Polymeric multilayer structures incorporating a layer of vinyl fluoride or vinylidene fluoride polymer which is bonded to a polar polymer layer

Polymeric multilayer structures incorporating a layer made of vinyl fluoride or vinylidene fluoride polymer which is bonded to a polar polymer layer with the use of a vinyl acetate polymer. The polymeric multilayer structures may be in the form of films, sheets, plates, pipes or hollow bodies which can be employed in particular in the field of protection against corrosion or ultraviolet rays.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to polymeric multi-layer structures 
incorporating a layer of vinyl fluoride or vinylidene fluoride polymer 
bonded to a polar polymer layer and more particularly such multilayer 
structures in which the vinyl fluoride or vinylidene fluoride polymer is 
bonded to the polar polymer with the use of a polymeric adhesive. 
2. Discussion of the Art 
Vinyl fluoride polymers and vinylidene fluoride polymers are thermoplastic 
polymers which have a combination of useful properties and, especially, 
high chemical inertness and outstanding resistance to weather and to 
ultraviolet rays. As a result, they find many applications in a great 
variety of fields and, in particular, in protection against corrosion of 
ultraviolet rays. However, they have the disadvantage of being relatively 
costly, which probably restricts their outlets. A suitable means of 
reducing the cost of articles fabricated of a vinyl fluoride or vinylidene 
fluoride polymer consists in employing these polymers in the form of 
polymeric multilayer structures (films, sheets, plates, pipes, hollow 
bodies, and the like) in which they are combined with other polymers 
which, furthermore, contribute their own properties and advantages such 
as, for example, mechanical strength, sealability, impermeability, scratch 
resistance and the like. However, the abovementioned fluorine-containing 
polymers adhere very poorly to other polymers, with the result that it is 
generally necessary to make use of adhesives, which are in most cases 
polymeric, to ensure adhesive bonding between the fluorine-containing 
polymers and other polymers. 
In French Patent No. FR-A-1,484,153 (The Dow Chemical Co.), it is 
recommended to bond a polyolefin layer to a fluorinated hydrocarbon 
polymer layer with the use of a polymeric adhesive consisting, preferably, 
of a copolymer of ethylene and vinyl acetate containing from approximately 
13 to 35% by weight of vinyl acetate. 
It has now been found that the use of such copolymers of ethylene and vinyl 
acetate to bond not a polyolefin but a polar polymer to a polymer of a 
fluorinated hydrocarbon, such as vinyl fluoride or vinylidene fluoride, 
gives multilayer complexes which are sensitive to delamination in the 
region of the fluorine-containing polymer layer. 
SUMMARY OF THE INVENTION 
The present invention aims to provide polymeric multilayer structures 
incorporating a layer of vinyl fluoride or vinylidene fluoride polymer, 
which is bonded to a polar polymer layer which do not have the 
abovementioned disadvantage. 
To this end, the invention provides polymeric multilayer structures 
incorporating a layer of vinyl fluoride or vinylidene fluoride polymer 
which is bonded to a polar polymer layer with the use of a vinyl acetate 
polymer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The term polymeric multilayer structures incorporating a layer made of a 
vinyl fluoride or vinylidene fluoride polymer which is bonded to a polar 
polymer layer is intended to denote multilayer structures containing at 
least one layer made of a vinyl fluoride or vinylidene fluoride polymer 
which is bonded to at least one polar polymer layer. The polymeric 
multilayer structures according to the invention can thus contain one or 
more layers made of a vinyl fluoride or vinylidene fluoride polymer which 
are bonded to one or more polar polymer layers, these layers being 
themselves capable of being bonded to other polymer layers. 
It has been found that, in contrast to the copolymers of ethylene and vinyl 
acetate which are recommended in the prior art, vinyl acetate polymers 
adhere perfectly to vinyl fluoride and vinylidene fluoride polymers. 
Furthermore, the said vinyl acetate polymers adhere perfectly to polar 
polymers. 
The invention thus lies substantially in the use of a vinyl acetate polymer 
to bond and cause to adhere a layer made of a vinyl fluoride or vinylidene 
fluoride polymer to a polar polymer layer in the production of multilayer 
structures. 
The term vinyl acetate polymer is intended to denote both the homopolymer 
and the binary copolymers of vinyl acetate and ethylene containing at 
least 50% by weight of vinyl acetate. The best results are obtained with 
binary copolymers of vinyl acetate and ethylene containing from 60 to 90% 
by weight of vinyl acetate and, still more particularly, with those 
containing from 70 to 85% by weight of vinyl acetate which are, 
consequently, preferred. 
