CA1038583A

CA1038583A - Method and apparatus for making oriented hollow plastic articles

Info

Publication number: CA1038583A
Application number: CA193,955A
Authority: CA
Inventors: Emery I. Valyi
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-03-05
Filing date: 1974-03-04
Publication date: 1978-09-19
Also published as: AU464755B2; DE2410085A1; DE2410085B2; CH577373A5; IT1003633B; BE811839A; GB1435646A; JPS5331505B2; FR2220363A1; SU605530A3; AU6622974A; JPS49119960A; FR2220363B1

Abstract

ABSTRACT OF THE DISCLOSURE

A method and apparatus for forming oriented hollow objects of moldable organic plastic material by injecting a parison in a parison die onto a blow core, partially expanding said parison to free it from surface contact with said blow core, axially extending the parison and finally expanding said parison by fluid pressure.

Description

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BACKGROUN~ 0~ THE INVENTION ; ~
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lhis invention relates to the art of blow molding articles of organic plastic material from a parison and has for its principal object the provision of impro~ed, oriented hollow articles and a method and apparatus for obtainlng same.
~ he art teaches various methods and appa~atus for obtaining blow molded articles of organic plastic material --from a parison, such as in U.S. Patent 39349,155 and Re.27,104.
Generally, these methods are characterized by forming a ;~-parison in a parison mold on a blow core, placing said formed parison and blow core into a blow mold and expanding said parison in the blow mold by mean~ of fluid pressure.
Naturally, the blowing procedure inherently pro e~ orientation in the plastlc due to expansion in a . ` .

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11 10~6583 radial direction; however it is highly desirable to produce orientation in the axial direction as well. Heretofore,~ ~-this has been done by re-heating the parison and, before blowing, axially orienting the parison, such as by stretching.
Such known methods are subject to clisadvantageous aspects. A particular disadvantage has been the dif~iculty of maintaining uniform wall thickness~ Ob~iously, eontrol of wall thickness distribution is quite important. Other difficulties include in~ufficient control of the parison dimensions and degree of orientation and time consuming and inconvenient operations.
Accordingly, it is a principal object o~ the present invention to provide improved, oriented hollow articles and a method and apparatus ~or obtaining same. -It is an additional object of the present invention ;-~
to provide a method and apparatus as aforesaid which is simple and conYenient to utilize, readily adapted to :
~ commercial operation and which results in an improved, ;~ oriented hollow article. ^
1 ~urther objects and advantages of th~ present invention will appear from the ensuing speci~ication.

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SUMMARY OF THE INVEN'rION

In accordance with the present invention, it has now ~ been found that the foregoing objects and advantages may be .;~
readily attained. The present invention provides a method of making hollow objects of moldable organic plastic material ,. ~ . . ~ .
wherein a parison is injected in a parison die onto a blow core in an injection station and thereafter finally expanded by fluid ~-pressure to form said hollow object, the improvement which is characterized in that the hollow object is oriented in the axial, , radial and tangential directions by positioning sald blow core with the parison thereon outside the injection station in a pre-forming station, partially expanding said parison by f:Luid pres-sure at said pre-forming station so as to free it from surface contact with said blow core, cooling or heating said parison at least in a region of its length followed by axially extending the partially expanded parison by means of said blow core, and finally expanding said partially expanded, axially extended parison at a blow station.
If it is desired to produce a muLtilayered parison, the blow core is first provided with a layer of one plas-tic and next, another plastic is pressure molded therearound, all :~
in accordance with my U.S. Patents ~os.3,349,155, 3,717,544 and

3,719,735. While the description to follow refers mainly to --parisons, it is understood that the method and apparatus of the present invention are applicable to such multilayered parisons , as well.
Also in accordance with the invention, there is pro-. . ~ . .
vided an apparatus for forming hollow objects of moldable organicplastic material which comprises a parison die having an outer die member and a blow core having walls forming the inner surface ~ q . . .
j thereof, means for introducing said plastic into said parison : ~

