Transparent planar heating film including transferred metal nanoparticles

Abstract

A transparent planar heating film includes metal nanoparticles that are disposed on at least a portion of a transparent adhesive film; and a transparent electrode that is completely covered by the transparent adhesive film and has a conductive surface that is laminated to and in direct contact with the metal nanoparticles via the transparent adhesive film. The heating temperature of the transparent planar heating film is a maximum of at least two times higher at the same power consumption than that of conventional planar heating films. Both the transparent adhesive film and the transparent electrode may be flexible so that the transparent planar heating film is flexible. In the transparent planar heating film, the metal nanoparticles may be bonded to desired locations on the conductive surface of the transparent electrode enabling selective heating.

Claims

1. A transparent planar heating film, comprising: metal nanoparticles that are disposed on at least a portion of a transparent adhesive film; and a transparent electrode that is completely covered by the transparent adhesive film and has a conductive surface that is laminated to and in direct contact with the metal nanoparticles via the transparent adhesive film.

2. The transparent planar heating film according to claim 1, wherein the conductive surface of the transparent electrode is made of a material selected from the group consisting of indium tin oxide (ITO), zinc oxide (ZnO), fluorine-doped tin oxide (FTO), and aluminum-doped zinc oxide (AZO).

3. The transparent planar heating film according to claim 1, wherein the metal nanoparticles are nanoparticles of a metal selected from the group consisting of Ag, Al, Au, Cu, W, Cr, Ti, and alloys thereof.

4. The transparent planar heating film according to claim 1, wherein the metal nanoparticles have an average diameter of 3 to 500 nm.

5. The transparent planar heating film according to claim 1, wherein the transparent adhesive film comprises an adhesive material disposed on a polymeric film comprising a polymeric material selected from the group consisting of polyethylene, polyethylene terephthalate, polyimide, polydimethylsiloxane (PDMS), polyester, polyurethane, polyamide, ethyl vinyl acetate, and combinations thereof.

6. The transparent planar heating film according to claim 1, wherein both the transparent adhesive film and the transparent electrode are flexible so that the transparent planar heating film is flexible.

7. The transparent planar heating film according to claim 6, wherein the transparent adhesive film and the transparent electrode are laminated in a roll-to-roll process.

8. The transparent planar heating film according to claim 1, wherein the metal nanoparticles are disposed on at least one predetermined portion of the transparent adhesive film so that selective heating of the laminated transparent electrode is enabled.

9. The transparent planar heating film according to claim 1, wherein the metal nanoparticles are disposed in a structure constituted to release heat when an electric current from the transparent electrode is received.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

(2) FIG. 1 is a flowchart illustrating a method for manufacturing a transparent planar heating film according to one embodiment of the present invention;

(3) FIG. 2 is a diagram illustrating the attachment of a metal nanoparticle film to a transparent electrode by a roll-to-roll process in accordance with one embodiment of the present invention;

(4) FIG. 3 shows a SEM image (left) of metal nanoparticles formed on a SiO.sub.2 substrate and a SEM image (right) of metal nanoparticles attached to an adhesive film in Example 1;

(5) FIG. 4 shows heating temperatures of transparent planar heating films manufactured in Example 1 and Comparative Example 1, which were measured as a function of applied voltage; and

(6) FIG. 5 shows temperature distributions of transparent planar heating films manufactured in Example 1 and Comparative Example 1.

DETAILED DESCRIPTION OF THE INVENTION

(7) The present invention is directed to a transparent planar heating film whose heating temperature is a maximum of at least two times higher at the same power consumption than that of conventional planar heating films and in which a metal nanoparticle film is bonded to a desired location on the surface of a transparent electrode, enabling selective heating, and a method for manufacturing the transparent planar heating film.

(8) The present invention will now be described in detail.

(9) A transparent planar heating film of the present invention includes a transparent electrode (also referred to as a “transparent flexible electrode”), metal nanoparticles transferred to the upper surface of the transparent electrode, and a transparent adhesive film attached to the upper surface of the metal nanoparticles.

(10) The transparent electrode receives external power and applies an electric current such that the electric current flows through the metal nanoparticles. Specifically, the transparent electrode may be made of a material selected from the group consisting of indium tin oxide (ITO), zinc oxide (ZnO), fluorine-doped tin oxide (FTO), and aluminum-doped zinc oxide (AZO).

