Manufacturing method for molded products

Abstract

To inhibit corrosion due to acid generation at the tip of the screw of twin-screw extruder in extrusion molding using poly(3-hydroxybutyrate) resin as the raw material.SOLUTION: In a melt extrusion process in which a resin composition containing a poly(3-hydroxyalkanoate) resin is melted and blended in a twin-screw extruder and the resulting melt is extruded, each tip of a pair of screws is eccentric in shape with the top (T) of the mountain (42a) displaced from the position of the screw's rotation axis (S) .SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for producing a molded article. [Background technology]

[0002] A technique using an extruder is known as a technique for producing resin pellets using a thermoplastic resin. For example, raw materials such as resin and additives are kneaded and heated and melted in the extruder, then extruded in the form of strands from a nozzle at the tip of the extruder, and then cut by a pelletizer to produce resin pellets.

[0003] In recent years, the separation and collection of food waste and composting have been promoted mainly in Europe, and there is a demand for biodegradable plastic products that can be composted together with food waste. In addition, the use of biodegradable plastics is expected to be used to combat marine pollution. In particular, poly(3-hydroxybutyrate)-based resins are attracting attention as a material that can solve the above problems because they can biodegrade even in seawater.

[0004] For example, Patent Document 1 discloses a technique in which a P3HA resin is melt-kneaded in a twin-screw extruder and then extrusion-molded. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2004-331913 A Summary of the Invention [Problem to be solved by the invention]

[0006] The present inventors, in the course of investigating a method for producing a molded article by extrusion molding using a poly(3-hydroxybutyrate)-based resin as a raw material, discovered that in this production method, when a twin-screw extruder is operated for a long period of time, acid is generated, which may corrode the tip of the screw.

[0007] One aspect of the present invention aims to provide a method for producing a molded product that can suppress corrosion caused by acid generation at the tip of the screw of a twin-screw extruder during extrusion molding using a poly(3-hydroxybutyrate) resin as a raw material. [Means for solving the problem]

[0008] In order to solve the above problems, a method for producing a molded body according to one embodiment of the present invention includes a melt extrusion step in which a resin composition containing a poly(3-hydroxyalkanoate) resin is melt-kneaded in a twin-screw extruder having a pair of screws and the resulting molten material is extruded, and a cooling step in which the molten material obtained after the melt extrusion step is cooled to obtain a molded body, wherein the tips of the pair of screws each have a peak protruding in the transport direction of the molten material, and the tips have an eccentric shape in which the tops of the peaks are positioned offset from the position of the rotation axis of the screws. Effect of the Invention

[0009] According to one aspect of the present invention, in extrusion molding using a poly(3-hydroxybutyrate) resin as a raw material, corrosion caused by acid generation at the tip of the screw of a twin-screw extruder can be suppressed. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a diagram showing a schematic configuration example of a twin-screw extruder used in the method for producing a molded body according to the embodiment of the present invention. [Diagram 2] FIG. 2 is a partial cross-sectional view showing the configuration of a screw cap that constitutes the tip of a screw in the twin-screw extruder shown in FIG. [Diagram 3] 3A to 3C are a front view, a side view, and a cross-sectional view taken along line AA in the side view, showing the configuration of a cap body of the screw cap shown in FIG. 2. [Figure 4] 3A to 3C are a front view, a side view, and a cross-sectional view taken along line AA and line BB in the side view, showing the configuration of the cap cover of the screw cap shown in FIG. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 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 each configuration described below, and various modifications are possible within the scope of the claims. In addition, 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 documents and patent documents described in this specification are incorporated herein by reference. In addition, 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 smaller than B)".

[0012] [Technical philosophy] As described above, the present inventors, in the course of studying a method for producing a molded product by extrusion molding using a P3HA-based resin as a raw material, have found that in this production method, when a twin-screw extruder is operated for a long time, the tip of the screw may corrode due to the generation of acid. In particular, when pellets are produced as a molded product using a resin composition in which a P3HA-based resin is blended so as to have a high melt viscosity, the corrosion of the tip of the screw was significant. When the tip of the screw corrodes in this way, the frequency of cleaning and replacing the screw increases, and the production efficiency of the molded product decreases. Such corrosion of the tip of the screw due to the generation of acid during extrusion molding using a P3HA-based resin as a raw material is a new problem newly discovered by the present inventors.

[0013] Therefore, the present inventors have intensively studied measures that can suppress the generation of acid (particularly crotonic acid). As a result, the present inventors have focused on the shape of the tip of the screw, and have found that by making the tip of the screw into a specific shape, the generation of crotonic acid can be reduced and corrosion of the tip of the screw can be suppressed, thereby arriving at the present embodiment.

