Radar-transparent high-luminance silver coating, and preparation method therefor and use thereof

Abstract

Disclosed in the present invention are a radar-transparent high-luminance silver coating, and a preparation method therefor and the use thereof. The high-luminance silver coating comprises: at least one aluminum pigment, with the weight percentage thereof being less than or equal to 1.5%; at least one silver pearlescent pigment, with the weight percentage thereof being 0.5-4.0%; and a solvent-type base material having a high content of an orienting agent, wherein the weight percentage of the effective content of the orienting agent in the solvent type base material is greater than 5%. In the present invention, a low addition amount of the aluminum pigment is used in combination with the silver pearlescent pigment having high covering properties to prepare the radar-transparent high-luminance silver coating in a base material system having a high content of the orienting agent; an increment in radar transmission loss caused by the silver coating is less than 0.5 dB, the optimal L15° is greater than 140, and the silver coating can also have good angle-dependent color shifting performance, flickering properties and covering power, and obvious metallic appearance; and the silver coating is expected to be applied to usage scenarios having requirements for both silver appearance and radar signal transparency.

Description

Radar-transparent high-brightness silver-colored coating and preparation method and use thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of radar-transparent silver-colored coatings. More particularly, it relates to a radar-transparent high-brightness silver-colored coating and a preparation method and use thereof. BACKGROUND

[0002] With the rapid development of automatic driving technology, the use of millimeter wave radar (frequency 77-81 GHz) is becoming more and more common. Several radars will be installed on each car or machine with automatic driving function, which are generally placed behind the bumpers or corresponding parts. For coatings without metal components, their use will not interfere with radar signals, while for metal effect coatings with silver appearance containing aluminum pigments, due to the high electrical conductivity and dense stacked lamellar structure of aluminum, the penetration of radar signals is greatly affected, with a loss of more than 3 dB, which brings challenges to the identification of radar systems.

[0003] Silver-colored pearlescent pigments with special wrapping layers based on mica flakes or alumina substrates are another kind of pigments that can achieve higher brightness, goniochromaticity and sparkling effect. CN103459515A discloses a high hiding power, high gloss silver-colored pearlescent effect pigment with metallic appearance, which wraps a coating containing ilmenite on the surface of a non-metallic flaky substrate. Through optimized formulation and process technology, the pigment has excellent goniochromaticity, brightness and sparkling effect, and has a silver appearance similar to silver powder. CN1784476A discloses an interference pigment with high hiding power, which also wraps an ilmenite-containing layer on a thin flaky inorganic substrate, improving the low hiding power problem of conventional pearlescent pigments and having a silver-gray or silver metallic appearance. However, compared with aluminum pigments, such products still have the defects of low hiding power and insufficient metallic feeling, and currently aluminum pigments cannot be completely replaced by pearlescent pigments. However, the dielectric properties possessed by such inorganic oxides are not possessed by aluminum pigments.

[0004] CN116018291A discloses a radar-compatible coating containing metal effect pigments, which adopts a double-layer stacked structure design, one layer does not contain metal effect pigments, and the other layer contains metal effect pigments. The thickness of the metal-containing pigment coating is reduced to improve the radar transmittance. However, the radar loss problem caused by the dense arrangement of aluminum pigments in the metal-containing coating still exists in this technical solution. In addition, the double-layer structure design is complex in preparation and has low feasibility, and the influence on hiding power, color tone and other performances is not disclosed. CN114222798A discloses a radar-transmissive coating composition using radar-transmissive pigments instead of metal aluminum pigments, which uses at least 50% of transmissive pigments to achieve the effect of reducing loss. However, the technical effect of this design is general, the lowest loss is controlled above 1.11dB, and there is a problem of insufficient brightness. At the same time, the influence on key performances such as flicker and hiding power is not disclosed.

[0005] In summary, even if the compatible system of silver pearl pigments and aluminum pigments is used in the prior art, it is difficult to achieve good compatibility of low radar transmittance loss and high brightness. The effect is generally poor, and it is urgent to develop a more effective technical solution to improve the compatibility of radar transmittance loss and high brightness.

[0006] SUMMARY

[0007] To solve the above problems, the first object of the present application is to provide a radar-transparent high-brightness silver coating.