The vinyl acetate polymers, homopolymers and copolymers with ethylene, are 
polymers which are well known in themselves. They can be manufactured by 
any of the conventional methods of polymerisation of ethylenically 
unsaturated monomers. They are usually maanufactured by aqueous emulsion 
polymerisation. 
The vinyl acetate polymers as defined above are polymers which are more or 
less sticky and, consequently, difficult to use. To overcome this 
disadvantage it is particularly advantageous to employ a vinyl acetate 
polymer coated with a thermoplastic polymer. According to a particularly 
preferred embodiment of the invention, use is therefore made of a vinyl 
acetate polymer coated with a thermoplastic polymer. As examples of such 
thermoplastic polymers, mention may be made of vinyl fluoride or 
vinyllidene fluoride polymers and vinyl chloride polymers. A particularly 
preferred thermoplastic coating polymer is polyvinyl chloride. The 
thermoplastic coating polymer is generally present in a proportion of at 
most approximately 10% by weight of the coated acetate polymer. 
Coating of the vinyl acetate polymer with a thermoplastic polymer may be 
carried out, for example, by addition of a vinyl acetate polymer latex to 
a thermoplastic polymer latex and coagulation of the mixture, for example 
by adding an electrolyte. 
The term vinyl fluoride or vinylidene fluoride polymer is intended to 
denote any polymers containing at least 85 mole % and, preferably, at 
least 90 mole % of monomer units derived from vinyl fluoride or vinylidene 
fluoride respectively. The vinyl fluoride or vinylidene fluoride polymers 
which are suitable for the production of multilayer structures according 
to the invention thus include both vinyl fluoride and vinylidene fluoride 
homopolymers and the vinyl fluoride or vinylidene fluoride copolymers 
containing monomer units derived from one or more comonomers. Preference 
is given to the polymers containing at least 90 mole % of monomer units 
derived from vinyl fluoride or vinylidene fluoride respectively, the 
remainder, where applicable, consisting preferably of monomer units 
derived from other fluoroolefins, such as vinylidene fluoride, vinyl 
fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene 
and hexafluoropropylene. Particularly preferred fluorine-containing 
polymers are vinyl fluoride homopolymer and vinylidene fluoride 
homopolymer and, still more particularly, vinylidene fluoride homopolymer. 
The term polar polymer is intended to denote the thermoplastic, elastomeric 
and thermosetting polymers resulting from polymerisation by polyaddition 
or by polycondensation which have a permanent dipole moment or, in other 
words, which contain dipole groups in their molecule. As examples of such 
polar polymers mention may be made of halogenated polymers such as vinyl 
chloride, vinylidene chloride and vinyl bromide polymers (homo- and 
copolymers), polymers containing nitrile groups such as polyacrylonitrile 
and acrylonitrile/styrene copolymers, cellulose-based polymers, 
polyketones, both aliphatic and aromatic polyesters, such as methyl or 
ethyl polyacrylates and polymethacrylates and polyethylene terephthalate, 
vinyl alcohol/ethylene copolymers (that is to say, vinyl acetate/ethylene 
copolymers in which at least 90% of the acetate groups have been converted 
by hydrolysis or alcoholysis into hydroxy groups), aromatic 
polycarbonates, polyamides or nylons and polyurethanes, which are all, 
moreover, well-known polymers. 
Preferred polar polymers are polyvinyl chloride, vinylidene chloride 
copolymers, vinyl alcohol/ethylene copolymers, polyethylene terephthalate, 
polymethyl methacrylate, aromatic polycarbonates derived from bisphenol A, 
nylons 6 and 66 and polyurethanes. 
Particularly preferred polar polymers are polyvinyl chloride, vinylidene 
chloride copolymers and vinyl alcohol/ethylene copolymers containing from 
approximately 15 to 35% by weight of ethylene. 
It is to be understood that each of the constituent polymers of the 
multilayer structures according to the invention may contain the usual 
additives employed when this polymer is used, such as, for example, 
lubricants, plasticisers, heat stabilisers, light stabilisers, particulate 
or fibrous fillers, pigments, and the like. It is particularly 
advantageous to incorporate an ultraviolet stabiliser in the vinyl 
fluoride or vinylidene fluoride polymer or in the adhesive polymer in 
order to protect the polar polymer. Similarly, it may be advantageous to 
incorporate a small quantity, for example up to approximately 10% by 
weight, of adhesive polymer in the constituent polymers of the multilayer 
structures. 
The method of producing the multilayer structures according to the 
invention is not critical. Use can thus be made of any of the usual 
methods of assembling polymer layers to produce the multilayer structures 
according to the invention. As an example of such a technique, mention may 
be made of hot gluing with the use of a solution of vinyl acetate polymer 
in a solvent or a mixture of suitable solvents. Solvents which are 
suitable for this assembly technique are, for example, aromatic 
hydrocarbons such as toluene, chlorinated hydrocarbons such as methylene 
chloride, ketones such as acetone and methyl ethyl ketone, ethers such as 
tetrahydrofuran and esters such as ethyl acetate and their mixtures. 
