JP5645458B2 - Coating composition used for forming resin film for structural color development - Google Patents

Description

  The present invention relates to a coating composition used for forming a structural color-developing resin film having concave portions in a regular arrangement for developing a structural color on a predetermined substrate.

  In the field of caps and containers, etc., it has been practiced to improve the commercial value by decorating the surface of containers and the like, but in recent years, chemicals using substances such as pigments from the viewpoint of recyclability and environmental suitability. Color development is becoming unacceptable. For this reason, various techniques for expressing a structural color (for example, a hologram image) that develops color using phenomena such as light diffraction and interference due to a fine periodic structure have been proposed as alternatives to chemical color development.

  For example, in Patent Document 1 below, a metal thin film layer having a thickness of 1000 mm is deposited on the surface of a thermoplastic synthetic resin base material to form a composite base material, and relief hologram irregularities are formed on the surface of the metal thin film layer of the composite base material. A method for replicating a relief hologram has been proposed in which the mold surface of a mold having a shape is brought into contact, and is molded by heating and pressing.

  However, it is difficult to form a fine periodic structure on a curved surface or an uneven surface by a conventional preparation method that forms a fine periodic structure by replicating a plate mold. In order to change it, it is necessary to create a new plate mold, and it is difficult to apply it to a small variety of products. In addition, if a fine periodic structure is formed on a flat plate and formed into a desired shape, there is a problem that the decoration effect is weakened.

  On the other hand, a method of forming a fine periodic structure by light irradiation and expressing a structural color has been proposed, for example, LIPS (Laser Induced Periodic Structures) (for example, see Non-Patent Document 1). This is a fine periodic structure formed on a material surface by laser irradiation in a self-organized manner, and a structure that expresses a structural color using this LIPS has also been proposed by the present applicant (Patent Document 2).

Japanese Patent Publication No. 3-60115 JP 2007-286113 A

Sylvain Lazare "Large scale excimer laser production of submicron periodic structures on polymer surface." Applied Surfa ce Science 69 (1993) 31-37 North-Holland

The structure that can express the structural color using the LIPS does not require a plate and can be changed by changing the scanning program. In addition, it can be easily applied to a curved surface or an uneven surface. Further, since it does not come into contact with the surface to be formed as in the case of using a plate mold, it has an excellent effect of enabling additional processing to a molded product.
However, a satisfactory structural color may not always be obtained depending on the material or state of the coating provided with the concave portions having a fine regular arrangement for forming a hologram image. In particular, when this coating is formed on the surface of the substrate, foreign matter (for example, lipid when touched with a finger) enters the recess formed on the coating surface, and as a result, a hologram image is formed. There is a problem that it becomes unclear or disappears in some cases. For this reason, it is necessary to further form a protective film on the surface of the coating.

  In addition, the present applicant uses a film containing a compound having an aromatic ring as a film in which a concave for forming a structural color is formed, and irradiates such a film with laser light having a periodic intensity distribution. According to PCT / JP2009 / 068052, a technique for expressing a stable and good structural color was proposed. However, even in this technique, when this film is formed on the surface, a concave portion for forming a hologram image is used. There is a problem that foreign matter enters into the film and the hologram image is damaged. For this reason, it is necessary to form a protective film on the surface of the film.

  In addition, when forming concave portions for structural color development in a resin coating using LIPS, the fluence during processing is large and a high-power laser oscillator must be used. From the viewpoint of cost reduction, low fluence is required. In the present situation, it is required to form a resin film that can be laser processed.

  Accordingly, an object of the present invention is to provide a coating composition for forming a resin film in which a recess for forming a structural color that can suppress the intrusion of foreign matter by laser processing at a low fluence is formed.

