Patent Application
20190247799
The present invention relates to the manufacturing of materials and structures. More particularly, it refers to methods and systems for manufacturing materials and structures from carbon nanotubes, also referred to as buckypaper (BP).
Carbon nanotubes (CNTs) are used in the manufacturing of high performance material and devices. Processes for the continuous manufacturing of CNT-based BPs have been disclosed in the last years. Such processes typically include making a suspension of CNTs dispersed in a liquid medium and filtering the suspension by moving a filter membrane through the suspension, such that the CNTs are deposited directly on the filter membrane as the fluid medium flows through the filter membrane. The continuous BP is then dried, after which it can be separated from the filter membrane. An example of this process is disclosed in U.S. Pat. No. 7,459,121B2.
US2016/0177511A1 discloses a method for continuous manufacturing of a CNT sheet in which a porous plate flanked by two guiding rollers acts as filtration area and is disposed within a suspension chamber filled with a suspension of CNTs. A filter paper is advanced to the filtration area. When vacuum pressure is applied, CNTs are deposited on the portion of the filter paper in contact with the filtration area. The portion of the filter paper with the deposited CNTs is then advanced to a drying area. After drying, the filter paper is separated from the continuous sheet of CNTs, thus obtaining a roll of filter paper and a roll of continuous sheet of CNTs.
A similar approach is disclosed in WO2016/019143A1, in which a volume of a CNT suspension is passed over a filter material and drawn through the filter material to provide a uniform dispersion of the CNTs over the filter material. The filter material is in the form of a continuous porous belt. The filtered CNT structure is dried prior to removing the CNT sheet from the porous filter material.
However, the time required for obtaining a sheet of CNTs of a predetermined thickness with the conventional manufacturing processes is relatively high, as a consequence of which these processes are of poor efficiency. Moreover, as the thickness of the CNT sheet increases, the thickness increasing rate slows down. In other words, the thickness vs filtering time curve has a non-linear behavior, as shown for example in
The present disclosure provides a new method and system for increasing the thickness of a sheet of CNTs or buckypaper (BP). A buckypaper is a thin sheet made from an aggregate of carbon nanotubes or carbon nanotube grid paper. Because when manufacturing a CNT sheet, its thickness increase rate is reduced as its thickness increases, obtaining the last portion of aimed thickness (typically several microns or μm) requires more time than the previous ones. The present disclosure provides a method that enables increasing the last portion of aimed thickness in a much faster process, in such a way that the above-mentioned slowing effect is minimized and the time required for obtaining the sheet of CNTs of a desired thickness is reduced. So, the aimed thickness of BP may be obtained as follows: First, a first amount of thickness of BP may be obtained by any conventional method, and then, a second amount of thickness (the remaining amount until the desired thickness is reached) may be additionally obtained by means of the method of the present disclosure. As a matter of example, the first amount of thickness may be around 85% of the aimed thickness. This may result in a time saving of about 25% for a same aimed thickness.
The buckypaper (or sheet of CNTs) whose thickness is increased may be obtained in the form of a continuous sheet, or in the form of batch portions (single portions). In the context of the present disclosure, a continuous sheet of material is an elongated sheet having a length that is orders of magnitude greater than the width of the sheet. The continuous sheet of material may be provided in the form of a roll of the sheet material. A continuous sheet of material may be obtained by performing a continuous manufacturing process. In the context of the present disclosure, a batch portion or single portion of material is a portion having length and width of same or similar order of magnitude.
The sheet of CNTs may be circular or rectangular or of any other shape. When it is rectangular, the sheet may be continuous (for example to be provided in a roll) or non-continuous, also referred to as batch or portion (for example a portion of length and width of similar order of magnitude). The width and length of the sheets of CNTs may vary depending on the manufacturing process.
The present disclosure also provides a new method and system for drying a wet sheet of CNTs, the drying method being continuous, intermittent or static. The drying method of this disclosure optimizes the drying stage in a process of manufacturing a sheet of CNTs, the sheets being either continuous or batch. With the proposed drying method, the thickness of the sheet of CNTs is increased, and therefore the manufacturing speed is also increased.
The present disclosure also provides a new method and system for manufacturing a sheet of CNTs, in which the stage of drying the wet sheet of CNTs (either continuous or batch) is optimized.
