Coating process, in particular by solvent-evaporation, for coating a substrate, in particular a substrate of complex shape, with a composite coating

Abstract

A process for coating a substrate (1) with a composite coating, the composite coating comprising a polymer matrix and particles, in particular reinforcing and / or functional particles, dispersed in said polymer matrix,the process comprising the steps of: a) dissolving a polymer in a solvent to obtain a polymer solution; b) dispersing said particles in the polymer solution to obtain a mixture; c) covering the substrate with said mixture; d) evaporating the solvent from the mixture which covers the substrate; wherein after step d), said substrate (1) coated with said composite coating comprising a polymer matrix and particles, in particular reinforcing and / or functional particles, dispersed in said polymer matrix is obtained; wherein in step b) the percentage ratio between the sum of the weight of the polymer in the mixture and the weight of said particles in the mixture / solvent volume in the mixture is from 0.1% to 30%, said percentage ratio being expressed according to the formula; (A) wherein in step c) the substrate (1) is immersed in said mixture.

Description

[0001] COATING PROCESS, IN PARTICULAR BY SOLVENT-EVAPORATION, FOR COATING A SUBSTRATE, IN PARTICULAR A SUBSTRATE OF COMPLEX SHAPE, WITH A COMPOSITE COATING

[0002] Field of the invention

[0003] The present invention relates to the field of substrate coating processes. Background art

[0004] The coating technologies for substrate functionalization which are adopted in industrial practice are PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition), electrodeposition (see for example US2020290084), electrolysis, fluid bed, thermal spray, painting and cladding.

[0005] The main criticalities of CVD are the high environmental impact and the temperature reached in the process. Furthermore, the coating is limited to the surfaces directly exposed to the vapor.

[0006] The main criticalities of PVD are the high environmental impact and the geometry of the sample which does not allow the application of the process continuously.

[0007] The main criticality of electrodeposition is the applicability thereof only to electrically conductive substrates.

[0008] The main criticalities of the electrolysis technique are the process toxicity and the poor adhesion of the coating to the substrate.

[0009] The main criticalities of the fluid bed technique are the timing and geometric limitations that the substrate must have in order to be coated.

[0010] The main criticalities of the cladding technique are related to the need to apply the coating to substrates being resistant to high temperatures. Furthermore, only coatings with a high thickness can be obtained with this technique.

[0011] The main criticalities of painting are the high environmental impact and the limitation of the materials that can be used.

[0012] Therefore, the need is felt to overcome the limitations of the background art. Summary of the invention

[0013] It is an object of the present invention to provide a coating process which allows coating a substrate without particular limitations imposed by the geometry of the substrate. In particular, it is an object of the invention to provide a process which allows coating a substrate without particular limitations imposed by the properties of the substrate, in particular a process which allows coating a substrate which is not necessarily electrically conductive.

[0014] In particular, it is an object of the invention to provide a coating process with low environmental impact and which can be carried out particularly easily.

[0015] The present invention achieves at least one of such objects, and other objects which will become apparent in light of the present description, by means of a process for coating a substrate, or body, or piece, or component, with a composite coating, the composite coating comprising a polymer matrix and particles, in particular reinforcing and / or functional particles, dispersed in said polymer matrix, the process comprising the steps of: a) dissolving a polymer in a solvent to obtain a polymer solution; b) dispersing said particles in the polymer solution to obtain a mixture; c) covering the substrate with said mixture; d) evaporating the solvent from the mixture which covers the substrate; wherein after step d), said substrate coated with said composite coating comprising a polymer matrix and particles, in particular reinforcing and / or functional particles, dispersed in said polymer matrix is obtained; wherein in step b) the percentage ratio between the sum of the weight of the polymer in the mixture and the weight of said particles in the mixture / solvent volume in the mixture is from 0.1 % to 30%, said percentage ratio being expressed according to the wherein in step c) the substrate (1 ) is immersed in said mixture; said process being in particular a solvent-evaporation coating process.

[0016] The invention further relates to a substrate according to claim 19.

