Multilayer structure

Structures built up from at least two layers one layer of which is built up from a polyalkylene phthalate ester film and one layer of which is built up from a polystyrene film.

The invention relates to a multilayer structure comprising at least two 
layers with 
(a) at least one layer, comprising a polyalkylene phtalate ester film. 
Multilayer structures comprising at least one layer comprising a 
polyalkylene phtalate ester film are general known. 
FR-A-2445223 describes multilayer structures comprising one layer of a 
polybutyleneterephtalate and one layer of a rubber modified polystyrene, 
bonded together by a bonding layer consisting of a special type of block 
copolymer (example 4-12). 
In manufacturing multilayer structures it is preferred to make structures 
not needing a special bonding layer. 
EP-A-0121883 describes multilayer structures built up from several layers 
in which at least one layer consists substantially of a mixture of a 
poly(1,4-butylene-terephthalate) having an extraordinarily high intrinsic 
viscosity of more than 1.5 parts/g and an amorphous copolyester copolymer 
built up from 1,4-cyclohexanedimethanol units, optionally ethylene glycol 
units and terephthalic acid or a mixture of terephthalic acid and 
isophthalic acid. A second layer may consist of poly(alkylene 
terephthalates), polycarbonates, poly(arylsulphones), polyacrylates, 
polymethacrylates, polyurethanes, polyamides, polyimides, polyamideimides, 
polyesterimides, polyesteramides, thermoplastic polymers and the like. The 
second layer preferably consists of a polycarbonate. According to 
EP-A-0121883 the above-mentioned mixture consisting of polybutylene 
terephthalate and the amorphous copolyester copolymer has good barrier 
properties and it can readily be processed in extrusion-coinjection-blow 
moulding. It is stated in EP-A-0121883 that layers of the above-mentioned 
mixture can readily be bonded to layers substantially consisting of other 
thermoplastic materials without the use of extra bonding layers. 
EP-A-0121883 therefore uses instead of a bonding layer a very special 
polyalkylene terephtalate based composition. 
EP-A-0128425 describes multilayer structures comprising one PET base layer 
and one foamed polystyrene layer. It has been indicated that the PET layer 
can be laminated on the foam layer by thermal adhesion or through a 
bonding layer. 
It has now been found that a polyalkylene terephtalate based film can be 
readily adhered onto a polystyrene or rubber modified polystyrene film 
without using a bonding layer. 
The multilayer structure according to the invention can therefore be 
characterised in that it comprises besides the above mentioned layer (a) 
b) at least one layer substantially consisting of a polystyrene film or a 
rubber modified polystyrene film, the layers (a) and (b) being juxtaposed 
and being bonded together by thermal adhesion without using a bonding 
layer. 
It is not an object of the invention to obtain rights for the structures 
which comprise a layer built up from a mixture of a polybutylene 
terephthalate having an intrinsic viscosity of more than 1.5 parts/g and 
an amorphous copolyester as described in EP-A-0121883. 
It is possible to obtain a further improved bonding between the layers (a) 
and (b) when layer (a) consists of a film out of a polyalkylene phthalate 
ester which is mixed with a functionalised polystyrene. 
(a) The layer comprising a polyalkylene phthalate ester film. 
The structure according to the invention comprises at least one layer (a) 
as defined hereinbefore. Layer (a) consists of a film out of a material 
comprising more than 50% by weight, preferably more than 80% by weight, 
calculated with respect to the sum of all polymeric constituents, one or 
more polyalkylene phthalate esters, optionally in combination with a 
functionalised polystyrene. 
Polyalkylene phthalate esters are compounds known per se. They are built up 
from units derived from one or more diols and one or more phthalic acids. 
Examples of suitable diols are ethanediol, butanediol, hexanediol, 
cyclohexanedimethanol, diethylene glycol, triethylene glycol and etherdiol 
compounds of the general formula H--0--[(CH.sub.2).sub.n --0]--.sub.m H. 
