig. 3 at 170 ° C in a supercritical inert gas atmosphere (disposed in Fig. 4, thickness 0.2 mm, groove width 2 mm, slit length). a foam molding die of 35 mm slit plate (Fig. 6, A, hollow portion is 0.2 mm thick), and after the temperature of the injected polylactic acid becomes 100 ° C, as shown in Fig. 6B, the hollow portion of the mold is used. After changing the thickness to 4 mm and foaming for 30 seconds to fill the hollow portion, the mold was cooled to 40 ° C for 30 seconds to produce the injection-molded article T11 of the present invention. Similarly, T12 was produced by crosslinking polylactic acid round particles (A2), (B2), and (C2). Further, T13 was produced by cross-linking polylactic acid round particles (A3), (B3), and (C3) in the same manner.

The expansion ratio of T11, T12, and T13 is 20 times. Heat resistance is excellent. The MI values measured at a pressure of 21.6 kg for T11, T12, and T13 were 0.4, 0.3, and 0.2, respectively. Further, by the GPC measurement of T11, T12, and T13, a significantly large high molecular weight substance having a polystyrene-converted molecular weight of 1.5 million or more was not detected.

(Example 4) Beads and injection foam molding: The mold of the water cutter portion of the injection molding machine described in the manufacturing machine 1 was exchanged into a mold having a small diameter hole of 0.8 mm. will 33.3 parts by weight of the crosslinked polylactic acid pellets (A1) produced in Production Examples 1 to 3, 33.3 parts by weight of (B1), and 33.3 parts by weight of (C1) were quantitatively supplied to a Henschel mixer, stirred and mixed, and sealed from the mixture. The addition funnel of the nitrogen gas is supplied to the extruder in a predetermined amount, and the amount of nitrogen gas which is 0.2% by weight of the polylactic acid foaming molding material is continuously supplied to the gas injection hole of the first stage, and the polylactic acid having a polystyrene equivalent molecular weight of 2 million or more is measured by GPC. In the environment of supercritical nitrogen, physically lowering the molecular weight, and mechanically pulverizing by applying a shearing force, and recombining to produce a diameter (1 mm) of the round particles of the polylactic acid foaming molding material of the present invention ( T4). Similarly, it is produced by round particles (A2), (B2), and (C2) (T5). Further, it is produced by the round particles (A3), (B3), and (C3) in the same manner (T6).

100 parts by weight of the above-mentioned round grains (T4) and 5 parts by weight of a solution of isobutane and methanol 2:1 were placed in a hot press, and kept at 70 ° C for 1 hour, and then cooled to room temperature to produce a foamed bead T4 of the present invention. . Similarly, expanded beads T5 were produced from round grains (T5). Further, the expanded beads T6 were produced from the round grains (T6) in the same manner.

The predetermined amounts of the beads T4, T5, and T6 were respectively added to a mold, and foamed by steam heating for 1 minute to produce a foamed molded article of the polylactic acid foamed molding material of the present invention. The expansion ratio of the foamed molded article was 28 times. Heat resistance is excellent. The MI value measured by the foam molding at 190 ° C and a pressure of 21.6 kg was T4 of 0.4, T5 of 0.3, and T6 of 0.2. Further, by the GPC measurement, a significantly large high molecular weight substance having a molecular weight of 1.5 million or more in terms of polystyrene was not detected.

(Comparative Example 4) Beads and injection foam molding: raw materials and Example 4 In the same manner, 33.3 parts by weight of the crosslinked polylactic acid round particles (A1) produced in Production Examples 1 to 3, 33.3 parts by weight of (B1), and 33.3 parts by weight of (C1) were used. In the same manner as in the fourth embodiment, the mold of the water cutter portion of the manufacturing machine 1 was exchanged into a mold having a small diameter of 0.8 mm, and the nozzle portion 6 was used in comparison with the fourth embodiment. The operating conditions were the same as in the fourth embodiment. However, since the die holes were clogged and only the linear or planar shaped objects were formed from the start of the operation, the round particles could not be produced. Further, because of the clogging of the mold, the vent hole 8 leaks and cannot continue to operate. The melt before reaching the die hole was taken out, and 1% by weight or more of a significantly large high molecular weight substance having a polystyrene equivalent of more than 2 million was measured by GPC. This is considered to be because there is no orifice portion which becomes a flow barrier of the polylactic acid melt in the subsequent stage of the thickened portion 21, so that the pressure at the outlet of the thickened portion is lowered and the pressure difference between the inlet and the outlet of the thickened portion is increased. The supercritical gas is separated from the polylactic acid melt to form a gas-only passage, causing degassing, and the polylactic acid melt cannot be heated by the super-flow through the thickening portion, and the cross-linked portion is accelerated by the heat generation in the thickened portion. Since the thermal decomposition is performed without the orifice portion, the resin pressure after the rear portion of the thickened portion is lowered, so that the flow direction cannot be concentrated, and the recombination is continued in the lateral direction of the flow for a long period of time without regularity.

