THERMALLY CONDUCTIVE AND ELECTRICALLY CONDUCTIVE NYLON COMPOUNDS

Abstract

A nylon compound is disclosed having good through plane thermal conductivity and improved physical strength. The compound comprises a combination of nylon, graphite, and long glass fibers. The through plane thermal conductivity of the compound ranges from about 1 W/m.Math.K to about 4 W/m.Math.K, as measured by the C-Therm Test described herein. This nylon compound is also electrically conductive, preferably having a surface resistivity ranging from about 1×10.sup.3 Ohm/sq to about 1×10.sup.5 Ohm/sq as measured by IEC 60093.

Claims

1. A thermally conductive nylon compound, comprising: a. polyamide resin, b. long glass fibers, c. graphite, d. optionally, metal soaps, and e. optionally, heat stabilizer, wherein the compound when molded into an article of 4 mm thickness has a through plane thermal conductivity ranging from about 1 W/m.Math.K to about 4 W/m.Math.K measured by C-Therm Test; wherein the through plane thermal conductivity of the compound when molded into article of 4 mm thickness is higher than a compound where long glass fibers are replaced with short glass fibers; and wherein the compound when molded into an article has a surface resistivity of less than about 1×10.sup.5 Ohm/sq as measured by IEC 60093.

2. An electrically conductive nylon compound, comprising: a. polyamide resin, b. long glass fibers, c. graphite, d. optionally, metal soaps, and e. optionally, heat stabilizer, wherein the compound when molded into an article has a through plane thermal conductivity ranging from about 1 W/m.Math.K to about 4 W/m.Math.K measured by C-Therm Test; wherein the compound when molded into an article has a surface resistivity of less than about 1×10.sup.5 Ohm/sq as measured by IEC 60093; wherein the surface resistivity of the compound is more electrically conductive than a compound where long glass fibers are replaced with short glass fibers; and wherein the weight percent of graphite in the compound is 35 or less.

3. The compound of claim 1 further comprising: f. additives selected from the group consisting of adhesion promoters; biocides; antibacterials; fungicides; mildewcides; anti-fogging agents; anti-static agents; bonding, blowing agents; foaming agents; dispersants; fillers; extenders; fire retardants; flame retardants; smoke suppressants; impact modifiers; initiators; lubricants; micas; pigments, colorants and dyes; plasticizers; processing aids; release agents; silanes, titanates and zirconates; slip agents; anti-blocking agents; stabilizers; stearates; ultraviolet light absorbers; viscosity regulators; waxes; and combinations of them.

4. The compound of claim 1 wherein the compound has ingredients ranging in amounts expressed in weight percent: (a) polyamide resin: 10-70 (b) long glass fiber: 10-40 (c) graphite: 20-50 (d) heat stabilizer: 0-1 (e) metal soaps: 0-1 (f) optional additives: 0-20.

5. The compound of claim 2 wherein the compound has ingredients ranging in amounts expressed in weight percent: (a) polyamide resin: 20-50 (b) long glass fiber: 20-25 (c) graphite: 30-35 (d) heat stabilizer: 0.1-0.4 (e) metal soaps: 0.1-0.4 (f) optional additives: 0-10.

6. The compound of claim 1, wherein the polyamide resin is selected from a group consisting of nylon 6; nylon 6,6; nylon 11; nylon 12; nylon 4,6; nylon 10,10; nylon 12,12; nylon 61; nylon 6T; nylon 9T; nylon 10T; nylon 61/66; nylon 6T/66; nylon 61/6T; copolyamides; and combinations thereof.

7. The compound of claim 1, wherein the compound when molded into an article has a surface resistivity ranging from about 1×10.sup.3 Ohm/sq to about 1×10.sup.5 Ohm/sq as measured by IEC 60093.

8. The compound of claim 1, in the form of a pellet wherein the average length of the long glass fiber is substantially the length of the pellet.

