CONDUCTIVE POLYASPARTIC ESTER BASED COMPOSITIONS

Abstract

A conductive composition for conductive coatings, gap fillers, caulks and fairing compounds that are useful for EMI shielding, electrical grounding, lightning strike protection, and reduced radar cross-section for low observability (LO), with improved resistance to exposure to water, oil and other fluids contains at least one aspartic ester, at least one isocyanate and a conductive filler.

Claims

1. A conductive composition comprising: at least one aspartic ester; at least one isocyanate; and conductive filler, wherein an amount of the conductive filler is greater than 50% by weight based on the weight of the conductive composition.

2. The conductive composition of claim 1, further comprising an organic solvent.

3. The conductive composition of claim 1, further comprising a catalyst.

4. The conductive composition of claim 1, wherein the conductive filler is selected from nickel, cobalt, silver, gold, silver plated aluminum, nickel plated aluminum, silver plated copper, tungsten clad graphite, nickel clad graphite, and graphite.

5. The conductive composition of claim 1, wherein the at least one aspartic ester has the formula (I): ##STR00003## wherein X represents an aliphatic residue; R.sup.1 and R.sup.2 independently represent C.sub.1 to C.sub.10 alkyl residues; and R.sup.3 and R.sup.4 independently represent hydrogen or an organic group that is inert towards isocyanate at temperatures of 100 C. or less.

6. The conductive composition of claim 5, wherein the at least one aspartic ester comprises a blend of at least two aspartic esters having the formula (I).

7. The conductive composition of claim 1, wherein the at least one isocyanate is selected from ethylene diisocyanate; 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), pentamethylene diisocyanate (PDI), isophorone diisocyanate (IPDI), 2,2,4- and 2,4,4-trimethyl-hexamethylene diisocyanate, the isomeric bis-(4,4-isocyanatocyclohexyl) methanes or mixtures thereof of any desired isomer content, benzene diisocyanate; 1,4-cyclohexylene diisocyanate, 1,12-dodecamethylene diisocyanate, 1,4-phenylene diisocyanate, 2,4- and/or 2,6-toluene diisocyanate (TDI) or hydrogenated 2,4- and/or 2,6-toluene diisocyanate, 1,5-naphthalene diisocyanate, 2,4- and 4,4-diphenylmethane diisocyanate (MDI), 1,3- and 1,4-bis-(2-isocyanato-prop-2-yl)-benzene (TMXDI), 1,3-bis(isocyanato-methyl)benzene (XDI), bis-(4-isocyanato-cyclohexyl)methane (H.sub.12MDI), (S)-alkyl 2,6-diisocyanato-hexanoates or (L)-alkyl 2,6-diisocyanatohexanoates and mixtures thereof.

8. The composition of claim 1, wherein it is a two-component composition consisting of a first component and a second component, which are produced, packed and stored separately from one another, the at least one isocyanate not being present in the same component as the at least one aspartic ester.

9. A cured conductive coating produced from the composition of claim 1.

10. An electrically conductive, sandable, fairing compound produced from the composition of claim 1

11. A method comprising applying the composition of claim 1 to a substrate, wherein the composition is applied as adhesive and/or sealant or as coating.

12. A bonded and/or sealed or coated article obtained from the method of claim 11, the article comprising an at least partly cured form of the composition.

13. The composition of claim 1, wherein an amount of the at least one aspartic ester is 5-30% by weight based on the weight of the conductive composition.

14. The composition of claim 1, wherein an amount of the at least one isocyanate is 5-20% by weight based on the weight of the conductive composition.

Description

DETAILED DESCRIPTION

[0021] The electrically conductive compositions of the present invention are two-component compositions. As used herein, the term two-component composition means a composition that includes at least two components that are stored/packaged separately because of their mutual reactivity. One component is a hardener/crosslinker component that includes at least one polyisocyanate. Another component is a binder component that includes at least one polyaspartic ester that is reactive with the polyisocyanate. The two components are typically not mixed until shortly before application of the composition to a substrate. It is advantageous that upon mixing, the pot life, i.e., working time, is sufficient to allow application of the composition to the substrate prior to curing of the composition.