[0008] The second object of the present application is to provide a preparation method of the high-brightness silver coating as described above.

[0009] The third object of the present application is to provide the use of the high-brightness silver coating as described above on a plastic substrate.

[0010] To achieve the above first object, the present application adopts the following technical solution:

[0011] The present application discloses a radar-transparent high-brightness silver coating, which comprises

[0012] at least one aluminum pigment, the weight percentage of which is ≤1.5%;

[0013] at least one silver pearl pigment, the weight percentage of which is 0.5-4.0%; and

[0014] a solvent-based binder containing a high content of orientation agent;

[0015] The effective content of the orientation agent in the solvent-based binder is >5% by weight.

[0016] Further, the silver-colored pearlescent pigment is selected from a group consisting of flaky substrates coated with iron oxide or titanium-iron oxide;

[0017] The flaky substrates comprise one or more of mica flakes, mica flakes coated with titanium oxide, aluminum oxide flakes, titanium dioxide flakes, glass flakes.

[0018] Further, the silver-colored pearlescent pigment has a D50 of 5-30 μm and an average thickness of 100-500 nm.

[0019] The aluminum pigment has a D50 of 5-30 μm and a solid content of 65-75%.

[0020] Further, the total weight percentage of the aluminum pigment and the silver-colored pearlescent pigment in the high-brightness silver-colored coating is controlled to be 1.5-5.0%.

[0021] Further, the weight ratio of the aluminum pigment and the silver-colored pearlescent pigment is 1:0.5-4.

[0022] Further, the high-brightness silver-colored coating has a dry film thickness of 10-25 μm.

[0023] To achieve the above-mentioned second object, the present application adopts the following technical solution:

[0024] The present application discloses a preparation method of the high-brightness silver-colored coating as mentioned above, comprising the following steps:

[0025] Preparation of solvent-based base and pre-dispersed aluminum pigment dispersion and silver-colored pearlescent pigment dispersion;

[0026] Adding the pre-dispersed aluminum pigment dispersion and the silver-colored pearlescent pigment dispersion into the solvent-based base, and after mixing uniformly, a radar-transparent silver-colored appearance coating is obtained.

[0027] Coating the silver-colored appearance coating on a plastic substrate and curing it, and the high-brightness silver-colored coating is obtained.

[0028] To achieve the above-mentioned third object, the present application adopts the following technical solution:

[0029] The present application discloses the use of the high-brightness silver-colored coating as mentioned above on a plastic substrate.

[0030] Further, the high-brightness silver-colored coating is used on bumpers, plastic parts of automobiles or plastic substrates of other intelligent devices.

[0031] Further, the high-brightness silver-colored coating has an L15° value of above 125, preferably above 140, and more preferably above 145.

[0032] The high-brightness silver coating has an increase in radar transmission loss caused by the high-brightness silver coating of <0.5 dB when applied to a plastic substrate.

[0033] The beneficial effects of the present application are as follows:

[0034] The present application uses low-content aluminum pigments and specific silver pearl pigments in combination, which ensures the reduction of radar transmission loss. After being combined with solvent-based binders containing high content of orientation agents, the flaky effect pigments can be fully arranged, and the obtained silver coating has high brightness, excellent goniochromicity, scintillation, hiding power and obvious metallic appearance. The silver coating is expected to be applied to scenarios that require silver appearance and radar signal transparency.

[0035] The silver pearl pigments selected by the present application are flaky substrate pigments wrapped with iron oxide or titanium iron oxide. The pearl pigments with high hiding power and silver appearance wrapped with ilmenite components are a new type of pearl product, which has goniochromicity, high brightness and scintillation effect similar to aluminum pigments, and can compensate for the influence of low-content aluminum pigments to a certain extent.

[0036] The present application controls the total addition amount and the ratio relationship between the aluminum pigments and the silver pearl pigments. On the one hand, it implicitly specifies the content of the solvent-based binder, which further specifies the content of the orientation agent, so that the full arrangement of the flaky effect pigments is ensured. On the other hand, through the amount relationship between the aluminum pigments and the silver pearl pigments, high brightness, excellent goniochromicity, scintillation, hiding power and obvious metallic appearance can be easily obtained.

