Method for manufacturing blow molded body

Abstract

To provide a method for manufacturing a blow molded article capable of suppressing defective molding.SOLUTION: A method for manufacturing a blow molded article using a rotary molding machine includes an input step and a molding step. The rotary molding machine has a mold 12 and a mold drive mechanism 10. The mold has a cavity in which the blow molded article is molded, and is configured to be openable and closable, and the mold drive mechanism is configured to rotate the mold around a revolution axis. In the input step, a molten resin is arranged in the cavity, and in the molding step, the mold is rotated around the revolution axis by the mold driving mechanism to mold the molten resin in the cavity. The molten resin is composed of resin that satisfies the following (a) and (b) in dynamic viscoelasticity measurement. (a)G'>290(Pa) (b)tanδ<4.60SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Various types of blow-molded resin containers have been proposed in the past (for example, Patent Document 1). The resin container disclosed in Patent Document 1 is configured to be able to be filled with various liquid medicines and the like, and is manufactured by blow molding. Blow molding is a molding method in which, for example, molten thermoplastic resin is sandwiched between split molds, air is injected into the molten resin to expand it, the molten resin is brought into close contact with the inner surface of the mold, and then cooled and solidified, and the container is removed from the mold as a blow-molded product. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-154940 Summary of the Invention [Problem to be solved by the invention]

[0004] Various manufacturing methods for blow molding have been proposed, including one that uses a rotary molding machine. In a rotary molding machine, multiple molds are arranged in a circular pattern. Molten resin is continuously supplied to the molds while they are rotating, and the molds to which the molten resin has been supplied are then closed one after another to blow air into the molten resin. In this manufacturing method, the orientation of the molten resin inside the mold changes as the mold rotates. This causes the relationship between the orientation of the molten resin and the direction of the force (e.g., gravity) acting on the molten resin to change over time (dynamically), which can lead to molding defects.

[0005] The present invention has been made in view of the above circumstances, and has as its object to provide a method for producing a blow-molded article that can suppress molding defects. [Means for solving the problem]

[0006] According to the present invention, there is provided a method for manufacturing a blow-molded body using a rotary molding machine, the method comprising a pouring step and a molding step, wherein the rotary molding machine has a mold and a mold drive mechanism, the mold has a cavity in which the blow-molded body is molded and is configured to be openable and closable, the mold drive mechanism is configured to rotate the mold around an axis of revolution, the pouring step involves placing molten resin in the cavity, and the molding step involves molding the molten resin in the cavity while rotating the mold around the axis of revolution using the mold drive mechanism, and the molten resin is composed of a resin that satisfies the following (a) and (b) in dynamic viscoelasticity measurement: (a) G'>290(Pa) (b) tanδ<4.60 tanδ:G'' / G' G': storage modulus of the molten resin at 190 degrees G): Loss modulus of the molten resin at 190 degrees

[0007] According to the present invention, the molten resin is made of a resin that satisfies the following (a) and (b) in dynamic viscoelasticity measurement: (a) G'>290(Pa) (b) tanδ<4.60 tanδ:G'' / G' G': storage modulus of the molten resin at 190 degrees G): Loss modulus of the molten resin at 190 degrees In other words, the molten resin has properties that take into account the dynamic changes in the direction of the force applied to the molten resin, and as a result, molding defects in the rotary molding machine can be suppressed.