9. The compound of claim 8, wherein the average length of the long glass fibers ranges from about 6 mm to about 25 mm.

10. The compound of claim 1, wherein the polyamide resin comprises polyamide 6,6 and polyamide 6 in a weight ratio in a range of about 1:1 to about 4:1.

11. An article made from the compound of claim 1, wherein the article is extruded or molded.

12. The article of claim 11 molded into a housing for a light emitting diode.

13. A method of making a compound of claim 1, comprising the steps of (a) gathering ingredients including polyamide resin, long glass fiber and graphite, (b) melt-mixing the polyamide resin and the graphite to form a polymer melt, (c) pultruding the long glass fiber through the polymer melt to form a compound, and (d) pelletizing the compound to form fiber reinforced pellets, wherein the length of the long glass fiber is substantially the length of the pellet.

14. The method of claim 13, wherein the long glass fiber is pultruded from a roving.

15. The method of claim 13, wherein the compound is extruded or molded into an article.

16. The compound of claim 2 further comprising: f. additives selected from the group consisting of adhesion promoters; biocides; antibacterials; fungicides; mildewcides; anti-fogging agents; anti-static agents; bonding, blowing agents; foaming agents; dispersants; fillers; extenders; fire retardants; flame retardants; smoke suppressants; impact modifiers; initiators; lubricants; micas; pigments, colorants and dyes; plasticizers; processing aids; release agents; silanes, titanates and zirconates; slip agents; anti-blocking agents; stabilizers; stearates; ultraviolet light absorbers; viscosity regulators; waxes; and combinations of them.

17. A method of making a compound of claim 2, comprising the steps of (a) gathering ingredients including polyamide resin, long glass fiber and graphite, (b) melt-mixing the polyamide resin and the graphite to form a polymer melt, (c) pultruding the long glass fiber through the polymer melt to form a compound, and (d) pelletizing the compound to form fiber reinforced pellets, wherein the length of the long glass fiber is substantially the length of the pellet.

18. The method of claim 17, wherein the long glass fiber is pultruded from a roving.

19. The method of claim 17, wherein the compound is extruded or molded into an article.

Description

EXAMPLES

[0037] Table 2 shows the list of ingredients and Table 3 shows the recipes for the Examples and Comparative Examples.

TABLE-US-00002 TABLE 2 Commercial Brand Name Ingredient and Purpose Source Edelgraphit NFL98 Graphite Edelgraphit GmbH Tufrov ® 4510 Long Glass Fiber PPG Industries (Silane sized) Roving (Average Fiber Diameter = 17 μm) Thermoflow ® 672 Short Glass Fiber Johns Manville 4 mm in length before breakage during processing Zytel ® FE210021 NC010 Polyamide 6,6 DuPont Alphalon ™ 27C Polyamide 6 ATT Polymers GmbH Brüggolen ® H 160 heat stabilizer and L. Brüggemann antioxidant mixture of KG phenolic antioxidants and synergists Ceasit ™ AV Calcium Stearate Bärlocher GmbH

TABLE-US-00003 TABLE 3 Recipes for Comparative Examples and Examples Example 1 Example A Example 2 Example B Example 3 Example C Example 4 Example D Formula LGF SGF LGF SGF LGF SGF LGF SGF Graphite 24.88% 25.00% 29.85% 30.00% 34.83% 35.00% 39.80% 40.00% Long Glass Fiber 24.88% 24.88% 24.88% 24.88% Short Glass fiber 25.00% 25.00% 25.00% 25.00% PA6,6 39.10% 39.50% 31.94% 33.00% 24.88% 26.00% 17.81% 17.50% PA6 10.65% 10.00% 12.84% 11.50% 14.93% 13.50% 17.01% 17.00% Heat stabilizer  0.30%  0.30%  0.30%  0.30%  0.30%  0.30%  0.30%  0.30% Calcium stearate  0.20%  0.20%  0.20%  0.20%  0.20%  0.20%  0.20%  0.20% .sup. 100% .sup. 100% .sup. 100% .sup. 100% .sup. 100% .sup. 100% .sup. 100% .sup. 100%

