Preform, method for producing same, and method for producing container

Abstract

Provided is a preform with which formation of a seal part to a high position on a side surface of the preform can be suppressed without reduction in an outer diameter of a parison.　The present invention provides a bottomed cylindrical preform. The preform is a direct blow-molded body. When an outer diameter at an open end of the preform is D1, the total height of the preform is L, and an outer diameter at a site where the outer diameter is maximized within the range of 0-0.2 L from the lower end of the preform is D, D1 / D is less than 1.

Description

Preform and manufacturing method thereof, and container manufacturing method

[0001] The present invention relates to a preform that can be suitably used in biaxially stretched blow molding, a method for producing the same, and a method for producing a container.

[0002] Patent Document 1 discloses a preform for biaxially stretched blow molding formed by direct blow molding.

[0003] JP 2016-101733 A

[0004] A preform formed by direct blow molding has a long, narrow seal formed at the bottom by welding the opposing surfaces of a cylindrical parison. This seal has relatively low strength and poor appearance. Therefore, if this seal is formed at a high position on the side of the preform, there are problems such as the preform being prone to rupture when the preform is biaxially stretched blow molded, or the seal mark being likely to be left on the side of the container formed by biaxial stretch blow molding. For this reason, it is desirable to prevent the seal from being formed at a high position on the side of the preform.

[0005] Generally, the longitudinal length of the seal portion is proportional to the outer diameter of the parison used in direct blow molding, so by reducing the outer diameter of the parison, it is possible to prevent the seal portion from being formed at a high position on the side surface of the preform. However, the smaller the outer diameter of the parison, the more difficult it becomes to blow air into the parison during direct blow molding, so it is desirable to prevent the seal portion from being formed at a high position on the side surface of the preform by a method other than reducing the outer diameter of the parison.

[0006] The present invention has been made in consideration of these circumstances, and provides a preform that can prevent the seal portion from being formed at a high position on the side of the preform without reducing the outer diameter of the parison.

[0007] According to the present invention, the following inventions are provided. [1] A cylindrical preform with a bottom, the preform being a direct blow-molded article, wherein D1 is the outer diameter at the open end of the preform, L is the total height of the preform, and D is the outer diameter at a portion of the preform where the outer diameter is largest within a range of 0 to 0.2L from the bottom end, so that D1 / D is less than 1. [2] The preform according to [1], wherein D1 / D is 0.85 or less. [3] The preform according to [1] or [2], wherein D1 / D is 0.50 or more. [4] A method for producing a preform according to any one of [1] to [3], comprising a step of forming a preform by direct blow-molding a cylindrical parison in a molten state, wherein D2 is the outer diameter of the parison, and D2 / D is 0.70 or less. [5] The method according to [4], wherein D2 / D1 is 0.60 or more. [6] A method for manufacturing a container, comprising a step of biaxially stretching blow molding a preform, wherein the preform is the preform described in any one of [1] to [3], and the biaxially stretching blow molding has a primary molding step and a secondary molding step, in which the preform is molded into an intermediate molded body having a shape between the preform and the container in the primary molding step, and the intermediate molded body is molded into the shape of the container in the secondary molding step.

[0008] In the preform of the present invention, the outer diameter D near the bottom is larger than the outer diameter D1 at the open end. If the outer diameter of the parison is constant, the larger the outer diameter D near the bottom, the lower the position of the longitudinal end of the seal portion. Therefore, according to the present invention, it is possible to prevent the seal portion from being formed at a high position on the side surface of the preform without reducing the outer diameter of the parison.

[0009] In addition, preforms are generally formed by injection molding, and in injection molding, if the outer diameter D near the bottom is made larger than the outer diameter D1 at the open end, an undercut occurs, making it difficult to make the outer diameter D near the bottom larger than the outer diameter D1 at the open end. For this reason, it has traditionally been recognized that the outer diameter D near the bottom of a preform is generally the same as or smaller than the outer diameter D1 at the open end, and this configuration is also used in Patent Document 1. In the present invention, despite this general recognition, the inventors realized that in direct blow molding, it is easy to make the outer diameter D near the bottom larger than the outer diameter D1 at the open end, and that by adopting such a configuration, it is possible to lower the position of the longitudinal end of the seal portion that is inevitably formed in direct blow molding, and this led to the completion of the present invention.