[0008] Various embodiments of the present invention will be described below as examples, and the embodiments shown below can be combined with each other. Preferably, the melt flow rate (MFR) of the molten resin is 0.80 to 2.00 g / 10 min. Preferably, there is provided a method wherein the melt tension (MT) of the molten resin is 14 to 35 mN. Preferably, the blow molded article has a mouth portion and a body portion, and the maximum outer diameter of the body portion is four times or more the outer diameter of the mouth portion. Preferably, the blow molded article has a pair of opposing parting lines, the mold is attached to the mold drive mechanism so that the pair of parting lines are aligned in a radial direction around the revolution axis, and the maximum outer diameter of the body portion is the distance between the pair of parting lines in the body portion. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view that schematically shows a rotary molding machine used in a blow molding method according to an embodiment. [Figure 2] FIG. 2 is an enlarged view of area A shown in FIG. [Figure 3] FIG. 3 is a front view showing the process of producing a container 1, which is a blow-molded product, using the rotary molding machine shown in FIG. [Figure 4] Fig. 4A is a schematic explanatory view of an extruder 21 for producing a molten resin. Fig. 4B is a cross-sectional view for explaining the schematic configuration of a die head 13. [Figure 5] FIG. 5 is a front view of the container 1 which is a blow molded article. [Figure 6] Fig. 6A is a lateral side view of the container 1 shown in Fig. 5. Fig. 6B is a BB end view shown in Fig. 6A. Fig. 6B shows positions 1 to 12 obtained by dividing the angle into 12 equal parts in the circumferential direction. [Figure 7] Fig. 7A is a diagram showing gravity acting on molten resin P in mold 12 located at position p3 shown in Fig. 3. Fig. 7B is a diagram showing gravity acting on molten resin P in mold 12 located at position p4 shown in Fig. 3. Figs. 7A and 7B are cross-sectional views showing the molten resin P cut along a plane passing through the contact surfaces with split molds 12a and 12b. [Figure 8]FIG. 8 is an explanatory diagram of the height position of the container 1 for explaining the wall thickness of the container 1. In FIG. [Figure 9] Fig. 9 is a graph plotting the wall thickness data shown in Table 4. The vertical axis corresponds to positions 1 to 19 in Fig. 8. The horizontal axis represents wall thickness in mm. [Figure 10] Fig. 10 is a graph plotting the thickness data shown in the figure. In Fig. 10, the vertical axis represents thickness in mm, and the horizontal axis corresponds to positions 1 to 12 shown in Fig. 6B. DETAILED DESCRIPTION OF THE INVENTION

[0010] Embodiment 1. Description of the container 1 configuration Hereinafter, an embodiment will be described with reference to the drawings. The container 1 shown in FIGS. 5 to 6B is a blow-molded body, and includes a body 2, a mouth 3, a hanging portion 4, and a cap 5. The container 1 is configured to be able to contain a liquid content, and is used, for example, as an infusion bottle for dripping a liquid medicine. The resin that constitutes the container 1 can be a thermoplastic resin that is suitable for blow molding, such as an olefin-based resin. In an embodiment, the resin that constitutes the container 1 is made of polypropylene, polyethylene, or a mixed resin thereof.

[0011] 5 to 6B, PL indicates the position of the parting line of the container 1 in the circumferential direction of the container 1. PL90 indicates a position that is at an angle of 90 degrees from the position of the parting line of the container 1 in the circumferential direction of the container 1.

[0012] The body 2 has a straight portion 2A and a pair of reduced diameter portions 2B. The straight portion 2A has a constant width in the direction of the major axis x and a constant width in the direction of the minor axis y. The reduced diameter portions 2B are formed so that their diameter decreases with increasing distance from the body 2. The container 1 is a flat container. Specifically, the width Tx of the straight portion 2A in the direction of the major axis x is wider than the width Ty of the straight portion 2A in the direction of the minor axis y. The width Tx is the maximum outer diameter of the body 2. The maximum outer diameter (width Tx) of the body 2 is the distance between a pair of parting lines in the body 2.

[0013] The width Tx is, for example, 90 mm, and the width Ty is, for example, 25 mm. Therefore, the ratio (Ty / Tx) of the width Tx to the width Ty is approximately 0.28. Here, when the flatness of the container 1 is defined as 1-(Ty / Tx), in this embodiment, the flatness f of the container 1 is 1-0.28=0.72. Note that the flatness f is not limited to this. Specifically, the flatness f can be set to, for example, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, or 0.90. The flatness f may also be defined within a range between any two of the numerical values ​​exemplified here. The functions and effects of this embodiment are remarkable in the case of a container with a relatively high flatness, such as a flatness f of 0.70 or more.