[0014] That is, the manufacturing method of the molded body according to this embodiment (hereinafter sometimes referred to as this manufacturing method) includes a melt extrusion process in which a resin composition containing a poly(3-hydroxyalkanoate)-based resin (hereinafter sometimes referred to as a P3HA-based resin) is melt-kneaded in a twin-screw extruder having a pair of screws, and the resulting molten material is extruded, and a cooling process in which the molten material obtained after the melt extrusion process is cooled to obtain a molded body, wherein the tips of the pair of screws each have a peak protruding in the transport direction of the molten material, and the tips have an eccentric shape in which the tops of the peaks are offset from the position of the rotation axis of the screws.

[0015] According to this manufacturing method, the tip of each of the pair of screws of the twin-screw extruder has an eccentric shape in which the top is positioned at a position offset from the rotation axis of the screw, thereby reducing the generation of crotonic acid and suppressing corrosion of the tip of the screw.

[0016] Furthermore, this manufacturing method can suppress marine pollution caused by waste, which can contribute to the achievement of the 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." The manufacturing method is described in detail below.

[0017] [Method for producing molded body] As described above, the present production method includes a melt extrusion step and a cooling step. In the melt extrusion step, a resin composition containing a P3HA resin is melt-kneaded in a twin-screw extruder having a pair of screws, and the resulting melt is extruded. In the cooling step, the melt after the melt extrusion step is cooled to obtain a molded product. The molded product obtained by the present production method may be any molded product made of a P3HA resin that can be extruded using a twin-screw extruder, and examples of such molded products include pellets, films, fibers, and foams. In particular, the present production method is suitably used for producing pellets.

[0018] (Melt extrusion process) The twin-screw extruder used in the melt extrusion step is not particularly limited as long as it can melt-knead the resin composition containing the P3HA resin, and a conventionally known twin-screw extruder can be used. Figure 1 is a schematic diagram showing an example of the configuration of a twin-screw extruder 100 used in this production method. The twin-screw extruder 100 shown in Figure 1 is preferably used for producing pellets.

[0019] As shown in FIG. 1, the twin-screw extruder 100 includes a motor 11, a reducer 12, a barrel section 20, a screw 50, and a die head 6. The twin-screw extruder 100 conveys a resin composition containing a P3HA resin as a raw material while melting it with the rotating screw 50. The twin-screw extruder 100 also conveys the melt of the resin composition while kneading it with the rotating screw 50. Here, as shown in the drawing, in this specification, the direction in which the resin composition (or the melt) is conveyed is referred to as the LD direction, and in the LD direction, the downstream side is the LDa side (front side), and the upstream side is the LDb side (rear side). The LD direction can also be said to be the extrusion direction of the melt in the melt extrusion process.

[0020] The motor 11 is a drive source for the screw 50. The rotational driving force output from the motor 11 is input to the screw 50 via the reducer 12, causing the screw 50 to rotate. The reducer 12 reduces the speed of the rotational driving force output from the motor 11 and increases the torque of the rotational driving force input to the screw 50.

[0021] The barrel portion 20 has a cylinder 21 which is a main body. The cylinder 21 forms a flow path (transport path) through which the resin composition or its melt is transported. A raw material hopper 22 is provided at the end of the cylinder 21 on the LDa side. Raw materials for the molded body are charged into the cylinder 21 through the raw material hopper 22.

[0022] The screw 50 is provided inside the cylinder 21 and supported so as to be freely rotatable. As described above, the screw 50 is driven to rotate by the motor 11. In FIG. 1, a similar screw 50 is provided behind the screw 50. These two screws 50 are arranged in parallel to each other and are similarly driven to rotate by the motor 11. In other words, the twin-screw extruder 100 is configured to include two screws 50 that are parallel to each other. In the following description, the two screws 50 included in the twin-screw extruder 100 are collectively referred to as "screw 50". The description of the screw 50 shown in FIG. 1 also includes the description of the other screw 50 not shown in FIG. 1.

[0023] The screw 50 includes a screw body 30 and a screw cap 40 (tip). The screw cap 40 constitutes the tip of the screw 50 on the LDa side. The screw cap 40 is provided at the end of the screw body 30 on the LDa side. The screw cap 40 is detachably attached to the screw body 30. Note that the member constituting the tip of the screw 50 on the LDa side is not limited to the screw cap 40, and any member that can be attached to the end of the screw body of a conventionally known twin-screw extruder can be used.

[0024] The screw body 30 is divided into five zones: a feed zone 31, a kneading zone 32a, a vent zone 33a, a kneading zone 32b, a vent zone 33b, and a pressure increase zone 34. From the LDa side to the LDb side, the feed zone 31, the kneading zone 32a, the vent zone 33a, the kneading zone 32b, the vent zone 33b, and the pressure increase zone 34 are arranged in this order.

[0025] The feed zone 31 is disposed at the end of the screw body 30 on the LDb side. The pressurization zone 34 is disposed at the end of the screw body 30 on the LDa side.

[0026] The feed zone 31 is intended to transport the raw material fed from the raw material hopper 22 to the LDa side. The pressurization zone 34 is intended to pressurize the molten material and extrude it to the die head 6.