[0022] These conductive compositions are useful as gap fillers and conductive coatings in electrical housing and enclosure assemblies, such as for telecommunication, automotive engine control modules, radar systems, GPS and avionic control system applications. The electrically conductive compositions described herein are also useful in aircraft assembly for electrical continuity. For example, the electrically conductive compositions may be used as a gap filler between adjacent panels of an aircraft, as fairings, as fastener filling materials and as an electrically conductive coating.

[0023] These conductive compositions include an isocyanate component, a polyaspartic ester component that is reactive with the isocyanate component, a catalyst, electrically conductive filler, and optionally one or more additives. The composition of the present invention has a long pot life and produces cured conductive coatings, gap fillers and fairings that are flexible and fluid resistant.

Polyisocyanate Component:

[0024] As used herein, the term polyisocyanate refers to compounds comprising at least two free isocyanate groups. Polyisocyanates include diisocyanates and diisocyanate reaction products comprising, for example, biuret, isocyanurate, uretdione, urethane, urea, iminooxadiazine dione, oxadiazine trione, carbodiimide, acyl urea, and/or allophanate groups.

[0025] The polyisocyanate suitable for inclusion in the compositions of the present invention are in various embodiments, aromatic, araliphatic, aliphatic or cycloaliphatic di- and/or polyisocyanates and mixtures of such isocyanates. In one embodiment, the diisocyanates are of the formula:

R.sup.1(NCO).sub.2, [0026] wherein R.sup.1 represents an aliphatic hydrocarbon residue having 4 to 12 carbon atoms, a cycloaliphatic hydrocarbon residue having 6 to 15 carbon atoms, an aromatic hydrocarbon residue having 6 to 15 carbon atoms or an araliphatic hydrocarbon residue having 7 to 15 carbon atoms.

[0027] Specific examples of suitable isocyanates include, but are not limited to, ethylene diisocyanate; 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), pentamethylene diisocyanate (PDI), isophorone diisocyanate (IPDI), 2,2,4- and 2,4,4-trimethyl-hexamethylene diisocyanate, the isomeric bis-(4,4-isocyanatocyclohexyl) methanes or mixtures thereof of any desired isomer content, benzene diisocyanate; 1,4-cyclohexylene diisocyanate, 1,12-dodecamethylene diisocyanate, 1,4-phenylene diisocyanate, 2,4- and/or 2,6-toluene diisocyanate (TIDI) or hydrogenated 2,4- and/or 2,6-toluene diisocyanate, 1,5-naphthalene diisocyanate, 2,4- and 4,4-diphenylmethane diisocyanate (MDI), 1,3- and 1,4-bis-(2-isocyanato-prop-2-yl)-benzene (TMXDI), 1,3-bis(isocyanato-methyl)benzene (XDI), bis-(4-isocyanato-cyclohexyl)methane (H.sub.12MDI), (S)-alkyl 2,6-diisocyanato-hexanoates or (L)-alkyl 2,6-diisocyanatohexanoates. In various embodiments, the polyisocyanate component may comprise a triisocyanate, such as, for example, 4-isocyanatomethyl-1,8-octane diisocyanate (triisocyanatononane or TIN); isomers thereof; or derivatives thereof.

[0028] Polyisocyanates having isocyanurate, biuret, allophanate, uretdione or carbodiimide groups are also useful as the isocyanate component of the present invention. Such polyisocyanates may have isocyanate functionalities of three or more and are prepared by the trimerization or oligomerization of diisocyanates or by the reaction of diisocyanates with polyfunctional compounds containing hydroxyl or amine groups. Preferred is the isocyanurate of hexamethylene diisocyanate. Further suitable compounds are blocked polyisocyanates, such as 1,3,5-tris-[6-(1-methyl-propylidene aminoxy carbonylamino)hexyl]-2,4,6-trioxo-hexahydro-1,3,5-triazine.

