JPH0753411B2 - Preform with internal wall and method for molding synthetic resin container with internal wall - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a preform for molding a synthetic resin container having an inner wall capable of withstanding the internal pressure caused by a filler, and a method for molding such a container.

[Background Art] A synthetic resin container is constructed by biaxially stretching a preform, and has a cylindrical body portion below a mouth portion, which is a part of the preform, and has an inner diameter larger than that of the mouth portion, a shoulder portion connecting the body portion and the mouth portion, and a bottom portion closing one end of the body portion. Conventional synthetic resin containers generally have large stretching ratios in the vertical and horizontal axes, and most of the body portions have a circular cross section. In the case of such synthetic resin containers, since the cross section of the body portion is circular,
The internal pressure stress caused by the contents is dispersed uniformly around the circumference of the body, and the mechanical strength of the body is guaranteed to a certain extent by the crystallization caused by biaxial stretching, so deformation of the body due to internal pressure caused by carbon dioxide, etc. can be sufficiently prevented.

However, when the body of a synthetic resin container is a rectangular bottle such as a triangle or a square, or when it has a flat, curved cross section like an ellipse, the internal pressure from the contents is concentrated on a portion of the side wall of the body, which can cause the side wall of the body, which has weak mechanical strength, to deform.

Furthermore, in the case of so-called wide-mouth containers, that is, containers made of synthetic resin in which the difference in the inner diameter of the mouth and the inner diameter of the body is relatively small, the transverse stretching ratio is small, so the mechanical strength of the container achieved by crystallization through biaxial stretching is poor. In the case of such wide-mouth containers, even if the shape of the body is circular in cross section,
There is a risk that deformation of the body due to internal pressure caused by the contents may not be reliably prevented.

To ensure the strength of this type of container, WO90/05674 discloses a bottle in which an internal spider is formed across the inside of the bottle, and this internal spider is biaxially stretched together with the side wall of the bottle.

However, in the biaxial stretch blow molding process for molding this type of bottle, the internal spider hinders smooth biaxial stretching of the preform compared to the biaxial stretching of a general cylindrical preform. In particular, since one end of the internal spider is connected to the inner surface of the side wall, the part of the side wall to which this internal spider is connected experiences a considerable amount of resistance during biaxial stretching. Therefore, the inventors have confirmed that, when the bottle is formed, a recess is likely to form on the outer surface of the side wall to which this internal spider is connected.
Such recesses significantly impair the appearance of the bottle.

Furthermore, the inventors' research has revealed that it is extremely difficult to mold this type of internal spider into a bottle with a uniform wall thickness without any wall deviations. This is because, unlike conventional types in which only the side walls are biaxially stretched, the internal spiders extending in various directions create resistance during stretching, preventing the bottle from being stretched to a uniform wall thickness.

Furthermore, when longitudinal axis stretching by a stretching rod and transverse axis stretching by blown air were performed for each partitioned area partitioned by the internal spider, it was observed that the internal spider was stretched in a biased direction due to various factors, resulting in axial misalignment.

Thus, when molding a bottle having an internal spider, it has been difficult to mold a bottle worthy of practical use without various improvements.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a preform that is optimal for molding a synthetic resin container having an inner wall.

A further object of the present invention is to provide a molding method for molding a synthetic resin container having an inner wall without impairing the appearance.

DISCLOSURE OF THE INVENTION A preform according to the present invention comprises a mouth portion, a cylindrical body portion,
The preform has a bottom portion closing one end of the body portion, and an inner wall formed from one side of the inner wall of the body portion to the other side and rising from the bottom, and is used for blow molding a synthetic resin container by biaxial stretching, and the thickness distribution of the inner wall in the horizontal axis direction of the preform is
The wall thickness is maximum at the end connected to the inner wall of the body, and the wall thickness transitions to become thinner toward the center.

The relatively thick portion of the inner wall located at the end connected to the inner wall of the barrel portion is easily stretched due to its high holding temperature, and is sufficiently stretched following the biaxial stretching of the barrel portion. The stretching force is relatively weaker toward the center of the inner wall, and the stretching is originally small. Therefore, if this portion is made relatively thin and a transition in thickness is formed between this portion and the maximum thickness, the inner wall will be smoothly stretched in its transverse direction and formed with a substantially uniform thickness after stretching. The portion near the center of the inner wall may be made substantially uniform in thickness within a certain range in the transverse direction.

In this case, the inner wall may have a thickness distribution in the longitudinal direction of the preform, with the thickness being maximum at the end connected to the bottom and gradually decreasing toward the top end, which is advantageous in ensuring a uniform thickness of the inner wall after stretching in the longitudinal direction without necessarily requiring a complex temperature distribution in the longitudinal direction in temperature control of the preform.

