Preform

Abstract

To provide a preform capable of selectively performing thinning of a container bottom part subjected to molding.SOLUTION: A preform 1 molded into a bottomed cylinder shape comprises a cylindrical trunk part 3, a mouth 2 opened on one end side of the trunk part 3, and a bottom part 4 for closing the other end side of the trunk part 3. A vertical cross-sectional shape of the bottom part 4 is made to be laterally elliptical arc-shaped, and a thickness of the bottom part 4 is made to be thinner than a thickness of the trunk part 3.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a preform for manufacturing a container made of synthetic resin by blow molding.

Background Art

[0002] Conventionally, a bottomed cylindrical preform is produced using a thermoplastic resin such as polyethylene terephthalate, and a container made of synthetic resin formed into a bottle shape from this preform by biaxial stretch blow molding or the like is used in a wide range of fields as a container containing various beverages, various seasonings, etc. as contents.

[0003] Among such containers made of synthetic resin, in the case of a beverage container containing a carbonated beverage, it is required to have pressure resistance capable of withstanding the pressure of carbon dioxide gas, and to be self-standing without the self-standing stability being impaired even when the inside of the container becomes a positive pressure. For this reason, for example, a pressure-resistant bottle having a bottom formed in a so-called petaloid shape as disclosed in Patent Document 1 is known.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in this type of container, there has been a demand for weight reduction and cost reduction by reducing the amount of resin used, and attempts have been made to form it as thin as possible.

[0006] However, in the case of a pressure-resistant bottle containing a carbonated beverage, there has been a limitation in reducing the thickness of the container, such as the need to form the container with a certain thickness in order to suppress the permeation of carbon dioxide gas.

[0007] Therefore, taking the above circumstances into consideration, the inventors diligently conducted research to selectively thin the bottom of the molded container, and as a result, completed the present invention. [Means for solving the problem]

[0008] The preform according to the present invention is a preform for manufacturing a synthetic resin container by blow molding, and is molded into a bottomed cylindrical shape including a cylindrical body, a mouth opening on one end of the body, and a bottom closing the other end of the body, outer bottom surface and inner bottom surface The vertical cross-sectional shape is such that it is a horizontal elliptical arc, and the thickness of the bottom is thinner than the thickness of the body. Furthermore, the flattening ratio of the inner bottom surface is made greater than the flattening ratio of the outer bottom surface. It is structured in that way. [Effects of the Invention]

[0009] According to the present invention, it becomes possible to selectively thin the bottom of the molded container. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing a preform according to an embodiment of the present invention. [Figure 2] This is an explanatory diagram illustrating, in an embodiment of the present invention, the relationship between a preform set in a blow molding die and a container in which the preform is molded into a predetermined container shape within the blow molding die. [Figure 3] Figure 1 is a schematic perspective view showing a container formed by blow molding the preform shown in Figure 1. [Figure 4] This is an explanatory diagram showing an outline of the preform related to the comparative example. [Figure 5] This is an explanatory diagram comparing a preform according to an embodiment of the present invention with a preform according to a comparative example. [Figure 6] This is an explanatory diagram showing a schematic of the bottom of a modified preform according to an embodiment of the present invention, and shows a longitudinal cross-section of the bottom. [Figure 7] This is an explanatory diagram illustrating the schematic of the bottom of another modified example of the preform according to the embodiment of the present invention, showing a longitudinal cross-section of the bottom. [Modes for carrying out the invention]

[0011] Preferred embodiments of the present invention will be described below with reference to the drawings.

[0012] Figure 1 is an explanatory diagram illustrating the schematic of the preform according to this embodiment, and shows a cross-section (longitudinal section) cut by a plane containing the central axis C, indicated by the dashed line in the figure. Note that in Figure 1, the hatching indicating the cross-section has been omitted, and the units of measurement for the dimensions shown in the figure are millimeters (mm).

[0013] Figure 2 is a schematic diagram illustrating the relationship between a preform 1 set in a blow molding die 100, indicated by a dashed line in the figure, and a container 10 formed from this preform 1 into a predetermined container shape within the blow molding die 100 by biaxial stretch blow molding or the like. Figure 3 shows an example of the molded container 10 in a perspective view. The container 10 is configured to be suitably used as a pressure-resistant bottle for carbonated beverages. Therefore, to ensure that self-supporting stability is not impaired even when the inside of the container becomes positive pressure, it is equipped with a so-called petaloid-shaped bottom 50, in which multiple (five in the illustrated example) legs 51 are arranged radially at equal intervals and rotationally symmetrically around the central axis of the container 10.

[0014] In this embodiment, the preform 1 can be molded using a thermoplastic resin by injection molding, compression molding, or the like, and is molded into a bottomed cylindrical shape including a cylindrical body 3, a mouth 2 that opens at one end of the body 3, and a bottom 4 that closes the other end of the body 3.

