US20070012572A1

US20070012572A1 - Method of producing mold used in production of hydrophobic polymer substrate

Info

Publication number: US20070012572A1
Application number: US11/335,024
Authority: US
Inventors: Seung-Mo Lee; Tai-Hun Kwon
Original assignee: Pohang University of Science and Technology Foundation POSTECH; Academy Industry Foundation of POSTECH
Current assignee: Pohang University of Science and Technology Foundation POSTECH; Academy Industry Foundation of POSTECH
Priority date: 2005-07-14
Filing date: 2006-01-19
Publication date: 2007-01-18
Also published as: JP2007022064A; DE102006002728A1; JP4297919B2; KR100605613B1

Abstract

Disclosed is a method of producing a mold for preparing a hydrophobic polymer substrate including forming an adhesion enhancer on a substrate, forming a first conductive layer on the adhesion enhancer, adhering a predetermined patterned hydrophobic template on the first conductive layer, forming a second conductive layer on the template to prepare a template assembly, metal electroplating on the template assembly to form a metal plating layer on the template assembly, and removing the first conductive layer, the second conductive layer, the adhesion enhancer, and the template from the template assembly.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2005-0063692 filed in the Korean Intellectual Property Office on Jul. 14, 2005, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method of producing mold used in production of a hydrophobic polymer substrate, and more particularly, to a method of producing mold used in production of a hydrophobic polymer substrate by an easy and simple process with large production and a large area.

BACKGROUND OF THE INVENTION

The wettability of a liquid to a surface of a solid such as a polymer material indicates an interaction between the surface of the solid and a molecule of liquid (adsorption of liquid to the surface of a solid), and a competitive phenomenon of adhesion between the solid and liquid and cohesion between molecules of the liquid. A larger cohesion than adhesion brings about a decrease in wettability, and less cohesion than adhesion brings about an increase in wettability.
Good wettability to liquid water relates to hydrophilic properties, and poor wettability relates to hydrophobic properties.
Such wettability can be quantitatively determined by measuring a contact angle of a solid surface. A contact angle of 90° or more indicates a hydrophobic surface and a contact angle of 150° or more indicates a super-hydrophobic surface. The hydrophobic properties mainly depend on chemical properties of the surface and of the micro- and nano-structures thereof. Recently, hydrophobic films have been widely required for various practical applications because of their characteristics such as self-cleaning, anti-fogging, and lack of surface friction fading caused by liquids.
W. Barthlott and C. Neinhuis reported various super-hydrophobic leaves in nature and the topology which results in the various phenomena in 1977. And various methods have been reported in the literature to construct hydrophobic surfaces by modifying structures of the surfaces. Conventionally, hydrophobic surfaces are fabricated with the help of chemical treatment for changing the surface energy of materials or for modifying the surface roughness, for example by polypropylene etching, plasma enhanced chemical vapor deposition (PECVD), plasma polymerization, plasma fluorination of polybutadiene, microwave anodic oxidation of aluminum, solidification of an alkylketene dimer, nanostructuring carbon film, polypropylene coating, carbon nanotube aligning, forming poly(vinyl) alcohol nanofibers, making the surface of polydimethylsiloxane porous, or oxygen plasma treatment.
Some of these methods produce hydrophobic surfaces by controlling the surface topography through complex chemical processes with toxic chemicals, and these methods mentioned above are generally time-consuming or costly. The produced surface from some of these methods is easily contaminated, causing a loss of hydrophobic properties, and some are unstable in the presence of other compounds.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a method of producing a mold used in production of a hydrophobic polymer substrate is by a simple process with a mass production.
One embodiment of the present invention is a method of producing a mold used in production of a hydrophobic polymer substrate. In the method, an adhesion enhancer is formed on a substrate and a first conductive layer is formed on the adhesion enhancer layer. A predetermined patterned hydrophobic template is adhered on the first conductive layer and a second conductive layer is formed on the hydrophobic template, thereby producing a template assembly. A metal plating layer is formed on the template assembly by metal electroplating and the template assembly is removed from the metal plating layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention:
FIG. 1 is a block diagram illustrating a procedure for producing a mold used in production of a hydrophobic polymer substrate of the present invention;
FIG. 2 is a scanning electron microscope (SEM) image showing micro- and nano-size surface structures of a mold used in production of a polymer substrate;
FIG. 3 is an enlarged photo of FIG. 2;
FIG. 4 is a drawing illustrating nickel plating of FIG. 1;
FIG. 5 is a schematic diagram illustrating ultraviolet-(UV) nanoimprint lithography equipment;
FIG. 6A is a SEM image of a lovegrass leaf;
FIG. 6B is an enlarged image of FIG. 6A;
FIG. 7 is a charge coupled device (CCD) photo of a water drop on the under-surface of a lovegrass leaf;
FIG. 8 is a photo of a nickel mold into which patterns of a lovegrass leaf are transferred, according to Example 1 of the present invention;
FIG. 9 is a photo showing a surface of a polymer substrate produced by using a nickel mold into which patterns of a lovegrass leaf are transferred, according to Example 1 of the present invention;
FIG. 10 is a CCD photo of a water drop on a polymer substrate produced by using a nickel mold into which patterns of a lovegrass leaf are transferred, according to Example 1 of the present invention; and
FIG. 11 is a CCD photo of a water drop on a polymer film according to Comparative Example 1.