From the viewpoint of preventing deformation due to internal pressure, it is sufficient that the upper end of the inner wall is formed up to a position midway along the body portion, not reaching the mouth portion. In this case, it is preferable that the height of the upper end of the inner wall near the center of the longitudinal axis of the preform is lower than the height of the upper end of the periphery on the side of the end connected to the inner wall of the body portion.
This is because the inner wall can be easily stretched near the center.

The height of this internal wall can be extended up to the opening of the mouth, or more preferably to the top surface of the mouth. In this case, the thickness of the internal wall within the mouth is set to be equal to or less than the minimum thickness of the internal wall within the body. In this way, the internal wall within the mouth is less susceptible to stretching, and the shape of the top seal can be retained within the mouth of a container blow-molded from this preform. When a cap is attached to this container, the bottom surface of the cap and the internal wall can separate it into multiple compartments.

The method for molding a synthetic resin container according to the present invention includes injection molding a preform having an open mouth, a cylindrical body having a bottom that is closed at one end, and an inner wall that is molded from one side of the inner wall of the body to the other and that rises from the bottom, and the bottom is stretched in the vertical axis direction by a plurality of stretch rods provided corresponding to a plurality of partitioned areas separated by the inner walls of the preform, and blow air is introduced into each of the plurality of partitioned areas separated by the inner walls to stretch them in the horizontal axis direction, and tip pieces are provided at the tips of the plurality of stretch rods, and each tip piece arranged in the partitioned area is positioned offset toward the vertical axis center of the preform from the center of the partitioned area, and the inner wall is stretched and guided in the vertical axis to biaxially stretch blow mold the synthetic resin container.

Stretching is performed in each area separated by the internal walls using a stretching rod and blow air. If the stretching rod is positioned approximately at the center of each area, a slight misalignment of the rod, differences in blow pressure between the areas, or variations in preform temperature can easily cause misalignment near the center of the vertical axis, which is the joint of the internal walls. Therefore, multiple end pieces are positioned offset near the center of the vertical axis, and the internal walls are stretched vertically straight down.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic, partially cutaway view of a synthetic resin container having an inner wall.

FIG. 2 is a plan view of the container shown in FIG.

FIG. 3 is a schematic explanatory view for explaining the arrangement of the inner walls of a container having a triangular cross section.

FIG. 4 is a schematic diagram illustrating the arrangement of the inner walls of a flat container having an elliptical cross section.

FIG. 5 is a schematic cross-sectional view of a container in which the upper end of the inner wall is flat.

FIG. 6 is a schematic cross-sectional view showing an embodiment in which the height of the inner wall is extended to the same height as the top surface of the mouth of the container.

FIG. 7 is a schematic cross-sectional view of a container in which the height of the inner wall is formed in a shape that allows for an airtight seal with an inner cap.

FIG. 8A is a schematic cross-sectional view showing a modified example of the shape of the upper end of the inner wall;
FIG. 2B is a cross-sectional view taken along line A-A of FIG.

9A is a schematic cross-sectional view of a preform for molding the container shown in FIG. 1, FIG. 9B is a cross-sectional view taken along the line B-B of FIG. 9A, and FIG. 9C is a schematic perspective view of the inner wall shown in FIG.

FIG. 10 is a schematic cross-sectional view of an injection molding apparatus for injection molding a preform.

FIG. 11 is a schematic cross-sectional view of a blow molding apparatus for biaxially stretching a preform to form a container.

FIG. 12 is a schematic explanatory view for explaining the planar arrangement of the stretching rods and air inlets shown in FIG.

FIG. 13 is a cross-sectional view of a preform used to mold the container of FIG.

FIG. 14 is a cross-sectional view of a preform used to mold the container of FIG.

FIG. 15 is a cross-sectional view of a modified example of the preform used to form the container of FIG.

FIG. 16 is a schematic vertical cross-sectional view showing an example of the distribution of the uniform thickness regions shown in FIG.

FIG. 17 is a schematic vertical cross-sectional view showing a temperature adjustment step for the preform of FIG.

18 and 19 are schematic explanatory diagrams showing examples of arrangements in which the stretching rods and the tip pieces are arranged offset from one another.

FIG. 20 is a schematic vertical cross-sectional view of a preform used to mold the container shown in FIG.

21 and 22 are schematic explanatory views showing examples of the arrangement of the stretch rod and the tip piece for the preform shown in FIG.

FIG. 23 is a schematic explanatory view showing a biaxial stretch blow molding process using the stretch rods of FIGS.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment in which the present invention is applied to the molding of a container made of polyethylene terephthalate (hereinafter abbreviated as PET) and having a rectangular cross section will be specifically described with reference to the drawings.

