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

(74) Agent

Bryn's Patent Office A / 5, Oslo.

(56) Published publications BRD (DE) publication no. 271 51 85 (B29D 9/00).

The present invention relates to the preparation of a composite material consisting of polyvinylidene fluoride, a polymer hereinafter referred to as PVF2, and a thermoplastic polymer incompatible with PVF2. This composite material is prepared by co-extrusion.

The technique of coextrusion of thermoplastic materials is well known in the industry, and is described in more detail in Polymer Plastics Technology and Engineering, vol. 3, pages 49-68: Coextruded filmsProcess and properties by JE Guillotte.

Generally, there are known three methods for coextrusion thermoplastic fabrics from a number of common extruders which correspond to the number of polymers to be extruded. The first method is to extrude the polymers separately and combine them as they leave the nozzle. The second method consists in feeding the material to a single nozzle from at least two extruders and the nozzle having as many channels as there are extruders and polymers to be extruded. The two polymer bands coalesce at the outlet of the nozzle, i.e., just before leaving it. The third method involves feeding a strip of material from the desired number of extruders to a belt distributor. In this distribution, the polymers will coalesce into a single band or wire which is then inserted into the nozzle. The respective feed rates of said extruders will in these processes provide an opportunity and arrangement for regulating the relative thickness of the polymers extruded.

While a variety of polymers can be co-extruded, it has not yet been possible to combine PVF2 with other polymers by this technique. This is because PVF2 is incompatible with other polymers, and it is further known that fluorinated resins do not readily adhere to most thermoplastic polymers. This difficulty in combining PVF2 with other thermoplastic substances is also present when using a lamination technique, ie. that one takes two pre-made films, one of PVF2 and the other of another desired thermoplastic polymer, and tries to make them cohesive by pressure and optionally using heat. In vain attempts have also been made with the help of a prefabricated film of PVF2 and films of polyvinyl chloride, polystyrene, polymethylmethacrylate or an acrylonitrile butene diene styrene copolymer leaving these extruder, i.e. in a substantially molten state. Even under these conditions, the two polymers can be easily separated after cooling.

If you want to combine PVF2 with another thermoplastic material that is incompatible with this, then today you have to use an adhesive or an adhesive. This process has the disadvantage of including the following three steps:

- You first make the film of PVF2.

A film is made of the thermoplastic material.

You glue and squeeze the films together.

This is usually impractical, takes a long time and requires the use of adhesive ₁₅ solvents based on solvents that can often be difficult to eliminate and prevent the composite material from being used immediately because the adhesive or glue has to dry for a certain amount of time. Furthermore, satisfactory composite material is not completely obtained, since the boundary phases between the two films can still be exposed to all the phenomena that otherwise give a separation. In other words, it can be said that the glue joint itself does not provide a uniform composite material, but merely places two thermoplastic elements side by side so as to obtain a heterogeneous final structure.

The present invention avoids these drawbacks and provides a process for producing a composite material consisting of at least one outer layer of polyvinylidene fluoride, an intermediate layer of polyalkylmethacrylate and a thermoplastic polymer incompatible with polyvinylidene fluoride, and this process is characterized by the polyalkyl methacrylate and the thermoplastic polymer incompatible with the polyvinylidene fluoride are co-extruded while the polyalkyl methacrylate acts as an intermediate binder.

In this way, a new, uniform, real composite material of homogeneous structure is obtained, the elements being firmly bonded to each other. This new composite has at least one outer surface

