JP4252570B2 - Pellet manufacturing method - Google Patents

Description

  The present invention relates to a method for producing pellets of a resin composition excellent in blocking resistance.

  General-purpose resins made from petroleum such as polypropylene and polyvinyl chloride are used in various fields such as household goods, household appliances, automobile parts, building materials, and food packaging because of their good processability and durability. Has been. However, these resin products have a disadvantage of good durability at the stage of finishing and discarding their functions, and are inferior in degradability in nature, and thus may affect the ecosystem.

  In order to solve such problems, thermoplastic resins and biodegradable resins include polylactic acid and copolymers of lactic acid and other aliphatic hydroxycarboxylic acids, aliphatic polyhydric alcohols and aliphatic polycarboxylic acids. Biodegradable resin compositions such as aliphatic polyesters derived from have been developed.

  Among these biodegradable resin compositions, polylactic acid resins are made from saccharides obtained from corn, straw, etc., and L-lactic acid is produced in large quantities by fermentation. Because of its extremely low carbon emissions, it is expected as an alternative to general-purpose resins made from petroleum.

  In addition, it has been used in the field of hard molded products because of its high rigidity and good transparency as a performance of polylactic acid resin, but when it is molded into a film or the like due to its brittleness, hardness, and lack of flexibility However, there were problems such as lack of flexibility and whitening when bent. In addition, a method for improving the heat resistance and the like by crystallizing polylactic acid by adding a crystal nucleating agent such as talc (Patent Document 1) has been proposed. However, when molding by injection, in order to crystallize polylactic acid in a short time, it was necessary to add a large amount of a crystal nucleating agent such as talc and to perform heat treatment at a mold temperature of 100 ° C. or higher.

  Various methods for adding a plasticizer have been proposed in order to adapt to the field of soft and semi-rigid molded products. For example, a technique of adding a plasticizer such as tributyl acetylcitrate or diglycerin tetraacetate is disclosed. When these plasticizers are added to polylactic acid and a film or sheet is formed by extrusion or the like, good flexibility is obtained, but because the resin is in an amorphous state, flexibility due to temperature changes near the glass transition point is obtained. The property changes markedly (temperature sensitivity) and the heat resistance at high temperatures is insufficient, so that the physical properties change significantly depending on the season, making it difficult to use in a high temperature environment.

On the other hand, when producing compound pellets for obtaining the above molded product, after melt-kneading in the polylactic acid resin, the strand-like melt is extruded from a die of a kneader, cooled with water, and then pelletized by a cutter device. The method of using after drying with the dryer which has a stirring function is taken. However, when drying at about 80 ° C with a dryer (hopper dryer) that does not have a stirring function, the polylactic acid resin is amorphous, so the pellets block in the apparatus and cannot be removed from the dryer. Will occur. In addition, there has been proposed a method (Patent Document 2) in which a composition obtained by adding a lubricant or a lubricant and a filler such as calcium carbonate to a polylactic acid resin is pelletized by hot cutting. However, when molding the obtained pellets by injection, it is necessary to add a large amount of a crystal nucleating agent such as talc in order to crystallize polylactic acid in a short time, and to perform heat treatment at a mold temperature of 100 ° C. or higher. there were. Moreover, in these compositions, the method of extruding a strand-like melt from a die of a kneader, cooling it with water, and then pelletizing it with a cutter device caused the same problems as with only a polylactic acid resin.
Japanese Patent No. 3410075 JP 2004-352844 A

  The subject of this invention is providing the method of manufacturing the pellet excellent in blocking resistance from the resin composition excellent in the crystallinity of polylactic acid-type resin.