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, die to form the parison on said blow core and a blow mold having ~
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a mold cavity to form said hollow article, the improvement ;~

which is characterized by a pre-forming station including a : ., :.
chamber with a cavity therein for partially expanding said --parison, means for juxtaposing said blow core with the formed parison thereon and said pre-forming station, means for par-tially expanding said parison with fluid pressure at said pre-forming station so as to free it from surface contact with said blow core, means for axially extending said pre-formed parison . . . ~
by said blow core, means for introducing said pre-formed, ~
axially extended parison into said blow mold, and means blowing ~ ;
the parison with fluid pressure in the blow mold to form a blown article which is oriented in khe axial, radial and tan- ;
i gential directions. ~;
`~ It can be readily seen that the hollow article of the present invention is characterized by highly improved pro- ; ;
perties by virtue of the fact that the walls thereof are con-trollably oriented in the axial, radial and tangential direc-.:.: :i .
tions~ It is known that orientation substantially improves the significant properties of plastics, as clarity, impact resistance, strength, resistance to permeation, etc. Among `1 the plastics that can be so improved are polystyrene, polyvinyl , chloride, polyolefins, as polyethylene and polypropylene, ; polyesters, polyamides, acrylics, acrylonitrile and metha- ;;
crylonitrile polymers. The controlled orientation in the axial, radial and tangential directions, which characterizes the .:
~ article of the present ~
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invention, therefore represents a significant advantage, j and an advantage which is obtained in a simple and -5 expeditious manner. : -.. , ' ~ ~
BRIE~ ~ESCRIP~ION 0~ ~RAWINGS -- ~
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. Figure 1 is an elevation, partly in section, ~ :
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showing the blow core in parison forming position in the ~.
parison die;
.. '~ Figure 2 is a view similar to Figure 1 showing .
~:~ the blow core retracted and the pre-~orming mold in position; ~.
: Figure 3 is a view similar to Figure 1 showing ~: .
.~ the blow core in position in the pre-forming mold~ with the parison pre-~ormed;
'15 Figure 3A is an enlarged sectiona1 view showing ;~
.1 the blow core and parison of Figure 3;
.. Figure 4 is a view similar to Figure 1 showing l the blow core retracted and the parison axially extended; :`
1 Figure 4A i9 an enlarged sectional view ~howing .
the blow core and parison of Figure 4; ; `~
il Figure 5 is a view similar to Figure 1 showing -.~ the blow core in blow position in the blow mold, with the - axially extended parison blown; :~
:"~ Figure 6 is a view similar to Figure 1 showing the blow mold in discharge position and the blow core : ~ :~

