Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/85—Investigating moving fluids or granular solids
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N2021/8411—Application to online plant, process monitoring
  • G01N2021/8416—Application to online plant, process monitoring and process controlling, not otherwise provided for
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/85—Investigating moving fluids or granular solids
  • G01N2021/8557—Special shaping of flow, e.g. using a by-pass line, jet flow, curtain flow
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/85—Investigating moving fluids or granular solids
  • G01N2021/8592—Grain or other flowing solid samples

Definitions

• the present invention relates to a method for measuring the color properties of a granulate in a moving granular stream, wherein a stationary or moving granular layer is produced from at least part of the moving granular stream with a uniform layer thickness, at this stationary or moving granular layer, the color properties (color loci) and, if appropriate, the part of the granulate stream from which the granulate layer with uniform layer thickness has been produced is recycled into the granulate stream, and the movement of the granular stream is optionally continued, and a device for measuring the color properties of a granulate in a moving granular stream comprising at least one unit for producing a stationary or moving granulate layer with a uniform layer thickness from the agitated granulate stream and at least one unit for measuring the color properties.
• colorants either in liquid or solid form or as a color batch, are intimately mixed with the actual polymers or polymer mixtures to be dyed in melt form or as a solid, homogenized in the melt and then mixed into a homogeneous, colored mass portionable form, such as granules brought.
• these are hitherto brought into a sheet-like form in an injection molding machine or by blow molding, calendering or extrusion, and these are measured using conventional colorimeters.
• the installation of an online measuring device has proved to be advantageous, which is above or below the flat surface. brought train over a distance of up to several centimeters of the color determined.
• the optics of the measuring device must be focused on the distance to the plastic web.
• the problem with the disclosed methods is that the samples must be taken from the continuous product stream and must be filled and measured in a complicated manner in special cuvettes.
• the company X-Rite offers a device under the product name Teleflash Compact, which makes it possible to determine color properties on flat bedding online.
• said device is directed at a specific distance to, for example, a conveyor belt on which a flat bed of the granules to be examined is applied, so that the ink can be measured online.
• the procedure disclosed by X-Rite gives large standard deviations of the individual measured values for granules with an average transmittance in the visible range of light from 400 to 700 nm measured on an injection-molded cast slab with a layer thickness of 2 mm of> 1%.
• this device it is not possible with this device to measure color values of transparent granules with sufficiently high sensitivity and accuracy.
• Jarochek, C. Litschke, C. in Kunststoffe international 12/2006, pages 40 to 42 disclose a method of online formulation and mixing of liquid colors to produce uniformly colored plastics from recycled plastic remnants.
• a dosing unit containing ink containers with the necessary primary colors is connected directly to a plasticizing screw in which the molten plastic and the color mixture are mixed.
• a molded article is prepared, whose color properties are determined with a corresponding color measuring unit.
• a difference may and this difference is compensated by changing the color mixing by means of the electronically controllable dosing unit.
• plastics 12/2006 method it is possible according to the presented in plastics 12/2006 method to produce plastics from recycled plastic residues with uniform color automatically.
• the problem with this method is that a shaped part has to be produced from the colored base granulate in order to be able to measure color properties.
• no colored granules are produced.
• the object of the present invention is therefore to provide a method for measuring color properties of a granulate which can be carried out directly on the agitated granulate stream, which originates, for example, from a continuous production process, without having to produce a sheet-like molded part from the granules. Furthermore, it is an object of the present invention to provide a method for measuring color properties of a granulate, which is characterized by a simple apparatus design and a cost-effective implementation. Furthermore, a method is to be provided, with which it is possible to examine the corresponding granulate directly and without delay with respect to its color properties. It is also an object of the present invention to provide a method for measuring color properties also on transparent granules. Another object is to determine from the colorimetric data obtained correction changes in the Farbdosiermengen and thereby to guide the color properties of the granules in a predefined target area.
