Thermoplastic polymers

Abstract

Thermoplastic polymers, for example fluoropolymers, are foamed by use of a solid formulation comprising thermoplastic polymer and manganese oxalate.

Claims

1. A method of preparing a foamed thermoplastic polymer which comprises: subjecting a mixture formed by contacting 1 to 36 wt % of a masterbatch with 64 to 99 wt % of a first thermoplastic polymer to be foamed to a temperature of greater than 300° C., wherein the masterbatch is in the form of melt-processed pellets which include 3 to 9 wt % of an oxalate compound, 2 to 10 wt % of a nucleator, and 87 to 95 wt % of a second thermoplastic polymer, wherein said second thermoplastic polymer has a melt-processing temperature of at least 250° C. and is a fluoropolymer, and wherein said oxalate compound comprises manganese oxalate.

2. The method according to claim 1, wherein said first thermoplastic polymer to be foamed is a fluoropolymer.

3. The method according to claim 2, wherein the first thermoplastic polymer to be foamed is a fluorinate ethylene propylene copolymer (FEP).

4. The method according to claim 1, wherein said mixture is subjected to a temperature of greater than 330° C.; and is subjected to a maximum temperature of less than 390° C.

5. The method according to claim 2, wherein said mixture is subjected to a temperature of greater than 330° C.; and is subjected to a maximum temperature of less than 390° C.

6. The method according to claim 1, wherein said first thermoplastic polymer to be foamed: (i) has a melting point of at least 250° C.; and/or (ii) has a continuous use temperature of at least 160° C.; and/or (iii) has a melt flow rate (MFR) at 372° C. and a 5.0 kg load assessed using ISO12086 in the range 1.2 to 36 g/10 min; and/or (iv) has a tensile strength, measured in accordance with ASTM D638, of at least 1500 psi; and/or (v) has a flexural modulus, in accordance with ASTM D790 at +23° C., of at least 70,000 psi; and/or (vi) has a tensile modulus, in accordance with ASTM D638, of at least 30,000.

7. The method according to claim 4, wherein said first thermoplastic polymer to be foamed is a fluoropolymer.

8. The method according to claim 4, wherein said first thermoplastic polymer to be foamed is a FEP.

9. The method according to claim 1, wherein said nucleator is boron nitride.

10. The method according to claim 1, wherein said first thermoplastic polymer to be foamed is a FEP and said nucleator is boron nitride.

Description

EXAMPLE 1—MANUFACTURE OF MANGANESE OXALATE MASTERBATCH CONCENTRATE

(1) Manganese oxalate was pre-blended with DuPont FEP106 pellets by tumble mixing. Tumble blends containing both 5 wt % and 10 wt % manganese oxalate were produced. The pre-blended mixture was then 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 manufacture process as this has the potential to cause premature foaming in subsequent use of the material if not removed. Improved dispersion of the manganese oxalate was observed after multiple extruder passes. The masterbatch is pelletised at the end of the process.

EXAMPLE 2—MANUFACTURE OF MANGANESE OXALATE MASTERBATCH CONCENTRATE WITH ALTERNATIVE RESIN

(2) Manganese oxalate was pre-blended with DuPont CJ99 pellets by tumble mixing. A tumble blend containing 5% wt manganese oxalate was produced. The pre-blended mixture was then fed by volumetric feeder into a 30 mm diameter twin screw extruder with length/diameter ratio of 22/1. The extruder temperature settings were 276/290/280/280/278/282/285° C. from the feed throat to the die respectively. The extruder is vented to allow the removal of water of hydration during the masterbatch manufacture process as this has the potential to cause premature foaming in subsequent use of the material if not removed. The dispersion of the manganese oxalate was improved after multiple passes through the extruder under these conditions. The masterbatch is pelletised at the end of the process.

EXAMPLE 3—MANUFACTURE OF A COMBINED MANGANESE OXALATE/BORON NITRIDE CONCENTRATE

(3) Manganese oxalate was pre-blended with DuPont CJ99 pellets by tumble mixing. A tumble blend containing 5.5% wt manganese oxalate was produced. The pre-blended mixture was then fed by volumetric feeder into a 30 mm diameter twin screw extruder with length/diameter ratio of 22/1. The extruder temperature settings were 276/290/280/280/278/282/285° C. from the feed throat to the die respectively. The resulting masterbatch was then pre-blended with 5 wt % boron nitride and extruded as a second step using exactly the same processing conditions as the previous step. The resultant formulation therefore contains 5.225% wt manganese oxalate and 5% wt boron nitride. The masterbatch is pelletised at the end of the process.

EXAMPLE 4—MEASUREMENT OF FOAMING

(4) The measurement of the density of the produced foams is 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−((p1/p2)*100)
where p1 and p2 are the densities of the foamed polymer and the unmodified polymer respectively.

EXAMPLE 5—MANUFACTURE OF FOAMED SAMPLES

(5) The manganese oxalate masterbatch was tumble blended with other pellets (e.g. nucleator and/or diluent resin) to be used in the formulations tested. The blend was then 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 and other FEP products. Different screw speeds were assessed in addition to the effect of the presence of nucleating agent (S164.1) or not. The processing conditions and results are summarised in Table 1. The diluent resin in all cases was DuPont FEP 106.

