JP2010184956A - Method for producing polylactic acid resin foamed particle for in-mold expansion molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a polylactic acid resin foamed particle to efficiently produce a polylactic acid resin foamed particle for in-mold expansion molding by reducing the number of adhesion of the polylactic acid resin foamed particle. <P>SOLUTION: This method for producing a polylactic acid resin foamed particle for in-mold expansion molding includes a step for feeding a polylactic acid resin composition which contains a polylactic acid resin and a thickener and has viscosity of 4,900-20,000 Pa s at 180°C to an extruder, then melting and kneading it in the presence of a foaming agent; a step for extruding the polylactic acid resin through a nozzle die 1 to obtain an extrudate, and cutting the polylactic acid resin extrudate with a rotary blade 5 into a particle while foaming to obtain a polylactic acid resin foamed particle, and scattering the polylactic acid resin foamed particle by cutting stress; and a step for making the polylactic acid resin foamed particle collide with a cooling member 4 disposed in front of the nozzle die 1 to cool. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing foamed polylactic acid resin particles for in-mold foam molding.

  Polylactic acid resin is a resin obtained by polymerizing naturally occurring lactic acid, is a biodegradable resin that can be decomposed by microorganisms existing in nature, and has excellent mechanical properties at room temperature. It attracts attention.

  The polylactic acid resin generally polymerizes D-lactic acid and / or L-lactic acid, or opens one or more lactides selected from the group consisting of L-lactide, D-lactide and DL-lactide. Manufactured by ring polymerization.

  In-mold foam molding has been proposed as a method for producing a polylactic acid resin foamed molded article by foaming polylactic acid resin foamed particles. The above-mentioned in-mold foam molding is a method in which polylactic acid resin foam particles are filled in a mold, and the polylactic acid resin foam particles are heated and foamed with a heat medium such as hot water or water vapor to produce polylactic acid resin foam particles. This is a method for producing a polylactic acid resin foamed molded article having a desired shape by fusing and integrating foamed particles with each other by the foaming pressure.

  In Patent Document 1, when continuously producing pre-expanded particles for in-mold molding using a biodegradable polyester resin, the biodegradable polyester resin and a foaming agent are kneaded with an extruder and foamed strands. The continuous production method of biodegradable polyester resin pre-foamed particles is disclosed, characterized in that the foamed strands are cut to obtain pre-foamed particles. As a method for cutting the foamed strand, it is disclosed that a so-called hot cut system in which the foaming strand is cut while being cooled is preferable (paragraph number [0030]).

  However, when producing the pre-expanded particles by cutting the foam strand, there is a problem that the pre-expanded particles are coalesced and the productivity is low.

  Further, Patent Document 2 uses an aerial hot cut method in which molten resin extruded from a die attached to the tip of an extruder is cut and pelletized by a rotating cutter while sliding the die surface and dropped into water and cooled. In the granulation method, there is described a granulation method in which the resin is poly-4-methyl-1-pentene, and cooling water is sprayed or sprayed to solidify a molten resin film formed on the die surface.

  In the above granulation method, in order to reduce the generation rate of coalescence pellets and grape-like pellets, cooling water is sprayed or sprayed on the die surface to solidify the molten resin film and peel it from the die surface. The adhesiveness with the surface is maintained well, and the sharpness when the molten resin is cut with a cutter is favorably maintained.

  However, in the above granulation method, there is a problem that cooling water is applied to the molten resin extruded from the die, the foaming of the molten resin is inhibited, and the expansion ratio of the molten resin is lowered. Further, since the cooling water is directly sprayed or sprayed on the die, nozzle clogging frequently occurs, and there is a problem that the particle diameter of the foamed particles and the foaming ratio vary.

JP 2002-302567 A Japanese Patent No. 3996695

  The present invention reduces the number of polylactic acid resin foam particles obtained by cutting a polylactic acid resin extrudate extruded from a nozzle mold with a rotary blade to reduce the number of polylactic acid resin foams for in-mold foam molding. Provided is a method for producing foamed polylactic acid resin particles for in-mold foam molding, which can efficiently produce particles (hereinafter sometimes abbreviated as “polylactic acid resin foamed particles”).

  The method for producing foamed polylactic acid resin particles for in-mold foam molding according to the present invention comprises a polylactic acid resin composition containing a polylactic acid resin and a thickener and having a viscosity at 180 ° C. of 4900 to 20000 Pa · s. Supplying to an extruder and melt-kneading in the presence of a foaming agent, and extruding a polylactic acid resin extrudate from a nozzle mold attached to the front end of the extruder, and foaming the polylactic acid resin extrudate The polylactic acid resin foamed particles are produced by cutting with a rotating blade that rotates while contacting the front end surface of the nozzle mold, and the polylactic acid resin foamed particles are scattered by cutting stress, and the polylactic acid. And a step of cooling the resin-based resin foam particles against a cooling member disposed in front of the nozzle mold.

  First, a manufacturing apparatus used for manufacturing the polylactic acid resin expanded particles will be described. In FIG. 1, reference numeral 1 denotes a nozzle mold attached to the front end of the extruder. This nozzle mold is preferable because the polylactic acid resin composition can be extruded and foamed to form uniform fine bubbles. As shown in FIG. 2, a plurality of nozzle outlet portions 11, 11... Are formed on the same virtual circle A at equal intervals on the front end surface 1 a of the nozzle mold 2. The nozzle mold attached to the front end of the extruder is not particularly limited as long as the polylactic acid resin composition does not foam in the nozzle.

  When the number of nozzles of the nozzle mold 1 is small, the production efficiency of the polylactic acid-based resin foamed particles is reduced. On the other hand, when the number is large, the polylactic acid-based resin extrudates extruded and foamed from adjacent nozzles are in contact with each other. Since the polylactic acid resin expanded particles obtained by coalescence or by cutting the polylactic acid resin extrudate may be coalesced, 2 to 80 are preferable, 5 to 60 are more preferable, and 8 to 50 Individual is particularly preferred.

  If the diameter of the nozzle outlet 11 in the nozzle mold 1 is small, the extrusion pressure may be too high and extrusion foaming may be difficult. On the other hand, if the diameter is large, the diameter of the polylactic acid resin expanded particles becomes large. Since the filling property to a metal mold | die falls, 0.2-2 mm is preferable, 0.3-1.6 mm is more preferable, 0.4-1.2 mm is especially preferable.

If the shear rate of the polylactic acid-based resin composition at the nozzle outlet 11 in the nozzle mold 1 is small, the expansion ratio of the polylactic acid-based resin expanded particles decreases or the bubbles of the polylactic acid-based resin expanded particles are coarse. On the other hand, if it is large, fracture may occur and stable extrusion foaming may not be possible, so 1000 to 30000 sec ⁻¹ is preferable, 2000 to 25000 sec ⁻¹ is more preferable, and 3000 to 20000 sec ^{−. 1} is particularly preferred.

The shear rate at the outlet 11 of the nozzle of the nozzle mold is calculated based on the following formula.
Shear rate (sec ⁻¹ ) = 4 × Q / (πr ³ )
However, Q is the volume extrusion rate (cm ³ / sec) of the polylactic acid resin composition (when calculating Q from the mass extrusion rate (g / sec), the density of the polylactic acid resin composition is 1 and .0g / cm ^3), r is the radius of the nozzle (cm).

  Further, in order to reduce fracture, the length of the land portion of the nozzle mold 1 is preferably 4 to 30 times the diameter of the outlet portion 11 of the nozzle of the nozzle die 1. 5 to 20 times the diameter of 11 is more preferable. This is because, if the length of the land portion of the nozzle mold is smaller than the diameter of the nozzle outlet portion of the nozzle mold, fracture may occur and stable extrusion foaming may occur. This is because, if the length of the land portion of the mold is larger than the diameter of the outlet portion of the nozzle of the nozzle mold, a large pressure is applied to the nozzle mold and extrusion foaming may not be performed.

  In the portion surrounded by the nozzle outlets 11, 11,... On the front end face 1a of the nozzle mold 1, the rotary shaft 2 is disposed so as to protrude forward. 2 penetrates the front part 41a of the cooling drum 41 which comprises the cooling member 4 mentioned later, and is connected with drive members 3, such as a motor.

  Further, one or a plurality of rotary blades 5, 5... Are integrally provided on the outer peripheral surface of the rear end portion of the rotary shaft 2, and all the rotary blades 5 are nozzles when rotating. The mold 1 is always in contact with the front end face 1a. When the plurality of rotary blades 5, 5,... Are integrally provided on the rotary shaft 2, the plurality of rotary blades 5, 5,. Each is arranged. 2 shows a case where four rotary blades 5, 5,... Are integrally provided on the outer peripheral surface of the rotary shaft 2 as an example.

  As the rotary shaft 2 rotates, the rotary blades 5, 5,... Are always in contact with the front end surface 1a of the nozzle mold 1 to form nozzle outlet portions 11, 11,. The polylactic acid resin extrudate that moves on the virtual circle A and is extruded from the outlet portions 11, 11...

  A cooling member 4 is disposed so as to surround at least the front end of the nozzle mold 1 and the rotating shaft 2. The cooling member 4 has a front circular front portion 41a having a larger diameter than the nozzle mold 1 and a cylindrical peripheral wall portion 41b extending rearward from the outer peripheral edge of the front portion 41a. And a bottom cylindrical cooling drum 41.

