JP5677227B2 - Opal, method for producing the same, paint and printed matter using the same - Google Patents

Description

  The present invention relates to an opal, a method for producing the same, a paint using the same, and a printed matter.

  Opal is not only naturally mined, but also artificially produced from silica particles. For example, Patent Document 1 discloses a thin film in which silica particles are regularly arranged. The thin film of this silica particle array has a periodic structure in which the plane orientation in the film plane is aligned, and the crack area ratio is 8% or less.

JP 2006-208453 A

  However, the silica particle array thin film as disclosed in Patent Document 1 is intended to form a single crystal. When viewed from the same direction, for example, when viewed in plan, the single crystal having the same plane orientation on the plane. Only the same hue was seen because it was only exposed, and there was a case where the play effect was poor.

  Furthermore, when the silica particle array thin film as in Patent Document 1 is used in the form of powder and used as a glittering material for paints, the silica particle array does not become a thin film but agglomerates because it has a structure that is difficult to cleave. In some cases, the mass per surface area was increased, and precipitation occurred without being dispersed in the paint. For this reason, if the powder of the silica particle array thin film is not used while being constantly stirred in the paint, the glitter material is likely to be uneven in coating, and is unsuitable as a glitter material used by mixing with the paint.

  The opal of the present invention is an opal comprising a group of silica particles having a plurality of different crystal structures, the silica particle group having one crystal structure and a silica particle having another crystal structure different from the one crystal structure Grooves are formed between the groups.

Further, opal production method of the present invention, a slurry-like dispersion in a proportion of 20 to 35 wt% of silica particles in water or an organic solvent, a is placed in a polyethylene terephthalate or aluminum substrate One step includes a second step of depositing the silica particles by drying the dispersion on the substrate, and a third step of firing the deposited silica particles.

  Furthermore, the coating material of the present invention contains the opal.

  Furthermore, the printed matter of the present invention is printed with the paint.

  According to the opal of the present invention, even when viewed from the same direction, different hues are exhibited simultaneously by having a plurality of plane orientations on the same plane, which is rich in a playable color effect.

  Moreover, according to the opal manufacturing method of the present invention, it is possible to mass-produce opal excellent in play-color effect in a thin film with good reproducibility.

  Furthermore, the paint of the present invention contains the opal. As described above, since this opal is easily cleaved into a thin film, it is easy to float and disperse in the paint as a bright material, so that the opal can be applied evenly, and a stable play effect after application Will be presented.

  Furthermore, since the printed matter of the present invention is printed with the paint, the opal has no unevenness and the paint has a sense of transparency.

It is a drawing substitute photograph of the surface of the conventional opal. It is a schematic diagram of the main surface of the opal in this embodiment. (A), (b) is the drawing substitute photograph of the main surface of the opal in this embodiment, (b) is the partial enlarged photograph in the dotted line of (a). It is a drawing substitute photograph of opal in this embodiment. It is a schematic diagram which shows the silica particle in the 1st process of the manufacturing method of the opal in this embodiment. It is a schematic diagram which shows the silica particle in the 2nd process of the manufacturing method of the opal in this embodiment. It is a schematic diagram which shows the silica particle in the 3rd process of the manufacturing method of the opal in this embodiment. It is a drawing substitute photograph which shows the silica particle in the 2nd process of the manufacturing method of the opal in this embodiment, (a) is before drying, (b) is after drying.

(opal)
Hereinafter, an embodiment of the opal of the present invention will be described with reference to the drawings.

  The present embodiment is an opal composed of a group of silica particles having a plurality of different crystal structures, and a group of silica particles having one crystal structure and a group of silica particles having another crystal structure different from the one crystal structure A groove is formed between the two.

  In general, opal emits a predetermined hue by causing Bragg diffraction due to the crystal structure (usually a hexagonal close-packed structure) of silica particles 2a as shown in FIG. 1, and the hue is the particles of silica particles 2a. It is determined by the diameter, interparticle distance and crystal structure.

