A radar-transparent high-brightness silver coating and its preparation method and use

Abstract

The present invention discloses a radar-transparent high-brightness silver coating, its preparation method and use. The high-brightness silver coating comprises at least one aluminum pigment, the weight percentage of which is ≤1.5%; at least one silver pearlescent pigment, the weight percentage of which is 0.5-4.0%; and a solvent-based base material containing a high content of a directing agent; wherein the weight percentage of the effective content of the directing agent in the solvent-based base material is greater than 5%. The present invention adopts a low-addition amount of aluminum pigment in combination with a silver pearlescent pigment with high hiding performance, and prepares a radar-transparent high-brightness silver coating in a base material system with a high content of a directing agent. The increase in radar transmission loss caused by the silver coating is less than 0.5dB, and the optimal L15° is greater than 140. At the same time, it can also have excellent angular color change, scintillation, hiding power and a distinct metallic appearance. The silver coating is expected to be used in scenarios where a silver appearance is required and radar signal transparency is required.

Description

Technical Field

[0001] The present invention relates to the technical field of radar-transparent silver coatings, and more particularly to a radar-transparent high-brightness silver coating, a preparation method thereof, and uses thereof. Background Art

[0002] With the rapid development of autonomous driving technology, the use of millimeter-wave radar (frequency 77-81GHz) is becoming increasingly common. Every car or machine with autonomous driving functions is equipped with several radars, generally placed behind the bumper or corresponding components. Coatings that do not contain metal components do not interfere with radar signals. However, metallic-effect coatings with a silver appearance containing aluminum pigments significantly affect radar signal penetration due to aluminum's high electrical conductivity and densely stacked layered structure, with losses reaching over 3dB, posing a challenge to radar system recognition.

[0003] Silver pearlescent pigments based on mica or aluminum oxide substrates with special coatings are another type of pigment that can achieve high brightness, angular color change, and a shimmering effect. CN103459515A discloses a pearlescent effect pigment with high hiding power and a metallic appearance, a high-gloss silver appearance. This pigment is coated with a coating containing ilmenite on the surface of a non-metallic flaky substrate. Through optimized formulations and process technologies, the pigment has excellent angular color change, brightness, and shimmering effects, and a silver appearance similar to silver powder. CN1784476A discloses an interference pigment with high hiding power. This pigment is also coated with a layer containing ilmenite on a thin flaky inorganic substrate. This improves the low hiding power of conventional pearlescent pigments and achieves a silvery or silver metallic appearance. However, compared to aluminum pigments, these products still have the disadvantages of low hiding power and insufficient metallic feel. Currently, aluminum pigments cannot be completely replaced by pearlescent pigments. However, the dielectric properties possessed by this inorganic oxide are not possessed by aluminum pigments.

[0004] CN116018291A discloses a radar-compatible coating containing metallic effect pigments. This technical solution utilizes a two-layer stacked structure: one layer contains no metallic effect pigments, and the other contains metallic effect pigments. Radar transmittance is improved by reducing the thickness of the metallic pigment coating. However, this technical solution still suffers from radar loss caused by the densely packed aluminum pigments in the metallic coating. Furthermore, the two-layer structure is complex to manufacture, making it difficult to implement. Furthermore, the impact on properties such as hiding power and hue is not disclosed. CN114222798A discloses a radar-transmissive coating composition that uses radar-transmissive pigments in place of metallic aluminum pigments. Using at least 50% of the transmissive pigments, the coating achieves reduced loss. However, this design offers limited technical benefits, with the minimum loss limited to above 1.11 dB. Furthermore, the coating suffers from insufficient brightness, and its impact on key properties such as scintillation and hiding power is not disclosed.

[0005] In summary, even if a compatible system of silver pearlescent pigments and aluminum pigments is used in the current existing technology, it is impossible to achieve a good balance between low radar transmission loss and high brightness. The results presented are generally mediocre. It is urgent to develop a more effective technical solution to improve the compatibility problem between radar transmission loss and high brightness. Summary of the Invention

[0006] To solve the above problems, a first object of the present invention is to provide a radar transparent high-brightness silver coating.

[0007] The second object of the present invention is to provide a method for preparing the high-brightness silver coating as described above.

