WO2001085435A1

WO2001085435A1 - Apparatus and method for blow-molding large containers

Info

Publication number: WO2001085435A1
Application number: PCT/US2001/014894
Authority: WO
Inventors: Paul E. Ewing, Jr.
Original assignee: Mott's, Inc.
Priority date: 2000-05-10
Filing date: 2001-05-09
Publication date: 2001-11-15
Also published as: AU2001259645A1

Abstract

The invention provides an apparatus and method for blow molding large containers previously considered too large to manufacture on small bottle rotary type blow-molding machines. The invention discloses a blow mold (12) for use in a rotary blow-molding machine which comprises at least two blow mold segments (22,24) which cooperatively define an interior container shaped cavity and a cooling circuit incorporated within each of the blow mold segments. In use coolant fluid is circulated through the cooling circuit to control the temperature of the mold. The invention also claims a method of making a plastic container. A preform is positioned in the above mold and inflated to form the container. Coolant fluid is then circulated through the cooling circuit, after which the container is removed from the mold.

Description

APPARATUS AND METHOD FOR BLOW-MOLDING LARGE CONTAINERS

TECHNICAL FIELD

The present invention relates generally to blow-molding large capacity plastic containers. More particularly, the invention concerns improvements made to large capacity molds used on rotary blow-molding machines.

BACKGROUND OF THE INVENTION Liquids, such as beverages, are commonly packaged in plastic containers. Nowadays, plastic containers are preferred over glass containers because of their light weight, flexibility, impact resistence and low production costs. Plastic containers are often prepared by blow-molding a thermoplastic preform in a blow-mold. A preferred thermoplastic is usually a strain hardenable plastic such as polyethylene terephthalate (PET). PET plastics have good transparency, high-gloss and excellent gas-barrier properties. They are also tough, have a high mechanical strength, are light weight, flexible as well as being impact, solvent and heat resistant. Manufacturing large thin- walled plastic containers from injection-molded parisons or preforms by direct stretch blow-molding has however proven to be more difficult. By large containers it is generally meant containers with internal volumes exceeding three liters. Conventional air blowing may cause non-uniformity of the container's wall thickness distribution and/or whitening of the plastic material. One way of overcoming some of these difficulties is by introducing an intermediate step into the manufacturing process prior to blow-molding the preform. The intermediate step comprises first forming a relatively large preform from the smaller injection molded preform, followed by the final blow-molding step. Such a process is disclosed in U.S. Patent No. 5,681,520 to oda. This intermediate step, however, further complicates the machinery and adds additional costs and time to the manufacturing process.

High speed blow-molding machines, which produce 5,000 to 50,000 bottles per hour, are often of the rotary type. Rotary blow-molding machines are also known as carousel or wheel type machines. Rotary blow-molding machines typically comprise multiple molds distributed symmetrically around a central hub. Each mold typically further consists of two identical mold halves which are capable of opening and closing. To produce a container, a tube shaped preform or parison is positioned between the mold segments and, the mold is closed and clamped shut around the parison to form an interior container shaped cavity defined by the inner walls of the mold halves. The inside of the preform is pressurized, to blow or inflate the preform outwards to form a container in the shape of the cavity defined by the inner surfaces of the mold. At the termination of the blow-molding operation, the mold is opened, and the blow-molded container removed.

Rotary blow-molding machines typically contain anywhere from approximately one to fifty molds per machine. These rotary blow-molding machines usually comprise two symmetrical mold halves surrounded by a separate cooling shell which clamps around the mold halves. The cooling shell holds the mold halves in place during the blow-molding process and circulates cooling fluid around the outside of the mold. This causes the mold to cool thereby solidifying the container prior to its removal. Due to practical size limitations, machines containing eight or more molds, are limited to producing smaller size containers of three liter internal volumes, or less. This limitation stems principally from the fact that the molds cannot open wide enough to accommodate and release larger diameter bottles without making contact with an adjacent mold or shell. One method of producing larger bottles on existing small bottle blow-molding machinery is disclosed in U.S. Patent No. 4,565,516 to Szajna. Szajna shows that larger size containers may be produced on existing machinery, by providing a mold which is capable of splitting in three, rather than the traditional two, mold sections. Such a system however calls for a complete redesign and replacement of the mechanisms used for opening and closing the molds and for removing the containers.

In light of the above it would be desirable to minimally adapt an existing rotary blow-molding machine so that it can produce larger containers than those for which the blow-molding machine was originally designed.