  Here, the silica particles 2a of the opal 1 of FIG. 1 are in a single crystal form arranged in the same crystal structure, but the opal 1 of this embodiment is not limited to a single crystal structure as shown in FIG. FIG. 2 shows a polycrystal with various crystal structures as shown in FIG.

  That is, as shown in FIG. 2, there are silica particle groups 2 having different crystal structures, and the grooves 5 are formed between the silica particle groups 2 having different crystal structures.

  The conventional opal is in a single crystal state in which the plane orientation of each silica particle group 2 is aligned on the same plane, and the particle arrangement is not different with the groove 5 as a boundary. Boundary where the surface orientation is different in a polycrystalline state in which silica particle groups 2 having a plurality of different crystal structures such as silica particle group 2 of packed structure 6 and silica particle group 2 of face-centered cubic structure 7 are assembled together Thus, the groove portion 5 is formed.

  As shown in FIG. 8, the groove portion 5 is not yet clearly formed before drying (a), but after drying (b), the polycrystalline opal 1 in which the groove portion 5 is more clearly formed is observed. Is done.

  As shown in FIG. 4, by having different crystal structures, even when the opal 1 is viewed from the same direction in a plan view, the opal 1 exhibits a different hue and has an excellent playable color effect. Can do.

  Examples of the crystal structure include structures such as a body-centered cubic structure, a simple cubic structure, an orthorhombic structure, and a tetragonal structure in addition to the hexagonal close-packed structure 6 and the face-centered cubic structure 7.

  The size of the silica particles 2a is not particularly limited, and for example, those having an average particle size of 200 to 300 μm are used. Within this range, it is advantageous in that it exhibits the most playable color effect by Bragg diffraction, and the sizes of these silica particles 2a are formed to be approximately equal to each other.

  By having such a groove portion 5 on the surface of the opal 1, cleavage is likely to occur on the surface, and the opal 1 having a small mass per surface area is likely to be formed. It floats in the paint and becomes easy to disperse.

  Further, since the surface resistance of the opal 1 is moderately increased, it is difficult for the opal 1 powder to settle even if it is mixed with the paint, and it is easy to float and disperse in the paint as a bright material.

  Alternatively, the same effect can be obtained by increasing the buoyancy of the opal 1 by attaching bubbles to the groove 5 as a starting point.

  The groove portion 5 refers to a space generated between the silica particle groups 2 when the silica particle groups 2 contract on the outermost surface of the opal 1 as the silica particles 2a aggregate. The groove 5 is often formed on the outermost surface, but is not limited to the outermost surface.

  Here, the outermost surface means a layer of silica particles 2a forming the outermost layer in the silica particle group 2 arranged on the surface of the opal 1 (first layer in FIG. 7).

  Furthermore, in this embodiment, it is preferable that the silica particle group 2 includes a silica particle group 2 having a hexagonal close-packed structure 6 and a silica particle group having a face-centered cubic structure 7.

  FIG. 2 is an enlarged view of the surface of the opal 1 of the present embodiment. When viewed in plan, the silica particle group 2 having the hexagonal close-packed structure 6 has the silica particles 2a in contact with each other at six points. The silica particle group 2 having the face-centered cubic structure 7 has a polycrystalline shape in which the silica particles 2a are in contact with each other at four points.

  The hexagonal close-packed structure 6 and the face-centered cubic structure 7 can exhibit different colors, and an excellent play-color effect can be obtained.

  Further, in the layer of the silica particles 2 a on the outermost surface of the opal 1, the hexagonal close-packed structure 6 and the face-centered cubic structure 7 are separated through a groove portion 5 (a gap portion along the broken line). The interval between the grooves 5 is about 0.05 to 0.2 μm.

  FIGS. 3A and 3B are SEM photographs showing the main surface of the opal 1 of the present embodiment, and the silica particle group 2 having the hexagonal close-packed structure 6 as shown in FIG. It can be seen that a groove 5 indicated by a broken line is formed between the silica particle group 2 having the cubic structure 7.

