Electrically conductive pressure sensitive adhesive tapes
US 3132204 A
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May 5, 1964 w. GIELLERUP 3,132,204
ELECTRICALLY CONDUCTIVE PRESSURE SENSITIVE ADHESIVE TAPES Filed July 27, 1962 INVENTOR.
i ,4rge vzy United States Patent 3 132,204 ELECTRICALLY C ONDUCTIVE PRESSURE SENSITIVE ADHESIVE TAPES Leon W. Giellerup, 527 Smith Place, Ridgewood, NJ. Filed July 27, 1962, Ser. No. 212,874 6 Claims. (Cl. 174-117) This invention relates to adhesive tapes and is more particularly concerned with electrically conductive pressure sensitive adhesive tapes.
conductive medium, the latter of which is generally a powdered substance, causes these particles to become coated with the adhesive, which in itself is inherently a non-conductor. Furthermore, the surfaces of powdered materials malnng up the electrically conductive medium, which are generally of metal such as aluminum, copper, silver, etc., tend to oxidize, and this oxidation causes the metal particles to lose their electrically conductive propertics, thus diminishing the ability of the metal particles to pass on the current.
Another disadvantage of electrically conductive adhesive tapes, where silver particles re used as the conductive medium, is that the relatively high cost of the silver particles makes the cost of this type of electrically conductive tape prohibitive for most conventional uses.
The present invention is intended to overcome the disadvantages specified above. In the first place, it has been found that a non-oxidizing material which has electricaily conductive properties may be employed with advantage in the production of electrically conductive adhesive tapes. In addition, this inventor has found that the particles of electrically conductive material may be cast on the pressure sensitive adhesive tape in such a manner that the coating of the individual particles of the electrically conductive material is avoided. It has, furthermore, been found that where this electrically conduct ve material is compacted by rolling under pressure, its conductivity is increased and resistance is substantially reduced.
The new article of manufacture produced in accordance with the invention lso has novel characteristics which allow the tape to conform to irregular surfaces, and to provide additional strength and tear resistance.
For a better understanding of this invention, reference is made to the drawings, in which:
FIGURE 1 is a perspective view on an enlarged scale of the conductive tape of this invention; and
FIGURE 2 is an end elevational view of said tape.
Referring to the drawings, 10 represents a ribbon or strip of metal foil of indefinite length, the outer edges of which are crimped at 11A and 11B to form a fold on each side of the metal strip. The ribbon of metal foil 10 may be of aluminum, copper or other conductive metal, or other conductive materials, which may bo'produced in thin sheets or strips. In the preferred form, the metal strip 10 is of an aluminum foil, whichis referred to as "dead soft," in which the temper or stiffness has been removed, so that the foil is readily ductile. The resulting ductility of the foil permits the tape to conform easily and permanently to irregular surfaces or objects. The thickness of the metal foil may vary with the needs and uses of the tape, but, for the usual purposes, a foil thickness of 0.002 inch is preferable.
A layer 12 of pressure sensitive adhesive is then cast upon the metal strip 10, so that the adhesive overlies the 3,132,204 Patented May 5, 1964 entire upper surface of the strip, including the crimped outer edges 11A and 113. After the layer 12 of adhesive has been cast on the strip 10, one or more stripes 13 of electrically conductive material are laid over the upper face of the pressure sensitiveadhesive, as shown in FIG URE 1 of the drawings, and the tape is then passed between a pair ofpressure rollers which compact and flatten the stripes of metal foil and the adhesive. The compacting of the stripes 13 of metal foil and the adhesive tends to increase the conductivity of the electrically conductive materials.
In the casting of the layer 12 of pressure sensitive adhesive on the metal strip 10, it has been found that vinyl ethyl ether polymer, such as that having high molecular weight and a reduced viscosity at 20 C. of 3.5 to 4.5, and a specific gravity at 20 C. of .0968, is satisfactory for this purpose and provides a favorable medium in the adhesive itself.
