U.S. patent application number 09/190516 was filed with the patent office on 2002-03-07 for multilayer foams.
Invention is credited to ESCHENLAER, GEORGES, MASON, JEFFFREY JOHN, VO, CHAU VAN.
Application Number | 20020026977 09/190516 |
Document ID | / |
Family ID | 8227766 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020026977 |
Kind Code |
A1 |
MASON, JEFFFREY JOHN ; et
al. |
March 7, 2002 |
MULTILAYER FOAMS
Abstract
The present invention concerns foamed products having a
plurality of coalesced extruded layers or layers of coalesced
strands of a foamed thermoplastic composition having a low
density.
Inventors: |
MASON, JEFFFREY JOHN;
(BUHLERTAL, DE) ; VO, CHAU VAN;
(SOUFFELWEYERSHEIM, FR) ; ESCHENLAER, GEORGES;
(SOUFFLENHEIM, FR) |
Correspondence
Address: |
STEPHEN S GRACE
P O BOX 1967
MIDLAND
MI
486411967
|
Family ID: |
8227766 |
Appl. No.: |
09/190516 |
Filed: |
November 12, 1998 |
Current U.S.
Class: |
156/78 ;
156/244.11 |
Current CPC
Class: |
B29C 44/468 20130101;
B29C 44/24 20130101 |
Class at
Publication: |
156/78 ;
156/244.11 |
International
Class: |
B32B 005/18 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 8, 1997 |
EP |
97121595.9 |
Claims
What is claimed is:
1. A method for producing a polymer or copolymer multilayer foam,
comprising the steps of: (a) providing at least one foamable
composition comprising at least one polymer or copolymer and a
blowing agent formulation, (b) extruding the composition through a
die having a plurality of orifices, (c) foaming the extruded
composition at a foaming temperature which is above the
glass-transition temperature or the melting temperature of the
polymer composition, (d) maintaining the foaming product at an
elevated temperature for a sufficient period of time to obtain
adhesion between individual foam layers, and (e) allowing the
foamed product to cool, characterized in that a foamed product is
obtained comprising a plurality of adherent foam layers, wherein at
least one of these foam layers extends across the whole breadth of
the foamed product.
2. The method of claim 1, wherein the polymer or copolymer
composition is selected from alkylene aromatic polymers or
copolymers and olefinic polymers or copolymers and mixtures
thereof.
3. The method of claim 1 wherein the blowing agent is selected from
hydrocarbons, ethers, lower alcohols, partially halogenated
hydrocarbons, water, carbon dioxide, nitrous oxides, nitrogen,
ammonia, air, noble gases and mixtures thereof.
4. The method of claim 1, wherein the multilayer foam comprises at
least three foam layers.
5. The method of claim 4, where the blowing agent formulation
exhibits a low evaporative cooling capacity during the foaming
process, and step (e) includes an accelerated cooling of the foamed
product.
6. The method of claim 4, where the blowing agent formulation
exhibits a high evaporative cooling capacity during the foaming
process, and step (d) includes a transfer of additional heat to the
foaming product.
7. The method of claim 1, wherein the polymer or copolymer
composition is substantially free from adhesive additives.
8. The method of claim 1, wherein the foaming temperature is
1.degree. C. to 50.degree. C. above the glass-transition
temperature or melting temperature of the polymer or copolymer.
9. The method of claim 1, further comprising co-extruding a first
polymer or copolymer composition through at least one first opening
of the multiorifice die, and a second polymer or copolymer
composition through at least one second opening of the multiorifice
die, wherein the first composition is different from the second
composition, and whereby a multilayer foam is produced comprising
at least one layer of the first polymer or copolymer foam and at
least one layer of the second polymer or copolymer foam.
10. The method of claim 9, wherein the first composition comprises
polypropylene and the second composition comprises polystyrene.
11. A polymer or copolymer multilayer foam, obtainable by the
method of claim 1.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to foamed products. More
Particularly, the present invention relates to foamed products
comprising a plurality of layers of a foamed thermoplastic
composition having a low density.
BACKGROUND OF THE INVENTION
[0002] Methods for producing foams comprising a plurality of
polymer layers are known. U.S. Pat. No. 4,053,341 discloses a
process for producing a laminate comprising a plurality of
cross-linked polyethylene foam layers having an anisotropic pore
structure in at least one internal layer. The internal layer
comprises a cross-linking agent and a large amount of blowing
agent, whereas the external layers comprise a cross-linking agent
and a small amount of blowing agent. The layers are welded at
160.degree. C. and heated at 190.degree. C. to 250.degree. C. to
foam the structure. A disadvantage of this process is that it
requires two steps: first welding and cross-linking the extruded
plastic layers, then foaming at a higher temperature. Further, the
process is limited to the production of a multi-layer foam sheet
with limited cross-section.
