JPH1113987A - Heat ray shielding plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat ray shielding plate which allows syrup to be easily injected in the inside of a mold, does not allow lamellar leaves to be sedimented within a molded item, and but allows syrup to be easily oriented in parallel with respect to the surface of the molded item only by injecting syrup. SOLUTION: A heat ray shielding plate comprises syrup polymerized with monomer solution in methyl methacrylate system and hardened therein by injecting syrup in a mold where aforesaid syrup includes 0.01 to 10 parts of lamellar leaves by weight and polymerization initiator, and a ratio (η1 /η2 ) of viscosity η1 at 6 min<-1> to viscosity η2 at 60 min<-1> for aforesaid monomer solution, is more than 1.3 in which viscosity is measured based on JIS K-7117. The thermic ray shielding plate is easy to manufacture, and allows lamellar leaves to be easily oriented in parallel with respect to the surface of a molded item.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a heat ray shielding plate.

[0002]

2. Description of the Related Art Conventionally, a heat selection shielding plate has been used for a lighting part,
A cool and bright daylighting window has been proposed which transmits visible light and blocks heat rays. An acrylic polymer having excellent transparency and weather resistance may be used as a base material of the heat ray shielding plate. On the other hand, acrylic polymers have excellent transparency, surface hardness, and weather resistance, and are widely used as building materials such as signboards and lighting covers, optical materials such as optical disc substrates, light guide plates, and optical fibers. The acrylic polymer can further be used as an acrylic composite material having functional and structural characteristics by adding a light diffusing agent, a pigment, a filler, an antistatic agent, and an inorganic filler such as glass fiber. Among these acrylic composite materials, plate-like flakes such as titanium dioxide-coated mica flakes, titanium oxide flakes, and basic lead carbonate flakes are added as inorganic fillers, and the plate surface is oriented parallel to the surface of the molded body. Heat ray shielding plates are conventionally known. As a production method, a syrup obtained by adding a plate-like flake and a polymerization initiator to an acrylic monomer or an acrylic partial polymer is poured into a mold having a desired shape, polymerized and cured, and then the mold is removed. There is a method of obtaining a molded body by pressing.
In this method, the dispersed plate-like flakes may settle during the period from injection into the mold to completion of polymerization curing,
There were problems such as the physical properties being different between the front and back surfaces of the obtained molded article, and the occurrence of warpage due to a temperature change.

As a method for preventing sedimentation of plate-like flakes, a method of increasing the viscosity by dissolving an acrylic polymer in an acrylic monomer, or increasing the viscosity of a syrup by partially polymerizing a part of the acrylic monomer. The method is general.

Further, in order to obtain an acrylic composite material having a sufficient heat ray shielding ability, it is necessary to orient the plate surface of the plate-shaped flake parallel to the surface of the molded product by some method. As a method therefor, a method is known in which syrup is poured into a mold and then subjected to electric vibration or a method of sliding. Japanese Patent Application Laid-Open No. Sho 62-268615 discloses that two endless belts facing each other and running opposite to each other using basic lead carbonate, fish scale, bismuth trichloride, and mica coated with titanium dioxide as plate-like flakes. A polymerization initiator in a monomer or partial polymer containing methyl methacrylate as a main component in a space formed by a gasket that runs between the belts on both sides near the two side ends and runs following the running of the belt, A method in which plate-like flakes are mixed, injected, and cured by heating and polymerization. The support and movement of two endless belts and the distance between the two endless belts are set by a carrier roll, and the polymerizable material is in a fluid state. At this time, a method of giving an amplitude up and down in a range of (L-1) mm to (L + 1) mm with respect to a desired plate thickness L at least once is shown.

On the other hand, the isotactic methyl methacrylate polymer and the syndiotactic methyl methacrylate polymer form a gel called a stereocomplex methyl methacrylate polymer in an organic solvent such as a methyl methacrylate monomer. It is widely known. The methyl methacrylate monomer solution of the stereocomplex methyl methacrylate polymer is a high-viscosity gel at room temperature. However, when heated, the viscosity sharply decreases to a low-viscosity sol. This so-called sol-gel transition occurs reversibly with temperature. For example, Japanese Patent Publication No. 47-14834 discloses that a high-viscosity gel obtained by dissolving this stereocomplex methyl methacrylate polymer in a polymerizable monomer is once heated to form a low-viscosity sol, To polymerize and cure at a temperature below the melting point of the gel.

