KR20120121939A - Coating composition for forming scratch resistant silica thin layers containing silica nano-particles of different sizes, method of preparing the same - Google Patents

Abstract

PURPOSE: A coating composition is provided to form a dense silica protection film without defects by using nano particles with different sizes, and to be sintered at temperature of 200 °C or less. CONSTITUTION: A coating composition comprises 85-90 weight% of surface treatment liquid comprising a silica precursor mixture which consists of tetraethoxysilane and methyltriethoxysilane, and 10-15 weight% of a silica nanoparticle mixture which consists of primary silica nanoparticles with the particle diameter of 4-18 nm and secondary nanoparticles with the particle diameter of 45-55 nm. The surface treatment liquid consists of 1-3 M of silica precursor mixture consisting of tetraetoxysilane and methyltriethoxysilane, 5-15 M of water, 0.01-0.1 M of acid catalyst, and 5-15 M of solvent.

Description

COATING COMPOSITION FOR FORMING SCRATCH RESISTANT SILICA THIN LAYERS CONTAINING SILICA NANO-PARTICLES OF DIFFERENT SIZES, METHOD OF PREPARING THE SAME}

The present invention relates to a coating composition for coating a metal surface based on two sizes of silica nanoparticles and a method for preparing the same, and more particularly, to the surface of metals using nano silica particles. The present invention relates to a coating composition for forming a scratch resistant silica protective film containing silica nanoparticles of two sizes providing scratch resistance and the like and a method of preparing the same.

The silica-based coating refers to a protective film that is applied to a surface of metal or plastic to improve physical and chemical durability. This protective film should have good physical and chemical bonding strength with the substrate, but at the same time, the protective film layer should be dense and the surface smooth.

The denseness of the protective film is correlated with corrosion resistance, and the smoothness of the surface is closely related to the scratch resistance, which is one of physical durability, and the characteristics such as optical transparency and reflectivity.

As such, through the dense protective film, the penetration of corrosive substances is effectively blocked, thereby improving corrosion resistance. In addition, the protective film with improved smoothness shows the surface of the cleaner product and improved results in scratch resistance are also obtained.

The subject technology of the present invention belongs to the field of physico-chemical protective coating coating based on inorganic silica. That is, a solution containing a silica precursor (precursor) or the like is formed for the purpose of imparting scratch and corrosion resistance properties to the surface of a metal, and the like, using a dip or spray-coating technique. To form a protective film.

In this technical field, the present invention aims to present a technique for obtaining a coating layer having excellent properties easily and stably compared to the conventional technology by adjusting the composition and content of the solution.

In general, inorganic silica is generally used as a material of scratch and corrosion resistant coatings. In particular, one of the most important characteristics in order to produce a scratch and corrosion resistance effect by spray coating on the metal surface is the density and smoothness of the coating layer. In other words, if the density is low, corrosion can easily occur due to the corrosive material passing through the coating layer, and if the smoothness is reduced, a part of the coating layer is easily damaged by external mechanical shock, and the fragments cause secondary scratches. Greatly falls.

In the existing technologies, first, in order to improve the density and smoothness of the surface layer at the same time, a large amount of commonly sprayed solution was applied to completely wet the surface layer. However, when the solution is applied too much, the coating layer finally obtained becomes too thick, which may cause a later peeling phenomenon. In general, the inorganic silica coating layer coated on the metal surface has a large difference from the metal in thermal expansion rate, so even a slight thermal shock causes stress (stress) that greatly exceeds the mechanical bond strength, and such stress causes a crack in the silica coating layer. do. However, in order to avoid such a problem, when the inorganic content of the solution is lowered to form a thin coating, the coating layer tends to become porous rather than thin. In this case, it is difficult to obtain a dense coating layer from the porous coating layer with a general heat treatment of about 400 to 500 ℃.

Therefore, it is not efficient to obtain a dense and high smooth thin film by adjusting the concentration or spraying amount of the coating solution as in the prior art, and a new silica coating composition which can obtain a stable dense and high smooth thin film in a relatively wide solution composition range is Required.

