EP2117805A2

EP2117805A2 - Cooling jig for extruding pctfe strings and method for extruding pctfe strings

Info

Publication number: EP2117805A2
Application number: EP08761978A
Authority: EP
Inventors: Yves Dugard; Eric Leforestier; Ludovic Luce; Jérôme CHAUVEAU
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2007-01-24
Filing date: 2008-01-24
Publication date: 2009-11-18
Also published as: JP2010516508A; FR2911536A1; US20100196643A1; WO2008104649A3; WO2008104649A2

Abstract

The invention relates to a method for making PCTFE strings, that comprises extruding PCTFE with an extruder connected to an assembly comprising a die and a metallic cooling jig, characterised in that a material is provided between the inner metallic wall of the cooling jig and the PCTFE such that the friction between the PCTFE and this material is lower than the friction between the PCTFE and the metal of the cooling jig.

Description

CONFORMER FOR THE EXTRUSION OF PCTFE JONCS AND METHOD

EXTRUSION OF PCTFE

FIELD OF THE INVENTION The present invention relates to a shaper for extruding PCTFE rods and to the method of manufacturing such rods using said shaper.

The technical problem

PCTFE is a fluorinated polymer which comprises chlorotrifluoroethylene (CTFE) as its main monomer and which is valued for its high chemical resistance and its interesting mechanical and electrical properties. However, it is a difficult to process polymer since it requires, unlike other crystalline polymers, particularly high extrusion temperatures (Table I). The melt viscosity of the PCTFE is high even for an extrusion temperature of the order of 290-300 ⁰ C and does not decrease markedly with the increase in temperature.

Table I

This makes the extrusion of PCTFE rods difficult because it is necessary to maintain the PCTFE in the molten state at high temperatures close to 290-300 ⁰ C without degrading it thermally. A "cold" zone (around 16O ⁰ C) is likely to cause the formation of a "plug" which prevents further extrusion and thus limits productivity.

A problem that the invention intends to solve is therefore to extrude PCTFE rods in a simple, regular manner, with good productivity and without the rods having irregularities. Another problem solved by the invention is to extrude the rods without thermal degradation of the PCTFE.

Prior art US 2834054 discloses a PCTFE extrusion process which is characterized by a particular extrusion temperature profile.

US 5833070 discloses a method of extruding PCTFE film or plate form of quenching the melt ("quench").

In neither of these two documents is the method of the invention described. Figures FIG. 1 represents an assembly 1 formed of the die 3 and the shaper 2. The zone A (shaper) is cooled by means of a cooling circuit 4 in which circulates a coolant and the zone B (die) is maintained at a high temperature using a heating collar 7. A thermal insulation 5 is disposed between the die 3 and the shaper 2. The shaper comprises a tube 6 formed of a material against which the rod slides. The melt enters the die 3 and leaves the shaper 2 (see direction of the arrows).

Fig. 2 shows the tube 6 out of the shaper.

BRIEF DESCRIPTION OF THE INVENTION The invention relates to a process for manufacturing PCTFE rods consisting in extruding PCTFE using an extruder connected to an assembly composed of a die and a metal shaper characterized by what is available between the inner metal wall of the shaper and the PCTFE material such that the friction of the PCTFE with this material is less than that of the PCTFE with the metal of the shaper.

Detailed description of the invention

PCTFE is a polymer comprising predominantly CTFE units. It may be a homopolymer of CTFE or a copolymer of CTFE and at least one other monomer copolymerizable with CTFE comprising by weight at least 75%, advantageously at least 85%, preferably at least 95% of CTFE . A suitable comonomer is, for example, vinylidene fluoride (VDF).

The PCTFE of the invention is in the form of a thermoplastic polymer advantageously having a ZST between 200 and 450 s, preferably between 300 and 450 s. ZST (Zero Strength Time) is defined according to ASTM D-1430 to characterize the molecular weight of PCTFE. Examples of commercial PCTFE, we can use the grades Neoflon ^® 300P M or M-400H of the Daikin company or Voltalef ^® 302 grade from Arkema.

The PCTFE may optionally be mixed with at least one additive commonly used in the thermoplastics industry. It may be for example a mineral or organic filler, a pigment or a dye, an antistatic, a flame retardant, ... The PCTFE may also be mixed with at least one other polymer with which it is compatible. It may be for example a fluoropolymer. It is necessary that the additive or the polymer is thermally stable at PCTFE extrusion temperatures. The proportion of PCTFE in the mixture is at least 80% by weight, advantageously at least 90%.

