A coating material for fabric having low infrared emissivity and a method for preparing the same

Abstract

The application discloses a coating with low infrared emissivity for fabric and a preparation method thereof. First, a preparation method of ITO-Ag composite microspheres with special-shaped surfaces is provided, which comprises the following steps: 1) modifying a low-emissivity filler powder with a specific particle size by using a silane coupling agent to obtain ITO surface modified powder; and 2) adding a solution containing an Ag source to carry out in-situ growth reaction. Based on the above-mentioned microspheres, the coating with low infrared emissivity for fabric is provided, which is composed of the following substances: water-based polyurethane emulsion, dispersing agent, ITO-Ag composite microspheres with special-shaped surfaces and pigments, wherein the water-based polyurethane emulsion accounts for 100% in mass, the dispersing agent accounts for 0.5-1%, the ITO-Ag composite microspheres with special-shaped surfaces account for 10-15%, and the pigments account for 5-10%. In the application, the silver particles are grown on the ITO in-situ, the glossiness of the infrared camouflage clothes is reduced under the condition of ensuring the camouflage performance of low emissivity, and the monodisperse particles obtained in-situ can also improve the agglomeration problem of the ITO-silver system.

Description

Technical Field

[0001] This invention belongs to the field of coatings, specifically relating to a coating for fabrics with low infrared emissivity and its preparation method. Background Technology

[0002] With the rapid development of science and technology, the research and application of optical and infrared detection technologies in the military field have become increasingly in-depth and sophisticated, giving rise to a wealth of research on optical and thermal infrared camouflage materials and technologies. Among these, camouflage coatings, due to their ease of use, low cost, convenient operation, and lack of limitation on the geometry of parts, have demonstrated greater advantages and have become the fastest-growing area of ​​camouflage technology research in recent years.

[0003] Camouflage coatings, as the most convenient, economical, and highly adaptable stealth technology, have been widely used in aerospace and military equipment. Applying optical camouflage coatings with different emissivity to the surface of weapons and equipment can reduce the probability of detection by optical and infrared reconnaissance equipment, thus achieving the purpose of camouflage. Currently, most camouflage coatings sold on the market are single-function optical camouflage coatings, with few products compatible with thermal infrared performance. Furthermore, the colors are limited, and the variety of colors is insufficient, making it difficult to meet the actual needs of weapons and equipment and restricting the development of thermal infrared camouflage coatings.

[0004] Traditional infrared camouflage coatings use low-emissivity Al powder as filler and polyurethane systems as binders. For example, patent CN108913018 B, "A Method for Preparing a High-Temperature Resistant Infrared Low-Emissivity Coating," uses Al powder, Ni powder, and polyacrylic resin, with filler prepared by ball milling aluminum powder. The final emissivity is as low as approximately 0.39. Another patent, CN103306131 B, describes an infrared low-emissivity tan stealth coating and its preparation method, using ITO and Ag as fillers. Ag is used to modify ITO, resulting in an infrared coating with an emissivity of 0.34. Other similar patents often change the type of filler metal or semiconductor to achieve a low emissivity of at least 0.3. However, because their particle size is relatively uniform, the surface tends to form a long-range ordered and short-range ordered photonic crystal structure during use, resulting in a glossy finish. This gloss affects camouflage performance regardless of whether the total internal reflection falls in the visible or infrared band. CN 113736327 A describes an optical and thermal infrared camouflage coating and its preparation method, using ball milling to prepare Al powder with a relatively dispersed particle size, improving the gloss effect. However, uniformly distributed particles are difficult to prepare, and the coating is prone to agglomeration during use. Using Ag to modify ITO also presents the problem of agglomeration, where the two fillers are very difficult to reconcile in the binder. Therefore, developing a coating that can solve the problem of coating gloss and has good infrared camouflage performance is of great practical significance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the inventors of this invention, based on the fact that Ag-modified ITO can achieve lower emissivity and that microspheres with non-uniform particle size can solve the problem of coating gloss, provide a method for preparing irregularly shaped ITO-Ag composite microspheres. This invention employs an in-situ growth method, activating ITO powder with a silane coupling agent, and then using AgNO3 for in-situ growth on the surface. During the growth process, the uniformity of particle size is effectively reduced, significantly minimizing the occurrence of gloss phenomena in the subsequent coating. Simultaneously, the Ag-modified ITO microparticles have low infrared emissivity, exhibiting excellent infrared camouflage properties and coating performance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing ITO-Ag composite microspheres with irregular surfaces.

