WO2007021275A2

WO2007021275A2 - Method and apparatus for forming a bottle

Info

Publication number: WO2007021275A2
Application number: PCT/US2005/029077
Authority: WO
Inventors: Daniel P. Soehnlen; Gregory M. Soehnlen
Original assignee: Creative Edge Design Group, Ltd.
Priority date: 2005-08-16
Filing date: 2005-08-16
Publication date: 2007-02-22
Also published as: WO2007021275A3

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 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 round 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. The parison is a hollow cylinder because that is a very stable shape or configuration, and because the fluid containers are often a generally round conformation. Thus, because the molten parison begins to immediately cool upon contact with the wall of the mold, it is desirable to have the molten plastic contact the inner surface of the mold at substantially the same time around the entire surface of the mold so that undesired stretching of the plastic does not occur. Likewise, known arrangements using round head tooling result in uneven wall thickness, and the inability to control the thickness of plastic at different locations in the mold. For example, the thickness of the plastic is usually greatest along the parting line of the mold halves. There are container configurations though requiring additional plastic at locations oriented at ninety degrees from the parting line and that are spaced furthest from the parting line. Heretofore, no simple effective manner of redistributing the plastic from one region to another has been achieved.

[0005] Accordingly, an effective and accurate method of forming a plastic container is needed and the resultant container is desired in a manner that can address one or more of: improved cycle time, increased process control, increased bottle strength without adding more plastic overall (and preferably by reducing the amount of plastic), more uniform parison velocity, and ease of redistributing plastic in forming a container.

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, non-round 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 a 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 such as air is then introduced into the hollow 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] One advantage resides in a method and apparatus for forming a plastic container with greater control of sidewall thickness.

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

[0013] Further benefits reside in maximizing the use of the plastic and developing accurate design parameters for shipping and handling.

[0014] Still another benefit is found in a container of increased strength using less resin.

[0015] 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

[0016] 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:

[0017] FIGURE 1 is a perspective view of a representative plastic container or bottle of the type formed in accordance with the present invention.

[0018] FIGURE 2 is a sectional view generally illustrating a two-part blow mold having a parison extending from a die and mandrel assembly of the present invention.

[0019] FIGURES 3 and 4 are longitudinal cross-sectional and plan views, respectively, of a die member according to the present invention.

[0020] FIGURES 5 ' and 6 are elevational and plan views, respectively, of a mandrel according to the present invention.

[0021] FIGURES 7-10 show elevational and a partial top plan view of a container with representative wall thickness values noted at selected locations - A -

Detailed Description of the Invention

[0022] Referring now to the drawings, wherein the showings illustrate preferred embodiments of the invention only and are not intended to limit same, FIGURE 1 shows a plastic container or bottle 20 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. This type of container has found commercial success in association with dairy products such as milk, although the invention should not be so limited to these specific uses and may find application in a wide variety of other applications that store fluid products such as water, oil, juice, powders, shampoos, detergents, etc. This list is not intended to be exhaustive but rather exemplary of the applicability of the present invention to related environments. Additional details of these types of containers may be found in commonly owned US Patents 6,050,455; 6,068, 161 ; 6,591 ,986; D461 , 414; the aspects of caseless shipping of these types of containers in US Patent 6,446,680, and the aspects of flexible filling disclosed in US Patent 6,371 ,172, the disclosures and details of each of these patents being incorporated herein by reference.

[0023] The container 20 includes a top surface or upper wall 22, bottom or lower surface 24 and a sidewall 26 molded integrally therewith, which sidewall in the illustrated embodiment includes four sidewall portions in which contiguous sidewall portions are disposed in substantially perpendicular relation to form a generally rectangular or square walled container. The top surface 22 and bottom 24 are of a generally square shape. One corner or an apex of contiguous sidewall portions preferably coincide with or form integrally molded handle 28. The handle 28 substantially proceeds from the top surface along the apex toward the bottom. A handle opening 30 dimensioned to receive fingers of a user is spaced inwardly from the handle and extends over a substantial height of the handle, and terminates before reaching the top surface and bottom.

[0024] The top surface 22 includes a stepped conformation having an upper surface, 30 and lower level planar portion 32 which is slightly vertically recessed from upper surface 30. An orifice or opening 34 is formed in the lower portion 32 for ingress and egress of the fluid (e.g., milk) or other material in container 10. A pouring lip 36 extends upwardly from the lower portion 32 to form a pouring spout 38 which in one embodiment is of generally diamond-shape (FIGURE 1 ) or in another embodiment is a conventional externally threaded round opening that is adapted to receive a closure cap (not shown).

[0025] The wall 26 is formed with a number of structural load distributing or load transferring features such as vertical ribs 40 which increase the sectional modulus of wall 26 and prevent bending and/or buckling. The ribs 40 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 26 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 US Patent No. 6,068,161. [0026] Referring in more detail to the drawings, FIGURE 2 shows a blow mold 50 comprising mold portions, or in this instance two mold halves 52, 54, movable between open and closed positions. Although illustrated in an open position, it will be appreciated that the cavity is preferably provided with a plurality of rib-like, projections (not shown) which provide for respective indentations in the plastic when the plastic is formed to shape. A molten parison 56 which is extruded vertically downwards through a die 60 having a die head 62 with generally rectangular passage 64 (FIGURES 3-4) disposed between the mold halves 52, 54. The parison 56 has at least a generally rectangular outer conformation formed by the die passage 64. The die opening may vary in cross-sectional area, i.e., passage 66 has ends 67, 68 flaring outward. The die further includes a stepped flange portion 69 on one end for engagement with an associated blow molding machine.

