Preforms, injection molds, resin container manufacturing equipment and manufacturing methods

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 Preforms, injection molds, resin container manufacturing equipment and manufacturing methods .

Background Art

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

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

[0004] Conventionally, for example, there are cases where the above requirements are met by using a preform with the bottom thickness set to about 1 / 2 of the body thickness and 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 with the same angle of 20° to 45°, and the connection part with the body part is formed in an arc shape, so that the wall thickness from the bottom to the body part gradually transitions and the whitening of the bottom surface is suppressed.

[0005] In recent years, a manufacturing method of 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 manufacturing method of the container, a resin container with good physical properties and appearance can be manufactured at a high-speed molding cycle.

Prior Art Documents

[0007] In the hot parison blow molding method, there is a suitable preform shape for each container, depending on the physical properties and stretch ratio of the container. For example, when manufacturing wide-mouthed, thin-walled resin containers such as cups, a flat, bowl-shaped preform is used. In this type of preform, the body thickness is set to be relatively thin, so if the bottom thickness is set to about half the body thickness, the bottom thickness of the preform becomes even thinner.

[0008] In the injection molding of the above-mentioned preform, the space at the bottom of the preform within the injection mold becomes very narrow, increasing the flow resistance of the molten resin near the gate. As a result, the shear heat generated by the molten resin during injection molding increases, causing the central bottom area of ​​the preform to become very hot. This makes it difficult to adequately cool the central bottom area of ​​the preform, making crystallization (whitening) due to slow cooling more likely to occur in the central bottom area of ​​the preform or container. In particular, when shortening the cooling time during injection molding and blow-molding a preform that has been demolded at a high temperature at a high stretch ratio, suppressing whitening in the central area of ​​the bottom becomes even more important.

[0009] Therefore, the present invention has been made in view of these problems. A preform or injection mold suitable for manufacturing resin containers in a high-speed molding cycle while suppressing whitening in the central area of ​​the bottom. The purpose is to provide. [Means for solving the problem]

[0010] One aspect of the present invention is a preform made of polyethylene terephthalate that is injection molded by a hot parison blow molding method or blow molding apparatus. The preform has a neck portion, a body portion, a bottom portion, and a gate portion projecting outward from the bottom portion, the neck portion is bottomed bowl-shaped with a diameter greater than the length from the upper end of the neck portion to the lower end of the bottom portion, the wall thickness of the bottom portion is 0.7 to 0.85 times the wall thickness of the body portion, the gate portion is tapered with an increasing diameter from the lower end of the gate portion toward the bottom portion, and a corner portion is formed between the gate portion and the outer surface of the bottom portion. Yes, they are. Another aspect of the present invention is an injection mold used in a hot parison blow molding method or blow molding apparatus for injection molding a polyethylene terephthalate preform. The injection molding die comprises an injection cavity mold that defines the outer shape of the preform, an injection core mold inserted into the injection cavity mold, a hot runner mold for supplying resin material, and a neck mold corresponding to the neck of the preform. The cavity mold has a tapered gate region connected to the hot runner mold and expanding toward the injection core mold at the bottom of the preform. The mold space of the preform is formed when the injection cavity mold, injection core mold, and neck mold are closed. The mold space is bowl-shaped with a bottom, where the inner diameter of the neck mold space is greater than the length from the upper end of the neck mold space to the lower end of the bottom of the injection cavity mold space. The spacing corresponding to the thickness of the bottom of the preform is set to a value of 0.7 to 0.85 compared to the spacing corresponding to the thickness of the body of the preform. A corner portion is formed between the gate region and the outer bottom surface of the injection cavity mold. Yes, they are. [Effects of the Invention]

[0011] By applying a preform or other injection mold according to one embodiment, resin containers can be manufactured in a high-speed molding cycle while suppressing whitening in the central area of ​​the bottom. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows an example of a preform according to this embodiment. [Figure 2] This figure shows an example of a resin container according to this embodiment. [Figure 3]It is a diagram schematically showing the configuration of the blow molding apparatus of the present embodiment. [Figure 4] It is a diagram showing a configuration example of the injection molding section. [Figure 5] It is a diagram showing a configuration example of the temperature adjustment section. [Figure 6] It is a flowchart showing the steps of the method for manufacturing a container. [Figure 7] It is a graph showing an example of the temperature change of the preform in the blow molding method of the present embodiment and the comparative example.

Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the embodiments, for the sake of easy understanding of the description, 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 indicate actual shapes, dimensions, etc.

[0014] <Explanation of Preform> First, referring 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] Further, 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 as compared with the wall thickness th2 of the body portion 13. That is, the preform 10 of the present embodiment has a relatively thicker bottom portion than the 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 portion with the stretching rod during the blow molding process, and the bottom portion is sufficiently cooled and solidified in the injection molding process.

[0017] At the center of the bottom portion 12 of the preform 10, a gate portion 14 is formed whose tip protrudes toward the outside of the bottom portion 12. 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 toward the base end side facing the bottom portion 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. In addition, at the corner portion 15 where the gate portion 14 and the outer surface of the bottom portion are connected on the base end side of the gate portion 14, a round (roundness, arc) is provided. The round is set so that its radius has a numerical value of, for example, 2.0 mm to 4.0 mm (preferably 2.1 mm to 3.0 mm).

[0018] The thickness of the bottom portion 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 of 0.70 to 0.9 (preferably 0.75 to 0.85). Further, 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 portion 12 from the upper end of the neck portion 11 to the upper end of the gate portion 14). The diameter D1 is set to, for example, 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 preform 10 is a thermoplastic synthetic resin, which can be appropriately selected depending on the application of the container. Specific examples of materials include PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PCTA (polycyclohexanedimethylene terephthalate), Tritan (Tritan®: a copolyester manufactured by Eastman Chemical Corporation), PP (polypropylene), PE (polyethylene), PC (polycarbonate), PES (polyethersulfone), PPSU (polyphenylsulfone), PS (polystyrene), COP / COC (cyclic olefin polymer), PMMA (polymethyl methacrylate: acrylic), and PLA (polylactic acid). The present invention is particularly effective when the material of preform 10 is a thermoplastic synthetic resin and a crystalline resin that is prone to whitening due to spherulite crystallization during injection molding (for example, PET or PEN).

[0020] <Container description> Next, an example of the container configuration of this embodiment will be described with reference to Figure 2. Figure 2(a) is a plan view of the container, and Figure 2(b) is a front view of the container. As shown in Figures 2(a) and (b), the container 1 is a wide-mouthed cup-shaped container with an open top and a closed bottom. The container 1 has a neck portion 2 facing the opening on the top side, a bottom portion 3 that closes the bottom 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 (inverted frustoconical shape) that narrows in diameter from the top side to the bottom side. In addition, the container 1 has a deep bottom, with the axial length (depth L) of the container being sufficiently longer than the inner diameter D of the container. The stretching ratio of the preform 10 in the longitudinal direction relative to the container 1 is set high, from 3.0 to 7.0 (preferably 3.5 to 6.0, more preferably 4.0 to 5.5).

[0021] <Description of blow molding equipment> Next, a blow molding apparatus 20 for manufacturing containers will be described with reference to Figure 3. Figure 3 is a schematic block diagram showing the configuration of the blow molding apparatus 20. The blow molding apparatus 20 of this embodiment is a hot parison type (also called a one-stage type) apparatus that blow molds the preform 10 by utilizing the heat retained during injection molding (internal heat quantity) without cooling the preform 10 to room temperature.

[0022] The blow molding apparatus 20 comprises an injection molding unit 21, a temperature control unit 22, a blow molding unit 23, a removal unit 24, and a transport mechanism 26. The injection molding unit 21, the temperature control unit 22, the blow molding unit 23, and the removal unit 24 are positioned at predetermined angles (for example, 90 degrees) around the transport mechanism 26.

