DE2107162A1 - Coating compound with electrical resistance and excellent abrasion resistance - Google Patents

Description

Patent attorneys
Dr. Gerhard KENICEL

757 B «! '!« Ii-j-a k'u-ü Jg

PT.W.-D. HEKLLl. ::: pl.-Ir. | fRMKERN

Dr. Lothar FEILER 9 1 fi 7 1 £ ^ SKfecbeaS0 _> £ daaid-8eliAii & Str. 3 C IU I IO C,

Globe Union Inc.,
Milwaukee, Wise, V.St.A.

Feb. 15, 1971

Dr.F / De

Coating compound with electrical resistance and excellent Abrasion resistance

The invention relates to coating compositions with electrical resistance, which are particularly used for the production of resistors and similar electrical elements are suitable. In particular, the invention relates to an electrical resistance Coating compositions made of synthetic resins, which are able to adhere to dielectric substrates and to the substrates and the off are able to impart high abrasion resistance to the coated substrates.

It has hitherto been customary to produce layers or coatings exhibiting (electrical) resistance from flowable, conductive synthetic resins with electrically conductive particles contained therein which are dispersed in a solution of a thermosetting polymer. There have also been numerous attempts to use such conductive synthetic resins for the production of an (electric) resistive coatings, in turn, in the production of in potentiometers and corresponding electrical devices, in which the resistance of the coating by sliding over contact arm or a corresponding contact device is "dismantled",

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used resistors are used.

To produce such an (electrical) resistor A wide variety of thermosetting polymers have been used with layers or coatings. To the mainly The polymers used include phenol / formaldehyde condensates and difunctional epoxy resins. Furthermore, the Use of mixtures of these epoxy resins with phenol / formaldehyde condensates, Melamine resins or urea / formaldehyde condensates and mixtures of phenol and urea / formaldehyde condensates suggested.

Often it is in the manufacture of carbonaceous resistors required several layers or coatings lying next to one another and exhibiting an (electrical) resistance produce, each having particles of different conductivity and between adjacent edges with each other are electrically connected. For example one of the coatings exhibiting an (electrical) resistance contain metal particles, e.g. silver particles, in order to achieve a Create low resistance band zone; the adjacent coating or layer can be considerably less Contain conductive particles, e.g. carbon particles, where creating a high resistance resistance zone; the the next coating or the next layer can in turn contain metal particles, e.g. silver particles, in order to form a further end zone (relatively low resistance). ·. ■ ".- '",' "- ;. '-. ·"' ■ -

To two-layer or multi-layer coated substrates with the The necessary electrical characteristics should be established by neighboring Layers with very different resistance with

'. .: '- r ■ ■■.; ■■ -3

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be electrically connected to each other in such a way that with an even or smooth transition of the resistance of. one Layer to the other a continuous current path is created. This requirement for a sliding, i.e. stepless electrical transition zone between layers or coatings of different resistance occurs particularly clearly in the manufacture of resistors for potentiometers, in which a contact arm over the resistor, i.e. from a layer to the other, being moved, in appearance. Used to apply such layers having an (electrical) resistance one of the most varied of procedures; such layers or coatings were, for example, sprayed on (the coating sma sse on the substrate), by extruding a free flowing film, by brushing on (the coating mass on the substrate), by applying (the coating compound to the Substrate) by means of rollers and the like. Manufactured. A particularly effective method for making coated substrates with particularly continuous electrical connections between adjacent layers or coatings is in the German patent application P ....... described.

It has now been shown that the hitherto used for the production of An (electrical) resistance exhibiting layers or coatings exhibiting conductive synthetic resins used for resistors often not the required wear resistance for long life in a potentiometer. the Layers or coatings made from the known synthetic resins seldom last more than about 5000 scans of the contact arm the end. The term "scanning process" is used here and hereinafter to mean the extent of contact that the contact arm has required to sweep a resistor of a given size from one end to the other and back again is.

T Ü 9 8 3 9/1 5 2 0

The object of the invention was now to provide an (electrical) Specify resistance coating compound for the production of resistors * which are calibrated in comparison to the previously known Coating compounds due to a significantly greater wear resistance excels.

The invention lay; based on the knowledge that the posed Task can be solved with a coating compound that consists of a mixture of certain thermosetting polymers and dispersed therein, finely divided, conductive particles.

ψ object of the invention is a coating composition having electrical resistance and excellent abrasion resistance, in the form of a mixture of about 30 to 95 wt .-% of a thermosetting polymeric material, consisting of a mixture of a trifunctional epoxy resin with a phenolic resin; from a mixture of an epoxy-modified phenolic resin with a phenolic resin; a mixture of a phenolic resin, a melamine resin or a precursor thereof with an epoxy-modified phenolic resin; from ein.Gemisch an epoxy-modified phenolic resin and a phenolic resin with an epoxy resin; or a melamine resin, and about 5 to 70% by weight of conductive particles dispersed therein.

