Dec. IO, 1946. c. L. sHAPlRo 2,412,296 A METHOD OF AND APPARATUS FOR DEPOLYMERIZING ACRYLATE RESINS Filed April 3, 1.944 lN VEN TOR. 6dr/ l. Jhd/:fra 4 free/vi y Patented Dec. 10, 1946 ,_ 2,412,296 UNITED STATES PATENT ori-'1cEffÍ> . 2,412,296 METHOD‘OF AND APPARATUS FOR DEPOLY MERIZING ACRYLATE RESINS - f Carl L. Shapiro, Beaver Falls, Pa. Application April 3, 1944, Serial No. 529,390 7 Claims. ’ (Cl. 260---486) l 2 The present invention is directed to the treat ment of acrylate resins such as those made from methacrylic acid and esters thereof. Resins of the acrylate type have been in use for some years and they ñnd a considerable ap plication in molding of various articles, usually by injection methods. In the course of such siderable velocity. Therefore, prior processes were Adependent upon the dissociation, volatiliza tion vof the product, and condensation thereof. The present invention also subjectsthe acrylate resin to temperatures above the dissociation point manufacture there is a considerable amount of Waste acrylate resin which is an important factor temperature used in the treatment is quite high, being usually above _400° C._ and Aas _high vas 1000° C. According to prior information,> such temperatures would, necessarily Ycompletely ,de-_ compose the resin to form useless end products. In accordance with the present invention, the in determining the cost of the molded article. It has been attempted to recover the same by various methods, among which is the treatment of the acrylate resin in order to decompose and for formation of the monomer from the resiniñed mass.V However, it differs` essentially inthat the depolymerize the same to form the monomer.À It time of treatment ofthe acrylate resin is__ex- was accomplished by placing the resin in a suit tremely short, usually amatter >of _a small'num ber of seconds. The heating ofthe resin isl in tense for the extremely short period of time, and able vessel and heating it to a temperature usually between 300° and 400° C., whereby decom position took place and dry distillation was the time and temperature are so correlatedas >to decompose the resin to form a liquid, product, effected. The condensate from the process was condensed and consisted to a large extent of the 20 that is, a product which after it is cooled isin monomer. the liquid state. This is accomplished Without However, this process was not capable of com mercial application for Various reasons. The monomer was quite impure and contained Various colored substances which were most difficult to remove. Also, some of the substances formed in volatilization- of any substantial amount of the end products, even though the temperatures used are far above the boiling points thereof~~ _ " The invention consists essentially in providing a trough or other container, having at the bottom thereof a moving conveyor or belt. The Aacrylate resin in the desired state vof subdivision, which may be irregular-shaped pieces of relatively‘small the decomposition operation and contained in the monomer tended to interfere with the further utilization thereof in the making of acrylate 30 size, is fed into the intake end of the trough, that resins. In order to overcome this, it was proposed to treat the relatively impure monomer in order to further purify the same. This was accomplished by distillation with steam of the monomer and the condensing of the distilled product. How CJ Cil ever, it required rather close control of the op eration, together with a considerable amount of equipment in order to fractionate the desired monomer from other substances present. Also, various difficulties arise where the acrylate resin 40 contains certain modifying agents which tend to contaminate the monomer after formation. The present invention is intended and adapted is, at the point where the traveling conveyor enters 'the apparatus. A' layer of _resin isi-so placed on the conveyor andwater is sprayed thereon so as to cover the layer of resin. As the mixture of Water andresin travels towards the opposite endl of the trough, there is provideda - direct flame of high intensity, such as an oxy acetylene type of flame. The flame cuts through the Water and acts intensively on the, resin;A depolymerizing the same, and immediately upon the reaction taking place the mixture on the _con-_v veyor is moved out of the zone of reaction‘with very little vaporization of either the water or the depolymerized product. The mixture is then to overcome the difñculties and disadvantages of prior methods and to provide a method of depoly 45 placed in a suitable vessel Where it is allowed merizing acrylate resins which is simple and effec to settle to form two layers, one of which is the tive and which