TWI414481B - Combined Preparation of Carbon Nanotube Composite Conductive Films with Metal Nanoparticles - Google Patents

Abstract

A production method of a carbon nano-tube complex conductive film bonded with metallic nano-particles includes the following steps: firstly preparing a carbon nano-tube complex bonded with metallic nano-particles, adding the carbon nano-tube complex into a predetermined quantity of a solvent to prepare a carbon nano-tube complex solution, further applying an ultrasound atomizing frequency such that the carbon nano-tube complex solution releases a plurality of atomized particles having the carbon nano-tube complex, and providing a carrying gas to transmit the atomized particles along a predetermined path to guide the atomized particles to a position over a stand placed with a substrate sheet. By means rotating the stand, the atomized particles are formed with a conductive film uniformly on the surface of the substrate sheet. Accordingly, the conductive film with lower resistance and better conductive performance can be produced.

Description

Method for preparing conductive film of carbon nanotube composite combined with metal nano particles

The invention relates to a method for producing a conductive film, in particular to a method for preparing a conductive film of a carbon nanotube composite combined with metal nanoparticles.

With the wide application and development of LCD screens, the development of transparent conductive materials has been a hot research topic. The transparent conductive films used in displays and touch panels should have the following basic characteristics: (1) Light transmittance in the visible range Both high conductivity and (2) must be made into a smooth surface film and can withstand the plasma process environment, (3) easy to etch to form a predetermined pattern, (4) large area uniformity (5) low production cost, (6) non-toxic and capable of recycling. Indium tin oxide (ITO) has the characteristics of low film resistance and visible light transmittance of 80% to 90%, and has become the most important source of transparent conductive film. However, indium in ITO raw materials. It is a rare metal, and the production is limited, resulting in unstable supply and high raw material costs. Therefore, the development of new alternative materials has become a major issue. In addition, the touch panel and the flexible panel which have been actively invested in the industry in recent years have disadvantages in that the ITO film is relatively soft and relatively durable in use and relatively low in reliability.

In view of the insufficient source of ITO and its application limit, nanocarbon tubes are a popular alternative material developed recently, mainly because of the excellent optical, electrical, magnetic and mechanical properties of nano carbon nanotube materials. Moreover, its macroscopic physical properties and chemical properties are directly related to the microscopic arrangement and quantity of the materials themselves, and can affect the applicable product end. At present, single-walled carbon nanotubes (single) that can be put into commercial application have been developed. -walled carbon nanotubes (referred to as SWNT) conductive film.

The single-walled carbon nanotube conductive film is mainly made by a filter method and a spray method. Among them, the filter method is to first synthesize SWNT by laser, pickle it with a high concentration of nitric acid solution, add it to a solvent containing a specific surfactant to form a carbon nanotube solution, and then filter it with a specific filter paper. The carbon nanotubes are parked on the surface of the filter paper to form a carbon nanotube membrane, and then the carbon nanotube membrane is transferred to a transparent substrate, and the filter paper portion is removed by acetone, leaving only the carbon nanotubes. A single-walled carbon nanotube conductive film ("Transparent, Conductive Carbon Nanotube Films", Z. Wu et., Science 2004 , 305, 1273, "Effect of SOCl2 Treatment on Electrical and Mechanical Properties of Single-Wall" Carbon Nanotube Networks", U. Dettlaff-Weglikowska et . , J. Am. Chem. Soc. , 2005, 127, 5125-5131).

The method for preparing a single-walled carbon nanotube conductive film by spraying method is to add a predetermined amount of single-walled carbon nanotubes and disperse it in a solvent containing a specific surfactant to form a carbon nanotube solution, which will After centrifugation of the carbon nanotube solution, a 50% portion of the upper layer of the solution is sprayed onto a poly(ethylene terephthalate, abbreviated as PET) substrate having a surface temperature maintained at 100 ° C. A single-walled carbon nanotube conductive film ("Effect of Acid Treatment on Carbon Nanotube-Based Flexible Transparent Conducting Films", J. Am. Chem. Soc. , 2007, can be obtained by washing and drying with deionized water . 129, 7758-7759).

In addition, although the carbon nanotubes themselves have excellent photoelectric characteristics, the contact resistance between the carbon nanotubes is still 10 ³ times that of the single carbon nanotubes. Therefore, the above-mentioned single-walled carbon nanotube conductive film Contact resistance between carbon nanotubes is still the focus of research to improve the conductivity of conductive films.

Although the academic and industry's active research and development, has developed a variety of transparent conductive films, and the manufacturing technology of single-walled carbon nanotube conductive film has also entered the stage of commercialization, and can replace the ITO film. Trends, but the related process technology will not be successful in a short period of time, in response to future needs, and create more humane interface products and soft electronic products, related to touch panels, flexible panels, transparent The process technology of liquid crystal displays such as electrodes will also be changed. Among them, the maturity of material technology will be a key element. Therefore, there is still a need to continuously develop different types of material technologies and improve the performance of existing materials to provide more elements. The choice and application, thereby improving product performance, reducing production costs and developing more advanced process technology.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method for producing a carbon nanotube composite conductive film incorporating metal nanoparticles in which the process is simplified and the conductivity can be further improved.

Therefore, the method for preparing a carbon nanotube composite conductive film incorporating metal nano particles comprises the following steps:

(i) separately dissolving a predetermined amount of the metal salt compound in an anhydrous organic solvent to prepare a first solution, and dissolving a predetermined amount of the carbon nanotubes in an anhydrous organic solvent to prepare a dispersion, and then After mixing and stirring the two, the temperature is raised to 100 ° C ~ 160 ° C at a predetermined heating rate and maintained at a constant temperature for a period of time to form a plurality of carbon nanotube composites combined with metal nanoparticles;

(ii) adding a predetermined amount of the carbon nanotube composite to a predetermined amount of solvent to prepare a carbon nanotube composite solution having a viscosity of 1 to 50 c.p;

(iii) applying an ultrasonic atomization frequency to the carbon nanotube composite solution, causing the carbon nanotube complex solution to release a plurality of atomized particles having the carbon nanotube complexes, and Providing a carrier gas for transporting the atomized particles along a predetermined path, wherein the atomized particles have a particle diameter of between 0.5 μm and 50 μm;

(iv) directing the atomized particles onto a susceptor on which a substrate sheet is placed, and by rotating the susceptor, the atomized particles are uniformly formed on the surface of the substrate sheet to form a carbon nanotube composite Conductive film.