[0037] The high-brightness silver coating provided by the present application can obtain good hiding power at a relatively thin dry film thickness (10-25 μm). When applied to a plastic substrate, the high-brightness silver coating has an increase in radar transmission loss of <0.5 dB, and the radar transmission loss is significantly reduced. Moreover, the preparation process of the high-brightness silver coating is simple, and does not require the double-layer stacked structure design reported in the prior art, which has higher feasibility. BRIEF DESCRIPTION OF DRAWINGS

[0038] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0039] Figure 1 shows a technical schematic diagram of the present application in improving radar transparency, wherein A in Figure 1 is a coating formed by a traditional metal effect pigment, and B is a coating obtained by using a silver appearance coating of the present application.

[0040] Figure 2 shows a cross-sectional SEM image of the high-brightness silver coating prepared in Example 6 of the present application.

[0041] Figure 3 shows a cross-sectional SEM image of the high-brightness silver-colored coating prepared in Example 8 of the present application. DETAILED DESCRIPTION

[0042] In order to more clearly illustrate the application, the following further describes the application with reference to the preferred embodiments and the accompanying drawings. Like reference numerals in the drawings denote like elements. It should be understood by those skilled in the art that the specific description given below is illustrative and not restrictive and is not intended to limit the scope of the application.

[0043] As used herein, the term "parts" refers to parts by weight, unless otherwise indicated.

[0044] Currently, the radar commonly used frequency is 24GHz or 77-81GHz band, which is installed behind the bumper or other automobile plastic parts, among which the 77-81GHz band radar is the most commonly used due to its small volume, strong anti-interference ability, policy access and other advantages. Since its wavelength is in the millimeter wave band of 1-10mm, it is called millimeter wave radar. Millimeter wave radar has strong penetration ability and can penetrate plastic substrates (polypropylene, polycarbonate, etc.) to achieve target recognition. However, as an electromagnetic wave, the millimeter wave radar energy is not enough to penetrate metal medium. For aluminum metal, a good conductor, the penetration depth of millimeter wave radar is only about a few hundred nanometers. Referring to Figure 1A, the aluminum effect paint commonly used in the automotive field generally contains about 1-6wt% of aluminum pigments. The higher the content, the closer the aluminum powder tends to form a dense and continuous structure, and the more layers are superimposed, resulting in a large loss of millimeter waves when penetrating such a coating.

[0045] Aluminum pigments are a kind of thin flake effect pigments obtained by grinding, generally having a size of 5-50μm, a thickness of about several hundred nanometers, and an outer surface generally having various additives such as oleic acid added during grinding. The aluminum pigment commonly used in automobiles is a silver dollar-shaped product with a size of 10-25μm, having a very high brightness, a delicate and strong metallic appearance, and unique performance that is difficult to replace. The indispensability of aluminum pigments and the demand for improvement of radar transmission rate are contradictory. However, with the popularization and use of silver pearl pigments, new possibilities are provided for the development of silver-colored coatings.

[0046] Pearlescent pigments are a kind of effect pigments prepared by wrapping a specific effect layer on the surface of a flaky inorganic oxide substrate. The general wrapping layer has a high refractive index, thereby producing interference with the internal substrate to form a product with specific effects. Pearlescent pigments include many categories, and there are corresponding products in various colors, sizes and various effects, which have been widely used in many fields, such as cosmetics, automobiles, household appliances, industrial equipment, etc. Pearlescent pigments have similar aluminum pigments in terms of goniochromaticity, high brightness and sparkling effect, but the hiding power is obviously lower. If silver pearlescent pigments are used alone, the metallic feeling is not ideal.

[0047] In order to better obtain a silver-colored coating with low radar transmission loss and high brightness, silver pearlescent pigments and aluminum pigments can be used in combination. Based on this idea, there are two specific solutions: the first solution is to design aluminum pigments and silver pearlescent pigments in a double-layer structure, which do not affect each other. The advantage mainly lies in the arrangement of the two types of flaky effect pigments without affecting each other. However, the design of a double-layer structure increases the complexity of the preparation process, which is not conducive to construction. The second solution is to design silver pearlescent pigments and aluminum pigments in a single-layer structure, that is, to mix silver pearlescent pigments and aluminum pigments into a uniform pigment. At this time, the amount of the two needs to be strictly controlled to reduce the arrangement of the two types of flaky effect pigments, control the amount of aluminum pigments to reduce radar transmission loss, and consider the maintenance of brightness, goniochromaticity, sparkling effect, metallic feeling and hiding power. However, it is actually difficult to balance, and even if a relatively balanced effect is obtained, it is difficult for a skilled person.

