JP6649628B2 - Decorative coating - Google Patents

Description

  The present invention relates to a decorative coating using silver nanoparticles.

  2. Description of the Related Art Conventionally, a vehicle such as an automobile is equipped with a radar device such as a millimeter-wave radar at a central position in front of the vehicle in order to measure an obstacle ahead of the vehicle or a distance from the vehicle. For example, radio waves such as millimeter waves emitted from the radar device are radiated forward through a front grill or an emblem of a vehicle manufacturer and are reflected by an object such as a vehicle ahead or an obstacle in front, and the reflected waves are reflected by the front grill or the like. To return to the radar device via the.

  Therefore, materials and paints that can provide a desired aesthetic appearance with little radio wave transmission loss and are often used for parts arranged in the beam path of the radar device, such as the front grill and the emblem, are often used on the surface of the resin base material. It is common practice to form decorative coatings. For example, Patent Literatures 1 and 2 disclose a decorative coating in which nanoparticles made of silver or a silver alloy are dispersed in a resin.

JP 2012-046665 A JP 2015-104707 A

However, the decorative film made of silver nanoparticles made of silver shown in Patent Document 1 tends to have a smaller L ^* value, which is a lightness index, as compared with a decorative film such as a chromium film formed by plating or an iridium film formed by sputtering. It is in.

  Furthermore, when silver nanoparticles are used, the decorative film does not appear to be a colorless metallic color, as seen from the results described later by the inventors, in which the original color of silver is colored yellow. When light is applied to such a decorative film, the silver nanoparticles vibrate due to the energy of the light, free electrons inside move, and the silver nanoparticles are polarized. As a result, a surface electromagnetic wave called surface plasmon poratolin is generated on the surface of the silver nanoparticles, a specific wavelength of light is absorbed, and the energy of the silver nanoparticles is amplified (surface plasmon resonance absorption). As a result, the constituent substances around the fine particles of silver nanoparticles receive amplification energy, which may cause discoloration of the decorative film.

Therefore, as shown in Patent Document 2, for example, when nanoparticles made of a silver alloy in which silver is added with another element are used, the decorative coating can be made to have a nearly colorless metallic color. The L ^* value of the decorative coating decreases.

The present invention has been made in view of such a point, and an object of the present invention is to improve the weather resistance and improve the L ^* value, which is a lightness index, by exhibiting a nearly colorless metallic color. To provide a decorative coating.

  In view of the above problem, the decorative coating according to the present invention is an electromagnetic-wave-transmitting decorative coating in which silver nanoparticles made of silver coated with an electrically insulating material are dispersed in a resin, The particles are plate-shaped silver nanoparticles, and the silver nanoparticles are formed on the silver nanoparticles, and the average particles of the silver nanoparticles as viewed from a direction orthogonal to a surface extending in a plane. It is characterized in that the diameter is 100 nm or more, and the aspect ratio, which is a value obtained by dividing the average particle diameter by the average particle thickness of the silver nanoparticles, is 10 or more.

ADVANTAGE OF THE INVENTION According to the decorative coating which concerns on this invention, by exhibiting a metal color near colorless, while improving the weather resistance of a decorative coating, L ^* value which is the lightness index of a decorative coating can be improved.

(A) is a schematic perspective view of the silver nanoparticles according to the embodiment of the present invention, and (b) is a plan view thereof. 3 is a photograph of a decorative coating according to Example 1. It is the figure which showed the waveform of the UV-vis spectrum of the aqueous solution which concerns on Example 1 and Comparative Examples 1-3. It is L ^* value of the decorative coating which concerns on Example 1, the comparative example 1, and a reference example. 4 is a photograph obtained by observing a cross section of the decorative coating according to Example 1 by SEM.

  Hereinafter, embodiments of the present invention will be described. As an example, the decorative coating according to the present embodiment constitutes a part of an emblem mounted on the surface of a resin base material serving as a front grill, and is a coating having electromagnetic wave permeability. Since the decorative coating according to the present embodiment is applied to the surface of a resin base material (front grill) located in the path of the millimeter wave radar device, it has a metallic luster in appearance, and has an electromagnetic wave transmittance ( (Electrical insulation).

