Method for forming hollow molded bodies, stretching rod used therefor, and injection stretch blow molding machine

Abstract

The present invention provides a method for molding a hollow molded body that can suppress deformation of the preform and shorten the molding cycle of the hollow molded body, as well as a stretching rod and an injection stretch blow molding machine used therefor. [Solution] In a method for manufacturing a hollow molded body, the method includes an injection molding step of injection molding a preform and a blow molding step of obtaining a hollow molded body by stretch blow molding the preform in a blow molding section, wherein the blow molding step includes a preform support step of inserting the tip of a stretch rod into the preform and supporting the preform by bringing the preform and the tip into contact, and a preform peeling step of supplying blow air into the preform to release the contact between the preform and the tip.

Description

Technical Field

[0001] The present invention relates to a method for forming a hollow molded body, an extension rod used therefor, and an injection stretch blow molding machine.

Background Art

[0002] An injection stretch blow molding machine is used for manufacturing hollow molded bodies such as bottles and cups made of synthetic resin.

[0003] For example, the injection stretch blow molding machine described in Patent Document 1 includes an injection molding section that injection-molds a preform, which is a raw material for a hollow molded body, using molten resin injected from an injection device; a blow molding section that blow-molds the preform injection-molded in the injection molding section into a desired hollow molded body such as a bottle or a cup; and a take-out section that sends out the hollow molded body blow-molded in the blow molding section to the outside of the machine.

[0004] Also known as an injection stretch blow molding machine is one that includes a temperature control engineering section for adjusting the temperature of the preform injection-molded in the injection molding section.

[0005] The injection molding section has an injection molding die including an upper die that is an injection core die, a lower die that is an injection cavity die, and a lip die. The lip die conveys the preform from the injection molding section to the blow molding section while supporting the injection-molded preform.

[0006] The preform molded in the injection molding section is cooled, whereby the outer surface and the inner surface are hardened, and a hard skin layer is formed. The properties such as the formation speed and hardness of the skin layer vary depending on the type of resin used for the raw material of the preform. Therefore, the timing of releasing the preform from the injection molding die (adjustment of the injection cooling time) and the time until blow molding in the blow molding section are adjusted according to the type of resin to form a desired container.

[0007] The blow molding section has a blow molding die that includes a split blow mold and a lip mold positioned corresponding to the blow molding section. Furthermore, the blow molding section includes a stretching rod that stretches the preform placed in the blow molding die. The stretching rod pushes down the sides (body) and bottom of the preform, thereby stretching the preform.

[0008] Furthermore, the blow molding section includes a blowing mechanism for blowing air into the preform when the preform is stretched using a stretching rod. The blowing mechanism inflates the preform, pressing its sides and bottom against the inner surface of the blow molding die to shape it into a hollow molded body.

[0009] The hollow molded body formed in the blow molding section is supported by a lip mold that was part of the blow molding die, and is removed from the blow molding die and moved to the removal section.

[0010] The hollow molded body, having been moved to the removal section, is released from the lip mold as the lip mold opens, and then proceeds to the removal section. As a result, the hollow molded body located in the removal section is sent out of the injection stretch blow molding machine. The lip mold, having released the hollow molded body, is then moved back to the injection molding section by the rotation of the turntable.

[0011] In this injection stretch blow molding machine, the preform, which has been injection molded in the injection molding section, is released from the injection molding die while being supported by a lip mold and moved to the blow molding section. The preform located in the blow molding section is stretched by a stretch rod, and blow air is blown into it to produce a hollow molded body. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Patent No. 7039089 [Overview of the project] [Problems that the invention aims to solve]

[0013] As the preform is molded in the injection molding section, its outer and inner surfaces harden upon cooling, forming a rigid skin layer. At this time, the core layer, which is sandwiched between the outer and inner skin layers, is still at a high temperature, and the resin is molten.

[0014] In this state, the preform is transported to the blow molding section, where the heat from the core layer warms the skin layer, causing it to melt and integrate with the core layer. In this state, the preform is held for a predetermined time (hereinafter referred to as the "intermediate time") until the entire preform reaches a temperature suitable for the downward stretching operation by the stretching rod and the blowing of blow air.

