High-temperature-resistant salt-fog-resistant wave-absorbing coating and preparation method thereof

Abstract

The invention provides a high-temperature-resistant and salt-fog-resistant wave-absorbing coating which is prepared from the following components in parts by weight: 26.9-32 parts of organic silicon resin, 54.8-57.7 parts of metal micro powder, 0.5-0.8 part of a dispersing agent, 0.5-0.8 part of an anti-settling agent, 1-1.5 parts of a salt-fog-resistant auxiliary agent and 10.6-13.2 parts of a solvent, the components are compounded and cured to obtain the high-temperature-resistant and salt-fog-resistant wave-absorbing coating, and particularly, the high-temperature-resistant and salt-fog-resistant wave-absorbing coating is prepared from the following components in parts by weight: 26.9-32 parts of organic silicon resin, 54.8-57.7 parts of metal micro powder, 0.5-0.8 part of The preparation method comprises the following steps: adding organic silicon resin, a solvent, a dispersing agent and a salt-spray-resistant additive into a reaction kettle, carrying out first dispersion stirring, adding an anti-settling agent, carrying out second dispersion stirring, adding metal micro-powder in batches, carrying out third dispersion stirring to obtain a wave-absorbing coating, spraying the wave-absorbing coating on a metal substrate, airing at room temperature, and drying at room temperature to obtain the wave-absorbing coating. And respectively baking at 55 DEG C, 100 DEG C and 250 DEG C to obtain the high-temperature-resistant salt-fog-resistant wave-absorbing coating. The wave-absorbing coating prepared by the preparation method disclosed by the invention can be free from blistering and cracking at 320 DEG C for 300 hours, and also can be free from obvious corrosion, wrinkling, cracking and falling off in a neutral salt mist environment for 480 hours.

Description

Technical Field

[0001] The invention belongs to the technical field of radar absorbing coatings, and in particular relates to a high temperature resistant and salt fog resistant radar absorbing coating and a preparation method thereof. Background Art

[0002] Absorbing coatings can reduce or eliminate the harm of electromagnetic waves to target protection carriers, and are widely used in electronic equipment and equipment. However, absorbing coatings usually face various complex use environments, such as: long-term temperature resistance environment of 320℃ or high humidity and high salt fog environment of the ocean. The common absorbing coatings currently used in the market are composed of organic resins and high-content metal micropowders, which are very prone to corrosion damage in 320℃ temperature resistance environment and salt fog environment. Therefore, a salt fog resistant absorbing coating that can withstand 320℃ for a long time is needed to meet the above usage requirements.

[0003] In view of this, this invention is proposed. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a high temperature resistant and salt fog resistant radar absorbing coating, which can achieve no blistering and cracking within 300 hours at a high temperature of 320°C, and no obvious corrosion, wrinkling, cracking and falling off within 480 hours in a neutral salt fog environment, thereby meeting the use requirements in a long-term temperature and salt fog resistant environment.

[0005] The purpose of the present invention is to be solved by the following technical solutions:

[0006] In one aspect, the present invention provides a high temperature resistant and salt fog resistant radar absorbing coating, wherein the radar absorbing coating comprises the following components in parts by weight:

[0007] 26.9-32 parts of organic silicon resin, 54.8-57.7 parts of metal powder, 0.5-0.8 parts of dispersant, 0.5-0.8 parts of anti-settling agent, 1-1.5 parts of salt spray resistant additive, 10.6-13.2 parts of solvent,

[0008] The high temperature resistant and salt fog resistant absorbing coating is obtained by compounding and curing the above components.

[0009] Furthermore, the thickness of the radar absorbing coating is 0.5 to 1 mm.

[0010] Furthermore, the organic silicone resin is methylphenyl silicone resin.

[0011] Furthermore, the metal powder is a flaky iron-silicon-chromium alloy powder, the powder D50 is 20 to 30 microns, and the powder thickness is 2 to 5 μm.

[0012] Furthermore, the salt spray resistance additive is zinc aluminum phosphate.

[0013] Furthermore, the solvent is prepared from xylene and n-butanol, and the mass ratio of xylene to n-butanol is 70:30.