As shown in FIGS. 1 and 2, the container 10 has an opening with an inner diameter a and a mouth portion 12 formed with a threaded portion 12a on the peripheral wall.
The body 14 has a rectangular cross section and an inner diameter b larger than the inner diameter a of the mouth 12. A shoulder 16 connects the mouth 12 and the body 14 in a curved shape that absorbs the difference between the inner diameters a and b with a predetermined curvature. A bottom 18 closes one end of the body 14.

The inner wall 20 formed inside this container 10 rises from the inner wall of the bottom 18 toward the mouth 12, and has side wall connecting ends 22 on each side of the side walls 14a to 14d of the body 14, which has a square cross section, and is formed in a shape that intersects in a cross shape at the center 24.

In this embodiment, the height position of the upper end 20a of the side wall 20 is the same as that of the mouth 12
It does not reach the upper part of the torso 14, i.e., the shoulder 16
The inner wall 20 is formed up to the vicinity of the lower end of the upper end 20
In this embodiment, the shape of a is such that the height at the side wall connecting ends 22 of the side walls 14a to 14d is the highest and the height at the center 24 where the inner wall 20 intersects with the center is the lowest.
It is formed in a curved shape with a continuously changing height.

In the case of a container 10 having a rectangular cross section as shown in FIG.
Each of the side walls 14a to 14d has a side wall connecting end 22 at the middle portion thereof, which cross at a center 24, and a bottom wall connecting end 26.
An upwardly rising interior wall 20 is formed inside the container 10. Thus, each of the side walls 14a-14d and the bottom 18
The side walls 14 are interconnected by a crisscross inner wall 20.
This makes it possible to significantly increase the mechanical rigidity of the portions 14a to 14d and the bottom portion 18.

The effect of forming the inner wall 20 is to
14a to 14d as well as increasing the rigidity of the side walls 14a to 14d
It is also possible to reduce the total internal pressure acting on the
That is, the total amount of internal pressure acting on the inner wall 20 is
The internal pressure acting on each of the side walls 14a to 14d of the body 14 can be reduced, which also makes it possible to prevent deformation of the body 14 due to the internal pressure.

In this embodiment, the height of the inner wall 20 is highest at the side wall connecting end 22 and lowest at the center 24 as shown in FIG. 1. This is because the upper end of the inner wall 20 is curved as shown in FIG. 1 during biaxial stretch blow molding, as will be described later.
This is because the shape of 20a is the easiest to mold.

3 shows an example in which the present invention is applied to a container 30 having a triangular cross section. In this embodiment, an inner wall 36 formed inside the container 30 is formed by a pair of walls 36 that rise from the bottom 34 and are connected to each side wall.
The inner walls 36 have side wall connecting ends 38a at the intermediate positions of the sides 32a to 32c, and extend radially from the center at 120 degree intervals so as to intersect at the center 38b.

4 shows an embodiment in which the present invention is applied to a container 40 having a flat cross section with a substantially elliptical cross section. In the case of such a flat container 40, an internal wall 46 is formed rising from a bottom 44 so as to connect the opposing side walls of a body 42 along the short axis Y. If necessary, a plurality of internal walls 46 parallel to the short axis Y can be provided in parallel to each other to more reliably prevent deformation of the body 42.

5 and 6 show the inner wall 20 in the embodiment shown in FIG.
5 shows a modification of the height of the inner wall 20. In the case of FIG. 5, the upper end 20a of the inner wall 20 is formed flat. In both the case shown in FIG. 5 and the case shown in FIG. 1, the upper end 20a of the inner wall 20 is formed flat.
6, the height of the inner wall 20 reaches only the middle position of the body 14, but the upper end 20a of the inner wall 20 is connected to the top surface 12b of the mouth 12.
6, by attaching a cap to the mouth 12, the inner surface of the cap seals the top surface 12b of the mouth 12 and the upper end 20a of the inner wall 20, so that even when different contents, such as different types of tea, spices, sweets, etc., are stored in each of the four storage compartments partitioned by the inner wall 20, the different types of contents can be prevented from moving between the compartments, making it possible to realize a container that can store different types of contents without mixing them in one container.

Figure 7 shows a modified example having the same function as Figure 6, in which the upper end 20a of the inner wall 20 does not reach the top surface 12b of the mouth 12, but is formed to a position halfway up the height of the mouth 12, and its upper end is formed flat. In this case, an inner cap 52 made of, for example, resin is usually attached inside the outer cap 50 to ensure airtightness, and the bottom surface 52a of this inner cap 52 and the upper end 20a of the inner wall 20 can be tightly sealed, thereby realizing a container that can be filled with different types of contents, as in Figure 6.

