JP2013203987A - Polylactic acid resin foam molded product and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polylactic acid resin foam molded product capable of retaining satisfactory mechanical strength for a long period of time, and to provide a method for producing the same.SOLUTION: A polylactic acid resin foam molded product is composed of at least a polylactic resin foam and a surface layer covering the whole surface thereof. The polylactic acid resin foam has a water amount of 1.5 wt.% or less, and the surface layer is composed of a moisture impermeable material having moisture permeability of 200 g/m_24 hours or less.

Description

  The present invention relates to a polylactic acid resin foamed molded article and a method for producing the same. More specifically, the present invention relates to a polylactic acid resin foam molded article (also referred to as “composite” or “composite molded article”) comprising at least a polylactic acid resin foam and a skin covering the entire surface thereof, and production thereof. Regarding the method.

  Polylactic acid resin is a resin obtained by polymerizing naturally occurring lactic acid. It is a biodegradable resin that can be decomposed by microorganisms existing in nature, and has excellent mechanical properties at room temperature. It attracts attention. In particular, with the recent increase in environmental awareness, the use of polylactic acid resins for various applications such as automobile-related parts and building materials has been advanced.

  For example, in JP 2012-7180 A (Patent Document 1), a foamable molten resin composition obtained by kneading a polylactic acid resin and a physical foaming agent in an extruder is extruded from a die to a low pressure region. A method for producing a polylactic acid-based resin foam molded body (foamed parison) is disclosed in which a formed cylindrical body having a foamed layer is sandwiched between molds. In this method, the polylactic acid-based resin has a melt tension at 190 ° C. of 3 cN or more, a water content of less than 300 ppm, and a calorific value (ΔHexo: −10 ° C.) determined by heat flux differential scanning calorimetry (cooling rate 10 ° C./min). / Min) is 20 J / g or more, so that the foamed parison can be molded.

  Japanese Patent Laid-Open No. 2006-152258 (Patent Document 2) discloses a foamed layer formed by extruding a foamable molten resin composition obtained by kneading a polylactic acid-based resin and a physical foaming agent into a low-pressure region from a die. A polylactic acid-based resin foam molded body (foamed parison) obtained by sandwiching and molding a cylindrical body having a mold and a method for producing the same are disclosed. In this foamed molded product, the endothermic amount (ΔHendo: 2 ° C / min) and the calorific value (ΔHexo: 2 ° C / min) determined by heat flux differential scanning calorimetry (temperature increase rate 2 ° C / min) for the molded foam layer. Minutes) (ΔHendo: 2 ° C./min−ΔHexo: 2 ° C./min) is 10 J / g or more and the melt tension at 190 ° C. is 2 cN or more, making it possible to form a foamed parison.

JP2012-7180A JP 2006-152258 A

There exists a subject that a void generate | occur | produces, when compounding a polylactic acid-type resin foam and another raw material as mentioned above. In addition, when the polylactic acid resin foamed molded product is used as a packaging material for structural members and electronic parts such as automobiles, trains and airplanes, especially when the polylactic acid resin foamed material is sealed with other materials, In use, there is a problem that the mechanical properties, particularly the compressive strength is lowered. In the prior art including the above-mentioned Patent Documents 1 and 2, enhancement of general mechanical properties has been studied, but the problem and the means for solving it are not described.
Then, this invention makes it a subject to provide the polylactic acid-type resin foaming molding which can hold | maintain favorable mechanical strength for a long period of time, and its manufacturing method.

  The inventors of the present invention have made extensive studies to solve the above problems, and as a result, the water in the polylactic acid resin foam promotes the generation of voids and the progress of the hydrolysis reaction at high temperatures. Focusing attention, for example, it has been found that the above-mentioned problems can be solved by adjusting the water content in the polylactic acid resin foam to a specific amount or less by vacuum drying or the like, and the present invention has been completed.

Thus, according to the present invention, it is composed of at least a polylactic acid-based resin foam and a skin covering the entire surface thereof, and the polylactic acid-based resin foam has a water content of 1.5% by weight or less, and the skin Is formed of a non-moisture permeable material having a moisture permeability of 200 g / m ² · 24 hours or less.

  Further, according to the present invention, there is provided a method for producing the above polylactic acid resin foam, wherein the polylactic acid resin foam has a water content of 1.5% by weight or less on the entire surface of the polylactic acid resin foam. Before or after covering with a skin, obtained by subjecting the polylactic acid resin foam to vacuum drying at a temperature of 70 ° C. or lower and a vacuum degree of 1 to 540 mmHg. A method of manufacturing a body is provided.

ADVANTAGE OF THE INVENTION According to this invention, the polylactic acid-type resin foaming molding which can maintain favorable mechanical strength for a long period of time, and its manufacturing method can be provided.
Therefore, the polylactic acid resin foamed molded article of the present invention can be suitably used as a structural member for automobiles, trains or airplanes, or a packaging material for electronic parts.

In the polylactic acid resin foamed molded article of the present invention, the polylactic acid resin foam is composed of polylactic acid resin foamed particles or a heat-fused body thereof, and the polylactic acid resin foamed particles are directed from the center toward the skin. When the radius is equally divided into four layers, P1, P2, P3 and P4 from the center, and the average bubble diameter of the bubbles present in the P4 layer region is 1, the average of the bubbles present in the P1 layer region When the cell diameter has physical properties of 1 to 100, and the polylactic acid resin foam has a volume of 0.01 to 1000 when the volume of the skin is 1, the polylactic acid resin foam molding The body was subjected to a heat and humidity test for 50 hours against a compressive strength CS ₀ measured before the test (when the test was 0 hour) for performing a heat and moisture resistance test for promoting hydrolysis (conditions: temperature 80 ° C., relative humidity 95%, 50 hours). Compressive strength CS ₅ measured later _The above effect is further exhibited when the physical properties are such that the ratio of ₀ is 50% or more.

It is the schematic cross section which showed an example of the manufacturing apparatus of an expanded particle. It is the schematic diagram which looked at the multi-nozzle mold from the front. It is a schematic diagram for demonstrating the measuring method of the average bubble diameter of an expanded particle.

The polylactic acid-based resin foamed molded product of the present invention (hereinafter also referred to as “foamed molded product”) is composed of at least a polylactic acid-based resin foam and a skin covering the entire surface thereof. It is characterized in that it has a moisture content of 5% by weight or less and the skin is made of a moisture-impermeable material having a moisture permeability of 200 g / m ² · 24 hours or less.

The polylactic acid resin foam of the present invention has a moisture content of 1.5% by weight or less.
If the water content exceeds 1.5% by weight, voids may be generated and mechanical properties, particularly compressive strength, may be reduced during long-term use. The water content is preferably 1.25% by weight or less, more preferably 1.0% by weight or less, and the lower limit is about 0.01% by weight.

