Patent Publication Number: US-2023151205-A1

Title: Resin composition, emitter, and tube for drip irrigation

Description:
TECHNICAL FIELD 
     The present invention relates to a resin composition, an emitter, and a drip irrigation tube. 
     BACKGROUND ART 
     In recent years, environmental pollution caused by plastics has become a problem, which leads to the increase of the demand for resin compositions that mainly contain biodegradable resins. Such resin compositions have attracted attention particularly in the fields of, for example, agricultural films and packaging containers. As a method for processing a resin composition into various shapes, molding such as injection molding is commonly used. 
     In a commonly used injection molding method, a resin composition is heated to a temperature higher than the melting point of the resin, and the resin composition with increased fluidity is poured into a mold. Subsequently, the resin composition is cooled to a temperature below the crystallization temperature of the resin to solidify the resin composition. However, poly(butylene adipate/terephthalate) (namely, (poly(butylene adipate-co-terephthalate), hereinafter also referred to as “PBAT”), which is known as a biodegradable resin, has a slow crystallization rate. Therefore, for processing a resin composition containing PBAT into a desired shape, a substantially long time is required between the procedures, namely pouring the resin composition into the mold, and removing the resin composition from the mold (hereinafter also referred to as “molding cycle time”). 
     With respect to the above disadvantages, a resin composition including PBAT with a metal salt of a phosphate (herein also referred to as “phosphate metal salt”), fatty acid sodium salt, talc, and/or the like added thereto is proposed (Patent Literature (hereinafter, referred to as PTL) 1). PTL 1 teaches that the phosphate metal salt and the like increases the crystallinity of the resin composition. 
     A resin composition including PBAT with polylactic acid (hereinafter also referred to as “PLA”) and an adipic acid-based plasticizer added thereto is also proposed (PTL 2). PTL 2 teaches that mixing relatively hard PLA and highly flexible PBAT can achieve both the desired flexibility and high impact strength. 
     In addition, a resin composition containing PBAT and thermoplastic starch is proposed (Non Patent Literature (hereinafter, referred to as NPL) 1). The technique of NPL 1 is supposed to improve moldability by adding the thermoplastic starch. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1 
         Japanese Patent Application Laid-Open No. 2013-133364 
         PTL 2 
         Japanese Patent Application Laid-Open No. 2014-5435 
       
    
     Non Patent Literature 
     
         
         NPL 1 
         Seligra P. G., et al., “Influence of incorporation of starch nanoparticles in PBAT/TPS composite films,” PolymInt, Vol. 65, pp. 938-945 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     Addition of the phosphate metal salt, talc, and the like to PBAT as in PLT 1 tends to lower the fluidity during injection molding, thereby making the molding of the resin composition difficult. In addition, the molded article of the resin composition of PLT 2 tends to have increased hardness due to PLA, and thus the flexibility derived from PBAT cannot be fully exhibited. It is also difficult to shorten the time required for injection molding (molding cycle time) with the use of this resin composition. 
     Further, regarding the technique described in NPL 1, the compatibility between PBAT and the thermoplastic starch is poor, which not only impairs the inherent flexibility of PBAT, but also lowers moldability. From the foregoing, there is a demand for a resin composition that is biodegradable, has excellent moldability, and can provide a molded product having appropriate flexibility. 
     An object of the present invention is to provide a resin composition that is biodegradable, can be easily molded in a short time, and can provide a molded article having appropriate flexibility. Another object of the present invention is to provide an emitter and a drip irrigation tube each containing the resin composition. 
     Solution to Problem 
     To achieve the above object, the present invention provides the following resin composition. 
     A resin composition containing 100 parts by mass of poly(butylene adipate/terephthalate) and 1 to 10 parts by mass of an aliphatic polyester represented by the following general formula 1: 
     
       
         
         
             
             
         
       
     
