JPH0585535A - Pressure resistant self-standing container which is formed by biaxial stretch molding - Google Patents

Abstract

PURPOSE:To improve self-standing performance and to reduce weakening due to stress cracking or whitening of leg parts by a method wherein at a lower part of a container body, besides a heat-crysterized bottom central part, valley parts, a divided bottom surface, the leg parts, curved parts and earthing parts, each having special shape, are provided. CONSTITUTION:In a pressure resistant container 1 which is formed by biaxially stretching saturated polyester resin, a heat-crysterized bottom central part 6 is provided. A container bottom surface is divided equally by an equal central angle, and valley bottom surfaces 4 which rise slantwise and outward from the bottom central part 6 and valley parts with valley side surfaces 7 to sandwich the valley bottom surfaces 4 are also provided. Further, divided bottom surface parts 5, divided equally by an equal central angle by the valley parts, are stretched from a peripheral edge of the bottom central part 6. On the other hand, a stretched body lower part 10 is defined by the valley parts, and tetra-trapezoid-shaped leg parts 3 are stretched from a body lower end part 2, which are defined by the valley side surfaces 7 and the divided bottom surface part 5. At a rising part adjacent to a body part of each bottom surface part divided equally by the valley parts, curved surface parts 8 are stretched. Further, an earthing part 9 formed of an arched bottom outer periphery which connects the curved parts 8 is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially stretch-molded self-standing pressure vessel having excellent pressure resistance.

[0002]

2. Description of the Related Art Containers for gas-containing beverages are required to have high resistance to internal pressure. Therefore, a biaxially stretch blow molded container using a saturated polyester resin such as polyethylene terephthalate having high strength is used.

The bottom of such a container has a hemispherical shell shape,
Internal pressure resistance is improved, but it cannot stand on its own. Therefore, a separately molded base cup is attached, and a hot-melt adhesive is used to fix the base cup to provide self-supporting property. However, the use of such a base cup requires that the base cup must be molded separately, needs to be mounted and fixed, the weight of the container is large and the shape is large, and the bottom of the container cannot be seen. Therefore, there are many drawbacks such as that the consumer cannot confirm that there is no foreign matter such as sediment on the bottom and that the bottom of the container is sealed by the base cup so that the pinhole test cannot be performed.

Due to these problems, a container that does not use a base cup has been proposed. For example, JP-A-57-19493
There is a container described in JP-A No. 9-167146, a container described in JP-A-1-267146, a container described in JP-B-61-1970, and the like. In each of these containers, legs are provided at the bottom of the container so that they can stand by themselves. As an example, the container described in Japanese Examined Patent Publication No. 61-9170 will be described. In this container, the bottom surface is divided into odd numbered parts at equal center angles by valley lines that are inclined upward from the center toward the outside. The other 2 opposite the line
A triangular pyramid where the part sandwiched by the valley lines of the book has ridges extending from the valley lines on both inclined side surfaces with the valley lines on both sides as the bases and the tip is cut off to form a flat bottom surface. The bottom portion of the biaxially stretch-molded pressure-resistant bottle which is formed into a leg portion by protruding into a shape. The ridgeline mentioned here refers to each bottom surface divided by a valley. That is, the divided bottom surface forms an inflexible surface that continuously rises upward with respect to the center-facing valley surface. The characteristic of this container is that each ridgeline including the valley line does not bend and does not invert in the middle, it is a simple curved shape in almost a single direction, and although it is divided, the entire bottom is a hemispherical shell. It is intended to maintain the performance of the shape. However, this container also has insufficient pressure resistance.

[0005]

SUMMARY OF THE INVENTION A major drawback of these biaxially stretch blow-molded containers having legs at the bottom is that the center of the bottom has a low strength. In biaxial stretch blow molding using a normal stretch rod, the center of the bottom cannot be sufficiently stretched and the strength is weak. Therefore, the center of the bottom is thermally crystallized. Although the strength of this part increased due to thermal crystallization, the peripheral edge of the thermal crystallization part was neither thick nor thick due to neither thermal crystallization nor stretching, resulting in a small strength and bulging outward due to internal pressure or stress. It causes cracking. In addition, if the container is dropped during storage due to internal pressure or due to buckling of the contents at the time of landing, the bulging portion further swells and the ground is often broken. Further, there is a problem of whitening and brittleness of the tips of the legs.

According to the research conducted by the present inventor, it has been found that the occurrence of stress cracking becomes remarkable as the number of legs increases. It is clear that this requires a large force to form the legs, so that a large stress occurs and stress cracking occurs.