[0014] Furthermore, the dispersant is BYK-110.

[0015] Furthermore, the anti-settling agent is polyamide wax 229.

[0016] On the other hand, the present invention provides a method for preparing a high temperature resistant salt fog resistant radar absorbing coating, wherein the preparation method is carried out according to the component raw materials included in the high temperature resistant salt fog resistant radar absorbing coating and the corresponding weight parts of the component raw materials, and specifically comprises the following steps:

[0017] (1) adding the silicone resin, solvent, dispersant and salt spray resistance additive into a mixing kettle, performing the first dispersion stirring for 5 to 8 minutes, then adding the anti-settling agent while dispersing and stirring, and performing the second dispersion stirring for 5 to 8 minutes after the anti-settling agent is added;

[0018] (2) Then, metal powder is added in 3 to 4 times while being dispersed and stirred. After the metal powder is added, a third dispersion and stirring is performed for 8 to 12 minutes. After the dispersion and stirring are completed, a high temperature resistant and salt fog resistant absorbing coating is obtained;

[0019] (3) After the obtained high temperature resistant and salt fog resistant absorbing coating is sprayed on the metal substrate with a thickness of 0.5 to 1 mm, it is placed at room temperature for 12 to 16 hours, and then baked at (55±5)°C for 6 to 12 hours, (100±10)°C for 6 to 12 hours, and 250°C for 6 to 12 hours, respectively, to obtain a high temperature resistant and salt fog resistant absorbing coating.

[0020] Furthermore, in step (1), the first dispersing stirring speed is 600-800 r / min, and the second dispersing stirring speed is 800-1000 r / min.

[0021] The third dispersion stirring speed in step (2) is 800-1000 r / min.

[0022] The room temperature in step (3) is (23±5)°C,

[0023] The metal substrate in step (3) includes a titanium alloy substrate or other metal substrates.

[0024] In step (3), the obtained high temperature resistant and salt fog resistant absorbing coating is sprayed on the metal substrate by air spraying.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention uses methylphenyl silicone resin as the coating matrix. During the high-temperature baking process at 250°C, the methylphenyl silicone resin molecules can form a dense network structure after curing and cross-linking, thereby evenly fixing the alloy powder in the coating. At the same time, the resin matrix and the alloy powder themselves have good heat resistance. The two can give the absorbing coating long-term heat resistance through synergistic effect. There is no blistering or cracking when baked at 320°C for 300 hours, and the heat resistance performance is excellent;

[0027] 2. Zinc aluminum phosphate is added to the radar absorbing coating provided by the present invention as a salt spray resistant additive. Zinc aluminum phosphate can react with the metal powder in the coating to form a dense phosphate protective film. In a salt spray environment, zinc and aluminum elements are more active than the alloy powder elements inside and corrode first, thereby protecting the alloy powder inside from corrosion temporarily. That is, through the sacrifice of zinc and aluminum elements, the salt spray resistance of the coating can reach more than 480 hours;

[0028] 3. The raw materials required for preparing the radar absorbing coating of the present invention are simple, the preparation method is simple and convenient, the production efficiency is high, and it is suitable for large-scale stable production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings are incorporated in and constitute a part of this specification and, together with the description, serve to explain the principles of the present invention.

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 The present invention is a flow chart of a method for preparing a high temperature resistant and salt fog resistant radar absorbing coating. DETAILED DESCRIPTION

[0032] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are merely examples consistent with some aspects of the present invention as detailed in the appended claims.

[0033] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0034] According to an embodiment of the present invention, the present invention provides a high temperature resistant and salt fog resistant absorbing coating, which comprises the following components in parts by weight: 26.9 to 32 parts of silicone resin, 54.8 to 57.7 parts of metal powder, 0.5 to 0.8 parts of dispersant, 0.5 to 0.8 parts of anti-settling agent, 1 to 1.5 parts of salt fog resistant additive, and 10.6 to 13.2 parts of solvent. The high temperature resistant and salt fog resistant absorbing coating is obtained by compounding and curing the above components.

