Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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583-140-0
TITLE OF THE INVENTION
PLASTIC LAMINATE COMPRISING AROMATIC
POLYETHER IMIDE AND AROMATIC POLYETHER SULFONE
BACKGROUND OF THE INVENTION
Field o~ the Invention:
The present invention relates to a new polymer laminate
with flame retardant properties comprising an aromatic
polyether imide and an aromatic polyether sulfone. The
aforementioned plastics belong to a group of aromatic polymers
that are called structural plastics or "engine~ring plastics".
They are characterized'by thermoformability, high heat
resistance, good impact strength and high strength values, but
differ in their fire behavior, e.g., in their flame retardant
properties.
Discussion of the Backqround:
A preferred field of application of structural plastics
lies in the extrusion of flat plastic webs with a uniform
thickness ranging from about 1 to 5 mm. They may be molded in
the thermally softened state into three dimensional molded
parts, which are used, for example, as the inner lining of
motor vehicles, ships or airplanes. For these applications a
dulled surface is desired. Therefore, the webs are directed
immediately following extrusion through an embossing calender,
where a granular dull structure is produced with a dulling
roller. This structure is to remain preserved during forming.
Aromatic polyether sulfones fulfill this requirement.
They can be formed under conditions under which the dull
structure of the surface is not lost. Unfortunately the
elongation at break of the aromatic polyether sulfones leave
much to be desired for many applications.
An important condition for the application of structural
plastics in airplane construction is the fulfillment of the
fire requirements according to the OSU test (Ohio State
University). It demands, starting August 1990, that a heatun,~ 14,1991 release rate
release velocity of 65 kW min/m2 and a heat h~ F Of 65
kW/m2 within the first 2 minutes of fire stress are not
exceeded; these measurement values are called HR and HRR.
The aromatic polyether sulfones in the pure form do not
satisfy the requirements of the OSU fire test. To meet this
standard, they must be mixed with flame resistant additives
Ju~ 14,1991 ~mechanical and physical~
Qthat, as a rule have a negative impact on the~f~notie~a~
properties.
Aromatic polyether imides are flame retardant, without
specific additives, as defined by the OSU fire test, but they
are too brittle for many applications. Therefore, they are
sometimes mixe~ with tougher, compatible polymers and thereby
exhibit an improved impact strength, However, such mixtures
have an unsatis~actory elongation at break. The OSU test is
also fulfilled by some mix~ures of this kind. It has been
further demonstrated that when thermoforming webs made of
these plastics, the embossed granular sur~ace structure does
~Q~7~21
not remain preserved, but rather the surface is smooth and
glossy, a feature that in undesired. The mandatory dull
structure must, therefore, be produced in a subsequent
operation by applying matt-finish paint.
Two different structural plastics are known from EP-A 195
229 and US-A 4 576 842, said plastics differ in their
allowable working temperatures to process into three layered
laminates by coextrusion. From these laminates heat resistant
kitchen dishes are produced by thermoforming. In many cases
it is preferred that the inner layer of the laminate has a
higher allowable working temperature than the outer layer in
other cases the reverse. The suitable structural plastics
also include polyether sulfones and polyether imides that are
used alternatively as the core layer material. Laminates that
have in common both of these two plastics are not known.
The invention is based on the problem of providing an
extruded plastic web made of structural plastic with flame
resistant properties and good mechanical properties. Above
all, a structural plastic with a high elongation at break and
toughness, that is provided with a surface structure, and can
be deformed in the softened state without loss of this
structure is provided for.
SUMMARY OF THE INVENTION
Accordingly, one object of this invention is provided by
a polymer laminate, characterized by a core layer made of an
2 ~ L '~ .~
aromatic po~yether imide or a mixture thereof with at most 40
wt.% of a compatible polymer material and cover layers that
are connected so as to adhere to both sides of the core layer
and which are made of an aromatic polyether sulfone.
The new laminates can be formed in the thermally softened
state while maintaining their surface structure.
Surprisingly, high elongation at break values, whlch can
exceed those of the individual plastics themselves are
obtained. Pure commercial polyether imide (Ultem 1000,
trademark of General Electric Co.) has in the form of extruded
webs, a tensile strength ranging from llO to 117 MPa and an
elongation at break ranging from 29 to 46%. When mixed with a
poly-~imide-siloxane) block copolymer (Ultem 1668, trademark
of General Electric Co.), the tensile strength drops to 92 to
102 MPa and the elongation at break to 19 to 39%. A tensile
strength of 97 MPa and an elongation at break of 67% were
measured on a coextruded laminate of the present invention
that bears on both sides 0.2 mm thick cover layers made of
aromatic polyether sulfone on a core layer made of the
aforementioned mixture. When pure polyether imide is used as
the core material, such layers have an even greater effect on
the properties of the plastic web. Through coextrusion with
0.2 mm thick cover layers made of polyether sulfone the
elongation at break ranging from 30 to 45 for the core
material alone increases to the astonishingly high value of 90
to 105% for the coextrudate. Similarly, the Gardner impact
strength of 1 J rises to over 18 joules.
