JP2012153907A - Method of producing expandable polylactic acid-based resin particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing expandable polylactic acid-based resin particles, by which the expandable polylactic acid-based resin particles excellent in mutual adhesiveness of expandable particles are obtained without using an adhesiveness-improving agent.SOLUTION: In the expandable polylactic acid-based resin particles, a polylactic acid-based resin that has an endothermic energy amount of 10 J/g, measured by differential scanning calorimetry at heating rate of 2°C/min, is used as a base resin. The method of producing the expandable polylactic acid-based resin particles includes: an impregnation step of impregnating 100 pts.wt of polylactic acid-based resin particles with 1 pt.wt or more of physical foaming agent; and a dissipation step of exposing the polylactic acid-based resin particles that is impregnated with the physical foaming agent under the condition of the temperature of 0 to 40°C to dissipate 10-60 wt.% of the physical foaming agent thus impregnated, thereby obtaining the expandable polylactic acid-based resin particles having a foaming agent content of 3.9 wt.% or lower.

Description

The present invention relates to secondary foaming and melting during molding that can be used for the production of molded foams of polylactic acid-based resin particles such as cushioning materials for packaging, agricultural boxes, fish boxes, automobile parts, building materials, and civil engineering materials. The present invention relates to a method for producing expandable polylactic acid-based resin particles capable of obtaining expanded particles having excellent adhesion.

Conventionally, foams made of general-purpose resins such as polyethylene resin, polypropylene resin, and polystyrene resin have been used in many fields because they are excellent in lightness, heat insulation, and buffering properties. On the other hand, in recent years, awareness of the global environment has increased, and environmental problems such as the exhaustion of petroleum resources have been raised. Instead of the above-mentioned general-purpose resins made from petroleum resources, plant-derived polylactic acid-based resins Is attracting attention. The polylactic acid-based resin is made from a plant such as corn as a starting material, and is an environment-friendly thermoplastic resin from the viewpoint of carbon neutral. Such polylactic acid-based resin is expected to increase versatility in the future. Similarly, polylactic acid-based resins are expected to be used as environmentally friendly plant-derived general-purpose foaming resins. Research has been conducted on foams made from polylactic acid-based resins. Development of a foamed particle molded body capable of obtaining a foam having a desired shape without being relatively restricted.

As a prior art related to a foam made of a polylactic acid-based resin, an expandable resin particle that absorbs a volatile foaming agent in a temperature range where the degree of crystallinity of an aliphatic polyester such as polylactic acid is in the range of 0 to 20%. Production method (Patent Document 1), containing 50 mol% or more of lactic acid component units, the difference between the endothermic amount and the calorific value in heat flux differential scanning calorimetry is 0 J / g or more and less than 30 J / g, and the endothermic amount is 15 J / g or more of expanded particles (Patent Document 2), polylactic acid resin expanded particles containing a fusion improver (Patent Document 3), and excellent fusibility between expanded particles, and low temperature (low pressure steam) ) And polylactic acid resin foamed particles (Patent Document 4) obtained by using the foamed polylactic acid resin particles are known.

JP 2000-136261 A JP 2004-83890 A JP 2006-282750 A JP 2006-282755 A

However, the foamed particle molded body made of a polylactic acid resin described in Patent Document 1 is a method in which foamable resin particles are filled in a mold and the resin particles are foamed with hot air, and at the same time, the particles are fused together. Therefore, the density variation in the part within the foamed particle molded body is relatively large, the fusion property between the foamed particles, the dimensional stability is insufficient, and the mechanical properties are also insufficient. .

In order to solve the problems of the foamed particle molded article described in Patent Document 1 and the like and to improve the fusion property between the foamed particles, dimensional stability, etc., the present inventors disclosed a crystal An attempt was made to produce foamed particles in a state where the polylactic acid-based resin was not crystallized using a functional polylactic acid-based resin, and to obtain a foamed particle molded body using the foamed particles. However, the polylactic acid-based resin expanded particles described in Patent Document 2 have been found to be improved in terms of the mutual fusing property and secondary expandability of the expanded particles during in-mold molding. In order to increase the temperature, it is desired to widen the heating temperature range in which a good molded product can be obtained at the time of in-mold molding.
Furthermore, the present inventors have found that in Patent Document 3 and Patent Document 4, in-mold molding at a low molding temperature is possible by adding a specific fusing property improving agent to the polylactic acid-based foamed resin particles. I found it. However, if the shape of the foamed particle molded body is complicated, the fusion between the foamed particles becomes insufficient, and if the thickness is large, the fusion between the foamed particles at the center of the foamed particle molded body becomes insufficient. This left room for improvement in terms of fusibility.

An object of the present invention is to provide a process for producing expandable polylactic acid resin particles, which can obtain polylactic acid resin expanded particles having excellent fusion properties between expanded particles without using a fusing property improving agent. And

As a result of intensive studies in view of the above problems, the present inventors have found that a foamable polylactic acid-based resin in which at least a part of the foaming agent present in the surface layer portion of the polylactic acid-based resin particles is impregnated with a physical foaming agent is diffused. The present inventors have found that polylactic acid-based resin foamed particles obtained by a production method for foaming particles become foamed particles having excellent in-mold moldability, and have reached the present invention.
That is, according to the present invention, the following methods (1) to (3) for producing expandable polylactic acid resin particles and expandable polylactic acid resin particles obtained by the production method are provided.
(1) Based on the heat flux differential scanning calorimetry described in JIS K7122 (1987), the mixture was heated to 30 ° C. higher than the end of the melting peak and melted, and kept at that temperature for 10 minutes. After cooling to 110 ° C. at a cooling rate of 2 ° C./min and keeping at that temperature for 120 minutes, after heat treatment to cool to 40 ° C. at a cooling rate of 2 ° C./min, melting again at a heating rate of 2 ° C./min Expandable polylactic acid resin particles having a base resin of polylactic acid resin having an endotherm (Rendo) in a DSC curve of 10 J / g or more obtained when heated to 30 ° C. higher than the end of the peak and melted A manufacturing method of
(I) an impregnation step of impregnating 100 parts by weight of the polylactic acid-based resin particles with 1 part by weight or more of a physical foaming agent;
(Ii) 10-60% by weight of the physical foaming agent impregnated with the polylactic acid resin particles impregnated with the physical foaming agent is diffused under a temperature of 0 to 40 ° C. A dissipation step for producing 3.9 wt% or less of expandable polylactic acid resin particles;
A process for producing expandable polylactic acid-based resin particles.
(2) The method for producing expandable polylactic acid-based resin particles according to (1), wherein the dissipation step is performed under a condition of a relative humidity of 40% or more.
(3) The method for producing expandable polylactic acid resin particles according to (1) or (2), wherein the main component of the physical foaming agent is carbon dioxide.

Note that in expandable polylactic acid resin particles, may the surface vicinity resin particles of the surface layer portion (S _{B) (or} simply the surface layer portion), the central portion of the central portion near the resin particles (C _{B) (or} simply center Part).

In the foamable polylactic acid resin particles produced by the production method of the present invention, the surface layer portion (S _B ) has a relatively larger amount than the center portion (C _B ) in the dissipation after impregnation with the physical blowing agent. Since the physical foaming agent is dissipated, when the expandable polylactic acid-based resin particles are expanded, the polylactic acid-based resin in which the crystallinity of the surface layer portion (S _B ) of the expanded particles is lower than that of the central portion (C _B ). Foamed particles are obtained, and a polylactic acid-based resin expanded particle molded body having excellent fusion property between the polylactic acid-based resin expanded particles can be obtained by in-mold molding of the expanded particles. Furthermore, since a polylactic acid resin having an endotherm (Rendo) of 10 J / g or more is used as a base resin, there are many components that can be crystallized. Therefore, the expandable polylactic acid resin particles obtained by the production method of the present invention The difference in crystallinity between the central part and the surface layer part of the polylactic acid-based resin foamed particles obtained by foaming can be widened, and a sufficient effect of improving the fusing property at the time of in-mold molding can be expected. Further, the foamed particle molded body obtained by further in-mold molding the polylactic acid resin foamed particles obtained by foaming the expandable polylactic acid resin particles produced by the production method of the present invention has a crystallinity by high temperature curing or the like. Increased heat resistance is high.

Furthermore, the polylactic acid-based resin foam particles obtained by foaming the expandable polylactic acid-based resin particles produced by the method of the present invention in which the dissipation step is performed under conditions of relative humidity of 40% or more have a surface layer thickness. Since the thickness becomes even thicker, the heat resistance of the polylactic acid-based resin expanded particles is increased, so that the heating temperature range in which a good expanded particle molded body can be obtained during in-mold molding can be expanded.
Furthermore, if the physical foaming agent is mainly composed of carbon dioxide gas, the ozone layer is not destroyed and is inexpensive, and the foamed polylactic acid resin particles can be used as a base resin for a polylactic acid resin. Because of its high solubility, it becomes foamable polylactic acid resin particles suitable for obtaining expanded particles with a low apparent density, and the dissipation rate of the foaming agent from the polylactic acid resin particles impregnated with the foaming agent is It is suitable for the production method of the present invention because it exhibits an appropriate speed in the adjustment of the amount of dispersion, particularly the amount of foaming agent escape in the surface layer portion.

It is an example of the DSC curve which shows the endothermic quantity (Rendo) of base-material resin measured with the heat flux differential scanning calorimeter. It is an example of the DSC curve which shows the endothermic quantity (Rendo) of base-material resin measured with the heat flux differential scanning calorimeter. It is an example of the DSC curve which shows the emitted-heat amount (Bexo) and the endothermic amount (Bendo) of the expanded particle measured with the heat flux differential scanning calorimeter. It is an example of the DSC curve which shows the emitted-heat amount (Bexo) and the endothermic amount (Bendo) of the expanded particle measured with the heat flux differential scanning calorimeter. It is an example of the DSC curve which shows the emitted-heat amount (Bexo) and the endothermic amount (Bendo) of the expanded particle measured with the heat flux differential scanning calorimeter. 2 is a scanning electron micrograph of a part of a cross-section obtained by dividing the polylactic acid foamed particles obtained in Example 1 into approximately two parts. 2 is a scanning electron micrograph of a part of a surface layer portion in a cross section obtained by dividing the polylactic acid foamed particles obtained in Example 1 into approximately two parts. 2 is a scanning electron micrograph of a part of a cross-section obtained by dividing the polylactic acid foamed particles obtained in Comparative Example 1 into approximately two parts. 2 is a scanning electron micrograph of a part of a surface layer portion in a cross-section obtained by dividing a polylactic acid foamed particle obtained in Comparative Example 1 into approximately two parts.

Hereinafter, the manufacturing method of the expandable polylactic acid-type resin particle of this invention and the expandable polylactic acid-type resin particle obtained by this method are demonstrated.
The method for producing expandable polylactic acid-based resin particles of the present invention (hereinafter sometimes simply referred to as expandable resin particles) includes:
Based on the heat flux differential scanning calorimetry described in JIS K7122 (1987), the mixture was heated to 30 ° C. higher than the end of the melting peak and melted, maintained at that temperature for 10 minutes, and then cooled at a cooling rate of 2 After cooling at 110 ° C / min to 110 ° C and keeping at that temperature for 120 minutes, after heat treatment cooling to 40 ° C at a cooling rate of 2 ° C / min, again at the end of the melting peak at a heating rate of 2 ° C / min Method for producing expandable polylactic acid-based resin particles using a polylactic acid-based resin having a heat absorption (Rendo) of 10 J / g or more in a DSC curve obtained when heated to a temperature higher than 30 ° C. as a base resin Because
(I) an impregnation step of impregnating 100 parts by weight of the polylactic acid-based resin particles with 1 part by weight or more of a physical foaming agent;
(Ii) 10-60% by weight of the physical foaming agent impregnated with the polylactic acid resin particles impregnated with the physical foaming agent is diffused under a temperature of 0 to 40 ° C. A dissipation step for producing 3.9 wt% or less of expandable polylactic acid resin particles;
It is characterized by including.
Hereinafter, the “method for producing expandable polylactic acid resin particles” of the present invention will be described in detail.