[0015] The same applies to injection stretch blow molding machines equipped with a temperature control process. After the temperature control process is complete, the preform is held for an intermediate period during the blow molding process until it reaches a temperature suitable for the overall stretching operation by the stretch rod and the injection of blow air.

[0016] The preform is then held in place for an intermediate period of time, after which it is pushed down and stretched by a stretching rod, and blown air is blown into it to blow-form a hollow molded body.

[0017] Figure 8 illustrates the deformation of the preform; (a) is a cross-sectional view showing the preform immediately after being transferred to the blow molding section, and (b) is a cross-sectional view showing the preform after shrinkage has progressed.

[0018] As shown in Figure 8(a), the preform retains its injection-molded shape immediately after being transferred to the blow molding section. However, as mentioned above, the skin layer of the preform melts and integrates with the core layer, and over time it shrinks due to residual stress from injection, pressure release due to mold opening, and thermal melting, causing its shape to deform from its injection-molded shape (see Figure 8(b)).

[0019] Here, the intermediate time is determined and set empirically from the shape, material, molding temperature, cooling temperature, etc. of the preform so that it is almost simultaneous with the point when the skin layer where the preform has crystallized melts and integrates with the core layer to become non-crystallized (hereinafter, this point is referred to as the "minimum point").

[0020] However, the minimum point changes depending on the thickness of the skin layer. When the preform is deformed by shrinkage, the thickness of the skin layer becomes thicker, and thus the minimum point also changes. Therefore, in order to make the end point of the intermediate time coincide with the point when the preform reaches the minimum point, it is necessary to make the intermediate time longer.

[0021] When the preform is stretched by a stretching rod and blow air is supplied in a deformed state, there is a problem that uneven wall thickness, rupture, etc. of the hollow molded body occur.

[0022] An object of the present invention is to provide a method for molding a hollow molded body that can suppress deformation of a preform and shorten the molding cycle of the hollow molded body, a stretching rod used therefor, and an injection stretch blow molding machine.

Means for Solving the Problems

[0023] The present invention includes an injection molding step of melting a synthetic resin material and injection molding a bottomed cylindrical preform in an injection molding section, a blow molding step of obtaining a hollow molded body by stretch blow molding the preform in a blow molding section, The blow molding step includes a preform support step of inserting a tip portion of a stretching rod into the preform, bringing the preform into contact with the tip portion, and supporting the preform, and a preform peeling step of supplying blow air into the preform to release the contact between the preform and the tip portion, and is a method for manufacturing a hollow molded body characterized by including the above steps.

[0024] The present invention also relates to a stretching rod used in the method for manufacturing the hollow molded body, which has a rod-shaped portion and a tip portion formed continuously at one end of the rod-shaped portion, wherein the tip portion has a peripheral wall portion having the same shape as the inner peripheral wall of the preform, and is characterized as a stretching rod.

[0025] Also, in the present invention, the tip portion is characterized in that a shoulder portion extending in a direction perpendicular to the axis of the rod-shaped portion is formed.

[0026] The present invention further relates to an injection stretch blow molding machine having an injection molding section for melting a synthetic resin material and injection molding a bottomed cylindrical preform, a blow molding section for forming a hollow molded body by stretching and blow molding the preform by extending a stretching rod, and a take-out section for taking out the hollow molded body outside the machine, wherein the blow molding process executed in the blow molding section includes a preform support process of inserting the tip portion of the stretching rod into the preform, bringing the preform into contact with the tip portion, and supporting the preform, and a preform peeling process of supplying blow air into the preform to release the contact between the preform and the tip portion, and is characterized as an injection stretch blow molding machine.

Advantages of the Invention

[0027] According to the present invention, the blow molding process includes a preform support process of inserting the tip portion of the stretching rod into the preform, bringing the preform into contact with the tip portion, and supporting the preform, and a preform peeling process of supplying blow air into the preform to release the contact between the preform and the tip portion. Therefore, the preform disposed in the blow molding section can be supported by the tip portion until the entire preform reaches a temperature suitable for the pressing and stretching operation by the stretching rod and the blowing of the blow air.

[0028] This suppresses inward shrinkage and deformation of the preform in the longitudinal and radial directions, thereby suppressing changes in the thickness of the skin layer due to preform shrinkage. Consequently, the thinness of the skin layer of the preform can be maintained, shortening the time it takes for the entire preform to reach a temperature suitable for the downward stretching operation by the stretching rod and the blowing of blown air. Thus, a method for molding hollow molded articles that suppresses preform deformation and shortens the molding cycle of the hollow molded article can be realized.

