CA1232555A

CA1232555A - Container and method and device for producing same

Info

Publication number: CA1232555A
Application number: CA000518907A
Authority: CA
Inventors: Torsten Nilsson; Kjell M. Jakobsen
Original assignee: PLM AB
Current assignee: Rexam AB
Priority date: 1981-11-26
Filing date: 1986-09-23
Publication date: 1988-02-09
Also published as: IT8268382A0; GB2153741B; US4991734A; AU9086782A; US4704243A; GB2113647A; SE428775B; IT1157099B; ZA828659B; ES517708A0; US4512735A; GB2153741A; GB8505623D0; DE3243908A1; JPS5899340A; MX154286A; SE8107044L; ES8307578A1; IE822807L; JPH0422783B2

Abstract

ABSTRACT OF THE DISCLOSURE

The disclosure describes a method of producing a container comprising a preform having a bottom closure of substantially amorphous material and a cylindrical portion which, at least adjacent the bottom closure, forms a ring-shaped region which consists of material oriented along the axis of the preform with an orien-tation corresponding to that produced in a sheet of the material stretched monoaxially to cause material flow, and reshaping the bottom closure to form a bulge directed towards the interior of the container. The container is also described.

Description

r - 5 The present invention relates to a container of thermo-plastic material, preferably of polyethylene terephtha-late or similar material and also to a method and a device for producing such a container and particularly a container with a central bottom part of amorphous, oriented and/or thermocrystallized material which forms a bulge directed towards the interior of the container which merges into an area of material round the cen-tral bottom part. Said area of material has undergone material flow through stretching and/or reshaping and has been contracted and/or acquired built-in stresses through heating whereby said area of material prevents the inward bulge from straightening out or turning inside out when the pressure inside the container is increased and,'or in connection with heating of the same.

In the field of packaging there exists a need for containers ofthermoplastic material capable of resisting an internal pressure of at least about 7 ~gf/cmZ for the storage of carbonated beverages, e.g. beer or soft drinks.
It has so far not been possible at reasonable cost to achieve can-shaped free-standing containers, for example, which under unfavourable conditions, e.g. at high ternperature, are deformed by such a negligible degree that the deformation can be accepted in regard to shape change, volume change, standing stability, etc.

It is mainly the bottom of the container that gives rise to problems since on deformation of the bottom the standing stability of the container is reduced. There ......

3~ 5 is also a risk of the bottom splitting or turning in-side out. In order to meet the demand for resistance to internal pressure and for standing stability, the bottom of the container has, in accordance with known techniques, a mainly spherical shape and the container is fitted with a separate base which is glued, welded or clipped into position on the container. Such a con-struction is naturally expensive owing to the extra manufacturing operations that the production and assem-bly of two separate parts entail. The amount of materialneeded for the bottom part of the assembled container is also undesirably large.

Free-standing containers so far known having no separate base are also lacking far too much in strength and in the attempts that have been made to use such containers for the purpose specified here they have split in connection with the rise in pressure that occurs during filling and the handling of filled packagings.

An indispensable requirement for packagings is that their costs can be accepted in regard to the end-price of the product in the consumer market. The packaging costs also weigh heavily because the packagings are manufactured and used in large series. In accordance with known techniques it has so far been possible, by using a large quantity of material in each packaging, to achieve a free-standing package of thermoplastic material with the ability to meet the previously spec-ified requirements, but the amount-of material used has been so great that the costs have become far too high to enable such packagings to be accepted.

In accordance with known techniques it is possible to produce bottles with a mouth portion of monoa~ially oriented material with a usually cylindrical container ~3~

body of biaxially oriented material and with a central - bottom part of amorphous or thermal crystallized mate-rial. Such containers have a body in which biaxial stretching of the material is obtained through a pro-cess in which the degree of stretching of the material in the axial direction of the container body and in the circumferential direction of the container body is mainly determined by the abili-~ty~lof the material itself to elongate when the preform is subjected to internal pressure in conjunction with being blown into the shape of the container. As a rule, insufficient stretching of the material along the axis of the con-tainer is obtained although in certain applications attempts have been made to improve this stretching by means of a mechanical device in the form of a mandrel which extends the preform along its axis in the initial stage of blowing it into thè shape of the`container.
Examples of this technique will be found in GB 1 536 194 and GB 2 052 367. The known technique described is solely related to the production of bottles and not to the production of containers in the nature of cans.