The new laminates largely fulfill the OSU fire test. An
HR value of 19 and an HRR value of 73 were found for PEI/PES
laminates of the invention. When polyether imide is mixed
with a poly-(imide/siloxane) block copolymer, the HR/HRR
values are reduced to g - 19/29 - 37.
~ DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
June .1~19,9~ '~ s
~ /~ de, An essential component of the core layer i~ an aromatic
June 14, l99l
f~ ~ olyether imide. Aromatic polyether ~mides that are suitable
~for the invention are known from the U.S. patents 3,847,867,
3,838,097 and 4,107,147. They are synthesized from repeating
units of the general formula I
~CO~ o ~CO'
The degrees of polymerization n lies preferably in the range
of 10 to 10,000 or optionally above. R denotes a bifunctional
aromatic group, which is bonded via ether oxygen atoms in the
met~ or para position to the phthalimide units. R can also
comprise several aromatic cores bonded preferably in the p, p'
position by a single bond or by heteroatoms such an -0-, -S-,
or by -S02- groups or alkylene groups such as methylene or
~. ,
~7~2~
2,2-propylene. The imide nitrogen atoms are linked by
identical aromatic groups R' that can, however, be different
~rom R. The preparation of aromatic polyether imides is
generally known. Especially preferred is a polymer comprising
repeating units of formula II.
L-Nf ~O~CCH3 ~0~ CO~, -1
To improve the impact strength and other properties, the
polyether imides can be mixed with other polymer material that
can be coextruded with said polyether imides and have a higher
strength. Such mixtures are manufactured by introducing the
two plastics into an extruder and mixing intimately in the
melt. The proportion of the mixing component is kept as small
as possible, in order to retain the flame resistant properties
of the polyether imide, but must be large enough to obtain the
required improvement of the toughness properties. An impact
strength ranging from 12 to 18 joules in the Gardner test (in
accordance with ASTM D 3029 - 28n) is adequate. As a rule,
additional quantities rangin~ from about 10 to 50 wt.%, based
on the weight of the mixture, are used.
Suitable compatible thermoplastic polymer materials with
higher strength are, e.g., aromatic polycarbonates and
aromatic poly-(imide-siloxane) block copolymers. Among the
~7~
aromatic polycarbonates, the derivatives of the ~isphenol A
are especially preferred. Other polycarbonate plastics can be
derived from other dihydroxyphenols, e.g., from
bis-(4-hydroxyphenyl)-methane, 2,2-bis-(4~hydroxy-3-
methylphenyl-)-propane, 4,4-bis-(4-hydroxyphenyl)-heptane.
Other polycarbonate plastics are known from US-A 2,999,835,
3,028,365 and 3,334,154.
Aromatic poly-(imide-siloxane) block copolymers are known
from EP-A 273 150. They can be described by the formula III,
[ ~CO~o-R-o~co~N R3-o'~R~;-o~);,;~ :11[
wherein n and m denots the degree of polymerization o* the
participating polyether imide and polysiloxane blocks; they
can have values ranging from 1 to 50. The variable a denotes
the number of the two blocks and can have values ranging from
1 to 10,000. R and R' are biEunctional aromatic groups, which
can have the same structure as in formula I. R" are aliphatic
or aromatic groups such an methyl, phenyl, cyanoethyl or
trifluoromethyl ethyl.
To form the cover layers, aromatic polyether sulfones
having a melt viscosity suitable for extrusion are used. The
MFI value (melt flow index) of the aromatic polyether sulfone
is at 360C, e.g., at about 30 cm /lO min.
The aromatic polyether sulfones are synthesized from
repeating units of the general structural formula
- (Ar - SO2 - Ar ~ ) n ~
where Ar donates a bifunctional, mono sr polynuclear aromatic
Ju 1 ~roup. ~referably the Ar groups comprise p-phenylene groups,
~ ~ w ~ch can bear optional substituents, like ~ewe~ line~r or
June 14 ,1991
~branched C1 l2 alkyl groups or cyclo C~ alkyl ~roups
Polynuclear Ar groups contain, for example, two such phenylene
groups, which can be coupled by a single bond or by an oxygen
or sulfur atom or by S02-, methylene or isopropylidene groups.
The aromatic polyether sulfones can be optionally modified
with flame resistant additives or similar auxiliary agents.