[0035] According to an embodiment of the present invention, the thickness of the radar absorbing coating is 0.5-1 mm.

[0036] According to an embodiment of the present invention, the organic silicone resin is a methylphenyl silicone resin, which can form a dense network structure after molecular curing and cross-linking, thereby evenly fixing the alloy powder in the coating. At the same time, the organic silicone resin and the alloy powder themselves have good heat resistance. Through the synergistic effect, the two can give the absorbing coating long-term heat resistance. There is no blistering or cracking when baked at 320°C for 300 hours, and the heat resistance performance is excellent.

[0037] According to an embodiment of the present invention, the metal powder is a flaky iron-silicon-chromium alloy powder, the powder D50 is 20-30 microns, and the powder thickness is 2-5 μm, which can provide the coating with the ability to reduce or eliminate electromagnetic waves.

[0038] According to an embodiment of the present invention, the salt spray resistant additive is zinc aluminum phosphate, which can react chemically on the surface of ferrous metal to form a dense protective film to prevent the penetration of water and corrosive ions. At the same time, the zinc and aluminum elements in zinc aluminum phosphate are amphoteric metals, which are more active than iron. When there are tiny corrosion cells on the surface of ferrous metal, zinc aluminum can be corroded first as sacrificial anodes, thereby protecting the ferrous metal.

[0039] According to an embodiment of the present invention, the solvent is prepared from xylene and n-butanol, and the mass ratio of xylene to n-butanol is 70:30. The solvent can significantly reduce the viscosity of the coating, has good compatibility with other components of the coating, and can adapt to construction in different environments by adjusting the ratio, thereby improving the adaptability of the product.

[0040] According to an embodiment of the present invention, the dispersant is BYK-110.

[0041] According to an embodiment of the present invention, the anti-settling agent is polyamide wax 229.

[0042] According to an embodiment of the present invention, the present invention provides a method for preparing a high temperature resistant and salt fog resistant radar absorbing coating, which specifically comprises the following steps:

[0043] (1) adding the silicone resin, solvent, dispersant and salt spray resistance additive into a mixing kettle, performing a first dispersion stirring for 5 to 8 minutes at a dispersion stirring speed of 600 to 800 r / min, adding the anti-settling agent while dispersing and stirring at a dispersion stirring speed of 600 to 800 r / min, and after the anti-settling agent is added, performing a second dispersion stirring for 5 to 8 minutes at a dispersion stirring speed of 800 to 1000 r / min to fully activate the anti-settling agent;

[0044] (2) Then, metal powder is added in 3 to 4 times while being dispersed and stirred at a speed of 800 to 1000 r / min. After the metal powder is added, the third dispersion and stirring is performed at a speed of 800 to 1000 r / min for 8 to 12 minutes. After the mixture is evenly dispersed, the dispersion and stirring is terminated to obtain a high temperature resistant and salt fog resistant absorbing coating;

[0045] (3) After the obtained high temperature resistant and salt fog resistant absorbing coating is air-sprayed on a metal substrate with a thickness of 0.5 to 1 mm, it is placed at room temperature (23±5)°C for 12 to 16 hours, and then baked at (55±5)°C for 6 to 12 hours, (100±10)°C for 6 to 12 hours, and 250°C for 6 to 12 hours, respectively, to obtain a high temperature resistant and salt fog resistant absorbing coating.

[0046] According to the embodiment of the present invention, the reaction kettle in the present invention can be replaced by a paint mixing cup, and the present invention uses a stirring, frosting and dispersing multi-purpose machine for dispersing and stirring.

[0047] According to the embodiment of the present invention, the heat-resistant and salt-fog-resistant radar-absorbing coating of the present invention is sprayed on a titanium alloy substrate or other metal substrate to form a long-term heat-resistant and salt-fog-resistant radar-absorbing coating thereon.

