JP4061620B2 - Mold for blow molding - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a blow mold, and more particularly to a blow mold that can control the generation of burrs at the bottom pinch-off portion of a container such as a casing.
[0002]
[Prior art]
As shown in FIG. 10, in the direct blow molding method, a parison P, which is a cylindrical molten resin, is extruded by an extruder 21 and the parison P is clamped in a split mold 1 for blow molding. In the lower part of the mold, the lower part of the molten resin is cut with a cutting blade disposed in the bottom pinch-off part 5 of the cavity 2 of the split mold 1 and thermally welded and sealed, and the upper part is a cylindrical molten resin with a parison cutter 22 The parison P having a bottomed cylindrical body is formed by cutting the upper portion of the mold, and then blow air is blown into the parison P from the top of the split mold 1 by an inserted air nozzle to form a molded product.
[0003]
8 and 9 show an example of a conventional split mold, and the split mold 1 as a whole is divided into two planes on one plane (main body split surface 11). ), The pinch-off line 14 formed by the cutting blade 6 is formed from 11 on the main body dividing surface on the bottom 3 bottom surface 4 of the mold cavity 2 in a flat cross section when the split mold 1 is closed. Located on the main body dividing line 13.
[0004]
Further, the width of the pinch-off portion 5, that is, the length of the pinch-off line 14 corresponding to the length in the left-right direction of the cutting blade 6 is a width obtained by flatly crushing a cylindrical parison having an outer diameter Dp into two. It is about 1.6 Dp, and a cutting line by a cutting blade having a length of about 1.6 Dp is inevitably formed on the bottom surface of the bottom of the container which is a molded product.
[0005]
Conventionally, with respect to the structure in the vicinity of the bottom pinch-off portion of the mold for blow molding, various improvements have been implemented from the viewpoint of improving the strength of the bottom seal portion of the container, which is a molded product, and the appearance. Describes a method of forming uneven pressing recesses on both sides of the pinch-off part to improve the strength of the bottom seal part of the laminated container in particular, and Patent Document 2 discloses a method from the pinch-off part below the pinch-off part. There is a description of a method for controlling the thickness of the bottom seal portion by providing a compression plate that sandwiches the protruding resin (burr).
[0006]
[Patent Document 1]
JP-A-7-88943 [Patent Document 2]
Japanese Patent Laid-Open No. 9-262902
[Problems to be solved by the invention]
As described above, a cutting line of approximately 1.6 Dp is usually formed on the bottom bottom surface of a container that is a direct blow molded product. However, in a container having a sufficiently large blow ratio, the formation range of this cutting line is the peripheral edge of the bottom surface. Since it does not reach the part, it is used for many purposes without any problems in appearance. However, in blow molding of a container with a low blow ratio, the pinch-off part is close to or equal in width to the bottom diameter at the bottom of the mold cavity, so that the parison is crushed flatly in the pinch-off process. The resin is deformed in the horizontal direction along the main body mold dividing surface located on the left and right from the left and right ends of the part, or the resin forming the parison flows, and as a result, the main body is divided not only at the bottom of the container but also at the side of the body directly above the bottom. In the vicinity of the line, the protruding resin remains, so-called burrs are formed, and burrs are left in the product container.
[0008]
For example, even in a container with a blow ratio of 2, the width of the pinch-off portion can be made smaller than the diameter of the bottom bottom surface of the container, but the resin that forms the parison when sandwiched and crushed by the pinch-off portion is pinched off. It flows in the horizontal direction along the main body dividing surface from the left and right ends of the part, and no burr marks remain near the main body parting line on the side surface of the barrel part directly above the bottom of the container, which is a molded product. Glossy spots or colored spots due to factors such as stretch spots, orientation spots, cooling spots, etc. accompanying flow changes occur.
[0009]
Further, when it is necessary to increase the wall thickness of the parison, even if the blow ratio is close to 3, the above-described gloss spots or color spots are generated.
[0010]
In addition, for example, in the field of cosmetics such as mascara and eyeliner, containers with a small size and a blow ratio of 1.6 or less are often used, and the appearance of the container is an important factor in merchantability. In such a container with a small blow ratio, the width of the pinch-off part that can be taken is the maximum diameter of the bottom surface of the mold cavity, so that it becomes smaller than 1.6 Dp, which is the width of the parison flattened, Since the parison is crushed not only in the pinch-off portion but also in the main body dividing surface in the vicinity of the pinch-off portion, burrs are inevitably generated in the vicinity of the main body dividing line on the side surface of the trunk portion immediately above the bottom.
