WO2009040291A1

WO2009040291A1 - Method and apparatus for measuring colour properties of plastic granules

Info

Publication number: WO2009040291A1
Application number: PCT/EP2008/062419
Authority: WO
Inventors: Peter Ittemann; Uwe Kleindienst; Bernd Niedermaier; Martin Klute; Norbert Mosbach
Original assignee: Basf Se
Priority date: 2007-09-21
Filing date: 2008-09-18
Publication date: 2009-04-02

Abstract

The present invention relates to a method for measuring the colour properties of granules in a moving stream of granules, said method comprising the following steps: (A) a stationary or moving layer of granules is produced from at least part of the moving stream of granules with a uniform layer thickness, (B) the colour properties of the layer of granules produced in step (A) are measured, and (C) that part of the stream of granules from which the layer of granules was produced in step (A) is returned to the stream of granules, if appropriate, and movement of the stream of granules is continued, if appropriate, and to an apparatus for carrying out the method.

Description

METHOD AND DEVICE FOR MEASURING COLOR CHARACTERISTICS

OF PLASTIC GRANULES

description

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.

During the production of colored plastic granules, 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.

To measure the color of these colored plastics, 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 problem with this approach is the long period between two sampling and measurements, which can be several minutes to sometimes hours. During this time, the possibility must be created to remove material with a different color from the production process. This is done according to the prior art so that after the first sampling, the continuously produced amount of colored granules is transferred to a quarantine bunker, after the second sampling is switched to another separate quarantine bunker and only after completion of the second measurement, i. After it has been established that the color obtained in the first quarantine bunker meets the requirements, this granulate can be supplied to further process steps such as processing or packaging.

In the case of flat parts, for example extrusion plates, 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. Here, the optics of the measuring device must be focused on the distance to the plastic web.

When measuring granules, there is the problem that reflection effects at the grain boundaries within the granules lead to falsified measurement results and thus to a large standard deviation of the individual measured values. To counteract this problem, specimens to be measured must be placed in a glass jar with specially made flat bottom made of special glass and then measured.

In Kunststoffe international 1/2005, pages 81 to 83 it is described that plastic granules can be measured by means of a revolving and coverable cuvette. Furthermore, it is revealed at www.hunterlab.com that pellets, granules or chips can be measured through the bottom of a special glass vessel.

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. For this purpose, 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, however, 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%. Thus, 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. For this purpose, 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. From the colored mixture thus obtained, a molded article is prepared, whose color properties are determined with a corresponding color measuring unit. By comparing the determined color properties of the finished part with the previously defined color properties, a difference may and this difference is compensated by changing the color mixing by means of the electronically controllable dosing unit. Thus, it is possible according to the presented in plastics 12/2006 method to produce plastics from recycled plastic residues with uniform color automatically. However, 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. In the process according to plastics 12/2006 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.

These objects are achieved by a method for measuring the color properties of a granulate in a moving granular stream, comprising the following steps:

(A) producing a stationary or moving granular layer comprising at least part of the moving granulated stream having a uniform layer thickness,

(B) Measurement of color properties on the granule layer produced in step (A) and

(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.

According to the invention it is possible to use all known to the expert granules. In a preferred embodiment, the granules used according to the invention contain at least one thermoplastic. An enumeration of 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 polystyrene (HIPS), polystyrene (PS) or copolymers of substituted styrenes, polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), polymethacrylimide, styrene-acrylonitrile polymers, copolymers of substituted styrenes and / or acrylic - nitrile compounds, alpha-methylstyrene-acrylonitrile polymers, aromatic polyester carbonates, halogenated polymers such as polyvinyl chloride, polyvinylidene chloride, polyphenylenether and mixtures thereof.

A detailed description of the thermoplastics which can be used according to the invention can be found in EP 0 800 554 B1 in Sections 0054 to 0132.

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. In general, 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. According to the invention, 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). Likewise, 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). According to the invention, however, it is also possible to use granules which are outside these limits. However, according to the invention it is also possible that non-uniform granules are used with regard to the particle size. 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. According to the invention, a granulate is preferably used, which is transparent. According to the invention, 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. Thus, it is possible according to the invention that 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. If 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. According to the invention, it is preferably possible for a granulate layer with a uniform layer thickness to be produced from the entire granulate stream. However, it is also possible for only one part of the granulate stream to form a granulate layer with a uniform layer thickness. 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. 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 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.

It is possible according to the invention that the granulate layer having a uniform layer thickness produced from the granulate stream is free, i. without external guidance in air, moving. By way of example, such a granulate layer having a uniform layer thickness can be produced by transporting granules on a slope with a reproducible layer thickness.

According to the invention, however, it is preferred that 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. In a preferred embodiment, 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.