DETAILED DESCRIPTION OF THE INVENTION

Conventionally, hydrophobic surfaces are fabricated with the help of chemical treatment for changing the surface energy of materials or for modifying the surface roughness, for example by polypropylene etching, plasma enhanced chemical vapor deposition (PECVD), plasma polymerization, plasma fluorination of polybutadiene, microwave anodic oxidation of aluminum, solidification of an alkylketene dimer, nanostructuring carbon film, polypropylene coating, carbon nanotube aligning, forming poly(vinyl) alcohol nanofibers, making the surface of polydimethylsiloxane porous, or oxygen plasma treatment.
Some of these methods produce hydrophobic surfaces by controlling the surface topography through complex chemical processes with toxic chemicals, and these methods mentioned above are generally time-consuming or costly. The produced surface from some of these methods is easily contaminated, causing a loss of hydrophobic properties, and some are unstable in the presence of other compounds.
The present invention relates to a method of producing a mold used in the production of a hydrophobic polymer substrate without chemical procedures.
Hereinafter, the inventive method will be illustrated in more detail in reference to the accompanying FIG. 1. An adhesion enhancer 5 is formed on a substrate 1 and then a first conductive layer 3 is formed on the adhesion enhancer 5 (A of FIG. 1).
The adhesion enhancer 5 acts to increase adhesion force between the substrate 1 and the first conductive layer 3, and is formed by depositing adhesion enhancing materials such as chromium or titanium on the substrate 1.
The substrate may be a silicon substrate such as silicon wafer.
The first conductive layer 3 is formed by depositing an electrically conductive material on the substrate 1. The electrically conductive material may be gold, copper or nickel, and the deposition may be performed by sputtering.
The thicknesses of the first conductive layer 3 and the adhesion enhancer 5 may be suitably controlled, for example, to about 800 Å for the first conductive layer 3, and about 200 Å for the adhesion enhancer 5.
A predetermined patterned hydrophobic template 7 is adhered on the first conductive layer 3 to partially cover the first conductive layer (B and C of FIG. 1). The hydrophobic template may be a hydrophobic plant leaf, examples of which include but are not limited to those of bamboo, lovegrass, silver maple tree, or tulip plant. The adhering step may be performed by using an epoxy-based binder to form an adhesion layer 8.
Thereafter, a second conductive layer 9 is formed on the hydrophobic template 7 and on the first conductive layer 3 which is not covered with the hydrophobic template 7 in order to impart the electrical conductivity to the hydrophobic template 7. The second conductive layer 9 is formed by gold or carbon ion coating. The thickness of the second conductive layer may be suitably controlled to mirror patterns of the hydrophobic template 7 and to be sufficient for plating.
The produced substrate 1, adhesion enhancer 5, first conductive layer 3, hydrophobic template 7, and second conductive layer 9 are referred to as a template assembly 10.
Metal electroplating is performed on the template assembly 10 to form a metal plating layer 20 on the second conductive layer (D of FIG. 1). The metal may be nickel, copper, silver, gold, zinc, or a tin-lead alloy, but is not limited thereto.
The template assembly 10 is removed from the electroplated template assembly to separate the template assembly 10 from the metal plating layer 20 (E of FIG. 1).
The removal is illustrated in more detail. The resulting metal-plated template assembly is immersed in a strong base solution to remove the substrate 1. The strong base solution may be a solution of KOH. Such a procedure is performed at a temperature of about 70° C.
The adhesion enhancer 5, the first conductive layer 3, and the second conductive layer 9 are removed from the resulting template assembly. The removal includes the following two steps. One step is that the resulting template assembly is immersed in an etching solution to remove the adhesion enhancer 5. The etching solution may be a solution including perchloric acid and ceric ammonium nitrate.
Thereafter, the resulting template assembly is immersed in a conductive material stripping solution to remove the first and second conductive layers 3 and 9. The stripping solution may be a mixture of hydrochloric acid, nitric acid, and water (approximately 240 ml:120 ml:400 ml), or a mixture of KI, I₂and water (approximately 4 g:1 g:40 ml).
The resulting material is dipped into a template removal solution to remove the hydrophobic template 7. The removal solution may be KOH. The dipping step may be performed at 55 to 65° C. As a result, a metal mold with a hydrophobic surface is produced (E of FIG. 1). The metal mold is useful for preparing a hydrophobic substrate.
