JP2011213906A - Polylactic acid-based resin foaming particle, method for producing the same, and foamed molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide resin foaming particles that provide a foamed molding having high porosity, water absorbability and biodegradability, and also have excellent moldability, a method for producing the same, and the foamed molding obtained from the resin foaming particles.SOLUTION: Polylactic acid-based resin foaming particles are provided, which have an open cell ratio of 25-50% and are spherical or generally spherical. The foamed molding obtained by performing in-mold molding of the polylactic acid-based resin foaming particles has a water absorption coefficient of 10-35%.

Description

  The present invention relates to polylactic acid-based resin expanded particles, a method for producing the same, and an expanded molded body. More specifically, the present invention provides a foamed molded product having high porosity, water absorption and biodegradability, and further has resin moldable particles excellent in moldability, a method for producing the same, and a foamed molded product obtained from the resin foamed particles. About.

  Conventionally, there are many foamable polystyrene resin foam moldings and polyolefin resin foam moldings having inter-particle voids as soil improvement materials that improve drainage in the fields of civil engineering, architecture, horticulture, etc. and sound absorbing members of automobiles Has been used.

  However, the foamed molded article did not exhibit high water absorption due to its resin composition, and as a result, it did not have water retention. For this reason, although the said foaming molding has the outstanding heat insulation, lightweight property, water resistance, etc., the use application had a limit.

  Accordingly, in view of the above-mentioned problems, resin foam particles having a through hole and a water-retaining material held therein, and a foam-molded article having a high porosity and water absorption, obtained by foam-molding the resin foam particles. Is described in Patent Document 1.

JP-A-9-118770

  The resin foam particles described in Patent Document 1 have a cylindrical shape provided with a through hole for the manufacturing method. For this reason, when molding resin foam particles in a mold, the resin foam particles may not be sufficiently filled into a foam molding machine for each batch, and as a result, a foam molded article having a desired bulk factor cannot be obtained. There was a problem with formability. In addition, there is also a problem that it is impossible to fill the foamed resin particles in a desired mold and it is impossible to obtain a foamed molded product having a complicated shape. Furthermore, not only does it require a dedicated manufacturing device for filling the water-retaining material into the resin foam particles having through-holes, but also the detachment of the water-retaining material from the resin foam particles is possible, and the resin foam particles are stable. Performance such as water absorption is not expected. On the other hand, the resin composition contained in the foamed molded article described in Patent Document 1 is not preferable from the viewpoint of the environment that does not exhibit biodegradability and is currently attracting much attention.

  In view of these problems, it is desired to provide a foamed molded article having high porosity, water absorption and biodegradability, and to provide resin foam particles having excellent moldability.

  Thus, according to the present invention, there are spherical or substantially spherical polylactic acid-based resin foamed particles having an open cell ratio of 25 to 50%, and a foamed molded product obtained by molding the polylactic acid-based resin foamed particles in a mold. A polylactic acid resin expanded particle having a water absorption of 10 to 35% is provided.

Moreover, according to the present invention, there is provided a method for producing polylactic acid-based resin expanded particles,
Supplying the polylactic acid resin to an extruder and melt-kneading under a foaming agent;
While 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 temperature of the nozzle mold is 210 to 235 ° C. Cutting with a rotary blade rotating at a rotational speed of 2000 to 10000 rpm while contacting the front end surface to produce the polylactic acid resin foamed particles, and scattering the polylactic acid resin foamed particles by cutting stress;
And a step of cooling the polylactic acid-based resin expanded particles by colliding with a cooling member disposed in front of the nozzle mold.

  According to the present invention, there is provided a foamed molded article obtained by molding the polylactic acid resin foamed particles in a mold.

  According to the present invention, it is possible to give a foamed molded article having high porosity, water absorption and biodegradability, and to obtain polylactic acid resin foamed particles having excellent moldability.

  According to the present invention, the polylactic acid-based resin expanded particles have a ratio (L / S) of 1.0 to 1.3 between the longest diameter L and the shortest diameter S of the polylactic acid-based resin expanded particles. In this case, it is possible to obtain a foamed molded article having further excellent moldability.

  According to the present invention, the polylactic acid-based resin expanded particles contain both D-form and L-form optical isomers as constituent monomer components, and contain the smaller of the D-form and L-form optical isomers. When the amount is less than 5 mol% or a polylactic acid resin containing only one of the optical isomers of D-form or L-form as a constituent monomer component is included, higher heat resistance Can be introduced into the foamed molded product.

  According to the present invention, when the polylactic acid-based resin expanded particles include 1.5 to 3.8 parts by weight of a foaming agent with respect to 100 parts by weight of the polylactic acid-based resin expanded particles, the polylactic acid-based resin expanded particles are desired. The foaming performance can be imparted.

According to the present invention, when the polylactic acid-based resin foamed particles have a bulk density of 0.06 to 0.15 g / cm ³ , a foamed molded product having a desired porosity can be obtained more easily.

  According to the present invention, when the polylactic acid-based resin expanded particles have a water absorption rate of 10 to 35%, a foamed molded product having a desired water absorption rate can be obtained more easily.

  According to the present invention, spherical or substantially spherical polylactic acid-based resin expanded particles can be more easily manufactured by using the manufacturing method of the present invention.

  According to the present invention, a foamed molded article having biodegradability can be obtained.

  According to the present invention, a foamed molded product having a higher porosity can be obtained.

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 nozzle metal mold from the front. 2 is a photograph of the polylactic acid resin expanded particles obtained in Example 1.

  According to the present invention, spherical or substantially spherical polylactic acid resin foamed particles having an open cell ratio of 25 to 50%, and 10 foam-molded articles obtained by in-mold molding of the polylactic acid resin foamed particles are 10 Polylactic acid-based resin expanded particles having a water absorption of ˜35% are provided.