• step (C) optionally, recycling the part of the granular stream from which the granule layer has been produced in step (A) into the granular stream and, if appropriate, continuing the movement of the granular stream.
• the method according to the invention serves to measure the color properties of a granulate which is present in a moving granulate stream.
• This agitated granulate stream may, for example, result from the continuous production of a corresponding granulate. It is also possible according to the invention that the invented The process according to the invention is carried out during filling and / or packaging of the corresponding granules, in which the granulate stream, which is filled, for example, into the packaging units, is subjected to the process according to the invention and thus compliance with the prescribed color is controlled.
• the granules used according to the invention contain at least one thermoplastic.
• suitable thermoplastics can be found, for example, in the Kunststofftaschenbuch (Hrsg. Saechtling) edition 1989, which also mentions sources of supply. Processes for the preparation of such thermoplastics are known to the person skilled in the art.
• Thermoplastics which can be used according to the invention are selected, for example, from the group consisting of polyoxymethylene homopolymers and copolymers, polycarbonates, polyesters, polymethacrylates and copolymers based on methyl methacrylate, polyamides, homo- and copolymers of olefins, polyether ketones, polyether sulfones, polyarylene sulfides, thermoplastic polyurethanes, crystalline polyarylates, polyacrylates, linear polyimides, polybenzimidazoles, polyhy- dantoins, polypyrroles, polyphosphazenes, silicones, methyl acrylate-acrylate-styrene polymers, acrylonitrile-butadiene-styrene polymers (ABS), acrylonitrile-styrene-acrylic ester polymers (ASA), Methacrylate-butadiene-styrene polymers (MBS), impact polystyren
• the thermoplastics may contain other additives and processing aids such as stabilizers, antioxidants, anti-heat and ultraviolet light decomposition aids, lubricants and mold release aids, colorants such as dyes and pigments, fibrous and powdery fillers and reinforcing agents, nucleating agents, plasticizers, etc.
• the amount is less than 70% by weight, preferably less than 40% by weight. It is possible according to the invention to measure granules which consist of a plastic. It is also possible according to the invention that granules are measured which contain two or more different plastics, so-called blends.
• Granules according to the invention are to be understood as meaning a quantity of particles from the corresponding plastic or mixture.
• the granules which can be used according to the invention have a particle size of 0.05 mm to 20 mm, preferably 0.5 to 7 mm.
• it is possible to use granules which have a uniform particle size distribution ie. the percentile d10 (sum of the smallest 10 mass% of the distribution) is more than 60% of the average diameter of the granules relative to the d50 (sum of the smallest 50% by mass of the distribution).
• the d90 (sum of the smallest 90% by mass of the distribution) is less than 140% of the average diameter of the granules relative to the d50 (sum of the smallest 50% by mass of the distribution).
• the particles may have a uniform shape, for example cylindrical, spherical, ellipsoidal, cube-shaped or irregularly shaped, but there may also be a mixture of different shapes.
• the granules used according to the invention may be opaque, i. be opaque to the human eye.
• a granulate is preferably used, which is transparent.
• transparent granules are to be understood as meaning granules which have an average transmission in the wavelength range of visible light of 400 to 700 nm measured on an injection molding wafer with a layer thickness of 2 mm of 1 to 95%, preferably 20 to 90%.
• the measurement of the color properties according to the method of the invention is carried out on a stationary or moving granular layer with a uniform layer thickness, which has been generated from a moving granular stream, for example by damming or decelerating the granular stream.
• the granulate layer produced rests during the measurement, ie has a speed of 0 m / s, or moves, ie has a speed> 0 m / s.
• the speed of the moving granule layer can be equal to the speed of the granule main stream or less than the speed of the granule main stream.
• the granulate layer produced from the agitated granulate stream moves, it generally has a velocity of> 0 to 2 m / s, preferably> 0 to 0.1 m / s.
• a granulate layer with a uniform layer thickness it is preferably possible for a granulate layer with a uniform layer thickness to be produced from the entire granulate stream.
