JP6398231B2 - Molding method for synthetic resin containers - Google Patents

Description

  The present invention relates to a synthetic resin container, more specifically a synthetic resin container having a bottom wall, a cylindrical side wall extending upward from the periphery of the bottom wall, and an annular flange extending radially outward from the upper end of the side wall. The present invention relates to a molding method for molding.

  As known in the art, as a container for food and drink, a circular or polygonal bottom wall, a cylindrical or inverted-conical cylinder extending upward from the periphery of the bottom wall, a polygonal cylinder or an inverted polygonal truncated cone-shaped side wall, and a side wall Synthetic resin containers having an annular or polygonal annular flange extending radially outward from the upper end are widely used in practice. After the contents are filled in the container, a sealing seal is attached to the annular flange, and the opening present on the upper surface of the container is sealed. As a simple molding method for molding such a container, a molding method in which a molten or soft synthetic resin mass is directly compression-molded into a final shape can be mentioned. Further, in Patent Documents 1 and 2 below, a molten or softened synthetic resin lump is molded by compression molding or extrusion molding into a flat or shallow dish-shaped circular or polygonal plate shape, and then applied. A molding method for thermoforming a pre-formed body into a final shape has also been proposed and put into practical use.

Japanese Patent No. 3970867 JP 2003-159743 A

  Thus, the molding method in which the synthetic resin block is directly compression-molded into the final shape and the conventional molding method disclosed in Patent Documents 1 and 2 described above include loads necessary for molding, that is, necessary molding. There is a problem that the load is excessive and the molding apparatus becomes large and expensive.

  The present invention has been made in view of the above-mentioned facts, and the main technical problems thereof are a bottom wall, a cylindrical side wall extending upward from the periphery of the bottom wall, and a ring extending radially outward from the upper end of the side wall. It is an object of the present invention to provide a new and improved molding method for molding a synthetic resin container having a shape flange with a required molding load considerably reduced as compared with the prior art.

As a result of diligent studies and experiments, the inventor has surprisingly surprisingly developed a plate-like preform having a thin central portion, a thick intermediate portion, and a thin peripheral portion by first compressing a synthetic resin mass in a molten or softened state. The body is then molded, and at least the thick middle part is in a melted or softened state. The thin middle part of the preform is displaced relative to the thin peripheral part in the direction of the central axis, and the thick middle part is ironed. It was found that a synthetic resin container having a required shape can be formed by a required molding load that is considerably reduced by molding the thick intermediate portion into a cylindrical shape while adding the above.

That is, according to the present invention, as a molding method for achieving the main technical problem, the bottom wall, the cylindrical side wall extending upward from the peripheral edge of the bottom wall, and the outer edge of the side wall extend radially outward. In a molding method for molding a synthetic resin container having an annular flange,
A primary molding step of molding a plate-shaped preform having a thin central portion, a thick intermediate portion, and a thin peripheral portion by compression molding a molten or soft synthetic resin mass;
At least the thick intermediate portion is in a molten or softened state. The thin central portion of the preform is displaced relative to the thin peripheral portion in the direction of the central axis, and the thick intermediate portion is squeezed. A secondary forming step of forming the thick intermediate portion into a cylindrical shape while adding ,
There is provided a molding method characterized by comprising:

