US2361435A - Coating articles carrying an insulating coating - Google Patents

Description

Oct. 31, 1944. r Q sw r I 2,361,435

comma ARTICLES. CARRYING AN INSULATING comma Filed Oct. 51; 1959 4? 2d may; .0. flzradz w eiiafi Patented Oct. 31, 1944 COATING ARTICLES CARRYING AN INSULATING COATING Milton 1). Swarts, Baltimore, and Kinloch N. Yellott, Cockeysvllle, Md., assignors to Far boil Paint Company, Inc., Baltimore, Md., a corporation of Maryland Application October 31, 1939, Serial No. 302,250 In Canada November 22, 1937 18 Claims.

The present invention relates to the coating of articles adapted to travel at high speeds with a cellulose derivative, said articles preferably carrying an undercoating acting primarily as a weather-proof and/or fire-retardant medium, although said under-coating 'may have other func- 1 tions.

The invention in its more specific aspect relates to the color coating of articles carrying a flame-proofing or weather-proofing coating, and which are adapted to be treated while traveling at high speeds, said articles being typified by wire conductors, cables, conduits, threads, ribbons, cords, tapes, gimps and the like. While the under-coating may be, as stated, any material which will weather-proof and flame-proof the conductor or other article being provided with a cellulose coating, preferably and usually the conductor which is being color coated carries a coating of pitch, such pitch coatings being well known in the prior art. Preferably, the pitch used to coat the article is an asphaltic pitch or a mixture of asphaltic pitch, stearine pitch, together with waxes and other materials. The pitch may contain a mineral filler.

The weather-proofed and flame-prooied jacketed electrical conductors now in use for the most part, are coated with stearine pitch or a material in which this is a major constituent. The stearine pitch may be used to impregnate and cover the fibrous Jacket of the conductor directly or the ilbrous jacket may be first impregnated with asphalt or other hydro-carbonaceous substances and then coated with the stearine pitch. In conductors of this type for the purpose of protection, beautification, improvement of the physical characteristics of the surface and/or for imparting thereto a distinctive coloration it is desirable and usual to apply to the pitch coated jacket an exterior color coating. Usually, although not necessarily, the color coating is provided with an additional coat of a sealing medium, which may assume various forms, but which is desirably a wax-like substance, as for example, parailin wax.

' In producing a colored jacketed conductor of the character herein set forth, the presence of the stearine pitch coating has always rendered the color coating of the conductors comparatively slow and dimcult operation. The stearine pitch is so readily softened and made tacky by ordinary paints and lacquers that a drying time cordance with the present invention, is relatively of at least fifteen seconds, or considerably more, a

is required when using prior art color coating materials. This drying time limits the speed at which the conductor may be color coated in a practical apparatus to about 126 to about 150 feet per minute or less. 1

In accordance with the presentinvention the articles being treated are provided with a coating, preferably a color coating, by applying to the articles a coating composition containing a cellulose derivative and a volatile solvent therefor having such a high rate of evaporation that the solvent of the color coating composition willnot be in contact with the pitch under-coating during the drying period for a suflicient length of time to materially attackthe pitch under-coating and render the same soft or tacky, said composition being applied while the article being treated is traveling at aielatively high rate of speed, which may vary from about 150 to 200 feet per minute as the lower limit, to about 650 to about 1000feet per minute as the upper limit.

The article being coated is only in contact with the coating composition presentin the coating pot for a relatively short period of time, usually less than a second, and during this short period of time the solvent of the coating composition, even if it is an active solvent for the under-coating, exercises relatively little solvent action upon the under-coating. In carrying out the present invention, the solvent medium for the nitrocellulose derivative, which has a high rate of evap-' oration or volatility of the order hereinafter pointed out, is usually, at least to some degree, a solvent for the under-coating of asphalt, stearine pitch, and the like, and,'therefore, the coating composition should not be in contact with the article carrying the under-coating during the coating step for such a period of time as to cause the solvent to act on the under-coating and cause softening and tackiness.

It is desired to point out that in contradistinction to the prior art the drying period, in acshort and that the speed at which the material is dried is exceedingly high as will hereinafter be pointed out in detail.

In order to illustrate the present invention, discuss the problems involved, and the solution of said problems, reference will be made to the accompanying drawing, in which:

Figure 1 is a plan view showing a jacketed conductor embodying the present invention Figure 2 is a perspective elevation of a suitable coating and drying device for carrying out the present invention. Figure 3 is a cross sectional view of the applicator pot taken on the line 3-4 of Figure 2. Figure 4 is a detail of the top sheave. Figure 5 is a detail oft-he wiping Basket. The coating and drying apparatus comprises an applicator pot i suitably located in a tower It, said applicator pot being provided with a partition 2, whereby there is formed a compartment 3 adapted to contain the color coating composition 5, and a wax coating compartment 4 adapted to contain a waxing material 6., Suitable upper and lower rolls 1 and 8 are provided, the wire 9, which is to be color coated, passing fromthe pay-off reel l0, under guide roll I I, and through the coating solution 5, contained in the applicator pot compartment 3. The wire 8 passes through the coating composition, through the wiping gasket i2, around the upper roll I, then back down and around the lower roll 8, then through the coating composition a second time, and, if necessary, through the coating composition a third time. Thereafter, the coated and dried wire passes through the waxing compartment 4 and then to the re-wind reel 13. The tower is preferably, although not necessarily, an air-conditioned chamber, that is, the chamber may be controlled from the standpoint of temperature and from the standpoint of humidity.

In a commercial process the coating applied to the wire 9 must become dried during the period of its travel from the applicator pot i to the top roll or sheave i. If the coating which has been applied to the wire is not dried by the time it touches the top roll 1, the coating will be marred or removed by the roll and, furthermore, portions of the wire carrying the coating will stick together when the wire is re-wound on the re-wind reel l3.

