Polyurethane microcapsule encapsulating internal liquid, hyperspectral stealth material for vegetation environment and preparation method and application thereof

Abstract

This invention relates to polyurethane microcapsules with internally encapsulated liquid, hyperspectral stealth materials for vegetated environments, their preparation methods, and applications, belonging to the technical field of spectral stealth and camouflage materials. This invention discloses a polyurethane microcapsule with internally encapsulated liquid, wherein the microcapsule has a polyurethane shell, and the liquid is encapsulated within the polyurethane shell; the particle size of the polyurethane microcapsule with internally encapsulated liquid is 5–50 μm, and the thickness of the polyurethane shell is 1–6 μm; the liquid includes an aqueous phase. This invention also discloses a hyperspectral stealth material for vegetated environments, which is prepared by mixing polyurethane microcapsules with internally encapsulated liquid with inorganic powder, dispersing the mixture in a viscous resin, and then curing it. This invention also discloses a preparation method for the hyperspectral stealth material for vegetated environments and its application in the field of military security.

Description

Technical Field

[0001] This invention belongs to the field of spectral stealth camouflage materials technology, and relates to a polyurethane microcapsule with internally encapsulated liquid, a hyperspectral stealth material for vegetated environments, and its preparation method and application. Background Technology

[0002] Camouflage and stealth are of paramount importance in military security. In terrestrial environments, traditional camouflage techniques primarily use methods such as camouflage, concealment, and coatings to make the appearance (mainly color) of a target object difficult to distinguish from its surroundings with the naked eye, thereby deceiving observers. However, with the development of remote sensing technology, especially hyperspectral detection technology that emerged in the 1980s, the shortcomings of traditional camouflage methods have become apparent.

[0003] First, traditional camouflage techniques, such as ghillie suits in the jungle or white sheets in the snow, are difficult to detect with the naked eye. However, if their spectra are detected against the surrounding environment, the differences become very obvious. Hyperspectral detection can achieve a spectral resolution of 5 nm or even lower. Under such high-resolution detection, the "metachromatic" phenomenon of traditional camouflage can be easily identified. Second, traditional camouflage is mainly aimed at the human eye, that is, camouflage in the visible light band (380–780 nm). However, the detection range of hyperspectral detection technology, in addition to the visible light band, usually includes the entire near-infrared band (780–2500 nm), which is a band that many traditional camouflage methods cannot cover, or even if they do, cannot effectively cover.

[0004] The purpose of camouflaging a target object to achieve the effect of "stealth" under hyperspectral detection means that the reflectance spectrum of the target object is highly consistent with the reflectance spectrum of the background environment within the spectral range, including visible light and near-infrared light.

[0005] In a wide variety of ground background environments, how to make a target object invisible to hyperspectral detection in a vegetated environment has always been a challenge in camouflage research. This is mainly due to the unique characteristics of the reflectance spectrum of plant green leaves.

[0006] The reflectance spectra of almost all green plant leaves have similar spectral line shapes and characteristics, which can be summarized into four main points: a weak reflectance peak appears near 550 nm, called the "green peak"; a sharp increase in reflectance occurs in the range of 680–750 nm, called the "red edge"; reflectance remains at a high level in the wavelength range of 750–1300 nm, a phenomenon called the "near-infrared plateau" or "near-infrared plateau"; and there are two relatively strong absorptions near 1450 nm and 1940 nm, which are due to the water contained in the green leaves of the plant and are therefore called the "water absorption valleys".

[0007] Therefore, how to enable materials to simultaneously simulate the aforementioned characteristics of the reflectance spectrum of green plant leaves with high accuracy, and to achieve stable and long-lasting simulation effects, is the key and challenge in making target objects in green vegetation environments undetectable under hyperspectral detection. Summary of the Invention

[0008] The purpose of this invention is to address the aforementioned problems in the existing technology by proposing a hyperspectral stealth material for vegetated environments, which is simple to prepare, has stable effects, and can highly accurately simulate the reflectance spectrum of green leaves. This material consists of polyurethane microcapsules containing an internal encapsulated liquid.