The invention has the beneficial effects that the carbon nanotube composite combined with the metal nanoparticle is prepared by using a carbon nanotube compound and a metal salt compound, and the conductive film product produced thereby can exhibit better conductivity and, in addition, through application The ultrasonic wave causes the carbon nanotube composite solution to form atomized particles, which facilitates the dispersion of the carbon nanotube composites, and is combined with a spin coating method to enable the carbon nanotubes to be on the substrate. The surface of the sheet uniformly forms a conductive film, and the invention has the advantages of relatively simple process technology and equipment, and can effectively save manufacturing cost.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments.

Referring to FIG. 1 and FIG. 2, a preferred embodiment of the method for fabricating a carbon nanotube composite conductive film incorporating metal nanoparticles comprises the following steps: Step 101 is to dissolve a predetermined amount of a metal salt compound, respectively. Preparing a first solution in an anhydrous ethylene glycol, and dissolving a predetermined amount of carbon nanotubes in an anhydrous ethylene glycol to prepare a dispersion, and then mixing and stirring the mixture to increase by 2 per minute. The temperature rise rate of °C~5°C is raised to 100°C~160°C and maintained at a constant temperature for 1-3 hours, so that the metal ions in the metal salt compound are reduced to metal nanoparticles and adhered to the carbon nanotubes to form After a plurality of carbon nanotube composites combined with metal nanoparticles, they are directly filtered while hot, washed several times with absolute ethanol, and vacuum dried at a temperature of 80 ° C to obtain the carbon nanotubes. Complex. The carbon nanotubes may be multi-walled nanotubes (MWNTs) or single-walled carbon nanotubes (SWNTs). In this embodiment, multi-walled walls are used. Carbon nanotubes.

It is worth noting that the main control parameters in this step are the reaction temperature and the heating rate. The main features of using ethylene glycol as the solvent here are: (1) Ethylene glycol itself is a solvent system with high viscosity, The high polarity feature helps to dissolve a small amount of metal salt compounds, and its high viscosity prevents metal ions from diffusing. By controlling the viscosity and the diffusion rate of metal ions by temperature rise, the generated metal nanoparticles can be suspended in Ethylene. The ratio of alcohol to the wall of the carbon nanotube tube. (2) Since the boiling point of ethylene glycol is 198 ° C, the first solution and the dispersion may be heated to a higher temperature to help lower the metal ion having a higher activity to a zero-valent metal atom, for example, Platinum ions must reach a high reduction ratio at 120 ° C, while silver ions need to be as high as 150 ° C to achieve the same effect. (3) The oxalic acid formed after the oxidation of ethylene glycol is also a good metal nanoparticle protection group. For the particle size control of the metal nanoparticle and the stability of the metal nanoparticle before it is bonded to the carbon nanotube Important role. However, the thermal decomposition temperature of oxalic acid is 175 °C. Therefore, in order to effectively exert the ratio of ethylene glycol and oxalic acid to reduce the aggregation of metal nanoparticles and bare suspension, the reaction temperature should be lower than 175 ° C, and should be higher than 100 ° C to facilitate the reduction of metal ions, therefore, here The step limits the final reaction temperature for the temperature rise to 100 ° C to 160 ° C.

In addition, the heating rate is related to the particle diameter of the formed metal nanoparticles and the ratio of the metal nanoparticles to which the amount of the metal ions originally added is attached to the carbon nanotubes, and the faster the rate of temperature rise, the formation The smaller the particle size of the metal nanoparticles, the lower the ratio of adhesion to the carbon nanotubes. For the preparation of a carbon nanotube composite in which platinum and silver nanoparticles are combined, an increase of 2 ° C per minute is defined as a slow temperature rise, and a rise of 5 ° C per minute is defined as a rapid temperature rise. The carbon nanotube composites with metal nanoparticles prepared at a heating rate of 2 ° C / min were observed by transmission electron microscopy to show that the metal nanoparticles attached to the walls of the carbon nanotubes were dense. The average particle diameter of the metal nanoparticles is 3.84 nm, and the actual particle size distribution ranges from 2 nm to 7 nm. The thermal analysis results obtained by calcination at 900 ° C show that the metal loading rate is 99 of the original metal addition amount. %, fully showing a high ratio of metal load. The carbon nanotube composites with metal nanoparticles prepared at a heating rate of 5 ° C / min were observed by a transmission electron microscope to show the density of metal nanoparticles attached to the wall of the carbon nanotubes. Below 2 ° C / min, and the average particle size of the metal nanoparticles is reduced to 3.00 nm, the actual particle size distribution range is enlarged to 1 nm ~ 7 nm, and the thermal analysis obtained by calcination at 900 ° C shows that the metal The load rate is only 89% of the original metal addition. Therefore, in the selection of the heating rate, it is necessary to cooperate with the subsequent application direction. When the catalytic or electrical conductivity is the main application direction, the slow heating rate of the metal nanoparticle adhesion ratio is selected, when the transmittance or the small particle is used. When the diameter is the main consideration, the faster heating rate is selected as the selection condition.

Wherein, the metal nanoparticles on the carbon nanotube composite are made of a metal selected from the group consisting of platinum, silver, gold, and the like. And the metal salt compound of the first solution is a substance selected from the group consisting of potassium tetrachloroplatinate (K ₂ PtCl ₄ ), silver nitrate (AgNO ₃ ), and tetrachloroauric acid (HAuCl ₄ ). By using different metal salt compounds, a carbon nanotube composite combined with different metal nanoparticles can be formed, and the nanocarbon tube composite can be controlled by adjusting the ratio of the amount of the metal salt compound to the carbon nanotube. The content of metal nanoparticles in the medium. The content of the metal nanoparticles in the carbon nanotube composites is preferably from 10% by weight to 40% by weight.

When the carbon nanotube composite has only one type of metal nanoparticle, as described above, a first mixture formed by mixing the first solution and the dispersion is heated to 100 ° C to 160 ° C. After maintaining a constant temperature for a period of time, direct thermal filtration can reduce the metal ions in the metal salt compound and bond them to the carbon nanotubes, thereby forming a carbon nanotube composite having a metal nanoparticle. Things.

