Method and apparatus for manufacturing resin containers

Abstract

This method for producing a resin container comprises an injection molding step for injection molding a bottomed cylindrical resin preform, and a blow molding step for blow molding the preform while the preform retains the heat from injection molding to produce a polygonal resin container having a plurality of corners in the circumferential direction. In the circumferential direction of the preform, the thickness of a first site corresponding to a wall surface of the container is greater than the thickness of a second site corresponding to a corner of the container, and the outer peripheral surface at the second site of the preform is positioned radially inward from the outer peripheral surface at the first site of the preform.

Description

Technical Field

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

Background Art

[0002] Containers for accommodating cosmetics, emulsions, etc. are required to have an appearance that is aesthetically pleasing to enhance consumers' purchasing desire. For thick-walled polygonal containers (e.g., rectangular containers) for accommodating this type of cosmetics, etc., glass bottles having a sense of weight and luxury and capable of maintaining a beautiful state even after repeated use are preferably used. However, glass bottles are heavy and easily broken, and the costs involved in transportation and manufacturing are also high. Therefore, replacing glass bottles with resin containers for containers for accommodating cosmetics, etc. has been considered.

[0003] Here, as one method for manufacturing a resin container, a hot parison blow molding method has been conventionally known. In the hot parison blow molding method, a resin container is blow molded using the retained heat during injection molding of a preform. Therefore, it is advantageous in that a resin container having various and excellent aesthetic appearances can be manufactured as compared with the cold parison method.

[0004] When blow molding a polygonal container, a difference occurs in the stretching ratio of the preform depending on the part of the container. Specifically, at the corners of the container body, the stretching ratio of the preform becomes larger than that of the wall surface of the container body. Therefore, in the manufacture of a polygonal container, due to the difference in the stretching ratio of the preform, for example, appearance defects such as columns on the wall surface of the body (band-shaped thick portions extending in the axial direction), loss of formability at the corners and ridge lines of the container, and uneven wall thickness (uneven stretching) of the container are likely to occur. In a general hot parison blow molding cycle, by adjusting the temperature of the preform before blow molding the container, the above-mentioned appearance defects of the container are alleviated to some extent.

[0005] Furthermore, when blow-molding a polygonal container with resin, for example, Patent Document 1 proposes that the inner circumference shape of the preform be shaped to correspond to the polygonal container, and that the wall thickness of the part corresponding to the container wall be thicker than the wall thickness of the part corresponding to the corner of the container. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Special Publication No. 6-71758 [Overview of the project] [Problems that the invention aims to solve]

[0007] Polygonal containers used to hold cosmetics and other products have high standards regarding their appearance. For example, a flat shape without protrusions is preferred for the body, and containers with columns in the body do not meet the specifications. On the other hand, cosmetic defects that occur on the body of polygonal containers have not been completely eliminated, and further improvements are requested.

[0008] Furthermore, when the container manufacturing cycle is shortened, the temperature control process after injection molding mainly involves cooling the preform. Therefore, when attempting to manufacture polygonal containers in a short manufacturing cycle, it becomes difficult to adjust the temperature distribution of the preform to suit the manufacturing of polygonal containers, making defects in the container's appearance more likely.

[0009] Therefore, the present invention has been made in view of these problems, and aims to provide a manufacturing method that can produce a polygonal resin container with excellent aesthetic appearance in a short manufacturing cycle. [Means for solving the problem]

[0010] A method for manufacturing a resin container according to one aspect of the present invention comprises an injection molding step of injection molding a bottomed cylindrical resin preform, and a blow molding step of blow molding the preform while it still contains the heat retained during injection molding to manufacture a polygonal resin container having multiple corners in the circumferential direction. In the circumferential direction of the preform, the wall thickness of the first portion corresponding to the wall surface of the container is thicker than the wall thickness of the second portion corresponding to the corner of the container. The outer surface of the preform's body is non-circular in the circumferential direction, in order to slow down the time it takes for the second portion to come into contact with the mold during blow molding. The outer surface of the second part of the preform is located radially inward from the outer surface of the first part of the preform. [Effects of the Invention]

[0011] According to one aspect of the present invention, a manufacturing method is provided that enables the production of resin polygonal containers with excellent aesthetic appearance in a short manufacturing cycle. [Brief explanation of the drawing]