[0014] In the embodiment, the width Tx (maximum outer diameter of the body 2) is at least four times the outer diameter T21 of the mouth 3, but is not limited to this. Specifically, the width Tx can be set to, for example, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, or 6.0 times the outer diameter T21. It may also be defined within a range between any two of the values ​​exemplified here. The functions and effects of this embodiment are particularly remarkable when manufacturing a container 1 in which the ratio between the outer diameter T2 of the mouth 3 and the width Tx of the body 2 satisfies this relationship.

[0015] The mouth 3 is formed in a cylindrical shape. In a direction parallel to the central axis of the mouth 3, one end of the mouth 3 is connected to the reduced diameter section 2B of the body 2, and the other end of the mouth 3 is connected to the cap 5 via a cut-off section 3a. The cut-off section 3a is a thin-walled portion of the container 1. The cap 5 is configured to be separable from the mouth 3 via the cut-off section 3a. In the embodiment, the outer diameter T21 of the mouth portion 3 is close to the diameter of the molten resin P (e.g., 16 mm), e.g., 16.5 mm, but is not limited to this. Specifically, the outer diameter T21 can be set to, for example, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, or 1.10 times the diameter of the molten resin P. Furthermore, the outer diameter T21 may be defined within a range between any two of the numerical values ​​exemplified here.

[0016] The suspending portion 4 has, for example, a circular opening formed therein, so that it can be hung on, for example, a hook. The suspending portion 4 is made of a solid plate-like member. The suspending portion 4 is connected to the reduced diameter portion 2B.

[0017] The longer the overall length T1 of the container 1, the more likely the effects of molding defects (drawdown), described below, become apparent during rotary molding. The overall length T1 can be set to, for example, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, or 4.0 times the width Tx of the body portion 2. The overall length T1 may also be defined within a range between any two of the values ​​exemplified here.

[0018] 2. Manufacturing method 2-1. Resin for blow molding 2-1-1. Dynamic viscoelasticity measurement The resin (molten resin) for blow molding in the manufacturing method according to the embodiment is made of polypropylene, polyethylene, or a mixture of these resins. This molten resin satisfies both the following conditions (a) and (b) in dynamic viscoelasticity measurement. Condition (a): G'>290(Pa) Condition (b): tanδ<4.60 Here, tan δ is expressed as G'' / G'. G' is the storage modulus of the molten resin at 190 degrees. G): Loss modulus of molten resin at 190 degrees.

[0019] In this specification, the dynamic viscoelasticity measurement is carried out by the following method. Measurement mode: Rotation mode (frequency dependent) Gap: 1.5~2.0mm Measurement jig: φ25mm parallel plate -Sample (molten resin) size: φ20mm Frequency: 0.1~100Hz Rotational distortion: 1% ·Measurement temperature: 190 degrees Measurement equipment: TA Instrument dynamic viscoelasticity measuring device (model number ARES-G2)

[0020] The inventors of the present invention have found that knowledge gained from measuring the dynamic viscoelasticity of molten resins can be utilized for molten resins in rotary molding, thereby improving the moldability of blow-molded articles. Molding methods that prevent the orientation of molten resin from tilting typically employ molten resins that take into account characteristics such as melt flow rate and melt tension, resulting in high-quality molded articles. However, the inventors discovered that even when using molten resins that focus solely on these characteristics, molding defects can occur in rotary molding. The inventors then discovered that the cause of these defects is the gradual tilting of the orientation of molten resin P, as shown in Figures 7A and 7B, resulting in a dynamic change over time in the relationship between the orientation of molten resin P and the direction of the force (gravity fg) acting on molten resin P. Specifically, in rotary molding, the molten resin just before the mold closes (just before the mold reaches position p2 shown in Figure 3) is in a stretched state (a state that is difficult to bend) due to the rotation of the already closed mold. When the mold closes, the upper and lower ends of the cylindrical molten resin are clamped and fixed within the mold, but the middle portion of the molten resin is free (not in contact with the mold cavity surface). This middle part is prone to drawdown and warping due to the influence of gravity, which changes over time (dynamically) as described above. If air is blown into the molten resin while it is warped, variations in thickness will occur, making it prone to molding defects.