[0009] The objective of this invention can be achieved through the following technical solutions:

[0010] A polyurethane microcapsule internally encapsulated with liquid, wherein the polyurethane microcapsule internally encapsulates liquid with polyurethane as the outer shell and the liquid is encapsulated inside the polyurethane shell.

[0011] The polyurethane microcapsules containing the encapsulated liquid have a particle size of 5–50 μm and a polyurethane shell thickness of 1–6 μm.

[0012] The liquid includes an aqueous phase liquid.

[0013] Preferably, the preparation process of the polyurethane microcapsules with internal encapsulation liquid includes: sequentially adding an aqueous phase liquid and an emulsifier to an oil phase liquid and stirring to obtain a reverse emulsion system, and then slowly adding isocyanate to react and obtain polyurethane microcapsules with internal encapsulation liquid.

[0014] Further preferably, in the preparation process of the polyurethane microcapsules containing the internal encapsulated liquid, the proportion of oil phase liquid added is 40-70 wt%, the proportion of aqueous phase liquid added is 10-20 wt%, the proportion of emulsifier added is 5-20 wt%, and the proportion of isocyanate added is 10-25 wt%.

[0015] Preferably, the reaction temperature of the reverse emulsion system with isocyanate is 50–65°C, and the reaction time is 0.25–18 h.

[0016] Further preferably, the isocyanate is completely added to the reverse emulsion system within 5 to 60 minutes.

[0017] Preferably, the stirring process speed is 200-700 rpm.

[0018] This invention requires strict control of the stirring rate to ensure that the aqueous phase is fully dispersed in the oil phase, forming a sufficient number of aqueous droplets of appropriate size, and to ensure that the core-shell structure of the microcapsules is not damaged by high-speed impact.

[0019] Preferably, the aqueous phase liquid in the cavity of the polyurethane microcapsule containing the internal encapsulated liquid comprises 40-90 wt% water and 10-60 wt% water-soluble organic solvent.

[0020] Further preferably, the water-soluble organic solvent is any organic solvent that is soluble in water.

[0021] More preferably, the water-soluble organic solvent includes one or more of ethylene glycol, 1,3-propanediol, 1,4-butanediol, glycerol, trimethylolpropane, pentaerythritol, and polyether polyol.

[0022] Preferably, the oil phase liquid and the aqueous phase liquid are immiscible, and the oil phase liquid includes one or more of benzene, toluene, xylene, trimethylbenzene, n-hexane, cyclohexane, n-octane, isooctane, hexadecane, and octadecane.

[0023] Preferably, the isocyanate includes one or more of lysine diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, toluene diisocyanate, and polymers thereof.

[0024] Preferably, the hydrophilic-lipophilic balance value of the emulsifier is less than 8.

[0025] Further preferred, the emulsifier includes one or more of the following: glyceryl monostearate, sorbitan monostearate, sorbitan monooleate, polyoxyethylene sorbitan ester, polyoxyethylene lanolin ether, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, lauric acid soap, calcium hydroxide, zinc hydroxide, and magnesium stearate.

[0026] This invention also discloses a hyperspectral stealth material for vegetated environments, which is prepared by mixing polyurethane microcapsules containing internally encapsulated liquid with inorganic powder, dispersing the mixture in a viscous resin, and then curing it.

[0027] The polyurethane microcapsules encapsulating the liquid in this invention serve to simulate the strong absorption at two points in the green leaf reflectance spectrum of plants, known as the "water absorption valleys," located near 1450 nm and 1940 nm, respectively. The inorganic powder enables the prepared material to simulate the spectral characteristics of the green leaf reflectance spectrum, such as the "green peak," "red edge," and "near-infrared plateau," while also serving as an auxiliary optimization tool for adjusting the overall reflectance of the material and simulating the "water absorption valleys." The resin acts as a carrier for the former two components, making the material readily applicable.

[0028] Preferably, the mass ratio of the polyurethane microcapsules containing the encapsulated liquid to the inorganic powder is (2-40):1.

[0029] Preferably, the hyperspectral stealth material for vegetation environments contains 40-80 wt% polyurethane microcapsules encapsulating liquid, 2-15 wt% inorganic powder, and 20-60 wt% viscous resin.

