Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.


  1. Advanced Patent Search
Publication numberUS2615857 A
Publication typeGrant
Publication dateOct 28, 1952
Filing dateDec 23, 1949
Priority dateDec 23, 1949
Publication numberUS 2615857 A, US 2615857A, US-A-2615857, US2615857 A, US2615857A
InventorsWalter J Clarke
Original AssigneeBell Telephone Labor Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Polyethylene-polyisobutylene composition
US 2615857 A
Previous page
Next page
Description  (OCR text may contain errors)

Oct. 28, 1952 w, CLARKE 2,615,857

POLYETHYLENE-POLYISOBUTYLENE COMPOSITION Filed Dec. 23, 1949 7 8 GEL POLYETHYLENE/N L/OU/D POLY/SOBUTYLENE //v l/EN TOR W J CLARKE A T TORNEV Patented Oct. 28, 1952 POLYETHYLENE-POLYISOBUTYLENE COMPOSITION Walter J. Clarke, Chatham, N. J assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 23, 1949, Serial No. 134,784


This invention relates to novel compositions useful for potting or embedding electrical apparatus.

The novel compositions of the present invention are particularly adapted to the potting of mechanically delicate and chemically sensitive apparatus such as germanium point contact rectifiers and transistors. Such point contact rectifiers or transistors may be made up of a body of germanium, or silicon, to which one or more electrical contacts are made by means of fine pointed wires, held frictionally, or otherwise, against the body. Since displacement of these wires on the surface of the body may result in defective or inoperative devices, it is necessary that some means be employed to prevent such displacement by the jarrin incident to manufacture and handling.

In order to protect these devices, it is common to embed the contact wires and at least the contact surface of the body in a suitable material which will lessen the chance of damage upon jarring. This is commonly accomplished by enclosing the device in hollow container and filling this container with the potting material.

There is a definite combination of properties which must be possessed by such a potting material. In view of the delicacy of the apparatus, the potting material must be capable of being reduced to a highly fluid state upon being heated to a moderately elevated temperature so that it can be poured into the container and caused to fill all the space in and around the device quickly and without the application of pressure. It must harden to a non-fluid state upon coolin to ordinary temperatures and must do so without setting up objectionable mechanical stresses which would tend to injure the device. It must be capable of withstanding the entire temperature range to which the device will be subjected in normal use, as from -40 C. to +85 C., without cracking, flowing or setting up undue mechanical stress. It must be as chemically inert as possible so that it will not exert a corrosive or otherwise degrading action upon the device. It must be chemically and physically stable throughout the life of the device. It must, moreover, not possess adverse electrical properties, such as excessive surface or volume current leakage due to electrolyte impurities.

The potting compounds of the present invention possess this requisite combination of properties to a greater degree than any material hitherto suggested for this purpose to applicants knowledge. These compounds are, at ordinary temperatures, gels of normally solid ethylene polymers (polyethylene) in a normally liquid butene polymer (polybutene, or particularly polyisobutylene) Since these potting compounds are true gels and, therefore, possess finite static shear strengths, they will not fiow except upon the exerting of a finite pressure, as contrasted with extremely viscous liquids which, although giving the appearance of rigidity, nevertheless have the zero static shear strength which is characteristic of liquids and, therefore, flow under infinitesimal pressure if given suflicient time.

These potting compounds may be contrasted with solids, on the other hand, in that they are soft and plastic and are, therefore, much more readily and permanently deformable under stress so that they do not set up undesirable mechanical strains and do not crack with temperature change.

Although these potting compounds are nonfiuid gels in the normal operating temperature range of the electrical apparatus, they are readily reduced to completely homogeneous liquids of sufficiently low viscosity to permit ready impregnation by heating to a moderately elevated temperature, such as slightly above C. When these homogeneous liquid solutions of polyethylene in polybutene are cooled to ordinary temperatures, the polyethylene becomes somewhat incompatible with the polybutene and small crystallite regions of polyethylene are formed throughout the body of liquid polybutene. The resultant intermolecular forces between the solid polyethylene and the liquid polybutene result in a non-fluid gel.

The components of the potting compounds of the present invention are stable hydrocarbons which are available commercially in a form in which they are free from electrolyte impurities and possess excellent electrical properties. They are chemically inert and, therefore, they exert no undesirable corrosive effect upon the electrical apparatus and they do not degrade even the sensitive germanium surface in germanium rectifiers. v i

Electrical apparatus embodying the potting compounds described above is shown in the accompanying drawing, which is a front elevation, partly in section, of a point contact rectifier.

