EP1272558A1

EP1272558A1 - Composite polymer/polymer material with high content in amorphous dispersed phase and preparation method

Info

Publication number: EP1272558A1
Application number: EP01923758A
Authority: EP
Inventors: Philippe Cassagnau; Alain Michel
Original assignee: Centre National de la Recherche Scientifique CNRS
Current assignee: Centre National de la Recherche Scientifique CNRS
Priority date: 2000-04-06
Filing date: 2001-04-06
Publication date: 2003-01-08
Also published as: JP2003530454A; AU2001250452A1; AU2001248492A1; EP1272557A1; CA2405282A1; FR2807440A1; WO2001077223A1; WO2001077222A1; US20030181596A1; US20030166778A1; JP2003532751A; CA2405111A1

Abstract

The invention concerns a micro-composite polymer/polymer material comprising an amorphous polymer (I) forming a dispersed phase localised inside a thermoplastic or elastomeric polymer (II) forming a matrix, the glass transition temperature of polymer (I) forming a dispersed phase being higher by at least 20 °C than the melting or softening point of matrix-forming polymer (II), and the amorphous polymer content (I) forming the dispersed phase being not less than 40 wt. %. The invention also concerns a method for obtaining said material comprising steps which consist in: extruding, at regulated temperature, said melted polymer mixture, said regulating temperature being decreasing from the feeding zone (A) to the die zone (F) of said extruding machine (1) so that the material temperature in said die zone (F) is lower than the temperature of recrystallisation or solidification of polymer (II), and higher than the melting or softening point of amorphous polymer (I); and cooling at room temperature the resulting micro-composite material.

Description

POLYMER / POLYMER COMPOSITE MATERIALS WITH HIGH AMORPHOUS DISPERSE PHASE CONTENT AND PROCESS FOR THEIR PREPARATION

The present invention relates to a process for the preparation of polymer / polymer micro-composite materials by temperature-controlled extrusion, as well as the resulting micro-composite materials.

The expression “polymer / polymer micro-composite material” designates a material comprising a mixture of immiscible polymers, one of which forms a phase dispersed in the other constituting the matrix. The polymer / polymer micro-composite materials are generally prepared by extrusion at constant or substantially increasing temperature from the supply zone to the die, this extrusion step being followed by a drawing step and an outlet quenching before being implemented again for the intended applications. In the case of a dispersed phase of amorphous polymer type, it is currently limited to contents of less than 20% (by weight) in the dispersed phase. Beyond that, one cannot control the morphology and the reproducibility of the final material obtained.

In general, the thermomechanical properties of the micro-composite materials available today are limited and insufficient for their subsequent use.

One of the objectives of the present invention is to provide polymer / polymer micro-composite materials heavily loaded with reinforcing polymer of amorphous polymer type, of defined morphology, stable and reproducible.

Another object of the invention is to provide a process for the preparation of the aforementioned micro-composite materials which can be implemented in a simple and reproducible manner with high contents in dispersed phase. Another object of ^the invention is to provide such a method of preparation - micro-composite materials as indicated above allowing to obtain improved thermomechanical properties to materials. Another objective of the present invention is also to provide polymer / polymer micro-composite materials which can be used as starting materials in processes for preparing shaped articles, without their thermomechanical properties being affected.

More specifically, according to a first aspect, the subject of the invention is a polymer / polymer micro-composite material, comprising an amorphous polymer (I) forming a localized dispersed phase within a thermoplastic or elastomeric polymer (II) forming a matrix, the glass transition temperature of the polymer (I) forming the dispersed phase being at least 20 ° C higher than the melting or softening temperature of the polymer (II) forming the matrix, and the content of amorphous polymer (I) forming the dispersed phase being greater than or equal to 40% by weight.

