Use of an ionic fluoropolymer as antistatic coating

Abstract

The present invention relates to the use of an ionic fluoropolymer in its H-form for the formation of an antistatic coating on a non-conductive substrate, and to a cable comprising an outermost non-conductive layer with a coating thereon which comprises an ionic fluoropolymer in its H-form.

Claims

1. An antistatic article comprising: a porous polymeric substrate; and a monolithic coating including an ionic fluoropolymer in its H-form on said porous polymeric substrate, wherein said monolithic coating is airtight and prevents air flow through said antistatic article, and wherein said monolithic coating does not contain particles.

2. The article of claim 1, wherein said polymeric substrate is a fluoropolymer.

3. The article of claim 1, wherein said fluoropolymer is selected from polytetrafluoroethylene (PTFE) and expanded polytetrafluoroethylene (ePTFE).

4. The article of claim 3, wherein an F/H ratio of said ionic fluoropolymer is above 1.

5. The article of claim 1, wherein an equivalent weight of said ionic fluoropolymer ranges from about 500 g/mol to about 2000 g/mol.

6. The article of claim 1, wherein said ionic fluoropolymer is selected from a fluoroionomer and a fluoropolyether.

7. The article of claim 1, wherein at least 25% of the ionizable groups present in said ionic fluoropolymer are in said H-form.

8. The article of claim 1, wherein said article has a charge decay time at 20 percent relative humidity of less than about 2 seconds.

9. The article of claim 1, wherein said ionic fluoropolymer in its H-form is present in said coating in a concentration from 5 wt % to 0.5 wt % solids.

10. An antistatic article comprising: a porous polymeric substrate comprising pores; and a monolithic coating including an ionic fluoropolymer in its H-form on said porous polymeric substrate, wherein said monolithic coating occludes pores in said porous substrate, wherein said monolithic coating does not contain particles, and wherein said monolithic coating is airtight and renders said antistatic article non-air permeable.

11. The article of claim 10, wherein said polymeric substrate is a fluoropolymer.

12. The article of claim 11, wherein said fluoropolymer is selected from polytetrafluoroethylene (PTFE) and expanded polytetrafluoroethylene (ePTFE).

13. The article of claim 10, wherein an equivalent weight of said ionic fluoropolymer ranges from about 500 g/mol to about 2,000 g/mol.

14. The article of claim 10, wherein said ionic fluoropolymer is selected from a fluoroionomer and a fluoropolyether.

15. The article of claim 10, wherein at least 25% of the ionizable groups present in said ionic fluoropolymer are in said H-form.

Description

(1) The present invention will be further illustrated by the examples described below, and by reference to the following figures:

(2) FIG. 1a: Schematic sectional view of an article (10) having a polymer porous substrate (20) and a monolithic coating (30) thereon.

(3) FIG. 1b: Schematic sectional view of an article (10) having a polymer porous substrate (20) and a coating (30) thereon, which is present on the inner and outer surface of the pores (inner coating).

METHODS AND EXAMPLES

(4) a) Charge Decay Time (CDT)

(5) Charge decay time (CDT) was measured in accordance with DIN EN 1149-3.

(6) b) Surface Resistivity

(7) Surface resistivity was measured in accordance with ASTM D 257 between two parallel electrodes with a square configuration.

(8) The control of environmental factors is important, since the surface restivity of a non-conductive polymeric substrate can change rapidly in response to humidity change. The accurate reporting of test results included the temperature and humidity of the samples before and during the surface resistivity measurement.

(9) c) Gurley Numbers

(10) Gurley numbers [s] were determined using a Gurley Densometer in accordance with ASTM D 726-58.

(11) The results are reported in terms of Gurley Number, which is the time in seconds for 100 cubic centimeters of air to pass through 6.54 cm.sup.2 of a test sample at a pressure drop of 1.215 kN/m.sup.2 of water.

(12) d) Frazier Numbers

(13) Frazier numbers [cfm] were determined using an Air Permeability Tester III FX 3300 (TEXTEST AG) in accordance with ASTM D 737.

(14) e) Mean Flow Pore Size [MFP, micrometer]

(15) MFP was measured using a PMI (Porous Materials Inc.) Capillary Flow Porometer CFP 1500 AEXLS. The membrane was completely wetted with Silwick (surface tension 20 mN/m). The fully wetted sample is placed in the sample chamber. The chamber is sealed, and gas is allowed to flow into the chamber behind the sample to a value of pressure sufficient to overcome the capillary action of the fluid in the pore of the largest diameter. This is the Bubble Point Pressure. The pressure is further increased in small increments, resulting in flow that is measured until the pores are empty of fluid. The applied pressure range was between 0 and 8.5 bar. Beside mean flow pore diameter, the largest and smallest pore diameters were detected.

