DE102008030732B4 - Process for the preparation of color concentrate granules for thermoplastics, color concentrate granules and their use - Google Patents

Abstract

Process for the production of color concentrate granules of reduced specific gravity for thermoplastics, comprising the steps of: a) mixing and melting a raw material mixture of pigments, plastics and optionally additives in an extruder, b) producing plastic strands from the plastic melt, c) cooling the plastic strands in a water bath; d) cutting the plastic strands to the desired length into granules in a granulator, characterized in that a propellant is added to the raw material mixture prior to extrusion, the extrusion being carried out at a temperature at which the propellant is completely decomposed to form gas , And that the gas formation takes place under pressure-tight conditions by the degassing zones of the extruder remain pressure sealed.

Description

The present invention relates to a process for the production of color concentrate granules of reduced weight for thermoplastics according to the claims. Furthermore, the invention relates to the color concentrate granules themselves and the use of color concentrate granules prepared according to the method of the invention for the production of colored molded parts from thermoplastic materials according to the claims.

In almost all areas of life, plastics with different colors are used. In the production of plastic for coloring is usually mixed with color pigments. The color pigments are in the form of color concentrates in granular form. Depending on the color, hue and color intensity, different amounts of such granulated color concentrates are necessary. Color granules are used in different areas of plastics processing, such. As in automotive parts, plastic packaging, toys or food containers.

In the production of these plastics, the color or additive concentrates are added in granular form to the polymer to be dyed. Such methods are in the DD 272 308 A1 , of the DD 247 015 A1 , of the DE 10 2005 014 024 A1 as well as in the DE 1 604 365 A described. In the DD 247 015 In a first process step, a polyolefin granule is ground at mass temperatures of less than 100 ° C., subjected to a residence time, and color pigments are metered in. Other color concentrates and processes for their preparation are also in the US 2002/0198122 A1 , of the US 2004/0214927 A1 and the WO 03/033571 A1 described. The blowing agents used therein are used in the actual production process of a plastic product, ie, when a base polymer is melted together with a concentrate, to improve the production process, wherein the blowing agent escapes.

In the DE 23 41 000 A1 describes a process for the preparation of color concentrates for the dyeing of molded polyester products, wherein 99.5 to 45 wt .-% powder polyester with 0.5 to 35 wt .-% of the pigment and / or 0.01 to 20 wt % of the dispersing agent and / or further additions are kneaded, filtered and granulated. Similar procedures are also in the EP 1 705 465 A2 described.

The DE 28 11 922 A1 describes a process for the preparation of resin color concentrates by coloring resins, wherein powdered or granular resins are intimately mixed at a temperature of about 35 ° to 150 ° C with a dye and a solid at normal temperature, but melted at the mixing temperature wax and this Mixture is cooled. The product is a fine to coarse-grained material, which is suitable as a "masterbatch" for thermoplastic and thermosetting resins.

In the DE 31 52 243 C2 discloses a process for producing a large, elongated, thermoplastic cell-structured body in which a thermoplastic polymer is mixed with a blowing agent. This creates bodies with a low-density cell structure, for example to produce foam bodies. The blowing agents used preferably comprise liquid fluorohydrocarbons. A similar procedure is also in the EP 1 148 086 B1 ( DE 601 13 473 T2 ).

In the production and coloring of the plastics, it must be ensured that the colorings are as uniform as possible and have the same color intensity over the entire product range. For opaque colors this is a minor problem, since smaller deviations of the color concentrate amount visually not noticeable. However, a bigger problem is with transparent or weak colorations. In such coloring often only 0.1 to 0.5% color concentrate are needed. This mixture would contain many natural colored plastic granules and extremely few color granules. In order to avoid the above-mentioned technical problems, such as streaking on the production part, unevenly dyed end products and fluctuating hiding power, mostly higher dosages of a less intensive concentrate are used. The mixture to be processed then contains more color granules of a less intense color concentrate.

