JPH05246416A - Self-standing bottle of synthetic resin - Google Patents

Abstract

PURPOSE:To decrease generation of stress cracks by a method wherein a non- stretched or low-stretched thick part at a bottom part of a self-standing bottle is extended from the center of the bottom part up to a substantially circular zone having a prescribed length of radius over a changing point of a shape, so that inner pressure resistance can be procured. CONSTITUTION:A self-standing bottle 30 is made of synthetic resin by biaxially orientated blowing. In this instance, a point apart, from a center 34a of a bottom part 34 by a prescribed distance is set as a changing point 42. More than three legs 40 leading to earthing parts 46 over sloped parts 44 which extend radially outward from the changing point 42, and in addition, slantwise and downward are arranged on the bottom part 34 at the substantially same central angle. On the other hand, a central range 38 on the inner side, which has a prescribed radius long enough to exceed the changing point 42 from the center 34a is formed of a non-stretched or low-stretched thick part 50. Further, a range on the outer side which at least includes the earthing part 46 is formed of a stretched thin part 52. A thick-to-thin part 54 connecting the thick part 50 and the thin part 52 is formed in the middle of the sloped parts 44.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially stretch blow-molded synthetic resin freestanding bottle, and more particularly to its bottom structure.

[0002]

2. Description of the Related Art As a bottom structure of a synthetic resin container having a carbonated beverage or the like as its content, a downwardly convex hemispherical structure is the best in order to ensure resistance to internal pressure. However, such a hemispherical bottom bottle cannot function as a self-supporting bottle unless a cap called a base cap is attached to the bottom.

Therefore, conventionally, a bottle structure has been proposed in which the bottom of the bottle is provided with an even or odd number of legs.
Its typical bottom structure is, for example, Jikken 3-55375.
It is shown in FIG. 1 of the publication. That is, such a bottle has the bottom structure shown in FIG. In addition, the first of the above publication
Since the thickness of the bottom portion is not disclosed in the drawing, FIG. 5 schematically shows only the shape without considering the thickness. The bottle shown in FIG. 5 has a bottom portion 14 that closes one end of a hollow cylindrical side wall portion 12. The bottom portion 14 has, for example, a spherical portion 16 that is curved at a constant radius R, and further, for example, an odd number of leg portions 20 that extend obliquely downward from the spherical portion 16 have approximately the same number with respect to the center 18. It is provided for each equal center angle. The leg portion 20 is connected to the spherical portion 16 at a change point 22 that is apart from the center 18 of the bottom portion 14 by a predetermined distance, and has an inclined portion 24 that extends obliquely downward from the change point 22 toward the outer side in the radial direction. . And this inclined portion 24
Is the lowest point of the ground. According to such a bottle bottom structure, the bottle 10 can be made to stand on its own by, for example, an odd number of leg portions 20.

[0004]

According to the experiments conducted by the present inventors, the bottle 10 having a bottom structure as shown in FIG.
It was found that stress cracks were likely to occur in the bottom portion 14 of the. The first cause of the stress cracks is that when the bottle 10 is transported along the bottling line that fills the bottle 10 with contents, the lubricant applied on the transport path promotes the stress cracks. It is thought to do. Secondly, it is considered that temperature cracks or environmental changes such as humidity in summer affect stress cracks. Thirdly, it is considered that a buckling load from above is applied when capping the bottle 10 after filling the contents. Further, according to further researches by the present inventors, such stress cracks are generated in the bottom portion 1.
It was confirmed that the change occurred significantly at the shape change point 22 in FIG. It is considered that this is because stress concentration occurs at the change point 22. In the bottle 10 in which the stress crack has occurred in this way, there is a problem that the crack propagates and the content leaks, and the commercial value of the bottle 10 is lost.

The present inventors also molded a bottle having the bottom structure shown in FIG. 6 and conducted a burst test for measuring the internal pressure when the bottle bursts. In the structure shown in FIG. 6, the change point 22 of the shape in the bottom portion 14 is
It is arranged at the center 18 of the.

