Polylactic acid resin composition

Abstract

A polylactic acid resin composition according to the present invention is configured by dynamically crosslinking a resin mixture containing a polylactic acid-based resin and cis-polyisoprene. The content of the polylactic acid-based resin is 280-950 parts by mass per 100 parts by mass of the cis-polyisoprene. The polylactic acid resin composition according to the present invention can be used in a wide range of usages, for example, molded products for automobiles, molded products for electrical products, molded products for agricultural materials, molded products for office use and molded products for daily necessities.

Description

[Technical Field]

[0001] The present invention relates to a polylactic acid resin composition, and more particularly to a polylactic acid resin composition with improved impact resistance. [Background technology]

[0002] Traditionally, polylactic acid (PLA), a type of bioplastic, has been widely used in various fields such as medical materials and agricultural materials. However, PLA itself has limitations in its applications due to its low impact resistance and flexibility, and improvements as a resin composition by using additives are desired. For example, in order to be used in automotive parts and components for home appliances, it is necessary to improve impact resistance and flexibility, as well as to possess thermoplastic properties.

[0003] On the other hand, copolymerization or alloying of polylactic acid, as well as the use of additives such as rubber, have been proposed to improve the impact resistance and flexibility of polylactic acid. However, most of the materials used in these processes are petroleum-derived products, raising concerns that they may compromise the biomass-derived characteristics of polylactic acid.

[0004] In response to this, polymer blends created by compounding polylactic acid with natural rubber have been proposed to improve the impact resistance and flexibility of polylactic acid using biomass-derived materials.

[0005] However, in such polymer blends, if the constituent polymers are incompatible with each other, the physical properties may not improve as designed. Therefore, it is considered important to devise ways to improve the interfacial affinity between polymers.

[0006] For example, resin compositions containing natural rubber such as epoxidized natural rubber and carbodiimide compounds in addition to polylactic acid have been reported with the aim of improving the impact resistance of polylactic acid (Patent Documents 1 and 2). However, these are unsuitable for industrial production due to poor working conditions and other reasons.

[0007] Furthermore, methods have been proposed to improve impact resistance by dynamically crosslinking natural rubber or Eucommia elastomer using peroxides (Patent Document 3 and Non-Patent Document 1). However, the presence of these peroxides can degrade other physical properties of polylactic acid. Moreover, the polylactic acid resin composition obtained by dynamic crosslinking polylactic acid and Eucommia elastomer in the presence of peroxides does not show a significant improvement in impact resistance, only slightly exceeding that of ABS. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2012-219151 [Patent Document 2] Japanese Patent Publication No. 2011-241317 [Patent Document 3] Japanese Patent Publication No. 2017-115041 [Non-patent literature]

[0009] [Non-Patent Document 1] Yukun Chen et al., ACS Appl. Mater. Interfaces 2014, 6, 3811-3816. [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The present invention aims to solve the above-mentioned problems, and its objective is to provide a polylactic acid resin composition that can improve impact resistance while taking advantage of the biomass-derived characteristics of polylactic acid. [Means for solving the problem]

[0011] The present invention relates to a polylactic acid resin composition, It is constructed by dynamically crosslinking a resin mixture containing polylactic acid resin and cis-type polyisoprene. The polylactic acid resin composition is such that the content of the polylactic acid resin is 280 to 950 parts by mass with respect to 100 parts by mass of the cis-type polyisoprene.

[0012] In one embodiment, the content of the polylactic acid resin is 290 to 570 parts by mass with respect to 100 parts by mass of the cis-type polyisoprene.

[0013] In one embodiment, the resin mixture further has the following formula (I):

[0014]

Chemical formula

[0015] (In formula (I), R 3 , R 2 and R 3 , and R 4 are each independently a group selected from the group consisting of a hydrogen atom and an optionally branched alkyl group having 1 to 8 carbon atoms).

[0016] In a further embodiment, R 1 , R 2 and R 3 in the above formula (I) are n-butyl groups, and R 4 is a hydrogen atom.

[0017] In one embodiment, the resin mixture further contains a crosslinking agent.

[0018] In a further embodiment, the crosslinking agent is selected from the group consisting of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and dicumyl peroxide.

