Method for producing resin pellet, resin pellet, and method for producing molded body

Abstract

The purpose of the present invention is to obtain a resin pellet capable of shortening the cooling time for a resin composition after being heated and melted during a molding process. The present invention involves, when a resin composition containing an aliphatic polyester resin is kneaded in an extruder (1) and thereafter extruded from a die head (2) to produce a resin pellet, setting the temperature of a cylinder (3) of the extruder (1) to equal to or lower than a temperature that is 30°C below the melting point peak temperature of the resin composition, and setting the temperature of the die head (2) is within a ±20°C range of the melting point peak temperature of the resin composition.

Description

Manufacturing method of resin pellets, resin pellets, and manufacturing method of molded body

[0001] The present invention relates to a method for producing resin pellets, a method for producing resin pellets, and a method for producing a molded article.

[0002] In recent years, there has been growing interest in the use of biodegradable plastics to combat marine pollution caused by plastics. However, a report compiled by the United Nations Environment Programme in 2015 pointed out that compostable plastics such as polylactic acid cannot be expected to decompose in a short period of time in the cold ocean, and therefore cannot be used to combat marine pollution.

[0003] In this context, poly(3-hydroxyalkanoate)-based resins (hereinafter sometimes referred to as "P3HA-based resins") are attracting attention as a material that can solve the above-mentioned problems because they are capable of biodegrading even in seawater.

[0004] Another known technique involves heating a thermoplastic biodegradable resin to form a molten resin, feeding the molten resin between dies, closing the dies to press-mold it, and cooling it to obtain a molded product.

[0005] However, because P3HA resins have a slow crystallization solidification rate, a long cooling time is required for solidification after the P3HA resin composition is heated and melted during molding, which poses a problem in terms of productivity.As a technology for solving such problems, for example, Patent Document 1 discloses a method for producing an injection-molded article of a P3HA resin, in which the heat-melting temperature of a molding material containing a P3HA resin is specified as the difference between the melting point peak temperature and the melting point peak end temperature in DSC (differential scanning calorimetry), and the mold temperature is specified to be 30°C to 80°C.

[0006] Patent Document 2 discloses a powder granulation product containing a thermoplastic resin powder. This powder granulation product is used as a molding material. This powder granulation product is a compression granulation product, and is produced by a compression granulator without undergoing a melt-kneading pelletization process for the thermoplastic resin powder as a raw material.

[0007] International Publication No. 2021 / 010054 Japanese Patent No. 7387950

[0008] Although the technology of Patent Document 1 is excellent, from another viewpoint, there is a need to develop a new technology that can increase the crystallization rate of the resin, shorten the cooling time of the resin composition after heat-melting during molding, and contribute to improving productivity. Also, the technology of Patent Document 2 has room for improvement in terms of increasing the crystallization solidification rate of the resin and shortening the cooling time of the resin composition after heat-melting during molding.

[0009] An object of one aspect of the present invention is to provide a method for producing resin pellets, resin pellets, and molded articles that can shorten the cooling time of a resin composition after heat-melting during molding.

[0010] In order to solve the above problems, a method for producing resin pellets according to one embodiment of the present invention is a method for producing resin pellets containing an aliphatic polyester-based resin, which includes a step of kneading a resin composition containing an aliphatic polyester-based resin in an extruder and then extruding the mixture from a die head, wherein the temperature of the cylinder of the extruder is set to the peak melting point temperature of the resin composition minus 30°C or less, and the temperature of the die head is set to a temperature within a range of ±20°C of the peak melting point temperature of the resin composition.

[0011] In order to solve the above-mentioned problems, another aspect of the present invention provides resin pellets made of a resin composition containing an aliphatic polyester resin, and the percentage of the resin pellets that buckle when subjected to a compression test in which a load of up to 400 N is applied in a direction perpendicular to the side surface of the resin pellets is 30% to 100%.

[0012] According to one aspect of the present invention, the cooling time of a resin composition after it has been heated and melted during molding can be shortened.

[0013] 1 is a diagram showing a schematic configuration example of a kneading extrusion device used in a method for producing resin pellets according to an embodiment of the present invention. 2 is a diagram showing a schematic configuration of a manufacturing device used in a method for producing a molded body according to an embodiment of the present invention. 3 is a graph for explaining evaluation of buckled resin pellets in Examples.

[0014] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more (including A and greater than A) and B or less (including B and less than B)."

[0015] [Technical Concept] While developing a new technology that can shorten the cooling time of a resin composition after heat-melting during molding and contribute to improving productivity, the present inventors focused on resin pellets used for the resin composition during molding, and thought that if resin pellets with a relatively high solidification peak temperature are used, the crystallization solidification rate of the resin pellets after heat-melting during molding can be increased, and the cooling time of the resin composition can be shortened.

[0016] Based on the above-mentioned idea, the present inventors conducted extensive research into methods for producing resin pellets with a high solidification peak temperature, and as a result, they discovered that resin pellets with a high solidification peak temperature can be produced by (1) employing a method of kneading in an extruder followed by extrusion from a die head, (2) controlling the temperature of the extruder cylinder within a specific range, and (3) controlling the temperature of the die head within a specific range, and thus arrived at the method for producing resin pellets according to this embodiment.

[0017] That is, the method for producing resin pellets according to this embodiment is a method for producing resin pellets containing an aliphatic polyester-based resin, and includes a step of kneading a resin composition containing an aliphatic polyester-based resin in an extruder and then extruding the mixture from a die head, in which the temperature of the cylinder of the extruder is set to the peak melting point temperature of the resin composition minus 30°C or less, and the temperature of the die head is set to a range of ±20°C of the peak melting point temperature of the resin composition.

[0018] According to the method for producing resin pellets of this embodiment, it is possible to obtain resin pellets with a high solidification peak temperature. Furthermore, if the resin pellets obtained by this method are used, the crystallization solidification rate of the resin pellets increases after heat melting during molding, and the cooling time of the resin composition can be shortened.

[0019] The powder granules of Patent Document 2 are compression granules, and are produced by a compression granulator without a melt-kneading pelletizing process for the raw material thermoplastic resin powder. That is, the method of producing the powder granules of Patent Document 2 does not employ a method of kneading in an extruder and then extruding from a die head, and the method underlying this method is fundamentally different from that of the present embodiment.

[0020] Furthermore, according to the method for producing resin pellets according to this embodiment, by using a marine biodegradable resin (for example, a P3HA-based resin), marine pollution due to waste can be suppressed, which can contribute to the achievement of Sustainable Development Goals (SDGs) such as Goal 12 "Ensure sustainable consumption and production patterns" and Goal 14 "Conserve and sustainably use the oceans and marine resources for sustainable development." This embodiment will be described in detail below.

[0021] [Method for producing resin pellets] As described above, the method for producing resin pellets according to this embodiment includes a step of kneading a resin composition containing an aliphatic polyester resin in an extruder and then extruding the mixture through a die head (hereinafter, this step may be referred to as a kneading-extrusion step). In the method for producing resin pellets according to this embodiment, the extrudate obtained by the kneading-extrusion step is cooled in a cooling step to obtain resin pellets.

[0022] The kneading / extrusion device for carrying out the kneading / extrusion step can be any conventionally known device as long as it is equipped with an extruder and a die head. Generally, a kneading / extrusion device having a die head attached to the tip of the extruder in the extrusion direction of the resin composition is used. Figure 1 is a diagram schematically showing an example of the configuration of a kneading / extrusion device 10 used in the method for producing resin pellets according to this embodiment.

[0023] As shown in Fig. 1, the kneading extrusion device 10 includes an extruder 1 and a die head 2. The extruder 1 conveys a raw material resin composition while kneading it with a rotating screw (not shown). The die head 2 is provided at the tip of the extruder 1 in the direction in which the resin composition is conveyed (extrusion direction).