Since the round pellets could not be produced in Comparative Example 4, the mold of the water cutter portion was exchanged into a mold having a normal hole of 3.2 mm in a state where the orifice portion 6 was removed. The operation was carried out in the same manner as in Example 4, and 33.3 parts by weight of (A1), 33.3 parts by weight of (B1), and 33.3 parts by weight of (C1) were quantitatively supplied to the extruder, and the diameter was produced in the state without the fracture opening portion. 5mm polylactic acid foam forming material round (T7). Similarly by round grains (A2), (B2), (C2) Manufacturing (T8). Further, it is produced by the round particles (A3), (B3), and (C3) in the same manner (T9).

100 parts by weight of the above-mentioned round granules (T7) and 5 parts by weight of a 2:1 solution of isobutane and methanol were placed in a hot press, and kept at 70 ° C for 1 hour, and then cooled to room temperature to produce expanded beads T7. Similarly, expanded beads T8 were produced from round grains (T8). Further, the expanded beads T9 were produced from the round grains (T9) in the same manner.

The predetermined amounts of the beads T7, T8, and T9 were respectively added to a mold, and foamed by steam heating for 1 minute to produce a foamed molded article of a polylactic acid foamed molding material. The expansion ratio of the foamed molded article was 15 times. The heat resistance is excellent, but the foam contains a large number of foaming chambers of 5 mm to 10 mm, and the strength is also weak, and it is judged that the practicality is lacking. The MI value measured at 190 ° C and a pressure of 21.6 kg of the foam molded article was T7 of 0.4, T8 of 0.3, and T9 of 0.2. It was measured by GPC to measure 1% by weight or more of a significantly large high molecular weight substance having a molecular weight of 2,000,000 or more in terms of polystyrene. It is considered that the high molecular weight is a cause of degassing and causes a large foaming chamber to be produced. Because it is foamed in the sealed space in the mold, the expansion ratio in appearance is up to 15 times. However, in the case of open space, it can be easily predicted that the expansion ratio will be further reduced due to the degassing of the large foaming chamber. In Comparative Example 4, the effect of the slit of the orifice portion was actually confirmed.

(Manufacturing Machine 3) Extrusion Forming Sheet Forming Machine: Fig. 9 shows a schematic configuration of a preferred extrusion foam forming sheet forming machine embodying the present invention. In Fig. 9, the structure and contents described in the manufacturing machine 1 are the same from the entrance of the Henschel mixer 1 to the rear stage gear pump 9. The PLA melt pressurized by the rear gear pump is one side cooled by the cooling unit 25 Cooling is supplied from the gas (2) in front of the T-shaped mold through the foaming gas injection hole 26, and melted into the PLA from the gas injection holes (a collection of a plurality of extremely small diameter injection holes) disposed at two or more places. injection. The sheet shape is ejected from the T-shaped mold 27, transferred to the pulling device 28, and further cooled by the cooling drum in the pulling unit 28 to produce the extruded foam molded sheet 30 of the present invention.

(Example 5) Extrusion-foamed molded sheet: 50 parts by weight of cross-linked polylactic acid round particles (A1) produced in Production Examples 1 to 3, using the extrusion-foamed molded sheet molding machine of the manufacturing machine 3, (B1) 25 parts by weight and (C1) 25 parts by weight are continuously supplied to the Henschel mixer in a quantitative manner, stirred and mixed, and are quantitatively supplied to the injection molding machine from an addition funnel sealed with nitrogen gas, and continuously quantitatively supplied from the initial gas injection hole. The polylactic acid foam molding material has a weight ratio of 1.0% by weight to 2:1 nitrogen and methanol, and the polylactic acid having a polystyrene equivalent molecular weight of 2 million or more measured by GPC is in a supercritical inert gas atmosphere, and is physically The orifice portion 6 which is mechanically pulverized by a low molecular weight and subjected to a shearing force is cooled by a cooling portion to a sheet having a thickness of 0.5 mm and a width of 30 cm which is cooled to 100 ° C, and is pressed and set to be maintained at 100 ° C. A 10 cm thick piece of traction device. After the foamed molded portion was held at 100 ° C for 30 seconds, the foamed molded piece T21 of the present invention was produced by being cooled to a fixed length by a cooling drum of 40 ° C and cooled to 5 ° C lower than the Tg of the polylactic acid. . Similarly, T22 was produced by crosslinking polylactic acid round particles (A2), (B2), and (C2). Further, T23 was produced by cross-linking polylactic acid particles (A3), (B3), and (C3) in the same manner.