  Further, a supply port 41c for supplying the cooling liquid 42 is formed in a portion of the peripheral wall portion 41b of the cooling drum 41 corresponding to the outside of the nozzle mold 1 so as to penetrate between the inner and outer peripheral surfaces. Yes. A supply pipe 41 d for supplying the cooling liquid 42 into the cooling drum 41 is connected to the outer opening of the supply port 41 c of the cooling drum 41.

  The coolant 42 is configured to be supplied obliquely forward along the inner peripheral surface of the peripheral wall portion 41b of the cooling drum 41 through the supply pipe 41d. Then, the coolant 42 spirals along the inner peripheral surface of the peripheral wall portion 41b of the cooling drum 41 by the centrifugal force accompanying the flow velocity when being supplied from the supply pipe 41d to the inner peripheral surface of the peripheral wall portion 41b of the cooling drum 41. Go forward as you draw. Then, the coolant 42 gradually spreads in the direction perpendicular to the traveling direction while traveling along the inner peripheral surface of the peripheral wall portion 41b, and as a result, the inner surface of the peripheral wall portion 41b in front of the supply port 41c of the cooling drum 41 is increased. The peripheral surface is configured to be entirely covered with the coolant 42.

  The cooling liquid 42 is not particularly limited as long as the polylactic acid-based resin expanded particles can be cooled, and examples thereof include water and alcohol, but water is preferable in consideration of the treatment after use.

  A discharge port 41e is formed on the lower surface of the front end portion of the peripheral wall portion 41b of the cooling drum 41 so as to penetrate between the inner and outer peripheral surfaces. A discharge pipe 41f is formed at the outer opening of the discharge port 41e. Are connected so that the polylactic acid-based resin expanded particles and the coolant 42 can be continuously discharged.

  Next, the polylactic acid resin used in the present invention will be described. As the polylactic acid resin used in the present invention, commercially available polylactic acid resins can be used. Specifically, D-lactic acid and L-lactic acid are copolymerized as monomers, or D-lactic acid or It can be obtained by polymerizing any one of L-lactic acid as a monomer or ring-opening polymerization of one or more lactides selected from the group consisting of D-lactide, L-lactide and DL-lactide. Any polylactic acid resin can be used.

  And when producing a polylactic acid-based resin, when the D isomer and L isomer are used in combination as a monomer, the proportion of the lesser optical isomer of the D isomer or L isomer is less than 5 mol%, or In the case where only one of the optical isomers of D-form or L-form is used as a monomer, that is, the polylactic acid-based resin has both D-form and L-form optical isomers as its constituent monomer components. And the content of the smaller optical isomer of D-form or L-form is less than 5 mol%, or any one of the D-form or L-form optical isomer as a constituent monomer component In the case where only the D-form or L-form is used as a monomer, the polylactic acid resin obtained has a higher crystallinity and a higher melting point. The smaller percentage When it mol% or more, according to the optical isomer is increased the smaller the resulting polylactic acid-based resin, its crystallinity decreases, the eventually amorphous.

  Therefore, in the present invention, a polymorphism containing both D-form and L-form optical isomers as a constituent monomer component and the content of the smaller of the D-form and L-form is less than 5 mol%. It is preferable to use a lactic acid-based resin or a polylactic acid-based resin containing only one optical isomer of either D-form or L-form as a constituent monomer component. By using such a polylactic acid-based resin, the heat resistance of the obtained polylactic acid-based resin expanded particles can be increased.

  Furthermore, the polylactic acid-based resin obtained by polymerizing the D-form and the L-form in combination as a monomer has a ratio of the lesser of the D-form and the L-form of less than 4 mol% of the optical isomer. A polylactic acid resin obtained by polymerizing a certain monomer is preferred, and a polylactic acid resin obtained by polymerizing a monomer in which the proportion of the optical isomer, whichever is smaller, of D-form or L-form is less than 3 mol% A lactic acid-based resin is more preferable, and a polylactic acid-based resin obtained by polymerizing a monomer in which the ratio of the optical isomer, which is the smaller of either the D-form or the L-form, is less than 2 mol% is particularly preferred.

  That is, a polylactic acid-based resin containing both optical isomers of D-form and L-form as a constituent monomer component, and the content of the smaller optical isomer of D-form or L-form is less than 4 mol%. Preferably, a polylactic acid-based resin that contains both D-form and L-form optical isomers as a constituent monomer component, and the content of the smaller of the D-form and L-form is less than 3 mol%. More preferably, a polylactic acid resin containing both D isomer and L isomer as constituent monomer components, and the content of the lesser of the D isomer and L isomer being less than 2 mol% Is more preferable.

  And as for the polylactic acid-type resin which contains D body and L body as a constituent monomer component, the ratio of the optical isomer of the smaller one of D body or L body decreases, and the polylactic acid resin becomes In addition to its crystallinity, the melting point increases. Therefore, the heat resistance of the foamed molded product obtained by filling the foamed particles in the mold and foaming is improved, and the foamed molded product can maintain its form even at a high temperature. Therefore, the foamed molded product can be taken out from the mold at a high temperature, the cooling time in the mold of the foamed molded product is shortened, and the production efficiency of the foamed molded product can be improved.

  Here, the content of D-form or L-form in the polylactic acid-based resin can be measured by the following method. The polylactic acid-based resin is freeze-pulverized and 200 mg of the polylactic acid-based resin powder is supplied into the Erlenmeyer flask, and then 30 ml of a 1N sodium hydroxide aqueous solution is added to the Erlenmeyer flask. Then, the polylactic acid resin is completely dissolved by heating to 65 ° C. while shaking the Erlenmeyer flask. Thereafter, 1N hydrochloric acid is supplied into the Erlenmeyer flask to neutralize it, a decomposition solution having a pH of 4 to 7 is prepared, and a predetermined volume is obtained using a volumetric flask.

  Next, after the decomposition solution is filtered through a 0.45 μm membrane filter, it is analyzed using a liquid chromatograph. Based on the obtained chart, the area ratio is calculated from the peak area derived from D-form and L-form as D Calculate body weight and L body weight. Then, the same procedure as described above was repeated 5 times, and the obtained D-form amount and L-form amount were arithmetically averaged to obtain the D-form amount and L-form amount of the polylactic acid resin.

HPLC system (liquid chromatograph): “PU-2085 Plus type system” manufactured by JASCO Corporation
Column: Product name “SUMICHIRAL OA5000” (4.6 mmφ × 250 mm) manufactured by Sumitomo Analysis Center
Column temperature: 25 ° C
Mobile phase: Mixture of 2 mM CuSO ₄ aqueous solution and 2-propanol
(CuSO ₄ aqueous solution: 2-propanol (volume ratio) = 95: 5)
Mobile phase flow rate: 1.0 ml / min Detector: UV 254 nm
Injection volume: 20 microliters

And polylactic acid-type resin expanded particles are manufactured by extrusion foaming. Therefore, the polylactic acid resin of the polylactic acid resin composition constituting the polylactic acid resin expanded particles has its melting point (mp), storage elastic modulus curve and loss obtained by dynamic viscoelasticity measurement. It is preferable that the temperature T at the intersection with the elastic modulus curve is adjusted so as to satisfy the following formula 1.
(Melting point of polylactic acid resin (mp) -40 ° C)
≦ (temperature T at the intersection) ≦ melting point of polylactic acid resin (mp) Formula 1

  Here, the storage elastic modulus obtained by the dynamic viscoelasticity measurement is an index indicating elastic properties in the viscoelasticity, and is an index indicating the elasticity of the bubble film in the foaming process. This is an index indicating the magnitude of the foaming pressure required to expand the bubbles against the contraction force of the bubble film.

  That is, if the storage elastic modulus obtained by the dynamic viscoelasticity measurement of the polylactic acid-based resin is low, when the cell membrane is stretched, the force that the cell membrane attempts to contract against the stretching force is small. As a result of the expansion of the foamed film easily due to the foaming pressure required for the production of lactic acid resin foamed particles, the foamed film expands excessively, resulting in bubble breakage, while measuring the dynamic viscoelasticity of the polylactic acid resin When the storage elastic modulus obtained in (2) is high, when the expansion force is applied to the cell membrane, the contraction force of the cell membrane against the expansion is large, and once the expansion pressure required for the production of the polylactic acid resin expanded particles is reached. Even if the bubbles expand, the bubbles contract as the foaming pressure decreases with time due to a temperature drop or the like.

  Further, the loss modulus obtained by dynamic viscoelasticity measurement is an index indicating a viscous property in viscoelasticity, and is an index indicating the viscosity of the bubble film in the foaming process. This is an index indicating the allowable range of how much can be expanded without breaking, and at the same time, the ability to expand the bubbles to the desired size by the foaming pressure and then maintain the expanded bubbles at that size It is also an indicator that indicates.

  That is, if the loss elastic modulus obtained by the dynamic viscoelasticity measurement of the polylactic acid-based resin is low, when the cell membrane is expanded by the foaming pressure required for the production of the polylactic acid-based resin expanded particles, On the other hand, if the loss elastic modulus obtained by the dynamic viscoelasticity measurement of the polylactic acid resin is high, the foaming force is converted into thermal energy by the cell membrane, and the polylactic acid resin expanded particles It becomes difficult to stretch the bubble membrane smoothly during production, and it is difficult to expand the bubbles.

  Thus, in producing polylactic acid resin foamed particles by foaming the polylactic acid resin composition, the polylactic acid resin is required to obtain the polylactic acid resin foamed particles in the foaming process. It is necessary to have an elastic force for expanding the bubble film appropriately without being broken by the foaming pressure, that is, a storage elastic modulus, and the bubble film is smoothly stretched without being broken by the foaming pressure to have a desired size. It is preferable to have a viscous force, that is, a loss elastic modulus, for maintaining the expanded bubbles in the size regardless of the decrease in the foaming pressure over time.

