JP3200259B2 - Biaxial stretch blow molding method for self-standing bottle and preform used therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for biaxially stretch-blowing a self-supporting bottle and a preform used for the method.

[0002]

2. Description of the Related Art In general, a self-supporting bottle is one of thin synthetic resin containers called twin-screw blow molded containers. When the content of a self-standing bottle, such as a carbonated beverage, as the bottom structure of the bottle body, is most preferably set to be a downwardly convex hemispherical shape in order to secure internal pressure resistance. However, such a bottle body having a hemispherical bottom cannot function as a free-standing bottle unless a cap called a base cap is attached to the bottom.

Therefore, a so-called one-piece bottle structure has been proposed in which an even or odd number of legs are provided at the bottom of the bottle. A typical bottom structure is disclosed, for example, in Japanese Utility Model Publication No. 3-5537. That Such bottles 7, having a bottom structure shown in FIG. The bottle shown in the figure 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 with a constant radius, and further has, for example, five legs 20 that extend diagonally below the spherical portion 16.
Are provided at substantially equal center angles 72 ° with respect to the center 18. The leg portion 20 is connected to the spherical portion 16 at a change point 22 which is a predetermined distance away from the center 18 of the bottom portion 14 and has an inclined portion 24 which extends obliquely downward from the change point 22 toward the outside in the radial direction. . And, this inclined portion 24
Is formed as the grounding portion 26. A valley 28 having substantially the same curvature as the vicinity of the center 18 is formed as a part of the spherical portion 16 between the adjacent legs 20, 20. According to such a bottle bottom structure, the bottle 10 can be made independent by the odd-numbered legs 20, for example.

A bottle of this type is obtained by biaxially stretch-blowing a bottomed cylindrical preform.

[0005]

When the above-described self-standing bottle having three or more legs 20 at the bottom is biaxially stretched and blow-molded, it is extremely difficult to form the legs 20 exactly as dimensioned and stably. Met. The reason will be described below.

Since the leg portion 20 protrudes beyond the spherical portion 16, the stretch ratio is large, and the valley portions 28, 28 on both sides are provided.
Is a relatively narrow area sandwiched between the valleys 28, and must be further extended after the valleys 28 reach the cavity surface of the blow cavity mold. In this case, the resin in the valley portion 28 that has reached the cavity surface first is cooled and hardly stretched, and the resin corresponding to the leg portion 20, which is the region between the valley portions 28, 28, is smaller than the valley portion 28. Since the resin temperature decreases as the film is further stretched, it becomes difficult to shape the leg portion 20 according to the shape of the cavity.
In addition, since three or more legs 20 are provided, it is considered that one of the legs 20 has an incomplete shape due to, for example, a change in the temperature of the preform before blow molding. However, the independence of the self-supporting bottle is significantly impaired.

In particular, it is desirable that the grounding surface of the leg portion 20 be a flat surface having a large grounding area in order to maintain the durability against the sideways fall of the bottle, that is, the so-called self-standing stability. However, if it is difficult to form the shape with the leg portion 20, it becomes difficult to obtain an edge portion located at the boundary between the flat surface and the leg portion wall surface,
In other words, the so-called edge portion is rounded, and the ground contact area is reduced, thereby impairing self-standing stability. Also, the legs 20
Even when the shape is formed, the thickness tends to be reduced due to the small amount of the resin stretched from the valley portion, whereby it is possible to ensure the impact strength at the time of dropping at the leg portion 20. May not be possible.

In order to improve the formability of the legs 20 which are difficult to shape, it is conceivable to increase the temperature at the bottom of the preform to facilitate stretching. And the desired wall thickness distribution of the self-supporting bottle cannot be obtained. It is also conceivable to increase the pressure of the blow air to promote the extension of the legs, but this requires an increase in the mold clamping force of the blow mold,
Increased mechanical strength requires larger equipment and higher air compressor capacity.

Accordingly, an object of the present invention is to form a self-supporting bottle capable of securing the self-standing stability by improving the shape of the legs protruding from the spherical bottom and ensuring the impact strength. And a preform used in the method.

[0010]

In order to achieve this object, a method according to the present invention comprises the steps of projecting downwardly from the apex of the spherical bottom at equal intervals in the circumferential direction of the spherical base having an outward convexity. A method of forming a self-standing bottle having three or more legs and having a valley between adjacent legs by biaxially stretching and blowing an injection-molded preform, comprising: At the time, with respect to the heat retained in the circumferential direction of the preform, a relationship was set such that the temperature of the region corresponding to the valley of the free-standing bottle could be higher than the temperature of the region corresponding to the legs of the free-standing bottle. Features.