[0030] Preferably, the inorganic powder includes one or more of CuO, KBr, TiO2, LiCl, Fe2O3, SiO2, Cr2O3, MnO2, MgCl2, BaSO4, CuSO4, CuSO4·5H2O, CrCl3, CrCl3·6H2O, FeSO4, FeSO4·7H2O, BaCl2, and BaCl2·2H2O.

[0031] Preferably, the viscous resin includes one or more of polyethylene, polymethyl methacrylate, polyvinyl alcohol, polystyrene, polyamide, polyethylene terephthalate, polyurethane, polydimethylsiloxane, epoxy resin, phenolic resin, alkyd resin, ethylene-vinyl acetate copolymer, acrylonitrile-butadiene-styrene copolymer, cellulose acetate, and cellulose nitrate.

[0032] Preferably, the curing temperature is 15–50℃ and the curing time is 1–24h.

[0033] This invention also discloses a method for preparing hyperspectral stealth materials for vegetated environments, the method comprising:

[0034] S1. Under continuous stirring, the aqueous phase is added to the oil phase and mixed thoroughly. Then, an emulsifier is added to obtain a reverse emulsion system. Isocyanate is then added and heated to react, resulting in polyurethane microcapsules containing encapsulated liquid.

[0035] S2. Polyurethane microcapsules containing internal liquid are mixed evenly with inorganic powder and then dispersed in viscous resin. After being mixed evenly, the mixture is cured to obtain a hyperspectral stealth material for vegetation environments.

[0036] Preferably, the polyurethane microcapsules containing the internal encapsulated liquid are further subjected to ultrasonic dispersion in anhydrous ethanol, followed by centrifugation, washing, and drying.

[0037] Further preferably, the ultrasonic dispersion, centrifugation and washing are all performed at room temperature, the ultrasonic dispersion frequency is 25-50 kHz, the washing refers to washing with anhydrous ethanol, and the drying process is carried out by forced air drying at 25-50°C for 0.1-10 hours.

[0038] This invention further discloses the application of a hyperspectral stealth material for vegetated environments in the field of military security.

[0039] Preferably, in the 380–2500 nm wavelength band, the normalized similarity of the hyperspectral stealth material for vegetation environments with fresh, untreated plant leaves can reach over 97%.

[0040] Preferably, in the 1300–2200 nm wavelength band of the reflectance spectrum, the normalized similarity of the hyperspectral stealth material for vegetation environments with fresh and untreated green leaves can reach more than 95%.

[0041] Preferably, under the reflection spectrum in the 1300–2200 nm band, the normalized similarity between the polyurethane microcapsules containing the encapsulated liquid and the green leaves of the plant (grapefruit leaves) can reach more than 98%.

[0042] Further optimization reveals that, due to the near-infrared absorption characteristics of the resin itself, the normalized similarity between the hyperspectral stealth material facing the vegetation environment and fresh, untreated plant leaves in the 1300–2200 nm reflectance spectrum is slightly lower than the normalized similarity between the polyurethane microcapsules containing the encapsulated liquid and fresh, untreated plant leaves.

[0043] The formula for calculating the normalized similarity between reflectance spectra is as follows:

[0044]

[0045] Where i refers to the wavelength of the test light, l1 and l2 represent the wavelength range of the calculated spectrum, and α i Let β be the reflectance of a measured sample at wavelength i. i Let i be the reflectance of another sample being measured at wavelength i.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1. The polyurethane microcapsules of the present invention, which encapsulate liquids internally, can stably lock water-based liquids inside the material, thereby accurately simulating the strong absorption at two points in the green leaf reflectance spectrum of plants, known as the "water absorption valleys," located at approximately 1450 nm and 1940 nm, respectively.

[0048] 2. The hyperspectral stealth material for vegetation environments of the present invention contains polyurethane microcapsules with internal encapsulated liquid. The polyurethane microcapsules with internal encapsulated liquid can encapsulate water-based liquids. These microcapsules are then mixed into resin, which actually plays a further role in sealing water. This constitutes a porous water-storing material with resin as the matrix and filled with sealed pores supported by a polyurethane shell.