[0023] (Conveying mechanism 26) The transport mechanism 26 includes a transport plate (not shown) that moves so as to rotate around an axis perpendicular to the plane of the paper in Figure 3. One or more neck molds 27 (not shown in Figure 1) that hold the neck of the preform 10 or resin container (hereinafter simply referred to as container) are arranged on the transport plate at predetermined angles. The transport mechanism 26 transports the preform 10 (or container) whose neck is held by the neck mold 27 to the injection molding section 21, temperature control section 22, blow molding section 23, and removal section 24 in that order by moving the transport plate by 90 degrees at a time. The transport mechanism 26 also includes a lifting mechanism (vertical mold opening and closing mechanism) and a mold opening mechanism for the neck mold 27, and performs operations related to lifting and lowering the transport plate, as well as mold closing and mold opening (release) in the injection molding section 21, etc.

[0024] (Injection molding section 21) As shown in Figure 4(a), the injection molding unit 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). In addition, an injection device 25 that supplies the resin material, which is the raw material for the preform, is connected to the injection molding unit 21.

[0025] The injection cavity mold 31 is a mold that defines the shape of the outer circumference of the preform 10. The hot runner mold 33 has a resin supply section 33a that introduces resin material from the injection device 25 into the mold. The injection core mold 32 is a mold that defines the shape of the inner circumference of the preform 10 and is inserted from above into the inner circumference 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 preform 10 described above. In the mold space S, the spacing th of the mold space corresponds to the thickness of the bottom 12. 1’ This is the spacing th of the mold space corresponding to the thickness of the body 13. 2’ It is set to a value of 0.7 to 0.85 compared to [the previous value].

[0027] As shown in Figure 4(b), in the injection cavity mold 31, the gate region S1 connected to the resin supply section 33a is formed in a tapered shape that widens in diameter as it approaches the injection core mold 32. Furthermore, at the exit of the gate region S1 facing the injection core mold 32, the corner portion 34 where the gate region S1 and the bottom outer surface are connected is rounded. 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 transport mechanism 26 are closed to form a preform-shaped mold space S. Then, resin material is poured into this preform-shaped mold space S from the injection device 25 via the hot runner mold 33, thereby manufacturing the preform 10 in the injection molding section 21.

[0029] On the other hand, the injection device 25 is a device in which a screw is rotatably and retractably installed inside the cylinder of the barrel, and is responsible for heating and melting the resin material and injecting it into the mold. The injection device 25 sequentially performs injection, holding pressure, and metering through the action of the screw.

[0030] The injection device 25 supplies resin material from a hopper to a cylinder where a screw is located, and performs plasticization, mixing, and metering of the resin material by rotating and retracting the screw. The injection device 25 then injects and fills the mold with molten resin by advancing the screw at high speed. Next, the injection device 25 injects and fills the mold with additional molten resin by advancing the screw at a low speed at a predetermined pressure to compensate for the shrinkage of the molten resin in the mold, and then holds the pressure in that state. The injection device 25 controls the movement speed of the screw (injection speed) when the resin material is being filled into the mold at high speed, and controls the pressure (holding pressure) after the resin material has been filled into the mold at high speed. The switch from speed control to pressure control is performed using the screw position or injection pressure as a threshold.

[0031] Furthermore, even when the mold of the injection molding unit 21 is opened, the neck mold 27 of the transport mechanism 26 remains closed and continues to hold and transport the preform 10. The number of preforms 10 that are simultaneously molded in the injection molding unit 21 (i.e., the number of containers that can be simultaneously molded in the blow molding apparatus 20) can be set as appropriate.

[0032] (Temperature adjustment section 22) The temperature control unit 22 equalizes the temperature of the preform 10 manufactured in the injection molding unit 21 and removes uneven heating, adjusting the temperature of the preform 10 to a temperature suitable for blow molding (for example, approximately 90°C to 105°C) and to have a temperature distribution suitable for the container shape to be formed. The temperature control unit 22 also has the function of cooling the preform 10, which is in a high-temperature state after injection molding.

[0033] Figure 5 shows an example of the configuration of the temperature control unit 22. The temperature control unit 22 has a cavity type (temperature control pot) 41 capable of housing a preform and an air introduction member 42 as a mold unit for temperature control.