[0011]
These burr marks, gloss spots, color spots, and the like are serious problems in terms of merchandise, especially in cosmetic containers, but no effective solution to such problems has been shown. Is the current situation. Even if the appearance is improved in the post-treatment process, a long process is required.
[0012]
The present invention was devised to solve the above-described problems of the prior art, and it is a technical problem to suppress the occurrence of burrs in the lateral direction from the right and left ends of the pinch-off portion, particularly at the bottom of the bottom in direct blow. Therefore, an object of the present invention is to create a mold for blow molding that can provide a blow molded container having a low blow ratio and excellent appearance without burr marks, gloss spots, and color spots on the side surface of the container near the bottom.
[0013]
[Means for Solving the Problems]
Of the present invention for solving the above technical problem, the means of the invention according to claim 1 is:
It is a split mold that has a main body dividing surface perpendicular to the mold clamping direction and has a pinch-off part in which a cutting edge for parison pinch-off is disposed on the bottom bottom surface of the mold cavity,
A flat cross section of the split mold in a closed state, a linear pinch-off line formed by a cutting blade on the bottom surface, a pair of main body dividing lines formed by a main body dividing surface at the left and right peripheral edges, and left and right of the pinch-off line Forming one bottom parting line from a pair of connecting lines connecting the ends and the left and right ends of the body parting line,
The connection line is configured to form a stepped bent portion that is substantially perpendicular to the pinch-off line, by means of the end dividing surfaces located at the left and right ends of the pinch-off portion,
It is in.
[0014]
According to the above configuration of the first aspect, a linear pinch-off line is formed at the center of the bottom surface of the mold cavity at the bottom pinch-off portion of the split mold by a cutting blade disposed on the bottom pinch-off portion of the mold cavity, and split at the left and right peripheral edges. A pair of main body dividing lines are formed by the main body dividing surface perpendicular to the mold clamping direction of the mold, and the connecting line connects this pinch-off line and the main body dividing line, and one bottom dividing line is formed on the bottom surface. Has been.
[0015]
In addition, the connection line is configured to form a stepped bent portion that is substantially perpendicular to the pinch-off line by means of the end split surfaces positioned at the left and right ends of the split mold pinch-off portion. That is, the bottom surface of the bottom of the conventional mold cavity has a configuration in which a stepped bent portion is inserted between the pinch-off line formed in a straight line and the main body dividing line.
[0016]
This end part split surface is configured to be formed substantially perpendicular to the left and right direction of the cutting blade at the left and right ends of the pinch off part, and the left and right ends of the pinch off part in the process of deforming the cylindrical parison into a flat shape at the pinch off part Functions to regulate the deformation in the horizontal direction from the side, or functions as a weir surface that stops the flow of the flat resin in the horizontal direction by pressing the cutting blade part, deformation of the parison between the main body split surfaces And block resin flow.
[0017]
Due to the effect of the stepped bent portion, that is, the end split surface as described above, the burr formation range when clamping the mold for blow molding is the range from the center of the bottom bottom surface of the mold cavity to the stepped bent portion. Therefore, it is possible to provide a container having a very good appearance with a low blow ratio and no burr marks, gloss spots, and color spots, which was difficult with a conventional mold.
[0018]
In addition, the structure of the mold structure according to claim 1 is such that the surface exhibiting a dam-like function against the deformation of the parison or the flow of the resin is based on the structure of the dividing surface of the portion below the bottom bottom surface of the cavity of the split mold. It is to be formed, and it is not necessary to add other components, moving parts, etc., just by changing the dividing method of the part below the bottom bottom of the normal mold cavity. The same productivity and durability can be exhibited even when compared to the mold for use.
[0019]
As a matter of course, the shape of the mold dividing surface is configured such that the forward and backward movement of the split mold, that is, the mold clamping mold opening is smoothly achieved.
[0020]
According to a second aspect of the present invention, in the first aspect of the present invention, the step height of the stepped bent portion is at least twice the thickness of the parison in blow molding.
[0021]
When the blow ratio exceeds about 1.6, the cylindrical parison is first folded into a flat shape at the pinch-off portion, and the thickness is approximately the parison wall thickness. It is cut twice so as to be crushed with a cutting blade. For this reason, by making the step height of the stepped bent portion at least equivalent to this thickness, it is possible to reliably prevent the resin from horizontally flowing from the left and right ends of the pinch-off portion due to the pressing force by the cutting blade. can do.