[0027] The kneading zones 32a and 32b are intended for kneading the resin composition or the melt, and are formed by a plurality of kneading discs or rotors.

[0028] The vent zones 33a and 33b are disposed on the LDa side of the kneading zones 32a and 32b, respectively. The vent zones 33a and 33b are intended to remove volatile matter and decomposition gases generated from the resin composition or the melt by kneading. The cylinder 21 is provided with vent ports 23a and 23b at positions corresponding to the vent zones 33a and 33b. The vent ports 23a and 23b are openings for discharging volatile matter and decomposition gases generated from the resin composition or the melt to the outside of the twin-screw extruder 100.

[0029] The form (structure, shape, size, pitch, etc.) of the screw grooves provided in each zone, i.e., feed zone 31, kneading zone 32a, vent zone 33a, kneading zone 32b, vent zone 33b, and pressure increase zone 34, is appropriately determined depending on the purpose of each zone described above and the type of resin composition, etc.

[0030] The die head 6 has a plurality of outlets from which the molten material is extruded. The molten material supplied to the die head 6 is extruded from the outlets of the die head 6 and formed into a strand (string or rope).

[0031] Although not shown in FIG. 1, a cutting section that cuts the molten material extruded from the die head 6 is provided on the LDa side of the twin-screw extruder 100. The cutting section includes a cutter that is driven to rotate. A plurality of cutter blades are attached to the cutter. By the rotational drive of the cutter, the strand-shaped molten material extruded from the die head 6 is cut to a predetermined length.

[0032] The melt extrusion process of the present manufacturing method using the twin-screw extruder 100 shown in Fig. 1 includes at least a melting process, a kneading process, and an extrusion process. The resin composition fed into the raw material hopper 22 is supplied to the feed zone 31. The resin composition supplied to the feed zone 31 is transported to the LDa side of the cylinder 21 while being melted (melting process). Next, the melt of the resin composition is transported to the kneading zone 32a or 32b (kneading process). The melt supplied to the kneading zone 32a or 32b is transported further to the LDa side of the cylinder 21 while being kneaded (mixed).

[0033] The molten material that has been through the melting and kneading processes in the cylinder 21 is further conveyed to the LDa side and supplied to the die head 6. The molten material supplied to the die head 6 is extruded from the outlet of the die head 6 (extrusion process). In the extrusion process, the molten material passes through the outlet of the die head 6 and is formed into a strand (string or rope).

[0034] The strand-shaped melt extruded from the discharge port of the die head 6 is cut to a predetermined length by the cutting process of the cutting unit. In other words, the melt extruded in the form of strands is divided into pellets. In this manufacturing method, the obtained pellet-shaped melt is then subjected to a cooling process.

[0035] In the melt extrusion process, the temperature at which the resin composition is melt-kneaded cannot be generally specified because it depends on the physical properties (melting point, weight average molecular weight, etc.) of the P3HA resin and the type of additive used. Regarding the temperature at which the resin composition is melt-kneaded, for example, in the melt extrusion process, the temperature of the melt at the time of extrusion (hereinafter sometimes referred to as the melt temperature) is preferably 170°C to 200°C, more preferably 180°C to 195°C. By keeping the melt temperature within the above range, it is possible to suppress deterioration in productivity due to a decrease in the average molecular weight of the resin composition and the occurrence of resin scorching on the resin composition.

[0036] In the melt extrusion process using the twin-screw extruder 100, the resin composition as the raw material is melted by heat generated mainly by the shearing action caused by the rotation of the screw 50. The melt is also kneaded (dispersively mixed and distributively mixed) mainly by the shearing action and elongation action caused by the rotation of the screw 50. The melt continues to generate heat even during kneading. This heat generation makes it possible to control the melt temperature within the above-mentioned numerical range. In order to maintain the melt temperature within the above-mentioned numerical range, the resin composition or the melt may be heated by a heating means such as a heater, or the resin composition or the melt may be cooled by a cooling means, as necessary.

[0037] Here, the present manufacturing method is characterized by the structure and shape of the tip of the screw of the twin-screw extruder used in the melt extrusion step described above. Fig. 2 is a partial cross-sectional view showing the configuration of the screw cap 40 constituting the tip of the screw 50 in the twin-screw extruder 100 shown in Fig. 1. Fig. 3 is a front view, a side view, and a cross-sectional view taken along line AA in the side view showing the configuration of the cap body 41 of the screw cap 40 shown in Fig. 2. Fig. 4 is a front view, a side view, and a cross-sectional view taken along line AA and line BB in the side view showing the configuration of the cap cover 42 of the screw cap 40 shown in Fig. 2.

[0038] The screw cap 40 includes a cap body 41 and a cap cover 42. The cap body 41 is screwed to the end of the screw body 30 on the LDa side. The cap cover 42 is screwed to the end of the cap body 41 on the LDa side.