[1] Polylactic acid resin particles (1) Base resin (a) Base resin Polylactic acid resin particles (hereinafter simply referred to as resin particles) used in the production of the expandable polylactic acid resin particles of the present invention The polylactic acid-based resin which is a base resin is a polymer containing 50 mol% or more of units derived from lactic acid in the resin. Examples of the polylactic acid resin include (a) a polymer of lactic acid, (b) a copolymer of lactic acid and another aliphatic hydroxycarboxylic acid, and (c) lactic acid, an aliphatic polyhydric alcohol, and an aliphatic polyvalent carboxylic acid. A copolymer of an acid, (d) a copolymer of lactic acid and another aliphatic polyvalent carboxylic acid, (e) a copolymer of lactic acid and an aliphatic polyhydric alcohol, (f) any one of (a) to (e) above The mixture by the combination of these, etc. is included. Specific examples of the lactic acid include L-lactic acid, D-lactic acid, DL-lactic acid or their cyclic dimer L-lactide, D-lactide, DL-lactide, or a mixture thereof. .

Examples of the other aliphatic hydroxycarboxylic acid in (b) include glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, and hydroxyheptanoic acid. Examples of the aliphatic polyhydric alcohol in (c) and (e) include ethylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, decamethylene. Examples include glycol, glycerin, trimethylolpropane, and pentaerythritol. Examples of the aliphatic polyvalent carboxylic acid in (c) and (d) include succinic acid, adipic acid, suberic acid, sebacic acid, dodecanedicarboxylic acid, succinic anhydride, adipic anhydride, trimesic acid, and propanetricarboxylic acid. , Pyromellitic acid, pyromellitic anhydride and the like.

Specific examples of the method for producing the polylactic acid resin include, for example, a method of direct dehydration polycondensation using lactic acid or a mixture of lactic acid and aliphatic hydroxycarboxylic acid as a raw material (for example, US Pat. No. 5,310,865). And a ring-opening polymerization method for polymerizing a cyclic dimer (lactide) of lactic acid (for example, a production method disclosed in US Pat. No. 2,758,987), lactic acid and A ring-opening polymerization method (for example, disclosed in US Pat. No. 4,057,537) in which a cyclic dimer of an aliphatic hydroxycarboxylic acid, for example, lactide or glycolide and ε-caprolactone is polymerized in the presence of a catalyst. And a method of directly dehydrating polycondensation of a mixture of lactic acid, an aliphatic dihydric alcohol and an aliphatic dibasic acid (for example, disclosed in US Pat. No. 5,428,126). Production method), a method in which lactic acid, an aliphatic dihydric alcohol, an aliphatic dibasic acid and a polymer are condensed in the presence of an organic solvent (for example, the production method disclosed in European Patent Application No. 071880). In the production of a polyester polymer by performing a dehydration polycondensation reaction in the presence of a lactic acid polymer in the presence of a catalyst, a method of performing solid phase polymerization in at least a part of the steps can be mentioned. The method is not particularly limited. In addition, a small amount of an aliphatic polyhydric alcohol such as glycerin, an aliphatic polybasic acid such as butanetetracarboxylic acid, a polyhydric alcohol such as a polysaccharide may be coexisted and copolymerized. The molecular weight may be increased by using a binder (polymer chain extender) such as a polyisocyanate compound. Further, it may be branched with a branching agent typified by a polyhydric aliphatic alcohol such as pentaerythritol.

The base resin in the present invention is preferably composed of 20 to 100 parts by weight of a crystalline polylactic acid resin (m) and 0 to 80 parts by weight of an amorphous polylactic acid resin (n) (provided that (m ) And (n) are 100 parts by weight.
When the ratio of the crystalline polylactic acid-based resin (m) in the base resin is less than 20 parts by weight, the foamed polylactic acid-based resin particles (A) are expanded, and the obtained polylactic acid-based resin expanded particles are further Even if the crystalline component of the foamed particle molded body obtained by in-mold molding is sufficiently crystallized by high-temperature curing or the like, the mechanical properties and heat resistance may be insufficient. From this viewpoint, the content of the crystalline polylactic acid resin (m) in the base resin is preferably 30 parts by weight or more, and more preferably 40 parts by weight or more.
The base resin in the present invention is preferably a mixture of 20 to 90 parts by weight of a crystalline polylactic acid resin (m) and 10 to 80 parts by weight of an amorphous polylactic acid resin (n). From the above viewpoint, the polylactic acid resin (m) is preferably a mixture of 30 to 80 parts by weight of the polylactic acid resin (m) and 20 to 70 parts by weight of the noncrystalline polylactic acid resin (n). It is particularly preferable from the above-mentioned viewpoint that it is a mixture of 40 to 80 parts by weight and an amorphous polylactic acid-based resin (n) 20 to 60 parts by weight (however, the total of parts by weight of (m) and (n) is 100 parts by weight). If it is in the above-mentioned range, it is sufficient when the crystalline component of the foamed particle molded body obtained by foaming the resin particles and further molding the obtained foamed particles in a mold is sufficiently crystallized by high-temperature curing or the like. Since it is possible to make a foamed particle molded body having heat resistance and also has an amorphous polylactic acid resin, the foamed particles obtained after foaming the resin particles become highly fusible, and further secondary foamed It becomes easy to adjust the sex.

(B) Endothermic amount in differential scanning calorimetry of base resin The polylactic acid-based resin that is the base resin is the above-mentioned polylactic acid-based resin in differential scanning calorimetry at a heating rate of 2 ° C./min described later. The endothermic amount (Rendo) is 10 J / g or more.
If the endothermic amount is 10 J / g or more, the foamed particle molded body obtained by foaming the expandable polylactic acid-based resin particles and then further molded in the mold is less likely to be deformed in a heated atmosphere by crystallization. To obtain a foamed particle molded body having heat resistance, rigidity and the like, and the difference in crystallinity between the central part and the surface layer part of the polylactic acid resin foamed particles obtained from the base resin described later It becomes easy to spread. From this viewpoint, the endothermic amount is preferably 15 J / g or more, and more preferably 20 J / g or more. On the other hand, the upper limit of the endothermic amount is not particularly limited, but is generally 70 J / g from the properties of a normal base resin.

In the present specification, the endothermic amount (Rendo) in the differential scanning calorimetry of the polylactic acid-based resin is a value obtained by the heat flux differential scanning calorimetry described in JIS K7122 (1987). However, 1 to 4 mg of polylactic acid resin is used as a test piece, and the condition adjustment of the test piece and the measurement of the DSC curve are performed according to the following procedure. Place the test piece in the container of the DSC apparatus, heat and melt to a temperature 30 ° C. higher than the end of the melting peak, hold at that temperature for 10 minutes, cool to 110 ° C. at a cooling rate of 2 ° C./min, After maintaining the temperature for 120 minutes, after heat treatment to cool to 40 ° C. at a cooling rate of 2 ° C./min, when again heating and melting to a temperature 30 ° C. higher than the end of the melting peak at a heating rate of 2 ° C./min To obtain the DSC curve obtained.
The endothermic amount (Rendo) of the polylactic acid resin, as shown in FIG. 1, is a point a where the endothermic peak departs from the low-temperature base line of the endothermic peak of the DSC curve, and the endothermic peak is on the high-temperature side. A point returning to the base line is a point b, and a value obtained from a straight line connecting the point a and the point b and an area of a portion surrounded by the DSC curve. Also, the device should be adjusted so that the baseline is as straight as possible. If the baseline is curved as shown in FIG. 2, the curved baseline on the low temperature side of the endothermic peak is the curved state of the curve. The point where the endothermic peak moves away from the curved low-temperature base line is point a, and the curved base line on the high-temperature side of the endothermic peak is maintained in the curved state of the curve. The point where the endothermic peak returns to the curved high temperature side baseline is drawn as point b.

In the measurement of the endothermic amount (Rendo), the condition of the test piece and the measurement conditions of the DSC curve were as follows: holding at 110 ° C. for 120 minutes, cooling rate of 2 ° C./min and heating rate of 2 ° C./min The reason for adopting it is to obtain the endotherm (Rendo) of the polylactic acid test piece that has been adjusted to a fully crystallized state or a state close to it by crystallization as much as possible. Because it is. As described above, the case where the polylactic acid resin is used as the test piece has been described. When the endothermic amount of the expanded particle is measured in the same procedure using the expanded particle as the test piece, the same value as the endothermic amount (Rendo) of the base resin is obtained. It becomes.
In the present specification, the crystalline polylactic acid-based resin has an endothermic peak exceeding 10 J / g in the DSC curve obtained by the above-described procedure for measuring the endothermic amount of the polylactic acid-based resin. The endothermic amount of the crystalline polylactic acid resin is usually 30 to 70 J / g. In addition, the non-crystalline polylactic acid resin in the present specification means that an endothermic peak of 2 J / g or less appears in the DSC curve obtained by the above-described procedure for measuring the endothermic amount of the polylactic acid resin, or no endothermic peak appears. Is.

(2) Other resin components and additives The base resin used in the production of the expandable polylactic acid-based resin particles of the present invention is blended with other resin components within a range that does not impair the object and effects of the present invention. Can do. The mixed resin of the polylactic acid resin and other resin preferably contains 50% by weight or more of polylactic acid resin, more preferably 70% by weight or more, and further preferably 90% by weight or more.
Examples of other resins that can be mixed with the polylactic acid-based resin include polyethylene-based resins, polypropylene-based resins, polystyrene-based resins, polyester-based resins, etc. Among them, biodegradable containing at least 35 mol% of aliphatic ester component units. Aliphatic polyester resins are preferred. Examples of the aliphatic polyester resin in this case include hydroxy acid polycondensates other than the polylactic acid resin, ring-opening polymerization products of lactones such as polycaprolactone, polybutylene succinate, polybutylene adipate, and polybutylene succinate adipate. And polycondensates of aliphatic polyhydric alcohols such as poly (butylene adipate / terephthalate) and aliphatic polycarboxylic acids.
For example, the base resin of the present invention may be colored by adding a coloring pigment or dye such as black, gray, brown, blue, or green. If colored resin particles obtained from the colored base resin are used, colored foamed particles and molded articles thereof can be obtained.
Examples of the colorant include organic and inorganic pigments and dyes. As such pigments and dyes, various conventionally known pigments can be used.

In addition, the base resin may be premixed with an inorganic substance such as talc, calcium carbonate, borax, zinc borate, aluminum hydroxide, calcium stearate, or an organic substance such as polyethylene wax or polypropylene wax, as a foam regulator. it can.
When an additive such as a color pigment, dye, or inorganic substance is added to the base resin, the additive can be added to the base resin as it is in the pelletizing step or the blowing agent impregnation step. It is preferable to make a master batch of the additive in consideration and knead it and the base resin in a pelletizing step so that the additive is uniformly contained in the base resin. The blending amount of the color pigment or dye varies depending on the color of the color, but it is usually preferably 0.001 to 5 parts by weight with respect to 100 parts by weight of the base resin. Moreover, it is preferable that the compounding quantity of an inorganic substance shall be 0.001-5 weight part with respect to 100 weight part of base resin, and also 0.02-1 weight part. By blending an organic material such as the above inorganic material or polyethylene wax into the base resin, it is possible to expect an effect of improving the expansion ratio, an improvement in the uniformity of the cell diameter, and an effect of adjusting the cell diameter.
Moreover, in the said method, mixing of additives, such as a flame retardant, an antistatic agent, a weathering agent, and a thickener, is also possible in the range which does not interfere with the effect of the manufacturing method of this invention.

(3) Production of polylactic acid-based resin particles In the production of polylactic acid-based resin particles, a strand cut method and underwater cut are performed using a base resin composed of a polylactic acid-based resin containing a crystalline polylactic acid-based resin as a raw material. It is obtained by adopting a well-known pelletizing method such as a method. As a specific example, a base resin or a resin composition containing additives as necessary is supplied to an extruder, melted, kneaded, extruded into a strand, and the strand-shaped extrudate is cooled with water. After cooling, the resin particles can be obtained by cutting to a predetermined length or cooling the extruded strand after cutting to a predetermined length or simultaneously with the cutting. Other resin particles can be produced by melting and kneading the base resin using an extruder, then extruding it into a plate or lump, cooling the extrudate with a cooling press or the like, and then crushing the cooling resin. For example, a well-known method such as a method obtained by breaking in a lattice shape can be employed. In addition, the cooling at the time of manufacturing the above resin particles is easy to adjust the ratio (Bexo / Bendo) of the heat generation amount (Bexo) of the foamed particles and the heat absorption amount (Bendo) of the foamed particles obtained in the subsequent steps. From this point, it is preferable to quench by submerging.