[0003] U.S. Pat. Nos. 4,107,247 and 4,206,165 and Canadian Patent
1,100,726 describe a method for the manufacture of a plastic
sandwich element in which a first extruder produces a foamed
cellular plastic at a defined temperature. A second extruder
produces a solid plastic at a temperature at least 14.degree. C.
(25.degree. F.) hotter than the temperature of the foamed cellular
core to promote foaming of the core. The resulting sandwich is
extruded through an extrusion die. A drawback of this process is
that there is only one single central foam layer confined between
two solid plastic films. Further, the resulting foam has
comparatively poor insulation and dimensional stability
properties.
[0004] U.S. Pat. No. 4,773,448 discloses a process for producing a
plastic pipe with a hard outer shell lined with an inner shell of
soft resilient plastic foam with a smooth axial passageway adapted
to be a conduit for liquid. An outer PVC shell is extruded and an
inner polyethylene foam material is simultaneously extruded inside
the PVC tube. A disadvantage of this process is that the maximum
cross-section is the size of the tube. Further, because of the
restrained foaming it is expected that the resulting foam exhibits
a very high foam density.
[0005] JP 50-107067 discloses a process for producing a
thermoplastic foam having a non-foamed skin layer by using
co-extrusion. A polyethylene foam having a polypropylene skin layer
and a polystyrene foam having a polyethylene skin are prepared. A
disadvantage of this process is that there is only one single
central foam layer confined between two solid skin layers.
[0006] Japanese Pat. No. 48-5100 discloses a process for producing
a multi-layer polystyrene foam having different foam densities, for
example, high density outside, low density inside, and a
reinforcement material in between. The material is used as pillars
in homes, exhibiting desired bending and strength properties. A
disadvantage of this process is that only foams having a
comparatively high density of 200 kg/m.sup.3 can be
manufactured.
[0007] Japanese Pat. No. 50-50473 discloses a laminated molded
product composed of a foam layer and a non-expanded thermoplastic
layer. Both layers are molded into a desired shape. The lamination
can take place separately using two extruders and two dies, or
simultaneously using two extruders and one multilayer die. A
disadvantage of the production process described therein is that
only products having a small cross-section and a high density are
obtained.
[0008] Laid-open Japanese Patent Application H7-112480 discloses a
rectangular molded resin product composed of a hollow multilayer
resin filled with a resin foam inside the hollow multilayer. The
material for the hollow multilayer is polypropylene. The foam is
polypropylene or polyurethane. The disadvantage of this
manufacturing process is that the molded resin product can have one
single foam layer only. Moreover, only products exhibiting a
restricted rectangular cross-section and a high foam density can be
produced.
[0009] U.S. Pat. No. 3,694,292 describes an extrusion head for
producing a multilayer blown tubular film.
[0010] Generally it has to be noted that considerable problems
arise with regard to corrugation of single layers when producing
multilayer foams. Particularly, when producing multilayer foams
which exhibit three or more foam layers, the foaming of the center
layer or layers takes place in a different environment as compared
to the outer layers.
[0011] Thus, there is a great need to provide a multilayer foam
having excellent insulating and dimensional stability properties at
a low density. It would also be desirable to provide a method for
producing a multilayer foam which is simple, inexpensive and
environmentally acceptable and results in products having good
physical properties.
SUMMARY OF THE INVENTION
[0012] In one aspect, the present invention thus pertains to a
method for producing a polymer or copolymer multilayer foam,
comprising the steps of: (a) providing at least one foamable
composition comprising at least one polymer or copolymer and a
blowing agent formulation, (b) extruding the composition through a
die having a plurality of orifices, (c) foaming the extruded
composition at a foaming temperature which is above the
glass-transition temperature or the melting temperature of the
polymer composition, (d) maintaining the foaming product at an
elevated temperature for a sufficient period of time to obtain
adhesion between individual foam layers, and (e) allowing the
foamed product to cool, characterized in that a foamed product is
obtained comprising a plurality of adherent foam layers, wherein at
least one of these foam layers extends across the whole breadth of
the foamed product.
[0013] In a further aspect, the invention relates to a polymer or
copolymer multilayer foam, obtainable by the method as described
above. This product has excellent properties with regard to thermal
insulation, dimensional stability, water diffusion resistance and
water vapor permeation resistance. Furthermore, the foam of the
present invention has a smooth, uniform surface equivalent to
current monolithic foams. This preferred appearance is obtained on
both sides of the final foam product without any additional
surface-modifying operations.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The foamable composition comprises at least one polymer or
copolymer. The composition may comprise a single polymer, a single
copolymer, mixtures of polymers, mixtures of copolymers or mixtures
of polymers and copolymers.
