Patent Description:
Radar is used in motor vehicles to detect objects for a variety of purposes, such as autonomous driving, adaptive cruise control, blind spot detection, automatic braking, and other advanced driver assistance systems. The radar sensor is typically mounted behind a component of the motor vehicle, typically a bumper or vehicle panel, so the component covers the radar device. In this regard, the radar signal must penetrate the bumper when traveling to an object to be detected, and then penetrate the bumper again when reflected off of the object and returning to the vehicle. The bumper, including any coatings applied to the surface of the bumper, can transmit, reflect, or absorb radar. Any reflection or absorption of the radar signal limits the effective detection range of the radar. For the radar to be useful for automatic braking or other advanced or autonomous driving features, the effective range of the radar must be at least as far as the braking distance of the vehicle at the driving speed.

If the component, e.g., the bumper or vehicle panel, behind which the radar is mounted is metal, the effective range of the radar is zero, so the components utilized are typically plastic or other non-metallic materials. The component includes the substrate, but also typically includes a coating overlying the substrate. Motor vehicle coatings typically include a basecoat, and often also include a primer coat and/or a clearcoat, with an interface between each layer. The radar typically used in motor vehicles for detecting objects is <NUM> giga hertz (GHz) band radar, which describes a category of radar that includes frequencies from about <NUM> to <NUM> (e.g., W Band).

<CIT> describes a method of forming a microstructured pigment flake, which method comprises: providing a microstructured dielectric core to a fluidized bed and encapsulating the microstructured dielectric core by chemical vapor deposition while in the fluidized bed so as to form an encapsulation layer encapsulating the microstructured dielectric core.

<CIT> discloses a multilayer material with an odd number (N) of layers, said multilayer material more specifically comprising at least three layers wherein each layer consists of a material A or of a material B different from A, said successive layers A and B being alternated and two adjacent layers having different refractive indices.

The transmission of radar through a typical bumper substrate and the coating layers thereon is therefore important for the effective operation of many vehicle radar systems. Further, many vehicle exterior coating or paint systems include ingredients that provide an aesthetically desirable appearance. For example, many coating systems use special effect ingredients, such as metallic effect ingredients or the like, to enhance the aesthetic appearance of the paint. Unfortunately, some of these ingredients can confound a radar system's functionality when applied to a component substrate, such as, for example, a plastic bumper substrate or the like, because these ingredients are not radar compatible (e.g., not substantially transparent or transmissive to radar signals) as they substantially reflect and/or absorb radar signals, thereby limiting or blocking transmission of the radar through the component panel.

Accordingly, it is desirable to provide special effect ingredients for radar compatible coatings that, for example, can be applied onto a component substrate to provide an aesthetic appearance while being substantially transmissive to radar. Furthermore, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with this background.

Dielectric pigments having a metallic appearance for radar compatible coatings and methods for making such dielectric pigments are provided herein. The dielectric pigment includes a flake. The flake has a thickness of from <NUM> to <NUM> and includes a plurality of alternating layers of dielectric materials including a first layer formed of a first dielectric material having a first refractive index in the visible spectrum range and a second layer disposed adjacent to the first dielectric layer and formed of a second dielectric material having a second refractive index in the visible spectrum range that is different than the first refractive index.

The method for making dielectric pigments as defined hereinabove and in the appended claims includes forming a plurality of alternating layers of dielectric materials overlying a substrate. Forming the plurality of alternating layers of dielectric material includes depositing a first layer of a first dielectric material overlying the substrate. The first dielectric material has a first refractive index in the visible spectrum range. A second layer of a second dielectric material is deposited overlying the first layer. The second dielectric material has a second refractive index in the visible spectrum range that is different than the first refractive index. The method further includes removing the substrate from the plurality of alternating layers of dielectric materials and breaking, crushing, and/or grinding the plurality of alternating layers into flakes to form the dielectric pigments.

The radar compatible coating includes one or more resins. Dielectric pigments are incorporated into the one or more resins and have a metallic appearance. Each of the dielectric pigments includes a flake a thickness of from <NUM> to <NUM>. The flake includes a plurality of alternating layers of dielectric materials including a first layer formed of a first dielectric material having a first refractive index in the visible spectrum range and a second layer disposed adjacent to the first dielectric layer and formed of a second dielectric material having a second refractive index in the visible spectrum range that is different than the first refractive index. Optionally, the radar compatible coating further includes one or more additives, one or more promoters, one or more curing agents, a water and/or solvent-based carrier, one or more colorants, one or more pigments, or combinations thereof.

