Patent Application
20230117887
The present invention relates to a coating apparatus for coating at least one side of a carrier with a paste.
A production process for such a coating of a carrier foil with a paste is known, for example, from the prior art from WO 2018/047054 A1 and is explained using the example of the manufacture of a negative electrode for lithium ion batteries. The carrier is in the form of a foil web, which is transported through the corresponding manufacturing/coating installation by way of rollers. In that case, the paste also contains graphite particles which can be oriented in a magnetic field. However, the transport has to be carried out very precisely, this is because, in order to obtain a precisely controllable orientation of the graphite particles, the carrier has to be guided in a precisely defined manner through the magnetic field.
In JP 2020053278 A, reference is made to the problem that, when using drying blowers to dry coatings, the carrier can sag as a result of the air flow. In order to compensate for this, a magnetic material is added to the electrode material, more precisely the coating on the carrier, and a permanent magnet is arranged in the vicinity of the carrier, in order to compensate for the sagging.
It is an object of the present invention to provide a coating apparatus which permits a more precise manufacturing operation with more precise positioning of the carrier.
The coating apparatus according to the present invention provides a transporting apparatus, by means of which the carrier foil to be coated is guided through the installation. The carrier foil itself is not a fixed constituent of the coating apparatus according to the present invention.
In the nomenclature used here, the carrier in turn comprises a foil as basic material and the coating applied to the foil. For the production of negative electrodes for lithium ion batteries, for example, use is made of copper foil, which is present in long webs. However, it has been proven that, in conventional methods according to the prior art, the transport of, in particular, long foil webs in relation to the force field or magnetic field is insufficiently precise and has hitherto regularly caused problems.
In addition, in the case of a coating, there are generally further requirements on the manufacturing process: As coating, by way of example, a paste composed of soft to liquid material is applied and subsequently dried. During the drying, the paste volume may shrink due to evaporation of constituents of the paste. The adhesion to the foil may cause the carrier overall to deform, bulge, wrinkle or crease. Furthermore, during the heating, which is employed for drying the paste, the carrier may expand or contract.
For example, it should be expected in the manufacture of lithium ion batteries that the copper foil used will expand upon heating, whereas a paste applied thereto contracts. The overall complex of the carrier, which comprises the foil and the paste, curves in that case, similar to a heating bimetallic strip through which current flows.
This can in turn lead to the carrier overall deforming, bulging, wrinkling or creasing. These effects have hitherto caused fundamental problems in the mounting and positioning and thus also in the transport and the manufacture, in particular, in the precise positioning, of the carrier in a force field.
The paste with which the carrier foil is, for example, coated may contain particles in platelet form, in which, for a majority of the particles, an ellipsoid approximating to the respective particle shape has two axes of similar length and one distinctly shorter axis.
The paste with which the carrier foil is, for example, coated may contain spherical particles, in which, for a majority of the particles, an ellipsoid approximating to the respective particle shape has three axes of similar length.
The paste with which the carrier foil is, for example, coated may contain acicular particles, in which, for a majority of the particles, an ellipsoid approximating to the respective particle shape has one long axis and two distinctly shorter axes.
If the paste with which the carrier foil is coated contains particles such as carbon-based particles, in particular, graphite particles, in particular, particles in platelet form, the uniform orientation of the particles can indeed in principle influence the distortion due to volume reduction during drying, however the orientation is prescribed by the desired production result and cannot be governed solely by a potential distortion. If possible, the coating may also comprise a material having thermoresponsive properties, but even these properties generally contribute only partially to the avoidance of distortions.
It is, for example, possible for particles to be oriented in the paste under the influence of a force field. Graphite particles can be oriented, for example, in a magnetic field, in particular, a temporal and/or spatial alternating magnetic field. If there are particles in the paste that are intended to be oriented, this process is advantageously carried out prior to and/or during the drying, since the particles in a completely dried and solidified mass of paste surrounding them are usually barely still able to move mechanically. The orientation of the particles can be performed, in part, at the same time as the drying process, so that the orientation of the particles is not completely or partially lost again during the drying, for example, due to an air flow or under the influence of shrinkage of the paste volume. It is also conceivable for the deformation which occurs during drying and shrinkage of the paste to be counteracted by active forming of the carrier. However, in order for foil to not lift out of the mounting arrangement in the case of such deformation, it is alternatively possible to employ the bearing apparatus according to the present invention which permits mounting in multiple directions, where appropriate in a contactless manner.
Apart from a paste which comprises a soft or liquid mass comprising particles as an essential component, it is also possible for dry coating with a powder to be effected. Depending on the application, the particles may also be oriented in the dry coating in a force field. It is also possible for the present invention to be used with this material.
The coating apparatus according to the present invention provides reliable and stable mounting, even if the carrier has a sensitive coating and a precise positioning is desired.
Correspondingly, the coating apparatus according to the present invention is distinguished in that the transporting apparatus comprises a bearing apparatus for the positionally stable mounting of the carrier in relation to a direction perpendicular to the transport plane, in which the carrier lies during transport, the bearing apparatus being able to be used to exert a force perpendicular to the transport surface. The bearing apparatus is fundamentally able to engage, with or without contact, with uncoated locations, on which no coating is present, or with coated locations. The bearing apparatus thus represents a mechanical constraint for the movement range perpendicular to the transport plane or to the surface of the carrier.
