WO2009045398A1

WO2009045398A1 - Vehicular axle and drive shafts

Info

Publication number: WO2009045398A1
Application number: PCT/US2008/011312
Authority: WO
Inventors: Andri E. Elia; Michael R. Day; Robert Espey; Glenn Steed; Andrew Wang; Nathan Keith
Original assignee: E.I. Du Pont De Nemours And Company; Morph Technologies, Inc.
Priority date: 2007-10-04
Filing date: 2008-10-01
Publication date: 2009-04-09
Also published as: WO2009045398A8

Abstract

Metal plated organic polymer compositions are useful as vehicular axle and drive shafts. Such shafts may have lighter weight, and/or superior corrosion resistance, than conventional metal drive shafts.

Description

VEHICULAR AXLE AND DRIVE SHAFTS

FIELD OF THE INVENTION

Metal plated organic polymers which are useful for vehicular axle and drive shafts.

TECHNICAL BACKGROUND

Vehicles such as automobiles, trucks, motorcycles, scooters, recreational and all terrain vehicles, farm equipment such as tractors, and construction equipment such as bulldozers and graders are of course important items in modern society, and they are made of a myriad of parts. Also important are stationary internal combustion engines such as those used to power generators . Many of these parts must have certain minimum physical properties such as stiffness and/or strength. Traditionally these types of parts have been made from metals such as steel, aluminum, zinc, and other metals, but in recent decades organic polymers have been increasingly used for such parts for a variety of reasons . Such polymeric parts are often lighter, and/or easier (cheaper) to fabricate especially in complicated shapes, and/or have better corrosion resistance. However such polymeric parts have not replaced metals in some applications because they are not stiff and/or strong enough, or have other property defi- ciencies compared to metal.

Thus vehicle manufacturers have been searching for ways to incorporate more polymeric materials into their vehicles for a variety of reasons, for example to save weight, lower costs, or provide more design freedom. Thus improved polymeric axle and drive shafts (ADSs) have been sought by vehicle manufacturers. It has now been found that metal plated organic polymeric ADSs have the properties desired. Metal plated polymeric parts have been used in vehicles, especially for ornamental purposes. Chrome or nickel plating of visible parts, including polymeric parts, has long been done. In this use the polymer is coated with a thin layer of metal to produce a pleasing visual effect. The amount of metal used is generally the minimum required to produce the desired visual effect and be durable .

US Patent 4,406,558 describes a gudgeon pin for an internal combustion engine which is metal plated polymer. US Patent 6,595,341 describes an aluminum plated plastic part for a clutch. Neither of these patents mentions ADSs.

SUMMARY OF THE INVENTION This invention concerns a vehicular axle or drive shaft, comprising an organic polymer composition which is coated at least in part by a metal .

This invention also concerns a vehicle, comprising an axle or drive shaft which comprises an organic polymer composition which is coated at least in part by a metal .

DETAILS OF THE INVENTION

Herein certain terms are used and some of them are defined below:

By an "organic polymer composition" is meant a composition which comprises one or more organic polymers. Preferably one or more of the organic polymers is the continuous phase.

By an "organic polymer" (OP) is meant a polymeric material which has carbon-carbon bonds in the polymeric chains and/or has groups in the polymeric chains which have carbon bound to hydrogen and/or halogen. Preferably the organic polymer is synthetic, i.e., made by man. The organic polymer may be for example a thermoplastic polymer (TPP) , or a thermoset polymer (TSP) . By a "TPP" is meant a polymer which is not crosslinked and which has a melting point and/or glass transition point above 30⁰C, preferably above about 100⁰C, and more preferably above about 150⁰C. The highest melt- ing point and/or glass transition temperature is also below the point where significant thermal degradation of the TPP occurs. Melting points and glass transition points are measured using ASTM Method ASTM D3418-82. The glass transition temperature is taken at the transition midpoint, while the melting point is measured on the second heat and taken as the peak of the melting endotherm.

By a "TSP" is meant a polymeric material which is crosslinked, i.e., is insoluble in solvents and does not melt. It also refers to this type of polymeric material before it is crosslinked, but in the final ADS, it is crosslinked. Preferably the crosslinked TSP composition has a Heat Deflection Temperature of about 50⁰C, more preferably about 100⁰C, very preferably about 150⁰C or more at a load of 0.455 MPa (66 psi) when measured using ASTM Method D648-07.