[0029] Furthermore, according to the present invention, since the tip portion has a peripheral wall portion that has the same shape as the inner peripheral wall of the preform, it can reliably support the inner peripheral wall of the preform, which is most prone to changes in thickness. This suppresses deformation of the preform and shortens the molding cycle of the hollow molded body.

[0030] Furthermore, according to the present invention, since the tip portion has a shoulder portion that extends in a direction perpendicular to the axis of the rod-shaped portion, by supplying blown air, air pressure can be applied in a direction that separates the preform and the tip portion. Therefore, even if the preform is supported by the tip portion, the preform and the tip portion can be separated, thus suppressing a decrease in the yield of the hollow molded product.

[0031] Furthermore, according to the present invention, since the injection stretch blow molding machine performs a preform support step and a preform peeling step, it is possible to provide an injection stretch blow molding machine that can suppress deformation of the preform and shorten the molding cycle of the hollow molded body. [Brief explanation of the drawing]

[0032] [Figure 1] This is a schematic plan view of the injection stretch blow molding machine 1. [Figure 2] This is a front view of the injection stretch blow molding machine 1. [Figure 3] This is a schematic cross-sectional view showing the inside of a blow molding die during the blow molding process. [Figure 4]This is a longitudinal cross-sectional view showing the extension rod. [Figure 5] This is a flowchart illustrating the blow molding process, where (a) is a flowchart of the blow molding process according to the prior art, and (b) is a flowchart of the blow molding process according to this embodiment. [Figure 6] This is an enlarged explanatory diagram showing the vicinity of the shoulder portion 23 in step 12. [Figure 7] This figure illustrates a comparative example using a conventional stretching rod. [Figure 8] This diagram illustrates the deformation of a preform. (a) is a cross-sectional view showing the preform immediately after it has been transferred to the blow molding section, and (b) is a cross-sectional view showing the preform after shrinkage has progressed. [Modes for carrying out the invention]

[0033] Hereinafter, an injection stretch blow molding machine 1 according to one embodiment of the present invention will be described in detail with reference to the drawings.

[0034] (Injection stretch blow molding machine) Figure 1 is a schematic plan view of the injection stretch blow molding machine 1 according to this embodiment. Figure 2 is a front view of the injection stretch blow molding machine 1. First, the overall configuration of the injection stretch blow molding machine 1 will be described with reference to Figures 1 and 2.

[0035] As shown in Figure 1, the injection stretch blow molding machine 1 according to this embodiment comprises three stations: an injection molding section 2, a blow molding section 3, and a removal section 4. Each of these stations—the injection molding section 2, the blow molding section 3, and the removal section 4—is arranged circumferentially with a distance of approximately 120° between them.

[0036] A hot runner mechanism (not shown) provided in the injection molding section 2 is connected to the injection device 6. This allows molten resin (e.g., polyethylene) to be filled into the injection molding section 2 from the injection device 6. In this invention, it is preferable to use an olefin-based resin such as polyethylene or polypropylene.

[0037] The injection stretch blow molding machine 1 is positioned above each station and further includes a rotating plate 50 for transferring preforms or hollow molded bodies to the next station. The rotating plate 50 is located within an intermediate base 51 and stops for a predetermined time when it reaches the position above each station.

[0038] A lip mold 11 for forming the lip portion of the preform and hollow molded body is provided on the lower surface of the rotating plate 50. The lip mold 11 grips the lip portion of the preform and hollow molded body, and as the rotating plate 50 rotates, the preform and hollow molded body are transferred to the next station.

[0039] The injection stretch blow molding machine 1 includes a control unit (not shown) that controls a series of operations. The control unit stores an operation program in a memory area (ROM) provided within the control unit, and controls the operations of the injection molding unit 2, blow molding unit 3, removal unit 4, rotating plate 50, etc., by executing the stored operation program.

