Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
- This invention relates to a method and a device
for manufacturing containers from plastic material by means of
a hollow mould, which comprises subjecting a heated mass of
plastic material in a softened deformabLe condition to an
external pressure greater than that between the material and the
interior surface of the moula.
A method by which a foil is softened by heating
and deformed by deep drawing or by a mechanical process is
- known per se from the art.
This known method has the drawback that deformation
of a moulded plastic article, starting from a mass of plastic
material, can only be effected within a small range of
temperature. The temperature at which the formation of the
plastic article is effected is so low that the homogeneity -
and the distribution of temperature in the article is often not
satisfactory. In order to improve this homogeneity and --
distribution of temperature extra provisions would be required,
which however, involve extra costs.
The invention aims to provide a method whereby
the aforementioned drawbacks are obviated to a considerable
extent. `
According to the invention a method of manufacturing
containers of plastic materials in a hollow mould open at one
end by subjecting the heated plastic layer which is in softened
deformable condition to a pressure greater than that between the
layer and the interior surface of the mould so as to cause the
layer to conform to the surface, and attaching a layer of
the plastic material to a supporting surface that presents
the material to the open end of the mould, sealing a
circumferential part of the layer to the mould around the
open end thereof and introducing a forming medium between the
supporting surface and the layer so that the layer is pressed
away from the supporting surface and conforms to the interior
~ ~ .
. .
'' ~ Lq~.9
- surface of the mould.
When applying this procedure deformation may be
! effected at higher temperatures than those of known procedures, -
j while homogeneity in the final product is also improved.
There is, as a matter of fact a very important
difference between the method according to the invention and
known methods, in which known methods, a heated plastic layer
, is pressed into a mould. In the latter case the plastic layer
j is drawn from the center to adapt the layer to the walls of the
mould. On performing the aforesaid method according to the
invention deformation is~, however, effected more gradually, as
the center of the layer of plastic material used for deformation,
is`still retained by the supporting surface when the material ;
between the retained portion and the circumferential part of
the layer sealed to the mould is already loose with respect to
this supporting surface and is subjected to a deformation due to
an external overpressure. In carrying out the method of the
invention the plastic material is subjected gradually from the
circumference to~ards the center, to the forces produced in
deforming the la~er, contrary to the known methods wherein -
deformation begins in the centre, whereby a totally different
distribution of forces is produced in the plastic layer. `
At the high temperature of which moulding is
effected and owing to the fact that the inner side of the layer
contacting the supportlng surface is hotter than the outer
side, the inner side of the container moulded from that layer
will be very smooth due to the high surface energy.
Advantageously the plastic layer is caused to
adhere to a supporting surface by applying pulverulent
synthe-tic material to the support and to heat this mass so that
it fuses together, in order to obtain a surface devoid of pores
on the side of the layer contacting the support.
--2-- ::
r~ :
. ~ , . . .
~ ~ .! , ' , . ', .,., i . ' '
,1~ ,! ~
~` ' .
The layer of plastic material may consist of
superposed layers of plastic materials, which are mutually -~
independent, while the dimensions o:E each layer and the degree
of fusion mutually differ and whereby, if desired, a layer is
constructed from independent parts, the composition of which
mutually differ.
The invention relates likewise to a device for
performing the method according to the invention comprising a
hollow mould open at one end, a support presenting a supporting
surface towards the open end of the mould and mounted for
movement towards and away from the open end while having a
heated deformable layer of plastic material adhering thereto,
means for causing the layer of plastic material to adhere to
the mould so as to be sealed thereto round the open end of the
mould, and means for supplying a forming medium between the
layer and the support while maintaining a pressure difference
between the medium and the interior of the mould to cause the
layer to conform to the inner surface of the mould. The forming
medium may be supplied from an annular chamber sealed to the
exterior of the mould and to the support, the annular chamber
being provided with an inlet and/or outlet for the forming
medium and the arrangement being such that the medium acts
between the said supporting surface and the plastic material so as
to separate the material from the support.
The invention is hereinafter clarified with
, .
;~ reference to examples of the invention shown in the accompanying
drawings, in which:-
Figures 1 to 4 represent four situations during
the formation of a plastic container by means of a device, only
one side of which is shown in cross-section;
Figures 5-8 show our phases of the formation of
a ~astic container by means of another device;
-3-
, .
Figures 9-13 show five different ways of applying
(by means of a mould) material to a support; and
Figures 14-17 show four different ways of applying ~-
various layers of m~terial.
:' ! ,
Figure 18 is a sectional eIevation of a third
device. -~
In Figures 1 to 8 are represented a hollow deep ;~
drawing mould l open at one end, support 2, the interior space 3
of the mould, a recess 4 in the upper edge of the mould, a -
flexible annular connection 5, a guide pin 6 and a plastic
layer 7. A cooling ring 8 is situated in a supporting plate 9
for the support 2. Around the pin 6 is a spring 10. A suction
i .~,, , ~ .,
channel 11 is shown in Figure 3.
Figures 9 to 11 show three ways of applying material
to the support 2 by means of a mould, the plastic layers 7
having different diameters.
Superposed layers may be applied consecutively
to the supporting surface of the support 2. Alternatively
juxtaposed layers may be appliedO A central- layer can for
example consist of polyethylene with a pigment, whereas two .
outer circumferential layers consist of colourless polyethylene.
Figures 14 to 17 show some results obtained in
applying layers when more ways of applying layers as shown in
Figures 9 to 13, are combined.