     where R 1  and R 4  each represent an alkyl group having 1 to 12 carbon atoms, R 2  and R 3  each represent an alkyl group having 2 to 5 carbon atoms, G represents an alkyl group having 2 to 12 carbon atoms, and n represents an integer of 2 to 10, and the amount of poly(butylene adipate/terephthalate) is 80 mass % or more based on the total mass of the resin composition. 
     The present invention also provides the following emitter. 
     An emitter for discharging an irrigation liquid in a tube, which allows the irrigation liquid to flow therethrough, at a constant rate from a discharge port, which allows an inside and the outside of the tube to communicate with each other, to an outside of the tube when the emitter is joined to an inner wall surface of the tube at a position corresponding to the discharge port, and the emitter includes an intake part for taking the irrigation liquid into the emitter, a discharge part for discharging the irrigation liquid to the discharge port, and a channel connecting the intake part and the discharge part, and the emitter contains the above-described resin composition. 
     The present invention also provides the following drip irrigation tube. 
     A drip irrigation tube including a tube and the above-described emitter disposed in the tube. 
     Advantageous Effects of Invention 
     A resin composition according to the present invention is biodegradable and can be efficiently molded in a short time. In addition, a resulting molded article from the resin composition has high flexibility. Therefore, the resin composition is applicable to various uses such as tubes for drip irrigation and emitters used therefor. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a cross-sectional view illustrating an exemplary drip irrigation tube obtained from the resin composition of the present invention; 
         FIG.  2 A  is a plan view of an emitter in the drip irrigation tube illustrated in  FIG.  1   ,  FIG.  2 B  is a bottom view of the emitter,  FIG.  2 C  is a left side view of the emitter, and  FIG.  2 D  is a right side view of the emitter; 
         FIG.  3    is a cross-sectional view taken along line A-A of  FIG.  2 A ; and 
         FIG.  4 A  is a bottom view of the emitter illustrated in  FIGS.  2 A to  2 D  before assembly,  FIG.  4 B  is a plan view of the emitter before assembly, and  FIG.  4 C  is a cross-sectional view taken along line A-A of  FIG.  4 A . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, the resin composition will be described in detail, and an emitter and a tube each containing the resin composition will then be described. 
     1. Resin Composition 
     A resin composition of the present invention contains poly(butylene adipate/terephthalate) (PBAT) and an aliphatic polyester having a specific structure. The amount of poly(butylene adipate/terephthalate) in the resin composition is 80 mass % or more. 
     As described above, it is difficult for a conventional resin composition containing PBAT to achieve both high fluidity during molding and a high crystallization temperature. In addition, there is another disadvantage such that addition of a crystal nucleating agent or the like for improving moldability lowers the flexibility of the resulting molded article. 
     The present inventors have found that adding an aliphatic polyester having a specific structure together with PBAT to a resin composition can lower the melt viscosity of the resin composition, and increase the crystallization temperature of the resin composition. These component allows the resin composition of the present invention to efficiently produce molded articles in a short molding cycle. In other words, the resin composition can be molded without any addition of other materials such as a hard resin (such as PLA) or a crystal nucleating agent. The aliphatic polyester does not lower the flexibility of the resulting molded article. Therefore, the resulting molded article has appropriate flexibility derived from PBAT. Such a resin composition is also applicable to molding materials of, for example, emitters that adjust the flow rate with, for example, a diaphragm in drip irrigation tubes. 
     In the following, components of the resin composition of the present invention will be described. The resin composition of the present invention may contain components in addition to PBAT and the aliphatic polyester. Examples of the additional components include aliphatic ester compounds and metal phosphates. 