The method of the present invention is characterized in that,
A step of injection molding a bottomed cylindrical preform in which the thickness of the region corresponding to the valley of the self-standing bottle is thicker than the thickness of the region corresponding to the legs of the self-standing bottle, The preform holding the heat at the time of injection molding is biaxially stretched and blow-molded in a blow cavity mold, and while the resin in the valley having a high holding heat is extended to the legs on both sides thereof, the shape of the legs is formed. And forming the self-standing bottle by dispensing.

The method of the present invention is characterized in that,
In the injection molding step, the neck part is held by a neck cavity mold that defines an outer wall of the neck part of the preform, and the preform is conveyed to the biaxial stretch blow molding step.

Further, the method of the present invention has a temperature control step of adjusting the temperature of the preform to an appropriate temperature for stretching before the biaxial stretching blow molding of the self-standing bottle. It is characterized in that set larger than a heat held in the region corresponding to heat held in the region corresponding to the valleys of the self-standing bottle legs freestanding bottle.

[0014] The method of the present invention is characterized in that
At the time of the temperature control step, on the inner surface of the preform, a core member that is in non-contact with a region corresponding to a valley of the self-supporting bottle and that is in contact with only a region corresponding to a leg portion of the self-standing bottle is characterized in that I have.

Further, the preform according to the present invention has three or more legs projecting below the apex of the spherical bottom at equal intervals in the circumferential direction of the outwardly projecting spherical bottom. In a preform for biaxially stretch-blowing a self-standing bottle having a valley between the adjacent leg portions, a thickness of a region corresponding to the valley portion of the self-standing bottle corresponds to the leg portion. It is characterized in that it is made thicker than the thickness of the region.

Further, according to the present invention, when the thickness of the region corresponding to the leg is defined as t1 and the maximum thickness of the region corresponding to the valley is defined as t2 = t1 + Δt, t1 //
25.ltoreq.t.ltoreq.t1 / 15.

Further, according to the present invention, in claim 6 or 7, the inner wall of the region corresponding to the leg is drawn with a first radius of curvature having a length R1 having a center on the central axis of the preform. The inner wall of a region defined by the first arc and corresponding to the valley is defined by a second arc drawn with a second radius of curvature having a length R2 (> R1), and has a second radius of curvature. On the normal passing through a point bisecting the second arc, is more than (R2-R) than the center of the first radius of curvature.
1 + Δt).

[0018]

According to the present invention, in the circumferential direction of a preform for forming a self-standing bottle at the time of injection molding or a temperature control step,
The heat holding amount of the region corresponding to the valley of the self-supporting bottle is different from that of the region corresponding to the leg. In other words, when performing injection molding, the heat holding amount in the valley is set by setting the thickness of the region corresponding to the valley to be thicker than the region corresponding to the leg in the preform to be injection-molded. And the temperature is set higher than that of the legs. Therefore, the region corresponding to the valley where the retained heat is high and the temperature is high begins to extend earlier than the region corresponding to the leg in the process of expanding with the blown air, and the region corresponding to the valley is blown. Even when the cavity surface is reached, the region corresponding to the leg is hardly stretched, so that it has sufficient retained heat. For this reason, the region having a high retained heat can be further extended toward the leg defining cavity surface.

In addition, when the temperature of an injection-molded preform is controlled in a state where the wall thickness is kept constant,
The heat holding amount in the region corresponding to the valley in the circumferential direction is made larger than the heat holding amount in the region corresponding to the leg. Therefore, the region corresponding to the valley in the circumferential direction of the preform has more heat than the region corresponding to the leg, and in the process of expanding by blow air, the stretching ratio is higher than that of the region corresponding to the leg. This promotes the stretching toward the leg defining cavity surface, and enhances the shapeability of the leg.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for forming a self-standing bottle to which the present invention is applied and a preform using the same will be specifically described with reference to the drawings.

The embodiment method described below is a method of forming a free-standing bottle 10 having the bottom structure shown in FIGS. Hereinafter, a method of forming the self-supporting bottle 10 will be described in the order of the steps. The following description relates to a method of changing the thickness of the preform to be injection-molded in the circumferential direction so as to change the amount of heat retained in the region corresponding to the legs and the valleys of the self-standing bottle .