Fundamentally, it is apparent that the distance between the applicator pot l and the top roll I and the speed of drying of the coating composition determine the speed or rate of travel per minute at which the wire 8 may be pulled through the coating composition 5.

In the apparatus now used for coating conductors, the distance from the coating vessel I to the top roll I varies between 1'7 and 55 feet. This distance is based upon practical considerations, as will be apparent from the following: The electric conductor which is treated usually comprises a bare wire A, a rubber sheathing B, a cotton sheathing C, which may or may not be impregnated with a waterproofing compound D, such as asphalt. To the wire thus treated there is usually applied a coating E of a flame-retardant material, said coating preferably being stearine pitch or a mixture of stearine pitch and other elements, as herein set forth. It is quite customary to cover the stearine pitch coating E with a color coating F. Upon the color coating F there is applied a wax-like coating G.

It is desired to point out that the color coating composition which'has hitherto been used comprises a pigmented alcohol soluble gum, or a pigmented cellulose compound or derivative dissolved in a combination of solvents.

More specifically, it has been the practice to provide the color coating over the setarine pitch by compounding an alcohol soluble gum with alcohol, or with alcohol together with other solvents, such as toluol, benzene and the like,'a pigment and suitable plasticizer. It has alsobeen proposed to provide a pigmented cellulose derivative with a mixture of suitable solvents, these solvents being those ordinarily found in cellulose lacquers. In this connection, it is desired to point out that celluloselacquers ordinarily contain a plurality of solvents; usually a fast solvent, such as acetone or ethyl acetate; a medium solvent, typified by butyl acetate: and a slow solvent, typified by amyl acetate, together with various other solvents such as alcohols, esters. he-

tones, ethers, and diluents, such as benzol. toluol, etc. However, the use of these hitherto known materials as a coating composition for a stearine pitch coating has involved material difficulties, since the stearine pitch became readily softened by the combination of solvents present in the coating composition.

It has been proposed to obviate the stickiness by subjecting the stearine pitch covered article to a curing step between the application of the first and second coats or by applying an intermediate coat or film such as silicate of soda under or between the lacquer coatings. However, this latter method has not been commercially successful for a variety of reasons which are well known.

Utilizing the color coating compositions which have been used in practice, it has been necessary to allow a relatively long period of time for the passage of the wire from the coating vessel I to the upper roll I. For example, in a tower which is 25 feet in height it has been necessa y to allow twelve to fifteen seconds for the passage of the wire from the coating vessel 1 to the upper roll 1, so that suflicient time may be allowed for the stearine pitch coating of the conductor to lose its stickiness as it passes from the coating vessel I to the upper roll I. If it i necessary to allow fifteen seconds for the coating to dry and the stearine pitch to lose its tackiness then the speed of travel of the conductor is limited to feet per minute. If it is necessary to allow twelve seconds to elapse, then the speed of travel of the conductor in order for the stearine pitch tolose its stickiness and the coating to dry, will be feet per minute. It is, therefore clear that the problem involved resides in correlating a high speed of travel of a conductor carrying an insulating coating adapted to be affected by the solvent of a color coating composition, with a color coating composition which has a fast rate of evaporation when applied over the insulating coating.

' In a specific application of the invention the conductor or other article adapted to be treated in accordance with the present invention carries a coating of stearine pitch, or a mixture of stearine pitch with an asphalt pitch, or a coating having the characteristics of stearine pitch or a mixture thereof with asphalt pitch.

It has been discovered that if a conductor carrying a flame-proofing coating, which in the preferred form is the commonly accepted prior art stearine pitch, has applied thereto a color-coat ing composition containing a cellulose derivative. capable of adhering to said conductor, and a solvent or mixture of solvents having such an onceedingly high rate of evaporation of the character hereinafter more specifically set forth. that the color coating of the conductor and the drying thereof may be carried out-at exceedingly high speeds, ranging from about to about 200 feet per minute, to about 800 to about 1000 feet per minute, said high speed of travel of the wire being possible because the solvent of the color coating inthepreferrcdformofthemventlomaresin.

It has been pointed out that the prior-art coating compositions contain medium or high boiling solvents, together with diluents, said solvents being incapable of volatilizing sumciently rapidly from the stearine pitch to prevent the same 5 from becoming soft and tackyto some extent.

Table I Vapour Solubility 8...... has; Boning y g gi g he? fleew range grav y a p e an an other i mm air 1 l esters Acetone 2.1 65-56 0. 791 180 2.01 -17 NC, AC Methyl acetate 2. 2 56-62 0. 932 170 2. 56 l3 NC, AC Special solvent A (Hiag) 2. 2 M 0-80-0. 90' 175 l8 NC, AC Solvent E-33 (I. G.) 2.3 62-60 0.895 173 1.91 -10 NC, AC

Special solvent EMA (Wackcr) 2. 3 60-75 0.893 -12 NC, A Solvent 13-14 (I. G.) 2. 4 52-62 0.873 194 l. 85 l0 NC, AC Special solvent (Hiag) Z 4 63-64 0-80-000 1 195 -l6 NC, AC Solvent E-l3 (I. G.) 2. 66-03 0. 885 186 1.07 NC, AC Special solvent C (Wanker) 2. 5 00-75 0. 87 l4 NC, AC

or 2% feet per second, this being necessary because sufficient drying time must elapse for the wire or conductor to be dried during its travel from the point of application of the coating solution to its next point of contact.

