In-line color mixer

Abstract

The method of producing a colored powder of a polymeric material includes the steps of selecting a feedstock of said polymeric material, pulverizing said polymeric material in a pulverizer to produce a powder, moving the powder directly from the pulverizer to a mixer; spraying a liquid formulation including a colorant into the powder within the mixer, and mixing the liquid formulation and powder.

Claims

1. A method of producing a colored powder of a polymeric material, the method comprising the steps of: (a) selecting a feedstock of polymeric material; (b) pulverizing the polymeric material in a pulverizer to produce a powder having a temperature greater than the ambient temperature; (c) moving the powder directly from the pulverizer to a mixer maintaining the powder at a temperature greater than the ambient temperature; (d) adding a colorant into mixer; (e) mixing the colorant and powder while the powder remains at a temperature greater than the ambient temperature.

2. The method of claim 1 wherein the pulverizer increases the temperature of the polymeric material during step (b) by at least 10 C.

3. The method of claim 1 wherein the pulverizer increases the temperature of the polymeric material during step (b) by at least 20 C.

4. The method of claim 1 wherein the pulverizer increases the temperature of the polymeric material during step (b) by at least 30 C.

5. The method of claim 1 wherein an outlet of the pulverizer is coupled to an inlet of the mixer.

6. The method of claim 1 wherein the temperature of the powder delivered into the mixer is at least 10 C. above ambient temperature.

7. The method of claim 1 wherein the temperature of the powder delivered into the mixer is at least 20 C. above ambient temperature.

8. The method of claim 1 wherein the temperature of the powder delivered into the mixer is at least 30 C. above ambient temperature.

9. The method of claim 1 wherein the mixer continuously conveys material from an inlet of the mixer to an outlet of the mixer.

10. The method of claim 1 wherein the colorant is a powder.

11. The method of claim 1 wherein the colorant is a liquid formulation.

12. The method of claim 11 further comprising: coating the powder at the temperature greater than the ambient temperature with a water component of the liquid formulation.

13. The method of claim 12 further comprising: driving off a portion of the water component upon contact in the mixer with the powder at the temperature greater than the ambient temperature.

14. The method of claim 1 further comprising: cleaning the mixer via cleaning ports in the mixer.

15. The method of claim 1 wherein the colorant is not introduced into the pulverizer.

16. The method of claim 1 further comprising: directly coupling an outlet of the pulverizer to an inlet of the mixer.

17. The method of claim 1 further comprising: spraying the colorant at the powder in the mixer.

18. The method of claim 17 wherein the colorant is a liquid.

19. The method of claim 1 further comprising: selecting a predetermined particle size of the powder via a sieve device.

20. A method of producing a colored powder of a polymeric material comprising the steps of: pulverizing a feedstock of polymeric material in a pulverizer to produce a powder having a temperature at least 10 C. greater than an ambient temperature; directly coupling an outlet of the pulverizer to an inlet of a mixer; moving the powder from the pulverizer to the mixer while maintaining the temperature at least 10 C. greater than the ambient temperature; spraying a colorant of a liquid formulation at the powder in the mixer; and continuously mixing the colorant and the powder in the mixer while the powder remains at the temperature at least 10 C. greater than the ambient temperature; wherein the continuously mixing step further comprises coating the powder with a water component of the liquid formulation and driving off a portion of the water component upon contact in the mixer with the powder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention may take physical form in certain parts and arrangement of parts, embodiments of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein:

(2) FIG. 1 which is a schematic representation of an apparatus for producing a colored powder, according to one embodiment;

(3) FIG. 2 is a perspective view of an apparatus for producing a colored powder, according to one embodiment;

(4) FIG. 3 is a perspective view of a paddle and paddle rod located within a mixer; according to one embodiment

(5) FIG. 4 is a cross-sectional view of mixer, according to one embodiment;

(6) FIG. 5 is a top view of a paddle and paddle rod, according to one embodiment;

(7) FIG. 6 is a side view of a paddle and paddle rod, according to one embodiment;