(16) f) Thickness

(17) For the substrate film thickness measurements reported herein, measurements were made using a Heidenhain thickness tester.

(18) Microscopic pictures were taken on LEO 1450 VP, samples were sputtered with gold. Cross-sections were prepared and thicknesses were measured.

(19) g) Flex Test

(20) A GORE High Flex Cable was fixed in an energy chain and flexed 1,000,000 cycles in the rolling flex test at room temperature. Traverse path: 1.30 m Velocity: 30 cycles/min Bend radius: 60 mm

(21) Surface resistance was measured before and after the test.

(22) f) Temperature/Humidity Test

(23) In accordance with IEC (International Electrotechnical Commission) -68-2-30 Damp Heat, the humidity test was performed at the temperature range 25 C. to 55 C. and 92 to 98% relative humidity for a total of 6 cycles.

(24) A dry heat test was performed in accordance with IEC 68-2-2 at 110 C. for 7 days.

EXAMPLES

Example 1

(25) The following example illustrates the advantage of ionic fluoropolymers in its H-form for the formation of antistatic coatings.

(26) An ePTFE membrane (area weight 20.5 g/m.sup.2, Gurley 11.6 s, surface resistance>10.sup.12 Ohm/square) was dipped in a mixture of 133.3 g Flemion F 950 in ethanol (6.0% solids, Ionomer, AGC), 216.7 g ethanol and 50 g water at 16 C. for 30 s.

(27) After drying at 160 C. for 5 min, the membrane was permeable to air (Frazier number 0.37) and showed a surface resistance of 2.55.Math.10.sup.6 Ohm/square at 65% rh and 21 C.

Example 2

(28) New commercial ionomers in water/alcohol dispersions with shorter side chain perform well to achieve antistatic surface properties on membranes.

(29) 50 g Aquivion hydroalcoholic Ionomer dispersion D83-15C (Solvay Solexis) was diluted with 300 g isopropylalcohol and 30 g water stirring constantly at 17 C. (measured solids 1.97% by weight).

(30) An ePTFE membrane (area weight 21.1 g/m.sup.2, Frazier 0.32, surface resistance>10.sup.12 Ohm/square) was coated with the solution D83-15C for 30 s. The lay down was 4.05 g/m.sup.2 after drying at 165 C. and 5 min. The surface resistance of the coated membrane was reduced to 1.367.Math.10.sup.7 Ohm/square at 65% rh and 21 C.

Example 3

(31) Another ePTFE membrane (area weight 54.8 g/m.sup.2, Frazier 0.35, surface resistance>10.sup.12 Ohm/square) was coated with the solution of Example 2 for 30 s. The lay down was 2.1 g/m.sup.2 after drying at 165 C. and 5 min. A surface resistivity of the coated membrane of 1.80.Math.10.sup.7 Ohm/square was measured at 65% rh and 21 C.

Example 4

(32) 50 g Aquivion aqeuous Ionomer dispersion D83-20B (Solvay Solexis) was mixed with 450 g ethanol stirring constantly at 16 C. (measured solids 2.0% by weight).

(33) An ePTFE membrane (area weight 21.1 g/m.sup.2, Frazier 0.32, surface resistance>10.sup.12 Ohm/square) was coated with the solution D83-20B for 30 s. The lay down was 5.43 g/m.sup.2 after drying at 165 C. and 5 min. The surface resistivity of the coated membrane of 2.067.Math.10.sup.7 Ohm/square was measured at 65% rh and 21 C.

Example 5

(34) Another ePTFE membrane (area weight 54.8 g/m.sup.2, Frazier 0.35, surface resistance>10.sup.12 Ohm/square) was coated with the solution of Example 4 for 30 s. The lay down was 5.82 g/m.sup.2 after drying at 165 C. and 5 min.

(35) Surface resistivity of 2.633.Math.10.sup.7 Ohm/square was measured at 65% rh and 21 C.

(36) Examples 3 to 5 describe the process to achieve antistatic properties at a variety of ePTFE membranes using a broad range of formulations.

Example 6

(37) The surface resistance of a non-air permeable Flemion F 950 (FSS-1, AGC) film (thickness 28 m) was 3.60.Math.10.sup.5 Ohm/square measured at 21 C. and 55% relative humidity.