The coating compositions exhibiting electrical resistance according to the invention are distinguished by excellent abrasion resistance and adhere to a wide variety of dielectric Substrates. As the polymeric materials used as binders and dispersants for the conductive particles are thermosetting and, furthermore, since the conductive particles should be dispersed uniformly in the mixture it proved particularly beneficial to that. Coating

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masses according to the invention in the form of solutions, in suitable. ' Solvents to be produced taking this into account it should be self-evident that the visual dimensions are in accordance with of the invention: the "in flowable; form on its dielectric rope Substrate applied, dried and finally dried hardened by heating, usually even lower Contains quantities of solvents. . ·

The named polymeric materials are particularly suitable

for the preparation of

Coating compounds with particles exhibiting high electrical resistance, e.g. carbon particles. In certain cases, for example when the 'conductive particles are in the respective coating compound. from metal particles, e.g. silver particles and the like exist, it is more difficult to ensure the desired abrasion resistance properties of the coating compositions according to the invention. However, it has been shown in an advantageous manner that, by adding certain solid lubricants to the respective Coating composition can improve the wear resistance of this and other coating compositions enough to to ensure the desired abrasion resistance.

For use in coating compositions according to the invention suitable solid lubricants are, for example. Molybdenum disul-. fid, tungsten disulfide, boron nitride, job selenide, tungsten selenide, Titanium telluride and mixtures thereof and similar lubricants, those with the respective polymeric material or the relevant conductive particles among those for curing the excess. or layers on the substrate required conditions "not react. Furthermore, the lubricant used in each case may electrical properties of the layers or coatings are not significantly affect. Usually based on the total solids content is at least about JO% by weight of the

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solid lubricant needed to. the abrasion resistance of the respective coating compound noticeably to improve ».

It has been shown that a Be stratification compound with about 45 to about 90% lubricant, e.g., molybdenum disulfide, which is essentially Has dielectric properties, for the formation of for the intended purpose particularly useful resistance Schictiten can be used, Preferably the amount of. Molybdenum disulphide in approximately the same amount as in the coating maase metal particles used correspond to "

The (electrically) resistive coating compositions according to the invention contain finely divided, electrically conductive particles uniformly in a practically non-conductive, thermosetting polymeric carrier. The polymeric carrier must adhere to the dielectric substrate during application and form a hard, solid matrix, in which the conductive particles remain dispersed after curing at elevated temperatures. Examples of suitable polymeric materials are thermosetting melamine resins or precursors thereof, for example melamine / formaldehyde condensates, methylated melamine / formaldehyde condensates, butylated melamine / formaldehyde condensates, butylated urea / formaldehyde condensates, Phe- w no! Resins, - z. BV Phenol / formaldehyde condensates, epoxy resins and epoxy-modified phenolic resins and mixtures thereof.

Of course, some need these thermosetting ones polymeric materials to accelerate the curing process Hardeners or catalysts. As already stated, it has sipYes shown that with the exception of melamine resins such as: e.g. the under the trade name .Resimene876 sold melamine resin, certain combinations or mixtures of these polymers

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must be applied to the unique coating compounds to be able to produce according to the invention.

Such combinations are advantageous from polymeric materials to mutual cross-linking *. Epoxy resins crosslink with phenol / formaldehyde condensates and also with melamine / formaldehyde condensates. It goes without saying that they are those according to the invention Pheriol resins used to remove such phenol / formaldehyde condensates, which include the heat-meltable phenolic novolak resins and the thermosetting one-stage phenolic resins. The novolaks are usually based on a molar ratio of formaldehyde to phenol of less than about 1: 1 prepared in the presence of a preferably acidic catalyst under suitable reaction conditions. Novolaks are permanently meltable and soluble and do not cross-link by themselves

To make the Kovolak resins infusible and thermosetting make them with an aldehyde donor or a supplier for methylene bridges or bonds further implemented are »The methylene bridges are supplied by connections, from which formaldehyde is produced. The latter in turn then provides further methylene bridges between neighboring ones Phenolic nuclei.

The one-stage phenolic resins are made with a larger molar ratio Formaldehyde to phenol than it is used in the manufacture of novolaks, "produced. Under the influence of alkaline Catalysts, the phenol reacts with aqueous formaldehyde, with one, two or all three phenolic ortho- and para positions, optionally with the formation of methylene bonds hydroxymethyl (methylol) groups are formed between phenol nuclei. Suitable phenolic resins are, for example

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commercially available under the trade names Bakelite BKS 2710, Varcum 1281 B 65, and BRPA 5570. Let these resins by simply heating them up in the heat-fixated, ddi. Cross-linked state, but usually runs this hardening does not cure quickly enough, so that consequently for acceleration hardener can be used for curing *

Suitable aldehyde donors - hardeners are, for example Hexamethylenetetramine, paraformaldehyde and sym-trioxane. Preferably the hardener consists of hexamethylenetetramine formed by the condensation of ammonia with formaldehyde. These P hardeners are called aldehyde donors because they rapidly cross-link when heated Bring novolak resins and the single-stage phenolic resins through methylene or equivalent bonds.

A suitable epoxy-modified phenolic resin is, for example the phenolic resin sold by Reichhold Chemicals, Inc. under the trade designation PLiOPHEN 23-983.