, 6 l retract ¦
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Figure 7 is a sectional view showing the improved article prepared in accordance with the pre~ent }~vention. : ~:
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.5 DETAILED DES~RIPTION
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j Referring to the drawings in more detail, a ~`
~ parison die 10 is shown having outer walls 11 which may :~
-~ be separable, depending upon the shape of the parison, .j adapted to form the outer surface of the parison walls and : ;~
having an end wall 12 shaped to form the end wall of the '7 parisonO The end wall 12 of the parison die has an injection opening 13 registering with an in~ection nozzle 14 through which the organic plastic material i~ injected into the 3 parison die. The parison die 10 is shown as split ~or ~i15 convenience in opening to release the formed parison. As indicated hereinabo~e, the plastics contemplated in accor-~l dance with the present in~ention are the moldable organic ~ plastic materials whose properties are improved by orienta- ~ ;
, tion, such as polyolefins as polyethylene, polypropylene l20 and copolymers thereof, polyvinyl chloride, polystyrene, ~:
;s adrylonitrile~ methacrylonitrile, polyvinylidene chloride, ~ . polycarbonates, polyesters, polyamides, etc~ .
In the case of multilayered parisons in which the layers are made of different plastic materials, the ;~
l25 deformatlon characteristics of all of said layers must be 1 taken into account, such chaFacteristics being known to ;~3~ . . . ~:
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those skilled in the artl and the step of axial extension must be conducted so as to be suitable for all of said layers at the same time. ~`
~he blow core 15 carried on a rod 16 is shown ~;
;~ 5 in ~igure 1 as disposed within the parison die 10 and is formed with cylindrical surface 17 and an end wall 18 ~;
shaped to form with the walls 11 and 12 of the parison di~, a die chamber in which the parison is formed. The blow core 15 is pro~ided with the usual blow passages 19 ~ ~-for admitting pressure ~luid to expand the parison into , !' the ~orm of the finished ar~icle. The blow core 15 i8 ~: .
hown to have an anterior portion 15a and a posterior :;f portion 15b, with the anterior portion 15a being arranged to be axially reciprocable by means of piston 207 actuated by suitable means, not shown, as shown more clearly in ~i Figures 4 and 4A in a manner to be described hereinbelow.
~he blow core rod 16 i9 connected to be actuated by a cross head 44 and a suitable hydraulic cylinder ~or advancing and retracting the blow core to its ~arious operating stations.
A neck ring which may be split and composed o~
members 52 and 53 mounted on a carrier 51 is connected to be shifted by a ~lee~e 60, cross head 61 and suitable hydraulic cylinder connected thereto 3 not shown. At the parison injection station in parison injection position, ''.:'i.' . ~ ' d ~,, . '.
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the neck ring i~ dis~osed adjacent the walls 17 of the `
parison dle and is adapted to shape the neck of the parison~
; and of the resulting blown article. A pre-forming mold 21 is formed with a cavity 22 shaped to pro~ide constraint ;~
for the partial e~pansion of the parison at the pre-forming station and having opening 24 on one side thereo~ to receive the blow core 1~. Si~ilarly, a blow mold 25 is provided formed with a caYity 26 shaped to form the finished article, i such as a bottle 23, also having on one side an opening 27 ~10 to recei~e the blow core 15 and pre-formed parison. Naturally, the pre-~orming mold 21 and/or the blow mold 25 may be ~;
made o~ one piece, or constructed as split, two-piece mold~
if desired. Also, if desired, the separate pre-forming ;~
mold 21 may be omitted, the parison introduced directly ~15 into blow mold 25 and the pre-forming operation conducted at the blow mold.
~igure 1 shows the parts in the parison injection station, with the blow core 15 in the parison die 10, the `
neck ring carrier 51 adjacent the parison die with both ;
the pre-~orming mold 21 and the blow mold 25 out of the ;
lj path of the blow oore. With the parts in this position -~ the plastic material is injected through the noz~le 14 into the inJection ca~ity to ~orm the parison 31.
In the second step shown in Figure 2, the parison ~25 die 10 is opened to release the parison and the blow core ,.'"~. : ', ' , ~' ` ' , '`'~
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V-246 ~ j :J I ~ )385~33 ¦ with the neck ring, and the parison die separated there~rom ¦ ~ufficiently to provide clearance for the pre-forming ¦ mold 21, which is then shifted transversely into the path ¦ of the blow core. It should be understood that variations ¦ of ~his movement will readil~ occur to those skilled in ¦ the art. Thus, instead of being movable in an axial direction ¦ only, the blow core may be rotatably mounted and mo~ed from ¦ injection stationj to pre-forming station, to blow molding ~;
¦ station.
~10 l In a third step as shown in Figure 3, the blow ;~
¦ core with the neck ring is advanced into the pre forming ;
¦ mold 21 and fluid is ~pplied under pressure through the ¦ blow core passages 19 to partially expand the parison so i~
as to free it from surface contact with the blow core, 1~ ¦ as elearly shown in ~igure 3A. ~he purpose of this step ¦ is to avoid the difficulties heretofore encountered cluring ~ ¦ axially extending the parison while in surface contact ;~
< ¦ with the blow core. For example, if the parison is axially ¦ extended while in surface contact with the blow core it ; 20 ¦ tends to thin out in localized regions due to the constraint ;
¦ caused by friction against the walls of the blow core. This ~i ¦ results in erratic and unpredictable thinning which often v leads to unnacceptable products.
Naturally, a pre-forming mold may at times be dispensed wnth in this step and the parison pre-formed .:''~, ., .
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without coni3traint by oontrolling the duration and/or degree of the fluid pressure. Alternatively9 this step ~ ;
