Method for molding hollow molded body, stretch rod and injection stretch blow molding machine used therein

Abstract

The present invention provides a method for molding a hollow molded article, which can suppress deformation of a preform and shorten the molding cycle of the hollow molded article, and a stretch rod and an injection stretch blow molding machine used therein. [Solution] In the method for manufacturing a hollow molded body, an injection molding process for injection molding a preform and a blow molding process for obtaining a hollow molded body by stretch blow molding the preform in a blow molding section are carried out, and in the blow molding process, a preform supporting process for inserting the tip of a stretch rod into the preform and bringing the preform into contact with the tip to support the preform, and a preform peeling process for supplying blow air into the preform to release the contact between the preform and the tip are carried out.

Description

[Technical field]

[0001] The present invention relates to a method for molding a hollow molded article, and a stretch rod and an injection stretch blow molding machine used therein. [Background technology]

[0002] 2. Description of the Related Art Injection stretch blow molding machines are used to manufacture hollow molded articles such as synthetic resin bottles and cups.

[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 the 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 an ejection section that sends the hollow molded body blow molded in the blow molding section out of the machine.

[0004] Also known as an injection stretch blow molding machine is one that is equipped with a temperature adjustment process section that adjusts the temperature of the preform injection molded in the injection molding section.

[0005] The injection molding section has an injection mold including an upper mold which is an injection core mold, a lower mold which is an injection cavity mold, and a lip mold. The lip mold supports the injection molded preform and transports the preform from the injection molding section to the blow molding section.

[0006] The preform molded in the injection molding section is cooled, which hardens the outer and inner surfaces and forms a hard skin layer. The speed at which the skin layer is formed and its properties, such as hardness, vary depending on the type of resin used as the raw material for the preform. Therefore, the timing at which the preform is released from the injection mold (adjusting the injection cooling time) and the time until blowing in the blow molding section are adjusted according to the type of resin to mold the desired container.

[0007] The blow molding section has a blow molding die equipped with a split blow mold and a lip mold located corresponding to the blow molding section. The blow molding section further has a stretch rod that stretches the preform placed in the blow molding die. The preform is stretched by pushing down the side (body) and bottom of the preform with the stretch rod.

[0008] The blow molding section also includes a blowing means for blowing air into the preform when the preform is stretched using the stretching rod. The blowing means inflates the preform, and the sides and bottom of the preform are pressed against the inner surface of the blow molding die to form a hollow molded body.

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

[0010] The hollow molded body moved to the removal section is released from the lip mold by opening the lip mold, and reaches the removal section. As a result, the hollow molded body located at the removal section is sent out of the injection stretch blow molding machine. The lip mold that released the hollow molded body moves again to the injection molding section by the rotation of the turntable.

[0011] In this manner, in the injection stretch blow molding machine, the preform injection molded in the injection molding section is released from the injection molding die while being supported by the lip mold and moved to the blow molding section, where the preform is stretched by a stretch rod and blown in with blow air to produce a hollow molded body. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Patent No. 7039089 Summary of the Invention [Problem to be solved by the invention]

[0013] The preform molded in the injection molding section is cooled to harden the outer and inner surfaces and form a hard skin layer. At this time, the core layer sandwiched between the outer and inner skin layers is still at a high temperature and the resin is in a molten state.

[0014] The preform is transported to the blow molding section in this state, and the heat from the core layer warms the skin layer, melting it and integrating it with the core layer. The preform is held in this state 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 stretch rod and the blowing of the blow air.

[0015] The same is true for injection stretch blow molding machines equipped with a temperature control step, in which the preform is held for an intermediate time after the temperature control step is completed until the entire preform reaches a temperature suitable for the downward stretching action by the stretch rods and for the blowing of blow air in the blow molding step.

[0016] After the preform is held for an intermediate time, it is pressed down by a stretching rod to perform a stretching operation and at the same time, blow air is blown into it to blow-mold a hollow molded body.

