JP5044337B2 - Polylactic acid-based resin expanded particles and the expanded particles molded body - Google Patents

Description

  The present invention relates to a polylactic acid resin foamed particle obtained by foaming polylactic acid resin particles containing a foaming agent, and foamed particles obtained by fusing the polylactic acid resin foamed particles to each other by in-mold molding. It relates to a molded body.

  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. Particle compacts are being developed.

As a prior art related to a foam made of a polylactic acid-based resin, a foam having foamability by absorbing a volatile foaming agent in a temperature range in which the degree of crystallinity of an aliphatic polyester such as polylactic acid is in the range of 0 to 20%. Resin particles (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 Particles having a particle size of 15 J / g or more (Patent Document 2), polylactic acid resin expanded particles containing a fusing property improver (Patent Document 3), and excellent fusibility between the expanded particles, and low temperature ( Polylactic acid resin expanded particles that can be molded in-mold with low-pressure steam) and polylactic acid resin expanded particles molded products obtained by using the expanded particles (Patent Document 4) are known.
The above-mentioned polylactic acid-based resin foamed particle molded body can obtain a foam having a desired shape without being subjected to relatively shape restrictions, and also has a physical property design according to the purpose such as lightness, shock-absorbing property and heat insulation. Since it is easy, it is particularly promising as having utility.

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

  However, in the foamed particle molded body made of polylactic acid-based resin described in Patent Document 1 and the like, 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 to each other. Therefore, there is a problem that 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. It was.

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 expanded polylactic acid-based resin was used to produce expanded particles in a state where the polylactic acid-based resin was not crystallized, and an attempt was made to obtain a expanded particle molded body using the expanded 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, it is desired to widen the heating temperature range in which a good molded body is obtained.
Furthermore, in Patent Documents 3 and 4, the present inventors include a specific fusing property improving agent in the polylactic acid-based foamed resin particles, whereby heating at a low molding temperature enables in-mold molding. I found out. 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.

  The present invention provides a foamed particle molded body having excellent fusion properties between foamed particles, and having a large thickness and a foamed particle molded body having a complicated shape, and having excellent fusion properties between foamed particles. Polylactic acid resin foam particles obtained by foaming expandable polylactic acid resin particles, and polylactic acid resin foam particles obtained by molding the polylactic acid resin foam particles in a mold The purpose is to provide a body.

  As a result of intensive studies in view of the above problems, the present inventors have found that a polylactic acid-based resin using a crystalline polylactic acid-based resin or a mixed resin of a crystalline polylactic acid-based resin and an amorphous polylactic acid-based resin as a base resin. In the resin foam particles, the crystallization of the foam particles is not progressed as a whole, and the crystallization of the surface layer portion of the foam particles is not proceeding more than the center portion of the foam particles. The present inventors have found that a foamed particle whose surface layer is thicker than the conventional one can solve the above problems, and has reached the present invention.

That is, according to the present invention, there are provided polylactic acid-based resin expanded particles and polylactic acid-based resin expanded particle molded bodies shown in the following [1] and [2], respectively.
[1] Apparent density is a polylactic acid-based resin foamed particles is ^{0.02g / cm 3 ~0.65g / cm 3} , are listed in the polylactic acid-based resin foamed particles to JIS K7122 (1987 year) Based on the heat flux differential scanning calorimetry, heated to 30 ° C higher than the end of the melting peak and melted, kept at that temperature for 10 minutes, then cooled to 110 ° C at a cooling rate of 2 ° C / min, After maintaining at that temperature for 120 minutes, after heat treatment to cool to 40 ° C. at a cooling rate of 2 ° C./min, heat again to a temperature 30 ° C. higher than the end of the melting peak at a heating rate of 2 ° C./min to melt. The endothermic amount (Rendo) in the DSC curve obtained at the time is 10 J / g or more,
Based on the heat flux differential scanning calorimetry, the polylactic acid in the DSC curve obtained when heated 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 Endothermic amount (Bendo: J / g) and calorific value (Bexo: J / g), and calorific value (Bs: J / g) of the surface layer portion of the polylactic acid based resin foamed particles The relationship with the calorific value (Bc: J / g) satisfies both the following formulas (1) and (2),
Polylactic acid resin foam characterized in that the ratio (Ts / Tm) of average surface layer thickness (Ts) and average cell membrane thickness (Tm) of the polylactic acid resin foamed particles is 5.0 to 40.0. particle.
(Bexo) / (Bendo)> 0.3 (1)
(Bs)> (Bc) (2)
[2] A molded article of polylactic acid resin expanded particles obtained by fusing the polylactic acid resin expanded particles according to [1] to each other by in-mold molding.

Hereinafter, the polylactic acid-based resin expanded particles of the present invention may be referred to as polylactic acid-based resin expanded particles (B), or simply expanded particles (B) or expanded particles, except for the description relating to comparative examples in the examples. The polylactic acid-based resin expanded particle molded body may be referred to as a polylactic acid-based resin expanded particle molded body (C), or simply a expanded particle molded body (C) or expanded particle molded body.
Further, the foamable polylactic acid resin particles before foaming to obtain the polylactic acid resin foam particles (B) can be expanded foamed polylactic acid resin particles (A), or simply foamable polylactic acid resin particles, or foamed. Sometimes referred to as conductive resin particles.
Incidentally, in the polylactic acid-based resin foamed particles (B), the surface layer portion of the expanded beads (hereinafter sometimes referred to the surface layer portion (S _B).) And the weight of the entire surface of the expanded beads, cut before the foamed particles The portion is cut out with a thickness as uniform as possible so that the weight is 1/5 to 1/3. On the other hand, the center part of the foamed particles (hereinafter sometimes referred to as the center part (C _B )) is the entire surface of the foamed particles cut out with a uniform thickness as much as possible, and the weight of the foamed particles before cutting out. The remainder of the expanded particles is 1/5 to 1/3 of the weight.
In the expandable polylactic acid resin particles (A), the vicinity of the surface layer portion including the surface layer portion of the expandable resin particles is referred to as the vicinity of the surface layer portion, and the vicinity of the center portion including the center portion of the expandable resin particles is the center portion. It is called neighborhood.

