KR101451425B1 - Surface modification method for self cleaning property of aluminium material - Google Patents

Abstract

The present invention relates to a method for modifying the surface of an aluminum material by imparting a lotus effect on the surface of the aluminum material with a self-cleaning ability, with the surface of the soft petal having superhydrophobic properties. For this purpose, the present invention relates to a method for manufacturing an aluminum alloy, comprising: anodizing an aluminum material to form anodized aluminum on the surface; Forming an irregularity on the anodized aluminum; And forming hydrophobic self-assembled monolayer films on the unevenness of the alumiminium. The present invention can be applied to all kinds of materials made of aluminum, and has a feature of easily and quickly imparting self-cleaning ability characteristics.

Soft petal effect, wet etching, hydrophobicity

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface modification method for self-

The present invention relates to a method for modifying the surface of an aluminum material by imparting a lotus effect on the surface of the aluminum material with a self-cleaning ability, with the surface of the soft petal having superhydrophobic properties.

Barthlott Wilhelm, a German botanist, observes the surface of various plant leaves with electron microscope. As the irregularities of the surface become more intense, the surface of the water repellent structure becomes stronger, and the surface of the water repellent structure becomes self- cleaning (self-cleaning). (Lee et al., 1997). The self-cleaning phenomena of plant leaves, such as lotus leaves, have been called the Lotus effect (Neinhuis C, Barthlott W, "Charaterization and distribution of water-repellent, ), 79, 667-677). The cause of this phenomenon in the natural world is that the surface of the leaves is coated with epicuticular wax, which has hydrophobic properties, and that the surface is formed in the form of protruding structures of micrometer or nanometer size. This surface structure can easily remove fine dust when applied to the surfaces of buildings, automobiles, trains, ships, etc., and since the water droplets themselves do not come into contact with the surface, it can prevent corrosion of the surface, It can be extended almost permanently.

In addition, as the semiconductor process technology developed, the micrometer unit structure was artificially made on the surface, and the petal effect was observed on such a surface. In recent years, as nanometer processing technology has been developed beyond the micro unit Studies on the effect of soft petal leaf have been made. However, as the size of the concavo-convex structure becomes smaller, the strength of the concavo-convex structure becomes weaker, and it is difficult to reduce the size, so it is not easy to improve the self-cleaning ability.

On the other hand, it is known that the following conditions must be satisfied in order for a certain surface to exhibit a soft petal effect.

First, the contact angle of the surface should exceed 150 °.

Second, the difference between the advancing angle and the receding angle should be minimized in the dynamic contact angle.

Anodic oxidation is a surface treatment in which an anode is added to a metal material and an anode is added to the solution to form an oxide film on the metal material. The coated oxide film has good corrosion resistance, durability, adhesion and the like depending on the kind of the oxide film. In addition, boric acid, phosphoric acid, sulfuric acid and chromic acid are used as the solution. Since the surface of the film is rugged, the surface of the film is subjected to a sealing treatment to improve the corrosion resistance, or a dyeing solution is put on the surface thereof to color the anode coating variously. These anodizing methods are used for decorative coatings for home appliances and machine parts, for building products that require weather resistance in severe outdoor environments, or for products that require corrosion resistance, such as aircraft parts. The most representative material of the anodic oxidation is Al, and the metal materials of Mg, Zn, Ti, Ta, Hf and Nb are also anodized.

One of the surface treatment methods of aluminum is anodic oxidation and anodic oxidation can form anodic aluminum oxide with regular nanometer unit structures on the surface, and a great many applications are being made in industry. And anodic oxidation is a relatively simple electrochemical reaction that can form a hard and transparent oxide film on the aluminum surface.

The present invention provides a method for modifying a surface to have a self-cleaning function by generating an anodic oxidation coating having a soft petal effect on aluminum.

For this purpose, the present invention relates to a method for manufacturing an aluminum alloy, comprising: anodizing an aluminum material to form anodized aluminum on the surface; Forming an irregularity on the anodized aluminum; And forming a hydrophobic self-assembled monolayer film on the concavo-convex portions of the alumiminium. The present invention also provides a surface modification method for imparting self-cleaning ability of an aluminum material. The anodic oxidation of the aluminum material may be selected from the group consisting of an aqueous acid method, a sulfuric acid method, a phosphoric acid method, a chromic acid method, a boric acid method, and a sulfamic acid method. The step of forming the irregularities of aluminum is performed by wet etching. Can be selected from phosphoric acid, nitric acid, and chromic acid based ones. In the step of forming the irregularities in the anodized aluminum, the static contact angle is preferably 150 ° or more, and the hydrophobic monomolecular film on the surface of the anodized aluminum is preferably formed by forming a silane group.

The present invention provides a method for imparting self-cleansing ability by imparting a soft petal effect to all kinds of materials made of aluminum by adding a simple treatment in addition to an anodic oxidation method, which is often used as a surface treatment method for aluminum. It is possible to modify the surface through easy manipulation and to directly impart specific functionality to it, and it has a differentiated methodology and objectivity and is industrially useful.

