Technical Field

The invention relates to the nanotechnological hybrid, reversibl thermochromic coating which detect the changes that will occur due to overheating for Aluminium terminals used in electrical components.

The invention is especially related with a coating originating from inorganic organic polymerization, doped with SiO2 nanoparticles, having the ability to change color at 70 °C and above and return to its former color when the temperature decreases. It can be applied with different coating methods and final coating material has long durability on metal surfaces with its increased hardness, adhesion and corrosion resistance behaviors.

The State of Art

Polymer technologies and materials are generally realized by condensation or addition polymerization. Condensation polymerization occurs when the building blocks combine during the monomer addition by removing small molecules such as alcohol, water, ammonia from the long skeleton formed. Especially the double bonds in the addition polymers join each other in a geometrical order by radical polymerization. Although other polymerization ways or examples exist, industrially important polymers and composites usually occur in these two types of polymer formation techniques. Among the condensation polymers, polyurethane formation, polyamide formation and sol-gel polymerization in inorganic organic polymer structures seem particularly important. Said polymer structures are generally thermally cured and known for their highly developed mechanical and physical properties.

Nanocomposite materials using polymeric structures consist of several different phases and one of these phases is in nanometric structure. If one of the phases is in nanometric level, a special interface is formed between the polymer and the nanostructure and the nanocomposite structure obtained due to the very large surface area of the nanometric structure causes very special mechanical and chemical properties. The ratio of surface area to volume allows to improve structure and properties to obtain new products in pharmaceutical, plastic composites, medical and energy materials.

For obtaining nanocomposite structures, sol-gel method is a way that was frequently used recently. Since it allows inorganic and organic hybrid structures to be combined at the molecular level, it provides wide advantages. In general, sol-gel technology is a method that can be explained on the basis of silica format, on from the Silicontetrahydroxide. If alkoxysilane compounds are taken as the beginning precursors of the reaction, a siloxane network is formed through hydrolysis and condensation reactions, as well as water and alcohol removal. Oligomers are formed first and then the inorganic polymer structure is formed. Industrially, using tetraethoxy silane (TEOS) or organic modified trialkoxysilane structures interesting materials with new properties can be produced by mixing epoxy, polyurethane, PVC, polyamide structures together with nanoparticles or quantum dots homogeneously. These materials are converted into structures with superhydrophobic, superhydrophilic, scratch resistant, abrasion resistant, enhanced optical properties and self-cleaning properties in addition to the general features of natural materials.

With the sol-gel technique, different phases are interacted at the molecular level and interactions are seen beyond just simple mixing. In this way, unique molecular nanocomposite structures are obtained. In general, the advantages of obtaining nanocomposites can be evaluated as follows;

• high surface area/volume ratio provides small filler spacing,

• better mechanical properties are achieved without loss of strength,

• improved optical properties are achieved because particle size and light transmittance are correlated.

Generally, the impact strength change and durability change drastically with the addition of nanostructures of nanocomposites. The formulation and evolution of properties vary with proper dispersion and homogenization of the nanoscale material. In this perspective nanoparticles have attracted great attention recently, especially due to their nanoelectronic, nanooptic and chemical catalysis effects. When the size of the nanoparticles is around 1-10 nm, it is easier to observe quantum effects, in other words, nanotechnological effects, especially when the quantum confinement becomes quite dominant. For example, if the band gap energy of semiconductor nanoparticles is developed in a controlled way, many new applications such as visible region catalysis and self-cleaning effects can be observed. The necessity of protecting the surface of nanoparticles used in nanocomposite structures plays an active role to develop novel optical and chemical properties as well as to prevent agglomeration of the particles due to unsaturated atoms on the surface. Therefore, it is known that the agglomeration phenomenon can be prevented by surface passivation by methods of attaching different polymeric or surface active agents, adsorption of different ligands to the surface. With these structures containing different numbers of attaching groups (dendates) adhered to the surface by physical or chemical means, the particle surface is protected from external factors and at the same time, nanocomposite dispersion is facilitated. The nanoparticles can be obtained by bottom up or top down methods. Especially when the synthesis methods are reviewed, La-Mer theory offers a linear formation theory in the synthesis of semiconductor nanoparticles. However, in metal oxide-type structures, for example, the Stober method can be used for particles that were surface modified and and size controlled in the fabrication of SiO2 nanoparticles.

The documents determined in the patent and literature research carried out for the state of the art are summarized below.

US 7,465,693 B2 describes a thermochromic structure that changes color with an adhesive or polymer structure, such as asphalt or cement, or that can be mounted on a traffic sign. This structure is used as an indication that the surface is at a temperature close to or below the freezing point of water.