According to the present invention, in a coating composition for forming a structural color-developing film in which concave portions having a regular arrangement for developing a structural color are formed by laser light irradiation , a polyesteramino resin or epoxy as a resin component A resin containing zinc oxide or titanium oxide having an average particle size of 2000 nm or less as inorganic ultraviolet absorbent particles, and the inorganic ultraviolet absorbent particles in an amount of 0.5 to 300 parts by weight per 100 parts by weight of the resin component A coating composition is provided which is characterized in that

In the coating composition of the present invention,
(1) The inorganic ultraviolet absorber has an average particle diameter of 2000 nm or less,
(2) The inorganic ultraviolet absorbent particles are zinc oxide or titanium oxide,
Is preferred.

  According to the coating composition of the present invention, a resin film is formed by applying it to a predetermined substrate and heat-treating the resin film, and this resin film has a regularly arranged structure by laser irradiation at a low fluence. A concave portion for color development can be formed. That is, if the fluence during processing is reduced, the energy of one pulse required for laser irradiation may be small. Then, a laser oscillator with a small pulse energy but a large pulse repetition frequency can be used, the number of machining points per unit time can be increased, and the machining speed can be improved. Laser processing can be performed using an oscillator, and productivity can be improved and costs can be reduced.

In addition, when a resin film formed using the coating composition of the present invention is irradiated with laser to form structural color-developing recesses, the surface of at least a part of the recesses is closed. It has been enclosed inside. Therefore, even if this film is exposed on the surface, foreign matter does not enter the recessed portion where the surface is closed. For example, even when this surface is touched or rubbed with a finger, The lipid does not enter the inside of the closed recess, and therefore, the structural color is not impaired by the invasion of foreign matter, and a good structural color can be stably expressed.
Incidentally, it can be easily confirmed by SEM observation that the surface of a part of the regularly arranged concave portions is closed.

It is a figure which shows an example of the cross-section of the recessed part for structural color coloring formed in the resin film formed using the coating composition of this invention. It is a figure which shows the SEM photograph of the surface of the resin film in which the recessed part for structural color development was formed. It is a schematic perspective view which shows the structure of the laser irradiation apparatus used for preparation of the laminated structure of this invention. It is a schematic diagram which shows the interference area | region of the light irradiated to the laminated structure of this invention.

<Concavity for structural color development>
First, the structural color developing recesses formed on the resin film formed using the coating composition of the present invention will be described.

  With reference to FIGS. 1 and 2, in the coating composition of the present invention, this is applied to the surface of a predetermined substrate 53 to form a resin film 50 for structural color development. In this case, the fine concave portions 55 for coloring the structural color are regularly arranged at substantially equal intervals by laser irradiation. That is, the interval and the size of the recesses 55 are close to the visible light wavelength (about 400 nm to 700 nm), and the formation of a large number of such recesses 55 causes light diffraction, resulting in the recesses 55. Interference of light due to the optical path difference occurs between the portion between the concave portion 55 and the concave portion 55 (convex portion), and thereby a structural color appears.

  Such a recess 55 is formed by irradiating a laser beam having a periodic intensity distribution described later, and its surface (upper part) is in an open state. Such a recess 55 is indicated by 55a. However, in the resin film 50 formed using the coating composition of the present invention, at least a part (or all in some cases) of such a recess 55 has a structure in which the surface is closed (the recess). 55 is shown as 55b) and is enclosed as a cavity inside the coating 50. That is, when laser irradiation is performed on the resin coating 50 formed according to the present invention, the concave portion 55b whose surface is closed can be formed.

  As shown in FIG. 2, when the surface of the coating film 50 on which such a recess 55 is formed is observed with an SEM, the recess 55a is observed as a clear black image, but the recess 55b is an unclear blurred black color. It can be recognized from being observed as an image.

  As described above, when the concave portion 55 for forming the structural color is formed in the resin film 50 formed using the coating composition of the present invention, the surface of at least a part of the concave portion 55 is closed. The foreign matter does not enter the recessed portion 55b, and therefore it is possible to effectively prevent the structural color from being deteriorated due to the foreign matter. That is, even in a form in which the coating film 50 is exposed on the surface, it is possible to reliably prevent foreign matter from entering all of the recesses 55, so that the coating 50 can be closed even if touched or rubbed with a finger. In addition, foreign matters such as lipids do not enter the recessed portion 55b. Therefore, when the resin film 50 is formed on the surface of a predetermined substrate using the coating composition of the present invention, in order to prevent the structural color from being deteriorated due to the entry of foreign matter into the recess 55, the film 50 is further formed thereon. The protective film can be omitted, and an increase in cost due to the formation of the protective film can be avoided.