In the use of the stripes 13 of electrically conductive material which are laid over the upper surface of the adhesive material 12, I prefer to employ metal powders of particles which are-corrosion resistant, such as corrosion-resistant copper powder having large particle size, of which 2% will pass through 150 mesh and from 55% to 70% will pass through 325 mesh. An example of the type of copper powder having the above characteristics is Resistox No. 150 RXA or No. 150 RXS, such as is used in the manufacture of sintered metal parts. Powdered aluminum which is corrosion-resistant has also been found satisfactory for this purpose.
A plurality of the stripes 13 of the corrosion-resistant metal powder is laid lengthwise the tape and over the adhesive 12, as shown in FIGURE 1. The tape is then passed between rollers which serve'to compact and flatten the stripes. The compacting of the adhesive and the stripes of metal powder increases the conductivity of the electrically conductive metal powders, without coating the metal particles with the adhesive material.
A strip of easily removable release paper 14 is then placed over the exposed surface ofthe adhesive 12 and the stripes 13 to protect the adhesive, and to prevent the adhesive from adhering to the metal foil backing when the tape is rolled up for shipment or storage. Also, the adhesive-free side of the metal foil backing 10 may be treated with conventional coatings of materials, such as silicones, to protect it and to prevent it from adhering to the adhesive surface when rolled and stored, thus avoiding the need to use release paper over the adhesive face.
In the preparation of the electrically conductive pressure sensitive adhesive tapes of this invention, it is important that the pressure sensitive adhesive not be permitted to coat the particles of the cross-section of the stripes of conductive materials applied in stripes to the upper surface of the adhesive. By the use of stripes of the electrically conductive metal powders, as shown and described above, the particles of metal producing the conductive characteristics are not isolated from each other and are in continuous contact. In addition, ,by keeping the particles of conductive material substantially out of direct contact with the adhesive, the corrosive effects of the adhesive upon the metal particles is minimized. It has also been found that an increase in the particle size (if the conductive material results in improved conduct vity.
In the use of the electrically conductive pressure sensitive tape, as shown and described above, the electrical conductivity showed low resistance and high inductance after prolonged use.
Having described my invention, I claim:
1. In a new article of manufacture, the combination of a metallic backing comprising a ribbon of metal foil, the outer edges of which are crimped to form a fold on each side of said ribbon, a layer of pressure sensitive adhesive overlying the upper surface of said ribbon, a plurality of stripes of compacted electrically conductive material overlying the upper face of the adhesive and lengthwise thereof, and a sheet of removable release paper overlying the exposed face of the adhesive and the stripes of electrically conductive material to protect the adhesive.
2. In a new article of manufacture, the combination of a flexible metal backing comprising a ribbon of metal foil, the outer edges of which are folded on each side of said ribbon, a layer of pressure sensitive adhesive overlying the upper surface of said ribbon, a plurality of stripes of compacted metal particles overlying the exposed face of the adhesive and extending lengthwise thereof, and a sheet of removable release paper covering the exposed face of the adhesive.
3. In a new article of manufacture, the combination of a ribbon of flexible metal foil, the outer edges of which are folded, a layer of pressure sensitive adhesive overlying the upper surface and the folded edges of said ribbon, and a plurality of stripes of compacted electrically conductive particles running lengthwise said ribbon and overlying the exposed face of the adhesive.
4. In a new article of manufacture, the combination of a ribbon of flexible metal foil, a layer of adhesive overlying one surface of said ribbon, and a plurality of stripes of metal particles overlying exposed face of the adhesive and extending lengthwise the ribbon.
5. In the production of electrically conductive adhesive 6. In the production of electrically conductive adhesive tape, the method of crimping the outside edges of a ribbon of metal foil of indefinite length" to form a fold on each side of said ribbon, casting a layer of adhesive over the upper surface of said ribbon and the crimped edges, laying a plurality of continuous stripes of electrically conductive powdered metal over the adhesive, said stripes extending lengthwise the adhesive, compacting the adhesive and the continuous stripes, and placing a strip of easily removable release paper over the exposed surface of the adhesive and the stripes.
References Cited in the file of this patent UNITED STATES PATENTS 1,984,356 Abott Dec. 18, 1934 2,831,049 Carbral Apr. 15, 1958 2,852,423 Bassett Sept. 16, 1958 3,029,303 Severino Apr. 10, 1962 3,060,062 Katz et al Oct. 23, 1962