[0008] The method for preparing ITO-Ag composite microspheres with irregular surfaces provided by the present invention includes the following steps:

[0009] 1) Low emissivity filler powder with a particle size of 50nm-100nm was modified by using a silane coupling agent to obtain ITO surface-modified powder.

[0010] 2) Add an Ag-containing solution to the ITO surface-modified powder to carry out an in-situ growth reaction to obtain the irregular ITO-Ag composite microspheres.

[0011] In step 1) of the above method, the silane coupling agent includes, but is not limited to, a series of silane coupling agents such as KH550, KH560, and KH570.

[0012] In step 1) of the above method, the low emissivity filler powder is a series of two-component low emissivity semiconductor materials, including but not limited to ITO, ATO, etc.

[0013] In step 1) of the above method, the specific method of the modification treatment is as follows: the silane coupling agent is added to the low emissivity filler powder of 50nm-100nm, and then a 95% ethanol aqueous solution is added to react.

[0014] The reaction conditions are: 20-25℃, reaction time 4 hours;

[0015] The mass ratio of the silane coupling agent to the low emissivity filler powder is 1:(2.8-3.75).

[0016] The volume ratio of the silane coupling agent to the 95% ethanol aqueous solution is 1:9.

[0017] In step 2) of the above method, the Ag source includes Ag NO3 and other Ag sources that can grow Ag particles on semiconductor materials by in-situ growth.

[0018] In step 2) of the above method, the mass ratio of the Ag source to the ITO surface-modified powder is 1:6.

[0019] In step 2) of the above method, NaBH4 is also added to the in-situ growth reaction, and the mass ratio of Ag source to NaBH4 is 3:1; the reaction conditions for the in-situ growth reaction are: room temperature (15-25℃) for 0.5-1h.

[0020] The irregular ITO-Ag composite microspheres prepared by the above method also fall within the scope of protection of this invention.

[0021] This invention employs in-situ growth of Ag particles from ITO to obtain composite microspheres with an irregular surface. This irregular surface makes it difficult for subsequent coatings to form a glossy finish, thus providing excellent infrared camouflage. Furthermore, compared to methods that modify ITO powder with Ag powder, the irregular ITO-Ag composite microspheres prepared by this invention are less prone to agglomeration, easier to mix, and have stronger affinity for coatings.

[0022] Secondly, the present invention provides a coating for fabrics having low infrared emissivity.

[0023] The coating for fabrics with low infrared emissivity provided by the present invention is composed of the following substances: 100% by mass of an aqueous polyurethane emulsion, 0.5-1% of a dispersant, 10-15% of the irregular ITO-Ag composite microspheres provided by the present invention, and 5-10% of a pigment.

[0024] According to one embodiment of the present invention, the fabric is coated with a coating having low infrared emissivity, which consists of the following substances: 100% by mass of an aqueous polyurethane emulsion, 1% of a dispersant, 15% of the irregularly shaped ITO-Ag composite microspheres provided by the present invention, and 8% of a pigment.

[0025] According to another embodiment of the present invention, the fabric is coated with a coating having low infrared emissivity, which consists of the following substances: 100% by mass of an aqueous polyurethane emulsion, 1% of a dispersant, 10% of the irregularly shaped ITO-Ag composite microspheres provided by the present invention, and 8% of a pigment.

[0026] Furthermore, the solid content of the aqueous polyurethane emulsion can be 20-45%, specifically 30%.