[0021] The above-mentioned melt flow rate and melt tension measurements are static tests in which force is slowly applied to the molten resin, and are therefore not considered sufficient for selecting resins in situations where the molten resin moves more dynamically. In contrast, dynamic viscoelasticity measurements apply stress to the sample that changes and oscillates over time, making them suitable for selecting resins for molding methods in which the relationship between the orientation of the molten resin P and the direction of the force (gravity fg) applied to the molten resin P changes dynamically. Therefore, the inventors performed blow molding using molten resins that took into account the results of dynamic viscoelasticity measurements, and were able to improve the moldability of the molded body.

[0022] In dynamic viscoelasticity measurement, a sample is subjected to a periodic small strain and the response to the strain is measured to obtain values ​​such as the storage modulus G', loss modulus G'', and tan δ (loss tangent). The storage modulus G' is an index corresponding to the strength of the solid (elastic) properties of a sample (molten resin). The loss modulus G'' is an index corresponding to the strength of the liquid (viscous) properties of the sample (molten resin). Tan δ is an index that indicates whether the properties of a sample (molten resin) are closer to solid (elastic) properties or liquid (viscous) properties. The inventors have found that a molten resin having a storage modulus G' of greater than 290 (Pa) and a tan δ of less than 4.60 can produce a good molded product with a good balance of viscosity and elasticity in a situation where the forces acting on the molten resin change dynamically, such as in rotary molding.

[0023] In rotary molding, centrifugal force acts on the molten resin P inside the mold 12 as it rotates. In this embodiment, the centrifugal force is small compared to gravity fg, but it may still impair moldability. However, the manufacturing method of this embodiment uses the molten resin P based on the results of the dynamic viscoelasticity measurement described above, so it is suitable even in situations where such centrifugal force acts.

[0024] In the embodiment, the lower limit of the storage modulus G' has been described as 290 (Pa), but this is not limited thereto. The lower limit (Pa) of the storage modulus G' can be, for example, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, or 600 (Pa).

[0025] In the embodiment, the upper limit of tan δ is described as 4.60, but this is not limited thereto. The upper limit of tan δ can be, for example, 1.70, 1.80, 1.90, 2.00, 2.10, 2.20, 2.30, 2.40, 2.50, 2.60, 2.70, 2.80, 2.90, 3.00, 3.10, 3.20, 3.30, 3.40, 3.50, 3.60, 3.70, 3.80, 3.90, 4.00, 4.10, 4.20, 4.30, 4.40, 4.50, or 4.60. In particular, as shown in the examples (Table 1) described below, when tan δ is less than 3.30, the moldability is all evaluated as "good," and therefore the resin is considered suitable as a molten resin for rotary molding.

[0026] 2-1-2. Melt flow rate (MFR) The MFR (g / 10 min) of the molten resin of this embodiment is preferably 0.80 to 2.00, because drawdown of the molten resin can be suppressed. The MFR (g / 10 min) of the molten resin is specifically, for example, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0 (g / 10 min), and may be defined within a range between any two of the numerical values ​​exemplified here.

[0027] MFR means a value obtained by measuring in accordance with JIS K-7210 at a test temperature of 190°C and a test load of 2.16 kg.

[0028] 2-1-3. Melt tension (MT) The MT (mN) of the molten resin is preferably 14 to 35. This is because it is possible to prevent pinholes from occurring in the blow-molded article during blow molding. The MT (mN) of the molten resin is specifically, for example, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, or 35 (mN), and may be defined within a range between any two of the numerical values ​​exemplified here.