[0012] [Figure 1] This is a longitudinal cross-sectional view of the preform according to this embodiment. [Figure 2] This is a cross-sectional view of the torso portion of the preform according to this embodiment. [Figure 3] Figure 2 is an enlarged view of the preform. [Figure 4] This diagram schematically shows the configuration of the blow molding apparatus according to this embodiment. [Figure 5] This figure shows an example of the configuration of the injection molding section. [Figure 6] This is a cross-sectional view along line AA in Figure 5. [Figure 7] This figure shows an example of the configuration of the temperature control unit. [Figure 8] This figure shows an example of the configuration of a blow-molded section. [Figure 9] This is a flowchart showing the steps involved in the manufacturing of the container. [Modes for carrying out the invention]

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

[0014] <Configuration Example of Preform and Container> First, referring to FIGS. 1 to 3, a configuration example of a preform 10 applied to the production of a resin container (hereinafter, also simply referred to as a container) 20 of the present embodiment will be described. FIG. 1 is a longitudinal sectional view of the preform 10 according to the present embodiment, FIG. 2 is a cross-sectional view of the body portion 13 of the preform 10 according to the present embodiment, and FIG. 3 is an enlarged view of the preform of FIG. 2. In FIGS. 1 and 2, the outline of the container 20 of the present embodiment is shown by a two-dot chain line.

[0015] The container 20 is formed by blow molding the preform 10. The container 20 of the present embodiment is a polygonal container having a quadrangular cross-sectional shape as shown in FIG. 2, and for example, contains lotion, emulsion, etc. inside. The container 20 has a neck portion 22 having a mouth portion 21 at the upper end, a cylindrical body portion 23 continuous from the neck portion 22, and a bottom portion 24 continuous from the body portion 23.

[0016] As shown in FIGS. 1 and 2, in the container 20, the wall surface portion (panel portion) 25 of the body portion 23 is made uniform in the axial direction (height direction) and the circumferential direction, and has a flat shape with almost no unevenness. Also, as shown in FIG. 2, for example, the corner portion 26 of the body portion 23 is thicker than the wall surface portion 25. Therefore, the inner peripheral side contour of the body portion 23 has a shape in which adjacent wall surface portions 25 are connected in a curved shape via the corner portion 26 without being recessed on the outer peripheral side at the corner portion 26. Note that the wall thickness of the bottom portion 24 of the container 20 is preferably formed thicker than the wall thickness of the body portion 23. [[ID=​​By forming the container 20 into a shape having the above-described wall thickness distribution, a high-class feeling and a sense of weight are emphasized, and the container 20 can be made closer to the image of a cosmetic container held by consumers. That is, since the aesthetic appearance of the container 20 can be enhanced, the container 20 can be used as a cosmetic container or the like for which appearance is important.

[0018] On the other hand, as shown in FIG. 1, the overall shape of the preform 10 is a bottomed cylindrical shape with one end open and the other end closed. The preform 10 includes a cylindrical body portion 13, a bottom portion 14 that closes the other end side of the body portion 13, and a neck portion 12 that is formed on the opening side of one end side of the body portion 13 and has a mouth portion 11.

[0019] As shown in FIGS. 2 and 3, the wall thickness of the body portion 13 of the preform 10 is different in the circumferential direction between a first portion 15 corresponding to the wall surface portion 25 of the container 20 and a second portion 16 corresponding to the corner portion 26 of the container 20. The first portion 15 and the second portion 16 are alternately arranged in four at equal intervals in the circumferential direction of the preform 10. That is, the first portion 15 and the second portion 16 are each formed at intervals of 90 degrees in the circumferential direction, and the phases of the first portion 15 and the second portion 16 are shifted by 45 degrees in the circumferential direction. Note that the wall thickness of the first portion 15 and the wall thickness of the second portion 16 are, for example, both substantially constant without change in the axial direction (height direction).

[0020] As shown in FIG. 3, in the first portion 15 of the body portion 13, the radial length from the axis Ax of the preform 10 to the outer peripheral surface of the preform is L1, and the radial length from the axis Ax to the inner peripheral surface of the preform is L2. Therefore, the wall thickness t1 of the first portion 15 of the preform 10 can be represented by L1 - L2.

