USRE22454E - Carbon black and the process of making same - Google Patents

Description

ReiseuedMar. 7, 1944 ."o F ca cannon BLACK AND, 'rnr: raocass or MAKING SAME William B. Wiegand, Ol'd Greenwich, C'onn., and Louis 'J. Venuto, New York, N. Y., assignors to Binney & Smith 00., New York, N. Y., a corporation of New Jersey No Drawing. Original No. 1,889,429, dated November 29, 1932, Serial No. 237,330, December 2, 1927. Application for reissue January 6, 1943,

Serial No. 411.496

8 Claims.

The important characteristics of carbon black which render it particularly valuable in the manufacture or rubber compositions, phonograph records, various wax and resin compositions, printers ink and other preparations, are its extremely fine state of subdivision together with the very essential property of'belng readily and uniformly dispersed in rubber, waxes, oils and the like. Carbon black, as manufactured, is such a very light fine powder that normally ten pounds, or less, occupy a package of'one cubic foot. It is accordingly expensive to pack, ship and store such a light bulky material, and handling the light powder causes it to fly in the airto such an extent that there is substantial loss of material. and an annoyance to workmen handling the material and breathing the dust.

Numerous attempts hav been made to overcome these objectionable properties of carbon black .and render it denser'and less dusty, but all such attempts heretofore have greatly changed the very essential physical properties of the carbon black which make it industrially valuable. Thus,

bon black as to all or substantially all of the by quickly removing the liquid by absorbing it into thewalls of a small porous container, or by displacing the original liquid by another in such a manner as to avoid free suspension of the particles, in a liquid phase.

The main object of our invention is to secure carbon black having the desired dispersive prop erties, greater density, freedom from dust, freedom from gritty particles, less absorbed or oceluded gases, reduced oil absorption than the ordinary powder form, and capable of considerable handling without crushing or dusting.

a We have discovered that we can improve'carabove mentioned properties without deleteriously afiecting any of the properties essential to its satisfactory industrial use, such as softness and dispersive qualities, and by a process which inor-great'er ability to wet the particles.

the carbon black may be made into a paste with I water or other volatile liquid such as gasoline, solvent naphtha, xylene, turpentine, carbon tetrachloride and the like, and the volatile liquid then distilled or evaporated, but the resulting cake is hard, the carbon particles tend to hold togetherin chunks, and they no longer disperse readily and uniformly as for example in rubber compositions.' Apparently the state of aggregation of the carbon particles has been changed.

. in such altered carbon blacks, and, as a matter of fact, the industrially essential physicalproperties, namely, easy and uniform dispersion, are so much impaired that such processes have never been a commercial success.

We find that when ,the original carbon black is added to a liquid to form a paste and the liquid slowLv distilled or evaporated, such treatment causes changes which are associated with a free meniscus, i. e. vortices, surface tension adhesion,

settlina. volume contraction of the black, and a in. veryqulckly with violent agitation. ying This procesa'if carried out under certain conditions, causes the carbon black to form into pellets which are hard enough to stand any ordinary shipment, or handling without dusting, flyingor breaking down, and which at the same time, are

easily crushed by moderate pressure, as between V the fingers or by the pressures commonly employed in the rolls of rubber compounding machinery, printers ink mixers and the like. The crushed particles have substantially their original softness and the material disperses freely with-.

out leaving any particles of undispersed carbon in the material.

While the pellet form is avery convenient form of the carbon black, the shape of the particles is not the most important characteristic of this novel carbon black. The properties enumerated above may be incorporated into the black in the which is substantially immiscible with the first andwhichhas greeterabilitytowetthecarbon particles. 'I'hemixtureisthenagitatedimtilthe fi st mentioned liquid ispnctically free from cealiquid is removed by evaporation.

Merely as an example of our improved proc-' ess, the operation may be carried out as follows: The carbon black is first mixed with water so as to form a comparatively thin paste with most of the occluded gases driven out. After thorough mixing gasoline is added and the whole,

mass thoroughly agitated. As a result substantially all of the carbon black floats on top of the water in the form of pellets and may be readily removed by filtering. decanting or the like.

These pellets may then be dried to-remove the absorbed gasoline and such moisture as there may be contained therein. Care should be taken to insure the complete wetting of the particles with the water, as otherwise the particles will be wet directly by the gasoline and in drying harsh particles may .result. In the drying operation the carbon black retains its globular, ball-like orv pellet form."

On the first addition of gasoline to the black and water paste, with agitation, the mass seems to thicken like an emulsion: then on further it seems to flocculate into granules; as

the agitation goes on, a slight creaming to the top of the pellets or a scum takes place, then gradually the pelletsiorm and float to the top.

' The end point is reached when the water below is free. of carbon, that is, is clear.