[0048] On the basis of the second solution, in order to maintain the effects of brightness and hiding power, the skilled person usually does not reduce the content of aluminum pigments too much, and the content is at least controlled above 2%. This is the lower limit of the development of aluminum pigment-containing formulations by the skilled person. If the radar transparent coating is pursued, that is, the radar loss value caused by the coating is below 1dB, since the skilled person usually intuitively believes that the addition of aluminum pigments will bring obvious radar loss, the radar transparent effect cannot be achieved, so the single silver pearlescent pigment is usually directly developed to completely replace the aluminum pigment, or the silver pearlescent pigment and aluminum pigment composite formulation is developed with the content of aluminum pigment above 2%, and the development of the composite formulation by further reducing the content of aluminum pigment is not attempted at all, which has become the inert thinking of the skilled person in development. However, surprisingly, the inventors found that based on the coating system of the present application, when a lower content of aluminum pigments (≤1.5%) is selected, there is almost no radar loss. On this basis, the present application combines and uses aluminum pigments and silver pearlescent pigments, as shown in FIG. 1B, to provide a radar transparent high-brightness silver coating. The black ellipse represents the aluminum pigment, and the white ellipse represents the silver pearlescent pigment. The combination of the two reduces the radar transmission loss. The high-brightness silver coating comprises

[0049] at least one aluminum pigment, the weight percentage of which is ≤1.5%;

[0050] at least one silver pearlescent pigment, the weight percentage of which is 0.5-4.0%; and

[0051] a solvent-based base containing a high content of orientation agent;

[0052] wherein the effective content of the orientation agent in the solvent-based base is >5% by weight.

[0053] The use of aluminum pigment mainly ensures the metallic luster of the coating, which is irreplaceable by pearlescent pigments at the present stage, but considering the loss of radar transmission caused by aluminum pigment, the weight percentage of aluminum pigment in the present application is controlled to be ≤1.0%. Due to the influence of the added amount, the low content of aluminum pigment significantly reduces the radar loss.

[0054] In one specific embodiment, the D50 of the aluminum pigment is 5-30 μm, and the solid content is 65-75%. The aluminum pigment contains structures in the shape of silver dollar, corn flake or other suitable shapes. The commonly used aluminum pigment suppliers for automobiles at present include Toyo Aluminum, Star Platinum, Zuxing, etc. As an example, the 4660NS (D50 is 9 μm) of Toyo Aluminum is used in the specific embodiment of the present application. The 4660NS has delicate metallic luster, high-brightness appearance and excellent goniochromatic performance, and is a representative product for automobiles.

[0055] Further, the weight percentage of the aluminum pigment in the high-brightness silver coating is ≤1.1%, and it is found through experiments that the radar loss caused by the aluminum pigment at this added amount can be basically ignored.

[0056] To eliminate the appearance problems such as brightness reduction caused by low content aluminum pigments, the silver-colored pearlescent pigments selected by the present application are flaky substrate pigments wrapped with iron oxide or titanium-iron oxide, and the flaky substrate pigments include one or more of mica flakes, titanium oxide coated mica flakes, aluminum oxide flakes, titanium oxide coated aluminum oxide flakes, titanium dioxide flakes, titanium oxide coated titanium dioxide flakes, glass flakes, and titanium oxide coated glass flakes; the D50 of the silver-colored pearlescent pigments is 5-30 μm, and the average thickness is 100-500 nm. The pearlescent pigments with high hiding and silver-colored appearance wrapped with ilmenite components are a new type of pearlescent product, which has similar aluminum pigment properties such as goniochromism, high brightness, and sparkling effect. The main suppliers of the silver-colored pearlescent pigments include Merck, Eckart, Global New Materials, and Kuncai Technology, etc. In a specific embodiment, the silver-colored pearlescent pigments are selected from the iriodin series of 9602 (D50 is 15 μm), 9605 (D50 is 23 μm), and 9612 (D50 < 15 μm) of Merck, and the OEM opaque silver series of superfine (D50 is 13 μm), fine (D50 is 18 μm), and medium (D50 is 23 μm) of Eckart. However, these products still do not solve the problem of low content aluminum pigments well.

