DE29923183U1 - Device for processing plastics - Google Patents

Description

M-W G 1051 A - 1 -

Device for processing of plastics

The invention relates to a device for processing plastics (plastics processing machine = KVM) or for producing plastic products from granular plastic raw material, in which the plastic raw material is converted from the solid granular state into the melt-flowing phase by the action of heat in a melting unit and is then formed into a finished plastic product in a closed product mold.

In the blow molding process, the granular plastic raw material is conveyed from a storage hopper via a feed line into an extruder (e.g. screw extruder) and there is converted from the solid phase into the melt-flowing phase under the influence of heat. Following the extruder, the melt-flowing plastic is brought into a hollow cylindrical shape in a circumferential distributor (e.g. spiral channel distributor) and pressed out of an adjustable ring nozzle as a tubular preform between the open halves of a blow mold. In the closed blow mold, the tubular preform is then usually blown into the finished product (e.g. bung barrel) using compressed air or another blowing medium and cooled until the finished product has sufficient dimensional stability and can be removed from the blow mold without affecting the geometric dimensions. Blow-molded plastic containers are usually cooled in a post-cooling device until the thick spots caused by the process (pinch welds, bung sockets) have completely cooled down.

In the injection molding process, the molten plastic is injected from the extruder into a negative mold under high pressure and after the plastic melt has cooled sufficiently, the finished product is removed from the injection mold.

In contrast, in the rotational molding process, the plastic granulate is filled into a heated rotating hollow mold and is deposited in a molten state on the inner wall of the hollow mold. After the hollow mold has cooled and the molten plastic has solidified or cooled, the finished product is removed from the opened mold. In this case, the heatable/coolable hollow mold is simultaneously a melting unit and a molding device. The invention is based on the knowledge that by heating the molten plastic,

Unstabilized plastic material that has been converted to a liquid or molten phase can react with oxygen molecules from the ambient air and, depending on the type of plastic material, more or fewer oxygen molecules can be deposited and bound. This has been found particularly in the case of high-purity, i.e. stabilizer-free, high-molecular HD-PE plastics (high density polyethylene such as Lupolen 4261 A, stabilizer-free) with highly branched molecular chains. However, the high-purity, stabilizer-free, high-molecular HD-PE plastics are of great interest in the manufacture of containers for storing and transporting expensive chemicals, particularly liquid, high-purity chemicals for the electronics industry.

It is an object of the present invention to provide a device for processing unstabilized polyethylene (PE) for the production of plastic products, in particular of sealable plastic hollow bodies (e.g. bung drums), which are preferably intended or can be used for quality-preserving storage and transport of high-purity chemicals (EC chemicals) that are extremely sensitive to any type of smallest contamination for the electronics industry (e.g. for chip production).

This object is achieved according to the features of patent claim 1. In the device according to the invention for producing plastic products from granular plastic raw material, the plastic raw material is converted from the cold granular state into the molten phase by the action of heat in a plastic melting unit, e.g. in an extruder, and is then formed into a finished plastic product in a closed product mold. In this case, the still cold granular plastic raw material is fed in and/or the granular plastic raw material is converted into the molten phase under an oxygen-free or almost oxygen-free inert gas atmosphere, preferably under a nitrogen atmosphere. This measure of displacing oxygen from the air by means of nitrogen shielding prevents oxidative damage to the unstabilized plastic material (disturbances in the lattice structures, knot formation, O2 deposition on the plastic molecular chains) when the granulate is drawn into the extruder screw and the heating that occurs during phase transformation (crystalline-amorphous).
The invention provides that the shaping and simultaneous cooling of the plastic product in the product mold (e.g. blow mold) also takes place under oxygen-free or almost oxygen-free inert gas atmosphere, ie,

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that an inert gas, preferably gaseous nitrogen, is used as the blowing medium, rather than air. This prevents the plastic from possibly entering into chemical reactions with the oxygen molecules in the blowing air when it is hot. Many processes are known from European patent EP 0 664 742 B1 and the prior art described at the beginning therein that use cold nitrogen or nitrogen-enriched or thus cooled air as the blowing medium; however, the purpose of all of these known processes is exclusively to shorten cycle times by accelerating the cooling of the blown plastic product. Shielding the hot plastic molecules against atmospheric oxygen in the heating phase is not previously known from this.
Preferably, the stabilizer-free HD-PE is a polyethylene with a specific density in a range from 0.940 to 0.970 g/cm ³ , in particular from 0.942 to 0.961 g/cm ³ , particularly preferably from 0.946 to 0.960 g/cm ³ , which in contact with the filling material, namely high-purity, liquid chemicals for the electronics industry (e.g. for microchip production), generates particularly small amounts of particles or releases them as contaminants.

