FI83843B - Mixing arrangement and method for mixing of plastic components - Google Patents

Description

83843

Mixing device and method for mixing plastic components Blandningsanordning och förfarande för blandning av plast-komponententer 5

The invention relates to an apparatus and a method for mixing plastic raw materials in a mixing apparatus. The mixing apparatus has a cylindrical mixing space with a mixing piston for shear mixing and auxiliary cylinders 10 for pumping the mixture. In the mixing method, mixing takes place alternately by pumping and shear mixing.

The apparatus and method can be used in particular for mixing small plastic batches as well as for mixing sensitive or highly reactive substances. The mixer is particularly well suited for use in adding a dopant to an electrically conductive polymer.

Various mixers in which several mixing methods are combined are already known e.g. U.S. Pat. No. 3,623,703, WO 89/00536 and U.S. Pat. No. 3,370,2075. These devices are intended to mix two reactants.

U.S. Pat. No. 3,623,703 discloses a device for mixing plastics, rubbers and the like. It has a perforated piston that mixes the ingredients as the piston is moved back and forth in the cylinder. The piston can also be rotated during mixing.

WO 89/00536 discloses an apparatus for homogenizing mixtures, which likewise has a piston-like mixing element. This homogenizer further has a cylindrical outlet 30 for the homogenized product at the opposite end of the piston rod.

U.S. Pat. No. 3,370,754 discloses an apparatus for mixing and dispersing two substances. The device has a perforated piston for mixing the substances and an auxiliary piston for adding the second component to the mixture. The device is intended for mixing two reactants, after which the reaction mixture can be metered into the desired location. Also in this device, the mixing can be enhanced by turning the mixing piston.

Mixing plastic raw materials with conventional mixers produces difficulties e.g. because plastic raw materials often behave like non-Newtonian fluids. In this case, a film is formed in the surface layers of the mixers, in which all mixing takes place while the majority of the raw material remains unmixed.

Another problem that arises in conventional equipment for mixing plastics 10 is that a relatively large batch of plastic is usually required, e.g. several kilos of raw material are needed for mixing with an extruder. This creates problems in the case of a small sample batch, mixing of a special polymer or expensive use of raw materials.

The object of the invention is to provide an apparatus and method, in particular for mixing small batches of plastic raw material. The device and method are characterized by what is stated in the claims.

The mixing device according to the invention can mix two or more components, which can be liquids or solids.

It is possible to build the mixing device according to the invention very tightly, in which case substances harmful to the working environment can be mixed in it. One group of such harmful substances is those used for doping electrically conductive plastics, 25 mm. iodine.

When the mixing device is sufficiently tight, the maintenance of pressures during the mixing and cooling phase can be controlled. If necessary, during the cooling step of the mixed plastic raw material, a compression pressure can be maintained with the mixing piston, thereby preventing the separation of gases from the plastic mixture.

The structure and surfaces of the mixing device are such that it is possible to produce corrosion-resistant raw materials such as structural ceramics or titanium.

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The mixing device according to the invention can be made from existing machines in the plastics industry with minor modifications. The body of the mixing device is formed by an injection molding machine to which the necessary accessories are attached. No major changes need to be made to the injection molding machine itself, the only required change will be its 5 control programs.

In a variation of the invention, a mixing piston or auxiliary piston is used to remove the pre-mixed material from the mixing slurry. In this case, the mixing device works like a conventional injection molding machine with a mold attached. The mixing device 10 is emptied while the plastic mixture is directed directly into the mold, so the shaping of the product takes place at the end of the mixing.

In the best embodiment of the invention, the mixing device has heating and cooling.

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The operation and advantages of the mixing device according to the invention will become apparent from the accompanying drawings and a detailed description of a preferred embodiment of the invention.

Figure 1 shows a sectional view of a device according to the invention when the parts of the device are separated.

Figure 2 shows the first mixing step.

Figure 3 shows the second mixing step.

Figure 4 shows the cooling step.

Figure 5 shows the test piece removal step.

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Figure 1 shows the mixing device 10 when its main parts, the mixing cylinder 1 and the bottom part 2, are separated. The mixing cylinder 1 has a cylindrical mixing space 11 in which a mixing piston 12 is arranged. The mixing piston 12 can move in a cylindrical mixing space 11, whereby the size of the mixing space 11 varies. In addition, 4,83843 mixing pistons 12 can be rotated. The mixing cylinder 1 may further have an opening 13 for adding the raw material 18 to be mixed.

The base part 2 has one or more auxiliary cylinders 14 with auxiliary pistons 15.

