JP2011225819A - Polylactic acid-based resin foam and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide polylactic acid-based resin foam improved in appearance, fusing property, and heat resistance.SOLUTION: The polylactic acid-based resin foam comprises at least a polylactic acid resin having an exothermic peak due to crystallization in measurement by a differential scanning calorimeter. When the shape of the exothermic peak is divided equally into first to four sections in this order from a lower temperature one, (1) a total calorific value of first, second, third, and fourth sections is 10 J/g or more, and (2) a total calorific value of the first, third, and fourth sections is 45% or more based on a total calorific value of the first, second, third, and fourth sections.

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 foamed molded article excellent in appearance and heat resistance and a method for producing the same.

Polylactic acid resin is a resin obtained by polymerizing naturally occurring lactic acid, is a biodegradable resin that can be decomposed by microorganisms existing in nature, and has excellent mechanical properties at room temperature. It attracts attention.
The polylactic acid resin generally polymerizes D-lactic acid and / or L-lactic acid or opens one or more lactides selected from the group consisting of L-lactide, D-lactide and DL-lactide. Manufactured by ring polymerization.
The polylactic acid-based resin has physical properties, particularly crystallinity, depending on the content ratio of D-form component (D-lactic acid and D-lactide-derived component) or L-form component (L-lactic acid and L-lactide-derived component) contained therein. Changes. Specifically, the polylactic acid-based resin obtained has lower crystallinity as the content ratio of the smaller optical isomer of the D-form component or L-form component contained therein increases, and eventually It becomes amorphous.

Further, as a method for producing a polylactic acid-based resin foam molded article, an in-mold foam molding method in which polylactic acid resin primary foamed particles are foamed in a mold has been proposed. In-mold foam molding is a method in which polylactic acid-based primary foamed particles filled in a mold are heated by a heat medium such as hot water or steam to be secondarily foamed, and the polylactic acid-based primary foamed particles are formed. This is a method for producing a polylactic acid-based resin foam molded article having a desired shape by fusing and integrating primary foam particles with foam pressure.
For example, in Japanese Patent No. 4225477 (Patent Document 1), a polylactic acid resin having a heat absorption (Rendo) of 10 J / g or more in differential scanning calorimetry at a heating rate of 2 ° C./min is used as a base resin, and heating is performed. The ratio (Bexo / Bendo) between the calorific value (Bexo) and the endothermic amount (Bendo) in differential scanning calorimetry at a rate of 2 ° C./min exceeds 0.20, and the endothermic amount (Bendo) and calorific value (Bexo) Using a foamed particle having a difference (Bendo-Bexo) of 0 J / g or more and less than 15 J / g, and forming the in-mold foam molded article by fusing the foamed particles together, and the mold obtained in the molding process A method for producing an in-mold foam-molded article is described which includes a curing step of maintaining the inner foam-molded article in an atmosphere having a temperature of [Tg + 5] to [Tg + 30] ° C. Furthermore, the ratio (bFexo / bFendo) between the calorific value (bFexo) and the endothermic amount (bFendo) of the in-mold foam molded product in the differential scanning calorimetry at a heating rate of 2 ° C./min is 0 to 0.20 by the curing process. It is described that an in-mold foam molded article having a difference (bFendo-bFexo) between an endothermic amount (bFendo) and a calorific value (bFexo) of 15 J / g or more can be obtained.

  Japanese Patent No. 4289547 (Patent Document 2) describes polylactic acid expanded particles containing 50 mol% or more of lactic acid component units. Specifically, the difference (ΔHendo: Bead−ΔHexo: Bead) between the endothermic amount (ΔHendo: Bead) and the calorific value (ΔHendo: Bead) in the heat flux differential scanning calorimetry of the expanded particles is 0 J / g or more and 30 J / g. Polylactic acid foamed particles having a heat absorption amount (ΔHendo: Bead) of 15 J / g or more are described.

Japanese Patent No. 4225477 Japanese Patent No. 4289547

Here, since the polylactic acid resin generally has a low crystallization rate, in order to crystallize the polylactic acid resin and obtain a polylactic acid resin foamed molded article having excellent heat resistance, during or after molding in the mold The curing process was necessary as the crystallization process.
However, the provision of a curing process is an increase in manufacturing cost, and the provision of a polylactic acid-based resin foam capable of forming a foam molded article having excellent appearance, fusion properties and heat resistance without providing a curing process is provided. It was desired.

As a result of intensive studies, the inventors of the present invention are polylactic acid resin foams containing a polylactic acid resin in which a part of an exothermic peak derived from crystallization is shifted to a low temperature side when measured with a differential scanning calorimeter. If it exists, it came to the present invention by surprisingly finding that a foamed molded article excellent in appearance, fusion property and heat resistance can be obtained without going through a curing process.
Thus, according to the present invention, it contains at least a polylactic acid-based resin, and the polylactic acid-based resin has an exothermic peak derived from crystallization when measured with a differential scanning calorimeter,
The exothermic peak is divided into four equal parts in the first, second, third and fourth sections from the lower temperature,
(1) The total calorific value of the first, second, third and fourth sections is 10 J / g or more,
(2) It has a shape in which the total amount of heat generated in the first, third, and fourth sections is 45% or more with respect to the total amount of heat generated in the first, second, third, and fourth sections. A polylactic acid-based resin foam is provided.

According to the present invention, there is also provided a method for producing the polylactic acid resin foam,
A polylactic acid resin primary foam having a bulk density of 0.05 to 0.5 g / cm ³ is heated for 10 to 300 seconds in a temperature range of glass transition temperature (Tg) −20 ° C. to glass transition temperature (Tg) + 5 ° C. Thus, a polylactic acid resin foam production method is provided, which is foamed to obtain a polylactic acid resin high-magnification foam having a bulk density of 0.02 to 0.2 g / cm ³ .