  That is, in the extrusion foaming process, it is preferable that both the storage elastic modulus and loss elastic modulus of the polylactic acid-based resin have values suitable for extrusion foaming, and the storage elastic modulus and loss suitable for such extrusion foaming. In order to impart an elastic modulus to the polylactic acid resin in the extrusion foaming process, the temperature T (below) at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by dynamic viscoelasticity measurement in the polylactic acid resin. More preferably, the expression “temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve” and the melting point (mp) of the polylactic acid resin preferably satisfy the following formula 1. 2 is adjusted so that the storage elastic modulus and loss elastic modulus of the polylactic acid resin are suitable for extrusion foaming while balancing the storage elastic modulus and loss elastic modulus of the polylactic acid resin. Cities, the polylactic acid-based resin foamed particles can be produced stably.

[Melting point of polylactic acid resin (mp) −40 ° C.]
≦ Temperature at the intersection T ≦ Melting point of polylactic acid resin (mp) Formula 1

[Melting point of polylactic acid resin (mp) -35 ° C.]
≦ Temperature at intersection T ≦ [melting point of polylactic acid resin (mp) −10 ° C.]
... Formula 2

  Further, the temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by the dynamic viscoelasticity measurement of the polylactic acid resin and the melting point (mp) of the polylactic acid resin are expressed by the above equation 1. The reason why it is preferable to adjust so as to satisfy will be described in detail below.

  First, the temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by dynamic viscoelasticity measurement of the polylactic acid resin exceeds 40 ° C. than the melting point (mp) of the polylactic acid resin. If it is low, the loss elastic modulus of the polylactic acid resin at the time of extrusion foaming is too large compared with the storage elastic modulus, so that the balance between the loss elastic modulus and the storage elastic modulus is lost.

  Therefore, if the foaming force suitable for the loss elastic modulus of the polylactic acid-based resin, that is, the foaming force matched to the viscosity of the polylactic acid-based resin, the foaming force is too large for the elastic force of the polylactic acid-based resin. The film is broken and bubbles are broken, and good polylactic acid resin expanded particles cannot be obtained. Conversely, the foaming force suitable for the storage elastic modulus of the polylactic acid resin, that is, the elasticity of the polylactic acid resin is reduced. If the combined foaming force is used, the foaming force is small for the viscosity of the polylactic acid-based resin, the polylactic acid-based resin is difficult to foam, and it is difficult to obtain good polylactic acid-based resin foamed particles.

  Further, when the temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by the dynamic viscoelasticity measurement of the polylactic acid resin is higher than the melting point (mp) of the polylactic acid resin, Since the storage elastic modulus of the polylactic acid resin at the time of foaming is too large compared to the loss elastic modulus, the balance between the loss elastic modulus and the storage elastic modulus is lost as described above.

  Therefore, if the foaming force suitable for the storage elastic modulus of the polylactic acid-based resin, that is, the foaming force matched to the elasticity of the polylactic acid-based resin, the foaming force is too large for the viscosity force of the polylactic acid-based resin, The film is broken and bubbles are broken, and good polylactic acid resin foam particles cannot be obtained. Conversely, the foaming force suitable for the loss elastic modulus of the polylactic acid resin, that is, the viscosity of the polylactic acid resin is adjusted. If the foaming force is high, the foaming force is small for the elastic force of the polylactic acid-based resin. Even if the polylactic acid-based resin foams once due to the foaming force, the bubbles shrink as the foaming force decreases over time. In other words, it becomes difficult to obtain good polylactic acid resin expanded particles.

  Then, the temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by the dynamic viscoelasticity measurement of the polylactic acid resin and the melting point (mp) of the polylactic acid resin are expressed by the above equation 1. As a method of adjusting so as to satisfy, as the weight average molecular weight of the polylactic acid resin increases, the storage elastic modulus curve and the loss elastic modulus curve obtained by the dynamic viscoelasticity measurement of the polylactic acid resin Since the temperature T at the intersection becomes high, a method for adjusting the weight average molecular weight of the obtained polylactic acid resin by adjusting the reaction time or reaction temperature during polymerization of the polylactic acid resin, before extrusion foaming or extrusion foaming A method of adjusting the weight average molecular weight of the polylactic acid resin sometimes using a thickener or a crosslinking agent is mentioned.

  Here, the melting point (mp) of the polylactic acid resin is measured in the following manner. That is, the differential scanning calorimetry of the polylactic acid resin is performed in accordance with JIS K7121: 1987, and the melting peak temperature in the obtained DSC curve is defined as the melting point (mp) of the polylactic acid resin. When there are a plurality of melting peak temperatures, the highest temperature is set.

  Further, the temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by the dynamic viscoelasticity measurement of the polylactic acid-based resin is the one measured in the following manner. First, polylactic acid resin particles are obtained in the same manner except that the foaming agent is not added in the procedure for producing the polylactic acid resin expanded particles.

The polylactic acid resin particles are dried for 3 hours at 80 ° C. under a reduced pressure of 9.33 × 10 ⁴ Pa. The polylactic acid-based resin particles are placed on a measurement plate heated to a temperature 40 to 50 ° C. higher than the melting point of the polylactic acid-based resin constituting the polylactic acid-based resin particles, and 5 in a nitrogen atmosphere. Leave to melt for minutes.

  Next, a flat circular pressure plate having a diameter of 25 mm is prepared, and the polylactic acid resin on the measurement plate is moved up and down until the distance between the opposing surfaces of the pressure plate and the measurement plate becomes 1 mm. Press in the direction. And after removing the polylactic acid-type resin which protruded from the outer periphery of a press plate, it is left to stand for 5 minutes.

  Thereafter, the dynamic viscoelasticity measurement of the polylactic acid resin is performed under the conditions of 5% strain, frequency 1 rad / sec, temperature drop rate 2 ° C./min, and measurement interval 30 sec to determine the storage elastic modulus and loss elastic modulus. taking measurement. Next, a storage elastic modulus curve and a loss elastic modulus curve are drawn with the horizontal axis as temperature and the vertical axis as storage elastic modulus and loss elastic modulus. In drawing the storage elastic modulus curve and the loss elastic modulus curve, the measurement values adjacent to each other are connected with a straight line based on the measurement temperature.

  And it can obtain by reading the temperature T in the intersection of the obtained storage elastic modulus curve and loss elastic modulus curve from the said graph. When the storage modulus curve and the loss modulus curve intersect each other at a plurality of locations, the highest temperature among the temperatures at the plurality of intersections of the storage modulus curve and the loss modulus curve is defined as the storage modulus curve. It is set as the temperature T in the intersection with a loss elastic modulus curve.

The temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by dynamic viscoelasticity measurement is a dynamic value commercially available from Reologica Instruments AB under the trade name “DynAlyser DAR-100”. It can be measured using a mechanical viscoelasticity measuring device.

  Then, the polylactic acid resin composition containing the polylactic acid resin and the thickener and having a viscosity at 180 ° C. of 4900 to 20000 Pa · s is supplied to an extruder and melt-kneaded in the presence of a foaming agent. Thereafter, the polylactic acid resin extrudate is cut by the rotary blade 5 while being extruded and foamed from the nozzle mold 1 attached to the front end of the extruder to produce polylactic acid resin expanded particles.

  The extruder is not particularly limited as long as it is a conventionally used extruder. For example, a single-screw extruder, a twin-screw extruder, and a tandem extruder in which a plurality of extruders are connected. Is mentioned.

  Since the polylactic acid resin extrudate in a molten state immediately after being extruded and foamed from the nozzle mold 1 is cut with a rotary blade, the polylactic acid resin extrudates are being cut together or between the polylactic acid resin expanded particles. When contacting after cutting of the polylactic acid resin extrudate, the polylactic acid resin foamed particles are likely to be bonded together.

  In particular, polylactic acid-based resins are hydrolyzed by heating in an extruder, resulting in a decrease in molecular weight due to resin degradation. As a result, the viscosity of the polylactic acid-based resin is decreased, and coalescence of the polylactic acid-based resin expanded particles is caused. Prone to occur.

  Here, as a method of suppressing the coalescence of the polylactic acid-based resin foamed particles, a method of reducing the number of nozzles of the nozzle mold or widening the interval between the nozzles is conceivable. The production efficiency of the polylactic acid-based resin expanded particles for use is reduced, which is not preferable.

  Therefore, in the present invention, a polylactic acid resin composition containing a polylactic acid resin and a thickener is supplied to the extruder. Thus, the viscosity of the polylactic acid resin composition is increased by adding a thickener to the polylactic acid resin.

  Furthermore, by adding a thickener to the polylactic acid resin, it prevents resin degradation due to hydrolysis in the extruder, prevents a decrease in the molecular weight of the polylactic acid resin, and reduces the viscosity of the polylactic acid resin composition. It also prevents.

  As described above, by adding a thickener to the polylactic acid resin, the viscosity of the polylactic acid resin composition is positively increased by the thickener while suppressing the decomposition of the polylactic acid resin. Even when polylactic acid resin extrudates or polylactic acid resin foam particles collide with each other during or after cutting the resin extrudates, it is effective for the polylactic acid resin foam particles to coalesce with each other. Has been reduced.

