Thermochromic film and method for producing thermochromic film

Abstract

The present invention provides a thermochromic film having economical and environmental advantages, since vanadium dioxide can be used without a doping process by decreasing the phase transition temperature of vanadium dioxide, and a method for manufacturing a thermochromic film, the method including: a forming step of coating a solution containing untreated vanadium oxide on a substrate to form a coating layer; and a manufacturing step of producing a thermochromic layer by subjecting untreated vanadium oxide to a phase change to vanadium dioxide through annealing using intense pulsed light (IPL).

Description

[Technical Field]

[0001] The present invention relates to a thermochromic film and a method for manufacturing a thermochromic film, and more particularly to a thermochromic film including a thermochromic layer whose phase transition temperature changes and a method for manufacturing a thermochromic film using IPL annealing.

[0002] The present invention was made with the support of the following problems. Project unique number: 2021-GJ-RD-0074 Department name: Ministry of Science, ICT and Technology of Korea Research management specialist: Korea Research Foundation Research project name: R&D Special Zone Development R&D Project Research topic: Development of a reversible heat-blocking functional window / door system using large-area inline spray coating Contribution rate: 1 / 2 Supervising agency: Songil Innotek Co., Ltd. Research period: 2021.06.01~2022.03.31 [Background technology]

[0003] As the shortcomings of conventional coal, oil, and nuclear energy sources become apparent, the need for developing new alternative energy sources has recently increased. However, controlling energy consumption is just as important. In fact, more than 60% of the energy consumed by an average household is used for heating and cooling. In particular, the energy consumed through windows in average homes and buildings accounts for as much as 24%. Therefore, various efforts are being made to reduce energy consumed through windows, from adjusting window size to installing highly insulated window glass.

[0004] For example, thermochromic glass has been studied, in which a thermochromic layer having thermochromism is coated on glass to adjust the inflow of energy through the control of infrared transmittance.

[0005] Thermochromism is a phenomenon in which the color of an oxide or sulfide of a transition metal changes reversibly at a transition temperature (or critical temperature). Coating glass with such a thermochromic material allows visible light to enter but blocks near-infrared and infrared rays above a certain temperature, producing thermochromic glass that prevents the room temperature from rising. This property can be used to block near-infrared light during the high summer temperatures, preventing the temperature from rising indoors, while allowing light energy from outside to enter during the low winter temperatures. The use of such thermochromic glass in building windows can be expected to result in significant energy savings.

[0006] Materials that exhibit the thermochromic effect include oxides or sulfides of various transition metals, but research has primarily focused on the use of vanadium dioxide (VO2), which has a transition temperature (phase transition temperature) of 68°C.

[0007] Vanadium dioxide has a relatively high phase transition temperature, making it difficult to use as is, especially in applications such as windows, and efforts are being made to lower the phase transition temperature. Recently, the phase transition temperature has been controlled by doping with tungsten or the like, but this doping method poses environmental issues due to the complicated process and post-process residue disposal, and also deepens hysteresis characteristics, so an alternative method is needed.

[0008] Vanadium dioxide (VO2) can be produced by inducing a phase change in vanadium pentoxide (VO5), and conventionally, this is achieved by applying a solution containing vanadium pentoxide (VO5) to a substrate and then performing a high-temperature heat treatment process. However, this heat treatment process has problems such as the unavoidable need for a diffusion barrier layer to prevent thermal diffusion, even though it reduces optical properties, and it is difficult to apply to heat-sensitive substrates such as polymers. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide a thermochromic film that can change the phase transition temperature of a thermochromic layer by changing the stress using a heat-shrinkable substrate, making it applicable to various fields, and that has economic and environmental advantages since it does not require the conventional complicated doping process and post-treatment process, and a method for manufacturing a thermochromic film that can induce a phase change of vanadium oxide without a diffusion barrier layer, and that can produce a thermochromic film even when the substrate is made of a heat-sensitive material such as a polymer substrate. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides a thermochromic film comprising: a heat-shrinkable substrate; and a thermochromic layer formed on the substrate, the thermochromic layer having a phase transition temperature that changes in response to heat shrinkage of the substrate.