[0039] The cap body 41 is a columnar member coaxial with the rotation axis S of the screw 50. The cap body 41 has a threaded portion 41a at the end on the LDb side. The threaded portion 41a is inserted into and screwed into a screw hole (not shown) provided at the end on the LDa side of the screw body 30. The entire screw body 30 is fixed by screwing the cap body 41 to the screw body 30.

[0040] The cap body 41 has a protruding portion 41b protruding in the LD direction at the end on the LDa side. A screw hole 41c is formed in the protruding portion 41b. The protruding portion 41b has a hexagonal prism shape.

[0041] When the cap body 41 is screwed to the screw body 30, a screw fastener such as a wrench is applied to the exposed protrusion 41b to perform the screw fastening. The side surface of the hexagonal column shape of the protrusion 41b is a surface that receives the fastener. When the screw fastening of the cap body 41 to the screw body 30 is completed, most of the cap body 41 is inserted into the screw body 30, and the protrusion 41b is exposed from the screw body 30.

[0042] The cap cover 42 is configured to cover the protruding portion 41b of the cap body 41. The cap cover 42 is disposed on the LDa side of the end portion on the LDa side of the screw body 30. Therefore, the external shape of the tip portion of the screw 50 corresponds to the external shape of the cap cover 42.

[0043] The cap cover 42 has a peak 42a protruding in the LD direction. The peak 42a has one apex T. The external shape of the cap cover 42 is an eccentric shape in which the apex T of the peak 42a is offset from the position of the rotation axis S of the screw 50. As can be seen from the front view and side view of FIG. 4, in this eccentric shape, the peak 42a is asymmetric with respect to the ridgeline formed by the apex T. Furthermore, as can be seen from the front view of FIG. 4, in the peak 42a, there is no intersection between the ridgeline formed by the apex T and the rotation axis S of the screw 50.

[0044] The cap cover 42 has an opening 42b at the end on the LDb side. The cap cover 42 has a threaded portion 42c in the opening 42b. The threaded portion 42c is inserted into and screwed into a screw hole 41c of the cap body 41. The screw fastening of the cap cover 42 to the cap body 41 firmly fixes the screw body 30 and the screw cap 40.

[0045] In the melt extrusion process of a resin composition containing a P3HA resin, when the twin-screw extruder 100 is operated for a long time, the P3HA resin is thermally decomposed to generate crotonic acid. This crotonic acid then enters the joint between the cap body 41 and the screw body 30 and the joint between the cap body 41 and the cap cover 42, causing corrosion of the tip of the screw 50. According to this manufacturing method, since the cap cover 42 constituting the tip has the eccentric shape as described above, it is possible to reduce the generation of crotonic acid and suppress corrosion of the tip of the screw 50 even when the twin-screw extruder 100 is operated for a long time.

[0046] The cap cover 42 also has a fastening portion 43. When the cap cover 42 is screwed to the cap body 41, a screw fastener such as a wrench is applied to the fastening portion 43 to perform the screw fastening. Therefore, the fastening portion 43 has two flat surfaces 43a for receiving the screw fastener. These two flat surfaces 43a extend parallel to the LD direction.

[0047] As shown in the BB cross-sectional view of Fig. 4, in a cross section perpendicular to the LD direction, the tightening portion 43 has an external shape that is a substantial rectangle made up of two parallel straight lines, sides L1 and L2, and two curved lines C1 and C2 that connect the sides L1 and L2. The sides L1 and L2 form two flat surfaces 43a that receive a screw fastener. In other words, the tightening portion 43 has a substantial quadrangular prism shape with two mutually opposing flat surfaces 43a and two curved surfaces resulting from the curved lines C1 and C2 on its side surfaces.

[0048] In general, the shape of the fastening part for screw fastening is, for example, a hexagonal prism. In addition, the side of the fastening part is provided with many flat surfaces for receiving the screw fastener so that the screw fastener can be easily attached, and the connecting parts between the flat surfaces are formed with edges. In the twin-screw extruder 100 used in this manufacturing method, the side of the fastening part 43 is formed with a minimum of two flat surfaces 43a for receiving the screw fastener, and the surfaces other than the flat surfaces 43a are formed with curved surfaces. By making the side of the fastening part 43 a curved surface with few edges in this way, the generation of crotonic acid due to the thermal decomposition of the P3HA resin can be further reduced.

[0049] 4, the tops T of the peaks 42a are curved, which can further reduce the generation of crotonic acid due to the thermal decomposition of the P3HA resin.

[0050] (Melt flow rate of molten material) In the melt extrusion process, the melt flow rate (MFR) of the melt cannot be generally defined because it depends on the physical properties (melting point, weight average molecular weight, etc.) and composition of the P3HA resin component in the resin composition. Regarding the melt flow rate of the melt, for example, the melt flow rate of the molded product such as pellets in the cooling process is preferably 6.0 g / 10 min or less, more preferably 4.0 g / 10 min or less. In addition, the lower the melt flow rate of the molded product, the better, but it is preferably 1.0 g / 10 min or more, more preferably 2.0 g / 10 min or more.