[0010] 2A is a perspective view of a preform 1 according to one embodiment of the present invention. The dashed-dotted lines in the figure represent the boundary lines where the curvature of the faces constituting the surface shape changes. The same applies to the other figures. 2A and 2B are a front view and a left side view, respectively, of the preform 1. This is a cross-sectional view showing the state immediately before inserting a blow pin 11 into the parison 6 in the manufacturing process of the preform 1. This is a cross-sectional view showing the state after inserting the blow pin 11 into the parison 6 from the state of FIG. 3 and then injecting pressurized fluid into the parison 6 to form the parison 6. This is a left side view showing the state after biaxially stretch blow molding the preform 1 to form a container 12.

[0011] The following describes embodiments of the present invention. The various features described in the following embodiments can be combined with each other. Each feature constitutes an invention independently. Elements in the following embodiments that are not defined in the claims are optional and can be omitted. Numerical values ​​disclosed in the following description may have any number of "0"s (e.g., one or two) added to the end. For example, "1.4" may have one or two "0"s added to the end to make it "1.40" or "1.400." Furthermore, when drawings with subnumbers (e.g., Figures 1A and 1B) are included, a reference to the drawing without the subnumber (e.g., Figure 1) refers to all drawings with the subnumbers (e.g., Figures 1A and 1B in the above example).

[0012] 1. Structure of Preform 1 A preform 1 according to one embodiment of the present invention will be described with reference to FIGS. 1 and 2. The preform 1 is used to manufacture a molded article, such as a container 12 shown in FIG. 5, by biaxial stretch blow molding, as described below. The preform 1 is cylindrical with a bottom, and includes a mouth portion 2 having an open end 1a and a main body portion 3. The preform 1 is provided with a flange 9, with the portion of the flange 9 closer to the open end 1a than the lower surface 9b thereof being the mouth portion 2, and the remaining portion being the main body portion 3. In biaxial stretch blow molding, the shape of the mouth portion 2 does not change, but the shape of the main body portion 3 does. The mouth portion 2 is provided with an engaging portion 2a, to which a mouth attachment member, such as a cap or pump, can be attached. In this embodiment, the engaging portion 2a is a male threaded portion 2c having an intermittent portion 2b, allowing a screw-type mouth attachment member to be attached to the mouth portion 2 in a stoppered manner. The flange 9 is configured to support the mouth portion 2 when the mouth attachment member is attached.

[0013] The main body 3 includes a barrel 4 and a bottom 5. The barrel 4 is disposed between the mouth 2 and the bottom 5. Of the main body 3, the portion that is visible when the preform 1 is viewed from the bottom 5 side along the direction in which the central axis C of the mouth 2 extends is the bottom 5, and the remaining portion is the barrel 4. The preform 1 is a direct blow molded article, and the main body 3 has an elongated seal portion 7 formed by sandwiching a cylindrical parison 6 between a pair of split molds 10 and welding the opposing surfaces of the parison 6 together during direct blow molding, as shown in FIG.

[0014] The seal portion 7 has a relatively low strength and an unattractive appearance. Therefore, if the seal portion 7 is formed at a high position on the preform 1, there are problems in that the preform 1 is likely to rupture when the preform 1 is biaxially stretched and blow-molded, and that a mark of the seal portion 7 is likely to be left on the side surface 12a (shown in FIG. 5) of the container 12 formed by biaxial stretching and blow-molding. For this reason, it is desirable to prevent the seal portion 7 from being formed at a high position on the side surface 1c of the preform 1.

[0015] Generally, the longitudinal length of the seal portion 7 is proportional to the outer diameter of the parison 6 used in direct blow molding, so by reducing the outer diameter of the parison 6, it is possible to prevent the seal portion 7 from being formed at a high position on the preform 1. However, the smaller the outer diameter of the parison 6, the more difficult it becomes to blow a pressurized fluid such as pressurized air into the parison 6 during direct blow molding, so it is desirable to prevent the seal portion 7 from being formed at a high position on the preform 1 by a method other than reducing the outer diameter of the parison 6. From the viewpoint of improving seal strength, it is preferable for the seal portion 7 to protrude from the bottom portion 5, but it does not have to protrude.

