HK1107300B - Apparatus and method for mixing liquid colour and method for colouring plastics with liquid colour - Google Patents

Description

Liquid pigment mixer and method for mixing liquid pigment

The invention relates to a liquid color mixer and a method for mixing liquid color, which is carried out with the color mixer and is suitable for the desired metering of liquid color in a plastic processing machine.

In the processing of plastics by melting of plastics, the coloration of the plastics is usually achieved by means of so-called masterbatches. Masterbatches are plastic pellets with a high pigment content, which are added to plastics during processing by melting in order to color the plastics. The use of masterbatches has the disadvantage that for each plastic type and each color, its own masterbatch needs to be produced and has to be kept in a warehouse for plastic processing. Short-term color changes or changes in hue are not possible, since new masterbatches have to be produced.

Instead of masterbatches, liquid pigments can also be used for coloring plastics, which are either fed to the plastics processing machine together with uncolored plastic granules or mixed with molten plastic in the processing machine. In this method, liquid pigments are used which are mixed for the desired shade, whereby for each desired color a corresponding liquid pigment is to be produced and has to be stored in a warehouse. A brief change of a new color or a change of shade cannot be achieved here either, since a new liquid pigment must be produced each time.

In WO 02/087849, it is proposed to supply a plurality of liquid colors separately to a plastics processing machine and to produce plastics having different color shades by dispensing the amounts of the various liquid colors in a formulaically controlled manner. However, this method has the disadvantage that, in many plastics processing machines, in the case of formulations with very different mixing ratios of the liquid pigments, a sufficiently homogeneous mixing of the liquid pigments with the plastics cannot be achieved, so that unevenly colored products are obtained.

A mixer and a mixing method are therefore needed, by means of which, even with very different proportions of liquid pigments, homogeneously mixed liquid pigments can be produced for the purpose of coloring plastics with liquid pigments according to a formulation, wherein the production of the mixture takes place directly before the processing of the plastics, according to the requirements of the plastics processing machine. The mixer must be able to mix reliably even thixotropic liquid pigments which flow only from a certain shear stress.

WO99/34905 discloses a mixer for manufacturing paint paints, wherein various liquid paints and one or more binder materials are dosed into a common chamber of the mixer and mixed in a subsequent vortex mixer before the mixture leaves the mixer. However, this mixer is not well suited for mixing liquid pigments of different viscosity and density without adding relatively large amounts of binder material as are required for coloring plastics, since the mixing of the liquid pigments is still not complete.

US 3,664,638 discloses a static mixer for mixing liquid pigments, wherein a plurality of helical mixing elements, each alternating in direction of rotation, are arranged in series within a tube. Static mixers of this type are known to the expert as screw mixers or Kenics mixers and are usually used for mixing the reaction components in the production of two-component plastics or two-component adhesives.

For the production of two-component plastics, dynamic mixers are also used, in which mixing elements known from helical mixers rotate in a mixing tube. In this mixer, the two components are fed axially at one end into the mixer, as in a static mixer.

However, the known axial feed of components, static helical mixers and mixers with rotating threaded mixing elements are not suitable for mixing liquid colors having different flow characteristics, such as liquid colors for plastics coloration, in different mixing ratios. When the viscosities of the liquid pigments to be mixed are different, for example, uneven mixing of the components having a greater viscosity occurs, whereby a mixture having a fluctuating hue is obtained. Similar problems arise when the liquid pigments have different densities or one or more of the liquid pigments have thixotropic flow characteristics.

JP-A3-60727 discloses a static mixer of spiral mixer construction in which nozzles are provided in the wall of the mixing tube to mix one liquid with another flowing through the tube. The mixer should have a high mixing efficiency when a small portion of the liquid is mixed by the nozzle in the wall of the mixing tube into a large liquid flow flowing through the mixing tube.

