US1766891A - Process of coloring granulated slate - Google Patents

Description

Patented June 24, 1930 UNITED STATES PATENT OFFICE HARRY C-. FISHER, 0F CINCINNATI, OHIO,

AS SIGNOR, BY NIESNE ASSIGNMENTS, TO

PROCESS OF COLORING GRANULATED SLATE No Drawing.

My invention relates to processes for coloring slate, particularly where done by means of silicate.

In the making of colored roofings of desired character, of the type in which slate forms the exposed surface, there are two modes of procedure, one being to cut the slate into tiles, and apply them to the roofs, and the other to crush the slate into granules, which because of its nature, are of laminated character, and roll these laminae into a mastic surface body so as to conceal the mastic beneath.

1 My invention applies to the latter mode of procedure, where the provision of various colors to suit the customer are desired, because of peculiarities of the action of coloring matter on slate granules, and the much greater economy in manufacture because much less coloring matter may be used, and higher temperatures of processing are possible, thereby cutting down operating time. Thus to color-coat a slate slab and thentry to fix the adherence and accomplish changes in the color itself by application of heat, will result in breaking up the slab, unless very careful slow heating and cooling can be practised.

Also, all slates have an inherent color which must be overcome; and the effect of heat on many slates is to darken their color, and all of these factors tend to produce a drab effect unless the coloring matter is of a nature which does not permit the colors of the slate itself to be substantially exposed. I

I have discovered that small particles of interspaced, adherent coloring matter on a granule of slate will give a desired color effect, when such particles of color on a slab of slate 'will not give a satisfactory'color result at all. I have discovered that adherence of certain coloring matters to particles of slate crus'hed'froin the slate body itself, will be much greater than the adherence to slabs of slate, because of a penetration factor, due to the fact that in-crushed slate the proportion ofsurface area cutting across the planes of cleavage is vastly greater than with slabs; and penetration of pigments occurs mostly parallel with the planes of cleavage.- Furthermore the general surface of granules 1s rougher than the surface of slabs; and this Application filed April 29,

1925. Serial No. 26,829.

promotes adherence of coloring both by penetration and by a mere clinging to the interstices of the surface. I

I have heretofore set forth in an application for Letters Patent Serial No. 603,369, filed November 15, 1922, a process for imposing color on granular slate by means of immersing the granules in a bath of sodium silicate of alkaline factor of .30, which I then boiled practically dry with agitation, followed by an oven treatment at 700 F. or thereabouts. This process was thus progressive and produced a colored granular mass in which dried silicate as distinguished from a glass was employed as the surface maintainmg medium. a This application for patent I have ceased to prosecute, and so far as concerns the basic principles and progressiveness of process, the present applicationis a continuation thereof. To review briefly then the requirements of a plrocess to produce artificially colored crushed s ate 1. The process must be economical both in time, labor and equipment cost and materials. 2. It is not practical to color large pieces of slate and crush them up because the color in no case penetrates more than the surface of the slate.

3. Also the color penetrates across the grains, so that crushing exposes a large amount of penetration surface facilitating spreading of the color. 4. Because of using the slate in granular form it can be handled with rapid heat treat ment, impossible with large pieces because they would split up. Accordingly the process must be particularly arranged for economy in connection with handling a large quantity of of the silicates, it is necessary to employ heats high enough in intensity to result in a translucent, whitish condition of the silicate, due

probably to foaming, and hence 1n a milky or translucent glassy adherent body of particles, which obscure the color of roasted slate granules and still give a pleasant color effect from the color of the silicate itself.

It is a very significant fact that in the use of silicates for binding bits of colored glass and the like to art objects, and in the use of silicates for impregnating porous bodies in the art of coloring marble and the like, that the temperatures used are far below anything that I find to be required for effectivly imparting a permanent water repellent coating to slate granules, for exposure to the weather on roofs, which coating has high adherence to the slate itself. The lack of penetrability of the 'sllicate into the slate bodies which I find to be resent, and the tight adherence which I gain, tend to establish that a sintering action takes place not only in the silicates themselves but between the silicates and the slate itself, at the surface thereof.