PVF2 and another surface of a thermoplastic polymer incompatible with said PVF2, characterized in that the two polymers are bonded to each other over their entire surface by a polyalkyl methacrylate which itself at least partially adheres to the entire surface of the two polymers to be joined. The interface phases between PVF2 and the polyalkylmethacrylate and the incompatible thermoplastic polymer and the polyalkylmethacrylate are in the form of an alloy which is believed to be formed by mixing the components together in a molten state, and this form of bonding between the components means that the composite can be considered to be uniform and homogeneous in structure, which is in contrast to so-called composite materials of heterogeneous structure which can easily be obtained by e.g. glue the surfaces together and get boundary phases where one can easily detect a transition zone. The product of the present invention may also be defined as a composite material consisting of three components formed by combining polyalkylmethacrylate and PVF2 and polyalkylmethacrylate and a thermoplastic polymer incompatible with PVF2. This material has at least one outer surface of PVF2 and one surface of the thermoplastic polymer incompatible with PVF2. The outer surface of PVF2 in the material is usually free of said polyalkylmethacrylate which acts as a binder. This is of course important when one wants the PVF2 to retain all its properties on the surface.

For economic reasons, the composite will usually have only one outer surface of PVF2, but the other outer surface consists of a thermoplastic polymer incompatible with PVF2. However, the thermoplastic polymer which is incompatible with PVF2 may act as an adhesive surface for another material. Thus, it is possible that the composite material of the present invention has both of its outer surfaces consisting of PVF2 with the following order of bonds between the three elements: PVF2 - polyalkylmethacrylate - thermoplastic polymer incompatible with PVF2 - polyalkylmethacrylate - PVF2. This is why, according to the present invention, the term polymer surface is incompatible with PVF2 as both an outer and an inner surface.

A product of this type which may have any form of the type commonly found in connection with thermoplastic agents, e.g. in the form of

568

<img file="NO155686B_D0001.tif" />

<img file="NO155686B_D0002.tif" />

<img file="NO155686B_D0003.tif" />

tubes, sleeves, profiles, films or sheets, and these can of course be formed by known methods such as heat forming, and will therefore have at least one outer surface which is resistant to various external forces such as corrosion etc ,, and will usually retain all the properties known to PVF2, but the other surface will have mechanical properties and, in general, all properties which characterize thermoplastic polymers incompatible with PVF2, at the same time as the product is made of a structurally homogeneous material.

This material is very advantageously prepared by coextrusion, which is very surprising when you know how difficult it is to attach PVF2 to a thermoplastic polymer. It has been found that if a polyalkylmethacrylate is extruded simultaneously with PVF2 and the incompatible thermoplastic polymer, and said polymethacrylate is placed between the two polymers, a composite material is produced in one stage where the material can be used immediately and where all the different layers are firmly bonded to each other.

Although all types of PVF2 give satisfactory results, the best results are obtained when using a PVF2 having a viscosity at 200 ° C between the minimum and maximum values ​​shown in the following table, at least two velocity gradients.

Speed ​​gradient Outer values ​​for apparent sec.^-1 viscosity in Poise

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

<td> 3,54</td><td>30 x 1 0⁵</td><td>20 0 x 1 05</td>

<td> 11,81</td><td>18 x 1 0⁵</td><td>93 x 10⁵</td>

<td> 35,4</td><td>11 x 10⁵</td><td>47 x 10⁵</td>

<td> 1 18</td><td>6.5 x 1o5</td><td>21 x 1 0 ⁵</td>

<td> 354</td><td>3.9 x 10?</td><td>10 x 10⁵</td>

<td> 1 181</td><td>2.3 x 10?</td><td>4.5 x 10⁵</td>

Apparent viscosity is measured in a known manner using a capillary rheometer, taking into account the Rabinowitch correction applied to non-Newtonian fluids.

In general, the thickness of the layer of PVF2 will not be important, but it is of course desirable for economic reasons to produce a composite material where the thickness of the layer of PVF2 is between 10 µm and up to approx. a half mm. In this context, PVF2 means not only the homopolymer, but also copolymers containing at least 70% by weight of PVF2 or mixtures of PVF2 and other polymers.

The polyalkylmethacrylate is preferably a polymethylmethacrylate or PMMA whose viscosity in the molten state can be selected within the range found for viscosities for commercially available PMMA, and it is well known in the industry how to possibly adjust the viscosity by adding smaller amounts of the material or by other polymer, provided that at least 75% by weight of polyalkylmethacrylate is retained.

