Preform, injection mold, and method and device for manufacturing resin container

Abstract

To provide a manufacturing method capable of manufacturing a resin container in a high-speed molding cycle while suppressing whitening in a central bottom region of a preform or container.SOLUTION: A method for manufacturing a resin container includes: an injection molding step of injection molding a preform made of resin and having a body portion and a bottom portion; a temperature adjustment step of adjusting a temperature of the preform manufactured in the injection molding step; and a blow molding step of blow-molding the preform having the adjusted temperature to manufacture a resin container. In the injection molding step, the preform is injection-molded using an injection mold in which a thickness of the bottom portion is 0.7 to 0.85 relative to a thickness of the body portion. Further, in the temperature adjustment step, a coolant is introduced into the preform to cool the bottom portion of the preform.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for manufacturing a resin container.

Background Art

[0002] Conventionally, as one of the methods for manufacturing a resin container, a hot parison blow molding method is known. The hot parison blow molding method is a method of blow molding a resin container using the retained heat during injection molding of a preform, and is advantageous in that it can manufacture a resin container that is more diverse and has an excellent aesthetic appearance compared to the cold parison method.

[0003] In the hot parison blow molding method, while the body portion of the preform is required to retain an amount of heat that can be stretched, the central region of the bottom of the preform is required to maintain a hardness such that it is not broken by a stretching rod.

[0004] Conventionally, for example, in some cases, a preform with a bottom thickness set to about 1 / 2 of the body thickness is used, and the above requirements are met by increasing the injection cooling efficiency of the bottom. Patent Document 1 discloses that in a cylindrical thin-walled preform, the bottom surface is formed as an inclined surface at the same angle of 20° to 45°, and the connection portion with the body portion is formed in an arc shape, so that the wall thickness gradually transitions from the bottom to the body portion to suppress whitening of the bottom surface.

[0005] In recent years, a method for manufacturing a container has been proposed in which the cooling time during injection molding is shortened, and a preform released at a high temperature is blow molded at a high stretching ratio (see, for example, Patent Document 2). According to the above method for manufacturing a container, a resin container with good physical properties and appearance can be manufactured at a high molding cycle speed.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the hot parison blow molding method, there is a preform shape suitable for each container according to specifications such as the physical properties of the container and the draw ratio. For example, when manufacturing a resin container with a wide mouth and thin walls such as a cup, for example, a flat bowl-shaped preform is applied. In this type of preform, since the wall thickness of the body part is set relatively thin, if the bottom thickness is set to about 1 / 2 of the wall thickness of the body part, the bottom thickness of the preform becomes even thinner.

[0008] In the injection molding of the above preform, the space at the bottom of the preform in the injection mold becomes very narrow, and the flow resistance of the molten resin in the vicinity of the gate portion increases. Then, the shear heat generation of the molten resin increases during injection molding, and the central region at the bottom of the preform becomes hot. As a result, it becomes difficult to sufficiently cool the central region at the bottom of the preform, and crystallization (whitening) due to slow cooling is likely to occur in the central region at the bottom of the preform and the container. In particular, when the cooling time during injection molding is shortened and the preform released at a high temperature is blow molded at a high draw ratio, suppression of whitening in the central region at the bottom becomes more important.

[0009] Therefore, the present invention has been made in view of such problems, and an object thereof is to provide a manufacturing method capable of manufacturing a resin container with a high molding cycle while suppressing whitening in the central region at the bottom of the preform and the container.

Means for Solving the Problems

[0010] A method for manufacturing a resin container according to an aspect of the present invention includes an injection molding step of injection molding a resin preform having a body portion and a bottom portion, a temperature adjustment step of adjusting the temperature of the preform manufactured in the injection molding step, and a blow molding step of blow molding the temperature-adjusted preform to manufacture a resin container. In the injection molding step, the preform is injection molded using an injection mold in which the wall thickness of the bottom portion is 0.7 to 0.85 times that of the body portion. Further, in the temperature adjustment step, a refrigerant is introduced into the preform to cool the bottom portion of the preform.

