JP2011213890A - Method for reducing odor in polylactic acid-based resin foamed particle, polylactic acid-based resin foamed particle, and foam molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reducing odor in polylactic acid-based foamed particles.SOLUTION: The method for reducing odor in polylactic acid-based foamed particles is characterized in that: odor derived from polylactic acid-based resin foamed particles is reduced by fluidizing the polylactic acid-based resin foamed particles in a container by a gas at a temperature of (T-40) to (T+15)°C (where T represents the glass transition temperature of the polylactic acid-based resin); and an average of odor intensity of a foam molded article obtained from the polylactic acid-based resin foamed particles having reduced odor is 3 or less in an odor test in which the odor of isovaleric acid diluted by 100,000 times is used as a standard odor indicating a level of 3 in odor intensity levels of from 0 to 5.

Description

  The present invention relates to a method for reducing odor in polylactic acid-based resin expanded particles, polylactic acid-based resin expanded particles, and an expanded molded article.

  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, Japanese Patent No. 4213200 proposes a technique for obtaining a foam molded body having a desired shape by molding polylactic acid resin foamed particles in a mold.

Japanese Patent No. 4213200

  By the way, in applications such as automobile-related parts and building materials, it is desired to reduce raw materials and additives-derived odors generated from the resin. In this respect, since the polylactic acid resin is a resin having relatively little odor, the odor has not been reduced so far. However, even in polylactic acid resins, odors derived from hydrolysis inhibitors added to impart durability, and odors derived from residual raw materials and decomposition products of polylactic acid resins may occur. The inventors thought that reducing these odors would be a future challenge.

Thus, according to the present invention, the polylactic acid resin expanded particles are made to flow in a container with a gas of (T-40) to (T + 15) ° C. (T is the glass transition temperature of the polylactic acid resin). Reduced odor derived from lactic acid-based resin expanded particles, the average value of odor intensity of foamed molded products obtained from polylactic acid-based resin expanded particles with reduced odor is the odor of isovaleric acid diluted 100000 times There is provided a method for reducing odor in polylactic acid-based resin expanded particles, which is 3 or less in an odor test with a reference odor of 3 in intensity from 0 to 5.
Further, according to the present invention, the foamed polylactic acid resin particles, wherein the polylactic acid resin foamed particles have an odor intensity of 0 to 5 levels of odor intensity of isovaleric acid diluted 100000 times. Thus, a foamed polylactic acid resin particle is provided, which gives a foamed molded product having an index of 3 or less in an odor test with a reference odor of 3.
Moreover, according to this invention, the foamable molded object obtained by carrying out the internal molding of the said polylactic acid-type resin expanded particle is provided.

According to the present invention, polylactic acid-based resin expanded particles with less odor can be obtained. As a result, it is possible to obtain a foamed molded article that can be used for applications such as automobile-related parts and building materials that require a low level of odor content.
Moreover, the polylactic acid-type resin expanded particle which gives a foaming molding with less odor can be obtained by putting the polylactic acid-type resin expanded particle in the container in the state which injected gas from the container lower part.
Furthermore, the polylactic acid-based resin expanded particles contain both D-isomer and L-isomer optical isomers, and the content of the lesser of the D-isomer or L-isomer is less than 5 mol%. Polyethylene which gives a foamed molded article excellent in heat dimensional stability by being derived from a component or derived from a monomer component containing only one of the optical isomers of D-form or L-form Lactic acid-based resin expanded particles can be obtained.

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.

The method of reducing odor in the polylactic acid-based resin expanded particles (hereinafter also simply referred to as expanded particles) of the present invention is as follows. The expanded particles are placed in a container at (T-40) to (T + 15) ° C. (T is a polylactic acid-based resin). It is a method of making it flow with the gas of glass transition temperature.
In the present invention, the odor is derived from a hydrolysis inhibitor added for imparting durability of the polylactic acid resin, a residual raw material of the polylactic acid resin, and a decomposition product. Examples thereof include compounds derived from hydrolysis inhibitors such as carbodiimide compounds, oxazoline compounds, epoxy compounds, isocyanate compounds, residual raw materials such as lactic acid monomers and lactides, and compounds derived from decomposition products.
In the present invention, since the foamed particles are flowed by blowing gas from the lower part of the container, the odor can be efficiently reduced. Here, the gas is air, an inert gas (for example, nitrogen) or the like, and usually air is used.