     Poly(Butylene Adipate/Terephthalate) (PBAT) 
     PBAT is a biodegradable resin. In the resin composition of the present invention, PBAT is the main component occupying 80% or more of the total amount of the resin composition. The content of PBAT is preferably 85 to 99 mass %, more preferably 90 to 99 mass %, based on the total amount of the resin composition. Content of PBAT within this range allows obtainment of a resin composition having desired flexibility and satisfactory process ability. 
     PBAT is a polymer obtained by condensation polymerization of adipic acid, terephthalic acid, and 1,4-butanediol. The amount of structural units derived from adipic acid in PBAT is preferably about 10 to 50 mol %, more preferably 15 to 40 mol %, based on the total amount of structural units constituting PBAT. The amount of structural units derived from terephthalic acid is preferably about 5 to 45 mol %, more preferably 8 to 35 mol %, based on the total amount of structural units constituting PBAT. The amount of structural units derived from 1,4-butanediol is preferably about 5 to 45 mol %, more preferably 10 to 30 mol %. 
     In addition to the structural units derived from adipic acid, terephthalic acid, and 1,4-butanediol, PBAT may partially contain structural units derived from additional components, so long as the objects and effects of the present invention are not impaired. Examples of the additional components include dihydroxy compounds such as diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, and polytetrahydrofuran; and hydroxycarboxylic acids such as glycolic acid, D-lactic acid, L-lactic acid, D,L-lactic acid, 6-hydroxyhexanoic acid, glycolide (1,4-dioxane-2,5-dione), D-dilactide (3,6-dimethyl-1,4-dioxane-2,5-dione), L-dilactide (3,6-dimethyl-1,4-dioxane-2,5-dione), and p-hydroxybenzoic acid. The amount of structural units derived from these additional components is preferably 30 mol % or less based on the total amount of structural units constituting PBAT. 
     The weight average molecular weight of PBAT is appropriately selected according to the application and molding temperature of the resin composition, and is preferably 3,000 to 1,000,000, more preferably 20,000 to 600,000, and even more preferably 50,000 to 400,000. The weight average molecular weight of PBAT is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene. A weight average molecular weight of PBAT within this range facilitates the adjustment of the fluidity to fall within a desired range during molding of the resin composition. 
     The viscosity of PBAT measured with a capillary rheometer at 200° C. and at a shear rate of 20 s −1  is preferably 1,000 to 3,000 Pa·s, more preferably 1,200 to 2,500 Pa·s. A viscosity within this range facilitates the adjustment of the viscosity of the resin composition to fall within a desired range, thereby facilitating the processing of the resin composition by, for example, injection molding. 
     PBAT may be prepared by polymerizing the above components, or may be a commercially available product. An example of the commercially available PBAT is Ecoflex manufactured by BASF. 
     Aliphatic Polyester 
     The aliphatic polyester is a polyester resin having a specific structure described below. A resin composition containing the aliphatic polyester has an increased melt viscosity, and can be cured (crystallized) at a relatively high temperature. 
     The amount of the aliphatic polyester is preferably 0.5 to 9 mass %, more preferably 1 to 8 mass %, based on the total amount of the resin composition. The amount of the aliphatic polyester based on 100 parts by mass of PBAT is 1 to 10 parts by mass, preferably 1 to 9 parts by mass, more preferably 2 to 8 parts by mass. An amount of the aliphatic polyester of 1 part by mass or more can improve the fluidity of a resin composition even at a relatively low temperature. An amount of the aliphatic polyester of 10 part by mass or more can lower the crystallization temperature of a resin composition, but may cause bleed-out in the resulting molded article. When the amount of the aliphatic polyester is within the above range, the resulting molded article has appropriate flexibility and thus can be applied to applications that require elasticity. 
     Adjusting the amount of the aliphatic polyester to fall within the above range can improve the moldability of the resin composition without lowering the inherent flexibility of PBAT. 
     The aliphatic polyester is a polymer represented by the following general formula 1. 
     
