JP2604499B2 - Biaxial stretch blow molded bottle - Google Patents

Description

The present invention relates to a biaxially stretched blow-molded bottle made of a saturated polyester resin or a polyacrylonitrile resin or the like, in particular, a self-supporting bottom portion having leg pieces bulging out. And a bottom structure of a pressure-resistant biaxially stretch blow-molded bottle having

[Conventional technology]

As a pressure-resistant biaxially stretch blow-molded bottle made of a saturated polyester resin or polyacrylonitrile resin, etc., the bottom of the bottle body is bulged into a hemispherical shell shape, and the bottom is bottomed separately from the bottle body. The base cup molded into a cylindrical shape,
The mainstream is one that is fitted and fixed in a form that provides a leg.

The bottle that combines this base cup with the bottom of the bottle body can exert sufficient internal pressure resistance due to the ability to give sufficient stretching deformation to the bottom of the bottle body and the mechanical structure of the bottom. The bottle has a superior function and effect as a pressure-resistant bottle.However, the base cup, which is a separate member from the bottle body, is a constituent member, making handling of the components cumbersome. A special work process for fitting and fixing the main body and the base cup is required,
The amount of synthetic resin material required to mold one bottle by the amount required for the base cup increases, which goes against resource saving, and the base cups made of different materials are assembled integrally, so From the viewpoint that cycling is difficult, etc., the use of a pressure-resistant bottle having a bottom portion of a self-standing type (hereinafter simply referred to as a self-standing type) in which leg pieces, which are one-piece bottles, are swelled has recently been studied. Has begun.

The self-supporting bottom has a plurality of legs bulging outward at equal intervals to make the bottle self-supporting. In addition, there is an effect that a larger amount of stretching can be given.

[Problems to be solved by the invention]

However, when a biaxially stretched blow-molded bottle whose bottom is formed into a self-supporting type is used as a pressure-resistant bottle, a problem arises in that a crack (crack) occurs in a region where the amount of stretching is insufficient at the bottom in a pressurized state.

As shown in FIG. 9, cracks 10
Is the unstretched region 7 where the stretching center point is not stretched at all.
And a bottom portion 4 having a point of origin A in an insufficiently stretched region 8 surrounded by a leg piece 5 which is greatly stretched and formed into a final shape and a reversal region 6 which is a valley wall wall and has insufficient stretching. Most often occur in a transverse configuration.

The cause of the crack 10 is that the empty bottle during storage in the warehouse receives a history of high temperature and high humidity environment and absorbs more than 4000 ppm (especially, the non-stretched portion tends to absorb moisture), and the pressure higher than normal (Such as when filling a carbonated beverage) and when a strong surfactant as a lubricant used to smoothly carry the sliding of the bottle in the filling line adheres. Occurs when conditions overlap. The condition of the occurrence of the crack 10 is as follows. First, a smaller crazing occurs due to the effect of a large internal residual stress (hereinafter, simply referred to as a stress) on the outer surface of the understretched region 8 of the bottom 4. Develops into cracks 10 within 1-2 days after pressing.

In general, the pressure resistance of a normal bottle at room temperature is
1717 kg / cm ² , whereas when the above-mentioned adverse conditions are added, around 5 kg / cm ² , that is, 1/3 of a normal bottle
Destruction by the action of internal pressure. From this, it can be said that the occurrence of the crack 10 is a fracture due to stress concentration based on crazing.

As a means for stabilizing the mechanical strength, heat resistance, and physical properties of the bottom portion of the synthetic resin biaxially stretched blow-molded bottle that is insufficiently stretched, a technique for crystallizing the bottom portion has been conventionally used. JP-A-62-39443, JP-A-62-193
No. 938, Japanese Unexamined Patent Publication No. 2-175226) are known, but these prior arts uniformly crystallize the entire central portion of the bottom portion, which is an unstretched portion, with a high density. Therefore, when the bottom is formed into a self-supporting type, stress at the boundary between the crystallized and unstretchable central portion and the peripheral portion that is stretched and deformed, that is, the concentration of stress is promoted. The occurrence of cracks can be seen at the beginning. Further, in the case of crystallizing the insufficiently stretched region at the bottom of the biaxially stretched blow-molded bottle, it is difficult to control the heating for crystallization or to regulate the heating region, and the processing operation is extremely troublesome. In addition, there are disadvantages that the number of working steps increases and the number of equipment days increases, and furthermore, there is a problem that the self-standing function is reduced due to deformation of the bottom due to crystallization.