EP-a 0090257 discloses a mixer for multi-component plastics, which has a mixing chamber and a piston rotating in the mixing chamber, wherein a shear gap is formed between the piston and the mixing chamber. The components are metered radially into the shear gap and leave the mixer through a discharge opening opposite the piston. The mixer induces laminar flow in the shear gap and has no means to move the contents of the shear gap in a direction opposite the discharge port.

The object of uniformly mixing liquid color materials even in the case of very different proportions of the liquid color materials and different flow properties of the liquid color materials is achieved by the mixer according to the invention and the method for mixing liquid color materials which is carried out with the mixer.

The subject of the invention is a mixer for liquid paints, comprising: a mixing tube having an outlet at an end thereof; a mixing element which is arranged in the mixing tube so as to be rotatable about the longitudinal axis of the mixing tube and has at least two mixing elements, wherein a part of the mixing elements move the contents of the mixer in the direction of the discharge opening and a part of the mixing elements move the contents of the mixer in the opposite direction, with the same direction of rotation of the mixing element; and at least two inlet openings for the liquid color, which are arranged in the region of the mixing body in the mixing tube wall between the mixing tube ends.

The invention also relates to a method for mixing liquid color materials, in which method at least two liquid color materials are mixed in a mixer according to the invention, wherein the liquid color materials are fed into the mixer via an inlet opening for the liquid color materials, while a mixing device is moved about the longitudinal axis of the mixing tube and the mixed liquid color materials leave the mixer via an outlet opening at the end of the mixing tube.

The invention also relates to a method for coloring plastics, in which at least two liquid colors are mixed with volumetric metering by the method for mixing liquid colors according to the invention and the mixed liquid colors are fed directly to a plastics processing machine.

Liquid pigments in the sense of the present invention are flowable formulations which comprise one or more pigments in dispersed form and/or one or more pigments in dissolved form. The liquid pigments may be liquid or paste-like and also include thixotropic formulations that flow when the shear force applied to them is above their flow limit. Preferably, these liquid pigments contain up to 10% by weight, in particular up to 5% by weight, of pigments.

The mixer according to the invention has a mixing tube, on one end of which the discharge opening for the mixed liquid color is located. The mixing tube is preferably designed such that it can be closed off at the end opposite the discharge opening during the mixing process, so that the liquid color mixed in the mixing tube can only leave the mixing tube through the discharge opening. A constant pressure holding valve may also be provided at the discharge opening, if desired, to ensure that no mixed liquid color is discharged from the discharge opening as long as no liquid color is fed into the mixer. The mixing tube preferably has a circular cross-section and may have a cylindrical or conical shape, wherein a cylindrical shape is particularly preferred.

A mixing mechanism is disposed in the mixing tube such that the mixing mechanism is rotatable about the longitudinal axis of the mixing tube. The mixing tube has at least two mixing elements, some of which move the contents of the mixer in the direction of the discharge opening and some of which move the contents of the mixer in the opposite direction, with the same direction of rotation of the mixing mechanism. By this different action of the mixing elements on the contents of the mixer, back mixing of the contents is induced in the mixer by the formation of a vortex. The mixing elements are preferably dimensioned such that they move through at least 80%, particularly preferably through at least 90%, of the cross section of the mixing tube during one revolution of the mixing device. By dimensioning this way, mixing can be brought about over the entire cross-section of the mixing tube. The mixing device is preferably designed such that it is exchangeable, in particular it can be withdrawn from the mixing tube without disassembly.

The mixing elements of the mixing mechanism preferably have the shape of a helical screw with an alternating reverse direction of rotation, as is known to the expert from mixing elements of helical mixers. However, other shapes of mixing elements may be used, such as a stirrer having oppositely positioned stirring blades. The mixing device preferably has at least 5, particularly preferably at least 9 mixing elements which each have a different action on the contents of the mixer.

The driving of the mixing mechanism to move the mixing mechanism may be performed in any manner. Preferably the mixing mechanism is driven by an electric motor. It is particularly preferred that the mixing mechanism is driven from the end of the mixing tube opposite the discharge opening by a shaft located on the longitudinal axis of the mixing tube. The mixing tube can be set in an oscillating or rotating movement by a drive, wherein a rotating movement is preferred. If several of the mixing elements reach all the way to the vicinity of the wall of the mixing tube, no additional mixing mechanism bearings are required in the mixing tube, if driven by a shaft located on the longitudinal axis of the mixing tube.

