Patented May 10, 1949 2,470,001

UNITED STATES PATENT oFFICE 2,470,001 PROCESS FOR PRODUCING UNFORMLY COLORED EXTRUDED ARTICLES FROM WNYLAROMATC RESNS Kenneth E. Stober, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware Application May 30, 1945, Seria No. 596,627 5 Claims. (C. 18-55) 1. 2 This invention relates to an improved process In so far as known, the new process is ap for producing uniformly colored articles from a plicable generally to mixing coloring materials resinous polymerized vinyl aro into thermoplastic resins formed by polymerizing matic compound. vinyl aromatic compounds or mixtures thereof. The coloring of a thermoplastic resin is usually Typical resins are the of styrene, p carried out by working a pigment or dye into chlorostyrene, p-ethyl styrene, p-ethoxy styrene, the uncolored resin on rolls or in a kneading vinyl naphthalene, and vinyl carbazole. At pres machine. This procedure, although effective, ent, the invention finds its greatest use in the necessarily involves all the limitations of batch coloring of . wise operation, especially the difficulty of main 0 The coloring materials employed are dyes sol taining uniformity of color from batch to batch. uble in the mononer from which the resin is In addition, during the mixing, the resin be formed, or finely-divided pigments. Most of comes highly heated, and while in that state is soluble dyes are effective. It is desirable to choose Often exposed to the air for a considerable period. a dye or pigment the color of which is not altered As a result of this exposure, dirt and dust tend 5 by exposure to the temperatures at which the to become included in the product, and molecular melt-blending step is carried out. Coloring ma degradation and even oxidative discoloration of terials which have been found especially suitable the resin often occur. are: With these difficulties in mind, it is the prin cipal object of the present invention to provide 20 Dyes: Color Index No. an improved process, applicable especially in Anthraquinone Blue Sky Base------1089 coloring vinyl aromatic resins such as polystyrene, Oil Red O------73. which permits continuous production of uni Oil Yellow 515------9 formly colored material and largely eliminates Pigments: Gardner page exposure of heated resin to the air. 25 Mapico Black.------1361. Basically, the new process involves first mak Mapico Brown------227 ing a color concentrate by mixing the coloring Monastral Fast Blue B------359 material into a dispersing medium, and then Titanox-A, I. O------1228 melt-blending the concentrate into the body of 1 Physical and Chemical Examination of Paints, War the resin to be colored. The blending is prefer 30 nishes, and Lacquers, 8th edition (1937). ably carried out continuously by delivering a stream of the color concentrate and a stream of The invention may be further explained with the resin, both in the molten state, in controlled reference to the accompanying drawing, in which proportions into a closed mixing zone and therein Fig. 1 is a flow diagram illustrating the color working the materials together to form a uni 35 ing of polystyrene, using styrene as the formly colored mass, and extruding the mass. color dispersing agent; and By operating in this manner, continuous produc Fig. 2 is a similar diagram illustrating the use tion of a uniformly colored product is possible, of polystyrene as the dispersing agent. and any given portion of the heated resin need In the process of Fig. 1, which is particularly be exposed to the air, if at all, for only a brief 40 useful with soluble dyes, the dye 3 and monomeric period. styrene 4 are charged into a mixer 5, such as The liquid dispersing medium used in making a tank provided with a propeller agitator, and the color concentrate either is the monomer of stirred together to produce a uniform liquid color the particular vinyl aromatic compound from concentrate, which is transferred to a closed stor which the resin to be colored has been formed, 45 age system 6. The relative proportions of dye or is a thermoplastic vinyl aromatic resinous and monomer may be varied within broad limits polyner. Such media are completely compatible depending on the intensity of color desired in with the resin to be colored, and, when mixed the final product, although dye concentrations therewith in small proportion, do not appreciably of the order of 0.05 to 5.0 per cent by weight of alter its mechanical or electrical properties, since the monomer are preferred. they are not, chemically speaking, foreign mate The polystyrene to be colored, which is usually rials. The liquid are especially effec maintained molten in a closed storage vessel , tive media for blending in soluble dyes, while the or which may be melted continuously as required, polymers, when molten, are, because of their is transferred by a metering pump 8 as a con much higher viscosity, preferred for suspending 55 tinuously flowing stream into an enclosed pigments. . blending and extruding system 9. At the same 2,470,001 3 4. time, a relatively much smaller strean of color to 50 per cent by weight of the . in the concentrate is metered by a pump ?o into the concentrate. mixer. The rates of delivery of the two pumps In mixing the color concentrate and the un and are carefully controlled at a constant colored polystyrene, the concentrate, in the plas ratio to insure uniform color intensity in the final 5 tic state, is metered as a stream by the feeder f4 product. In general, best results are obtained into the mixing and extruding system 9, in which when the stream of color concentrate represents it is mixed with a larger metered stream of un between 1 and 3 percent by weight of the polymer colored polystyrene from the reservoir T. Mix stream. ing and extrusion of the blended product are car In the blending system 9, which is maintained 10 ried out as described with respect to Fig. 1. at a temperature at which the polystyrene is The following examples will further illustrate freely fluid, e. g. at least 200° C., and preferably the invention: getherabout 250°mechanically C., the two by streamsa kneading are workedor stirring to Eacample 1 action, without exposure to the air, to produce a In coloring polystyrene according to the process uniformly colored plastic mass. This mass is then of Fig. 1, a color concentrate was prepared by forced through an extrusion orifice, preferably as stirring 0.20 pounds of Oil Red O dye into 100 fast as it is produced, and the extruded product pounds of monomeric styrene. This mixture was is drawn away and cooled to final form. then metered at a rate of 2.60 pounds per hour This melt-blending of color