A lightweight radar absorbing material and its applied coating

Abstract

This application relates to the technical field of electromagnetic wave absorbing materials, and particularly to a lightweight radar absorbing material and its applied coating. The lightweight radar absorbing coating is composed of the following components by weight: film-forming resin 25-30%, additives 0-15%, and the balance is modified absorbent; the modified absorbent is prepared by blending and modifying a core-shell magnet and a coating emulsion; the core-shell magnet is prepared by atomically depositing strontium oxide on the surface of iron oxide; the coating emulsion is composed of polycarbonate polyol, diisocyanate, and a catalyst. The coating prepared from the above components effectively takes into account both lightweight and anti-radar effects, and has extremely remarkable effects when applied to special fields such as aircraft.

Description

Technical Field

[0001] The present application relates to the technical field of electromagnetic wave absorbing materials, and more specifically, to a lightweight radar wave absorbing material and its application coating. Background Art

[0002] Radar wave absorbing coatings are formed by curing radar wave absorbing paints coated on the surfaces of mobile and fixed targets. They can absorb and attenuate incident radar waves and convert electrical energy into heat energy for dissipation, thereby endowing targets such as aircraft, missiles, and ships with radar stealth functions.

[0003] The radar wave absorbing paints in related technologies mainly consist of absorbents and film-forming agents. Among them, the absorbents are metal particles and ferrite particle absorbents, and the film-forming agents are resin materials with excellent adhesion and toughness. Excellent radar wave absorption effects can be obtained through the bonding of the film-forming agent and the wave absorption of the absorbent.

[0004] However, due to the defect that the metal particles and ferrite particle absorbents used have a large density, the coating area per square meter will increase in weight by 4 - 5 kg, thus limiting their application. Although there are reports in the existing literature on replacing them with other lightweight absorbents, it is often impossible to take into account their wave absorption effects. Therefore, a lightweight radar wave absorbing material and its application coating are specifically provided. Summary of the Invention

[0005] In order to achieve both lightweight and wave absorption performance and thus broaden the application fields of existing radar wave absorbing paints, the present application specifically provides a lightweight radar wave absorbing material and its application coating.

[0006] In a first aspect, the present application provides a lightweight radar wave absorbing paint, adopting the following technical solution:

[0007] A lightweight radar wave absorbing paint is composed of the following components by weight:

[0008] Film-forming resin 25 - 30%, additives 0 - 15%, and the balance is a modified absorbent;

[0009] The modified absorbent is prepared by blending and modifying a core-shell magnet and a coating emulsion;

[0010] The core-shell magnet is prepared by depositing strontium oxide on the surface of magnetite by the deposition method;

[0011] The coating emulsion consists of polycarbonate polyol, diisocyanate, and a catalyst.

[0012] By adopting the above technical solution, the modified absorbent prepared by blending and modifying the core-shell magnet and the coating emulsion effectively combines the characteristics of both by using magnetite as the core and a thin strontium oxide layer as the shell. Thus, when applied to the wave-absorbing coating, it can endow the coating with light weight and excellent wave-absorbing effect. In addition, the use of the coating emulsion effectively ensures the bonding force between the absorbent and the coating matrix.

[0013] Preferably, the weight ratio of the core-shell magnet to the coating emulsion is 1:(0.3 - 0.5).

[0014] Preferably, the specific preparation steps of the core-shell magnet are as follows:

[0015] S1. First, mix magnetite, strontium salt solution and citric acid, and add ammonia water dropwise to adjust the pH to neutral. After the water is evaporated, a magnet gel is obtained.

[0016] S2. Then, vacuum-dry the magnet gel obtained in S1, remove citric acid, and finally calcine it at 1000 - 1200 °C for 3 - 5 h to obtain the core-shell magnet.

[0017] Preferably, the strontium salt solution is an aqueous solution of strontium nitrate with a mass percentage of 8 - 10%.

[0018] Preferably, the weight ratio of magnetite, strontium nitrate and citric acid is 1:(0.3 - 0.5):(0.8 - 1.0).

[0019] By adopting the above technical solution, the core-shell magnet obtained by the above process and components effectively combines the effects of light weight and high wave-absorbing performance by screening the thickness and composition of the oxide layer. In addition, due to the use of a specific amount of the coating emulsion, the uniformity and coverage rate of the coating are ensured.