In addition, the carbon nanotube composites may have two or more kinds of metal nanoparticles. For example, when the carbon nanotube composites have platinum and silver metal nanoparticles, the preparation method is Dissolving a predetermined amount of potassium tetrachloroplatinate in anhydrous ethylene glycol to prepare the first solution, and then mixing with a dispersed liquid phase containing a carbon nanotube to form the first mixed liquid, and rising by 2 ° C per minute~ After the temperature is raised to 100 ° C to 160 ° C at a rate of 5 ° C and maintained at a constant temperature for 1 to 3 hours, the platinum ions can be reduced to platinum nanoparticles and respectively bonded to the carbon nanotubes. At this time, the chamber is cooled first. Warming, adding a second solution to the first mixture to form a second mixture, the second solution is prepared by dissolving a predetermined amount of silver nitrate in anhydrous ethylene glycol, and the second mixture is prepared by After stirring, the temperature is raised to 100 ° C ~ 160 ° C at a temperature increase rate of 2 ° C ~ 5 ° C per minute and maintained at a constant temperature for a period of time, then the silver ions in the silver nitrate are reduced to silver nanoparticles and respectively bonded to the platinum On the rice particles to form a naphthalene containing two kinds of metal nanoparticles, platinum and silver. Carbon nanotube composite. Since the adhesion between the silver nanoparticle and the wall of the carbon nanotube is not as strong as that of the platinum nanoparticle, and the raw material price of platinum is close to 100 times that of the silver, in order to increase the carbon nanotube composite in the conductive product Commercially useful value, firstly bound to the carbon nanotubes with a small amount of platinum nanoparticles, and then the silver nanoparticles are indirectly bonded to the carbon nanotubes through the platinum nanoparticles, therefore, by using two The metal nanoparticle can achieve the predetermined effect of attaching the metal nanoparticle to the carbon nanotube, and at the same time reduce the raw material cost. Among them, the weight of the platinum nanoparticle and the silver nanoparticle is preferably 1:5 to 1:20. If the balance between the raw material cost and the adhesion effect is considered, it is more preferably 1:10, and the content of the platinum nanoparticle and the silver nanoparticle in the carbon nanotube composite is preferably 20% by weight. The optimum loading efficiency (i.e., the total metal adhesion rate) is expressed as the ratio of the weight of the metal nanoparticles attached to the carbon nanotubes to the weight of the metal ions in the metal salt compound.

Step 102 is to prepare a carbon nanotube composite solution 30, and add 1 part by weight of the carbon nanotube composite and 1 part by weight of the surfactant component to 1000 to 1,000,000 parts by weight of the solvent respectively to prepare a viscosity value. In the carbon nanotube composite solution 30 of 1 to 50 c.p, the above viscosity value is a value measured at room temperature.

The surfactant component is for preventing the aggregation of the carbon nanotube composites, and is a substance selected from the group consisting of a sulfated alcohol (ROSO ₃ ^- M ⁺ ) , alkylsulfonate (formula RSO ₃ ^- M ⁺ ), α-olefin sulfonate (alpha-olefinsulphonate, abbreviated as AOS, of the formula RCH=CH(CH ₂ ) _n -SO ₃ M) Quaternary ammonium salt ), ethylene oxide (also known as polyethylene glycol, polyoxyethylene, POE for short), polyoxyethylene alkyl ether (also known as fatty alcohol polyoxyethylene ether, ether alcohol, alcohol ethoxylate, referred to as AE, The formula is RO(CH ₂ CH ₂ O) _n H), and combinations thereof.

Preferably, the surfactant is a substance selected from the group consisting of sodium C ₄ ~ C ₁₈ linear alkyl sulfonate (formula RSO ₃ ^- Na ⁺ ), C ₄ ~ C ₁₈ straight Potassium alkane sulfonate (formula RSO ₃ ^- K ⁺ ), linear alkyl sodium sulfate of C ₄ ~ C ₁₈ (formula of ROSO ₃ ^- Na ⁺ ), linear alkyl group of C ₄ ~ C ₁₈ Potassium sulfate (formula of ROSO ₃ ^- K ⁺ ), sodium C ₄ ~ C ₁₈ linear alkylbenzene sulfonate (formula RC ₆ H ₄ SO ₃ ^- Na ⁺ ), linear chain of C ₄ ~ C ₁₈ Potassium alkylbenzene sulfonate (formula RC ₆ H ₄ SO ₃ ^- K ⁺ ), linear C ₄ -C ₁₈ linear alkyl benzene sulphate (formula: ROC ₆ H ₄ SO ₃ ^- Na ⁺ ), C ₄ to C ₁₈ linear alkyl benzene sulfate (formula: ROC ₆ H ₄ SO ₃ ^- K ⁺ ), C ₂ to C ₁₆ linear alkyl quaternary ammonium salt, α-olefin sulfonate (abbreviation is the AOS, the formula _{RCH = CH (CH 2) n} -SO 3 M, where, n = 14 ~ 16, and M is an alkali metal ion group), alkyl polyoxyethylene alkyl is a C ₂ ~ C ₁₆ of Ether (abbreviated as AE, the formula is RO(CH ₂ CH ₂ O) _n H, n=5~30), and combinations thereof. Thereby, a better dispersion effect can be achieved. In the present embodiment, sodium dodecyl sulfate (SDS) is selected as the surfactant.

Wherein the solvent is a liquid selected from the group consisting of water, ethanol, isopropanol and acetone, and in the present embodiment, water is used as a solvent. When preparing, adding the carbon nanotube complex and the surfactant to the solvent, the probe type ultrasonic shock diffuser with power of 750W can be used first (model: Sonics & Materials, Inc. "SONICS The VCX 750") was applied to the carbon nanotube composite solution 30 at 20% power for 5 minutes and at 30% power for 5 minutes to prevent the carbon nanotube composites from aggregating and uniformly dispersed.