Accordingly, a first object of the present invention is to provide a silica protective film having a high surface pencil hardness of 6H to 9H, and to form a protective film having excellent adhesion without using environmentally harmful substances and only by coating using a conventional coating treatment technique. The present invention provides a coating composition for forming a scratch resistant silica protective film containing silica nanoparticles of two sizes.

And a second object of the present invention is to provide a method for producing a paint composition to enable the production of the coating composition described above.

In order to achieve the first object of the present invention described above, in one embodiment of the present invention is 85 to 90% by weight of the surface treatment liquid containing a silica precursor mixture consisting of tetraethoxysilane and methyltriethoxysilane, and the diameter It provides a coating composition for forming a scratch-resistant silica protective film comprising 10 to 15% by weight of a mixture of silica nanoparticles composed of first silica nanoparticles having a diameter of 4 to 18 nm and second silica nanoparticles having a diameter of 45 to 55 nm.

In order to achieve the second object of the present invention, in an embodiment of the present invention, the solvent is mixed with 5 to 15M, 5 to 15M of water, and 0.01 to 0.1M of an acid catalyst to generate a mixed solution, and tetra Mixing 0.5 to 2.5 M of ethoxysilane and 0.5 to 2.5 M of methyltriethoxysilane to produce a silica precursor mixture in a total range of 1 to 3 M, and a surface treatment solution 85 to a mixture of the mixed solution and the silica precursor mixture. The coating solution was prepared by mixing and stirring 10-15 wt% of the silica nanoparticles containing 90 wt% of the first silica nanoparticles having a particle size of 4 to 18 nm and second silica nanoparticles having the particle size of 45 to 55 nm. It provides a method for producing a coating composition for forming a scratch-resistant silica protective film comprising the step of producing.

The coating composition according to the present invention can form a dense and defect-free silica protective film by using a mixture of silica nanoparticles of different sizes.

In addition, the coating composition of the present invention is capable of sintering at 200 ° C. or lower, which is lower than that of the existing technology. In general, in order to improve the hardness and compactness of the silica protective film, a high temperature heat treatment process is performed, but the present invention may not only improve the hardness of the silica protective film by adding two kinds of nanoparticles formed of spherical silica particles. By filling the free space between the particles through the two kinds of nanoparticles, the silica protective film can be dense even without a high temperature heat treatment process.

In addition, the coating composition of the present invention is uniformly mixed with the nanoparticles of the two sizes using a surface modification technique. In general, the silica nanoparticles are easily synthesized into the coating composition, but aggregation or precipitation of nanoparticles easily occurs, but the present invention controls the change of the interaction between nanoparticles by inducing electric field changes on the surface of particles by changing pH or synthesis composition. This change improves the repulsive force between the particles and improves the stability as a coating composition.

In addition, by using the coating composition according to the present invention, it is possible to impart improved corrosion resistance, abrasion resistance, and scratch resistance to a metal surface than a conventional coating paint, and can be applied to a simple coating method.

In addition, the present invention provides a good appearance beauty to the mobile phone case and provides uniform paint adhesion to the front surface of the mobile phone case.

1 is a schematic diagram showing a binding relationship between two kinds of silica nanoparticles according to an embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating a binding relationship between two kinds of silica nanoparticles and one kind of silica nanoparticles of FIG. 1.
3 is a flowchart illustrating a method of preparing a coating composition according to an embodiment of the present invention.
Figure 4 is a flow chart showing a surface treatment method of the coating composition according to an embodiment of the present invention.
5 is a schematic view for explaining a dip coating method for forming a uniform coating protective film.
6 is a TEM photograph for explaining a coating composition according to an embodiment of the present invention.
7 and 8 are SEM photographs for explaining the silica protective film formed of the coating composition of the present invention.
9 is a graph showing the results of the coin polarization test of the silica protective film formed of the coating composition of the present invention.
10 is a test report showing the pencil hardness of the silica protective film formed of the coating composition of the present invention.

Hereinafter, with reference to the accompanying drawings, a coating composition for forming a scratch-resistant silica protective film containing silica nanoparticles of two sizes according to preferred embodiments of the present invention (hereinafter referred to as 'silica protective film-forming coating composition') It will be described in detail.

