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This invention relates to improvements in mastic-coated metal sheets for structural purposes as in sidings and in roofing, piping, containers and other means in which metal sheeting is used; and to methods of providing such mastic-coated metal.
In the present invention a bituminous mastic layer, that is non-flowing, non-cracking and practically non-water absorptive, is strongly bonded to smooth-surfaced, flat or corrugated metal such as iron, steel, aluminum and the like, thereby providing metal structural means having heat-insulating, soundproof, waterproof and weather-resistant surfaces.
To provide such surfaces on metals, particularly of a type that does not crack or is not readily broken loose from metal by sudden shock or otherwise, a mastic is prepared from coaldigestion pitch, a finely divided filler, and fibers preferably precoated with bituminous material.
Coal-digestion pitch comprises coal dispersed by digestion in a heat-liquefiable bituminous medium which contains heavy hydrocarbon oil, or to which heavy hydrocarbon oil containing a preponderating proportion of aromatic hydrocarbons or constituents is added during or preferably after the digestion and dispersion process, or during or preferably after thermal decomposition of coal in such process.
In preparing the coal-digestion pitch, coal, such as bituminous coals or coking coals including either high or low volatile bituminous coal, and certain commercial non-coking bituminous coals, is heated while admixed with tar or pitch.
The temperature of the mixture while stirring the latter, is gradually increased over an extended period of time to substantially 300° C. or preferably to a temperature in the approximate range of 3000 C. to 3100 C. The temperature employed is generally not lower than about 270' C. nor higher than about 350° C.
To obtain a pitch of highly desirable characteristics for the purposes of the present invention, either before but preferably after dispersion of coal in the tar and/or pitch in the ,digestion process, there is added the above-mentioned heavy hydrocarbon oil which is preferably heavy water gas tar heavy oil and which latter is preferred above light water gas tar heavy oil and above coal tar heavy oil. These heavy hydrocarbon oils are high-boiling distillates obtained by distilling the corresponding tars and separating the distillate recoverable above approximately 300° C. Only a minor proportion (about 15 per cent or less) of the oil boils below 300° C.
The boiling points may be within the approximate range of 250° C. to 450' C.
Heavy water gas tar heavy oils, which are substantially aromatic in character, are obtained by distillation from heavy water gas tar which in turn is obtained from water-gas generator plants in which Bunker-C or similar grades of residual petroleum fuel oil are used for carburetting.
Heavy water gas tar is also known as residuum tar and is thus termed to distinguish it from what was formerly known as water gas tar or is known today specifically as light water gas tar. Light water gas tar heavy oil is obtained from light water gas tar which is produced in the carburetter of a water gas plant when petroleum distillates are used as carburetting agents.
Depending upon the proportions of coal, tar and/or pitch, and/or heavy oil, in the coal-digestion pitches, the latter pitch products have been prepared with ring and ball softening points in the approximate range of 35° C. to 150° C., all exhibiting improved rheological properties, as well as considerably better temperature susceptibilities (less change in viscosity with temperature change) and greater resistance to flow than the commonly used bitumens. This is particularly true when the heavy oil employed in the pitch is heavy water gas tar heavy oil and is even more apparent when this oil is used in conjunction with heavy water gas tar or pitch as the heat-liquefiable bitumen. Though the same proportions of coal, tar and oil are used in preparing these pitches and though the products have the same softening points, they have different penetrations depending on the oil used. By including heavy water gas tar heavy oil, coaldigestion pitches of higher softening point, or with the same softening point as other coaldigestion pitches similarly prepared with other oils, are producible with higher penetrations at low temperatures.
The following, by way of illustration, are examples of coal-digestion pitch that is employed in the present invention: A. About 187 parts by weight of heavy water gas tar and about 47 parts by weight of powdered bituminous coal are heated together in a still preferably while stirring. The temperature is gradually raised to a temperature of about 3050 C. over a period of approximately five and one-half hours. This temperature is maintained for about four hours during which time there results a distillate of about 5 to 6% based on the tar. At the end of this time heating is discontinued and the 66 mixture permitted to cool. After about forty minutes and while the temperature is slowly dropping, about 54 parts by weight of heavy water gas tar heavy oil are stirred into the heattreated coal and tar mass. The resulting product is discharged from the still at around 225* C. The softening point of this product is about 102° C., and the penetration at 320 F. Is 14; at 77" F. is 20.5; and at 115° F. is 40.