FIG. 2 shows an injection molding process of a preform 30 used for molding the self-standing bottle 10. This preform 30 has a neck portion 32 on the opening end side,
It has a cylindrical body 34 below it, and its lower end is configured as a closed bottom 38. The preform 30 is injection molded using a neck mold 40, an injection core mold 42 and an injection cavity mold 48. Neck type 40
Functions as a neck cavity of the neck portion 32 in the injection molding step, and thereafter functions as a conveying means of the preform 30 or the self-standing bottle 10. The injection cavity mold 48 defines the outer wall of the body 34 and the bottom 38 below the neck 32 of the preform 30.
The injection cavity mold 48 has a gate for introducing a resin such as PET (polyethylene terephthalate) from the bottom 38 side of the preform 30, and has a built-in cooling medium passage 49 for cooling the preform after injection molding. are doing.

The injection core mold 42 defines the inner wall of the preform 30, and has a rod-shaped core pin 44 that follows the shape of the inner wall of the preform 30. In the present embodiment, the cross-sectional shape at the tip of the core pin 44 is a special shape.

FIG. 3 shows a cross-sectional shape of the core pin 44 in the AA cross section shown in FIG. This core pin 44
Has a substantially circular cross section drawn with a first radius of curvature R1 having a center at the center P1 of the core pin 44, but is chamfered at equal intervals in the circumferential direction (72 ° intervals in this embodiment). A portion 47 is provided. The chamfered portion 47 has a maximum chamfering amount Δt at the center of the chamfering area, and has a width (indicated by reference numeral 46) in which the chamfering amount gradually decreases toward both sides. In the present embodiment, the contour of the chamfered portion 47 is an arc drawn by a radius of curvature R2 longer than the first radius of curvature R1, and this region is referred to as a second arc region 46. As a result, in the AA cross section in FIG. 2, the second arc regions 46 and the first arc regions 45 drawn with the first radius of curvature R1 are alternately formed at 36 ° intervals. become. The center P2 of the second radius of curvature R2 is set at a position (R2-R1 + At) away from the center P1 on a normal passing through the center point of the second arc region 46.

FIG. 4 shows a cross section taken along the line AA of the preform 30 formed by using such a core pin 44 as shown in FIG. As shown in the figure, the area corresponding to the chamfered portion 47 of the core pin 44 has a thickness t2 (= t1 + Δ) which is thicker by the maximum chamfer amount Δt than the thickness t1 of the other areas.
It can be seen that it is molded as the thick part 37 of t). The region corresponding to the thick portion 37 is a valley located between the five legs 20 formed on the bottom 10 side when the preform 30 is biaxially stretched and blow-molded to form the self-standing bottle 10. It corresponds to the section 28. Accordingly, a region corresponding to the thick portion 37 is referred to as a valley-corresponding region 36, and a region located between the two valley-corresponding regions 36, 36 is referred to as a leg-corresponding region 35.

Next, the axial length of the thick portion 37 on the lower end side of the preform 30 will be described with reference to FIGS.

In FIG. 7, the point S1 at which the leg 20 of the free-standing bottle 10 starts from the spherical portion 16 is set at a height position which is separated from the vertex 18 on the lower end side of the spherical portion 16 by a distance L1. ing. On the other hand, as shown in FIG. 1, the starting point S2 on the upper end side in the axial direction where the thick portion 37 of the preform 30 starts.
Is set at a height of a distance L2 from the vertex at the lower end of the bottom portion 14 of the preform 30. This thick part 3
The position S3 at the lower end in the axial direction where the end of the step 7 is
Is a position at which it intersects the spherical bottom portion 14. The relationship between the distances L1 and L2 is L1> L2.

The preform 30 having such a shape
Is molded in a mold-clamped state at the injection molding station shown in FIG. 2, for example, by filling PET resin,
Immediately after the filling is completed, cooling is performed in the injection cavity mold 48. Then, after the preform 30 is cooled to a temperature at which the preform 30 can be taken out, the mold is opened, and the preform 30 is conveyed to the next temperature control station using the neck mold 40.

Here, the injection molded preform 30
Has a large heat capacity in a region with a large thickness and is difficult to be cooled, and thus has a high retained heat. Therefore, in the section AA shown in FIG. 2, the region 36 corresponding to the valley portion, which becomes the thick portion 37, has high retained heat, and the region 35 corresponding to the leg has lower retained heat.