[0034] The cavity mold 41 is a mold having a temperature-controlled space that is approximately the same shape as the preform 10 manufactured in the injection molding section 21. A flow path (not shown) for a temperature-controlled medium (refrigerant) is formed inside the cavity mold 41. Therefore, the temperature of the cavity mold 41 is maintained at a predetermined temperature by the temperature-controlled medium. The temperature of the temperature control medium in the cavity type 41 is not particularly limited, but can be appropriately selected within a range of, for example, 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 unit (not shown) and a fitting core 44, and is inserted inside the neck mold 27 and the preform 10. When inserted into the neck mold 27, the air introduction member 42 is in airtight contact with the neck portion 11 of the preform 10. 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 forms a passage for guiding compressed air (air, gaseous refrigerant) from the air supply unit, and the tip of the air introduction rod 43 is inserted near the bottom surface of the preform 10. In addition, an opening 43a is formed at the tip of the air introduction rod 43 facing the bottom of the preform 10 for supplying compressed air into the preform 10.

[0037] The mating core 44 makes 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 shape 27, maintaining airtightness between the preform 10 and the air introduction member 42. The tip of the mating core 44 is inserted into or abuts against the neck portion 11 of the preform 10. An opening 45 is also formed at the tip of the mating core 44 for exhausting air from inside the preform 10. The space between the air introduction rod 43 and the mating core 44 forms an exhaust passage connected to an air exhaust section (not shown).

[0038] (Blow-molded section 23) The blow molding unit 23 manufactures a container by performing stretch blow molding on the preform 10 whose temperature has been controlled by the temperature control unit 22. The blow molding unit 23 includes a blow cavity mold, which is a pair of split molds corresponding to the shape of the container, a bottom mold, a stretching rod, and an air introduction member (none of which are shown). The blow molding unit 23 blow-moldes the preform 10 while stretching it. This allows the preform 10 to be shaped into the shape of the blow cavity mold, thereby manufacturing the container.

[0039] (Removal section 24) The removal section 24 is configured to release the neck portion of the container manufactured in the blow molding section 23 from the neck mold 27 and remove the container to the outside of the blow molding apparatus 20.

[0040] <Explanation of blow molding method> Next, a blow molding method using the blow molding apparatus 20 of this embodiment will be described. Figure 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 mold space, which is shaped like a preform and formed by the injection cavity mold 31, the injection core mold 32, and the neck mold 27 of the transport mechanism 26, thereby manufacturing a preform 10.

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

[0043] Since the gate region S1 of the injection cavity mold 31 has a tapered shape that widens towards the injection core mold 32, the flow velocity of the resin flowing through the gate region S1 decreases as it approaches the outlet of the gate region S1, and the flow resistance of the resin also decreases. Furthermore, since the corner portion 34 at the exit of the gate region S1 is rounded, vortices are less likely to form in the resin flow at the corner portion 34. Therefore, the resin flow at the exit of the gate region S1 tends to become a laminar flow that flows along the curved surface into the bottom region, and the increase in flow resistance due to vortices is also suppressed.

[0044] Furthermore, the spacing th of the mold space corresponds to the thickness of the bottom 12. 1’ This is the spacing th of the mold space corresponding to the thickness of the body 13. 2’ Compared to conventional molds, the values ​​are 0.7 to 0.85, and the gap at the bottom is wider compared to conventional molds where the bottom thickness is approximately half the body thickness. Therefore, in the bottom region of the mold space S, the resin flows more easily toward the body compared to conventional molds, and the resin flow resistance is also reduced.

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

[0046] From the viewpoint of manufacturing containers in a high-speed molding cycle, it is preferable to open the mold in step S101 without allowing 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 this case, since the preform 10 is not cooled in the injection mold without holding pressure, the phenomenon of shrinkage and sink marks occurring due to the preform 10 shrinking during the cooling time can be suppressed.

[0047] On the other hand, when the preform 10 is cooled minimally within the injection mold, the time required to cool the resin material after the injection of the resin material in the injection molding section 21 (cooling time) is preferably 1 / 2 or less of the time required to inject the resin material (injection time). Furthermore, the above cooling time can be made even shorter than the time required to inject the resin material, depending on the weight of the resin material. For example, the cooling time is more preferably 2 / 5 or less of the time required to inject the resin material, even more preferably 1 / 4 or less, and particularly preferably 1 / 5 or less.

