JPS6236726Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a stretched blown polyester hollow body.
More specifically, the present invention relates to a stretched and blown polyester hollow body whose bottom part has high fracture resistance against drop impacts, vibrations during transportation, and the like. Stretch-blown polyester hollow bodies are characterized by their transparency,
It has attracted attention for its excellent properties such as gloss, strength, impact resistance, and gas barrier properties, and has recently been increasingly used in food containers. Injection molded bottomed parisons are often used as the raw material for such stretch-blown hollow bodies. However, in this type of bottomed parison, a gate portion during injection molding, usually called a sprue, protrudes from the center outer surface of the bottom. Depending on the type of polyester resin, this sprue may
Whitening may occur during injection molding (for example, in the case of polyethylene terephthalate). If stretch blow molding is performed with this whitened sprue attached while crushing the sprue between the stretching tip and the bottom of the mold, a white cloud-like cloudy part will spread around the center of the bottom of the hollow body. This cloudy part is usually brittle due to crystallization and is easily torn by impact or vibration. In order to prevent such defects, for example,
No. 52-109565, etc., proposes a method of cutting and removing the sprue from the bottom of the parison with a cutter or the like before stretch-blow molding, but even in this case, most of the area near the center of the bottom of the stretch-blow molded hollow body is not stretched. Because it is not stretched, its strength is lower than other stretched parts. Therefore, if the bottom part has the shape shown by 1 (solid line) in Figure 1, normally the part 2 near the center will not hit other objects, but if the bottom part is filled with contents and a falling impact force is applied. When the bottom part bulges downward as indicated by 1' (dotted line), the bottom bulges out at 2' near the center.
There is a problem in that they are likely to collide with the floor surface and cause cracks, etc. The above problem can be prevented by making the bottom wall thick enough or by making the recess height at the bottom sufficiently large so that the center area 2' does not come into contact with the floor during a fall. This leads to problems such as increasing the amount of water used and decreasing the internal volume. The present invention was devised in view of the problems of the conventional stretch-blown polyester hollow bodies mentioned above. The object of the present invention is to provide a stretch-blown polyester hollow body that is less prone to cracking. In order to achieve the above object, the present invention provides a polyester hollow body formed by stretch blowing using an injection molded parison having a sprue at the bottom, the bottom of the hollow body being a peripheral edge having a ground plane, the peripheral edge connected to the ground surface, 10~
a first recess formed of a substantially flat panel section that extends diagonally upward and inward with a 25 degree slope; 2 recesses, the diameter of the second recess is larger than the diameter of the starting end of the sprue, and the first recess and the second recess have an outer surface with a radius of curvature of 2 to 15 mm. The object of the present invention is to provide a stretched-blown polyester hollow body, which is characterized in that the polyester hollow bodies are connected through a curvature portion. The present invention will be described below with reference to the drawings which are examples. In FIGS. 2 and 3, reference numeral 4 denotes a stretched blown polyester hollow body (the cross section can take any shape such as circular or elliptical), and its bottom 5 is a ground plane 6a.
It has a peripheral edge 6 that is connected to the body wall 7, and a substantially flat surface that connects with the inside of the peripheral edge 6 and extends obliquely upward (in the case of FIG. 2, it has a slightly curved surface that is convex inward). (This shape will also be referred to as substantially flat in this specification) It has a main recess 8 formed by the panel part 9, and a central recess 10 formed in the center of the bottom part 5 in connection with the panel part 9. ing. The panel part 9 and the bottom part 11 of the central recess 10 have a slope larger than that of the panel part 9 (for example, about 30 degrees with respect to the axis of the hollow body).
They are connected by a rising portion 12 having a certain angle. The slope of the panel section 9 (relative to the horizontal plane of the figure, i.e. the ground plane) is preferably relatively small, i.e. between 10 and 25 degrees. If it is smaller than 10 degrees, the depth of the recess will not be sufficient to protect the center of the bottom in the event of a fall impact, etc. If it is larger than 25 degrees, the above-mentioned protection effect will not particularly increase, but rather the inner volume will be reduced. This is because it will lead to a decrease. The panel portion 9 and the rising portion 12 are connected via a curvature portion 13. Preferably, the radius of curvature (of the outer surface) of the curved portion 13 is approximately 2 to 15 mm. In the case of a fall impact, etc., when the bottom part is turned outward, the area near the boundary between the panel part 9 and the curved part 13 first comes into contact with the floor surface, etc. It is important to prevent cracks at weak points. If the radius of curvature is smaller than about 2 mm, the above-mentioned relaxation effect will not be sufficient, while if it is larger than about 15 mm, the bottom part 11 of the central recess will bulge downward and be easily torn when subjected to a fall impact. Although the outer surface of the bottom portion 11 is substantially flat, traces of cutting the sprue from the bottom of the parison before stretch blow molding remain. If the outer surface of the bottom portion 11, that is, the bottom surface, is not substantially flat, for example, if the bottom surface is convex downward in a spherical shape, the bottom surface is likely to hit the floor surface etc. when a fall impact is applied, and this may cause damage. It has the disadvantage of being easy to use. For example, if the bottom has a dome-like shape, that is, it is convex inward, the cloudy, crystallized, originally brittle part at the center of the bottom has been subjected to relatively large processing, as mentioned above. Furthermore, it becomes brittle and has the disadvantage of being easily torn or cracked by impact, vibration, etc. The bottom portion 11 and the rising portion 12 are also connected via a curvature portion 14 having a radius of curvature approximately equal to that of the curvature portion 13, but the diameter of the outer surface side of the bottom portion 11 is
It is desirable that it be larger than the maximum diameter of the cut sprue (usually the diameter of the interface with the bottom of the parison). The diameter is usually about 3 to 5 mm, but the area near the center of the bottom within this range is hardly stretched, and there are also areas where the influence of whitening remains, resulting in low strength. It is also undesirable for the diameter of the bottom portion 11 to be larger than about 20 mm. This is because if the length exceeds about 20 mm, the bottom portion 11 will bulge downward in the event of a fall impact, etc., making it more likely to collide with the floor or the like. The depth of the main recess 8 and the central recess 10 from the ground surface 6a depends on the diameter, wall thickness, strength, internal volume of the container, etc. of the bottom, but when a drop impact is applied, the center of the bottom will be close to the floor surface etc. The depth is usually set in the range of about 3 to 10 mm, so that it is as shallow as possible without touching the surface. The drawn and blown polyester hollow body of the present invention has a bottom formed by two recesses, a main recess and a central recess, and the bottom of the central recess is almost flat, so that it can be filled with contents and sealed. Even if the bottom bulges downward due to a drop impact or repeated vibrations, the relatively strong outer periphery of the central recess, which has an outer surface curvature radius within a predetermined range, will collide with the floor first. or contact, so that the vicinity of the center of the central concave portion, where the strength is the weakest, does not come into contact with the floor surface or the like. Therefore, it has the effect of preventing leakage of contents due to cracks, etc. In addition, the panel forming the main recess forms an inclination of 10 to 25 degrees with respect to the ground plane and extends diagonally upward and inward, making it possible to secure a relatively large internal volume while also being able to withstand the impact of falling. This has the advantage that the recess depth is sufficient to protect the center of the bottom. Furthermore, since the panel portion is substantially flat, it has the advantage that it is difficult to flip outward due to the arch effect even when a fall impact is applied. A specific example will be explained below. Specific Example A stretch-blown polyethylene terephthalate container having a circular cross section, a bottom of the type shown in FIG. 2, and the following specifications was prepared. Note that the sprue of the parison was previously cut and removed at its base. The diameter of the bottom peripheral part (ground plane 6a) is 70 mm, the diameter of the panel part 9 is 60 mm, the diameter of the central concave part (circle) is 15 mm, the radius of curvature of the curved part 13 is 4 mm, the average thickness of the bottom part is 1.5 mm, the average thickness of the body part is thickness
0.4mm, the slope of the panel part 9 is 18 degrees, the maximum depth of the panel part 9 is 4mm, the depth of the central recess from the ground plane is 6mm,
Container internal volume 1000c.c. For comparison, a container similar to the above except that the central concave portion was not provided, and a container similar to the above except that the radius of curvature of the outer surface of the curvature portion 13 was set to 1 mm and 17 mm were prepared. Next, each of these 10 containers was filled with tap water and sealed, vertically dropped from a height of 120 cm with the bottom facing down up to 10 times, and the number of damaged containers was determined.
The results are shown in Table 1.

