Note: Descriptions are shown in the official language in which they were submitted.
' 1~7~175
-- 1 --
The invention relates to the manufacture of
articles from a thermoplastic of polyester or polyamide
type, preferably of polyethylene terephthalate, the art-
icles being formed from an element which consists of an
edge part which surr~unds a body in an arrangement in which
the latter is sunk relativeto the edge part. The elementis
formedfrom a blank of mainly amor~hous material or from a
material having a crystallinity of less than 10%.
The blank consists, for example, of a flat plate, a
blank shell or the like. The body or parts
thereof are shaped by stretching the blank until that
material flows which is located within the material
sections of the blank~ which form the edge part in the
element, the material stretched up to flowing in the
body assuming a crystallinity of between lC%and 25%,
whilst the crystallinity in the ~aterial in the edge
~, . .
part and in the unstretched parts retains its original
value of less than lO~o. The edge part is severed
from the body, the latter being elongated in the axial
direction by a number of drawing steps, whilst the dimen-
sions of the ~ody at right angles thereto are reduced
at the same time. The body of the element of the drawn
part is reshaped by a blow-mouldipg process to give the
article.
In the manufacture of products from thermo-
~r~
,
1~73175
-- 2 --
plastics, the starting material is in most cases a
virtually flat blank. Either an end product is formed
here substantially in one deformation step, or a pre-
moulding is formed for later reshaping to give the end
product. The shaping of the blank is effected,
according to methods known at present, either by the
blow-moulding process or by the thermc-forming process.
In the blow-moulding process~ thick sections are as a
rule obtained in the bottom. In the thermo-forming
process, either so-called negative thermo-forming or so-
called positive thermo-forming is used. In the
negative thermo-forming process, a thin bottom is
obtained, whilst a thick bottom is obtained in the posi-
tive thermo-forming process.
- In negative thermo-forming, a warm sheet or a
warm film is placed over cavities, after which the
material of the film or the sheet is pressed and sucked
into the cavities by external pressure and internal
reduced pressure. This has the result that the
material is stretched and becomes thin, when it is
sucked into the particular cavities. If the cavity
is a cup, a thin stretched bottom and a wall thickness
increasing in the direction of the edge of the cup are
obtained.
In positive thermo-forming the cup mould forms
a projecting body and the material of the film or sheet
is pressed and sucked over this projecting body. This
has the result that the material on the upper part of the
projecting body, that is to say the bottom of the cup,
!
7317~i
-- 3 --
remains thick and essentially unstretched, whilst the
thickness of the material decreases to-Yards the edge of
the cup.
To obtain an adequate material thickness in the
bottom part of the cup in negative thermo~forming, a
sufficient thickness in the starting material must be
chosen. To obtain an adequate thickness in the edge
zone of the cup by positive thermo-forming, which is
necessary for stability of the cup, a sufficient thick-
ness of starting material must likewise be chosen.
In negative thermo-forming, the material zones between
the shaped cups remain uninfluenced and are subsequently
severed, after the manufacture of the actual cups.
In positive thermo-forming, the material between the
cups is drawn into recesses and severed from the cups
formed. In positive thermo-forming, cup bottoms are
thus obtained which have substantially the same thick-
hess as the starting material. Both forming processes
require an unnecessarily high consumption of material,
which is of economic importance in the mass production of
articles.
The present invention eliminates certain disad-
vantages connected with the technology hitherto known.
The invention is suitable preferably for the
manufacture of articles from thermoplastics of the poly-
ester or polyamide type. Examples of such materials
are polyethylene terephthalate, polyhexamethylene-
adipamide, polycaprolactam, polyhexamethylene-sebacamide,
polyethylene 2,6- and l,~-naphthalate, polytetramethylene
.
