EP1244735A1

EP1244735A1 - Production of thermoplastic molding compounds using magnesium oxide

Info

Publication number: EP1244735A1
Application number: EP00985191A
Authority: EP
Inventors: Peter Ittemann; Rainer Theysohn
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1999-12-23
Filing date: 2000-12-18
Publication date: 2002-10-02
Also published as: US20020190425A1; DE19962570A1; KR20020063262A; WO2001048070A1

Abstract

The invention relates to a method for processing plastic materials of the acrylnitril-butadiene-styrene type (ABS) or the acrylnitril-styrene-acrylic ester type (ASA) by extrusion and/or injection molding. The inventive method is characterized in that a magnesium oxide that has a citric acid number of < 1500 sec, preferably of < 800 sec is used as an additive during extrusion and/or injection molding. The inventive method allows reduction of plaque-formation during the processing of the above-mentioned plastic materials to a minimum. The quality of the molded articles obtained is improved and any processes required for cleaning the processing machines used are substantially reduced.

Description

Production of thermoplastic molding compositions using

magnesia

The present invention relates to the field of plastics processing. More specifically, the present invention relates to a method in which magnesium oxide of a certain quality is used in the extrusion and injection molding of ABS and ASA plastic parts to prevent deposits. The invention also relates to thermoplastic molded parts which can be obtained by this process.

The production of molded parts for many thermoplastics is often done by so-called extrusion or injection molding. Frequently, both steps are used in succession, with the extrusion resulting in a granulate which is used in the subsequent injection molding in order to obtain a molded part. Both methods have in common that they involve melting the plastics and pressing out the melt obtained through nozzles.

In the case of practically all plastics, partial decomposition is observed as a result of processing at high temperatures and the application of pressure during the extrusion process from the extrusion or injection molding device. This is also the case with plastics of the type ABS (acrylonitrile-butadiene-styrene) and ASA (acrylonitrile-styrene-acrylic ester), and with one reason for the occurrence of so-called molding. In addition to the decomposition products, this mold covering also contains oligomers and polymers of the ones used Educt monomers, which are in the plastic, as well as other outgassing components. On the one hand, this mold coating accumulates in the mold itself, in the nozzles and in the degassing openings and thus interferes with the shaping and the extrusion process.

On the other hand, deposits often appear on the molded components themselves. These often interfere due to the dark color, furthermore the molded covering with oily consistency often proves to be annoying when printing, gluing and electroplating. The result is a loss of quality of the molded components.

To remove the mold covering, the production process must be interrupted after a certain extrusion length or number of injection molding processes in order to mechanically clean the mold, the nozzles and the degassing ducts. This causes machine downtime and production downtime, and the cleaning process also ties up labor. Furthermore, a certain percentage of the molded parts obtained must also be discarded, which is of course undesirable.

It would therefore be desirable to be able to carry out the extrusion and injection molding in such a way that only a slight formation of mold deposits occurs. The object of the present invention is therefore to provide a method which makes it possible to suppress or even prevent this formation of mold deposits when processing ABS and ASA in the described methods.

This object is achieved by a method of processing by extrusion and / or injection molding of plastics of the acrylonitrile-butadiene-styrene (ABS) and of the acrylonitrile-styrene-acrylic ester (ASA) type, characterized in that a magnesium oxide which has a citric acid number of <1,500 seconds, is used as an additive in extrusion and / or injection molding. It has been found that the use of magnesium oxide can greatly reduce or even suppress the formation of mold deposits and oily deposits. The apparatus can be cleaned at much greater intervals, and significantly fewer molded parts have to be discarded.

Magnesium oxide which can be used according to the present invention must have a certain activity against acids. More specifically, the magnesium oxide must have basic groups that are available within a certain time to neutralize acids. Although the mode of action of the magnesium oxide is not exactly known in the present invention, it can be said that the basic properties of the magnesium oxide mentioned are crucial.

The basic properties are expressed by the so-called citric acid number. This test measures the time after which a given amount of citric acid is neutralized by a given amount of magnesium oxide. For this purpose, an amount of 2.6 g of citric acid is dissolved in 100 ml of water and added together with 0.01 g of phenolphthalein to a stirred dispersion of 1.7 g of magnesium oxide in 100 ml of water at once. The time it takes for the color of the phenolphthalein to change from colorless to pink is measured. The shorter the time, the easier the basic groups for neutralizing acids are available. The test described is thus a measure of the availability of basic groups on the water-wettable surface of the magnesium oxide.

Good results in connection with the present invention were achieved with magnesium oxide qualities which have a citric acid number of <1,500 seconds. Better results could be achieved with magnesium oxide qualities with a citric acid number of <800 seconds, whereby the best results could be achieved with magnesium oxide with a citric acid number of <600 seconds. A magnesium oxide of the qualities described can be achieved, for example, by firing the magnesium oxide below certain temperatures. Magnesium oxide, which was fired at temperatures below 900 ° C., generally has an activity which is described by a citric acid number of <1,500 seconds. When firing at temperatures <750 ° C, citric acid numbers of <800 sec are reached, and if the firing process is carried out at even lower temperatures, an oxide of even higher activity can be produced. Magnesium oxide with a citric acid number <600 sec can be obtained by firing at temperatures <700 ° C.