Suitable phthalic acids are terephthalic acid and isophthalic acid. As 
phthalic acids are particularly suitable terephthalic acid and isophthalic 
acid. A small quantity of, for example, up to 20 mol.% of the phthalic 
acid may be replaced by other dicarboxylic acids, for example, adipic 
acid. 
The polyalkylene phthalate esters may be branched. 
Particularly suitable in the structures according to the invention are the 
polyalkylene phthalate esters the alkylene units of which are derived for 
more than 80 mol.% from terephthalic acid. It is possible as such to use a 
polybutylene terephthalate having an intrinsic viscosity of less than 1.5 
parts/g. Suitable are polybutylene terephthalate esters having an 
intrinsic viscosity of 0.7 to 2.0, preferably from 0.7-1.5 parts/g 
(measured in a 60/40 mixture of phenol/tetrachloroethane at 25.degree. 
C.). 
Layers constructed from the above-mentioned polyalkylene phthalate ester 
films have a good bonding to polystyrene film layers without the use of 
special intermediate layers of bonding material. 
In those cases in which particularly high requirements are imposed upon the 
bonding, it is possible according to the invention to use a layer from a 
polyalkylene phthalate ester which is mixed with an agent to improve the 
bonding. As an agent to improve the bonding may be used in the structures 
according to the invention a functionalised polystyrene incorporated in 
the layer consisting substantially of the polyalkylene phthalate ester. 
Functionalised polystyrene is to be understood to include polymers which 
comprise units derived from styrene or styrene derivatives and which also 
comprise units with reactive groups, i.e. groups which can enter into a 
physical ineraction with the polyalkylene phthalate ester. Examples of 
such groups are carboxylate groups or derivatives thereof, methacrylate 
groups, hydroxyl groups, epoxy groups, amine groups, oxazoline groups, 
sulphonate groups or derivatives thereof, nitrile groups, carbonate groups 
or derivatives thereof, amide groups and imide groups. 
The units with reactive groups may be incorporated in the functionalised 
polystyrene in various manners, for example, in the form of random 
copolymers and block copolymers. Another manner consists in that the said 
units are grafted on a styrene polymer. 
Suitable examples of functionalised polystyrene are the generally known 
styrene-maleic anhydride copolymers or the rubber-modified embodiments 
thereof and polystyrene on with reactive groups such as oxazoline groups. 
These products are commercially available: the first-mentioned as 
DYLARK.RTM. from Messrs. ARCO, the second group as developmental polymer 
XUS-40056.01 from Dow Chemical Company. Furthermore suitable are the 
polystyrenes with methacrylate or hydroxyl terminal groups (commercially 
available as CHEMLINK.RTM. from the Sartomer Company). 
The addition of S-MA to PET for improving the adhesive properties has been 
described in UK-A-2076832. EP-A-0205145 describes multilayer structures in 
which one layer comprised a polymer having reactive pendant cyclic imino 
ether groups and one adjecent layer comprises a polymer with groups 
coreactive with said cyclic imino ether groups. As such special copolymers 
having carboxyl groups, amino groups, amide group and the like are used. 
The graft copolymers as described in US-A-3,786,116 are also suitable. 
These graft copolymers consist of a back bone which comprises 
ethylenically unsaturated monomers each having more than 1 vinylidene 
group (for example, alkyl esters of (meth)acrylic acid). Linear polymeric 
side chains in the form of polymers or copolymers having a molecular 
weight from 5,000 to 50,000 with more than one polymerisable moiety per 
(co)polymer chain are grafted on the said grafting base, said 
polymerisable moiety being present at the end of the chain. An example of 
such a side chain is a polystyrene chain with terminal vinyl groups. 
The weight ratio of used functionalised polystyrene to polyalkylene 
phthalate ester preferably is between 0.01:1 and 0.1:1. 
(b) The layer consisting substantially of polystyrene or a modified 
polystyrene 
The structures according to the invention comprise at least one layer 
consisting substantially of polystyrene film or a rubber modified 
polystyrene film. "Consisting substantially of" is to be understood to 
mean that the material of which the layer in question consists, is built 
up from polystyrene or rubber modified polystyrene for more than 50% by 
weight, preferably more than 80% by weight, calculated with respect to the 
sum of all polymeric constituents. 
