Manufacturing method and manufacturing device for resin container

Abstract

This manufacturing method for a resin container made of high-density polyethylene includes: an injection molding step for injection-molding a preform; a temperature adjustment step for adjusting the temperature of the preform; and a blow molding step for blow-molding the preform to form a resin container. The blow molding step includes: a primary blowing step for introducing a pressurized gas into the preform and blow-molding the preform into an intermediate molded body having a size equal to or smaller than that of the resin container; an exhausting step for exhausting the pressurized gas and heat-shrinking the intermediate molded body; and a secondary blowing step for manufacturing the resin container by blow-molding the intermediate molded body which, after the heat-shrinkage of the intermediate molded body, has a lower temperature than the preform at the start of the primary blowing step.

Description

Resin container manufacturing method and manufacturing device

[0001] The present invention relates to a method and an apparatus for manufacturing a resin container, and more particularly to a method and an apparatus for manufacturing a resin container having high ESCR performance and sufficient rigidity.

[0002] Chemicals containing surfactants such as bleach have the effect of chemically degrading various plastic materials, so containers containing these chemicals are required to have high environmental stress cracking resistance (ESCR).One of the materials suitable for manufacturing such containers is polyethylene, particularly high-density polyethylene (HDPE), which has excellent physical properties such as chemical resistance and impact resistance.

[0003] Conventionally, attempts have been made to improve the ESCR performance of manufactured containers by adjusting the manufacturing conditions and additives of the polyethylene resin material. For example, Patent Document 1 proposes improving chemical resistance and ESCR performance by using a polyethylene resin having a melt flow rate and density within a predetermined range and performing stretch blow molding at a predetermined temperature and pressure.

[0004] Patent No. 7375359

[0005] In general, materials with high ESCR performance are often designed so that molded articles produced using them have high ductility, and therefore the rigidity of the molded articles tends to be low. In recent years, there has been a demand for lighter resin containers as a measure to address environmental issues. However, when attempting to reduce the weight of a container produced using a material with high ESCR performance, the low rigidity can result in the container becoming excessively soft and making it difficult to use as a container. Conversely, when a container is produced using a material that can increase rigidity, even if it is possible to reduce the weight, the ESCR performance can be reduced. Therefore, there is a need for a container manufacturing method that can achieve both sufficient rigidity to enable lightweight containers and high ESCR performance.

[0006] The present invention has been made in consideration of these problems, and aims to provide a method and apparatus for manufacturing a resin container that has high ESCR performance while providing sufficient rigidity to enable the container to be lightweight.

[0007] One aspect of the present invention is a method for manufacturing a resin container made of high-density polyethylene, comprising: an injection molding process for manufacturing a bottomed resin preform by injection molding; a temperature adjustment process for adjusting the temperature of the manufactured preform; and a blow molding process for blow molding the temperature-adjusted preform to manufacture a resin container.The blow molding process is characterized by comprising: a primary blowing process for introducing pressurized gas into the preform and blow-molding the preform into an intermediate molded body of the same size as or smaller than the resin container; an exhaust process for evacuating the pressurized gas introduced in the primary blowing process and thermally shrinking the intermediate molded body; and a secondary blowing process for blow-molding the intermediate molded body, which has reached a lower temperature than the preform at the start of the primary blowing process after thermal shrinkage of the intermediate molded body, to manufacture a resin container.

[0008] According to one aspect of the present invention, it is possible to provide a method for manufacturing a resin container that has high ESCR performance while also having sufficient rigidity to enable the container to be lightweight.

[0009] FIG. 1 is a diagram showing an example of a resin container manufactured by a method for manufacturing a resin container according to the present invention. FIG. 2 is a diagram schematically showing an example of the configuration of a manufacturing apparatus for a resin container according to an embodiment. FIG. 3 is a flowchart showing the steps of a method for manufacturing a resin container according to an embodiment. FIG. 4 is a schematic diagram explaining a blow molding step in a method for manufacturing a resin container according to an embodiment. FIG. 5 is a diagram showing ESCR test results for a resin container manufactured at a mold temperature of 20°C in a blow molding step. FIG. 6 is a diagram showing ESCR test results for a resin container manufactured at a mold temperature of 80°C in a blow molding step. FIG. 7 is a diagram showing rigidity evaluation test results for a resin container. FIG. 8 is a diagram schematically showing another example of the configuration of a manufacturing apparatus that is a one-step system. FIG. 9 is a diagram schematically showing an example of the configuration of a manufacturing apparatus that is a two-step system.

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the embodiments, in order to make the description easier to understand, structures and elements other than the main parts of the present invention will be described in a simplified or omitted manner. In addition, the same elements will be given the same reference numerals in the drawings. Note that the shapes, dimensions, etc. of each element shown in the drawings are shown schematically and do not represent the actual shapes, dimensions, etc.