The injection-molded preform 30 is conveyed to a temperature control step (not shown), preferably with its neck 32 held by a neck mold 40. In this temperature control step, it is possible to provide a temperature distribution that is suitable for stretching in a temperature control pot that is divided into zones in the longitudinal direction of the preform 30 having the retained heat during injection molding. At this time, the valley equivalent region 36 and the leg equivalent region 3 of the preform 30
Even if the temperature of the valley portion 5 is controlled by the zone temperature control portion set to a uniform temperature control temperature in the circumferential direction, the valley portion corresponding region 36 is the thick portion 37 and therefore the leg portion corresponding region. It will have a retained heat higher than 35. After the completion of this temperature control step, the preform 30 is conveyed by the neck mold 40 to the next step of the blow molding step.

FIG. 1 shows a blow molding step for blow-molding the self-standing bottle 10 from the preform 30 whose temperature has been adjusted. In this blow molding station, a neck mold 40 for holding the neck 32 of the preform 30 whose temperature has been adjusted, a blow cavity mold 60, and a blow core mold 70.
Are clamped as shown in FIG. Then, blow air is introduced into the preform 30 from the blow core mold 70, and the stretching rod 72 is driven longitudinally, whereby the preform 30 is biaxially oriented. Here, the blow cavity mold 60 has a cavity surface 62 corresponding to the external shape of the self-standing bottle 10 shown in FIGS. 7 and 8 . In particular, the area defining the bottom 14 of the self-supporting bottle 10 includes a valley 2
Cavity surfaces 64 for defining the spherical bottom portion 16 including the holes 8 and cavity surfaces 66 for defining the leg portions 28 are alternately formed in the circumferential direction.

By the way, in a so-called one-stage blow molding apparatus for continuously performing the blow molding of the self-standing bottle 10 from the injection molding of the preform 30, the preform 30
Is transported by the neck mold 40, so that the relative positional relationship between the neck mold 40 and the preform 30 during injection molding is maintained at the blow molding station. Therefore, in the mold clamping state shown in FIG. 1, the leg-corresponding region 35 and the valley-corresponding region 36 of the preform 30 are located at positions corresponding to the corresponding cavity surfaces 64 and 66 of the blow cavity mold 60 in the circumferential direction. Can be set to

When the blow air is introduced and the extension rod 72 is driven on the vertical axis after the mold clamping, the preform 30 sequentially reaches the cavity surface 62 from the upper end side thereof,
The shape setting of the self-standing bottle 10 is performed. By the way, in this embodiment, the valley-corresponding region 36 of the preform 30 has a higher retained heat because it is thicker than the leg-corresponding regions 35 on both sides thereof. Therefore, the valley-corresponding region 36 having a high retained heat in advance begins to extend earlier than the leg-corresponding region 35 in the process of expanding with blow air. Finally, the bottom 38 side of the preform 30 reaches the spherical cavity surface 64 of the blow cavity 60. As a result, the valley-equivalent region 36 of the preform 30 reaches the cavity surface 64, and cooling is immediately started. Even when the valley-corresponding region 36 reaches the cavity surface 64, since the leg-corresponding region 35 is hardly stretched, it still has a sufficient retained heat. Therefore, the leg-equivalent region 36 still having a high retained heat is used as the leg defining cavity surface 66.
The shapeability when further stretching toward is improved.

As described above, according to the method of the present embodiment, the extension of the leg-corresponding region 35 can be promoted by using the relatively high retained heat of the valley-corresponding region 36. Even if the pressure is set low, the self-standing bottle 10 with good shape stability can be formed. The blow pressure can be preferably 30 kg / cm 2 or less. Since molding can be performed with such a low blow pressure, safety can be improved and the mold clamping force can be reduced, so that the apparatus can be downsized. Further, since the capacity of the air compressor for introducing the blow air can be reduced, the cost of the apparatus can be reduced.

According to the experiment of the present inventors, the preform 3
0, the thickness t1 of the body 34 is 2.5 mm ≦ t1 ≦ 4.5.
mm, the maximum value Δt of the thickness increase in the thick portion 37 of the preform 30 is 0.1 mm ≦ Δt ≦
It was found that setting to 0.3 mm is good. If this is defined from the relationship between the thicknesses t1 and Δt, it can be set in the range of t1 / 25 ≦ Δt ≦ t1 / 15.