Effects of the Invention

[0011] According to an aspect of the present invention, a resin container can be manufactured with a high molding cycle while suppressing whitening in the central region of the bottom portion of the preform and the container.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the embodiments, for easier understanding, the structures and elements other than the main part of the present invention will be described in a simplified or omitted manner. Also, in the drawings, the same elements are denoted by the same reference numerals. Note that the shapes, dimensions, etc. of each element shown in the drawings are schematically shown and do not represent actual shapes, dimensions, etc.

[0014] <Explanation of preform> First, with reference to FIG. 1, a configuration example of a preform 10 applied to the production of a resin container (hereinafter also simply referred to as a container) of the present embodiment will be described. FIG. 1(a) shows the overall shape of the preform 10, and FIG. 1(b) is a partial enlarged view of the vicinity of the gate portion 14 in FIG. 1(a). Note that the preform 10 in FIG. 1 is applied, for example, when manufacturing a wide-mouth and thin-walled container (see FIG. 2) such as a cup.

[0015] As shown in FIG. 1(a), the overall shape of the preform 10 is a flat bottomed bowl shape that is convex downward. A cylindrical neck portion 11 that opens upward is formed on the upper side of the preform 10, and a bottom portion 12 faces the lower side of the preform 10. Also, between the neck portion 11 and the bottom portion 12, they are connected by a body portion 13 over the entire circumferential direction. Note that the above shape of the preform 10 is merely an example, and for example, the preform 10 may be a bottomed cylindrical shape extending in the longitudinal direction.

[0016] Also, in the preform 10 of the present embodiment, the wall thickness th1 of the bottom portion 12 is set to a value of 0.7 to 0.85 compared to the wall thickness th2 of the body portion 13. That is, the preform 10 of the present embodiment has a relatively thicker bottom wall thickness compared to a conventional preform in which the bottom thickness is set to about 1 / 2 of the body thickness. In the hot parison blow molding method, the bottom thickness is set to about 1 / 2 of the body thickness so as not to break the bottom with a stretching rod during the blow molding process, and the bottom is sufficiently cooled and solidified in the injection molding process.

[0017] At the center of the bottom 12 of the preform 10, a gate portion 14 with a tip protruding outward from the bottom 12 is formed. The gate portion 14 is a resin introduction mark from a hot runner mold 33 described later, and is formed in a tapered shape that expands in diameter from the tip side of the gate portion 14 toward the base end side facing the bottom 12. Therefore, as shown in Fig. 1(b), the gate portion 14 has a larger diameter dimension d2 on the base end side than the diameter dimension d1 on the tip side. Note that at the corner portion 15 where the gate portion 14 and the outer surface of the bottom are connected on the base end side of the gate portion 14, a round (rounded, arc) shape is provided. The round shape is set, for example, so that its radius has a numerical value from 2.0 mm to 4.0 mm (preferably from 2.1 mm to 3.0 mm).

[0018] The thickness of the bottom 12 is set to be thinner than the diameter dimension d1 of the gate portion. For example, when the diameter dimension d1 is set to 1, it is set to a value from 0.70 to 0.9 (preferably from 0.75 to 0.85). Also, in the preform 10, for example, the maximum diameter D1 (the diameter of the neck portion 11) is set to be longer than the length L1 (the length of the bottom 12 from the upper end of the neck portion 11 to the upper end of the gate portion 14). The diameter D1 is set, for example, to be 1.5 times to 3.0 times (preferably 1.5 times to 2.5 times, more preferably 1.7 times to 2.3 times) the length L1.

