KR20170071678A - Graphene Oxide having enhanced dispersibility, and a method of making a surface-treated steel plate thereby - Google Patents

Abstract

In order to compensate for the fact that the graphene oxide is poorly dispersed in a non-polar solvent or a weakly polar solvent, an alkyl group having a different length at the edge portion of graphene oxide is synthesized to improve dispersibility in a non-polar solvent, And a method for producing a surface-treated steel sheet by coating the graphene / polymer coating solution.

Description

TECHNICAL FIELD The present invention relates to a method for improving the dispersibility of graphene oxide and a method for manufacturing a surface-treated steel sheet using the same,

TECHNICAL FIELD The present invention relates to a method for producing a steel sheet having surface treated by introducing alkyl groups having different lengths into graphene oxide to improve dispersibility in a solution.

Generally, graphite is a material having a typical layered structure, in which plate-shaped two-dimensional graphenes in which carbon atoms are connected in a hexagonal shape are laminated. Graphene is a typical single flat sheet with 3 carbon atoms bonded by SP2 hybrid orbital bond, and is integrated in a hexagonal crystal lattice.

In graphite, the bond between carbon atoms in graphene constituting each layer is very strong as a covalent bond, but the bond between graphene and graphene is van der Waals bond, which is very weak compared to the covalent bond described above.

Graphene refers to one layer of graphite, that is, a surface layer of graphite, in which graphene has a very thin two-dimensional structure with a thickness of about 4 angstroms because the bond between graphene and graphene is weak in graphite . These graphenes have found very useful properties that differ from conventional materials.

The most notable feature is that when electrons move from graphene, the mass of electrons flows like zero, which means that electrons flow at the rate at which light travels in vacuum, that is, the flux. These graphenes also have an unusual half-integer quantum Hall effect on electrons and holes.

In addition, the electron mobility of the graphenes known to date is known to have a high value of about 20,000 to 50,000 cm 2 / Vs. As described above, due to the excellent properties of graphene, it has attracted attention as a substitute material for transparent electrodes such as next-generation silicon or ITO (INDIUM TIN OXIDE).

In addition, graphene has a merit that it is very easy to process 1-dimensional or 2-dimensional nanopatterns composed of only carbon, which is a relatively light element. In addition, it can control the semiconductor-conductor properties, Since diversity can be used to fabricate a wide range of functional devices such as sensors and memories, many people are working hard to obtain a large-area graphene film easily in order to commercialize the graphene.

Solution processes are widely used to easily coat graphene onto substrates with large areas. However, in order to use such a solution process, the dispersibility of graphene / graphene oxide is very important.

Graphene oxide shows good dispersibility in polar solvents, but dispersibility is poor in nonpolar solvents or in solvents with weak polarity. Also, when the dispersibility is poor, the physical properties of the coated steel sheet are poor.

For application to aqueous or solvent-type polymer solutions for steel sheet coating, it is necessary to ensure dispersibility for various solvents.

Korean Patent Publication No. 2015-0076632 Korean Patent Registration No. 1535178

Accordingly, the present invention intends to improve the dispersibility in a non-polar solvent by synthesizing an alkyl group at the edge portion of graphene graphene oxide in length.

Another aspect of the present invention is to produce an alkyl-reduced graphene oxide having a high reduction ratio to produce a high-quality graphene-coated steel sheet.

In order to improve the dispersibility, the present invention improves the dispersibility by introducing alkyl groups having different lengths to the edges of graphene oxide.

Alkyl-reduced graphene oxide with graphene oxide modified with alkylamine reacts with amine group of alkylamine and carboxyl group of graphene oxide to form amide bond and bond alkyl group to edge of graphene.

The alkylamine may be at least one alkylamine having an alkyl group of C5 to C19. As preferred specific examples of the alkylamine, at least one of hexylamine, decylamine, octadecylamine, and the like is possible and is not limited within a range that is obvious to a person skilled in the art. When the number of carbon atoms is less than C4, the carbon length is too short to ensure dispersion stability. In the case of C20 or more, the carbon length is long when coating the steel sheet, so that the stability of the curing dispersion is easy. However, Can be deteriorated.