[0017] FIG. 8 is a diagram illustrating deformation of the preform, where (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 in an advanced state of shrinkage.

[0018] As shown in Fig. 8(a), the preform immediately after being transferred to the blow molding section retains the injection-molded shape. However, as described above, the skin layer of the preform melts and becomes integrated with the core layer, and the preform shrinks over time due to residual stress caused by injection, pressure release caused by mold opening, thermal melting, etc., and the shape deforms from the injection-molded shape (see Fig. 8(b)).

[0019] The intermediate time is empirically determined and set based on the shape, material, molding temperature, cooling temperature, etc. of the preform so that it is approximately the same time as the point at which the crystallized skin layer of the preform melts, becomes integrated with the core layer, and becomes 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, and when the preform deforms due to shrinkage, the thickness of the skin layer increases, which also changes the minimum point. Therefore, the intermediate time must be further extended in order to match the end point of the intermediate time with the point at which the preform reaches the minimum point.

[0021] If the preform is stretched by the stretch rod and blown with air is supplied while the preform is in a deformed state, there is a problem that uneven thickness and bursting of the hollow molded article may occur.

[0022] An object of the present invention is to provide a method for molding a hollow molded body, which is capable of suppressing deformation of a preform and shortening the molding cycle of the hollow molded body, and a stretch rod and an injection stretch blow molding machine used therein. [Means for solving the problem]

[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 process includes: a preform supporting step of inserting a tip end of a stretch rod into the preform and bringing the preform into contact with the tip end to support the preform; and a preform peeling step of supplying blow air into the preform to release the contact between the preform and the tip end.

[0024] The present invention also relates to a stretch rod used in the method for producing a hollow molded body, the stretch rod having a rod-shaped portion and a tip portion formed continuous to one end of the rod-shaped portion, The tip portion is a stretch rod having a peripheral wall portion having the same shape as the inner peripheral wall of the preform.

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

[0026] The present invention also provides an injection molding unit that melts a synthetic resin material and injection molds a bottomed cylindrical preform; a blow molding section for stretch-blow-molding the preform by stretching a stretch rod to form a hollow molded body; and a removal unit for removing the hollow molded body from the injection stretch blow molding machine, The blow molding process performed in the blow molding section is a preform supporting step of inserting a tip end of a stretch rod into the preform and bringing the preform into contact with the tip end to support the preform; and a preform peeling step of supplying blow air into the preform to release the contact between the preform and the tip end portion. Effect of the Invention

[0027] According to the present invention, the blow molding process includes a preform supporting process in which the tip of a stretch rod is inserted into the preform and brought into contact with the tip to support the preform, and a preform peeling process in which blow air is supplied into the preform to release the contact between the preform and the tip. Therefore, the preform placed in the blow molding section can be supported by the tip until the entire preform reaches a temperature suitable for the downward stretching action by the stretch rod and the blowing of the blow air.

[0028] This makes it possible to suppress the 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 shrinkage of the preform. As a result, 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 action by the stretch rod and for blowing in the blow air. This makes it possible to realize a molding method for a hollow molded body that suppresses deformation of the preform and shortens the molding cycle of the hollow molded body.

[0029] According to the present invention, the tip portion has a peripheral wall portion having the same shape as the inner peripheral wall of the preform, and therefore can reliably support the inner peripheral wall of the preform, which is the area where thickness layer changes are most likely to occur, thereby suppressing deformation of the preform and shortening the molding cycle of the hollow molded body.

[0030] According to the present invention, the tip portion is formed with a shoulder extending in a direction perpendicular to the axis of the rod-shaped portion, so that by supplying blow air, air pressure can be applied in a direction in which the preform and the tip portion move apart. Therefore, even if the preform is supported at the tip portion, the preform and the tip portion can be peeled away from each other, so that a decrease in the yield of hollow molded bodies can be suppressed.