The subject of the invention is also a process for the preparation of such composite materials, characterized in that it comprises the steps consisting in:

- Introducing, at a regulated temperature into the feed zone (A) of an extruder (1), a mixture (2) comprising said polymers (I) and (II), the regulation temperature in this zone being greater than the melting or softening temperature of each of the polymers of said mixture (2);

- Extruding, at a controlled temperature, said mixture of polymers in the molten state, said control temperature being decreasing from the supply zone (A) to the zone of the die (F) of said extruder (1) so that the material temperature in said zone of the die (F) is lower than the recrystallization or solidification temperature of the polymer (II) and higher than the melting or softening temperature of the amorphous polymer (I); and

- cool the resulting micro-composite material to room temperature.

The invention also relates to a method for obtaining shaped objects, using, as starting material, a micro-composite material as mentioned above at a controlled temperature such that, throughout the formation of the shaped object, the material temperature remains below the melting or softening temperature of the polymer forming the dispersed phase of the micro-composite material used.

The inventors have demonstrated that by treating a mixture of polymers (or copolymers) chosen by a “dynamic quenching” process as defined below, it was possible to obtain, in a reproducible and stable manner, micro-composite materials with a high content of amorphous dispersed phase, having improved thermomechanical properties.

The invention is described in more detail below with reference to the drawings in which: - Figure 1 shows schematically the extrusion step of the process according to the invention;

- Figures 2 and 3 are photographs taken with a scanning electron microscope showing the morphology of materials obtained from an ethylene vinyl acetate (EVA) / polycarbonate (PC) 50/50 mixture respectively by a traditional process and by the process dynamic quenching according to the invention;

- Figure 4 is a comparative diagram showing the thermodynamic behavior of the materials of Figures 2 and 3 obtained respectively, according to a traditional process (À) and according to the dynamic quenching process of the invention (u), as well as EVA alone (Φ), at a stress frequency ω equal to 1 rad / sec.

In general, in the process of the invention, a mixture of polymers is first produced comprising at least the polymer (I), intended to form the dispersed phase (called “polymer (I) forming dispersed phase”) and the polymer (II) intended to form the matrix (known as “polymer (II) forming matrix”). The term “polymer”, within the meaning of the invention, indifferently designates one or more polymers and or copolymers.

The polymers (I) and (II) are specifically immiscible polymers, that is to say, within the meaning of the invention, immiscible polymers in the molten state, under the conditions of their use for the preparation of the desired materials, as well as in the final extruded material.

In general, the choice of polymers used in the invention is made so that the crystallization or solidification temperature of the polymer (I) intended to form the dispersed phase is significantly higher than the melting or softening temperature polymer (II) intended to form the matrix. By "clearly higher temperature" is meant a difference of at least 20 ° C between the temperatures considered, and preferably a difference ranging from 30 ° C to 50 ° C. A difference of the order of 30 ° C (that is to say advantageously between 25 and 40 ° C, and typically between 28 and 35 ° C) is more particularly preferred.

The polymer (II) can be chosen from semi-crystalline or amorphous thermoplastic polymers, or also from elastomers.

Among the examples of polymers suitable as polymer (II) forming a matrix, mention may be made of polymers or copolymers of vinyl acetate and of acrylic esters, more particularly polymers or copolymers of ethylene / vinyl acetate or ethylene / acrylic esters . Typically, the polymer (II) is an ethylene / vinyl acetate (EVA) polymer.

The polymer (I) is in turn specifically chosen from amorphous polymers.

Among the amorphous polymers suitable for the purposes of the invention, mention may be made of polycarbonates, polystyrenes and acrylic and methacrylic polyesters or their mixtures. Typically, the polymer (I) forming a dispersed phase is a polycarbonate. The method of the invention is implemented in an extruder. It is the skill of the person skilled in the art to make the choice of the characteristics of the extruder to be used in particular so as to relatively quickly obtain a homogeneous melt mixture of polymers taking into account the physicochemical characteristics of the extruded material.

The extruder used is preferably a twin screw extruder, the length / diameter ratio of which is advantageously greater than or equal to 34.