The skin covering the entire surface of the polylactic acid resin foam of the present invention has a moisture permeability of 200 g / m ² · 24 hours or less.
When the moisture permeability exceeds 200 g / m ² · 24 hours, voids may be generated and mechanical properties, particularly compressive strength, may be reduced during long-term use. The moisture permeability is preferably 195 g / m ² · 24 hours or less, more preferably 190 g / m ² · 24 hours or less, further preferably 185 g / m ² · 24 hours or less, and the lower limit is 10 ^-6 g / m ² · About 24 hours. However, depending on the material of the skin, for example, a metal material has a moisture permeability of zero.

(Polylactic acid-based resin expanded particles (hereinafter also referred to as “expanded particles”))
(1) Polylactic acid resin As the polylactic acid resin, a commercially available polylactic acid resin can be used. Specifically, 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 -Ring-opening polymers of one or more lactides selected from the group consisting of lactides.
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, the copolymer of D-form and L-form in which the proportion of the smaller optical isomer of D-form or L-form is 5 mol% or more increases as the smaller optical isomer increases. Tend to be low and eventually become amorphous.

Therefore, 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 into complicated spaces is desired.
The former polylactic acid resin D-form and L-form copolymer preferably has a ratio of the lesser of the D-form and L-form of the optical isomer of less than 4 mol%. It is more preferably less than mol%, and particularly preferably less than 2 mol%.

In addition, the polylactic acid resin may contain a hydrolysis inhibitor carbodiimide compound, an oxazoline compound, an epoxy compound, an isocyanate compound, and the like.
Moreover, as said carbodiimide compound, what is necessary is just to have at least 2 carbodiimide group represented by (-N = C = N-) in a molecule | numerator, and as a polyvalent carbodiimide compound which has two or more carbodiimide groups, , Poly (4,4′-dicyclohexylmethanecarbodiimide), poly (4,4′-diphenylmethanecarbodiimide), poly (1,6-hexamethylenecarbodiimide), poly (1,3-cyclohexylenecarbodiimide), poly (1, 4-cyclohexylenecarbodiimide), poly (3,3′-dimethyl-4,4′-diphenylmethanecarbodiimide), poly (naphthylenecarbodiimide), poly (p-phenylenecarbodiimide), poly (m-phenylenecarbodiimide), poly ( 1,3,5-triisopropylbenzene carbodi Examples thereof include polycarbodiimide compounds such as (imide), poly (tolylcarbodiimide), and poly (diisopropylcarbodiimide).
The polycarbodiimide compound is commercially available, for example, from Nisshinbo under the trade name “Carbodilite LA-1”.

The isocyanate compound may have two or more isocyanate groups, and the polyvalent isocyanate compound having two or more isocyanate groups may be a polyfunctional aromatic isocyanate, a polyfunctional aliphatic isocyanate, an aromatic polyisocyanate. Either an isocyanate or an aliphatic polyisocyanate may be used, for example, diisocyanate compounds such as diphenylmethane diisocyanate, tolylene diisocyanate, xylene diisocyanate, hexamethylene diisocyanate; triphenylmethane triisocyanate, tris (p-isocyanatophenyl) thiophos Examples thereof include phyto and polymethylene polyphenyl polyisocyanate.
Moreover, as the compound having an epoxy group, an acrylic / styrene compound having an epoxy group is preferable, and an acrylic monomer having an epoxy group and a styrene monomer are contained as constituent monomer components. Vinyl polymers are preferred.

  Examples of the acrylic monomer having an epoxy group include glycidyl methacrylate, glycidyl acrylate, (3,4-epoxycyclohexyl) methyl methacrylate, and (3,4-epoxycyclohexyl) methyl acrylate. . Examples of the styrene monomer include styrene, α-methylstyrene, t-butylstyrene, chlorostyrene, and the like.

Further, the acrylic / styrene compound having an epoxy group may contain a monomer other than an acrylic monomer having an epoxy group and a styrene monomer as a constituent monomer component. Examples of the body include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate. An acrylate etc. are mentioned.
Acrylic / styrene compounds having an epoxy group are commercially available from Toa Gosei Co., Ltd. under the trade names “ARUFON UG-4000”, “ARUFON UG-4010”, “ARUFON UG-4030”, “ARUFON UG-4040”, “ARUFON UG-”, for example. 4070 ".

  Examples of the oxazoline compound include 2,2′phenylene bis (2-oxazoline), 2,2′phenylene bis (4-methyl-2-oxazoline), and 2,2′phenylene bis (4,4′-dimethyl-2). -Oxazoline), 2,2'-ethylenebisoxazoline, 2,2'-tetramethylenebisoxazoline, 2,2'-ethylenebis (4-methyl-2-oxazoline) and the like.

Here, when the foamed particles are obtained by the extrusion foaming method, the polylactic acid resin has a melting point (mp) at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by dynamic viscoelasticity measurement. It is preferable that the temperature T is adjusted so as to satisfy the following formula (A).
(Mp−40 ° C.) ≦ (temperature T at intersection) ≦ mp (A)
Here, the storage elastic modulus obtained by the dynamic viscoelasticity measurement is an index indicating elastic properties in the viscoelasticity, and is an index indicating the elasticity of the bubble film in the foaming process. This is an index indicating the magnitude of the foaming pressure required to expand the bubbles against the contraction force of the bubble film.

  That is, 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 with which 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 foamed particles, the bubble film may extend excessively, resulting in 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. For this reason, even if the bubbles once expand at the foaming pressure required for the production of the foamed particles, the bubbles may contract as the foaming pressure decreases with time due to a temperature drop or the like.

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.
In other words, if the loss elastic modulus obtained by the dynamic viscoelasticity measurement of polylactic acid resin is low, the cell membrane can be easily broken when the cell membrane is stretched by the foaming pressure required for producing the expanded particles. May end up. On the other hand, if the loss elastic modulus obtained by the dynamic viscoelasticity measurement of the polylactic acid resin is high, the foaming force is converted into thermal energy by the foam film, and the foam film is smoothly stretched during the production of the foamed particles. And it can be difficult to inflate the bubbles.
As described above, in producing foamed particles by foaming polylactic acid-based resin, the foaming process has an elastic force for appropriately expanding without breaking the cell membrane due to foaming pressure, that is, storage elastic modulus. It is preferable. In addition, the foaming force smoothly expands without breaking the bubble film, and the viscous force to maintain the bubble expanded to the desired size regardless of the decrease in foaming pressure over time, that is, It is preferable to have 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 to satisfy the following formula (A), more preferably to satisfy the following formula (B). By this adjustment, the foamed particles can be stably produced by making the extrusion foamability good while balancing the storage elastic modulus and the loss elastic modulus.
(Mp−40 ° C.) ≦ Temperature at intersection T ≦ mp (A)
(Mp−35 ° C.) ≦ temperature at intersection T ≦ (mp−10 ° C.) (B)
Furthermore, the reason why the temperature T and the melting point (mp) of the polylactic acid resin are preferably adjusted to satisfy the above formula (A) 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 and bubbles are broken. 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 against the viscous force is small, and the polylactic acid-based resin is difficult to foam, and good foamed 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 foam film breaks to cause good foaming. Particles may not be obtained. Conversely, 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, and even if the polylactic acid-based resin once foams, As the foaming power decreases, the air bubbles contract, and good foamed 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 formula (A), the reaction time or reaction temperature is adjusted during the polymerization of the polylactic acid resin. And a method of adjusting the weight average molecular weight of the polylactic acid resin to be obtained, and a method of adjusting the weight average molecular weight of the polylactic acid resin before or during extrusion foaming using a thickener or a crosslinking agent.