B. A mixture prepared from aplroximately 174 parts by weight of coke oven tar and approximately 58 parts by weight of pulverized bituminous coal is heated to about 3000 C. over a period of seven to eight hours. The heating is discontinued and about 72 parts by weight of heavy water gas tar heavy oil are added whereupon the heating is resumed at about 300' C. for an additional one to two hours. Then another 15 parts by weight of heavy water gas tar heavy oil are added whereafter the heating is discontinued and after thorough mixing the product is permitted to cool. The softening point of the product is about 89' C. and the penetration at 32° F. is 24; at 77° F. is 38; and at 115° F. is 67.
In either Example A or B, the heavy water gas tar heavy oil may be substituted by light water gas tar heavy oil provided high melting coke oven pitch is included in the composition; though the heavy water gas tar heavy oil alone is preferred.
Without the high melting coke oven pitch, less light water gas tar heavy oil may be included, which tends to result in a material of poorer weather resistance.
C. A still is charged with 310 parts by weight of crude light water gas tar and 40 parts of light water gas tar heavy oil. To this mixture 40 parts of molten high melting coke oven pitch having a melting point of 145* C. (cube in air), and 72 parts of pulverized coal are added. This mixture is heated to 300° C. in approximately one hour and maintained at about 300* C. for approximately three hours with agitation, 23 parts of distillate being removed. The residual pitch has a softening point of 88° C. (ring and ball) and penetrations at 32* F. (200 grams, 60 seconds) of 20, at 77* F. (100 grams, 5 seconds) of 32 and at 115° F. (50 grams, 5 seconds) of 61.
In some cases, one to two parts by weight of sulfur may be included in the coal-digestion mixture, or air may be introduced for varying periods. The air and sulfur serve as dehydrogenating agents by which with subsequent addition of heavy water gas tar heavy oil, the characteristics of the pitch may alternatively be adjusted.
The fillers employed in the mastic may be sand, clay, slate dust and the like or mixtures thereof.
The fibers may be mineral, vegetable or animal fibers or mixtures thereof including asbestos, cotton (such as that reclaimed from tires), hair and so forth. As previously indicated, it is preferable, particularly if the mastic is not subsequently dip-coated, to precoat the fibers. For this purpose there are employed tars such as coal tars including coke oven tar, horizontal retort tar, and vertical retort tar; heavy water gas tar and light water gas tar; oil-gas tar, Pintsch gas tar; wood tar; pitches of such tars; oils from such tars; asphalt; mixtures of these bituminous substances; or coal digestion pitches either molten or dispersed in volatile solvent. If desired, any water repellent material may be used to precoat the fibers but it should preferably be miscible or compatible with the bituminous material in the mastic. For instance, a non-aromatic petroleum dis-tillate should not be used to precoat the fibers, if a tar derived composition is to be used in the mast.c.
The precoating of the fibers is preferably accomplished in a Banbury mixer, though this is a also done by dip-coating and then centrifuging to remove the excess coating material In a Banbury mixer, about 15 parts by weight of coaldigestion pitch, such as exemplified above, satisfactorily coats about 85 parts by weight of fiber. A rubber roll mill, pug mill, or a Banbury mixer may be used to prepare the mastic. The fillers and bituminous material used in the mastic are first mixed together and then the fibers, either precoated or untreated, are added and mixed with' the first two ingredients. When using a rubber roll mill, the bituminous material is melted on the heated rolls and then the filler and fibers are successively added and mixed. When using a pug mill, the melted bituminous material and filler are mixed in the mill, and the fibers are mixed with the resulting mixture in a pug mill, a rubber mill or in a Banbury mixer.
The proportions of constituents employed in the mastic may vary widely. Too much of the bituminous material of a low softening point should not be used if the mastic is to be pliable and yet retain its pressure-molded form. To avoid brittleness, the coal-digestion pitch should not be' too high-melting or be present in too small proportions. In other words, pliability is increased while retaining the non-flowing properties of the mastic by increasing the amount of bituminous~ material or fibers, or by using a bituminous material of lower softening point. Less pliable products are obtained by increasing the amount of filler, decreasing the amount of bituminous material, or by using bituminous material of higher softening point.
