Method and device for manufacturing resin container

Abstract

This method for manufacturing a resin container comprises: an injection molding step for injection-molding a bottomed cylindrical resin preform; and a blow molding step in which the preform is blow-molded in a state including holding heat during injection molding, and a polygonal container made of a resin having a plurality of corners in the circumferential direction is manufactured. In the circumferential direction of the preform, the wall thickness of a first portion corresponding to the wall surface portion of the container is thicker than the wall thickness of a second portion corresponding to the corner portion of the container, and the outer circumferential surface of the second portion of the preform is located radially inward of the outer circumferential surface of the first portion 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] In order to increase consumers' desire to buy, containers for cosmetics, emulsions, etc. require the containers themselves to have an aesthetically pleasing appearance. Among thick-walled polygonal containers (e.g., rectangular containers) for containing such cosmetics, it is preferred to use glass bottles that have a sense of heaviness and luxury and can maintain a beautiful state even after repeated use. However, glass bottles are heavy and fragile, and the cost of transportation and manufacturing is also high. Therefore, with regard to containers for containing cosmetics, etc., research is being conducted to replace glass bottles with resin containers.

[0003] Here, as one of the methods for manufacturing resin containers, a hot parison blow molding method has been known in the past. The hot parison blow molding method uses the heat retained during injection molding of the preform to blow-mold the resin container. Therefore, compared with the cold parison method, it is advantageous in that a variety of resin containers with excellent appearance can be manufactured.

[0004] In the case of blow-molding polygonal containers, the stretching ratio of the preform varies depending on the location of the container. Specifically, at the corners of the container body, the stretching ratio of the preform becomes larger than that of the wall of the container body. Therefore, in the manufacture of polygonal containers, due to the difference in the stretching ratio of the preform, poor appearances such as columns (band-shaped thick-walled parts extending axially) on the wall of the body, reduced shaping properties at the corners and edges of the container, and uneven thickness (uneven elongation) of the container are likely to occur. In a general hot preform blow molding cycle, the poor appearance of the container is alleviated to some extent by adjusting the temperature of the preform before blow molding the container.

[0005] In addition, in the case of using resin blow molding to form a polygonal container, for example, in Patent Document 1, it is proposed to set the inner circumferential side shape of the preform to a shape corresponding to the polygonal container, and to make the wall thickness of the portion corresponding to the wall surface of the container thicker than the wall thickness of the portion corresponding to the corner of the container.

[0006] Prior Art Literature Patent Literature Patent Document 1: Japanese Patent Publication No. 6-71758 Summary of the invention

[0007] Problems to be solved by the invention In polygonal containers for storing cosmetics, etc., the requirements for the appearance of the container are high. For example, the main body is preferably a flat shape without bumps, and containers with columns in the main body do not meet the specifications. On the other hand, the appearance defects generated in the main body of the polygonal container have not been completely eliminated at present, and further improvement is desired.

[0008] In addition, when the manufacturing cycle of the container is shortened, the cooling of the preform is mainly performed in the temperature adjustment process after injection molding. Therefore, when a polygonal container is to be manufactured in a short manufacturing cycle, it is difficult to adjust the temperature distribution of the preform in a manner suitable for the manufacture of the polygonal container, and the appearance of the container is more likely to be poor.

[0009] Therefore, the present invention has been made in view of such a problem, and an object of the present invention is to provide a method for manufacturing a polygonal container made of resin with excellent appearance in a short manufacturing cycle.

[0010] Technical solutions to solve problems A method for manufacturing a resin container according to one embodiment 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 retaining heat during injection molding to manufacture a resin polygonal container having a plurality of corners in the circumferential direction. In the circumferential direction of the preform, a first portion corresponding to a wall portion of the container has a thicker wall thickness than a second portion corresponding to a corner of the container, and an outer peripheral surface of the second portion of the preform is located radially inward of an outer peripheral surface of the first portion of the preform.

[0011] Effects of the Invention According to one aspect of the present invention, it is possible to provide a method for manufacturing a polygonal container made of resin and having an excellent appearance in a short manufacturing cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a longitudinal sectional view of the preform according to the present embodiment.

[0013] Figure 2 It is a cross-sectional view of the main body portion of the preform according to the present embodiment.

[0014] Figure 3 yes Figure 2 Magnified view of the preform.