[0057] Further, the total weight percentage of the aluminum pigments and the silver-colored pearlescent pigments in the high-brightness silver-colored coating is controlled at 1.5-5.0%, and exemplarily, the total weight percentage of the aluminum pigments and the silver-colored pearlescent pigments in the high-brightness silver-colored coating can be 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0058] Further, the weight ratio of the aluminum pigments and the silver-colored pearlescent pigments is 1:0.5-4, and exemplarily, the weight ratio of the aluminum pigments and the silver-colored pearlescent pigments can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, etc. In a specific embodiment, when the weight ratio of the aluminum pigments and the silver-colored pearlescent pigments is 1:1-2, the high-brightness silver-colored coating has higher brightness and lower radar transmission loss.

[0059] The brightness is represented by the L15° value close to the reflection angle, and the L15° value of the high-brightness silver-colored coating is at least above 125.

[0060] The orienting agent is a kind of rheological additive that must be added in the coating system of flaky effect pigment. The commonly used orienting agent includes but is not limited to polyethylene wax, polyamide wax, ethylene vinyl acetate wax, butyl acetate cellulose, silicate, etc. The principle is to increase the viscosity and thixotropy of the coating system, strengthen the dispersion and prevent the flaky effect pigment from sinking to the bottom. When drying, it can also support the arrangement of flaky effect pigment. In the coating system, about 1-5 wt% of orienting agent is generally added. In order to make up for the poor hiding power of low content aluminum pigment and silver color pearl pigment, the effective content of orienting agent in the silver color coating system of the present application is increased and controlled at >5 wt%. This is beneficial to the full arrangement of flaky effect pigment to achieve high brightness and hiding power. The skilled person can further adjust the amount of suitable orienting agent according to different base systems, for example, the effective content of orienting agent in solvent-based base can be controlled at >6 wt%, >7 wt%, >8 wt%, >9 wt%, >10 wt%, >11 wt%, >12 wt% or >13 wt%.

[0061] The high-brightness silver color coating obtained by the present application has a relatively thin thickness, with a dry film thickness of 10-25 μm, preferably 10-20 μm. Without the action of high content of orienting agent, the coating system of the present application cannot achieve good hiding power with low content of aluminum pigment in the application of thin coating. In a specific embodiment, the orienting agent is selected from one or more of Eastman CAB 531-1, DISPARLON 4200-10 (effective ingredient 10 wt%) of Nanben Chemical, and CERAFAK 103 of BYK. Eastman CAB 531-1 is a butyl acetate cellulose with a higher butyryl content than Eastman CAB 381 type cellulose ester. Through the combination of butyl acetate cellulose and thermoplastic acrylic resin, a tough film with good scratch resistance and weather resistance can be obtained. The hydroxyl content and solubility characteristics of Eastman CAB 531-1 and Eastman CAB 381 are similar, both of which can be dissolved in various solvents. Eastman CAB 531-1 is a softer resin, which requires lower plasticizer modification compared with Eastman CAB 381 ester. DISPARLON 4200-10 is a non-dissolved paste-like swelling dispersion flow body mainly composed of a dispersible oxidized polyethylene wax, which has little effect on the viscosity of the coating and is not easily affected by the type of pigment and vehicle. It can be used as a settling preventing agent for almost all pigment dispersion coating, and can produce stable gel structure with pigments, fillers, etc. in the coating, thereby imparting excellent thixotropic properties to the coating and preventing pigment settlement and coating sagging. CERAFAK 103 is a dispersion of ethylene acrylic acid copolymer wax, which is suitable for solvent-based effect coating system and can improve the orienting effect of effect pigment and reduce in-can settling.