  The decorative film includes at least silver nanoparticles made of silver dispersed in the decorative film and a light-transmissive binding resin that binds the silver nanoparticles. The silver nanoparticles are covered with an electrically insulating material as a protective material. The protective material is preferably a resin that has good adhesion to the silver nanoparticles and has good affinity for the binding resin. By using the protective material for the silver nanoparticles, it is possible to prevent the aggregate of the silver nanoparticles from acting as an electromagnetic wave transmission barrier. The “resin” in the present invention corresponds to the binding resin in the present embodiment, and the “electrically insulating material” corresponds to the protective material in the present embodiment.

  The binding resin is a light-transmitting polymer resin, and examples thereof include an acrylic resin, a polycarbonate resin, a polyethylene terephthalate resin, an epoxy resin, and a polystyrene resin.

  When a binding resin of the type exemplified above is selected, a resin having a carbonyl group in the resin is preferred. For example, when an acrylic resin is selected as the binding resin, it is preferable to select an acrylic resin having a carbonyl group as the protective material.

  As described above, by using an acrylic resin having a carbonyl group as the protective material, the adhesion to the silver nanoparticles 1 can be increased, and by selecting the same resin as the binding resin, the affinity with the binding resin can be improved. Can be increased.

  As shown in FIGS. 1A and 2, the silver nanoparticles 1 are nanoparticles made of silver and are plate-shaped particles. “Nanoparticles” as used herein refers to particles having an average particle size on the order of nanometers.

  As shown in FIG. 2, the plate-like silver nanoparticles 1 are formed of silver nanoparticles 1 viewed from a direction orthogonal to a planar surface 1 a (see FIG. 1) formed on the silver nanoparticles 1. Has an average particle diameter D of 100 nm or more, and the aspect ratio, which is a value obtained by dividing the average particle diameter D by the average particle thickness t of the silver nanoparticles 1, is 10 or more.

  Here, as shown in FIG. 1 (b), the average particle diameter D is equal to the circle of the silver nanoparticles 1 viewed from a direction perpendicular to the surface 1a with respect to any 50 silver nanoparticles 1. Is drawn, the area of the region of the silver nanoparticle 1 outside the circle (protruding from the circle) and the area of the region inside the circle that do not include the silver nanoparticle 1 become the same area. The diameter of the circle.

  On the other hand, as shown in FIG. 1A, the average particle thickness t of the silver nanoparticles 1 is an average value of the measured thickness of the silver nanoparticles with respect to arbitrary 50 silver nanoparticles. FIG. 2 shows silver nanoparticles having an average particle diameter of 321 nm and an average particle thickness of 21 nm. When measuring the average particle diameter D and the average particle thickness t, it can be measured by extracting silver nanoparticles within a certain range of the SEM image or the TEM image on the image.

  In the present embodiment, by setting the average particle diameter D of the silver nanoparticles 1 to 100 nm or more, the silver nanoparticles 1 can be arranged on the resin substrate on the design surface side without tilting, and therefore, the light reflection The area can be increased. Further, the peak in the vicinity of the wavelength of 400 to 500 nm (visible light region) in the light absorption band of the decorative film can be leveled, and the decorative film can exhibit a nearly colorless metallic color.

Specifically, in the present embodiment, the plasmon absorption wavelength of the decorative coating can be shifted to outside visible light. Thus, it is not necessary to use nanoparticles made of a silver alloy in which a second element such as nickel is added to silver. As a result, the weather resistance of the decorative film can be improved (discoloration can be suppressed), and the L ^* value, which is the lightness index of the decorative film, can be improved. The more preferable average particle diameter D of the silver nanoparticles 1 is 250 nm or more.

  Furthermore, in the present embodiment, since the aspect ratio of the silver nanoparticles 1 is 10 or more, the silver nanoparticles 1 can be arranged on the resin substrate on the design surface side without inclination, so that the light reflection area is increased. be able to. The more preferable aspect ratio of the silver nanoparticles 1 is 15 or more.