[0031] Furthermore, according to the present invention, since the injection stretch blow molding machine executes a preform supporting process and a preform peeling process, 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 description of the drawings]

[0032] [Figure 1] FIG. 1 is a schematic plan view of an injection stretch blow molding machine 1. [Diagram 2] FIG. 1 is a front view of an injection stretch blow molding machine 1. [Diagram 3] FIG. 2 is a schematic cross-sectional view showing the inside of a blow molding die during a blow molding process. [Figure 4]FIG. 2 is a longitudinal sectional view showing a stretch rod. [Diagram 5] 1A and 1B are flowcharts illustrating a blow molding process, where FIG. 1A is a flowchart of the blow molding process according to a conventional technique, and FIG. 1B is a flowchart of the blow molding process according to the present embodiment. [Figure 6] 1 is an enlarged explanatory view showing the vicinity of a shoulder portion 23 at a step 12. FIG. [Figure 7] FIG. 1 is a diagram illustrating a comparative example using a conventional stretch rod. [Figure 8] 1A and 1B are diagrams illustrating deformation of a preform, where (a) is a cross-sectional view showing a preform immediately after being transferred to a blow molding section, and (b) is a cross-sectional view showing a preform in an advanced state of shrinkage. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0034] (Injection stretch blow molding machine) Fig. 1 is a schematic plan view of an injection stretch blow molding machine 1 according to this embodiment. Fig. 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 Figs. 1 and 2.

[0035] 1, an injection stretch blow molding machine 1 according to this embodiment includes three stations: an injection molding section 2, a blow molding section 3, and an ejection section 4. The injection molding section 2, the blow molding section 3, and the ejection section 4 are arranged circumferentially at intervals of approximately 120° from each other.

[0036] A hot runner mechanism (not shown) provided in the injection molding section 2 is connected to an 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 the present invention, it is preferable to use an olefin resin represented by polyethylene, polypropylene, etc.

[0037] The injection stretch blow molding machine 1 further includes a rotating plate 50 disposed above each station for transporting the preform or hollow molded body to the next station. The rotating plate 50 is provided within an intermediate base 51, and stops for a predetermined time when it reaches a position above each station.

[0038] A lip mold 11 for forming the lip portion of the preform and the hollow molded body is provided on the lower surface of the rotating plate 50. The lip mold 11 holds the lip portion of the preform and the hollow molded body, and as the rotating plate 50 rotates, the preform and the 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, for example, a memory area (ROM) provided in the control unit, and controls operations in the injection molding unit 2, the blow molding unit 3, the take-out unit 4, the rotating plate 50, etc. by executing the stored operation program.

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

[0041] Next, the rotating plate 50 rotates, and the lip mold 11 gripping 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 gripped by it descend toward the blow molding section 3. As a result, the preform is transferred to the blow molding section 3.

[0042] The preform is transferred to the blow molding section 3 and stretch-blowed in a blow molding die in the blow molding section 3. In this way, a hollow molded body is formed from the preform.

[0043] When the molding of the hollow molded body is completed, the blow molding die is opened and the molded hollow molded body is released from the blow molding die. After that, the lip die 11 rises while gripping the lip portion of the hollow molded body.

[0044] The rotating plate 50 rotates, and the lip mold 11 gripping the lip portion of the hollow molded body moves toward 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] When the hollow molded body reaches the removal section 4, the lip of the hollow molded body is released from the lip mold 11, and the hollow molded body falls toward a container removal opening (not shown) of the removal section 4. As a result, the hollow molded body passes through the container removal opening and is removed to the outside of the injection stretch blow molding machine 1.

[0046] (Molding cycle) The injection stretch blow molding machine 1 continuously carries out an injection molding process of injection molding a preform in an injection molding section 2, a blow molding process of stretch blow molding the preform molded in the injection molding process into a hollow molded body in a blow molding section 3, and an ejection process of sending the hollow molded body molded in the blow molding process out of the molding machine in a ejection section 4.