It is known that polyethylene terephthalate, henceforth abbreviated to PET, which i's stretched monoaxially and particularly biaxially about three times in the direc-tion of each axis acquires extremely good material properties, see US 4 153 667, for example. An extremely sure and effective technical method of achieving such stretching is to stretch the material until it undergoes flow. Examples of technlques where such stretching occurs are given in GB 2 052 365 and GB 2 052.367.

PET which is stretched so that it undergoes flow has, as stated above, extremely high tensile strength combined with little elongation. In connection with reshaping pre-c-ms corlain-.ns such. ..ate- -l it ls there'ore .._ - ~3~5 possible to stretch the material further in the earlier stretching direction in order to obtain the desired shape of the container.

Further, on heating PET which has been stretched and thereby oriented, the material shrinks in the stretch-ing direction. Shrinking occurs both when stretching has been carried so far that flow has occurred in the mate-rial and also in the case of lesser stretching condi-tions and regardless of whether stretching is monoaxial or multiaxial~ e.g. biaxial. These properties accentuate the problems associated with reshaping a preform into a container.

The physical properties mentioned above do not apply solely to PET but to a greater or lesser degree also to many other thermoplastic materials. Examples of such materials are polyhexamethylene-adipamide, polycapro-lactum, polyhexamethylene-sebacamide, polyethylene-

2.6-naphthalate and polyethylene-1.5-naphthalate, poly-tetramethylene-1.2-dioxybenzoate and copolymers of ethylene terephthalate, ethylene isophthalate and other similar polymer plastics.

The present invention relates to a container of chiefly can type as well as a method and a device for producing such a container The container has a central bottom part which consists chiefly of amorphous, oriented and/or thermocrystallized material, the said central bottom part being surrounded by a ring-shaped area of oriented material. The central bottom part is displaced inwards towards the centre of the container and as a result a ring-shaped standing surface is created adjacent to and principa]ly outside the central bottom part. The ring-shaped area of mate-rial is formed through stretching to flow of mainlyamorphous material which, as in a tubular blank, is situated adjacent the bottom closure of the blank and which before stretching is a ring-shaped and mainly amorphous part of materlal in the blank. In cer-tain applications the ring-shaped part of material in the blank is at least partially situated at a shorter distance from the axis of the blank than the material forming the mainly cylindrical walls of the blank.
Through stretching to flow, the material in the ring-shaped section is oriented chiefly along the axis of the container, to which is added a certain preferably lesser orientation in the circumferential direction of the material. The ring-shaped area of material accord-ingly forms in the container a transition between thematerial in the container body and the central bottom part of the container.

The material stretched to flow in the ring-shaped area has undergone a certain degree of shrinking by the mate-rial being heated to a temperature higher than TG. How-ever, the central bottom part situated inside the ring-shaped area of material prevents complete shrinkage corresponding to the raised temperature of the material whereby forces are built into the ring-shaped material which act to contract (shrink) the material still further. As a result, the ring-shaped area of material has an extremely small tendency to elongate and pre-vents the inward bulge of the central bottom part from straightening out and/or turning inside out as a result of raised internal pressure in the container and/or raised temperature of the container material.

The material in the ring-shaped area has in the case of PET a maximum crystallization of approximately 17%
which has arisen in connection with stretching of the material to flow, to which is added thermal crystalliza-tion which has been formed in connection with heat treatment of the material and which amounts to a maximum of about 15% and is preferably less than 10%.

In a preferred version of the invention, all material in the cylindrical portion of the blank is stretched to flow, whereby the parts of material which are situated nearest the bottom closure of the stretched blank corre-spond to the ring-shaped area of material. In a contai-ner which has been shaped from such a blank, the con-tainer body and mouth portion of the material consist of material oriented along the axis of the container with an orientation corresponding to the orientation the material is given in connection with monoaxial stretching to flow. In addition to orientation along the axis of the container, the material also has a certain preferably lesser orientation in the circum-ferential direction of the container as well as certain preferably lesser thermal crystallization.

In an initial application of the preferred version, the container has the shape of a straight cylinder whose walls consist of material oriented along the axis.

In a second application the walls of the container, in addition to the axial orientation, have an orienta-tion in the circumferential direction of the container.

In a third application, the central bottom part containsparts of material, the original thickness of which has been reduced through compression to an extent which gives the material improved properties corresponding to the material properties obt2ined in connection with stretching the material to flow. In the case of PET, for example, such improved properties begin to appear at approximately two-fold compression. In accordance with the invention it is possible to shape these reinforced parts of material in the form, for example, of squares, concentric rings, ribs directed towards the walls of the container body, and as combinations of these.