[0027] The aqueous polyurethane emulsion used in this invention can be prepared according to methods disclosed in the prior art, such as the following method: PEG is weighed into a three-necked flask, heated and stirred, then diisocyanate and a catalyst are added for reaction, followed by the addition of a hydrophilic chain extender for chain extension, and the reaction continues. During this process, a viscosity reducer is added to lower the viscosity of the reaction system. The entire reaction is carried out under a nitrogen atmosphere. After the reaction is completed, the temperature is lowered to 40°C, a neutralizing agent is added for neutralization while stirring is maintained, and finally, the mixture is cooled to room temperature. Deionized water is added for high-speed emulsification, and excess solvent is removed by rotary evaporation to obtain an aqueous polyurethane emulsion (WPU) with a solid content of approximately 30%.

[0028] In the above method for preparing aqueous polyurethane emulsion, the molecular weight of PEG can be 2000-5000.

[0029] The diisocyanates include, but are not limited to, isoflurone diisocyanate, toluene diisocyanate, etc.

[0030] The catalysts include, but are not limited to, dibutyltin dilaurate (DBDTL).

[0031] The hydrophilic chain extenders include, but are not limited to, 2,2-dihydroxymethylbutyric acid (DMBA), diethylene glycol, etc.

[0032] The viscosity reducers include, but are not limited to, butanone, ethylene glycol, etc.

[0033] The neutralizing agents include, but are not limited to, triethylamine (TEA), melamine, etc.

[0034] Furthermore, the dispersant includes, but is not limited to, polyvinyl alcohol PVA2000, polyvinyl alcohol PVA4000, polyvinyl alcohol PVA1500, polyacrylic acid 2000, etc.

[0035] Furthermore, the pigment can be selected from common inorganic pigments on the market, such as any one of the camouflage pigments, specifically green pigment.

[0036] The present invention also provides a method for preparing the coating with low infrared emissivity for the above-mentioned fabric, comprising the following steps: adding a dispersant to an aqueous polyurethane solution, weighing and adding irregularly shaped ITO-Ag composite microspheres, adding pigment, and stirring until there are no obvious particles, thereby obtaining the coating.

[0037] Thirdly, the present invention provides an infrared low emissivity coated fabric.

[0038] The low infrared emissivity coating provided by the present invention is prepared by the following method: the coating with low infrared emissivity is applied to the white fabric by a scraping method, and then the fabric sample is dried to obtain the coating.

[0039] In the above method, the thickness of the coating formed by the coating material with low infrared emissivity is 150-350 μm, specifically 150 μm, 200 μm, or 250 μm.

[0040] In the above method, the drying temperature is 120-160℃ and the drying time is 6-7 hours.

[0041] The infrared low emissivity coated fabric provided by this invention has a view-view-independent infrared reflection peak and good applicability to clothing fabrics.

[0042] While basic coating research primarily focuses on brushing onto boards and walls, and coating properties such as adhesion and emissivity are well-established, significant issues arise when applied to individual combat clothing. This limitation hinders the development of infrared camouflage for individual combat uniforms. Existing technologies mainly involve developing new materials (such as organic infrared absorbing materials and composite infrared camouflage inserts), but their invention maturity and industrialization levels still have a long way to go, preventing immediate mass production. This invention utilizes an existing low-emissivity semiconductor filler system, employing in-situ growth of silver particles on ITO. This reduces the gloss of the infrared camouflage clothing while maintaining low emissivity camouflage performance. Simultaneously, the monodisperse particles obtained through in-situ growth also mitigate the aggregation problem of the ITO-silver system, providing a method for individual soldier infrared camouflage that is closest to industrialization.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1) This invention is simple to operate, requires no equipment modification, and reduces costs;

[0045] 2) The ITO in-situ growth of Ag particles used in this invention results in an irregular surface that makes it difficult for the subsequent coating to form a glossy surface.

[0046] 3) This invention uses in-situ growth of Ag particles from ITO, which, compared to the method of modifying ITO powder with Ag powder, is less prone to agglomeration, easier to mix, and has stronger affinity for coatings.