[0047] In the injection stretch blow molding machine 1, lip dies 11 are provided at three locations so that the lip dies 11 simultaneously correspond to the three positions of the injection molding section 2, the blow molding section 3, and the removal section 4.

[0048] The three lip dies 11 are attached to a rotating plate 50, and the rotating plate 50 is rotated 120 degrees in one direction and stopped, and when it stops, it descends, then ascends, and after that it rotates 120 degrees in one direction again, and the same stopping, descending, and ascending movements are repeated thereafter, so that the corresponding positions of the lip dies 11 advance in sequence.

[0049] In the injection stretch blow molding machine 1, the three lip dies 11 simultaneously change their corresponding positions and move in sequence, so that the molding cycle for a hollow molded body and the next molding cycle proceed with a one-step lag between each other.

[0050] (extension rod) Fig. 3 is a schematic cross-sectional view showing the inside of a blow molding die during a blow molding process, and Fig. 4 is a vertical cross-sectional view showing a stretch rod.

[0051] The stretch rod 20 is composed of a rod-shaped portion 21 extending 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 a round rod shape having an axis that extends straight, and the other end in the axial direction is inserted into the blow core 30.

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

[0054] The shoulder portion 23 is formed so as to extend perpendicularly from the axis line around the circumferential direction of the axis line. As shown in Fig. 3, the shoulder portion 23 is formed at a position that forms the same horizontal plane as the lower end of the lip portion of the preform or at a position close to the position when the stretch rod 20 is inserted into the preform.

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

[0056] The peripheral wall portion 24 is a generally 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. Since the preform of this embodiment is formed so that the inner peripheral wall tapers toward the axis toward the inside bottom formed on the opposite side to the lip portion, the peripheral wall portion 24 is formed in a shape that is parallel to the inner peripheral wall of the preform, that is, so that the peripheral wall tapers toward the axis as it moves toward one direction in the axial direction.

[0057] The shape of the peripheral wall portion 24 is not limited to the above-mentioned shape, and may be formed to 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 tapered. If the preform is formed to be a square prism or a sphere, the shape of the peripheral wall portion 24 may be set to fit the inner peripheral wall of the preform.

[0058] Moreover, the peripheral wall portion 24 is preferably shaped so that a small gap (about 0.1 mm to 2.0 mm) is formed between it and the inner peripheral wall of the preform, which allows it to be smoothly inserted into the preform.

[0059] The bottom portion 24 is continuous with one end portion 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) 5 is a flow chart for explaining a blow molding process, where (a) is a flow chart for the blow molding process according to the conventional technology, and (b) is a flow chart for the blow molding process according to this embodiment. Below, the blow molding process of this embodiment will be explained while comparing it with the blow molding process of the conventional technology.

[0061] (Step S1) In the conventional blow molding process, the blow molding process starts with the lip mold 11 being placed in the blow molding section 3 (step S1). The process proceeds to step S2.

[0062] (Step S2) In step S2, the preform transferred to the blow molding section 3 is lowered with its lip portion clamped by the lip mold 11, and placed at the blow position, where the blow mold is clamped.The process proceeds to step S3.

[0063] (Step S3) In step S3, the process waits until a predetermined blow core lowering waiting time T1 has elapsed. When the blow core lowering waiting time T1 has elapsed, the process proceeds to step S4.

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

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

[0066] (Step S6) In step S6, the stretch rod is stretched to contact the bottom inside the preform, stretching the preform downward and simultaneously supplying blow air to the flow passage of the blow core 30. This causes the preform to be blown and a hollow molded body is formed. Then, the process proceeds 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, and then the process proceeds to step S8.

[0068] (Step S8) In step S8, the blow mold is released and the mold is released, and the process proceeds to step S9.

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

[0070] In the blow molding process of this embodiment, steps S1, S2 and steps S7 to S9 are the same as those in the blow molding process according to the conventional technology, and therefore descriptions thereof will be omitted to avoid duplication.