       
         
         
             
             
         
       
     
     In the general formula, R 1  and R 4  each independently represent an alkyl group having 1 to 12 carbon atoms. The number of carbon atoms of each of R 1  and R 4  is more preferably 3 to 11, even more preferably 5 to 10. R 1  and R 4  may be linear or branched. R 1  and R 4  may be the same or different to each other. 
     In the general formula, R 2  and R 3  each independently represent an alkyl group having 2 to 5 carbon atoms. Typically, R 2  and R 3  are structures derived from dicarboxylic acids. When the number of carbon atoms of R 2  and R 3  is 2 to 5, the affinity between the aliphatic polyester and the above-described PBAT is increased, the melt viscosity of the resin composition is more likely to be lowered, and PBAT is more likely to be crystallized. R 2  and R 3  may be branched, but are more preferably linear. R 2  and R 3  may be different to each other, but usually are the same structure. R 2  and R 3  particularly preferably has 4 carbon atoms, namely a structure derived from adipic acid. 
     In the general formula, G represents an alkyl group having 2 to 12 carbon atoms and usually is a diol-derived structure. The number of carbon atoms of G is preferably 2 to 10, more preferably 3 to 8. G may be linear or branched. When the number of carbon atoms of G is within the above range, the affinity between the above-described PBAT and the aliphatic polyester is more likely to increase. 
     In the general formula, n represents an integer of 2 to 10, preferably 2 to 9, and more preferably 2 to 8. The number represented by n can be adjusted according to, for example, the viscosity of the aliphatic polyester. The viscosity of the aliphatic polyester measured at 25° C. at an angular frequency of 1 Hz with the use of an coaxial double-cylinder rotational viscometer is preferably 100 to 10,000 mPa·s, more preferably 300 to 5,000 mPa·s. A viscosity of the aliphatic polyester within this range facilitates the adjustment of the viscosity of the resin composition to fall within a desired range. 
     The weight average molecular weight of the aliphatic polyester is preferably 400 to 8,000, more preferably 500 to 5,000, even more preferably 800 to 3,000. A weight average molecular weight of the aliphatic polyester within this range facilitates the adjustment of the viscosity of the aliphatic polyester to fall within a desired range, thereby facilitating the mixing with PBAT. The weight average molecular weight of the aliphatic polyester is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene. 
     The aliphatic polyester can be prepared, for example, by polymerizing a dicarboxylic acid and a diol by a known method. Examples of the dicarboxylic acid used in the preparation include glutaric acid, adipic acid, and pimelic acid. Examples of the diol used in the preparation include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,5-hexanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,7-heptanediol, 1,8-octanediol, and 1,2-octanediol. 
     Aliphatic Ester Compound 
     The resin composition may further contain an aliphatic ester compound having a structure derived from a fatty acid having 2 to 5 carbon atoms. An aliphatic ester compound herein is a low-molecular-weight ester compound having two or less ester bonds per molecule. Examples of the aliphatic ester compound include reaction products of dicarboxylic acids each having alkyl group of 2 to 5 carbon atoms with monohydric alcohols. 
     When the resin composition contains the aliphatic ester compound, the aliphatic ester compound functions as a crystallization accelerator, more likely to increase the crystallization temperature of the resin composition. An excessive amount of the aliphatic ester compound may impair the flexibility of the resulting molded article. Therefore, the amount of the aliphatic ester compound is preferably 5 parts by mass or less, more preferably 0.1 to 4 parts by mass, based on 100 parts by mass of PBAT. When the amount of the aliphatic ester compound is within this range, the resulting molded article is less likely to be excessively hard. 
     The aliphatic ester compound preferably has a structure derived from glutaric acid, adipic acid, or pimelic acid, and particularly preferably has a structure derived from adipic acid. When the aliphatic ester compound has a structure derived from adipic acid, the affinity between the above-described PBAT and the aliphatic ester compound becomes excellent, allowing the aliphatic ester compound to promote crystallization of PBAT. 
     Examples of the alcohols to be reacted with adipic acid and the like include linear or branched monohydric alcohols having 2 to 12 carbon atoms. Examples of the monohydric alcohols include ethanol, butanol, isobutyl alcohol, isononyl alcohol, isodecyl alcohol, 2-ethylhexanol, n-octanol, n-decyl alcohol, and butyl diglycol. 
     The molecular weight of the aliphatic ester compound is preferably 150 to 500, more preferably 200 to 450, even more preferably 250 to 400. A molecular weight of the aliphatic ester compound within this range can improve the crystallinity of the resin composition. 
     Phosphate Metal Salt 
     The resin composition may further contain a phosphate metal salt having a specific structure. The phosphate metal salt functions as a crystal nucleating agent; thus a resin composition containing the phosphate metal salt has a high crystallization temperature. 
     An excessive amount of the phosphate metal salt may lower the flexibility of the resulting molded article. Therefore, the amount of the phosphate metal salt is preferably 5 parts by mass or less, more preferably 0.1 to 2 parts by mass, based on 100 parts by mass of PBAT. When the amount of the phosphate metal salt is within this range, the resulting molded article is less likely to be excessively hard. 
     The phosphate metal salt is represented by the following general formula 2. 
     