Since the polylactic acid-based resin expanded particles (B) have a (Bexo) / (Bendo) ratio of more than 0.3, there are over 30% of uncrystallized regions among the regions that can be crystallized in the expanded particles. And the calorific value (Bs: J / g) based on the crystallization of the surface layer part (S _B ) exceeds the calorific value (Bc: J / g) based on the crystallization of the central part (C _B ) For this reason, since the crystallinity of the central portion (C _B ) is relatively high and the crystallinity of the surface layer portion (S _B ) is low, the foamed particles are mutually bonded when heated in in-mold molding. Therefore, the polylactic acid-based resin expanded particle molded body obtained by fusing the polylactic acid-based resin expanded particles to each other has excellent fusion properties. Further, since the polylactic acid-based resin expanded particles (B) have an average surface layer thickness (Ts) larger than the average cell membrane thickness (Tm), the shrinkage of the expanded particles during heating of the polylactic acid-based resin expanded particles Since foaming can be suppressed and the heat resistance of the foamed particles becomes high, the heating temperature range in which a good foamed particle molded body can be obtained during molding of the foamed particles is widened, and the secondary foamability is further increased. It will be good.

Hereinafter, the polylactic acid-based resin expanded particles (B) and the polylactic acid-based resin expanded particles (C) of the present invention will be described.
The polylactic acid-based resin expanded particles (B) of the present invention are obtained by (i) impregnating a polylactic acid-based resin particle with a physical foaming agent, and (b) one of the foaming agents from the polylactic acid-based resin particle impregnated with the foaming agent. And (iii) foaming the foaming agent-impregnated polylactic acid resin particles in which part of the foaming agent is diffused to produce the polylactic acid resin foamed particles (B) of the present invention. Is possible.
In addition, by adding a physical foaming agent during the production of the resin particles, the production of the resin particles and the impregnation with the foaming agent can be performed in one step.
The polylactic acid-based resin expanded particle molded body (C) of the present invention can be produced by (III) in-mold molding of the polylactic acid-based resin expanded particles (B).
First, the polylactic acid-type resin particle used for manufacture of a polylactic acid-type resin expanded particle (B) is demonstrated.

[1] Polylactic acid-based resin particles The polylactic acid-based resin particles used in the production of the expandable polylactic acid-based resin particles (A) of the present invention are extruded by blending additives necessary for the base resin. Can be manufactured by a strand cutting method, an underwater cutting method, or the like.
(1) Base resin (a) About base resin The polylactic acid resin, which is a base resin used in the production of the expandable polylactic acid resin particles (A), contains 50 moles of units derived from lactic acid in the resin. % Containing polymer. 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 polyhydric carboxylic acid, (e) a copolymer of lactic acid and an aliphatic polyhydric alcohol, (f) any one of (a) to (e) 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 resin as the base resin is the above-mentioned polylactic acid resin in differential scanning calorimetry at a heating rate of 2 ° C./min described later. A heat absorption amount of 10 J / g or more is preferable.
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 (A) and further molded in-mold is deformed under heating atmosphere by being crystallized. It is easy to increase 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. From this viewpoint, the heat absorption is more preferably 15 J / g or more, and further preferably 20 J / g or more. On the other hand, the upper limit is not particularly limited, but the endothermic amount is generally 70 J / g from the properties of ordinary base resin.

The endothermic amount in the differential scanning calorimetry of the polylactic acid-based resin can be determined based on 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.
As shown in FIG. 1, the endothermic amount of the polylactic acid resin is defined as point a where the endothermic peak is separated from the low temperature side baseline of the endothermic peak of the DSC curve, and the endothermic peak reaches the high temperature side baseline. The return point is defined as a point b, and a value obtained from a straight line connecting the points a and 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 addition, in the measurement of the endothermic amount, the reason for adopting the holding condition at 110 ° C. for 120 minutes, the cooling rate of 2 ° C./min, and the heating rate of 2 ° C./min as the condition adjustment of the test piece and the measurement condition of the DSC curve. Is intended to determine the endothermic amount of a polylactic acid test piece which has been adjusted to a state where the crystallizable region is completely crystallized or close to it, by maximizing the crystallization of the polylactic acid test piece. Because of that. As described above, the case where the polylactic acid resin is used as the test piece has been described. When the endothermic amount (Rendo) 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 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 In the base resin used in the production of the polylactic acid-based resin expanded particles (B) of the present invention, other resin components are blended within a range that does not impair the purpose and effect 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 above polylactic acid resins, ring-opening polymers of lactones such as polycaprolactone, polybutylene succinate, polybutylene adipate, polybutylene succinate adipate , 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.
Further, by the above method, it is possible to add additives such as flame retardants, antistatic agents, weathering agents, thickeners and the like within a range not impeding the effects of the present invention.

(3) Production of resin particles In the production of resin particles, a known pelletizing method such as a strand cut method or an underwater cut method using a base resin composed of a polylactic acid resin containing a crystalline polylactic acid resin as a raw material. It is obtained by adopting. 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. Examples of the production method include obtaining the resin particles by cooling 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] The polylactic acid resin foamed beads of the present invention for the polylactic acid-based resin foamed particles (B) (B) is polylactic acid resin foamed apparent density of 0.02g ^/ cm ³ ~0.65g ^/ cm 3 Based on the heat flux differential scanning calorimetry described in JIS K7122 (1987), the polylactic acid resin foamed particles are heated to a temperature 30 ° C. higher than the end of the melting peak and melted. After maintaining at that temperature for 10 minutes, cooling to 110 ° C. at a cooling rate of 2 ° C./min, holding at that temperature for 120 minutes, and then cooling to 40 ° C. at a cooling rate of 2 ° C./min. The endothermic amount (Rendo) in the DSC curve obtained when heating and melting at a heating rate of 2 ° C./min up to 30 ° C. higher than the end of the melting peak is 10 J / g or more, and the heat flux differential running A temperature that is 30 ° C. higher than the end of the melting peak from normal temperature (normal temperature refers to a temperature of about 23 ° C. (hereinafter the same)) at a heating rate of 2 ° C./min without heat treatment based on the calorimetric method. Endothermic amount (Bendo: J / g) and exothermic amount (Bexo: J / g) of the polylactic acid-based resin expanded particles in the DSC curve obtained when heated to 1, and the surface layer portion of the polylactic acid-based resin expanded particles The relationship between the calorific value (Bs: J / g) and the calorific value (Bc: J / g) at the center satisfies both the following formulas (1) and (2), and the average surface layer of the polylactic acid-based resin expanded particles The ratio (Ts / Tm) of the thickness (Ts) and the average cell membrane thickness (Tm) is 5.0 to 40.0.
(Bexo) / (Bendo)> 0.3 (1)
(Bs)> (Bc) (2)

