KR102873707B1 - Method for producing a conductive coating containing graphene on natural leather or synthetic leather, and natural leather or synthetic leather thus obtained - Google Patents

Abstract

A method for producing a thermally and electrically conductive coating on natural or synthetic leather, comprising the deposition of several layers based on an aliphatic polyurethane having an intermediate layer having a thickness of 10 to 50 μm, wherein at least 90% of the intermediate layer comprises graphene nano-platelets having lateral dimensions (x, y) of 50 to 50000 nm and a thickness (z) of 0.34 to 50 nm and a C/O ratio ≥ 100:1.

Description

Method for producing a conductive coating containing graphene on natural leather or synthetic leather, and natural leather or synthetic leather thus obtained

The present invention relates to a method for producing a conductive coating containing graphene on natural or synthetic leather, and to natural or synthetic leather coated in this way.

It is known in the art to make non-naturally conductive substrates, such as natural leather, tanned leather or natural or synthetic textile articles, electrically and/or thermally conductive by applying conductive materials such as graphene.

WO 2015/103565 A1 describes the application of a conductive ink containing graphene to a wide variety of substrates, including leather and tanned leather. The graphene may be present in any form, for example, as an oxide, or may contain oxygen and carbon in any ratio from 1:1 to 2000:1, or may be functionalized with hydroxyl, carboxyl, or epoxy groups, or may be mixed with graphite in any ratio from 1 to 99 wt%. The conductive ink may be applied by any method, such as painting, dyeing, powder coating, lamination, extrusion, electrodeposition, lithography, and many other methods, although no specific examples of application are provided.

WO 2020/002979 A1 describes tanned leather treated to be heat-dispersible and electrically conductive, and a related treatment method. The method comprises directly impregnating the tanned leather with an aqueous bath containing graphene particles by mixing in a drum after tanning and before finishing. The graphene particles are thus trapped within the pores of the collagen matrix of the tanned leather, and are then dried by heating to 70°C.

CN 108330704A discloses graphene ultrafine fiber polyurethane synthetic leather and a method for producing the same. The graphene ultrafine fiber polyurethane synthetic leather comprises a surface layer, a middle layer, and an adhesive layer. The synthetic leather is produced from the following components: a high-performance water-based non-yellowing polyurethane resin, nylon, graphene, an ultrafine fiber polyurethane synthetic substrate, an abrasion-resistant agent, a light-resistant agent, a flame-retardant masterbatch, and water. The production method comprises the steps of weighing raw materials; treating graphene; mixing and stirring the raw materials; filtering the solution through a filter net; and applying the components onto a base fabric to produce leather.

CN 105735002A discloses a method for producing polyurethane modified with graphene and synthetic leather with high physical properties. The graphene-modified polyurethane is characterized by first subjecting graphene to lipophilic modification, then dispersing the modified graphene in a polyurethane solution, and producing the modified polyurethane using conventional dry and wet processes. By introducing graphene, the polyurethane can be strengthened and toughened, making it applicable to the production of various synthetic leathers.

US 2020/062914 A1 discloses a polyurethane film comprising a polyurethane resin and graphene, characterized in that the graphene is present in an amount of 1 to 30 wt% based on the total weight of the film.

However, prior art embodiments do not provide an optimal solution to the problem of effectively maintaining the thermal and electrical dissipative properties of tanned leather or synthetic leather over time. In fact, graphene applied to a surface can be removed by friction and surface wear.

Moreover, using conventional solutions, it is impossible to obtain a surface finish that has a specific aesthetic effect, both in terms of the presence of decorative surface decoration and the morphological structure of the surface. This problem is particularly critical for synthetic leather, which must mimic tanned leather in both appearance and surface morphology to provide a "hand feel" with a slight roughness that can be felt to the touch.

Accordingly, it is an object of the present invention to provide a method for producing a thermally and electrically conductive coating on natural or synthetic leather, which is stable and retains its properties over time.

Another object of the present invention is to provide a method for producing a thermally and electrically conductive coating on natural or synthetic leather, which is adapted to provide a surface finish having a specific aesthetic effect, both in relation to the presence of a decorative pattern on the surface and to the morphological structure of the surface.

A further object of the present invention is to provide natural or synthetic leather provided with a thermally and electrically conductive coating, and optionally with a decorative pattern and/or a specific surface shape on the surface.

