JP4679283B2 - Bottom structure of plastic container - Google Patents

Description

  The present invention relates to a bottom structure of a synthetic resin container.

In the conventional synthetic resin container, for the purpose of achieving both self-supporting property and pressure resistance, the bottom of the container is inflated downward to form a curved wall, and the curved wall is inflated intermittently in the circumferential direction. Some have a bottom structure that includes a plurality of legs that surround the central portion as an upper bottom wall (see, for example, Patent Document 1).
Japanese Patent No. 3138051

  In particular, the above conventional bottom structure smoothly connects the ground contact portion of the leg portion and the upper bottom wall without forming a corner portion, and the smooth curved surface portion is continuously connected to other portions as well. Thus, when the internal pressure of the container increases, the self-supporting property is ensured while allowing some expansion.

  By the way, when using carbonated beverages containing fruit juice as the contents, it is common to perform sterilization by keeping the contents at a temperature of 65 ° C. for 10 minutes after filling the container with low-temperature contents. is there.

  However, when the conventional bottom structure is filled with a highly volatile content such as a carbonated beverage at a relatively low temperature and sterilized by heating, the internal pressure of the container continues to be very large for a long time. The upper bottom wall surrounded by bulges out to the outside and may cause a phenomenon of so-called bottom falling.

  In addition, in the conventional bottom structure, when the container is dropped with the contents filled, stress tends to concentrate on the upper bottom wall surrounded by a plurality of legs, and cracks and cracks are formed on the upper bottom wall. Etc. may be generated.

  The present invention has been made on the basis of such fact recognition, and the problem to be solved is that the internal pressure of the synthetic resin container becomes very large, such as heating highly volatile contents. However, the object is to provide a bottom structure that is excellent in drop strength without falling off the bottom.

The bottom structure of the synthetic resin container according to the present invention is formed by inflating the lower end of the body portion of the synthetic resin container downward in the body axis direction to form a curved wall and intermittently inflating the curved wall in the circumferential direction. A bottom portion structure of a synthetic resin container including a plurality of legs surrounding the central portion of the curved wall as an upper bottom wall, wherein the outer wall of the leg has an upper end at a position where the curved wall starts to bend The lower end is a position connected to the heel portion formed on the outer edge of the grounding portion, and the curvature between the upper end and the lower end is 1.5 times or more with respect to the height in the axial direction of the flat portion connected in a straight line or the outer wall. The curved wall that forms a curved portion having a radius and the effective diameter of the lower end is 92% or less of the effective diameter of the upper end, and the curved wall that connects the side walls of each leg portion has a width at the body side end that is on the upper bottom wall side. Form a valley bottom that is at least 1.2 times the width of the edge, and crystal of the upper bottom wall Degree is characterized in that 30% or less.

  According to the present invention, the outer shape of the outer wall of the leg, the width of the trunk side end and the upper bottom wall side end of the valley bottom formed by the curved wall connecting the side walls of each leg, and the leg and curve By defining the crystallinity of the upper bottom wall surrounded by the wall, the internal pressure of the container is very high, such as when sterilizing by heating after filling highly volatile contents such as carbonated beverages with fruit juice. Even if the large state continues for a long time, the upper bottom wall does not expand to the outside of the container to cause a bottom drop. In particular, the drop strength is excellent because the crystallinity of the upper bottom wall where stress due to drop impact is likely to concentrate is 30% or less.

  Therefore, according to the present invention, it is possible to provide a bottom structure of a synthetic resin container that is excellent in drop strength without falling down even under conditions in which the internal pressure of the container becomes very large.

  In the present invention, if the shape and numerical values described above are defined, various changes can be made in the configuration of the other parts, but the leg part is interposed through a heel part whose outer wall is curved outward of the container. If the grounding part is provided with an upper bottom inclined wall that is curved to the inside of the container and is connected to the upper bottom wall, the internal pressure of the container is increased because the rigidity is increased due to the shape of the upper bottom inclined wall. Even if becomes slightly larger, it is possible to further suppress the deterioration of the independence due to the falling of the bottom or the expansion of the bottom.

  Further, according to the present invention, the upper bottom wall, which is the central portion of the curved wall surrounded by a plurality of legs, may be flat or curved. However, when the upper bottom wall is flat, stress is easily concentrated when the container is dropped. Since the stress can be further dispersed in the upper bottom wall, it is effective in improving the drop strength. Further, when the upper bottom wall is curved inward of the container, the bottom falling phenomenon can be prevented more.