(2) Production of expanded particles Expanded particles can be produced by a known method. For example, the following extrusion foaming method is mentioned.
First, a polylactic acid resin is supplied to an extruder and melt kneaded in the presence of a foaming agent. Thereafter, the polylactic acid resin extrudate is extruded and foamed from the nozzle mold shown in FIGS. 1 and 2 attached to the front end of the extruder.
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.

  Moreover, what is conventionally used widely is used as a foaming agent. For example, chemical blowing agents such as azodicarbonamide, dinitrosopentamethylenetetramine, hydrazoyldicarbonamide, sodium bicarbonate; saturated aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, hexane, dimethyl ether, etc. Examples include physical foaming agents such as ethers, carbon dioxide, and nitrogen. Of these, 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 the foaming agent is small, the foamed particles may not be foamed 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 foamability may be reduced, and good foamed particles may not be obtained. In addition, the expansion ratio of the expanded particles may be too high to control the crystallinity. Therefore, the amount of the foaming agent is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 4 parts by weight, and particularly preferably 0.3 to 3 parts by weight with respect to 100 parts by weight of the polylactic acid resin.
In addition, it is preferable that a bubble regulator is added to an extruder. However, since many of the bubble regulators act as crystal nucleating agents for the expanded particles, it is preferable to use a bubble regulator that does not promote crystallization of the polylactic acid resin. Examples of such a bubble regulator include polytetrafluoroethylene powder and polytetrafluoroethylene powder modified with an acrylic resin.
On the other hand, if the amount of the air conditioner supplied to the extruder is small, the bubbles of the 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 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.

The polylactic acid-based resin extrudate extruded from the nozzle mold 1 continues into the cutting step. 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. .
All the rotary blades 5 are always rotating in contact with the front end face 1a of the nozzle mold 1. The polylactic acid resin extrudate extruded and foamed from the nozzle mold 1 is subjected to atmospheric air at a certain time interval due to shear stress generated between the rotary blade 5 and the edge of the nozzle outlet 11 in the nozzle mold 1. It is cut into foamed 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 non-foamed portion, which continues from the non-foamed portion immediately after being discharged from the nozzle outlet portion 11 of the nozzle mold 1. The foamed part.

  The non-foamed portion maintains its state from when it is projected from the outlet 11 of the nozzle of the nozzle mold 1 until foaming is started. The time during which this 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.

When the extrusion temperature of the polylactic acid-based resin (the temperature of the polylactic acid-based resin at the tip of the extruder) is low, fracture occurs and the obtained expanded particles are easily attached to each other. On the other hand, when the extrusion temperature of the polylactic acid-based resin is high, the decomposition of the polylactic acid-based resin is accelerated, and the foamability and open cell ratio of the expanded particles are likely to be lowered. Accordingly, the extrusion temperature is preferably 10 to 50 ° C. higher than the melting point of the polylactic acid resin, more preferably 15 to 45 ° C. higher than the melting point of the polylactic acid resin, and 20 times higher than the melting point of the polylactic acid resin. A temperature of ~ 40 ° C is particularly preferred.
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. The unfoamed portion immediately after being discharged from the outlet portion 11 is cut to produce expanded particles.

Since the obtained 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 expanded particles is covered with a skin layer having no bubble cross section. Therefore, the foamed particles have excellent foamability with no loss of foaming gas, have a low open cell ratio, and are excellent in surface heat-fusibility.
The surface of the expanded particle is formed from a skin layer in which the cell cross section is not exposed. For this reason, when foamed particles are used for in-mold foam molding, the heat-fusibility between the foamed particles is good, and the resulting foamed molded product has no surface unevenness and excellent appearance and excellent mechanical strength. doing.
The material constituting the skin is not particularly limited as long as it does not impair the effects of the present invention and can be practically used as a foam molded article. Specifically, a resin material such as a sheet or a film reinforced with the resin itself or a fiber material, a metal material such as aluminum, and the like can be given.

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 it is less than 2000 rpm, the polylactic acid resin extrudate may not be cut by the rotary blade 5. For this reason, the foam particles may coalesce or the shape of the foam particles may be non-uniform. If it exceeds 10,000 rpm, the following problems may occur. The first problem is that the initial velocity of the foamed particles may be increased when the cutting stress due to the rotary blade is increased and the foamed particles are scattered from the nozzle outlet toward the cooling member. As a result, the time from when the polylactic acid resin extrudate is cut until the foamed particles collide with the cooling member is shortened, and foaming of the foamed 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.

The foamed particles are scattered outward or forward simultaneously with the cutting due to the cutting stress by 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 foamed particles continue to foam until they collide with the cooling drum 41, and grow into a substantially spherical shape by foaming.
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 foam particles that collide with the inner peripheral surface of the peripheral wall portion 41b of the cooling drum 41 are immediately cooled to stop foaming. . Thus, after cutting the polylactic acid resin extrudate with the rotary blade 5, the foamed particles are immediately cooled with the cooling liquid 42, so that the degree of crystallinity of the polylactic acid resin constituting the foamed particles is increased. It is possible to prevent the foaming particles from being excessively foamed while being able to prevent the rise.
Accordingly, the foamed particles exhibit excellent foamability and heat-fusibility during in-mold foam molding. The crystallinity of the foamed particles can be increased during in-mold foam molding to improve the heat resistance of the polylactic acid resin, and the resulting foam molded article 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. The degree of crystallinity of the polylactic acid resin constituting the particles increases, and the heat-fusibility of the expanded particles may decrease. Therefore, the temperature is preferably 0 to 45 ° C, more preferably 5 to 40 ° C, and particularly preferably 10 to 35 ° C.
And the degree of crystallinity of the obtained expanded particles is preferably 30% or less, more preferably 3 to 28%, and particularly preferably 5 to 26%. The degree of crystallinity of the expanded particles can be adjusted by the time from when the polylactic acid resin extrudate is extruded from the nozzle mold 1 until the expanded particles collide with the coolant 42 and the temperature of the coolant 42.

