COMPOSITIONS FOR FORMING ANTISTATIC COATINGS AND ARTICLES COATED WITH THE COMPOSITIONS

Abstract

This invention relates to a coating composition comprising an ionomer having a polymer backbone and side chains, the side chains comprising ionic groups, wherein the ionic groups are sulfonic acid groups and sulfonate groups, from 50 to 95% of the total number of sulfonic acid groups and sulfonate groups are in the sulfonate form, and the sulfonate groups have counter ions M selected from the group consisting of lithium, sodium, magnesium, calcium, and mixtures thereof. This invention also relates to an article comprising a polymeric substrate having an antistatic coating thereon, wherein the antistatic coating is formed from the inventive coating composition. The article may be a cable, a cable cover or a cable jacket.

Claims

1. A coating composition comprising: an ionomer having a polymer backbone and side chains, wherein the side chains comprise ionic groups in an acid form and ionic groups in a salt form, wherein the ionic groups in the acid form are sulfonic acid groups and the ionic groups in the salt form are sulfonate groups, wherein from 50 to 95% of the ionic groups are sulfonate groups, and wherein the sulfonate groups have counter ions M selected from the group consisting of lithium, sodium, magnesium, calcium, and mixtures thereof.

2. The coating composition of claim 1, wherein the ionomer is a perfluorinated ionomer.

3. The coating composition of claim 1, wherein the ionomer has repeating units of the structural formula; wherein x is in a range from 1 to 14, wherein y=1, wherein m is in a range from 0 to 3, wherein n is in a range from 1 to 5, and wherein (H, M) means that either a sulfonic acid group or a sulfonate group is be present.

4. The coating composition of claim 1, wherein the ionomer has an equivalent weight of from 800 to 1200 g/mol.

5. The coating composition of claim 1, wherein from 60 to 80% of the ionomer groups are sulfonate groups.

6. The coating composition of claim 1, wherein the counter ion M is lithium, or lithium in combination with sodium, or lithium in combination with magnesium, or lithium in combination with calcium, or sodium.

7. The coating composition of claim 1, wherein the coating composition is a solution and does not contain particles, or is a dispersion and does not contain particles different from the ionomer particles.

8. The coating composition of claim 1, wherein the coating composition does not contain compounds capable of forming complexes with counter ions of the sulfonate groups.

9. (canceled)

10. An article comprising: a polymeric substrate; and an antistatic coating thereon, wherein the coating is formed from the coating composition claimed in claim 1.

11. The article of claim 10, wherein the polymeric substrate is porous or nonporous, and wherein when the polymeric substrate is porous, the antistatic coating is at least partially impregnated within pores of the polymeric substrate.

12. The article of claim 10, wherein the polymeric substrate is a perfluorinated polymer or a partially fluorinated polymer.

13. The article of claim 10, wherein the polymeric substrate is in tape form or sheet form having two main surfaces, and wherein the antistatic coating is provided on one or on both surfaces of the polymeric substrate.

14. The article of claim 10, wherein the polymeric substrate is in tape form or sheet form having two main surfaces, wherein the antistatic coating is provided on one of the main surfaces, and wherein an adhesive layer is provided on the opposing main surface.

15. The article of claim 10, wherein the article is a cable cover.

16. The article of claim 15, wherein two cable covers are laminated together with an adhesive therebetween to form a cable jacket having an electrostatic coating.

17. The article of claim 10, wherein the article is a cable comprising an outermost electrically non-conductive layer and an antistatic coating thereon.

18. The article of claim 10, wherein the article is a cable comprising at least one conductor and/or conduit and/or channel.

19. The article of claim 10, wherein the polymeric substrate is ePTFE provided on a conductor.

20. The article of claim 10, wherein the polymeric substrate is ePTFE provided on an arrangement comprising at least one wire and/or other conductor and/or conduit.