In the present invention, the aluminum surface is changed to anodized aluminum by anodization, and wet etching is performed to form innumerable irregularities of nanometer size on the surface of the anodized aluminum, and a hydrophobic self-assembled monolayer is formed on the surface thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings, wherein like reference numerals will be understood to refer to the same or similar components.

The anodic oxidation of aluminum can be achieved by forming a layer of aluminum oxide (Al ₂ O ₃ ) on the surface of aluminum metal by electrochemical electrolytic method to form functional layers such as hardness, corrosion resistance, abrasion resistance, . When + and - electrodes are given in a certain liquid to oxidize aluminum, it can be said that several balls are formed and a single film is formed on the aluminum surface. In the cathode, a lot of lead is used, and aluminum is placed in the anode. In the anode, oxygen is generated and oxidation occurs. Oxidation means that aluminum forms a hole due to the combination with oxygen, and aluminum dissolves. In the case of forming a thin film, relatively low voltage is applied, but in the present invention, it is desirable to apply a relatively high voltage because a certain thickness is to be formed. The temperature also affects the film formation. Generally, in the soft anodizing method, the work is performed at a temperature of about 20 ° C., but depending on the conditions, the work may be performed in a low temperature environment. In the hard anodizing method, Is preferable. The soft anodized film is a film treatment method aimed at preventing the corrosion of aluminum metal and maximizing the ornamental effect by various color treatments. Since the hard oxide film has a thick coating layer and a high hardness, . The hard anodized film is treated with functional film to hard anodically oxidize the original aluminum metal surface to increase its functionality and properties. In addition to reinforcing the ductility of aluminum, Can be supplemented.

As the anodic oxidation method, it is possible to use a method such as a hydrochloric acid method, a sulfuric acid method, a phosphoric acid method, a chromic acid method, a boric acid method and a sulfamic acid method. In the case of the hard anodic oxidation method, To form a porous layer on the surface of the substrate. The acid method has the advantage that the initial film thickness increases linearly with time and is thick, strong and has good corrosion resistance, and superposition technique is important. The formed film can be adjusted in thickness and shape according to various production conditions. The thickness increase rate of the hard anodized film can be changed by the alloy component of the aluminum metal, and the additional dimension due to the increase in thickness after the anodic oxidation treatment is slightly different depending on the kind of the alloy.

Aluminum is anodized to partially modify the surface and wet it to form innumerable irregularities of nanometer size. The etching solution is fluorinated acid and vaginal

A mixture of hydrochloric acid and nitric acid, a mixture of nitric acid and cerium (IV) and nitric acid and water, a mixture of nitric acid and cerium (IV) and perchloric acid, and a mixture of nitric acid and nitric acid. Water, phosphoric acid, nitric acid, acetic acid and

Water, or a mixture of phosphoric acid, nitric acid and water. Chromic acid-based solutions are also used, but their use is being reduced in consideration of environmental factors. Among them, a phosphoric acid-based etchant is widely used because it is stable, has a low cost, has little influence on other insulating films, and has excellent controllability of etching. As the cap metal or barrier metal, Ti or Ti-W may be used. On the other hand, the shape of the concavities and convexities is preferably controlled in a tapered shape. In the case where the concentration of nitric acid in the etching solution is high, cracks may be generated on the surface of the irregularities, and the etching solution seeps into the boundary surface to cause a so-called etching trace.

It is preferable that the static contact angle of the unevenness formed through such a process is adjusted to be equal to or more than 150 degrees in order to sufficiently exhibit the effect of the lotus flower, and it is preferable that the difference between the forward angle and the backward angle is reduced. Since the difference between the advancing angle and the retraction angle is gradually reduced after the static contact angle becomes 150 ° or more, it is necessary to continue the wet etching process until the above condition is reached.

Next, a hydrophobic self-assembled membrane is formed on the surface of the surface-treated aluminum. This is to modify the surface so that the lotus effect can be exerted even more. Molecular self-assembly is the formation of thin films that have functional properties at desired locations on the solid surface by unitary molecules assembled through spontaneous intermolecular interactions to form a specific structure. The formation of self-assembled monolayer on the alumina surface, which is an element of anodic aluminum oxide, can be achieved by using a silane compound. It is known that the -OH functional group on the alumina surface is covalently bonded to form a dense monolayer. The hydrophobic self-assembled monolayer film can impart hydrophobicity to the aluminum surface using a compound containing a functional group of a fluoroalkyl group or the like.

Hereinafter, the present invention will be described by way of examples of the present invention.