Coating composition for forming a silica protective film according to an embodiment of the present invention is a corrosion-resistant, abrasion-resistant, scratch-resistant coating protective film using a sol-gel method through the hydrolysis and polycondensation reaction of silica nanoparticles of different sizes and silica precursor It is an environmentally friendly and economical coating agent to form.

Specifically, the coating composition is a silica precursor mixture consisting of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES), a surface treatment solution containing water, an acid catalyst, and a solvent, and two kinds of silica Colloids with added nanoparticles are used.

Hereinafter, the characteristics of each component for each component of the present invention will be described in more detail.

The coating composition for forming a silica protective film according to an embodiment of the present invention includes a silica precursor mixture.

The silica precursor mixture is formed by mixing silica precursors TEOS and MTES.

At this time, the TEOS is used to form a stable network structure of the silica polymer, the MTES is used to increase the flexibility of the network.

As the silica precursor mixture according to the present invention, TEOS may include 0.5 to 2.5 molarity (M). At this time, when the content of TEOS contained in the silica precursor mixture is less than 0.5 molar concentration, the hardness may be weakened due to the decrease of the content of the silica precursor, and when the content of the TEOS exceeds 2.5 molar concentration, the content of the silica precursor is increased to make the stainless steel material The paint composition cured at the surface becomes brittle, and cracks may occur during the drying process.

MTES in the silica precursor mixture according to the present invention may contain 0.5 to 2.5 molar concentrations. At this time, when the content of MTES contained in the silica precursor mixture is less than 0.5 molar concentration, the flexibility of the network is lowered. When the content of MTES exceeds 2.5 molar concentration, the network structure is loosely deformed and the hardness of the cured coating protective film is lowered.

The silica precursor mixture is preferably included in the surface treatment liquid such that the total molar concentration of the two kinds of silica precursors described above is 1 to 3.

This is because when the total molar concentration of the silica precursor in the amount of chemical molar concentration exceeds 3 molar concentration, the amount of ethanol, water and silica nanometer colloid necessary for it is not sufficiently mixed. As such, when the capacity of the mixed solution of ethanol, water and silica nanoparticle colloids is insufficient compared to the silica precursor mixture, the reaction is less likely to occur, making it difficult to synthesize a stable coating composition and improving hardness and density by low temperature process. Degrades. In addition, when the total molar concentration is less than 1 molar concentration, compared to the silica nanoparticles added, small silica precursors do not form sufficient silica networks between the nanoparticles in response to the synthesis of the coating composition, resulting in physical properties of the silica protective film. Is lowered.

In addition, the silica precursor mixture preferably has a pH of 1 to 3 levels. If the pH is less than 1, a corrosion reaction occurs on the metal surface on which the coating composition is deposited. On the contrary, when the pH exceeds 3, the stability of the coating composition decreases with time, causing a problem of gelation instead of sol. Can be. Such selection of the appropriate pH range is an important factor in the present invention.

The coating composition for forming a silica protective film according to an embodiment of the present invention includes water.

The water is added for the hydrolysis reaction of the silica precursor mixture, it is possible to use soft water, distilled water, deionized water or filtered tap water containing no substance, preferably distilled water.

The water may be included in the surface treatment solution of the present invention at a concentration of 5 to 15 moles, preferably 4 moles per mole concentration of the silica precursor mixture. However, since a variable such as quantitative loss may occur during the synthesis of the coating composition, the hydrolysis reaction occurs completely when the water contains more than 4 molar concentrations per molar concentration of the silica precursor mixture.

At this time, if the content of the water contained in the surface treatment solution of the present invention is less than 5 molar concentration, the hydrolysis rate of the silica precursor mixture is low, condensation reaction is not performed well, the silica network formation is reduced. If the water content exceeds 15 molar concentrations, the hydrolysis rate of the silica precursor mixture is too high, causing gelation and deteriorating the stability of the solution.

The coating composition for forming a silica protective film according to an embodiment of the present invention includes an acid catalyst.