SUMMARY OF THE INVENTION

According to the present invention there is provided a blow mold for use in a rotary blow-molding machine. The blow mold comprises at least two blow mold segments which cooperatively define an interior container shaped cavity and a cooling circuit incorporated within each of the blow mold segments. In use coolant fluid is circulated through the cooling circuit to control the temperature of the mold.

The invention further provides a mold for blow molding large hollow plastic containers on a rotary blow molding machine. The blow mold comprises first and second mold segments which cooperatively define an interior shaped cavity where the cavity has at least one interior dimension greater than at least about 130mm. The mold segments have inner and outer walls and at one end together define an opening for receiving a blow mold preform. Each of the segments define at least one passage between the inner and outer walls for passage of liquid coolant therethrough.

An inlet and an outlet on each of the segments communicates with the at least one passage for connection to a coolant source. The blow mold segments are configured and dimensioned to be received in clamps of the rotary blow molding machine without a separate cooling shell therearound. Still further, the invention provides a rotary blow-molding machine for forming plastic containers. The machine comprises a plurality of blow molds positioned about a central hub of the rotary machine. Each blow mold comprises at least two blow mold segments which cooperatively define an interior container shaped cavity, and a cooling circuit incorporated within each of the blow mold segments. According to the invention there is also provided a method of making a plastic container. A blow mold is provided comprising at least two blow mold segments which cooperatively define an interior container shaped cavity and a cooling circuit incorporated within each of the mold segments. A preform is positioned in the mold and inflated to form the container. Coolant fluid is then continuously or intermittently circulated through the cooling circuit, after which the container is removed from the mold. The present invention thus allows for the manufacture of containers previously considered too large to manufacture on small bottle rotary type blow-molding machines.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is diagrammatic top view of a rotary type blow-molding machine according to the invention; FIG. 2 is an isometric view of a split blow mold according to the invention;

FIGS. 3A-D are orthographic views of a split blow mold according to the invention;

FIG. 4 is a cross sectional view along line AA' of FIG. 3 A; FIG. 5 is a diagrammatic top view of a rotary type blow-molding machine according to the invention;

FIG. 6 is another diagrammatic top view of a rotary type blow-molding machine according to the invention;

FIG. 7 illustrates a plastic bottle made in accordance with the mold of the invention; and FIG. 8 illustrates a method for forming a plastic bottle in accordance with the invention.

Like reference numerals refer to corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, there is shown a simplified diagrammatic top view of a rotary blow-molding machine 10. Molds 12 are equally spaced from one another and positioned at a set radius 14, on a blow wheel 16, around a central hub 18 of the rotary blow-molding machine 10. The molds 12 are capable of rotating about the central hub 18. High speed, high volume, small rotary blow-molding machines, as utilized by the present invention, typically include more than four molds per machine. Examples of rotary blow-molding machines are disclosed in U.S. Patent Nos. 4,801,260 to Odes and 5,683,729 to Valles, which are incorporated by reference herein.

Referring to FIG. 2, there is shown an isometric view of a split blow mold 20 for use in a rotary type blow-molding machine. Mold 20 preferably consists of two mold segments 22 and 24, split along a radial plane 26 (also shown in FIGS. 1 and 6). Mold segments 22 and 24 cooperatively define an interior container shaped cavity (not shown). It should however be appreciated that more than two mold segments may be utilized. Each mold segment is preferably a mirror image of the other. The mold 20 is capable of opening and/or closing in a hinged manner about said radial plane 26. The mold segments 22 and 24 align at their upper edge, to form a support ring 30. The support ring 30 defines an opening 38 which is capable of receiving a preform therein, forming a seating with the support ring 30. Vents 32 are provided to allow any air present in the molds to escape when a container is being blow-molded. A cooling circuit is formed within each mold segment as will be described below.

A coolant inlet 34 and coolant outlet 36 allow coolant to be circulated through the cooling circuit. The coolant acts to cool down the mold so as to reduce the temperature of a container formed within the mold 20. The cooled container thus rapidly solidifies, aiding in its removal from the mold 20 on completion of the blow molding process.

Referring to FIGS. 3A-C, there is shown orthographic views of a segment of the split blow mold of FIG. 2. The bottom view shown in FIG. 3C illustrates the coolant inlet 34 and coolant outlet 36, described above. _v It should be noted that the location of the coolant inlet 34 and the coolant outlet 36 may be interchanged. The side view, shown in FIG. 3B shows an outer wall of the mold 40, whereas front a view, shown in FIG. 3A, clearly displays the vent holes 32 and the mold's inner wall 48. The mold segments, when clamped together, define an interior container shaped cavity. A portion of the interior cavity is formed by the inner wall 48 of each mold segment. Furthermore, the mold segments have mating surfaces to conform to the shape of the cavity.

