U.S. patent application number 14/816257 was filed with the patent office on 2015-11-26 for foamed polyester extrusion equipment which can be used in plants for producing sheets, boards or tubes of foamed polyester.
This patent application is currently assigned to COSTRUZIONI MECCANICHE LUIGI BANDERA S.P.A.. The applicant listed for this patent is COSTRUZIONI MECCANICHE LUIGI BANDERA S.P.A.. Invention is credited to Franco Bandera, Enrico Venegoni.
Application Number | 20150336319 14/816257 |
Document ID | / |
Family ID | 41319796 |
Filed Date | 2015-11-26 |
United States Patent
Application |
20150336319 |
Kind Code |
A1 |
Bandera; Franco ; et
al. |
November 26, 2015 |
FOAMED POLYESTER EXTRUSION EQUIPMENT WHICH CAN BE USED IN PLANTS
FOR PRODUCING SHEETS, BOARDS OR TUBES OF FOAMED POLYESTER
Abstract
Foamed polyester extrusion equipment has two co-rotating screws
defining with an internal walls of an insulated frame, first
degassing zone between a feeding zone at a feeding inlet for
polyester and a first tight zone, a second degassing zone
downstream of the first degassing zone, foaming agent inlet zone
downstream of the second degassing zone and a pumping end zone for
melted material downstream of the foaming agent zone. The first
degassing zone carries out forced atmospheric degassing at lower
temperature and has a first vent stack adjacent the first tight
zone. The second degassing zone carries out vacuum degassing at a
temperature equal to or greater than the melting point of the
treated polyester material. The first degassing zone has, upstream
of the first vent stack, a nozzle for inlet of preheated nitrogen
gas to entrain vapours.
Inventors: |
Bandera; Franco; (Busto
Arsizio VA, IT) ; Venegoni; Enrico; (Busto Arsizio
VA, IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
COSTRUZIONI MECCANICHE LUIGI BANDERA S.P.A. |
Busto Arsizio VA |
|
IT |
|
|
Assignee: |
COSTRUZIONI MECCANICHE LUIGI
BANDERA S.P.A.
Busto Arsizio VA
IT
|
Family ID: |
41319796 |
Appl. No.: |
14/816257 |
Filed: |
August 3, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13142906 |
Sep 6, 2011 |
9114562 |
|
|
PCT/IB2009/007929 |
Dec 29, 2009 |
|
|
|
14816257 |
|
|
|
|
Current U.S.
Class: |
425/4C |
Current CPC
Class: |
B29C 48/405 20190201;
B29C 48/691 20190201; B29C 48/40 20190201; B29C 48/57 20190201;
B29C 48/501 20190201; B29C 48/307 20190201; B29K 2067/00 20130101;
B29C 48/767 20190201; B29K 2105/26 20130101; B29C 44/3446 20130101;
B29C 48/09 20190201; B29C 48/37 20190201; B29C 48/387 20190201;
B29C 48/08 20190201; B29C 48/55 20190201 |
International
Class: |
B29C 47/76 20060101
B29C047/76; B29C 47/00 20060101 B29C047/00; B29C 47/36 20060101
B29C047/36; B29C 44/34 20060101 B29C044/34 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 30, 2008 |
IT |
MI2008A 002348 |
Claims
1. Foamed polyester extrusion equipment comprising a thermo
regulated frame provided with a feeding inlet of pure and/or
recycled polyester material, inside of said frame two co-rotating
screws are arranged, said co-rotating screws defining with the
internal walls of said frame a first degassing zone interposed
between a feeding zone placed at said feeding inlet and a first
tight zone, a second degassing zone placed downstream from said
first degassing zone and separated from the latter through said
first tight zone, a foaming agent inlet zone placed downstream from
said second degassing zone and separated from the latter through a
second tight zone and a pumping end zone of the melted material
placed downstream from said foaming agent inlet zone, wherein: said
first degassing zone is adapted to carry out a forced atmospheric
degassing at a temperature lower than the melting point of a
treated polyester material and comprises a first vent stack placed
at a first segment of said first degassing zone adjacent to said
first tight zone, said second degassing zone is adapted to carry
out a vacuum degassing at a temperature equal to or greater than
the melting point of said treated polyester material and said first
degassing zone comprises, upstream from said first vent stack, a
nozzle for the inlet of preheated nitrogen gas into said first
degassing zone adapted to entrain vapours present in said first
zone towards the atmosphere carrying out said forced atmospheric
degassing.
