JP5188232B2 - Method for producing foamed polylactic acid resin particles for in-mold foam molding - Google Patents

Description

  The present invention relates to a polylactic acid resin foamed particle for in-mold foam molding (hereinafter referred to as “polylactic acid resin foamed particle”) which can obtain a polylactic acid resin foamed molded article having excellent heat resistance and mechanical strength by in-mold foam molding. Is sometimes abbreviated as “)”.

  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.

  And the physical property, especially crystallinity of the obtained polylactic acid-type resin changes with the content ratio of D body component or L body component contained in this polylactic acid resin. Specifically, the polylactic acid-based resin obtained has crystallinity as the content ratio of the smaller optical isomer of the D-form component or L-form component contained in the polylactic acid-type resin increases. Decreases and eventually becomes amorphous.

  Further, in-mold foam molding has been proposed as a method for producing a polylactic acid resin foamed molded body 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.

  Specifically, Patent Document 1 discloses that an isocyanate group ≧ 2.0 equivalents / mol in polylactic acid having a molar ratio of L-form to D-form of 95/5 to 60/40, or 40/60 to 5/95. A resin composition obtained by aging under a predetermined condition a resin composition obtained by reacting 0.5 to 5% by weight of the polyisocyanate compound with respect to the polylactic acid is disclosed. Then, particles are produced from the resin composition, the particles are impregnated with a foaming agent and a foaming auxiliary agent, and the resulting foamable particles are pre-foamed to produce pre-foamed particles. It is disclosed that a molded product having a desired shape is formed by filling the product into foam.

  However, the polylactic acid resin constituting the resin composition has a molar ratio of the smaller optical isomer component of the L-form component or D-form component of 5 mol% or more, and the polylactic acid resin is crystalline. The properties were low or non-crystalline and inferior in heat resistance. Therefore, the heat resistance of the molded body obtained from this resin composition is not sufficient, and is about 50 ° C. at most, which causes a problem in practical use.

  Therefore, in the above method, as the polylactic acid resin constituting the resin composition, the polylactic acid resin with high crystallinity in which the molar ratio of the smaller optical isomer of the L-form or D-form is less than 5 mol% Alternatively, it is conceivable to use a polylactic acid resin having high crystallinity containing only the smaller optical isomer of the L-form or D-form. However, since the particles made of the resin composition are impregnated with a foaming agent to form expandable particles, and the expandable particles are heated to be prefoamed, the heat of the polylactic acid resin is applied by heat applied in the prefoaming process. Crystallization proceeds. As a result, the obtained pre-expanded particles become pre-expanded particles having a high degree of crystallinity, and the fusing property is lowered. Therefore, the molded body obtained by using such pre-expanded particles has a problem that the meltability is poor and the mechanical strength is low.

  Furthermore, although the polylactic acid-based resin has high crystallinity and excellent heat resistance, as the crystallinity increases, the fusibility of the expanded particles decreases and the brittleness increases. There is also a problem that the impact resistance of the resin-based resin foamed molded product is lowered.

Patent Document 2 discloses a polylactic acid resin containing a polylactic acid resin and a vinyl polymer containing a monomer unit having a functional group having reactivity with a carboxyl group and / or a hydroxyl group as a constituent unit. The composition has a strain of 0.1% at 200 ° C., a shear viscosity of 800 to 2000 Pa · s at a frequency of 100 rad / s, a uniaxial elongation rate of 1.0 sec ⁻¹ , and a uniaxial elongation strain of 1.0 to 4. A polylactic acid resin composition characterized by a strain hardening degree λ of uniaxial elongational viscosity at 0 of 0.4 to 0.8 has been proposed, a direct blow molded article, an inflation molded article, a foam molded article, It has been disclosed that it has rheological properties advantageous for molding of an extruded molded body and the like, and a molded product can be obtained using this polylactic acid resin composition.

  However, Patent Document 2 describes that a foam is produced by extrusion foaming using a polylactic acid resin composition, but does not disclose in-mold foam molding at all.

  As described above, in-mold foam molding is one in which polylactic acid resin foamed particles are foamed in the mold, and the polylactic acid resin foamed particles are fused and integrated by the foaming pressure of the polylactic acid resin foamed particles. However, unlike extrusion foaming, it is necessary to consider the fusibility between the foamed polylactic acid resin particles.

  Therefore, as disclosed in Patent Document 2, even though an extruded foam can be produced by adding a foaming agent to the polylactic acid resin composition, the obtained extruded foam is cut into particles to form expanded particles. Even if the foamed particles were used for in-mold foam molding, the foamed particles lacked the fusibility, and a good polylactic acid resin foam could not be obtained.