The resin particle average diameter (D) and [resin particle average length (L) / resin particle average diameter (D)] obtained by cutting the strand-like extrudate are appropriately determined depending on conditions such as foaming method and mold shape. Selected. D is preferably 0.1 to 5 mm, more preferably 0.3 to 4 mm, and L / D is preferably 1.0 to 1.5.
Moreover, the average weight per resin particle is preferably 0.05 to 10 mg, more preferably 0.1 to 4 mg from the viewpoints of productivity and foaming agent impregnation properties. The shape of the resin particles is not particularly limited, and can be various shapes such as a spherical shape and a rod shape in addition to a columnar shape (pellet shape).

When the base resin is hygroscopic when the base resin is melt kneaded and extruded into a strand or the like as described above, it is preferable to dry the base resin in advance. If a resin that absorbs a large amount of water is supplied to the extruder, it will adversely affect the uniformity of the foamed foam bubbles obtained by foaming the resin particles obtained in the subsequent process. When the base resin is melt-kneaded in an extruder in order to obtain resin particles, the physical properties may be lowered, for example, the melt flow rate (MFR) of the base resin becomes extremely large.
In order to suppress deterioration of the base resin, a method of removing moisture from the base resin by vacuum suction using an extruder with a vent port can be employed. Moreover, it is also possible to set the upper limit temperature of the extrusion temperature condition so that the physical properties of the base resin do not deteriorate. The obtained resin particles are preferably stored in an environment where hydrolysis does not proceed by avoiding high temperature and high humidity conditions.

[2] Method for producing expandable polylactic acid-based resin particles
(I) an impregnation step of impregnating 100 parts by weight of the polylactic acid-based resin particles with 1 part by weight or more of a physical foaming agent;
(Ii) The polylactic acid resin particles impregnated with the physical foaming agent are exposed to a temperature of 0 to 40 ° C. to dissipate 10 to 60% by weight of the impregnated physical foaming agent, and the amount of the foaming agent impregnated A process of dissipating foamed polylactic acid resin particles having a weight of 3.9% by weight or less,
It is characterized by including.
The production method of expandable polylactic acid-based resin expanded particles will be described below.

(1) Physical foaming agent impregnation step The physical foaming agent impregnation step is a step of impregnating 100 parts by weight of the polylactic acid resin particles with 1 part by weight or more of a physical foaming agent.
(I) Physical foaming agent As the physical foaming agent, conventionally known ones, propane, isobutane, normal butane, isohexane, normal hexane, cyclobutane, cyclohexane, isopentane, normal pentane, cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, Chlorofluoromethane, trifluoromethane, 1,1,1,2-tetrafluoroethane, 1-chloro-1,1-difluoroethane, 1,1-difluoroethane, 1-chloro-1,2,2,2-tetrafluoro Examples include organic physical foaming agents such as ethane, or inorganic physical foaming agents such as nitrogen, carbon dioxide, argon, air, and water, or a mixture of two or more selected from them. And an inexpensive inorganic physical foaming agent is preferable. , Or it is further preferable that the carbon dioxide as a main component.
In the present invention, the main component of the physical foaming agent is most preferably carbon dioxide. If the main component of the physical foaming agent is carbon dioxide, it is highly compatible with the polylactic acid resin, which is the base resin of the expandable polylactic acid resin particles, so it is suitable for obtaining expanded particles with a low apparent density. Polylactic acid resin particles.
Further, since the impregnated carbon dioxide gas escapes from the foamable polylactic acid resin particles at an appropriate rate, it is suitable for dissipating the physical foaming agent in the present invention, and the foamable polylactic acid resin particles are foamed. It becomes easy to adjust the crystallinity of the surface layer part and the center part of the polylactic acid-based resin foamed particles obtained by the treatment. The phrase “the main component of the physical foaming agent is carbon dioxide” means that 60 mol% or more of the physical foaming agent is carbon dioxide, more preferably 70 mol% or more, and even more preferably 80 mol% or more. .

(B) Impregnation method of physical foaming agent Next, an impregnation example in which the polylactic acid resin particles are impregnated with a physical foaming agent will be described.
As the impregnation method of the physical foaming agent, when the polylactic acid resin particles are produced in the pelletizing process by an extruder, the physical foaming agent is pressed into the extruder to produce the polylactic acid resin particles and the foaming agent. It is also possible to perform the impregnation in one step, but from the viewpoint of adjusting the impregnation amount of the physical foaming agent, adjusting the impregnation temperature of the physical foaming agent, adjusting the crystallinity of the foamable resin particles described later, and the like. A method in which polylactic acid resin particles are impregnated with a physical foaming agent in an aqueous medium is preferred. In this case, the resin particles can be impregnated with the physical foaming agent by placing the aqueous medium and the resin particles in the airtight container, and then pressing the physical foaming agent into the airtight container and stirring.
As the aqueous medium, water is preferably used, and more preferably ion-exchanged water. However, the aqueous medium is not limited to water, and any aqueous medium that does not dissolve the polylactic acid resin and can disperse the resin particles. Can be used. Examples of the aqueous medium other than water include ethylene glycol, glycerin, methanol, ethanol, and the like. The aqueous medium includes a mixed solution of water and an organic solvent such as the alcohol.
The impregnation temperature of the physical foaming agent is preferably 10 to 50 ° C, more preferably 20 to 40 ° C. Considering the operability and efficiency of impregnation, the above temperature range is preferable. Moreover, if it is the said temperature range, the crystallinity degree of the resin particle can be accelerated | stimulated moderately, and adjustment of crystallization is easy.
The pressure of the physical foaming agent in the gas phase impregnation during the gas phase impregnation when impregnating the resin particles with the physical foaming agent or the liquid layer impregnation is the apparent density of the target foamed particles. Although it varies depending on (foaming ratio), it is usually 0.5 to 5.0 MPa (G), and the impregnation time is about 0.2 to 7 hours.

(C) Impregnation amount of foaming agent The impregnation amount of the physical foaming agent needs to be impregnated in an amount that also takes into account the dissipation due to the dissipation of the physical foaming agent in the next step. The impregnation amount of the physical foaming agent is 1 part by weight or more, preferably 2 parts by weight or more, and more preferably 3 parts by weight or more with respect to 100 parts by weight of the polylactic acid resin particles.
The upper limit of the impregnation amount is 10 to 60% by weight of the physical foaming agent as described in claim 1 of the present invention, so that the resin particle foaming agent impregnation amount is 3.9% by weight or less. The amount is approximately 10 parts by weight with respect to 100 parts by weight of the lactic acid resin. If the impregnation amount is less than 1 part by weight, the foamable resin particles may not be sufficiently foamed when heated and foamed after dissipation of the physical foaming agent. There is a possibility that the treatment time takes a long time during the dissipation or the crystallization of the resin particles is easy to proceed, so that the fusion property at the time of in-mold molding of the obtained foamed particles may be insufficient.
The amount of impregnation (parts by weight) of the physical foaming agent with respect to 100 parts by weight of the resin particles is obtained by the following equation (3).
Physical foaming agent impregnation amount (parts by weight) = [(polylactic acid resin particle weight after physical foaming agent impregnation−polylactic acid resin particle weight before physical foaming agent impregnation) / polylactic acid resin particles before physical foaming agent impregnation Weight] × 100 (parts by weight) (3)
The weight of the polylactic acid-based resin particles impregnated with the physical foaming agent in the above formula (3) is the physical foaming agent-impregnated polylactic acid measured 10 minutes after the physical foaming agent is impregnated and taken out to the atmospheric pressure This refers to the weight of resin particles. The weight of the polylactic acid resin particles after impregnation with the physical foaming agent when the polylactic acid resin particles are impregnated with the physical foaming agent in an aqueous medium in an airtight container is the atmospheric pressure after impregnation with the physical foaming agent. It is the weight of the physical foaming agent impregnated polylactic acid resin particles measured after removing the moisture on the surface of the resin particles with air or a centrifuge, and after 10 minutes have passed since being taken out to atmospheric pressure. Measured.

(D) When carbon dioxide gas is used as the physical foaming agent Hereinafter, the case where carbon dioxide gas is used as the physical foaming agent will be described.
The amount of carbon dioxide impregnation is 1 part by weight or more, preferably 2 parts by weight or more, and more preferably 3 parts by weight or more with respect to 100 parts by weight of the polylactic acid resin, as described above. When the impregnation amount is less than 1 part by weight, there is a possibility that the resin particles may not be sufficiently foamed during foaming after dissipation of the foaming agent. When the agent escapes, the treatment time takes a long time, or if carbon dioxide gas is impregnated into the polylactic acid resin, the glass transition temperature is lowered, resulting in a relatively high crystallization speed. There is a possibility that the fusibility at the time of in-mold molding of the foamed particles obtained in the subsequent process will be insufficient.

The carbon dioxide impregnation temperature is preferably 10 to 50 ° C., more preferably 20 to 40 ° C., as described above. Considering the operability and efficiency of impregnation, the above temperature range is preferable. Moreover, if it is the said temperature range, it will be easy to adjust so that crystallization of a resin particle may be suppressed.
In particular, when carbon dioxide is used as the foaming agent, the impregnation temperature is preferably (−0.6X + 50) ° C. or lower, where X (weight%) represents the amount of carbon dioxide impregnated with respect to the resin particles. When the temperature exceeds (−0.6X + 50) ° C., the crystallization is extremely advanced particularly in a highly crystalline polylactic acid resin, and a predetermined foaming ratio may not be obtained. In addition, when foamed particles obtained in a subsequent process are molded in the mold, if the expandability of the foamed particles and the fusion property between the foamed particles are reduced, the foamed particles must be molded at a higher temperature. In some cases, it may be an uneven foamed particle molded body.
Further, the pressure of the carbon dioxide foaming agent in the gas phase impregnation at the time of gas phase impregnation when impregnating the resin particles with carbon dioxide or the gas phase impregnation in the liquid container impregnation is determined by the apparent density ( Usually, it is 0.5 to 5.0 MPa (G), and the impregnation time is about 0.2 to 7 hours.

(E) Use of fusibility improver Expandable polylactic acid resin particles obtained by the production method of the present invention even when no fusibility improver is contained in the polylactic acid resin when impregnating the foaming agent When foaming polylactic acid resin foamed particles obtained by foaming a foam, it is possible to produce a foamed molded article with high fusibility, but the foamed polylactic acid resin particles of the present invention are foamed. When the agent is impregnated, a fusion improver may be contained in the polylactic acid resin for the purpose of further improving the fusion property.
When using expandable resin particles containing a fusibility improver, it is more preferable that the content of the fusibility improver in the vicinity of the surface layer portion is larger than the content in the vicinity of the center portion of the foamed particle, and only in the vicinity of the surface layer portion. More preferably, an adhesion improver is present.
Here, the fusing property improving agent means one having a function of lowering the glass transition temperature of the polylactic acid resin by being contained in the polylactic acid resin. The specific degree of decrease in the glass transition temperature depends on the type and amount of the fusibility improver used, but it is preferable to decrease the midpoint glass transition temperature by 0.5 to 20 ° C., and decrease by 1 to 15 ° C. What is made to do is more preferable. In addition, the said midpoint glass transition temperature is a value measured by the measuring method mentioned later.
Examples of the fusibility improver include those used as plasticizers for polylactic acid resins. Glycerin derivatives such as glycerin fatty acid esters, ether ester derivatives, glycolic acid derivatives, citric acid derivatives, adipic acid derivatives, rosin Preferred examples include single or plural mixtures selected from derivatives and tetrahydrofurfuryl alcohol derivatives.

Examples of the method for incorporating the fusion improver into the polylactic acid resin particles include a method of incorporating the fusion improver into the resin particles at the time of impregnation with the foaming agent, or before or after the impregnation.
Also, when foaming resin particles, which will be described later, is foamed with a heating medium using a foaming machine, for example, a fusing improver is adhered to the surface of the resin particles in the foaming machine. While spraying in the form of mist or after spraying in the form of mist, the heating medium is introduced into the foaming machine and foamed, or the heating medium added with the fusing property improving agent is introduced into the foaming machine and foamed. The method of spraying a fusion improving agent on the surface of the resin particle is mentioned. Furthermore, you may spray in the shape of a mist so that it may adhere to the surface of a foamed particle after completion | finish of foaming.