The epoxy resins which can be used according to the invention are polymeric reaction products of polyfunctional halohydrins with polyhydric phenols. Such resins are known to those skilled in the art as epoxy resins, epoxides, glycidyl ethers, or atherepoxides. The polyfunctional halohydrins suitable for the production of the epoxy resins include, for example, epichlorohydrin, glycerol dichlorohydrin and the like. Typical polyhydric phenols are the resorcinols and 2,2-bis (hydroxyphenyl) alkanes, ie compounds which are formed by condensation of phenols with aldehydes and ketones, such as _o formaldehyde, acetaldehyde, propionaldehyde, acetone and the like. " The epoxy resins often contain terminal epoxy groups, but they can also contain both terminal epoxy groups

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as well as terminal hydroxyl groups. Particularly Trifunctional ones are suitable when mixed with phenolic resins Epoxy resins, for example that from Union Carbide sold under the trade name Bakelite ERL 0510 trifunctional epoxy resin.

For the production of an (electrical) resistance having coating composition according to the invention, various Commercially available epoxy resins are used. Examples are those from the Bakelite Company under the trade names ERL.277 # »ERL 4221 and BRL 3794 and BXKB 4466, which are available from Shell Chemical Corporation under the trade names Epon 1001 »Epα» 1004, Epon 1007 » Epon 1009 and Epon 828 sold epoxy resins "by the Ciba Company, Ine "under the trade names Araldite 6010 and 6020 sold epoxy resins and those of the General Mills Chemical Division sold under the trade names GenEpoxy 175 »190 and 525 GenEpoxyharzea

In addition to the usual epoxy resins, other epoxy intermediates and modified epoxy resins can also be used in the preparation of the coating compounds according to the invention often contain reactive diluents such as styrene oxide, octylene oxide _s Ällylglycidylather, Bu. ty lglycidyl ethers, phenylglycidyl ethers and similar reactive compounds in amounts of up to about 20 to JO parts of diluent per 100 parts of epoxy resins. Examples of such modified epoxy resins are commercially available under the trade names Bakelite ERL 2795 »ERL 4289, EHL 2774, Araldite 502, GenEpoxy M- 180 and Epon 815

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sustainable. Of course, in the present case, the term "epoxy resin ¹¹ " should be understood to mean both the customary epoxy resins of the type described and the modified epoxy resins and the epoxy resin intermediates.

When preparing the respective combinations or mixtures of for the production of the coating compositions according to Resins suitable for the invention have shown that the individual proportions can be varied.

In the case of coating compounds that consist of a mixture of a trifunctional epoxy resin (e.g. Bakelite ERL 0510) and a Phenol / formaldehyde condensate (e.g. Bakelite BES 2710) can usually have about the weight ratio of phenolic resin to epoxy resin 3: 1 to about 5: 1, preferably about 4: 1.

The mixtures of epoxy-modified phenolic resins (e.g. PLYOPHElT 23-983) and a Hieno! Resin (e.g. Bakelite BES 2710) usually contain these resins in weight ratios from about 1: 2 to 1: 1, preferably from about 1: 1.5. If an epoxy resin is added to this mixture, it is used in the Usually in the same weight as the epoxy modified one Phenolic resin used. For example, it contains a particularly effective combination of phenolic resin and epoxy-modified phenolic resin and epoxy resin, the individual resins in a weight ratio of 1.5 s 1: 1. If necessary, smaller amounts can also be used be used on Bpoxaiiarsen ''.

When these phylol resin mixtures are melamine resins or melamine resin precursors j such as hexamethoxymethylmelamine, are added, the melamine resin usually serves as a hardener or as a crosslinking agent. Consequently, it will be in relatively low levels Amounts atapgeted. So these mixtures, based on

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the total weight of the mixture »about 50 to 65% phenolic resin, 30 to 50% of the epojy-modified phenolic resin and about Contains 5 to 10% of the melamine resin.,

If the melamine resins are used alone, they can, based on the total solids content of the coating, make up about 30 to about 60 weight percent.

Of course, determine the amount, type and size of the Conductive used in the flowable, conductive synthetic resins Particles the resistance of the material «As a result of their different conductivity, carbon particles have a the production of layers or coatings exhibiting (electrical) resistance has proven to be particularly effective » The carbon particles can contain about 4 to about 60% by weight of the flowable, Make out the coating compound containing solvent. It is preferred for the production of flowable coating compositions suitable viscosity about 7 to about 30 weight percent carbon particles used · If the content of carbon particles is 60% by weight exceeds the viscosity of the flowable coating mass often too high to use in a suitable way, e.g. by means of a coating eater to be able to apply. At a Content of coal particles below about 7 wt .-% exercise the after Curing or crosslinking of the polymeric carrier between the carbon particles formed polymeric pores or bubbles on the electrical properties of the layer or the coating opposite influence. It has been shown, for example, that the bulk level of the (electrical) resistive top coat at this low carbon content is excessively high and consequently cannot be accepted for commercial products.

It was found "that metal particles" such as

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Silver, platinum and other noble metal particles, copper particles, stainless steel particles and the like can also be used as conductive particles in a coating composition according to the invention. Such metal-containing coating compounds are particularly suitable for forming the ind zones of a resistor. Depending on the metal used and the resistance desired, the level of metal particles can vary considerably. It has been shown that silver particles in amounts of about 30 to about 50% by weight, based on the weight of the solvent-containing coating compound, are particularly suitable for producing a band with a resistance which is 1% of the total resistance of the resistance element . Of course, lower amounts of metal particles, such as "may be in the order of 10 GeWc-%, or greater amounts of metal particles, Z _0, in the order of 65% Gew.r- f for the production of layers or coatings of a different (electrical ) Resistor can be used.

