Nickel-coated graphite filled silicone composite

Abstract

The present invention is a composition comprising a) a hydrolyzable polyorganosiloxane; b) an organosiloxane crosslinking agent; c) nickel-coated graphite particles; d) a condensation cure catalyst; e) an adhesion promoter; and f) a thixotropic agent. The composition of the present invention provides a composite material with low volume resistivity and high shielding effectiveness.

Description

[0001] Nickel-Coated Graphite Filled Silicone Composite

[0002] Background of the Invention

[0003] The present invention relates to a nickel-coated graphite filled silicone composite. The demand for electromagnetic interference (EMI) shielding materials is rapidly growing, driven by the increasing autonomy in automotive systems and the evolution of 5G technology. The expanded frequency range, fast data transfer rates, and the proliferation of connected devices require uninterrupted communication, while higher density packaging in electronics demands advanced shielding solutions. Moreover, the rising concern over electromagnetic pollution emphasizes the need for robust EMI shielding technologies. Electrically conductive silicone composites (ECSCs) have emerged as highly attractive solutions for EMI shielding applications due to their unique electrical and mechanical properties. They offer a range of advantages compared to conventional metal and organic materials, including excellent dispersibility, strong adhesion to various substrates, adjustable modulus, high flexibility, high-temperature stability, low flammability, and toxicity. These properties position electrically conductive silicone adhesives (ECSAs) as desired materials for high-performance EMI applications. ECSAs are commonly applied as adhesives, sealants, and gaskets, facilitating rapid dispensing for efficient processing. Typically, an ECSC consists of electrically conductive fillers dispersed in a non-conductive silicone matrix at a concentration above their percolation threshold. The commonly used electrically conductive fillers range from carbon black for applications requiring relatively lower conductivity and EMI shielding to pure metal powders such as silver, as well as metal-coated materials such as silver-coated copper, silver-coated aluminum for high-conductivity, high-EMI shielding applications. There is a growing demand for cost-effective and highly conductive ECSAs with acceptable shielding effectiveness.

[0004] Summary of the Invention

[0005] The present invention addresses a need in the art by providing a composition comprising, based on the weight of the composition a) from 5 to 50 weight percent of a hydrolyzable polyorganosiloxane; b) from 0.1 to 10 weight percent of an organosiloxane crosslinking agent; c) from 30 to 90 weight percent of nickel-coated graphite particles; d) from 0.01 to 5 weight percent of a condensation cure catalyst; e) from 0.1 to 10 weight percent of an adhesion promoter; and f) from 0.01 to 10 weight percent of a thixotropic agent. The composition of the present invention provides a composite material with low volume resistivity and high shielding effectiveness. Detailed Description of the Invention

[0006] The present invention is a composition comprising, based on the weight of the composition a) from 5 to 50 weight percent of a hydrolyzable polyorganosiloxane; b) from 0.1 to 10 weight percent of an organosiloxane crosslinking agent; c) from 30 to 90 weight percent of nickel- coated graphite particles; d) from 0.01 to 5 weight percent of a condensation cure catalyst; e) from 0.01 to 10 weight percent of an adhesion promoter; and f) from 0. 1 to 10 weight percent of a thixotropic agent.

[0007] As used herein, the term “hydrolyzable polyorganosiloxane” refers to a linear or branched polyorganosiloxane functionalized with groups that react with water, then condense to form a crosslinking network of Si-O-Si linkages. The hydrolyzable polyorganosiloxane is preferably represented by one or more compounds of Formula 1 :

[0008] Formula 1 : where R is either of Fragment 1 or Fragment 2: where each R1is independently Ci-Ce-alkyl or phenyl; each R2is independently C(0)CH3, Ci-Ce-alkyl, or N=C(R3)z, where each R3is independently Ci-C4-alkyl; R4is Ci-Ce-alkyl, phenyl, OR2, or -(Rs)y-vinyl, where R5is a divalent Ci-Cn-linear or branched hydrocarbyl group, and y is 0 or 1; and n is from 50 to 1000. The compound of Formula 1 functionalized with Fragment 1 (R1and R2= Me in each case) can be prepared in accordance with Scheme 1: Scheme 1: where the catalyst is preferably a platinum catalyst.

[0009] The compound of Formula 1 functionalized with Fragment 2 (R1, R2, and R4= Me in each case) can be synthesized in accordance with Scheme 2:

[0010] Scheme 2: where the catalyst is preferably a titanate or tin catalyst.

[0011] In one aspect, the hydrolyzable polyorganosiloxane is a mixture of hydrolyzable polyorganosiloxanes of different degrees of polymerization. In another aspect, the hydrolyzable polyorganosiloxane may contain T and / or Q structural units: As used herein, an organosilane crosslinking agent refers to an organosilicon compound containing hydrolyzable groups such as Si-Ci-C4-alkoxy, Si-OC(O)CH3, and Si-O-N=C(R3)2 groups. Preferably, the organosilane crosslinking agent, when used, is one or more compounds of Formula 2:

[0012] Formula 2 where R6is -OR2or -(R5)y-vinyl; and R7is R6, Ci-C4-alkyl, or phenyl. R2is preferably methyl or ethyl for the compound of Formula 2.