In a further preferred embodiment, 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. At the point where step (B) of the process according to the invention takes place, a sufficiently large transparent surface is present in the opaque tube, through which the measurement of the color properties can be carried out. Thus, 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. These are provided with 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.

To carry out the process in such a way that the stationary or moving granular layer is produced by guiding the agitated granulate stream in a tube has the advantage that the material does not have to be handled openly and thus possible dust contamination is prevented.

The individual process steps (A), (B) and (C) are described in detail below:

Step (A):

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.

In order that the color properties of the granulate can be reliably and accurately measured in step (B) of the process according to the invention, in 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.

In a preferred embodiment, 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. In a particularly simple embodiment, a part of the tube is closed at the bottom by a suitable device and filled with the granules to be examined. Preferably, 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. Thus, in a preferred embodiment of the method according to the invention, 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.

In a further embodiment, 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. For this purpose, 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. As described, a stationary granulate layer having a uniform layer thickness can then be formed with the branched-off part.

If color properties of opaque granules are determined by the method according to the invention, then 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.

It is according to the invention required that the granule layer produced in step (A) of the method according to the invention has an approximately uniform layer thickness. Thus, it is avoided that due to interacting light beams different absorbance intensities are measured and thus a high standard deviation of the individual measured values occur with each other.

Step (B): 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.

In the case of the SpectraProbe XE LAV, the application for the in-line measurement of granules is also described. In the description, however, it is expressly pointed out that only every minute a measurement can be performed and every 30 minutes, a recalibration of the meter is necessary. This is impractical for material removal detection.

Other measuring instruments with which the color properties of granules can be measured are also described at www.hunterlab.com.

Furthermore, with the device TELEFLASH Compact from X-Rite, granules can also be measured in a small bowl. In this device, however, the maintenance of a large distance between the surface to be measured and the device is necessary.

In a particularly preferred embodiment, the device for measuring the color properties of the granules to be examined at an angle of 45 to 90 °, preferably 65 to 90 °, relative to the granule layer produced in step (A), attached. In a preferred embodiment, 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. It is possible according to the invention that the frequency with which the granulate stream is moved and stopped is adapted to the measuring frequency. Thus, it is possible that one or more measurements are made per stop of the granule stream. In the method according to the invention, the stationary granule layer is generated at least as long as it takes to perform at least one measurement according to step (B).

It is inventively preferred to generate a measured value every two to ten seconds, depending on the discharge quantity. Since 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. In the case of measurements which show that the measured color properties do not match the predefined color properties, 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.

In a preferred embodiment of the method according to the invention, 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. Thus, 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. By changing 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):

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.

Depending on whether a part has been separated from the entire moving granulate stream in step (A) of the process according to the invention in order to produce a stationary or moving granulate layer with a uniform layer thickness, recycle takes place in step (C) of the process according to the invention of the separated part into the main stream. The recycling 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.

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. If, in step (A) of the process according to the invention, a granulate layer having a uniform layer thickness is produced which has a lower velocity than the granulate stream from which it was produced, 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. Methods for this are known to the person skilled in the art.

In a preferred embodiment of the method according to the invention, in 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. In this preferred embodiment, 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.

In a preferred embodiment, step (B) or step (C) of the process according to the invention is followed by the following step (D):

(D) Comparison of the measured in step (B) color properties of the granules with predetermined color properties.

In 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).

The comparison in 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. Furthermore, 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.

In a further preferred embodiment of the method according to the invention, if the measured color properties deviate from the previously defined color properties, 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. For example, in the tube in which the granulate stream moves, 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.

In a further preferred embodiment, if the measured color properties deviate from the previously defined color properties, 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.

Thus, in a preferred embodiment of the method according to the invention, 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. By changing the color composition, the color of the granules can then be adapted to the previously set color properties. In a preferred embodiment, by suitable Farbrezeptier programs and automatically adjustable scales 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.

In the case of simple color recipes with few coloring additives, this can be done with the aid of stored color tables, with the aid of simple algorithms and appropriate feedback to the metering device or completely ab initio with the aid of stored color spectra of the starting materials and the colorants, e.g. with the help of color theories such as Kubelka-Munk.

The present invention also relates to an apparatus for carrying out the above-mentioned method.

In a preferred embodiment, 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.

In a further embodiment, 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.

With regard to the granules, the granule layer, the measurement and all other parameters, including with respect to the preferred embodiments, what has been said with regard to the method according to the invention applies.

characters

Figures 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.

In the figures, the reference numerals have the following meanings:

1 colorants, e.g. Colored batches, liquid colors, etc. 2 Controllable dosing device, e.g. Scale, pump etc.

3 polymer or polymer blend

4 extruder or mixer

5 discharging and granulating unit

6 Reservoir volume for impounding the granulate bed 7 Color measuring device 8 units for regulated damming of the granulate flow, z. B. flap, vibrating trough, weir etc.

