WO2006015286A1

WO2006015286A1 - Method and apparatus for forming a bottle

Info

Publication number: WO2006015286A1
Application number: PCT/US2005/027141
Authority: WO
Inventors: Daniel P. Soehnlen; Gregory M. Soehnlen
Original assignee: Creative Edge Design Group, Ltd.
Priority date: 2004-07-29
Filing date: 2005-07-29
Publication date: 2006-02-09

Abstract

A die head assembly for blow molding a plastic container such as a fluid container used commercially in the dairy industry, for example, is disclosed. The die head assembly includes a die member with an opening and a mandrel at least partially received in the opening. One of the die member opening and the external surface of the mandrel has a generally rectangular conformation. The parison introduced therein is forced into corner regions of the blow mold. The assembly and method removes ovalization of the parison and allows the plastic to reach the corners of the mold with less stretching. A plastic container results with walls having a greater control of sidewall thickness.

Description

METHOD AND APPARATUS FOR FORMING A BOTTLE

Field of the Invention

[0001] The invention relates to a method and apparatus for forming a container, particularly a plastic container formed from a thermoplastic material by blow molding.

Background of the Invention

[0002] Plastic containers are often made by blow molding. Such a method generally uses a mold having a partitioned mold such as two mold halves. The interior surface of the mold has a contour which corresponds to a desired final external contour of the container. Die head assemblies for extruding plastic parisons used for blow molding bottles typically include an elongate, generally cylindrical ortapering cylindrical blow mandrel and a die bushing having a circular opening that receives the mandrel. The mandrel and die bushing define an annular die opening through which molten plastic is extruded from the head as a parison. The location of the mandrel in the die bushing controls the wall thickness of the parison.

[0003] A molten hollow cylindrical parison is introduced in between the mold halves of the open blow mold, the blow mold is closed, and the parison is blown to shape by pressurized air. Particularly, pressurized air is introduced into a central passage of the parison such that the molten plastic is urged outwardly and engages the inner walls of the blow mold so as to assume the shape thereof. The pressurized air is fed through the die head assembly, for example through a central passage of the mandrel, which extends axially inward from one end of the blow mold. [0004] The annular die opening has a circular inner wall and a circular outer wall, a conformation that has been commonly used for forming fluid containers, e.g., plastic milk containers or milk bottles. The die head assembly with the annular die opening is conventionally used irrespective of the final shape of the bottle. Because the molten plastic immediately begins to cool and harden upon contact with the mold wall, variations in thickness result in the final container because the distance over which the plastic moves outwardly toward the mold wall from the central axis of the parison differs. Unfortunately, this results in an inefficient use of plastic since the primary concern is to provide sufficient plastic at desired geometric locations of the container and oftentimes extra or excess plastic is directed to regions where it is unnecessary.

[0005] A more efficient and accurate use of the plastic in forming containers is needed.

Summary of the Invention

[0006] An improved method and apparatus is provided for forming plastic containers.

[0007] Generally, the method comprises introducing a parison into a blow mold and forming the parison to a desired container shape by means of a unique mandrel and die head arrangement.

[0008] A parison having a generally rectangular outer conformation is introduced into a cavity of the blow mold. After closing the blow mold, the parison is urged outwardly in the mold cavity to engage the inner surface of the blow mold to assume the shape thereof.

[0009] In forming the container of the present invention, the molten parison is extruded from an extrusion die head having a generally rectangular passage. The mandrel has a body having a generally rectangular outer surface. As such, the parison is located closer to corners of the mold walls and initially urged toward the corners.

While the parison is in heated, moldable condition the blow mold halves are closed therearound. Pressurized fluid is then introduced into the parison to urge the parison outwardly against the mold walls and form the plastic container.

[0010] The invention provides a method and apparatus for forming a plastic container which initially urges the parison toward corners of the mold cavity thereby allowing the parison to reach the corners of the mold with less stretching.