[0013] Examples of specific suitable organosilane crosslinking agents include vinyltrimethoxysilane, methyltrimethoxysilane, isobutyltrimethoxysilane, and tetraethyl orthosilicate. The concentration of the organosilane crosslinking agent is present at a concentration in the range of from 0.1 or from 0.3 or from 0.7 weight percent, to 10 or to 5 or to 3 or 2 weight percent, based on the weight of the composition.

[0014] The nickel-coated graphite particles preferably have a Dso particle size in the range of from 50 pm or from 80 pm or from 100 pm, to 200 pm or to 150 pm or to 120 pm, as measured by laser scattering based on volume distribution. The concentration of the nickel-coated graphite particles is in the range of from 30 or from 50 or from 60 weight percent, to 90 or to 80 or to 70 weight percent, based on the weight of the composition.

[0015] The condensation cure catalyst is preferably a titanate catalyst such as titanium diisopropoxy bis(ethylacetoacetate) or tetra-n-butyl titanate or tetra-isobutyl titanate. The concentration of the condensation cure catalyst is in the range of from 0.01 or from 0.1 or from 0.5 weight percent, to 10 or to 5 or to 2 weight percent, based on the weight of the composition.

[0016] The adhesion promoter is a hydrolyzable silane that promotes adhesion of the composition to the desired substrate. Preferred adhesion promoters include those illustrated in Formula 3 :

[0017] Formula 3 where R2is preferably methyl or ethyl; Y is a bivalent linear or branched Ci-Ce hydrocarbyl group, preferably linear propylenyl; X is a glycidyl ether group, a thiol group, an aminoethyl amine group, a silatrane group, a methacryloyloxy group, an acryloyloxy group, or a cyano group. Glycidyl either, aminoethyl amine, silatrane, and thiol groups, as shown below, are preferred: up where R2is preferably methyl or ethyl. Alternatively, Y and X together form an OR2group.

[0018] A thixotropic agent is included in the composition to control viscosity. Examples of suitable thixotropic agents include carbon nanotubes, carbon nanofibers, fumed silica, and zinc oxide. The concentration of the thixotropic agent is in the range of from 0.01 or from 0.1 or from 0.3 weight percent, to 10 or to 5 or to 2 weight percent, based on the weight of the composition.

[0019] The composition advantageously comprises a processing aid to enhance dispensability and electrical performance. The processing aid is a polydimethylsiloxane of the formula (CH3)3SiO-(Si(CH3)2-O)z-Si(CHs)3 where z is from 0 to 5 or to 4 or to 3. Examples of processing aids include octamethyltrisiloxane and decamethyltetrasiloxane at a concentration typically in the range of from 1 to 10 weight percent, based on the weight of the composition. The composition of the present invention provides composites with the desired low volume resistivities and high shielding effectiveness. Examples

[0020] In the following example, Fi so refers to a hydrolyzable polyorganosiloxane of Formula 1, Fragment 1, with each R1and R2= methyl, and n = 780; Fmiso refers to a polymer of Formula 1, Fragment 1, with each R1and R2= methyl, and n = 150.

[0021] General Procedure for Preparing Moisture Cure Compositions

[0022] Fin78o and Fin i o and octamethyltrisiloxane were loaded into a vessel and blended with a speed mixer at 2000 rpm for 30 s. The contents were then hand mixed, then speed mixed once again at 2000 rpm for 30 s. Half of the filler material (either nickel coated graphite or nickel coated aluminum) was loaded into the vessel, and the contents were speed mixed at 2000 rpm for 30 s. The contents were then hand mixed, then speed mixed once again at 2000 rpm for 30 s. The contents, which heated upon mixing, were allowed to cool to room temperature. Then, the remaining half of the filler material was added to the vessel, with the repeated cycle of speed mixing, hand mixing, and speed mixing as before. The mixture was allowed to cool to room temperature, and the crosslinker and adhesion promoter were added. The contents were speed mixed at 2000 rpm for 60 s, then the thixotropic agent was added. The contents were speed mixed, hand mixed, and speed mixed as before, and then catalyst was added to the blend. The contents were speed mixed at 2000 rpm for 60 s, then hand mixed, then mixed at 1200 rpm in vacuo for 15 s. The mixture was then packed into 30 cm3syringes, then applied to a Teflon substrate with a drawdown bar to a thickness of from 1 mm to 1.5 mm. The slab was allowed to cure at ambient conditions for 7 d.