FIG. 3D is a close up view of the heel 42 of the mold segment 40, as shown in FIG 3 A. The heel 42 consists of a heel segment 46 of the mold segment, which may or may not be split with the wall at 47. If the heel segment 46 is split at 47, then a bolt 45 in a bolt hole 51 is used to secure the heel segment 46 to the wall. The bolt hole 51 can also be seen in FIG. 3C. The heel segment 46 does not come into contact with the cooling channel 54 and therefore is cooled by conduction between the heel segment 46 and wall. The base of the mold 49 may be cooled by cooling channel 44 which passes through the base of the mold. The heel segment 46 may also cool through conduction between the base 49 and the heel segment 46. The cooling channel 54 does not pass through the heel segment 46, due to size and/or strength considerations.

Referring to FIG. 4, there is shown a simplified cross sectional view along line AA' of FIG. 3 A, showing a either mold segment 22 or 24. Preferably approximately half of the container mold interior cavity 50 is defined by the mold's inner wall 48. A cooling circuit comprising a plurality of hollow cooling channels 54 circulates coolant between the mold's inner wall 48 and outer wall 40. Coolant is circulated through the cooling channel 54 by introducing the coolant into cooling channel 54 at cooling inlet 34, and expelling it from cooling channel 54 at cooling outlet 36, or vice versa. Molds for small bottle blow-molding machines are typically manufactured from aluminum. The mold of the present invention, however, is preferably manufactured out of a strong steel material, such as stainless steel.

Stainless steel is preferred as the new mold segments have a reduced wall thickness to accommodate the cooling circuit and thus have to withstand a greater load per unit area. By eliminating the necessity of providing a separate cooling shell unit, the mold of the present invention allows for larger volume molds to be used on current small bottle rotary blow-molding machines.

FIGS. 5 and 6, show diagrammatic top views of a rotary type blow-molding machine 10 in operation. Mold segments 22 and 24 are held in the jaws of a clamp 54. Actuator means 56 are provided for forcing the mold segments 22 and 24 towards or away from one another. Such actuator means 56 may for example be mechanical, pneumatic or hydraulic devices. Mold segments 22 and 24 are hinged about radial plane 26, as best seen in FIG. 6. Ejecting means 58 are provided for removing a formed container 60 from between the mold segments 22 and 24. The larger volume mold segments 22 and 24 an unloading phase to get the bottle 60 out from between the mold segments 22 and 24. This is accomplished by mounting less molds in a large frame machine, such as for example mounting sixteen molds on a twenty-two mold machine. Thus, sufficient maneuvering room 62 (FIG. 5) is provided to allow the mold segments 22 and 24 to open without making contact with adjacent clamps 54. Referring to FIG. 7, there is shown a plastic bottle 64 made by utilizing the above described mold. A wide variety of liquids may be stored in such a plastic bottle, for example carbonated or non carbonated liquids, as well as hot or cold liquids. The bottle is preferably made from a strain hardenable plastic such as a polyethylene terephthalate (PET), due to PET's superior properties. Blow-molding can produce many types of containers, including bottles having symmetrical cross-sections, which is usually the case for pressurized containers, or bottles having rectangular cross sections, as shown here. Complex shapes such as handles 66 and ribs 68, may also be formed on the container by providing for such in the mold.

Referring to FIG. 8, there is shown a method 70 for forming a plastic bottle in accordance with the invention. Firstly, a mold as described above is provided 72. A preform is loaded into a hopper/sorter or the like and is thereafter positioned 74 on a mandrel. The preform may be made by injection molding, or equivalent process, and comprises of a bottle neck, complete with threads, attached to an elongate test tube like plastic article. The preform is heated 76,' in an oven or the like, to above the plastic transition temperature. The preform is positioned 78 between the mold segments which are then forced towards one another by actuator means, and the mold is closed 80, thus developing the internal mold cavity. The mold may also close first and the preform thereafter be lowered into the mold. The preform may then be stretched 82 further into the cavity by means of a stretch rod. The inside of the preform is pressurized, so as to blow or inflate 84 the preform outwards to form a container in the shape of the cavity defined within the mold. Prior to the inflating step 84, the preform may first receive a brief preblow of pressurized air. This prior preblow step, is undertaken to release the preform from the stretch rod without allowing the preform to come into contact with the cavity walls, as if the blown preform makes contact with the cavity walls, the semi-molten plastic tends to set, negatively effecting the blow- molded product. Coolant is then circulated 86 through the cooling circuit of the mold which aids in the solidification of the container. At the termination of the blow- molding operation, the mold is opened 88, and the blow-molded container removed 90 onto a conveyor or the like. The process may then be repeated.

