SI25955A - Electrically conductive coating - Google Patents

Abstract

Electrically conductive coating allows to ensure the electrical conductivity of various surfaces such as wood, plastics, metals, ceramics, plasters, glass, etc. The coating is quick-drying and waterproof. It adheres well to surfaces and is partially flexible, which reduces problems with cracking of the coating. It is intended primarily for use in heating elements, capacitive sensors, protection against electromagnetic radiation, electrolytic coating of non-conductive materials, manufacture of electronic circuits and devices, enabling thermal conductivity of the surface, etc. It provides good surface conductivity, which can be further adjusted by the method of application of the coating and the final mechanical treatment.

Description

ELECTRIC CONDUCTIVE COATING

The subject of the invention is an electrically conductive carbon-based coating that ensures the electrical conductivity of the surface to which it is applied, and a process for applying and subsequently treating the coating to ensure adequate application quality to each surface. In the context of this application, the term "coating" refers to a composition that is applied to a surface and then treated appropriately to ensure the appropriate quality of the final application to each surface. The coating is waterproof and flexible. It is intended for application to various materials such as wood, plastics, paper, ceramics, plasters, metal, glass, textiles, etc. The coating is formulated in liquid form with solid conductive particles dispersed in a suitable solvent, the liquid coating being applied to the surface in known ways to apply the liquid coating to the surface, such as by spray application, brush application, roller application or in any other way known to those skilled in the art of applying liquid coatings. The coating can be formulated in powder form, the powder being mixed with a solvent before use. The application in this case takes place in the same way as in the above-described procedure for applying the coating in liquid form. Regardless of the coating formulation used and the coating technology used, the final coating can be further processed by compression, which increases the conductivity or reduces the layer resistance, and makes it easier to determine the conduction range, while ensuring better adhesion, lower application thickness and look with metallic luster.

BACKGROUND OF THE INVENTION:

Nowadays, it is important for both consumers and industry that products and devices are compact, inexpensive and easy to use. The main progress in this is made possible by new materials and new ways of using them. The conductive coating presented in the present invention enables this in a number of different devices as a main component or as an additive that enables miniaturization and simplification of production, especially series production. The main purpose of the coating according to the invention is to provide the conductivity of surfaces for the transmission of various signals, protection against interference or the conversion of electric current into heat, for example when used in a resistance heater. In addition, there are a number of new applications in sensor and other devices, which are enabled by the coating properties according to the invention, especially excellent adhesion to different surfaces, flexibility, water resistance, different application options, the possibility of post-treatment of the application in terms of increasing conductivity. price advantage.

Comparable graphite-based coatings currently appearing on the market have low conductivity. Possibilities of increasing the conductivity of coatings by using conductive fillers and special binders have already been presented, which greatly increases the number of components and increases the cost of production due to expensive raw materials and complex manufacturing processes (eg DE202014009744U1, DE202016106096U1,

CN104231749A, CN103146259B, US20150240099A1, JP3400236B2,

GB2526591A, US 2012/0020033 A1).

Currently known coatings, which enable the conductivity of surfaces, are mostly water-based and have a long drying time, which limits the possibilities of application to some surfaces. Also, their adhesion on different surfaces is poorer and their conductivity is lower. As a result, the application process can be quite complicated.

Conductive coatings, paints and inks for industrial use are often applied by a screen printing process, which is otherwise suitable for creating specific patterns on the substrate, but presents greater difficulties when applied to larger surfaces, especially when applied by spraying.

The conductive coating according to the invention enables the conductivity of the final product using standard materials. The production process is simple and safe, raw materials are widely available, which allows to simplify the entire production process compared to the competition. The presented coating is also useful on several different substrates such as paper, cardboard, wood, textiles, artificial and natural fibers, ceramics, concrete, stone, glass, plastics. By using different solvents, the applicability of the coating on different surfaces can be ensured. An additional advantage is that the coating is quick-drying, which is desirable especially in the serial production of products. Flexibility of the final application is a very desirable property, as it enables the conductivity of materials that are exposed to bending and various deformations such as various foils, textiles, fibers, paper, etc.

The technical problem solved by the submitted electrically conductive coating is the formulation of such a coating that provides water resistance, flexibility, high electrical conductivity and good adhesion to various surfaces with the possibility of further processing to ensure higher conductivity, which similar coatings do not show. The coating is quick-drying and enables various finding techniques suitable for industrial and domestic use. Due to its composition, it is not limited to use at low voltage, but can be used at all voltages with adequate protection with electrical insulation. Also, the presented conductive coating has a completely new formula, which has not been used for similar coatings so far.

Additionally, the coating according to the invention can be formulated in powder form, i.e. in powder, to which a solvent is later added according to the required application. The conductivity of the coating is regulated by changing the ratio of the components, by the thickness of the coating and by mechanical treatment, for example by compressing the final coating, which is not possible with similar coatings.

