U.S. patent application number 13/768385 was filed with the patent office on 2013-08-29 for extensional flow heat exchanger for polymer melts.
This patent application is currently assigned to ARMACELL ENTERPRISE GMBH. The applicant listed for this patent is Armacell Enterprise GmbH. Invention is credited to Frederic GAUDER, Mika MELLER.
Application Number | 20130225710 13/768385 |
Document ID | / |
Family ID | 45656049 |
Filed Date | 2013-08-29 |
United States Patent
Application |
20130225710 |
Kind Code |
A1 |
MELLER; Mika ; et
al. |
August 29, 2013 |
EXTENSIONAL FLOW HEAT EXCHANGER FOR POLYMER MELTS
Abstract
An extensional flow static heat exchanger with at least two
components of tubular cooling elements arranged in a flow passage,
wherein the components are successively arranged in the flowing
direction, each component having a first and a second set of at
least two cooling elements, the cooling elements of the first set
being angularly offset to the cooling elements of the second set,
the cross sections of the cooling elements have a convex profile on
the upstream and downstream side or a droplet shape, the cooling
elements of the first and the second set, respectively of the
adjacent component are arranged at least partially in the space
between two cooling elements of the first and second set,
respectively of the previous component, a process for producing a
low density extruded thermoplastic foam material and a low density
extruded thermoplastic foam material.
Inventors: |
MELLER; Mika; (Jarvenpaa,
FI) ; GAUDER; Frederic; (Verviers, BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Armacell Enterprise GmbH; |
|
|
US |
|
|
Assignee: |
ARMACELL ENTERPRISE GMBH
Muenster
DE
|
Family ID: |
45656049 |
Appl. No.: |
13/768385 |
Filed: |
February 15, 2013 |
Current U.S.
Class: |
521/182 ;
165/104.19 |
Current CPC
Class: |
F28D 7/1623 20130101;
B29C 44/3419 20130101; F28D 7/0058 20130101; F28F 1/00
20130101 |
Class at
Publication: |
521/182 ;
165/104.19 |
International
Class: |
F28F 1/00 20060101
F28F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 17, 2012 |
EP |
12155955.3 |
Claims
1. An extensional flow static heat exchanger (10) with at least two
components (20) of tubular cooling elements (25) arranged in a flow
passage adapted to be flown through by a flow medium in a flowing
direction, characterized in that the components (20) are
successively arranged in the flowing direction, each component (20)
comprises a first set (21) and a second set (22) of at least two
cooling elements (25), wherein each cooling element comprises at
least two cooling tubes, the cooling elements (25) of the first
(21) and the second set (22) are spaced substantially parallel to
each other in a plane running substantially perpendicularly to the
flowing direction, the cooling elements (25) of the first set (21)
being angularly offset to the cooling elements of the second set
(22) with respect to the longitudinal axis of the flow passage, and
the cross sections of the cooling elements (25) have a convex
profile on the upstream and downstream side with regard to the flow
direction or a droplet shape, the cooling elements (25) of the
first set (21) of the adjacent component (21b) are arranged at
least partially in the space between two cooling elements (25) of
the first set (21) of the previous component (21a), and the cooling
elements (25) of the second set (22) of the adjacent component
(22b) are arranged at least partially in the space between two
cooling elements (25) of the second set (22) of the previous
component (22a).
2. The extensional flow static heat exchanger (10) according to
claim 1, wherein the cooling elements (25) of the first set (21)
are positioned in a 90.degree..+-.5.degree. angle to the cooling
elements (25) of the second set (22).
3. The extensional flow static heat exchanger (10) according to
claim 1, wherein the first set (21) of cooling elements (25) are
arranged in a distance to the second set (22) of cooling elements
(25) of not less than 50% and not more than 200% in reference to
the diameter of one tube of a cooling elements (25).
4. The extensional flow static heat exchanger (10) according to
claim 1, wherein the tubes of the cooling element (25) are arranged
with a distance of not less than 0.5 cm and not more than 6 cm.
5. The extensional flow static heat exchanger (10) according to
claim 1, wherein a vacuum area is positioned downstream after the
exchanger (10) exit.
6. The extensional flow static heat exchanger (10) according to
claim 1, wherein the cooling elements (25) of the first (21) and
second (22) set of the adjacent component (21b, 22b) are arranged
tessellated to the cooling elements (25) of the first (21) and the
second (22) set of the previous component (21a, 22a).