JP 2000-17037 A JP 2005-239932 A

  The present invention provides a method for producing polylactic acid resin foamed particles for in-mold foam molding, which can obtain a polylactic acid resin foam molded article having excellent heat resistance and mechanical strength by in-mold foam molding.

The method for producing foamed polylactic acid resin particles for in-mold foam molding according to the present invention comprises a polylactic acid resin containing more than 95 mol% of an L-form component as a constituent monomer component and 95 D-form components as a constituent monomer component. A polylactic acid-based resin containing more than mol%, and 80 to 98% by weight of any one of the above polylactic acids, and 2 to 20% by weight of the other polylactic acid. The extruded polylactic acid resin mixture is supplied to an extruder, melted and kneaded in the presence of a foaming agent, and extruded and foamed from a nozzle mold attached to the front end of the extruder to produce an extruded foam. was prepared polylactic acid resin foamed beads by cutting the particulate in the atmosphere by the rotary blade rotating at a rotational speed of 2000~10000rpm while contacting the front end face of the nozzle die, the polylactic acid-based resin foamed A step of scattering the child by the cutting stresses, characterized in that the polylactic acid-based resin foamed particles and a step of cooling by colliding a cooling member which is arranged in front of the nozzle die.

  First, 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 the L isomer are used in combination as a monomer, the ratio of the greater optical isomer of the D isomer or L isomer is greater than 95 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 greater of the D isomers and L isomers is greater than 95 mol%, or the constituent monomer component is any one of the D isomers and L isomers In the case of containing only the lactic acid resin, the resulting polylactic acid resin has high crystallinity and a high melting point. On the other hand, when the D-form and the L-form are used in combination as a monomer and the ratio of the larger of the D-form or L-form is 95 mol% or less, the larger the optical isomer decreases, the greater the amount obtained. The resulting polylactic acid resin has low crystallinity and eventually becomes amorphous.

  Therefore, in the present invention, a polymorphism containing both D-form and L-form optical isomers as a constituent monomer component and a content of the greater of the D-form and L-form is more than 95 mol%. Lactic acid-based resin or polylactic acid-based resin containing only one optical isomer of either D-form or L-form as a constituent monomer component, that is, L-form component or D-form component as constituent monomer component A polylactic acid resin containing more than 95 mol% of any one of the above is used. By using such a polylactic acid-based resin, the heat resistance of the obtained polylactic acid-based resin expanded particles can be increased.

  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, it is a polylactic acid resin containing both D isomer and L isomer as constituent monomer components, and the content of the greater of the D isomer and L isomer is more than 95 mol%. Alternatively, by using a polylactic acid-based resin containing only one of the optical isomers of D-form or L-form as a constituent monomer component, the foam particles are filled in a mold and foamed. The heat resistance of the obtained foamed molded product is also 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.

  Furthermore, as a polylactic acid-based resin obtained by polymerization using both D-form and L-form as monomers, the ratio of either the D-form or L-form, which is larger, is more than 96 mol%. A polylactic acid resin obtained by polymerizing monomers is preferable, and a polylactic acid resin obtained by polymerizing a monomer in which the proportion of the optical isomer of either D-form or L-form is greater than 97 mol%. A resin is more preferable, and a polylactic acid-based resin obtained by polymerizing a monomer in which the ratio of the optical isomer, whichever is larger of D-form or L-form, is more than 98 mol% is particularly preferred.

  That is, a polylactic acid resin containing both D isomer and L isomer as a constituent monomer component and having a larger content of the D isomer or L isomer than 96 mol% is preferable. More preferred is a polylactic acid-based resin that contains both D isomer and L isomer as constituent monomer components, and the content of the larger of the D isomer and L isomer is more than 97 mol%. More preferred is 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 greater of the D-form and L-form is more than 98 mol%. .

  Furthermore, in the present invention, a polylactic acid-based resin (hereinafter referred to as “polylactic acid-based resin A”) containing more than 95 mol% of L-form component as a constituent monomer component, and a D-form component from 95 mol% as a constituent monomer component. By mixing a large amount of polylactic acid resin (hereinafter referred to as “polylactic acid resin B”) in a predetermined ratio, the melt viscoelasticity of the polylactic acid resin is suitable for obtaining extruded foam particles, The extrusion foamability of lactic acid resin is improved.