[0024] The extruder 1 has a cylinder 3 and a raw material hopper 4. The cylinder 3 is the main body of the extruder 1 and forms a flow path (conveyance path) through which the resin composition and its kneaded product are conveyed. The cylinder 3 is provided with the raw material hopper 4. The raw material for the resin pellets is charged into the cylinder 3 via the raw material hopper 4.

[0025] Any conventionally known extruder can be used as the extruder 1 as long as it has a rotating screw for kneading and conveying the resin composition. Examples of the extruder 1 include a single-screw extruder and a twin-screw extruder, with a twin-screw extruder being preferred.

[0026] Although not shown in FIG. 1 , the rotating screw provided in the extruder 1 can have a conventionally known structure. As an example, the rotating screw can have a structure including a feed zone, a kneading zone, a kneading zone, and a pressurization zone. The feed zone is intended to transport raw materials fed from the raw material hopper 4 in the extrusion direction. The pressurization zone is intended to pressurize the kneaded material and extrude it into the die head 2. The kneading zone is intended to knead the resin composition. The vent zone is intended to remove volatiles and decomposition gases generated from the resin composition by kneading. The screw grooves (structure, shape, size, pitch, etc.) provided in each of the feed zone, kneading zone, vent zone, and pressurization zone can have conventionally known structures and are appropriately determined depending on the purpose of each of the above-mentioned zones and the type of resin composition.

[0027] The die head 2 has a plurality of discharge ports through which the kneaded material is extruded. The kneaded material supplied to the die head 2 is extruded from the discharge ports and formed into a strand shape (string shape, rope shape).

[0028] The kneading / extrusion process of the resin pellet manufacturing method using the kneading / extrusion device 10 shown in Fig. 1 includes at least a kneading process and an extrusion process. In the extruder 1, a resin composition charged into a raw material hopper 4 is supplied to a cylinder 3. The resin composition supplied to the cylinder 3 is kneaded in a kneading zone and transported toward a die head 2 (kneading process).

[0029] Then, the kneaded material that has undergone the kneading process in the cylinder 3 is supplied to the die head 2. The kneaded material supplied to the die head 2 is extruded from the discharge opening of the die head 2 (extrusion process). In the extrusion process, the kneaded material passes through the discharge opening of the die head 2 and is formed into a strand shape (string shape, rope shape).

[0030] The strand-like kneaded material extruded from the discharge port of the die head 2 is cut to a predetermined length by the cutting process of the cutting unit. In other words, the kneaded material extruded in the form of strands is divided into pellets. Then, in the method for producing resin pellets, the obtained pellet-like kneaded material is subjected to a cooling process.

[0031] In the cooling step, the semi-molten material obtained after the kneading / extrusion step is cooled to obtain a molded product. As a method for cooling the semi-molten material in the cooling step, a conventionally known cooling method used in extrusion molding technology can be adopted. In addition, the cooling method can be appropriately selected depending on the shape of the molded product to be obtained, etc.

[0032] For example, when resin pellets are formed using the kneading extrusion apparatus 10 shown in Figure 1, the cooling methods can be broadly divided into two: a cold cut method and a die face cut method. The cold cut method includes a method in which the semi-molten material extruded from the die head 2 is cooled through a water tank while a strand-shaped molded product is withdrawn and then shredded (strand cut method). The die face cut method is a method in which the semi-molten material extruded from the discharge port of the die head 2 is cut with a rotating cutter while in contact with the surface of the die head 2 or while a small gap is maintained.

[0033] The die face cutting method can be further divided into three methods based on the cooling method: underwater cutting (hereinafter sometimes referred to as UWC), watering cutting (hereinafter sometimes referred to as WRC), and hot cutting (hereinafter sometimes referred to as HC). The UWC method involves filling a chamber attached to the tip of the die head 2 with cooling water adjusted to a predetermined pressure so that it contacts the resin discharge surface of the die head 2, and cutting the semi-molten material extruded from the discharge port of the die head 2 underwater. The WRC method involves placing a cooling drum connected to the die head 2 downstream from the die head 2, through which cooling water flows along its inner surface, and cooling the semi-molten material cut by the cutter in the air under the cooling water. The HC method involves cutting the semi-molten material with a cutter in the air, and cooling the cut semi-molten material in the air. Examples of the HC method include a mist cutting method that further includes a step of spraying a mixed mist of water and air.

[0034] The kneaded material extruded from the discharge port of the die head 2 is in a semi-molten state, so there is no need to rapidly lower the temperature of the kneaded material for solidification. Therefore, in the cooling step, even if the kneaded material extruded from the discharge port of the die head 2 is cooled in air as in the HC method, the desired resin pellets can be obtained in a short time.

[0035] In the method for producing resin pellets according to this embodiment, the temperature of the cylinder 3 of the extruder 1 and the temperature of the die head 2 are controlled so that the resin composition contained in the obtained resin pellets is not completely melted but is in a semi-molten state. That is, in the method for producing resin pellets according to this embodiment, the temperatures are controlled as follows in the kneading step and the extrusion step.

[0036] First, in the kneading step, the temperature of the cylinder 3 of the extruder 1 is set to the melting point peak temperature of the resin composition minus 30°C or less. The temperature of the cylinder 3 can be measured, for example, by attaching a heat sensor such as a thermocouple to the cylinder 3. The temperature of the cylinder 3 refers to the temperature of the portion of the cylinder 3 from the raw material hopper 4 side to the tip on the die head 2 side, excluding the portion directly below the raw material hopper 4. The temperature of the cylinder 3 may be set in any manner as long as it is within the above-mentioned temperature range. For example, the cylinder 3 may be divided into zones and different temperatures may be set between these zones, or the same temperature may be set between the zones.

[0037] In the kneading process of the resin composition using the extruder 1, the raw material resin composition tends to melt due to heat generated mainly by shearing action caused by the rotation of the screw. Furthermore, the melt is kneaded (dispersively mixed and distributively mixed) mainly by shearing action and elongation action caused by the rotation of the screw. Heat generation in the melt continues even during kneading. Therefore, in the kneading process, the temperature of the cylinder 3 of the extruder 1 is set so as to suppress, to some extent, melting of the resin composition due to heat generated by the shearing action caused by the rotation of the screw. To maintain the temperature of the cylinder 3 at or below −30° C., the melting point peak temperature of the resin composition, the resin composition may be cooled by a cooling means, as necessary.

[0038] The lower the temperature limit of the cylinder 3, the better, but it is generally 10°C or higher. If the temperature is too low, condensation will form on the cylinder 3, so the lower limit of the temperature of the cylinder 3 is preferably 10°C or higher. For example, when the resin composition contains a P3HA-based resin, the temperature of the cylinder 3 is set to 10°C to 120°C, preferably 30°C to 90°C.

[0039] In the extrusion process, the temperature of the die head 2 is set within the range of the peak melting point temperature of the resin composition ±20° C. That is, the temperature of the die head 2 is set so that the range of the peak melting point temperature of the resin composition −20° C.≦the temperature of the die head 2≦the peak melting point temperature of the resin composition +20° C. The temperature of the die head 2 can be measured, for example, by a temperature sensor such as a thermocouple attached to the die head 2.

[0040] In the extrusion step, the resin composition may melt due to the heat of compression when passing through the die head 2. In the method for producing resin pellets according to the present embodiment, the temperature of the die head 2 is set within the above-mentioned range, so that the resin composition does not completely melt due to the heat of compression even when passing through the die head 2, but remains in a semi-molten state.

