WO2011145391A1 - ポリ乳酸系樹脂発泡粒子および該発泡粒子成形体 - Google Patents
ポリ乳酸系樹脂発泡粒子および該発泡粒子成形体 Download PDFInfo
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- WO2011145391A1 WO2011145391A1 PCT/JP2011/057104 JP2011057104W WO2011145391A1 WO 2011145391 A1 WO2011145391 A1 WO 2011145391A1 JP 2011057104 W JP2011057104 W JP 2011057104W WO 2011145391 A1 WO2011145391 A1 WO 2011145391A1
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
- C08J9/12—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a physical blowing agent
- C08J9/122—Hydrogen, oxygen, CO2, nitrogen or noble gases
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
- C08G63/06—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from hydroxycarboxylic acids
- C08G63/08—Lactones or lactides
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/16—Making expandable particles
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/16—Making expandable particles
- C08J9/18—Making expandable particles by impregnating polymer particles with the blowing agent
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/22—After-treatment of expandable particles; Forming foamed products
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/22—After-treatment of expandable particles; Forming foamed products
- C08J9/228—Forming foamed products
- C08J9/232—Forming foamed products by sintering expandable particles
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L67/00—Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers
- C08L67/04—Polyesters derived from hydroxycarboxylic acids, e.g. lactones
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2205/00—Foams characterised by their properties
- C08J2205/04—Foams characterised by their properties characterised by the foam pores
- C08J2205/052—Closed cells, i.e. more than 50% of the pores are closed
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
- C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
- Y10T428/2989—Microcapsule with solid core [includes liposome]
Definitions
- the present invention relates to a polylactic acid-based resin expanded particle suitable for in-mold molding and an in-mold molded body of the expanded particle.
- the polylactic acid-based resin is made from a plant such as corn as a starting material, and is a low environmental load thermoplastic resin from the viewpoint of carbon neutral.
- Such polylactic acid-based resins are expected to be used as environmentally friendly plant-derived foaming general-purpose resins, and research on foams using polylactic acid-based resins as raw materials has been conducted.
- the polylactic acid-based resin foamed particle molded body is molded into a desired shape in the mold without being restricted by the same shape as the conventional polystyrene resin foamed particle molded body and polyolefin resin foamed particle molded body.
- the invention described in Patent Documents 1 to 7 has been made promising as having the possibility of being able to easily design physical properties according to purposes such as lightness, shock-absorbing properties, and heat insulating properties. .
- Patent Document 1 discloses an expandable resin particle of an aliphatic polyester such as polylactic acid impregnated with a volatile foaming agent such as n-pentane in a temperature range where the crystallinity is in the range of 0 to 20%. Is disclosed.
- foamable resin particles are filled in a mold and the resin particles are foamed by hot air, and at the same time, the particles are fused to each other. Therefore, the density variation between the parts of the 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.
- Patent Document 2 contains 50 mol% or more of lactic acid component units, the difference between the endothermic amount and the calorific value in heat flux differential scanning calorimetry is 0 J / g or more and less than 30 J / g, and the endothermic amount is 15 J / g.
- Expanded particles made of a polylactic acid-based resin in a state where the crystallization has not sufficiently progressed are disclosed.
- the polylactic acid-based resin expanded particles described in Patent Document 2 have been recognized to be improved in terms of the mutual fusing property and secondary expandability of the expanded particles at the time of in-mold molding.
- the fusion between the foamed particles may be insufficient.
- the fusion between the foamed particles at the center of the molded body is not good. There was room for improvement in terms of fusibility, such as being sufficient.
- Patent Documents 3 and 4 disclose that a mold by heating at a molding temperature lower than that containing no specific heat-fusibility improver is contained in polylactic acid resin particles. Polylactic acid-based resin expanded particles that can be molded internally are disclosed. However, the foamed particles described in Patent Document 3 and Patent Document 4 are also fused with each other in the case of trying to obtain a foamed particle molded body having a complicated shape and thickness similar to the foamed particle described in Patent Document 2. It left room for improvement in terms of wearability.
- Patent Document 6 discloses expanded particles obtained by producing an extruded foam and cutting it. This can obtain a polylactic acid resin foam excellent in heat resistance and mechanical strength by in-mold molding.
- a polylactic acid resin having a relatively high crystallinity it is necessary to use a polylactic acid resin having a relatively high crystallinity. Therefore, the degree of crystallinity of the polylactic acid resin constituting the expanded particles tends to be high, so that the fusion property is high. There is a problem that a good foamed particle molded body cannot be obtained stably.
- Patent Document 7 a polylactic acid resin containing a foaming agent is extruded from an extruder through a nozzle mold, and the extrudate is cut with a rotary blade while foaming to produce polylactic acid resin foamed particles.
- a method for producing polylactic acid-based resin foam particles in which particles are scattered by cutting stress and collided with a cooling member disposed in front of a nozzle mold for cooling. According to this method, a rapid cooling operation immediately after extrusion foaming is indispensable in order to obtain expanded particles having good in-mold formability, but it is difficult to obtain expanded particles having a high expansion ratio due to the rapid cooling operation. Have.
- the present invention is not limited to the target shape of the foamed particle molded body, and is suitable for in-mold molding that can stably produce a polylactic acid-based resin foamed particle molded body having excellent fusion properties between foamed particles.
- An object of the present invention is to provide lactic acid-based resin expanded particles.
- the following polylactic acid-based resin expanded particles are provided.
- Foamed particles having a polylactic acid-based resin as a base resin and obtained under the following condition 1 in accordance with the heat flux differential scanning calorimetry described in JIS K7122 (1987)
- the endothermic amount of the entire expanded particle (Br: endo) [J / g], the endothermic amount of the surface portion of the expanded particle (Brs: endo) [J / g], and the endothermic amount of the center portion of the expanded particle (Brc: endo) [ J / g] satisfies the following formulas (1) and (2):
- Condition 1 [Measurement sample adjustment] (Sample for measuring endotherm of foam particle surface layer) A surface layer portion including the surface of the expanded particles is cut to collect the surface layer portion to obtain a
- a measurement sample having a weight of 1/6 to 1/4 of the weight of the expanded particles before the cutting process is collected from the entire surface of one expanded particle. (Sample for measuring endotherm at the center of expanded particles)
- the entire surface of the foam particles is removed by cutting, and the remainder of the foam particles that are 1/5 to 1/3 of the weight of the foam particles before the cutting treatment is collected as a measurement sample.
- the value is determined based on the DSC curve obtained at that time.
- the expanded particle comprises a core layer composed of a polylactic acid resin and an outer layer located on the surface side of the core layer and composed of a polylactic acid resin.
- the difference [(A)-(B)] between the softening point (A) [° C.] of the lactic acid resin and the softening point (B) [° C.] of the polylactic acid resin constituting the outer layer exceeds 0 ° C. and 105 ° C.
- [6] A molded article of polylactic acid resin expanded particles having a bulk density of 15 to 300 g / L, wherein the polylactic acid resin expanded particles according to any one of [1] to [5] are integrally fused.
- the entire expanded particles have a specific endothermic amount (Br: endo) [J / g], and the endothermic amount (Brs: endo) [J / g] of the surface layer of the expanded particles.
- the endothermic amount (Brc: endo) [J / g] at the center of the expanded particle satisfy a specific relationship, so that the crystallization management of the base resin of the expanded particle is easy.
- a polylactic acid-based resin expanded particle molded body having excellent fusion property can be obtained under in-mold molding conditions over a wide temperature range.
- the polylactic acid-based resin foamed particles of the present invention it is possible to obtain a foamed particle molded body having a large thickness or a foamed particle molded body having a complicated shape. Furthermore, in the polylactic acid-based resin expanded particles of the present invention, the endothermic amount (Bfc: endo) [J / g] and the calorific value (Bfc: exo) [J / g] at the center of the expanded particle have a specific relationship. By satisfying, it becomes a foamed particle with good secondary foaming property and shrinkage resistance especially during molding in the mold, temperature adjustment at the time of molding in the mold is easy, and shrinkage rate of the obtained foamed particle molded body becomes small. .
- the polylactic acid-based resin expanded particles of the present invention comprises a core layer composed of a polylactic acid-based resin and an outer layer composed of a polylactic acid-based resin located on the surface side of the core layer, Difference [(A)-(B)] between the softening point (A) [° C.] of the polylactic acid resin constituting the core layer and the softening point (B) [° C.] of the polylactic acid resin constituting the outer layer
- the temperature exceeds 0 ° C. and is equal to or lower than 105 ° C.
- the endothermic amount (Br: endo, Brs: endo, Brc: endo) and the like are appropriately adjusted.
- the polylactic acid-based resin foamed particle molded body of the present invention has a good appearance and excellent fusion property between the foamed particles, the physical properties of the base resin and the effect of improving physical properties due to sufficient foaming are sufficient. It is an excellent one that can be expressed.
- the polylactic acid-based resin expanded particle molded body of the present invention which has been sufficiently increased in crystallinity by heat treatment (heat set), is further excellent in mechanical properties when used at room temperature in combination with the above-described physical property improving effect. It becomes.
- FIG. 1 is an example of a DSC curve showing the endothermic amount (Br: endo) of a measurement sample obtained by a heat flux differential scanning calorimeter.
- FIG. 2 is an example of a DSC curve showing the endothermic amount (Br: endo) of a measurement sample obtained by a heat flux differential scanning calorimeter.
- FIG. 3 is an example of a DSC curve showing a calorific value (Bfc: exo) and an endothermic amount (Bfc: endo) of a measurement sample obtained by a heat flux differential scanning calorimeter.
- FIG. 1 is an example of a DSC curve showing the endothermic amount (Br: endo) of a measurement sample obtained by a heat flux differential scanning calorimeter.
- FIG. 2 is an example of a DSC curve showing the endothermic amount (Br: endo) of a measurement sample obtained by a heat flux differential scanning calorimeter.
- FIG. 3 is an example of a DSC curve showing
- FIG. 4 is an example of a DSC curve showing a calorific value (Bfc: exo) and an endothermic amount (Bfc: endo) of a measurement sample obtained by a heat flux differential scanning calorimeter.
- FIG. 5 is an example of a DSC curve showing a calorific value (Bfc: exo) and an endothermic amount (Bfc: endo) of a measurement sample obtained by a heat flux differential scanning calorimeter.
- FIG. 6 is a drawing showing the relationship between the foamed particle surface layer part and the foamed particle center part in the foamed particles having a core layer and an outer layer.
- the base resin constituting the polylactic acid-based resin expanded particles of the present invention (hereinafter also simply referred to as “expanded particles”) is a polylactic acid-based resin.
- the polylactic acid resin is made of polylactic acid or a mixture of polylactic acid and another resin.
- this polylactic acid is a polymer which contains 50 mol% or more of component units derived from lactic acid.
- polylactic acid examples include (a) a polymer of lactic acid, (b) a copolymer of lactic acid and another aliphatic hydroxycarboxylic acid, and (c) a lactic acid, an aliphatic polyhydric alcohol, and an aliphatic polycarboxylic acid.
- the polylactic acid also includes what are called stereocomplex polylactic acid and stereoblock polylactic acid. Specific examples of 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.
- aliphatic hydroxycarboxylic acids in (b) above include glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, hydroxyheptanoic acid, and the like.
- examples of the aliphatic polyhydric alcohol in the above (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.
- the aliphatic polycarboxylic acids in (c) and (d) are succinic acid, adipic acid, suberic acid, sebacic acid, dodecanedicarboxylic acid, succinic anhydride, adipic anhydride, trimesic acid, propanetricarboxylic acid. , Pyromellitic acid, pyromellitic anhydride and the like.
- Specific examples of the method for producing polylactic acid used in the present invention 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, disclosed in US Pat. No. 5,310,865). Production method), ring-opening polymerization method for polymerizing cyclic dimer (lactide) of lactic acid (for example, production method disclosed in US Pat. No.
- 2,758,987 cyclic dimer of lactic acid and aliphatic hydroxycarboxylic acid
- a ring-opening polymerization method in which lactide or glycolide and ⁇ -caprolactone are polymerized in the presence of a catalyst for example, a production method disclosed in US Pat. No. 4,057,537), lactic acid, aliphatic dihydric alcohol, and aliphatic dihydric acid.
- a method of directly dehydrating polycondensation of a mixture of basic acids for example, the production method disclosed in US Pat. No.
- lactic acid and aliphatic dihydric acid A method of condensing an alcohol, an aliphatic dibasic acid and a polymer in the presence of an organic solvent (for example, a production method disclosed in European Patent Publication No. 071880 A2), dehydration polycondensation of a lactic acid polymer in the presence of a catalyst
- an organic solvent for example, a production method disclosed in European Patent Publication No. 071880 A2
- dehydration polycondensation of a lactic acid polymer in the presence of a catalyst there can be mentioned, for example, a method of performing solid phase polymerization in at least a part of the steps, but the production method is not particularly limited.
- 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 by a branching agent typified by a polyhydric aliphatic alcohol such as pentaerythlit.
- the polylactic acid used in the present invention is preferably blocked at the molecular chain end.
