WO2019118361A1

WO2019118361A1 - Color monitoring and dosing system for mixtures of polymers

Info

Publication number: WO2019118361A1
Application number: PCT/US2018/064774
Authority: WO
Inventors: Christopher Small; John STANDISH
Original assignee: Colormatrix Holdings, Inc.
Priority date: 2017-12-13
Filing date: 2018-12-10
Publication date: 2019-06-20

Abstract

Modifications to conventional dosing and thermoplastic processing machines are made for detecting in nearly real-time the presence of either off-shade or off-color thermoplastic material being fed for processing into intermediate or final shapes of polymer articles. Image capture by a camera occurs before the melt-mixing commences and is responsive to unacceptable contrast percentages or color ΔE values detected in the off-shade thermoplastic material or the off-color thermoplastic material, respectively.

Description

COLOR MONITORING AND DOSING SYSTEM FOR MIXTURES OF

POLYMERS

CLAIM OF PRIORITY

[0001] This application claims priority from U.S. Provisional Patent

Application Serial Number 62/598,276 bearing Attorney Docket Number 12017028 and filed on December 13, 2017, which is incorporated by reference.

FIELD OF THE INVENTION

[0002] This invention relates to the use of a camera to monitor the color of polymer mixtures for nearly real-time color correction.

BACKGROUND OF THE INVENTION

[0003] Thermoplastic has taken the place of other materials in a variety of industries. In the packaging industry, thermoplastic has replaced glass to minimize breakage, reduce weight, and reduce energy consumed in

manufacturing and transport. In other industries, thermoplastic has replaced metal to minimize corrosion, reduce weight, and provide color-in-bulk products.

[0004] Reuse and recycling of thermoplastic is one aspect of

environmental sustainability. Previously used thermoplastic, so-called “regrind” from both post-consumer-recycling sources and production waste is increasingly being used as good stewardship of available material resources.

[0005] First use thermoplastic, called“virgin thermoplastic” is made by polymerization and large scale processes in which there are precise and predictable color controls. Within the CIE L*a*b* color system, the precise and predictable color of virgin thermoplastic falls within about 1 to 3 DE, the combined variance of the AL* grayscale, the Aa* green-magenta scale, and the Ab* blue-yellow scale.

[0006] Unfortunately regrind thermoplastic from either post-consumer- recycling sources or internal production lacks precision and predictable color controls. Indeed, in some parts of the thermoplastic processing industry, such as the extrusion blow molding (EBM) industry, the amount of regrind thermoplastic content can range from 20 to 80 weight percent. Every moment of regrind feeding can encounter a color of regrind thermoplastic which is different from the color of the virgin thermoplastic.

[0007] More specifically, with EBM manufacturing, there is always a considerable amount of waste material created when the mold is closed and the part is molded. This waste material is trimmed off, granulated to create "re grind", and the re-grind is used again in the EBM process.

[0008] Because of the amount of re-grind in EBM manufacturing, it is common to feed and mix three separate streams into the EBM extruder: (a) virgin un-colored thermoplastic material; (b) regrind thermoplastic materials from waste trimmings as described above; and (c) color concentrate.

[0009] Sometimes, in addition to these three streams, there is a fourth stream of post-consumer recycle (PCR) thermoplastic material being fed also. The PCR thermoplastic is typically either matched by the supplier to be close to or the same as the color of the regrind thermoplastic or close to or the same as the color of the virgin thermoplastic.

[00010] The amount of color concentrate to be used in EBM

manufacturing is determined by the percentage amount of regrind thermoplastic that is used relative to the percentage amount of virgin thermoplastic that is used. When higher levels of re-grind thermoplastic are used, more or less color concentrate is required depending on the color of the virgin thermoplastic.