73 17
-- 4 --
l,2-dihydroxybenzoate and copolymers of ethylene
terephthalate, ethylene isophthalate and similar
polymers. The description of the invention below
relates mainly to polyethylene terephthalate, called
PET in the further text, but the invention is not
restricted exclusively to the use of either this material
or other materials already mentioned; instead, it is
also suitable for many other thermoplastics.
For a better understanding of the existing
problem and of the invention, several characteristic
properties of the polyester polyethylene terephthalate
are described belcw. From the literature, for example
Properties of Polymers, by D.W. van Krevelen, Elsevier
Scientific Publishing Company, 1976, it is known that the
properties of the material change when amorphous poly-
ethylene terephthalate is oriented. Some of these
changes are shown in the diagrams, Figures 14.3 and 14.4
on pages 3 7 and 319 in the book "Properties of Polymers".
The symbols used in the discussion below correspond to
the symbols in the said book.
PET, like many other thermoplastics, can be
oriented by stretching the material. Normally this
stretching takes place at a temperature above the glass
transition temperature Tg of the material. The
strength properties of the material are improved by
orienting. The literature shows that~ in the case of
the thermoplastic PET, an increase in the stretching
ratioJ~, that is to say the quotient of the length of
the stretched material and the length of the unstretched
2 7 317
_ 5
material, also leads to an increase in the improvement
of the material properties. When the stretching ratio
is increased from about 2 to a little more than 3~
particularly large changes in the material properties
are obtained. The strength in the direction of orien-
tation is here markedly improved, whilst at the same time
the density ~ and likewise the crystallinity Xc rises and
the glass transition temperature Tg is raised. It can
be seen from the diagram on page 317 that, after stretch-
in~ with~ assuming the value of 3.1, the material with-
stands a force per unit area, which corresponds to ~ = 10,
coupled with a very sm~ll elongation, whilst the elonga-
tion at ~ = 2.8 i$ substantially larger. In the
further test, the term "step1' issometimes used to desig-
nate orienting which is obtained by stretching, or
a reduction in thickness by at least about 3 times,
and which leads to the marked improvements of t~e material
properties, indicated above.
The diagrams quoted abcve show changes which are
obtained on mono-axial orientation of the material.
In biaxial orientation, similar effects are obtained in
both directions of orientation. Orientation is
carried out as a rule by successive stretchings.
Improved material properties, corresponding to
those which are obtained by the "step" defined above, are
also obtained if an amorphous material is stretc~ed until
it flows and, before flowing, the ma~erial is at a tem-
perature which is below the glass transition temperature
Tg. In a rod being drawn, a reduction of the diameter
~2 7~17 J
~ about 3 times results in th~ flow zone. On
drawing, the flow zone is continuously displaced into
the a~orphous mat~rial, whilst at the same time the
material, which has already undergone the state of
flowing, absorbs the tensile forces of the test rod
without an additio~al permanent stretching.
According to the invention, an element is pro-
duced which consists of an edge part and a cup part,
starting from a substantially flat blank of amorphous
material or having a crystallinity of less than io%. The
material in annular sections in ~he blank is transformed
into the state of flow by a drawlng process. The cup
part is formed in this way. In certain applications, the
ratio between the radial and the axial expansion
of the cup is such that production of the beaker in
a single drawing step is not possible. According to
tne invention, the desired ratios are obtained by a
number of redrawing steps of the cup, the diameter of the
cup being reduced in each redrawing step~ whilst the
thickness of the material remains more or less unchanged.
The cup part of the element or the drawn cup is
reshaped by a blow-moulding process to give the article
According to the invention, an element is
obtained which consists of an edge part and a cup part,
the material preferably being of more or less uniform
thickness and orientation in the entire bottom of the
cup part (cup). In a certain embodiment of the
invention, the material in the bottom part of the cup
1~7317Si
-- 7 --
moreover consists completely or partially of material of
the same thickness as that of the material of the wall.
The remaining sections of ma*erial have the thickness
and material properties of the material.