[Table] As shown above, when the center recess is not provided, all containers are damaged by 5 drops, but for the containers of this invention with a center recess, about half (6) are broken even after 10 drops. was not damaged. In addition, the curvature part 1
When the radius of curvature of No. 3 was 1 mm and 17 mm, the number of undamaged containers was 3 and 2, respectively.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view near the bottom of a conventional hollow body;
FIG. 2 is a partially sectional front view of an embodiment of the hollow body of the present invention, and FIG. 3 is a bottom view of the hollow body of FIG. 4... Stretched blown polyester hollow body, 5... Bottom, 6... Periphery, 6a... Ground plane, 8... Main recess (first recess), 9... Panel part, 10... Center recess ( second recess).

Claims (1)

[Scope of utility model registration request] In a polyester hollow body formed by stretch blowing using an injection molded parison having a sprue at the bottom, the bottom of the hollow body has a peripheral edge having a ground plane, and a peripheral edge that is connected to the circumferential edge and is connected to the ground plane. a first recess formed of a substantially flat panel section that extends obliquely upward and inward with an inclination of 10 to 25 degrees; , the diameter of the second recess is larger than the diameter of the starting end of the sprue, and the first recess and the second recess are
A stretched blown polyester hollow body, characterized in that the outer surfaces are connected via a curvature portion having a radius of curvature of 2 to 15 mm.