[0020] Preferably, the weight ratio of the polycarbonate polyol, diisocyanate and catalyst is 1:(0.2 - 0.4):(0.01 - 0.02).

[0021] Preferably, the hydroxyl value of the polycarbonate polyol in the coating emulsion is 40 - 60 mgKOH / g, and the isocyanate index of the diisocyanate is 1.0 - 1.2.

[0022] Preferably, the blending and modification steps of the core-shell magnet and the coating emulsion are as follows:

[0023] First, mix the coating emulsion at 80 - 100 °C for 0.5 - 1.0 h, then add the core-shell magnet, and raise the temperature to 100 - 120 °C and continue to mix for 1.5 - 2.5 h to obtain the modified absorbent.

[0024] By adopting the above technical solution, the polycarbonate polyol, diisocyanate and catalyst used can form polycarbonate-based polyurethane during the blending process, and then excellent curing effect and bonding strength can be imparted to the coating after mixing. In addition, due to the characteristics of the material itself, the mechanical properties and corrosion resistance of the coating can be effectively guaranteed.

[0025] Preferably, the auxiliary agent is one or more of a toughening agent, a surfactant, a dispersant and a leveling agent.

[0026] By adopting the above technical solution, the above auxiliary agents can be selectively added according to the actual coating performance, and the requirements of the coating in other performance aspects can be effectively met through the compounding of the auxiliary agents.

[0027] In the second aspect, the present application provides a lightweight radar absorbing material, adopting the following technical solution:

[0028] A lightweight radar absorbing material is prepared by blending and modifying a core-shell magnet and a coating emulsion. The core-shell magnet is prepared by depositing strontium oxide on the surface of magnetite by the deposition method, and the coating emulsion is composed of a polycarbonate polyol, a diisocyanate and a catalyst.

[0029] By adopting the above technical solution, the absorbing material obtained through the above raw materials and steps can not only be applied to coating products, but also be cured on the surface of the object to be protected against radar through other products or forms, and the anti-radar effect during its application can be effectively guaranteed.

[0030] To sum up, the present application has the following beneficial effects:

[0031] 1. The modified absorbent prepared by blending and modifying the core-shell magnet and the coating emulsion in the present application effectively guarantees the lightweight characteristics and radar absorbing effect of the coating by using magnetite as the core and a thin layer of strontium oxide as the shell, while the use of the coating emulsion guarantees the adhesion and cementing effect after curing;

[0032] 2. The core-shell magnet prepared by a specific process and components in the present application can further achieve the balance between lightweight and high radar absorbing performance by optimizing the thickness and composition of the oxide layer. In addition, due to the use of a specific amount of the coating emulsion, the uniformity and coverage rate of the coating are guaranteed;

[0033] 3. The polycarbonate polyol, diisocyanate and catalyst used in the present application can form polycarbonate-based polyurethane during the blending process, and then excellent curing effect, bonding strength and corrosion resistance can be imparted to the coating after melt coextrusion;

[0034] 4. The microwave absorbing material obtained through specific raw materials and steps in this application can not only be applied to coating products, but also be cured on the surface of the object to be radar-proof through other products or forms, which can effectively ensure the radar-proof effect during its application. The light weight feature significantly broadens its application fields. Detailed implementation manners

[0035] The following further elaborates on this application in conjunction with examples.

[0036] Preparation examples

[0037] Preparation example 1

[0038] A core-shell magnet is prepared as follows:

[0039] S1. First, mix iron tetroxide, strontium salt solution and citric acid, and add ammonia water to adjust the pH to 7.0. After the water is evaporated, a magnet gel is obtained.

[0040] The strontium salt solution is an aqueous solution of strontium nitrate with a mass percentage of 10%.

[0041] The weight ratio of iron tetroxide, strontium nitrate and citric acid is 1:0.3:1.0.

[0042] S2. Then, vacuum-dry the magnet gel obtained in S1 at 110 °C, remove citric acid by combustion in air, and finally calcine it at 1000 °C for 5 h to obtain the core-shell magnet.

[0043] Preparation examples 2 - 3

[0044] A core-shell magnet, which is different from Preparation example 1 in that the component situation of the strontium salt solution used is different, as shown in the following table.

