Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-02-22
2003-06-10
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S366000, C524S835000, C526S242000, C526S250000
Reexamination Certificate
active
06576703
ABSTRACT:
The invention relates to a process for the preparation directly from polymerization of fluoropolymers aqueous dispersions, having a multimodal or bimodal distribution of the particle sizes and to the dispersion obtainable by a high conversion preparation process; said dispersions having an average diameter in the range 100 nm-400 nm, preferably 150 nm −300 nm, the fraction of small particles having diameter between 10 and 100 nm is in the range 1.5-35% by weight, preferably 3-259 by weight; the ratio between the average diameter of the small particles with respect to the average diameter of the dispersion obtained from the polymerization being in the range 0.025-0.6.
In particular the invention relates to a radical polymerization process of tetrafluoroethylene (TFE) and copolymers thereof in aqueous emulsion, using a specific dosage of surfactants of which at least one is a component of a microemulsion.
From the literature (J. G. Brodnyan, Trans. Soc. Rheology, 12:3 (1968), 357; J. S. Chong, E. B. Christiansen, A. D. Baer, J. Appl. Pol. Sci., v.15 (1971), 2007; P. -L. Kuo, C. -J. Chen, J. Polymer Sci. Pol. Chemistry, 31 (1993), 99; C. Chang, R. L. Powell, J. Rheol., 38 (1994), 85; Emulsion polymerization and emulsion polymers. Ed. A. Lovell, M. S. El-Aasser, J. Wiley & Sons, Chichester, 1997, p. 450) it is known that polymeric latexes with a bimodal distribution of the particle diameters with respect to those with a monomodal distribution have a lower viscosity, the concentration being equal. This allows to obtain latexes having a higher concentration not exceeding a certain viscosity, for example up to 74% by volume with a viscosity lower than 1,000 cP. This leads, for example, to a better capability of the film formation and better tensile properties of the film.
Lately (F. Chu, J. Guillot, A. Guyot, Colloid. Polym. Sci., 276 (1998), 305; F. Chu, J. Guillot, A. Guyot, J. Applied Polymer Sci., 70 (1998), 2667) it has been shown for the polymers based on styrene, butyl acrylate and methylmethacrylic acid, that latexes with multimodal, in particular trimodal, distributions of the particle diameters, have more advantageous rheological and colloidal properties with respect to bimodal latexes and much more advantageous with respect to monomodal latexes. For example, a latex can be obtained having a solid content up to 80% by volume and minimum viscosity in the case of trimodal distribution of the particle diameters with ratio by weight among large/average/small particles equal to 80/10/10.
The above mentioned literature and U.S. Pat. No. 4,657,966, U.S. Pat. No. 4,385,157, U.S. Pat. No. 5,668,207 refer to hydrogenated polymer latexes and fluoropolymer latexes are not mentioned.
In U.S. Pat. No. 5,576,381 it is described how to obtain PTFE latexes with a bimodal distribution of the particle diameters by mixing a latex having a particle diameter in the range 180 nm—400 nm with another latex having an average diameter in a ratio from 0.3 to 0.7 with respect to the particle diameter of the first latex. The process requires the carrying out of two separate polymerization operations with a subsequent mixing in a specific ratio. This complicates the production process, since it requires the separate production of two types of latex and the increase of the storage volumes. Besides, the latex polymerization process with small particles requires to work at a low polymerization conversion, i.e. with low productivity, and it does not allow to obtain the particles having a diameter lower than 100 nm with the typical conversions of the industrial scale. As operating example the preparation of a latex having an average particle diameter of 100 nm the conversion being 10% by weight, is reported. In this patent it is stated that the fluoropolymer latexes with bimodal distribution of the particle sizes can be obtained by carrying out a polymerization reaction with subsequent additions of a surfactant. No example is reported on this aspect. From the examples, bimodal or multimodal distributions of the particle diameters are not obtained from the polymerization. On the other hand, it is known that subsequent additions of surfactants commonly used for the polymerization of tetrafluoroethylene based fluoropolymers, as for example described in U.S. Pat. No. 3,009,892 and U.S. Pat. No. 3,391,099 with the purpose to increase the latex stability and the conversion, do not give bimodal or multimodal distributions of the particle diameters. Experiments carried out by the Applicant (see comparative Examples) have shown that by using during the PTFE polymerization subsequent additions of ammonium perfluorooctanoate or of ammonium salt of perfluoropolyether acid as surfactants, multimodal distributions are not obtained.
The patent application WO 98/58984 mentions the possibility to obtain fluoropolymer latexes having a bimodal distribution of the particles directly from the polymerization but it is not indicated anyway how this result can be obtained.
U.S. Pat. No. 4,864,006 uses a microemulsion based on (per)fluoropolyethers for the polymerization of fluorinated polymers and indicates that all the surfactant necessary for the polymerization is fed into the reactor under the form of microemulsion. Besides, it is indicated that the whole microemulsion must be introduced into the reactor before the starting of the reaction. The amount of the used microemulsion must be higher than 0.05 ml of perfluoropolyether for 1 liter of water. Tests carried out by the Applicant (see comparative Examples) have shown that by operating under the conditions indicated in the patent dispersions with multimodal distributions of the particle diameters are not obtained.
In U.S. Pat. No. 4,380,618, U.S. Pat. No. 5,789,508 and WO 97/08214 for the PTFE polymerization and copolymers thereof surfactants of formula:
F—(CF
2
—CF
2
)
n
—CH
2
—CH
2
—SO
3
M, wherein M=H, NH
4
, Na, Li, K are used. Multimodal distributions of the particle diameters are not obtained (see the Examples).
In U.S. Pat. No. 4,038,230 it is described how to obtain large spherical PTFE particles by using a non reactive perfluorinated oil phase, for example perfluorobutane, together with the surfactant. Multimodal distributions of the particle diameters are not reported.
In U.S. Pat. No. 3,526,614 in order to obtain a sufficiently large particle diameter, the addition of polivalent metal salts, such as Zn
2+
, is used. This technique allows to control the final diameter of the PTFE particles, but multimodal distributions of the particle diameters are not reported.
U.S. Pat. No. 5,523,346 uses for the PTFE polymerization a microemulsion based on polymerizable unsaturated liquid monomers in order to obtain small PTFE particles. This method does not allow to obtain multimodal distributions of the particle diameters. Besides, it is well known that by operating under these conditions it is extremely dangerous due to the explosiveness of the liquid tetrafluoroethylene.
In patent application WO 96/22315 a perfluorinated microemulsion is used in order to obtain small particles of thermoprocessable fluoropolymers. Multimodal distributions of the particle diameters are not obtained.
U.S. Pat. No. 3,925,292 and U.S. Pat. No. 5,789,083 relate to a mixture formed by a dispersion of PTFE and by a dispersion of a thermoplastic copolymer of tetrafluoroethylene. In said patents it is neither reported nor described that the obtained single latexes have a multimodal distribution of the particle diameters. It is not indicated that said mixture can be directly obtained from the polymerization process.
In EP 969,027 in the name of the Applicant, a polymerization process in microemulsion to obtain PTFE particles or PTFE copolymers having a size 5-60 nm, is described. Bimodal distribution is not described.
The need was felt of a polymerization technique able to give PTFE dispersions having a multimodal distribution as defined below.
It is therefore an object of the present invention a process for the preparation of a dispersion based on tetrafluoroethytlene (TFE) homopolymers
Kapeliouchko Valery
Marchese Enrico
Arent Fox Kintner & Plotkin & Kahn, PLLC
Ausimont S.p.A.
Yoon Tae H.
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