[0022]
When the blow ratio is approximately 1.6 or less, the pinch-off portion width needs to be approximately 1.6 Dp or less, and it is necessary to regulate the deformation of the parison in the lateral direction. Although set, this height can be determined according to conditions such as the shape of the container, the blow ratio, the parison diameter and the wall thickness.
[0023]
The invention according to claim 3 is the invention according to claim 1 or 2,
The direction of the pinch-off line passing through the center of the bottom bottom surface of the mold cavity is a direction that forms a predetermined center angle with the direction of the body parting line, in a flat cross section in the mold closed state of the mold.
Connecting the left and right ends of the pinch-off line and the left and right ends of the main body dividing line in a substantially straight line to form a connecting line;
Forming a bottom parting line substantially axisymmetrically with respect to the center of the bottom surface;
It is in.
[0024]
The structure of claim 3 is formed by inclining the formation direction of the pinch-off line from the direction of the main body dividing line, and by this inclination, the left and right ends of the pinch-off line and the left and right ends of the main body dividing line are positioned in steps. It is the structure which connected in substantially linear form and formed the step-shaped bending part. Further, the step height of the stepped bent portion can be adjusted by the inclination angle, that is, the center angle.
[0025]
Moreover, since the dividing surface of the portion below the bottom bottom surface of the mold cavity can be formed in a simple shape as a whole, the width of the pinch-off portion can be formed over substantially the entire width of the bottom surface, and lower blow The resin flow path of the resin serving as a burr is simple because the resin has no residual resin and can be easily maintained.
[0026]
According to a fourth aspect of the present invention, in the third aspect of the invention, the central angle is set to 45 ° or less.
[0027]
The above-mentioned configuration according to claim 4 determines the upper limit of the center angle. However, if the center angle is too large, that is, if the pinch-off line is inclined too much from the direction of the main body dividing line, the surface is greatly inclined in the pinch-off process of blow molding. In this case, the flat crushing of the parison is performed, and the pinch-off process cannot be smoothly achieved.
[0028]
As described above, the step height of the stepped bend is adjusted by the center angle, so the lower limit of the center angle is the required step height, the size of the container to be molded, the thickness of the parison, etc. Therefore, a value that can be used as a guideline geometrically can be determined.
[0029]
According to a fifth aspect of the present invention, in the first or second aspect of the present invention, the direction of the pinch-off line passing through the center of the bottom bottom surface of the mold cavity is divided into the main body in the flat section in the mold closed state of the split mold. The direction is the same as the direction of the line, and the step-shaped bent part is formed substantially symmetrically from the left and right ends of the pinch-off line.
[0030]
In the above-described configuration according to the fifth aspect, since the crushing of the parison by the pinch-off portion is achieved in a plane perpendicular to the clamping direction of the split mold, the pinch-off process can be achieved more stably and the step can be achieved. The step height of the bent portion can be made sufficiently high, and the deformation of the parison in the left-right direction can be reliably regulated.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
1 to 3 show a split mold 1 which is a first embodiment of a blow mold according to the present invention. FIG. 1 shows a rear portion of a pair of split molds 1 divided into two parts in the front and rear directions. 1 is an overall perspective view of a split mold 1b, and one front split mold 1a is substantially axisymmetric with respect to a rear split mold 1b. The split mold 1 is for molding a container having a cylindrical body having a blow ratio of 1.8.
[0032]
FIG. 8 shows an example of a conventional split mold. The split mold 1 as a whole is divided into two parts in the front-rear direction by a main body split surface 11 perpendicular to the clamping direction (the direction of the white arrow in FIG. 8). Further, the cutting blade 6 is disposed along the main body dividing surface 11 to form the pinch-off portion 5, whereas the split mold 1 of the first embodiment as shown in FIG. In the mold cavity 2, the split surface is formed by a step-shaped surface at the bottom 3 and the bottom surface 4 of the mold cavity 2, and the cutting blade 6 is disposed in a direction inclined at a certain angle from the main body split surface 11. Part 5 is formed.
[0033]
Moreover, the end part dividing surface 12 is formed and arranged substantially perpendicular to the left and right direction of the cutting blade 6 at the left and right ends of the pinch-off part 5, and the end part dividing surface 12 is recessed from the main body dividing surface 11 at the left end part. The right end portion is formed to protrude from the main body dividing surface 11.