Conveniently, the side wall is an upright cylinder or an inverted frustum cylinder whose size gradually decreases downward. Preferably, in the secondary molding step, a first molding die member having a cylindrical molding recess opened upward, and a columnar body corresponding to the molding recess of the first molding die member, to the first mold member said first mold member between a lowered position which is allowed to enter into the molding in the recess of the raised position and said first mold member located above the molded recesses A second mold member that is relatively moved, and an annular restraining member that is positioned at a restraining position that faces the peripheral region surrounding the molding recess on the upper surface of the first mold member. forming apparatus that is used, allowed position on the molding recess of the thin-walled central portion and the thick middle portion by placing the front molded body on an upper surface of said first mold member, then the restraining member The first mold member and the restraining member positioned at the restraining position The said thin peripheral portion of the front molded body captured between and allowed move said second mold member to the lowered position from the raised position thereafter. Further, a lower mold assembly composed of a columnar lower inner member and a cylindrical lower outer member surrounding the lower inner member, and a cylindrical shape surrounding the columnar inner member and the upper inner member. A molding apparatus comprising an upper mold assembly composed of upper and outer members is used, and in the primary molding process, a synthetic resin mass is supplied to the upper surface of the lower inner member, and the lower mold assembly The upper molding assembly is lowered relative to the lower inner member and the upper inner member, and the thin central portion of the preform is compression-molded between the lower inner member and the upper outer member. The thin peripheral edge is compression-molded between the outer member and the outer peripheral edge of the lower inner member or the outer peripheral edge of the lower inner member and the inner peripheral edge of the lower outer member and the outer peripheral edge of the upper inner member. The thick intermediate portion is compression-molded between the upper portion and the inner peripheral edge portion of the upper and outer members, In the shape step, the lower inner member and the upper inner member is moved down, the thick middle portion of the front compact is formed into a tubular shape, it is also preferable.

  According to the molding method of the present invention, as clearly understood from the examples and comparative examples described later, a container having a required shape can be molded with a considerably reduced required molding load.

The simplified sectional view showing the initial stage of the primary forming process in the suitable embodiment of the forming method of the present invention. The simplified sectional view showing the final stage of the primary forming process in a suitable embodiment of the forming method of the present invention. The simplified sectional view showing the initial stage of the secondary fabrication process in a suitable embodiment of the fabrication method of the present invention. The simplified sectional view showing the final stage of the secondary fabrication process in a suitable embodiment of the fabrication method of the present invention. The simplified sectional view showing the initial stage of the primary forming process in other suitable embodiments of the forming method of the present invention. The simplified sectional view showing the last stage (initial stage of a secondary fabrication process) of the primary fabrication process in other suitable embodiments of the fabrication method of the present invention. The simplified sectional view showing the last stage of the secondary fabrication process in other suitable embodiments of the fabrication method of the present invention. FIG. 4 is a simplified cross-sectional view showing a molding method in Comparative Example 1. FIG. 6 is a simplified cross-sectional view showing a molding method in Comparative Example 2. The diagram which shows the measurement result in an Example and Comparative Examples 1 and 2. FIG.

  The preferred embodiments of the molding method of the present invention will be described below in more detail with reference to the accompanying drawings.

  Referring to FIGS. 1 and 2, in a preferred embodiment of the molding method of the present invention, a primary molding process is performed using a molding apparatus generally designated by numeral 2. The molding apparatus 2 includes a first mold member 4 and a second mold member 6 positioned above the first mold member 4 and moved up and down relative to the first mold member 4. A molding device is used. A disc-shaped molding recess 8 is formed on the top surface of the first mold member 4 as a whole, and an annular groove 10 is formed on the bottom surface of the molding recess 8. The cross-sectional shape of the groove 10 is generally an isosceles triangle, and the deepest portion, that is, the lowermost portion is formed in an arc shape. The second mold member 6 has a flat lower surface that extends substantially horizontally. As shown in FIG. 1, in the mold open state in which the second mold member 6 is spaced upward from the first mold member 4, the center of the molding recess 8 of the first mold member 4 is formed. A molten or softened synthetic resin mass 12 is supplied. Examples of suitable synthetic resins constituting the synthetic resin mass 12 include polypropylene, polyethylene, polyethylene terephthalate, and the like. Next, the second mold member 6 is lowered to the closed position shown in FIG. 2, and the synthetic resin mass 12 is compression molded into the pre-molded body 14. The preform 14 has a disk shape as a whole, and has a thin central portion 16, a thick intermediate portion 18, and a thin peripheral portion 20. Thereafter, the second mold member 6 is raised to the position shown in FIG. 1, and the molded preform 14 is taken out from the first mold member 4. If desired, the first mold member 4 can be moved up and down instead of or in addition to moving the second mold member 6 up and down.