When the bulk density of the foamed particles is small, the open cell ratio of the foamed particles may increase, and the foaming force necessary for the foamed particles may not be imparted during foaming in the in-mold foam molding. On the other hand, if it is large, the foamed particles obtained have non-uniform bubbles, and the foamability of the foamed particles during in-mold foam molding may be insufficient. Therefore, the bulk density is preferably 0.02~0.6g / cm ^3, more preferably ^{0.03~0.5g / cm 3, 0.04~0.4g / cm} 3 is particularly preferred.
If the open cell ratio of the foamed particles is high, the foamed particles hardly foam at the time of in-mold foam molding, the fusion property between the foamed particles is lowered, and the mechanical strength of the resulting foamed molded product is lowered. Sometimes. Therefore, the open cell ratio is preferably less than 20%, more preferably 10% or less, and particularly preferably 5% or less. The open cell ratio of the expanded particles is adjusted by adjusting the extrusion foaming temperature of the polylactic acid resin from the extruder, the supply amount of the foaming agent to the extruder, and the like.
In addition, if the particle size of the expanded particles is small, the expandability of the expanded particles may be reduced during in-mold expansion molding. On the other hand, if it is large, the filling property of the foamed particles in the mold may be lowered during the foam molding in the mold. Therefore, 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.

Divide the radius from the center of the polylactic acid-based resin expanded particle into four equal parts to form a layer region of P1, P2, P3, and P4 from the center, and the average bubble diameter of the bubbles present in the P4 layer region is 1 It is preferable that the average bubble diameter of the bubbles existing in the P1 layer region is 1 to 100. FIG. 3 is a schematic diagram for explaining a method for measuring the average cell diameter of the expanded particles. Specific measurement methods will be described in detail in Examples.
When the average bubble diameter of the bubbles existing in the P1 layer region is less than 1, the surface layer becomes too thick and it may be difficult to foam. On the other hand, if the average cell diameter exceeds 100, the cell membrane may be easily broken and the specified expansion ratio may not be reached. A preferable range of the average cell diameter is 1.1 to 95, and a more preferable range is 1.2 to 90.

(Method for producing polylactic acid-based resin foam molding)
The polylactic acid-based resin foam in the present invention means polylactic acid-based resin expanded particles or a heat-fused body thereof. That is, the polylactic acid resin foamed molded article of the present invention is obtained by filling the material constituting the skin with the polylactic acid resin foamed particles or the thermal fusion product thereof.
The method for producing a polylactic acid-based resin foamed molded article includes a polylactic acid-based resin before or after the water content of 1.5% by weight or less of the polylactic acid-based resin foam covers the entire surface of the polylactic acid-based resin foam with a skin. The foam is obtained by subjecting the foam to vacuum drying at a temperature of 70 ° C. or less and a degree of vacuum of 1 to 540 mmHg.
That is, the step of covering the polylactic acid-based resin foam with a skin may be performed before or after vacuum drying, and may be appropriately selected depending on the material of the skin, its shape, and the like.

The vacuum drying is not particularly limited as long as the moisture content of the polylactic acid resin foam can be 1.5% by weight or less. When the temperature and the degree of vacuum are low, the drying time may be long, and may be appropriately set depending on the material used and its state.
A drying temperature is 30-70 degreeC normally, Preferably it is 45-65 degreeC.
The degree of vacuum is 1 to 540 mmHg, more preferably 50 to 500 mmHg.
The drying time is usually 0.1 to 20 hours, preferably 0.5 to 10 hours.

  For example, the foamed particles obtained as described above are filled in a cavity of a mold and heated to foam the foamed particles. By this heating, the foamed particles can be fused and integrated with each other by their foaming pressure, so that a foamed molded article having excellent meltability can be obtained. Moreover, since the crystallinity degree of the polylactic acid-type resin which comprises a foamed particle can be raised by this heating, the foaming molding excellent in heat resistance can be obtained.

  In addition, it does not specifically limit as a heating medium of foamed particle, Hot air, warm water, etc. other than water vapor | steam are mentioned. Of these, it is preferable to use warm water. This is because hot water is liquid and has a large specific heat, so that a high amount of heat necessary for foaming can be sufficiently imparted to the foamed particles in the mold even when the temperature is low. Therefore, the foamed particles can be sufficiently heated and foamed without overheating. For this reason, the foamed particles can be strongly heat-bonded and integrated with each other by their foaming force without causing thermal contraction of the surface of the foamed particles as occurs when steam or hot air is used as the heating medium. As a result, the obtained foamed molded article has excellent mechanical strength and excellent appearance.

In addition, since the in-mold foam molding can be performed at a lower pressure than when high-pressure steam is used, the design strength of the mold can be kept low. Therefore, a mold having a complicated shape can be molded, and a compact mold can also be molded. As a result, the productivity of the foamed molded product can be improved.
When the temperature of the water used as the heating medium is low, foaming of the foam particles filled in the mold becomes insufficient, and the heat-fusibility between the foam particles is lowered. Therefore, the mechanical strength and appearance of the foamed molded product may be deteriorated. On the other hand, if it is high, water must be in a high-pressure state, and a large facility such as a boiler is required. Therefore, the temperature of water is preferably 60 to 100 ° C, more preferably 70 to 99 ° C, and particularly preferably 80 to 98 ° C.

The method for heating the foamed particles by supplying warm water to the foamed particles filled in the mold is not particularly limited. For example, (1) a method for supplying warm water instead of water vapor to a known in-mold foam molding machine (2) A method of molding with water vapor using a known in-mold foam molding machine (3) A method of immersing a mold filled with foamed particles in warm water. Of these, the method (3) is preferable, even if the mold has a complicated shape, in which the entire mold, that is, the polylactic acid resin foamed particles can be heated and foamed uniformly.
If the heating time of the foamed particles filled in the mold with hot water is short, the foamed particles are not sufficiently heated and the thermal fusion between the foamed particles is insufficient, or the crystallinity of the foamed particles is sufficient. May not rise. As a result, the heat resistance of the obtained foamed molded product may be lowered. On the other hand, when it is long, the productivity of the foamed molded product is lowered. The heating time is preferably 20 seconds to 1 hour.

After the in-mold foam molding, the foam molded body formed in the mold can be taken out by cooling and then opening the mold. If the cooling temperature of the foamed molded product is high, the foamed particles may not be sufficiently solidified. As a result, when it is taken out from the mold, it may swell and may not become a foamed molded product according to the cavity shape of the mold. Therefore, the cooling temperature is most preferably 0 so that the surface temperature of the foamed molded product is preferably 50 ° C. or less, more preferably 0 to 45 ° C., particularly preferably 0 to 40 ° C. It can set so that it may become -35 degreeC.
The cooling method is not particularly limited, but (1) a method of leaving the mold in an atmosphere of 50 ° C. or lower, (2) a method of spraying water or air of 50 ° C. or lower to the mold, and (3) a mold. Is immersed in water at 50 ° C. or lower. Among these, the cooling method (3) is preferable because even the mold having a complicated shape can cool the entire mold uniformly. The cooling time can be appropriately adjusted according to the cooling method and the size of the mold. For example, when the mold is immersed in water at 50 ° C. or lower, 1 to 10 minutes is preferable.