The present invention is a method for producing pellets from a resin composition containing a polylactic acid-based resin, a plasticizer and a crystal nucleating agent, and comprising the following steps (1), (2) and (3) Provide manufacturing method.
Step (1): Melting and kneading the resin composition with a kneader, and extruding the strand from the die of the kneader Step (2): The strand extruded from the die of the kneader is placed in a liquid medium at 40 ° C. or less to reach 0. Step (3) of cooling for 5 to 5 seconds: Step (3a) of holding the strand cooled in step (2) in an atmosphere of 40 ° C. or lower for at least 10 seconds and / or in an atmosphere of 70 to 90 ° C. or a liquid medium Holding for at least 3 seconds (3b)

  According to the production method of the present invention, pellets of a crystallized resin composition can be efficiently obtained in a short time. Moreover, the pellets obtained by the production method of the present invention are excellent in blocking resistance, and can be efficiently dried even in a dryer having no stirring function during drying.

[Polylactic acid resin]
The polylactic acid resin used in the present invention has biodegradability based on JIS K6953 (ISO 14855) “Aerobic and ultimate biodegradation and disintegration tests under controlled aerobic compost conditions”. The polyester resin which has is preferable.

  Here, the polylactic acid resin is polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid. Examples of the hydroxycarboxylic acid include glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxypentanoic acid, hydroxycaproic acid, hydroxyheptanoic acid and the like, and glycolic acid and hydroxycaproic acid are preferable. A preferred molecular structure of polylactic acid is composed of 20 to 100 mol% of either L-lactic acid or D-lactic acid and 0 to 20 mol% of each enantiomer. The copolymer of lactic acid and hydroxycarboxylic acid is composed of 85 to 100 mol% of either L-lactic acid or D-lactic acid and 0 to 15 mol% of hydroxycarboxylic acid units. These polylactic acid-based resins can be obtained by dehydrating polycondensation using L-lactic acid, D-lactic acid, and hydroxycarboxylic acid as a raw material by selecting one having a required structure. Preferably, it can be obtained by ring-opening polymerization by selecting a desired structure from lactide, which is a cyclic dimer of lactic acid, glycolide, which is a cyclic dimer of glycolic acid, and caprolactone. Lactide includes L-lactide which is a cyclic dimer of L-lactic acid, D-lactide which is a cyclic dimer of D-lactic acid, meso-lactide obtained by cyclic dimerization of D-lactic acid and L-lactic acid, and D-lactide. There is DL-lactide, which is a racemic mixture of lactide and L-lactide. Any lactide can be used in the present invention. However, the main raw material is preferably D-lactide or L-lactide.

  Examples of commercially available polylactic acid-based resins include Cargill Dow Polymers, Inc., trade name: Nature works; Mitsui Chemicals, Inc., trade name: Raisia; Kanebo Gosei Co., Ltd., trade name: Lactron; Ink Chemical Industry Co., Ltd., trade name: Puramate; Toyobo Co., Ltd., trade name: Viro Ecole; Toyota Motor Corporation, Eco Plastic, etc.

[Plasticizer]
The plasticizer used in the present invention is not particularly limited and includes plasticizers used for general biodegradable resins. From the viewpoint of promoting crystallization of polylactic acid-based resins, two or more in the molecule. A compound having an ester group of 2 to 9, particularly 3 to 9 is preferable. Examples of such compounds include esters of polyvalent carboxylic acids and polyethylene glycol monoalkyl ethers, alkyl ether esters of polyhydric alcohols, and the like.

  The average molecular weight of the plasticizer used in the present invention is preferably from 250 to 700, more preferably from 300 to 600, still more preferably from 350 to 550, particularly preferably from the viewpoint of bleed resistance and volatile resistance. Is 400-500. The average molecular weight can be obtained by calculating the saponification value by the method described in JIS K0070 and calculating from the following formula.

    Average molecular weight = 56108 × (number of ester groups) / saponification value

