US2888357A - Thermal insulation material - Google Patents

Description

United States Patent THERMAL INSULATION MATERIAL Charles U. Pittman, Penn Township, Allegheny County,

Pa., and John C. Christensen, Scotch Plains, N.J., assignors to Koppers Company, Inc., a corporation of Delaware No Drawing. Application May 26, 1954 Serial No. 432,616

3 Claims. (Cl. 106-202) This invention relates to improved thermal insulation material and methods of preparing the same.

There has been a considerable increase in the need for an inexpensive thermal insulation and coating material for surfaces generally under moderately high temperature conditions, and particularly where the use of presently available, high-priced, insulation materials is not economically justifiable. In manufacturing plants, for instance, where exposed storage tanks, process tanks, piping, and other equipment can be advantageously insulated to avoid thermal losses, the cost of satisfactory insulating materials for such purposes is frequently found to be prohibitive.

The bituminous compositions of the present invention are provided not only to satisfy the need for an eco nomical, effectively heat-insulating coating material but also are provided to serve as coverings that are longerlasting from the standpoint of weathering, and that are protective against corrosion, and relatively less affected in certain respects by aqueous and other solvents. In many plants referred to above, processes are employed that require the use of solvents, which if accidentally spilled on most commonly used coatings, particularly those containing certain well-known bitumen or other binders, severely damage such coatings. The most widely used solvents are derived from petroleum, and it has been observed that the applied bituminous coatings, hereinbelow described, are notably resistant to the spillage indicated. Water, including rain and moisture, also known to have a noticeable solvent effect on certain bituminous materials, has substantially less on the bituminous coating hereinafter designated and it offers greater resistance to the penetration of water and aqueous solutions.

In accordance with the present invention, a bituminous, filled product is provided for use in preventing heat or cold losses. It has definite thermal insulation characteristics and properties that render it particularly useful at temperatures up to about 300 F. and down through temperatures in the atmospheric range. It fulfills a need for thermal insulation for metallic containers or tanks, and pipings, and other industrial plant structures that require insulation and that are exposed to atmospheric or weather conditions.

The product includes coal tar or pitch which contains substances that render it highly effective in preventing corrosion, and in preventing erosion of a coating. Coal tar pitch, with a softening point up to approximately 190 F., that is plasticized with a heavy oil, is a preferred constituent of the insulating coating for obtaining firm adhesiveness without brittleness. Coal, such as bituminous coal, highor preferably low-volatile, is preferably added to the tar or pitch and digested therein to provide a pitch with less susceptibility to change of viscosity with change of temperature. in temperature susceptibility makes it possible to use the binder over a wider temperature range than straight distilled coal tar pitch.

The improvement A bituminous binder is prepared by uniformly dispersing powdered bituminous coal in molten pitch or tar and digesting the mixture. Before, during or after the dispersion process, a heavy coal tar oil, such as a heavy residue creosote oil, is added to pitch, more being added to a hard pitch than to a soft pitch to obtain the desired characteristics, including penetration and softening-point as well as other plastic and bonding characteristics. Variation in the pitch or tar, or variation in the coal or in the oil causes a variation in composition. Variationin the residue of the heavy creosote oil, the use of a suitable different oil, namely, a heavy hydrocarbon oil having a preponderating proportion of aromatichydrocarbons or constituents, such as the above coal tar heavy oil, water-gas tar heavy oils, and others, for instance, and use of different coals, require different proportions of these materials to obtain the aforementioned characteristics.

