LU83774A1 - PROCESS FOR IMPROVING ACID RESISTANCE OF SYNTHETIC ORGANIC FIBERS AND TISSUES - Google Patents

Description

* 1

The present invention relates to the chemical treatment of synthetic organic fibers and fabrics, and more particularly to a method of coating organic fibers with polytetrafluoroethylene to improve acid resistance and other properties.

Hitherto it has been known to coat polytetrafluoroethylene with synthetic and / or mineral fabrics, such as glass fabrics, in order to improve the dirt removal characteristics thereof and to increase its durability (see for example the patent ”.

from the USA No. 3,968,297). In the latter patent, the coating method consists in first applying a base coating of a tetravalent titanium oxide polymer, a zirconium oxide polymer or an oxide polymer of tin. A top coating is then applied to this base coating by means of an unsintered aqueous dispersion of polytetrafluoroethylene particles.

It has also been proposed in the past to coat elastomeric materials such as bu-tadiene-acrylonitrile copolymers with unsintered polytetrafluoroethylene particles by first softening the surface of the polymer with a solvent and then bonding the particles. 25 polytetrafluoroethylene cules on the softened surface (see eg US Patent 3,200,006). The U.S. Patent No. 3,511,682 describes a process in which the elastomer is coated with a thin film of polytetrafluoroethylene and then the film is sintered using an open flame on the surface of the elastomer.

Those skilled in the art will realize that the prior art methods for coating both mineral and organic materials require multiple operations, specific base coatings, solvents and / or sintering at a relatively high temperature.

2

These procedures can weaken certain fibers and certain synthetic organic tissues such as polyaramides.

The E.ü.A. No. 4,232,087 describes a new process for coating organic fibers with polytetrafluoroethylene in the presence of a determined class of chromium complexes. By the process of this invention, synthetic organic fibers and fabrics such as polyaramides 10 can be coated with polytetrafluoroethylene, which improves their soil removal characteristics, acid resistance, hydrophobicity and oleophobicity in one. operation, without the need for solvents, flames, sophisticated base coatings, etc.

The process does not adversely modify the treated fibers, i.e. it does not weaken, stiffen, or otherwise alter the basic properties desired for which fibers and fabric have been selected. This method is particularly advantageous for the treatment of non-woven filter fabrics made from synthetic organic fibrous materials. The treated filter cloths are particularly useful for air filtration when the filter cloth is to be exposed to acid vapors such as sulfuric acid vapors and liquids containing this acid.

However, the woven fabrics treated by the U.S. patent process No. 4,232,087 are not always completely coated with polytetrafluoroethylene. Photomicrographs with a scanning electron microscope of woven fabrics treated by the method described in this patent show that the hydrophobic particles of polytetrafluoroethylene do not adequately penetrate into the empty spaces where the warp and weft threads cross. The uncoated portions of the wires are obviously exposed to degradation by acids when exposed to acids as discussed above. It is believed that penetration does not occur because the resin particles agglomerate at the intersection of the wires.

The process of the present invention avoids agglomerating particles at the intersections of the wires, allowing the polytetrafluoroethylene particles to enter the voids between the intersections of the wires. After evaporation of the volatile materials present in the carrier fluid and subsequent hardening of the residual solids, a single layer of polytetrafluoroethylene particles is included on the unitary fibers included in a matrix of residual solids. The method of the invention provides a woven fabric which is very resistant to degradation by acids due to its hydrophobic surface which remains after exposure, for example to hot sulfuric acid.

The subject of the invention is a process for improving the acid resistance, hydrophobicity, oleophobicity and dirt-removing properties of synthetic organic fibers, comprising coating the fibers with particles of polytetra fluorethylene, in the presence of water, a water-soluble chromium complex of a fluorinated chain chemical compound when characterized in part by a molecular structure consisting of a polar end and a a non-polar fluorocarbon end which is both organophobic and hydrophobic, of a cationic fluoropolymer and of a surfactant.

The term "chromium complex of a long chain fluorinated chemical compound" herein refers to a compound which comprises a chromium coordination complex with a fluorinated substituted hydrocarbon moiety, such as substituted amino or sulfonylamino alkyl derivatives having preferably at least 6 carbon atoms and preferably from 6 to 30 carbon atoms.

The method of the invention can be used for k.

vs .

4 to improve acid resistance, hydrophobicity, oleophobia and soil removal characteristics of a wide variety of synthetic organic fibers such as, for example, polyamides, pcly-5 esters, polyolefins. es etc. The process is particularly advantageous for treating polyaramides such as Nomex fibers. In a preferred embodiment of the invention, filter fabrics based on Nomex fibers and yarns are treated to improve the above properties. The filtering fabrics which can be treated by the process of the invention can be woven or nonwoven fabrics or composites thereof such as woven screens on which a nonwoven web is needled. As described above, the method of the invention is particularly advantageous for improving the acid resistance of woven fabrics and composite fabrics containing a woven structure.