The adverse effect on the viscosity of the resistive synthetic resins is less pronounced in the case of metal particles. The main consideration, which is decisive for the maximum amount of metal particles used, the abilities w ness of the polymeric carrier in the coating composition to attach the particles to the coated substrate adherent.

As a rule, for one part by weight of metal particles 0.25 to 1 part by weight of the resinous carrier and for about 1 part by weight of carbon particles about 0.5 to 2 parts by weight of resin needed.

As a rule, coating compounds are used that either only Ko & lepartjUcel. or contain only metal particles; ge

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109 839 / 1B 2 0 )

gebeaenfal}. ”However, coating dimensions also work

Kisehangen do different metal particles or mixtures

from Mötiallpe ^ i ^ tlö, qnd carbon particles are used.

The KoblepertiSceX can be used in different. Forms of crystalline or amorphous form, such as those found in commercial products, ethylene black or furnace black, are used. · Oftmai be the coal particles prior to use in the preparation of the Be layer ungsma lake "according to the Erfinduag aenfffre Stux ^ long the GrÖSenordnung calcined in air at elevated temperatures, i of about 1090 ° to 165o C ^0. The particles can range in size from about 10 to about 400 microns, and mixtures of larger or smaller particles can be used.

«In general, the metal particles are considerably larger than the carbon particles and can have a particle size of about 10 to about 400 microns *

Of course, the resistance of the conductive, particulate synthetic resin coating compound is determined by the Hexode on conductive particles used; the resistance changes inversely to the amount of particles used

numerous of the heat-fixable polymers or polymers used as carriers or binders for the conductive particles have the same viscosities that are higher

they are desirable on the field of application of the invention, it is often necessary to control the viscosity of the Ittitfsünigen KunetherEoateriels an organic compound which eim ^ osungewittel represents for dae polymers "to use Bteee LÖBungaiittel may with the polymeric carrier not reagie reu and vüeMn epenügend be fleeting to get out of the «appii-

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to remove the adorned coating by evaporation. Geöighete solvent include aliphatic Aikohole, such as ethanol, Isöbutanol, etc. * aliphstische ketones, How METB ^ iäthylketoii ¹ "Methylisobuty ketone! And the like"., Cyclic ketones such as isophorone, glycol ethers such as Ithylenglykol-n-butyl.-ättier, itüylengXykolätiüylather and the like, as well as aromatic hydrocarbons * such as benzene, toluene, xylenes and the like. Since, as already mentioned, the solvents can mainly be used to control the viscosity of the resistive synthetic resin material: the amount of solvent is considerable different, its »that is about 5 to about 70% by weight of the flowable coating mass to be applied to the substrate is * · '..;""-' ■■ · ^.: ■ -.- · .;: V . ~ .; '".-. · ■". "■■""": .- ■ ;;: '. - - ' - ■ -

Various additives and auxiliaries can be used in the preparation of the coating compositions according to the invention. On wearing the same on a dielektrisciif s S, üsfrat »'to facilitate. It has been shown, for example, that the occurrence of surface irregularities can be avoided if bilicon oils and other appropriate wetting agents are used. Optionally, polymeric Dickungsiäittel, Metäll-cross-linking inhibitors such as catechol, and the like may _f. Yerwendet Werdes * In general, such additives make a relatively small proportion, ie "about 1 to 5 Glichtsteiie of the coating material from. Furthermore, when mixing the individual components of the respective coating material, catalysts and hardeners for the polymeric siager can be added, as already stated.

The viscosity of the (electrical) resistance exhibiting Beechichtunesmasee according to the invention should be sufficient to ensure the formation of the edges ^{in every 1 layer.}

afford, feraerÄuss ^ eiofe move the viscosity in a range

INSPECTED

which allows the coating to flow onto the dielectric substrate. Resistive (electrical) resins with viscosities from about 10OG centipoise up to 80,000 centipoise, measured on a Brookfield viscometer at a spindle speed of 10 rpm, can be used , will. Of course, the type of application of the coatings, e.g. by spraying on, roller coating, applying with the aid of a coating knife or a brush, sieving through silk and the like, determines the respective minimum viscosity of the synthetic resin used. As a rule, viscosities of at least about 200 oentipoise (measured with a Brookfield viscometer at a spindle speed of 10 rpm) are ^{required for application 1} with the aid of a coating knife. Preferably, the viscosities of the polymeric materials used are in the range between about 3000 and about 20,000 oentipoise ». .

When loading with a coating knife one also preferably uses such an (electrical) resistance coating on substances that have thixotropic properties; Bi ^ these substances can be applied more easily with the help of a knife edge. They also ensure that the edges between adjacent layers create the (required) uniform electrical transition from one resistive layer to the other. In. As a rule, the thixotropic index of these substances can be between about 1.5 and about 40, preferably between about 2 and about 20, the term "thixotropic index" is intended here and below to mean the ratio of the viscosity of a substance to be% , e; t # er b.eet ^ öarnten - Movement to viscosity (the same sub instead of ») b # i tipi & v > - change movement to be understood eft | webnifecre viscosity by means of a BröokfieId-

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Viscometers at '; a spindle speed of 0.5 revolutions per minute is measured, viscosities between about 200,000 and about 800,000 or more.

