CA1079014A

CA1079014A - Method of injection-blow molding biaxially-oriented hollow plastic containers

Info

Publication number: CA1079014A
Application number: CA246,311A
Authority: CA
Inventors: Robert J. Kobylarz; John A. Marcinek
Original assignee: Emhart Industries Inc
Current assignee: Emhart Industries Inc
Priority date: 1975-03-03
Filing date: 1976-02-23
Publication date: 1980-06-10
Also published as: IT1056763B; FR2302839A1; FR2302839B1; SE7601488L; DE2608742A1; JPS5314590B2; GB1536466A; CH612875A5; JPS51111874A; BE838918A

Abstract

METHOD OF INJECTION-BLOW MOLDING
BIAXIALLY-ORIENTED HOLLOW PLASTIC CONTAINERS
ABSTRACT
A biaxially-oriented hollow plastic container is molded by injecting plastic around a core pin in an injection mold and forming the finish of the bottle in a neck ring mold which forms part of the parison mold. After the parison has been temperature conditioned, the core pin, neck ring mold assembly and parison are removed from the injection (parison) mold as a unit. The core pin is then removed from the unit, further temperature conditioning takes place, and the neck ring mold transfers the parison into a split blow mold. The blow mold closes around the parison and a stretch rod enters the parison. As the stretch rod stretches the parison, a blow medium is injected into the parison, which is blown and stretched into the final biaxially oriented container shape.

Description

10790~
BACKGROUND OF THE INVENTION
Field of the Invention. This invention relates to a method of making a plastic container, and particularly to a method for injection-blow molding a biaxially-oriented hollow plastic container.
Description of the Prior Art. Machines for forming plastic bottles by the injection-blow technique are known from U. S. Patents Nos. 2,290,129; 2,789,312; 2,853,736; 2,914,799;
3,011,216; 3,100,913; 3,339,231; 3,412,186; 3,480,993 and 3,584,337 among others. Further, many attempts have been made to devise a method for forming biaxially-oriented hollow plastic containers. Biaxial orientation of plastic is known, for ex-ample, from the U. S. Patent to Goldman et al, No. 3,231,642.
Axial stretching and blowing of a parison is old in the glass-ware forming art from U. S. Patent to Blair et al, No. 688,924, and axial stretching followed by blowing to form a biaxially-oriented plastic bottle is known from the U. S. Patent to Scalora, No. 3,470,282.
However, although certain methods are known, none of the known techniques have met with much commercial success in injection-blow molding biaxially-oriented hollow plastic con-tainers.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a new and improved process for injection-blow molding of biaxially-oriented hollow plastic containers.
This object and other objects and advantages are achieved by an improved method which comprises injection molding a plastic parison about a core pin in an injection, or parison, 107901~
mold and forming the finish of the container in a neck ring mold which forms part of the parison mold; after the parison is formed, it is temperature conditioned within the parison mold so that the parison may be biaxially oriented and molded during the forming of the parison into its final container shape. After the parison has been properly temperature conditioned, the core pin, neck ring mold assembly and parison are removed as a unit from the parison mold. The purpose in removing the neck ring, core pin and parison as a unit from the parison mold after the parison has been formed is to allow the core pin to be easily removed from the parison. The removal of the core pin is made easy because after the parison has been removed from contact with the parison mold, we have found that the parison body will expand slightly radially outwardly as the core pin is being ex-tracted from the parison. The core pin is then removed from the above-mentioned unit prior to disposition of the parison in the blow mold so that the parison does not adhere to the core pin during subsequent forming operations and so that a further temp-erature conditioning of the parison body may take place to allow the heat stored in the inner portion of the parison body between the two outer surfaces thereof to reheat the two outer surfaces so that the temperature of the two outer surfaces approaches the temperature of the inner portion of the parison body. The object of this further temperature conditioning step is to have the parison body at as near an equilibrium temperature throughout its wall thickness as possible in order to have optimum orient-ation during the stretching and blowing of the parison body into -~its final container shape; furthermore, the core pin must be removed in order to form narrow neck containers, such as soda bottles, beer bottles, etc. If the parison were to be stretched ~'' ' 107901~
on a core pin, as is the case in the above-mentioned Scalora patent, the parison would neck in on the core pin as it is stretched, thereby preventing further uniform stretching of the parison. The parison held by the neck ring mold is then trans-ferred to a blow mold by neck ring mold transfer means. The blow mold is closed around the parison~ A stretch rod enters the parison and stretches it towards the end of the blow mold, and a blow medium is injected into the parison which is thereby blown and stretched into its final container form.
~0 In further accord with the present invention the blowing of the parison may commence substantially simultaneously with the stretching of the parison by the stretch rod. The blowing of the parison while stretching may serve two functions:
it prevents the parison from necking in on the stretch rod and it speeds up the process of forming the parison into its final container shape.
In further accord with the present invention the blowing and stretching of the parison may take place through the neck ring, the stretch rod being part of the blowhead assembly, or the stretching and blowing may take place after the neck ring mold assembly has been removed from the blow mold, the blow mold itself supporting the parison therein, with different sealing means for the blow air being utilized.
The foregoing and other objects, features and advan-tages of the present invention will become more apparent in light of the following detailed description of a preferred em-bodiment thereof, as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a partial schematic plan view of a portion of a machine taken along line 1-1 of Fig. 3.