[0008] The third object of the present invention is to provide a use of the high-brightness silver coating as described above applied to a plastic substrate.

[0009] In order to achieve the above first purpose, the present invention adopts the following technical solutions:

[0010] The present invention discloses a radar transparent high brightness silver coating, the high brightness silver coating comprising

[0011] At least one aluminum pigment, the weight percentage of which is ≤1.5%;

[0012] At least one silver pearlescent pigment, the weight percentage of which is 0.5-4.0%; and

[0013] Solvent-based binders with high directing agent content;

[0014] Wherein, the effective content of the directing agent in the solvent-based base material is greater than 5% by weight.

[0015] Furthermore, the silver pearlescent pigment is selected from a flaky substrate wrapped with iron oxide or titanium iron oxide;

[0016] The flaky substrate comprises one or more of mica flakes, mica flakes coated with titanium oxide, aluminum oxide flakes, titanium dioxide flakes, and glass flakes.

[0017] Furthermore, the silver pearlescent pigment has a D50 of 5-30 μm and an average thickness of 100-500 nm;

[0018] The aluminum pigment has a D50 of 5-30 μm and a solid content of 65-75%.

[0019] Furthermore, the total weight percentage of the aluminum pigment and the silver pearlescent pigment in the high-brightness silver coating is controlled to be 1.5-5.0%.

[0020] Furthermore, the weight ratio of the aluminum pigment to the silver pearlescent pigment is 1:0.5-4.

[0021] Furthermore, the dry film thickness of the high-brightness silver coating is 10-25 μm.

[0022] In order to achieve the above second purpose, the present invention adopts the following technical solutions:

[0023] The present invention discloses a method for preparing the high-brightness silver coating as described above, comprising the following steps:

[0024] Formulate solvent-based binders and pre-dispersed aluminum pigment dispersions and silver pearlescent pigment dispersions;

[0025] Adding pre-dispersed aluminum pigment dispersion and silver pearlescent pigment dispersion to the solvent-based base material and mixing them evenly to obtain a radar-transparent silver appearance coating;

[0026] The silver appearance paint is applied to the plastic substrate and allowed to cure.

[0027] In order to achieve the third object, the present invention adopts the following technical solutions:

[0028] The present invention discloses the use of a high brightness silver coating as described above applied to a plastic substrate.

[0029] Furthermore, the high-brightness silver coating is used on bumpers, automotive plastic parts, or plastic substrates of other smart devices.

[0030] Furthermore, the L15° value of the high-brightness silver coating is greater than 125, preferably greater than 140, and more preferably greater than 145;

[0031] When the high-brightness silver coating is applied on a plastic substrate, the radar transmission loss increase caused by the high-brightness silver coating is less than 0.5 dB.

[0032] The beneficial effects of the present invention are as follows:

[0033] The present invention combines a low-aluminum pigment with a specific silver pearlescent pigment to reduce radar transmission loss. Combined with a solvent-based binder containing a high content of a directing agent, the flaky effect pigments are fully aligned, resulting in a silver coating with high brightness, excellent angular color variability, scintillation, hiding power, and a distinct metallic appearance. This silver coating is expected to be used in applications that require a silver appearance while also being transparent to radar signals.

[0034] The silver pearlescent pigment selected in the present invention is a flaky base pigment coated with iron oxide or titanium iron oxide. It is a pearlescent pigment with high hiding power and silver appearance coated with ilmenite components. It is a new type of pearlescent product with angular color variation, high brightness and shimmering effect similar to aluminum pigment, which can compensate for the impact of low aluminum content pigment to a certain extent.

[0035] The present invention controls the total amount of aluminum pigment and silver pearlescent pigment added and the ratio between the two. On the one hand, it implicitly specifies the content of the solvent-based binder, and further specifies the content of the orienting agent, so that sufficient arrangement of the flake effect pigments is ensured. On the other hand, the ratio between the amount of aluminum pigment and silver pearlescent pigment makes it easier to obtain high brightness, excellent angular color change, sparkle, hiding power and a distinct metallic appearance.