In certain applicat~ons, the bottom is more or less
completely flat, whilst in other applications the bottom
consists of parts which are axially displaced relative
to the axis of the cup. In this case, in certain
embodiments, annular edge sections are formed adjoining
the lower edge of the wall, whilst in other embodiments
central bottom sections are displaced further away from
the upper opening edge of the element.
The element consists of an edge part which
surrounds a ~ody which is sunk relative to the edge
part. The material in the edge part is mainly amor-
phous or has a crystallinity of less than 10%. The
body has a wall part and a bottom part. The wall part
consists of material which has been drawn at a tempera-
ture below the glass transition temperature Tg, until
flow sets in, and in which the crystallinity is between
lOo~and 25%. In the basic design of the element, the
bottom consists of mainly amorphous material or of
material having a crystallinity of less than 10%. In
embodiments of the invention, the bottom consists, as
desired, of material which has been drawn at a tem-
perature below the glass transition temperature Tg and
at a crystallinity between 10%and 25%, until flow sets
in, that is to say of a material having properties which
1~ 73 175
mainly are identical to the material properties of the
wall part of the element,or of material sections which
have been drawn until flow sets in and which alternate
with material sections of mainly amorphous material or
materlal having a crystallinity of less than 10%. In
certain embodiments, the material zones already mentioned
are displaced in the axial direction relative to the
lower edge of the wall part.
During the production of an element, a mainly
flat blank of thermoplastic, having a crystallinity of
less than 10%,is clamped in ~t a temperature below the
glass transition temperature Tg between counter-holders,
so that a zone is formed which is completely surrounded
by the clamped-in material sections. A press device
the contact surface of which is smaller than the surface
area of the zone, is applied against this zone. Thus,
a closed strip-like material zone is formed between the
clamped-in material sections of the blank and that part
of the zone which is in contact with the press device.
Subsequently, a drive mechanism s~ifts the press device
relative to the counter-holder, while the press device
remains in contact with the zone. The material in the
strip-like zone is thus stretched in such a way that flow
of the material occurs, the material being oriented,
whilst at the same time the thickness of the material is
reduced by about 3 times in the case of PET. The wall
part of the element is formed during the stretching pro-
cess.
Since the circumference of the contact surface
~ ~ 73175
_ 9 _
of the press device is smaller than the inner
circumference of the clamping devices, the
material which adjoins the edge of the press device is
subjected to the greatest stress, for which reason the
flow of the material normally starts at this point.
The effect thus resulting is ~urther reinforced by the
fact that the transition from the contact surface of the
press device to the side walls of the press device is
made relatively sharp-edged. When flow has set in,
the zone of flow of the material is gradually shifted in
the direction of the clamping devices. In certain
application examples, the press step is interrupted when
the flow zone has reached the press devices. In
other application examples, the press step continues,
renewed flowing of the material takir.g place adjoining
the edges of the press device and being displaced from
these zones towards the centre of the material. ~hen
all the material which is in contact with the contact
surface-of the press device has undergone flow, that -
material between the clamping devices which is located
next to the inner circumference of the clamping devices
is utilised for a further drawing step in certain appli-
cation examples. To make this possible, a somewhat
elevated temperature in this material is normally required.
The starting temperature, however, is still below the
glass transition temperature Tg.
- Incer~n a~plication examples, accelerated cooling
of the drawn material is necessary. In this case, the
press d~ioe is preferably provided with a cooling device
~ 73 175
-- 10 --
which is arranged in such a way that the zones of the
material, which flow during drawing of the material, are
in contact with the cooling deviceL
In certain applications~ the flow of the material
is caused to start adjoining the clamping devices.
This is accomplished by providing the clamping devices
with heating devices which raise the temperature of those
material sections where flow is to start. The tem-
perature in the ma~erial, however, is still below the
glass transiti~n temperature Tg of the material.
When flow has set in, this continues in the
direction of the contact surface of the press device
and, in some cases which may occur, it continues past
the transition from the side walls to the contact surface
of the press device. To ensure that the clamping
devices retain the blank in the future edge sections of
the element, the clamping devices are as a rule provided
with cooling devices.