9 points for discharging off-spec goods

10 evaluation computers 1 1 off-spec goods

12 on-spec goods

13 vibrating trough

Examples:

General structure (see FIG. 1):

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. In another embodiment, 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).

Example 1 :

The color plates used are a 0.05% BLUE colorant-containing SAN batch and a second 0.02% red-violet colorant-containing SAN batch.

These batches are coated at a dosage of 0.32 wt% (0.05% blue batch) and 0.15 wt% (0.02% red violet batch). added to the resulting granules. The two Farbbatche are intimately mixed together with Luran 368 R natural granules and Luran 368 R - natural melt in an extruder in the melt and this mixture discharged through a nozzle head and granulated. The resulting transparent colored granules slip through gravity through a pipe system to a rotary valve. The granules accumulate on this slowly rotating conveyor. The rotary speed of the rotary valve is controlled via a signal generator above the measuring device in the pipe to ensure a constant accumulation height. With this method, 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. At some point in time, 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. One recognizes an accuracy of dE 0.05-0.3 from measurement to measurement.

To prove the operation, a balance (2) is turned off for 30 seconds to determine the effects on the color measurement readings. The measuring frequency is 10 measurements / min. 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.

For color adjustment, the color location of the colored granules is determined. 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. After comparison with the desired value, 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):

As Aufstauorgan a vibrating trough (13) is used. This branches off a partial flow of the granules for color measurement. In this case, material that differs slightly from the color specification may also be fed directly to the further feed by overlaying granules at the upper T-piece. Therefore, this structure is more suitable for determining long-term color deviations than current failure of Farbdosiereinrichtungen.

Example 3 (FIG. 1):

In this case, the Aufstauorgan (8) is a flap in the granule tube.

The following sequence takes place: • The flap closes

• Granules accumulate in the pipe

• Measurement of the filling condition of the pipe via max-level measurement

• When reaching the max level: triggering the measurement

• Evaluation of the measurement bez. Deviation from specified dE values • Depending on the measurement result, switch the lower switch to "off-spec" or "on-spec" goods.

• Opening the flap

• emptying of the accumulated granulate

• After a defined time after opening the flap or detecting a min alarm, the flap is switched to the "closed position" again

• Cycle starts again.

Example 4 (Figure 1):

In this embodiment, 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.

Claims

claims

1. A method for measuring the color properties of a granulate in a moving

Granule stream comprising the following steps:

(A) producing a stationary or moving granular layer of at least a portion of the moving granular stream having a uniform layer thickness,

(B) Measurement of the color properties of the granule layer produced in step (A) and

(C) optionally recycling the portion of the granular 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.

2. The method according to claim 1, characterized in that the granules are transparent.

3. The method according to claim 1 or 2, characterized in that the granules used contains at least one thermoplastic material.

4. The method according to claim 3, characterized in that the thermoplastic material is selected from the group consisting of Polyoxymethylenhomo- and copolymers, polycarbonates, polyesters, polymethacrylates and copolymers 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, polyhydantoins, 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-resistant polystyrene (HIPS), polystyrene (PS) or copolymers of substituted styrenes, polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), polymethacrylimide , Styrene-acrylonitrile polymers, copolymers substituted styrene and / or acrylonitrile compounds, alpha-methylstyrene-acrylonitrile polymers, aromatic polyestercarbonates, halogenated polymers such as polyvinyl chloride, polyvinylidene chloride, polyphenylene ethers and

Mixtures thereof.

5. The method according to any one of claims 1 to 4, characterized in that the layer thickness produced in step (A) is 2 mm to 150 mm.

6. The method according to any one of claims 1 to 5, characterized in that a stationary granule layer is formed by at least a portion of the agitated granular stream is stopped.

7. The method according to any one of claims 1 to 5, characterized in that a moving granular layer is formed with a uniform layer thickness by granules is accumulated by suitable devices.

8. The method according to any one of claims 1 to 7, characterized in that followed by step (C), the following step (D):

9. The method according to claim 8, characterized in that in a deviation of the measured color properties of the predetermined color properties, the granules in question is discharged from the granular stream.

10. The method according to claim 8, characterized in that at a deviation of the measured color properties of the predetermined color properties, this deviation is reduced by changing the color dosage in the production of the granules.

1 1. Apparatus for carrying out a method according to one of claims 1 to 10.

12. The device according to claim 11, characterized in that it comprises at least one unit for generating a stationary or moving granular layer with a uniform layer thickness of the moving granular stream and at least one unit for measuring the color properties.

13. The apparatus of claim 1 1 or 12, characterized in that it comprises at least one unit for comparing the measured color properties with predetermined color properties.

14. Device according to one of claims 11 to 13, characterized in that it comprises at least one unit for discharge of a portion of the granules from the granular stream.