The substrate or the base to be coated with a coating compound according to the invention is a dielectric, insulating material which is used for fastening the coatings on the surface of the respective substrate or the. relevant document must be effective. Examples of suitable such materials are "foils," tapes, films and the like made of polymers, for example phenolic resins, polyvinyl chloride, polyethylene, epoxy resins and the like, glass, ceramic materials, treated papers and similar materials, of course the substrate can be coated in full by means of a coating ^{knife edge +} coating} 'on the other hand, the substrate can also be coated under a coating knife edge or some other application device in the form of head-to-tail connection steneh &eji; Foils or sanders or as a continuous flexible film are now moved and then pulled off on a take-up roller. · .- ';:;

The coating compositions according to the invention can be applied to the dielectric substrate, for the production of extremely thin layers a thickness of about 0.013 mm to about 0.51inni can be applied. As a rule, there is a flowable coating compound Solvent is contained) the layers after the removal "des Solvents, e.g. by drying, thinner. the after drying and fixing on the Substrate biäzii shrink about 6Q ^ or more. Consequently can the solvent-free coatings or layers have a strength in on the order of about 0.006 to about 0.25 mm.

■ ♦ ■ a roller or _: another application device

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Of course, the coating compositions must according to the invention / _e attaching -Ie.s coating are gekartet on the dielectric substrate by a Erwärae for fixing BZV., As a rule, the coated substrate is first few minutes TFIs to a temperature of about 95 ° for about 149 ⁰ C heated to dry or pre-cure the coating; then the substrate for final curing of the polymeric carrier is heated for one-half to 4 hour (s) to a temperature of about 121 ° to 177 ⁰ G.

It has been shown that with a coating compound Wear-resistant layers or coatings that can be produced according to the invention in a hardness test (for example by means of a penetration test device according to Knoop) a different micro-hardness have · Scr, for example, the use of a coating compound with a phenolic resin usually leads to cured Coatings or layers having hardness values on the order of about 60 to about 70; dis use of. Coating Melamine-type sleeves provide layers or coverings, whose hardness is of the order of about: 15 to about JO (These hardness values are obtained with a load of 25 g and polished test pieces of the layers or coatings) <>

After the layers or coatings have been fixed on the substrate, resistance elements for the production of potentiometers and other variable resistors can be produced by punching, cutting out and the like »several resistance elements from the coated substrate. circular, be moon shaped, rectangular and the like _a. The way in which such resistance elements are produced is described in more detail below. The special form of certain sector-shaped elements is in the German patent application P .... », *. described.

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The following examples are intended to explain the invention in more detail.

Example I.

This example illustrates the preparation of an (electrical) resistance coating composition with a mixture of a phenolic, epoxy and epoxy modified phenolic resin for the production of carbon-containing cons stand elements for a potentiometer "

The coating composition had the following percentages by weight Composition:

Components % by weight

Coal particles ^ ¹ ^ 23.2

Phenolic resin ^ 20.6

Epoxy modified phenolic resin ^K ^ '12 .7

Epoxy resin '*''12.5

Hexamethylenetetramine. 1.4

Methyl ethyl ketone 6.0

Isophorone 25.59

Eluorcarbon-i'ietzr-ittel ^) Q _t Q1

100.00

(1) Carbon particles of a diameter you

54 mj ^ (from Columbian Carbon Co. sold under the trade name Statex 93)

(2) 56% solution of the resin in ethanol (sold by Union Carbide Co ₀ under the trade name BIS 2710)

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(3) 60% solution of the resin in isopropanol (sold by the company Fellchhold Chemical Co ₀ under the trade name PMOPHJSK. ^ - 98.5)

(4) 55% solution of the resin in a mixture from methyl isbutyl ketone and Tulucl (from the Shell Chemical Go company. sold under the trade name Epon 1007)

(5) (from Minnesota Mining and Manufacturing Co. sold under the trade name FX-173)

The components mentioned were first mixed in a disperser mixer and then ground in a ball mill for 24 hours until the carbon particles were uniformly dispersed in the resins and solvents, forming a flowable, plastic coating compound a dielectric substrate =, i-ho, a phenolic resin-based tape sold by Synthane Corporation and having a dielectric strength greater than 1000 megohms, a thickness of 0.51 mm, and a length of about 71 cm Using a coating knife, coated with the coating compound mentioned in a wet thickness of approximately 0.08 μm.

The coated phenolic resin tape was then cured for 10 minutes at a temperature of about 93 ° C and then dried for 1 hour at a temperature of about 16J ⁰ C to the coating or the layer · anchor on the tape.

