Blown film molding device, sizing ring of blown film molding device, and movable member of sizing ring of blown film molding device

Abstract

To provide a technique that suppresses molding defects.SOLUTION: An inflation forming apparatus includes a sizing ring that forms an insertion hole through which bubbles pass. The sizing ring includes a hole diameter variable mechanism that varies the hole diameter of the insertion hole. The hole diameter variable mechanism has a movable member that defines the insertion hole. The movable member includes a curved surface forming part that forms a curved surface on a wall surface of the insertion hole.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an inflation molding apparatus, a sizing ring of the inflation molding apparatus, and a movable member of the sizing ring of the inflation molding apparatus. [Background technology]

[0002] An inflation molding device extrudes molten resin from a die into a tube shape and blows air into the inside of the tube to inflate it and form a thin film (see, for example, Patent Document 1). There are two types of inflation molding devices: an upward type that extrudes molten resin upward, and a downward type that extrudes molten resin downward.

[0003] The inflation molding device is equipped with a sizing ring. The sizing ring determines the outer diameter of the bubble, which is a tubular resin film. The sizing ring forms an insertion hole through which the bubble passes. A film of refrigerant, such as cooling water, is formed between the wall of the insertion hole and the bubble. The outer diameter of the bubble is smaller than the diameter of the insertion hole by the thickness of the refrigerant film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-231266 Summary of the Invention [Problem to be solved by the invention]

[0005] Previously, when changing the outer diameter of a bubble, it was necessary to change the diameter of the insertion hole and replace the sizing ring. Replacing the sizing ring was a cumbersome task and a heavy workload. Replacement took time, during which resin film production was halted. Furthermore, replacing the sizing ring required stopping molding, which resulted in resin loss when molding was restarted.

[0006] Therefore, a sizing ring equipped with a hole diameter changing mechanism for changing the hole diameter of the insertion hole is conceivable. The hole diameter changing mechanism has a plurality of movable members that define the insertion hole and are arranged continuously in the circumferential direction of the insertion hole. The movable members are movable in both directions, to decrease the hole diameter and to increase the hole diameter.

[0007] The wall surface of the insertion hole is formed by the side surface of the movable member. If the side surface of the movable member is flat, the wall surface of the insertion hole is formed by multiple flat surfaces, and the insertion hole has a polygonal shape. Therefore, the distance between the wall surface of the insertion hole and the bubbles varies in the circumferential direction of the insertion hole. In areas with a wider distance, a larger amount of cooling water flows than in areas with a narrower distance, and the time it takes for the bubbles to solidify is shorter.

[0008] The portion of the bubble that takes less time to solidify is less stretched by the pair of pinch rolls than the portion that takes longer, and is therefore more likely to become thicker. As a result, the thickness of the bubble becomes uneven in the circumferential direction of the bubble. The appearance of the bubble also becomes uneven, with visible streaks.

[0009] One aspect of the present invention provides a technique for suppressing molding defects. [Means for solving the problem]

[0010] A blown film molding apparatus according to one aspect of the present invention includes a sizing ring that forms a through-hole through which a bubble passes. The sizing ring includes a hole diameter changing mechanism that changes the hole diameter of the through-hole. The hole diameter changing mechanism has a movable member that defines the through-hole. The movable member includes a curved surface forming portion that forms a curved surface on the wall of the through-hole. The curved surface forming portion has a deforming portion that is elastically deformable, and a side surface of the deforming portion forms the curved surface. The curved surface forming portion changes the shape of the curved surface in response to a change in the diameter of the insertion hole. [Effects of the Invention]