is capable of quickly depolymeriz ing said resins With a minimum of labor and apparatus. _ _ liquid depolymerized resin. _ '_ . The process may be controlled so as to givey any desired mixture of liquid products. It is possible It is well known thatl acrylate resins begin to 50 to control the time and temperature of the _reac tion to give the monomer as the principal orvsole dissociate when heated to a temperature of about reaction product. However, for the purpose of 200° C., and that the dissociation, if allowed to proceed for a suiiicient length of time, will pro the preseni-Í invention it is not necessary nor even duce the monomer. At higher temperatures, say desirable in many cases to decomposethe resin 300°-400° C., this action takes place with a 60n 55 t0 the monomer. In a preferred operation of the` 2,412,296 3 , invention, the depolymerization is caused to» take place to form a mixturey of polymers of low mo 4 Y _ . . stances, such as plasticizers, other resins, sta bilizers, and the like. Usually such additional substances do not interfere with the operation of lecular Weight, the mixture being liquid in char the process and most of them are not unduly de-Y acter. Usually such polymers contain from 2 to 5 acrylate radicals in the molecule. There may Ul composed in the operation. However, if such de composition does occur, then a simple distillation also be present molecules of a higher molecular operation will remove the liquid polymers and any weight which are semi-solid in character. Be cause of the presence of the lower liquid poly monomer which may be present, from vthe addi-` tional « substances. However, »the heating step is ' mers, such higher vpolymers are dissolved ktherein vand a liquid product results. Sucha liquid mix so short Vthat usually. î'additions contained in . ture has a boiling point above the boiling point acrylate resins remain in their initial form. Be-v » of water, and this facilitates the operation in thatì ¿cause of the short time of treatment, there is very little if any discoloration in the liquid prod the tendency to volatilize under vthe high tem-V peratures used is minimized. -Such .a .product 'has' ` the further advantage that in order 'to 'transform ' the same into an acrylate resin, the zpolyrneriza-` tion reaction takes place much moreA readily than with the monomer, with less reagent and in a shorter time. nots..> ,In-any'case, lsuch discoloration may be I 'removed by usual color-absorbing materials. Although the invention has been described by means ofV a single specific example of the opera.- ' -tion thereof, 'it will be apparent to those skilled’ in the jart that various changes in the details of l The products of the present invention may be 20 the invention may be made Within the scope of directly mixed with acrylate resin and themix ture subjected to molding. Also, it is possible> tomixthe .products of thepresent invention with the invention. For .instancethe .apparatus need notvlbe strictly in the lshape of a trough, but other equivalent forms may be used. Itis even possible the scrap acrylate resi-n which in itself is no to dispense with a trough as such .and construct longer. useable for furthermolding operationsbe causeof the chemical changes-taking place ,dur the traveling conveyorV in such a mannerthat lit performs the vfunctions ofthe trough._rThe .resin ing theV molding process. .Such a mixture .has substantially the qualities of an unmolded mul may be Vintroduced .into .the apparatus'in thecold state, but if desired some heating thereof may- tiple acrylate resin. ÍOr, the .productmay he be performed in order to facilitate and shorten mixed with’benzoylperoxide or the like and sub the depolymerization reaction by the .direct fiame. In "place of water, other. liquids of suitablechar. jected topolymerization to form a molding com position.. l-It .may be made in >any desired form, such as rods, sheets, .or the like,’and the same subdivided to give granulesfof the desired size. acter or aqueous solutions Vmay be used. V>rIfhese and other changes may be made in `the'details of the'invention withinthe spiritY thereof, and the 4In the accompanying drawing, constituting .a 35 invention is to be broadly construed and not .to be limited except by the .character ofthenc'laimsap- . part hereof, and 'in which 1like reference char acters Vindicate v.like parts, the single -iigure is a pended hereto. perspective view of an apparatus particularly What .I claim is: . . , . adapted for depolymerizing acrylate resins to l. A method of .depolymerizing acrylate .resins form liquid polymers «in accordance with thepres 40 which comprises wetting .said resin'with an aque~ ent invention. Y ' Y There is .provided a trough l, the