Description

[0083] In the following, the invention is further illustrated by working examples, some of which refer to the accompanying Figures, wherein:

[0084] FIG. 1 visualizes the surface resistance of various coated samples;

[0085] FIGS. 2 to 5 illustrate surface resistances of samples having coatings with different sulfonic acid:sulfonate ratios and different counter ions;

[0086] FIG. 6 visualizes the results for all coatings shown in FIGS. 2 to 5;

[0087] FIG. 7 illustrates the surface resistance of coated samples (different counter ions);

[0088] FIGS. 8 to 11 compare ionomer solutions used for preparing the coatings, the surface resistances of which are shown in FIGS. 2 to 5.

EXAMPLE 1

[0089] Preparation of Coating Formulations Comprising Inventive Coating Compositions

[0090] An ionomer solution selected from the materials described in table 1 is stirred by the use of a magnetic stirrer at a rate of 600 revolutions per minute. The solution is kept under constant stirring during the next preparation steps.

[0091] Subsequently a specific amount of water as depicted in table 2 is added over a time frame of 1 minute. The solution is stirred for additional 10 minutes without any additional treatment. In a subsequent step a specific amount of a neutralization agent or neutralization agent mixture as depicted in table 2 is added over a time frame of 30 s. The mixture is ready to be used for coating purposes after an additional stirring period of 5 h in a closed container. During this time period the neutralization agent dissolves slowly and reacts with the sulfonic acid ionomer to form the respective salt forms. After completion of the described process steps the coating solution should be free from any neutralization agent precipitate or polymer gel content.

TABLE-US-00001 TABLE 1 Fluorinated Ionomers Trade name Manufacturer Composition Flemion FSS-2 Asahi Glas 9-11 wt % solution in ethanol Nation D2020 Chemours 20-22 wt % solution 34% water, 46% lower aliphatic alcohols Aquivion D72-25BS Solvay 25 wt % solution in water

TABLE-US-00002 TABLE 2 Formulations based on Flemion FSS-2 Formulation Stoi- chiometry Weight Valence (Degree Target Ionomer Solution Solution Equivalent Neutral- Molecular Neutral- Factor of Proton Metal weight conc. Ionomer weight ization weight ization Counter- neutral- Weight Sample Content Counterion Ionomer Ionomer content Ionomer agent of agent agent ion ization) Water Na+ 20 10 2 909 NaAcetate 82.03 0.1444 1 0.8 4 D 7 20 Na+ 20 10 2 909 NaAcetate 82.03 0.1083 1 0.6 4 D 8 40 Na+ 20 10 2 909 NaAcetate 82.03 0.0722 1 0.4 4 D 9 60 20 10 2 909 non 0 4 D 10 100 Li+ 20 10 0.667 909 LiAceta- 102.02 0.0599 1 0.8 4 tex2H2O D 11 20 Na+ 1.333 909 NaAcetate 82.03 0.0962 1 0.8 Li+ 20 10 1.333 909 LiAceta- 102.02 0.1197 1 0.8 4 tex2H2O D 12 20 Na+ 0.667 909 NaAcetate 82.03 0.0482 1 0.8 Li+ 20 10 1 909 LiAceta- 102.02 0.0673 1 0.6 4 tex2H2O D 13 40 Na+ 1 909 NaAcetate 82.03 0.0541 1 0.6 Li+ 20 10 1 909 LiAceta- 102.02 0.0449 1 0.4 4 tex2H2O D 14 60 Na+ 1 909 NaAcetate 82.03 0.0361 1 0.4 Li+ 20 10 2 909 LiAceta- 102.02 0.0898 1 0.4 4 tex2H2O D 15 60 H+ Li+ 20 10 2 909 LiAceta- 102.02 0.1347 1 0.6 4 tex2H2O D 16 40 D 17 20 Li+ 20 10 2 909 LiAceta- 102.02 0.1796 1 0.8 4 tex2H2O Li+ 20 10 1 909 LiAceta- 102.02 0.1207 1 1.075 4 tex2H2O D18 0 Mg++ 1 909 MgAceta- 214.45 0.1268 2 1.075 tex4H2O D19 0 Mg++ 20 10 2 909 MgAceta- 214.45 0.2536 2 1.075 4 tex4H2O Li+ 20 10 1.5 909 LiAceta- 102.02 0.1347 1 0.8 4 tex2H2O D 20 20 Mg++ 0.5 909 MgAceta- 214.45 0.0472 2 0.8 tex4H2O Li+ 20 10 1 909 LiAceta- 102.02 0.0898 1 0.8 4 tex2H2O D 21 20 Mg++ 1 909 MgAceta- 214.45 0.0944 2 0.0944 2 tex4H2O Li+ 20 10 1.333 909 LiAceta- 102.02 0.0898 1 0.6 4 tex2H2O D 22 40 Mg++ 0.667 909 MgAceta- 214.45 0.0472 2 0.6 tex4H2O Li+ 20 10 1 909 LiAceta- 102.02 0.0449 1 0.4 4 tex2H2O D 23 60 Mg++ 1 909 MgAceta- 214.45 0.0472 2 0.4 tex4H2O D 24 40 Mg++ 20 10 2 909 MgAceta- 214.45 0.1416 2 0.6 4 tex4H2O ESD 15 2 Li+ 20 10 2 909 LiAceta- 102.02 0.2193 1 0.98 4 tex2H2O ESD 25 2 Na+ 20 10 2 909 NaAcetate 82.03 0.1769 1 0.98 4 Ca++ 1 909 CaAcetatex- 158.17 0.0850 2 0.98 H2O ESD 23 2 Li+ 20 10 1 909 LiAceta- 102.02 0.1097 1 0.98 6 tex2H2O (%) w(g) w % w(g) Mw (g/mol) Mw (g/mol) w(g) w(g)