[0029] Examples of suitable commercially available polyisocyanates include: aliphatic polyisocyanate based on hexamethylene diisocyanate (HDI) from Vencorex Chemicals under the trade names TOLONATE HDT-LV and TOLONATE HDT-LV2; from SAPICI under the trade names POLURENE MT 100 LV and POLURENE MT 100 LLV; and from Covestro AG under the trade names DESMODUR N3200, DESMODUR N3300, DESMODUR N3600, DESMODUR N3800, and DESMODUR N3900.

[0030] In various embodiments of the curable conductive composition, the amount of isocyanate is 5-20% by weight, or 7-15% by weight, or 8-12% by weight, based on the weight of the curable conductive composition.

Polyaspartic Ester Component:

[0031] Various embodiments of the compositions of the present invention include a blend of two or more polyaspartic esters. Polyaspartic esters useful in the compositions of the present invention include compounds of formula (I):

##STR00002##

[0032] In compounds of formula (I), the residue X is preferably obtained from an n-valent polyamine selected from ethylenediamine, 1,2-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, 2,5-diamino-2,5-dimethylhexane, 2,2,4- and/or 2,4,4-trimethyl-1,6-diaminohexane, 1,11-diaminoundecane, 1,12-diaminododecane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane, 2,4- and/or 2,6-hexahydrotoluylene-diamine, 2,4- and/or 4,4-diaminodicyclohexylmethane, 3,3-dimethyl-4,4-diaminodicyclohexylmethane, 2,4,4-triamino-5-methyldicyclohexyl-methane, and polyether polyamines with aliphatically-bound primary amino groups and having a number average molecular weight, Mn, of 148 to 6000 g/mol where the number average molecular weight is determined according to ASTM D 3750-79, (1985).

[0033] The residue X, in one embodiment, is obtained from 1,4-diaminobutane, 1,6-diaminohexane, 2,2,4- and/or 2,4,4-trimethyl-1,6-diaminohexane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane, 4,4-diaminodicyclohexylmethane or 3,3-dimethyl-4,4-diaminodicyclohexylmethane.

[0034] The phrase inert to isocyanate groups under the reaction conditions, which is used to define groups R.sup.1 and R.sup.2, means that these groups do not have Zerevitinov-active hydrogens (CH-acid compounds; cf. Rmpp Chemie Lexikon, Georg Thieme Verlag Stuttgart), such as OH, NH or SH.

[0035] R.sup.1 and R.sup.2, independently of one another, are in some embodiments C.sub.1 to C.sub.10 alkyl residues, in certain embodiments methyl or ethyl residues. Where X is the residue obtained from 2,4,4-triamino-5-methyldicyclohexylmethane, R.sup.1 and R.sup.2 are preferably ethyl. R.sup.3 and R.sup.4 may be identical or different and represent hydrogen or organic groups which are inert towards isocyanate groups at a temperature of 100 C. or less, in some embodiments hydrogen or C.sub.1 to C.sub.10 alkyl residues, in certain embodiments hydrogen, methyl or ethyl residues. In some embodiments, R.sup.3 and R.sup.4 are both hydrogen. In formula I), n is in some embodiments an integer from 2 to 6, in other embodiments 2 to 4.

[0036] The production of polyaspartic esters takes place in known manner by reacting the corresponding primary polyamines of the formula (II):

XNH.sub.2].sub.n(II) [0037] with maleic or fumaric acid esters of the formula (III):

R.sup.1OOCCR.sup.3CR.sup.4COOR.sup.2(III) [0038] where R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are as defined above for formula (I). Examples of suitable maleic or fumaric acid esters are dimethyl maleate, diethyl maleate, dibutyl maleate, and the corresponding fumarates.

