Composite material consisting of polyvinylidene fluoride and a thermoplastic polymer incompatible therewith and process for producing this material by coextrusion

<^This invention relates to a composite material consisting of polyvinylidenefluoride, a polymer referred to as PVF₂ lor short, and a thermoplastic polymer incompatible with PVFg. This composite material is obtained by cocxtrasion. .

The technique of coextrusion of thermoplastics is well known and is described in particular in POLYMER. PLASTICS TECHNOLOGY AND ENGDWIING, Volume 3, pages 49 to 68: ”Coextruded films - Process anΛ properties” by John E. GUHiLOTTE.

Generally, three methods of coextruding thermoplastics from a number of conventional extruders equal to the number of polymers to be extruded are known. The first process consists in extruding the polymers separately and combining ;them as they leave the aie. The second process consists in feeding a single die from at least two extruders,* the die having as many channels as there are extraders and hence polymers to be extruded. The fluxes of polymers combine at the lips of the die, i.e. substantially just before leaving the die. The third process consists in feeding a flux distributor from the desired number of extraders־ In this distributor, the polymers combine to form a single flux which is fed into the die. In these processes, the respective delivery rates of the exiracers generally provide a means of regulating the relative thicknesses of the polymers extraded.

Whereas numerous polymers can be coextraded, it has not been possible to combine PVF₂ with other polymers using this technique. The reason for this is the fact that PVI?₂ is incompatible with other polymers and also the well-known fact that fluorinated resins do not readily adhere to the majority of thennoplastic polymers. This difficulty in combining FVF₂ with other thermoplastics is also encountered when the technique of lamination is applied, ־which consists in taking too prefabricated films, one of PVF₂,the other of any desired thermoplastic, and attempting to make them adhere to each other under pressure with the application of heat. Attempts

¹ . ׳. . • at lamination have also been made, without success, starting from a prefabricated film of PVF₂ and films of polyvinyl chloride, polystyrene, polymethyl methacrylate or an aciylonitrilc-butadienestyrene copolymer leaving the extruder, i.e. in a virtually molten state. Even under these conditions, the two polymers are easily separated after cooling.

As matters stand, if it is desired to combine PVF₂ with another thcmoplastic incompatible therewith, an adhesive has to be used. This method has the disadvantage of comprising three steps:

— preparation of the film of PVF₂ ן — preparation of the film of thermoplastic — adhesive bonding and pressing the films together.

These operations are impractical, slow, generally require the use of adhesives based on solvents which are difficult to elimi nate and do not enable the composite material to be used immediately owing to the time needed to dry the adhesive. Moreover, the composite material obtained is not unified, the interfaces still being susceptible to all the phenomena which are liable to cause detachment. Consequently, one could say that adhesive bonding does not produce a unified composite material but simply juxtaposes thermoplastic elements to give a heterogeneous final structure.

This invention remedies these disadvantages and provides a means of obtaining a new, unified, truly composite material of homogeneous structure, wherein the elements arc firmly bonded to one mother. This new composite material, 1«״i־B 1 *<־?“* ^{onc outcr}surface of FVTj »nd one surface of thermoplastic polymer incompatibl vith FVF₂, is characterised in that the t.<0 polymers are each other over their entire surface by moans of a polyaUyl methaorylnto which is itself at least partially joined firmly to the entire surface of the two polymers to be bonded. The interfaces between the PVT, and polyallyl methacrylate and the incompatible • thermoplastic polymer and the polyalkyl methacrylate aro in the form of an alloy such that one could imagine it as being the result of mixing the components together in a molten state, for example, whilst this form of bondin’ between the components means that the composite material can be regarded as unified and homogencous in structure, os opposed to a so-called composite material of heterogeneous structure which might be obtained, for example, by adhesive bonding, wherein, in this latter case, the interfaces which would have no transitional zone would be clearly marked and vulnerable. The product according to the invention may also bo defined as a composite material consisting of three eomponen formed by the combining of polyalkyl methacrylate and FZF, and polyallyl methacrylate and a thermoplastic polymer incompatible with PVT , this material having at least one outer surface of PV?₂and. one surface of thermoplastic polymer incompatible with PVT,.