Further, a steel sheet is coated with a coating composition composed of the alkyl-reduced graphene oxide of the present invention and a solvent to provide a steel sheet having improved physical properties. The kind of the ground steel sheet coated with the alkyl amidated graphene oxide of the present invention is not particularly limited, and for example, a cold-rolled steel sheet; Hot - rolled steel; galvanized steel; Aluminum-plated steel sheet; Copper, magnesium, iron, manganese, titanium, zinc, or a mixture thereof, or a mixture of two or more of these metals, It may be an aluminum alloy plate added.

The solvent used for the alkyl aminated graphene oxide to coat the steel sheet may be either polar or non-polar solvent, preferably toluene, chloroform, NMP, THF or DCM.

As a preferred embodiment of the present invention, there is provided a method for coating a steel sheet with a mixture of an alkylaminated graphene oxide and a solvent of the present invention.

1) heating graphene oxide to 90 DEG C in DMF for 48 hours;

2) reducing the graphene oxide with an alkylamine to obtain an alkylaminated graphene oxide;

3) dispersing the alkyl aminated graphene oxide in a solvent to obtain an on-coating composition; And

4) coating the coating composition on a steel sheet, and then drying the coating composition to produce a high-quality graphene-coated steel sheet.

In the method of producing the graphene-coated steel sheet of the present invention, the above-described alkylaminated graphene oxide, a solvent and the like can be applied.

Alkylaminated graphene oxide having improved dispersibility by the method according to the present invention has excellent properties such as corrosion resistance, workability, and adhesion after coating with a steel sheet because of easy compatibility with a polymer solution for coating steel.

In addition, by easily dispersing graphene oxide, which has dispersibility only in a polar solvent, in a nonpolar solvent, it can be applied to various coating polymer solutions, and it is easy to secure the physical properties of the graphene coated steel sheet.

FIG. 1 shows the O1s spectrum (b) of the XPS C1s spectrum (a) of the graphene oxide (GO) and the alkyl reduced graphene oxide (alkyl-rGO), and (c) the C1s spectrum.
Figure 2 shows the Raman spectrum of graphene oxide (GO) and alkyl-reduced graphene oxide (alkyl-rGO).
Fig. 3 shows the results of the dissolution test of graphene oxide (GO) and alkyl-reduced graphene oxide (alkyl-rGO).
4 shows changes in absorbance of the supernatant depending on each solvent.
Figure 5 shows an SEM image of a dispersed upper layer droplet graphene in NMP.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

According to the present invention, it is possible to provide a steel sheet which is surface-treated by coating the coating solution with a non-polar solvent by synthesizing an alkyl group having different lengths at the edge of graphene oxide.

First, hexylamine, decylamine, and octadecylamine were reacted with graphene oxide to synthesize alkyl-reduced graphene oxide (alkyl-rGO) having different alkyl groups.

The synthesized alkyl-reduced graphene oxide (alkyl-rGO) was confirmed to have proceeded well by X-ray photoelectron spectroscopy (XPS). First, the XPS C1s graph of graphene oxide (GO) in FIG. 1 (a) shows large bond peaks of carbon and oxygen, whereas in the C1s graph of alkyl-reduced graphene oxide (alkyl-rGO) (Fig. 1 (c)). This is because many of the functional groups bound to graphene oxide were reduced because the graphene oxide was heated in DMF at 90 ° C. for 48 hours during the synthesis of alkyl-reduced graphene oxide (alkyl-rGO). When the C1s peak of this alkyl-reduced graphene oxide (alkyl-rGO) is divided into several peaks as shown in Fig. 1 (c), it can be seen that a C-N bond peak is newly formed. As a result, it was confirmed that the carboxyl group of graphene oxide and the amide group of the alkylamine reacted to form a C-N bond, that is, an amide bond.

We also compared the C1s and O1s peaks of XPS to confirm that three different alkyl-reduced graphene oxide (alkyl-rGO) were synthesized using amines of different alkyl lengths. Because the synthesis proceeded under the same conditions, the reduction of each alkyl-reduced graphene oxide (alkyl-rGO) would have occurred to a similar extent. Therefore, in terms of elemental analysis, the longer the alkyl group is, the greater the amount of carbon should be, while having similar amounts of oxygen. 1 (b) and 1 (c), it can be seen that the amount of oxygen decreases sharply as the length of the alkyl group increases as the amount of carbon is almost the same. In other words, if the amount of oxygen is the same, since the amount of carbon increases as the length of the alkyl group increases, it can be confirmed that the synthesis of alkyl-reduced graphene oxide (alkyl-rGO) has been successfully performed according to the length of the alkyl group.