Figure 14 shows the result when consecutive .
layers are applied as shown in Fig. 9 and 10, the central layer
having a composition different from that of the two other
layers. The central layer can for example consist of poly-
ethylene with a pigment, whereas the two outer layers consist
of col~urless polyethylene.
Figure 15 represents two layers formed according
to the way of Figures 9 and 11 and Figure 16 shows~two layers
formed as a combination of the application method shown in
-4-
9 and 13.
Figure 18 shows another embodiment of device
according to the invention. This device corresponds
substantially with that as represented in Figures 5 to 8. To
~- the device a mobile piston 12 with a resilient rim 13 is added,
which presses against the wall of the mould. In the wall a
pocket 14 is provided with an inlet and outlet. At the lower
end of the mould is an inlet or outlet 15 for fluid.
In performing the method one proceeds as follows:
At or above fusion temperature firstly one or more
layers of pulverulent plastic material, e.g. polyethylene or
polypropylene are applied to the support, heated a temperature
; ranging from 200 to 400C~, according to any of the embodiments
as represented in Figures 9 to 13. The layers may be
differently composed and coloured, they may also have different
shapes e.g. circular, square or stap-shaped. The pulverulent
material can be deposited by means of a fluid bed technique
. or by electrostatic deposition, but it is also possible to apply
the plastic material as a suspension or solution or even as a
film.
~ Thereupon support 2 is brought over the mould 1
; (Figure 1 and S) and closed in an air-tight manner by the
flexible connection 5. The plastic layer on the support has a
temperature such that the plastic layer in contact with the
surface of the support is melted and is devoid of pores. This
temperature which is considerably above the melting point
amounts to e.g. 300C for polyethylene, the melting point of
which is 180C. The support 2 is thereupon applied against the
mould (Figure 2 and 6) whereupon the plastic layer 7 is cooled
down at the location of the upper edge of the mould 1 by means
of the cooling ring 80 Thereafter the support 2 and the upper
edge of the mould are moved apart (see Figures 3 and 7) whereby
a circumferential part of the plastic layer still adheres to the
-5-
J
.~ lg
~ edge of the mould in the recess 4. By exerting pressure in
the annular chamber formed by the flexible connection 5, the - `
support 2 and the` plastic layer and by creating a vacuum in
the interior 3 of the mould (via suction channel 11) the still
; more or less liquid, or plastic layer will be pressed into
the mould and cover the wall of the mould 1, as shown in
Figures 4 and 8. The annular chamber formed by the flexible
connection 5 is providea with an inlet and, if required, an
outlet for fluid.
- 10 Thus a plastic container can be formed in a simple
manner, for instance in one second. The support 2 can be
constructed flat, (Figures 5 to 8). It is also possible to
construct the support as depicted in Figures l to 4. The
support 2 has then already for the greater part the desired
shape (first shape) of the container and after removing the
plastic layer 7 from the support 2, only a slight deformation
; of the plastic layer will be necessary. -~
In Figure 18 a different construction of the
device is represented. Here a flat support 2 is positioned over
20 a mould 1 with a movable piston-shaped bottom 13. First the
plastic layer 7 is caused to adhere to the edge of the mould,
as described hereinbefore or by means of a ring clamping the
upper edge, thereupon the layer is loosened from the support by
means of air pressure (e.g. an overpressure ranging from 0.5 to
3 atmospheres) and subsequently pressed into the mould. The
container takes its final configuration when the piston is
moved downwards. The temperature of the mould is then maintained
at a value ranging e.g. from 160 to 170 for polyethylene by
- causing heated liquid to flow through the pocket 14.
During the downward movement of the piston 12, the
heat`ed ~liquid can be replaced with cooling liquid whereby a
forced cooling is achieved. By adding cooling oil, the
article in its first shape is cooled down to lO to 15 degrees
6-
. ~ ~
7~
below the crystalline fusion point, whereupon the article in
its first shape is drawn deep by means of overpressure until
a final configuration is imparted thereto, the area of which is
up to twice as large as the area of thb starting shape prior to
drawing which drawing process can also be e-Efected at a next
moulding station.
An inlet and/or outlet 15 for the medium can
facilitate the reciprocation of the piston.
The piston may be constructed with a resilient
rim 13 which may be pressed against the tapering wall by means
of fluid pressure. Consequently the plastic layer will remain
on top of the piston and not flow down around the piston.
The support may be manufactured from e.g. metal,
synthetic material or metal with a plastic coating. The centre
of the support may be arranged to be cooled.
Since the plastic layers, when the same still
contacts the support, will be hotter on its inner - than its
outer side, the inner side in this case being that side of the
plastic layers contacting ~he support, the inner side will be
hotter when the layer is pressed into the- mould, so that a
~` well shaped inner side is obtained. The mould being cooled, the
container cools down rapidly, resulting in less loss of time
for solidifying. As one starts by thoroughly heating the plastic
layers on the support, the result will be that the said layer
for moulding any articles (containers) is properly and homogen-
eously distributed, at the same time being free from stresses.
Arbitrary pressures can be selected for removing
the plastic material from the support, by a pressure ranging
from 0.5 to 3 atmospheres is preferableO The plastic layer
has e.g. a thickness ranging from 0.5 to 3 mm. For the process
of deformation, the temperature of the support preferably
ranges from 260 to 300C.
-7-
' ~:
