US1755891A - Process of dispersing coagulated bodies - Google Patents

Description

' tionedfor dispersion by compounding No Drawing.

Patented Apr. 22, 1930 UNI ED STATES PATENT OFFICE WILLIAM BEACH PRATT, OF WELLESLEY, MASSACHUSETTS, ASSIGNOR, BY MESNE AS- SIGNMENTS TO DISPERSIONS PROCESS, INCL, OF DOVER, DELAWARE, A. CORPORA- TION or DELAWARE PROCESS OF DISPERSIN'G COAGULATED BODIES Application filed July 10,

' ess .by which the globules of these previously coagulated bodies may be separated and dispersed in an aqueous medium, and I have therein described more particularly a process in which the coagulated mass is first condi there with such organic water-conveying colloids as glue, albumin, dextrine or the like, and is then dispersed in water by the use of an organic agent such as certain saponins or soap bark extract; and I have described these organic conditioning and dispersing agents as being for the purpose of carrying into the rubber mass a certain quantity of Water and of permitting the globules to slide or slip by each other during a stretching and pulling operation, as a result of all of which the interfacial tension of the globules is reduced, the surface tension of the globules is increased, and the globules permitted to separate from each other as the disperse phase of the dispersion in which water constitutes the continuous phase. While in some cases, according to the uses to which the dispersion is to be employed, it is desirable to practice the two steps of first conditioning the rubber for dispersion and then dispersing it by the use of a dispersing agent,nevertheless I have discovered that this can be carried out practically in 'a single step if a suflicient quantity of colloidalmaterial be employed, so that it will function both as a water conveyor and also as a lubricating agent for the globules. It constitutes in this case a protective coating for the globules and permits their separation and dispersion in the aqueous medium. For example, I have found that by employing animal glue in the proportion of one part by weight of glue to one part by weight of crude rubber, it'is possible to effect the dispersion of the-rubber in water Without utilizing any dispersing agent. In this ca e, the 'g u m y 1924. Serial No. 725,207.

the rubber on the usual compounding roll, elther in whole or in part, and the mixture placed ina two blade mixer, such as described in my previous application, and water gradually added thereto, with the remainder of the glue in the event that the entire amount of glue was not compounded with the rubber. Other colloids may likewise be employed if used in suflicient quantity. I have found that the mechanical operation of mixing the colloid into the rubber, the introduction of water and the time schedules employed in the entire operation differ according to the different types of colloidal substances which are used or when different dispersing agents are employed. \Vhere it is desired to employ a smaller amount of glue, the best results are secured by also employing in the dispersing operation a small quantity of another dispersing agent which supplements the action of'the colloid and decreases the surface tension of the water and increases the surface tension of the rubber with a consequent decrease in the interfacial tension of the rubber globules. And in those cases where it is not desired to employ such a large proportion of glue as 50% of themass, the dispersion may be effected by working in 5% of glue together with 10% of water upon a standard compounding roll, and then removing the mass to a two-bladed mixer, and then gradually adding to the mass 10% of water together with 2% to 5% of saponin or soap bark extract. But, instead of employing two different agents in effecting the ultimate dispersion, I may employ, as hereinbefore stated, a single material, provided it is used in sufficient quantities to act both as awater conveyor and also as a lubricant in permitting the relative slipping and ultimate dispersion of the rubber globules.

Bearing in mind the functions to be performed by the substances employed in effecting the separation of the globules and their dispersion in water, I have discovered that other organic and inorganic water-conveying colloids, such as sea moss or Irish moss, clays, and other organic-substances of a colloidal nature may be employed, according to the characteristics which one-desires to securein i theform of paint for application to other surfaces whereon it is spread by a brush or spray, the nature of the dispersion should be such that the rubber globues will not again become adherent during the spreading operation but will adhere and form a continuous film only-upon the removal of the water. In

' some cases likewise it is desirable that the dispersion itself shouldnot be of a tacky nature such as may be imparted thereto by an excess of certain classes of glue.