7. A process for producing low density extruded thermoplastic foam
material wherein a polymer-gas mixture is fed into an extensional
flow static heat exchanger (10) according to claim 1.
8. The process according to claim 7, wherein the polymer material
is a thermoplastic material, virgin or recycled, or a mixture or
blend of any of them.
9. The process according to claim 7, wherein the polymer-gas
mixture further includes at least one of nucleating agent(s), flame
retardant(s), or elastomeric impact modifier(s).
10. The process according to claim 7, wherein the cooling elements
(25) of the extensional flow static heat exchanger (10) are cooled
down to a temperature not more than 10.degree. C. above the
solidification point of the polymer-gas mixture.
11. The process according to claim 7, wherein the polymer material
is PET, PBT, PC, PEEK, PEI, PMI, PMMA, PS, PVC or PA, or a mixture
or blend of any of them.
12. The process according to claim 7, wherein at least 75% of the
polymer material is PET.
13. The process according to claim 12, wherein the PET material
comprises at least 70% recycled, post-consumer PET (r-PET).
14. The process according to claim 12, wherein the cooling elements
(25) of the extensional flow static heat exchanger (10) are cooled
down to a temperature between 265.degree. and 285.degree. C.
15. A low density extruded thermoplastic foam material with a
density between 12 kg/m.sup.3 to 50 kg/m.sup.3 according to ISO
845, which is obtainable by the process according to claim 7.
16. The low density extruded thermoplastic foam material according
to claim 15 with a density between 12 to 50 kg/m.sup.3, which is
obtainable by reactive extrusion of PET resin.
17. A foamed article manufactured from a material according to
claim 15.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to European Patent
Application No. 12155955.3 filed Feb. 17, 2012, which is
incorporated herein in its entirety.
[0002] The invention refers to an extensional flow static heat
exchanger with at least two components of tubular cooling elements
arranged in a flow passage adapted to be flown through by a flow
medium in a flowing direction, wherein the components are
successively arranged in the flowing direction, each component
consists of a first set and a second set of at least two cooling
elements. The cooling elements of the first and the second set are
spaced substantially parallel to each other in a plane running
substantially perpendicularly to the flowing direction, the cooling
elements of the first set being angularly offset to the cooling
elements of the second set with respect to the longitudinal axis of
the flow passage, and the cross sections of the cooling elements
have a convex profile on the upstream and downstream side with
regard to the flow direction or a droplet shape, the cooling
elements of the first set of the adjacent component are arranged at
least partially in the space between two cooling elements of the
first set of the previous component, and the cooling elements of
the second set of the adjacent component are arranged at least
partially in the space between two cooling elements of the second
set of the previous component. Moreover, the invention refers to a
process for producing a low density extruded thermoplastic foam
material and a low density extruded thermoplastic foam material
obtainable by the above mentioned process.
[0003] Physical foaming of thermoplastic material is a very
challenging art. One needs first to melt the material and mix it
with any required additives, then keep the material under high
pressure and inject the physical blowing agent (hence physical
foaming) and then homogenize the mixture and bring the material
mixture to a temperature close to its solidification point.
Furthermore, the pressure in the extrusion die must remain high
enough for the physical blowing agent to remain in the mixture.
When low density foams, typically between 300 kg/m.sup.3 and even
down to 12 kg/m.sup.3, are in question, maintaining high pressures
and low temperatures gets very challenging. Dropping down the
temperature by several, even tens, of degrees is not simple, and
many different ideas have been tested and patented.
[0004] Already among the very first thermoplastic foam patents, the
need for cooling of the melt has been mentioned, and in many cases
even patented. The two most common ways to cool down the melt is to
use either a dynamic or a static cooling device, in the latter case
it is a static heat exchanger. Typical dynamic cooling device
configuration is a tandem-line, where the first extruder (typically
a twin-screw extruder) acts as melting and homogenization
equipment, and the second extruder, typically a single-screw, is
cooled both from exterior (barrel) and from the interior (screw).
Such has been described for example in DE 1914584, U.S. Pat. No.
4,958,933 and U.S. Pat. No. 4,022,858.
[0005] Static heat exchangers are compact and cost efficient
equipment, which typically employ both distributive mixing and
cooling. The most known device is a Colombo melt cooler, where the
material is pushed through numerous small, cooled orifices
(channels). The surface area of the cooled metal (wall of the
channel) is very large, so the material is cooled down very
effectively (for example EP 0071016). However, this type of heat
exchanger is based on laminar flow, and the material is subjected
to a significant amount of shear deformation (see FIG. 1B for
description of laminar flow and shear deformation).