       
         
         
             
             
         
       
     
     In the general formula, A 1  and A 2  each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. A 1  and A 2  may be the same or different to each other. In the general formula, A 3  to A 6  each independently represent an alkyl group having 1 to 12 carbon atoms. A 3  to A 6  may be the same or different to each other. A 1  to A 6  may be linear or branched. 
     M represents at least one metal atom selected from the group consisting of alkali metal atoms, alkaline earth metal atoms, and transition metal atoms. Examples of M include Li, Na, K, Al, Mg, and Ca, with Li, Na, Al being more preferred. In the general formula, n represents 1 or 2. 
     Additional Components 
     The resin composition may contain components in addition to the above described components, so long as the objects and effects of the present invention are not impaired. Examples of the additional components include ultraviolet absorbers and antioxidants for the purpose of preventing deterioration. 
     Methods for Preparing and Molding Resin Composition 
     The above described resin composition can be prepared, for example, by mixing components such as PBAT, an aliphatic polyester, an aliphatic ester compound, and a phosphate metal salt, and kneading the mixture by a known method. 
     The melt viscosity of the resin composition at 200° C. is preferably 300 to 1,500 Pa·s, more preferably 500 to 1,200 Pa·s. A melt viscosity of the resin composition within this range can increase the fluidity, allowing easy application of the resin composition for the production of molded products having a fine structure, such as an emitter of a drip irrigation tube described below. The melt viscosity is measured with a capillary rheometer at a shear rate of 20 s −1 . 
     The crystallization temperature of the resin composition is preferably 50 to 95° C., more preferably 60 to 85° C. A crystallization temperature within this range allows the resin composition to be cured in a relatively short time, thereby shortening the cycle time during the molding. The crystallization temperature is measured by a differential scanning calorimeter. Specifically, the crystallization temperature is the value observed as the peak top of exotherm during the cooling procedure in a chart obtained by heating the resin composition from room temperature to 200° C. at a rate of 10° C./min, holding the temperature at 200° C. for 5 minutes, and then cooling the resin composition to −50° C. at a rate of −10° C./min. 
     Any known molding method can be used for molding the resin composition. Examples of the molding methods include injection molding, extrusion molding, blow molding, compression molding, transfer molding, and calendar molding. In particular, injection molding is preferred. The injection molding may be of any type, such as insert molding, gas-assisted injection molding, or injection compression molding. 
     2. Drip Irrigation Tube (Emitter and Tube) 
     The resin composition of the present invention may be used in any application that requires biodegradability, for example, for emitters and tubes of drip irrigation tubes. Biodegradable emitter and tube can be buried in soil or composted when they are no longer needed, thus can be treated without imposing a burden on the environment. However, applications of the resin composition are not limited to emitters and tubes. In addition, an emitter can be formed, for example, by injection molding the resin composition described above, and a tube can be formed, for example, by extrusion molding the resin composition described above. 
     Hereinafter, an exemplary drip irrigation tube (emitter and tube) to which the resin composition of the present invention can be applied will be described with reference to the drawings. However, the emitter and tube of the present invention are not limited to the structures described below. 
       FIG.  1    is a cross-sectional view of drip irrigation tube  100 . As illustrates in  FIG.  1   , drip irrigation tube  100  includes tube  110  and one or more emitters  120 . The resin composition may be applied to both tube  110  and emitter  120 . Examples of irrigation liquids flowing through tube  110  include water, liquid fertilizers, pesticides, and mixtures thereof. 
     Tube  110  is a pipe for allowing an irrigation liquid to flow therethrough. Tube  110  includes plurality of discharge ports  111  for discharging the irrigation liquid, at predetermined intervals (for example, 200 mm or more and 500 mm or less) along the axial direction of the tube. The opening of discharge port  111  of tube  110  may have any diameter, so long as the irrigation liquid can be discharged therefrom. In the embodiment illustrated in  FIG.  1   , the diameter of the opening of discharge port  111  is 1.5 mm Tube  110  may have any cross-sectional shape and cross-sectional area perpendicular to the axial direction of the tube, so long as emitter  120  can be disposed inside tube  110 . 
     Emitter  120  is a member to be joined to inner wall surface  112  of tube  110  at a position corresponding to discharge port  111 . Emitter  120  is a member for adjusting the discharge amount of irrigation liquid from drip irrigation tube  100 . Tube  110  and emitter  120  may be joined by any method, and may be welded or joined with an adhesive. 
       FIG.  2 A  is a plan view of emitter  120  and  FIG.  2 B  is a bottom view of emitter  120 .  FIG.  2 C  is a left side view of the emitter, and  FIG.  2 D  is a right side view of the emitter.  FIG.  3    is a cross-sectional view taken along line A-A of  FIG.  2 A . 
     As illustrated in  FIGS.  2 A to  2 D , emitter  120  has a substantially rectangular shape with rounded corners. Emitter  120  may have any size, which may be appropriately determined based on the desired amount of irrigation liquid to be discharged from discharge port  111 . In the present embodiment, emitter  120  has a long side length of 19 mm, a short side length of 8 mm, and a height of 2.7 mm. 