(Odor reduction conditions)
The container used in the present invention is a container capable of causing particles in the container to flow while blowing gas from the lower part of the container, and the shape of the container is not particularly limited as long as there is a gas blowing port in the lower part. The container usually has a discharge port in the upper part for discharging the blown gas. In the lower part of the container, it is preferable to provide a countersink plate for preventing foam particles from entering the blowing port. A number of holes through which gas can normally pass are provided in the eye plate. This hole may have a shape that blows gas vertically or may have a shape that blows obliquely. From the viewpoint of increasing the odor reduction efficiency, it is preferable to use a countersunk plate having holes of both shapes. Furthermore, in order to increase the odor reduction efficiency, a stirring device may be provided in the container. As such a container, for example, a fluidized bed drying apparatus generally used for drying granular materials can be used. Specifically, a swirl type fluidized bed drying apparatus with a built-in bug (for example, Slit Flow (registered trademark) (FBS type) manufactured by Okawara Seisakusho) can be used.

In the method of the present invention, the expanded particles may be put into the container before the gas is blown from the lower part of the container, or may be put into the container with the gas blown from the lower part of the container. Among these, it is preferable from the viewpoint of improving the odor reduction efficiency that the gas is blown from the lower part of the container into the container.
The temperature of the gas used in the present invention is a temperature of (T-40) to (T + 15) ° C. when the glass transition temperature of the polylactic acid resin is T ° C. When the temperature is lower than (T-40) ° C., the odor may not be sufficiently reduced. When the temperature is higher than (T + 15) ° C., the foamed particles may be bonded to each other, and the crystallinity of the foamed particles may be increased, so that molding may not be possible. More preferable gas temperatures are (T-20) to (T + 15). In addition, the glass transition temperature of the polylactic acid-type resin said here means the glass transition temperature said by JISK7121-1987.

The gas flow rate is greater than or equal to the minimum flow rate required to cause the expanded particles in the container to flow and can vary depending on the particle size and amount of the expanded particles in the container.
The flow rate of the gas can be changed according to the air volume of the blown gas, and the fluidity can be adjusted by adjusting the air volume. When the air volume is small, the expanded particles may not flow sufficiently. Moreover, when there is much air volume, foamed particles may be scattered. In order to make the expanded particles flow more efficiently, a preferable range of the air volume is 0.1 to 2.0 m / second, and a more preferable range is 0.5 to 1.6 m / second. The appropriate air volume can be determined by the pressure loss experienced when the blown gas passes through the expanded particles. The pressure loss is preferably in the range of 1 to 10 kpa, more preferably in the range of 2 to 6 kpa. If the pressure loss due to the foamed gas particles is within this range, the foamed particles can be reliably flowed.

  The gas blowing time varies depending on the gas temperature and the flow velocity. When the gas temperature is constant, the time decreases as the flow velocity increases, and conversely, the time increases as the flow velocity decreases. On the other hand, when the gas flow rate is constant, the time is shortened if the temperature is high, whereas the time is long if the temperature is low. In any case, the odor contained in the foamed molded product obtained from the polylactic acid resin foamed particles is the odor intensity of isovaleric acid diluted 100000 times. In the odor test, the average value of the odor intensity is 3 or less.

(Polylactic acid resin foamed 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 -One or two or more ring-opened polymers of lactide selected from the group consisting of lactide.
Here, the copolymer of D-form and L-form in which the ratio of the lesser optical isomer of D-form or L-form is less than 5 mol%, and the single weight of either D-form or L-form The coalescence tends to increase in crystallinity and melting point as the smaller optical isomer decreases. On the other hand, a copolymer of D-form and L-form in which the ratio of the smaller optical isomer of D-form or L-form is 5 mol% or more increases 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 in complicated spaces is desired.
In addition, the latter polylactic acid-based resin can improve the heat resistance of a foamed molded product obtained by filling foamed particles in a mold and foaming, so that the foamed molded product maintains its form even at high temperatures. it can. 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.
Further, in the copolymer of D-form and L-form, the ratio of the smaller one of D-form and L-form is preferably less than 4 mol%, and less than 3 mol%. More preferably, it is particularly preferably less than 2 mol%.