  The thickener is not particularly limited as long as it is an additive that increases the viscosity of the polylactic acid resin composition by being contained in the polylactic acid resin, but it contains a carbodiimide compound, an isocyanate compound, and an epoxy group. And a compound containing an oxazoline group are preferable, and the effect of suppressing the hydrolysis of the polylactic acid resin in the Oshiyama machine is high, and the decrease in the molecular weight of the polylactic acid resin due to resin degradation can be effectively prevented. A carbodiimide compound is more preferable. In addition, a thickener may be used independently or 2 or more types may be used together.

  As a strong rubodiimide compound, it is sufficient that the molecule has two or more carbodiimide groups represented by (—N═C═N—), and as a polyvalent carbodiimide compound having two or more carbodiimide groups, For example, poly (4,4′-dicyclohexylmethanecarbodiimide), poly (4,4′-biphenylmethanecarbodiimide), poly (1,6-hexamethylenecarbodiimide), poly (1,3-cyclohexylenecarbodiimide), poly (1,4-cyclohexylenecarbodiimide), poly (3,3′-dimethyl-4,4′-diphenylmethanecarbodiimide), poly (naphthylenecarbodiimide), poly (p-phenylenecarbodiimide), poly (m-phenylenecarbodiimide) Poly (1,3,5-triisopropylbenzene carbodi De), poly (tolyl carbodiimide), polycarbodiimide compounds such as poly (diisopropylcarbodiimide) and the like. In addition, as a polycarbodiimide compound, it is marketed by the Nisshinbo Co., Ltd. by the brand name "Torubodilite LA-1."

  The isocyanate compound may be any polyvalent isocyanate compound having two or more isocyanate groups, and may be any of polyfunctional aromatic isocyanate, polyfunctional aliphatic isocyanate, aromatic polyisocyanate or aliphatic polyisocyanate, for example. May be.

  Specifically, as the isocyanate compound, for example, diphenylmethane diisocyanate, tolylene diisocyanate, xylene diisocyanate, hexamethylene diisocyanate, triphenylmethane triisocyanate, tris (p-isocyanatophenyl) thiophosphite, polymethylene polyphenyl polyisocyanate Etc.

  In addition, the epoxy group-containing compound is preferably an acrylic / styrene compound containing an epoxy group, and the constituent monomer component contains an epoxy monomer containing an epoxy group and a styrene monomer. More preferred is a vinyl polymer.

  Examples of the acrylic monomer containing an epoxy group include glycidyl (meth) acrylate, glycidyl (meth) acrylate, (3,4-epoxycyclohexyl) methyl (meth) acrylate, and (3,4-epoxycyclohexyl). ) Methyl (meth) acrylate and the like. In the present invention, (meth) acryl means acryl or methacryl. Examples of the styrene monomer include styrene, α-methylstyrene, t-butylstyrene, chlorostyrene, and the like.

  Furthermore, as a constituent monomer component, a vinyl polymer containing an acrylic monomer containing an epoxy group and a styrene monomer contains an acrylic monomer containing an epoxy group and a styrene monomer. A monomer other than the body may be contained as a constituent monomer component. Examples of such a monomer include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate. , Methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate and the like.

  Acrylic / styrene compounds containing an epoxy group are available from Toagosei Co., Ltd. under the trade names “ARUFON UG-4000”, “ARUFON UG-4010”, “ARUFON UG-4030”, “ARUFON UG-4040”, “ARUFON UG-”, for example. 4070 ".

  Examples of the oxazoline compound include 2,2′-phenylenebis (2-oxazoline), 2,2′-phenylenebis (4-methyl-2-oxazoline), and 2,2′-phenylenebis (4,4′- Dimethyl-2-oxazoline), 2,2′-ethylenebisoxazoline, 2,2′-tetramethylenebisoxazoline, 2,2′-ethylenebis (4-methyl-2-oxazoline), and the like.

  When the viscosity at 180 ° C. of the polylactic acid resin composition is low, when the polylactic acid resin extrudate extruded and foamed from the nozzle mold is cut with a rotary blade, the polylactic acid resin foam particles collide with each other. On the other hand, if it is high, the foamability of the polylactic acid resin composition is lowered, and when the in-mold foam molding is performed using the polylactic acid resin foamed particles, the heat fusion property between the polylactic acid resin foamed particles is Is reduced to 4900 to 20000 Pa · s, 4900 to 19000 Pa · s is preferable, and 4900 to 18000 Pa · s is more preferable.

  In addition, the viscosity in 180 degreeC of a polylactic acid-type resin composition is measured in the following way. First, polylactic acid resin particles are obtained in the same manner except that the foaming agent is not added in the procedure for producing the polylactic acid resin expanded particles.

  Next, a test piece having a flat circular shape having a diameter of 25 mm and a thickness of 3 mm is prepared from the polylactic acid resin particles at 180 ° C. using an injection molding machine. The specimen is heated to 80 ° C. for 3 hours.

  Thereafter, the test piece is placed on the plate, and the test piece is left to stand at 180 ° C. for 5 minutes in a nitrogen atmosphere to be completely melted. Next, a pair of flat plate-shaped pressing plates having a diameter of 25 mm are prepared. After disposing the test piece between the pair of pressing plates, the test piece is heated at 180 ° C. for 5 minutes, and then the test piece is crushed until its thickness becomes 1 mm, from the outer periphery of the pressing plate. The protruding polylactic acid resin composition is removed to prepare a test specimen. The pair of pressing plates is set so that both surfaces thereof are horizontal. After leaving the test body for 5 minutes, the viscosity of 0 to 60 seconds is measured in a state where the upper pressing plate is rotated so that the horizontal pressure is a constant pressure of 100 Pa on the test body. The arithmetic average value of the viscosity of the test specimen for 60 seconds is defined as the viscosity at 180 ° C. of the polylactic acid-based resin composition. In addition, when the bubble has generate | occur | produced in the test body after a viscosity measurement, the viscosity of this test body is not employ | adopted.

  And if there is little quantity of the carbodiimide compound supplied to an extruder, the fall of the molecular weight of the polylactic acid-type resin in an extruder cannot be suppressed, or the viscosity of a polylactic acid-type resin composition is fully raised. However, when the polylactic acid resin expanded particles collide with each other, the polylactic acid resin expanded particles are easily bonded to each other. On the other hand, if the polylactic acid resin expanded particles are too large, the viscosity of the polylactic acid resin composition becomes too high. When the in-mold foam molding is performed using the polylactic acid-based resin expanded particles, the heat-fusibility between the polylactic acid-based resin expanded particles may be reduced. Therefore, with respect to 100 parts by weight of the polylactic acid-based resin 0.01-5 weight part is preferable and 0.03-4.5 weight part is more preferable.

  Further, as the foaming agent, those conventionally used are used, for example, chemical foaming agents such as azodicarbonamide, dinitrosopentamethylenetetramine, hydrazoyldicarbonamide, sodium bicarbonate; propane, normal butane, Saturated aliphatic hydrocarbons such as isobutane, normal pentane, isopentane, hexane, ethers such as dimethyl ether, chlorofluorocarbons such as methyl chloride, 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, monochlorodifluoromethane, Examples thereof include physical blowing agents such as carbon dioxide and nitrogen, dimethyl ether, propane, normal butane, isobutane and carbon dioxide are preferred, propane, normal butane and isobutane are more preferred, and normal butane and isobutane are particularly preferred. In addition, a foaming agent may be used independently or 2 or more types may be used together.

  If the amount of foaming agent supplied to the extruder is small, the polylactic acid resin foamed particles may not be foamed to the desired foaming ratio, while if large, the foaming agent acts as a plasticizer. Since the viscoelasticity of the polylactic acid resin composition in a molten state is excessively lowered and foamability may be reduced and good polylactic acid resin expanded particles may not be obtained. 0.1 to 5 parts by weight is preferable, 0.2 to 4 parts by weight is more preferable, and 0.3 to 3 parts by weight is particularly preferable.

  In addition, it is preferable that a bubble regulator is supplied to the extruder. However, since many of the bubble regulators act as crystal nucleating agents for the polylactic acid resin expanded particles, crystallization of the polylactic acid resin is not promoted. It is preferable to use a bubble regulator, and as such a bubble regulator, polytetrafluoroethylene powder or polytetrafluoroethylene powder modified with an acrylic resin is preferred.

  In addition, as the amount of the air conditioner supplied to the extruder, if the amount is small, the bubbles of the polylactic acid-based resin expanded particles become coarse, and the appearance of the resulting polylactic acid-based resin foam molded product may be deteriorated, If the amount is too large, foam breakage may occur when the polylactic acid resin composition is extruded and foamed, and the closed cell ratio of the polylactic acid resin foamed particles may be reduced. It is preferably 01 to 3 parts by weight, more preferably 0.05 to 2 parts by weight, and particularly preferably 0.1 to 1 part by weight.

  And the polylactic acid-type resin extrudate extruded from the nozzle metal mold | die 1 continues to a cutting process. The polylactic acid resin extrudate is cut by rotating the rotary shaft 2 and rotating the rotary blades 5, 5... Disposed on the front end surface 1 a of the nozzle mold 1, preferably at a constant rotational speed of 2000 to 10000 rpm. Rotate to do.

  All the rotary blades 5 are always rotating while being in contact with the front end face 1a of the nozzle mold 1, and the polylactic acid resin extrudate extruded and foamed from the nozzle mold 1 includes the rotary blade 5 and the nozzle mold. 1 is cut into the air at regular time intervals to form polylactic acid-based resin expanded particles by the shear stress generated between the nozzle 11 and the edge of the nozzle outlet 11. At this time, water may be sprayed onto the polylactic acid resin extrudate in a range where the cooling of the polylactic acid resin extrudate does not become excessive.