  The polylactic acid-based resin mixture obtained by mixing the polylactic acid-based resin A and the polylactic acid-based resin B at a predetermined ratio has a melt viscoelasticity suitable for producing extruded foam particles as described above. The reason for this is that the polylactic acid resins A and B are partially stereocomplexed in the process of being melt-kneaded in the extruder, so that the van derder is formed between the polylactic acid resin A and the polylactic acid resin B. Wahls force is generated, and the interaction improves the melt viscoelasticity of the polylactic acid resin mixture. The polylactic acid resin mixture has a melt viscosity and melt tension suitable for extrusion foaming and is a good polylactic acid resin. Expanded particles can be obtained.

  A partially stereocomplexed polylactic acid resin exhibits a new melting peak due to stereocomplexation at a temperature of 200 ° C. or higher in a differential scanning calorimeter (DSC). It can be easily confirmed that a complex has been formed.

  If the content of the polylactic acid-based resin A or the polylactic acid-based resin B in the polylactic acid-based resin mixture is small, the melt tension of the polylactic acid-based resin mixture becomes too high, resulting in high foaming. On the other hand, if the polylactic acid resin foamed particles are large, the effect of modifying the melt viscoelasticity of the polylactic acid resin mixture becomes insufficient, and good polylactic acid resin foamed particles cannot be obtained.

  Therefore, in the polylactic acid resin mixture, the content of the polylactic acid resin of the larger one of the polylactic acid resin A or the polylactic acid resin B is 80 to 98% by weight, and the polylactic acid resin A or polylactic acid. The content of the polylactic acid resin in the smaller one of the resin B is limited to 2 to 20% by weight.

  That is, in the polylactic acid resin mixture, the polylactic acid resin A is 80 to 98% by weight and the polylactic acid resin B is 2 to 20% by weight, or the polylactic acid resin A is 2 to 20% by weight and the polylactic acid resin. The resin B needs to be 80 to 98% by weight.

  Further, in the polylactic acid resin mixture, the content of the polylactic acid resin of the larger one of the polylactic acid resin A or the polylactic acid resin B is 85 to 97% by weight and the polylactic acid resin A or polylactic acid The content of the less polylactic acid resin in the resin B is preferably 3 to 15% by weight, and the polylactic acid resin in the larger one of the polylactic acid resin A or the polylactic acid resin B is preferred. It is more preferable that the content of the polylactic acid resin is 88 to 96% by weight and the smaller one of the polylactic acid resin A or the polylactic acid resin B is 4 to 12% by weight.

  In addition, since the polylactic acid resin mixture is industrially inexpensive and suitable for mass production, the polylactic acid resin A is cheaper and easily available than the polylactic acid resin B. preferable.

  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): Product name “PU-2085 Plus 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. Specifically, the polylactic acid-based resin mixture is supplied to an extruder, melted and kneaded in the presence of a foaming agent, and then extruded and foamed from a mold attached to the tip of the extruder to produce an extruded foam. The foamed polylactic acid resin can be produced by cutting the extruded foam into particles. Examples of the form of the extruded foam include a strand form and a sheet form, and a strand form is preferable. However, in order to efficiently and stably produce polylactic acid-based resin foamed particles, as described later, extrusion Extrusion foam is produced from a nozzle mold attached to the front end of the machine, and the extruded foam immediately after being extruded from the nozzle mold is continuously cut with a rotary blade to produce polylactic acid resin foam particles. It is preferable to manufacture.

  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.

  When the polylactic acid-based resin A and the polylactic acid-based resin B are melt-mixed by an extruder, compression of the extruder is performed in order to uniformly and effectively modify the melt viscoelasticity of the polylactic acid-based resin mixture. The temperature of the part is preferably adjusted to 200 to 250 ° C, more preferably 210 to 240 ° C, and particularly preferably 215 to 235 ° C.

  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.

  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. From the above, the viscoelasticity of the molten polylactic acid resin is too low and the foamability is lowered, and it is not possible to obtain good polylactic acid resin expanded particles, or the expansion ratio of the polylactic acid resin expanded particles is too high. Since the degree of crystallinity may not be controlled, it is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 4 parts by weight, and 0.3 to 3 parts by weight with respect to 100 parts by weight of the polylactic acid resin mixture. Part is particularly preferred.

  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.

  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 is extruded and foamed, and the closed cell ratio of the polylactic acid resin foamed particles may be reduced. Therefore, 0.01% relative to 100 parts by weight of the polylactic acid resin mixture. -3 parts by weight is preferable, 0.05-2 parts by weight is more preferable, and 0.1-1 part by weight is particularly preferable.

