CA1116650A - Corrosion resistant emi shielding gasket - Google Patents

Corrosion resistant emi shielding gasket

Info

Publication number
CA1116650A
CA1116650A CA 305874 CA305874A CA1116650A CA 1116650 A CA1116650 A CA 1116650A CA 305874 CA305874 CA 305874 CA 305874 A CA305874 A CA 305874A CA 1116650 A CA1116650 A CA 1116650A
Authority
CA
Grant status
Grant
Patent type
Prior art keywords
gasket
shell
particles
core
rubber
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA 305874
Other languages
French (fr)
Inventor
Robert F. Jasse
John F. Broderick
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Chomerics Inc
Original Assignee
Chomerics Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Grant date

Links

Classifications

    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01PWAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00Auxiliary devices
    • H01P1/04Fixed joints
    • H01P1/042Hollow waveguide joints
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K9/00Screening of apparatus or components against electric or magnetic fields
    • H05K9/0007Casings
    • H05K9/0015Gaskets or seals

Abstract

Abstract of the Disclosure Form stable gasket providing corrosion resistance, the gasket comprising a core of a plastic matrix binder and electrically conductive metal particles, the particles being homogeneously dispersed therethrough in an amount sufficient to provide electromagnetic energy shielding, and an outer electrically non-conductive insulator shell of the thickness of a film encapsulating the core, said shell being penetrable by said particles when said gasket is squeezed between the two waveguide flanges or other sur-faces in order to make electrical contact therewith.

Description

1~16~

EMI (ELECTROMAGNETIC ENERGY) gaskets such as shown in U.S. Patent 3,140,342, are now conventionally used in radar, communications equipment and guidance system applications to prevent the escape of or exclude the entry of electromagnetic energy. While gaskets of the type shown in Patent 3,140,342, in use to date, essentially prevent corrosion of enclosures in environments such as salt spray, and rain, the military and manufacturers for the military have for a long time desired an EMI gasket construction which would provide even greater assurance that in long term use corrosion of enclosures caused by exposed metal particles in the gasket coming into contact with salt water and the enclosure would be prevented.
The present invention provides a solution to the long felt need of the military and manufacturers for the military in that water is essentially prevented from coming into contact with the metal particles of the gasket.
The invention provides a form stable shielding gasket for use in preventing the escape of electromagnetic energy and preventing corrosion of exposed surfaces in contact therewith comprising a core of compressible plastic matrix binder having electrically conductive metal particles dis-persed therethrough in an amount sufficient to provide electromagnetic energy shielding and an insulator polymer shell completely encapsulating the entire core whereby no metal particles are exposed to the atmosphere absent sufficient compression of the gasket, said shell being penetratable by a sufficient number of particles in the direction of compression to cause the shell portion being compressed to become a conductor and act in the same manner as the core in providing electromagnetic energy shielding.

Brief Description of the Drawings Figure 1 illustrates in a sectional view an O
ring gasket of this invention in place to provide EMI shielding;
Figure 2 is a top plain view of an O ring gasket of this invention;
Figure 3 is a sectional view taken along lines 3-3 in Figure 2;
Figure 4 is the gasket of Figure 1-3 shown compressed;
Figure 5 is an enlarged view of a portion of the gasket in section showing the constructive particles penetrating the shell andmaking electrical contact with the flange;
Figure 6 is a plan view of a washer gasket o~ this invention;
Figure 7 is a sectional view taken along line 707; and Figure 8 is a plan view of a rectangular gaske~
of this invention.