[0029] MT means the tension when a strand is extruded from an orifice with a diameter of 2.095 mm and a length of 8 mm at a test temperature of 190°C and an extrusion speed of 10 mm / min using a melt tension tester, and this strand is wound around a roller with a diameter of 80 mm at a winding speed of 16 rpm.

[0030] 2-2. Manufacturing equipment As shown in Figures 1 to 4B, in the method for producing a blow-molded article according to the embodiment, a molten resin melted in an extruder 21 is extruded from the extruder 21 to form a cylindrical molten resin, and the molten resin is blow-molded to obtain a blow-molded article (container 1). This production method can be carried out using a rotary molding machine. As shown in Figures 1 to 4B, the rotary molding machine, for example, includes the extruder 21, a mold drive mechanism 10, and a plurality of molds 12.

[0031] 2-2-1. Extruder 21 As shown in FIG. 4A, the extruder 21 includes a cylinder 23, a resin inlet 25, a screw 27, a temperature control unit 29, a resin extrusion outlet 28, and a die head 13.

[0032] Resin inlet 25 is a so-called hopper, through which raw resin is introduced. The form of the raw resin is not particularly limited, but is usually in pellet form. The raw resin is a resin for blow molding that has the above-mentioned properties. After being introduced into cylinder 23 through resin inlet 25, the raw resin is heated and melted within cylinder 23 to become molten resin. The raw resin is also transported toward resin extrusion outlet 28 provided at one end of cylinder 23 by the rotation of screw 27 arranged within cylinder 23.

[0033] The screw 27 is disposed within the cylinder 23, and by its rotation, kneads the molten resin while conveying it toward the resin extrusion port 28. A gear device 26 is provided at one end of the screw 27, and the screw 27 is driven to rotate by the gear device 26.

[0034] The temperature control unit 29 is configured to individually control a plurality of temperature control units provided along the cylinder 23 to control the temperature of each part of the cylinder 23. The temperature control unit 29 can also control the temperature of the die head 13 for forming the molten resin and the temperature of the connecting part 20 between the cylinder 23 and the die head 13.

[0035] The molten resin is extruded from the resin extrusion port 28 and injected into the die head 13 through the connecting part 20. As shown in FIG. 4B , the die head 13 includes a cylindrical die outer cylinder 41 and a mandrel 43 housed therein, and the molten resin extruded from the cylinder 23 is stored in the space 47 between them. After a predetermined amount of the molten kneaded resin has been stored in the space 47, the ring-shaped piston 45 is pushed down vertically, thereby extruding the molten kneaded resin from the die slit 49 and forming a cylindrical molten resin P.

[0036] 2-2-1. Die drive mechanism 10 and die 12 As shown in FIG. 3, the mold driving mechanism 10 has multiple molds 12 arranged on a circle centered on the revolution axis C. The mold driving mechanism 10 is configured to rotate the molds 12 at a predetermined cycle, for example, by a power source (e.g., a motor) not shown. Each mold 12 is located at a predetermined rotation radius r around the revolution axis C. The rotation radius r corresponds to the distance from the revolution axis C to the portion of each mold 12 that is closest in a straight line to the revolution axis C. The container 1 has a pair of opposing parting lines, and the molds 12 are attached to the mold driving mechanism 10 so that the pair of parting lines are aligned radially around the revolution axis C. Therefore, a plane parallel to the contact surface between the split molds 12a and 12b is perpendicular to the extension direction of the revolution axis C.