In a further preferred embodiment, the stabilizer-free HD-PE is a polyethylene with a specific density in a range from 0.940 to 0.970 g/cm ³ , in particular from 0.942 to 0.961 g/cm ³ , particularly preferably from 0.946 to 0.960 g/cm ³ , which releases at most one of the following ionic impurities in contact with basic, neutral or acidic, high-purity chemicals:

Al = 60 ng/g, Ca = 60 ng/g, Fe = 63 ng/g, Mg = 16 ng/g,

Ti = 4 ng/g, Zn = 6 ng/g, Mn = 0.3 ng/g, Cu = 1.5 ng/g.

The unstabilized HD-PEs are also characterized by an extremely low content of catalyst residues, which means that these materials release particularly small amounts of ionic impurities when in contact with both basic and acidic, high-purity chemicals. In addition, comparatively few particles are formed by any interaction between the chemicals to be stored or transported and the material. The particle content preferably remains below the following limits:

Particles with a size < = 0.5 pm : content max. 5/ml liquid,

Particles with a size < = 0.2 μηι: content max. 50/ml liquid,

Particles with a size < = 0.1 pm: content max. 500/ml liquid.

Particularly preferred for the manufacture of the containers is HD-PE, which

sold under the brand name Lupolen® 6021 D or HD-PE, which is offered under the brand name Lupolen® 4261AQ149. This material is of sufficient purity to be used in containers for high-purity chemicals. In addition, this material is easy to extrude and process using blow molding technology.

Furthermore, the plastic used to manufacture the container can consist of an HD-PE from the group Lupolen® 5261 D ₁ Lupolen® 4261AQ135, Hostalen® GM6255, Fina® 56020, Borealis® 8214, Stamylan® 7731, Stamylan® 7890 or Daplen® AH 5493 or comprise a mixture of two or more of the HD-PE's of this group.

In an embodiment of the invention, the plastic product is designed as a sealable hollow body, wherein the inert gas atmosphere from the shaping phase is contained in the hollow body and remains enclosed therein at least until the hollow body has finally cooled down.

In the manufacturing process, the inert gas heated up during the shaping and/or cooling of the plastic product is advantageously subsequently used to inertize the still cold granular plastic raw material.
In a preferred embodiment of the invention, pure or almost pure gaseous nitrogen is used as the inert gas, with the gaseous nitrogen being conveniently generated on site by means of a nitrogen generator (N2 unit) that is directly connected to the plastic processing machine. In order to ensure optimum process control, the state variables of oxygen content, temperature, pressure and flow rate of the inert gas are measured by means of sensors (= probes) or corresponding measuring devices and these measured values are used as control variables for process control.

The device or plastic processing machine (= KVM) for producing plastic products from granular plastic raw material, in which the plastic raw material is converted from the solid granular state into the molten phase in a melting unit by the action of heat and is then formed into a finished plastic product in a closed product mold, differs according to the invention from the known prior art in that the storage hopper or the feed line for conveying the cold granular plastic raw material into the plastic melting unit (= extruder in blow molding or injection molding or product mold in rotational molding) is provided with an inlet line for a gaseous inert medium, preferably nitrogen N2, through which the inert gas is introduced and protects the plastic material to be processed from oxidation damage.

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The invention is explained and described in more detail below with reference to embodiments shown in the drawings. They show:

Figure 1 shows a blow moulding machine according to the invention in side view,
Figure 2 is a schematic partial sectional view of a blow molding machine according to the invention,

Figure 3 shows a bung drum manufactured according to the method according to the invention,
Figure 4 shows a reusable container produced according to the method according to the invention,

Figure 5 shows a method according to the invention for a pallet container
manufactured plastic inner container and
Figure 6 the pallet container with the plastic inner container like Fig. 5

In Figure 1, in the blow molding machine shown, reference number 1 designates a circumferential distributor with an annular extrusion nozzle for extruding a tubular preform. An extruder 2 with a raw material hopper 3 on the input side is connected to the circumferential distributor 1. In the lower area of the blow molding machine there is a hydraulic unit 4 for operating the horizontally movable holder 6 for the two blow mold halves, which is enclosed by a protective grid 5.