(11) The metal nanoparticles receive an electric current from the transparent electrode to release heat. Particularly, due to the presence of the metal nanoparticles transferred to the upper surface of the transparent electrode, the transparent planar heating film of the present invention has a maximum of at least two-fold higher heating temperature at the same power consumption than conventional planar heating films without metal nanoparticles. The use of the transparent adhesive film allows the transparent planar heating film of the present invention to have latent heat properties. Specifically, it takes a 20 to 30% longer time until the elevated temperature of the transparent planar heating film according to the present invention falls to room temperature after power is cut off than that of conventional planar heating films. Therefore, the use of the transparent planar heating film according to the present invention can reduce energy consumption. The metal nanoparticles are not especially limited but are preferably selected from the group consisting of Ag, Al, Au, Cu, W, Cr, and Ti nanoparticles.

(12) The metal nanoparticles have an average diameter of 3 to 500 nm, preferably 5 to 300 nm. If the average diameter of the metal nanoparticles is less than the lower limit defined above, no improvement in heat release properties cannot be expected. Meanwhile, if the average diameter of the metal nanoparticles exceeds the upper limit defined above, the metal nanoparticles are very difficult to transfer to the adhesive film or, even if transferred, the haze of the transparent planar heating film increases greatly, resulting in low flexibility as well as poor visibility of the heating film.

(13) The use of the transparent adhesive film in combination with the metal nanoparticles allows the transparent planar heating film of the present invention to have latent heat properties and assists in facilitating the bonding of the metal nanoparticles to the transparent electrode. The transparent adhesive film is not especially limited as long as it has the above-mentioned characteristics but is preferably made of at least one material selected from the group consisting of polyethylene, polyethylene terephthalate, polyimide, polydimethylsiloxane (PDMS), polyester, polyurethane, polyamide, and ethyl vinyl acetate.

(14) The present invention also provides a method for manufacturing a transparent planar heating film.

(15) Specifically, the method of the present invention includes (A) depositing a thin metal film on a surface-treated substrate, (B) physically treating the deposited thin metal film to form metal nanoparticles, (C) separating the metal nanoparticles from the substrate with an adhesive film, and (D) attaching the metal nanoparticles attached to the adhesive film to a transparent electrode such that the metal nanoparticles are brought into contact with the transparent electrode.

(16) In step (A), a thin metal film is deposited on a surface-treated substrate.

(17) The substrate is made of a material that can withstand subsequent physical treatment performed to form metal nanoparticles and facilitates separation of the metal nanoparticles. Specifically, any semiconducting or insulating material (such as an oxide or nitride) except a metal or metal alloy may be used without particular limitation for the substrate. Preferably, the substrate is selected from the group consisting of silicon, glass, and SiO.sub.2 substrates.

(18) The surface of the substrate is treated with an organic solvent. This surface treatment facilitates the separation of metal nanoparticles in the subsequent step.

(19) The material for the thin metal film is not limited to a particular metal but is preferably selected from Ag, Al, Au, Cu, W, Cr, Ti, and alloys thereof. Any known deposition process may be used without particular limitation to deposit the thin metal film. Preferably, the thin metal film is deposited by a process selected from the group consisting of physical vapor deposition (PVD), chemical vapor deposition, spray coating, roll coating, bar coating, dip coating, and spin coating.

(20) The thickness of the deposited thin metal film is in the range of 1 to 25 nm, preferably 1 to 15 nm. If the thickness of the thin metal film is less than the lower limit defined above, no improvement in heat release properties cannot be expected. Meanwhile, if the thickness of the deposited thin metal film exceeds the upper limit defined above, metal nanoparticles are impossible to transfer to an adhesive film in the subsequent step and no improvement in heat release properties cannot be expected.

(21) Next, in step (B), the deposited thin metal film is physically treated to form metal nanoparticles.

(22) The physical treatment may be thermal treatment such as heating or photo treatment such as light irradiation.

(23) The thermal treatment is performed at 80 to 400° C., preferably 100 to 300° C. for 1 to 60 minutes, preferably 1 to 30 minutes. The thermal treatment is performed under ambient air, vacuum or inert gas conditions. If the thermal treatment temperature and time are outside the respective preferred ranges defined above or satisfy only one of the two conditions, the thin metal film is not formed into metal nanoparticles or, even if formed, the average diameter of the metal nanoparticles is outside the range defined above, resulting in poor heat release properties.