[0011] According to one aspect of the present invention, by forming a curved surface on the wall surface of the insertion hole, the roundness of the insertion hole can be improved and molding defects can be suppressed. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an inflation molding apparatus according to one embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing an example of the second cooling device of FIG. [Figure 3] 3A and 3B are perspective views showing a sizing ring according to one embodiment, in which FIG. 3A is a perspective view showing a state in which the hole diameter is maximum, and FIG. 3B is a perspective view showing a state in which the hole diameter is minimum. [Figure 4] 4A and 4B are cross-sectional views showing a sizing ring according to one embodiment, in which FIG. 4A is a cross-sectional view showing a state in which the hole diameter is at its maximum, and FIG. 4B is a perspective view showing a state in which the hole diameter is at its minimum. [Figure 5] 5A and 5B are perspective views showing an example of a leaf spring, in which FIG. 5A is a perspective view showing the leaf spring in a state before deformation, and FIG. 5B is a perspective view showing the leaf spring in a state after deformation. [Figure 6] FIG. 6 is a plan view showing an example of a curved surface formed by a leaf spring. [Figure 7] 7A and 7B are perspective views showing an example of rubber, where FIG. 7A is a perspective view showing the state of the rubber before deformation, and FIG. 7B is a perspective view showing the state of the rubber after deformation. [Figure 8] 8A and 8B are perspective views showing an example of a curved surface of a blade, where FIG. 8A is a perspective view and FIG. 8B is a plan view. [Figure 9] FIG. 9 is a plan view showing an example of an insertion hole formed by the blade shown in FIG. 8(B). DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and their description may be omitted. In this specification, the X-axis, Y-axis, and Z-axis directions are perpendicular to each other. The X-axis and Y-axis directions represent the horizontal direction, and the Z-axis direction represents the vertical direction.

[0014] An inflation molding apparatus 1 according to one embodiment will be described with reference to Figure 1. The inflation molding apparatus 1 includes a die 10, a first cooling device 20, a second cooling device 30, a pair of stabilizer plates 40, and a pinch roll 50. The inflation molding apparatus 1 is a downward-type apparatus in which resin is extruded downward from the die 10. However, the present invention is also applicable to an upward-type inflation molding apparatus in which resin is extruded upward from the die 10.

[0015] Molten resin is supplied to the die 10 from an extruder (not shown). The supplied molten resin is extruded from a ring-shaped resin discharge port 11 formed in the die 10. Air is appropriately ejected into the extruded molten resin from air ejection ports 12 formed inside the resin discharge port 11. This forms a bubble B, which is a tubular resin film.

[0016] The first cooling device 20 is disposed below the die 10. The first cooling device 20 sprays cooling gas onto the bubbles B to cool them. The second cooling device 30 is disposed below the first cooling device 20. The second cooling device 30 cools the bubbles B by bringing cooling water into contact with the bubbles B. Details of the second cooling device 30 will be described later. The bubbles B are cooled by the first cooling device 20 and the second cooling device 30 and solidify.

[0017] A pair of stabilizer plates 40 are disposed below the second cooling device 30 and guide the bubble B between a pair of pinch rolls 50. The pair of pinch rolls 50 are disposed below the stabilizer plates 40. The pair of pinch rolls 50 pull down the guided bubble B and fold it flat. A winder 60 winds up the folded resin film to form a film roll R.

[0018] An example of the second cooling device 30 will be described with reference to FIG. 2. The second cooling device 30 includes a water tank 31, a sizing ring 32, a first cylindrical member 33, a second cylindrical member 34, and a rotation mechanism 35. The water tank 31 stores cooling water to be supplied to the sizing ring 32. The sizing ring 32 determines the outer diameter of the bubbles B. The sizing ring 32 has an insertion hole 32a through which the bubbles B pass. The first cylindrical member 33 is placed on the bottom 31a of the water tank 31 and supports the sizing ring 32 at a predetermined height from the bottom 31a of the water tank 31. The second cylindrical member 34 extends downward from the bottom 31a of the water tank 31 and surrounds the bubbles B to prevent the cooling water from scattering. The rotation mechanism 35 rotates the sizing ring 32.