[0006] Other alternative static heat exchangers are so called
Sulzer mixers (EP 0727249, EP 1437173 and EP 1123730), which are
typically cooled only from the exterior, and the mixing elements
are used to move the molten material randomly in the mixer and move
new material close to the cooled surface. Company Fluitec has
recently improved the design of Sulzer mixer by incorporating also
interior cooling (EP 1067352 and EP 2113732). A similar idea is
described also in EP 0074570 and EP 0884549 where the tubes inside
the exchanger are cooled down. All of these designs have the
disadvantage that the cooling elements are in a 0.degree. to max.
60.degree. angle with the flow. Because the material will travel in
the direction of least resistance, only a small part of the flow
goes through in between the tubes, whereas most of the flow takes
place in the direction of the tubes, that its flow is of laminar
flow type. The flow lines in a heat exchanger similar to Sulzer or
Fluitec design is depicted in terms numerical simulation of the
flow in
http://www.fluitec.ch/cms/download.php?f=3cb2fbf0e4f60e6142c39044452bfd7d-
. Because of laminar flow, the shear deformation is the dominant
type of deformation, and shear deformation is widely known as the
main cause for heating in polymer melts. The difference between
extensional deformation in converging flow and shear deformation in
laminar flow is depicted in FIGS. 1A and 1B.
[0007] Also, as a combination of static and dynamic cooling devices
was introduced by Colombo, where the melt is transported by an
extruder and pushed through a static heat exchanger (U.S. Pat. No.
4,324,493) which is built around the extruder. To our knowledge,
this also did not find commercial application, most likely because
of excessive shear heating in the small channels. Furthermore other
designs have been patented and introduced, such as EP 1426099, EP
2181827, DE 1213385, DE 19803362 and U.S. Pat. No. 6,622,514, but,
to our knowledge, these are not commercially used.
[0008] The main disadvantage of existing cooling devices, whether
static or dynamic, is that the cooling capacity is limited, mostly
because of their design, where laminar flow, that is shear
deformation, is dominantly present. Shear deformation creates shear
heating and a significant part of the removed energy (heat) is
therefore regenerated in the heat exchanger. Furthermore, in many
cases, such as the Sulzer mixer, the amount of cooled surface in
respect to throughput is very limited. In order to improve surface
per throughput ratio, some attempts have been made to use several
static heat exchangers, which has improved the processing in some
cases (DE 19958037, DE19848537 and U.S. Pat. No. 4,746,477), but
this approach cannot be used for all materials due to increased
pressure drop and long residence times.
[0009] Therefore, the existing static heat exchangers, or melt
coolers, are not ideal for thermally sensitive materials, such as
PET, PBT, PC, PEEK, PEI, PMI, PMMA, PS, PVC, PA, and other
engineering plastics, as they either create too much heat due to
laminar flow, or have too long residence times due to oversized
design. However the use of extensional heat exchanger is not
limited to thermally sensitive materials, as the amount of
generated heat in comparison to removed heat is negligible and
therefore use of such also for commodity foams such as polyolefins
and polystyrenes would be of an advantage.
DESCRIPTION OF THE INVENTION
[0010] The subject matter of the invention is an extensional flow
static heat exchanger with at least two components of tubular
cooling elements arranged in a flow passage adapted to be flown
through by a flow medium in a flowing direction, characterized in
that [0011] the components are successively arranged in the flowing
direction, [0012] each component consists of a first set and a
second set of at least two cooling elements (25), wherein each
cooling element consists of at least two cooling tubes, [0013] the
cooling elements of the first and the second set are spaced
substantially parallel to each other in a plane running
substantially perpendicularly to the flowing direction, [0014] the
cooling elements of the first set being angularly offset to the
cooling elements of the second set with respect to the longitudinal
axis of the flow passage, and [0015] the cross sections of the
cooling elements have a convex profile on the upstream and
downstream side with regard to the flow direction or a droplet
shape, [0016] the cooling elements of the first set of the adjacent
component are arranged at least partially in the space between two
cooling elements of the first set of the previous component, and
[0017] the cooling elements of the second set of the adjacent
component are arranged at least partially in the space between two
cooling elements of the second set of the previous component.
[0018] A further subject matter of the invention is a process for
producing low density extruded thermoplastic foam material wherein
a polymer-gas mixture is fed into the extensional flow static heat
exchanger according to the invention.