[0038] Table 4a provides the mixing conditions for the Comparative Examples and Table 4b provides the mixing conditions for the Examples. The Comparative Examples and Examples were processed using a counter-rotating twin screw extruder, one configuration for twin screw extrusion and a second configuration adding an impregnation box for pultrusion, respectively. All of the ingredients for the Comparative Examples and the Examples were fed through the extruder's main hopper at the throat, except that the long glass fibers for the Examples were added to the polymer melt following the extrusion process via an attached pultrusion line described further below. The graphite was added in the form of a powder for the Comparative Examples and in the form of a graphite masterbatch for the Examples. The composition of the graphite masterbatch was nylon 6 (29.4%), graphite (70%), heat stabilizer (0.3%) and calcium stearate (0.3%). Although the graphite was added in different forms, it was determined to not materially affect the resulting compounds.

[0039] To process the long glass fiber material for the Examples, a pultrusion line configuration was attached to the extruder. The polymer melt matrix was prepared by adding all of the ingredients, excluding the long glass fibers, into the extruder's main hopper for mixing through multiple heated zones in the twin screw extruder. The polymer melt then flowed from the extruder into an impregnation box, which was positioned on the pultrusion line downstream from the extruder. The polymer melt coated the long glass fibers that were pulled as continuous roving filaments along a single axis through the impregnation box. The compound emerging from the impregnation box was cooled in a wet bath and pelletized for later injection molding into pellets having a length of 12 mm.

TABLE-US-00004 TABLE 4a Mixing Conditions All Comparative Examples Extruder Type Coperion twin screw (co-rotating) extruder (26 mm) Order of Addition All ingredients were mixed together and fed into the extruder's main hopper for twin screw agitating rotation through the 8 zones at progressively higher temperatures. Zone 1 290° C. Zone 2 300° C. Zone 3 310° C. Zone 4 320° C. Zone 5 325° C. Zone 6 330° C. Zone 7 335° C. Zone 8 340° C. Die 340° C. RPM 350 rpm Pellet Size  6 mm

TABLE-US-00005 TABLE 4b Mixing Conditions All Examples Extruder Type Coperion twin screw (co-rotating) extruder (50 mm) set up as a pultrusion line Order of Addition All ingredients were mixed together and fed into the extruder's main hopper for preparation of the polymer melt, except the long glass fiber which was added as a glass roving through the impregnation box for spreading and impregnating by the polymer melt. Zone 1 290° C. Zone 2 300° C. Zone 3 310° C. Zone 4 320° C. Zone 5 325° C. Zone 6 330° C. Zone 7 335° C. Zone 8 340° C. Die Impregnation box (345° C.) RPM 350 rpm Pellet Size  12 mm

[0040] As a result of the extrusion method used to incorporate short glass fibers into the Comparative Examples, there was significant breakage of the fibers into smaller pieces having a length of about 0.4 mm or less. This breakage was likely due, at least in part, to the rotational stress exerted on the short glass fibers from the extrusion process. On the other hand, as a result of being able to use a pultrusion process to incorporate long glass fibers into the Examples, there was minimal breakage, resulting in long glass fibers in the polymer compound having the length of about 12 mm.

[0041] Table 5 gives the molding conditions in an Arburg molding machine for both the Examples and the Comparative Examples.