(6) TABLE-US-00001 TABLE 1 Loading of foaming Loading of masterbatch nucleator Void of Example 1 masterbatch Screw Density content Sample (wt %) (wt %) rpm (g/cm3) (%) 1 5% 5% 10 1.36 37.222 2a 10% — 18 1.06 50.972 3b 10% — 18 1.01 53.241 3a 10% 5% 18 1.09 49.722 3b 10% 5% 18 1.06 50.926

EXAMPLE 6—MANUFACTURE OF FOAMED SAMPLES USING PELLETS FROM EXAMPLE 2

(7) The manganese oxalate masterbatch was tumble blended with other pellets (e.g. nucleator and/or diluent resin) to be used in the formulations tested. The blend was then added at the feed throat of a single screw extruder with different temperature profiles (T1=280/300/350/400/390/380/380° C.; T2=280/300/350/400/380/370/370 and T3=290/310/360/400/390/380/380° C. from the feed throat to the die) in order to find the optimum processing temperature. Different screw speeds were assessed in addition to the effect of the presence of nucleating agent (S164.1) or not. The processing conditions and results are summarised in Table 2. The diluent resin in all cases was DuPont FEP CJ99.

(8) TABLE-US-00002 TABLE 2 Loading of foaming Loading of masterbatch nucleator Void Sam- of Example masterbatch Temp Screw Density content ple 2 (wt %) (wt %) profile rpm (g/cm3) (%) 4a 5% — T1 10 1.91 11.136 4b 5% — T1 20 1.89 12.093 4c 5% — T1 30 1.86 13.488 4d 5% — T1 40 1.84 14.419 4e 5% — T1 50 1.70 20.930 4f 5% — T3 20 1.82 15.35 4g 5% — T3 40 1.84 14.42 4h 5% — T3 50 1.49 30.70 5a 10% — T3 20 1.58 26.51 5b 10% — T3 40 1.35 37.21 6a 5%   5% T3 20 1.26 41.40 6b 5%   5% T3 40 1.20 44.19 7a 10% 2.5% T3 10 1.62 24.65 7b 10% 2.5% T3 20 1.45 32.56 7c 10% 2.5% T3 40 0.97 54.88 8a 10%   5% 13 20 1.21 43.72 8b 10%   5% T3 40 1.03 52.09

EXAMPLE 7—MANUFACTURE OF FOAMED SAMPLES USING PELLETS FROM EXAMPLE 3

(9) The combined masterbatch containing both manganese oxalate and boron nitride produced in example 3 was tumble blended with diluent resin pellets to produce the formulations tested. The blend was then added to the feed throat of a single screw extruder using the temperature profile T3 as described in example 6 (i.e. T3=290/310/360/400/390/380/380° C. from the feed throat to the die). Different screw speeds were assessed and the diluent resin in all case was DuPont FEP CJ99. The results are summarised in Table 3.

(10) TABLE-US-00003 TABLE 3 Loading of foaming masterbatch Void of Example Screw Density content Sample 3 (wt %) rpm (g′cm3) (%)  9a 5% 20 1.57 26.98  9b 5% 40 1.25 41.86  9c 5% 50 1.08 49.77 10a 10% 20 1.17 45.58 10b 10% 40 0.89 58.60 10c 10% 50 0.77 64.19
From these results the synergistic effect of manufacturing the masterbatch with the incorporation of a single type of masterbatch pellet comprising both manganese oxalate and the boron nitride nucleating agent is evident. For example, in example 6 samples 6a and 6b are analogous to samples 10a and 10b in example 7. In examples 10a and 10b the density is reduced compared to similar samples produced by utilising separate nucleator and foaming agent masterbatches. In addition, sample 9b indicates that using half the active ingredient can result in similar density reductions when a combined masterbatch approach is made.

EXAMPLE 8—MANUFACTURE OF A COMBINED MANGANESE OXALATE/BORON NITRIDE MASTERBATCH BY AN ALTERNATIVE METHOD

(11) Dupont CJ99 resin was tumble blended with manganese oxalate and boron nitride (each at concentrations of 5 wt %). The resultant mixture was then fed by volumetric feeder into a 30 mm diameter twin screw extruder with length/diameter ratio of 22/1. The extruder temperature settings were 276/290/280/280/278/282/285° C. from the feed throat to the die respectively. The extruder is vented to allow the removal of water of hydration during the masterbatch manufacture process as this has the potential to cause premature foaming in subsequent use of the material if not removed. The dispersion of the additives was improved after multiple passes through the extruder under these conditions. The masterbatch is pelletised at the end of the process.

EXAMPLE 9—MANUFACTURE OF FOAMED WIRE FROM PELLETS OF EXAMPLE 8

(12) The combined masterbatch containing both manganese oxalate and boron nitride produced in example 8 was tumble blended with diluent resin pellets (Dupont FEP 9494) at a ratio of 10% wt. the resultant composition was extruded onto 24AWG bare copper using a 38 mm single screw extruder with LID ratio of 24/1 and a standard FEP screw. The extruder was fitted with a 6.35 mm die with a 1.5 mm tip. A temperature profile of 290/310/370/400/405/405/410/410/425 was used from tip to die with a screw speed of 34 rpm. The resultant insulation had a density of 1.262 g/cm3 and a void content of 41%.

(13) Thus, it is clear from the experiments undertaken that the manganese oxalate masterbatch can advantageously be used to foam the high performance (high melting) thermoplastic. Other high melting thermoplastics may be foamed in a similar manner. i.e. by the manufacture of a masterbatch/compound containing the manganese oxalate foaming agent or a masterbatch/compound containing manganese oxalate foaming agent and boron nitride nucleating agent.

(14) As an alternative to the use of a masterbatch as described, a mixture comprising manganese 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/manganese oxalate/boron nitride mixture can be used directly to make foamed products.

(15) 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.