It has further been found that the quality of the polyalkyl methacrylate and, optionally, also for PVF2, should be chosen according to the viscosity of the incompatible thermoplastic material in its molten state. Excellent results are obtained when the viscosity of the polymethylmethacrylate lies between the outer limits of a velocity gradient given below and measured at 200 ° C. However, these values ​​are not absolute because one can easily modify the viscosity as a function of extrusion temperature.

Speed ​​gradient Values ​​for apparent sec · -¹ Viscosity in Poise ___

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

<td> 3,54</td><td>1 00 x 1 0³</td><td>500 x 1 0³</td>

<td> 1 1 ,81</td><td>50 x 10³</td><td>280 x 1 0³</td>

<td> 35,4</td><td>25 x 10⁵</td><td>150 x 1 0³</td>

<td> 118</td><td>13 x 1 0³</td><td>80 x 10³</td>

<td> 354</td><td>7x10?</td><td>50 x 1 0³</td>

<td> 1181</td><td>3.5 x 1 0³</td><td>30 x 1 0³</td>

The thickness of the polyalkyl methacrylate is adjusted in each case, but should be between a few µm and 200 µm. It is uneconomical and inappropriate to have greater thickness because the polyalkyl methacrylate would then affect the mechanical properties of the finished material.

The thermoplastic polymer incompatible with PVF2 may be, inter alia, a chlorinated vinyl polymer such as polyvinyl chloride or polyvinylidene chloride, a styrene polymer such as a polystyrene or toughened polystyrene, a polycarbonate, a polyurethane, a graft copolymer of styrene-acrylonitrile acrylonitrile or elastomeric elastomeric elastomeric elastomeric elastomeric elastomeric This layer of thermoplastic polymer can be of any desired thickness, i.e. 20 pm to a few millimeters. This thermoplastic polymer layer may contain additives, plasticizers, stabilizers, dyes or other known additives.

The apparatus used to make the composite material consists of ₁₅ extruders, a nozzle and preferably a distributor, all of the usual type used in extrusion of thermoplastic fabrics. The thickness of each layer is regulated by the feed rate of each extruder.

2Q For the present purpose, the temperature of the nozzle should be between 180 and 280 ° C, depending on the material being extruded. The temperature of the extruders are those normally used for simple extrusion of each polymer.

In order to ensure a final satisfactory bond between the three polymers, it is preferable to carry out the coextrusion of the three polymers so that the materials leave the extruders together, at least at the nozzle lips. In some cases, an unsatisfactory bond may occur and for this purpose it is preferred that the effluent material of PVF2, thermoplastic polymer and polyalkyl methacrylate be in contact with each other over a certain distance before reaching the nozzle lips. Instead of using a multi-channel nozzle, a known type distributor can be placed between the extruder outlet and a single channel nozzle.

As a variant, a coextrusion technique using three composite materials can be prepared: PVF2155686 polyalkylmethacrylate - thermoplastic polymer incompatible with PVF2 polyalkylmethacrylate - PVF2.

The following examples illustrate the invention.

Viscosity was measured with an Instron Model 3211 capillary rheometer with a capillary 50.8 mm long and had a nozzle diameter of approx. 1.27 mm.

Example 1

3 SMTP - Kaufman extruders were used. The first to have a degassing system had a diameter of 120 mm and a screw length 33 times the diameter. It was used for extrusion of an acrylonitrile butadiene styrene copolymer (ABS), while the second extruder had a diameter of 50 mm (Super - 2 x 50), and was used for polymethylmethacrylate (PMMA), while the third, which had a diameter of 40 mm, was used for PVF2.

These three extruders fed materials to a distribution cylinder which itself was attached to a conventional flat nozzle which provided a flat approx. 4 mm thick, followed by a calender and an ordinary plate extruder.