  In the present invention, the ratio of the recesses 55b whose surfaces are closed is not critical, but generally, the total number of the recesses 55 (the total number of the recesses 55a and 55b) is 10% or more, particularly 30% or more. Most preferably, the number of the concave portions 55b is preferably 50% or more, and the number of the concave portions 55a whose surfaces are open can be made zero. That is, if the number of the recesses 55b is too small, when the coating is exposed on the surface, the ratio of the recesses 55 into which foreign matter enters increases, so that it is difficult to prevent structural color deterioration. Because it ends up.

<Coating composition>
The coating composition of the present invention, which can form the resin film 50 in which the concave portion 55b whose surface is closed as described above is formed by laser irradiation, is coated with an inorganic ultraviolet ray absorption together with a resin component which is a film forming material. Agent particles. That is, the addition of the inorganic ultraviolet absorber enables laser processing at a low fluence, and at the same time forms a concave portion with a closed surface.

That is, the formation of the recess 55 in the coating 50 is performed by irradiating laser light. The laser irradiation part absorbs the laser beam, generates heat, pyrolyzes and volatilizes, so that the recess 55 is formed. However, the laser light is coherent light, and the wavelength of the laser light used for forming the recess 55 is short and is in the ultraviolet region (less than 400 nm). For this reason, by dispersing the inorganic ultraviolet absorber, the laser absorptivity is enhanced, and the recess 55 is effectively formed at the laser irradiated portion. In this case, as the resin that is a matrix, a resin that transmits the laser beam to be irradiated is used, and specifically, a polyesteramino resin or an epoxy resin is used.

By the way, when the film forming material itself (that is, a resin that is a film forming material) absorbs laser light having a periodic intensity distribution to be irradiated to form the recess 55, the surface of the coating 50 As a result, laser ablation progresses from the inside toward the inside, and as a result, a large number of formed recesses 55 are open surfaces (that is, recesses 55a).
On the other hand, in the resin film 50 formed using the coating composition of the present invention, when the inorganic ultraviolet absorber dispersed in the film 50 is added to the film 50, the ultraviolet ray is absorbed. Since laser ablation progresses starting from the absorbent, it is presumed that the degree of progress of this ablation is reflected in the shape of the recess 55. That is, when laser ablation occurs excessively, the progress reaches the surface of the coating 50, and the concave portion 55a is formed with the surface opened, but part of the laser ablation progresses depending on the concentration of the ultraviolet absorber. Under the influence of unevenness, unevenness of the intensity of the irradiated laser light, or unevenness of the thickness of the coating 50, the progress does not reach the surface of the coating 50, and as a result, a concave portion 55b whose surface is closed is formed. It is estimated.

Further, the formation of the concave portion 55b whose surface is closed can be realized even when an organic ultraviolet absorber is added. However, when an organic ultraviolet absorber is used, the amount added per resin component is considerably smaller than that of the inorganic ultraviolet absorber. Compared to inorganic UV absorbers, the UV absorbing ability is high, and if added in the same amount as inorganic UV absorbers, laser ablation occurs excessively, forming a recess 55b with a closed surface. This is because it becomes difficult to do. As understood from this, when an organic ultraviolet absorber is used, the amount of addition is small, so that laser processing with a large fluence is required.
On the other hand, when an inorganic ultraviolet absorber is used according to the present invention, it can be added in a large amount compared to an organic ultraviolet absorber. As a result, the structure color is reduced by laser irradiation at a low fluence. It is possible to form a color developing recess. When the fluence during processing is reduced, an inexpensive laser oscillator with low output can be used, and at the same time, the energy of one pulse required for laser irradiation may be small. In this case, a laser oscillator having a small pulse energy but a large pulse repetition frequency can be used, the number of machining points per unit time can be increased, and the machining speed can be improved. Thus, in the present invention, by using an inorganic ultraviolet absorber, productivity can be improved and cost can be reduced.