Since the polylactic acid-based resin foam according to the present invention can quickly increase the degree of crystallinity at the time of in-mold molding, it is possible to provide a foam molded article excellent in appearance, fusion property and heat resistance.
Furthermore, the total amount of heat generated in the first, second, third and fourth sections is 12 J / g or more,
When the total amount of heat generated in the first, second, third, and fourth sections is 50% or more with respect to the total amount of heat generated in the first, second, third, and fourth sections, the appearance and fusion properties And heat resistance can be improved more.
The polylactic acid-based resin contains a monomer component composed of both optical isomers of lactic acid or lactide in the D-form and L-form, and the content of the smaller optical isomer of the D-form or L-form is 5 When it is less than mol% or is derived only from the monomer component consisting of either one of the optical isomers of D-form and L-form, the appearance, fusion property and heat resistance can be further improved.

Furthermore, when the polylactic acid-based resin has an endothermic amount of an endothermic peak of crystal melting of 30 J / g or more, it is possible to further improve the appearance, the fusibility and the heat resistance.
Further, polylactic acid resin foam, obtained by foaming by heating the polylactic acid resin primary foam bulk density of 0.05~0.5g / cm ³ 0.02~0.2g In the case of a polylactic acid resin high-magnification foam having a bulk density of / cm ³ , the appearance, fusing property and heat resistance can be further improved.
Furthermore, the polylactic acid resin primary foam having a bulk density of 0.05 to 0.5 g / cm ³ is 10 to 300 in a temperature range of glass transition temperature (Tg) −20 ° C. to glass transition temperature (Tg) + 5 ° C. When it is foamed by heating for 2 seconds to obtain a polylactic acid resin high-magnification foam having a bulk density of 0.02 to 0.2 g / cm ³ as a polylactic acid resin foam, appearance, fusing property and heat resistance It is possible to easily produce a polylactic acid-based resin foam that can improve the temperature.

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. 2 is a DSC curve of Example 1. 2 is a DSC curve of Example 2. 2 is a DSC curve of Comparative Example 1. 3 is a DSC curve of Comparative Example 2.

(Exothermic peak)
The polylactic acid resin foam according to the present invention (hereinafter also referred to as a foam) has an exothermic peak derived from crystallization (exothermic when transitioning from amorphous to crystalline) when measured with a specific differential scanning calorimeter (DSC). Corresponding to the quantity). Specifically, this exothermic peak is divided into the first, second, third and fourth divisions from the lower temperature,
(1) The sum of the calorific values (hereinafter also referred to as total calorific values) of the first, second, third and fourth sections is 10 J / g or more,
(2) A shape in which the total amount of heat generated in the first, third, and fourth sections is 45% or more of the total amount of heat generated in the first, second, third, and fourth sections. ing. In short, the size of the exothermic peak is specified in the configuration (1), and the lateral extension of the exothermic peak is specified in the configuration (2). Note that the total calorific value and calorific value are absolute values and correspond to the area of the exothermic peak. Moreover, although the exothermic peak derived from crystallization differs depending on the type of polylactic acid resin, it usually appears in the range of 60 to 110 ° C.

The defining method of the total calorific value and the calorific values of the first, second, third and fourth classifications is described in the column of Examples.
The foam may be in the form of particles or an aggregate of particles. However, it is preferable that the foam is in the form of particles because it is easy to handle in subsequent foam molding.
By the way, the case where it uses for crystalline polylactic acid resin is illustrated in the said patent document. However, when the inventors actually used the method exemplified in the patent literature for a highly crystalline polylactic acid resin having a D-form amount of 5 mol% or less, the polylactic acid resin is produced by the plasticizing effect of carbon dioxide used as a foaming agent. It has been confirmed that foaming cannot be performed even when heated with water vapor (see Comparative Examples 3 and 4).

(1) Exothermic peak size (total calorific value)
If the total calorific value is less than 10 J / g, the degree of crystallinity is increased, so that the heat-fusability between the polylactic acid resin foams is reduced during in-mold molding, and the mechanical strength of the resulting foam molded article And the appearance deteriorates. A preferable total heat generation amount is 12 J / g or more, and a more preferable total heat generation amount is 14 J / g or more. Moreover, since it takes time until crystallization is completed when the total calorific value is large, the upper limit of the total calorific value is preferably 35 J / g.

(2) Horizontal extension of exothermic peak Generally, the exothermic peak of crystalline polylactic acid resin has a substantially triangular shape. On the other hand, in the polylactic acid resin constituting the foam of the present invention, two peaks or two peaks in which the above-described peak of heat generation and another peak of heat generation were further developed on the lower temperature side were synthesized. A substantially trapezoidal shape or a substantially semicircular shape is shown. Other exothermic peaks on the low temperature side have not been chemically elucidated yet. However, the inventors believe that the polylactic acid-based resin is an exothermic peak derived from a crystal precursor crystallized very slightly by the action of stretching of the resin by heating and foaming (foaming including a crystal precursor). The body is called modified foam). The inventors believe that this low-temperature exothermic peak contributes to relatively rapid crystallization as compared to a polylactic acid resin having a general peak of exothermic peaks.
In addition, even if the above crystal precursor is generated, the total heat quantity of the exothermic peak does not decrease so much, so that the crystallization progresses quickly without hindering fusion during molding, and foam molding with excellent appearance and heat resistance You can get a body.

  When the total amount of heat generated in the first, third, and fourth sections is less than 45% of the total amount of heat generated in the first, second, third, and fourth sections, the appearance and heat resistance are excellent. It is difficult to obtain a foamed molded product. A more desirable ratio is 50% or more, and still more preferably 55% or more. The upper limit of the ratio is preferably 65% or less. Further, the calorific value of the first section is preferably a ratio of 25% or more of the total calorific value of the first, second, third and fourth sections, and preferably a ratio of 30% or more. More preferred. The inventors consider that the first section is a section mainly including the crystal precursor. Note that the second category is the category that occupies the largest proportion in the case of a mountainous exothermic peak.