[0071] (Step S10) In step S10, the blow core 30 is lowered and the tip 22 of the stretch rod 20 is inserted into the internal space of the preform until the bottom 25 contacts the bottom of the interior of the preform. When the tip 22 reaches the bottom of the interior of the preform, the process proceeds to step S11. In step S10, the inner wall of the preform comes into contact with the peripheral wall portion 24 due to shrinkage, and the preform is supported by the peripheral wall portion 24. This process of supporting the preform from the inside by the peripheral wall portion 24, which is performed in step S10, is also called a preform supporting process.

[0072] (Step S11) In step S11, the process waits until a predetermined stretch rod elongation waiting time T4 has elapsed. When the stretch rod waiting time T4 has elapsed, the process proceeds to step S12.

[0073] (Step S12) In step S12, the stretch rod 20 is extended and contacts the bottom inside the preform, stretching the preform downward while blow air is supplied to the flow path of the blow core 30. This blows the preform and shapes a hollow molded body. Proceed to step S7. In step S12, the contact between the inner peripheral wall of the preform and the peripheral wall portion 23 is peeled off by the blow air. Therefore, step S12 includes a preform peeling step.

[0074] (Extension rod extension waiting time T4) Here, the stretch rod extension waiting time T4 is set to a time shorter than the stretch rod extension waiting time T2, the reason for which will be explained below.

[0075] The skin layer of the preform shrinks and its thickness varies depending on the location due to integration with the core layer, residual stress due to injection, pressure release due to mold opening, etc. In order for the entire preform to reach a temperature suitable for the downward stretching action by the stretch rod and for blowing air, the preform needs to be decrystallized.

[0076] However, as described above, when the thickness of the skin layer changes due to shrinkage, the time required for the preform to become amorphized varies depending on the location, and the time required for the entire preform to reach a temperature suitable for the downward stretching action by the stretch rod and for blowing air (hereinafter sometimes referred to as the "minimum point") becomes longer. In other words, the stretch rod stretching waiting time T2 in the prior art 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, which 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 immediately after 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 makes it possible to suppress the shrinkage and deformation of the preform in the longitudinal and radial directions, and therefore to suppress changes in the thickness of the skin layer due to shrinkage of the preform, so that the thickness of the skin layer can be maintained at approximately the same thickness as when it was molded.

[0079] This shortens the time until the entire preform becomes amorphized, and therefore shortens the time until the entire preform reaches a temperature suitable for the downward stretching operation by the stretch rod and the blowing of the blow air. Therefore, the stretch rod extension waiting time T4 can be set to be shorter than the stretch rod extension waiting time T2.

[0080] (Shoulder 23) 6 is an enlarged explanatory view showing the vicinity of the shoulder portion 23 in step 12. The shoulder portion 23 is formed at the tip portion 22 of the stretch rod 20. The shoulder portion 23 is formed so as to be located in a position that is flush with the lower end of the lip portion (in the vicinity of the connection position with the peripheral wall portion of the preform) or in the vicinity thereof when the tip portion 22 is inserted into the internal space of the preform in step 11.

[0081] By forming the shoulder portion 23, the preform is supported by the lip mold 11 and the tip portion 22, so that the change in thickness of the skin layer due to shrinkage can be suppressed.

[0082] When blow air is supplied in step 12, it flows down the flow passage 31 formed in the blow core 30 and reaches the shoulder 23. Since the shoulder 23 is formed extending perpendicularly from the axis around the circumferential direction of the axis, the blow air is changed in course by 90 degrees and proceeds in a direction away from the axis of the preform. As a result, the inner peripheral wall of the preform that has been in contact with the peripheral wall 24 due to shrinkage is peeled off from the peripheral wall 24, and a flow passage is formed between the inner peripheral wall of the preform and the peripheral wall 24.