The inorganic ultraviolet absorber described above is added in an amount of 0.5 to 300 parts by weight, particularly 5 to 200 parts by weight, per 100 parts by weight of the resin component in the coating composition . The larger the amount, the more the concave portion 55 can be formed by laser irradiation at a low fluence. However, when the amount is larger than the above range, it becomes difficult to form the concave portion 55b whose surface is closed.

In the coating composition of the present invention, as the inorganic ultraviolet absorber, any inorganic ultraviolet absorber may be used as long as it has sensitivity to the wavelength of the laser beam irradiated for forming the recess 55. In particular, zinc oxide or titanium oxide is used in the present invention. Thereby, for example, laser processing can be performed with a YAG laser having a wavelength of 355 nm. These zinc oxide and titanium oxide can be used alone or in combination.

The particle size of the inorganic ultraviolet absorber is preferably smaller than the interval and size of the structural color developing recesses 55 formed by laser irradiation, and the interval and size of these recesses 55 are in the visible light wavelength. In consideration of setting to a close level (usually about 1 to 2 μm), the average particle diameter (volume center diameter D ₅₀ by laser diffraction scattering method) is 2000 nm or less, particularly 1000 nm or less, and most preferably 200 nm or less. It is good to be in.

  Furthermore, as the inorganic ultraviolet absorber to be used, those having improved dispersibility with respect to the resin by surface treatment can be used. Such surface treatment does not adversely affect the formation of the recess 55 by laser irradiation. However, depending on the type of the resin component used in the coating composition, the formed resin film 50 may become cloudy. If such cloudiness occurs, the visibility of the structural color will be reduced, so use. It is necessary that an appropriate surface treatment is performed according to the type of resin.

As the surface treatment agent used for the above surface treatment, for example, a metal salt of a higher fatty acid is generally used. For example, a saturated or unsaturated fatty acid having 10 to 22 carbon atoms, particularly 14 to 18 carbon atoms such as capric acid or undecane. Saturated fatty acids such as acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, etc. Metal salts (for example, zinc salts, calcium salts, etc.) can be exemplified, and an appropriate one can be selected according to the type of the resin component and used in an appropriate amount.
Further, a surface treatment using a silicon compound such as a silane coupling agent, methicone, or dimethicone may be performed.
Furthermore, a hydrophilic treatment using a metal oxide such as ZrO ₂ , ZnO ₂ , Al (OH) ₃ may be performed.

  In the coating composition of the present invention, a resin capable of forming a film is used as a resin component, that is, a film forming material (matrix) of the film 50, and as described above, it is used particularly for forming the recess 55. A resin having excellent transparency to laser light, for example, a resin having a light transmittance of 70% or more is preferably used. That is, when a laser beam having low transparency with respect to the laser beam used for forming the recess 55 is used, it is difficult for the laser beam to enter the inside of the coating 50, so that it is particularly difficult to form the closed recess 55b. This is because there is a tendency. In other words, it is preferable to form the concave portion 55 (hereinafter sometimes simply referred to as laser processing) using a laser beam having a high transmittance with respect to the film forming material of the coating 50. is there.

Therefore, as the resin component in the coating composition of the present invention , from the above viewpoint, polyester amino resins and epoxy resins that have been conventionally used as resin components for paints are used.

Incidentally, the polyester amino resin and epoxy resin used as the resin component in the present invention have the most preferable dispersibility of zinc oxide and titanium oxide when laser processing is performed with a YAG laser having a wavelength of 355 nm.

The coating composition of the present invention is prepared by dissolving or dispersing the above-described resin component and inorganic ultraviolet absorbent in an appropriate organic solvent or water or the like according to the type of the resin component. These solvents may be used in such an amount that the viscosity of the coating composition becomes a viscosity suitable for coating.
The coating on the predetermined substrate can be performed by any means such as brushing, dipping, spray spraying, etc., and after coating, the coating film is appropriately heat treated to cure the coating film as described above. A resin film 50 for forming the concave portions 55 for forming the structural color is formed.