(Polylactic acid resin)
As the polylactic acid resin, commercially available polylactic acid resins can be used. Specifically, a copolymer of D-lactic acid and L-lactic acid, a homopolymer of any one of D-lactic acid (D-form) or L-lactic acid (L-form), D-lactide (D-form), L -A ring-opening polymer of one or more lactides selected from the group consisting of lactide (L-form) and DL-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.
Moreover, since the latter polylactic acid-based resin can improve the heat resistance of the foamed molded product obtained by filling the modified foamed material in the mold and performing secondary foaming, the foamed molded product can be heated at a high temperature. The form can be maintained. 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%.

Here, when the primary foam is obtained by the extrusion foaming method, the polylactic acid resin has a melting point (mp) and a storage elastic modulus curve and a loss elastic modulus curve obtained by dynamic viscoelasticity measurement. It is preferable that the temperature T at the intersection 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 primary foam, 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 primary foam, 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 the polylactic acid resin is low, the cell membrane can be easily formed when the cell membrane is stretched by the foaming pressure required for producing the primary foam. It may be torn. 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 made smooth during the production of the primary foam. It may be difficult to expand and it may be difficult to expand the bubbles.

  Thus, in producing a primary foam by foaming a polylactic acid-based resin, in the foaming process, an elastic force, ie, storage elastic modulus, for appropriately expanding without breaking the cell membrane due to foaming pressure is obtained. It is preferable to have. In addition, the foam force smoothly expands without breaking the bubble film, and the viscous force to maintain the expanded bubble to the desired size regardless of the decrease in the foam pressure over time, that is, It preferably has a loss elastic modulus.

That is, in the extrusion foaming process, it is preferable that both the storage elastic modulus and loss elastic modulus of the polylactic acid-based resin have values suitable for extrusion foaming, and the storage elastic modulus and loss suitable for such extrusion foaming. In order to impart an elastic modulus to the polylactic acid resin in the extrusion foaming process, the temperature T (below) at the intersection of the storage elastic modulus curve and the loss elastic modulus curve obtained by dynamic viscoelasticity measurement in the polylactic acid resin. (Referred to as “temperature T”) and the melting point (mp) of the polylactic acid-based resin are preferably adjusted so as to satisfy the following formula 1, more preferably satisfy the formula 2. By this adjustment, the primary foam can be stably produced with good extrusion foamability 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
Furthermore, the reason why it is preferable to adjust the temperature T and the melting point (mp) of the polylactic acid resin so as to satisfy the 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. A primary foam may not be obtained. Conversely, if the foaming force suitable for the storage elastic modulus of the polylactic acid-based resin, that is, the foaming force matched to the elasticity, the foaming force with respect to the viscous force is small, and the polylactic acid-based resin is difficult to foam, and a good primary A foam 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, when 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. The secondary foam 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 a good primary foam 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. The weight average molecular weight is preferably in the range of 5.0 × 10 ⁴ to 40 × 10 ⁴ .
The foam may contain other components as necessary. Examples of other components include flame retardants, antistatic agents, colorants, antioxidants, heat stabilizers, ultraviolet absorbers, hydrolysis inhibitors, and the like.

(Production of primary foam)
The primary foam can be produced by a known method. For example, the following extrusion foaming method is mentioned. The following method is one method when the primary foam is in the form of particles.
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 general-purpose 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 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, methyl chloride, 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 primary foam 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 is lowered, and a good primary foam may not be obtained. In addition, the expansion ratio of the primary foam 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 primary foam, 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.

  Moreover, when there is little quantity of the bubble regulator supplied to an extruder, the bubble of a primary foam becomes coarse and the external appearance of the foaming molding obtained may fall. On the other hand, when the polylactic acid-based resin is extruded and foamed, the foam may be broken to lower the closed cell ratio of the primary foam. 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 a primary foam. 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 resin (the temperature of the polylactic acid resin at the tip of the extruder) is low, fracture occurs and the obtained primary foams are easily attached. 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 primary foam 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 primary foam is manufactured by cutting at the unfoamed portion immediately after being discharged from the outlet portion 11.

Since the obtained primary foam cuts the polylactic acid resin extrudate at its unfoamed portion, there is no cell cross section on the surface of the cut portion. The entire surface of the primary foam is covered with a skin layer having no bubble cross section. Accordingly, the primary foam has excellent foamability without any loss of foam gas, has a low open cell ratio, and is excellent in surface heat-fusibility.
The surface of the primary foam is formed from a skin layer in which the cell cross section is not exposed. Therefore, when the modified foam derived from the primary foam is used for in-mold foam molding, the heat-fusibility between the modified foams is good, and the resulting foam molded body has no surface unevenness and has an appearance. It has excellent mechanical strength as well as excellent.

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 primary foams may be united with each other, or the shape of the primary foam may be uneven. If it exceeds 10,000 rpm, the following problems may occur. The first problem is that when the cutting stress due to the rotary blade increases and the primary foam is scattered from the outlet portion of the nozzle toward the cooling member, the initial speed of the primary foam may be increased. . As a result, the time from when the polylactic acid resin extrudate is cut until the primary foam collides with the cooling member is shortened, and foaming of the primary foam is 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 primary foam is scattered outward or forward simultaneously with the cutting by the cutting stress of the rotary blade 5 and immediately collides with the inner peripheral surface of the peripheral wall portion 41 b of the cooling drum 41. The primary foam continues to foam until it collides with the cooling drum 41 and grows 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 primary foam that collides with the inner peripheral surface of the peripheral wall portion 41b of the cooling drum 41 is immediately cooled and foamed. Stop. Thus, after cutting the polylactic acid resin extrudate with the rotary blade 5, the primary foam is immediately cooled with the cooling liquid 42, so that the polylactic acid resin constituting the primary foam can be obtained. The crystallinity can be prevented from increasing, and the primary foam can be prevented from excessively foaming.
Therefore, the primary foam exhibits excellent foamability and heat-fusibility during in-mold foam molding. It is possible to improve the heat resistance of the polylactic acid resin by increasing the crystallinity of the primary foam during in-mold foam molding, 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 secondary foam may be high, and the heat-fusibility of the primary foam may be reduced. 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 primary foam is preferably 30% or less, more preferably 3 to 28%, and particularly preferably 5 to 26%. The degree of crystallinity of the primary foam can be adjusted by the time from when the polylactic acid-based resin extrudate is extruded from the nozzle mold 1 until the primary foam collides with the coolant 42 and the temperature of the coolant 42. .