The mixer according to the invention also has at least two inlet openings for the liquid color, which are arranged in the region of the mixing means in the wall of the mixing tube between the ends of the mixing tube. The liquid color is thus fed to the mixing tube radially through the wall of the mixing tube, rather than axially on the end of the mixing tube. The inlet opening for the liquid color is in this case preferably arranged such that at least 60%, particularly preferably more than 80%, of the length of the mixing device is located between the inlet opening and the outlet opening at the end of the mixing tube. The inlet openings for the liquid color are preferably located in one to three planes, particularly preferably in only one plane, transverse to the longitudinal axis of the mixing tube. The inlet port may additionally be provided with a shut-off valve or check valve to prevent the mixed liquid color from flowing back from the mixer into the conduit leading to the inlet port.

The inlet openings for the liquid color and the mixing means are preferably arranged such that, when the mixing means are moved, at least one mixing element of the mixing means moves past each inlet opening at a small distance, preferably at a distance of less than 1mm, in particular at a distance of less than 0.5 mm. This achieves high shear forces next to the inlet opening for the liquid color and better mixing.

The mixer according to the invention may additionally have one or more additional inlet openings for flushing liquid and/or compressed air, preferably both for flushing liquid and compressed air, in order to be able to empty and clean the mixer when changing colors. Additionally, the mixer may also have one or more discharge openings which allow emptying independently of the discharge opening(s) on the end of the mixing tube. The inlet openings for flushing liquid and/or compressed air and, if appropriate, additional outlet openings are preferably arranged radially in the vicinity of one end of the mixing tube or axially at one end of the mixing tube.

The method according to the invention for mixing liquid pigments is carried out in a mixer according to the invention. In this case, the liquid color is fed into the mixer via the inlet opening for the liquid color, while the mixing element is moved about the longitudinal axis of the mixing tube and the mixed liquid color leaves the mixer via the outlet opening at the end of the mixing tube. Preferably, all ports, except the inlet port for the liquid color and the outlet port at the end of the mixing tube, remain closed during the mixing process, so that the liquid color fed in through the inlet port can only leave the mixing tube after mixing through the outlet port at the end of the mixing tube. In particular the end of the mixing tube opposite the discharge opening remains closed during mixing.

The mixing mechanism movement during the liquid color input can be carried out in an oscillating or rotating manner, wherein a rotating movement is preferred. The rotational movement is particularly preferably carried out at a substantially constant rotational speed. The speed of movement of the mixing means can be selected by the expert within wide limits depending on the nature of the liquid color to be mixed. The speed of movement is at least selected to be so high that uniform mixing is achieved. The speed of movement is limited upwards only by the presence of voids on the mixing element. As long as gas, for example air, is also contained in the mixer, the speed of movement is preferably selected to be low in order to avoid mixing in bubbles and to achieve bubble-free mixing.

The process for mixing liquid pigments according to the invention is preferably carried out continuously or discontinuously. In the case of continuous operation, the liquid color is fed in a predetermined volume ratio, so that a continuous flow of mixed liquid color leaves the mixer. In the case of intermittent implementation of the method, the liquid color is supplied alternately always in a predetermined volume ratio in a first time interval, while no liquid color is supplied in a subsequent second time interval. In intermittent operation the mixed liquid color leaves the mixer only during the first time interval and not during the second time interval.