Accordingly, one aspect of the present invention relates to a method for producing a thermally and electrically conductive coating containing graphene on natural leather or on a textile substrate for the production of synthetic leather, comprising the steps of:

a) forming an inner layer comprising at least one aliphatic polyurethane having a thickness of 10 to 50 μm, which is applied on the natural leather or textile substrate;

b) forming at least one intermediate layer applied on the inner adhesive layer (A) and having a thickness of 10 to 50 μm, wherein the intermediate layers each comprise at least one aliphatic polyurethane and graphene nano-platelets, wherein at least 90% of the graphene nano-platelets have lateral dimensions (x, y) of 50 to 50000 nm and a thickness (z) of 0.34 to 50 nm, and wherein the C/O ratio is ≥ 100:1;

c) A step of forming an outer layer comprising at least one aliphatic polyurethane having a thickness of 2 to 10 μm and applied on the intermediate layer (B).

Another aspect of the present invention relates to natural or synthetic leather comprising a coating comprising:

(A) an inner adhesive layer in contact with the natural leather or textile substrate and comprising at least one aliphatic polyurethane having a thickness of 10 to 50 μm;

(B) an intermediate layer overlapping the inner adhesive layer (A) and having a thickness of 10 to 50 μm, the intermediate layer comprising at least one aliphatic polyurethane and graphene nano-platelets, wherein at least 90% of the graphene nano-platelets have lateral dimensions (x, y) of 50 to 50000 nm and a thickness (z) of 0.34 to 50 nm, and the C/O ratio is ≥ 100:1;

(C) An outer layer comprising at least one aliphatic polyurethane having a thickness of 2 to 10 μm and overlapping the intermediate layer (B).

The present invention is also described below with reference to the attached drawings.
- Figure 1 is a schematic cross-sectional view of a first embodiment of synthetic leather according to the present invention;
- Figure 2 is a schematic cross-sectional view of a second embodiment of synthetic leather according to the present invention.

In this description, the term "tanned leather" or "natural leather" means the final product obtained by processing animal skin.

In this description, the term "synthetic leather" or "artificial leather" or "imitation leather" means a natural or synthetic textile substrate coated with a film of a plastic material having a surface finish that imitates tanned leather or natural leather.

As used herein, the term "textile substrate" refers to a substantially flat substrate, such as a fabric, nonwoven fabric, polymer film, or membrane. With respect to fabrics, these may be made from natural, artificial, or synthetic fibers. With respect to nonwoven fabrics and polymer films or membranes, these are typically made from artificial fibers or synthetic resins.

Natural or synthetic leather having a coating according to the present invention can be used in clothing or other articles, for example in the furniture sector, for example in seats, sofas, etc., including seats and seats in the automotive sector, where heat and electrical dissipation properties are particularly advantageous.

With regard to heat dissipation, natural or synthetic leather having a coating according to the present invention can not only evenly distribute absorbed heat, but also ensure breathability to maximize user comfort.

In relation to electrical dissipation, this leads to an effective dissipation of charges which are mainly formed through rubbing and tend to accumulate on the surface of the article, reducing the user's comfort or causing even greater defects.

In order to increase the electrical and thermal conductivity of natural or synthetic leather and to make these conductivity properties stable and long-lasting, the present invention provides for applying a multilayer coating as described above directly onto natural or tanned leather, or onto a textile substrate adapted for producing synthetic leather.

With respect to the material from which the textile substrate is made, it is mentioned that it may be natural, artificial, or synthetic. If the textile substrate is a nonwoven fabric or a polymer film or membrane, the material forming it is generally artificial or synthetic.

Useful natural fibers include, for example, wool, silk, and cotton. Useful man-made fibers include modified or regenerated cellulose fibers, such as viscose and cellulose acetate. Useful synthetic fibers include polyamides, such as aromatic polyamides (aramids), polyesters, polyurethanes, polyacrylonitrile, polycarbonates, polypropylene, polyvinyl chloride, and mixtures thereof. Fabrics obtained from blends of natural, man-made, and synthetic fibers can also be advantageously used.

For example, according to an embodiment of the present invention referring to natural leather or tanned leather schematically illustrated in FIG. 1, the coating is applied to a substrate (10) made of a textile or tanned leather substrate according to the following steps:

a) A step of forming an inner adhesive layer (A) comprising at least one aliphatic polyurethane having a thickness of 10 to 50 μm and in contact with the natural leather or textile substrate, and then heating the inner adhesive layer at a temperature of 70 to 100°C for 1 to 10 minutes;

b) forming at least one intermediate layer (B) overlapping on the inner adhesive layer (A) and having a thickness of 10 to 50 μm, wherein the intermediate layer (B) comprises at least one aliphatic polyurethane and graphene nano-platelets, wherein at least 90% of the graphene nano-platelets have lateral dimensions (x, y) of 50 to 50000 nm and a thickness (z) of 0.34 to 50 nm, and wherein the C/O ratio is ≥ 100:1, followed by a step of heating at a temperature of 70 to 100°C for a time of 1 to 10 minutes;

c) A step of forming an outer layer (C) comprising at least one aliphatic polyurethane having a thickness of 2 to 10 μm and overlapping the intermediate layer (B), and then heating the outer layer (C) at a temperature of 100 to 160°C for 1 to 10 minutes.