[0015] According to the present invention a multilayer foam is
composed of a plurality of polymer or copolymer foam layers. These
foam layers may be comprised of the same or of different foamable
compositions. The multilayer foam comprises at least two and
preferably at least three foam layers. At least one of these foam
layers is a homogeneous foam layer, that is, a monolithic foam part
extending across the whole breadth of the foam. This homogeneous or
monolithic foam layer is obtained by extruding the foamable
composition through an orifice which extends across the whole
breadth of the die, for example, a slit, or through a continuous
orifice, for example, a circle.
[0016] The present invention relates to such multilayer foams
composed of a variety of such monolithic layers, but also to such
foams comprising at least one layer extending across the whole
breadth of the foam and at least one layer which is comprised of a
plurality of individual coalescent foam strands.
[0017] By means of the process for the production of multilayer
foams according to the invention, it becomes possible to obtain
foams having a greater overall thickness, or to produce them in a
simpler manner. Moreover, the resulting multilayer foams have an
oriented structure and offer an improved thermal insulation
performance at the same density or thickness compared to monolithic
foams. Furthermore, they exhibit an excellent dimensional stability
and strength with similar or, more preferably, substantially
equivalent water permeation resistance and water absorption
properties as compared to monolithic foams.
[0018] It has been discovered that polymer or copolymer multilayer
foams, for example, multilayer foams consisting of a plurality of
monolithic layers or multilayer foams having one or more layers
consisting of a plurality of individual coalesced strands can be
produced on-line without using adhesive additives or any additional
mechanical devices to enhance the adhesion between strands or
layers.
[0019] The multilayer foam can be made from any foamable polymer or
copolymer, for example, alkylene aromatic polymers, such as
polystyrene or styrene-based copolymers, olefinic polymers or
copolymers, such as, polyethylene, polypropylene or copolymers of
polyethylene or polypropylene with other olefinic monomers,
polyurethanes, acrylic polymers or any other plastic materials
which can be foamed.
[0020] In a preferred embodiment the polymer or copolymer
composition is comprised, exclusively or as part of a blend, of an
alkylene aromatic polymer or copolymer. An alkylene aromatic
polymer according to the present invention is preferably comprised
of monovinylidene aromatic monomers. Preferred examples thereof are
styrene, alkylstyrenes, for example, styrenes having at least one
C.sub.1-C.sub.4 alkyl substituent located on the aromatic ring
and/or on the vinylidene residue, and halogenated styrenes.
Specific examples are styrene, .alpha.-methylstyrene, a styrene
having at least one alkyl and/or halo substituent on the aromatic
ring, such as o-methylstyrene, m-methylstyrene, p-methylstyrene, or
the corresponding ethylstyrenes or chlorostyrenes, vinylxylene or
mixtures thereof. An alkylene aromatic copolymer is comprised of
alkylene aromatic monomers and other polymerizable monomers,
wherein the alkylene aromatic monomers preferably are present in an
amount of at least 50 percent by weight, more preferably in an
amount of at least 70 percent by weight, and most preferably in an
amount of at least 85 percent by weight based on the weight of the
total monomers. The other polymerizable monomers preferably are
selected from acrylic-monomers, for example, acrylonitrile, acrylic
acid, and acrylic esters such as butyl acrylate, or from mono or
poly unsaturated olefinic monomers, for example, ethylene,
propylene, butadiene, and isoprene, or mixtures thereof.
[0021] According to a further preferred embodiment of the present
invention the polymer or copolymer composition is comprised, solely
or as part of a blend, of an olefinic polymer, for example, a
polymer comprised of olefinic or poly-olefinic monomers. Preferred
examples are homopolymers of ethylene or propylene, copolymers of
ethylene or propylene with one or more C.sub.4-C.sub.8
.alpha.-olefins and inter- or copolymers of ethylene or propylene
and at least one non-olefinic comonomer, wherein the olefinic
monomers preferably are present in an amount of at least 50 percent
by weight, more preferably in an amount of at least 70 percent by
weight, most preferably in an amount of at least 85 percent by
weight based on the weight of the total monomers. The non-olefinic
polymerizable monomers preferably are selected from acrylic
monomers, monovinylidene aromatic monomers or mixtures thereof.
[0022] The blowing agent in the method of the present invention can
be selected from any known blowing agent suitable for the
respective polymer, for example, from aliphatic or cycloaliphatic
compounds including hydrocarbons, ethers, lower alcohols,
halogenated hydrocarbons, especially partially halogenated
hydrocarbons, and "inorganic" blowing agents such as water, carbon
dioxide, nitrous oxides such as NO, NO.sub.2 and N.sub.2O,
nitrogen, ammonia, noble gases such as argon and air, or mixtures
thereof. Inorganic blowing agents can also be produced in situ by
adding chemical compounds to the composition which decompose and
generate gas, such as known typically in the art, for example,
azo-type compounds for the generation of N.sub.2, ammonium
compounds of the generation of NH.sub.3 and mixtures of carbonates
and acids for the generation of CO.sub.2.