[0037] Each mold 12 includes split molds 12a and 12b. As shown in FIG. 2, the split molds 12a and 12b move in a direction parallel to the revolution axis C (see arrow Ar in FIG. 2), thereby opening and closing each mold 12. Each mold 12 rotates clockwise in FIG. 3. At positions p0 and p1 shown in FIG. 3, the mold 12 is fully open. Then, between positions p1 and p2, the mold 12 begins to close, and is fully closed at position p2. Between positions p2 and p6, the mold 12 is fully closed. At this time, the molten resin P is molded within the mold 12. Between positions p6 and p7, the mold 12 begins to open, and is fully open at position p7.

[0038] 2-2. Manufacturing process The method for manufacturing a blow-molded article according to the embodiment includes a loading step, a molding step, and a removal step.

[0039] The mold 12 is in the most open state between positions p0 and p1, and then gradually closes as it moves from position p1 to position p2. The injection process corresponds to the timing from position p1 to position p2. As it moves from position p1 to position p2, molten resin P is placed between the cavities of the split molds 12a and 12b, and the split molds 12a and 12b close together. The temperature of the molten resin P supplied from the die head 13 is 190°C, but this does not have to be exactly the same. For example, the functions and effects of the embodiment can be achieved as long as the temperature of the molten resin P supplied from the die head 13 is 180°C to 200°C. Note that in the embodiment, the molten resin P is described as being composed of polypropylene, polyethylene, or a mixed resin thereof. However, it is preferable to adjust the temperature of the molten resin depending on the type of resin used as the molten resin P.

[0040] The molding process is performed between positions p2 and p6. In the molding process, air is supplied into the cylindrical molten resin P in the mold 12 to shape the molten resin P in the cavity cv, thereby forming a molded body. In the molding process, the posture of the cylindrical molten resin P in the mold 12 changes as shown in FIGS. 7A and 7B. Therefore, the relationship between the posture of the molten resin P and the direction of the force (gravity fg) applied to the molten resin P changes over time (dynamically). However, in the embodiment, as described above, a molten resin that takes into account the results of dynamic viscoelasticity measurement is used, thereby making it possible to suppress molding defects.

[0041] Examples of molding defects include accelerated drawdown of the molten resin P due to a change in the above-mentioned relationship over time, resulting in pinholes, unmolded portions, and variations in wall thickness in the molded product. For example, at position w1 shown in Figures 7A and 7B, the molten resin P becomes thin when it is drawn down, making it more likely to develop pinholes. Note that position w1 corresponds to the upper position of the reduced diameter portion 2B of the container 1. In particular, the effects of drawdown are likely to be significant under manufacturing conditions in which air supply into the molten resin P begins after the mold 12 is at the bottom dead center (position p4 in Figure 3). Other examples include a phenomenon in which molten resin P overflows the cavity cv at the mouth of the container (a portion with a small diameter), resulting in burrs, and a phenomenon in which burrs generated in a previous molding shot remain in the mold and penetrate into the next molded product (burr jamming). Position w2 shown in Figures 7A and 7B is a position where burrs are likely to occur when molten resin P is drawn down. Position w2 corresponds to the position of the mouth 3 of the container 1.

[0042] When producing a blow-molded article that satisfies the above-mentioned numerical range for the flattening f or when producing a blow-molded article that satisfies the above-mentioned numerical ranges for the outer diameter T2 of the mouth portion 3 and the width Tx of the body portion 2, the degree of expansion of the molten resin P tends to increase, and the effects of drawdown tend to become more pronounced. Furthermore, when the above-mentioned numerical ranges for the outer diameter T21 of the mouth portion 3 and the diameter of the molten resin P are satisfied, the production conditions result in a small clearance between the mouth portion 3 and the molten resin P, and burrs and burr bite tend to become more pronounced. However, by using the molten resin according to the embodiment, the above-mentioned molding defects are particularly effectively suppressed.

[0043] In the molding process, the weight of the molten resin P placed in each mold 12 is 22.6 (g) in this embodiment, but is preferably set to, for example, 15 to 30 (g). Furthermore, the weight (g) of the molten resin P placed in each mold 12 can be set to, for example, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 (g). The weight of the molten resin P placed in each mold 12 can also be defined within a range between any two of the numerical values ​​exemplified here.