[0015] As the thermoplastic resin to be used, any resin capable of blow molding can be used. More specifically, thermoplastic polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, amorphous polyarylate, polylactic acid, polyethylene furanoate or copolymers thereof can be used. In particular, ethylene terephthalate-based thermoplastic polyesters such as polyethylene terephthalate can be preferably used. These resins may be mixed in two or more kinds, or blended with other resins. Polycarbonate, acrylonitrile resin, polypropylene, propylene-ethylene copolymer, polyethylene, etc. can also be used. Further, the preform 1 is not limited to being formed into a single layer, and can also be formed into a multilayer including a gas barrier layer or the like according to the characteristics required for the container 10.

[0016] The preform 1 is heated as necessary to be in a softened state capable of blow molding, and then set in the blow mold 100. The portion from directly below the mouth portion 2 to the bottom portion 4 is stretched in the axial direction (vertical direction) by a stretch rod as necessary, and is stretched in the axial direction and the circumferential direction (lateral direction) by the blow air blown into the preform 1. Then, by transferring the cavity shape of the blow mold 100, the stretched portion of the preform 1 is formed into the shoulder portion 30, the body portion 40, and the bottom portion 50 of the container 10.

[0017] Here, in the present embodiment, in the state shown in FIG. 1 with the mouth portion 2 facing upward, the vertical, horizontal, and longitudinal and lateral directions of the preform 1 are defined.

[0018] As shown in FIG. 2, the mouth portion 2 of the preform 1 is not stretched by blow molding and remains as the mouth portion 2 of the container 10. For this reason, in the figure, these are denoted by the same reference numerals. The mouth portion 2 of the preform 1, and by extension, the mouth portion 2 of the container 10 is a portion that serves as an injection outlet for the contents, and a screw thread 21 for attaching a lid body (not shown) is provided on the side surface of the open end side of the mouth portion 2 formed in a cylindrical shape.

[0019] Furthermore, the mouth portion 2 is provided with an annular neck ring 22 that protrudes outward along the circumferential direction. The preform 1 is typically formed by starting from the portion directly below the neck ring 22 supported by the blow molding die 100, and extending the portion below that point to form the shoulder portion 30, body portion 40, and bottom portion 50 of the container 10, as described above.

[0020] In this embodiment, when blow-molding the preform 1 in this manner, in order to selectively thin the wall thickness of the bottom 50 of the molded container 10, the vertical cross-sectional shape of the bottom 4 of the preform 1 is made to be a horizontal elliptical arc with its major axis perpendicular to the central axis C, so that the wall thickness of the bottom 4 is thinner than that of the body 3. Furthermore, according to this embodiment, by making the vertical cross-sectional shape of the bottom 4 of the preform 1 a horizontal elliptical arc, it is possible to thin the wall thickness of the bottom 50 of the molded container 10 while suppressing a decrease in the environmental stress corrosion cracking resistance (ESCR) of the bottom 50. In this invention, the term "elliptical arc" includes not only elliptical arcs formed by a series of circular arcs whose radius of curvature changes monotonically, but also shapes that can be considered as such elliptical arcs.

[0021] The reason for this will be explained by comparing it with an example of a preform that the inventors considered during the process of completing the present invention.

[0022] Figure 4 is an explanatory diagram illustrating the schematic of preform 1c, which is used as a comparative example, and shows a longitudinal cross-section of preform 1c in the same manner as in Figure 1. In preform 1 shown in Figure 1 and preform 1c shown in Figure 4 as a comparative example, the length along the axial direction, particularly the length h along the axial direction from directly below the neck ring 22 to the stretched portion below it, is made equal so that the longitudinal stretching ratio during blow molding is the same.

[0023] In Figure 4, the parts of preform 1c that are not stretched by blow molding are indicated by the same reference numerals as those used for preform 1 in Figure 1.

[0024] As shown in Figure 4, conventional preforms are molded with a hemispherical bottom. In the comparative example shown in Figure 4, when molding the preform 1c by injection molding or the like, a core mold (not shown) that molds the inner circumferential surface of the preform 1c is slightly stretched so that the bottom 4c is molded to be thinner by that amount.

[0025] To explain in more detail, focusing on the longitudinal cross-sectional shape of the bottom portion 4c, in the comparative example shown in Figure 4, the outer and inner bottom surfaces of the bottom portion 4c are formed to be semicircular in shape with a constant radius of curvature in their longitudinal cross-section. The center of curvature of the inner bottom surface moves along the axial direction by the amount by which the core mold is stretched, relative to the center of curvature of the outer bottom surface. Consequently, the upper edge of the inner bottom surface also moves along the axial direction by the same amount as the core mold is stretched. As a result, the wall thickness of the bottom portion 4c decreases towards the tip of the bottom portion 4c, starting from the upper edge of the outer bottom surface.