  In a preferred embodiment of the molding method of the present invention, a secondary molding step is performed following the primary molding step. The description will be continued with reference to FIG. 3 and FIG. 4. In the secondary molding step, a molding apparatus indicated by the whole number 22 is used. The molding apparatus 22 includes a first mold member 24, a second mold member 26, and a restraining member 28. Formed on the upper surface of the first mold member 24 is a generally cylindrical recess 30 that is open upward. The outer peripheral edge of the lower end of the molding recess 30 has an arc shape in the sectional view, and the inner diameter is gradually reduced downward, and the outer peripheral edge of the upper end of the molding recess 30 is also arced in the sectional view. The inner diameter is gradually increased upward. The second mold member 26 has a cylindrical shape as a whole. The second mold member 26 is moved upwardly from the first mold member 24 (the lifted position shown in FIG. 3) and the molding recess 30 of the first mold member 24. It can be moved up and down between the lowered position (the lowered position shown in FIG. 4) entered. The outer diameter of the second mold member 26 is, for example, about 0.5 to 2.0 mm smaller than the inner diameter (the inner diameter other than the lower end and the upper end) of the molding recess 30 of the first mold member 24. . The restraining member 28 has an annular plate shape and surrounds a raised position (a raised position shown in FIG. 3) spaced upward from the first mold member 24 and a molding recess 30 on the upper surface of the first mold member 24. It is selectively positioned at the working position (the working position shown in FIG. 4) that opposes the peripheral region with some gap. The inner diameter of the restraining member 28 is substantially the same as the outer diameter of the second molding member 26.

  In the secondary molding process performed using the molding apparatus 22, a mold in which a second molding member 26 and a restraining member 28 are spaced apart from the first molding member 24 as shown in FIG. 3. In the open state, the preform 14 is supplied onto the first mold member 24. The thin central portion 16 of the preform 14 is located above the central region of the molding recess 30, the thick intermediate portion 18 is located above the peripheral region of the molding recess 30, and the thin peripheral portion 20 is the first mold. Located on the upper surface of the member 24. At least the thick intermediate portion 18 of the preform 14, usually the entire preform 1, is melted or softened. Next, the restraining member 28 is lowered together with the second mold member 26 or the restraining member 28 is lowered prior to the lowering of the second mold member 26 to be brought into the restraining position shown in FIG. It is done. When the restraining member 28 is positioned at the restraining position shown in FIG. 4, the lower surface of the restraining member 28 is positioned with a slight gap with respect to the upper surface of the thin peripheral edge 20 of the preformed body 14, or the preformed body. 14 is brought into contact with the upper surface of the thin peripheral edge 20. If desired, some restraining force can be applied to the thin peripheral edge 20 of the preform 14 by the restraining member 28. Further, instead of holding the restraining member 28 at a predetermined restraining position, the restraining member 28 is allowed to move up and down, and the restraining member 28 is thinned by the weight of the restraining member 28 itself. It can also be made to press against the upper surface of the plate.

  The second mold member 26 lowered together with the restraining member 28 or separately from the restraining member 28 to the position indicated by a two-dot chain line in FIG. It begins to act on the meat middle part 18. As the second mold member 26 is lowered, the thin central portion 20 of the pre-formed body 14 is displaced downward with respect to the thin peripheral edge portion 16, and the thick intermediate portion 18 is deformed into a cylindrical shape. Thus, when the second mold member 26 is lowered to the lowered position shown in FIG. 4, the circular bottom wall 34, the cylindrical side wall 36 extending upward from the peripheral edge of the bottom wall 34, and the upper end of the side wall radially outward. A synthetic resin container 32 having an annular flange 38 extending substantially horizontally is formed. The molded container 32 can be taken out from the molding apparatus 22 by raising the second mold member 26 and the restraining member 28 as appropriate to bring the mold into an open state. For example, first, both the second mold member 26 and the restraining member 28 are raised to raise the container 32 from the molding recess 30 of the first mold member 24, and then the raising of the restraining member 28 is stopped. Only the second mold member 24 is raised and the container 32 is released from the second mold member 26.