When the bulk density of the primary foam is small, the open cell ratio of the primary foam increases, and the foaming force necessary for the primary foam may not be imparted during the high-magnification foaming process. On the other hand, if it is large, the cells of the resulting primary foam may become non-uniform, and the foamability of the primary foam during the high-magnification foaming process 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.
When the open cell ratio of the primary foam is high, the modified foam hardly foams during the high-magnification foaming process or in-mold foam molding, and the fusion property between the modified foams becomes low. The mechanical strength of the foamed molded product may be lowered. 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 primary foam 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.

  Moreover, if the particle size of the primary foam is small, the foamability of the primary foam may be reduced during the high-magnification foaming process. On the other hand, if it is large, the filling property of the modified foam into the mold may be lowered during in-mold foam molding. 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.

(Production method of modified foam)
The crystal precursor can be generated by heating or stretching the primary foam, and is preferably generated by heating and stretching by foaming in the high-magnification foaming process.
If the heating temperature is low, crystallization does not proceed and a crystal precursor may not be produced. Further, as the heating temperature becomes higher than the glass transition temperature (Tg), normal crystallization may proceed instead of the crystal precursor. As crystallization progresses, the heat-fusibility between the polylactic acid resin foams may be reduced during in-mold molding, and the mechanical strength and appearance of the resulting foam molded article may be reduced. A preferable heating temperature is Tg-20 ° C to Tg + 5 ° C, more preferably Tg-15 ° C to Tg + 3 ° C, and further preferably Tg-10 ° C to Tg + 1.

In addition, if the heating time is short, the crystal precursor may not be sufficiently generated, and if it is long, the crystal may be crystallized through the crystal precursor. Therefore, the heating time is preferably 10 to 300 seconds, more preferably 20 to 270 seconds, and further preferably 30 to 240 seconds.
In addition, as the heating medium for heating the modified foam, dry air is preferable.
Here, for example, by the above high magnification foaming process, the primary foam bulk density of 0.05 to 0.5 g / cm ^3, modified foam bulk density of 0.02~0.2g / cm ³ It can be. Here, the modified foam preferably has a bulk density that is 1.6 times higher than the bulk density of the primary foam.

Prior to the high-magnification foaming step, the primary foam may be impregnated with an inert gas to improve the foaming power of the primary foam. By improving the foaming power of the primary foam, a modified foam having a high foaming ratio can be obtained quickly without increasing the crystallinity even at a low temperature. In addition, as an inert gas, a carbon dioxide, nitrogen, helium, argon etc. are mentioned, for example.
Examples of the method of impregnating the primary foam with the inert gas include a method of impregnating the inert gas by placing the primary foam in an inert gas atmosphere having a pressure higher than normal pressure in a pressure vessel. It is done.

  When the inert gas is carbon dioxide, the primary foamed particles are placed in a carbon dioxide atmosphere of 0.1 to 1.5 MPa for 20 minutes to 24 hours to impregnate the primary foam with carbon dioxide. It is preferable to improve the foamability. Moreover, since the atmosphere temperature at the time of impregnation may raise the crystallinity degree of a primary foam, 0-40 degreeC is preferable, 5-35 degreeC is more preferable, and 10-30 degreeC is still more preferable.

(Foamed molded product)
The modified foam thus obtained is filled in a cavity of a mold and heated to further foam the modified foam. By this heating, the modified foams can be fused and integrated with each other by their foaming pressure, so that it is possible to obtain a foamed molded article having excellent meltability. Moreover, since the crystallinity degree of the polylactic acid-type resin which comprises a modified foam 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 a modified foam, 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 modified foam in the mold even when the temperature is low. Therefore, the modified foam can be sufficiently heated and foamed without being heated too much. Therefore, the modified foams can be strongly heat-bonded and integrated with each other by their foaming force without causing the thermal shrinkage of the surface of the modified foams that 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 modified foam filled in the mold becomes insufficient, and the heat-fusibility between the modified foams decreases. 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 of heating the modified foam by supplying warm water to the modified foam filled in the mold is not particularly limited. For example, (1) warm water instead of water vapor in a known in-mold foam molding machine And (2) a method of immersing a mold filled with the modified foam in warm water. Among these, the method (2) is preferable because even the mold having a complicated shape can uniformly heat and foam the entire mold, that is, the modified foam.
If the heating time of the modified foam filled in the mold with hot water is short, the heating of the modified foam is insufficient, and the thermal fusion between the modified foams becomes insufficient, or the modified foam is formed. The crystallinity of the body may not increase sufficiently. 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 modified foam 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 modified foam may be further impregnated with an inert gas to improve the foaming power of the modified foam. By improving the foaming force, the fusion property between the modified foams can be 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.

  As a method for further impregnating the modified foam with an inert gas, for example, the primary foam is placed in an inert gas atmosphere having a pressure equal to or higher than normal pressure in a pressure vessel. The method of impregnating with an active gas is mentioned. The inert gas may be impregnated before filling the modified foam into the mold, or impregnated by placing the modified foam in the mold and placing it in an inert gas atmosphere together with the mold. May be. When the inert gas is carbon dioxide, it is preferable to leave the modified foam in a carbon dioxide atmosphere of 0.1 to 1.2 MPa for 20 minutes to 24 hours. The pressure is based on atmospheric pressure.