Preference is given, however, to ethyl acetate. In practice, hot gluing 
with the use of a solution of vinyl acetate polymer is carried out by 
coating cold, for example with the aid of a doctor blade, a film, a sheet 
or a plate made of a vinyl fluoride or vinylidene fluoride polymer (or of 
a polar polymer) with a solution of vinyl acetate polymer, drying the 
coating and hot-pressing the coated (precoated) film, sheet or plate onto 
a film, sheet or plate made of a polar polymer (or of a vinyl fluoride or 
vinylidene fluoride polymer). 
The optimum hot gluing temperature and time will be evaluated 
experimentally in each particular case. They depend, in particular, on the 
nature of the polar polymer, the thickness of the assembled polymer layers 
and the additives employed which may be incorporated in the various 
polymers. 
Other usual assembly techniques for the polymer layers which are suitable 
for producing the multilayer structures according to the invention are 
those in which the constituent polymers are employed at a temperature 
which is at least equal to their softening temperature, such as 
heat-lamination (hot-pressing of the polymer layers preformed, for 
example, by extrusion), coextrusion and coextrusion-lining. 
The choice of one or other of these assembly techniques will be made as a 
function of the properties, particularly heat properties, of the polar 
polymer which is to be bonded to the vinyl fluoride or vinylidene fluoride 
polymer. 
Polymeric multilayer structures which are preferred are those produced by 
assembling by hot gluing or by heat-lamination, by coextrusion or by 
coextrusion-lining and which incorporate three layers, in this case and in 
order a layer of vinyl fluoride or vinylidene fluoride polymer, a layer of 
vinyl acetate polymer and a layer of polar polymer, the latter being 
preferably chosen from polyvinyl chloride, vinylidene chloride copolymers 
and vinyl alcohol/ethylene copolymers containing approximately 15 to 35% 
by weight of ethylene. 
The thickness of the constituent polymer layers of the multilayer 
structures according to the invention and the total thickness of the said 
structures are not critical and naturally depend on the use for which they 
are intended. The polymeric multilayer structures according to the 
invention may therefore be in the form of films, sheets, plates, pipes, 
hollow bodies, and the like. 
The polymeric multilayer structures according to the invention may be 
advantageously employed in the form of films, sheets, plates, pipes or 
hollow bodies, in the areas of application requiring high chemical 
inertness, such as the chemical, pharmaceutical and food-processing 
industries, or a high resistance to ultraviolet rays, such as, for 
example, in the manufacture of agricultural or greenhouse films. As 
non-restrictive, practical examples of uses of multilayer complexes 
according to the invention, attention may be drawn to corrosion-resistant 
multilayer pipes incorporating a layer of rigid polyvinyl chloride, 
multilayer films and sheets for agriculture, incorporating a layer of 
polyvinyl chloride or polymethyl methacrylate, multilayer tarpaulins and 
sails incorporating a layer of polyurethane or polyethylene terephthalate, 
in which the layers consisting of the abovementioned polar polymers are 
bonded to a layer made of a vinyl fluoride or vinylidene fluoride polymer, 
and preferably of polyvinylidene fluoride, with the use of a vinyl acetate 
polymer. 
The following examples illustrate the invention without, however, 
restricting it. 
Example 1, according to the invention, relates to a three-layer coextruded 
tubular structure incorporating, in this order, a layer (A) made of a 
vinylidene fluoride homopolymer (thickness: 200 .mu.m), a layer (B) made 
of a vinyl acetate/ethylene copolymer containing 88% by weight of vinyl 
acetate (thickness: 200 .mu.m) and a layer (C) of flexible polyvinyl 
chloride (thickness: 540 .mu.m). 
Example 2, for reference, relates to a three-layer coextruded structure 
similar to that of Example 1, except that the adhesive polymer (layer B) 
is an ethylene/vinyl acetate copolymer containing 61% by weight of 
ethylene. 
To manufacture the three-layer coextruded structures of Examples 1 and 2, 
three extruders (A) (B) (C) are arranged, feed a special coextrusion head. 
The displayed heating temperatures are, from the feed zone to the pumping 
zone respectively: 
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200.degree. C.-210.degree. C. 
for extruder A 
90.degree. C.-140.degree. C. 
for extruder B 
155.degree. C.-165.degree. C.-180.degree. C.-180.degree. C. 
for extruder C 
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The extruders A, B and C supply, respectively, the layers A, B and C of the 
coextruded structure. 
Examples 3 and 4, according to the invention, relate to five-layer 
structures obtained by coextrusion-lining. 