[0092] Explanation of Table 2:

[0093] Sample D10 contained Flemion FSS-2 in the fully protonated form, while samples D18 and D19 contained Flemion FSS-2 in salt form, i.e. without sulfonic acid groups. Samples ESD 15, ESD 23, and ESD 25 each contained 2% of the ionic groups in the sulfonic acid form. Therefore, samples D10, D18, D19, ESD 15, ESD 23, and ESD 25 are comparative samples, while the remaining samples are samples according to this invention.

[0094] In the column stoichiometry the degree of neutralization is indicated. Some samples, for example samples D11 and D12, contain two different counter ions. In such cases the total degree of neutralization is indicated, and the ratio of the counter ions can be seen in the column ionomer content.

EXAMPLE 2

[0095] Preparation of Coated Cable Cover

[0096] Coating solutions prepared according to the procedures described in Example 1. Preparations of formulations had been coated on a Gore composite membrane part no. 10131349-WH (made from ePTFE membrane 10346174) by the use of a Wet Film Applicator Rod (wire wound applicator) made from of a 5 mm steel rod and wound 500 micrometer diameter wire.

[0097] For this purpose approximately 0.5 g of the respective solution is applied on the ePTFE membrane surface (piece of 6.011 cm in rectangular shape). Subsequent to the first coating procedure the coated specimen was dried for 5 min at 110 C. in a forced air convection oven. Note that in the coating solutions obtained in Example 1 the reaction participants are present in an equilibrium. The reaction is completed, and the target degree of neutralization achieved, by removing the weak acid from the equilibrium. Supporting the removal by heating is preferable in order to speed up the process.

[0098] The coating and drying procedures were repeated up to 4 times in order to generate specimen with systematically varying coating weight per area. By means of this subsequent process a broad range of coated ePTFE composite membranes had been prepared which are described in table 3. Each assignment given contains information about the coating solution used and the number of subsequent coating runs.

[0099] For example, sample D 10 4 is made from coating solution D 10 according to table 2, and had been coated and dried 4 times. D 10 4 is coated with 0.001170 g ionomer per square centimeter (11.7 g/m2).