[0011] <Overview of Resin Container> First, an example of the shape of a resin container 1 manufactured by the resin container manufacturing method according to this embodiment will be described. Fig. 1 is a front view showing an example of the resin container 1. As shown in Fig. 1, the resin container 1 includes a cylindrical neck portion 3 having an opening 2 at its upper end, a cylindrical body portion 4 connected to the neck portion 3, and a bottom portion 5 continuing from the lower end side of the body portion 4. This resin container 1 is intended to be used for storing, transporting, etc., chemicals that have the property of degrading resin materials, such as bleach containing a surfactant, and is formed using high-density polyethylene (HDPE), which has excellent chemical resistance, waterproofing, impact resistance, insulating properties, etc.

[0012] In this embodiment, the resin container 1 is formed by forming a bottomed preform 20 by injection molding, and then stretch-blow molding the preform 20. That is, the resin container 1 of this embodiment is formed by the injection stretch-blow molding method (ISBM). An example of the shape of the preform 20 used to manufacture the resin container 1 is shown by the dashed line in FIG. 1 .

[0013] The resin container 1 manufactured by the resin container manufacturing method according to this embodiment has high ESCR performance and sufficient rigidity to enable the container to be made lighter (thinner-walled). The manufacturing method and manufacturing apparatus for the resin container 1 will be described below.

[0014] 2 is a plan view schematically showing the configuration of the blow molding apparatus 10, which is an apparatus for manufacturing the resin container 1 according to this embodiment. The blow molding apparatus 10 is an example of an apparatus for manufacturing the resin container 1, and employs a hot parison method (also referred to as a one-stage method) in which the resin container 1 is blow-molded by utilizing the heat retained (internal heat) during injection molding without cooling the resin preform 20 to room temperature.

[0015] The blow molding apparatus 10 includes an injection molding section 11, a temperature adjustment section 12, a blow molding section 13, a take-out section 14, an injection device 15, and a conveying mechanism 16. The injection molding section 11, the temperature adjustment section 12, the blow molding section 13, and the take-out section 14 are arranged at positions rotated by a predetermined angle (e.g., 90 degrees) around the conveying mechanism 16.

[0016] (Transport mechanism 16) The transport mechanism 16 includes a transport plate (not shown) that moves in a rotational direction around an axis perpendicular to the plane of the paper in Fig. 2. The transport plate is composed of a single disk-shaped flat plate member or a plurality of roughly fan-shaped flat plate members divided into individual molding stations. One or more neck molds 26 (see Fig. 4) that hold the neck portion 202 of the preform 20 (or the neck portion of an intermediate molded body 30 described below, or the neck portion 3 of the resin container 1) are arranged at predetermined angles on the transport plate.

[0017] The transport mechanism 16 includes a rotation mechanism (not shown) that intermittently rotates the transfer plate counterclockwise, for example, when viewed from above. This allows the transport mechanism 16 to transport the preform 20 (or intermediate molded body 30, resin container 1) whose neck portion 203 is held by the neck mold 26, in the order of injection molding section 11, temperature adjustment section 12, blow molding section 13, and removal section 14. In the transport mechanism 16, the preform 20 is transported to each section in an upright position with the neck portion 203 positioned on the upper side and the longitudinal direction of the preform 20 aligned vertically. The transport mechanism 16 also includes an elevation mechanism (vertical mold opening / closing mechanism) and a mold opening mechanism for the neck mold 26, and performs operations for raising and lowering the transfer plate and operations related to mold closing and mold opening (mold release) in the injection molding section 11, etc.

[0018] (Injection molding section 11) The injection molding section 11 uses an injection mold to manufacture the preform 20. As shown in Fig. 2, the injection molding section 11 is connected to an injection device 15 that supplies a resin material that is a raw material of the preform 20.

[0019] 1, the overall shape of the preform 20 is a cylindrical shape with one end open and the other end closed. The preform 20 has a neck portion 203 formed at one end with an opening 202, a body portion 204 connected to the neck portion 203 and formed into a cylindrical shape, and a bottom portion 205 connected to the body portion 204 and closing the other end.

[0020] As described above, the material of the resin container 1 in this embodiment, i.e., the material of the preform 20, is high-density polyethylene. It is preferable to use this high-density polyethylene with a melt flow rate (MFR) of 0.1 to 10 g / 10 min (test temperature 190°C, test load 2.16 kg), more preferably 0.2 to 7 g / 10 min (test temperature 190°C, test load 2.16 kg).

[0021] Furthermore, in this embodiment, the high-density polyethylene used as the material for the preform 20 is one that is considered to have a relatively low ESCR performance. This is because if a material with a high ESCR performance is used, the rigidity of the manufactured container will be low, making it difficult to reduce the weight. By using a material with a low ESCR performance and manufacturing the container by the method for manufacturing a resin container of the present invention described below, it is possible to manufacture a resin container 1 that has high ESCR performance and sufficient rigidity to enable weight reduction.