  The thickness of the coating film 50 formed using the coating composition as described above is sufficient as long as it can form the concave portion 55 described above, and is generally at least 0.5 μm or more, particularly 1 to 15 μm. In this range, it is set according to the use of the base material 53 on which the resin film 50 is formed. Further, the coating 50 does not necessarily have to be formed on the entire surface of the base material 53, and can be formed on a part of the surface of the base material 53 in a desired pattern.

  In addition, the resin film 50 formed using the coating composition of the present invention has a form in which at least a part of the recess 55 formed by laser irradiation is closed, and the structural color is developed by mixing foreign substances. Therefore, the coating 50 can be provided so as to be exposed on the outer surface, and can be used without providing a protective layer thereon. In the case where a protective layer is provided on the resin coating 50, the protective layer is made to be laser transmissive, so that after forming the protective layer, laser irradiation is performed to form the concave portions 55 for structural color development. Can also be formed.

  Furthermore, when the adhesiveness between the base material 53 and the coating film 50 is poor, an adhesive resin layer can be appropriately provided between the base material 53 and the coating film 50. Such an adhesive resin layer is formed with an appropriate thickness by an adhesive resin known per se, for example, an unsaturated carboxylic acid-modified olefin resin such as maleic anhydride-modified polyethylene.

  As the base material 53 on which the resin coating 50 for the structural color development as described above is provided on the surface, various materials conventionally used for packaging bodies such as metal, glass, plastic, paper, etc., depending on the application. For example, a cap, a can lid, a can, a bottle, a cup, a tray, a pouch, a sheet, a film, and the like may be used in various forms depending on the application.

  Further, the surface of the substrate 53 on the side where the coating 50 is provided preferably has an average surface roughness Ra (JIS B-0601) of 10 μm or less, particularly 3 μm or less. As a result, a smooth coating 50 can be formed, and the concave portion 55 having a fine periodic structure having a regular arrangement can be easily formed by laser processing, and the structural color by the concave portion 55 is clearly projected, and the decorative property is improved. A structural color such as a high hologram image can be formed.

  The resin film 50 formed using the above-described coating composition is provided with the concave portions 55 (open concave portions 55a) by laser processing by irradiating the above-described inorganic ultraviolet absorber with laser light having a sensitivity in a predetermined pattern. And is formed by forming a closed recess 55b).

  A laser beam irradiation apparatus for performing such laser processing has the structure shown in FIG. 3, and the irradiation apparatus 10 indicated as a whole includes a laser oscillator 11, a beam splitter (transmission type). A diffractive optical element) 12, a collimator element 13, a light beam selection element 14, and a condensing element 15.

The laser oscillator (laser light source) 11 outputs a laser. In the present invention, a YAG laser, a YVO ₄ laser, a YLF laser, or the like can be preferably used.
In order to form the concave portion 55 on the surface of the coating film 50 described above, it is necessary to be a high power pulse laser, and when a structural color is expressed by a fine periodic structure, in order to efficiently develop color with visible light, The pitch of the fine periodic structure is preferably about 0.5 to 2 μm. In order to process the periodic structure with high accuracy, it is necessary to set the wavelength of the laser light to an ultraviolet wavelength region shorter than this pitch. Since the formation of the recess 55 is due to decomposition (laser ablation) of a resin or the like using interference of laser light, it is necessary to use a laser with high coherency. For this reason, the said laser can be used suitably.
In addition, these pulse lasers have a repetition frequency of several Hz to several tens of MHz, but since the stored energy is released in a very short time width of several ps to several tens ns during this repetition period, a small input is required. High peak power can be efficiently obtained from energy.