[0045] Table: Comparison table of the component situation of the strontium salt solution in Preparation examples 2 - 3

[0046]

[0047]

[0048] Preparation examples 4 - 6

[0049] A core-shell magnet, which is different from Preparation example 1 in that the amount of iron tetroxide in S1 remains unchanged, and the component ratio of each material is different, as shown in the following table.

[0050] Table: Comparison table of the component dosage ratio in Preparation examples 4 - 6

[0051] Group Allocation ratio of each material group Preparation Example 4 The weight ratio of iron oxide, strontium nitrate and citric acid is 1:0.4:0.9 Preparation Example 5 The weight ratio of iron oxide, strontium nitrate and citric acid is 1:0.5:0.8 Preparation Example 6 The weight ratio of iron oxide, strontium nitrate and citric acid is 1:0.8:1.2

[0052] Preparation examples 7 - 12

[0053] A modified absorbent is prepared by blending a core-shell magnet and a coating emulsion in a weight ratio of 1:0.3. The core-shell magnet is prepared in Preparation Examples 1-6 respectively, and the specific corresponding relationship is as follows in the table:

[0054] Table: Comparison table of the usage of the modified absorbent in Preparation Examples 7-12

[0055] Group Modified absorbent Preparation Example 7 Prepared from Preparation Example 1 Preparation Example 8 Prepared from Preparation Example 2 Preparation Example 9 Prepared from Preparation Example 3 Preparation Example 10 Prepared from Preparation Example 4 Preparation Example 11 Prepared from Preparation Example 5 Preparation Example 12 Prepared from Preparation Example 6

[0056] The coating emulsion is composed of polycarbonate polyol (hydroxyl value 60mgKOH / g), diisocyanate (HDI / isocyanate index is 1.0) and catalyst (stannous octoate) in a weight ratio of 1:0.2:0.01;

[0057] The specific steps of the above blending modification are as follows: First, mix the coating emulsion at 100°C for 0.5h, then add the core-shell magnet, and raise the temperature to 120°C and continue to mix for 1.5h to obtain the modified absorbent.

[0058] Preparation Examples 13-15

[0059] A modified absorbent, which is different from Preparation Example 7 in that the weight ratio of the core-shell magnet and the coating emulsion is different, and the specific corresponding relationship is shown in the following table.

[0060] Table: Comparison table of the weight ratio of the core-shell magnet and the coating emulsion in Preparation Examples 13-15

[0061] Group Weight ratio of core-shell magnet and coating emulsion Preparation Example 13 The weight ratio of core-shell magnet and coating emulsion is 1:0.4 Preparation Example 14 The weight ratio of core-shell magnet and coating emulsion is 1:0.5 Preparation Example 15 The weight ratio of core-shell magnet and coating emulsion is 1:0.8

[0062] Preparation Examples 16-18

[0063] A modified absorbent, which is different from Preparation Example 7 in that the dosage of each component of the coating emulsion is different, and the specific corresponding relationship is shown in the following table.

[0064] Table: Comparison table of the dosage of each component of the coating emulsion in Preparation Examples 16-18

[0065]

[0066]

[0067] Preparation Examples 19-21

[0068] A modified absorbent, which is different from Preparation Example 7 in that the usage of the polycarbonate polyol and / or the diisocyanate is different, and the specific corresponding relationship is shown in the following table.

[0069] Table: Comparison table of the usage of the polycarbonate polyol and / or the diisocyanate in Preparation Examples 19-21

[0070]

[0071] Preparation Examples 22-24

[0072] A modified absorbent, which is different from Preparation Example 7 in that the operating parameters of the blending modification are different, and the specific corresponding relationships are shown in the following table.

[0073] Table: Comparison of operating parameters for blending and modification in Preparation Examples 22-24

[0074]

[0075] The performance test selected the lightweight absorbing coatings prepared in the following embodiments and / or comparative examples as test objects, and after curing, tested their surface density (kg / m 2 ) and wave absorbing performance, each group was tested three times in parallel, and the average value of the test results was recorded;

[0076] The thickness of the cured coating of the lightweight absorbing paint is 0.3mm, and the absorbing performance is characterized by its reflectivity (dB) in the 8GHz-18GHz frequency band. The specific testing steps and standards refer to GJB2038A-2011 "Test Method for Reflectivity of Radar Absorbing Materials".