[0048] In order to further verify the efficacy of the heat-resistant and salt-fog-resistant absorbing coating of the present invention, the following examples are provided for further explanation:

[0049] Example 1

[0050] This embodiment 1 provides a heat-resistant and salt-fog-resistant radar-absorbing coating, which includes the following components in parts by weight:

[0051] 26.9 parts of organic silicon resin, 57.7 parts of metal powder, 0.6 parts of dispersant, 0.6 parts of anti-settling agent, 1 part of salt spray resistant additive, 13.2 parts of solvent,

[0052] The preparation process of a heat-resistant and salt-fog-resistant radar-absorbing coating of the present invention is as follows:

[0053] (1) adding the silicone resin, solvent, dispersant and salt spray resistance additive into a mixing kettle, performing a first dispersion stirring at a dispersion stirring speed of 600 r / min for 8 min, then adding the anti-settling agent while dispersing and stirring at a dispersion stirring speed of 600 r / min, and after the anti-settling agent is added, performing a second dispersion stirring at a dispersion stirring speed of 800 r / min for 8 min to fully activate the anti-settling agent;

[0054] (2) Then, metal powder is added three times while dispersing and stirring at a speed of 800 r / min. After the metal powder is added, the third dispersion stirring is performed at a speed of 800 r / min for 12 minutes. After the mixture is evenly dispersed, the dispersion stirring is terminated to obtain a high temperature resistant and salt fog resistant absorbing coating;

[0055] (3) The obtained high temperature resistant and salt fog resistant absorbing coating is sprayed on the surface of a 50*50*3mm titanium alloy substrate, and the above-mentioned heat resistant and salt fog resistant absorbing coating is sprayed by air until the coating thickness is (1±0.05)mm, each spraying is two crosses, and the spraying interval is 5min. After the final spraying thickness reaches (1±0.05)mm, it is placed at room temperature (23±5)℃ for 16h, and then baked at 60℃ for 12h, 100℃ for 12h, and 250℃ for 12h, respectively, to obtain a heat resistant and salt fog resistant absorbing coating.

[0056] Example 2

[0057] This embodiment 2 provides a heat-resistant and salt-fog-resistant radar-absorbing coating, which includes the following components in parts by weight:

[0058] 32.9 parts of organic silicon resin, 54.8 parts of metal powder, 0.5 parts of dispersant, 0.5 parts of anti-settling agent, 1 part of salt spray resistant additive, 10.6 parts of solvent,

[0059] The preparation process of a heat-resistant and salt-fog-resistant radar-absorbing coating of the present invention is as follows:

[0060] (1) adding the silicone resin, solvent, dispersant and salt spray resistance additive into a mixing kettle, performing a first dispersion stirring at a dispersion stirring speed of 650 r / min for 7 min, then adding the anti-settling agent while dispersing and stirring at a dispersion stirring speed of 650 r / min, and after the anti-settling agent is added, performing a second dispersion stirring at a dispersion stirring speed of 850 r / min for 7 min to fully activate the anti-settling agent;

[0061] (2) Then, metal powder is added three times at a speed of 850 r / min while dispersing and stirring. After the metal powder is added, the third dispersion stirring is performed at a speed of 850 r / min for 11 minutes. After the mixture is evenly dispersed, the dispersion stirring is terminated to obtain a high temperature resistant and salt fog resistant absorbing coating;

[0062] (3) The obtained high temperature resistant and salt fog resistant absorbing coating is sprayed on the surface of a 50*50*3mm titanium alloy substrate, and the above-mentioned heat resistant and salt fog resistant absorbing coating is sprayed by air until the coating thickness is (1±0.05)mm, each spraying is two crosses, and the spraying interval is 5min. After the final spraying thickness reaches (1±0.05)mm, it is placed at room temperature (23±5)℃ for 16h, and then baked at 60℃ for 12h, 100℃ for 12h, and 250℃ for 12h, respectively, to obtain a heat resistant and salt fog resistant absorbing coating.