The inventors have observed that, when manufacturing a sheet of CNTs by applying vacuum and a filter material, for example as disclosed in WO2016/019143A1, some CNTs get trapped in the pores of the mentioned filter. The inventors have also observed that, due to such trapping forces, the dimensions of the sheet of CNTs cannot change during drying. In the present disclosure, the wet sheet of CNTs is separated from any filter material. In other words, the wet sheet of CNTs is dried without filter material or support. This way the effect of the CNTs trapped in the filter material pores is eliminated, thus enabling changes in dimensions during drying, in particular increasing the thickness. This means that, when the process for increasing the thickness of a sheet of CNTs is applied during the manufacturing process of a sheet of CNTs, the wet sheet of CNTs is dried after separating the CNTs sheet from the filter material. Or, when the process for increasing the thickness of a sheet of CNTs is applied long after the manufacturing process of the sheet of CNTs, for example when the sheet of CNTs is provided/commercialized together with a support, the sheet of CNTs is separated from the support, then soaked in an aqueous solution, such as in water, and finally the drying process for increasing its thickness is applied.
The methods and systems of this disclosure enable the obtaining of sheets of CNTs, either continuous or batch, at a relatively fast rate compared to conventional setups due to the increasing in thickness achieved in the proposed drying stage.
The method for increasing the thickness of a sheet or CNTs or buckypaper of the present disclosure may be applicable to any sheet of CNTs or buckypaper obtained from any conventional manufacturing process. The areal weight of the sheet of CNTs prior to applying the drying method of the present disclosure, may be adjusted by tailoring the manufacturing conditions, such as the concentration of the CNT suspension, the applied vacuum pressure, the filtration speed, the filtration duration, the type of filter (for example of the grillage) or a combination thereof, during the manufacturing process.
The thickness of the sheets of CNTs obtained in the method of the present disclosure, that is to say, dried after separating the sheet of CNTs from any support, such as a filter support, has been observed to be substantially higher than the thickness of sheets of CNTs dried prior to separating the sheet of CNTs from the filter support, considering identical sheets of CNTs and identical drying conditions. In particular, it has been observed that the thickness of sheets of CNTs of the present disclosure (dried without any support material, that is to say, after separating the sheet of CNTs from the any support material) is up to 15% larger than the thickness of sheets of CNTs dried prior to separating the sheet of CNTs from any support. In some embodiments of the invention, it is up to 13% larger, or up to 11% larger, or up to 8% larger or up to 6% larger.
In some embodiments of the invention, the thickness of the resulting sheet of CNTs, which has been increased up to 15% with respect to drying before separation of sheet and support, varies between 40 and 100 μm (1 μm=1 micron=10−6 meters).
In order to apply the method for increasing the thickness of a sheet of CNTs, a wet sheet of CNTs is used. The wet sheet of CNTs may be obtained by applying a conventional method for manufacturing sheets of CNTs. In embodiments of the invention, it is obtained as follows: in a container filled with a liquid solution comprising CNTs at certain concentration, submerging a vacuum tank having a lower surface forming a grillage; moving an elongated filtering membrane along the lower surface of the vacuum tank while vacuum is applied on the elongated filtering membrane in such a way that in the surface of the filtering membrane opposed to the surface in contact with the lower surface of the vacuum tank CNTs are deposited forming a continuous sheet of CNTs of constant thickness; taking the filtering membrane together with the continuous sheet of CNTs out of the container; washing the continuous sheet of CNTs disposed on the filtering membrane or on a support element in a second container filled with cleaning solution; taking the continuous sheet of CNTs together with the filtering membrane or the support element (54) out of the second container. In order to apply the method of the invention, the continuous sheet of CNTs is separated from the filtering membrane or the support element. Alternatively, the wet sheet of CNTs may be obtained by soaking in an aqueous solution a dry sheet of CNTs. For example, the dry sheet of CNTs may be in the form of a roll of continuous sheet of CNTs, or a portion of sheet of CNTs, that has been manufactured by any conventional manufacturing process.
A first aspect of the invention refers to a method for increasing the thickness of a sheet of CNTs, comprising: providing a wet sheet of CNTs, wherein the sheet of CNTs is either a continuous sheet of CNTs or a portion of sheet of CNTs, wherein the wet sheet of CNTs is the result of applying a process for manufacturing a sheet of CNTs; separating the wet sheet of CNTs from any filter or support element; drying the wet sheet of CNTs by applying heat from a heat source.
In embodiments of the invention, the wet sheet of CNTs being the result of applying a process for manufacturing a sheet of CNTs, is obtained by soaking in a liquid medium a dry sheet of CNTs already manufactured.
In embodiments of the invention, the sheet of CNTs is continuous or a single portion thereof (batch portion).
In embodiments of the invention, the drying stage implies a continuous advancing of the sheet of CNTs, or an intermittent advancing thereof, or is static.
In embodiments of the invention, the sheet of CNTs is a continuous sheet of CNTs and the drying of the wet continuous sheet of CNTs is done as follows: moving forward the wet continuous sheet of CNTs in a longitudinal direction until a portion thereof is disposed within a drying unit comprising the heat source, the heat source being configured to provide heat to a drying area, the drying unit further comprising screening means for delimiting said drying area, in such a way that the portion of continuous sheet of CNTs is subject to heat only until while it is under the drying area.