(2) Dissipation process of physical foaming agent The physical foaming agent dissipation process is a process of dissipating a part of the physical foaming agent in the polylactic acid resin particles impregnated with the physical foaming agent. As a result of the dissipation, the foaming agent concentration in the vicinity of the surface layer portion of the impregnated resin particles becomes lower than the foaming agent concentration in the vicinity of the center portion of the foamed particles. Is obtained, which is relatively advanced from the vicinity of the surface layer portion. Therefore, since the crystallinity of the surface layer portion (S _B ) of the expanded particles obtained by expanding the expandable resin particles after the dissipation can be maintained relatively low, the expanded particles were heated in the in-mold molding. At this time, the foamed particles are easily fused to each other, and it is possible to obtain foamed particles having excellent meltability.

The method for escaping the physical foaming agent is illustrated below.
After the operation of impregnating the foaming agent into the resin particles, the foaming agent-impregnated resin particles are taken out from the sealed container, the aqueous medium is removed and dried, and then left to stand under atmospheric pressure or reduced pressure. After the aqueous medium is removed, the foaming agent is removed from the container. A method of introducing impregnated resin particles and introducing a replacement gas such as an inert gas from one end of the container to forcibly disperse the foaming agent, without removing the foaming agent-impregnated resin particles from the sealed container after the impregnation of the foaming agent A method of releasing the foaming agent in a suspended state in an aqueous medium after releasing the pressure of the airtight container or after taking out the foaming agent-impregnated resin particles from the airtight container and transferring it to another container Is mentioned. In order to dissipate the foaming agent in the vicinity of the surface layer of the foaming agent-impregnated resin more efficiently, the foaming agent is introduced by introducing a replacement gas such as a method of standing under atmospheric pressure or an inert gas into the container. A method of dissipating is preferred.

The ambient temperature when the physical foaming agent is dispersed is preferably 0 ° C to 40 ° C. If the dissipation temperature is 0 ° C or higher, it is possible to dissipate industrially in a short time. On the other hand, if it is 40 ° C or lower, the amount of dissipation of the target foaming agent is easy to adjust. Impregnated with a foaming agent so that the calorific value (Bs: J / g) of the surface layer portion of the polylactic acid-based resin foamed particles of the present invention obtained in the subsequent step is larger than the calorific value (Bc: J / g) of the central portion. The density | concentration of the foaming agent which exists in the surface layer part of the resin particle can be efficiently made lower than the density | concentration of the foaming agent which exists inside. More preferably, the dissipation temperature of the blowing agent is 10 ° C to 30 ° C.
Further, the pressure for the dissipation treatment needs to be lower than the partial pressure of the physical foaming agent when impregnated with the physical foaming agent, but the pressure is preferably less than half of the partial pressure of the foaming agent when impregnated with the physical foaming agent, more preferably Is below atmospheric pressure. Further, 10 to 60% by weight of the physical foaming agent impregnated under these conditions is dissipated to obtain expandable polylactic acid resin particles having a foaming agent impregnation amount of 3.9% by weight or less. If the foamable polylactic acid resin particles have a foaming agent dissipation rate of 10 to 60% by weight and a foaming agent impregnation amount of 3.9% by weight or less, the surface layer of the polylactic acid resin particles after the foaming agent dissipation step The amount of the foaming agent in the vicinity of the part is kept lower than the amount of the foaming agent in the vicinity of the central part, and as a result, the crystallization of the surface layer part becomes difficult to proceed, so that the foamed particles obtained in the subsequent step Crystallization of the surface layer portion is suppressed, and when the foamed particles are molded in the mold, the foamed particles are easily fused to each other. From this viewpoint, the foaming agent dissipation rate is more preferably 20% by weight to 50% by weight.
The “foaming agent dissipation rate” representing the proportion of the physical foaming agent dissipated among the physical foaming agents impregnated in the polylactic acid resin particles is a value determined by the following formula (4).
Foaming agent dissipation rate (% by weight) = [(physical foaming agent impregnation amount (g) −physical foaming agent impregnation amount (g)) / (physical foaming agent impregnation amount (g))] × 100 (4)
In the formula (4), the physical foaming agent impregnation amount is a value obtained by subtracting the resin particle weight (g) before impregnating the physical foaming agent from the physical foaming agent impregnated resin particle weight (g) used in the dissipation step. The amount of physical foaming agent impregnation after dissipation is a value obtained by subtracting the weight (g) of resin particles before impregnation with the physical foaming agent from the weight (g) of physical foaming agent impregnation resin particles after dissipation. The term “after dissipating” here means that 10 minutes have elapsed since the end of the dissipating process. In addition, when the physical foaming agent is dissipated by the method of dissipating the physical foaming agent in a state of being suspended in an aqueous medium, the resin particles are immediately taken out to the atmospheric pressure after the dissipation process is finished. Measure the resin particle weight (g) after evacuation by measuring the weight of the resin particles after 10 minutes from the removal of the surface moisture with air etc. .

The humidity condition for dissipating the foaming agent is preferably 40% relative humidity (RH) or more, more preferably 50% RH or more. When the humidity condition is 40% RH or more, the moisture content of the expandable resin particles obtained after the dissipation treatment can be maintained at a high value of 0.5% by weight or more, for example. Since the polylactic acid resin foam particles obtained in this way have a larger surface layer thickness, the heat resistance of the polylactic acid resin foam particles is improved. The heating temperature range obtained can be expanded. From this point of view, the humidity condition when the foaming agent is dissipated is more preferably 50% RH or more. In addition, the water content in the normal state of a polylactic acid-type resin composition is less than 0.5 weight%.
In order to obtain the dissipation temperature and dissipation rate of the physical foaming agent described above, the dissipation treatment time of the foaming agent is preferably approximately 30 minutes to 6 hours, more preferably 1 hour to 5 hours. is there. If the treatment time is 30 minutes or more and 6 hours or less, it is sufficient to dissipate the foaming agent, and sufficient foaming agent can be left for foaming.

The temperature and time conditions are preferably such that the product of the dissipation treatment temperature (° C.) and the treatment time (hour) is 10 (° C. · hour) or more and 200 (° C. · hour) or less, more preferably 20 (° C. The temperature and time conditions are preferably such that the time is not less than 150 (° C./hour), and the temperature and time conditions are most preferably not less than 30 (° C. · hour) and not more than 100 (° C. · hour).

(3) Expandable polylactic acid resin particles Expandable polylactic acid resin particles are foamed by impregnating 100 parts by weight of polylactic acid resin particles with at least 1 part by weight of a physical foaming agent and then impregnating the physical foaming agent. The polylactic acid-based resin particles are exposed to a temperature of 0 to 40 ° C. to dissipate a part of the physical foaming agent, the dissipation factor of the physical foaming agent is 10 to 60% by weight, and the amount of foaming agent impregnation is 3. It can be obtained by using expandable polylactic acid resin particles of 9% by weight or less. This inevitably increases the dissipation from the vicinity of the surface layer portion of the expandable polylactic acid-based resin particles, and the concentration of the blowing agent in the vicinity of the surface layer portion of the resin particles is lower than the concentration of the blowing agent in the vicinity of the central portion.
In addition, when an inorganic physical foaming agent such as an organic physical foaming agent or carbon dioxide gas is contained, the polylactic acid resin composition is in a state in which crystallization is likely to proceed because the glass transition temperature is lowered. As a result, by passing through the dissipation step, the vicinity of the surface layer portion of the expandable polylactic acid-based resin particles becomes more difficult to crystallize than the vicinity of the center portion, and in the expanded particle obtained through the subsequent expansion step, the center of the expanded particle The crystallinity in the vicinity of the portion is relatively higher than the crystallinity in the vicinity of the surface layer portion. This is because it is difficult to directly check the concentration distribution of the physical foaming agent because the foamable polylactic acid resin particles are small, but the polylactic acid resin obtained by foaming the foamable polylactic acid resin particles. It can be confirmed by comparing the calorific value described later between the central portion and the surface layer portion of the resin foam particles.

Since the degree of crystallinity of the surface layer portion (S _B ) of the expanded particles obtained by expanding the expandable polylactic acid resin particles after the dissipation step of the present invention is maintained relatively low, It becomes possible to obtain expanded particles having high adherence. Further, even if a foamed particle molded body having a large thickness or a foamed particle molded body having a complicated shape is molded, it is also possible to obtain a foamed particle molded body in which the foamed particles at the center are mutually fused. Incidentally, by using the expanded beads, but not the mechanism is uncertain can be molded fusion rate is high foamed bead molded article, the heating value of the surface layer portion of the expanded beads (S _B) is believed to be due to not decrease. That is, it is considered that since the crystallization of the foam particle surface layer portion (S _B ) has not progressed, the foam particle surface layer portion is in a state of being easily softened and the foam particles are easily fused. Therefore, if the calorific value (Bs) of the surface layer part (S _B ) in the expanded particles is larger than the calorific value (Bc) of the central part (C _B ), it means that the crystallization of the surface layer part (S _B ) has not progressed. As shown, it becomes easy to fuse the expanded particles. In addition, since the crystallization of the central portion (C _B ) has progressed, the heat resistance of the expanded particles themselves can be improved, and shrinkage of the expanded particles due to in-mold molding can be suppressed. The range of in-mold molding heating temperature conditions that can be obtained can be widened.

[3] Method for Producing Polylactic Acid Resin Expanded Particles The method for producing polylactic acid resin foam particles is described in the above method for producing expandable polylactic acid resin particles. (I) 100 parts by weight of the polylactic acid resin particles An impregnation step of impregnating at least 1 part by weight of a physical foaming agent with respect to the liquid, and (ii) exposing the polylactic acid resin particles impregnated with the physical foaming agent to a temperature of 0 to 40 ° C. to impregnate the physical foaming (Iii) Expandable polylactic acid resin particles following the dissipation step of dispersing 10 to 60% by weight of the agent to obtain expandable polylactic acid resin particles having a foaming agent impregnation amount of 3.9% by weight or less Foam
Polylactic acid-based resin expanded particles can be obtained.
The process of foaming expandable polylactic acid resin particles will be described below.

(1) Foaming Step In the foaming step, the foamable resin particles that have finished the physical foaming agent dissipation step are heated and foamed. As a method of heating and foaming the expandable particles, a conventionally known method can be employed. Among them, a method in which foamed resin particles are filled in a sealed container and foamed by introducing water vapor or a mixed heat medium of water vapor and air is preferable. Also, the method of foaming by immersing in warm water for a certain time is industrially preferable because the temperature of the warm water is relatively easy to adjust. In addition, if the airtight container is provided with an opening valve for exhausting the heating medium, the atmospheric temperature in the airtight container can be easily maintained constant, and it is easy to obtain expanded particles having a uniform apparent density.

In the above method, the temperature condition for heating the foamable resin particles impregnated with the foaming agent, that is, the foaming temperature is usually (Tg of the base resin, where Tg is the midpoint glass transition temperature of the base resin. −50) ° C. to (Tg + 50) ° C. is preferable, and (Tg−40) ° C. to (Tg + 40) ° C. is more preferable. When the foaming temperature is less than (Tg-50) ° C., sufficient foaming is difficult to occur, and when it exceeds (Tg + 50) ° C., the closed cell ratio of the foamed particles is reduced and the foamed particles exhibit good moldability. This causes a problem that it is difficult to obtain. When the foaming agent is impregnated into the base resin, foaming occurs even at a temperature equal to or lower than the midpoint glass transition temperature of the base resin. In particular, when the foaming agent is carbon dioxide, the foaming temperature is preferably (Tg-40) ° C to (Tg + 40) ° C, more preferably (Tg-30) ° C to (Tg + 30) ° C.

In the present specification, the measurement of the midpoint glass transition temperature (Tg) of the base resin is obtained as the midpoint glass transition temperature of the DSC curve obtained by heat flux differential scanning calorimetry based on JIS K 7121 (1987). Value. More specifically, the midpoint glass transition temperature (Tg) is measured according to 3 of JIS K7121 (1987). Condition of test piece (3) According to “When measuring glass transition temperature after performing a certain heat treatment”, put the test piece into the vessel of the DSC apparatus, and a temperature 30 ° C. higher than the end of the melting peak. The temperature was raised at a heating rate of 10 ° C./min until it was dissolved by heating, held at that temperature for 10 minutes, then adjusted to 0 ° C. at a cooling rate of 10 ° C./min, and then heated at a rate of 10 ° C. It is obtained from a DSC curve obtained when the temperature is raised from 0 ° C. to 30 ° C. higher than the end of the melting peak at / min.