Here, the silica particle group 2 having the hexagonal close-packed structure 6 and the silica particle group 2 having the face-centered cubic structure 7 are listed, but the silica particle group 2 having other crystal structures and the like also exist. Is preferred.

  In addition, as shown in FIG. 3, the silica particle 2a may have a part where a part of the silica particle 2a is shed.

  Even if the crystal structures are different, some of the grooves 5 may not be formed. This is because the silica particle groups 2 having different crystal structures may be fused via an impurity that lowers the melting point before they break apart.

  Moreover, even if there is a portion where the crystal structure sandwiching the groove portion 5 has the same plane orientation, the effect of the present application is not hindered.

  In addition, due to the influence of the gap due to the groove portion 5, even if the silica particle groups 2 have the same crystal structure, they may be separated at the groove portion 5, but this further increases the surface resistance of the opal 1, so that It is preferable in that it floats in the paint and easily disperses.

  Furthermore, in this embodiment, the silica particle group having one crystal structure is a silica particle group having a hexagonal close-packed structure, and the silica particle group having the hexagonal close-packed structure is 40% in the entire particle group. It is preferable to contain ~ 80%.

  Thereby, the play color effect which has blue-red color development can be exhibited.

  Furthermore, this embodiment is a plate-like body having two main surfaces, and the thickness of the plate-like body is preferably 0.5 to 10 μm.

  Here, in this specification, the main surface is two large surfaces facing each other on the front and back of the plate-like body, and the occurrence of cracks due to stress concentration on the thin portion of the opal 1 can be reduced. It is preferable that two main surfaces are substantially parallel at the point which can do.

  By setting the thickness to 0.5 μm or more, the opal 1 can have a certain strength or more, and by setting the thickness to 10 μm or less, it can exhibit a transparent play effect as shown in FIG. it can.

  In FIG. 4, the opals 1 that are different from each other when viewed from the same direction are shown. For example, it can be seen that the polycrystalline structure opal 1b has a plurality of plane orientations on the same plane, thereby simultaneously exhibiting different hues.

  Here, the opal 1 powder may contain the opal 1 that does not have the groove 5 separated along the groove 5 in addition to the opal 1 of the present application. For example, the single crystal structure opal 1a in FIG. 4 corresponds to this.

  Further, in the case of the opal 1 powder, even if only one outermost layer of the opal 1 is partially cleaved and peeled off, the Bragg diffraction can be performed.

  This is because only the first layer on the outermost surface is easily peeled off due to the stress difference between the first layer and the second layer.

  For example, the first layer in FIG. 7 is in a state where it can be easily peeled off from the second layer of silica particles 2a due to the stress caused by the aggregation of the silica particles 2a.

Furthermore, since the surface area is larger than the mass, it is easy to float and disperse in the paint as a bright material. In particular, the ratio (S / W) of the mass (W) of the opal 1 and the sum (S) of the surface areas of the two main surfaces is in the range of 6 × 10 ^{−5 to} 6 × 10 ^−6. preferable.

  The average thickness can be measured by observing the cross section of an arbitrary opal 1 with a microscope.

  In this case, the groove portion 5 may be formed not only on one main surface but also on the other main surface (that is, both the front and back surfaces), thereby further reducing the precipitation of the silica particles 2a.

Furthermore, in this embodiment, the number of silica particles per unit area on the main surface is preferably 16 / μm ² or more.

  As a result, Bragg diffraction is likely to occur on the main surface, so that a stable play effect and brightness can be obtained.

  For example, the number per unit area of the silica particles 2 a on the main surface can be measured by measuring the number per unit area of the silica particles 2 a on the cross section of the opal 1. Specifically, the cross section of the opal 1 is magnified 3000 to 10,000 times in the secondary electron image of the SEM, and the number of silica particles 2a in 1 μm square is counted. Then, the density may be calculated in terms of the mass of the silica particles 2a.

  Furthermore, in this embodiment, the flatness of the main surface is 10 μm or less, and the arithmetic average surface roughness Ra of the main surface is 1 μm or less.