[0023] The blowing agent is generally used in an amount of from 0.5
to 25 weight percent, preferably of from 1 to 15 weight percent
based on the total weight of the foamable composition.
[0024] Examples of suitable aliphatic or cycloaliphatic compounds
are ethane, ethylene, propane, propylene, butane, isobutane,
butylene, isobutene, pentane, neopentane, isopentane, cyclopentane,
hexane, heptane, cyclohexane and mixtures thereof. Suitable
examples of ethers are dimethyl ether (DME), methyl ethyl ether, or
diethyl ether. Suitable examples of lower alcohols are methanol,
ethanol, propanol, isopropanol, butanol, pentanol, hexanol and
mixtures thereof, wherein ethanol is preferred. Among the
"inorganic" blowing agents, carbon dioxide or carbon dioxide/water
mixtures are preferred. Examples of partially halogenated
hydrocarbons are chloroethane, chlorodifluoromethane (R-22),
1-chloro-1,1-difluoroethane (R-142b), 1,1,1,2-tetrafluoroethane
(R-134a), 1,1,2,2-tetrafluoroethane (R-134),
2-chloro-1,1,1,2-tetrafluoroethane (R-124), pentafluoroethane
(R-125), 1,1-difluoroethane (R-152a), 1,1,1-trifluoroethane
(R-143a), 1-fluoroethane (R-161), difluoromethane (R-32),
1,1,1,3,3-pentafluoropropane (HFC-245 fa),
1,1,1,3,3-pentafluorobutane (HFC-365 mfc) and mixtures thereof.
[0025] Preferable in all cases are blowing agent compositions which
have no ozone depletion potential (ODP), namely fluorinated
alkanes, inorganic blowing agents, alcohols, hydrocarbons, ethers
or combinations thereof. Particularly suitable, for example, for
alkylene aromatic polymers and copolymers, or for olefinic polymers
and copolymers, are blowing agent compositions composed primarily
of carbon dioxide, and mixtures of carbon dioxide with water or
ethanol or isopropanol or dimethyl ether or mixtures of two or more
of these. Compositions based on (i) 1,1,1,2-tetrafluoroethane, (ii)
1,1,2,2-tetrafluoroethane, (iii) 1,1-difluoroethane, (iv) mixtures
of two or more of these, or (v) mixtures of each compound or
mixture with ethanol or isopropanol or dimethyl ether or water or
carbon dioxide or mixtures of two or more of these are also
particularly suitable in the practice of the present invention.
Additionally, compositions based on dimethyl ether and mixtures of
dimethyl ether with water or ethanol or isopropanol or carbon
dioxide or mixtures of two or more of these are also suitable in
the practice of the present invention. Other suitable blowing
agents are hydrocarbons, such as propane, butane, pentane or
mixtures thereof. Furthermore, mixtures of suitable hydrocarbons
with dimethyl ether, carbon dioxide, and partially halogenated
hydrocarbons are also suitable in the practice of the present
invention.
[0026] When preparing the multilayer foam according to the present
invention it is in some cases preferred that a control of the foam
temperature based on the thermodynamic nature of the blowing agent
formulation is carried out in steps (d) and (e) as described above.
In some cases, when using a blowing agent formulation comprising a
blowing agent or a mixture of blowing agents which exhibits a low
evaporative cooling capacity during the foaming process, an
accelerated cooling during step (e) of the process is preferred to
obtain a product having excellent quality. Examples of suitable low
evaporative cooling capacity blowing agents are carbon dioxide,
nitrogen, noble gases, nitrous oxides and air. In contrast, when
using a blowing agent formulation comprising a major amount of a
blowing agent or a mixture of blowing agents which exhibits a high
evaporative cooling capacity during the foaming process, it was
found that an additional transfer of heat to the composition during
step (d) was beneficial in some cases to obtain satisfactory
results.
[0027] The additional transfer of heat can be accomplished, for
example, by also heating the composition to a temperature above the
foaming temperature as it passes through the extrusion die, or by
heating the environment directly adjacent to the extrusion die face
to such an extent that a sufficiently high foam surface temperature
is maintained throughout the point in time at which the expanding
foam structures coalesce. Said heating can be accomplished in
various ways such as known in the art, all such that (a) the
extrusion die structure, or (b) the individual foam strand surfaces
are heated above the bulk foaming composition temperature.