[0019] The material of the preform 10 is a thermoplastic synthetic resin, which can be appropriately selected according to the use of the container. Specific types of materials include, for example, PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PCTA (policyclohexane dimethylene terephthalate), Tritan (registered trademark: copolyester manufactured by Eastman Chemical Company), PP (polypropylene), PE (polyethylene), PC (polycarbonate), PES (polyethersulfone), PPSU (polyphenylsulfone), PS (polystyrene), COP / COC (cyclic olefin polymer), PMMA (polymethyl methacrylate: acrylic), PLA (polylactic acid), and the like. It should be noted that the present invention is particularly effective when a thermoplastic synthetic resin and a crystalline resin that are likely to cause whitening due to spherulitic crystallization during injection molding (for example, PET or PEN) are selected as the material of the preform 10.

[0020] <Description of the container> Next, with reference to FIG. 2, a configuration example of the container of the present embodiment will be described. FIG. 2(a) is a plan view of the container, and FIG. 2(b) is a front view of the container. As shown in FIGS. 2(a) and 2(b), the container 1 is a wide-mouth cup-shaped container with an open top and a closed bottom. The container 1 has a neck portion 2 facing the opening on the upper surface side, a bottom portion 3 closing the bottom surface side, and a body portion 4 connecting the neck portion 2 and the bottom portion 3. The body portion 4 of the container 1 has a tapered shape (an inverted truncated cone shape) that tapers from the upper surface side to the bottom surface side. Further, the container 1 has a sufficiently long axial length (depth L) in the axial direction of the container compared to the inner diameter D of the container and is formed with a deep bottom. The longitudinal stretching ratio of the preform 10 with respect to the container 1 is set as high as 3.0 to 7.0 (preferably 3.5 to 6.0, more preferably 4.0 to 5.5).

[0021] <Description of the blow molding device> Next, with reference to FIG. 3, a blow molding apparatus 20 for manufacturing a container will be described. FIG. 3 is a block diagram schematically showing the configuration of the blow molding apparatus 20. The blow molding apparatus 20 of the present embodiment is a hot parison method (also referred to as a one-stage method) apparatus that performs blow molding by utilizing the retained heat (internal heat quantity) during injection molding without cooling the preform 10 to room temperature.

[0022] The blow molding apparatus 20 includes an injection molding section 21, a temperature adjustment section 22, a blow molding section 23, a take-out section 24, and a transfer mechanism 26. The injection molding section 21, the temperature adjustment section 22, the blow molding section 23, and the take-out section 24 are arranged at positions rotated by a predetermined angle (for example, 90 degrees) around the transfer mechanism 26.

[0023] (Transfer mechanism 26) The transfer mechanism 26 includes a transfer plate (not shown) that moves so as to rotate around an axis perpendicular to the plane of FIG. 3. On the transfer plate, one or more neck molds 27 (not shown in FIG. 1) for holding the neck of the preform 10 or a resin container (hereinafter simply referred to as a container) are arranged at each predetermined angle. The transfer mechanism 26 transports the preform 10 (or container) with its neck held by the neck mold 27 in the order of the injection molding section 21, the temperature adjustment section 22, the blow molding section 23, and the take-out section 24 by moving the transfer plate by 90 degrees each time. Note that the transfer mechanism 26 further includes a lifting mechanism (a vertical mold opening and closing mechanism) and a mold opening mechanism for the neck mold 27, and also performs operations such as lifting the transfer plate and operations related to mold closing and mold opening (releasing) in the injection molding section 21 and the like.

[0024] (Injection molding section 21) As shown in FIG. 4(a), the injection molding section 21 includes an injection cavity mold 31, an injection core mold 32, and a hot runner mold 33, and manufactures the preform 10 by injection molding. The injection cavity mold 31 and the hot runner mold 33 are fixed to the machine base of the blow molding apparatus 20 in an integrated state. On the other hand, the injection core mold 32 is fixed to a core mold lifting mechanism (not shown). Further, an injection device 25 for supplying a resin material, which is the raw material of the preform, is connected to the injection molding section 21.

[0025] The injection cavity mold 31 is a mold that defines the shape of the outer periphery of the preform 10. The hot runner mold 33 has a resin supply portion 33a that introduces the resin material from the injection device 25 into the mold. The injection core mold 32 is a mold that defines the shape on the inner peripheral side of the preform 10 and is inserted from above into the inner peripheral sides of the neck mold 27 and the injection cavity mold 31.

