Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-06-28
2002-10-22
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S249000, C526S250000, C526S253000, C526S255000
Reexamination Certificate
active
06469116
ABSTRACT:
The present invention relates to amorphous fluoropolymer manufactured articles for optical, electronic and chemical applications.
Specifically, the invention relates to the preparation of manufactured articles in the form of selfsupported capillaries and pipes and selfsupported films having a high thickness and high purity combined with good mechanical and optical properties; the preparation of manufactured articles in the form of semipermeable membranes for separation processes such as filtering, reverse osmosis and gaseous separation. More specifically, the membranes have an improved selectivity in the gaseous separation, for example for the oxygen in admixture with nitrogen, combined with a good permeability.
It is known in the art the preparation of films having an high transmittance and low refractive index, by dissolving an amorphous fluoropolymer in a solvent, filtering the solution and then using the spin coating to coat glassy substrates having a low thickness. This procedure is described in EP 416,528, wherein as fluoropolymer, an amorphous copolymer formed by perfluoro-2,2-dimethyl-1,3-dioxole (PDD) in amount comprised between 30% and 99% by moles and by tetrafluoroethylene (TFE), is used. The obtained films have a substantially uniform thickness in the range 0.3-20 &mgr;m and have a transmittance higher than 90% at wave lengths in the range 190-800 nm. The amorphous fluoropolymers forming the above films have a refractive index lower than the glass one and such as to allow the use thereof in anti-reflex layers in optical systems.
U.S. Pat. No. 4,948,851 describes manufactured articles obtained by the amorphous polymers mentioned in EP '528, in particular selfsupported films having a thickness in the range 100-400&mgr;m, prepared by molding of the melted amorphous polymer. The so obtained films contain impurities derived from materials with which they come into contact, for example molding plates. Tests carried out by the Applicant have shown that it is not possible to obtain by a single casting process, films having so high thicknesses. With these copolymers it is indeed possible to prepare selfsupported films by casting with a thickness in the range 20-25 &mgr;m.
U.S. Pat. No. 5,051,114 confirms what said above: the films obtained by deposition from casting have a thickness in the order of 25 &mgr;m; those obtained from melt have a thickness of one order magnitude superior. The obtained films can be used supported on porous substrates to form composite membranes useful for enriching and/or separating gaseous mixtures. In this patent selectivity values for the O
2
and N
2
from 2.0 to 2.4, depending on the PDD dioxole content in the PDD/TFE copolymer, are reported. It is shown that by increasing the dioxole content, the oxygen permeability increases but the selectivity decreases. Further data on the gas-selectivity are in chapter 22 of P. R. Resnick e W. H. Buck in “Modern Fluoro-polymers” (1997), wherein in the case of PDD/TFE copolymers membranes in molar ratio 87:13 obtained by casting, a 5.0 value for the CO
2
and N
2
and 4.4 for the H
2
and N
2
is indicated.
In all the prior art described herein no mention is made to the preparation by casting of selfsupported hollow small pipes and/or capillaries, having the combination of good mechanical and optical properties. Neither the preparation by casting of selfsupported films with thicknesses higher than 25 &mgr;m, which combine good mechanical and optical properties is reported. Indeed, when the films are obtained by molding of the melted amorphous polymer, they have a higher thickness and therefore good mechanical properties, but they have also contamination problems which compromise the optical properties of the final product.
The Applicant has surprisingly found that it is possible to obtain by the casting process from solution in a single step, manufactured articles such as selfsupported hollow small pipes and/or capillaries and fluoropolymer membranes or films having a high thickness and such as to overcome the drawbacks of the prior art. Besides, the membranes obtained by using said films, surprisingly have an improved selectivity in the gaseous separation, combined with a good permeability, with respect to those of the prior art above described.
It is therefore an object of the present invention self-supported manufactured articles of amorphous fluoropolymers obtained by casting from solution in a single step, characterized in that they are obtained by the polymerization of a monomer having structure (I), optionally and preferably with a monomer having a structure (II):
CF
2
=CY
1
Y
2
(II)
wherein: R
f
is a C
1
-C
5
perfluoroalkylic radical; X
1
and X
2
are selected from F and CF
3
; Y
1
and Y
2
are selected from F, Cl, H, CF
3
, OR
f
; having a refractive index lower than 1.35, trasmittance higher than 90% in the wave length 300-2,000 nm, and thickness higher than 20-25 &mgr;m.
The manufactured articles of the invention show good mechanical properties which make it possible their use in a selfsupported form.
In order to obtain the selfsupported manufactured articles of the present invention the amorphous copolymer obtained by the above mentioned polymerization must have a composition in which the dioxole (I) is in the range 20%-100% by moles, preferably 40%-80% by moles.
The dioxoles (I) are reported in EP 633,256; preferably 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole (TTD) is used.
The comonomers (II) are tetrafluoroethylene, (C
1
-C
5
) perfluoroalkylvinylethers, trifluoroethylene, hexafluoropropene, chlorotrifluoroethylene, vinylidene fluoride; tetrafluoroethylene (TFE) is preferably used.
The manufactured articles of the invention are obtained by a process comprising the preparation of a solution of the amorphous polymer in a solvent up to a viscosity such that the solution can be handled and subsequently deposited by casting in a single step on a support of a defined configuration.
More specifically, in order to obtain the manufactured articles in form of small pipes or capillaries, the so obtained solution is let flow in glass tubular supports having a predefined internal diameter. When the fluid has wet all the support internal surface, the solution feeding is stopped and the so coated support is kept under filtered inert gas, preferably nitrogen or air, so as to take away the solvent, continuously renewing the so deposited polymer surface. The glass support is then thermally treated to completely dry the polymer; after this step the support internally coated by the dry polymer is completely dipped in water for some hours. By cutting with a cutter for glass the tubular support, a part of the internal pipe of fluorinated polymer is uncovered and by a simple mechanical operation the polymer is completely taken off from the glass. Depending on the viscosity and the solvent, it is possible to obtain hollow small pipes having external diameter sizes in the mm order or real capillaries with external diameter in the &mgr;m hundred order.
In order to obtain manufactured articles in the form of films, the amorphous polymer solution above described is deposited with a stratifying knife having a definite thickness on a flat and smooth support. After thermal treatment for the solvent removal a dry film is obtained. Depending on the solution viscosity and the support type the film has thicknesses in the range 25 &mgr;m-150 &mgr;m and shows good mechanical and optical properties.
With the above described method for films, also manufactured articles in the form of selfsupported thick membranes, optionally used on suitable supports for the obtainment of composite membranes, are obtained. To obtain asymmetrical membranes it is possible to use the phase inversion method as, for example, reported in the publication by K. Kimmerle and H. Strathmann, Desalination, 79, 283-302 (1990). According to this method, after the solution deposition, the support coated by the polymer is dipped in a coagulation bath formed by a non-solvent at a determined temperature. As non-solvents, the ali
Arcella Vincenzo
Drioli Enrico
Grippaldi Giuseppina
Maccone Patrizia
Arent Fox Kintner Plotkin & Kahn
Ausimont S.p.A.
Zitomer Fred
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