[0015] Figure 4 It is a figure which shows typically the structure of the blow molding apparatus which concerns on this embodiment.

[0016] Figure 5 It is a figure which shows the structural example of an injection molding part.

[0017] Figure 6 yes Figure 5 AA line section view.

[0018] Figure 7 It is a diagram showing a configuration example of a temperature adjustment unit.

[0019] Figure 8 It is a figure which shows the structural example of a blow molding part.

[0020] Fig. 9 This is a flowchart showing the steps of a method for manufacturing a container. DETAILED DESCRIPTION

[0021] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0022] In the embodiments, in order to make the description easy to understand, the structures and elements other than the main parts of the present invention are simplified or omitted for description. In addition, in the drawings, the same symbols are marked for the same elements. It should be noted that the shapes, sizes, etc. of the elements shown in the drawings are schematically represented, and therefore do not represent the actual shapes, sizes, etc.

[0023] <Example of the structure of preform and container> First, refer to Figures 1 to 3 Next, a structural example of the preform 10 used for manufacturing the resin container (hereinafter, also simply referred to as a container) 20 according to the present embodiment will be described.

[0024] Figure 1 is a longitudinal sectional view of a preform 10 according to the present embodiment. Figure 2 is a cross-sectional view of the main body 13 of the preform 10 according to the present embodiment. Figure 3 yes Figure 2 It should be noted that Figure 1 , Figure 2 In FIG. 1 , the outline of the container 20 of the present embodiment is shown by a two-dot chain line.

[0025] The container 20 is formed by blow molding the preform 10. Figure 2 As shown, the container 20 of this embodiment is a polygonal container having a quadrilateral cross-sectional shape, and contains, for example, lotion, emulsion, etc. The container 20 has a neck 22 having a mouth 21 at the upper end, a tubular body 23 continuous from the neck 22, and a bottom 24 continuous from the body 23.

[0026] like Figure 1 , Figure 2As shown, in the container 20, the wall surface portion (plate portion) 25 of the main body portion 23 is uniformly walled in the axial direction (height direction) and the circumferential direction, and has a flat shape with almost no unevenness. Figure 2 As shown, for example, the corner portion 26 of the main body 23 is thicker than the wall portion 25. Therefore, the contour of the inner peripheral side of the main body 23 is not recessed toward the outer peripheral side at the corner portion 26, and the adjacent wall portions 25 are connected to each other in a curved shape via the corner portion 26. It should be noted that the wall thickness of the bottom 24 of the container 20 is preferably formed thicker than the wall thickness of the main body 23.

[0027] By making the container 20 have the above-mentioned wall thickness distribution, the sense of luxury and weight can be emphasized, and the container 20 can be made closer to the impression of a cosmetic container held by consumers. That is, the appearance of the container 20 can be improved, so the container 20 can be used as a cosmetic container where appearance is important.

[0028] On the other hand, Figure 1 As shown, 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 main body 13 formed in a cylindrical shape; a bottom 14 that closes the other end of the main body 13; and a neck 12 that is formed on the open side of one end of the main body 13 and has a mouth 11.

[0029] like Figure 2 , Figure 3 As shown in FIG. 1 , the wall thickness of the main body 13 of the preform 10 is different in the circumferential direction at the first portion 15 corresponding to the wall portion 25 of the container 20 and the second portion 16 corresponding to the corner portion 26 of the container 20. Four of the first portion 15 and four of the second portion 16 are alternately arranged at equal intervals in the circumferential direction of the preform 10. That is, the first portion 15 and the second portion 16 are 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. It should be noted that the wall thickness of the first portion 15 and the wall thickness of the second portion 16 are both substantially constant without changing in the axial direction (height direction), for example.

[0030] like Figure 3 As shown, for the first portion 15 of the main body 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.

[0031] On the other hand, in the second portion 16 of the main body 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). In addition, 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 expressed by L3-L4.

[0032] As described above, the radial length L1 from the axis Ax to the outer peripheral surface of the preform at the first portion 15 is different from the radial length L3 from the axis Ax to the outer peripheral surface of the preform at the second portion 16. Therefore, the outer peripheral surface of the main body 13 of the preform 10 is non-circular, and the outer peripheral surface of the second portion 16 is located radially inward of the outer peripheral surface of the first portion 15.