[0034]
Further, in the first embodiment, a part of the mold below the bottom 3 bottom surface 4 of the mold cavity 2 is formed by a separate semi-cylindrical bottom block body 7 and fitted and assembled. By making such a combination, it becomes easy to manufacture the split mold, it is possible to vent the gas during blow molding along the combination surface, and the pinch-off part including the cutting blade 6 by changing the metal material There is an advantage that the wear resistance in the vicinity of 5 can be improved.
[0035]
With reference to FIG. 2, the details of the division of the mold in a flat cross section in the mold closed state of the mold 1 will be described. On the bottom surface 4 of the bottom 3 of the mold cavity 2, a pair of linear pinch-off lines 14 formed by the butting of the cutting blade 6 and a pair of main body dividing surfaces 11 positioned at the left and right peripheral edges of the bottom surface 4. From the main body parting line 13 and the pair of connecting lines 16 that connect the left and right ends of the pinch-off line 14 and the left and right ends of the main part parting line 13, a single bottom parting line 17 is provided so as to be axially symmetric with respect to the center of the bottom surface 4. Is formed.
[0036]
In this embodiment, the connecting wire 16 is formed along the circular arc of the circular fitting line 18 formed in the vicinity of the periphery of the bottom surface 4 by the fitting combination surface of the bottom block body 7 described above. The bottom surface of the connecting line 16 is made inconspicuous.
[0037]
Further, the pinch-off line 14 passes through the center of the bottom 3 of the bottom 3 that is circular, and the direction thereof is formed in a direction inclined at a predetermined center angle α from the direction of the main body dividing line 13. Further, the connecting line 16 is formed from the end dividing surfaces 12 positioned at the left and right ends of the pinch-off portion 5, and the stepped bent portions 15 are formed at substantially right and left ends at the left and right ends of the pinch-off line 14.
[0038]
FIG. 3 is an explanatory view showing a pinch-off process by the split mold 1 of the present embodiment in a plan view. The parison P is sandwiched between the pinch-off portions 5 provided with the cutting blades 6 as the mold clamping progresses and is flattened. However, the stepped bent portions 15 formed at the left and right ends of the pinch-off line 14 are pinched off. Since the end split surfaces 12 formed at the left and right ends of the portion 5 serve as a weir, it is possible to prevent the flow of the flattened resin toward the main body split surface 11 in the left-right direction due to the pressing of the cutting blade 6. it can.
[0039]
As can be seen from FIGS. 2 and 3, the main body dividing surface 11 in which the direction of the cutting blade 6 is perpendicular to the mold clamping direction of the split mold 1 (the direction of the white arrow in FIG. 3A). Although the center angle α is deviated from this direction, the pinch-off process can be smoothly achieved if α is in the range of up to 45 °.
[0040]
Further, by making the step height h of the step-shaped bent portion 15 formed from the end portion dividing surface 12 at least twice the thickness of the parison P, the flow of the resin to the lateral direction and the main body dividing surface 11 is ensured. Can be blocked. (See Fig. 3 (b))
[0041]
As described above, FIG. 8 shows an example of a conventional split mold, which is used to mold a container having a cylindrical body having a blow ratio of 1.8, similar to the split mold of the first embodiment. It is. As described above, in the conventional split mold 1, the whole is divided into the front and rear parts by the main body dividing surface 11 perpendicular to the mold clamping direction (the direction of the white arrow in FIG. 8), and along the main body dividing surface 11. The pinch-off part 5 is formed by disposing the cutting blade 6.
[0042]
FIG. 9 is an explanatory view showing the pinch-off process by the split mold 1 of FIG. When the mold is closed (see FIG. 9C), the pinch-off line 14 and the main body dividing line 13 are formed in a straight line, so that the resin crushed in the pinch-off process also flows in the left-right direction and the main body is divided. In the case of a container having a small blow ratio, particularly, a burr mark remains in the vicinity of the body parting line mark position on the side surface of the trunk portion immediately above the bottom part, or even if the burr mark does not reach the burr mark or color spots. Will occur.
[0043]
4 to 7 show a split mold 1 which is a second embodiment of the blow mold according to the present invention. 4 and 5 are overall perspective views of the rear mold 1b and the front mold 1a of the pair of split molds 1 divided in the front and the rear, respectively, and a cylindrical body having a blow ratio of 2 It is for shape | molding the container which has.