may be performed in the blow mold whereby the parison 4 is first pre-formed within the confines of the b~ow mold ~ithout expanding it into conformity there~ith. The parison is then axially extended to reach the length of the blow mold cavity and only then is it expanded into ~ull conformity with the blow mold.
In the fourth step, as shown in ~igure 4, the `
parison is axially extended by moving the anterior por-tion 15a of the blow core 15 in an axial direction by means of piston 20 as clearly shown in Figure 4A. Alter-natively, if desired, the same effect can be achieved by moving the entire blow core 15 in an axial direction. ~his step conveniently stretches the parison longitudinally ` ~
be~ore blowing, without the problems noted heretofore, ~ ;
~; and thereby produces orientation in the axial direction ~ -as well as the orientation subsequently produced by blowing.
It can be seen that reheating is not required and frictional ~; 20 discontinuities are avoide~. In this step both the pre-~orming mold and the blow mold are spaced from the blow "., . , . .
~ core.
',.~'A , In the fifth step, as shown in ~igure 5, the :''' :
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¦ blow core with the neck ring and with the axially extended ¦ parison i5 positioned in the blow mold 25 and fluid i~ ~ ;
¦ supplied under pressure through the blow core passages ¦ to blow the pre-formed and axially extended parison into . ~ .. ..
¦ the form of the blow mold cavity 26 to form the bottle 23. ~ ;
Depending upon the shape of the pre-formed and axially -¦ extended parison, it may be so positioned through the ¦ neck opening of the blow mold, or the blow mold may be ~`
¦ opened to admit the parison.
¦ When the article ha~ cooled to its proper state, ., the neck ring members 51 and 52 are separated, the neck 1 ring carrier 51 retracted and the blow mold is shifted out ;~ ¦ of the path o~ the blow core into discharge position as ¦ shown in ~igure 6, wherein the finished article is extracted ¦ there~romO During the extraction step, the blow core is ¦ returned to the parison die as shown in ~igure 1 for the ~." . I
~ ¦ n~xt cycle. Extraction of the article may be ~acilitated ;i ¦ by applying air pressure or mechanical actuators, such as ¦ ejector pins, through opening 88.
¦ It can be readily seen that the finished article ¦ of the present invention is characterized by many advantages.
~:i ¦ In particular, the side walls thereo~ are controllably ¦ oriented in the axial, radial and tangential directions ¦ without longitudinal discontinuities or thinning. ~urther-3 25 more, the article of the present invention has substantially . ' .~ .
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~niform wall thickness. The uniform w~l thickness in an ~ article 90 oriented is highly advantageous.
.. ~. A.s part of the method accord:ing to the present . i~nyent.ion, it is possible to carry out the steps of axial a.nd/or radial orientation at the tempe:ratures that are .
. :su-i~.ted -to produce the best properties in a given plastic. . ~
~ T.hus,.a coo.ling dwell may be introduced before axially ~ ~m : .e.xten.d.ing the parison. Alternatively, the parison or . pred~-te.rmined regions thereof may be heated to reduce the : 1~ .degree of orientation in such regions. .
.Naturally, the present invention is quite versatile . and.a wide variety of articles of varying oonfigura~ions ~ay be readily prepared. If desired, the present invention `~
~ ¦ may be performed on a continuous basis or inter~ittently.
`.1 15 ~or example, the process may be interrupted at any convenient ~ .stage~ the product stored or shipped to another location ;~ and the process subsequently completed, such as shipping `~
. the molded parison from one location to another.
~his invention may be embodied in other forms or :~
oarried out in other ways without departing from the spirit ~
l or essential characteristics thereof. The present embodi- ;
.~; . ment is therefore to be considered as in all respects `~ ! illustrative and not restrictive, the scope of the invention .. i ¦ being indicated by the appended claims, and all changes . ~ which come within the meaning and range of e~uivalency :.
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i' are intended to be embraced therein.
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Claims

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

1. In a method of making hollow objects of moldable organic plastic material wherein a parison is injected in a parison die onto a blow core in an injection station and there-after finally expanded by fluid pressure to form said hollow object, the improvement which is characterized in that the hollow object is oriented in the axial, radial and tangential directions by positioning said blow core with the parison thereon outside the injection station in a pre-forming station, partially expanding said parison by fluid pressure at said pre-forming station so as to free it from surface contact with said blow core, cooling or heating said parison at least in a region of its length followed by axially extending the partially expanded parison by means of said blow core, and finally ex-panding said partially expanded, axially extended parison at a blow station.

2. A method according to claim 1 wherein an axially reciprocable portion of said blow core extends said parison.

3. A method according to claim 1 wherein the neck of the parison is confined while said parison is partially expanded, axially extended and finally expanded.

4. A method according to claim 1 wherein the final expansion step is performed at the pre-forming station.

5. A method according to claim 1 wherein the parison is partially expanded without constraint by controlling the fluid pressure with respect to duration or degree or both.

6. A method according to claim 1 wherein a multilayered parison is formed on said blow core, and wherein the resultant multilayered article is oriented in the axial, radial and tangential directions.