More specifically, and by way of illustration, the softening point of the bituminous constituent of the mastic is about 75* C. to about 150* C. For the production of a non-brittle non-flowing, pliable mastic, the bituminous constituent employed, when its softening point is above about 90° C., has a penetration of not less than 10 at 32* F. and not more than about 70 at 115° F. In the stiffer mastics for instance the penetration of the bituminous constituent having a softening point of at least 75* C. is 0 at 32° F., 0 to 5 at 77° F., and 15 to 35 at 115* F.
Specifically, and for purposes of illustration, as to the proportions of the constituents of the mastic, the bituminous constituent varies from about 25 percent by weight to about 60 percent by weight (generally about 30 to about 50); the fibers are present to the extent of at least about 10 percent by weight; and the filler up to about 65 percent by weight, but generally of the order of 40 to 55 percent.
Examples of mastics employed in products of the present invention, and as illustrated In the accompanying drawings, are as follows: Example 1.-A pliable but non-flowing mastic surface for flat and corrugated metal sheets is 65 prepared by adding to 52 parts by weight of molten coal-digestion pitch, such as that exemplified above and more particularly in Example A, 40 parts by weight of slate dust and 8 parts by weight of fiber precoated with 15% by weight (based on the weight of fiber) of the coal-digestion pitch.
The pitch and slate dust are first mixed on a rubber mill or in a pug mill or in a Banbury mixer, and the coated fiber is incorporated in the resulting mixture in a Banbury mixer.
Example 2.-A less pliable mastic is prepared by compounding 325 parts by weight of coaldigestion pitch of about 75* C. softening point (ring and ball), 575 parts by weight of slate dust, and 100 parts by weight of fiber precoated with 15% by weight (based on the weight of fiber) of coal-digestion pitch, coal tar pitch or other pitch, tar, or high-boiling tar distillate.
Mastic-coated metal sheets of the types illustrated herein, are manufactured by sheeting out the mastic between calender rolls to a desired thickness. The resulting mastic sheet while still warm, but not necessarily so, is superposed on the metal which is preferably precoated with coaldigestion pitch of substantially the same composition and physical characteristics (melting point and penetrations) as the coal-digestion pitch in the mastic, or is precoated with a suitable adhesive, though the mastic adheres strongly without either upon compression. Moderate pressure and heat are applied to the,metal and/or to the mastic to complete the coating operation.
Sticking of the mastic to molding faces is minimized by applying a thin film of a lubricating oil or grease preferably of petroleum origin to the mold surfaces, or by applying a light covering of finely divided mineral aggregate such as ground talc or slate dust or stone dust or the like, or by simultaneous use of both of these treatments.
A mastic-coated metal sheet of outstanding merit is prepared by coating the metal with mastic compounded as set forth above with coal-digestion pitch of Example A, in which mastic, the fiber is precoated with the latter pitch; by precoating the metal with this pitch or with cement made from this pitch; and by dip-coating the mastic-coated metal with this pitch. Various types of surface treatments are then applied as illustrated below.
For certain purposes, the mastic is alternatively prepared from asphalt of about 100° C. (or above) softening point, or is prepared from coal tar pitch or other pitches of high softening points (1200 to 1400 C.) mixed with 30% to 40% heavy oil such as heavy water gas tar heavy oil or other oil of high aromaticity and with a boiling point above about 3000 C. These bituminous substances are mixed with the desired proportion of filler and fiber (preferably precoated), after which the mastic is sheeted and applied to bitumen-coated metal surfaces. The mastic-coated metal product, prepared with mastics compounded with these alternative materials, is preferably finally coated with coal-digestion pitch, particularly of the type described in Example A, for reasons set forth below.
Products of the present invention including preformed or other structural means are diagrammatically illustrated by way of example in the accompanying drawings in which Figs. 1 to 8 are cross-sectional views of fragments of masticcoated metal structures. Similar reference characters in the various figures designate similar or substantially similar features.