[0022] Specifically, in this embodiment, high-density polyethylene having a durability of less than 1000 hours in an ESCR (environmental stress crack resistance) test in accordance with ASTM D1693 (using a 10 wt % solution of Igepal (registered trademark) CO-630 as a surfactant and storing at a temperature of 50°C, the durability is defined as the time until 50% of the sample breaks) is used as the material, and preferably high-density polyethylene having a durability of less than 500 hours in the same test is used as the material.

[0023] Generally, the higher the density of high-density polyethylene, the higher its rigidity. In this embodiment, in order to impart high rigidity to the manufactured resin container 1, high-density polyethylene having a density of 0.954 g / cm is used as the material. ３ Use the one that is equal to or greater than this.

[0024] The injection molding section 11 includes an injection cavity mold, an injection core mold, and a hot runner mold (none of which are shown) that guides molten resin (high-density polyethylene) supplied from an injection device 15 into a mold space. The injection cavity mold and the injection core mold are examples of injection molds. In the injection molding section 11, the molten resin injected from the injection device 15 is introduced into a mold space (a space that defines the outer shape of the preform 20) defined by the injection mold, thereby molding the preform 20 having the above-mentioned shape.

[0025] (Temperature Adjustment Unit 12) After being released from the injection molding die, the injection-molded preform 20 is transported to the temperature adjustment unit 12 by the transport mechanism 16. The temperature adjustment unit 12 is equipped with a temperature adjustment die (not shown), and cools (or heats) the preform 20, which is in a high-temperature state after injection molding, by placing it in the temperature adjustment die maintained at a predetermined temperature. The temperature adjustment unit 12 also has the function of adjusting the temperature distribution of the preform 20 to a predetermined state before transport to the blow molding unit 13.

[0026] The temperature control mold of the temperature control unit 12 has a temperature control pot (temperature control pot or heating pot) that controls the temperature of the preform 20 from the outside, and a temperature control rod (temperature control rod or heating rod) that controls the temperature of the preform 20 from the inside. Note that the temperature control mold in this embodiment is preferably a combination of a heating pot and a temperature control rod.

[0027] (Blow molding unit 13) The blow molding unit 13 performs stretch blow molding on the preform 20 whose temperature has been adjusted in the temperature adjustment unit 12, to produce the resin container 1. As shown in Fig. 4, the blow molding unit 13 includes a blow molding die 21 and a stretch rod 22. The blow molding die 21 also includes a blow cavity die 23, which is a pair of split dies corresponding to the shape of the resin container 1, and a blow bottom die 25. The blow molding unit 13 also includes a blow core die 24 having an insertion hole 27 formed therein, and the insertion hole 27 is configured so that the stretch rod 22 can be inserted therethrough so as to be movable in the vertical direction. The blow core die 24 having the insertion hole 27 also functions as an air inlet / outlet member for introducing and emitting pressurized gas (blow air).

[0028] The blow molding section 13 stretches the preform 20 placed in the blow molding die 21 in the longitudinal direction by the stretching rod 22, and also stretches it in the radial direction by the pressurized gas supplied from the air inlet / outlet member. As a result, the preform 20 is shaped into the shape of the blow cavity die 23, and the resin container 1 can be manufactured.

[0029] (Removal section 14) The removal section 14 is configured to release the neck section 3 of the resin container 1 manufactured in the blow molding section 13 from the neck mold 26 and remove the resin container 1 to the outside of the blow molding device 10.

[0030] <Explanation of Container Manufacturing Method> Next, a method for manufacturing the resin container 1 using the blow molding apparatus 10 of this embodiment will be described. Fig. 3 is a flowchart showing the steps of the method for manufacturing the resin container 1.

[0031] (Step S101: Injection Molding Process) First, in the injection molding section 11, resin is injected from the injection device 15 into a preform-shaped mold space formed by the injection cavity mold, the injection core mold, and the neck mold 26 of the transport mechanism 16 to manufacture the preform 20. Then, after the injection of the resin material (filling and pressure holding) is completed, or after a minimum cooling time provided after the completion of the injection has elapsed, the mold of the injection molding section 11 is opened.

[0032] Although not particularly limited, from the viewpoint of manufacturing a container with a high-speed molding cycle, it is preferable to shorten the cooling time of the preform 20 in the injection molding mold after the injection (filling and pressure holding) of the resin material is completed in step S101 and then open the mold.

[0033] When the injection molding of the preform 20 is completed, the mold in the injection molding section 11 is opened and the preform 20 is released from the injection cavity mold and the injection core mold. Next, the transfer plate of the transport mechanism 16 moves so as to rotate by a predetermined angle, and the preform 20 held in the neck mold 26 is transported to the temperature adjustment section 12 while retaining the heat retained during injection molding.