The auxiliary pistons 15 can move in the auxiliary cylinders 14 so that the volume of the auxiliary cylinders 14 varies according to the movement of the auxiliary pistons 15. The auxiliary pistons 15 may have their own means for moving them or they may have only a return spring.

Each of the main parts 1 and 2 of the mixing device 10 may have heating devices for heating and melting the substance to be mixed, most preferably electric resistors 16. Correspondingly, for cooling, there may be means, which are best piping 17 for coolant circulation.

At the same time, Fig. 1 shows a mixing step in which the raw material 18 to be mixed is added to the mixing device 10. Usually, the main parts 1 and 2 of the mixing device 10 are then already attached to each other.

In the first mixing step shown in Fig. 2, the substance 18 to be mixed is entirely in the mixing space 11. The mixing in the first stage takes place by rotating the mixing piston 12. If the substances to be mixed 18 are solid, they are melted by electric resistors 16 in the first stage.

Fig. 3 shows a second mixing step in which the substance to be mixed 18 is pumped into the auxiliary cylinders 14. This is done by pushing the mixing piston 12 into the mixing space 11. The auxiliary pistons 15 in the auxiliary cylinders 14 protrude deeper into the auxiliary cylinders 14.

Figure 4 shows the cooling step. After the required number of mixing steps shown in Figures 2 and 3 have been repeated, the mixed product 19 can be cooled by introducing a coolant into the piping 17. In this case, the mixed product 19 can be cooled under pressure and thus the separation of gases from the plastic can be prevented.

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Figure 5 shows the test piece removal step. The cooled, mixed product 19 is removed from the mixing device 10 by separating the main parts of the mixing device 10, the mixing cylinder 1 and the bottom part 2, from each other.

In one embodiment of the mixing device 10, the substance to be mixed 18 is added as a solid, e.g. in the form of granules, which are melted by means of heating devices in the mixing device 10, preferably electric resistors 16. The mixing device 10 can also be implemented without the opening 13 shown in Fig. 1. In this case, the raw material 18 to be mixed is added to the mixing space 11 with the base part 2 and the mixing cylinder 1 separated.

Correspondingly, cooling devices can be connected to the mixing device 10, e.g. channels 17 surrounding the mixing space 11 for the circulation of coolant. It is most preferred to use water as the coolant.

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There are several options for restoring the auxiliary pistons 15 in the auxiliary cylinders 14. The movements and recovery of the auxiliary pistons 15 can be controlled hydraulically.

. . Another alternative is to provide the auxiliary pistons 15 of the auxiliary cylinders 14 with a return spring, whereby the auxiliary cylinders 14 are emptied with the movements of the mixing piston 12.

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Claims (11)

Mixing device (10) for mixing plastic components, characterized in that it comprises a cylindrical mixing space (11), a mixing piston (12) rotating in the mixing space (11) and moving in its axial direction, at least one auxiliary cylinder (14) connected to the mixing space (11), the mixing piston (12) pushes the mixture, and the auxiliary piston (15) moving in each auxiliary cylinder (14) to return the mixture to the mixing space (11). Mixing device according to Claim 1, characterized in that the mixing device (10) has means (16) for heating the substance (18) to be mixed. Mixing device according to Claim 1 or 2, characterized in that the mixing device (10) has channels (17) for circulating the liquid to cool or heat the substance to be mixed. Mixing device according to one of the preceding claims 1 to 3, characterized in that the movement of the auxiliary pistons (15) of the auxiliary cylinders (14) is controlled hydraulically or by a spring for emptying the auxiliary cylinders (14). Mixing device according to one of the preceding claims 1 to 4, characterized in that the mixing device (10) is sealed in order to control the escape of harmful substances. 25 Mixing device according to one of the preceding claims 1 to 5, characterized in that construction ceramic is used as the raw material for the mixing device (10). 6 83843 Mixing device according to one of the preceding claims 1 to 6, characterized in that the mixing cylinder (1) and the base part (2) of the mixing device (10) are fastened to the table of the injection molding machine. 8. A method for mixing plastic rolls using two different mixing methods, characterized in that shear mixing is used in the first mixing step and pumping mixing in the second mixing step. A method according to claim 8, characterized in that in the first shear mixing step the rotating mixing piston (12) mixes the polymer blend and in the second pumping mixing step the rotating mixing piston (12) pushes the mixture into the auxiliary cylinders (14), after which the auxiliary pistons (14) 15) push the mixture back into the mixing space (11). Method according to Claim 8 or 9, characterized in that it comprises a plurality of successive cutting and pumping mixing steps. Method according to one of Claims 8 to 10, characterized in that it comprises first a heating step and finally a cooling step. 15 8 83843