Product with antistatic properties

Details Product with antistatic properties Product with antistatic properties

1999-11-17

2001-11-13

Cain, Edward J. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S495000

Reexamination Certificate

active

06316537

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a product provided with antistatic properties.
2. Description of the Background
Appropriate thermoplastics are increasingly replacing metal as a material in piping systems which transport combustible fluids, e.g. motor fuel piping systems for vehicles or aircraft, or supply piping in gas stations. This results in savings in weight and in production costs, but in turn gives rise to the disadvantage that electrostatic charges can arise.
Under certain conditions the electrostatic charge created by the flow of motor fuel or solvent can discharge extremely rapidly and produce holes in the pipeline wall, through which the motor fuel or, respectively, the solvent can escape. On contact with hot components in the vicinity, or if sparks are generated, motor fuel or solvent can ignite and cause a fire in the vehicle or installation. In partly filled tanks where the motor fuel can move around freely, the electrical charge can also cause explosion of ignitable mixtures within these.
It is known that this problem can be avoided by providing the components of the piping system with antistatic properties. For example, DE 40 25 301 C1 describes antistatic motor fuel piping for motor vehicles which is composed of at least two different layers of polymer. At least one of the layers has been modified with electrically conducting additives, such as conductivity black. Although the motor fuel piping is described in that text as peroxide-resistant, it has become apparent that this applies only to layers which do not comprise the carbon black. The test conditions used take no account of the damage to the relatively thin layer provided with antistatic properties. It has now also been found that the conductivity blacks used hitherto have a disadvantageous catalytic action. Pipes provided with these and having two or more layers show serious deterioration in low-temperature impact strength even after a relatively short time on storage in peroxide-containing motor fuels (sour gas), e.g. to the Ford specification FLTM AZ 105-01, PN180 or the GM specification GM213M, PN50. Another problem which has been found is that the ageing of pipes of this type having two or more layers is markedly more rapid on exposure to heat, e.g. in the engine compartment, with attendant embrittlement.
EP-A-0 730 115 is based upon the recognition that the resistance to peroxide-containing motor fuels of pipes having two or more layers and provided with antistatic properties is improved by using no conductivity black, and using graphite fibrils in its place. However, in practice this improvement is insufficient in many cases. In addition, ageing on exposure to heat continues here to be at a level inappropriately high for practical purposes. A further factor is that graphite fibrils are very expensive.
EP-A-0 745 763 describes a motor fuel filter made from plastic. Its casing is composed of at least three layers, and the inner and the outer layer are composed of a plastic provided with conductive properties. Electrically conducting additives mentioned are, inter alia, conductivity black and graphite fibrils. This motor fuel filter suffers from the disadvantages discussed above.
The object was therefore to produce products provided with antistatic properties and having both high resistance to peroxide-containing motor fuels or solvents and low susceptibility to heat-ageing.
SUMMARY OF THE INVENTION
This object was achieved by means of a product made from plastic and composed, at least in part, of a thermoplastic molding composition which comprises polyamide and comprises from 3 to 30% by weight, preferably from 10 to 25% by weight and particularly preferably from 16 to 20% by weight, of a conductivity black, wherein the conductivity black is defined by the following parameters:
a) Dibutyl phthalate (DBP) absorption to ASTM D2414 of from 100 to 300 ml/100 g, preferably from 140 to 270 ml/100 g;
b) a specific surface area, measured via nitrogen absorption to ASTM D3037, of from 30 to 180 m
2
/g, preferably from 40 to 140 m
2
/g;
c) an ash content to ASTM D1506 of less than 0.1%. by weight, preferably below 0.06% by weight, particularly preferably below 0.04% by weight, and
d) a grit content of not more than 25 ppm, preferably not more than 15 ppm and particularly preferably not more than 10 ppm.
For the purposes of the present invention, grit is hard coke-like particles which arise as a result of cracking reactions in the preparation process.
DETAILED DESCRIPTION OF THE INVENTION
Two embodiments of this invention are possible:
1. The product made from plastic is entirely composed of this molding composition, i.e. it has a one-layer structure.
2. The product made from plastic is composed of at least two layers, where at least one layer is composed of the molding composition used according to the invention and the other layers are composed of another molding composition which has not been rendered antistatic. For example, the article is composed of 2, 3, 4, 5, 6 or even more layers. If the product made from plastic is hollow, the antistatic layer may be an outer layer or have its location in the middle. However, it is usefully the innermost layer.
In the case of a hollow product made from plastic, e.g. a pipe, the antistatic layer may also preferably cover the entire extent of the hollow article. However, it may also cover just a relatively small part of this extent, and so may be executed in the form of a straight or spiral band.
A function of the non-antistatic layers is to give the product the required functional properties, such as strength, impact strength, flexibility or barrier action with respect to motor fuel components. Except in specialized designs, the individual layers here should adhere firmly to one another, and this can be brought about using an adhesion promoter if the layers are not mutually compatible.
Suitable materials and configurations of layers for systems conveying motor fuels can be found, for example, in DE-A 40 25 301, 41 12 662, 41 12 668, 41 37 430, 41 37 431, 41 37 434 , 42 07 125, 42 14 383, 42 15 608, 42 15 609, 42 40 658, 43 02 628, 43 10 884, 43 26 130, 43 36 289, 43 36 290, 43 36 291, 44 10 148, 44 18 006, 195 07 026, 196 41 946, and also WO-A-93/21466, Wo-A-93/25835, WO-A-94/09302, WO-A-94/09303, WO-A-95/27866, WO-A-95/30105, EP-A-0 198 728, EP-A-0 558 373 and EP-A-0 730 115. In the case of the hollow profiles or hollow articles disclosed in these texts, one of the layers may have been provided according to the invention with antistatic properties, or an additional antistatic layer is added.
The molding composition provided with antistatic properties may comprise at least 10% by weight, preferably at least 40% by weight and particularly preferably at least 70% by weight, of any desired polyamide. The other layers are composed, for example, of a polyamide molding composition, of a polyolefin molding composition, or of a rubber, or, in the case of a barrier layer for motor fuel constituents or solvents as in the prior art of a molding composition based on thermoplastic polyester, polyvinylidene fluoride (PVDF), ETFE or THV, or of polyolefins, or ethylene-vinyl alcohol copolymer (EVOH). For suitable embodiments reference should be made to the abovementioned patent applications.
Possible polyamides here are primarily aliphatic homo and copolyamides. Examples which may be mentioned are nylon−4, 6, −6, 6, −6, 12, −8, 10 and −10, 10 and the like. Preference number is given to nylon−6, −10, 12, −11, −12 and −12, 12. [The polyamides are identified as in the international standard, where the first number(s) give(s) the number of carbon atoms in the starting diamene and the final number(s) give(s) the number of carbon atoms in the dicarboxylic acid. If only one number is given, this means that the starting material was an &agr;, &ohgr;-aminocarboxylic acid or the lactam derived therefrom—H. Domininghaus, Die Kunststoffe und ihre Eigenschaften [Plastics an

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