In FIG. 2, the morphology of the metal mold is shown enlarged by 3500 times and by 6500 times in FIG. 3. As shown in FIGS. 2 and 3, the metal mold has a hydrophobic surface.
Hereinafter, the metal electroplating process will be illustrated in more detail with accompanying FIG. 4, which shows electroplating. In the present invention, a metal electroplating procedure is preferred and nickel electroforming procedure is more preferred, but the metal plating process is not limited thereto.
The nickel electroplating is performed by using the template assembly 10 shown in FIG. 1 as a cathode and nickel as an anode in a nickel plating solution. The nickel plating solution includes 300 to 500 g/L of nickel sulfamate (Ni(SO₃NH₂)₂), 20 to 60 g/L of nickel chloride (NiCl₂.6H₂O), and 20 to 80 g/L of boric acid (H₃BO₃).
The nickel electroplating is performed at a nickel plating solution temperature of 50 to 55° C. and a pH of 3.8 to 4.5. The current density is set to 0.37 to 1.20 mA/dm². The current density may be constant or alternatively is increased by step by step during the electroplating.
When the nickel electroplating is performed outside of the above conditions, a mold having poor resolution may be produced, pits may be formed on the mold, or the plating is not performed. A temperature of the nickel plating solution of the less than 50° C. of increases resistance of the nickel plating solution, which causes poor current flow. A temperature of more than 55° C. restricts the type of material to be plated. Furthermore, a pH of more than 4.3 produces hydroxides of Ni which prevent the plating, and a pH of less than 3.7 causes corrosion of the materials in the plating solution.
The metal mold has an inverse pattern of micro- and nano-size structures of the surface of the hydrophobic leaf, and is useful for a hydrophobic polymer substrate replicating micro- and nano-structures of hydrophobic plant leaves by using a UV-nanoimprint lithography technique. The mold is also applicable for injection molding or hot embossing. In particular, the mold is useful for applications in which films are produced in a short time under mass production.
UV-nanoimprint lithography equipment used in UV-nanoimprint lithography using the mold is shown in FIG. 5. As shown in FIG. 5, the UV-nanoimprint lithography equipment includes a pneumatic cylinder 50, a vacuum chuck 52 fixing the metal mold 54, a transparent quartz substrate 60 through which UV rays pass, a glass substrate 58 on which a photopolymer 57 is coated, a UV lamp 66 which cures the photopolymer, a reflector 68, and a UV shutter 64 which controls the irradiation time of the UV rays.
A hydrophobic polymer substrate production using the UV-nanoimprint lithography equipment will be illustrated.
A curable photopolymer composition is coated on a glass substrate 58 on a transparent quartz substrate 60 to form a curable photopolymer layer 57. The curable photopolymer composition includes a curable photopolymer and an initiator.
The curable photopolymer may be any one as long as it is cured by ultraviolet rays. The photopolymer may include, but is not limited to, epoxy resin, acrylic resin, or acrylate-based resin such as ethylene glycol diacrylate or polyimide. The photoinitiator may be an anthraquinone-based compound such as 1-chloro anthraquinone, or an epoxide-based compound.
The mixing ratio between the photopolymer and the initiator is not critical and may be suitably controlled. In particular, the initiator is used in a sufficient amount to initiate a curing reaction.
The coated amount of the photopolymer composition may be suitably controlled, for example to 30 to 40 μl per cm²when a template to be used has an area of 5×5 cm².
Thereafter, the hydrophobic metal mold 54 is located on the curable photopolymer layer 57 and then ultraviolet rays are irradiated to them while they are under pressure. The curable photopolymer layer is thereby cured to form a hydrophobic patterned film.
The irradiating step is preferably performed while a pressure of 150 kPa or more and more preferably 150 to 500 kPa is applied. In addition, it is preferable that the pressure while irradiating is kept constant. The time for the irradiating step may be controlled according to the amount and type of curable photopolymer. Generally, 600 seconds or more are required to completely cure 1 ml of the curable photopolymer, and more precisely 600 seconds to 30 minutes.
The hydrophobic polymer substrate is applicable to fields where self-cleaning is required, such as tiles, varnish, construction, clothing, tools for the kitchen, or for fields in which a decrease in flowing resistance is required fields, such as aeronautics, shipping crafts, or automobiles.
The following examples illustrate the present invention in more detail. However, it is understood that the present invention is not limited by these examples.