[0011] The present invention also provides a method for producing a thermochromic film, which includes the steps of: applying a solution containing untreated vanadium oxide (VOx) onto a substrate to form a coating layer; and annealing the untreated vanadium oxide using intense pulsed light (IPL) to transform it into vanadium dioxide, thereby producing a thermochromic layer. [Effects of the Invention]

[0012] The thermochromic film according to the present invention can change the phase transition temperature of the thermochromic layer using a heat-shrinkable substrate without complicated doping and post-treatment processes, and has economic and environmental advantages.

[0013] In addition, the manufacturing method of the present invention has the advantage that it is possible to induce a phase change of vanadium oxide by using IPL annealing without a diffusion prevention layer that would deteriorate optical properties, and that it is possible to manufacture a thermochromic film even when the substrate is made of a heat-sensitive material such as a polymer substrate. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing the structure of a thermochromic film according to the present invention. [Figure 2] FIG. 2 is a diagram showing the stress direction during thermal shrinkage of the substrate according to the present invention. [Figure 3] FIG. 3 is a diagram for easily explaining the shrinkage direction and stress direction during thermal shrinkage of the base material. [Figure 4] FIG. 4 is a graph showing the measured transmittance of the thermochromic film prepared in Example 1. [Figure 5] FIG. 5 is a graph showing the thermochromic properties of the thermochromic film produced in Example 2. [Figure 6] FIG. 6 is a graph showing the thermochromic properties of the thermochromic film produced in the control group of Example 2. [Figure 7] FIG. 7 is a graph showing the thermochromic properties of the thermochromic film produced in the control group of Example 2. [Figure 8] FIG. 8 is a graph showing the thermochromic properties of the thermochromic film produced in Example 3. BEST MODE FOR CARRYING OUT THE INVENTION

[0015] The terms used in this specification will be briefly explained below, and the present invention will be described in detail.

[0016] The terms used in the present invention are generally used and widely used as much as possible, taking into consideration the functions of the present invention. However, these terms may change depending on the intentions of engineers in the relevant field, precedents, the emergence of new technologies, etc. In addition, in certain cases, the applicant may arbitrarily select terms, and in such cases, the meanings thereof will be described in detail in the relevant description of the invention. Therefore, the terms used in the present invention should be defined based on the meanings of the terms and the overall content of the present invention, rather than simply the names of the terms.

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. Furthermore, in the drawings, parts that are not relevant to the description are omitted in order to clearly explain the present invention, and similar parts are designated by similar reference numerals throughout the specification.

[0018] The present invention will now be described in detail with reference to the accompanying drawings.

[0019] FIG. 1 is a diagram showing the structure of a thermochromic film according to the present invention, FIG. 2 is a diagram showing the stress direction during thermal shrinkage of a substrate according to the present invention, and FIG. 3 is a diagram for easily explaining the shrinkage direction and stress direction during thermal shrinkage of a substrate.

[0020] The thermochromic film of the present invention includes a substrate 100 and a thermochromic film 200 .

[0021] Specifically, the thermochromic film of the present invention relates to a thermochromic film comprising a substrate 100 having heat shrinkability; and a thermochromic layer 200 formed on the substrate, the phase transition temperature of which changes due to the thermal shrinkage of the substrate 100.

[0022] The substrate 100 has the property of shrinking when heat is applied, and the shrinking force acts as stress on the thermochromic layer, which can change the phase transition temperature of the thermochromic layer. For example, stress may be generated in the thermochromic layer 200 from the edge to the center when the substrate 100 is thermally shrunk (see FIG. 2). For example, the thermal shrinkage rate of the substrate 100 may be about 2%, and in this case, stress of about 2 GPa may be generated in the thermochromic layer 200.

[0023] The present invention induces a change in the phase transition temperature of the thermochromic layer 200 by changing the stress of the substrate 100, and ultimately controls the thermochromic properties of the thermochromic layer 200.

[0024] In one example, the phase transition temperature of the thermochromic layer 200 may decrease when the substrate 100 is thermally contracted. The rate of change in the phase transition temperature varies depending on the magnitude of stress caused by thermal contraction. For example, when the thermal contraction rate of the substrate 100 is 2% and the resulting stress is 2 GPa, the phase transition temperature may decrease by about 10°C.