  Specifically, a foamed molded article having a water absorption rate of 10 to 35%, that is, high water absorption and biodegradation, is obtained by in-mold molding polylactic acid resin foamed particles having an open cell ratio of 25 to 50%. A foamed molded product having properties can be obtained. In addition, since the polylactic acid-based resin foamed particles are spherical or substantially spherical, they have excellent fluidity and moldability compared to conventional foamed particles such as columns and cylinders. Here, the open cell ratio means a ratio of open cells other than closed cells contained in the polylactic acid resin expanded particles. On the other hand, the porosity means the ratio of the interparticle voids not occupied by the expanded particles of the foam molded article. In addition, about these measuring methods etc., it explains in full detail in an Example.

The polylactic acid resin foamed particles, foamed molded product and the like obtained in the present invention will be described below.
(Polylactic acid resin foamed particles)
(1) Polylactic acid-based resin In the present invention, a resin in which lactic acid is polymerized by an ester bond can be used as the polylactic acid-based resin. From the viewpoint, a copolymer of D-lactic acid and L-lactic acid, a homopolymer of either D-lactic acid (D-form) or L-lactic acid (L-form), D-lactide, L-lactide and DL-lactide A ring-opening polymer of one or more lactides selected from the group consisting of

Polylactic acid-based resins are aliphatic monomers such as glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, hydroxyheptanoic acid, etc., as long as they do not affect the foam molding process or desired physical properties. Hydroxycarboxylic acid;
Aliphatic polycarboxylic acids such as succinic acid, adipic acid, suberic acid, sebacic acid, dodecanedicarboxylic acid, succinic anhydride, adipic anhydride, trimesic acid, propanetricarboxylic acid, pyromellitic acid, pyromellitic anhydride;
Aliphatic polyhydric alcohols such as ethylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, decamethylene glycol, glycerin, trimethylolpropane, pentaerythritol, etc. May optionally be included.

  In addition, the polylactic acid resin used in the present invention may be an alkyl group, a vinyl group, a carbonyl group, an aromatic group, an ester group, an ether group, an aldehyde, as long as it does not affect the foam molding process and desired physical properties. Other functional groups such as a group, an amino group, a nitrile group, and a nitro group may be included. Moreover, it may be bridge | crosslinked with the isocyanate type crosslinking agent etc., and may couple | bond together with bonds other than an ester bond. Furthermore, a polylactic acid-type resin may be used independently and 2 or more types may be used together.

  When manufacturing a polylactic acid-type resin, it does not specifically limit as a manufacturing method of a polylactic acid-type resin, All can use a well-known method. Specifically, a lactide method in which lactide is polymerized in the presence of a catalyst such as tin (II) octoate; a direct polymerization method in which a lactic acid compound is heated under reduced pressure in a solvent such as diphenyl ether to perform polymerization while removing water; Examples of the polymerization method include a melting method in which polymerization is performed while melting a lactic acid compound.

  The polylactic acid-based resin used in the present invention can be reduced in molecular weight by hydrolysis of ester bonds with moisture contained in the environment, and finally decomposed into carbon dioxide and water by microorganisms. Specifically, it may be decomposed in about 1 week in compost. For this reason, the polylactic acid-based resin foamed particles obtained by the present invention and the foamed molded product thereof are biodegradable, which is preferable from the viewpoint of the environment that is currently a major problem.

  In addition, the polylactic acid resin can be easily impregnated with a desired amount of foaming agent. The polylactic acid resin also has a high gas barrier property against the foaming agent. For this reason, in this invention, the polylactic acid-type resin expanded particle which has a high open cell ratio can be obtained, As a result, the foaming molding which has a high porosity can also be obtained easily.

  Here, a copolymer of D-form and L-form in which the proportion of the lesser optical isomer of D-form or L-form is less than 5 mol%, and the single weight of either D-form or L-form The coalescence tends to increase in crystallinity and melting point as the smaller optical isomer decreases. On the other hand, a copolymer of D-form and L-form in which the ratio of the smaller optical isomer of D-form or L-form is 5 mol% or more increases the crystallinity as the smaller optical isomer increases. Tends to be low and eventually become amorphous. Thus, for example, the former polylactic acid-based resin can be used in applications where high heat resistance is desired, and the latter polylactic acid-based resin can be used in applications where improvement in filling properties in complicated spaces is desired.

  Further, the latter polylactic acid resin can improve the heat resistance of a foamed molded product obtained by filling a foamed product with polylactic acid resin foamed particles in a mold, and the foamed molded product has a high temperature. However, the form may be maintained. Accordingly, the foam molded body can be taken out from the mold at a high temperature, the cooling time in the mold of the foam molded body is shortened, and the production efficiency of the foam molded body may be improved.

  For this reason, from the above viewpoint, the copolymer of D-form and L-form preferably has a ratio of the lesser of optical isomers of D-form or L-form of less than 5 mol%. More preferably, it is less than mol%.

Here, when polylactic acid-based resin expanded particles are obtained by extrusion foaming, the polylactic acid-based resin has a melting point (mp), a storage elastic modulus curve and a loss elastic modulus curve obtained by dynamic viscoelasticity measurement. It is preferable to adjust so that the temperature T at the intersection of
(Melting point of polylactic acid resin (mp) -40 ° C)
≦ (temperature T at the intersection) ≦ melting point of polylactic acid resin (mp) Formula 1

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

  That is, when 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. Therefore, as a result of the foaming film easily extending due to the foaming pressure required for the production of the polylactic acid-based resin foamed particles, the bubble film may be excessively stretched to cause bubble breakage. On the other hand, when the storage elastic modulus obtained by the dynamic viscoelasticity measurement of the polylactic acid-based resin is high, when the expansion force is applied to the cell membrane, the contraction force of the cell membrane resists the expansion. Therefore, even if the bubbles expand once at the foaming pressure required for the production of the polylactic acid-based resin expanded particles, the bubbles may shrink as the foaming pressure decreases over time due to a temperature drop or the like. is there.