If the crystallinity of the foamed molded product is low, the heat resistance may decrease. On the other hand, if it is high, the foamed molded product may become brittle. Therefore, the crystallinity is preferably 40 to 65%, more preferably 45 to 64%, and particularly preferably 50 to 63%.
In addition, a metal mold | die is not specifically limited, For example, you may be comprised from the iron-type metal, the aluminum-type metal, the copper-type metal, the zinc-type metal etc. Among these, it is preferable that it is comprised from the aluminum-type metal from a heat conductive and workable viewpoint.

Furthermore, before the in-mold foam molding, the foamed particles may be further impregnated with an inert gas to improve the foaming power of the foamed particles. By improving the foaming force, the fusibility between the foamed particles is improved at the time of in-mold foam molding, and further excellent mechanical strength can be imparted to the resulting foam molded article. Examples of the inert gas include carbon dioxide, nitrogen, helium, and argon.
Examples of the method of impregnating the expanded particles with an inert gas include a method of impregnating the expanded particles with an inert gas by placing the expanded particles in an inert gas atmosphere having a pressure equal to or higher than normal pressure. The inert gas may be impregnated before the expanded particles are filled in the mold, or may be impregnated by placing the expanded particles in the inert gas atmosphere after filling the expanded particles in the mold. When the inert gas is carbon dioxide, it is preferable to leave the expanded particles in a carbon dioxide atmosphere of 0.1 to 1.5 MPa for 20 minutes to 24 hours. The pressure is based on atmospheric pressure.

The foamed particles further impregnated with an inert gas may be heated and foamed in the mold as they are, and heated and foamed before filling the foamed particles into the mold to produce foamed particles with a high expansion ratio. Then, it may be filled in a mold and heated and foamed. By using such expanded particles with a high expansion ratio, a foamed molded article with a high expansion ratio can be obtained. In addition, as a heating medium for heating the expanded particles, dry air is preferable.
In addition, even when filling into a mold after forming expanded particles with a high expansion ratio, the expanded particles are placed in an inert gas atmosphere of 0.1 to 1.5 MPa, preferably carbon dioxide for 20 minutes to 24 minutes. It is preferable that the foamed particles are impregnated with an inert gas to improve foamability over time.
As the temperature for forming expanded particles with a high expansion ratio, if the temperature is high, the degree of crystallinity of the polylactic acid-based resin may increase, and the heat-fusibility between the expanded particles may decrease. The mechanical strength and appearance of the molded body may be reduced. Therefore, the temperature is preferably less than 70 ° C.

  In addition, after completion of the polylactic acid-based resin foam molded article, even if the moisture content is adjusted by the above-described vacuum drying, the polylactic acid-based resin foam is further adjusted by adjusting the moisture content by the above-described vacuum drying, It may be combined to obtain a polylactic acid resin foam molded article.

(Polylactic acid resin foam molding)
The polylactic acid resin foamed molded article of the present invention preferably has a volume of 0.01 to 1000, where the volume of the skin is 1.
If the volume of the foam is less than 0.01, the skin becomes too much to be able to take advantage of the light weight characteristic of the foam, and the skin material may be expensive and may be expensive. On the other hand, when the volume of the foam exceeds 1000, the skin may be too thin and may be broken. A preferred range for the volume of the foam is 0.02 to 500.

The polylactic acid resin foamed molded article of the present invention has a compressive strength measured before (when the test is 0 hour) a moisture and heat resistance test for promoting hydrolysis (conditions: temperature 80 ° C., relative humidity 95%, 50 hours). It is preferable that the compressive strength CS ₅₀ measured after 50 hours of moist heat resistance test with respect to CS ₀ has a physical property of 50% or more.
The higher this ratio, the longer the stability can be expected. Preferably it is 55% or more, More preferably, it is 60% or more, The upper limit is about 100%.

The polylactic acid resin foamed molded product can be obtained by combining a polylactic acid resin foam with a known method.
As such a composite method, a method of covering the entire surface of the foam with a film, a method of covering the foam with a fiber reinforced plastic (hand lay-up method, spray-up method, SMC press method, RTM method, vacuum bag) A molding method, a filament wind method, etc.), a method of filling a metal having a cavity and covering the entire surface of the foam.

  The resulting polylactic acid-based resin foamed molded article is used for shock absorbers such as household appliances (cushion materials), electronic parts, various industrial materials, food containers, etc., automobile-related parts (for example, door interior cushioning materials) Energy absorbers, sun visors, tibia pads, etc.), and particularly suitable for structural members of automobiles, trains or airplanes, or for packaging materials of electronic parts.

Hereinafter, the present invention will be specifically described with reference to production examples, examples and comparative examples. However, the following production examples and examples are only exemplifications of the present invention, and the present invention is limited to the following production examples and examples. Not.
In the examples and comparative examples, the obtained polylactic acid resin foamed molded products were evaluated as follows.

(amount of water)
Using a polylactic acid resin foamed molded article as a sample, 0.05 g was accurately weighed, and using a trace moisture measuring device (manufactured by Hiranuma Sangyo Co., Ltd., model: AQ-2100), the moisture content (by Karl Fischer method at a heating temperature of 150 ° C.) %).

(Compression test)
The compressive strength is measured by the method described in JIS K6767: 1999 “Foamed Plastics—Polyethylene—Test Method”. That is, using a Tensilon universal testing machine UCT-10T (manufactured by Orientec Co., Ltd.), the compression strength at the time of 25% compression (at the time of 10 mm displacement) is set at a compression speed of 10 mm / min for a test body of 50 mm × 50 mm × 20 mm. taking measurement.
The compressive strength before the wet heat resistance test of the sample for compressive strength test (at 0 hour) and the compressive strength after 50 hours of the wet heat resistance test are measured, and the ratio of the latter to the former is calculated.
From the obtained results, 50% or more is evaluated as “◯”, and less than 50% is evaluated as “×”.