[0025] In one embodiment, the substrate 100 has a curved surface, and the curvature of the curved surface can be gradually deformed during thermal contraction. Referring to Figure 3, the end of the curved surface moves in direction B during thermal contraction, and the curvature of the curved surface can be gradually deformed. Furthermore, as the curvature of the curved surface gradually deforms, stress (also referred to as compressive stress) can be applied to the thermochromic layer 200 formed on the substrate 100 in direction A.

[0026] In one example, the substrate 100 may include a shape memory polymer (SMP). A shape memory polymer is a polymer that has the property of returning to its original shape. It refers to a polymer material that memorizes a shape arranged under specific conditions and then returns to its original shape when the condition is further applied, even after the model is changed. In the present invention, the shape memory polymer has heat shrinkability, and in this case, the specific condition for the shape memory polymer may be the application of heat.

[0027] The glass transition temperature of the shape memory polymer may be 30°C or higher, 40°C or higher, 50°C or higher, 60°C or higher, 70°C or higher, 80°C or higher, or 100°C or higher. As long as the glass transition temperature is within the above range, the type of shape memory polymer is not particularly limited and can be appropriately selected in consideration of realizing desired physical properties. For example, the shape memory polymer may be a urethane-based shape memory polymer. Urethane-based shape memory polymers have the advantage of being able to exhibit shape memory properties even at low temperatures due to low glass conductivity, and are easy to handle and process.

[0028] In one embodiment, the thermochromic layer may include vanadium oxide. For example, the vanadium oxide may be vanadium dioxide. Specifically, the thermochromic layer 200 may include vanadium dioxide clusters. The term "vanadium dioxide clusters" refers to aggregates formed by adhesion between vanadium dioxide particles through a sintering process after removing the organic solvent from a solution containing vanadium dioxide particles. Because vanadium dioxide clusters exhibit thermochromic properties due to a phase transition, the present invention ultimately allows for the control of the phase transition temperature of the thermochromic layer 200 through the magnitude of stress in the substrate 100, thereby enabling adjustment of the thermochromic properties.

[0029] The thickness of the substrate 100 may be in the range of 50 to 200 μm, but is not particularly limited thereto, and the magnitude of the stress applied to the thermochromic layer can be controlled by adjusting the thickness of the substrate.

[0030] The thermochromic film may have a maximum transmittance of 50% or more in the 400 to 800 nm region. max ) is 50% or more, 55% or more, 60% or more, or 65% or more, and the minimum transmittance (OP) in the 2000 to 3000 nm region at any temperature above the critical temperature min ) may be 70% or less, 60% or less, specifically 55% or less, 50% or less, or 40% or less. max If the value is 50% or more, the visible light transmittance is high, ensuring a clear field of view. min If the value is 65% or less, the infrared blocking effect is excellent.

[0031] The thermochromic film can satisfy the condition of the following general formula 1. [General formula 1] △IR=BP min -Op min ≧10%

[0032] In the general formula 1, BP minshows a minimum transmittance between 2000 and 3000 nm at any temperature below the critical temperature, and OP min indicates the minimum transmittance in the range of 2000 to 3000 nm at any temperature equal to or higher than the critical temperature. Here, the temperature equal to or lower than the critical temperature may be, for example, 20 to 30°C, specifically 25°C, and the temperature equal to or higher than the critical temperature may be, for example, 60 to 90°C, specifically 80°C. When the ΔIR value (%) is 10% or higher, specifically 20% or higher, 25% or higher, 30% or higher, or 35% or higher, the effect of blocking / transmitting infrared rays is excellent.

[0033] The present application also relates to a method for producing the thermochromic film, which includes, for example, applying a thermochromic precursor solution onto a heat-shrinkable substrate and photosintering the thermochromic precursor solution to form a thermochromic layer.

[0034] In one example, the thermochromic precursor solution may include vanadium oxide.

[0035] The present application relates to yet another method for producing thermochromic films using IPL annealing.