JP11323708 A2, which is one of the patent applications of the Japanese, defines a composition containing microencapsulated pigment that changes color reversibly with temperature increase. This polymer composition can be used in the form of a mesh and defines a thermoplastic resin.

GB2401710 Al describes a warning device that will act as a thermochromic indicator if the temperature on a door surface increases. It is also possible to perceive it as a warning sign in fire situations. The thermochromic indicator can be obtained with a thermochromic ink or a luminescent thermochromic mixture. US 9404200 B2 describes a thermochromic building material. In this way, color-controlled materials were produced by means of 3D printing. This material, which can change color through the melting or extrusion process, is clearly defined.

In US 10837143 B2, thermoregulatory nano-coatings for paper materials are described. Here, a nanostructured phase change material and a protective layer are used together. In this way, top coatings or surface paints that respond sensitively to temperature are obtained.

EP3816243 Al describes a thermochromic dye that can be printed by the ink jet method. This paint contains an organic solvent, a binder containing at least one resin, heat and moisture sensitive pigment and another pigment formulation to act as a temperature sensor and humidity sensor. In this system, a special composition is created by choosing the pigment color and paint color complementary to each other, and this composition is compatible with the system called ink jet. As a result, a pigment formulation with thermochromic properties is obtained.

WO2015135949 Al describes a microemulsion containing microencapsulated thermochromic leuco dyes and a multimicroencapsulation structure associated with this structure. 5-30% pigment, 30-50% a polymeric structure, 1-10% an emulsifying agent and 30-60% a solvent, and the leucocolorants can be spironolactone, fluorene or spiropyran type structures. In this structure, a thermochromic emulsion formulation emerges from a polymeric coating, an oil-based solvent, microencapsulation of thermochromic pigments and combining this structure with a water-based gelatin and polyamide or polyurea type structure.

Brief Description of the Invention

The present invention relates to nanotechnological coatings that change color reversibly with temperature for aluminum terminal blocks used in electrical components, which meet the above- mentioned requirements, eliminate all disadvantages and provide bring some additional advantages.

The invention is inspired by current situations and aims to solve the above-mentioned disadvantages. The main objective of the present invention is to obtain a coating material that can be formed with a size-adjustable SiCT nanostructure, an inorganic-organic hybrid polymer structure, an epoxy-containing resin, a microencapsulated pigment structure and preferably together with surface agents, can be applied to aluminum surfaces and can change color around 70°C. In this way, a paint mixture with enhanced nanotechnological and physical properties, which can provide reversible color transformation on the applied metal surfaces can be defined.

Another objective of the invention is to obtain a nanotechnological coating that changes color and can be applied by spray method which will be used on aluminum terminal blocks used in electrical components. In this way, excessive temperatures generated by electrical leakages can be determined. The nanotechnological mixture developed within the scope of the invention contains the desired and modifiable ratio and chemical properties.

The structural and characteristic features of the invention and all its advantages will be understood more clearly due to the detailed explanation below, and therefore this evaluation should be made by taking this figure and detailed explanation into consideration.

Figures to Help Explain the Invention

Figure 1: Cross sectional view SEM image for thermochromic surface coating.

Figure 2: SEM images of SiCE nanoparticles used to improve the physical properties of the thermochromic hybrid system.

Detailed Description of the Invention

In this detailed description, the invention is described in such a way that it does not have any limiting effect on the production of hybrid, thermochromic nanocomposite coating for metal surfaces.

This invention relates to the nanotechnological coating and its preparation forthe cases that occurs as a result of the heating of aluminum terminals used in electrical components. The coating comprises at least one thermochromic pigment encapsulated, SiCE nanoparticles that are used to improve physical properties and whose sizes can be controlled, at least one epoxy resin, at least one silane initiator compound, at least one aluminum compound suitable for use as a curing agent. In addition, optionally, it is possible to include solvents (EtOH, IPA, Butyl Glycol, Acetone), which can be used for different purposes when necessary in the homogeneous coating formulation. Solvents are components that are preferably used to adjust viscosity and are an input to the coating. Coating can be applied on metal surfaces with preparation of a homogeneous coating formulation. In this way, by using different application methods, it defines a system that can change color and become transparent at 70 ± 2 °C on aluminum terminals. Theoretically reversibl thermochromic effect is stable infinitely and coating formulation has strength on surfaces.