2. Foamed polyester extrusion equipment according to claim 1,
wherein said first degassing zone comprises an extractor hood,
adapted to activate the draught of said first vent stack carrying
out said forced atmospheric degassing, on top of said first vent
stack.
3. Foamed polyester extrusion equipment according to claim 2
wherein said extractor hood is arranged on top of said first vent
stack.
4. Foamed polyester extrusion equipment according to claim 3,
wherein said extractor hood is arranged away from a mouth of said
first vent stack and it can be brought close to said first vent
stack in order to activate the draught of the vent stack.
5. Foamed polyester extrusion equipment according to claim 1,
wherein said second degassing zone comprises a first segment in
which a second vent stack is provided, followed by a second segment
in which a third vent stack is provided, said first and second vent
stack being connected to at least one vacuum member, wherein said
first and second segment are linked to form a single degassing
zone.
6. Foamed polyester extrusion equipment according to claim 1,
wherein downstream from said second tight zone said foaming agent
inlet zone comprises a second nozzle for the inlet of at least one
foaming agent in said treated polyester material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 13/142,906 filed Jun. 30, 2011, which was a 371
application of PCT/IB2009/007929 filed Dec. 29, 2009, both of which
are incorporated herein by reference, which claimed priority on
Italian patent application MI2008A 002348 filed Dec. 30, 2008,
which priority claim is repeated here.
FIELD OF THE INVENTION
[0002] The present invention refers to a foamed polyester extrusion
equipment.
SUMMARY OF THE INVENTION
[0003] In particular, the equipment according to the present
invention can be used in plants for producing sheets, boards or
tubes of foamed polyester, preferably of the type operating
continuously. In the field of foamed polymer extrusion, plants for
producing sheets or boards of foamed synthetic thermoplastic
polymers, such as PS, PE, PP and PU are more common than plants
used for the extrusion of foamed polyester.
[0004] This is due to the fact that the aforementioned synthetic
thermoplastic polymers are materials which are characterised by a
high melt strength and are very hydrophobic and thus do not undergo
hydrolysis. They are thus able to maintain a sufficiently high
absolute viscosity and a high melt strength which make it possible
to obtain high quality foamed products and properties which are
suitable for the final use in the industrial fields of packaging,
coating and so on. In particular, the high absolute viscosity and
the high melt strength ensure that the gas bubbles, which are
formed during the foaming step of the extrusion process, when the
material is still melted, remain trapped in it without them
breaking and consequently releasing gas.
[0005] Contrarily, since polyester is a highly hygroscopic material
and since it is subject to strong hydrolysis, it has, if not
appropriately dehumidified before the extrusion process, viscosity
and melt strength properties which are insufficient in order to
obtain a foamed final product having a high enough quality.
[0006] This is due to the fact that in the case in which there is
humidity, during the extrusion process, and in particular when the
material is in molten state, a strong hydrolysis takes place which
causes the material to degrade by reducing the mechanical
properties of the polyester, and in particular, the intrinsic
viscosity, the absolute viscosity and the melt strength.
[0007] Such a phenomenon is particularly noticeable in the case in
which post-consumption recycled materials or recycled industrial
scrap and foamed or non foamed thermoforming residue, co-extruded
with non foamed polyester or laminated with films of various
thermoplastic materials, are used, which have low intrinsic and
absolute viscosity and a particularly high initial humidity
level.