[0036] The manufacturing method includes the steps of coating a substrate with a solution containing untreated vanadium oxide (VOx) to form a coating layer; and annealing the untreated vanadium oxide to vanadium dioxide through intense pulsed light (IPL) annealing to form a thermochromic layer. In this specification, the term "untreated vanadium oxide" refers specifically to vanadium oxide that does not undergo a phase change. The untreated vanadium oxide may exist in the form of particles or ions in a solution, and various known solvents capable of dissolving vanadium oxide may be used without limitation. The coating may be performed by various methods, such as spin coating, slot die coating, or spray coating.

[0037] The method of the present invention uses IPL instead of conventional high-temperature heat treatment, making it possible to produce a thermochromic film even when the substrate is made of a heat-sensitive material such as a polymer substrate.

[0038] For example, the untreated vanadium oxide (VOx) can be vanadium pentoxide (V2O5).

[0039] In order to prevent the induction of a phase change in vanadium oxide using IPL and the deformation of the heat-sensitive polymer substrate, it is important to optimize and set the specific annealing conditions, such as the annealing atmosphere, type of light, applied voltage (output voltage), pulse width, pulse number (number of repeated light irradiations), and pulse interval (frequency).

[0040] In one example, the annealing may be performed in a vacuum or air atmosphere. Specifically, the vacuum atmosphere may be a vacuum atmosphere of 1 to 20 Torr.

[0041] In the manufacturing method according to the present application, various IPL conditions such as pulse width, pulse interval, and number of repetitions, which will be described later, must be optimized depending on whether the annealing is performed in a vacuum or air atmosphere to induce a phase change in vanadium oxide. The optimized values ​​of the annealing conditions may differ depending on whether the annealing is performed in a vacuum or air atmosphere.

[0042] For example, in a vacuum atmosphere, the output voltage of the ultrashort pulsed light may be in the range of 1500 to 1900 V. As the output voltage increases, the phase change occurs more efficiently, but physical deformation of the polymer film may occur. An appropriate voltage at which physical deformation does not occur may be in the range of 1500 to 1750 V.

[0043] As another example, in an air atmosphere, the output voltage of the ultrashort pulsed light may be in the range of 1700 to 2000 V. As the output voltage increases, the phase change occurs more efficiently, but physical deformation of the polymer film may occur, and an appropriate voltage at which physical deformation does not occur may be in the range of 1750 to 1900 V.

[0044] The annealing can be performed by repeatedly irradiating light with a certain pulse interval and pulse width. To induce a phase change in vanadium oxide, the pulse interval, pulse width, and number of repetitions must be adjusted to an optimized range, as described below, depending on whether the atmosphere is vacuum or air.

[0045] Specifically, in a vacuum atmosphere, the pulse width may be within a range of 1 to 4 ms. Furthermore, in a vacuum atmosphere, the pulse interval may be within a range of 0.2 to 1 Hz. As the pulse interval decreases, the average power applied per second increases, thereby reducing the process time. The average power is determined by the output voltage, pulse width, and pulse interval. However, if the pulse interval is less than 0.2 Hz, the accumulated heat energy may be released to the bed, preventing a phase change from occurring. If the pulse interval exceeds 1 Hz, the bed temperature may rise rapidly, causing physical deformation of the polymer film.

[0046] In one example, the number of repetitions of annealing (or light irradiation) in a vacuum atmosphere may be in the range of 20 to 200. As the number of repetitions increases, the visible light transmittance and infrared light transmittance of the thermochromic layer produced improve; however, if the number of repetitions exceeds a certain number, the substrate may be deformed and the transmittance may decrease. For example, the infrared light transmittance improves up to 200 repetitions, but decreases above 250 repetitions. Therefore, the number of repetitions is preferably 20 to 200 repetitions, 50 to 200 repetitions, 100 to 200 repetitions, or approximately 200 repetitions.