[0041] In order to maintain the temperature of the die head 2 within a range of ±20°C of the peak melting point temperature of the resin composition, the kneaded material may be heated by a heating means such as a heater, or the kneaded material may be cooled by a cooling means, as necessary. From the viewpoint of making the resin composition semi-molten after passing through the die head 2, the temperature of the die head 2 is preferably set within a range of ±25°C of the peak melting point temperature, more preferably within a range of ±10°C of the peak melting point temperature. For example, when the resin composition contains a P3HA-based resin, the temperature of the die head 2 is set to 120°C to 170°C, preferably 135°C to 155°C.

[0042] Here, the melting peak temperature is the melting point peak temperature in differential scanning calorimetry analysis and is defined as follows. An aluminum pan is filled with 4 mg to 10 mg of a resin sample, and the resin sample is melted using a differential scanning calorimetry analyzer by heating from 30°C to 160°C at a rate of 10°C / min under a nitrogen stream. The endothermic curve obtained when the temperature is increased from 30°C to 160°C at this rate is taken as the melting point peak temperature. For resin samples with melting point peak temperatures of 160°C or higher, the upper measurement limit can be appropriately adjusted to be within the melting point peak temperature +10°C to +20°C. When the resin sample is a resin composition, the melting point peak temperature is measured for the entire resin composition. When the resin sample is a resin pellet, the melting point peak temperature is measured for the entire resin pellet.

[0043] In the method for producing resin pellets according to this embodiment, a resin composition having one peak melting point temperature may be used, or a resin composition having two or more peak melting point temperatures may be used. In the method for producing resin pellets according to this embodiment, when the resin composition has two or more peak melting point temperatures, the highest temperature among the two or more peak melting point temperatures is used as the peak melting point temperature.

[0044] The peak melting temperature of the resin composition is not particularly limited, but is preferably 100° C. to 200° C., and more preferably 130° C. to 170° C. Furthermore, for example, when the resin composition contains a P3HA-based resin, the peak melting temperature is preferably 130° C. to 170° C., and more preferably 135° C. to 160° C. When the peak melting temperature is in the above numerical range, the resin composition can be melted without thermal decomposition, and therefore has excellent processability.

[0045] Furthermore, in the method for producing resin pellets according to the present embodiment, the retention rate of the weight-average molecular weight between the resin composition before kneading and the resin pellets obtained after kneading is preferably 85.0% to 100.0%, and more preferably 90.0% to 100.0%. By having the retention rate of the weight-average molecular weight within the above numerical range, it is possible to suppress a decrease in the mechanical strength of a molded article produced using the resin pellets according to the present embodiment as a raw material.

[0046] The weight average molecular weight can be determined as a molecular weight converted into polystyrene by gel permeation chromatography (GPC) (RI monitor "L-3000" manufactured by Hitachi, Ltd.) using polystyrene gel ("K-G" (1 tube) and "K-806L" (2 tubes) manufactured by Showa Denko K.K.) as columns and chloroform as a mobile phase.

[0047] The weight average molecular weight of the resin composition before kneading is not particularly limited, but is preferably 100,000 to 1,000,000, more preferably 150,000 to 800,000, and even more preferably 200,000 to 600,000. In particular, when the resin composition contains a P3HA-based resin, the weight average molecular weight of the resin composition before kneading is not particularly limited, but is preferably 100,000 to 1,000,000, more preferably 150,000 to 800,000, and even more preferably 200,000 to 600,000. Furthermore, the weight average molecular weight of the resin pellets obtained after kneading is not particularly limited, but is preferably 80,000 to 800,000, more preferably 120,000 to 640,000, and even more preferably 160,000 to 480,000. In particular, when the resin composition contains a P3HA-based resin, the weight average molecular weight of the resin pellets obtained after kneading is not particularly limited, but is preferably 80,000 to 800,000, more preferably 120,000 to 640,000, and even more preferably 160,000 to 480,000.

[0048] When the weight average molecular weight of the resin composition before kneading and the weight average molecular weight of the resin pellets obtained after kneading are each within the above numerical ranges, appropriate mechanical strength can be obtained and an excessive increase in melt viscosity can be suppressed, resulting in excellent moldability and processability.

[0049] [Resin Composition] The resin composition used in the method for producing resin pellets according to this embodiment contains an aliphatic polyester-based resin. The aliphatic polyester-based resin is not particularly limited, but is preferably biodegradable, and is more preferably a P3HA-based resin. In this specification, "P3HA-based resin" refers to a resin having the general formula: [-CHR-CH ２ -CO-O-] (wherein R is C ｎ H ２ｎ＋１and n is an integer of 1 or more and 15 or less.) as a repeating unit.

[0050] More specifically, the P3HA-based resin preferably contains 3-hydroxybutyrate (3HB) units. The P3HA-based resin is preferably one or more selected from the group consisting of poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (P3HB3HV3HH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxydecanoate), and combinations thereof. The P3HA-based resin may contain only one type, or may contain two or more types.

[0051] The P3HA resin is preferably a P3HA resin produced by a microorganism (a microbially produced P3HA resin). A microbially produced P3HA resin is usually composed only of D-form (R-form) polyhydroxyalkanoate monomer units. Among the microbially produced P3HA resins, P3HB, P3HB3HH, P3HB3HV, P3HB3HV3HH, and P3HB4HB are preferred because of ease of industrial production, with P3HB, P3HB3HH, P3HB3HV, and P3HB4HB being more preferred.

[0052] P3HA-based resins can also be produced by, for example, the method described in International Publication No. 2010 / 013483. Commercially available P3HA-based resins include Kaneka Biodegradable Polymer PHBH (registered trademark) manufactured by Kaneka Corporation.

[0053] The P3HA resin also contains at least one copolymer of a 3HB unit and another hydroxyalkanoate unit, and the 3-hydroxybutyrate unit in the poly(3-hydroxyalkanoate) resin accounts for 65.0 to 99.0 mol %, preferably 68.0 to 98.5 mol %, more preferably 70.0 to 98.5 mol %, and even more preferably 70.0 to 98.0 mol %, of all repeating units (100 mol %).

[0054] When the composition ratio of the 3HB repeating unit is 65.0 mol% or more, the rigidity of the P3HA-based resin is improved, the crystallization rate is accelerated, burrs are reduced, and productivity tends to be improved. On the other hand, when the composition ratio of the 3HB repeating unit is 99.0 mol% or less, the melting point is below the thermal decomposition temperature, making stable and continuous production possible. The monomer composition ratio of the P3HA-based resin can be measured by gas chromatography or the like (see, for example, International Publication No. 2014 / 020838).

[0055] In the kneading / extrusion step, a resin composition containing the P3HA-based resin is used to produce resin pellets. The resin composition used in the kneading / extrusion step is not particularly limited as long as it contains the P3HA-based resin and can be extruded into resin pellets.

[0056] The resin composition may contain two or more P3HA resins having different composition ratios of 3HB repeating units and / or different weight average molecular weights.

[0057] The resin composition may contain other resins besides the P3HA resin, provided that the effects of the present invention are not impaired. Examples of such other resins include aliphatic polyester resins such as polybutylene succinate adipate, polybutylene succinate, polycaprolactone, and polylactic acid, and aliphatic aromatic polyester resins such as polybutylene adipate terephthalate, polybutylene sebatate terephthalate, and polybutylene azelate terephthalate. Only one type of other resin may be contained, or two or more types may be contained.

[0058] The content of the other resin is not particularly limited, but is preferably 50 parts by weight or less, more preferably 40 parts by weight or less, and even more preferably 30 parts by weight or less, relative to 100 parts by weight of the total P3HA resin. The lower limit of the content of the other resin is not particularly limited, and may be 0 parts by weight.

[0059] The resin composition does not necessarily contain an inorganic filler, but preferably further contains an inorganic filler. When the resin composition contains an inorganic filler, the crystallization rate is improved, and effects such as reducing burrs and improving the production cycle are achieved.