  Hereinafter, the bottom structure of the synthetic resin container according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view of an essential part showing an entire bottle 10 as an embodiment of the present invention from the front, and FIG. 2 is a bottom view thereof. 3 is a cross-sectional view taken along the line XX of FIG. 2, and FIG. 4 is a perspective view showing the bottom 15 of the bottle 10 from below. Further, FIG. 5 is an enlarged view of a main part showing the bottom 15 from the back.

  The bottle 10 is a so-called PET bottle formed by biaxial stretching blow molding of polyethylene terephthalate (PET) resin, and as shown in FIG. The shoulder portion 13 is connected to the neck portion 12 provided with the ring 12a, and the bottom portion 15 is connected to the shoulder portion 13 via the trunk portion 14.

  The bottom 15 has a dome-shaped curved wall 2 connected to the cylindrical wall 1 by inflating the lower end of the body 14 downward along the axis O as shown in FIG. As shown in FIG. 2, the curved wall 2 is intermittently inflated in the circumferential direction around the axis O, and has five legs 4 surrounding the central portion 3 of the curved wall 2 as an upper bottom wall. Thereby, as shown in the cross-sectional part of FIG. 3, the bottom part 15 can form a space inside the cylindrical wall 1, the curved wall 2, the upper bottom wall 3 and the leg part 4 and can be filled with the contents.

  As shown in FIG. 2, the leg portion 4 includes an outer wall 5 connected to the cylindrical wall 1, a side wall 6 rising from the curved wall 2 together with the outer wall 5, and an upper bottom inclined wall 7 connected to the upper bottom wall 3. A grounding portion 9 is formed in a portion surrounded by a heel portion 8 that is curved outward of the container.

  As shown in FIG. 3, the cylindrical wall 1 is curved with a radius of curvature R 1 from a position b hanging from the upper end a by ΔL 1 and connected to the upper end c of the curved wall 2. The curved wall 2 starts to bend from the upper end c to the outer side of the container with a radius of curvature R2, and from the middle of the curved wall 2 to the outer side of the body 14 by a radius of curvature R3, with a position offset by L2 from the upper end c. Then, it is connected to the outer edge d of the upper bottom wall 3.

  As shown in FIG. 3, the outer side wall 4 starts with the upper end c of the curved wall 2, and the upper end c and the lower end e form a flat portion that is connected in a straight line, and the effective diameter φ1 of the lower end e is the upper end c. Is set to 92% (φ1 = 0.92 × φ2) or less of the effective diameter φ2. More preferably, the effective diameter φ1 of the lower end e is set to 87% (φ1 = 0.87 × φ2) or less of the effective diameter φ2 of the upper end c.

  The lower end e of the outer side wall 4 is connected to the outer edge f of the ground contact portion 9 via a heel portion 8 having a curvature radius R5. Furthermore, although the upper bottom inclined wall 7 connected to the inner edge g of the ground contact portion 9 can be formed of either a flat surface or a curved surface, this embodiment is curved to the outside of the container with a radius of curvature R6 and is also a bent portion. Curved from h to the inside of the container with a radius of curvature R7 and connected to the outer edge d of the upper bottom wall 3 together with the curved wall 2. When the upper bottom inclined wall 7 is formed of a curved surface, the curvature radius R6 is preferably 45 mm or less.

  Furthermore, as shown in FIG. 2, the curved wall 2 connecting the side walls 6 of the legs 4 has a valley bottom where the width W1 of the body side end is 1.2 times or more than the width W2 of the upper bottom wall side end. Form. More preferably, the valley bottom is formed so that the width W1 at the body side end is at least twice as large as the width W2 at the upper bottom wall side end.

  Thereby, the bottle 10 is held by the five legs 4 swelled intermittently around the axis O from the curved wall 2 of the bottom 15. In this embodiment, as shown in FIG. 2, the leg portion 4 has a configuration in which the intermediate portion of the curved wall 2 forming the valley bottom is narrowed as the connecting portion 6a with the curved wall 2 protrudes toward the curved wall 2 side. However, in the present invention, if the width W1 of the body side end is 1.2 times or more, preferably 2 times or more than the width W2 of the upper bottom wall side end, the valley bottom formed by the curved wall 2 is used. It does not matter what the external shape is. For example, the curved wall 2 that forms the valley bottom by extending the connecting portion 6a in a straight line may be configured to be tapered toward the upper bottom wall 3.

  The bottle 10 further sets the crystallinity of the upper bottom wall 3 to 30% or less. Specifically, the crystallinity is adjusted by adjusting the temperature of the upper bottom wall 3 during blow molding. In this case, for example, in the two-stage blow molding, it is preferable to adjust the bottom part temperature of the primary blow mold, the bottom heating temperature of the heat shrinking process, the bottom part temperature of the secondary blow mold, etc. Then, it becomes easy to make the upper bottom wall thickness 1 mm or less. Further, when adjusted as described above, when the crystallinity is suppressed to 30% or less as in the present invention, the molded product (bottle 1) is stretched and thinned, so that thermal crystallization hardly occurs and crystallization is suppressed. Can be effective.