Furthermore, if the bottom surface is divided into even numbered parts at equal center angles by the valleys, the deformation occurs asymmetrically, so that there is a risk that the container may tilt and fall over during transportation.

Further, it seems that the self-sustaining stability is improved by cutting off the tip of the ridge to form a flat ground contact surface, but when the gas-containing beverage is filled, internal pressure causes an inflection of the connection between the flat surface and the ridge. It was found that the swelling and the ground contact part moved to the center side of the bottom part, and the diameter of the arc connecting the ground contact surface supporting the bottle body when it stood up became small and the self-sustaining stability deteriorated. The present invention is a novel invention that solves all such drawbacks.

[0009]

MEANS FOR SOLVING THE PROBLEMS The present invention relates to "1. A. A thermally crystallized bottom central portion arranged at the bottom center of a biaxially stretched pressure resistant container made of a saturated polyester resin, and B. Biaxially stretched. The bottom of the pressure vessel is equally divided by an equal angle, and the bottom of the valley is inclined upward from the center of the bottom to the outside.
A valley portion having both side surfaces sandwiching the bottom surface of the valley, and C.I. A split bottom portion equally divided by the valley portion at an equal center angle and extended from the peripheral portion of the thermally crystallized bottom center portion; The extended lower end of the trunk portion is partitioned by a valley portion, and the elongated leg portion having a square trapezoidal shape by the valley side surface, the divided bottom surface portion, and the trunk portion lower end portion; A stretched curved surface portion which is arranged at a rising portion following the trunk portion of each bottom portion that is evenly divided by a valley portion; A pressure resistant self-supporting container biaxially stretch-molded, comprising: a ground contact portion having an arcuate bottom outer periphery connecting the curved surfaces of the rising portion. 2. The biaxially stretch-molded pressure-resistant self-supporting container according to item 1, wherein the bottom of the valley is composed of a single curved surface having no inflection portion and rising outward from the peripheral edge of the thermally crystallized bottom. 3. The bottom part, which is divided into equal parts by the valley part, is composed of a single curved surface having no inflection part that descends from the peripheral edge of the thermally crystallized bottom part toward the rising part. Molded pressure resistant self-supporting container. 4. The biaxially stretch-molded pressure-resistant self-supporting container according to any one of items 1 to 3, in which the bottom surface of the container is evenly divided at an equal center angle. 5. The biaxially stretch-molded pressure-resistant self-supporting container according to any one of items 1 to 4, in which the bottom surface of the container is equally divided into four equal angles. 6. The biaxial stretch-molded pressure resistance according to any one of items 1 to 5, wherein the bottom part excluding the leg part is formed of a hemispherical surface having a radius of half the diameter of the lower end of the body part. Freestanding container. 7. The pressure resistant self-supporting container biaxially stretch-molded according to any one of items 1 to 6, wherein the divided bottom surface portion is thinned by extending from the peripheral edge of the thermally crystallized bottom portion. Regarding

As the saturated polyester resin used in the present invention, polyethylene terephthalate resin is most suitable in terms of strength, transparency, and gas barrier property.

[0009]

In the present invention, the center of the bottom is thermally crystallized. Thermal crystallization of the center of the bottom is a means used in ordinary biaxial stretch blow molding as described above. In blow molding using an ordinary stretched rod, the strength of the center of the bottom is small because the center of the bottom is not sufficiently stretched, and therefore heat crystallization is performed to increase the strength of the center of the bottom. However, even if such a thermal crystallization part is provided, its peripheral edge is not stretched, so that it becomes thick and has low strength, and it is deformed or cracked due to internal pressure. In order to increase the strength of the center of the bottom, blow molding was carried out substantially without restraint, and the center of the bottom was also stretched to become a stretched hemisphere, and the strength was greatly improved. However, this container cannot stand on its own.

On the other hand, in order to make the container self-supporting, the stretch-blow-molded hemispherical bottom portion is further finish-blow-molded by using a mold to form a split bottom surface and a leg portion. Whitening occurred on the rising part connected to the lower end of the trunk. According to the research conducted by the present inventor, this whitening is caused by over-stretching, and thus has the drawbacks of being brittle, easily cracked, and having a large gas permeation amount. Since this part is a grounding part, brittleness is a serious drawback.

Further studies have shown that this overstretching occurs because the bottom is stretched. Since it is further stretched near the rising part of the stretched thin bottom,
Over-stretching occurs because the thickness of the stretched material is small. In order to prevent overstretching, various investigations were made, and it was attempted to arrange a thick portion that is stretched at the time of forming the legs at the center of the bottom. However, stretching is necessary in order to increase the strength of the entire bottom portion, and when stretched, the thickness becomes uniform and no thick portion remains.