[0023] Table 1 summarizes the materials and their amounts in parts per hundred. NCG refers to nickel coated graphite (D50 = 80 m to 120 pm) ; NCA refers to nickel coated aluminum (D50 = 80 pm); OMTS refers to octamethyltrisiloxane; IBTMS refers to isobutyltrimethoxysilane; API refers to l-methoxy-3,7-bis{ {3-(trimethoxysilyl)propoxy {methyl} silatrane + glycidoxypropyltrimethoxysilane; TEOS refers to tetraethoxysilane; BTMSH refers to 1,6-Bis(trimethoxysilyl)hexane; and Catalyst refers to titanium ethyl acetoacetate complex. Carbon Nanotube refers to Tuball Matrix 601 Carbon Nanotube (by OCSiAl). Table 1 - Materials used to Prepare Composition

[0024] Measurement of Volume Resistivity (VR)

[0025] Volume resistivity was performed on drawdown slabs using a Pro4 instrument connected to an inline 4-point probe. The thickness of the sample was measured at 5 points on the cure slab using a micrometer, averaged, and entered into the program. A 75-mA current was used for the measurements. The volume resistivity was measured on 5 points of the slab and averaged.

[0026] Shielding Effectiveness (SE) Measurement

[0027] Shielding effectiveness measurements were conducted according to ASTM D-4935 (“Standard

[0028] Test Method for Measuring the Electromagnetic Shielding Effectiveness of Planar Materials”) by connecting a Keysight network analyzer, with a frequency range from 100 kHz to 8.5 GHz, to a circular coaxial transmission line holder, EM 2107A Shielding Effectiveness Text Fixture from Electro-Metrics. This procedure allows for broadband analysis of conductive samples for electromagnetic shielding effectiveness. The measurement was conducted on a flat drawdown slab of cured material that was sandwiched in the center of the transmission line. Table 2 illustrates the Volume Resistivity (VR) and Average Shielding Effectiveness (SE) of the slabs. N.C. means not conductive (very high resistance). Table 2 - Volume Resistivity and Average Shielding Effectiveness of Slabs

[0029] The example cured slabs of the present invention demonstrated good performance for both electrical conductivity and shielding effectiveness.

Claims

Claims:

1. A composition comprising, based on the weight of the composition a) from 5 to 50 weight percent of a hydrolyzable polyorganosiloxane; b) from 0.1 to 10 weight percent of an organosiloxane crosslinking agent; c) from 30 to 90 weight percent of nickel-coated graphite particles; d) from 0.01 to 5 weight percent of a condensation cure catalyst; e) from 0.1 to 10 weight percent of an adhesion promoter; and f) from 0.01 to 10 weight percent of a thixotropic agent.

2. The composition of Claim 1 wherein the hydrolyzable polyorganosiloxane is one or more compounds of Formula 1 :Formula 1 where R is either of Fragment 1 or Fragment 2:where each R1is independently Ci-Ce-alkyl or phenyl; each R2is independently C(O)CH3, Ci-Ce-alkyl, or N=C(R3)2, where each R3is independently Ci-C4-alkyl; R4is Ci-Ce-alkyl, phenyl, OR2, or -(R5)y-vinyl, where R5is a divalent Ci-Cn-linear or branched hydrocarbyl group, and y is 0 or 1; and n is from 50 to 1000.

3. The composition of Claim 2 wherein each R is Fragment 1, wherein the organosiloxane crosslinking agent is a compound of Formula 2:Formula 2 where each R2is methyl or ethyl; and R7is OR2or Ci-C4-alkyl.

4. The composition of Claim 3 wherein each R1is methyl or phenyl; wherein the thixotropic agent is selected from the group consisting of carbon nanotubes, carbon fibers, fumed silica, and ZnO; and wherein the adhesion promoter is a compound of formula 3:Formula 3 where Y is a bivalent linear or branched Ci-Ce hydrocarbyl group; X is a glycidyl ether group, a thiol group, an aminoethyl amine group, a silatrane group, a methacryloyloxy group, an acryloyloxy group, or a cyano group; or Y and X together form an OR2group.

5. The composition of Claim 4 wherein Y is a linear propylenyl group; and X is an aminoethyl amine group or a silatrane group.

6. The composition of Claim 2 wherein each R is fragment 1; the concentration of the nickel- coated graphite particles is in the range of from 50 to 70 weight percent, based on the weight of the composition; and the nickel-coated graphite particles have a Dso particle size in the range of from 50 m to 200 pm.

7. The composition of Claim 1 which further comprises from 1 to 10 weight percent, based on the weight of the composition, of a polydimethylsiloxane of the formula:(CH3)3SiO-(Si(CH3)2-O)z-Si(CH3)3where z is from 0 to 5.

8. The composition of Claim 6 which further comprises from 1 to 10 weight percent, based on the weight of the composition, of octamethyltrisiloxane.

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