In contradistinctio'n to the prior art practice,

( and in accordance with the'present invention, the

coating composition only requires, instead of from about twelve to fifteen seconds to dry, usually about one and one-half to three seconds. In other words, in a twenty-five foot tower if one and one-half seconds are required for drying, the wire can travel at approximately sixteen and onehalf feet per second, which is approximately 1000 feet per minute. If three seconds are required for drying, then the wire can travel approximately eight feet per-second in covering the twentyflve feet, this being roughly about 500 feet per minute. The important point is that in the past the speed at which the conductors were coated were limited largely by the time required for the coating to dry, and when employing as a constituent of the color coating composition a solvent which did not evaporate very quickly from the undercoating, as typified by asphalt, stearine pitch, and the like, necessarily the speed of travel was slow. With the utilization of a color coating composition having a solvent which has a volatility of the character herein set forth, the limitation as to speed is governed substantially Of the above, acetone functions best as a solvent for the color coating composition.

Methyl acetate, which has just a little slower rate of evaporation, also gives excellent results, and especially so when mixed with relatively small proportions of methyl alcohol. It may be stated that special solvent E43, above set forth, consists chiefly of methyl acetate and a relatively small proportion ofmethyl alcohol.

Special solvents E-ll and E-ll, while possessing about the same properties, are different in that E-II has a greater speed of solution and.

forms solutions of nitrocellulose and cellulose acetate of lower viscosity than E t-l4.

Special solvent EMA (Wacker) is somewhat less volatile than acetone or methyl acetate, but has properties similar to the above referred to special solutions.

It may be stated that in the mixed solvents above set forth, which are essentially mixtures of some or all of the following: methyl acetate,

entirely by the mechanical difllculties'involved in handling conductors at high speeds of about 600 feet to about 900 feet per minute. It is clear ethyl acetate, acetone, methyl alcohol and the acetals, the methyl alcohol functions to produce a desirable effect on the viscosity of the cellulose solutions and on their uniformity of drying. Of course, in all of the above, low boiling solvents are present in the composite solvents which are really azeotropic mixtures. These mixed solvents are advantageous in that not only do they have an exceedingly high rate of evaporation, as for example, between 2.2 and 2.5 (based on the volatility of ether as 1), but they dissolve the cellulose ethers and esters to form solutions of exceptionally low viscosity which evaporate very smoothly;

It is within the province of the present inven tion to employ in the color coating composition a solvent which has a high rate of volatility, based on ether as 1, with a solvent, which has a slightly less high rate of evaporation or volatility, based on ether as 1, to thereby form a composite solvent having a rate of volatility between '2 and 2.8, said composite solvent having such a rate of evaporation as to enable it to be used in a color coating composition which will 'allow wire coated therewith to dry while traveling at relatively high speeds, as for example, to 200 to 400 to 450 feet per minute, or 150 to 200 to 700 feet per minute, or 150 to 200 to 950 feet per minute.

Some of these secondary solvents are solvents for nitro-cellulose and acetate cellulose; some of them are solvents only for thenitro-cellulose;

and some of them have no solvent action on the cellulose derivative. However, necessarily, those secondary solvents which have no solvent action upon the cellulose derivative must be employed in relatively small quantities.

While in Table I there have been set forth certain mixed solvents which have a relative volatility based on ether, these mixed solvents have a volatility ranging between 2.2 and 2.8. Other mixed solvents may be made by combining a solvent having a high relative volatility, as for example, methyl acetate with a small proportion of a secondary solvent, which has a relative volatility higher than 2.8, to thereby produce a composite azeotropic solvent, which does not have a relative volatility compared to ether of higher than 2.6 or 2.7, or 2.6, 2.7, or 2.8, the preferred composite azeotropic solvents having volatility numbers of about 2.2, or 2.3, or, in certain cases, 2.4, but certainly not higher than 2.8.

In Table II, which follows, there is set forth secondary solvents which may be combined with the primary solvents set forth in Table I.

Table 11 Solubility for cellulose ethers and esters Relative Solven volatility Ethyl acetate Carbon tetrachloride.

Benzene Light petroleum Trichloroethylene.

Ethylene chloride Iso-propyl acetate Ethyl propionate Toluene Iso-butyl acetate swm swees w s \IWWHHDINHWOI In the above table symbols NC and AC indicate the solubility of cellulose ethers and esters in the respective solvents.

The following are examples of suitable coating compositions:

Example I Per cent Metallic red oxide 33.33 Filmscrap or cellulose nitrate 7.82 Shellac .78 Acetone 56.97 Methyl alcohol .94 Beta naphthol .16

Example 11 Per cent Chrome green 5.5 Yellow iron oxide 8.5 Titanium dioxide 3.6 Lamp black .93 Prussia blue .93 Filmscrap 8.8 Camphor .28 Shellac 3.42 Methyl alcohol 2.97 Beta naphthol .14 Acetone 64.93

Example III Per cent Metallic red oxide 27.5 Filmscrap r cellulose nitrate 8.7 Shellac 1.2 Acetone 61.08 Methyl alcohol 1.41

Beta naphthol .10

Example IV Per cen American whiting 9.65 Asbestine 5.60 5 Red iron oxide 15.30 Film scrap 7.15 Alkyd resin 3.28 Aluminum stearate 0.87 Beta naphthol 0.005 Hydrogenated petroleum fraction 7.95

Acetone 50.195

Example V Per cent Titanium dioxide 37.0

Ferric oxide yellow 1.88 Lead chromate 7.08 Red iron oxide 1.25 Film scrap 5.16 Alkyd resin 3.96

Maleic anhydride resin 2.475 Blown castor oil 1.88 Methyl acetate 33.40 Methyl alcohol- 5.91 Beta naphthol 0.005 In the above examples for the methyl alcohol and hydrogenated petroleum fraction there may be substituted other secondary solvents,