The laser oscillator 11 has a function of adjusting the number of irradiation pulses. The laser oscillator 11 can also control the energy density (fluence: energy per pulse irradiation area) by adjusting the laser output.
The energy density can be controlled not only by adjusting the laser output in the laser oscillator 11, but also by changing the irradiation beam diameter with the same laser output.

As already described, the resin film 50 formed using the coating composition of the present invention can form the recess 55 by laser irradiation at a low fluence (for example, 90 mJ / cm ² or less). This is the greatest advantage of the invention.

  The beam splitter 12 is a transmissive optical element that diffracts because fine concave portions or convex portions are periodically engraved on the surface, and divides laser light into a plurality of light beams.

  For example, a synthetic quartz plano-convex lens having a focal length of 200 mm can be used as the collimator element 13. In this case, the collimator element 13 is placed at a position 200 mm from the beam splitter 12. The collimator element 13 passes a plurality of light beams divided by the beam splitter 12.

The light beam selection element 14 is placed at a position where the light beam that has passed through the collimator element 13 is focused, blocks a light beam unnecessary for interference among a plurality of light beams, and allows only the necessary light beam to pass.
For example, a synthetic quartz plano-convex lens having a focal length of 100 mm can be used as the light condensing element 15, and the light flux that has passed through the light flux selecting element 14 is condensed, and the light fluxes intersect and interfere with each other.
In addition, as a collimator element and a condensing element, optical elements, such as a Fresnel lens and a GRIN (Graded-Index) lens, can be used besides a convex lens.

As shown in FIG. 4, the interfering area has a high intensity region distribution, and the laminated structure 20 indicated by 20 is irradiated in this region. At this time, the interval (period) d of the high intensity region in the interference region varies depending on the crossing angle θ of the light beams. The period d in the high intensity region can be obtained by the following equation using the laser wavelength λ and the crossing angle θ of the luminous flux.
d = λ / (2 sin (θ / 2))

That is, the laminated structure (20) in which the coating film 50 is formed on the surface of the base material 53 is disposed at a predetermined distance from the light condensing element 15 of the laser light irradiation device 10. This position is an interference region where a plurality of light beams intersect with each other through the condensing element 15 (see FIG. 4).
The laser light irradiation device 10 outputs laser light, the beam splitter 12 divides the laser light to form a plurality of light beams, and the light collecting element 15 crosses the plurality of light beams to form an interference region, The structure 20 is irradiated. Here, the laser beam is absorbed by the ultraviolet absorber in the coating (50) of the laminated structure 20. In addition, since the laser light irradiation is performed in the interference region, a periodic light intensity distribution is excited on the surface of the coating 50, the occurrence of laser ablation becomes significant in the high intensity portion, and the recess 55 is formed. . In the present invention, the ultraviolet absorber is dispersed in the coating 50, and laser ablation occurs due to the absorption of the dispersed ultraviolet absorber, so that there is some variation in the degree of laser ablation. An open concave portion 55a and a concave portion 55b whose surface is closed are generated, and the concave portions 55 (the concave portions 55a and the concave portions 55b) formed in this way are formed at the same period as the periodic intensity distribution of the laser beam. The Rukoto.

  The excellent effect of the present invention will be described in the following experimental example.

<Example 1>
Zinc oxide fine particles having an average particle size of 25 nm (MZY-505S, oleophilic) having an average particle diameter of 25 nm are added to a polyester amino paint in an amount of 20 parts by weight based on 100 parts by weight of the resin component of the paint. Was formulated. This paint was applied to one side of an aluminum plate (thickness: 200 μm) to prepare a sample. At this time, the thickness of the coating is about 2 μm. A Q switch pulse YAG laser third harmonic (wavelength 355 nm) was used as the laser light to be irradiated. The pulse width of the pulse YAG laser is 5 ns.
This sample was irradiated with one pulse at a fluence (laser irradiation energy density) of 60 mJ / cm ² using a laser beam irradiation apparatus from the side where the film was formed. As a result, a rainbow-colored structural color was observed and the color did not disappear even after rubbing with a finger.
Moreover, when the surface was observed with the scanning electron microscope (SEM), as shown in FIG. 2, it turned out that the recessed part open | released by the film and the recessed part with which the surface was closed were formed. Moreover, from this SEM photograph, the recessed part with which the surface was closed was 80% of all the recessed parts.

