US2353991A - Process for forming plastic solutions and incorporating solid filling material therein - Google Patents

Description

' July 18, 1944.

' CJE. BOU TWELL PROCESS FOR FORMING PLASTIC SOLUTIONS AND INCORPORATING SOLID FILLING MATERIAL THEREIN.

Filed Sept. 2, 1941 SOLVENT .STORAGE 65 A A PUMP /0 MIX/N6 IEJJEL CONDENSER "7 /4 33 M J /e /JB' 26 Z3 Z8 2/ ame/var:

ll fi 24 /7 61 ARE/veg E. Bou TWEL L1 Patented July 18, 1944 PROCESS FOR FORMING PLASTIC SOLU- TIONS AND INCORPORATING SOLID FILL- ING MATERIAL THEREIN Clarence E. Boutwell, Birmingham, Ala.

Application September 2, 1941, Serial No. 409,218

' Claims. (Cl. 106-493) This invention relates to a process for the rapidand thorough dispersion of plasticizers and cellulose into a solution, and for incorporating filling material into plastic solutions and the like, such as finely divided solid material in cellulosic'plastics, phenolic-aldehyde resins, while in solution, and the like, and has for an object the provision of a process of the character desi nated which shall be effective to bring about a uniform dispersion of such material, in a minimum of time, in a liquid solution preparatory to forming a plastic into a solid, which dispersion shall be free of lumps or masses of unwetted solid material.

In my prior Patent No. 2,219,587, issued September'28, 1940, there is disclosed and claimed a printing plate composition comprising a cellulosic plastic material and a mineral filler up to approximately 30% by volume. By using ordinary mixing methods heretoforeknown to me, it has required from 24 to 48 hours to efiect a thorough dispersion of the filling material in the plastic while in solution. By the process herein disclosed I have been enabled to reduce the time required'for thorough mixing to from 3 to 4 hours, and have obtained a better,-more complete dispersion. I

In the carrying out of my invention I contemplate employing an excess of a volatile solvent such as acetone, alcohol, or a mixture of ether and alcohol, to aid in producing the dispersion, and removing and recovering the ex cess solvent as mixing proceeds to completion. I further contemplate introducing air into the mixture along with the solid material, to aid in the dispersion and to act as a vehicle in removing the volatile solvent from the mixture.

My invention further contemplates, in its preferred embodiment, a grinding action on the materials while they are being incorporated into the plastic solution whereby to provide a quicker, more thorough incorporation thereof into the liquid plastic solution and to insure against lumps, or masses of agglomerated material passing into the solution.

The single figure of the accompanying drawing, forming a part of this application, illustrates conduit l2 controls the flow of'solvent. to the vessel. A pipe |l is'connected tothe bottom of the vessel I0 and has a control valve l6 therein. At I1 is a T connectionto which abranch conduit l8 for the admission of solids into the nular gear 23 and an'inside spur gear-24 with a crescent shaped projection 26 extendingfrom diagrammatically, by way of example, apparatus adapted to carry out my invention.

Referring to the drawing, I show a closed vessel l0, preferably having a hopper bottom as shown, for the mixture of solvent, plasticizers, plastic and filler. At II is shown a storage vessel for the solvent. A conduit |2 leads from the vessel II to the vessel It, and a valve l3 in the the casing and dividing: the space between the two gears, as shown. The solution enters the casing of the pump 22 through the conduit H at 21, and is discharged at 28 into, aconduit 29 which discharges it-backinto thevessel Ill. As will be seen in the further description of my inventidn, a gear pump is preferably employed, due to its grinding action on the solid material passing therethrough. A gear pump of a form difierentirom that herein shown may, of course,-.be employed,v so. longas it produces a circulation of the materials being mixed coupled with a grinding action on the solid material.

A conduit 30 is connected to the upper end of the vessel l0 and leads to a pump 3| which may be a rotary sliding vane pump, as shown. The pump 3| discharges through a conduit 35 to a condenser 32 into which a cooling solution is introduced at 33 and passes out at 34. A by-pass 36 having a valve 31 therein connects the conduits 30 and 35. Thisvalve controls the flow of vapor from the vessel ID to the condenser 32 when the pump 3|v is not in operation. Condensate is collected in a vessel 38.

Assuming that the plastic employed is cellulose acetate and it is desired to incorporate therein a filler, such as lead carbonate or iron oxide, I Proceed as follows: I first run into the vessel III a solvent, such as acetone, alcohol, or a mixture of ether and alcohol, in an amount about twice that required in the finished product before drying. The pump 22 is then started to bring about a circulation of the solvent through the pump and the piping system back into the vessel Ill. The valve 31 is then opened and the required plasticizers are added through the fun-- nel 2| and branch pipe |8 and are circulated through the pump 22 until thoroughly dissolved in the solvent. Next, the cellulose acetate is introduced into the confined stream of the solvent in the pipe H by feeding it slowly through cordance with my invention.

the branch conduit II. In passing into the stream and through the pump 22, the minute particles of cellulose acetate are each exposed to the maximum quantity of solvent before they have an opportunity to agglomeraie. Thus the cellulose acetate is thoroughly incorporated into the solent and a smooth, uniform dispersion is made. I have found that the required amount of cellulose acetate may thus be thoroughly dissolved in the solvent in around 30 minutes. This time, of course, may vary with the size of the batch and the size and speed of the pump.