:~L07901'~

Fig. 2 is a partial schematic plan view of the portion of the machine shown in Fig. 1 in a position wherein the parison and blow molds are open.
Fig. 3 is a sectioned elevation of a portion of a machine which may be utilized to perform the present invention.
Fig. 4 is a schematic sectioned elevation of a parison mold including a neck ring mold assembly and a core pin disposed therein and showing plastic having been injected thereinto.
Fig. 5 is a schematic sectioned elevation showing the core pin, neck ring mold assembly and parison after having been removed from the parison mold.
Fig. 6 is a schematic sectioned elevation showing the neck ring mold assembly and parison after the core pin has been removed.
Fig. 7 is a schematic sectioned elevation showing the neck ring mold assembly and parison disposed in the blow mold after the parison, held by the neck ring assembly, has been transferred from the parison mold to the blow mold by the neck ring mold transfer means and a method of sealing for blow air between the blowhead and neck ring mold assembly.
Fig. 8 is a schematic sectioned elevation showing the stretch rod commencing to stretch the parison in the blow mold.
Fig. 9 is a schematic sectioned elevation showing the stretch rod in its final position.
Fig. 10 is a schematic sectioned elevation showing the parison after it has been formed to its final container shape in the blow mold.
Fig. 11 is a schematic sectioned elevation showing -the neck ring assembly open and the container being ejected from the blow mold.

.

107901~
Fig. 12 is a schematic sectioned elevation showing an alternative method of sealing for blow air between the stretch rod and the neck ring mold assembly.
Fig. 13 is a schematic sectioned elevation showing still another method of sealing for blow air between the blow-head and the blow mold.
Fig. 14 is a schematic sectioned elevation showing another method of sealing for blow air between the blowhead and the parison.
Fig. 15 is a partial schematic view of an alternative machine which may be utilized to practice the present invention.
Like numerals denote the same elements wherever they appear on the drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, a parison mold 2 is -provided having a parison body cavity 4 therein. The parison mold 2 is preferrably a split mold having halves 2a and 2b, although it can be a solid mold. A split neck ring mold assembly 6 is disposed within the parison mold 2 and forms the finish portion 8 of the parison. The neck ring mold assembly 6 cooper-ates with the cavity 4 to form the complete parison mold. A
core pin 10 is inserted through the neck ring and into the parison body cavity. Plastic is injected into the parison mold through inlet 12 by an injector 13, shown schematically, which may be any of the plastic injection machines well-known in the art, such as the Fellows Corporation Model 150 injection molding machine. ~ -After the plastic has been injected into the parison mold 2 and the parison 14 is formed, the parison 14 is temperature conditioned in the parison mold. The temperature conditioning -of the plastic parison 14 is necessary to optimize the biaxial orientation of the plastic container. The temperature condition-ing is accomplished by control of several variables, some of which are: 1) the temperature of the injection mold; 2) the temperature of the core pin; 3) the temperature of the neck ring;
4) the length of the injection period; 5) the length of time the parison is retained in the parison mold; and 6) the parison wall thickness. The variables are controlled by maintaining each of them at a predetermined value, depending on the type of plastic material being utilized. For example, if the plastic being utilized is polyethylene terepthalate (melt temperature about 540 F), the temperature of the injection mold and the core pin is maintained at about 50 F; the injection time is seven seconds; the parison is retained in the parison mold for about ~
18 seconds after completion of the injection step; and the -parison wall thickness is about 0.150 inches~ The parison will be at a temperature of about 200 F and ready for stretching and blowing into the final biaxially oriented container form.
If the plastic is a nitrile resin, for example, (melt temperature about 350 F), the temperature of the upper half of the parison mold (including the finish) is maintained at about 115 F, while ~ -the lower half of the mold is maintained at about 150 F; the temperature of the core pin is maintained at about 190 F; the parison requires about 5.8 seconds for injection of the plastic ; -and is retained in the parison mold for an additional 8 seconds after completion of the injection period; the parison has a wall thickness of about 0.150 inches. The parison will be at a temperature of about 290 F and ready for forming to the final biaxially oriented container shape by stretching and blowing.