[0039] In various embodiments, the production of polyaspartic esters from the above-mentioned starting materials takes place within the temperature range of 0 C. to 100 C. The starting materials are used in amounts such that there is at least one, preferably one, olefinic double bond for each primary amino group. Any starting materials used in excess can be separated off by distillation following the reaction. The reaction can take place in the presence or absence of suitable solvents, such as methanol, ethanol, propanol, dioxane, or mixtures thereof.

[0040] Examples of suitable aspartic ester functional amines are those commercially available from Arnette Polymers under the trade names ALl 138 and ALl 146; from Covestro LLC under the trade names DESMOPHEN NH 1420 and DESMOPHEN NH 1520; and from Cargill under the trade names ALTOR 201 and ALTOR 205.

[0041] In various embodiments of the curable conductive composition, the amount of aspartic ester is 5-30% by weight, or 7-25% by weight, or 8-20% by weight, based on the weight of the curable conductive composition.

Conductive Fillers:

[0042] Conductive fillers that are suitable for the conductive composition include, for example, nickel, cobalt, silver, gold, silver plated aluminum, nickel plated aluminum, silver plated copper, tungsten clad graphite, nickel clad graphite, and graphite.

[0043] In various embodiments of the curable conductive composition, the amount of conductive fillers is greater than 50% by weight, or 50-80% by weight, or 50-75% by weight, based on the weight of the curable conductive composition.

Catalyst:

[0044] The conductive composition may include a catalyst. The catalyst, if present, is generally included in the binder, i.e., aspartic acid containing, component. Examples of suitable catalysts include deionized water, carboxylic acids, and 1,4-butanediol.

[0045] In various embodiments of the curable conductive composition, the amount of catalyst is 0-3% by weight, or 0.05-1.0% by weight, or 0.1-0.5% by weight, based on the weight of the curable conductive composition.

Solvent:

[0046] The two-component compositions disclosed herein may include one or more organic solvents. The presence of solvent is useful for achieving acceptable working life, as well as the evaporation of solvent to induce shrinkage of the conductive composition, which improves conductivity. Suitable solvents that may be used in the compositions of the present invention include esters, ketones, aromatic hydrocarbons such as ethyl acetate, butyl acetate, methoxypropylacetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, toluene, xylene, solvent naphtha 100, parachlorobenzotrifluoride (PCBTF) and mixtures thereof.

[0047] The amount of solvent used may depend on the method by which the curable composition is applied, and the curing conditions used. For example, more solvent will be used if it a sprayable conductive coating is desirable. For applications where the curable conductive composition is to be used as a fairing, the amount of solvent used will allow sufficient working life and allow the fairing material to be sanded after 6 to 8 hours after application.

[0048] In various embodiments of the curable conductive composition, the amount of solvent is 0.01-50% by weight, or 0.01-10% by weight, or 0.01-0.5% by weight, based on the weight of the curable conductive composition.

Manufacturing Process:

[0049] The aspartic ester(s), conductive filler, and optionally solvent and catalyst are combined in a suitable mixer. The resulting paste is the Part A of a two-part kit.

[0050] The isocyanate(s) and solvent(s) are combined and mixed until the isocyanates have dissociated into the solvent homogeneously. This is the Part B of the two-part kit.

[0051] The Part A and the Part B are then packaged into suitable containers that protect against the degradation of the materials, for instance due to moisture ingress.