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. It may be either an isocyanate or an aliphatic polyisocyanate, for example, diisocyanate compounds such as diphenylmethane diisocyanate, tolylene diisocyanate, xylene diisocyanate, hexamethylene diisocyanate; triphenylmethane triisocyanate, tris (p-isocyanatophenyl) thiophos Phyto, polymethylene polyphenyl polyisocyanate and the like.
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, (3,4-epoxycyclohexyl) methyl acrylate, and the like. . 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 1.
(Melting point of polylactic acid resin (mp) -40 ° C)
≦ (temperature T at the intersection) ≦ melting point of polylactic acid resin (mp) Formula 1
Here, the storage elastic modulus obtained by the dynamic viscoelasticity measurement is an index indicating elastic properties in the viscoelasticity, and is an index indicating the elasticity of the bubble film in the foaming process. This is an index indicating the magnitude of the foaming pressure required to expand the bubbles against the contraction force of the bubble film.

  That is, when the storage elastic modulus obtained by the dynamic viscoelasticity measurement of the polylactic acid-based resin is low, when the cell membrane is stretched, the force that the cell membrane attempts to contract against the stretching force is small. Therefore, as a result of the foaming film easily extending due to the foaming pressure required for the production of the 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.
That is, 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 the production of 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 a polylactic acid-based resin, in the foaming process, the foam film has an elastic force for appropriately stretching without breaking the foam film, that is, a storage elastic modulus. It is preferable. In addition, the foam force smoothly expands without breaking the bubble film, and the viscous force to maintain the expanded bubble to the desired size regardless of the decrease in the foam pressure over time, that is, It 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 so as to satisfy the following formula 1, more preferably satisfy the formula 2. By this adjustment, the foamed particles can be stably produced by making the extrusion foamability good while balancing the storage elastic modulus and loss elastic modulus.
[Melting point of polylactic acid resin (mp) −40 ° C.]
≦ Temperature at the intersection T ≦ Melting point of polylactic acid resin (mp) Formula 1
[Melting point of polylactic acid resin (mp) -35 ° C.]
≦ Temperature at the intersection T ≦ [Melting point of polylactic acid resin (mp) −10 ° C.] Formula 2
Further, the reason why the temperature T and the melting point (mp) of the polylactic acid resin are preferably adjusted so as to satisfy the above formula 1 will be described in detail below.

First, when the temperature T is lower than the melting point (mp) of the polylactic acid resin by more than 40 ° C., the loss elastic modulus of the polylactic acid resin at the time of extrusion foaming is too large compared to the storage elastic modulus. In addition, the balance between the loss elastic modulus and the storage elastic modulus is lost.
Therefore, if the foaming force suitable for the loss elastic modulus of the polylactic acid-based resin, that is, the foaming force matched to the viscosity, the foaming force with respect to the elastic force is too large, and the bubble film is broken and bubbles are broken. Expanded particles may not be obtained. On the contrary, if the foaming force suitable for the storage elastic modulus of the polylactic acid-based resin, that is, the foaming force matched to the elasticity, the foaming force with respect to the viscous force is small, and the polylactic acid-based resin is difficult to foam, and good 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 bubble film is broken to cause bubble breakage and good foaming. Particles may not be obtained. On the contrary, if the foaming force suitable for the loss elastic modulus of the polylactic acid-based resin, that is, the foaming force matched to the viscosity, the foaming force with respect to the elastic force is small. As the foaming power decreases, the air bubbles contract, and good 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-based resin so as to satisfy the above formula 1, the reaction time or the reaction temperature is adjusted during the polymerization of the polylactic acid-based resin. Examples thereof include a method of adjusting the weight average molecular weight of the lactic acid resin, 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, a 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, hydrazoyl dicarbonamide, 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 unfoamed portion, which continues from the unfoamed portion immediately after being discharged from the nozzle outlet portion 11 of the nozzle mold 1 and the unfoamed portion. The foamed part.
The non-foamed portion maintains its state from when it is projected from the outlet 11 of the nozzle of the nozzle mold 1 until foaming is started. The time for which the unfoamed part is maintained can be adjusted by the resin pressure at the nozzle outlet 11 of the nozzle mold 1, the amount of foaming agent, and the like. When the resin pressure at the nozzle outlet 11 of the nozzle mold 1 is high, the polylactic acid resin extrudate does not foam immediately after being extruded from the nozzle mold 1 and maintains an unfoamed state. The adjustment of the resin pressure at the nozzle outlet 11 of the nozzle mold 1 can be adjusted by the nozzle diameter, the extrusion amount, the melt viscosity and the melt tension of the polylactic acid resin. By adjusting the amount of the foaming agent to an appropriate amount, the polylactic acid resin can be prevented from foaming inside the mold, and the unfoamed portion can be reliably formed.