The drying unit may comprise a plurality of rollers configured to rotate freely and to guide the continuous sheet of CNTs along its longitudinal direction, forcing the continuous sheet of CNTs to adopt soft convex and concave curvatures in an alternate way.
The plurality of rollers may comprise a central roller disposed under the drying area and lateral rollers disposed under the screening means.
The drying unit may comprise two conveyor belts configured to guide the continuous sheet of CNTs in its longitudinal direction, the conveyor belts being longitudinally disposed above and below the continuous sheet of CNTs, respectively.
At least one of the conveyor belts may be made of a porous material or comprises a grillage, in order to favour the entrance of heat and also to favour liquid evaporation, therefore reducing the drying time.
In embodiments of the invention, the heating source is an infrared irradiation source or a convection source or hot air source, or an ultra-violet (UV) irradiation source or an electrical resistance (ER) radiation source, or a conduction source.
Because the wet sheet of CNTs is dried without the support, such as filtering support, with which it has been manufactured, the thickness of the resulting sheet of CNTs is increased. The resulting sheet of CNTs has uniform thickness increase without causing any irregular deformations such as wrinkles and buckling.
A second aspect of the invention refers to a method for manufacturing a continuous sheet of CNTs, comprising: in a container filled with a liquid solution comprising CNTs at certain concentration, submerging a vacuum tank having a lower surface forming a grillage; moving an elongated filtering membrane along the lower surface of the vacuum tank while vacuum is applied on the elongated filtering membrane in such a way that in the surface of the filtering membrane opposed to the surface in contact with the lower surface of the vacuum tank CNTs are deposited forming a continuous sheet of CNTs of constant thickness; taking the filtering membrane together with the continuous sheet of CNTs out of the container; separating the continuous sheet of CNTs from the filtering membrane or the support element; drying the continuous sheet of CNTs by applying the method already disclosed.
Prior to separating the continuous sheet of CNTs from the filtering membrane or the support element, the method may comprise washing the continuous sheet of CNTs disposed on the filtering membrane or on a support element in a second container filled with cleaning solution; taking the continuous sheet of CNTs together with the filtering membrane or the support element out of the second container.
Thanks to the optimized drying stage, in which the sheet of CNTs is separated from the filter support with which it has been manufactured before drying the sheet of CNTs, the invention provides a sheet of CNTs with increased thickness with respect to conventional ones, considering similar conditions (filtering and optionally washing stage). The resulting sheet of CNTs has uniform thickness increase without causing any irregular deformations such as wrinkles and buckling.
A third aspect of the invention refers to a system for increasing the thickness of a sheet of CNTs, the system comprising a drying unit comprising a heat source configured to provide heat to a drying area, the drying area being configured to receive the sheet of CNTs.
In embodiments of the invention, the sheet of CNTs is continuous, the drying area being configured to receive the wet continuous sheet of CNTs as it moves forward in its longitudinal direction, the drying unit further comprising screening means for delimiting said drying area, in such a way that the portion of continuous sheet of CNTs is subject to heat only until while it is under the drying area.
In embodiments of the invention, the drying area may comprise means for preventing deformation of the continuous sheet of CNTs during the drying stage, said means being either a plurality of rollers configured to rotate freely and to guide the continuous sheet of CNTs along its longitudinal direction, forcing the continuous sheet of CNTs to adopt soft convex and concave curvatures in an alternate way, or two conveyor belts configured to guide the continuous sheet of CNTs in its longitudinal direction.
Additional advantages and features of the invention will become apparent from the detail description that follows and will be particularly pointed out in the appended claims.
To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate an embodiment of the invention, which should not be interpreted as restricting the scope of the invention, but just as an example of how the invention can be carried out. The drawings comprise the following figures:
As a matter of example, but without limitation, a possible method that may be used for manufacturing a wet sheet of CNTs is disclosed in view of
After the filtering stage of
Next, different embodiments of the drying stage for increasing the thickness of a sheet of CNTs according to the present invention are disclosed. The sheet of CNTs must be wet (for example, as it comes from the washing stage illustrated in
For example, if the method for increasing the thickness of the sheet of CNTs is applied after the washing stage shown in
In embodiments of the invention, an infrared (IR) irradiation source is used. In embodiments of the invention, a convection source or hot air source is used. Other radiation sources, such as a ultra-violet (UV) irradiation source or an electrical resistance (ER) radiation source, may be used instead. The thickness of the resulting dry sheet of CNTs has been increased.
In the embodiments represented in
Next, some experiments that have been carried out are described.