Therefore, the present invention was conceived in order to solve the problems in the conventional example described above, and the cracks generated in the bottom formed into a self-supporting type have a poorly stretched area including an unstretched area, and a curved wall shape. Eliminating the concentration of stress on the insufficiently stretched area and the inversion area, focusing on the fact that stress concentrates on the outer surface of the inversion area such as a valley line wall having an inversion point and acts on the inversion area, Accordingly, it is an object of the present invention to reliably prevent the occurrence of cracks at the bottom of a biaxially stretch blow molded bottle made of synthetic resin, which is formed into a self-standing type.

[Means for solving the problem]

Means of the present invention for solving the above technical problem is to form a plurality of leg pieces bulging out at equal intervals and to form a valley line wall between the leg pieces, which is a reversal area having a wall reversal point at a curved reversal point. A biaxially stretched blow-molded bottle made of synthetic resin having a free-standing bottom portion, on the outer surface of an insufficiently stretched region where stretching is insufficient, including an unstretched region where the stretching center point of the bottom is located, Shaping a large number of stress concentration-reducing functional parts that cause local thickness changes, such as fine irregularities or linear ridges or grooves.

In the case of a free-standing bottom, strong stress concentrates on the bulging base end of the leg, that is, in the insufficiently stretched region near the portion where the leg rises. Since the stress also concentrates on the inversion region, it is desirable to form a large number of stress concentration reducing portions on the outer surface of the valley line wall which is the inversion region.

In addition, as the stress concentration reducing function part, a small projecting protruding piece shape, a small recessed concave shape, and a linear ridge or groove shape along an arc centered on the stretching center point are used. Appropriate.

[Action]

Since a large number of fine stress concentration reducing functional portions are formed in the understretched region, the stress generated in the understretched region is dispersed by the large number of fine stress concentration reducing portions, and a specific stress is reduced. Inability to concentrate on the point.

Therefore, even if crazing occurs in the insufficiently stretched region, stress does not concentrate on one crazing, and it becomes impossible for the crazing to develop into a crack.

In addition, since it does not crystallize the understretched region, it does not require a troublesome and delicate heat treatment for crystallization, and only forms the stress concentration reducing portion in the understretched region. Therefore, the bottle is formed into the final shape only by the conventional simple biaxial stretch blow molding process.

Similarly, since the insufficiently stretched region is not crystallized, there is no possibility that the moldability is reduced due to crystallization, thereby achieving the molding of the bottle while maintaining good moldability.

Most of the stress at the bottom of the biaxially stretched blow-molded bottle acts concentrated on the stretch-deficient region. Since relatively large stress also acts on the inversion region, which is a valley line wall in a state of being in a state, fine crazing may also occur in this inversion region, and therefore, this inversion region By forming a large number of stress concentration reducing functional parts, cracks can be more reliably prevented from occurring.

The structure of the stress concentration-reducing function part includes those that protrude or depress in an uneven shape, and those that become a linear ridge or groove. Since the stress concentration reducing function part is formed, the stress itself generated in the understretched area is reduced, and the stress generated in the understretched area is dispersed to individual stress concentration reducing function parts. , Which makes it impossible for stress to concentrate at a particular location.

In the case of a linear ridge or groove, a large number of fine lines or grooves are formed on the outer surface of the insufficiently stretched area, and the stress in the insufficiently stretched area acts on the outer surface of the insufficiently stretched area. The stress is prevented from dispersing by the large number of fine linear ridges or grooves, thereby preventing the stress from concentrating on a specific crazing and developing into a crack.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a front view of a big-foot type biaxially stretched blow-molded bottle 1 in which the present invention is carried out, in which the bottom portion 4 is cut away. The bottle 1 is formed by injection molding into a bottomed cylindrical shape. A mouth portion 3 is continuously provided at an upper end of a cylindrical body 2 which is biaxially stretch blow-molded from a reform 1 'and has a cylindrical shape, and a bottom portion 4 is continuously provided at a lower end.