However, as a result of the burst test of the bottle having the structure shown in FIG. 6, it was found that the pressure resistance was further lowered as compared with the bottle having the bottom structure shown in FIG. That is, in the case of the bottle shown in FIG. 5, 20 kg /
While it does not burst even when an internal pressure of cm ² or more is applied,
In the case of the bottle shown in FIG. 6, the standard value is 10 kg /
It was impossible to clear even cm ² .

As described above, the bottom structure of FIG. 5 is excellent in order to secure the internal pressure resistance, but there is no measure capable of preventing the occurrence of stress cracks.

[0008] Therefore, an object of the present invention is to provide a synthetic resin self-supporting bottle having a bottom portion which is resistant to stress cracks while ensuring internal pressure resistance.

[0009]

According to the present invention, in a self-supporting bottle made of a biaxially stretch blow-molded synthetic resin, a point separated by a predetermined distance from the center of the bottom is defined as a change point of the bottom shape, and a radius from the change point. In the bottom portion, there are three or more leg portions provided at substantially equal center angles through an inclined portion that extends obliquely downward outward in the direction and reach the ground contact portion, and the change point is exceeded from the center. An inner substantially circular region having a predetermined radius of length is composed of an unstretched or low-stretched thick portion, and an outer region including at least the ground portion is constituted of a stretched thin portion,
A thickness transition portion connecting the thick portion and the thin portion is formed in the middle of the inclined portion.

[0010]

According to the present invention, the inner pressure resistance is enhanced by forming the shape change point at the bottom at a point distant from the center of the bottom by a predetermined distance. Moreover, the wall thickness at this change point is formed as a thick wall portion in which the wall thickness remains relatively because it is unstretched or low stretched during the biaxial stretch blow molding process. Therefore, even if stress is concentrated at the change point of this shape, the generation of stress cracks is prevented by ensuring the wall thickness. The most molecularly unstable portion is a transition portion of wall thickness from a portion that is amorphous due to unstretched to a relatively stretched oriented crystallized portion.
If these points are not taken into consideration, stress cracks are most likely to occur when the thickness transition portion and the shape change point coincide with each other. According to the present invention, such a wall thickness transition portion that is unstable in terms of molecular structure is formed radially outside the shape change point at the bottom portion, that is, in the middle of the inclined portion at the leg portion, thereby ensuring pressure resistance. In addition, the occurrence of stress cracks is reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a self-supporting bottle to which the present invention is applied will be specifically described below with reference to the drawings.

In FIGS. 1 and 2, the self-standing bottle 30 according to this embodiment has a bottom portion 34 that closes one end of a hollow cylindrical side wall portion 32. The bottom portion 34 has a downwardly convex hemispherical portion 36. Further, three or more leg portions 40, for example, five leg portions 40 are connected to the hemispherical portion 36 in the circumferential direction of the center 34a of the bottom portion 34 at equal center angles. The connection point between the leg portion 40 and the hemispherical portion 36 is the center 3 of the bottom portion 34.
It is a point separated from 4a by a predetermined distance, preferably 3 mm or more, and this point is a change point 42 of the shape of the bottom portion 34. Each leg 40 has an inclined portion 44 extending radially outward from the change point 42 and obliquely downward.
The lowest point of the inclined portion 44 is a position having a diameter smaller than the maximum diameter of the side wall portion 32, and the lowest point is the ground contact portion 46. That is, the shape of the bottom portion 34 is the leg portion 40.
When viewed from one section including
a hemispherical portion 36 over the change point 42 on the opposite side beyond a.
Is formed, and the shape curved upward from the center 34a to the change point 42 is folded obliquely downward at the change point 42, and the leg portion 40 is formed from the change point 42 to the other side wall 32. There is.

Next, the thickness of the bottom portion 14 will be described with reference to FIG.