  Moreover, the loss elastic modulus obtained by the dynamic viscoelasticity measurement is an index indicating a viscous property in viscoelasticity. Specifically, it is an index indicating the viscosity of the bubble film in the foaming process. In particular, in the foaming process, it is an index indicating an allowable range of how much the bubble membrane can be stretched without being broken. At the same time, after the bubbles are expanded to a desired size by the foaming pressure, the expanded bubbles are expanded in size. It is also an indicator that shows the ability to maintain the same.

  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, It can easily be torn. On the other hand, if the loss elastic modulus obtained by dynamic viscoelasticity measurement of polylactic acid resin is high, the foaming force is converted into thermal energy by the foam film, and the foam film is smoothed during the production of polylactic acid resin foam particles. It may be difficult to expand the air bubbles, and it may be difficult to expand the bubbles.

  Thus, in producing polylactic acid resin foamed particles by foaming polylactic acid resin, in the foaming process, the elastic force to stretch appropriately without breaking the cell membrane due to foaming pressure, that is, storage elasticity It is preferable to have a rate. In addition, the foam force smoothly expands without breaking the bubble film, and the viscous force to maintain the expanded bubble to the desired size regardless of the decrease in the foam pressure over time, that is, It preferably has a loss elastic modulus.

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. (Referred to as “temperature T”) and the melting point (mp) of the polylactic acid-based resin are preferably adjusted so as to satisfy the following formula 1, more preferably satisfy the formula 2. This adjustment makes it possible to improve the extrusion foamability while balancing the storage elastic modulus and loss elastic modulus, and stably produce the polylactic acid-based resin expanded particles.
[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 the intersection T ≦ [Melting point of polylactic acid resin (mp) −10 ° C.] Formula 2

  Furthermore, the reason why it is preferable to adjust the temperature T and the melting point (mp) of the polylactic acid resin so as to satisfy the formula 1 will be described in detail below.

  First, when the temperature T is lower than the melting point (mp) of the polylactic acid resin by more than 40 ° C., the loss elastic modulus of the polylactic acid resin at the time of extrusion foaming is too large compared to the storage elastic modulus. In addition, 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, the foaming force with respect to the elastic force is too large, and the bubble film is broken to cause bubble breakage and good polylactic acid -Based resin expanded particles may not be obtained. Conversely, 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, the foaming force with respect to the viscous force is small, and the polylactic acid-based resin is difficult to foam, and good polylactic acid -Based resin expanded particles may not be obtained.

  If the temperature T is higher than the melting point (mp) of the polylactic acid resin, the storage elastic modulus of the polylactic acid resin at the time of extrusion foaming is too large compared to the loss elastic modulus. Therefore, the balance between the loss elastic modulus and the storage elastic modulus may be 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, the foaming force with respect to the viscous force is too large, and the bubble film is broken to cause bubble breakage and good polylactic acid-based Resin foam particles may not be obtained. On the contrary, 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, the foaming force with respect to the elastic force is small. As the foaming power decreases, the air bubbles contract, and good polylactic acid resin expanded particles may not be obtained.

  As the weight average molecular weight of the polylactic acid resin increases, the temperature T increases. Therefore, in order to adjust the temperature T and the melting point (mp) of the polylactic acid resin so as to satisfy the above-mentioned formula 1, the reaction time or the reaction temperature is adjusted during the polymerization of the polylactic acid resin. Examples thereof include a method of adjusting the weight average molecular weight of the lactic acid-based resin and a method of adjusting the weight average molecular weight of the polylactic acid-based resin before or during extrusion foaming using a thickener or a crosslinking agent.

  In the present invention, the polylactic acid-based resin particles may contain a resin component such as a polystyrene-based resin or a polyolefin-based resin, as long as the desired physical properties and molding process are not affected. In addition, the polylactic acid-based resin particles include, other than the above, an air conditioner such as talc, calcium silicate, calcium stearate, synthetically or naturally produced silicon dioxide, ethylene bis-stearic acid amide, methacrylate ester-based copolymer; Flame retardants such as allyl isocyanurate hexabromide; colorants such as carbon black, iron oxide and graphite may be included.

(2) Production of polylactic acid-based resin expanded particles In the present invention, polylactic acid-based resin expanded particles are known as long as the shape of the obtained polylactic acid-based resin expanded particles is spherical or substantially spherical (elliptical spherical or oval). It can manufacture by the method of. Specifically, using a commercially available extruder, polylactic acid resin foamed particles are produced by granulation by underwater cutting, strand cutting, etc. while melt extruding polylactic acid resin in the presence of a foaming agent. it can.

According to the present invention, it is possible to more easily produce spherical or substantially spherical polylactic acid resin expanded particles having a high open cell ratio,
Supplying a polylactic acid resin to an extruder and melt-kneading under a foaming agent;
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 at a nozzle mold temperature of 210 to 235 ° C., the front end surface of the nozzle mold Cutting with a rotating blade rotating at a rotational speed of 2000 to 10000 rpm while in contact with the resin to produce polylactic acid resin foamed particles, and scattering the polylactic acid resin foamed particles by cutting stress;
A method for producing the polylactic acid-based resin expanded particles, which includes the step of colliding and cooling the cooling member in which the polylactic acid-based resin expanded particles are disposed in front of the nozzle mold.

Hereinafter, although the manufacturing method which can be used by this invention is illustrated, this invention is not limited to the following manufacturing methods.
First, a polylactic acid resin is supplied to an extruder and melt kneaded in the presence of a foaming agent. Thereafter, a polylactic acid resin extrudate is extruded from the nozzle mold shown in FIGS. 1 and 2 attached to the front end of the extruder, and while the polylactic acid resin extrudate is foamed, the nozzle mold of 210 to 235 ° C. Polylactic acid resin foam particles are produced by cutting with a rotating blade rotating at a rotational speed of 2000 to 10,000 rpm while contacting the front end surface of the nozzle mold at a temperature, and the polylactic acid resin foam particles are scattered by cutting stress. . The extruder is not particularly limited as long as it is a conventionally used extruder. Examples thereof include a single-screw extruder, a twin-screw extruder, and a tandem type extruder in which a plurality of extruders are connected.