I have discovered that certain inorganic materials such as colloidal clays or equivalent argillaceous material. may be employed in performing the function of both a water 2 conveyor and a lubricating agent in effecting the dispersion of the previously coagulated bodies, that relatively small quantities of these bodies will function properly in effect:

ing the dispersion without the addition of other agents, such for example as saponin,

soap bark extracts, or the like, that, when these colloidal clays are employed in effecting the dispersiomthe dispersion is remarkably stable even under pressure, and that the dispersed globules of rubber are not adherent until the removal of more or less of the aqueous medium; so that, even if an agent ordinarily employed for coagulation (such as acetic acid) is added to the dispersion, it does .40, not effect the coagulation of the rubber glob-' ules. Another advantage, which follows from the employment of colloidal clay as the dispersing agent, is that it may supplant a part of the usual pigments such as whiting,

5 talc, magnesia or the like, in efiecting a disersi'on of a rubber compound in which these atter materials are employed. The colloidal clay may be worked dry, together with the other compounding materials such as sul-.

5o phur, organic or inorganic accelerators, pignrents, softeners, rubber substitutes, etc2, into the rubber mass by the standard compounding mill in which the smooth surfaced rolls are separated fromjeach other and are driven at different speeds, or a small quantity of water may be added to the clay so that it is compounded with the rubber while in a moistened state. It should be borne in mind, however, that, inasmuch as one of the functions of the colloidal clay is that of .a water conveyorforvthe purpose of assisting in the introduction of water into the interglobular spaces of the rubber mass, the clay should be moistened before it is compounded with the 4 {rubber or that the compounding operation should not be carried to such anextent that 1 ,In any event; after the clay has been compounded with the rubber mass, it maynow be placed in a mixer of the character of a dough mixer, wherein the mass will be subjected to a stretching and pulling operation, and water is gradually added to the mass during the operation of the machine. It is noted that as the water is gradually mixed with the mass, the mass swells; ahd finally, as the operation continues with the gradual addition of water, a paste as smooth as butter results in which the rubber globules are dispersed in the aqueous medium. One may continue to add water until the mass is of the consistency of cream; and by the addition of more water the dispersion becames of the consistency and general appearance of milk. In this condition, acids such as acetic acid may be added to the mass without the coagulation or mechanical adhesion of the rubber globules. In its paste form, the mass may be spread with a spreading machine, and it may be painted on to a surface with a brush or by means of an air nozzle; and in anycase, with the removal of water by evaporation, forced drying or the like, the rubber globules adhere and coalesceto form a continuous rubber film.

One may employ say 10% to 15% ,of certain colloidal clays in effecting the dispersion of such coagulated rubbers as smoked sheet, pale crepe, fiup river fine para and thelike in dispersing the rubber globules to a size and form similar to thatin which they exist in the serum of the latex as drawn fromthe rubber tree. By way of example, one may compound with 85% of pale crepe 15% of colloidal clay, (e. g. bentonite or Wilkenite) to which 10% of water has been added, and then, after the compounding operation has been completed, by introducing the mass into a Werner and Pfleiderer, Ross or Day mixer, and then gradually adding water during the mixing operatioh, a paste of the desired consistency'is produced.

It is not necessary that the colloidal clay should be initially compounded with the rubher, as it may be added to the mixer together with water so that it is worked into the rubber during the pulling and stretching of the mass which takes place in the mixer. While the crude rubber, even before it is worked on the compounding mill so as to soften it and render it more or less plastic, may be introduced into the mixing machinetogether with the desired proportion of the colloidal clay, and be dispersed,provided not too much water is gradually added, nevertheless it is for economic reasons that I prefer tocworkthe moistened clay into the rubber on the compounding mill as I am enabled thereby greatly to shorten the whole process of eifecting the dispersion.

I have previously pointed out that, where it is desirable to effect the dispersion of a rubber compound containing as its components such materials as whiting, magnesia or the like, the colloidal clay may be used to supplant a part of these materials. Thus, for example, in dispersing a compound which would ordinarily consist of rubber pounds, whiting'25 pounds, zinc oxide 15 pounds, litharge 10 pounds, barytes 10 pounds, mineral rubber 10 pounds, and sulphur 5 pound s, Ihave found that the whiting may be reduced to 23 pounds and the barytes reduced to 8 pounds; andthat, by employing 7 pounds of colloidal clay and compounding this with the rubber and water, and then adding the remainder of the compounding materials as noted, I effeet a dispersion, simply by the gradual addition of water to the mixer during the mixing operation.

