Thermoplastic polymers

Abstract

Thermoplastic polymers, for example fluoropolymers, are foamed by use of a solid formulation comprising thermoplastic polymer and an oxalate compound which includes a moiety selected from potassium, calcium, titanium, iron, cobalt, nickel, copper, zinc, zirconium and barium.

Claims

1. A formulation for use in preparing a foamed thermoplastic polymer, said formulation comprising a thermoplastic polymer and an oxalate compound, wherein said oxalate compound includes a moiety selected from a group consisting of zinc and zirconium, wherein said oxalate compound includes 1 wt % or less of water, wherein said formulation is in the form of pellets which are homogenous, wherein said thermoplastic polymer has a melt processing temperature of at least 250 C., wherein said thermoplastic polymer is a fluoropolymer.

2. A formulation according to claim 1, wherein, in said pellets, the sum of the wt % of oxalate compound(s) and thermoplastic polymer(s) is at least 98 wt %.

3. A formulation according to claim 1, wherein said formulation comprises a solid master batch.

4. A formulation according to claim 1, wherein said formulation comprises a solid master batch which includes 3 to 15 parts by weight of said oxalate compound and 85 to 97 parts by weight of said thermoplastic polymer.

5. A formulation according to claim 1, wherein said formulation comprises 5 to 15 wt % of said oxalate compound and 85 to 95 wt % of said thermoplastic polymer.

6. A formulation according to claim 1, wherein said fluoropolymer is fluorinated ethylene-propylene copolymer.

7. A formulation according to claim 1, wherein said formulation includes less than 0.5 wt % of water.

8. A formulation according to claim 1, wherein said pellets have a volume in the range 2-50 mm.sup.3.

9. A formulation according to claim 1, wherein said pellets include 1 to 10 wt % of said oxalate compound, 0 to 10 wt % of a nucleator and 89 to 99 wt % of said thermoplastic polymer.

10. A formulation according to claim 1, wherein said pellets include 3 to 9 wt % of said oxalate compound, 2 to 10 wt % of said nucleator and 87 to 95 wt % of said thermoplastic polymer.

11. A formulation according to claim 1, wherein said formulation comprises 0.2 to 1 wt % of zirconium or zinc oxalate and 99.0 to 99.8 wt % of said thermoplastic polymer.

12. A formulation according to claim 1, wherein said formulation comprises 1 to 30 wt % of zirconium or zinc oxalate and 70 to 99 wt % of fluoropolymer.

13. A formulation according to claim 1, wherein 100% of the particles of said oxalate compound would pass through a sieve of mesh size 200 m.

14. A formulation for use in preparing a foamed thermoplastic polymer, said formulation comprising a thermoplastic polymer and an oxalate compound, wherein said oxalate compound is selected from zinc oxalate and zirconium oxalate, wherein said oxalate compound includes 1 wt % or less of water, wherein said formulation is in the form of pellets which are homogenous, wherein said thermoplastic polymer has a melt processing temperature of at least 250 C. and is a fluoropolymer, wherein said pellets have a volume in the range 2-50 mm.sup.3, wherein said pellets include 1 to 10 wt % of said oxalate compound, 0 to 10 wt % of a nucleator and 89 to 99 wt % of said thermoplastic polymer.

15. A formulation according to claim 14, wherein said pellets include 3 to 9 wt % of said oxalate compound.

16. A formulation according to claim 15, wherein said fluoropolymer is fluorinated ethylene-propylene copolymer.

17. A formulation according to claim 15, wherein, in said pellets, the sum of the wt % of oxalate compounds and thermoplastic polymers is at least 99 wt %; and wherein said pellets have a volume in the range 4-30 mm.sup.3.

18. A formulation according to claim 14, wherein, in said pellets, the sum of the wt % of oxalate compounds and thermoplastic polymers is at least 98 wt %.

Description

EXAMPLE 1GENERAL PROCEDURE FOR MANUFACTURE OF OXALATE MASTERBATCH CONCENTRATE

(1) An oxalate selected from those described above is pre-blended with DuPont FEP106 pellets by tumble mixing to produce tumble blends containing both 5 wt % and 10 wt % oxalate. The pre-blended mixture can be fed by volumetric feeder into a 30 mm diameter twin screw extruder with let-down ratio of 22/1. The extruder temperature settings are suitably 255/255/260/260/265/270/270 C. from the feed throat to the die respectively. Improved dispersion of the oxalate is observed after multiple extruder passes. The masterbatch is pelletised at the end of the process.

EXAMPLE 2GENERAL PROCEDURE FOR MEASUREMENT OF FOAMING

(2) The measurement of the density of produced foams may be carried out using an AG 104 density balance manufactured by Mettler Toledo. The sample is weighed both in air and in water to obtain the density of the material under investigation. The resultant density is used in the calculation of the void content as follows
Void content=100((1/2)*100)
where 1 and 2 are the densities of the foamed polymer and the unmodified polymer respectively.