[0027] The die head assembly further includes a mandrel 70 (FIGURES 5-6) received in the die opening 64. The mandrel 70 comprises a body 72 having a radially outward tapering flange on one end defining a generally rectangular outer surface 74. The mandrel further includes a central air feed and discharge passage 76 extending longitudinally therethrough. The discharge passage 76 communicates with the interior of the generally rectangular parison 56 when the blow mold is closed. [0028] With continued reference to FIGURE 2, the die 60 and centrally arranged mandrel 70 define a generally rectangular passage or space 78 therebetween that has a substantially constant thickness therearound. As such, the parison is initially extruded from the die in the direction of arrow A (having both longitudinal and radial directional components). This, together with the generally rectangular contour of the die 60 and mandrel 70 assembly, has the effect that upon pressurizing the molten parison interior, the parison 56 is directed or urged into the corner regions of the blow mold (the regions that form two of the corners of the plastic container and are located ninety degrees from the parting line). This arrangement 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 sidewall thickness that assures that plastic reaches those regions of the mold where desired or needed.

[0029] 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 and enclosing the parison within the mold cavity. The blowing medium, usually pressurized air, is introduced through the central air feed and discharge passage 76 of the mandrel, as indicated by arrow B in FIGURE 2, to expand the parison against the interior surface of the mold cavity. Thereafter, the pressure is reduced to a residual value in order to stabilize the formed parison/plastic (not shown) in the blow mold 50 and prevent it from collapsing. After cooling, the container is removed from the mold 50. [0030] FIGURES 7-10 illustrate a container used as a milk bottle, for example, with representative wall thicknesses formed in a blow molding process. The numerical values are provided in pairs and demonstrate the difference from blow molding with a conventional round head tooling (referenced as "ovalized") relative to the square head tooling of the present invention. For example, in FIGURE 7 the wall thickness along the parting line is substantially changed by using the square head tooling. Along the upper surface at the parting line, the wall thickness is decreased from 0.040" to 0.036" along the handle (left-hand side as shown), is reduced from 0.041" to 0.033" along the central rib region, and increased under the pour lip or spout from 0.022" to 0.027" (as shown at the right-hand side of FIGURE 6). In the elevational view of FIGURE 8, the desired increase in wall thickness at regions ninety degrees from the parting line is exemplified by the increase from 0.010" to 0.016" achieved with the square head tooling on the left- hand side and the increase from 0.011" to 0.016" on the right-hand side. Along the handle, the desired removal of plastic at the parting line is exemplified at the upper surface (as also noted in Figure 6) by the dimensions 0.040" to 0.036", along a mid- region of the container handle with a decrease from 0.032" to 0.025" with the square head tooling, to the same wall thickness of the bottom surface (0.033" for both the ovalized and square head tooling).

[0031] FIGURE 9 further illustrates the desire to exhibit greater control on the placement of plastic at selected regions of the mold than was able to be achieved with conventional round head tooling. The plastic is either increased or substantially the same along the central rib region (note comparative dimensions of 0.0155" to 0.0160", of 0.021 " to 0.019", and of 0.019" to 0.019" as one proceeds from the upper region of the central rib to the bottom surface). Beneath the pour spout, the wall thickness is desirably increased (compare 0.024" to 0.026") while the plastic is substantially reduced in the side panel portions that extend between the corners of the container and that are not intended to carry the vertical loads and forces of the ribs and corner regions of the container. Thus, the reductions from 0.030 to 0.019" for the square head tooling along the left hand portion as shown, and from 0.028" to 0.018" along the right-hand portion as shown.

[0032] Likewise, FIGURE 10 further demonstrates the greater control of locating the plastic at desired regions in a blow molding operation. Particularly, the side panel portions that are not intended to carry or bear substantial vertical loads are substantially thinner or have reduced sidewall thickness (0.031" to 0.015" along the left-hand portion of FIGURE 10, and 0.031" to 0.018" on the right-hand side). The thickness along the base surface is substantially unchanged.

[0033] Using the square head tooling of the present invention provides a designer and manufacturer of plastic containers greater flexibility and control of the final product. Plastic can be moved to corner regions much more quickly without encountering stretching issues associated with conventional head tooling. Greater strength is achieved in the illustrated containers where the corners of the container serve as load bearing columns to transfer forces from an upper layer to a lower layer of stacked containers. Although a cylindrical parison is a very stable shape, the squared parison can still be controlled with great accuracy by keeping the same pressure and same overall die gap opening and thereby resulting in substantially the same velocity profile for the parison (which improves cycle time since the parison does not swing as much), and yet the hollow square shape of the parison is more closely related to the final shape or configuration of the container. Where round head tooling resulted in undesired thickness along the parting line, this plastic can be redistributed to other regions where it is desired, and the square head tooling geometry facilitates movement of the plastic to mold wall corner locations oriented ninety degrees from the parting line. [0034] Whereas round head tooling may require approximately 85 grams of resin per container, the present invention decreases the resin content to approximately 70 grams for the same dimensioned container. Just as important, however, is the fact that reduced resin content (and therefore reduced cost) still achieves a stronger container since the plastic is redistributed to areas where the plastic is needed. Overall strength is increased by as much as 10-15%.

[0035] 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.