[0060] The inorganic filler is not particularly limited, but examples thereof include talc, diatomaceous earth, white clay, clay, calcium carbonate, manganese carbonate, magnesium carbonate, barium sulfate, mica, silica, alumina, zircon, iron oxide, zinc oxide, titanium oxide, silicon nitride, boron nitride, aluminum nitride, silicon carbide, graphite, carbon black, ferrite, graphite, quartz, glass fiber, glass particles, etc. These may be used alone or in combination of two or more.

[0061] The content of the inorganic filler is, for example, 0 to 60 parts by weight, preferably 5 to 50 parts by weight, more preferably 10 to 40 parts by weight, and particularly preferably 15 to 35 parts by weight, relative to 100 parts by weight of the total P3HA-based resin. When the content of the inorganic filler is within the above range, a sufficient crystallization rate and toughness can both be achieved.

[0062] The resin composition may also contain additives that can be used with the P3HA-based resin, provided that the effects of the present invention are not impaired. Examples of such additives include colorants such as pigments and dyes, odor absorbers such as activated carbon and zeolite, fragrances such as vanillin and dextrin, plasticizers, antioxidants, weather resistance improvers, UV absorbers, crystal nucleating agents, lubricants, release agents, water repellents, antibacterial agents, and sliding properties improvers. Only one type of additive may be contained, or two or more types may be contained. The content of these additives can be appropriately determined by those skilled in the art depending on the intended use.

[0063] Furthermore, the resin composition does not need to contain a nucleating agent. In the resin composition, the nucleating agent has the function of promoting the crystallization of the P3HA-based resin and accelerating the crystallization rate of the resin composition. According to this embodiment, since the obtained resin pellets are in a semi-molten state, the crystallization rate of the resin pellets can be accelerated even if the resin composition does not contain a nucleating agent.

[0064] It is known that poly(3-hydroxybutyrate) (P3HB) also acts as a crystal nucleating agent by accelerating the crystallization rate of a resin composition. In this specification, the term "crystal nucleating agent" does not refer to a resin that has the function of accelerating the crystallization rate of such a resin composition. In other words, in this specification, the definition of a crystal nucleating agent is a non-resin component that promotes the crystallization of a P3HA-based resin and has the function of accelerating the crystallization rate of a resin composition.

[0065] Examples of such crystal nucleating agents include sugar alcohol compounds derived from natural products such as erythritol, pentaerythritol, galactitol, mannitol, and arabitol; polysaccharides such as chitin and chitosan; polyols such as aliphatic alcohols (polyols), polyvinyl alcohol, and polyethylene oxide; sodium benzoate, potassium benzoate, lithium benzoate, calcium benzoate, magnesium benzoate, barium benzoate, lithium terephthalate, sodium terephthalate, potassium terephthalate, calcium oxalate, sodium laurate, and lauric acid. Potassium urate, sodium myristate, potassium myristate, calcium myristate, sodium octacosanoate, calcium octacosanoate, sodium stearate, potassium stearate, lithium stearate, calcium stearate, magnesium stearate, barium stearate, sodium montanate, calcium montanate, sodium toluate, sodium salicylate, potassium salicylate, zinc salicylate, aluminum dibenzoate, potassium dibenzoate, lithium dibenzoate, sodium β-naphthalene organic sulfonates such as sodium p-toluenesulfonate and sodium sulfoisophthalate; carboxylic acid amides such as behenamide, ethylenestearamide, ethylenebislauricamide, palmitic acid amide, hydroxystearic acid amide, erucic acid amide, and trimesic acid tris(t-butylamide), and carboxylic acid esters such as laurate, palmitate, oleate, stearate, erucate, N-oleyl palmitate, N-oleyl oleate, N-oleyl stearate, N-stearyl oleate, N-stearyl stearate, N-stearyl erucate, methylene bisstearate, ethylene bislaurate, ethylene biscaprate, ethylene bisoleate, ethylene bisstearate, ethylene biserucate, ethylene bisisostearate, butylene bisstearate, and p-xylylene bisstearate;Examples of suitable compounds include dicarboxylic acid derivatives such as dimethyl adipate, dibutyl adipate, diisodecyl adipate, and dibutyl sebacate; cyclic compounds having a functional group C═O and one or more functional groups selected from the group consisting of NH, S, and O in the molecule, such as indigo, quinacridone, and quinacridone magenta; sorbitol derivatives such as bisbenzylidene sorbitol and bis(p-methylbenzylidene) sorbitol; compounds containing a nitrogen-containing heteroaromatic nucleus, such as pyridine, triazine, and imidazole; phosphate ester compounds, bisamides of higher fatty acids, and metal salts of higher fatty acids. In this embodiment, these exemplified compounds do not necessarily need to be contained in the resin composition.

[0066] [Resin pellets] The resin pellets according to this embodiment are not in a completely molten state in which the resin composition constituting the resin pellets is completely melted, but are in a semi-molten state in which a portion of the resin composition is melted and the remaining portion is not melted. The resin pellets according to this embodiment are resin pellets made of a resin composition containing an aliphatic polyester resin, and the percentage of the resin pellets that buckle when subjected to a compression test in which a load of up to 400 N is applied in a direction perpendicular to the side of the resin pellets is 30% to 100%. The resin pellets according to this embodiment are, for example, resin pellets produced by the method described in the above section [Method for producing resin pellets].

[0067] The compression test to measure the percentage of buckled resin pellets is performed using a texture analyzer (TA.XTplus, manufactured by Eiko Seiki Co., Ltd.). Specifically, a 4 mm diameter cylinder probe is used to apply a load perpendicular to the side of the resin pellet at a compression rate of 0.3 mm / sec, and the load (N) and displacement (mm) are measured. The behavior of the load-displacement curve (see Figure 3) obtained from this measurement is then used to evaluate whether or not buckling occurs in the resin pellet. Specifically, under the above compression rate conditions, the load on the side of the resin pellet is increased until a load of 400 N is applied. If a yield point appears on the load-displacement curve, the resin pellet is evaluated as having buckled.

[0068] The resin pellets according to this embodiment are evaluated as having buckling in a proportion of 30% to 100%, and are in a semi-molten state with a relatively high peak solidification temperature. Therefore, by using the resin pellets according to this embodiment, the crystallization and solidification rate of the resin pellets increases after heating and melting during molding, and the cooling time of the resin composition can be shortened.

[0069] Furthermore, in the resin pellets according to this embodiment, the resin composition does not contain a nucleating agent. The definition of a nucleating agent is as described above. According to this embodiment, the resin pellets obtained are in a semi-molten state, so that the crystallization solidification rate of the resin pellets can be increased even if the resin composition does not contain a nucleating agent.

[0070] From the viewpoint of promoting the crystallization and solidification of the resin pellets, the resin pellets according to this embodiment preferably have a peak solidification temperature of 90°C to 120°C, more preferably 100°C to 110°C. The resin pellets according to this embodiment preferably have a peak melting point temperature of 130°C to 170°C, more preferably 135°C to 160°C. Furthermore, the resin pellets according to this embodiment preferably have a difference between the peak melting point temperature and the peak solidification temperature of 0°C to 60°C, more preferably 10°C to 45°C.

[0071] The peak solidification temperature is the peak solidification temperature in differential scanning calorimetry, and is defined as follows: 4 mg to 10 mg of a resin sample is filled into an aluminum pan, and the resin sample is solidified by lowering the temperature from 160°C to 30°C at a rate of 10°C / min using a differential scanning calorimetry analyzer under a nitrogen stream. The temperature at which the heat release is maximized in the heat release curve obtained is defined as the peak solidification temperature. When the resin sample is a resin pellet, the peak solidification temperature is measured for the entire resin pellet.