TABLE-US-00003 TABLE 3 Coated composite membranes and their coating weight per area (wpa) Coating 1 Coating 2 Coating 4 D 7 1 D 7 2 D 7 4 0.000203172 0.000474143 0.001040208 Coating wpa (g/cm2) D 8 1 D 8 2 D 8 4 0.000224189 0.000488626 0.00107861 D 9 1 D 9 2 D 9 4 0.000215856 0.00052086 0.001065049 D 10 1 D 10 2 D 10 4 0.000277277 0.000544377 0.00116991 D 11 1 D 11 2 D 11 4 0.000258221 0.000570761 0.001147378 D 12 1 D 12 2 D 12 4 0.000305281 0.000584498 0.001069266 D 13 1 D 13 2 D 13 4 0.000262479 0.000512281 0.001102956 D 14 1 D 14 2 D 14 4 0.000228575 0.000519893 0.001062184 D 15 1 D 15 2 D 15 4 0.000254392 0.000581662 0.001114562 D 16 1 D 16 2 D 16 4 0.00027332 0.000588471 0.00105552 D 17 1 D 17 2 D 17 4 0.000276743 0.00055194 0.001085872 D 18 1 D 18 2 D 18 4 0.000252231 0.000551926 0.001042748 D 20 1 D 20 2 D 20 4 0.000222722 0.000579988 0.001048266 D 21 1 D 21 2 D 21 4 0.000252061 0.000500246 0.001062138 D 22 1 D 22 2 D 22 4 0.000225999 0.000538138 0.001135215 D 23 1 D 23 2 D 23 4 0.000234281 0.000566128 0.001111635 D 24 1 D 24 2 D 24 4 0.000218511 0.000511475 0.001098411 Coating 1 Coating 2 Coating 3 Coating 4 Coating 5 ESD 15 1 ESD 15 2 ESD 15 3 ESD 15 4 ESD 15 5 0.00025 0.00055 0.0008 0.001200 0.00135 ESD 25 1 ESD 25 2 ESD 25 3 ESD 25 4 ESD 25 5 0.000145 0.000430 0.00065 0.000820 0.001170 ESD 23 1 ESD 23 2 ESD 23 3 ESD 23 4 ESD 23 5 0.000203 0.000467 0.000764 0.001061 0.001240

EXAMPLE 3

[0100] Measurement of Surface Resistance

[0101] It was established that the surface resistance of ionomer coated substrates decreases with increasing coating weight. FIGS. 1A to 1O visualize this surface resistance decrease for some of the samples listed in Table 3, and also visualize that coating weights exceeding a weight per area (wpa) of about 10 g/m.sup.2 have low impact on surface resistance. This is also evident from the results shown in FIG. 7 and table 9.

[0102] As the surface resistance of ionomer coatings correlates with the amount of material on the tape surface and the air humidity during testing, a subset of samples with comparable coating laydown was selected for electrical characterization.

[0103] The surface resistance of the selected coated samples was measured with a geometry consisting of two rectangular aluminum electrodes spanning a square inch shaped surface area. The measurement is performed as follows: an electrode as described is positioned on the coated specimen and connected with a voltage generator. A one kilogram weight is applied on the electrode in order to generate a consistent initial pressure at the electrode/sample contact surface. Thereafter a voltage of 100 V DC is applied and the current through the surface layer is measured in time intervals of seconds. The results are stored as surface resistance values in digital form. For the purpose of the current comparison the surface resistance data points at a measuring time of 60 seconds were evaluated and compared.

[0104] ASTM D257-07 describing the implementation of surface resistance measurements was used as guidance for the described test methodology.

[0105] Table 4 shows the results and respective testing conditions (see also FIG. 6).

TABLE-US-00004 TABLE 4 Sample Riso[Ohm] wpa (g/cm2) % rH T ( C.) D 7 4 2.4E+07 0.001040 38.4 22.8 D 8 4 1.0E+07 0.001078 38.4 22.8 D 9 4 5.8E+06 0.001065 38.4 22.8 D 10 4 4.0E+05 0.001169 38.4 22.8 D 11 4 2.2E+07 0.001147 38.4 22.8 D 12 4 1.1E+07 0.001069 38.4 22.8 D 13 4 7.2E+06 0.001102 38.4 22.8 D 14 4 2.4E+06 0.001062 38.4 22.9 D 15 4 1.6E+06 0.001114 38.2 23.0 D 16 4 4.9E+06 0.001055 38.1 23.0 D 17 4 1.3E+07 0.001085 38.2 23.0 D 18 4 9.9E+07 0.001042 38.5 23.0 D 20 4 3.1E+07 0.001048 38.6 23.0 D 21 4 3.9E+07 0.001062 38.3 23.0 D 22 4 8.0E+06 0.001135 38.6 23.0 D 23 4 7.6E+06 0.001111 38.3 23.0 D 24 4 2.1E+07 0.001098 37.9 23.0 ESD 15 4 2.5E+07 0.0012 41.4 22.0 ESD 25 5 1.9E+07 0.00117 50.8 23.8 ESD 23 4 6.1E+07 0.001061 41.8 23.4

[0106] FIGS. 2 to 5 and corresponding tables 5 to 8 illustrate surface resistances of samples having coatings with different sulfonic acid:sulfonate ratios and different counter ions.