When the maximum value Δt of the increase in thickness is below the lower limit of the above range, the increase in thickness is too small, and it is possible to stably improve the formability of the leg-corresponding region 35. Can not. When Δt exceeds the upper limit of the above range, the valley-corresponding region 36 is excessively stretched, so that the thickness of the valley 28 of the self-supporting bottle 10 becomes thin and the mechanical strength is deteriorated. Further, the thickness change in the circumferential direction of the preform 30 becomes large, and in the cooling step after injection molding, the thick part 37 is cooled and whitened and crystallized, thereby significantly impairing the appearance of the self-standing bottle 10.

The inner wall shape of the thick portion 37 of the preform 30 has a contour drawn by a second radius of curvature R2 longer than the first radius of curvature R1 defining the inner wall of the other body as shown in FIG. Preferably, it is defined by a line. The reason is as follows.

First, in order to improve the shapeability of the free-standing bottle leg 28, the valley-corresponding region 36 which becomes the thick portion 37 of the preform 30 has a certain width in the circumferential direction. There must be. At this time, the chamfered portion 47 shown in FIG.
When a straight line located inside by Δt from a circle drawn with the first radius of curvature R1 is used as a chamfering method of
The width of the chamfered area 46 becomes extremely narrow. Also,
Assuming that the center P2 of the second radius of curvature R2 shown in FIG. 3 is positioned outside the chamfered portion 47, that is, positioned outside the outer shape of the core pin 44 in the radial direction, an arc is drawn. The width of the chamfered area is further reduced as compared with the case of drawing with a straight line. Therefore, forming the chamfered portion 47 by the method shown in FIG. 3 is a method that can ensure the widest circumferential width of the valley-corresponding region 36 that becomes the thick portion 37. Further, by defining the chamfered area 46 by the contour drawn by such a second radius of curvature R2, the maximum thickness increase Δt is obtained at the center of the chamfered area 46, and as it goes to both sides thereof, The wall thickness is gradually reduced, and relatively smoothly intersects the contours of the leg equivalent region 35 at both ends of the valley equivalent region 36. Therefore,
Since the change in the thickness is gentle, the injection moldability is improved. In addition, since there is no large thickness change point in the body portion 34 of the preform 30, a boundary line having a clearly different stretching amount does not occur in the self-standing bottle 10 as the final molded product.

Incidentally, Japanese Patent Publication No. Hei 3-14618 discloses that
In order to reinforce the bottom of a plastic bottle having a champagne bottle-shaped bottom structure, a technique of forming a thick rib on an inner wall on the bottom side of a preform is disclosed. However, the ribs formed on the preform are intended to remain as reinforcing ribs on the champagne-shaped bottom of the bottle obtained by blow molding the preform. It is completely different in terms of configuration and effect. On the other hand,
Japanese Patent Application Publication No. 51876 discloses a technique in which a thick rib is provided on the inner wall on the bottom side of the preform. However, these ribs are formed at positions corresponding to the legs of the free-standing bottle, and by blowing this preform, the thickness of the legs is made equal to or greater than the thickness of the bottle body. This is completely different from the principle of the present invention.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention. The bottom structure of the self-supporting bottle 10 to which the present invention is applied is not limited to the above-described structure having the five legs 20, and at least three or more odd or even legs 2.
What is necessary is just to have 0. In the method of the present invention, 1
Although the self-standing bottle 10 is blow-molded by the stage method, the blow molding method of the one-stage method is not limited to the method having the temperature control step as described above, and the preform 30 after the injection step is heated. The present invention can also be applied to a system in which the toner is carried into a blow molding process without going through a conditioning process.
In this case, when the mold is opened after injection molding of the preform 30,
The retained heat of the thick portion 37 of the preform 30 is increased, and the formation of the leg portion 20 can be improved similarly to the above embodiment.

Next, another embodiment of the present invention will be described.

The embodiment shown in FIG. 5 is directed to a preform injection-molded to have a uniform thickness, and if the temperature control temperature is different between a region corresponding to a valley and a region corresponding to a leg in the circumferential direction. Shows how to make it work.

FIG. 5 shows the structure of the temperature control unit 100. The temperature control unit 100 has a bottomed cylindrical preform 130 formed with a uniform thickness distribution in an injection molding station. Is carried in.

As shown in FIG. 5, the structure of the temperature control section 100 is composed of a heating pot 102 and a temperature control core 104. The temperature control core 104 is a preform 1
When inserted, the tip contacts the bottom inner surface of the preform 130 and contacts the inner peripheral surface in a range from this bottom position to immediately below the neck portion. can do. This temperature control core 1
Reference numeral 04 is for maintaining the inner peripheral surface of the preform 130 at a lower temperature than the outer peripheral surface in the case of the present embodiment.
Therefore, although not shown, the temperature control core 104 has a structure in which a temperature control medium such as water or oil can be circulated in the longitudinal direction of the preform 130. The heating pot 102
Is heated from the outer peripheral surface of the preform 130,
In cooperation with the temperature control core 104, the temperature distribution in the longitudinal direction of the preform 130 is set to a state in which an optimum amount of blow stretching can be obtained.