[0016] In this embodiment, as shown in Fig. 2A, if the outer diameter at the open end 1a of the preform 1 is D1 and the total height of the preform 1 is L, and the outer diameter at a portion of the preform 1 where the outer diameter is greatest within a range of 0 to 0.2L from the lower end 5a is D, then a configuration is adopted in which D1 / D is less than 1 (0.76 in this embodiment). The lower end 5a indicates the lowest position excluding the seal portion 7 when the preform 1 is held upright as shown in Fig. 2A. The total height L is the length in the direction of the central axis C between the lower end 5a and the open end 1a.

[0017] In a preform having such a configuration, the outer diameter D near the bottom 5 is larger than the outer diameter D1 at the open end 1a. If the outer diameter of the parison 6 shown in FIG. 3 is constant, the larger the outer diameter D near the bottom 5, the lower the position of the longitudinal end 7a of the seal portion 7. Therefore, according to this embodiment, the seal portion 7 is prevented from being formed at a high position on the side surface 1c of the preform 1 without reducing the outer diameter of the parison 6. L is, for example, 50 to 80 mm (64.5 mm in this embodiment), and preferably 55 to 75 mm. This value may be, for example, 50, 55, 60, 65, 70, 75, or 80 mm, or may be in a range between any two of the values ​​exemplified here.

[0018] D1 / D is preferably 0.85 or less. In this case, the position of the end 7a can be further lowered. Furthermore, D1 / D is preferably 0.50 or more. If this value is too small, the blow ratio in direct blow molding may become too large near the bottom 5, resulting in the preform 1 being too thin-walled. Furthermore, since the outer diameter of the parison 6 is usually set smaller than the outer diameter D1 at the open end 1a, if D1 is too small, the outer diameter of the parison 6 also becomes small, which may make it difficult to inject pressurized fluid into the parison 6. Furthermore, if D is too large, stretching near the bottom 5 during biaxial stretch blow molding is likely to be insufficient, and the improvement in impact resistance (drop strength, tensile strength) due to stretching is likely to be insufficient.

[0019] D1 / D is, for example, 0.50 to 0.99, specifically, for example, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, or 0.99, and may be in a range between any two of the numerical values ​​exemplified here, or any value greater than or equal to the range. D is, for example, 20 to 30 mm (25.2 mm in this embodiment), specifically, for example, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 mm, and may be in a range between any two of the numerical values ​​exemplified here. D1 is, for example, 14 to 24 mm (19.3 mm in this embodiment), specifically, for example, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24 mm, or may be in a range between any two of the values ​​exemplified here.

[0020] If the height position of the end 7a from the lower end 5a of the preform 1 is L1, then L1 / L is, for example, preferably 0.30 or less (0.20 in this embodiment), and more preferably 0.25 or less. L1 / L is preferably 0.05 or more. If the outer diameter of the parison 6 is reduced to reduce L1 / L, it may become difficult to inject the pressurized fluid into the parison 6. L1 / L is, for example, 0.05 to 0.30, such as 0.05, 0.10, 0.15, 0.20, 0.25, or 0.30, and may be in a range between any two of the numerical values ​​exemplified here, or may be greater than or equal to any of these values.

[0021] If the height position of the boundary 1b between the body portion 4 and the bottom portion 5 from the lower end 5a is L2, L2 / L is, for example, 0.05 to 0.30, such as 0.05, 0.10, 0.15, 0.20, 0.25, or 0.30, and may be a range between any two of the values ​​exemplified here, or may be greater than or less than any of these values. The outer surface of the bottom portion 5 is preferably hemispherical. In this case, the radius of curvature R of the outer surface of the bottom portion 5 coincides with the height position L2 of the boundary 1b.

[0022] The thickness of the thickest portion of the preform 1 is, for example, 0.5 to 3.0 mm (1.5 mm in this embodiment), preferably 1.0 to 2.0 mm. Specifically, the thickness may be, for example, 0.5, 1.0, 1.5, 2.0, 2.5, or 3.0 mm, or may be in a range between any two of the values ​​exemplified here.