[0036] The high-brightness silver coating provided by the present invention achieves excellent hiding power at a relatively thin dry film thickness (10-25 μm). When applied to a plastic substrate, the increased radar transmission loss caused by the high-brightness silver coating is less than 0.5 dB, significantly reducing radar transmission loss. Furthermore, the high-brightness silver coating is simple to prepare, eliminating the need for a double-layer stacking structure as reported in prior art, making it more feasible. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0038] Figure 1 A technical schematic diagram of the present invention in improving radar transparency is shown, wherein Figure 1 A is a coating formed by traditional metallic effect pigments, and B is a coating obtained by using the silver appearance coating of the present invention.

[0039] Figure 2 A cross-sectional SEM image of the high-brightness silver coating prepared in Example 6 of the present invention is shown.

[0040] Figure 3 A cross-sectional SEM image of the high-brightness silver coating prepared in Example 8 of the present invention is shown. DETAILED DESCRIPTION

[0041] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the following detailed description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0042] As used herein, unless otherwise indicated, the term "parts" refers to parts by weight.

[0043] Currently, radars placed behind bumpers or other plastic automotive parts typically operate at frequencies of 24 GHz or 77-81 GHz. Radars in the 77-81 GHz band are the most commonly used due to their small size, strong anti-interference capabilities, and regulatory approval. Because their wavelengths fall within the millimeter wave band of 1-10 mm, they are referred to as millimeter-wave radars. Millimeter-wave radars have strong penetrating power and can identify targets through plastic substrates (such as polypropylene and polycarbonate). However, as electromagnetic waves, millimeter-wave radars lack sufficient energy to penetrate metal media. For good conductors like aluminum, the penetration depth of millimeter-wave radars is only a few hundred nanometers. Figure 1 Medium A, an aluminum-effect coating commonly used in the automotive field, generally contains about 1-6wt% of aluminum pigment. The higher the content, the more the aluminum powder tends to form a dense, continuous structure of flakes, and the multiple layers are superimposed, resulting in greater loss of millimeter waves when penetrating such a coating.

[0044] Aluminum pigments are flaky effect pigments obtained by grinding, typically 5-50μm in size and hundreds of nanometers thick. Their surface is typically coated with various additives added during grinding, such as oleic acid. Aluminum pigments commonly used in automotive applications are silver-dollar-like products with a size of 10-25μm. They offer high brightness, a delicate and intense metallic appearance, and unique properties that make them difficult to replace. The indispensability of aluminum pigments is in conflict with the need for improved radar transmittance. However, the promotion and use of silver pearlescent pigments has opened up new possibilities for the development of silver-look coatings.

[0045] Pearlescent effect pigments are produced by coating a specific effect layer on the surface of an inorganic oxide flaky substrate. The coating typically has a high refractive index, which interferes with the underlying substrate, creating a specific effect. Pearlescent effect pigments include a wide variety of products, available in various colors, sizes, and effects. They are widely used in various fields, such as cosmetics, automotive, home appliances, and industrial equipment. Pearlescent effect pigments offer similar angular color shift, high brightness, and a shimmering effect to aluminum pigments, but their hiding power is significantly lower. Using silver pearlescent pigments alone can produce an unsatisfactory metallic effect.

[0046] In order to better obtain a silver appearance coating with low radar transmission loss and high brightness, silver pearlescent pigments and aluminum pigments can be compounded. Based on this idea, there are two specific solutions: the first solution is to design the aluminum pigment and the silver pearlescent pigment according to a double-layer structure, which does not affect each other. Its advantage is mainly reflected in the fact that the arrangement of the two types of flake effect pigments does not affect each other. However, the double-layer structure design will increase the complexity of the preparation process and is not conducive to construction. The second solution is to design the silver pearlescent pigment and the aluminum pigment according to a single-layer structure, that is, to mix the silver pearlescent pigment and the aluminum pigment into a uniform pigment. At this time, it is necessary to strictly control the amount of the two. It is necessary to reduce the influence of the arrangement of the two types of flake effect pigments and control the amount of aluminum pigment to reduce radar transmission loss. It is also necessary to consider the maintenance of multiple performance aspects such as brightness, angular color, scintillation effect, metallic feel and hiding power. However, it is actually very difficult to take all of them into account. Even obtaining a relatively balanced effect is very difficult for technicians.