[0062] The solvent-based base also conventionally adds acrylic resin, solvent and dispersant. In a specific embodiment, the acrylic resin is selected from solvent-based acrylic resin, such as DIC's ACRYDIC ZHL-1063, ACRYDIC WML-350, etc., accounting for 15wt% of the weight of the solvent-based base. The solvent is selected from xylene, ethyl acetate and isobutyl alcohol, and the oriented butyl acetate cellulose agent needs to be dispersed in advance using ethyl acetate and isobutyl alcohol to obtain a dispersion liquid for use. The dispersant is selected from BYK-192. Since the solvent-based base has little effect on the radar transmission loss of other materials in addition to the orientation agent, those skilled in the art can replace the above-mentioned products used as examples in the examples while ensuring the basic performance of the coating, and the increase in radar transmission loss caused by different silver coatings obtained is basically equivalent.

[0063] The high-brightness silver coating developed by the present application is obtained based on a solvent-based coating system, which can exhibit low radar loss, high brightness, excellent goniochromicity, hiding power and sparkling effect. However, in the current development of water-based systems, the arrangement of aluminum pigments is poor, the hiding power is low, the brightness is very low, and the technical effect is not obvious.

[0064] The present application also provides a preparation method for preparing the high-brightness silver coating as described above, comprising the following steps:

[0065] Preparation of a solvent-based base and pre-dispersed aluminum pigment dispersion and silver pearl pigment dispersion;

[0066] Add the pre-dispersed aluminum pigment dispersion and silver pearl pigment dispersion to the solvent-based base, mix uniformly, and obtain a radar-transparent silver appearance coating;

[0067] Coat the silver appearance coating on the plastic substrate containing the primer and cure it, and the high-brightness silver coating is obtained.

[0068] Further, the curing conditions are 60-80°C baking for 20-30min.

[0069] Further, the thickness of the primer is 10-15μm, and the present application also includes a varnish layer coated on the high-brightness silver coating, and the thickness of the varnish layer is 30-40μm.

[0070] The present application also provides a use of the high-brightness silver coating as described above applied to a plastic substrate.

[0071] Further, the high-brightness silver coating is used on bumpers, plastic parts of automobiles or plastic substrates of other intelligent devices.

[0072] Further, the high-brightness silver coating has an L15° value of 125 or more, preferably 140 or more, and more preferably 145 or more.

[0073] The high-brightness silver coating has a radar transmission loss increase value of <0.5 dB when applied to a plastic substrate. In the present application, the radar transmission loss increase value refers to the difference in radar transmission loss caused by the addition of aluminum pigments and silver pearl pigments in the high-brightness silver coating compared to before the addition.

[0074] The following will be further described in combination with the following specific solutions.

[0075] Solvent-based base

[0076] The formulation of the solvent-based base containing a high content of the orienting agent is also important for achieving the technical effects of the present application. In order to illustrate the effect of the high content of the orienting agent, two solvent-based bases, Base A and Base B, were prepared for comparative analysis, wherein Base A is a formulation containing a high content of the orienting agent, and Base B is a formulation containing a low content of the orienting agent.

[0077] Table 1 Formulation of solvent-based base Note: CAB 531-1 dispersion is prepared by dispersing CAB 531-1 into isobutyl alcohol and butyl acetate.

[0078] Coating requirements

[0079] A 3 mm thick PP plate (black, size 150*200 mm) was sequentially sprayed (ecogun machine spraying) with Flex700 primer (product of Axalta Coating Systems), the color paint of the examples and comparative examples of the present application, and Flex200 / AP2000 clear paint (product of Axalta Coating Systems), with thicknesses as shown in Table 2, and then placed flat in an oven at 80°C for 30 min. The following tests were then performed: optical indicators were tested using a BYK-MAC tester, and radar transmission loss was tested using a Rohde & Schwarz QAR device.

[0080] Table 2 Summary of information of each coating

[0081] Comparative Examples 1-7

[0082] The comparative examples in this group provide the formulations of seven silver-colored coatings, and the specific formulations are shown in Table 3.

