EP2559620B1 - Method for packaging polycrystalline silicon - Google Patents

Description

The invention relates to a method for packaging polycrystalline silicon.

Polycrystalline silicon (polysilicon) is predominantly deposited by means of the Siemens process from halosilanes such as trichlorosilane and then comminuted as little as possible in contamination into polycrystalline silicon fragments.

For applications in the semiconductor and solar industries, the least possible contaminated polysilicon fraction is desired. Therefore, the material should also be packed with low contamination before it is transported to the customer.

Typically, polysilicon fracture for the electronics industry is in 5 kg bags with a weight tolerance of +/- max. 50 g packed. For the solar industry polysilicon breakage is in bags with a weight of 10 kg and a weight tolerance of +/- max. 100 g usual.

Tubular bag machines, which are in principle suitable for packaging of silicon fracture, are commercially available. A corresponding packaging machine is for example in DE 36 40 520 A1 described.

When Polysiliciumbruch is a sharp-edged, non-free-flowing bulk material with a weight of each Si fragments of up to 2500 g. Therefore, it must be ensured during packaging that the material does not puncture the usual plastic bags during filling, or even completely destroyed in the worst case.

To prevent this, the commercial packaging machines are to be suitably modified for the purpose of packaging polysilicon.

Out EP 1 334 907 B1 a device for cost-effective fully automatic transporting, weighing, portioning, filling and packaging of a high-purity polysilicon fracture is known, comprising a polysilicon fracture chute, a polysilicon fracture weighing device connected to a hopper, baffles made of silicon, a filling device consisting of a high-purity plastic film forms a plastic bag comprising a deionizer which prevents static charge and thus particle contamination of the plastic film, a plastic bag filled with polysilicon fracture, a flowbox mounted above the conveyor trough, weighing device, filling device and sealing device, which prevents particle contamination of the polysilicon fracture , a conveyor belt with a magnetic inductive detector for the welded polysilicon filled plastic bag, wherein all components, the come in contact with the polysilicon, reinforced with silicon or clad with a highly wear-resistant plastic.

It has been found that in such devices often jamming of the silicon fragments in the filling device occurs. This is disadvantageous because it leads to increased downtime of the machine.
Also penetrate the plastic bag, which also leads to a shutdown of the plant and contamination of the silicon.

DE 10 2007 027 110 A1 discloses a method for packaging polycrystalline silicon in which polycrystalline silicon is filled by means of a filling device into a free hanging, finished shaped bag, the filled bag being subsequently closed, characterized in that the bag is made of high purity plastic with a wall thickness of 10 to 1000 microns, wherein the filling device comprises a free-hanging energy absorber made of a non-metallic low-contamination material, which is introduced before filling the polycrystalline silicon in the plastic bag and via which the polycrystalline silicon is filled into the plastic bag, and the free-hanging energy absorber is then removed from the polycrystalline silicon filled plastic bag and the plastic bag is sealed.

By such a method that provides an energy absorber within the plastic bag, punctures of the plastic bag can be largely prevented. A disadvantage of this method, however, is that it still comes to jamming. This occur in this process, especially in the energy absorber. This further leads to production stoppages and requires manual intervention, which entails a contamination of the silicon.

DE 32 21 436 A1 discloses an apparatus for filling bags, consisting of an outer bag, and arranged in this, open-top inner bag made of plastic film, with a hopper, with a filled sacks supporting and transporting off conveyor, the bags during filling up to support on the conveyor are lowered.

The object of the invention is to avoid such jamming of the silicon, and to accomplish a nachzerkleinerungsarmes packaging of the silicon.

The object is achieved by a method for packaging polycrystalline silicon, in which polycrystalline silicon is filled by means of a filling device in a plastic bag, wherein the filling device comprises a freely suspended energy absorber made of a non-metallic low-contamination material, characterized in that the plastic bag pulled over the energy absorber is filled polycrystalline silicon and the plastic bag is lowered during filling down so that silicon slips into the plastic bag, wherein prior to the beginning of the lowering movement of the plastic bag whose cross section is reduced by a suitable device and gradually during filling or after filling is increased to accomplish a controlled filling of the plastic bag with polycrystalline silicon.