[0047] 4) This invention employs in-situ growth of Ag particles from ITO. The Ag particles on the surface of the ITO modify the final coating emissivity to less than 0.3. Therefore, the preparation method provided by this invention has high practical value and economic benefits. Attached Figure Description

[0048] Figure 1 This is a scanning electron microscope image of the ITO-Ag composite powder prepared in Example 1;

[0049] Figure 2 This is a scanning electron microscope image of the ITO-Ag composite powder prepared in Example 2;

[0050] Figure 3The image shows a scanning electron microscope (SEM) image of the ITO-Ag composite powder prepared in Example 3. Detailed Implementation

[0051] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0052] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0053] Example 1

[0054] 10 ml of silane coupling agent KH550 was added to 30 g of ITO powder with a particle size of 100 nm, followed by 90 mL of 95% (v / v) ethanol aqueous solution. The mixture was reacted at 25 °C for 4 h, and then filtered to obtain 30 g of ITO surface-modified powder. 100 ml of 5% (w%) AgNO3 solution and 1.66 g of NaBH4 were added to the above system for in-situ growth (reaction temperature 25 °C; reaction time 1 h) to obtain ITO-Ag composite powder. The structural characterization diagram is shown below. Figure 1 As shown. By Figure 1 It can be seen that the Ag particles have grown onto the ITO powder.

[0055] Weigh 200 ml of PEG-400 into a three-necked flask, heat to 68 °C and stir at 240 rpm. Then add 40 ml of isoflurane diisocyanate (IPDI) and two drops of dibutyltin dilaurate (DBDTL) catalyst. React for 3 h, then add 2 ml of hydrophilic chain extender 2,2-dimethylolbutyric acid (DMBA) for chain extension and continue the reaction for 2 h. During this period, add 10 ml of butanone to reduce the viscosity of the reaction system. The entire reaction is carried out under a nitrogen atmosphere. After the reaction is complete, cool to 40 °C, add stoichiometric amounts of triethylamine (TEA) (molar amount equal to the carboxyl group content in the DMBA structure) for neutralization and keep stirring for 0.5 h. Finally, cool to room temperature, add 100 ml of deionized water and emulsify at high speed for 1 h. Remove excess solvent by rotary evaporation to obtain a waterborne polyurethane emulsion (WPU) with a solid content of approximately 30%.

[0056] To a waterborne polyurethane solution with a solid content of approximately 30% (100% by mass), 1% by mass of polyvinyl alcohol (PVA2000) dispersant was added. Then, 15% by mass of low-emissivity filler (ITO-Ag composite powder) of waterborne polyurethane was added, followed by 8% by mass of green pigment. The mixture was stirred until no obvious particles remained, yielding a low-emissivity coating suitable for fabrics. A doctor blade coating method was used, adjusting the blade parameters to control the coating thickness to 200 μm. The low-emissivity coating was applied to a white greige fabric, and the fabric sample was dried in an oven at 140°C for 6 hours to obtain a green infrared low-emissivity coated fabric. The emissivity of this coating was measured to be 0.26 using an IR-2 dual-band emissivity meter.

[0057] Example 2

[0058] 10 ml of silane coupling agent KH650 was added to 30 g of ATO powder with a particle size of 80 nm, followed by 90 mL of 95% (v / v) ethanol solution. The mixture was reacted at 25 °C for 4 h, and then filtered to obtain 30 g of ATO surface-modified powder. 100 ml of 5% (w%) AgNO3 solution and 1.66 g of NaBH4 were added to the above system for in-situ growth (reaction temperature 25 °C; reaction time 1 h) to obtain ATO-Ag composite powder. The structural characterization diagram is shown below. Figure 2 As shown. By Figure 2 It can be seen that the Ag particles have grown onto the ATO powder.