(2) polylactic acid resin foamed polylactic acid-based resin foamed particles obtained by the foaming for particles has an apparent density of ^{0.02g / cm 3 ~0.65g / cm 3} , the heat flux differential scanning calorimetry Thus, the endothermic amount of the expanded resin particles (Bendo: J) in the DSC curve obtained when heating at a heating rate of 2 ° C / min from room temperature to a temperature 30 ° C higher than the end of the melting peak without heat treatment. / G) and the calorific value (Bexo: J / g) [(Bexo) / (Bendo)] is more than 0.3, and the calorific value (Bs: J / g) of the surface layer part is the calorific value of the central part. It is larger than the amount (Bc: J / g).
In addition, it is preferable to preserve | save polylactic acid-type resin expanded particles on the conditions which do not hydrolyze avoiding high temperature and humid conditions.

(B) Apparent Density Apparent density expanded polylactic acid resin ^{particles, 0.02g / cm 3 ~0.65g / cm} 3 are preferred. That is, the apparent density of the polylactic acid-based resin expanded particles is preferably 0.03 g / cm ³ or more, and more preferably 0.04 g / cm ³ or more from the viewpoint of avoiding a possibility that the shrinkage rate after in-mold molding is increased. On the other hand, the upper limit is preferably 0.45 g / cm ³ or less from the viewpoint of avoiding the possibility of variation in physical properties of the foamed particle molded body obtained by in-mold molding, since the density variation of the expanded particles tends to be large. More preferred is cm ³ or less.
The apparent density of the polylactic acid-based resin expanded particles is measured as follows.
Prepare a measuring cylinder containing water at 23 ° C, and wire over 500 expanded foam particles (weight W1 of the expanded particle group) left in the measuring cylinder at a relative humidity of 50%, 23 ° C and 1 atm for 2 days. Divide (W1 / V1) the weight W1 (g) of the expanded particles placed in the graduated cylinder by the volume V1 (cm ³ ) of the expanded particles read from the rise in the water level. Ask for.

(B) Relationship between the endothermic amount of the expanded particles in the differential scanning calorimetry and the calorific value of the expanded particles The polylactic acid resin expanded particles have an endothermic amount of the expanded particles in the differential scanning calorimetry at a heating rate of 2 ° C./min ( The relationship between Bendo (J / g) and the calorific value (Bexo: J / g) of the expanded particles satisfies the following formula (1).
(Bexo) / (Bendo)> 0.3 (1)
If the (Bexo) / (Bendo) ratio is greater than 0.3, foaming during in-mold molding has many regions that are uncrystallized compared to regions that can be crystallized in the foamed particles. The particles are excellent in mutual fusion property. Moreover, it can crystallize in post processes, such as high temperature curing, and can improve the heat resistance of a foamed particle molded object, and a mechanical physical property. In the above formula (1), the upper limit of the value of (Bexo) / (Bendo) is 1, preferably 0.8, and more preferably 0.7.
The exothermic amount (Bexo) and endothermic amount (Bendo) of the expanded particles are values determined by heat flux differential scanning calorimetry described in JIS K7122 (1987). However, the test piece is 1 to 4 mg of expanded particles, and the condition adjustment and DSC curve measurement of the test piece are performed according to the following procedure.

A test piece is put in a container of a DSC apparatus, and a DSC curve is obtained when the temperature is raised from room temperature to 30 ° C. higher than the end of the melting peak at a heating rate of 2 ° C./min without heat treatment. In this case, the room temperature generally means a temperature of about 23 ° C. (hereinafter the same).
The exothermic amount (Bexo) of the expanded particles is defined as a point c where the exothermic peak is separated from the low temperature side baseline of the DSC curve, and a point d where the exothermic peak returns to the high temperature side baseline. A value obtained from a straight line connecting the points c and d and the area of the portion surrounded by the DSC curve. Further, the endothermic amount (Bendo) of the expanded particles is defined as a point e where the endothermic peak is separated from the low-temperature base line of the endothermic peak of the DSC curve, and a point f where the endothermic peak returns to the high-temperature base line. , And a value obtained from a straight line connecting the points e and f and the area of the portion surrounded by the DSC curve.

However, the apparatus is adjusted so that the baseline in the DSC curve is as straight as possible. If the baseline is inevitably curved, the curved baseline on the low temperature side of the exothermic peak is extended to the high temperature side while maintaining the curved state of the curve. The point at which the exothermic peak deviates from the point c, and the curved base line on the high temperature side of the exothermic peak is extended to the low temperature side while maintaining the curved state of the curve, and the exothermic peak appears on the curved high temperature side baseline Let the point to return be a point d. Further, the base line curved at the low temperature side of the endothermic peak is extended to the high temperature side while maintaining the curved state of the curve, and the point at which the endothermic peak moves away from the curved base line at the low temperature side is the endothermic point. Drawing is performed to extend the curved base line on the high temperature side of the peak to the low temperature side while maintaining the curved state of the curve, and the point where the endothermic peak returns to the curved high temperature side baseline is defined as a point f.

For example, in the case shown in FIG. 3, the heat generation amount (Bexo) of the expanded particles is obtained from the area surrounded by the straight line connecting the points c and d and the DSC curve determined as described above, and determined as described above. The endothermic amount (Bendo) of the expanded particles is obtained from the area surrounded by the straight line connecting the points e and f and the DSC curve. In the case shown in FIG. 4, since it is difficult to determine the points d and e as described above, the intersection of the straight line connecting the points c and f determined as described above and the DSC curve. Is determined as a point d (point e) to determine the heat generation amount (Bexo) and the heat absorption amount (Bendo) of the expanded particles. In addition, as shown in FIG. 5, when a small exothermic peak occurs on the low temperature side of the endothermic peak, the exothermic amount (Bexo) of the foamed particles is the first exothermic peak area A in FIG. It is determined from the sum of the area B of the second exothermic peak. That is, the area A is defined as a point c where the exothermic peak moves away from the low temperature side baseline of the first exothermic peak, and a point d where the first exothermic peak returns to the high temperature side baseline. It is assumed that the area A is a portion surrounded by a straight line connecting the point d and the DSC curve. The area B is defined as a point g where the second exothermic peak is separated from the low temperature side baseline of the second exothermic peak, a point f where the endothermic peak returns to the high temperature side baseline, and a point g. The intersection of the straight line connecting the point f and the DSC curve is defined as a point e, and the area B of the portion surrounded by the straight line connecting the point g and the point e and the DSC curve is defined. On the other hand, in FIG. 5, the endothermic amount (Bendo) of the expanded particles is a value obtained from the area surrounded by the straight line connecting the point e and the point f and the DSC curve.
In the measurement of the exothermic amount (Bexo) and endothermic amount (Bendo), the reason for adopting a heating rate of 2 ° C./min as the measurement condition of the DSC curve is that the exothermic peak and the endothermic peak are separated as much as possible. This is based on the inventor's knowledge that a heating rate of 2 ° C./min is suitable when determining the endothermic amounts (Bendo) and (Bexo / Bendo) by heat flux differential scanning calorimetry.

(C) a surface layer portion (S _B) heating value and the central portion (C _B) polylactic acid-based resin foamed particles obtained relationships expandable polylactic acid resin particles and foaming the heat value of the expanded beads, the Since the relationship between the calorific value (Bs) of the surface layer part (S _B ) and the calorific value (Bc) of the central part (C _B ) of the expanded particles satisfies the following formula (2), the surface layer part is more than the central part. Foam with many uncrystallized parts, excellent fusion between foam particles during molding, and excellent fusion between foam particles even if the thickness is large or the shape is complicated It is also possible to obtain a particle compact. In addition, since the central part is more crystallized than the surface layer part, the heat resistance of the expanded foam as a whole is improved, so that the molding temperature range during in-mold molding can be increased. As a result, according to the expanded particles of the present invention, the range of molding pressure can be expanded.
(Bs)> (Bc) (2)
The calorific values (Bs) and (Bc) are the same as the measurement method of the calorific value (Bexo) of the expanded particles, except that the surface layer part (S _B ) and the central part (C _B ) are 1 to 4 mg. Can be obtained. The surface layer portion (S _B ) of the expanded particles is as uniform as possible from the entire surface of the expanded particles to a weight that is 1/5 to 1/3 of the weight of the expanded particles before cutting. The part that is cut out. On the other hand, the center part (C _B ) is a foamed particle that cuts and removes the entire surface of the foamed particle with a uniform thickness as much as possible, and has a weight of 1/5 to 1/3 of the weight of the foamed particle before cutting. Say the rest.

The samples of the surface layer portion of the expanded beads (S _B), subjected the surface layer portion (S _B) a cutter knife, the collecting and measuring surface section (S _B) performs a cutting process using a microtome or the like including a surface do it. However, 5 minutes total weight of the particle weight of the original foamed particles of the surface layer portion excised from always excised and one expanded beads entire surface of one of the expanded particles as noted point for the (S _B) Excise so that it is 1 to 1/3 of the above. If the weight of the excised surface layer part (S _B ) is 1/5 to 1/3 of the original foam particle weight, it will not contain a large amount of the foam layer inside the particle. The amount can be measured accurately. Furthermore, when the surface layer part obtained from one expanded particle is less than 1-4 mg, it is necessary to repeat the said operation about several expanded particle.
On the other hand, the foam layer method sample preparation in the central portion (C _B), a cutting process with a cutter knife or the like for the purpose of leaving the foam layer of the central portion which does not include the surface layer portion (S _B) (C _B) It is necessary to conduct and measure. When preparing a sample of the foam layer in the center (C _B ), the foam layer should have a thickness that is as uniform as possible from the cut surface after the entire surface of one foam particle is always cut out. Leave the foamed layer in the center (C _B ) so that it is excised. At this time, the weight of the foam layer in the central portion (C _B ) left in the excision operation needs to be set to one fifth to one third of the particle weight of the original foam particles, and the original foam. It is preferable that the particle shape is as similar as possible. Furthermore, when the foamed layer of the center part (C _B ) obtained from one expanded particle is less than 1 to 4 mg, it is necessary to repeat the above operation and use a plurality of expanded particles.

The calculation method of the thickness of the surface layer portion of the expanded particles cut out to be 1/5 to 1/3 of the weight of the original expanded particles is as follows.
First, the weight (g) of the expanded particles is derived from the following equation.
W = (4/3) π (R ₁ ) ³ ρ
Where W is the weight of the expanded particle (g), R ₁ is the radius of the sphere assuming the expanded particle is a sphere (cm), and ρ is the apparent density assuming that the expanded density of the expanded particle is generally constant (g / Cm ³ ).
Next, the thickness S ₁ from the surface layer of the expanded particles cut out so that the surface layer portion of the expanded particles becomes one third of the particle weight of the original expanded particles is calculated as follows.
(2/3) × (4/3) π (R ₁ ) ³ ρ = (4/3) π (R ₂ ) ³ ρ
R ₂ = 0.873R ₁
S ₁ = R ₁ −R ₂ = 0.127R ₁
Where R ₂ is the radius of a sphere that is 2/3 the weight of W.

Similarly, the thickness S ₂ from the surface of the expanded beads to be cut out as a surface layer portion of the expanded beads is 1/5 becomes 0.072R _1. Therefore, in order for the surface layer portion (S _B ) of the expanded particles to be 1/5 to 1/3 or less of the particle weight of the original expanded particles, the surface layer portion (S _B ) of the expanded particles is as uniform as possible. It will be cut out from the surface layer with a thickness of 0.072R _{1 to} 0.127R ₁ cm so as to have a thickness.
Next, the central part (C _B ) is cut out and removed so that the entire surface of the foamed particles has a uniform thickness as much as possible, and the remaining part becomes one fifth to one third of the particle weight of the original foamed particles. The remaining radius R ₃ (cm) of the center of the expanded particle, which is one third of the particle weight of the original expanded particle thus cut out, is derived as follows.
(1/3) × (4/3) π (R ₁ ) ³ ρ = (4/3) π (R ₃ ) ³ ρ
R ₃ = 0.693R ₁
Similarly, the radius R ₄ (cm) of the remaining foamed particle central part in which the central part of the foamed particle is 1/5 of the particle weight of the original foamed particle is R ₄ = 0.585R ₁ .

Therefore, in order to cut out the foamed particles so that the center part (C _B ) of the foamed particles is 1/5 to 1/3 of the particle weight of the original foamed particles, the radius of the center part is set to 0. The excision work is performed so as to be 585R _{1 to} 0.693R ₁ cm.
Here, as an example, a substantially spherical expanded particle having an apparent density of 0.15 g / cm ³ and a diameter of 0.3 cm was cut into a surface layer portion (S _B ) and a central portion (C _B ) by the above method. At that time, the weight (g) of the expanded particles, the thicknesses S ₁ and S ₂ cut out from the surface layer, and the radii R ₃ and R ₄ of the central part are 0.019 cm, 0.011 cm, 0.104 cm, and 0.088 cm, respectively. It becomes.