[0019] The present invention also relates to a method for producing a polylactic acid resin composition, a step of mixing a polylactic acid resin and a cis-type polyisoprene to obtain a resin mixture; and a step of heat-kneading the resin mixture to dynamically crosslink the resin mixture; It includes, The method involves a polylactic acid resin content of 280 to 950 parts by mass per 100 parts by mass of cis-type polyisoprene.

[0020] In one embodiment, the content of the polylactic acid resin is 290 to 720 parts by mass per 100 parts by mass of the cis-type polyisoprene.

[0021] The present invention also relates to a resin molded article containing the above-mentioned polylactic acid resin composition. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a resin composition with improved impact resistance compared to polylactic acid. The polylactic acid resin composition of the present invention also has thermoplastic properties, which makes it possible to provide a wide range of resin molded articles. Furthermore, the polylactic acid resin composition of the present invention can utilize readily available biomass-derived materials as constituent components, further enabling its application to industrial production processes. [Brief explanation of the drawing]

[0023] [Figure 1] These are scanning electron microscope (SEM) images showing the surface state of observation thin sections prepared from resin samples (E5), (E6), (E8), and (E9) obtained in Examples 5, 6, 8, and 9, as well as Comparative Example 1, and (C1). [Modes for carrying out the invention]

[0024] The present invention will be described in detail below.

[0025] (Polylactic acid resin composition) The polylactic acid resin composition of the present invention is constructed by dynamically crosslinking a resin mixture containing a polylactic acid-based resin and cis-type polyisoprene.

[0026] In the resin composition of the present invention, the polylactic acid-based resin constituting the resin mixture refers collectively to resins based on polylactic acid that are biodegradable (for example, those that can be decomposed by microorganisms in various natural environments such as soil, compost, freshwater, or seawater). Examples of polylactic acid-based resins include polymers and copolymers containing L-lactic acid and / or D-lactic acid as monomer units, and copolymers of L-lactic acid and / or D-lactic acid as monomer units with other organic acids such as glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, and 6-hydroxycaproic acid as other monomer units; and / or other alcohols such as vinyl alcohol and butanediol. When the polylactic acid-based resin contains the above-mentioned other monomer units, these other monomer units are preferably present in a proportion of 50 mol% or less, and more preferably in a proportion of 0.1 mol% to 50 mol%. In the present invention, for reasons of its versatility and ease of availability, the polylactic acid resin is preferably poly(L-lactic acid) composed of L-lactic acid as a monomer unit.

[0027] The weight-average molecular weight of the polylactic acid resin is preferably 10,000 to 1,000,000, more preferably 50,000 to 500,000. If the weight-average molecular weight of the polylactic acid resin is less than 10,000, the mechanical properties of the resulting polylactic acid resin composition may deteriorate, potentially impairing its versatility as a molded resin product. If the weight-average molecular weight of the polylactic acid resin is more than 1,000,000, the moldability of the resulting polylactic acid resin composition may deteriorate.

[0028] Polylactic acid resins may be obtained, for example, by ring-opening polymerization of lactide or dehydration condensation of L- and / or D-lactic acid, or by heating polymerization of L- and / or D-lactic acid under reduced pressure in a predetermined organic solvent such as diphenyl ether. Alternatively, polylactic acid resins may be produced from biomass using methods known to those skilled in the art. Biomass is not necessarily limited, but examples include plant materials such as corn, sweet potatoes, potatoes, and sugarcane, as well as combinations thereof.

[0029] The content of polylactic acid resin is set, for example, based on the content of cis-type polyisoprene, as described later. For example, if the content of cis-type polyisoprene is 100 parts by mass, the content of polylactic acid resin is preferably 280 to 950 parts by mass, more preferably 290 to 720 parts by mass, and even more preferably 350 to 570 parts by mass. If the content of polylactic acid resin is less than 280 parts by mass, the amount of polylactic acid resin contained in the resulting resin composition will be relatively lower compared to the amount of other components, which may deviate from the objective of providing a polylactic acid resin composition that is, for example, biomass-derived and has excellent biodegradability. If the content of polylactic acid resin exceeds 950 parts by mass, the amount of polylactic acid resin contained in the resulting resin composition will be relatively higher compared to the amount of other components, which may cause the resin composition to exhibit undesirable properties of polylactic acid resin (for example, reduced impact resistance or flexibility).