[0028] Examples of blowing agents having a high evaporative cooling
capacity are hydrocarbons, ethers, partially halogenated
hydrocarbons, water or mixtures comprising as a major component at
least one of such blowing agents.
[0029] It should be noted that in many cases the temperature
control as described above is not an essential feature to obtain
multilayer foam products having an excellent quality. However,
especially when using a polymer or copolymer composition comprising
an alkylene aromatic polymer or copolymer and when preparing a foam
having at least one layer comprising a plurality of individual
strands, the temperature control may be of great importance. A
detailed description of the temperature control may be found in the
co-pending application by the same applicants having the title,
"Low Density Strand Foams."
[0030] Apart from the blowing agent, the composition may also
comprise further additives, such as nucleating agents, extrusion
aids, antioxidants, flame retardants, colorants, or pigments.
Examples of pigments are carbon black or titanium dioxide or
graphite and other compounds known in the art which may further
enhance the thermal insulation properties of foamed products.
[0031] According to the present invention, foam structures
comprising a plurality of layers and having a large cross-section
can be produced. The present invention is particularly suitable for
producing foamed products having excellent thermal insulation
characteristics with cross-sections of at least 150 cm.sup.2 or
more, more preferably at least 500 cm.sup.2 or more. It should,
however, be noted that also foams having smaller cross-sections can
be produced with the same advantages as previously described. The
cross-sectional area of individual foam layers can be varied over a
broad range. Usually the cross-section of a single foam layer is in
the range of from 1 cm.sup.2 up to 500 cm.sup.2, preferably of from
2 cm.sup.2 to 250 cm.sup.2.
[0032] By the process as described above a cellular foam product
can be obtained. In some cases, the cells of at least one foam
layer may have an anisotropic shape, that is, the cell size is
different when measured in different orientations (horizontal,
vertical and extrusion).
[0033] Surprisingly, it was found that the polymer or copolymer
composition can be substantially free from adhesive additives, for
example, ethyl vinyl alcohol copolymer (EVA), ethyl acrylic acid
copolymer (EAA), or other adhesive agents known in the art.
Preferably, the adhesive additives are present in an amount lower
than 5 weight percent, more preferably in an amount of lower than 1
weight percent based on the total polymer or copolymer composition.
Most preferably, the composition is free from adhesive
additives.
[0034] The use of adhesive additives, while not necessary for the
easy production of, the final properties of or the excellent
performance of the foams of this invention, may, however, be
employed additionally such as is known in the art. Delivery methods
of such adhesive additives would include mixing in the polymer,
addition during any stage of the extrusion process or application
of suitable adhesives during or after passage through the extrusion
die, all such as known in the art.
[0035] According to the present invention, the polymer and blowing
agents preferably are mixed in a mixer or in the extruder, and
afterwards the mixed composition is cooled down prior to extrusion.
Then, the composition, usually being in the form of a gel, is
forced through a plurality of die orifices, preferably through a
die plate comprising a plurality of openings, where at least one
such opening is so designed that a monolithic foam layer extending
across the whole breadth of the foam is produced. The individual
foam layers can be planar or corrugated, discontinuous, for
example, having ends, or continuous, for example, being in the form
of a circle.
[0036] When a foam having at least one layer comprised of a
plurality of individual strands is produced, the composition
preferably is forced through a die plate comprising a plurality of
small holes in a suitably desired spatial arrangement, for example,
in an oscillating form such as a sinus wave, honeycomb, square, saw
tooth or triangular saw tooth wave pattern.
[0037] According to the present invention it is preferred that the
first contact between individual foam layers occurs after the
departure from the respective die orifices. Further, it is
preferred that the process according to the present invention is
not carried out in a closed molding box but rather that a free
molding of the foam product is conducted, optionally in an
intermediate space between two plates. Furthermore, it is preferred
in the process according to the invention that the total area of
the openings of the dies used is .ltoreq.10 percent, more
preferably .ltoreq.5 percent, and most preferably .ltoreq.3 percent
in relation to the cross-section transverse to the direction of
extrusion of the resulting product.
[0038] In order to enhance the self-adhesion between individual
layers or strands, the foaming temperature is above the glass
transition temperature or the melting temperature of the polymer or
copolymer. The difference in temperature is preferably 1.degree. C.
to 50.degree. C., more preferably 2.degree. C. to 40.degree. C. and
most preferably 5.degree. C. to 30.degree. C. Furthermore, it is
preferred that the theoretical diameter of an individual strand (T)
or the theoretical thickness of an individual layer (T) is at least
as high as the distance between the orifices (D) or the distance
between the slits (D). The ratio T/D which is designated as
cohesion ratio (C) is thus preferably greater than or equal to 1,
more preferably the cohesion ratio is greater than or equal to 1.2.