  In the present invention, the polylactic acid resin composition is prevented from foaming in the nozzle of the nozzle mold 1. The polylactic acid-based resin composition is not yet foamed immediately after being ejected from the nozzle outlet 11 of the nozzle mold 1 and begins to foam after a short time has elapsed since ejection. Therefore, the polylactic acid-based resin extrudate is in the process of foaming extruded before the non-foamed portion, which continues from the non-foamed portion immediately after being discharged from the nozzle outlet portion 11 of the nozzle mold 1. The foamed part.

  The non-foamed portion maintains its state from when it is projected from the outlet 11 of the nozzle of the nozzle mold 1 until foaming is started. The time during which the unfoamed portion is maintained can be adjusted by the resin pressure at the nozzle outlet 11 of the nozzle mold 1, the amount of foaming agent, and the like. When the resin pressure at the nozzle outlet 11 of the nozzle mold 1 is high, the polylactic acid resin extrudate does not foam immediately after being extruded from the nozzle mold 1 and maintains an unfoamed state. The resin pressure at the nozzle outlet 11 of the nozzle mold 1 can be adjusted by adjusting the nozzle diameter, the extrusion amount, the melt viscosity and the melt tension of the polylactic acid resin composition. By adjusting the amount of the foaming agent to an appropriate amount, the polylactic acid resin composition can be prevented from foaming inside the mold, and the unfoamed portion can be reliably formed.

  Since all the rotary blades 5 cut the polylactic acid resin extrudate while being always in contact with the front end face 1a of the nozzle mold 1, the polylactic acid resin extrudate is formed on the nozzle mold 1. Polylactic acid-based resin foamed particles are produced by cutting at an unfoamed portion immediately after being discharged from the outlet portion 11 of the nozzle.

  Since the obtained polylactic acid-based resin expanded particles cut the polylactic acid-based resin extrudate at the unfoamed portion, there is no cell cross section on the surface of the cut portion. The entire surface of the polylactic acid-based resin expanded particles is covered with a skin layer having no cell cross section. Therefore, the polylactic acid-based resin foamed particles have excellent foamability without foaming gas removal, a low open cell ratio, and excellent surface heat-fusibility.

  When the polylactic acid-based resin expanded particles are used for in-mold foam molding, the surface of the polylactic acid-based resin expanded particles is formed from a skin layer in which the cell cross section is not exposed. The fusing property is good, and the obtained polylactic acid resin foamed molded article has no surface unevenness and excellent appearance and has excellent mechanical strength.

  As described above, the rotary blade 5 rotates at a constant rotational speed, but the rotational speed of the rotary blade 5 is preferably 2000 to 10,000 rpm, more preferably 3000 to 9000 rpm, and particularly preferably 4000 to 8000 rpm.

  This is because when the rotary blade 5 is below 2000 rpm, the polylactic acid resin extrudate cannot be reliably cut by the rotary blade 5, and the polylactic acid resin foam particles are bonded together, This is because the resin foam particles may have non-uniform shapes.

  On the other hand, if the rotational speed of the rotary blade 5 exceeds 10,000 rpm, the following problems are likely to occur. The first problem is that when the cutting stress due to the rotary blade is increased and the polylactic acid resin foam particles are scattered from the nozzle outlet toward the cooling member, the initial speed of the polylactic acid resin foam particles is high. Become. As a result, the time from when the polylactic acid resin extrudate is cut until the polylactic acid resin expanded particles collide with the cooling member is shortened, resulting in insufficient expansion of the polylactic acid resin expanded particles. The expansion ratio of the resin-based resin expanded particles may be lowered. The second problem is that the wear of the rotary blade and the rotary shaft is increased and the life of the rotary blade and the rotary shaft may be shortened.

  Then, the polylactic acid-based resin foam particles obtained as described above are scattered outward or forward simultaneously with the cutting by the cutting stress by the rotary blade 5, and are spread on the inner peripheral surface of the peripheral wall portion 41b of the cooling drum 41. Clash immediately. The polylactic acid-based resin expanded particles continue to expand until they collide with the cooling drum 41, and the polylactic acid-based resin expanded particles grow into a substantially spherical shape by expansion.

  The inner peripheral surface of the peripheral wall portion 41b of the cooling drum 41 is entirely covered with the cooling liquid 42, and the polylactic acid resin foamed particles that collide with the inner peripheral surface of the peripheral wall portion 41b of the cooling drum 41 are immediately cooled, Foaming of the polylactic acid resin expanded particles stops. Thus, after the polylactic acid resin extrudate is cut by the rotary blade 5, the polylactic acid resin foamed particles are immediately cooled by the cooling liquid 42. While preventing the crystallinity degree of lactic acid-type resin from raising, the polylactic acid-type resin expanded particle is prevented from foaming too much.

  Therefore, the polylactic acid-based resin expanded particles exhibit excellent foamability and heat-fusibility during in-mold foam molding. The polylactic acid resin foamed particles can be improved in heat resistance of the polylactic acid resin composition by increasing the crystallinity of the polylactic acid resin foamed particles during in-mold foam molding. It has high heat resistance.

  In addition, when the temperature of the coolant 42 is low, the nozzle mold located in the vicinity of the cooling drum 41 is excessively cooled, which may adversely affect the extrusion foaming of the polylactic acid-based resin composition. The degree of crystallinity of the polylactic acid resin constituting the polylactic acid resin expanded particles is increased, and the heat fusion property of the polylactic acid resin expanded particles may be lowered. 5-40 degreeC is more preferable and 10-35 degreeC is especially preferable.

  And the degree of crystallinity of the obtained polylactic acid-based resin expanded particles is preferably 30% or less, more preferably 3 to 28%, and particularly preferably 5 to 26%. The degree of crystallinity of the polylactic acid-based resin expanded particles depends on the time from when the polylactic acid-based resin extrudate is extruded from the nozzle mold 1 until the polylactic acid-based resin expanded particles collide with the coolant 42, It can be adjusted by temperature.

  Here, the degree of crystallinity of the polylactic acid-based resin expanded particles is measured while using a differential scanning calorimeter (DSC) while raising the temperature at a rate of temperature increase of 10 ° C./min according to the measurement method described in JIS K7121. Based on the measured amount of cold crystallization per 1 mg and heat of fusion per 1 mg, it can be calculated by the following formula.

If the bulk density of the polylactic acid-based resin expanded particles obtained in this way is small, the open cell ratio of the polylactic acid-based resin expanded particles increases, and the polylactic acid-based resin expanded particles become foamed during foaming in in-mold foam molding. On the other hand, there is a possibility that the necessary foaming force cannot be imparted. On the other hand, if it is large, the resulting foam of the polylactic acid resin foamed particles becomes uneven, and foaming of the polylactic acid resin foamed particles during in-mold foam molding 0.02 to 0.6 g / cm ³ is preferable, 0.03 to 0.5 g / cm ³ is more preferable, and 0.04 to 0.4 g / cm ³ is particularly preferable. preferable.

  And when the open cell ratio of the polylactic acid-based resin expanded particles is high, the polylactic acid-based resin expanded particles hardly foam at the time of in-mold foam molding, and the fusion property between the polylactic acid-based resin expanded particles becomes low, Since the mechanical strength of the obtained polylactic acid-based resin foam molded article may be lowered, it is preferably less than 20%, more preferably 10% or less, and particularly preferably 5% or less. The open cell ratio of the polylactic acid-based resin expanded particles is adjusted by adjusting the extrusion foaming temperature of the polylactic acid-based resin composition from the extruder, the supply amount of the foaming agent to the extruder, and the like.

Here, the open cell ratio of the polylactic acid-based resin expanded particles is measured in the following manner. First, a sample cup of a volumetric air comparison type hydrometer is prepared, and the total weight A (g) of polylactic acid resin expanded particles in an amount satisfying about 80% of the sample cup is measured. Next, the volume B (cm ³ ) of the entire polylactic acid-based resin expanded particles is measured by a 1-1 / 2-1 atmospheric pressure method using a hydrometer. The volumetric air comparison type hydrometer is commercially available, for example, from Tokyo Science Co. under the trade name “1000 type”.

  Subsequently, a wire mesh container is prepared, the wire mesh container is immersed in water, and the weight C (g) of the wire mesh container in the state immersed in the water is measured. Next, after all the polylactic acid-based resin expanded particles are put in the wire mesh container, the wire mesh container is immersed in water, and the wire mesh container and the wire mesh container are immersed in water. The weight D (g) of the total amount of the polylactic acid-based resin expanded particles put in the container is measured.

Then, the apparent volume E (cm ³ ) of the polylactic acid resin foamed particles is calculated based on the following formula, and the following formula is calculated based on the apparent volume E and the volume B (cm ³ ) of the entire polylactic acid resin foamed particles. Thus, the open cell ratio of the polylactic acid-based resin expanded particles can be calculated. The volume of 1 g of water was 1 cm ³ .
E = A + (CD)
Open cell ratio (%) = 100 × (EB) / E

  In addition, if the particle diameter of the polylactic acid-based resin expanded particles is small, the foamability of the polylactic acid-based resin expanded particles may be reduced during in-mold foam molding. Since the filling property of the polylactic acid-based resin foamed particles may be lowered, 0.5 to 5.0 mm is preferable, 1.0 to 4.5 mm is more preferable, and 1.5 to 4 mm is particularly preferable.