On the other hand, the cross-sectional shape of the tip of the temperature control core 104 in contact with the inner surface of the bottom of the preform 130 and the vicinity thereof is set as shown in FIG.

That is, FIG. 6 shows a cross-sectional shape of the temperature control core 104 along the line BB in FIG.

The temperature control core 104 has a center at the center P1 similar to the core pin 44 shown in FIG.
Although a substantially circular cross section obtained by a first radius of curvature R1 corresponding to the radius of the inner peripheral surface of 0 is formed, the chamfered portions 106 are arranged at equal intervals in the circumferential direction (in this embodiment, at intervals of 72 °). Is provided. This chamfer 106 has a maximum chamfer amount Δt set at the center of the chamfer area,
It has a width (indicated by reference numeral 110 ) that gradually decreases toward both sides. Although the surface of the chamfered portion 106 may be a flat surface, for example, similarly to the core pin 44 shown in FIG. 3, the contour of the chamfered portion 106 has a curvature radius R2 longer than the first curvature radius R1. Can be formed on the set surface. When the region formed with the first radius of curvature R1 is the first region 108,
The area where the chamfer 106 is formed is referred to as the second area 11
Set to 0. Thereby, in the circumferential direction of the temperature control core 104,
This means that the first regions 108 and the second regions 110 are alternately formed at 36 ° intervals. Each of these areas
These are associated with the legs and the valleys of the free-standing bottle when the preform 130 is stretch blow-molded. In other words, the first region 108 corresponds to the leg of the self-supporting bottle (the portion indicated by the symbol M in FIG. 6), and the second region 110 corresponds to the valley of the self-supporting bottle (the symbol V in FIG. 6). Part shown). In addition,
The center position P2 of the second radius of curvature R2 is, as in the case shown in FIG. 3, on the normal passing through the center of the second region, at a position (R2−R1 + Δt) away from the center P1. Is set to

Therefore, when such a temperature control core 104 is inserted into the preform 130, the relationship shown in FIG. 6 with the inner peripheral surface of the preform 130 is set. That is, the first region of the temperature control core 104 is in contact with the inner peripheral surface near the bottom of the preform 130, and the second region is in a non-contact relationship.

On the other hand, the length of the chamfered portion 106 in the axial direction is as follows.

That is to say, FIG.
In the position S1 at which the base of the leg 20 of the self-standing bottle when blow-molded starts to extend from the spherical portion 16,
The position is set at a distance L1 from the vertex 18 on the lower end side of the spherical portion 16. In addition, the leg 20 starting to extend from the spherical portion 16 must be formed so that the lowest point of the inclined portion 24 that extends diagonally downward toward the outside in the radial direction from the center 18 of the bottom portion 14 is not formed as the ground contact portion 26. No.
For this reason, it is necessary to secure the maximum amount of extension over the inclined portion 24 and the contact portion 26 which is the lowest point thereof. Therefore, the chamfered portion 106 of the temperature control core 104 is
0 where the base of 0 starts to extend from the spherical portion 16
The length starting from the position S2 (see FIG. 5) corresponding to 1 is set. Then, from the position S2, the temperature control core 1
As it reaches the tip of 04, it is continuously changed to a depth approaching the chamfering depth (Δt). By the way, this Δ
With respect to t, for example, when Δt = 0.2 mm, it was confirmed that the leg portions had better shapeability than the one using the normal injection core without chamfering. Further, the present inventor has confirmed through experiments that when the above-mentioned Δt is set to 0.3 mm, the formability is further improved. Where Δ
When the experiment was performed with t set to 0.4 mm, crystallization proceeded and whitening occurred. Therefore, it is preferable that the upper limit of Δt is about 0.3 mm. Note that the whitened state refers to the degree to which the whitened state starts to become opaque instead of completely whitened.