8A and 8B show a modification of the interior wall 20 shown in Fig. 1. In the embodiment of Fig. 8, the interior wall 60 is connected to the bottom 18 and the bottom wall connecting end.
The height H1 of the cross-shaped portion is relatively small, and in the region covering the height range H2 above the cross-shaped portion, each side wall 14
The inner walls 60 are connected to the container 10 only at the side wall connecting ends 64 connected to 14a through 14d, and do not intersect at the center.

Even with such an internal wall 60, sufficient mechanical strength is ensured near the bottom 18 by the internal wall 60 having a cross-sectional shape, and the side walls 14a to 14b on each side of the rectangle in the body 14 are
The inner walls 60 connected to each other at the side wall connecting ends 64 ensure mechanical strength, and the inner wall 60 is resistant to the internal pressure of the contents.
Deformation of the bottom 14 and bottom 18 can be similarly prevented.
In particular, the inner wall 60 near the center of the vertical axis has a low height H1, so when tilting the container 10 to transfer the contents into a cup or when drinking it directly by mouth, there is minimal risk that the inner wall will obstruct the outflow of the contents.

Next, an embodiment of the molding method of the present invention will be described with reference to FIG. 9 and subsequent figures.

9A shows an injection-molded preform 70 as an intermediate for molding the container 10 shown in FIG. 1. This preform 70 has a shape similar to that of a conventional preform in that it has an open mouth portion 72, a body portion 74 connected to this mouth portion 72 and having a circular cross section, and a bottom portion 76 that closes one end of this body portion 74. Furthermore, the preform 70 has
It is molded from one side to the other of the inner wall of the body portion 74, and
It has an inner wall 78 that rises from the bottom 76 at a predetermined height.
In the illustrated embodiment, the upper end 80 of the interior wall 78 is flat and has the same height at its center and periphery.
It is desirable to set the thickness of the inner wall 78 to the dimensions shown in FIGS. 9B and 9C.

Furthermore, when the dimensions of the inner wall 78 are _a1 ; thickness _a2 at the center connecting end 82 on the upper end 80 side; thickness _a3 at the side wall connecting end 84 on the upper end 80 side; thickness _a4 at the center connecting end 82 on the bottom wall connecting end 86 side; thickness at the side wall connecting end 84 on the bottom wall connecting end 86 side, it is desirable that _a1 < _a2 < _a3 < _a4 .

The reasons for setting these dimensions will be described later, but the above dimensions are set from the viewpoint of making the thickness of the inner wall 20 of the container 10 shown in FIG. 1 uniform.

10 shows an injection molding apparatus for the preform 70. This injection molding apparatus includes a mouth molding die 90 for molding the mouth 72 of the preform 70, an injection cavity die 92 for setting the outer walls of the body 74 and bottom 76 of the preform 70, and
The injection cavity mold 92 is made up of an injection core mold 94 for defining the inner walls of the body 74 and bottom 76 and the inner wall 78. A gate 96 is provided at the center of the bottom of the injection cavity mold 92, and a gate 96 is provided for injection of the molten material.
The PET resin is filled through this gate 96 into a bottom molding area 98, a body molding area 100, and a mouth molding area 102 in that order, and further into an inner wall molding area 104 defined by the injection core mold 94, thereby injection molding the preform 70.
Cooling sections 106 for cooling the resin by circulating a refrigerant are provided at positions corresponding to the four regions partitioned by the internal walls 78 of the mold 70 .

After the preform 70 is injection molded, the injection core mold 94 is first driven upward to release the preform 70, and then the mouth mold 90 is driven upward to release the preform 70.
While holding 70, preform 70 is removed from injection cavity mold 92 and driven. Thereafter, preform 70 is transported by mouth forming mold 90 to a temperature control step (not shown), where it is controlled to a temperature suitable for stretching, and then transported to the biaxial stretch blow molding step shown in FIG.

In this biaxially stretched blow molding process, a blow cavity mold 110 and a bottom mold 112 having a cavity shape substantially similar to the outer wall of the body 14, shoulder 16, and bottom 18 of the container 10 shown in FIG.
is disposed above which is provided, for example, a blow core mold 114 which can be driven up and down. In this biaxial stretch blow molding process, first the bottom mold 112 is driven upward so as to surround the preform 70 conveyed by the mouth mold 90, and then the blow cavity mold 110, which is made up of two split molds, is driven to close. Thereafter, the blow core mold 114 is driven so as to be inserted into the mouth 72 of the preform 70 via the mouth mold 90.