[0021] On the other hand, in the second portion 16 of the body portion 13, the radial length from the axis Ax to the outer peripheral surface of the preform is L3, which is shorter than L1 of the first portion (L1 > L3). Also, the radial length from the axis Ax to the inner peripheral surface of the preform in the second portion 16 is L4, which is longer than L2 of the first portion 15 (L4 > L2). Therefore, the wall thickness t2 of the second portion 16 of the preform 10 can be represented by L3 - L4.

[0022] As described above, the radial length L1 from the axis Ax at the first part 15 to the outer surface of the preform is different from the radial length L3 from the axis Ax at the second part 16 to the outer surface of the preform. Therefore, the outer surface of the body portion 13 of the preform 10 is non-circular, and the outer surface of the second part 16 is located radially inward from the outer surface of the first part 15.

[0023] Similarly, the radial length L2 from the axis Ax in the first part 15 to the inner surface of the preform is different from the radial length L4 from the axis Ax in the second part 16 to the inner surface of the preform. Therefore, the inner surface of the body 13 of the preform 10 is also non-circular, and the inner surface of the first part 15 is located radially inward from the inner surface of the second part 16.

[0024] Furthermore, compared to the second part 16, the outer surface of the preform in the first part 15 is located radially outward, and the inner surface of the preform is located radially inward. Therefore, the wall thickness t1 of the first part of the preform 10 is greater than the wall thickness t2 of the second part (t1>t2).

[0025] <Description of container manufacturing equipment> Figure 4 is a schematic diagram showing the configuration of the blow molding apparatus 30 of this embodiment. The blow molding apparatus 30 is an example of a container manufacturing apparatus and employs a hot parison method (also called a one-stage method) in which the container is blow-molded by utilizing the heat retained during injection molding (internal heat quantity) without cooling the preform 10 to room temperature.

[0026] The blow molding apparatus 30 comprises an injection molding section 31, a temperature control section 32, a blow molding section 33, a removal section 34, and a transport mechanism 36. The injection molding section 31, the temperature control section 32, the blow molding section 33, and the removal section 34 are positioned at predetermined angles (for example, 90 degrees) around the transport mechanism 36.

[0027] (Conveying mechanism 36) The transport mechanism 36 includes a transport plate (not shown) that moves in a rotational direction about an axis perpendicular to the plane of the paper in Figure 4. The transport plate consists of a single disc-shaped flat plate member or a plurality of substantially fan-shaped flat plate members divided for each molding station. One or more neck-shaped plates 36a (not shown in Figure 4) for holding the neck portion 12 of the preform 10 (or the neck portion 22 of the container 20) are arranged on the transport plate at predetermined angles.

[0028] The transport mechanism 36, equipped with a rotating mechanism (not shown), moves a transport plate to transport the preform 10 (or container 20), whose neck portion 12 is held by the neck mold 36a, to the injection molding section 31, the temperature control section 32, the blow molding section 33, and the removal section 34 in that order. The transport mechanism 36 is further equipped with a lifting mechanism (vertical mold opening and closing mechanism) and a mold opening mechanism for the neck mold, and also performs operations related to lifting and lowering the transport plate, as well as mold closing and mold opening (release) in the injection molding section 31, etc.

[0029] (Injection molding section 31) The injection molding unit 31 manufactures the preforms 10 shown in Figures 1 to 3 by injection molding. An injection device 35 is connected to the injection molding unit 31 to supply the raw materials (resin material) for the preforms 10.

[0030] Figure 5 shows an example of the configuration of the injection molding unit 31, and Figure 6 is a cross-sectional view taken along line AA of Figure 5. The injection molding unit 31 includes an injection cavity mold 41 and an injection core mold 42. The injection cavity mold 41 is fixed to the machine base of the blow molding apparatus 30. The injection core mold 42 is fixed to a core mold lifting mechanism (not shown).

[0031] The injection cavity mold 41 is a mold that defines the outer circumference shape of the body 13 of the preform 10. A resin supply unit (hot runner) 43 for introducing resin material from the injection device 35 is connected to the lower side of the injection cavity mold 41. On the other hand, the injection core mold 42 is a mold that defines the inner circumference shape of the preform 10 and is inserted from above into the inner circumference side of the injection cavity mold 41.