Thus with this invention greater assurance of corrosion resis-tance is now possible. In addition to the foregoing, the present invention provides a gasket that can be constructed to withstand the deleterious effects caused by gasoline or other solvents which attach the polymer bind-er matrix portion of the gasket.
Detailed Description of the Invention This invention is directed to an EMI shielding gasket having a core of plastic matrix binder with electrically conductive metal particles homogeneously dispersed therethrough in an amount sufficient to provide EMI
shielding, and an outer electrically insulator shell of the thickness of a film encapsulating the core, said shell being penetrable by said particles, and extending to the outer surface thereof when the gasket is squeezed be-tween two surfaces e.g., the metal flanges of a waveguide to make electri-cal contact with said flanges.
The remainder of the shell which is not being compressed seals out water and other materials e.g., oils, gasoline, etc., that may deleter-iously effect the binder or metal particles.
Thus with this invention water, salt or other materials are essen-tially kept away from the metal in the gasket and corrosion is thus pre-vented. In addition, by suitably selecting the polymer used for forming the shell, materials such as gasoline and other solvents which may attack the plastic matrix binder or the particles themselves and are yet essentially sealed out.
With this invention the shell conforms to the shape of the gasket and may be formed by dipping the core one or more times in a liquid solu-tion containing the shell forming material and a solvent therefore. There-after the solvent is permitted to evaporate at room temperature.

5~1 When compressed, the particles penetrate the shell to provide a contact surface and yet are still surrounded in the hori~ontal plane by the shell. In this manner the particles are further protected in this invention.
As used herein "metal particles" include the noble metals such as silver, gold, as well as nickel, copper, silver coated copper, and other metals well known in the art, such as disclosed in U.S. Patent 3,140,342, 3,202,488, and 3,194,860. As used herein the phrase "metal particles" are also intended to include particles such as glass, silica, polymer or other non-conductive materials having an outer layer or coating of metal e.g., silver, gold or other noble metals or coated with an outer layer of non-noble metal such as nickel, copper, etc., or particles of conductive polymer (i.e., polymer having electrically conductive metal e.g., such as particles dispersed therethrough) all of which, for the purpose of this invention are also referred to as metal particles. The art sometimes refers to electrically conductive metal particles as conductive powder and it is intended that particles used herein include conductive powders.
In general the core of this invention will contain about 10 to 80 volume per cent of electrically conductive particles although the amount of particles will depend upon the particular application and the amount of other fillers e.g., foam rubber, silica, etc., as well known in the art (see U.S.
Patents 3,140,342 and 3,583,930).
Preferably the loading of particles for a good general purpose EMI
gasket will be this amount, about 25 to 40% of silver coated copper being most preferred.

Since this invention does not revolve around the precise volume percent of the particles present and is a matter of choice depending upon the circum-stances, it is intended that this invention can cover all EMI gaskets as long as they contain sufficient electrically conductive metal particles to make the binder in which they are homogeneously dispersed sufficiently elec-trically conductive to provide suitable EMI shielding.
In general to provide good EMI shielding, i.e., the central binder core with particles should have a volume resistivity of less than 10 ohm centimeters, and preferably less than 1 ohm centimeter.
In this invention the particles are irregularly shaped, or are of other shapes, such as flakes or plates and generally spherically shaped par-ticles. Suitable average maximum dimensional sizes for the particles may be between 100 mils to 0.05 mils as set forth in United States Patent 3,140,342, and most preferably have an average dimension of 1 to 3 mils.
The insulator film forming the shell of this invention is prefer-ably of a thickness of about .1 to 2 mil with .2 to .5 mils being most pre-ferred. The films forming the shell of this invention may preferably com-prise insulator plastics of a combination of plastic such as silicone poly-mers, e.g., silicone rubber, fluorosilicone rubber, urethane polymers, vinyl polymers, e.g., vinyl chloride polymers, acrylate polymers, ethylene poly-mers, propylene polymers, neoprene, ethyl propylene rubber and a host of others, sufficiently soft in comparison with the hardness of the particles to be penetrable thereby.
Other suitable plastics may be selected from those set forth in the book entitled Plastics In The Modern World authored by E. G. Couyens and V. E. Yarsley, published by Penguin Books9 Inc. Baltimore, Maryland and copyright 1968 by the authors. In particular, certain polymers such as the thermo-softening (thermoplastic) plastics disclosed on pages 76 to 95 may be used or thermohardening ~thermosetting) plastics such QS the polyurethanes and epoxides may also conveniently be used.