  Among such plasticizers, from the viewpoint of excellent moldability and impact resistance of the resin composition, an ester of succinic acid and polyethylene glycol monomethyl ether having an average added mole number of ethylene oxide of 2 to 4, adipic acid and Esters with polyethylene glycol monomethyl ether having an average addition mole number of ethylene oxide of 2-3, esters of polyethylene glycol monomethyl ether with 1,3,6-hexanetricarboxylic acid and ethylene oxide having an average addition mole number of 2-3, etc. Ester of polyvalent carboxylic acid and polyethylene glycol monomethyl ether; ester of acetic acid and glycerin in an average of 3 to 9 moles of ethylene oxide adduct, ester of acetic acid and ethylene oxide in an average of 4 to 9 moles of polyethylene glycol Multivalent alcohol such as Alkyl ether esters are more preferred. From the viewpoint of excellent moldability of the resin composition, impact resistance and bleed resistance of the plasticizer, an ester of succinic acid and ethylene oxide with polyethylene glycol monomethyl ether having an average addition mole number of 2-3, adipic acid and diethylene glycol monomethyl Esters with ether, esters with 1,3,6-hexanetricarboxylic acid and diethylene glycol monomethyl ether, esters with acetic acid and glycerin in average 3 to 6 mol of ethylene oxide adducts, and average added moles of acetic acid and ethylene oxide in 4 Even more preferred are esters of ~ 6 with polyethylene glycol. From the viewpoint of moldability of resin composition, impact resistance and bleed resistance of plasticizer, volatilization resistance and irritating odor, esters of succinic acid and triethylene glycol monomethyl ether, ethylene oxide average of acetic acid and glycerin 3 Particularly preferred are esters with 6 molar adducts. These plasticizers may be used alone or in combination of two or more.

  In addition, it is preferable that the ester of this invention is all the esterified saturated ester from a viewpoint of fully exhibiting the function as a plasticizer.

  The reason why the effect of the present invention is improved by the plasticizer is not clear, but the plasticizer has two or more ester groups in the molecule, and an average added mole number of ethylene oxide of 2 to 9 (further It preferably has a methyl group, and preferably has two or more.) The heat resistance and the compatibility with the polylactic acid resin are good. Therefore, the bleed resistance is improved and the softening effect of the polylactic acid resin is also improved. By improving the softening of the polylactic acid-based resin, it is considered that the growth rate is also improved when the polylactic acid-based resin is crystallized. As a result, by performing the step (2) and the step (3) according to the present invention, the crystallization of the strand extruded from the die of the kneader proceeds within 60 seconds, and a pellet excellent in blocking resistance is obtained. it is conceivable that.

[Crystal nucleating agent]
In the present invention, as the crystal nucleating agent, at least one selected from the group consisting of an organic nucleating agent and an inorganic nucleating agent can be used.
The organic nucleating agent used in the present invention is preferably a compound having a hydroxyl group and an amide group in the organic nucleating agent molecule from the viewpoint of crystallization promotion of the polylactic acid resin and the bloom resistance of the organic nucleating agent. More preferably, it is an aliphatic compound having at least two and having at least two amide groups. The melting point of the organic nucleating agent is preferably 65 ° C or higher, more preferably 70 ° C to 220 ° C, and still more preferably 80 to 190 ° C.

  The reason why the effect of the present invention is improved by the organic nucleating agent is not clear, but if it has two or more of the above functional groups, the interaction with the polylactic acid resin is improved and the compatibility is improved. It is thought that it is caused by fine dispersion in the resin. Probably by having one or more, preferably two or more hydroxyl groups, the dispersibility in the polylactic acid resin is improved, and one or more amide groups, preferably two. By having two or more, it is considered that the compatibility with the polylactic acid resin is improved. When the melting point of the crystal nucleating agent is higher than the heat treatment temperature of the strand and not more than the kneading temperature of the resin composition, the dispersibility is improved by dissolving the crystal nucleating agent at the time of kneading. Since stabilization and heat processing temperature can be raised, it is preferable also from the viewpoint of improving the crystallization speed of the polylactic acid resin. The preferred crystal nucleating agent is considered to precipitate a large number of fine crystals quickly in the cooling process from the resin melt state, and is also preferable from the viewpoint of improving transparency and crystallization speed.

  Examples of the organic nucleating agent used in the present invention include hydroxy fatty acid monoamides such as 12-hydroxy stearic acid monoethanolamide, methylene bis 12-hydroxy stearic acid amide, ethylene bis 12-hydroxy stearic acid amide, hexamethylene bis 12-hydroxy stearic acid. And hydroxy fatty acid bisamides such as amides. From the viewpoint of crystallization promotion of polylactic acid resin and bloom resistance of organic nucleating agent, ethylene bis 12-hydroxystearic acid amide and hexamethylene bis 12-hydroxystearic acid amide are preferable.