[0033] Similarly, the radial length L2 from the axis Ax to the inner circumference of the preform at the first portion 15 is different from the radial length L4 from the axis Ax to the inner circumference of the preform at the second portion 16. Therefore, the inner circumference of the main body 13 of the preform 10 is also non-circular, and the inner circumference of the first portion 15 is located radially inwardly of the inner circumference of the second portion 16.

[0034] The first portion 15 has an outer circumferential surface of the preform radially outward and an inner circumferential surface of the preform radially inward compared to the second portion 16. Therefore, the wall thickness t1 of the first portion of the preform 10 is greater than the wall thickness t2 of the second portion (t1>t2).

[0035] <Description of container manufacturing apparatus> Figure 4 1 is a diagram schematically showing the structure of a blow molding device 30 of the present embodiment. The blow molding device 30 is an example of a container manufacturing device, and adopts a hot preform method (also called a one-stage method) in which the preform 10 is blow-molded into a container by effectively utilizing the retained heat (internal heat) during injection molding without cooling the preform 10 to room temperature.

[0036] The blow molding device 30 includes an injection molding unit 31, a temperature adjustment unit 32, a blow molding unit 33, a take-out unit 34, and a conveying mechanism 36. The injection molding unit 31, the temperature adjustment unit 32, the blow molding unit 33, and the take-out unit 34 are arranged at positions rotated by a given angle (for example, 90 degrees) around the conveying mechanism 36.

[0037] (Conveying mechanism 36) The conveying mechanism 36 has Figure 4The transfer plate (not shown) is a transfer plate that moves in a rotation direction about an axis perpendicular to the paper plane. The transfer plate is composed of a single disk-shaped flat plate member or a plurality of roughly fan-shaped flat plate members divided for each molding station. On the transfer plate, one or more neck molds 36a ( Figure 4 (not shown in the figure).

[0038] The conveying mechanism 36 includes a rotating mechanism (not shown), and by moving the transfer plate, the preform 10 (or container 20) with the neck 12 held by the neck mold 36a is conveyed in the order of the injection molding section 31, the temperature adjustment section 32, the blow molding section 33, and the removal section 34. It should be noted that the conveying mechanism 36 also includes a lifting mechanism (vertical mold opening and closing mechanism) and a neck mold opening mechanism, and also performs the actions of lifting and lowering the transfer plate, closing the mold, and opening (demolding) the injection molding section 31, etc.

[0039] (Injection molding section 31) The injection molded part 31 is manufactured by injection molding. Figures 1 to 3 The preform 10 shown. An injection device 35 for supplying a raw material (resin material) of the preform 10 is connected to the injection molding section 31 .

[0040] Figure 5 3 is a diagram showing a structural example of the injection molding portion 31. Figure 6 yes 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 table of the blow molding device 30. The injection core mold 42 is fixed to a core mold lifting mechanism (not shown).

[0041] The injection cavity mold 41 is a mold that defines the outer peripheral shape of the main body 13 of the preform 10. A resin supply portion (hot runner) 43 that introduces the 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 peripheral shape of the preform 10, and is inserted into the inner peripheral side of the injection cavity mold 41 from the upper side.

[0042] like Figure 5 As shown, in the injection molding section 31, the injection cavity mold 41, the injection core mold 42, and the neck mold 36a of the conveying mechanism 36 are closed to form a mold space for the preform 10. Then, a 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.

[0043] Figure 6The figure shows a cross section (a section perpendicular to the axial direction) of the injection cavity mold 41 and the injection core mold 42 when the injection molding portion 31 is closed. The inner peripheral surface of the injection cavity mold 41 of the present embodiment is formed into a shape in which the area 41b of the second portion is cut from the outside by the amount of four surfaces, and in the injection cavity mold 41, the area 41b of the second portion is located radially inwardly than the area 41a of the first portion. In addition, the area 42a of the first portion of the outer peripheral surface of the injection core mold 42 of the present embodiment is cut by the amount of four surfaces, and the area 42a of the first portion of the injection core mold 42 is located radially inwardly than the area 42b of the second portion. By combining the above-mentioned injection cavity mold 41 and injection core mold 42, injection molding can be achieved. Figure 3 A preform 10 having a wall thickness distribution is shown.