[0077] Example

[0078] Examples 1-3

[0079] A lightweight radar absorbing coating, the raw material components and dosage are as follows (per 100kg):

[0080] Table: Raw material components and their weights in Examples 1-3 (kg)

[0081]

[0082] The modified absorbent is prepared according to Preparation Example 7, and the film-forming resin is PPS polyphenylene sulfide resin.

[0083] Comparative Example 1

[0084] A radar absorbing coating, which differs from Example 1 in that the modified absorbent is replaced by an equal amount of ferroferric oxide powder, and other conditions and raw material selection are the same as those of the present application.

[0085] The coatings prepared in Examples 1-3 and Comparative Example 1 were taken as test objects, and their surface densities (kg / m 2 ) and wave absorbing performance, the test results are averaged and recorded in the table below.

[0086] Table: Performance test results of Examples 1-3 and Comparative Example 1

[0087]

[0088]

[0089] As can be seen from the above table, the lightweight radar absorbing coatings obtained in Examples 1-3 all have lightweight and excellent anti-radar stealth effects after curing, and their areal density is only 1.00-1.05 kg / m 2 , which is 17-21% lower than that of Comparative Example 1; the reflectivity in the 8 GHz-18 GHz frequency band is as high as -2.3--2.4 dB, achieving the same performance as that in Comparative Example 1;

[0090] In summary, combining the data of the examples and comparative examples, the reasons may be as follows:

[0091] The modified absorber prepared by blending and modifying the core-shell magnet and the coating emulsion effectively combines the characteristics of both by using magnetite as the core and strontium oxide thin layer as the shell, so that it can endow the absorber with lightweight and excellent absorbing effects after being applied to the absorbing coating; in addition, it can be seen from Examples 1-3 that the preferred amount of the film-forming resin is 25-30%, and the preferred amount of the modified absorber is 70-75%. As for the additives, they can be added and designed according to the performance requirements of the product. Thanks to the use of the film-forming resin and the coating emulsion, its weather resistance is also strong. As for the amount of the modified absorber, it should not be too high or too low, otherwise it is very easy to affect the balance between lightweight and anti-radar.

[0092] Examples 4-8

[0093] A lightweight radar absorbing coating, which is different from that of Example 1 in that the usage of the modified absorber used is different, and the specific corresponding relationship is shown in the following table.

[0094] Table: Comparison table of the usage of the modified absorber in Examples 4-8

[0095] Group Modified absorbent Example 4 Prepared from Preparation Example 8 Example 5 Prepared from Preparation Example 9 Example 6 Prepared from Preparation Example 10 Example 7 Prepared from Preparation Example 11 Example 8 Prepared from Preparation Example 12

[0096] Extract the coatings prepared in Examples 4-8 above as the test objects, and then test their areal density (kg / m 2 ) and absorbing performance respectively, and the test results are averaged and recorded in the following table.

[0097] Table: Performance test results of Examples 4-8

[0098]

[0099]

[0100] As can be seen from the above table, the lightweight radar absorbing coatings obtained in Examples 4-8 all have lightweight and excellent anti-radar stealth effects after curing, and their areal density is only 0.92-1.05 kg / m2 , its reflectivity in the 8 GHz - 18 GHz frequency band is as high as -2.1 to -2.4 dB;

[0101] Combining the above with the data of the examples, the possible reasons are analyzed as follows:

[0102] For the core-shell magnet obtained by the above process and components, through the screening of the thickness and composition of the oxide layer, the effects of light weight and high wave absorption performance are effectively balanced. In addition, thanks to the use of a specific amount of coating emulsion, the uniformity and coverage rate of its coating are also guaranteed; in addition, it can be seen from Examples 4 - 5 that when the amount of strontium salt is certain, its concentration and specific selection basically have no impact on the final product performance, and it has been verified that the preferred strontium salt solution is an aqueous strontium nitrate solution with a mass percentage of 8 - 10%, which is only related to its reaction rate.