(Use of foamed molded products)
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. Can be used for lower limb impact absorbing materials, floor raising materials, automobile interior materials such as tool boxes).

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

(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.

(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.

(Open cell ratio)
The open cell ratio is measured as follows.
First, a sample cup of a volumetric air comparison type hydrometer is prepared, and the total weight A (g) of foamed particles in an amount satisfying about 80% of the sample cup is measured. Next, the volume B (cm ³ ) of the entire expanded particle is measured by a 1-1 / 2-1 atmospheric pressure method using a hydrometer. The volumetric air comparison type hydrometer is commercially available, for example, from Tokyo Science Co. under the trade name “1000 type”.
Subsequently, a wire mesh container is prepared, the wire mesh container is immersed in water, and the weight C (g) of the wire mesh container in the state immersed in the water is measured. Next, after all of the foam particles are put in the wire mesh container, the wire mesh container is immersed in water, and the wire mesh container in the water soaked state and the foam particles placed in the wire mesh container The weight D (g) combined with the total amount of was measured.
Then, the apparent volume E (cm ³ ) of the expanded particles is calculated based on the following formula, and the open cell ratio of the expanded particles is calculated by the following formula based on the apparent volume E and the entire volume B (cm ³ ) of the expanded particles. To do. The volume of 1 g of water is 1 cm ³ .
E = A + (CD)
Open cell ratio (%) = 100 × (EB) / E

(DSC measurement)
The degree of crystallinity, calorific value, endothermic amount, and melting point are measured as follows.
The expanded particles or the expanded molded article is collected as a 4 mg sample. In accordance with the measurement method described in JIS K7121, the obtained sample was heated from 30 ° C. to 210 ° C. at a rate of 10 ° C./min, and a differential scanning calorimeter (DSC: manufactured by SII Nano Technology Co., Ltd.) Using a differential scanning calorimeter “DSC 6220 type”), the calorific value per 1 mg and the heat of fusion are measured. The degree of crystallinity is calculated by substituting both calories into the following equation.

Next, a procedure for defining the calorific value of the expanded particles or the expanded molded body will be described.
First, a straight line portion between an exothermic peak derived from crystallization of a DSC curve and an endothermic peak of crystal melting is drawn as a baseline. Mark the two intersections that intersect the extension of the baseline on the low temperature side of the exothermic peak from the point that is far from the base line on the high temperature side of the exothermic peak (for example, reference symbol a in FIG. 3). A value obtained from the base line between the two intersections (the base line of the exothermic peak) and the area surrounded by the DSC curve is defined as the total calorific value.
Further, three perpendicular quadrants that divide the base line between the two intersections of the exothermic peak into four are extended to draw a line that intersects the DSC curve. The exothermic peak is divided into four sections surrounded by a base line between two intersections, three vertical quadrants, and a DSC curve. The four sections are referred to as the first, second, third and fourth sections from the lower temperature (left side), and the values obtained from the areas of the respective sections are the first, second, third and fourth. The calorific value of the category.

The reason why the baseline is drawn from the high temperature side of the exothermic peak is that the gentle endothermic peak, which is derived from glass transition, enthalpy relaxation, and dissipation of the foaming agent from the expanded particles, is close to the exothermic peak. This is because the base line cannot be drawn from the low temperature side of the exothermic peak.
In addition, the endothermic amount of the expanded particles or the foamed molded article is a point where a straight line portion between the exothermic peak derived from crystallization of the DSC curve and the endothermic peak of crystal melting is drawn as a baseline, and the temperature is away from the baseline on the low temperature side of the endothermic peak. To a value obtained from the area of the portion surrounded by the baseline and the DSC curve up to the point where the endothermic peak returns to the baseline on the high temperature side. However, when a small exothermic peak appears on the low temperature side of the endothermic peak, the area of the portion surrounded by the baseline and DSC curve from the point where the endothermic peak and the baseline intersect and the point where the high temperature side of the endothermic peak returns to the baseline. The value obtained from
The melting point (mp) of the polylactic acid-based resin is defined as the melting point (mp) of the polylactic acid-based resin at the peak temperature of the melting peak in the obtained DSC curve. When there are a plurality of melting peak apexes, the highest temperature is set.

(The bulk density)
The bulk density of the expanded particles refers to that measured in accordance with JIS K6911: 1995 “General Test Method for Thermosetting Plastics”. That is, it measures using the apparent density measuring device based on JISK6911, and measures the bulk density of foamed particle based on a following formula.
Bulk density of expanded particles (g / cm ³ )
= [Mass of measuring cylinder with sample (g) -Mass of measuring cylinder (g)]
/ [Capacity of measuring cylinder (cm ³ )]

(Apparent density)
The apparent density of the foamed molded product is measured by the method described in JIS K6767: 1999 “Foamed Plastics and Rubber—Measurement of Apparent Density”.
(Heat-resistant)
The obtained foamed molded product is left in an electric oven maintained at 120 ° C. for 22 hours. And the dimension of the foaming molding before and behind leaving in an electric oven is measured, a dimensional change rate is computed based on a following formula, and it evaluates as heat resistance. In addition, let the dimension of a foaming molding be an arithmetic mean value of the dimension of a vertical direction, a horizontal direction, and a height direction.
Dimensional change rate (%) = 100 × (dimension after heating−dimension before heating) / dimension before heating

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 %, Obtained by dynamic viscoelasticity measurement, 100 parts by weight at the intersection of storage elastic modulus curve and loss elastic modulus curve, 13 parts by weight, polytetrafluoroethylene powder (Asahi Glass Co., Ltd.) as a bubble regulator Product name “Fullon L169J”) 0.1 parts by weight was supplied to a single screw extruder having a diameter of 65 mm and melt-kneaded. In the single screw extruder, the polylactic acid resin was first melt-kneaded at 190 ° C. and then melt-kneaded while raising the temperature to 220 ° C.
Subsequently, from the middle of the single-screw extruder, the polylactic acid-based polylactic acid in a melted state so that butane comprising 35% by weight of isobutane and 65% by weight of normal butane is 1.2 parts by weight with respect to 100 parts by weight of the polylactic acid-based resin. It was press-fitted into the resin and uniformly dispersed in the polylactic acid resin.