[0026] The mold space S formed by the injection cavity mold 31 and the injection core mold 32 has a shape that follows the above-mentioned preform 10. In the mold space S, the interval th of the mold space corresponding to the thickness of the bottom portion 12 1’ is set to a value of 0.7 to 0.85 compared to the interval th of the mold space corresponding to the thickness of the body portion 13. 2’

[0027] As shown in FIG. 4(b), in the injection cavity mold 31, the gate region S1 connected to the resin supply portion 33a is formed in a tapered shape that expands in diameter as it goes toward the injection core mold 32. At the exit of the gate region S1 facing the injection core mold 32, a roundness is added to the corner portion 34 where the gate region S1 and the outer surface of the bottom portion are connected. The radius of curvature of the corner portion 34 is, for example, 1 mm or more.

[0028] In the injection molding section 21, the injection cavity mold 31, the injection core mold 32, and the neck mold 27 of the transfer mechanism 26 are closed to form a mold space S in the shape of a preform. Then, by flowing the resin material from the injection device 25 through the hot runner mold 33 into such a mold space S in the shape of a preform, the preform 10 is manufactured in the injection molding section 21.

[0029] On the other hand, the injection device 25 is a device in which a screw is provided rotatably and reciprocally in the cylinder of the barrel, and is responsible for the function of heating and melting the resin material and injecting it into the mold. The injection device 25 performs injection, pressure holding, and metering in order by the action of the screw.

[0030] The injection device 25 supplies the resin material from the hopper to the cylinder in which the screw is disposed, and plasticizes, kneads, and measures the resin material by the rotation and backward movement of the screw. Then, the injection device 25 injects and fills the molten resin into the mold by advancing the screw at high speed. Next, the injection device 25 advances the screw at a low speed with a predetermined pressure to additionally inject and fill the molten resin into the mold so as to compensate for the shrinkage amount of the molten resin in the mold, and the pressure holding is performed in that state. When the injection device 25 fills the resin material into the mold at high speed, it controls the moving speed (injection speed) of the screw, and after the resin material is filled into the mold at high speed, it controls by pressure (pressure holding force). The switching from speed control to pressure control is performed using the screw position or the injection pressure as a threshold value.

[0031] Note that even when the mold of the injection molding unit 21 is opened, the neck mold 27 of the transfer mechanism 26 is not opened and holds and transfers the preform 10 as it is. The number of preforms 10 simultaneously molded in the injection molding unit 21 (that is, the number of containers that can be simultaneously molded by the blow molding device 20) can be set as appropriate.

[0032] (Temperature adjustment unit 22) The temperature adjustment unit 22 equalizes the temperature of the preforms 10 manufactured in the injection molding unit 21 and removes uneven temperature, and adjusts the temperature of the preforms 10 to a temperature suitable for blow molding (for example, about 90°C to 105°C) and a temperature distribution suitable for the shape of the container to be shaped. Further, the temperature adjustment unit 22 also has a function of cooling the preforms 10 in the high-temperature state after injection molding.

[0033] FIG. 5 is a diagram showing a configuration example of the temperature adjustment unit 22. The temperature adjustment unit 22 includes, as a mold unit for temperature adjustment, a cavity mold (temperature adjustment pot) 41 capable of accommodating the preform and an air introduction member 42.

[0034] The cavity mold 41 is a mold having a temperature-controlled space with substantially the same shape as the preform 10 manufactured in the injection molding section 21. Inside the cavity mold 41, a flow path (not shown) through which a temperature-adjusting medium (refrigerant) flows is formed. Therefore, the temperature of the cavity mold 41 is maintained at a predetermined temperature by the temperature-adjusting medium. Note that the temperature of the temperature-adjusting medium of the cavity mold 41 is not particularly limited, but for example, it can be appropriately selected within a range of 5°C to 80°C, preferably between 30°C and 60°C.