Step 103 is to apply an ultrasonic atomization frequency to the carbon nanotube composite solution 30 to atomize the carbon nanotube composite solution 30. The atomization refers to the carbon nanotube composite solution 30. A plurality of atomized particles 31 with such carbon nanotube composites are released and a carrier gas 32 is provided to transport the atomized particles 31 along a predetermined path. Wherein, the carbon nanotube composite solution 30 is contained in an atomization container 33, and the liquid level of the solution 30 is maintained at a fixed height by a siphon tube 34, thereby generating the supersonic frequency super The acoustic wave element 35 is constantly located at a fixed depth below the liquid surface to control the fixation of the energy received by the liquid level of the solution, and the particle size of the generated atomized particles 31 can be maintained. The siphon tube 34 is connected between the atomization container 33 and a liquid storage container 38. The liquid storage container 38 is placed on a lifting seat 39 to be vertically displaced by the linkage thereof, and can thereby control the The liquid level in the atomizing container 33. Preferably, in order to maintain the dispersed state of the carbon nanotube composite in the carbon nanotube composite solution 30 flowing to the liquid storage container 38, an additional one is usually added to the liquid storage device 38. A probe-type ultrasonic oscillating disperser (not shown) continues to act on the solution that is returned to the reservoir 38.

In the present embodiment, the ultrasonic atomization frequency of 1.65 MHz is used (the ultrasonic atomizer used in this embodiment is: Pro-Wave Electronic Corp M165D25, M165D20), and these The particle size of the atomized particles 31 is between 0.5 μm and 50 μm, and preferably between 2 μm and 7 μm. In the present embodiment, the particle size of the atomized particles 31 is matched with the ultrasonic atomization frequency. It is maintained at approximately 3 μm.

In order to meet the required particle size, the frequency range of the ultrasonic wave can be estimated by the following formula to adjust to the required atomized particle size 31 more quickly:

Where D is the particle size of the atomized particles, T is the surface tension coefficient (N/cm), ρ is the solution density (g/cm ³ ), f is the ultrasonic atomization frequency (Hz), and α is 0.34. Value. (Ultrasonics Volume 22, Issue 6, November 1984, Pages 259-260)

Preferably, the flow rate of the carrier gas 32 is from 1 L/min to 200 L/min. In the present embodiment, the flow rate of the carrier gas 32 is set to 22 L/min, and the carrier gas 32 is nitrogen.

Step 104 is spin coating, and the atomized particles 31 are guided onto a susceptor 37 on which a substrate sheet 36 is placed. By rotating the susceptor 37, the atomized particles 31 are placed on the substrate sheet 36. The surface uniformly forms a conductive film.

When the rotating cloth is rotated, the susceptor 37 is pre-treated by one wet spin coating and one preliminary film spin coating, and then repeated periodic re-filming spin coating is repeated, and the repulsion is repeated. In the film spin coating, the rotation is sequentially changed through a cycle of a low speed, a medium speed, and a high speed. In this embodiment, the low speed is preferably 300 to 450 r.p.m., and the medium speed is preferably controlled at 450 to 900 r.p.m., and the high speed is preferably 1200 to 6000 r.p.m. Among them, the rotational speed of the wet spin coating is 300r.pm and 450r.pm alternately, and the rotational speed of the preliminary film spin coating is from 450r.pm to 6000r.pm, and then enters the cycle. Sexual re-filming rotation.

Step 105 is hot pressing, applying a predetermined pressure to the substrate sheet 36 provided with the conductive film at a predetermined temperature, so that the conductive film is compacted and compacted to form a denser and stable structure, and the A tight junction is formed between the carbon nanotube composites to help reduce the surface resistance of the conductive film, so that the conductive film can exhibit better conductivity.

Preferably, when hot pressing is performed, a pressure of 1 to 200 kg/cm ² is applied at a temperature of 50 ° C to 110 ° C for 30 seconds to 30 minutes, and in the present embodiment, 100 kg / is applied at a temperature of 70 ° C. The pressure of cm ² is hot pressed for 30 minutes, but this should not limit the hot pressing time. Generally, the longer the hot pressing, the better the conductivity, but the increase in conductivity after hot pressing for more than 30 minutes is not significant, so the hot pressing time Should be controlled within 30 minutes.

Step 106 is cleaning. The substrate sheet 36 having a conductive film is firstly rinsed in deionized water for 5 to 30 minutes, and soaked for 2 hours for water exchange, repeated 5 times, and then soaked in ethanol for 2 hours, and then at a temperature of 60 ° C. A vacuum is applied, whereby the surfactant remaining in the conductive film can be removed to prevent the residual impurities from causing a decrease in the conductivity of the conductive film. After the cleaning is completed and dried, the finished carbon nanotube composite conductive film bonded to the metal nanoparticle is bonded to the substrate sheet 36.

It is worth mentioning that, in step 102, in addition to using only the carbon nanotube composite prepared in step 101 to prepare a solution of the carbon nanotube complex with a solvent, a predetermined ratio of unbound metal nanoparticles may also be used. The pure carbon nanotubes are mixed with the carbon nanotube composite combined with the metal nanoparticles to be added into the solvent to prepare a nanocarbon tube composite solution, and in step 103, the atomized particles are simultaneously carried The carbon nanotube composites and the pure carbon nanotubes. Thereby, the carbon nanotube composite with the best load efficiency is mixed with the pure carbon nanotube to achieve the desired electrical conductivity, and the amount of metal nanoparticles used in the conductive film can be reduced to reduce the cost. When the two carbon nanotubes overlap, as long as the single-sided carbon nanotubes have the metal nanoparticles, the wall connecting the two carbon nanotubes can be achieved to achieve the effect as a conductive passage. Therefore, the carbon nanotubes are mixed. The composite and the pure carbon nanotubes still achieve a predetermined conductivity.

<Specific Example 1 - Preparation of Nano Carbon Tube Composites Bonded with Platinum Nanoparticles>

150.2 mg of purified and heat-treated carbon nanotubes were ultrasonically dispersed in 100 ml of anhydrous ethylene glycol solution under nitrogen atmosphere, and K ₂ PtCl ₄ (which was sufficiently dissolved in 100 ml of anhydrous ethylene glycol) 79.9mg, no crystal water), transferred to a non-aqueous ethylene glycol dispersion containing carbon nanotubes under a nitrogen atmosphere by a double-ended needle, and after fully stirring, the temperature is gradually raised by 2 ° C per minute. The reaction was terminated at 160 ° C and at a constant temperature of 2 hours. The formed carbon nanotube composite was collected by hot filtration and washed with absolute ethanol for several times, and then vacuum dried at 80 ° C for 12 hours to obtain a carbon nanotube composite A loaded with 20 wt% of platinum nanoparticles. Further, in the same manner as described above, the amount of K ₂ PtCl ₄ was changed to 212.8 mg to obtain a carbon nanotube composite B loaded with 40 wt% of platinum nanoparticles. Wherein, the function of the above-mentioned double-ended needle is that the solution system in two nitrogen atmospheres can be effectively transferred from one side to the other side, and does not contact the outside air, for example, a needle for blood drawing, because the needle is connected to the blood vessel side, Connecting the blood bag is a double-ended needle.