(1) Production of polylactic acid-based resin expanded particles (B) Polylactic acid-based resin expanded particles (B) are obtained by (i) impregnating polylactic acid-based resin particles with a physical foaming agent, (b) dissipation of physical foaming agent, And (c) production by foaming.
Production examples of the polylactic acid resin expanded particles (B) will be described below.
(A) Impregnation of physical foaming agent (a-1) 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- An organic physical foaming agent such as 1,2,2,2-tetrafluoroethane, or an inorganic physical foaming agent such as nitrogen, carbon dioxide, argon, air, water, or a mixture of two or more selected from them. Among them, an inorganic physical foaming agent that does not destroy the ozone layer and is inexpensive is preferable. From this viewpoint, it is more preferable that the physical foaming agent contains nitrogen, air, or carbon dioxide as the 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. .

(I-2) 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.
In addition, the water used as an aqueous medium may act as a foaming agent as described above.
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, adjustment of the crystallinity degree of the resin particle 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.

(A-3) 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, which is the next step. The impregnation amount of the physical foaming agent is 1 to 30 parts by weight, preferably 2 to 20 parts by weight, and more preferably 3 to 15 parts by weight with respect to 100 parts by weight of the polylactic acid resin particles before impregnation with the physical foaming agent. When the impregnation amount is less than 1 part by weight, there is a risk that the resin particles may not be sufficiently foamed when heated and foamed after the physical foaming agent escapes, while when the impregnation amount exceeds 30 parts by weight, When the physical foaming agent is dissipated, it takes a long time to process, or the crystallization of the resin particles is likely to proceed, so that there is a possibility that the obtained foam particles may have insufficient fusion properties during molding in the mold. .
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.

(A-4) When carbon dioxide gas is used as a physical foaming agent Hereinafter, a case where carbon dioxide gas is used as a physical foaming agent will be described.
The amount of carbon dioxide impregnation is 1 to 30 parts by weight, preferably 2 to 20 parts by weight, and more preferably 3 to 15 parts by weight 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, while when the impregnation amount exceeds 30 parts by weight. When the next blowing agent escapes, the treatment time takes a long time, or when carbon dioxide gas is impregnated in the polylactic acid-based resin, the glass transition temperature is lowered, resulting in a relatively high crystallization speed. There is a possibility that crystallization proceeds excessively and the fusibility at the time of in-mold molding of the foamed particles obtained in the subsequent process becomes 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.
In addition, 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 liquid layer impregnation is the apparent density of the target foam 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.

(A-5) Use of fusibility improver When impregnating a polylactic acid resin particle with a foaming agent, the resin particle is obtained by foaming the polylactic acid resin without containing the fusibility improver. When molding the foamed polylactic acid-based resin particles, it is possible to produce a foamed particle molded body having a high fusing property. When the foamable polylactic acid-based resin particles (A) are impregnated with a foaming agent, In addition, for the purpose of further improving the fusibility, a polylactic acid resin may contain a fusibility improver.
When the expandable polylactic acid resin particles (A) containing a fusing property improving agent are used, it is more preferable that the content of the fusing property improving agent in the vicinity of the surface layer portion is larger than the content in the vicinity of the central portion of the expanding particle. Further, it is more preferable that the fusing property improving agent exists only in the vicinity of the surface layer portion.
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 containing the fusion improving agent in the polylactic acid-based resin particles include a method in which the resin particle contains the fusion improving agent before or after impregnation with the foaming agent.
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.

(B) Dissipation of physical foaming agent Dissipation of physical foaming agent 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 dissipating the foaming agent is exemplified 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 for dissipating the blowing agent 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 can be easily adjusted. The concentration of the blowing agent present in the surface layer portion is set so that the calorific value (Bs: J / g) of the surface layer portion of the polylactic acid-based resin expanded particles of the invention is larger than the calorific value (Bc: J / g) of the central portion The concentration can be made lower than the concentration of the blowing agent present in the central portion. More preferably, the dissipation temperature of the blowing agent is 10 ° C to 30 ° C.
The humidity condition for dissipating the blowing agent is preferably 40% or higher relative humidity (RH). 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%.

The pressure of the dissipation treatment needs to be lower than the partial pressure of the foaming agent when impregnated with the 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 less than atmospheric pressure. It is. Further, the foaming agent dissipation rate to be dissipated under these conditions is 10% to 60% by weight of the foaming agent impregnated in the foaming agent-impregnated resin particles after the impregnation of the foaming agent. Therefore, if the dissipation factor of the foaming agent is 10 to 60% by weight, the amount of the foaming agent in the vicinity of the surface layer portion of the polylactic acid-based resin particles that has undergone the foaming agent dissipation step is more concentrated than the amount of the foaming agent in the vicinity of the center portion. Is kept low, and as a result, the crystallization of the surface layer portion is difficult to proceed, so that the crystallization of the surface layer portion of the expanded particles obtained in the subsequent process is suppressed, and when the expanded particles are molded in the mold The expanded 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 obtained by the following equation (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 step. Measuring the resin particle weight (g) after evacuation by measuring the weight of the resin particle 10 minutes after it is taken out to atmospheric pressure, with the surface of the resin particle removed with air or the like And
In order to adjust to the above dissipation rate at the dissipation temperature 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 or more. 5 hours or less. If the treatment time is 30 minutes or more and 6 hours or less, it is sufficient to dissipate the foaming agent, and a foaming agent sufficient for foaming can be left in the resin particles.
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).