The operation may be carried on at ordinary atmospheric temperatures, except that of course the rubber heats to some extent during the preliminary milling or mixing operation. This heating, however, may be controlled by cooling the rolls of the compounding mill and by cooling the mixer, which is ordinarily provided with a water jacket for this purpose. The water may be employed at seasonable temperatures orit may be heated to a temperature not exceeding 70 C. Bearing in mind, however, that at temperatures below 20 C. the rubber becomes tough and it is more ditficult to introduce water into the mass, whereas at temperatures above C. the rubber becomes tacky as 'well as plastic and will tend to cause an adhering of globule to globule which retards the dispersing action of the mediums employed, the operations should be carried on at a reasonable mean temperature between 20 and 70 C. If rubber is heated to a high temperature of say 300 to 400 F., depolymerization or breaking down of the globules occurs and the rubber loses the characteristics of crude'rubber, and if then dispersed the dispersed particles are not those of crude rubber. By my process the crude rubber is notheated to a point of depolymerization, and the rubber globules are separated and dispersed as such.

Colloidal clays, such as found on the market, vary to some extent in their efliciency in effecting a dispersion of a coagulated body such as cruderubber or crude rubber compound, and different colloidal clays require a difierent schedule of time and proportion to rubber in elfecting the dispersion.

It is quite possible that colloidal clay has the effect of separating from the coagulated rubber globules such organic substances as may have been initially in the rubber latex, and which, because of their lower softening point, tend to increase the interfacial tension and adherence of the rubber globules in the the colloidal clays which I employ in the dispersion of the rubber compound may perform a function additional to that previously pointed out, (that is, of acting as a water con vey'er and as providing a protective coating for the individual globules and of permitting them to slip relatively to each other), to

wit :-of cleaning the rubber globules of such foreign substances as the resins or other organic bodies which are incorporated in the rubber mass during the coagulation of the rubber globules from the serum. Be that as it may, however, and whether my theory be correct, it is the fact that by the use of such colloidal clays it is possible to separate the globules of rubber which had originally been adherent in the coagulated crude rubber mass and to restore them to substantially their initial form in the water medium.

When the water is removed from the dispersion by drying or otherwise, the film or mass which is left may be vulcanized by the hot cure or the cold cure with the same factors in-relation to vulcanization that obtain with a sample of the same crude rubber before dispersion. That is, with the same time and temperature schedules and with the same sulphur addition that are used in Vulcanizing a sample of the crude rubber, from which the dispersion was made, to produce a given result, the dispersion itself on removal of water may be vulcanized to produce the same result. 4

I have herein referred to the fact that substantially any crude rubber or compound containing crude rubber may be dispersed by the process herein outlined, so that I have not attempted to specify in detail the various compounds which may be dispersed. It may be stated generally, however, that any rubber compound which is capable of vulcanization may, after being prepared, be dispersed in accordance with the process, and, upon removal of the contained water, be vulcanized. Furthermore, where the compound is not to be vulcanized but is to be used in the form of a paint or other plastic. I may compound with the rubber prior to its dispersion such continuous bodies as boiled linseed oil, China wood oil, rape oil, corn oil, fish oil, or animal oil, together with coloringpigmentsinafinely divided state; and, in some instances Where it is desired, the compound before dispersion may be colored by suitable dyes such as will not be injuriously affected by thewater; or, on the other hand, a water-soluble dye may be dissolved in the water which is employed for the dispersion of the mass, and left in the resulting compound upon the evaporation of j compound and incorporated therein suitable the water. Where'oils are compounded with \the rubber, there may be also added to the organic or "inorganic drying agents which will set oils without affecting the rubber. Ordinarily such driers are added when the compound is not to be vulcanized, and therefore does not contain sulphur.