  As the foaming agent, those conventionally used are used. For example, chemical blowing agents such as azodicarbonamide, dinitrosopentamethylenetetramine, hydrazoyl dicarbonamide, sodium bicarbonate; saturated aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, hexane, dimethyl ether, etc. Examples include ethers, chlorofluorocarbons such as methyl chloride, 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, monochlorodifluoromethane, and physical foaming agents such as carbon dioxide and nitrogen. Among these, from the viewpoint of imparting high foamability to the polylactic acid-based resin expanded particles, a physical foaming agent is preferable, and normal butane and isobutane are more preferable. A foaming agent may be used alone or two or more kinds may be used in combination as long as the foam molding process and desired physical properties are not affected.

  Here, if the amount of the foaming agent contained in the polylactic acid resin expanded particles is small after production, the polylactic acid resin expanded particles may not be expanded to a desired expansion ratio. On the other hand, if the amount is too large, the foaming agent acts as a plasticizer, so that the viscoelasticity of the molten polylactic acid-based resin is too low, and the foamability is lowered, making it impossible to obtain good polylactic acid-based resin expanded particles. is there. In addition, the expansion ratio of the polylactic acid-based resin expanded particles may be too high to control the crystallinity. Therefore, the amount of the foaming agent is preferably 1.5 to 3.8 parts by weight and more preferably 1.6 to 3.0 parts by weight with respect to 100 parts by weight of the polylactic acid resin foamed particles.

  In addition, it is preferable that a bubble regulator is added to the extruder, but since many of the bubble regulators act as crystal nucleating agents for the polylactic acid resin foamed 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.

  On the other hand, when the amount of the air conditioner supplied to the extruder is small, the air bubbles of the polylactic acid-based resin expanded particles become coarse, and the appearance of the obtained foamed molded product may be deteriorated. On the other hand, when the polylactic acid-based resin is extruded and foamed, foam breakage may occur, and the closed cell ratio of the polylactic acid-based resin expanded particles may decrease. Therefore, the amount of the air conditioner is preferably 0.01 to 3 parts by weight, more preferably 0.05 to 2 parts by weight, and particularly preferably 0.1 to 1 part by weight with respect to 100 parts by weight of the polylactic acid resin. preferable.

  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 with a motor 3 and rotating the rotary blade 5 disposed on the front end surface 1a of the nozzle mold 1 at a constant rotational speed of 2000 to 10000 rpm. It is preferable.

  All the rotary blades 5 are always rotating in contact with the front end face 1a of the nozzle mold 1. The polylactic acid-based resin extrudate extruded and foamed from the nozzle mold 1 is in the atmosphere at regular intervals due to shear stress generated between the rotary blade 5 and the edge of the nozzle outlet 11 in the nozzle mold 1. Is cut into polylactic acid-based resin expanded particles. 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.

  It is preferable that the polylactic acid resin does not foam in the nozzle of the nozzle mold 1. Therefore, immediately after the polylactic acid-based resin is discharged from the nozzle outlet portion 11 of the nozzle mold 1, the polylactic acid-based resin has not yet been foamed, and starts to foam after a short time has elapsed since being discharged. Therefore, the polylactic acid-based resin extrudate is in the process of foaming extruded before the unfoamed portion, which continues from the unfoamed portion immediately after being discharged from the nozzle outlet portion 11 of the nozzle mold 1 and the unfoamed portion. 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 for which the unfoamed part 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 adjustment of the resin pressure at the nozzle outlet 11 of the nozzle mold 1 can be adjusted by the nozzle diameter, the extrusion amount, the melt viscosity and the melt tension of the polylactic acid resin. By adjusting the amount of the foaming agent to an appropriate amount, the polylactic acid resin can be prevented from foaming inside the mold, and the unfoamed portion can be reliably formed.

  In the present invention, the polylactic acid-based resin foamed particles are foamed at a nozzle mold temperature of preferably 210 to 235 ° C, more preferably 215 to 230 ° C. When the temperature of the nozzle mold is not included in the range of 210 to 235 ° C., it may be impossible to produce the desired spherical or substantially spherical polylactic acid resin expanded particles having a high open cell ratio. That is, the polylactic acid-based resin expanded particles may have an irregular shape such as a columnar shape. Here, the temperature of the nozzle mold means a temperature at a position of 7 mm from the flow path closest to the mold.

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

  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.

  Moreover, it is preferable that the rotary blade 5 is rotating at a constant rotational speed. The rotational speed of the rotary blade 5 is preferably 2000 to 10000 rpm, more preferably 3000 to 9000 rpm, and further preferably 4000 to 8000 rpm.

  If this is less than 2000 rpm, it will be difficult to reliably cut the polylactic acid resin extrudate with the rotary blade 5. Therefore, the polylactic acid-based resin expanded particles may be united with each other, and the shape of the polylactic acid-based resin expanded particles may be nonuniform.

  On the other hand, if it exceeds 10,000 rpm, the following problems may 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, and the foaming of the polylactic acid resin expanded particles becomes insufficient. . 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 is shortened.

（式中、
Ｄｎ：金型のノズル径（ｃｍ）
Ｑ：一穴あたりの吐出量（ｇ／ｈｒ）
Ｒ：カッター刃回転数（ｒｐｍ）
Ｎ：カッター刃枚数（枚）
Ｘ：得られる発泡粒の倍数（ｇ／ｃｍ³））
を満たすことが好ましい。式３の関係を満たさない場合、同様に、所望の球状ないし略球状のポリ乳酸系樹脂発泡粒子を製造することができず、成形性等に影響を与えることがある。 Furthermore, the amount of discharge and the number of rotations of the extruder are expressed by Equation 3:

(Where
Dn: Mold nozzle diameter (cm)
Q: Discharge amount per hole (g / hr)
R: Cutter blade rotation speed (rpm)
N: Number of cutter blades (sheets)
X: Multiple of the obtained foamed particles (g / cm ³ ))
It is preferable to satisfy. If the relationship of Formula 3 is not satisfied, the desired spherical or substantially spherical polylactic acid resin expanded particles cannot be produced in the same manner, which may affect moldability and the like.