[0035] The air introduction member 42 has an air introduction rod 43 connected to an air supply section (not shown) and a fitting core 44, and is inserted inside the neck mold 27 and the preform 10. The air introduction member 42 is airtightly abutted against the neck portion 11 of the preform 10 in a state of being inserted into the neck mold 27. Both the air introduction rod 43 and the fitting core 44 are hollow cylindrical bodies, and the air introduction rod 43 is concentrically arranged inside the fitting core 44.

[0036] The inside of the air introduction rod 43 constitutes a flow path for guiding compressed air (air, gaseous refrigerant) from the air supply section, and the tip of the air introduction rod 43 is inserted to near the bottom surface of the preform 10. Further, an opening 43a for supplying compressed air into the preform 10 is formed at the tip of the air introduction rod 43 facing the bottom of the preform 10.

[0037] The fitting core 44 is in close contact with the inner circumference or upper end surface of the neck portion 11 when the air introduction rod 43 is inserted into the neck mold 27, and maintains airtightness between the preform 10 and the air introduction member 42. The tip of the fitting core 44 is inserted or abutted to the position of the neck portion 11 of the preform 10. Further, an opening 45 for exhausting air from the preform 10 is formed at the tip of the fitting core 44. Also, the space between the air introduction rod 43 and the fitting core 44 constitutes an exhaust flow path connected to an air exhaust section (not shown).

[0038] (Blow molding section 23) The blow molding section 23 performs stretch blow molding on the preform 10 whose temperature has been adjusted by the temperature adjustment section 22 to manufacture a container. The blow molding section 23 includes a blow cavity mold which is a pair of split molds corresponding to the shape of the container, a bottom mold, a stretch rod, and an air introduction member (all not shown). The blow molding section 23 performs blow molding while stretching the preform 10. Thereby, the preform 10 can be shaped into the shape of the blow cavity mold to manufacture a container.

[0039] (Take-out section 24) The take-out section 24 is configured to release the neck portion of the container manufactured by the blow molding section 23 from the neck mold 27 and take out the container to the outside of the blow molding apparatus 20.

[0040] <Explanation of the blow molding method> Next, the blow molding method by the blow molding apparatus 20 of the present embodiment will be described. FIG. 6 is a flowchart showing the steps of the blow molding method.

[0041] (Step S101: Injection molding process) In step S101, in the injection molding section 21, resin is injected from the injection device 25 into the preform-shaped mold space formed by the injection cavity mold 31, the injection core mold 32, and the neck mold 27 of the transfer mechanism 26, and the preform 10 is manufactured.

[0042] The resin injected from the injection device 25 is filled into the mold space S between the injection cavity mold 31 and the injection core mold 32 through the gate region S1 of the injection cavity mold 31 from the resin supply section 33a of the hot runner mold 33.

[0043] Since the gate region S1 of the injection cavity mold 31 has a tapered shape that expands toward the injection core mold 32, the flow rate of the resin flowing through the gate region S1 decreases toward the outlet of the gate region S1, and the flow resistance of the resin also decreases. In addition, since the corner portion 34 is rounded at the exit of the gate region S1, vortices are less likely to occur in the resin flow at the corner portion 34. Therefore, the resin flow at the exit of the gate region S1 is likely to become a laminar flow that flows along the curved surface into the bottom region, and an increase in flow resistance due to vortices is also suppressed.

[0044] Furthermore, the interval th of the mold space corresponding to the thickness of the bottom portion 12 1’ is a value of 0.7 to 0.85 compared to the interval th of the mold space corresponding to the thickness of the body portion 13 2’ and the interval at the bottom is wider compared to a conventional mold in which the bottom thickness is about 1 / 2 of the body thickness. Therefore, in the bottom region of the mold space S, the resin flows more easily toward the body portion compared to the conventional case, and the flow resistance of the resin also becomes smaller.

[0045] After the injection (filling and holding pressure) of the resin material is completed, or after the minimum cooling time provided after the completion of injection, the injection mold of the injection molding section 21 is opened.