[0026] Here, in the longitudinal section of the preform 1c, the portion where the radius of curvature changes from the outer bottom surface of the bottom 4c toward the outer circumferential surface of the body 3c is defined as the upper edge of the outer bottom surface, and similarly, the portion where the radius of curvature changes from the inner bottom surface of the bottom 4c toward the inner circumferential surface of the body 3c is defined as the upper edge of the inner bottom surface.

[0027] In contrast, in the preform 1 shown in Figure 1, the outer and inner bottom surfaces of the bottom 4 are arranged in a transverse elliptical arc shape in its longitudinal section. Depending on the flattening ratio (1 - [minor radius] / [major radius]), the thickness of the bottom 4 decreases towards the tip of the bottom 4, resulting in a thinner wall compared to the thickness of the body 3. As a result, compared to the comparative example, the boundary between the body 3 and the bottom 4, or in other words, the starting point where the thickness of the bottom 4 decreases, has shifted towards the tip of the bottom 4 (see Figure 5).

[0028] Here, the wall thickness of the bottom 4 and bottom 4c is measured along a perpendicular line perpendicular to the tangent line passing through the intersection of their outer bottom surfaces and the tangent line. Figure 5 shows the longitudinal cross-sectional shape of the bottom 4 of the preform 1 in this embodiment (center in the figure) and the longitudinal cross-sectional shape of the bottom 4c of the preform 1c in the comparative example (left in the figure), such that the maximum wall thickness (wall thickness at the point where the wall thickness decreases) and the minimum wall thickness (wall thickness at the tip) are equal. On the right side of the figure, the wall thickness change from the body 3 to the tip of the bottom 4 in this embodiment is shown by a solid line, and the wall thickness change from the body 3c to the tip of the bottom 4c in the comparative example is shown by a dashed line.

[0029] Therefore, in this embodiment, the boundary between the body portion 3 and the bottom portion 4 shifts towards the tip side of the bottom portion 4, resulting in a longer axial length of the body portion 3 compared to the comparative example. For example, the axial length h3 of the body portion 3 in the preform 1 shown in Figure 1 is approximately 5% longer than the axial length h3c of the body portion 3c in the preform 1c shown in Figure 4.

[0030] Then, as the body portion 3 becomes longer, if the amount of resin allocated to the parts formed on the shoulder portion 30 and body portion 40 of the molded container 10 is adjusted so that the wall thickness of these portions is maintained at the same level as when using preform 1c shown as a comparative example, the wall thickness of the body portion 3 becomes thinner compared to the comparative example. For example, the wall thickness t3 of the body portion 3 of preform 1 shown in Figure 1 is approximately 3% thinner than the wall thickness t3c of the body portion 3c of preform 1c shown in Figure 4.

[0031] As a result, according to this embodiment, the maximum wall thickness of the bottom 4 (corresponding to the wall thickness of the body 3) can be reduced, and at the same time, the minimum wall thickness at its tip can also be reduced. For example, the minimum wall thickness t4c at the tip of the bottom 4c of the preform 1 shown in Figure 4 is approximately 3% thinner than the minimum wall thickness t4c at the tip of the bottom 4 of the preform 1 shown in Figure 1.

[0032] As described above, this embodiment allows for easy and balanced adjustment of the amount of resin allocated to each part of the preform 1 so that the thickness of the shoulder portion 30 and body portion 40 of the molded container 10 reaches the desired thickness, while ensuring sufficient resin is allocated to the parts formed on these portions, and reducing the amount of resin allocated to the part formed on the bottom portion 50. As a result of reducing the amount of resin allocated to the part formed on the bottom portion 50 of the molded container 10, the bottom portion 50 is formed in a more elongated state, improving formability and increasing the degree of oriented crystallinity. This makes it possible to selectively thin the bottom portion 50 while suppressing a decrease in the environmental stress corrosion cracking resistance (ESCR) of the bottom portion 50.

[0033] In this embodiment, in order to more effectively achieve such effects, it is preferable that the inner bottom surface and the outer bottom surface of the bottom portion 4 are formed such that their respective vertical cross-sectional shapes are horizontal elliptical arcs, with their respective upper edges located within a range of ±1 mm along the axial direction, and it is particularly preferable that their respective upper edges are located on the same plane perpendicular to the axial direction. Furthermore, it is preferable that the centers of the inner and outer bottom surfaces of the bottom portion 4 (the intersection of the major and minor axes) in the longitudinal section are located within ±1 mm along the axial direction, and it is particularly preferable that their centers coincide.