[0047] On the basis of the second solution, in order to maintain the brightness and hiding power, technicians usually do not reduce the aluminum pigment too low, and its content is controlled at least above 2%, which is already the lower limit for technicians to develop aluminum pigment formulas. If the coating pursues radar transparency, that is, the radar loss caused by the coating is increased by less than 1dB, since technicians usually intuitively believe that as long as aluminum pigment is added, it will cause obvious radar loss and the radar transparency effect cannot be achieved, they generally directly develop single silver pearlescent pigments to completely replace aluminum pigments, or maintain the aluminum pigment content above the lower limit of 2% to develop a composite formula of silver pearlescent pigments and aluminum pigments. They will not try to continue to reduce the aluminum pigment content to develop a composite formula. This has become the inertial thinking of technicians. However, surprisingly, the inventors found that based on the coating system of the present invention, when a lower content of aluminum pigment (≤1.5%) is selected, there is almost no radar loss. On this basis, the present invention uses a combination of aluminum pigments and silver pearlescent pigments, see Figure 1 In B, a radar-transparent high-brightness silver coating is provided. The black oval represents aluminum pigment and the white oval represents silver pearlescent pigment. The combination of the two reduces radar penetration loss. The high-brightness silver coating contains

[0048] At least one aluminum pigment, the weight percentage of which is ≤1.5%;

[0049] At least one silver pearlescent pigment, the weight percentage of which is 0.5-4.0%; and

[0050] Solvent-based binders with high directing agent content;

[0051] Wherein, the effective content of the directing agent in the solvent-based base material is greater than 5% by weight.

[0052] The use of aluminum pigment mainly ensures the metallic texture of the coating, which is irreplaceable by pearlescent pigments at this stage. However, considering the loss effect of aluminum pigment on radar transmittance, the weight percentage of aluminum pigment is controlled below 1.0% in the present invention. Due to the influence of the added amount, the radar loss caused by the low content of aluminum pigment is significantly reduced.

[0053] In one embodiment, the aluminum pigment has a D50 of 5-30 μm and a solids content of 65-75%. The aluminum pigment includes a silver dollar-shaped, corn flake-shaped, or other suitable shapes. Commonly used aluminum pigment suppliers for automotive applications include Toyo Aluminum, Star Platinum, and Zuxing. For example, Toyo Aluminum's 4660NS (D50 of 9 μm) is used in this embodiment. 4660NS offers a delicate metallic feel, a high-brightness appearance, and excellent angular color shift, making it a representative product for automotive applications.

[0054] Furthermore, the weight percentage of the aluminum pigment in the high-brightness silver coating is ≤1.1%. Experiments have found that the radar loss caused by the aluminum pigment at this addition amount is basically negligible.

[0055] In order to eliminate the appearance problems such as brightness reduction caused by low content of aluminum pigment, the silver pearlescent pigment selected in the present invention is a flaky base pigment coated with iron oxide or titanium iron oxide. The flaky base pigment includes one or more of mica flakes, mica flakes coated with titanium oxide, aluminum oxide flakes, aluminum oxide flakes coated with titanium oxide, titanium dioxide flakes, titanium dioxide flakes coated with titanium oxide, glass flakes, and glass flakes coated with titanium oxide. The D50 of the silver pearlescent pigment is 5-30μm and the average thickness is 100-500nm. The pearlescent pigment with high hiding and silver appearance coated with ilmenite component is a new type of pearlescent product with angular color variation, high brightness and sparkling effect similar to aluminum pigment. The main suppliers of the silver pearlescent pigment include Merck, Aika, Global New Materials and Kuncai Technology. In one embodiment, the silver pearlescent pigment is selected from Merck's iriodin series 9602 (D50 of 15 μm), 9605 (D50 of 23 μm), and 9612 (D50 <15 μm), and Aika's OEM opaque silver series superfine (D50 of 13 μm), fine (D50 of 18 μm), and medium (D50 of 23 μm). However, these products still do not effectively solve the hiding power problem caused by low aluminum content.