The new laminates are producad in a well-known manner
through coextrusion of the core and cover layer naterial. The
materials are melted in separated extruders and fed into a
coextrusion adapter, whereby they are uni~ed into a three
layered strand. Said strand is extruded at temperatures
ranging from about 300 to 380C from a flat die in the shape
o~ a flat web of uniform thickness. It can be, e.g., 500 to
2,500 mm wid~. The total thickness o~ the web can range from
1 to 5, preferably from 1 to 3 mm. 0.05 - O.5 mm, pre~erably
O.2 to 0.5 mm o~ said thickness are allocated to the cover
.
layers, respectively. If said cover layers are relatively
thin, e.g., less than 0.2 mm thick, the improved strength
values are not always obtained. With cover layers of greater
thicknes~ there is the danger that the OSU fire test will not
.
be fulfilled. Thus, the core material comprises about 60 to
80 wt.% of the new laminates; and the cover layer material
comprises 20 to 40 wt.%. It must be mentioned that in many
ca es with this construction a cost saving is achieved with
respect to the web having uniform thickness and made of pure
core material, since the polyether sulfones are as a rule less
expensive than the modified polyether imides.
If a surface structure is desired, the extru~ion-hot
multilayer web can be directed immediately following
coextrusion through an embossing calendar, where the surface
structure of the embossing roller is molded on the surface of
the web and is stabilized ~elow the softening temperature
through cooling. Preferably, a granular dull structure is
produced with a dulling roller. As a rule it suffices if one
of the cover layers is structured in this manner.
Molded par~s having three dimensional shapes such as
elements for the inner lining of airplanes can be produced
from the lamina~es of the invention in vacuum forming machines
with positive tools. In so doing, the back side of the
laminate abuts preferably the tool surface, whereas the
structured front side is free. Forming at negative tools with
structured surfaces is possible but less usable.
To form, the laminate is heated to 270 to 300C. To this
end, a heating station comprising an upper and bottom heating
J~ 14,1991
~ t is suitable. The thermoplastically softened web,is-~dYe~
June~14~ 199 ~ ~ ~ cd in a clamping frame, grasping the edge, _
(/ is directed to a position above the forming tool,
~~; ~
J~
--10--
un~ 14 1991 its
and placed against this surface by means of a vacuum. To
~c. ~ guarantee accurate detail forming, it can be expedient to heat
the tool. Following cooling below the softening temperature,
venting occurs and the molded part is removed.
Other features of the invention will become apparent in
the course of the following description of exemplary
embodiments which are given for illustration of the invention
and are not intended to be limiting thereof.
EXAMPLES
Embodiment
Undyed commercial polyether imide extrusion molding
compound (trade name ~Ultem 1000", trademark of General
Electric Co.) and pigmented polyether sulfone extrusion
molding compound (trade name ~Ultrason E 3000, trademark of
BASF AG) are melted in separate extruders and united into a
three layer strand in a coextrusion adapter. Said strand is
introduced into an extrusion flat die and extruded at 350C in
the shape of a 2~5 mm thic~ web, which contains the polyether
imide as core layer and a 0.3 mm thick cover layer made of
polyether sulfones on each side of the core layer. The
extruded web is taken over by an embossing calender, where itune~4,1991 smoothed
is pe~ibd~ or dulled on one surface and is cooled below the
softening temperature. The web is divided with a separating
device into sheets of desired size.
~7~21
For comparison purposes a uniformly thick web made of
polyether imide was extruded alone. The following mechanical
properties were determined on the extrudates.
_ single layer laminate of
comparison the invention
material
tensile strength (MPa) 110 110
modulus of elasticity (MPa) 3300 3300
elongation at break (%)29 - 46 90 - 105
Gardner impact strength (J) approx. 1 > 18
OSU fire test values
HR ~kW min/m2) 9 - 22 12 - 19
HRR (kW/m2) 72 - 76 73 - 77
The laminate of the present example displays a
significantly improved Gardner implact strength as compared
with the single layer material.
Embodiment 2
A three layer laminate and a single layer comparison
material are manufactured as in embodiment 1, but in place of
polyether imide its mixture with a poly-(imide-siloxane)-block
copolymer is added. This mixture is commercially available
under the name "Ultem 1668" (trademark of General Electric
Co . ) .
The following mechanical properties were determined on
the extrudates.
~ ~1 L1 7 i~
-12-
_ _ _ single layer laminate of
comparison the invention
material
tensile strength (MPa)90 - 100 97
modulus of elasticity (MPa) 3300 3300
elongation at break (%)19 - 39 67
Gardner impact strength ~J) > 18 > 18
OSU fire test values
HR (kW min/m2) 0 - 30 9 - 19
HRR (kW/m2) 17 - 55 29 - 37
The lamina-te of the present example displays a
significantly improved elongation at break strength.
Obviously, numerous modifications and variations of the
present invention are possible in light of the abave
teachings. It is therefore to be understood that within the
scope of the appended claims, the invention may be practiced
otherwise than as specifically described herein.