[0047] In another example, in an air atmosphere, the pulse width may be within a range of 0.1 to 1 ms, for example, 0.2 to 1 ms, 0.3 to 1 ms, 0.4 to 1 ms, or 0.5 to 1 ms. Furthermore, in an air atmosphere, the pulse interval may be within a range of 1.0 to 3.0 Hz, for example, 1.1 to 3.0 Hz, 1.2 to 3.0 Hz, 1.0 to 2.5 Hz, 1.1 to 2.5 Hz, 1.2 to 2.5 Hz, 1.0 to 2.0 Hz, 1.1 to 2.0 Hz, or 1.2 to 2.0 Hz. As the pulse interval decreases, the average power applied per second increases, thereby reducing the process time. The average power is determined by the output voltage, pulse width, and pulse interval. However, if the pulse interval is less than 1.0 Hz, the accumulated heat energy may be released to the bed and the phase change may not occur, and if it exceeds 3.0 Hz, the bed temperature may rise too rapidly and physical deformation of the polymer film may occur.

[0048] In one example, the number of repetitions of annealing (or light irradiation) in an atmospheric environment may be in the range of 200 to 400. As the number of repetitions increases, the visible light transmittance and infrared light transmittance of the resulting thermochromic layer improve; however, if the number of repetitions exceeds a certain number, the substrate may be deformed and the transmittance may decrease. For example, the infrared light transmittance improves up to 400 repetitions, but decreases above 450 repetitions. Therefore, the number of repetitions is preferably 200 to 400 repetitions, 200 to 350 repetitions, 200 to 300 repetitions, or about 250 repetitions.

[0049] In one embodiment, the substrate may be selected from glass, quartz, or a polymer film. In particular, considering the utility of the flexible device, a polymer film may be selected as the substrate. The type of such a polymer film is not particularly limited, but may be a polyolefin film (e.g., cycloolefin, polyethylene, polypropylene, etc.), a polyester film (e.g., polyethylene terephthalate, polyethylene naphthalate), polyvinyl chloride, or a cellulose-based film (e.g., triacetyl cellulose).

[0050] Specifically, the polymer film may include a polymer having a glass transition temperature of 70°C or higher, 80°C or higher, 90°C or higher, 100°C or higher, 110°C or higher, or 120°C or higher. As long as the glass transition temperature is within the above range, the type of polymer is not particularly limited and can be appropriately selected in consideration of realizing desired physical properties. For example, when the polymer film is a polyethylene naphthalate film, excellent heat resistance can be realized.

[0051] Furthermore, the polymer film may be stretched, for example, uniaxially or more, and have a shrinkage rate of less than 3% when exposed to 120°C for 1 hour. When a stretched polymer film is used, it can have excellent mechanical strength and can prevent shrinkage at high temperatures. A polymer film satisfying these conditions can be selected from known materials.

[0052] When annealing in an air atmosphere, the thickness of the coating layer and the amount of untreated vanadium oxide (VO X The average particle size of the powder must also be controlled within the following range:

[0053] In one example, the thickness of the coating layer may be 10 to 300 nm or less, and untreated vanadium oxide (VO X The average particle size of the granules may be 1 to 40 nm or less. In this specification, the average particle size may be the average particle size measured by D50 particle size analysis, unless otherwise specified.

[0054] The present invention will be described in detail below based on the examples. However, the examples described in the specification and the configurations illustrated in the drawings are merely the most preferred embodiments of the present invention and do not fully represent the technical ideas of the present invention. Therefore, it should be understood that there may be various equivalents and modifications that can replace them at the time of filing this application.

[0055] Example 1 A solution containing vanadium dioxide was applied to a substrate containing a urethane-based shape memory polymer (SMP) using a spin coater (ACE-200, Dong-A Trading, Korea) to form a 10 × 10 mm 2 The size was coated onto glass at 1000 rpm for 30 seconds and dried to produce a thermochromic film.

[0056] The transmittance of the thermochromic films prepared in the examples was measured at 2500 nm using a spectrophotometer (JASCO V-770, JASCO, USA) when the temperature was increased from 25°C to 80°C and then decreased, and the results are shown in Figure 4. As a control, glass was used instead of the shape memory polymer.

[0057] Vanadium dioxide exhibits thermochromic properties due to a phase transition, so the temperature at which the transmittance changes in Figure 4 can be considered the phase transition temperature of vanadium dioxide. Therefore, when using an SMP substrate, it was confirmed that the phase transition temperature of vanadium dioxide decreased by 6.4°C due to the application of compressive stress.