[0056] Furthermore, the total weight percentage of the aluminum pigment and the silver pearlescent pigment in the high-brightness silver coating is controlled at 1.5-5.0%. For example, the total weight percentage of the aluminum pigment and the silver pearlescent pigment in the high-brightness silver coating can be 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0057] Furthermore, the weight ratio of the aluminum pigment to the silver pearlescent pigment is 1:0.5-4. Exemplarily, the weight ratio of the aluminum pigment to the silver pearlescent pigment 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 pigment to the silver pearlescent pigment is 1:1-2, it has higher brightness and lower radar transmission loss.

[0058] Brightness is represented by the L15° value near the reflection angle, and the L15° value for the high brightness silver coating is at least above 125.

[0059] Directing agents are a type of rheological additive that must be added to coating systems for flake effect pigments. Commonly used directing agents include, but are not limited to, polyethylene wax, polyamide wax, ethylene vinyl acetate wax, cellulose butyl acetate, and silicates. Their principle is to increase the viscosity and thixotropy of the coating system, enhance dispersion, prevent the flake effect pigments from settling, and support the flake effect pigments in their proper alignment during drying. Generally, approximately 1-5 wt% of directing agent is added to the coating system. To compensate for the poor hiding power of low-content aluminum pigments and silver pearlescent pigments, the effective directing agent content in the silver coating system of the present invention is increased to >5% by weight. This facilitates the proper alignment of the flake effect pigments, achieving high brightness and hiding power. The amount of directing agent used can be further adjusted based on the specific binder system. For example, the effective directing agent content in a solvent-based binder can be controlled to above 6%, 7%, 8%, 9%, 10%, 11%, 12%, or 13% by weight.

[0060] The high-brightness silver coating obtained by the present invention is relatively thin, with a dry film thickness of 10-25 μm, preferably 10-20 μm. Without the high content of a directing agent, the coating system of the present invention cannot achieve good hiding power when applied in thinner coatings using low levels of aluminum pigment. In one embodiment, the directing agent is selected from one or more of Eastman's CAB 531-1, Kusumoto Chemical's DISPARLON 4200-10 (active ingredient 10 wt%), and BYK's CERAFAK 103. Eastman CAB 531-1 is a cellulose butyl acetate with a higher butyryl content than Eastman CAB 381 cellulose ester. Combining cellulose butyl acetate with thermoplastic acrylic resins produces tough films with excellent scratch and weather resistance. Eastman CAB 531-1 and Eastman CAB 381 have similar hydroxyl content and solubility characteristics, making them soluble in a wide range of solvents. Eastman CAB 531-1 is a softer resin, requiring less plasticizer modification than Eastman CAB 381 esters. DISPARLON 4200-10 is a non-soluble, paste-like, swellable dispersion based on a dispersible oxidized polyethylene wax. It has a minimal effect on coating viscosity and is not easily affected by pigment or vehicle. It can be used as an anti-settling agent for nearly all pigment dispersions. It reacts with pigments and fillers in the coating to produce a stable colloidal structure, imparting excellent thixotropic properties to the coating, thereby preventing pigment settling and also preventing sag. CERAFAK 103 is a dispersion of ethylene acrylic acid copolymer wax suitable for solvent-based effect coating systems. It can improve the orientation effect of effect pigments and reduce in-can sedimentation.

[0061] The solvent-based binder also typically contains an acrylic resin, a solvent, and a dispersant. In one embodiment, the acrylic resin is selected from solvent-based acrylic resins, such as DIC's ACRYDIC ZHL-1063 and ACRYDIC WML-350, and constitutes 15% by weight of the solvent-based binder. The solvent is selected from xylene, ethyl acetate, and isobutanol. The oriented butyl acetate cellulose agent must be pre-dispersed in ethyl acetate and isobutanol to obtain a dispersion for use. The dispersant is selected from BYK-192. Because the other materials in the solvent-based binder, besides the oriented agent, have a minimal impact on radar transmission loss, those skilled in the art can interchange the products used in the examples, while maintaining the coating's basic properties. The resulting silver coatings exhibit substantially equivalent increases in radar transmission loss.