For the reasons set out above, magnesium oxide which has been fired at temperatures <900 ° C., preferably <750 ° C., is generally used in the present invention. Even better results were achieved with magnesium oxide, which was fired at temperatures of <700 ° C.

The amount of magnesium oxide used is 0.02-10% by weight, preferably 0.05-5% by weight and most preferably 0.1-1% by weight, based on the amount of plastic used.

The use of magnesium oxide with the properties described above makes it possible to avoid the formation of mold deposits during the extrusion and injection molding of ABS and ASA. On the one hand, a significantly lower formation of mold deposits in the mold, the nozzles and the degassing openings is observed. On the other hand, less oily coating occurs on the molded parts, of which only a small part therefore has to be discarded. Adhesiveness, printability and galvanizability are also improved. It is advantageous to use a fine-particle magnesium oxide, since plastic parts can be obtained which have good mechanical properties. This can be determined by determining the impact strength. Good results regarding the impact strength could be achieved if magnesium oxide with a grain size was used in which 90% of all particles have a diameter of <30 μm (d90 <30 μm). Better results were obtained with a magnesium oxide with a grain size d90 <15 μm, and the best results were obtained with a magnesium oxide with a grain size d90 <8 μm.

Plastics in which the described use of magnesium oxide gives the positive results described are copolymers of styrene, namely plastics of the acrylonitrile-butadiene-styrene (ABS) type and of the arylnitrile-styrene-acrylic ester (ASA) type. In connection with the present invention, ABS plastics are understood to mean those plastics which are specified in the draft for the European standard ISO 2580-1. These are styrene / acrylonitrile copolymers with a continuous phase based on copolymers of styrene / alkyl-substituted styrene and acrylonitrile and a disperse elastomeric phase, predominantly based on butadiene, admixtures of other new components may be present. These other components can be monomers or polymers of compounds other than acrylonitrile, butadiene and substituted or unsubstituted styrene, these new components not being present in more than 30% by weight. If the new component is a polymer, it is dispersed in a matrix made of a styrene-acrylonitrile copolymer. Monomers that may be present are acrylic esters, butadiene, maleic anhydride and other anhydrides, and N-phenyl maleic esters and other maleic esters.

In connection with the present invention, ASA plastics are understood to mean those plastics which are specified in the draft for the European standard ISO 6402-1. ASA is a plastic with a continuous phase based essentially on a styrene-acrylonitrile copolymer and a disperse elastomer phase based mainly on acrylic esters. There may be other new components. If these are monomers other than acrylonitrile, substituted or unsubstituted styrene or acrylic esters, they are in a weight amount of no more than 30% available. If these are polymers, they are not present in an amount by weight of not more than 15% based on acrylonitrile, substituted or unsubstituted styrene or acrylic ester. Furthermore, these polymers are dispersed in a matrix made of a stryol-acrylonitrile copolymer. The monomers mentioned above are acrylic esters, butadiene, maleic anhydride and other anhydrides, or N-phenyl-maleic acid esters and other maleic acid esters.

The method according to the invention can be used in the production of all thermoplastic plastic bodies and plastic parts made of ABS or ASA, which are produced by extrusion or injection molding. Such extruded or injection molded parts are known to a person skilled in the art, and it is not possible within the scope of the present application to list them exhaustively and comprehensively. It includes extruded granulate, semi-finished products and extruded finished parts as well as moldings, plates and profiles that can be produced by extrusion or injection molding. These plastic bodies and plastic parts obtainable by extrusion and / or injection molding according to the method of the present invention are a further subject of the invention.

Particularly preferred molded parts that can be produced by the process according to the invention are injection-molded chip cards and game components, housings for electrical and electronic parts, for example kitchen machines, shavers, telephones, vacuum cleaners, monitor housings, keyboards, electric lawn mowers, toy trains, washing machines, dishwashers, refrigerators , Parts for the interior of motor vehicles, for example center consoles, door side panels, speedometer housings, fan nozzles, buttons and switches and for outdoor use on motor vehicles, for example hub caps, exterior mirrors (colored, painted or galvanized), galvanized emblems, radiator grills, spoilers. The present invention is now explained in more detail in the following examples.

In the following Examples 1-8 while an ABS polymer was the quality Terluran ^®, KR2876 / 1 (manufacturer: BASF AG) mixed with the appropriate amount of additive and extruded on a twin-screw extruder ZSK 30 at 250 ° C and from the obtained strands a granulate made. The granules thus obtained were placed in an injection molding machine where, after melting, they were injected into a tie-rod weld mold. In such a form, the injection molding of a tension rod takes place from the two sides of the head. This ensures that both melting fronts meet in the middle and form a weld line. Since no degassing openings are provided, mold deposits easily appear in the vicinity of the weld line, which allow the formation of mold deposits to be assessed after a short time. After 350 shots, the mold was disassembled and the formation of mold deposits was assessed.