By a polymeric "composition" is meant that the organic polymer is present together with any other additives usually used with such a type of polymer (see below) . By "coated with a metal" is meant part or all of one or more surfaces of the ADS is coated with a metal. The metal does not necessarily directly contact a surface of the organic polymer composition. For example an adhesive may be applied to the surface of the organic polymer and the metal coated onto that. Any method of coating the metal may be used (see below) .

By "metal" is meant any pure metal or alloy or combination of metals. More than one layer of metal may be present, and the layers may have the same or different compositions .

Axles and drive shafts are common on self propelled vehicles. In front engine, rear wheel drive vehicles, drive shafts typically transmit power from the transmission to a differential on an axle. In the axle housing the differential transmits the power to the axle shaft (s), which in turn transfer the power to the wheels, thereby moving the vehicle. Traditionally these axles have been made of metal, but continuous wound fiber composites have also been used, at least for drive shafts. However such composites are expensive to produce. Sometimes the drive shaft is in two or more segments connected by a universal joint, universal joints also being used to connect the drive shaft to the transmission and/or differential. In four-wheel drive vehicles there are often two drive shafts, one to the front axle and one to the rear axle. Front wheel drive vehicles typically do not have a common drive shaft but have axle shafts driving each wheel .

Drive shafts are usually circular in cross section, and to reduce weight often hollow, in other words often essentially large tubes or pipes. Axle shafts are also usually circular in cross section but usually solid. However axles may in some cases be solid, and drive shafts may be tubular. The axle and drive shafts herein may have the same configuration. They are metal coated at least in part, and preferably completely because of the large dynamic loads they have to endure . The metal coating may also improve their corrosion resistance compared with metal shafts. Thus the metal coated OP composition ADSs herein are lighter than metal shafts but more easily fabricated and cheaper than composite shafts. In addition to the contribution of overall weight reduction, the reduced rotational mass will also offer opportunities for improved performance and reduced fuel consumption.

One, some or all of the axle and drive shafts in a vehicle may be made of the metal coated OP composition. Useful TSPs include epoxy, phenolic, and melamine resins. Parts may be formed from the thermoset resin by conventional methods such as reaction injection molding or compression molding.

Useful TPPs include poly (oxymethylene) and its co- polymers; polyesters such as poly (ethylene terephtha- late) , poly (1, 4-butylene terephthalate) , poly(l,4- cyclohexyldimethylene terephthalate), and poly(l,3- poropyleneterephthalate) ; polyamides such as nylon-6,6, nylon-6, nylon-12, nylon-11, and aromatic-aliphatic co- polyamides; polyolefins such as polyethylene (i.e. all forms such as low density, linear low density, high density, etc.), polypropylene, polystyrene, polystyrene/poly (phenylene oxide) blends, polycarbonates such as poly (bisphenol-A carbonate); fluoropolymers including perfluoropolymers and partially fluorinated polymers such as copolymers of tetrafluoroethylene and hexafluoropro- pylene, poly(vinyl fluoride), and the copolymers of ethylene and vinylidene fluoride or vinyl fluoride; poly- sulfides such as poly (p-phenylene sulfide); polyetherke- tones such as poly (ether-ketones) , poly (ether-ether- ketones) , and poly (ether-ketone-ketones) ; poly (etherimides) ; acrylonitrile-1, 3-butadinene-styrene copolymers; thermoplastic (meth) acrylic polymers such as poly (methyl methacrylate) ; and chlorinated polymers such as poly(vinyl chloride), polyimides, polyamideimides, vinyl chloride copolymer, and poly (vinylidene chloride) . "Thermotropic liquid crystalline polymer" (LCP) herein means a polymer that is anisotropic when tested using the TOT test or any reasonable variation thereof, as de- scribed in U.S. Patent 4,118,372, which is hereby incorporated by reference. Useful LCPs include polyesters, poly (ester-amides) , and poly (ester-imides) . One preferred form of LCP is "all aromatic", that is all of the groups in the polymer main chain are aromatic (except for the linking groups such as ester groups) , but side groups which are not aromatic may be present. The TPPs may be formed into parts by the usual methods, such as injection molding, thermoforming, compression molding, extrusion, and the like.

The OP, whether a TSP, TPP or other polymer composition may contain other ingredients normally found in such compositions such as fillers, reinforcing agents such as glass and carbon fibers, pigments, dyes, stabilizers, toughening agents, nucleating agents, antioxidants, flame retardants, process aids, and adhesion promoters. Another class of materials may be substances that improve the adhesion to the resin of the metal to be coated onto the resin. Some of these may also fit into one or more of the classes named above.