The speed of rotation of the screws as well as the rate of supply of polymers can be adapted by a person skilled in the art so as to limit self-heating and to satisfy the temperature condition explained below.

With reference to FIG. 1, the barrel of an extruder 1 is seen, for which the supply zone A, an intermediate zone I and the zone of the die F have been shown diagrammatically, subject respectively to regulation temperatures defined as explained. below. A die 3 is also placed at the outlet of the extruder.

The mixture of polymers 2 is introduced into the feed zone A of the extruder 1. The regulation temperature T _a is higher than the melting or softening temperature of each of the polymers of said mixture. The polymers are then quickly melt-mixed so that the polymer forming the minority phase is dispersed homogeneously in the other polymer.

It is generally recalled that the regulation temperature corresponds to the temperature applied (set temperature) to the barrel of the extruder and takes account in particular of the thermal phenomena which can occur at the level of the installation and the self-heating of the treated material which may occur during the extrusion operation. The choice of the regulation temperature depends on the polymers used.

The extrusion operation is continued on the polymer blend in the molten state up to the zone of the die F where it will undergo a “dynamic quenching”. The expression “dynamic quenching” designates a controlled cooling operation, carried out in the extruder, upstream of the die, which causes recrystallization or solidification of the polymer forming phase dispersed in the matrix-forming polymer, under the shear forces and the mechanical stresses imposed by the extruder (rotation of the screws). A polymer / polymer micro-composite material with specific and controlled morphology is thus obtained, having improved thermomechanical properties as explained below.

To this end, the regulation temperature T _fil in the zone of the die F is fixed so that the temperature of the material located in this zone is lower than the recrystallization or solidification temperature of the polymer (I) forming dispersed phase. The regulation temperature T _fil is advantageously at least 20 ° C lower than the recrystallization or solidification temperature of the polymer (I) forming the dispersed phase, and it is preferably 30 ° C to 50 ° C lower at this temperature .

In other words, the temperature in the zone of the die F is significantly lower than the temperature of the supply zone A and it follows a decreasing profile between said zones passing through an intermediate zone I where the temperature T, is lower than that of zone A but does not yet correspond to the “dynamic quenching” temperature.

At the outlet of the die 3, the material is simply cooled to room temperature.

By implementing the method of the invention, a material with controllable and reproducible morphology is obtained, heavily loaded with reinforcing polymer without this high content of polymer (I) decreasing the cohesion properties of the material. According to the invention, the content of polymer (I) forming dispersed phase is specifically greater than 40% by weight (ie greater than 35% by volume) relative to all of the polymers. In particular so as not to obtain materials which are too fragile, it is generally preferred that this content of polymer (I) is less than 60% by weight, and advantageously less than 50% - by weight. Thus, the content of polymer (I) can typically be between 40 and 45% by weight. In the material obtained at the end of the process of the invention, the amorphous polymer (I) is present in finely dispersed form and the dispersed amorphous phase is generally present in the form of rods dispersed in the matrix. The size of these rods is generally of the order of 1 μm. Whatever the exact morphology of the dispersed phase, the average size of the polymer globules (I) dispersed within the polymer (II) matrix is generally of the order of a micron.

A typical example of the morphology obtained according to the “dynamic quenching” method of the invention is given in FIG. 3. By way of comparison, it is observed, in FIG. 2, that a co-continuity of the phases is obtained, by a conventional process in which the quenching operation is carried out independently after extrusion. In this case, it is not possible to access a defined, stable and reproducible morphology, in particular because this morphology considerably depends on the conditions for implementing the method.

The composite materials obtained in accordance with the present invention retain their morphology and therefore their properties at temperatures below the melting or softening temperature of the polymer (I) forming their dispersed phase. The materials obtained according to the process of the invention therefore constitute interesting intermediate products which can serve as starting materials for the preparation of shaped articles. In this context, they can be implemented according to various techniques chosen according to the shaped object that one wishes to obtain. The processes for preparing shaped articles using the micro-composite materials of the invention as starting materials can thus consist, for example, in one or more extrusion, injection and / or molding.