The aluminium compund used in the invention can be composed of different alkoxide components of aluminum. Aluminum trisecondary butoxide, aluminum triethoxide, aluminum triisop yloxide type components can be given as examples. By adding complex-forming ligands such as ethylene diamine, EDTA, acetylacetone, ethylacetoacetate to these components, the airsensitive feature of the aluminum alkoxide compound is blocked and a stable complex is formed. Generally, the ligands mentioned herein are added directly to the alkoxide compound in different equivalent amounts for complex formation. The exothermic reaction during the formation of this complex should be controlled. Aluminum compound is added to the system after sufficient mixing and dispersion. After this addition, dispersion continues, preferably for 30 minutes or another more suitable time. It is more convenient to store the aluminum compound in a nitrogen and argon environment due to its rapid hydrolysis and condensation properties.

The silane precursor compounds are epoxy silane, mercapto silane, aminosilane, tetraethoxy silane, methyltriethoxy silane etc. and / or their mixed mixtures in different equivalent amounts. The properties and contents of these mixtures are adjusted by determining the properties of the material to be obtained in the final. Different starting amounts can be mixed, for example for water repellency or crosslinking properties, or for secondary polymerization purposes different side groups are vectorized.

Said silane precursor compound is prepared alone or with other functional silane compounds by adding the necessary amounts of water for hydrolysis and condensation. Hydrolysis and condensation rate are important and it is necessary to pay attention to this point while preparing the mixtures. The said water addition is made in proportion to the calculation of the alkoxide amounts. Preferably, mixtures after hydrolysis and condensation for at least 12 hours are considered usable. Especially mixtures containing amine groups should be used more quickly as they cause additional polymerization.

The rate of hydrolysis and condensation is important in the preparation of these mixtures and it is necessary to pay attention to this condensation rates while preparing the mixtures. Trialkoxy silanes which having functional side groups may not form a transparent mixture when compared with other silanes because their hydrolysis and condensation rates are different. However, since the nanocomposite structure to be obtained will already contain a black-based color, such differences are of little importance. This silane mixture contains different functional groups and side groups suitable for cross-linking for the next step, and at the same time, a suitable environment should be provided for the removal of the condensation products, which we call shrinkage after hydrolysis and condensation.

First, the silane mixture is mixed in certain proportions and acidic water is added proportinally to the calculation of the alkoxide amounts. The Stober method was used in a modified way to obtain SiO2 nanoparticles. In order to increase the physical strength of the thermochromic hybrid nanocomposite structures to be obtained (scratch, adhesion, abrasion resistance and corrosion test), the surface and dimensions of these nano-sized particles can be precisely controlled. For the synthesis of nanoparticles, firstly, base is added to the system mixed which is composed of Isopropyl alcohol and distilled water. In this system, especially ammonia, methylamine type bases can be used. As a result of a certain mixing time, silane initiators can be added to this reaction environment individually or in a mixed manner to produce surface modified particles. Especially after the basic mixture is obtained, the pH value of the solution should be above pH=10. It is known that the pH value being below this point will affect the hydrolysis and condensation reactions and affect the formation of nanoparticles. Nanoparticles are obtained in a spherical manner after the reaction carried out at a certain rpm speed and at room temperature. If the surface is desired to be modified, TEOS initiator can be used with trialkoxysilans. As the reaction volume increases, the volume ratios can change. After the fabrication, the nanoparticles are washed with water and alcohol-based solvents at the end of the reaction, dried and stored for the nanocomposite structure after chemical analysis, crystallinity and thermal characterization.

The resulting nanoparticles are obtained in a very precise monodisperse and size controllable manner, as evidenced by SEM (Scanning Electron Microscopy-Scanning Electron Microscopy) analyses. In the invention, additional additives provided by S iO 2 nanoparticles such as anti-scratch, filling properties and hardness strengthen the nanotechnological character of the coating. Particles such as ZrC>2, AI2O3, SiC, BN can also be used instead of monodisperse SiCL- In the use of nanoparticles, it is important that the dimensions are nano-sized and transparent polymers that will show transparent properties and that they will not prevent thermochromic color change. The nanoparticles used should have properties like SiCT nanoparticles. The important thing is not the presence of monodisperse particles, but the particles that provide the formation of a transparent polymeric structure due to their size.

Epoxy resins are used to modulate the chemical and physical properties of the nanocomposite structure. In addition to linear or Bis Phenol A based epoxies, other desired epoxy resins can also be used. Said epoxy resins are added to the coating mixture and mixed preferably at a speed of around 2000 - 4000 rpm. This mixing time can preferably be between 2-4 hours depending on the homogeneity. Especially in the final composition, linear epoxies can be preferred in order to prevent unwanted yellowing of the nanocomposite. However, both structures are suitable for the invention. The thermal resistance of aromatic structures is suitable for the system. In one embodiment of the invention, it is also possible to add the epoxy partially piecemeal. It is also possible to use any other desired epoxy resins.