[0017] It is highlighted that the immersion of the substrate in the mixture and the selection of the aforesaid range have a synergistic effect in particular of obtaining an optimal coating. In particular, such features allow the formation of a homogeneous and continuous layer of composite coating, allow a correct control of the thickness, and allow adequately coating even a substrate having a complex geometry. Advantageously, the process according to the invention is adapted to make a polymer matrix composite coating with particle reinforcement on substrates, even having complex geometries. For example, the particles can be particles of a filler. In particular, the process utilizes the solvent-evaporation technology.

[0018] Advantageously, a process according to the invention allows coating a substrate, even of complex shape, without particular limitations imposed by the geometry of the substrate.

[0019] Advantageously, a process according to the invention allows coating a substrate without particular limitations imposed by the properties of the substrate, in particular the process allows coating a substrate which is not necessarily electrically conductive.

[0020] Advantageously, a process according to the invention is of low environmental impact and particularly easy to be carried out.

[0021] The coating can advantageously confer a functionalization for thermal and / or electrical and / or mechanical and / or shielding purposes.

[0022] In particular, advantageously, a process according to the invention allows conferring physical and / or chemical and / or mechanical surface properties which are improved with respect to the same properties of the substrate without said coating. In particular, by means of said process, in particular solvent-evaporation process, and using particles of materials with specific properties, it is possible to transfer the latter to the substrate, obtaining a homogeneous and functional coating.

[0023] Therefore, advantageously, a process according to the invention allows improving the surface properties of the substrate.

[0024] Advantageously, there is no specific limitation on the type of particles which can be used. In particular, particle reinforcements preferably having a maximum size, i.e. , a maximum dimension, from 1 nm to 900 pm can be used, with the possibility of using ceramic, polymer, metal, bio-origin materials or innovative materials such as carbon allotropes (nanotubes, diamond, graphene and derivatives, and fullerenes), 2D materials (hexagonal boron-nitrate, molybdenum disulfide / tungsten, M-Xenes, LDH, etc.) or 1 D materials (BNNT, MOS2NT, BPNT, etc.).

[0025] By means of the process according to the invention it is possible to transfer the specific properties of the particles (e.g., fillers) to the substrate having a substantially two-dimensional or three-dimensional geometry, even of complex shape, making a homogeneous and functional coating.

[0026] Advantageously, there is no specific limitation on the material forming the polymer matrix of the coating, which can be for example a polymer of a thermoplastic, thermosetting, or elastomeric nature.

[0027] The corresponding solvent, e.g., water, alcohols, polar solvent, non-polar solvent, organic solvent, inorganic solvent, is chosen as a function of the polymer used.

[0028] The process imposes no particular limitations either in terms of material of the substrate and the shape thereof (which can also be a 3D complex shape).

[0029] Advantageously, since the process does not include the use of electric current, it does not need the presence of an electrically conductive substrate, and given the absence of high temperatures, has no limitations related to a possible thermal degradation.

[0030] For example, the process allows obtaining coatings on metals, synthetic polymers, bio-origin polymers (e.g., paper), natural polymers (wood and derivatives thereof), glass, composites, ceramics, minerals or rocks.

[0031] The substrate or component obtained at the end of the process has improved properties with respect to the substrate without coating. For example, the coated substrate can have one or more of the following features: high thermal and / or electrical conduction, resistance to corrosion and / or environmental degradation, protection from biological and / or viral agents, hydrophobicity and / or surface tension properties, flame retardant properties, resistance to wear and / or increased hardness, fatigue resistance and / or self-healing.

[0032] The advantages of a process according to the invention include: process versatility; absence of geometric and / or chemical-physical limitations of the substrate; reduced costs; high industrial scalability; limited and / or negligible environmental impacts (as a function of the polymer forming the matrix); high surface properties which can be functionalized based on the selected particles (e.g., fillers).

[0033] Given the high versatility of the process according to the invention, the industrial uses are highly varied including, by way of non-limiting example, the following: structural applications both indoors and outdoors due to the resistance to aggressive environmental agents conferrable by the coating to the substrate; use in furniture components by virtue of the antibacterial and antiviral properties conferrable to the substrate, or increase in the tribological properties of mechanical components.

[0034] Possible areas of application can be for example: aerospace, construction, health, precision mechanics, nano- and microelectronics, design and furniture, ships, thermal applications.

[0035] Further features and advantages of the invention will become more apparent in light of the detailed description of exemplary but non-exclusive embodiments.