The introduction of the liquid color into the inlet opening for the liquid color preferably takes place by volumetric metering. In this case, the liquid color is introduced in a predetermined volume flow in predetermined volume proportions which are obtained from the formulation for the desired color. Volumetric metering is preferably achieved by means of positive-displacement pumps, in which the volume to be delivered is positively generated by mechanical movement of the pump. Suitable positive-displacement pumps are, for example, piston pumps, rotary-piston pumps and gear pumps. For the metering of liquid color, preferably a double piston pump is used, in which liquid color is metered alternately from one of the two pistons, while the other piston is filled, thereby metering a constant volume flow. A homogeneous combination of mixed liquid colors can be reproducibly achieved by volumetric dosing with a positive-displacement pump, without fluctuations in the regulation of the dosing leading to fluctuations in color. Furthermore, the volumetric metering allows the flow rate of the mixed liquid color leaving the mixer to be precisely adjusted, so that the liquid color can be metered directly into the plastics processing machine by means of the method according to the invention. The metering can be carried out continuously in a continuously operating plastics processing machine, for example in an extruder. It is also possible to dose discontinuously into discontinuously operating plastics processing machines, such as injection molding machines.

The volumetric metering of the liquid color in the mixer according to the invention is preferably controlled by the plastics processing machine so that it can be metered directly into the plastics processing machine without an intermediate container. In the mixer according to the invention, the controlled dosing of liquid color by the plastic processing machine is particularly advantageous for dosing discontinuously operating plastic processing machines, for example injection molding machines.

The direct metering into the plastics processing machine by the method according to the invention makes it possible to change the color or to change the color shade during the processing of the plastics in a short time without the need for a prior preparation of the color mixture or a change of the color container on the plastics processing machine.

It is particularly preferred to use positive-feed pumps for the metering of liquid color, which pumps are driven by stepping motors. Such a pump has the advantage over a continuously driven pump with a variable-speed drive that the dosing rate, which is precise and can be set constant, has a much wider range. The range from minimum to maximum dosing rates in variable-speed drives is generally not greater than 1: 100, whereas ranges greater than 1: 1000 can be achieved by driving with a stepper motor. It is thus possible to adjust a greater mixing ratio range without changing the pump and thus to produce a greater number of shades. In particular, an electric piston burette driven by a stepper motor is suitable for dosing liquid color.

The introduction of liquid color into the liquid color inlet in the process according to the invention can always take place continuously or in a clocked manner. By back-mixing in the mixing tube, homogeneous mixing can be achieved by means of the mixer according to the invention even with a clocked feed of one or more liquid colours, without temporal fluctuations in the composition, when the ratio between the mean residence time of the mixed liquid colours in the mixer and the duration of a beat is greater than 5: 1, preferably greater than 10: 1. The duration of a beat according to the invention is the sum of the duration of the individual steps of feeding the color into the mixer and the duration of the pause between two such color feeding steps. The possibility of a clocked input also makes it possible by the method according to the invention to mix the liquid pigments used in very different proportions reproducibly and without color fluctuations.

In order to change the color, it is advantageous in the method according to the invention to interrupt the mixing process and to wash the mixer with rinsing liquid, in order to obtain mixed liquid color with a changed, homogeneous composition as quickly as possible and in order to keep the amount of waste generated during the color change small. For this purpose, the supply of liquid color is first interrupted and the mixing tube is emptied by supplying compressed air. The mixing tube is then filled at least once with a rinsing liquid and the mixing device is moved in order to detach liquid color adhering to the mixing tube and to the mixing device from the rinsing liquid. The mixing tube is then emptied again by supplying compressed air and the liquid color is then supplied again in different proportions. If the liquid color is metered directly into the plastics processing machine in the method according to the invention, the contents of the mixing tube emptied with compressed air and the first portion of the liquid color mixed in a changed ratio are expediently fed into a separate collection container during the cleaning process before the direct metering into the plastics processing machine is continued. In principle any liquid which dissolves or disperses the components of the liquid pigment is suitable as flushing liquid.

The flushing operation is preferably carried out in such a way that at the end of the flushing operation all the lines connected to the mixing line are filled with liquid. By avoiding air cushions in the feed lines, a uniform flow of mixed liquid pigment can be obtained from the mixer during the subsequent mixing process.