In each of the above steps a), b) and c) of the present invention, the aliphatic polyurethane is applied in the form of an aqueous dispersion.

According to another embodiment of the present invention, for example in relation to synthetic leather as schematically illustrated in FIG. 2, a coating comprising the following layers is applied to a suitable textile substrate (20):

(A) an inner adhesive layer (A) in contact with the natural leather or textile substrate and comprising at least one aliphatic polyurethane having a thickness of 10 to 50 μm;

(B) a first intermediate layer (B) overlapping on the inner adhesive layer (A) and having a thickness of 10 to 50 μm, comprising at least one aliphatic polyurethane and graphene nano-platelets, wherein at least 90% of the graphene nano-platelets have lateral dimensions (x, y) of 50 to 50000 nm and a thickness (z) of 0.34 to 50 nm, and a C/O ratio of ≥ 100:1;

(B1) A second intermediate layer (B1) applied to the first intermediate layer (B) and having a thickness of 10 to 50 μm, which, as in the first intermediate layer (B), also comprises one or more aliphatic polyurethanes and graphene nano-platelets, wherein at least 90% of the graphene nano-platelets have lateral dimensions (x, y) of 50 to 50000 nm and a thickness (z) of 0.34 to 50 nm, and the C/O ratio is ≥ 100:1.

(C) An outer layer (C) having a shape having depressions and/or roughness mimicking the surface morphology of tanned leather, which is superimposed on the second intermediate layer (B1) and comprises at least one aliphatic polyurethane having a thickness of 2 to 10 μm.

In this second embodiment, the intermediate layer (B) is advantageously present when the outermost layer (C) is formed with depressions and/or roughness that mimic the surface morphology of tanned leather. Since the depressions expose or can expose areas of the second intermediate layer (B1) containing graphene to the atmosphere, the presence of two intermediate layers (B) and (B1) ensures the permanence of a sufficient amount of graphene in the coating, ensuring that the electrical and heat dissipation properties are maintained. With regard to the method for forming the coating on tanned leather and on a textile substrate, it is possible to deposit the various layers (A), (B), (B1) and (C) directly on the tanned leather or on the textile substrate, or indirectly by depositing the layers in the reverse order (C), (B1), (B) and (A) on an external support, for example a release paper. Next, the deposited layer is coupled to a tanned leather or textile substrate, the layer (A) is brought into contact therewith, and finally the release paper is detached to expose the outer layer (C).

Accordingly, according to one aspect, the present invention is a method for producing a thermally and electrically conductive coating containing graphene on natural leather or on a textile substrate for the production of synthetic leather, characterized in that it comprises the following steps:

i. For the manufacture of an outer layer (C) having a thickness of 2 to 10 μm, a step of spreading an aqueous dispersion of one or more aliphatic polyurethanes on a paper substrate and then heating the dispersion at a temperature of 70 to 90°C for 1 to 10 minutes;

ii. For the formation of an intermediate layer (B) having a thickness of 10 to 50 μm, an aqueous dispersion of at least one aliphatic polyurethane and graphene nano-platelets is spread on the layer (C), wherein at least 90% of the graphene nano-platelets have lateral dimensions (x, y) of 50 to 50000 nm and a thickness (z) of 0.34 to 50 nm, and a C/O ratio of ≥ 100:1, followed by a step of heating at a temperature of 70 to 100°C for 1 to 10 minutes;

iii. A step of spreading an aqueous dispersion of at least one aliphatic polyurethane on the intermediate layer (B) to form an inner adhesive layer (A) having a thickness of 10 to 50 μm;

iv. A step of coupling the coating composed of the paper substrate, the layers (C), (B) and (A) with the natural or synthetic leather, wherein the natural or synthetic leather is brought into contact with the inner adhesive layer (A), and then heated at a temperature of 100 to 160°C for 1 to 10 minutes; and

v. A step of separating the paper substrate from the outer layer (C).