[0103] It can also be seen from Examples 10 - 12 that the preferred weight ratio of magnetite, strontium nitrate and citric acid is 1:(0.3 - 0.5):(0.8 - 1.0). Any adjustment within this range is not likely to affect the various performances of this application. When exceeding this ratio, the anti-radar effect will also decrease correspondingly with the increase in the amount of strontium nitrate used. At this time, blindly pursuing light weight is no longer advisable.

[0104] Examples 9 - 11

[0105] A lightweight radar absorbing coating, which is different from Example 1 in that the usage of the modified absorbent is different, and the specific corresponding relationship is shown in the following table.

[0106] Table: Comparison table of the usage of modified absorbents in Examples 9 - 11

[0107] Group Modified absorbent Example 9 Prepared from Preparation Example 13 Example 10 Prepared from Preparation Example 14 Example 11 Prepared from Preparation Example 15

[0108] Comparative Example 2

[0109] A lightweight radar absorbing coating, which is different from Example 1 in that the used coating emulsion is replaced by an equal amount of polyurethane, and other reaction conditions and raw material selections are the same as those in Example 1.

[0110] Extract the coatings prepared in the above Examples 9 - 11 and Comparative Example 2 as test objects, and then test their surface density (kg / m 2 ) and wave absorption performance respectively, and record the average test results in the following table.

[0111] Table: Performance test results of Examples 9 - 11 and Comparative Example 2

[0112]

[0113] As can be seen from the above table, the lightweight radar absorbing coatings obtained in Examples 9-11 all have lightweight and anti-radar stealth effects after curing. Their areal density is only 0.76-0.98 kg / m 2 , and their reflectivity in the frequency band of 8 GHz - 18 GHz is as high as -2.0 - -2.4 dB, showing varying degrees of improvement compared to Comparative Example 2;

[0114] Based on the above, combining the data of the examples and comparative examples, the possible reasons are analyzed as follows:

[0115] The polycarbonate polyol, diisocyanate and catalyst used can form polycarbonate-type polyurethane during the blending process, and then can endow the coating with excellent curing effect and bonding strength after mixing. Obviously, Comparative Example 2 cannot achieve the above conditions. In addition, due to the characteristics of the material itself, the mechanical properties and corrosion resistance of the coating can be effectively guaranteed.

[0116] That is, the use of the coated emulsion effectively guarantees its bonding strength with the coating matrix, but the dosage ratio with the core-shell magnet needs to be designed and controlled separately. The preferred weight ratio of the core-shell magnet to the coated emulsion is 1:(0.3 - 0.5). Adjustments within this range are not likely to affect its anti-radar effect. However, if the dosage of the coated emulsion exceeds this range, although it endows the coating with a lighter characteristic, its anti-radar effect will be reduced accordingly. The specific ratio can be adjusted according to the actual product requirements.

[0117] Examples 12 - 20

[0118] A lightweight radar absorbing coating, which is different from Example 1 in that the usage of the modified absorbent is different, and the specific corresponding relationship is shown in the following table.

[0119] Table: Comparison table of the usage of modified absorbents in Examples 12 - 20

[0120]

[0121]

[0122] Extract the coatings prepared in the above Examples 12 - 20 as test objects, and then test their areal density (kg / m 2 ) and wave absorption performance respectively. The test results are averaged and recorded in the following table.

[0123] Table: Performance test results of Examples 12 - 20

[0124]

[0125] As can be seen from the above table, the lightweight radar-absorbing coatings obtained in Examples 12-20 all have lightweight and excellent anti-radar stealth effects after curing. Their areal density is only 1.05 kg / m 2 , and their reflectivity in the 8 GHz - 18 GHz frequency band is as high as -2.4 dB. In summary, combining the data of the examples, it can be seen that due to the polycarbonate polyol, diisocyanate and catalyst used, the main purpose is to synthesize polycarbonate-based polyurethane, which can then endow the coating with excellent curing effects and bonding strength after mixing, so the influence on the above areal density and reflectivity is relatively small;

[0126] Therefore, it can be seen from Examples 12-14 that the dosage ratio of each component only affects the reaction temperature and time during the blending process to ensure the formation of the final polycarbonate-based polyurethane. Considering the actual operation efficiency, the weight ratio of polycarbonate polyol, diisocyanate and catalyst in the coating emulsion is 1:(0.2 - 0.4):(0.01 - 0.02).