  The polylactic acid-based resin foam particles are scattered outward or forward simultaneously with the cutting by the cutting stress of the rotary blade 5 and immediately collide with the inner peripheral surface of the peripheral wall portion 41 b of the cooling drum 41. The polylactic acid-based resin foamed particles continue to foam until they collide with the cooling drum 41, and grow into a spherical or substantially spherical shape by foaming.

  Next, the obtained polylactic acid resin foamed particles are cooled by colliding with a cooling member disposed in front of the nozzle mold. Specifically, 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-based resin foam particles that collide with the inner peripheral surface of the peripheral wall portion 41b of the cooling drum 41 are It cools immediately and the foaming stops. In this way, after the polylactic acid resin extrudate is cut by the rotary blade 5, the polylactic acid resin foam particles are immediately cooled by the cooling liquid 42, thereby forming the polylactic acid resin foam particles. The crystallinity of the lactic acid resin can be prevented from increasing, and the polylactic acid resin foamed particles can be prevented from excessively foaming.

  Accordingly, the polylactic acid-based resin expanded particles exhibit excellent foamability and heat-fusibility during in-mold foam molding. The crystallinity of the polylactic acid-based resin expanded particles can be increased during in-mold foam molding to improve the heat resistance of the polylactic acid-based resin, and the resulting foam-molded product has excellent heat resistance.

  If the temperature of the cooling liquid 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 resin. On the other hand, if it is high, the degree of crystallinity of the polylactic acid-based resin constituting the polylactic acid-based resin expanded particles becomes high, and the heat-fusibility of the polylactic acid-based resin expanded particles may be lowered. Therefore, the temperature is preferably 0 to 45 ° C, more preferably 5 to 40 ° C, and particularly preferably 10 to 35 ° C.

  In order to use the said manufacturing method, the polylactic acid-type resin expanded particle of this invention is spherical shape or substantially spherical shape (refer FIG. 3). Since the polylactic acid-based resin expanded particles of the present invention have the above-mentioned shape, for example, the polylactic acid-based resin expanded particles are excellent in fluidity and expanded as compared with polylactic acid-based resin expanded particles having a columnar shape, a cylindrical shape, a needle shape, or a flake shape. It is excellent in filling properties to a molding machine, and as a result, it is excellent in moldability. Furthermore, a foamed molded article having a desired complicated shape can be easily produced. Spherical or substantially spherical means that the projected view of the polylactic acid-based resin expanded particles includes from spherical particles to elliptical particles.

  Further, the ratio (minor axis / major axis) of the longest diameter (major axis) to the shortest diameter (minor axis) of the polylactic acid resin expanded particles is preferably 1.0 to 1.3 by measurement using calipers. More preferably, it is the range of 1.0-1.2. When the minor axis / major axis is not included in the range of 1.0 to 1.3, there may be a problem in terms of filling into the foam molding machine, resulting in variations among the foam molded articles, The desired formability may not be obtained. The minor axis / major axis = 1 means a true sphere.

  The polylactic acid-based resin expanded particles have an open cell ratio of 25 to 50%, preferably 25 to 45%, more preferably 25 to 40%. When the open cell ratio is not included in 25 to 50%, a foamed molded article having a desired porosity may not be obtained. When the open cell ratio is larger than 50%, the fusion property between the polylactic acid-based resin expanded particles is lowered, and the mechanical strength of the obtained foamed molded product may be lowered. The open cell ratio of the polylactic acid-based resin expanded particles can be adjusted by adjusting the extrusion foaming temperature of the polylactic acid-based resin from the extruder, the supply amount of the foaming agent to the extruder, and the like. Also, the distribution of open cells is excellent.

Polylactic acid-based resin foamed particles are preferably bulk density 0.06~0.15g / cm ³ (bulk multiples 8-20 fold), more preferably a bulk density 0.08~0.15g / cm ³ (bulk multiples 8 ~ 16 times). When the bulk density is greater than 0.15 g / cm ³ , the weight of the obtained foamed molded product is increased, which may be impractical. On the other hand, when the bulk density is less than 0.06 g / cm ³ , the strength of the obtained foamed molded product is lowered, and it may be difficult to use it for a structural member or the like.

  Moreover, since the polylactic acid-based resin expanded particles of the present invention contain a polylactic acid-based resin as a resin component, the obtained polylactic acid-based resin expanded particles preferably have a water absorption rate of 10 to 35%, more preferably 15 to 35%. Have These high water absorption rates also indicate that the foamed molded article of the present invention has excellent water retention.

  The average particle diameter of the polylactic acid-based resin expanded particles is preferably 1.0 to 5.0 mm, and more preferably 1.5 to 4.0 mm. When the average particle diameter is larger than 5.0 mm, the filling property of the polylactic acid-based resin foam particles into the foam molding machine may be lowered, and the strength of the obtained foam molded body may be lowered. Moreover, when smaller than 1.0 mm, the bulk specific gravity of a foaming molding may be affected.

  The degree of crystallinity of the polylactic acid-based resin expanded particles is preferably 15 to 30%, and more preferably 15 to 25%. When the crystallinity is not included in the above range, foamability may be affected. 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 cooling liquid 42, It can also be adjusted by temperature.

(3) Method for Producing Foam Molded Body Next, the obtained polylactic acid resin foamed particles are heat-treated using a known foam molding machine to heat-fuse the polylactic acid resin foamed particles with each other. In-mold molding can be performed on the foamed molded article.

  In the present invention, in order to mold polylactic acid resin foamed particles having a high open cell ratio in a mold, the obtained foamed molded article preferably has a porosity of 10 to 45% by volume, more preferably 15 to 40% by volume. Have When the porosity is higher than 45% by volume, the strength of the foamed molded product may be lowered. On the other hand, if the porosity is lower than 10% by volume, it may not be possible to impart desired water permeability and sound absorption to the foamed molded article. Here, the porosity means the ratio of the inter-particle void portion that is not occupied by the expanded particles of the foam molded article.