EXAMPLE 3GENERAL PROCEDURE FOR MANUFACTURE OF FOAMED SAMPLES

(3) Oxalate masterbatch is tumble blended with other pellets (e.g. nucleator and/or diluent resin) to be used in formulations. The blend may then be added at the feed throat of a single screw extruder with a temperature profile of 280/300/330/380/360/360/340 C. from the feed throat to the die as this is representative of processing conditions used in the manufacture of wire and cable. Different screw speeds may be assessed in addition to the effect of the presence of nucleating agent (S164.1) or not.

(4) The oxalate masterbatch can be used to foam the high performance (high melting) thermoplastic. Other high melting thermoplastics may be foamed in a similar manner.

(5) As an alternative to the use of a masterbatch as described, a mixture comprising oxalate (e.g. 0.25-2 wt %) and thermoplastic polymer may be made, in a manner analogous to that described in Example 1, except that the mixture can be used directly in manufacturing a foamed sample without needing to be diluted. Such a mixture could also incorporate nucleator (e.g. boron nitride) at an appropriate concentration (e.g. 0.25 to 2 wt %) so the thermoplastic polymer/oxalate/boron nitride mixture can be used directly to make foamed products.

(6) In a further alternative, nucleator (e.g. boron nitride) may be included in the masterbatch of Example 1 at a suitable level and the Example 3 method used to produce a foamed product, without addition of separate oxalate and boron nitride masterbatches.

EXAMPLE 4MANUFACTURE OF IRON II OXALATE MASTERBATCH CONCENTRATE

(7) Iron (II) oxalate was pre-blended with DuPont FEP106 pellets by tumble mixing to produce tumble blends containing 5 wt % oxalate. The pre-blended mixture was fed by volumetric feeder into a 30 mm diameter twin screw extruder with let-down ratio of 22/1. The extruder temperature settings were 255/255/260/260/265/270/270 C. from the feed throat to the die respectively. The extruder is vented to allow the removal of water of hydration during the masterbatch manufacturing process as this has the potential to cause premature foaming in subsequent use of the material if not removed. Improved dispersion of the oxalate is observed after multiple extruder passes. The masterbatch was pelletised at the end of the process.

EXAMPLE 5MANUFACTURE OF ZINC OXALATE MASTERBATCH CONCENTRATE

(8) Zinc oxalate was pre-blended with DuPont FEP106 pellets by tumble mixing to produce tumble blends containing 5 wt % oxalate. The pre-blended mixture was fed by volumetric feeder into a 30 mm diameter twin screw extruder with let-down ratio of 22/1. The extruder temperature settings were 255/255/260/260/265/270/270 C. from the feed throat to the die respectively. The extruder is vented to allow the removal of water hydration. Improved dispersion of the oxalate is observed after multiple extruder passes. The masterbatch was pelletised at the end of the process.

EXAMPLE 6MANUFACTURE OF FOAMED SAMPLES FROM EXAMPLE 1 AND EXAMPLE 2 MASTERBATCHES

(9) Pellets of oxalate masterbatch is tumble blended with other pellets (e.g. nucleator and/or diluent resin) to be used in formulations. The blend may then be added at the feed throat of a single screw extruder with a temperature profile of 280/300/330/380/360/360/340 C. from the feed throat to the die as this is representative of processing conditions used in the manufacture of wire and cable. The density and void content of the resultant foams was measured with the following results

(10) Iron (II) Oxalate

(11) Density 1.215

(12) Void content 44%

(13) Zinc Oxalate

(14) Density 1.732

(15) Void content 21%

EXAMPLE 7MANUFACTURE OF FOAMED SAMPLES FROM EXAMPLE 1 AND EXAMPLE 2 MASTERBATCHES

(16) The procedure of Example 6 was followed except the temperature profile was 280/300/330/380/380/400/410 C. from the feed throat to the die. The density and void content of the resultant foams was measured with the following results

(17) Iron (II) Oxalate

(18) Density 0.978

(19) Void content 55%

(20) Zinc Oxalate

(21) Density 1.245

(22) Void content 42%

(23) The oxalate masterbatch can be used to foam the high performance (high melting) thermoplastic. Other high melting thermoplastics may be foamed in a similar manner.

(24) As an alternative to the use of a masterbatch as described, a mixture comprising oxalate (e.g. 0.25-2 wt %) and thermoplastic polymer may be made, in a manner analogous to that described in Example 1, except that the mixture can be used directly in manufacturing a foamed sample without needing to be diluted. Such a mixture could also incorporate nucleator (e.g. boron nitride) at an appropriate concentration (e.g. 0.25 to 2 wt %) so the thermoplastic polymer/oxalate/boron nitride mixture can be used directly to make foamed products.

(25) In a further alternative, nucleator (e.g. boron nitride) may be included in the masterbatch of Example 1 at a suitable level and the Example 3 method used to produce a foamed product, without addition of separate oxalate and boron nitride masterbatches.

(26) The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.