Example 1 (comparative example)

Terluran ^® KR2876 / 1 white was injected in the injection molding machine described above under the conditions described without the addition of additives. The formation of a hard mold covering with a brown edge could be observed.

Example 2 (comparative example)

Terluran ^® KR2876 / 1 white was first extruded without the addition of MgO and the granules obtained were processed as described in Example 1. The formation of a mold deposit in the same amount and with the same appearance as in Example 1 was again observed.

Example 3 (comparative example) The procedure was as described in Example 2, but using 0.5% by weight of dehydrotalcite of the formula [Mg4.5Al ₂ (OH) ₁₃ ] ²⁺ [(CO ₃ ^{2 "} ) ₃ • 5H ₂ O] ^2" Kyowa Chemical Industry Company were added. Compared to Example 2, the amount of molding was reduced, but a brown border was still visible.

Example 4 (comparative example)

The procedure was as described in Example 2, with 0.5% by weight CaCO ₃ having a particle size d85 <50 μm being added. After the injection molding, the formation of a coating was observed which was identical in quantity and appearance to that obtained in Example 2.

Example 5 (comparative example)

The procedure was as described in Example 2, with 0.5% by weight of ZnO having a particle size d85 <5 μm being added. Compared to example 2, the amount of the topping could be reduced, but a brown edge still appeared.

Example 6

The procedure was as described in Example 2, but using 0.5% by weight of MgO. This had a grain size of d50 approx. 2.0 μm and d90 approx. 7.7 μm and had been fired at 700 ° C. After the injection molding process, it was found that the amount of molding had been significantly reduced compared to Example 2, and a brown edge could no longer be found. The material thus obtained had an impact strength according to ISO 179/1 eA of 23.3 KJ / m ² . Example 7

The procedure was as described in Example 6, the grain size of the MgO used being d50 approx. 4.0 μm and d90 approx. 15 μm. After the injection molding process, it was again found that the amount of mold coating had been reduced in comparison to Example 2 and that there was no longer a brown edge. The impact strength of the material according to ISO 179 / leA was 19.8 KJ / m ² .

Example 8

The procedure was as described in Example 6, the MgO used having been fired at 1200 ° C. and having a grain size of d50 of approximately 5 μm. Compared to Example 2, a reduction in the mold deposit was found, but the formation of a brown edge was still observed.

Example 9 (comparative example)

ABS granules of the quality Terluran ^® EGP-7 (manufacturer: BASF AG) were turned into tubes on an extruder ZSK 40 with tube tool

Outside diameter of 21.4 mm and 2.0 mm wall thickness extruded. During a running time of approx. 30 minutes, a black, oily coating built up on the upper edge of the ring nozzle. This was extruded from time to time

Torn pipe and led to dark streaks on the top of this pipe. The contaminated pipe sections had to be discarded. A cleaning of the

Nozzle was not possible without damaging the soft, melt-like surface of the tube. It was also not possible to detach the covering without damaging the pipe, there were visible streaks and streaks on the surface

Pipe on. The effect described is particularly disadvantageous in the case of tubes with a small diameter which are wound up after extrusion and which require large run lengths. Example 10

The procedure was as described in Example 9. However, 0.3% by weight of MgO which had been fired at 700 ° C. was added to the granules to be extruded. The grain size of this MgO was d50 approx. 2.0 μm and d90 approx. 7.7 μm.

After intensive mixing of the powder with the granulate, this was in the

ZSK 40 extruder processed. After a running time of 30 minutes, it was found that only a barely visible coating had built up at the upper edge of the ring nozzle. However, the amount was so small that this coating did not extrude from it

Pipe was carried away. The tube obtained was in perfect condition

Surface quality.

Claims

claims

1. A method of processing by extrusion and / or injection molding of plastics of the acrylonitrile-butadiene-styrene (ABS) or of the acrylonitrile-styrene-acrylic ester (ASA) type, characterized in that a magnesium oxide which has a citric acid number of <1,500 sec. preferably <800 sec, most preferably <600 sec, is used as an additive in extrusion and / or injection molding.

2. The method according to claim 1, characterized in that the magnesium oxide has been fired at a temperature of <900 ° C, preferably <750 ° C, most preferably <700 ° C.

3. The method according to claim 1 or 2, characterized in that the grain size of the magnesium oxide at values of d90 <30 microns, preferably d90 <15 microns, most preferably d90 <8 microns.

4. ABS or ASA plastic body or plastic part, can be produced by the method according to any one of claims 1 to 3 and containing one

Magnesium oxide as set out in one of these claims.

5. Plastic body according to claim 4 in the form of granules

6. Plastic part according to claim 4 in the form of a thermoplastic molding.

7. Thermoplastic molded part according to claim 6, in the form of an extruded semi-finished product or an extruded finished part, in particular a plate, a profile or a shaped body.

8. Thermoplastic molded part according to claim 6 in the form of an injection molded part.

, Injection molded part according to claim 8, in the form of a chip card or a game component.

10. Injection molded part according to claim 8, in the form of an electrical or electronic part, a motor vehicle interior part or a part for outdoor use on motor vehicles.