Lowering the color pigment concentration in the granules and increasing the dosage of the colored pigment granules in the plastic mixture is a cost factor. Although the material costs for the color concentrate fall due to the lower pigment concentration, since a larger amount of color concentrate granules must be used, the production process becomes considerably more expensive. For example, with a 4% color concentrate dosage, the cost is almost twice that of adding 2%. It should be noted that the costs are usually calculated on the basis of the specific gravity of the granules, ie. H. a larger amount of granules automatically leads to higher costs. A reduction in the pigment concentration in the color concentrate granules thus does not lead to the desired result of a cost-efficient production process.

It is an object of the present invention to provide a process for producing color concentrate granules in which the specific gravity of the color concentrate granules is reduced.

This object is achieved by a method having the features of patent claim 1.

• a) Vermischung und Aufschmelzung einer Rohstoffmischung aus Pigmenten, Kunststoffen und gegebenenfalls Additiven in einem Extruder,
• b) Erzeugen von Kunststoffsträngen aus der Kunststoffschmelze,
• c) Abkühlen der Kunststoffstränge in einem Wasserbad,
• d) Schneiden der Kunststoffstränge auf die gewünschte Länge zu Granulatkörnern in einem Granulator. Das Verfahren ist dadurch gekennzeichnet, dass der Rohstoffmischung vor der Extrusion ein Treibmittel zugesetzt wird, wobei die Extrusion bei einer Temperatur durchgeführt wird, bei der das Treibmittel unter Gasbildung zersetzt wird, und dass die Gasbildung unter druckdichten Bedingungen erfolgt, indem die Entgasungszonen des Extruders druckdicht verschlossen bleiben.

The procedure is defined in the individual steps as follows:

• a) mixing and melting of a raw material mixture of pigments, plastics and optionally additives in an extruder,
• b) producing plastic strands from the plastic melt,
• c) cooling the plastic strands in a water bath,
• d) cutting the plastic strands to the desired length to granules in a granulator. The process is characterized in that a blowing agent is added to the raw material mixture prior to extrusion, wherein the extrusion is carried out at a temperature at which the blowing agent is decomposed to form gas, and that the gas formation takes place under pressure-tight conditions by pressure-tight sealing of the degassing zones of the extruder stay closed.

The invention is based on reducing the specific gravity of the color concentrate granules by gas formation during the production process. As a result, a larger amount of granules in the plastic manufacturing process can be used, as was previously the case. The granules are the same dimensions lighter than the granules previously known from the prior art. In the manufacturing process can continue to work with the same weight ratio of natural plastic and concentrate, but the volume ratio changes in favor of the color concentrate.

Due to the higher volume fraction of the granules of the color concentrate to achieve a more uniform coloring and ink coverage of the plastic. The coloring is distributed homogeneously over the entire surface of the plastic. Local intensity differences do not occur.

The production process according to the invention is carried out as follows: The raw materials, such as pigments, plastics and optionally additives, are introduced premixed into an extruder. In the extruder, the plastic mass is melted and incorporated the pigments and additives evenly in the plastic melt. Subsequently, the melt is pressed to produce plastic strands through a perforated plate from the extruder. The resulting plastic strands are then pulled through a water bath, so that the liquid plastic cools. In the following process, the plastic strand is cut to the desired length into individual granules in a granulator. The granules have uniform dimensions.

The extruder has multiple degasification zones that are normally used to allow vaporized moisture to escape to improve product quality. In the method according to the invention, however, it is provided that the degassing zones remain sealed pressure-tight.

In the method according to the invention, it is provided that voids are formed by gas formation in the individual granules. These cavities require a reduced filling of the granules with color concentrate mass. This reduces the specific weight. The gas inclusion (CO ₂ ) is inventively achieved in that the composition is supplied to a blowing agent prior to extrusion. This blowing agent is at a certain temperature of the solid (powdery) or liquid state in the gaseous state. Since the extruder is pressure-tight, the resulting gas can not escape and forms due to the formation of gas in the plastic melt microbubbles. The pressure-tight conditions are necessary so that the microbubbles are retained until they exit the extruder. Otherwise the bubbles would burst.