The outer surface or surfaces of PVT₂ of the composite material is er are usually free from polyaUyl methacrylate acting as a binder. This is understandable if it is intended that the Ρ»₂ should return all its intrinsic properties on the surface. ,

For chiefly economic reasons, this composite naterxal generally has only one.outer surface of PVFg, with the other

Thus, inventthe surface consisting of the thermoplastic polymer which is incompatible with PVF^^^However, the thermoplastic polymer incompatible with PVF_ may act as an attachment surface for another material» it is possible for this composite material according to the ion to have both its outer surfaces consisting of PVFg with following succession of bonds between the three elements: FVF״ - polyalkyl methacrylate - thermoplastic polymer incompatible ־with PVF_O - polyalkyl methacrylate - PVF״. This is why, according to the invention, the surface of polymer incompatible with PVFg may mean both an outer surface and an inner surface«

A product of this kind, which may take any of the forms usually found with thermoplastics, such as for example tubes, sleeves, profiles, films and sheets, the last of which can themselves be re-formed by knoivn methods such as thermoforming, for example, • is of great value, since it has at least one outer surface which is resistant to weathering and generally has all the properties peculiar to PVT , and another surface having mechanical properties and in general all the properties peculiar to thermoplastic polymers which are incompatible with PV?₂, whilst being in the form of a structur ally unified and homogeneous material.

׳׳ This material is obtained, very advantageously, by coextrus! ionj which is all the more surprising in view of the notorious j . . difficulty of making PVF^ adhere to a thermoplastic polymer. It has been found that if a polyalkyl methacrylate is coextruded simul- taneously with PVF״ and the incompatible thermoplastic material ¹ 80 that the polymethacrylate is located between the two polymers, * a composite material is obtained in one step, which can be used

I immediately and wherein all the different layers are firmly bonded ί'

I . .

I .י ־

I to one another. The invention thus also relates to the process for producing a composite material consisting of FVFg and thermoplastic polymer incompatible with the FVFg, characterised in that the PVFg» a polyallcyl methacrylate and a thermoplastic polymer incompatible with PVF״ are coextruded, with the polyalkyl methacrylate serving M * as intermediate binder.

Although all PVF״’s give satisfactory results, the best results are obtained with a PVT״ within a range of apparent viscosily at 200°C such that, at least for two velocity gradients in the following table, it has apparent viscosities falling between the two extreme apparent .viscosities indicated.

<td rowspan="2"> Velocity gradient -1 sec</td><td colspan="2"> Values of apparent viscosities in poises</td>

<td> minimum</td><td> maximum</td>

<td> 3.54</td><td> 30^0³</td><td> 20¾ 10³</td>

<td> 11.81</td><td> 18x10³</td><td> 93xlO³</td>

<td> 35.4</td><td> llxlO³</td><td> 47xlO³</td>

<td>¹¹⁸</td><td> 6.540³</td><td> 21xl0³</td>

<td> 354</td><td> 3,940³</td><td> 10xl0³</td>

<td> • 1181</td><td> 2.3^0³</td><td> 4.5_x10³</td>

' The apparent viscosities shown are measured in know manner using a capillary rheometer, taking into account the Rabinowitch correction applied to non—Newtonian liquids.

Although, generally speaking, the thickness of the layer of fvf₂ is not important, it is preferable for economic reasons to produce a composite material wherein the thickness of the layer of PVT₂ is between 10 microns and several tenths of a millimetre.

Moreover, by PVT,, is meant not only the homopolymer but also the copolymers containing at least 7055 by weight of FWg or mixtures of

PVFg with other polymers.

The polyalkyl methacrylate is preferably; a polymethyl methacrylate or Mtt the viscosity of which, in the molten state, nay be selected within th־ range 1־ viscosities of commercially available PMMA's, whilst, the nan skilled in the art would know of poss' me moans of adjusting the viscosity to the desired viscosity by for example nixing with small quantities of charges or another polymer, provided that at least 7$ by weight of polyalkyl methacrylate was retained.