[0107] FIG. 2 and table 5 compare coatings having 100%, 60%, 40%, and 20% sulfonic acid groups, the remainder being sulfonate groups having lithium has a counter ion.

[0108] FIG. 3 and table 6 compare coatings having 100%, 60%, 40%, and 20% sulfonic acid groups, the remainder being sulfonate groups having sodium as a counter ion.

[0109] FIG. 4 and table 7 compare coatings having 100%, 60%, 40%, and 20% sulfonic acid groups, the remainder being sulfonate groups having both lithium and sodium as counter ions.

[0110] FIG. 5 and table 8 coatings having 100%, 60%, 40%, 20%, and 0% sulfonic acid groups, the remainder being sulfonate groups having both lithium and magnesium as counter ions

[0111] FIG. 6 visualizes the results for all coatings shown in FIGS. 2 to 5, and some further coatings (see table 4).

[0112] It is evident that the surface resistance decreases with increasing ratio of sulfonic acid groups to sulfonate groups. Furthermore, when coatings having the same ratio of sulfonic acid groups to sulfonate groups are compared, coatings having lithium as a counter ion yield the lowest surface resistance, and also coatings having sodium as counter ion yield very good results. Coatings containing both lithium and sodium as counter ions perform better than coatings containing lithium in combination with a different counter ion.

[0113] Therefore, from the view point of surface resistance, it appears desirable to use ionomers having 100% sulfonic acid groups, but it has been shown, that ionomers comprising sulfonate groups may also provide low surface resistance, in particular, when lithium is used as a counter ion.

[0114] In tables 5 to 8 and FIGS. 1A to 1O and 2 to 5, numerical values are indicated in German style (with e.g., 0,000200 g/cm.sup.2 meaning 200 g/cm.sup.2).

TABLE-US-00005 TABLE 5 Sample % H+ Riso[Ohm] wpa (g/cm2) % rH T ( C.) D 10 4 100 4.02E+05 0.001170 38.4 22.8 D 15 4 60 1.64E+06 0.001115 38.2 23 D 16 4 40 4.94E+06 0.001056 38.1 23 D 17 4 20 1.33E+07 0.001086 38.2 23

TABLE-US-00006 TABLE 6 Sample % H+ Riso[Ohm] wpa (g/cm2) % rH T ( C.) D 10 4 100 4.02E+05 0.001170 38.4 22.8 D 9 4 60 5.81E+06 0.001065 38.4 22.8 D 8 4 40 1.02E+07 0.001079 38.4 22.8 D 7 4 20 2.41E+07 0.001040 38.4 22.8

TABLE-US-00007 TABLE 7 Sample % H+ Riso[Ohm] wpa (g/cm2) % rH T ( C.) D 104 100 4.02E+05 0.001170 38.4 22.8 D 14 4 60 2.41E+06 0.001062 38.4 22.9 D 13 4 40 7.17E+06 0.001103 38.4 22.8 D 12 4 20 1.11E+07 0.001069 38.4 22.8

TABLE-US-00008 TABLE 8 Sample % H+ Riso[Ohm] wpa (g/cm2) % rH T ( C.) D 10 4 100 4.02E+05 0.001170 38.4 22.8 D 23 4 60 7.64E+06 0.001112 38.3 23 D 22 4 40 8.03E+06 0.001135 38.6 23 D 21 4 20 3.85E+07 0.001062 38.3 23 D 18 4 0 9.92E+07 0.001043 38.5 23

[0115] The superiority of lithium, sodium, magnesium and calcium as counter ions is illustrated by FIG. 7. FIG. 7 shows the surface resistance of ePTFE membranes coated with Flemion FSS-2 ionomers having different counter ions versus coating weight per area. The samples were prepared as described in examples 1 and 2, and the particulars of the coating formulation are indicated in table 9. The straight line visualizes the influence of the counter ion/counter ion combination on conductivity. In FIG. 7, numerical values are indicated in German style.