The pellets are then screened off byany o the various methods, placed in an oven or a recovery-apparatus and freed from solvent and water. It has been found that by use of this method the drying'has little or no harmful effect upon the particle. Low temperature dryin and high temperature drying (around 400 Fahrenheit) leave the particle in a good soft condition. There are however various factors which will influence this.

' If there is no organic residue decomposed by heat, there will be no binding of the particle.

lf'there is, a harshness will result due to the decomposition or gumming of the residue. If

too much gasoline is used, the particles will compact to comparatively hard pellets. If there is too much water and not enough gasoline, an inferior product will result.

The control however of the above process does not necessarily have tobe delicate. A rather wide margin of safety exists.

Merely as an example of --the relative proporv 28,!!! bon. This liquid is then separated and the other dirtying or dusting. Apparently the outer surface portion or shell of each pellet is slightly more compact than theinner part, but still porous. In shipping or storing, we find that approximately twice the number of pounds of these pellets can be placed in a container of a given size than is the case with the untreated carbon black. Thus, expense is reduced for shipment or storage.

It will be noted that during the agitation and separation any grit which there may be in the carbon black may settle to the bottom, while the pellets float to the top and thus the-purification of the carbon black will be effected at the same time the pellets are formed.

The pellets will not pack down in the bottom of a bag or other shipping container as in the case with untreated black and may be stored in bins and delivered through chutes to the point of use, without caking or sticking. The non-flying properties permit better control of the mixing in rubber or other composition, facilitate weighing, result in a substantial saving of material by eliminating mechanical loss, and add to the comfort of the operator.

The process. of the present invention when carried out as described above yields substantially pure carbon black, but we find that the present invention can be employed for the manufacture of carbon black containing other materials uniformly distributed through or absorbed by the black, without loss of dispersibility. For example in its application in the rubber industry, ithas been attempted to incorporate various other substances with the black, such as accelerators. softeners and anti-oxidants.

When this is done by adding the said additional tions which we have found to operate satisfactorily, we give the following by weight:

substance and the carbon black to a liquid in which the added ingredient is soluble, and subsequently evaporating or distilling the liquid, the resulting .carbon black is hard and has lost its ready dlspersibility, as noted above. We find that the addition of substantial proportions of certain other substances to either of the liquids used in the process of the present invention does not impair the dispersibility of the resulting carbon black. Thus for example hexamethylene tetra-mine and various water soluble xanthates may be. added to the watercontaining the carbon black or such substances as diphenyl-guanidine, thiocarbanilide, various amine oleates or stearates, or anti-oxidants, such as hydroquinone, resorcinol or naphthylamine may be added to the gasoline, benaol or water insoluble phase up to the limit of their respective solubilities, without qualities of the re- Part8 Carbon 5 Water r 40') 80 658011118 7 t0 9 In carrying out our improved process with these proportions, the mass may be thoroughly shaken or otherwise agitated for about five min-' utes and the resulting pellets will be of about onesixteenth of an inch in diameter and will be fairly uniform in size.

The pellets are very porous, of substantially spherical or globular form, have a smooth somewhat lustrous outer surface which is not easily broken by handlin are more compact than um treated carbon, are fragile under light pressure.

and may be easily reduced to soft minute particles which cannot be told from the original particles except that possibly they have a more unctuous feel. j They somewhat resemble lead shot and may be rolled in the hand without suiting carbon black. I

There are various factors which enter into theprocessandthesemaybevariedtoget the. pellets harder or softer or larger or smaller. Among these factors are the thickness of the paste, the amount of gasoline used, the adding of the gasoline in bulk or a little at a time, speed of agitation, temperature, type of gasoline used, and character of the carbon black; In using gasoline, it is desirable touss a high grade, such for instance that commonly known as aviation gasoline, in which there is a minimum amount of high boiling constituents. Other liquids, such as benrbl, chloroform, toluol, carbontetrachloride, nlol, turpentine, or carbon di-8il1phldQ,'Iil&y" bB; used. It is important that theliquid be one ity of over one,

the pellets to the top of the water, but they grades or different kinds, or grades applied to other fine applications depend upon their dispersibility. For example, precipitated magnesium carbonride, chloroform, carbon di-sulphide, or any other of like character having a specific gravwill not cause the flotation of will simply sink to the bottom. They can however be recovered by filtration or screening.

Some creaming agents have greater wetting power than gasoline, and therefore require a lesser amount to bring about the end point.

In general it is preferable that the cream ing agent be completely volatile so as the carbon pure. In special cases it is not necessary where the residue will impart special properties to the pellet.