The electrically conductive coating according to the invention includes at least a conductive filler and a binder. The conductive filler includes graphite particles and carbon black. Graphite can be natural or artificial, the graphite particles being of various shapes, namely in the form of powder and / or rods and / or cloths, and the size of the graphite particles being from 0.5 to 200 micrometers, preferably from 5 to 50 micrometers. The stated graphite particle size dimension refers to the longest dimension of an individual particle shape. Carbon black can be any of a variety of types, preferably a highly conductive carbon black such as, but not limited to, SuperP. The carbon black particles can be of various shapes, namely in the form of powder and / or sticks and / or cloths, etc .., the size of the carbon black particles being between 0.5 to 200 micrometers, preferably from 5 to 100 micrometers. The stated particle size dimension carbon black refers to the longest dimension of an individual particle shape. In some applications, especially in the production of paint for IR heaters, the specific surface of Carbon black is also important. A specific area of 50 m2 per gram or more is preferred. The carbon black content of the graphite in the conductive filler is from 5% by weight to 15% by weight, preferably from 8% by weight to 13% by weight.

Additionally, the conductive filler may include additives to increase conductivity in the form of conductive metal particles, for example silver or copper, and / or other various forms of graphite, for example graphene, carbon nanotubes, and the like. The size of these particles is between 0.5 and 200 micrometers, preferably 5 to 50 micrometers. Mass ratio of additives to increase conductivity: graphite is smaller than the ratio of carbon black to graphite, depending on the desired properties of the coating and the material used, preferably between 1:10 and 1: 100.

The binder ensures the adhesion of the coating to the surface of the substrate, the flexibility of the final application and allows a good connection between the particles of the conductive filler in a way that allows electrical conductivity. The binder is polyvinyl butyral, hereinafter PVB, in the form of a powder with a particle size between 0.5 and 200 micrometers, preferably 5 to 100 micrometers. The binder content with respect to the conductive filler in the conductive coating is from 10% by weight to 30% by weight, preferably from 13% by weight to 18% by weight.

The electrically conductive coating of the invention further includes a solvent for formulating the coating in liquid form. Suitable solvents are organic solvents in which the binder is soluble. A suitable solvent is selected from, but not limited to, ethanol, isopropyl alcohol or butanol, or a mixture thereof. To ensure the legally prescribed limits for the content of volatile organic compounds and other purposes, such as regulating the drying time, etc. the solvent can be diluted with various substances, preferably water, so that instead of 96% ethanol, for example, either 80% or 60% ethanol is used. It should be borne in mind that such dilution can change the quality of the final application in terms of resistance, adhesion to different materials and the appearance of the application. The drying time is also extended. The content of the binder, i.e. polyvinyl butyral, relative to the solvent is from 2 wt% to 20 wt%, preferably from 5 wt% to 8 wt%.

Various additives can be added to the conductive coating to suit its specific use. In addition to the aforementioned additives to increase the conductivity, which can optionally be added to the conductive filler, the conductive coating may additionally include additives to strengthen the coating structure (eg: ground carbon fibers, glass fibers), additives to prevent sedimentation (eg: fumed silica ), additives for changing the appearance of the coating, for changing the structure of the coating (eg: additives to increase the specific application surface), for changing the physical (eg: additives to increase or decrease the viscosity) and chemical properties of the coating (eg: additives for better adhesion) on specific surfaces, reduced reactivity, fungicidal additives, etc.).

The viscosity of the final coating formulation in liquid form is generally between 19 mPas and 500 mPas.

The type of PVB used (ie molar mass, number of butyrai groups) depends on the desired properties of the final coating such as water resistance, viscosity of the liquid coating, solubility in organic solvents. PVB with an average molecular weight of 50,000 or more is preferred so that the viscosity of the coating can be determined and with a number of butyrai groups of 75% mol or more to determine the water resistance of the final application. PVB with good solubility in organic solvents such as ethanol, isopropyl alcohol, butanol, etc., and a suitable viscosity in solution for the desired application technique is used.

The layer resistance of the dry coating is between 2 Ω and 1.5 kQ, depending on the substrate, the thickness of the coating and the final treatment of the coating.

The process of making the coating consists of appropriate mixing of the basic components.

To make the coating formulation in powder form, all components, ie conductive filler, binder and optionally the above-mentioned various additives, are mixed with a suitable powder mixer, preferably a mixer providing a high shear force. Stirring is carried out until the mixture is completely homogeneous. Finally, if necessary, the homogeneous mixture is ground again in a mill, preferably in a roller mill or ball mill, or in a similar powder mill, to obtain a homogeneous mixture of powder particles. The powder coating can be added to other coatings as an additive or mixed with a solvent and applied in liquid form. A mixer that provides a high shear mixer or any other mixer designed to mix dust particles and liquids is best for mixing the powder coating into the solvent. The main advantage of powder coating is easy storage, long shelf life and easy transport.