The essential functional elements of the blow molding machine according to the invention with a schematic representation of the plastic material flow are shown in Figure 2. The granular plastic raw material 10 is conveyed from the storage hopper 12 into the screw extruder 14 and is converted there from the solid to the melt-flowing state partly by supplied electrical heat energy and partly by internal frictional heat. The melt-flowing plastic strand emerging from the extruder 14 is brought to a hollow cylindrical material shape in the circumferential distributor 16 and extruded through an adjustable annular extrusion nozzle 18 as a tubular preform 20 between the horizontally movable, open blow mold halves 22. A nitrogen generator 24 (N2 unit) is shown to the side next to the blow mold halves, in which pure nitrogen is generated by air splitting. It is shown schematically that the nitrogen generator 24 is connected to the storage hopper 12 via a connecting line 26. The connecting line 26 is guided through a gas filter 44, in which any particles are filtered out. Furthermore, a connecting line 28 leads to the blowing mandrel 30 and a connecting line 32 through the nozzle core 34 to the extrusion nozzle 18. These connecting lines 28, 32 are also connected via a corresponding

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appropriate gas filter. Gaseous nitrogen N2 is introduced into the storage hopper 12 via the connecting line 26 to render the plastic granulate 10 inert. When the tubular preform 20 is pressed out of the extrusion nozzle 18, gaseous nitrogen is passed through the nozzle core 34 via the connecting line 32 and flushes the interior of the preform 20 and prevents atmospheric oxygen from reaching the hot plastic material. As soon as the beginning of the tube approaches the blowing mandrel 30, gaseous nitrogen can also be blown into the interior of the tube for flushing purposes. After the blow mold halves are closed, the tubular preform 20 is blown into the finished product shape via the blowing mandrel and/or the connecting line 32 with a pressurized blowing medium, preferably gaseous nitrogen (e.g. from a pressure vessel not shown in the drawing). The ingress of air from the outside into the tubular preform or the extruded hot plastic material is not critical, since possible O2 molecule deposits there cannot have any adverse effects on the high-purity filling material later contained in the finished blown hollow body.
Other important design features are that

the inlet line for introducing gaseous inert gas into the storage hopper or into the feed line for conveying the cold granular plastic raw material is connected to an inlet line for introducing gaseous inert gas into the product mold;

the inlet line for introducing gaseous inert gas into the storage hopper or into the feed line and/or the inlet line (e.g. blow mandrel) for introducing gaseous inert gas into the product mold is connected to a nitrogen generator (N2 unit);

the inlet line for introducing gaseous inert gas into the storage hopper or into the feed line and/or the inlet line (e.g. blow mandrel) for introducing gaseous inert gas into the product mold is/are equipped with measuring sensors (= probes) for determining the state variables oxygen content, temperature, pressure and flow rate of the inert gas, and these measured state values are used as control variables for controlling the process sequence;

the plastic processing machine is designed as a blow molding machine with movable blow mold halves for shaping the molten plastic material and with at least one extruder as a melting unit, in which the plastic raw material can be converted from the solid granular state into the molten phase by the action of heat.
The following drawings show preferred products that

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are manufactured using the process according to the invention with nitrogen shielding. Figure 3 shows a 220 litre bung drum which was manufactured in one piece and in one layer from Lupolen 4261 A without stabilizer.

Figure 4 shows a manually manipulable 50 litre reusable barrel made from high-purity HD-PE material.
Figure 5 shows a partially sectioned side view of the blow-molded inner container for a pallet container, as shown, for example, in Figure 6 .

In one embodiment, the containers according to the invention are made in one piece and in one layer from high molecular weight, stabilizer-free and low catalyst residue polyethylene (HD-PE). In another embodiment, the containers according to the invention are made from two or more layers using a co-extrusion process, with only the innermost layer then consisting of high-purity HD-PE.

These containers manufactured from the special plastic materials mentioned according to the process of the invention are all suitable for use with high-purity liquid chemicals for the electronics industry.