[0044] In the removal step, the mold 12 is opened and the blow-molded article is removed from the mold 12. The removal step corresponds to the timing from position p6 to position p7.

[0045] The way in which gravity fg acts on the molten resin P varies depending on the rotation period and rotation radius of the mold 12. The rotation period and rotation radius are preferably set as follows: The rotation period is the time required for each mold 12 to make one revolution around the revolution axis C. The rotation period of the mold 12 can be set to, for example, 15 to 45 seconds. Specifically, the rotation period (seconds) can be set to, for example, 15, 20, 25, 30, 35, 40, or 45 seconds. The rotation period may also be defined within a range between any two of the numerical values ​​exemplified here. The rotation radius r can be set to, for example, 200 to 800 mm. Specifically, the rotation radius r (mm) can be set to, for example, 200, 250, 300, 350, 400, 450, 50, 550, 600, 650, 700, 750, or 800 mm. The rotation radius r can also be defined within a range between any two of the numerical values ​​exemplified here. [Example]

[0046] 3. Working Example A blow-molded article (container 1) was produced using an extruder 21, a mold drive mechanism 10, and a mold 12, and the blow-molded article was evaluated. The resins used as raw material resins were polypropylene, polyethylene, or a mixed material of polypropylene and polyethylene shown in Table 1 (Examples) and Table 2 (Comparative Examples). Table 1 shows the properties of the resins of Examples 1 to 10. Table 2 shows the properties of the resins of Comparative Examples 1 to 6. Table 3 shows details of the resins of the Examples in Table 1 and the Comparative Examples in Table 2. Examples 4 to 9 are mixed materials of polypropylene and polyethylene, and the ratios (%) are mass ratios. The temperature of the molten resin P is controlled to 190°C by temperature control unit 29. The rotation radius r of the rotary molding machine is 410 (mm), and the rotation period is 27.3 seconds.

[0047] Whether a blow-molded article is a good product or not is judged based on the presence or absence of molding defects (such as the occurrence of pinholes or unmolded areas) as described above. Note that the symbols ○ and △ in Table 1 both indicate that a good blow-molded article was obtained, while the symbol × in Table 2 indicates that the blow-molded article was a defective product. Furthermore, the symbol △ in Table 1 indicates that adjustments to the rotary molding machine (for example, the injection angle of the molten resin) were sometimes required during the manufacturing process. The molten resin P used in manufacturing the containers 1 of Examples 1 to 9 satisfied both the condition (a): G' > 290 (Pa) and the condition (b): tan δ < 4.60. All of these containers 1 were non-defective. In contrast, the molten resin P used in manufacturing the containers 1 of Comparative Examples 1 to 6 did not satisfy at least one of the condition (a): G' > 290 (Pa) and the condition (b): tan δ < 4.60. These containers were found to have molding defects such as pinholes and unmolded portions, and were therefore defective.

[0048] [Table 1]

[0049] [Table 2]

[0050] [Table 3]

[0051] The dimensions and weight of the container 1 manufactured in the example will be described with reference to FIGS. 5 to 6B. The overall length T1 of the container 1 is 258 (mm). The width Tx of the body 2 is 90 (mm). The width Ty of the body 2 is 25 (mm). The outer diameter T21 of the mouth portion 3 is 16.5 (mm). The height and width T22 of the mouth portion 3 is 18.6 (mm). The height T31 of the hanging portion 4 is 20 (mm). The width T32 of the hanging portion 4 is 20 (mm). The wall thickness T33 of the hanging portion 4 is 1.7 (mm). The height and width T41 of the cap portion 5 is 27 (mm). The width T42 of the cap portion 5 is 23.5 (mm). The weight of the container 1 is 19.5 g.