• the layer thickness of the granule layer having a uniform layer thickness formed from at least part of the granulate stream used according to the invention must be selected at least such that the light irradiated into the granules has sufficient opportunity to interact with the color of the granules.
• this layer thickness is preferably 2 mm to 150 mm, more preferably 2 to 60 mm. Larger thicknesses are also possible, but then show only minor effects on the measured values.
• the measuring surface required for the method according to the invention is 4 mm 2 to 1600 mm 2 , with circular measuring surfaces being preferred. Particularly preferred are diameters of 10 to 200 mm.
• the measuring surface of the device can also be limited by additional apertures between the granulate layer and the measuring aperture of the device.
• the granulate layer having a uniform layer thickness produced from the granulate stream is free, i. without external guidance in air, moving.
• a granulate layer having a uniform layer thickness can be produced by transporting granules on a slope with a reproducible layer thickness.
• the stationary or moving granulate layer to be examined with a uniform layer thickness is produced from the agitated granulate stream by passing the granulate stream in a transparent tube with a corresponding diameter.
• the transparent tube is made of glass or a special glass or a plastic selected from the group consisting of polycarbonate, polyolefin, poly-styrene-acrylonitrile, polymethyl methacrylate and other transparent plastics.
• the tube in which the agitated granulate stream is fed to produce a granular layer having a uniform layer thickness is not transparent, but opaque.
• a sufficiently large transparent surface is present in the opaque tube, through which the measurement of the color properties can be carried out.
• the tube through which the granule stream to be tested is guided, thereby producing a granulate layer with a uniform layer thickness consists in a particularly preferred embodiment of a non-transparent layer. th material, z. As of metal or other non-transparent material.
• a transparent measuring window wherein this measuring window in a preferred embodiment has a diameter of 2 to 400 mm, preferably 10 to 200 mm.
• the transparent window is preferably made of a material selected from the group consisting of glass, special glass with a certain wavelength permeability, for example borosilicate glass, polycarbonate, polyethylene, poly-styrene-acrylonitrile, polymethyl methacrylate or other transparent plastics.
• Step (A) of the method according to the invention comprises generating a stationary or moving granular layer of at least part of the moving granular stream having a uniform layer thickness.
• step (A) a stationary or moving granular layer must be produced from at least part of the agitated granulate stream having a uniform layer thickness.
• the uniform layer thickness is necessary to provide high measurement accuracy, i. small standard deviations of the individual measured values from each other.
• a stationary granule layer is formed by stopping at least a portion of the agitated granular stream.
• Suitable devices for stopping a granular stream are known to those skilled in the art. An example of such devices is a rotary valve or a flap.
• a part of the tube is closed at the bottom by a suitable device and filled with the granules to be examined.
• the stationary granule layer is produced by damming the granulate stream in a tube.
• the stationary granule layer formed in this way has a uniform layer thickness, which preferably corresponds to the diameter of the tube. In a further embodiment it is ensured that there is a moving granulate layer with a uniform layer thickness.
• This granulate layer with a uniform layer thickness can preferably be produced by the granulate stream moving past the measuring window.
• the speed of the accumulated granulate stream is generally> 0 to 2 m / s, preferably> 0 to 0.1 m / s.
• a moving, preferably slowly moving, granular layer with a uniform layer thickness is formed by granules being accumulated by suitable devices. Suitable devices are known in the art.
• a stationary or moving granulate layer having a uniform layer thickness is produced from only one part, for example 0.1 to 99% by weight, of the moving granulate stream.
• devices known from the person skilled in the art for example a switch, are branched off from the moving granulate stream, the part forming the granulate layer being branched off.
• a stationary granulate layer having a uniform layer thickness can then be formed with the branched-off part.