Thereafter, after the molten polylactic acid-based resin is cooled to 190 ° C. at the front end of the extruder, the poly-nozzle mold 1 attached to the front end of the single-screw extruder is subjected to polyslurry at a shear rate of 7621 sec ⁻¹ . 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 the rotary blade 5 to produce substantially spherical primary 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 the production of the primary expanded particles, first, the rotating shaft 2 was not attached to the multi-nozzle mold 1 and the cooling member 4 was retracted from the multi-nozzle mold 1. In this state, the 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 a rotary blade 5 produced primary expanded particles.

The primary expanded 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 primary expanded 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 primary expanded particles had a particle size of 2.2 to 2.6 mm, a bulk density of 0.2 g / cm ³ , and a crystallinity of 19.3%.
Next, the primary expanded particles are put in a sealed container, and carbon dioxide is injected into the sealed container at a pressure of 1.0 MPa and left at 25 ° C. for 6 hours to form carbon dioxide into the primary expanded particles. Impregnated with carbon.

The primary foamed particles were taken out from the pressure vessel, immediately supplied to a hot air dryer equipped with a stirrer, and heated and foamed for 3 minutes with 54 ° C. dry hot air while stirring. As a result, modified expanded particles having a high expansion ratio having a particle size of 2.8 to 3.5 mm, a bulk density of 0.047 g / cm ³ and a crystallinity of 22.3% were obtained. When this modified foamed particle was measured by DSC, the peak derived from crystallization showed a double peak shape. Further, when the exothermic peak is divided into four equal parts by temperature and the first, second, third, and fourth divisions are made from the lowest temperature, the first, third, and fourth divisions in the heat quantity of the exothermic peak The total proportion of heat was 58.9%.
Next, the modified foamed particles are placed in a sealed container, and carbon dioxide is injected into the sealed container at a pressure of 0.8 MPa and left at 25 ° C. for 24 hours to form carbon dioxide into the modified foamed particles. Impregnated with carbon.

Subsequently, the modified foamed particles were filled into a cavity of an aluminum mold. The inner dimension of the cavity of the mold was a rectangular parallelepiped shape having a length of 300 mm × width of 300 mm × height of 30 mm. 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 part with an opening width of 1 mm at each supply port, the highly foamed particles filled in the mold do not flow out of the mold through this supply port, but from outside the mold through the supply port into the cavity. It was configured so that water could be supplied smoothly.
Next, the mold filled with the modified foamed particles was completely immersed in warm water maintained at 85 ° C. in a heated water tank for 40 seconds. By this immersion, hot water is supplied to the foam particles in the cavity of the mold through the mold supply port, whereby the modified foam particles are heated and secondarily foamed, and the modified foam particles are integrated by heat fusion. Thus, a foamed molded product was obtained.

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. The mold was taken out from the cooling water tank, and the mold was opened to obtain a rectangular parallelepiped foam molded body. The obtained foamed molded article had an apparent appearance with an apparent density of 0.047 g / cm ³ . The performance evaluation results are shown in Table 1.

(Example 2)
Modified foamed particles were obtained in the same manner as in Example 1 except that the temperature of the hot air in the hot air dryer was 47 ° C. and the heating time was changed to 210 seconds. The obtained modified foamed particles had a particle size of 2.5 to 3.4 mm, a bulk density of 0.058 g / cm ³ , and a crystallinity of 23.1%. When this modified foamed particle was measured by DSC, the peak derived from crystallization showed a substantially semicircular shape. Further, when the exothermic peak is divided into four equal parts by temperature and the first, second, third, and fourth divisions are made from the lowest temperature, the first, third, and fourth divisions in the heat quantity of the exothermic peak The total amount of heat was 54.5%.
Next, a foamed molded article was obtained from the obtained modified foamed particles in the same manner as in Example 1. The obtained foamed molded article had an apparent appearance with an apparent density of 0.058 g / cm ³ . The performance evaluation results are shown in Table 1.

(Example 3)
Modified foamed particles were obtained in the same manner as in Example 1 except that the heating time in the hot air dryer was changed to 240 seconds. The obtained modified foamed particles had a particle size of 2.8 to 3.6 mm, a bulk density of 0.044 g / cm ³ , and a crystallinity of 25.0%. When this modified foamed particle was measured by DSC, the peak derived from crystallization showed a double peak shape. Further, when the exothermic peak is divided into four equal parts by temperature and the first, second, third, and fourth divisions are made from the lowest temperature, the first, third, and fourth divisions in the heat quantity of the exothermic peak The total amount of heat was 55.5%.
Next, a foamed molded article was obtained from the obtained modified foamed particles in the same manner as in Example 1. The obtained foamed molded article had an apparent appearance with an apparent density of 0.044 g / cm ³ . The performance evaluation results are shown in Table 1.

Example 4
Modified foamed particles were obtained in the same manner as in Example 1 except that the temperature of the hot air in the hot air dryer was 41 ° C. and the heating time was changed to 300 seconds. The obtained modified foamed particles had a particle size of 2.2 to 3.2 mm, a bulk density of 0.065 g / cm ³ , and a crystallinity of 20.2%. When this modified foamed particle was measured by DSC, the peak derived from crystallization showed a substantially semicircular shape. Further, when the exothermic peak is divided into four equal parts by temperature and the first, second, third, and fourth divisions are made from the lowest temperature, the first, third, and fourth divisions in the heat quantity of the exothermic peak The total proportion of heat was 48.6%.
Next, a foamed molded article was obtained from the obtained modified foamed particles in the same manner as in Example 1. The obtained foamed molded article had an apparent appearance with an apparent density of 0.065 g / cm ³ . The performance evaluation results are shown in Table 1.