SUMMARY OF THE INVENTION

[00011] Thus, it becomes important to know how much re-grind is being used and to control the amount of color concentrate being dosed into the extruder so that both (a) the correct shade or color values are obtained and (b) the amount of color concentrate is not over-used and wasted. [00012] But, the amount of regrind thermoplastic and possibly its shade or color can vary from hour to hour or day to day depending on which regrind thermoplastic is used with which virgin thermoplastic. If there is a process disruption, for example, there will be a need to incorporate more regrind thermoplastics to re-use the thermoplastic of the off- specification molded parts which had been made, particularly on those occasions when the off- specification thermoplastic is due to a larger than acceptable DE affecting both shade and color.

[00013] Feeding of the three streams is often done with gravimetric blenders that sit on the process floor some distance from the extruder. These blenders are not suitable for use with liquid color because liquid color is better added to the process at the feed throat of the extruder for EBM manufacturing.

[00014] Also, regrind thermoplastic can be created in other molding processes such as sheet and film extrusion or injection molding. The requirement to control color concentrate dosing as regrind levels change can have applicability in these other types of molding processes as well.

[00015] Therefore, the art of thermoplastic processing, in which shade fidelity, or preferably color fidelity, is continuously required, needs a reliable, real-time means for monitoring the shade of the feed stream, or preferably the CIELAB or RGB color of the feed stream, of thermoplastic materials of both virgin and regrind origin before final shaping into a polymer article.

[00016] The present invention solves this problem for shade or color fidelity monitoring by placing a camera at a location in the polymer processing equipment downstream from the feeding hopper and upstream from the throat of the melt mixing chamber of the polymer processing equipment, whether a profile extruder or a molding machine. The camera captures images identifying the differences of shade, and preferably color, of the feed stream of

thermoplastic against an established index of shade, or preferably color, between 100% virgin thermoplastic and 100% regrind thermoplastic. [00017] The camera is connected electronically to a conventional dosing machine for transmission of the images to the dosing machine. Software will compare the image from the camera with the established index and, if necessary, software will cause the output of that comparison to instruct the dosing machine to inject liquid color concentrate of a pre-determined amount into a space between the feeding hopper and the throat to correct the shade, or preferably color, of the thermoplastic moving through the polymer processing equipment to match the conditions being monitored as the mixture of virgin thermoplastic and regrind thermoplastic move past the camera. The camera monitors the shade or preferably color of the mixture and communicates the numerical value to the conventional dosing machine for comparison with the established index stored in memory of the conventional dosing machine and if necessary, to alter the dosage of liquid color concentrate.

[00018] In one embodiment, the amount of the liquid color concentrate to be injected during the thermoplastic processing is directly in response to the content of the regrind thermoplastic detected as a weight percentage of regrind thermoplastic between the extremes of 0% regrind thermoplastic and 100% regrind thermoplastic, as such percentage of shade difference is detected by the camera operating in grayscale and communicated to the conventional dosing machine for comparison with the established index. To the extent that the dosing of colorant needs to change as a result of the comparison with the established index, the conventional dosing machine increases or decreases the amount of colorant being dosed into the thermoplastic processing machine.

[00019] In a second embodiment, the amount of liquid color concentrate to be injected during thermoplastic processing is directly in response to the color variances detected by a color sensor, such as a color camera or a spectrophotometer as a specific type of camera of any of AL* grayscale, Aa* green-magenta scale, or Ab* blue-yellow scale, or any combination of them in the CIELAB system or alternatively using the RGB system. [00020] In effect, the first embodiment is a contrast monitoring system of the blend of virgin and regrind thermoplastic while the second embodiment is a full color monitoring system of the average color of the blend of two different thermoplastics.

[00021] For the first embodiment, by use of this monitoring and dosing system, shade or contrast correction to a precision of about ± 5% in the scale between 100% virgin thermoplastic and 100% regrind thermoplastic is now possible according to the amount of regrind thermoplastic and the amount of virgin thermoplastic being fed into the thermoplastic processing equipment. Significantly, with a shade of the regrind thermoplastic precise to within ± 5%, knowing the amount of regrind thermoplastic identifies the shade of the regrind thermoplastic, allowing for the camera to detect contrast and transmit that amount numerically to the software in the conventional dosing machine.