[0030] In the polylactic acid resin composition of the present invention, the cis-type polyisoprene constituting the resin mixture may be, for example, derived from biomass, chemically synthesized, or a combination thereof. For example, it is preferable that the cis-type polyisoprene is obtained from a biomass-derived material, as this allows for the provision of an environmentally friendly resin composition when combined with the polylactic acid resin. Furthermore, in the present invention, such cis-type polyisoprene may be chemically modified as appropriate with maleic anhydride groups, maleimide groups, epoxy groups, etc.

[0031] Biomass containing cis-type polyisoprene includes, for example, plant tissues composed of plant roots, stems (trunks), leaves, samaras (pericarps and seeds), and bark, as well as combinations thereof. Examples of plant bodies comprising these include, but are not limited to, Palaquim gutta. Cis-type polyisoprene can be obtained from such plant bodies using methods known in the art.

[0032] The number-average molecular weight (Mn) of cis-type polyisoprene is preferably 10,000 to 3,000,000, more preferably 15,000 to 1,000,000, and even more preferably 30,000 to 100,000.

[0033] The weight-average molecular weight (Mw) of cis-type polyisoprene is preferably 10,000 to 3,000,000, more preferably 15,000 to 1,000,000, and even more preferably 30,000 to 100,000.

[0034] In the polylactic acid resin composition of the present invention, the resin mixture may further contain trans polyisoprene in addition to the cis polyisoprene described above.

[0035] Trans-type polyisoprene may be derived from biomass, chemically synthesized, or a combination thereof. For example, it is preferable that the trans-type polyisoprene is obtained from biomass-derived materials, as it can be used in combination with the polylactic acid resin to provide an environmentally friendly resin composition. Furthermore, in the present invention, such trans-type polyisoprene may also be chemically modified as appropriate with maleic anhydride groups, maleimide groups, epoxy groups, etc.

[0036] Trans-type polyisoprene is abundantly contained in plant tissues such as roots, stems (trunks), leaves, samaras (fruit skins and seeds), and tree barks in plants such as Eucommia ulmoides Oliver and Mimusops balata, and can be obtained from the plant bodies by using methods known in the art.

[0037] The number average molecular weight (Mn) of trans-type polyisoprene is preferably 10,000 to 1,500,000, more preferably 50,000 to 1,500,000, and even more preferably 100,000 to 1,500,000.

[0038] The weight average molecular weight (Mw) of trans-type polyisoprene is preferably 1×10 3 ~5×10 6 [[ID=​​​​​​​​​​​​​​​Both cis-type and trans-type polyisoprene preferably have a particle form and exist in a state where they form a sea-island structure, finely dispersed in the matrix of the polylactic acid resin. The average particle size of cis-type and / or trans-type polyisoprene having such a particle form is preferably 0.1 μm to 100 μm, more preferably 0.1 μm to 10 μm. The impact resistance of the polylactic acid resin composition of the present invention containing cis-type and / or trans-type polyisoprene is improved by having particles that satisfy this average particle size range. The average particle size of cis-type and / or trans-type polyisoprene can be calculated, for example, by etching the cross-section of a sample piece made of the obtained polylactic acid resin composition with a solvent such as n-hexane to remove the polyisoprene particles present in the cross-section, surface-treating the resulting pores (corresponding to the particle size of cis-type and / or trans-type polyisoprene contained in the polyresin composition) using a sputtering method such as gold deposition, and then measuring the radius of the surface-treated pores through the field of view of an electron microscope image.

[0041] In the polylactic acid resin composition of the present invention, the resin mixture further comprises the following additive: Formula (I):

[0042] [ka]

[0043] (In formula (I), R 1 , R 2 and R 3 , and R 4 Each of these compounds independently contains a group (which is selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 8 carbon atoms, which may be branched).

[0044] The compound represented by formula (I) is a compound having a boiling point of 120°C to 250°C, preferably 125°C to 230°C, at 1 atmosphere (1 mm bar). Specific examples of compounds represented by formula (I) include triethyl citrate (TEC), tributyl citrate (TBC), tributyl o-acetylcitrate (ATBC), tris(2-ethylhexyl) o-acetylcitrate (ATEHC), and combinations thereof. The relationship between these specific compounds and their boiling points is shown in Table 1 below.

[0045] [Table 1]

[0046] Furthermore, in this invention, it is preferable that the auxiliary agent contains tributyl citrate (TBC) because it is readily available and can provide even better impact resistance to the resulting resin composition.