[0011] The invention provides a method and apparatus for forming a plastic container with more consistent sidewall thickness.

[0012] Yet another benefit is the ability to consistently and repeatedly mold containers.

[0013] A further benefit resides in forming containers having a more uniform wall thickness in order to maximize the use of the plastic and develop accurate design parameters for shipping and handling. [0014] Still other benefits and advantages of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description.

Brief Description of the Drawings

[0015] The invention may take physical form in certain parts and arrangements of parts, preferred embodiments and methods of which will be described in detail in this specification. The accompanying drawings form a part of the invention and show:

[0016] FIGURE 1 is a prospective view of a plastic dispenser container formed according to the present invention.

[0017] FIGURE 2 is a sectional view illustrating a two-part blow mold having a parison positioned on a die and mandrel assembly.

[0018] FIGURES 3 and 4 are elevational and plan views, respectively, of a die member according to the present invention.

[0019] FIGURES 5 and 6 are elevational and plan views, respectively, of a mandrel according to the present invention.

Detailed Description of the Preferred Embodiments

[0020] Referring now to the drawings, wherein the showings illustrate the preferred embodiments of the invention only and are not intended to limit same, FIGURE 1 shows a plastic container 10 formed according to the present invention. The container may be a standard 3-liter or 1 -gallon size container or any other size. Those of ordinary skill will recognize that the container structures described herein are generally scalable to achieve different sizes comprising a blow-molded plastic, although different manufacturing techniques may be used. The container 10 comprises a top surface 12, bottom 14 and a wall 16 molded integrally therewith. The top surface 12 and bottom 14 are of a generally rectangular shape with a corner or an apex thereof preferably coinciding with integrally molded handle 18. The handle proceeds from the top surface along the apex. A handle opening dimensioned to receive a user's fingers is spaced inwardly from the handle and extends over a substantial height of the handle but terminates before reaching the top and bottom.

[0021] The top surface 12 includes a stepped conformation having an upper surface 20 and lower level deck portion 22 which is slightly vertically recessed from upper surface 20. An orifice 24 is formed in deck portion 22 for egress of the liquid - A -

(e.g., milk) or other material contained in container 10. A pouring lip 26 extends upwardly from the deck portion 22 to form a pouring spout 28 which is of generally diamond-shape.

[0022] The wall 16 is formed with a number of structural load distributing or load transferring features such as vertical ribs 30 which increase the sectional modulus of wall 16 and prevent bending and/or buckling. The ribs 30 are preferably of a "V" shape in cross-section, with the apex of the "V" extending inward of the container and are substantially continuous along the longitudinal height of the container. This structure permits the construction of manufacturing molds without the presence of undercuts, which are inefficient from a manufacturing standpoint. Preferably, vertical ribs 30 are incorporated into vertical surfaces of wall 16 in an effort to reduce the unbraced length of the wall and limit deflections. A more complete description of the above described container is set forth in commonly owned U.S. Patent No. 6,068,161 , the details of which are expressly incorporated herein by reference

[0023] Referring in more detail to the drawings, FIGURE 2 shows a blow mold

50 comprising two mold halves 52, 54 movable between open and closed positions and shown in an open position. The cavity is preferably provided with a plurality of rib-like, projections (not shown) which provide for respective indentations in the parison 56 when it is formed to shape. These indentations in the walls of the finished container serve to stiffen the container as described above with reference to the container of FIGURE 1. A thermally plasticated parison 56 which is extruded vertically downwards through a die 60 having a die head 62 with generally rectangular passage 64 disposed between the mold halves 52, 54. The parison 56 is generally annular having at least a generally rectangular outer conformation. The die opening 64 includes a generally cylindrical passage 66 having ends 67, 68 flaring radially outward. The die further includes a stepped flange portion 69 on one end for engagement with an associated blow molding machine. [0024] The die head assembly further includes a mandrel 70 partially received in the die opening 64. With reference to FIGURES 3-6, the die 60 and blow mandrel 70 according to the invention are shown for carrying out the method according to the invention. The blow mandrel 70 comprises a mandrel body 71 having a radial flange 73 on one end defining a generally rectangular outer surface 74. The mandrel further includes a central air feed and discharge passage 72 located in its main axis. The discharge passage 72 communicates with the interior of the generally rectangular parison 56 when the blow mold has been closed.