As shown in FIG. 3 and FIG. 4, respectively, a carbon nanotube composite A loaded with 20 wt% of platinum nanoparticles observed under a transmission electron microscope (TEM), and a load of 40 wt. The morphology of the carbon nanotube composite B of the % platinum nanoparticle is effective for the adhesion of the platinum nanoparticle to the wall of the carbon nanotube tube, and the carbon nanotube composites A and B are respectively grooved. After 15 minutes of sonication, the clarified sample was taken for TEM observation, and it was shown that the platinum nanoparticles remained attached to the carbon nanotubes stably after the ultrasonic action. In addition, as shown in FIG. 5, the carbon nanotube composite A is first dispersed by ultrasonic waves, and is atomized by ultrasonic waves into atomized particles and deposited on the carbon-coated copper mesh of the TEM sample stage, and then observed by TEM. As a result, it was revealed that the platinum nanoparticles were able to be bonded to the carbon nanotubes after being subjected to ultrasonic vibration dispersion and atomization treatment, and showed excellent adhesion to the carbon nanotube wall. The carbon nanotube composite combined with the metal nanoparticle formed by the invention method can withstand the processing procedures of ultrasonic dispersion and atomization applied during the film formation, and can be smoothly formed into the nano carbon. Tube composite conductive film products.

<Specific Example 2 - Preparation of a carbon nanotube composite in which platinum and silver nanoparticles are combined>

150.1 mg of purified and heat-treated carbon nanotubes were ultrasonically dispersed in 100 ml of anhydrous ethylene glycol solution under nitrogen atmosphere, and K ₂ PtCl ₄ (which was sufficiently dissolved in 100 ml of anhydrous ethylene glycol) 7.2mg, no crystal water), use a double-headed needle to transfer it into the anhydrous ethylene glycol dispersion containing carbon nanotubes under nitrogen atmosphere, stir well, and then slowly heat up at 2 °C per minute. To 160 ° C, and constant temperature for 2 hours. After the solution was cooled to room temperature, an anhydrous glycol solution in which AgNO ₃ (54.1 mg) was sufficiently dissolved was added under a nitrogen atmosphere, and after sufficiently stirring, the temperature was slowly raised to 160 ° C by 2 ° C per minute. The reaction was terminated after 2 hours of constant temperature. The formed carbon nanotube composite was collected by hot filtration and washed with absolute ethanol for several times, and then vacuum dried at 80 ° C for 12 hours to obtain a carbon nanotube composite loaded with 20 wt% of platinum/silver nanoparticles. C, wherein the weight ratio of platinum to silver is 1:10.

As shown in Fig. 6, the morphology of the carbon nanotube composite C loaded with 20 wt% of platinum/silver nanoparticle observed under a transmission electron microscope (TEM) can be clearly observed from the figure. The dense metal nanoparticles attached to the tube wall of the carbon nanotube show that the effect of adhering to the wall of the carbon nanotube can still be achieved by using two different metal nanoparticles.

In addition, when the carbon nanotube composite C was measured by an energy dispersive spectrometer (EDS), the weight ratio of platinum to silver was 8.85:91.15, and the original addition amount was 1:10. Very close, showing that the metal complex ratio can be precisely controlled by the two-stage reduction synthesis described above.

Thermogravimetric analysis of carbon nanotube composites A, B, C, purified carbon nanotubes (Pure CNT) and raw unpurified carbon nanotubes (Raw CNT), respectively, at 10 ° C / min The heating rate was raised to 900 ° C under air conditions. The results are shown in Fig. 7. The residual amounts of the carbon nanotube composites A and B were 21.9% and 42.2%, respectively, and the final residual metal ratio and the original metal used. The proportion of the compound in the carbon nanotube composite is very close, showing that the platinum nanoparticle and the carbon nanotube wall have excellent interaction, so that a high load ratio can be obtained, and the measured residual amount More than 20% by weight and 40% by weight of the originally added platinum ion should be partially residual graphite combined with platinum metal, which is difficult to oxidize and volatilize in an air environment of 900 ° C. In addition, the carbon nanotube complex C combined with platinum and silver nanoparticles prepared by two-stage reduction may have a lower initial residual concentration, resulting in a ratio of the final residual metal slightly lower than the proportion of the originally added metal. However, the residual metal ratio is still quite close to the proportion of the original metal compound in the carbon nanotube composite, showing the carbon nanotube complex C combined with platinum and silver nanoparticles prepared by two-stage reduction. High metal nanoparticle loading ratios can also be obtained.

<Specific Example 3 - Metal Nanoparticle Adhesion Test>

The carbon nanotube composites loaded with 10 wt%, 20 wt%, and 40 wt% of platinum nanoparticles were separately prepared by the method of <Specific Example 1> , and the weight ratio of platinum to silver was 1 by the method of <Specific Example 2> . : 5, 1:10 and 1:20, each preparation of carbon nanotube composites loaded with 10wt%, 20wt%, 40wt% platinum/silver nanoparticles, the above-mentioned carbon nanotube composites respectively in a high temperature furnace Ashing at 750 ° C and measuring the weight of the residual metal (corresponding to the total weight of the metal nanoparticles attached to the carbon nanotubes), and dividing the weight by the weight of the metal ions in the initially added metal salt compound, The result was the total adhesion rate of the metal nanoparticles, and the experimental results were summarized in Table 1 below.

According to the results of Table 1, in the case of considering high adhesion rate and raw material cost (reducing the amount of platinum), a carbon nanotube composite showing 20 wt% of platinum/silver nanoparticle was observed, when Pt:Ag = 1:10. The best metal nanoparticle adhesion rate can be obtained with a relatively small amount of platinum.