(C) Foaming of expandable polylactic acid-based resin particles In the foaming step of expandable polylactic acid-based resin particles, the foamable resin particles (ii) after the dissipation of the foaming agent are heated and foamed. As a method of heating and foaming the expandable resin particles, a conventionally known method can be employed. Among them, a method in which foamed resin particles are filled in an airtight container, and a foam or a mixed heat medium of steam and air is introduced and foamed 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 the foaming temperature exceeds (Tg + 50) ° C., the closed cell ratio of the foamed particles is lowered and good in-mold moldability is exhibited. There arises a problem that it is difficult to obtain expanded particles. By impregnating the base resin with the foaming agent, the expandable resin particles are foamed even below 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) is a value obtained as the midpoint glass transition temperature of the DSC curve obtained by heat flux differential scanning calorimetry based on JIS K 7121 (1987). More specifically, the midpoint glass transition temperature is the same as that in JIS K7121 (1987) 3. 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 particles (B)
The obtained by the production examples and the like polylactic acid-based resin foamed particles (B) has an apparent density of a polylactic acid-based resin foamed particles is ^{0.02g / cm 3 ~0.65g / cm 3} , the polylactic acid Based on the heat flux differential scanning calorimetry described in JIS K7122 (1987), the resin expanded particles are heated to a temperature 30 ° C. higher than the end of the melting peak, and kept at that temperature for 10 minutes. Then, 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, again at a heating rate of 2 ° C./min The endothermic amount (Rendo) in the DSC curve obtained when heating and melting to a temperature 30 ° C. higher than the end of the melting peak is 10 J / g or more, and heat treatment based on the heat flux differential scanning calorimetry The endothermic amount of the polylactic acid-based resin expanded particles (Bendo: J / g) in the DSC curve obtained when heated from room temperature to 30 ° C higher than the end of the melting peak at a heating rate of 2 ° C / min. ) And calorific value (Bexo: J / g), and the relationship between the calorific value (Bs: J / g) of the surface layer portion of the polylactic acid-based resin expanded particles and the calorific value (Bc: J / g) of the central portion. Both the following formulas (1) and (2) are satisfied,
The ratio (Ts / Tm) of the average surface layer thickness (Ts) and the average cell membrane thickness (Tm) of the polylactic acid-based resin expanded particles is 5.0 to 40.0.
(Bexo) / (Bendo)> 0.3 (1)
(Bs)> (Bc) (2)
The polylactic acid-based resin expanded particles (B) obtained by foaming are preferably stored under conditions that avoid hydrolysis at high temperatures and high humidity.

(B) Apparent Density Apparent density expanded polylactic acid resin particles (B) is ^{0.02g / cm 3 ~0.65g / cm 3} .
The apparent density of the polylactic acid-based resin expanded particles (B) 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 becomes large. 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 resin expanded particles (B) 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) Measurement of endothermic amount (Rendo) after heat treatment of polylactic acid-based resin expanded particles (B) The polylactic acid-based resin expanded particles (B) of the present invention are JIS K7122 using 1 to 4 mg of expanded particles as a test piece. 1987), and heated to a temperature 30 ° C. higher than that at the end of the melting peak to be melted, kept at that temperature for 10 minutes, and then cooled at a rate of 2 ° C./min. After cooling to 110 ° C. and keeping at that temperature for 120 minutes, the heat treatment is cooled to 40 ° C. at a cooling rate of 2 ° C./min. The endothermic amount (Rendo) in the DSC curve obtained when melting by heating to a high temperature is 10 J / g or more.
When the endothermic amount is less than 10 J / g, there are too few components to crystallize in the polylactic acid-based resin expanded particles (B), and the expanded particle molded body obtained by in-mold molding is completely crystallized Even if it makes it, there exists a possibility that improvement in heat resistance, rigidity, etc. which are hard to deform | transform in a heating atmosphere may become inadequate. From this viewpoint, the heat absorption is more preferably 15 J / g or more, and further preferably 20 J / g or more. On the other hand, the upper limit is not particularly limited, but the endothermic amount is generally 70 J / g from the properties of ordinary base resin. If the endothermic amount (Rendo) is within the above range, the base resin has many components that can be crystallized. It is easy to increase the difference in degree.
The endothermic amount (Rendo) is substantially the same as the “endothermic amount in differential scanning calorimetry of the base resin”.

(C) Relationship between the endothermic amount of the expanded particles and the exothermic amount of the expanded particles in differential scanning calorimetry without performing heat treatment based on the heat flux differential scanning calorimetry described in JIS K7122 (1987), The endothermic amount (Bendo: J / g) and calorific value of the expanded polylactic acid resin particles in the DSC curve obtained when heating from room temperature to 30 ° C higher than the end of the melting peak at a heating rate of 2 ° C / min ( The relationship with Bexo: J / g) satisfies the following formula (1).
(Bexo) / (Bendo)> 0.3 (1)
If the (Bexo) / (Bendo) ratio is greater than 0.3, the amount of uncrystallized material is greater than the amount of crystals that the foamed particles have when they are completely or mostly crystallized. Therefore, the mutual fusion property of the foamed particles at the time of in-mold molding is excellent. 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 mg 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.
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 obtaining a high endothermic amount (Bendo) and (Bendo-Bexo) by heat flux differential scanning calorimetry.