(38) The surface resistance of a nonair permeable GORE-SELECT 55 series (W.L. Gore & Associates, Inc.) film (thickness 26 m) was 1.93.Math.10.sup.5 Ohm/square measured at 21 C. and 55% relative humidity.

(39) Charge decay time results of less than 0.01 s at 20% rh indicate antistatic properties for both pure ionomeric films.

(40) Example 6 shows inherent antistatic properties of free standing films of ionic fluoropolymers in its H form.

Example 7

(41) The following example illustrates the performance of ionic fluoropolymers partially in its H-form (50% of total number) for the formation of antistatic coatings.

(42) A ePTFE membrane as used in Example 1 was dipped in a mixture of 133.3 g Flemion F 950 in ethanol (6.0% solids, Ionomer, AGC), 216.7 g ethanol and 0.344 g sodium acetate (water free, 0.0042 mol) dissolved in 49.656 g water at 16 C. for 30 s (total time after complete wetting).

(43) After drying at 160 C. for 5 min, the membrane was permeable to air (Frazier number 0.19) and showed a surface resistance of 67.35.Math.10.sup.6 Ohm/square at 65% rh and 21 C. About 50% of the ionic groups were in the H-form.

(44) A similar ePTFE membrane was dipped in a mixture of 133.3 g Flemion F 950 in ethanol (6.0% solids, Ionomer, AGC), 216.7 g ethanol and 0.412 g potassium acetate (water free, 0.0042 mol) dissolved in 49.588 g water at 16 C. for 30 s (total time after complete wetting).

(45) After drying at 160 C. for 5 min, the membrane was permeable to air (Frazier number 0.10) and showed a surface resistance of 74.50.Math.10.sup.6 Ohm/square at 65% rh and 21 C. About 50% of the ionic groups were in the H form.

Example 8

(46) A flat cable for high flex and harsh environments from W.L. GORE GmbH (outer layer PTFE, GORE HIGH FLEX Cable) was pretreated in an ultrasonic bath. After drying, the surface was additionally cleaned with methylethylketone.

(47) The cable outer surface was exposed to an 6.0% by weight Flemion F 950 (FSS-1, AGC) solution in ethanol for 60 s.

(48) After drying at 165 C. for 3 min, the surface resistance was measured. Both outer ePTFE sides of the cable showed a resistance between 3.Math.10.sup.8 and 9.Math.10.sup.8 Ohm/square at 21 C. and 55% relative humidity.

Example 9

(49) In accordance with the procedure of Example 8, a planar cable configuration for high flex and harsh environments GSC-06-25743-00 AWM 21090 (W.L. GORE GmbH) was treated with Flemion F 950 (FSS-1, AGC) solution. The results shown in Table 1 represent the surface resistance measured at the coated flat cable configuration at 20 C. and 33% relative humidity.

(50) TABLE-US-00001 TABLE 1 Planar cable surface properties GSC-06-25743-00 after antistatic treatment Surface Surface Surface resistance resistance Surface resistance after after resistance after flex temperature temperature (Ohm/ test.sup.1 cycling.sup.2 cycling.sup.3 Sample square).sup.0 (Ohm/square) (Ohm/square) (Ohm/square) 1side A 2.03 .Math. 10.sup.7 5 .Math. 10.sup.9-1 .Math. 10.sup.10 Not tested Not tested 1side B 1.00 .Math. 10.sup.7 1 .Math. 10.sup.7-4 .Math. 10.sup.8 Not tested Not tested 2side A 2.7 .Math. 10.sup.7 Not tested 2.45 .Math. 10.sup.8 1.258 .Math. 10.sup.9 2side B 2.57 .Math. 10.sup.7 Not tested 3.25 .Math. 10.sup.8 3.850 .Math. 10.sup.9 .sup.024 C. and 30% relative humidity .sup.1number of flexes: 1,000,000 .sup.2cycle: Damp heat test .sup.3cycle: Dry heat test

(51) As shown by the data in Examples 1 to 9, the use of ionic fluoropolymers mainly in its H form enhances antistatic properties at surfaces. Coatings were produced using different formulations of ionic fluoropolymers. Superior performance was achieved when the coatings were applied at ePTFE surfaces, such as membranes or flat cable configurations. All data represent an assessment of humidity dependence of surface resistivity for formulation selected from different equivalent weight of ionic fluoropolymers.

(52) Fitness for use testing of antistatic coated cables under harsh environment showed excited durability performance of the coating.