In a first experiment, a first portion of sheet of CNTs produced by means of a conventional method for manufacturing sheets of CNTs (using a dispersion of multi-wailed CNTs in a liquid medium, with random orientation, followed by filtration through a filtering membrane with the aid of vacuum) has been subjected to a conventional drying stage, that is to say, it has been dried without separating the sheet of CNTs from the filter support (or support, in general), with which the sheet of CNTs is washed. The dimensions of the portion of sheet of CNTs are approximately 70 mm (70 millimeters=0.07 m) (length)×46 mm (width). It has been dried with an infrared (IR) source of radiation (power of 1100 W, distance of 45 cm between the CNT sheet and the infrared lamp). A second portion of sheet of CNTs is produced by means of exactly the same manufacturing method. It has the same dimensions as the first one. In fact, in some experiments the same BP has been cut in two portions (or more) that have been dried differently to have comparable results. However, instead of drying the sheet of CNTs without separating the sheet of CNTs from the filter support with which the sheet of CNTs was washed, both elements were separated and the method of the invention was applied. In particular, a system similar to the one shown in
Therefore, an increase of 13% was obtained. This experiment proves the capacity of the method of the invention to increase the thickness of the resulting sheet of CNTs. It is remarked that this comparison has been established, instead of comparing the same wet portion of sheet of CNTs before and after applying the method of the invention, because it is extremely complicated to correctly measure the thickness of a wet sheet of CNTs. Besides, the purpose of the method is to increase its thickness with respect to sheets of CNTs manufactured by means of conventional methods, in which the stage of drying is performed without separating the sheet of CNTs from the filter element.
In a second experiment, it has been proved that the thickness is increased for a wide range of thickness. First, three portions of sheet of CNTs were produced by means of a conventional method for manufacturing sheets of CNTs, but with different filtering times in order to obtain sheets of CNTs with different thickness. The three of them were subjected to a conventional drying stage, that is to say, they were dried without separating the sheet of CNTs from the filter support (or support, in general), with which each sheet of CNTs was washed. The dimensions of the portions of sheets of CNTs were approximately 45 mm (length)×45 mm (width). They were dried with an infrared (IR) source of radiation (power of 1100 W, distance of 45 cm between the CNT sheet and the infrared lamp). Next, three additional portions of sheet of CNTs were produced by means of exactly the same manufacturing method. They had the same dimensions as the first three ones. However, instead of drying the sheets of CNTs without separating the sheet of CNTs from the filter support with which each sheet of CNTs was washed, in the three cases both elements were separated and the method of the invention was applied. In particular, a system similar to the one described for the first experiment was used. The following table summarizes the results:
As can be observed, in all the cases an increase of at least 11% was achieved. In particular, in two cases it was of 13%. This experiment proves the capacity of the method of the invention to increase the thickness of the resulting sheet of CNTs for sheets of CNTs of different thickness.
In a third experiment, it has been proved that the thickness is increased for a wide range of thickness also when the heating source is an air heater instead of an infrared source of radiation. First, three portions of sheet of CNTs were produced by means of a conventional method for manufacturing sheets of CNTs, but with different filtering times in order to obtain sheets of CNTs with different thickness. The three of them were subjected to a conventional drying stage, in this case with an air heater (2 h at 105° C.). In other words, they were dried without separating the sheet of CNTs from the filter support (or support, in general), with which each sheet of CNTs was washed. The sheets of CNTs had similar dimensions as in the previous experiments. Next, three additional portions of sheet of CNTs were produced by means of exactly the same manufacturing method. They had the same dimensions as the first three ones. However, instead of drying the sheets of CNTs without separating the sheet of CNTs from the filter support with which each sheet of CNTs was washed, in the three cases both elements were separated and the method of the invention was applied. In particular, a system similar to the one described for the first and second experiments, was used. The following table summarizes the results:
As can be observed, if an air heater is used instead of an infrared source of radiation, an increase in the thickness of the resulting sheet of CNTs is also achieved. However, the increase is larger when an infrared source of radiation is used.
Although the former experiments refer to “static” or batch portions of sheets of CNTs, that is to say, portions of sheets of CNTs of width and length of the same order of magnitude, these experiments have also been performed in a dynamic configuration (with continuous sheets of CNTs, for example provided in rolls). In all the cases, an increase in the thickness of the resulting sheets of CNTs, similar to the ones shown in experiments 1-3, has been observed.
In sum, the method of the invention permits to save production time, thus increasing efficiency, thanks to the obtained increase in the thickness of the sheet of CNTs. For example, the graph represented in
In this text, the term “comprises” and its derivations (such as “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.
The invention is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the invention as defined in the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18382078.6 | Feb 2018 | EP | regional |