[0083] Table 3

[0084] The formulations provided in Table 3 were prepared and tested for radar transmission loss under different sample structures, as shown in Table 4. As the content of aluminum pigment decreased, the radar transmission loss decreased accordingly. When the content of aluminum pigment decreased to 1.5 parts (No. 5), the effect on radar transmission loss was not obvious. When the content of aluminum pigment decreased to 1 part (No. 4), there was almost no effect on radar transmission loss. By comparing the samples of No. 1 and No. 2, the sample without any effect pigment had slightly higher radar transmission loss than the pure PP plate, which was due to the loss caused by the conductivity of the primer. In addition, by testing the samples of No. 9 and No. 10, it was found that the silver pearl pigment 9602 and OEM superfine opaque silver almost did not produce radar transmission loss, indicating that the use of such materials for the development of radar transmission coating was feasible.

[0085] Table 4

[0086] Comparative Examples 8-10

[0087] The present comparative examples provide the formulations of three silver-colored coatings, as shown in Table 5.

[0088] Table 5

[0089] The components of Comparative Example 5 were replaced with the components of Comparative Examples 8-10 to prepare the coatings according to the formulations of No. 8 in Table 4, and the brightness, goniochromicity, scintillation, and hiding power were tested. The effects of the effect pigments on the performance of the base A and base B were compared, and the results are shown in Table 6. By comparing the formulations of No. 11 and No. 13, it can be seen that the FI of the coating prepared with base B decreased, and the L15° decreased significantly, which was due to the poor arrangement of the aluminum pigment. Therefore, even with the same amount of base, the hiding power of the base B system will decrease, and the granularity and sparkle of the coating will also change, which may be caused by the non-parallel arrangement of the aluminum flakes. In the system provided by the present application, it was finally determined that the base A containing a high content of directional agent was used for subsequent experimental research.

[0090] Table 6

[0091] Examples 1-9

[0092] The present examples provide the formulations of nine silver-colored coatings, as shown in Table 7.

[0093] Table 7

[0094] The coating was prepared by replacing Comparative Example 5 with the components of Examples 1-9 in the scheme of No. 8 in Table 4 respectively, and the brightness, flop, sparkle, hiding power and radar transmission loss were tested, and the results are shown in Table 8.

[0095] Table 8 Note: Nos. 4, 8, 9 and 10 in Table 7 are control groups.

[0096] The results show that:

[0097] Comparative Example 5 is a formula sample containing 5 parts (5%) of aluminum pigment. From the results, it can be seen that it has excellent hiding power, brightness and sparkle performance, and in addition, the metal feeling of the naked eye appearance is the best. Comparative Example 1 is a formula sample with 1 part (1.04%) of aluminum pigment, compared with Comparative Example 5, the hiding power decreases significantly, the brightness decreases, and most importantly, the metal feeling of the naked eye appearance decreases, which is not as delicate and strong as Comparative Example 5. This may be because the aluminum pigment in the coating is already a discontinuous structure, and the decrease in hiding power can be clearly observed, and there are a large number of gaps. Although achieving radar transparency will cause a certain degree of loss of metal feeling, which is unavoidable, but if the naked eye can clearly observe the difference, it is difficult to meet the basic requirements of customers.

[0098] Comparative Examples 6 and 7 are two kinds of silver pearl pigments used in the examples of the present application, which are used to prepare samples without aluminum pigment. From the results, it can be seen that whether it is brightness, flop effect or hiding power, there is a big difference from Comparative Example 5, and the metal feeling is relatively low.

[0099] Examples 1-6 are samples prepared by using 4 parts of different types of silver pearl pigments and mixing 1 part of aluminum pigment. Compared with Comparative Example 1, the hiding power is significantly improved, the brightness of L45° is significantly improved, and the metal feeling of the naked eye appearance is significantly improved. Only the L15° is lower than that of Comparative Example 1, which may be because the silver pearl pigment covers the surface of the aluminum pigment, affecting the mirror reflection effect. In addition, the particle size of the silver pearl pigment has a regular influence on the results. Examples 4-6 show that the larger the particle size, the higher the L15° brightness, the higher the FI value, the lower the hiding power, and the better the sparkle effect. By adjusting the particle size used, products with corresponding indicators can be developed.