[0052] The wall thickness dimensions of the body portion 2 of the container 1 produced in the examples will be outlined with reference to Figures 5 to 6B, Figures 8 to 10, Tables 4 and 5. Table 4 is a table showing the wall thickness of the container 1 shown in Figure 8, with the unit of wall thickness being mm. In Table 4, positions 1 to 19 arranged vertically (in the column direction) correspond to positions 1 to 19 shown in Figure 8. In Table 4, the horizontal direction (in the row direction) correspond to positions 1 to 12 shown in Figure 6B. Table 5 is a table showing the wall thickness at circumferential positions at position 9 in Figure 8. In Table 5, the unit of wall thickness is mm.

[0053] Since the straight portion 2A of the body portion 2 is the portion where the molten resin P is largely stretched during blow molding, the thickness of the straight portion 2A of the body portion 2 (positions 3 to 15 in Figure 9) is thinner overall than the tapered portion 2B of the body portion 2 (positions 1, 2, 16 to 18 in Figure 9) and the mouth portion 3 (position 19 in Figure 9). At positions PL and PL90, the thickness of the straight portion 2A of the body 2 (positions 3 to 15 in Figure 9) is distributed within a range of 0.156 to 0.656 (mm). At positions PL and PL90, the thickness of the reduced diameter portion 2B of the body 2 (positions 1, 2, 16 to 18 in Figure 9) is distributed within a range of 0.159 to 1.128 (mm). In the reduced diameter portion 2B, the thickness increases rapidly from the straight portion 2A, which is thinner, to the mouth portion 3 or the hanging portion 4, which are thicker. The circumferential thickness of the intermediate portion (position 9 in FIG. 9) of the straight portion 2A of the body portion 2 is distributed within the range of 0.254 to 0.607 (mm).

[0054] [Table 4]

[0055] [Table 5] [Explanation of symbols]

[0056] 1: Container 2: Body 2A: Straight section 2B: Reduced diameter part 3: Mouth 3a: Cut-off section 4: Hanging part 5: Cap part 10: Mold drive mechanism 12: Mold 12a: Split mold 12b: Split mold 13: Die head 20:Connection part 21: Extruder 23: Cylinder 25:Resin inlet 26: Gear device 27: Screw 28:Resin extrusion port 29: Temperature control unit 41: Die outer cylinder 43: Mandrel 45: Ring-shaped piston 47:Space 49: Die slit C: Revolution axis P: Molten resin cv: cavity fg :Gravity x :Long axis y: short axis

Claims

1. A method for producing a blow-molded article using a rotary molding machine, The method includes a charging step and a molding step, the rotary molding machine has a mold and a mold drive mechanism, the mold has a cavity in which the blow molded article is molded, and is configured to be openable and closable; the mold drive mechanism is configured to rotate the mold around a revolution axis; In the introducing step, a molten resin is placed in the cavity, In the molding step, the molten resin in the cavity is molded while the mold is rotated around the revolution axis by the mold drive mechanism; The method, wherein the molten resin satisfies the following (a) and (b) in dynamic viscoelasticity measurement and is composed of a resin containing polypropylene: (a) G'>290 (Pa) (b) tanδ<3.30 tan δ: G″ / G′ G': storage modulus of the molten resin at 190 degrees G″: loss modulus of the molten resin at 190 degrees

2. 10. The method of claim 1, The melt flow rate (MFR) of the molten resin is 0.80 to 2.00 g / 10 min.

3. 3. The method of claim 1 or claim 2, The melt tension (MT) of the molten resin is 14 to 35 mN.

4. The method according to any one of claims 1 to 3, The blow molded article has a mouth portion and a body portion, The method, wherein the maximum outer diameter of the body is at least four times the outer diameter of the mouth.

5. 5. The method of claim 4, The blow molded article has a pair of opposing parting lines, the mold is attached to the mold driving mechanism so that the pair of parting lines are aligned in a radial direction about the revolution axis, The method, wherein the maximum outer diameter of the body portion is the distance between the pair of parting lines in the body portion.

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