[0034] (Step S102: Temperature Adjustment Step) Subsequently, in the temperature adjustment section 12, the preform 20 is accommodated in a temperature adjustment mold, and temperature adjustment is performed to bring the temperature of the preform 20 close to a temperature (e.g., 120°C to 150°C) suitable for stretch blowing in the next blow molding step.

[0035] After the temperature adjustment step, the transfer plate of the transport mechanism 16 moves so as to rotate by a predetermined angle, and the temperature-adjusted preform 20 held by the neck mold 26 is transported to the blow molding section 13 .

[0036] (Blow Molding Process) Subsequently, the resin container 1 is blow molded in the blow molding section 13. The blow molding process in the present invention is configured to include a primary blowing process in step S103, an exhausting process in step S104, and a secondary blowing process in step S105.

[0037] As a result of extensive research, the inventors have found that the ESCR performance of the resin container 1 produced can be improved by stretching a high-density polyethylene preform 20 twice, in a primary blowing process and a secondary blowing process, as described below. Furthermore, they have found that in blow molding using this method, as the temperature during stretching of the preform 20 (the temperature of the blow molding mold 21 or blow cavity mold 23 with which the stretched preform 20 comes into contact) increases, the density and rigidity of the produced resin container 1 increase, but the ESCR performance decreases. The improvement in ESCR performance achieved by the two blowing processes is thought to be due to reduced unevenness in the elongation of the preform 20, allowing the resin container 1 to be configured with a more uniform wall thickness distribution. This is also thought to be due to an increased degree of molecular chain orientation in the stretching direction of the high-density polyethylene.

[0038] Based on this knowledge, the temperature of the mold (blow molding die 21 or blow cavity die 23) used in the blow molding step of this embodiment is set to a temperature lower than the optimum blowing temperature of high-density polyethylene (about 130°C) or a temperature slightly lower than the optimum blowing temperature, in order to achieve both high ESCR performance and high rigidity. Specifically, the temperature of the blow molding die 21 or blow cavity die 23 is set between 10°C and 125°C, and more preferably between 20°C and 80°C. This makes it possible to suppress a sudden temperature drop and solidification of the high-density polyethylene when the stretched preform 20 or intermediate molded body 30 comes into contact with the blow cavity die 23.

[0039] It is also desirable to set the molding time (blowing time) of the primary blowing step shorter than the molding time of the secondary blowing step, thereby minimizing the decrease in the retained heat (temperature) of the preform 1 in the primary blowing step and allowing the intermediate molded body 30 to maintain a retained heat (temperature) sufficient to enable stretching in the secondary blowing step.

[0040] In this embodiment, the primary blowing step and the secondary blowing step are performed using the same mold, which shortens the time required for the blow molding step, facilitates temperature control of the preform 20 during stretching and the intermediate molded body 30 (or the blow molding mold 21 or blow cavity mold 23) described below, and reduces costs.

[0041] 4A, in the primary blowing step, first, the blow cavity mold 23 is closed, and the preform 20 is placed in a mold space (a space that defines the outer shape of the resin container 1) formed by the blow cavity mold 23 and the blow bottom mold 25. Thereafter, the blow core mold 24 is lowered to abut against the neck 203 of the preform 20. Then, the stretching rod 22 is lowered to press against the inner surface of the bottom 205 of the preform 20, and while vertical axis stretching is performed as necessary, pressurized gas (blow air) is supplied from the blow core mold 24 to horizontally stretch the preform 20, thereby obtaining an intermediate molded body 30.

[0042] The pressure of the pressurized gas supplied to the preform 20 in the primary blowing step is set lower than the pressure of the pressurized gas in the secondary blowing step described below in order to prevent rupture of the preform 20. The pressure of the pressurized gas in the primary blowing step can be set to, for example, 0.03 to 0.6 MPa, preferably 0.05 to 0.3 MPa.

[0043] Furthermore, the stretch blowing in the primary blowing step is carried out for a relatively short time so that the blown preform 20 (intermediate molded body 30) can maintain a temperature sufficient to enable further blow molding in the secondary blowing step described below (i.e., so that the preform 20 is not cooled too much). That is, the primary blowing step ends when the intermediate molded body 30 is obtained, in which the preform 20 is expanded to a size that just touches the inner wall of the blow cavity mold 23, as shown in Figure 4(A).