According to one embodiment, the method also provides step ii'. after step ii.:

ii'. A step of spreading an aqueous dispersion of at least one aliphatic polyurethane and graphene nano-platelets on the layer (B) to form an intermediate layer (B1) having a thickness of 10 to 50 μm, wherein at least 90% of the graphene nano-platelets have lateral dimensions (x, y) of 50 to 50000 nm and a thickness (z) of 0.34 to 50 nm, wherein the C/O ratio is ≥ 100:1, followed by a step of heating at a temperature of 70 to 100°C for 1 to 10 minutes.

The method comprising step ii' leads to obtaining a coating comprising two intermediate layers (B) and (B1) as defined above.

Indirect deposition methods are preferred when creating a coating on a textile substrate. In this case, the method actually produces artificial leather with thermal and electrical conductivity properties.

Furthermore, with regard to the formation of a coating on tanned leather or textile substrates, in the first case, it is not necessary to create a surface finish that mimics tanned leather, but it may be desirable to provide a specific surface finish to tanned leather. Instead, in the second case, a surface finish that mimics leather should be created.

Surface finishes imitating tanned leather can be produced by a variety of known methods. Figure 2 schematically illustrates the production of a surface finish on an outermost, intermediate layer (B1), schematically represented by a series of triangles. In this case, the outer layer (C) is applied by a cylinder engraved with a dotted pattern filled with the material of the layer (C) and deposited on the layer (B1).

Each of the layers (A), (B), (B1) and (C) comprises as a main component at least one aliphatic polyurethane present in an amount of at least 80 wt% of each single layer, preferably at least 90 wt% of each single layer.

Each layer (A), (B), (B1) and (C) further comprises at least one component selected from the group consisting of a leveling agent, a crosslinking agent and a thickener. Preferably, each layer comprises all of these agents.

Leveling agents that can be advantageously used are fluorinated surfactants or mixtures thereof.

Crosslinking agents that can be advantageously used are polyethylene amines or mixtures thereof.

Thickeners that can be advantageously used are natural or synthetic thickeners.

Examples of inorganic natural thickeners include layered silicates, such as bentonite. Examples of organic natural thickeners include proteins, such as casein or polysaccharides. Natural thickeners selected from agar, gum arabic, and alginate are particularly preferred.

Examples of synthetic thickeners are generally liquid solutions of synthetic polymers, particularly polyacrylates.

Preferably, graphene is present in the layer (B) or layer (B1) in an amount of 0.5 to 15 wt%, more preferably 1.5 to 10 wt%, more preferably 2 to 8 wt% of the total weight of the layer.

Graphene is composed of at least 90% graphene nano-platelets having lateral dimensions (x, y) of 50 to 50000 nm and thickness (z) of 0.34 to 50 nm.

Preferably, at least 90% of the graphene nano-platelets have lateral dimensions (x, y) of 100 to 10000 nm and a thickness (z) of 0.34 to 10 nm, more preferably lateral dimensions (x, y) of 200 to 8000 nm, even more preferably 500 to 5000 nm, and a thickness (z) of 0.34 to 8 nm, even more preferably 0.34 to 5 nm.

The graphene nano-platelets have a C/O ratio of ≥ 100:1, preferably ≥ 200:1.

Graphene is a material composed of a single layer of ^sp2 hybridized carbon atoms arranged in a dense, highly crystalline, and regular hexagonal honeycomb structure.

Several methods for the production of graphene are known from the scientific and patent literature, such as chemical vapor deposition of oxidized forms of graphene oxide (GO), epitaxial growth, chemical exfoliation, and chemical reduction.

The applicant, Directa Plus S.p.A., is the owner of patents and patent applications relating to methods for producing structures comprising layers of graphene, such as EP 2 038 209 B1, WO 2014/135455 A1, and WO 2015/193267 A1. The latter two patent applications describe a method for producing dispersions of pristine graphene, which allows for obtaining graphene nanoplatelets having the dimensions required for the practice of the present invention and a C/O ratio of ≥ 100:1. This ratio is important because it defines the maximum amount of oxygen bonded to the carbon forming graphene. In fact, the best properties of graphene, derived from high crystallographic quality, are obtained when the amount of oxygen is minimal.

That is, pristine graphene having a C/O ratio of ≥ 100 and the dimensional characteristics defined above is manufactured and marketed by Directa Plus S.P.A. under the brand name G+ ^® .

The C/O ratio in the graphene used in the method according to the present invention is determined by elemental analysis performed by an elemental analyzer (CHNS O) that provides weight percentages of various elements. The C/O ratio is obtained by normalizing the obtained values to the atomic weights of C and O species and calculating the ratio.