[0025] With continued reference to FIGURE 3, the die 60 and centrally arranged mandrel 70 define a generally rectangular space 78 therebetween that has a substantially constant thickness therearound. As such, the parison is initially extruded out laterally or obliquely from the die, in the direction of arrow A. This, together with the generally rectangular contour of the die 60 and mandrel 70 assembly, has the effect that upon pressuring the thermally plasticated parison interior, the parison 56 is forced into the so-called corner region of the blow mold (the region that forms the corners of the plastic container) and bears against the wall of said corner region. As such, this removes ovalization of the parison 56 and allows the plastic to reach the corners of the mold 50 with less stretching and provides a plastic container with a consistent sidewall thickness.

[0026] In operation, the parison 56 is continuously extruded from the die 60 in a generally rectangular outer conformation and flows laterally and downwardly between the mold halves 52, 54. The mold halves are brought together pinching the parison. The parison is formed into shape by pressurizing its interior. The blowing medium, usually air, is introduced through the central air feed and discharge passage 72, as indicated by arrow B, into the parison to expand the parison until it bears against the mold cavity 58. Thereafter, the pressure used to form the parison 56 to shape is reduced to a residual value in order to stabilize the formed parison (not shown) in the blow mold 50 and prevent it from collapsing. After cooling, the finished container is removed from the mold 50. When the mandrel 70 is removed from the container, an opening remains which serves to receive milk in the case of a milk container. [0027] The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

1. A method of blow molding a plastic container comprising the steps of: providing thermally plasticated parison into an associated mold; forming the thermally plasticated parison into a generally annular parison having at least a generally rectangular outer conformation; introducing a pressurized fluid into an interior of the thermally plasticated parison by introduction of a blowing medium mandrel into the parison for urging the parison into engagement with the associated mold; and cooling the inflated parison thereby forming the plastic container, and removing the plastic container from the blow mold

2. The method of claim 1 further comprising the step of forming an inner portion of the parison into a rectangular conformation.

3. The method of claim 1 wherein the parison forming step includes advancing a thermally plasticated parison through a generally rectangular passage between a die and mandrel set which initially urges the parison laterally or obliquely downwards from the die.

4. The method of claim 3 wherein the die includes a generally rectangular opening.

5. The method of claim 3 wherein the mandrel has a generally rectangular outer surface.

6. The method of claim 3 wherein the mandrel is hollow having a central air feed and discharge passage and the pressurized fluid is introduced into the parison through the passage.

7. The method of claim 1 wherein the introducing step includes the step of using pressurized air.

8. The method of claim 1 wherein said parison is made from high density polyethylene.

9. A die head assembly for blow molding a plastic container having a generally parallelepiped conformation, the die head assembly comprising: a die member having an opening therethrough; a mandrel at least partially received in the die member opening; and at least one of the die member opening and an external surface of the mandrel having a generally rectangular conformation.

10. The invention of claim 9 wherein both the die member and the mandrel outer surface have a generally rectangular conformation.

11. The invention of claim 9 wherein the mandrel includes an internal passage adapted to receive pressurized fluid therethrough for urging a thermally plasticated parison toward an associated mold.

12. The invention of claim 11 wherein the internal passage extends generally longitudinally through the mandrel.

13. The invention of claim 9 wherein the die member and the mandrel define a space therebetween that has a substantially constant thickness therearound.

14. The invention of claim 13 wherein the space has a non-round contour.

15. The invention of claim 13 wherein the space has a generally rectangular conformation.