The theoretical diameter of each strand or thickness of each layer
can be calculated based on the foam volume expansion and the line
speed determination. The foam volume can be calculated from mass
balance and foaming temperature. It can also be deduced from the
foam density measurement.
[0039] Further, the present invention comprises using conventional
co-extrusion technology to co-extrude multiple polymer/blowing
agent systems. The nature of each polymer or each blowing agent can
be different. It is, however, important that the foaming
temperature is above the glass-transition temperature or the
melting temperature of each polymer or copolymer, and preferably
the cohesion ratio is equal to or larger than 1.
[0040] When producing a multilayer foam comprising multiple
polymer/blowing agent systems, the present invention comprises
co-extruding a first polymer or copolymer through at least one slit
of the multiorifice die and a second foamable polymer or copolymer
through at least one second slit of the multiorifice die, whereby a
foam composition is produced comprising at least one layer of the
first polymer or copolymer foam and at least one layer of the
second polymer or copolymer foam.
[0041] For example, the outer layers of a foam composition can be
made of an olefinic polymer such as polypropylene with a
hydrocarbon blowing agent, for example, butane, and the inner layer
or layers are made with an alkylene aromatic polymer, such as
polystyrene, and, for example, CO.sub.2 and/or hydrofluorocarbons
as blowing agent. The resulting composite foam offers a very good
insulation value, thanks to the extruded polystyrene foam core, and
a high service temperature and good chemical resistance due to the
performance of the polypropylene outer shell.
[0042] A polymer or copolymer multilayer foam, for example, an
alkylene aromatic and/or olefinic polymer or copolymer foam, which
is obtainable by the method of the present invention preferably has
a density of up to 150 kg/m.sup.3. More preferably, the density is
from 16 to 80 kg/m.sup.3.
[0043] The expansion of the foam after leaving the extrusion die
can be carried out in a normal atmospheric environment. For the
expansion, however, also a sub-atmospheric environment, for
example, partial vacuum, a super-atmospheric environment, for
example, overpressure, and atmospheres having various gaseous
compositions, for example, an elevated CO.sub.2 content, can be
selected, such as is known in the art.
[0044] The foamed product may be transported by various conveying
devices as known in the art, for example, continuous belts, or
rollers. These devices may additionally comprise means for
temperature control as appropriate.
[0045] Further, the foamed product which is produced according to
the present invention is suitable for use in processes involving
devices for reducing density after initial foam expansion, for
example, infrared ovens, steam ovens, hot air ovens, or
combinations of such devices.
[0046] If desired, the foamed product can be subjected to
post-treatment procedures, such as embossing, remelting and other
techniques known in the art to modify the outer surface of the
foamed product. It should, however, be noted that according to the
present invention a product with a smooth, uniform surface
substantially equivalent to current monolithic foams is obtained,
which in many cases does not require any surface-modifying
operations.
[0047] By using the present invention, a foam having a large
cross-section and a low density can be produced. This invention is
suitable for production of foams with an average cell size ranging
from 25 to 3000 micrometers (.mu.m), preferably 50 to 2000 .mu.m,
and more preferably 100 to 1500 .mu.m. This foam presents a
superior thermal insulation performance and dimensional stability
in comparison with the foams of the prior art.
[0048] The multilayer foam according to the present invention
preferably has an improvement in the thermal conductivity by at
least 1.5 percent, more preferably by at least 3 percent, and most
preferably by at least 5 percent over a monolithic foam having the
same density and thickness and produced from the same
polymer/blowing agent composition. "Monolithic" as used herein
means a single, integral unit.
[0049] A preferred feature of the process and resulting foam
according to the present invention is that at least one layer of
the foam structure is composed of a plurality of closed-cells,
preferably a closed-cell content as measured by ASTM D 2856-90 of
at least 90 percent, and more preferably at least 95 percent. More
preferably, all layers of the foam product are composed of a
substantially closed-cell foam.
[0050] A further advantage of the foam according to the present
invention over the prior art foams is that continuous layers in the
direction of extrusion can be obtained. Further, it is preferred
that according to the present invention the interface between
individual strands or layers substantially does not exhibit any
zones or only very small zones having an increased foam
density.
[0051] A further preferred feature of the foam according to the
present invention is that a minimum tensile strength, for example,
as measured by ASTM D-1623 of at least 20 kPa, more preferably of
at least 100 kPa and most preferably 250 kPa or higher is obtained.
Further, the shear strength of the foamed product, for example, as
measured by ASTM C-273 is preferably at least 10 kPa, more
preferably at least 100 kPa and most preferably 250 kPa or
higher.