  Thereby, since irregular reflection is suppressed on both main surfaces, the opal 1 having high luminance can be obtained.

  In the present specification, for example, a measuring method using an optical flat is used for the flatness. An optical interference fringe is generated by bringing a reference flat (optical flat) into contact with a work (opal) that has been completely flattened, and a short-wavelength light source is applied thereto. Measure the degree. In other words, this is a comparative measurement between the workpiece and the optical reference standard (optical flat). It is assumed that the surface roughness is up to the mirror surface. In addition, for example, a laser beam is used instead of the short wavelength light source and reflected optically to generate interference fringes, which are digitally processed or manually analyzed. For example, in the case of measurement with a three-point gauge, a three-point gauge comparative measurement is possible if it is on the micron order.

  About the measuring method of arithmetic mean surface roughness, it can confirm by measuring the main surface of arbitrary opal 1 with an atomic force microscope.

  Furthermore, this embodiment can be used as a paint containing opal, and can also be applied to cosmetic lamé.

  Furthermore, as a printed matter printed with the paint of this embodiment, it can be applied to wallpaper, wrapping paper, advertising bodies, etc., and the opal 1 has a groove portion 5 on its surface, so that it adheres to the paint solidified by drying. The opal 1 can be hardly peeled off from the printed matter.

Further, the present invention is not limited to a printed material printed with a paint, and can be applied to a resin molded product formed by mixing with various resins such as acrylic, epoxy, and urethane including the opal 1 of the present embodiment. There are uses such as materials.

  Alternatively, not limited to the above-described resin, the opal 1 may be mixed with a colorless and transparent water-based or oil-based solvent-type ink to form a paint.

(Opal production method)
Next, the manufacturing method of the opal of this invention is demonstrated using FIGS.

  This embodiment is a first step in which a slurry-like dispersion containing 20 to 35% by mass of silica particles in water or an organic solvent is disposed on a polyethylene terephthalate or aluminum substrate with a predetermined thickness, the substrate The method includes a second step of depositing the silica particles by drying the dispersion liquid, and a third step of firing the deposited silica particles.

  The wettability between the slurry-like dispersion 4 having 20 to 35% by mass of the silica particles 2a and the substrate 3 made of polyethylene terephthalate or aluminum is appropriate (for example, the contact angle between the substrate 3 and water is 20 to 45 degrees, Alternatively, the contact angle between the substrate 3 and the organic solvent is 20 to 25 degrees), and thus the production of the opal 1 of the present embodiment that could not be realized conventionally can be realized.

  Such an organic solvent preferably has a certain degree of polarity that is soluble in water. Specific examples include methanol, ethanol, isopropyl alcohol, chloroform, ether, acetone, and the like.

  When the contact angle is large, the dispersion liquid 4 becomes spherical, and the dispersoid 2a in the dispersion liquid 4 aggregates at one place due to the influence of the surface tension, so that the silica particle group 2 having a single crystal structure is easily formed. If it is small, the dispersion 4 spreads and the silica particles (dispersoids) 2a are too far apart from each other, so that it is difficult to form the silica particle group 2 having a crystal structure.

  The silica particles 2a can be adjusted, for example, by the following method.

  First, 100 parts by mass of colloidal silica and 100 parts by mass of methanol are mixed, and the resulting mixture is centrifuged at 10,000 rpm for about 1 hour in a centrifuge.

  Furthermore, after discarding only the supernatant and replenishing with methanol, the silica particles 2a can be obtained by repeating the centrifugal separation again several times.

  The concentration of the silica particles 2a in the dispersion 4 is appropriately adjusted according to the substrate 3 to be used. For example, from the viewpoint of dispersion of the silica particles 2a and ease of colloidal particle formation, the silica particles 2a are prepared so as to form a slurry having a concentration of 20% by mass to 35% by mass.

  The substrate 3 made of polyethylene terephthalate or aluminum in FIGS. 5 to 7 needs to have a smooth surface, and the flatness and surface roughness of the substrate 3 are directly reflected in the surface properties of the opal 1.