This type of self-supporting bottle 30 is formed by biaxial stretch blow molding, and as is well known in this process, a stretch rod for extending the bottom wall of the preform in the longitudinal direction and a preform are introduced into the preform. And blowing air.
Therefore, the bottom center region where the stretching rod is stretch-guided in the longitudinal direction by contact or non-contact is a region which is unstretched or hardly stretched. Therefore, the central region 38 of the bottom portion 34 of the self-supporting bottle 30 is formed as a thick wall portion 50 having a relatively thick wall thickness as compared with the wall thickness of the other stretched portions. The thick portion 50 has a center 34 a of the bottom portion 34.
Although it is formed as a substantially circular area around, in the present embodiment, the thick portion 50 is formed up to the area radially outward of the change point 42, that is, up to an intermediate position of the inclined portion 44. On the other hand, from the lower end side of the inclined portion 44 to the grounding portion 46
The outer side wall portion 32 and the outer side wall portion 32 are oriented in the biaxial direction in the biaxial stretch blow molding process, and as a result, the thin portion 5 is formed.
Formed as 2. Between the thick-walled portion 50 on the center side and the thin-walled portion 52 on the outer side thereof, the thin-walled portion 5 is thinner than the thick-walled portion 50.
It is formed as a wall thickness transition portion 54 whose wall thickness changes relatively gradually up to the wall thickness of 2. In this embodiment, the wall thickness transition portion 54 is formed radially outside the transition point 22, that is, at an intermediate position of the inclined portion 44.

Next, the density of the bottom portion 34 of the self-supporting bottle 30 will be described.

The density of the thick wall portion 50 is low because the region is unstretched or low stretched, and is 1.35 g / cm ³ or less, and particularly the density of the center 34a is 1.345 g / cm ^3.
It will be ³ or less. On the other hand, since the thickness transition portion 54 is a region that transitions from the amorphous state to the crystalline state, the thickness transition portion 54 has a lower density than the biaxially oriented side wall portion 32 and the like, and the density thereof is 1.35.
The above is 1.36 g / cm ³ or less. In particular, the density of the thickness transition portion 54 is often 1.35 g / cm ³ unit. Since the thin portion 52 has a relatively high degree of biaxial orientation, its density is higher than that of the thickness transition portion 54, and is usually 1.36 g / cm ³ or more.

According to the bottom structure of the self-supporting bottle 30 of this embodiment, there is a change point 42 of the shape at the bottom 34, but this change point 42 is present at a position apart from the center 34a by a predetermined distance. Further, since the bottom structure other than the legs 40 is configured as the hemispherical portion 36 having a constant radius R, for example, relatively high internal pressure resistance can be ensured. This freestanding bottle 30
A burst test in which the inner wall of the bottle was ruptured by applying an inner pressure to the inner wall of the bottle was confirmed to have a high inner pressure resistance of 20 kg / cm ² or more. In particular, this internal pressure resistance is 3 m from the center 34a to the change point 42.
It was found that when it was m or more, it was good.

Further, such a self-supporting bottle 30 is conveyed along a bottling line for filling the contents thereof, and at that time, even if a lubricant is applied and formed on the conveying line, the contents thereafter. It was found that stress cracks are unlikely to occur even when the product is filled. The reason is that, in the self-standing bottle 30 of the present embodiment, the position of the wall thickness transition portion 54, which is molecularly unstable, and the position of the change point 42 of the shape in which stress concentration is most likely to occur at the bottom portion 34, coincide. This is because there is no change point 42 at which the stress concentration occurs.
This is because the reinforcement is achieved by configuring as 0.

As described above, in the self-supporting bottle 30 according to this embodiment, the thick portion 50 constitutes a substantially circular region having a predetermined radius with a length beyond the change point 42 from the center 34a, so that the internal pressure resistance is improved. It was possible to sufficiently reduce the occurrence of stress cracks while ensuring the above.

As described above, in the self-supporting bottle 30 of this embodiment,
The thick portion 50 is enlarged radially outward of the conventional bottle. A method of molding the self-supporting bottle 30 having such a bottom structure is achieved by increasing the descending speed of the stretching rod or delaying the timing from the start of descending the stretching rod to the introduction of the primary blown air.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention.

FIGS. 3 and 4 show modifications of the shape of the central region 38 in the bottom portion 30. In the structure shown in FIG. 3, the central region 38 is configured as a flat portion 60 that is substantially perpendicular to the vertical axis, rather than a part of the downwardly convex hemispherical portion. Further, the inclined portion 44 from the change point 42 to the grounding portion 46 has the first inclined portion 44 having different inclination angles.
a and the second inclined portion 44b. Also in the case of the embodiment shown in FIG. 3, the area of the thick portion 50 is the flat portion 6
0 and the first inclined portion 44a on the outside thereof extend to an intermediate region.