The OP (composition) should preferably not soften significantly at the expected maximum operating temperature of the ADSs. Since it is often present at least in part for enhanced structural purposes, it will better maintain its overall physical properties if no softening occurs. Thus preferably the OP has a melting point and/or glass transition temperature and/or a Heat Deflection Temperature at or above the highest use temperature of the OP. The OP composition (without metal coating) should also preferably have a relatively high flexural modulus, preferably at least about 1 GPa, more preferably at least about 2 GPa, and very preferably at least about 10 GPa. Flexural modulus is measured by ASTM Method D790-03, Pro- cedure A, preferably on molded parts, 3.2 mm thick (1/8 inch) , and 12.7 mm (0.5 inch) wide, under a standard laboratory atmosphere. Since these are structural parts, and are usually preferred to be stiff, a higher flexural modulus improves the overall stiffness of the metal coated ADS .

The OP composition may be coated with metal by any- known methods for accomplishing that, such as vacuum deposition (including various methods of heating the metal to be deposited) , electroless plating, electroplating, chemical vapor deposition, metal sputtering, and electron beam deposition. Preferred methods are electroless plating and electroplating, and a combination of the two. Although the metal may adhere well to the OP composition without any special treatment, usually some method for improving adhesion will be used. This may range from simple abrasion of the OP composition surface to roughen it, addition of adhesion promotion agents, chemical etching, functionalization of the surface by ex- posure to plasma and/or radiation (for instance laser or UV radiation) or any combination of these. Which methods may be used will depend on the OP composition to be coated and the adhesion desired. Methods for improving the adhesion of coated metals to many OPs are well known in the art. More than one metal or metal alloy may be plated onto the organic resin, for example one metal or alloy may be plated directly onto the organic resin surface because of its good adhesion, and another metal or alloy may be plated on top of that because it has a higher strength and/or stiffness.

Useful metals and alloys to form the metal coating include copper, nickel, iron-nickel, cobalt, cobalt- nickel, and chromium, and combinations of these in different layers. Preferred metals and alloys are copper, nickel, cobalt, cobalt-nickel, and iron-nickel, and nickel is more preferred.

The surface of the organic resin of the structural part may be fully or partly coated with metal. In dif- ferent areas of the part the thickness and/or the number of metal layers, and/or the composition of the metal layers may vary.

When electroplating it is known that grain size of the metal deposited may be controlled by the electroplat- ing conditions, see for instance U.S. Patents 5,352,266 and 5,433,797 and U.S. Patent Publications 20060125282 and 2005020525, all of which are hereby included by reference. In one preferred form at least one of the metal layers deposited has an average grain size in the range of about 5 nm to about 200 nm, more preferably about 10 nm to about 100 nm. In another preferred form of electroplated metal, the metal has an average grain size of at least 500 nm, preferably at least about 1000 nm, and/or an average maximum grain size of about 5000 nm. For all these grain size preferences, it is preferred that that thickest metal layer, if there is more than one layer, be the specified grain size.

The thickness of the metal layer (s) deposited on the organic resin is not critical, being determined mostly by the desire to minimize weight while providing certain minimum physical properties such as modulus, strength and/or stiffness. These overall properties will depend to a certain extent not only on the thickness and type of metal or alloy used, but also on the design of the struc- tural part and the properties of the organic resin composition.

In one preferred embodiment the flexural modulus of the metal coated ADS is at least about twice, more preferably at least about thrice, the flexural modulus of the uncoated OP composition. This is measured in the following way. The procedure used is ISO Method 178, using molded test bars with dimensions 4.0 mm thick and 10.0 mm wide. The testing speed is 2.0 mm/min. The composition from which the ADSs are made is molded into the test bars, and then some of the bars are completely coated (optionally except for the ends which do not affect the • test results) with the same metal using the same procedure used to coat the ADS. The thickness of the metal coating on the bars is the same as on the ADS. If the thickness on the ADS varies, the test bars will be coated to the greatest metal thickness on the ADS. The flexural moduli of the coated and uncoated bars are then measured, and these values are used to determine the ratio of flex- ural moduli (flexural modulus of coated/flexural modulus of uncoated) . Generally speaking the thicker the metal coating, the greater the flexural modulus ratio between the uncoated and coated OP part .