[0044] The raw material of the preform 10 is a thermoplastic synthetic resin, which can be appropriately selected according to the specifications of the container 20. Specific types of materials include, for example, PET, PEN (polyethylene naphthalate), PCTA (polycyclohexanedimethanol terephthalate), Tritan (Tritan (registered trademark): copolyester manufactured by Eastman Chemical), PP (polypropylene), PE (polyethylene), PC (polycarbonate), PES (polyethersulfone), PPSU (polyphenylsulfone), PS (polystyrene), COP / COC (cyclic olefin polymer), PMMA (polymethyl methacrylate: propylene), PLA (polylactic acid), etc. In addition, additives such as coloring materials may be added to the resin material.

[0045] It should be noted that even when the mold of the injection molding section 31 is opened, the neck mold 36a of the conveying mechanism 36 does not open but holds and conveys the preform as it is. The number of preforms 10 that can be simultaneously molded by the injection molding section 31 (that is, the number of containers 20 that can be simultaneously molded by the blow molding device 30) can be appropriately set.

[0046] (Temperature adjustment unit 32) The temperature adjustment unit 32 adjusts the temperature of the preform 10 delivered from the injection molding unit 31 by equalizing the temperature, eliminating temperature deviation, and adjusting the temperature distribution, and adjusts the temperature of the preform 10 to a temperature suitable for final blow molding (e.g., about 90° C. to 105° C.). In addition, the temperature adjustment unit 32 also has the function of cooling the preform 10 in a high-temperature state after injection molding.

[0047] Figure 7 1 is a diagram showing a configuration example of the temperature adjustment section 32. For example, the temperature adjustment section 32 is a structure in which a cavity mold 51 (temperature adjustment tank mold) capable of accommodating the preform 10, a cooling core 52 (air introduction and outlet core), and a cylindrical cooling rod 53 (air introduction and outlet rod) are combined.

[0048] The cooling core 52 is a cylindrical mold inserted into the inner side of the neck mold 36a, and a cooling rod 53 is concentrically arranged with an annular gap inside the cooling core 52. When the cooling core 52 is inserted into the neck mold 36a, it is in close contact with the inner periphery or upper end surface of the neck 12 of the preform 10, and maintains airtightness with the preform 10. In addition, the inner side of the cooling rod 53 and the gap between the cooling rod 53 and the cooling core 52 constitute a supply path and an exhaust path for compressed air, respectively. Figure 7 , an example is shown in which the inner side of the cooling rod 53 is connected to the supply path of compressed air, and the gap between the cooling rod 53 and the cooling core 52 is connected to the exhaust path of compressed air, but the supply path and the exhaust path of compressed air may be in the opposite relationship. As described above, the temperature adjustment unit 32 blows compressed air into the preform 10, thereby cooling the preform 10 by cooling with compressed air and heat exchange by contact with the cavity mold.

[0049] It should be noted that, when compressed air is introduced into the preform 10 by the temperature regulating section 32, the preform 10 may be pre-blown by the temperature regulating section 32 before blow molding to form an intermediate molded body (not shown) having a main body with a larger diameter than the preform 10. In addition, when pre-blowing is performed by the temperature regulating section 32, the cavity mold 51 of the temperature regulating section 32 is composed of a pair of split molds divided in the axial direction.

[0050] (Blow molding section 33) The blow molding section 33 performs biaxial stretch blow molding on the preform 10 whose temperature has been adjusted by the temperature adjustment section 32 , thereby manufacturing the container 20 .

[0051] Figure 8 3 is a diagram showing a structural example of the blow molding unit 33. The blow molding unit 33 includes a pair of split molds corresponding to the shape of the container 20, namely, a blow cavity mold 61, a bottom mold 62, a fitting core (blow core, a cylindrical air introduction and deduction member) 63, and a stretch rod 65.

[0052] A stretching rod 65 is concentrically arranged inside the fitting core 63 so as to be able to advance and retreat in the axial direction. The fitting core 63 is a cylindrical mold inserted into the inside of the neck mold 36a. When inserted into the neck mold 36a, the fitting core 63 is in close contact with the inner periphery or the upper end surface of the neck 12 of the preform 10, and maintains airtightness with the preform 10 during blow molding. In addition, the gap between the inside of the fitting core 63 and the stretching rod 65 constitutes a supply path and an exhaust path for compressed air (blow air). The above-mentioned blow molding section 33 performs blow molding by blowing compressed air into the preform 10 while stretching the preform 10. In this way, the preform 10 can be shaped into the shape of the blow cavity mold 61 to manufacture the container 20.