[00022] For the second embodiment, by use of this monitoring and dosing system, color correction to an acceptable precision within a DE of from about 1 to about 3 is now possible regardless of the origin and color of the regrind thermoplastic being fed into the thermoplastic processing equipment.

[00023] One aspect of the invention is a system comprising (a) a dosing machine and (b) a thermoplastic processing machine, wherein the thermoplastic processing machine is modified to include a camera in electronic

communication with the dosing machine, wherein the camera detects and communicates potential shade or color variance in thermoplastic flowing through the thermoplastic processing machine, wherein the dosing machine responds to the communication from the camera by comparing an electronically communicated image from the camera with an established index of shade or color to determine any variance and then dosing liquid color concentrate to the thermoplastic processing machine, if there is any shade or color variance from the image and the index, for shade or color correction purposes before melt mixing commences in the thermoplastic processing machine. [00024] To elaborate about the first embodiment, the purpose of the system is to (a) use a camera to obtain an image of a mechanical mixture of virgin thermoplastic and colored regrind thermoplastic; and (b) use software to compare the image to create a measure of the weight percent of virgin thermoplastic and weight percent of regrind thermoplastic in the mixture of two thermoplastics. Then, with knowledge of the weight percent of regrind thermoplastic, the correct dosing amount of liquid color concentrate can be determined and then dosed in nearly real time to the polymer processing machine between the hopper and the feed throat. Image analysis takes advantage of the fact that virgin thermoplastic and regrind thermoplastic have distinctly different colors that can be evaluated with image analysis software, based on the image obtained from the camera and communicated to the dosing machine, to establish the index stored in memory and used by software for comparison with the image detected by the camera in nearly real time.

[00025] Other benefits of the first embodiment of the system include regular monitoring and reporting of regrind thermoplastic levels for quality assurance and use of simpler mixing and color dosing equipment than the floor mounted gravimetric feeders and blenders used for pellet color concentrates as conventionally used at the time of this document.

[00026] More specifically, there is a focus in this document on how to address particular issues with EBM manufacturing, in which there is both a target color and opacity required for the finished EBM parts, the conventional use of color concentrate to be mixed with virgin un-colored resin and regrind from the process to achieve that target color, and the conventional circumstance that regrind thermoplastic is used at different levels in the EBM process from hour to hour, or day to day, thereby requiring the amount of color concentrate needs to be adjusted to achieve the target color.

[00027] EBM processing has been more often used solid color concentrate, also called masterbatch, than liquid color concentrate. The automated contrast and color correction system of this document increases the likelihood of the use of liquid color concentrate because of its precise dosing capabilities. Though liquid color concentrate cannot be gravimetrically blended with mixtures of polymers at a distance from the feed throat of the EBM machine, the system described herein now permits liquid color concentrate being fed at the feed throat of the EBM machine with more precise responsiveness to mixture changes in the feed stream than can a solid color masterbatch remote from that feed stream.

[00028] The invention is further described with reference to the Drawing.

BRIEF DESCRIPTION OF THE DRAWING

[00029] Fig. 1 is partially a plan view and partially a cut-away view of the existing thermoplastic processing equipment with the addition of modifications to provide the monitoring and dosing system of the invention.

[00030] Fig. 2 is a cut-away view of one embodiment of the monitoring portion of the system.

[00031] Fig. 3 is a cut-away view of a second embodiment of the monitoring portion of the system.

EMBODIMENTS OF THE INVENTION

[00032] FIG. 1 shows in plan view a dosing machine 10 for liquid color concentrate and shows in cut-away view upstream portions of a thermoplastic processing machine 20.

[00033] The machines 10 and 20 have two types of interconnection. The first is a camera 30 configured to be positioned inside the thermoplastic processing machine 20 and in electronic communication with the dosing machine 10. The second is a liquid tube 40 configured to be positioned downstream of the camera 30 in the thermoplastic processing machine but also in liquid communication with the dosing machine 10.