Thus, the thick intermediate portion 18 of the pre-formed body 14 is not displaced by simply displacing the thin central portion 16 of the pre-formed body 14 with respect to the thin peripheral edge portion 20 without acting a member. However, as can be clearly understood by referring to FIGS. 3 and 4, the peripheral portion of the second mold member 26 is allowed to act on the thick intermediate portion 18 of the preform 14. If the thick intermediate portion 18 is deformed while applying a so-called ironing action to the thick intermediate portion 18, the thick intermediate portion 18 can be satisfactorily deformed as required with sufficient stability. On the other hand, if the second mold member 26 is lowered without restraining the thin peripheral edge portion 20 of the pre-formed body 14 by the restraining member 28 and the thick intermediate portion 18 is deformed, the thin peripheral edge portion 20 becomes the second peripheral edge portion 20. Then, there is a tendency that the mold member 24 is displaced upward from the upper surface of the mold member 24 and then immerses into the molding recess 30, which obstructs the molding of the container 32 as required.

  In the embodiment described above, the composite has a circular bottom wall 34, a cylindrical side wall 36 extending upward from the periphery of the bottom wall 34 and an annular flange 38 extending substantially horizontally radially outward from the upper end of the side wall. The resin container 32 is molded, but the molded container is not limited to such a shape. For example, instead of the cylindrical shape, the side wall can be formed in an inverted truncated cone shape whose outer diameter gradually increases upward. Further, the bottom wall can be made into a polygonal shape instead of a circle, the side wall can be made into a polygonal cylinder or an inverted polygonal pyramid shape, and the flange can be made into a polygonal ring.

5 to 7 show another preferred embodiment of a forming method constructed according to the present invention. In another embodiment, the molding apparatus 102 performs both the primary molding process and the secondary molding process. The molding apparatus 102 includes a lower mold assembly 104 and an upper mold assembly 106. The lower molding assembly 104 includes a cylindrical lower inner member 108 and a cylindrical lower outer member 110 surrounding the lower inner member 108. In the state shown in FIG. 5, a molding recess 112 opened upward is defined on the upper surfaces of the lower inner member 108 and the lower outer member 110. The molding recess 112 is a circular plate shape as a whole, it has been made forms the annular groove 114 and the central raised portion 116. The annular groove 114 has an outer peripheral surface that extends straight in the vertical direction in the sectional view and a bottom surface or an inner peripheral surface that extends in an arc shape in the sectional view. The upper mold assembly 106 includes a cylindrical upper inner member 118 and a cylindrical upper outer member 120 surrounding the upper inner member 118. A circular depression 122 is formed at the center of the lower surface of the upper inner member 118. A shallow annular groove 124 is formed in the lower surface of the upper outer member 120, and the inner peripheral edge of the lower surface of the upper outer member 120 is slightly inclined upward in the radial direction.

  The primary molding process using the molding apparatus 102 will be described. As shown in FIG. 5, in the mold open state in which the upper mold assembly 106 is spaced upward from the lower mold assembly 104, the lower mold assembly A synthetic resin mass 126 in a molten or softened state is supplied to the central portion of the molding recess 112 of the three-dimensional body 104. Next, the upper mold assembly 106 is lowered relative to the lower mold assembly 104 to the position shown in FIG. 6, and thus the pre-molded body 128 is compression molded. The molded preform 128 is generally disk-shaped and has a thin central portion 130, a thick intermediate portion 132, and a thin peripheral portion 134.