[0023] The preform 1 preferably includes a crystalline resin layer made of a crystalline resin that crystallizes upon stretching. In this case, the crystalline resin layer crystallizes when the preform 1 is biaxially stretched and blow-molded, improving impact resistance. Furthermore, while elastomers have been added to containers formed by direct blow molding to enhance impact resistance, in this embodiment, the crystalline resin layer improves impact resistance through crystallization, making it possible to reduce the amount of elastomer added and facilitating the realization of a mono-material container. Examples of crystalline resins include polyolefins such as polyethylene and polypropylene. Furthermore, if impact resistance is improved by crystallization, the wall thickness of the container formed by biaxially stretching and blow-molding the preform 1 can be reduced, thereby reducing the amount of resin used.

[0024] When the preform 1 has a single layer structure, it is preferable that the entire preform 1 is a crystalline resin layer. When the preform 1 has a multilayer structure, it is preferable that at least one layer is a crystalline resin layer. In addition, in one example, when the preform 1 has a multilayer structure, it is preferable that it has a gas barrier layer made of a gas barrier resin such as EVOH, and it is more preferable that the gas barrier layer is sandwiched between a pair of crystalline resin layers.

[0025] 3 and 4, the preform 1 can be manufactured by a method including a step of forming a preform by direct blow molding a tubular parison 6 in a molten state. Direct blow molding can mold the parison 6 using a pair of split molds 10 configured to be able to open and close. In the closed state, the pair of split molds 10 includes a cavity 10b having a cavity surface 10a corresponding to the outer surface shape of the preform 1. With the parison 6 placed in the cavity 10b, pressurized fluid can be blown into the parison 6 to mold the parison 6 into the shape of the preform 1.

[0026] In one example, this blow molding can be carried out by a method including a parison clamping step, a parison cutting step, a blow pin inserting step, an air blowing step, and a removal step.

[0027] In the parison clamping process, the parison 6 is placed between a pair of split molds 10 in an open state, and then, as shown in FIG. 3 , the pair of split molds 10 is closed to clamp the parison 6 between the pair of split molds 10. The pair of split molds 10 includes a pinch-off portion 10c and an opening 10d. The pinch-off portion 10c is located below the cavity 10b and is configured to clamp the parison 6 at the pinch-off portion 10c to form a seal portion 7. The opening 10d is provided to communicate with the outside of the split mold 10, and the parison 6 is not clamped at the opening 10d, maintaining its cylindrical shape. A flash 6c is formed below the pinch-off portion 10c.

[0028] Next, in the parison cutting step, the parison 6 is cut above the pair of split molds 10. As a result, an opening end 6a is formed in the parison 6.

[0029] Next, in the blow pin insertion step, the blow pin 11 is inserted into the parison 6 from the open end 6a, and in this state, pressurized fluid is blown into the parison 6 through a flow path 11d within the blow pin 11, thereby molding the parison 6 into the shape of the preform 1. The blow pin 11 is tapered toward its tip, which makes it easier to insert the blow pin 11 into the parison 6. As shown in Figures 3 and 4, the outer peripheral surface 11c of the blow pin 11 preferably abuts against the inner peripheral surface 6b of the parison 6 at a portion corresponding to the mouth portion 2 of the preform 1, thereby improving the dimensional accuracy of the inner peripheral surface 6b.

[0030] A counter plate 10e is provided on the pair of split molds 10, and a cut ring 11a is provided on the blow pin 11. With the parison 6 placed between the counter plate 10e and the cut ring 11a, the edge 11b of the cut ring 11a is pressed against the counter plate 10e, thereby cutting the parison 6.

[0031] Assuming that the outer diameter of the parison 6 is D2, it is preferable that D2 / D is 0.70 or less (0.61 in this embodiment). As the outer diameter D2 of the parison 6 increases, the seal portion 7 formed in the preform 1 becomes longer, and the height position of the end 7a tends to increase. However, by setting D2 / D to 0.70 or less, the height position of the end 7a is prevented from increasing. Furthermore, it is preferable that D2 / D is 0.40 or more. By setting D2 / D to 0.40 or more, it becomes easier to blow pressurized fluid into the parison 6. In particular, when the outer peripheral surface 11c of the blow pin 11 inserted from the open end 6a is brought into contact with the inner peripheral surface 6b of the parison 6, a blow pin 11 with a relatively large diameter is used, so the technical significance of increasing D2 / D is particularly significant. Specifically, D2 / D is, for example, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, or 0.70, and may be in a range between any two of the numerical values ​​exemplified here, or may be greater than or less than any of these values.