As soon as the cellulose acetate has been thoroughly dissolved, the filling material is introduced.

through the branch conduit It, being added slowly, the rate of feed being controlled by the valve l9, This method of feeding the material into a confined stream of solution prevents agglomeration of masses of material which would otherwise have to be separated by heating. With a uniform feed of filling material introduced thus into the plastic solution, and with the pump 22 running, it will be seen that there must result a uniform dispersion of the solid material in the liquid. In addition, the action of the gears 23 and 2 grinds the solid material into the solution, prevents its lumping, and insures a thorough wetting of every particle of the solid material.

The action of the pump 22 creates a partial vacuum in the intake conduit I, so that a considerable amount of air is drawn into the mixture with the materials added through the funnel 2|. I have found that the air aids in the rapid mixing which I obtain, and also acts as a carrier for the solvent which is volatilized in the operation. It also increases the gaseous volume in the vessel i0. Accordingly, while-the mixing is proceeding, the valve 81 is left open to permit the excess mixture of air and volatilized solvent to pass out of the vessel Hi to the condenser 32 where a cooling solution chills the solvent and condenses it for recovery in thevessel 38. When the mixing is completed, and with the circulating pump 22 still in operation, the valve 31 is closed and the pump II is started, creating a partial vacuum in the vessel Ill and drawing the solvent out of the mixture to be condensed in the condenser 32. By this procedure, I find that I recover about one-half of the original solvent employed, leaving the mixture of a consistency such that it may be spread upon a smooth plate to form a sheet, extruded, or otherwis treated, and dried to evaporate the remaining solvent and produce plates, sheets, rods, or whatever form the final product may take. It is understood, 0'! course, that the solvent thus evaporated may be recovered, if desired, by well known means;

When the mixing is completed, the contents of the vessel Ill may be discharged by means of a valve 40 connected to the conduit l4 directly beneath the vessel HI.

While the specific example given is a mixture of a cellulosic plastic, one or more solvents, plasticizers and solid filler material, other uses of my invention and other solid-liquid mixtures will at once suggest themselves to those skilled in the art that may advantageously b mixed in ac- It is well known that the production of a uniform dispersion of a relatively high percentage of filling material in cellulose acetate, or other cellulosic plastics, with thereupon as are specifically set forth in the appended claims.

What I claim is:

1. A process of incorporating solid filler material in plastics which comprises forming a solution of the plastic in a volatile solvent, forcibly circulating the solution in a confined restricted path, introducing solid filler material and grinding it into the solution while circulating in said path, maintaining a sub-atmospheric pressure in the path at the point of introduction of the solid material, and evaporating the solvent.

2. In a process of incorporating solid filler material in plastics, the steps which comprise forming a solution of the plastic, forcibly circulating the solution in a confined path, introducing solid filler material into the solution while circulating in said path, admitting 'air to the solution along with the solid material, separating air and volatilized solvent from the mixture, and condensinl the solvent.

3. A process of incorporating solid filler material in plastics which comprises forming a solution of the plastic, forcibly circulating the solution in a confined path, introducing solid filler material into the solution while circulating in said path, admitting air to the solution along with the solid material, separating air and volatilized solvent from the mixture, condensing the solvent, and grinding the solid material into the solution as it is introduced thereinto.

4. The method of forming a cellulosic plastic mixture containing up to 30% of solid mineral filler by volume, which comprises forcibly circulating a volatile solvent in a confined restricted path, adding cellulosic plastic to the solvent in said path and continuing the circulation until the plastic is thoroughly dissolved, slowly adding the solid material to the solution while circulating in said path, submitting the solid material to a grinding action while introducing it, continuing th circulation until the solid material is thoroughly dispersed and maintaining a partial vacuum in the restricted path at the point of introduction of the plastic and the solid material to induce a flow of air into the path at said point.

5. The method of forming a cellulosic plastic mixture containing up to 30% of solid mineral filler by volume, which comprises forcibly circulating a volatile solvent in a confined path, adding the cellulosic plastic to the solvent in said path and continuing the circulation until the plastic is thoroughly dissolved, slowly adding solid filler material to the solution while circulating in said path, admitting air into the solution along with the solid material, separating the air and volatilized solvent from th mixture, and condensing the solvent.

CLARENCE E. BOUTWELL.

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