[0049] 3. In this invention, polyurethane microcapsules containing internal liquid are blended with inorganic powder in resin. Although the normalized similarity to the reflectance spectrum of green leaves is reduced, it can be better coated on the surface of the equipment. The reduction in normalized similarity is mainly due to the vibration of the chemical bonds in the resin itself, especially the vibration of C-H bonds, which will produce specific absorption in the near-infrared region. These absorptions are often redundant and interfering for the reflectance spectrum of green leaves that we want to simulate.

[0050] 4. The preparation method of the polyurethane microcapsules containing internally encapsulated liquid and the hyperspectral stealth material for vegetation environments of the present invention is simple and controllable, and is easy to scale up for production.

[0051] 5. The hyperspectral stealth material of the present invention, designed for vegetated environments, can simulate the reflectance spectrum of natural green plant leaves in the range of 380–2500 nm with high precision under normal temperature and pressure, and can be efficiently applied in the field of military security. Attached Figure Description

[0052] Figure 1 This is a morphological diagram of the polyurethane microcapsules containing the encapsulated liquid in Example 1.

[0053] Figure 2 This is a complete morphological image of a single polyurethane microcapsule in Example 1.

[0054] Figure 3 This is a morphological image of the rupture of a single polyurethane microcapsule in Example 1.

[0055] Figure 4 The reflection spectra of the polyurethane microcapsules containing the encapsulated liquid in Example 1 and the green leaves of the plant (grapefruit leaves) in the 1300-2200 nm wavelength range are shown.

[0056] Figure 5 The normalized reflectance spectra of the hyperspectral cloaking material and the green leaves (grapefruit leaves) of the plant in the 380-2500nm band in Example 1 are shown. Detailed Implementation

[0057] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0058] Example 1

[0059] Preparation of polyurethane microcapsules with internal liquid encapsulation:

[0060] A mixture of 5g deionized water and 5g 1,4-butanediol (aqueous phase) was added to 35g toluene (oil phase) and stirred until fully mixed. Then, 10g Span-80 and 1g Tween-80 were added to the above reaction system to obtain a stable reverse emulsion system. The temperature of the reaction system was then maintained at 60°C, and 10g toluene diisocyanate was added to the above reaction system over 15 minutes to initiate the polyurethane synthesis reaction, and the reaction was maintained for 4 hours. The mechanical stirring rate was maintained at 500 rpm throughout the process.

[0061] The obtained product was ultrasonically dispersed in anhydrous ethanol at a frequency of 20 kHz, then centrifuged at 4000 rpm for 10 minutes and washed with anhydrous ethanol several times. After drying, polyurethane microcapsules containing encapsulated liquid were obtained.

[0062] Figures 1-3 The morphology of the polyurethane microcapsules containing the internally encapsulated liquid was shown in the image, confirming that it was indeed a capsule structure; the morphology of the broken capsules was also examined. Figure 3 The polyurethane microcapsules containing the encapsulated liquid have a particle size of 15.1 μm and a polyurethane shell thickness of 1.9 μm. Figure 4 The normalized similarity of the reflectance spectra of polyurethane microcapsules containing internal liquid and green leaves (grapefruit leaves) in the 1300–2200 nm wavelength range can reach 98.92%.

[0063] Preparation of hyperspectral stealth materials for vegetated environments:

[0064] Take 0.6g of the polyurethane microcapsule containing the internal encapsulated liquid, mix it with 0.03g of Cr2O3 powder by stirring, and then disperse it in 0.36g of uncured viscous epoxy resin. Stir and mix evenly, and then heat to 40℃ to cure the resin for 20h to obtain a hyperspectral stealth material for vegetated environments.

[0065] Figure 5The normalized reflectance spectra of the hyperspectral stealth material for vegetated environments and the green leaves of a plant (pomelo leaf) in the 380–2500 nm band showed a normalized similarity of 97.85%. The normalized similarity of the hyperspectral stealth material for vegetated environments and the green leaves of a plant (pomelo leaf) in the 1300–2200 nm band reached 95.01%.