[0051] The MFR of the molded product is measured using a melt indexer (X419 mounted type L260: manufactured by Tateyama Scientific Industrial Co., Ltd.) at a load of 5 kg and a measurement temperature of 165° C. in accordance with JIS K 7210-1.

[0052] In the melt extrusion process, the higher the MFR of the melt, the lower the melt viscosity of the melt. A melt with a relatively low MFR has a high melt viscosity, and is therefore more susceptible to screw corrosion caused by crotonic acid. On the other hand, for a melt with a relatively high MFR, for example, 10.0 g / 10 min or more, screw corrosion caused by crotonic acid is unlikely to occur. According to this manufacturing method, since the tip of the screw is eccentric as described above, screw corrosion caused by crotonic acid can be suppressed even when the MFR of the melt is in a relatively low range of 6.0 g / 10 min or less.

[0053] Furthermore, if the melt viscosity of the molten material is low (if the MFR of the molten material is high), there is a tendency for this to be effective against resin scorching. When the MFR of the molten material is in the relatively low range of 6.0 g / 10 min or less, the melt viscosity of the molten material becomes high, making resin scorching more likely to occur. According to this manufacturing method, since the tip of the screw has an eccentric shape as described above, resin scorching can be suppressed even when the MFR of the molten material is in the relatively low range of 6.0 g / 10 min or less.

[0054] (Poly(3-hydroxyalkanoate) resin) In this manufacturing method, a P3HA resin is used as a raw material for the resin composition. In this specification, the term "P3HA resin" refers to a 3-hydroxyalkanoic acid repeating unit represented by the general formula: [-CHR-CH2-CO-O-] (wherein R is C n H 2n+1 where n is an integer of 1 or more and 15 or less.) is a polyhydroxyalkanoate containing this as a repeating unit.

[0055] More specifically, the P3HA resin preferably contains 3-hydroxybutyrate (3HB) units. The P3HA resin is preferably one or more selected from the group consisting of poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HB3HV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (P3HB3HV3HH), and combinations thereof. The P3HA resin may contain only one type, or may contain two or more types.

[0056] 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, and P3HB, P3HB3HH, P3HB3HV, and P3HB4HB are more preferred, in terms of ease of industrial production.

[0057] The P3HA resin can also be produced by, for example, the method described in International Publication No. 2010 / 013483. Commercially available P3HA resins include Kaneka Biodegradable Polymer PHBH (registered trademark) manufactured by Kaneka Corporation.

[0058] The P3HA resin also contains at least one copolymer of 3HB units and other hydroxyalkanoate units, and the 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin account 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 %).

[0059] When the composition ratio of the 3HB repeating unit is 65.0 mol% or more, the rigidity of the P3HA resin is improved, the crystallization speed 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 lower than the thermal decomposition temperature, so stable and continuous production is possible. The monomer composition ratio of the P3HA resin can be measured by gas chromatography or the like (see, for example, International Publication No. 2014 / 020838).

[0060] The molecular weight of the P3HA resin is not particularly limited as long as it shows substantially sufficient physical properties for the intended use. The weight average molecular weight of the P3HA resin is preferably in the range of 100,000 to 1,000,000, more preferably 150,000 to 800,000, further preferably 200,000 to 700,000, and particularly preferably 250,000 to 650,000. When the weight average molecular weight is 100,000 or more, appropriate mechanical strength is obtained. In addition, when the molecular weight is 1,000,000 or less, the increase in melt viscosity can be suppressed, and the moldability is excellent.

[0061] The weight average molecular weight can be measured by gel permeation chromatography (GPC) (Shodex GPC-101, manufactured by Showa Denko K.K.), using a polystyrene gel (Shodex K-804, manufactured by Showa Denko K.K.) as a column, and using chloroform as a mobile phase, and can be calculated as a molecular weight converted into polystyrene. In this case, a calibration curve is prepared using polystyrenes with weight average molecular weights of 31,400, 197,000, 668,000, and 1,920,000. As the column for the GPC, a column appropriate for measuring the molecular weight may be used.

[0062] In the melt extrusion step, a resin composition containing the above-mentioned P3HA resin is extrusion molded. The resin composition used in the melt extrusion step is not particularly limited as long as it contains the above-mentioned P3HA resin and can be extruded.

[0063] The resin composition may contain two or more types of P3HA resins having different composition ratios of 3HB repeating units and / or different weight average molecular weights.

[0064] The resin composition may contain other resins besides the P3HA resin, so long as the effect of the present invention is 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 sebate terephthalate, and polybutylene azelate terephthalate. Only one type of other resin may be contained, or two or more types may be contained.

[0065] 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.

[0066] The resin composition does not need to contain an inorganic filler, but preferably further contains an inorganic filler. By containing an inorganic filler in the resin composition, the crystallization speed is improved, and effects such as reducing burrs and improving the production cycle are achieved.