[0019] A further subject matter of the invention is a low density
extruded thermoplastic foam material with a density between 12
kg/m.sup.3 to 50 kg/m.sup.3 according to ISO 845, which is
obtainable by the above mentioned process.
[0020] Preferably a low density extruded thermoplastic foam
material with a density between 12 to 45 kg/m.sup.3, is obtainable
by the above mentioned process
[0021] The low density extruded thermoplastic foam material shows a
thermal conductivity of less than 0.028 W/mK according to EN
12667.
[0022] Moreover, the low density extruded thermoplastic foam
material shows an average cell size determined by optical
microscopy according to ASTM D3576 between 0.20 and 0.8 mm, more
preferably between 0.25 and 0.75 mm.
[0023] The density of the material is measured according to ISO
845, the average cell size was determined by optical microscopy
according to ASTM D3576, the thermal conductivity was determined
according to EN 12667.
BRIEF DESCRIPTION OF THE FIGURES
[0024] The invention will be described in more detail below with
reference to examples shown in the drawings.
[0025] FIG. 1: Schematic description of A) extensional deformation
in flow through a convergence and B) shear deformation in laminar
flow;
[0026] FIG. 2: Flow through a convergence;
[0027] FIG. 3: Schematic three-dimensional diagram showing one
component consisting of a first set and a second set of three
cooling elements each;
[0028] FIG. 4: Schematic three-dimensional diagram showing two
components, wherein the cooling elements of the first and second
set of the adjacent component are arranged at least partially in
the space between two cooling elements of the first and second set
of the previous component;
[0029] FIG. 5: Extensional flow heat exchanger described in this
invention;
[0030] FIG. 6: Flow path lines in the extensional flow heat
exchanger. The arrows indicate areas of acceleration, hence
extensional deformation;
[0031] FIG. 7: Density as a function of level of blowing agent. The
circled area represents results obtained with the extensional flow
heat exchanger.
DETAILED DESCRIPTION OF THE INVENTION
[0032] The invention presented here describes a compact heat
exchanger which has been designed to minimize the laminar flow,
namely shear deformation (laminar flow in FIG. 1B), within the
exchanger, while maximizing the amount of cooled surface and
distributive mixing by extensional deformation. The extensional
deformation in this case is generated by acceleration of the fluid
through a convergence (converging flow in FIG. 1A). It is widely
known that extensional deformation is much more efficient for
dispersive mixing than shear deformation (Grace, H. P., Chem. Eng.
Commun., 14, (1982), 225-277; Bentley, B. J., and Leal, L. G., J.
Fluid Mech., 167 (1986), 241-283), and some mixers based on
extensional deformation have been developed for that purpose (such
as U.S. Pat. No. 5,451,106 and US 2003/0142582 and CN
101259750).
[0033] FIG. 2 depicts extensional deformation in a converging flow
in more detail: a capillary die (or any similar obstacle) is
located in a larger tube to restrict the flow (without this
restriction, only laminar flow would take place). In region A the
flow lines converge, producing both shear and extensional
deformation of the fluid (corresponds to FIG. 1A). Extensional
effects dominate in this region due to acceleration of the fluid,
and only close to the walls some shear deformation takes place. The
larger the ratio of convergence (d.sub.B/d.sub.C) is, the higher
the amount of extensional deformation is. In region B the shear
deformation dominates due to laminar flow (corresponds to FIG. 1B).
By minimizing the length of the region B, (I.sub.C.about.0), and by
using round entry and exit profiles, the amount of shear
deformation is minimized and mostly extensional deformation takes
place. This has been the purpose in the design of the heat
exchanger introduced in this invention.
[0034] The concept of converging flow has been used in this case,
where the so called "extensional flow heat exchanger" consists of a
number of converging and diverging sections which are created by
staggered cooling elements, i.e. each cooling element is at a
different position than the previous, in order to cool down the
exiting, diverging melt also from the middle. The converging
sections were simply implemented by using cooled, high pressure
steel tubes, keeping the distance of the tubes (e.g. tubes with a
diameter of 12 mm) constant in both sideways and downstream
direction. Characteristic for such an extensional flow heat
exchanger is that the cooling elements (tubes in this case) stand
in an angle (e.g. 90.degree..+-.5.degree.) to the flow of the
polymer, i.e. they are perpendicular to the flow. This forces the
material to go through the convergence (extensional deformation),
and not to follow the direction of cooling elements, thus creating
unwanted shear deformation. The ratio of convergence
(d.sub.B/d.sub.C) was kept close to 2 throughout the heat exchanger
in order not to generate significant pressure drop.