[0072] [Method for Manufacturing a Molded Body] The method for manufacturing a molded body according to this embodiment is a method for manufacturing a molded body using the resin pellets according to this embodiment or resin pellets obtained by the method for manufacturing a resin pellet according to this embodiment. The manufacturing method includes a supplying step and a molding step. In the supplying step, a molding material including the resin pellets is heated and melted to a temperature equal to or higher than the peak melting point temperature of the resin pellets, and the resulting molten molding material is supplied between a pair of molds by being discharged from a discharge portion. In addition, in the molding step, the pair of molds is closed, and the flowable molten molding material is press-molded and cooled. The molded body obtained by the method for manufacturing a molded body according to this embodiment is a press-molded body. According to the method for manufacturing a molded body according to this embodiment, a material including the resin pellets according to this embodiment, which has a relatively high solidification peak temperature, is used as the molding material. Therefore, the molten material obtained after heating and melting in the supplying step has a fast crystallization and solidification rate of the resin pellets. Therefore, when the molten molding material is press-molded and cooled in the molding step, the cooling time of the molten molding material can be shortened.

[0073] FIG. 2 is a diagram showing a schematic configuration of a manufacturing apparatus 100 used in the method for manufacturing a molded body according to this embodiment.

[0074] As shown in Fig. 2, the molding apparatus 100 includes a pair of molds for filling a molten resin composition containing resin pellets. The lower mold of the pair of molds is shown in Fig. 2. The molding apparatus 100 includes a molten resin generation section 11 and a supply section 12.

[0075] The molten resin generation section 11 heats a material containing resin pellets to generate a molten resin composition. The molten resin generation section 11 includes a raw material input section for inputting the material containing resin pellets. The molten resin generation section 11 also includes a melt-kneading device that melts and kneads the raw materials input from the raw material input section. The molten resin generation section 11 may also include a mixing device that mixes the raw materials, as necessary. While FIG. 2 shows a configuration in which the molten resin generation section 11 includes an extruder as the melt-kneading device, the configuration of the molten resin generation section 11 is not limited to the configuration shown in FIG. 2.

[0076] The supply unit 12 has a discharge unit 12a that discharges the molten resin composition generated in the molten resin generation unit 11. The supply unit 12 supplies the molten resin composition between the pair of molds by the discharge unit 12a. In the configuration shown in Fig. 2, the supply unit 12 is configured to discharge the molten resin composition from the discharge unit 12a to the lower mold. After a predetermined amount of molten resin composition is supplied to the lower mold, the upper mold is placed on the lower mold, thereby supplying the molten resin composition between the pair of molds.

[0077] The manufacturing apparatus 100 also includes a molding unit (not shown). The molding unit closes a pair of molds to press-mold and cool the flowable molten resin composition. The molding unit includes a heat press molding machine that heat-presses the pair of molds, and a cooling device that cools the pair of molds after the heat press is complete. Any device used in press molding can be used for the heat press machine and the cooling device. For example, the cooling device may include a pair of cooling plates that sandwich the pair of molds, and the cooling plates may be used to cold-press the pair of molds.

[0078] 2, the manufacturing method of a molded body using the manufacturing apparatus 100 first performs the above-described supply step. That is, molding material including resin pellets is introduced from a raw material introduction section into the molten resin production section 11. Then, in the molten resin production section 11, the molding material is kneaded while being heated to a temperature equal to or higher than the peak melting point temperature of the resin pellets and melted.

[0079] The mode of the melt-kneading is not particularly limited as long as a melt-kneaded resin composition can be obtained. Specific examples of the melt-kneading step include the following methods (a1) and (a2): (a1) A method in which a resin composition containing resin pellets is prepared by mixing or blending using a mixer or the like, and then the resin composition is supplied to a melt-kneading device and melt-kneaded; (a2) A method in which raw materials for a resin composition containing resin pellets are supplied to a melt-kneading device, and a resin composition is prepared (completed) in the melt-kneading device, and the resin composition is melt-kneaded.

[0080] In the method (a1), the order in which the raw materials for the resin composition containing resin pellets are mixed or blended (dry blended) is not particularly limited. In the method (a2), the order in which the raw materials for the resin composition containing resin pellets are supplied to the melt-kneading device is not particularly limited.

[0081] In the method (a1), the mixing device is not particularly limited, and examples thereof include a ribbon blender, a flash blender, a tumbler mixer, and a super mixer.

[0082] In the methods (a1) and (a2), the melt-kneading device is not particularly limited, and examples thereof include an extruder, a kneader, a Banbury mixer, a roll, etc. Because of their excellent productivity and convenience, an extruder is preferred as the melt-kneading device, as shown in the molten resin generating section 11 in Fig. 2, and a twin-screw extruder is more preferred.

[0083] The temperature when melt-kneading the resin composition is equal to or higher than the peak melting point temperature of the resin pellets, and cannot be generally specified because it depends on the physical properties of the resin pellets (melting point, weight average molecular weight, etc.) and the type of additive used. Regarding the temperature when melt-kneading the resin composition, for example, when the resin pellets contain P3HA resin, the temperature of the melt-kneaded resin composition discharged from the discharge port (hereinafter sometimes referred to as the composition temperature) is preferably 140°C to 190°C, more preferably 150°C to 180°C, and even more preferably 160°C to 170°C. If the composition temperature is 150°C or lower, unmelted P3HA-based resin may be generated. On the other hand, if the composition temperature is 180°C or higher, the P3HA-based resin may be thermally decomposed.

[0084] Next, in the supplying step, the molten molding material obtained by melt-kneading is supplied between the pair of molds by being discharged from the discharge part. At this time, the molten molding material is discharged from the discharge part into the pair of molds while still in a molten state. In this way, the molten molding material is supplied between the pair of molds in a flowable state.

[0085] The method for supplying the molten material for molding between the molds is not particularly limited as long as the molten material discharged from the discharge part can be supplied between the pair of molds. From the viewpoint of reliably supplying the molten material between the pair of molds, it is preferable to first discharge the molten material from the discharge part to the lower mold, supply a predetermined amount of the molten resin composition to the lower mold, and then place the upper mold on the lower mold, thereby supplying the molten material between the pair of molds.

[0086] The configuration of the discharge section is not particularly limited as long as it is capable of discharging the molten material, and any conventionally known configuration can be used. From the viewpoint of improving the productivity of the press-molded body, it is preferable that the discharge section be configured to be able to quantitatively discharge the molten material. Examples of such a discharge section configuration include a configuration equipped with a gear pump and a configuration equipped with an automatic opening and closing nozzle. Specific examples of the discharge section include a plunger-type discharger, a pre-plunger-type discharger, and a screw-type discharger.

[0087] Next, in the molding step, the pair of dies are closed and the flowable molten material for molding is press-molded and cooled. In the supply step, the molten material is supplied between the pair of dies in a molten state, so that even when the pair of dies are closed in the molding step, the molten material can flow within the space between the pair of dies.

[0088] After the molten material is supplied between the pair of dies in the supplying step, the pair of dies are subjected to heat pressing using a heat press molding machine in the molding step. Then, the pair of dies after the heat pressing is cooled to perform press molding. After press molding, the pair of dies are opened to obtain a press-molded body.

[0089] The heat press molding machine used in the molding step is not particularly limited as long as it is configured to be able to heat press the pair of dies to which the molten material has been supplied. Any conventionally known device can be used as the heat press molding machine.

[0090] In addition, in order to allow the molten material supplied between the pair of dies to flow, the pair of dies are preferably preheated. The heating temperature of the pair of dies may be any temperature that can maintain the composition temperature of the molten material, preferably within ±30°C of the composition temperature of the molten material, and more preferably the same temperature as the composition temperature of the molten material.