l07sal~
The parison may be temperature conditioned by controlling the temperature of the core pin 10. This can be accomplished by disposing a tube 7 in a chamber 9 in the core pin 10 as shown in Fig. 3. The tube 7 is connected at its upper end to a source of fluid (now shown) via a fluid inlet 11. The tube 7 has an outlet into the chamber 9 near the lower end of the core pin 10.
Fluid flowing through the inlet 11 passes through the tube 7 and into the chamber 9. From the chamber 9 the fluid flows up through the core pin and out through a fluid outlet 15. By regulating the temperature of the fluid flowing through the core pin, the temperature of the core pin may be controlled. The temperature of the parison mold 2 and the blow mold 18 may be controlled in a manner well-known in the art. One type of cooling for the neck ring 6, the parison mold 2 and the blow mold 18 is shown in Fig. 3. Coolant passages 17 may be drilled in the neck ring 6, passages 19 may be drilled in the parison mold 2, and passages 21 may be drilled in the blow mold 18.
The fluid inlets and outlets for these coolant passages have been omitted for clarity in the drawings. Another method of cooling neck rings, parison molds and blow molds which is well-known in the art, is by blowing cool air over them.
After the parison has been properly temperature con-ditioned, the neck ring mold assembly 6, the core pin 10 and the parison 14 are removed from the parison mold as a unit, shown generally by the numeral 16 in Fig. 5. The unit 16 may be re-moved by opening the parison mold 2 and the blow mold 18, having halves 18a and 18b,as shown in Figs. 1 and 2 by moving platen 20, on which mold halves 2b and 18b are disposed, away from fixed platen 22, on which mold halves 2a and 18a are disposed. A
hydraulic cylinder (not shown), for example, could be connected ' to shaft 24 for this purpose. The turret 26, on which are disposed two neck ring mold assemblies 6, is then moved away from fixed platen 22 as shown best in Fig. 2.
The unit 16 may also be removed as shown in Fig. 15, by opening the parison mold 2 or by raising the neck ring mold assembly transfer arm 28, and rotating the arm 28 to a mid-position as shown in Fig. 15. The subsequent step of removing the core pin 10 from the parison may now be accomplished (see Fig. 6) and a further conditioning of the parison takes place which allows the parison body to approach an equilibrium temp-erature as explained heretofore. After the core pin 10 has been removed, the turret 26, including neck ring assembly 6 holding the finish 8 of the parison 14, may be rotated 180 by rotating shaft 27 to transfer the parison to the split blow mold 18 as in Figs. 1 and 2, or by further rotation of the neck ring mold assembly transfer arm 28 to the blow mold 18 as shown in Fig.
15. The parison is now in the blow mold 18 as shown in Fig. 7 (or the finish 8 of the parison is supported in the blow mold as shown in Figs. 13 or 14 if the neck ring assembly has been re~urned to the parison mold).
Still referring to Fig. 15, the neck ring mold assembly 6 may now be returned to the parison mold by rotating the neck ring mold assembly transfer arm 28 back to the parison mold 2, while the finish 8 of the parison 14 is supported by the blow mold 18 itself as shown in Figs. 13 or 14. After the neck ring mold assembly 6 has been removed from the blow mold 18, the blow-head 30 descends to the blow mold. The neck ring mold assembly need not be returned to the parison mold prior to stretching and blowing. Both these cteps may be accomplished through the neck ring mold assembly 6 as shown in Figs. 7-10 and 12. The iQ7~014 stretch rod 32 may be disposed with the blowhead 30. The stretch rod 32 is caused to enter the parison, as shown sequen-tially in Figs. 7, 8 and 9, thus stretching the parison 14 to the end of the blow mold cavity opposite to the end through which the stretch rod 32 enters the blow mold 18. The parison is blown to its final container shape by injecting air into the interior thereof, preferrably through orifices 34 (see Figs. 3 and 10) in stretch rod 32. The parison may be stretched by the stretch rod 32 before being blown to its final shape, but pre-ferrably the blowing step commences simultaneously with stretch-ing. This is especially true when tall narrow neck containers are being produced because the simultaneous blowing during the stretching operation prevents the parison 14 from necking in on the stretch rod 32, which can cause too much cooling of the parison and prevention of proper biaxial orientation and container formation. In most cases only a small volume of air at low pressure is necessary to prevent parison-stretch rod contact.
It will be easily understood by those skilled in the art that the ~tretching and blowing of the container into its final bi-axially oriented container shape is the same whether the neckring 6 is in place at the blow mold 18 or has been returned to the parison mold 2 prior to the final forming, the only differ-ence being the method of sealing the blow air.
After the container has been stretched and blown to its final container shape as shown in Fig. 10, the split blow mold lB opens. If the blowing and stretching has taken place through the neck ring mold assembly 6, the latter also opens and the container is removed from the blow mold either by ejecting the container as shown in Fig. 11, or by removing it _g_ .. . . . . .. . . . .