If an intake port is not necessary to make the currently desired liquid color mixture, the liquid color input conduit leading to the intake port is at least partially filled with mixed liquid color from the mixing tube after liquid color input begins. This is preferably done in such a way that: the pump for feeding the liquid color operates for a short time in the reverse feed direction. By filling the inlet line at least partially with the mixed liquid color, it is possible to avoid: the liquid color that is currently being mixed is contaminated with unwanted liquid color from the access ports that are not currently being used. In an alternative embodiment, the feed line leading to the unwanted inlet opening is also at least partially filled with rinsing liquid during the rinsing process.

In the method according to the invention for mixing liquid colors, it is also possible to additionally feed other flowable components or preparations to the at least two liquid colors via inlet openings arranged in the wall of the mixing tube. In the production of liquid pigments for coloring plastics, it is also possible, for example, to admix Ultraviolet (UV) stabilizers, antioxidants, flame retardants, softeners or additives for improving impact resistance, in order to add them to the plastics together with the mixed liquid pigments.

Fig. 1 shows a preferred embodiment of the mixer according to the invention, with a mixing element in the form of a helical spiral, additional inlets for flushing liquid and compressed air and metering of liquid color by means of a volumetrically metered double-piston pump,

FIG. 2 shows a graph of liquid color flow versus time t with continuous operation of the mixer, the first liquid color at flow rate F₁Continuously dosed and the second liquid colour at a flow rate F₂Timed rationing with one beat of duration t₁，

FIG. 3 shows a graph of liquid color flow versus time t for intermittent operation of a mixer with a first liquid color at a flow rate F₁Continuously dosed and the second liquid colour at a flow rate F₂Rhythmically dosing; in the intermittent operation, the two liquid pigments are always in the first time interval t₂Is dosed and the dosing of the two liquid colours is performed at a second time interval t₃The upper one of the interrupts is interrupted,

fig. 4 shows a preferred embodiment of the mixer according to the invention, with two mixing pipes.

In the embodiment of fig. 1, the mixer comprises a cylindrical mixing tube 1 with a discharge opening 2 at the lower end of the mixing tube 1. A mixing element 3, which is rotatable about the longitudinal axis of the mixing tube 1 and is driven by an electric motor via a shaft 8, is arranged in the mixing tube 1. The mixing device 3 has a total of 5 mixing elements 3a, 3b in the form of helical spirals whose directions of rotation are alternately reversed, which, during one revolution of the mixing device 3, move through a cross section greater than 80% of the mixing tube 1. In the case of the same direction of rotation of the mixing mechanism 3, the first partial mixing element 3a moves the contents of the mixer in the direction of the discharge opening and the second partial mixing element 3b in the opposite direction. The mixer furthermore has two inlet openings 4, 5 for the liquid color 6, 7, which are arranged in the mixing tube wall between the two ends of the mixing tube 1 in a plane transverse to the longitudinal axis of the mixing tube 1 in the region of the mixing means 3, so that more than 60% of the length of the mixing means 3 is located between the inlet openings 4, 5 and the outlet opening 2 at the end of the mixing tube 1. The inlet openings 4, 5 for the liquid colors 6, 7 and the mixing means 3 are in this case arranged such that one mixing element 3b moves past the inlet openings 4, 5 at a distance of less than 0.5mm when the mixing means is moved. The mixer also has an additional inlet 9 for rinsing liquid 10 and compressed air 11.

In a particularly preferred embodiment according to the invention, the two liquid colors 6, 7 are fed into the mixing tube 1 via the inlet openings 4, 5 for the liquid colors 6, 7 by means of a double-piston pump 13, 14, while the mixing means 3 rotates about the longitudinal axis of the mixing tube 1. The end of the mixing tube 1 opposite the outlet opening 2 and the additional inlet opening 9 are kept closed, so that the entire quantity of liquid color 6, 7 fed in through the inlet openings 4, 5 leaves the mixer as mixed liquid color 12 via the outlet opening 2 and a valve 15. The double-piston pumps 13, 14 are driven by stepping motors in this case, so that the liquid colors 6, 7 can be fed to the mixer in a clocked manner, the ratio of the duration of one cycle to the average residence time of the mixed liquid colors in the mixer being selected to be less than 1: 10. The mixed liquid color 12 is fed directly into the plastics processing machine, wherein the volumetric metering of the liquid colors 6, 7 is controlled by the plastics processing machine.