The present invention thus allows larger bottles to be made on fewer high output small bottle rotary blow-molding machines, instead of several low output machines (typically four molds or less) reducing capital cost, utility and labor.

Previous small bottle machines, utilizing standard molds, shells and clamps, were capable of making containers of up to approximately 120mm (130mm at most) diameter. By diameter it is meant, any internal dimension comparable to a diameter of a round container, such as for example the diagonal of the cross section of a square container. The method of the present invention allows bottles with diameters of larger thanl30mm, to be produced (4 liter bottles) on the same machines which could previously only produce bottles of up to 3 liters.

The foregoing descriptions of specific embodiments of the present invention are presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, obviously many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. A blow mold for use in a rotary blow-molding machine wherein said blow mold comprises: at least two blow mold segments which cooperatively define an interior container shaped cavity; and a cooling circuit incorporated within each of said blow mold segments, such that in use coolant fluid is circulated through said cooling circuit to control the temperature of said mold.

2. An apparatus according to claim 1, wherein said cooling circuit comprises: an inlet for ingress of cooling fluid into said cooling circuit; at least one cooling channel between inner and outer walls of said blow mold for circulating coolant therein; and an outlet for egress of the cooling fluid from said cooling circuit, said inlet and outlet communicating with said at least one channel.

3. An apparatus according to claim 2, wherein said blow mold segments further comprise vents in said inner walls for allowing air present in the blow mold to escape when a container is being blow-molded.

4. An apparatus according to claim 1, wherein said cavity has a diameter greater or equal to 130mm.

5. A mold according to claim 1 , wherein said blow mold is made of a steel material.

6. An apparatus according to claim 5, wherein said steel material is stainless steel.

7. An apparatus according to claim 1 , wherein portions of the blow mold sections are cooled by conduction.

8. A mold for blow molding large hollow plastic containers on a rotary blow molding machine, said blow mold comprising: first and second mold segments which cooperatively define an interior shaped cavity wherein said cavity has at least one interior dimension greater than at least about 130mm, said mold segments having inner and outer walls and at one end together defining an opening for receiving a blow mold preform; each said segment defining at least one passage between said inner and outer walls for passage of liquid coolant therethrough; and an inlet and an outlet on each said segment communicating with said at least one passage for connection to a coolant source; said blow mold segments being configured and dimensioned to be received in clamps of the rotary blow molding machine without a separate cooling shell therearound.

9. An apparatus according to claim 8, wherein portions of the mold sections are cooled by conduction.

10. A rotary blow-molding machine for forming plastic containers, said machine comprising: a plurality of blow molds positioned about a central hub of said rotary machine, wherein each blow mold further comprises: at least two blow mold segments which cooperatively define an interior container shaped cavity; and a cooling circuit incorporated within each of said blow mold segments.

11. An apparatus according to claim 10, wherein said cooling circuit comprises: an inlet for ingress of cooling fluid into said cooling circuit; a cooling channel for circulating coolant between inner and outer walls of said blow mold; and an outlet for egress of the cooling fluid from said cooling circuit.

12. An apparatus according to claim 10, wherein said plurality of blow molds is less or equal to 16 blow molds.

13. An apparatus according to claim 10, wherein said mold is made of a steel material.

14. An apparatus according to claim 13, wherein said steel material is stainless steel.

15. An apparatus according to claim 10, wherein said cavity has a diameter greater or equal to 130mm.

16. An apparatus according to claim 10, wherein portions of the blow molds are cooled by conduction.

17. A method of making a plastic container, said method comprising the steps of: providing a blow mold comprising: at least two blow mold segments which cooperatively define an interior container shaped cavity; and a cooling circuit incorporated within each of said mold segments; positioning a preform in the mold; inflating said preform to form said container; circulating coolant fluid through the cooling circuit; and removing said container from said mold.

18. A method according to claim 17, wherein the method further comprises the step of heating the preform prior to the inflating step.