  Examples of the inorganic nucleating agent used in the present invention include silicates such as talc, smectite, kaolin, mica, and montmorillonite, silica, and inorganic compounds such as magnesium oxide. From the viewpoint of dispersibility, the average particle size is 0.1. An inorganic compound of ˜20 μm is preferable, and 0.1 to 10 μm is more preferable. Among the inorganic compounds, silicate is preferable and talc is more preferable from the viewpoint of promoting crystallization of the polylactic acid resin.

[Resin composition]
The resin composition of the present invention contains a polylactic acid resin, a plasticizer, and a crystal nucleating agent. As a particularly preferred combination of the polylactic acid resin, plasticizer, and crystal nucleating agent (organic nucleating agent and / or inorganic nucleating agent) in the resin composition of the present invention, the polylactic acid resin is polylactic acid, and the plasticizer is succinic acid. An ester with triethylene glycol monomethyl ether, the organic nucleating agent is at least one selected from ethylene bis 12-hydroxystearic acid amide and hexamethylene bis 12-hydroxystearic acid amide, and the inorganic nucleating agent is talc.

  As described above, the resin composition has the effects of the present invention by containing a polylactic acid resin, a plasticizer, and a crystal nucleating agent. Therefore, even if the plasticizer or crystal nucleating agent is added alone to a polylactic acid resin, particularly polylactic acid, the effect of the present invention cannot be obtained.

The content of the polylactic acid resin in the resin composition of the present invention is preferably 50% by weight or more, more preferably 60% by weight or more, and still more preferably from the viewpoint of achieving the object of the present invention. 70% by weight or more.
The content of the plasticizer in the resin composition of the present invention is preferably 5 to 60 parts by weight, and 7 to 50 parts by weight with respect to 100 parts by weight of the polylactic acid resin from the viewpoint of obtaining bleeding resistance and a sufficient crystallization rate. Part is more preferable, and 10 to 40 parts by weight is further preferable.
When an organic nucleating agent is used as the crystal nucleating agent, the content of the organic nucleating agent in the resin composition of the present invention is preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the polylactic acid resin, and 0.3 to 3 parts by weight is more preferable, and 0.5 to 2 parts by weight is particularly preferable.
When an inorganic nucleating agent is used as the crystal nucleating agent, the content of the inorganic nucleating agent in the resin composition of the present invention is preferably 0.1 to 150 parts by weight with respect to 100 parts by weight of the polylactic acid resin, 100 parts by weight is more preferable, 0.3 to 50 parts by weight is still more preferable, and 0.5 to 20 parts by weight is particularly preferable.

  The resin composition can further contain a hydrolysis inhibitor in addition to the crystal nucleating agent and the plasticizer. Examples of the hydrolysis inhibitor include carbodiimide compounds such as polycarbodiimide compounds and monocarbodiimide compounds, and polycarbodiimide compounds are preferable from the viewpoint of moldability of the resin composition, and the heat resistance, impact resistance and organic nucleus of the resin composition are preferred. From the viewpoint of the bloom resistance of the agent, a monocarbodiimide compound is preferred.

  Examples of the polycarbodiimide compound include poly (4,4′-diphenylmethanecarbodiimide), poly (4,4′-dicyclohexylmethanecarbodiimide), poly (1,3,5-triisopropylbenzene) polycarbodiimide, and poly (1,3,5). -Triisopropylbenzene and 1,5-diisopropylbenzene) polycarbodiimide and the like, and examples of the monocarbodiimide compound include N, N'-di-2,6-diisopropylphenylcarbodiimide.