[00034] The dosing machine 10 is commercially available from several manufacturers, with the preferred supplier being The ColorMatrix Corporation of Berea, Ohio. Under the brand of FlexCart™, several sizes of dosing machines 10 are commercially available and are configured to have software responsive to the color of the thermoplastic material being detected by the camera 30 to pump liquid color concentrate through liquid tube 40 into the thermoplastic processing machine. The pumping by machine 10 can be either volumetric or gravimetric, with the latter being preferred.

[00035] FIG. 2 shows a cut-away view of one embodiment of the modifications to be made to a conventional thermoplastic processing machine 20. The machine 20, explained as thermoplastic material moves downstream, typically has a hopper 22 in a conical shape for gathering and feeding the thermoplastic material to a feed throat 24 for entry into a melt mixing chamber 26, usually having a rotating screw and heating elements to melt and mix the thermoplastic material for shaping by extrusion, molding, or both. The shaping may be intermediate, such as formation of cylindrical pellets for later melt mixing into final polymer article shape. Alternatively, the shaping may be final by interconnection of the melt-mixing chamber with a profile extrusion die or with an injection mold or an extrusion die connected to a blow molding machine (EBM).

[00036] The camera 30 can be a AL* grayscale detector, a full color camera, or a spectrophotometric sensor, depending on the complexity of the monitoring and correcting desired. The camera can capture images and communicate electronically to the dosing machine 10 as often as deemed necessary for precise dosing according to the needs of the market. The camera 30 can capture images periodically or continuously for the monitoring of variances in the thermoplastic mixture flowing by the camera.

[00037] The camera 30 is deployed to a location downstream from the hopper 22 and upstream from the feed throat 24. Optionally but preferably, one or more baffles 32 and 34 redirect the flow or movement of the thermoplastic material in order for the camera 30 to be both protected from the thermoplastic flow and positioned to detect precisely the color of that thermoplastic flowing by the camera 30.

[00038] If the camera 30 detects unacceptable shade or color of thermoplastic material flowing from the hopper 22 and toward the feed throat 24, the dosing machine 20 responds by pumping liquid color concentrate through tube 40 to dosing point 42 which is before melt mixing in chamber 26 commences. In other words, the camera 30 detects a change in concentration of the regrind thermoplastic in the feed stream, as compared with the established index, then software in the dosing machine 10 causes the dosing level of color concentrate to increase or decrease until acceptable precision is obtained.

[00039] The commercial dosing machines already are equipped with sophisticated software for precise dosing of liquid color concentrate. Without undue experimentation, a person skilled in writing source code in the language of the software could author the software necessary to permit responses by the machine 10 to detection by camera 30 to off-shade or off-color thermoplastic flowing by the camera 30 in order to control the dosing of liquid color concentrate through tube 40 for combining with the thermoplastic at dosing point 42. It is estimated that the duration of time from detection of off-shade or off-color material to dosing of liquid color concentrate can range from seconds to minutes. Preferably, software in the dosing machine 10 will evaluate several images detected by the camera 30 over an acceptable period of time with use of statistical rules to confirm that there has been a real and sustained change in the amount of regrind thermoplastic, before software directs to dosing machine 10 to alter the amount of dosing of color concentrate. In this fashion, the system of dosing machine 10 and processing machine 20 as modified, can provide essentially“real-time” shade or color correction of the thermoplastic feed stream within acceptable precision of ± 5%, having significant and sometimes dominating amounts of regrind thermoplastic. [00040] FIG. 3 is also a cut-away view, but of a second embodiment of the modifications to machine 20. The modifications are the different placement of camera 30 and baffles 132 and 134 with the addition of baffle 136 in the centerline of the thermoplastic material flow. The camera 30 is positioned in a protected location with a close view of the color of the thermoplastic for detection and possible correction.