Also, it was confirmed by using Raman spectroscopy that graphene oxide was reduced during the alkyl functionalization (FIG. 2). A downshift of the G peak of alkyl-reduced graphene oxide (alkyl-rGO) was observed compared to graphene oxide, which is evidence that graphene oxide was reduced during the course of the reaction. As a ratio of the D / G peak, graphene quality can be confirmed. It can be confirmed that the graphene oxide is increased in the D / G ratio by progressing the reaction with the alkyl-reduced graphene oxide (alkyl-rGO). The reason for this is that the reduction reaction occurs during the synthesis of the alkyl-reduced graphene oxide (alkyl-rGO), and the functional groups are separated and defects are generated in place.

In order to confirm the dispersion stability of the alkyl-rGO compounds synthesized in this way, five kinds of solvents (NMP, THF, DCM, Chloroform, Toluene) were dispersed. When the dispersion was observed immediately after the ultrasonic dispersion, it was confirmed that the three alkyl-reduced graphene oxides (alkyl-rGO) were well dispersed regardless of the solvent, while the graphene oxide was not dispersed in the non-polar toluene . After 2 days, the graphene oxide was mostly submerged in the four solvents except NMP, and after two weeks, the alkyl-reduced ruthenium oxide (alkyl-rGO) except for hexyl-reduced graphene oxide ) Showed excellent dispersibility in all solvents (Fig. 3).

After 2 weeks of dispersion, the supernatant of each solution was taken separately and UV-Vis spectroscopy was used to confirm the dispersion concentration according to each type of graphene (FIG. 4). As a result, it was confirmed that the longer the alkyl length was, the larger the hydrophobic property was, and the dispersion stability in the polar solvent was deteriorated and the dispersion stability in the non-polar solvent was increased. However, in general, alkyl-reduced graphene oxide (alkyl-rGO), which is more hydrophobic than graphene oxide which is hydrophilic in polar solvents, has excellent dispersion stability.

When a spin-coated SEM image (FIG. 5) and a UV-Vis spectroscopy (FIG. 4) of a dispersed upper layer liquid of NMP are taken together, it can be seen that in the case of octadecyl-rGO It is predicted that the dispersibility is good because it has a hydrophobic property and it has a long alkyl group on the edge though it has poor releasability in NMP which is a polar solvent. From these results, it has been found that the introduction of an appropriate alkyl group into graphene oxide can improve the dispersion stability although the peeling property is slightly lowered in the polar solvent as well as the non-polar solvent.

Grapina  Preparation of coating solution

The graphene dispersion solution is mixed with an organic resin to obtain a graphene dispersion coating solution.

According to one example, the graphene oxide may be included in an amount of 5 to 80 parts by weight, preferably 25 to 75 parts by weight, based on 100 parts by weight of the graphene oxide coating solution. If the content of the graphene dispersion is less than 5 parts by weight, the graphene content in the final product may be too small to exhibit excellent physical properties of graphene. On the other hand, if the graphene oxide content exceeds 80 parts by weight, The adhesion of the pin coating layer may be deteriorated or it may be difficult to secure a uniform graphene coating layer.

The organic resin uniformly disperses the graphene oxide and serves as a binder in coating. Examples of the organic resin may be a mixture of one or more kinds selected from the group consisting of water-dispersible urethane resin, water-dispersible acrylic resin, water-soluble epoxy resin, water-soluble polyester resin and water-soluble amino resin, no. The water-dispersible urethane resin is preferably used. More preferably, it may be selected from the group consisting of an aqueous dispersion urethane resin having a carboxyl group or a hydroxy group, an aqueous dispersion urethane resin modified with an acrylic monomer, an aqueous dispersion urethane resin modified with a vinyl monomer, , And most preferably an aqueous dispersion urethane resin using a polycarbonate polyol.

According to one example, the organic resin may be contained in an amount of 25 to 70 parts by weight, preferably 40 to 55 parts by weight, based on 100 parts by weight of the graphene coating solution. If the content of the organic resin is less than 25 parts by weight, the adhesion to the surface of the base steel sheet may be deteriorated and it may be difficult to form a uniform graphene coating layer. If the content exceeds 70 parts by weight, the viscosity of the graphene oxide coating solution The workability may be deteriorated.