The carbodiimide compounds may be used alone or in combination of two or more in order to satisfy the moldability, heat resistance, impact resistance and bloom resistance of the organic nucleating agent of the resin composition. Poly (4,4′-dicyclohexylmethanecarbodiimide) is obtained from carbodilite LA-1 (manufactured by Nisshinbo Co., Ltd.), poly (1,3,5-triisopropylbenzene) polycarbodiimide and poly (1,3,5). -Triisopropylbenzene and 1,5-diisopropylbenzene) polycarbodiimide are stabuxol P and stabuxol P-100 (Rhein Chemie), N, N'-di-2,6-diisopropylphenylcarbodiimide is stabuxol 1 (Rhein Chemie) Can be purchased and used.
The content of the hydrolysis inhibitor in the resin composition is preferably 0.05 to 7 parts by weight with respect to 100 parts by weight of the polylactic acid resin from the viewpoint of promoting crystallization of the polylactic acid resin. Part by weight is more preferable, and 0.5 to 4 parts by weight is particularly preferable.

  The resin composition includes an aliphatic polyester such as polybutylene succinate, polybutylene succinate / adipate or polyethylene succinate as a resin component other than polylactic acid; polybutylene succinate / terephthalate, polybutylene adipate / terephthalate or poly Aliphatic aromatic copolyesters such as tetramethylene adipate / terephthalate can be contained as long as the object of the present invention is not hindered.

  In addition to the above, the resin composition may further contain other components such as a hindered phenol or phosphite antioxidant, or a hydrocarbon wax or a lubricant that is an anionic surfactant. The content of each of the antioxidant and the lubricant is preferably 0.05 to 3 parts by weight, more preferably 0.1 to 2 parts by weight with respect to 100 parts by weight of the polylactic acid resin.

  The resin composition includes an antistatic agent, an antifogging agent, a light stabilizer, an ultraviolet absorber, a pigment, an inorganic filler, an antifungal agent, an antibacterial agent, a foaming agent, a flame retardant, and the like as components other than the above. It can contain in the range which does not prevent achievement of the objective of this invention.

[Method for producing pellet of resin composition]
The manufacturing method of the pellet of the resin composition of this invention is a method which has the said process (1), a process (2), and a process (3).

  In the step (1), the resin composition is preferably melt-kneaded at a melting point (Tm) or higher of the polylactic acid resin. Specific examples of the melt-kneading can be performed by an ordinary method, for example, the above-mentioned plasticizer, organic nucleating agent and / or inorganic nucleating agent while melting the polylactic acid resin using a twin screw extruder or the like. And a method of kneading using a metering pump. When the production amount is small, the polylactic acid resin and the organic nucleating agent and / or the inorganic nucleating agent may be dry blended and then melted simultaneously. As a method for uniformly dry blending, a ribbon blender, a hensil mixer, a tumbler mixer, or an air blender can be used. From the viewpoint of dispersibility of the plasticizer, organic nucleating agent and / or inorganic nucleating agent, the melt kneading temperature is preferably not less than the melting point (Tm) of the polylactic acid resin, more preferably in the range of Tm to Tm + 100 ° C. More preferably, it is the range of Tm-Tm + 50 degreeC. For example, when the polylactic acid resin is polylactic acid, the temperature is preferably 170 to 240 ° C, more preferably 170 to 220 ° C. Moreover, when melt-kneading using a biaxial extruder etc., the temperature of die | dye has the preferable range of 140-170 degreeC from a viewpoint of stability of the strand extruded.

  In addition, melting | fusing point (Tm) of polylactic acid-type resin is a value calculated | required from the crystal melting endothermic peak temperature by the temperature rising method of the differential scanning calorimetry (DSC) based on JIS-K7121.