For convenience of phraseology, I use the term rubber to includebalata or gutta percha,

which like crude rubber are originally in thec form of globules inthe serum of the natural sap of the plant and which are coagulated or coat, and that, on coagulation of the rubber globules, the colloidal coatings are dehydrated and adhere together; A deformation of the globules takes place, with the.

decrease in the surface tension of the globules and the increase of the areas of their interfacial contact, asthe protective coatings become ineffective in maintaining-the globules separate from each other. Doubtless, 'this adhesion of the coatings and hence of the globules is .assisted by the resinous or other substances which are present in the natural latex and which are more or less adhesive in character. Colloidal clay does not, in my opinion, form a coating or film for the globules of precisely the same character as that which initially protects the globules in the latex( It is inorganic and while it is lubricating in its nature when moistened,

and, performs the function in the rubber dispersion of maintaining the globules separate from each other and permitting freedom of movement, it differs from the natural coating of the globules in that, while the natural coatings are affected and are easily caused to coagulate by the addition of acids to the mass, the colloidal clay coatings are not thus affected. Irrespective, however, of whether the theories advanced are or are not correct, it is the fact that in following the procedure hereinbefore stated one may disperse such' coagulated bodies as crude or reclaimed rub; ber-in water in globular form without affecting the chemical or physical characteristics of the rubber, sothat on removal of the water the recoagulated rubber may be employed for the purposes and cured with the same vulcanization factors as the initial body before dispersion.

\Vhat I claim is: 1. An aqueous disperson of non-polymer- 6 ized previously-coagulated rubber and an inorganic'colloid which is not in excess of 15% by weight of rubber,'in which the rubber I I globules possess the same characteristics as those before the rubber was dispersed, said dispersion resulting from the kneading and stretchingjof a coherent, plastic mass of-rub her in the presence of such colloid while gradually adding water. vI 2. An aqueous dispersion of an initiallyc-oagulated body such as rubber, ba'lata or gutta-pe'rcha, together with not in excess of 15% by'weight of colloidal clay, in which the .dispersed globules are of substantially the a form as 'in the original latex, and having 35 similar freedom of movement, said dispersion resulting from the manipulation of a coherient, plastic mass of rubber in the presence of I v the colloidal clay and water. I

41 A non-sticky aqueous dispersion of previously-coagulated rubber, comprising sepal rated crude rubber globules, and a colloid, Y said globules being coagulated with diificulty, if at all, upon the addition of acetic acid to the mass, but, said globules coagulating upon removal of the water from the mass, said dis persion resulting from the manipulation of a coherent, plastic mass of rubber in the presence of such colloid and water.

5. A non-sticky aqueous paste comprising 1 previously-coagulated rubber, vulcanizing agents 'and a colloid all dispersed in water, said colloid being not in vexcess-of 15% by weight of the rubber and being such as to 'render the mass diflicult'to coagulate with acids, but such paste forming a continuous cohering film on removal of the water, said dispersion resulting from the manipulation of a coherent, plastic mass of rubber in the presence of such colloid and water. .6. A process of dispersing crude rubber in water, which comprises p-ullin and stretching a coherent mass of such ru her while at low temperature and at atmospheric pressure in the presence'of water and an inorganic colv112i loid until the rubber in the water.

7. A process of dispersing crude rubber in water, whichcomprises firs'tincorporatingcolloidal cla into the coherent rubber mass, and 12 then whil e the product is below the temperature of depolymerization mixin water a with the resulting product while su jecting the mass to a stretching or operation until the rubber disperses'in the Water.

separates and disperses v i v '7 tion of water thereto, untilfthe rubber sepab'er dispersed as minute, undecomposed pars n testimony whereof I have aifixedmy sig- I rates into its constituent globules, without changing the 'chemical characteristics of the rubber. f

9. An aqueous dispersion comprising rubticles in an aqueous medium containing an inorganic colloid as the dispersing agent, said particles coagulating upon the removal of water from the dispersion to form a continuous', coherent body, said dispersion resulting from the manipulation of a coherent, plastic mass of rubber in the presence of such colloid and water.

10. An aqueous dispersion comprising rubber dispersed as minute, undecomp'osed particles in an aqueous medium containing colloidal clay as the dispersing agent, said particles coagulating upon the removal of wa ter from the dispersion to form a continuous, coherent body, said dispersion resulting from the kneading and stretching of a coherent,

plastic mass of rubber in the presence of colloidal clay while gradually adding water.

11. A process which comprises manipulating a coherent plastic mass of rubber without decomposition in the presence of'an inorganic colloid and water until the rubber dis erses as minute particles in the aqueous me ium.

12. A process whichcompri'ses manipulating below decomposin temperatures a coherent plastic mass of ru ber 1n the presence of colloidal clay, and gradually adding water while the mass is being manipulated until the rubber disperses as minute particles in the a ueous medium.

nature. 7

WILLIAM BEACH PRATT.