(Average bubble diameter)
Calculation is based on the average chord length measured according to the test method of ASTM D2842-69.
Specifically, the polylactic acid-based resin expanded particles are cut in an arbitrary direction, and the polylactic acid-based resin expanded particles are equally divided into four radii from the central portion toward the epidermis, and P1, P2, and P3 are respectively formed from the central portions. And a P4 layer region, and a scanning electron microscope at a section of each of the P1 layer region and the P4 layer region is magnified 100 times and photographed.
Next, the average chord length (t) of each bubble is calculated based on the following formula from the number of bubbles on a straight line having a length of 60 mm in each photograph taken.
Average chord length (t) = 60 / (number of bubbles × photo magnification)
And the bubble diameter D in each photograph is calculated by the following formula, and the arithmetic mean of the bubble diameters in each photograph is taken as the average bubble diameter of the styrene resin foam molded article.
Bubble diameter D = t / 0.616
Each average bubble diameter calculated | required from these is compared and evaluated.

(Production Example 1)
Polylactic acid resin expanded particles were produced as follows.
First, a crystalline polylactic acid resin (manufactured by Unitika Ltd., product name: Terramac HV-6250H, melting point: 169.1 ° C., D-form ratio: 1.2 mol%, L-form ratio: 98.8 mol%, Weight average molecular weight: 2.5 × 10 ⁴ ) 100 parts by weight and 0.1 part by weight of polytetrafluoroethylene powder (manufactured by Asahi Glass Co., Ltd., product name: Fullon L169J) as a bubble regulator The mixture was first melt-kneaded at 190 ° C. and then melt-kneaded while raising the temperature to 220 ° C.
Subsequently, from the middle of the single-screw extruder, butane consisting of 35% by weight of isobutane and 65% by weight of normal butane as a foaming agent was melted so as to be 1.0 part by weight with respect to 100 parts by weight of the polylactic acid resin. The solution was press-fitted into a polylactic acid resin and uniformly dispersed in the polylactic acid resin.

Then, after cooling the molten polylactic acid resin to 200 ° C. at the front end of the single screw extruder, each of the multi-nozzle molds 1 (see FIGS. 1 and 2) attached to the front end of the single screw extruder. Polylactic acid resin foamed particles are produced by extruding and foaming polylactic acid resin from the nozzle at a shear rate of 7639 seconds- ¹ and rotating with a rotating blade rotating at 4800 rpm while contacting the front end surface of the multi-nozzle mold. did. The temperature of the multi-nozzle mold was maintained at 200 ° C. The polylactic acid-based resin foamed particles were blown outward or forward by the cutting stress of the rotary blade, and were immediately cooled by colliding with the cooling water flowing along the inner surface of the cooling drum.
The cooled polylactic acid resin foamed 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 surface of the obtained polylactic acid-based resin expanded particles was entirely covered with a skin layer. There was no bubble cross section in the skin layer.

The multi-nozzle mold 1 had 20 nozzles having a diameter of 1.0 mm at the outlet portion 11 and was arranged at equal intervals on a virtual circle A having a diameter of 139.5 mm.
Four rotary blades 5 are integrally provided at equal intervals in the circumferential direction of the rotary shaft 2 on the outer peripheral surface of the rear end portion of the rotary shaft 2, and each rotary blade 5 is a multi-nozzle mold 1. It is configured to move on the virtual circle A while always in contact with the front end face 1a.
In addition, a cylindrical cooling drum 41 having an inner diameter of 315 mm was provided around the multi-nozzle mold 1, and the cooling water 42 flowed spirally inside thereof.
In the figure, 3 is a driving motor, 41a is a front part, 41b is a peripheral wall part, 41c is a supply port, 41d is a supply pipe, and 41f is a discharge pipe.

  The average bubbles of the bubbles present in the P4 layer region are obtained by dividing the radius from the center of the obtained polylactic acid resin expanded particles into four equal areas from the center to the layer regions of P1, P2, P3 and P4. When the diameter was 1, the average bubble diameter of the bubbles present in the P1 layer region was 2.0.

Next, the obtained polylactic acid-based resin expanded particles are put into a sealed container having an internal volume of 10 L, and carbon dioxide (CO ₂ ) is pressed into the sealed container through a pressure regulating valve at a pressure of 1.0 MPa, and the temperature is 20 After leaving at 24 ° C. for 24 hours, the polylactic acid resin expanded particles impregnated with carbon dioxide were taken out with the pressure in the sealed container set to atmospheric pressure.
The polylactic acid-based resin expanded particles impregnated with carbon dioxide were put into a warm air generator and heated at a hot air temperature of 60 ° C. for 3 minutes to secondary-expand the polylactic acid-based resin expanded particles.

  Next, the obtained polylactic acid-based resin expanded particles are placed in a sealed container having an internal volume of 10 L, carbon dioxide is injected into the sealed container at a pressure of 0.6 MPa, and left at a temperature of 20 ° C. for 24 hours to be polylactic acid-based. The resin foam particles were impregnated with carbon dioxide.

  Next, the obtained 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 100mm * width 300mm * height 30mm. Further, in order to allow the inside of the mold cavity to communicate with the outside of the mold, a circular supply port having a diameter of 8 mm is arranged at intervals of 20 mm in the mold. Furthermore, each supply port is provided with a grid portion having an opening width of 1 mm so that the polylactic acid resin foam particles filled in the mold do not 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 supply port.

Next, a mold filled with polylactic acid-based resin expanded particles was completely immersed in warm water maintained at a temperature of 95 ° C. in a 300 L heated water tank for 1 minute. As a result, warm water is supplied to the polylactic acid resin foam particles in the mold cavity through the mold supply port, the polylactic acid resin foam particles are heated and foamed, and the polylactic acid resin foam particles are integrated by heat fusion. did.
Next, the mold was taken out from the heated water tank, and the mold was completely immersed in water maintained at a temperature of 20 ° C. in a cooling water tank having another internal volume of 300 L for 5 minutes. As a result, the polylactic acid resin foam molded body in the mold was cooled.
Next, 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-based resin foam molded article had a very excellent appearance, and its density was 0.05 g / cm ³ .

Example 1
The polylactic acid-based resin foam molded body obtained in Production Example 1 is vacuum-dried for 60 minutes in a vacuum dryer (manufactured by Tabai Espec Co., Ltd. (currently Espec Co., Ltd.)) at a temperature of 40 ° C. and a vacuum of 360 mmHg Went.
Next, the dried polylactic acid resin foamed molded article is cut in half, and one of them is cut into a size of 50 mm × 50 mm × 20 mm for a compressive strength test, and an ethylene-vinyl alcohol copolymer film having a high barrier property (Co., Ltd.) Made by Kuraray, product name: EVAL EF-F, moisture permeability 70g / m ² · 24 hours), covering the entire surface of the molded product and heat-sealing the boundary, composite of film and polylactic acid resin foam molding A sample for compressive strength test as a body was obtained.
The volume of the polylactic acid resin foam when the volume of the epidermis was 1 was 280.