[0008] In order to avoid such a phenomenon, it is known to make the
polyester undergo advance drying, with the purpose of eliminating
the humidity incorporated inside and outside of each granule, up to
20 parts per million. However, such a procedure is costly and
obtains modest results.
[0009] Also equipment for the extrusion of foamed polyester is
known which does not require the material to undergo the
preliminary drying step.
[0010] Such equipment is generally made up of a twin co-rotating
screw extruder connected in series to a single screw extruder, in
which the twin screw extruder has the purpose of melting and mixing
the pure and/or recycled polyester with some additives adapted to
increase the molecular weight, and thus the viscosity and the melt
strength of the polyester, and to take as much humidity as possible
away from the melted material, whereas in the single screw
extruder, the injection of the foaming agents, their mixing with
the melted material as well as a moderate cooling of the material
before the extrusion, take place. The known equipment has the
drawback of obtaining a final product having low quality due to
there being no advance drying and because the humidity is only
taken away when the material is already melted.
[0011] Moreover, the plant comprising both a twin screw extruder,
as well as a single screw extruder causes there to be a substantial
complexity with high plant costs, as well as higher energy
consumption, maintenance costs and so on.
[0012] The purpose of the present invention is that of avoiding the
aforementioned drawbacks and in particular that of conceiving a
piece of foamed polyester extrusion equipment which is able to
offer a high quality final product without requiring long and
costly preventive drying processes.
[0013] Another purpose of the present invention is that of
providing a piece of foamed polyester extrusion equipment which
offers optimal extrusion results whilst maintaining a generally
simple structure and eliminating the need for a single screw
extruder placed in series.
[0014] These and other purposes according to the present invention
are reached by making foamed polyester extrusion equipment as
outlined in the independent claim.
[0015] Further characteristics of the foamed polyester extrusion
equipment are object of the dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The characteristics and the advantages of the foamed
polyester extrusion equipment according to the present invention
shall become clearer from the following description, given as an
example and not for limiting purposes, with reference to the
attached schematic drawings in which:
[0017] FIG. 1 is a top schematic view and partially, in section of
a piece of foamed polyester extrusion equipment according to the
present invention;
[0018] FIG. 2 is a top view of a plant for producing sheets, boards
or tubes of foamed polyester using the extrusion equipment
according to the present invention;
[0019] FIG. 3a is a schematic representation of a first product
which can be obtained with the foamed polyester extrusion equipment
and process according to the present invention;
[0020] FIG. 3b is a schematic representation of a second product
which can be obtained with the foamed polyester extrusion equipment
and process according to the present invention; and
[0021] FIG. 4 is an enlarged view of a detail of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] With reference to the figures, a piece of foamed polyester
extrusion equipment is shown, wholly indicated with reference
numeral 10.
[0023] Such equipment 10 for the extrusion of foamed polyester,
hereafter in brief also called foamed polyester extruder, is used
in a plant 100 for producing the sheet, board or tube in foamed
polyester which also comprises, downstream from the foamed
polyester extruder 10, a filter changer 30, a geared pump 40, a
layering device 50, an extruder head 60, as well as a calender 70
for cooling and forming the sheet, the board or tube.
[0024] The extruder 10 for foamed polyester according to the
present invention comprises a thermoregulated frame 11, for example
using oil, inside which two co-rotating screws 12 are arranged,
i.e., rotating in the same rotation direction, fed through a
feeding inlet 14. Preferably, the co-rotating screws 12 are of the
parallel intermeshing self-cleaning type and have an L/D ratio
(length over diameter) preferably of between 35 and 55, and more
preferably from 42 to 52.
[0025] The dosing of the polyester material is carried out by means
of a plurality of gravimetric metering devices 80, which feed a
feeding inlet 14 of the foamed polyester extruder 10, by
gravity.