<Comparative Example 1>
A benzotriazole ultraviolet absorber (ADEKA STAB LA-31 manufactured by ADEKA Co., Ltd.) was added to the polyester amino paint in an amount of 1 part by weight based on 100 parts by weight of the resin component of the paint to prepare a paint. This paint was applied to one side of an aluminum plate (thickness: 200 μm) to prepare a sample. At this time, the thickness of the coating is about 1 μm.
This sample was irradiated with one pulse from the side where the film was formed using a laser beam irradiation apparatus. As a result, a rainbow-colored structural color was observed and the color did not disappear even after rubbing with a finger. At this time, the fluence was 150 mJ / cm ² .

<Examples 2 to 5>
The same zinc oxide fine particles as in Example 1 were added to paints of various resin compositions in an amount of each part by weight based on 100 parts by weight of the resin component to prepare a paint. Confirmation of the presence of structural color and the change after rubbing the surface with a finger on a sample (coating thickness: about 1 to 5 μm) prepared by applying this to an aluminum plate. The results are shown in Table 1.

<Example 6>
Add 150 parts by weight or 200 parts by weight of zinc oxide fine particles with an average particle size of 25 nm (Made by Teika Co., Ltd., MZ-500, hydrophilic) to the epoxy paint with respect to 100 parts by weight of the resin component of the paint. Then, paint was prepared. A sample (coating thickness: about 5 μm) prepared by applying this to an aluminum plate was irradiated with laser in the same manner as before.
As a result, a rainbow-colored structural color was observed and the color did not disappear even after rubbing with a finger. Moreover, when 150 weight part was added, compared with Example 5, the cloudiness of the coating film was weak and the visibility of color development was favorable.

<Example 7>
40 parts by weight of titanium oxide fine particles (Ishihara Sangyo Co., Ltd., TTO-55 (D), hydrophilic) having an average particle diameter of 40 nm are added to epoxy paint with respect to 100 parts by weight of the resin component of the paint. Then, paint was prepared. This paint was applied to one side of an aluminum plate (thickness: 200 μm) to prepare a sample. A sample (coating thickness: about 2 μm) prepared by applying this to an aluminum plate was irradiated with laser in the same manner as before.
As a result, a rainbow-colored structural color was observed and the color did not disappear even after rubbing with a finger.

<Example 8>
The same zinc oxide fine particles as in Example 1 were added to the epoxy paint in an amount of 40 parts by weight with respect to 100 parts by weight of the resin component of the paint to prepare the paint. This paint was applied to one side of an aluminum plate (thickness: 200 μm) to form a film, and then a polyesteramino paint was applied on the film to form a protective layer. A sample was prepared in this way. At this time, the thickness of the coating is about 3 μm, and the thickness of the protective layer is about 6 μm.
This sample was irradiated with a pulse YAG laser third harmonic (wavelength 355 nm) from the side where the coating film and the protective layer were formed using a laser beam irradiation device at a fluence of 60 mJ / cm ² . As a result, a rainbow-colored structural color was observed and the color did not disappear even after rubbing with a finger. At this time, the regularly arranged concave portions exist at the interface with the protective layer on the very outermost surface of the coating.

50: Resin coating for structural color development 53: Substrate 55: Concave for structural color development 55a: Concave with open surface 55b: Concave with closed surface

Claims (1)

In a coating composition for forming a structural color-developing film in which concave portions of a regular arrangement for forming a structural color are formed by laser light irradiation , including polyesteramino resin or epoxy resin as a resin component, inorganic type It contains zinc oxide or titanium oxide having an average particle diameter of 2000 nm or less as the ultraviolet absorber particles, and the inorganic ultraviolet absorber particles are added in an amount of 0.5 to 300 parts by weight per 100 parts by weight of the resin component. A coating composition characterized by