[0052] A further preferred feature of a foam according to the
present invention is that there are substantially no voids when
cutting the foam perpendicular to the direction of extrusion.
Preferably, the void area is less than 1 percent, and more
preferably less than 0.5 percent based on the total cross-section
of the foam. Most preferably, there are no voids at all.
[0053] The substantially voidless multilayer foams have at least
substantially equal water vapor permeability and water diffusion
resistance as comparable monolithic foams.
[0054] The following examples are for illustrative purposes only
and do not limit the scope of the invention. Unless otherwise
stated, all parts and percentages are given by weight.
EXAMPLE 1
[0055] A multilayer foam (Sample ML1) was produced using a 5.08 cm
(2 inch) extruder, consisting of a polymer-copolymer blend with a
glass transition temperature of 103.degree. C., composed of 90 phr
(parts per 100 of resin) polystyrene, 10 phr
styrene-.alpha.-methyl-styrene copolymer, 0.8 phr of additives,
comprising of extrusion aids and colorants, and 4.5 phr of carbon
dioxide. The foaming temperature was set at 114.degree. C. The gel
was extruded into atmospheric pressure through a plate of 3 slits
having a slit opening height of 1.0 mm. The distance between the
slit centers was 17.0 mm. The multilayer foam a composed of 3 foam
layers was produced without any adhesive material. The foam had a
density of 39.3 kg/m.sup.3, a cell size of 0.30 mm (vertical), 0.23
mm (extrusion) and 0.29 mm (horizontal) and a cross-section of
11,600 mm.sup.2. The cohesion ratio C (the ratio of the thickness
of individual layer and the distance between slit centers) was
1.38.
[0056] Another multilayer foam (Sample ML2) was prepared using the
process as described above, but using 4.6 phr CO.sub.2, a slit
opening height of 0.9 mm and a distance between slit centers of
12.7 mm. The density of this foam was 45.6 kg/m.sup.3, cell size
0.16 mm (vertical), 0.12 mm (extrusion) and 0.12 mm (horizontal).
The cross-section was 7,020 mm.sup.2 and the cohesion ratio C was
1.36.
[0057] A further multilayer foam (Sample ML3) was prepared using
the formulation as described above, but using a 8.9 cm (3.5 inch)
extruder and a plate having five open slits. The density of this
foam was 38.6 kg/m.sup.3, the cell size was 0.35 mm (vertical), 0.2
mm (extrusion) and 0.28 (horizontal). The cross-section was 30,000
mm.sup.2 and the cohesion ratio C was 1.81.
[0058] The data are shown in Table I. Samples ML1, ML2 and ML3
clearly show that excellent performance in mechanical strength,
interlayer adhesion, thermal insulation performance, dimensional
stability, and resistance to water permeation and diffusion were
achieved by the process described in this invention.
EXAMPLE 2
[0059] A multilayer foam (Sample ML4) was produced using a 1.9 cm
(3/4 inch) extruder and using polystyrene as polymer and a mixture
of HFC-134a and ethanol as blowing agent. The 3-layer foam produced
had a low density and showed excellent interlayer adhesion. The
data are shown in Table II.
EXAMPLE 3
[0060] A polyethylene multilayer foam was produced using a 1.9 cm
(3/4 inch) extruder and using HCFC-142b as blowing agent (Sample
ML5). The 3-layer foam produced showed excellent interlayer
adhesion. The data are shown in Table II.
EXAMPLE 4
[0061] A polystyrene multilayer foam was produced using a 1.9 cm
(3/4 inch) extruder, carbon dioxide as the blowing agent and carbon
black as the additive (Sample ML6). The 3-layer foam produced had a
low density and showed excellent interlayer adhesion. The data are
shown in Table II.
1 TABLE I Sample Sample Sample Unit ML1 ML2 ML3 PROCESS DATA PS phr
90 90 90 SaMS phr 10 10 10 Additive phr 0.8 0.85 1.4 HBCD (fire
retardant) phr 0 0 2.5 CO.sub.2 phr 4.5 4.6 4.7 Slit opening, h mm
1.0 0.9 0.9 Distance between slit mm 18.0 13.6 13.6 centers, D
Number of slits open, n slits 3 3 5 Foaming temperature .degree. C.