[0040] In the injection stretch blow molding machine 1, when molten resin is filled into the injection molding die in the injection molding section 2, the body and bottom of the preform are molded in the cavity die 12, and the lip portion of the preform is molded in the lip die 11. After the molding of the preform is complete, the lip die 11 and core die 13 rise, and the preform, with its lip portion held by the lip die 11, is released from the injection molding die. Then, the lip die 11, which has risen to a predetermined position, stops, and the mold opening of the injection molding die is completed.

[0041] Next, the rotating plate 50 rotates, and the lip mold 11, which grips the lip portion of the preform, moves toward the blow molding section 3. When the lip mold 11 reaches a position above the blow molding section 3, the lip mold 11 and the preform it grips descend toward the blow molding section 3. This transfers the preform to the blow molding section 3.

[0042] The preform is transferred to the blow molding section 3, where it is stretched and blown in the blow molding die. This process forms a hollow molded body from the preform.

[0043] Once the molding of the hollow molded body is complete, the blow molding die is opened, and the molded hollow molded body is released from the blow molding die. Subsequently, the lip mold 11 rises while gripping the lip portion of the hollow molded body.

[0044] As the rotating plate 50 rotates, the lip mold 11, which is gripping the lip portion of the hollow molded body, moves towards the removal section 4. When the lip mold 11 reaches a position above the removal section 4, the lip mold 11 descends toward the removal section 4. As a result, the hollow molded body is transferred to the removal section 4.

[0045] Upon reaching the removal section 4, the grip of the hollow molded body lip by the lip mold 11 is released, and the hollow molded body falls toward the container outlet (not shown) of the removal section 4. As a result, the hollow molded body passes through the container outlet and is removed from the injection stretch blow molding machine 1.

[0046] (Molding cycle) The injection stretch blow molding machine 1 continuously performs the following steps in a series: an injection molding step in which a preform is injected and molded in the injection molding section 2; a blow molding step in which the preform molded in the injection molding step is stretch blow molded into a hollow molded body in the blow molding section 3; and a removal step in which the hollow molded body molded in the blow molding step is sent out of the molding machine in the removal section 4.

[0047] The injection stretch blow molding machine 1 has three lip molds 11, which are formed so that the lip molds 11 simultaneously correspond to the injection molding section 2, the blow molding section 3, and the removal section 4.

[0048] The three lip-shaped parts 11 are assembled to the rotating plate 50. The rotating plate 50 is rotated 120 degrees in one direction and stopped, then it descends when it stops, then rises, and then rotates 120 degrees in one direction again. The stopping, descending, and rising movements are repeated in the same manner, so that the corresponding positions of the lip-shaped parts 11 advance in sequence.

[0049] In the injection stretch blow molding machine 1, the three lip molds 11 move sequentially, simultaneously changing their corresponding positions, so that the molding cycle of the hollow molded body and the next molding cycle are each staggered by one process.

[0050] (Extendable rod) Figure 3 is a schematic cross-sectional view showing the inside of a blow molding die during the blow molding process. Figure 4 is a longitudinal cross-sectional view showing a stretched rod.

[0051] The extension rod 20 consists of a rod-shaped portion 21 that extends in the axial direction and a tip portion 22 connected to one end of the rod-shaped portion 21.

[0052] The rod-shaped portion 21 is formed in the shape of a round rod having a straight axis, and its other end in the axial direction is inserted through the blow core 30.

[0053] The tip portion 22 has a shoulder portion 23 that is connected to one end of the rod-shaped portion 21 in the axial direction and extends radially outward from the axis (in the direction away from the axis), a peripheral wall portion 24 that is connected to the shoulder portion 23 and extends toward one side in the axial direction, and a bottom portion 25 that is connected to the end of the peripheral wall portion 24 on one side in the axial direction.

[0054] The shoulder portion 23 is formed extending perpendicularly from the axis around the circumferential direction of the axis. As shown in Figure 3, when the stretching rod 20 is inserted into the preform, the shoulder portion 23 is formed to be in the same horizontal plane as, or near, the lower end of the lip portion of the preform.

[0055] Furthermore, in the present invention, "formed to extend perpendicularly from the axis around the circumferential direction of the axis" also includes cases in which the shoulder portion 23 is formed to extend at an inclination of approximately +5 degrees and -5 degrees with respect to the axis around the circumferential direction of the axis.