[0059] Weigh 200 ml of PEG-500 into a three-necked flask, heat to 68 °C and stir at 240 rpm. Then add 40 ml of toluene diisocyanate and two drops of dibutyltin dilaurate (DBDTL) catalyst, and react for 3 h. Then add 2 ml of hydrophilic chain extender 2,2-dimethylolbutyric acid (DMBA) for chain extension and continue the reaction for 2 h. During this period, add 10 ml of butanone to reduce the viscosity of the reaction system. The entire reaction is carried out under a nitrogen atmosphere. After the reaction is completed, cool to 40 °C, add stoichiometric amounts of triethylamine (TEA) (molar amount equal to the carboxyl group content in the DMBA structure) for neutralization and keep stirring for 0.5 h. Finally, cool to room temperature, add 100 ml of deionized water and emulsify at high speed for 1 h. Remove excess solvent by rotary evaporation to obtain a waterborne polyurethane emulsion (WPU) with a solid content of approximately 30%.

[0060] To a waterborne polyurethane solution with a solid content of approximately 30% (100% by mass), 1% by mass of polyvinyl alcohol (PVA4000) dispersant was added. Then, 10% by mass of low-emissivity filler (ATO-Ag composite powder) of waterborne polyurethane was added, followed by 8% by mass of green pigment. The mixture was stirred until no obvious particles remained, yielding a low-emissivity coating suitable for fabrics. A doctor blade coating method was used, adjusting the blade parameters to control the coating thickness to 250 μm. The low-emissivity coating was applied to a white greige fabric, and the fabric sample was dried in an oven at 160°C for 6 hours to obtain a green infrared low-emissivity coated fabric. The emissivity of this coating was measured to be 0.28 using an IR-2 dual-band emissivity meter.

[0061] This invention utilizes in-situ growth of Ag particles from ATO, which, compared to methods of modifying ATO powder with Ag powder, reduces agglomeration, facilitates mixing, and enhances coating affinity. The low-emissivity coating prepared in this embodiment, suitable for fabrics, exhibits a hydrodynamic particle size (D50) reduction from 4 μm to 1.5 μm.

[0062] Example 3

[0063] 10 ml of silane coupling agent KH570 was added to 30 g of ITO powder with a particle size of 50 nm, followed by 90 mL of 95% (v / v) ethanol solution. The mixture was reacted at 25 °C for 4 h, and then filtered to obtain 30 g of ITO surface-modified powder. 100 ml of 5% (w%) AgNO3 solution was added to the above system to carry out an in-situ growth reaction (reaction temperature 25 °C; reaction time 0.5 h) to obtain ITO-Ag composite powder. The structural characterization diagram is shown below. Figure 3 As shown. By Figure 3 It can be seen that the Ag particles have grown onto the ITO powder.

[0064] Weigh 200 ml of PEG-1000 into a three-necked flask, heat to 68 °C and stir at 280 rpm. Then add 40 ml of isoflurane diisocyanate (IPDI) and two drops of dibutyltin dilaurate (DBDTL) catalyst. React for 3 h, then add 2 ml of hydrophilic chain extender 2,2-dimethylolbutyric acid (DMBA) for chain extension and continue the reaction for 2 h. During this period, add 10 ml of butanone to reduce the viscosity of the reaction system. The entire reaction is carried out under a nitrogen atmosphere. After the reaction is complete, cool to 40 °C, add stoichiometric amounts of triethylamine (TEA) (molar amount equal to the carboxyl group content in the DMBA structure) for neutralization and keep stirring for 0.5 h. Finally, cool to room temperature, add 100 ml of deionized water and emulsify at high speed for 1 h. Remove excess solvent by rotary evaporation to obtain a waterborne polyurethane emulsion (WPU) with a solid content of approximately 30%.

[0065] A 1% (by mass) dispersant, polyvinyl alcohol (PVA1500), was added to an aqueous polyurethane solution with a solid content of approximately 30% (100% by mass). Then, 15% (by mass) of a low-emissivity filler (ITO-Ag composite powder) was added, followed by 8% (by mass) of a green pigment. The mixture was stirred until no obvious particles remained, yielding a low-emissivity coating suitable for fabrics. A doctor blade coating method was used, adjusting the blade parameters to control the coating thickness to 150 μm. The low-emissivity coating was applied to a white greige fabric, and the fabric sample was dried in an oven at 120°C for 7 hours to obtain a green infrared low-emissivity coated fabric. The emissivity of this coating was measured to be 0.29 using an IR-2 dual-band emissivity meter.