1079~14 with a take-out mechanism such as is commonly used in the glassware forming art.
Figs. 7-10, 12, 13 and 14 show different methods of sealing the blow air within the blow mold 18. In Figs. 7-10 the seal 36 is disposed between the blowhead 30 and the neck ring mold assembly 6. Fig. 12 shows another method of sealing blow air in which a seal 38 is disposed in a neck ring mold insert 39 to seal around the upper portion 40 of the stretch rod 22. In Figs. 13 and 14 the neck ring mold assembly 6 has been transferred back to the parison mold 2 prior to blowing and stretching. Therefore, the seal 42 in Fig. 14 is disposed in the blowhead 30 and abuts the top of the parison finish 8.
In Fig. 13 the seal 44 is disposed between the blowhead 30 and the blow mold 18; in this configuration there is no sealing pressure on the finish of the container.
There has thus been described an improved method of injection-blow molding biaxially-oriented hollow plastic con-tainers in accordance with the present invention. It should be understood by those skilled in the art that while a preferred embodiment has been shown herein to teach my invention, various changes and omissions in the form and detail thereof may be made therein without departing from the spirit and scope of the invention which is to be limited only as set forth in the following claims.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The method of forming a biaxially-oriented hollow plastic container in an injection-blow molding machine which has a parison body mold, a split neck ring mold operable between open and closed positions whereby said neck ring mold is adapted to cooperate with said parison body mold to define a parison cavity, a core pin operable to and from an active position at said parison mold, means for injecting plastic into said parison mold around said core pin, transfer means for moving said split neck ring mold and the parison formed in said parison cavity out of said parison mold and to a split blow mold, a split blow mold operable between open and closed posi-tions, a stretch rod operable to and from an active position at said blow mold, means for forming the parison into its final container shape at said blow mold, including a blowhead operable to and from an active position at said blow mold, and means for removing the final container from said blow mold, the improved method of forming the biaxially-oriented hollow plastic con-tainer, comprising:
disposing said core pin and said neck ring mold in said parison mold;
injecting plastic into said parison mold around said core pin, thereby forming the parison body and forming the finish of the container in said neck ring mold;
temperature conditioning the parison body in said parison mold to a predetermined plastic orientation temperature;
removing said core pin, neck ring mold and parison as a unit from the parison mold so that the parison body is removed from contact with said parison mold;
extracting said core pin from said parison after said unit is removed from said parison mold and after and while said parison has and is slightly expanded in the radial outward direction from said core pin;
further temperature conditioning the parison body after the core pin has been extracted to allow the heat stored in the inner portion of the parison body between the two outer surfaces thereof to reheat said two outer surfaces so that the temperature of said two outer surfaces approaches the tempera-ture of said inner portion of said parison body;
transferring said parison in said neck ring mold without said core pin to said blow mold;
closing said blow mold around said parison;
forming said parison into its final container shape in said blow mold by blowing and stretching said parison;
opening said neck ring mold, and opening said blow mold and removing the final con-tainer from said blow mold.

2. A method of forming a biaxially-oriented hollow plas-tic container as defined in claim 1, wherein the parison is formed into its final container shape in said blow mold by stretching and injecting a blowing medium through said neck ring mold and into the interior of said parison.

3. A method of forming a biaxially-oriented hollow plas-tic container as defined in claim 1, additionally comprising the steps of opening said neck ring mold after said parison has been transferred to said blow mold by said transfer means;
supporting said parison in said blow mold; and removing said neck ring mold from said blow mold prior to forming said parison into its final container shape.

4. A method of forming a biaxially-oriented hollow plastic container defined in claim 2, wherein the step of forming said parison into its final container shape in said blow mold includes commencing the blowing simultaneously with the stretching of the parison by the stretch rod.

5. A method of forming a biaxially-oriented hollow plastic container as defined in claim 3, wherein the step of forming said parison into its final container shape in said blow mold includes commencing the blowing simultaneously with the stretching of the parison by the stretch rod.

6. A method of forming a biaxially-oriented hollow plastic container as defined in claim 4, wherein the step of forming said parison into its final container shape addition-ally comprises forming a seal between said neck ring mold and said blowhead.

7. A method of forming a biaxially-oriented hollow plastic container as defined in claim 5, wherein the step of forming said parison into its final container shape addition-ally comprises forming a seal between said blowhead and said parison.

8. A method of forming a biaxially-oriented hollow plastic container as defined in claim 5, wherein the step of forming said parison into its final container shape addition-ally comprises forming a seal between said blowhead and said blow mold.