A characteristic feature of this blow core mold 114 in this embodiment is that it has stretch rods 120 and blow air introduction sections 122 at positions corresponding to the four areas partitioned by the internal wall 78 of the preform 70. The planar arrangement of the stretch rods 120 and blow air introduction sections 122 is as shown in Figure 12. In this embodiment, the internal wall 78 of the preform 70
A stretch rod 120 is disposed at approximately the center of each of the four regions partitioned by the stretch rods 120. An air inlet 124 provided at the end of a blow air inlet 122 is opened and disposed at a position avoiding the position of the stretch rod 120. In this biaxial stretch blow molding process, after each mold is disposed as described above, the four stretch rods 120 are
are driven downward to stretch the preform 70 in the vertical axis, and blow air is introduced from the air inlets 124 at the ends of the four blow air inlets 122, respectively, so that the preform 70 is biaxially stretched and blow-molded in the vertical and horizontal axis directions. In this case, for example, by driving the four stretching rods 120 with the same drive source, each region defined by the four internal walls 78 of the preform 70 can be stretched in the vertical axis at the same speed. Furthermore,
The blow air blown in from each of the four blow air introduction parts 122 is made to have a substantially uniform pressure within the four areas partitioned by the internal wall 78, thereby making it possible to obtain the container 10 by blow molding.
This makes it possible to prevent uneven thickness and deformation of the inner wall 20.

The wall thickness dimensions _a1 to _a4 of the inner wall 78 of the preform 70 are
The reason for the above setting is as follows.

According to an experiment, the inventors have found that when the body 74 and bottom 76 of the preform 70 are stretch-blow molded along the vertical and horizontal axes,
It was found that the sidewall connection end 84 of the inner wall 78 of the preform 70 tends to be stretched more easily than the center connection end 82, and furthermore, the bottom wall connection end 86 tends to be stretched more easily than the top end 80. It is believed that the sidewall connection end 84 side is pulled by the body 74 and is subjected to a greater stretching force. Therefore, if the wall thicknesses _a1 and _a2 of the center connection end 82 and the sidewall connection end 84 at the top end 80 of the inner wall 78 of the preform 70 are the same, the wall thickness at the center 24 of the inner wall 20 of the container 10 after biaxial stretch blow molding will be thick and the wall thickness at the sidewall connection end 22 will be thin, making it impossible to mold with a uniform wall thickness. This significantly impairs the appearance, particularly with transparent resins such as PET resin.

Furthermore, if the inner wall 78 has a uniform thickness in the horizontal direction, the center is difficult to stretch, making it difficult for the side wall connecting end 84 to stretch in accordance with the side wall, which can result in the formation of recesses in the bottle side wall.

Therefore, the thickness in the horizontal direction is set to _a1 < _a2 and _a3 < _a4 ,
The side wall connecting end 84 side is made thicker to increase the holding temperature, allowing for stretching in accordance with the side wall. Furthermore, the center 82 side, which receives less stretching force, is made thinner in advance, so that the final thickness is nearly uniform with the well-stretched side wall connecting end 84 side.

The dimensions of the upper end 80 and the bottom wall connecting end 86 of the inner wall 78 of the preform 70 in the longitudinal direction are generally the same as those of the injection core mold 94.
However, it was found that the thickness deviation phenomenon, in which the thickness of the inner wall 20 of the container 10 on _the bottom wall connecting end 26 side becomes thin _, cannot be eliminated with a dimensional difference of the draft taper.
The dimensional difference between the wall thicknesses to achieve _a2 < _a4 is equal to or greater than the normal draft taper, and if it is appropriately set according to the longitudinal elongation ratio of the container 10, it is possible to achieve a substantially uniform wall thickness from the lower end to the upper end of the inner wall 20 of the container 10. In addition, since it is easy to achieve a temperature distribution in the temperature control process in the longitudinal direction, the thickness of the inner wall 78
The thickness distribution may be provided only in the horizontal axis direction.

Furthermore, experiments conducted by the inventors have shown that a curved upper end 20a of the inner wall 20 of the container 10, such that the side wall connecting end 22 is higher and the center 24 is lower, as shown in FIG. 1 , provides good moldability. This is because the center 24 of the inner wall 20 is particularly susceptible to longitudinal stretching, particularly as a result of the longitudinal stretching using the four stretch rods 120, resulting in the upper end 20a being lower than the height of the side wall connecting end 22. However, the loss of wall thickness resulting from the curved upper end 20a of the inner wall 20 has the advantage of reducing the total amount of resin material required to mold the preform 70. Furthermore, it has been found that the loss of wall thickness does not significantly affect the mechanical strength of the body 14 of the container 10 compared to when the upper end 20a of the inner wall 20 is flat, as shown in FIG. 5 .
That is, even in the case shown in Fig. 1, the height position of the upper end 20a of the side wall connecting end 22 of the inner wall 20 is approximately the same height as that shown in Fig. 5. This is because, as long as the height of the upper end 20a at the side wall connecting end 22 can be ensured, the mechanical strength of the body 14 up to that height position can be ensured to a degree that is sufficient to prevent deformation of the body 14 due to the internal pressure of the contents.