ABS (Ugikral SF 10 436), PMMA (Altulite 2 710) and PVF₂ (Foraflon 1,000 HD) were trading products. The viscosity of ABS, measured at 220 ° C, was 75.10-3 at a velocity gradient of 5.6 sec.^-^ and 10.10 ^ Poise at a gradient of 2 sec. 'k The viscosity of PMMA measured at 200 ° C was 110-10-3 at a gradient of 5.6 sec.^-^ and 14.10 ^ at a gradient of 2 sec ~ k

Finally, the viscosity measured at 200 ° C for PVF2 was 141.10 ^ and 8.8.10 ^ Poise for velocity gradients of 3.5 and 8, respectively. 354 sec. ”L.

The temperature in the extruders ranged from 190 to 210 ° C for ABS, from 180 to 200 ° C for PMMA and from 180 to 220 ° C for PVF₂.

The distributor and nozzle had a temperature of 210 ° C. The film was inserted between the cylinders on a calender which was heated to 80 ° C.

Total supply was approx. 300 kg / hour. The supply from the three extruders was controlled to give a finished composite material consisting of ABS (4 mm), PMMA (30 µm) and PVF2 (100 µm). These three layers were perfectly fused to each other immediately after the nozzle. After cooling, a composite material with homogeneous structure was obtained and one surface consisted of PVF2 while the other consisted of ABS.

Example 2

Example 1 was repeated, but this time a distributor was used by means of which a material consisting of five layers could be prepared. The same polymers and the same extruder temperatures were used, and a composite sheet was prepared which consisted of a 75 µm thick layer of PVF2, 50 µm PMMA, 3 mm ABS, a 50 µm thick layer of PMMA and finally 75 µm PVF2. Thus, the material consisted of five layers that are perfectly attached to each other. After cooling, a composite material was obtained with homogeneous structure and with two outer surfaces of PVF2 while the core consisted of ABS.

Example 3

A Kestermann K 107 twin screw extruder for polyvinyl chloride (PVC) (Ekavyl SL 66), an STMP extruder, 30 mm in diameter, for polymethylmethacrylate (PMMA) (Resarite Kox 125), and a Kaufmann extruder, 40 mm in diameter, were used for PVF2 ( Preflon 4,000 HD).

These three extruders brought the material into a distributor which itself is attached to a tube extruder head. A conventional vacuum-type mold and an extraction system completed the apparatus.

The three polymers were co-extruded at their normal extrusion temperatures, i.e. 160-200 ° C for PVC, 180-200 ° C for PMMA and 180-200 ° C for

PVF2 · The extruder head and distributor were kept at a temperature between 195 and 200 ° C.

A tube having an outer diameter of 50 mm was obtained, made of successive layers of PVC (about 3 mm thick), a layer of PMMA (about 50 µm thick) and an inner layer of PVF2 (about 75 µm thick). The three polymers existed as a composite material with homogeneous, uniform structure.

Example 4

All three extruders in Example 3 were used and these ended in a distributor and a tube extruder head. The apparatus also consisted of a conventional bottle forming and blowing system through which the three polymers could be extruded and blown.

In the first extruder a PVC (Ekavyl SK 55B) was placed, in the second a PMMA (Resarite Kox 125 ”) and in the third PVF2 (Floraflon 1000 HD”). The respective temperatures were 160-180 ° C, 180-190 ° C and 190-200 ° C, and the distributor and nozzle had a temperature of 190 ° C.

A coextruded product was prepared which was blown in the usual manner into a bottle. The three extruders were attached to the distributor in such a way that the bottle had an inner layer of PVF2 (about 100 µm thick), an intermediate layer of PMMA (about 80 µm thick), and finally an outer layer of PVC (about 8 µm). / 10 mm thick).

The three layers of the bottle were perfectly fused immediately after the expulsion head. After cooling, the bottle will consist of a composite material with a homogeneous and uniform structure.

<img file="NO155686B_D0004.tif" />