[0044]
Also in this embodiment, the dividing surface is formed by a step-shaped bent surface in the portion below the bottom 3 bottom surface 4 of the mold cavity 2, but the arrangement direction of the cutting blade 6 is the same as that of the conventional split mold. Similarly, a pinch-off portion 5 is formed as a direction along the main body dividing surface 11.
[0045]
In addition, end split surfaces 12 are formed and arranged at right and left ends of the pinch-off portion 5 so as to be substantially perpendicular to the left-right direction of the cutting blade 6, and as shown in FIGS. 4 and 5 at the left and right ends of the pinch-off portion 5. The rear split mold 1b is formed with an ear-shaped recess 8b from the main part split surface, and the front split mold 1a is formed with a protrusion 8a. Clamping of the split mold 1 is achieved while fitting into the recess 8b.
[0046]
Also in this embodiment, a part of the mold below the bottom 3 bottom surface 4 of the mold cavity 2 is formed by separate block bodies 7a and 7b and is assembled and assembled.
[0047]
The details of the division will be described with reference to FIG. Formed on the bottom surface 3 of the bottom 3 of the mold cavity 2 are a pinch-off line 14, a pair of main body parting lines 13, and a fitting surface of the projecting part 8 a and the concave part 8 b, and the left and right ends of the pinch-off part 5 and the main body parting line 13. One bottom parting line 17 is formed so as to be symmetric with respect to a pair of ear-shaped connecting lines 16 connecting the left and right ends of the two.
[0048]
The pinch-off line 14 is in the same direction as the main body dividing line 13, and the connecting line 16 forms a step-shaped bent portion 15 having a step height h substantially perpendicular to the left and right ends of the pinch-off line 14. The width of the pinch-off portion 5, that is, the length in the left-right direction of the pinch-off line 14 is approximately 1.2 Dp (Dp indicates the outer diameter of the parison P), and is shorter than the width 1.6 Dp where the parison is flattened.
[0049]
FIG. 7 is an explanatory view showing a pinch-off process by the split mold 1 of the second embodiment. The cylindrical parison P is crushed into a flat shape and deformed into an oval shape. However, when the flat parison P is in a certain flat state, as shown in FIG. 7 (b), an ear shape of the front mold 1a is formed. The end dividing surface 12 that forms a part of the protruding portion 8a having the shape of FIG. 8 functions as a weir surface, and further deformation in the lateral direction is prevented. Thereafter, the left and right end dividing surfaces The parison P is crushed within a range of 12 widths, and excess resin is forced to flow below the biting blade 6.
[0050]
In the split mold 1 of the second embodiment, since the parison P is crushed by the pinch-off portion 5 on a plane perpendicular to the clamping direction, the pinch-off process can be achieved more stably.
[0051]
In the description of the split molds of the first and second embodiments, the molding of a container having a blow ratio of 1.8 or 2 has been described. However, as described above, the pinch-off portion 5 has a width of approximately 1.6 Dp. Even in a narrower case, if the step height h of the stepped bent portion 15 is sufficiently high, the deformation of the cylindrical parison P can be restricted within the range of the width of the pinch-off portion 5, and the blow of the present invention can be controlled. The molding die can sufficiently handle the molding of containers with a blow ratio of about 1.6 or less. The blow ratio ranges from about 1 to 3, and the burr forming range in the blow molding can be set at the bottom of the mold cavity. It is possible to provide a container having a very good appearance free from burrs, gloss spots, and color spots on the side surface of the body portion.
[0052]
【The invention's effect】
Since the present invention has the above-described configuration, the following effects can be obtained.
In the first aspect of the invention, the end split surfaces located at the left and right ends of the pinch-off part restrict the deformation of the parison in the lateral direction, and the resin flow from the left and right ends of the pinch-off part in the lateral direction. It is possible to provide a container that functions as a weir surface to be stopped and has a very excellent appearance without a burr mark, a glossy spot, and a color spot on the side surface at a bottom blow ratio, which is difficult with a conventional mold.
[0053]
Also for a container having a blow ratio of about 1.6 or less, the burr formation range can be set to the bottom bottom range.
[0054]
In addition, since the surface that functions as the weir surface is formed by the configuration of the mold dividing surface, there is no need to add other components, movable parts, etc. The same productivity and durability can be exhibited as compared with the above.
[0055]
In the invention according to claim 2, in the case of a container having a blow ratio of more than about 1.6 in particular, by setting the step height of the stepped bent portion to at least twice the wall thickness of the parison in blow molding. In addition, it is possible to reliably stop the resin from entering the main body dividing surface from the left and right ends of the pinch-off portion.