[0100] Examples 7-8 are samples adjusting the amount of aluminum pigment and silver pearl pigment, which are used to improve the problem of insufficient brightness of Examples 1-6. By reducing the amount of silver pearl pigment, it is found that the L15° is significantly improved, and the L45° brightness can still be maintained, only the hiding power decreases slightly. In terms of comprehensive performance, it is considered that Examples 7-8 are better examples.

[0101] Example 9 is a sample with further reduced aluminum pigment to 0.5 parts (0.5% by weight). From the test results of radar transmission loss, it can be seen that further reducing the amount of aluminum pigment has little effect on improving radar transmission loss, because 1 part (1% by weight) of aluminum pigment has almost no loss, and it is also found that the brightness, hiding power and other properties of example 9 are significantly decreased, and the appearance of the metal feeling is insufficient, which shows that a certain amount of aluminum pigment is necessary to obtain a metallic silver appearance.

[0102] In summary, under the premise of ensuring radar transparency, the performance of the silver and metallic appearance coating developed by the present application is still excellent.

[0103] Performance test 1

[0104] The cross-sectional structure SEM images of the coatings obtained in test numbers 19 and 21 are shown in Figures 2 and 3, respectively. It can be found that the flaky structure of the aluminum pigment and the silver pearl pigment is well arranged parallel to the coating. The coating of test number 21 contains less silver pearl pigment, so more gaps are found in the coating.

[0105] Performance test 2

[0106] The gloss and distinctness of the coatings obtained in test numbers 4, 8, 19 and 20 were tested, and the results are shown in Table 9. It can be seen from the results that the addition of silver pearl pigment has no effect on the gloss and distinctness of the coating.

[0107] Table 9

[0108] Obviously, the above examples of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description, and it is impossible to enumerate all the embodiments here. Any obvious changes or variations derived from the technical solutions of the present application are still within the protection scope of the present application.

Claims

1. A radar-transparent, high-gloss silver-colored coating, characterized in that The high-brightness silver coating comprises at least one aluminum pigment, the weight percentage of which is ≤1.5%; at least one silver-colored pearlescent pigment, the weight percentage of which is 0.5-4.0%; and a solvent-based base containing a high content of orientation agent; wherein the effective content of the orientation agent in the solvent-based base is >5% by weight.

2. The high brightness silver color coating according to claim 1, characterized in that, The silver-colored pearlescent pigment is selected from a flaky substrate containing iron oxide or titanium-iron oxide coating; The flaky substrate comprises one or more of mica flake, mica flake containing titanium oxide coating, aluminum oxide flake, titanium dioxide flake, glass flake.

3. The high brightness silver color coating according to claim 1, characterized in that, The D50 of the silver-colored pearlescent pigment is 5-30 μm, and the average thickness is 100-500 nm; The D50 of the aluminum pigment is 5-30 μm, and the solid content is 65-75%.

4. The high brightness silver color coating according to claim 1, characterized in that, The total weight percentage of the aluminum pigment and the silver-colored pearlescent pigment in the high-brightness silver coating is controlled to be 1.5-5.0%.

5. The high brightness silver color coating according to claim 4, characterized in that, The weight ratio of the aluminum pigment and the silver-colored pearlescent pigment is 1:0.5-4.

6. The high brightness silver color coating according to claim 1, wherein The dry film thickness of the high-brightness silver coating is 10-25 μm.

7. The process for producing a high-brightness silver-colored coating according to any one of claims 1 to 6, characterized in that, The steps include: preparing a solvent-based base and pre-dispersed aluminum pigment dispersion and silver-colored pearlescent pigment dispersion; adding the pre-dispersed aluminum pigment dispersion and silver-colored pearlescent pigment dispersion to the solvent-based base, mixing uniformly to obtain a radar-transparent silver-colored appearance coating; applying the silver-colored appearance coating to a plastic substrate and curing it, and the high-brightness silver coating is obtained.

8. Use of the high-brightness silver coating according to any one of claims 1-6 on a plastic substrate.

9. Use according to claim 8, characterized in that, The high-brightness silver coating is used on bumpers, plastic parts of automobiles, or plastic substrates of other intelligent devices.

10. Use according to claim 8, characterized in that, The L15° value of the high-brightness silver coating is above 125, preferably above 140, and more preferably above 145; the radar transmission loss increase value caused by the high-brightness silver coating is <0.5 dB.

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