[0026] The fed polyester material can be entirely made up of pure
material, it can be a mixture of pure material and recycled
material, or it can entirely be recycled material.
[0027] In the case in which recycled material is used, it is
generally polyester, in particular polyethylene terephthalate
(PET), in flakes from the mechanic recycling of post-consumption
bottles or from the grinding of industrial scrap and thermoforming
residue. The mixture generally contains foamed or non foamed
material, or even material from the grinding of laminated
products.
[0028] The types of mechanically recycled polyester material more
frequently used are PET and PET copolymers containing moderate
percentages of isophthalic acid, dietilenglicol,
cyclohexanedimethanol (CHDM) and similar or polylactide (PLA) or
polylactide copolymers. The dosage is very important since not only
does it define the capacity of the production plant 100, but also
the geometry of the screws 12 and their speed, the filling level of
the screws 12 themselves in the degassing and foaming agent inlet
zones of the foamed polyester extruder 10.
[0029] The feeding is preferably carried out in a way such as to
obtain some screws 12 with an "open throat", i.e., not completely
full of material.
[0030] In general, in addition to the gravimetric metering devices
80 which feed the foamed polyester, additional metering devices are
foreseen for feeding solid additives or compounds thereof.
[0031] In general, the additives comprise chain extenders or
crosslinking agents, like tetracarboxylic acid anhydrides,
preferably piromellitic dianhydride (PMDA) or tri- or
tetracarboxylic acids, and are used in percentages from 0.1% to
about 3%, preferably from 0.1% to 0.5%, on the fed polyester.
[0032] Generally the tri- or tetracarboxylic crosslinking agents
are used together with metal salts of the Groups I, II and III of
the periodic table of the elements, in particular sodium and
calcium carbonates, in a percentage which is similar to that of the
crosslinking agent.
[0033] It is moreover possible to add nucleating agents and
stabilizers of the cells of foamed material, like for example talc,
to the fed polyester material. Other additives that can be fed by
the gravimetric metering devices 80, are colouring agents,
antiflame agents or fillers or mineral fillers like calcium
carbonate and so on.
[0034] Otherwise, polyester compounds already comprising some of
such solid additives are fed to the foamed polyester extruder 10,
again through the gravimetric metering devices 80.
[0035] The fed material is treated between the two screws 12 so as
to be made advance inside the extruder 10.
[0036] The structure of the screws 12 is such as to define, with
the internal walls of the frame 11, two degassing zones separated
from one another by a first tight zone 15, for example, made
through a combination of cams or possibly through one or more
reverse threads.
[0037] In a first degassing zone A,B arranged between the feeding
inlet 14 and the first tight zone 15 the initial heating, of the
polyester material fed up to a temperature lower than its melting
point, and an atmospheric degassing, takes place.
[0038] In a second degassing zone C,D arranged between the first
tight zone 15 and a second tight zone 22 which separates it from a
zone E in which the foaming agents are introduced, a vacuum
degassing takes place at temperatures higher than or equal to the
melting point of the treated polyester material.
[0039] According to the present invention, the first degassing zone
A,B is made in such a manner, that in it, a forced atmospheric
degassing takes place whereas the temperature to which the material
is brought is kept lower than the melting point of the polyester in
order to keep the material in a solid state or at the maximum
sintered.
[0040] For such a purpose, the atmospheric degassing zone A,B is
for example provided with an extractor hood 19 arranged on top of a
first vent stack 13 for the discharge of gas.
[0041] The extractor hood 19 is arranged away from the mouth of the
first vent stack 13 and it can preferably be brought close to it in
order to activate the draught of the vent stack.
[0042] The depression exerted by the extractor hood 19 is such as
to have on the not yet melted material a pressure which is
substantially comparable to atmospheric pressure so that there is
not a removal of the still solid material.
[0043] The first vent stack 13 is constructed so that it promotes
the draught through a suitable profile of its section which
slightly but gradually decreases from the bottom upwards.