[0062] The high-brightness silver coating developed in the present invention is obtained based on a solvent-based coating system, and can exhibit low radar loss, high brightness, and excellent angular color variation, hiding power, and sparkling effects. However, in the current development of water-based systems, due to poor arrangement of aluminum pigments, low hiding power and very low brightness, the technical effect is not obvious.

[0063] The present invention also provides a method for preparing the high-brightness silver coating as described above, comprising the following steps:

[0064] Formulate solvent-based binders and pre-dispersed aluminum pigment dispersions and silver pearlescent pigment dispersions;

[0065] Adding pre-dispersed aluminum pigment dispersion and silver pearlescent pigment dispersion to the solvent-based base material and mixing them evenly to obtain a radar-transparent silver appearance coating;

[0066] The silver appearance paint is applied to the plastic substrate containing the primer and allowed to cure.

[0067] Furthermore, the curing condition is baking at 60-80° C. for 20-30 minutes.

[0068] Furthermore, the thickness of the primer is 10-15 μm. The present invention further comprises a varnish layer coated on the high-brightness silver coating, and the thickness of the varnish layer is 30-40 μm.

[0069] The present invention also provides a use of the high-brightness silver coating as described above applied on a plastic substrate.

[0070] Furthermore, the high-brightness silver coating is used on bumpers, automotive plastic parts, or plastic substrates of other smart devices.

[0071] Furthermore, the L15° value of the high-brightness silver coating is greater than 125, preferably greater than 140, and more preferably greater than 145;

[0072] When the high-brightness silver coating is applied to a plastic substrate, the increase in radar transmission loss caused by the high-brightness silver coating is less than 0.5 dB. In the present invention, the increase in radar transmission loss refers to the difference in radar transmission loss caused by the addition of aluminum pigment and silver pearlescent pigment to the high-brightness silver coating compared to the addition of the aluminum pigment and silver pearlescent pigment.

[0073] The following will be further explained in conjunction with the following specific plans.

[0074] Solvent-based binders

[0075] The formulation of the solvent-based binder containing a high content of directing agent is equally important for achieving the technical effects of the present invention. To illustrate the effect of a high content of directing agent, the present invention prepared two solvent-based binders for comparative analysis: Base A and Base B. Base A is a formulation containing a high content of directing agent, while Base B is a formulation containing a low content of directing agent.

[0076] Table 1 Solvent-based base material formula

[0077]

[0078]

[0079] Note: CAB 531-1 dispersion was prepared by dispersing CAB 531-1 in isobutanol and butyl acetate.

[0080] Coating requirements

[0081] 3mm thick PP panels (black, 150 x 200mm) were sprayed (using an ecogun sprayer) with Flex700 primer (Nippon Paint), the color paints from the examples and comparative examples, and Flex200 / AP2000 clearcoat (Nippon Paint) in the thicknesses shown in Table 2. The panels were then placed flat in an oven and baked at 80°C for 30 minutes. The following performance tests were then conducted: optical performance was tested using a BYK-MAC tester, and radar transmission loss was tested using a Rohde & Schwarz QAR device.

[0082] Table 2 Summary of coating information

[0083] coating Dry film thickness Flex700 Primer 10μm Silver appearance coating of the embodiment or comparative example of the present invention 20μm Flex200 / AP2000 varnish 35μm

[0084] Comparative Examples 1-7

[0085] This group of comparative examples provides 7 formulas of silver appearance coatings. The specific formulas are shown in Table 3.

[0086] Table 3

[0087]

[0088] Using the formula provided in Table 3 and referring to the sample structures in Table 4, radar transmission loss was then tested for different sample structures. Table 4 shows that radar transmission loss decreases with decreasing aluminum pigment content. When the aluminum pigment content is reduced to 1.5 parts (No. 5), the effect on radar transmission loss is no longer significant. When it is further reduced to 1 part (No. 4), the effect is almost negligible. Comparing samples No. 1 and No. 2, the sample without any effect pigment has slightly higher radar transmission loss than the pure PP board. This is due to losses caused by the conductivity of the primer. Furthermore, testing of samples No. 9 and No. 10 revealed that silver pearlescent pigment 9602 and OEM superfine opaque silver produce almost no radar transmission loss, demonstrating the feasibility of using these materials in the development of radar-transparent coatings.