TABLE-US-00006 TABLE 5 Molding Conditions All Comparative Examples and Examples Arburg molding machine Drying Conditions before Molding: Temperature (° C.) 80° C. Time (hours) 4 Temperatures: Nozzle (° C.) 290 Zone 1 (° C.) 280 Zone 2 (° C.) 290 Zone 3 (° C.) 300 Mold (° C.) 110 Speeds: Screw RPM (%) 350 mm/s % Shot - Inj Vel Stg 1 80 cm3/s % Shot - Inj Vel Stg 2 80 cm3/s % Shot - Inj Vel Stg 3 80 cm3/s % Shot - Inj Vel Stg 4 80 cm3/s % Shot - Inj Vel Stg 5 80 cm3/s Pressures: Hold Stg 1 (mPa) - 750 Bar Time (sec) Hold Stg 2 (mPa) - 750 Bar Time (sec) Timers: Injection Hold (sec) 5 Cooling Time (sec) 25 Operation Settings: Shot Size (ccm) 35 Cushion (ccm) 1.8

[0042] Once molded the sample shots from each Example and Comparative Example were tested for shrinkage, strength, thermal conductivity, impact resistance and surface resistivity. Table 6 describes the test methods used to obtain the test results for the Examples and Comparative Examples shown in Table 7.

TABLE-US-00007 TABLE 6 Test Methods ASH content ISO 3451 Specific gravity ISO 1183 Shrinkage % ISO 294-4 Tensile Strength Mpa ISO 527 Tensile Modulus Mpa ISO 527 Tensile elongation % ISO 527 Flexural Strength Mpa ISO 178 Flexural Modulus Mpa ISO 178 Thermal conductivity Through C-Therm Test plane W/m.K (Internal method described below) Notched charpy Impact kJ/m.sup.2 ISO-179/1eA Unnotched charpy Impact ISO-179/1eU kJ/m.sup.2 Surface resistivity (Ohm/sq) IEC 60093 Heat Deflection Temperature ISO 75 method C (HDT) (MPa) Unnotched charpy Impact ISO-179/1eU kJ/m.sup.2 (−30° C.)

[0043] Internal Methods

[0044] Thermal conductivity can be represented in two ways: “through plane” and “in plane”. For purposes of the examples the through plane thermal conductivity was measured by the modified transient plane source method using the C-Therm TCi™ Thermal Conductivity Analyzer (also referred to as the “C-Therm Test” defined for purposes of this disclosure and the claims).

[0045] The dimensions of the tensile bars for the C-Therm tests were 172 mm×10 mm×4 mm and the tensile bar type was ISO 527—Type 1A. Each example was run as a new test, selecting “Ceramics” as the test method from the C-Therm Test's standard options and using water as the contact agent.

[0046] The C-Therm test uses a one-sided, interfacial, heat reflectance sensor that applies a momentary, constant heat source to the sample. Both thermal conductivity and effusivity are measured directly to provide a detailed overview of the thermal characteristics of the sample material by applying a known current to the sensor's heating element providing a small amount of heat. The heat provided results in a rise in temperature at the interface between the sensor and the sample—typically less than 2° C. This temperature rise at the interface induces a change in the voltage drop of the sensor element. The rate of increase in the sensor voltage is used to determine the thermo-physical properties of the sample material.

[0047] The thermal conductivity is calculated based on the time rate of steady state heat flow through a unit area of the sample induced by a unit temperature gradient in a direction perpendicular to that unit area, W/m.Math.K.

[0048] Table 7 shows the test method results for the Examples and Comparative Examples.