For changing the color, the mixer shown in fig. 1 is particularly preferably cleaned in that the dosing of the liquid color 6, 7 is first stopped and the valve 15 is closed, through which the mixed liquid color 12 is fed to the plastics processing machine. Compressed air 11 is then fed in through the additional inlet 9 and the contents of the mixing tube 1 are discharged as a waste stream 16 through the valve 15 into a collection container. The mixing tube 1 is then completely filled with rinsing liquid 10 via the additional inlet opening 9 with the valve 15 closed, the mixing mechanism 3 rotating and the mixing tube 1 being vented via a not shown vent opening at the upper end of the mixing tube 1. After about 30 seconds, during which the mixing device 3 continues to rotate, compressed air 11 is introduced through the additional inlet 9 and the contents of the mixing tube 1 are emptied as a waste stream 16 into a collection container via the valve 15. The rinsing process was then repeated two more times. The rotational speed of the mixing device 3 is then reduced and the liquid color 6, 7 is dosed in the new ratio, wherein the valve 15 is initially kept open in such a way that the mixed liquid color is fed as a waste stream 16 to the collection container. After a quantity of liquid color 6, 7 has been dosed, which corresponds to the volume of the mixing tube 1 and thus displaces air from the mixing tube 1, the rotational speed of the mixing element 3 is increased again to the original value. After a metered amount of liquid color 6, 7, which corresponds to two to three times the volume of the mixing tube 1, the valve 15 is switched in such a way that the mixed liquid color 12 is fed again to the plastics processing machine.

In the embodiment of fig. 4, the mixer comprises two mixing tubes 1, each having an outlet opening 2, a mixing means 3 and inlet openings 4, 5. These inlet openings 4, 5 are supplied with liquid color 6, 7 by means of double-piston pumps 13, 14, wherein in each double-piston pump the pistons can be driven independently of one another and the liquid color can be dosed from each of the two pistons independently of one another into each of the two mixing tubes by means of a correspondingly arranged valve. The two mixing lines are connected to one another via a valve 15 in the form of a four-way valve, so that one of the mixing lines is selectively connected via a line to a device in which the mixed liquid color 12 is dosed, while the other mixing line is connected to a collecting container for a waste stream 16. In addition to the inlet 9 for the rinsing liquid 10, the mixer preferably has valves 17, by means of which the rinsing liquid 10 or the compressed air 11 can also be fed into the mixing tube 3 via the outlet 2, and an additional outlet 18 for the waste stream 19 on the end of the mixing tube 3 opposite the outlet 2. The additional valve 17 and the discharge 18 make it possible to flush the mixing tube thoroughly in both directions and thus to effectively purge the mixing tube in order to change the color.