;6~

In addition, because of their high temperature properties sili-cone polymers are most preferred for military applications and flurosilicone polymers are most preferred for use in environments in which gasoline or other solvents are liable to be present.
The matrix binder used in the gasket of this invention may be any of those conventionally used in the art, e.g., as shown in Patent No.
3,140,342. The plastic binder is preferably resilient and compressible and is most preferably an elastomer.
The matrix binder is also preferably of a hardness greater than the shell so that when the gasket is compressed the particles will penetrate through the thin shell.
The matrix binders which may be used are well known in the art, see United States Patent 3,140,342 with silicone polymers, e.g., rubber being the most preferred for its high temperature and elastomeric properties. How-ever, this invention does not preclude the use of thermoplastic polymers such as polyvinylchloride, polyethylene, polypropylene, polyamides or thermo-hardening plastics.
Accordingly, the term "plastic" as used herein is intended to in-clude resins and elastomers (rubber) besides the conventionally accepted plastics such as polyethylene and the epoxides. The plastic matrix and the shell of this invention can thus be thermosetting or thermoplastic, depend-ing upon the use to which the gasket is to be put, e.g., asphalts, poly-urethane, polyesters, acrylates, polyamides and natural rubber.
The term "matrix binder" means something holding or capable of holding embedded within another object to which it gives shape or form.
The gasket herein has a stable form or shape (termed form stable~
i.e., it substantially retains its shape until compressed when in use unlike an adhesive that is spreadable when taken out of a can or tube.
Reference should now be had to Figures 1 to 5 which illustrate an 0 ring gasket at 20 in place in a waveguide joint consisting of wave guide 16~i~5~

sections 30 and 31 ending in two flanges 30-1 and 31-1 held together in a manner to compress the gasket as shown by closure bolts 32.
Figure 3 illustrates the gasket section showing the core of binder and metal particles 20-1 having an outer shell 20-2. Figures 1 and 4 illus-trate the shape of this gasket after squeezing with the portions 20-2a thereof serving as the electrical contacts to these flanges.
Figure 5 illustrates a view of the 20-2a portion showing particles 22 in both the core binder 20-1 and penetrating into the shell portion 20-2a to electrically contact flange 31-1 when the gasket is compressed. Figures 6, 7 and 8 show other gasket configurations and Figure 7 shows in section the central core 35 surrounded by ~he non-conductive shell 36.
The gaskets when uncompressed exhibit a resistance greater than 1000000 ohms between opposite points, e.g., 37 and 38 in Figure 2. When the gasket is compressed as in Figure 4 points 39 and 40 would be less than 10 ohms and in most cases less than .3 ohms if the ID of the 0 ring was 2"
and the diameter of the 0 ring section was 125 mils.
The core, e.g., 20-1 of this invention has a volume resistivity less than 10 ohms centimeters and preferably less than 1 ohm centimeter.
The following examples illustrate the invention.
EXAMPLE l A molded electrically conductive core in the shape of an "0" ring with a 1/8" diameter cross sectional rim and a 2" internal diameter was made using 80% by weight of silver coated copper powder prepared as disclosed in Example 1 of United States Patent No. 3,140,342 and 20% by weight of Dow Corning 440 silicone rubber. The material was molded as is taught in United States Patent No. 3,140,342 (Figure 2) and cured to form an "0" ring. A
shell forming mixture comprising 100 grams Dow Corning 9605 (1 part RTV*
silicone rubber) and 75 grams toluene was prepared. The molded "0" ring was washed with toluene and dried at room temperature (68 - 72F). The washed "0" ring core was then immersed in the shell forming mixture for 15 seconds *room temperature vulcanizing _ 7 -and then removed and left suspended so that an excessive coating would flow to the lowest point of the gasket. After coating the flow stopped and a smooth and even coating remained on the gasket surface. The shell formed on the core was permitted to cure for 16 hours at room temperature.
EXAMPLE II
The conductive core was prepared as in Example I and then washed as in Example I. A shell forming mixture was prepared from Dow Corning A
4000 (Part A and B) silicone rubber as follows:
Part A 100 grams Part B 4.5 grams toluene solvent 90 grams Thereafter the core was immersed in the mixture for 15 seconds and then sus-pended to dry as in Example I.
EXAMPLE III
.
The conductive core was prepared as in Example I and then washed as in Example I. A shell forming mixture was prepared from 100 grams of flurosilcone rubber RTV Dow Corning 94034 and 160 grams of methylisobutyl ketone (MIBK). Thereafter the core was immersed in the mixture for 15 sec-onds and then suspended to dry as in Example I.
EXAMPLE IV
No. 1250 extruded 0 ring strips, round strips (15 feet with 62 mil diameter) sold by Chomerics, Inc., Woburn, Massachusetts, was singly coated with the shell forming mixture of Example I as taught therein after being washed with toluene. No. 1250 O ring is silicone rubber filled with silver powder.
EXAMPLE V
No. 1250 stock as in Example IV was double coated with the shell forming mixtures of Examples II and III by immersing and then drying and then repeating the process of immersing and drying a second time.