(8) FIG. 7 is a perspective view of a shaft located within a mixer, according to one embodiment;

(9) FIG. 8 is a perspective view of an interior of a mixer, according to one embodiment;

(10) FIG. 9 is a side view of a mixer, according to one embodiment;

(11) FIG. 10 is a top view of a mixer, according to one embodiment;

(12) FIG. 11 is a perspective view of an apparatus for producing a colored powder, according to one embodiment; and

(13) FIG. 12 is a perspective view of an apparatus for producing a colored powder, according to one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

(14) Referring now to the drawings wherein the showings are for purposes of illustrating embodiments of the invention only and not for purposes of limiting the same, and wherein like reference numerals are understood to refer to like components, FIGS. 1-10 show an apparatus 20 including a pulverizer 30 which is arranged to deliver uncolored pulverized polymer powder via its outlet 40 directly into a mixer 60 via its inlet 80. A spray device 100 is operatively connected to the mixer 60 and is arranged to produce a spray 120 of a colored liquid formulation which is directed at the pulverized polymer powder thereby to color the powder. The powder and liquid formulation are mixed resulting in an evenly colored powder passing from an outlet 140 of the mixer, after which the colored powder may be stored for subsequent use in rotational molding. Further details on the apparatus are provided below.

(15) The pulverizer 30 may be of conventional design. It is arranged to receive pelletized polymer and pulverize it to produce a powder of predetermined particle sizes. During pulverization the polymer becomes heated, for example to a temperature of the order of 50-60 C. due to the mechanical work done on it.

(16) The mixer 60 is closely coupled to the pulverizer and is arranged to receive the heated powder from the pulverizer. Suitably, the outlet 40 of the pulverizer and inlet 80 of the mixer are directly coupled to one another so that powder may be continuously fed from the pulverizer to the mixer without a significant drop in temperature of the powder on passing between pulverizer and mixer. Thus, powder entering the mixer is suitably at an elevated temperature which is approximately the same as the temperature of the powder within the pulverizer.

(17) In this way, the powder is still hot due to the mechanical work done on it by the pulverizer 30. The additional heat produces greater color adhesion than would the cooled powder. This process happens without the additional step of re-heating the powder when it enters into the mixing apparatus.

(18) The mixer 60 is a mechanical mixer, for example a paddle mixer, and is arranged to develop a fluidized bed in which the powder and liquid formulation can be intimately mixed. The mixer has a paddle 71 and a paddle rod 61. The paddle rod 61 is connected to the shaft 62. The top of the paddle rod 61 contains a weld cap 65. Additionally, the mixer 60 has cleaning ports 64, which are holes or apertures in a cylindrical paddle rod 61. The cleaning ports 64 facilitate easy cleaning of the device. In one embodiment, a water or cleaning fluid source is operatively connected to the shaft 62. The cleaning fluid then travels through the shaft 62 into each of the paddle rods 61. The cleaning fluid travels through the paddle rods 61 and exits the cleaning ports 64 on each paddle rod 61. In some embodiments, the shaft 62 may also include cleaning ports 64.

(19) The spray device 100 comprises a low pressure (e.g. 5-15 psi) air atomizing nozzle which is arranged to spray a continuous stream of liquid formulation into the powder at relatively low velocity. It is preferred to avoid the liquid formulation being sprayed so forcefully that it penetrates the mass of powder and contacts walls of the mixer. It is also preferred to direct substantially the entire spray of formulation at the powder itself and avoid coating walls of the mixer. Any coating of walls of the mixer may result in regions of relatively concentrated color being produced in the powder which is undesirable.

(20) The liquid formulation comprises water as a vehicle and a colorant, for example a dye or pigment. It suitably has a viscosity measured on a Brookfield viscometer at 20 rpm using a #6 spindle of 100-50,000 centipoises immediately prior to entering the spray device 100.

(21) The use of water as a vehicle is believed to facilitate coating of the liquid formulation, in particular the colorant, on the powder particles. In this regard, the fact the powder is hot at the time it is contacted with the liquid formulation leads to some water being driven off from droplets of formulation which contact the relatively hot powder. This makes the droplets less mobile and more likely to remain adhered to powder particles.