The bottom part 4 has an unstretched area 7 where the stretching center point is located, a leg piece 5 which swells downward and provides a leg which gives the bottle 1 a self-supporting function, and a position between the leg piece 5. A reversal area 6 which is a valley wall, and an unstretched area 8 including an unstretched area 7 and a rising portion of the leg piece 5 and surrounded by a leg piece 5 or a valley line wall or the like which is sufficiently stretched. Is composed of
A stress concentration reducing function portion 9 is formed in the stretch insufficient region 8.

As shown in FIG. 2 and FIG. 3, the distribution form of the stress concentration reducing function portion 9 formed in the insufficient stretching region 8 is as follows.
A form almost uniformly dispersed in the entire area of the stretching insufficient region 8, the fourth
As shown in the figure, a form distributed along a spiral line centered on the unstretched area 7, and as shown in FIG. 5, a form distributed on a concentric circle centered on the unstretched area 7 Further, as shown in FIG. 6, it is possible to adopt various forms such as a form intermittently distributed on a concentric circle centered on the unstretched area 7.

FIG. 7 is an enlarged sectional view showing an example of the structure of the stress concentration reducing function portion 9. FIG. 7 (a) shows a sectional structure of the stress concentration reducing function portion 9 shaped like a protruding piece. FIG. 7 (b) shows a sectional structure of the stress concentration reducing function portion 9 which is depressed and formed in a concave shape, and FIG. 7 (c) shows a stress concentration reduction portion which is engraved linearly and formed in a groove shape. The sectional structure of the functional part 9 is shown, and FIG. 7 (d) shows the sectional structure of the stress concentration reducing functional part 9 protruding linearly.

7 (a) and 7 (b) are suitable for being formed in the distribution form shown in FIG. In the case of the stress concentration reducing function portion 9 of the linear ridge or groove of (d),
Although it is advantageous to mold in the distribution form shown in FIGS. 4 to 6, even if the unevenness-shaped stress concentration reducing function portion 9 is molded in the distribution form shown in FIGS. good.

Also, as shown in FIG. 4 to FIG. 6, when the stress concentration reducing function portions 9 are arrayed and formed along a predetermined line, the manufacture of a blow mold for forming the bottle 1 becomes easy. .

Incidentally, the stress concentration reducing function portion 9 formed on the bottom 4 of one bottle 1 does not mean that the structure must be unified, and even if the stress concentration reducing function portions of various structures are mixed. good.

FIG. 8 shows a stress concentration reducing function portion 9 formed in a protruding piece shape.
Are uniformly distributed in the understretched region 8 and the stress concentration reducing function portion 9 is also formed in the inversion region 6.
FIG. 3 is a partially enlarged view showing details of the embodiment shown in the figure, wherein each stress concentration reducing function part 9 has a height from the outer surface of the understretched area 8 of 0.2 mm and a skirt on the outer surface of the understretched area 8. Although the diameter of the part is set to 1.6 mm, the height of only the stress concentration reducing function part 9 located outside indicated by a double circle in FIG. The degree of local stress generated by molding the functional part 9
The periphery is reduced.

In the form shown in FIG.
The results of an experiment comparing the degree of cracking of 100 bottles of the bottle 1 embodying the present invention and 100 bottles of the bottle without forming the stress concentration-reducing function portion 9 are shown below. Show.

In the experiment, the amount of moisture absorbed was 5000 ppm in the state of an empty bottle, and a high-concentration surfactant was applied to the bottom 4, and the filling amount of carbonated water was 4.5 vol.

In the case of a conventional bottle in which the stress concentration reducing function portion 9 is not formed on the bottom 4, cracks occurred in 34 out of 100 bottles, whereas the present invention in which the stress concentration reducing function portion 9 was formed on the bottom 4 was used. In the case of bottle 1 that was implemented, no cracks occurred in all 100 bottles.

