Process for producing colour concentrate

Abstract: Continuous strands of color concentrate are metered into the feed zone of a screw-melter polymer extruder where they are cut into pellets by the shearing action of the flights of a rotating screw against the extruder housing. These pellets are mixed within the extruder with a thermoplastic polymer to be colored and this mixture is then melted and extruded into a useful article, for example, a fiber for textile or carpeting end-use. Additionally, color concentrates can be first formed into continuous strands and stored conveniently on a spool for subsequent metering into the polymer extruder.

Description: This invention relates to melt extruding a colour concentrate as a continuous strand and winding the strand on a spool. DE-A-3523661 concerns the feeding of colorants in the form of ribbons via tubes, a cutter and twin rolls into the storage hopper at the feed section of an extruder for extruding plastics. In this manner the feeding of colorants to the extrusion process can be controlled precisely by regulating the advance of the ribbons. US-A-3905937 concerns colour concentrates for colouring polymeric materials comprising a colourant, a deflocculating agent and a polymeric carrier, i.e. a polyester. Patent Abstracts of Japan, Vol. 9, No. 132 (M 385) (1855) (JP 60-15116) discloses an apparatus whereby thermoplastic resin and moulding colorant are fed by different routes to a hopper and thence to an extruder screw. Whilst resin and colorant are delivered forward of the screw they are melted and kneaded and the uniformly mixed resin and colorant delivered to an extruding die to obtain the desired coloured resin. According to this invention a process for forming a colour concentrate comprises compounding a pigment with a thermoplastic polymer, melting said compounded material and extruding said melted compounded material as a continuous strand. After extrusion the continuous strand is precisely metered by nip rolls to maintain a constant weight-per-unit length ratio and thereafter wound onto a spool. Additionally, colour concentrates can be first formed into continuous strands and stored conveniently on a spool for subsequent metering into the polymer extruder. Screw-melter polymer extruders useful in this invention are of the single to twin-screw type. These extruders typically have a barrel housing with a rotatable screw longitudinally positioned therein for the purpose of moving a thermoplastic polymer flake or pellet from the feed zone into the melting zone of the extruder. The screw comprises a shaft rotatably mounted longitudinally within the housing and having a flight positioned spirally about and projecting from the surface of the shaft to a location touching the wall of the barrel housing. In operation of the flight wipes the inner surface of the barrel. The invention is described with reference to Fig. 1 which is a schematic diagram illustrating the process of the invention. Fig. 1 shows a process for making a continuous strand color concentrate according to this invention. A coloring material, such as a pigment, is compounded with a thermoplastic polymer, such as nylon or polyethylene, in an intermixer 10, for example, a Banbury mixer. A batch of compounded color concentrate is thoroughly blended and then transferred to and melted in an extruder 12 from which it can be passed through a screen filter 14 to remove agglomerates of color concentrate. Meter pump 15 then transfers the melt to extrusion die 16 from which color concentrate strands 30 are extruded. Individual strands 30 pass through quench bath 18 and are guided by pins 24, 26 and form a single multi-strand cable 34 of color concentrate. The cable 34 is precisely metered by nip rolls 35, 37 to maintain weight per unit length at a constant value and is then wound up on spool 28. Controlling the weight per unit length of the color concentrate cable is important in ensuring good color uniformity of the thermoplastic polymers to be colored. While rolls 35, 37 can be smooth, they may be knurled or toothed to facilitate precise metering of the cable. The strand and subsequent cable diameters are optimized for flexibility to ensure windability on the spool. The spool 28 can later be used to provide a continuous color concentrate cable to a polymer coloring process. As cable 34 is passed through quench bath 18, guide rolls 22, 20 may be used to press the individual color concentrate strands together while still tacky, thereby improving the cohesiveness of the strands in cable 34. Although rolls 22, 20 can be smooth, they may be knurled or toothed to facilitate the tacking together of the strands which pass betweem them. In addition to the multi-strand cable process described above, it may be possible with relatively flexible color concentrates or with relatively narrow diameter strands to extrude a single-strand and wind this strand onto a spool for later use. The colored thermoplastic polymers produced as described herein have many uses, particularly as synthetic fibers for the textile and carpet industry. In general, the process described herein provides color concentrates in a convenient form for use in many methods of manufacture for thermoplastic polymer material, including moldings, blow-moldings and the like wherein uncolored thermoplastics are pre-mixed or mixed with color concentrates prior to article formation. The addition of multiple colors of concentrates conveniently results in high versatility in the selection and fine adjustment of colors for the thermoplastic polymers. Individual metering of the multiple ends of color concentrate further aids the adjustment of color in the thermoplastic polymer.

Claims: A process for forming a colour concentrate comprising compounding a pigment with a thermoplastic polymer, melting said compounded material and extruding said melted compounded material as a continuous strand, wherein after extrusion the continuous strand is precisely metered by nip rolls to maintain a constant weight-per-unit length ratio and thereafter wound onto a spool.

Inventors: FINTEL WILLIAM ACHARD, FINTEL, WILLIAM ACHARD
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1989
Main classification: B29C47
IPC codes: B29B7, B29C47, C09D7