The heat resistance of the sheets T21, T22, and T23 is excellent. Foamed molded body The MI values of T21, T22, and T23 measured at a pressure of 21.6 kg were 0.4, 0.3, and 0.2, respectively. By the GPC measurement, a significantly large high molecular weight substance having a molecular weight of 1.5 million or more in terms of polystyrene was not detected.

The above is only the embodiment of the present invention, and the scope of the present invention is not limited thereto. The simple equivalent changes and modifications made by the content of the patent application and the contents of the patent specification of the present invention are still the patents of the present invention. Covered by the scope.

Claims (12)

A polylactic acid foam molding material is a polylactic acid (A), (B), and (C) having a composition ratio of three kinds of D bodies and L bodies, and has a total of 0.2 parts by weight based on 100 parts by weight of the above polylactic acid. And 2.0 parts by weight of an epoxy group or a polyisocyanate-based crosslinking agent, which does not contain polylactic acid having a polystyrene-equivalent molecular weight of 2,000,000 or more as measured by GPC, and the polylactic acid (A): (B): The weight ratio of (C) is 25~50:25~50:25~50 [but (A)+(B)+(C)=100], and JIS K7210 with 190 °C and pressure of 21.6kg is The MI value measured as follows is 0.05 to 5; wherein the composition ratio (D/L) of the D body and the L body in the polylactic acid (A), (B), and (C) is the polylactic acid (A) In the middle, D _A /L _A =5~20/95~80 [but D _A +L _A =100], in the above polylactic acid (B), D _B /L _B =(D _A +3~D _A +10)/(L _A -3~L _A -10) [but D _B +L _B =100], in the above polylactic acid (C), D _C /L _C =(D _B +3~D _B + 10) / (L _B -3~L _B -10) [but D _C + L _C = 100]. The polylactic acid foam molding material according to claim 1, which contains 0.5 to 5 parts by weight of calcium carbonate or talc fine particles. A foamed molded article comprising the polylactic acid foam molding material according to claim 1 or 2. The foamed molded article according to claim 3, which is maintained in a form after being injected with hot water at 90 °C. A method for producing a polylactic acid foam molding material, which is a method for producing a polylactic acid foam molding material having a MI value of 0.05 to 5, which is measured at 190 ° C and a pressure of 21.6 kg of JIS K7210. And comprising: a product produced by a crosslinking reaction between 100 parts by weight of polylactic acid composed of D body and L body and 0.2 to 2.0 parts by weight of a crosslinking agent having an epoxy group or a polyisocyanate group In the environment of supercritical inert gas, physically or mechanically lowering the product and then combining it to obtain three kinds of crosslinked polylactic acid (A) having different composition ratios of D body and L body. And (B) and (C) a cross-linked polylactic acid preparation step, and the cross-linked polylactic acid (A), (B) and (C) are 25 to 50:25 to 50:25 to 50 [but ( A) The weight ratio of +(B)+(C)=100] is mixed, and the polystyrene-reduced polylactic acid having a polystyrene-converted molecular weight of 2 million or more in the GPC obtained by melting the obtained mixture is in a supercritical inert gas. a step of physically or mechanically lowering and then recombining; wherein the ratio of the D body to the L body in the crosslinked polylactic acid (A), (B), and (C) is (D/L) Yes, in the foregoing Linked polylactic acid (A) for _{D A / L A = 5 ~} 20/95 ~ 80 [ but _{D A + L A = 100]} , in the cross-linked polylactic acid (B) for D _B / L _B = ( D _A +3~D _A +10)/(L _A -3~L _A -10) [but D _B +L _B =100], which is D _C /L _C = in the aforementioned crosslinked polylactic acid (C) (D _B +3~D _B +10)/(L _B -3~L _B -10) [but D _C +L _C =100]. A method for producing a polylactic acid foam molding material, which is a method for producing a polylactic acid foam molding material having a MI value of 0.05 to 5, which is measured at 190 ° C and a pressure of 21.6 kg of JIS K7210. The method includes: preparing polylactic acid (A), (B), and (C) having different composition ratios of the D body and the L body, and the polylactic acid (A), (B), and (C) are 25~ a step of mixing 50:25~50:25~50 [but (A)+(B)+(C)=100], and 100 parts by weight of the polylactic acid mixture prepared by the foregoing steps, and having Polylactic acid having a polystyrene-equivalent molecular weight of 2 million or more in GPC measurement by a GPC measurement of a crosslinking reaction between 0.2 to 2.0 parts by weight of an epoxy group or a polyisocyanate group crosslinking agent, and the polylactic acid is supercritical In the