[0044] (Step S104: Exhaust Step) Next, the exhaust step is carried out. In the exhaust step, after the primary blow step is completed, the pressurized gas that had been introduced into the intermediate molded body 30 is temporarily exhausted. As shown in FIG. 4(B) , since the intermediate molded body 30 blown in the primary blow step still maintains a high temperature, the pressurized gas is exhausted and the pressure is released, causing thermal shrinkage of the intermediate molded body 30. The exhaust step ends upon completion of this thermal shrinkage or during thermal shrinkage. The time until thermal shrinkage is completed varies depending on the characteristics of the high-density polyethylene material, the temperatures of the preform 20 (intermediate molded body 30) and the blow molding die 21, etc., but in this embodiment, it is, for example, about 0.5 seconds to several seconds.

[0045] (Step S105: Secondary Blowing Process) In the subsequent secondary blowing process, pressurized gas is again supplied from the blow core mold 24 to the intermediate molded body 30 after thermal shrinkage, thereby stretching each portion. The pressure of the pressurized gas supplied to the intermediate molded body 30 in the secondary blowing process is set higher than the pressure of the pressurized gas in the primary blowing process. The pressure of the pressurized gas in the secondary blowing process can be set to, for example, 0.7 to 3.5 MPa, preferably 1.0 to 2.0 MPa. As a result, as shown in FIG. 4(C), the intermediate molded body 30 is cooled in a bulged state so as to be in close contact with the inner wall of the blow cavity mold 23, and is shaped into the shape of the final product, the resin container 1.

[0046] The secondary blowing step is carried out while the intermediate molded body 30 has a temperature (heat) that allows it to be stretched. The blow molding of the intermediate molded body 30 in the secondary blowing step is carried out at a lower temperature than the blow molding of the preform 20 in the primary blowing step. In other words, the intermediate molded body 30 that has undergone the evacuation step is at a lower temperature than the preform 20 at the start of the primary blowing step, and the secondary blowing step is carried out on this intermediate molded body 30. The temperature of the intermediate molded body 30 at the start of the secondary blowing step may be, for example, about 80°C.

[0047] As described above, in the blow molding process of the present invention, the preform 20 is blow-molded once in the primary blowing step into an intermediate molded body 30 of a size equal to or smaller than the resin container 1, and then the pressure is released in the exhausting step to cause thermal shrinkage of the intermediate molded body 30. Thereafter, in the secondary blowing step, the intermediate molded body 30 is stretched again at a temperature lower than the temperature of the preform 20 at the start of the primary blowing step, thereby producing the resin container 1.

[0048] In a manufacturing method in which a resin container is molded from a preform through a single stretch-blow process, uneven stretching occurs in different regions due to the shape of the preform, bias in temperature distribution, etc., which results in large variations in the resin thickness of the resin container 1 (thick and thin portions are formed irregularly), resulting in uneven orientation of the molecular chains of the high-density polyethylene. In other words, the degree of orientation of the molecular chains in the stretching direction is high in regions that are sufficiently stretched, while the degree of orientation of the molecular chains remains low in regions that are not sufficiently stretched (e.g., near the outer periphery of the bottom). The fact that some regions with low orientation remain in the manufactured resin container in this way is thought to be one cause of the deterioration of ESCR performance.

[0049] In contrast, in the method for manufacturing a resin container 1 according to the present invention, the preform 20 is molded into an intermediate molded body 30 having a size similar to that of the resin container 1 in the primary blowing step, the intermediate molded body 30 is thermally shrunk in the exhausting step, and then the intermediate molded body 30 is stretched in the secondary blowing step at a temperature lower than that of the preform 20 at the start of the primary blowing step. This is thought to result in the resin container 1 having a more uniform wall thickness distribution (less unevenness in the degree of orientation of the molecular chains of the high-density polyethylene), improving the ESCR performance of the manufactured resin container 1. Furthermore, in this embodiment, the high-density polyethylene used as the material has a relatively low ESCR performance and a density of 0.954 g / cm. ３ Since the above-mentioned materials are used, the resin container 1 produced has sufficient rigidity.

[0050] As described above, in the method for manufacturing a resin container 1 according to the present invention, the ESCR performance of the resin container 1 can be improved by setting the temperature when stretching the preform 20 lower within the above-mentioned temperature range, and the rigidity of the resin container 1 can be improved by setting the temperature when stretching the preform 20 higher. Therefore, by adjusting the temperature of the mold used in the blow molding process, a resin container 1 having the desired ESCR performance and rigidity can be manufactured.

[0051] (Step S106: Container Removal Process) When blow molding is completed as described above, the blow cavity mold 23 is opened. This allows the resin container 1 to be removed from the blow molding section 13. Next, the transfer plate of the conveying mechanism 16 moves a predetermined angle, and the resin container 1 is transported to the removal section 14. In the removal section 14, the neck portion 3 of the resin container 1 is released from the neck mold 26, and the resin container 1 is removed to the outside of the blow molding apparatus 10.