     Emitter  120  includes intake part  131 , discharge part  137 , and groove  132  (channel  142 ) connecting intake part  131  with discharge part  137 . Intake part  131  is for taking in irrigation liquid from the tube  110  side. Discharge part  137 , disposed at a position corresponding to discharge port  111  of tube  110 , is for discharging the irrigation liquid to discharge port  111  of tube  110 . In the present embodiment, emitter  120  further includes flow rate adjusting part  136  between channel  142  and discharge part  137 . 
     Intake part  131  is a structure for taking irrigation liquid into emitter  120 . Intake part  131  is disposed in emitter  120  on the surface side (the side closer to the center of the axial direction of tube  110 ). Intake part  131  includes intake side screen part  146  and intake through hole  147 . Intake side screen part  146  is a structure for preventing floating matter in the irrigation liquid from entering intake through hole  147 . 
     As illustrated in  FIG.  2 B , groove  132  is disposed in emitter  120  on the back side (on the side of the inner wall surface  112  of tube  110 ). The region surrounded by groove  132  and tube  110  serves as channel  142  for the irrigation liquid. Groove  132  may have any shape, so long as groove  132  connects intake through hole  147  of intake part  131  with flow rate adjusting part  136 . The shape of groove  132  may be straight, curved, or zigzag. In the present embodiment, a straight groove and a zigzag groove are combined. The zigzag region can reduce the pressure of the irrigation liquid taken from intake part  131 . 
     Flow rate adjusting part  136  is a structure for adjusting the discharge amount of the irrigation liquid that has been taken into emitter  120 . As illustrated in  FIG.  3   , flow rate adjusting part  136  includes base  161 , diaphragm part  153 , communication hole  151 , communicating groove  162 , and notched groove  150  (see  FIG.  4 B ). In flow rate adjusting part  136 , diaphragm part  153  faces base  161 , communication hole  151  connects the surface of base  161  with the back side of the emitter  120 , communicating groove  162  is disposed in base  161 , and notched groove  150  is for taking in the irrigation liquid from groove  132  (channel  142 ) toward flow rate adjusting part  136  (toward an area between base  161  and diaphragm part  153 ). In flow rate adjusting part  136 , the irrigation liquid is taken into the area between base  161  and diaphragm part  153  via notched groove  150  and allowed to flow toward discharge part  137  via communication hole  151 . 
     Emitter  120  including such flow rate adjusting part  136  is formed of first main body  120   a  and second main body  120   b . For easy understanding of the structure of flow rate adjusting part  136 ,  FIGS.  4 A to  4 C  illustrate a structure of emitter  120  before assembling, namely the structures of first main body  120   a  and second main body  120   b .  FIG.  4 A  illustrates the back side structures of first main body  120   a  and second main body  120   b  and  FIG.  4 B  illustrates the front side structures of first main body  120   a  and second main body  120   b .  FIG.  4 C  is a cross-sectional view taken along line A-A of  FIG.  4 A . For producing emitter  120 , first main body  120   a  and second main body  120   b  are separated from each other at hinge  123  that connects the bodies, and then second main body  120   b  is fitted to the back side of first main body  120   a . At this time, first main body  120   a  and second main body  120   b  are fitted to each other in such a way that base  161  faces diaphragm part  153 . 
     Notched groove  150  is used to appropriately guide the irrigation liquid introduced from groove  132  (channel  142 ) to the area between base  161  and diaphragm part  153 . Notched groove  150  may have any shape, so long as the above function can be exhibited. In the present embodiment, notched groove  150  is formed in a straight line. 
     Base  161  is a region where diaphragm part  153  contacts when diaphragm part  153  is deformed by the pressure of the irrigation liquid. Base  161  may have any shape. Base  161  may have a shape of a curved or flat surface. In the present embodiment, base  161  has a shape of a flat surface. Notched groove  150  is formed in a part of the flat surface where base  161  is disposed. 
     Communication hole  151  is used to allow the irrigation liquid having flowed into the area between base  161  and diaphragm part  153  to flow toward discharge part  137  of tube  110 . In the present embodiment, communication hole  151  opens onto the central portion of base  161 . The size of the opening of communication hole  151  is also not limited and can be set as appropriate. 
     Communicating groove  162  is for guiding the irrigation liquid to communication hole  151  even when diaphragm part  153  is bent and is in contact with base  161 . One end of communicating groove  162  communicates with communication hole  151 . The other end of communicating groove  162  is disposed outside the region where diaphragm part  153  is brought into contact with base  161 . 
     Diaphragm part  153  may have any configuration so long as the diaphragm part can bend toward base  161  due to the pressure of the irrigation liquid flowing through tube  110 . In the present embodiment, the shape of diaphragm part  153  in plan view is circular. In the present embodiment, diaphragm part  153  is formed integrally with other components of emitter  120  (intake part  131  and channel  142 ). 
     Discharge part  137  is a region for temporarily storing the irrigation liquid configured to flow toward the emitter  120  side via through hole  151  of flow rate adjusting part  136  described above. The irrigation liquid that has reached discharge part  137  is discharged to the outside from discharge port  111 . 