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. Accordingly, the foamed particles have excellent foamability with no loss of foaming gas, a low open cell ratio, and excellent surface heat-sealing property.
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. is doing.

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 10,000 rpm, more preferably 3000 to 9000 rpm, and still more 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 by 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 expanded 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.

(Manufacturing method of foam molding)
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. Accordingly, 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 immersing a mold filled with expanded particles in warm water, and the like. Of these, the method (2) 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 onto 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, the size of the mold, and the like. 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 foam particles may be further impregnated with an inert gas to improve the foam power of the foam 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. In addition, as an inert gas, a carbon dioxide, nitrogen, helium, argon etc. are mentioned, for example.
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. The foamed particles are heated and foamed before filling the foamed mold into the mold, so that the foamed particles have 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. Accordingly, the temperature is preferably less than 70 ° C.

  The obtained foamed molded products are used as cushioning materials (cushion materials) for home appliances, electronic parts, various industrial materials, food containers, etc., automobile-related parts (for example, vehicle damper core materials, door interior cushioning materials, etc. For example, an impact energy absorbing material. Particularly suitable for automobile interior materials (for example, lower limb impact absorbers, floor raising materials, tool boxes, etc.) from the viewpoint of obtaining a foamed molded article having a low odor, that is, an average odor intensity of 3 or less in an odor test. It can also be used.

Hereinafter, although an example is given and explained further, the present invention is not limited by these examples. Various measurement methods and production conditions described in the examples will be described below.
(D or L content)
The content of D-form or L-form in the polylactic acid resin is 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 is repeated 5 times, and values obtained by arithmetically averaging the obtained D-form amount and L-form amount are defined as the D-form amount and L-form amount of the polylactic acid resin.
HPLC apparatus (liquid chromatograph): “PU-2085 Plus type system” manufactured by JASCO Corporation
Column: Sumitomo Analysis Center Co., Ltd. trade name “SUMICIRAL OA5000” (4.6 mmφ × 250 mm)
Column temperature: 25 ° C
Mobile phase: 2MMCuSO ₄ mixture of aqueous solution and 2-propanol (CuSO ₄ solution: 2-propanol (volume ratio) = 95: 5)
Mobile phase flow rate: 1.0 ml / min Detector: UV254 nm
Injection volume: 20 microliters

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

(Temperature T at the intersection of storage modulus curve and loss modulus curve)
The temperature T at the intersection of the storage modulus curve and the loss modulus curve is measured as follows.
First, polylactic acid resin particles are obtained in the same manner except that the foaming agent is not added.
The polylactic acid resin particles are dried for 3 hours at 80 ° C. under a reduced pressure of 9.33 × 10 ⁴ Pa. Placed on a measurement plate heated to 40-50 ° C. higher than the melting point of the polylactic acid resin constituting the polylactic acid resin particles and allowed to stand for 5 minutes in a nitrogen atmosphere to melt Let
Next, a flat circular pressure plate having a diameter of 25 mm is prepared, and the polylactic acid resin on the measurement plate is moved up and down until the distance between the opposing surfaces of the pressure plate and the measurement plate becomes 1 mm. Press in the direction. And after removing the polylactic acid-type resin which protruded from the outer periphery of a press plate, it is left to stand for 5 minutes.