114 114 117 Foam density, fresh kg/m.sup.3 40.4 44 -- Foam cell
size mm 0.3 -- -- Foam volume, V mm.sup.3/s -- 512000 1110000 Foam
linear speed, L mm/s -- 73 37 Foam board cross-section, S mm.sup.2
11600 7020 30000 Layer Thickness, T mm 23.5 17.3 23 Cohesion ratio,
T/D 1.31 1.27 1.69 FOAM PROPERTIES Void content % 0 0 <1% Foam
thickness mm 70 53 115 Aged density kg/m.sup.3 39.3 45.6 39.4 Cell
size, vertical mm 0.30 0.16 0.33 Cell size, extrusion mm 0.23 0.12
0.27 Cell size, horizontal mm 0.29 0.12 0.34 Closed cell content %
94 >99.7 95.1 Compressive strength, kPa 355 450 260 vertical
Compressive strength, kPa 230 550 265 extrusion Compressive
strength, kPa 215 305 175 horizontal Tensile strength, full kPa 105
375 -- specimen Shear strength, extrusion kPa 190 380 -- Lambda
value, 10.degree. C. mW/m .multidot. K 34.8 34.5 33.9 DIN 18164, WD
test at 30 % 1.2 1 2.1 days, average Water vapor permeance,
.mu.-value -- 149 -- SIA 279 Water pickup, by % vol 0.65 0.20 --
immersion, SIA 279 Freeze-thaw water pickup, % 2.4 0.82 -- SIA
279
[0062]
2 TABLE II Sample Sample Sample Unit ML4 ML5 ML6 PROCESS DATA
Polymer type PS PE PS Additive phr 0.9 0.2 0.9 Carbon black phr --
-- 5 Carbon dioxide phr -- -- 4.7 HCFC-142b phr -- 12 -- HFC-134a
phr 6 -- -- Ethanol phr 1.4 -- -- Slit opening, h mm 0.5 .06 0.6
Distance between mm 6.2 6.3 6.3 slit centers, D Number of slits
slits 3 3 3 open, n Foaming temperature .degree. C. 127 109 126
Foam density, fresh kg/m.sup.3 44 55 44 Foam board cross- mm.sup.2
700 300 550 section, S FOAM PROPERTIES Void content % 0 0 0 Foam
thickness mm 22.5 10.5 19.2
EXAMPLE 5
[0063] The thermal conductivity of a multilayer polystyrene foam
versus two monolithic polystyrene foams was tested. In all cases a
polystyrene formulation with carbon dioxide as blowing agent was
used. The foaming conditions were the same in all cases.
[0064] The results are shown in Table III. The multilayer foam,
showing an improvement in thermal conductivity of 4-4.2 percent,
clearly illustrates the advantage that foams of the present
invention demonstrate when compared to foams produced by means of
the prior art.
3 TABLE III Multilayer foam Monolithic foam Average thickness, mm
115 120 120 Cell size, thickness 0.33 0.3 0.36 direction, mm Aged
foam density, kg/m.sup.3 39.4 39.8 36.7 Thermal conductivity, 33.9
35.3 35.4 mW/m .multidot. K, 10.degree. C. mean temperature, 90
days age
EXAMPLE 6
[0065] The dimensional stability and water permeation resistance of
a multilayer foam (Sample ML2) versus a monolithic polystyrene foam
was tested. In all cases a polystyrene formulation with carbon
dioxide as a blowing agent was used. The foaming conditions were
the same in all cases.
[0066] The results are shown in Table IV. A direct comparison of
multilayer foam ML2 with a monolithic foam of similar density and
vertical cell size showed that the multilayer foam had improved
water permeation resistance (".mu.-value") and better dimensional
stability (as measured by DIN 18164) versus a similar monolithic
foam.
4 TABLE IV Multilayer foam (ML2) Monolithic foam Average thickness,
mm 53 50 Aged foam density, kg/m.sup.3 45.6 44.5 Vertical cell
size, mm 0.16 0.18 Dimensional change, DIN 18164, 1.0 1.1 WD test
at 30 days age, average % Resistance to water vapor 149 130
permeation, SIA 279, .mu.-value
EXAMPLE 7
[0067] A multilayer foam having a center layer comprising a
plurality of individual strands was produced using polystyrene as
polymer and carbon dioxide as blowing agent. The data are shown in
Table V. This multilayer foam demonstrates that one or more layers
of the foam structure can be composed of multiple strands while
maintaining the capacity to make a low density, zero void content
foam with good interlayer and interstrand adhesion.
5 TABLE V Unit Sample PROCESS DATA Polymer type PS Additive phr 0.6
Carbon dioxide phr 4.5 Slit opening, h mm 0.6 Distance between slit
centers, D mm 6.3 Number of slit rows slits 3 Top/bottom slit,
number of openings 1 Center slit, number of openings 3 Left/right
side openings, width mm 1.6 Center opening, width mm 2.6 Foaming
temperature .degree. C. 127 Foam density, fresh kg/m.sup.3 42.6
Foam volume, V mm.sup.3/s 24000 Foam linear speed, L mm/s 22 Foam
board cross-section, S mm.sup.2 660 Layer thickness, T mm 7.5 Size
of interstrand cavities mm.sup.2 none
* * * * *