[0047] The content of the additive is preferably 3% to 30% by mass, more preferably 5% to 20% by mass, relative to the total polylactic acid resin composition. If the content of the additive is less than 3% by mass, the resulting resin composition may not have sufficient impact resistance. If the content of the additive exceeds 30% by mass, the impact resistance of the resulting resin composition will hardly change, which may be unproductive.

[0048] In the present invention, dynamic crosslinking of a resin mixture containing a polylactic acid resin and cis-type polyisoprene is performed, for example, by the resin mixture containing a suitable crosslinking agent.

[0049] The polylactic acid resin and cis-type polyisoprene described above are inherently incompatible with each other even when simply blended. However, these two components can be made compatible by dynamic crosslinking in the presence of an appropriate crosslinking agent.

[0050] The crosslinking agent that can be used in the polylactic acid resin composition of the present invention is pre-blended in the resin mixture together with the polylactic acid resin and cis-type polyisoprene. By dynamically crosslinking such a resin mixture, the resulting resin composition can be provided with superior physical properties (e.g., impact resistance) compared to an uncrosslinked resin.

[0051] Examples of crosslinking agents include organic peroxides (e.g., 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and dicumyl peroxide, and combinations thereof); sulfur; organosulfur compounds; organonitroso compounds (e.g., aromatic nitroso compounds); oxime compounds; metal oxides (e.g., zinc oxide and magnesium oxide, and combinations thereof); polyamines; metalloids and their compounds (e.g., metalloids such as selenium and tellurium, and their compounds, and combinations thereof); resin crosslinking agents (e.g., alkylphenol formaldehyde resins and brominated alkylphenol formaldehyde resins, and combinations thereof); organoorganosiloxane compounds having two or more SiH groups in the molecule; and combinations thereof. For example, it is preferable to use organic peroxides as crosslinking agents for the following reasons: they prevent a decrease in the mechanical properties of the resin composition itself due to the decomposition of polylactic acid resins and cis-type polyisoprene during crosslinking; they do not particularly require large-scale equipment for crosslinking; and they are readily available as reagents and materials for industrial production.

[0052] The crosslinking agent content can preferably be set based on the cis-type polyisoprene content. In the present invention, for example, if the cis-type polyisoprene content is 100 parts by mass, the crosslinking agent content is preferably 0.3 to 50 parts by mass, more preferably 2.8 to 48 parts by mass, and even more preferably 4 to 45 parts by mass. If the crosslinking agent content is less than 0.3 parts by mass, it becomes difficult to perform appropriate dynamic crosslinking in the resulting resin composition, and satisfactory impact resistance may not be provided. If the crosslinking agent content exceeds 50 parts by mass, the dynamic crosslinking formed in the resulting resin composition becomes so-called over-crosslinking, which strongly constrains each constituent molecule, and may worsen the moldability of the resin composition itself.

[0053] The polylactic acid resin composition of the present invention may further contain other additive materials as needed. Examples of other additive materials include fillers, nucleating agents, plasticizers, vulcanization accelerators, antioxidants, and flexibility imparters, as well as combinations thereof.

[0054] Examples of fillers, though not limited to them, include cellulose powder, carbon black, silica, talc, and titanium dioxide, as well as combinations thereof.

[0055] The nucleating agent is not particularly limited as long as it can promote the crystallization of the polylactic acid resin, and either an inorganic or organic nucleating agent can be used. The nucleating agent is preferably organic, and more preferably, examples include a homopolymer containing lactic acid (units) with a different chirality from the polylactic acid resin as monomer units, and a copolymer containing the lactic acid units and other monomer units (for example, polysaccharides such as starch and glucomannan, monosaccharides such as glucose, disaccharides such as sucrose and maltose, and oligosaccharides such as cyclodextrin).

[0056] The plasticizers, vulcanization accelerators, and antioxidants are not particularly limited, and commercially available ones may be used, for example.

[0057] Examples of flexibility-imparting agents, though not limited to them, include polycaprolactone.

[0058] The content of other additives is not particularly limited, and any amount can be selected by those skilled in the art, taking into consideration the content of the polylactic acid resin, polyisoprene, and auxiliary agents.

[0059] The polylactic acid resin composition of the present invention is constructed by dynamically crosslinking a resin mixture containing a polylactic acid resin, cis-type polyisoprene, and optionally trans-type polyisoprene, auxiliary agents, crosslinking agents and / or other additive materials.