  Moreover, since the polylactic acid-based resin expanded particles of the present invention contain a polylactic acid-based resin as a resin component, the obtained foamed molded article is 10 to 35%, preferably 15 to 35%, more preferably 15 to 33%. Has water absorption. These high water absorption rates also indicate that the foamed molded article of the present invention has excellent water retention.

  Since the foamed molded article of the present invention has a high porosity, water absorption and biodegradability, it can be used as a heat insulating material for building materials, a cushioning material for packaging, an interior material for vehicles, and the like. Moreover, it can also be used as a soil conditioner and a humidity control material.

EXAMPLES Hereinafter, although an Example is given and further demonstrated, this invention is not limited by these Examples.
<Content of D-form or L-form of polylactic acid-based resin expanded particles>
The content of D-form or L-form in the polylactic acid resin can be measured by the following method.
The polylactic acid resin is freeze-pulverized and 200 mg of the polylactic acid resin powder is supplied into the Erlenmeyer flask, and then 30 ml of 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, the decomposition solution is filtered through a 0.45 μm membrane filter and then analyzed using liquid chromatography. Based on the obtained chart, the area ratio is determined from the peak area derived from the D-form and the L-form as the abundance ratio. The amount and L body mass are calculated. Then, the same procedure as described above is repeated 5 times, and the obtained D-form amount and L-form amount are arithmetically averaged to obtain the D-form amount and L-form amount of the polylactic acid resin.

Measurement conditions for liquid chromatography HPLC apparatus (liquid chromatography): manufactured by JASCO Corporation, product name PU-2085 Plus system column: manufactured by Sumitomo Analysis Center, Inc., product name SUMICHILAR OA5000 (4.6 mmφ × 250 mm)
Column temperature: 25 ° C
Mobile phase: Mixed solution 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 μl

<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 measures using the apparent density measuring device based on JISK6911, and measures the bulk density of a polylactic acid-type resin expanded particle based on a 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 measuring cylinder (cm ³ )]

<Bulk multiple of polylactic acid resin expanded particles>
The bulk multiple of the polylactic acid-based resin expanded particles is a value obtained by dividing the polylactic acid resin density of 1.25 g / cm ³ by the bulk density obtained by the above measurement.

<Open cell ratio of polylactic acid-based resin expanded particles>
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-based resin expanded 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-based resin expanded particles. Thus, the open cell ratio of the polylactic acid-based resin expanded particles can be calculated. The volume of 1 g of water is 1 cm ³ .
E = A + (CD)
Open cell ratio (%) = 100 × (EB) / E

<Evaluation of Open Cell Distribution of Polylactic Acid Resin Expanded Particles>
The evaluation of the open cell distribution of polylactic acid resin foamed particles is that 10 arbitrary polylactic acid resin foamed particles are cut vertically at half the position with respect to the long diameter, and the cut surface is 100 times with a scanning electron microscope. Were evaluated at the following magnifications and evaluated according to the following criteria.
Cell membrane tears are observed throughout the polylactic acid resin foamed particles: ○
No tearing of the cell membrane is observed in the entire polylactic acid resin expanded particles: ×

<Foaming agent content of polylactic acid-based resin expanded particles>
5-20 mg of polylactic acid resin expanded particles are precisely weighed and used as a measurement sample. This measurement sample is set in a pyrolysis furnace (manufactured by Shimadzu Corporation: PYR-1A) maintained at 180 to 200 ° C., and the measurement sample is sealed and heated for 120 seconds to release the foaming agent component. Using this released foaming agent component, a chart of the blowing agent component is obtained under the following conditions using a gas chromatograph (manufactured by Shimadzu Corporation: GC-14B, detector: FID). Based on the calibration curve of the foaming agent component measured in advance, the foaming agent content of the polylactic acid resin foamed particles is calculated from the obtained chart.

Measurement condition column for gas chromatography: “Shimalite 60/80 NAW” (φ3 mm × 3 m) manufactured by Shinwa Kako Co., Ltd. Column temperature: 70 ° C.
Detector temperature: 110 ° C
Inlet temperature: 110 ° C
Carrier gas: Nitrogen carrier gas Flow rate: 60 ml / min

<Measurement of particle size of polylactic acid resin expanded particles>
The particle diameter of the polylactic acid-based resin expanded particles is determined by measuring the longest diameter (major axis) and the shortest diameter (minor axis) of each polylactic acid-based resin expanded particle with a vernier caliper. The length of the resin foam particles in the direction perpendicular to the cut surface is measured, and the arithmetic average value of the major axis, minor axis and length of the polylactic acid resin foam particles is taken as the particle diameter of the polylactic acid resin foam particles.

<L / S measurement of polylactic acid resin expanded particles>
The L / S of the polylactic acid-based resin expanded particles is calculated as an arithmetic average value using a caliper, where L is the longest diameter (major axis) and S is the shortest diameter (minor axis) of each polylactic acid-based resin expanded particle. To do.