- the hydrolysis in the production process of the polylactic acid-based resin expanded particles can be more reliably suppressed, and the polylactic acid-based resin expanded particles that can withstand in-mold molding can be easily obtained.
- the durability of the polylactic acid-based resin expanded particle molded body (hereinafter also simply referred to as expanded particle molded body) obtained by in-mold molding is improved.
- a carbodiimide compound As said terminal blocker, a carbodiimide compound, an oxazoline compound, an isocyanate compound, an epoxy compound etc. can be used, for example.
- carbodiimide compounds are preferred.
- aromatic monocarbodiimide such as bis (dipropylphenyl) carbodiimide (for example, Stabaxol 1-LF manufactured by Rhein Chemie), aromatic polycarbodiimide (for example, Stabaxol P manufactured by Rhein Chemie, Stabaxol P400 manufactured by Rhein Chemie)
- aliphatic polycarbodiimides such as poly (4-4′-dicyclohexylmethanecarbodiimide) (for example, Carbodilite LA-1 manufactured by Nisshinbo Chemical Co., Ltd.).
- end-capping agents may be used alone or in combination of two or more.
- the content of the end-capping agent is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 3 parts by weight per 100
- the polylactic acid used in the present invention is preferably a modified polylactic acid resin modified with one or more modifiers selected from a carbodiimide compound, an epoxy compound, and an isocyanate compound, More preferred is a modified polylactic acid modified with a carbodiimide compound.
- the base resin constituting the expanded particles of the present invention can be mixed with other resins as described above within a range not impairing the objects and effects of the present invention.
- the mixed resin of polylactic acid and other resins is used as the base resin.
- the constituent requirements of the endothermic amount and calorific value in the present invention not the base resin made of a mixed resin, but only polylactic acid among the polylactic acid and other resins constituting the base resin is the above-mentioned in the present invention. It is only necessary to satisfy the constituent requirements for the amount of heat absorbed and the amount of heat generated.
- the mixed resin of polylactic acid and other resin preferably contains 50% by weight or more of polylactic acid, more preferably 70% by weight or more, and still more preferably 90% by weight or more.
- polyester resins examples include polyethylene resins, polypropylene resins, polystyrene resins, polyester resins, and the like. Among them, biodegradable aliphatic compounds containing at least 35 mol% of aliphatic ester component units Polyester resins are preferred.
- aliphatic polyester resin examples 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.
- lactones such as polycaprolactone
- polybutylene succinate polybutylene adipate
- polybutylene succinate adipate polybutylene succinate adipate
- Polycondensates of aliphatic polyhydric alcohols such as poly (butylene adipate / terephthalate) and aliphatic polycarboxylic acids.
- the expanded particles are obtained by adding, to the base resin, for example, expanded particles and expanded particle molded bodies that are colored by a conventionally known coloring method such as adding a coloring pigment or dye such as black, gray, brown, blue, or green.
- a coloring pigment or dye such as black, gray, brown, blue, or green.
- a colored pigment or dye is added to the polylactic acid resin particles, the dispersion medium, and the foaming agent in the pressure-resistant sealed container.
- the colorant include organic and inorganic pigments and dyes. Known pigments and dyes can be used.
- flame retardants include flame retardants, antistatic agents, weathering agents, conductivity-imparting agents and the like in addition to the colorants.
- the additives when additives such as color pigments and dyes are directly added to the base resin, the additives can be kneaded into the base resin as they are, but usually the master of the additive in consideration of dispersibility and the like. It is preferable to prepare a batch and knead it with the base resin.
- the above-mentioned additive varies depending on the type of additive, it is usually preferably 0.001 to 20 parts by weight, more preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the base resin.
- the polylactic acid-based resin expanded particles of the present invention have a polylactic acid-based resin as a base resin, the expanded particles have a specific endothermic amount (Br: endo), and the endothermic amount of the surface layer of the expanded particles ( It will be described in detail that Brs: endo) and the endothermic amount (Brc: endo) at the center of the expanded particle have a specific relationship.
- the endothermic amount (Br: endo) [J / g] of the entire expanded particles after heat treatment, obtained under the following condition 1 by the heat flux differential scanning calorimetry, is as follows (1 ) The expression must be satisfied. (Br: endo)> 25 (1)
- (Br: endo) is more than 25 [J / g] when the heat treatment is performed under the condition that the crystallization of the polylactic acid constituting the expanded particles is sufficiently advanced. This means that the amount of the crystal component of the expanded particles by lactic acid is large.
- (Br: endo) is preferably 30 J / g or more, and more preferably 35 J / g or more.
- the upper limit of (Br: endo) is approximately 70 J / g, and further 60 J / g.
- the fact that the relationship of the formula (2) is satisfied means that when the expanded particles are heat-treated under the condition that the crystallization of the polylactic acid constituting the expanded particle surface layer portion and the expanded particle central portion is sufficiently advanced, This means that the amount of the polylactic acid crystal component constituting the surface layer portion is less than the amount of the polylactic acid crystal component constituting the center portion of the expanded particle.
- the foamed particles satisfying the relationship of the formula (2) are those in which the crystallinity of the polylactic acid at the center of the foamed particles is increased by sufficient heat treatment.
- the degree it means that the foamed particles as a whole satisfy the above formula (1). That is, the expanded particles satisfying the relationship of the formula (2) can improve the heat resistance of the entire expanded particles by heat treatment.
- the polylactic acid on the surface layer of the expanded particle has a lower crystallinity than the center of the expanded particle even after sufficient heat treatment. Therefore, the expanded particle satisfying the relationship of formula (2) has a low softening point on the surface of the expanded particle. It is. Therefore, the foamed particles are foamed particles that can exhibit excellent fusing properties in the thermal fusing properties between the foamed particles at the time of in-mold molding regardless of the heat history before and after the production of the foamed particles. From this point of view, in order to further improve the fusibility of the surface of the expanded particle, the endothermic amount (Brs: endo) of the expanded particle surface layer is preferably 35 J / g or less (including 0).
- the endothermic amount (Brc: endo) of the center part of the expanded particle is preferably 30 J / g or more, and more preferably 35 J / g or more.
- the upper limit of (Brc: endo) is approximately 70 J / g, and further 60 J / g.
- (Brc: endo) and (Brs: endo) preferably have a calorific value difference of 3 J / g or more, and further a calorific value difference of 4 J / g or more.
- the polylactic acid constituting the foamed particle surface layer within the range satisfying the formula (2) may be amorphous polylactic acid or a mixed resin of amorphous polylactic acid and crystalline polylactic acid. Good.
- the values of (Brc: endo) and (Brs: endo) are greatly different from the reason of the above-mentioned fusing property, but actually, they are not so different.
- the reason for this is, for example, the case where the polylactic acid-based resin particles for obtaining foamed particles are adjusted by a core layer having a specific softening point difference described later and an outer layer positioned on the surface side with respect to the core layer. It can be considered that it is difficult to collect (Brs: endo) by measuring a portion consisting only of the outer layer as a surface layer portion of the expanded particle from the relationship of cutting out the expanded sample from the expanded particle.
- the endothermic amount (Br: endo) [J / g] of the whole expanded particle, the endothermic amount (Brs: endo) [J / g] of the surface layer of the expanded particle, and the endothermic amount (Brc) of the center of the expanded particle : Endo) [J / g] is a measured value obtained under the following condition 1 in accordance with the heat flux differential scanning calorimetry described in JIS K7122 (1987).
- the foamed particles are basically used as a measurement sample without being cut.
- the surface layer portion including the surface of the expanded particles is cut to collect the surface layer portion to obtain a measurement sample.
- a measurement sample having a weight of 1/6 to 1/4 of the weight of the expanded particles before the cutting process is collected from the entire surface of one expanded particle.
- the surface layer portion may be cut using a cutter knife, a microtome, etc., and the surface layer portion may be collected and used for measurement.
- the entire surface layer portion of one foamed particle must be excised and the weight of the surface layer portion excised from one foamed particle is the weight of the foamed particle before cutting. It should be within the range of 1/6 to 1/4. (Sample for measuring endotherm at the center of expanded particles)
- the entire surface of the foam particles is removed by cutting, and the remainder of the foam particles that are 1/5 to 1/3 of the weight of the foam particles before the cutting treatment is collected as a measurement sample.
- a cutting process may be performed with a cutter knife or the like for the purpose of cutting out an internal foam layer that does not include the surface of the foam particles, and the center of the foam particles may be used for measurement.
- the entire surface of one foamed particle must be excised, and 5 minutes of the weight of the foamed particle before cutting so as to have the same center as possible.
- the center part of the expanded particle is cut out in the range of 1 to 1/3. At this time, the cut out measurement sample is as similar as possible to the shape of the expanded particles before the cutting process.
- the (Br: endo), (Brs: endo), and (Brc: endo) are measured and defined for a sample collected as follows.
- the first test sample is obtained by cutting and collecting the surface portion of one randomly selected expanded particle. This cutting collection is performed so that the entire outer peripheral surface of the foam particles is removed and the weight of the first test sample is 1/6 to 1/4 of the weight of the foam particles before cutting;
- C The surface portion of other randomly selected foamed particles is cut away to leave the second test sample.
- This excision is performed so that the entire outer peripheral surface of the foamed particles is cut, and the weight of the second test sample is 1/5 to 1/3 of the weight of the foamed particles before the excision; (D) If the weight of the second test sample obtained is less than 1 mg, then one or more further expanded particles selected at random until a total of 1-4 mg of the second test sample is obtained. Repeat procedure (c); (E) randomly selecting one more expanded particle to obtain a third test sample; (F) Each of the first test sample 1 to 4 mg, the second test sample 1 to 4 mg, and the third test sample 1 to 4 mg is heated and melted to a temperature 30 ° C. higher than the melting peak end temperature, and kept at that temperature for 10 minutes. Then, after cooling to 110 ° C.
- the heat flux differential scanning calorimetry is performed in accordance with JIS K7122 (1987) to obtain a DSC curve by heating and melting at a temperature 30 ° C.
- (Brs: endo) is The heat value of the endothermic peak in the DSC curve of the first test sample
- (Brc: endo) is the heat amount of the endothermic peak in the DSC curve of the second test sample
- (Br: endo) is It is a calorie
- the endothermic amount (Br: endo) is defined as point a where the endothermic peak is separated from the low-temperature side baseline of the second endothermic peak of the DSC curve, and the endothermic peak is the base on the high-temperature side.
- a point returning to the line is a point b, and is a value obtained from a straight line connecting the point a and the point b and the area of the portion indicating the endothermic amount surrounded by the DSC curve.
- the apparatus should be adjusted so that the baseline is as straight as possible. If the baseline is inevitably curved as shown in FIG. 2, the curved baseline on the low temperature side of the endothermic peak should be Perform drawing to maintain the curved state and extend to the high temperature side.
- Point a is the point where the endothermic peak is away from the curved low temperature side baseline, and the curved base line on the high temperature side of the endothermic peak is the curved state of the curve.
- a point where the endothermic peak returns to the curved high temperature side base line is plotted as point b.
- the endothermic amount (Brs: endo) and the endothermic amount (Brc: endo) are determined from the second DSC curve in the same manner as (Br: endo), and a straight line connecting the point a and the point b, and the DSC It is calculated
- the measurement condition of the DSC curve of the measurement sample is 120 ° C. holding for 120 minutes, 2 ° C./min.
- the reason for adopting the cooling rate and the heating rate of 2 ° C./min is that the endothermic amount (Br: endo), (Brs: endo), (Br): This is because the purpose is to obtain (Brc: endo).
- the foamed polylactic acid resin particles of the present invention have a specific endothermic amount (Br: endo), so that the foamed particles can be molded in the mold after the heat treatment, or the foamed particles can be molded after the foamed particles are molded in the mold.
- a foamed particle molded body excellent in mechanical strength and compressive strength at high temperature can be obtained.
- the expanded particle has an endothermic amount (Brs: endo) of the surface portion of the expanded particle even though the entire expanded particle satisfies a specific endothermic amount (Br: endo) condition.
- the softening temperature of the surface of the foamed particles can be kept low regardless of the thermal history of the foamed particles, and the meltability during in-mold molding It is an excellent expanded particle.
- the endothermic amount (Bfc: endo) [J / g] and the calorific value of the center of the expanded particles before heat treatment, which are determined by the heat flux differential scanning calorimetry method under the following condition 2, (Bfc: exo) [J / g] preferably satisfies the following formula (3). 40> [(Bfc: endo)-(Bfc: exo)]> 10 ... (3)
- a DSC curve obtained when heating and melting from 23 ° C. to 30 ° C. higher than the end of the melting peak at a heating rate of 2 ° C./min (hereinafter also referred to as the first DSC curve).
- the (Bfc: endo) and (Bfc: exo) are measured and defined as follows.
- (H) The surface portion of one randomly selected expanded particle is cut away to leave the fourth test sample. This excision is performed so that the entire outer peripheral surface of the foamed particles is cut, and the weight of the fourth test sample is 1/5 to 1/3 of the weight of the foamed particles before the excision;
- (I) If the weight of the obtained fourth test sample is less than 1 mg, one or more additional expanded particles randomly selected until a total of 1-4 mg of the fourth test sample is obtained. Repeat procedure (h);
- (J) With respect to 1 to 4 mg of the fourth test sample, heat flux differential scanning calorimetry in which the fourth test sample is heated from 23 ° C.