Claims

1. A method for preparing ITO-Ag composite microspheres with special-shaped surfaces, comprising the following steps: 1) modifying 50-100 nm particle size low-emissivity filler powder by using a silane coupling agent to obtain ITO surface modified powder; the low-emissivity filler powder is ITO; 2) adding AgNO3 solution to the ITO surface modified powder, then adding NaBH4 to perform in-situ growth reaction, thereby obtaining the ITO-Ag composite microspheres with special-shaped surfaces.

2. The method of claim 1, wherein: In the step 1), the silane coupling agent is at least one of KH550, KH650 and KH570.

3. The production method according to claim 1 or 2, characterized by: In the step 1), the modification process is as follows: the silane coupling agent is added to the low-emissivity filler powder with a particle size of 50-100 nm, then a 95% volume fraction ethanol aqueous solution is added to perform reaction. The reaction conditions are: 20-25℃, reaction for 4 hours. The mass ratio of the silane coupling agent to the low-emissivity filler powder is 1:(2.8-3.75). The volume ratio of the silane coupling agent to the 95% concentration ethanol aqueous solution is 1:

9.

4. The production method according to claim 1 or 2, characterized by: In the step 2), the mass ratio of AgNO3 to the ITO surface modified powder is 1:

6. The mass ratio of AgNO3 to NaBH4 is 3:

1. The reaction conditions of the in-situ growth reaction are: normal temperature reaction for 0.5-1 h.

6. A coating material for fabrics having a low infrared emissivity, characterized by:

5. The ITO-Ag composite microspheres with special-shaped surfaces prepared by the method of any one of claims 1-4.

7. The coating of claim 6, wherein: A method for preparing a fabric coating with low infrared emissivity, comprising the following steps: adding a dispersant with a mass fraction of 0.5-1% to a waterborne polyurethane solution with a solid content of 30% and a mass of 100%, weighing the ITO-Ag composite microspheres with special-shaped surfaces of claim 5 with a waterborne polyurethane mass fraction of 10-15%, and then adding pigments with a waterborne polyurethane mass fraction of 5-10%, and stirring until no obvious particles are observed, thereby obtaining the fabric coating with low infrared emissivity. The dispersant is at least one of polyvinyl alcohol PVA2000, polyvinyl alcohol PVA4000 and polyvinyl alcohol PVA1500.

8. The coating according to claim 6 or 7, characterized in that: Alternatively, the pigments are inorganic pigments. The waterborne polyurethane emulsion is prepared by the following method: weighing PEG into a three-necked flask, heating and stirring, then adding diisocyanate and a catalyst to react, then adding a hydrophilic chain extender to perform chain extension, continuing to react, adding a viscosity reducer to reduce the viscosity of the reaction system during the reaction, and performing the whole reaction under nitrogen atmosphere; after the reaction is completed, cooling to 40℃, adding a neutralizing agent to neutralize and keep stirring, finally cooling to room temperature, adding deionized water to emulsify at high speed, removing excess solvent by rotary evaporation, and obtaining the waterborne polyurethane emulsion. The molecular weight of the PEG is 2000-5000. The diisocyanate is isophorone diisocyanate or toluene diisocyanate. The catalyst is dibutyltin dilaurate. The hydrophilic chain extender is 2,2-dimethylol butyric acid. The viscosity reducer is butanone or ethylene glycol. The neutralizing agent is triethylamine or melamine.

9. An infrared low-emissivity coated fabric, which is obtained by coating the fabric sample with the coating material with low infrared emissivity according to any one of claims 6-8 by using a blade coating method and then drying the fabric sample.

10. The infrared low emissivity coated fabric of claim 9, wherein: The thickness of the coating layer formed by the coating material with low infrared emissivity is 150-350 μm. Or, the temperature for drying is 120-160 °C and the time is 6-7 hours.

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