concentrate and 20 into a mixer-extruder such as that described uncolored resin may be carried out in any type above. At the same time, molten uncolored poly of enclosed mechanical mixing equipment, pref styrene at about 250 C. having an average molec erably one in which the materials are worked to ular weight of about 100,000, and a volatile Con gether while in continuous flow. The extrusion tent of 1.0 per cent was metered as a stream at a of the colored mixture as it is formed may like rate of 260 pounds per hour into the mixer wise be accomplished in various machines. A extruder. The resulting extruded material was particularly convenient apparatus, in which a a uniformly colored, commercially acceptable screw extruder is fitted with special mixing disks, product, showed no change in average molecular and which in a single machine performs the func weight, and had a volatile content of 1.3 per tions both of mixing and of extrusion on a con 30 cent. tinuously moving stream of material, is described Eacample 2 in a patent application Serial No. 596,626 filed In coloring polystyrene according to the proc May 30, 1945 by the present applicant. Suitable ess of Fig. 2, a color concentrate was made by machinery for drawing the extruded plastic away plastically working together 100 pounds of Mapico from the extrusion orifice and cooling it is de 3 5 Brown pigment and 500 pounds of polystyrene. scribed in applicant's application Serial No. This concentrate was then fed as a stream into 549,375, filed August 14, 1944, now abandoned in a mixer-extruder at a rate of 4 pounds per hour, favor of continuing application Serial No. 783,252, together with a stream of 400 pounds per hour of filed October 31, 1944. uncolored polystyrene at a temperature of 250° During the mixing of the color concentrate 4) C. The resulting extruded product was a uni into the heated resin, the liquid monomer por formly colored, commercially acceptable material, tion of the concentrate tends to polymerize, and What is claimed is: is in large part converted to non-volatile poly 1. A continuous process for producing uniform mers which become mixed throughout the resin. ly colored articles from thermoplastic resinous A part of the monomer may persist as such polymerized vinyl aromatic compounds which through to the extrusion step, at which point it comprises: forming a color concentrate by mix is usually lost by volatilization from the extruded ing together a coloring material and a polymer product. In any case, the monomer in the color ized vinyl aromatic compound, delivering a stream concentrate does not appear to affect the proper of the color concentrate in the molten state and ties or appearance of the extruded colored resi a relatively much larger stream of the molten in any way. W uncolored resinous compound to a closed mixing The process of Fig. 2 is useful primarily in in Zone maintained at a temperature of at least corporating pigments into the resins, although it 200 C. and therein working the materials to may also be used in adding dyes. In the first 55 gether to form a uniformly colored mass while step of this process, the pigment f is mixed with still in stream form, and continuously extruding polystyrene, usually uncolored molten polymer the mass. from the reservoir , although polymer from 2. A continuous process for producing uniform another source, which need not be of the same ly colored articles from polystyrene which com molecular weight as the resin to be colored, may prises: forming a color concentrate by mixing also be used. The mixing is preferably, though 60 together a coloring material and polystyrene at not necessarily, effected at a temperature at a temperature at which the latter is plastic, de which the polymer is plastic, in any convenient livering a molten stream of the color concen mixing equipment 2, such as a plasticator, and trate and a relatively much larger stream of the resulting color concentrate is transferred to molten uncolored polystyrene to a closed mixing storage 3. The color concentrate may be stored Zone maintained at a temperature of at least molten, or, often more conveniently, may after 200 C. and therein working the materials to gether to form a uniformly colored mass while mixing be extruded into rod which can be cooled still in stream form, and continuously extruding and cut up into granules, which are stored and the mass. later remelted as needed. . . 3. A process according to claim 2 wherein the The relative proportions of pigment and poly coloring material is a finely-divided pigment. mer in the concentrate are not critical, the con 4. In a process for producing uniformly colored centration being chosen to secure the desired thermoplastic resinous polymerized vinyl aro color intensity in the final product. In ordinary natic compounds wherein a coloring material is cases, the pigment usually represents from 10 75 mixed with the resinous polymer, the improve 2,470,001 5 6 ment which comprises: first forming a fluid mix and continuously removing a stream of the col ture of a coloring material and a polymer of the Ored maSS from the Zone. vinyl aromatic compound, delivering a stream of KENNETH. E. STOBER. such fluid mixture and a relatively much larger REFERENCES CITED stream of the uncolored resin in the molten state 5 in controlled proportions to a mixing zone and The following references are of record in the therein working the materials together while still le of this patent: in stream form to produce a uniformly colored mass, and continuously removing a stream of the UNITED STATES PATENTS colored mass from the Zone. O Number Name Date 5. In a process of producing uniformly colored 1,528,291 Dreyfus ------Mar. 3, 1925 resinous polystyrene wherein a coloring material 1,627,195 OStromislensky ----- May 3, 1927 is mixed with the Said resin, the improvement 1966,327 Wood ------July 10, 1934 which comprises: forming a color concentrate by 2,074,285 Studt ------Mar. 16, 1937 mixing together a coloring material and poly 5 2,109,592 Macht et al. ------Mar. 1, 1938 styrene at a temperature at which the latter is 2.279,067 Shapiro ------Apr. 7, 1942 plastic, delivering a molten stream of the color 2,303,340 Dreyfus ------Dec. 1, 1942 concentrate and a relatively much larger stream 2,326,531 Gates ------Aug. 10, 1943 of molten uncolored polystyrene in controlled 2,374,069 Balthis ------Apr. 17, 1945 proportions to a closed mixing Zone maintained 20 FOREIGN PATENTS at a temperature of at least 200° C. and therein working the materials together while still in Number Country Date stream form to produce a uniformly colored mass, 498,679 Great Britain ------Jan. 9, 1939