- the difference [(Bfc: endo) ⁇ (Bfc: exo)] in the above equation (3) is the difference between the crystallized portion already present in the center of the foamed particle when the heat flux differential scanning calorimetry is performed, In the temperature rising process, the endothermic amount (Bfc: endo), which is the energy absorbed when the center part of the expanded particle crystallizes, and the center part of the expanded particle in the temperature rising process of differential scanning calorimetry of heat flux Represents the difference from the calorific value (Bfc: exo), which is the energy released by crystallization, and the smaller the difference, the less the crystallization of the foamed particle center before the heat flux differential scanning calorimetry.
- the difference [(Bfc: endo) ⁇ (Bfc: exo)] has a wide secondary foaming property when foamed particles are molded in-mold and a wide molding temperature range in which a molded product with foamed particles is good when molded in-mold. From the viewpoint, it is preferable to be within the above range. Further, from the viewpoint of secondary foaming properties, it is preferably 35 J / g or less, particularly 30 J / g or less.
- the difference [(Bfc: endo) ⁇ (Bfc: exo)] is further 15 J / g or more, particularly 20 J / g, from the viewpoint of easy temperature adjustment at the time of in-mold molding and prevention of shrinkage of the in-mold foam molding. The above is preferable.
- the endothermic amount (Bfc: endo) is preferably 30 to 70 J / g.
- the endothermic amount (Bfc: endo) is too small, the mechanical strength of the foamed particle molded body, particularly the mechanical strength at high temperatures, may be insufficient.
- (Bfc: endo) is more preferably 35 J / g or more.
- the upper limit of (Bfc: endo) is approximately 70 J / g, and further 60 J / g.
- the calorific value (Bfc: exo) is 5 to 30 J / g, more preferably 10 to 10 in relation to the difference [(Bfc: endo) ⁇ (Bfc: exo)] and the endothermic amount (Bfc: endo). 25 J / g is preferable from the viewpoint of excellent secondary foamability and moldability of the foamed particles.
- the calorific value (Bfc: exo) and the endothermic amount (Bfc: endo) of the expanded particles are the heat flux differential scanning calorimetry described in JIS K7122 (1987) as described above (Condition 2).
- the calorific value (Bfc: exo) and the endothermic amount (Bfc: endo) are measured according to the following criteria.
- the exothermic amount (Bfc: exo) of the expanded particles is defined as a point c where the exothermic peak departs from the low-temperature base line of the first DSC curve, and a point d where the exothermic peak returns to the high-temperature base line.
- the endothermic amount (Bfc: endo) of the expanded particles is defined as a point e where the endothermic peak departs from the low temperature side baseline of the first DSC curve, and the endothermic peak returns to the high temperature side baseline. Is a point f, and a value obtained from the area connecting the straight line connecting the point e and the point f and the endothermic amount surrounded by the DSC curve.
- the apparatus is adjusted so that the baseline in the first DSC curve is as straight as possible.
- 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
- 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.
- the calorific value (Bfc: exo) of the foamed particles is obtained from the area of the portion showing the calorific value surrounded by the straight line connecting the points c and d defined as described above and the DSC curve.
- the endothermic amount (Bfc: endo) of the expanded particles is obtained from the area of the portion indicating the endothermic amount surrounded by the straight line connecting the point e and the point f determined as described above and the DSC curve.
- the intersection of the straight line connecting the points c and f determined as described above and the DSC curve 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.
- the exothermic amount (Bfc: exo) of the expanded particles is the area of the first exothermic peak in FIG. It is obtained from the sum of A and 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.
- the area A of the portion showing the heat generation amount surrounded by the straight line connecting the point d and the DSC curve 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.
- An intersection point between the line connecting the point f and the DSC curve is defined as a point e, and an area B indicating the amount of heat generated between the line connecting the point g and the point e and the DSC curve is shown.
- the endothermic amount (Bfc: endo) of the expanded particles is a value obtained from the area of the portion indicating the endothermic amount surrounded by the straight line connecting the points e and f and the DSC curve.
- the reason why the heating rate of 2 ° C./min is adopted as the measurement condition of the DSC curve is that the exothermic peak and the endothermic peak are as much as possible.
- a heating rate of 2 ° C./min is preferred when separating and obtaining an accurate endothermic amount (Bfc: endo) and [(Bfc: endo) ⁇ (Bfc: exo)] by heat flux differential scanning calorimetry. This is based on the knowledge of the inventors.
- the polylactic acid-based resin expanded particles satisfying the formulas (1) and (2), and further the formula (3) are composed of a core layer composed of a polylactic acid-based resin and another polylactic acid-based resin. It can be obtained by producing expanded particles comprising an outer layer covering the core layer. However, in the expanded particles of the present invention, the outer layer does not need to cover the entire core layer, and as long as the expanded particles satisfy the expressions (1) and (2), the resin constituting the core layer is expanded. There may be a portion exposed on the particle surface.
- FIG. 6 shows an example of the relationship between the foamed particle surface layer portion 3 and the foamed particle central portion 4 in the foamed particles having the core layer 1 and the outer layer 2.
- 1 is a core layer (inner part surrounded by an inner solid line)
- 2 is an outer layer (part surrounded by an outer solid line and an inner solid line)
- 3 is a foamed particle surface layer part (outer solid line).
- 4 indicates a central part of the foamed particle (an inner part surrounded by a broken line on the inner side).
- the softening point (B) [° C.] of the polylactic acid resin constituting the outer layer is lower than the softening point (A) [° C.] of the polylactic acid resin constituting the core layer, and the softening point (A) And the softening point (B) [(A) ⁇ (B)] is preferably more than 0 ° C. and not more than 105 ° C., more preferably 15 to 105 ° C., and still more preferably 20 ⁇ 105 ° C. Expanded particles having the difference within the above range are obtained by a method described later, such as coextrusion of a polylactic acid resin showing a softening point (B) and a softening point (A) constituting the outer layer and the core layer.
- the softening point (B) of the polylactic acid resin constituting the outer layer is the polylactic acid resin constituting the core layer from the viewpoint of the handleability of the foamed particles and the mechanical strength at high temperatures of the obtained foamed particle molded body.
- the softening point (A) is within the above range, and is preferably 50 ° C. or higher, more preferably 55 ° C. or higher, and particularly preferably 65 ° C. or higher.
- the softening point in this specification means the Vicat softening temperature measured by the A50 method based on JIS K7206 (1999).
- a measurement test piece after the polylactic acid resin is sufficiently dried using a vacuum oven, it is pressurized under the conditions of 200 ° C. and 20 MPa, and an air venting operation is performed as necessary so that bubbles are not mixed.
- a test piece having a length of 20 mm ⁇ width of 20 mm ⁇ thickness of 4 mm is prepared, and the test piece is annealed in an oven at 80 ° C. for 24 hours and used for measurement.
- “HDT / VSPT test apparatus MODEL TM-4123” manufactured by Ueshima Seisakusho Co., Ltd. can be used.
- the weight ratio of the resin forming the core layer and the resin forming the outer layer is 99.9: 0.1 to 80:20. It is preferably 99.7: 0.3 to 90:10, more preferably 99.5: 0.5 to 92: 8. If the weight ratio of the resin forming the outer layer of the expanded particles is too small, the thickness of the outer layer portion of the expanded particles is too thin and the effect of improving the fusing property at the time of molding of the expanded particles is reduced. It becomes easy for the melt
- the weight ratio of the resin forming the outer layer is too large, the resin forming the outer layer foams more than necessary, and there is a possibility that the fusion property at the time of in-mold molding of the foamed particles is lowered. Furthermore, there is a possibility that the mechanical properties of the foamed particle molded body are likely to be lowered.
- the resin forming the outer layer in the present invention is foamed. Accordingly, since the weight ratio between the resin forming the core layer of the foamed particles and the resin forming the outer layer is within the above range, the fusion strength between the foamed particles is increased, so that the obtained foam is obtained.
- the particle compact has excellent mechanical properties, and the mechanical properties are further improved by increasing the proportion of the core layer that contributes to improving the physical properties of the expanded particles.
- the adjustment of the weight ratio of the resin forming the core layer in the foamed particles and the resin forming the outer layer is performed by forming a core layer of polylactic acid-based resin particles (hereinafter also referred to as resin particles). This is done by adjusting the weight ratio of the resin forming the outer layer and the resin forming the outer layer.
- the endblocker for the polylactic acid resin constituting the expanded particles is preferably added to at least the core layer, and more preferably added to both the core layer and the outer layer. Since the polylactic acid resin constituting at least the core layer, preferably both the core layer and the outer layer, is end-capped, hydrolysis during the production of the expanded particles of the resin can be suppressed, and the expanded particles can be stably produced. become able to. Furthermore, hydrolysis during foamed particle molded body production can be suppressed, leading to stable production of the foamed particle molded body, and being able to withstand use under high temperature and humidity even when used as a product, etc. Durability improvement can be expected.
- the thickness of the outer layer of the expanded particles it is preferable that the thickness is thinner because bubbles are less likely to be generated in the outer layer and the mechanical properties of the expanded expanded product are improved.
- the outer layer is too thin, there is a concern about the effect of improving the fusibility between the expanded particles, but if the thickness is within the following range, the effect of improving the fusibility is sufficiently exhibited. That is, the average thickness of the outer layer of the expanded particles is preferably 0.1 to 20 ⁇ m, more preferably 0.2 to 10 ⁇ m, and particularly preferably 0.3 to 5 ⁇ m.
- the average thickness of the outer layer of the resin particles may be adjusted by adjusting the weight ratio of the outer layer and the core layer at the resin particle stage.
- the average thickness of the outer layer of the resin particles varies depending on the weight of the resin particles, the expansion ratio, etc., but is preferably 2 to 100 ⁇ m, more preferably 3 to 70 ⁇ m, and particularly preferably 5 to 50 ⁇ m.
- the average thickness of the outer layer of the expanded particles is measured as follows.
- the expanded particles are roughly divided into two equal parts, and the thickness of the outer layer at four locations on the upper, lower, left and right sides of the cross section is determined from the photograph of the enlarged cross section, and the average is defined as the thickness of the outer layer of one expanded particle.
- This operation is performed for 10 expanded particles, and the value obtained by arithmetically averaging the thicknesses of the outer layers of the expanded particles is taken as the average thickness of the outer layers of the expanded particles.
- the average thickness of the outer layer of resin particles is also measured by the same method.
- the thickness of the four outer layers may not be measured by any means, but in that case, the four outer layer thicknesses that can be measured randomly are obtained.
- the average is the thickness of the outer layer of one foamed particle or resin particle.
- the apparent density of the foamed particles of the present invention is preferably 25 to 400 g / L, more preferably 40 to 200 g / L, from the viewpoint of excellent lightness, in-mold moldability, and mechanical properties. If the apparent density is too small, the shrinkage rate after in-mold molding may increase, and if the apparent density is too large, the apparent density will tend to vary widely, and the foamed particles at the time of heat molding in the mold This leads to variations in expansibility, fusibility, and apparent density, and there is a risk of deterioration in physical properties of the obtained foamed particle molded body.
- the apparent density of the expanded particles in this specification is measured as follows.
- the expanded particles are allowed to stand for 10 days in a temperature-controlled room under conditions of atmospheric pressure, relative humidity 50%, and 23 ° C.
- the weight W1 (g) of the expanded particle group of about 500 ml left in the same constant temperature room for 10 days is measured, and the measured expanded particle group is water having a temperature of 23 ° C. using a tool such as a wire mesh. Sink into a measuring cylinder containing.
- the average cell diameter of the polylactic acid-based resin expanded particles of the present invention is preferably 30 to 500 ⁇ m, and preferably 50 to 250 ⁇ m, from the viewpoints of further improving the in-mold moldability and the appearance of the obtained expanded foam molded body. It is more preferable that
- the average cell diameter of the expanded particles is measured as follows. Based on an enlarged photograph obtained by photographing a cut surface obtained by dividing the expanded particle into approximately equal parts by a microscope, it can be obtained as follows. In the enlarged photograph of the cut surface of the expanded particle, four line segments passing through the approximate center of the bubble cut surface are drawn from one surface of the expanded particle to the other surface. However, the line segments are drawn so as to form radial straight lines extending in eight directions at equal intervals from the approximate center of the bubble cut surface to the cut particle surface. Next, the total number N of bubbles that intersect the four line segments is determined.
- a total sum L ( ⁇ m) of the lengths of the four line segments is obtained, and a value (L / N) obtained by dividing the total L by the total N is defined as an average cell diameter of one expanded particle.
- This operation is carried out for 10 expanded particles, and the value obtained by arithmetically averaging the average cell diameter of each expanded particle is taken as the average cell diameter of the expanded particles.
- the closed cell ratio of the foamed particles of the present invention is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. If the closed cell ratio is too small, the secondary foamability of the foamed particles tends to be inferior, and the mechanical properties of the resulting foamed particle molded body tend to be inferior.
- the polylactic acid-based resin constituting the base resin of the expanded particles at least the polylactic acid-based resin that constitutes the core layer has the molecular chain end blocked as described above. It is preferable for obtaining a high closed cell ratio.