Polystyrenes are to be understood to include polymeric compounds which 
comprise units derived from styrene or styrene derivatives such as 
alphamethyl styrene or halogenated styrene. These polymers may be modified 
with a rubber, for example a polybutadiene rubber (so-called high-impact 
polystyrene). The thickness of layer (a) usually is between 0.05 to 4.0 
mm, that of layer (b) is between 0.05 and 10 mm. 
The structures according to the invention may be built up from two or more 
layers. For example, the structure according to the invention may be built 
up from a layer consisting of a polyalkylene phthalate ester film and a 
juxtaposed layer bonded thereto and consisting substantially of 
polystyrene or a rubber modified polystyrene. A structure built up from 
three layers may consist, for example, of a central layer consisting of a 
polyalkylene phthalate ester film and two enveloping layers consisting 
substantially of polystyrene or a modified polystyrene films. It is also 
possible to combine the structure according to the invention with layers 
consisting substantially of other thermoplastic materials, for example, 
polycarbonate, polyvinyl chloride. 
The structure according to the invention may be obtained according to a 
method generally known for such structures. For example, the structure can 
be obtained by laminating the individual layers obtained in a seperate 
extrusion step or also by coextrusion by means of a die specially suited 
for coextrusion. "Coinjection moulding" is also a suitable technique. Any 
desired article can be manufactured from the structure according to the 
invention, for example, by cold deformation, thermal deformation, blow 
moulding, and the like. The adhesion between the different film layers is 
thereby obtained by bonding them together at elevated temperature, 
possibly in combination with pressure. 
The structure according to the invention is suitable for example, to 
manufacture therefrom packaging materials in the form of holders, cups, 
and the like. 
In the manufacture of the structures according to the invention or in the 
manufacture of articles therefrom, a considerable quantity of waste 
material may occur. This waste material may be ground, a mixture of the 
various materials which are present in the structure according to the 
invention being formed. Articles can be manufactured from these mixtures 
by injection moulding. It is another object of the invention to also 
obtain exclusive rights for these mixtures. 
The composition of these mixtures depends on the structure according to the 
invention from which they have been obtained. In general, these mixtures 
comprise 5-95% by weight of polyalkylene phthalate ester and 95-5% by 
weight of polystyrene or a modified polystyrene, calculated with respect 
to the quantity of polyalkylene phthalate ester plus (modified) 
polystyrene. A functionalised polystyrene may also be present in the 
mixtures.

The invention will now be described in greater detail with reference to the 
ensuing specific examples. 
EXAMPLE I 
Several different films were manufactured having a composition as indicated 
hereinafter (TABLE A). The films were prepared by pressing the materials 
in a mould (dimension of the pressed layers: 180.times.50.times.0.65 mmm). 
The materials were first heated in the mould to just below their softening 
point and were kept at that temperature for 30 seconds. The material was 
then brought under a pressure of 25 kN for minutes. The films were then 
cooled in air. 
TABLE A 
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Film No. Composition (% by weight) 
______________________________________ 
1 High-impact polystyrene (having 9.5% by 
weight of rubber and 20-25% by weight of gel 
fraction). 
2 Polybutylene terephthalate (PBT) (intrinsic 
viscosity 1.18 parts/g. 
3 80% by weight of PBT + 20% by weight of high- 
impact polystyrene. 
4 80% by weight of PBT + 20% by weight of 
polystyrene functionalised with oxazoline. 
5 80% by weight of PBT + 20% by weight of 
rubber-modified styrene-maleic anhydride 
copolymer (DYLARK .RTM. 250). 
6 50% by weight of PBT + 50% by weight of 
DYLARK .RTM. 250. 
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Various structures, each consisting of one film I and one of the films 2 to 
6 inclusive were manufactured from the layers thus obtained. 