Thus, apparent density 0.15 g / cm ^3, when the expanded beads are generally spherical diameter 0.3 cm, the surface layer portion of the expanded beads _{(S B)} is as uniform as possible in thickness from the surface layer portion of the expanded beads _{(S B)} cut out the entire surface of the expanded beads so that a cut-out surface portion 5 minutes 1 to become part of one third of the weight of the total weight the original expanded beads (S _B), the foamed particle surface To 0.11 mm to 0.19 mm. On the other hand, the central portion (C _B ) cuts out and removes the entire surface of the foamed particles so as to have a uniform thickness as much as possible, and becomes 1/5 to 1/3 of the particle weight of the original foamed particles. It is the remaining part and refers to a part having a radius from the center of the foamed particle of 0.88 mm or more and 1.04 mm or less.
Further, other expanded particles are cut out in the same manner, and the surface layer portion (S _B ) and the central portion (C _B ) are 1 mg to 4 mg for measurement.
From the sample thus obtained, the calorific value (Bs) of the surface layer portion (S _B ) and the calorific value (Bc) of the center portion (C _B ) of the expanded particles are measured by differential scanning calorimetry.

(D) Ratio of average surface layer thickness (Ts) and average cell membrane thickness (Tm) of foamed polylactic acid resin particles Foamed particles obtained by foaming the expandable polylactic acid resin particles are polylactic acid resin foams. The ratio (Ts / Tm) of the average surface layer thickness (Ts) to the average bubble film thickness (Tm) of the particles is 5.0 to 40.0, preferably 6.0 to 25.0, more preferably 7.0. The polylactic acid-based resin expanded particles in such a state are durable because the average surface layer thickness (Ts) with respect to the average cell membrane thickness (Tm) is larger than that of the conventional one. Covered with a smooth skin, the foam particles have a high apparent heat resistance, and when heated with a heating medium such as steam or hot air during molding, the foam particles can be prevented from shrinking or breaking. Molding temperature range for obtaining good expanded particle compacts Spreads, and those more suitable for forming a good polylactic acid-based resin foamed bead molded article.

(D-1) Measurement of average surface layer thickness (Ts) of expanded particles The average surface layer thickness (Ts) of expanded particles is measured as follows.
The foamed particles are roughly divided into two, and the cut surface is photographed with a scanning electron microscope. In the obtained cross-sectional photograph, the value at which the length between the bubble located on the outermost side of the expanded particle and connected in the circumferential direction and the surface of the expanded particle becomes the minimum value is set to the connected bubble on all the photos. The arithmetic average value of these values is taken as the surface layer thickness of the expanded particles. This operation is performed for a large number (at least 30 or more) of expanded particles, and the arithmetic average value of the surface layer thickness of each expanded particle is defined as the average surface layer thickness (Ts).
In addition, there are cases where bubbles exist independently or several times continuously outside the connected bubbles, but these are rarely present separately from the group of bubbles forming the expanded particles, and are ignored. It shall be possible. In order to accurately measure the surface layer thickness, it is necessary to divide the expanded particles substantially in half so that the skin portion is not wrinkled.

(D-2) Measurement of average cell diameter of expanded particles The average cell diameter of expanded particles is measured as follows.
The foamed particles are roughly divided into two, and the cut surface is photographed with a scanning electron microscope. In the obtained cross-sectional photograph, draw straight lines at equal intervals in the eight directions from the vicinity of the center of the foamed particle cut surface, count all the number of bubbles intersecting the straight line, the total length of the straight line is the number of counted bubbles The value obtained by dividing is taken as the cell diameter of the expanded particles. This operation is performed for a large number (at least 30 or more) of foamed particles, and the arithmetic average value of the bubble diameters of the foamed particles is defined as the average bubble diameter.
In the measurement of the bubble diameter of each expanded particle, the bubbles that intersect even part of the straight line are counted. Further, in the above measurement, the reason why the straight lines are drawn at equal intervals in the eight directions from the vicinity of the center of the expanded surface of the foamed particle is measured if the straight lines are drawn at equal intervals in the eight directions from the vicinity of the center of the expanded surface of the expanded particle. This is because a stable bubble diameter value can be obtained even if the shape of the bubbles varies depending on the direction on the expanded particle cut surface.

(D-3) Calculation of average cell membrane thickness (Tm) of expanded particles The average cell membrane thickness (Tm) of the expanded particles is calculated from the average cell diameter d measured by the above method using the following formula (5). Calculated.
V _S = (ρf−ρg) / (ρs−ρg) = [(d + Tm) ³ −d ³ ] / (d + Tm) ³ ... (5)
Where V _S is the volume fraction of the base resin, ρf is the apparent density (g / cm ³ ) of the expanded particles, ρs is the density of the base resin (g / cm ³ ), and ρg is the gas density (g / Cm ³ ), d is the average bubble diameter (μm), and Tm is the average bubble film thickness (μm). Since (ρf and ρs) >> ρg in the equation (5), ρg is set to 0 (g / cm ³ ), and Vs = ρf / ρs. Accordingly, the average bubble film thickness Tm (μm) can be calculated by the equation Tm = d [(X / (X−1)) ^1/3 −1] (where X = ρs / ρf). . If the average cell diameter d of the expanded particles is determined by this formula, the average cell thickness (Tm) of the expanded particles is determined.
The above equation (5) is a relational expression between the average bubble diameter and the average bubble film thickness when the bubble shape is regarded as a sphere. “Plastic Foam Handbook” Issued on May 28), page 222, section “1.3.2”.

When these foamed particles are used, it is possible to mold a foamed particle molded body having excellent fusion properties between the foamed particles under a wide range of in-mold molding temperature conditions. Since the use of the expanded beads, the reason can be molded foamed bead molded article excellent in fusion bonding of the expanded beads another, but is not certain, it not progressed crystallization of the foamed particle surface layer portion (S _B), Obtained from expandable resin particles that are easily softened at the surface layer of the expanded particles, are easily fused to the expanded particles, and the physical foaming agent is dispersed under high humidity conditions. It is considered that the foamed particles are formed by forming a thicker skin than the conventional one and preventing the shrinkage and foam breakage of the foamed particles during in-mold molding.

[4] Production of Polylactic Acid Resin Foamed Particle Molded Article A method for producing a polylactic acid resin foamed particle molded article is described in the method for producing polylactic acid resin foamed particles.
(I) an impregnation step of impregnating 1 part by weight or more of a physical foaming agent with respect to 100 parts by weight of the polylactic acid resin particles;
(Ii) The polylactic acid resin particles impregnated with the physical foaming agent are exposed to a temperature of 0 to 40 ° C. to dissipate 10 to 60% by weight of the impregnated physical foaming agent, and the amount of the foaming agent impregnated A process of dissipating foamed polylactic acid resin particles having a weight of 3.9% by weight or less,
(Iii) a step of foaming the expandable polylactic acid-based resin particles to obtain polylactic acid-based resin expanded particles;
Subsequently, (iv) the polylactic acid-based resin expanded particles can be obtained by in-mold molding the polylactic acid-based resin expanded particles to fuse the expanded particles to each other.

(1) Molding of polylactic acid-based resin foamed particles In the above (iv) foamed particle in-mold molding step, after the foamed particles are filled in the mold, the foamed particles are heated with a heating medium such as steam or steam and air. Thus, it is preferable to fuse the expanded particles to each other. As described above, when the heat molding is performed, the foamed particles are fused and integrated to obtain a foamed particle compact. As a mold for molding in this case, a generally used mold or a steel belt used in a continuous molding apparatus described in JP 2000-15708 A or the like is used. Further, as the heating means, a steam is usually used, and the heating temperature only needs to be a temperature at which the foamed particle surface portion melts, and a steam pressure of 0.1 to 0.25 MPa (G) is usually adopted. Is done.
A foamed particle molded body obtained by in-mold molding of polylactic acid-based resin expanded particles is superior to the conventional polylactic acid resin expanded particle molded body in the fusion property between the expanded particles.

(2) impregnation of pressurized gas into polylactic acid-based resin expanded particles When producing a expanded particle molded body, prior to in-mold molding, an inorganic gas such as air, nitrogen, carbon dioxide gas, etc. in advance to the polylactic acid-based resin expanded particles, Alternatively, it is preferable to impregnate with an organic gas such as butane. Among the inorganic gas and organic gas, carbon dioxide is preferable from the viewpoint of handling. By impregnating the expanded particles with gas, in-mold molding, secondary foaming properties such as a decrease in gaps between the expanded particles, mold shape reproducibility, and curing recovery after molding the expanded particle molded body are improved. . The amount of impregnation gas into the expanded particles is preferably in the range of 0.05 to 4 mol / (1000 g expanded particles), more preferably 0.1 to 2 mol / (1000 g expanded particles).

In addition, the gas amount (mol / 1000 g foamed particles) in the foamed particles is obtained by the following formula (6).
Gas amount in expanded particles (mol / 1000 g expanded particles) =
[Gas increase (g) × 1000] / [Gas molecular weight (g / mol) × Expanded particle weight (g)] (6)
The gas increase amount (g) in the above equation (6) is obtained as follows.
Take out 500 or more foamed particles filled in the mold, and the pressure inside the foamed particles is increased by impregnating gas, and within 60 seconds, constant humidity and humidity at 50% relative humidity and 23 ° C atmospheric pressure It moves to a chamber, puts on the balance in the constant temperature and humidity chamber, takes out the foamed particles, and reads the weight after 120 seconds. The weight at this time is defined as Q (g). Next, the foamed particles are allowed to stand for 240 hours in the same constant temperature and humidity room at 50% relative humidity and 23 ° C. atmospheric pressure. The high-pressure gas in the expanded particles permeates through the cell membrane over time and escapes to the outside, so the weight of the expanded particles decreases accordingly, and after 240 hours the equilibrium is reached. stable. The weight of the expanded particles after 240 hours is measured in the same constant temperature and humidity chamber, and the weight at this time is defined as S (g). Any of the above weights shall be read up to 0.0001 g. The difference between Q (g) and S (g) obtained by this measurement is defined as the gas increase amount (g) in the equation (6).
As a method of impregnating the expanded particles with the inorganic gas or the organic gas, as is well known, there is a method in which the expanded particles are put in a closed container and the inside of the container is pressurized with an inorganic gas or an organic gas. The amount of impregnating gas of the particles can be increased.

(3) Curing after in-molding The foamed particle molded body obtained by the in-mold molding described above is in an atmosphere of [Tg + 5] to [Tg + 30] ° C. when the intermediate glass transition temperature of the base resin is Tg. It is preferable to go through a curing process for holding for a certain time.
When the temperature of the curing process is less than [Tg + 5] ° C., it is necessary for a long time to crystallize the polylactic acid-based resin and there is no effect of improving the heat resistance of the foamed particle molded body, resulting in poor heat resistance. A foamed particle molded body is obtained. In this respect, the curing temperature is preferably [Tg + 8] ° C. or higher, and more preferably [Tg + 10] ° C. or higher. Moreover, when it exceeds [Tg + 30] degreeC, a foamed particle molded object will raise | generate a deformation | transformation and it will become difficult to obtain a favorable expanded particle molded object. From this viewpoint, [Tg + 25] ° C. or lower is preferable, and [Tg + 20] ° C. or lower is more preferable.
Moreover, as time to hold | maintain under said temperature atmosphere at a curing process, 1 hour or more is preferable from a viewpoint of heat resistance improvement, 3 hours or more are preferable, and especially 5 hours or more are preferable. On the other hand, the upper limit is usually 36 hours from the viewpoint of preventing the foamed particle molded body from being deformed or discolored. From the above viewpoint and productivity balance, 24 hours or shorter is more preferable, and 12 hours or shorter is particularly preferable.