Oxidized graphene, like graphene obtained through the reduction of graphene oxide ("GO"), has been found to possess characteristics and properties that differ from those of pristine graphene. For example, the electrical and thermal conductivity characteristics, as well as the mechanical strength characteristics, of pristine graphene are higher than those of GO and its reduction products, due to the presence of numerous network defects and imperfections in the crystalline structure induced by the reduction reaction.

The network defects in the nano-platelets can be evaluated using Raman spectroscopy by analyzing the intensity and shape of peak D located at 1350 cm ^{-1 .}

According to the embodiment described in the above-mentioned patent document by the applicant Directa Plus S.P.A., the process for producing pristine graphene is carried out continuously by continuously feeding graphite flakes into a high-temperature expansion stage, continuously discharging the expanded graphite thus obtained into an aqueous medium, and continuously subjecting the expanded graphite dispersed in the aqueous medium to an exfoliation and size reduction treatment carried out by ultrasonic treatment at high pressure and/or a homogenization method.

As described in these patent documents, the final dispersion of graphene nano-platelets obtained can be concentrated or dried depending on the final form desired for the graphene.

The purpose of drying the dispersion is to obtain a dry powder that is readily redispersible in a variety of matrices, solvents and polymers, both where liquids are undesirable or unmanageable at the process level or where water cannot be used due to chemical incompatibility.

A significant advantage of the manufacturing methods described in patent documents WO 2014/135455 A1 and WO 2015/193267 A1 lies in their ability to operate without the use of surfactants. Indeed, the graphene nanoplatelets thus obtained are very clean, both due to their high C/O ratio and the absence of foreign substances, such as surfactants, that could contaminate them. Indeed, the absence of surfactants has been shown to result in graphene with substantially higher electrical conductivity than graphene obtained using methods that use surfactants. This improves the performance of graphene in many applications.

Pristine graphene nanoplatelets, having at least 90% lateral dimensions (x, y) of 50 to 50,000 nm and a thickness (z) of 0.34 to 50 nm and a C/O ratio of ≥ 100:1, have high electrical conductivity. Furthermore, it has been shown that when a dispersion of graphene nanoplatelets is formed in the presence of a surfactant, it tends to deposit on its surface and promotes its aggregation.

In this description, the dimensions of the graphene nanoplatelets are defined with reference to the system of Cartesian axes x, y, z, and it is understood that the particles may be substantially flat platelets, but may also have irregular shapes. In any case, the lateral dimensions and thicknesses given with respect to the directions x, y, and z are to be intended as the maximum dimensions in each of the aforementioned directions.

The lateral dimensions (x, y) of the graphene nano-platelets are determined by directly measuring them using a scanning electron microscope (SEM) after diluting the final dispersion in deionized water at a ratio of 1:1000 and applying it dropwise onto a silicon oxide substrate arranged on a plate heated to 100°C, within the scope of the above-described preparation method.

Alternatively, if the nanoplatelets are available in a dry state, SEM analysis is performed directly on the powder deposited on double-sided carbon adhesive tape. In both cases, measurements are performed on at least 100 nanoplatelets.

The thickness (z) of graphene nanoplatelets is determined using atomic force microscopy (AFM), a subnanometer-resolution profilometer widely used for surface and nanomaterial characterization (primarily morphological). This type of analysis is commonly used to assess the thickness of graphene flakes prepared by any method, thereby determining the number of layers forming the flake (single layer = 0.34 nm).

Thickness (z) can be measured using a dispersion of nanoplatelets diluted 1:1000 in isopropanol, 20 ml of which is collected and subjected to sonication in an ultrasonic bath (Elmasonic S40) for 5 minutes. The nanoplatelets are then deposited as described for SEM analysis and directly scanned with an AFM tip, where the measurements provide a topographic image of the graphene flakes and their profiles on the substrate, enabling accurate thickness measurements. Measurements are performed on more than 50 nanoplatelets.

Alternatively, if dry nanoplatelets are available, the powder was dispersed in isopropanol at a concentration of 2 mg/L, 20 ml of which was collected and subjected to sonication in an ultrasonic bath (Elmasonic S40) for 30 min. The nanoplatelets were then deposited as described for SEM analysis and scanned using an AFM.