<Water absorption rate of polylactic acid-based resin expanded particles>
The water absorption of the polylactic acid-based resin expanded particles was determined by measuring the weight W1 immediately after drying 150 cm ³ of the polylactic acid-based resin expanded particles in an oven at 100 ° C. for 1 hour. After dipping for 30 minutes, the weight W2 of the foamed molded product after removing moisture on the surface of the foamed particles is measured, and the water absorption is measured from the following equation.
Water absorption (%) = (W2−W1) / W1 × 100

<Water absorption rate of foam molded article>
The water absorption of the foamed molded product was measured by measuring the weight W1 immediately after drying a 100 mm × 100 mm × 40 mm test piece collected from the foamed molded product in an oven at 100 ° C. for 1 hour, and measuring the foam molded product. After being immersed in water for 30 minutes, the weight W2 of the foamed molded product after removing moisture on the surface of the foamed particles is measured, and the water absorption is measured from the following equation.
Water absorption (%) = (W2−W1) / W1 × 100
The water absorption rate of the foamed molded product is evaluated according to the following criteria.
When the water absorption of the foamed molded product is 10 to 35%: ○ (pass)
When the water absorption of the foamed molded product is not included in 10 to 35%: × (failed)

<Porosity of foam molded article>
The porosity of the polylactic acid resin foamed molded product can be determined by the following equation (1).
Porosity: V (volume%) = [(B−C) ÷ B] × 100 (1)
B: Apparent volume of foamed molded product (cm ³ )
C: True volume of the foamed molded product (cm ³ )
The apparent volume: B (cm ³ ) of the foam molded article is calculated from the outer dimensions of the foam molded article. In addition, the true volume of the foamed molded product: C (cm ³ ) is the actual volume of the foamed molded product obtained by subtracting the volume of the void from the apparent volume B: the increased volume when the foamed molded product is submerged in water. Is C.
The porosity of the foam molded product is evaluated according to the following criteria.
1. When the porosity of the foamed molded product is 10 to 45% by volume: ○ (pass)
2. When the porosity of the foamed molded product is not included in 10 to 45% by volume: × (failed)

<Appearance of foam molding>
The appearance of the polylactic acid-based resin foam molded article is evaluated visually according to the following criteria.
When inter-particle voids are seen in the appearance of the foamed molded product: ○ (pass)
When there are no interparticle voids on the appearance of the foamed molded article: × (Fail)

Example 1
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% 100 parts by weight of a temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by dynamic viscoelasticity measurement, and polytetrafluoroethylene powder (manufactured by Asahi Glass Co., Ltd.) as a bubble adjusting agent , Trade name "Fullon L169J") 0.1 parts by weight 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 was first melt-kneaded at 190 ° C. and then melt-kneaded while raising the temperature to 220 ° C.
Subsequently, in the middle of the single-screw extruder, a polylactic acid system in a molten state so that butane composed of 35% by weight of isobutane and 65% by weight of normal butane becomes 1.7 parts by weight with respect to 100 parts by weight of the polylactic acid resin. It was press-fitted into the resin and uniformly dispersed in the polylactic acid resin.
Thereafter, after cooling the molten polylactic acid resin, shearing is performed from each nozzle of the multi-nozzle mold having 20 nozzles having a diameter of 1.0 mm at the outlet portion attached to the front end of the single screw extruder. Polylactic acid-based resin was extruded and foamed at a speed of 7639 sec ⁻¹ . The multi-nozzle mold attached to the front end of the single screw extruder was set at 225 ° C. The extruded polylactic acid resin foam was cut by a so-called hot cut method to obtain polylactic acid resin foam particles. In the cutting step, the polylactic acid resin extrudate is cut by rotating the rotating shaft and rotating the rotary blade disposed on the front end surface of the nozzle mold at a constant rotation speed of 4000 rpm.

The resulting polylactic acid-based resin expanded particles are
The average particle size is 2.60 mm,
The bulk density is 0.10 g / cm ³ ;
L / S is 1.1,
The open cell rate is 28.4%,
The water absorption is 22.5%,
It contained 1.7 parts by weight of a foaming agent with respect to 100 parts by weight of the expanded polylactic acid resin particles.

  Next, the polylactic acid-based resin expanded particles are placed in a sealed container, and carbon dioxide is pressed into the sealed container at a pressure of 0.30 MPa and left at room temperature for 3 hours to leave the polylactic acid-based resin. The 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 200mm x width 200mm x height 30mm. 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 resin foamed particles in the mold cavity through the mouth, and the polylactic acid resin foamed particles were heated and foamed to heat-seal the polylactic acid resin foamed particles together.

  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 article having a void.

Example 2
A butane composed of 35% by weight of isobutane and 65% by weight of normal butane as a foaming agent was pressed into a polylactic acid resin in a molten state so as to be 2.5 parts by weight with respect to 100 parts by weight of the polylactic acid resin. Polylactic acid resin foamed particles and a foamed molded article were obtained in the same manner as in Example 1 except that they were uniformly dispersed in the lactic acid resin.

The resulting polylactic acid-based resin expanded particles are
The average particle size is 2.71 mm,
The bulk density is 0.09 g / cm ³ ;
L / S is 1.1,
The open cell rate is 47.3%,
The water absorption rate is 32.1%,
It contained 2.5 parts by weight of a foaming agent with respect to 100 parts by weight of the expanded polylactic acid resin particles.

Comparative Example 1
A butane comprising 35% by weight of isobutane and 65% by weight of normal butane as a foaming agent is pressed into a polylactic acid resin in a molten state so as to be 1.0 part by weight with respect to 100 parts by weight of the polylactic acid resin. Polylactic acid-based resin expanded particles were obtained in the same manner as in Example 1 except that the lactic acid-based resin was uniformly dispersed and the nozzle mold temperature was 210 ° C.

The resulting polylactic acid-based resin expanded particles are
The average particle size is 2.25 mm,
The bulk density is 0.20 g / cm ³ ;
L / S is 1.1,
The open cell rate is 5.3%,
The water absorption is 6%,
1.0 part by weight of a foaming agent was contained with respect to 100 parts by weight of the expanded polylactic acid resin particles.

The obtained polylactic acid-based resin expanded particles were treated in the same manner as in Example 1 to obtain a polylactic acid-based resin expanded molded body. The obtained polylactic acid resin foamed molded article was a molded article having no voids and having no water absorption and void ratio.
Comparative Example 2
Crystalline polylactic acid resin (trade name “TERRAMAC HV-6250H” manufactured by Unitika Ltd.), melting point: 169.1 ° C., D-form ratio: 1.2 mol%, L-form ratio: 98.8 mol%, dynamic viscosity 100 parts by weight of a temperature T at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by elastic measurement, and polytetrafluoroethylene powder (manufactured by Asahi Glass Co., Ltd., trade name “Fluon”) L169J ") 0.1 parts by weight 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 was first melt-kneaded at 190 ° C. and then melt-kneaded while raising the temperature to 220 ° C.