(D) a surface layer portion (S _B) heating value and the central portion (C _B) polylactic acid-based resin foamed particles obtained relationship expandable polylactic acid resin particles and heating value (A) to foam in the foamed particles (B) is the difference between the endothermic amount of the expanded particles (Bendo: J / g) and the exothermic amount of the expanded particles (Bexo: J / g) in the differential scanning calorimetry at the heating rate of 2 ° C./min as described above. The relationship satisfies the following formula (1), and the relationship between the calorific value (Bs) of the surface layer portion (S _B ) and the calorific value (Bc) of the central portion (C _B ) of the expanded particles is expressed by the following formula ( 2) is satisfied, the surface layer portion has more uncrystallized portions than the center uncrystallized portion. Therefore, the foamed particle molded body has excellent fusion properties between foamed particles at the time of in-mold molding and excellent mechanical properties. Can be obtained. Moreover, when the crystallization of the center part has progressed to some extent, since the heat resistance of the foamed particles as a whole is improved, the in-mold molding temperature range can be expanded.
(Bexo) / (Bendo)> 0.3 (1)
(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 cut out from the entire surface of the expanded particles with a thickness as uniform as possible so that it is 1/5 to 1/3 the weight of the expanded particles before cutting. The central part (C _B ) is a part of the surface of the foamed particles that is cut out and removed with a uniform thickness as much as possible. The weight of the foamed particles before cutting is 1/5 to 1/3 of the weight. The remainder of the expanded particles.

The test pieces of the surface layer portion of the expanded beads (S _B), the surface layer portion (S _B) of the cutter knife, the surface portion subjected to cutting processing using a microtome or the like (S _B) were collected containing the surface of the foamed particles Can be used for measurement. 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) It is excised with a thickness that is as uniform as possible so that it becomes 1 to 1/3. If the weight of the excised surface layer portion (S _B ) is 1/5 to 1/3 of the original expanded particle particle weight, the amount of heat generated in the surface layer portion without containing a large amount of the expanded layer inside the expanded particle 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, as a method of the central portion foamed layer of the test piece (C _B) preparation, cutting processing 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 perform measurement. The point to be noted when preparing the test piece of the foamed layer in the central part (C _B ) is that the foamed layer has a thickness that is as uniform as possible from the cut-out surface after always cutting out the entire surface of one foamed particle. Is removed, leaving the foamed layer in the center (C _B ). 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 one fifth to one third of the particle weight of the original expanded particles, the thickness as uniform as possible from the surface layer portion (S _B ) of the expanded particles. Thus, the thickness of 0.072R _{1 to} 0.127R ₁ cm is cut out from the surface layer.

Next, the central part (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. The remaining foamed particles are referred to, and the radius R ₃ (cm) of the center of the remaining foamed particles, which is one third of the particle weight of the original foamed particles cut out as described above, 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 (S _B) 5 minutes 1 to 3 fold lower than to become part of the weight of the total weight the original foamed particles, the foamed particles The portion from 0.11 mm to 0.19 mm from the surface. 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 expanded particles, and refers to a portion having a radius from the center of 0.88 mm to 1.04 mm.
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 test piece thus obtained, the calorific value (Bs) of the surface layer portion (S _B ) and the calorific value (Bc) of the central portion (C _B ) of the expanded particles are measured by differential scanning calorimetry.

(E) Ratio of average surface layer thickness (Ts) and average cell membrane thickness (Tm) of polylactic acid-based resin expanded particles (B) The present invention is obtained by foaming the expandable polylactic acid-based resin particles (A). The expanded particles (B) have a ratio (Ts / Tm) of the average surface layer thickness (Ts) to the average cell membrane thickness (Tm) of the polylactic acid-based resin expanded particles of 5.0 to 40.0, preferably 6. It is 0-25.0, More preferably, it is 7.0-18.0, The polylactic acid-type resin expanded particle (B) of such a state is the average surface layer thickness (Ts) with respect to average cell membrane thickness (Tm). Since the value is larger than that of conventional foam particles, the heat resistance of the foam particles is increased by being covered with a strong skin, and when heated by a heating medium such as steam or hot air during in-mold molding Can prevent shrinkage and foam breakage of foamed particles, good foamed particles The molding temperature range in which a child molded body can be obtained is widened, and it becomes more suitable for molding a good molded body of polylactic acid resin particles.

(E-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.

(E-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.

(E-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).
The above formula is a relational expression between the average bubble diameter and the average bubble film thickness. “Plastic Foam Handbook” (published by Nikkan Kogyo Shimbun, published on February 28, 1973), “1. This is described in section 3.2. If the average cell diameter of the foamed particles of the present invention is determined by the formula (5), the average cell membrane thickness (Tm) of the expanded particles is determined.

When the above-mentioned expanded particles are used, it is possible to mold expanded particle molded articles having excellent fusion properties between expanded particles under a wide range of in-mold molding conditions. In-mold molding such as thick and complex shapes Even if it is difficult to obtain, a good molded product can be obtained. Since the use of the expanded beads, a mechanism capable of forming a 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), At the time of in-mold molding, the surface layer of the foamed particles is easy to soften, the foamed particles are easily fused together, and the foamed particles have a thicker skin than conventional ones. In this case, it is considered that the expansion of the in-mold molding temperature range in which a good foamed particle molded body can be obtained by preventing shrinkage and foam breakage of foamed particles, and these are considered to be the combined effects.