[0063] Example 3

[0064] This embodiment 3 provides a heat-resistant and salt-fog-resistant radar-absorbing coating, which includes the following components in parts by weight:

[0065] 31.9 parts of organic silicon resin, 54.8 parts of metal powder, 0.5 parts of dispersant, 0.5 parts of anti-settling agent, 1.5 parts of salt spray resistant additive, 10.8 parts of solvent,

[0066] The preparation process of a heat-resistant and salt-fog-resistant radar-absorbing coating of the present invention is as follows:

[0067] (1) adding the silicone resin, solvent, dispersant and salt spray resistance additive into a mixing kettle, performing a first dispersion stirring at a dispersion stirring speed of 700 r / min for 6 min, then adding the anti-settling agent while dispersing and stirring at a dispersion stirring speed of 700 r / min, and after the anti-settling agent is added, performing a second dispersion stirring at a dispersion stirring speed of 900 r / min for 6 min to fully activate the anti-settling agent;

[0068] (2) Then, metal powder is added in four portions at a speed of 900 r / min while being dispersed and stirred. After the metal powder is added, the mixture is dispersed and stirred for 10 min for the third time at a speed of 900 r / min. After the mixture is evenly dispersed, the dispersion and stirring are terminated to obtain a high temperature resistant and salt fog resistant absorbing coating;

[0069] (3) The obtained high temperature resistant and salt fog resistant absorbing coating is sprayed on the surface of a 50*50*3mm titanium alloy substrate, and the above-mentioned heat resistant and salt fog resistant absorbing coating is sprayed by air until the coating thickness is (1±0.05)mm, each spraying is two crosses, and the spraying interval is 5min. After the final spraying thickness reaches (1±0.05)mm, it is placed at room temperature (23±5)℃ for 16h, and then baked at 60℃ for 12h, 100℃ for 12h, and 250℃ for 12h, respectively, to obtain a heat resistant and salt fog resistant absorbing coating.

[0070] Example 4

[0071] This embodiment 4 provides a heat-resistant and salt-fog-resistant radar-absorbing coating, which includes the following components in parts by weight:

[0072] 32 parts of organic silicon resin, 54.8 parts of metal powder, 0.8 parts of dispersant, 0.8 parts of anti-settling agent, 1 part of salt spray resistant additive, 10.6 parts of solvent,

[0073] The preparation process of a heat-resistant and salt-fog-resistant radar-absorbing coating of the present invention is as follows:

[0074] (1) adding the silicone resin, solvent, dispersant and salt spray resistance additive into a mixing kettle, performing a first dispersion stirring at a dispersion stirring speed of 800 r / min for 5 min, then adding the anti-settling agent while dispersing and stirring at a dispersion stirring speed of 800 r / min, and after the anti-settling agent is added, performing a second dispersion stirring at a dispersion stirring speed of 1000 r / min for 5 min to fully activate the anti-settling agent;

[0075] (2) Then, metal powder is added in four portions at a speed of 1000 r / min while being dispersed and stirred. After the metal powder is added, the mixture is dispersed and stirred for a third time at a speed of 1000 r / min for 8 minutes. After the mixture is evenly dispersed, the dispersion and stirring are terminated to obtain a high temperature resistant and salt fog resistant radar absorbing coating;

[0076] (3) The obtained high temperature resistant and salt fog resistant absorbing coating is sprayed on the surface of a 50*50*3mm titanium alloy substrate, and the above-mentioned heat resistant and salt fog resistant absorbing coating is sprayed by air until the coating thickness is (1±0.05)mm, each spraying is two crosses, and the spraying interval is 5min. After the final spraying thickness reaches (1±0.05)mm, it is placed at room temperature (23±5)℃ for 16h, and then baked at 60℃ for 12h, 100℃ for 12h, and 250℃ for 12h, respectively, to obtain a heat resistant and salt fog resistant absorbing coating.

[0077] Performance Testing

[0078] The heat-resistant and salt-fog-resistant absorbing coatings prepared in Examples 1-4 were subjected to performance tests respectively. The appearance of the coatings was visually inspected, the coating thickness was measured with a micrometer, the adhesion was tested using the GB / T 5210-2006 double-column method, the heat resistance was tested using the GB / T 1735-2009 method, and the salt spray resistance was tested using the GJB 150.11A-2009 method.

[0079] The test results are shown in Table 1.