The cellulose compound may be film scrap, 0 cellulose nitrate, cellulose acetate, ethyl cellulose,

cellulose formate, propionate and butyrate, any of the higher fatty acid cellulose compounds, or any of the cellulose materials commonly used in the manufacture of lacquers. While the cellulose base used in lacquers is suitable for carrying out the present invention, as pointed out, these lacquer compositions themselves cannot be used because practically all of them contain a plurality of solvents and diluents, and some of these solvents and diluents make the stearine pitch or its equivalent tacky. It is to be noted that in the examples, there is present a small percentage of shellac or other resin, together with a solvent for the resin, such as methyl alcohol, benzene, toluol, or the like. The shellac and other resins set forth are examples of a material present in the coating composition which confers on the latter the proper adhesive properties during the process of applying the coating to the stearine pitch E, and

also inducing the proper adhesion of the dried coating or film to the stearine pitch base. Instead of using resins of the character set forth, any resin or fossile gum, together with a proper solvent, may be used for the purpose specified. Alternatively, gums of the class known as synthetic gums may be used. More specifically, the synthetic resins may be phenol formaldehyde condensation products, furfural condensation products, and urea formaldehyde condensation products, alkyd resins, and the like. Broadly, the natural and synthetic resins are applicable. The resins and resins are set forth as an example of a material functioning to increase the adherence of the cellulose derivative fllm to the stearine pitch, that is,'as an example of a material which keeps the cellulose derivative solution from wiping oil. the wire too cleanly as it passes through the aperture [2a of the wiping gasket II, and also induces the proper adhesion of the dried coating or fllm to the stearine pitch base. This adhesion of the color coating to the stearine pitch covered conductor should be sufllci'ent to allow the conductor to be flexed and bent or twisted without the color coating flaking oil. It is not necessary thatthefllmbemfiicientiyelastictostand adru- I camphor.

tic bend without cracking. There is no objection to cracking provided the color coating does not readily flake off when the conductor is straightened to its original formii, The opacity of the color coating is preferably suilicient to cover the dark stearine pitch and produce the desired color. When dark colors are used a very thin film is suflicient but when light colors such as light green, yellow, white, ivory, etc., are'required it is desirabl that the film be appreciably thicker.

The present invention is not limited to the use of the resins. Any material which will perform this function may be used, and considered from this point, the invention resides in the combination of a pigmented cellulose derivative with a solvent having the characteristics set forth, together with an agent which will function to increase the adherence of the cellulose derivative solution to the stearine pitch of its equivalent.

While ethyl alcohol and methyl alcohol, have been set forth as solvents for the shellac, rosin or resin that is used, it is obvious that any other solvent for the adhesion-inducing agent may be used, provided it is not present in such proportions asto bring the volatility of the composite solvent to a point greater than 2.8 or thereabouts, the latter number being based on ether having a volatility of unity. Some of the resins specified are soluble in the primary solvent, as for example, acetone and methyl acetate, and in that case it will not be necessary to add an extra solvent for the adhesion-inducing agent, although in some cases it may be desirable, because the solvent for the adhesion-inducing agent will perform other functions in the composition.

Reierringto Examples I to V inclusive, it is to be noted that the solvent for the adhesion-inducing agent, as for example, methyl alcohol is only present in a small proportion, ranging from about 1% to 8%. The criterion is that the solvent for the adhesion-inducing agent should be present in a proportion sufllcient to dissolve said agent and, further, in the preferred form of the invention, to keep the volatility number of the composite solvent not greater than 2.8 or 2.9. Preferably, the coating composition should contain a plasticizer. When film scrap or Celluloid is used as a cellulose derivative base, the latter already contains thev plasticizer. However, if the cellulose derivative does not contain the plasticizer it is preferably added to the composition in a small percentage.

Any of the plasticizers well known in the prior art may be used, as for-example, a small percentage of It is also desirable that the coating composition carry a small amount of material acting as an insecticide or a fungicide, as for ex ample, beta naphthol.

The color coating cgmposition has added there: to a pigment, which may be any opaque substance capable of being mixed and/or ground into the vehicle, as for example, zinc oxide, iron oxide, and the like.

In compounding the color coating composition, the film scrap or the ceileulose derivative is dissolved in the solvent, as for example, acetone, and the adhesion-inducing agent, as for example, shellac, is. dissolved in a solvent therefor. The two solutions are then mixed in the proportions set forth in the examples, and the pigment is then mixed in or ground in in amill, such as a ball mill. More specifically, 7.82 pounds of film scrap are dissolved in 56.97 pounds of acetone, then .78 of a pound of shellac is dissolved in .94 of a pound of alcohol, making 1.72 pounds of shellac solution. The two solutions are then mixed and the pigment is added and thereafter the beta naphthol. The entire mixture is then ground in a ball mill,

It is recognized that the viscosity of the cellulose derivative composition or solution may be reduced by varying the amount of solvent, as for example, acetone, to produce a thicker or more viscous solution. In other words, the present invention is not limited to a cellulose nitrate or a cellulose acetate solution of the character set forth in the specific examples.

Cellulose solutions of various viscosities may be used, varying anywhere from extremely low viscosity, such as one-half second cotton, to a very high viscosity, such as sixty second cotton. In the preferred form of the invention, the nitrocellulose is in the form of film scrap.

It is desired to point out that the coating which is applied to the wire 9 is exceedingly thin. The criterion as to the thickness of the coating is that the coating must be of such a character as to cover the wire with the thinnest film which will give the desired opacity and at the same time.

fulfil the physical characteristics hereinbefore pointed out.

When once the thickness of the coating has been determined, the wiper i2 is set so as to apply a coating having the predetermined thickness. Therefore, while the viscosity of the cellulose solution is an item to be considered, the thickness of the final coating is not determined by the viscosity of the cellulose solution, but by the adjustment or the gasket l2.

v The gasket I2 is provided with a, central aperture Ila. The size of this aperture is usually slightly smaller than the diameter of the stearine pitch coated wire. The diameter is slightly smaller than the diameter of the coated wire because the gasket which is of thin flexible rubber gives as the wire is pulled through. In this way, the size of the hole is increased. In carrying out the present invention, the hole was made smaller than the standard hole for a standard or normal sized wire because with the high increase in the speed of wire travel the hole flexed more and became larger.