[0034] Here, in the longitudinal section of the preform 1, the upper edge of the outer bottom surface is defined as the boundary where the radius of curvature changes from monotonically decreasing to increasing, extending from the outer bottom surface of the bottom 4 toward the outer circumferential surface of the body 3. Similarly, the upper edge of the inner bottom surface is defined as the boundary where the radius of curvature changes from monotonically decreasing to increasing, extending from the inner bottom surface of the bottom 4 toward the inner circumferential surface of the body 3.

[0035] Furthermore, when molding the inner and outer bottom surfaces so that their longitudinal cross-sectional shape is a horizontal elliptical arc, it is preferable that their respective flattening ratios be between 0.22 and 0.42. If the flattening ratios of the longitudinal cross-sections of the inner and outer bottom surfaces fall below the above range, it tends to become difficult to fully obtain the effect of making the longitudinal cross-sectional shape of the bottom 4 of the preform 1 a horizontal elliptical arc. On the other hand, if the ratio exceeds the above range, the bottom 4 of the preform 1 becomes thinner, and the amount of resin allocated to the part formed into the bottom 50 of the molded container 10 tends to be insufficient, which is undesirable in suppressing a decrease in the environmental stress corrosion cracking resistance of the bottom 50.

[0036] If the amount of resin allocated to the portion formed on the bottom 50 of the molded container 10 is insufficient, the thickness of the central part of the bottom 4 of the preform 1 can be adjusted, for example, by making the flatness ratio of the inner bottom surface greater than the flatness ratio of the outer bottom surface, as shown in Figure 6. In this configuration, it is preferable to adjust the thickness of the central part of the bottom 4 of the preform 1 to be 0.1 to 0.5 mm thick.

[0037] Figure 6 shows an example where the thickness of the central part of the bottom 4 of the preform 1 is adjusted to be 0.3 mm thicker by increasing the flatness of the inner bottom surface compared to the case where the flatness of the inner bottom surface and the outer bottom surface are equal.

[0038] Alternatively, or in addition to the above, as shown in Figure 7, the thickness of the central part of the outer bottom surface of the bottom 4 of the preform 1 can also be adjusted by uniformly raising the central part of the outer bottom surface. In this configuration, it is preferable to raise the central part of the outer bottom surface in a circular shape to a height of 0.1 to 0.5 mm in a range of 35 to 55% of the outermost diameter D of the bottom 4, including the upper edge of the outer bottom surface, and it is preferable that the center of the circularly raised part lies on the central axis C.

[0039] Figure 7 shows an example in which the thickness of the central part of the bottom 4 of the preform 1 is adjusted by raising a circular area of ​​approximately 44% of the outermost diameter D of the bottom 4 to a height of 0.3 mm relative to the outer bottom surface. In the example shown in Figure 7, the raised area is clearly shown for ease of understanding, but it is preferable to raise it smoothly relative to the outer bottom surface.

[0040] In this way, by adjusting the thickness of the central part of the bottom 4 of the preform 1, it is possible to compensate for any shortage of resin allocated to the portion formed on the bottom 50 of the molded container 10. However, in any embodiment, it is preferable to adjust the thickness of the central part of the bottom 4 of the preform 1 so that the entire bottom 4 is stretched in a balanced manner.

[0041] Although the present invention has been described above with reference to preferred embodiments, it goes without saying that the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the present invention.

[0042] For example, the above-described embodiment can be selectively thinned at the bottom 50 while suppressing carbon dioxide permeation by making the wall thickness of the shoulder portion 30 and body portion 40 of the molded container 10 a desired thickness. Therefore, it is particularly suitable for pressure-resistant bottles containing carbonated beverages, but it is not limited to this. It can also be appropriately applied to various containers for non-carbonated beverages. [Explanation of symbols]

[0043] 1 Preform 2 Mouth 3 Torso 4 Bottom

Claims

1. A preform for manufacturing a synthetic resin container by blow molding, It is formed into a bottomed cylindrical shape, including a cylindrical body, a mouth opening at one end of the body, and a bottom closing the other end of the body. The vertical cross-sectional shapes of the outer and inner bottom surfaces of the bottom are made to be in the shape of a horizontal elliptical arc, so that the thickness of the bottom is thinner than the thickness of the body, A preform characterized in that the flatness ratio of the inner bottom surface is greater than that of the outer bottom surface.

2. The preform according to claim 1, wherein the upper edges of the inner bottom surface and the outer bottom surface are located within a range of ±1 mm along the axial direction.

3. The preform according to claim 1 or 2, wherein the flatness ratio of the outer bottom surface and the inner bottom surface is 0.22 to 0.

42.

4. The preform according to any one of claims 1 to 3, wherein the central part of the outer bottom surface is raised in a circular shape to a height of 0.1 to 0.5 mm relative to the outer bottom surface, in a range of 35 to 55% of the diameter of the outermost part of the bottom surface.

Images