[0019] The water tank 31 has a circular shape in a plan view, but is not particularly limited to this, and is open at the top. An insertion hole 31b through which the bubbles B pass is formed in the bottom 31a of the water tank 31. A cooling water supply port 31c is also formed in the bottom 31a of the water tank 31. An overflow pipe 36 is attached to the bottom 31a of the water tank 31. The overflow pipe 36 extends above the sizing ring 32 and has an outlet 36a at its upper end. Cooling water is supplied through the supply port 31c and discharged through the outlet 36a. The cooling water level WH is determined by the position of the outlet 36a and is maintained at a predetermined level above the sizing ring 32. A cooling water film is formed between the wall surface of the insertion hole 32a of the sizing ring 32 and the bubbles B. The cooling water cools the bubbles B as it flows down between the wall surface of the insertion hole 32a and the outer periphery of the bubbles B.

[0020] A plurality of (for example, four) plates 37 are fixed to the outer peripheral surface 31d of the water tank 31. A first bolt 71 is screwed vertically downward into each of the plurality of plates 37. The first bolts 71 are provided, for example, at equal intervals in the circumferential direction. The first bolts 71 pass through the plates 37, and the tips of the first bolts 71 each abut against the upper surface 70a of the mounting base 70. The water tank 31 is supported on the mounting base 70 via the plurality of first bolts 71. The first bolts 71 and the plates 37 form a ball screw mechanism, and turning the first bolts 71 moves the plates 37, and therefore the water tank 31, in the vertical direction. In other words, the height of the water tank 31 is adjusted.

[0021] A plurality of (for example, four) support members 73 are fixed to the upper surface 70a of the mounting table 70. A second bolt 72 is threaded horizontally into each of the plurality of support members 73 toward the central axis of the water tank 31. The second bolts 72 are provided, for example, at equal intervals in the circumferential direction. The second bolts 72 penetrate the support members 73, and the tips of the second bolts 72 each abut against the outer peripheral surface 31d of the water tank 31. The plurality of second bolts 72 position the water tank 31 horizontally. For example, the water tank 31 is positioned horizontally so that the central axis of the sizing ring 32 coincides with the central axis of the resin discharge port 11 of the die 10.

[0022] The sizing ring 32 is a component that determines the outer diameter of the bubble B by the diameter of the insertion hole 32a. A film of cooling water is formed between the wall surface of the insertion hole 32a and the bubble B. Therefore, the outer diameter of the bubble B is smaller than the diameter of the insertion hole 32a by the thickness of the cooling water film. As will be described in detail later, the sizing ring 32 is equipped with a hole diameter varying mechanism 100 (see FIG. 3) that varies the hole diameter of the insertion hole 32a. This eliminates the need to replace the sizing ring 32 when changing the outer diameter of the bubble B. Note that a coolant other than cooling water may be used. Furthermore, a cooling gas may be used as a refrigerant instead of a coolant.

[0023] The first cylindrical member 33 is provided so that its central axis extends vertically. The lower end of the first cylindrical member 33 is spigot-fitted to the bottom 31a of the water tank 31. The sizing ring 32 is placed on the upper end of the first cylindrical member 33. In other words, the sizing ring 32 is supported by the first cylindrical member 33. The upper end of the first cylindrical member 33 is spigot-fitted to the sizing ring 32, specifically to the second holding member 132 described below.

[0024] The second cylindrical member 34 extends downward from the bottom 31a of the water tank 31. The second cylindrical member 34 has the same inner diameter as the insertion hole 31b of the water tank 31, and surrounds the bubble B to prevent the cooling water from scattering.

[0025] The rotation mechanism 35 rotates the sizing ring 32. The rotation mechanism 35 rotates the sizing ring 32, for example, once every 20 to 30 minutes. The sizing ring 32 is rotated when the insertion hole 32a of the sizing ring 32 is not a perfect circle. When the insertion hole 32a is not a perfect circle, the distance between the wall surface of the insertion hole 32a and the bubbles B varies in the circumferential direction of the insertion hole 32a. In areas with a wider distance, a larger amount of cooling water flows than in areas with a narrower distance, and the time required for the bubbles B to solidify is shorter. In areas where the bubbles B take less time to solidify, they are less likely to be stretched by the pair of pinch rolls 50 and are more likely to become thicker than in areas with a longer distance. As a result, the thickness of the bubbles B becomes uneven in the circumferential direction of the bubbles B.