The coating of the organic fibers and fabrics made thereof can be carried out by a conventional technique of application of an aqueous dispersion to a fiber or a fabric, for example by spraying, application by roller or by the bar, immersion etc ...

The fibers to be coated are preferably in the form of a woven fabric which is saturated by immersion in the aqueous dispersion of polytetrafluorethylene particles. Immersion of the tissue may be followed by compression or other operation to partially remove the excess aqueous dispersion from the immersed tissue, so as to adjust the amount of aqueous dispersion retained in the substance of the tissue . The wet fabric can then be dried by any conventional means, for example in a drying rack, under radiant or microwave heaters, etc. The drying is preferably carried out at temperatures <s : 5 lower than the boiling point of water, and better still between 65 and 82 ° C in an oven with air circulation. This process is used to prevent explosive destruction of the fiber coating when the vaporization takes place at or above the boiling point of water. The amount of polytetrafluoroethylene particles and residues of the aqueous treatment dispersion added is preferably about 2 to 12% by weight of the fabric, and more preferably about 10% (the contribution of polytetrafluoroethylene being of about 40 to 70% of the solids added). In the preferred embodiment of the process of the invention, the polytetrafluoroethylene particles have on average about 0.05 to about 0.5 microns in diameter.

After drying, that is to say removal of the water, the treated fabric is advantageously subjected to a heat treatment, by heating at a temperature of 175 to 190 ° C. for approximately 30 minutes.

In the process of the invention, it is necessary to add the polytetrafluoroethylene particles in the presence of a water-soluble chromium complex of a fluorinated chain chemical compound when characterized in part by a molecular structure composed of a polar end or head, and a non-polar end, 'or tail, which is both organophobic and hydrophobic.

It has been reported that the polar head of complexes of the complex compound with the fiber body and polytetrafluoroethylene particles are drawn to the non-polar fluorocarbon tail of the coordinating complex and are held there by Van der Waals forces .

The chromium complex therefore behaves as an exceptional chemical coupling agent between the organic fiber and the polytetrafluoroethylene particles, giving a coating of high stability and having great advantages.

6 * t

To obtain as far as possible penetration of the hydrophobic particles of polytetrafluoro-thylene in the voids between the intersections of the threads in the woven fabrics, the coating of the fibers also kills in the presence of a cationic fluoropolymer. The cationic fluoropolymers stabilize the dispersion of polytetrafluoroethylene with respect to the agglomeration of the particles, in particular at the intersections of the threads in the woven fabrics subjected to the treatment in accordance with the invention. As an example of preferred cationic fluoropolymers, mention will be made of those which are miscible with water such as the fluorocarbon-sulfonyl acrylamides and polymerized methacrylamides, such as those described in the patent of the * E.U.A. No. 2,995,542, etc. Such fluoropolymers are sold commercially under the trade names "Zepel" and "Nalan" from EA DuPont of Nemours and Co, Wilmington, Delaware. Other examples of these fluoropolymers are: copolymers of trifluorochlo-retethylene and one or more other olefinically unsaturated monomers, such as vinylidene fluoride, vinyl chloride, vinyl acetate, methyl methacrylate, and styrene, resins fluorinated acrylics such as polymers of 1,1-dihydroperfluorobutyl acrylate and copolymers of n-butyl acrylate, N-methyl.ol acrylamide and at least 35% by weight of a methacrylate corresponding to the formula CH3 0 CH2 = i -i'-0 -CH2CH2 (CF2) mCF3 in which m represents an integer from 1 to 13.

3q The proportion of cationic fluoropolymer used in the treatment dispersion is advantageously from 5 to. 15%, preferably around 12% relative to the weight of the dispersion.

The treatment dispersion preferably also contains a surfactant. The term surfactant 7 or "surfactant" is a generic term used to describe a chemical compound (1) which is soluble in at least one phase of the system, (2) which has an amphipatic structure, (3) whose molecules form 5 monomolecular layers oriented at the phase interfaces, (4) which has an equilibrium concentration, in the form of a solute at the phase interface, greater than its concentration in the mass of the solution, (5) which forms micelles when the concentration in the form of a solute in the solution exceeds a characteristic limit value and, (6) which combines several of the following functional properties: massage, wetting, emulsification, solubilization and dispersion. generally classified as anionic, cationic or nonionic agents. In the process of the invention, the preferred surfactants are those of the nonionic type. Nonionic surfactants are generally b ien known; the same is true of their preparation. Examples of these include alkylphenoxypoly (ethyleneoxy) ethanols such as octylphenoxypoly (ethylenoxy) ethanols and nonylphenoxypoly (ethylenoxy) ethanols whose polyoxyethylene moieties have an average length of 8 to 15 units. Other nonionic surfactants which can be used are, for example, polyoxyethylenes, polyoxypropylenes, long-chain alkylphosphine oxides, long-chain alkylamine oxides, etc. The proportion of agent surfactant used in the treatment dispersion may be from about 0.001 to 1% by weight relative to the dispersion, preferably from about 0.1%.

