Note: Descriptions are shown in the official language in which they were submitted.
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Process for the coloring of plastics with liquid colorant
and liquid colorant container suitable for this purpose
The invention relates to a process for the coloring of
plastics in a continuously operated extruder or an
intermittently operating injection-molding machine, and to
a liquid colorant container suitable for the process, which
can be used to achieve consistent and reproducible coloring
of plastics, even with a liquid colorant that has not been
precisely standardized.
The feeding of liquid colorant into a continuously operated
extruder or an intermittently operating injection-molding
machine is a simple method of coloring plastics during
their processing. Use of liquid colorant in this way can
avoid maintaining inventory of colored plastics.
In order to achieve consistent and reproducible results
when coloring with liquid colorant, the usual method uses
liquid colorants with standardized properties and meters
the liquid colorants for production of a certain color in
each case with constant weight or volume. However,
standardization of the properties of a liquid colorant
requires additional operations and is particularly
difficult in the case of liquid colorants which are metered
not only by weight but also by volume, and for which it is
therefore not only the color strength that has to be
standardized but also the density of the liquid colorant.
WO 02/087849 discloses a process in which one or more
liquid colorants are introduced into a continuously
operated plastics-processing machine, where the metering of
the liquid colorant takes place with a metering device
according to fixedly prescribed formulations.
DE 197 28 733 Al discloses a process in which liquid
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colorant is metered into the conveying path of the
injection material, leading to the mold cavities, in an
intermittently operating injection-molding machine.
Prescribed amounts of liquid colorant are metered here.
In both of the known processes, differences in the
substance properties of the liquid colorant which have an
effect on its color strength inevitably lead to deviations
in the coloring of the plastic.
DE 35 05 036 Al discloses a process for the controlled
addition of colorant concentrates into a screw-based
machine, where a spectrometer attached to the screw-based
machine is used to measure the color intensity of the
colored mixture, and the measured signal is used to control
the addition of solid colorant concentrates to the screw-
based machine. The process achieves uniform coloring in the
event of variations in the color strength of the colorant
concentrates, but requires modification of the machine with
an expensive spectrometer.
EP 131 414 describes a method for the production of color
mixtures by using a metering device to meter dye from a
container which comprises a memory element in which
information relating to the color properties of the dye is
stored. In this method, the metering device reacts to
information stored in the memory element in order to meter
an amount of dye required to achieve the prescribed color.
EP 131 414 contains no reference to coloring of plastics.
There continues to be a need for a process which uses
liquid colorant for the coloring of plastics and which
dependably achieves a consistent and reproducible result
during the coloring process, even when using a liquid
colorant which has not been precisely standardized.
It has now been found that this object can be achieved by a
process in which liquid colorant is metered from a
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container which has a machine-readable memory element in
which data relating to substance properties of the liquid
colorant present in the container are stored, where the
metering device reads from the memory element of this
container data relating to substance properties of the
liquid colorant and uses the read data to adjust or control
the amount of liquid colorant metered.
The invention provides a process for the coloring of
plastics by metering of liquid colorant from a liquid
colorant metering device, connected to least one liquid
colorant container, into a continuously operated extruder
or an intermittently operating injection-molding machine,
characterized in that at least one container is used which
comprises at least one machine-readable memory element in
which data on substance properties of the liquid colorant
present in the container are stored, and the metering
device reads from the machine-readable memory element of
the container at least a portion of the data on substance
properties of the liquid colorant present in the container,
and adjusts or controls the amount of liquid colorant
metered with the read data.
The invention also provides a liquid colorant container
comprising at least one machine-readable memory element in
which data on substance properties of the liquid colorant
present in the container are stored, wherein data on the
density of the liquid colorant are stored in the machine-
readable memory element.
The process of the invention uses a liquid colorant
container which comprises at least one machine-readable
memory element. For the purposes of the invention, machine-
readable memory elements are those from which a data-
processing system can read data directly. Printed barcodes
are an example of machine-readable memory elements from
which a data-processing system can read data directly and
optically, whereas printed text is not a machine-readable
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memory element for the purposes of the invention, since the
data present in the text cannot be directly read into a
machine.
Machine-readable memory elements preferably used are
barcodes, magnetic strips, electrically contacted memory
elements, and memory elements readable via radio frequency.
The machine-readable memory elements used can be memory
elements that are only readable, examples being barcodes or
ROM memory elements. Writable memory elements are equally
suitable, examples being magnetic strips or EEPROM memory
elements. A preferred embodiment uses memory elements
readable via radio frequency which are known to the person
skilled in the art as RFID tags.
In one embodiment of the invention, the design of the
liquid colorant container is such that when the container
is connected to a metering device for the liquid colorant,
the machine-readable memory element is oriented in a
predetermined orientation with respect to the metering
device so that the metering device can read data from the
memory element.