[0036] The dependent claims describe particular embodiments of the invention.

[0037] Brief description of the figures

[0038] In the description of the invention reference is made to the accompanying drawing, given by way of non-limiting example, in which:

[0039] Fig. 1 shows an example of a substrate, or body, which can be coated by a process according to the present invention.

[0040] Description of exemplary embodiments of the invention

[0041] Exemplary embodiments of a process for coating a substrate 1 , or body, or piece, or component, with a composite coating are described, the composite coating comprising a polymer matrix and particles, in particular reinforcing and / or functional particles, dispersed in said polymer matrix.

[0042] In all the embodiments, the process comprises the steps of: a) dissolving a polymer in a solvent to obtain a polymer solution; b) dispersing said particles in the polymer solution to obtain a mixture; c) covering, at least partially for example completely, the substrate 1 with said mixture; d) evaporating the solvent from the mixture which covers the substrate 1 ; wherein after step d), said substrate 1 coated with said composite coating comprising a polymer matrix and particles, in particular reinforcing and / or functional particles, dispersed in said polymer matrix is obtained; said process being in particular a solvent-evaporation coating process.

[0043] Furthermore, advantageously, in step c) the substrate 1 is immersed in said mixture. Immersion is particularly advantageous since it allows the substrate to be homogeneously coated, even if the substrate has a complex shape. For example, in step c) the substrate is placed in a container containing the mixture, and for example in step d) the substrate can be left in the container or be extracted from the container.

[0044] Preferably, in step c) the substrate 1 is completely immersed in the mixture.

[0045] Furthermore, advantageously, in step b) the percentage ratio between the sum of the weight of polymer in the mixture and the weight of said particles in the mixture I solvent volume in the mixture, in particular at room temperature, is from 0.1 % to 30%, said percentage ratio being in particular expressed according to the formula grams of polymer in mixture + grams of said particles in mixturen / liters of solvent in mixture

[0046] Such a ratio substantially defines the coating / solvent ratio, defined as the weight / volume percentage between the materials forming the matrix and the reinforcement (i.e., the particles) and the volume of solvent, in particular at room temperature. "Room temperature" means in particular a temperature between 20 and 25 °C, preferably about 25 °C.

[0047] Ratios less than 0.1 % preclude the formation of a continuous layer of composite coating, not conferring improved properties to the substrate.

[0048] Ratios above 30% result in a viscosity such that there is not correct control of the thickness. Furthermore, it is difficult to define the details in complex geometries, such as lack of localized coating, occlusion of holes or indentations and modification of angles on sharp edges, for example.

[0049] Therefore, the immersion of the substrate in the mixture and the selection of the aforesaid range have a synergistic effect in particular of obtaining an optimal coating. In particular, such features allow the formation of a homogeneous and continuous layer of composite coating, allow a correct control of the thickness, and allow adequately coating even a substrate having a complex geometry.

[0050] Said substrate 1 , or body, or piece, or component, can be a non-planar substrate, in particular not having a completely flat surface.

[0051] Said substrate 1 , or body, or piece, or component, can have a shape, in particular a complex shape, having at least one curved portion and / or at least one undercut and / or at least one hole or opening.

[0052] In general, the substrate 1 , or body, or piece, or component, can have a complex shape. Complex shape means in particular a shape having high curvature variations and / or high point features with respect to the overall size of the substrate. In addition, or alternatively, a substrate of complex shape can have any holes or areas not visible by simple projection views, such as undercuts and / or internal or limited access areas.

[0053] The polymer usable to make the polymer matrix, i.e. , the polymer usable in step a), can be selected from: thermosetting polymers; thermoplastic polymers; elastomeric polymers; natural polymers (e.g., cellulose, starch, proteins); polysaccharide gels.

[0054] The solvent used in step a) is selected as a function of the polymer.

[0055] For example, the solvent used in step a) can be selected from: water, polar organic solvents (e.g., ethanol and butyl acetate), apolar organic solvents (e.g., hexane, benzene), mixtures of organic solvents and / or water, mixtures of commercial solvents such as turpentine and slow solvent.