[0053] (Taking out portion 34) The take-out section 34 is configured to release the neck portion 22 of the container 20 manufactured by the blow molding section 33 from the neck mold 36 a and take the container 20 out of the blow molding device 30 .

[0054] <Description of the method for manufacturing the container> Next, a method for manufacturing a container using the blow-molding device 30 of the present embodiment will be described. Fig. 9 1 is a flowchart showing the steps of a method for manufacturing the container 20 .

[0055] (Step S101: Injection molding process) First, in the injection molding section 31, resin is injected from the injection device 35 into a mold space in the shape of a preform formed by the injection cavity mold 41, the injection core mold 42, and the neck mold 36a of the conveying mechanism 36, thereby manufacturing the preform 10. Then, after the injection (filling and holding pressure) of the resin material is completed, or after a minimum cooling time set after the injection is completed, the injection mold of the injection molding section 31 is opened.

[0056] Although not particularly limited, from the perspective of manufacturing containers with a fast molding cycle, in step S101, it is preferred that the mold is opened without providing cooling time for the preform 10 in the injection mold after the injection (filling and holding pressure) of the resin material is completed.

[0057] On the other hand, when the preform 10 is cooled to a minimum in the injection mold, the time for cooling the resin material (cooling time) after the injection molding unit 31 completes the injection of the resin material is preferably less than 1 / 2 of the time for injecting the resin material (injection time). In addition, the above cooling time can be set shorter than the time for injecting the resin material according to the weight of the resin material. For example, the cooling time is more preferably less than 2 / 5, more preferably less than 1 / 4, and particularly preferably less than 1 / 5 relative to the injection time of the resin material. Moreover, the cooling time can also be set to 0. It should be noted that the cooling time and the injection time are parameters that the operator can arbitrarily set for the blow molding device 30 as part of the molding conditions of the preform.

[0058] In addition, regarding the main body 13 of the preform 10 of the present embodiment, the wall thickness t1 of the first portion 15 corresponding to the wall surface portion 25 of the container 20 is thick, and the wall thickness t2 of the second portion 16 corresponding to the corner portion 26 of the container 20 is thin. Since the retained heat of the preform 10 increases in proportion to the wall thickness, the retained heat of the first portion 15 is relatively high and the retained heat of the second portion 16 is relatively low in the circumferential direction of the main body 13 of the preform 10.

[0059] When the injection molding of the preform 10 is completed, the injection molding section 31 is opened, and the preform 10 is demolded from the injection cavity mold 41 and the injection core mold 42. Next, the transfer plate of the conveying mechanism 36 is moved in a manner of rotating by a predetermined angle, and the preform 10 held in the neck mold 36a is conveyed to the temperature regulating section 32 while retaining the heat during injection molding.

[0060] (Step S102: Temperature Adjustment Process) Next, in the temperature adjustment section 32 , temperature adjustment is performed to bring the temperature of the preform 10 close to a temperature suitable for final blow molding.

[0061] In the temperature adjustment process, the transfer plate is lowered, so that the preform 10 held in the neck mold 36a is accommodated in the cavity mold 51, and the cooling core 52 is in contact with the neck 12 of the preform 10, and the cooling rod 53 (air introduction and extraction rod) is inserted into the preform 10. Then, the temperature of the preform 10 is adjusted by blowing compressed air (blowing compressed air) from the cooling core 52 and / or the cooling rod 53 in contact with the neck 12 of the preform 10. Thus, the temperature of the preform 10 is adjusted so that it does not fall below the temperature suitable for blow molding, and the temperature deviation generated during injection molding is also reduced.

[0062] It should be noted that the preform 10 may be pre-blown by the temperature regulating section 32 before (or after) the cooling (cooling blow molding) of the preform by compressed air by the temperature regulating section 32 to form an intermediate molded body (not shown) having a main body with an enlarged diameter compared to the preform 10.

[0063] After the temperature adjustment step, the transfer plate of the conveying mechanism 36 moves so as to rotate by a predetermined angle, and the temperature-adjusted preform 10 held by the neck mold 36 a is conveyed to the blow molding section 33 .

[0064] (Step S103: Blow molding process) Next, in the blow molding section 33 , the container 20 is blow-molded.