  Subsequently, in the middle of the single-screw extruder, the polylactic acid-based polylactic acid in a melted state so that butane comprising 35% by weight isobutane and 65% by weight normal butane is 0.7 parts by weight with respect to 100 parts by weight of the polylactic acid-based resin It was press-fitted into the resin and uniformly dispersed in the polylactic acid resin.

Thereafter, after the molten polylactic acid resin is cooled, it is extruded and foamed from each nozzle of a multi-nozzle mold attached to the tip of a single screw extruder at a shear rate of 5659 sec ⁻¹ to form a strand-shaped polylactic acid resin. Extruded foam was produced. The temperature of the multi-nozzle mold was maintained at 220 ° C.

  Subsequently, the strand-shaped polylactic acid-based resin extruded foam is cooled by air cooling over a distance of 60 cm from the tip of each nozzle of the multi-nozzle mold, and then the strand-shaped polylactic acid-based resin extruded foam is 2 m. Over the water surface in the cooling water tank and cooled. In addition, the water temperature in a cooling water tank was 30 degreeC.

  The multi-nozzle mold was provided with 15 nozzles having a diameter of 1.0 mm at the outlet portion, and the land portion had a length of 7 mm. The resin temperature when extrusion foaming from the nozzle of the multi-nozzle mold is inserted between the tip of the single screw extruder and the mold, and a thermocouple is inserted in the center of the breaker plate. It was 204 degreeC when measured by doing.

The strand-shaped polylactic acid-based resin extruded foam is sufficiently drained, and the polylactic acid-based resin extruded foam is cut into a cylindrical shape every 2.3 mm using a fan cutter type pelletizer. Resin foam particles were obtained.
The resulting polylactic acid-based resin expanded particles are
The average particle size is 2.4 mm,
The bulk density is 0.15 g / cm ³ ;
L / S is 1.1,
The open cell rate is 22.4%,
The water absorption is 3.9%,
It contained 0.7 parts by weight of a foaming agent with respect to 100 parts by weight of the polylactic acid resin expanded particles.
The obtained polylactic acid-based resin expanded particles were treated in the same manner as in Example 1 to obtain a polylactic acid-based resin expanded molded body. The obtained polylactic acid-based resin foamed molded article did not have large voids, and was a molded article having low water absorption and low porosity.

  In Table 1, the raw material seed | species of an Example and a comparative example, the evaluation result of a foaming molding, etc. are shown.

Table 1 shows that a foamed molded article having a high porosity can be obtained by using the polylactic acid-based resin foamed particles of the present invention. This indicates that the foamed molded article of the present invention has excellent water permeability. It also shows.
It also shows that a foamed molded article having a beautiful appearance, that is, excellent moldability can be obtained.
Furthermore, it also shows that a foamed molded article having high water absorption, that is, excellent water retention can be obtained.

  Therefore, since the polylactic acid-based resin foamed particles of the present invention give a foamed molded product having high porosity, water absorption and biodegradability, and further excellent moldability, the foamed molded product of the present invention comprises a soil improver and It can also be used as a humidity control material.

1a Front end surface 2 of nozzle mold 1 Rotating shaft 3 Driving member 4 Cooling member 5 Rotating blade 11 Nozzle outlet 41 Cooling drum 41a Cooling drum front 41b Cooling drum peripheral wall 41c Cooling drum supply port 41d Cooling drum supply port 41d Supply pipe 41e Cooling drum discharge port 41f Cooling drum discharge pipe 42 Cooling drum coolant A Rotary blade folder

Claims (9)

  It is a spherical or substantially spherical polylactic acid resin foamed particle having an open cell ratio of 25 to 50%, and the foamed product obtained by molding the polylactic acid resin foamed particle in a mold has a water absorption of 10 to 35%. Polylactic acid resin foamed particles characterized by having   The polylactic acid-based resin expanded particles have a ratio (L / S) of 1.0 to 1.3 between the longest diameter L and the shortest diameter S of the polylactic acid-based resin expanded particles. The polylactic acid-based resin expanded particles described.   The polylactic acid-based resin expanded particles contain both D-form and L-form optical isomers as constituent monomer components, and the content of the smaller of the D-form and L-form is 5 mol%. The polylactic acid-based resin according to claim 1 or 2, comprising a polylactic acid-based resin that is less than or contains only one optical isomer of either D-form or L-form as a constituent monomer component Expanded particles. 4. The poly according to claim 1, wherein the polylactic acid-based resin expanded particles contain 1.5 to 3.8 parts by weight of a foaming agent with respect to 100 parts by weight of the polylactic acid-based resin expanded particles. Lactic acid resin foam particles. The polylactic acid-based resin expanded particles according to any one of claims 1 to 4, wherein the polylactic acid-based resin expanded particles have a bulk density of 0.06 to 0.15 g / cm ³ .   The polylactic acid-based resin expanded particles according to any one of claims 1 to 5, wherein the polylactic acid-based resin expanded particles have a water absorption rate of 10 to 35%. It is a manufacturing method of the polylactic acid-based resin expanded particles according to any one of claims 1 to 6,
Supplying the polylactic acid resin to an extruder and melt-kneading under a foaming agent;
While 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 temperature of the nozzle mold is 210 to 235 ° C. Cutting with a rotary blade rotating at a rotational speed of 2000 to 10000 rpm while contacting the front end surface to produce the polylactic acid resin foamed particles, and scattering the polylactic acid resin foamed particles by cutting stress;
And a step of cooling the polylactic acid-based resin expanded particles by colliding with a cooling member disposed in front of the nozzle mold.   The foaming molding which molded the polylactic acid-type resin expanded particle as described in any one of Claims 1-6 in-mold.   The foamed molded product according to claim 8, wherein the foamed molded product has a porosity of 10 to 45% by volume.

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