Further, the relative humidity in the curing process is preferably 40% RH or less because if the relative humidity is high, the foamed particle molded body tends to be hydrolyzed and the foamed particle molded body inferior in mechanical properties may be formed. From the above viewpoint, 30% RH or less is more preferable, and 20% RH or less is more preferable. On the other hand, the lower limit of 0% RH is preferably 5% RH or more because there is a possibility that a special apparatus may be required to satisfy the condition.
Moreover, when the time of the whole curing process is 100%, from the above viewpoint, the time when the relative humidity exceeds 40% RH is preferably 50% or less, and more preferably 25% or less.
When curing, the foamed particle molded body may be in the form as it is, but if the temperature is high, the foamed particle molded body may be deformed. In such a case, it is preferable to fix the foamed particle molded body with a jig or the like for fixing the shape.
According to the curing step, since the crystallization can be performed based on the midpoint glass transition temperature of the base resin, a foamed particle molded body with improved heat resistance can be obtained efficiently. In addition, the heating medium in a curing process is normally performed with a hot air. The foamed particle molded body is more excellent in heat resistance by performing the curing step. Specifically, the heat resistance is preferably within 4%, more preferably within 3%, and more preferably within 2% of the heating dimensional change after standing for 22 hours in an atmosphere at 90 ° C. Is more preferable. If the absolute value of the heating dimensional change rate exceeds 4%, the use range may be narrowed, such as being difficult to use in the field used near 90 ° C. Although depending on the composition of the polylactic acid resin constituting the expanded particle molded body, the expanded particle molded body having heat resistance within the above range can be obtained through the curing step. The heating dimensional change rate (%) is [(the size of the foamed particle molded body after heating at 90 ° C. for 22 hours (mm) −the dimension of the foamed particle molded body before heating (mm)) / before the heating] Dimension of foamed particle molded body (mm)] × 100, which is a value determined by the formula, and the heating dimensional change rate of the foamed particle molded body in this specification is the heating dimensional change rate of each part determined by the above formula Of these, the value of the part having the largest absolute value of the dimensional change rate is adopted.

(4) Foamed particle molded body The foamed particle molded body thus obtained is obtained from foamed particles that have good secondary foaming properties during molding in the mold and good fusion between the foamed particles, so there are few gaps between the foamed particles. The foamed particle molded body has good appearance and fusion in the vicinity of the center of the foamed particle molded body.
Furthermore, when the crystallization of the foamed particle molded body is promoted, the heat resistance is improved, so that the degree of crystallization can be efficiently increased and the heat resistance can be improved by passing through the curing step described above.
The shape of the foamed particle molded body is not particularly limited, and the shape can be various shapes such as a container shape, a plate shape, a cylindrical shape, a column shape, a sheet shape, and a block shape. The foamed particle molded body is excellent in dimensional stability and surface smoothness.
Apparent density (a) Apparent Density foamed bead molded article is preferably 0.02~0.65g / cm ^3, more preferably 0.03~0.45g / cm ^3.
The apparent density of the foamed particle molded body is obtained by dividing the weight WM (g) of the foamed particle molded body by the volume VM (cm ³ ) determined from the external dimensions of the foamed particle molded body and converting the unit (WM / VM). Desired.

(B) Fusion rate The fusion rate of the foamed particle molded body is preferably 50% or more, and more preferably 60% or more from the viewpoint of exhibiting sufficient mechanical properties such as bending strength of the molded body.
The fusion rate can be measured by the following method. That is, the foamed particle molded body was cut by about 3 mm in the thickness direction of the foamed particle molded body with a cutter knife, and then the foamed particle molded body was broken from the cut portion by hand. Next, the number of expanded particles (n) present on the fractured surface and the number of expanded particles (b) whose material was destroyed were measured, and the ratio (b / n) between (n) and (b), It can be obtained by an expression.
Fusing rate (%) = (b / n) × 100 (7)
Since the polylactic acid-based resin foamed particle molded body uses a low environmental load thermoplastic resin as the base resin, conventional polystyrene-based resin foamed particle molded body and polyolefin-based resin foamed particle molded body are used. It can be preferably used as a substitute for conventional fields, for example, fish boxes, packaging cushioning materials, automobile interior materials and the like.

Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.
The evaluation methods and the like in the examples are described below.
In addition, the DSC apparatus used in the following Examples and Comparative Examples is a product name: DSC-Q1000 manufactured by TA Instruments Japan Co., Ltd.
(1) About base resin (a) Measurement of endothermic amount (Rendo) “[1] About polylactic acid resin particles, (1) Base resin, (b) Endothermic amount in differential scanning calorimetry of base resin The measurement method described in the section is adopted.
(B) Measurement of midpoint glass transition temperature The measurement method described in the above section “[3] Production method of polylactic acid-based resin expanded particles, (1) Foaming step” was adopted.

(2) Expandable polylactic acid resin particles (a) Physical foaming agent impregnation amount The physical foaming agent impregnation amount (% by weight) with respect to the polylactic acid resin particles is obtained from the following formula.
Physical foaming agent impregnation amount (% by weight) = [(polylactic acid resin particle weight (g) after physical foaming agent impregnation−polylactic acid resin particle weight (g) before physical foaming agent impregnation) / before physical foaming agent impregnation Of polylactic acid resin particles (g)] × 100
(B) Physical foaming agent dissipation rate The physical foaming agent dissipation rate (% by weight) relative to the resin particles was determined from the following formula.
[(Physical foaming agent impregnation amount (g) −physical foaming agent impregnation amount after dissipation (g)) / (physical foaming agent impregnation amount (g))] × 100 (%)
(C) Moisture content The moisture content of the expandable polylactic acid resin particles was measured based on the method B-water vaporization method of JIS K7251 (2002).

(3) Polylactic acid resin expanded particles (a) A graduated cylinder containing water with an apparent density of 23 ° C. was prepared, and the graduated cylinder was allowed to stand for 2 days under the conditions of 50% relative humidity, 23 ° C. and 1 atm. 1,000 foam particles (weight W1 of the foam particle group) were submerged using a wire mesh, and the expanded particle group was placed in a graduated cylinder at a volume V1 (cm ³ ) of the foam particle group read from the rise in water level. The weight W1 (g) was obtained by dividing (W1 / V1).
(B) Heat generation (Bexo) and heat absorption (Bendo)
"[3] Production method of polylactic acid-based resin expanded particles, (2) Regarding polylactic acid-based resin expanded particles, (b) Relationship between the heat absorption amount of the expanded particles and the calorific value of the expanded particles in differential scanning calorimetry" The measurement method described in the section was adopted.
(C) Heat value (Bc) at the center and heat value (Bs) at the surface layer
The measurement method described in the section “[3], (2), (c) Relationship between the calorific value of the surface layer part (S _B ) and the calorific value of the central part (C _B )” of the expanded particles was adopted.
(D) Average surface layer thickness and average cell membrane thickness of resin foam particles “[3], (2), (d) Average surface layer thickness (Ts) and average cell membrane thickness (Tm) of polylactic acid resin foam particles Using the method described in the section “Ratio of No.”, 50 foamed particles were measured. Note that ρg was 0 (g / cm ³ ) and ρs was 1.26 (g / cm ³ ).

(4) Foamed particle molded body (a) Secondary foamability The secondary foamability shown in Table 1 was evaluated by visually observing the foamed particle molded body according to the following criteria.
A: There is no gap between the expanded particles on the surface of the expanded particle molded body, and the shape of the corner of the molded body is the same as the shape of the mold.
○: There are almost no gaps between the expanded particles on the surface of the expanded particle molded body, and the shape of the corner of the molded body is almost the same as the shape of the mold.
Δ: There are few gaps between the expanded particles on the surface of the expanded particle molded body, and the shape of the corner of the molded body is slightly rounder than the shape of the mold.
X: There are many gaps between the expanded particles on the surface of the expanded particle molded body, and the shape of the corner of the molded body is rounder than the shape of the mold.

(B) Fusing rate The foamed particle molded body was cut with a cutter knife in the thickness direction of the foamed particle molded body by about 3 mm, and then the foamed particle molded body was broken by hand from the cut portion. Next, the number (n) of the expanded particles existing on the fracture surface and the number (b) of the expanded material particles are measured, and the ratio (b / n) of (n) and (b) is 100%. A certain [(b / n) × 100] (%) was defined as the fusion rate.
(C) Evaluation of fusion at the center part The center part of the fracture surface of the foamed particle molded body fractured by the measurement of the fusion rate was visually observed, and the degree of fusion was evaluated as follows.
A: All foamed particles are not peeled off at the particle interface, and the foamed particles themselves are broken.
○: Most of the expanded particles are not peeled off at the particle interface, and the expanded particles themselves are broken.
Δ: Many foamed particles are peeled off at the interface, and few foamed particles are destroyed.
X: Almost all foamed particles are peeled off at the particle interface.
(D) Apparent density of the foamed particle molded body The apparent density of the foamed particle molded body is a volume VM (cm ^{In 3} ), the weight WM (g) of the foamed particle molded body was divided (WM / VM) and converted into a unit of kg / m ³ .

[Example 1]
(1) Production of Resin Particles Crystalline polylactic acid (manufactured by Mitsui Chemicals, Inc., trade name: Lacia H-100, density 1.26 g / cm ³ , endotherm 49 J / g, listed as crystalline resin in Table 1) .) 50 parts by weight and amorphous polylactic acid (Mitsui Chemicals, trade name: Lacia H-280, density 1.26 g / cm ³ , endotherm 0 J / g, listed as amorphous resin in Table 1) 200 weight ppm of polyethylene wax (manufactured by Toyo Petrolite Co., Ltd., trade name: Polywax 1000, number average molecular weight 2200) was added to the blend with 50 parts by weight, and these were melted in an extruder. Kneaded and extruded into strands. Next, the strand was quenched and solidified in water at about 25 ° C. and then cut to obtain non-crosslinked resin particles having a length (L) / diameter (D) of 1.3 and an average weight of 1.1 mg per piece. Obtained. The midpoint glass transition temperature of the obtained resin particles was 57 ° C.

As a result of measuring the endothermic amount (Rendo) of the obtained resin particles, a DSC curve as shown in FIG. 1 was obtained. Table 1 shows the measured endotherm (Rendo).

(2) Impregnation with foaming agent In an autoclave having an internal volume of 5 liters (L), 3000 ml of ion-exchanged water and 0.5 g of aluminum oxide (product name: Aerooxide), sodium dodecylbenzenesulfonate (Daiichi Kogyo Seiyaku) Co., Ltd., trade name: Neogen S20A) 0.2 g, resin particles 1000 g were added, and glycerol diacetomonocaprylate (manufactured by Riken Vitamin Co., Ltd., trade name: Riquemar PL-019) as a fusion improver Was added in an amount of 0.5 part by weight based on 100 parts by weight of the resin particles.
Next, after adjusting the temperature in the autoclave to 30 ° C. (impregnation temperature shown in the column of impregnation conditions in Table 1), carbon dioxide (CO ₂ ) was press-fitted into the autoclave through the pressure regulating valve, and the autoclave The pressure in the gas phase is adjusted to 2 MPa (G) (impregnation pressure shown in the column of impregnation conditions in Table 1) and maintained for 5.5 hours (retained for the time shown in the column of impregnation conditions in Table 1). Time)) held and impregnated with carbon dioxide.
Thereafter, the pressure in the autoclave was reduced to atmospheric pressure, and then the resin particles were taken out. The extracted resin particles were freed of adhering moisture by a centrifuge.
Moisture on the surface of the obtained resin particles was further removed with air, and the amount of the resin particles impregnated with the physical foaming agent was measured 10 minutes after taking out from the autoclave and found to be 6.3% by weight.

(3) Dissipation of foaming agent The foaming agent-impregnated resin particles are placed in a polyethylene bag, and left at room temperature of 25 ° C. and humidity of 50% RH for 2 and a half hours with the bag mouth open, A treatment to dissipate a part of the impregnated carbon dioxide gas was performed. The amount of impregnation of the foaming agent after the dissipation treatment measured after 10 minutes from the end of the foaming agent dissipation treatment was 3.5% by weight. From the amount of foaming agent impregnation before and after the foaming agent dissipation treatment, the foaming agent dissipation rate of the resin particles was 45% by weight. The water content of the expandable resin particles after the dissipation treatment was 1.1% by weight.

(4) Foaming of polylactic acid-based resin foamable resin particles After filling the foamable resin particles after the foaming agent dissipation treatment into a sealed container with a pressure regulating valve, the temperature is adjusted to 96 ° C with steam and air. The mixed heat medium thus introduced was introduced for 8 seconds and heated to obtain expanded and expanded non-crosslinked expanded particles. At this time, the maximum temperature in the foaming machine was 82 ° C. The apparent density of the expanded particles, the calorific value (Bexo), the endothermic amount (Bendo), the ratio (Bexo / Bendo) and the difference (Bendo-Bexo), the calorific value (Bs) of the surface layer portion, the calorific value of the central portion Table 1 shows the amount (Bc), ratio (Bs / Bc), average surface layer thickness (Ts), average bubble film thickness (Tm), and ratio (Ts / Tm).