[0060] Herein, the term "dynamic crosslinking" as used herein refers to the formation of a crosslinked structure of cis-type polyisoprene obtained by kneading a resin mixture, specifically the fine dispersion of crosslinked cis-type polyisoprene in the resin composition due to shear force during kneading, resulting from the reaction of cis-type polyisoprene with a crosslinking agent. Such dynamic crosslinking in a resin composition can be easily altered by those skilled in the art, for example, by varying the conditions in the kneading process described later.

[0061] The polylactic acid resin composition of the present invention has a sea-island structure in which cis-type polyisoprene is finely dispersed in the matrix of the polylactic acid resin, and exhibits improved impact resistance compared to polylactic acid resin alone. As a result, the polylactic acid resin composition of the present invention can be used in various resin molded products (for example, molded products for automobiles, molded products for electrical products, molded products for agricultural materials, molded products for office use, and molded products for daily necessities) that were difficult to manufacture using conventional polylactic acid resin alone due to its lack of impact resistance, etc.

[0062] (Method for producing polylactic acid resin composition) In the production of the polylactic acid resin composition of the present invention, first, the above-mentioned polylactic acid resin and cis-type polyisoprene, along with trans-type polyisoprene, auxiliary agents, crosslinking agents and / or other additive materials as needed, are mixed to form a resin mixture.

[0063] In obtaining a resin mixture, polylactic acid resin, cis-type polyisoprene, trans-type polyisoprene, auxiliary agents, crosslinking agents, and other additives can be mixed in various orders. In one embodiment, the polylactic acid resin and cis-type polyisoprene are pre-mixed and kneaded at a predetermined temperature, and then a crosslinking agent is added to this mixture to form a resin mixture (in this case, other additives may be added after kneading using a kneading device described later). Alternatively, in another embodiment, the polylactic acid resin, cis-type polyisoprene, and crosslinking agents, etc., can be directly introduced into a kneading device as described later, or mixed in a separate container to form a resin mixture.

[0064] Next, the resin mixture is kneaded under heat.

[0065] Various types of kneading equipment can be used for this mixing process. Examples of kneading equipment, though not limited to them, include segment mixers, Banbury mixers, Brabender mixers, pressure kneaders, single-screw extruders, twin-screw extruders, and open rolls.

[0066] The temperature required for kneading can be set to any temperature by those skilled in the art, taking into account the melting point of the polylactic acid resin used and / or the decomposition initiation temperature of cis-type polyisoprene. The kneading temperature is preferably 140°C to 250°C, more preferably 150°C to 220°C, and even more preferably 160°C to 200°C. If the kneading temperature is below 140°C, it may be difficult to knead the resin mixture uniformly. If the kneading temperature exceeds 250°C, the molecular weight of the polylactic acid resin and / or cis-type polyisoprene may decrease, potentially degrading the mechanical properties of the resulting resin composition.

[0067] The time required for mixing is not necessarily limited, as it can vary depending on the total amount of resin mixture used, the ratio of the polylactic acid resin, cis-type polyisoprene, trans-type polyisoprene, auxiliary agents, crosslinking agents, and other additives that make up the resin mixture, and can be set to any time by those skilled in the art. The time required for mixing is preferably 3 to 60 minutes, more preferably 5 to 30 minutes. If the mixing time is less than 3 minutes, dynamic crosslinking within the resin mixture may be insufficient, and the impact resistance of the resulting resin composition may not be significantly improved compared to that of polylactic acid resin alone. If the mixing time exceeds 60 minutes, the molecular chains of the polylactic acid resin and / or cis-type polyisoprene within the resin mixture may be cleaved, which may reduce the mechanical properties of the resulting resin composition.

[0068] Through the above kneading process, the resin mixture is dynamically crosslinked to obtain a resin composition having a sea-island structure consisting of a polyisoprene component dispersion phase composed of cis-type polyisoprene and optionally trans-type polyisoprene, and a polylactic acid component matrix phase.

[0069] In this way, the polylactic acid resin composition of the present invention is produced.

[0070] The polylactic acid resin composition of the present invention is characterized by its thermoplasticity due to the polylactic acid resin component, despite the crosslinking of the polyisoprene component. Therefore, the polylactic acid resin composition of the present invention can be molded into any resin molded product using known thermoplastic resin molding methods such as extrusion molding, injection molding, blow molding, and compression molding, and molding apparatus using such methods. Furthermore, the resin molded product obtained in this manner can be further remolded. [Examples]

[0071] The present invention will be described more specifically below with reference to examples. However, the present invention is not limited to these examples.