In the apparatus shown in this drawing, a wafer l of rectifier material, such as germanium, is mounted upon and permanently fixed to an electrically conductive base 2 which is externally threaded. The base 2 is screwed into one end of an internally threaded container 3. Into the other end of the container 3 is screwed an externally threaded, electrically insulating sleeve 0. through the center of which passes an electrically conducting lead 5 on the end of which is mounted a pointed contact wire so situated that its pointed end makes electrical contact with the surface of the wafer i The space defined by the container 3 and the members closing each end is filled with the gel potting compound 7' described above. This potting compound is applied by heating it to a temperature sufficient to convert it to a homogeneous liquid and it is poured into the opening 3 until the space is filled. The compound is then allowed to cool and to gel to its non-fluid state.

Devices of this type have been subjected to three drops from a height of 60 inches at room temperature without injury and have also withstood iive cycles from 55 C. to +80 C. without injury.

A very suitable potting gel according to the present invention is made up of 7.5 per cent by weight of polyethylene having a molecular weight of about 12,000, as determined by the Staudinger method, 92 cent polyisobutylene having a molecular weight of about 3,000 and 0.5 per cent of an antioxidant, such as polymerized trimethyl dihydroquinoline. This composition is prepared by mixing the ingredients together at a tempera-- ture above the melting point of the polyethylene, such as 130 C. to 135 C., until a clear homogeneous mass is obtained.

Soft gels suitable for the present invention can be formed in similar manner from other low molecular weight polyethylenes having a molecular weight between 4,000 and 15,000 or preferably between 7,000 and 15,000. Any viscous liquid polybutene, as of molecular weight between 2,000 and 7,000, or preferably between 2,000 and 5,000, may be used. Particularly when the mixture is to be maintained at elevated temperatures in its state in contact with air, it is desirable that an antioxidant in suitable amount, as from 0.1 per cent to 1 per cent be added.

The gels of the present invention may be formed with widely varying proportions of polyethylene and polybutene. Preferably, the amount of polyethylene in the gel is between per cent and 35 per cent although gels of satisfactory properties may be produced when the amount of polyethylene is as high as 90 per cent, particularly when the lower molecular weight polyethylenes are used. The remainder of the composition, aside from the antioxidant, if any, is polybutene, as discussed above, and therefore the proportions of this ingredient vary preferably from 65 per cent to 95 per cent, although as little as 10 per cent may be present.

Examples of other of the gels of the present invention are one formed from 90 per cent of polyethylene of molecular weight of about 4,000 and 10 per cent of polyisobutylene of molecular weight of about 3,000, together with 0.5 per cent of antioxidant added to this'mixture, and one formed from 60 per cent of polyethylene of molecular weight of about 7,000 and 40 per cent of polyisobutylene of molecular weight of about 3,000, together with 0.5 per cent of antioxidant added to this mixture.

These gels have been described above as applied to the potting of point contact translating devices. Obviously, their advantageous properties as set forth above fit them for the potting of other electrical apparatus.

The invention has been described in terms of its specific embodiments and, since certain modifications and equivalents will be apparent to those skilled in the art, this description is intended to be illustrative of, and not to constitute a limitation upon, the scope of the invention.

What is claimed is:

1. A composition consisting essentially of a gel of between about 5 per cent and about 35 per cent of polyethylene having a molecular weight between about 4,000 and about 15,000 and the remainder a viscous, liquid polyisobutylene having a molecular weight between about 2,000 and about 7,000.

2. A composition as described in claim 1 wherein the composition contains an antioxidant.

3. A composition consisting essentially of about 7.5 per cent of polyethylene of molecular weight of about 12,000 and the remainder po1yisobuty1- one or" molecular weight of about 3,000.

4. A composition as described in claim 3 wherein the composition contains an antioxidant.

5. A composition as described in claim 4 wherein the antioxidant is 0.5 per cent of polymerized trimethyl dihydroquinoline.


REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,934,297 Eibner et al Nov. 7, 1933 1,980,483 Blackley Nov. 13, 1934 2,064,752 Ingram Dec. 15, 1936 2,129,722 Woodhouse Sept. 13, 1933 2,274,031 Bannon Feb. 24, 1942 2,339,958 Sparks Jan. 25, 1944 2,406,405 Salisbury Aug. 27, 1946 2,414,300 Hamilton Jan. 14, 1947 2,432,116 McLean et a1 Dec. 9, 1947 2,432,594 Thompson et al. Dec. 16, 1947 2,435,245 Strain Feb. 3, 1948 2,452,977 Kitchin Mar. 1, 1949 2,472,933 Brittain et a1 June 14, 1949 2,475,641 Rosenberg July 12, 1949 OTHER REFERENCES Hunter et al.: British Plastics, Mar. 1945, pages 94-96. 1

Rubber Age, Apr. 1946, page 72.

Plastics (of Chicago), Dec. 1948, pages 12 and 29.

