FIELD OF THE INVENTION
This invention relates primarily to aqueous fluoropolymer dispersion employing a strong oxidizing agent as a coagulating electrolyte. More particularly, the present invention relates particularly to coagulation process in fluoropolymer dispersion treatment employing a strong oxidizing agent as a coagulating electrolyte. The invention further relates to coagulating agent which results in improved powder properties like- higher whiteness index, improved particle size distribution, bulk density and extrusion.
BACKGROUND OF THE INVENTION
It is known that the Fluoropolymer powders are obtained by the polymerization in dispersion. In coagulation process a sufficient amount of surfactant is used so as to be able to stabilize the Fluoropolymer colloidal particles and a soft stirring is applied during the polymerization to avoid the polymer coagulation (precipitation). Subsequently the latex obtained from said process is coagulated and the powder obtained from the coagulation is called "coagulated powder". The conventional coagulation process comprises the following steps:
- latex dilution with water, optionally addition of a destabilizing electrolyte,
- latex mechanical stirring to obtain the formation of aggregates/gels,
- granulation (coagulation) of the aggregates/gels by mechanical stirring,
- Fluoropolymer flotation from water,
- mechanical separation of the wet powder from the dispersion medium.
WO 2013/169566 Al titled "Fluoropolymer dispersion treatment employing hypochlorite salts or nitrite salts to reduce fluoropolymer resin discoloration" discloses Fluoropolymer dispersion treatment employing hypochlorite salts or nitrite

salts to reduce fluoropolymer resin discoloration. It discloses a process for reducing thermally induced discoloration of fluoropolymer resin produced by polymerizing fluoromonomer in an aqueous dispersion medium to form aqueous fluoropolymer dispersion and isolating said fluoropolymer from said aqueous medium to obtain said fluoropolymer resin. The process comprises: exposing the aqueous fluoropolymer dispersion to oxidizing agent selected from the group consisting of hypochlorite salts and nitrite salts.
In prior arts, carbonate salts or strong acids were used as coagulant in Fluoropolymer dispersion treatment employing hypochlorite salts or nitrite salts to reduce fluoropolymer resin discoloration.
For instance, Fluoropolymer fine powders are transformed by the lubricated extrusion process to obtain the manufactured articles. The lubricated extrusion process is much more productive and easily automatable the more the fine powders are flowing and have a high apparent density. Besides, the average particle diameter is preferably higher than 400 micron and the particle diameter distribution as above defined should be at least higher than 50%, preferably higher than or equal to 60% to obtain an improved flow.
It is usually desirable for fluoropolymer resin to be clear white in color and, in resin prone to discoloration due to residual ionic impurities, a gray, brown or yellow color sometimes quite dark forms upon heating. It has been discovered that this discoloration of fluoropolymer resin can be reduced by employing a strong oxidizing agent as a coagulating electrolyte in the coagulation process of fluoropolymer dispersion.
Therefore, there was a strong need to develop the usage of a strong oxidizing agent as a coagulating electrolyte in the coagulation process of fluoropolymer dispersion resulting in higher whiteness index, improved particle size distribution and bulk density and extrusion.

There was a need for an improved process which may reduces discoloration by at least about 30% as measured by % change in L* on the CIELAB color scale.
There was need for development of a sole coagulant which can be used as a coagulating agent for dispersion and also for reducing the discoloration without addition of any other separate coagulant or any additional treatment.
To fulfill this need, a strong oxidizing agent like alkali metallic chlorates is required which acts as a coagulant for the fluoropolymer dispersion that also increases the rate of coagulation by around 25% compared to the conventional coagulation methods utilizing carbonates, strong acids, etc.
OBJECTIVES OF THE INVENTION
The main objective of this invention is to provide a coagulation process in fluoropolymer dispersion employing a strong oxidizing agent as a coagulating electrolyte that overcomes the aforestated problems.
Another objective of this invention is to provide a coagulation process in fluoropolymer dispersion having reduced discoloration and improved fluoropolymer resin properties.
Yet another objective of this invention is to provide a coagulating agent which may reduce coagulation time at least by 25 % in comparison to the conventional coagulation techniques.
Yet another objective of this invention is to provide a process for the preparation of fluoropolymer powder that is having sole oxidizing agent which may also act as sole coagulating agent in fluoropolymer dispersion treatment process.