Thereafter, the dynamic viscoelasticity measurement of the polylactic acid resin is performed under the conditions of 5% strain, frequency 1 rad / sec, temperature drop rate 2 ° C./min, and measurement interval 30 sec to determine the storage elastic modulus and loss elastic modulus. taking measurement. Next, a storage elastic modulus curve and a loss elastic modulus curve are drawn with the horizontal axis as temperature and the vertical axis as storage elastic modulus and loss elastic modulus. In drawing the storage elastic modulus curve and the loss elastic modulus curve, the measurement values adjacent to each other are connected with a straight line based on the measurement temperature.
And temperature T is obtained by reading the intersection of the obtained storage elastic modulus curve and loss elastic modulus curve. When the storage elastic modulus curve and the loss elastic modulus curve intersect each other at a plurality of locations, the highest temperature among the temperatures at the plurality of intersections of the storage elastic modulus curve and the loss elastic modulus curve is defined as a temperature T.
Also, the temperature T is the value of Relogica Instruments A. It measures using the dynamic viscoelasticity measuring apparatus marketed with the brand name "DynAlyser DAR-100" from B company.

(Glass-transition temperature)
Measured according to the method described in JIS K7121-1987 “Method for Measuring Transition Temperature of Plastic”. That is, using a differential scanning calorimeter (DSC), about 6 mg of expanded particles were measured at a temperature rising rate of 10 ° C./min to a measuring temperature of 20 ° C. to 100 ° C., and the intermediate glass transition temperature was calculated by the method described in JIS K7121-1987. To do. This intermediate glass transition temperature is defined as the glass transition temperature in the present specification.

(Particle size)
The diameter of the expanded particles is measured directly using a caliper as follows. That is, the longest diameter (major axis) and the shortest diameter (minor axis) on the cut surface of the expanded particle are measured, and the length of the expanded particle in the direction perpendicular to the cut surface is measured. The arithmetic average value of the major axis, minor axis, and length of 30 expanded particles is defined as the particle size.

(Crystallinity)
The crystallinity is measured as follows.
The expanded particles or the expanded molded article is collected as a 4 mg sample. While the obtained sample was heated at a rate of 10 ° C./min in accordance with the measurement method described in JIS K7121, a differential scanning calorimeter (DSC: differential scanning calorimeter “ DSC 6220 Model ") is used to measure the amount of cold crystallization and heat of fusion per mg. The degree of crystallinity is calculated by substituting both calories into the following equation.

(Odor test)
Performed by 5 professional or skilled odor test panels.
Panels shall be those that have been recognized as having a normal olfaction by the method of selecting two panels using the following standard odor.
1. 5 types of standard odor

2. Panel selection method (1) Test paper (number 14 cm, width 7 mm; hereinafter referred to as “smell paper”) with the numbers 1 to 5 in a set of 5 sheets, and any two odors The paper is immersed in a reference odor liquid (one type) to the tip of about 1 cm, and the remaining three sheets are similarly immersed in odorless liquid paraffin.
(2) Give this set of five scented papers to the subject (limited to those over 18 years old) and have them select the two scented papers that have been smelled with the reference odor liquid using the sense of smell.
(3) The procedure of (1) and (2) is performed for five types of reference odor liquids, and those who correctly answer all of them are recognized as having a normal olfactory sense.
(4) The above test shall be taken every 5 years or less (within 3 years for those over 40 years old) and it is necessary to confirm that they have normal olfaction.