[0127] It can be seen from Examples 15-17 that the use of the above polycarbonate polyol and / or diisocyanate only affects the reaction temperature and time during the blending process to ensure the formation of the final polycarbonate-based polyurethane. The hydroxyl value of the polycarbonate polyol is preferably 40 - 60 mgKOH / g, and the isocyanate index of the diisocyanate is preferably 1.0 - 1.2.

[0128] It can be seen from Examples 18-20 that the preferred blending and modification steps are as follows:

[0129] First, mix the coating emulsion at 80 - 100 °C for 0.5 - 1.0 h, then add the core-shell magnet and raise the temperature to 100 - 120 °C and continue to mix for 1.5 - 2.5 h to obtain the modified absorbent;

[0130] The above conditions can effectively ensure the uniformity and coverage of the coating emulsion on the core-shell magnet, and then effectively ensure the mechanical properties and bonding strength of the coating after the coating is cured and formed.

[0131] This specific application example is only an interpretation of the present application and does not limit the present application. Those skilled in the art can make modifications to this application example without creative contributions according to needs after reading this specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A lightweight radar absorbing coating, characterized in that, It consists of components with the following weights: Film-forming resin 25 - 30%, additives 0 - 15%, and the balance is modified absorbent; The modified absorbent is prepared by blending and modifying a core-shell magnet and a coating emulsion; The core-shell magnet is prepared by depositing strontium oxide on the surface of magnetite by the deposition method; The coating emulsion consists of polycarbonate polyol, diisocyanate, and a catalyst; The specific preparation steps of the core-shell magnet are as follows: S1. First, mix magnetite, strontium salt solution, and citric acid, and add ammonia water dropwise to adjust the pH to neutral. After the water is evaporated, a magnet gel is obtained; The strontium salt solution is an aqueous solution of strontium nitrate with a mass percentage of 8 - 10%; The weight ratio of magnetite, strontium nitrate, and citric acid is 1:(0.3 - 0.5):(0.8 - 1.0); S2. Then, vacuum-dry the magnet gel obtained in S1, remove citric acid, and finally calcine it at 1000 - 1200 °C for 3 - 5 h to obtain the core-shell magnet.

2. The lightweight radar absorbing coating according to claim 1, wherein, The weight ratio of the core-shell magnet to the coating emulsion is 1:(0.3 - 0.5).

3. The lightweight radar absorbing coating according to claim 2, wherein The weight ratio of polycarbonate polyol, diisocyanate, and the catalyst is 1:(0.2 - 0.4):(0.01 - 0.02).

4. The lightweight radar absorbing coating according to claim 1, characterized in that, The hydroxyl value of polycarbonate polyol in the coating emulsion is 40 - 60 mgKOH / g, and the isocyanate index of diisocyanate is 1.0 - 1.

2.

5. The lightweight radar absorbing coating according to any one of claims 1-4, characterized in that, The blending and modification steps of the core-shell magnet and the coating emulsion are as follows; First, mix the coating emulsion at 80 - 100 °C for 0.5 - 1.0 h, then add the core-shell magnet, and raise the temperature to 100 - 120 °C and continue to mix for 1.5 - 2.5 h to obtain the modified absorbent.

6. The lightweight radar absorbing coating according to claim 1, characterized in that: The additive is one or more of a toughening agent, a surfactant, a dispersant, and a leveling agent.

7. A lightweight radar absorbing material, characterized in that: It is prepared by blending and modifying a core-shell magnet and a coating emulsion. The core-shell magnet is prepared by depositing strontium oxide on the surface of magnetite by the deposition method. The coating emulsion consists of polycarbonate polyol, diisocyanate, and a catalyst; The specific preparation steps of the core-shell magnet are as follows: S1. First, mix magnetite, strontium salt solution, and citric acid, and add ammonia water dropwise to adjust the pH to neutral. After the water is evaporated, a magnet gel is obtained; The strontium salt solution is an aqueous solution of strontium nitrate with a mass percentage of 8 - 10%; The weight ratio of magnetite, strontium nitrate, and citric acid is 1:(0.3 - 0.5):(0.8 - 1.0); S2. Then, vacuum-dry the magnet gel obtained in S1, remove citric acid, and finally calcine it at 1000 - 1200 °C for 3 - 5 h to obtain the core-shell magnet.

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