[00041] These two embodiments and many others possible provide a very consistent representation of the thermoplastic flowing past the camera 30 to cause a waterfall-like flow of thermoplastic material due to positioning of the baffles 32, 34, 132, 134, and 136 and others of similar structure between the hopper 22 and feed throat 24, similar in design to how pellet concentrate dosing systems add pellets into a flood fed extrusion line.

[00042] Another embodiment of the invention is contemplated, which employs a digital camera to capture an image of the then current mixture of virgin thermoplastic and regrind thermoplastic.

[00043] Image analysis software can be used to characterize the area of virgin thermoplastic and the area of regrind thermoplastic in the image.

[00044] Image analysis software then can then employ a difference in RGB color of the virgin thermoplastic and regrind thermoplastic, or simply a difference in contrast if the image were to be displayed in grayscale values.

[00045] The area values can then be used to determine the weight percent of virgin thermoplastic and regrind thermoplastic, because the density of the regrind is very similar to that of the virgin thermoplastic, area percent should be proportional to weight percent.

[00046] Knowledge of the weight percent of virgin thermoplastic and regrind thermoplastic can then be used to adjust the amount of liquid color dosed to a feed-throat of the EBM machine.

[00047] If there is an existing gravimetric feeder and blender in connection with the EBM machine, the image analysis approach of this invention can be used with such existing equipment. [00048] By comparison, a new installation could utilize less expensive and less complex volumetric feeders to feed virgin thermoplastic and regrind thermoplastic to make the over-all system for liquid color concentrate in the dosing machine be less expensive and less complex to use.

[00049] Yet another embodiment of the invention is contemplated, using a camera feature within a cellular phone for which may software applications (“apps”) are available for nominal or reasonable cost. Some apps are known to allow the camera on the phone and the phone’s software to measure color of an image.

[00050] In this embodiment, instead of measuring areas of virgin thermoplastic and regrind thermoplastic in the feed stream of the polymer processing machine, one could measure the color of the mix in the system of color used by the app.

[00051] If for example, red regrind thermoplastic was mixed with natural colored virgin thermoplastic, the image analysis in the cellular phone app would evaluate different shades of pink depending upon the amount of red regrind detected in the image. If the app measures in RGB values and the dosing machine uses software to measure CIELAB values, the conversion from RGB to CIELAB is possible because the two color systems are mathematically related.

[00052] A benefit of this embodiment is that if the regrind thermoplastic contains bottles originally made with virgin thermoplastic and no color, or contains bottles made during a color cleanout (“purge”) of the polymer processing machine, then camera will see an average color and account for the amount of regrind thermoplastic that does not contain the target color value of the final part made by EBM.

[00053] There are commercial spectrophotometers and colorimeters with software that can measure the color of a sample of pellets and regrind pellets. These types of equipment are likely to be more expensive to use than the embodiments described above. USEFULNESS OF THE INVENTION

[00054] The modifications to dosing machine 10 and thermoplastic processing machine 20 are suitable for detecting in nearly real-time the presence of off-shade or off-color thermoplastic material being fed for processing into intermediate or final shapes of polymer articles. The monitoring occurs before the melt-mixing commences and is responsive to unacceptable contrast percentages or color DE values, respectively, detected in the thermoplastic material within view of the camera 30 of any type.

[00055] Any polymer processing is a candidate for this system of interconnected dosing and processing machines. But because of the amount of manufacturing waste during extrusion blow molding (EBM) processing, the system is particularly suitable for EBM processing.

[00056] As an example, a digital camera can capture an image of the blend of virgin thermoplastic and regrind thermoplastic wherein the virgin thermoplastic resin is a light-colored polymer pellet whereas the regrind thermoplastic is colored red by the color concentrate in use for the EBM manufacturing and obtained from the waste material trimmings.

[00057] In this example, the image obtained by the camera and communicated to the doser will be evaluated by software to measure the area of virgin thermoplastic as well as the area of red regrind thermoplastic in the image. This area determination of both types of thermoplastic present within the image can be used by software using statistical methods to estimate the weight percent of each type of thermoplastic in the stream of thermoplastic material about to enter the feed throat of the EBM machine.