Therefore, it was considered to utilize the conventional unfavorable problem, that is, the thick portion which is not stretched and which is generated at the peripheral edge when the thermal crystal region is provided at the center of the bottom. If the center of the bottom of the preform is thermally crystallized and stretched in advance to form a container, a hemispherical shell-shaped bottom having the center of the thermally crystallized bottom is formed. Since the peripheral portion of the center portion of the thermally crystallized bottom is difficult to be stretched, a thick portion that is neither thermally crystallized nor oriented crystallized remains. If this bottom part is further subjected to blow blow molding using a mold for forming the leg part, the resin remaining on the peripheral edge of the center part of the thermally crystallized part is stretched and becomes thin. It was clarified that overstretching can be prevented. In addition, the peripheral edge of the thermally crystallized bottom portion is also sufficiently stretched, and the strength of this portion is greatly improved. Since the wall thickness is uniform and there is no thick portion, stress cracking is prevented. Furthermore, in the obtained container, the thickness of the peripheral portion of the center portion of the thermally crystallized bottom is also uniform, and there is no residual resin forming the thick portion, so the total resin areal weight can be reduced.

In the present invention, the bottom surface of the container is equally divided at equal center angles. Since the bottom portions having the same structure have substantially the same strength, the deformation tends to occur similarly in the same structure portion. If it is divided into odd numbers, the structure is asymmetrical, so deformation also occurs asymmetrically, and the self-sustaining stability deteriorates, and there is a risk of falling during transportation. If it is divided into even numbers, even if deformation occurs, the structure is symmetrical, so deformation also occurs symmetrically, and deterioration of self-sustaining stability can be prevented. Therefore, even division is preferable, but the present invention also includes odd division.

In the present invention, the valley bottom surface that equally divides the bottom surface at an equal center angle forms a part of a hemispherical surface which is inclined upward toward the outside from the peripheral edge of the thermally crystallized bottom center portion. The bottom of the container is essentially a hemispherical shell or a semi-elliptical spherical shell stretched by blow molding, and the legs are arranged on this hemispherical shell to provide self-supporting property, and the valley bottom is this hemisphere. It shows that it is the remaining part of the shell. The most preferred container bottom is one of the diameter of the lower end of the body
It is a hemispherical shell with a radius of / 2. In this substantially hemispherical shell bottom, approximately 90% of the required stretching is achieved by unconstrained blow molding, and finally the legs are formed in the mold by finish blow molding. Since it is sufficiently hemispherically stretched by unconstrained blow molding, even if the legs are formed, the strength of the bottom is very large due to the action of the valley bottom which is a part of the hemispherical shell. The central portion of the bottom is thermally crystallized, and the peripheral portion thereof is also sufficiently stretched by stretching, so that the strength of the entire bottom portion is very large and the pressure resistance is excellent.

As described above, when the legs are formed on the bottom portion of the hemispherical shell obtained by stretch blow molding, stress cracking becomes remarkable as the number of legs increases. This is because a large amount of force is required to form the legs and a large amount of stress is generated, resulting in stress cracking. Therefore, the smaller the number of legs is, the better the self-sustaining stability is when the number of legs is 2, which is the minimum number.
With four, the self-sustaining stability and stability over time were very good. With six, the occurrence of stress cracking increased slightly. In this way, the number of legs is not too large,
It is preferably a book.

The present invention will now be described with reference to the drawings.

FIG. 1 shows a side surface of a container of the present invention, and 1 is a container. Reference numeral 2 denotes a lower end portion of the trunk, on which leg portions 3 are formed. The leg portion 3 is formed in a rectangular trapezoidal shape by the extended trunk lower end portion 10 partitioned by the valley bottom surface 4, the valley side surface 7, and the divided bottom surface portion 5.

FIG. 2 is a plan view showing the bottom,
Is a valley bottom surface, 5 is a divided bottom surface portion, and 6 is a thermally crystallized bottom center portion. Reference numeral 7 denotes a side surface of the valley, which forms a valley portion together with the bottom surface of the valley. The bottom surface of the divided valley is connected to the lower end of the body extended by a curved surface portion 8 which is inclined downward from the peripheral edge of the center of the bottom toward the rising portion and is arranged at the rising portion.