(Example 5)
Modified foamed particles were obtained in the same manner as in Example 1 except that the temperature of the hot air in the hot air dryer was changed to 62 ° C. The obtained modified foamed particles had a particle size of 2.7 to 3.6 mm, a bulk density of 0.043 g / cm ³ , and a crystallinity of 26.1%. When this modified foamed particle was measured by DSC, the peak derived from crystallization showed a double peak shape. Further, when the exothermic peak is divided into four equal parts by temperature and the first, second, third, and fourth divisions are made from the lowest temperature, the first, third, and fourth divisions in the heat quantity of the exothermic peak The total percentage of heat was 48.4%.
Next, a foamed molded article was obtained from the obtained modified foamed particles in the same manner as in Example 1. The obtained foamed molded article had an apparent appearance with an apparent density of 0.043 g / cm ³ . The performance evaluation results are shown in Table 1.

(Example 6)
Modified foamed particles were obtained in the same manner as in Example 1 except that the temperature of the hot air in the hot air dryer was changed to 57 ° C. The obtained modified foamed particles had a particle size of 2.6 to 3.6 mm, a bulk density of 0.045 g / cm ³ , and a crystallinity of 24.7%. When this modified foamed particle was measured by DSC, the peak derived from crystallization showed a double peak shape. Further, when the exothermic peak is divided into four equal parts by temperature and the first, second, third, and fourth divisions are made from the lowest temperature, the first, third, and fourth divisions in the heat quantity of the exothermic peak The total rate of heat was 55.9%.
Next, a foamed molded article was obtained from the obtained modified foamed particles in the same manner as in Example 1. The obtained foamed molded article had an apparent appearance with an apparent density of 0.045 g / cm ³ . The performance evaluation results are shown in Table 1.

(Example 7)
As the polylactic acid resin, crystalline polylactic acid resin (“Ingeo 4032D” manufactured by NatureWorks, melting point (mp): 166.2 ° C., D-form ratio: 1.3 mol%, L-form ratio: 98.7% ) Modified foaming in the same manner as in Example 1 except that 100 parts by weight and 2 parts by weight of a master batch of an acrylic / styrene compound having an epoxy group as a crosslinking agent and a polylactic acid resin were used. Particles were obtained. The master batch of an acrylic / styrene compound having an epoxy group and a polylactic acid resin is an acrylic / styrene compound having an epoxy group (trade name “ARUFON UG-4030” manufactured by Toagosei Co., Ltd., weight average molecular weight: 11000. , Epoxy value: 1.8 mmol / g) and 30% by weight of polylactic acid resin (trade name “LACEA H-100” manufactured by Mitsui Chemicals, Inc.). The obtained modified foamed particles had a particle size of 2.6 to 3.4 mm, a bulk density of 0.051 g / cm ³ , and a crystallinity of 18.2%. When this modified foamed particle was measured by DSC, the peak derived from crystallization showed a substantially semicircular shape. Further, when the exothermic peak is divided into four equal parts by temperature and the first, second, third, and fourth divisions are made from the lowest temperature, the first, third, and fourth divisions in the heat quantity of the exothermic peak The total rate of heat was 52.8%.
Next, a foamed molded article was obtained from the obtained modified foamed particles in the same manner as in Example 1. The obtained foamed molded article had an apparent appearance with an apparent density of 0.051 g / cm ³ . The performance evaluation results are shown in Table 1.

(Example 8)
Modified foamed particles were obtained in the same manner as in Example 7 except that 1 part by weight of talc was added at the time of melt kneading in a polylactic acid resin extruder. The obtained modified foamed particles had a particle size of 2.7 to 3.8 mm, a bulk density of 0.048 g / cm ³ , and a crystallinity of 20.2%. When this modified foamed particle was measured by DSC, the peak derived from crystallization showed a substantially trapezoidal shape. Further, when the exothermic peak is divided into four equal parts by temperature and the first, second, third, and fourth divisions are made from the lowest temperature, the first, third, and fourth divisions in the heat quantity of the exothermic peak The total amount of heat was 53.3%.

(Comparative Example 1)
The primary expanded particles obtained in Example 1 were supplied into a sealed container. Carbon dioxide was injected into the sealed container at a pressure of 0.3 MPa (G) and left at 25 ° C. for 24 hours to impregnate the primary foamed particles with carbon dioxide.
Next, a foam-molded article was obtained from the primary foamed particles impregnated with carbon dioxide in the same manner as in Example 1. The obtained foamed molded product was swollen as a whole and had a poor appearance.
When the primary foamed particles were measured by DSC, the peak derived from crystallization showed a sharp and substantially triangular shape. Further, when the exothermic peak is divided into four equal parts by temperature and the first, second, third, and fourth divisions are made from the lowest temperature, the first, third, and fourth divisions in the heat quantity of the exothermic peak The total proportion of heat was 36.5%. The performance evaluation results are shown in Table 1.

(Comparative Example 2)
Highly expanded particles were obtained in the same manner as in Example 1 except that the temperature of the hot air in the hot air dryer was changed from 52 ° C to 68 ° C. The obtained highly expanded particles had a particle size of 2.8 to 3.6 mm, a bulk density of 0.041 g / cm ³ , and a crystallinity of 31.5%. When this highly expanded particle was measured by DSC, the peak derived from crystallization showed a substantially triangular shape of a mountain. Further, when the exothermic peak is divided into four equal parts by temperature and the first, second, third, and fourth divisions are made from the lowest temperature, the first, third, and fourth divisions in the heat quantity of the exothermic peak The total proportion of heat was 35.5%.
Next, a foam-molded article was obtained from the obtained highly expanded particles in the same manner as in Example 1. The resulting polylactic acid resin foamed molded article had a very good appearance with a density of 0.041 g / cm ³ , but the inside was not fused. The performance evaluation results are shown in Table 1.