The acid catalyst may be hydrochloric acid, silicic acid, acetic acid, acetic acid, sulfuric acid, nitric acid, ascorbic acid, tartaric acid, or malic acid, but hydrochloric acid may be used to prevent stability of the coating composition, that is, aggregation or precipitation of silica nanoparticle colloids. It is preferable to use. More specifically, when synthesizing a silica sol using organic silica precursors such as GPTMS and MAPTS, nitric acid can maintain a sol state more stably than hydrochloric acid, but inorganic silica precursors TEOS and MTES are used as silica precursors. Thus, when synthesizing a silica sol, it is possible to maintain a sol state in which silica nanoparticles are evenly dispersed in hydrochloric acid than nitric acid.

The acid catalyst included in the surface treatment liquid according to the present invention contains 0.01 to 0.1 molar concentration. At this time, when the content of the acid catalyst contained in the surface treatment solution is less than 0.01 molar concentration, the hydrolysis rate is lowered, the gelation time of the coating composition for forming a silica protective film is faster, the stability of the coating composition is lowered. In addition, when the content of the acid catalyst contained in the surface treatment solution exceeds 0.1 molar concentration, the viscosity of the coating composition is lowered, not only the practicality as a coating agent is lowered, but also the acidity of the coating composition is too high to affect the metal material. have.

The coating composition for forming a silica protective film according to an embodiment of the present invention includes a solvent.

The solvent is a common solvent used in the silica precursor together with water, and any solvent can be used as long as it can be mixed with the water smoothly to cause hydrolysis and condensation reactions, which are important reactions in sol-gel synthesis. Although an alcohol solvent is preferable, it is preferable to use it. Specifically, ethanol or isopropyl alcohol (IPA) may be used as the alcohol solvent, and it is preferable to use more stable ethanol. The ethanol or isopropyl alcohol also serves to replace the moisture absorbed by the silica precursor during the sol-gel reaction.

The solvent included in the surface treatment liquid according to the present invention contains 5 to 15 molar concentrations. At this time, if the content of the solvent contained in the surface treatment solution is less than 5 molar concentrations, the reaction rate decreases due to the uneven reaction between the silica precursor and water, and the content of the solvent contained in the surface treatment solution exceeds 15 molar concentrations. The viscosity of the lower surface coating composition is lowered, and the practicality as the coating composition is lowered.

As such, the above-described silica precursor mixture, water, acid catalyst, and solvent constitute a surface treating solution, and the surface treating solution contains 85 to 90 wt% based on 100 wt% of the total coating composition.

At this time, when the content of the surface treatment solution is less than 85% by weight or more than 90% by weight, the performance of the corrosion resistance, abrasion resistance and scratch resistance of the silica protective film formed of the coating composition may be reduced.

The coating composition for forming a silica protective film according to an embodiment of the present invention includes a silica nanoparticle mixture.

The silica nanoparticle mixture is to synthesize an inorganic silica network by a sol-gel reaction with the silica precursor mixture, consisting of two kinds of silica nanoparticles having different nanometer sizes, colloid containing an aqueous or other solvent medium Can be mixed in a state.

Here, two kinds of silica nanoparticles are added to improve the corrosion resistance, abrasion resistance, and scratch resistance of the coating protective film, the first silica nanoparticles having a diameter of 4 to 18 nm and the second silica nanoparticles having a diameter of 45 to 55 nm. Particles are used. In other words, spherical silica nanoparticles having different diameters are used as the two kinds of silica nanoparticles.

In this case, when the size of the first silica nanoparticles is less than 4nm, the advantage of hardness improvement due to the addition of the silica nanoparticles is lost, and when the size of the first silica nanoparticles exceeds 18nm, the gap between the second silica nanoparticles is increased. You will not see the effect of entering and filling the free space.

In addition, when the size of the second silica nanoparticles is less than 45nm, the void space between the second silica nanoparticles becomes narrow, making it difficult for the first silica nanoparticles to fill the void space, and the size of the second silica nanoparticles is 55 When the thickness exceeds nm, the specific surface area of the particles is reduced, and the formation of the network made of the silica precursor is lowered, so that a rigid structure cannot be achieved.