  As specific examples of step (2) and step (3) of the present invention, a strand extruded from a die such as a twin-screw extruder is rapidly cooled with a liquid medium of 40 ° C. or less stored in a water tank or the like [step (2)]. And immediately crystallize the strand by preheating in an atmosphere of 40 ° C. or lower (step (3a)), and then cut the pellet to obtain pellets, and the strand extruded from a die such as a twin screw extruder, a water tank, etc. The strand is rapidly cooled with a liquid medium of 40 ° C. or less (step (2)) and immediately kept in an atmosphere of 70 to 90 ° C. (preferably 70 to 80 ° C.) or in a liquid medium to crystallize the strand [step ( 3b)], and then a method of cutting to obtain pellets, a strand extruded from a die such as a twin-screw extruder, etc., and rapidly cooling with a liquid medium of 40 ° C. or less stored in a water tank or the like [step (2)], Immediately due to residual heat in an atmosphere of 40 ° C or less The strand is crystallized [step (3a)], and held in an atmosphere of 70 to 90 ° C. (preferably 70 to 80 ° C.) or in a liquid medium for crystallization (step (3b)) and then cut. (In the case where the step (3a) and the step (3b) are performed simultaneously, the order may be either).

The temperature of the liquid medium in step (2) and step (3b) can be determined by measuring the liquid medium in a place that is not extremely affected by the heat of the strand extruded from the die with an alcohol thermometer or the like. For example, it is preferable to measure the temperature of the liquid medium at a distance of 5 cm or more from the strand with an alcohol thermometer or the like.
The temperature in the atmosphere of the step (3a) can be obtained by measuring the temperature of the room in which the device is placed with an alcohol thermometer or the like. For example, it is preferable to measure the temperature 1-5 cm away from the strand with an alcohol thermometer or the like.
The temperature in the atmosphere of the step (3b) can be determined, for example, by measuring the temperature in a tunnel in which a hot air device or an infrared heater is mounted with an alcohol thermometer or the like, and is about 1 to 2 cm away from the strand. It is preferable to measure the temperature with an alcohol thermometer or the like.

From the viewpoint of promoting crystallization of the polylactic acid-based resin and obtaining pellets excellent in blocking resistance, the strand cooling time in the step (2) is 0.5 to 5 seconds, and preferably 1 to 3 seconds.
In the step (3), in the case of only the step (3a), the holding time of the step (3a) is at least 10 seconds, and the crystallization of the polylactic acid resin is promoted to obtain a pellet excellent in blocking resistance. And from a viewpoint of productivity, 10 to 30 seconds are preferable, and 15 to 30 seconds are more preferable.
In the step (3), when only the step (3b) is used, the holding time of the step (3b) is at least 3 seconds, and the crystallization of the polylactic acid-based resin is promoted to obtain pellets excellent in blocking resistance. And from a viewpoint of productivity, 3 to 20 seconds are preferable, and 10 to 20 seconds are more preferable.
In the step (3), when the step (3a) and the step (3b) are performed, the holding time of the step (3a) is at least 10 seconds, and the holding time of the step (3b) is at least 3 seconds. From the viewpoint of promoting crystallization of the polylactic acid-based resin and obtaining pellets excellent in blocking resistance and from the viewpoint of productivity, the holding time in the step (3a) is preferably 10 to 30 seconds, more preferably 15 to 30 seconds. The holding time in the step (3b) is preferably 3 to 10 seconds, and more preferably 5 to 10 seconds.
The strand diameter is preferably 2 mm to 5 mm from the viewpoint of productivity.

  Moreover, the temperature which cools the strand in a process (2) with a liquid medium is 40 degrees C or less from a viewpoint of the ease of taking-out of a strand, and crystallization promotion of a polylactic acid-type resin, and 5-30 degreeC is preferable, 10-10 25 degreeC is more preferable and 15-25 degreeC is further more preferable. In the step (3), the temperature in the atmosphere in the step (3a) is 40 ° C. or less, preferably 5 to 40 ° C., more preferably 10 to 40 ° C., from the viewpoint of promoting crystallization of the polylactic acid resin. More preferably, -40 ° C. The temperature maintained in the atmosphere or liquid medium in the step (3b) is 70 to 90 ° C., and preferably 70 to 80 ° C. from the viewpoint of promoting crystallization of the polylactic acid resin.