For use as ADSs, it is also important in many in- stances that the plated OP composition be tough, for example be able to withstand impacts. It has surprisingly been found that some of the metal plated OP compositions of the present invention are surprisingly tough. It has previously been reported (M. Corley, et al . , Engineering Polyolefins for Metallized Decorative Applications, in Proceedings of TPOs in Automotive 2005, held June 21-23, 2005, Geneva Switzerland, Executive Conference Management, Plymouth, MI 48170 USA, p. 1-6) that unfilled or lightly filled polyolefin plaques have a higher impact energy to break than their Cr plated analog. Indeed the impact strength of the plated plaques range from 50 to 86 percent of the impact strength of the unplated plaques. As can be seen from Examples 2-7 below, the impact maximum energies of the plated plaques are much higher than those of the unplated plaques. It is believed this is due to the higher filler levels of the OP compositions used, and in the present parts it is preferred that the OP composition have at least about 25 weight percent, more preferably about 35 weight percent, especially preferably at least about 45 weight percent of filler/reinforcing agent present. A preferred maximum amount of filler/reinforcing agent present is about 65 weight percent . These percentages are based on the total weight of all ingredients present. Typical reinforcing agents/fillers include carbon fiber, glass fiber, aramid fiber, particulate minerals such as clays (various types), mica, silica, calcium carbonate (including limestone), zinc oxide, wollastonite, carbon black, titanium dioxide, alumina, talc, kaolin, microspheres, alumina trihydrate, calcium sulfate, and other minerals.

It is preferred that the ISO179 impact energy (see below for procedure) of the metal plated ADS be 1.2 times or more the impact energy of the unplated OP composition, more preferably 1.5 times or more. The test is run by- making bars of the OP composition, and plating them by the same method used to make the ADS, with the same thickness of metal applied. If the ADS is metal plated on both sides (of the principal surfaces) , the test bars are plated on both sides, while if the ADS is plated on one side (of the principal surfaces) the test bars are plated on one side. The impact energy of the plated bars are compared to the impact energy of bars of the unplated OP composition. Preferably the metal coating will about 0.010 mm to about 10 mm thick, more preferably about 0.025 mm to about 8 mm thick, very preferably about 0.050 to about 4.0 mm thick, and especially preferably about 0.10 to about 1.0 mm thick. It is to be understood that any minimum thickness mentioned above may be combined with any maximum thickness mentioned above to form a different preferred thickness range. The thickness required to attain a certain flexural modulus is also dependent on the metal chosen for the coating. Generally speaking the higher the tensile modulus of the metal, the less will be needed to achieve a given stiffness (flexural modulus) . Preferably the flexural modulus of the uncoated OP composition is greater than about 200 MPa, more prefera- bly greater than about 500 MPa, and very preferably- greater than about 2.0 GPa.

Example 1

Zytel® 70G25, a nylon 6,6 product containing 25 weight percent chopped glass fiber available from E.I. DuPont de Nemours & Co., Inc. Wilmington, DE 19898 USA, was injection molded into bars whose central section was 10.0 mm wide and 4.0 mm thick. Before molding the polymer composition was dried at 80°C in a dehumidified dryer. Molding conditions were melt temperature 280-300⁰C and a mold temperature of 80⁰C. Some of the bars were etched using Addipost® PM847 etch, reported to be a blend of ethylene glycol and hydrochloric acid, and obtained from Rohm & Haas Chemicals Europe. Less than 1 μm of copper was then electrolessly deposited on the surface, followed by 8 μm of electrolytically deposited copper, followed by 100 μm of nickel, on all surfaces. The flexural modulus was then determined, as described above, on the uncoated and metal coated bars. The uncoated bars had a flexural modulus of 7.7 GPa, and the metal coated bars had a flex- ural modulus of 29.9 GPa.

Examples 2-7

Ingredients used, and their designations in the tables are: Filler 1 - A calcined, aminosilane coated, kaolin, Polarite^® 102A, available from Imerys Co., Paris, France .

Filler 2 - Calmote^® UF, a calcium carbonate available from Omya UK, Ltd., Derby DE21 6LY, UK.

Filler 3 - Nyad^® G, a wollastonite from Nyco Minerals, Willsboro, NY 12996, USA.

Filler 4 - M10-52 talc manufactured by Barretts Minerals, Inc., Dillon, MT, USA. Filler 5 - Translink^® 445, a treated kaolin available from BASF Corp., Florham Park, NJ 07932, USA.