The following detailed description is merely exemplary in nature and is not intended to limit the various embodiments or the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

A vehicle "component," as used herein, includes a plastic or polymeric substrate with an overlying coating. The term "overlying," as used herein, means the overlying material may be physically touching the underlying substrate, or the overlying material may be physically separated from the underlying substrate by an intervening material, such as an overlying layer that may be separated from an underlying substrate by another layer. It is understood that a component may be rotated or moved, so reference to one component overlying another refers to a particular orientation, with the understanding that the actual component may be rotated into a different orientation. The term "vehicle," as used herein, refers to a motor vehicle, such as a car, truck, airplane, or other device propelled through space with a motor or engine. The term vehicle includes vehicles propelled by a motor burning fuel for power, and a vehicle propelled by an engine using electricity. The overlying coating of the component includes one or more of a primer, a basecoat, and a clearcoat.

Various embodiments contemplated herein relate to dielectric pigments having a metallic appearance for a radar compatible coating that, for example, can be applied onto a component substrate to provide an aesthetic appearance while being substantially transmissive to radar. As used herein, the term "radar compatible" is understood to mean substantially transparent or transmissive to radar signals with relatively low (e.g., radar signal loss is less than about <NUM>%, or <NUM> dB) or no transmission loss of the radar signal while traveling through the designated medium.

Referring to <FIG>, a cross-sectional view of a radar compatible coating <NUM> that includes dielectric pigments <NUM> incorporated therein in accordance with an exemplary embodiment is provided. The radar compatible coating <NUM> is disposed on a substrate <NUM>. The substrate <NUM> may be a part, a component such as a vehicle body or trim panel, for example, a bumper fascia, skin, or trim portion.

In an exemplary embodiment, the radar compatible coating <NUM> is a paint or coating composition that is applied to the substrate <NUM> in an uncured or wet state and that is subsequently cured and/or dried. Paint formulation may be, for example, a primer formulation, a sealer formulation, a basecoat formulation, a clearcoat formulation, a topcoat formulation, and/or a tinted coat formulation. In an exemplary embodiment, the radar compatible coating <NUM> is a basecoat.

The radar compatible coating <NUM> includes a paint or resin matrix <NUM>. Non-limiting examples of resins that may be present in the paint or resin matrix <NUM> include one or more types of resins, such as an acrylic resin, an epoxy resin, a polyurethane resin, and/or the like. In addition to the dielectric pigments <NUM> incorporated therein, the radar compatible coating <NUM> may include various other ingredients such as various additives, promoters, curing agents, a water and/or solvent-based carrier that flashes off during drying or curing of the paint formulation, colorants, and other pigments that may add special effect and/or color without significantly deteriorating the radar transparency or transmissivity of the coating <NUM>.

In the uncured state, the radar compatible coating <NUM> may be sprayed or otherwise deposited onto the underlying substrate <NUM> using conventional techniques. For example, the radar compatible coating <NUM> may be deposited onto the underlying substrate <NUM> via an applicator, such as a spray gun, for example in a refinishing paint setting or alternatively, in an industrial painting setting. In another example, the applicator may be a printhead, for example in a refinishing paint setting or alternatively, in an industrial painting setting. In yet another example, the applicator may be a rotary bell applicator, for example in an industrial painting setting. Once cured and/or dried, the radar compatible coating <NUM> provides an aesthetic appearance, protection and/or improved durability to the underlying substrate <NUM> and is substantially transparent or transmissive to radar signals with relatively low radar signal loss.

In an exemplary embodiment, the dielectric pigments <NUM> include or are in the form of flakes <NUM> that have a highly reflective or metallic appearance in the visible spectrum range. As used herein, the "visible spectrum range" is understood to mean wavelengths of from about <NUM> about <NUM>.

In an exemplary embodiment, each flake <NUM> includes a plurality of alternating layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> of dielectric materials <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. Adjacent layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are formed of different dielectric materials <NUM>, <NUM>, <NUM>, <NUM>, <NUM> that have different refractive indexes in the visible spectrum range. In an exemplary embodiment, the alternating layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> of dielectric materials <NUM>, <NUM>, <NUM>, <NUM>, <NUM> with different refractive indexes improves the total reflection of light in the visible spectrum range to provide a highly reflective, mirror-like or metal appearance. In particular, an incoming light ray(s) (indicated by single headed arrow <NUM>) traveling through the paint or resin matrix <NUM>, which has a refractive index of, for example about <NUM>, impinges on the flake <NUM> and portions of the light ray(s) <NUM> are reflected back (indicated by arrows <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) at each interface where there is a change in refractive index to improve the total reflection of the light ray <NUM> from the flake <NUM> and provide an enhanced metal appearance. Multiple reflection, absorption, and transmission events occur at each interface between the alternating layers.