[0032] As shown in Figure 5, in the injection molding section 31, the injection cavity mold 41, the injection core mold 42, and the neck mold 36a of the transport mechanism 36 are closed to form the mold space for the preform 10. Then, the resin material is injected from the injection device 35 through the hot runner mold 43 from the bottom of the mold space, thereby manufacturing the preform 10 in the injection molding section 31.

[0033] Figure 6 shows cross-sections (cross-sections perpendicular to the axial direction) of the injection cavity mold 41 and injection core mold 42 when the injection molding section 31 is closed. In this embodiment, the inner circumferential surface of the injection cavity mold 41 is formed such that the second region 41b is cut out by four sides from the outside, and the second region 41b is located radially inward of the first region 41a in the injection cavity mold 41. In addition, in this embodiment, the outer circumferential surface of the injection core mold 42 is cut out by four sides of the first region 42a, and the first region 42a in the injection core mold 42 is located radially inward of the second region 42b. By combining the above injection cavity mold 41 and injection core mold 42, it becomes possible to injection mold a preform 10 with the wall thickness distribution shown in Figure 3.

[0034] Furthermore, the raw materials for the preform 10 are thermoplastic synthetic resins, which can be appropriately selected according to the specifications of the container 20. Specific examples of materials include PET, 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). Additives such as colorants may also be added to the resin material.

[0035] Furthermore, even when the mold of the injection molding section 31 is opened, the neck mold 36a of the transport mechanism 36 remains closed and continues to hold and transport the preform. The number of preforms 10 that are simultaneously molded in the injection molding section 31 (i.e., the number of containers 20 that can be simultaneously molded in the blow molding apparatus 30) can be set as appropriate.

[0036] (Temperature adjustment section 32) The temperature control unit 32 equalizes the temperature of the preform 10 transported from the injection molding unit 31, removes uneven heating, and adjusts the temperature distribution to adjust the temperature of the preform 10 to a temperature suitable for the final blowing (for example, approximately 90°C to 105°C). The temperature control unit 32 also has the function of cooling the preform 10, which is in a high-temperature state after injection molding.

[0037] Figure 7 shows an example of the configuration of the temperature control unit 32. For example, the temperature control unit 32 is configured by combining a cavity type 51 (temperature control pot type) capable of housing the preform 10, a cooling core 52 (air inlet / outlet core), and a cylindrical cooling rod 53 (air inlet / outlet rod).

[0038] The cooling core 52 is a cylindrical mold inserted inside the neck mold 36a, and cooling rods 53 are concentrically arranged inside the cooling core 52 with an annular gap between them. When inserted into the neck mold 36a, the cooling core 52 is in close contact with the inner circumference or upper end surface of the neck portion 12 of the preform 10, maintaining airtightness with the preform 10. The inside of the cooling rods 53 and the gap between the cooling rods 53 and the cooling core 52 constitute a compressed air supply passage and an exhaust passage, respectively. Figure 7 shows an example where the inside of the cooling rods 53 is connected to the compressed air supply passage and the gap between the cooling rods 53 and the cooling core 52 is connected to the compressed air exhaust passage, but the relationship between the compressed air supply passage and the exhaust passage may be reversed. As described above, the temperature control unit 32 can cool the preform 10 by blowing compressed air into the preform 10, through cooling by compressed air and heat exchange through contact with the cavity mold.

[0039] Furthermore, when compressed air is introduced into the preform 10 in the temperature control unit 32, the preform 10 may be pre-blown in the temperature control unit 32 prior to blow molding to form an intermediate molded body (not shown) with a larger diameter than the preform 10. Also, when pre-blowing is performed in the temperature control unit 32, the cavity mold 51 of the temperature control unit 32 is composed of a pair of split molds divided along the axial direction.

[0040] (Blow-molded section 33) The blow molding section 33 manufactures the container 20 by performing biaxial stretch blow molding on the preform 10 whose temperature has been controlled in the temperature control section 32.

[0041] Figure 8 shows an example of the configuration of the blow molding section 33. The blow molding section 33 comprises a blow cavity mold 61, which is a pair of split molds corresponding to the shape of the container 20, a bottom mold 62, a fitting core (blow core, cylindrical air introduction / exit member) 63, and a stretching rod 65.