[0046] From the viewpoint of manufacturing the container with a high-speed molding cycle, in step S101, it is preferable to open the mold without providing a cooling time for the preform 10 in the injection mold after the injection (filling and holding pressure) of the resin material is completed. In the above case, since the preform 10 is not cooled in a state without holding pressure in the injection mold, an event in which the preform 10 shrinks and sinks can also be suppressed during the cooling time.

[0047] On the other hand, when performing the minimum cooling of the preform 10 in the injection mold, the time (cooling time) for cooling the resin material after the injection of the resin material is completed in the injection molding section 21 is preferably 1 / 2 or less with respect to the time (injection time) for injecting the resin material. Further, the above cooling time can be made shorter with respect to the time for injecting the resin material according to the weight of the resin material. For example, the cooling time is more preferably 2 / 5 or less, even more preferably 1 / 4 or less, and particularly preferably 1 / 5 or less with respect to the injection time of the resin material.

[0048] When the injection mold is opened in step S101, the preform 10 is released from the injection cavity mold 31 and the injection core mold 32 in a high-temperature state where the outer shape can be maintained. Next, the transfer plate of the transfer mechanism 26 moves so as to rotate by a predetermined angle, and the preform 10 in a high-temperature state held by the neck mold 27 is transferred to the temperature adjustment unit 22.

[0049] Also, referring to FIG. 7, the temperature change of the preform 10 in the blow molding method of the present embodiment will be described. The vertical axis in FIG. 7 indicates the temperature of the preform 10, and the horizontal axis in FIG. 7 indicates time. In FIG. 7, an example of the temperature change of the preform 10 of the present embodiment is shown in (A) in FIG. 7. Also, an example of the temperature change of the preform in the comparative example described later is shown in (B) in FIG. 7. Note that the blank between each process is the time required for transferring the preform 10 or the container, etc., and all have the same length.

[0050] In the comparative example (conventional method), as shown in (B) of FIG. 7, the preform is cooled to a temperature lower than or substantially the same as the blow temperature in the mold of the injection molding section.

[0051] On the other hand, in the present embodiment, as described above, since there is no (or the cooling time is very short) cooling time of the preform 10 in the injection mold, the skin layer (surface layer in a solidified state) of the preform is thinner than before, and the core layer (inner layer in a softened state or a molten state) is formed thicker than before. That is, compared with the comparative example, the thermal gradient between the skin layer and the core layer is large, and the preform 10 with a high heat retained at a high temperature is formed.

[0052] The preform 10 of the present embodiment is released from the injection molding section 21 at a demolding temperature higher than that of the comparative example and transferred to the temperature adjustment unit 22. Along with the movement to the temperature adjustment unit 22, the preform 10 proceeds with temperature equalization due to heat exchange (heat conduction) between the skin layer and the core layer. Also, due to contact with the outside air, the preform 10 is slightly cooled from the outer surface. However, the temperature of the preform 10 of the present embodiment is maintained in a very high state compared with the comparative example until it is carried into the temperature adjustment unit 22.

[0053] (Step S102: Temperature Adjustment Process) Subsequently, in the temperature adjustment unit 22, cooling and temperature adjustment are performed to bring the temperature of the preform 10 closer to the temperature suitable for the final blow (blow temperature). The blow temperature is set, for example, between 90°C and 105°C for PET resin. Note that in some cases, a lower blow temperature can improve the draw orientation of the preform 10 and enhance the strength (physical properties) of the container. Therefore, the blow temperature can be set, for example, between 90°C and 95°C for PET resin.

[0054] As shown in FIG. 7, in the temperature adjustment unit 22, the temperature of the preform 10 is lowered to the blow temperature, and then the temperature of the preform 10 is maintained at the blow temperature until blow molding is performed. In the temperature adjustment unit 22, since the preform in a high-temperature state is rapidly cooled, whitening (clouding) due to spherulite formation crystallization that may occur when slowly cooled is suppressed.