In Fig. 1, a sectional view is shown of a fragment of a flat mastic-coated metal sheet I in which a thick layer 2 of the herein-described improved type of mastic containing coal-digestion pitch is directly bonded to the metal surface by application of moderate heat and pressure. A similar view of a corrugated mastic-coated metal sheet is shown in Fig. 5 in which the mastic layer 3 may be pre-corrugated to conform with the corrugations of the metal sheet 4, or it may be impressed on the metal surface to form a uniformly coated corrugated sheet. At the same time granules or mineral dusts 5 may be impressed into the surface of the mastic.
In Figs. 2 and 6, the articles illustrated include a precoated metal sheet I and 4, respectively. The thick mastic layers 6 and 7 respectively, are bonded to the precoated sheets I and 4 with moderate pressure and while the mastic is warm.
Whether or not a mastic layer is prepared from coal-digestion pitch, it is preferred to coat the metal with non-brittle and non-flowing coaldigestion pitch. This is applied by dipping the metal in a bath of the molten pitch and slowly withdrawing at a decelerating rate to provide a coating of appropriate uniform thickness. Before the pitch coating 8 (Fig. 2) or 9 (Fig. 6) is cold and hard the mastic layer is pressed on the coated surface. An interpenetration of the binders in the coating and in the mastic takes place readily and firm bonding with interlocking is accomplished.
An adhesive or cement applied directly to the metal surface as at 10 in Fig. 3, or to a precoated metal surface as at ii in Fig. 4, may also serve in bonding the mastic layers 12 and 13, respectively, in place. With a mastic layer prepared from coal-digestion pitch or with such layer and the metal surface precoated with a coating 14 containing coal-digestion pitch, a cement having a similar pitch base is preferably employed. A solvent employed in the cement assists in furthering the interpenetration, referred to above, of the materials of contacting layers and thereby further enhances the bonding qualities of coal-digestion pitch surfaces.
In preparing the above-mentioned bituminous cement in a preferred manner for cold application, a low-boiling solvent, such as coal tar naphtha, is added slowly at room temperature to molten coal-digestion pitch with agitation. The agitation is continued until all the solvent has been introduced, and the temperature of the final mixture has dropped to a substantial extent below the boiling point of the solvent.
Solvent naphtha in the above procedure may in whole or in part be replaced by other lowboiling coal tar solvents; fractions of heavy water gas tar and of light water gas tar distillates; and petroleum distillates of high aromaticity or containing a preponderating proportion of aromatics. The boiling point ranges of these solvents may be from about 100° C., or 1350 C., or from 1500 C. to about 2000 C., depending upon the drying properties desired. The boiling points may also range higher than 2000 C., as shown in the following table, depending upon the use of the cement: Distillation of typical solvents 60 Sample Source First Drop....
65 io%-----20%------30%.--------. 40%- ----50%------........-50% 60% -----70% -.........80% ----70 90%-------95%-------(1) Coal Tar OC.
105 127 138 148 157 164 168 173 175 179 184 195 (2) Coal Tar °C.
145 160 165 169 171 174 176 177 179 182 188 198 (3) Heavy W. G. Tar oC.
140 153 163 173 182 191 203 207 216 225 * 242 258 (4) Light W. G. Tar °C.
148 175 187 201 209 218 225 228 233 241 258 280 The relative rate of evaporation of solvent and consequent setting-up time of the adhesive at 75 atmospheric temperatures may be changed as de3,478,100 7 sired by proper choice of an aromatic solvent or solvent fraction, If relatively quick-drying adhesives are desired, the lower boiling solvents of any of the sources mentioned may be selected for use, but if slower setting cements are required the higher boiling fractions are selected for incorporation in the cement. In the above table, solvents (1) and (2) provide a relatively quick-drying cement; (3) provides a slightly slower drying cement; and (4) a 10 considerably slower drying cement, Coal tar solvent naphtha, when employed in the cement, is prepared from coal tar distillate from which most of the tar acids, and in some instances the tar bases, have been removed. Material boiling below 100* C. is preferably removed to prevent too rapid setting of the cement upon application, and to minim';e fire hazards arising from too low boiling distillates if present. Coal tar solvents and solvents of high aromaticity are particularly compatible with coal-digestion pitches and prevent undesirable sludging and separation of different ingredients into layers.