[0066] Example 2

[0067] A mixture of 7.5g deionized water and 2.5g trimethylolpropane (aqueous phase) was added to 35g toluene (oil phase) and stirred until fully mixed. Then, 10g Span-80 was added to the above reaction system to obtain a stable reverse emulsion system. Next, the temperature of the reaction system was maintained at 60℃, and 10g phenyl diisocyanate trimer was added to the above reaction system over 10 minutes to initiate the polyurethane synthesis reaction and maintain the reaction for 4 hours. The mechanical stirring rate was maintained at 400rpm throughout the above process.

[0068] The obtained product was ultrasonically dispersed in anhydrous ethanol at a frequency of 45 kHz, then centrifuged at 4000 rpm for 10 minutes and washed with anhydrous ethanol several times. After drying, polyurethane microcapsules containing encapsulated liquid were obtained.

[0069] Take 0.5g of the prepared polyurethane microcapsule containing internal encapsulation liquid, mix it with 0.05g of CrCl3·6H2O powder and 0.03g of KBr powder by stirring, and then disperse it in 0.42g of uncured viscous polyethylene. Stir and mix evenly, and then heat to 40℃ to cure the resin for 20h to obtain a hyperspectral stealth material for vegetated environments.

[0070] The normalized similarity of the hyperspectral stealth material for vegetated environments with the reflectance spectra of plant leaves (grapefruit leaves) in the 380–2500 nm band can reach 98.10%.

[0071] Example 3

[0072] A mixture of 75g deionized water and 5g polyether polyol (aqueous phase) was added to 40g isooctane (oil phase) and stirred until fully mixed. Then, 8.5g Atmul-67 was added to the above reaction system to obtain a stable reverse emulsion system. Next, the temperature of the reaction system was maintained at 60℃, and 10g hexamethylene diisocyanate was added to the above reaction system over 15 minutes to initiate the polyurethane synthesis reaction and maintain the reaction for 6 hours. The mechanical stirring rate was maintained at 500rpm throughout the process.

[0073] The obtained product was ultrasonically dispersed in anhydrous ethanol at a frequency of 30 kHz, then centrifuged at 4000 rpm for 10 minutes and washed with anhydrous ethanol several times. After drying, polyurethane microcapsules containing encapsulated liquid were obtained.

[0074] Take 0.5g of the prepared polyurethane microcapsules containing internal encapsulated liquid, mix them with 0.03g of Cr2O3 powder, 0.03g of FeSO4·7H2O powder and 0.04g of LiCl powder by stirring, and then disperse them in 0.40g of uncured viscous polydimethylsiloxane. Stir and mix evenly, and then heat to 40℃ to cure the resin for 20h to obtain a hyperspectral stealth material for vegetated environments.

[0075] The normalized similarity of the hyperspectral stealth material for vegetated environments with the reflectance spectra of plant leaves (grapefruit leaves) in the 380–2500 nm band can reach 98.24%.

[0076] Example 4

[0077] A mixture of 5g deionized water, 2g 1,4-butanediol, and 1g pentaerythritol (aqueous phase) was added to 35g toluene (oil phase) and stirred until fully mixed. Then, 10g Arlacel-80 was added to the above reaction system to obtain a stable reverse emulsion system. Next, the temperature of the reaction system was maintained at 60°C, and 10g isophorone diisocyanate was added to the above reaction system over 15 minutes to initiate the polyurethane synthesis reaction and maintain the reaction for 4 hours. The mechanical stirring rate was maintained at 500 rpm throughout the process.

[0078] The obtained product was ultrasonically dispersed in anhydrous ethanol at a frequency of 30 kHz, then centrifuged at 4000 rpm for 10 minutes and washed with anhydrous ethanol several times. After drying, polyurethane microcapsules containing encapsulated liquid were obtained.

[0079] Take 0.75g of the polyurethane microcapsules containing the internal encapsulated liquid, mix them with 0.03g of Cr2O3 powder and 0.01g of TiO2 powder by stirring, and then disperse them in 0.22g of uncured viscous phenolic resin. Stir and mix evenly, and then heat to 40℃ to cure the resin for 20h to obtain a hyperspectral stealth material for vegetation environments.