By a slow heating over many hours below say 300 Fahrenheit, it is possible to obtain a highly glossed, and essentially transparent film of silicate on any mineral body, but this coating is not of permanent nature, being gradually soluble, and susceptible to certain chemical changes. Slow heating is not practical in commercial coloring of granulated slate, as it is too expensive, so that by my improvement I obtain economical processing, an assurance of permanence, a tighter bond, a surfacing hiding the darkened slate, practical freedom from spotty appearance if too little of the material is used, and probably a sintering action between the silicates of the coating and the silicates of the slate.

Furthermore I have discovered that in the process of baking a soluble silicate to the requlred degree of insolubility on granulated slate particles, the application of heat and agitation must be controlled to give the desired eflects without a balling up of the materials in such a way that they will not come apart into granular form again. Thus my process involves progressive heat action on the particles accompanied by agitation, which first makes the surfaces coated with SlllCate dry enough to be non-adherent and then dehydrates and foams the silicate to the proper degree of hardness and insolubility,

and resistance to atmospheric exposure. The

amount of silicate used is readily controlled of themselves .the invention which I wish to claim in this application, in which I cover the processes necessary for best heat treatment for slate treated with colorin solutions, and the idea broadly of ,artifical y coloring slate by granulation and subjection to solutions or suspensions which when the slate is roasted will give an adherent coloring, particularly to treatments where silicate is involved.

The first process which I will describe relates to the use of colored silicates. In the action of-forming silicate, which is soluble, such as silicate of factor 1 Na O to 3.25 SiO I add during the reaction in the furnace, according to principles adopted in making colored glass,'sufiicient pigmenting agent, in any suitable form, to become distributed in the glass. By control of the proportions of sodium compounds in the furnace, I provide for the desired solubility of the final silicate, and I have found that a silicate of factor 1 Na O to 3.25 SiO will serve my purposes excellently. The materials from the furnace are treated in the usual manner to bring them to take up water, as in the usual practices of manufacture of water soluble sodium silicates.

The slate which is crushed in the usual manner from the form in which it is extracted from the ground, is mixed in with the silicate ande with water, using no more water than is required. Thus to give small proportions, which may be expanded as much as desired, I use 6 grams of sodium silicate of the color desired, and mix this in 12 grams of water. 100 grams of slate is then mixed up in the solution so as to thoroughly coat each particle.

The coated slate is then passed through a roasting kiln, in which the products of combustion, or the heated air is arranged with counter-flow to the passage of the slate.

The temperature is controlled so that at the introduction of the slate, it will not be raised to a point of frothing of the silicate, until the silicate coating on the granules has developed a surface skin. During this perlod agitation is carried on as much as posslble without crushing the granules, and such agitation as is carried on will not develop slate dust, as this, if any, appears to be held by the silicate coatings.

When the slate has passed through a zone of skin drying it moves into a higher heat zone which causesthe silicate to whiten or to foam, and brings it to the desired degree of insolubility (and there is some agglomeration into balls). I have found a temperature of 900 to 1000 F. and above, with a top limit so far as our practice has developed it, of 1700 F. or thereabouts, will give the effect desired, namely the uniform and permanent coloring of slate granules by means of a surface coating without causing any substantial adherence of the granules to each other during the coloring process. I find that the temperatures and conditions named will produce these results satisfactorily, but I do not wish to limit myself to this point. a Temperatures in a furnace, with relation to the material within them, as stated by me, are readings from instruments which I have; and the proper temperatures will vary somewhat with conditions. Essentially there should be a skin-drying accompanied by agitation to bring the slate to a non-adhesive condition before anyrapid drying and particularly before any whitening or foaming is attempted.