The odor test is as follows.
The foamed moldings obtained in Examples or Comparative Examples are taken out after being placed in a constant temperature bath at 55 ° C. for 1 hour, and left at 23 ° C. for 24 hours.
Thereafter, a flat rectangular plate-shaped test piece having a length of 100 mm, a width of 100 mm, and a thickness of 30 mm was cut out from the foamed molded body, and the test piece was put into a stainless steel container with a lid having a diameter of 160 mm and a depth of 200 mm, and the entire stainless steel container was 60 ° C. After being placed in a constant temperature bath for 1 hour, it is taken out and left at 23 ° C. for 30 minutes.
Next, the smell of isovaleric acid (made by Daiichi Yakuhin Sangyo Co., Ltd.) diluted 100000 times is sniffed, and this is used as the standard odor (3 out of 0-5 odor intensity).
Next, open the lid of the stainless steel container a little and smell the odor inside the container. If it is stronger (stronger odor) than the above standard odor, the odor intensity is 5, and if it is slightly stronger (strong odor), the odor intensity is the same (4) The odor intensity is 3 when the odor is easily sensed, the odor intensity is 2 when the odor is slightly weak (a weak odor that understands what odor is), the odor intensity is 1 when the odor is weak (a odor that can be finally detected), and the odor intensity is 0. After the test, the average value of the odor intensity by the five persons who performed the above test is obtained, and the case where the value is 3 or less is regarded as acceptable.

(Bulk density of expanded particles)
The expanded particles are filled into a graduated cylinder to a scale of 500 cm ³ . The graduated cylinder is visually observed from the horizontal direction, and if any one of the expanded particles reaches a scale of 500 cm ³ , the filling of the expanded particles into the graduated cylinder is terminated at that point.
Next, the mass of the expanded particles filled in the graduated cylinder is weighed to the second significant figure after the decimal point, and is defined as the mass W (g).
Then, the bulk density of the expanded particles is calculated by the following formula.
Bulk density (g / cm ³ ) = W / 500

Example 1
Expanded particles were produced using the production apparatus shown in FIGS. First, crystalline polylactic acid resin (trade name “TERRAMAC HV-6250H” manufactured by Unitika Ltd., melting point (mp): 169.1 ° C., D-form ratio: 1.2 mol%, L-form ratio: 98.8 mol %, Temperature T at the intersection of storage elastic modulus curve and loss elastic modulus curve obtained by dynamic viscoelasticity measurement: 138.8 ° C., glass transition temperature: 58 ° C.) 0.1 parts by weight of polytetrafluoroethylene powder (trade name “Fluon L169J” manufactured by Asahi Glass Co., Ltd.) was supplied to a single screw extruder having a diameter of 65 mm and melt kneaded. In the single screw extruder, the polylactic acid resin was first melt-kneaded at 190 ° C. and then melt-kneaded while raising the temperature to 220 ° C.
Subsequently, in the middle of the single screw extruder, the polylactic acid-based polylactic acid in a molten state so that butane composed of 35% by weight isobutane and 65% by weight normal butane is 1.0 part by weight with respect to 100 parts by weight of the polylactic acid-based resin. It was press-fitted into the resin and uniformly dispersed in the polylactic acid resin.

Thereafter, after the molten polylactic acid-based resin is cooled to 200 ° C. at the front end of the extruder, the polypolylactic acid resin is cooled at a shear rate of 7639 sec ⁻¹ from each nozzle of the multi-nozzle mold 1 attached to the front end of the single screw extruder. A lactic acid resin was extruded and foamed. The temperature of the multi-nozzle mold 1 was maintained at 200 ° C.
The multi-nozzle mold 1 has ten nozzles having a diameter of the outlet portion 11 of 1.0 mm, and all the outlet portions 11 of the nozzle are assumed to be on the front end face 1a of the multi-nozzle die 1. Are arranged at equal intervals on a virtual circle A of 139.5 mm.
Then, four rotary blades 5 are integrally provided at equal intervals in the circumferential direction of the rotary shaft 2 on the outer peripheral surface of the rear end portion of the rotary shaft 2, and each rotary blade 5 is a multi-nozzle mold 1. It is configured to move on the virtual circle A while always in contact with the front end face 1a.