[0035] An extensional flow static heat exchanger 10 according to
the invention consists of at least two components 20 of tubular
cooling elements 25 arranged in a flow passage adapted to be flown
through by a flow medium in a flowing direction, wherein the
components 20 are successively arranged in the flowing direction
and each component 20 consists of a first set 21 and a second set
22 of at least two cooling elements 25, wherein each cooling
element consists of at least two cooling tubes. The cooling
elements 25 of the first 21 and the second set 22 are spaced
substantially parallel to each other in a plane running
substantially perpendicularly to the flowing direction. The cooling
elements 25 of the first set 21 being angularly offset to the
cooling elements of the second set 22 with respect to the
longitudinal axis of the flow passage. The cross sections of the
cooling elements 25 have a convex profile on the upstream and
downstream side with regard to the flow direction or a droplet
shape. The cooling elements 25 of the first set 21 of the adjacent
component 21b are arranged at least partially in the space between
two cooling elements 25 of the first set 21 of the previous
component 21a. The cooling elements 25 of the second set 22 of the
adjacent component 22b are arranged at least partially in the space
between two cooling elements 25 of the second set 22 of the
previous component 22a.
[0036] Preferably, the cooling elements 25 of the first set 21 are
positioned in a 90.degree..+-.5.degree. angle to the cooling
elements 25 of the second set 22.
[0037] Furthermore, depending on rheological characteristics of the
polymer and of the polymer-gas mixture, different sizes and shapes
of tubing, for example round, oval or droplet shape, wherein the
droplet has a convex profile on the upstream side and different
distances between the tubes may be used.
[0038] The tubes in the cooling elements 25 may have different
diameters. The diameter of a tube depends on the cooling range, the
required cooling efficiency and the throughput of the extruder. The
diameter of a tube in a cooling element 25 is at least 2.5 mm in
diameter and not more than 120 mm in diameter, preferably between
10 to 30 mm in diameter.
[0039] The space between two adjacent tubes in a cooling element 25
is defined as 50 to 200 of the diameter of one tube of the cooling
elements 25. The tubes of the cooling element 25 are preferably
arranged with a distance of not less than 4 mm and not more than 60
mm. The distance of the tubes in the cooling elements 25 depends on
the throughput and required cooling efficiency.
[0040] The first set 21 of cooling elements 25 are arranged in a
distance to the second set 22 of cooling elements 25 of not less
than 50% and not more than 200% in reference to the diameter of one
tube of the cooling elements 25.
[0041] Preferably, the cooling elements 25 of the first 21 and
second 22 set of the adjacent component 21b, 22b are arranged
tessellated to the cooling elements 25 of the first 21 and the
second 22 set of the previous component 21a, 22a.
[0042] In another embodiment, a vacuum area is positioned
downstream after the exchanger 10 exit, more specifically the
exiting foam (extrudate) is subjected to pressure lower than
atmospheric pressure. With such vacuum treatment even lower
densities may be possible, as has been shown in U.S. Pat. No.
6,291,539.
[0043] FIG. 3 shows a schematic diagram of one component 20
consisting of a first set 21 and a second set 22 of cooling
elements 25 with three tubes each. In this embodiment, the tubes of
the cooling elements 25 are arranged with a distance of 100% of the
diameter of one tube of the cooling elements 25. The distance of
the cooling elements 25 depends on the throughput and the required
cooling efficiency.
[0044] FIG. 4 shows a schematic three-dimensional diagram of two
components 20, wherein the first (previous) component 21a, 22a and
the second component 21b, 22b are arranged successively in the
flowing direction (see arrowhead in FIG. 4). The distance between
the tubes in the cooling elements 25 in this embodiment is 100% in
reference to the diameter of the tubes. The cooling elements 25 of
the first set 21 are positioned in a 90.degree..+-.5.degree. angle
to the cooling elements 25 of the second set 22. In this
embodiment, the cooling elements 25 of the first 21 and second 22
set of the adjacent component 21b, 22b are arranged tessellated to
the cooling elements 25 of the first 21 and the second 22 set of
the previous component 21a, 22a.
[0045] FIG. 5 shows the extensional flow heat exchanger used in
this work. Here the material flows from left to right, and each of
the vertical 21 and horizontal 22 cooling elements (steel tubes)
are cooled down by thermal oil, as is also the exterior shell of
the exchanger, to a temperature close to solidification point of
the polymer-gas mixture. This temperature depends on the level of
gas, and may be easily adjusted by thermal regulator. In the case
of PET which was used in this work this temperature may vary from
265.degree. to 285.degree. C., depending on raw material(s),
additives, and target density.