[0065] First, the blow cavity mold 61 is closed to accommodate the preform 10 in the mold space, and the fitting core 63 is lowered, so that the fitting core 63 contacts the neck 12 of the preform 10. Then, the stretching rod 65 (longitudinal axis stretching member) is lowered to press the bottom 14 of the preform 10 from the inner surface, and the preform 10 is stretched in the longitudinal axis while supplying blow air from the fitting core 63 as needed, thereby stretching the preform 10 in the transverse axis.

[0066] When the preform 10 is bulged by the introduction of the blow air, the first portion 15 of the main body 13 of the preform 10 is pressed against the area of ​​the wall surface of the blow cavity mold 61, and the second portion 16 enters the area of ​​the corner of the blow cavity mold 61. As a result, the preform 10 is bulged in a manner that closely adheres to the mold space of the blow cavity mold 61 and is shaped, and blow-molded into a container 20. It should be noted that the bottom mold 62 is controlled in the following manner: before the blow cavity mold 61 is closed, it waits at a position below that does not contact the bottom 14 of the preform 10, and quickly rises to the molding position before or after the mold is closed.

[0067] In the hot parison blow molding, the greater the internal heat retained by the preform 10, the easier it is for the preform 10 to deform. As described above, the first portion 15 of the preform 10 is thicker and retains higher heat than the second portion 16, so the first portion 15 deforms earlier than the second portion 16 during blow molding.

[0068] During blow molding, the first portion 15 of the preform 10 contacts the blow mold earlier than the second portion 16 while being stretched in the transverse axis. After contacting the blow mold, the first portion 15 of the preform 10 is continuously stretched 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 is nearly uniform, and the wall of the container 20 moves from the center of the wall portion 25 toward the corner 26.

[0069] In addition, as described above, the second portion 16 of the preform 10 has a lower thermal conductivity than the first portion 15 and is less likely to deform, so the second portion 16 is stretched later than the first portion 15. Furthermore, since the outer peripheral surface of the second portion 16 is located radially inward of the outer peripheral surface of the first portion 15, the distance from the outer peripheral surface of the second portion 16 to the corner of the blow mold is greater than when the outer peripheral shape of the main body of the preform 10 is circular. Therefore, the time until the second portion 16 of the preform 10 contacts the corner of the blow mold is sufficiently longer than the time until the first portion 15 contacts the wall portion of the blow mold. Therefore, the wall portion 25 of the container 20 is sufficiently stretched during blow molding.

[0070] In addition, the wall thickness t2 of the second portion 16 before blow molding is thinner than the wall thickness t1 of the first portion 15, but during blow molding, the wall of the container 20 moves toward the corner 26. Therefore, when the second portion 16 contacts the corner of the blow mold, the wall thickness of the corner of the container 20 becomes larger and the heat is also high. As a result, it is easy to clearly shape the edge and ridgeline at the corner 26 of the container 20.

[0071] (Step S104: Container Removal Process) When the blow molding is completed, the blow cavity mold 61 is opened. Thus, the container 20 can be moved from the blow molding section 33.

[0072] Next, the transfer plate of the conveying mechanism 36 moves by a predetermined angle, and the container 20 is conveyed to the take-out section 34. In the take-out section 34, the neck 22 of the container 20 is released from the neck mold 36a, and the container 20 is taken out of the blow molding device 30.

[0073] The above is the end of one cycle of the container manufacturing method. Then, by moving the transfer plate of the conveying mechanism 36 by a predetermined angle, the above-mentioned steps S101 to S104 are repeated. It should be noted that when the blow molding device 30 is operated, the manufacturing of four sets of containers with a time difference of one step each is performed in parallel.

[0074] In addition, in the structure of the blow molding device 30, the injection molding process, the temperature adjustment process, the blow molding process, and the container removal process are of the same length. Similarly, the conveying time between the processes is also of the same length.

[0075] Hereinafter, the effects of this embodiment will be described.

[0076] Regarding the preform 10 used in manufacturing the container 20 of the present embodiment, in the circumferential direction, the wall thickness t1 of the first portion 15 corresponding to the wall portion 25 of the container 20 is thicker than the wall thickness t2 of the second portion 16 corresponding to the corner portion 26 of the container 20. In addition, the outer peripheral surface of the second portion 16 of the preform 10 is located radially inward of the outer peripheral surface of the first portion 15 of the preform 10.