[0080] Table 1 Performance test results of heat-resistant and salt-fog-resistant radar absorbing coating examples 1-4

[0081]

[0082] It can be seen that the high temperature resistant and salt fog resistant absorbing coating prepared by the present invention has high temperature resistance, can achieve no blistering and cracking for 300 hours at 320°C, has salt fog resistance, can achieve no obvious corrosion, wrinkling, cracking and falling off for 480 hours in a neutral salt fog environment, thereby meeting the use requirements in a long-term temperature and salt fog resistant environment.

[0083] The above description is only a specific embodiment of the present invention, so that those skilled in the art can understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention.

[0084] It should be understood that the present invention is not limited to what has been described above and that various modifications and changes may be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A high temperature resistant and salt fog resistant radar absorbing coating, characterized in that: The absorbing coating comprises the following components in parts by weight: 26.9-32 parts of organic silicon resin, 54.8-57.7 parts of metal powder, 0.5-0.8 parts of dispersant, 0.5-0.8 parts of anti-settling agent, 1-1.5 parts of salt spray resistant additive, 10.6-13.2 parts of solvent, The high temperature resistant and salt fog resistant absorbing coating is obtained by compounding and curing the above components.

2. The high temperature resistant and salt fog resistant absorbing coating according to claim 1, characterized in that: The thickness of the radar absorbing coating is 0.5-1 mm.

3. The high temperature resistant and salt fog resistant absorbing coating according to claim 1, characterized in that: The organic silicone resin is methyl phenyl silicone resin.

4. The high temperature resistant and salt fog resistant absorbing coating according to claim 1, characterized in that: The metal powder is a flaky iron-silicon-chromium alloy powder, the powder D50 is 20 to 30 microns, and the powder thickness is 2 to 5 μm.

5. The high temperature resistant and salt fog resistant radar absorbing coating according to claim 1, characterized in that: The salt spray resistance additive is zinc aluminum phosphate.

6. The high temperature resistant and salt fog resistant radar absorbing coating according to claim 1, characterized in that: The solvent is prepared from xylene and n-butanol, and the mass ratio of the xylene to n-butanol is 70:

30.

7. The high temperature resistant and salt fog resistant radar absorbing coating according to claim 1, characterized in that: The dispersant is BYK-110.

8. The high temperature resistant and salt fog resistant radar absorbing coating according to claim 1, characterized in that: The anti-settling agent is polyamide wax.

9. A method for preparing a high temperature resistant and salt fog resistant radar absorbing coating, characterized in that: The preparation method is based on the raw materials and weight portions of the raw materials included in the high temperature resistant and salt fog resistant absorbing coating according to any one of claims 1 to 8, and specifically comprises the following steps: (1) adding the silicone resin, solvent, dispersant and salt spray resistance additive into a mixing kettle, performing the first dispersion stirring for 5 to 8 minutes, then adding the anti-settling agent while dispersing and stirring, and performing the second dispersion stirring for 5 to 8 minutes after the anti-settling agent is added; (2) Then, metal powder is added in 3 to 4 times while being dispersed and stirred. After the metal powder is added, a third dispersion and stirring is performed for 8 to 12 minutes. After the dispersion and stirring are completed, a high temperature resistant and salt fog resistant radar absorbing coating is obtained; (3) After the obtained high temperature resistant and salt fog resistant absorbing coating is sprayed on the metal substrate with a thickness of 0.5 to 1 mm, it is placed at room temperature for 12 to 16 hours, and then baked at (55±5)°C for 6 to 12 hours, (100±10)°C for 6 to 12 hours, and 250°C for 6 to 12 hours, respectively, to obtain a high temperature resistant and salt fog resistant absorbing coating.

10. The method for preparing the high temperature resistant and salt fog resistant radar absorbing coating according to claim 9, characterized in that: In step (1), the first dispersing stirring speed is 600-800 r / min, and the second dispersing stirring speed is 800-1000 r / min. The third dispersion stirring speed in step (2) is 800-1000 r / min. The room temperature in step (3) is (23±5)°C, The metal substrate in step (3) includes a titanium alloy substrate or other metal substrates. In step (3), the obtained high temperature resistant and salt fog resistant absorbing coating is sprayed on the metal substrate by air spraying.

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