As a thermochromic encapsulated pigment, a pigment that changes color reversibly at 70 C and above, transforms from black-dark green to a transparent state is used. Generally, LCR HALLCREST Reversible Thermochromic Screen Ink 70 pigment is used as the active thermochromic agent. The condition of this encapsulated pigment against acids and bases should be considered. In addition, its dispersion should be carried out well. Thermochromic capsules consist of a dye called leuco, dye improvers, and components that serve to control temperature. It generally contains structures smaller than 10 microns.

For the synthesis process, first of all, the hydrolysis and condensation reactions of alkoxysilanes are completed and nano-sized SiCL nanoparticles are added to each other and homogenization takes place with the addition of epoxy resin. A stirring speed of 1500 rpm to 3000 rpm can be used. Then, after adding the thermochromic pigment, homogenization is completed in approximately 4-6 hours with a controlled dispersion rate. The expression “low mixing speed” in the text represents the 500-800 rpm range. Otherwise, the pigment structure in the core/shell structure deteriorates and thermochromic properties are not observed.

When particle and pigment homogenization is ended, aluminum compound is added accordingly into the formulation and mixing procedure continues for another 30 minutes. Afterwards, it is applied to the desired surface by spray, if desired, with viscosity adjustment, serigraphically, dipping or spin coating. A degreasing procedure is carried out before coating the aluminum terminal blocks. This procedure usually involves cleaning the metal in an ultrasonic bath at 70- 80 °C in a detergent solution. The degreasing procedure represents the removal of oil from the substrate by dissolving it using a surfactant (detergent nature). For this, agitation and surface cleaning are carried out by means of an ultrasonic bath by placing the metal structure in hot water with detergent. Henkel, P3 Almeco 18 can be used for this process, but a general detergent does the same.

In one embodiment of the invention, alcohol-based solvents can be added for system viscosity at the beginning or at another appropriate time. Generally, this addition is between 5-10%, and the dispersion process can be extended after the addition as necessary. Addition of pigments important for dispersion should not be carried out with alcohol.

In the invention, aluminum terminals are cleaned beforehand with a detergent solution, preferably in an ultrasonic bath at 70 °C, and are thoroughly washed and dried as a result of the degreasing process. The cleaning process is important for the adhesion of the substrate. Therefore, more than one cleaning operation can be performed if necessary.

The coating, which is the subject of the invention, is applied to the surface (aluminum terminals) with the final composition using different coating methods (such as dip coating, spray coating, spin coating for flat surfaces). Double or, if necessary, triple layers can be used. The coating mixture is thermally cured, preferably at 140 - 170 °C, preferably for 10 - 30 minutes.

Preferably, coating thickness between 5-150 microns can be applied in the invention. The curing system can be monitored with FT-IR or thermally. As a result, a system with inorganic organic hybrid and reversible thermochromic properties is obtained. The following ratios can be used with different modifications for the thermochromic system;

For example, the weight ratios for the synthesis process;

• Solvents in the range of 3-8%,

• Precursor silane in the range of 50-70%,

• Epoxy resin in the range of 10-25%.

• SiCh nanoparticle in the range of 1-5%

• Aluminum compound in the range of 10-25%

• Thermochromic pigment in the range of 5-15%

In this process, the compositions vary depending on the properties of the product to be obtained.

In the present invention, generally, solid, liquid and resinous products are used together after pretreatment if necessary. The input materials are transformed into a standard industrial paint and become ready to cure with heat. Solvent can be used for dilution and hydrolysis condensation adjustment if desired. Applications are carried out at room temperature.

As seen in Figure 1, nano-sized SiO2 nanoparticles were produced by the modified Stober method and used in thermochromic nanocomposite structure. As seen in Figure 2, it shows a compact coating feature with the nanoparticles in the coating formulation.

In this text, the usage area and preferred application area of the invention are given specifically. However, it is clear that a person skilled in the art can also apply the whole, part, essential features and/or characterizing part of the invention to other purposeful fields. Therefore, it is obvious that such structuring will lack the criteria of innovation, and especially of overcoming the state of the art. Numerous specific details are set forth in the specification to provide a full understanding of the invention. However, it is possible to obtain the invention based on the technical features defined in the claim without using all of the mentioned details or alternatives. The component alternatives mentioned for the invention should not be considered as being limited to those listed.