[3] About expandable polylactic acid-based resin particles (A) The expandable polylactic acid-based resin particles (A) become polylactic acid-based resin expanded particles (B) by foaming, and are a physical foaming agent. And the water content is 0.5% by weight or more.
As described above, the expandable polylactic acid resin particles (A) can be produced by impregnating the polylactic acid resin particles with a physical foaming agent and then dissipating the foaming agent.
When dispersing the foaming agent, for example, if the humidity condition is 40% RH or more, the water content of the resin particles obtained after the dissipation treatment can be 0.5% by weight or more.
In such dispersion, the physical foaming agent is relatively dissipated from the vicinity of the surface layer portion of the resin particle, and the physical foaming agent concentration in the vicinity of the surface layer portion of the resin particle is the foaming agent concentration in the vicinity of the center portion of the particle. It is assumed that it will be lower.
In addition, when an inorganic physical foaming agent such as an organic physical foaming agent or carbon dioxide gas is contained, the glass transition temperature of the polylactic acid resin is lowered, so that the crystallization of the crystalline polylactic acid resin composition is likely to proceed. It becomes.
As a result, by passing through the dissipation step, the foaming agent concentration in the vicinity of the surface layer portion of the expandable resin particles is lower than the foaming agent concentration in the vicinity of the center portion of the impregnated resin particles, so that the vicinity of the center portion of the resin particles near the center portion In the expanded particles obtained through the subsequent expansion step, the crystallinity in the vicinity of the center of the expanded particles is relatively higher than the crystallinity in the vicinity of the surface layer. This is confirmed by the fact that the calorific value (Bs) of the surface layer part (S _B ) of the expanded particles obtained by foaming after the dissipation is higher than the calorific value (Bc) of the central part (C _B ). . Since the foaming agent concentration in the vicinity of the surface layer portion of the expandable resin particles can be kept relatively low, the expanded particles obtained in the subsequent step have a low surface layer portion crystallinity and a high fusion rate between the expanded particles. It will be a thing.

[4] Polylactic acid-based resin expanded particle molded body (C) The expanded particle molded body (C) is obtained by fusing the polylactic acid-based resin expanded particles (B) to each other.
(1) In-mold molding of polylactic acid-based resin expanded particles (B) The polylactic acid-based resin expanded particles (C) are molded into each other by molding the polylactic acid-based resin expanded particles (B) in the mold. It can be obtained by fusing. Moreover, it is preferable that the foamed particle molded body (C) obtained by fusing the polylactic acid resin expanded particles (B) of the present invention to each other further undergo a curing process.
In in-mold molding, it is preferable that the foamed particles are fused together by heating the foamed particles with a heating medium such as steam or a mixed medium of steam and air after filling the foamed particles in the mold. As described above, when the heat molding is performed, the foamed particles are well fused with each other to obtain an expanded foamed particle molded body. 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. As the heating means, steam is usually used, and the heating temperature is a temperature at which the surface of the foamed particles melts during in-mold molding.
The foamed particle molded body (C) obtained by in-mold molding of the polylactic acid-based resin expanded particles (B) is superior to the conventional polylactic acid resin expanded particle molded body in the fusion property between the expanded particles, for example, 30 mm to 50 mm. It is possible to form a foamed particle molded body with a thickness of 0.1 to 0.25 MPa (G) steam.

(2) Impregnation of polylactic acid-based resin expanded particles (B) with pressurized gas When producing the expanded particle molded body (C), prior to in-mold molding, the polylactic acid-based resin expanded particles (B) are previously air, It is preferable to impregnate an inorganic gas such as nitrogen or carbon dioxide or 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).

The amount of impregnated gas (mol / 1000 g expanded particles) is obtained by the following equation (6).
Impregnation gas amount (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-mold molding The foamed particle molded body (C) obtained by the above in-mold molding has [Tg + 5] to [Tg + 30] ° C. when the midpoint glass transition temperature of the base resin is Tg. It is preferable to go through a curing process for holding for a certain time in an atmosphere.
When the temperature of the curing process is [Tg + 5] ° C. or higher, it becomes possible to perform the polylactic acid resin in a relatively short time to crystallize, and the effect of improving the heat resistance of the foamed particle molded body is obtained. It becomes a foamed particle molded body which is more excellent in heat resistance. In this respect, the curing temperature is more preferably [Tg + 8] ° C. or higher, and further preferably [Tg + 10] ° C. or higher. Moreover, when it is [Tg + 30] degrees C or less, it becomes possible to prevent a deformation | transformation of a foamed particle molded object (C), and to obtain a favorable expanded particle molded object. In this respect, [Tg + 25] ° C. or lower is more preferable, and [Tg + 20] ° C. or lower is still 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 or less from the viewpoint of preventing the foamed particle molded body (C) 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 (C) may be hydrolyzed to form a foamed particle molded body having poor mechanical properties. . From the above viewpoint, 30% RH or less is more preferable, and 20% RH or less is more preferable. On the other hand, a lower limit of 0% RH is preferably 5% RH or more because a special device is 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 (C) may be in the form as it is, but in order to prevent deformation of the foamed particle molded body (C) when the temperature is high, the foamed particle molded body may be fixed with a jig for fixing the shape. It is preferable to fix (C).
According to the curing step, the foamed particle molded body (C) having improved heat resistance can be obtained efficiently since it can be crystallized based on the midpoint glass transition temperature of the base resin. In addition, the heating medium in a curing process is normally performed with a hot air.

  The foamed particle molded body (C) of the present invention 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 (C)
The foamed particle molded body (C) of the present invention can be obtained from foamed particles having good secondary foamability and good fusion between the foamed particles at the time of in-mold molding. This is a foamed particle compact with good fusion in the vicinity of the center of the particle compact.
Furthermore, since the heat resistance is improved when the crystallization of the foamed particle molded body (C) is promoted, the degree of crystallization can be increased efficiently and the heat resistance can be improved through the curing process described above. .
The shape of the expanded particle molded body (C) 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 of the present invention is excellent in dimensional stability and surface smoothness.

Apparent density (a) Apparent Density PP bead molding (C) is preferably from 0.02~0.65g / cm ^3, more preferably 0.03~0.45g / cm ^3.
The apparent density of the foamed particle molded body (C) is calculated by dividing the weight WM (g) of the foamed particle molded body by the volume VM (cm ³ ) obtained from the outer dimensions of the foamed particle molded body (WM / VM). Is required.