In one version of the invention the container is stable in shape up to a certain raised temperature. This has been achieved through heating of the material at least to the said temperature. Also a certain degree of thermal crystallization arises in the material in addition to the crystallization arising through orientation.

In certain versions the material in the central bottom part has a raised thermal crystallization compared with the other material of the container.

In other versions the central bottom part is arranged with thicker reinforced sections of material which form a pattern of squares, concentric rings, radial ribs, etc. The reinforced sections of material preferably have a raised thermal crystallization.

In the case of PET and with the material stretched to flow, the material in the container body and in the mouth portion has a crystallization in the 15-33% range, preferably in the 15-25% range. Crystallization con-sists partly of the crystallization arising in connec-tion with orientation of the material and partly of thermal-conditioned crystallization. The crystalliza-tion arising through orientation amounts in the case of biaxial orientation to a theoretical maximum of about 33~ but in the majcrity of applica ions orientation con2itions are used which limit the crystallization achleved through orientation to about 25%.

In the above-mentioned initial application of the invention the crystallization arising through orienta-tion is limited to a maximum of about 17~ to which is added, where applicable, thermal crystallization amounting to a maxirnum of about 15~ and preferably less than 10%.

Inthe second application the crystallization arising through orientation may reach the stated theoretical maximum of about 33% but in most applications has a value in the 15-25% range to which is added, where applicable, thermal crystallization amounting to a maximum of 15% and preferably less than 10~.

Depending on which alternative version of the bottom part is chosen, crystallization in the material of the bottom part varies from a few per cent up to about 25-30%, where the thermal-conditioned crystallization is usually less than 10-15%.

The crystallization values given in this patent appli- --cation are based on the theory aavanced in the publica-tion"Die Makromolekulare Chemie" 176, 2459-2465 (1975).
The values refer to the material PET. In applications of the invention using other materials, crystallization values characteristic of these materials will of course be obtained.

For the production of a container in accordance with the invention a tubular blank of mainly amorphous ma-terial is used. The tube is closed at one end. The mate-rial in the walls of the tube are stretched to flow at least in a ring-shaped area of material adjacent the bottom closure of the blank.

In a preferred version of the invention the material ~I!Lf~3 r ~j is stretched by passing the whole blank through a draw ring at the same time as a mandrel occupies the inte-rior of the blank. In this way the blank is elongated by an amount corresponding to the reduction in the thickness of the walls of the blank. In the case of PET the elongation is about three times. During the passage of the blank through the draw ring, at the transition between the material that has already passed through the draw ring and the material that is just about to pass through it, a transitional zone is formed between material stretched along the axis of the blank, i.e.
oriented material, and material which has not yet been stretched, i.e. chiefly amorphous material. Heat is released in connection with the molecules restructuring, which takes place during the passage of the material through the draw ring. Both the internal mandrel and the draw ring are maintained at a temperature in the vicinity of or in the range of the glass transition temperature of the material, henceforth designated TG.
As a rule, passages for this purpose are arranged in - -both the mandrel and the draw ring to carry liquid for regulating the temperature of the mandrel and draw ring respectively. In the event of excessively high temperature in the material at the transitional zone, 2~ contact between the material and the draw ring is lost in parts of the transitional zone, which leads to unwanted effects in the material that is to pass through, or has passed through, the draw ring. In conjunction with its passage through the draw ring the material is temporarily allowed to assume a temperature somewhat in excess of TG. In the case of PET, temperature in excess of 105C are as a rule unsuitable. Described in patént application DEOS 31 21 524.6 laid open June 9, 1982 is a version of material stretching using draw rings as described in brief ahove.