[0091] The pressing pressure of the pair of dies by the heat press molding machine is not particularly limited, but is preferably 50 KN to 300 KN, and more preferably 100 KN to 200 KN. Setting the pressing pressure within the above numerical range has the advantage of making it easier to obtain a press-molded body with a uniform thickness.

[0092] The pressing time of the pair of dies in the heat press molding machine is not particularly limited, but is preferably 5 to 60 seconds, and more preferably 10 to 30 seconds. Setting the pressing time within the above range has the advantage of making it easier to obtain a press-molded product with a uniform thickness.

[0093] The method for cooling the pair of molds after the hot pressing is not particularly limited, and examples thereof include a method in which the pair of molds after the hot pressing is sandwiched between a pair of cooling plates and subjected to cold pressing.

[0094] In this method, the pressing pressure during cold pressing is not particularly limited, but is preferably 10 KN to 300 KN, and more preferably 30 KN to 100 KN. Setting the pressing pressure within the above numerical range has the advantage of producing a press-molded body with a uniform thickness.

[0095] Furthermore, the method for producing a molded body according to this embodiment can shorten the press time (cooling time) during cold pressing. The press time during cold pressing is preferably 30 to 600 seconds, and more preferably 60 to 300 seconds. Even if the press time is set short within the above numerical range, there is an advantage in that the resin pellets are sufficiently solidified, making it easy to remove the press-molded body.

[0096] The temperature of the cooling plate used in the cooling press is not particularly limited, but is preferably 10° C. to 60° C., and more preferably 20° C. to 50° C. Setting the temperature of the cooling plate within the above numerical range has the advantage that the resin pellets are sufficiently solidified, making it easy to remove the press-molded body.

[0097] That is, one embodiment of the present invention is as follows.

[0098] <1> A method for producing resin pellets containing an aliphatic polyester-based resin, comprising a step of kneading a resin composition containing an aliphatic polyester-based resin in an extruder and then extruding the mixture through a die head, wherein the temperature of the cylinder of the extruder is set to a melting point peak temperature of the resin composition minus 30°C or less, and the temperature of the die head is set to a range of ±20°C of the melting point peak temperature of the resin composition.

[0099] <2> The method for producing resin pellets according to <1>, wherein the retention rate of the weight average molecular weight between the resin composition before kneading and the resin pellets obtained after kneading is 85.0% to 100.0%.

[0100] <3> The method for producing resin pellets according to <2>, wherein the weight average molecular weight of the resin composition before kneading is 100,000 to 1,000,000.

[0101] <4> The method for producing resin pellets according to <2> or <3>, wherein the weight-average molecular weight of the resin pellets obtained after kneading is 80,000 to 800,000.

[0102] <5> The method for producing resin pellets according to any one of <1> to <4>, wherein the resin composition has a peak melting point of 100°C to 200°C.

[0103] <6> The method for producing resin pellets according to any one of <1> to <5>, wherein the aliphatic polyester resin is a poly(3-hydroxyalkanoate) resin.

[0104] <7> The method for producing resin pellets according to <6>, wherein the poly(3-hydroxyalkanoate)-based resin is at least one selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxydecanoate).

[0105] <8> Resin pellets made of a resin composition containing an aliphatic polyester-based resin, wherein the percentage of resin pellets that buckle when subjected to a compression test in which a load of up to 400 N is applied in a direction perpendicular to the side surface of the resin pellets is 30% to 100%.

[0106] <9> The resin pellet of <8>, wherein the resin composition does not contain a crystal nucleating agent.

[0107] <10> Resin pellets according to <8> or <9>, having a peak solidification temperature of 90°C to 120°C.

[0108] <11> The resin pellet according to any one of <8> to <10>, having a melting point peak temperature of 130°C to 170°C.

[0109] <12> The resin pellet according to any one of <8> to <11>, wherein the difference between the melting point peak temperature and the solidification peak temperature is 0°C to 60°C.

[0110] <13> A method for producing a molded body using resin pellets obtained by any one of the methods for producing resin pellets according to <1> to <7>, comprising: a supplying step of heating and melting a molding material containing the resin pellets to a temperature equal to or higher than the peak melting point temperature of the resin pellets, and discharging the obtained molten molding material from a discharge part to supply it between a pair of molds; and a molding step of closing the pair of molds, press-molding the flowable molten molding material, and cooling it.

[0111] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0112] <Differential Scanning Calorimetry Analysis Evaluation> The melting peak temperature and solidification peak temperature of the resin pellets or resin compositions of Examples 1 to 9, Comparative Examples 1 to 4, and Reference Examples 1 and 2 were measured by the following method.

[0113] An aluminum pan was filled with 4 to 10 mg of sample, and using differential scanning calorimetry, the sample was heated from 30°C to 160°C at a rate of 10°C / min under a nitrogen stream and held at 160°C for 3 minutes. The sample was then cooled from 160°C to 20°C at a rate of 10°C / min. The melting point peak temperature was determined as the temperature at which the endothermic heat was maximized in the endothermic curve obtained when the sample melted during the sample temperature increase. The solidification peak temperature was determined as the temperature at which the exothermic heat was maximized in the exothermic curve obtained when the sample solidified during the sample temperature decrease.

[0114] <Evaluation of Solidification Properties> The solidification properties of the resin pellets of Examples 1 to 9, Comparative Examples 1 to 4, and Reference Examples 1 and 2 were evaluated by the following method.

[0115] Press molding was performed using the following method, and solidification properties were evaluated based on the presence or absence of deformation of the molded body obtained after demolding. Using a tabletop plunger-type melt extrusion machine (manufactured by Nakatsuji Mold Industry Co., Ltd.), the resin pellets obtained in Examples 1 to 9, Comparative Examples 1 to 4, and Reference Examples 1 and 2 were heated to 160°C to form a molten resin. The molten resin was then supplied to the lower mold by ejecting it into a lower mold preheated to a desired temperature. The lower mold to which the molten resin had been supplied was then closed with an upper mold preheated to 160°C, thereby supplying the molten resin between the pair of molds. The pair of molds to which the molten resin had been supplied were subjected to heat pressing using a heat press molding machine (manufactured by Mikado Technos Co., Ltd., VS38-2525) at a pressure of 125 kN for a pressing time of 10 seconds. Immediately after the heat pressing, the pair of molds were sandwiched between upper and lower cooling plates heated to 25°C, and press molding was performed by performing a cooling press at a pressure of 30 kN for a pressing time of 90 seconds. After press molding, the molded body obtained upon release from the mold was evaluated for deformation as follows: Deformation of the molded body upon release from the mold indicates that the solidification property of the resin pellets used is insufficient.

[0116] Good: No deformation of the molded body. Bad: Deformation of the molded body.

[0117] (Example 1) Using a twin-screw extruder (Technovel MFU25TW-60HG-NH), the raw material poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (sometimes referred to as P3HB3HH) (weight average molecular weight Mw 380,000, 3HH ratio 6 mol%, melting point peak temperature 147 ° C. evaluated by differential scanning calorimetry analysis) resin powder was kneaded in a cylinder (set temperature 60 ° C.) and extruded from the nozzle of a die head (set temperature 140 ° C.) attached to the tip of the twin-screw extruder. The strand extruded from the nozzle of the die head was air-cooled at room temperature (20 ° C. to 25 ° C.) and then cut to obtain resin pellets.

[0118] As a result of differential scanning calorimetry analysis, the obtained resin pellets had a melting point peak temperature of 146° C. and a solidification peak temperature of 103° C. The solidification property evaluation result was good. These evaluation results are shown in Table 1.