If small pellets are desired, a lesser amount of gasoline or other liquid should be used in respect to' the amount of water and carbon, and greater agitation should-be employed. To secure large pellets, we use a larger amount of gasoline and slower agitation. In practice, we

'do 'not consider a size larger than one-quarter of an inch desirable. There are many kinds, varieties of carbon black and often identification of the particular kind or grade is difllcult. With our improved process the may be made into pellets of different sizes so that identification is facilitated, for instance, very small pellets may be made for printers ink and 1arger ones for rubber, etc.-

It is possible also to ultimate pellet stage. It will come out as an amorphous mass somewhat flaky and flufl'y, and must be separated from the mixture by filtration.

The flake form of the material is produced by incorporating the black in water, as described above, and immersing in the mixture a porous material which is wet with gasoline, or other liquid "as before described. wing to the preferential wetting power of the gasoline, the carbon particles leave the water and are wetted by the gasoline, building up a layer instead of forming globules or pellets as is the case when the agitation method is used. The surface on which the black is deposited may be a rotating porous cylinder, with the gasoline supplied to the inside, the layerot'black being continuously scraped off the cylinder, as it rotates.

Another method of producing the flake form is 'to crush the pellets before evaporating" the solvent, as between rolls, and then evaporating the gasoline, or other volatile liquid.

The whole process of' pends upon the selective wetting power w ch the various solvents exert on the carbon bl ck.

We use the term "carbon black" in its broad rather than limited meaning, and 'by such term include lamp black, gas black and other black analogous carbon substances for use as pigments or fillers.

We find that the present invention can be powders whose industrial ate, zinc oxide, titanium oxide, barium sulfate,

and certain tales and clays are diilicult to disto leave reduce the fiyingof the black by not carrying the above treatment to its perse in rubber or oil on account of absorbed air and tendency to fly as dust, and we find that these powders can be manufactured in denser form, with elimination of most of the absorbed air and without loss of dispersibility, by the process of the present invention.

In the foregoing we have referred to agita-, tion of the mixture,'but we do not wish to be vrestricted to any particular kind of agitating apparatus. For batch operation the agitation may be accmomplished by violent shaking, rotating or tumbling of the container, and for continuous operation the agitation may be by any means which will impart rapid changes in the direction and/or velocity of the flow of themixture stream, as for instance,

apertured obstructions or bailles in a conduit.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is: a

1. Substantially pure carbon black in the form of round smooth-surfaced aggregates less than one-quarter of an inch in diameter, free from.

binder and porous throughout in such degree that approximately twice the number of pounds of aggregates of fairly uniform size can be placed in a container of a given size than is the case with the untreated carbon black.

2. Substantially pure carbon black in the form oi round smooth-surfaced aggregates less than one-quarter of an inch in diameter, free from binders and porous throughout in suchv de ree that approximately twice the number of pounds of aggregates of fairly uniform size can be placed.

.. in a container of a given size than is the case pellet formation -declear, separating the with the untreated carbon black, the aggregates being sufficiently hard and flowable to prevent the formation of dust, and yet sufficiently friable and dispersible for use as a component in the manufacture of rubber and other products.

3. The process of treating carbon black which includes the steps of mixing th carbon black with a liquid to form a very thin paste, addin a second liquid in smaller-amount and which, is immiscible with the first liquid, agitating, separating the carbon black and second liquid from the first liquid, and then separating the carbon black and the second liquid.

4.,The method which includes wetting carbon black with water, bringing the mixture into contact with a liquid having greaterwetting properties whereby the carbon black is substantially separated from the water, and evaporating the second liquid from the carbon black to leave asgregates of porous fragile structure readily reducible to the original state of flne-subdivision.

. 5. The process which includes wetting carbon black with water, bringing itand gasoline into contact under conditions causing the gasoline to displace substantially all of the water from-the carbon black, removing the carbon black mass wetted with the gasoline, and evaporating the gasoline. 6. The following process, mixing 40 to parts of water and 5 parts of carbon black to form a thin paste, adding '7 to 9 parts of gasoline, agitating until the carbon black forms in pellets in the gasoline and leaves the water substantially pellets and the water, and drying the pellets.

,7. The process of treating compounding ma terials in a fine state of subdivision to bring them into a more compact form for use in plastic and coating composition which consists in wetting it with one liquid in which the finely divided rnaterial is substantially insoluble and with which it does not react chemically, subsequently agitating it with a second similarly inactive liquid immiscible with the first and having greater wetting properties, separating the material from the first liquid, and drying to obtain the material in a more compact form.

8. The process of treating carbon black, which consists in wetting it with one liquid in which the finely divided material is substantially insoluble" and with which it does not coact chemically, subsequently agitating it with a second similarly inactive liquid immiscible with the first and having greater wetting Pr p rties, separating the carbon black from the first liquid and drying to obtain the carbon black in more compact form.