  Here, the particle diameter of the polylactic acid-based resin expanded particles can be measured directly using a caliper with the diameter of the polylactic acid-based resin expanded particles. Specifically, the longest diameter (major axis) and the shortest diameter (minor axis) at the cut surface of each polylactic acid-based resin expanded particle are measured, and the direction perpendicular to the cut surface at each polylactic acid-based resin expanded particle is measured. The length is measured, and the arithmetic average value of the major axis, minor axis, and length of the polylactic acid-based resin expanded particles is defined as the particle size of the polylactic acid-based resin expanded particles.

  The polylactic acid resin foam particles thus obtained are filled in a mold cavity and heated to foam the polylactic acid resin foam particles, thereby foaming the polylactic acid resin foam particles and expanding the foam particles. To obtain a polylactic acid resin foam molded article having a desired shape excellent in fusion property and heat resistance by fusing together with each other by their foaming pressure and increasing the crystallinity of the polylactic acid resin. Can do.

  The heating medium for the polylactic acid-based resin foam particles filled in the mold is not particularly limited, and examples include hot air and hot water in addition to water vapor, but it is preferable to use water at 60 to 100 ° C. . This is because water is in a liquid state and has a large specific heat, so that a high amount of heat necessary for foaming can be sufficiently imparted to the polylactic acid resin foamed particles in the mold even at a low temperature. .

  Therefore, the polylactic acid resin foamed particles can be sufficiently heated and foamed without overheating the polylactic acid resin foamed particles, and the polylactic acid resin produced when steam or hot air is used as a heating medium. Without causing thermal shrinkage on the surface of the foamed particles, the polylactic acid resin foamed particles can be firmly heat-fused and integrated with each other by their foaming force, and the resulting polylactic acid resin foam molded article is excellent. It has excellent mechanical strength and appearance.

  And, compared to using high-pressure steam, in-mold foam molding can be performed at a low pressure, so that the design strength of the mold can be kept low, and a mold having a complicated shape can be easily manufactured. In addition, the mold itself can be made compact so that the handleability can be improved, and the productivity of the polylactic acid resin foamed molded product can be improved.

  If the temperature of the water used as the heating medium is low, the polylactic acid resin foam particles filled in the mold are insufficiently foamed and the polylactic acid obtained by reducing the heat-fusibility between the polylactic acid resin foam particles On the other hand, the mechanical strength and appearance of the resin-based resin molded article may be reduced. On the other hand, if it is high, water must be in a high pressure state, and large equipment such as a boiler is required. 70-99 degreeC is more preferable and 80-98 degreeC is especially preferable.

  The method of heating the polylactic acid resin expanded particles by supplying water at 60 to 100 ° C. to the polylactic acid resin expanded particles filled in the mold is not particularly limited. For example, (1) conventionally used A method of supplying 60-100 ° C. water in place of water vapor into the mold in the in-mold foam molding machine, and (2) a mold filled with polylactic acid-based resin expanded particles in water at 60-100 ° C. Examples include a method of immersing and supplying water to the polylactic acid-based resin expanded particles, and even when the mold has a complicated shape, the entire mold, that is, the polylactic acid-based resin expanded particles is heated uniformly throughout. The method (2) is preferred because it can be foamed.

  If the heating time of the polylactic acid resin expanded particles filled in the mold with water is short, the heating of the polylactic acid resin expanded particles is insufficient and the thermal fusion between the polylactic acid resin expanded particles is insufficient. Or the crystallinity of the polylactic acid-based resin expanded particles may not be increased sufficiently, and the heat resistance of the resulting polylactic acid-based resin foam may decrease. Since only the productivity of the molded body is lowered, 20 seconds to 1 hour is preferable.

  And after heating the polylactic acid-based resin foamed particles with water at 60 to 100 ° C. to perform in-mold foam molding, after cooling the polylactic acid-based resin foam molded body formed in the mold, the mold is A polylactic acid-based resin foam molded body having a desired shape can be obtained by opening.

  When the cooling of the polylactic acid resin foamed molding formed in the mold is high, the polylactic acid resin foamed particles in the mold are not sufficiently solidified, and the mold expands when removed from the mold. Therefore, the surface temperature of the polylactic acid resin foamed molded product is preferably 50 ° C. or lower, more preferably 0 to 45 ° C. Thus, it cools so that it may become especially preferably 0-40 degreeC, Most preferably, it will be 0-35 degreeC.

  Here, the method for cooling the polylactic acid-based resin foam molded body formed in the mold is not particularly limited, but (1) a method of leaving the mold in an atmosphere of 50 ° C. or lower, (2) a mold There are a method of spraying water or air of 50 ° C or less to the mold, and a method of (3) immersing the mold in water of 50 ° C or less. Even if the mold has a complicated shape, the entire mold is cooled uniformly. Therefore, the cooling method (3) is preferable. The cooling time may be appropriately adjusted according to the cooling method, the size of the mold, and the like. For example, when the mold is immersed in water of 50 ° C. or lower, 1 to 10 minutes is preferable.

  When the crystallinity of the obtained polylactic acid-based resin foamed molded product is low, the heat resistance of the polylactic acid-based resin foamed molded product is reduced. On the other hand, when the crystallinity is high, the polylactic acid-based resin foamed molded product becomes brittle. Therefore, it is preferable to adjust the in-mold foam molding conditions so that it is preferably 40 to 65%, more preferably 45 to 64%, and particularly preferably 50 to 63%. In addition, since the crystallinity degree of a polylactic acid-type resin foaming molding is the same as the measuring method of the crystallinity degree of a polylactic acid-type resin expanded particle, the description is abbreviate | omitted.

  The material forming the mold is not particularly limited, and examples thereof include iron-based metal, aluminum-based metal, copper-based metal, and zinc-based metal, and aluminum is used from the viewpoint of thermal conductivity and workability. Base metals are preferred.

  Furthermore, before the in-mold foam molding, the foamed polylactic acid resin particles may be further impregnated with an inert gas to improve the foaming power of the polylactic acid resin foam particles. Thus, by improving the foaming power of the polylactic acid-based resin foamed particles, the fusion property between the polylactic acid-based resin foamed particles is improved at the time of in-mold foam molding, and the resulting polylactic acid-based resin foamed molded product is even better. Has high mechanical strength. Examples of the inert gas include carbon dioxide, nitrogen, helium, and argon, and carbon dioxide is preferable.

  As a method for impregnating the polylactic acid-based resin expanded particles with an inert gas, for example, by placing the polylactic acid-based resin expanded particles in an inert gas atmosphere having a pressure higher than normal pressure, A method of impregnating with an inert gas can be mentioned. In such a case, an inert gas may be impregnated before filling the polylactic acid resin expanded particles into the mold, but the entire mold is inactive after the polylactic acid resin expanded particles are filled into the mold. It may be placed in a gas atmosphere and the polylactic acid resin expanded particles may be impregnated with an inert gas. When the inert gas is carbon dioxide, the polylactic acid-based resin expanded particles are allowed to stand for 20 minutes to 24 hours in a pressurized atmosphere of carbon dioxide of 0.1 to 1.5 MPa with respect to atmospheric pressure. It is preferable to do.

  As described above, when the polylactic acid resin foam particles are impregnated with an inert gas, the polylactic acid resin foam particles may be heated and foamed in the mold as they are. It may be heated before being filled into the mold and subjected to secondary foaming to form secondary foamed particles with higher foaming, then filled into the mold and heated and foamed. By using such secondary expanded particles, it is possible to obtain a polylactic acid resin foamed molded article having a high expansion ratio. In addition, as a heating medium for heating the polylactic acid-based resin expanded particles, dry air is preferable.

  Even when secondary foam particles are filled in a mold and molded, secondary foaming is performed in a pressurized atmosphere of an inert gas of 0.1 to 1.5 MPa with respect to atmospheric pressure, preferably in a carbon dioxide atmosphere. It is preferable to leave the particles for 20 minutes to 24 hours to impregnate the secondary foamed particles with an inert gas to improve foamability.

  If the temperature at which the polylactic acid-based resin expanded particles are secondarily expanded to obtain highly expanded secondary expanded particles is high, the crystallinity of the polylactic acid-based resin increases, and the heat of the secondary expanded particles increases. Less than 70 ° C. is preferable because the melt strength is lowered and the mechanical strength and appearance of the resulting polylactic acid resin foamed molded article are lowered.

  As described above, the method for producing foamed polylactic acid-based resin particles for in-mold foam molding of the present invention is to rotate at a predetermined number of revolutions while keeping the rotary blade always in contact with the front end surface of the nozzle mold and extrude from the nozzle mold. Since the foamed polylactic acid resin extrudate is cut by the rotary blade, the polylactic acid resin extrudate can be reliably cut to obtain substantially spherical polylactic acid resin foamed particles. Therefore, when polylactic acid resin foam particles are used for in-mold foam molding, the polylactic acid resin foam particles are foamed almost uniformly in all directions, and the foam particles are firmly heat-sealed in each direction. Integrate.

  Furthermore, in the method for producing foamed polylactic acid resin particles for in-mold foam molding according to the present invention, a polylactic acid resin composition containing a polylactic acid resin and a thickener is supplied to an extruder. While the viscosity of the resin composition is increased by the thickener, the polylactic acid resin is hydrolyzed by heating in the extruder to reduce the molecular weight of the polylactic acid resin, and the viscosity of the polylactic acid resin composition is decreased. As a result, the polylactic acid resin extrudates are in contact with each other during the cutting of the polylactic acid resin extrudate, or the polylactic acid resin expanded particles are cut after the polylactic acid resin extrudate is cut. Even if they collide with each other, it is difficult to coalesce, and it is possible to efficiently produce polylactic acid-based resin expanded particles.