FIG. 3 is a view showing a part of the bottom part cut along the axis of the body part, and the leg part is omitted on one side to clearly show the valley bottom surface 4. As can be seen from the valley bottom surface 4, the bottom portion is essentially a hemispherical shell having a radius of half the diameter of the trunk lower end portion 2. The divided bottom surface portion 5 is formed by bulging downward from the hemispherical shell, forms a slope that does not bend from the peripheral edge of the thermally crystallized central portion 6 toward the rising portion, and extends at the curved surface 8 of the rising portion. It is connected to the lower end 10 of the body. 9 is a grounding part. The arc connecting the grounding parts of each leg becomes the grounding part of the container. If there is no thick portion around the center of the thermally crystallized bottom, whitening occurs due to overstretching at the rising portion including the ground contact portion when the leg portion is formed. The bottom surface as a whole forms a concave surface that descends from the center of the bottom toward the periphery of the bottom to prevent grounding of the center. Since stress is generated when there is an inflection portion on the division bottom surface 5, the inflection portion bulges due to internal pressure, and this portion becomes the ground contact portion, so that the ground contact arc becomes small and the self-sustaining stability deteriorates.

Comparative Test Example A container having a content of 1.5 liters shown in FIGS. 1 to 3 and using a polyester resin. The elements of the container are as shown in Table 1.

Comparative Example 1 A container was used in which the bottom center portion thermally crystallized on the bottom surface was not arranged. Others were the same as those in the example.

[0020]

[Table 1]

(Note) Number of divisions: number of equally divided division bottoms

Test Method Test 1 In each example, 100 G of 4G. V. The number of stress cracking after storage at 30 ° C. and a humidity of 80% and the number of deformed strains were examined. The results are shown in Table 2.

[0023]

[Table 2]

Test 2 The number of occurrences of whitening at the tip of the leg after forming the leg was counted. In addition, 4G. V. Of carbonated water was dropped into the concrete floor from 1.2 rice above and the number of broken legs was counted. The results are shown in Table 3.

[0025]

[Table 3]

From the test results, it is understood that the container of the present invention is excellent in stress cracking resistance and deformation resistance of the leg portion against whitening.

[0027]

The present invention has the effects of being highly self-sustaining, less stress cracking, and less brittle due to whitening of the legs.

[Brief description of drawings]

FIG. 1 is a side view of a container of the present invention.

FIG. 2 is an explanatory diagram of a container bottom portion.

FIG. 3 is an explanatory view showing a vertical cross-sectional view of the bottom of the container.

[Explanation of symbols]

 1 Container 2 Lower End of Body 3 Bottom 4 Bottom of Valley 5 Split Bottom 6 Center of Thermally Crystallized Bottom 7 Side of Valley 8 Curved Surface 9 Grounding Part 10 Lower End of Extension Body

Claims (7)

[Claims] 1. A. A thermally crystallized bottom center portion arranged at the center of the bottom of a biaxially stretched pressure-resistant container made of a saturated polyester resin; A bottom surface of the valley that is inclined upward from the center of the bottom to divide the bottom surface of the pressure-resistant container stretched biaxially at equal center angles.
A valley portion having both side surfaces sandwiching the bottom surface of the valley, and C.I. A split bottom portion equally divided by the valley portion at an equal center angle and extended from the peripheral portion of the thermally crystallized bottom center portion; The extended lower end of the trunk portion is partitioned by a valley portion, and the elongated leg portion having a square trapezoidal shape by the valley side surface, the divided bottom surface portion, and the trunk portion lower end portion; A stretched curved surface portion which is arranged at a rising portion following the trunk portion of each bottom portion that is evenly divided by a valley portion; A pressure resistant self-supporting container biaxially stretch-molded, comprising: a ground contact portion having an arcuate bottom outer periphery connecting the curved surfaces of the rising portion. 2. The pressure resistant self-supporting container biaxially stretch-molded according to claim 1, wherein the valley surface is a single curved surface having no inflection portion which rises outward from the peripheral edge of the thermally crystallized bottom portion. 3. The bottom surface, which is divided into equal parts by the valley bottom, is composed of a single curved surface having no inflection part which descends from the peripheral edge of the thermally crystallized bottom center toward the rising part. The biaxially stretch-molded pressure-resistant freestanding container described. 4. The bottom surface of the container is evenly divided at equal center angles,
The biaxially stretch-molded pressure-resistant self-supporting container according to any one of claims 1 to 3. 5. The biaxially stretch-molded pressure-resistant self-supporting container according to claim 1, wherein the bottom surface of the container is divided into four equal-angled parts. 6. The bottom excluding the legs has a diameter of 1 at the lower end of the body.
The biaxially stretch-molded pressure-resistant self-supporting container according to any one of claims 1 to 5, which is formed of a hemispherical surface having a radius of / 2. 7. The biaxially stretch-molded pressure-resistant self-supporting container according to claim 1, wherein the divided bottom surface portion is thinned by extending from the peripheral portion of the thermally crystallized bottom center portion.