In the concentrated final dispersion or in the dried form obtained after drying, at least 90% of the graphene nano-platelets preferably have lateral dimensions (x, y) of 50 to 50000 nm and a thickness (z) of 0.34 to 50 nm, and a C/O ratio of ≥ 100:1. Preferably, at least 90% of the graphene nano-platelets have lateral dimensions (x, y) of 100 to 10000 nm and a thickness (z) of 0.34 to 10 nm, more preferably 200 to 8000 nm, even more preferably 500 to 5000 nm, and a thickness (z) of preferably 0.34 to 8 nm, more preferably 0.34 to 5 nm.

Graphene nanoplatelets having the above-mentioned features of dimensions and purity, and therefore having a very low oxygen content as defined by the above-mentioned C/O ratio and not being functionalized with other molecules, have proven to be particularly suitable for application on tanned leather or on textile substrates in the method according to the invention to form thermal and electrical circuits capable of evenly dissipating heat and electrostatic charge along the circuit.

The dispersion to be applied on the tanned leather or textile substrate of the present invention for forming each of the layers (A), (B), (B1) and (C) is in the form of a thick liquid or paste, wherein the dispersion liquid is preferably water or a mixture of water and another solvent and/or dispersant.

The term "thick liquid or paste" means an aqueous dispersion containing from 20 to 70 wt% solids, preferably from 25 to 60 wt% solids, more preferably from 30 to 50 wt% solids. In this dispersion, at least 90 wt% of the solids consist of aliphatic polyurethane and graphene nano-platelets.

The aqueous dispersion for forming each of layers (A), (B), (B1) and (C) further comprises at least one component selected from the group consisting of a leveling agent, a crosslinking agent and a thickener as described above. Preferably, the aqueous dispersion of the aliphatic polyurethane comprises all of these agents.

The aqueous dispersion for forming the layer (B) or layer (B1) comprises 0.5 to 15 wt%, more preferably 1 to 10 wt%, more preferably 1.4 to 8 wt% of graphene nano-platelets.

The aqueous dispersion is prepared by mixing an aliphatic polyurethane or aliphatic polyurethanes with one or more of the other components as defined above.

The preparation of the aqueous dispersion is preferably carried out by introducing the polyurethane pre-dispersed in water into a receptacle while stirring with a rotary stirrer, and then introducing the graphene, leveling agent, crosslinking agent, and thickener therein. The dispersion is stirred until a uniform dispersion is obtained. Typically, stirring is performed at a rotation speed of 1,000 to 2,500 revolutions per minute (rpm) for 1 to 2 hours.

According to one aspect of the present invention, the dispersion has a viscosity of 4000 to 30000 cPs, or mPa·s, as measured using a Fungilab series Viscolead PRO rotational viscometer, impeller R6, speed 10 rpm (revolutions per minute). Measured at T = 20°C. The viscosity of the composition is preferably in the range of 10000 to 20000 cPs, or mPa·s. The viscosity is also controlled by the amount of the thickener.

After applying the dispersion onto each layer of the substrate and/or the preformed coating, a step of heating the layers at an increasing temperature of 70 to 100°C for a time of 2 to 10 minutes follows. After the preparation of the last layer, heating is carried out at a higher temperature of 100 to 160°C, preferably 120 to 160°C, to effect crosslinking of the components and curing of the layer.

Depending on the operating mode, the heating step is performed sequentially in two ovens.

When the layers are deposited in the order of (C), (B), and (A) on the release paper and then coupled to the substrate via the layer (A), the coupling is performed before the last heating step. This is then performed while maintaining two ovens at different temperatures, so that the already coupled substrate is first inserted into a first oven at a temperature of 70 to 100°C to perform evaporation of the liquid, and then inserted into a second oven at a temperature of 120 to 160°C to perform crosslinking of the components and curing of the layers. The total duration of the heat treatment is 1 to 10 minutes.

In connection with the method for forming a coating on tanned leather and textile substrates, when the deposition of the various layers is carried out in the reverse order (C), (B1), (B) and (A) on an external support, such as a release paper, the coupling of the preformed layer to the tanned leather or textile substrate is carried out by means of a roller which presses the layer (A) onto the substrate before introduction into a second oven at a higher temperature, i.e. before the step of crosslinking the layer (A). In this way, crosslinking of the layer (A) takes place after contact with and adhesion to the substrate. After exiting the second oven, the release paper is detached, exposing the outer layer (C).