SUMMARY OF THE INVENTION
The present invention relates to coagulation of fluoropolymer dispersion and a process for preparing the same.
In accordance with an aspect of the invention, there is provided a coagulation of aqueous fluoropolymer dispersion employing oxidizing agent, comprising the steps of:
a) dilution of a fluoropolymer or modified fluoropolymer latex obtained from the
polymerization in dispersion (emulsion)
up to a concentration from 5 to 35% w/w of fluoropolymer, preferably from 8 to 30% w/w of fluoropolymer or modified fluoropolymer; and optional filtration of the obtained diluted latex,
b) addition of alkali metallic chlorate electrolyte solution, to the fluoropolymer or modified fluoropolymer latex. Preferred concentrations are about 0.1 weight percent to about 7 weight percent based on the weight of fluoropolymer solids. Preferably, the exposing of the aqueous fluoropolymer dispersion to alkali metallic chlorates is carried out at a temperature of about 10°C to about 90 °C.
c) granulation (coagulation) of the gel obtained in step b) by mechanical stirring, maintaining the stirring until fine powder flotation,
d) separation of the underlying water from the wet fine powder.
A process for preparing coagulated fluoropolymer fluoropolymer dispersion comprising the steps of:
a. cooling down fluoropolymer latex to a temperature below fluoropolymer's
transition temperature
b. stirring the fluoropolymer latex continuously at low temperature
c. exposing the fluoropolymer latex composition with strong oxidizing agent
slowly to form diluted latex;

d. increasing stirring of diluted latex to form complete coagulated
fluoropolymer resin; thereafter decreasing rpm
e. collecting coagulated fluoropolymer resin, filtering coagulated resin; and
f drying coagulated fluoropolymer resin to form coagulated fluoropolymer fluoropolymer dispersion.
The fluoropolymer composition useful in the present invention comprises of coagulation of aqueous fluoropolymer dispersion employing Alkali metal chlorate acts as a sole coagulating agent and reduces the coagulation time at the least by 25 %.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above and other features, aspects, and advantages of the subject matter will be better understood with regard to the following description and accompanying drawings.
Figure 1. Flowchart for the process for preparing coagulated fluoropolymer dispersion using strong oxidizing agent
DETAILED DESCRIPTION OF THE INVENTION
Discussed below are some representative embodiments of the present invention. The invention in its broader aspects is not limited to the specific details and representative methods. Illustrative examples are described in this section in connection with the embodiments and methods provided.
It is to be noted that, as used in the specification, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a composition containing "a compound" includes a mixture of two or more compounds. It should also be noted that the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise.

The expression of various quantities in terms of "%" or "% w/w" means the percentage by weight of the total solution or composition unless otherwise specified. All cited references are incorporated herein by reference in their entireties. Citation of any reference is not an admission regarding any determination as to its availability as prior art to the claimed invention.
The invention provides a novel process for the coagulation of fluoropolymer resin which has an improved particle size distribution, bulk density and a higher whiteness index. It has been discovered that the discoloration of fluoropolymer resin caused by residual ionic impurities can be reduced by: exposing the aqueous fluoropolymer dispersion to a strong oxidizing agent like alkali metallic chlorates. Preferably, the process reduces the thermally induced discoloration by at least about 30% as measured by % change in L* on the CIELAB color scale. The highlight of this invention is that not only does it reduce the discoloration but also acts as a sole coagulating agent for the dispersion. This eliminates the need for a separate coagulating agent. Thermal history of fluoropolymer resin or residual ionic impurities can also cause discoloration of the fluoropolymers and the other conventional coagulating agents result in poor particle size distribution and bulk density. Utilizing strong oxidizing agents like alkali metallic chlorates coagulates the fluoropolymer dispersion at a rate of around 25% faster than the conventional coagulating agents like carbonates, strong acids, etc.
The said fluoropolymer fine powders are transformed by the lubricated extrusion process to obtain the manufactured articles. The lubricated extrusion process is much more productive and easily automatable the more the fine powders are flowing and have a high apparent density. Besides, the average particle diameter is preferably higher than 400 micron and the particle diameter distribution as above defined should be at least higher than 50%, preferably higher than or equal to 60% to obtain an improved flow.
The present invention discloses a continuous coagulation process of fluoropolymer or modified fluoropolymer fine powders, comprising:

a) dilution of a fluoropolymer or modified fluoropolymer latex obtained from the polymerization in dispersion (emulsion) up to a concentration from 5 to 35% w/w of fluoropolymer, preferably from 8 to 30% w/w of fluoropolymer or modified fluoropolymer; and optional filtration of the obtained diluted latex,
b) addition of alkali metallic chlorate electrolyte solution, to the fluoropolymer or modified fluoropolymer latex. Preferred concentrations are about 0.1 weight percent to about 7 weight percent based on the weight of fluoropolymer solids. Preferably, the exposing of the aqueous fluoropolymer dispersion to alkali metallic chlorates is carried out at a temperature of about 10°C to about 90 °C.
c) granulation (coagulation) of the gel obtained in step b) by mechanical stirring, maintaining the stirring until fine powder flotation,
d) separation of the underlying water from the wet fine powder.
A process for preparing coagulated fluoropolymer dispersion comprising the steps of: g. cooling down fluoropolymer latex to a temperature below fluoropolymer's
transition temperature h. stirring the fluoropolymer latex continuously at low temperature i. exposing the fluoropolymer latex composition with strong oxidizing agent
slowly to form diluted latex; j. increasing stirring of diluted latex to form complete coagulated
fluoropolymer resin; thereafter decreasing rpm k. collecting coagulated fluoropolymer resin, filtering coagulated resin; and 1. drying coagulated fluoropolymer resin to form coagulated fluoropolymer
fluoropolymer dispersion.
In an embodiment, the process for preparing coagulated fluoropolymer dispersion includes exposing the aqueous fluoropolymer dispersion to oxidizing agent selected from the group consisting of alkali metal chlorate salts.

In an embodiment, discoloration in the process of coagulation of fluoropolymer dispersion may be reduced by at least about 30% as measured by % change in L* on the CIELAB color scale.
In an embodiment, the solids content of said dispersion during said exposing to said oxidizing agent may ranges from about 5 weight % to about 35 weight %.
In an embodiment, the aqueous fluoropolymer dispersion may be exposed to oxidizing agent may be carried out at a temperature of about 10°C to about 90°C.
In an embodiment, the exposing of said aqueous fluoropolymer dispersion to said coagulating agent is carried out by adding alone said coagulating agent.
In an embodiment, the coagulating agent may be added to said aqueous fluoropolymer dispersion in an amount of about 0.1 weight % to about 7 weight percent based on weight of fluoropolymer solids.
In an embodiment, the oxidizing agent may be carried out for a time period of about 5 minutes to about 25 minutes.
In an embodiment, the fluoropolymer resin may have an induced discoloration value (L*i) at least 4 L units on the CIELAB color scale below the L* value of equivalent fluoropolymer resin of commercial quality manufactured using carboxylic acid fluorosurfactant with high and low levels of fluorine.
In an embodiment, the coagulation process may include latex of 1 kg 5 kg and said
latex is stirred from 100 rpm to 700 rpm.
In an embodiment, the coagulation process may increase stirring to rpm up to 1500
for completing coagulation at step (d)
In an embodiment, the coagulation process may comprises of stirring for 5min to 25
min and rpm is decreased to 250 rpm at step d.

In an embodiment, the coagulation process may comprises of drying of fluoropolymer coagulated resin at 150 degree C to 220 degree C for about 16 hours to 30 hours.
In an embodiment, fluoropolymer particle size distribution may ranges from 450 microns to 550 microns.
In an embodiment, bulk density of fluoropolymer may ranges from 450 g/1 to 500 g/1
In an embodiment, extrusion of fluoropolymer may be carried at 30 MPa to 34 MPa
In an embodiment, whiteness index of fluoropolymer may ranges from 70 to 98.
In an embodiment, fluoropolymer may consists of PTFE, PFA, FEP, PVDF and PTFE micropowder.
In an embodiment, fluoropolymer may consist of fine powder PTFE wherein
- particle size distribution of fine power PTFE ranges from 400 microns to 650 microns;
- bulk density of fine powder PTFE ranges from 350 g/1 to 600 g/1;
- extrusion of fine powder PTFE is carried at 30 MPa to 45 MPa; and
- whiteness index of fine powder ranges from 70 to 98.
Advantages of the present invention:
It is usually desirable for fluoropolymer resin to be clear white in color and, in resin prone to discoloration due to residual ionic impurities, a gray, brown or yellow color sometimes quite dark forms upon heating. It has been discovered that this discoloration of fluoropolymer resin can be reduced by employing a strong oxidizing agent as a coagulating electrolyte in the coagulation process of fluoropolymer dispersion. The process reduces such discoloration by at least about 30% as measured