[0052] In this manner, one container production cycle in the method for producing a resin container 1 is completed. Thereafter, the transfer plate of the conveying mechanism 16 is moved a predetermined angle, and the above-described steps S101 to S106 are repeated. When the blow molding apparatus 10 is in operation, the production of four sets of containers is carried out in parallel, with a time difference between each step. Due to the structure of the blow molding apparatus 10, the injection molding step, temperature adjustment step, blow molding step, and container removal step are all the same length of time. Similarly, the transport time between each step is also the same length.

[0053] Examples The present invention will be described below with reference to examples, but the present invention is not limited to the examples below. The technical scope of the present invention is defined by the scope of the claims or equivalents thereof.

[0054] The resin containers of Examples 1 and 2 were manufactured by the method for manufacturing a resin container (a method in which two blow molding steps are performed) described in the above embodiment. The difference between Examples 1 and 2 is that the temperature of the mold (blow cavity mold) used in the blow molding step was set to 20°C in Example 1, whereas it was set to 80°C in Example 2. Both Examples 1 and 2 were manufactured using high-density polyethylene with low ESCR performance (HJ451 manufactured by Japan Polyethylene Corporation, ESCR test durability time 200 hours in accordance with ASTM D1693, density 0.955 g / cm). ３ ) was used as the material, the container volume was 600 ml, and the container weight was 30 g assuming a lightweight container.

[0055] In Comparative Examples 1 and 2, resin containers were produced by a conventional method for producing a resin container, i.e., a method in which a resin container is obtained by a single stretch blow without performing the primary blow step, the exhaust step, and the secondary blow step in the blow molding process. In Comparative Example 1, the temperature of the mold used in the blow molding process was set to 20°C, and in Comparative Example 2, the temperature of the same mold was set to 80°C. In Comparative Examples 1 and 2, similarly to Examples 1 and 2, resin containers were produced using high-density polyethylene with low ESCR performance (HJ451 manufactured by Japan Polyethylene Corporation, ESCR test durability time 200 hours in accordance with ASTM D1693, density 0.955 g / cm). ３ ) was used as the material, the container volume was 600 ml, and the container weight was 30 g.

[0056] Furthermore, as Comparative Examples 3 and 4, resin containers were produced by the conventional method for producing resin containers, similar to Comparative Examples 1 and 2. In both Comparative Examples 3 and 4, the temperature of the mold used in the blow molding process was set to 20°C. Comparative Example 3 used a high-density polyethylene with high ESCR performance (HB332EK manufactured by Japan Polyethylene Corporation, ESCR test durability time of 1000 hours or more in accordance with ASTM D1693, density 0.953 g / cm). ３The container volume was 600 ml, and the container weight was 35 g, assuming a container that was not lightweight. In addition, in Comparative Example 4, high-density polyethylene (HB332EK manufactured by Japan Polyethylene Corporation, ESCR test durability time of 1000 hours or more in accordance with ASTM D1693, density 0.953 g / cm) with high ESCR performance was used, similar to Comparative Example 3. ３ ) was used as the material, the container volume was 600 ml, and the container weight was 30 g assuming a lightweight container.

[0057] First, the ESCR performance of Examples 1 and 2 was evaluated. Figures 5 and 6 show the results of the ESCR test for Examples 1, 2, Comparative Examples 1, and 2. The ESCR test was conducted by filling each container with 60 ml of bleach, equivalent to 10% of the capacity, sealing it, and storing it in an insulated tank at 65°C, and measuring the time until damage to the container was confirmed. In this test, a product with a durability of 200 hours or more was evaluated as having practical ESCR performance.

[0058] 5 shows the ESCR test results for Example 1 and Comparative Example 1, which were produced at a mold temperature of 20° C. The durability of Comparative Example 1 was 175 hours, which is shorter than the practical durability of 200 hours, whereas the durability of Example 1 was 320 hours, which showed high ESCR performance that far exceeded the standard of 200 hours.

[0059] 6 shows the ESCR test results for Example 2 and Comparative Example 2, which were produced at a mold temperature of 80° C. The durability of Comparative Example 2 was 101 hours, which was an even lower ESCR performance than Comparative Example 1, whereas the durability of Example 2 was 246 hours, which was inferior to Example 1 but still showed a sufficiently high ESCR performance for practical use.

[0060] These results confirm that by using the resin container manufacturing method of the present invention, it is possible to manufacture resin containers with high ESCR performance that are sufficiently practical for use as containers for chemicals such as bleach, even when high-density polyethylene material with relatively low ESCR performance is used as the material.

[0061] Next, the rigidity of the containers in Examples 1 and 2 was evaluated. Fig. 7 shows the results of the rigidity evaluation test for Examples 1, 2, Comparative Examples 3, and 4. The rigidity evaluation test was performed based on the magnitude of the load (generated reaction force) when the side of the container was partially deformed. Specifically, in an environment of 22°C, a vertical force was applied to the center of the body of a container placed on its side in a testing device, and the load was measured when a deformation of 10 mm occurred.