Depending upon the proportion of coal, tar and/or pitch, and/or heavy oil, in socalled coal-digestion pitches, or on the proportion of such oil added to these pitches the resulting pitch products have been prepared with Ring & Ball softening points in the approximate range of C. to 150 C., all exhibiting improved rheological properties, as well as considerably better temperature susceptibilities, and greater resistance to flow than the commonly used bitumens, when in layers or on surfaces in vertical position as Well as in inclined position. The pro-portions are adjusted not only to obtain a desired softening point but also to obtain a desired combination of penetration characteristics suitable for conditions of use. For example, coal-digestion pitches are prepared with softening points above 90 C. and penetrations of not less than 10 at 32 F. and not more than 70 at 115 F.; others are prepared with softening points of .at least C. and penetrations of 0 at 32 F., 0 to 5 at 77 F., and 15 to 35 at 115 F.; and still others with softening points of about 52 C. up to about 80 C. and penetrations of above 10 at 32 F., above substantially 60 at 77 F. and of substantially 230 to 300 at P. All

such coal-digestion pitches show no tendency to flow in coatings above temperatures at which the pitch flows when the coal is omitted.

A more specific example of a pitch-heavy oil mixture that gives highly satisfactory results in insulating coatings of the present invention is one prepared from heavy creosote oil (approximately 80% residue) and a pitch in which coal has been uniformly dispersed by thermal digestion. Such coal-digestion pitch is prepared by heating together the following substances in approximately the proportions (by weight) indicated, to obtain a pitch with a softening point (R. & B.) in the approximate range of 210 to 215 F., and with penetrations at 77 F. and 115 F. in approximate ranges of 9 to 13 and 20 to 30, respectively:

Percent Coal tar pitch (softening point in the approximate range of to F.) 40 to 45 Heavy residue creosote oil (approximately 80% residue) 30 to 40 Pulverized low-volatile coal 20 to 25 In preparing the coal-digestion pitch from the ingredients referred to above, the mixture is stirred while gradually increasing the temperature over an extended period of time to substantially 300 C. or preferably to a temperature in the approximate range of 300 C. to 320 C. Preferred minimum and maximum temperatures for digestion are 290 C. and 340 C., respectively. While the mixing continues, constituents of the coal at the temperature employed appear to undergo a dissolution in the tar or pitch. Depending on the temperature and the time of digestion, it has in certain instances been impossible to detect chemical change in the coal, and in other instances such change has been detectable. Control tests comprising softening point and penetration determinations are employed to provide a pitch having desired characteristics.

The heavy oil added to the coal tar pitch or to the coal-digestion pitch for the purpose of plasticizing it is a high-boiling distillate obtained by distilling tar and separating the distillate recoverable above approximately 300 C. Only a minor proportion (about percent or less) of the oil boils below 300 C. The boiling points may be within the approximate range of 250 C. to 450 C.

To permit cold application of the coating material principally by spraying, as distinct from trowelling or brushing, a solvent is added to reduce the consistency or viscosity. The solvent medium should be such that a coating dries rapidly enough to prevent sagging, but not so quickly that shrinkage is accompanied by cracking of the coating. To retard evaporation of the more highly volatile solvents and therefore to prevent shrinkage cracking upon solvent evaporation, a compatible, relatively higher boiling solvent is mixed with a lower boiling solvent or solvents in proportions which will also impart at least a temporary plasticizing effect and thereby to some extent prevent an applied thick coating not only from cracking but also from becoming brittle and from losing adhesion when in service on heated surfaces.

Xylol, toluol and benzol, for instance, when used by themselves as solvent media, are generally found to evaporate too rapidly during spray application and subse quent setting. Examples of combinations of solvents which are found to serve satisfactorily in the compositions herein referred to, are xylol and trichlorobenzene, or xylol and methylnaphthalene. Other compatible volatile solvents may be substituted for xylol, and other aromatic, evaporation-retardant, miscible solvents may be substituted for trichlorobenzene or methylnaphthalene.

Material of low thermal conductivity is included in the bituminous binder in sufficiently high proportions to provide effective insulation. Solid particles of porous insulating material such as cork, vermiculite, and the like, and discrete fiber particles of asbestos and the like, are advantageously employed for this purpose. It has been found preferable to use a uniform mixture of the porour cork or similar particles and the fibers of asbestos. The asbestos serves not only as an insulator, but also is a means for forming a fibrous matrix throughout a coating, for increasing resistance to slippage and cracking, and for providing a desired consistency suitable for spray application.

