US1773105A - Resistance paint and art of making resistances - Google Patents

Description

Patented Aug. 19, 1930 UNITED STATES PATENT ol-"rica LESTER L. J ONES, OF ORADELL, NEW JERSEY, AND ALOIS SCHMIDT, OF NEW YORK, AND

JOSEPH JONES, OF WHITE PLAINS, NEW YORK, ASBIGNORS TO TECHNIDYNE CORPO- RATION, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK RESISTANCE PAINT AND ART OF MAKING RESISTANCES ll'o Drawing.

manufacture of capacity and inductance-free,

resistances and to a resistance paint for making the same.

As is well known, capacity and inductancefree high resistance elements are made in the art by any of a number of methods, such as by impregnating paper strips or other material with various kinds of carbon inks, by surfacing paper or the like with graphite streaks or lines, by painting insulating bases with graphite and other compositions, or by depositing thin films of metal on insulating bases such as glass tubes or the like. These resistances, although compact, inductance and capacityfree, possess a number of disadvantages either in the process of manufacture of the same or in service, the inked and graphited paper resistances being, for instance, quite micophonic, generally destructible in use, and incapable of carrying any considerable current, the metallic film resistances being unstable by reason of the change in the resistance value thereof which takes place due to the crystallization or oxidation of the thin metal film, and the graphited painted or coated resistances being comparatively diflicult to make. due to the necessity of compacting the graphite layer by hand or other means. Some of these resistance elements are i also open to the common and serious objection that the resistance values thereof for a given type or make vary within wide limits, it being diflicult to manufacture the resistances of uniform value, especially where the same are produced by quantity production methods.

The manufacture of resistance units which do not possess the above-stated objections and drawbacks, and which are characterized by being non-microphonic, stable in value or magnitude, of large current-carrying capacity, durable, and capable of being manufactured uniformly in desired values within wide ranges, and especially without the necessity of manual or mechanical compacting operations, is a prime desideratum of our present invention.

In the copending application of Lester L. Jones et al. Ser. No. 61,326 filed Oct. 8, 1925,

Application filed February 11, 1927. Serial No. 187,583.

there is disclosed a resistance paint or material and resistances made therefrom, which resistance paint is capable of being applied to such insulating substances, as glass, porcelain, bakelite and the like and capable of being applied by a coating or painting process to produce the resistance element, the coating of resistance material comprising finely divided graphite held in a binder such as an alkaline silicate, the resistance coatings produced by such material forming very thin and continuous and unbroken films having a comparatively low specific resistance.

This coating material or paint, as disclosed in said copending application, while possessing the advantageous characteristics described therefor, is found to be hygroscopic; and this hygroscopic characteristic results in an increase of resistance of the resistance units when the same are allowed to stand and absorb moisture, especially when not in use. This disadvantage may be minimized by sealing the resistance units hermetically in tubes and by coating them with waterproof insulating coating such as lacquer. Our present invention contemplates an improved resistance paint which possesses all the desirable characteristics found in the resistance paint disclosed in said copending application, and which in addition is fully nonhygroscopic.

Further important objects of our present invention reside in the provision of a resistance paint or coating material which may be painted on a mica surface and which forms resistance coatings on mica, glass and other bases capable of being electroplated so that suitable and highly eflicient contact terminals may be made therefor.

To the accomplishment of the foregoing and such other objects as may hereinafter appear, our invention consists in the method, the resistance elements and resistance material hereinafter particularly described and sought to be defined in the claims.

We have discovered'that the desired objects of the invention may be obtained by employing a resistance material composed of finely divided graphite mixed with a binder and vehicle consisting of a metallic phosphate in phosphoric acid. In compounding the reresistance material the a bite, preferably a colloidal graphite, is mixe with a solution of aluminum in phosphoric acid to form a freely 5 flowing paint. The aluminum in the phosphoric acid produces an aluminum hosphate; and in the pre aration of the a uminum hosphate it has en found desirable to add a uminum to the hosphoric acid in such an amount as just faifl to produce a precipitate. Addition of more than this amount, which would produce a precipitate, is undesirable because of the presence in the paint of large particles formed by the precipitate which interfere with the production of a smooth, uniform film. On the other hand, the addition of an insufiicient quantity of aluminum or aluminum phosphate is undesirable mainly because of the more highly acid 9 condition of the resulting paint, which tends to destroy the colloidal nature of the graphite, causing clotting of the paint with streakiness in the film. We therefore prefer to use a solution of aluminum in phosphoric acid in l a slight excess of phosphoric acid, aluminum being added in such an amount, as described, as just fails to produce a precipitate. The aluminum phosphate may also be prepared by the addition of C. P. aluminum p osphate to phosphoric acid in sufficient quantity to just avoid the formation of any precipitate.

The paint thus compounded may be applied. to glass or porcelain rods or to any glazed or enameled surface, and may equally be applied to mica to form resistance coatings of very thin films of the order of magnitude of 0.1 to 0.25 thousandths of an inch, such coatings being formed in continuous and unbroken layers. The paint may be applied to the insulating material by means of a brush or b dipping or by any other method. To pro uce resistances of predetermined values, the same may be applied in a continuous coating on cylindrical bases and then parts spirally removed in the manner described in the conding application of L. L. Jones, Ser. No. 6,026, filed Oct. 27, 1924, to form a spiral film of a iven value.

After t e bases are coated with the paint and air-dried, the painted unit is preferably heated to approximately 500 C. for a period of approximately one hour. The heat treatment causes areduction of the electrical resistance in the film to approximately 1% of its air dried value. The coating thus formed is tough and durable and may be made more or less glassy, depending upon therelative amounts of aluminum phosphate and colloidal graphite used.

films having a resistance of the order of 1,000 ohms Her inch with a width of one inch may be ma e to have permanent non-microphonic characteristics. Resistance films of a higher order of resistance may be made by using a Bythe use,of our invention, resistance of finely divided graphite may be employed with good results, such as the finely divided graphite commercially known as air floated,

graphite.