[0046] FIG. 6 depicts in more detail the path lines (flow of
material) inside the heat exchanger, and the purpose of laying the
tubes 21a, 21b, 21c (black dots) in different position compared to
the previous layer: within each converging section the material is
accelerated through the convergence and the external layer gets
cooled down. The arrows in FIG. 6 indicate the areas of
acceleration, hence areas of extensional deformation. As the
material meets the second layer 21b of cooled tubes, the internal,
and much warmer, material becomes now the new external layer and is
cooled down. This is done multiple times so that the whole melt
becomes homogeneously cooled down. In one embodiment a total number
16 layers and a total number of 104 steel, high pressure tubes is
used. This creates a total area of 0.570 m.sup.2 of metal surface
which may be cooled down and is in contact with the polymer-gas
mixture. For comparison purposes, a similar size of Sulzer
Mixer.RTM. has 0.095 m.sup.2 of cooled metal per polymer-gas
mixture, and a Fluitec Mixer.RTM. roughly 0.2 m.sup.2 of cooled
surface (estimated from the drawings presented in the previously
mentioned patent).
[0047] In the process for producing low density extruded
thermoplastic foam material according to the invention, an
extruder, preferably a twin-screw extruder is equipped with an
extensional flow static heat exchanger 10.
[0048] In the process according to the invention, a polymer-gas
mixture is fed into the equipment, i.e. the extruder, equipped with
an extensional flow static heat exchanger 10.
[0049] Preferably the polymer material is a thermoplastic material,
virgin or recycled, or a mixture or blend of any of them.
[0050] Virgin thermoplastic material (resin) according to this
invention is a polymer that has never been made into a finished
product. It is the new polymer that any factory gets directly from
the manufacturer of the polymer.
[0051] Recycled or post-consumer thermoplastic material (resin)
according to this invention is a material that has at least once
been made into a finished product. The material has been extracted
from industrial or household waste by means of recycling, where a
substantial part of contaminants and dirt has been removed.
[0052] The polymer material is Polyethylene terephthalate (PET),
Polybutylene terephthalate (PBT), Polycarbonate (PC),
Polyetheretherketone (PEEK), Polyetherimid (PEI), Polymethacrylimid
(PMI), Polymethylmethacrylat (PMMA), Polystyrene (PS),
Polyvinylchloride (PVC) or Polyamide (PA), or a mixture or blend of
any of them.
[0053] The polymer-gas mixture consists also of nucleating agent(s)
and/or flame retardant(s), and/or elastomeric impact modifier(s).
Typical nucleating agents are present in unmolten form and may
compose for example of talc, calcium carbonate, glass spheres,
nanoclays, PTFE particles. Possible flame retardant systems are for
example halogenated flame retardants (with or without
antimonytrioxide), phosphor based flame retardants, metal stannates
and expandable graphites. Elastomeric impact modifiers may be
selected from a large group of polymeric materials, including
thermoplastic elastomers such as styrenic block copolymers (SEBS,
SBS, SIBS, etc.), acrylates (EBA, EMA, EEA, etc.), polyolefins,
polyamines, polyurethanes, copolyesters, and even so called
interpolymers.
[0054] In one embodiment of the process according to the invention,
the cooling elements 25 of the extensional flow static heat
exchanger 10 are cooled down to a temperature not more than
10.degree. C. above the solidification point of the polymer-gas
mixture.
[0055] In one embodiment of the process according to the invention,
the polymer-gas mixture comprises at least 75% wt (based on the
total amount of the polymer-gas mixture) of PET.
[0056] Preferably, the PET material consists of at least 70 wt %
(based on the total amount of PET) of recycled, post-consumer PET
(r-PET).
[0057] The viscosity of the resin may be increased during the
extrusion foaming process by means of chain extenders. A typical
virgin resin has an intrinsic viscosity from 0.65 to 0.85 dl/gm,
whereas foaming is very difficult with resins having intrinsic
viscosity below 1.0 dl/gm (measured according to ASTM D4603 using
60% Phenol and 40% Tetrachlorethane solution). The choice and
amount of chain extenders depend on the targeted end-product, but
as a guideline the intrinsic viscosity of the foam is higher than
1.2 dl/gm.