The concept of the invention also comprises the
possibility that, by a number of drawing steps which are
arranged onP after the other, both in the wall part and
in the bottom p~rt of the body, material sections are
obtained which alternately consist of material sections
which have been drawn until flow sets in and have in this
way been given a reduced wall thickness, and undrawn
material sections which have retained their wall thick-
ness. In material sections located in the bottom part
of the body, a displacement of the material in the axial
direction of the body also takes place in certain appli-
',
~ ~731~S
cation examples in conjunction with the drawing step,
The edge part is removed from the element formedand the element is reshaped by a number of drawing steps.
These drawing steps take place at a temperature below the
glass transition temperature Tg and effect a reduction
of the diameter of the cup, whilst the length of the
body is extended at the same time in the axial direction
T~e drawing step effects exclusively a redistribution of
the material without flow setting in.
The cup formed after the end of the drawing step
has an opening at one end, whilst it has a bottom part
at the other end. ~epending on the manner in which the
elementhasbeen shaped, the bottom part consists wholly or
partially of amorphousmaterial orof unoriented material. In
the first-mentioned case, the bottom part thus retains
the thickness of the starting material in the amorphous
zone or in the amorphous zones. The amorphous material
is suitable for use as a fixing material for welding
additional parts to the cup. This requirement will be
present, for example, when the cup is used as a container
and the bottom part of the cup simultaneously represents
the bo'tom part.of the container. In this case9 it is
advantageous to weld an external foot to the container.
The cup shaped in the manner described possesses an
spening part which, if appropriate after reworking, is
preferably expanded in such a way that a beaded edge
results, the stability of the beaded edge being increased
by heating up to the maximum crystallisation temperature
of the material. The beaded edge is thus outstandingly
~ L~73175
-- 12 --
suitable for fitting, for example, a loose lid of a suit-
able material, for example metal, by crimping.
In another application example, the drawing step
at the cup is interrupted so that parts of the cup have
a reduced diameter compared with the initial diameter.
By removing the bottom from this part of smaller diameterJ
expanding the edge formed and stabilising the opening
which has been formed in the manner described in the pre-
ceding section, a mouth part is obtained which is suit-
able for fitting, for example, a closure or a crown cap.
The other still open part of the cup is closed, for
example, by an end disc, in a manner similar to that
already described,
In the blow-moulding process, the starting point
is either a cup which has been severed in the normal way
from the edge part of the element, or from a newly drawn
cup. By blow-moulding against warm mould walls, the
cup, the material of which is at a temperature above the
glass transition temperature Tg, is reshaped in such a
way that it has exactly the form of the intended end
product. In certain applications, a warm blowing
mandrel is used in order to prevent excessive cooling of
the material during the blow-moulding step.
It can be seen from what has been said that the
combination of drawing, until flow sets in to obtain an
element, redrawing of the cup of the element formed and
a blow-moulding step offers many optional possibilities
for the shaping of different types of articles.
An article produced in the manner described
1,
73.1~5
- 13 -
above is thus not only suitable for use as a container,
but many applications are possible.
The invention will be clescribed in more detail by
reference to a number of illustrations in which
Figures 1 - 2 show optional embodiments of bands suitable
for reshaping,
Figure 3 shows an element having a bottom part of the
body, consisting mainly of amorphous
.
material,
Figures 4 - lO show the principles of devices for drawing
of the element,
Figure ll shows a part of a device for redrawing o~
the cup of the element,
Fi~ure 12 shows the cup of the element before
. redrawing,
; Figure 13 shows the cup of the element after partial
redrawing,
Figure 14 shows the cup of the element after complete
redrawingj
. Figure 15 shows the cup o~ the element, having the
part of the cup, which was partially
redrawn, according to Figure 13, after
renewed redrawing,
Figure 16 shows a container produced from a cup
according to Figure 15~ .-
Figures 17 - 19 show the counterparts to Figures 12 - 14,
the bottom part of the cup having sections
of amorphous material and
Fi~ures20 - 22 show optional em~odiments of blow-moulded
~73~7,5
articles.