[0044] Advantageously, such a first vent stack 13 is positioned
near to the tight zone 15, and in particular at a first segment B
of the atmospheric degassing zone A,B adjacent to the tight zone
15, in which the releasing speed of the water vapours and of
volatile substances is greater, since, in such a first segment B,
the temperature of the material is kept at a level of around
10.degree. C. lower than the melting point of the treated
material.
[0045] By means of the forced atmospheric degassing a large amount
of the humidity of the polyester material fed into the extruder 10
is taken away without preventive drying, as well as a large amount
of the pollutants which often come with recycled material.
[0046] In this way the hydrolysis of the polyester material, which
would otherwise be very high once reached the melting point of the
polyester and higher temperatures, is minimised.
[0047] In addition or as an alternative to the provision of the
extractor hood 19, the Applicant has found during the development
of the forced atmospheric degassing that the effectiveness of such
a degassing, in terms of hydrolysis and yellowing of the material
containment, substantially increases by introducing a stream of
preheated nitrogen gas into a second segment A of the first
degassing zone A,B interposed between the feeding zone, placed at
the feeding inlet 14, and the first segment B of the first
degassing zone A,B placed at the first vent stack 13.
[0048] Such a flow of preheated nitrogen has an entrainment action
on the vapours towards the first vent stack 13 which, in such a
way, takes away even more of the humidity from the polyester
material entraining it out through the first vent stack 13.
[0049] The flow rate of the nitrogen gas is regulated through a
first flow regulation device 16.
[0050] For such a purpose, at the second segment A of the
atmospheric degassing zone A,B, thus interposed between the feeding
inlet 14 and the first vent stack 13, a first nozzle 18 for the
inlet of nitrogen gas is preferably foreseen.
[0051] Before entering into the foamed polyester extruder 10, the
nitrogen gas is heated by means of a heater 17 and subsequently
introduced through such a first nozzle 18. The flow rate of the
flow of nitrogen gas introduced is of between 200 l/h and 1500 l/h,
and preferably between 200 l/h and 800 l/h wherein the flow rate is
measured when the gas is at room temperature. At the first tight
zone 15 most of the melting of the material takes place.
[0052] The series of cams and/or the possible reverse threads of
the screws 12 are full of melted material, so as to obtain the gas
tight seal between the first degassing zone A,B in which the
heating of the solid and the forced atmospheric degassing of the
not yet melted material take place, and the second degassing zone
C,D downstream from the first tight zone 15 and upstream from the
second tight zone 22, in which the material completes the melting
and undergoes a vacuum degassing while it mixes and reacts with the
chain extender and crosslinking agents.
[0053] Preferably, the vacuum degassing takes place at a residual
pressure lower than or equal to 10 mbar. Taking away the water
vapours promotes the chain extender and crosslinking reactions in
the melted polyester polymer.
[0054] In the example case of PET, in the second degassing zone C,D
downstream from the first tight zone 15, the polyester is
preferably kept at temperatures of between 280.degree. C.
295.degree. C., and preferably equal to 290.degree. C., with a
relatively low level of material in the screws 12 and a high
rotation speed of the latter.
[0055] Preferably, the level of material in the screws 12 in the
vacuum degassing zone C, D is of between 40%/60%, and preferably
equal to 50%. Moreover, the rotation speed of the screws 12 is
preferably of between 200 rpm and 350 rpm, and more preferably of
between 250 rpm/300 rpm.
[0056] The equipment 10 for the extrusion of foamed polyester
according to the present invention is thus able, in the case of
PET, to obtain a measurement of the final intrinsic viscosity of
the material having values of between 0.9 dl/g and 1.8 dl/g.
[0057] The vacuum degassing is carried out in the second degassing
zone C, D. For such a purpose, the second degassing zone C, D has a
first segment C in which a second vent stack 20 is provided,
followed closely by a further segment D in which a third vent stack
21 is provided preferably connected independently to its vacuum
member (not illustrated).