Data on substance properties of the liquid colorant present
in the container are stored in the machine-readable memory
element. Preferably, data on one or more of the following
properties are stored in the memory element: hue, color
strength, lightness, color saturation, hiding power,
transparency, and density of the liquid colorant. The data
relating to hue, lightness, and color saturation are
preferably stored in the form of the parameters L, a, and
b, or the parameters L, Cab, and hab of the CIELAB system,
or the parameters X, Y, and Z corresponding thereto.
Further data on the liquid colorant present in the
container may also be stored in the machine-readable memory
element, such as for example the weight of the liquid
colorant present in the container, or one or more product
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identification numbers.
In the process of the invention, at least one liquid
colorant container is connected to a liquid colorant
metering device. The data on properties of the liquid
5 colorant present in the container are read completely or in
part by the metering device and the amount of liquid
colorant metered is adjusted or controlled with these data.
The reading of the data can be brought about by the user of
the metering device, for example in that the user reads the
data with a barcode-reader from a barcode attached to the
container and transfers the data from the barcode-reader to
the metering device.
In another embodiment, the reading of the data takes place
automatically upon connecting the container to the metering
device, for example by a coupling between the container and
the metering device which electrically contacts the memory
element, or by an RFID tag reader integrated into the
metering device. It is preferable that with an exchange of
a liquid colorant container the metering device
automatically reads data from the machine-readable memory
element of the container newly connected to the metering
device.
Preferably, metering devices in which the metering of the
liquid colorant takes place continuously or intermittently
at constant flow rates are used in the process of the
invention.
In a preferred embodiment of the process of the invention,
the metering device reads from the memory element of the
container data on the density of the liquid colorant
present in the container and adjusts or controls volumetric
metering of the liquid colorant with the read data. This
embodiment allows consistent and reproducible coloring
using liquid colorants, which have been standardized to a
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constant color strength based on weight, and do not have a
precisely standardized density. This embodiment
particularly preferably uses commercially available liquid
colorant containers which are additionally labeled with a
barcode in which the density of the liquid colorant present
in the container is stored. This embodiment permits the use
of commercially available liquid colorants, standardized to
a constant color strength based on weight, with metering
devices with volumetric metering of the liquid colorant.
In another preferred embodiment of the process of the
invention, the metering device reads from the machine-
readable memory element data on the weight of the liquid
colorant present in the container and uses the read data to
monitor the residual amount of liquid colorant in the
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stoppage of colorant metering when the container has been
emptied, even when containers with different filling weight
are used. When writable memory elements are used, it is
moreover possible to save in the memory element the
remaining residual amount of liquid colorant in the
container. This permits changeover between only partly
filled containers and permits monitoring of the remaining
residual amount in the container even when the metering
device is connected to a container which is only partly
filled and avoidance of unintended emptying of the
container during the metering process.
In another preferred embodiment of the process of the
invention, the metering device is connected to at least two
liquid colorant containers and mixes at least two liquid
colorants with one another. Each of the containers
connected to the metering device has a machine-readable
memory element, in which data on the hue of the liquid
colorant present in the container are stored, and the
metering device adjusts or controls the mixing ratio of the
liquid colorants with the read data.
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It is preferable that, in addition to the hue, data on
lightness and color saturation in the form of the
parameters L, a, and b, or the parameters L, Cab, and hab of
the CIELAB system, or the parameters X, Y, and Z
corresponding thereto are stored in the memory element.
Using the read data, and setpoint values for the parameters
L, a, and b, or L, Cab, and hab, or the parameters X, Y, and
Z corresponding thereto, of the liquid colorant, deposited
in the metering device, a correction for the mixing ratio
can be calculated in the metering device to obtain a mixed
liquid colorant, which achieves a consistent and
reproducible coloring even in the event of deviations of
the parameters L, a, and b, or L, Cab, and hab or the
parameters X, Y, and Z corresponding thereto, from the
specified value. The correction can sometimes also require
the metering of further liquid colorants which are not
required for the formulation with the specified values. The
person skilled in the art is aware of suitable methods for
the calculation of the correction, for example from G. A.
Klein, Farbenphysik fur industrielle Anwendungen [Color
physics for industrial applications], Verlag Springer.
Using this embodiment, it is possible to obtain a mixed
liquid colorant which achieves a consistent and
reproducible coloring even starting from liquid colorants
which have not been precisely standardized. Even when using
standardized liquid colorants, this embodiment of the
inventive process can achieve an even better
reproducibility of the coloring, because deviations from
the specified value, which remain even after
standardization, can be compensated during the metering
process.
The process of the invention can achieve consistent and
reproducible coloration of preparations in the form of
liquids, pastes, powders, or granules, even when using
liquid colorants which have not been precisely
standardized.