  Subsequent to the primary molding step as described above, a secondary molding step is performed. In this secondary molding step, the lower inner member 108 and the upper inner member 118 sandwiching the thin central portion 130 of the pre-formed body 134 between them until the position shown in FIG. The lower outer member 110 and the upper outer member 120 sandwiching the peripheral edge portion 134 are lowered relative to each other. As a result, the thin central portion 130 of the pre-formed body 128 is displaced with respect to the thin peripheral edge portion 134 of the pre-formed body 128, and the thick intermediate portion 132 of the pre-formed body 128 is deformed into a cylindrical shape or an inverted conical first cylindrical shape. Thus, a container 136 having a circular bottom wall 138, a cylindrical or inverted frustoconical side wall 140, and an annular flange 142 is formed. If desired, instead of lowering the lower inner member 108 and the upper inner member 118 simultaneously, the lower inner member 108 can be lowered first, and then the upper inner member 118 can be lowered. As clearly understood by referring to FIGS. 6 and 7, when the thick intermediate portion 132 of the preformed body 128 is deformed, the upper inner member 118 is moved to the thick intermediate portion 132 of the preformed body 128. Add a so-called ironing action. The molded container 136 can be taken out of the molding apparatus 102 by opening the molding apparatus 102 in an appropriate manner.

Next, examples and comparative examples will be described.
Example Polypropylene sold under the trade name “Prime Polypro B251VT” from Prime Polymer Co., Ltd. as a synthetic resin material, melted from an extruder, extruded from a synthetic resin, and manually cut from an extrusion port (diameter 10 mm), A substantially cylindrical synthetic resin lump (10.3 g) was obtained. Next, the synthetic resin mass was compression-molded using a molding apparatus as illustrated in FIGS. 1 and 2 to form a pre-molded body having a shape as illustrated in FIG. The various dimensions of the molded pre-molding were as follows.

Outer diameter D1 ... 80.0mm
Outer peripheral edge diameter D2 of the thick middle part 63.0mm
Maximum thick part diameter D3 of the thick middle part 49.0mm
Inner peripheral edge diameter D4 of the thick middle part 28.8mm
Thin center thickness T1 ... 1.0mm
Maximum thickness T2 in the thick middle part 5.1 mm
Thin peripheral edge thickness T3 ... 1.7mm

Next, the preform was molded into a container as illustrated in FIG. 4 using a molding apparatus as illustrated in FIGS. 3 and 4. The temperature of the surface of the thick intermediate portion of the preformed body during the molding of the preformed body was approximately 160 ° C. Further, during the molding of the preform, the gap between the upper surface of the first mold member and the lower surface of the restraining member was maintained at 1.8 mm. Various dimensions of the molded container were as follows.

Center thickness of bottom wall t1, ... 1.0mm
Thickness t2 of the peripheral edge of the bottom wall ... 2.0mm
Flange thickness t3 ... 1.7mm
Total height h of container 29.7mm

Necessary for lowering the second mold member and fluctuations in the distance between the bottom surface of the molding recess of the first mold member and the lower surface of the second mold member during the molding of the preform into the container. The load variation was measured. The result was as shown in FIG. The variation in the distance between the bottom surface of the molding recess of the first mold member and the bottom surface of the second mold member was obtained by measuring the descending length of the second mold member with a laser displacement meter.

Comparative Example 1
Using a molding apparatus as illustrated in FIG. 8, the container was molded under substantially the same conditions as in the example except that the 200 ° C. synthetic resin mass 212 was directly compression molded into the container. Measure the change in the gap between the bottom surface of the molding recess 230 of the first mold member 224 and the bottom surface of the second mold member 226 and the load required to lower the second mold member 226. did. The result is as shown in FIG. 10, and the required load became excessive when molding the side wall by raising the synthetic resin along the inner peripheral surface of the molding recess 230.