[0056] The peripheral wall portion 24 is a substantially cylindrical portion that is connected to the shoulder portion 23 and extends in one direction in the axial direction, and has the same shape as the inner peripheral wall of the preform. In this embodiment, the preform is formed in a shape in which the inner peripheral wall tapers toward the axis toward the bottom of the interior formed on the opposite side of the lip portion, so the peripheral wall portion 24 is formed in a shape parallel to the inner peripheral wall of the preform, that is, the peripheral wall tapers toward the axis toward one direction in the axial direction.

[0057] The shape of the peripheral wall portion 24 is not limited to the shape described above, and it is sufficient if it is formed to be the same shape as the inner peripheral wall of the preform. For example, if the preform has a cylindrical internal space, the peripheral wall may be cylindrical rather than tapering. If the preform is formed in the shape of a rectangular prism or a sphere, the shape of the peripheral wall portion 24 may be set to follow the inner peripheral wall of the preform.

[0058] Furthermore, it is preferable that the peripheral wall portion 24 has a shape that creates a small gap (approximately 0.1 mm to 2.0 mm) between it and the inner peripheral wall of the preform. This allows for smooth insertion into the preform.

[0059] The bottom portion 24 is connected to one end of the peripheral wall portion 23 in the axial direction and has the same shape as the bottom shape inside the preform.

[0060] (Blow molding process) Figure 5 is a flowchart illustrating the blow molding process, where (a) is a flowchart of the blow molding process according to the prior art, and (b) is a flowchart of the blow molding process according to this embodiment. The blow molding process of this embodiment will be described below in comparison with the blow molding process of the prior art.

[0061] (Step S1) In the conventional blow molding process, the blow molding process begins with the lip mold 11 positioned in the blow molding section 3 (step S1). Proceed to step S2.

[0062] (Step S2) In step S2, the preform transferred to the blow molding section 3 is lowered with its lip portion held by the lip mold 11, positioned at the blowing location, and the blow mold is clamped. Proceed to step S3.

[0063] (Step S3) In step S3, the system waits until a predetermined waiting time T1 for the blow core to descend has elapsed. Once the waiting time T1 has elapsed, the system proceeds to step S4.

[0064] (Step S4) In step S4, the blow core 30 descends and is inserted into the lip section together with the extension rod. At this time, the tip of the extension rod is not in contact with the bottom inside the preform. Proceed to step S5.

[0065] (Step S5) In step S5, the system waits until the extension rod waiting time T2 has elapsed. Once the extension rod waiting time T2 has elapsed, the system proceeds to step S6.

[0066] (Step S6) In step S6, the stretching rod is extended and contacts the bottom of the preform, stretching the preform downwards while blow air is supplied to the flow path of the blow core 30. This blows the preform and forms a hollow molded body. Proceed to step S7.

[0067] (Step S7) In step S7, the blow-molded hollow molded body is cooled until a predetermined cooling time T3 has elapsed. Proceed to step S8.

[0068] (Step S8) In step S8, the mold clamping of the blow mold is released and the mold is demolded. Proceed to step S9.

[0069] (Step S9) In step S9, the lip mold 11 is raised, causing the hollow molded body held in the lip mold 11 to rise and be transferred to the removal section 4. In this way, the blow molding process is completed.

[0070] In the blow molding process of this embodiment, steps S1, S2 and steps S7 to S9 perform the same operations as in the blow molding process of the prior art, so their explanation will be omitted to avoid duplication.

[0071] (Step S10) In step S10, the blow core 30 is lowered, and the tip 22 of the extension rod 20 is inserted into the internal space of the preform until the bottom 25 contacts the bottom of the preform. Once the tip 22 reaches the bottom of the preform, the process proceeds to step S11. In step S10, the preform shrinks, causing its inner circumferential wall to contact the circumferential wall portion 24, and is supported by the circumferential wall portion 24. This process of supporting the preform from the inside with the circumferential wall portion 24, as performed in step S10, is also called the preform support process.

[0072] (Step S11) In step S11, the system waits until a predetermined extension rod waiting time T4 has elapsed. Once the extension rod waiting time T4 has elapsed, the system proceeds to step S12.