[0119] Example 2 Resin pellets were obtained in the same manner as in Example 1, except that the cylinder temperature was set to 30°C and the die head temperature was set to 145°C.

[0120] As a result of differential scanning calorimetry analysis, the obtained resin pellets had a melting point peak temperature of 147° C. and a solidification peak temperature of 104° C. The solidification property evaluation result was good. These evaluation results are shown in Table 1.

[0121] Example 3 Resin pellets were obtained in the same manner as in Example 1, except that the cylinder temperature was set to 90°C and the die head temperature was set to 135°C.

[0122] As a result of differential scanning calorimetry analysis, the obtained resin pellets had a melting point peak temperature of 146° C. and a solidification peak temperature of 103° C. The solidification property evaluation result was good. These evaluation results are shown in Table 1.

[0123] Example 4 Resin pellets were obtained in the same manner as in Example 1, except that the cylinder temperature was set to 30°C and the die head temperature was set to 155°C.

[0124] As a result of differential scanning calorimetry analysis, the obtained resin pellets had a melting point peak temperature of 147° C. and a solidification peak temperature of 103° C. The solidification property evaluation result was good. These evaluation results are shown in Table 1.

[0125] Example 5 Resin pellets were obtained in the same manner as in Example 1, except that the cylinder temperature was set to 110°C and the die head temperature was set to 125°C.

[0126] As a result of differential scanning calorimetry analysis, the obtained resin pellets had a melting point peak temperature of 147° C. and a solidification peak temperature of 103° C. The solidification property evaluation result was good. These evaluation results are shown in Table 1.

[0127] Comparative Example 1 Resin pellets were obtained in the same manner as in Example 1, except that the cylinder temperature was set to 145°C, the die head temperature was set to 145°C, and the strands extruded from the nozzle of the die head were immersed in water at 50°C for water cooling.

[0128] As a result of differential scanning calorimetry analysis, the obtained resin pellets had a melting point peak temperature of 148° C. and a solidification peak temperature of 83° C. The solidification property was evaluated as poor. These evaluation results are shown in Table 1.

[0129] Comparative Example 2 Resin pellets were obtained in the same manner as in Example 1, except that the cylinder temperature was set to 165°C, the die head temperature was set to 165°C, and the strands extruded from the nozzle of the die head were immersed in water at 50°C for water cooling.

[0130] As a result of differential scanning calorimetry analysis, the obtained resin pellets had a melting point peak temperature of 148° C. and a solidification peak temperature of 81° C. The solidification property was evaluated as poor. These evaluation results are shown in Table 1.

[0131] (Reference Example 1) Resin pellets were obtained in the same manner as in Comparative Example 1, except that a raw material pre-blended with 1 wt % of pentaerythritol, a nucleating agent, was used in addition to the P3HB3HH resin powder. Differential scanning calorimetry analysis showed that the resulting resin pellets had a melting point peak temperature of 148°C and a solidification peak temperature of 97°C. The solidification property evaluation results were good. These evaluation results are shown in Table 1.

[0132] (Example 6) As the raw material P3HB3HH, a resin powder having a weight average molecular weight Mw of 580,000, a 3HH ratio of 11 mol%, and a melting point peak temperature of 145 ° C. as determined by differential scanning calorimetry analysis was used, and the cylinder temperature was set to 30 ° C. and the die head temperature was set to 165 ° C. Resin pellets were obtained in the same manner as in Example 1.

[0133] As a result of differential scanning calorimetry analysis, the obtained resin pellets had a melting point peak temperature of 148° C. and a solidification peak temperature of 104° C. The solidification property evaluation result was good. These evaluation results are shown in Table 1.

[0134] Example 7 Resin pellets were obtained in the same manner as in Example 6, except that the cylinder temperature was set to 60°C and the die head temperature was set to 155°C.

[0135] As a result of differential scanning calorimetry analysis, the obtained resin pellets had a melting point peak temperature of 148° C. and a solidification peak temperature of 103° C. The solidification property evaluation result was good. These evaluation results are shown in Table 1.

[0136] Example 8 Resin pellets were obtained in the same manner as in Example 6, except that the cylinder temperature was set to 90°C and the die head temperature was set to 145°C.

[0137] As a result of differential scanning calorimetry analysis, the obtained resin pellets had a melting point peak temperature of 149° C. and a solidification peak temperature of 103° C. The solidification property evaluation result was good. These evaluation results are shown in Table 1.

[0138] Example 9 Resin pellets were obtained in the same manner as in Example 6, except that the cylinder temperature was set to 110°C and the die head temperature was set to 130°C.

[0139] As a result of differential scanning calorimetry analysis, the obtained resin pellets had a melting point peak temperature of 148° C. and a solidification peak temperature of 102° C. The solidification property evaluation result was good. These evaluation results are shown in Table 1.

[0140] Comparative Example 3 Resin pellets were obtained in the same manner as in Example 6, except that the cylinder temperature was set to 145°C, the die head temperature was set to 145°C, and the strands extruded from the nozzle of the die head were immersed in water at 50°C for water cooling.

[0141] As a result of differential scanning calorimetry analysis, the obtained resin pellets had a melting point peak temperature of 149° C. and a solidification peak temperature of 85° C. The solidification property was evaluated as poor. These evaluation results are shown in Table 1.

[0142] Comparative Example 4 Resin pellets were obtained in the same manner as in Example 6, except that the cylinder temperature was set to 165°C, the die head temperature was set to 165°C, and the strands extruded from the nozzle of the die head were immersed in water at 50°C for water cooling.

[0143] As a result of differential scanning calorimetry analysis, the obtained resin pellets had a melting point peak temperature of 148° C. and a solidification peak temperature of 83° C. The solidification property evaluation result was poor. These evaluation results are shown in Table 1.

[0144] Reference Example 2 Resin pellets were obtained in the same manner as in Comparative Example 3, except that a raw material prepared by blending pentaerythritol as a nucleating agent in advance to a concentration of 1 wt % in addition to the P3HB3HH resin powder was used.

[0145] As a result of differential scanning calorimetry analysis, the obtained resin pellets had a melting point peak temperature of 148° C. and a solidification peak temperature of 99° C. The solidification property evaluation result was good. These evaluation results are shown in Table 1.

[0146] From the results in Table 1, it can be seen that in the methods of Comparative Examples 1 to 4, i.e., the method in which the cylinder temperature of the extruder was set to the melting point peak temperature of the raw resin powder minus 30°C or more and the die head temperature of the extruder was set within the range of the melting point peak temperature of the resin powder ±20°C, pellets with a low solidification peak temperature were obtained, and the solidification property evaluation results showed poor, indicating insufficient solidification property.

[0147] In contrast, in the methods of Examples 1 to 9, i.e., the method in which the cylinder temperature of the extruder was set to be equal to or lower than the peak melting point temperature of the raw resin powder -30°C and the die head temperature of the extruder was set within a range of the peak melting point temperature of the resin powder ±20°C, pellets with a high solidification peak temperature were obtained, the solidification property evaluation results were good, and it was possible to obtain resin pellets with a fast crystallization solidification rate.

[0148] In Reference Examples 1 and 2, resin pellets with a high solidification peak temperature were obtained, the solidification evaluation results were good, and it was possible to obtain resin pellets with a fast crystallization solidification rate, compared to Comparative Examples 1 to 4. However, the pellets of Reference Examples contain pentaerythritol, a crystal nucleating agent, which has problems in that it may adhere to the mold surface during molding and contaminate the mold, and that it may gradually bleed out after molding, inhibiting printability and heat sealability on the surface.

[0149] <Evaluation of Weight Average Molecular Weight> The Mw (weight average molecular weight) of the resin pellets obtained in Examples 1 to 9, Comparative Examples 1 to 4, and Reference Examples 1 and 2 was evaluated by the following method.