[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 while still at a high temperature that maintains its outer shape. Next, the transfer plate of the transfer mechanism 26 moves to rotate by a predetermined angle, and the high-temperature preform 10, held in the neck mold 27, is transported to the temperature control unit 22.

[0049] Furthermore, the temperature change of the preform 10 in the blow molding method of this embodiment will be explained with reference to Figure 7. The vertical axis of Figure 7 represents the temperature of the preform 10, and the horizontal axis represents time. In Figure 7, an example of the temperature change of the preform 10 in this embodiment is shown in Figure 7(A). An example of the temperature change of the preform of the comparative example described later is shown in Figure 7(B). The gaps between each process represent the time required for transporting the preform 10 or the container, etc., and are all of the same length.

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

[0051] In contrast, in this embodiment, as described above, there is no (or very short) cooling time for the preform 10 in the injection mold, so the skin layer (the solidified surface layer) of the preform is thinner than conventionally formed, and the core layer (the softened or molten inner layer) is thicker than conventionally formed. In other words, compared to the comparative example, the thermal gradient between the skin layer and the core layer is larger, and a preform 10 with high temperature and high heat retention is molded.

[0052] In this embodiment, the preform 10 is demolded from the injection molding section 21 at a higher demolding temperature than the comparative example and transported to the temperature control section 22. As it moves to the temperature control section 22, the preform 10 undergoes temperature equalization through heat exchange (heat conduction) between the skin layer and the core layer. In addition, the preform 10 is slightly cooled from the outer surface by contact with the outside air. However, the temperature of the preform 10 in this embodiment remains at a much higher level than the comparative example until it is transported to the temperature control section 22.

[0053] (Step S102: Temperature adjustment process) Next, the temperature control unit 22 performs cooling and temperature adjustment to bring the temperature of the preform 10 closer to a temperature suitable for the final blowing (blow temperature). The blow temperature is set to 90°C to 105°C, for example, for PET resin. However, a lower blow temperature may result in better stretch orientation of the preform 10, which can increase the strength (physical properties) of the container. For this reason, the blow temperature may be set to 90°C to 95°C, for example, for PET resin.

[0054] As shown in Figure 7, in the temperature control 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 control unit 22, the preform is rapidly cooled from a high temperature state, so whitening (clouding) due to spherulite formation and crystallization that may occur when cooled slowly is suppressed.

[0055] In the temperature control process, as shown in Figure 5, first the preform 10 is placed in the cavity mold 41. Next, the air introduction member 42 is inserted into the neck of the preform 10 placed in the cavity mold 41. At this time, the neck 11 of the preform 10 and the fitting core 44 are in close contact, maintaining airtightness between them.

[0056] Subsequently, the preform 10 is subjected to a cooling blow. In the cooling blow of the preform 10 in this 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] During the cooling blow, compressed air is ejected from the opening 43a of the air introduction rod 43, so the bottom 12 of the preform 10 facing the opening 43a of the air introduction rod 43 comes into contact with the low-temperature compressed air. The preform 10 is cooled from the inside by the compressed air flowing through it, but the temperature of the compressed air gradually increases as it moves towards the body 13 and neck 11 due to heat exchange with the preform 10. Therefore, during the cooling blow, the bottom 12 of the preform 10 is cooled locally more strongly than the neck 11 and body 13 of the preform 10. The rapid cooling of the bottom 12 of the preform 10 by the cooling blow described above effectively suppresses whitening in the central area of ​​the bottom of the preform 10.

[0058] Furthermore, compared to conventional preforms in which the bottom thickness of the preform 10 is approximately half the thickness of the body, the bottom 12 of the preform 10 in this embodiment has a relatively thicker wall thickness, resulting in greater heat retention at the bottom 12. However, as described above, the bottom 12 is locally cooled by the temperature control unit 22, which reduces the heat retention at the bottom 12, thus suppressing excessive stretching of the bottom 12 during blow molding of the container (for example, fracture of the bottom 12).