Furthermore, with regard to the thickness of the inner wall 78 of the preform 70, the following points must be taken into consideration in order to position the upper end 20a of the inner wall 20 in the area of the mouth 12 of the container 10 as shown in Figures 6 and 7. That is, the area of the mouth 12 is hardly stretched during biaxial stretch blow molding, and therefore it is desirable to mold the thickness of the inner wall 78 in the area of the mouth 72 of the preform 70 as thin as possible, taking into account that it will not be stretched.

Next, various preform shapes used for molding synthetic resin containers having an inner wall will be described.

Fig. 13 is a cross-sectional view of a preform used to form the container shown in Fig. 4. This preform 130 has an inner wall 134 extending from the bottom across a body 132 having a circular cross section.
The thickness of the inner wall 134 is represented by the symbols a ₁ and a 2 used in FIG.
When a ₂ , a ₃ , and a ₄ are used with the same definition, a ₁ <
_a2 and _a1 < _a3 < _a4 .

Fig. 14 is a longitudinal sectional view of a preform used to form the container shown in Fig. 6. This preform 140 has a top end with a mouth portion 1
The inner wall 1 rises from the bottom 146, which is flush with the top surface of 42.
The inner wall 148a in the body 144 has a bottom 1
The thickness is a maximum of _a3 at the connecting end 148c with 46, and there is a thickness transition until it reaches a thinner thickness _a1 near the upper end within the body 144.
The inner wall 148b present in the mouth portion 142 preferably has a thickness _a0 equal to or thinner than the minimum thickness _a1 in the body portion 144. That is, as shown in FIG. 14, the inner wall 148b has a thickness
The wall thickness may transition from _a1 to _a0 , or may be substantially equal to _a1 , because the objective is to barely stretch the inner wall 148b within the mouth portion 142. It is particularly preferred that the thinner inner wall 148b within the mouth portion 142 be conditioned to a lower temperature than other regions that will be stretched in a temperature conditioning step prior to the biaxial stretch blow molding step.

In the case of the container shown in Figure 7, where the inner wall does not reach the top surface of the mouth portion 12 but exists within the mouth portion 12, the thickness of the inner wall existing within the mouth portion of the preform may be set in the same manner as in Figure 14.

15 shows a cross-sectional view of another preform 150 for molding the container shown in FIG. 1. An inner wall 154 that crosses the inside of the body 152 and intersects in a crisscross pattern at the center has a uniform thickness region 154a with a thickness of _a1 near the center of the vertical axis. This inner wall 154 has a thickness transition portion 154b where the thickness transitions from _a1 to a maximum thickness _a2 from the end of the uniform thickness region 154a to the connecting end 156 to the inner wall of the body.
The reason for ensuring this is that this region is less stretchable than the surrounding area, and after molding into a container, it becomes thicker than the rest, causing uneven thickness of the inner wall. In particular, in the case of transparent containers such as PET, uneven thickness of the inner wall significantly impairs the appearance. Therefore, by thinning the less stretchable region in advance, uneven thickness of the inner wall of the blow-molded container is prevented. From this perspective, the distribution of the uniform thickness region 154a is as follows:
16, it is desirable that the inner wall 154 has a shape of, for example, approximately a quarter circle on the upper end side and center side. The outer side of this uniform thickness region 154a is preferably formed to be relatively thick so that it can be easily stretched.

FIG. 17 shows the temperature control step for the preform of FIG.
A temperature control core 160 is inserted into the preform 150, and a temperature control pot 164 is disposed around the temperature control core 160.
In this example, a temperature control medium such as hot water or oil is circulated in the jacket 162, and the wall of the preform 150 is cooled to a temperature suitable for stretching.
The temperature control core 160 does not come into contact with this region, weakening the cooling effect on that region. Similarly, the cooling effect is weakened on the shoulder portion 158, i.e., the joint between the neck portion and the body portion, which needs to be sufficiently stretched. Figure 17 shows an example of cooling the preform 150, but conversely, if a heater or the like is built into the temperature control core to heat the preform, efficient radiant heating can be achieved by narrowing the distance between the temperature control core and the uniform thickness region and the shoulder portion compared to other regions.