Next, the compressive strength test sample was heat and moisture resistant at a temperature of 80 ° C., a relative humidity of 95%, and a time of 50 hours in a low-temperature constant temperature and humidity chamber (manufactured by Isuzu Seisakusho, model: HPAV-120-20). A test was conducted.
Next, the compressive strength (test 0 hour) of the test piece that was not subjected to the moist heat resistance test and the compressive strength of the test piece after 50 hours of the moist heat resistance test were measured, and 50 hours against the compressive strength of the 0 hour moist heat resistance test. When the ratio (percentage) of the subsequent compressive strength was calculated, it was 50% or more (65%).
In addition, about 50 mg of a molded product in the vicinity of 10 mm from the center of the cut surface of the other dried polylactic acid resin foamed molded product, which was halved, was measured for moisture content by the Karl Fischer method. %Met.

(Example 2)
The polylactic acid resin foamed molded article obtained in Production Example 1 was subjected to the same process as in Example 1 except that it was vacuum dried for 60 minutes under the conditions of a temperature of 50 ° C. and a vacuum of 360 mmHg. The moisture content of the molded body was measured, and a sample for a compressive strength test, which was a composite of a film and a polylactic acid-based resin foam molded body, was prepared to evaluate the compressive strength after the wet heat resistance test.
The moisture content was 0.61%, and the ratio of the compressive strength after 50 hours to the compressive strength after 0 hours of the moist heat resistance test was 50% or more (68%).

(Example 3)
The polylactic acid resin foamed molded product obtained in Production Example 1 was subjected to the same process as in Example 1 except that it was vacuum dried for 60 minutes under the conditions of a temperature of 60 ° C. and a vacuum of 360 mmHg. The moisture content of the molded body was measured, and a sample for a compressive strength test, which was a composite of a film and a polylactic acid-based resin foam molded body, was prepared to evaluate the compressive strength after the wet heat resistance test.
The moisture content was 0.51%, and the ratio of the compressive strength after 50 hours to the compressive strength after 0 hours of the moist heat resistance test was 50% or more (68%).

Example 4
The polylactic acid resin foamed molded product obtained in Production Example 1 was subjected to the same process as in Example 1 except that it was vacuum dried for 60 minutes under the conditions of a temperature of 65 ° C. and a vacuum of 360 mmHg. The moisture content of the molded body was measured, and a sample for a compressive strength test, which was a composite of a film and a polylactic acid-based resin foam molded body, was prepared to evaluate the compressive strength after the wet heat resistance test.
The moisture content was 0.35%, and the ratio of the compressive strength after 50 hours to the compressive strength after 0 hours of the moist heat resistance test was 50% or more (75%).

(Example 5)
Except that the polylactic acid-based resin expanded particles obtained in Production Example 1 were used to produce a composite with metallic aluminum, and that vacuum drying was performed for 60 minutes at a temperature of 60 ° C. and a vacuum of 360 mmHg. In the same manner as in Example 1, the moisture content was measured, and the compressive strength after the wet heat resistance test was evaluated.
The moisture content was 0.77%, and the ratio of the compressive strength after 50 hours to the compressive strength after 0 hours of the moist heat resistance test was 50% or more (65%).

A composite was prepared as follows.
The polylactic acid resin expanded particles obtained in Production Example 1 are placed in an aluminum tube (moisture permeability of 0 g / m ² · 24 hours) having an outer diameter of 50 mm × 100 mm × thickness that is open at both ends. It was fastened with (mesh 16 mesh).
Next, the aluminum tube filled with the polylactic acid-based resin expanded particles was completely immersed in warm water maintained at a temperature of 95 ° C. in a 300 L heated water tank for 1 minute. As a result, hot water is supplied to the polylactic acid-based resin expanded particles in the aluminum tube through the mesh of the wire mesh, the polylactic acid-based resin expanded particles are heated and foamed, and the polylactic acid-based resin expanded particles are thermally fused and integrated with each other. A composite with a polylactic acid resin foamed molded product was obtained.
The volume of the polylactic acid resin foam when the volume of the skin was 1 was 6.
Next, the aluminum pipe was taken out from the heated water tank, and the aluminum pipe was completely immersed in water maintained at a temperature of 20 ° C. in a cooling water tank having another internal volume of 300 L for 5 minutes. As a result, the polylactic acid resin foam molded body in the aluminum tube was cooled.
The obtained composite is vacuum-dried under the above-mentioned conditions, and is halved. One end of the composite is sealed with an aluminum plate, and the compact is 10 mm from the center of the other cut surface. Was subjected to moisture measurement.

(Example 6)
Using the polylactic acid resin foam molded article obtained in Production Example 1, a composite with FRP (glass fiber reinforced resin) was prepared, and vacuum drying was performed for 60 minutes under conditions of a temperature of 60 ° C. and a vacuum degree of 360 mmHg. Except that, the moisture content was measured in the same manner as in Example 1, and the compressive strength after the wet heat resistance test was evaluated.
The moisture content was 0.69%, and the ratio of the compressive strength after 50 hours to the compressive strength after 0 hours of the moist heat resistance test was 50% or more (70%).

A composite was prepared as follows.
The polylactic acid-based resin foam molded body obtained in Production Example 1 is cut into a specified size (45 mm × 45 mm × 15 mm) and cured in advance to a glass cloth (manufactured by Nittobo, product name: WF 230 N 100). (Polyester resin, manufactured by Epoch, product name: Aero Car Range) put in FRP (moisture permeability of 170 g / m ² · 24 hours) that has been hardened, and a sample for compressive strength test of a 50 mm × 50 mm × 20 mm composite Obtained. The cut polylactic acid resin foamed molded article was used as a moisture content measurement sample.
The volume of the polylactic acid resin foam when the volume of the skin was 1 was 12.

(Example 7)
Using the polylactic acid resin foam molded article obtained in Production Example 1, a composite with CFRP (carbon fiber reinforced resin) was prepared, and vacuum drying was performed for 60 minutes under conditions of a temperature of 60 ° C. and a vacuum degree of 360 mmHg. Except that, the moisture content was measured in the same manner as in Example 1, and the compressive strength after the wet heat resistance test was evaluated.
The moisture content was 0.80%, and the ratio of the compressive strength after 50 hours to the compressive strength after 0 hours of the moist heat resistance test was 50% or more (65%).

A composite was prepared as follows.
The polylactic acid resin foam molded body obtained in Production Example 1 is cut into a specified size of 50 mm × 50 mm × 20 mm, and the surface is coated with a carbon fiber cloth prepreg (product name: F6347B-05P). A sample for compressive strength test of a 50 mm × 50 mm × 20 mm composite was obtained by the autoclave method. The moisture permeability of CFRP was 170 g / m ² · 24 hours. The cut polylactic acid resin foamed molded article was used as a moisture content measurement sample.
The volume of the polylactic acid resin foam when the volume of the epidermis was 1 was 50.