In order to provide a specific three-dimensional shape to the outer layer (C), for example to imitate natural leather, the outer layer (C) is manufactured with depressions or roughness suitable to provide a tactile feel similar to tanned leather. According to one embodiment, the imitation of tanned leather through the formation of depressions or roughness is carried out directly on the intermediate layer (B) or (B1), as shown in FIG. 2, and this layer is deposited on a release paper provided with depressions and/or roughness. Referring again to FIG. 2, the protective outer layer (C) is then deposited on the thus formed layer (B1) by a treatment consisting in applying the outer layer (C) by means of a cylinder imprinted with a dot-like pattern filled with the material of the layer (C), as shown in FIG. 2, and this being deposited on the layer (B1).

The total thickness of the coating including all layers is 42 to 160 μm, preferably 45 to 120 μm, more preferably 47 to 90 μm.

Application of the dispersion on a textile substrate or tanned leather forms a thermally and electrically dispersive coating characterized by the following parameters:

i. A thermal conductivity greater than 1 W/mK. It should be considered that the thermal conductivity of metals is typically > 20 W/mK, and that of insulating polymers is typically < 0.1 W/mK.

ii. Electrical conductivity, expressed as a surface resistivity of about 10 to 10 ⁸ Ω, i.e., the coating is substantially conductive.

Application of the dispersion onto tanned leather or textile substrates makes it possible to obtain coatings that are substantially electrically and heat dissipative.

When applied on textile substrates, the coating also imitates tanned leather, making it possible to obtain electrically and thermally dissipative imitation leather.

Accordingly, the articles obtained in this way can be advantageously used in the manufacture of articles in the clothing and furniture sectors, including seats and seating for the automobile sector.

The following examples illustrate some embodiments of the present invention and are provided as non-limiting examples.

Example

Each layer of the coating is manufactured using two types of aqueous aliphatic polyurethanes:

PU 1 - Viscosity = 1346 cP (20.5℃); ~ 35% solids content.

PU 2 - Viscosity = 53.4 cP (20.5℃); ~ 34% solids content.

Graphene was composed of nano-platelets manufactured by Directa Plus, dispersed in paste form (Paste G+) in aqueous dispersions of polyurethanes PU 1 and PU 2.

The paste G+ used consisted of 23.5% water and 76.5% graphene nanoplatelets (pure G+). Furthermore, a crosslinker, X-LINK 100 (dry residue 99%; polyaziridine) and a leveling agent, LEV 3F (dry residue 3.5-5.5; mixture of fluorinated surfactants) were also used. In the dispersion step, paste G+ was dispersed in polyurethane using a Cowles Dissolver DISPERMAT® CN40 disperser. The specifications of the machine were as follows: power 2.2 kW; rotation speed 0 - 5500 rpm (revolutions per minute); torque 7.2 Nm. The material was treated at 4000 - 5000 rpm (revolutions per minute) for 15 minutes. The prepared dispersion contained 5% graphene G+.

Example 1

Formation of the coating shown in Fig. 1

Textile substrate 10: Nonwoven fabric of polyester microfibers.

Layer (C): Thickness 5 μm; Weight 3 g/m ² ; Oven temperature: 85℃

Composition:

The layer (C) is spread on a release paper to provide an aesthetic effect with an organic geometric structure that mimics natural leather. The coating is performed on the release paper.

Layer (B): Thickness 20 μm; Weight 17 g/m ² ; Oven temperature: 85℃.

This is spread over the layer (C).

Composition:

Layer (A): Thickness 22 μm; Weight 38 g/m ² ;

Composition:

This is spread on layer (B). It is heated to 110°C in a first oven, coupled to a textile substrate, and heated to 150°C in a second crosslinking and curing oven.

The total weight of the coating was 58 g/m ² . The amount of graphene in the coating was 0.51 g/m ² , which is equivalent to 0.9%.

Example 2

Formation of the coating shown in Fig. 2

Textile substrate 20: Nonwoven fabric of polyester microfibers.

Layer (C): Thickness 4 μm; Weight 7 g/m ² ; Oven temperature: 85℃

Composition:

Layer (C) is applied onto layer (B1) by the “mill punti” method as described above as a final treatment when other layers are manufactured and coupled to the textile substrate.

Layer (B1) : Thickness 25 μm; Weight 40 g/m ² ; Oven temperature: 85℃.

This is spread on a release paper structured with depressions that provide a three-dimensional effect mimicking natural leather.

Composition:

Layer (B): Thickness 33 μm; Weight 45 g/m ² ; Oven temperature: 95℃.

This is spread on the layer (B1).

Composition:

Layer (A): Thickness 35 μm; Weight 50 g/m ² ; Oven temperature: 95℃.

Composition:

This is spread on layer (B). It is heated to 110°C in a first oven, coupled to a textile substrate, and heated to 150°C in a second crosslinking and curing oven.