To make the coating formulation in liquid form, each of the powder components separately, i.e. the conductive filler, the binder and optionally the above-mentioned various additives, is first ground to the required size, if necessary. The grinding of individual ingredients takes place in a mill for grinding powder particles or solids, ie it can be in a roller mill ("roller mili") or a ball mill ("bali mili"), etc. or in any other mill providing grinding to particles of the required size. The PVB is then mixed into the solvent at room temperature in such a way that the PVB is completely dissolved. This can be done with a mixer designed to mix dust particles into a liquid, especially a high-shear mixer as well as other suitable mixers. Carbon black is then added to the mixture, stirring until a homogeneous mixture is obtained. Graphite and the other various fillers mentioned above are then mixed into the homogeneous mixture in such a way that the mixture is completely homogeneous. A mixer that provides a high shear mixer or any other mixer designed to mix dust particles and liquids is best for mixing conductive fillers and other various additives.

The prepared coating is filled into containers suitable for storage or transport. Care must be taken to avoid the formation of sediment during the production stages, because in this case the coating no longer has the desired properties, especially in terms of the conductivity of the final application.

The coating formulated in liquid form is applied to the substrate by various techniques known to those skilled in the art. Suitable application techniques include, but are not limited to: brush application, roller application, spray application (ultrasonic nozzles, air), spin coating. After applying the coating to the substrate, drying follows until the formation of the final coating. Drying can be accelerated by heating the coating with hot air, in an oven, via IR radiation, by electric current, by electromagnetic waves (eddy currents) and other methods known to those skilled in the art.

The composition can be adapted to different applications in terms of composition, especially in terms of particle size and raw materials used. This is especially important when used in series production, as it allows the use of existing devices and tools and eliminates the need for major changes in production lines.

A special feature of the presented coating is also the possibility of processing the final application, ie the coating after application. Exposing the dry final coating to pressure increases the conductivity, which has not been presented in the segment of conductive coatings so far. By compressing, we can increase the conductivity of the entire surface or only part of the surface. For compacting larger surfaces, it is suitable to press with rollers or a press, which can also be part of the process of applying the coating to the substrate, such as but not limited to roller application. With the compression process, it is possible to further determine the part of the application surface that will have higher conductivity. Namely, if a die is present on the compression roller or on the press, the impression of the die becomes more conductive than the rest of the coated area. The conductivity can be increased from 10% to 200% depending on the uncompressed dry final application, the increase in conductivity depending on the substrate, the composition of the coating and the pressure used. Thus, by continuously changing the pressure during the processing of different parts of the coating, it is also possible to continuously change the resistance of the coating, which is interesting for use in sensor, heating and some other applications. By pressing and polishing, the coating also gets a shiny metallic appearance, which is an added advantage when using the coating as part of a finished room architecture or product design, as it eliminates the need for additional application of paint or covering the coating. The pressure required to improve the coating depends on the substrate. Each compression of the coating will increase its conductivity, and it is preferable to use compression with a pressure of 1.5 MPa and more. The compression pressure itself depends on the substrate and the application of the coating.

The coating or its components can be used as an additive in the production of other coatings, adhesives, plastics, foils, plasters, paints and similar products and semi-finished products as an additive to improve electrical and thermal conductivity and transmit other properties inherent in the presented coating.

Performance examples

EXAMPLE 1:

5.5 g of PVB (KT-30H, manufactured by Kunshan Chemtech Co. Ltd.) are slowly dissolved in 130 ml of 99% isopropyl alcohol. The mixture is stirred with a stirrer at room temperature until the PVB is completely dissolved. In all steps, we use a mixer that provides a high shear mixer with a rotation speed of 1000 rpm or more. Stir at room temperature. Then slowly stir in 5 g Carbon black (SuperP Li, manufacturer lmerys Graphite and Carbon). Mix the mixture with a mixer until completely homogeneous (15 minutes) Finally, add another 37 g of graphite (particle size <50 micrometers (> 99.5%), manufacturer Merck KGaA) and mix the mixture with a mixer until completely homogeneous (15 minutes). Immediately after mixing with the roller, the coating is applied to a glass substrate measuring 50 x 80 x 1 mm.

The sample is dried for 15 minutes. The measured layer resistance is 136 Ω and the thickness is 36 pm. Compress the sample in a hydraulic press at a pressure of 5 MPa. The layer resistance after compression is 63.4 Ω.