[0067] 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 kinds.

[0068] 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, based on 100 parts by weight of the total P3HA resin. When the content of the inorganic filler is within the above range, both a sufficient crystallization rate and toughness can be achieved.

[0069] The resin composition may contain additives that can be used together with the P3HA resin, as long as they do not impair the effects of the present invention. Examples of such additives include colorants such as pigments and dyes, odor absorbents such as activated carbon and zeolite, fragrances such as vanillin and dextrin, plasticizers, antioxidants, weather resistance improvers, ultraviolet absorbers, crystal nucleating agents, lubricants, release agents, water repellents, antibacterial agents, and sliding property 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 set by those skilled in the art depending on the purpose of use.

[0070] (cooling process) In the cooling step, the molten material after the melt extrusion step is cooled to obtain a molded product. The cooling method of the molten material in the cooling step can be a conventionally known cooling method used in extrusion molding technology. The cooling method can be appropriately set depending on the shape of the molded product to be obtained.

[0071] For example, when pellets are formed using the twin-screw extruder 100 shown in Fig. 1, the cooling method can be roughly divided into two methods: a cold cut method and a die face cut method. The cold cut method includes a method in which the molten material extruded from the die head 6 is cooled through a water tank while a strand-shaped molded body is taken out and then chopped (strand cut method). The die face cut method is a method in which the molten material extruded from the discharge port of the die head 6 is cut by a rotating cutter while in contact with the surface of the die head 6 or while leaving a small gap.

[0072] The die face cutting method is further divided into the following three methods based on the difference in the cooling method. That is, the underwater cutting (hereinafter sometimes referred to as UWC) method, the watering cutting (hereinafter sometimes referred to as WRC) method, and the hot cutting (hereinafter sometimes referred to as HC) method. The UWC method is a method in which cooling water adjusted to a predetermined pressure is filled in a chamber attached to the tip of the die head 6 so as to contact the resin discharge surface of the die, and the molten material extruded from the discharge port of the die is cut underwater. The WRC method is a method in which a cooling drum connected to the die head 6, through which cooling water flows along the inner peripheral surface of the cooling drum, is disposed downstream from the die head 6, and the molten material cut by the cutter in the air is cooled in the cooling water. The HC method is a method in which the molten material is cut by the cutter in the air, and the cut molten material is cooled in the air. The HC method also includes a mist cutting method that further includes a step of spraying a mixed mist of water and air.

[0073] The amount of crotonic acid in the molded product in the cooling step is preferably 10.0 mg or less, more preferably 8.0 mg or less, even more preferably 5.0 mg or less, and particularly preferably 3.0 mg or less per kg of poly(3-hydroxyalkanoate) resin. By controlling the content of crotonic acid in the molded product within the above numerical range, corrosion of the tip of the screw in the twin-screw extruder can be suppressed.

[0074] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0075] That is, one embodiment of the present invention is as follows.

[0076] <1> A melt extrusion step of melt-kneading a resin composition containing a poly(3-hydroxyalkanoate)-based resin in a twin-screw extruder 100 having a pair of screws and extruding the resulting melt; A cooling step of cooling the molten material after the melt extrusion step to obtain a molded product, The tip end of each of the pair of screws 50 has a ridge portion 42a protruding in the conveying direction LD of the molten material, the tip portion has an eccentric shape in which a top T of the ridge portion 42a is shifted from the position of a rotation axis S of the screw 50, the method for producing a molded body comprising the steps of:

[0077] <2> The screw 50 includes a screw body 30 and a screw cap 40 detachably attached to the screw body 30. The screw cap 40 constitutes the tip portion. <1> A method for producing a molded body.

[0078] <3> The screw cap 40 is A cap body 41 that is screwed onto the screw body 30; a cap cover 42 that is screwed to the cap body 41; The cap cover 42 is The fastening portion 43 is for fastening with a screw fastener, and the thread portion 42a is provided. The fastening portion 43 has two flat surfaces 43a for receiving the screw fastener, and the two flat surfaces 43a extend parallel to the conveying direction LD of the molten material, In a cross section perpendicular to the conveying direction LD of the melt, The external shape of the fastening portion 43 is as follows: Two sides are two straight lines L1 and L2 parallel to each other and constituting two planes 43a for receiving the screw fastener; A substantially rectangular shape formed by two curves C1 and C2 connecting the two sides. <2> A method for producing a molded body.

[0079] <4> The poly(3-hydroxyalkanoate)-based resin is at least one selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate), and combinations thereof. <1> ~ <3> A method for producing any one of the molded bodies described above.

[0080] <5> The melt flow rate of the molded body in the cooling step is 6.0 g / 10 min or less. <1> ~ <4> A method for producing any one of the molded bodies described above.

[0081] <6> In the melt extrusion step, the temperature of the melt during extrusion is 170°C to 200°C. <1> ~ <5> A method for producing any one of the molded bodies described above.