(B) Fusion rate The fusion rate of the foamed particle molded body (C) is preferably 50% or more, more preferably 60% or more from the viewpoint of exhibiting sufficient mechanical properties such as bending strength of the molded body. preferable.
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 expanded particle molded body of the present invention uses a low environmental load thermoplastic resin as a base resin, the conventional polystyrene-based resin expanded particle molded body and polyolefin-based resin expanded particle molded body Can be preferably used as a substitute for the fields in which has been used, 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.
The DSC apparatus used in Examples and Comparative Examples of the present invention is a product name: DSC-Q1000 manufactured by TA Instruments Japan Co., Ltd.
(1) Polylactic acid-based resin particles (i) Midpoint glass transition temperature The midpoint glass transition temperature of polylactic acid-based resin particles is the same as that in 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 heated and dissolved, held at that temperature for 10 minutes, and then adjusted to 0 ° C. at a cooling rate of 10 ° C./min, and then heated at a rate of 10 ° C. It was determined from the DSC curve obtained when the temperature was raised from 0 ° C./min to a temperature 30 ° C. higher than the end of the melting peak.
(2) About expandable polylactic acid-based resin particles (i) Amount of impregnated foaming agent The amount of impregnation (parts by weight) of a physical foaming agent into resin particles was determined from the following formula.
Physical foaming agent impregnation amount (parts 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 (parts by weight)
(Ii) Foaming agent dissipation rate The physical blowing agent dissipation rate (%) with respect 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 (%)
(Iii) Moisture content The moisture content of the expandable polylactic acid resin particles was measured by the method B-water vaporization method of JIS K7251 (2002).

(3) Polylactic acid-based resin expanded particles (i) Apparent density A graduated cylinder containing ethanol at 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. 1000 foam particles (weight W1 of the foam particles group) were sunk using a wire mesh, and the foam particles group was placed in a graduated cylinder at a volume V1 (cm ³ ) of the foam particle group read from the rise in the ethanol water level. The weight W1 (g) was divided (W1 / V1).
(Ii) Endothermic amount (Rendo) in DSC curve after heat treatment of polylactic acid resin expanded particles
Based on the heat flux differential scanning calorimetry described in JIS K7122 (1987), the polylactic acid resin foamed particles are heated to a temperature 30 ° C. higher than the end of the melting peak and melted. After maintaining for 1 minute, cooling to 110 ° C. at a cooling rate of 2 ° C./min, holding at that temperature for 120 minutes, and then heat treatment to cool to 40 ° C. at a cooling rate of 2 ° C./min, again heating rate of 2 ° C. The endothermic amount (Rendo) in the DSC curve obtained when melted by heating to a temperature 30 ° C. higher than at the end of the melting peak at / min was measured.
(Iii) Heat generation (Bexo) and heat absorption (Bendo)
Regarding “[2] Polylactic acid-based resin expanded particles (B), (2) Polylactic acid-based resin expanded particles (B), (C) Endothermic amount of expanded particles and calorific value of the expanded particles in differential scanning calorimetry The measurement method described in the section “No.

(Iv) Calorific value (Bc) at the center and calorific value (Bs) at the surface layer
Regarding “[2] Polylactic acid-based resin expanded particles (B), (2) Polylactic acid-based resin expanded particles (B), (D) Heat generation amount of the surface layer portion (S _B ) of the expanded particles and the central portion (C _B The measurement method described in the section “Relation with calorific value”) was adopted.
(V) Method for Measuring Average Surface Layer Thickness and Average Cell Film Thickness of Resin Expanded Particles “[2] Polylactic acid based resin expanded particles (B) (2) Polylactic acid based expanded resin particles (B), (e) Using the same method as described in the section “Ratio of average surface layer thickness (Ts) and average cell membrane thickness (Tm) of polylactic acid-based resin expanded particles (B)”, measurement was performed for 50 expanded particles each. went. Since (ρf and ρs) >> ρg in equation (5), assuming that ρg is 0 (g / cm ³ ), Vs = ρf / ρs. Therefore, the average bubble film thickness Tm (μm) is expressed by the following equation: Tm = d [(X / (X−1)) ^1/3 −1] (where X = ρs / ρf = 1.26 / ρf). Calculated.

(4) About foamed particle molded body (i) 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.
(Ii) Fusing rate 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 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 particles whose material was destroyed by the expanded particles themselves were measured, and the ratio (b / n) of (n) and (b) The fusion rate was [(b / n) × 100] (%), which is 100 minutes.
(Iii) Center part fusion evaluation The center part of the fracture surface of the expanded foam 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.
(Iv) Apparent density of 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 wt ppm of polyethylene wax (manufactured by Toyo Petrolite Co., Ltd., trade name: Polywax 1000, number average molecular weight 2200) is added to 50 parts by weight of the blend, and these are melted and kneaded in an extruder. 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.

(2) Impregnation of blowing agent Next, in an autoclave having an internal volume of 5 liters (L), 3000 ml of ion-exchanged water, 0.5 g of aluminum oxide (trade name: Aerooxide), sodium dodecylbenzenesulfonate (No. 1) Made by Ichi Kogyo Seiyaku Co., Ltd., trade name: Neogen S20A (0.2 g) and resin particles (1000 g) were added, and glycerol diacetomonocaprylate (manufactured by Riken Vitamin Co., Ltd., trade name: Riquemar PL) -019) 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.
Next, after reducing the pressure in the autoclave to atmospheric pressure, the resin particles were taken out. The resin particles taken out 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 after 10 minutes from taking out from the autoclave, and found to be 6.3 parts by weight.