[0026] Rotation mechanism 35 rotates sizing ring 32, thereby rotating the thick and thin portions of bubble B in the circumferential direction of bubble B. This prevents the thick portions of bubble B from piling up on top of each other when winder 60 forms film roll R. This prevents unevenness from forming on the outer periphery of film roll R, and prevents distortion of the resin film.

[0027] The rotation mechanism 35 may rotate the sizing ring 32 by rotating the water tank 31. By rotating the sizing ring 32 together with the water tank 31, it is not necessary to place the components of the rotation mechanism 35 inside the water tank 31, and it is possible to suppress the swaying of the cooling water inside the water tank 31. As a result, it is possible to prevent uneven thickness of the bubble B due to the swaying of the cooling water inside the water tank 31.

[0028] Rotation mechanism 35 includes, for example, a drive unit 80 and a transmission mechanism 81. Drive unit 80 is, for example, a motor or a gear motor, and outputs rotational force. Transmission mechanism 81 is a mechanism that transmits the rotational force generated by drive unit 80 to water tub 31, and includes an external gear 82 and a bearing 83. External gear 82 is fitted onto output shaft 80a of drive unit 80.

[0029] The bearing 83 is disposed so as to surround the bubble B. The central axis of the bearing 83, the central axis of the sizing ring 32, and the central axis of the water tank 31 are substantially aligned.

[0030] Bearing 83 includes an inner ring 83a and an outer ring 83b. Inner ring 83a is fixed to a frame (not shown). Outer ring 83b is fixed to water tank 31. Outer ring 83b is indirectly fixed to water tank 31 by being fixed to mounting table 70, but may also be fixed directly to water tank 31. External teeth 83c that mesh with external gear 82 are formed on the outer periphery of outer ring 83b.

[0031] When the external gear 82 rotates in accordance with the rotation of the output shaft 80a, the outer ring 83b rotates. As described above, the outer ring 83b is fixed to the water tub 31. In addition, the sizing ring 32 is fixed to the water tub 31. Therefore, when the outer ring 83b rotates, the sizing ring 32 rotates.

[0032] Preferably, the rotation mechanism 35 may rotate (i.e., rotate back and forth) the water tank 31 within a predetermined angular range (e.g., a predetermined angular range of 360° or less), thereby preventing twisting of a hose (not shown) connected to the supply port 31c.

[0033] An example of a hole diameter varying mechanism 100 for the sizing ring 32 will be described with reference to Figures 3 to 6. As shown in Figures 3 and 4, the hole diameter varying mechanism 100 varies the hole diameter of the insertion hole 32a. The hole diameter varying mechanism 100 has a plurality of movable members 110 (e.g., 32 members) that define the insertion hole 32a and are arranged continuously in the circumferential direction of the insertion hole 32a. The movable members 110 are movable in both directions, that is, in a direction to decrease the hole diameter and a direction to increase the hole diameter.

[0034] The insertion hole 32a of the sizing ring 32 is defined by the multiple movable members 110, and the wall surface of the insertion hole 32a is formed by the side surfaces of the multiple movable members 110. The height of the wall surface of the insertion hole 32a is determined by the height of the movable members 110. The height of the wall surface is set to a height sufficient to define the outer diameter of the bubble B.

[0035] 5, the movable member 110 has a blade 111 having, for example, a triangular prism shape. The blade 111 has an upper surface 111a, a lower surface 111b, a first side surface 111c, a second side surface 111d, and a third side surface 111e. The upper surface 111a and the lower surface 111b are triangular and tapered toward the inside in the radial direction of the sizing ring 32. The first side surface 111c, the second side surface 111d, and the third side surface 111e are rectangular.

[0036] A first protrusion 121 is provided on an upper surface 111a of the blade 111. The first protrusion 121 is inserted into a first slit 131a (see FIG. 3) of a first holding member 131. Meanwhile, a second protrusion (not shown) is provided on a lower surface 111b of the blade 111. The second protrusion is inserted into a second slit 132a (see FIG. 3) of a second holding member 132. The first protrusion 121 and the second protrusion are arranged on the same vertical line.