In an exemplary embodiment, the dielectric materials <NUM>, <NUM>, <NUM>, <NUM>, <NUM> of adjacent layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> have one layer with a refractive index of from about <NUM> to about <NUM> and the other layer with a refractive index of from about <NUM> to about <NUM>, for example, from about <NUM> to about <NUM> and from about <NUM> to about <NUM>, respectively.

In an exemplary embodiment, the dielectric materials <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are selected from the group of semi-conductors or insulators. In an exemplary embodiment, the dielectric materials <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are selected from the group of metal oxides. In an exemplary embodiment, the dielectric materials of adjacent layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are SiO<NUM> and TiO<NUM>, respectively, for example alternating layers of SiO<NUM> and TiO<NUM> throughout the stack of layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

In an exemplary embodiment, the thickness of each layer <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, the number layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and the concentration of the dielectric pigments <NUM> in the coating <NUM> is designed or formulated to further enhance and improve the total reflection of the light ray <NUM> from the flake <NUM>. In an exemplary embodiment, each of the alternating layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> have a corresponding thickness of from about <NUM> to about <NUM>, for example from about <NUM> to about <NUM>. In an exemplary embodiment, the plurality of alternating layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is from about <NUM> to about <NUM> layers, for example from about <NUM> to about <NUM> layers. Each of the flakes <NUM> has an overall thickness of from about <NUM> to about <NUM>, for example of from about <NUM> to about <NUM>. In an exemplary embodiment, each of the flakes has a radius of from about <NUM> to about <NUM>. In an exemplary embodiment, the dielectric pigments <NUM> are present in the radar compatible coating <NUM> in an amount of about <NUM> to <NUM>%, of the radar compatible coating <NUM>.

As discussed above, the dielectric pigments <NUM> are substantially transparent to radar. In an exemplary embodiment, the dielectric materials that form the alternating layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> of the dielectric pigments <NUM> each have a corresponding dielectric constant of about <NUM> or less, for example from about <NUM> to about <NUM> in the radar frequency range of from about <NUM> to about <NUM>. In an exemplary embodiment, the dielectric materials that form the alternating layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> of the dielectric pigments <NUM> each have a corresponding permittivity of about <NUM> or less, for example about <NUM> to about <NUM> in a radar frequency range of from about <NUM> to about <NUM>.

<FIG> illustrates a method <NUM> for making dielectric pigments having a metallic appearance for a radar compatible coating in accordance with an exemplary embodiment. <FIG> illustrates a screen shot <NUM> of details of a layer structure <NUM> of a candidate dielectric pigment within a paint or resin matrix generated from one or more predictive models in accordance with an exemplary embodiment. In an exemplary embodiment, the one or more predictive models utilizes two or more predictive models. For example, a first predictive model that is configured to predict a corresponding color for each of one or more candidate dielectric pigments within a paint or resin matrix, and a second predictive model that is configured to predict a radar property for each of the one or more candidate dielectric pigments within the paint or resin matrix. Predictive models that are configured to predict colors for candidate formulations are well-known in the industry. A non-limiting example of predictive model that is used to predict colors for candidate formulations is described in <CIT>, which is owned by the assignee of the present application. Two non-limiting examples of predictive models that are used to predict radar properties, such as a radar transmission property, for example, a permittivity response of an ingredient, a coating formulation, and/or a coating formed from the coating formulation, is described in <CIT>, and <CIT>, which are owned by the assignee of the present application.

Further, <FIG> is a graphical representation of reflection and transmission at <NUM> degrees over a broad wavelength ranging including the visible spectrum range of the layer structure <NUM> of the candidate dielectric pigment depicted in <FIG>. <FIG> is a graphical representation of reflection and transmission from <NUM> to <NUM> degrees in the visible spectrum range of the layer structure <NUM> of the candidate dielectric pigment depicted in <FIG>. <FIG> is a graphical representation of reflection and transmission from <NUM> to <NUM> degrees in the visible spectrum range of the layer structure of the candidate dielectric pigment depicted in <FIG>. <FIG> illustrates a table of corresponding visible appearances values including a color of the layer structure <NUM> of the candidate dielectric pigment depicted in <FIG>.

Referring to <FIG>, the method <NUM> includes predicting (STEP <NUM>), using a processor and the one or more predictive models as described above, the corresponding layer structure <NUM>, a corresponding visible appearance including a color (shown in <FIG>) additional predictive capabilities include real-time optimization and visualization of predicted reflectance, transmittance, absorptance throughout the desired wavelength range (<FIG>. An example color rendering as a function of the angle of incidence can also be shown (<FIG>), and additional tabular data can be included to provide specific color information including tristimulus values CIEXYZ and CIELAB values as well as hue and chroma information, and a corresponding radar property for each of the one or more candidate dielectric pigments within the paint or resin matrix. The dielectric pigments that corresponds to one of the one or more corresponding candidate dielectric pigments within the paint or resin matrix that is the same or substantially similar in appearance to a target metal-containing coating including the color is generated (STEP <NUM>) based at least in part on the corresponding visible appearance including the color and the corresponding radar properties for the one of the one or more candidate dielectric pigments.