To give full temperature ranges dependent upon the accurac of present day -instru ments, in terms 0 the readings of which I speak 'I state as .a low limit of heat, a temperature of around 300 degrees Fahrenheit, but the heat treatment at this range will have to be very long. At 600 degrees Fahrenheit maximum temperature, the better ranges of effects and more economical processing begins to be more predominant, and the semiopaque quality as compared to the transparent quality begins to have considerable efl'ect. At 900 degrees maximum temperaturethe time factor is well cut down and the best grade of effects can be obtained, and with proper agitation, counterflow and care in use of materials, up to 1700 degrees Fahrenheit is pfi'actical, using soluble silicates to begin Wit The higher heats used in the latter steps of the process more rapidly dehydrate the silicate, cause it to whiten, decrease its solubility; and it adheres tightly to the surfaces of the slate granules in small nodules which are visible in the microscope. Also the dehydrated silicate is of semi opaque non transparent condition so that it obscures the dark color of the heated slate. A mass of the colored granules will give a true color efi'ect, although not completely coated. In the formula given the'color will be that of the silicate used as a coating.

The use of sufficient silicate with my-process would probably fully coat each granule, without resulting in permanent agglomeration of'the material and this has been attained in commercial practice and is the ideal condition. But slate slabs covered with nodules of color will give a drab effect, while the same coating on granular slate gives a bright color. This is an optical-effect that is easily demonstrable, but hard-to explain.

Another way of obtaining colored silicate coatings is to use colorless silicate to begin with, and add the coloring matter during the slate treatment process. Thus I may employ, giving small quantities, as before, 2- grams of chromic oxide, 6 grams of silicate of A factor 1 Na O to 3.25 SiO mixed with 12 cc. of water.

The slate is treated in'the same way as before and gives a bright green color to the final product. I

Another way of obtaining a pigmented surfacing for slate granules is to form a metal glass on the granules, instead of a dehydrated silicate. The treatment of the material is the same. Stating proportions 10 gm. of lead acetate and 10 gm. of silicate factor 1 Na O to 3.25: SiO are mixed with 30 cc. of water. The coloring matter can be added to the mixture or the silicate colored in the first place, as in the first example. 400 gm. of slate is then mixed with the products of the reaction so as to be surface coated thereby. After dehydration the high temperatures in the roaster must be at the high end of the range heretofore given, in order subsequently to fuse the silicate and lead compounds, to form a lead glass. As a flux some borax can be used. This type of process is covered by my application for patent, Serial No. 22878, filed April 13, 1925.

In any of my processes of coloring, the features of importance involved here are substantially the same. The granules will come out of the roaster substantially without coalescing; and if any masses are formed these will break up, upon cooling, into the original granules. The whitening or frothing of thesilicate gives the clouded nature to the dehydratd substance; an amount of silicate may be used suflicient onlyto coat the granules in specks rather than completely, thus lessening the tendency to agg'lomerate, and the agitation and heat treatment is graduated to give a preliminary skin before the frothy stage is reached, thereby avoiding permanent agglomeration even if, and this I state upon belief, there is more than enough silicate used to fully coat each granule in a dehydrated or glazed condition.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is

1. A granular slate, surface-coated with a body of dehydrated soluble silicate. '2. A granular slate, surface-coated with-a body of dehydrated soluble silicate, said silicate containing a pigmenting agent.

- 3. A anular mineral matter coated with a body of dehydrated soluble silicate, said silicate containing a pigmenting agent said mineral material being of a character to withstand a roasting treatment.

4. A process of coloring. crnshedmineral matter, which consists in'treating the crushed mineral matter with a water solution of aii alkaline silicate together with a suspended pigment, and dehydrating without chemically changing the silicate, to a weather permanent condition, accompanied by agitation suflicient to prevent formation of balls during the dehydration, said mineral material being of a character to withstand a roasting treatment.