[0058] In one embodiment of the process according to the invention,
the cooling elements 25 of the extensional flow static heat
exchanger 10 are cooled down to a temperature between 265.degree.
and 285.degree. C.
[0059] Also higher density foams are possible to manufacture using
this technology, and the foam is characterized by having improved
cellular structure, more specifically finer and more uniform cells
throughout the foam.
[0060] This type of heat exchanger may be easily scaled up or down
in size to fit the specific needs of heat transfer and throughput
of the extruder.
[0061] It is made in industrial scale with throughput higher than
100 kg/hr, preferably over 300 kg/hr.
[0062] According the invention, a low density extruded
thermoplastic foam material with a density of 12 to 50 kg/m.sup.3
is obtainable by the above mentioned process.
[0063] Preferably a low density extruded thermoplastic foam
material with a density between 12 to 45 kg/m.sup.3, according to
ISO 845, is obtainable by reactive extrusion of PET resin.
[0064] Most preferably a low density extruded thermoplastic foam
material with a density below 40 kg/m.sup.3, is obtainable by
reactive extrusion of PET resin.
[0065] Reactive extrusion according to this invention means that
the melt viscosity and melt strength of the material is increased
by means of chain extension.
[0066] A foamed article can be manufactured with the above
described material.
Comparative Example 1
[0067] A medium size Sulzer mixer and low throughput: a twin-screw
extruder FG-75.2 with a screw diameter of 75 mm (manufactured by
Fagerdala Benelux) was equipped with a SMB-R 120 Sulzer mixer
(cooled area per kilo throughput at 40 kg/hr=526 kg/h*m.sup.2). The
equipment was used to foam polyethyleneterephtalate (Ramapet
9921.RTM. from Indorama) using a low level of nucleating agent,
chain extender package (see EP 2253659A1 for description) and a
physical blowing agent. The amount of physical blowing agent was
slowly increased until the foam became unstable (observed as rough
surface and holes within the foam). The Sulzer mixer was set to
265.degree. C., as any further reduction did lead to increased
pressure drop in the exchanger, indicating freezing
(solidification) of the melt. The pressure drop in the mixer was
measured as 16 bars and the minimum density possible with this
equipment was 54 kg/m.sup.3. Average cell size was determined being
1.03 mm by optical microscopy according to ASTM D3576. It is also
noted that cell size varied a lot throughout the sample, having
larger cells and voids in the middle of the foam. The thermal
conductivity was determined after 4 months of tempering at RT as
0.028 W/mK according to EN 12667.
Comparative Example 2
[0068] A large Sulzer mixer and high throughput: a twinscrew
extruder BC-180 with a screw diameter of 180 mm (manufactured by BC
Foam) was equipped with the largest possible Sulzer mixer SMB-R 200
(cooled area per kilo throughput at 450 kg/hr=1052 kg/h*m.sup.2).
The equipment was used to foam polyethylene terephthalate (Ramapet
9921.RTM. from Indorama) using a low level of nucleating agent,
chain extender package and a physical blowing agent. The amount of
physical blowing agent was slowly increased until the foam became
unstable. The Sulzer mixer was set to 268.degree. C., as any
further reduction did lead to increased pressure drop in the
exchanger. The pressure drop in the mixer was measured as 18 bars
and the minimum density possible with this set-up was 64
kg/m.sup.3. Average cell size was determined being 1.12 mm by
optical microscopy according to ASTM D3576. It is also noted that
cell size varied throughout the sample, having larger cells and a
few voids in the middle of the foam. The thermal conductivity was
determined after 3 months of tempering at RT as 0.028 W/mK
according to EN 12667.
Comparative Example 3
[0069] Fluitec mixer: a twin-screw extruder MIC27/GL-40D with a
screw diameter of 27 mm and 40D length (manufactured by Leistritz)
was equipped with a CSE XR DN150 type of Fluitec heat exchanger.
The equipment was used to foam polyethylene terephthalate (Ramapet
9921.RTM. from Indorama) using a low level of nucleating agent,
chain extender package and a physical blowing agent. The Fluitec
heat exchanger temperature was varied between 275.degree. and
248.degree. C., and no freezing of the melt was observed. However,
due to a long residence time of the line, good quality foam was not
obtained. Average cell size was not determined.