The method <NUM> further includes forming (STEP <NUM>) a plurality of alternating layers of dielectric materials overlying a substrate. In one example, the plurality of alternating layers of dielectric materials that correspond to the layer structure <NUM> of the one of the one or more candidate dielectric pigments that is the same or substantially similar in appearance to a target metal-containing coating is deposited overlying a mylar film substrate. This includes depositing (STEP <NUM>) a first layer of a first dielectric material overlying the mylar film substrate, wherein the first dielectric material has a first refractive index in the visible spectrum range; and depositing (STEP <NUM>) a second layer of a second dielectric material overlying the first layer, wherein the second dielectric material has a second refractive index in the visible spectrum range that is different than the first refractive index. In an exemplary embodiment, the layers are deposited using a physical vapor deposition (PVD) process. In an exemplary embodiment, a sol gel dipping process may optionally be used to deposit outer SiO<NUM> layers on the dielectric pigments to improve robustness for mixing the dielectric pigments into the paint or resin matrix.

The method <NUM> continues by removing (STEP <NUM>) the substrate (e.g., the mylar film substrate, for example by dissolving the mylar or by mechanical means) from the plurality of alternating layers of dielectric materials. Either before, during or after removing (STEP <NUM>), the plurality of alternating layers are broken, crushed, and/or ground into flakes to form the dielectric pigments. The grinding process is intended to create a flake that is of an appropriate diameter to ensure geometric compatibility with various application processes discussed in paragraph [<NUM>]. For instance, an example flake diameter range could be <NUM> to <NUM> microns. In certain instances, sieving could be used in order to control the flake diameter and size distribution.

Referring to <FIG>, a computer <NUM> may be used as a device to implement the techniques and methods described herein. The computer <NUM> may include an input device <NUM>, such as a keyboard <NUM>, a mouse <NUM>, electronic communication devices such as a modem, or a variety of other communication devices. The input device <NUM> communicates with a processor <NUM> (processing unit) and/or a memory <NUM> of the computer, where the processor <NUM> and the memory <NUM> communicate with each other. A wide variety of processor <NUM> and memory <NUM> embodiments are known to those skilled in the art. The computer <NUM> also includes an output device <NUM>, such as the monitor illustrated. Other exemplary embodiments of an output device <NUM> include a modem, a printer, or other components known to those skilled in the art. The methods and techniques described above may be implemented on the computer <NUM>.

A computer readable medium <NUM> embodies a computer program, where the computer program directs the computer to implement the method and techniques described above. The computer readable medium may be an SD card, a USB storage medium, a floppy disk, a CD-ROM, a DVD, a hard drive, or other devices that are readable by a computer, and that include memory for saving the computer program. In some embodiments, the computer program may be electronically downloaded to the computer, but the downloaded computer program is saved on a tangible device somewhere.

In an exemplary embodiment, the computer program directs the computer to request input from the input device <NUM>, wherein the requested input is directed towards obtaining a reflectance measurement of a target coating to characterize a color of the target coating. The computer program directs the processor <NUM> to generate one or more candidate formulas to determine color matching to the color of the target coating, where the processor <NUM> may access one or more mathematical/predictive model(s), an algorithm for example a genetic algorithm, or a software implemented expert system to generate the candidate formulas. The computer program directs the processor <NUM> to access or otherwise cooperative with one or more predictive models to predict the corresponding color in the corresponding radar property for each of the one or more candidate formulas. Simultaneously or subsequently, the computer program directs the processor <NUM> to generate a radar compatible coating composition that is the same or substantially similar in appearance to the target coating including color based at least in part on the corresponding color in the corresponding radar property for a selected one of the candidate formulations. The computer program directs the output device <NUM> to present the radar compatible coating composition including its associated color and radar property, and/or any other information as mentioned above.

Claim 1:
A dielectric pigment (<NUM>) having a metallic appearance for a radar compatible coating (<NUM>), the dielectric pigment comprising:
a flake (<NUM>) having a thickness of from <NUM> to <NUM> and comprising a plurality of alternating layers (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) of dielectric materials including a first layer formed of a first dielectric material having a first refractive index in the visible spectrum range and a second layer disposed adjacent to the first dielectric layer and formed of a second dielectric material having a second refractive index in the visible spectrum range that is different than the first refractive index.