[0056] Preferably, the percentage weight ratio of said particles in the mixture and said polymer in the mixture is from 10% to 90%, said percentage ratio being in particular expressed according to the formula - - - - - - %. grams of polymer in mixture

[0057] Ratios less than 10% do not allow the establishment of a continuous and effective network of particles (filler), significantly decreasing performance, e.g., thermal and / or electrical conduction of the coating. The interaction between the particles (fillers) and the external environment is also reduced, inhibiting the specific functions of the particles such as: antibacterial properties, hydrophobic or hydrophilic properties, catalytic functions, and reduced surface friction functions.

[0058] Ratios above 90% do not allow a suitable fixing to the substrate, thus making the coating substantially unusable.

[0059] Concentrations in the identified range allow obtaining good or excellent performance, maintaining a suitable adhesion of the coating to the substrate.

[0060] Preferably, in step a) the concentration of polymer, in particular in the solvent, is from 0.01 % to 50% by weight, said concentration being in particular expressed accordin to the formula

[0061] ® Preferably, in step b) the concentration of said particles in the mixture is from 0.01 % to 50% by weight, said concentration being in particular expressed according to the formula

[0062] Optionally, one or more additive materials, in particular surfactants and / or tensides, can be added to the mixture, adapted to improve the dispersion of the particles in the solvent and thus improve the coating uniformity. Such materials comprise, by way of example: CTAB, SDS, PEG, Hydroxypropyl cellulose, Hydroxymethyl cellulose, Hydroxypropyl methylcellulose, Lauryl ethoxy sulfate, Benzalkonium chloride, Polyacrylic acid, or combinations thereof.

[0063] The ratio between said one or more materials and said particles (fillers) is definable by percentage weight ratio. The percentage weight ratio between said one or more materials and the particles can be up to 100% by weight, in particular from 0% (without said materials) to 100%.

[0064] The use of additive(s), in particular surfactant(s) and / or tenside(s), is optional in the case of particles easily dispersible in the chosen solvent, reducing the cost, complexity, and environmental impact of the coating technology. The adoption of one or more additives is useful if a homogeneous and stable dispersion of the particles (fillers) in the solvent is not observed, which leads to formation of localized clusters in the coating or alteration of the concentration of the particles in suspension over time. Concentrations above 100% do not bring significant improvements to the quality of the dispersion, but alter the environmental and economic impact of the product and the performance of the latter.

[0065] Preferably, before said step c), a pre-treatment step of the substrate 1 is provided to remove surface impurities from the substrate and / or promote the adhesion of the composite coating; in particular said pre-treatment comprises a treatment of mechanical and / or chemical and / or electrochemical and / or physical type.

[0066] Examples of mechanical treatments are: sandblasting, shot peening, tumble finishing, hammer peening, and lapping.

[0067] Examples of chemical treatments are: acid etching, basic etching; degreasing and / or pickling, electropolishing. Examples of physical treatments are: use of laser beam, use of cold plasma, use of hot plasma, corona treatment, use of electron beam, use of ion beam, use of UV light, cleaning by ionized air.

[0068] Preferably, in step b) the dispersion of said particles is carried out by mechanical and / or magnetic and / or ultrasonic and / or compressed air stirring.

[0069] Optionally, there is provided a step of curing the polymer matrix of the composite coating and / or altering the composite coating, in particular by heat treatment and / or UV and / or sintering; said step of curing and / or altering the composite coating being in particular carried out after step d).

[0070] Preferably, said coating has a thickness from 1 pm to 2 mm.

[0071] Preferably, said particles have a maximum size (i.e., maximum dimension) from 1 nm to 900 pm. In other words, preferably, the maximum dimension among the three dimensions of each particle is preferably in the aforesaid range.

[0072] Preferably, said particles have at least one dimension less than or equal to 100 nm. This feature is advantageous, since allows a stable and homogeneous dispersion. Preferably, none, one, or two dimensions of said particles are greater than 100 nm. Preferably, said particles are one or more of the following: fullerenes, carbon dots, carbon onions, quantum dots, nanoparticles, nanotubes, nanowires, nanobars, nanoribbons, graphene (in particular graphene nanoplatelets), hexagonal boron nitrate, bisulfides, monolayer of transition metal chalcogenides. The above- mentioned particles are Low Dimensional Materials.

[0073] Such particles are advantageous in particular because they allow a stable and homogeneous dispersion, and thus allow obtaining a particularly homogeneous coating. Furthermore, they have thermal and / or electric properties.