[0058] Such vent stacks 20, 21 define a tandem vacuum degassing
since the sections C and D of the second degassing zone are not
separated from one another by any tight zone. Such an arrangement
makes it possible to have a large vacuum degassing zone and thus a
greater surface for the gas to be exchanged with the treated
polyester material.
[0059] Moreover, the absence of intermediate tight zones between
the sections C and D, intended for the vacuum degassing of the
melted material, avoids the thermal degradation of the material due
to local over-heating and amplifies the total length of the vacuum
degassing zone obtaining in such a way a material having an overall
higher final intrinsic viscosity.
[0060] The distance between the second 20 and the third 21 vent
stack is preferably of between 8/15 diameters, and more preferably
between 10/12 diameters.
[0061] The ratio L/D (length over diameter) of the vacuum degassing
zone C,D, from the first tight zone 15 to the second tight zone 22,
is preferably between 20/33, and more preferably between 25/30.
[0062] The second tight zone 22 is preferably obtained
by--inserting two reverse threads on the screws, so as to make the
level of melted material rise locally until the screws 12
themselves are filled.
[0063] In this way gas interaction between the second vacuum
degassing zone C, D placed upstream from the second tight zone 22
and the foaming agent inlet zone E downstream from the latter 22,
is avoided.
[0064] The foaming agent inlet zone E placed downstream from the
second tight zone 22 has a second nozzle 23 for introducing, in
contact with the melted material, a foaming agent, preferably
nitrogen gas.
[0065] In the case of nitrogen gas, the gas pressure inside the
foaming agent inlet zone E is kept stable at values from 8 bar to
40 bar, preferably from 20 bar to 30 bar, by means of a second flow
regulation device 24.
[0066] In these conditions, with a temperature of the melted
polyester material, in the example case of PET, between 280.degree.
C. and 290.degree. C., the absorption of nitrogen gas is equal to
about 0.2%/0.3% by weight with respect to the polyester flow
rate.
[0067] Other inert gases can be used as foaming agents, in
particular carbon dioxide or also other agents foaming from liquids
which are easily vaporized, measured by means of a volumetric pump,
for example hydrocarbons like hexane or aliphatic and aromatic
hydrocarbons or also liquefied carbon dioxide.
[0068] The pumping end zone F of the extruder 10 is characterised
by a very close pitch thread that promotes a progressive increase
in the level of melted polymer in the screws 12 until they have
been filled completely to be able to create the pressure necessary
for the material to be discharged for its filtration through the
filter changer 30.
[0069] Downstream from the filter changer 30 the material is fed to
a gear pump 40, which provides the pressure necessary for the final
extrusion through the layering device 50 and the extruder head
60.
[0070] At the outlet from the extruder head 60 the foaming of the
material and the formation of the sheet take place through the
calender chill roll stack 70.
[0071] In the illustrated embodiment, a flat head is indicated as
an extruder head 60.
[0072] However, the head 60 can also be of the annular type,
allowing a particularly effective type of cooling of the sheet.
[0073] The final product 90 can be made up of a mono-layer sheet
91, as schematised in FIG. 3a, or multilayer, as illustrated in
FIG. 3b in which a structure 90' is represented with three layers
in which the layer of foamed material 91 is part of a sandwich
structure with two outer layers 92 of material compatible with the
foamed material 91 itself.
[0074] The multilayer structure 90' can be obtained through
co-extrusion of the foamed material 91 with non foamed compatible
materials fed into the layering device 50 by independent extruders
(not illustrated). In FIG. 4 the introduction into the layering
device of non foamed compatible material is represented with the
reference numeral 25.
[0075] The lamination of the layer 91 of foamed polyester with
suitable films 92, for example with polyethylene and/or other
materials like for example tie-resins, is a method used to obtain
structures in which the layer of foamed polyester 91 is covered on
one or both sides of the non foamed material 92.