- the closed cell ratio of the expanded particles is measured as follows.
- the expanded particles are allowed to stand for 10 days in a temperature-controlled room at atmospheric pressure, relative humidity of 50% and 23 ° C.
- the apparent volume Va is accurately measured by the submersion method as follows using the foamed particles after curing having a bulk volume of about 20 cm 3 as a measurement sample.
- the measurement is performed by an air-comparing hydrometer 930 manufactured by Toshiba Beckman Co., Ltd. according to the procedure C described in ASTM-D2856-70.
- the true volume Vx of the working sample is measured.
- Closed cell ratio (%) (Vx ⁇ W / ⁇ ) ⁇ 100 / (Va ⁇ W / ⁇ ) ... (4)
- Vx the sum of the true volume of the expanded particles measured by the above method, that is, the volume of the resin constituting the expanded particles and the total volume of bubbles in the closed cell portion in the expanded particles (cm 3 )
- Va The apparent volume of the expanded particles (cm 3 ) measured from the rise in the water level after the expanded particles are submerged in a graduated cylinder containing water.
- W Weight of the foam particle measurement sample (g) ⁇ : Density of resin constituting expanded particles (g / cm 3 )
- a polylactic acid-based resin expanded particle molded body By performing in-mold molding using the expanded particles of the present invention, a polylactic acid-based resin expanded particle molded body can be obtained.
- the shape is not particularly limited, and a plate shape, a column shape, a container shape, and a block shape can be obtained as a three-dimensional complicated shape or a particularly thick one.
- the foamed particle molded body is composed of the specific foamed particles, the foamed particles have excellent heat-fusibility between the foamed particles, and are rigid and compressed by heat treatment of the polylactic acid resin constituting the foamed particles.
- the foamed particle molded body is excellent in heat resistance such as strength and dimensional stability.
- the bulk density of the foamed particle molded body obtained as described above is preferably 15 to 300 g / L, more preferably 25 to 180 g / L from the viewpoint of being lightweight and excellent in mechanical properties. preferable.
- the closed cell ratio of the foamed particle molded body is preferably 60% or more, more preferably 70% or more, and further preferably 80% or more. If the closed cell ratio is too low, mechanical properties such as compression strength of the foamed particle molded body may be lowered.
- the measurement of the closed cell ratio of the foamed particle molded body was performed by cutting a sample of 25 ⁇ 25 ⁇ 30 mm from the center of the foamed particle molded body (cutting off all skin) and using it as a measurement sample. It can be obtained in the same manner as the measurement.
- the foamed particle molded article is excellent in the fusion property between the foamed particles, and the fusion rate is preferably 50% or more, more preferably 60% or more, and particularly preferably 80% or more.
- a foamed particle molded body having a high fusion rate is excellent in mechanical properties, particularly bending strength.
- the fusing rate means a material destruction rate based on the number of fractured surface foamed particles when the foamed particle molded body is ruptured. The unfused part does not break the material and peels at the interface of the foamed particles. To do.
- the manufacturing method of the polylactic acid-type resin expanded particle of this invention is demonstrated.
- the method for producing the expanded particles of the present invention include an extrusion foaming method, a gas impregnation pre-foaming method, a dispersion medium releasing foaming method, and other foaming methods based on these methods and principles.
- the extrusion foaming method includes, for example, melt-kneading a polylactic acid resin in an extruder, press-fitting a physical foaming agent into the extruder, and kneading to obtain a foamable molten resin.
- This is a method for producing expanded particles by cutting a strand-like foam obtained by extrusion.
- the resin particle production process, the foaming agent impregnation process, and the foaming process are performed as one process using one extruder.
- Japanese Patent Application Laid-Open No. 2007-100025 and International Publication WO 2008/123367 refer to Japanese Patent Application Laid-Open No. 2007-100025 and International Publication WO 2008/123367.
- the gas-impregnated pre-foaming method for example, after melt-kneading a polylactic acid-based resin with an extruder, resin particles are produced by extruding and cutting into strands, and the resin particles are filled in a pressure-resistant sealed container, By injecting a physical foaming agent into the pressure vessel, the resin particles are impregnated with the foaming agent to produce foamable resin particles.
- the foamable resin particles are put into a pre-foaming machine, and steam, hot air, or their This is a method of obtaining foamed particles by foaming expandable resin particles by heating with a heating medium such as a mixture.
- a strand cut method, an underwater cut method or the like can be appropriately selected.
- a liquid phase impregnation method or a gas phase impregnation method can be appropriately selected.
- the resin particle production process, the foaming agent impregnation process, and the foaming process are performed as separate processes. For this method, refer to JP-A Nos. 2000-136261 and 2006-282750.
- the dispersion medium releasing foaming method is, for example, producing a resin particle by melt-kneading a polylactic acid resin with an extruder and then extruding it into a strand shape and cutting it, and the resin particle is placed in an aqueous medium in a closed container.
- the foamed resin particles are produced by impregnating with a physical foaming agent by dispersing and heating to form foamable resin particles, and releasing the foamable resin particles together with an aqueous medium from a closed container at a foaming suitable temperature.
- the resin particle production step, the foaming agent impregnation step, and the foaming step can be performed as separate steps, but the foaming agent impregnation step and the foaming step are usually performed as one step.
- the production method of the polylactic acid-based resin expanded particles will be described in detail with a focus on the dispersion medium release foaming method.
- the resin particles can be produced by a strand cut method, an underwater cut method, or the like in which additives necessary for the base resin are blended, extruded, and pelletized.
- a strand cut method an underwater cut method, or the like in which additives necessary for the base resin are blended, extruded, and pelletized.
- it is required to satisfy the above formulas (1) and (2). Therefore, it is preferable to produce resin particles composed of a core layer and an outer layer.
- Resin particles comprising the core layer and the outer layer are described in, for example, Japanese Patent Publication No. 41-16125, Japanese Patent Publication No. 43-23858, Japanese Patent Publication No. 44-29522, Japanese Patent Publication No. 60-185816, and the like. Further, it can be manufactured using a co-extrusion technique.
- an apparatus in which a core layer forming extruder and an outer layer forming extruder are connected to a coextrusion die is generally used.
- a polylactic acid resin and an additive as necessary are supplied to the core layer forming extruder and melt-kneaded, and another polylactic acid resin and, if necessary, an additive are added to the outer layer forming extruder. Is supplied and melt-kneaded.
- Each melt-kneaded product is joined in the die to form a multi-layered structure consisting of a cylindrical core layer and an outer layer covering the side surface of the core layer, and from the pores of the die attached to the die outlet at the tip of the extruder.
- the strand-like extrudate having a multilayer structure is extruded, cooled by submerging the strand-like extrudate, and then cut by a pelletizer so that the weight of the resin particles becomes a predetermined weight, thereby producing resin particles having a multilayer structure.
- the resin particles can also be produced by cooling the strand-like extrudate having a multilayer structure after cutting or simultaneously with the cutting so that the weight of the resin particles becomes a predetermined weight.
- the average weight per resin particle is preferably 0.05 to 10 mg, and more preferably 0.1 to 4 mg. If the average weight is too light, the production of resin particles becomes special. On the other hand, when the average weight is too heavy, the density distribution of the obtained foamed particles may be increased, or the filling property during in-mold molding may be deteriorated.
- As the shape of the resin particles a columnar shape, a spherical shape, a prismatic shape, an elliptical spherical shape, a cylindrical shape, or the like can be adopted. Foamed particles obtained by foaming such resin particles have a shape substantially corresponding to the shape of the resin particles before foaming.
- the polylactic acid resin which is a constituent component of the base resin
- a method of removing moisture from the polylactic acid-based resin by performing vacuum suction using an extruder with a vent port can be employed. By removing water from the polylactic acid-based resin, it is possible to suppress the generation of bubbles in the resin particles and improve the stability during extrusion production.
- the foaming agent impregnation step and the foaming step in the dispersion medium releasing foaming method will be described.
- the resin particles are dispersed and heated together with the dispersion medium and the physical foaming agent in the pressure resistant container, or the resin particles are dispersed and heated together with the dispersion medium in the pressure resistant container, and then physically foamed.
- the resin particles are impregnated with a physical foaming agent by press-fitting an agent into the pressure vessel to obtain expandable resin particles.
- the expandable resin particles are expanded by releasing the expandable resin particles together with the dispersion medium under a pressure lower than that in the pressure vessel, thereby obtaining expanded particles.
- a foaming aid can be added in advance to the resin particles.
- the foaming aid include inorganic substances such as talc, calcium carbonate, borax, zinc borate, aluminum hydroxide, silica, polytetrafluoroethylene, polyethylene wax, polycarbonate, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, High molecular weight materials such as polycyclohexanedimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, silicone, methyl methacrylate copolymer, and crosslinked polystyrene can be employed.
- polytetrafluoroethylene, polyethylene wax, cross-linked polystyrene and the like are preferable in the present invention, and hydrophobic polytetrafluoroethylene powder is more preferable.
- the foaming aid When adding a foaming aid to the base resin, the foaming aid can be kneaded into the base resin as it is, but in consideration of dispersibility, etc. It is preferable to knead the base resin.
- the apparent density and cell diameter of the foamed particles of the present invention change depending on the amount of foaming aid added, the effect of adjusting them can be expected.
- polylactic acid-based resins are easily hydrolyzed, it is preferable to avoid the hydrophilic substances as much as possible and to select and add hydrophobic substances as additives to the base resin.
- a hydrophobic foaming aid as the foaming aid, the effect as a foaming aid can be obtained while suppressing deterioration due to hydrolysis of the polylactic acid-based resin. In this case, it is possible to reduce the apparent density (improve the foaming ratio) and make the bubble diameter uniform while sufficiently suppressing the hydrolysis of the polylactic acid resin.
- dispersion medium releasing foaming method for example, resin particles are dispersed in a dispersion medium such as water in a pressurizable closed container (for example, an autoclave), a dispersant is added, and a required amount of foaming agent is added. After impregnating and pressurizing and stirring under heating for a required time to impregnate the polylactic acid resin particles with the foaming agent, the container contents are released below the pressure inside the container to lower the pressure range, thereby foaming the resin particles, Expanded particles are obtained. At the time of this discharge, it is preferable to discharge the container with back pressure.
- the expanded particles obtained by the above-described method are subjected to a normal curing step under atmospheric pressure and can be pressurized again. And is subjected to a pressure treatment with a pressurized gas such as air at a pressure of, for example, 0.01 to 0.10 MPa (G) to increase the pressure in the foamed particles. Then, by using a heating medium such as hot air, steam or a mixture of air and steam, expanded particles having a lower apparent density can be obtained (this process is hereinafter referred to as two-stage foaming).
- a heating medium such as hot air, steam or a mixture of air and steam
- the production method of the foamed particles is as described above.
- a gas impregnation prefoaming method and a dispersion medium releasing foaming method are preferred, and a dispersion medium releasing foaming method is particularly preferred.
- any resin that does not dissolve the polylactic acid resin particles can be used.
- the dispersion medium other than water include ethylene glycol, glycerin, methanol, ethanol and the like. Water is preferable.
- a dispersant when dispersing the resin particles in the dispersion medium, a dispersant can be added to the dispersion medium as necessary.
- the dispersant include inorganic substances such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, titanium oxide, zinc oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, kaolin, mica, and clay, and polyvinylpyrrolidone.
- Water-soluble polymer protective colloid agents such as polyvinyl alcohol and methylcellulose.
- an anionic surfactant such as sodium dodecylbenzenesulfonate or sodium alkanesulfonate can be added to the dispersion medium.
- These dispersing agents can be used in an amount of 0.05 to 3 parts by weight per 100 parts by weight of the resin particles, and these dispersing aids can be used in an amount of 0.001 to 0.3 parts by weight per 100 parts by weight of the resin particles. .
- blowing agent examples include hydrocarbons such as butane, pentane and hexane, organic physical blowing agents such as halogenated hydrocarbons such as trichlorofluoromethane, dichlorofluoromethane, tetrachlorodifluoroethane, and dichloromethane, carbon dioxide, nitrogen,
- An inorganic physical foaming agent such as an inorganic gas such as air or water can be used alone or in combination of two or more.
- a physical foaming agent mainly composed of an inorganic physical foaming agent such as carbon dioxide, nitrogen or air. More preferred is carbon dioxide.
- inorganic physical foaming agent as a main component means that the inorganic physical foaming agent in 100 mol% of the total physical foaming agent is 50 mol% or more, preferably 70 mol% or more, more preferably 90 mol% or more. Means that.
- the addition amount of the physical foaming agent can be appropriately adjusted according to the type of foaming agent, the blending amount of the additive, the apparent density of the desired foamed particles, and the like.
- the inorganic physical foaming agent is generally used in an amount of 0.1 to 30 parts by weight, preferably 0.5 to 15 parts by weight, and more preferably 1 to 10 parts by weight per 100 parts by weight of the base resin.
- a known in-mold molding method can be employed.
- a compression molding method, a cracking molding method, a pressure molding method, a compression filling molding method, a normal pressure filling molding method for example, Japanese Patent Publication No. 46-38359, Japanese Patent Publication No. 51
- a conventionally known foamed particle molding die No. 22951, JP-B-4-46217, JP-B-6-22919, JP-B-6-49795, etc.
- the foam particles are filled into a cavity of a conventionally known thermoplastic resin foam particle molding mold that can be heated and cooled and that can be opened and closed and sealed,
- the expanded particles are expanded by supplying water vapor with a saturated vapor pressure of 0.01 to 0.25 MPa (G), preferably 0.01 to 0.20 MPa (G) and heating the expanded particles in a mold, Examples thereof include a batch type in-mold molding method in which the foamed particle molded body obtained by fusing and then cooling is taken out from the cavity, and a continuous in-mold molding method described later.
- the water vapor supply method As the water vapor supply method, a conventionally known method in which heating methods such as one-side heating, reverse one-side heating, and main heating are appropriately combined can be adopted. In particular, a method of heating the expanded particles in the order of preliminary heating, one-side heating, reverse one-side heating, and main heating is preferable.
- the foamed particle molded body continuously supplies the foamed particles into a mold formed by a belt that moves continuously along the upper and lower sides of the passage, and the saturated vapor pressure is reduced when passing through the steam heating region. 0.01 to 0.25 MPa (G) of water vapor is supplied to expand and fuse the expanded particles, and then cooled by passing through a cooling region, and then the obtained expanded expanded particles are taken out from the passage, It can also be produced by a continuous in-mold molding method (for example, see JP-A-9-104026, JP-A-9-104027, JP-A-10-180888, etc.) in which the length is sequentially cut.
- a continuous in-mold molding method for example, see JP-A-9-104026, JP-A-9-104027, JP-A-10-180888, etc.
- foamed particles obtained by the above method are filled into a pressurizable sealed container, and foaming is performed by increasing the pressure in the foamed particles by pressurizing with a pressurized gas such as air. After the pressure in the particles is adjusted to 0.01 to 0.15 MPa (G), the foamed particles are taken out from the container and molded in the mold, thereby further improving the moldability of the foamed particles in the mold. I can do it.
- Examples 1 to 4, Examples 6 to 9, Comparative Examples 2 and 3 An extruder provided with a co-extrusion die for forming a multilayer strand on the outlet side of an extruder for forming a core layer having an inner diameter of 65 mm and an extruder for forming an outer layer having an inner diameter of 30 mm was used.
- the core layer forming extruder and the outer layer forming extruder were respectively supplied with the polylactic acid-based resin forming the core layer and the outer layer shown in Table 1 at the ratio shown in Table 1, and melt-kneaded. .
- the melt-kneaded product is introduced into the co-extrusion die, merged within the die, and co-extruded as multi-layer strands having an outer layer formed on the side surface of the core layer from the pores of the die attached to the tip of the extruder.
- the resulting strand was cooled with water, cut with a pelletizer so as to have a weight of about 2 mg, and dried to obtain multilayer resin particles.
- polytetrafluoroethylene powder (trade name: TFW-1000, manufactured by Seishin Enterprise Co., Ltd.) is supplied in a master batch to the polylactic acid resin of the core layer so that the content becomes 1000 ppm by weight as a foam regulator. did.
- a phthalocyanine green pigment was added to the outer polylactic acid resin in a master batch so that the content was 100 ppm.
- polylactic acid-based resin expanded particles were produced using the resin particles.
- 1 kg of the resin particles obtained as described above was charged into a 5 L sealed container equipped with a stirrer together with 3 L of water as a dispersion medium, and 0.1 parts by weight of aluminum oxide as a dispersant was further added to the dispersion medium.
- 0.01 part by weight of surfactant (trade name: Neogen S-20F, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., sodium alkylbenzene sulfonate) was added.
- the temperature was raised to 5 ° C.
- the addition amount (parts by weight) of the dispersant and the surfactant is an amount with respect to 100 parts by weight of the polylactic acid resin particles.
- Table 1 shows the production conditions (pressure inside the sealed container and foaming temperature) of the polylactic acid-based resin foamed particles. In addition, Table 1 shows the results of measuring various physical properties of the obtained expanded particles.
- Example 5 The foamed particles obtained in Example 1 were pressurized with air to give an internal pressure of 0.18 MPa (G), and then heated with a mixed medium of steam and compressed air, whereby a foaming atmosphere temperature of 58 was obtained. Two-stage foaming was performed at 0 ° C. to obtain foamed particles shown in Table 1.
- Example 10 Using the multilayer resin particles obtained in Example 1, polylactic acid resin foamed particles were produced as follows. First, 1 kg of the obtained multilayer resin particles was charged into a 5 L airtight container equipped with a stirrer together with 3 L of water as a dispersion medium, and a surfactant (trade name: Neogen S-20F, 1st 0.004 part by weight was added as an active ingredient amount (sodium alkylbenzene sulfonate manufactured by Kogyo Seiyaku Co., Ltd.). In addition, the addition amount (part by weight) of the surfactant is an amount with respect to 100 parts by weight of the polylactic acid resin particles. Next, after adjusting the temperature to 30 ° C.
- a surfactant trade name: Neogen S-20F, 1st 0.004 part by weight was added as an active ingredient amount (sodium alkylbenzene sulfonate manufactured by Kogyo Seiyaku Co., Ltd.
- Comparative Example 1 Polylactic acid-based resin foaming was carried out in the same manner as in Example 1 except that a single-layer polylactic acid resin particle was produced using an extruder provided with a strand-forming die on the outlet side of the core layer-forming extruder having an inner diameter of 65 mm. Particles were obtained.
- Table 1 shows the production conditions (pressure inside the sealed container and foaming temperature) of the polylactic acid-based resin foamed particles. In addition, Table 1 shows the results of measuring various physical properties of the obtained expanded particles.
- a foamed particle molded body was produced using the foamed particles.
- the foamed particles obtained in Examples and Comparative Examples were filled into flat plate molds having a length of 200 mm ⁇ width of 250 mm ⁇ thickness of 20 mm and 50 mm (Examples 1-2, 2-2, and 5-2), and steam was added.
- In-mold molding was performed by pressure molding by heating to obtain a plate-like foamed particle molded body.
- the heating method is to supply steam for 5 seconds with the double-sided drain valve open, perform preheating (exhaust process), and then supply steam from the moving side for 5 seconds with the fixed drain valve open.
- steam was supplied for 10 seconds from the stationary side with the moving side drain valve opened, and then heated at the molding heating steam pressure (vapor pressure) shown in Tables 2 and 3.
- Appearance evaluation is performed by observing the surface of the foamed particle molded body, evaluating the case where the particle gap due to secondary foaming failure of the foamed particles is not conspicuous as “ ⁇ ”, and evaluating the case where it is conspicuous as “x”. It was.
- the evaluation of the fusing property was performed based on the ratio (the fusing rate) of the number of foam particles whose material was broken out of the foam particles exposed on the fracture surface when the foamed particle molded body was broken. Specifically, the foamed particle molded body was cut by about 10 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. Next, the number (b) of foam particles present on the fracture surface and the number (b) of the foam particles whose material was destroyed were measured, and the ratio (b / n) of (b) and (n) was expressed as a percentage. It was set as the fusion rate (%). Tables 2 and 3 show the fusion rate values.
- the bulk density of the foamed particle molded body was measured as follows. The bulk volume was determined from the external dimensions of the foamed particle molded body that was allowed to stand for 24 hours or more in an environment of a temperature of 23 ° C. and a relative humidity of 50%. Next, the weight (g) of the foamed particle compact was precisely weighed. The bulk density (g / L) of the foamed particle molded body was determined by dividing the weight of the foamed particle molded body by the bulk volume and converting the unit.
- Internal pressure The internal pressure of the foamed particles when producing the foamed particle molded body or two-stage foaming is a part of the foamed particles immediately before filling the in-mold molding machine or just before the two-stage foaming machine is charged (hereinafter referred to as a foamed particle group). was measured as follows.
- the expanded particles are not allowed to pass through, but the air It was housed in a bag of about 70 mm ⁇ 100 mm with a large number of needle holes of a size that can pass freely, and moved to a constant temperature and humidity chamber under an atmospheric pressure with an air temperature of 23 ° C. and a relative humidity of 50%. Subsequently, a bag containing foam particles was placed on the balance in the constant temperature and humidity chamber, and the weight was read. This weight measurement was performed 120 seconds after the above expanded particle group was taken out from the pressurized tank.
- the weight at this time was defined as Q (g).
- the bag containing the expanded particles was left in the same temperature and humidity chamber for 10 days. Since the pressurized air in the expanded particles permeates the bubble wall and escapes to the outside as time passes, the weight of the expanded particles group decreases accordingly, and after 10 days, the weight has reached equilibrium. Stable. Therefore, after 10 days, the weight of the bag containing the expanded particle group was measured again in the same temperature and humidity chamber, and this weight was defined as U (g).
- the difference between Q (g) and U (g) was defined as the increased air amount W (g), and the internal pressure P (MPa) of the expanded particles was calculated by the following equation (5).
- the internal pressure P corresponds to a gauge pressure.
- M is the molecular weight of air, and here, a constant of 28.8 (g / mol) is adopted.
- R is a gas constant, and here, a constant of 0.0083 (MPa ⁇ L / (K ⁇ mol)) is adopted.
- T means an absolute temperature, and since an atmosphere of 23 ° C. is adopted, it is a constant of 296 (K) here.
- V means the volume (L) obtained by subtracting the volume of the base resin in the expanded particle group from the apparent volume of the expanded particle group.
- the apparent volume of the expanded particles is determined by submerging the entire amount of expanded particles taken out of the bag after 10 days of curing into water in a graduated cylinder containing 100 cm 3 of 23 ° C. water immediately in the same temperature and humidity chamber.
- the volume Y (cm 3 ) of the expanded particle group is calculated from the increment of the scale at the time of making it, and this is obtained by converting this to liter (L) units.
- the volume (L) of the base resin occupying in the foam particle group is the foam particle weight (difference between U (g) and the weight Z (g) of the bag having a large number of needle holes). It is determined by dividing the particle by the density (g / cm 3 ) of the resin obtained by defoaming the particles with a heat press.
- the apparent density (g / cm 3 ) of the expanded particle group is obtained by dividing the weight of the expanded particle group (difference between U (g) and Z (g)) by the volume Y (cm 3 ). Desired.
- the foamed particle group weight (difference between U (g) and Z (g)) is 0.5000 to 10.0000 g and the volume Y is 50 to 90 cm 3.
- a group of expanded particles is used.
- Heating-resistant The heat resistance of the foamed particle molded body was evaluated.
- a test piece was placed in a gear oven maintained at 120 ° C. and heated for 22 hours. Thereafter, the sample was left in a constant temperature and humidity chamber at 23 ° C. and a relative humidity of 50% for 1 hour, and the heating dimensional change rate was determined from the dimensions before and after heating using the following formula (6).