EXAMPLE 1

Chromium was sputtered on a 4-inch diameter silicon wafer to form an adhesion enhancer, and gold was sputtered on the adhesion enhancer to form a first conductive layer. The thickness of the first conductive layer was about 800 Å and that of the adhesion enhancer was about 200 Å.
A bamboo leaf was adhered on the first conductive layer using an epoxy-based binder (Trademark: LICTITE, PRISM 401), and gold ion coating was performed on the bamboo leaf to form a second conductive layer, thereby obtaining a template assembly. The thickness of the second conductive layer was about 3 Å.
Using the template assembly as a cathode, a nickel metal as an anode, nickel electroplating was performed in a nickel plating solution to form a nickel plating layer on the template assembly. The nickel plating solution included 320 g/L of nickel sulfamate ((Ni(SO₃NH₂)₂), 50 g/L of nickel chloride (NiCl₂.6H₂O), and 35 g/L of boric acid (H₃BO₃). The electroplating was performed at a temperature of the nickel plating solution in 55° C. at a pH of 4.1. The anode current collector was set to 0.37 mA/dm²for 240 minutes, at 0.61 mA/dm²for 780 minutes, at 1.20 mA/dm²for 2340 minutes and finally at 1.20 mA/dm²for 2400 minutes.
The nickel plating layer template assembly was immersed in a 70° C. solution of KOH to remove silicon, and the resulting template assembly was immersed in an adhesion enhancer etching solution (Trademark: CR-7SK, Cyanteck Corporation) to remove the adhesion enhancer. The etching solution included perchloric acid and ceric ammonium nitrate.
The obtained template assembly was immersed in a conductive layer removal solution including a mixture of KI, I₂and water (about 4 g:1 g:40 ml ratio) to remove the first and second conductive layers. Thereafter, the template assembly from which silicon, chrome and gold were removed was immersed in a 60° C. KOH solution to remove the bamboo leaf, thereby obtaining a nickel mold.
The nickel mold was attached on a vacuum chuck 52 of UV-nanoimprint lithography equipment in a vacuum chamber as shown in FIG. 5. A curable photopolymer composition including a curable epoxy photopolymer and an epoxide initiator (available from Ventico, RenShape SL 5180) was coated on a glass substrate 58 on a quartz substrate 60 to form a curable photopolymer layer 57. At this time, the coated amount of the photopolymer was 1 ml per cm²of the nickel mold.
Thereafter, air and dust were removed from the vacuum chamber and pressure was applied to a pneumatic cylinder 50. The pressure was maintained at 400 kPa or more.
Under constant pressure, UV was irradiated from a UV lamp 66 to reach the curable photopolymer layer 57 via a UV shutter 64 and the quartz substrate 60. The curable photopolymer layer was cured while the hydrophobic structure of the nickel mold was replicated to the curable photopolymer layer, thereby obtaining a replicated hydrophobic polymer substrate. The UV irradiation was performed for 660 seconds and the UV lamp 66 was an MRL 1500 UV lamp available from SEM Co., Ltd.
When the UV irradiation was completed, the vacuum chamber was depressurized followed by detaching the replicated film from the nickel mold 54, thereby producing a hydrophobic polymer substrate.