According to one example, the graphene dispersion coating solution may further comprise at least one corrosion resistance improving agent selected from the group consisting of inorganic metal sols, rust inhibitors, organometallic complexes and crosslinking agents. The corrosion resistance improving agent is added to 100 parts by weight of the graphene coating solution, 0.1 to 5 parts by weight, preferably 0.5 to 4 parts by weight, more preferably 1 to 4 parts by weight.

The inorganic metal sol serves to improve the corrosion resistance. Specific examples thereof include, but are not limited to, silica sol, alumina sol, titania sol, and zirconia sol, or a mixture of two or more thereof.

Rust inhibitors also serve to improve corrosion resistance, including metal compounds such as aluminum or aluminum aluminum; An aqueous solution of phosphoric acid of hexaammonium heptamolybdate tetrahydrate; zinc; molybdenum; Fluorine; Boric acid; A mixture thereof or a phosphate solution thereof, but is not limited thereto.

The organometallic complex improves the adhesion property by the condensation reaction with the base steel sheet, particularly the zinc-plated steel sheet and the hydrogen bond formation, and thereby improves the corrosion resistance of the base steel sheet, and the silane coupling agent, Zirconium-based coupling agents, and mixtures of two or more thereof. However, the present invention is not limited thereto.

The crosslinking agent serves to crosslink the organic resin through cross-linking with a carboxyl group or a hydroxy group contained in the organic resin, thereby enhancing the adhesion and corrosion resistance of the coating layer. The crosslinking agent has a carbodiimide group But are not limited to, a compound selected from the group consisting of a melamine crosslinking agent, an isocyanate crosslinking agent, an aziridine crosslinking agent, and a mixture thereof.

According to one example, the graphene dispersion coating solution may further include at least one of an antifoaming agent, a smoothing agent, a wax, and a solvent. Such additives may be added in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the graphene oxide coating solution .

The solvent may be water, ethanol or a mixture thereof. In order to improve wettability and dispersibility of the graphene coating solution, it is preferable that 0.1 to 10% by weight of ethanol is contained as a mixture of water and ethanol. However, the content of the solvent in the graphene dispersion coating solution is not particularly limited and may be appropriately selected depending on the content of the above-mentioned components.

The component contents of the coating composition were varied as shown in Table 1 for Examples and Comparative Examples.

Grapina Dispersion  Coating layer formation

Next, a graphene dispersion coating solution is applied on a base steel sheet to form a graphene dispersion coating layer.

In the present invention, the kind of the base steel sheet is not particularly limited, and for example, a cold-rolled steel sheet; Hot - rolled steel; galvanized steel; Aluminum-plated steel sheet; Copper, magnesium, iron, manganese, titanium, zinc, or a mixture thereof, or a mixture of two or more of these metals, But it is not necessarily limited to these.

Also, in the present invention, the method of applying the graphene dispersion coating solution onto the base steel sheet is not particularly limited. For example, any of spray coating, bar coating, roll coating, gravure coating, dip coating and solution cast coating But the present invention is not limited thereto.

[Comparative Example]

The grafting reaction was carried out by graphening with alkylamines having carbon atoms of C0, C2, C4, C20 and C22 (Comparative Examples 1 to 5) and then dispersing them in a solvent to improve the dispersibility in the non- To prepare a surface-treated steel sheet

[Example]

(Examples 1 to 7), and dispersed in a solvent to improve the dispersibility in the non-polar solvent to obtain a solvent-type graphene / A polymer coating solution was prepared and coated to prepare a surface-treated steel sheet

(1) scratch resistance

The pencil hardness was measured in order to evaluate the scratch resistance, and the pencil hardness was measured according to JIS K5600-5-4KS. Here, the pencil hardness is measured sequentially from 9B to 9H, and the closer to 9B the hardness is, the closer to 9H the harder the hardness.

F: Excellent scratch resistance

B: My Scratchy Dread

◎: HB or more

○: B or more to F or less

DELTA: 4B or more to 2B or less

×: 5 B or less

(2) Corrosion resistance

The initial wetness of the coated specimens was evaluated by continuous spraying of 5% saline at 35, 95% humidity. The evaluation results were evaluated in the following manner.

◎: No more than 480 hours.