[0077] In the present embodiment, the wall thickness of the first portion 15 is made thicker than the wall thickness of the second portion 16, so that the heat retention of the first portion 15 becomes higher, and the first portion 15 is deformed earlier than the second portion 16 during blow molding. In addition, since the outer peripheral surface of the second portion 16 is located radially inward of the outer peripheral surface of the first portion 15, the time until the second portion 16 contacts the corner of the blow mold is sufficiently longer than the time until the first portion 15 contacts the wall surface of the blow mold. As a result, the first portion 15 is sufficiently stretched during blow molding, so that the generation of columns on the wall surface 25 of the container 20 and the uneven thickness at the wall surface 25 are suppressed.

[0078] In addition, in the present embodiment, as the first portion 15 is stretched in the transverse axis, when the second portion 16 contacts the blow mold, the wall thickness of the corner portion of the container 20 becomes larger, and the heat retention is also high. Therefore, it is easy to clearly shape the edge and ridgeline at the corner portion 26 of the container 20, and the processing accuracy and appearance of the polygonal container can be further improved.

[0079] In addition, in the present embodiment, the deformation of the first portion 15 and the second portion 16 during blow molding is adjusted according to the wall thickness distribution and the shape of the outer peripheral surface of the preform 10. Therefore, even when it is difficult to sufficiently adjust the temperature of the preform after injection molding, it is easy to obtain a container 20 with excellent appearance, as in the case where the cooling time of the preform 10 in the injection molding mold is shortened and the container is manufactured in a fast manufacturing cycle.

[0080] In addition, in the present embodiment, the inner circumferential surface of the first portion 15 of the preform 10 is located radially inwardly of the inner circumferential surface of the second portion 16 of the preform 10. Thus, the wall thickness of the first portion 15 can be made thicker than the wall thickness of the second portion 16 to increase the heat retention of the first portion 15, and thus the first portion 15 can be deformed more easily than the second portion 16 during blow molding.

[0081] The present invention is not limited to the above-described embodiments, and various improvements and design changes may be made without departing from the gist of the present invention.

[0082] For example, the container manufactured by the manufacturing method of the present invention is not limited to a square container with a quadrilateral cross section as in the above embodiment. For example, the manufacturing method of the present invention can also be used to manufacture a polygonal container with a cross section of a triangle or pentagon or more, or an elliptical container. In addition, the manufacturing method of the present invention can also be used to manufacture a flat container with different dimensions in the short axis direction and the long axis direction of the cross section.

[0083] The embodiments disclosed herein are illustrative in all aspects and should not be considered restrictive. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all modifications within the scope and meanings equivalent to the claims.

[0084] Explanation of symbols 10: preform; 13: main body; 15: first part; 16: second part; 20: container; 23: main body; 25: wall part; 26: corner; 30: blow molding device; 31: injection molding part; 32: temperature adjustment part; 33: blow molding part; 41: injection cavity mold; 42: injection core mold.

Claims

1. A method for manufacturing a resin container, comprising: an injection molding step of injection molding a resin preform in a bottomed cylindrical shape; and The blow molding step comprises blow molding the preform while it is kept hot including during injection molding, to produce a polygonal container made of resin having a plurality of corners in the circumferential direction. In the circumferential direction of the preform, the wall thickness of a first portion corresponding to the wall surface portion of the container is thicker than the wall thickness of a second portion corresponding to the corner portion of the container. The outer peripheral surface of the second portion of the preform is located radially inward of the outer peripheral surface of the first portion of the preform.

2. The method for manufacturing a resin container according to claim 1, wherein: The inner peripheral surface of the first portion of the preform is located radially inward of the inner peripheral surface of the second portion of the preform.

3. The method for manufacturing a resin container according to claim 1, wherein: The method for manufacturing a resin container further includes, before the blow molding, a temperature adjustment step of adjusting the temperature of the preform manufactured in the injection molding step.

4. A manufacturing device for a resin container, comprising: an injection molding section that injection molds a bottomed cylindrical preform made of resin; and a blow molding section that blows the preform while it is still hot, including during injection molding, to produce a polygonal container made of resin having a plurality of corners in a circumferential direction, The injection molding section injection molds the preform, and the preform has a shape in which the wall thickness of a first portion corresponding to the wall surface portion of the container in the circumferential direction is thicker than the wall thickness of a second portion corresponding to the corner portion of the container, and the outer peripheral surface of the second portion is located radially inner than the outer peripheral surface of the first portion.

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