Flory Jour. Am. Chem. Soc, vol. 65, Mar. 1943, pages 373-382.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1934297 *Dec 12, 1930Nov 7, 1933Consortium Elektrochem IndCompounds of polymerized vinyl esters and fatty oils
US1980483 *Nov 3, 1932Nov 13, 1934Ici LtdResin and resin forming compound
US2064752 *Mar 12, 1934Dec 15, 1936Monsanto ChemicalsPreservation of rubber
US2129722 *Jul 14, 1934Sep 13, 1938Du PontEsters of methacrylic acid
US2274031 *Feb 25, 1938Feb 24, 1942Standard Oil Dev CoInsulated electrical conductor
US2339958 *Sep 14, 1939Jan 25, 1944Jasco IncComposition of matter containing polyethylene and polyisobutylene
US2342116 *Jun 28, 1938Feb 22, 1944Int Cigar Mach CoVibrating feed for cigar machines
US2406405 *May 19, 1941Aug 27, 1946Sperry Gyroscope Co IncCoaxial condenser crystal and method of making same
US2414300 *Dec 28, 1943Jan 14, 1947Callenders Cable & Const CoElectrical insulating compounds
US2432594 *Aug 18, 1943Dec 16, 1947Union Switch & Signal CoRectifying detector for high-frequency alternating electric currents
US2435245 *Feb 5, 1944Feb 3, 1948Du PontStabilized polymers of ethylene
US2462977 *Mar 28, 1945Mar 1, 1949Western Union Telegraph CoCable joint
US2472938 *Mar 1, 1945Jun 14, 1949Gen Electric Co LtdPoint-contact rectifier
US2475641 *Oct 29, 1946Jul 12, 1949John Archer CarterPrompting system
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2697268 *Dec 30, 1950Dec 21, 1954Sylvania Electric ProdDiode fabricating apparatus
US2726357 *Oct 22, 1952Dec 6, 1955Columbia Broadcasting Syst IncSemiconductor device
US2768100 *Sep 30, 1953Oct 23, 1956Bell Telephone Labor IncSurface treatment of germanium circuit elements
US2785349 *Jun 7, 1952Mar 12, 1957Int Standard Electric CorpElectric semi-conducting devices
US2924584 *Jun 20, 1956Feb 9, 1960Du PontComposition comprising polyethylene and an ethylenically unsaturated aliphatic hydrocarbon of 20-35 carbon atoms and article thereof
US2993028 *May 26, 1958Jul 18, 1961Montedison SpaIsotactic polypropylene-polyisobutene blend and method for making same
US3132104 *Apr 7, 1959May 5, 1964Rockwell Mfg CoPlug valve lubricant and sealant compositions
US3283890 *Jun 22, 1964Nov 8, 1966United Shoe Machinery CorpThermoplastic adhesive rods or strips
US3484533 *Sep 29, 1966Dec 16, 1969Texas Instruments IncMethod for fabricating semiconductor package and resulting article of manufacture
US3526522 *Oct 18, 1967Sep 1, 1970Gillette CoInk follower composition and method therefor
US3656857 *Dec 2, 1969Apr 18, 1972Gillette CoA ball point pen ink reservoir containing an improved ink follower
US3964010 *Oct 8, 1974Jun 15, 1976Okazaki TasukuSimple, small-sized fuse
US4622344 *Mar 5, 1984Nov 11, 1986Bend Research, Inc.Recovery of ammoniacal copper with novel organogels
US4771534 *Nov 30, 1987Sep 20, 1988Mold-Masters LimitedMethod of manufacture of injection molding nozzle electrical terminal
US5232113 *Oct 11, 1991Aug 3, 1993Aluminum Company Of AmericaVenting resealable container closure and associated method of manufacture
US6028126 *Oct 7, 1998Feb 22, 2000Bic CorporationInk follower compositions
U.S. Classification524/87, 174/521, 257/E23.119, 29/855, 336/96, 438/126, 524/490, 257/E21.502, 525/240, 174/76, 148/33, 264/272.17, 524/585, 438/127
International ClassificationB29C70/84, C08L23/22, H01L23/16, B29C70/70, H01B3/22, H01G4/22, H01L29/00, H01L23/29, H01L21/56, C08L23/06, H01B3/18, H01G2/12
Cooperative ClassificationB29C70/84, H01G4/221, H01L23/16, B29C70/70, H01L21/56, B29K2023/06, C08L23/22, C08L23/06, H01L23/293, H01L29/00, H01B3/18, H01G2/12, B29L2031/3406, H01B3/22
European ClassificationH01L29/00, H01L23/16, C08L23/22, C08L23/06, B29C70/84, B29C70/70, H01B3/18, H01G2/12, H01L21/56, H01G4/22B, H01L23/29P, H01B3/22