[0037] The hole diameter varying mechanism 100 has a first holding member 131. The first holding member 131 holds the blade 111 so that it can move freely in a direction that changes the hole diameter of the insertion hole 32a. The first holding member 131 is a thin, annular member. The first holding member 131 has first slits 131a, the same number as the number of blades 111, formed at equal intervals in the circumferential direction. When viewed from above, the first slits 131a extend linearly and are inclined counterclockwise as they move radially inward of the sizing ring 32.

[0038] The hole diameter varying mechanism 100 also includes a second holding member 132. The second holding member 132 holds the blade 111 so as to be movable in a direction that changes the hole diameter of the insertion hole 32a. The second holding member 132 is a member having the same shape and size as the first holding member 131. That is, the second holding member 132 is a thin-walled, annular member. The second holding member 132 has second slits 132a, the same number as the number of blades 111, formed at equal intervals in the circumferential direction. When viewed from above, the second slits 132a extend linearly and are inclined clockwise as they extend radially inward of the sizing ring 32. That is, when viewed from above, the second slits 132a are inclined in the opposite direction to the first slits 131a.

[0039] As shown in Fig. 4, the first side surface 111c of one blade 111 contacts the second side surface 111d of the adjacent blade 111. The first side surface 111c and the second side surface 111d are sliding surfaces that are vertical planes. When viewed from above, the first side surface 111c and the second side surface 111d are inclined clockwise as they move radially inward of the sizing ring 32. Multiple blades 111 overlap in the radial direction of the sizing ring 32.

[0040] When the first holding member 131 is rotated clockwise relative to the second holding member 132 as viewed from above, the first protrusion 121 moves radially inward along the first slit 131a, and the second protrusion moves radially inward along the second slit 132a. As a result, the blade 111 moves radially inward, and the diameter of the insertion hole 32a of the sizing ring 32 becomes smaller.

[0041] On the other hand, when the first holding member 131 is rotated counterclockwise relative to the second holding member 132 as viewed from above, the first protrusions 121 move radially outward along the first slits 131a, and the second protrusions move radially outward along the second slits 132a. As a result, the blades 111 move radially outward, and the diameter of the insertion holes 32a of the sizing ring 32 increases.

[0042] Here, the case where the first holding member 131 is rotated relative to the second holding member 132 has been described, but the second holding member 132 may be rotated relative to the first holding member 131.

[0043] Although the case has been described here in which the first side surface 111c and the second side surface 111d are inclined clockwise as they move radially inward of the sizing ring 32 when viewed from above, the first side surface 111c and the second side surface 111d may also be inclined counterclockwise as they move radially inward of the sizing ring 32 when viewed from above. In the latter case, the first slit 131a is inclined clockwise as it moves radially inward of the sizing ring 32. In the latter case, the second slit 132a is inclined counterclockwise as it moves radially inward of the sizing ring 32.

[0044] As shown in FIG. 6, multiple movable members 110 are provided continuously in the circumferential direction of the insertion hole 32a. The wall surface of the insertion hole 32a is formed by the side surface of the movable member 110. If the movable member 110 were made up of only the blade 111 and the first side surface 111c of the blade 111 were flat, the wall surface of the insertion hole 32a would be formed by multiple flat surfaces, and the insertion hole 32a would have a polygonal shape. In this case, as described above, the thickness of the bubble B would be uneven in the circumferential direction of the bubble B. Furthermore, the appearance of the bubble B would also be uneven, resulting in visible streaks.

[0045] Therefore, as shown in FIG. 6, the movable member 110 includes a curved surface forming portion 112 that forms a curved surface 32a1 on the wall surface of the insertion hole 32a. The insertion hole 32a can be rounded, improving the roundness of the insertion hole 32a. As a result, the distance between the wall surface of the insertion hole 32a and the bubble B can be made uniform, and the thickness of the bubble B can be made uniform. Furthermore, the appearance of the bubble B can be made uniform, reducing appearance defects such as streaks. This prevents molding defects.