environment of an inert gas, a step of recombining physically or mechanically, and then combining the D body and the L body in the polylactic acid (A), (B), and (C) (D) /L) is, in the above polylactic acid (A), D _A /L _A = 5 to 20/95 to 80 [but D _A + L _A = 100], and in the above polylactic acid (B), D _B / L _B = (D _A +3~D _A +10) / (L _A -3~L _A -10) [but D _B +L _B =100], in the aforementioned polylactic acid In (C), it is D _C /L _C =(D _B +3~D _B +10)/(L _B -3~L _B -10) [but D _C +L _C =100]. A method for producing a foamed molded article of a polylactic acid foam molding material, which is a polylactic acid foam molding material having a MI value of 0.05 to 5, which is measured by JIS K7210 at 190 ° C and a pressure of 21.6 kg. A method of foaming a molded article, comprising: by using 100 parts by weight of polylactic acid composed of a D body and an L body, and 0.2 to 2.0 parts by weight of a crosslinking agent having an epoxy group or a polyisocyanate group; The ratio of the ratio of the three D-forms to the L-forms produced by the cross-linking reaction between the products produced by super-molecularization of the product in a supercritical or inert gas environment The cross-linked polylactic acid preparation step of the different cross-linked polylactic acid (A), (B) and (C), and the cross-linked polylactic acid (A), (B) and (C) are 25 to 50: 25~50:25~50 [but (A)+(B)+(C)=100] is mixed in a weight ratio, and the polystyrene-converted molecular weight measured by GPC obtained when the melted mixture is obtained is more than 2 million. The polylactic acid is formed by a physical or mechanical low molecular weight in a supercritical and inert gas atmosphere to form a polylactic acid foam molding material, and the polylactic acid foam molding material is produced. a step of foaming and molding at a temperature higher than a softening point and at a temperature of 110 ° C or lower; wherein the ratio of the D body to the L body in the crosslinked polylactic acid (A), (B), and (C) (D/L) Is, in the above-mentioned crosslinked polylactic acid (A), D _A /L _A = 5 to 20/95 to 80 [but D _A + L _A = 100], and D in the aforementioned crosslinked polylactic acid (B) _B / L _B = (D _A +3~D _A +10) / (L _A -3~L _A -10) [but D _B + L _B = 100], in the aforementioned crosslinked polylactic acid (C) D _C /L _C =(D _B +3~D _B +10)/(L _B -3~L _B -10) [but D _C +L _C =100]. The method for producing a foamed molded article of a polylactic acid foam molding material according to claim 7, wherein 0.5 to 5 parts by weight of calcium carbonate or talc fine particles are added to 100 parts by weight of the mixture. A method for producing a foamed molded article of a polylactic acid foam molding material, which is a polylactic acid foam molding material having a MI value of 0.05 to 5, which is measured by JIS K7210 at 190 ° C and a pressure of 21.6 kg. A method of foaming a molded article, comprising: preparing polylactic acid (A), (B), and (C) having three different compositions of D and L, and the polylactic acid (A), (B) and (C) a step of mixing at a weight ratio of 25 to 50:25 to 50:25 to 50 [but (A) + (B) + (C) = 100], and by the foregoing steps The polystyrene-equivalent molecular weight measured by GPC measured by a crosslinking reaction between 100 parts by weight of the polylactic acid mixture and 0.2 to 2.0 parts by weight of a crosslinking agent having an epoxy group or a polyisocyanate group is 2,000,000 or more. Polylactic acid, which is physically or mechanically low-molecularized in a supercritical inert gas environment and then combined to produce a polylactic acid foam molding material, and the polylactic acid foam molding material is softened at a softening point. a step of foaming and molding at a temperature of 110 ° C or lower; wherein the composition ratio (D/L) of the D body and the L body in the polylactic acid (A), (B), and (C) is The polylactic acid (A) for _{D A / L A = 5 ~} 20/95 ~ 80 [ but _{D A + L A = 100]} , in the polylactic acid (B) for _{D B / L B = (D} A + 3~D _A +10)/(L _A -3~L _A -10) [but D _B +L _B =100], in the above polylactic acid (C) is D _C /L _C =(D _B +3 ~D _B +10)/(L _B -3~L _B -10) [but D _C +L _C =100]. The method for producing a foamed molded article of a polylactic acid foam molding material according to claim 9, wherein 0.5 to 5 parts by weight of calcium carbonate or talc fine particles are added to 100 parts by weight of the polylactic acid mixture. A foamed molded article produced by the production method according to any one of claims 7 to 10. The foamed molded article according to claim 11, wherein the foamed molded article is maintained in a form after being injected with hot water at 90 °C.