  (First Step) As shown in FIG. 5, the dispersion liquid 4 is quickly disposed on the substrate 3 with a uniform thickness, and the dispersion liquid 4 is repelled by water repellency or the like and the amount to be disposed does not decrease. Since the substrate 3 desirably has good wettability with the dispersion 4, the dispersion 4 is in a slurry state, and a substrate 3 made of polyethylene terephthalate or aluminum is used.

  (Second Step) Next, as shown in FIG. 6, the dispersion medium 4a is removed from the dispersion 4 disposed on the substrate 3 by heating means. At this time, the surface orientation of the outermost silica particle group 2 varies depending on the degree of aggregation of the outermost silica particles 2a, particularly the difference in the aggregation rate of the silica particles 2a.

  This is due to the fact that the distribution of the droplets of the dispersion liquid 4 causes a local distribution of the aggregation rate on the droplet surface.

  In order to quickly produce an aggregate of the silica particles 2a, an infrared heater, hot air drying, or the like can be used as the heating means.

  (Third step) Next, as shown in FIG. 7, grooves 5 are formed on the outermost surface of the heated and dried silica particle group 2, and by firing the silica particles 2a in this state, The silica particles 2a are fused and fixed.

  Furthermore, in the present embodiment, in the first step, the dispersion is preferably applied at 10 to 100 μm using a bar coater.

  Although it is most preferable in that the bar coater is applied thinly and uniformly, other means such as dipping or a dispenser may be used if possible.

  Furthermore, this embodiment is preferably dried at a drying temperature of 60 to 80 ° C. and a heating rate of 5 to 10 ° C./second in the second step.

  Thereby, the silica particles 2a on the outermost surface of the opal 1 can be locally aggregated as shown in FIG.

  Further, within this temperature increase rate range, the droplets of the dispersion 4 are gradually dried from the end portions, and the silica particles 2a are sequentially aligned along the substrate surface, so that the flatness of the silica particle group 2 is small. Tend to be. As a result, the silica particle group 2 tends to have a constant hue in the same direction.

  When the flatness is large, various hues tend to be mixed and become white.

  Furthermore, in the present embodiment, the firing in the third step is preferably performed at 500 to 900 ° C. for 1 to 10 hours.

  Thereby, the polycrystalline silica particles 2a on the outermost surface of the opal 1 can be fused and fixed as shown in FIG.

  Moreover, by gradually drying the droplets of the dispersion 4 so as not to boil, the droplets are dried so that the alignment of the silica particles 2a is not disturbed, and the surface roughness of the silica particle group 2 tends to be reduced. is there. As a result, the surface of the silica particle group 2 is regularly arranged, so that Bragg diffraction is improved and irregular reflection on the surface is reduced.

  If the opal 1 of the present embodiment obtained by the above manufacturing method is pulverized into powder and mixed with a paint such as ink or paint, the following printing method can be performed, for example.

  For example, it is most preferable to use a gravure coater as a printing method, coating with a film thickness of 3 to 30 μm is possible, and it can be applied to various substrates and the control of the coating distance is easy.

  In addition to gravure coaters, slot die coaters are resistant to the effects of substrate thickness, dust, etc., and can handle a wide range of speeds from low to high.

  In addition, the CAP coater can be applied with a film thickness of 0.1 to 5 μm, and can realize high-precision coating with a uniformity of ± 2%.

  (Sample Preparation) As an example, an opal 1 based on the conditions shown in Table 1 was prepared (sample numbers 2 to 23), and an opal based on Patent Document 1 was prepared as a conventional example (sample number 1).

  When the obtained sample 1 was observed by SEM, it had a single crystal structure (only the hexagonal close-packed structure 6) as shown in FIG.

  Further, when the obtained sample 4 was observed by SEM, it had a hexagonal close-packed structure 6 and a face-centered cubic structure 7 as shown in FIGS.

  In the first step, the dispersion 4 was prepared by using water as the dispersion medium 4a and the concentration of the silica particles 2a serving as the dispersoid being prepared, and using a bar coater as the coating means.