65~

EXAMPLE VI - VII
A CHO-SEAL (R) rectangular gas~et #1215 silicone rubber and silver coated copper sold by Chomerics, Inc. was single coated with the shell form-ing mixtures of Examples I, II and III as set forth therein.
While particular embodiments of the present invention have been described~ they are intended to be exemplary only, with the true scope and spirit of the invention being indicated in the following claims.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A form stable shielding gasket for use in preventing the escape of electromagnetic energy and preventing corrosion of exposed surfaces in contact therewith comprising a core of compressible plastic matrix binder having electrically conductive metal particles dispersed therethrough in an amount sufficient to provide electromagnetic energy shielding and an insulator polymer shell completely encapsulating the entire core whereby no metal particles are exposed to the atmosphere absent sufficient compres-sion of the gasket, said shell being penetratable by a sufficient number of particles in the direction of compression to cause the shell portion being compressed to become a conductor and act in the same manner as the core in providing electromagnetic energy shielding.
2. The gasket of claim 1 in which the resistance between two points on the shell opposite to each other is greater than 1,000,000 ohms when the gasket is uncompressed.
3. The gasket of claim 1 in which the resistance between opposite points on the shell which are compressed towards each other sufficiently to cause the particles under said points to penetrate the shell is less than 10 ohms.
4. The gasket of claim 1 in which the shell is rubber.
5. The gasket of claim 1 in which the shell is .1 to .5 mils thick.
6. The gasket of claim 1 in which the particles are silver, gold, silver coated copper, silver coated glass, or nickel.
7. The gasket of claim 6 in which the binder is silicone rubber and the shell is silicone rubber.
8. The gasket of claim 6 in which the binder is silicone rubber and the shell is flurosilicone rubber.
9. The gasket of claim 6 in which the volume per cent of particles is 10 to 80 volume per cent and the particles have an average maximum dimension of .5 to 10 mils.
10. The gasket of claim 9 in which the binder is silicon rubber and the shell is .1 to 1 mil thick and is silicone rubber or flurosilicone rubber.
CA 305874 1977-06-30 1978-06-20 Corrosion resistant emi shielding gasket Expired CA1116650A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US81189077 true 1977-06-30 1977-06-30
US811,890 1977-06-30

Publications (1)

Publication Number Publication Date
CA1116650A true CA1116650A (en) 1982-01-19

Family

ID=25207869

Family Applications (1)

Application Number Title Priority Date Filing Date
CA 305874 Expired CA1116650A (en) 1977-06-30 1978-06-20 Corrosion resistant emi shielding gasket

Country Status (5)