• the layer thickness is generally not critical as long as a closed layer is present. Since, in a preferred embodiment, granules are used which have an average transmission in the visible range of light of 1 to 95%, it is necessary to choose the thickness of the granulate stream used according to the invention at least so that the light irradiated into the granules receives sufficient opportunity to interact with the color of the granules. Important for the reproducibility and comparability of the measured values is a uniform layer thickness for all measurements of a series. Depending on the transparency, shape and particle size of the granules, this layer thickness is preferably 2 to 150 mm. Larger layer thicknesses are also possible, but then show only minor effects on the measured values.
• the granule layer produced in step (A) of the method according to the invention has an approximately uniform layer thickness.
• Step (B) of the method according to the invention comprises the measurement of the color properties on the granule layer produced in step (A).
• Devices for measuring the color properties of stationary or moving granule layers are known to the person skilled in the art. Examples of suitable devices are disclosed, for example, in "Application Note” Hunterlab Feb 1999, VoI 11, No 2, “Color Measurement of Plastic Pellets Using Hunter Lab Instruments", available at www.hunterlab.com. It describes the use of the ColorFlex 45/0, ColorQuest 45/0, Labscan, Miniscan, Color Quest Sphere, Ultrascan and SpectraProbe XE LAV color measurement devices.
• a spectrophotometer is used to measure the color properties. This spectrophotometer can be mounted at a distance of 0 cm, ie direct contact with the granulate or the transparent pane, up to 200 cm, preferably 0 to 80 cm from the granule layer produced in step (A).
• the color properties are measured according to the invention by light in the visible range, ie 400-700 nm, particularly preferably by the light of a xenon lamp (one or more xenon flashes, optionally filtered to illuminant "D65".)
• the measurement is preferably carried out in 0745 ° optics. If the meter is used in production, for example, in the immediate vicinity of the hot granules, the device can be provided in a preferred embodiment with an internal air purge, which cools the electronic parts to a maximum of 50 0 C.
• the measuring frequency of a preferably used measuring device is 1 to 100 spectral evaluations per minute, more preferably 3 to 20 per minute.
• Each spectral evaluation can, for example, be based on an averaging of up to 100 individual measurements in a very short sequence, for example in the millisecond range of the lightning light frequency, depending on the desired accuracy.
• the frequency with which the granulate stream is moved and stopped is adapted to the measuring frequency.
• the stationary granule layer is generated at least as long as it takes to perform at least one measurement according to step (B).
• the granulate layer produced from the agitated granulate stream preferably continues to move between the individual measurements, a different part of the granulate stream is detected by each individual measurement.
• the corresponding granules can be discharged.
• the storage volume required for discharge can be easily calculated below the measurement and depends on the measuring time / measuring frequency as well as the volume flow and the cross-sectional area.
• the measured spectrum can be further processed to Lab or LCh or yellow values.
• the original spectrum is stored in a computer and can be used for color formulation calculation.
• the color properties which are preferably measured in step (B) of the method according to the invention are represented by means of the CIE-Lab color space system.
• the method according to the invention it is possible with the method according to the invention to determine the color loci which result from the parameters L, a and b of the CIE-Lab color space system.
• L, a and b or the evaluation delta E or the color difference of a given color location in different measurements on the granular layer generated from the granulate Ström can thus be detected, whether and how the color locus, and thus the color of the granules change.
• the measurement which can be carried out in step (B) of the method according to the invention is so fast and has such a low standard deviation that it is reproducible with a standard deviation from measurement to measurement of ⁇ 0.8 dE, preferably ⁇ 0.5 dE, more preferably ⁇ 0.3 dE, the color can be determined in the Lab color space. Due to the rapidity and the accuracy of the method according to the invention, it is suitable to discern color deviations, for example due to dosing disturbances of the colorant or due to the change in the intrinsic color of the polymer to be colored so quickly that the faulty Material can be discharged directly after the measurement. This eliminates the need for quarantine bunkers when transported in granulate silos. This dosing failures can be detected very quickly and targeted the resulting granules are discharged.