Further, the cooling member 4 includes a cooling drum 41 including a front circular front part 41a and a cylindrical peripheral wall part 41b extending rearward from the outer peripheral edge of the front part 41a and having an inner diameter of 315 mm. It was. 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 forwarded along the inner surface of the peripheral wall portion 41b. It was flowing in a spiral.
A polylactic acid-based resin extruded and foamed from the outlet portion 11 of each nozzle of the multi-nozzle mold 1 is rotated by the rotary blade 5 disposed on the front end surface 1a of the multi-nozzle mold 1 at a rotation speed of 4800 rpm. The extrudate was cut with a rotary blade 5 to produce substantially spherical expanded particles. The polylactic acid-based resin extrudate was composed of an unfoamed portion immediately after being extruded from the nozzle of the multi-nozzle mold 1 and a foamed portion in the course of foaming continuous with the unfoamed portion. And the polylactic acid-type resin extrudate was cut | disconnected in the opening end of the exit part 11 of a nozzle, and the cutting | disconnection of the polylactic acid-type resin extrudate was performed in the unfoamed part.

In producing foamed 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 polylactic acid resin extrudate is extruded and foamed from a single screw extruder, and the polylactic acid resin extrudate is extruded from the nozzle of the multi-nozzle mold 1 and the unfoamed portion. It was confirmed that it was composed of a foaming part in the middle of foaming. Next, after attaching the rotating shaft 2 to the multi-nozzle mold 1 and disposing the cooling member 4 at a predetermined position, the rotating shaft 2 is rotated, and the polylactic acid resin extrudate is placed at the opening end of the outlet portion 11 of the nozzle. Cutting with the rotary blade 5 produced foamed particles.
The foamed particles were blown outward or forward by the cutting stress of the rotary blade 5, collided with the cooling water 42 flowing along the inner surface of the cooling drum 41 of the cooling member 4, and immediately cooled.
The cooled foamed particles were discharged together with the cooling water 42 through the discharge port 41e and the discharge pipe 41f of the cooling drum 41, and then separated from the cooling water 42 by a dehydrator. The obtained expanded particles had a particle size of 2.2 to 2.6 mm, a crystallinity of 18%, and a bulk density of 0.2 g / cm ³ .

Next, using a fluidized bed drying apparatus (model: FB-0.5; bed height 600 mm) manufactured by Okawara Seisakusho Co., Ltd., 20 kg of the foamed particles were increased by 68 ° C. from the glass transition temperature T ° C. of the polylactic acid resin. Was introduced into the apparatus being blown from the bottom at a speed of 1.0 m / sec (pressure loss: 1.0 kPa). The fluidized bed drying apparatus was provided with a countersink plate (a countersink area of 0.05 m ² ) for preventing foam particles from entering the blowing port. After charging, the expanded particles were treated for 6 hours to reduce odor. Next, it was cooled to room temperature (about 25 ° C.), and the expanded particles were taken out from the fluidized bed dryer. The crystallinity of the expanded particles was 23%.
Next, the expanded particles are put in a sealed container, and carbon dioxide is injected into the sealed container at a pressure of 0.3 MPa and left at 20 ° C. for 24 hours to impregnate the expanded particles with carbon dioxide. It was.

Subsequently, the foamed particles were filled into a cavity of an aluminum mold. In addition, the internal dimension of the cavity of a metal mold | die was made into the rectangular parallelepiped shape of length 30mm * width 300mm * height 300mm. The mold was provided with a total of 252 circular supply ports with a diameter of 8 mm at intervals of 20 mm in order to communicate the inside of the mold cavity and the outside of the mold. By providing a grid portion with an opening width of 1 mm at each supply port, the foamed particles filled in the mold do not flow out of the mold through the supply port, and water flows from the outside of the mold into the cavity through the supply port. Is configured so that it can be supplied smoothly.
Next, the mold filled with the expanded particles in hot water maintained at 90 ° C. in a heated water tank was completely immersed for 5 minutes. By this immersion, hot water is supplied to the foamed particles in the mold cavity through the mold supply port, whereby the foamed particles are heated and foamed, and the foamed particles are thermally fused and integrated to obtain a foamed molded product. It was.

Next, the mold was taken out from the heated water tank. And the metal mold | die was completely immersed over 5 minutes in the water maintained at 20 degreeC in a cooling water tank. The foamed molded body in the mold was cooled by this immersion.
After the mold was taken out of the cooling water tank, the mold was opened to obtain a rectangular parallelepiped foam molded body. When the odor test of the obtained foamed molded product was performed, the average odor intensity was 2.6. Therefore, it was found that the odor of the expanded particles is also reduced.
Various measurement results are shown in Table 2.