The total weight of the coating was 142 g/m ² . The amount of graphene in the coating was 2.55 g/m ² , which is equivalent to 1.8%.

Claims (12)

A method for manufacturing a thermally and electrically conductive coating containing graphene, wherein the thermally and electrically conductive coating is applied on a leather substrate, the method comprising:
a) forming an inner layer (A) comprising at least one aliphatic polyurethane having a thickness of 10 to 50 μm and applied on the leather substrate;
b) forming at least one intermediate layer (B; B1) each having a thickness of 10 to 50 μm, each comprising at least one aliphatic polyurethane and graphene nano-platelets, wherein at least 90% of the number of the graphene nano-platelets have a lateral dimension in each of the x- and y-directions of 50 to 50000 nm and a thickness (z) of 0.34 to 50 nm, and a carbon-to-oxygen ratio of ≥ 100:1;
c) a step of forming an outer layer (C) comprising at least one aliphatic polyurethane having a thickness of 2 to 10 μm and applied on one of the at least one intermediate layer (B; B1)
Includes,
A method for producing a thermally and electrically conductive coating containing graphene, wherein the inner layer (A) and the outer layer (C) do not contain graphene. A method for producing a thermally and electrically conductive coating containing graphene, characterized in that in each of steps a), b) and c), the aliphatic polyurethane is applied in the form of an aqueous dispersion. A method for producing a thermally and electrically conductive coating containing graphene, characterized in that the aqueous dispersion further comprises at least one component selected from the group consisting of a leveling agent, a crosslinking agent, and a thickener in the second paragraph. A method for producing a thermally and electrically conductive coating containing graphene, characterized in that the method comprises, after each of steps a) and b), a heat treatment at a temperature of 70 to 100° C., and after step c), a heat treatment at a temperature of 100 to 160° C., wherein each of the heat treatments is performed for a time period of 1 to 10 minutes. A method for producing a thermally and electrically conductive coating containing graphene, wherein the deposition of the layers (A, B, B1, C) is performed in the reverse order (C, B1, B, A) on an external support in any one of claims 1 to 3, and then the thus deposited layers are coupled to the leather substrate so that the inner layer (A) comes into contact with the leather substrate, and finally the external support is detached to expose the outer layer (C). A method for producing a thermally and electrically conductive coating containing graphene, wherein the leather substrate comprises a textile substrate for producing natural leather or synthetic leather, according to any one of claims 1 to 3. An inner adhesive layer (A) in contact with the leather substrate and comprising at least one aliphatic polyurethane having a thickness of 10 to 50 μm;
At least one intermediate layer (B, B1) superimposed on the inner adhesive layer (A), each having a thickness of 10 to 50 μm, wherein each of the at least one intermediate layer (B, B1) comprises at least one aliphatic polyurethane and 1.5 to 10 wt.% of graphene nano-platelets based on the total weight of the layer, wherein at least 90% of the number of the graphene nano-platelets has a lateral dimension in each of the x- and y-directions of 50 to 50000 nm and a thickness (z) of 0.34 to 50 nm, and wherein the carbon-to-oxygen ratio is ≥ 100:1;
An outer layer (C) superimposed on one of the above one or more intermediate layers (B, B1) and comprising one or more aliphatic polyurethanes having a thickness of 2 to 10 μm.
A leather substrate comprising a coating characterized by including: A leather substrate, characterized in that in claim 7, each of the layers (A, B, B1 and C) comprises, as its main component, at least one aliphatic polyurethane present in an amount of at least 80 wt%, or at least 90 wt%, of each individual layer. A leather substrate according to claim 7 or 8, characterized in that the graphene is present in each of the at least one intermediate layer (B, B1) in an amount of 2 to 8 wt% based on the total weight of the layer. A leather substrate according to claim 7 or 8, characterized in that the graphene comprises graphene nano-platelets having a lateral dimension in each of the x- and y-directions of 100 to 10,000 nm and a thickness (z) of 0.34 to 10 nm, or a lateral dimension in each of the x- and y-directions of 200 to 8,000 nm or 500 to 5,000 nm and a thickness (z) of 0.34 to 8 nm or 0.34 to 5 nm. A leather substrate according to claim 7 or 8, characterized in that the graphene comprises graphene nano-platelets having a carbon-to-oxygen ratio of ≥ 100: 1 or a carbon-to-oxygen ratio of ≥ 200: 1. A leather substrate comprising a textile substrate for the production of natural leather or synthetic leather according to claim 7 or 8.