With the preferred embodiment of the mixer according to fig. 4, it is possible to: when changing color, the liquid color is prepared in the second mixing tube in a new, changed mixing ratio, and is dosed by the first mixing tube in the old mixing ratio. This shortens the interruption time for changing the color, since for changing the color it is only necessary to flush or replace the line for mixing the liquid color 12, which is led from the valve 15 to the device used, while the cleaning of the mixing tube can take place without interrupting the dosing of the liquid color. The liquid colours 6, 7 are still dosed in the old mixing ratio into the first mixing pipe and the mixed liquid colours are obtained in the old mixing ratio through the valve 15, while the second mixing pipe is flushed and emptied with flushing liquid 10 and compressed air 11 as described above. In addition to the flushing liquid and compressed air being supplied through the inlet opening 9 and being evacuated through the valve 15, it is also preferred if the flushing liquid and compressed air are additionally supplied in the opposite direction by the valve 17 for flushing and evacuation through the outlet opening 18. The second mixing tube is then filled with liquid color at the new mixing ratio as described above, while the dosing of liquid color into the first mixing tube continues at the old mixing ratio. For this purpose, the two pistons of a double-piston pump 13, 14 are driven in such a way that one of the pump pistons doses into the first mixing line according to the old mixing ratio and the other pump piston doses into the second mixing line according to the new mixing ratio. If during this process one of the pump pistons, i.e. the pump piston metering into the first mixing tube, has to be filled, the filling of the second mixing tube is interrupted, and for the continuous metering changeover to the still filled second pump piston, the first pump piston is filled and then the filling of the second mixing tube is continued, so that the continuous metering into the first mixing tube is not interrupted. Preferably, the pump piston which is not needed for dosing into the first mixing tube is filled in each double-piston pump before the second mixing tube is filled, the dosing from the filled piston into the first mixing tube is switched over in all pumps, the second pump piston which is not needed for dosing into the first mixing tube is also filled in, and the filling of the second mixing tube is started. In this way, the filling of the second mixing tube can generally be ended before a changeover between the pistons of the dual-piston pump is required for dosing into the first mixing tube.

Examples of the invention

The test was carried out in a mixer according to fig. 1 having a mixing tube 1 with an inner diameter of 8.3mm and a length of 10 cm. The mixing tube has two inlet openings 4, 5, each having a diameter of 1.5mm, spaced apart from the outlet opening 2 by a distance of 8 cm. As mixing means 3, a 8mm diameter, 93mm long helical mixer MR 08-12 from Mixpac was used, which has 12 mixing elements in the form of helical, respectively inverted helices. The mixing mechanism was rotated by a 1500 rpm motor. For the metering of liquid color, an electric burette of the Hamilton company, type PSD/8, is used as the piston pump 13, 14.

Example 1

A red and a white liquid pigment Polytrend 700 from Colortrend are fed intermittently radially into the mixer via two different inlet openings 4, 5 in a volumetric flow of 1.8ml/min in a volume ratio of 10: 9. The time interval for feeding the liquid color and the time interval for interrupting the feeding are each 10 seconds. To evaluate the mixing quality, a few drops were thinly extracted from the mixed liquid pigment obtained at the discharge port 2 on a microscope slide and visually evaluated. The unevenness or fluctuation of hue was not determined in the mixed liquid pigment.

Example 2 (comparative example)

Example 1 was repeated, but the two liquid pigments were not fed radially through the inlet openings 4, 5, but axially through the inlet opening on the end of the mixer opposite the discharge opening 2. The mixed liquid pigment had clearly recognizable fluctuations in hue.

Claims (22)

1. A mixer for liquid paint comprising:

a) a mixing tube (1) having an outlet opening (2) at the end of the mixing tube,

b) a mixing element (3) which is arranged in the mixing tube so as to be rotatable about the longitudinal axis of the mixing tube and has at least two mixing elements (3a, 3b), wherein, with the same direction of rotation of the mixing element, a part of the mixing elements move the contents of the mixer in the direction of the outlet opening and a part of the mixing elements move the contents of the mixer in the opposite direction, and

c) at least two inlet openings (4, 5) for liquid color (6, 7) which are arranged in the region of the mixing means in the wall of the mixing tube between the ends of the mixing tube, wherein the inlet openings (4, 5) and the mixing means (3) are arranged such that, when the mixing means are moved, at least one mixing element (3a, 3b) of the mixing means moves with a spacing of less than 1mm next to each inlet opening.

2. The mixer of claim 1, wherein: the mixing tube (1) has a cylindrical shape.

3. A mixer according to claim 1 or 2, wherein: the mixing elements (3a, 3b) of the mixing means (3) have the shape of helical spirals having alternately opposite directions of rotation.

4. A mixer according to claim 1 or 2, wherein: the mixing elements (3a, 3b) of the mixing device (3) are moved through at least 80% of the cross section of the mixing tube (1) during one revolution of the mixing device.