<Microstructure Formation of Aluminum Surface>

Hard anodization of aluminum forms anodic aluminum on the aluminum surface and wet etching to produce nanostructured microstructures on the aluminum surface. First, the aluminum substrate is placed in a 25% perchloric acid ethanol solution and a potential of 20 V is applied for about 5 minutes. Keep the temperature at 7 ° C. Then, anodic oxidation was carried out in 0.3M oxalic acid solution at 0 ° C and 40V for 5 minutes. Anodic oxidation was carried out in a 0.3M oxalic acid solution at 0 ° C and 140V for 6 hours, immersed in a chromic acid solution (chromic oxide 9g + phosphoric acid 20.3ml + distilled water = 500ml) at 65 ° C for 12 hours, Lt; RTI ID = 0.0 &gt; primarily &lt; / RTI &gt; Followed by secondary anodization. Anodic oxidation was carried out in a 0.3M oxalic acid solution at 0 ° C and 40V for 5 minutes and anodic oxidation in a 0.3M oxalic acid solution for 6 hours at 0 ° C and 140V. Then, wet etching is performed for 20 minutes, 40 minutes, 60 minutes, and 80 minutes in a phosphoric acid solution (5.765 g phosphoric acid + distilled water = 500 ml) at 30 ° C.

FIG. 1 shows a scanning electron microscope photograph of the surface of anodized aluminum produced by the hard anodization process. As the wet etching time increases, sharp nanometric protrusions appear clearly on the aluminum surface.

&Lt; Formation of microstructure of aluminum surface through soft anodization >

The aluminum substrate is placed in a 25% perchloric acid ethanol solution and a potential of 20 V is applied for about 5 minutes. Keep the temperature at 7 ° C. Then, anodic oxidation was carried out in 0.3M oxalic acid solution at 0 ° C and 40V for 5 minutes. Chromic acid solution (chromic oxide 9g + phosphoric acid 20.3ml + distilled water = 500ml) is immersed for 12 hours at 65 ° C to remove the anodic aluminum primarily formed on the surface. Followed by secondary anodization. Anodic oxidation was carried out in a 0.3M oxalic acid solution at 0 ° C and 40V for 5 minutes. Thereafter, wet etching is performed at a predetermined time interval while maintaining the temperature at 30 ° C in a phosphoric acid solution (5.765 g of phosphoric acid + distilled water = 500 ml).

&Lt; Formation of hydrophobic monomolecular film &

The surface of the anodized aluminum fabricated above was washed with 5% Nochromix solution for 20 minutes at room temperature, washed again with distilled water, dried in vacuum, and then immersed in 0.1% volume% HDFS (heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane) n-hexane solution for 10 minutes, then taken out and washed with n-hexane and distilled water.

FIG. 2 is a result of measuring the static contact angle of a sample in which a hydrophobic self-assembled monolayer is formed on a hard anodized aluminum surface. As the wet etching time increases, the static contact angle increases more than 150 °.

FIG. 3 is a graph showing changes in forward and backward angles in a sample in which a hydrophobic self-assembled monolayer is formed on a soft anodized aluminum surface. As the wet etching time increases, the static contact angle increases to 150 ° or more, and the difference between the forward angle and the backward angle decreases sharply.

As described above, the technical structure of the present invention is implemented in other specific forms while retaining the technical concept of the present invention or essential conditions, namely, the concept of wet etching followed by anodization of aluminum and formation of hydrophobic self-assembled film It is to be understood that the embodiments described herein are to be interpreted in all aspects as illustrative and not restrictive.

Therefore, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. .

FIG. 1 is a photograph showing a change in surface structure according to wet etching time using an anodic aluminum oxide phosphoric acid solution formed through hard anodization in an oxalic acid solution. FIG.

FIG. 2 is a graph in which a static contact angle is increased to 150 ° or more according to a wet etching time using an anodic aluminum oxide phosphoric acid solution formed through hard anodization in an oxalic acid solution.

FIG. 3 is a graph in which the static contact angle is increased to 150 ° or more and the difference between the forward angle and the backward angle is decreased according to the wet etching time using the anodic aluminum oxide phosphoric acid solution formed through the soft anodization in the oxalic acid solution.

Claims (7)

Forming an anodized aluminum on the surface by hard anodizing the aluminum material at a temperature of -5 to 0 占 폚; Wet etching with a chromic acid-based solution to form tapered irregularities on the hard anodized aluminum; And forming a hydrophobic self-assembled monolayer film on the unevenness of the aluminum. The method according to claim 1, Wherein the anodic oxidation of the aluminum material is selected from the group consisting of a sulfuric acid method, a phosphoric acid method, a chromic acid method, a boric acid method, and a sulfamic acid method. delete delete 3. The method according to claim 1 or 2, Wherein the step of forming the irregularities on the anodized aluminum forms a static contact angle of 150 ° or more. 3. The method according to claim 1 or 2, Wherein the hydrophobic monomolecular film on the surface of the anodized aluminum forms a silane group. The method according to claim 6, Wherein the formation of the silane group is formed using a silane having hydrophobic properties by having a chemical structure comprising a fluoroalkyl group.

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