EXAMPLE 2:

Slowly dissolve 45 g of PVB (KT-30H, manufactured by Kunshan Chemtech Co. Ltd.) in 630 g of 96% denatured ethanol. Stir the mixture with a blender until the PVB is completely dissolved. In all steps, we use a mixer that provides a high shear mixer with a rotation speed of 1000 rpm or more. Stir at room temperature. Stir in 25 g of carbon black (SuperP Li, manufactured by lmerys Graphite and Carbon) and mix with a blender (15 minutes). Finally, add 300 g of graphite (particle size <50 micrometers (> 99.5%), manufactured by Merck KGaA). The mixture is stirred with a mixer on high shear for at least 15 min. Using a paint roller, apply a coat of coating to a glass substrate measuring 50 x 80 x 1 mm immediately after mixing. Allow the application to dry for 15 minutes.

The measured layer resistance is 159 Ω. The thickness of the sample is 25 pm. The sample is compressed in a hydraulic press with a pressure of 2.5 MPa. The measured layer resistance after compression is 127 Ω.

The layer resistance is measured in both cases with a four-point probe and calculated according to the formula R = 4,532 x (V / l), where V is the voltage measured between the two internal contacts, I is the current measured between the two external contacts (Electrical Measurement, Signal Processing, and Displays. Ed. John G. Webster. CRC Press, 2003, Chapter 7-1. Heaney, Michael B. Electrical Conductivity and Resistivity. ”Thickness was measured with a contact profilemeter.

EXAMPLE 3:

Mix 5 g of Carbon black (SuperP Li, manufactured by lmerys Graphite and Carbon) and 37 g of graphite (particle size <50 micrometers (> 99.5)) with a high-shear mixer. %), manufacturer Merck KGaA). When the mixture is completely homogeneous (mixing time 5 minutes), another 5.5 g of PVB (KT-30H, manufactured by Kunshan Chemtech Co. Ltd.) is added. Stir again until the mixture is completely homogeneous (mixing time 5 minutes). To the mixture of carbon black, graphite and PVB add 130 ml of 99% isopropyl alcohol and the resulting mixture is mixed with a mixer, which provides a high shear force ("High-shear mixer"). Mixing time is 15 minutes, or. until the mixture is completely homogeneous.

Claims (10)

PATENT APPLICATIONS An electrically conductive coating, wherein the coating comprises at least a conductive filler and a binder, and the binder content relative to the conductive filler in the conductive coating is from 10 wt% to 30 wt%, wherein the conductive filler includes graphite particles and carbon black, and the carbon black content relative to graphite in the conductive filler is from 5 wt% to 15 wt%, and the binder is polyvinyl butyral. The electrically conductive coating according to claim 1, wherein the graphite is natural or artificial and the graphite particles are in the form of powder and / or rods and / or cloths, and the graphite particle size is from 0.5 to 200 micrometers, preferably from 5 to 50 micrometers. Electrically conductive coating according to claims 1 and 2, wherein carbon black is highly conductive carbon black and the carbon black particles are in the form of powder and / or rods and / or cloths, and the particle size of carbon black is between 0.5 to 200 micrometers, preferably from 5 to 50 micrometers. Electrically conductive coating according to the preceding claims, wherein the conductive filler further comprises conductivity enhancing additives in the form of conductive metal particles and / or other various forms of graphite, and the weight ratio between the conductive enhancing additives and graphite is between 1:10 and 1: 100, and the size of the conductive particles is between 0.5 to 200 micrometers, preferably from 5 to 50 micrometers. Electrically conductive coating according to the preceding claims, wherein the polyvinyl butyral has an average molecular weight of at least 50,000 and the number of butyral groups is at least 75% mol and the polyvinyl butyral is in powder form with a particle size between 0.5 and 200 micrometers, preferably 5 to 100 micrometers. Electrically conductive coating according to the preceding claims, wherein the coating further comprises an organic solvent in which the polyvinyl butyral is soluble, the solvent being selected from ethanol, isopropyl alcohol or butanol or a mixture thereof, and wherein the polyvinyl butyral content is based on solvent of 2% wt. up to 20% by weight, and the viscosity of the final coating formulation in liquid form is between 19 mPas and 500 mPas. Electrically conductive coating according to the preceding claims, wherein the layer resistance of the dry coating is between 2 Ω and 1.5 kO. Electrically conductive coating according to the preceding claims, wherein the dry top coat of the conductive coating is subjected to compression with a pressure of at least 1.5 MPa, the electrical conductivity being increased from 10% to 200% relative to the uncompressed dry top coat. Use of an electrically conductive coating to increase the electrical conductivity of the surface of the substrate to which it is applied, wherein the electrically conductive coating is applied in liquid form to the surface of the substrate, followed by drying until a final coating is formed. Use according to claim 9, wherein the entire surface or part of the surface of the substrate with the applied dry top coat of conductive coating is subjected to compression with a pressure of at least 1.5 MPa, to increase the electrical conductivity of all or part of the surface from 10% to 200%.