[0042] A stretching rod 65 is concentrically arranged inside the fitting core 63 so as to be able to move back and forth in the axial direction. The fitting core 63 is a cylindrical mold inserted inside the neck mold 36a, and when inserted into the neck mold 36a, it is in close contact with the inner circumference or upper end surface of the neck portion 12 of the preform 10, maintaining airtightness with the preform 10 during blow molding. The gap between the inside of the fitting core 63 and the stretching rod 65 constitutes a supply passage and an exhaust passage for compressed air (blow air). The blow molding unit 33 performs blow molding by blowing compressed air into the preform 10 while stretching the preform 10. As a result, the preform 10 is shaped into the shape of the blow cavity mold 61, and the container 20 can be manufactured.

[0043] (Removal section 34) The removal section 34 is configured to release the neck portion 22 of the container 20 manufactured in the blow molding section 33 from the neck mold 36a, and to remove the container 20 to the outside of the blow molding apparatus 30.

[0044] <Explanation of container manufacturing method> Next, the method for manufacturing a container using the blow molding apparatus 30 of this embodiment will be described. Figure 9 is a flowchart showing the steps for manufacturing the container 20.

[0045] (Step S101: Injection molding process) First, in the injection molding section 31, resin is injected from the injection device 35 into a mold space shaped like a preform, formed by the injection cavity mold 41, the injection core mold 42, and the neck mold 36a of the transport mechanism 36, thereby manufacturing a preform 10. Then, after the injection (filling and holding pressure) of the resin material is completed, or after a minimum cooling time provided after the completion of injection, the injection mold of the injection molding section 31 is opened.

[0046] While not particularly limited, from the viewpoint of manufacturing containers in a high-speed molding cycle, it is preferable to perform mold opening in step S101 without allowing a cooling time for the preform 10 in the injection mold after the completion of resin material injection (filling and holding pressure). On the other hand, when performing minimal cooling of the preform 10 within the injection mold, the time for cooling the resin material after the injection of the resin material is completed in the injection molding section 31 (cooling time) is preferably 1 / 2 or less of the time for injecting the resin material (injection time). Furthermore, the above cooling time can be made shorter than the time for injecting 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 injection time of the resin material, even more preferably 1 / 4 or less, and particularly preferably 1 / 5 or less. Moreover, the cooling time may be set to 0. Note that the cooling time and injection time are parameters that the operator can arbitrarily set for the blow molding apparatus 30 as part of the molding conditions of the preform.

[0047] Furthermore, in this embodiment, the body portion 13 of the preform 10 has a thicker first portion 15 corresponding to the wall portion 25 of the container 20 (thicker t1), and a thinner second portion 16 corresponding to the corner portion 26 of the container 20 (thicker t2). Since the heat retained by the preform 10 increases in proportion to the thickness, the heat retained by the first portion 15 is relatively high and the heat retained by the second portion 16 is relatively low in the circumferential direction of the body portion 13 of the preform 10.

[0048] Once the injection molding of the preform 10 is complete, the injection molding section 31 opens and the preform 10 is released from the injection cavity mold 41 and the injection core mold 42. Next, the transfer plate of the transport mechanism 36 moves to rotate by a predetermined angle, and the preform 10, held in the neck mold 36a, is transported to the temperature control section 32 while still retaining the heat from the injection molding process.

[0049] (Step S102: Temperature adjustment process) Next, the temperature control unit 32 adjusts the temperature of the preform 10 to bring it closer to a temperature suitable for the final blowing.

[0050] In the temperature control process, as the transfer plate descends, the preform 10 held in the neck mold 36a is housed in the cavity mold 51, and the cooling core 52 comes into contact with the neck portion 12 of the preform 10, and the cooling rod 53 (air inlet / outlet rod) is inserted into the preform 10. Subsequently, compressed air is blown into the preform 10 from the cooling core 52 and / or the cooling rod 53 that are in contact with the neck portion 12 of the preform 10 (compressed air is blown through) to control the temperature. As a result, the temperature of the preform 10 is adjusted so that it does not fall below the temperature suitable for blow molding, and the uneven temperature that occurred during injection molding is also reduced.

[0051] Alternatively, the temperature control unit 32 may pre-blow the preform 10 before (or after) cooling the preform with compressed air (cooling blow) in the temperature control unit 32, thereby forming an intermediate molded body (not shown) with a larger diameter than the preform 10.

[0052] After the temperature adjustment process, the transfer plate of the transport mechanism 36 moves to rotate by a predetermined angle, and the temperature-adjusted preform 10 held in the neck mold 36a is transported to the blow molding section 33.