<Specific Example 4 - Preparation of Nano Carbon Tube Composites Bonded with Metal Nanoparticles Conductive film and test for flexural resistance >

(1) The following four samples were prepared separately: Sample I: purified carbon nanotubes, sample II: carbon nanotube composites prepared with 20 wt% of gold nanoparticles in the manner shown in <Specific Example 1 (where metal The salt compound is HAuCl ₄ in an amount of 65.2 mg), the sample III: 20 wt% platinum/silver nanoparticle nanotube complex (Pt: Ag = 1:10), and the sample IV: from 20 wt% platinum/silver The carbon nanotube mixture obtained by mixing the carbon nanotube composite III (Pt: Ag = 1:10) of the nanoparticle with the pure carbon nanotube containing no metal nanoparticle in a ratio of 1:1 (equivalent a carbon nanotube composite of 10 wt% platinum/silver nanoparticle).

(2) The above four samples I~IV were respectively arranged into a 10 mg/L carbon nanotube complex solution: 10 mg of sample I~IV and 10 mg of SDS were respectively added to 1 L of deionized water, and the power was first 750 W. Probe-type ultrasonic oscillator diffuser (model: Sonics & Materials, Inc. "SONICS The VCX 750") was applied to the carbon nanotube composite solution at 20% power for 5 minutes and at 30% power for 5 minutes to prevent the carbon nanotube composites from aggregating and uniformly dispersed.

(3) Atomization: The ultrasonic atomizer is placed at a depth of 3.0 cm below the liquid surface, and the temperature of the solution is maintained at 30 ° C, and an ultrasonic atomization frequency of 1.65 MHz is provided to act on the carbon nanotube composite. The solution solution can reach an atomization rate of 25 to 30 ml/hr, and the atomized particles have a particle diameter of about 3 μm, and the carrier gas is fed into the gas pipe connected to the container containing the sample I~IV solution, and the carrier is carried. The gas flow rate was 22 L/min.

(4) spin coating: the carrier gas guides the atomized particles onto a susceptor of a spin coater, and the substrate sheet placed on the susceptor is rotated synchronously with the susceptor for spin coating Before, the substrate sheet was washed with deionized water for 40 seconds at a speed of 500 rpm, and then washed with alcohol at a speed of 800 rpm for 60 seconds, and then spin coating of the ultrasonic atomized particles. .

When the spin coating of the ultrasonic atomized particles is performed, the pretreatment is performed by one wet spin coating and one preliminary film spin coating, and the periodic recoating spin coating is repeated a plurality of times. Among them, the rotational speed of the wet spin coating is 300r.pm and 450r.pm alternately, and the rotational speed of the preliminary film spin coating is from 450r.pm to 6000r.pm, and then enters the cycle. Sex re-filming spin coating. During the coating process, the susceptor is continuously rotated in a staged cycle as shown in FIG. 9, and the interval (I) represents the change in the rotational speed of the wet spin coating, and the interval (II) represents the preliminary film forming spin coating. The stepwise speed change, the sections (III), (IV), and (V) are all stepwise rotational speed changes of the re-filming spin coating, thereby enabling the atomized particles to be uniformly applied to the base. The surface of the sheet is controlled, and the film thickness of the carbon nanotube composite conductive film can be controlled by the length of the spin coating. In Figure 9, the different stages are represented by different letters, and the speed and time represented by them are organized as shown in Table 2 below. The time of each stage in Table 2 should not be limited, and can be adjusted according to actual needs.

The spin coating time is controlled from 10 minutes to 60 minutes to control the spin coating time to achieve the design specifications of the multilayered nano-carbon nanotube conductive film, which is mainly by adjusting c~ The time of f is used to adjust the thickness of the conductive film of the carbon nanotube composite.

(5) Hot pressing: the temperature of the upper and lower stampers of a hot press is raised to 70 ° C, and the temperature is maintained for 1 hour, and the temperature fluctuation is controlled below ± 0.25 ° C, and four pieces of 5 cm × 5 cm PET sheets are cut. And rinsing the PET sheets in a cleaning sequence of deionized water, ethanol, deionized water, acetone, deionized water, respectively, and sandwiching the two conductive sheets to form the conductive film (sample I, respectively) a substrate sheet made of ~IV, and then a 10 cm×10 cm stainless steel jig is superposed on the PET sheet, and the combined substrate sheet, PET sheet and stainless steel jig are placed on top of the hot press. Between the stampers, a pressure of 100 kg/cm ² was applied and hot pressed for 30 minutes.

(6) Cleaning: The hot-pressed conductive film substrate sheet is cleaned in the manner described in the foregoing step 106, and the carbon nanotube conductive film I (made of the sample I) can be separately obtained, and the metal naphthalene is combined. The carbon nanotube composite conductive film II~IV of rice particles (made of samples II~IV, respectively).

<Flexibility test>

Referring to Fig. 8, the obtained substrate sheet with conductive films I to IV was cut into a test piece 51 of 1 cm × 2 cm, and the conductivity of the test piece 51 before being bent was measured. Then, the opposite sides of the longer side of the test piece 51 are respectively fixed to a fixed clip 52, and a movable clip 53 spaced apart from the fixed clip 51, and the movable clip 53 is biased toward the opposite side. The fixing clip 51 is displaced to the opposite side of the long side of the test piece 51 by a distance of 1 cm, and further displaced to a distance of 0.5 cm on the opposite side of the long side of the test piece 51, the test piece 51 will follow The movement of the movable clamp 53 is bent and bent, and then the movable clamp 53 is displaced away from the fixed clamp 52, and the test piece 51 is returned to a flat state, and the test piece 51 is measured to be bent. The folded sheet resistance repeats the above-described operation of flexing and bending the test piece 51, and the test piece 51 is again measured once after returning to the flat state, and the sheet resistance can be correspondingly reacted by the change of the sheet resistance. The change in conductivity, the more stable the sheet resistance value, the more stable the conductivity.