[0046] As shown in FIG. 5, the curved surface forming portion 112 has a deforming portion 113 that is elastically deformable, for example. The side surface of the deforming portion 113 forms the curved surface 32a1. The curved surface forming portion 112 changes the shape of the curved surface 32a1 in response to changes in the diameter of the insertion hole 32a. Specifically, the smaller the diameter of the insertion hole 32a, the smaller the radius of curvature of the curved surface 32a1. Therefore, the circularity of the insertion hole 32a can be maintained even when the diameter of the insertion hole 32a changes.

[0047] The deformation portion 113 includes, for example, a leaf spring 113A. The leaf spring 113A is provided at the tip of the blade 111. The blade 111 is a rigid body that supports the leaf spring 113A so that it can be deformed. The shape of the leaf spring 113A can be controlled to some extent by the rigid body.

[0048] The leaf spring 113A elastically bends when it comes into contact with the first side surface 111c of the adjacent blade 111. The smaller the diameter of the insertion hole 32a, the greater the bending of the leaf spring 113A. The side surface of the leaf spring 113A forms a curved surface 32a1. The height of the leaf spring 113A is approximately the same as the height of the blade 111, for example.

[0049] 6, a plurality of leaf springs 113A may be overlapped in the radial direction of the sizing ring 32. This allows the wall surfaces of the insertion hole 32a to be formed only by the side surfaces of the leaf springs 113A, thereby improving the roundness of the insertion hole 32a.

[0050] Next, a modified example of the deforming portion 113 will be described with reference to FIG. 7. As shown in FIG. 7, the deforming portion 113 may be a part of the blade 111, or may include a triangular prism-shaped rubber 113B. The rubber 113B is provided at the tip of the blade 111, and elastically bends when it comes into contact with the first side surface 111c of the adjacent blade 111. The smaller the diameter of the insertion hole 32a, the greater the bending of the rubber 113B. The side surface of the rubber 113B forms a curved surface 32a1.

[0051] A plurality of rubber pieces 113B may overlap in the radial direction of the sizing ring 32. This allows the wall surfaces of the insertion hole 32a to be formed only by the side surfaces of the rubber pieces 113B, thereby improving the roundness of the insertion hole 32a.

[0052] In addition to the triangular prism-shaped rubber 113B, the blade 111 also includes a quadrangular prism-shaped rubber mounting portion 114 to which the rubber 113B is attached. The upper and lower surfaces of the rubber mounting portion 114 are trapezoidal and tapered toward the inside in the radial direction of the sizing ring 32. The rubber 113B is attached to the side surface of the tip side of the rubber mounting portion 114.

[0053] The rubber mounting portion 114 is made of a material harder than the rubber 113B, such as metal, and maintains a preset shape regardless of changes in the diameter of the insertion hole 32a. In other words, the rubber mounting portion 114 is a rigid body that supports the rubber 113B in a deformable manner. The shape of the rubber 113B can be controlled to some extent by the rigid body.

[0054] 8 and 9, modified examples of the curved surface forming portion 112 will be described. The curved surface forming portion 112 may maintain the shape of the curved surface 32a1 in a preset shape regardless of changes in the diameter of the insertion hole 32a.

[0055] The curved surface forming portion 112 is provided, for example, at the tip of the first side surface 111c. The curved surface forming portion 112 has, for example, a curved surface 112a and a flat surface 112b. The flat surface 112b is provided on the same plane as the second side surface 111d. The curved surface 112a is formed so as to round the corner between the flat surface 112b and the first side surface 111c. The inclination angle of the curved surface 112a with respect to the flat surface 112b decreases toward the radially inner side of the sizing ring 32. The curved surface 112a corresponds to the curved surface 32a1.

[0056] The curved surface 112a may have a smaller radius of curvature toward the inside in the radial direction of the sizing ring 32. Compared to when the curved surface 112a has a constant radius of curvature overall, this can suppress a decrease in the circularity of the insertion hole 32a due to a change in the hole diameter of the insertion hole 32a.