- Heating dimensional change rate (%) ((dimension after heating ⁇ dimension before heating) / dimension before heating) ⁇ 100 ... (6)
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Abstract
Description
[1]ポリ乳酸系樹脂を基材樹脂とする発泡粒子であって、JIS K7122(1987年)に記載されている熱流束示差走査熱量測定法に準拠して下記の条件1にて求められる該発泡粒子全体の吸熱量(Br:endo)[J/g]、該発泡粒子表層部の吸熱量(Brs:endo)[J/g]及び該発泡粒子中心部の吸熱量(Brc:endo)[J/g]が下記(1)式及び(2)式を満足することを特徴とするポリ乳酸系樹脂発泡粒子。
(Br:endo)>25 ・・・(1)
(Brc:endo)>(Brs:endo)≧0 ・・・(2)
条件1
[測定試料の調整]
(発泡粒子表層部の吸熱量測定試料)
発泡粒子の表面を含む表層部分を切削処理して表層部分を集めて試験片とする。なお、切削処理にあたっては1個の発泡粒子の表面全面から、切削処理前の発泡粒子の粒子重量の1/6~1/4の重量の測定試料を採取することとする。
(発泡粒子中心部の吸熱量測定試料)
発泡粒子の表面全面を切削除去し、切削処理前の発泡粒子の粒子重量の1/5~1/3の重量となる発泡粒子残部を測定試料として採取することとする。
[吸熱量の測定]
それぞれの吸熱量、(Br:endo)、(Brs:endo)、または(Brc:endo)の測定値は、ポリ乳酸系樹脂発泡粒子、該発泡粒子の表層部から採取された測定試料または該発泡粒子の中心部から採取された測定試料1~4mgをJIS K7122(1987年)に記載されている熱流束示差走査熱量測定法に準拠して、融解ピーク終了温度より30℃高い温度まで加熱溶融させ、その温度に10分間保った後、冷却速度2℃/minにて110℃まで冷却し、その温度に120分間保った後、冷却速度2℃/minにて40℃まで冷却する熱処理後、再度、加熱速度2℃/minにて融解ピーク終了時よりも30℃高い温度まで加熱溶融させる際に得られるDSC曲線に基づいて求められる値とする。
[2]JIS K7122(1987年)に記載されている熱流束示差走査熱量測定法に準拠して下記の条件2にて求められる前記発泡粒子中心部の吸熱量(Bfc:endo)[J/g]と発熱量(Bfc:exo)[J/g]とが下記(3)式を満足することを特徴とする前記[1]に記載のポリ乳酸系樹脂発泡粒子。
40>[(Bfc:endo)-(Bfc:exo)]>10 ・・・(3)
条件2
[吸熱量および発熱量の測定]
吸熱量(Bfc:endo)および発熱量(Bfc:exo)の測定は、前記条件1の発泡粒子中心部の吸熱量測定試料の調整方法により、発泡粒子の中心部から採取された測定試料1~4mgをJIS K7122(1987年)に記載されている熱流束示差走査熱量測定法に準拠して、加熱速度2℃/minにて23℃から融解ピーク終了時よりも30℃高い温度まで加熱溶融させる際に得られるDSC曲線に基づいて求められる値とする。
[3]ポリ乳酸系樹脂発泡粒子の見かけ密度が25~400g/Lであることを特徴とする前記[1]又は[2]に記載のポリ乳酸系樹脂発泡粒子。
[4]ポリ乳酸系樹脂発泡粒子の平均気泡径が30~500μmであることを特徴とする前記[1]~[3]のいずれかに記載のポリ乳酸系樹脂発泡粒子。
[5]発泡粒子が、ポリ乳酸系樹脂により構成される芯層と、該芯層に対して表面側に位置しポリ乳酸系樹脂により構成される外層とからなり、前記芯層を構成するポリ乳酸系樹脂の軟化点(A)[℃]と前記外層を構成するポリ乳酸系樹脂の軟化点(B)[℃]との差[(A)-(B)]が0℃を超え105℃以下であることを特徴とする前記[1]~[4]のいずれかに記載のポリ乳酸系樹脂発泡粒子。
[6]前記[1]~[5]のいずれかに記載のポリ乳酸系樹脂発泡粒子が一体的に融着してなる嵩密度15~300g/Lのポリ乳酸系樹脂発泡粒子成形体。
更に、本発明のポリ乳酸系樹脂発泡粒子においては、発泡粒子中心部の吸熱量(Bfc:endo)[J/g]と発熱量(Bfc:exo)[J/g]とが特定の関係を満たすことにより、特に型内成形時の二次発泡性と耐収縮性が良好な発泡粒子となり、型内成形時の温度調整が容易で、得られる発泡粒子成形体の収縮率が小さなものになる。
更に、本発明のポリ乳酸系樹脂発泡粒子においては、ポリ乳酸系樹脂により構成される芯層と、該芯層に対して表面側に位置しポリ乳酸系樹脂により構成される外層とからなり、前記芯層を構成するポリ乳酸系樹脂の軟化点(A)[℃]と前記外層を構成するポリ乳酸系樹脂の軟化点(B)[℃]との差[(A)-(B)]が0℃を超え105℃以下であることにより、上記の吸熱量(Br:endo,Brs:endo,Brc:endo)等が的確に調整されたものとなる。
また、本発明のポリ乳酸系樹脂発泡粒子成形体は、外観良好で発泡粒子相互の融着性にも優れるものであるため、基材樹脂の有する物性と十分な発泡に伴う物性向上効果を十分に発現することができる優れたものである。また、熱処理(ヒートセット)により充分に結晶化度が高められた本発明のポリ乳酸系樹脂発泡粒子成形体は、上記物性向上効果と相俟って常温使用時の機械的物性において更に優れるものとなる。
本発明のポリ乳酸系樹脂発泡粒子(以下、単に「発泡粒子」ともいう。)を構成する基材樹脂は、ポリ乳酸系樹脂である。該ポリ乳酸系樹脂は、ポリ乳酸、或いはポリ乳酸と他の樹脂との混合物からなる。なお、該ポリ乳酸は、乳酸に由来する成分単位を50モル%以上含むポリマーであることが好ましい。該ポリ乳酸としては、例えば(a)乳酸の重合体、(b)乳酸と他の脂肪族ヒドロキシカルボン酸とのコポリマー、(c)乳酸と脂肪族多価アルコールと脂肪族多価カルボン酸とのコポリマー、(d)乳酸と脂肪族多価カルボン酸とのコポリマー、(e)乳酸と脂肪族多価アルコールとのコポリマー、(f)これら(a)~(e)の何れかの組合せによる混合物等が包含される。また、該ポリ乳酸には、ステレオコンプレックスポリ乳酸、ステレオブロックポリ乳酸と呼ばれるものも包含される。なお、乳酸の具体例としては、L-乳酸、D-乳酸、DL-乳酸又はそれらの環状2量体であるL-ラクチド、D-ラクチド、DL-ラクチド又はそれらの混合物が挙げられる。
具体的には、ビス(ジプロピルフェニル)カルボジイミド(例えば、ラインケミー社製Stabaxol 1-LF)などの芳香族モノカルボジイミド、芳香族ポリカルボジイミド(例えば、ラインケミー社製Stabaxol P、ラインケミー社製Stabaxol P400など)、ポリ(4-4’-ジシクロヘキシルメタンカルボジイミド)などの脂肪族ポリカルボジイミド(例えば日清紡ケミカル(株)製カルボジライトLA-1)などが挙げられる。
これらの末端封鎖剤は単独で使用しても良く、あるいは2種以上を組み合わせて使用しても良い。
また、末端封鎖剤の含有量は、ポリ乳酸100重量部あたりに0.1~5重量部が好ましく、0.5~3重量部がより好ましい。
着色剤としては、有機系、無機系の顔料、染料などが挙げられる。このような、顔料及び染料としては、公知のものを用いることができる。
上記添加剤は、添加剤の種類によっても異なるが、通常、基材樹脂100重量部に対して0.001~20重量部、更に0.01~5重量部とすることが好ましい。
(Br:endo)>25 ・・・(1)
上記(1)式において、(Br:endo)が25[J/g]超であることは、発泡粒子を構成しているポリ乳酸の結晶化が充分に進む条件にて熱処理した場合、該ポリ乳酸による発泡粒子の結晶成分の量が多い状態になることを意味している。すなわち、充分な熱処理により発泡粒子を構成しているポリ乳酸の結晶化度を高めることにより、結晶化度の高められた発泡粒子成形体を得ることができることを意味する。したがって、最終的に得られる発泡粒子成形体の機械的強度、高温時の圧縮強さ等の耐熱性が高められることが期待できる。このような観点から、(Br:endo)は、30J/g以上、更に35J/g以上であることが好ましい。また、(Br:endo)の上限は、概ね70J/g、更に60J/gである。
(Brc:endo)>(Brs:endo)≧0 ・・・(2)
一方、発泡粒子表層部のポリ乳酸は、充分な熱処理によっても結晶化度が発泡粒子中心部より低いことから、(2)式の関係を満たす発泡粒子は、発泡粒子表面の軟化点が低いものである。したがって、該発泡粒子は、発泡粒子製造前後の熱履歴によらず型内成形時の発泡粒子相互の熱融着性において優れた融着性を発現できる発泡粒子である。かかる観点から、発泡粒子表面の融着性をより向上させるために、発泡粒子表層部の吸熱量(Brs:endo)は35J/g以下(0も含む)が好ましい。また、発泡粒子の中心部の耐熱性、機械的強度を向上させるために、発泡粒子中心部の吸熱量(Brc:endo)は30J/g以上、更に35J/g以上であることが好ましい。また、(Brc:endo)の上限は、概ね70J/g、更に60J/gである。
また、(Brc:endo)と(Brs:endo)とは、3J/g以上の熱量差、更に4J/g以上の熱量差を有することが好ましい。なお、前記(2)式を満足する範囲において、発泡粒子表層部を構成しているポリ乳酸は、非晶性ポリ乳酸でも非晶性ポリ乳酸と結晶性ポリ乳酸との混合樹脂であってもよい。
[測定試料の調整]
(発泡粒子全体の吸熱量測定試料)
発泡粒子を基本的には切断することなく測定試料とすることとする。
(発泡粒子表層部の吸熱量測定試料)
発泡粒子の表面を含む表層部分を切削処理して表層部分を集めて測定試料とする。なお、切削処理にあたっては1個の発泡粒子の表面全面から切削処理前の発泡粒子の粒子重量の1/6~1/4の重量の測定試料を採取することとする。具体的には、表層部分をカッターナイフ、ミクロトーム等を用いて切削処理を行い、該表層部分を集めて測定に供すればよい。但し、この際の留意点としては、1個の発泡粒子の該表層部分全面を必ず切除し、且つ1個の発泡粒子から切除した該表層部分の重量が切削処理前の発泡粒子の粒子重量の6分の1~4分の1の範囲内となるようにする。
(発泡粒子中心部の吸熱量測定試料)
発泡粒子の表面全面を切削除去し、切削処理前の発泡粒子の粒子重量の1/5~1/3の重量となる発泡粒子残部を測定試料として採取することとする。具体的には、発泡粒子の表面を含まない内部の発泡層を切り出すことを目的にカッターナイフ等で切削処理を行い、該発泡粒子中心部を測定に供すればよい。但し、この際の留意点としては、1個の発泡粒子の表面全面を必ず切除し、且つ発泡粒子の中心とできる限り同じ中心をもつように切削処理前の発泡粒子の粒子重量の5分の1~3分の1の範囲内で発泡粒子中心部を切り出す。この際、切り出された測定試料は、切削処理前の発泡粒子の形状とできる限り相似の関係にあるようにする。
それぞれの吸熱量、(Br:endo)、(Brs:endo)、または(Brc:endo)の測定値は、ポリ乳酸系樹脂発泡粒子、該発泡粒子の表層部から採取された試験片または該発泡粒子の中心部から採取された測定試料1~4mgをJIS K7122(1987年)に記載されている熱流束示差走査熱量測定法に準拠して、融解ピーク終了温度より30℃高い温度まで加熱溶融させ、その温度に10分間保った後、冷却速度2℃/minにて110℃まで冷却し、その温度に120分間保った後、冷却速度2℃/minにて40℃まで冷却する熱処理後、再度、加熱速度2℃/minにて融解ピーク終了時よりも30℃高い温度まで加熱溶融させる際に得られるDSC曲線(以下、2回目のDSC曲線ともいう。)に基づいて求められる値とする。なお、(Brs:endo)、(Brc:endo)の測定試料採取にあたり、1個の発泡粒子から得られる測定試料が1~4mgに満たない場合には上記測定試料採取操作を複数個の発泡粒子に対して行い1~4mgの範囲内で測定試料を調整する必要がある。また、(Br:endo)の測定試料採取にあたり、1粒の発泡粒子の重量が4mgを超える場合には発泡粒子を2等分するなど同形状に等分して1~4mgの範囲内で測定試料を調整する必要がある。
(a)無作為に選ばれた一つの発泡粒子の表面部分を切削収集して第1試験試料得る。この切削収集は発泡粒子の外周表面が全て除かれ、かつ第1試験試料の重量が切削前の発泡粒子の重量の1/6~1/4となるよう行う;
(b)収集した第1試験試料の重量が1mgに満たない場合は、合計1~4mgの第1試験試料が得られるまで、無作為に選ばれた一つ以上の更なる発泡粒子について上記(a)の手順を繰り返す;
(c)無作為に選ばれた他の発泡粒子の表面部分を切除して第2試験試料を残す。この切除は発泡粒子の外周表面が全て切削され、第2試験試料の重量が切除前の発泡粒子の重量の1/5~1/3となるよう行う;
(d)得られた第2試験試料の重量が1mgに満たない場合は、合計1~4mgの第2試験試料が得られるまで、無作為に選ばれた一つ以上の更なる発泡粒子について上記(c)の手順を繰り返す;
(e)さらに一つの発泡粒子を無作為に選び第3試験試料得る;