  Here, an example of a production apparatus used for producing an extruded foam by extrusion foaming from a nozzle mold and continuously cutting the extruded foam with a rotary blade to produce polylactic acid resin foamed particles explain. In FIG. 1, reference numeral 1 denotes a nozzle mold attached to the front end of the extruder. This nozzle mold is preferable because it can form a uniform fine cell by extruding and foaming a polylactic acid resin. 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 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, while when large, the extruded foams that are extruded and foamed from nozzles adjacent to each other come into contact with each other, Or since polylactic acid-type resin expanded particles obtained by cut | disconnecting an extrusion foam may unite, 2-80 pieces are preferable, 5-60 pieces are more preferable, and 8-50 pieces are especially preferable.

  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 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 become 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 (when Q is calculated from the mass extrusion rate (g / sec), the density of the polylactic acid resin is 1.0 g / cm ³ ), r is the radius (cm) of the nozzle.

  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,. It moves on the imaginary circle A, and it is comprised so that the extrusion foam extruded from the exit part 11, 11, ... of a nozzle can be cut | disconnected sequentially and continuously.

  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. A bottom cylindrical cooling drum 41 is provided.

  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 due to 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.

  Subsequently, the extruded foam extruded from the nozzle mold 1 continues to the cutting step. The extruded foam 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 at a constant rotational speed of 2000 to 10,000 rpm.

  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 extruded foam that is extruded and foamed from the nozzle mold 1 is the rotary blade 5 and the nozzles in the nozzle mold 1. Due to the shear stress generated between the edge of the outlet portion 11 and the outlet portion 11, the foamed polylactic acid resin particles are cut in the atmosphere at regular time intervals. At this time, water may be sprayed onto the extruded foam in a range where the extruded foam is not excessively cooled.

  In the present invention, the polylactic acid resin is prevented from foaming in the nozzle of the nozzle mold 1. The polylactic acid-based resin is not yet foamed immediately after being discharged from the nozzle outlet portion 11 of the nozzle mold 1, and starts to foam after a short time has elapsed since being discharged. Therefore, the extruded foam is composed of an unfoamed portion immediately after being discharged from the nozzle outlet portion 11 of the nozzle mold 1 and a foaming portion in the process of foaming that is continuous with the unfoamed portion and is extruded prior to the unfoamed portion. It consists of.

  Since all the rotating blades 5 cut the extruded foam in a state where it is always in contact with the front end face 1a of the nozzle mold 1, the extruded foam is removed from the nozzle outlet 11 of the nozzle mold 1. Polylactic acid-based resin expanded particles are produced by cutting at the unfoamed portion immediately after being discharged.

  Since the obtained polylactic acid-based resin expanded particles are obtained by cutting the extruded foam 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 falls below 2000 rpm, the extruded foam cannot be reliably cut by the rotary blade 5, and the polylactic acid-based resin expanded particles are combined, or the polylactic acid-based resin expanded particles are This is because the shape may be non-uniform.

  On the other hand, if the rotational speed of the rotary blade 5 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 extruded foam is cut until the polylactic acid resin foam particles collide with the cooling member is shortened, resulting in insufficient foaming of the polylactic acid resin foam particles. The expansion ratio of the particles is 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 is 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. In this way, after the extruded foam is cut by the rotary blade 5, the polylactic acid resin foam particles are immediately cooled by the cooling liquid 42, so that the crystallinity of the polylactic acid resin foam particles is increased. While preventing, 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. And the crystallinity degree of polylactic acid-type resin foaming particle can be raised at the time of in-mold foam molding, and the heat resistance of polylactic acid-type resin can be improved, and the obtained polylactic acid-type resin foam molding is excellent in heat resistance. It has sex.

  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. Since the degree of crystallinity of the polylactic acid-based resin constituting the lactic acid-based resin expanded particles is increased, and the heat-fusibility of the polylactic acid-based resin expanded particles may be lowered, 0 to 45 ° C. is preferable, 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%. By setting the crystallinity of the polylactic acid-based resin expanded particles to 30% or less, the fusing property of the polylactic acid-based resin expanded particles is improved, the thermal fusion between the expanded particles is excellent, and the mechanical strength is excellent. A lactic acid resin foamed molded product can be obtained. Further, during the in-mold foam molding process, the crystallinity of the polylactic acid resin expanded particles can be increased to improve the heat resistance of the polylactic acid resin, and the resulting polylactic acid resin foam molded article is excellent. It has fusibility and heat resistance.