Using a punching tool, the coated substrate was

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Tool several corresponding sector-shaped resistance elements punched out with a resistance of 500 ohms each. These elements each had an outside diameter of about 1.39 cm, a radial width of about 2.97 mm and an included angle between the centers of the terminal openings of about 62 °. This element is sized and of a type as used in that provided by Globe-Union, Inc. under the trade name Centralab ^ Model 3 Potentiometer distributed potentiometers are included. About the wear and tear resistance of one (electrical) resistor having coating on the resistor element became a contact resistance-changing test such as he in the Centralab Specification Mr. 0-4BB-1 is described, carried out

w

In this test, the resistor element is placed in a Model 3 potentiometer unit with a silver-plated phosphor bronze contact ssm ₉ that rests on the resistor element at a pressure of about 70 kg / ca. The unit is then mounted on a test device which rotates the contact arm over the resistance element at a rate of 50 scans per minute. The total number of times of scanning was measured by means of a counter. The "potentiometer unit is also (electrically) conductively connected to an electronic resistance meter with a Χ-Ύ - coordinate recorder that records the noise level, ie the change in resistance across the resistance element at a constant current of 1 milliampere. This test is in the As a rule, continued until the noise level exceeds a value of 1% of the total resistance or until the surface of the coating shows signs of damage or damage to the contact arm that is visible by periodic visual inspection.

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elements according to the test procedure described shown that the coatings on the individual resistor elements more than 90,000 scans or visible damage or damage to the layer surface or the contact arm survived. The test was then interrupted.

Example II

This example illustrates the wear resistance and the improvement in the number of scans that occur when using coating compounds with certain Achieve melamine resins as a polymeric carrier for carbon particles leaves. For the production of a flowable coating compound the following ingredients were used in the following amount:

Components weight -%

Coal particles ^ · 1? »4) in air

¹¹ "^. '3i5) calcined

(5) _2f3 )

Melamine resins ^ 44.5

p-toluenesulfonic acid. 0.27

Methyl ethyl ketone ". 12.03

Ethylene glycol n-butyl ether 20 _t 0

100.00

(1) Carbon particles with a diameter of

60 mp (sold by Carbot Carbon Co. under the trade name Regal SR IS )

(2) Coal particles with a diameter of 17 mf- »(from Columbian Carbon Co.

sold under the trade name Conductex SC)

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(3) Carbon particles with a diameter of 42 (from Cabot Carbon Go under the trade name Sterling V expelled)

(4) 56% solution of the resin in isooutancl

(from Monsanto Co. under four trade names Resimene 876 distributed)

When preparing this coating, the p-Toluenesulfonic acid, methyl ethyl ketone, ethylene glycol and the n-butyl ether is poured into a vessel with a capacity of about 3 »8 liters and mixed by means of a dispersator until the sulfonic acid is dissolved. The melamine resin was then added and mixed. After adding the carbon particles and mixing for 1/2 hour, the resulting mixture was bead milled for 16 hours marry.

The coating composition obtained in the manner described was applied to a phenolic resin tape (of the type used in Example I) in a wet thickness of 0.08 mm, whereupon the tape was ^{dried for 4 minutes at a temperature of 149 °} C. and for 2 hours at hardened at a temperature of 121 ^{0 C »}

As described in Example I, the coated Phenolic resin substrate sector-shaped resistor elements punched out and in the Model 3 potentiometer unit on the Number of possible scans examined. In these examinations it was found that with the help of the coating composition according to this example have an (electrical) resistance having coatings produced, the more than 50,000 scanning processes survive.

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Example IH

This example illustrates the use of an (electrical) resistance exhibiting coating compound a mixture of a phenolic resin and a trifunctional one Epoxy resin as a polymeric carrier for Kohl ep articles.

It became an (electrical) resistive one Coating compound prepared with the following composition:

Components ■

Coal particles ^ (2)

(3)

Phenolic resin ^ 'Trifunctional epoxy resin Methyl ethyl ketone.

17.4 ) in air 3.5 ) calcined 2.3 36.8 4.9 4.2 1O ₅ O 4.0 16.8

0? Oluene
Cyclohexanone

. .-. / · 100.0

■ - ■ - (1) Shelf SSF-S

(2) Gonductex SC

(3) Sterling V.

(4) BES 2710

(5) ERL 0510 (sold by Union Carbide)

:. The coating compound was prepared by first adding the Phenolic and epoxy resin dissolved in the solvent mixture and were then ground for 16 hours in a ball mill.

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The resulting flowable coating composition was applied by spraying through a nozzle with an atomizing pressure of 2.1 kg / cm onto a phenolic resin tape (of the type used in Example I) in a wet thickness of 0.08 mm. The tape was then dried for 10 minutes at a temperature of 93 ⁰ G and then cured for 1/2 hour at a temperature of about 163 ^{0 O.} Sector-shaped resistor elements for use in a Model 3 potentiometer that withstood more than 50,000 scans were then cut in the manner described in Example I.

example IV

This example illustrates the use of a coating composition to produce an electrically resistive coating that can withstand a very large number of scans. The polymeric carrier consists of. the coating composition of this example composed of a mixture of a phenolic resin and an epoxy-modified phenolic resin.