[0059] Furthermore, in the temperature control section 22, the preform 10 remains in contact with the cavity mold 41, which is maintained at a predetermined temperature by compressed air pressure from the inside. Therefore, during the temperature control process, the temperature of the preform 10 is adjusted from the outside so that it does not fall below a temperature suitable for blow molding, and uneven heating that occurred during injection molding is also reduced. In addition, during the temperature control 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 transport mechanism 26 moves to rotate by a predetermined angle, and the temperature-adjusted preform 10 held in the neck mold 27 is transported to the blow molding section 23.

[0061] (Step S103: Blow molding process) Next, the container 1 is blow-molded in the blow molding section 23. First, the blow cavity mold is closed to house the preform 10 in the mold space, and the air introduction member (blow core) is lowered so that it contacts the neck of the preform 10. Then, the stretching rod (longitudinal stretching member) is lowered to press the bottom of the preform 10 from the inside, and while performing longitudinal stretching as needed, blow air is supplied from the air introduction member to stretch the preform 10 horizontally. As a result, the preform 10 expands and is shaped to fit tightly into the mold space of the blow cavity mold, and is blow-molded into the container 1. The bottom mold waits in a lower position that 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 process) Once the blow molding is complete, the blow cavity mold and bottom mold are opened. This allows the container 1 to move out of the blow molding section 23. Next, the transport plate of the transport mechanism 26 moves to rotate by a predetermined angle, and the container 1 is transported to the removal section 24. In the removal section 24, the neck of the container 1 is released from the neck mold 27, and the container 1 is removed to the outside of the blow molding apparatus 20.

[0063] This completes the series of steps in the blow molding method. Subsequently, the transfer plate of the transport mechanism 26 is moved to rotate by a predetermined angle, thereby repeating each of the steps S101 to S104 described above. During operation of the blow molding apparatus 20, the manufacture of four sets of containers 1, each with a time difference between each step, is carried out in parallel.

[0064] Due to the structure of the blow molding apparatus 20, the time the transfer plate is stopped in the injection molding section 21, temperature control section 22, blow molding section 23, and removal section 24 is the same length. Similarly, the transport time of the transfer plate between each section is also the same length.

[0065] The effects and advantages of this embodiment will be described below. In the injection molding process (S101) of this embodiment, a resin preform 10 having a body portion 13 and a bottom portion 12 is injection molded, and the preform 10 is released from the mold at a high temperature that maintains the outer shape of the preform. In this injection molding process (S101), an injection mold is used in which the wall thickness of the bottom portion 12 is 0.7 to 0.85 times that of the wall thickness of the body portion 13. Compared to conventional molds, the injection mold of this embodiment has a wider gap between the bottom portions 12, which reduces the resistance of resin flow at the bottom of the preform. Therefore, shear heat generation at the bottom of the preform during injection molding is reduced, and excessive heat accumulation in the central area of ​​the bottom of the preform can be suppressed.

[0066] Furthermore, in the temperature control step (S102) of this embodiment, a cooling blow is performed by introducing compressed air into the preform 10 to cool the bottom 12 of the preform 10. This reduces shear heat generation at the bottom of the preform and, in conjunction with the rapid cooling of the bottom of the preform, suppresses whitening in the central area of ​​the bottom of the preform 10. As a result, even in high-speed molding cycles where the preform 10 is demolded at high temperatures, highly transparent and high-quality containers can be manufactured.

[0067] Furthermore, the gate region S1 of the injection cavity mold 31 is tapered, widening towards the bottom, and the resin flow velocity and flow resistance decrease as they approach the exit of the gate region S1. Therefore, tapering the gate region S1 can further reduce shear heat generation at the bottom of the preform.

[0068] Furthermore, because the corner portion 34 connecting the gate region S1 and the bottom outer surface is rounded, flow resistance due to vortices is less likely to occur at the exit of the gate region S1. Therefore, rounding the corner portion 34 of the injection cavity mold 31 can further reduce shear heat generation at the bottom of the preform.