Preferably in connection with the recently described stretching of the material in the walls of the blank, the bottom closure is given a shape largely coinciding with the final shape of the central bottom part of the container that is to be shaped. Shaping of the bottom part takes place by means of a die and a stamp or punch placed on the internal mandrel and arranged on an external element respectively and adjustable relative to each other along the axis of the mandrel. Reshaping of the bottom closure normally takes place at a temperature in the TG
range. However, reshaping in some embodiments of the invention also takes place above or below the TG range.
The major portion of the material in the bottom part is therefore, also immediately after the actual reshaping process, chiefly amorphous or alternatively th~rmal-ly crystallized.
.
Through reshaping of the bottom closure of the blank as described in the foregoing paragraph the stamp moves the material in the bottom closure, during the latter part of its relative movement towards the die, in a direction towards the opening part of the blank at the same time as the bottom closure is arched towards the inside of the blank. The increase in the profile length of the material in the bottom part thereby received results in the material in the bottom closure, which merges the material in the wall of the blank which is axially oriented and stretched to flow, being subjected to such high tensile forces that material flow occurs in the aforementioned transitional zone at material temperatures in the TG range or below. In this connectiOr, in addition to the material in the wall of the blank already stretched to flow, a ring of material stretched to flow is formed which outwardly limits the other-"ise chiefly amorphous material in the bottom part s and forms the transition between the mainly cylindrical portion of the container and the central bottom part of the container. The forming space which arises between the stamp and the die when their movements towards each . other have terminated is adapted to the desired final shape of the bottom of the container which is in the pro-cess of manufacture or is adapted to a shape suitable for the next reshaping stage. Depénding on the desired proper-ties of the material inside the ring of stretched mate-rial, the forming space is designed in order to form orprocess reinforcement ribs, etc. in the bottom part in accordance with the alternatives mentioned above. In certain applications the stamp and/or die have a raised temperature through which the material in the bottom lS part underyoes thermal crystallization simultaneously with reshaping of the bottom part.

In the next stage the mouth opening of the blank is en-larged or reduced in size, which is most simply accom-plished by pressing the blank down over a conical man-drel or a sleeve. The maximum permissible increase inthe circumference of the opening is adapted to the material stretching necessary in order to obtain mate-rial flow. In the case of PET the maximum permissible increase is about three times. During reshaping of the mouth the material has a temperature in excess of TG.
The temperature~is further chosen in regard to and normally higher than the maximum temperature the container will be exposed to in use.

In one version of the invention the remaining material in the blank is heated to the same temperature, which means that the material stretched to flow shrinks. The amorphous material in the bottom part of the blank is also subjected to shrinkage forces when heated which tend to restore the mainly amorphous material in the bottom part to the shape the material had before it was reshaped by means of the stamp and die. The ring of material stretched to flow nevertheless prevents a return to the original shape because the ring contracts and does not allow amorphous material adjacent to the ring to move back to the positions the material had before reshaping of the bottom part. Depending on the degree of thermal crystallization it is desired to achieve in the material in the bottom part, the material is retained at the temperature specified above for a shorter or longer pe-riod of time. The blank treated in this manner now forms a finished container or a preform completely lacking in a tendency to shrinkage at all temperatures below the temperature at which shaping of the mouth section and shrinking of the stretched material was achieved.

In cases where the preform is to be reshaped, which usually takes place in a blowing mould, the preform is heated to a blowing temperature higher than the TG
of the material but lower than the temperature at which the mouth portion was shaped. Shape changing of the preform when the temperature of the material is adjusted to reshaping temperature is avoided in this way.

The preform is preferably preheated and obtains its final temperature adjustment to blowing temperature in the blowing mould in that the preform is heated additionally in it or, alternatively, in that it cools slightly when it is placed in the blowing mould. Temperature adjust-ment is carried out in accordance with a known technique, e.g. by means of an internal mandrel, circulating liq-uid, hot mould walls, etc. With the material in the preform at blowing temperature the interior of the pre-form is pressurized and the preform is expanded until it is in contact with the walls of the blowing mouid while the profile length of the material is simulta-neously retained. This is achieved by moving the bottom of the preform towards the opening of the preform while simultaneously moving the central bottom part of the blowing mould. In the final stage of forming the con-tainer the moved central bottom part forms in the blow-ing mould even transitional surfaces with adjacent sur-faces at the same time as the expanded preform is in contact with all forming surfaces in the blowing mould.
Through contact with the forming surfaces of the blowing mould, thermal crystallization of the material is added in one alternative version of the invention in addition to the crystallization of the material obtained through the axial and transversal stretching.

In certain applications, thermal crystallization of the material in the container is concluded in conjunction with the recently described final forming of the pre-form and, in certain applications, also in conjunction with the forming of the central bottom part.

In accordance with the invention it is possible to pro-uuce a container which is shape-permanent on being heaced to temperature in the vicinity of the blowing temperature of the material and/or the temperature of the forming surfaces of the blowing mould. The blowing temperature and the temperature of the forming surfaces of the blowing mould are usually lower than the temperature at which the material in the mouth portion of the blank was reshaped.