5. A mixer according to claim 1 or 2, wherein: the inlet openings (4, 5) for the liquid color (6, 7) are arranged such that at least 60% of the length of the mixing means (3) is located between the inlet opening and the outlet opening (2) at the end of the mixing tube (1).

6. A mixer according to claim 1 or 2, wherein: the inlet openings (4, 5) for the liquid color (6, 7) are located in a plane transverse to the longitudinal axis of the mixing tube (1).

7. A mixer according to claim 1 or 2, wherein: the mixing element (3) is driven by a shaft (8) located on the longitudinal axis of the mixing tube (1) from the end of the mixing tube opposite the discharge opening (2).

8. A mixer according to claim 1 or 2, wherein: it has one or more additional inlet openings (9) for flushing liquid (10) and compressed air (11).

9. A mixer according to claim 1 or 2, wherein: it has two mixing pipes (1), the discharge openings (2) of which are connected via a valve (15) to a common line for the mixed liquid color (12).

10. A mixer according to claim 1 or 2, wherein: it comprises at least two double piston pumps (13, 14), wherein the liquid color can be dosed into each of the two mixing tubes independently of each other by the two pistons of one double piston pump.

11. A method for mixing liquid pigments, characterized by: at least two liquid colors (6, 7) are mixed in a mixer according to claim 1 or 2, wherein the liquid colors are fed to the mixer through inlet openings (4, 5) for the liquid colors, and the mixing means (3) is moved about the longitudinal axis of the mixing tube (1) and the mixed liquid colors (12) leave the mixer through outlet openings (2) at the end of the mixing tube.

12. A method according to claim 11, characterized in that: the mixing mechanism (3) rotates around the longitudinal axis of the mixing tube (1).

13. A method according to claim 11 or 12, characterized in that: during mixing, the end of the mixing tube (1) opposite the discharge opening (2) remains closed.

14. A method according to claim 11 or 12, characterized in that: at least one of these liquid colors (6, 7) is fed to the mixer in a clocked manner, wherein the ratio of the mean residence time of the mixed liquid color in the mixer to the duration of a beat is greater than 5: 1.

15. The method of claim 14, wherein: at least one of the liquid colors (6, 7) is fed to the mixer by means of a pump, which is driven by a stepping motor.

16. A method according to claim 11 or 12, characterized in that: these liquid colors (6, 7) are supplied to the mixer in a volumetrically dosed manner.

17. The method of claim 16, wherein: the volumetric metering of the liquid color (6, 7) is carried out in a forced manner.

18. A method according to claim 11 or 12, characterized in that: no liquid color is fed into at least one inlet opening (5), and the feed line leading to this inlet opening (5) is at least partially filled with mixed liquid color from the mixing tube after the beginning of the feeding of liquid color.

19. A method according to claim 11 or 12, characterized in that: to change colors

a) Interrupting the supply of liquid color (6, 7),

b) the mixing tube (1) is evacuated by feeding compressed air (11),

c) filling the mixing tube with a rinsing liquid (10) and moving the mixing device (3),

d) evacuating the mixing tube (1) by feeding compressed air (11), an

e) The introduction of the liquid color (6, 7) is continued in another ratio.

20. A method according to claim 11 or 12, characterized in that: using a mixer with two mixing tubes (1) and feeding at least two liquid pigments (6, 7) into one of the mixing tubes, while in the other mixing tube the color is changed

a) The mixing tube (1) is evacuated by feeding compressed air (11),

b) filling the mixing tube with rinsing liquid (10) and moving the mixing means (3), an

c) The mixing tube (1) is evacuated by feeding compressed air (11).

21. Method for coloring plastic, characterized in that: mixing at least two liquid colours (6, 7) according to the method of claim 16 or 17 and feeding the mixed liquid colours (12) directly to a plastics processing machine.

22. The method of claim 21, wherein: the volumetric dosing of the liquid color (6, 7) is controlled by the plastic processing machine.