5. A process of coloring crushed mineral matter, which consists in treating the crushed mineral matter with a water solution of an alkaline silicate together with a suspended pigment, and dehydrating without chemically changing the silicate, to a weather permanent condition accompanied byagitation sufiicient to prevent formation of balls during the dehydration, said alkaline silicate having about three times as much SiO as it has Na O, said mineral material being of a character to withstand a roasting treatment.

6. A process of forming colored mineral matter for surfacing, which consists in crushing natural slate to granular form, mixing the granuules with a wet body of soluble silicate and coloring matter, and then treating the resultant mass with heat to permanently cause adhesion of the silicate to the granules with concurrent agitation of the mass.

der application of heat, which consists in applying coloring matter to the granular material by means of a wet adhesive capable of dehydration to permanent condition and then subjecting the granules to heat suflicient to dehydrate said adhesive at a rate which causes the aqueous condition thereof by its evolution to impart a pufiiness to the adhesive thus renderin it non-transparent said mineral granules fileing of a character to withstand a roasting treatment.

9. A process of forming colored material for surfacing, which consists in crushing natural slate to granular form mixing the granules with a wet body of soluble silicate in the presence 9f coloring matter, and then treating the resultant coated granules with heat and agitation to permanently cause adhesion of the silicate to the granules, insuflicient silicate being used to more than fully coat physically the individual granules.

10. A process of forming colored material for surfacing, which consists in crushing natural slate to granular form, mixing the granules with a wet body of silicate in the presence of coloring matter, and then treatingthe resultant coated granules with heat to permanently cause adhesion of the silicate to the granules, said heat treatment being at sufficiently high degree to cause whitening of thesilicate, forming a non-transparent coating, that obscures the color of the slate granules resulting from the heat treatment.

11. A process of forming colored material for surfacing, which consists in crushing natural slate to granular form, mixing the granules with a wet body of silicate in the presence of coloring matter, and then treating the resultant coated granules with heat to permanent-ly cause adhesion of the silicate to the granules, said heat treatment being controlled to first form a skin on the coated granules, in the presence of agitation, and then at sufficiently higher temperature to cause a whitening of the silicate.

12. A-process of forming colored material for surfacing, which consists in crushing natural slate to granular form, mixing the granules with a wet body of silicate in the presence of coloring matter, and then treating the resultant coated granules with heat to permanently cause adhesion ofthe silicate to the granules, said heat treatment being controlled to first form a skin on the coated granules in the presence of agitation and then at sufliciently higher temperature to rapidly and thoroughly dehydrate the silicate.

13. A surfacing material comprising granulated slate, each granule covered with a coat: ing of coloring matter in an inorganic binder, said binder permanently afiixed to the granule, and non-transparent.

14. A surfacing material comprising granulated slate covered with permanently adhering interspaced particles of combined nontransparent coloring matter and non-transparent, dehydrated soluble silicate.

15. A process of forming a mineral surfacing material for exposure to the weather, which consists in crushing slate to granular form, wetting the slate with a dissolved silicate in the presence of pigmenting matter,

and roasting the slate to a temperature of not less than 600 degrees Fahrenheit.

16. A process of forming mineral surfaccate in the presence of pigmentingfmatter,

and then roasting the slate to a temperature of between 900 degrees Fahrenheit, or thereabouts, and 1700 degrees Fahrenheit, or thereabouts.

17 A process for forming artificially colored granular mineral matter, which consists in coating the granular matter with a soluble silicate and coloring matter, and then passing the granules through a kiln with agitation, said kiln operated by an influx of heat in counterflow to the granular material, for

the pur ose described said mineral matter being a character to withstand a roast- 1 ing treatment.

18. A process for forming artificially colored granular mineral matter which consists in coating the granular matter with a soluble silicate and coloring matter, and then passing the granules through a kiln with agitation, said kiln operated by an influx of heat in counterflow. to the granular material, for the purpose described, the ultimate temperature to which the granular material is raised being 600 degree Fahrenheit and upwardly said mineral matter being of a'character to withstand a roasting treatment.

HARRY C. FISHER.