Figures 11 and 16 are on the same sheet of drawings.
Figures 1 - 2 show a band or a blank 14', 14" of
thermoplastic, the bands or blanks being seen from above.
In the figures, annular material zones 16', 16" or 17', 17"
are represented. Moreover, a material zone 15', 15" is
indicated which is surrounded by the original annular
material zone 17', 17". The material zone 16 marks that zone
which, cn drawing of the blank, is clamped in between the
clamping devices 30 a-b (see Figure 4). The material zone 15
marks that zone which, on drawing of the blank, is in contact
with the press face of the press device 20 (see Figure 4).
The material zone 17 marks that zone which, on drawing of the
blank, is brought into the state of flow.
An element 10 consisting of an edge part 12 of the
body 13 is seen in Figure 3. The body in turn consists of a
wall part 18 and a bottom part 11. In the figure, the wall
part consists of drawn material of reduced thickness compared
with the thickness of the starting material. The bottom part
11 consists of material which, while retaining its material
properties, has been displaced in the axial direction of
the body. Moreover, a zone 19 is marked in which material
belonging to the edge part 12 had been transformed into
the state of flow.
In Figures 4-8, a number of clamping devices 30
which fix the blank 14 can be seen. A press device 20
having a press face 21 is located between the clamping
devices 30. In Figure 4, the press device is in a
~ 73~75
-- 15 --
position in which -the press.face 21 is located directly
next to the upper surface of the blank 14. In Figure 5,
the press device was shifted downwards, flow of the
material.having started. In Fi~ure 6, the press
device has been shi~ted to such an extent that an element
according to Figure 3 has been formed. In Figure 7,
the press device was yet further shifted, further flow of
the material having taken place. An element 10'. has
thus been formed, the body 13' of which has a bottom part
llt the central sections of which consist of amorphous
undrawn material which is surrounded by drawn oriented
material in which flow has taken place. Finally, in
Figure 8, the press device 20 has been shifted to such
an extent that virtually the entire material in the
bottom part 11" of the body 13" has undergone flow.
An element 10" has thus been formed in which both the
wall part.and the bottom part o~ the body have a reduced
wall thickness because the material has been in the state
of flow and has-at the same time been oriented.: .
In Figures 9 - 10, an .optional embodiment of the
cla.mping devices .~3 a-b is represented, which are pro-
vided with cooling channels 31 and heating channels 34.
In.the figures, only the feedline for the heating
channels is shown, whilst the di~charge line for the
heating channels is located behind the feedline in the
figu~es and is indicated by the upward-pointing arrow.
The cooling channels, like the heating channels, are
covered by plate-like covers 35, the other surface of
which at the same time represents the contact surface of
1273175
-- 16 --
the clamping devices for clamping the blank. An
insulation 32 separates the cooled zone of the clamping
devices from the heated zone. In certain applications,
the heating channels are used as the cooling channe1s
in the same way. I
Furthermore, the figures show an optional embodi- !
ment of a press device 20a which also has cooling
channels 22. The cooling channels are covered
by a cooling jacket 23 which at the same time represents
the outer contact surface of the press device opposite
the material during the process of drawing the latter.
Figure 9 shows a position of the press device, which
corresponds to the position shown in Figure 5, and
Figure 10 shows a position of the press device, which
corresponds to the position in Figure 8. The press
device is constructed with a face of rotationally
symmetrical curvature, which is shaped in such a way that,
on drawing within the flow range, the material is always
in contact with the cooling Jacket, whilst that material
which has not yet been in the state of flow is not in
contact at any point with any device in the zone between
the press device and the clamping devices.