As regards the extrusion process of PCTFE rods, it consists in extruding the PCTFE (in the form of powder or granules) using an extruder connected to a set formed of a die and the shaper of the invention.

The die has a function of bringing the melt leaving the extruder and shaping to give the 1 ^st to form ring. The die must keep the polymer melt at a material temperature T> 250 ° C, and without areas where the polymer could stagnate. Advantageously, this temperature is> 300 ° C to facilitate shaping.

The function of the shaper is to shape the molten material and to solidify it. It is made of a metal such as for example steel. The shape of the shaper is adapted to the shape of the ring that is desired. Generally, it is desired to prepare a cylindrical ring and the shaper is in this case of cylindrical symmetry. The internal diameter of the shaper is then equal to or substantially equal to the outer diameter of the ring. It is also conceivable to obtain other shapes for the rod, for example square section, and the shaper then has the appropriate geometry.

The shaper has a means of removing calories from the PCTFE to solidify the PCTFE before it leaves the shaper. A cooling circuit using a coolant such as a silicone oil for example can be advantageously used (see Fig.1). The exchange of calories is such that at a point of the shaper, over the entire section of the ring, the temperature of the PCTFE is below its crystallization temperature. Preferably, the rod of PCTFE leaves the shaper at a temperature of 90 ^° C. maximum. Cooling all the way along the shaper markedly influences the crystallinity of the polymer, thus the mechanical characteristics of the solid PCTFE.

It was found that there should be no contact between the inner metal wall of the shaper and the PCTFE because, in this case, the extrusion is very difficult or impossible, probably because the PCTFE, especially in the solid state or semi-solid, has a friction with the metal surfaces so that the rod can no longer or almost no longer advance in the shaper, which brakes or even blocks the extrusion. The use of a lubricant that would be added to PCTFE (such as an oil or grease) is not recommended because its thermal degradation can cause a significant coloration of PCTFE. It is necessary to arrange between the inner metal wall of the shaper and the PCTFE a material such that the friction of the PCTFE with this material is lower (at the same temperature) than that of the PCTFE with the metal of the shaper. The material can make the shape of a tube that is slid into the shaper and against which the ring slides along the length of the shaper (implied during the advance of the ring inside the shaper). An effective material for reducing friction is PTFE (polytetrafluoroethylene). By friction is meant above all the friction of solid PCTFE rather than liquid PCTFE. The combination PCTFE / PTFE is particularly interesting because:

The friction between these two fluoropolymers is weak;

• PTFE itself exhibits high thermal resistance at the extrusion temperatures envisaged.

The invention also relates to the use of said material to improve the preparation of the PCTFE rod, more specifically to the use of a material inside a shaper such that the friction of the PCTFE with this material is lower. to that of the PCTFE with the metal of the shaper.

Advantageously, it is also possible to have a thermal insulator between the die and the shaper so as not to create a "cold" point at the level of the die and thus to maintain a PCTFE always melted. The insulation must be able to withstand high temperatures on the die side and have low thermal conductivity. The insulation may for example be made of a composite consisting of glass fabric, glass mat, wick (roving) or mica paper alloyed with at least one resin resistant to high temperatures. For example, it may be PARMITHERM ^® 41140 marketed by Insulants of the East, Zl West, BP 46, 28, av. des Erables 54182 Heillecourt.

Downstream of the shaper, it is advantageous to have a brake device to exert a back pressure on the rod. This device makes it possible to compensate for the withdrawal of the polymer during its cooling in the shaper. It also improves the shape of the ring and in the case of a cylindrical ring, to obtain a perfectly cylindrical shape.

The method of the invention provides the following advantages: • the extrusion has a high productivity (no stop extrusion);

• the rods do not show any degradation (black color for example); no

• the rods do not have visible cooling layers;

• In the case of a cylindrical ring, a perfectly cylindrical shape is obtained, which therefore requires little reworking thereafter.

As regards productivity, it has been found that it is possible to obtain a productivity of at least 120 cm of extruded rod per hour for a 17 mm diameter cylindrical rod. The methods described above did not make it possible to obtain such productivity. The process of the present invention applies to PCTFE but also to the PCTFE-based mixture described above.