Comparative Example 2
A substantially cylindrical synthetic resin mass 212 (5.2 g) is compression-molded to form a disk-shaped preform 314 having an outer diameter of 86 mm and a thickness of 1.0 mm, and this preform 314 is shown in FIG. Except that the container was molded using the molding apparatus as shown, the container was molded under substantially the same conditions as in the example, and the bottom surface of the molding recess 330 of the first mold member 324 at this time The change in the gap with the lower surface of the second mold member 326 and the change in the load required to lower the second mold member 326 were measured. The result is as shown in FIG. 10, and an excessive molding load was required to deform the preformed body 314 and mold the side wall.

2: Molding apparatus for primary molding process 12: Synthetic resin block 14: Pre-molded body 16: Thin center portion of the pre-molded body 18: Thick middle portion of the pre-molded body 20: Thin peripheral edge portion of the pre-molded body 22: Molding device for secondary molding process 24: First mold member 26: Second mold member 28: Restraining member 30: Molding recess 32: Container 34: Bottom wall of container 36: Side wall of container 38: Container 102: Molding apparatus for primary molding process and secondary molding process 104: Lower mold assembly 106: Upper mold assembly 108: Lower inner member 110: Lower outer member 112: Molding recess 118: Upper inner Member 120: Upper outer member 126: Synthetic resin block 128: Pre-formed body 130: Thin center portion of the pre-formed body 132: Thick middle portion of the pre-formed body 134: Thin peripheral portion of the pre-formed body 136: Container 138: Container Bottom wall 1 0: the side wall of the container 142: Container flange

Claims (4)

A molding method for molding a synthetic resin container having a bottom wall, a cylindrical side wall extending upward from the peripheral edge of the bottom wall, and an annular flange extending radially outward from the upper end edge of the side wall,
A primary molding step of molding a plate-shaped preform having a thin central portion, a thick intermediate portion, and a thin peripheral portion by compression molding a molten or soft synthetic resin mass;
At least the thick intermediate portion is in a molten or softened state. The thin central portion of the preform is displaced relative to the thin peripheral portion in the direction of the central axis, and the thick intermediate portion is squeezed. A secondary forming step of forming the thick intermediate portion into a cylindrical shape while adding ,
A molding method comprising:   The molding method according to claim 1, wherein the side wall has an upright cylindrical shape or an inverted frustum cylindrical shape whose size gradually decreases downward. In the secondary molding step, a columnar body which corresponds to the molding recess of the first mold member, said first mold member having a molding recess of the opened tubular upwardly, said first relative between the raised position and the lowered position is brought enters the molding in the recess of said first mold member located above the molding recess of the mold member relative to the mold members of the first And a molding apparatus comprising an annular restraining member positioned at a restraining position positioned opposite to a peripheral region surrounding the molding recess on the upper surface of the first molding member. Is used,
Allowed position on the molding recess of the thin-walled central portion and the thick middle portion by placing the front molded body on an upper surface of said first mold member, then allowed to position the restraining member to the restraining position The thin peripheral edge of the preform is restrained between the first mold member and the restraining member, and then the second mold member is moved from the raised position to the lowered position.
The molding method according to claim 1 or 2. A lower mold assembly composed of a columnar lower inner member and a cylindrical lower outer member surrounding the lower inner member, and a columnar upper inner member and a cylindrical upper member surrounding the upper inner member A molding device comprising an upper mold assembly composed of an outer member is used,
In the primary molding step, a synthetic resin lump is supplied to the upper surface of the lower inner member, the upper molding assembly is lowered relative to the lower mold assembly, and the lower inner member and the lower inner member are The thin central portion of the preform is compression molded with the upper inner member, and the thin peripheral edge is compression molded between the lower outer member and the upper outer member, and the outer peripheral edge of the lower inner member The thick intermediate portion is compression molded between the outer peripheral edge of the lower inner member and the inner peripheral edge of the lower outer member and the outer peripheral edge of the upper inner member and the inner peripheral edge of the upper outer member. And
In the secondary molding step, the lower inner member and the upper inner member are lowered, and the thick intermediate portion of the preform is molded into a cylindrical shape.
The molding method according to claim 1 or 2.

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