(22) It should be appreciated that, since no colorant is introduced into the pulverizer 30, it does not need to be cleaned between color changes. Furthermore, mixers 60 and/or spray devices 100 may be sufficiently inexpensive that it is cost effective to dedicate respective mixers/spray devices to particular colors. When it is desired to produce powder of a different color, one mixer/spray device used to produce one color may be replaced with a spray device dedicated to production of a different color. Thus, it may not be necessary to undertake extensive cleaning between color changes.

(23) Furthermore, it should be appreciated that the process described can be used to continuously produce colored powder from polymer pellets with great efficiency. Additionally, by contacting liquid formulation with heated powder from the pulverizer, not only is the coloring process improved but also less energy is needed to dry the colored powder after is preparation.

(24) The powder may be used as a feedstock to a rotational molding apparatus. Alternatively, it could be used in other coating processes or in melt-processing to produce components.

(25) With reference to FIGS. 11 and 12, an apparatus 200 for producing a colored powder of a polymeric material can include a pulverizer P arranged to deliver uncolored pulverized polymer powder from the outlet of the pulverizer P directly into a mixer 220 via the inlet 290 of the mixer 220. The apparatus 200 can function and operate in the same manner as the previously described apparatus 20. The pulverizer P can include a control panel 240, which houses a controller for the pulverizer. The pulverizer P can include a milling chamber 260, mill motors 250 and 252, a vibratory feeder 270, and an inlet tube 280 for the milling chamber 260. The mixing chamber 220 can include a mixer inlet 290, a mixer outlet 292, a spray nozzle 296, and a drive motor 300. The spray nozzle 296 sprays a colorant into the mixing chamber 220 to color the pulverized polymer powder. The mixing chamber 220 can have a generally semi-circular cross-section with a substantially curved or rounded lower or bottom portion and a substantially flat upper or top portion. Many other shapes and configurations for the mixing chamber 220 have been contemplated and are within the scope of this invention. A cabinet or housing 210 can include a container of colorant and a pump for transferring the colorant from the container to the spray nozzle 296. The housing 210 can enclose the container of colorant and the pump within the interior of the housing. In some embodiments, the pump can be either a progressive cavity pump or a peristaltic pump. The housing 210 can include a controller 230 for the pump. The controller 230 controls the amount of colorant the pump provides to the spray nozzle 296. The colorant can be a liquid or a powder. A hose or tube can fluidly connect the container to the pump and the pump to the nozzle. The housing 210 can include wheels, rollers, or casters for readily moving and positioning the housing. The mixing chamber 220 can be operatively connected or attached to the housing 210. In some embodiments, the mixing chamber 220 can be fixedly attached to the housing 210 to form a single unit, which can be moved or transported together. The housing 210 can be easily moved for cleaning the mixing chamber 220 offline.

(26) The controller 230 can be integrated with the controls 240 of the pulverizer P to deliver the proper amount of colorant to the mixing chamber 220 for the corresponding amount of pulverized powder. The controller 230 determines the proper amount of colorant to match the production rate of the pulverizer P. In some embodiments, the controller 230 controls the amount of colorant provided to the mixing chamber 220 based upon the feed rate of the pulverizer P. In other embodiments, the controller 230 controls the amount of colorant provided to the mixing chamber 220 based upon the speed of an extrusion screw. In other embodiments, the controller 230 controls the amount of colorant provided to the mixing chamber 220 based upon the flow rate of the pulverized powder. In other embodiments, the controller 230 controls the amount of colorant provided to the mixing chamber 220 based upon the weight basis of the material delivered to the mixing chamber 220.

(27) The invention is not restricted to the details of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

(28) Numerous embodiments have been described herein. It will be apparent to those skilled in the art that the above methods and apparatuses may incorporate changes and modifications without departing from the general scope of this invention. It is intended to include all such modifications and alterations in so far as they come within the scope of the appended claims or the equivalents thereof.