◯: Initial screening after 240 hours.

△: Initial call after 120 hours.

×: Initial call before 72 hours.

(3) Bending property

The surface of the coated specimen was bent by 180 °, then inserted into a vise and tightened to a flat surface. (0, 1, 2, 3T-Bending). A scotch tape was attached to the curved coating film, and when the coating film was peeled off, the state of peeling off the tape was evaluated.

◎: 0T, 1T, 2T, 3T No peeling.

○: 1T, 2T, 3T No peeling.

?: 2T, 3T No peeling.

X: 3T Micro crack occurred.

(4) Adhesiveness

The coated specimens were cut with a cutter so as to have a width of 1 mm and a length of 1 mm to prepare 100 pieces, and 3M tape was attached and then peeled off to evaluate the adhesion of the coating. The evaluation results were evaluated in the following manner.

◎: No abnormality.

○: 10 or less eliminated.

△: Within 50 pieces.

×: Completely eliminated.

(5) Lubrication

The lubricity was measured using a drag bead friction tester (load 1,000 kgf, speed 1,000 mm / min, distance 100 mm).

?: Friction coefficient less than 0.15

?: Friction coefficient 0.15 or more and less than 0.30

X: Friction coefficient 0.30 or more

Remarks Scratch resistance Corrosion resistance Bending property Attachment Lubricity Comparative Example 1 × × × △ × Comparative Example 2 × × △ △ × Comparative Example 3 △ × ○ △ △ Comparative Example 4 △ △ × × ○ Comparative Example 5 × △ × × ○ Example 1 ○ ◎ ○ ◎ △ Example 2 ◎ ◎ ◎ ◎ ○ Example 3 ◎ ◎ ◎ ◎ ○ Example 4 ◎ ◎ ◎ ◎ ○ Example 5 ◎ ○ ◎ ◎ ○ Example 6 ○ ○ ○ ◎ ○ Example 7 ○ ○ △ ○ ○

The surface properties of graphene oxide (GO) and three kinds of alkyl-reduced graphene oxide (alkyl-rGO) were mixed with a polymer solution and coated on a steel sheet (FIG. 5).

Alkyl-reduced graphene oxide (alkyl-rGO) having excellent dispersion stability has more stable dispersibility even in a polymer solution for steel plate coating, and thus has more excellent properties such as corrosion resistance, workability, and adhesion after steel plate coating.

When the dispersibility is lowered as in the case of graphene oxide, compatibility with the coating solution is lowered, and a phenomenon such as aggregation on the surface after coating occurs, which causes defects and deteriorates physical properties such as corrosion resistance.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be obvious to those of ordinary skill in the art.

Claims (8)

A steel sheet coated with a coating composition comprising an alkyl reduced graphene oxide, a binder and a solvent,
The alkyl-reduced graphene oxide is a reduction reaction product of graphene oxide and an alkylamine,
Wherein the alkylamine is at least one of alkylamines having C5 to C19 carbon atoms.
The graphene-coated steel sheet according to claim 1, wherein the alkylamine is at least one of hexylamine, decylamine and octadecylamine.
The graphene-coated steel sheet according to claim 1, wherein the solvent is toluene, chloroform, NMP, THF or DCM.
The graphene-coated steel sheet according to claim 1, wherein graphene oxide is contained in an amount of 5 to 80 parts by weight based on 100 parts by weight of the coating composition.
The graphene-coated steel sheet according to claim 1, wherein 25 to 70 parts by weight of an organic resin is contained as a binder with respect to 100 parts by weight of the coating composition.
The graphene-coated steel sheet according to claim 1, wherein the coating composition further comprises at least one corrosion inhibitor selected from inorganic metal sols, rust inhibitors, organometallic complexes and crosslinking agents.
The graphene-coated steel sheet according to claim 6, wherein the crosslinking agent is at least one selected from the group consisting of a compound having a carbodiimide group, a melamine crosslinking agent, an isocyanate crosslinking agent, an aziridine crosslinking agent, .
Heating the graphene oxide to 90 DEG C in DMF for 48 hours;
Reducing the graphene oxide with an alkylamine to obtain an alkyl-reduced graphene oxide;
Dispersing the alkyl-reduced graphene oxide in a binder and a solvent to obtain a coating composition; And
Coating the coating composition on a steel sheet, and drying the coating composition.

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