  Here, the silver nanoparticles 1 contained in the entire decorative coating are preferably 85 to 99% by mass. Here, when the content of the silver nanoparticles is less than 85% by mass, the metallic luster due to the silver nanoparticles may not be sufficient, and when the content exceeds 99% by mass, the silver nanoparticles due to the binding resin may be insufficient. May not be sufficient.

Further, the thickness of the decorative film is preferably 300 nm or more. If the thickness is smaller than this, the concealing property of the resin substrate by the silver nanoparticles 1 becomes low, and a sufficient L ^* value may not be obtained for the decorative coating.

  An embodiment according to the present invention will be described below.

(Example 1)
An aqueous solution containing plate-shaped silver nanoparticles having an average particle diameter of 350 nm and an average particle thickness of 18 nm on a surface extending in a plane was prepared. The silver nanoparticles are coated with an acrylic resin having a carbonyl group as an electrically insulating material. The average particle diameter and the average particle thickness of the silver nanoparticles before coating with the protective material were measured by SEM.

  Specifically, the average particle diameter of the silver nanoparticles is, for a given 50 silver nanoparticles, when a circle is drawn, the area of the region of the silver nanoparticle protruding from the circle and the inside of the circle The area of the region that does not include silver nanoparticles is the average value of the diameter of the circle when the area is the same.

  On the other hand, the average particle thickness of the silver nanoparticles is an average value of the measured thickness of the silver nanoparticles for any 50 silver nanoparticles. When the value obtained by dividing the average particle diameter of the silver nanoparticles of Example 1 by the average particle thickness is defined as the aspect ratio of the silver nanoparticles, the aspect ratio of the silver nanoparticles according to Example 1 is 19.4. become. Next, the silver nanoplate aqueous solution was replaced with a 1-methoxy-2-propanol solution, and an acrylic resin was added as a binder thereto, followed by stirring to obtain a paint for a decorative coating.

  The obtained paint was put into a spray applicator, and was applied from the design side of an automobile emblem (work made of transparent resin). Specifically, while rotating the work, the gun of the spray applicator was reciprocated at a constant speed, and the paint was applied evenly until the required film thickness was obtained.

  Here, the volatility of the solvent was controlled to arrange the plate-like silver nanoparticles in the same direction. Specifically, in Example 1 and Examples 2 and 3 to be described later, the paint was applied under the conditions of a temperature of 28 to 32 ° C. and a humidity of 30 to 50% RH. After the application, the coating was dried under a condition of 10 to 15 minutes until it was put into a curing oven, and then heated in an oven at 80 ° C. for 30 minutes or more to cure the binder and form a decorative film on the work.

The aqueous solution before adding an acrylic resin as a binder to form a paint for a decorative film was diluted, and the UV-vis spectrum was measured with a spectrophotometer. The result is shown in FIG. Furthermore, L ^* of the decorative film was measured using a color difference meter (Konica Minolta CR-400). The results are shown in FIG. L ^* is a lightness index of the color system specified in the CIE 1976 color system. Table 1 shows the ratio when the predetermined L ^* value is set to 100%. In addition, the cross section of the decorative coating according to Example 1 was observed by SEM. The result is shown in FIG.

(Example 2)
In the same manner as in Example 1, a decorative film was formed on the surface of the work. The difference from Example 1 is that the silver nanoparticles have an average particle diameter of 257 nm and an aspect ratio of 15.0. As in Example 1, the decorative coating according to Example 2 was measured for L ^* value. Table 1 shows the results.

(Example 3)
In the same manner as in Example 1, a decorative film was formed on the surface of the work. The difference from Example 1 is that the average particle diameter of the silver nanoparticles is 482 nm and the aspect ratio is 22.6. As in Example 1, the L ^* value of the decorative film according to Example 3 was measured. Table 1 shows the results.

(Comparative Example 1)
In the same manner as in Example 1, a decorative film was formed on the surface of the work. The difference from Example 1 is that the silver nanoparticles are spherical in shape and the average particle size is 25 nm. In the same manner as in Example 1, the UV-vis spectrum of the aqueous solution of the paint for decorative coating according to Comparative Example 1 before the addition of the acrylic binder was measured, and the L ^* value of the decorative coating was measured. The results are shown in FIGS. 3 and 4 and Table 1.