These solid insulating materials are of varying particle size. Though a coarse ground cork may be used, cork that is finely ground is preferred. Of the various grades of asbestos that are available, such as those known as the crude grade, long fiber, short fiber, paper stock, cement stock, shingle stock, and floats, the short fiber grade is preferred. Asbestos designated as 7M asbestos has been found suitably effective in the insulating composition applied by spraying.

Instead of using porous solid insulating materials, such as cork, in dry form, it is preferred that they be immersed in water before introducing them into the bituminous and solvent mixture. Water is not included for the purposes of forming an emulsion but on the contrary the cork is soaked in water to fill the pores. When this water-treatment is omitted, it is found that the bitumen, solvent, and filler composition more readily becomes thickened upon standing and eventually is more likely to become difficult or even impossible to spray, or to convey through piping, with standard equipment. Apparently, the water in the pores of porous fillers pre 4 vents absorption and adsorption of the non-aqueous fluids or infiltration of the bituminous and solvent constituents. The solid suspension, furthermore, remains uniformly distributed in the bituminous vehicle for long periods of time.

The following examples, presented for purposes of illustration, more particularly indicate preferred compositions for use in providing thermal insulation, and methods of preparing the same:

Example 1.A coal-digestion pitch is prepared, as set forth above, from 40 to 45% by Weight of coal tar pitch (softening point 120-130 F.), 30 to 40% by weight of heavy residue creosote oil, and 20 to 25% by weight of pulverized low-volatile coal. About to by weight of this pitch with a softening point of about 210 to 215 F. and penetrations of about 9 to 13 at 77 F., and 20 to 30 at F., is mixed with from about 15 to about 20% by weight of heavy creosote oil (with about 80% residue). The resulting pitchheavy oil mixture has a softening point in an approximate range of F. to F. Xylol and methylnapthalene or trichlorobenzene are added to the pitchheavy oil mixture to thin it. A mixture of cork particles and asbestos fiber is employed in such proportions that the fiber has a strengthening effect on an insulating layer, and the particles of cork and asbestos in an applied layer are close together and are separated from each other by a relatively thin film of the bituminous binder when the coating is dry.

Example 2.A composition for use in providing thermal insulation is prepared by mixing together 20.5% by weight of a pitch-heavy oil mixture, with a softening point of approximately 156 F., prepared as set forth hereinabove; 34% by weight of industrial xylol; 11.5% by weight of crude methyl-naphthalene; 8% by weight of 7M asbestos fiber; 10% by weight of cork (ground to approximately inch particle size) and 16% by Weight of Water which is adsorbed by the cork upon soaking or immersion prior to adding it to the dissolved pitch-heavy oil mixture.

Example 3.A composition useful in providing thermal insulation of metal tanks is prepared by mixing together 27.7% by weight of a pitch-heavy oil mixture, with a softening point of approximately 160 F, prepared as set forth above; 30.3% by Weight of industrial xylol; 10.1% by Weight of crude methylnaphthalene; 7.1% by weight of 7M asbestos fiber; 8.3% by weight of finely ground cork (particle size is approximately inch to a minimum of approximately inch in diameter) and 16.5% by weight of water which is absorbed by the cork, the pores of which are filled with the water upon immersion prior to adding it to the pitch and solvent mixture.

The above exemplified compositions may be applied directly to metal surfaces such as the exteriors of metal tanks. These compositions are maintainable indefinitely in a readily sprayaole state, and spraying thereof is effected with equipment such as a spray gun and a pump of the type known as Alemite Versatal pump, or Moyno pump. After application of a coating to a surface, the volatile solvent evaporates, and an ultimate dry, hardened layer remains which has a high insulation value. Such a layer may be approximately /8 inch to approximately inch, or preferably A1 inch, in thickness. With a dry layer of a thickness of A1 inch or more, heat-flow through metal can be reduced by well over 65%.

Various changes may be made in the details of the various compositions without departing from the invention or sacrificing the advantages thereof. It is understood that the invention embraces not only the applied coating having the composition described, but also mixtures adapted for the formation of such coating.