[0072] (Example 1: Preparation and testing of a dynamically crosslinked resin sample (E1)) In a laboplast mill (4C150-01, manufactured by Toyo Seiki Co., Ltd.) equipped with a segment mixer temperature-controlled to 180±10℃, 36.0g of polylactic acid (PLA) pellets (Terramac TE-2000, manufactured by Unitika Ltd.) and 4.0g of cis-type polyisoprene (CPI) (manufactured by Sigma-Aldrich) as a rubber component were added. The mixture was melt-kneaded at 180℃ at 25rpm for 1 minute, then cooled to 150℃, and further melt-kneaded at 150℃ at 25rpm for 3 minutes to obtain a kneaded product. This product was then further kneaded at 160℃ at 25rpm for 20 minutes to obtain a dynamically crosslinked resin sample (E1).

[0073] The following tests were performed on this resin sample (E1).

[0074] (Tensile test) The resin sample (E1) obtained above was molded into a film with a thickness of 500 ± 100 μm and a width of 4 mm. This film was subjected to a tensile test in accordance with JIS K 6251 using a small benchtop testing machine (Shimadzu Corporation EZ-Graph) with a load cell of 500 N. The test conditions were a crosshead speed of 10 mm / min and a specimen length of 20 mm. The maximum stress (MPa) and Young's modulus (GPa) were obtained from the resulting stress-strain curve. Furthermore, toughness was calculated from the integral value of the stress-strain curve of the above tensile test. The results are shown in Table 2.

[0075] (Impact test / Impact strength measured by Charpy impact test) The resin sample (E1) obtained above was finely cut, and strips for Charpy impact testing (80 × 10 × 4 mm) were molded using a small injection molding machine (Thermo Fisher Scientific, Model: HAAKE MiniJet Pro). The test pieces were given a single notch using a notching tool (INSTRON). For the Charpy impact test, an impact testing machine (Ueshima Seisakusho Co., Ltd.) was used, and the test was conducted in accordance with JIS K 7111-1. The obtained impact strengths are shown in Table 2.

[0076] (Example 2: Preparation and testing of a dynamically crosslinked resin sample (E2)) In a laboplast mill (4C150-01, manufactured by Toyo Seiki Co., Ltd.) equipped with a segment mixer temperature-controlled to 180±10℃, 36.0g of polylactic acid (PLA) pellets (Terramac TE-2000, manufactured by Unitika Ltd.) and 4.0g of cis-type polyisoprene (CPI) (manufactured by Sigma-Aldrich) as a rubber component were added. The mixture was melt-kneaded at 180℃ at 25rpm for 1 minute, then cooled to 150℃, and further melt-kneaded at 150℃ at 25rpm for 3 minutes to obtain a kneaded product.

[0077] Next, 0.5 g of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (Luperox101, manufactured by Arkema Yoshitomi Co., Ltd.) was added to the compound obtained above as a crosslinking agent and kneaded at 160°C at 25 rpm for 20 minutes. Then, 0.15 g of an antioxidant (Irganox1520L, manufactured by BASF Japan Ltd.; 4,6-bis(octylthiomethyl)-o-cresol) was added and kneaded for 5 minutes to obtain a dynamically crosslinked resin sample (E2). The obtained resin sample (E2) was tested in the same manner as in Example 1. The results are shown in Table 2.

[0078] (Examples 3 and 4: Preparation and testing of dynamically crosslinked resin samples (E3) and (E4)) Resin samples (E3) and (E4) were obtained by dynamic crosslinking in the same manner as in Example 2, except that the content of PLA, CPI, crosslinking agent, and antioxidant used was changed as shown in Table 2. The obtained resin samples (E3) and (E4) were tested in the same manner as in Example 1. The results are shown in Table 2.

[0079] (Example 5: Preparation and testing of a dynamically crosslinked resin sample (E5)) A resin sample (E5) was obtained by dynamic crosslinking in the same manner as in Example 1, except that the content of PLA and CPI used was changed as shown in Table 2. The obtained resin sample (E5) was tested in the same manner as in Example 1. The results are shown in Table 2.