(f)第1試験試料1~4mg、第2試験試料1~4mg、第3試験試料1~4mgのそれぞれについて、融解ピーク終了温度より30℃高い温度まで加熱溶融させ、その温度に10分間保った後、冷却速度2℃/minにて110℃まで冷却し、その温度に120分間保った後、冷却速度2℃/minにて40℃まで冷却する熱処理後、再度、加熱速度2℃/minにて融解ピーク終了時よりも30℃高い温度まで加熱溶融させる熱流束示差走査熱量測定をJIS K7122(1987年)に準拠して行い、DSC曲線を求める;および
(g)(Brs:endo)は第1試験試料のDSC曲線における吸熱ピークの熱量であり、(Brc:endo)は第2試験試料のDSC曲線における吸熱ピークの熱量であり、(Br:endo)は第3試験試料のDSC曲線における吸熱ピークの熱量である。
40>[(Bfc:endo)-(Bfc:exo)]>10
・・・(3)
[測定試料の調整]
(発泡粒子中心部の吸熱量および発熱量測定試料)
前記条件1の発泡粒子中心部の吸熱量測定試料の調整方法と同様に発泡粒子の表面全面を切削除去し、切削処理前の発泡粒子の粒子重量の1/5~1/3の重量となる発泡粒子残部を測定試料として採取することとする。
[吸熱量および発熱量の測定]
吸熱量(Bfc:endo)および発熱量(Bfc:exo)の測定は、発泡粒子の中心部から採取された測定試料1~4mgをJIS K7122(1987年)に記載されている熱流束示差走査熱量測定法に準拠して、加熱速度2℃/minにて23℃から融解ピーク終了時よりも30℃高い温度まで加熱溶融させる際に得られるDSC曲線(以下、1回目のDSC曲線ともいう。)に基づいて求められる値とする。なお、1個の発泡粒子から得られる測定試料が1~4mgに満たない場合は上記測定試料採取操作を複数個の発泡粒子に対して行い1~4mgの範囲内で測定試料を調整する必要がある。
(h)無作為に選ばれた一つの発泡粒子の表面部分を切除して第4試験試料を残す。この切除は発泡粒子の外周表面が全て切削され、第4試験試料の重量が切除前の発泡粒子の重量の1/5~1/3となるよう行う;
(i)得られた第4試験試料の重量が1mgに満たない場合は、合計1~4mgの第4試験試料が得られるまで、無作為に選ばれた一つ以上の更なる発泡粒子について上記(h)の手順を繰り返す;
(j)第4試験試料1~4mgについて、第4試験試料が加熱速度2℃/minにて23℃から融解ピーク終了時よりも30℃高い温度まで加熱する熱流束示差走査熱量測定をJIS K7122(1987年)に準拠して行い、DSC曲線を求める;および
(k)(Bfc:endo)と(Bfc:exo)は、それぞれ、第4試験試料のDSC曲線における吸熱ピークと発熱ピークの熱量である。
発泡粒子の発熱量(Bfc:exo)は1回目のDSC曲線の発熱ピークの低温側のベースラインから発熱ピークが離れる点を点cとし、発熱ピークが高温側のベースラインへ戻る点を点dとして、点cと点dとを結ぶ直線と、DSC曲線に囲まれる発熱量を示す部分の面積から求められる値とする。また、発泡粒子の吸熱量(Bfc:endo)は、1回目のDSC曲線の吸熱ピークの低温側のベースラインから吸熱ピークが離れる点を点eとし、吸熱ピークが高温側のベースラインへ戻る点を点fとして、点eと点fとを結ぶ直線と、DSC曲線に囲まれる吸熱量を示す部分の面積から求められる値とする。但し、1回目のDSC曲線におけるベースラインはできるだけ直線になるように装置を調節することとする。また、どうしてもベースラインが湾曲してしまう場合は、発熱ピークの低温側の湾曲したベースラインをその曲線の湾曲状態を維持して高温側へ延長する作図を行い、該湾曲した低温側のベースラインから発熱ピークが離れる点を点c、発熱ピークの高温側の湾曲したベースラインをその曲線の湾曲状態を維持して低温側へ延長する作図を行い、該湾曲した高温側ベースラインへ発熱ピークが戻る点を点dとする。更に、吸熱ピークの低温側の湾曲したベースラインをその曲線の湾曲状態を維持して高温側へ延長する作図を行い、該湾曲した低温側のベースラインから吸熱ピークが離れる点を点e、吸熱ピークの高温側の湾曲したベースラインをその曲線の湾曲状態を維持して低温側へ延長する作図を行い、該湾曲した高温側ベースラインへ吸熱ピークが戻る点を点fとする。
図6において、1は芯層(内側の実線で囲まれた内側部分)を、2は外層(外側の実線と内側の実線で囲まれた部分)を、3は発泡粒子表層部(外側の実線と外側の破線で囲まれた部分)を、4は発泡粒子中心部(内側の破線で囲まれた内側部分)をそれぞれ示す。
なお、外層を構成するポリ乳酸系樹脂の軟化点(B)は、発泡粒子の取り扱い性および得られる発泡粒子成形体の高温時の機械的強度の観点から、芯層を構成するポリ乳酸系樹脂の軟化点(A)との関係が上記範囲であると共に、50℃以上、更に55℃以上、特に65℃以上が好ましい。
従って、発泡粒子の芯層を形成している樹脂と外層を形成している樹脂との重量比が前記範囲内にあることにより、発泡粒子間の融着強度が強くなることから、得られる発泡粒子成形体は機械的物性に優れたものとなり、また、発泡粒子の物性向上に寄与する芯層の割合が大きくなることにより更に機械的物性に優れたものとなる。
なお、発泡粒子における芯層を形成している樹脂と外層を形成している樹脂の重量比の調整は、後記ポリ乳酸系樹脂粒子(以下、樹脂粒子ともいう。)の芯層を形成している樹脂と外層を形成している樹脂の重量比を調整することにより行なわれる。
発泡粒子を大気圧下、相対湿度50%、23℃の条件の恒温室内にて10日間放置する。次に、同恒温室内にて、10日間放置した約500mlの発泡粒子群の重量W1(g)を測定し、重量を測定した発泡粒子群を金網などの道具を使用して温度23℃の水の入ったメスシリンダー中に沈める。次に、金網等の道具の体積を差し引いた、水位上昇分より読みとられる発泡粒子群の容積V1(L)を測定し、メスシリンダーに入れた発泡粒子群の重量W1を容積V1で割り算(W1/V1)することにより見かけ密度を求める。
発泡粒子を略二等分した切断面を顕微鏡で撮影した拡大写真に基づき、以下のとおり求めることができる。発泡粒子の切断面拡大写真において発泡粒子の一方の表面から他方の表面に亘って、気泡切断面の略中心を通る4本の線分を引く。ただし、該線分は、気泡切断面の略中心から切断粒子表面へ等間隔の8方向に伸びる放射状の直線を形成するように引くこととする。次いで前記4本の線分と交わる気泡の数の総数N(個)を求める。4本の各線分の長さの総和L(μm)を求め、総和Lを総和Nで除した値(L/N)を発泡粒子1個の平均気泡径とする。この作業を10個の発泡粒子について行い、各発泡粒子の平均気泡径を相加平均した値を発泡粒子の平均気泡径とする。
発泡粒子を大気圧下、相対湿度50%、23℃の条件の恒温室内にて10日間放置し養生する。次に同恒温室内にて、嵩体積約20cm3の養生後の発泡粒子を測定用サンプルとし下記の通り水没法により正確に見かけの体積Vaを測定する。見かけの体積Vaを測定した測定用サンプルを十分に乾燥させた後、ASTM-D2856-70に記載されている手順Cに準じ、東芝・ベックマン株式会社製空気比較式比重計930により測定される測定用サンプルの真の体積Vxを測定する。そして、これらの体積Va及びVxを基に、下記の(4)式により独立気泡率を計算し、N=5の平均値を発泡粒子の独立気泡率とする。
独立気泡率(%)=(Vx-W/ρ)×100/(Va-W/ρ)
・・・(4)
ただし、
Vx:上記方法で測定される発泡粒子の真の体積、即ち、発泡粒子を構成する樹脂の容積と、発泡粒子内の独立気泡部分の気泡全容積との和(cm3)
Va:発泡粒子を、水の入ったメスシリンダーに沈めて、水位上昇分から測定される発泡粒子の見かけの体積(cm3)
W:発泡粒子測定用サンプルの重量(g)
ρ:発泡粒子を構成する樹脂の密度(g/cm3)
なお、該融着率は、発泡粒子成形体を破断した際の破断面発泡粒子の個数に基づく材料破壊率を意味し、融着していない部分は材料破壊せず、発泡粒子の界面で剥離する。
本発明の発泡粒子の製造方法としては、押出発泡方法、ガス含浸予備発泡方法、分散媒放出発泡方法、或いはこれらの方法、原理を基本としたその他の発泡方法が挙げられる。
該芯層と外層とからなる樹脂粒子は、例えば、特公昭41-16125号公報、特公昭43-23858号公報、特公昭44-29522号公報、特開昭60-185816号公報等に記載された共押出成形法技術を利用して製造することができる。
該平均重量が軽すぎる場合には、樹脂粒子の製造が特殊なものになる。一方、該平均重量が重すぎる場合には、得られる発泡粒子の密度分布が大きくなったり、型内成形時の充填性が悪くなったりするおそれがある。
該樹脂粒子の形状は、円柱状、球状、角柱状、楕円球状、円筒状等を採用することができる。かかる樹脂粒子を発泡して得られる発泡粒子は、発泡前の樹脂粒子形状に略対応した形状となる。
分散媒放出発泡方法においては例えば前記樹脂粒子を耐圧容器内で分散媒及び物理発泡剤と共に分散させて加熱したり、或いは樹脂粒子を耐圧容器内で分散媒と共に分散させて加熱し、次いで物理発泡剤を上記耐圧容器内へ圧入したりすることにより、樹脂粒子に物理発泡剤を含浸させて発泡性樹脂粒子とする。次いで、該発泡性樹脂粒子を耐圧容器内よりも低い圧力下に分散媒と共に放出することにより発泡性樹脂粒子を発泡させて発泡粒子を得ることができる。
上記発泡助剤のうち、本発明では、ポリテトラフルオロエチレン、ポリエチレンワックス、架橋ポリスチレン等が好ましく、更に、疎水性のポリテトラフルオロエチレン粉末が好ましい。
この場合には、ポリ乳酸系樹脂の加水分解を十分に抑制しつつ、見かけ密度の低下(発泡倍率の向上)及び気泡径の均一化を図ることができる。
なお、押出発泡法と比較して見かけ密度が低い発泡粒子を得ることができ、型内成形性に優れ、物性の良好な発泡粒子が得られるという観点から、発泡粒子の製法としては、上記のガス含浸予備発泡方法や分散媒放出発泡方法が好ましく、特に分散媒放出発泡方法が好ましい。
該分散剤としては、酸化アルミニウム、第三リン酸カルシウム、ピロリン酸マグネシウム、酸化チタン、酸化亜鉛、塩基性炭酸マグネシウム、塩基性炭酸亜鉛、炭酸カルシウム、カオリン、マイカ、及びクレー等の無機物質や、ポリビニルピロリドン、ポリビニルアルコール、メチルセルロースなどの水溶性高分子保護コロイド剤が挙げられる。また、分散助剤として、ドデシルベンゼンスルホン酸ナトリウム、アルカンスルホン酸ナトリウム等のアニオン性界面活性剤などを分散媒に添加することもできる。
これら分散剤は、樹脂粒子100重量部あたり0.05~3重量部使用することができ、これら分散助剤は、樹脂粒子100重量部あたり0.001~0.3重量部使用することができる。
なお、無機系物理発泡剤を主成分とするとは、全物理発泡剤100モル%中の無機系物理発泡剤が50モル%以上、好ましくは70モル%以上、より好ましくは90モル%以上含まれることを意味する。
例えば、従来公知の発泡粒子成形金型を用いる、圧縮成形法、クラッキング成形法、加圧成形法、圧縮充填成形法、常圧充填成形法(例えば、特公昭46-38359号公報、特公昭51-22951号公報、特公平4-46217号公報、特公平6-22919号公報、特公平6-49795号公報等参照)などが挙げられる。
内径65mmの芯層形成用押出機および内径30mmの外層形成用押出機の出口側に多層ストランド形成用の共押ダイを付設した押出機を用いた。
芯層形成用押出機および外層形成用押出機に、それぞれ表1に示す芯層および外層を形成するポリ乳酸系樹脂を、表1に示す割合で、夫々の押出機に供給し、溶融混練した。その溶融混練物を前記の共押ダイに導入してダイ内で合流して押出機先端に取り付けた口金の細孔から、芯層の側面に外層が形成された多層ストランドとして共押出し、共押出されたストランドを水冷し、ペレタイザーで重量が略2mgとなるように切断し、乾燥して多層樹脂粒子を得た。
なお、芯層のポリ乳酸系樹脂には気泡調整剤としてポリテトラフルオロエチレン粉末(商品名:TFW-1000、(株)セイシン企業製)を含有量が1000重量ppmとなるようにマスターバッチで供給した。また、外層のポリ乳酸系樹脂にはフタロシアニングリーン系顔料を含有量が100ppmとなるようにマスターバッチで添加した。
まず、前記のようにして得られた樹脂粒子1kgを分散媒としての水3Lと共に撹拌機を備えた5Lの密閉容器内に仕込み、更に分散媒中に、分散剤として酸化アルミニウム0.1重量部、界面活性剤(商品名:ネオゲンS-20F、第一工業製薬社製、アルキルベンゼンスルホン酸ナトリウム)を有効成分量として0.01重量部を添加した。次いで、撹拌下で表1に示す発泡温度より5℃低い温度まで昇温し、密閉容器内に発泡剤としての二酸化炭素を表1に示す圧力より0.2MPa(G)低い圧力になるまで圧入しその温度で15分間保持した。次いで、発泡温度まで昇温し、表1に示す圧力になるまで二酸化炭素を圧入し、表1に示す発泡温度で15分間保持した。その後、二酸化炭素にて背圧を加えながら内容物を大気圧下に放出して表1に示す見かけ密度のポリ乳酸系樹脂発泡粒子を得た。なお、分散剤、界面活性剤の添加量(重量部)は、ポリ乳酸系樹脂粒子100重量部に対する量である。
また、得られた発泡粒子の諸物性を測定した結果を表1に示す。
実施例1で得られた発泡粒子を用いて、空気により加圧処理を行い内圧0.18MPa(G)を付与した後、スチームと圧縮空気との混合媒体により加熱することにより、発泡雰囲気温度58℃下で二段発泡を行い表1に示す発泡粒子を得た。
実施例1にて得られた多層樹脂粒子を用いて、次のようにポリ乳酸系樹脂発泡粒子を作製した。