(Comparative Example 3)
70 parts by weight of crystalline polylactic acid resin (“LACEA H140” manufactured by Mitsui Chemicals, melting point (mp): 152.1 ° C., D-form ratio: 4.0 mol%, L-form ratio: 96.0 mol%) 30 parts by weight of an amorphous polylactic acid resin (“LACEA H280” melting point (mp) manufactured by Mitsui Chemicals, Inc .: none, D-form ratio: 11 mol%, L-form ratio: 89 mol%) 2 parts by weight are supplied to a single screw extruder having a diameter of 54 mm, melt kneaded, extruded in a strand form from a multi-nozzle mold attached to the tip of the single screw extruder, cooled in water at 25 ° C., and cut. Columnar polylactic acid resin particles having a diameter of 1.1 mm and a length of 1.9 mm were obtained.
Next, 1000 g of the polylactic acid resin particles are supplied into a 5-liter pressure vessel and sealed, and carbon dioxide is injected into the sealed vessel at a pressure of 3 MPa (G) for 4 hours at an ambient temperature of 25 ° C. Then, the polylactic acid resin particles were impregnated with carbon dioxide.
Next, the polylactic acid resin particles impregnated with carbon dioxide were put into a foaming machine, and steam adjusted to 65 ° C. was introduced for 5 seconds and heated. However, the polylactic acid resin particles were slightly clouded and did not foam. Further, even when the steam temperature was raised to 90 ° C., it only became cloudy, and even when the steam introduction time was extended to 180 seconds, only fine foaming occurred.

(Comparative Example 4)
50 parts by weight of crystalline polylactic acid resin (“Ingeo 4032D” manufactured by NatureWorks, melting point (mp): 166.2 ° C., D-form ratio: 1.3 mol%, L-form ratio: 98.7%) and amorphous Columnar polylactic acid having a diameter of 1.1 mm and a length of 1.9 mm in the same manner as in Comparative Example 1 with 50 parts of a polylactic acid resin (“LACEA H280” manufactured by Mitsui Chemicals) and 0.2 part of talc as a bubble regulator Resin particles were obtained.
Subsequently, 1000 g of the polylactic acid resin particles are supplied into a 5 liter pressure vessel and sealed, and carbon dioxide is injected into the sealed vessel at a pressure of 3 MPa (G), and the pressure is reduced to 0.1 at an atmospheric temperature of 10 ° C. The polylactic acid resin particles were impregnated with carbon dioxide for 5 hours.
Next, the polylactic acid resin particles impregnated with carbon dioxide were put into a foaming machine, and steam adjusted to 65 ° C. was introduced for 5 seconds and heated. However, the polylactic acid resin particles were slightly clouded and did not foam. Further, even when the steam temperature was raised to 90 ° C., it only became cloudy, and even when the steam introduction time was extended to 180 seconds, it only became cloudy.

From Table 1, when the modified foamed particles in which the total amount of heat of the first, third, and fourth categories occupies 45% or more of the total heat generation of the exothermic peak, appearance, fusion It can be seen that a foamed molded article excellent in heat resistance and heat resistance can be obtained.
In addition, the DSC curves of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in FIGS. In the figure, X means an exothermic peak derived from crystallization.

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 Exit: 41f Discharge pipe: 42 Coolant: A Virtual circle: Exothermic peak derived from X crystallization: a Two intersections where the baseline extension line and the DSC curve intersect

Claims (6)

Including at least a polylactic acid-based resin, the polylactic acid-based resin having an exothermic peak derived from crystallization when measured with a differential scanning calorimeter,
The exothermic peak is divided into four equal parts in the first, second, third and fourth sections from the lower temperature,
(1) The total calorific value of the first, second, third and fourth sections is 10 J / g or more,
(2) It has a shape in which the total amount of heat generated in the first, third, and fourth sections is 45% or more with respect to the total amount of heat generated in the first, second, third, and fourth sections. Polylactic acid resin foam characterized by the following. The total amount of heat generated in the first, second, third and fourth sections is 12 J / g or more,
2. The poly according to claim 1, wherein the total calorific value of the first, third, and fourth sections is 50% or more of the total calorific value of the first, second, third, and fourth sections. Lactic acid resin foam.   The polylactic acid-based resin is a monomer component composed of both D-form and L-form optical isomers of lactic acid or lactide, and the content of the lesser of the D-form or L-form is less than 5 mol%. The polylactic acid-based resin foam according to claim 1 or 2, wherein the polylactic acid-based resin foam is derived only from a monomer component consisting of an optical isomer of either D-form or L-form.   The polylactic acid resin foam according to any one of claims 1 to 3, wherein the polylactic acid resin has an endothermic amount of an endothermic peak of crystal melting of 30 J / g or more. 0.02-0.2 g / obtained by foaming the polylactic acid-based resin foam by heating a polylactic acid-based resin primary foam having a bulk density of 0.05-0.5 g / cm ^3. The polylactic acid resin foam according to any one of claims 1 to 4, which is a polylactic acid resin high-magnification foam having a bulk density of cm ³ . A method for producing a polylactic acid-based resin foam according to any one of claims 1 to 5,
A polylactic acid resin primary foam having a bulk density of 0.05 to 0.5 g / cm ³ is heated for 10 to 300 seconds in a temperature range of glass transition temperature (Tg) −20 ° C. to glass transition temperature (Tg) + 5 ° C. To produce a polylactic acid resin high-magnification foam having a bulk density of 0.02 to 0.2 g / cm ³ .

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