Country Link
JP (1) JPS54116056A (en)
CA (1) CA1116650A (en)
DE (1) DE2827676A1 (en)
FR (1) FR2396388A1 (en)
GB (1) GB1600710A (en)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0399028A1 (en) * 1988-11-10 1990-11-28 Vanguard Products Corporation Dual elastomer gasket shield for electronic equipment
US5068493A (en) * 1988-11-10 1991-11-26 Vanguard Products Corporation Dual elastomer gasket shield for electronic equipment
US5107070A (en) * 1988-11-10 1992-04-21 Vanguard Products Corporation Dual elastomer gasket for protection against magnetic interference
US5141770A (en) * 1988-11-10 1992-08-25 Vanguard Products Corporation Method of making dual elastomer gasket shield for electromagnetic shielding
US5641438A (en) * 1995-01-24 1997-06-24 Bunyan; Michael H. Method for forming an EMI shielding gasket
US5910524A (en) * 1995-01-20 1999-06-08 Parker-Hannifin Corporation Corrosion-resistant, form-in-place EMI shielding gasket
US6096413A (en) * 1993-09-10 2000-08-01 Chomerics, Inc. Form-in-place EMI gaskets
US6303180B1 (en) 1993-09-10 2001-10-16 Parker-Hannifin Corporation Form-in-place EMI gaskets
US6410846B1 (en) 1998-12-15 2002-06-25 Vanguard Products Corporation Electromagnetic interference shielding device
US6613976B1 (en) 1998-12-15 2003-09-02 Vanguard Products Corporation Electromagnetic interference shielding gasket
US6635354B2 (en) 1995-01-20 2003-10-21 Parker-Hannifin Corporation Form-in place EMI gaskets
US6784363B2 (en) 2001-10-02 2004-08-31 Parker-Hannifin Corporation EMI shielding gasket construction

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* Cited by examiner, † Cited by third party
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JPS5826381B2 (en) * 1979-04-28 1983-06-02 Shinetsu Polymer Co
DE3024888A1 (en) * 1980-07-01 1982-02-04 Bayer Ag Composite material for shielding electromagnetic radiation
FR2488054B1 (en) * 1980-07-29 1984-06-15 Ducros Emile
US4434541A (en) * 1980-12-22 1984-03-06 Chomerics, Inc. Electromagnetic shielding
DE3101519C2 (en) * 1981-01-19 1986-07-10 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt, De
FR2509949B1 (en) * 1981-07-15 1984-10-26 Aerospatiale
US4508640A (en) * 1981-11-24 1985-04-02 Showa Denko Kabushiki Kaisha Electromagnetic wave-shielding materials
EP0110548B1 (en) * 1982-10-29 1987-06-24 Plessey Overseas Limited Conductive gaskets
US4539433A (en) * 1982-11-24 1985-09-03 Tdk Corporation Electromagnetic shield
FR2537786B1 (en) * 1982-12-14 1990-01-12 Caplatex Sa Electrically conductive joint, in particular for electromagnetic shielding and method for manufacturing such a seal
JPS61149399U (en) * 1985-03-07 1986-09-16
JPS61195096U (en) * 1985-05-27 1986-12-04
JPS63174496U (en) * 1987-01-21 1988-11-11
US4932673A (en) * 1988-02-01 1990-06-12 Hughes Aircraft Company Emi suppression gasket for millimeter waveguides
US5045635A (en) * 1989-06-16 1991-09-03 Schlegel Corporation Conductive gasket with flame and abrasion resistant conductive coating
DE69019826D1 (en) * 1989-07-17 1995-07-06 Gore & Ass Sealing of metallized microporous polytetrafluoroethylene electromagnetic shielding.
JPH0748593B2 (en) * 1990-11-13 1995-05-24 北川工業株式会社 Method of manufacturing an electromagnetic wave shielding packing material
DE4345582B4 (en) * 1993-06-14 2005-01-13 Emi-Tec Elektronische Materialien Gmbh Dispensed, electrically-conductive, resilient plastic seal completing electromagnetic screening, comprises screening profile consisting of overlapping and adjacent strands
DE4319965C3 (en) 1993-06-14 2000-09-14 Emi Tec Elektronische Material A process for the production of a housing with electromagnetic screening
DE4340108C3 (en) * 1993-11-22 2003-08-14 Emi Tec Elektronische Material Shielding and process for its preparation
US6325391B1 (en) * 1998-11-12 2001-12-04 Rosemount Inc. PTFE window seal with EMI shielding
DE102011013458A1 (en) * 2011-03-09 2012-09-13 Valeo Systèmes d'Essuyage windshield wiper drive