Another reason for forming a thin uniform thickness region near the center of the longitudinal axis is to prevent axial misalignment when the inner wall is biaxially stretched. As described above, the stretching operation using the stretching rod and blow air is performed for each region defined by the inner wall.
In this case, misalignment of the inner wall joints near the center of the vertical axis is likely to occur due to misalignment of the stretch rods located approximately in the center of each compartment, differences in blow pressure between compartments, and variations in preform temperature. If the inner wall is relatively thin near the center of the vertical axis and therefore less likely to be stretched at a low temperature, the joints of the inner wall are less likely to become misaligned. From this perspective, it is better to form the thin, uniform thickness region along the center of the vertical axis from the top end of the inner wall to the end connecting to the bottom, rather than following the distribution shown in Figure 16.

Figures 18 and 19 show examples of the arrangement of multiple stretch rods used in the biaxial stretch blow molding process.
11 is that the stretch rods 170 arranged in each partitioned area are arranged offset toward the center of the longitudinal axis of the preform 70. In the case of FIG. 18, a tip block 172 having a rectangular cross section is provided at the tip of each stretch rod 170.
19, a tip block 174 having a circular cross section is provided at the tip of each extension rod 170. In both cases, the tip blocks 172 and 174 are not in contact with the inner wall 78,
The inner wall 78 is disposed near a corner 176 where the two inner walls 78, 78 that form one partition area intersect. The reason for this arrangement is to prevent axial misalignment of the cross-shaped joint of the inner wall 78 and to guide the inner wall 78 vertically straight downward.
In particular, the tip piece 172 having a contour shape that corresponds more to the shape of the corner 176 as shown in FIG. 18 can more effectively prevent axial misalignment of the joint portion.

20 is a longitudinal sectional view of a preform 180 used to form the container shown in FIG.
In order to form the internal walls 60 having clearly different heights, the container 10 has a first internal wall 182 having a height of approximately H1 near the center of the vertical axis and a second internal wall 184 having a height of H3 provided around the periphery including the end side connected to the body internal wall. The first internal wall 182 has a height H1 that is approximately the same as the internal wall 60 having a low upper end height of the blow-molded container 10. This is because the first internal wall 182 is hardly stretched by a method described below.

This method will be explained using Figures 21 to 23.
21 and 22 show examples of the arrangement of a stretch rod 190 and its tip pieces 192 and 194 used in the biaxial stretch blow molding process.
18 and 19, the stretching rod 190 is arranged in each partitioned area, offset toward the center of the longitudinal axis of the preform. Furthermore, the tip pieces 192, 194 arranged at the tip of this rod 190 contact both sides of the first inner wall 182, and sandwich it from both sides. In the case of FIG. 21, the tip pieces 192
22, the cross section of the tip piece 194 is circular, so it is not in contact with the corner 186 but is in line contact with the two first internal walls 182, sandwiching the internal walls 182 from both sides.

The biaxial stretch blow molding process using the stretch rods of Figures 21 and 22 is shown in Figure 23. In this figure, a preform 180 is held by a neck mold 200 and placed in a blow cavity mold 202. Furthermore, a blow core 204 is inserted into the opening of the preform 180.
This blowing core 204 is inserted into the four extension rods 1
21 and 22, the first inner wall 192, 194 is supported so that it can be raised and lowered, and for example, blow air can be blown in from the periphery of the rod 190.
82 is sandwiched between end pieces 192 and 194 on both sides, and the first interior wall 182 is hardly stretched in either the vertical or horizontal axis. On the other hand, the second interior wall 184 is relatively thick and easily stretched, and is biaxially stretched together with the body portion. As a result, a container 10 having an interior wall 60 as shown in FIG. 8 is formed.

The present invention is not limited to the above examples.
Various modifications are possible within the scope of the present invention.

In the above-described embodiments, the cross-sectional shape of the container 10 is an angular cross-section such as a triangle or a rectangle, or a flattened ellipse, but even when the present invention is applied to a container having a circular cross-section, the mechanical strength of the body and bottom can be ensured to prevent deformation due to the internal pressure of the contents, just like in the above-described embodiments. Furthermore, applying the present invention to a so-called wide-mouth container with a low longitudinal elongation ratio is preferable because it can strengthen the reinforcement of the body, which has low mechanical strength. However, the fact that the present invention can prevent deformation due to the internal pressure of the contents can also be applied to containers other than wide-mouth containers.