In addition, the mixing ratio of the first silica nanoparticles and the second silica nanoparticles used in the silica nanoparticle mixture is preferably 4: 6 to 6: 4, more preferably in a ratio of 5: 5. . In other words, 40 to 60 wt% of the first silica nanoparticles are used, and 40 to 60 wt% of the second silica nanoparticles, based on 100 wt% of the silica nanoparticle mixture. This is because the spherical particles and free space used in the cube become about 1: 1 by volume ratio.

Meanwhile, as the colloid containing the silica nanoparticle mixture of the present invention, the silica nanoparticle colloid to which the first silica nanoparticles are added and the silica nanoparticle colloid to which the second silica nanoparticles are added are mixed at a ratio of about 1: 1. The prepared silica nanoparticle colloid can be used. Specifically, the silica nanoparticle colloids to which the first silica nanoparticles are added are H.C. Starck's LEVASIL? 300/30 (trade name) can be used, and the silica nanoparticle colloid to which the second silica nanoparticles are added is H.C. Starck's LEVASIL? 50/50 (brand name) can be used.

As shown in FIG. 1, when two kinds of silica nanoparticles having different particle sizes are used, relatively small particles fill a void space of a relatively large particle, and thus, a silica protective film having a more compact structure ( Coating protective film).

Specifically, the silica protective film added with silica nanoparticles has a higher hardness than that of the silica protective film composed only of a silica precursor, and the silica protective film containing large silica nanoparticles has a higher hardness than the silica protective film containing small silica nanoparticles. Is improved. However, when a single large particle is added as shown in FIG. 2, it is difficult to have a dense structure due to the clearance between the particles. In order to compensate for these disadvantages, the density of the silica protective film is improved by using a mixture of particles of different sizes (first silica nanoparticles and second silica nanoparticles). In addition, in this case, the specific surface area of the silica nanoparticles is increased to improve the physical properties of the coating layer even at low temperature heat treatment.

The silica nanoparticle mixture included in the paint composition according to the present invention contains 10 to 15% by weight based on 100% by weight of the total coating composition. In this case, when the content of the silica nanoparticle mixture included in the coating composition of 100% by weight is less than 10% by weight, the low temperature heat treatment curing time is long, and thus the hardness is lowered. In addition, when the content of the silica nanoparticle mixture included in the coating composition of 100% by weight exceeds 15% by weight, the content of the silica nanoparticles is increased, so that the silicon thin film cured on the metal surface becomes brittle, and cracks are generated during the drying process. May occur and the adhesion may be reduced.

As such, the coating composition consists of a surface treatment solution and a mixture of silica nanoparticles.

In addition, the present invention provides a method for preparing a coating composition for forming a silica protective film using the above-described components.

Figure 3 is a flow chart for explaining a method for producing a silica protective coating formed coating composition of the present invention.

Referring to Figure 3, the coating composition according to the present invention to solve the problem of growth and aggregation or precipitation of the silica nanoparticles generated during the synthesis and for the stability of the solution, first Water and hydrochloric acid are mixed with ethanol as a solvent and stirred to produce a mixed solution (step S10). Next, to prepare a silica precursor mixture of a mixture of silica precursor TEOS and MTES (step S20). Then, the mixture mixture is mixed with a silica precursor mixture and an ethanol-based or silica-based silica nanoparticle colloid at the same time to the synthesized coating composition was stirred at room temperature for 3 to 5 hours to induce the hydrolysis and condensation polymerization reaction (S30). step). In this case, the surface treatment liquid mixed with the mixed solution and the silica precursor mixture is added to include 85 to 90% by weight based on 100% by weight of the coating composition, the silica nanoparticle mixture is 10 to 15 based on 100% by weight of the coating composition It is added to include the weight percent. Here, when using the silica nanoparticle colloid as the silica nanoparticle mixture, the amount of the aqueous or other solvent medium included in the colloid is included in the surface treatment liquid.

More specifically, in the step S10, after the addition of ethanol, distilled water, hydrochloric acid is carried out a process for stirring for 25 minutes to 60 minutes at room temperature to create a well mixed state. In this step, as the total volume of the mixed solution increases, the stirring time is preferably increased.

In step S20, TEOS and MTES, which are silica precursors, are sequentially added to the stirrer, followed by agitation at room temperature to sufficiently mix each silica precursor.

