AU574690B2

AU574690B2 - Contact stabilization coating of electrical contact surfaces

Info

Publication number: AU574690B2
Application number: AU30141/84A
Authority: AU
Inventors: William Michael Dayton Wright
Original assignee: D W Electrochemicals Ltd
Current assignee: D W Electrochemicals Ltd
Priority date: 1983-05-30
Filing date: 1984-05-23
Publication date: 1988-07-14
Anticipated expiration: 2004-05-23
Also published as: EP0144399A1; WO1984004848A1; AU3014184A; CA1217892A; JPS60501482A

Description

CONTACT STABILIZATION COATING MATERIAL FOR ELECTRICAL

CONTACT SURFACES

This invention relates to contact stabilization materials; that is, materials that are used to stabilize or enhance current flow characteristics between contacting surfaces for electrical contact purpoces.

BACKGROUND OF THE INVENTION

In any electrical contact, the actual contacting surfaces are not perfectly smooth or continuously planar. Indeed, such contacting surfaces, if magnified sufficiently, may have the general appearance of a lunar landscape, or even that of a mountain range. In other words, the contacting surfaces, themselves, may be very rough, having a number of peaks and a number of pits or valleys. The actual electrical transmission — i.e., the transmission of electrical current from one contact surface to the other — therefore occurs only at those places where there is real physical contact between the material of the one surface and the material of the other surface.

Such electrical contacting surfaces, in general, where the contact stabilization material of the present invention is particularly useful, are those that may be used in circumstances where relatively high current

OMFI _ transfers between the contacting surfaces — relatively high being several milliamperes up to several amperes or more — as well as micropower installations where extremely low currents are expected to pass between contacting surfaces.

For example, high current applications may include plug-in communications and stand by power applications such as may be used by ground surface personnel when working with and communicating to personnel on board commercial jet aircraft and the like. Low power and micropower applications include low level video, radio frequency, audio frequency and computer circuitry and connections therefore.

In any electrical contact situation, between contacting surfaces, there may be surface resistance due to oxidized metal or other foreign materials, and if there is any varnish present, there may be sufficiently higher resistance that virtual insulation between the contacting surfaces may occur under certain conditions.

For example, in high current applications, there may be heating deformation due to resistance of the materials of the contacting surfaces, or due to the presence of surface resistance material, such that there is a possibility of chemical reaction that may take place due to the heat. Moreover, if there is a

OMPI further material present, such as previous materials that have been attempted to be used for the same purposes as the material of the present invention, there may be a chemical reaction between the contact 5 metal and a trapped gas film that may have developed due to the heat, and either the gas film or the chemical reaction may further cause anomalous behaviour of the near-contact boundry in the contact region.

In such micropower current applications as low "^•-¹ current or power level video cable connectors, radio frequency or audio frequency connectors, or cable connectors between computer components or peripheral components, there may be occasions when there is not a sufficient signal power available to ensure that there -^■-* is a reliable maintenance of signal flow. Where the signals involved are alternating complex waveform signals, such as audio signals from a cartridge, reading head or laser head, the current flow may be momentarily interrupted at zero-crossing conditions — 0 that is, where the voltage potential between the contact surfaces changes from a directed positive to a directed negative potential, or vice versa — and the current flow may only be re-established after there has been sufficient voltage rise to breakdown the potential 5 gap between the surfaces or of the material between the surfaces. In radio frequency circuitry, this discontinuous - behaviour at zero-crossing, may lead to line reflections that may add artifacts to the signal. For example, with video signals, the zero-crossing discontinuity that may occur between contacting surfaces may show up as video ghosts or as imperfect chroma demodulation, due to apparent noise.

In computer circuitry, zero-crossing or other contact-induced signal or data artifacts may appear as increased noise, and in certain circumstances there may be rectification artifacts — particularly in binary data flow conditions — where program crashes, incorrect data transmission, or spurious parity or cyclic redundancy error conditions may occur. A prior attempt in the electrical industry, particularly in respect of micropower audio frequency applications as well radio frequency and computer data transmission applications, has been to use octadecyl alcohol-doped palm oil, or similar materials. It has been found, generally, that it is not possible or commercially feasible to attempt to obtain the substantially perfectly planar contacting surfaces that might otherwise be expected to be helpful, and therefore contact stabilization materials have appeared to be warranted at least in prior micropower circumstances.

O PI However, in any vulcanizable vegetable oil, such- as palm oil or otherwise, there is a propensity for the oils to cross-link during their use, particularly in the presence of metallic materials that could act as catalyst. This cross-linking amounts to the creation of a varnish, by which a virtual insulative property then occurrs. Thus, using such materials as octadecyl alcohol-doped palm oil, initial results where encouraging, but they then proved to be of no value if not of negative value due to the varnishing and consequent contact insulating characteristics that have developed.

There have been other materials developed that can exhibit both low resistance and high resistance, and which may be electrically activated so as to be switched from one of those resistance states to the other. Those materials are particularly referred to be United States Patent No. 4,359,414, issued November 16, 1982 in the name of MASTRANGELO et al.