We have also found that zinc oxide may be used in lace of aluminum or aluminum phosphate orming a zinc phosphate. This composition employing zinc phosphate is also non-hygroscopic but 1s more subject to attack by acid during electroplating. We have also found experimentally that a composition of approximately one part of zinc to 27 parts of phosphoric acid by weight gives a. binder which is less subject to disintegration by sulphuric acid than any other preparation, though even this optimum pro ortion is not as good as the aluminum p osphate. The addition of from 3% to 5% by weight of aluminum to the above optimum zinc phosphate composition will also produce an acid insoluble film of desirable characteristics. In this composition the acid resistance is apparently mainly due to the aluminum present, while the addition of zinc appears to have its chief utility in the production of a paint of more syrupy character which may be required in the painting of certain surfaces where the more freely flowing liquid would drain undesirably.

Films of high resistance and up to 50,000 ohms per inch in one-inch widths may be made from the above compositions by .baking to lower temperatures, as for example, approximately 150 C. These films, however, are not as reliable as the films baked at higher temperatures, since they do not maintain the stable characteristics of the films produced at the higher temperatures.

We have found after considerable experimentation that the resistance paint of our present invention possesses the following very desirable characteristics:

1. The paint adheres perfectly to glass, porcelain, lavite, mica, etc.

2. The paint can be applied or painted in a smooth, even film on these materials. When working on mica, we have found that slight warming of the mica facilitates the formation of a smooth, even film.

3. The painted units may be baked to form a smooth, adherent coating on the above materials.

4. 'During the baking process the coating or paint contracts and compacts the graphite into a homogeneous mass having a very low resistance as compared to the initial resistance. For example, the drop in resistance during bakin is found to be of the order of 100 to 1, as aibrestated; and this compacting of the graphite insures a non-microphonic or noiseless resistance.

5. The baked coating is relatively insoluble in sulphuric acid, so that it becomes practical to electroplate copper, nickel or silver contacts at the terminals. To the electroplated terminals conducting leads may be soldered or terminal bands may be clamped about the electroplated terminals to make efiicient connecting means to the resistance paint.

6. The baked coating is absolutely nonhygroscopic so that the unit suffers no deterioration due to exposure to moisture, nor does the resistance vary due to any moisture absorption.

The manner of painting the resistance material and making the resistance elements and the many advantages thereof will in the main be fully apparent from the above detailed description thereof. While we have described the preferred form of our invention and the preferred process thereof, it will be apparent that many modifications and changes may be made therein Without departing from the spirit of the invention defined in the following claims.

We claim:

1. A resistance paint having the property of being coatable to form very thin electrically conductive films and comprising a suspended solution of finely divided graphite in a binder and vehicle consisting of a metallic phosphate in a slight excess of phosphoric acid.

2. A resistance paint having the property of being coatable to form very thin electrically conductive films and comprising a colloidal solution of colloidal graphite in a binder and vehicle of a metallic phosphate and phosphoric acid.

3. A resistance paint having the property of being coatable to form very thin electricaL ly conductive films and comprising a colloidal solution of colloidal graphite in abinder and vehicle consisting of a metallic phcsphate in a slight excess of phosphoric ac1 4:. A resistance paint comprising a suspended solution of finely divided graphite in a binder and vehicle of aluminum phosphate and phosphoric acid.

5. A resistance paint comprising a colloidal solution of colloidal graphite in a binder and vehicle consisting of aluminum phgsphate in a slight excess of phosphoric aci 6. The method of constructing resistance units which consists in coating an insulating base with a paint consisting of finely divided graphite suspended in a metallic phosphate and phosphoric acid solution, and in baking the said coated base to a temperature of about 500 C. for approximately one hour.

7. A resistance element comprising a base provided with a coated resistance material consisting of finely divided graphite held in a binder of a metallic phosphate and phosphoric acid.

8. A resistance element comprising a base provided with a coated resistance material consisting of finely divided graphite in a binder and vehicle of a metallic phosphate in a slight excess of phosphoric acid.

9. A resistance element comprising a base provided with a coated resistance material consisting of a colloidal graphite in a binder of a metallic phosphate in a slight excess of phosphoric acid.

10. A resistance paint having the property of being coatable to form very thin electrically conductive films and comprising a colloidal solution of finely divided conducting particles held in a binder and vehicle of a metallic phosphate and phosphoric acid.

11. A resistance element comprising a base provided with a coated resistance film having a thinness of the order of magnitude of 0.25 thousandths of an inch and consisting of finely divided conducting particles held in a binder of a metallic phosphate and phosphoric acid.

12. A resistance paint comprising finely divided carbon in suspension in a binder of metallic phosphate and phosphoric acid.

13. A resistance paint comprising finely divided carbon in suspension in aluminum phosphate and phosphoric acid.

14;. A resistance paint'comprising finely divided carbon incorporated in a binder consisting of aluminum phosphate in an almost neutral solution of phosphoric acid.

15. A resistance element comprising a base provided with a coated resistance material consisting of finely divided carbon held in a binder of a metallic phosphate and phosphoric acid.

16. A resistance clement comprising a base provided with a coated resistance material cons sting of finely divided carbon in a bind- Br 3f aluminum phosphate and phosphoric acl Signed at New York in the county of New York and State of New York this eighth day of February, A. D. 1927.

LESTER L. JONES. ALOTS SCHMIDT. JOSEPH JONES.