The invention is also described with reference to a number of figures, where Fig. 1 shows an axial cross-section through a blank consisting chiefly of amorphous material, Fig. 2 shows an axial cross-section through a preform formed from the blank as in Fig. 1, Fig. 3 shows the preform as in Fig. 2 with reshaped bottom, Fig. 3a shows the area A in Fig. 3 in detail, Fig. 4 shows the preform after it has been heated for relieving of the material stresses quilt into the material of the cylindrical part of the pre-form in conjunction with forming of the preform, Fig. 4a shows the area B in Fig. 4 in detail, Fig. 5 a--c show versions of a container formed through reshaping of the mouth portion of the preform as in Fig. 4, Fig. 6 shows a container formed through reshaping of the container as in Fig. 5b, Fig. 7 shows a device for reshaping the bottom part of the preform, Figs. 8-10 show a device for reshaping a preform into a container as in Fig. 6 in various stages of the reshaping process.

Depicted in Fig. 1 is a tubular blank 10 of chiefly amorphous material with a cylindrical portion 12 and a closure 14 at one end.

Fig. 2 shows a preform 20 rormed from the blank 10 through stretching of the material in the cylindrical portion 12 of the blank 10 to flow. The preform thus formed has a cylindrical portion 22 and a bottom part 24.

Figures 3 and 3a show the preform as in Fig. 2 with reshaped bottom part 24a. In certain applications the bottom part 24 is reshaped with the material at a tem-perature in a range lower than the thermoelastic temper-ature range of the material (in or below thè TG range). The increase of the profile length of the bottom part 24 that reshaping entails means that the preform as in Figs. 3 and 3a is provided in conjunction with reshaping with a ring-shaped area of material 25a stretched to flow, henceforth also designated ring-shaped transition, which is formed of amorphous material which in blank 10 is situated in the transition between the closure 14 of the blank and the cylindrical portion 12 of the blank.
The corresponding arèa of material in the preform as in Fig. 2 has undergone a certain degree of stretching, although less than the stretching that corresponds to material slow. On reshaping of the bottom part 24 the recently-mentioned prestretched area of material is subjected to additional stretching with the result that material flows. Accordingly, material flows in the blank 10 and the material, which flows, is situated closer to the axis of the blank than the mate-rial which in the blank forms the cylindrical portion 12.
The material of the ring-shaped transition has a smaller initial radius than the material in the cylindrical por-tion. Also indicated in the figures is a standing sur-face with the reference number 26a and the mouth portion of the preform with the reference number 27a.

In another version the bottom part 24 ls reshaped with the material at a temperature within the thermoelastic temperature range of the material. As a result, the profile length of the bottom part increases in conjunc-~3~

tion with reshaping as the thickness of the material in the bottom part decreases duxing simultaneous elongation of the material. The equivalent to the ring-shaped transi-tion of materia1 which is stretched to flow as aescribed in the previous paragraph in this application consists of a ring-shaped area of material stretched to flow which was formed during the passage of the blank through the draw ruing and which is situated adjacent the bottom part 24 of the blank. Figures

3 and 3a are also representative of the ring-shaped area of material which is formed according to this version and which is accoraingly assigned reference number 25a in the figures.

Figs.~4 and 4a show the preform as in Figs. 3 and 3a which has been heated to a temperature higher than the lS TG range of the material. In the case of PET the mate-rial has been heated to a temperature preferably higher than the TG range by at least about 40C, i.e. has been heated to at least about 120C. Through heating, the preform is given a smaller axial length and the cylin-drical portion 22b a smaller diameter (cf. the figures).
The reduction of the diameter of the ring-shaped tran-sition 25a results in the bottom part 24b of the pre-form 20b being given a sharper bend than the bottom part 24a and it consequently bulges deeper into the cylin-arical portion than the bottom part 24a. In the version of the invention where the ring-shaped transition 25a is formed by amorphous material closer to the axis of the blank than the material in the cylindrical walls of the blank, the contracting effect in the ring-shaped transition 25a is intensified, which as a rule results in greater inward bulging of the bottom part 24b into the cylindrical portion 22b.

Figs. 5 a-c show alternative versions of an initial version of containers 30a, 30b and 30c according to the ~;~3~

invention which are formed by preform 20b being reshaped in lts mouth portion 27b. In Fig. 5a the container 30a has a flared mouth portion 37a, in Fig. 5b the container 30b has a mainly conical flared mouth S portion 37b, and in Fig. 5c a constric-ted mouth portion 37c. The mouth portions are adapted for folding together with a sealing end-section which, however, is not shown in any of the figures. Indicated in these with reference designations 34a - 34c are a central bottom part, with 35a - 35c the ring-shaped transitions and with 36a - 36c the ring-shaped standing surfaces.