[0080] (Examples 6 and 7: Preparation and testing of dynamically crosslinked resin samples (E6) and (E7)) Resin samples (E6) and (E7) were obtained by dynamic crosslinking in the same manner as in Example 2, except that the content of PLA, CPI, crosslinking agent, and antioxidant used was changed as shown in Table 2. The obtained resin samples (E6) and (E7) were tested in the same manner as in Example 1. The results are shown in Table 2.

[0081] (Comparative Example 1: Testing of a resin sample (C1) consisting solely of PLA) A resin sample (C1) was obtained using only 40.0 g of polylactic acid (PLA) pellets (Terramac TE-2000, manufactured by Unitika Ltd.) as the polylactic acid-based resin. The obtained resin sample (C1) was tested in the same manner as in Example 1. The results are shown in Table 2.

[0082] [Table 2]

[0083] As shown in Table 2, the resin samples (E1) to (E7) obtained in Examples 1 to 7 all showed improved impact strength compared to the resin sample (C1) of Comparative Example 1, which was composed of polylactic acid alone. Furthermore, the resin samples (E1) to (E7) of Examples 1 to 7 showed significantly lower maximum stress in tensile tests while improving toughness compared to the resin sample (C1) of Comparative Example 1. This trend can be confirmed even in the absence of crosslinking agents and antioxidants by mixing predetermined amounts of polylactic acid resin and cis-type polyisoprene and dynamically crosslinking them (Examples 1 and 5), but it was particularly pronounced in the presence of the crosslinking agent and antioxidant (Examples 2 to 4, 6 and 7).

[0084] (Example 8: Preparation and testing of a dynamically crosslinked resin sample (E8)) In a laboplast mill (4C150-01, manufactured by Toyo Seiki Co., Ltd.) equipped with a segment mixer temperature-controlled to 180±10℃, 36.0g of polylactic acid (PLA) pellets (Terramac TE-2000, manufactured by Unitika Ltd.) as a polylactic acid resin, 4.0g of cis-type polyisoprene (CPI) (manufactured by Sigma-Aldrich) as a rubber component, and 4.0g of tributyl citrate (TBC) as an auxiliary agent were added. The mixture was melt-kneaded at 180℃ at 25rpm for 1 minute, then cooled to 150℃, and further melt-kneaded at 150℃ at 25rpm for 3 minutes to obtain a kneaded product.

[0085] Next, 1 g of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (Luperox101, manufactured by Arkema Yoshitomi Co., Ltd.) was added to the compound obtained above as a crosslinking agent and kneaded at 160°C at 25 rpm for 20 minutes. Then, 0.3 g of an antioxidant (Irganox1520L, manufactured by BASF Japan Ltd.; 4,6-bis(octylthiomethyl)-o-cresol) was added and kneaded for 5 minutes to obtain a dynamically crosslinked resin sample (E8). The obtained resin sample (E8) was tested in the same manner as in Example 1. The results, along with those of Example 6, are shown in Table 3.

[0086] [Table 3]

[0087] As shown in Table 3, the resin sample obtained in Example 8 (E8) showed a significant improvement in both toughness and impact strength compared to the resin sample obtained in Example 6 (E6), which did not contain the auxiliary agent TBC.

[0088] (Example 9: Preparation and testing of a dynamically crosslinked resin sample (E9)) In a laboplast mill (4C150-01, manufactured by Toyo Seiki Co., Ltd.) equipped with a segment mixer temperature-controlled to 180±10℃, 32.0g of polylactic acid (PLA) pellets (Terramac TE-2000, manufactured by Unitika Ltd.) and 8.0g of cis-type polyisoprene (CPI) (manufactured by Sigma-Aldrich) as a rubber component were added. The mixture was melt-kneaded at 180℃ at 25rpm for 1 minute, then cooled to 150℃, and further melt-kneaded at 150℃ at 25rpm for 3 minutes to obtain a kneaded product.

[0089] Next, 0.8 g of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (Luperox101, manufactured by Arkema Yoshitomi Co., Ltd.) was added to the compound obtained above as a crosslinking agent and kneaded at 160°C at 25 rpm for 20 minutes. Then, 0.24 g of an antioxidant (Irganox1520L, manufactured by BASF Japan Ltd.; 4,6-bis(octylthiomethyl)-o-cresol) was added and kneaded for 5 minutes to obtain a dynamically crosslinked resin sample (E9). The obtained resin sample (E9) was tested in the same manner as in Example 1. The results, along with those of Examples 5 and 6 and Comparative Example 1, are shown in Table 4.