TABLE-US-00008 TABLE 7 Test Results of Comparative Examples and Examples Properties Example1 Example A Example 2 Example B Example 3 Example C Example 4 Example D ASH glass % 23.4 25.1 25.04 24.8 26.18 25.3 26.03 24.9 ASH graphite % 19.28 23.5 28.13 29.5 33.92 33.9 37.01 39.2 Specific gravity 1.48 1.55 1.61 1.6 1.67 1.65 1.76 1.72 Shrinkage % 0.22 0.25 0.24 0.25 0.3 0.22 0.26 0.3 Tensile Strength Mpa 129 109 92.9 100 59.3 87 77 50 Tensile Modulus Mpa 14,700 17,640 15,790 18,900 14,740 17,102 16,940 18,470 Tensile elongation % 1.9 1 0.8 0.85 0.4 0.7 0.52 0.3 Flexural Strength 178 151 158 136 141 127 138 113 Mpa Flexural Modulus 12,100 11,600 12,640 12,320 13,180 13,362 15,750 14,675 Mpa Thermal conductivity 1.1 1.21 1.92 1.43 2.27 1.98 3.4 3.11 Through plane W/m .Math. K Notched Charpy 11 5.3 8.3 4.6 6.8 5.5 6.1 4.3 Impact kJ/m.sup.2 Unnotched Charpy 45.2 22 29.5 16.6 18.5 14 13.2 11 Impact kJ/m.sup.2 Surface resistivity 1.50E+03 2.00E+05 6.00E+04 2.00E+06 2.00E+04 1.80E+05 4.40E+04 1.00E+04 (Ohm/sq) Heat Deflection 225 194 213 187 202 190 (Not 190 Temperature (MPa) tested) Unnotched charpy 38.9 19.6 25 17.7 20.5 13.2 17.7 10.2 Impact kJ/m.sup.2 (−30° C.)

[0049] The examples tested both short glass fibers (the Comparative Examples) and long glass fibers (the Examples) in thermally conductive and electrically conductive nylon compounds containing graphite. While both types of glass fibers increased the strength of the nylon compound, the Examples containing long glass fibers had higher impact strength and flexural strength compared to the Comparative Examples containing short glass fibers.

[0050] The thermal conductivity of the Examples had a through plane thermal conductivity ranging from about 1 W/m.Math.K to about 4 W/m.Math.K measured by C-Therm Test on molded samples having a thickness of 4 mm. Unpredictably, the thermal conductivity of Examples 2, 3 and 4 was also higher compared to the respective Comparative Examples, with Example 2 having a thermal conductivity 34% higher than Comparative Example B. It is noted that the content of graphite (ASH) was 4.22% greater for Comparative Example A than Example 1 in spite of the original starting materials seen in Table 3, which explains the slightly higher thermal conductivity compared to Example 1. Therefore, the slightly higher through plane thermal conductivity for Comparative Example A is discounted by that actually higher graphite content. Additionally, the heat deflection temperature increased by 12% or greater in Examples 1, 2 and 3 that were tested compared to the respective Comparative Examples.

[0051] Finally, the surface resistivity (Ohm/sq) of each of the Examples was electrically conductive, having a surface resistivity of less than about 1×10.sup.5 Ohm/sq as measured by IEC 60093. Moreover, Examples 1, 2, and 3 were unexpectedly lower (i.e., more electrically conductive and less electrically insulative) compared to their respective Comparative Examples A-C. Indeed, Examples 1-3 are within the range of electrically conductive materials, whereas Comparative Examples are within the range of being electrically dissipative. Because glass is electrically insulative, it is counterintuitive that longer glass fibers would reduce surface resistivity, all other variables being constant.

[0052] Further comparison shows more unpredictable results in this combination of ingredients where long glass fiber has replaced short glass fiber in the comparison between Example 4 and Comparative Example D. Although, the advantage of thermal conductivity for Example 4 and Comparative Example D was consistent with Examples 1-3 vs. Comparative Examples A-C, the surprising advantage of less surface resistivity using longer glass fibers was lost because Comparative Example D had less surface resistivity than Example 4. While not being limited to a particular theory, it is believed that the weight percent loading of graphite above 35 weight percent contributed more to the electrical properties of the compound than did the glass fiber length.

[0053] Glass fibers are known for their ability to reinforce polymer matrices. In addition, short glass fibers and long glass fibers would be expected to contribute similarly to the properties of thermal conductivity, surface resistivity and heat deflection temperature in nylon compounds. Surprisingly, however, long glass fibers achieved superior characteristics for applications requiring thermal management (i.e. through plane thermal dissipation), increased heat deflection temperature, and electrical conductivity.

[0054] The invention is not limited to the above embodiments. The claims follow.