During the production process, stable mounting in the transport plane is not only advantageous for being able to apply the paste precisely during the coating but also for exposing the carrier to a force field in a defined manner. In particular, it is advantageous for positioning the carrier in the force field in a precisely defined manner, for example, for orienting it precisely in relation to the apparatus generating the force field and for positioning it at a precisely defined distance in relation to the apparatus generating the force field. In general, use is typically made of permanent magnets for generating a magnetic field, which is why it is particularly important that the carrier is positioned at the predetermined, well-defined distance from the permanent magnets, so that the particles to be oriented are exposed to the intended field strength required for orienting the particles. Such stable mounting can be obtained by way of the coating apparatus according to the present invention. In particular, the distance of the carrier from the magnets has to be precisely defined over the entire surface on which the magnetic field acts on the carrier. With respect to its mounting arrangement, the coating apparatus according to the present invention can also dispense with convex foil guidance, which is conventionally used in the prior art but can be significantly more complex to implement.
In an embodiment variant, the distance between the foil and the magnet is preferably between 0 mm-200 mm, preferably between 0 mm-20 mm, particularly preferably 1 mm-4 mm.
In refinements of the present invention, use can, for example, be made of the following bearing apparatuses or combinations of bearing apparatuses.
The carrier may rest on one or more roller bearings. The roller bearings provide a mechanical constraint so that the carrier does not sag in the direction of gravitational force. They have the advantage that they can co-rotate with the translational movement of the carrier, thus also bring about only small friction forces, which also consequently might not influence the carrier (for instance, by abrasion, electrostatic charging or the like).
Instead, grinding bearings are also possible, which do not co-rotate upon contact with the carrier but rather remain rotationally fixed. In general, areal grinding bearings are not usable since they have a large contact surface in contact with the carrier and thus lead to high friction forces. It is generally possible to use thin wires or plastics threads which are stretched transversely or at an angle with respect to the transporting direction. The carrier rests on the wire or thread and slides over it. On account of the extremely small contact surface, usually only small friction forces occur between carrier and thread or wire. Such mounting can usually be implemented cost-effectively, in a space-saving manner with a small structural height and also without relatively great technical effort.
There are various possibilities for the arrangement or the combination of bearings: roller bearings or grinding bearings are generally used in the case of contact with solid surfaces. To reduce the friction, provision may also be made of a liquid cushion, such that the carrier slides over this cushion.
With respect to surfaces composed of soft material or liquid coatings, it is in turn advantageous to use contactless bearings. In the case of a gas bearing or air bearing, for example, a gas flow, advantageously an air flow, is generated on a surface. The carrier can then slide on this gas cushion. The friction forces are regularly negligibly low. Nevertheless, a gas bearing should be dimensioned such that it does not hinder the drying operation, especially if it is arranged on the coating side. It is particularly advantageous for a gas bearing to be designed such that it can be arranged above the magnets in an areal manner, and has a small thickness, advantageously between 1 mm-4 mm. In this configuration, the magnetic field penetrates the gas bearing and acts on the carrier. This allows precise mounting of the foil parallel to the magnets.
It is advantageously also possible to use a vacuum bearing, which provides negative pressure, for example, by way of a vacuum pump or a blower. The vacuum bearing suctions the carrier and thus exerts a force action on it. This arrangement can also be used to press the carrier against another bearing.
In addition, electromagnetic bearings such as eddy-current bearings or electrostatic bearings are also conceivable, which permit similarly low friction forces as gas bearings. Nevertheless, it is necessary for the material to be mounted to have corresponding properties, for example, allowing an electrostatic charge or the generation of eddy currents.
Contactless bearings such as gas bearings or electromagnetic bearings can especially be used on the coating side. These can effectively prevent the carrier from bending or bulging excessively perpendicular to the transport plane, but without contacting or damaging the soft or partially liquid coating in doing so. At the same time, the gas bearings according to the refinement of the present invention make it possible for the access to the foil, that is to say during the drying operation, for example, to not be hindered.
Overall, it is advantageous for all the bearings to be oriented such that the straightness of the foil perpendicular to the foil transporting direction is ensured, in order to avoid any bulging, creasing or wrinkling of the foil, wherein contactless bearings can permit a certain amount of play in a lateral direction.
The following bearing arrangements are considered as a starting point. It is fundamentally possible for conventional rollers, via which the carrier band is guided, to then each be arranged between the respective magnets in the transporting direction, so that the field lines are not disturbed by the rollers. However, rollers require a comparatively large amount of space. On account of the one-sided mounting, the foil may lift off from the rollers. Lifting-off of the foils during the orienting operation increases the distance from the magnets, that is to say the particles may be oriented only to an insufficient extent.