The proportion of these solvents to be used in the cement depends upon the desired consistency of the product. A relatively viscous product, suitable preferably for warm weather or warm climate use, and better for daubing, rather than brush application, is made from a mix of approximately 80% by weight of coal-digestion pitch 30 layer. (softening point about 750 C. to about 125° C.), and 20% by weight of a selected solvent. A more fluid product, suitable for easy application in warm weather or warm climates, is made with about 75% by weight of such coal-digestion pitch 35 and 25% by weight of a selected solvent. A product fluid enough (specific Engler viscosity, 50 c. c. at 500 C., of approximately 18) for convenient application at low to moderate temperatures is made with about 70% by weight of such coal- 40 digestion pitch and 30% by weight of a selected solvent, A very fluid cement for brush or spray application is made with 60 parts by weight of coal-digestion pitch (softening point about 75° C. to about 1250 C.) and about 40 parts by weight of a selected solvent (boiling range 100° C. to 200* C.). The specific Engler viscosity of such a cement is approximately 5 (50 c. c. at 500 C.).
A fluid cement generally suitable for brush or spray application to pitch coated articles, is made by cutting back 60 parts to 55 parts by weight of molten coal-digestion pitch of relatively high melting point with 40 to 45 parts by weight of aromatic solvent (boiling range about 100* to 55 200 C.) , thus producing an adhesive, quick dryIng bituminous cement, that is applied cold, and having an Engler specific viscosity of approximately 8 to 15 (50 c. c. at 250 C.).
Fillers, such as, slate dust or flour, finely divided talc or clay may be added to the cement, if desired, to the extent of 25 to 30%, or even-up to 35% ov tho e of 2 to 30 or.en a -t 35% to provide a desired weather-resistant adhesive.
ton of the pitch in a ma-gestion pitch describedompostion of the coal-digestion pitch described in Exemployed for producing various color schemes. A ample A above, it is preferred to use this pitch in the cement or dip-coating since better bonding is obtained than in cases where the compositions are different as indicated above. The same is true in the case of the coal-digestion pitches described in the other examples. Advantageous resuits are obtained however for bonding purposes by employing for instance a heavy water gas tarheavy water gas tar heavy oil--coal-digestion pitch in the mastic and a coal tar-heavy water gas tar heavy oil-coal-digestion pitch in the dipcoating or in the cement, or vice versa; or a light water gas tar-light water gas tar heavy oilcoal-digestion pitch in the mastic and a heavy water gas tar-heavy water gas tar heavy oilcoal-digestion pitch in the dip-coating material or in the cement, or vice versa; and so forth.
Figs. 7 and 8 are illustrative of a mastic-coated metal sheet product that is dip-coated as a unit in molten coal-digestion pitch. After a metal sheet is mastic-coated, a dip-coat 15 and I (Figs. 7 and 8, respectively) is particularly applied if the fiber in the mastic has not been precoated as set forth above. Such a dip-coat is also applied if the mastic coat is prepared from bituminous materials less weather-resistant or having' less desirable rheological properties than mastics prepared from coal-digestion pitch particularly of the type described in Example A.
Only a thin coating of such coal-digestion pitch is needed on ordinary asphaltic, or conventional tar or pitch or other bituminous mastic coating 17, to provide structural means having superlor weather-resistant and rheological properties over wide temperature ranges. These properties are Improved by Increase of depth of penetration of the dip-coating material into the mastic In some instances the hot dip-coating is subsituted by the cold application of compositions such as the above-described cements with selected solvents.
An article to be hot dip-coated is submerged in the molten coal-digestion pitch having a consistency appropriate for forming a relatively thin coating on the article upon its withdrawal. If the pitch in the bath has a higher melting point than the melting point of the bitumen in the mastic coat the time for submergence is less than that for coating with pitch of a lower melting point. The time may be long enough to permit some penetration which, if desired, may also be obtained by applying pressure. The withdrawal of an article, particularly masticcoated metal sheets or panels of large dimensions, is preferably at a decelerating rate to obtain a uniform coating. The total time of submergence of the lowermost portions of a sheet should not be such as to result in any substantially different change in physical or structural condition of a lowermost portion from that of an uppermost portion.