The structures were manufactured by pressing the films one on the other at 
250.degree. C. for 2 minutes under a pressure of 25 kN. 
The mutual bonding strength of the layers in the resulting two-layer 
structures was determined as follows. The two film layers were separated 
from each other mechanically (by means of a knife) over a length of 40 mm. 
The ends obtained were each bent at an angle of approximately 90.degree. 
with the two-layer structure and clamped in a drawing machine. The layers 
were pulled apart at a pulling rate of 5 mm/min. 
The force occurring when the two layers detached (fracture) was determined. 
The found values are recorded in TABLE B. 
TABLE B 
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Structure built up 
from layer Nos. Force when the layers detached (N) 
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2 & 1 4 
3 & 1 1.3 
4 & 1 12.8 
5 & 1 12.5 
6 & 1 24 
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It may be seen from the results of TABLE B that the laminate according to 
the invention has a good bonding between the various layers, even in case 
of the combination of film layer 1 with film layer 2 or 3. A further 
improvement in bonding strength is obtained by using film layers 
comprising a functionalized polystyrene, in particular the laminates with 
a layer 4, 5 or 6. 
EXAMPLE II 
Two structures, each built up from a layer of high-impact polystyrene film 
having a rubber content of 8-10% by weight and a gel fraction of 20-25% by 
weight and a layer of polybutylene terephthalate film (PBT having an 
intrinsic viscosity of 1.10 parts/g) were manufactured by coextrusion in a 
Reifenhauser extruder. In the first case the layer consisted of pure PBT 
film; in the second case it consisted of a film out of a mixture of 90% by 
weight of PBT and 10% by weight of DYLARK.RTM.250 (as used in Example I*). 
In the coextrusion in a Reifenhauser extruder the PBT/DYLARK mixture was 
prepared directly in the coextruder. The high-impact polystyrene was 
supplied through the main extruder. 
A procedure similar to that as described in Example I was followed for 
determining the bonding strength between the layers: the layers were 
separated from each other mechanically over a certain length. The end of 
one of the two layers was bent back over an angle of approximately 
180.degree. . The ends of the detached layers were clamped in a drawing 
machine. The force occurring when the two layers detached (fracture) was 
determined. The found values are recorded in TABLE C. 
TABLE C 
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Force when the layers 
Structure detached (N) 
______________________________________ 
.cndot. high-impact polystyrene/PBT 
0.3 
.cndot. high-impact polystyrene/PBT 
&gt;35 
+ DYLARK .RTM. 250 
______________________________________ 
It may also be seen from TABLE C that bonding occurs already in structures 
with layers consisting of (high-impact) polystyrene and PBT. This bonding 
may be considerably improved by using a polymer mixture which comprises a 
functionalised polystyrene. 
EXAMPLE III 
In the same manner as described in Example I, three film layers were 
manufactured from: 
(a) a mixture of 80 parts by weight of polyethylene terephthalate (=PET 
having an intrinsic viscosity of 0.70 parts/g measured in a 60/40 mixture 
of phenol and tetrachloroethane at 30.degree. C.) and 20 parts by weight 
of high-impact polystyrene. 
(b) a mixture of 80 parts by weight of the same PET and 20 parts by weight 
of DYLARK.RTM.250. 
(c) high-impact polystyrene. 
The same product as was used in Example I was used as a high-impact 
polystyrene. The layers were compressed at 250.degree. C. Two multilayer 
structures were manufactured: the first from a film layer of PET +HIPS in 
combination with a film layer of HIPS; the second from a film layer of 
PET+DYLARK.RTM.250 in combination with a film layer of HIPS. The said 
layers were pressed one on the other at a temperature of 250.degree. C. 
The bonding strength was determined in the same manner as in Example I. The 
results are recorded in TABLE D. 
TABLE D 
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Force when the layers 
Structure built up from 
detached (N) 
______________________________________ 
PET + HIPS film and 
11.0 
HIPS film 
PET + DYLARK .RTM. 250 
14.5 
film and HIPS film 
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