[0076] This type of lamination can be carried out during the
calendering step of the foamed material or in outlet from the
calender 70 or, completely separately, with or without the use of
gluing compatibilizing agents.
[0077] The extrusion process of foamed polyester according to the
present invention thus comprises the following steps.
[0078] Initially, a step of forced atmospheric degassing of the non
pre-dried polyester material at a temperature lower than the
melting point of such treated polyester material, takes place in an
atmospheric degassing zone A, B.
[0079] In particular, the temperature of the polyester material
during the atmospheric degassing step remains at least 10.degree.
C. lower than its melting point.
[0080] The step of forced atmospheric degassing takes place for
example, through an activation step of the draught of the first
vent stack 13 placed at the atmospheric degassing zone A, B.
[0081] The activation of the draught of the first vent stack 13 can
be carried out by bringing an extractor hood 19 close to the inlet
of the first vent stack 13, said extractor hood 19 being positioned
on top of the same first vent stack 13.
[0082] Preferably, the step of forced atmospheric degassing can in
addition or as an alternative be carried out through the
introduction of a flow of preheated nitrogen gas for the
entrainment of the vapours towards the atmosphere.
[0083] In such a case, the preheated nitrogen gas is introduced
with a flow rate d of between 200 l/h and 1500 l/h, and preferably
between 200 l/h and 800 l/h wherein the flow rate is measured when
the gas is at room temperature.
[0084] Subsequently the melting of the polyester material and a
step of vacuum degassing of the melted material in a vacuum
degassing zone C, D, comprising at least two degassing vent stacks
20, 21 connected to at least one vacuum member take place, the
vacuum degassing zone C, D being arranged downstream from the
atmospheric degassing zone A, B and sealingly separated from the
latter A, B.
[0085] Subsequently, a step of measuring the foaming agent and its
mixing with the melted polyester material takes place in a foaming
agent inlet zone E placed downstream from the vacuum degassing zone
C, D and sealingly separated from the latter C, D.
[0086] The foaming agent is preferably nitrogen gas and is
introduced in contact with the melted material with a pressure kept
stable at values from 8 bar to 40 bar, and preferably from 20 bar
to 30 bar.
[0087] Finally, the feeding of the polyester material to a filter
and to a gear pump take place in order to generate the pressure
necessary for the final extrusion through the layering device 50
and the extruder head 60, and the foaming of the material at the
outlet of the extruder head 60 as well as the forming of the sheet
through the calender chill roll stack 70.
[0088] From the description carried out the characteristics of the
equipment object of the present invention should be clear just as
the relative advantages should also be clear.
[0089] Thanks to the particular construction of the foamed
polyester extrusion equipment according to the present invention it
is possible to obtain excellent quality end products even from
recycled post-consumption materials without needing to previously
dry the material to be treated whilst keeping the complete
structure of the extruder simple.
[0090] Indeed, the forced atmospheric degassing eliminates a large
amount of the water molecules present in the material before its
melting takes place and thus before the hydrolysis reaction takes
place at a particularly high speed.
[0091] In addition, the particular configuration of the vacuum
degassing zone makes it possible to reduce the thermal degradation
suffered by the material while passing in the extruder, as well as
to optimise the mixing and the rapid reaction with the
chain-extender and crosslinking agents.
[0092] Overall, a material is obtained, having a greater intrinsic
and absolute viscosity and a higher degree of melt strength that is
able to keep the bubbles of gas, which are formed during the
foaming step, trapped inside the material still melted without them
breaking and consequently releasing gas.
[0093] Finally, it should be clear, that the equipment thus
conceived can undergo numerous modifications and variants, all
covered by the invention; moreover, all the details can be replaced
by technically equivalent elements. In practice the materials used,
as well as the sizes, can be any according to the technical
requirements.
* * * * *