[0073] (Step S12) In step S12, the stretching rod 20 is extended and contacts the bottom of the preform, stretching the preform downwards, while blow air is supplied to the flow path of the blow core 30. This blows the preform and forms a hollow molded body. The process proceeds to step S7. In step S12, the contact between the inner circumferential wall of the preform and the circumferential wall portion 23 is separated by the blow air. Therefore, step S12 includes a preform separation step.

[0074] (Extending rod waiting time T4) Here, the extension rod waiting time T4 is set to be shorter than the extension rod waiting time T2. The reason for this will be explained.

[0075] The skin layer of the preform shrinks due to integration with the core layer, residual stress from injection molding, and pressure release during mold opening, resulting in variations in thickness depending on the area. For the entire preform to reach a temperature suitable for downward stretching by the stretching rod and blowing in blown air, the preform needs to become amorphous.

[0076] However, as mentioned above, when the thickness of the skin layer changes due to shrinkage, the time required for the preform to become non-crystallized varies from place to place. This increases the time required for the entire preform to reach a temperature suitable for the downward stretching operation by the stretching rod and the blowing of blown air (hereinafter sometimes referred to as the "minimum point"). In other words, the stretching rod extension waiting time T2 in the conventional technology is set to a time that takes into account the change in the thickness of the skin layer.

[0077] In contrast, in this embodiment, the tip portion 22 has a peripheral wall portion 24, and the peripheral wall portion 24 is formed in a shape parallel to the inner peripheral wall of the preform. Furthermore, the tip portion 22 is inserted into the internal space of the preform as soon as step S2 is completed. When the preform begins to shrink, the inner peripheral wall of the preform comes into contact with the peripheral wall portion 24, and the internal space of the preform is reinforced by the peripheral wall portion 24.

[0078] This suppresses inward shrinkage and deformation of the preform in both the longitudinal and radial directions. Therefore, it is possible to suppress changes in the thickness of the skin layer due to preform shrinkage, and thus maintain the thinness of the skin layer at approximately the same thickness as during molding.

[0079] This shortens the time it takes for the entire preform to become noncrystallized, thus reducing the time it takes for the entire preform to reach a temperature suitable for the downward stretching operation by the stretching rod and the blowing of compressed air. Therefore, the stretching rod extension waiting time T4 can be shorter than the stretching rod extension waiting time T2.

[0080] (Shoulder 23) Figure 6 is an enlarged explanatory diagram showing the vicinity of the shoulder portion 23 in step 12. The shoulder portion 23 is formed on the tip portion 22 of the extension rod 20. The shoulder portion 23 is formed to be in a position that is on the same plane as, or near, the lower end of the lip portion (near the connection point with the peripheral wall portion of the preform) when the tip portion 22 is inserted into the internal space of the preform in step 11.

[0081] Because the shoulder portion 23 is formed, the preform is supported by the lip-shaped portion 11 and the tip portion 22, which helps to suppress changes in the thickness of the skin layer due to shrinkage.

[0082] In step 12, when blow air is supplied, the blow air flows down the channel 31 formed in the blow core 30 and reaches the shoulder portion 23. Since the shoulder portion 23 is formed extending perpendicularly from the axis around the circumferential direction of the axis, the blow air changes its course by 90 degrees and travels away from the axis of the preform. As a result, the inner circumferential wall of the preform, which was in contact with the circumferential wall portion 24 due to contraction, is separated from the circumferential wall portion 24, and a channel is formed between the inner circumferential wall of the preform and the circumferential wall portion 24.

[0083] The blown air moves downward, peeling the inner circumferential wall of the preform away from the circumferential wall portion 24, reaching the bottom, and further expanding the preform to form the hollow molded body. By forming the shoulder portion 23 in this way, shrinkage of the preform is suppressed and peeling of the preform can be performed smoothly.

[0084] [Table 1] JPEG2026048528000002.jpg54170

[0085] Table 1 is a comparison table showing an example of forming a hollow molded body using a conventional blow molding process, a comparative example of forming a hollow molded body by performing the blow molding process of the present invention using a conventional stretching rod, and an example of forming a hollow molded body by performing the blow molding process of the present invention using the stretching rod of the present invention.

[0086] In the conventional example, comparative example, and example, the preform was molded from the same material. Specifically, the case in which the preform was molded from polyethylene was described.