What is claimed is:

1. A composition for use in thermal insulation on tanks, pipes and other exposed industrial plant metal structures, the said composition consisting essentially of an intimate and homogeneous mixture of coal-digestion pitch, heavy hydrocarbon oil plasticizer for said pitch, a. volatile solvent medium compatible with said pitch and said plasticizer, and cork in which the pores are occupied by water for preventing infiltration of the pitch and solvent media,f said composition being sprayable underpressure for providing an insulating coating, for preventing transference of heat from or through heat-conductive surfaces of said metal structures at temperatures below substantially 300 F., resistant to penetration by water-and resistant to removal from such structures by spillage of solvents including petroleum and distillates.

2. A composition for use in thermal insulation on tanks, pipes and other exposed industrial plant metal structures, the said composition consisting essentially of an intimate and homogeneous mixture of coal-digestion pitch, heavy hydrocarbon oil plasticizer for said pitch, a volatile solvent medium compatible with said pitch and said plasticizer, and cork and discrete particles of asbestos fiber, pores in which are occupied by water for preventing infiltration of the pitch and solvent media, said composition being sprayable under pressure for providing an insulating coating, for preventing transference of heat from or through heat-conductive surfaces of said metal structures at temperatures below subtantially 300 F., resistant to penetration by water and resistant to removal from such structures by spillage of solvents including petroleum and distillates.

3. A composition for use in thermal insulation on tanks, pipes and other exposed industrial plant metal structures, the said composition consisting essentially of an intimate and homogeneous mixture of coal-digestion pitch, heavy hydrocarbon oil plasticizer for said pitch, a volatile solvent medium containing xylol and methylnaphthalene compatible with said pitch and said plasticizer, and cork and asbestos, pores in said cork occupied by water for preventing infiltration of the pitch and solvent media, said composition being sprayable under pressure for providing an insulating coating, for preventing transference of heat from or through heat-conductive surfaces of said metal structures at temperatures below substantially 300 F., resistant to penetration by water and resistant to removal from said structures by spillage of solvents including petroleum and distillates.

References Cited in the file of this patent UNITED STATES PATENTS 1,253,454 Abraham Jan. 15, 1918 1,398,613 Watson Nov. 29, 1921 1,970,164 Breuer Aug. 14, 1934 2,142,584 Ferguson Jan. 3, 1939 2,459,520 Greenshields Jan. 18, 1949 2,701,219 Fair Feb. 1, 1955 2,722,869 Archer Nov. 8, 1955 2,749,250 Christansen et al. June 5, 1956 FOREIGN PATENTS 129,495 Switzerland Dec. 17, 1928 112,032 Australia .9, Dec. 12, 1940

Claims (1)

1. A COMPOSITION FOR USE IN THERMAL INSULATION ON TANKS, PIPES AND OTHER EXPOSED INDUSTRIAL PLANT METAL STRUCTURES, THE SAID COMPOSITION CONSISTING ESSENTIALLY OF AN INTIMATE AND HOMOGENEOUS MIXTURE OF COAL-DIGESTION PITCH, HEAVY HYDROCARBON OIL PLASTICIZER FOR SAID PITCH, A VOLATILE SOLVENT MEDIUM COMPATIBLE WITH SAID PITCH AND SAID PLASTICIZER, AND CORK IN WHICH THE PORES ARE OCCUPIED Y WATER FOR PREVENTING INFILTRATION OF THE PITCH AND SOLVENT MEDIA, SAID COMPOSITION BEING SPRAYABLE UNDER PRESSURE FOR PROVIDING AN INSULATING COATING, FOR PREVENTING TRANSFERENCE OF HEAT FROM OR THROUGH HEAT-CONDUCTIVE SURFACES OF SAID METAL STRUCTURES AT TEMPERATURES BELOW SUBSTANTIALLY 300* F,. RESISTANT TO PENETRATION BY WATER AND RESISTANT TO REMOVAL FROM SUCH STRUCTURES BY SPILLAGE OF SOLVENTS INCLUDING PETROLEUM AND DISTILLATES.