It has also boon found that the quality of the polyalkyl methacrylate and possibly that of the PVF_־ should be chosen in accordance Kith the viscosity of the incompatible thermoplastic material in the molten state. Excellent results are obtained with viscosities of polymethyl methacrylate between the limits given for a velocity gradient given below and measured at 200°C. However, these values are not restrictive, because the nan skilled in the art can modify the viscosities as a taction oi the extrusion temper-

<td rowspan="2"> attire. Velocity gradient - 1 * sec</td><td colspan="2"> Value of apparent viscosities in poises</td>

<td> minimum</td><td> maximum</td>

<td> 3.54</td><td> 100 x 10⁵</td><td> 500 x io⁵</td>

<td> 11.81</td><td> 50 x 10⁵</td><td> 280 x 10⁵</td>

<td> 35.4</td><td> 25 x 10⁵</td><td> 150 x IO’</td>

<td> 118</td><td> 15 x 10⁵</td><td> 80 x 105</td>

<td> 354</td><td> 7 x 10⁵</td><td> 50 x IO⁵</td>

<td> ’ 1181</td><td> 3.Ji. * 1³ט</td><td> 30 x IO⁵</td>

-^The thickness of polyalkyl methacrylate is adjusted, according to the'par.ticular case, between several microns and 200 microns.

Generally speaking, it is ™!advisable to work with greater thickncsses owing to the part which the polyalkyl methacrylate would play in the mechanical properties of the whole.

The thermoplastic polymer incompatible with FVF₂ may be, inter alia, a chlorinated vinyl polymer such as polyvinyl chloride or polyvinylidene chloride, a styrene polymer such as polystyrene^or toughened polystyrene, a polycarbonate, a polyurethane, a/copolymer of styrene- acrylonitrile- acrylic elastomer, or a copolymer of acrylonitrile - butadiene - styrene. This layer of thermoplastic polymer may be of any desired thickness, generally from several tens of microns to several millimetres. Obviously, this thermoplastic polymer may contain charges, plasticisers, stabilisers, dyes or other conventional adjuvants.

The apparatus used for producing the composite material eoncists of extruders, a die and preferably a flux distributor, all of the conventional type currently used in the field of the coextrusion of thermoplastics. The thickness of ־־־h layer is regulated by the delivery reie of each extruder.

For the purposes of the invention, the temperature of the die is between 180 and 280°C, depending on the materials coextruded. The temperatures of the extruders are those normally used for the simple extrusion of each of the polymers.

To ensure satisfactory final cohesion between the three polymors, it is recommended to proceed with the cocxtrusion of these three polymers 0־ that the materials leaving, the extruders are combined, at the latest, at the lips of the die. In certain cases, tho cohesion obtained may leave something to be desired and for this reason it is preferable for the fluxes of TO,, thermoplastic and polyalkyl methacrylate leaving the extruder to travel together in contact with one another before reaching the lips of the die. In this case, instead of a die with several channels, a flux distributor is interposed between the outlet from the extruders and a singlechannel die.

As a variant, using ths coextrusion technique with at least three extruders, the following composite material is obtained which has throe components: PVF_־ - polyallyl methacrylate - thermoplastic polymer incompatible with Wl?₂ - polyalkyl methacrylate - W,.

The following examples illustrate the object of the invention.

me viscosity is measured with ־η ΒΒΠΙΟΝ Model 3211 capillary rheometer having a capillary about 50.8 mm (2 in.) long lor a norzle diameter 01 about 1.27 mm (0.05 in.).

EXAMPLE 1

Throe SMTP - KAUFMAN extruders are used, the first of which, comprising a degasifying system, i⁴^ ־״ 120 ־^has “ screw length of 33 times its diometor. It is used to extrude the acrylonitrile - butadiene - styrene copolymer (ABS), whilst the second is 50 mm in diameter (Super - 2 x 50) ־־d is used for the polymothyl methacrylate (Mil) and the third, with a diameter al 40 ram, is used for the PVFg.

These three extruders feed a flux distributing cylinder which is itself fixed to an ordinary Hat die intended to produce a sheet about ־. m thick, followed by a calender and a conventional drawing apparatus far the extrusion of sheets.

The ABS is BGHOIAL SF 10 36&lt;׳ made by the company Produits

Chirnqucs Ugine IWltaan־« ,־ FHMA is ALTOLITB 2 710 nude by Messrs. ALTULOR end the PVF₀ is ΙΌΪΙΑΕΕΟΝ 1 000 HD made by the company Produits Chimiques Ugine Kuhlmann. The viscosity of the ABS, measured at 220°C, is 75.10⁵ poises at a velocity gradient of 5.6 eec and 10.10³ poises at a gradient of 2 sec¹־. The viscosity 01 the 1 PUMA measured ai 200°C is 110.10³ at a gradient of 5.6 ־־־ and &lt;T «•1

14.10^ג at a gradient of 2 sec .