• Step (C) of the process according to the invention optionally comprises recycling the part of the granulate stream from which the granule layer has been produced in step (A) into the granular stream and optionally continuing the movement of the granular stream.
• step (C) of the process according to the invention of the separated part into the main stream can be done, for example, by supplying the separated part to the main stream with devices known to the person skilled in the art, for example a T-pipe section.
• step (A) of the process according to the invention If, in step (A) of the process according to the invention, a stationary granulate layer has been produced from the agitated granulate stream, the movement of the granular stream stopped in step (A) is continued in step (C) of the process according to the invention. If, for example, in step (A) of the process according to the invention at least a portion of the granular stream has been stopped by a flap to produce the granule layer with uniform layer thickness, then in step (C) of the inventive method, the movement of the granular stream is continued by the flap is opened again.
• step (C) is carried out by the granulate stream or the part of the granular stream the granule layer has been produced with a uniform layer thickness, is fed back to the promotion.
• step (A) the granule layer is produced with a uniform layer thickness by reducing the speed of at least part of the granule mainstream, so that there is a slowly moving granule layer with a uniform layer thickness at which the measurement according to step (A) B) is performed.
• step (C) is carried out by returning the portion of the granular stream or the entire granular stream whose rate has been reduced in step (A) to recovery. Additional steps may optionally follow the process steps (A), (B) and, if appropriate, (C) which are mandatory according to the invention.
• step (B) or step (C) of the process according to the invention is followed by the following step (D):
• step (D) Comparison of the measured in step (B) color properties of the granules with predetermined color properties.
• step (D) of the process according to the invention the color properties of the granules measured in step (B) are compared with predetermined color properties. This comparison can be made in any manner known to those skilled in the art, for example manually or electronically. In a preferred embodiment, an electronic data processing unit with appropriate software is used for step (D).
• step (D) of the method according to the invention is used, for example, to check, in the case of a granulate whose color has previously been determined in sample production, whether the resulting color of the granulate matches the previously set target value.
• the measured color location (Lab values, or LCh or x, y, z coordinates or other representations of coordinates of the color locus) or the measured color, expressed by the wavelength-dependent transmission values, can be used for quality assurance and documentation thereof to ensure in that uniformly colored granules are obtained over a longer period of production.
• the granules in question are discharged from the granulate stream.
• Suitable devices for discharging a portion of the granules from the moving granular stream are known in the art.
• a switch may be installed which, on the one hand, passes on the granulate stream containing granules, which has the correct color, into the corresponding production or packaging process and, on the other hand, a part of the granules in the granular stream, which is not the correct color, separated from the main granulate stream.
• this deviation is reduced by changing the color dosage during the production of the granules. ed. It is possible according to the invention to determine, by comparing the measured color properties and the predetermined color properties, how the actual color properties differ from the predetermined color properties. After determining this difference, a command can then be given to the color dosing unit to change the color mixture so that the color properties obtained largely match the predefined color properties, ie, the previously determined color deviation dE is further reduced.
• the determined deviation of the color properties of the measured granules with the previously set color properties is passed on to a dosing unit for the color mixture.
• the color of the granules can then be adapted to the previously set color properties.
• this adjustment and readjustment of the dosage can also be carried out fully automatically during the process. This means that in the case of color deviations the recipe change which has become necessary is calculated and the latter adapts the metering device of the ink / inkjet / liquid ink accordingly, for example manually or fully automatically.
• the present invention also relates to an apparatus for carrying out the above-mentioned method.
• the device according to the invention comprises at least one unit for producing a stationary or moving granulate layer from the moving granular stream and at least one unit for measuring the color properties.
• the device according to the invention has at least one unit for comparing the measured color properties with predetermined color properties. In a further preferred embodiment, the device according to the invention has at least one unit for discharging part of the granulate from the granulate stream.
• FIG. 1 to 7 show the following:
• FIG. 1 shows a general structure of a device which can be used according to the invention.