(5) In-mold molding of polylactic acid-based resin expanded particles In-mold molding was performed as follows using the obtained expanded particles.
The foamed particles are filled into a sealed container, pressurized with air, impregnated into the foamed particles so that the amount of impregnation with air is 0.33 (mol / 1000 g), and then 250 (mm) wide by 200 (mm) wide. × thickness 50 compression rate of 20% in a mold having a molding space portion (mm) (bulk volume of the expanded beads before compression to be filled into the mold (cm 3) ^- mold volume after clamping (cm ³ )) × 100 / mold inner volume after clamping (cm ³ )) (%), and molded in-mold at molding pressure (steam pressure) shown in Table 1. The bulk volume (cm ³ ) of the foamed particles before compression filled in the mold is the weight (g) of the foamed particles filled in the mold at the bulk density (g / cm ³ ) of the foamed particles. The bulk density (g / cm ³ ) of the foamed particles is the volume of the foamed particles (cm ³ ) indicated by the scale of the graduated cylinder when the foamed particles are placed in an empty graduated cylinder. It is a value obtained by dividing the weight (g) of the expanded particles. Table 1 shows the in-mold molding conditions and the evaluation results of the obtained foamed particle molded body.
FIG. 6 shows a scanning electron micrograph of a cross-section obtained by dividing the polylactic acid foamed particles obtained in Example 1 into approximately two parts. In FIG. 7, the scanning electron micrograph which expanded further the surface layer part in the cross section which divided the polylactic acid foamed particle obtained in Example 1 into about 2 is shown.

[Example 2]
In Example 2, the same resin particles as in Example 1 were used, and carbon dioxide gas was impregnated without adding glycerol diacetomonocaprylate (manufactured by Riken Vitamin Co., Ltd., trade name: Riquemar PL-019) when impregnating the foaming agent. I let you. The foaming agent dissipation treatment and foaming were performed under the same conditions as in Example 1. In-mold molding was performed under the same conditions as in Example 1 except that the foamed particles were not impregnated with air under pressure. The evaluation results of the obtained foamed particle molded body are shown in Table 1.

[Comparative Examples 1 and 2]
In Comparative Example 1 and Comparative Example 2, the same resin particles as in Example 1 were used and impregnated with carbon dioxide gas as a blowing agent under the conditions described in Table 1. In Comparative Example 1 and Comparative Example 2, foaming particles were obtained by performing foaming under the same conditions as in Example 1 immediately after the foaming agent impregnation without performing the foaming agent dissipation treatment. Here, “immediately after the impregnation” means that the impregnation was performed within 10 minutes from the end of the impregnation to the start of foaming. In-mold molding was performed under the same conditions as in Example 1 except that the foamed particles were not impregnated with air and the molding pressure was 0.2 MPa (G). The evaluation results of the obtained foamed particle molded body are shown in Table 1.
FIG. 8 shows a scanning electron micrograph of a part of a cross-section obtained by dividing the polylactic acid foamed particles obtained in Comparative Example 1 into approximately two parts. In FIG. 9, the scanning electron micrograph which expanded further the surface layer part in a part of the cross section which divided the polylactic acid foamed particle obtained by the comparative example 1 substantially into two is shown.

[Example 3, Example 4]
In Example 3 and Example 4, the same resin particles as used in Example 1 were used, and the blowing agent carbon dioxide gas was used under the same conditions as in Example 1 except that the retention time of the blowing agent impregnation condition was 5 hours. Impregnated. Next, after reducing the pressure in the autoclave to atmospheric pressure, the resin particles were taken out and the adhering moisture was removed with a centrifuge.
The obtained expandable resin particles are put into a cylindrical container (fluidized bed drying apparatus) having an inner diameter of 10 cm and a depth of 25 cm, and air with adjusted humidity is introduced from the lower part of the container, and the temperature in the container is 25 ° C. and humidity is 40% RH. In this state, the foaming agent dissipation treatment of the expandable resin particles was performed for 1 hour in Example 3 and for 2 hours in Example 4. Next, the foamable resin particles after the dissipation treatment were foamed under the same conditions as in Example 1. In-mold molding was performed under the same conditions as in Example 2 except that the obtained foamed particles were subjected to a molding pressure of 0.2 MPa (G). The evaluation results of the obtained foamed particle molded body are shown in Table 1.

[Example 5]
In Example 5, the same resin particles as used in Example 1 were used, and the blowing agent carbon dioxide gas was impregnated under the same conditions as in Example 1 except that the retention time of the blowing agent impregnation condition was 5 hours. Next, after reducing the pressure in the autoclave to atmospheric pressure, the resin particles were taken out and the adhering moisture was removed with a centrifuge.
The obtained expandable resin particles are put into a cylindrical container (fluidized bed drying apparatus) having an inner diameter of 10 cm and a depth of 25 cm, and dry air is introduced from the lower part of the container to bring the container to a temperature of 25 ° C. and a humidity of 15% RH. The foaming agent dissipation treatment of the expandable resin particles was performed for 2 hours. Next, the foamable resin particles after the dissipation treatment were foamed under the same conditions as in Example 1.
The obtained foamed particles were filled in a mold having a molding space portion of width 250 (mm) × length 200 (mm) × thickness 10 (mm) at a compression rate of 50% without being subjected to pressure impregnation treatment with air. In-mold molding was performed under the same conditions as in Example 1 except that the molding pressure was 0.16 MPa (G). The evaluation results of the obtained foamed particle molded body are shown in Table 1.
[Comparative Example 3]
In Comparative Example 3, the same resin particles as in Example 1 were used and impregnated with carbon dioxide gas as a foaming agent under the conditions described in Table 1. In Comparative Example 3, foaming particles were obtained by performing foaming under the same conditions as in Example 1 immediately after the impregnation of the foaming agent without performing the foaming agent dissipation treatment. In-mold molding was performed under the same conditions as in Example 1 except that the foaming particles were not impregnated with air and the molding pressure was 0.16 MPa (G). The evaluation results of the obtained foamed particle molded body are shown in Table 1.
[Reference Example 1]
The expanded particles obtained in Comparative Example 3 were compressed into a mold having a molding space portion of width 250 (mm) × length 200 (mm) × thickness 10 (mm) without performing pressure impregnation treatment with air. Filled at 50% and molded in-mold under the same conditions as in Comparative Example 3. The evaluation results of the obtained foamed particle molded body are shown in Table 1.

[Example 6]
In Example 6, the same resin particles as in Example 1 were used, and the blowing agent carbon dioxide gas was impregnated under the same conditions as in Example 3. Next, after reducing the pressure in the autoclave to atmospheric pressure, the foaming agent was dispersed for 2 hours while stirring in the autoclave. Next, the expandable resin particles were taken out from the autoclave, and the adhering moisture was removed with a centrifuge. Then, the expandable resin particles after the dissipation treatment were expanded under the same conditions as in Example 3. The obtained expanded particles were molded in-mold under the same conditions as in Example 3. The evaluation results of the obtained foamed particle molded body are shown in Table 1. In Table 1, values in parentheses are estimated values.

なお、表１において重量部とはポリ乳酸系樹脂粒子１００重量部に対する値である。

In Table 1, “parts by weight” is a value relative to 100 parts by weight of the polylactic acid resin particles.

[Summary of Examples and Comparative Examples]
From Examples 1 to 6, the foamed particles obtained from the expandable resin particles produced by the process of the present invention and subjected to the dissipation treatment of the physical foaming agent have a large calorific value in the surface layer portion and are used for in-mold molding. It can be seen that a foamed particle molded body having excellent secondary foamability and a high fusion rate can be obtained. Furthermore, from Examples 1 to 4 and 6, the expanded particles obtained from the expandable resin particles of the present invention are those in which a foamed particle molded body having a thickness of 50 mm and good secondary expandability and fusion property can be obtained. I understand. Further, from Examples 1 and 2, the foamed particles obtained from the foamable resin particles of the present invention have a secondary foaming property of the foamed particle molded body even when the molding pressure is set low and 0.16 MPa (G). It can be seen that a foamed particle molded body having a thickness of 50 mm and excellent fusion properties up to the center is obtained. Further, from the comparison result between Example 1 and Example 2, the expanded foam obtained from the expandable resin particle of Example 1 to which the fusion improver is added is secondary expanded than that of Example 2. The foamed particle molded bodies obtained in Examples 1 and 2 were inferior to each other, although they were somewhat superior in properties. From the comparison of Examples 1 and 2, from the foamable resin particles subjected to the dissipation treatment of the present invention without containing a fusibility improver, a foamed particle molded article having a good secondary foamability and fusibility is obtained. It can be seen that the resulting expanded particles can be obtained.
On the other hand, from Comparative Examples 1 and 2, the foamable resin particles that were not subjected to the physical foaming agent dissipation treatment were not sufficiently fused with the foamed particle molded body even at a high heating steam pressure. It is extremely low in the fusion of the central part of the resin, and although it is not shown in the table, it is possible to obtain a foamed particle molded body having a thickness of 50 mm that is excellent in fusion property between the foamed particles even if the heating steam pressure is further increased. I could not do it.
Moreover, the expandable polylactic acid resin particles produced by the production method of the present invention obtained in Examples 1 to 4 and 6 are those in which the water content of the expandable resin particles is adjusted to be high in the dissipation treatment. The polylactic acid foamed particles obtained by foaming the foamable resin particles showed a large ratio between the average surface layer thickness and the average cell thickness (see FIG. 7). On the other hand, the expandable polylactic acid resin particles obtained in Comparative Examples 1 to 3 were not subjected to dissipation treatment, and the expandable polylactic acid resin particles obtained in Example 5 were subjected to dissipation treatment. However, since the water content is low, the polylactic acid foamed particles obtained by foaming those foamable resin particles showed a small ratio between the average surface layer thickness and the average cell thickness (see FIG. 9). ) Note that the magnifications of the photographs in FIGS. 7 and 9 are the same.
Examples 3 to 6 are obtained by changing the dissipation treatment method of the physical foaming agent, and are not limited to the dissipation treatment by standing. It can be seen that the expandable resin particles of the present invention can be produced.

Although the expandable polylactic acid resin particles of the present invention obtained in Example 5 have a low water content, the expanded particles obtained from the expandable resin particles due to the dissipation treatment of the physical foaming agent are Since the surface layer portion has a large calorific value, a 10 mm-thick foamed particle molded article having a good secondary foaming property and fusing property can be obtained. In addition, the expanded particle obtained from the expandable resin particle of Example 5 is fused rather than the expanded particle obtained from the expandable resin particle to which the fusibility improver is added without performing the dissipation treatment shown in Reference Example 1. The rate showed a large value.
In the foamable resin particles of Reference Example 1, a foamed particle molded body having a thickness of 10 mm could be formed by in-mold molding in the foamed particles obtained from the foamable resin particles. It was difficult to obtain a good foamed particle molded body.

Claims (3)

Based on the heat flux differential scanning calorimetry described in JIS K7122 (1987), the mixture was heated to 30 ° C. higher than the end of the melting peak and melted, maintained at that temperature for 10 minutes, and then cooled at a cooling rate of 2 After cooling at 110 ° C / min to 110 ° C and keeping at that temperature for 120 minutes, after heat treatment cooling to 40 ° C at a cooling rate of 2 ° C / min, again at the end of the melting peak at a heating rate of 2 ° C / min Method for producing expandable polylactic acid-based resin particles using a polylactic acid-based resin having a heat absorption (Rendo) of 10 J / g or more in a DSC curve obtained when heated to a temperature higher than 30 ° C. as a base resin Because
(I) an impregnation step of impregnating 100 parts by weight of the polylactic acid-based resin particles with 1 part by weight or more of a physical foaming agent;
(Ii) 10-60% by weight of the physical foaming agent impregnated with the polylactic acid resin particles impregnated with the physical foaming agent is diffused under a temperature of 0 to 40 ° C. A dissipation step for producing 3.9 wt% or less of expandable polylactic acid resin particles;
A process for producing expandable polylactic acid-based resin particles. The method for producing expandable polylactic acid-based resin particles according to claim 1, wherein the dissipation step is performed under a condition of a relative humidity of 40% or more. The manufacturing method of the expandable polylactic acid-type resin particle of Claim 1 or 2 whose main component of the said physical foaming agent is a carbon dioxide gas.

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