[0080] The normalized similarity of the hyperspectral stealth material for vegetated environments with the reflectance spectra of plant leaves (grapefruit leaves) in the 380–2500 nm band can reach 97.63%.

[0081] Example 5

[0082] Compared with Example 1, the difference is that in the preparation process of the hyperspectral stealth material for vegetation environment, 0.6g of the polyurethane microcapsules with internal encapsulation liquid were mixed with 0.09g of Cr2O3 powder by stirring and then dispersed in 0.30g of uncured viscous epoxy resin. After stirring and mixing evenly, the mixture was cured.

[0083] The normalized similarity of the hyperspectral stealth material for vegetated environments with the reflectance spectra of plant leaves (grapefruit leaves) in the 380–2500 nm band can reach 97.32%.

[0084] Example 6

[0085] Compared with Example 1, the difference is that in the preparation process of the hyperspectral stealth material for vegetation environment, 0.6g of the polyurethane microcapsules with internal encapsulation liquid were mixed with 0.20g of Cr2O3 powder by stirring and then dispersed in 0.19g of uncured viscous epoxy resin. After stirring and mixing evenly, the mixture was cured.

[0086] The normalized similarity of the hyperspectral stealth material for vegetated environments with the reflectance spectra of green plant leaves (grapefruit leaves) in the 380–2500 nm band is 95.65%.

[0087] Example 7

[0088] Compared with Example 1, the difference is that in the preparation process of the hyperspectral stealth material for vegetation environment, 0.6g of the polyurethane microcapsules with internal encapsulation liquid were mixed with 0.01g of Cr2O3 powder by stirring and then dispersed in 0.38g of uncured viscous epoxy resin. After stirring and mixing evenly, the mixture was cured.

[0089] The normalized similarity of the hyperspectral stealth material for vegetated environments with the reflectance spectra of plant leaves (grapefruit leaves) in the 380–2500 nm band is 93.13%.

[0090] Example 8

[0091] Compared with Example 1, the difference lies in the preparation process of the polyurethane microcapsules with internal encapsulation liquid. A mixture of 6g deionized water and 6g 1,4-butanediol (aqueous phase) was added to 26g toluene (oil phase), and stirred until fully mixed. Then, 11g Span-80 and 1g Tween-80 were added to the above reaction system to obtain a stable reverse emulsion system. Next, the temperature of the reaction system was maintained at 60°C, and 16g toluene diisocyanate was added to the above reaction system over 15 minutes to initiate the polyurethane synthesis reaction, which was maintained for 4 hours. The mechanical stirring rate was maintained at 500 rpm throughout the process.

[0092] The resulting product consists mostly of irregular polyurethane powder particles, with very few polyurethane microcapsules containing liquid encapsulation. However, the surface of the microcapsules is smoother, and their size has increased to over 35 μm.

[0093] The normalized similarity of the hyperspectral stealth material for vegetated environments with the reflectance spectra of plant leaves (grapefruit leaves) in the 380–2500 nm band is 93.57%.

[0094] Example 9

[0095] Compared to Example 1, the difference lies in the preparation process of the polyurethane microcapsules with internal encapsulation liquid. In this process, a mixture of 4g deionized water and 4g 1,4-butanediol (aqueous phase) was added to 27g toluene (oil phase), and stirred until fully mixed. Then, 10g Span-80 and 1g Tween-80 were added to the above reaction system to obtain a stable reverse emulsion system. Next, the temperature of the reaction system was maintained at 60°C, and 20g toluene diisocyanate was added to the reaction system over 15 minutes to initiate the polyurethane synthesis reaction, which was maintained for 4 hours. The mechanical stirring rate was maintained at 500 rpm throughout the process.

[0096] The yield of polyurethane microcapsules containing encapsulated liquid in the obtained products was significantly low, with most being non-microcapsule polyurethane debris.