COMPARATIVE EXAMPLE 1

A polymer film was produced by irradiating UV to a photosensitive resin composition (Ventico, RenShape SL 5180) for 660 seconds.
FIG. 6A shows a SEM image enlarged by 2000 times of micro- and nano-structures of a bamboo leaf, and FIG. 6A shows a SEM image enlarged by 6000 times thereof. FIG. 7 shows a water drop on the under-surface of a bamboo leaf after 5 μl of water was dropped to the leaf. The contact angle was measured and was found to be 152°.
FIG. 8 shows a SEM image of the nickel mold to which the structure of the bamboo leaf was replicated according to Example 1, and FIG. 9 shows a SEM image of the polymer substrate produced by using the nickel mold.
FIG. 10 shows a water drop on the under-surface of the polymer film after 5 μl of water was dropped to the polymer substrate. The contact angle was found to be 150° which is about 2° different from that of the bamboo leaf, thereby indicating a good hydrophobic property.
FIG. 11 shows a water drop on the polymer substrate according to Comparative Example 1 after 5 μl of water was dropped to the polymer substrate. The contact angle was found to be 56°.
It is shown from the results that the modification of the structure of the surface increases the contact angle by 94° and makes it hydrophobic.
As described above, the mold of the present invention can be repeatedly used over a long time because of the inherent durability of nickel. The nickel mold is applicable to various applications such as UV-nanoimprint lithography, hot embossing, and injection molding. Furthermore, the polymer substrate made by using the mold renders use for a long time without deformation or denaturation because the polymer used has good durability.
Furthermore, the polymer substrate of the present invention is applicable to various fields such as tiles, varnishes, construction, clothing, tools for the kitchen, aeronautics, shipping crafts, or automobiles, as well as microchips.

Claims

1. A method of producing a mold for producing a hydrophobic polymer substrate, comprising;

forming an adhesion enhancer on a substrate;

forming a first conductive layer on the adhesion enhancer;

adhering a predetermined patterned hydrophobic template on the first conductive layer;

forming a second conductive layer on the template and on the first conductive layer to prepare a template assembly;

metal electroplating on the template assembly to form a metal plating layer on the template assembly to produce a metal plated template assembly;

removing the template assembly from the metal plated template assembly to separate the template assembly and the metal plating layer.

2. The method of claim 1, wherein the adhesion enhancer is formed by depositing on the substrate a material selected from the group consisting of Cr and Ti.

3. The method of claim 1, wherein the first conductive layer is formed by sputtering on the adhesion enhancer a conductive material selected from the group consisting of gold, copper, and nickel.

4. The method of claim 1, wherein the second conductive layer is formed by gold or carbon ionic coating.

5. The method of claim 1, wherein the hydrophobic template is a hydrophobic leaf.

6. The method of claim 5, wherein the hydrophobic leaf is a leaf of one or more selected from the group consisting of bamboo, lovegrass, trident maple, and tulip plant.

7. The method of claim 1, wherein the metal electroplating is a nickel electroplating.

8. The method of claim 7, wherein the nickel electroplating is performed by using a nickel plating solution including 200 to 330 g/L of nickel sulfamate, 30 to 60 g/L of nickel chloride, and 30 to 60 g/L of boric acid.

9. The method of claim 8, wherein the nickel plating is performed at 50 to 55° C., a pH of 3.8 to 4.5, and a current density of 0.37 to 1.20 mA/dm².