  Further, in the above method for producing foamed polylactic acid resin particles for in-mold foam molding, when the thickener is a carbodiimide compound, hydrolysis of the polylactic acid resin in the Oshiyama machine is further suppressed, The decrease in the molecular weight due to the decomposition of the resin is suppressed to suppress the decrease in the viscosity of the polylactic acid resin more effectively, and the polylactic acid resin foamed particles can be produced more efficiently.

It is the schematic cross section which showed an example of the manufacturing apparatus of the polylactic acid-type resin expanded particle for in-mold foam molding. It is the schematic diagram which looked at the multi-nozzle mold from the front.

1 Nozzle mold 2 Rotating shaft 3 Drive member 4 Cooling member
41 Cooling drum
42 Coolant 5 Rotary blade

  In the present invention, the weight average molecular weight of the polylactic acid resin, the degree of dispersion, the bulk density of the polylactic acid resin foamed particles, the ratio of coalesced particles and the moldability, and the heating dimensional change rate of the polylactic acid resin foam molded article are as follows. The one measured by the point.

(Weight average molecular weight and dispersity of polylactic acid resin)
In each Example and Comparative Example, polylactic acid resin particles were prepared in the same manner except that no foaming agent was used, and about 30 mg of the obtained polylactic acid resin particles were dissolved in 10 ml of chloroform. After filtration through a 45 μm chromatographic disk, the weight average molecular weight in terms of polystyrene and the degree of dispersion were measured using an HPLC apparatus (liquid chromatograph) (trade name “Detector 484, Pump 510” manufactured by Water).

As measurement conditions,
Column: Showa Denko Co., Ltd. Trade name “Shodex GPC K-806L” (φ8.0 mm × 300 mm) Two column temperature: 40 ° C.
Mobile phase: Chloroform mobile phase Flow rate: 1.2 ml / min Injection / pump temperature: Room temperature Detection: UV254 nm
Injection volume: Standard polystyrene for 50 ml calibration curve:
Product name "Shodex" manufactured by Showa Denko KK Weight average molecular weight 1030000
Weight average molecular weight 5480000,3840000,355000,102000,37900,9100,2630,495 manufactured by Tosoh Corporation

(Bulk density of polylactic acid resin foamed particles)
The bulk density of the polylactic acid-based resin expanded particles refers to that measured according to JIS K6911: 1995 “General Test Method for Thermosetting Plastics”. That is, it measured using the apparent density measuring device based on JISK6911, and measured the bulk density of the polylactic acid-type resin expanded particle based on the following formula.

Bulk density (g / cm ³ ) of foamed polylactic acid resin
= [Mass of measuring cylinder with sample (g) -Mass of measuring cylinder (g)]
/ [Capacity of graduated cylinder (cm ³ )]

(Fused particle ratio)
Scoop up the obtained polylactic acid resin expanded particles in a 5 ml container, count the number A of polylactic acid resin expanded particles in the container, and at least 2 polylactic acid resin expanded particles. The number B (number) of coalesced particles formed by coalescence was counted and calculated based on the following formula. The coalesced particles were counted as one piece.
Fused particle ratio (%) = 100 × B / A

(Formability)
Polylactic acid-based resin expanded particles are placed in a sealed container, and carbon dioxide is injected into the sealed container at a pressure of 0.30 MPa and left at room temperature for 24 hours to form carbon dioxide into the polylactic acid-based resin expanded particles. Impregnated with carbon.

  Next, the polylactic acid-based resin expanded particles were filled in a cavity of an aluminum mold. In addition, the internal dimension of the cavity of a metal mold | die was a rectangular parallelepiped shape of length 30mm x width 300mm x height 300mm. In addition, a total of 252 circular supply ports having a diameter of 8 mm were formed at intervals of 20 mm in order to allow the inside of the mold cavity to communicate with the outside of the mold. Each supply port is provided with a grid portion having an opening width of 1 mm, and the polylactic acid resin foam particles filled in the mold are formed so as not to flow out of the mold through the supply port. The water can be smoothly supplied from the outside of the mold into the cavity through the mold supply port.

  And the water maintained at 95 degreeC was stored in the heating water tank, and the metal mold | die filled with the polylactic acid-type resin expanded particle was completely immersed in the water in this heating water tank over 5 minutes, Water was supplied to the polylactic acid-based resin expanded particles in the mold cavity through the supply port, and the polylactic acid-based resin expanded particles were heated and expanded so that the polylactic acid-based resin expanded particles were integrated by heat fusion.

  Next, the mold was taken out from the heated water tank. And the water maintained at 20 degreeC was stored in another cooling water tank, and the metal mold | die was completely immersed in this cooling water tank over 5 minutes, and the polylactic acid-type resin foaming molding in a metal mold | die was cooled. .

The appearance of the polylactic acid resin foamed molded article obtained by the above method was visually observed and evaluated according to the following criteria.
○: The polylactic acid resin foamed particles had good elongation, and the polylactic acid resin foamed molded product was molded into a cavity shape.
X: There were many coalesced particles, and the elongation of the polylactic acid-based resin expanded particles was poor, so the appearance of the polylactic acid-based resin foamed molded article was poor.

(Heating dimensional change rate)
A polylactic acid resin foamed molded article was molded in the same manner as the procedure for measuring moldability. The obtained polylactic acid resin foamed molded product was left in an electric oven maintained at 120 ° C. for 22 hours.

Next, the dimensions of the polylactic acid resin foamed molded product before and after being left in the electric oven were measured, and the heating dimensional change rate was calculated based on the following formula. In addition, the dimension of the polylactic acid-type resin foaming molding was made into the arithmetic mean value of the dimension of a vertical direction, a horizontal direction, and a height direction.
Heating dimensional change rate (%) = 100 × (dimension after heating−dimension before heating) / dimension before heating

Example 1
The polylactic acid resin foamed particles for in-mold foam molding were produced using the production apparatus shown in FIGS. First, crystalline polylactic acid resin (trade name “TERRAMAC HV-6250H” manufactured by Unitika Ltd.), melting point (mp): 169.1 ° C., D-form ratio: 1.2 mol%, L-form ratio: 98.8 mol %, Obtained by dynamic viscoelasticity measurement, 100 parts by weight at the intersection of storage elastic modulus curve and loss elastic modulus curve, T: 138.8 ° C., poly (4,4′-dicyclohexyl as a thickener) Methane carbodiimide) (trade name “Carbodilite LA-1” manufactured by Nisshinbo Co., Ltd.) 0.2 parts by weight and 0.1 part by weight of polytetrafluoroethylene powder (trade name “Fluon L169J” manufactured by Asahi Glass Co., Ltd.) as a foam regulator. The polylactic acid resin composition was supplied to a single screw extruder having a diameter of 65 mm and melt kneaded. In the single screw extruder, the polylactic acid resin composition was first melt-kneaded at 180 ° C. and then melt-kneaded while raising the temperature to 210 ° C.

  Subsequently, in the middle of the single screw extruder, the polylactic acid-based polylactic acid in a molten state so that butane composed of 35% by weight isobutane and 65% by weight normal butane is 1.0 part by weight with respect to 100 parts by weight of the polylactic acid-based resin. The mixture was press-fitted into the resin composition and uniformly dispersed in the polylactic acid resin.

Thereafter, after the molten polylactic acid resin composition is cooled to 180 ° C. at the front end of the extruder, the shear rate is 18118 sec ⁻¹ from each nozzle of the multi-nozzle mold 1 attached to the front end of the single screw extruder. The polylactic acid resin composition was extruded and foamed. Note that the temperature of the multi-nozzle mold 1 was maintained at 220 ° C.

  The multi-nozzle mold 1 has 20 nozzles having an outlet portion 11 having a diameter of 0.5 mm, and all the outlet portions 11 of the nozzle are assumed to be on the front end surface 1a of the multi-nozzle die 1. Are arranged at equal intervals on a virtual circle A of 139.5 mm.

  Then, four rotary blades 5 are integrally provided at equal intervals in the circumferential direction of the rotary shaft 2 on the outer peripheral surface of the rear end portion of the rotary shaft 2, and each rotary blade 5 is a multi-nozzle mold 1. It is configured to move on the virtual circle A while always in contact with the front end face 1a.

  Furthermore, the cooling member 4 includes a cooling drum 41 including a front circular front portion 41a and a cylindrical peripheral wall portion 41b extending rearward from the outer peripheral edge of the front portion 41a and having an inner diameter of 315 mm. It was. Then, the cooling water 42 is supplied into the cooling drum 41 through the supply pipe 41d and the supply port 41c of the drum 41, and the cooling water 42 at 20 ° C. is moved forward along the inner surface of the peripheral wall portion 41b. It was flowing in a spiral.

  The rotary blade 5 disposed on the front end face 1a of the multi-nozzle mold 1 is rotated at a rotation speed of 4800 rpm, and the polylactic acid-based resin extruded and foamed from the outlet portion 11 of each nozzle of the multi-nozzle mold 1 The extrudate was cut with a rotary blade 5 to produce substantially spherical polylactic acid-based resin expanded particles. The polylactic acid-based resin extrudate was composed of an unfoamed portion immediately after being extruded from the nozzle of the multi-nozzle mold 1 and a foamed portion in the process of foaming continuous with the unfoamed portion. The polylactic acid resin extrudate was cut at the open end of the outlet portion 11 of the nozzle, and the polylactic acid resin extrudate was cut at the unfoamed portion.