〔The invention's effect〕

The present invention has the above-described configuration, and has the following effects.

Since stress can be prevented from concentrating on a specific portion in the understretched region at the bottom, even if crazing occurs at the bottom, for example, the crazing does not develop into a crack, and thereby cracks at the bottom can be prevented. Generation can be almost completely prevented, and a self-standing bottle having a bottom that exhibits stable strength against internal pressure can be obtained.

Since the stress concentration reducing portion formed at the bottom of the bottle is formed by a normal biaxial stretch blow molding operation of the bottle, the forming is simple and stable productivity can be obtained. .

Since the stress concentration reduction function part is only in the shape of fine uneven pieces or linear ridges or grooves,
Good moldability of the bottle can be stably maintained without lowering the moldability of the bottle.

[Brief description of the drawings]

FIG. 1 is a front view in which the bottom of a biaxially stretched blow-molded bottle having a free-standing bottom as an embodiment of the present invention is broken. FIG. 2 is a bottom view showing an embodiment of the present invention in which the stress concentration reducing function portions are uniformly distributed in the understretched region and the inversion region. FIG. 3 is a longitudinal sectional view of the embodiment shown in FIG. FIG. 4 is a bottom view showing an embodiment of the present invention in which a stress concentration reducing function portion is arranged along a spiral line. FIG. 5 is a bottom view showing an embodiment of the present invention in which the stress concentration reducing function portions are arranged on a plurality of concentric circles centering on the stretching center point. FIG. 6 is a bottom view showing an embodiment of the present invention in which the stress concentration reducing function portion is intermittently arranged on a plurality of concentric circles centered on the stretching center point. FIG. 7 is a partially enlarged longitudinal sectional view showing an example of a sectional structure of the stress concentration reducing function part. FIG. 7 (a) shows the stress concentration reducing function part shaped like a protruding piece, and FIG. FIG. 7 (b) shows the stress concentration reducing function portion which is depressed in a hole shape, FIG. 7 (c) shows the stress concentration reducing function portion cut in a linear groove shape, and FIG. 7 (d) shows the linear shape. The stress concentration reducing function portions each formed in the shape of a ridge are shown. FIG. 8 is a partially enlarged bottom view showing a specific arrangement of the stress concentration reducing function portion in the embodiment of the present invention shown in FIG. FIG. 9 is a bottom view of a conventional bottle having cracks. DESCRIPTION OF SYMBOLS 1; bottle, 1 '; preform, 2; trunk, 3; mouth, 4; bottom, 5; leg, 6; inversion area, 7; unstretched area, 8; 9; stress concentration reduction function part, 10; crack, A; origin.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-202424 (JP, A) JP-A-57-106055 (JP, A)

Claims (5)

(57) [Claims] 1. A plurality of leg pieces (5) bulging out at equal intervals, and a valley line wall is formed between the leg pieces (5), the valley line wall being a reversal area (6) having a curved reversal point. A biaxially stretched blow-molded bottle (1) made of synthetic resin having a free-standing bottom (4), comprising an unstretched area (7) in which the stretching center point of the bottom (4) is located. On the outer surface of the insufficiently stretched region (8) where the stress is insufficient, a large number of stress concentration-reducing functional portions (9) that cause local thickness change, such as fine irregularities or linear ridges or grooves, are formed. Biaxially stretch blow molded bottle. 2. A plurality of stress concentration reducing portions (9) are formed on the outer surface of the inversion region (6) of the bottom portion (4).
4. The biaxially stretch blow-molded bottle according to item 1. 3. The biaxially stretch blow-molded bottle according to claim 1, wherein the stress concentration reducing function portion (9) has a small protruding piece shape. 4. The method according to claim 1, wherein the stress concentration reducing function portion has a small recessed shape.
Axial stretch blow molded bottle. 5. The biaxially stretched blow-molded bottle according to claim 1, wherein the stress concentration reducing portion (9) has a linear ridge or groove shape along an arc centered on the stretching center point. body.