- Heating of the material with the ~d of the
heating channels 34 has the purpose of increasing the
readiness of the material to flow.Heating is limited, how-
ever, in such a way thatthe temperature of the material
is always lower than the glass transition temperature Tg.
Heating makes it possible to allow the drawing step of
the material to continue a little into the zone between
1273~7tj
17
the jaws of the clamping devices, as shown in Figure 10.
Another optional application, where the increased readi-
ness of the material to flow is exploited, is obtained
when, during the drawing step, the zone of initial flow
of the material is directed to the zone next to the inner
edges of the clamping devices. After flow has taken
place, the flow zone is gradually displaced in the
direction away from the clamping devices towards the
bottom of the press device, as the press device gradually
shifts downwards as in the figures.
The result of this is that ~low always propagates
in the same direction, and a new start of flow is avoided,
such as takes place when the embodiment of the invention
shown in ~igures 4 - 8 is used.
Figure 11 shows a device for redrawing
the element formed before. In the figure which shows
only a part of the device, a press plunger 40, a counter-
holder ring 41, a clamping ring 42 and a wall part 18 i~
the element are seen, the wall part being in the process
of shaping. Moreover, the bottom 11" in the body 13
of the element is seen. The clamping ring 42 is pro-
vided with a calibration device 43 which determines the
thickness o$ the material, drawn anew, in the wall
part 18.
Figure 12 shows an element body 50 which has been
formed by means of the press device 20a according to
Figure 9 and in which the edge part of the element has
been produced ~rom the body, In Figure 13, the shaping
process of the body 50 was initiated with the aid of a
7~ ~75
- 18 -
device shown in Figure 11. The shaping process has
progressed to such an extent that a mainly cylindrical
larger part, having the same diameter as the body 50, and
a shorter part 59 have been formed. In Figure 14, the
shaping process has been completed, a mainly cylindrical
body 52 of the same diameter as in the shorter part in
Figure 13 having been formed.
Figure 15 shows a body 53, the shorter part 59
of which has been reshaped with the aid 'of a dev.-.
ice shbwn in Figure ll for the purpose of further reducing
the diameter of the shorter part 59'. There is a
transition 58 between the shorter cylindrical part 59'
and the larger part of the body 53.
Figure 16 shows a bottle-like container 70~pro-
duced from a body 53 according to ~igure 15. The bottom
part of the shorter part 59' has been severed and
replaced by a closure 55, for example a cap. The
mouth edges formed on severing the bottom part were
expanded and beaded, after which the material in the
beaded material zones has preferably been givenan increased
crystallinity as a result of heating the material up to
the crystallisation temper~ture. This gives additional
strength at the moubh edge so that the latter
is well suited for closing the container, for example
by means of a cap or a crown cork. The transition,
already mentioned, between the shorter part and the larger
part of the body now forms a bottle neck 58'. The
figure also shows how an end disb 56 is fixed at the
other end of the container ?~ after the container has
~ 73 17~
-- 19 --
been filled. As a result of expanding, beading and
heating of the material, material sections are here also
obtained which are suitable, for example, for fitting
an end disc. by crimping,in order to close-the
container
Figures 17 - 19 show counterparts to Figures
12 - 14. Thefigures showhow an element body, formed from
the body 11' according to Figure 7, is subjected to an
axial lengthening, with simultaneous reduction in the dia-
meter of the body, and forms an almost completely cylin-
drical body 61, the bottom part of this body consisting
of a material section 62 of mainly amorphous material
During the shaping process, an intermediate form of the
body results, which is marked 60 in Figure 18.
In the embodiment of the invention in which a
. body is formed which comprises an amorphous bottom sectlon,.
a.material zoneisa~.obtained which is suitable as a fixing .
material for welding on additional parts ~o- the body.