(Comparative Example 2)
In the same manner as in Example 1, a decorative film was formed on the surface of the work. The difference from Example 1 is that the average particle diameter of the silver nanoparticles is 25 nm and the aspect ratio is 1.5. Similarly to Example 1, in the case of Comparative Example 2, the UV-vis spectrum and the L ^* value were measured. The results are shown in Table 1 and FIG.

(Comparative Example 3)
In the same manner as in Example 1, a decorative film was formed on the surface of the work. The difference from Example 1 is that silver alloy (Ag-Ni) nanoparticles obtained by adding Ni to silver were used instead of silver nanoparticles made of silver. Further, the difference from Example 1 is that the shape is spherical and the average particle size is 25 nm. As in Example 1, the UV-vis spectrum was measured in Comparative Example 3 as well. The result is shown in FIG.

(Reference example)
As a reference example, a workpiece was prepared by sputtering iridium as a decorative coating on the surface of a work. As in Example 1, the L ^* value was measured for the decorative coating according to the reference example. The results are shown in FIG.

(result)
The decorative coatings according to Comparative Examples 1 and 2 have a color close to yellow, and as shown in FIG. 3, the UV-vis spectrum of the aqueous solution of the paint for decorative coatings according to Comparative Examples 1 and 2 before the addition of the acrylic binder was shown. And a peak was present at a wavelength of 400 to 500 nm including the visible light region. In Comparative Example 3, since the nanoparticles of the Ag—Ni alloy were used, the peak was leveled. On the other hand, the decorative coating according to Example 1 has a nearly colorless metallic color, and the UV-vis spectrum of the aqueous solution before the addition of the acrylic binder of the coating for decorative coating as shown in FIG. At wavelength, no peak was present.

As shown in FIG. 4, the L ^* value of the decorative coating according to Example 1 was higher than those of Comparative Example 1 and the reference example. Furthermore, as shown in Table 1, when comparing the L ^* value of enamel coating according to Comparative Example 2 and Comparative Example 1, the direction of L ^* value of Comparative Example 2 using the plate-shaped silver nanoparticles, spherical It was about 5% higher than that of Comparative Example 1 using silver nanoparticles. Furthermore, the L ^* values of the decorative coatings according to Examples 1 to 3 were larger than those of Comparative Examples 1 and 2.

  From these results, since the decorative coatings according to Comparative Examples 1 and 2 have a peak at a wavelength of 400 to 500 nm including the visible region and have a color close to yellow, the weather resistance of the decorative coatings due to surface plasmon resonance absorption. Sex is not enough.

On the other hand, when the Ag-Ni nanoparticles are used as in Comparative Example 3, the above-mentioned peak of the decorative film can be suppressed, and the weather resistance of the decorative film is improved as compared with Comparative Examples 1 and 2. Can be done. However, in this case, as shown in Table 1, the L ^* value of the decorative coating may decrease.

In the decorative coating according to Examples 1 to 3, by using silver nanoparticles of a predetermined size and shape, a metallic color close to colorless without adding a new element to silver is exhibited, as described above. It is considered to be excellent in weather resistance and the L ^* value of the decorative film will be high. This is considered to be because, as shown in FIG. 5, the silver nanoparticles dispersed in the decorative film were arranged without inclination on the resin substrate on the design surface side.

  Although the present invention has been described in detail with reference to the embodiment, the specific configuration is not limited to the embodiment and the example, and there are design changes without departing from the gist of the present invention. These are included in the present invention.

  1: silver nanoparticles, 1a: surface of silver nanoparticles, D: average particle diameter, t: average particle thickness

Claims (1)

An electromagnetic wave permeable decorative coating in which silver nanoparticles made of silver coated with an electrically insulating material are dispersed in a resin,
The silver nanoparticles are plate-like silver nanoparticles,
The silver nanoparticles are formed on the silver nanoparticles, the silver nanoparticles have an average particle diameter of 100 nm or more as viewed from a direction perpendicular to a surface extending in a plane, and the average particles An aspect ratio, which is a value obtained by dividing a diameter by an average particle thickness of the silver nanoparticles, is 10 or more.

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