[0090] Furthermore, thin sections for observation were prepared by freeze-fracturing this resin sample (E9), and the surface condition was observed using a scanning electron microscope (SEM) (SU-3500, Hitachi High-Tech Corporation). The obtained SEM images are shown in Figure 1.

[0091] Furthermore, SEM images were obtained for the resin samples (E5) and (E6) and (C1) obtained in Examples 5 and 6, as well as Comparative Example 1, in the same manner as described above. The obtained SEM images are shown in Figure 1.

[0092] (Example 10: Preparation and testing of a dynamically crosslinked resin sample (E10)) A resin sample (E10) was obtained by dynamic crosslinking in the same manner as in Example 9, except that the content of PLA, CPI, crosslinking agent, and antioxidant used was changed as shown in Table 4. The obtained resin sample (E10) was tested in the same manner as in Example 1. The results are shown in Table 4. Furthermore, an SEM image of the obtained resin sample (E10) was obtained in the same manner as in Example 9. The obtained SEM image is shown in Figure 1.

[0093] [Table 4]

[0094] As shown in Table 4, it can be seen that increasing the content of the crosslinking agent used tends to increase the impact strength of resin samples (E5) to (E9).

[0095] As shown in Figure 1, compared to the resin sample of Comparative Example 1 (C1), the resin sample of Example 5 (E5), which did not contain a crosslinking agent, showed significant aggregation of cis-type polyisoprene in the SEM image, forming large spherical clumps. In contrast, the resin samples obtained in Examples 6, 9, and 10 (E6), (E9), and (E10), which had crosslinking agents added, did not show the large spherical clumps observed in the SEM image of Example 5, indicating that the aggregation of cis-type polyisoprene was eliminated. [Industrial applicability]

[0096] According to the present invention, it is useful in various resin molded products (for example, molded products for automobiles, molded products for electrical products, molded products for agricultural materials, molded products for office use, and molded products for daily necessities) that were difficult to achieve with conventional polylactic acid resins alone.

[0097] This application claims priority under Japanese Patent Application No. 2023-024939, filed with the Japan Patent Office on 21 February 2023, all of which are incorporated herein by reference.

Claims

1. A polylactic acid resin composition, It is constructed by dynamically crosslinking a resin mixture containing a polylactic acid-based resin, cis-type polyisoprene, and a crosslinking agent. The content of the polylactic acid resin is 280 to 950 parts by mass per 100 parts by mass of the cis-type polyisoprene, and A polylactic acid resin composition in which the crosslinking agent is contained in an amount of 12.5 to 50 parts by mass per 100 parts by mass of cis-type polyisoprene.

2. The polylactic acid resin composition according to claim 1, wherein the content of the polylactic acid resin is 290 to 720 parts by mass per 100 parts by mass of the cis-type polyisoprene.

3. The aforementioned resin mixture is further divided into the following formula (I): 【Chemistry 1】 (In formula (I), R １ , R ２ and R ３ , and R ４ The polylactic acid resin composition according to claim 1, wherein each of the compounds is independently represented by a hydrogen atom and a group selected from the group consisting of a branched alkyl group having 1 to 8 carbon atoms.

4. R in formula (I) １ , R ２ and R ３ is an n-butyl group, and R ４ The polylactic acid resin composition according to claim 3, wherein is a hydrogen atom.

5. The polylactic acid resin composition according to claim 1, wherein the crosslinking agent is selected from the group consisting of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and dicumyl peroxide.

6. A method for producing a polylactic acid resin composition, A process of obtaining a resin mixture by mixing a polylactic acid resin, cis-type polyisoprene, and a crosslinking agent; and A step of heating and kneading the resin mixture to dynamically crosslink the resin mixture; It includes, The content of the polylactic acid resin is 280 to 950 parts by mass per 100 parts by mass of the cis-type polyisoprene, and A method wherein the crosslinking agent is contained in an amount of 12.5 to 50 parts by mass per 100 parts by mass of cis-type polyisoprene.

7. The method according to claim 6, wherein the content of the polylactic acid resin is 280 to 720 parts by mass per 100 parts by mass of the cis-type polyisoprene.

8. A resin molded article containing the polylactic acid resin composition according to any one of claims 1 to 5.

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