[0082] <7> the amount of crotonic acid in the molded body in the cooling step is 10.0 mg or less per 1 kg of poly(3-hydroxyalkanoate) resin; <1> ~ <6> A method for producing any one of the molded bodies described above. EXAMPLES

[0083] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0084] <Poly(3-hydroxyalkanoate) resin> The poly(3-hydroxyalkanoate) resin used was as follows: P3HA-1: P3HB3HH (average content ratio 3HB / 3HH = 95 / 5 (mol% / mol%), weight average molecular weight = 610,000) P3HA-2: P3HB3HH (average content ratio 3HB / 3HH = 94 / 6 (mol% / mol%), weight average molecular weight = 620,000) P3HA-3: P3HB3HH (average content ratio 3HB / 3HH = 94 / 6 (mol% / mol%), weight average molecular weight = 540,000) P3HA-4: P3HB3HH (average content ratio 3HB / 3HH = 94 / 6 (mol% / mol%), weight average molecular weight = 200,000) P3HA-5: P3HB3HH (average content ratio 3HB / 3HH = 95 / 5 (mol% / mol%), weight average molecular weight = 230,000) P3HA-6: P3HB3HH (average content ratio 3HB / 3HH = 85 / 15 (mol% / mol%), weight average molecular weight = 670,000).

[0085] <Method for measuring weight-average molecular weight of poly(3-hydroxyalkanoate) resin> The method for measuring the weight average molecular weight of the poly(3-hydroxyalkanoate) resin is described below.

[0086] To measure the weight-average molecular weight using gas chromatography (Nexwra: manufactured by Shimadzu Corporation), 5 mg of each poly(3-hydroxyalkanoate) resin was weighed out, 5 ml of chloroform was added thereto, and the mixture was heated at 60° C. to prepare a sample. Using the sample, detection was performed by setting the mobile phase to chloroform, the flow rate to 1.0 ml / min, and the column oven to 40° C.

[0087] <Evaluation Method of Obtained Resin Composition and Pellets> (Method of measuring resin temperature (melt temperature)) The temperature of the strands produced in the examples and comparative examples was measured using a radiation thermometer (manufactured by HORIBA: IT-545S). Specifically, the temperature of the strand-shaped molten material immediately after it was discharged from the die hole was measured.

[0088] (Method of measuring MFR of pellets) The melt flow rate (MFR) of the pellets obtained in the examples and comparative examples was evaluated according to JIS K 7210-1. The melt flow rate (MFR) was measured using a melt indexer (X419 mounted L260: manufactured by Tateyama Scientific Industrial Co., Ltd.) by preheating 6.0 to 7.0 g of pellets in a cylinder in the device at 165°C for 5 minutes while loading them with a 5.0 kgf weight, and then measuring the weight of the sample extruded at 30 second intervals, and calculating and evaluating the weight by the following formula multiplied by a coefficient. Formula for calculating MFR: MFR (g / 10min) = measured weight (g) × 20.

[0089] (Method for quantifying crotonic acid) The crotonic acid content of the pellets obtained in the examples and comparative examples was measured by LC / TOFMS. The crotonic acid content was expressed in mg / kg-P3HA units.

[0090] The LC / TOFMS method used an HPLC device (NexeraX2: manufactured by Shimadzu Corporation). The column was Inertsil ODS-3 4.6 x 100 mm, mobile phase A was 0.1% phosphoric acid water 85%, mobile phase B was acetonitrile 15%, the flow rate was 0.8 mL / min, the column oven was set at 40°C, and detection was performed using a PDA detector (cutoff wavelength 210 nm).

[0091] The analytical sample was prepared as follows: 0.5 g of the pellets of the Examples and Comparative Examples was extracted with 4 mL of acetonitrile for 2 hours. The extracted solution was filtered, heated to 40°C and purged with nitrogen, and concentrated to 1 mL. The solution was further diluted 10 times with water and used as the analytical sample.

[0092] (Whether or not the resin is discolored) After production was completed under the conditions of the following Examples and Comparative Examples, the presence or absence of discoloration of the resin at the tip of the screw was visually confirmed.

[0093] (Whether or not the screw is corrosive) After production was completed under the conditions of the following Examples and Comparative Examples, the entire screw was visually inspected for the presence or absence of corrosion.

[0094] Example 1 22 parts by weight of P3HA-1 and 78 parts by weight of P3HA-2 were blended to obtain a P3HA resin. 0.5 parts by weight of behenic acid amide, a lubricant, was mixed with 100 parts by weight of the P3HA resin and dry blended to obtain a resin composition. The obtained resin composition was melt-kneaded at 150°C using a twin-screw extruder (manufactured by Japan Steel Works, Ltd.: TEX65αIII-59.5ABW-8V) with a die hole of φ10 mm, and the discharge rate was set to 250 kg / hr to produce strands. The obtained strands were then pelletized by continuous cutting using a water tank and a pelletizer whose temperature was adjusted to 50°C. In Example 1, a screw in which the screw cap at the tip was changed to a screw cap 40 having an eccentric cap cover 42 shown in FIG. 4 was used as the screw of the twin-screw extruder. The resulting pellets had a 3-hydroxybutyrate / 3-hydroxyhexanoate ratio of 94.8 / 5.2 (mol % / mol %) and a MFR of 3.2 g / 10 min.