───────────────────────────────────────────────────────── Continued from the front page (51) Int.Cl. ⁶ Identification symbol Internal reference number FI Technical marking location B29C 49/20 7619-4F B65D 23/00 // B29L 22:00

Claims (14)

[Claims] [Claim 1] A preform having a mouth, a cylindrical body, a bottom closing one end of the body, and an internal wall formed from one side of the body inner wall to the other and rising from the bottom, which is used for blow molding a synthetic resin container by biaxial stretching, wherein the thickness distribution of the internal wall in the horizontal axis direction is maximum at the end connected to the body inner wall and has a thickness transition that becomes thinner toward the center. [Claim 2] A preform having an internal wall according to claim 1, wherein the internal wall further has a thickness distribution in the longitudinal axis direction, the thickness being maximum at the end connected to the bottom portion, and having a thickness transition that becomes thinner toward the upper end. [Claim 3] A preform having an internal wall according to claim 2, characterized in that the internal wall has a uniform thickness region formed in a region near the center of the vertical axis, and the thickness transition is formed from the maximum thickness in the vertical axis direction and the horizontal axis direction to the end of the uniform thickness region. 4. A preform having an internal wall according to claim 1, wherein the upper end of said internal wall is formed to a position midway along said body portion but not reaching said mouth portion. [Claim 5] A preform having an internal wall according to claim 4, wherein the height of the upper end of the internal wall near the center of the vertical axis of the preform is lower than the height of the upper end of the periphery on the side of the end connected to the inner wall of the body portion. [Claim 6] A preform having an internal wall according to claim 5, wherein the internal wall near the center where the upper end height is low is a region of substantially uniform thickness in the horizontal axis direction of the preform, and the thickness transition is formed in the horizontal axis direction from the maximum thickness at the connecting end with the body inner wall to the end of the uniform thickness region. [Claim 7] In claim 1, the upper end of the inner wall is molded to a position flush with the top surface of the mouth portion, and the thickness of the inner wall existing within the mouth portion is:
A preform having an inner wall, characterized in that the thickness is equal to or less than the minimum thickness of the inner wall present in the body portion. [Claim 8] A preform having an internal wall according to claim 1, wherein the upper end of the internal wall is formed to a position midway within the mouth portion but does not reach the top surface of the mouth portion, the upper end is formed as a flat surface, and the thickness of the internal wall within the mouth portion is equal to or less than the minimum thickness of the internal wall within the body portion. [Claim 9] A method for molding a synthetic resin container, comprising: injection molding a preform having an open mouth, a cylindrical body having a closed bottom at one end, and an internal wall formed from one side of the internal wall of the body to the other and rising from the bottom; stretching the bottom in the axial direction using a plurality of stretch rods provided corresponding to a plurality of partitioned areas separated by the internal walls of the preform; and introducing blow air into each of the plurality of partitioned areas separated by the internal walls to stretch them in the horizontal axis; and providing tip pieces at the tips of the plurality of stretch rods, each of the tip pieces arranged in the partitioned areas being biased toward the vertical axis center of the preform rather than the center of the partitioned area, thereby stretching and guiding the internal wall in the vertical axis, thereby biaxially stretching and blow molding a synthetic resin container. 10. The method according to claim 9, wherein the inner wall comprises three or more walls extending in a radial direction,
A method for molding a synthetic resin container, characterized in that each wall is joined on the central axis to form a joint, and the multiple end pieces have a contour shape corresponding to the corner shape where two walls forming one partition area intersect, and guide the joint on the central axis in a vertical direction. [Claim 11] According to claim 9, in the injection molding step, a preform is injection molded in which the upper end of the inner wall is formed up to a position midway through the body portion that does not reach the mouth portion, and the height of the upper end near the center of the vertical axis of the preform is lower than the height of the upper end around the connecting end side with the inner wall of the body portion, and in the biaxial stretch blow molding step, the plurality of tip pieces come into contact with the inner wall near the center axis of the preform,
A method for molding a synthetic resin container, characterized in that the inner wall near the center is sandwiched and stretched along the longitudinal axis. 12. The method according to claim 11, wherein the inner wall comprises three or more walls extending in a radial direction,
A method for molding a synthetic resin container, characterized in that each wall is joined on the central axis to form a joint, the multiple end pieces have a contour shape that contacts the corner where two walls that form one partition area intersect, and the end pieces sandwich the joint on the central axis from each direction to perform vertical axis stretching. [Claim 13] A method for molding a synthetic resin container according to claim 9, characterized in that, before the biaxial stretching blowing process, there is a temperature control process in which the inner and outer surfaces of the body of the preform and both surfaces of the internal wall are controlled to a temperature suitable for stretching, and in this temperature control process, a temperature distribution is imparted in which at least the upper region of the internal wall has a controlled temperature higher than that of the lower region. [Claim 14] A method for molding a synthetic resin container according to claim 13, characterized in that the temperature control process uses a temperature control core to control the temperature of the inner surface of the body and both sides of the internal wall, and the temperature control core is locally brought close to or into contact with the area of the internal wall that is to be set to a high temperature control temperature.