MW G 1051 A -8-

Reference number list

1 Circumferential distributor 2 Extruders 3 Raw material funnel 4 Hydraulic station 5 Protective grille 6 Blow mold holder 7 Removal device 10 K'stoff raw material 12 Storage hopper 14 Screw extruder 16 Circumferential distributor 18 Extrusion nozzle 20 hoses. Preform 22 Blow mold half 24 N2 generator 26 N2 connecting line 24-12 28 N2 connecting line 24-30 30 Blow mandrel 32 N2 connecting line 24-34 34 Nozzle core 36 220 litre bung barrel 38 50 litre reusable keg 40 K'stoff inner container 42 1000 litre pallet container 44 Gas filter

Claims (18)

1. Plastics processing machine (= KVM) for producing plastic products from granular plastic raw material, in which the plastic raw material is converted from the solid granular state into the molten phase in a melting unit by the action of heat and is then formed into a finished plastic product in a closed product mold, characterized in that the storage hopper (3) or the feed line for conveying the cold granular plastic raw material into the plastics melting unit (= extruder in blow molding or injection molding or product mold in the rotational molding process) (2) is provided with an inlet line (26) for gaseous inert gas, preferably N ₂ . 2. Plastic processing machine according to claim 1, characterized in that the inlet line (26) for introducing gaseous inert gas into the storage hopper (3) or into the feed line for conveying the cold granular plastic raw material is connected to an inlet line (28, 32) for introducing gaseous inert gas into the product mold (22). 3. Plastic processing machine according to claim 1 or 2, characterized in that the inlet line (26) for introducing gaseous inert gas into the storage hopper (3) or into the feed line and/or the inlet line (28, 32) for introducing gaseous inert gas (e.g. via the blow mandrel 30) into the product mold (22) is connected to a nitrogen generator (24) (N ₂ unit). 4. Plastic processing machine according to claim 1, 2 or 3, characterized in that the inlet line (26) for introducing gaseous inert gas into the storage hopper (3) or into the feed line and/or the inlet line (28, 32) for introducing gaseous inert gas into the product mold (22) is/are equipped with measuring sensors (= probes) for determining the state variables oxygen content, temperature, pressure and flow rate of the inert gas. 5. Plastic processing machine according to claims 1, 2, 3 or 4, characterized by a design as a blow molding machine with movable blow mold halves (22) for shaping the molten plastic material and with at least one extruder (2) as a melting unit, in which the plastic raw material can be converted from the solid granular state into the molten phase by the action of heat. 6. Plastic container, made in one piece and in one layer from high molecular weight, high purity, stabilizer-free polyethylene (HD-PE), preferably from Lupolen 4261 A stabilizer-free or comparably pure plastic material on a plastic processing machine according to at least one of the preceding claims 1 to 5, characterized in that the polyethylene (HD-PE) is free of damaged lattice structures (oligomers) after the processing process and can be used for the use (= storage and transport) of highly sensitive filling goods such as CE chemicals for the electronics industry. 7. Plastic container, one-piece, but multi-layered consisting of at least two or more coextruded layers, in which at least the inner layer comprises a high molecular weight, high purity, stabilizer-free polyethylene (HD-PE), preferably Lupolen 4261 A stabilizer-free or comparably pure plastic material, the container being produced on a blow molding machine according to at least one of the preceding claims 1 to 6, characterized in that the polyethylene (HD-PE) of the inner layer is free of damaged lattice structures (oligomers) after the processing process, and the container can be used for use (= storage and transport) of highly sensitive filling goods such as CE chemicals for the electronics industry. 8. Plastic container made from granular plastic raw material on a blow molding system according to at least one of the preceding claims 1 to 7, characterized in that the plastic raw material is a stabilizer-free polyethylene (HD-PE) with a specific density in a range from 0.940 to 0.970 g/cm ³ , in particular from 0.942 to 0.961 g/cm ³ , particularly preferably from 0.946 to 0.960 g/cm ³ , which, in contact with basic, neutral or acidic, high-purity chemicals (EC chemicals) for the electronics industry, releases at most one of the following ionic contaminants up to an upper limit as follows:
Al = 60 ng/g, Ca = 60 ng/g, Fe = 63 ng/g, Mg = 16 ng/g,
Ti = 4 ng/g, Zn = 6 ng/g, Mn = 0.3 ng/g, Cu = 1.5 ng/g. 9. Plastic container according to claim 8, characterized in that the plastic material has an extremely low content of catalyst residues such that this material releases particularly small amounts of ionic impurities in contact with neutral, basic and/or acidic, high-purity chemicals (EC chemicals), with comparatively few particles being formed by any interaction between the chemicals to be stored or transported and the material, and with the content of particles of different sizes formed remaining below the following limit values:
Particles with a size < = 0.5 µm: content max. 5/ml liquid,
Particles with a size < = 0.2 µm: content max. 50/ml liquid,
Particles with a size < = 0.1 µm: content max. 500/ml liquid. 10. Plastic processing machine (= KVM) for producing plastic products from granular plastic raw material, in which the plastic raw material is converted from the solid granular state into the molten phase in a melting unit by the action of heat and is then formed into a finished plastic product in a closed product mold, characterized in that the storage hopper (3) or the feed line for conveying the cold granular plastic raw material into the plastic melting unit (= extruder in blow molding or injection molding or product mold in the rotational molding process) (2) is provided with an inlet line (26) for gaseous inert gas, preferably N ₂ . 11. Plastic processing machine according to claim 10, characterized in that the inlet line (26) for introducing gaseous inert gas into the storage hopper (3) or into the feed line for conveying the cold granular plastic raw material is connected to an inlet line (28, 32) for introducing gaseous inert gas into the product mold (22). 12. Plastic processing machine according to claim 9 or 11, characterized in that the inlet line (26) for introducing gaseous inert gas into the storage hopper (3) or into the feed line and/or the inlet line (28, 32) for introducing gaseous inert gas (e.g. via the blow mandrel 30) into the product mold (22) is connected to a nitrogen generator (24) (N ₂ unit). 13. Plastic processing machine according to claim 9, 10, 11 or 12, characterized in that the inlet line (26) for introducing gaseous inert gas into the storage hopper (3) or into the feed line and/or the inlet line (28, 32) for introducing gaseous inert gas into the product mold (22) is/are equipped with measuring sensors (= probes) for determining the state variables oxygen content, temperature, pressure and flow rate of the inert gas. 14. Plastic processing machine according to at least one of the preceding claims 9 to 13, characterized by a design as a blow molding machine with movable blow mold halves (22) for shaping the molten plastic material and with at least one extruder (2) as a melting unit, in which the plastic raw material can be converted from the solid granular state into the molten phase by the action of heat. 15. Plastic container, made in one piece and in one layer from high molecular weight, high purity, stabilizer-free polyethylene (HD-PE), preferably from Lupolen 4261 A stabilizer-free or comparably pure plastic material according to at least one of the preceding process claims 1 to 9 on a plastic processing machine according to at least one of the preceding claims 10 to 14, characterized in that the polyethylene (HD-PE) is free of damaged lattice structures (oligomers) after the processing process and can be used for the use (= storage and transport) of highly sensitive filling goods such as CE chemicals for the electronics industry. 16. Plastic container, one-piece but multi-layered, consisting of at least two or more coextruded layers, in which at least the inner layer comprises a high molecular weight, high purity, stabilizer-free polyethylene (HD-PE), preferably Lupolen 4261 A stabilizer-free or comparably pure plastic material, the container being produced according to at least one of the preceding process claims 1 to 9 on a blow molding machine according to at least one of the preceding claims 10 to 14, characterized in that the polyethylene (HD-PE) of the inner layer is free of damaged lattice structures (oligomers) after the processing process, and the container can be used for use (= storage and transport) of highly sensitive filling goods such as CE chemicals for the electronics industry. 17. Plastic container made from granular plastic raw material according to at least one of the preceding process claims 1 to 9 on a blow molding system according to at least one of the preceding claims 10 to 14, characterized in that the plastic raw material is a stabilizer-free polyethylene (HD-PE) with a specific density in a range from 0.940 to 0.970 g/cm ³ , in particular from 0.942 to 0.961 g/cm ³ , particularly preferably from 0.946 to 0.960 g/cm ³ , which, in contact with basic, neutral or acidic, high-purity chemicals (EC chemicals) for the electronics industry, releases at most one of the following ionic contaminants up to an upper limit as follows:
Al = 60 ng/g, Ca = 60 ng/g, Fe = 63 ng/g, Mg = 16 ng/g,
Ti = 4 ng/g, Zn = 6 ng/g, Mn = 0.3 ng/g, Cu = 1.5 ng/g. 18. Plastic container according to claim 17, characterized in that the plastic material has an extremely low content of catalyst residues such that particularly small amounts of ionic impurities are released from this material both in contact with neutral, basic and/or acidic, high-purity chemicals (EC chemicals), with comparatively few particles being formed by any interaction between the chemicals to be stored or transported and the material, and with the content of particles of different sizes formed remaining below the following limit values:
Particles with a size < = 0.5 µm: content max. 5/ml liquid,
Particles with a size < = 0.2 µm: content max. 50/ml liquid,
Particles with a size < = 0.1 µm: content max. 500/ml liquid.