The following non-limiting examples are given by way of illustration of the invention. In these examples, the following tests were used: Acid resistance: The acid resistance of treated fabrics is% 8 determined by carrying out 15 cyclic immersions of wound ends of the fabric in 0.2% sulfuric acid for 15 seconds followed by heating in an oven for 10 minutes at 177 ° C. The fabric 5 is then subjected to a resistance test using an untreated fabric as a control.

Breaking strength: The test is carried out as described in standard ASTM D1682 de Breaking load and elongation at break of fabrics "(Breaking Load and Elongation of

Textile Fabrics ".

Example 1

An aqueous dispersion is prepared by mixing 1 part of the chromium complex (Cr III) of 15 N-ethyl-N-heptadecylfluoro-octane sulfonyl glycine in isopropyl alcohol (52%) and water (15%) (FC 805, Minnesota Mining and Manufacturing Co, Minneapolis, Minnesota), 7.5 parts of a dispersion of polytetrafluoroethylene resin (Teflon 30, EI

20 DuPont de Nemours and Co), 37.5 parts of a fluoropolymer, fluorocarbon sulfonyl acrylamide (Zepel RN, EI DuPont de Nemours and Co), 0.1 part of an octylphenoxypoly (ethylenoxy) ethanol including poly-xyethylene chain has an average length of 8 to 10 units + 25 (Triton X-100, Rhorn and Haas Co, Philadelphia, Pa) and 53.9 parts of water. The mixture is stirred to obtain a uniform dispersion.

We obtain a 3x1 cross-woven filter fabric weighing 220 g / m2, made of po-30 lyaramide (Nomex) threads. The fabric is immersed in the dispersion described above so as to obtain a 100% wet fixation (relative to the initial dry weight of the fabric). The fabric is then dried in a drier at 80 ° C, then the coating is cured for 15 minutes at 180 ° C.

9

The physical properties of the treated fabric obtained are then examined and compared to that of the untreated fabric. The results of this examination are as follows: 5 fixation of solids in% 10.3 retention of resistance in% after 15 75.0 acid / heating cycles

Example 2

The procedure of Example 1 above is repeated, except that the aqueous dispersion used therein is replaced by an aqueous dispersion prepared by mixing 1.5 parts of FC 805, 6.25 parts of Sepel RI, 11.25 parts of Teflon 30, 0.1 part of Triton 15 X-100 and 80.9 parts of water. The results of the physical examination are as follows: fixation of solids in% 9.0 conservation of resistance in% after 15 69.7 20 acid / heating cycles

Example 3

This is not an example, according to the invention, but a comparative example.

Following the procedure of Example 1 · '' above, but replacing the aqueous dispersion 25 used therein by a dispersion consisting of 2 parts of FC 805, 10 parts of Teflon 30 and 88 parts of water , a treated fabric is obtained having the following 5 physical properties: fixation of solids in% 10/5 30 retention of resistance in% after 15 8.4 acid / heating cycles

Example 4

Following the procedure of Example 1 above, but replacing the aqueous dispersion used therein with a dispersion consisting of 1 part of FC 805, 6.5 parts of Teflon 30, 0.1 part of Triton X-100, 6.5 parts of a fluoropolymer, the fluorocarbon sulfonyl acrylamide (Teflon Μ, EI DuPont from 5 Nemours and Co.) and 91, 9 parts of water, a treated fabric is obtained having the properties following: fixing of solids in% 4.7 conservation of resistance in% after 15 91.1 10 acid / heating cycles

Claims (7)

1. Process for improving the acid resistance of synthetic organic fibers, characterized in that the fibers are coated with polytetrafluoro-retylene particles, in the presence of water, with a soluble chromium complex in 1 water from a long chain fluorinated chemical characterized in part by a molecular structure consisting of a polar end and a non-polar fluorocarbon end which is both organophobic and hydrophobic, a cationic fluoropolymer and a agent * 10 surfactant. 2. Method according to claim 1, characterized in that the chromium complex is the chromium complex (Cr XII) of N-ethyl-N-heptadecylfluoroctane sulfonyl glycine. 15 3) Method according to claim 1, characterized in that the particles have an average diameter of 0.05 to 0.5 microns. 4. Method according to claim 1, characterized in that the coating increases the weight of the fibers from 2 to 12%. Λ » , 5) Process according to claim 1, characterized in that the organic fibers are poly-aramid fibers. 6. Method according to claim 1, characterized in that the fibers are in a woven fabric. 7. A method of improving the acid resistance of a fabric woven from textile yarns of synthetic organic fibers, characterized in that a) the fabric is saturated with an aqueous dispersion of 1. a polytetrafluoroethylene; 2. a cationic fluoropolymer; 3. a surfactant; and k * t »r 12 4. a water-soluble chromium complex of a long chain fluorinated chemical characterized in part by a molecular structure consisting of a polar end and a fluo-5 end non polar carbon which. is both organophobic and hydrophobic; b) the saturated fabric is dried at. a temperature below the boiling point of water; and c) the dried fabric is heat treated. k v - »