[0053] (Step S103: Blow molding process) Next, the container 20 is blow-molded in the blow molding section 33. First, the blow cavity mold 61 is closed to house the preform 10 in the mold space, and the fitting core 63 is lowered so that it comes into contact with the neck portion 12 of the preform 10. Then, the stretching rod 65 (vertical axis stretching member) is lowered to press the bottom portion 14 of the preform 10 from the inside, and the preform 10 is stretched horizontally by supplying blow air from the fitting core 63 while performing vertical axis stretching as needed.

[0054] When the preform 10 expands due to the introduction of blow air, the first portion 15 of the body 13 of the preform 10 is pressed against the wall area of ​​the blow cavity mold 61, and the second portion 16 enters the corner area of ​​the blow cavity mold 61. As a result, the preform 10 expands and is shaped to closely fit the mold space of the blow cavity mold 61, and is blow-molded into the container 20. The bottom mold 62 waits in a lower position that does not come into contact with the bottom 14 of the preform 10 before the blow cavity mold 61 is closed, and is controlled to quickly rise to the molding position before or after the mold is closed.

[0055] In hot parison blow molding, the greater the internal heat content of the preform 10, the easier it is for the preform 10 to deform. As described above, the first part 15 of the preform 10 is thicker and contains more heat than the second part 16, so during blow molding, the first part 15 deforms before the second part 16.

[0056] During blow molding, the first portion 15 of the preform 10 is stretched along the lateral axis and contacts the blow mold before the second portion 16. After contacting the blow mold, the first portion 15 of the preform 10 continues to stretch until the second portion 16 contacts the corner of the blow mold. As a result, the thickness of the wall portion 25 of the container 20 becomes more uniform, and the material of the container 20 moves from the center of the wall portion 25 towards the corner 26.

[0057] Furthermore, as described above, the second portion 16 of the preform 10 retains less heat and is less prone to deformation than the first portion 15, so the second portion 16 is stretched later than the first portion 15. Moreover, since the outer surface of the second portion 16 is located radially inward from the outer surface of the first portion 15, the distance from the outer surface of the second portion 16 to the corner of the blow mold is larger compared to the case where the outer shape of the body of the preform 10 is circular. Therefore, the time it takes for the second portion 16 of the preform 10 to contact the corner of the blow mold is considerably longer than the time it takes for the first portion 15 to contact the wall of the blow mold. As a result, the wall portion 25 of the container 20 is sufficiently stretched during blow molding.

[0058] Furthermore, although the wall thickness t2 of the second part 16 before blow molding is thinner than the wall thickness t1 of the first part 15, the wall of the container 20 moves towards the corner 26 during blow molding. Therefore, when the second part 16 contacts the corner of the blow mold, the wall thickness of the corner of the container 20 increases, and the retained heat also increases. This makes it easier to clearly define edges and ridges at the corner 26 of the container 20.

[0059] (Step S104: Container removal process) Once the blow molding is complete, the blow cavity mold 61 is opened. This allows the container 20 to be moved out of the blow molding section 33. Next, the transport plate of the transport mechanism 36 moves by a predetermined angle, and the container 20 is transported to the removal section 34. In the removal section 34, the neck portion 22 of the container 20 is released from the neck mold 36a, and the container 20 is removed to the outside of the blow molding apparatus 30.

[0060] This completes one cycle in the container manufacturing process. Subsequently, the transfer plate of the transport mechanism 36 is moved by a predetermined angle, and steps S101 to S104 described above are repeated. During operation of the blow molding apparatus 30, the manufacturing of four sets of containers, each with a time difference between each step, is carried out in parallel. Furthermore, due to the structure of the blow molding apparatus 30, the injection molding process, temperature adjustment process, blow molding process, and container removal process each have the same duration. Similarly, the transport time between each process is also the same duration.

[0061] The effects and advantages of this embodiment will be described below. In the manufacturing of the container 20 of this embodiment, the preform 10 has a thickness t1 of the first portion 15 corresponding to the wall portion 25 of the container 20 that is greater in the circumferential direction than the thickness t2 of the second portion 16 corresponding to the corner portion 26 of the container 20. Furthermore, the outer circumferential surface of the second portion 16 of the preform 10 is located radially inward from the outer circumferential surface of the first portion 15 of the preform 10.