     In emitter  120 , irrigation liquid taken in from intake part  131  flows into flow rate adjusting part  136  via groove  132  (channel  142 ). In flow rate adjusting part  136 , the irrigation liquid is taken into the area between base  161  and diaphragm part  153  via notched groove  150 . When the pressure of the irrigation liquid in tube  110  is low, diaphragm part  153  of flow rate adjusting part  136  is substantially parallel with base  161 , and the irrigation liquid easily flows toward discharge part  137 . On the other hand, when the pressure of the irrigation liquid in tube  110  increases, diaphragm part  153  of flow rate adjusting part  136  bends toward base  161  as the material of the present invention has appropriate flexibility. As a result, the gap between diaphragm part  153  and base  161  is reduced, making it difficult for the irrigation liquid to flow from the communication hole  151  side toward discharge part  137 . When the pressure of the irrigation liquid in tube  110  is very high, diaphragm part  153  is brought into close contact with base  161 . That is, diaphragm part  153  covers base  161 . However, even in this case, a certain amount of irrigation liquid flows into communication hole  151  via communicating groove  162 . 
     When the pressure of the irrigation liquid flowing through tube  110  is low, the amount of irrigation liquid taken into emitter  120  would be reduced, and when the pressure of the irrigation liquid flowing through tube  110  is high, the amount of irrigation liquid taken into emitter  120  would be increased. The amount of the irrigation liquid flowing into the discharge part  137  side is adjusted by flow rate adjusting part  136  as described above in the present invention. Therefore, regardless of the pressure of the irrigation liquid in tube  110 , the amount of the irrigation liquid flowing from communication hole  151  toward discharge part  137  can be kept substantially constant. 
     EXAMPLES 
     The present invention will be described in detail based on Examples, but the present invention is not limited to these Examples. 
     Preparation of Materials 
     PBAT: product name Ecoflex C1200, manufactured by BASF 
     Aliphatic polyester B-1: PN7650 (adipic acid-based polyester, viscosity measured with a coaxial double-cylinder rotational viscometer at 25° C. at an angular frequency of 1 Hz: 3,000 mPa·s), manufactured by ADEKA CORPORATION 
     Aliphatic polyester B-2: PN7160 (adipic acid-based polyester, viscosity measured with a coaxial double-cylinder rotational viscometer at 25° C. at an angular frequency of 1 Hz: 150 mPa·s), manufactured by ADEKA CORPORATION 
     Aliphatic polyester B-3: D623 (adipic acid-based polyester, viscosity measured with a coaxial double-cylinder rotational viscometer at 25° C. at an angular frequency of 1 Hz: 3,000 mPa·s), manufactured by J-PLUS Co., Ltd. 
     Aliphatic ester compound: diisononyl adipate (viscosity measured with a coaxial double-cylinder rotational viscometer at 25° C. at an angular frequency of 1 Hz: 16 mPa·s), manufactured by FUJIFILM Wako Pure Chemical Corporation, 
     Phosphate metal salt: sodium 2,2′-methylenebis(4,6-di-tert-butylphenyl) phosphate, manufactured by Tokyo Chemical Industry Co., Ltd. 
     Example 1 
     Preparation of Resin Composition 
     A resin composition was obtained by mixing 100 parts by mass of PBAT and 1 part by mass of aliphatic polyester B-1 and kneading the mixture at 160° C. for 5 minutes with a two-roll mill. 
     Examples 2 to 13 and Comparative Examples 1 to 6 
     Resin compositions were prepared in the same manner as in Example 1, except that the amounts of the components were changed as shown in Tables 1 and 2. 
     Evaluation 
     For Examples and Comparative Examples, the melt viscosities of the resin compositions at 200° C., the crystallization temperatures of the resin compositions, the evaluation of the appearance of molded articles, and the presence or absence of bleed-out were observed by the following methods. Tables 1 and 2 show the results. 
     Measurement of Melt Viscosity of Resin Composition at 200° C. 
     The viscosity of each resin composition at 200° C. was measured with a capillary rheometer at a shear rate of 20 s −1 . The obtained melt viscosity was evaluated according to the following criteria. 
     Excellent: 1,200 Pa·s or less 
     Good: more than 1,200 Pa·s and 1,500 Pa·s or less 
     Poor: more than 1,500 Pa·s 
     Measurement of Crystallization Temperature of Resin Composition 
     Each resin composition was scraped to remove a thin slice with a cutter or the like. The obtained sliced sample (about 8 mg) was inserted into a pan for DSC measurement and brought into close contact with the pan. The crystallization temperature of the sample was measured by using a differential scanning calorimeter (product name DSCvesta, manufactured by Rigaku Corporation,). Specifically, the sample was heated to 200° C. at the rate of 10° C./min, held for 5 minutes, and then cooled to −50° C. at the rate of −10° C./min. In the obtained chart, the peak top of exotherm in the cooling procedure was taken as the crystallization temperature of the resin composition. 
     Evaluation of Appearance of Molded Article with Cycle Time of 20 Seconds 
     Each resin composition was introduced into an injection molding machine (product name SE30S, manufactured by Sumitomo Heavy Industries, Ltd.), heated to 200° C., and introduced into a mold at 60° C. to obtain an molded article having a structure illustrated in  FIGS.  4 A to  4 C . After cooling for 10 seconds, the molded article was removed from the mold. The time required for injection molding (cycle time) was 20 seconds. An emitter was assembled from the molded article. The obtained emitters were evaluated for appearance visually and with a light microscope. Evaluation criteria are as follows. 
     Excellent: No appearance defects was found 
     Good: Minor sink marks or minor short shots were found 
     Poor: Sink marks, short shots, warping and twisting occurred, or molding was impossible 
     Observation of Bleed-Out from Molded Article 
     The emitters prepared as described above were left at room temperature for one week. Subsequently, the surface condition of each emitter was visually checked to observe the presence or absence of bleed-out. Evaluation criteria are as follows. 
     Excellent: No bleed-out was observed 
     Good: A small amount of bleed-out was observed 
     Poor: A large amount of bleed-out was observed 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
               