  The concentration and coating thickness of the silica particles (dispersoid) 2a in the dispersion 4 were variously changed as shown in Table 1. PET, aluminum, and glass were used as the material of the substrate 3.

  In the second step, an infrared heater was used as the heating means, and the drying temperature and the heating rate were variously changed as shown in Table 1.

  Moreover, in the 3rd process, the opal 1 was obtained by baking in a baking crucible as a baking means.

  As shown in Table 1, various changes were made as shown in Table 1, with a firing temperature of 700 ° C. and a firing time of 5 hours as standard conditions.

  The opal 1 obtained by firing in the third step was peeled off from the substrate 3 with a rim bar, pulverized with a ball mill, and pulverized to obtain an evaluation sample having a long side of 2-3 mm.

  The sample preparation conditions are shown in Table 1 below.

  (Sample evaluation) Ten arbitrary evaluators were selected, and the main surface of the obtained opal 1 was observed at a magnification of 20 times using a factory microscope, and the hue, transparency, play-color effect, and dispersibility were compared. When there were 10 people who felt superior to the example (Sample 1), it was judged as ◯, when it was 9-6 people, Δ, when it was 5 people or less, it was judged as x.

  Table 2 shows the opal 1 produced under the sample preparation conditions shown in Table 1 and the sample evaluation results.

  Hereinafter, the evaluation results will be described.

  Sample No. 1 was a comparative example (conventional example), and since it was not a thin film, the thickness was increased, the color became white, the hue was weak, and transparency was lacking. In addition, since only the hexagonal close-packed structure 6 is used, when viewed from the same direction, only the same hue can be seen, so that the play color effect is poor. Moreover, since it does not become a thin film, the dispersibility may be poorly precipitated in the paint, which is not within the range that can be used as a bright material for the paint.

  In sample numbers 2 to 6, the correspondence between the ratio of the types of crystal structures (the hexagonal close-packed structure 6 and the face-centered cubic structure 7) and hue, transparency, play-color effect, and dispersibility was confirmed.

  As a result, Sample Nos. 3, 4 and 5 are more likely to generate good Bragg diffraction due to the regular crystal structure having a high density of silica particles 2a, and are superior to Sample No. 2 in terms of hue. In addition, a plurality of types of hues were obtained depending on the balance of the ratio of the hexagonal close-packed structure 6 and the face-centered cubic structure 7, which was superior to the sample number 6 in terms of the play color effect.

  In sample numbers 7 to 10, the correspondence between the thickness of Opal 1 and hue, transparency, play-color effect, and dispersibility was confirmed.

  As a result, Sample Nos. 8 and 9 have a deep hue and excellent transparency, excellent hue due to stronger Bragg diffraction than Sample No. 7, and are thinner and thinner than Sample No. 10 in terms of transparency. It was.

  In addition, it turned out that what the silica particle 2a arranged is obtained even if the thickness of the opal 1 is 1 micrometer (thickness for 4 particles) or less like the samples 7 and 8.

  In Sample Nos. 11 to 14, the flatness of the opal 1 was controlled by the rate of temperature increase, and correspondence with hue, transparency, play-color effect, and dispersibility was confirmed.

  In Sample Nos. 12, 13, and 14, by slowing the rate of temperature rise, the droplets of the dispersion 4 are gradually dried from the end portions, and the silica particles 2a are sequentially aligned along the substrate surface, and the silica particles group The flatness of 2 is reduced.

  As a result, the silica particle group 2 tends to have a constant hue in the same direction, which is superior to the sample number 11 in terms of hue.

  In sample numbers 15 to 18, the surface roughness of the opal 1 was controlled by the drying temperature, and the correspondence between hue, transparency, play-color effect, and dispersibility was confirmed.

  In Sample Nos. 16, 17, and 18, the droplets of the dispersion liquid 4 are gradually dried so as not to boil, whereby the droplets are dried so that the alignment of the silica particles 2a is not disturbed. The surface roughness can be reduced.