[0062] In this embodiment, by making the thickness of the first part 15 thicker than that of the second part 16, the heat retention of the first part 15 is increased, and during blow molding, the first part 15 deforms before the second part 16. Also, since the outer surface of the second part 16 is located radially inward from the outer surface of the first part 15, the time until the second part 16 contacts the corner of the blow mold is sufficiently longer than the time until the first part 15 contacts the wall of the blow mold. As a result, the first part 15 is sufficiently stretched during blow molding, so that the generation of columns in the wall portion 25 of the container 20 and uneven thickness in the wall portion 25 are suppressed.

[0063] Furthermore, in this embodiment, as the first portion 15 is stretched along its lateral axis, the thickness of the corners of the container 20 increases and the heat retention also increases when the second portion 16 comes into contact with the blow mold. Therefore, it becomes easier to clearly define edges and ridges at the corners 26 of the container 20, thereby improving the processing accuracy and appearance of the polygonal container.

[0064] Furthermore, in this embodiment, the deformation of the first portion 15 and the second portion 16 during blow molding is adjusted by the thickness distribution and the shape of the outer surface of the preform 10. Therefore, even when it is difficult to adequately control the temperature of the preform after injection molding, such as when shortening the cooling time of the preform 10 in the injection molding die to manufacture containers in a high-speed manufacturing cycle, it becomes easier to obtain a container 20 with an excellent aesthetic appearance.

[0065] Furthermore, in this embodiment, the inner surface of the first portion 15 of the preform 10 is located radially inward from the inner surface of the second portion 16 of the preform 10. This makes the wall thickness of the first portion 15 thicker than that of the second portion 16, thereby increasing the heat retention of the first portion 15, and making the first portion 15 more easily deformable than the second portion 16 during blow molding.

[0066] 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.

[0067] For example, the containers manufactured by the manufacturing method of the present invention are not limited to rectangular containers with a square cross-section, as in the above embodiment. For example, the manufacturing method of the present invention may be applied to manufacture containers with a triangular cross-section, a polygonal cross-section with pentagons or more, or an elliptical cross-section. Furthermore, the manufacturing method of the present invention may be applied to manufacture flattened containers in which the dimensions in the short axis direction and the dimensions in the long axis direction differ in the cross-section.

[0068] 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]

[0069] 10…Preform, 13…Body, 15…First part, 16…Second part, 20…Container, 23…Body, 25…Wall, 26…Corner, 30…Blow molding machine, 31…Injection molding section, 32…Temperature control section, 33…Blow molding section, 41…Injection cavity mold, 42…Injection core mold

Claims

1. An injection molding process in which a bottomed cylindrical resin preform is injection molded, The process includes a blow molding step in which the preform is blow-molded while retaining the heat from injection molding to produce a polygonal resin container having multiple corners in the circumferential direction, In the circumferential direction of the preform, the thickness of the first portion corresponding to the wall of the container is greater than the thickness of the second portion corresponding to the corner of the container. The outer surface of the body of the aforementioned preform is non-circular in the circumferential direction. In order to slow down the time it takes for the second portion to come into contact with the mold during blow molding, the outer circumferential surface of the second portion of the preform is positioned radially inward from the outer circumferential surface of the first portion of the preform. A method for manufacturing resin containers.

2. The inner circumferential surface of the first portion of the preform is located radially inward from the inner circumferential surface of the second portion of the preform. A method for manufacturing a resin container according to claim 1.

3. The process further includes a temperature adjustment step, prior to the blow molding, in which the temperature of the preform manufactured in the injection molding step is adjusted. A method for manufacturing a resin container according to claim 1.

4. An injection molding section for injection molding a bottomed cylindrical resin preform, The system includes a blow molding section that blow-moldes the preform while it is still containing the heat retained during injection molding to produce a polygonal resin container having multiple corners in the circumferential direction, The injection molding section is, In the circumferential direction, the thickness of the first portion corresponding to the wall surface of the container is greater than the thickness of the second portion corresponding to the corner of the container, the outer circumferential surface of the body is non-circular in the circumferential direction, and the preform is injection molded such that the outer circumferential surface of the second portion is located radially inward from the outer circumferential surface of the first portion in order to delay the time until the second portion contacts the mold during blow molding. Manufacturing equipment for plastic containers.

Images