Whatever the treatment applied, during the formation of the shaped articles, the processing temperature of the micro-composite materials according to the invention (that is to say the material temperature) must specifically remain below the temperature of melting or softening of the polymer (I) forming the dispersed phase. In the case generally, this material temperature is preferably at least 20 ° C lower, and more preferably 30 ° C to 50 ° C lower, than the melting or softening temperature of the polymer (I) forming the dispersed phase.

The processes for the preparation of shaped objects using the micro-composite materials described above, under the controlled temperature conditions indicated above, constitute a particular object of the invention.

The characteristics and advantages of the invention will appear in more detail, in the light of the examples set out below.

EXAMPLES

MATERIAL AND METHOD

For the production of the examples described below, a co-rotating twin screw extruder with interpenetrated screws was used. All screw elements have two threads. The diameter of the screws is 34 mm and the distance between centers is 30 mm. The length / diameter ratio (L / D) of the extruder is L / D = 34.

The sheath has nine successive and independent parts for regulating the temperature determining three zones, the supply zone A, the intermediate zone I and the zone of the die F, shown diagrammatically in FIG. 1.

These heating zones are also equipped with a pressurized water circuit, controlled by a solenoid valve allowing the evacuation of the calories produced by viscous dissipation of the polymers which is introduced by the mechanical shearing of the screws. This system considerably limits self-heating phenomena.

The different heating zones of the sheath are illustrated in FIG. 1.

The die consists of a flat die type coat rack having the following dimensions: width L = 50 mm, length 1 = 30 mm and thickness h = 2 mm. The sector is also regulated independently of the other zones but does not have a water regulation system. For the entire process described, the speed of rotation of the screws is fixed at 160 rpm and the total feed rate of the extruder at 3 kg / h. The two polymers (polymer forming matrix and polymer forming dispersed phase) are introduced together into the feed zone A of the extruder. The polymer material temperature is controlled by two infrared (IR) temperature sensors. These sensors measure and control the actual temperature of the molten polymers. They are located in the intermediate zone ₄ and at the head of the die 3. A pressure sensor makes it possible to measure and control the pressure at the inlet of the die 3. The tensile tests were carried out on samples cut out at prevails on the extruded bands. The values given for each sample are taken from the average of ten tests. The test specimens are of the H3 type according to standard NF T51-034.

The test conditions are as follows: - Device: INSTRON 1175, the jaws are self-tightening, pneumatic (force sensor 1 kN)

- Temperature: room temperature (23 ° C).

- Test speed: 50 mm / min

In linear viscoelasticity, the threshold flow stress is measured at 120 ° C. The temperature range of use of the material is defined as being the region where the material does not flow for applied stresses lower than the critical stress Gp (flow threshold). The use temperature, defined according to this threshold stress criterion, must therefore be lower than the melting or softening temperature of the dispersed phase.

EXAMPLE 1 EVA / PC composite

The matrix consists of a copolymer of ethylene and vinyl acetate containing 28% by weight of vinyl acetate. It is an Atochem copolymer with commercial reference Evatane 2803. Its melting point is 80 ° C. and its crystallization temperature is close to 50 ° C.

The dispersed phase consists of polycarbonate (PC), a Bayer product of commercial reference Makrolon 2658.

50% by weight of polycarbonate are dispersed according to the method of the invention in the EVA matrix.

The temperature setpoints for the different temperature control zones are given in table 1.

TABLE 1

The material temperatures indicated by the infrared sensors as well as the pressure measured at the head of the die are given in table 2:

TABLE 2

A fine dispersion of the PC phase is obtained by the process of the invention and thus makes it possible to have a high concentration of PC while retaining the cohesion properties of the material for the use temperatures below the glass transition temperature. polycarbonate. EXAMPLE 2 (Comparative example)

By a conventional implementation process, a co-continuous morphology of the two phases is obtained as shown in FIG. 2.