[0097] The normalized similarity of the hyperspectral stealth material for vegetated environments with the reflectance spectra of green plant leaves (grapefruit leaves) in the 380–2500 nm band is 90.05%.

[0098] Example 10

[0099] Compared with Example 1, the difference lies in the preparation process of the polyurethane microcapsules with internal encapsulation liquid. A mixture of 6g deionized water and 6g 1,4-butanediol (aqueous phase) was added to 20g toluene (oil phase), and stirred until fully mixed. Then, 10g Span-80 and 5g Tween-80 were added to the above reaction system to obtain a stable reverse emulsion system. Next, the temperature of the reaction system was maintained at 60°C, and 19g toluene diisocyanate was added to the above reaction system over 15 minutes to initiate the polyurethane synthesis reaction, which was maintained for 4 hours. The mechanical stirring rate was maintained at 500 rpm throughout the process.

[0100] No polyurethane microcapsules containing encapsulated liquid were found in the product.

[0101] The normalized similarity of the hyperspectral stealth material for vegetated environments with the reflectance spectra of plant leaves (grapefruit leaves) in the 380–2500 nm band is 90.18%.

[0102] Example 11

[0103] The difference compared to Example 1 is that toluene diisocyanate is added to the reverse emulsion system within 1 minute.

[0104] No polyurethane microcapsules containing encapsulated liquid were found in the product.

[0105] The normalized similarity of the hyperspectral stealth material for vegetated environments with the reflectance spectra of plant leaves (grapefruit leaves) in the 380–2500 nm band can reach 91.32%.

[0106] Comparative Example 1

[0107] Compared with Example 1, the difference is that polyurethane microcapsules without internal encapsulation liquid were not added. The material prepared in this way has a normalized similarity of only 92.74% with the normalized reflectance spectrum of plant green leaves (grapefruit leaves) in the 380-2500nm band.

[0108] Comparative Example 2

[0109] Compared with Example 1, the difference is that no inorganic powder was added. The material prepared has a normalized similarity of only 90.63% with the green leaves of the plant (grapefruit leaves) in the normalized reflectance spectrum of the 380-2500nm band.

[0110] As can be seen from the above, the polyurethane microcapsules with internal encapsulation liquid and the hyperspectral stealth material for vegetated environments prepared by this invention exhibit a high normalized similarity in the reflectance spectrum within the 380–2500 nm range to the reflectance spectrum of fresh, untreated plant leaves. In Example 9, the polyurethane microcapsules were broken and could not simulate water peaks; instead, their own spectral characteristics negatively impacted the normalized similarity. In Comparative Example 1, the polyurethane microcapsules without internal encapsulation liquid only exhibited the properties of inorganic powder and resin. In Examples 10 and 11, polyurethane microcapsules without internal encapsulation liquid were not prepared and also failed to simulate water peaks, resulting in poor and fluctuating normalized similarity.

[0111] In summary, the polyurethane microcapsules containing encapsulated liquid and the hyperspectral stealth material designed for vegetated environments of this invention can achieve a normalized similarity of over 97% with the reflectance spectrum of fresh, untreated green leaves in the 380–2500 nm range at room temperature and pressure over a relatively long period of time; thus, it can be efficiently applied in the field of military security.

[0112] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A polyurethane microcapsule encapsulating an internal liquid, characterized in that, The polyurethane microcapsule encapsulating liquid inside has a polyurethane shell, and the polyurethane shell encapsulates liquid inside; The polyurethane microcapsule encapsulating liquid inside has a particle size of 5-50 μm, and the polyurethane shell has a thickness of 1-6 μm; The liquid in the cavity of the polyurethane microcapsule encapsulating liquid inside is an aqueous liquid, and the aqueous liquid comprises 40-90 wt% of water and 10-60 wt% of a water-soluble organic solvent; The water-soluble organic solvent comprises one or more of ethylene glycol, 1,3-propanediol, 1,4-butanediol, glycerol, trimethylolpropane, pentaerythritol, and polyether polyol; The preparation process of the polyurethane microcapsule encapsulating liquid inside comprises: sequentially adding an aqueous liquid and an emulsifier into an oil phase liquid to obtain a reverse emulsion system, and then slowly adding isocyanate to prepare the polyurethane microcapsule encapsulating liquid inside; wherein the oil phase liquid is added in an amount of 40-70 wt%, the aqueous liquid is added in an amount of 10-20 wt%, the emulsifier is added in an amount of 5-20 wt%, and the isocyanate is added in an amount of 10-25 wt%; The reaction temperature of the reverse emulsion system and the isocyanate is 50-65℃, and the reaction time is 0.25-18h; the isocyanate is added into the reverse emulsion system within 5-60 minutes; The polyurethane microcapsule encapsulating liquid inside has a normalized similarity of 95% or more in the reflectance spectrum of the 1300-2200 nm wave band with fresh and untreated plant green leaves.