[0032] Furthermore, it is preferable that D2 / D1 be 0.60 or more (0.80 in this embodiment). By making D2 / D1 0.60 or more, it becomes easier to inject the pressurized fluid into the parison 6. In particular, when the outer peripheral surface 11c of the blow pin 11 inserted from the opening end 6a is brought into contact with the inner peripheral surface 6b of the parison 6, a blow pin 11 with a relatively large diameter is used, so the technical significance of increasing D2 / D1 is particularly significant. It is preferable that D2 / D1 be 0.95 or less. If D2 / D1 is too large, the pair of split molds 10 will easily pinch the parison 6 at the portion corresponding to the mouth portion 2. Specifically, D2 / D1 may be, for example, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, or 0.95, and may be within a range between any two of the values ​​exemplified here, or may be greater than or less than any of these values.

[0033] 2. Manufacturing Method of Container 12 As shown in FIG. 5 , the container 12 can be manufactured by biaxially stretching blow molding the preform 1. Biaxial stretching blow molding is preferably performed using a method including a primary molding step and a secondary molding step. In the primary molding step, the preform 1 is molded into an intermediate molded body having a shape between that of the preform 1 and the container 12. In the secondary molding step, the intermediate molded body is molded into the shape of the container 12. The intermediate molded body has a smaller wall thickness than the preform 1, so heating unevenness is less likely to occur. Therefore, by performing biaxial stretching blow molding in two stages, unevenness in the wall thickness of the container 12 due to heating unevenness can be suppressed. Furthermore, when the container 12 has a flat-shaped portion, unevenness in the wall thickness of the container 12 is likely to occur, so performing biaxial stretching blow molding in two stages is particularly preferable. Furthermore, when the preform 1 includes a polyolefin layer, unevenness in the wall thickness of the container 12 is also likely to occur, so performing biaxial stretching blow molding in two stages is particularly preferable.

[0034] 1: preform, 1a: opening end, 1b: boundary, 1c: side, 2: mouth portion, 2a: engagement portion, 2b: intermittent portion, 2c: male thread portion, 3: main body portion, 4: barrel portion, 5: bottom, 5a: lower end, 6: parison, 6a: opening end, 6b: inner peripheral surface, 6c: flash, 7: seal portion, 7a: end portion, 9: flange, 9b: lower surface, 10: split mold, 10a: cavity surface, 10b: cavity, 10c: pinch-off portion, 10d: opening, 10e: counter plate, 11: blow pin, 11a: cut ring, 11b: edge, 11c: outer peripheral surface, 11d: flow path, 12: container, 12a: side, C: central axis

Claims

1. A cylindrical preform with a bottom, the preform being a direct blow molded article, wherein, when the outer diameter at the open end of the preform is D1 and the total height of the preform is L, the outer diameter at a portion of the preform where the outer diameter is greatest within a range of 0 to 0.2L from the bottom end of the preform is D, D1 / D is less than 1.

2. A preform according to claim 1, wherein D1 / D is 0.85 or less.

3. A preform according to claim 1, wherein D1 / D is 0.50 or more.

4. A method for manufacturing a preform according to any one of claims 1 to 3, comprising a step of forming a preform by direct blow molding a tubular parison in a molten state, wherein, when the outer diameter of the parison is D2, D2 / D is 0.70 or less.

5. The method according to claim 4, wherein D2 / D1 is 0.60 or more.

6. A method for manufacturing a container, comprising a step of biaxially stretching blow molding a preform, wherein the preform is a preform as defined in any one of claims 1 to 3, and the biaxially stretching blow molding comprises a primary molding step and a secondary molding step, wherein the primary molding step molds the preform into an intermediate molded body having a shape between the preform and the container, and the secondary molding step molds the intermediate molded body into the shape of the container.

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