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Fluoropolymer composition

a technology of fluoropolymer and composition, applied in the field of fluoropolymer composition, can solve the problems of increasing the melt viscosity of the blend, affecting the shear rate of the molded article, so as to achieve the effect of reducing melt viscosity, reducing melt viscosity and improving shear ra

Inactive Publication Date: 2007-05-24
EI DU PONT DE NEMOURS & CO
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention relates to melt-mixed compositions containing non-melt flowable polytetrafluoroethylene (PTFE) and melt-fabricable perfluoropolymer that exhibit desirable viscosities for melt fabrication and do not become brittle upon increasing shear rates. The compositions have a thixotropy that allows them to flow at high shear rates, making them suitable for melt fabrication processes such as extrusion and injection molding. The PTFE in the compositions acts as a reinforcing agent, providing strength and flexibility to the composition. The compositions can also be made into transparent or translucent articles. The patent text also describes a novel dispersion structure where the PTFE is present in small particles within the perfluoropolymer continuous phase, which further enhances the properties of the compositions.

Problems solved by technology

When the amount of PTFE is more than 2 parts by weight, two disadvantageous results are disclosed: the melt viscosity of the blend increases significantly and the molded article tends to become brittle .
These are the same effects as adding filler to a polymer, except that in the case of adding PTFE to FEP, the disadvantageous effects arise with even small additions of the PTFE to the FEP.

Method used

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Examples

Experimental program
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Effect test

examples

Test Procedures

[0048] The procedures for determining melt creep viscosity, standard specific gravity (SSG), melt flow rate (MFR), core / shell polymer composition, and average core / shell polymer particle size (RDPS) reported in the Examples are disclosed earlier herein. The determination of melt viscosity is also disclosed earlier herein. All of the core / shell polymers and separate melt-fabricable perfluoropolymers disclosed in the Examples exhibited a melt viscosity less than about 5×104 Pa·s at 350° C. and shear rate of 101 s−1.

[0049] The thixotropy of the melt blends described in the Examples is determined by capillary rheometry method of ASTM D 3835-02 in which the melt temperature of the polymer in the rheometer is 350° C. This method involves the extrusion of molten polymer through the barrel of a Kayeness® capillary rheometer at a controlled force to obtain the shear rate desired. The results are reported in the Examples as melt viscosity change (reduction), Δη in Pa·s in in...

example 1

[0056] Core / shell polymer when the shell polymer is FEP and the proportion of core to shell is widely varied, is made in this Example. A cylindrical, horizontal, water-jacketed, paddle-stirred, stainless steel reactor having a length to diameter ratio of about 1.5 and a water capacity of 10 gallons (37.9 L) was charged with 50 pounds (22.7 kg) of demineralized water and 330 mL of a 20 wt % solution of ammonium perfluorooctanoate surfactant in water. With the reactor paddle agitated at 46 rpm, the reactor was heated to 60° C., evacuated and purged three times with tetrafluoroethylene (TFE). The reactor temperature then was increased to 103° C. After the temperature had become steady at 103° C., the pressure of the reactor was raised to 250 psig (1.75 MPa) using TFE. Fifty milliliters of an initiating solution consisting of 1.04 wt % APS and 0.94 wt % KPS in water was injected to the reactor, then this same initiator was added at 0.5 mL / min. After polymerization had begun as indicated...

examples 2-6

[0057] Examples 2 through 6 were prepared in a manner similar to Example 1, with the proportions of core and shell altered by changing the relative amounts of TFE fed during each phase of polymerization. Details are given in Table 1 below.

TABLE 1PTFEHFPPEVEHFPPEVETensileExampleCore,Content,Content,Content inContent inMFR,Strength,ElongationΔη,Numberwt %wt %wt %Shell, wt %Shell, wt %g / 10 minMPaat Break, %Pa · s17.6%6.841.377.411.48026.735712936211.5%6.421.437.251.620.423.83936273315.4%6.411.477.571.740.721.33586495419.2%6.181.697.652.09024.93949000526.9%5.831.817.982.48020.93389113639.0%5.081.308.342.12017.323510344

Each of the polymerizations was carried out to a solids content of 33.8 to 35.8 wt % and the RDPS of the polymer particles ranged from 194 to 261 nm (0.194 to 0.261 micrometers). As compared to the reduction in melt viscosity of 101 Pa·s for typical FEP by itself (Comparison Example A), the core / shell polymer of the present invention exhibits a much greater melt viscosi...

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Abstract

A melt-mixed composition of non-melt flowable polytetrafluoroethylene (PTFE) and melt-fabricable perfluoropolymer is provided that exhibits thixotropy at increasing shear rate in the molten state and high elongation at break even at PTFE concentrations well above 4 wt %, based on the combined weight of the PTFE and the perfluoropolymer, e.g. at least 200% up to at least 30 wt % PTFE, the composition also exhibiting the structure of a dispersion of submicrometer-size particles of the PTFE in a continuous phase of the melt-fabricable perfluoropolymer.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] This invention relates to fluoropolymer compositions of polytetrafluoroethylene and other perfluoropolymers. [0003] 2. Description of Related Art [0004] U.S. 2004 / 0242783 A1 discloses a blend of tetrafluoroethylene / hexafluoropropylene copolymer, commonly called FEP, and polytetrafluoroethylene (PTFE), the PTFE imparting the improved extrusion property of reduced cone breaks during melt draw down extrusion coating of wire. The PTFE content of the blend is disclosed to be 0.03 to 2 parts by weight based on 100 parts by weight of the copolymer. When the amount of PTFE is more than 2 parts by weight, two disadvantageous results are disclosed: the melt viscosity of the blend increases significantly and the molded article tends to become brittle [0027]. These are the same effects as adding filler to a polymer, except that in the case of adding PTFE to FEP, the disadvantageous effects arise with even small additions of the...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C08L27/12
CPCC08F114/26C08F259/08C08L27/18C08L51/003C08L2205/02C08F2/00C08L2666/02C08L2205/025Y10S525/902
Inventor BURCH, HEIDI ELIZABETHVENKATARAMAN, SUNDAR KILNAGARATEN, RALPH MUNSON
Owner EI DU PONT DE NEMOURS & CO
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