  The degree of crystallinity of the polylactic acid-based resin expanded particles is adjusted by the time from when the extruded foam is extruded from the nozzle mold 1 until the polylactic acid-based resin expanded particles collide with the coolant 42, and the temperature of the coolant 42. can do.

  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.

  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.

  And the temperature at the time of making an inert gas impregnate polylactic acid-type resin expanded particle has preferable -40-25 degreeC, and its -10-20 degreeC is more preferable. This is because when the temperature is low, the polylactic acid-based resin expanded particles are cooled too much, and the polylactic acid-based resin expanded particles cannot be sufficiently heated at the time of in-mold foam molding. This is because the heat-sealing property is lowered, and the mechanical strength of the obtained polylactic acid resin foamed molded product may be lowered. On the other hand, if the temperature is high, the amount of impregnation of the inert gas into the polylactic acid resin expanded particles becomes low, and sufficient foamability may not be imparted to the polylactic acid resin expanded particles. This is because crystallization of the resin foam particles is promoted, the heat-fusibility of the polylactic acid resin foam particles is lowered, and the mechanical strength of the resulting polylactic acid resin foam molding may be lowered.

  The pressure when impregnating the polylactic acid-based resin expanded particles with an inert gas is preferably 0.2 to 1.6 MPa, and more preferably 0.28 to 1.2 MPa. When the inert gas is carbon dioxide, 0.2 to 1.5 MPa is preferable, and 0.25 to 1.2 MPa is more preferable. This is because, when the pressure is low, the impregnation amount of the inert gas into the polylactic acid resin foamed particles becomes low, and sufficient foamability cannot be imparted to the polylactic acid resin foamed particles. This is because the mechanical strength of the resin foam molding may be lowered.

  On the other hand, when the pressure is high, the degree of crystallinity of the polylactic acid-based resin expanded particles increases, the heat-fusibility of the polylactic acid-based resin expanded particles decreases, and the mechanical strength of the resulting polylactic acid-based resin foamed molded product increases. It is because it may fall.

  Furthermore, the time for impregnating the polylactic acid resin expanded particles with the inert gas is preferably 20 minutes to 24 hours, more preferably 1 to 18 hours, and particularly preferably 3 to 8 hours. When the inert gas is carbon dioxide, 20 minutes to 24 hours are preferable. This is because if the impregnation time is short, the polylactic acid resin expanded particles cannot be sufficiently impregnated with the inert gas. On the other hand, if the impregnation time is long, the production efficiency of the polylactic acid-based resin foamed molded product is lowered.

  Thus, by impregnating the polylactic acid resin expanded particles with an inert gas at −40 to 25 ° C. and a pressure of 0.2 to 1.6 MPa, the degree of crystallinity of the polylactic acid resin expanded particles can be improved. While suppressing the rise, foamability can be improved, and therefore, during the in-mold foam molding, the polylactic acid resin foam particles can be firmly heat-sealed and integrated with sufficient foaming force, and the mechanical strength In particular, it is possible to obtain a polylactic acid resin foam molded article having excellent impact strength.

  In addition, 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 a mold as they are. Before the foamed particles are filled into the mold, they may be heated and subjected to secondary foaming, and the foamed particles are further 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.

  And as the temperature at the time of foaming the polylactic acid-based resin expanded particles to obtain secondary expanded particles, if the temperature is high, the crystallinity of the polylactic acid-based resin increases, and the heat-fusible properties between the secondary expanded particles Is lower, and the mechanical strength and appearance of the resulting polylactic acid resin foamed molded article are reduced.

  Even when the secondary foamed particles are filled in a mold and molded, the secondary foamed particles are not treated under the same conditions and in the same manner as when the polylactic acid resin foamed particles are impregnated with an inert gas. It is preferable to impregnate the active gas to improve the foamability of the secondary foamed particles.

  When both the polylactic acid-based resin expanded particles and the secondary expanded particles are impregnated with an inert gas, the inert gas may be the same or different, but is preferably the same.

Further, the fusion rate of the obtained polylactic acid resin foamed molded article is preferably 40% or more, more preferably 50% or more, and particularly preferably 60% or more. In addition, the fusion rate of a polylactic acid-type resin foaming molding means what was measured in the following way. First, the polylactic acid resin foamed molded body is bent and cut from a predetermined location. Then, the total number N ₁ of foam particles exposed on the cut surface of the polylactic acid resin foam molded article is visually counted, and the foamed particles whose material is broken, that is, the number N ₂ of the divided foam particles is calculated. It can be counted visually and the fusion rate can be calculated based on the following formula.
Fusing rate (%) = 100 × number of particles of expanded foam particles N ₂ / total number of expanded particles N ₁

  As described above, the method for producing foamed polylactic acid resin particles for in-mold foam molding of the present invention comprises a polylactic acid resin containing more than 95 mol% of an L-form component as a constituent monomer component and D as a constituent monomer component. A polylactic acid-based resin containing more than 95 mol% of body components, 80 to 98% by weight of any one of the above polylactic acids, and 2 to 20% by weight of the other polylactic acid % Polylactic acid resin mixture is used, the melt viscoelasticity of the polylactic acid resin is suitable for obtaining extruded foam particles, and the extrusion foamability of the polylactic acid resin is improved.