[0056]
In the invention according to claim 3, since the dividing surface is formed in a simple shape, it is possible to form the pinch-off portion across the entire width of the bottom surface, which corresponds to a container having a lower blow ratio. It is possible to provide a mold that is excellent in durability and easy to maintain without resin residue.
[0057]
In the invention according to claim 4, the pinch-off process can be smoothly achieved by setting the angle formed by the main body parting line and the pinch-off line to 45 ° or less.
[0058]
In the invention of claim 5, since the crushing of the parison by the pinch-off portion is achieved on a surface perpendicular to the mold clamping direction of the split mold, the pinch-off process can be achieved more stably, In addition, since the step height can be made sufficiently high, the deformation of the parison can be regulated more surely.
[Brief description of the drawings]
FIG. 1 is an overall perspective view showing a rear mold of a mold according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional plan view taken along the line AA in FIG. 1 in the mold closed state of the split mold according to the first embodiment of the present invention.
FIG. 3 is an explanatory view showing the pinch-off process by the split mold according to the first embodiment of the present invention in a plane sectional view similar to FIG.
FIG. 4 is an overall perspective view showing a rear split mold among split molds according to a second embodiment of the present invention.
FIG. 5 is an overall perspective view showing a front part mold part of the mold part of the second embodiment of the present invention.
FIG. 6 is a cross-sectional plan view taken along the line BB in FIG. 4 in the mold closed state of the split mold according to the second embodiment of the present invention.
FIG. 7 is an explanatory view showing a pinch-off process using a split mold according to a second embodiment of the present invention in a plan sectional view similar to FIG.
FIG. 8 is an overall perspective view showing a rear part mold part of an example of a conventional mold part.
9 is an explanatory view showing a pinch-off process by the split mold of FIG. 8 in the same manner as FIG. 3;
FIG. 10 is an explanatory view showing a mold-clamping process of blow molding.
[Explanation of symbols]
1; Split mold 1a; Front split mold 1b; Rear split mold 2; Mold cavity 3; Bottom 4; Bottom 5; Pinch-off part 6; Cutting blade 7; Bottom block body 7a; Projection 8b; Recess 11; Main body dividing surface 12; End dividing surface 13; Main body dividing line 14; Pinch-off line 15; Step-like bent part 16; Connecting line 17; Bottom dividing line 18; 21; Extruder 22; Parison cutter P; Parison α; Center angle h;

Claims (5)

It has a main body dividing surface (11) perpendicular to the clamping direction, and a parison (P) pinch-off cutting blade (6) is arranged on the bottom (3) bottom surface (4) of the mold cavity (2). It is a split mold (1) having a pinch-off part (5) divided into front and rear, and in a flat cross section in the mold closed state of the split mold (1), the cutting blade (6 ) Formed by a linear pinch-off line (14), a pair of main body dividing lines (13) formed by the main body dividing surface (11) on the left and right peripheral edges, and left and right ends of the pinch-off line (14) A bottom parting line (17) is formed from a pair of connecting lines (16) connecting the left and right ends of the main body parting line (13), and the connecting line (16) is connected to the pinch-off part (5). A blow molding die configured to form the pinch-off line (14) and a stepped bent portion (15) substantially perpendicular to the end split surfaces (12) positioned at the left and right ends. The mold for blow molding according to claim 1, wherein the step height (h) of the step-shaped bent portion (15) is at least twice the thickness of the parison (P) in blow molding. The direction of the pinch-off line (14) passing through the center of the bottom (3) bottom surface (4) of the mold cavity (2) in the flat section in the mold closed state of the split mold (1) A direction forming a predetermined center angle (α) with the direction, the left and right ends of the pinch-off line (14) and the left and right ends of the main body dividing line (13) are connected substantially linearly to form a connecting line (16), and the bottom surface The blow mold according to claim 1 or 2, wherein the bottom parting line (17) is formed substantially axially symmetrical with respect to the center of (4). The blow mold according to claim 3, wherein the central angle (α) is 45 ° or less. The direction of the pinch-off line (14) passing through the center of the bottom (3) bottom surface (4) of the mold cavity (2) in the flat section in the mold closed state of the split mold (1) The blow molding die according to claim 1 or 2, wherein the step-shaped bent portion (15) is formed in the same direction as the direction, and is substantially symmetrical from the left and right ends of the pinch-off line (14).

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