This morphology is not stable and depends considerably on the conditions of implementation.

The thermomechanical properties measured are compared in table 18 to the reference samples obtained by a conventional process of implementation on the same extruder (identical speed and speed of the screws).

TABLE 3

Figure 4 shows the thermomechanical behavior of the two types of material measured by the variation of the elastic modulus according to the temperature for a stress frequency ω equal to 1 rad / s.

Claims

1. Polymer / polymer micro-composite material, comprising an amorphous polymer (I) forming a dispersed phase localized within a thermoplastic polymer or elastomer (II) forming a matrix, the glass transition temperature of the polymer (I) forming a dispersed phase being at least 20 ° C higher than the melting or softening temperature of the polymer (II) forming the matrix, and the content of amorphous polymer (I) forming the dispersed phase being greater than or equal to 40% by weight.

2. Material according to claim 1, characterized in that the amorphous polymer (I) forming a dispersed phase is chosen from polycarbonates, polystyrenes, acrylic or methacrylic polyesters, or mixtures of these compounds.

3. Material according to claim 1 or claim 2, characterized in that the amorphous polymer (I) forming dispersed phase is. polycarbonate.

4. Material according to any one of claims 1 to 3, characterized in that the dispersed phase is in the form of rods.

5. Material according to any one of claims 1 to 4, characterized in that the average size of the polymer globules (I) dispersed in the polymer matrix (II) is of the order of a micron.

6. Material according to any one of claims 1 to 5, characterized in that the glass transition temperature of the amorphous polymer (I) forming dispersed phase is 30 ° C to 50 ° C above the melting or softening temperature of polymer (II) forming a matrix.

7. Material according to claim 6, characterized in that the glass transition temperature of the amorphous polymer (I) forming dispersed phase is 30 ° C higher than the melting or softening temperature of the polymer (II) forming the matrix.

8. Material according to any one of the preceding claims, characterized in that the polymer (II) forming a matrix is chosen from polymers or copolymers of vinyl acetate and acrylic esters.

9. Material according to claim 8, characterized in that the polymer (II) forming a matrix is chosen from polymers or copolymers of ethylene / vinyl acetate or ethylene / acrylic ester.

10. Material according to claim 9, characterized in that the polymer (II) forming a matrix is ethylene vinyl acetate (EVA).

11. Process for the preparation of a polymer / polymer micro-composite material according to any one of claims 1 to 10, characterized in that it comprises the steps consisting in:

- Introducing, at a regulated temperature into the feed zone (A) of an extruder (1), a mixture (2) comprising said polymers (l) and (II), the regulation temperature in this zone being greater than the melting or softening temperature of each of the polymers of said mixture (2);

- cool the resulting micro-composite material to room temperature.

12. Method according to claim 1 1, characterized in that the regulation temperature in the zone of the die (F) is lower by at least minus 20 ° C at the recrystallization or solidification temperature of the polymer (II).

13. The method of claim 12, characterized in that the regulation temperature in the area of the die (F) is 30 ° C lower than

50 ° C at the recrystallization or solidification temperature of the polymer (II).

14. Method according to any one of claims 1 1 to 13, characterized in that the mixture of polymers in the molten state is extruded in a twin-screw extruder.

15. The method of claim 14, characterized in that the extruder has a length / diameter ratio (L / D) greater than or equal to 34.

16. A method of preparing a shaped article, using, as starting material, a micro-composite material according to any one of claims 1 to 10, or a micro-composite material obtained at the end of 'A method according to any one of claims 11 to 15, the temperature being controlled during the formation of said shaped article so that the material temperature remains below the melting or softening temperature of the polymer (I) forming the dispersed phase of said micro-composite material.

17. The method of claim 16, characterized in that the material temperature remains at least 20 ° C lower than the melting or softening temperature of the polymer (I) forming the dispersed phase of the micro-composite material.