[0083] The blown air advances downward while peeling off the inner peripheral wall of the preform from the peripheral wall portion 24, reaches the bottom, and further spreads the preform to form a hollow molded body. By forming the shoulder portion 23 in this manner, shrinkage of the preform can be suppressed and the preform can be smoothly peeled off.

[0084] [Table 1] JPEG0007672757000002.jpg54170

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

[0086] In all of the conventional example, comparative example, and working example, the preforms were molded from the same material. Specifically, the preforms were molded from polyethylene.

[0087] <In the case of conventional blow molding process> FIG. 7 is a diagram illustrating a blow molding process when a stretch rod according to the prior art is used. The preform that has been injection molded in the injection molding section is transferred to the blow molding section, where the blow molding process begins. The preform, with its lip portion clamped by the lip mold 11, is lowered to the blow position, and the blow mold is clamped.

[0088] Next, the blow core is waited for 3.0 seconds to elapse as a blow core lowering waiting time, and after 3.0 seconds has elapsed, the blow core is lowered and inserted into the lip portion together with the stretch rod.

[0089] Next, the stretch rod is waited for 4.5 seconds to elapse as a stretch rod extension waiting time, and after 4.5 seconds has elapsed, the stretch rod is extended to contact the bottom inside the preform while stretching the preform downward and supplying blow air to the flow path of the blow core to form a hollow molded body.

[0090] The blow molded hollow body is cooled until a predetermined cooling time has elapsed, after which the blow mold is released from the clamping state to release the hollow body.

[0091] Finally, the lip mold is raised to raise the hollow molded body held by the lip mold and transfer it to the removal section.

[0092] In the conventional blow molding process, the waiting time for the blow core to descend is set to 3.0 seconds, and the waiting time for the stretch rod to extend is set to 4.5 seconds, so that the time it takes for the preform to reach its minimum point is set to 3.0 seconds + 4.5 seconds = 7.5 seconds.

[0093] 100 hollow molded bodies were molded using the blow molding process of the conventional technology, and the molded hollow molded bodies were visually checked for the presence of ruptures, or extremely thin or thick areas (strong thickness deviations). If any hollow molded bodies with such problems were found, they were rated as not moldable, and if none were found, they were rated as moldable. The evaluation results are shown in Table 1.

[0094] <Example> The blow molding process of the present invention was carried out using a stretch rod 20 to form a hollow molded body. The preform injection molded in the injection molding section is transferred to the blow molding section 3, where the blow molding process begins. The preform, with its lip portion clamped by the lip mold 11, is lowered and placed at the blow position, and the blow mold is clamped. The preform in this example is molded using the same material and mold as the preform used in the conventional blow molding process described above.

[0095] Next, without setting a blow core lowering waiting time, the blow core was lowered, and the blow core 30 was inserted into the lip portion together with the stretch rod 20, and the tip portion 22 was inserted into the inside of the preform to carry out the preform supporting step.

[0096] Next, the stretch rod was held for a waiting time of 2.0 seconds, after which the stretch rod 20 was extended to contact the bottom of the interior of the preform, thereby stretching the preform downward and supplying blow air to the flow path of the blow core 30 to form a hollow molded body.

[0097] The blow-molded hollow body was cooled until a predetermined cooling time (the same time as in the case of a conventional blow molding process) had elapsed, after which the blow mold was released from its clamping state to release the hollow body.

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

[0099] In this embodiment, the blow core lowering waiting time was set to 0 seconds, the stretch rod extension waiting time was set to 2.0 seconds, and the time until the preform reached the minimum point was set to 0 seconds + 2.0 seconds = 2.0 seconds.

[0100] 100 hollow molded bodies were molded by carrying out the embodiment, and the molded hollow molded bodies were visually inspected to evaluate whether they could be molded. No ruptures or extremely thin or thick areas were found in any of the hollow molded bodies, and they were in good condition.