[0089] Table 4

[0090] Serial number Sample structure Radar penetration loss / dB 1 PP board 0.88 2 PP board + FLEX700 primer 1.01 3 PP board + FLEX700 primer + base material A + FLEX200 varnish 0.99 4 PP board + FLEX700 primer + comparative example 1 + FLEX200 varnish 1.04 5 PP board + FLEX700 primer + comparative example 2 + FLEX200 varnish 1.22 6 PP board + FLEX700 primer + comparative example 3 + FLEX200 varnish 1.76 7 PP board + FLEX700 primer + comparative example 4 + FLEX200 varnish 3.2 8 PP board + FLEX700 primer + comparative example 5 + FLEX200 varnish 4.4 9 PP board + FLEX700 primer + comparative example 6 + FLEX200 varnish 0.99 10 PP board + FLEX700 primer + comparative example 7 + FLEX200 varnish 1.08

[0091] Comparative Examples 8-10

[0092] This group of comparative examples provides three formulas for silver exterior coatings. For specific formulas, see Table 5.

[0093] Table 5

[0094] Components Comparative Example 8 / part Comparative Example 9 / part Comparative Example 10 / part Base A 60 / / Base material B / 60 60 Butyl acetate 35 35 35 4660NS 2.5 5 2.5 OEM medium opaque silver 2.5 / 2.5

[0095] Referring to the solution with sequence number 8 in Table 4, the coating was prepared by replacing the components of Comparative Example 5 with those of Comparative Examples 8-10. The coatings were then tested for brightness, angular color variability, sparkle, and hiding power, and the effects of base materials A and B on the performance of the effect pigments were compared. The results are shown in Table 6. A comparison of the solutions with sequence numbers 11 and 13 shows that due to the addition of less directing agent, the FI of the coating decreased, and L15° was significantly reduced. This is due to the poor alignment of the aluminum pigment. Therefore, even with the same amount of base material added, the hiding power of the base material B system decreased. Furthermore, the granularity and sparkle of the coating also changed, likely due to the aluminum flakes not being arranged in parallel and forming an angle. Under the system provided by the present invention, base material A, which contained a high content of directing agent, was ultimately selected for subsequent experimental studies.

[0096] Table 6

[0097]

[0098]

[0099] Examples 1-9

[0100] This group of examples provides 9 formulas for silver appearance coatings. See Table 7 for specific formulas.

[0101] Table 7

[0102]

[0103] Referring to the solution No. 8 in Table 4, the components of Comparative Example 5 were replaced with those of Examples 1-9 to complete the preparation of the coating, and the brightness, angular heterochromaticity, scintillation, hiding power and radar transmission loss were tested. The results are shown in Table 8.

[0104] Table 8

[0105]

[0106] Note: No. 4, 8, 9, and 10 in Table 7 serve as the control group.

[0107] Result description:

[0108] 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 scintillation performance. In addition, the metallic feel of the naked eye is the best. Comparative Example 1 is a formula sample with the aluminum pigment dosage reduced to 1 part (1.04%). Compared with Comparative Example 5, the hiding power is significantly reduced, the brightness is reduced, and the most important thing is that the metallic feel of the naked eye is reduced. It is not as delicate and strong as Comparative Example 5. This may be because the aluminum pigment is already a discontinuous structure in the coating, and the decline in hiding power can be clearly found, and there are a lot of gaps. Although achieving the effect of radar transparency will cause a certain degree of loss of metallic feel, which is unavoidable, if the difference can be clearly observed by the naked eye, it will be difficult to meet the basic requirements of customers.

[0109] Comparative Examples 6 and 7 were prepared using two silver pearlescent pigments used in the examples of the present invention to prepare samples without aluminum pigment. The results show significant differences in brightness, angular flop, and hiding power compared to Comparative Example 5, with a relatively low metallic feel.