In Example 3, a two-layer coextruded structure manufactured using a flat 
die and consisting of a layer made of a vinylidene fluoride copolymer 
containing 5% by weight of monomer units derived from a fluoroolefin 
(average thickness: 800 .mu.m) and a layer of vinyl acetate/ethylene 
copolymer containing 60% by weight of vinyl acetate (average thickness: 
170 .mu.m) is lined continuously at the exit of the abovementioned flat 
die and at a low pressure with a non-preheated three-layer structure 
consisting of a textile coated on both faces with flexible polyvinyl 
chloride (total thickness: 800 .mu.m). 
In Example 4 and according to the operational procedure described in 
Example 3, the two-layer coextruded structure of Example 3 is lined 
continuously with a non-preheated three-layer structure consisting of a 
textile coated on both faces with polyurethane elastomer (total thickness: 
200 .mu.m). 
Collated in Table I are the results of the evaluation of adhesion, measured 
as the peel strength of the multilayer structures according to Examples 1 
to 4. The peel strength is measured in a Frank type 650 tensometer using a 
method based on the ASTM standard D 1876-72. 
Examples 5 to 12, according to the invention, relate to the hot gluing of a 
layer made of vinylidene fluoride homopolymer (film with a thickness of 
100 .mu.m) on a polar polymer layer with the use of a 
vinyl-acetate/ethylene copolymer containing 75% by weight of vinyl 
acetate, coated with polyvinyl chloride representing 7.5% by weight of the 
coated vinyl acetate copolymer. 
Using a 150 .mu.m wire spreader, the polyvinylidene fluoride film is coated 
with a solution of vinyl acetate copolymer at a concentration of 30% by 
weight in ethyl acetate, the coating is dried for 6 hours at ambient 
temperature, after which a second layer of vinyl acetate copolymer (as a 
solution at a concentration of 30% by weight in ethyl acetate) is applied 
under the same conditions, and the coating is dried for 24 hours at 
ambient temperature. The total thickness of the dry coating is 90 .mu.m. 
The precoated polyvinylidene fluoride film is pressed hot onto a polar 
polymer layer for 20 minutes under a pressure of 46 kg/cm.sup.2 in a 
Lafarge press maintained at 120.degree. C., and then the complex is 
transferred to a cold press and held therein at ambient temperature for 10 
minutes under the same pressure. 
Example 13, for reference, relates to hot gluing of a layer made of 
vinylidene fluoride homopolymer (film with a thickness of 100 .mu.m) on a 
layer of rigid polyvinyl chloride (film with a thickness of 200 .mu.m) 
with the use of an ethylene/vinyl acetate copolymer containing 61% by 
weight of ethylene. 
Using a 150 .mu.m wire spreader, the polyvinylidene fluoride film is coated 
with a solution of ethylene copolymer at a concentration of 40% by weight 
in tetrahydrofuran, which is applied in two layers according to the 
operating procedure of Examples 5 to 12. The total thickness of the dry 
coating is 120 .mu.m. The precoated polyvinylidene fluoride film is 
pressed in accordance with the operating procedure of Examples 5 to 12 
onto the rigid polyvinyl chloride film. 
The nature of the polar polymer and the thickness of the polar polymer 
layer employed in Examples 5 to 13, together with the results of the 
evaluation of the peel strength of the multilayer structures obtained by 
hot gluing in Examples 5 to 13, are collated in Table II. 
TABLE I 
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Method of producing Peel 
Example 
the multilayer strength, 
no. structure Polar polymer 
newtons/cm 
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1 coextrusion Flexible poly- 
&gt;10 
vinyl chloride 
2 coextrusion Flexible poly- 
3.77 
vinyl chloride 
3 coextrusion Flexible poly- 
&gt;10 
lining vinyl chloride 
4 coextrusion Polyurethane 
7.55 
lining elastomer 
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TABLE II 
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Polar polymer Peel 
Example Layer strength, 
no. Nature thickness newtons/cm 
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5 Vinyl alcohol/ethylene 
50 .mu.m 
12.50 
copolymer containing 20% 
by weight of ethylene 
6 Polyethylene terephthalate 
50 .mu.m 
15 
7 Nylon 6 30 .mu.m 
8.93 
8 Vinylidene chloride/vinyl 
20 .mu.m 
12.40 
chloride copolymer 
9 Rigid polyvinyl chloride 
200 .mu.m 
21.90 
10 Polymethyl methacrylate 
4 mm 19.45 
11 Polyurethane elastomer 
0.8 mm 14.62 
12 Aromatic polycarbonate 
4 mm 15.00 
derived from bisphenol A 
13 Rigid polyvinyl chloride 
200 .mu.m 
4.74 
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