  Therefore, the polylactic acid-based resin expanded particles obtained by the production method of the present invention have a high expansion ratio, a high closed cell ratio and excellent foamability, and exhibit a sufficient foaming pressure at the time of in-mold foam molding. It is possible to obtain a polylactic acid resin foam molded article having excellent mechanical strength and high mechanical strength.

  And as mentioned above, since the polylactic acid-based resin containing more than 95 mol% of either L-form or D-form as a constituent monomer component is used, the obtained polylactic acid-based resin expanded particles are: Its crystallinity is high and it has excellent heat resistance.

  Therefore, the obtained polylactic acid-based resin expanded particles exhibit excellent foamability and heat-sealability in in-mold foam molding, and the resulting polylactic acid-based resin molded product has appearance, heat resistance and mechanical strength. Is excellent.

  Furthermore, the heat resistance of the polylactic acid resin foam molded article obtained by in-mold foam molding using the polylactic acid resin foam particles is excellent, and at the time of in-mold foam molding, the polylactic acid resin foam molded article has a high temperature. However, since the form can be maintained, the cooling time in the mold of the foam molded product can be shortened, and the production efficiency of the foam molded product can be improved.

  In the method for producing foamed polylactic acid-based resin particles for in-mold foam molding of the present invention, the extrusion blade is extruded and foamed from the nozzle mold by rotating the rotary blade at a predetermined rotational speed while always contacting the front end surface of the nozzle mold. When the foam is cut with the rotary blade, the extruded foam can be cut reliably to obtain substantially spherical polylactic acid-based resin expanded particles whose entire surface is covered with a skin layer. 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.

  And, when the polylactic acid resin foamed particles are scattered by the cutting stress when cutting the extruded foam and collide with the cooling member and immediately cooled, the crystallinity of the polylactic acid resin is suppressed Excellent heat-sealability in in-mold foam molding.

  When a polylactic acid resin is extruded and foamed and a nozzle mold is used as the mold, the resulting polylactic acid resin foamed particles have fine bubbles and a low open cell ratio.

  In the present invention, the bulk density of the polylactic acid-based resin expanded particles, the apparent density of the polylactic acid-based resin foam molding, and the average molecular weight of the polylactic acid-based resin are those measured according to the following procedures.

(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 measuring cylinder (cm ³ )]

(Apparent density of polylactic acid resin foam molding)
The apparent density of the polylactic acid-based resin foamed molded product refers to that measured by the method described in JIS K6767: 1999 “Measurement of foamed plastic and rubber-apparent density”.

(Average molecular weight of polylactic acid resin)
30 mg of polylactic acid resin was dissolved in 4 ml of chloroform to prepare a solution. Using this solution, the average molecular weight of the polylactic acid-based resin was measured under the following conditions using the following measuring apparatus.
Measuring device: HPLC manufactured by Tosoh Corporation (pump: DP-8020, autosampler: AS
-8020, detector: UV-8020, RI-8020)
Column: GPC K-806L × 2 (manufactured by Shodex)
Measurement conditions: column temperature (40 ° C.), mobile phase (chloroform)
Mobile phase flow rate (1.2ml / min)
Pump temperature (room temperature), measurement time (25 minutes), detection (RI)
Injection volume (50 microliters)

Example 1
The polylactic acid resin foamed particles for in-mold foam molding were produced using the production apparatus shown in FIGS. First, 95 parts by weight of polylactic acid resin A (trade name “Lacia H-100” manufactured by Mitsui Chemicals, L-form component: 98.8 mol%, D-form ratio: 1.2 mol%) and polylactic acid resin B (Number average molecular weight: 100,000, weight average molecular weight: 180,000, L-form component: 0 mol%, D-form ratio: 100 mol%) 5 parts by weight of a polylactic acid-based resin mixture and a cell regulator prepared by dry blending in advance As a polytetrafluoroethylene powder (trade name “Fluon L169J” manufactured by Asahi Glass Co., Ltd.) 0.1 part by weight was supplied to a single screw extruder having a diameter of 40 mm and melt kneaded. In addition, the polylactic acid-type resin B used what was pelletized using the twin screw extruder whose aperture is 30 mm.