2. The internally encapsulated liquid polyurethane microcapsule according to claim 1, wherein, The preparation process of the polyurethane microcapsule encapsulating liquid inside comprises: 5g of deionized water and 5g of 1,4-butanediol are mixed into 35g of toluene, and stirred to fully mix; then 10g of Span-80 and 1g of Tween-80 are added to the mixture to obtain a stable reverse emulsion system; then the temperature of the reverse emulsion system is kept at 60℃, and 10g of toluene diisocyanate is added into the reverse emulsion system within 15 minutes to start the polyurethane synthesis reaction in the system, and the reaction is kept for 4 hours; the above process is kept at a mechanical stirring speed of 500rpm; the obtained product is ultrasonically dispersed in anhydrous ethanol at a frequency of 20kHz, and then washed with anhydrous ethanol for 10 minutes and multiple times at a speed of 4000rpm, and then dried at 35℃ under a blast for 1h, to obtain the polyurethane microcapsule encapsulating liquid inside.

3. A hyperspectral cloaking material for a vegetated environment, characterized in that, The vegetation environment-oriented hyperspectral stealth material is prepared by mixing the polyurethane microcapsule encapsulating liquid inside of claim 1 with inorganic powder, dispersing in viscous resin, and curing; The content of the polyurethane microcapsule encapsulating liquid inside in the vegetation environment-oriented hyperspectral stealth material is 40-80 wt%, the content of the inorganic powder is 2-15 wt%, and the content of the viscous resin is 20-60 wt%.

4. The vegetation-oriented hyperspectral stealth material according to claim 3, characterized in that, The inorganic powder comprises one or more of CuO, KBr, TiO2, LiCl, Fe2O3, SiO2, Cr2O3, MnO2, MgCl2, BaSO4, CuSO4, CuSO4·5H2O, CrCl3, CrCl3·6H2O, FeSO4, FeSO4·7H2O, BaCl2, BaCl2·2H2O; The viscous resin comprises one or more of polyethylene, polymethyl methacrylate, polyvinyl alcohol, polystyrene, polyamide, polyethylene terephthalate, polyurethane, polydimethylsiloxane, epoxy resin, phenolic resin, alkyd resin, ethylene-vinyl acetate copolymer, acrylonitrile-butadiene-styrene copolymer, cellulose acetate, cellulose nitrate.

5. The vegetation-oriented hyperspectral stealth material according to claim 3, wherein, The curing temperature is 15-50 DEG C, and the curing time is 1-24 h.

6. A method of preparing a vegetation-oriented hyperspectral stealth material according to claim 3, characterized by, The preparation method comprises: S1, under the condition of continuous stirring, the water phase is added to the oil phase, mixed fully, then the emulsifier is added to obtain a reverse emulsion system, and then the isocyanate is continuously added to carry out a heating reaction to obtain; S2, the polyurethane microcapsule of the internal encapsulation liquid is mixed uniformly with the inorganic powder by stirring, then dispersed in the viscous resin, and then stirred and mixed uniformly to obtain the hyperspectral stealth material facing the vegetation environment through curing.

7. Use of the vegetation-oriented hyperspectral stealth material according to claim 3 in the field of military security, characterized in that, Under the reflection spectrum of 380-2500 nm, the normalized similarity between the hyperspectral stealth material facing the vegetation environment and the fresh and untreated plant green leaves is more than 97%.

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