The coating compound had the following composition as a percentage by weight:

Ingredients wt .- $ Coal particles ^ '' . _: 21.6) in

"ί ² \ 5.4) calcined

Phenolic resin ^ * '29 .5

Epoxy modifiedβ phenolic resin '**' 17.2 Methyl ethyl ketone 6.0

Isophorone 20.5

100.0

- 25 - 109839/1520

- 25 - '. ■

(1) States

(2) Conducted SO ■ · '' · ['- ..: - "^:;; (5) BIB 2710 ^.: ·:;.' ■■ · '(4) PiarOPHBSH 23-9835J

Bex preparing these Beschichtungsm & sse elm batch of 1000 was made -g by the phenolic resin

. epoxy-modified phenal resin, methyl ethyl ketone and the Mixed isophorone for 5 minutes in a *>, 8 1 vessel » The carbon particles were then mixed in for 1/2 hour "and the resulting mixture in a ball mill for 1/2 hour

. marry. The coating compound obtained in this way would be closed; lent applied by einas coating knife to an existing of a phenolic resin eand in a wet thickness of about 0.08 mm, dried for 4 minutes at a Temperotur From about i4g- ° C ■ and 2 hours at a temperature of 163 ⁰ C. ge ^ '^:; hardens. '

^: From the coated. " Phenolic resin tape was punched out and assembled in the same way as described in Example I for a Model 3 potentiometer unit. ! Line investigation of these sector-shaped resistance elements showed that their coatings, made from a coating compound according to S} 2j £, lasted over 400,000 scanning processes without their surface being significantly impaired or the contact arm visibly damaged.

- Example V

This example illustrates the use of solid sliding agents, for example molybdenum disulfide, in the preparation of a (electric) resistors # SSD having Beschichtüngsmassen according to the invention ^'1' ■: ■■ ^'■': -

Q9839 / 1520 - «. ■ INSPECTBD

The following ingredients became one for manufacture a metal endzone suitable for a resistance element b Filber-containing coating compound prepared:. ;

\ - ■ t

Ingredients · ·. Wt .- $ ;

Silver flake » ^k ; ^tJ 30.0

Mojybdenum disulfide 25.0

Hienol resin ^ '■ 20,1 Ipo ^ y-modified phenolic resin ^';;; 11.8

Hexamethoxyme thy Ime larain ^ '1,4'

Brenzlca techin 0.4

Isophorone 11 jj>

(from the company Metal JJisinfc © ÄT-ating o,

(2) BIB 2710

O) PM) HiEi 23-983

(4) Cymel 301 (¥ on the FJx'ma American Distribute cyanamide)

In the manner described in Example I, the coating compound obtained was applied to a phenolic resin tape, whereupon sector-shaped resistance elements were punched out of this and their service life (during operation) was examined. It has been found that the _r check of the described coating composition

09839/1520

Coatings made according to the invention withstood more than 50,000 scans.

Example VI

This example again illustrates the advantages which when solid lubricants are used to improve the abrasion resistance of metal-containing, a resistance having coatings can be achieved. First of all, the components listed below were used to create a presentation fair prepared:

Components by weight

Silver flakes ^ ** 40.0 Phenolic resin ^ ' 26.8 Bpoxy-modified phenolic resin ^ ' 1Γ.7 Hexamethoxymethy ! Melamine ^ '" 1.8 Catechol o _s 5 Polyaeres thickener ^^ 0.25 Isophorone 14.95

100i00

(1> # 75O (from! Irma Ketal Disintegrating Co. expelled)

(2} 5% solution of the resin in ethanol BBS 2710 (sold by Union Carbide). ;

C3) 60% solution of the resin in isopropanol PLlOiKES 23-985 (tone from Reichhold Gbesical Co.)

Helamine / PorBaldehyde condensate, Cymel 301 (from American Cyanamid expelled)

- 28 109839/1620

(5) Thixotrol ST (from Baker ' Chemical sold) ■

The coating compound obtained was then applied with the aid of a coating knife to the substrate made of a phenolic resin in a wet thickness of about 0.08 mm, ^{dried for 4 1/2 minutes at a temperature of about 149 °} C. and for 2 hours at one temperature hardened by about 16 ^ ^{0 C.} Finally, in the manner described in Example I, suitable sector-shaped base elements were punched out of the coated phenolic resin substrate for use and investigation in a Model 3 potentiometer and their service life was examined. In these investigations it has been shown that coatings from the very even coating compound slide out less than 50% of the casting process.

There was yet another BeschicJituix ^ sEasoc eter following Composition made:

Components% by weight

Molybdenum disulfide. 40.0

Phenolic resin ^ 26.8

ψ Epoxy-modified phenolic resin ^ '15 »7

Hexame thoxyme thylme1amine ^ ' 1,8

Catechol 0.50

Polymeric thickener ^ 0.25

Isophorone 14.95

100.00

This second coating compound (which corresponded in its composition to the first coating compound, but with except that the silver flakes were replaced by molybdenum disulfide) were in a weight ratio of 1: 1 with the previous one prepared silver-containing coating mass mixed

- 29 109839/1520

BATH ORIGINAL.

and the mixture obtained with the help of a coating knife in a wet thickness of about 0.08 mm on the phenolic resin tapes applied. The tapes eventually became among those used in curing the first silver-containing coating composition cured conditions applied. A test of the wear resistance of the coating according to the above Scanning or rotating procedures indicated that the coating withstood more than 50,000 scans.