[0055] In the temperature adjustment process, as shown in FIG. 5, first, the preform 10 is accommodated in the cavity mold 41. Subsequently, an air introduction member 42 is inserted into the neck portion of the preform 10 accommodated in the cavity mold 41. At this time, the neck portion 11 of the preform 10 and the fitting core 44 are in close contact with each other, and an airtight state between the two is maintained.

[0056] Thereafter, cooling blow of the preform 10 is performed. In the cooling blow of the preform 10 of the present embodiment, compressed air is introduced from the air introduction rod 43 to the bottom side of the preform 10, and the compressed air is exhausted from the neck side of the preform 10.

[0057] In the cooling blow, since compressed air jets out from the opening 43a of the air introduction rod 43, low-temperature compressed air contacts the bottom 12 of the preform 10 facing the opening 43a of the air introduction rod 43. The preform 10 is cooled from the inside by the compressed air flowing inside, but the temperature of the compressed air gradually rises as it exchanges heat with the preform 10 and heads towards the body portion 13 and the neck portion 11. Therefore, in the cooling blow, the bottom 12 of the preform 10 is locally cooled more strongly than the neck portion 11 and the body portion 13 of the preform 10. By rapidly cooling the bottom 12 of the preform 10 in the above-described cooling blow, whitening in the central region of the bottom 12 of the preform 10 is effectively suppressed.

[0058] Further, compared with a conventional preform 10 in which the bottom thickness is about 1 / 2 of the body thickness, the wall thickness of the bottom 12 of the preform 10 of the present embodiment is relatively thick, so the heat retained by the bottom 12 becomes large. However, as described above, since the heat retained by the bottom 12 is reduced by locally cooling the bottom 12 with the temperature adjustment unit 22, excessive stretching of the bottom 12 (for example, breakage of the bottom 12) during blow molding of the container is suppressed.

[0059] Further, the preform 10 in the temperature adjustment unit 22 continues to contact the cavity mold 41 maintained at a predetermined temperature under the pressure of the compressed air from the inside. Therefore, in the temperature adjustment process, the preform 10 is temperature-adjusted so as not to fall below the temperature suitable for blow molding from the outside, and further, the temperature deviation generated during injection molding is reduced. In addition, in the temperature adjustment process, the shape of the preform 10 is maintained by the cavity mold 41 and does not change significantly.

[0060] After the temperature adjustment process, the transfer plate of the transfer mechanism 26 moves so as to rotate by a predetermined angle, and the temperature-adjusted preform 10 held by the neck mold 27 is transferred to the blow molding unit 23.

[0061] (Step S103: Blow molding process) Subsequently, in the blow molding unit 23, blow molding of the container 1 is performed. First, the blow cavity mold is closed, and the preform 10 is accommodated in the mold space. By lowering the air introduction member (blow core), the air introduction member abuts against the neck portion of the preform 10. Then, the stretching rod (vertical axis stretching member) is lowered to hold the bottom of the preform 10 from the inner surface, and while performing vertical axis stretching as necessary, blow air is supplied from the air introduction member to stretch the preform 10 in the horizontal axis. As a result, the preform 10 bulges and is shaped so as to be in close contact with the mold space of the blow cavity mold, and is blow-molded into the container 1. The bottom mold waits at a lower position where it does not contact the bottom of the preform 10 before the blow cavity mold is closed, and quickly rises to the molding position before or after the mold is closed.

[0062] (Step S104: Container removal step) When the blow molding is completed, the blow cavity mold and the bottom mold are opened. As a result, the container 1 can be moved from the blow molding section 23. Subsequently, the transfer plate of the transfer mechanism 26 moves so as to rotate by a predetermined angle, and the container 1 is transferred to the take-out section 24. At the take-out section 24, the neck portion of the container 1 is released from the neck mold 27, and the container 1 is taken out of the blow molding apparatus 20.

