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Concentrated fluoropolymer dispersions stabilized with anionic polyelectrolyte dispersing agents

Inactive Publication Date: 2007-12-06
EI DU PONT DE NEMOURS & CO
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0010]The invention further provides a process for reducing the fluorosurfactant content of and concentrating an aqueous fluorosurfactant-containing fluoropolymer dispersion comprising stabilizing fluoropolymer dispersion comprising fluoropolymer particles having an average size of about 10 to about 400 nm and a solids content of about 15 to about 55 wt % with anionic polyelectrolyte dispersing agent, contacting the stabilized fluorosurfact

Problems solved by technology

Coatings of polytetrafluoroethylene (PTFE) homopolymers and modified PTFE provide the highest heat stability among the fluoropolymers, but unlike tetrafluoroethylene (TFE) copolymers, cannot be melt processed to form films and coatings.
For some specialized fluoropolymer coating dispersions, common nonionic surfactants such as alkyl phenol ethoxylates or aliphatic alcohols ethoxylates for stabilization are unsuitable.
However because of environmental concerns and because fluorosurfactants are expensive, processes have been developed for reducing and recovering fluorosurfactant from aqueous fluoropolymer dispersions.

Method used

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  • Concentrated fluoropolymer dispersions stabilized with anionic polyelectrolyte dispersing agents
  • Concentrated fluoropolymer dispersions stabilized with anionic polyelectrolyte dispersing agents
  • Concentrated fluoropolymer dispersions stabilized with anionic polyelectrolyte dispersing agents

Examples

Experimental program
Comparison scheme
Effect test

example 1

[0072]Several samples of 200 grams of as-polymerized (raw) PTFE dispersion at 41 wt % solids are placed in 8-ounce glass jars. The jars are approximately ¾ full.[0073]Sample 1 contains only as-polymerized PTFE dispersion.[0074]Sample 2 contains as-polymerized PTFE dispersion stabilized with 1.22 wt % TAMOL® 681 (active ingredient basis) based on the dry weight of PTFE.[0075]Sample 3 contains as-polymerized PTFE dispersion with 6 wt % of wet US Filter A-244-OH ion exchange resin[0076]Sample 4 contains as-polymerized PTFE dispersion stabilized with 1.22 wt % TAMOL® 681 based on the dry weight of PTFE and 6 wt % of wet US Filter A-244-OH ion exchange resin.

[0077]The jars are placed on a Brunnell Wrist Action Shaker and shaken on a speed setting of 1 at room temperature, a suitable setting to get good mixing of the ion exchange resin and PTFE dispersion in Samples 3 and 4.[0078]Sample 1 containing only PTFE dispersion is ⅔ coagulated after shaking for about 1.5 hours.[0079]Sample 2 cont...

example 2

Shear Stability as Measured by Gel Time

[0082]To establish an effective level of TAMOL® 681, samples of as-polymerized PTFE dispersion and TAMOL® 681 are sheared in a Waring blender at high speed until the dispersion gelled. The resulting Gel Times are shown below in Table 1. The shear stability is found to be highly dependent on concentration of TAMOL®. The wt % Tamol 681 is expressed on the basis of active ingredients relative to PTFE solids.

TABLE 1wt % TAMOL ® 681Gel Time, seconds0.3520.7041.0531.49431.75727

example 3

Fluorosurfactant Removal

[0083]A dispersion containing 1.75 wt % TAMOL® 681 (active ingredients basis) in as-polymerized PTFE with 41 wt % solids is prepared. Additional ammonium hydroxide is added to insure the pH remains above 9.5. Varying level of A-244-OH ion exchange resin are added and the samples are shaken on the Brunnell Wrist Action Shaker at a speed setting of 1 for 3 hours. The samples are then analyzed for APFO levels based on the total dispersion weight. The results are shown below.

TABLE 2wt % A-244-OH ResinAPFO, ppm1.28793.54345.82328.114910.599.812.864

[0084]The results indicate that the TAMOL® 681 provides sufficient stability to allow ion exchange to reduce the level of APFO in fluoropolymer dispersions. It is also a good indication that the ion exchange resin is not removing the TAMOL® as well as the APFO.

[0085]The rate of ion exchange can be further improved by using additional ion exchange resin or by increasing the temperature at which the ion exchange is conduct...

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Abstract

An aqueous fluoropolymer dispersion comprising fluoropolymer particles having an average particle size of about 10 to about 400 nm. The dispersion has a solids content of at least about 35 to about 70 wt % and comprises about 0.03 wt % to about 10 wt % anionic polyelectrolyte dispersing agent based on the weight of fluoropolymer solids. The dispersion has a Gel Time of at least about 100 seconds.

Description

FIELD OF INVENTION[0001]The present invention relates to concentrated fluoropolymer dispersions and more particularly to concentrated stabilized dispersions with reduced fluorosurfactant content.BACKGROUND OF THE INVENTION[0002]Fluoropolymers are applied to a wide number of substrates in order to confer release, chemical and heat resistance, corrosion protection, cleanability, low flammability, and weatherability. Coatings of polytetrafluoroethylene (PTFE) homopolymers and modified PTFE provide the highest heat stability among the fluoropolymers, but unlike tetrafluoroethylene (TFE) copolymers, cannot be melt processed to form films and coatings. Therefore, other processes have been developed for applying coatings of PTFE homopolymers and modified PTFE. One such process is dispersion coating which applies the fluoropolymer in dispersion form. Dispersions used in coating processes are usually in a concentrated form and contain a significant quantity of nonionic surfactant, e.g. 6-8 w...

Claims

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Application Information

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IPC IPC(8): D06P1/52C09B67/00
CPCC08K3/24C08L1/08C08L27/18C08L33/02C08L33/14C09D127/18C08L79/08C08L2666/26C08L2666/04C08L2666/20
Inventor CAVANAUGH, ROBERT JOHNJONES, CLAY WOODWARD
Owner EI DU PONT DE NEMOURS & CO
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