In addition, the step S30 is a process in which the hydrolysis and condensation reactions occurring in the silica precursor and the silica nanoparticles are performed to allow the reaction to occur at the same time without partial reaction than when the silica precursor material is sequentially added. If the reaction between the silica precursor and the silica nanoparticles occurs separately, aggregation and precipitation of the silica particles occur. In this step, in order to sufficiently react the hydrolysis and the polycondensation reaction, stirring is performed for 3 to 5 hours. In this step, silica nanoparticle colloids having different sizes of silica nanoparticles, for example, first silica nanoparticles having a diameter of 4 to 18 nm and second silica nanoparticles having a diameter of 45 to 55 nm are added.

On the other hand, the present invention provides a surface treatment method of the coating composition for producing a silica protective film (coating protective film) on the metal surface by using the above-described coating composition.

Figure 4 is a flow chart for explaining the surface treatment method of the coating composition of the present invention.

Referring to Figure 4, the surface treatment method according to an embodiment of the present invention is a dip coating step (S300) for forming a silica protective film on the surface of the metal product, and a heat treatment step (S400) for producing a dense coating surface It may further include an alkali degreasing step (S100) and pickling step (S200) before the coating step (S300), if necessary.

In general, when a small amount of a substance that induces a chemical reaction is included on the surface of a product made of a material such as stainless steel, it may be fatally damaged to form a coating protective film. Therefore, the alkaline degreasing step (S100) is performed to remove the material causing the chemical reaction on the surface of the metal product. More specifically, the alkaline degreasing step (S100) is 50 to 150 g of sodium hydroxide (NaOH) and 0.5 to 2.5 g of a surfactant (for example Triton X-100) in 1 L of water (for example, distilled water). It is wrapped in a gauze cut to fit the size of the metal product in an alkaline cleaning solution prepared by heating to about 110 ℃ soaked for 10 to 20 minutes and then ultrasonically washed with distilled water 2 to 5 times.

In the pickling step (S200), 120 to 240 g of a solution obtained by synthesizing chromic acid (CrO ₃ ) and acetic acid (CHCOOH) in a ratio of 20: 1 in 1 L of distilled water was heated to 50 to 100 ° C., and the alkali was added to the pickling solution. The degreasing step (S100) soaked alkali degreased metal product for 30 seconds or more, preferably 1 to 3 minutes, washed with distilled water 2 to 5 times, removing water with an air gun to dry about 45 ℃ Dry in an oven for 10 to 40 minutes.

In the immersion coating step (S300), 85 to 90% by weight of a silica precursor mixture consisting of TEOS 0.5 to 2.5M and MTES 0.5 to 2.5M, ethanol 5 to 20M, water 5 to 20M, and hydrochloric acid 0.01 to 0.1M And a coating composition comprising 10 to 15% by weight of the silica nanoparticle mixture to form a coating layer on the surface of the metal product (the metal product subjected to the pickling step) by using a surface treatment method such as a dip coating method. Referring to FIG. 5, the stainless steel sheet 20 is supported on the coating composition 10, and then the stainless steel sheet 20 is separated from the coating composition 10 at a constant rising speed of 3 to 6 mm / sec. The coating layer is formed two to three times with a uniform thickness of nm, preferably about 550 nm. Since the whole coating layer formed from such a coating composition shows high adhesiveness when it is 1-3 micrometers thick, it is good to form a coating layer 2-3 times. In addition, if the rising speed of the stainless steel sheet is less than 3 mm / sec, the thickness of the coating layer becomes thin, and this role decreases as a protective film. If the rising speed is more than 6 mm / sec, the thickness of the coating layer becomes thick and peeling phenomenon occurs. Done.

In the heat treatment step (S400) after drying the stainless steel sheet formed with the coating layer through the immersion coating step (S300) for 8 to 15 minutes at 40 to 50 ℃, heat treatment at 150 to 200 ℃ for 40 to 80 minutes A process of forming a silica coating film is performed. As such, the reason for carrying out the aging process at low temperature (40 to 50 ° C.) before the high temperature heat treatment process is excellent by inducing a complete reaction of the hydrolysis and condensation reactions that may occur before all the ethanol and water are evaporated. To form a silica protective film.