When the plastic strands are pressed out of the perforated plate, the microbubbles can expand because the atmospheric ambient pressure is substantially lower than the mass pressure in the plastic mass. The expansion of the gas bubbles causes cavities to be formed in the plastic strand that result in the desired volume expansion. The hollow plastic strand is, as described above, fed to a water bath and then granulated to form individual granules.

Citric acid, azodicarbonamides, sulfohydrazides or sodium bicarbonate are preferably used as blowing agents. The person skilled in the art also discloses further blowing agents which lead to the desired formation of gas and thus to the formation of cavities in the plastics material. The dosage of the propellant is preferably between 0.05 and 5%. The exact dosage of the blowing agent depends on the respective plastic mixture.

The temperature in the extruder depends on the particular blowing agent used. For example, the temperature will be about 200 ° C with the addition of citric acid. At this temperature, complete decomposition of the blowing agent takes place. The individual decomposition temperatures are different for each propellant and must be determined.

The method can be used for all plastic melts. Exemplary plastics are all polyolefins such as PE, PP, HDPE and LDPE. Furthermore, all technical plastics such as ABS, SAN, and PA can be treated with the method according to the invention.

After granulation, the product is checked for the possible presence of propellant residues. This can be done for example with an injection molding machine. Injection molded parts are made with about 2% color concentrate addition. With a microscope, these can then be examined for the presence of gas bubbles. After the test, the entire production process can be aligned.

The granules produced according to the invention differ even optically from the conventionally produced granules. Due to the formation of voids due to gas formation, the granules produced according to the invention have a profiled surface structure.

Due to the reduced specific weight, a larger amount of granular mass in the plastic dyeing process can be used, which causes a more uniform coloring of the plastic and significantly reduces costs.

The invention further relates, in a further aspect, to the use of color concentrate granules produced in accordance with the process of the invention for the production of colored molded parts from thermoplastics.

The following example serves to illustrate the invention.

Example:

Pigments, additives and plastic mass are premixed and then introduced into an extruder. 2% citric acid per kg color concentrate is added as propellant. The premixed composition is then extruded in the extruder at a temperature of about 200 ° C. At this temperature, complete decomposition of the blowing agent takes place.

Claims (8)

Process for the production of color concentrate granules of reduced specific gravity for thermoplastics, comprising the steps of: a) mixing and melting a raw material mixture of pigments, plastics and optionally additives in an extruder, b) producing plastic strands from the plastic melt, c) cooling the plastic strands in a water bath; d) cutting the plastic strands to the desired length into granules in a granulator, characterized in that a propellant is added to the raw material mixture prior to extrusion, the extrusion being carried out at a temperature at which the propellant is completely decomposed to form gas , And that the gas formation takes place under pressure-tight conditions by the degassing zones of the extruder remain pressure sealed. A method according to claim 1, characterized in that the blowing agent is added in a concentration between 0.05 and 5%. Method according to one of claims 1 to 2, characterized in that the blowing agent is added in a concentration of 2%. Method according to one of claims 1 to 3, characterized in that are used as the blowing agent citric acid, azodicarbonamides, sulfohydrazides or sodium bicarbonate. Method according to one of claims 1 to 4, characterized in that the extrusion takes place at a temperature of 200 ° C. Method according to one of claims 1 to 5, characterized in that are used as plastics poly-olefins such as PE, PP, HDPE, LDPE or engineering plastics such as ABS, SAN, PA. Color concentrate granules for coloring and additivation of thermoplastics, produced by a process according to one of claims 1 to 6. Use of color concentrate granules produced by a process according to one of claims 1 to 6 for the production of colored molded parts from thermoplastics.