It has been found that this can prevent jamming of the silicon.

The inventive method also uses an energy absorber, as already known from the prior art. However, the filling process itself differs from the procedure described in the prior art. During filling with silicon, the plastic bag is lowered down. The presence of the energy absorber further prevents piercing of the plastic bag, as it is protected by the energy absorber from hard impact of the silicon. At the same time it is ensured by lowering the plastic bag that no jamming occur in the energy absorber.

Preferably, the energy absorber comprises a balance.

This balance is preferably made of a hard metal or ceramic or carbides.

The preferably prefabricated bag is pulled over the weighing container and filled by turning the whole unit nachzerkleinerungsarm.

The balance is preferably designed as a sieve and is located at a bottom of the energy absorber or the storage container.

Preferably, a jarring mechanism is provided to eliminate jamming altogether and to accomplish a better separation.
Such a vibrating mechanism can be generated for example by ultrasound.

A further preferred embodiment provides for a balance with transfer to an energy absorber.

The plastic bag is pulled over the energy absorber, then the scales incl. Sieve open, then opened a case brake and closed and then lowered the bag under wave motions and / or shaking.

As a fall brake is preferably a device that is pressed against plastic bag or energy absorber.
As a result, the cross section of the plastic bag or the energy absorber is first reduced, then released controlled.
This makes it possible to control the product flow and to achieve a low-backflow filling of the silicon into the prefabricated bag.

Preferably, the energy absorber consists of a non-metallic low-contamination material.

Unlike DE 10 2007 027 110 A1 the energy absorber is not introduced into the plastic bag before filling the polycrystalline silicon, but the plastic bag is pulled over the energy absorber.

Preferably, the plastic bag is pulled over the energy absorber by means of a suitable handling system. For example, an articulated robot is suitable for this purpose.

According to the method of the invention, the polycrystalline silicon is introduced into the plastic bag via the energy absorber.

During filling, the plastic bag is moved downwards.

This is preferably done by means of suitable gripper systems.

After the filling process, the plastic bag is preferably closed.

Beforehand, the plastic bag is preferably evacuated by sucking air out of the plastic bag and then welding it.

In this case, a handle hole punched into the plastic bag and any supernatant of the bag can be removed after welding for ease of handling.

In contrast to the fixed position of the free-hanging prefabricated bag, it is possible with the present invention that a flexible, non-pinch, low-penetration filling operation is possible via the flexible positioning of the bag gripper by means of handling systems.

The method described is suitable both for packaging polysilicon fracture for solar applications and polysilicon fracture for the electronics industry. In particular, these methods are suitable for packaging sharp-edged, up to 10 kg polycrystalline silicon fragments. The advantages are particularly noticeable in the presence of fragments with an average weight of more than 80 g.

The plastic bag is preferably made of a high purity plastic. These are preferably polyethylene (PE) polyethylene terephthalate (PET) or polypropylene (PP) or composite films.

A composite film is a multilayer packaging film from which flexible packaging is made. The individual film layers are usually extruded or laminated or laminated. The packaging is mainly used in the food industry.

Preferably, the plastic bag during filling with polysilicon fracture by means of at least two elements on Held bag and moved away from the energy absorber away and after completion of the filling process by means of these grippers a closure device, preferably a welding device supplied.

The plastic bag preferably has a thickness of 10 to 1000 microns.

The energy absorber is preferably made of a non-metallic low-contamination material. It is preferably in the form of a funnel or hollow body.