[0101] <Comparative Example in which the blow molding process of the present invention was carried out using a conventional stretch rod> The blow molding process of the present invention was carried out using a conventional stretch rod to form hollow molded bodies. The preform injection molded in the injection molding section is transferred to the blow molding section 3, where the blow molding process begins. The preform, with its lip portion clamped by the lip mold 11, is lowered and placed at the blow position, and the blow mold is clamped. The preform in this example was molded using the same material and mold as the preform used in the conventional blow molding process and in the example described above.

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

[0103] Next, the stretch rod was held for a waiting time of 2.0 seconds, after which the conventional stretch rod was extended to contact the bottom of the inside of the preform while stretching the preform downward and supplying blow air to the flow path of the blow core to form a hollow molded body.

[0104] The blow-molded hollow body was cooled until a predetermined cooling time (the same time as in the case of a conventional blow molding process) had elapsed, after which the blow mold was released from its clamping state to release the hollow body.

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

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

[0107] A comparative example was carried out to mold 100 hollow molded bodies, and the molded hollow molded bodies were visually inspected to evaluate whether they could be molded. Several of the molded hollow molded bodies were found to have ruptures or extremely thin or extremely thick areas (uneven thickness), and therefore were evaluated as not being moldable. In addition, because ruptures and strong uneven thickness were observed, it is presumed that the preforms were stretch-blow molded in a state where they had not reached the minimum point in some areas. The results of the examples and comparative examples 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 if the time to the minimum point was shortened by 5 seconds compared to the conventional blow molding process. Also, as is clear from the results of the comparative example, the conventional stretch rod without the tip portion 22 cannot suppress the change in thickness of the preform, so it requires a longer time to reach the minimum point.

[0109] From the above, by carrying out the preform supporting process using the stretch rod 20 having the tip portion 22 with the peripheral wall portion 24 of the present invention, 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 makes it possible to suppress inward shrinkage and deformation of the preform in the longitudinal and radial directions.

[0110] Therefore, according to the present invention, since the change in thickness of the skin layer due to shrinkage of the preform can be suppressed, the thickness of the skin layer can be maintained at approximately the same thickness as when the preform was molded. This shortens the time until the entire preform becomes amorphized, and therefore shortens the time until the entire preform reaches a temperature suitable for the downward stretching operation by the stretch rod and the blowing of the blow 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 rod 21 Rod-shaped part 22 Tip 23 Shoulder 24 Peripheral wall section 25 Bottom 30 Blow Core 31 Flow Path 50 Rotating Plate

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; A blow molding step of obtaining a hollow molded body by stretch blow molding the preform in a blow molding section, The blow molding process includes: a preform supporting step of inserting a tip end of a stretch rod into the preform and bringing the preform into contact with the tip end to support the preform; A preform peeling step of supplying blow air into the preform to release contact between the preform and the tip portion, The stretch rod has a rod-shaped portion and a tip portion formed continuous with one end of the rod-shaped portion, A method for producing a hollow molded article, wherein the tip portion has a peripheral wall portion having the same shape as an inner peripheral wall of the preform.

2. A stretching rod used in the method for producing a hollow molded body according to claim 1, A stretch rod, wherein the tip portion is formed with a shoulder portion extending in a direction perpendicular to the axis of the rod-shaped portion.

3. an injection molding section that melts a synthetic resin material and injection molds a bottomed cylindrical preform; a blow molding section for stretch-blow-molding the preform by stretching a stretch rod to form a hollow molded body; and a removal unit for removing the hollow molded body from the injection stretch blow molding machine, The blow molding process performed in the blow molding section is a preform supporting step of inserting a tip end of a stretch rod into the preform and bringing the preform into contact with the tip end to support the preform; A preform peeling step is carried out in which blow air is supplied into the preform to release the contact between the preform and the tip portion, The stretch rod has a rod-shaped portion and a tip portion formed continuous with one end of the rod-shaped portion, 2. An injection stretch blow molding machine comprising: a tip portion having a peripheral wall portion having the same shape as an inner peripheral wall of the preform;

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