In addition, as a means to hold | maintain in the atmosphere of a process (3b), it can carry out by allowing a strand to pass through the tunnel in which the hot air apparatus and the infrared heater were mounted | worn inside, for example. The holding means in the step (3b) is preferably performed in a liquid medium from the viewpoint of thermal efficiency.
The liquid medium used in step (2) and step (3b) is preferably a low-viscosity liquid having a boiling point of 100 ° C. or higher, such as water, ethylene glycol, or silicon oil, from the viewpoint of safety and handleability. Water is more preferred. The temperature of the liquid medium is preferably maintained stably by, for example, circulating the liquid medium with a temperature control device.

  In the production method of the present invention, the presence or absence of crystallization of the pellet can be confirmed using a differential scanning calorimetry (DSC) apparatus. The pellet is finely cut, 15 mg is weighed in an aluminum pan, and measured from room temperature to 200 ° C. at a temperature increase rate of 8 ° C./min. At that time, if an exothermic peak of cold crystallization is observed, the pellet is amorphous, and if not observed, the pellet is crystallized. Furthermore, the temperature is measured from 200 ° C. to room temperature at a rate of 5 ° C./min. At that time, an exothermic peak of melt crystallization is observed, and it is confirmed that the pellet is crystalline.

  The resin compositions used in the following examples and comparative examples are shown together in Table 1.

* 1 Polylactic acid resin; manufactured by Mitsui Chemicals, LACEA H-400
* 2 Plasticizer: Diester of succinic acid and triethylene glycol monomethyl ether
* 3 Organic nucleating agent: Ethylene bis 12-hydroxystearic acid amide (Nippon Kasei Co., Ltd., SLIPAX H)
* 4 Inorganic nucleating agent: Nihon Talc Co., Ltd., Micro Ace P-6
* 5 Hydrolysis inhibitor; Nisshinbo product, Carbodilite LA-1
* 6 Organic nucleating agent: hexamethylene bis 12-hydroxystearic acid amide (Nihon Kasei Co., Ltd., Sripacks ZHH)
* 7 Plasticizer: Acetic acid ester of 6 mol adduct of glycerin with ethylene oxide
* 8 Inorganic nucleating agent; Mizusawa Chemical Co., Ltd., Mizukacil P-526

Examples 1-7, Comparative Examples 1-7
Using a biaxial extruder [Berstorf ZE40A × 40D (screw diameter: 用 い 43 mm L / D = 37.2)], the polylactic acid resin and organic nucleating agent in the resin compositions (A to G) shown in Table 1 , Inorganic nucleating agent, hydrolysis inhibitor powder, etc. are dry blended in advance with a hensil mixer and charged into a hopper, and the plasticizer is melted and kneaded at a cylinder temperature of 160-170 ° C. by extrusion and extruded from a die. The processed strand (step (1)) having a diameter of 4 mm was processed under various conditions shown in Tables 2 and 3, and then cut to obtain pellets. In steps (2) and (3b), water was used as the liquid medium.

  Next, the presence or absence of crystallization of the pellets thus obtained, blocking resistance immediately after cutting, blocking resistance after 80 ° C. × 5 hours and bleeding resistance were evaluated by the following methods. These results are shown in Tables 2 and 3.

<Pellet crystallization>
The pellet is finely cut, 15 mg is weighed in an aluminum pan, and measured from room temperature to 200 ° C. at a temperature increase rate of 8 ° C./min. At that time, if an exothermic peak of cold crystallization is observed, the pellet is amorphous, and if not observed, the pellet is crystallized. At that time, the temperature is further decreased from 200 ° C. to room temperature at a rate of 5 ° C./min, and an exothermic peak of melt crystallization is observed to confirm that the pellet is crystalline.
The presence or absence of crystallization of the pellets was confirmed by the above method.

<Blocking resistance (immediately after cutting)>
About 5 kg of the pellet immediately after cutting the strand was stored in a net basket (30 cm × 30 cm × 30 cm), and it was confirmed whether or not blocking would be caused by the residual heat.
If the blocking resistance was good, it was rated as ◯, and if it was poor, it was marked as x.

<Blocking resistance (after 80 ° C. × 5 hours)>
About 5 kg of the obtained pellets were stored in a net basket (30 cm × 30 cm × 30 cm) and dried at 80 ° C. for 5 hours using a hot air dryer.
After drying, it was evaluated as ◯ if the blocking resistance was good, and x if it was poor.