In order to obtain the precise distance between the foil and the magnet, spacers, which rest on the magnets, may be used. However, such mounting fundamentally also constitutes one-sided mounting, that is to say lifting-off of the foil is still possible. It only prevents the distance between foil and magnet from becoming too small. In addition, this conventional mounting is associated with difficulties, because a spacer constitutes a grinding bearing, and scratches in the foil can occur due to the friction. The process stability may no longer be ensured.
According to one exemplary embodiment, gas bearings, such as air bearings, can then be used. A contactless air bearing can be used, in particular, on the coated side, such that, irrespective of which bearing is used on the opposite side (for example, a contacting roller or grinding bearing or a contactless gas bearing), there is a double-sided mounting arrangement, which engages with the opposite sides.
If the individual bearings are connected in series (in the transporting direction), the distance between adjacent bearings may, in principle, be between 1 cm and 8 m, preferably 1 cm-50 cm, depending on which bearings are used.
In order for the air bearing arranged on the coating side, for example, the upper air bearing, to not disrupt the drying process and for there to not be poor access for the drying, a vacuum bearing for exerting a pressing force may be provided. This vacuum bearing can be arranged on the same side of the carrier as the other bearings, since it suctions the foil, that is to say acts in the opposite direction to the force direction of the other bearings. The vacuum bearing can preferably be designed with a vacuum pump.
The coating apparatus serves for the final completion of the coating, such that the coating apparatus also comprises, according to the present invention, an orienting apparatus in order to be able to orient the particles in the paste. The orienting apparatus generates the force field, under the influence of which the particles are oriented. In the case of graphite particles of platelet form in flake form or elongate form, use can be made of temporally or spatially alternating magnetic fields. In general, permanent magnets are essentially arranged in stacks and oriented such that the orientation of their magnetic fields spatially varies, with the result that the carrier moving through the fields is subjected to a temporally alternating magnetic field in relation to a point that is fixed relative to the carrier. In order to obtain coated carriers of constant quality, a stable positioning of the carrier, which is made possible by a coating apparatus according to the present invention, is advantageous particularly when passing through the magnetic fields.
The bearing apparatus advantageously mounts the carrier perpendicular to the transport plane in a stable position. In an advantageous exemplary embodiment of the present invention, the bearing apparatus is thus configured for at least two-sided or for multi-sided mounting of the carrier. With regard to the distance from elements generating a magnetic field, the bearing elements may, for example, be arranged in an opposite manner above and below the transport plane or the carrier. The bearings may also engage in a U-shaped manner around the carrier in the peripheral region and thus form a three-sided bearing.
Two or more bearings may be connected in series along the transport path, in order to obtain particularly stable mounting over the corresponding region. The bearings may be arranged in an opposite manner at the individual locations along the transport path or directly in series at various locations. In this way, in spite of the length of the foil web, sagging of the latter is prevented or reduced.
In a preferred embodiment of the present invention, at least two gas bearings are connected in series, wherein a vacuum bearing for exerting a pressing force perpendicular to the transporting direction is provided on the same side as where the gas bearings are located. In this way, the stability can be increased, in particular.
The carrier may be distorted during drying of the paste, which generally leads to a disruptive bulge perpendicular to the transport plane. With regard to such a bulge, it may be advantageous to use, for example, a grinding bearing which restores the shape of the carrier or of the foil.
A bearing force on the coated side can fundamentally also be brought about by convex foil guidance. The foil then passes along a longer path than in a straight line; the guidance of the foil with a constant change in direction on the circular arc-shaped path section also has the effect that the carrier foil receives a certain pressing action. However, especially when orientation is also intended to be effected at the same time on this transport path section, it is necessary for a convex force field or magnet surface to be produced there, which is difficult in technical terms. The convex guidance can also be effected only within a determined scope, since the coating apparatus generally permits only a determined angular range in terms of geometry.
Nevertheless, in one embodiment of the present invention, it is also possible for convex foil guidance to be used in combination with at least one air bearing. For the drying process, all the bearings may be arranged on one side, such that, for example, the coated side is accessible to a drying process.
Exemplary embodiments of the present invention are illustrated in the drawings and are explained in more detail below with further details and advantages being given.
Different types of carriers 1a, 1b, 1c which can be processed or transported by means of a coating apparatus according to the present invention are schematically illustrated in
The ground 4 is depicted in order to indicate the direction of gravitational force.
The sagging of the carrier 1 can be reduced by supporting the latter at more locations that lie closer together. However, a prerequisite for this is that the bearings 12 are smaller, in order to not significantly influence the magnetic field through the magnets 3. Such an embodiment can be achieved using grinding bearings in the form of spacers 12 as shown in
Friction effects can, by contrast, be reduced or avoided by way of air bearings 22, as is illustrated in
According to
A contacting bearing such as a grinding or roller bearing could damage the coating on the foil top side. An air bearing in turn could, as shown in
Another option having a two-sided mounting effect similar to in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 105 658.6 | Mar 2021 | DE | national |
This application is a continuation of International Application No. PCT/EP2022/056012 filed Mar. 9, 2022, which designated the United States, and claims the benefit under 35 USC § 119(a)-(d) of German Application No. 10 2021 105 658.6 filed Mar. 9, 2021, the entireties of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2022/056012 | Mar 2022 | US |
| Child | 18057858 | US |