Due to the previous several flexings, the sheet resistance of the conductive film is unstable, and it is impossible to make a clear comparison. Therefore, the test pieces of the conductive films I~IV are respectively bent 50 times to make the sheet resistance. After the (conductivity) is stabilized, it is officially entered into the flexural resistance test. Among them, the sheet resistance values after stabilization for 50 times are conductive film I (CNT/PET) ≒ 3K Ω / □, conductive film II (20% Au-CNT / PET) ≒ 157 Ω / □, conductive film III (20%) Ag/Pt-CNT/PET) ≒175Ω/□, and conductive film IV (10% Ag/Pt-CNT/PET) ≒229Ω/□, and the film measured by bending 100 times, 250 times and 500 times The resistance is compared with the sheet resistance of bending 50 times, and the results are shown in Table 3 below:

The test results show that the sheet resistance of the CNT/PET test piece is increased by 10% after 100 times of bending, the sheet resistance of the sheet after the bending of 250 times is increased by 20%, and the sheet resistance after the bending of 500 times is increased by 20%, and the metal nanometer is combined. The test piece of the conductive film II~IV made of the carbon nanotube composite of the particle not only has a sheet resistance lower than that of the CNT/PET test piece after being bent 50 times, and it passes 100 times, 250 times, After 500 bends, the rate of change of sheet resistance is also reduced to 3% or less, or even almost no change. It is shown that the carbon nanotubes are doped with highly conductive metal nanoparticles and made into a conductive film, which has better resistance to bending. Flexibility, according to this, it can be explained that the conductive film of the carbon nanotube composite combined with the metal nanoparticle can also improve the electrical conductivity by reducing the contact resistance between the carbon nanotubes by the metal nanoparticles, and also contributes to Improve the stability of the conductive film structure.

The sheet resistance value of the conductive film generally applicable is in the range of 10 to 800 Ω/cm ² , and the sheet resistance of the conductive film used in the general touch panel is 200 to 800 Ω/cm ² , and the present invention is explained by the above results. The sheet resistance of the produced conductive film has met the application specifications and has practical application value.

In summary, the present invention combines the production method of a carbon nanotube composite conductive film of metal nanoparticles to obtain the following effects and advantages, thereby achieving the object of the present invention:

1. Since there is only a small contact area between the carbon nanotubes and the carbon nanotubes, the contact resistance between the carbon tubes is much higher than other possible resistances of the carbon nanotube film and becomes the main source of resistance by making a predetermined amount. The metal nanoparticle adheres to the carbon nanotube, and forms a conductive film formed by forming a contact point on the tube wall to form an effective high-conductivity channel and having a rough surface and adhering the carbon nanotube composite of the metal nanoparticle. The contact resistance is easily reduced by the change of external force, so that the carbon nanotube composite conductive film prepared by the method of the invention can effectively improve the electrical conductivity and has the value of commercial application.

2. By preparing a carbon nanotube composite solution combined with metal nanoparticles, and providing a specific ultrasonic frequency, the nanocarbon tube composite solution is formed into atomized particles, and coated by a carrier gas. On the rotating substrate sheet, a conductive film having a uniform thickness can be obtained, which shows that the present invention can produce a low-resistance and better conductive carbon nanotube composite conductive film in a readily available device and a relatively simple process. The simplified process can meet the advantages of practical and economic benefits.

3. The results of the flexural resistance test show that the conductive film prepared by the manufacturing method of the present invention has a plurality of flexural properties, and the electrical conductivity thereof still meets the required application specifications, so that the manufacturing method of the present invention can be produced. A conductive film that is flexible and structurally more stable.

4. The thickness of the finally obtained conductive film can be controlled by the length of the spin coating to correspondingly produce conductive films with different transmittances and different resistance specifications, so that the manufacturing method of the present invention can be adjusted in a relatively simple control manner. The quality of the products is used in conjunction with different grades of application products.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

30. . . Nano carbon tube composite solution

31. . . Atomized particle

32. . . Carrying gas

33. . . Atomizing container

34. . . siphon

35. . . Ultrasonic component

36. . . Substrate sheet

37. . . Pedestal

38. . . Liquid container

39. . . Lifting seat

51. . . Conductive film test piece

52. . . Fixed clamp

53. . . Activity holder

1 is a flow chart showing a preferred embodiment of a method for producing a conductive film of a carbon nanotube composite incorporating a metal nanoparticle according to the present invention;

Figure 2 is a schematic view showing the combination of the devices used in the preferred embodiment;

Figure 3 is a transmission electron microscope photograph showing the case where a plurality of metal (platinum) nanoparticles are bonded to a carbon nanotube;

Figure 4 is a transmission electron microscope photograph showing the case where a plurality of metal (platinum) nanoparticles are bonded to a carbon nanotube;

Figure 5 is a transmission electron microscope photograph showing the case where a plurality of metal (platinum) nanoparticles are bonded to a carbon nanotube;

Figure 6 is a photomicrograph of a transmission electron microscope illustrating the case where a plurality of metal (platinum/silver) nanoparticles are bonded to a carbon nanotube;

Figure 7 is a graph showing the results of thermogravimetric analysis of carbon nanotube composite samples A, B, and C;

Figure 8 is a schematic view showing the process of conducting a flexural test on a conductive film test piece produced by the method of the present invention; and

Fig. 9 is a schematic view showing the change of the rotational speed set at different times when the preferred embodiment performs spin coating.

Claims (19)