[0058] Example 2 A solution containing vanadium pentoxide was applied to a 10 × 10 mm 2 The glass was coated with the size at 1000 rpm for 30 seconds.

[0059] Then, the film was subjected to IPL treatment 100 times at 1900V, 2ms, 0.5Hz in a vacuum atmosphere of 1 Torr to produce a thermochromic film.

[0060] FIG. 5 is a graph showing the thermochromic properties of the thermochromic film produced in Example 2, and FIGS. 6 and 7 are graphs showing the thermochromic properties of the thermochromic film produced in the control group of Example 2.

[0061] Specifically, FIG. 6 is a graph showing the thermochromic properties of a thermochromic film produced by drying at room temperature instead of the IPL treatment in Example 2, and FIG. 7 is a graph showing the thermochromic properties of a thermochromic film produced by heat treatment at 500°C for 1 hour in a vacuum atmosphere of 1 Torr instead of the IPL treatment in Example 2.

[0062] Referring to the drawings, it can be seen that the thermochromic film dried at room temperature does not exhibit thermochromic properties because no phase change of vanadium oxide occurs (see FIG. 6), whereas the heat-treated thermochromic film exhibits thermochromic properties due to a phase change of vanadium oxide (see FIG. 7). It was also confirmed that the thermochromic film manufactured by the IPL process according to the present invention in a vacuum atmosphere also underwent a phase change and exhibited the same effect as the heat-treated thermochromic film (see FIG. 5).

[0063] Example 3 A solution containing vanadium pentoxide with an average particle size of 40 nm or less was applied to a 10 × 10 mm 2 The glass was coated with the particle size at 1000 rpm for 30 seconds, and the thickness of the coating layer was 300 nm.

[0064] Then, the film was subjected to IPL treatment 300 times at 1750V, 0.5ms, 1.2Hz in an air atmosphere to produce a thermochromic film.

[0065] FIG. 8 is a graph showing the thermochromic properties of the thermochromic film produced in Example 3.

[0066] From Figures 6, 7 and 8, it was confirmed that the thermochromic film manufactured by the IPL treatment according to the present invention in an air atmosphere also underwent a phase change and exhibited the same effect as the heat-treated thermochromic film. [Explanation of symbols]

[0067] 100 Base material 200 thermochromic layer

Claims

1. a heat-shrinkable substrate comprising a shape memory polymer (SMP); and A thermochromic film containing vanadium oxide and a thermochromic layer formed on the substrate, the thermochromic layer having a phase transition temperature that changes due to thermal contraction of the substrate.

2. The thermochromic film according to claim 1 , wherein the thermochromic layer has a phase transition temperature that decreases when the substrate is thermally shrunk.

3. The thermochromic film according to claim 1 , wherein the substrate has a curved surface, and the curvature of the curved surface is gradually deformed during heat shrinkage.

4. The thermochromic film according to claim 1 , wherein the shape-memory polymer has a glass transition temperature of 30° C. or higher.

5. The thermochromic film according to claim 1 , wherein the shape-memory polymer is a urethane-based shape-memory polymer.

6. The thermochromic film according to claim 1, wherein the thickness of the substrate is in the range of 50 to 200 μm.

7. The thermochromic film according to claim 1, wherein the laminate has a maximum transmittance of 50% or more in the 400 to 800 nm region.

8. 2. The thermochromic film according to claim 1, wherein the laminate has a minimum transmittance of 70% or less in the 2000 to 3000 nm region at any temperature equal to or higher than the critical temperature.

9. The thermochromic film according to claim 1, wherein the laminate satisfies the condition of the following general formula 1: [General formula 1] △9R=BPP ｍｉｎ -Yes ｍｉｎ ≧10% In the general formula 1, BP ｍｉｎ indicates a minimum transmittance between 2000 and 3000 nm at any temperature below the critical temperature, and OP ｍｉｎ exhibits a minimum value of transmittance between 2000 and 3000 nm at any temperature above the critical temperature.

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