[00058] There are commercially available digital cameras for this purpose. There is commercial software that is used for image analysis. The software may require some customization by a person having ordinary skill in the art who is experienced in authoring uses of image analysis for controlling the dosing of liquid color concentrate. But that software authoring should not require undue experimentation by that person. [00059] Because images can be captured by the camera and analyzed rapidly using the software, moving averages of the regrind thermoplastic weight percent can be used to control the output of the color dosing unit, such as a FlexCart™ liquid color dosing machine fluidly connected to an EBM machine. While the dosing machine in this embodiment involves liquid colors, uses liquid color concentrate, it is contemplated that one could use the same approach to control the dosing of pelletized color concentrate, also called a color masterbatch.

[00060] Another aspect contemplated for this invention is the use of less expensive volumetric feeders to feed virgin thermoplastic and regrind thermoplastic, allowing for a less complex and expensive system for regrind management.

[00061] Another aspect contemplated for this invention addresses the circumstance where the optical contrast between virgin thermoplastic and regrind thermoplastic is not easily differentiating. One could dose UV stabilizer rather than color, especially if the color of the regrind thermoplastic and the virgin thermoplastic are essentially the same.

[00062] Also, one could add a small amount of optical brightener to the additive being dosed such that the optical brightener will create contrast in the image being monitored when the mixture of virgin thermoplastic and regrind thermoplastic is illuminated with a light source which contains UV energy.

[00063] The invention is not limited to the above embodiments. The claims follow.

Claims

What is claimed is:

1. A system comprising:

(a) a dosing machine and

(b) a thermoplastic processing machine,

wherein the thermoplastic processing machine is modified to include a camera in electronic communication with the dosing machine,

wherein the camera detects and communicates potential shade or color variance in thermoplastic flowing through the thermoplastic processing machine,

wherein the dosing machine responds to the communication from the camera by comparing an electronically communicated image from the camera with an established index of shade or color to determine any variance and then dosing liquid color concentrate to the thermoplastic processing machine, if there is any shade or color variance determined from the image and the index, for shade or color correction purposes before melt-mixing commences in the thermoplastic processing machine.

2. The system of Claim 1, wherein the camera detects and communicates potential shade or color variance between virgin thermoplastic and regrind thermoplastic.

3. The system of Claim 1 or Claim 2, wherein the camera is deployed in the thermoplastic processing machine protected by at least one baffle from flow of the thermoplastic.

4. The system of Claim 3, wherein the camera is deployed in a location downstream from a hopper and upstream from a feed throat of the thermoplastic processing machine.

5. The system of any one of Claims 1-4, wherein the camera detects a change in concentration of regrind thermoplastic in the flow of the

thermoplastic, as compared with the established index.

6. The system of any one of Claims of 1-5, wherein the camera detects an area of virgin thermoplastic and an area of regrind thermoplastic.

7. The system of any one of Claims 1-6, wherein the camera is a digital camera assessing difference in contrast of virgin thermoplastic and regrind thermoplastic.

8. The system of any one of Claims 1-7, wherein the camera is a digital camera assessing difference in RGB color of virgin thermoplastic and regrind thermoplastic.

9. The system of any one of Claims 1-8, wherein the camera is a digital camera assessing difference in L*a*b* color of virgin thermoplastic and regrind thermoplastic.

10. The system of any one of Claims 1-9, wherein electronic communication between the camera and dosing machine permits the dosing machine to compare an image from the camera with the established index in the dosing machine.

11. The system of any one of Claims 1-6, wherein the camera is a spectrophotometer.

12. The system of any one of Claims 1-10, wherein the camera is a video camera.

13. The system of any one of Claims 1-10, wherein the camera is a grayscale detector.

14. The system of any one of Claims 1-13, wherein the thermoplastic processing machine is an extrusion blow molding machine.

15. The system of any one of Claims 1-14, wherein the dosing machine also doses optical brightener to the thermoplastic processing machine in addition to liquid color concentrate.