At this time, if the high temperature heat treatment is performed at a temperature of less than 150 ℃ ethanol and water used in the synthesis of the solution is left in the coating layer to deteriorate the characteristics of the silica protective film. In addition, when the high temperature heat treatment is performed at a temperature exceeding 200 ° C., cracks may occur due to a difference in thermal expansion rates between the metal substrate and the silica protective layer at high temperatures, and the process cost increases.

Hereinafter, the present invention will be described in detail with reference to the preferred embodiments. It should be noted, however, that the present invention is not limited to the following examples.

Example 1

* Preparation of Coating Composition

1. 10M of distilled water and 0.03M of hydrochloric acid were mixed with 6M of ethanol as a solvent, and the mixture was stirred for 30 minutes to prepare a mixed solution.

2. A silica precursor mixture was prepared by mixing silica precursors TEOS 1M and MTES 1M.

3. 1.3 kg of the silica nanoparticle mixture in which the silica nanoparticles having a diameter of 10 nm and the silica nanoparticles having a diameter of 50 nm were added in a ratio of 1: 1 to 8.7 kg of the coating solution mixed with the mixed solution and the silica precursor mixture. And all of them were mixed.

4. Then, the synthesized solution was stirred at room temperature for 5 hours to induce hydrolysis and condensation polymerization to complete the coating composition.

6 is a TEM photograph taken of the coating composition prepared in Example 1.

Referring to FIG. 6, it was observed that 10 nm silica nanoparticles and 50 nm silica nanoparticles present in the coating composition according to the present invention were well dispersed without aggregation.

Comparative Example 1

Preparation of the coating composition under the same experimental conditions as in [Example 1], except that silica nanoparticles having a diameter of 10 nm and silica nanoparticles having a diameter of 50 nm were added at a ratio of 1: 1. The coating composition was prepared using 1.3 kg of silica nanoparticles having a diameter of 50 nm instead of 1.3 kg of the particle mixture.

Comparative Example 2

Preparation of the coating composition under the same experimental conditions as in [Example 1], except that silica nanoparticles having a diameter of 10 nm and silica nanoparticles having a diameter of 50 nm were added at a ratio of 1: 1. The coating composition was prepared without adding 1.3 kg of the particle mixture.

[Example 2]

* Formation of silica protective film

1. The specimen was coated twice by a immersion coating method using the coating composition prepared in [Example 1] at a constant rising speed of 4 mm / sec to form a coating layer having a uniform thickness. At this time, the thickness of the coating layer formed by one coating was about 550 nm, and the thickness of the entire coating layer was about 1.1 μm.

2. The specimen coated with the coating composition was placed in a drying oven and first dried at 50 ° C. for 10 minutes, and then heat-treated at 200 ° C. for 60 minutes to form a dense silica protective film.

7 and 8 are SEM pictures of the coating protective film formed through Example 2.

Referring to FIGS. 7 and 8, it was observed that the specimen treated with the coating composition according to the present invention was formed with a silica protective film having a predetermined thickness without a fine crack on its surface.

≪ Comparative Example 3 &

The coating composition was prepared under the same experimental conditions as in [Example 2], but instead of using the coating composition prepared through [Example 1], the coating protective film was coated on the specimen using the coating composition prepared through [Comparative Example 1]. Formed.

≪ Comparative Example 4 &

Prepare a coating composition under the same experimental conditions as in [Example 2], but instead of using the coating composition prepared in [Example 1] using a coating composition prepared in [Comparative Example 2] coating protective film on the specimen Formed.

<Experimental Example 1>

* Potentiodynamic polarization test and results of specimens treated with the coating composition of the present invention

After mounting the specimen in which the silica protective film was formed in the 3-electrode cell through [Example 2], it was immersed in 0.1M HCl aqueous solution for 1 hour, and then the working sample, the carbon electrode, A reference (Ag / AgCl (sat.KCl)) was connected to measure the current change according to the change in the potential value of -0.25 to 0.5V. The result is shown through FIG.