  In the production of the polylactic acid-based resin expanded particles described above, first, the rotating shaft 2 was not attached to the multi-nozzle mold 1 and the cooling member 4 was retracted from the multi-nozzle mold 1. In this state, the polylactic acid resin extrudate is extruded and foamed from a single screw extruder, and the polylactic acid resin extrudate is extruded from the nozzle of the multi-nozzle mold 1 and the unfoamed portion. It was confirmed that it was composed of a foaming part in the middle of foaming. Next, after attaching the rotating shaft 2 to the multi-nozzle mold 1 and disposing the cooling member 4 at a predetermined position, the rotating shaft 2 is rotated, and the polylactic acid resin extrudate is placed at the opening end of the outlet portion 11 of the nozzle. Polylactic acid resin foamed particles were produced by cutting with a rotary blade 5.

  The polylactic acid-based resin foamed particles are blown outward or forward by the cutting stress of the rotary blade 5, collide with the cooling water 42 flowing along the inner surface of the cooling drum 41 of the cooling member 4 and immediately cool down. It was done.

The cooled polylactic acid-based resin expanded particles were discharged together with the cooling water 42 through the discharge port 41e of the cooling drum 41, and then separated from the cooling water 42 by a dehydrator. The obtained polylactic acid-based resin expanded particles had a particle size of 1.0 to 2.2 mm and a bulk density of 0.20 g / cm ³ .

  The surface of the obtained polylactic acid-based resin expanded particles was entirely covered with a skin layer. There was no bubble cross section in the skin layer.

  Next, the polylactic acid-based resin expanded particles are put in a sealed container, and carbon dioxide is injected into the sealed container at a pressure higher by 0.3 MPa than the atmospheric pressure and left at 20 ° C. for 24 hours. Then, the polylactic acid resin expanded particles were impregnated with carbon dioxide.

  Subsequently, the polylactic acid-based resin expanded particles were filled in a cavity of an aluminum mold. In addition, the internal dimension of the cavity of a metal mold | die was a rectangular parallelepiped shape of length 30mm x width 300mm x height 300mm. In addition, a total of 252 circular supply ports having a diameter of 8 mm were formed at intervals of 20 mm in order to allow the inside of the mold cavity to communicate with the outside of the mold. Each supply port is provided with a grid portion having an opening width of 1 mm, and the polylactic acid resin foam particles filled in the mold are formed so as not to flow out of the mold through the supply port. The water can be smoothly supplied from the outside of the mold into the cavity through the mold supply port.

  Then, water maintained at 95 ° C. is stored in the heated water tank, and the mold filled with the polylactic acid resin foam particles is completely immersed in the water in the heated water tank for 5 minutes to supply the mold. Water was supplied to the polylactic acid-based resin expanded particles in the cavity of the mold through the mouth, and the polylactic acid-based resin expanded particles were heated and expanded to integrate the polylactic acid-based resin expanded particles by heat fusion.

  Next, the mold was taken out from the heated water tank. And the water maintained at 20 degreeC was stored in another cooling water tank, and the metal mold | die was completely immersed in this cooling water tank over 5 minutes, and the polylactic acid-type resin foaming molding in a metal mold | die was cooled. .

  The mold was taken out from the cooling water tank, and the mold was opened to obtain a rectangular parallelepiped polylactic acid resin foam molded product. The obtained polylactic acid resin expanded resin foamed molded article had a very excellent appearance.

(Example 2)
Poly (4,4′-dicyclohexylmethanecarbodiimide) (trade name “Carbodilite LA-1” manufactured by Nisshinbo Co., Ltd.) was changed to 2.0 parts by weight instead of 0.2 parts by weight, and the diameter of the outlet part 11 was set to be 0.00. A multi-nozzle mold 1 having 40 nozzles of 7 mm and all nozzle outlets 11 being arranged at equal intervals on a virtual circle A having a diameter of 139.5 mm Except that the polylactic acid resin composition was extruded and foamed from each nozzle of the mold 1 at a shear rate of 4952 sec ⁻¹ , the polylactic acid resin foam particles and the polylactic acid resin foam molding were obtained in the same manner as in Example 1. It was.

The obtained polylactic acid-based resin expanded particles had a particle size of 1.6 to 2.4 mm and a bulk density of 0.20 g / cm ³ . Further, the obtained polylactic acid resin foamed molded article had a very excellent appearance.

(Example 3)
Poly (4,4′-dicyclohexylmethanecarbodiimide) (trade name “Carbodilite LA-1” manufactured by Nisshinbo Co., Ltd.) was changed to 0.05 parts by weight instead of 0.2 parts by weight, and the diameter of the outlet 11 was 1. Using a multi-nozzle mold 1 having 20 nozzles of 0 mm and all nozzle outlet portions 11 being arranged at equal intervals on a virtual circle A having a diameter of 139.5 mm, a multi-nozzle Except that the polylactic acid resin composition was extruded and foamed from each nozzle of the mold 1 at a shear rate of 4529 sec ⁻¹ , polylactic acid resin foam particles and a polylactic acid resin foam molded article were obtained in the same manner as in Example 1. It was.

The obtained polylactic acid-based resin expanded particles had a particle size of 1.8 to 2.8 mm and a bulk density of 0.20 g / cm ³ . Further, the obtained polylactic acid resin foamed molded article had a very excellent appearance.

Example 4
As a thickener, 0.2 part by weight of poly (4,4′-dicyclohexylmethanecarbodiimide) (trade name “Carbodilite LA-1” manufactured by Nisshinbo Co., Ltd.) and an acrylic / styrene compound containing an epoxy group and polylactic acid A polylactic acid resin foamed particle and a polylactic acid resin foam molded article were obtained in the same manner as in Example 1 except that 0.5 part by weight of the master batch with the resin was used.

  The masterbatch of an acrylic / styrene compound containing an epoxy group and a polylactic acid resin is an acrylic / styrene compound containing an epoxy group (trade name “ARUFON UG-4030” manufactured by Toagosei Co., Ltd., weight average molecular weight). 11000, epoxy value: 1.8 mmol / g) 30% by weight, and polylactic acid resin (trade name “LACEA H-100” manufactured by Mitsui Chemicals, Inc.) 70% by weight.

The obtained polylactic acid-based resin expanded particles had a particle size of 1.0 to 2.2 mm and a bulk density of 0.20 g / cm ³ . Further, the obtained polylactic acid resin foamed molded article had a very excellent appearance.

(Example 5)
The same procedure as in Example 1 was conducted except that poly (4,4′-dicyclohexylmethanecarbodiimide) (trade name “Carbodilite LA-1” manufactured by Nisshinbo Co., Ltd.) was changed to 4.0 parts by weight instead of 0.2 parts by weight. Polylactic acid-based resin expanded particles and a polylactic acid-based resin expanded molded body were obtained.

The obtained polylactic acid-based resin expanded particles had a particle size of 1.0 to 2.2 mm and a bulk density of 0.20 g / cm ³ . Further, the obtained polylactic acid resin foamed molded article had a very excellent appearance.

(Comparative Example 1)
Polylactic acid-based resin foamed particles were obtained in the same manner as in Example 1 except that poly (4,4′-dicyclohexylmethanecarbodiimide) was not used. Landing particles were generated.

The obtained polylactic acid-based resin expanded particles had a particle size of 1.0 to 2.2 mm and a bulk density of 0.20 g / cm ³ .

(Comparative Example 2)
Polylactic acid as in Example 1 except that poly (4,4′-dicyclohexylmethanecarbodiimide) (trade name “Carbodilite LA-1” manufactured by Nisshinbo Co., Ltd.) was changed to 6 parts by weight instead of 0.2 parts by weight. An attempt was made to produce the expanded resin-based resin particles, but the pressure during extrusion was too high to produce the expanded polylactic acid-based resin particles.

  The viscosity of the polylactic acid resin composition was measured, and the results are shown in Table 1. The weight average molecular weight (Mw) and dispersity of the polylactic acid resin constituting the polylactic acid resin composition were measured, and the results are shown in Table 1. The coalesced particle ratio and moldability of the polylactic acid-based resin expanded particles, and the heating dimensional change rate of the polylactic acid-based resin expanded molded body were measured, and the results are shown in Table 2.

Claims (4)

A step of supplying a polylactic acid resin composition containing a polylactic acid resin and a thickener and having a viscosity at 180 ° C. of 4900 to 20000 Pa · s to an extruder and melt-kneading in the presence of a foaming agent; A polylactic acid resin extrudate is extruded from a nozzle mold attached to the front end of the extruder, and the polylactic acid resin extrudate is foamed and cut by a rotating blade that rotates while contacting the front end surface of the nozzle mold. To produce foamed polylactic acid resin particles, the polylactic acid resin foam particles are scattered by cutting stress, and the polylactic acid resin foam particles collide with a cooling member disposed in front of the nozzle mold. And a step of cooling the product, and a method for producing foamed polylactic acid-based resin particles for in-mold foam molding. Whether the polylactic acid-based resin contains both D-form and L-form optical isomers as constituent monomer components, and the content of the lesser of the D-form and L-form is less than 5 mol% Alternatively, the polylactic acid resin expanded particles for in-mold foam molding according to claim 1, wherein the constituent monomer component contains only one optical isomer of either D-form or L-form. Manufacturing method. The method for producing expanded polylactic acid resin particles for in-mold foam molding according to claim 1 or 2, wherein the thickener is a carbodiimide compound. The in-mold foam molding according to any one of claims 1 to 3, wherein 0.01 to 5 parts by weight of a thickening agent is supplied to the extruder with respect to 100 parts by weight of the polylactic acid resin. For producing polylactic acid-based foamed resin particles.

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