In the alternative version of a container 30d shown in Fig. 6 the contour length of the material stretched to flow in the mouth portion 37d of the container, the cylindrical portion 32d of the container, and in the ring-shaped transitional zone 35d coincides with the corresponding contour length of the mouth portion 27b, the cylindrical section 22b and the ring-shaped tran-sitional zone 35b. The central bottom part 34d of the container is not as thick as the central bottom part 24b of the preform 20b. In a preferred version, the central bottom part is also thinner in the parts closest to the axis of the container. Between the central bottom part 34d and the ring-shaped standing surface 36d of the container is the ring-shaped area 35d of material stretched to flow which stabilizes the shape of the bottom part 34d and prevents the bottom part from turning inside out when the pressure in the container rises and/
or when the container is heated. The ring-shaped area of material 35d corresponds in preform 20a to the ring-shaped area of material 25a. From the figure it is also evident that the material in the cylindrical portion 32d and the mouth portion 37d of the container lS stretched in the circumferential direction of the container in addi-tion to its stretching along the axis of the container.

This (circumferential) stretching amounts at maximum to a stretching which gives rise to material flow.

Fig. 7 shows the principle oE a clevice for reshaping a preform 20 as in Fig. 2 into a preform 20a as in Fig. 3.
Depicted in the figure is a locating body 40 with a cylindrical cavity 41, the diameter of which corresponds to the outside diameter of the preform 20. A manarel with a diameter adapted to the inside aiameter of preform 20 is an initial forming element 42 which is movable along the axis of the cavity and relative to a second forming element 43. The first forming element is situated inside preform 20 and the second forming element is situated on the other side of the bottom part 24 of the preform. The first forming element 42 presents a concave forming surface 44 to the bottom part 24 and the second forming element presents a convex forming surface 45 to the bottom part. For the sake of simplicity, the drive elements for the movement of the forming elements are omitted in the figure but drive elements can be arranged in accordance with any already known technique. Further, the movement of the forming elements towards each other is controlled in such a manner that in the final forming position the distance between the forming surfaces of the forming elements corresponds to the thickness of the reshaped bottom part 24a. Depicted in the figure are stops 46 which regulate the maximum movement of the first forming element 42 in a direction towards the locating body 40. By means of double-headed arrows A and B the directions of movement of the first and second forming elements respectively are marked.

Figs. 8 10 show a version of a device for final forming of a preform as in Fig. 3 or Fig. 4. Even though a pre-form 20b shrunk through heating is shown in Fig. 8, it ~3~ 5 is just as easy to use the device for reshaping of a preform 20a.

The figures show a blowing mould 50 with two mould halves 51 a, b. At the lower part of the blowing mould is a cylindrical cavity 52 bounded by the two mould halves 51 a, b and with a diameter adapted to the diameter of preforrn 20b in order to permit the preform to pass into the cavity. In the cavity the blowing mould is arranged with a bottom part 53 which is movable in the cavity and in the direction of the double-headed arrow D to assume the position shown in Fig. 10 at one of its end positions. The bottom part 53 corresponds to the previously-mentioned second forming element 43 and like it is arranged with a con-vex forming surface 55. A mainly cylindrical mandrel 56 with a diameter mainly coinciding with the inside diameter of preform 20b and adapted to permit the man-drel to pass into the preform corresponds to the pre-viously-mentioned first forming element 42 and like it is arranged with a concave forming surface 54. At its upper part the mandrel is arranged with a part 57 of larger diametex and terminates in a flat-like part 58 with a lower contact surface 59 adapted to abut against an upper contact surface 60 a, b on the mould halves 51 a, b. The mandrel 56 is capable of moving back and forth in the direction of arrow C to assume the position shown in Figs. 9 and 10 at one of its end positions. The blow-ing mould halves 51 a,b- have at their upper parts 61 a,b a shape adapted to the shape of the mandrel in part 57 of larger diameter whereby, with the mandrel 56 in the end position shown in Figs. 9 and 10, a form-ing space adapted to the shape of the mouth portion of the future container is formed between the mandrel and the upper parts of the blowing mould halves. Further, with the mandrel and bottom part 53 in the positions shown in Fig. 10, a corresponding forming space for the :~L2~ 5 central bottom part 34c of the future container is formed.