CRITERIA FOR A SUITABLE CONTACT STABILIZATION MATERIAL

A contact stablization material, in order to be particularly effective, at micropower and higher power levels, and at frequencies ranging from DC to 500 mHz, must have the following properties, some of which may

ΪUREXj?

O PI s , IPO appear to be contradictive at first glance:

First, any effective contact stablization material must exhibit conductive effects when it is used between conductive surfaces such as metals, particularly as in metal-to-metal electrical contact applications.

However, the material should not exhibit conductive properties when it is applied to insulators, such as the insulating material between the outer conductive shell and the inner conductive stud or wire used in co-axial radio frequency and video connectors, or the insulating material between adjacent data terminal strips for computer connectors.

The contact stabilization material should be sufficiently liquid, or be capable of being carried in a liquid that is otherwise chemically inert, so that it may be readily and easily applied to the electrical contact surfaces. Alteratively, the material may be semi-liquid at room temperatures but liquid at higher working temperatures. Moreover, the contact stabilization material should have a sufficiently high surface tension that capillary action will cause the material to migrate between contacting electrical surfaces when they are connected together according to their usual application means, and at their working temperature.

At the same time, the contact stabilization

O PI material should have a sufficiently low vapour pressure _ so as to remain in place for the service life of the connector contact surfaces, even when the material is spread in very thin film thicknesses. In contradistinction to the prior vulcanizable vegetable oils such as octadecyl alcohol-doped palm oil, a good contact stabilization material such as that which is contemplated by the present invention must ■ exhibit characteristics such that if the material catalyses or aids in any reaction within the material in the presenses of the metal of the contact surfaces, then the resultant catalysed or cross-linked material should also exhibit the same properties as those spoken herein. In other words, if cross linkage occurs or other reactions occur such that a cross-linked or longer molecule than exists, that cross-linked or longer molecule should be benign as to any adverse characteristics.

When any contact stabilization material is used, it should have sufficient detergent action so that any embedded or coated continant that may be present on any contact surface, should be lifted or washed or wiped away when the contact stabilization material is applied. At the same time, the contact stabilization material must be such that it does not degrade the _{n Λ lnΛOΛO} PC 84/04848

commonly used plastics or other structural or insulative materials that are used in electronic or electrical applications.

Likewise, the contact stabilization material

5 should be non-corrosive as to any metals that are used, either in the contact surfaces or otherwise where the stabilant material may come into physical contact or proximity with them.

For safety reasons, the contact stabilization -_0 material should have low toxicity.

Finally, the cost of the contact stabilization coating material for coating electrical contact surfaces should be sufficiently low that Its benefits are not more costly or expensive than the problems that

15 the use of the contact stabilant material eliminates.

DESCRIPTION OF CONTACT STABILANT MATERIALS ACCORDING TO THE PRESENT INVENTION

It has been learned that, particularly as

20 determined during tests of octadccyl alcohol-doped palm oil as a contact stabilization material, that apart from the question of "varnishing", there is also the problem that the use of a material having too low molecular weight appeared to result in a material that

25 was highly fugitive. This may also have been because the material had either too hiβh a vapour pressure, or

OMPI its viscosity was too low. Moreover, for any given amount of material used in a contact-to-contact situation, the lower molecular weight materials seemed to show a much greater propensity for cross-linking. This was probably because of the greater number of bond sites that existed, per molecule. The electrical environment in the contact situation appeared also to assist in generating the cross-linking reactions.

On the other hand, according to the present invention, contact stabilization coating materials for use with electrical contact surfaces, by coating the same, are provided that comprise co-polymers or block polymers of polyoxypropylene together wth polyoxyethylene, or a plurality of block polymers of polyoxypropylene together with polyoxyethylene. Such materials, especially when they have lower molecular weights, may be quite fluid and tend to "leak" or be runny. However, when cross-linking occurred, it- has been found that the longer molecular chains that then developed are still benign, and exhibit all the desired characteristics as discussed above.

Block polymers of polyoxypropylene together with polyoxyethylene, having molecular weights in the range of 1,000 to 3,000 were found to be most useful, and particularly those having a molecular weight in the range of 1,400 to 2,800. On the other hand, higher molecular weight block poylmers, which may have a semi-liquid or waxy appearance at room temperatures, are quite suitable for use with elevated temperature surfaces, and show the necessary capillary action at those te pertures. The physical properties of the material, therefore, can be altered as required; particularly as may be determined by the operating or ambient temperature of the contact surfaces.

The block polymers ^" are useful when the polyoxypropylene and polyoxyethylene were present in the range of 2% to 98%., by weight, of either of them, with the other component being present in the range of 98% to 2%, by weight; but more usually, each is present in the range of 20% to 80%, and vice-versa. The block polymers, when first produced, have a distinctly yellow colouration, but the colouration may disappear or become quite reduced, in time.