It is preferably made of textile material (eg Gore- ^Tex® - PTFE fabric or polyester / polyamide fabric), plastics (eg PE, PP, PA, or copolymers of these plastics). Particularly preferably it consists of a rubber-elastic plastic, z. As PU, rubber or rubber ethylene ethylene acetate (EVA), with a Shore A hardness between 30 A and 120 A, preferably 70 A.

The closing of the plastic bag can be done for example by means of welding, gluing, sewing or positive locking. Preferably, it is done by welding.

Preferably, the filling device consists of a filling unit and the freely suspended energy absorber which is connected to the filling unit. Preferably, the free-hanging energy absorber has the form of a freely suspended movable flexible hose or one of the other forms mentioned, which are hereinafter to be understood for the sake of simplicity by the term hose with.

The plastic bag is pulled over the movable flexible tube and the poly-break is introduced into the bag via the filling unit and the flexible tube.

The filling unit is preferably a funnel, a conveyor trough or a chute, which is provided with a Contaminated material or consist of a low-contamination material.

The free-hanging energy absorber absorbs a large part of the kinetic energy of the polysilicon crack falling in the bag. It protects the walls of the plastic bag from contact with the sharp-edged polycrystalline silicon and prevents puncturing of the plastic bag. The fact that after filling the plastic bag is pulled down, there is no jamming of the polycrystalline silicon in the energy absorber.

Preferably, the polysilicon is first portioned and weighed prior to packaging.

The filling unit is designed so that the finest particles and chippings of the polysilicon are removed before or during filling. For example, particles with an edge length of less than 16 mm can be sieved off safely.

For this purpose, a product stream of polysilicon fragments is preferably transported via a conveyor trough, by means of at least one sieve, wherein the sieve may be a perforated plate, a bar screen, an optopneumatic sorting or another suitable device, separated into coarse and fine fragments by means of a dosing scale weighed and dosed to a target weight, discharged via a discharge chute and transported to a packaging unit.

Preferably, the at least one sieve and the dosing scales at least partially comprise on their surfaces a low-contamination material, such as e.g. a carbide.

Portioning and weighing of the polysilicon fracture is preferably by means of a dosing unit for a polysilicon dosing and packaging apparatus comprising a conveyor trough suitable for conveying a product stream of debris, at least one sieve suitable for separation the product stream into coarse and fine fragments, a Groβosierrinne for coarse debris and a Feinosierrinne for fine fragments, a dosing scale for determining the dosing, wherein the at least one screen and the dosing scale at least partially comprise a hard metal on their surfaces.

Such a dosing unit serves to dose polysilicon fragments of a certain size class as accurately as possible before packaging.

By separating the product stream into coarse and fine particles, a more accurate dosing of the polysilicon is possible.

The weighed amount of polysilicon fragments is packed in a foil pouch after dosing and a possible cleaning step according to the method described above.

The dosing unit comprises at least one sieve, e.g. a bar screen suitable for separating the bridging pieces of the initial product stream into a coarse and fine metering trough.

Preferably, the metering unit comprises two screens, more preferably bar screens.

Coarse or larger polysilicon fragments are transported in a coarse dosage trough.

Fine or smaller polysilicon fragments are transported in a fine metering trough.

The size distribution of the polysilicon fragments in the starting product stream depends inter alia on the preceding comminution processes. The type of division into coarse and fine fragments and the size of the coarse or fine fragments depend on the desired end product, which is to be dosed and packaged.

A typical fraction size distribution includes pieces of sizes 5-170 mm.

For example, fragments below a certain size can be removed from the dosing unit by means of a sieve, preferably by means of a rod sieve, in conjunction with a discharge channel. So it can be accomplished that only fragments of a very specific size class are dosed.

By transporting the polysilicon on the conveyor again arise undesirable product sizes. These can be removed again, for example, by separating them in the dosing scale. For this purpose, the balance is equipped with an opening, an exchangeable separation mechanism and an evacuation unit.

The removed smaller fragments are reclassified in downstream processes, dosed and packaged or put to another use.