[0074] As already mentioned, said particles can also be innovative materials such as carbon allotropes (nanotubes, diamond, graphene and derivatives, and fullerenes), 2D materials (hexagonal boron-nitrate, molybdenum disulfide / tungsten, M-Xenes, LDH, etc.) or 1 D materials (BNNT, MOS2NT, BPNT, etc.).

[0075] Preferably, said particles are particles of one or more (i.e., are) low dimensional materials (LDMs), in particular 0D, preferably fullerenes, carbon dots, carbon onions, quantum dots, nanoparticles, and / or 1 D, preferably nanotubes, nanowires, nanobars, nanoribbons, and / or 2D, preferably graphene, hexagonal boron nitrate, bisulfides, monolayer of transition metal chalcogenides.

[0076] "Low dimensional material" means in particular a nanomaterial, i.e. , having at least one dimension less than 100 nm, which extends along 0, 1 or 2 preferential directions, i.e., LDM 0D, LDM 1 D, and LDM 2D, respectively.

[0077] The fibers are not classified as LDMs.

[0078] The evaporation of the solvent in step d) can be carried out, for example, at room temperature or at a higher temperature than the room temperature.

[0079] Optionally, the substrate 1 coated with said coating is coated with at least one further coating layer, preferably made of metal.

[0080] For example, said further coating layer can be from 1 pm to 2 mm.

[0081] Optionally, said further coating layer is made by electrodeposition and / or chemical vapor deposition (CVD) and / or physical vapor deposition (PVD) and / or cladding.

[0082] An advantageous example includes coating a substrate 1 which is not electrically conductive with a polymer matrix composite coating in which electrically conductive particles are dispersed, and optionally applying a further coating layer by electrodeposition, for example.

[0083] The invention further relates to a substrate 1 coated with said composite coating comprising a polymer matrix and particles, in particular reinforcing and / or functional particles, dispersed in said polymer matrix, obtained by a process according to the present invention.

[0084] Optionally, the substrate is removed from the substrate coated with said coating, so as to obtain a three-dimensional structure, in particular self-standing, consisting of said coating; in particular wherein the substrate is removed by chemical and / or thermal etching and / or by deflating the substrate and / or by disassembling the substrate. For example, the substrate to be coated can be a deflatable or disassemblable mandrel, such as similar to those used in filament winding; or the substrate to be coated can be a friable resin.

[0085] On the structure resulting from the removal of the substrate, a treatment can optionally be carried out to further increase the surface properties, for example through at least one treatment chosen from mechanical treatment, chemical treatment, electrochemical treatment, and treatment by means of concentrated energy beams.

[0086] Optionally, the structure resulting from the removal of the substrate can be fixed to another structure, preferably obtained by a process according to the present invention.

[0087] For example, on a structure having electrical conductivity, it is possible to achieve a subsequent metallization to make a connection with another structure feasible by means of the brazing technique.

[0088] Optionally, at the end of the product life, it is possible to recover the constituent raw materials, said particles and the polymer matrix by means of an appropriate solvent for a possible reuse and / or for an appropriate subsequent disposal process.

[0089] In an experimental example, a substrate made by additive manufacturing, in particular of the FFF type, was coated. The substrate was made of PLA (Polylactic acid). A solution was then prepared using polyacrylic acid (as a polymer for polymer matrix formation) and water (as a solvent). The particles dispersed in step b) were graphene nanoplatelets GNPs, in particular in a 1 :1 ratio by weight. The mixture was conveniently sonicated and then used to coat the substrate by immersion. The process was characterized by a high ease of implementation and once the samples were obtained, they were tested using an instrument capable of measuring electrical resistance, by recording a decrease in electrical resistance ranging from 10E+09 0 to 10E+04 0 with respect to the uncoated substrate. A reduction in the volume of wear in the flat ball test equal to 65% with respect to the uncoated substrate was recorded.