(Comparative Example 1)
Except that the polylactic acid resin foam molded article obtained in Production Example 1 was dried without being subjected to vacuum conditions, the water content of the polylactic acid resin foam molded article was measured in the same manner as in Example 1, Furthermore, a sample for a compressive strength test, which is a composite of a film and a polylactic acid resin foamed molded product, was prepared, and the compressive strength after the wet heat resistance test was evaluated.
The moisture content was 4.8%, and the compressive strength after 50 hours with respect to the compressive strength after 0 hours of the moist heat resistance test was less than 50% (10%).

(Comparative Example 2)
Except that the polylactic acid resin foam molded article obtained in Production Example 1 was dried without being subjected to vacuum conditions, the water content of the polylactic acid resin foam molded article was measured in the same manner as in Example 2, Furthermore, a sample for a compressive strength test, which is a composite of a film and a polylactic acid resin foamed molded product, was prepared and the compressive strength after the wet heat resistance test was evaluated.
The moisture content was 4.0%, and the compressive strength after 50 hours with respect to the compressive strength after 0 hours of the moist heat resistance test was less than 50% (10%).

(Comparative Example 3)
Except that the polylactic acid resin foam molded article obtained in Production Example 1 was dried without being subjected to vacuum conditions, the water content of the polylactic acid resin foam molded article was measured in the same manner as in Example 3, Furthermore, a sample for a compressive strength test, which is a composite of a film and a polylactic acid resin foamed molded product, was prepared, and the compressive strength after the wet heat resistance test was evaluated.
The moisture content was 2.8%, and the compressive strength after 50 hours with respect to the compressive strength after 0 hours of the moist heat resistance test was less than 50% (20%).

(Comparative Example 4)
Except that the polylactic acid resin foam molded article obtained in Production Example 1 was dried without being subjected to vacuum conditions, the water content of the polylactic acid resin foam molded article was measured in the same manner as in Example 4, Furthermore, a sample for a compressive strength test, which is a composite of a film and a polylactic acid resin foamed molded product, was prepared, and the compressive strength after the wet heat resistance test was evaluated.
The moisture content was 2.5%, and the compressive strength after 50 hours with respect to the compressive strength after 0 hours of the moist heat resistance test was less than 50% (20%).

(Comparative Example 5)
Except that the polylactic acid resin foam molded article obtained in Production Example 1 was dried without vacuum conditions, the water content of the polylactic acid resin foam molded article was measured in the same manner as in Example 5, Furthermore, a sample for a compressive strength test, which is a composite of metallic aluminum and a polylactic acid resin foamed molded product, was prepared, and the compressive strength after the wet heat resistance test was evaluated.
The moisture content was 4.5%, and the compressive strength after 50 hours was 0% (7%) with respect to the compressive strength of the wet heat resistance test 0 hours.

(Comparative Example 6)
Except that the polylactic acid resin foam molded article obtained in Production Example 1 was dried without being subjected to vacuum conditions, the water content of the polylactic acid resin foam molded article was measured in the same manner as in Example 6, Furthermore, a sample for compressive strength test, which is a composite of FRP (glass fiber reinforced resin) and a polylactic acid resin foamed molded product, was prepared, and the compressive strength after the wet heat resistance test was evaluated.
The moisture content was 4.0%, and the compressive strength after 50 hours with respect to the compressive strength after 0 hours of the moist heat resistance test was less than 50% (5%).

(Comparative Example 7)
Except that the polylactic acid resin foam molded article obtained in Production Example 1 was dried without vacuum conditions, the water content of the polylactic acid resin foam molded article was measured in the same manner as in Example 7, Furthermore, a sample for compressive strength test, which is a composite of CFRP (carbon fiber reinforced resin) and a polylactic acid resin foamed molded product, was prepared, and the compressive strength after the wet heat resistance test was evaluated.
The moisture content was 4.0%, and the compressive strength after 50 hours with respect to the compressive strength after 0 hours of the moist heat resistance test was less than 50% (8%).

  Compared with the conventional polylactic acid-based resin foamed molded products (Comparative Examples 1-7), the polylactic acid-based resin foamed molded products (Examples 1-7) have a compressive strength after a moist heat resistance test for promoting hydrolysis. It can be seen that there is little decrease in the strength, the strength can be maintained for a long time, and it can be used stably as various structural members and packing materials.

DESCRIPTION OF SYMBOLS 1 Multi-nozzle metal mold | die 1a Front end surface 2 Rotating shaft 3 Motor 4 Cooling drum 5 Rotating blade 11 Outlet part 41 Cooling drum 41a Front part 41b Peripheral wall part 41c Supply port 41d Supply pipe 41e Discharge port 41f Discharge tube 42 Cooling water A Virtual circle C Foamed particle center P1, P2, P3, P4 Four equal areas from the center of the foamed particle

Claims (6)

It is composed of at least a polylactic acid resin foam and a skin covering the entire surface thereof, the polylactic acid resin foam has a water content of 1.5% by weight or less, and the skin is 200 g / m ² · 24 hours. A polylactic acid-based resin foamed molded article comprising a non-moisture permeable material having the following moisture permeability. The polylactic acid-based resin foam is composed of polylactic acid-based resin foam particles or a heat-fused body thereof,
The polylactic acid-based resin expanded particles are divided into four equal radii from the central portion toward the epidermis to form P1, P2, P3 and P4 layer regions from the central portion, respectively, and the average of the bubbles present in the P4 layer region The polylactic acid-based resin foam-molded article according to claim 1, having a physical property in which an average cell diameter of bubbles present in the P1 layer region is 1 to 100 when the cell diameter is 1.   The polylactic acid-based resin foam molded article according to claim 1 or 2, wherein the polylactic acid-based resin foam has a volume of 0.01 to 1000, where the volume of the skin is 1. The polylactic acid-based resin foamed molded product was measured for compressive strength CS ₀ before performing a heat-and-moisture resistance test (conditions: temperature 80 ° C., relative humidity 95%, 50 hours) for promoting hydrolysis. for polylactic acid resin foamed molded article according to any one of claims 1 to 3 ratio of the compressive strength CS ₅₀ measured after the wet heat test 50 hours has physical properties at least 50%.   The polylactic acid-based resin foamed molded product according to any one of claims 1 to 4, wherein the polylactic acid-based resin foamed molded product is for a structural member of an automobile, a train or an airplane, or a packaging material for an electronic component.   It is a manufacturing method of the polylactic acid-type resin foam molding as described in any one of Claims 1-5, and the water content of 1.5 weight% or less of the said polylactic acid-type resin foam is said polylactic acid-type resin. Polylactic acid obtained by subjecting the polylactic acid-based resin foam to vacuum drying at a temperature of 70 ° C. or lower and a vacuum degree of 1 to 540 mmHg before or after covering the entire surface of the foam with a skin. For producing a resin-based resin foam molded article.