The articles in Figs. 5, 6, 7 and 8 exemplify the application of granules or dusts 5 or 18 either lightly or deeply impressed, and bonded with or without a coating such as a dip-coat of coaldigestion pitch, or cold-applied cement coat prepared from coal-digestion pitch and solvent, or a bituminous paint coat with or without inert filler. The surfacing granules or dusts, including slate dust, clay, sand and others, as well as e solid, inert, oil- and water-insoluble, heat-resistant mineral, or metallic, or artificial pigment particles. Colored granules or dusts are employed for producing various color schemes. A coal-digestion pitch coat serves excellently for anchoring the surfacing particles to mastic-coated metal. For certain purposes pigmented bituminous paints or metal paints such as aluminum or bronze paints containing a bituminous vehicle may be applied for heat and light reflection.
In forming and bonding the mastic layer to a 76 metal sheet, molding temperatures and pressures respectively are employed, for instance, of about 750 C. to about 1500 C. depending upon the me!ting point of the binder, and of from about 200 lbs. per sq. in. to about 2000 lbs. per sq. in. depending upon the thickness of a sheet and amount of compression required.
Besides the desirable characteristics referred to above, the mastic-coated metal article of th1 present invention has unique water-repelling properties, thereby eliminating corrosion or rusting of the metal. In comparative tests with conventional mastic coats, after immersing in water for ten days at room temperature and also at 500 C., a change in weight of only 1% is noted in the improved mastic coat; whereas other commercially known bituminous mastics submitted to similar tests show increases in weight of 15% to 25%. The hot dip application of the improved pitch as a precoat, dries a metal surface, and the finally hardened coat prevents rusting, and 2( furtherance of rusting if the metal surface is rusted before coating; and prevents rusting even of unpickled metal surfaces.
An improved pitch of the type used herein tolerates excessive bending while also adhering 2 strongly to a metal surface. In the use of the improved pitch coating on metal such as galvanized iron, the adhesion of the coating is strikingly demonstrated by gently peeling off or stripping the coating with a knife or other sharp-edged instru- 3 ment. In the peeling operation the galvanizing coat is removed with the pitch coating.
What is claimed is: In a metal structural element having a layer of filler- and fiber-containing bituminous mastic bonded directly to metal surface of said element, the said layer of mastic and said metal element both being in sealed-in relationship to a coating of coal-digestion pitch containing heavy water gas tar heavy oil, said pitch in combination with said oil having a softening point of about 90" C. to about 1500 C. and penetrations of not less than 10 at 32° F. and not more than 70 at 1150 F., and the said pitch containing the said oil preventing penetration of water to the metal surface and being non-flowing at high atmospheric temperatures and being non-embrittling at low atmospheric temperatures, thereby preventing removal of said layer from said metal surface.
WILLIAM F. FAIR, JR.
REFERENCES CITED The following references are of record in the file of this patent: UNITED STATES PATENTS Number 407,195 441,036 1,277,755 1,289,537 1,362,888 1,698,267 1,701,926 1,863,186 1,864,971 1,875,458 1,925,005 2,158,772 2,184,139 2,212,122 2,249,412 2,304,773 2,325,594 2,395,041 2,395,853 Name Date Garrison ---------- July 16, 1889 Siebel ------------ Nov. 18,1890 Robertson -------- Sept. 3, 1918 Porter ---------- Dec. 31, 1918 Mullin ------------- Dec. 21, 1920 Kirschbraun -------- Jan. 8, 1929 Kirschbraun ------ --Feb. 12, 1929 Burns ----------- June 14, 1932 Young et al.--------- June 29, 1932 Hill -------------- Sept. 6, 1932 Rose -------------- Aug. 29, 1933 Beckwith ---------- May 16, 1939 Cunnington ---........ Dec. 19, 1939 Miller --.-------- Aug. 20, 1940 Yeager ------------ July 15, 1941 Anderton ---------- Dec. 15, 1942 Denman ------------ Aug. 3, 1943 Fair ...........-----.. Feb. 19, 1946 Fair -------------- Mar. 5, 1946