The invention relates to a method for preparing a conductive film of a carbon nanotube composite combined with metal nano particles, comprising the following steps: (i) separately dissolving a metal salt compound in an anhydrous ethylene glycol to prepare a first solution, and The rice carbon tube is dissolved in an anhydrous ethylene glycol to prepare a dispersion liquid, and then the two are mixed and stirred, and then heated to a temperature of 100 ° C to 160 ° C at a temperature increase rate of 2 ° C to 5 ° C per minute and maintained at a constant temperature of 1 to 3 Hours to form a plurality of carbon nanotube composites bonded with metal nanoparticles, the metal salt compound being a substance selected from the group consisting of potassium tetrachloroplatinate, silver nitrate and tetrachloroauric acid; The carbon nanotube composite is added to a solvent to prepare a carbon nanotube composite solution having a viscosity of 1 to 50 c.p, which is a liquid selected from the group consisting of water, ethanol, Isopropanol and acetone; (iii) applying a supersonic atomization frequency to the carbon nanotube composite solution to release the nanocarbon tube composite solution to release a plurality of ruthenium carbon nanotube complexes Atomizing the particles and providing a carrier gas to transport the atomized particles along a predetermined path Wherein the particle size of these particles is between atomized 0.5μm ~ 50μm, and the frequency of the applied ultrasonic atomization by the formula Calculated, where D is the particle size of the atomized particles, T is the surface tension coefficient (N/cm), ρ is the solution density (g/cm ³ ), f is the ultrasonic atomization frequency (Hz), and α is 0.34 And (iv) directing the atomized particles onto a susceptor on which a substrate sheet is placed, and by rotating the susceptor, the atomized particles are uniformly formed on the surface of the substrate sheet. Nano carbon tube composite conductive film. The method for preparing a carbon nanotube composite conductive film combined with a metal nanoparticle according to claim 1, wherein in the step (i), the metal nanoparticles are in the carbon nanotubes The content in the composite is from 10% by weight to 40% by weight. The method for preparing a carbon nanotube composite conductive film incorporating metal nanoparticle according to claim 2, wherein in the step (i), the metal on the carbon nanotube composite The nanoparticles are made of a metal selected from the group consisting of platinum, silver, gold, and the like. The method for producing a conductive film of a carbon nanotube composite bonded with a metal nanoparticle according to claim 3, wherein in the step (i), forming the nanoparticle combined with the metal nanoparticle After the carbon tube composite, it is filtered first, and washed and dried by an anhydrous organic solvent to obtain the carbon nanotube composites. The method for producing a conductive film of a carbon nanotube composite bonded with a metal nanoparticle according to claim 2, wherein in the step (i), the first solution and the dispersion are mixed to form a The first mixed liquid is heated to 100 ° C ~ 160 ° C at a temperature increase rate of 2 ° C ~ 5 ° C per minute and maintained at a constant temperature for 1-3 hours, first cooled to room temperature, and then added to the first mixed liquid The second solution is formed by forming a second mixed solution prepared by dissolving another metal salt compound in an anhydrous organic solvent, and the second mixed solution is stirred by 2 ° C ~ 5 per minute after stirring. The heating rate of °C is raised to 100 °C ~ 160 °C and maintained at a constant temperature for 1-3 hours. Forming a carbon nanotube composite incorporating two kinds of metal nanoparticles. The method for preparing a carbon nanotube composite conductive film incorporating metal nanoparticle according to claim 5, wherein in step (i), the metal nanoparticle on the carbon nanotube composite The particles include platinum nanoparticles and silver nanoparticles, and the weight ratio of the platinum nanoparticles to the silver nanoparticles is 1:5 to 1:20. The method for producing a conductive film of a carbon nanotube composite bonded with a metal nanoparticle according to claim 6, wherein in the step (i), the metal nanoparticles are in the carbon nanotubes The content in the composite is substantially 20% by weight, and the weight ratio of the platinum nanoparticle to the silver nanoparticle is substantially 1:10. The method for producing a conductive film of a carbon nanotube composite bonded with a metal nanoparticle according to claim 6, wherein in the step (i), the metal salt compound of the first solution is substantially tetrachloride Potassium platinumate, the metal salt compound in the second solution is substantially silver nitrate, and the metal nanoparticles on the carbon nanotube composites comprise platinum nanoparticles directly bonded to the carbon nanotubes, and the combination Silver nanoparticles on platinum nanoparticles. The method for producing a conductive film of a carbon nanotube composite bonded with a metal nanoparticle according to claim 5, wherein in the step (ii), a predetermined ratio of the pure nanoparticle of the unbonded metal nanoparticle is used. The carbon nanotubes are mixed with the carbon nanotube composite combined with the metal nanoparticles to be added into the solvent to prepare a carbon nanotube composite solution, and in the step (iii), the atomized particles are simultaneously carried The carbon nanotube composites and the pure nano Carbon tube. The method for producing a conductive film of a carbon nanotube composite bonded with a metal nanoparticle according to claim 9 of the invention, wherein in the step (ii), in the carbon nanotube composite solution or the solvent An surfactant component is added and the surfactant component is used to prevent aggregation of the carbon nanotube complexes. The method for preparing a carbon nanotube composite conductive film combined with a metal nanoparticle according to claim 10, wherein the surfactant component is a substance selected from the group consisting of: sulfuric acid of alcohol An ester salt, an alkyl sulfonate, an alpha olefin sulfonate, a fourth ammonium salt, an ethylene oxide system, a polyoxyethylene alkyl ether, and combinations thereof. The method for preparing a carbon nanotube composite conductive film combined with a metal nanoparticle according to claim 11, wherein the surfactant component is a substance selected from the group consisting of C ₄ ~C ₁₈ linear sodium alkyl sulfonate, C ₄ ~ C ₁₈ linear alkyl sulfonate, C ₄ ~ C ₁₈ linear sodium alkyl sulfate, C ₄ ~ C ₁₈ linear alkyl sulfate Potassium, C ₄ ~ C ₁₈ linear sodium alkylbenzene sulfonate, C ₄ ~ C ₁₈ linear alkyl benzene sulfonate, C ₄ ~ C ₁₈ linear sodium alkyl benzene sulfate, C ₄ ~ C _a linear linear alkyl benzene sulphate of ₁₈ , a C ₂ -C ₁₆ linear alkyl quaternary ammonium salt, an α-olefin sulfonate, an alkyl group of a C ₂ -C ₁₆ polyoxyethylene alkyl ether, and A combination of the same. The method for producing a carbon nanotube composite conductive film incorporating metal nanoparticle according to claim 12, wherein the surfactant component is selected from sodium dodecyl sulfate. The method for preparing a carbon nanotube composite conductive film combined with a metal nanoparticle according to claim 11 further comprises a step (v) after the step (iv), wherein the step (v) is cleaning, Used to remove the surfactant remaining in the conductive film. The method for producing a conductive film of a carbon nanotube composite bonded with a metal nanoparticle according to claim 11, wherein in the step (ii), the carbon nanotube composite solution has 1 part by weight. The surfactant component, 1 part by weight of the carbon nanotube composite, and 1000 to 1,000,000 parts by weight of the solvent. The method for producing a carbon nanotube composite conductive film incorporating metal nanoparticle according to claim 15, wherein in the step (iii), the atomized particles have a particle diameter of 2 μm to 7 μm. The method for preparing a carbon nanotube composite conductive film combined with a metal nanoparticle according to claim 16, wherein in the step (iii), the carrier gas has a flow rate of 1 L/min to 200 L. /min. The method for preparing a carbon nanotube composite conductive film combined with a metal nanoparticle according to claim 14 , further comprising a step (a) between the step (iv) and the step (v) And the step (a) is hot pressing, applying a predetermined pressure to the substrate sheet provided with the conductive film at a predetermined temperature for compacting the conductive film. The method for preparing a carbon nanotube composite conductive film combined with a metal nanoparticle according to claim 18, wherein in the step (a), applying 1 to 200 at a temperature of 50 ° C to 110 ° C The pressure of kg/cm ² is hot pressed for 30 seconds to 30 minutes.