  Hereinafter, as a reference technique, a method for measuring the crystallinity of the PET resin will be exemplified. There are various methods for measuring the degree of crystallinity, but a density method based on density measurement is easily used. Here, an example of calculating the degree of crystallinity from the following formula (1) based on the sample density is illustrated.

X = dc × (d−da) / d × (dc−da) (1)
X: crystallinity, d: sample density
da: density of completely amorphous PET (1.335 g / cm ³ )
dc: Theoretical density of fully crystallized PET (1.501 g / cm ³ )
However, the density measurement conforms to JIS K-7112 (density gradient tube method / D method).

  The upper bottom wall 3 surrounded by the legs 4 may have a dome shape that protrudes outside the container along the axis O. However, as shown in a region A in FIG. It is preferable to constitute a part.

  According to the present invention, the outer shape of the outer wall 5 of the leg 4 and the width W1 of the body side end and the upper bottom wall side end of the valley bottom formed by the curved wall 2 connecting the side walls 6 of each leg 4 to each other. , W2 and the upper bottom wall 3 surrounded by the legs 4 and the curved wall 2 are specified for crystallinity so that they are sterilized by heating after filling with highly volatile contents such as carbonated beverages containing fruit juice. As described above, even if the state where the internal pressure of the bottle 10 is very large continues for a long time, the upper bottom wall 3 does not expand to the outside of the bottle 10 to cause a bottom drop. In particular, the drop strength is excellent because the crystallinity of the upper bottom wall 3 where stress due to drop impact tends to concentrate is reduced to 30% or less.

  Therefore, according to the present invention, it is possible to provide a bottom structure of a PET bottle that is excellent in drop strength without falling down even under conditions where the internal pressure of the bottle 1 becomes very large.

  Further, in the present invention, the leg portion 4 is connected to the grounding portion 9 via the heel portion 8 formed by the outer wall 5 being curved toward the outside of the bottle, and the grounding portion 9 is curved toward the inner side of the bottle to the upper bottom wall 3. If the upper bottom inclined wall 7 to be connected is provided, the rigidity increases due to the shape of the upper bottom inclined wall 7, and even if the internal pressure of the bottle 1 increases somewhat, the independence deteriorates due to the bottom drop or the bottom 15 expansion. Can be suppressed.

  Further, in the present invention, the upper bottom wall 3 surrounded by the plurality of legs 4 may be flat or curved, but when the upper bottom wall 3 is flat as in the present embodiment, stress is applied when the bottle 1 is dropped. Since the stress can be further dispersed in the upper bottom wall 3 that tends to concentrate, it is effective in improving the drop strength. Further, when the upper bottom wall 3 is curved inward of the bottle 1, the bottom falling phenomenon can be further prevented.

  What has been described above is one embodiment of the present invention, and various modifications can be made within the scope of the claims. For example, even if the number of legs is three or more, it may be an even number or an odd number. However, when the number of legs is five, as in this embodiment, the bottom drop and the drop strength are most excellent.

It is principal part sectional drawing which shows the whole PET bottle which is one form of this invention from the front. It is a bottom view of the same form. It is XX sectional drawing of FIG. It is a perspective view which shows the bottom part in the same form from the downward direction. It is a principal part enlarged view which shows the bottom part in the same form from a back surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder wall 2 Curved wall 3 Upper bottom wall 4 Leg part 5 Outer side wall 6 Side wall 7 Upper bottom inclined wall 8 Heel part 9 Grounding part

Claims (1)

The lower end of the body portion of the synthetic resin container is inflated downward in the body axis direction to form a curved wall, and the curved wall is intermittently inflated in the circumferential direction to surround the central portion of the curved wall as an upper bottom wall. In the bottom structure of a synthetic resin container provided with a plurality of legs,
The outer wall of the leg part has a position where the curved wall starts to bend as an upper end, and a position connected to a heel part formed on the outer edge of the grounding part as a lower end,
Between the upper end and the lower end, a flat portion connected in a straight line or a curved portion having a radius of curvature of 1.5 times or more with respect to the axial height of the outer wall and an effective diameter of the lower end are effective at the upper end. 92% or less of the diameter,
The curved walls connecting the side walls of each leg portion form a valley bottom where the width of the body side end is 1.2 times or more the width of the upper bottom wall side end, and the crystallinity of the upper bottom wall is 30 % Bottom structure of a synthetic resin container.

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