Comparative Example 1

* Coin testing and results of specimens treated with different coating compositions

A sample prepared with a silica protective film through [Comparative Example 2] and [Comparative Example 3] was mounted on a 3-electrode cell, and soaked in 0.1 M HCl solution for 1 hour. A carbon rod (counter electrode) and a reference (Ag / AgCl (sat.KCl)) were connected to measure the current change according to the change in the potential value of -0.25 to 0.5V. The result is shown through FIG.

Comparative Example 2

* Coin polarization test and results of specimens without coating composition

A standard specimen was mounted on a 3-electrode cell and immersed in 0.1 M HCl solution for 1 hour, followed by a working electrode, a counter electrode, and a reference (Ag / AgCl (sat.KCl). ) Was measured to change the current according to the change in the potential value of -0.25 to 0.5 V. The result is shown through FIG.

As shown in FIG. 9, the specimen treated with the coating composition to which two kinds of silica nanoparticles (silica nanoparticles having diameters of 10 nm and 50 nm) were added was treated with one type of silica nanoparticles having a diameter of 50 nm. It can be seen that the corrosion resistance is improved compared to the specimen treated with a coating composition without the addition of silica nanoparticles). In particular, the comparison of the corrosion current (corrosion current) of the specimen with no coating and the silica protective film formed using the existing coating composition, and the specimen formed with the silica protective film using the coating composition of the present invention In the case of the specimen formed with the silica protective film using the coating composition shows the lowest value. That is, it was interpreted that the silica protective film formed through the coating composition of the present invention provides a dense coating surface, and thus the corrosion resistance property is improved.

<Experimental Example 2>

* Pencil hardness test and results of the specimen treated with the coating composition of the present invention

The hardness of the pencil was measured using a pencil hardness tester [Yoshimitsu, Japan] based on the specimen in which the silica protective film was formed through [Example 2] under a 500g load. The result is shown through FIG.

As shown in FIG. 10, the silica protective film of the present invention exhibited a pencil hardness of 6H, which was confirmed to be excellent in scratch resistance.

Although the above has been described with reference to the preferred embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. It will be appreciated.

Claims (6)

85 to 90% by weight of a surface treatment liquid comprising a silica precursor mixture consisting of tetraethoxysilane and methyltriethoxysilane; And
A coating composition for forming a scratch resistant silica protective film comprising 10 to 15% by weight of a mixture of silica nanoparticles composed of first silica nanoparticles having a diameter of 4 to 18 nm and second silica nanoparticles having a diameter of 45 to 55 nm. The method of claim 1, wherein the surface treatment liquid
For forming a scratch resistant silica protective film, characterized by consisting of 1 to 3M of silica precursor mixture consisting of tetraethoxysilane and methyltriethoxysilane, 5 to 15M of water, 0.01 to 0.1M of acid catalyst, and 5 to 15M of solvent. Coating composition. The method of claim 1, wherein the silica nanoparticle mixture is
A coating composition for forming a scratch-resistant silica protective film, characterized in that consisting of 40 to 60% by weight of the first silica nanoparticles and 40 to 60% by weight of the second silica nanoparticles. The method of claim 1 or 2, wherein the silica precursor mixture is
A coating composition for forming a scratch resistant silica protective film, comprising 0.5 to 2.5 M of tetraethoxysilane and 0.5 to 2.5 M of methyltriethoxysilane. The method of claim 1,
The acid catalyst is hydrochloric acid, and the solvent is a coating composition for forming a scratch resistant silica protective film, characterized in that ethanol. Mixing and stirring 5 to 15 M of solvent, 5 to 15 M of water, and 0.01 to 0.1 M of an acid catalyst to generate a mixed solution;
Mixing 0.5 to 2.5 M of tetraethoxysilane and 0.5 to 2.5 M of methyltriethoxysilane to produce a total of 1 to 3 M silica precursor mixture; And
Silica in which first silica nanoparticles having a particle size of 4 to 18 nm and second silica nanoparticles having a particle size of 45 to 55 nm are mixed in 85 to 90 wt% of the surface treatment solution in which the mixed solution and the silica precursor mixture are mixed. 10 to 15% by weight of the nanoparticles mixed and stirred to produce a coating solution comprising the step of producing a coating composition for forming a scratch-resistant silica protective film.

Images