Moreover, the contact stabilization material of . the present invention may comprise a plurality of block polymers of polyoxypropylene together with polyoxyethylene.

It has been found, in keeping with the desirable characteristics as discussed above, that use of the contact stabilization material according to this invention, being a block polymer of polyoxypropylene and polyoxyethylene, or a plurality of block polymers, is such that the gaps between the surfaces of the _ contact surfaces act as if they were filled with a good electrical conductor; or in any event, that there is a discernible virtual conductivity between the contact surfaces, and therefore in the signal circuit.

Thus, discontinuity effects between surfaces are virtually eliminated, with zero-crossing distortion of complex signals being substantially non-existant. It has also been noted that, in radio frequency applications, where previously a signal strength loss of up to 6 dB may have occurred even in such contact situations as silver-to-silver BNC connectors, those signal strength drops have been eliminated.

Improvements in signal transmission from contact surface to contact surface in video applictions where easily discerned, due to the improvement in picture sharpness and colour accuracy. Improvements in audio frequency signal transmission has also been readily discerned, even to a relatively untrained ear. Still other tests, where contact stabilization materials according to the present invention where used on all edge card connectors and micro chip sockets in computer hardware, resulted in the virtual elimination of system crashes or other data transmission or cyclic redundancy error conditions occuring.

A study of the electrical operating conditions in electrical contact situations, using the contact - stabilization material of the present invention, suggests that the conductive mechanism is in the nature of a tunnel diode transmission effect. The film thickness effects exhibited by the contact stabilization material of the present invention are such that normal insulation gaps, however, as in co-axial connectors or computer edge card connectors, are not adversely affected. Frequency tests have been made, ranging from DC up to 500 mHz, and while there appeared to be some frequency dependency, various results were not consistent, and appeared in all events to be accounted for by variations in the connector/cable/test equipment performances.

No adverse affects have been encountered in field trials, where the contact stabilization material has been used in a variety of applications that duplicate normally commercial applications, even though a certain build up of dust has been observed on wetted and exposed surfaces of non-environmental protected connectors. In any event, no gross varnishing effects where noted; and while some cross-linkage was noted on a connector having pins that were made of a high-sulphur brass, the thicker or cross-linked material performed as a contact stabilization material

OMPI just as well as the original material without any apparent varnishing or insulation or resistance effects.

The contact stabilization materials of the present invention have been used in avionics applications, operating from minus 40 degrees C to plus 30 degrees C, without observable adverse effects.

Finally, the toxicity of block polymers of polyoxypropylene together with polyoxyethylene was tested, with the observation that the LD (50) level that is, the lethal dosage level for 50%. of the study group of white mice being tested — was about 5 grams per kilogram of body weight. That level, in fact, is about half of that for common hair shampoo. There has been described a contact stabilization material for coating electrical contacting surfaces, which has all . of the properties that have been described above as being desirable for such materials. Moreover, test results have been described as to the observations made — there being no generally meaningful quantitative results, except as noted showing the use of the contact stabilization materials of the present invention in a wide variety of frequency domains, power transmission situations, and environmental or ambient operating conditions. The scope of the present invention, however, is defined by the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. A contact stabilization material for coating electrical contact surfaces, comprising at least one block polymer of polyoxypropylene together with polyoxyethylene.

2. The material of claim 1, when a liquid.

3. The material of claim 1, comprising a plurality of block polymers of polyoxypropylene together with polyoxyethylene.

4. The material of claim 1, 2 or 3, having a molecular weight in the range of 1000 to 3000.

5. The material of claim 1, 2 or 3, having a molecular weight in the range of 1400 to 2800.

6. The material of claim 1, 2 or 3, when cross-linked.

7. The material of claim 1, 2 or 3, where one of said polyoxypropylene and polyoxyethylene is present in the range of 2% to 98% by weight, and the other of said polyoxypropylene and polyoxyethylene is present in the range of 98% to 2% by weight.

OMPI

8. The material of claim 1, 2 or 3, where one of said polyoxypropylene and polyoxyethylene is present in the range of 20% to 80% by weight, and the other of said polyoxypropylene and polyoxyethylene is present in the range of 80% to 20% by weight.

9. The material of claim 1, 2 or 3, having a surface tension sufficiently high that said material will migrate between nominally contacting electrical contact surfaces.

10. The material of claim 1, 2 or 3, having a sufficiently low vapour pressure that said material will not evaporate even when spread in very thin film thicknesses.

11. A contact stabilization material for coating electrical contact surfaces, containing at least one co-polymer or block polymer of polyoxypropylene together with polyoxyethylene, together with a chemically inert liquid carrier.

12. The material of claim 11, containing a plurality of block polymers of polyoxypropylene together with polyoxyethylene.

OMPI

13. The material of claim 11 or 12, where said liquid carrier is an alcohol.

14. The material of claim 11 or 12, where the molecular weight of any said block polymer is between 1000 and 3000.

15. The material of claim 11 or 12, where the molecular weight of any said block polymer is between 1400 and 2800.