[0110] Examples 1-6 were prepared using four parts of silver pearlescent pigment of different types mixed with one part of aluminum pigment. Compared to Comparative Example 1, their hiding power was significantly improved, and the brightness at L45° was significantly increased, significantly improving the metallic appearance to the naked eye. However, L15° was lower than Comparative Example 1, likely due to the silver pearlescent pigment coating the aluminum pigment surface, which affected the specular reflection effect. Furthermore, the particle size of the silver pearlescent pigment had a regular effect on the results. Examples 4-6 show that larger particle size increases L15° brightness, improves FI value, slightly reduces hiding power, and improves the shimmering effect. By adjusting the particle size used, it is possible to develop products with corresponding performance indicators.

[0111] Examples 7-8, which adjust the dosage of aluminum pigment and silver pearlescent pigment, were used to improve the insufficient brightness of Examples 1-6. By reducing the amount of silver pearlescent pigment, L15° was significantly improved, while L45° brightness was maintained, with only a slight decrease in hiding power. Based on overall performance, Examples 7-8 are considered superior.

[0112] Example 9 further reduces the aluminum pigment content to 0.5 parts (0.5%). Radar transmission loss test results show that further reducing the aluminum pigment content has little effect on improving radar transmission loss, as 1 part (1%) of aluminum pigment already results in almost no loss. Furthermore, Example 9 exhibits significant declines in brightness, hiding power, and other properties, and the metallic appearance is also lacking, indicating that a certain amount of aluminum pigment is necessary to achieve a metallic silver appearance.

[0113] In summary, while ensuring radar transparency, the performance of the silver, metallic-looking coating developed by the present invention is still excellent.

[0114] Performance Test 1

[0115] The cross-sectional SEM images of the coatings obtained from test numbers 19 and 21 are shown in Figure 2 and Figure 3 It can be found that the flake structures of the aluminum pigment and the silver pearlescent pigment are well arranged parallel to the coating. Since the coating No. 21 contains less silver pearlescent pigment, more gaps are found in the coating.

[0116] Performance Test 2

[0117] The glossiness and distinctness of image indexes of the coatings obtained from Nos. 4, 8, 19 and 20 were tested. The results are shown in Table 9. From the results, it can be seen that the addition of silver pearlescent pigment has no effect on the glossiness and distinctness of image indexes of the coatings.

[0118] Table 9

[0119]

[0120]

[0121] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A radar-transparent, high-brightness silver 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 pearlescent pigment, the weight percentage of which is 0.5-4.0%; as well as Solvent-based binders with high directing agent content; Wherein, the weight percentage of the effective content of the directing agent in the solvent-based base material is greater than 5%; The silver pearlescent pigment is selected from a flaky substrate wrapped with titanium iron oxide; The flaky substrate comprises one or more of mica flakes, aluminum oxide flakes, titanium dioxide flakes, and glass flakes; The silver pearlescent pigment has a D50 of 5-30 μm and an average thickness of 100-500 nm; The aluminum pigment has a D50 of 5-30 μm and a solid content of 65-75%; The total weight percentage of the aluminum pigment and the silver pearlescent pigment in the high-brightness silver coating is controlled to be 1.5-5.0%; The weight ratio of the aluminum pigment to the silver pearlescent pigment is 1:0.5-4.

2. The high-brightness silver coating according to claim 1, characterized in that The dry film thickness of the high-brightness silver coating is 10-25 μm.

3. The method for preparing a high-brightness silver coating according to any one of claims 1 to 2, characterized in that: The steps include: Formulate solvent-based binders and pre-dispersed aluminum pigment dispersions and silver pearlescent pigment dispersions; Adding pre-dispersed aluminum pigment dispersion and silver pearlescent pigment dispersion to the solvent-based base material and mixing them evenly to obtain a radar-transparent silver appearance coating; The silver appearance paint is applied to the plastic substrate and allowed to cure.

4. Use of the high-brightness silver coating according to any one of claims 1 to 2 applied on a plastic substrate.

5. The use according to claim 4, characterized in that The high-brightness silver coating is used on automobile plastic parts or plastic substrates of other smart devices.

6. The use according to claim 4, characterized in that The L15° value of the high-brightness silver coating is greater than 125; The increase in radar transmission loss due to the high brightness silver coating is less than 0.5 dB.

7. The use according to claim 4, characterized in that The L15° value of the high-brightness silver coating is above 140.

8. The use according to claim 4, characterized in that The L15° value of the high-brightness silver coating is above 145.

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