  Subsequently, from the middle of the single-screw extruder, the polylactic acid-based polylactic acid in a melted state so that butane comprising 35% by weight of isobutane and 65% by weight of normal butane is 1.2 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. In the single screw extruder, the supply unit was 190 ° C, the compression unit was 230 ° C, and the weighing unit was 200 ° C.

  Thereafter, a polylactic acid resin was extruded and foamed at a resin temperature of 202 ° C. from each nozzle of the multi-nozzle mold 1 attached to the front end of the single screw extruder.

  The multi-nozzle mold 1 has two nozzles having a diameter of the outlet portion 11 of 0.5 mm, and all the outlet portions 11 of the nozzles are assumed to be on the front end surface 1a of the multi-nozzle die 1. Is arranged on the imaginary circle A of 120.5 mm at a position facing the diameter direction. The multi-nozzle mold 1 was held at 200 ° C.

  Two rotary blades 5 are integrally provided on the outer peripheral surface of the rear end portion of the rotary shaft 2 at equal intervals in the circumferential direction of the rotary shaft 2, that is, at positions facing the diameter direction of the rotary shaft 2. The rotary blades 5 are configured to move on the virtual circle A in a state where they are always in contact with the front end face 1a of the multi-nozzle mold 1.

  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.

  And the rotary blade 5 arrange | positioned in the front end surface 1a of the multi-nozzle metal mold | die 1 is rotated at the rotation speed of 4800 rpm, and the extrusion foam foamed and extruded from the exit part 11 of each nozzle of the multi-nozzle metal mold | die 1 is used. Cutting with the rotary blade 5 produced substantially spherical polylactic acid resin foamed particles. The extruded foam consisted 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 extruded foam was cut at the open end of the outlet portion 11 of the nozzle, and the extruded foam was cut at the unfoamed portion.

  In the production of the above-mentioned polylactic acid-based resin expanded particles, 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 extruded foam is extruded and foamed from the extruder, and the extruded foam is immediately after being extruded from the nozzle of the multi-nozzle mold 1 and the foaming part in the process of foaming continuous with the unfoamed part. It was confirmed that 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 extruded foam is rotated at the opening end 11 of the nozzle at the rotating end 5. To produce polylactic acid resin expanded particles.

  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 2.2 to 2.6 mm.

  In addition, when the melting peak temperature of the obtained polylactic acid-type resin expanded particle was measured with the differential scanning calorimeter (DSC), the melting peak was able to be confirmed at 169.1 degreeC and 220.1 degreeC.

  Next, the polylactic acid-based resin expanded particles are put in a sealed container, carbon dioxide is pressed into the sealed container at a pressure of 0.3 MPa, and left at 20 ° C. for 24 hours to be polylactic acid-based. The resin foam 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. Further, in order to make the mold communicate with the inside of the mold cavity and the outside of the mold, circular supply ports having a diameter of 8 mm were formed at intervals of 20 mm. 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 of 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)
Polylactic acid resin expanded particles in the same manner as in Example 1 except that polylactic acid resin A was changed to 90 parts by weight instead of 95 parts by weight, and polylactic acid resin B was changed to 10 parts by weight instead of 5 parts by weight. And the polylactic acid-type resin foaming molding was obtained. The obtained polylactic acid resin foamed molded article had a very excellent appearance.

  In addition, when the melting peak temperature of the obtained polylactic acid-type resin expanded particle was measured with the differential scanning calorimeter (DSC), the melting peak was able to be confirmed at 169.1 degreeC and 220.1 degreeC.

(Example 3)
As polylactic acid resin A, polylactic acid resin A (L-form component: 95.8 mol%, D-form component: 4.2 mol%) commercially available from Mitsui Chemicals under the trade name “Lacia H-140” ) Was used in the same manner as in Example 2 to obtain polylactic acid resin expanded particles and a polylactic acid resin expanded foam. The obtained polylactic acid resin foamed molded article had a very excellent appearance.

  In addition, when the melting peak temperature of the obtained polylactic acid-type resin expanded particle was measured with the differential scanning calorimeter (DSC), the melting peak was able to be confirmed at 168.9 degreeC and 220.7 degreeC.