[0087] <In the case of a conventional blow molding process> Figure 7 illustrates the blow molding process using a conventional stretching rod. The preform, which has been injection molded in the injection molding section, is transferred to the blow molding section to begin the blow molding process. The preform is lowered with its lip portion held by the lip mold 11, positioned at the blowing location, and the blow mold is clamped.

[0088] Next, wait for 3.0 seconds to elapse as the blow core descent waiting time. After 3.0 seconds, lower the blow core and insert it into the lip section together with the extension rod.

[0089] Next, a waiting period of 4.5 seconds is set for the extension of the stretching rod. After 4.5 seconds, the stretching rod is extended and brought into contact with the bottom of the preform, stretching the preform downwards while blown air is supplied to the flow path of the blow core to form the hollow molded body.

[0090] Then, the blow-molded hollow body is cooled until a predetermined cooling time has elapsed, and after that, the mold clamp of the blow mold is released and the hollow body is demolded.

[0091] Finally, by raising the lip mold, the hollow molded body held in the lip mold is raised and transferred to the removal section.

[0092] In conventional blow molding processes, the waiting time for the blow core to descend is set to 3.0 seconds, and the waiting time for the stretching rod to extend is set to 4.5 seconds. Therefore, the time required for the preform to reach its minimum point is set to 3.0 seconds + 4.5 seconds = 7.5 seconds.

[0093] One hundred hollow molded bodies were formed using a conventional blow molding process. The formed hollow molded bodies were visually inspected for any ruptures, extremely thin areas, or extremely thick areas (severe wall thickness variations). If any hollow molded bodies exhibiting such problems were found, they were deemed unsuitable for molding; otherwise, they were deemed suitable for molding. The evaluation results are shown in Table 1.

[0094] <Examples> A hollow molded body was formed by performing the blow molding process of the present invention using the stretching rod 20. The preform, injection-molded in the injection molding section, is transferred to the blow molding section 3 to begin the blow molding process. The preform is lowered with its lip portion held by the lip mold 11, positioned at the blowing location, and the blow mold is clamped. The preform in this embodiment was molded using the same material and mold as the preform used in the conventional blow molding process described above.

[0095] Next, without setting a waiting time for the blow core to descend, the blow core was lowered, and the blow core 30 was inserted into the lip portion together with the extension rod 20, and the tip portion 22 was inserted into the preform to perform the preform support process.

[0096] Next, the stretching rod was set to wait for 2.0 seconds. After 2.0 seconds, the stretching rod 20 was extended and brought into contact with the bottom of the preform, stretching the preform downwards while blow air was supplied to the flow path of the blow core 30 to form the hollow molded body.

[0097] Then, the blow-molded hollow body was cooled for a predetermined cooling time (the same time as in the conventional blow molding process), and after that, the mold clamp of the blow mold was released and the hollow body was demolded.

[0098] Finally, the lip mold was raised, and the hollow molded body held in the lip mold was raised and transferred to the removal section 4.

[0099] In this embodiment, the waiting time for the blow core to descend was set to 0 seconds, and the waiting time for the extension rod to extend was set to 2.0 seconds. The time until the preform reaches its minimum point was set to 0 seconds + 2.0 seconds = 2.0 seconds.

[0100] The example was performed to form 100 hollow molded bodies, and the formed hollow molded bodies were visually inspected to evaluate whether the form was satisfactory. No ruptures, extremely thin areas, or extremely thick areas were found in any of the hollow molded bodies, indicating good quality.

[0101] <Comparative example in which the blow molding process of the present invention was performed using a conventional stretching rod> A hollow molded body was formed by performing the blow molding process of the present invention using a conventional stretching rod. The preform, injection-molded in the injection molding section, is transferred to the blow molding section 3 to begin the blow molding process. The preform is lowered with its lip portion held by the lip mold 11, positioned at the blowing location, and the blow mold is clamped. The preform in this embodiment was molded using the same material and mold as the preform used in the conventional blow molding process and the embodiment described above.

[0102] Next, without setting a waiting time for the blow core to descend, the blow core was lowered, and the blow core was inserted into the lip portion together with the conventional extension rod. The tip of the conventional extension rod was then inserted into the preform to perform the preform support process.

[0103] Next, a waiting period of 2.0 seconds was set for the extension of the extension rod. After 2.0 seconds, the conventional extension rod was extended and brought into contact with the bottom of the preform, while the preform was stretched downwards. At the same time, blown air was supplied to the flow path of the blow core to form the hollow molded body.