Liquid passages 62 a, b, 63 and 64 are arranged in the mould halves 51 a,b, in the bottom part 53 of the blow-ing mould,and in the mandrel 56 for heating or cooling of the respective elements.

In order to simplify the figures, the passages for the pressure medium, as well as all drive elements fox the movements of the mould halves 51, the bottom part 53 and the mandrel 56, are omitted.

In the introductory part of the description an explana-tion was given as to how a preform is obtained. Reshap-ing of preform 20 into the versions 20a and 20b is begun in an application example in a device as shown in jig. 7.
The preform 20 is placed over the mandrel 42 and with the aid of it is introduced into cavity 41 until the bottom part 24 of the preform abuts against the convex surface 45 of the second forming element 43. The mandxel then con-tinues its movement towards the second forming element until a forming space corresponding to the shape of the desired bottom part 24a ox the preform 20a is formed between the convex surface 45 of the forming element 43 and the concave surface 44 of the mandrel.

In an initial application example the material then has at least in the lower part of the preform 20 a tempera-ture in the TG range or below, whereby the formationof the ring-shaped transition 25a is concluded in accord-ance with the forming stages described in the foregoing paragraph.

In a-second appli-ation example the material in the lower part of the preform 20 has a temperature higher than the TG range, whereby the material has rubber-like Via properties and reshaping takes place during successive stretching of the material in the bottom part 24. Depend-ing on which of the versions of the central bottom part is desired in the container which is being manufactured, the material in the bottom part is heated or cooled on coming into contact with the concave and convex surfaces 44, 45.

A comparison of Figs. 7 and 8 will clearly show that reshaping of preform 20 into the preform 20a can also take place in a device as shown in Fig. 8, whereby pre-form 20a is formed during the initial stage of forming the container 30d.

When using a device as shown in Figs. 8-10 the mouth portion of the future container is also formed during the initial stage of reshaping the preform through part 57 of the mandrel 56 having a larger diameter moving the material radially outwards towards the upper parts 61 a, b of the mould halves. The preform is then as a rule able to withstand the axial forces without under-going deformation. In cases where the processing tem-perature and the material have been so chosen that the axial strength of the preform is insufficient, forming of the mouth portion of the future container can be carried out more suitably in a separate device having a cylindrical cavity for supporting the preform more or less along its entire length.

Through heating of the material in preform 20a it is transformed, as has already been described, into the pre-form 20b. Heating of the preform 20a takes place in accord-ance with an alternative version of the invention in separate heating ovens while in another version heating takes place in the slowing mould 50. Versions also naturally exist in which heating in ovens is combined 123~r~ US

with adjusting the temperature in the blowing mould. Tem-peratures of interest in connection with the various forming stages have been dealt with in the introductory part of the description.

Regardless of whether a heated preform 20a or a heat-treated preform 20b has been inserted into blowing mould 50 after the mandrel 56 has been moved to its lower po-sition, the preform is transformed into the shape shown in Fig. 9. In certain applications this corresponds to the desired end product while in other applications the mandrel has a larger axial length in order to permit certain reshaping and heat treatment of the material in - bottom part 34b.

In the event that a container 30d is to be produced the interior of the container 30b, which is now to be regarded as an intermediate product, is pressurized and as a result the walls of the intermediate product are blown out or expanded to make contact with the forming surfaces ox the mould halves 51 a, b at the same time as the bottom part 53 of the blowing mould is moved upwards and so permits reshaping to take place with retention of the profile length of the section of material of the inter-mediate product consisting of material stretched to flow. In its upper position (Fig. 10) the concave form-ing surface 54 and the convex forming surface 55 inter-act for the formation of a forming space adapted to the shape of the central bottom part 34d of the desired con-tainer.

The liquid passages 62 a, b, 63 and 64 then carry hot or cold liquid, depending on which of the versions men-tioned in the introductory part of _he description is aimed at in the individual application examp]e. Through simultaneous retention of the internal pressure in the 3~ 5 formed container and supplying heat to the forming surfaces, a container is producted where thermal crystallization is also obtained in the parts of the material which are crystallized through stretching of the material.

In the above description it has been stated that the blank and the preform respectively have a cylindrical portion. Nat-urally, the cross-section of both the blank and the pre-form as well as that of the formed container, does not need to be circular since in accordance with the inven-tion other shapes are also suitable.

The description and the figures have mainly described the application of the invention to a preform whose cylindrical portion consists of material that has been strechted to flow. From the description it is also plainly evident that the invention is applicable for the pro-duction of a container from a preform where only an area of material adjacent to the bottom closure of the pre-form consists of material that has been stretched to flow.