Example 4
The polylactic acid-based resin expanded particles before impregnation with carbon dioxide obtained in Example 1 were supplied and sealed in a 10-liter pressure vessel, and carbon dioxide was pressed into the pressure vessel at a pressure of 1.0 MPa. The polylactic acid-based resin expanded particles were impregnated with carbon dioxide by being allowed to stand at 20 ° C. for 6 hours.

The polylactic acid-based resin expanded particles are taken out from the pressure vessel, and the polylactic acid-based resin expanded particles are immediately supplied to a hot-air dryer equipped with a stirrer. The mixture was heated for 3 minutes for foaming to obtain secondary foamed particles foamed to high foaming with a bulk density of 0.06 g / cm ³ .

  The obtained secondary foamed particles are supplied into a sealed container, and carbon dioxide is injected into the sealed container at a pressure of 0.8 MPa and left at 20 ° C. for 24 hours to obtain secondary foamed particles. Was impregnated with carbon dioxide.

  Subsequently, the secondary expanded particles were filled into the mold cavity used in Example 1. Then, water maintained at 85 ° C. is stored in the heated water tank, and the mold filled with the secondary foam particles is completely immersed in the water in the heated water tank for 3 minutes, and then passed through the mold supply port. Water was supplied to the secondary foam particles in the cavity of the mold, and the secondary foam particles were heated and foamed to integrate the polylactic acid resin foam 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.

(Comparative Example 1)
Polylactic acid resin expanded particles in the same manner as in Example 1 except that the polylactic acid resin A was 99 parts by weight instead of 95 parts by weight, and the polylactic acid resin B was 1 part by weight instead of 5 parts by weight. However, gas holes due to foam breakage occurred intermittently, and the polylactic acid-based resin expanded particles could not be stably produced.

  In addition, when the melting peak temperature of the obtained polylactic acid-based resin expanded particles was measured with a differential scanning calorimeter (DSC), the melting peak could be confirmed only at 169.6 ° C.

(Comparative Example 2)
Polylactic acid resin expanded particles in the same manner as in Example 1 except that the polylactic acid resin A was changed to 78 parts by weight instead of 95 parts by weight, and the polylactic acid resin B was changed to 22 parts by weight instead of 5 parts by weight. And the polylactic acid-type resin foaming molding was obtained.

  The obtained polylactic acid-based resin expanded particles and polylactic acid-based resin expanded molded articles were about 23%, respectively, compared to the polylactic acid-based resin expanded particles and polylactic acid-based resin expanded molded articles obtained in Example 1. It was about 27% heavier. The polylactic acid resin foamed molded article had a low fusion rate of 30%.

  The bulk density, crystallinity and average particle diameter of the obtained polylactic acid resin foamed particles, and the apparent density and fusion rate of the obtained polylactic acid resin foam molded article were measured. The results are shown in Table 1. Indicated. In addition, the average particle diameter of the polylactic acid-based resin expanded particles is arbitrarily extracted from the obtained polylactic acid-based resin expanded particles, and the particle diameter of each of the polylactic acid-based resin expanded particles is measured as described above. This is an arithmetic average of particle sizes.

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.

Explanation of symbols

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

  The polylactic acid resin foamed particles produced by the production method of the present invention exhibit excellent foamability and heat-fusibility in in-mold foam molding. Therefore, the obtained polylactic acid-based resin molded article is excellent in appearance, heat resistance and mechanical strength, and can be suitably used for applications such as building materials and automobile interior materials.

Claims (2)

A polylactic acid-based resin containing more than 95 mol% of L-form component as a constituent monomer component, and a polylactic acid-based resin containing more than 95 mol% of D-form component as a constituent monomer component In the presence of a blowing agent, a polylactic acid-based resin mixture containing 80 to 98% by weight of one of the polylactic acids and 2 to 20% by weight of the other polylactic acid is fed to an extruder. An extruded foam is produced by melt-kneading and extrusion-foaming from a nozzle die attached to the front end of the extruder, and the extruded foam is brought into contact with the front end surface of the nozzle die at a rotational speed of 2000 to 10,000 rpm. and cut into a particulate in the atmosphere to produce a polylactic acid-based resin foamed particles by a rotating blade which rotates, a step of scattering by cleavage stress the polylactic acid-based resin foamed particles, the polylactic acid resin Mold foam method for manufacturing a molded polylactic acid resin foamed particles, characterized in that the foam particles and a step of cooling by colliding a cooling member which is arranged in front of the nozzle die. The bulk density of the polylactic acid-based resin expanded particles is 0.02 to 0.6 g / cm ^Three The method for producing expanded polylactic acid resin particles for in-mold foam molding according to claim 1, wherein:

Images