[0104] Then, the blow-molded hollow body was cooled for a predetermined cooling time (the same time as in the conventional blow molding process), and after that, the mold clamp of the blow mold was released and the hollow body was demolded.

[0105] Finally, the lip mold was raised, and the hollow molded body held in the lip mold was raised and transferred to the removal section 4.

[0106] In the comparative example, the waiting time for the blow core to descend was set to 0 seconds, as in the example, and the waiting time for the extension rod to extend was set to 2.0 seconds. The time until the preform reached its minimum point was set to 0 seconds + 2.0 seconds = 2.0 seconds.

[0107] The comparative example was performed to form 100 hollow molded bodies, and the formed hollow molded bodies were visually inspected to evaluate whether they could be formed. Several of the formed hollow molded bodies were found to have ruptures, or areas that were extremely thin or extremely thick (uneven wall thickness), so they were evaluated as unformable. Furthermore, because ruptures and severe uneven wall thickness were observed, it is presumed that the preform was stretch-blow molded while partially failing to reach the minimum point. The results of the example and comparative example are shown in Table 1.

[0108] <Consideration> As shown in Table 1, according to the embodiment of the present invention, the preform could be shaped even with a 5-second reduction in the time to the minimum point compared to the conventional blow molding process. Furthermore, as is clear from the results of the comparative example, in a conventional stretching rod where the tip portion 22 is not formed, it is not possible to suppress the change in the thickness of the preform, and therefore a longer time to the minimum point is required.

[0109] From the above, by performing the preform support process using the stretching rod 20 on which the tip portion 22 having the peripheral wall portion 24 of the present invention is formed, the inner peripheral wall of the preform comes into contact with the peripheral wall portion 24, and the internal space of the preform is reinforced by the peripheral wall portion 24. This demonstrates that it is possible to suppress inward shrinkage and deformation of the preform in both the longitudinal and radial directions.

[0110] Therefore, according to the present invention, it is possible to suppress changes in the thickness of the skin layer due to the shrinkage of the preform, and thus maintain the thinness of the skin layer at approximately the same thickness as when the preform was molded. This shortens the time it takes for the entire preform to become noncrystallized, and thus shortens the time it takes for the entire preform to reach a temperature suitable for the downward stretching operation by the stretching rod and the blowing of blown air. [Explanation of Symbols]

[0111] 1. Injection stretch blow molding machine 2 Injection molding section 3. Blow molding section 4. Removal section 13-core type 20 Extension Rods 21 Rod-shaped part 22 Tip 23 Shoulder 24 Peripheral wall section 25 Bottom 30 Blow Core 31 Flow channels 50 Rotating Plates

Claims

1. An injection molding process in which a synthetic resin material is melted and a bottomed cylindrical preform is injection molded in an injection molding section, The process includes a blow molding step to obtain a hollow molded body by stretch blow molding the preform in a blow molding section, The blow molding process described above is: A preform support step involves inserting the tip of the stretching rod into the preform and bringing the preform and the tip into contact to support the preform. A method for manufacturing a hollow molded article, comprising a preform peeling step of supplying blown air into the preform to release contact between the preform and the tip.

2. A stretching rod used in a method for manufacturing a hollow molded body according to claim 1, comprising a rod-shaped portion and a tip portion formed in connection with one end of the rod-shaped portion, The extension rod is characterized in that the tip portion has a circumferential wall portion that has the same shape as the inner circumferential wall of the preform.

3. The extension rod according to claim 3, characterized in that the tip portion has a shoulder portion that extends in a direction perpendicular to the axis of the rod-shaped portion.

4. An injection molding section that melts synthetic resin material and injection molds a bottomed cylindrical preform, A blow molding section that forms a hollow molded body by stretching a stretching rod to form the aforementioned preform, An injection stretch blow molding machine having a removal section for removing the hollow molded body from the machine, The blow molding process performed in the blow molding section is as follows: A preform support step involves inserting the tip of the stretching rod into the preform and bringing the preform and the tip into contact to support the preform. An injection stretch blow molding machine characterized by performing a preform peeling step of supplying blow air into the preform to release contact between the preform and the tip.

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