In the-examples given, the percentage of adhesion-inducing agent varies from .78% to about 6.50%. While the above examples set forth the preferred mixtures it is recognized that the amount of resin, including shellac, alkyd resins, and the glyptals preferably varies roughly between .5% to 10%, and may under some circumstances be as high as 20%. When' the resin varies as set forth, the solvent will vary as set forth. In other words, as the resin varies from .5% to 10% the solvent therefor may vary from about .5% to 6 or 6.50% or even higher, subject to the limitation that the solvent for the resin should not confer upon the composite solvent of the coating composition a volatility number greater than 2.8 or 2.9, .based on ether having a volatility number of unity.

It mayb pointed out that the percentage of ingredients in the above mixtures maybe con siderably varied and still come within the spirit .-pmsent may be considerably varied. A higher percentage of shellac or resin improves adhesion but somewhat decreases the speed .of drying. However, the resin is present in such a small amount that it can be substantially increased from the standpoint of a percentage increase and still not greatly vary the properties of the final coating composition. For example, the solvent for the film scrap may be 98%% acetone or methyl acetate, or any substitution product of acetone or any ketone, said solvent having a volatility varying between about 2.1 and 2.4, based on ether as unity, together with about 1%% of methyl alcohol or other secondary solvent. The secondary solvent may run from 3% to 8% and in exceptional cases may be considerably higher. The quantity of secondary solvent that may be added can be stated in a slightly different manner. The secondary solvent, as for example, methyl alcohol, ethyl alcohol, benzene and the like, may be added in excess of that required for solution of the resin, provided the drying rate of the composition is not slowed up enough to materiallyreduce the speed of travel below 450 to 1000 feet per minute. However, in the preferred form of the invention it is contemplated to add only so much secondary solvent as will dissolve the adhesion-inducing agent, typified by shellac. resin or any other material which will function to increase the adhesion properties of the coating composition. In this connection it may be stated that while the resin is the preferred adhesioninducing agent, it is recognized that there may be substituted therefor other adhesion-inducing agents, and the invention in its broadest form, contemplates the addition to the color coating composition of any adhesion-inducing agent where the presence of such an agent is necessary.

It is desired to point out that the cellulose derivative may be a cellulose ether or ester, or any substituted compounds thereof, or mixtures of the same. More specifically. the cellulose compounds may be the cellulose acetates, the cellulose nitrates, or the cellulose xanthates, or the like. In connection with the use of these cellulose compounds in the color coating composition it is desired to state that the solvent therefor is one which has a low enough surface tension to allow its fast evaporation and, further, that the surface tension of the solvent is such as to enable the solvent to be quickly released from contact with the stearine pitch or other insulating medium and thereby inhibit the production of any stickiness in the stearine pitch. a

The stearine pitch, which is preferably used on the conductors treated in accordance with the present invention, typifies the residue which remains in the retorts from which is distilled by vacuum distillation, such free fatty acids as stearic, palmitic, oleic, myristic and the like, such as may be obtained from oleo stearine, lard oil,

cotton-seed, soya bean oil, corn oil, and the like,

position of the character herein set forth for t e l In one aspect of the invention the article carries a protective coating, which may be weatherprooiing or flame-proofing in character, and in the preferred form the article is impregnated or coated with asphalt, stearine pitch, or the like.

While the invention has been described in connection with the flame-proofing of an electrical conductor, it is recognized that the basic concept of the invention may be applied to other articles carrying a coating of any kind of material, but

preferably a material typified by asphalt, stearine pitch, or the like, which during drying under normal circumstances would be softened or made tacky if there was applied thereto a coating composition of the character herein described, containing a solvent having a volatility number greater than about 2.8 or about 2.9.

More specifically, textile and/or paper filaments, threads, ribbons, cords, tapes, gimps, and the like, which have a coating or impregnation of asphalt, stearine pitch, or similar hydrocarbonaceous material, may be coated and dried in accordance with the present invention. The present invention may also be used in the production of tire tape. Ordinary tire tape is impregnated on both sides with an asphaltic compound, such 200 feet to 450 to 1000 feet per minute.

Insulating tape, which is commonly designated as tire tape, but which, of course, may be used for various other purposes if treated as above set forth improved durability and appearance and does not discolor other articles which come in contact with it. It may be used for splices in electrical conductors.

If the article to be treated is cylindrical or Ovll in form it may be passed through a coating composition and treated in an apparatus of the charthe like may have applied thereto, while they are traveling at the rate of between 150 to 200 feet and 850 to 1000 feet per minute, a coating composition containing a cellulose derivative and a volatile solvent therefor, having a volatility between 2 and 2.8 or 2.0, said solvent of the color coating composition being substantially a nonsolvent for the asphalt, stearine pitch and the It is recognised that the adhesion-inducing agent of the coating composition may be natural or synthetic gum or resin, such as fcssile gum, or any of the synthetic resins, as for example, glyptal resins, alkyd resins, phenol formaldehyde condensation products. urea formaldehyde condensation products, and the like.

The adhesion-inducing agent is one that is compatible with the cellulose derivative med. By compatible is meant that the nitro-cellulose and gum form a 1 solution, and.