The invention is applicable in connection with the pro-duction of containers from both injection-moulded and extruded blanks.

In addition to the above description the invention will be evident from the following patent claims.

This application is a divisional of Canadian Patent Application No. 415,918 filed November 18, 1982.

Claims

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

1. A method of producing a container comprising a preform having a bottom closure of substantially amorphous material and a cylindrical portion which, at least adjacent the bottom closure, forms a ring-shaped region which consists of material oriented along the axis of the preform with an orientation corresponding to that produced in a sheet of the material stretched monoaxially to cause material flow, and reshaping said bottom closure to form a bulge directed towards the interior of the container.

2. A method as claimed in claim 1 wherein the material in said bottom closure during reshaping to form the inward bulge is at a temperature within or below the range of the glass transition temperature of the material, whereby the amorphous material in said bottom closure is stretched to flow at least in the region adjacent the stretched material in said ring-shaped region.

3. A method as claimed in claim 1, wherein said inward bulge is moved during blowing of the preform along the axis of the preform towards the center of the preform and relative to the cylindrical portion of the preform to maintain the contour length of the material.

4. A method as claimed in claim 3 comprising reducing the thickness of the material during the reshaping thereof to form the central bottom portion of the resulting container.

5. A method as claimed in claim 3 comprising heating the material to a temperature within the thermal crystal-lization range.

6. A method as claimed in claim 3 comprising heating the material to a temperature above the temperature at which thermal crystallization of the material is a maximum.

7. A method as claimed in claim 3 comprising expanding a mouth portion of the preform in an initial stage of forming the container.

8. A method as claimed in claim 4 further comprising heating the material in said ring-shaped region to a temperature above the region of the glass transition temperature range of the material, and blowing at least the material in said cylindrical portion outwardly at forming temperature to contact forming surfaces in a blow mold.

9. A method as claimed in claim 8 comprising expanding a mouth portion of the preform in an initial stage of forming the container and before blowing.

10. A container of polyethylene terephthalate or similar thermoplastic material comprising a body, a closed bottom portion of curved shape which bulges inwardly into thy body, and an annular region joining said bottom and body, said annular region including a ring-shaped region which is constituted of material which is oriented and under internal pre-stress tending to contract said ring-shaped region, the combination of the orientation and internal pre-stress of said ring-shaped region serving as a means for preventing said inwardly curved bottom portion from straightening out or turning inside-out.

11. A container as claimed in claim 10 wherein said annular region provides a standing surface for the container.

12. A container as claimed in claim 10 wherein said bottom portion is substantially amorphous.

13. A container as claimed in claim 10 wherein said bottom portion is substantially thermocrystallized.

14. A container as claimed in claim 10 wherein said ring-shaped region includes material which has been squeezed radially outwards.

15. A container as claimed in claim 11 wherein said ring-shaped region is situated between said standing surface and the axis of the container.

16. A container as claimed in claim 11 wherein said standing surface is situated between said ring-shaped region and the axis of the container.

17. A container as claimed in claim 10 wherein said standing surface is at least partially formed by said ring-shaped region.

18. A container as claimed in claim 10 wherein said body comprises a wall of biaxially stretched material.

19. A container as claimed in claim 18 wherein said wall is stretched axially by a multiple of its original length to provide crystallization with axial orientation.

20. A container as claimed in claim 19 wherein said ring-shaped region merges with said wall and said orien-tation of the material of said ring-shaped region is provided by said crystallization with axial orientation obtained by axial stretching of said wall.

21. A container as claimed in claim 20 wherein said wall has biaxial orientation.

22. A container as claimed in claim 10 wherein the material of said body is oriented along the axis of the container with an orientation corresponding to that arising in a sheet of material which is stretched monoaxially to cause material flow.

23. A container as claimed in claim 22 wherein the material of said body is additionally oriented in the circumferential direction of the container with an orientation corresponding at most to that arising in a sheet of material when stretched monoaxially to cause material flow.

24. A container as claimed in claim 10 wherein the material in the body and ring-shaped region has a crystallization of between 15-33% and the material in said bottom portion has a maximum crystallization of approximately 30%.

25. A container as claimed in claim 10 wherein said ring-shaped region is laterally bulged with respect to said body.

26. A container as claimed in claim 10 wherein said body is heat set.

27. A container as claimed in claim 10 wherein said body is thermocrystallized.