Claims

CLAIMS1. A process for coating a substrate (1 ) or body with a composite coating, the composite coating comprising a polymer matrix and particles, in particular reinforcing and / or functional particles, dispersed in said polymer matrix, the process comprising the steps of: a) dissolving a polymer in a solvent to obtain a polymer solution; b) dispersing said particles in the polymer solution to obtain a mixture; c) covering the substrate with said mixture; d) evaporating the solvent from the mixture which covers the substrate; wherein after step d), said substrate (1 ) coated with said composite coating comprising a polymer matrix and particles, in particular reinforcing and / or functional particles, dispersed in said polymer matrix is obtained; wherein in step b) the percentage ratio between the sum of the weight of the polymer in the mixture and the weight of said particles in the mixture / solvent volume in the mixture is from 0.1 % to 30%, said percentage ratio being expressed according to thewherein in step c) the substrate (1 ) is immersed in said mixture.

2. The process according to claim 1 , wherein said particles have a maximum size from 1 nm to 900 pm.

3. The process according to claim 1 or 2, wherein said particles have at least one dimension less than or equal to 100 nm.

4. The process according to any one of the preceding claims, wherein none, one or two dimensions of said particles are greater than 100 nm.

5. The process according to any one of the preceding claims, wherein said particles are one or more of the following: fullerenes, carbon dots, carbon onions, quantum dots, nanoparticles, nanotubes, nanowires, nanobars, nanoribbons, graphene, hexagonal boron nitrate, bisulfides, monolayer of transition metal chalcogenides.

6. The process according to any one of the preceding claims, wherein said substrate (1 ) is a non-planar substrate.

7. The process according to any one of the preceding claims, wherein said substrate (1 ) has a shape, in particular a complex shape, having at least one curved portion and / or at least one undercut and / or at least one hole or opening.

8. The process according to any one of the preceding claims, wherein the percentage weight ratio of said particles in the mixture and said polymer in the mixture is from 10% to 90%, said percentage ratio being in particular expressed according to the formula9. The process according to any one of the preceding claims, wherein in step a) the polymer concentration, in particular in the solvent, is from 0.01 % to 50% by weight, said concentration being in particular expressed according to the formula grams of polymer in the polymer solutionn / grams of polymer solution10. The process according to any one of the preceding claims, wherein in step b) the concentration of said particles in the mixture is from 0.01 % to 50% by weight, said concentration being in particular expressed according to the formula grams of said particles in mixturen / grams of mixture11. The process according to any one of the preceding claims, wherein before said step c), there is provided a step of pre-treating the substrate (1 ) to remove surface impurities from the substrate and / or promote the adhesion of the composite coating; in particular wherein said pre-treatment comprises a treatment of mechanical and / or chemical and / or electrochemical and / or physical type.

12. The process according to any one of the preceding claims, wherein in step b) the dispersion of said particles is carried out by stirring, in particular mechanical and / or magnetic and / or ultrasonic and / or compressed air stirring.

13. The process according to any one of the preceding claims, wherein there is provided a step of curing the polymer matrix of the composite coating and / or altering the composite coating, in particular by heat treatment and / or UV and / or sintering; said step of curing and / or altering the composite coating being in particular carried out after step d).

14. The process according to any one of the preceding claims, wherein said coating has a thickness from 1 pm to 2 mm.

15. The process according to any one of the preceding claims, wherein said particles are particles of one or more low dimensional materials (LDMs), in particular 0D, preferably fullerenes, carbon dots, carbon onions, quantum dots, nanoparticles, and / or 1 D, preferably nanotubes, nanowires, nanobars, nanoribbons, and / or 2D,preferably graphene, hexagonal boron nitrate, bisulfides, monolayer of transition metal chalcogenides.

16. The process according to any one of the preceding claims, wherein the substrate(1) coated with said coating is coated with at least one further coating layer, preferably made of metal.

17. The process according to claim 16, wherein said further coating layer is obtained by electrodeposition and / or chemical vapor deposition (CVD) and / or physical vapor deposition (PVD) and / or cladding.

18. The process according to any one of the preceding claims, wherein the substrate is removed from the substrate coated with said coating, so as to obtain a three- dimensional structure consisting of said coating; in particular wherein the substrate is removed by chemical and / or thermal etching and / or by deflating the substrate and / or by disassembling the substrate.

19. A substrate (1 ), or body, coated with said composite coating comprising a polymer matrix and particles, in particular reinforcing and / or functional particles, dispersed in said polymer matrix, obtained by means of a process according to any one of the preceding claims.

Images