7. whenailowedtodryleavesambstantiallyhomo present invention. to color coat at relatively high speeds, the wax coating may be applied to the wire in molten form after the conductor has been given a color coating. In other words, it is possible to apply the wax coating in molten form by passing the conductor through the wax bath present in chamber 4, instead of spraying on the hot wax-like coating, as has been the usual prior art practice. Prior to the present invention the conductor with the dried color coating travelled so slowly that it could not be passed through molten paraflln or wax, because the color coating and the under-coating of stearine pitch became softened or melted. In contradistinction, employing the present invention the time of passage through the molten wax is so short that there is no material softening of the color coating composition or the under-coating of the conductor. However, conductors produced in ac cordance with the present invention may be given a wax-like coating by spraying on a thin film of a paraffin emulsion. Likewise, it is desired to point out that while the conductor is preferably coated with the color coating composition by passing the conductor through the composition in the applicator pot I, it is obvious that the coating composition may be applied in other ways, as by spraying the composition coating thereon, since, due to the particular solvent employed in the color coating composition, there is practically a flash drying, a substantially so.

This application'is a continuation in part of application Serial No. 174,682, filed Nov. 15, 1937.

What is claimed is:

1. The method of providing an article carrying a protective coating of pitch with an adherable cellulosic coating, comprising depositing an adherable homogeneous cellulosic coating on the article, and drying the deposited coating while the article during said coating and drying steps is traveling at a linear speed varying between 200 and 1,000 feet per minute, said coating composition containing a cellulose derivative dissolved in an organic solvent, and preventing the pitch coating from becoming soft and tacky during the coating and drying steps by having the coating time-period so short that the solvent component of the coating composition exerts during coating little softeningactionon the pitch coating, and by having the solvent medium of the coating composition characterized by t e property of being so quickly released during drying from the coating composition and from the surface of the pitch coaitng as tov inhibit any substantial softening action on the pitch coating, said solvent medium consisting essentially of a solvent selected from the group consisting of a low boiling point ketone, methyl acetate and ethyl acetate, said solvent medium having a relative volatility varying between 2v and 2.9, base on ether having unit volatility. V 1

2. The methodof providing anar'ticle carrying a protective coating of pitch with an adherable cellulosic coating, comprising depositing an adherable homogeneous cellulosic coating on the article, and drying the deposited coating while the article during said coating and drying steps is traveling at a linear speed varying between 200 and 1,000 feet per minute, said coating composition containirgg a cellulose derivative dissolved in an organic olvent, and preventing the pitch coating from becoming soft and tacky during the coating and drying steps by having the coating time-period so short that the solvent component of the coating composition exerts during coating little softening action on the pitch coating, and by having the solvent medium of the coating composition characterized by the property of being so quickly released during drying from the coating composition and from the surface of the pitch'coating as to inhibit any a substantial softening action on the pitch coating, said solvent medium consisting essentially of a low boiling point ketone, said solvent medium having a relative volatility varying between 2 and 2.9, based on ether having unit volatility.

able cellulosic coating, comprising depositing an adherable homogeneous cellulosic'coating on the article, and drying the deposited coating while the article during said coating and drying steps is traveling at a linear speed varying between 200 and 1,000 feet per minute, said coating composition containing a cellulose derivative dissolved in an organic solvent, and preventing the pitch coating from becoming soft and tacky during the coating and drying steps by having the coating time period so short that the solvent component of the coating composition exerts during coating little softening action on the pitch coating, and by having the solvent meduim of the coating composition characterized by the 40 property of being so quickly released during drying from the coating composition and from the surface of the pitch coating as to inhibit any substantial softening action on the pitch coating, said solvent medium consisting essentially of methyl acetate, said solvent medium having a relative volatility varying between 2 and 2.9, based on ether having unit volatility.

4. The method of providing an article carrying a protective coating of pitch with an adherable cellulosic coating, comprising depositing an adherable homogeneous cellulosic coating on the article, and drying the deposited coating while the article during said coating and drying steps is traveling at a linear speed varying between 2.00 and 1,000 feet per minute, said coating composition containing a cellulose derivative dissolved in an organic solvent, and preventing the pitch coating from becoming soft and tacky during the coating and drying steps by having the coating time-period so short that the solvent component of the coating composition exerts during coating little softening action on the pitch coating, and by having the solvent medium of the coating composition characterized by the property of being so quickly released during'drying from the coating composition and from the surface of the pitch coating as to inhibit any substantial softening action on the pitch coating, said solvent medium consisting essentially of acetone, said solvent medium having a relative .-.volatility varying between 2 and 2.9, based on positing on said conductor an adherable homogeneous cellulosic coating, and drying the deposited coating while the conductor during said coating and drying steps is traveling at a linear speed varying between" 200 and 1,000 feet per minute, said coating composition containing a cellulose derivative dissolved in an organic solvent, and preventing the pitch coating from becoming soft and tacky during the coating and drying steps 'by having the coating time-period so short that the solvent component of the coating composition exerts during coating little softening action on the pitch coating, and by having the solvent medium of the coating composition characterized by the property of being so quickly released during drying from the coating composition and from the surface of the pitch coating as to inhibit any substantial softening action on the pitch coating, said solvent medium consisting essentially ofa solvent selected from A the group consisting of a low boiling point ketone, methyl acetate and ethyl acetate, said solvent medium having a relative volatility varyin between 2 and 2.9, based on ether having unit volatility.

6. The method of providing an electrical condu r carrying a protective coating of pitch with an adherable cellulosic coating, comprising depositing on said conductor an adherable homogeneous cellulosic coating, and drying the deposited coating while the conductor during said coating and drying steps is traveling at a linear speed varying between 200 and 1,000 feet per minute, said coating composition containing a cellulose derivative dissolved in an organic solvent, and preventing the pitch coating from becoming soft and tacky during the coating and drying steps by having the coating time-period so short that the solvent component of the coating composition exerts during coating little softening action on the pitch coating, and by having the solvent medium of the coating composition characterized by the property of being so quickly released during drying from the coating composition and from the surface of the pitch coating as to inhibit any substantial softening action on the pitch coating, said solvent medium consisting essentially of a low boiling point ketone, said solvent medium having a relative volatility varying between 2 and 2.9, based on ether having unit volatility.