GF 1 - Chopped (nominal length 3.2 mm) glass fiber, PPG^® 3660, available from PPG Industries, Pittsburgh, PA 15272, USA. GF 2 - Chopped (nominal length 3.2 mm) glass fiber, PPG^® 3540, available from PPG Industries, Pittsburgh, PA 15272, USA.

HSl - A thermal stabilizer containing 78% KI, 11% aluminum distearate, and 11% CuI (by weight) . HS2 - A thermal stabilizer contain 7 parts KI, 11 parts aluminum distearate, and 0.5 parts CuI (by weight) .

Lube - Licowax® PE 190 - a polyethylene wax used as a mold lubricant available from Clariant Corp. Charlotte, NC 28205, USA. Polymer A - Polyamide-6 , 6 , Zytel^® 101 available from E.I. DuPont de Nemours & Co., Inc. Wilmington, DE 19810, USA.

Polymer B - Polyamide-6, Durethan^® B29 available from Laxness AG, 51369 Leverkusen, Germany. Polymer C - An ethylene/propylene copolymer grafted with 3 weight percent maleic anhydride.

Polymer D - A copolyamide which is a copolymer of terephthalic acid, 1, 6-diaminohexane, and 2-methyl-l, 5- diaminopentane, in which each of the diamines is present in equimolar amounts.

Polymer E - Engage^®8180, an ethylene/1-octene copolymer available by Dow Chemical Co., Midland, MI, USA. Wax 1 - N, N' -ethylene bisstearamide Wax 2 - Licowax^® OP, available from Clariant Corp. Charlotte, NC 28205, USA.

The organic polymer compositions used in these examples are listed in Table 1. The compositions were made by melt blending of the ingredients in a 30 mm Werner & Pfleiderer 30 mm twin screw extruder.

Table 1

The test pieces, which were 7.62x12.70x0.30 cm plaques or ISO 527 test bars, 4 mm thick, gauge width 10 mm, were made by injection molding under the conditions given in Table 2. Before molding the polymer compositions were dried for 6-8 hr in dehumidified air under the temperatures indicated, and had a moisture content of <0.1% before molding. Table 2

These test specimens were then etched in sulfochro- mic acid or Rohm & Haas Chrome free etching solution, and rendered conductive on all surface by electroless deposition of a very thin layer of Ni. Subsequent galvanic deposition of 8 μm of Cu was followed by deposition of a 100 μm thick layer of fine grain N-Fe (55-45 weight) using a pulsed electric current, as described in US Patent 5,352,266 for making fine grain size metal coatings.

The samples were tested by one or both of the following methods:

ISO 6603-2 - Machine Instron^® Dynatup Model 8250, Support Ring 40 mm dia, Hemispherical Tup 20 mm dia, Velocity 2.2 m/s, Impacter weight 44.45 kg, Temperature 23°C, Condition dry as made. Test were run on the plaques described above .

ISO 179-leU - Sample Unnotched, Pendulum energy 25 J, Impact velocity 3.7 m/s, Temperature 23°C, Condition dry as made. Tests were run on the gauge part of the ISO 527 test bars described above.

Testing results are given in Table 3. Table 3

Claims

CLAIMS What is claimed is:

1. A vehicular axle or drive shaft, comprising, an organic polymer composition which is coated at least in part by a metal .

2. The vehicular axle or drive shaft as recited in claim 1 wherein said organic polymer, if a thermoplastic has a melting point and/or a glass transition point of about 150⁰C or more, or if a thermoset has a heat deflec- tion temperature of 150°C or more at a load of 0.455 MPa.

3. The vehicular axle or drive shaft as recited) in claim 1 or 2 wherein said axle or drive shaft is metal coated on the exterior and/or interior of said axle or drive shaft .

4. The vehicular axle or drive shaft as recited in any one of claims 1 to 3 wherein at least one layer of said metal coating has an average grain size of about 5 nm to about 200 nm.

5. The vehicular axle or drive shaft as recited in any one of claims 1 to 3 wherein a thickest layer of said metal coating has an average grain size of at least about 500 nm.

6. The vehicular axle or drive shaft as recited in any one of claims 1 to 5 wherein said metal coating is about 0.010 mm to about 10 mm thick.

7. The vehicular axle or drive shaft as recited in any one of claims 1 to 5 wherein said metal coating is about 0.025 mm to about 10 mm thick.

8. A vehicle, comprising, an axle or drive shaft of any one of claims 1 to 7.