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

[0070] In the above embodiment, a hot parison type 4-station blow molding apparatus was described as an example. However, the blow molding apparatus of the present invention is not limited to the above embodiment, and may be applied to other blow molding apparatuses other than the 4-station type, as long as they include an injection molding section, a temperature control section, and a blow molding section.

[0071] Furthermore, the embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

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

Claims

1. A preform made of polyethylene terephthalate, which is injection molded by a hot parison blow molding method or blow molding apparatus, The preform has a neck portion, a body portion, a bottom portion, and a gate portion that protrudes outward from the bottom portion, and the diameter of the neck portion is greater than the length from the upper end of the neck portion to the lower end of the bottom portion, The thickness of the bottom portion is 0.7 to 0.85 times the thickness of the body portion. The gate portion is tapered, with its diameter increasing from the lower end of the gate portion toward the bottom. A corner portion is formed between the gate portion and the outer surface of the bottom portion. Preform.

2. The preform according to claim 1, wherein the radius of curvature of the corner portion is 1 mm or more.

3. The thickness of the bottom portion is 0.70 to 0.90 of the diameter dimension at the tip of the gate portion. The preform according to claim 2.

4. An injection mold used in a hot parison blow molding method or blow molding apparatus for injection molding a preform made of polyethylene terephthalate, The injection mold comprises an injection cavity mold that defines the outer periphery shape of the preform, an injection core mold inserted into the injection cavity mold, a hot runner mold for supplying resin material, and a neck mold corresponding to the neck portion of the preform. The cavity mold is connected to the hot runner mold and has a tapered gate region that widens toward the injection core mold, located at the bottom of the preform. The injection cavity mold, the injection core mold, and the neck mold are closed to form the mold space of the preform. The mold space is in the shape of a bottomed bowl, where the inner diameter of the neck mold space is greater than the length from the upper end of the neck mold space to the lower end of the bottom of the injection cavity mold space. The spacing corresponding to the thickness of the bottom of the preform is set to a value of 0.7 to 0.85 compared to the spacing corresponding to the thickness of the body of the preform. The diameter of the bottom of the injection core mold is four times or more the diameter of the base end of the gate region. Injection mold.

5. The injection molding die according to claim 4, wherein the radius of curvature of the corner portion is 1 mm or more.

6. The gap at the bottom of the mold space is 0.70 to 0.90 with respect to the diameter dimension at the tip of the gate region. The injection mold according to claim 5.

7. It comprises at least an injection molding section, a temperature control section, a blow molding section, an extraction section, and a transport mechanism. The injection molding unit has an injection mold for a preform as described in claim 4, and injects a preform, The temperature control unit cools the bottom of the preform by introducing a refrigerant into the preform that has been transported from the injection molding unit by the transport mechanism. The blow molding section blow-moldes the temperature-controlled preform to manufacture a resin container. Manufacturing equipment for plastic containers.

8. The temperature control unit comprises a cavity mold, which is a mold for temperature control, and an air introduction member. The refrigerant is compressed air, which is introduced into the preform housed in the cavity via an air introduction member. The apparatus for manufacturing a resin container according to claim 7.

9. In the injection molding section, the preform is demolded at a temperature high enough to maintain its outer shape. The apparatus for manufacturing a resin container according to claim 8.

10. A method for manufacturing a resin container, comprising at least an injection molding step, a temperature control step, and a blow molding step, In the injection molding process, the preform described in claim 1 is injection molded, In the temperature adjustment step, a coolant is introduced into the preform that has been transported from the injection molding step to cool the preform. In the blow molding process, the temperature-controlled preform is blow-molded to manufacture a resin container. A method for manufacturing resin containers.

11. In the temperature adjustment step, the preform is placed in a cavity mold, which is a mold for temperature adjustment. Compressed air, which is a refrigerant, is introduced into the interior of the preform from an air introduction member that is in contact with the preform. A method for manufacturing a resin container according to claim 10.

12. In the injection molding process, the preform is demolded at a temperature high enough to maintain its outer shape. A method for manufacturing a resin container according to claim 11.

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