TABLE-US-00009 TABLE 9 Formulation Stoi- chiometry Weight Valence (Degree Target Ionomer Solution Solution Equivalent Neutral- Molecular Neutral- Factor of Proton Metal weight conc. Ionomer weight ization weight ization Counter- neutral- Weight Sample Content Counterion Ionomer Ionomer content Ionomer agent of agent agent ion ization) Water Li+ 20 10 2 909 LiAceta- 102.02 0.2193 1 0.98 4 tex2H2O ESD 15 2 Na+ 20 10 2 909 NaHydroxide 40.0 0.0860 1 0.98 8 ESD 16 2 +10 g isopro- panol K+ 20 10 2 909 KAcetate 98.14 0.2110 1 0.98 8 ESD 18 2 +10 g isopro- panol Ca++ 20 10 2 909 CaAcetatex- 158.17 0.1700 2 0.98 8 H2O ESD 20 2 Li+ 20 10 1 909 LiAceta- 102.02 0.1097 1 0.98 6 tex2H2O ESD 22 2 Mg++ 1 909 MgAcetate*4 214.45 0.1153 2 0.98 H2O Li+ 20 10 1 909 LiAceta- 102.02 0.1097 1 0.98 6 tex2H2O ESD 23 2 Ca++ 1 909 CaAcetatex- 158.17 0.0850 2 0.98 H2O (%) w(g) w % w(g) Mw (g/mol) Mw (g/mol) w(g) w(g)

[0116] The comparison of specimen samples having ionomer coatings comprising different counter ions, as illustrated in FIG. 7, proves that the counter ions and counter ion combinations, respectively, used in the present invention are superior to different counter ion such as exemplified by potassium. For example, when comparing coatings comprising lithium to coatings comprising potassium as counter ion, the surface resistance achieved with lithium is more than 2 orders of magnitude lower than the surface resistance achieved with potassium as the counter ion.

EXAMPLE 4

[0117] Discoloration of Coated ePTFE Tape

[0118] The unintended interactions of ionomer coatings with contacting materials were investigated by a worst case test procedure. Ionomer solutions described in the previous sections were added to paper tissue which reacts rapidly with H+ based ionomers generating an intense discoloration effect by a reaction of sulfonic acid with cellulose and paper additives present at its surface. The staining reaction is interpreted as an effective indicator for unintended ionomer reactions.

[0119] The procedure had been performed as follows: Some drops of the polymer solutions according to table 2 were added onto paper tissue and dried at room temperature for 3 hours. Then the impregnated paper was aged at a temperature of 130 C. for 2 hours in a forced air convection oven. During this time frame the indicator paper shows, depending on the coating composition, different degrees of yellowing which strongly correlates with the concentration of H+ in the ionomer used.

[0120] FIGS. 8 to 11 compare ionomer solutions used for preparing the coatings, the surface resistances of which are shown in FIGS. 2 to 5. Thus, the results shown in FIG. 8 must be compared to the results shown in FIG. 2, the results shown in the FIG. 9 must be compared to the results shown in FIG. 3, the results in FIG. 10 must be compared to the results in shown in FIG. 4, and the results shown in FIG. 11 must be compared to the results shown in FIG. 5.

[0121] It is evident from FIGS. 8 to 11 that discoloration increases with increasing ratio of sulfonic acid groups to sulfonate groups. In particular after aging at elevated temperature discoloration was dramatic in the case of ionomers having a high sulfonic acid content. Therefore, from the view point of discoloration, it appears desirable to have a low sulfonic acid content. When comparing surface resistances and discoloration effects, it can be established that ionomers having a molar ratio of sulfonic acid groups to sulfonate groups in a range from about 2:8 to 2:3, and having lithium as a counter ion, are most advantageous.