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 8 
                 9 
                 10 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Compo- 
                 PBAT 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 sition 
                 Aliphatic 
                 B-1 
                 1 
                   
                   
                 5 
                   
                   
                 10 
                   
                 4 
                 3 
               
               
                 (parts by 
                 polyester 
                 B-2 
                   
                 1 
                   
                   
                 5 
               
               
                 mass) 
                   
                 B-3 
                   
                   
                 1 
                   
                   
                 5 
                   
                 10 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 Aliphatic ester 
                   
                   
                   
                   
                   
                   
                   
                   
                 1 
                 2 
               
               
                   
                 compound 
               
               
                   
                 Phosphate metal 
               
               
                   
                 salt 
               
               
                 Evaluation 
                 Melt viscosity 
                 Good 
                 Good 
                 Good 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
               
               
                   
                 Crystallization 
                 69 
                 69 
                 69 
                 70 
                 70 
                 70 
                 69 
                 70 
                 71 
                 71 
               
               
                   
                 temperature 
               
               
                   
                 Appearance 
                 Excellent 
                 Good 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
               
               
                   
                 Bleed-out 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
                 Good 
                 Excellent 
                 Good 
                 Good 
                 Excellent 
                 Excellent 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Example 
                 Example 
                 Example 
                 Comp. 
                 Comp. 
                 Comp. 
                 Comp. 
                 Comp. 
                 Comp. 
               
               
                   
                 11 
                 12 
                 13 
                 Ex. 1 
                 Ex. 2 
                 Ex. 3 
                 Ex. 4 
                 Ex. 5 
                 Ex. 6 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Composition 
                 PBAT 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 (parts by 
                 Aliphatic 
                 B-1 
                 5 
                 5 
                 5 
                   
                   
                   
                   
                 15 
                   
               
               
                 mass) 
                 polyester 
                 B-2 
               
               
                   
                   
                 B-3 
                   
                   
                   
                   
                   
                   
                   
                   
                 15 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 Aliphatic ester 
                 1 
                 2 
                 2 
                   
                 2 
                 3 
                 3 
                   
                   
               
               
                   
                 compound 
               
               
                   
                 Phosphate metal 
                   
                   
                 0.5 
                   
                   
                   
                 0.5 
               
               
                   
                 salt 
               
               
                 Evaluation 
                 Melt viscosity 
                 Excellent 
                 Excellent 
                 Excellent 
                 Poor 
                 Poor 
                 Poor 
                 Poor 
                 Excellent 
                 Excellent 
               
               
                   
                 Crystallization 
                 71 
                 71 
                 79 
                 38 
                 71 
                 72 
                 79 
                 68 
                 68 
               
               
                   
                 temperature 
               
               
                   
                 Appearance 
                 Excellent 
                 Excellent 
                 Excellent 
                 Poor 
                 Poor 
                 Poor 
                 Poor 
                 Poor 
                 Poor 
               
               
                   
                 Bleed-out 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
                 Excellent 
                 Poor 
                 Poor 
               
               
                   
               
            
           
         
       
     
     As shown in Tables 1 and 2, resin compositions containing an aliphatic polyester having a specific structure with respect to 100 parts by mass of PBAT had low melt viscosity at 200° C. (Examples 1 to 13). In these Examples, the crystallization temperature was 69° C. or more, and molding could be performed in a relatively short time. 
     On the other hand, when the amount of an aliphatic polyester having a specific structure exceeds 10 parts by mass with respect to 100 parts by mass of PBAT, bleed-out is more likely to occur (Comparative Examples 5 and 6). In addition, resin compositions including no aliphatic polyester resin had increased melt viscosity at 200° C. (Comparative Examples 1 to 4). 
     This application is entitled to and claims the benefit of Japanese Patent Application No. 2020-077697 filed on Apr. 24, 2020, the disclosure of which including the specification and drawings is incorporated herein by reference in its entirety. 
     INDUSTRIAL APPLICABILITY 
     The resin composition of the present invention can be buried in soil or composted after the use without imposing a burden on the environment. In addition, a molded article can be efficiently produced from the resin composition. Therefore, the resin composition can be used in a wide variety of applications such as drip irrigation tubes (such as emitters and tubes) and various packaging members. 
     REFERENCE SIGNS LIST 
     
         
           100  Drip irrigation tube 
           110  Tube 
           111  Discharge port 
           112  Inner wall surface 
           120  Emitter 
           120   a  First main body 
           120   b  Second main body 
           123  Hinge 
           131  Intake part 
           132  Groove 
           136  Flow rate adjusting part 
           137  Discharge part 
           142  Channel 
           146  Intake side screen part 
           147  Intake through hole 
           150  Notched groove 
           151  Communication hole 
           153  Diaphragm part 
           161  Base 
           162  Communicating groove