Examples

Example:

Was used Voltalef ^® 302 (PCTFE), marketed by Arkema having a ZST between 300 and 450 s. The polymer was extruded using a COLLIN 030 mm extruder under the following conditions: screw speed: 11 rpm extrusion temperature profile: 40/280/280/280/28 ⁰ C temperature of the die: 28O ⁰ C shaper: 70 ^° C ring diameter: 17 mm counterweight: 1000 g on a lever arm of 250 mm

A ring having the following characteristics was obtained: density: 2.14 g / cm ³ threshold stress: 47-49 MPa rupture stress: 37-40 MPa elongation rupture: 150-200% crystallinity: approximately 70%

The productivity of the extrusion was 120 cm / hour.

Example 2

Was used Voltalef ^® 302 (PCTFE), marketed by Arkema having a ZST between 300 and 450 s. The polymer was extruded using a COLLIN 030 mm extruder under the following conditions: screw speed: 15-20 rpm extrusion temperature profile: 35/280/280/280/28 ⁰ C temperature of the die: 27O ⁰ C shaper: 5-5O ⁰ C ring diameter: 17 mm counterweight: 1000 g on a lever arm of 250 mm A ring having the following characteristics was obtained: density: 2.13 g / cm ³ threshold stress: 46-48 MPa rupture stress: 37-40 MPa elongation rupture: 150-200% crystallinity: approximately 70%

The productivity of the extrusion was 400-500 cm / hour.

Example 3

Was used Voltalef ^® 302 (PCTFE), marketed by Arkema having a ZST between 300 and 450s. The polymer was extruded using a COLLIN 030 mm extruder under the following conditions: screw speed: 12 rpm extrusion temperature profile: 35/280/290/290/300 ⁰ C die temperature: 300 ⁰ C shaper: -18 ⁰ C ring diameter: 8 mm counterweight: 1000 g on a lever arm of 250 mm

A ring having the following characteristics was obtained: density: 2.12-2.13 g / cm ³ threshold stress: 45-47 MPa rupture stress: 37-40 MPa elongation rupture: 150-200% crystallinity: about 65- 70%

The productivity of the extrusion was 900 cm / hour.

Claims

1. Process for manufacturing PCTFE rods consisting in extruding PCTFE with the aid of an extruder connected to an assembly (1) composed of a die (3) and a metal shaper (2), characterized in that there is disposed between the inner metal wall of the shaper (2) and the PCTFE a material such that the friction of the PCTFE with this material is less than that of the PCTFE with the metal of the shaper (2).

2. The method of claim 1 wherein the rod PCTFE slides on the material.

3. The method of claim 1 or 2 wherein a tube (6) formed of the material is disposed between the inner metal wall and the PCTFE.

4. The method of claim 1 or 2 wherein the material takes the form of a tube (6) disposed between the inner metal wall and the PCTFE.

5. Method according to one of claims 1 to 4 wherein the material is PTFE.

6. Method according to one of claims 1 to 5 wherein the shaper (2) has a means of removing calories from PCTFE.

7. Method according to one of claims 1 to 6 wherein at a point of the shaper (2), over the entire section of the rod, the PCTFE temperature is below its crystallization temperature.

8. Method according to one of claims 1 to 7 wherein the temperature of the PCTFE rod at the output of the shaper (2) is at most 9O ⁰ C.

9. Method according to one of claims 1 to 8 wherein there is a thermal insulator (5) between the die (3) and the shaper (2).

10. A method according to any one of claims 1 to 9 wherein there is a brake device downstream of the shaper (2) exerting a back pressure on the rod.

11. Process according to any one of claims 1 to 10 in which the PCTFE is replaced by a mixture based on PCTFE and an additive and / or a polymer, comprising by weight at least at least 80%, advantageously at least 90% PCTFE.

12. Ring of PCTFE or a mixture as described in claim 11 obtainable by the method according to one of claims 1 to 11.

13. Use of a material inside a shaper intended to prepare rods PCTFE or a mixture as defined in claim 11 such that the friction of the PCTFE or the mixture with this material is lower than that PCTFE or the mixture with the metal of the shaper (2).

14. Use according to claim 13 wherein the material is in the form of a tube (6) disposed between the inner metal wall of the shaper (2) and the PCTFE or the mixture.

The use of claim 14 wherein the material is PTFE.