Compositions – Electrically conductive or emissive compositions – Elemental carbon containing
Reexamination Certificate
1998-06-12
2001-01-09
Kopec, Mark (Department: 1751)
Compositions
Electrically conductive or emissive compositions
Elemental carbon containing
C524S495000, C524S910000
Reexamination Certificate
active
06171523
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to electrically conductive resin blends and methods for preparing them. More particularly, it relates to the preparation of conductive blends which are ductile and have excellent paint adhesion.
Blends of polyphenylene ethers and polyamides are currently in wide use for the fabrication of such articles as exterior body parts for automobiles. Their use in such areas is particularly advantageous by reason of the combination of the excellent properties of polyphenylene ethers, which include temperature stability and impact resistance, with those of polyamides, which include solvent resistance. It is known that polyphenylene ether-polyamide blends containing more than a rather low minimum threshold proportion of polyamide are incompatible unless special compatibilization steps are taken, and therefore such blends are usually prepared with the addition of a suitable compatibilizing compound.
It is also well known that external automobile parts must be painted. In recent years, electrostatic powder coating methods of painting are becoming more widely used by reason of their convenience and environmental advantages, particularly minimization of volatile emissions. For powder coating to be successful, it is necessary for the resinous article to have a relatively high surface electrical conductivity.
U.S. Pat. No. 5,484,838 describes a method of increasing thermal conductivity by incorporating electrically conductive carbon black into a polymer blend. Similarly, Japanese Kokai 2/201,811 describes the incorporation of conductive carbon black into polyphenylene ether-polyamide compositions, and more particularly into the polyamide continuous phase thereof. A further constituent of such polyphenylene ether-polyamide compositions is usually an impact modifier, most often a block copolymer of styrene and a diene such as butadiene or isoprene which block copolymer may be subsequently hydrogenated. As described, the conductive compositions are prepared by first blending the carbon black with the polyamide and subsequently introducing the polyphenylene ether, impact modifier and compatibilizer, optionally in combination with polystyrene.
In another known method for producing conductive blends, the initial step combines the polyphenylene ether, compatibilizer and impact modifiers and the polyamide and carbon black are then individually added, typically at successive downstream addition ports in an extruder. This method has the advantage that formation of the compatibilized polyphenylene ether-polyamide blend precedes addition of the carbon black, improving blend morphology.
It has been discovered, however, that such blends are frequently characterized by low ductility; i.e., they are brittle. Moreover, adhesion of electrostatically deposited paints to such blends is erratic. It appears that there are chemical differences between the paints employed in Europe, for example, and those employed in the United States in that the former but not the latter have uniformly high adhesion to the surface of the resin blend.
It is of interest, therefore, to provide electrically conductive polyphenylene ether-polyamide blends with improved ductility and improved adhesion to a wide variety of electrostatically applied paints.
SUMMARY OF THE INVENTION
The present invention provides conductive resin blends and a method for making them. Said resin blends have the desired high ductility and excellent adhesion to diverse types of electrostatic powder coatings, including those employed in many regions of the world. They may be prepared in a single pass through a melt blending apparatus such as an extruder.
In one of its aspects, the invention is a method for preparing a conductive resinous composition which comprises:
I. melt blending, to form a first resin blend:
(A) a polyphenylene ether resin;
(B) at least one impact modifying polymer comprising at least 40% by weight of ethylenically unsaturated structural units; and
(C) an effective proportion of a non-polymeric functionalizing compound capable of reacting in the melt with polyphenylene ethers and polyamides; and
II. melt blending said first resin blend with
(D) a polyamide composition comprising (i) at least 20% by weight of at least one polyamide consisting essentially of structural units of the formula
—NH—R
1
—CO— (I)
with any balance being (ii) at least one polyamide consisting essentially of structural units of the formula
—NH—R
2
—NH—CO—R
3
—CO—, (II)
wherein each of R
1-3
is an alkylene radical, said polyamide introduced in this step being in particulate form; and
(E) an effective proportion of conductive carbon black having a volatiles content less than 1.0% by weight;
to form a final resin blend comprising polyamide as a continuous phase and polyphenylene ether, impact modifying polymer and carbon black as one or more dispersed phases, said final resin blend having a bulk electrical resistivity of at most 200 KOhm-cm and, in the falling dart impact test, a total energy at 23° C. of at least 48 joules and a failure mode other than fully brittle; the weight ratio of reagent D to the combination of reagents A, B and C in said final resin blend being at least about 0.75.
Another aspect of the invention is conductive polyphenylene ether-polyamide compositions prepared by the above-described method.
DETAILED DESCRIPTION; PREFERRED EMBODIMENTS
The polyphenylene ethers employed as reagent A according to the present invention (the term “reagent” being employed herein without regard to whether a chemical reaction involving said material actually occurs) are known polymers comprising a plurality of structural units of the formula
wherein in each of said units independently, each Q
1
is independently halogen, primary or secondary lower alkyl (i.e., alkyl containing up to 7 carbon atoms), phenyl, haloalkyl, aminoalkyl, hydrocarbonoxy, or halohydrocarbonoxy wherein at least two carbon atoms separate the halogen and oxygen atoms; and each Q
2
is independently hydrogen, halogen, primary or secondary lower alkyl, phenyl, haloalkyl, hydrocarbonoxy or halohydrocarbonoxy as defined for Q
1
. Most often, each Q
1
is alkyl or phenyl, especially C
1-4
alkyl, and each Q
2
is hydrogen.
Both homopolymer and copolymer polyphenylene ethers are included. The preferred homopolymers are those containing 2,6-dimethyl-1,4-phenylene ether units. Suitable copolymers include random copolymers containing such units in combination with (for example) 2,3,6-trimethyl-1,4-phenylene ether units. Also included are polyphenylene ethers containing moieties prepared by grafting onto the polyphenylene ether in known manner such materials as vinyl monomers or polymers such as polystyrenes and elastomers, as well as coupled polyphenylene ethers in which coupling agents such as low molecular weight polycarbonates, quinones, heterocycles and formals undergo reaction in known manner with the hydroxy groups of two polyphenylene ether chains to produce a higher molecular weight polymer, provided a substantial proportion of free OH groups remains.
The polyphenylene ether has an intrinsic viscosity greater than about 0.25, most often in the range of about 0.25-0.6 and especially 0.4-0.6 dl/g, as measured in chloroform at 25° C.
The polyphenylene ethers are typically prepared by the oxidative coupling of at least one monohydroxyaromatic compound such as 2,6-xylenol or 2,3,6-trimethylphenol. Catalyst systems are generally employed for such coupling; they typically contain at least one heavy metal compound such as a copper, manganese or cobalt compound, usually in combination with various other materials.
Particularly useful polyphenylene ethers for many purposes are those which comprise molecules having at least one aminoalkyl-containing end group. The aminoalkyl radical is typically located in an ortho position to the hydroxy group. Products containing such end groups may be obtained by incorporating an appropriate primary or secondary monoamine such as di-n-butylamine or dimethylamine as one of the constituents of the ox
Giammattei Mark
Haaf William R.
Hossan Robert
Richards William D.
Silvi Norberto
General Electric Company
Kopec Mark
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