  As a result, the surface of the silica particle group 2 has a regular arrangement, so that Bragg diffraction is improved, and irregular reflection on the surface is reduced, which is superior to the sample number 15 in terms of hue density and transparency. It was.

  In sample numbers 19 and 20, the correspondence between the material of the substrate 3 and the hue, transparency, play color effect, and dispersibility was confirmed.

  As a result, the same effect as in the case of using polyethylene terephthalate could be obtained with the aluminum sample No. 19.

  When the glass of sample number 20 was used, it was a comparative example, and since the wettability between the glass and the dispersion liquid 4 was poor, it was water-repellent, resulting in large spherical droplets and granular opals. For this reason, only a hue due to a single crystal structure was exhibited, and since it was thick, it was cloudy. Moreover, even if it mixes with a coating material, it precipitated because it was a big spherical shape.

  In sample numbers 21 to 24, correspondences between the degree of firing (firing temperature, firing time) and hue, transparency, play-color effect, and dispersibility were confirmed.

  As a result, Sample Nos. 22 and 23 are not overfired as compared with Sample No. 21 and are not insufficiently calcined as compared with Sample No. 24. Therefore, stable Bragg diffraction can be obtained with a stable crystal structure. Excellent in terms.

  As described above, it was found that Sample Nos. 3 to 5, 8, 9, 12 to 14, 16 to 19, 22, and 23 exhibited excellent hue, transparency, color play effect, and dispersibility.

  Samples Nos. 2, 6, 7, 10, 11, 15, 21, and 24 are also embodiments of the present application and have characteristics superior to those of Comparative Examples 1 and 20.

1: Opal 1a: Single crystal structure opal 1b: Polycrystalline structure opal 2: Silica particle group 2a: Silica particles (dispersoid)
3: Substrate 4: Dispersion 4a: Dispersion medium 5: Groove 6: Hexagonal close-packed structure 7: Face-centered cubic structure

Claims (13)

An opal comprising a group of silica particles having a plurality of different crystal structures,
An opal in which a groove is formed between a group of silica particles having one crystal structure adjacent on the surface and a group of silica particles having another crystal structure different from the one crystal structure. The opal according to claim 1, wherein the groove has a bent portion in a plan view. The opal according to claim 1 or 2 , wherein the silica particle group includes a silica particle group having a hexagonal close-packed structure and a silica particle group having a face-centered cubic structure. The silica particle group having the one crystal structure is a silica particle group having a hexagonal close-packed structure,
The opal according to any one of claims 1 to 3 , wherein the silica particle group having the hexagonal close-packed structure is contained by 40 to 80% in the entire silica particle group. The opal according to any one of claims 1 to 4 , wherein the opal is a plate-like body having two main surfaces, and the thickness of the plate-like body is 0.5 to 10 µm. The opal according to claim 5 , wherein the number of silica particles per unit area on the main surface is 16 / μm ² or more. The opal according to claim 5 or 6 , wherein the flatness of the main surface is 10 µm or less, and the arithmetic average surface roughness Ra of the main surface is 1 µm or less. The slurry dispersion in a proportion of 20 to 35% by weight of water or silica particles in an organic solvent, a first step to place a polyethylene terephthalate or aluminum substrate, on the substrate, the dispersion An opal production method comprising a second step of depositing the silica particles by drying and a third step of firing the deposited silica particles. The manufacturing method of the opal of Claim 8 arrange | positioned on the said board | substrate by apply | coating the said dispersion liquid by the thickness of 10-100 micrometers using a bar coater in the said 1st process. The method for producing opal according to claim 8 or 9 , wherein, in the second step, drying is performed at a drying temperature of 60 to 80 ° C and a temperature increase rate of 5 to 10 ° C / second. The method for producing opal according to any one of claims 8 to 10 , wherein, in the third step, baking is performed at 500 to 900 ° C for 1 to 10 hours. A paint comprising the opal according to any one of claims 1 to 7 . A printed matter printed with the paint according to claim 12 .