This result clearly shows the advantages that ♦ when mixing coating compositions containing a solid lubricant into coating compositions containing silver in the Can be achieved in terms of the desired wear resistance. It can also be seen from these results that from the coating compositions according to the invention an (electrical) Produce resistive, microdimensional layers or coatings that cool down 50,000 or more scanning processes permit,

Example VII

In the manner described in Example I and under the conditions specified there, numerous other one (electrical) resistance is produced, however, the polymeric carriers used according to the invention are replaced by other polymeric carriers, such as phenolic resins » Mixtures of phenolic resins and difunctional epoxy resins ^ Polybutadiene, diallyl isophthalate, and others have been replaced. In each case it has been shown that the respective coating considerably fewer scanning processes on the resistance element, i.e. only about 2Q0Q up to 10,000 scanning processes, withstood

- 30 109839/1520 "*

Claims (16)

Claims 1.) Coating compound with electrical resistance and excellent Abrasion resistance, in the form of a mixture of about JO to 95% by weight of a thermosetting polymeric material, consisting of a mixture of a trifunctional epoxy resin with a phenolic resin; from a mixture of an epoxy-modified Phenolic resin with a phenolic resin; from a mixture of a phenolic resin, a melamine resin or a precursor of which with an epoxy-modified phenolic resin; from a mixture of an epoxy-modified phenolic resin and a phenolic resin with an epoxy resin; or a melamine resin, and about 5 to about 70% by weight of conductive particles dispersed therein. 2 «) coating compound according to claim 1, characterized in that that the conductive particles consist of carbon particles having an average particle size of about 10 to about 400 millimicrons exist. 3 ») coating compound according to claim 1, characterized in that that the conductive particles consist of metal particles and that the coating compound ι based on their total weight, additionally at least about 30% by weight of a solid Contains lubricant. 4 ») coating compound according to claim 3, characterized in that» that the metal particles are silver particles and the solid lubricant made of molybdenum disulfide consists. -; - 5 ·) Beschichtunsmas se according to claim 1, characterized that in the mixture of tri- - 31 109839/1520 functional epoxy resin and phenolic resin these resins in one Contain weight ratio of about 1: 3 to about 1: 5 6.) coating compound according to claim 1, characterized in that that in the mixture used in each case of epoxymodif ized phenolic resin and phenolic resin, these resins in one Weight ratio of from about "1: 2 to about 1: 1" are. 7.) Coating composition according to claim 1, characterized in that in the mixture used in each case of phenolic resin, epoxy-modified phenolic resin and melamine resin, these resins in a weight ratio of etird 2: 1: 0.5 to about 1: 1: 0, 2 contain sincL 8.) Beschich.uungsm0.8se according to claim i, characterized by that in the mixture of epoxymodif used in each case iced phenolic resin, phenolic resin and 3po; -iy resin these Resins are included in a weight ratio of 1: 2: 1 to 1: 1: 1. · 9 ·) Coating composition according to one or more of the preceding Claims, characterized in that it contains a solvent for the polymeric carrier. 10.) Coating compound after; Claim 91 characterized in that that the solvent, about 5 to about 70 wt .-% of the total weight of the coating composition. 11.) Electrical resistance element with much improved Lifetime, consisting of a dielectric carrier or a dielectric base / and one applied to it! - 32 109839/15 20 Excellent abrasion-resistant coating, characterized in that the coating consists of a mixture of about 30-95% by weight a thermosetting polymeric material consisting of a mixture of a trifunctional epoxy resin with a phenolic resin; from a mixture of an epoxy-modified phenolic resin with a phenolic resin; from a mixture of a phenolic resin, one Melamine resin or a precursor thereof with an epoxy-modified phenolic resin; from a mixture of an epoxy-modified Phenolic resin and a phenolic resin with an epoxy resin; or a melamine resin, and about 5 to about 70% by weight is formed on conductive particles dispersed therein. 12.) Resistance element according to claim 11, characterized in that the coating as conductive particles with carbon particles an average particle size of from about 10 to about 400 millimicrons. 13 ·) Aries stand element according to claim 11, characterized in that dex ¹ coating contains metal particles as conductive particles and, based on the total weight of the coating, additionally contains at least about 30% by weight of a solid lubricant. 14.) Resistance element according to claim 13, characterized in that " It is not possible that the coating is made of silver pepper as a metal particle and as a solid lubricant contains molybdenum sulphide. 15) Resistance element according to claim 11, characterized in that that in the mixture forming the polymeric carrier of the coating of trifunctional epoxy resin and phenolic resin contain these resins in a weight ratio of about 1: 3 to about 1: 5 are. 16.) Resistance element according to claim 11, characterized in that in which the polymeric carrier of the coating forming Ge - 33 109839/1520 "^ mixed from © poxyHsodif! seventh phenol hara u »ci. this Hsrae in a weight ratio of about 1: .- 2 to it contains about 1 s 1, 1? ο) Widerstaxidseleraenfc asofe A & spruoia H ₃ οβΦ, ϊ;? eb. - characterized in that the polymeric carrier :? ds8 -libar-r / ugs forming mixture of phenolic resins ep ^ rj-modified © ^5;! Pfesnolharz and lelsminharzj this Harss ia sisiea ßawiohta ^ erMl-böis voa about 2 s 1 ί O _S 5 to about 1? 1 ι O _? 2 estteites. are, 1S _Q ) üidsrafcsÄdseleiaent aaoSi claim 1I ₅ dacliiroa characterized ₅ daS in the Gemisefi from spo: ^ - modified Pheaolha ^ K, Piisa.clherz and Eposyhsrs these resins in einoii Ge ^ i.cctsysri tos 1 ^ 2: 1 to 1 2 1 si enthaitea sindο 10-963S / 1B2Q