まず、得られた多層樹脂粒子1kgを分散媒としての水3Lと共に撹拌機を備えた5Lの密閉容器内に仕込み、更に分散媒中に、界面活性剤(商品名:ネオゲンS-20F、第一工業製薬社製、アルキルベンゼンスルホン酸ナトリウム)を有効成分量として0.004重量部を添加した。なお、界面活性剤の添加量(重量部)は、ポリ乳酸系樹脂粒子100重量部に対する量である。
次いで、撹拌下で温度30℃に調整した後、密閉容器内に発泡剤としての二酸化炭素を表1に示す圧力2.0MPa(G)になるまで圧入し、3時間保持し二酸化炭素を含浸させた。
次に、密閉容器内の圧力を大気圧に減圧した後、樹脂粒子を取り出した。取り出した樹脂粒子は、遠心分離機にて付着水分を除去した。
得られた樹脂粒子の表面の水分をエアーによりさらに除去し、上記密閉容器から取り出してから10分経過後に二酸化炭素含浸量を測定したところ、5.8重量部であった。
前記発泡剤含浸樹脂粒子を、温度23℃、相対湿度50%の雰囲気下で2時間30分静置して該樹脂粒子に含浸された炭酸ガスの一部を逸散させた。この発泡剤逸散処理を終えてから10分経過後に測定される逸散処理後の発泡剤含浸量は、3.7重量部であった。
この発泡性樹脂粒子を圧力調整弁の付いた密閉容器内に充填した後、95℃に調整したスチームと圧縮空気との混合媒体を8秒間導入して加熱することにより、雰囲気温度81℃下で発泡し、表1に示す見かけ密度のポリ乳酸系樹脂発泡粒子を得た。
内径65mmの芯層形成用押出機の出口側にストランド形成用ダイを付設した押出機を用い、単層のポリ乳酸樹脂粒子を作製した以外は、実施例1と同様にしてポリ乳酸系樹脂発泡粒子を得た。
前記の方法により測定した。
前記の方法により測定した。
前記の方法により測定した。
まず、実施例、比較例で得られた発泡粒子を縦200mm×横250mm×厚さ20mm及び50mm(実施例1-2、2-2、及び5-2)の平板成形型に充填し、スチーム加熱による加圧成形により型内成形を行なって板状の発泡粒子成形体を得た。加熱方法は両面の型のドレン弁を開放した状態でスチームを5秒間供給して予備加熱(排気工程)を行ったのち、固定側のドレン弁を開放した状態で移動側よりスチームを5秒間供給し、次いで移動側のドレン弁を開放した状態で固定側よりスチームを10秒間供給した後、表2及び表3に示す成形加熱スチーム圧力(蒸気圧)で加熱した。
このようにして得られた発泡粒子成形体について、下記の各種物性を評価し、その結果を厚さ20mmの成形体については表2に、厚さ50mmの成形体については表3に示す。
外観評価は、発泡粒子成形体の表面を観察し、表面に発泡粒子の二次発泡不良による粒子間隙が目立たない場合を「○」として評価し、目立つ場合を「×」として評価することにより行った。
融着性評価は、発泡粒子成形体を破断した際の破断面に露出した発泡粒子のうち、材料破壊した発泡粒子の数の割合(融着率)に基づいて行った。具体的には、発泡粒子成形体を、カッターナイフで発泡粒子成形体の厚み方向に約10mmの切り込みを入れた後、切り込み部から発泡粒子成形体を破断させた。次に、破断面に存在する発泡粒子の個数(n)と、材料破壊した発泡粒子の個数(b)を測定し、(b)と(n)の比(b/n)を百分率で表して融着率(%)とした。融着率の値を表2及び表3に示す。
発泡粒子成形体の嵩密度は、次のように測定した。
温度23℃、相対湿度50%の環境下で24時間以上放置した発泡粒子成形体の外形寸法から嵩体積を求めた。次いで該発泡粒子成形体の重量(g)を精秤した。発泡粒子成形体の重量を嵩体積にて除し、単位換算することにより発泡粒子成形体の嵩密度(g/L)求めた。
発泡粒子成形体を作製する際、或いは二段発泡する際の発泡粒子の内圧は、型内成形機充填直前、或いは二段発泡機投入直前の発泡粒子の一部(以下、発泡粒子群という)を使用して次のように測定した。
加圧タンク内にて内圧が高められた型内成形機充填直前、或いは二段発泡機投入直前の発泡粒子群を加圧タンクから取り出してから60秒以内に、発泡粒子は通過させないが空気は自由に通過できるサイズの針穴を多数穿設した70mm×100mm程度の袋の中に収容して気温23℃、相対湿度50%の大気圧下の恒温恒湿室に移動した。続いてその恒温恒湿室内の秤に発泡粒子群の入った袋を乗せて重量をよみとった。この重量の測定は、上記した発泡粒子群を加圧タンクから取り出してから120秒後におこなった。この時の重量をQ(g)とした。続いてその発泡粒子群の入った袋を同恒温恒湿室に10日間放置した。発泡粒子内の加圧空気は時間の経過とともに気泡壁を透過して外部に抜け出すため発泡粒子群の重量はそれに伴って減少し、10日間後では平衡に達しているので実質的にその重量は安定した。よってこの10日間後に再度その発泡粒子群の入った袋の重量を同恒温恒湿室内にて測定し、この重量をU(g)とした。Q(g)とU(g)の差を増加空気量W(g)とし、下記の(5)式により発泡粒子の内圧P(MPa)を計算した。なお、この内圧Pはゲージ圧に相当する。
但し、上式中、Mは空気の分子量であり、ここでは28.8(g/モル)の定数を採用する。Rは気体定数であり、ここでは0.0083(MPa・L/(K・mol))の定数を採用する。Tは絶対温度を意味し、23℃の雰囲気を採用されているので、ここでは296(K)の定数である。Vは発泡粒子群の見かけ体積から発泡粒子群中に占める基材樹脂の体積を差し引いた体積(L)を意味する。
なお、以上の測定においては、上記発泡粒子群重量(U(g)とZ(g)との差)が0.5000~10.0000gで、かつ体積Yが50~90cm3となる量の複数個の発泡粒子群が使用される。
発泡粒子成形体の耐熱性を評価した。JIS K6767(1999年)に記載されている熱的安定性(高温時の寸法安定性・B法)に準拠して、120℃に保ったギアオーブン内に試験片を入れ22時間加熱を行った後取り出し、23℃、相対湿度50%の恒温恒湿室に1時間放置し、加熱前後の寸法より下記(6)式を用いて加熱寸法変化率を求めた。
加熱寸法変化率(%)=((加熱後の寸法-加熱前の寸法)/加熱前の寸法 )×100
・・・(6)
2 外層
3 発泡粒子表層部
4 発泡粒子中心部
Claims (6)
- ポリ乳酸系樹脂を基材樹脂とする発泡粒子であって、JIS K7122(1987年)に記載されている熱流束示差走査熱量測定法に準拠して下記の条件1にて求められる該発泡粒子全体の吸熱量(Br:endo)[J/g]、該発泡粒子表層部の吸熱量(Brs:endo)[J/g]及び該発泡粒子中心部の吸熱量(Brc:endo)[J/g]が下記(1)式及び(2)式を満足することを特徴とするポリ乳酸系樹脂発泡粒子。
(Br:endo)>25 ・・・(1)
(Brc:endo)>(Brs:endo)≧0 ・・・(2)
条件1
[測定試料の調整]
(発泡粒子表層部の吸熱量測定試料)
発泡粒子の表面を含む表層部分を切削処理して表層部分を集めて試験片とする。なお、切削処理にあたっては1個の発泡粒子の表面全面から、切削処理前の発泡粒子の粒子重量の1/6~1/4の重量の測定試料を採取することとする。
(発泡粒子中心部の吸熱量測定試料)
発泡粒子の表面全面を切削除去し、切削処理前の発泡粒子の粒子重量の1/5~1/3の重量となる発泡粒子残部を測定試料として採取することとする。
[吸熱量の測定]
それぞれの吸熱量、(Br:endo)、(Brs:endo)、または(Brc:endo)の測定値は、ポリ乳酸系樹脂発泡粒子、該発泡粒子の表層部から採取された測定試料または該発泡粒子の中心部から採取された測定試料1~4mgをJIS K7122(1987年)に記載されている熱流束示差走査熱量測定法に準拠して、融解ピーク終了温度より30℃高い温度まで加熱溶融させ、その温度に10分間保った後、冷却速度2℃/minにて110℃まで冷却し、その温度に120分間保った後、冷却速度2℃/minにて40℃まで冷却する熱処理後、再度、加熱速度2℃/minにて融解ピーク終了時よりも30℃高い温度まで加熱溶融させる際に得られるDSC曲線に基づいて求められる値とする。 - JIS K7122(1987年)に記載されている熱流束示差走査熱量測定法に準拠して下記の条件2にて求められる前記発泡粒子中心部の吸熱量(Bfc:endo)[J/g]と発熱量(Bfc:exo)[J/g]とが下記(3)式を満足することを特徴とする請求項1に記載のポリ乳酸系樹脂発泡粒子。
40>[(Bfc:endo)-(Bfc:exo)]>10 ・・・(3)
条件2
[吸熱量および発熱量の測定]
吸熱量(Bfc:endo)および発熱量(Bfc:exo)の測定は、前記条件1の発泡粒子中心部の吸熱量測定試料の調整方法により、発泡粒子の中心部から採取された測定試料1~4mgをJIS K7122(1987年)に記載されている熱流束示差走査熱量測定法に準拠して、加熱速度2℃/minにて23℃から融解ピーク終了時よりも30℃高い温度まで加熱溶融させる際に得られるDSC曲線に基づいて求められる値とする。 - ポリ乳酸系樹脂発泡粒子の見かけ密度が25~400g/Lであることを特徴とする請求項1又は2に記載のポリ乳酸系樹脂発泡粒子。
- ポリ乳酸系樹脂発泡粒子の平均気泡径が30~500μmであることを特徴とする請求項1~3のいずれかに記載のポリ乳酸系樹脂発泡粒子。
- 発泡粒子が、ポリ乳酸系樹脂により構成される芯層と、該芯層に対して表面側に位置しポリ乳酸系樹脂により構成される外層とからなり、前記芯層を構成するポリ乳酸系樹脂の軟化点(A)[℃]と前記外層を構成するポリ乳酸系樹脂の軟化点(B)[℃]との差[(A)-(B)]が0℃を超え105℃以下であることを特徴とする請求項1~4のいずれかに記載のポリ乳酸系樹脂発泡粒子。
- 請求項1~5のいずれかに記載のポリ乳酸系樹脂発泡粒子が一体的に融着してなる嵩密度15~300g/Lのポリ乳酸系樹脂発泡粒子成形体。
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EP3124527A1 (en) | 2015-07-30 | 2017-02-01 | JSP Corporation | Expanded polylactic acid resin beads and molded article of expanded polylactic acid resin beads |
JP2021512992A (ja) * | 2018-12-12 | 2021-05-20 | ヒューヴィス コーポレーションHuvis Corporation | 低融点樹脂を含む発泡体およびこれを含む成形体 |
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WO2012086305A1 (ja) | 2010-12-21 | 2012-06-28 | 株式会社ジェイエスピー | ポリ乳酸系樹脂発泡粒子及びポリ乳酸系樹脂発泡粒子成形体 |
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JP2017031290A (ja) * | 2015-07-30 | 2017-02-09 | 株式会社ジェイエスピー | ポリ乳酸系樹脂発泡粒子及びポリ乳酸系樹脂発泡粒子成形体 |
US10633504B2 (en) | 2015-07-30 | 2020-04-28 | Jsp Corporation | Expanded polylactic acid resin beads and molded article of expanded polylactic acid resin beads |
JP2021512992A (ja) * | 2018-12-12 | 2021-05-20 | ヒューヴィス コーポレーションHuvis Corporation | 低融点樹脂を含む発泡体およびこれを含む成形体 |
JP7132342B2 (ja) | 2018-12-12 | 2022-09-06 | ヒューヴィス コーポレーション | 低融点樹脂を含む発泡体およびこれを含む成形体 |
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JPWO2011145391A1 (ja) | 2013-07-22 |
US20130059154A1 (en) | 2013-03-07 |
KR20130092405A (ko) | 2013-08-20 |
EP2573133A1 (en) | 2013-03-27 |
TW201209089A (en) | 2012-03-01 |
KR101728195B1 (ko) | 2017-04-18 |
EP2573133A4 (en) | 2014-07-23 |
US9206296B2 (en) | 2015-12-08 |
BR112012029328A2 (pt) | 2016-07-26 |
JP5717204B2 (ja) | 2015-05-13 |
EP2573133B1 (en) | 2016-08-10 |
CN102884115B (zh) | 2015-04-22 |
CN102884115A (zh) | 2013-01-16 |
TWI513748B (zh) | 2015-12-21 |
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