EXAMPLES

[0052] In the following exemplary compositions, the materials used in preparing the compositions are: [0053] Aspartic Ester A: a 100% solids content aspartic ester functional amine, having an amine number of approx. 201 mg KOH/g, viscosity of 1450 mPa.Math.s, commercially available from Covestro LLC as DESMOPHEN NH 1420. [0054] Aspartic Ester B: a 90% solids (by volume) content, zero VOC, aspartic ester functional amine, commercially available from Duraamen Engineered Products, Inc. as PERDURE P90, Part A. [0055] Isocyanate A: an aliphatic polyisocyanate resin based on hexamethylene diisocyanate, NCO content 23.01.0%, viscosity of 600150 mPa.Math.s, commercially available from Vencorex Chemicals as TOLONATE HDT-LV2. [0056] Isocyanate B: a 90% solids (by volume) content, zero VOC aliphatic polyisocyanate resin, commercially available from Duraamen Engineered Products, Inc. as PERDURE P90, Part B. The viscosity of Aspartic Ester B mixed 1:1 with Isocyanate B is 250-300 mPa.Math.s.

Solvent A: Acetone.

[0057] Electrically Conductive Filler A: Nickel-clad, ca. 60% nickel content, irregular-shaped graphite powder, 40-120 microns in size, commercially available from Weber Manufacturing, Midland, Ontario, Canada. [0058] Electrically Conductive Filler B: A silver-clad aluminum powder, 30-60 micron in size, ca. 12% silver content, produced by Parker Hannifin Corporation, Chomerics Division, Woburn, Massachusetts.

Example 1

[0059] A two-component conductive composition was prepared as follows: Component 1A: This component was prepared containing a blend of an aspartic ester, catalyst (deionized water) and electrically conductive filler. Component 1B contained a blend of Isocyanate A and Solvent A.

TABLE-US-00001 TABLE 1 Example 1 Amount (wt basis) Component 1A Aspartic Ester A 144.9 Catalyst (deionized water) 1.6 Electrically Conductive Filler A 724.7 Component 2A Isocyanate A 96.6 Solvent A 32.2 Total 1000

[0060] The resistivity of the mixed and cured conductive composition was measured over time, as shown in Table 2.

TABLE-US-00002 TABLE 2 24-hour resistivity 96-hour resistivity 168-hour resistivity (/sq) (/sq) (/sq) Example 1 0.187 0.101 0.063

Example 2

[0061] A two-component conductive composition was prepared as follows: Component 2A: This component was prepared containing a blend of a solvated aspartic ester, catalyst (deionized water) and electrically conductive filler. Component 2B was composed solely of a solvated isocyanate, Isocyanate B.

TABLE-US-00003 TABLE 3 Example 2 Amount (wt basis) Component 1B Aspartic Ester B 142.7 Catalyst (deionized water) 1.4 Electrically Conductive Filler B 713.2 Component 2B Isocyanate B 142.7 Total 1000

[0062] The resistivity of the mixed and cured conductive composition was measured over time, as shown in Table 4.

TABLE-US-00004 TABLE 4 24-hour resistivity 96-hour resistivity 168-hour resistivity (/sq) (/sq) (/sq) Example 1 0.700 0.547 0.336

[0063] The conductive compositions of the present invention, upon mixing of the two components, have a working life of at least 20 minutes. Upon curing of the conductive compositions, the conductive compositions have a through resistance of less than 10, a surface resistivity of less than 1 /sq, and a hardness of at least 60 Shore A.

[0064] The conductive compositions described herein were evaluated for chemical resistance and found to have a volume swell of less than 5%, and in some embodiments less than 1%, when exposed to the following fluids for three (3) days at room temperature: JP-8 jet fuel (MIL-DTL-83133), hydraulic fluid (MIL-PRF-83282), and de-icing fluid (AMS-1424). The equation used for determining volume swell is as follows:

[00001]$\mathrm{Volume}\mathrm{Swell}\%=\frac{\left(m_{\mathrm{af}}-m_{\mathrm{wf}}\right)-\left(m_{\mathrm{ai}}-m_{\mathrm{wi}}\right)}{\left(m_{\mathrm{ai}}-m_{\mathrm{wi}}\right)}100$ [0065] wherein, a is air, w is water, i is initial and f is final. The method for measuring these masses is described in ASTM D792.

[0066] Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification. While a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.