[0057] The above describes the embodiments of the inflation molding apparatus, the sizing ring of the inflation molding apparatus, and the movable member of the sizing ring of the inflation molding apparatus according to the present invention, but the present invention is not limited to the above embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These changes also naturally fall within the technical scope of the present invention. [Explanation of symbols]

[0058] 1. Blown film molding equipment 32 Sizing Ring 32a Insertion hole 32a1 curved surface 100 Variable hole diameter mechanism 110 Movable parts 112 Curved surface forming part B Bubble

Claims

1. An inflation molding apparatus including a sizing ring that forms a through hole through which a bubble passes, the sizing ring includes a hole diameter varying mechanism that varies the hole diameter of the insertion hole, the hole diameter varying mechanism has a movable member that defines the insertion hole, the movable member includes a curved surface forming portion that forms a curved surface on a wall surface of the insertion hole, the curved surface forming portion has a deforming portion that is elastically deformed, and a side surface of the deforming portion forms the curved surface; The curved surface forming unit changes the shape of the curved surface in accordance with a change in the diameter of the insertion hole.

2. The inflation molding apparatus according to claim 1 , wherein the curved surface forming portion has a rigid body that supports the deforming portion so that the deforming portion can be deformed.

3. The inflation molding apparatus according to claim 1 or 2, wherein the deformation portion includes a leaf spring.

4. An inflation molding apparatus including a sizing ring that forms a through hole through which a bubble passes, the sizing ring includes a hole diameter varying mechanism that varies the hole diameter of the insertion hole, the hole diameter varying mechanism has a movable member that defines the insertion hole, the movable member includes a curved surface forming portion that forms a curved surface on a wall surface of the insertion hole, The curved surface has a radius of curvature that decreases toward the inside in the radial direction of the sizing ring.

5. A sizing ring of an inflation molding apparatus, Equipped with a variable hole diameter mechanism that changes the diameter of the insertion hole through which the bubble passes, the hole diameter varying mechanism has a movable member that defines the insertion hole, the movable member includes a curved surface forming portion that forms a curved surface on a wall surface of the insertion hole, the curved surface forming portion has a deforming portion that is elastically deformed, and a side surface of the deforming portion forms the curved surface; The curved surface forming portion changes the shape of the curved surface in accordance with a change in the diameter of the insertion hole.

6. A sizing ring of an inflation molding apparatus, Equipped with a variable hole diameter mechanism that changes the diameter of the insertion hole through which the bubble passes, the hole diameter varying mechanism has a movable member that defines the insertion hole, the movable member includes a curved surface forming portion that forms a curved surface on a wall surface of the insertion hole, A sizing ring for an inflation molding apparatus, wherein the curved surface has a radius of curvature that decreases toward the inside in the radial direction of the sizing ring.

7. A movable member of a sizing ring of an inflation molding apparatus, comprising: a sizing ring that forms a through-hole through which a bubble passes; the sizing ring having a hole diameter varying mechanism that varies the hole diameter of the through-hole; and the hole diameter varying mechanism having a movable member that defines the through-hole, the movable member includes a curved surface forming portion that forms a curved surface on a wall surface of the insertion hole, the curved surface forming portion has a deforming portion that is elastically deformed, and a side surface of the deforming portion forms the curved surface; The curved surface forming portion is a movable member of a sizing ring of an inflation molding device that changes the shape of the curved surface in response to changes in the diameter of the insertion hole.

8. A movable member of a sizing ring of an inflation molding apparatus, comprising: a sizing ring that forms a through-hole through which a bubble passes; the sizing ring having a hole diameter varying mechanism that varies the hole diameter of the through-hole; and the hole diameter varying mechanism having a movable member that defines the through-hole, the movable member includes a curved surface forming portion that forms a curved surface on a wall surface of the insertion hole, The movable member of the sizing ring of the inflation molding apparatus, wherein the curved surface has a radius of curvature that decreases toward the inside in the radial direction of the sizing ring.

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