Preferably, the dosing unit comprises a fine particle chute. This can be designed einschwenkbar. Depending on the desired target product (fractional size distribution), this is used to screen fines and separate them from the product stream for fine dosing.

The dosage of the polysilicon over the two dosing channels can be automated.

Particularly advantageous is the use of hard metal elements for sieve and dosing scale. At least the screen and the dosing scale should at least partially have carbide on their surfaces.

By hard metals is meant sintered Carbidhartmetalle. In addition to conventional tungsten carbide-based hard metals, there are also hard metals, preferably titanium carbide and titanium carbide Titanium nitride as hard materials, wherein the binder phase thereby comprises nickel, cobalt and molybdenum. Their use is also preferred in the context of the method according to the invention.

Preferably, at least the mechanically stressed, wear-sensitive surface areas of the sieve and the metering balance comprise cemented carbide or ceramic / carbides. Preferably, at least one screen is made entirely of hard metal.

Sieve and dosing scales may be partially or fully coated with a coating. The coating used is preferably a material selected from the group consisting of titanium nitride, titanium carbide, aluminum titanium nitride and DLC (Diamond Like Carbon).

It has been found that the use of hard metal elements improves the mechanical stability of the dosing unit. In addition, the maintenance intervals of the dosing unit become significantly larger, since the hard metal elements wear less than the silicon and plastic cladding used in the prior art.

Surprisingly, it has been found that the contamination of silicon by the use of hard metal does not significantly increase over the use of silicon or plastic liners. This concerns in particular the contamination with tungsten and cobalt.

The dosing unit also makes it possible to divide the silicon product flow over a controlled swirl chute into several dosing and packaging systems and thus a combination of several dosing systems, which are filled with a starting product and are transported to different packaging machines after dosing and weighing.

The dosing system includes separation mechanisms (sieves) that screen out unwanted, smaller, product sizes and then deliver them to the upstream processes (sieving, classifying). Preferably, the polysilicon fragments are packaged in two plastic bags.

The packaging in a first plastic bag is carried out as previously mentioned using an energy absorber.

Subsequently, the first plastic bag is closed.

Preferably, the sealed bag is then transferred via a gripping system or a conveyor belt to a machine part for attaching a second bag.

Alternatively, the polysilicon may also be filled into two nested bags.

After welding the inner bag this slips down to the bottom of the outer bag and this can also be welded.

In another embodiment, the inner and outer bags are completely inserted into one another, the inner bag is welded, folded over and, after optional control, the outer bag is welded.

Claims (6)

1. Method for packaging polycrystalline silicon, in which a plastic bag is filled with polycrystalline silicon by means of a filling device, the filling device comprising a freely suspended energy absorber consisting of a nonmetallic low-contamination material, characterized in that the plastic bag is pulled over the energy absorber and filled with polycrystalline silicon, and the plastic bag is lowered downward during the filling, so that silicon slides into the plastic bag, wherein the cross section of the plastic bag is reduced by means of a suitable device before the start of its lowering movement, and is increased gradually during the filling or after the filling, in order to achieve controlled filling of the plastic bag with polycrystalline silicon.
2. Method according to Claim 1, characterized in that the plastic bag consists of polyethylene (PE), polyethylene terephthalate (PET) or polypropylene (PP) or composite sheet.
3. Method according to Claim 1, wherein the energy absorber consists of a nonmetallic low-contamination material and has the shape of a funnel, a tube or a hollow body.
4. Method according to one of Claims 1 to 3, wherein the storage container or energy absorber comprises a weighing balance.
5. Method according to Claim 1, wherein the storage container or energy absorber comprises a weighing balance which is configured as a screen and is located at the bottom of the energy absorber or storage container.
6. Method according to one of Claims 1 to 5, wherein a mechanism is provided which produces a wave-like and/or shaking movement of the storage container or energy absorber during the filling, in order to be able to fully prevent sticking and achieve better separation.