7. The method of providing an electrical conductor carrying a protective coating of pitch with an adherable cellulosic coating, comprising depositing on said conductor an adherable homoeneous cellulosic coating, and drying the deposited coating while the conductor during .said

coating and drying steps is traveling at a linear speed varying between 200 and 1,000 feet per minute. said coating composition containing a cellulose derivative dissolved in an organic sol vent, and preventing the pitch coating from becoming soft and tacky during the coating and drying steps by having the coating time-period so short that the solvent component of the coating composition exerts during coating little softening action on the pitch coating, and by having the solvent mediumof the coating composition characterized by the property of being so quickly released during drying from the coating composition and from the surface of the pitch coating as to inhibit any substantial softenin action on the pitchcoating, said solvent medium conslstingessentially of acetone, said solvent meaccuse dium having a relative volatility varying between 2 and 2.9, based on ether having unit volatility.

8. The method of providing an electrical conductor carrying a protective coating of pitch with an adherable cellulosic coating, comprising depositing on said conductor an adherable homogeneous cellulosic coating, and drying the deposited coating while the conductor during said coating and drying steps is traveling at a linear speed varying between 200 and 1,000 feet per minute, said coating composition, containing a cellulose derivative together with an organic soluble resin of the class consisting of natural and synthetic resins, said resin being compatible with the cellulose derivating, and present in the coating composition in an amount which increases the adhesion of the cellulosic coating to the pitch coating; and preventing the pitch coating from becoming soft and tacky during the coating and drying steps by having the coatingtime period so short that the solvent component of the coating compomtion exerts during coating little softening action on the pitch coating, and by having the solvent medium of the coating composition characterized by the property of being so quickly released during drying from the coating composition and from the surface of the pitch coating as to inhibit any substantial softening action on the pitch coating, said resin and cellulose derivative being dissolved in a composite organic solvent consisting essentially of a low boiling point ketone together with a resin solvent, the latter being present in a minor proportion insufiicient to increase the volatility number of the composite solvent medium to greater than 2.9, said volatility number being based on ether having unit volatility.

9. The method of providing an electrical conductor carrying a protective coating of pitch with an adherable cellulosic coating, comprising depositing on said conductor an adherable homogeneous cellulosic coating, and drying the deposited coating while the conductor during said coating and drying steps is traveling at a linear speed varying between 200 and 1,000 feet per minute, said coating composition containing a cellolose derivative together with an organic soluble resin of the class consisting of natural and synthetic resins, said resin being compatible with the cellulose derivative, and present in the coating composition in an amount which increases the adhesion of the cellulosic coating to the pitch coating; and preventing the pitch coating from becoming soft and tach during the coating and drying steps by having the coating time-period so short that the solvent component of the coating composition exerts during coating little softening action on the pitch coating, and by having the solvent medium of the coating composition characterized by the property of being so quickly released during drying from the coating composition and from the surface of the pitch coating as to inhibit any substantial soiteningaction on the pitch coating; said rain and cellulose derivative being dissolved in a composite organic solvent consisting essentially of coating, comprising depositing on said conductor an adherable homogeneous cellulosic coating, and drying the deposited coating while the conductor during said coating and drying steps is traveling at a linear speed varying between 200 and 1,000 feet per minute, said coating composition containing a substantial proportion of pigment and 7% to of a cellulose derivative based on the weight of the composition, said cellulose derivative being dissolved in an organic solvent, and preventing the pitch coating from becoming soft and tacky during the coating and drying steps by having the coating time period so short that the solvent component of the coating composition exerts during coating little softening action on the pitch coating, and by having the solvent medium of the coating composition characterized by the property of being so quickly released during drying from the coating composition and from the surface of the pitch coating as to inhibit any substantial softening action on the pitch coating, said solvent medium being present in the coating composition in an amount of about 40% to 65% based on the weight of the coating composition, said solvent medium consisting essentially of a solvent selected from the group consisting of a low boiling point ketone, methyl acetate and ethyl acetate, said solvent medium having a relative volatility varying between 2 and 2.9 based on ether having unit volatility.

11. The method of providing an electrical conductor carrying a protective coating of pitch with an adherable cellulosic coating, comprising depositing on said conductor an adherable homogeneous cellulosic coating, and drying the deposited coating while the conductor during said coating and drying steps is traveling at a linear speed varying between 500 and 1,000 feet per minute, the drying time varying from about 1 seconds to about 3 seconds for each -foot unit of the conductor, and preventing the pitch coating from becoming soft and tacky during the coating and drying steps by having the coating time period so short that the solvent component of the coating composition exerts during coating little softening action on the pitch coating, and by having the solvent medium of the coating composition characterized by the propertyof being so quickly released during drygeneous cellulosic coating, and drying the de-' posited coating while the conductor during said coating and drying steps is traveling at a linear speed varying between 500 and 1,000 feet per minute, said coating composition containing a cellulose derivative dissolved in an organic solvent, and preventing the pitch coating from becoming soft and tacky during the coating and drying steps by having the coating time-period so short that the solvent component of the coating composition exerts during coating little softening action on the pitch coating, and by having the solvent medium of the coating composition characterized by the property of being so quickly released during dry-ing from the coating composition and from the surface of the pitch coating as to i it any substantial softening action on the p tch coating, said solvent medium consisting essentially of a solvent selected from the group consisting of a low boiling point ketone, methyl acetate and ethyl acetate, said solvent medium having a relative volatility varying between 2 and 2.9, based on ether having unit volatility.