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* Cited by examiner, † Cited by third party
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US2674644A (en) * 1952-01-22 1954-04-06 Metal Textile Corp Shielding and sealing gasket for electronic equipment
US2885459A (en) * 1955-11-02 1959-05-05 Pulsifer Verne Sealing and conducting gasket material
DE1214759B (en) * 1962-03-22 1966-04-21 Western Electric Co Thermocouple having at least one consisting of a bismuth-antimony alloy leg
US3194860A (en) * 1962-10-02 1965-07-13 John E Ehrreich Manufacture of reinforced conductive plastic gaskets
US3140342A (en) * 1963-07-05 1964-07-07 Chomerics Inc Electrical shielding and sealing gasket
US3303440A (en) * 1964-03-30 1967-02-07 Parker Hannifin Corp Radio frequency joints
US4065197A (en) * 1974-06-17 1977-12-27 Chomerics, Inc. Isolated paths connector
JPS5648952B2 (en) * 1975-01-31 1981-11-18
US3969572A (en) * 1975-03-05 1976-07-13 Ncr Corporation Electromagnetic interference shielding gasket for light-weight equipment enclosures

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5068493A (en) * 1988-11-10 1991-11-26 Vanguard Products Corporation Dual elastomer gasket shield for electronic equipment
US5107070A (en) * 1988-11-10 1992-04-21 Vanguard Products Corporation Dual elastomer gasket for protection against magnetic interference
US5141770A (en) * 1988-11-10 1992-08-25 Vanguard Products Corporation Method of making dual elastomer gasket shield for electromagnetic shielding
EP0399028B1 (en) * 1988-11-10 1998-02-18 Vanguard Products Corporation Dual elastomer gasket shield for electronic equipment
EP0399028A1 (en) * 1988-11-10 1990-11-28 Vanguard Products Corporation Dual elastomer gasket shield for electronic equipment
US6331349B1 (en) 1993-09-10 2001-12-18 Parker-Hannifin Corporation Form-in-place EMI gaskets
US6096413A (en) * 1993-09-10 2000-08-01 Chomerics, Inc. Form-in-place EMI gaskets
US6303180B1 (en) 1993-09-10 2001-10-16 Parker-Hannifin Corporation Form-in-place EMI gaskets
US6635354B2 (en) 1995-01-20 2003-10-21 Parker-Hannifin Corporation Form-in place EMI gaskets
US5910524A (en) * 1995-01-20 1999-06-08 Parker-Hannifin Corporation Corrosion-resistant, form-in-place EMI shielding gasket
US6056527A (en) * 1995-01-24 2000-05-02 Bunyan; Michael H. Apparatus for forming a gasket
US5641438A (en) * 1995-01-24 1997-06-24 Bunyan; Michael H. Method for forming an EMI shielding gasket
US6613976B1 (en) 1998-12-15 2003-09-02 Vanguard Products Corporation Electromagnetic interference shielding gasket
US6410846B1 (en) 1998-12-15 2002-06-25 Vanguard Products Corporation Electromagnetic interference shielding device
US6784363B2 (en) 2001-10-02 2004-08-31 Parker-Hannifin Corporation EMI shielding gasket construction

Also Published As

Publication number Publication date Type
JPS54116056A (en) 1979-09-10 application
CA1116650A1 (en) grant
DE2827676A1 (en) 1979-01-18 application
FR2396388A1 (en) 1979-01-26 application
GB1600710A (en) 1981-10-21 application

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