bottom of which consists of -a travelling conveyor or Abelt 2, which is held in place by a plate 5 underlying trough .I. Belt 2 is continuous and .is rotated around rollers 4; .'I‘he belt .moves from .the in coming `or intake end `3 of `the trough, to the dis-` charge end 6. '.Amethacrylate resin in relatively small sized pieces is 'introduced'through .funnelr'l at end 310i ~ trough ÍI, forming `a layer -8 von the moving belt. ThroughA pipe 9 water is .introduced and Ydis tributed rley spray `lll over material 8. .The amount of water is-sufiicient to rthoroughly wet the particles of resin and maybe sufficient »to form a water layer thereover, as shown at ll. Through a tube _I2 there is introduceda mixture of oxygen .and acetylene, forming a series of frames .I3 projecting downwardly and impinging upon the >layer 1I l.. At this point depolymeriza tion takes .place and the mixture of depolymer ized resin .and water .in the liquid state .passes out through 6 .and into .container l5. .The material settles ltherein, forming an upper layer .I6 .of wa ‘ terand alowerlayer 4Il of liquid depolymerized 65 i ous liquid, subjecting the same tothe actionof a. direct ilame of relatively high `temperature above 400° C. fora short time to. decompose said resin to a liquid, and rapidly >removing said Aprod uct from 4the zone of Vreaction to prevent volatili zation of .said product. „ ' » ' i2’.` A method of depolymerizingacrylate resins which comprises subdividing said resin to Aprovide particles of relatively small lsize, wetting said resin with an aqueous liquid, subjecting the same to the action of a direct dame of relatively high temperature above`400° C.l for alshort time to ole-y c'ompose saidrresin toa liquid, and rapidly .re moving said >product from` the `zone. of ‘reaction to _prevent volatilization oisaid product. k ` Y ' 3. Ainethod of depoly'merizing acrylate .resins which comprises piacing'saidresin on a travelling conveyor, wetting .said resin with .an aqueous liquid, subjecting thev same to 'the action of a4 direct iiame of relatively high temperature above 400° C. for a short time to .decompose said resin to a liquid, and rapidly removing said productY from the zoneof reaction toprevent volatilization of said product. ' ` '4. yA method of. depolymerizing acrylate .resins which comprises placing said .resin on a traveling product. conveyor, wetting said resin with anaqueous liquid, passing said mixtureunder av gas .flame emulsion with the 'liquid monomer or liquid poly» and during said passage subjecting the .sameto mer. after .it is depolymerized. The liquid may 75) the .action of said direct name of relatively high. 'Incorporated in the water in pipe .9 may be .a ` detergent or wetting agent whichr willform an subsequently lbe Yeither separated `mechanically from .the emulsion or polymerized in the .emul sion to 'its polymers. f '.'Ihe 'invention may be operated vwith acrylate resins whichhave been vmixed with other `Sub 75 temperature above 400° C.r for a short ltime .to decompose said .resin vto a liquid, and` rapidly .re-. moving said product from the Zone of .reaction to prevent volatilization »of said product. ` ` 45. A method of depolymeriz-ing .acrylate .resins ' 2,412,296 6 which comprises wetting said resin with an aque ous liquid, subjecting the same to the action of a direct flame of relatively high temperature above 400° C. for a short time to decompose Said resin to a liquid, and rapidly removing said prod uct from the zone of reaction to prevent volatili zation of said product, pouring said product into tively high temperature above 400° C. for a short time to decompose said resin to a liquid, said ñame being at the discharge end of said conveyor, and rapidly removing said product from the zone of reaction to prevent volatilization of said product. 7. A method of depolyrnerizing acrylate resins which comprises subdividing said resin to provide particles of relatively small size, wetting said a vessel, allowing the same to stand to form an aqueous layer and a liquid acrylate layer, and resin With an aqueous liquid, said liquid having 10 a wetting agent dissolved therein, subjecting the recovering the latter. 6. A method of depolymerizing acrylate resins same to the action of a direct ñame of relatively which comprises wetting said resin with an aque ous liquid, providing a trough, the bottom of high temperature above 400° C. for a short time to decompose said resin to a liquid, and rapidly ‘ which is a traveling conveyor, placing said resin removing said product from the zone of reaction on the incoming end of said conveyor, subjecting 15 to prevent volatilization of said product. the same to the action of a direct flame of rela CARL L. SHAPIRO.