[0095] Example 2 Resin pelletization was performed in the same manner as in Example 1, except for the following (1) and (2). (1) 40 parts by weight of P3HA-3, 8 parts by weight of P3HA-4, 22 parts by weight of P3HA-5, and 30 parts by weight of P3HA-6 were blended to obtain a P3HA resin. 1.0 part by weight of behenic acid amide and 0.5 part by weight of erucic acid amide, which are lubricants, were mixed with 100 parts by weight of the P3HA resin and dry-blended to obtain a resin composition. (2) The discharge rate was set to 400 kg / hr. The ratio of 3-hydroxybutyrate / 3-hydroxyhexanoate in the obtained pellets was 91.2 / 8.8 (mol% / mol%), and MFR was 5.9 g / 10 min.

[0096] Example 3 Resin pelletization was carried out in the same manner as in Example 1, except for the following (1) and (2). (1) 0.5 parts by weight of behenic acid amide and 0.5 parts by weight of erucic acid amide, which are lubricants, were mixed with 100 parts by weight of P3HA resin (P3HA-1) and dry-blended to obtain a resin composition. (2) The discharge rate was set to 300 kg / hr. The ratio of 3-hydroxybutyrate / 3-hydroxyhexanoate in the obtained pellets was 95 / 5 (mol% / mol%), and MFR was 4.0 g / 10 min.

[0097] Comparative Example 1 Except for changing the cap cover at the tip of the screw of the twin-screw extruder to a conventionally known cap cover, resin pelletization was performed in the same manner as in Example 1. The cap cover used in Comparative Example 1 is not eccentric as shown in Fig. 4, but is concentric with the rotation axis of the screw, and is a standard cap for a twin-screw extruder (model number: TEX65αIII) manufactured by Japan Steel Works, Ltd.

[0098] The evaluation results of Examples 1 to 3 and Comparative Example 1 are shown in Table 1.

[0099] [Table 1]

[0100] From the results in Table 1, in Examples 1 to 3 in which the screws having the cap covers with the eccentric shapes shown in FIG. 4 were used as the screws of the twin-screw extruder, no corrosion of the screws was observed. [Industrial Applicability]

[0101] The manufacturing method of the present invention is applicable to agriculture, fisheries, forestry, horticulture, medicine, hygiene products, clothing, non-clothing, packaging, It can be suitably used in the fields of automobiles, building materials, and others. [Explanation of symbols]

[0102] 30 Screw body 40 Screw Cap 41 Cap body 42 Cap cover 42a Mountain 43 Fastening part 43a plane 50 Screw 100 Twin Screw Extruder L1, L2 sides C1, C2 curve

Claims

1. a melt extrusion step of melt-kneading a resin composition containing a poly(3-hydroxyalkanoate)-based resin in a twin-screw extruder having a pair of screws and extruding the resulting melt; A cooling step of cooling the molten material after the melt extrusion step to obtain a molded product, a tip end of each of the pair of screws has a ridge portion protruding in a conveying direction of the molten material, The tip portion has an eccentric shape in which the top of the peak is positioned offset from the position of the rotation axis of the screw.

2. The screw includes a screw body and a screw cap detachably attached to the screw body, The method for producing a molded article according to claim 1 , wherein the screw cap constitutes the tip portion.

3. The screw cap is a cap body that is screwed to the screw body; a cap cover that is screwed to the cap body, The cap cover is The screw fastener has a fastening portion for fastening the screw fastener and the thread portion. The fastening portion has two flat surfaces for receiving the screw fastener, the two flat surfaces extending parallel to a conveying direction of the melt; In a cross section perpendicular to the conveying direction of the molten material, The external shape of the fastening portion is Two sides that are two parallel straight lines constituting two planes for receiving the screw fastener; The method for producing a molded article according to claim 2 , wherein the molded article has a substantially rectangular shape constituted by two curves connecting the two sides.

4. The method for producing a molded article according to any one of claims 1 to 3, wherein the poly(3-hydroxyalkanoate)-based resin is one or more selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate), and combinations thereof.

5. The method for producing a molded body according to any one of claims 1 to 3, wherein the molded body has a melt flow rate of 6.0 g / 10 min or less in the cooling step.

6. The method for producing a molded article according to any one of claims 1 to 3, wherein in the melt extrusion step, the temperature of the molten material during extrusion is 170°C to 200°C.

7. The method for producing a molded article according to any one of claims 1 to 3, wherein the amount of crotonic acid in the molded article in the cooling step is 10.0 mg or less per 1 kg of poly(3-hydroxyalkanoate) resin.

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