Finally, the viscosity, measured at 200°C, of the FVFg is 141.10⁵ and 8.8.10⁵ poises for velocity gradients, in sec , of 5.5 and 354, respectively.

The temperatures to which the extruders are heated range from I90 to 210°C for the ABS, from 180 to 200°C for the PUMA and from 180 to 220°C for the PVFg.

The flux distributor and the die are at 210 C. The film is received between the cylinders of a calender heated to 80 C.

The total delivery is about 500 kg/hour. The deliveries of the three extruders are regulated so as to obtain finally a composite material containing ABS 4 mm thick, PMMA 50 microns thick and PVT 100 microns thick. These three layers are perfectly fused to one another as soon as they leave the die. After cooling, a composite material of homogeneous structure is obtained one surface of which consists of PVF״ whilst the other consists of ABS. it

EXAMPLE 2

Using a flux distributor with which a material consisting of five layers can be obtained as it leaves the die, Example 1 is repeated so as to obtain, with the same polymers and the same extruders heated to the same temperatures, a composite sheet having in succession a 75 nicroh layer of PVF₂, a 50 micron layer of ΡΗΜΑ, a&lt;^mm^layer of ABS, a 5° micron layer of HINA and finally a 75 micron layer of PVF״. The composite material obtained comprises five layers which are perfectly fused to one another. After cooling, a composite material of homogeneous structure is obtained which has two outer surfaces of PVl.^ whilst its centre consists of f ABS.

EXAMPLE 5

A KESTEEHANN K 107 two-screw extruder is used for the polyvinyl chloride (PVC) (EKAVYL SL 66 made by Produits Chimiques Ugine Kuhlmann), an SO extruder 30 mm in diameter is used for the polymethyl methacrylate (PIUIA) (iffiSARITE KOX 125 made by Messrs RESARTE) and a KAUliMAN extruder 40 rm_;in diameter is used for the PVF - F0RAFL0N 4 000 HD made by Produits Chimiques Ugine Kuhlmann.

These three extruders supply a flux distributor which is ־ itself fixed to a tube extruding head. A conventional vacuum-type former and a dra'vdng system complete the apparatus.

The three polymers are coextruded at their normal extrusion temperatures, i.e. 160-200°C for the PVC, 180-200°C for the PMMA and 180-200°C for the PVF״. The extrusion head and the flux distributor are maintained at between 195 aud 200 Co ^X A tube with an external diameter of 5θ mm is obtained, made up successively of a layer of PVC about 3 mm thick, a layer of PI1MA about 50 microns thick and an inner layer of PV?₂ about 75 microns thick. The three polymers take the form of a composite material with a homogeneous, unified structure.

EXAMPLE 4

All throe extruders in Example 5 are used, ending in a flux distributor and a tube extruding head. The apparatus also comprises ! ' a conventional bottle-moulding and Mowing system with ״Mob the three polymers can be coextruded and blown.

In the first extruder is placed a PVC (EKAVIL SK 55^ made by Produits Cbimigues Ugino Kuhlmann), in the second a BHl (EESAMTE KOX 125 made by Messrs. IttSAME) and in the third FVFj (FOMPLON 1 000 ΙΠ) made by Produits Chimiquos Ugino Kuhlmann) The tempera iures reached arc, respectively16 ־O-1SO°C, 180-190°C and 190-200’c, • the flux distributor and discharge nozzle are at 190 C.

A coextruded parison is obtained which is Ms» in conventional manner to obtain a bottle. The three extruders had been fixed to the flux distributor in such a way that the bottle bos an inner layer of PVFg about 100 microns thick, on intermediate layer of ΡΜΜΛ a 80 microns thick and finally an outer layer of PVC shout 8/10 thick.

The three layers of the bottle obtained are perfectly fused to one another os soon as they leave the extrusion head. Alter cooling, the bottle is in tho form of 0 eomposito material with a homogeneous, unified structure.