<Bleed resistance (after 80 ° C x 5 hours)>
About 5 kg of the obtained pellets were stored in a net basket (30 cm × 30 cm × 30 cm) and dried at 80 ° C. for 5 hours using a hot air dryer.
After drying, if the bleed resistance derived from the plasticizer was good, it was rated as ◯, and if it was poor, it was marked as x.

  From the results shown in Table 2, the pellets produced by subjecting the strands extruded from the dies of the kneader after melt-kneading the resin compositions (A to G) to the steps (2) and (3) of the present invention were obtained. It crystallized and was excellent in blocking resistance and bleed resistance. On the other hand, from the results shown in Table 3, the pellets obtained by melt-kneading the resin compositions (A to G) and then treating the strands extruded from the dies of the kneader with only conventional water cooling are in an amorphous state and are resistant to blocking. It was inferior in nature.

Examples 8-11, Comparative Examples 8-10
Using a biaxial extruder [Berstorf ZE40A × 40D (screw diameter: Ф 43 mm L / D = 37.2)], the polylactic acid resin and organic nucleating agent in the resin composition (H to N) shown in Table 1 , Inorganic nucleating agent, hydrolysis inhibitor powder, etc. are dry blended in advance with a hensil mixer and charged into a hopper, and the plasticizer is melted and kneaded at a cylinder temperature of 160-170 ° C. by extrusion and extruded from a die. The processed strand (step (1)) having a diameter of 4 mm was processed under various conditions shown in Table 4, and then cut to obtain pellets. In steps (2) and (3b), water was used as the liquid medium.

  Next, the presence or absence of crystallization of the pellets thus obtained, blocking resistance immediately after cutting, blocking resistance after 80 ° C. × 5 hours and bleeding resistance were evaluated in the same manner as in Examples 1 to 7. . These results are shown in Table 4.

  From the results of Table 4, the pellets produced from the resin composition (H to K) of the present invention through the steps (1) to (3) of the present invention are crystallized and have excellent blocking resistance and bleed resistance. Met. On the other hand, the pellets produced through the steps (1) to (3) of the present invention from the comparative resin composition (L to N) containing no plasticizer or crystal nucleating agent are in an amorphous state and have a blocking resistance. It was inferior.

From the above results, when pellets are produced by the method of the present invention from a resin composition containing a polylactic acid resin, a plasticizer, and a crystal nucleating agent, the crystallized pellets can be efficiently obtained. It turns out that it is excellent in blocking property and does not need to use the special dryer which has a stirring function in the case of drying.

Claims (6)

A method for producing pellets from a resin composition containing a polylactic acid-based resin, a plasticizer and a crystal nucleating agent, comprising the following steps (1), (2) and (3).
Step (1): The resin composition was melt-kneaded with a kneading machine, process step (2) for extruding a strand from a die kneader: 2 from die kneader in extruded liquid medium 40 ° C. below the strand ~ Step (3) of cooling for 5 seconds: Step (3a) of holding the strand cooled in step (2) in an atmosphere of 40 ° C. or lower for at least 10 seconds and / or in an atmosphere of 70 to 90 ° C. or in a liquid medium Holding for at least 3 seconds (3b)   The manufacturing method according to claim 1, wherein the strand has a diameter of 2 to 5 mm.   The production method according to claim 1 or 2, wherein the plasticizer is a compound having 2 or more ester groups in the molecule and an average added mole number of ethylene oxide of 2 to 9.   The method according to claim 1, wherein the crystal nucleating agent is at least one selected from the group consisting of an organic nucleating agent and an inorganic nucleating agent.   The process according to claim 4, wherein the organic nucleating agent is a compound having a hydroxyl group and an amide group in the molecule. The content of the plasticizer is 5 to 60 parts by weight, the content of the organic nucleating agent is 0.1 to 5 parts by weight and / or the content of the inorganic nucleating agent is 0.1 to 100 parts by weight of the polylactic acid resin. The manufacturing method in any one of Claims 1-5 which is 150 weight part.