Comparative Example 4
[0070] Fluitec mixer: a twin-screw extruder Coperion ZSK30 MC with
30 mm screw diameter and 48D length was equipped with a CSE XR
DN150 type of Fluitec heat exchanger. The equipment was used to
foam polyethylene terephthalate (Ramapet 9921.RTM. from Indorama)
using a low level of nucleating agent, chain extender package and a
physical blowing agent. The Fluitec heat exchanger temperature was
varied between 275.degree. and 248.degree. C., and no freezing of
the melt was observed. This extruder was characterized of having
much shorter residence time than the extruder used in Comparative
example 3. However, good quality foam was not obtained due to lack
of pressure.
Comparative Example 5
[0071] Comparative example 1 was repeated, but targeting an end
density of 100 kg/m.sup.3 (measured 99.2 kg/m.sup.3). The Sulzer
mixer was set to 267.degree. C., as any further reduction did lead
to an increased pressure drop in the exchanger, indicating freezing
of the melt. The pressure drop in the mixer was measured as 17
bars. The average cell size was determined being 0.84 mm by optical
microscopy according to ASTM D3576. It is also noted that cell size
varied throughout the sample, having somewhat larger cells in the
middle of the foam. The thermal conductivity was determined after 4
months of tempering at RT as 0.031 W/mK according to EN 12667.
Innovative Example 1
[0072] Heat exchanger of this invention: a twin-screw extruder with
a screw diameter 75 (manufactured by Fagerdala Benelux) was
equipped with an extensional flow heat exchanger shown in FIG. 5
(cooled area per kilo throughput=108 kg/h*m.sup.2). The equipment
was used to foam polyethylene terephthalate (Ramapet 9921.RTM. from
Indorama) using a low level of nucleating agent, chain extender
package and a physical blowing agent. The amount of physical
blowing agent was slowly increased until the foam became unstable.
The heat exchanger was set to 272.degree. C., as any further
reduction did lead to increased pressure drop in the exchanger,
indicating possible freezing of the material. The pressure drop in
the mixer was measured as 22 bars and the minimum density possible
with this equipment was 35 kg/m.sup.3. This is to our knowledge by
far the lowest ever produced density foam made of PET by physical
foaming (without use of vacuum) and the cellular structure of the
foam was much more uniform and contained in average smaller cells
than foam from any of the comparative examples. Average cell size
was determined being 0.29 mm by optical microscopy according to
ASTM D3576. It is also noted that cell size was very uniform
throughout the sample, nevertheless the "spaghettis" (due to
multihole die) were visible and the walls of the spaghettis had
even smaller cells. The thermal conductivity was determined after 4
months of tempering as 0.025 W/mK according to EN 12667.
Innovative Example 2
[0073] Heat exchanger of this invention: Innovative example 1 was
repeated, but using recycled polyethylene terephthalate, r-PET
(from Meister Recycling GmbH) and a low level of nucleating agent
(<1.0%), chain extender package (at a 50% higher level than
usual) and a physical blowing agent. The amount of physical blowing
agent was slowly increased until the foam became unstable. The heat
exchanger was set to 271.degree. C., as any further reduction did
lead to increased pressure drop in the exchanger. The minimum
density possible with this equipment was 37.5 kg/m.sup.3. Average
cell size was determined being 0.38 mm by optical microscopy
according to ASTM D3576. It is also noted that cell size was very
uniform throughout the sample, nevertheless the "spaghettis" were
again visible and the walls of the spaghettis had even smaller
cells. The thermal conductivity was determined after 3 months of
tempering as 0.026 W/mK according to EN 12667.
[0074] Innovative example 3
[0075] Innovative example 1 was repeated, but adjusting the blowing
agent level for a density of 100 kg/m.sup.3 (measured 98.6
kg/m.sup.3). The heat exchanger was set to 274.degree. C., as any
further reduction did lead to increased pressure drop in the
exchanger, indicating possible freezing of the material. The
average cell size was determined being 0.42 mm by optical
microscopy according to ASTM D3576. It is also noted that cell size
was very uniform throughout the sample, and the "spaghettis" were
not visible but the product was very homogeneous throughout the
sample. The thermal conductivity was determined after 4 months of
tempering as 0.027 W/mK according to EN 12667.
[0076] FIG. 7 shows the achieved density as a function of level of
hydrocarbon based blowing agent. The diamond and round shaped
points indicate results from two different extrusion lines
indicated in comparative examples 1 and 2, whereas the circled area
(square points) represents the results achieved with the help of
the extensional flow heat exchanger 10, according to the invention.
A power law fit is shown to correlate with the results. The lowest
possible density achieved in physical foaming with such an
extrusion line is 12 kg/m.sup.3 using polyethylene and a
hydrocarbon blowing agent.
* * * * *
References