On the other hand, the one shown in FIG.
8 is composed of a flat portion 62 as in the case of FIG. 3, but this flat portion 62 is formed at a position projecting inward of the bottle, so that the hemispherical portion 36 and the flat portion 62 are formed.
A stepped portion 64 is formed at the boundary between and. Also in the case of the structure shown in FIG. 4, in addition to the area of the flat portion 62, the thick portion 50
It extends to an intermediate position of the outer inclined portion 44.

In addition to the above, the inclined portion 44 is not limited to the one inclined in a plane, and may be one inclined while curving with a predetermined curvature. The spherical portion 36 may be smoothly connected using a plurality of different curvatures. Furthermore, each of the above-described embodiments applies the present invention to a plurality of leg portions 40.
Although the example is shown in which the invention is applied to a self-supporting bottle having an even number of legs 40, it can be similarly applied to a self-supporting bottle having an even number of legs 40. In the case of a free-standing bottle having an even number of legs, the sectional structure of the bottom portion including the legs has a symmetrical shape.
A self-supporting bottle having an even number of legs is inferior in pressure resistance to a self-supporting bottle having an odd number of legs, but it is possible to ensure a predetermined pressure resistance by considering the wall thickness setting. A bottle that can reduce stress cracks can be realized.

[0025]

As described above, according to the present invention, the unstretched or low-stretched thick-walled portion at the bottom of the self-supporting bottle has a substantially circular shape having a predetermined radius whose length exceeds the change point of the shape from the center of the bottom. By extending to the region, it can be strengthened by increasing the wall thickness at the change point where stress concentration is likely to occur, and the thickness transition part, which is the most unstable in terms of material structure, is set at a position where stress concentration does not occur. Therefore, while securing the internal pressure resistance,
It is possible to reduce the occurrence of stress cracks.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a cross-sectional structure of a bottom portion of an embodiment in which the present invention is applied to a self-standing bottle having an odd number of leg portions.

FIG. 2 is a bottom view of the self-supporting bottle shown in FIG.

FIG. 3 is a cross-sectional view showing a modified example in which the bottom center region is formed of a flat portion.

FIG. 4 is a cross-sectional view showing a modified example in which a flat part in the central region of the bottom part is projected inside the bottle.

FIG. 5 is a cross-sectional view schematically showing the bottom of a conventional self-supporting bottle.

FIG. 6 is a cross-sectional view schematically showing a bottom structure in which a change point of the shape at the bottom is set at the center of the bottom.

[Explanation of symbols]

 30 Self-supporting bottle 32 Side wall part 34 Bottom part 34a Center 36 Hemispherical part 40 Leg part 42 Change point 44 Inclined part 46 Ground contact part 50 Thick part 52 Thin part 54 Part thickness transition part

Claims (3)

[Claims] 1. A biaxially stretch blow-molded self-supporting bottle made of synthetic resin, wherein a point separated by a predetermined distance from the center of the bottom is defined as a bottom shape change point, and extends obliquely downward outward in the radial direction from this change point. An inner side having three or more legs provided at substantially equal center angles at the bottom through the existing sloped portion to the grounding portion, and having a predetermined radius of a length beyond the change point from the center The substantially circular region is composed of an unstretched or low-stretched thick part, and at least the outer region including the grounding part is composed of a stretched thin part, and the thickness transition connecting the thick part and the thin part A self-standing bottle made of synthetic resin, characterized in that a portion is formed in the middle of the inclined portion. 2. The self-standing bottle made of synthetic resin according to claim 1, wherein the change point is separated from the center of the bottom by 3 mm or more. 3. The density of the thick portion is 1.35 g / cm ³ or less, and the density of the thickness transition portion is 1.35 or more and 1.36 g / cm ^{3 according to} claim 1 or 2.
The following is, and the density of the thin portion is higher than the density of the thickness transition portion, a self-supporting bottle made of synthetic resin.