[0062] As shown in the figure, in the case of Comparative Examples 3 and 4, which were manufactured by the conventional method using a material with high ESCR performance, the load measured in Comparative Example 3, which assumed a container that was not lightweight, was 6.6 N, but the load measured in Comparative Example 4, in which the weight was reduced in anticipation of weight reduction, was 4.1 N, confirming that reducing the weight of the container (by making it lighter) significantly reduced rigidity.

[0063] On the other hand, in Example 1, although a container weight of 30 g was manufactured assuming a lightweight container, the measured load was a high value of 6.8 N, which was equal to or higher than that of Comparative Example 3. Moreover, in Example 2, which was produced using a mold temperature higher than that of Example 1, an even higher value of 7.8 N was observed.

[0064] These results confirmed that by using the method for manufacturing a resin container according to the present invention, it is possible to manufacture a resin container that has high rigidity even when the container weight is 30 g, which is an assumed weight reduction, and that combines high ESCR performance with high rigidity. Furthermore, it was confirmed that in the method for manufacturing a resin container according to the present invention, the rigidity of the resin container can be further improved by setting a higher mold temperature in the blow molding process.

[0065] The effects of this embodiment will be described below. According to this embodiment, a method for manufacturing a resin container using high-density polyethylene as a material includes a primary blowing step, an exhaust step, and a secondary blowing step as a blow molding process. In the primary blowing step, pressurized gas is introduced into a preform 20, and the preform 20 is blow-molded into an intermediate molded body 30 having a size equal to or smaller than the resin container 1, which is the final product. In the exhaust step, the pressurized gas introduced into the preform 20 (intermediate molded body 30) is exhausted, causing the intermediate molded body 30 to thermally shrink. In the secondary blowing step, after the intermediate molded body 30 has thermally shrunk, the intermediate molded body 30, which has reached a temperature lower than that of the preform 20 at the start of the primary blowing step, is blow-molded to produce the resin container 1.

[0066] According to the method for manufacturing a resin container of this embodiment, the preform 20 is stretched in the primary blowing step to form an intermediate molded body 30 having a size similar to that of the resin container 1, and then the pressure is released once in the exhausting step to thermally shrink the intermediate molded body 30. After that, in the secondary blowing step, the intermediate molded body 30, which has reached a temperature lower than that of the preform 20 at the start of the primary blowing step, is stretched again to manufacture the resin container 1. As a result, areas that were insufficiently stretched due to uneven stretching during the primary blowing step are selectively stretched during the secondary blowing step, and the ESCR performance of the resin container 1 can be improved.

[0067] Furthermore, because the resin container manufacturing method of this embodiment can improve the ESCR performance of the resin container 1, it is possible to use high-density polyethylene as the material, which has the properties of relatively low ESCR performance but high density. This makes it possible to impart high rigidity to the manufactured resin container 1. Therefore, the resin container manufacturing method of this embodiment can manufacture a resin container 1 that has high ESCR performance and sufficient rigidity to enable the container to be lightweight.

[0068] In particular, the high-density polyethylene used as the material may be one having a durability of less than 1000 hours in the ESCR test in accordance with ASTM D 1693, and preferably one having a durability of less than 500 hours in the same test. In other words, since high-density polyethylene, which has a relatively low ESCR performance but a high density, can be used as the material, it is possible to impart higher rigidity to the resin container 1 produced.

[0069] In this embodiment, the high-density polyethylene used as the material has a density of 0.954 g / cm ３ Generally, the higher the density of high-density polyethylene, the higher its rigidity, so by using high-density polyethylene with a higher density as the material, it is possible to impart higher rigidity to the resin container 1 to be manufactured.

[0070] In this embodiment, the primary blow step and the secondary blow step are performed using the same mold, which shortens the time required for the blow molding step, facilitates temperature control of the preform 20 and the intermediate molded body 30 (or the blow molding mold 21 or the blow cavity mold 23), and reduces costs.

[0071] In this embodiment, the temperature of the mold used in the blow molding step is set between 10° C. and 125° C., and more preferably between 20° C. and 80° C. In this way, by using a mold that is lower in temperature than conventional molds and performing stretching twice, in a primary blow step and a secondary blow step, the ESCR performance of the resin container 1 can be improved.

[0072] The present invention is not limited to the above-described embodiment, and various improvements and design changes may be made without departing from the spirit of the present invention. For example, in the above-described embodiment, a configuration in which exhaust is performed after the primary blowing process and then the secondary blowing process is performed immediately thereafter has been described. However, a configuration in which exhaust is performed after the primary blowing process, and then pressurized gas is supplied again at the same pressure as in the primary blowing process, and then the secondary blowing process is performed subsequently may also be used. In this way, localized elongation unevenness in the preform 20 can be further reduced, and ESCR performance can be further improved.