By rendering the material crystalline, a zone of extreme
dimènsional stability is obtained, whereby it becomes
possible to use the container for storing liquids under
pressure, for example béverages to which carbonic acid
has been added, without a risk of deforming the bottom
part. The concept of the invention also comprises the
replacement of the plane embodiment of the bottom part by
a convex or concave face, depending on the particular
wishes which apply corresponding to the individual appli-
cations. -
Figures 20 - 22 show.optional embodiments of
1~ 73 ~75
- 20 -
blow--moulded containers. - All the containers are closed
by end discs in the manner already described in connec-
tion with Figure 16. Of course, this combination of
a blow-moulded container and an end disc is to be
regarded only as an example of the possibilities avail-
able for closure.
Figure 20 shows an embodiment in which all the
material in the blow-moulded container consists of
material previously drawn. The container is formed
from a body part either according to Figure 12 or accord-
ing to Figure 14
Figure 21 shows an embodiment of a blow-moulded
container which has been formed from a body part accord-
ing to Figure 17 or ~igure l9. On blow-moulding, the
amorphous material zone 22 remained in the amorphous
state without change, and it represents a thicker section
in the bottom part of the container. In certain
embodiments, this section is heated up to the crystal-
lisation temperature of the material in order to form
a bottom sectlon which is particularly suitable for
withstanding deformation forces, for example~forces due
to an internal pressure in the container. The amor-
phous material is also suitable for the purpose of weld-
ing additional plastic parts thereto.
Figure 22 shows an embodiment of a blow-moulded
container ~Ihich has been formed from a body part, the
bottom of the body part consisting alternately of
material sections, which have been drawn until flow sets
in, and of those material sections which have retained
1~ 73 ~75
- 21 -
their original thickness. In this way, a simple
amorphous material section 21 has been formed which is
surrounded by an annular amorphous section 72 which is
located below the central section. The central section
and the annular section are connected by material which
has been drawn urt~ flowsets in. The a~nular material
section thus forms standing surfaces for the container.
The parts forming the shell of the container are as a
rule shaped from redrawn material. ~t least in the
cases where the container has a relatively large a~ial
dimension, such redrawing is necessary.
Blow-moulding is carried out in any known manner
at a temperature of the material, which is above-the
glass transition temperature Tg. Normally, blow- -
moulding takes place against heated mould walls. In
certain illustrative embodiments, a heated elongate
blow mandrel is required in order to avoid excessive
cooling of the material during the blow-moulding step.
The material oriented by flow possesses improved
strength properties in the direction of orienting, which
is largely the same as the direction of drawing the
material Since the material has been heated to a
temperature above the glass transition temperature Tg,
there are no difficulties in a blow-moulding process
with regard to reshaping the element by stretching the
material in a direction which is mainly at right angles
to the said direction of orienting. An element reshaped
in this way forms, for example, a container having a
central shell surface of a diameter which exceeds the
` 1~7;~175
-- 22 --
diametPr of the opening, and havlng a bottom which con-
sists of a standing surface which represents the tran-
sition between the lower edge of the shell surface and
the bottom surface, the bottom surface either being
slightly concave or consisting of annular material sec-
tions which are displaced relative to one another in the
axial direction of the container.
The 2bove description merely represents examples
for the application of the invention. The invention
allows of course that a number of combinations of drawing
steps take piace, zones of drawn and undrawn materlal
also forming alternately. ~or example, the body con-
~ sists of wall parts with sections which contain undrawn
material, whilst the bottom part consists of sections,
for example annular sections, which contain undrawn
material and which are displaced in the axial direction
of -the body relative to the lower edge of the wall part.
The concept of the invention comprises manv
optional embodiments. According to one of these, drawing
until the material in the body of the element flows is
effected by a numberof successive drawing steps, the con-
tact area of the press device decreasing for each drawing
step. The result of this is t~at the width of the
material zone 15 is adapted to the extent to which the
drawing step has proceeded.
In addition to the above description, the inven-
tion is also comprised by the attached patent claims.
This application is a division of Canadian Application
No. 352,907 filed May 28, 1980~
I
1.
