Tetrafluoroethylene copolymer fine powder resin
AssigneeE. I. Du Pont de Nemours and Company
InventorRobert Victor Poirier
Life of this patent
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Abstract
Good extrusion at high reduction ratios is obtained with a non-melt-fabricable tetrafluoroethylene fine powder resin whose particles have an inner portion and an outer portion, each portion being composed of a copolymer of tetrafluoroethylene and a selected comonomer, in which the comonomer content of the copolymer in the inner portion is greater than the comonomer content in the copolymer in the outer portion. Such particles are obtained by polymerizing tetrafluoroethylene and a desired amount of the selected comonomer in an aqueous dispersion medium, then lowering the amount of comonomer available, and continuing the polymerization.
Claims21
An aqueous polymer dispersion comprising a dispersion of non-melt-fabricable tetrafluoroethylene polymer particles in water at a solids content of between about 10 and about 65 weight percent;
- said particles having an average size of between about 0.1 and 0.5.mu.;
- said particles having at least two portions, an outer portion and an adjacent inner portion, each portion consisting essentially of a copolymer of units of tetrafluoroethylene and at least one comonomer having the formula ##STR11## wherein R.sub.1 independently if F or H;
- R.sub.2 independently is F or Cl;
- R.sub.3 can be Cl, --R.sub.F, --OR.sub.F,--R'.sub.F H, --OR'.sub.F H, --R'.sub.F Cl, --OR'.sub.F Cl, or ##STR12## Wherein R.sub.F is linear perfluoroalkyl of 1-5 carbon atoms, and R'.sub.F is linear perfluoroalkylene (perfluorinated alkane diradical) of 1-5 carbon atoms in which the designated substituent is an omega substituent;
- and when R.sub.2 is F, R.sub.1 and R.sub.3 taken together can be ##STR13## or the formula ##STR14## wherein R.sub.5 and R.sub.6 are independently --CF.sub.3 or --CClF.sub.2 ;
- said inner copolymer portion containing a higher percentage of said comonomer than the outer copolymer portion;
- the total comonomer content present in the particle, the amount of comonomer present in the copolymer of each portion, and the amount of each portion within such particles being sufficient to produce on AWG 22 wire a sintered coating having no more than 5 flaws per 100 meters of coated wire when said particles are paste extruded at a reduction ratio of 2840:1, the flaws being detected by subjecting the sintered coated wire to a high voltage spark tester at 2KV and 3000Hz;
- the copolymers of the inner portion and the outer portion combined containing an amount of comonomer which is low enough to maintain the non-melt-fabricable nature of the polymer particles.
A process for preparing an aqueous dispersion of tetrafluoroethylene polymer particles which comprises
- 1. subjecting tetrafluoroethylene and at least one comonomer of the formula ##STR15## wherein R.sub.1 independently is F or H;
- R.sub.2 independently is F or Cl;
- R.sub.3 can be Cl, --R.sub.F, --OR.sub.F, --R'.sub.F H, --OR'.sub.F H, --R'.sub.F Cl, --OR'.sub.F Cl, or ##STR16## wherein R.sub.F is linear perfluoroalkyl of 1-5 carbon atoms, and R'.sub.F is linear perfluoroalkylene (perfluorinated alkane diradical) of 1-5 carbon atoms in which the designated substituent is an omega substituent;
- and
- when R.sub.2 is F, R.sub.1 and R.sub.3 taken together can be ##STR17## or the formula ##STR18## wherein R.sub.5 and R.sub.6 independently are --CF.sub.3 or --CCLF.sub.2 ;
- wherein the mole ratio of the amount of the comonomer to the tetrafluoroethylene is between about 0.0005 and about 0.05, to polymerizing conditions to temperature and pressure in an aqueous medium having dissolved therein a free-radical initiator and a dispersing agent and at an agitation level of from between about 2 to 12 joules/sec.-1. until the polymer solids content is between about 20 and 50% of the weight of the resulting dispersion;
- 2. subjecting the aqueous dispersion obtained in step (1) to tetrafluoroethylene and said comonomer in a mole ratio of comonomer to tetrafluoroetylene of between about 0.0001 and 0.005, provided said ratio is less than that in step (1) under polymerizing conditions of temperature and pressure and at an agitation level of from between about 2 to 12 joules/sec.-1. until the solids content is between about 35 and 65% of the weight of the resulting dispersion and is at least about 15% greater than the solids content of the dispersion obtained in step (1).
Dependencies are inferred from the claim text.