Example 2
Expanded particles and foamed molded articles were obtained in the same manner as in Example 1 except that the temperature of the warm air during the odor reduction step was 48 ° C., which was 10 ° C. lower than the glass transition temperature of the polylactic acid resin (average odor strength 2 .6). The crystallinity of the expanded particles was 20%.
Various measurement results are shown in Table 2.
Example 3
Expanded particles and foamed molded articles were obtained in the same manner as in Example 1 except that the temperature of the hot air during the odor reduction step was 28 ° C., which was 30 ° C. lower than the glass transition temperature of the polylactic acid resin (average odor strength 2 .8). The crystallinity of the expanded particles was 18%.
Various measurement results are shown in Table 2.

Comparative Example 1
A foamed molded product was obtained in the same manner as in Example 1 except that the odor reducing step was not performed (average odor intensity 3.7). The crystallinity of the expanded particles was 18%.
Various measurement results are shown in Table 2.
Comparative Example 2
Expanded particles and a foamed molded article were obtained in the same manner as in Example 1 except that the temperature of the warm air during the odor reduction step was 8 ° C., which was 50 ° C. lower than the glass transition temperature of the polylactic acid resin (odor 3.6). ). The crystallinity of the expanded particles was 18%.
Various measurement results are shown in Table 2.
Comparative Example 3
While trying to obtain expanded particles with reduced odor in the same manner as in Example 1 except that the temperature of the hot air during the odor reduction step was 78 ° C. which was 20 ° C. higher than the glass transition temperature of the polylactic acid resin, Since the foamed particles were bonded together, molding was impossible. The crystallinity of the expanded particles was 40%.
Various measurement results are shown in Table 2.

  From Examples 1 to 3 and Comparative Examples 1 to 3, when the glass transition temperature of the expanded particles is T ° C., the expanded particles are blown while blowing a gas (air) from (T-40) to (T + 15) ° C. from the bottom of the container. Foamed particles that give foamed molded articles that, when fluidized, give an average value of odor intensity of 3 or less in an odor test in which the odor of isovaleric acid diluted 100000 times is the standard odor of 0 to 5 levels of odor intensity. You can see that

1 nozzle mold: 1a front end surface: 2 rotation shaft: 3 motor: 4 cooling member: 5 rotation blade: 11 outlet part: 41 cooling drum: 41a front part: 41b peripheral wall part: 41c supply port: 41d supply pipe: 41e exhaust Outlet: 41f Discharge pipe: 42 Cooling water liquid: A virtual circle

Claims (4)

  Polylactic acid-based resin expanded particles are derived from polylactic acid-based resin expanded particles by flowing them in a container with a gas at (T-40) to (T + 15) ° C. (T is the glass transition temperature of the polylactic acid-based resin). The average value of the odor intensity of the foamed molded article obtained from the polylactic acid resin expanded particles with reduced odor is reduced to 100000 times the odor of isovaleric acid, and the odor intensity is 3 in 0 to 5 stages. A method for reducing odor in polylactic acid-based resin expanded particles, characterized in that it is 3 or less in an odor test with a standard odor of   Monomer component in which the polylactic acid-based resin expanded particles contain both D-form and L-form optical isomers, and the content of the lesser of the D-form and L-form is less than 5 mol% The odor in the polylactic acid-based resin expanded particles according to claim 1 or 2, derived from a monomer component containing only one of the optical isomers of D-form or L-form Reduction method.   The polylactic acid-based resin expanded particles obtained by the method according to claim 1 or 2, wherein the polylactic acid-based resin expanded particles have an odor intensity of an isovaleric acid diluted 100000 times. A polylactic acid-based resin expanded particle, which gives a foamed molded product having an odor intensity of 3 or less in an odor test with a standard odor of 3 in 0 to 5 odor intensity.   A foam molded article obtained by in-mold foam molding of the polylactic acid resin foamed particles according to claim 3.

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