[0150] The Mw of the P3HA resin was measured by dissolving the P3HA resin in chloroform, heating it in a hot water bath at 60°C for 0.5 hours, filtering the soluble matter through a disposable PTFE filter with a 0.45 μm pore size, and then performing GPC measurement on the filtrate under the following conditions. The evaluation results are shown in Table 2.

[0151] GPC measurement device: RI monitor (L-3000) manufactured by Hitachi, Ltd. Column: K-G (1 column), K-806L (2 columns) manufactured by Showa Denko K. Sample concentration: 3 mg / ml. Free liquid: chloroform solution. Free liquid flow rate: 1.0 ml / min. Sample injection amount: 100 μL. Analysis time: 30 min. Standard sample: standard polystyrene.

[0152] <Compression Test Evaluation> Compression tests of the resin pellets obtained in Examples 1 to 9, Comparative Examples 1 to 4, and Reference Examples 1 and 2 were conducted using a texture analyzer (TA.XTplus, manufactured by Eiko Seiki Co., Ltd.). A load was applied perpendicular to the side of the resin pellet using a 4 mm diameter cylinder probe at a compression rate of 0.3 mm / sec, and the load (N) and displacement (mm) were measured. Whether or not buckling occurred in the resin pellets was evaluated based on the behavior of the load-displacement curve obtained by the measurement. Specifically, under the above compression rate conditions, the load on the side of the resin pellet was increased until a load of 400 N was applied. If a yield point occurred on the load-displacement curve, as shown in Figure 3, the resin pellets were evaluated as having buckled. The number of resin pellets evaluated for buckling was determined by performing a compression test evaluation on 20 randomly selected resin pellets, and the number of resin pellets that reached a yield point was evaluated. The evaluation results are shown in Table 2.

[0153] Regarding the evaluation results of Mw (weight average molecular weight), as is clear from the results shown in Table 2, when a P3HB3HH resin powder with an Mw of 380,000 was used as a raw material, the Mw was 370,000 in Example 1, 370,000 in Example 2, 360,000 in Example 3, 360,000 in Example 4, 360,000 in Example 5, 320,000 in Comparative Example 1, 310,000 in Comparative Example 2, and 320,000 in Reference Example 1. In Examples 1 to 5, the retention of weight average molecular weight between the resin composition before kneading and the resin pellets obtained after kneading was 85.0% to 100.0%. On the other hand, in Comparative Examples 1 and 2, the retention of weight average molecular weight between the resin composition before kneading and the resin pellets obtained after kneading was less than 85.0%. Compared to the resin pellets obtained in Comparative Examples 1 and 2, the resin pellets obtained in Examples 1 to 5 exhibited a high weight average molecular weight, and it was possible to suppress the change in molecular weight before and after melt kneading.

[0154] Even when a P3HB3HH resin powder with a Mw of 580,000 was used as the raw material, as is clear from the results shown in Table 2, the Mw was 540,000 in Example 6, 530,000 in Example 7, 540,000 in Example 8, 530,000 in Example 9, 480,000 in Comparative Example 3, 460,000 in Comparative Example 4, and 480,000 in Reference Example 2. In Examples 6 to 9, the weight-average molecular weight retention rates were 85.0% to 100.0% for the resin composition before kneading and the resin pellets obtained after kneading. On the other hand, in Comparative Examples 3 and 4, the weight-average molecular weight retention rates were less than 85.0% for the resin composition before kneading and the resin pellets obtained after kneading. Compared to the resin pellets obtained in Comparative Examples 3 and 4, the resin pellets obtained in Examples 6 to 9 exhibited a high weight-average molecular weight, and it was possible to suppress the change in molecular weight before and after melt-kneading.

[0155] Regarding the results of the compression test evaluation, buckling did not occur in any of the 20 resin pellets obtained in Comparative Examples 1 to 4. In contrast, buckling was observed in 6 out of 20 pellets in Example 1, 7 out of 20 pellets in Example 2, 6 out of 20 pellets in Example 3, 7 out of 20 pellets in Example 4, 7 out of 20 pellets in Example 5, 7 out of 20 pellets in Example 6, 8 out of 20 pellets in Example 7, 6 out of 20 pellets in Example 8, and 7 out of 20 pellets in Example 9. In Examples 1 to 9, the percentage of resin pellets that buckled when subjected to a compression test in which a load of up to 400 N was applied perpendicularly to the side of the resin pellets was within the range of 30% to 100%. On the other hand, in Comparative Examples 1 to 4, the percentage of resin pellets that buckled when subjected to a compression test in which a load of up to 400 N was applied perpendicularly to the side of the resin pellets was less than 30%.

[0156] These results are thought to be due to the fact that strands of the P3HA resin were discharged from the nozzle of the die head without being completely melted when producing the resin pellets in Examples 1 to 9. That is, (1) by producing a press-molded body using the resin pellets of Examples 1 to 9, it is possible to suppress a decrease in the molecular weight of the resin pellets, and (2) it is thought that the obtained resin pellets form a non-uniform structure as solidification progresses starting from unmelted resin scattered within the strands, and buckling occurs at the boundaries of the structure during the compression test.

[0157] REFERENCE SIGNS LIST 1 Extruder 2 Die head 3 Cylinder 4 Raw material hopper 10 Kneading extrusion device 11 Molten resin generating section 12 Supply section 12a Discharge section 100 Manufacturing device

Claims

1. A method for producing resin pellets containing an aliphatic polyester resin, comprising the steps of kneading a resin composition containing an aliphatic polyester resin in an extruder and then extruding the mixture through a die head, wherein the temperature of the cylinder of the extruder is set to the peak melting point temperature of the resin composition minus 30°C or less, and the temperature of the die head is set to within ±20°C of the peak melting point temperature of the resin composition.

2. The method for producing resin pellets according to claim 1, wherein the retention rate of the weight average molecular weight between the resin composition before kneading and the resin pellets obtained after kneading is 85.0% to 100.0%.

3. The method for producing resin pellets according to claim 2, wherein the weight average molecular weight of the resin composition before kneading is 100,000 to 1,000,000.

4. The method for producing resin pellets according to claim 2, wherein the weight average molecular weight of the resin pellets obtained after kneading is 80,000 to 800,000.

5. The method for producing resin pellets according to claim 1, wherein the resin composition has a peak melting point of 100°C to 200°C.

6. The method for producing resin pellets according to claim 1, wherein the aliphatic polyester resin is a poly(3-hydroxyalkanoate) resin.

7. The method for producing resin pellets according to claim 6, wherein the poly(3-hydroxyalkanoate) resin is one or more selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxydecanoate).

8. Resin pellets made of a resin composition containing an aliphatic polyester resin, wherein the percentage of resin pellets that buckle when subjected to a compression test in which a load of up to 400 N is applied in a direction perpendicular to the side of the resin pellets is 30% to 100%.

9. The resin pellet according to claim 8, wherein the resin composition does not contain a crystal nucleating agent.

10. The resin pellet according to claim 8, wherein the peak solidification temperature is 90°C to 120°C.

11. The resin pellet according to claim 8, having a peak melting point of 130°C to 170°C.

12. The resin pellet according to claim 8, wherein the difference between the peak melting temperature and the peak solidification temperature is 0°C to 60°C.

13. A method for producing a molded body using resin pellets obtained by the method for producing resin pellets according to any one of claims 1 to 7, comprising: a supply step of heating and melting a molding material containing the resin pellets to a temperature equal to or higher than the peak melting point temperature of the resin pellets, and supplying the obtained molten molding material between a pair of molds by discharging it from a discharge part; and a molding step of closing the pair of molds and press-molding the flowable molten molding material and cooling it.

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