(24) Examples of light sources for the photo treatment include, but are not particularly limited to, infrared lamps, xenon lamps, YAG lasers, argon lasers, carbon dioxide lasers, and XeF, XeCl, XeBr, KrF, KrCl, ArF and ArCl excimer lasers, which are generally at powers of 10 to 5000 W. The power of a light source used in the present invention is in the range of 100 to 1000 W.

(25) In steps (C) and (D), the metal nanoparticles are separated from the substrate with an adhesive film (step (C)) and the metal nanoparticles attached to the adhesive film are attached to a transparent electrode such that the metal nanoparticles are brought into contact with the transparent electrode (step (D)).

(26) Specifically, an adhesive film is attached to one surface of the substrate/metal nanoparticles structure formed in step (B) where the metal nanoparticles are formed, and is then detached from the substrate. As a result, the metal nanoparticles are separated from the substrate and are attached to the adhesive film. The resulting adhesive film attached with the metal nanoparticles is referred to as “metal nanoparticle film”.

(27) The metal nanoparticle film separated from the substrate is attached to a transparent electrode to manufacture a transparent planar heating film.

(28) The metal nanoparticles are less likely to be directly formed on the upper surface of the transparent electrode. Thus, the metal nanoparticle film is attached to the transparent electrode in the present invention instead of forming the metal nanoparticles on the transparent electrode.

(29) A heating film manufactured by directly transferring metal nanoparticles to an adhesive film and attaching the metal nanoparticles to a transparent electrode has a non-uniform heating temperature and is not flexible, unlike the heating film of the present invention in which metal nanoparticles are directly formed from a thin metal film. A heating film using a thin metal film instead of metal nanoparticles has poor latent heat properties and cannot be activated for a long time.

(30) The following examples are provided to assist in further understanding of the invention. However, these examples are intended for illustrative purposes only. It will be evident to those skilled in the art that various modifications and changes can be made without departing from the scope and spirit of the invention and such modifications and changes are encompassed within the scope of the appended claims.

Example 1

(31) A SiO.sub.2 substrate was immersed in a DTS solution (a mixture of 1 ml of trichlorododecylsilane and 20 ml of toluene) at room temperature for 1 h, sonicated in toluene, and deposited with silver (Ag) to a thickness of 10 nm using a thermal evaporator. The deposited thin silver film was annealed in a furnace at 200° C. for 20 min to form metal nanoparticles with an average diameter of 130 nm. The metal nanoparticles formed on the SiO.sub.2 substrate are shown in the left SEM image of FIG. 3. An adhesive film was attached to the surface of the SiO.sub.2 substrate where the metal nanoparticles were formed, and was then detached from the substrate. At this time, the metal nanoparticles were naturally separated from the substrate. The resulting adhesive film attached with the metal nanoparticles (see the right SEM image of FIG. 3) was attached to a transparent electrode by using a roll-to-roll process, as illustrated in FIG. 2, such that the metal nanoparticles were brought into contact with the transparent electrode, completing the manufacture of a transparent planar heating film.

Comparative Example 1

(32) Fluorine-doped tin oxide (FTO) was deposited on a PET substrate to manufacture a planar heating film.

Test Example

Test Example 1: Measurement of Heat Release Properties

(33) FIG. 4 shows heating temperatures of the transparent planar heating films manufactured in Example 1 and Comparative Example 1, which were measured as a function of applied voltage, and FIG. 5 shows temperature distributions of the transparent planar heating films manufactured in Example 1 and Comparative Example 1. Each of the transparent planar heating films shown in FIG. 5 was attached to a portion of the transparent electrode.

(34) As shown in FIG. 4, the transparent planar heating film of Example 1 showed much higher heating temperatures than that of Comparative Example 1 at the same voltages. The heat released from the transparent planar heating film of Example 1 reached a maximum of 120° C. Particularly, when a voltage of 6 V or above was applied, the heating temperature of the transparent planar heating film of Example 1 was at least twice that of Comparative Example 1.

(35) As shown in FIG. 5, the transparent planar heating film of Example 1 showed high heating temperatures compared to that of Comparative Example 1. FIG. 5 confirms planar heat release from the transparent planar heating film of Example 1 other than local heat release.

(36) Due to its high transmittance and low sheet resistance, the transparent planar heating film of the present invention can be used in various applications where high optical transparency is required.