[0073] Furthermore, for example, in the above embodiment, the primary blowing step and the secondary blowing step are performed using the same mold (blow cavity mold), but it is also possible to perform the primary blowing step and the secondary blowing step using separate molds. In this case, it becomes possible to change the temperature and dimensions of the molds in each blowing step, and it is possible to manufacture a resin container while more precisely and accurately controlling the temperature of the preform 20 (intermediate molded body 30), the size of the intermediate molded body 30, and the like.

[0074] 8 shows an example of a blow molding apparatus 10A that, like the blow molding apparatus 10 described above, is a hot parison type (one-step system) but performs the primary and secondary blowing steps using different molds. The blow molding apparatus 10A differs from the blow molding apparatus 10 only in the configuration of the blow molding section 13a. The blow molding section 13a includes a primary mold (primary blow cavity mold) 21a for the primary blowing step and a secondary mold (secondary blow cavity mold) 21b for the secondary blowing step, and each mold is configured to be slidable based on the position of the neck mold 26 (preform 20). The preform 20 is primarily blown in the primary mold 21a, evacuated and shrunk, and molded into an intermediate molded body 30, which is then shaped into the shape of the resin container 1 in the secondary mold 21b.

[0075] The present invention may also be implemented using a cold parison method (two-step method) rather than a hot parison method (one-step method). Figure 9 shows an example of a blow molding apparatus 10B using the cold parison method. The blow molding apparatus 10B includes at least a supply section 101 that introduces room-temperature preforms 20 into the apparatus 10B, a plurality of preform holders 201 that hold necks 203 of the preforms 20, a conveying section 103 that continuously circulates and conveys the preform holders 201, a heating section 102 that is disposed within the conveying section 103 and heats the preforms 20 to a temperature suitable for blowing, a transfer section 104 that sends the heated preforms 20 to a blow molding section 105, the blow molding section 105 that molds the preforms 20 into containers 1, and an unloading section 106 that discharges the containers 1 from the apparatus 10B. The blow molding section 105 may perform the primary blowing step and the secondary blowing step using the same mold (blow cavity mold), or may perform the primary blowing step and the secondary blowing step using different molds.

[0076] 8 and 9, the set temperatures of the blow molds may be different between the primary blowing step and the secondary blowing step. For example, the mold temperature in the primary blowing step may be 125°C, and the mold temperature in the secondary blowing step may be 10°C.

[0077] Furthermore, the embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0078] DESCRIPTION OF SYMBOLS 1...Resin container, 10...Blow molding device (apparatus for manufacturing a resin container), 11...Injection molding section, 12...Temperature adjustment section, 13...Blow molding section, 14...Removal section, 20...Preform, 30...Intermediate molded body

Claims

1. A method for manufacturing a resin container made of high-density polyethylene, comprising: an injection molding process for manufacturing a bottomed resin preform by injection molding; a temperature adjustment process for adjusting the temperature of the manufactured preform; and a blow molding process for blow molding the temperature-adjusted preform to manufacture a resin container, wherein the blow molding process comprises: a primary blowing process for introducing pressurized gas into the preform and blow molding the preform into an intermediate molded body of the same size as or smaller than the resin container; an exhaust process for evacuating the pressurized gas introduced in the primary blowing process and thermally shrinking the intermediate molded body; and a secondary blowing process for blow molding the intermediate molded body, which has a temperature lower than that of the preform at the start of the primary blowing process after the thermal shrinkage of the intermediate molded body, to manufacture the resin container.

2. The method for manufacturing a resin container according to claim 1, wherein the high-density polyethylene has a durability of less than 500 hours in an environmental stress crack resistance test in accordance with ASTM D1693.

3. The high-density polyethylene has a density of 0.954 g / cm ３ The method for producing a resin container according to claim 1, characterized in that:

4. The method for manufacturing a resin container according to claim 1, wherein the primary blowing step and the secondary blowing step are carried out using the same mold.

5. The method for manufacturing a resin container according to claim 1, characterized in that the temperature of the mold used in the primary blowing step is 10°C to 125°C.

6. An apparatus for manufacturing a resin container made of high-density polyethylene, comprising: an injection molding section that manufactures a bottomed resin preform by injection molding; a temperature adjustment section that adjusts the temperature of the manufactured preform; and a blow molding section that blow molds the temperature-adjusted preform to manufacture a resin container, wherein the blow molding section introduces pressurized gas into the preform and blow-moldes the preform into an intermediate molded body of the same size as or smaller than the resin container, and then vents the introduced pressurized gas to thermally shrink the intermediate molded body, and after the thermal shrinkage is completed, blow-moldes the intermediate molded body, which has a lower temperature than the preform at the start of processing in the blow molding section, to manufacture the resin container.

Images