• FIG. 2 shows the measuring accuracy of the color measuring device from measurement to measurement in the granulate flow.
• FIG. 3 shows the change in the dE value after simulated scale failure.
• FIG. 4 shows the deviation of the color in the case of balance failure measured at the b value in the lab color space.
• FIG. 5 shows the change of the color locus in the a-b color plane after correction of the dosing devices (2) of the color plates.
• FIG. 6 shows a special embodiment of the device from FIG. 1, in which a vibrating channel (13) is used as an accumulation element (8).
• FIG. 7 shows the fluctuation from measured value to measured value in example 4.
• Controllable dosing device e.g. Scale, pump etc.
• the coloring substances e.g. Farbbatche, liquid colors or pigments are in storage tanks 1. From there they are dosed together with a metering device 2 with the polymers or polymer blends as granules or melt 3 in an extruder 4. After the granulation unit 5, the granules fall into a unit which accumulates the granules. 8 This can be done either by a flap (open / closed) or merely by braking and forming a moving granulate layer with an average stationary layer height. The granules 6 thus accumulated are measured with a color measuring device 7. Subsequently, either the flap is opened, so that this granulate can continue to flow again and then closed this flap again for the next series of measurements.
• a metering device 2 with the polymers or polymer blends as granules or melt 3 in an extruder 4. After the granulation unit 5, the granules fall into a unit which accumulates the granules. 8 This can be done either by a flap
• the granules continue to slip. If the color measuring device 7 has detected an exceeding in dE compared to the preset tolerance range with the aid of the evaluation computer 10, a switch 9 switches to offware 11 ("off-spec product") , so that the color is returned to the tolerance range, then the downstream switch 9 switches back accordingly to "commodity" 12 (on-spec product).
• offware 11 off-spec product
• the color plates used are a 0.05% BLUE colorant-containing SAN batch and a second 0.02% red-violet colorant-containing SAN batch.
• the granulate slowly slips past a transparent measuring window in the pipe to which a Hunterlab XE gauge is connected.
• This meter generates a spectrum every 12 seconds from which the connected computer calculates L, a, b values.
• the meter is informed that the following measurements will set the "STANDART" for that production, after which dE will be generated in addition to the L, a, b values.
• FIG. 2 shows the measuring accuracy of the color measuring device from measurement to measurement in the granulate flow.
• FIG. 3 shows the change in the dE value after simulated scale failure. After only 18 seconds you have a deviation in the dE of 2 units. Previously, a tolerable deviation of 1, 5 units dE was set. Since this has been exceeded, the switch (9) located further down switches to "off-spec goods" (11) before the part of the measured granulate flow arrives there, thus providing a 100% discharge of the off-spec goods.
• the color deviation can also be detected by the accompanying change of the a or b value in the Lab color space.
• FIG. 4 shows the deviation of the color in the case of balance failure measured at the b value in the lab color space. After only a few seconds, the measured value deviates by several units from the statistical mean value.
• FIG. 5 shows the change of the color locus in the ab color plane after correction of the metering devices (2) of the color plate;
• FIG. 5 shows the individual measured values in the color plane.
• a dosing change leads to a color change.
• the metered color batch quantities of the metering devices are changed accordingly and the resulting color location is compared with the desired value.
• Example 2 (FIG. 6):
• the Aufstauorgan (8) is a flap in the granule tube.
• the unit for controlled damming of the granular flow (8) is realized by installing a "weir" in the drainpipe after the granulating unit which accumulates the granules in front of it.
• the height of the granules reaches the weir height and the granules will flow over it is not completely filled, the irradiated layer thickness fluctuates more than in Examples 1 and 2.
• the deviation from measured value to measured value is correspondingly greater
• Figure 7 shows the fluctuation from measured value to measured value in Example 4.

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Citations (4)

• 2008
  • 2008-09-18 WO PCT/EP2008/062419 patent/WO2009040291A1/de active Application Filing

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