(3) Dissipation of foaming agent The foaming agent-impregnated resin particles are put in a polyethylene bag and left at room temperature 25 ° C. and humidity 50% RH for 2 and a half hours with the bag mouth opened, A treatment to dissipate a part of the impregnated carbon dioxide gas was performed.
The amount of foaming agent impregnation after the dissipation treatment measured after 10 minutes from the end of the foaming agent dissipation treatment was 3.5 parts 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 expandable polylactic acid-based resin 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 foamed non-crosslinked expanded particles. At this time, the maximum temperature in the foaming machine was 82 ° C. Apparent density, endothermic amount (Rendo), exothermic amount (Bexo), endothermic amount (Bendo), ratio (Bexo / Bendo) and difference (Bendo-Bexo), surface layer portion calorific value (Bs), central portion Table 1 shows the calorific value (Bc) and ratio (Bs / Bc), average surface layer thickness (Ts), average bubble diameter, 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 in a sealed container, pressurized with air, impregnated into the foamed particles so that the amount of impregnated gas of air is 0.33 (mol / 1000 g), and then 250 (mm) × 200 (mm) ) X compression rate 20% in a mold having a molding space portion with a thickness of 50 (mm) (bulk volume of foamed particles before compression filled in the mold (cm ³ ) −mold inner volume after mold clamping (cm ³ )) × 100 / The mold inner volume after clamping (cm ³ )) (%) was filled and molded in-mold at the 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 part of a cross-section obtained by dividing the polylactic acid foamed particles of the present invention obtained in Example 1 into approximately two parts. In FIG. 7, the scanning electron micrograph which expanded further the surface layer part in the part of the cross section which divided the polylactic acid expanded particle of this invention obtained in Example 1 into the substantially two parts 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.

[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 same conditions as in Examples 3 and 4. After removing the adhering moisture, it was placed in the same cylindrical container as used in Example 3 and Example 4, and in Comparative Example 3, foaming was performed for 2 hours at a temperature of 25 ° C. and a humidity of 15% RH by introducing dry air. The foaming agent dissipation treatment of the conductive resin particles was performed. Next, the foamable resin particles after the dissipation treatment were foamed under the same conditions as in Example 1. The foamed particles thus obtained were molded in-mold under the same conditions as in Example 2 except that the molding pressure was 0.20 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 in Example 1 were used, and carbon dioxide gas as a foaming agent 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.

[Summary of Examples and Comparative Examples]
In Example 1, even if the foamed particle molded body had a large thickness, the secondary foamability was excellent and the fusion rate was high. Even when the molding pressure was set to a low molding pressure such as 0.16 MPa (G), the fusion was excellent up to the center of the foamed particle molded body.
As shown in FIG. 7, the polylactic acid foamed particles of the present invention obtained in Example 1 were obtained by treating the foaming agent under the condition of 50% RH to obtain expandable resin particles having a high water content. The surface layer of the polylactic acid foamed particles obtained by foaming the resin particles had a large thickness, and the ratio of the average surface layer thickness to the average cell membrane thickness showed a large value.
In Example 2, no fusion improver was used, but even a foamed particle molded body having a large thickness was excellent in secondary foamability and a high fusion rate. Further, even when the molding pressure was as low as 0.16 MPa (G), the center of the foamed particle molded body was fused.
On the other hand, in Comparative Example 1 and Comparative Example 2, the foamed particle molded body was not sufficiently fused even at a high heating steam pressure, and particularly the fusion at the center of the foamed particle molded body was extremely low. Even if the steam pressure was increased, it was not possible to obtain a foamed particle molded body having a thickness of 50 mm showing good fusion properties.
As shown in FIG. 9, the polylactic acid foamed particles obtained in Comparative Example 1 did not dissipate the foaming agent, so the photo of the polylactic acid foamed particles surface layer part is the photograph of the surface layer part of Example 1 However, the thickness of the surface layer was observed to be smaller than that of Example 1, and the ratio of the average surface layer thickness to the average bubble film thickness showed a small value. Moreover, the value of the calorific value of the surface layer portion of the expanded particles was small, and the crystallization of the expanded particle surface layer portion was progressing.
In Examples 3, 4, and 5, the same effect as the foaming agent dissipation step by standing can be confirmed by the foaming agent dissipation step other than standing, and even if the foamed particle molded body has a large thickness, An excellent secondary foaming property and a high fusion rate were obtained.
Comparative Example 3 is an example in which the dissipation step was performed under low humidity conditions, and the obtained foamed particle molded article had poorer fusibility and secondary foamability than Examples 3 and 4. .

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

It is an example of the DSC curve which shows the endothermic amount of the base resin and the endothermic amount (Rendo) of the foamed particles measured by heat-treating the test piece with a heat flux differential scanning calorimeter. It is an example of the DSC curve which shows the endothermic amount of the base resin and the endothermic amount (Rendo) of the foamed particles measured by heat-treating the test piece with a 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 without heat-processing a test piece with a 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 without heat-processing a test piece with a 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 without heat-processing a test piece with a 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 of the present invention obtained in Example 1 into approximately two parts. 2 is a scanning electron micrograph of a part of the surface layer portion in a cross-section obtained by dividing the polylactic acid foamed particles of the present invention 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.

Claims (2)

Apparent density is a polylactic acid-based resin foamed particles is ^{0.02g / cm 3 ~0.65g / cm 3} , the heat flux differential listed the polylactic acid-based resin foamed particles to JIS K7122 (1987 year) Based on the scanning calorimetry, it is heated and melted to a temperature 30 ° C. higher than the end of the melting peak, kept at that temperature for 10 minutes, and then cooled to 110 ° C. at a cooling rate of 2 ° C./min. After maintaining for 120 minutes, after heat treatment to cool to 40 ° C. at a cooling rate of 2 ° C./min, it is obtained again by heating to a temperature 30 ° C. higher than the end of the melting peak at a heating rate of 2 ° C./min. The endothermic amount (Rendo) in the DSC curve is 10 J / g or more,
Based on the heat flux differential scanning calorimetry, the polylactic acid in the DSC curve obtained when heated 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 Endothermic amount (Bendo: J / g) and calorific value (Bexo: J / g), and calorific value (Bs: J / g) of the surface layer portion of the polylactic acid based resin foamed particles The relationship with the calorific value (Bc: J / g) satisfies both the following formulas (1) and (2),
Polylactic acid resin foam characterized in that the ratio (Ts / Tm) of average surface layer thickness (Ts) and average cell membrane thickness (Tm) of the polylactic acid resin foamed particles is 5.0 to 40.0. particle.
(Bexo) / (Bendo)> 0.3 (1)
(Bs)> (Bc) (2)   A polylactic acid resin foamed particle molded body obtained by fusing the polylactic acid resin foamed particles according to claim 1 to each other by in-mold molding.