by % change in L* on the CIELAB color scale. In addition to this, it does improve the particle size distribution, bulk density and the extrusion.
The present invention is more particularly described in the following examples that are intended as illustration only, since numerous modifications and variations within the scope of the present invention will be apparent to those of skill in the art. Unless otherwise noted, all parts, percentages, and ratios reported in the following examples are on a weight basis, and all reagents used in the examples were obtained or are available from the chemical suppliers.
Experiment 1:
The polymerization process was carried out in a 150 L reactor with 70 L of de-ionized water. Oxygen was removed from the reactor until its concentration was less than 10 ppm. After that, the surfactant/s (less-fluorinated), 300 ppm, was added in one shot into the reactor. Thereafter, the addition of Tetrafluoroethylene (TFE) caused an increase in the pressure to 24 bar and the temperature was increased to 90 °C. After attaining the operating pressure and temperature a solution comprising an initiator Disuccinic Acid Peroxide (DSAP) or Ammonium Persulphate (APS) was added into the reactor in one shot for initiating the polymerization process. After completion of the polymerization process the PTFE particles were coagulated, using the said coagulating agent. The coagulated particles were separated from the mother liquor and washed with cold water, steam treated and dried at a temperature of 220 °C to get the PTFE resin.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive.

The following examples illustrate the basic methodology and versatility of the present invention.
Examples
Following, batches of PTFE Fine Powder were prepared according to the present invention: Examples: In Example 1, Specifications of Examples 1 is presented in the following Table 1.
Table 1.

Property Evaluation procedure Units Example 1
Appearance - -
Bulk Density g/1 475
Particle Size D50 urn 520
Extrusion MPa -31
CIELAB L~ 92.13, a--0.9,
b ~ - 3 (for
fluorinated
surfactants) L ~ 95,
a ~ 0.30, b ~ 2.50
(for non-
fluorinated
surfactants)
Whiteness index 98 (fluorinated
surfactant) and 80
(Non fluorinated
surfactant)

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive.

We Claim:

1. A process for preparing coagulated fluoropolymer dispersion comprising the
steps of:
a) cooling down fluoropolymer latex to a temperature below fluoropolymer's transition temperature
b) stirring the fluoropolymer latex continuously at low temperature
c) exposing the fluoropolymer latex composition with strong oxidizing agent slowly to form diluted latex;
d) increasing stirring of diluted latex to form complete coagulated fluoropolymer resin; thereafter decreasing rpm
e) collecting coagulated fluoropolymer resin, filtering coagulated resin; and
f) drying coagulated fluoropolymer resin to form coagulated fluoropolymer fluoropolymer dispersion.

2. The process of claim 1 wherein said process includes exposing the fluoropolymer dispersion to oxidizing agent selected from the group consisting of alkali metal chlorate salts and said exposing of said fluoropolymer dispersion to said oxidizing agent is carried out by adding alone said oxidizing agent.
3. The process of claim 1 wherein said process reduces discoloration by at least about 30% as measured by % change in L* on the CIELAB color scale.
4. The process of any of the preceding claims wherein the solids content of said
dispersion during said exposing to said oxidizing agent is about 5 weight % to
about 35 weight %.
5. The process of any of the preceding claims wherein said exposing the
fluoropolymer dispersion to oxidizing agent is carried out at a temperature of
about 10°C to about 30°C.

6. The process of any of the preceding claims wherein the exposing to the oxidizing agent is carried out for a time period of about 5 minutes to about 25 minutes.
7. The process of claim 1 wherein said oxidizing agent is added to said fluoropolymer dispersion in an amount of about 0.1 weight % to about 7 weight percent based on weight of fluoropolymer solids.
8. The process of any of the preceding claims wherein the fluoropolymer resin has an i induced discoloration value (L*i) at least 4 L units on the CIELAB color scale below the L* value of equivalent fluoropolymer resin of commercial quality manufactured using carboxylic acid fluorosurfactant with high and low levels of fluorine.
9. The process of claim 1 wherein said process includes latex of 1 kg to 5 kg and
said latex is stirred from 100 rpm to 700 rpm.
10. The process of claim 1 wherein said process comprising increasing stirring to
rpm up to 1500 for completing coagulation at step d; wherein said process
comprising stirring for 5 min to 25 min and rpm is decreased to 250 rpm at step
(d).
11. The process of claim 1 wherein said process comprising drying of
fluoropolymer coagulated resin at 150 degree C to 290 degree C for about 16
hours to 30 hours.
12. The process of claim 1 wherein fluoropolymer consists of PTFE, PFA, FEP, PVDF and PTFE micropowder.
13. The process of claim 1 wherein fluoropolymer consist of fine powder PTFE, wherein

- particle size distribution of fine power PTFE ranges from 400 microns to 650 microns;
- bulk density of fine powder PTFE ranges from 350 g/1 to 600 g/1;
- extrusion of fine powder PTFE is carried at 30 MPa to 45 MPa; and
- whiteness index of fine powder ranges from 70 to 98.