The legs 20 of the self-standing bottle 10 are
As shown in the figure, the grounding portion 2 located at the lowest point of the slope 24 and the slope 24 from the changing point 22 of the spherical portion 16.
6 must be stretched. For this reason, the chamfer amount Δt needs to be set to a depth at which the heat transfer from the preform 130 can be suppressed and the heat holding amount at which the stretching amount can be obtained can be secured. Thereby, the preform 13 by the second region 110 of the temperature control core 104 is formed.
By suppressing heat absorption from zero, the preform 13
The temperature drop in the region corresponding to the valley of 0, that is, the second region 110 is suppressed.

The temperature control core 104 having such a structure
Is inserted into the preform 130 when the preform 130 is conveyed to the temperature control section and set.

Accordingly, in the outer peripheral surface of the temperature control core 104, the first region 108 contacts the inner peripheral surface of the preform 130 in the circumferential direction, and the second region 110
Non-contact with the inner peripheral surface of Therefore, the temperature control pot 102
The preform 130 heated by the temperature control core 10
4 at the point in contact with the first region 108.
Heat transfer to zero is performed. Thus, in the circumferential direction of the preform 130, the second region 11 of the temperature control core 104
The state where the heat holding amount at the portion facing 0 is kept high. As described above, the preform 130 in which the heat holding amount is different between the region corresponding to the valley and the region corresponding to the leg in the self-standing bottle is conveyed to the blow molding process after the temperature control process.

In the blow molding step, blow molding using the blow cavity 60 shown in FIG. 1 is performed in the same manner as in the case of the preform 30 injection-molded with the core pins 44 shown in FIG. By the way, the preform 130 used for blow molding is formed in the first region 108 in the circumferential direction.
The temperature of the second region 110 is higher than that of the second region 110. That is, the second region 110 is the first region 108
Heat absorption by the temperature control core 104 is smaller than that of
A large amount of heat is retained and the temperature is kept high. Therefore, when the blow air is introduced after the blow cavity mold 60 is clamped, the preform 130 sequentially reaches the cavity surface from the neck portion side, and the shape of the self-standing bottle is formed. In this embodiment, the preform 130
, The first region 1 in which the second region 110 is a region corresponding to the legs located on both sides thereof.
It has a higher retained heat than 08. For this reason, in the process of inflation by blow air, it begins to expand earlier than the region corresponding to the leg. On the other hand, the second region 110 is cooled when it reaches the spherical cavity surface of the blow cavity mold 60, but in this region, the retained heat is increased more than in the first region 108 corresponding to the legs. So
Further stretching can be performed for shaping in the first region 108 corresponding to the leg. Therefore, the area corresponding to the legs of the free-standing bottle can be made a flat surface from which the grounding area of the grounding portion can be sufficiently large. Moreover, in the stretching for shaping the grounding portion into a flat surface, the heat holding amount for the stretching at that portion is sufficiently secured, so that the edge portion shaped by the cavity surface of the blow cavity mold 60 is formed. The shape does not become round, and the shapeability can be improved.

According to the present embodiment, the preform for which the temperature distribution in the circumferential direction is set may have a uniform thickness. Therefore, injection molding does not require special thickness control, so that there is no need to make injection molding equipment including an injection mold special. In addition, when the heat holding amount is made different, it can be carried out without changing the temperature control conditions in the circumferential direction of the temperature control pot. Therefore, it is necessary to make the structure of the temperature control section in the molding apparatus special. Absent.

[0056]

As described above, according to the method of the present invention, in the circumferential direction of the preform to be subjected to blow molding, the stretching of the region corresponding to the valley and the region corresponding to the leg of the self-standing bottle is performed. By making the ratio different, it is possible to improve the shapeability at the leg. In other words, in order to make the above-mentioned stretching ratio different, during injection molding of the preform, the thickness of the region corresponding to the valley sandwiched between two adjacent legs on the bottom side of the free-standing bottle is equivalent to the leg. Thicker than the thickness of the region to be formed. In addition, when such a change in the thickness is not set, but the thickness is made uniform, the amount of heat radiation from the area corresponding to the valley is released to the area corresponding to the leg during the temperature control step. Keep it below the calorific value. Thereby, when the self-supporting bottle is biaxially stretched and blow-molded from this preform, the relatively high retained heat in the valley-like region can be used to promote the stretching of the leg-like region on both sides thereof. In addition, the shape of the legs of the self-standing bottle can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a blow molding station of an apparatus for carrying out a method of the present invention.

FIG. 2 is a schematic sectional view of an injection molding station of the apparatus of the embodiment.

FIG. 3 is a sectional view taken along line AA of the core pin shown in FIG. 2;

FIG. 4 is a cross-sectional view of the preform shown in FIG. 2, taken along AA.