[0063] Thus, a series of steps of the blow molding method are completed. Thereafter, by moving the transfer plate of the transfer mechanism 26 so as to rotate by a predetermined angle, the steps from S101 to S104 described above are repeated. During the operation of the blow molding apparatus 20, the production of four sets of containers 1 with a time difference for each step is executed in parallel.

[0064] Note that due to the structure of the blow molding apparatus 20, the time during which the transfer plate stops at the injection molding section 21, the temperature adjustment section 22, the blow molding section 23, and the take-out section 24 is the same length. Similarly, the transfer time of the transfer plate between each section is also the same length.

[0065] Hereinafter, the effects of the present embodiment will be described. In the injection molding process (S101) of the present embodiment, a resin preform 10 having a body portion 13 and a bottom portion 12 is injection molded, and the preform 10 is demolded in a high-temperature state where the outer shape of the preform can be maintained. In this injection molding process (S101), an injection mold in which the wall thickness of the bottom portion 12 is 0.7 to 0.85 with respect to the wall thickness of the body portion 13 is used. The injection mold of the present embodiment has a wider interval at the bottom portion 12 compared to the conventional mold, and the flow resistance of the resin at the preform bottom is reduced. Therefore, the shear heat generation at the preform bottom during injection molding is reduced, and it is possible to suppress excessive heat accumulation in the central region of the preform bottom.

[0066] Further, in the temperature adjustment process (S102) of the present embodiment, a cooling blow is performed in which compressed air is introduced into the preform 10 to cool the bottom portion 12 of the preform 10. By cooling the preform bottom rapidly in combination with the reduction of shear heat generation at the preform bottom, whitening in the central region of the preform bottom of the preform 10 is suppressed. Thereby, even in a high-speed molding cycle in which the preform 10 is demolded in a high-temperature state, a container with high transparency and high quality can be manufactured.

[0067] Also, the gate region S1 of the injection cavity mold 31 is in a tapered shape that expands in diameter toward the bottom, and the flow velocity and flow resistance of the resin decrease toward the outlet of the gate region S1. Therefore, by making the gate region S1 in a tapered shape, the shear heat generation at the preform bottom can be further reduced.

[0068] In addition, since the corner portion 34 connecting the gate region S1 and the outer surface of the bottom has a rounded shape, it is difficult to generate flow resistance due to vortices at the outlet of the gate region S1. Therefore, by rounding the corner portion 34 of the injection cavity mold 31, the shear heat generation at the preform bottom can be further reduced.

[0069] The present invention is not limited to the above embodiment, and various improvements and design changes may be made without departing from the spirit of the present invention.

[0070] In the above-described embodiment, as an example of the blow molding apparatus, a hot parison type four-station type apparatus configuration was described. However, the blow molding apparatus of the present invention is not limited to the above-described embodiment, and may be applied to other blow molding apparatuses other than the four-station type as long as it includes an injection molding section, a temperature adjustment section, and a blow molding section.

[0071] In addition, the embodiments disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all changes within the meaning and scope equivalent to the claims are included.

Explanation of Reference Numerals

[0072] 1... Container, 10... Preform, 12... Bottom, 14... Gate portion, 15... Corner portion, 20... Blow molding apparatus, 21... First injection molding section, 22... Temperature adjustment section, 23... Blow molding section, 25... Injection device, 26... Conveying mechanism, 31... Injection cavity mold, 32... Injection core mold, 34... Corner portion, 41... Cavity mold, 42... Air introduction member, S... Mold space, S1... Corner region

Claims

【Claim 1】 An injection molding step of injection molding a resin preform having a body portion and a bottom portion; A temperature adjustment step of adjusting the temperature of the preform manufactured in the injection molding step; A blow molding step of blow molding the temperature-adjusted preform to manufacture a resin container, the method for manufacturing a resin container comprising: In the injection molding step, the preform is injection molded using an injection mold in which the wall thickness of the bottom portion is 0.7 to 0.85 times the wall thickness of the body portion; In the temperature adjustment step, a refrigerant is introduced into the preform to cool the bottom portion of the preform A method for manufacturing a resin container.

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