13. The method of providing an electrical conductor carrying a protective coating of pitch with an adherable cellulosic coating, comprising depositing on said conductor an adherable hOXIlO- geneous cellulosic coating, and drying the deposited coating while the conductor during said coating anddrying steps is traveling at a linear taining a cellulose derivative dissolved in an organic solvent together with an organic soluble resin of the class consisting of natural and synthetic resins, said resin being compatible with the cellulose derivative, and present in the coating composition in an amount which increases the adhesion of the cellulosic coating to the pitch coating; and preventing the pitch coating from becoming soft and tacky during the coating and drying steps by having the coating time-period so short that the solvent component of the coating composition exerts during coating little sof tening action on the pitch coating, and by having the solvent medium of the coating composition characterized by the property of being so quickly released during drying from the coating composition and from the surface of the pitch coating as to inhibit any substantial softening action on .the pitch coating, said solvent medium consisting essentially of a low boiling point ketone together with a resin solvent, the latter being present in a minor proportion insuflicient to increase the volatility number of the composite solvent medium to greater than 2.9, said volto about 3 seconds for each 25-foot unit of the conductor, said coating composition containing a cellulose derivative dissolved in an organic sol.

vent together with an organic soluble resin of the class consisting of natural and synthetic resins, said resin being compatible with the cellulose derivative, and present in the coating composition'in an amount which increases the adhesion of the cellulosic coating to the pitch coata ing; and preventing the pitch coating from being action on the pitch coating, and by having v the solvent medium of the coating composition characterized by the property of being so quickly released during drying from the coating composition and from the surface of the pitch coating as to inhibit any substantial softening action on the pitch coating, said solvent medium consisting essentially of methyl acetate together with a resin solvent, the latter being present in a minor proportion insufllcient to increase the volatility number of the compositev 'solvent medium to greater than 2.9, said volatility number being based on ether having unit volatility.

15. The method of providing an electrical con ductor carrying a protective coating of pitch with an adherable cellulosic coating, comprising depositing on said conductor an adherable homogeneous cellulosic coating, and drying the deposited coating while the conductor during said coating and drying steps is traveling at a linear speed varying between 500 and 1,000 feet per minute, the drying time varying from about 1 seconds to about 3 seconds for each 25-foot unit of the conductor, said coating composition con taining a,cellulose derivative dissolved in an organic solvent together with an organic soluble resin of the class consisting of natural and synthetic resins, said resin being compatible with the cellulose derivative, and present in the coating composition in an amount which increases the adhesion of the cellulosic coating to the pitch coating; and preventing the pitch coating from becoming soft and tacky during the coating and drying steps by having the coating time-period so short that the solvent component of the coating composition exerts during coating little softening action on the pitch coating, and by having the solvent medium of the coating *composition characterized by the property of being so quickly released during drying from the coating ,composition and from the surface of the pitch and a top sheave, the steps of depositing on the' pitch an adherable homogeneous cellulosic coating and drying the deposited coating while the conductor during said coating and drying steps is traveling'at a linear speed varying between 200 and L000 feet per minute, said coating composition containing a cellulose derivative and a highly volatile solvent medium which evaporates during the period of travel from the bottom sheave to the top sheave with such rapidity that it is not in contact with the pitch coating for a time-period suflicient to soften and make said pitch coating tacky, said high rate of evapora- Y tion enabling the conductor coating to dry while traveling the given distance between the sheaves at the linear speed set forth; said solvent medium consisting essentially of a solvent selected from the group consisting of a low'boiling point ketone, methyl acetate and ethyl acetate, said solvent medium having a relative volatility varying between 2 and 2.9, based on ether having unit volatility.

17. In the art of coating an electrical conductor carrying a protective coating of stearine pitch in a coating apparatus provided with a bottom sheave and a top sheave, the steps of depositing on the stearine pitch an adherable homogeneous cellulosic coating, and drying the deposited coating while the conductor during said coating and drying steps is traveling at a linear speed varying between 500 and 1,000 feet per minute, said coating composition containing a cellulose derivative dissolved in an organic solvent together with an organic soluble resin of the class consisting of natural and synthetic resins, said resin being compatible with the cellulose derivative and present in the coating composition in an amount which increases the adhesion of the cellulosic coating to the stearine pitch coating, the solvent medium of the coating composition evaporating during the period of travel of the conductor from the bottom sheave to the top sheave with such rapidity that said solvent is not in contact with the stearing pitch coating for a time-period suflicient to soften and make said a pitch coating tacky, said high rate of evaporation enabling the conductor coating to dry while traveling the given distance between the sheaves at the linear speed set forth, said solvent medium consisting essentially of a low boiling point ketone together with a resin solvent, the latter being present in a minor proportion insufllcient to increase the volatility number of the composite solvent medium to greater than 2.9, said volatility number being based on ether having unit volatility. I

18. In the art of coating an electrical conductor carrying a protective coating of stearine pitch in a coating apparatus provided with a bottom sheave and a top sheave, the steps of depositing on the stearine pitch an adherable homogeneous cellulosic coating, and drying the deposited coating while the conductor during said coating and drying steps is traveling at a linear speed varying between 500 and 1,000 feet per minute, said coating composition containing a cellulose derivative dissolved in an organic solvent together with an organic soluble resin of the class consisting of natural and synthetic resins, said resin being compatible with the cellulose derivative and present in the coating composition in an amount which increases the adhesion of the cellulosic coating to the stearine pitch coating, the solvent medium of the coat: ing composition evaporating during the period of travel of the conductor from the bottom sheave to the top sheave with such rapidity that said solvent is not in contact with the stearlne pitch coating for a time-period sufllcient to soften and make said pitch coating tacky, said high rate of evaporation enabling the conductor coating to dry while traveling the given distance between the sheaves at the linear speed set forth, said solvent medium consisting essentially of methyl acetate together with a resin solvent, the

latter being present in a minor proportion insumcient to increase the volatility number of the composite solvent medium togreaterthan 2.9, said volatility number being based onether having unit volatility.

MILTON D. SWAR'IZ. KINIDCH N. YELLO'I'I.

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