FIG. 5 is a cross-sectional view showing a structure of a temperature control station used in a molding method according to another embodiment of the present invention.

6 is a cross-sectional view for explaining a relationship between a temperature control core and a preform used in the temperature control station shown in FIG.

FIG. 7 is a cross-sectional view of the bottom of a free-standing bottle blow-molded by the apparatus of the embodiment.

FIG. 8 is a bottom view of the self-standing bottle blow-molded by the apparatus of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Self-standing bottle 14 Bottom part 16 Spherical part 20 Leg 28 Trough 30 Preform 35 Leg equivalent area 36 Valley equivalent area 37 Thick part 40 Neck type 44 Core pin 45 True circle area 46 Chamfer area 47 Chamfer area 62-66 Cavity surface 104 Temperature control core 106 Chamfered portion 108 First region corresponding to leg 110 Second region corresponding to valley

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI // B29L 22:00 (56) References JP-A-4-239440 (JP, A) JP-A-4-201838 (JP, A JP-A-4-154535 (JP, A) JP-A-3-26513 (JP, A) JP-A-59-115816 (JP, A) JP-A-4-275130 (JP, A) 5537 (JP, Y2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 49/00-49/80 B29B 11/00-11/14 B65D 1/00-1/48

Claims (8)

(57) [Claims] 1. An outwardly projecting spherical bottom is projected at a regular interval in the circumferential direction below the apex of the spherical bottom.
A method of forming a self-standing bottle having at least two legs and having a valley between the adjacent legs by biaxially stretching and blowing an injection-molded preform. With respect to the heat retained in the circumferential direction of the preform, a relationship is set such that the temperature of the region corresponding to the valley of the free-standing bottle can be higher than the temperature of the region corresponding to the legs of the free-standing bottle. A biaxial stretch blow molding method for a self-standing bottle. 2. A bottomed cylindrical shape according to claim 1, wherein the thickness of a region corresponding to said valley of said free-standing bottle is thicker than the thickness of a region corresponding to said legs of said free-standing bottle. Injection molding of the preform, and biaxial stretching blow molding of the preform holding the heat at the time of injection molding in a blow cavity mold, so that the holding heat is high.
While extending the valleys of the resin to the leg portion side on both sides, biaxial stretch blow molding method of free-standing bottle, characterized in that and a step of molding the self bottle performs a shape out of the legs. 3. The biaxial stretch blow molding process according to claim 2, wherein the neck portion is held by a neck cavity mold that defines a neck portion outer wall of the preform in the injection molding process. A method for biaxially stretch-blowing a self-standing bottle , comprising conveying the bottle . 4. The method according to claim 1, further comprising a temperature adjusting step of adjusting the temperature of the preform to an appropriate stretching temperature before the biaxial stretching blow molding of the self-standing bottle. in the circumferential direction of the preform, biaxially oriented blow molding method of free-standing bottle, characterized in that set larger than a heat held in the region corresponding to the heat held in the region corresponding to the valleys of the self-standing bottle legs freestanding bottle . 5. The self-standing bottle according to claim 4, wherein, in the temperature control step, a region corresponding to a valley of the self-standing bottle on the inner surface of the preform is not contacted and corresponds to a leg of the self-standing bottle. A biaxial stretch blow molding method for a self-standing bottle , comprising disposing a core member in contact only with a region to be formed. 6. A projection projecting downward from a vertex of the spherical bottom at an equal interval in a circumferential direction of the spherical bottom having an outward convex.
In the preform for biaxially stretch-blowing a self-standing bottle having at least two legs and having a valley between the adjacent legs, the thickness of a region corresponding to the valley of the self-standing bottle Wherein the thickness of the preform is larger than the thickness of a region corresponding to the leg. 7. The method according to claim 6, wherein the thickness of the region corresponding to the leg is t1, and the maximum thickness of the region corresponding to the valley is t2 = t1 + Δt.
A preform, wherein t 1/25 ≦ Δt ≦ t 1/15. 8. The first inner surface of the preform, wherein an inner wall of a region corresponding to the leg portion is drawn with a first radius of curvature having a length R1 having a center on a center axis of the preform. The inner wall of the region defined by the arc and corresponding to the valley is defined by a second arc drawn with a second radius of curvature having a length R2 (> R1), and has a center of the second radius of curvature. The position is (R2-R) higher than the center position of the first radius of curvature on a normal passing through a point bisecting the second arc.
(1 + Δt). A preform set at a position shifted by (1 + Δt).