[0006]

As a method of preventing sedimentation of plate-like flakes, a method of dissolving an acrylic polymer in an acrylic monomer, or a method of partially polymerizing an acrylic monomer to partially polymerize a syrup. In the method of increasing the viscosity, a syrup having a considerably high viscosity must be obtained in order to obtain a sufficient anti-settling effect. Such a high-viscosity syrup is available from JI
When the viscosity was measured by a method based on SK-7117,
6min viscosity eta ₂ of the ratio of the viscosity eta ₁ and 60min ^-1 at ^-1 (η ₁ / η ₂₎ is close to 1, the same viscosity after filling into viscosity and mold when injected into a mold It is. Therefore, it becomes difficult to inject into the mold. Further, in this method, a sufficient effect cannot be obtained when a plate-like flake having a large particle size or a plate-like flake having a large density difference from an acrylic monomer is added.

In addition, a method of applying electric vibration, a method of sliding, a method of using an endless belt, or the like, which is a method of orienting the plate surface of the plate-shaped flake parallel to the surface of the molded article, is used. In the method of orienting by the method, it is necessary to control the viscosity of the syrup and the timing of orienting well, and the degree of orientation of the molded article tends to be uneven.

In the method disclosed in Japanese Patent Publication No. 47-14834, in which a high-viscosity gel is raised into a low-viscosity sol by injecting it into a mold, it is difficult for the inorganic filler to settle by the completion of polymerization curing. When the polymerization temperature is increased, the radical polymerization initiator used for the decomposition is decomposed, and the generated radical cures the polymerizable monomer. Therefore, if the operation of injecting into the mold is not performed promptly, the viscosity rapidly increases due to polymerization during the injection, and it becomes particularly difficult to inject into the mold having a small clearance.

In view of such circumstances, the present inventor has conducted intensive studies on the heat ray shielding plate. As a result, the viscosity was measured by a method in accordance with JIS K-7117, and the viscosity η ₁ at 6 min ⁻¹ and 60 were measured.
A syrup containing a plate-like flake and a polymerization initiator is poured into a mold into a methyl methacrylate-based monomer solution having a viscosity η ₂ ratio (η ₁ / η ₂ ) at min ^-1 of 1.3 or more. By polymerizing and curing, it is easy to inject into the mold and the plate-shaped flakes do not settle in the molded product. They found that they could be manufactured and completed the present invention.

[0010]

That is, the present invention provides a JI
The viscosity was measured by a method according to SK-7117, and 6 mi
viscosity eta ₂ of the ratio of the viscosity eta ₁ and 60min ^-1 at n ^-1 (η ₁
/ Η ₂ ) is injected into a mold with a syrup containing 0.01 to 10 parts by weight of a plate-like flake and a polymerization initiator in a methyl methacrylate-based monomer solution having 1.3 or more, and polymerized and cured. The present invention relates to a heat ray shielding plate.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The viscosity was measured by a method according to JIS K-7117, viscosity eta ₂ of the viscosity eta ₁ and 60min ^-1 at 6min ^-1
In the method for preparing a methyl methacrylate-based monomer solution having a ratio (η ₁ / η ₂ ) of 1.3 or more, various conventionally known viscosity modifiers can be used. As the viscosity modifier, those which are compatible with the base resin and have a small difference in the refractive index are preferable, and the isotactic methyl methacrylate polymer alone, or the isotactic methyl methacrylate polymer and the syndiotactic methacrylic acid are used. A syrup in which both methyl-based polymers are dissolved in a methyl methacrylate-based monomer is more preferable. The isotactic methyl methacrylate polymer in the present invention means a polymer having a methyl methacrylate unit as a main component and having a methyl methacrylate unit chain isotacticity of 50% or more in a triad display. And, if necessary, a copolymer with another copolymerizable monomer. Preferably, the isotacticity is 70% or more, more preferably 7% or more.
5 to 95%.

Other copolymerizable monomers are known ones, for example, methacrylic acid such as ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate and 2-hydroxyethyl methacrylate. Esters: Methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, etc .; unsaturated acids such as methacrylic acid, acrylic acid; acrylonitrile ,
Monofunctional monomers such as methacrylonitrile and styrene.
Further, (poly) alkylene glycol di (meth) acrylate, allyl (meth) acrylate,
It is a polyfunctional monomer containing two or more unsaturated double bonds in the molecule, such as trimethylolpropane tri (meth) acrylate and divinylbenzene.

The proportion of each monomer unit in the isotactic methyl methacrylate-based copolymer is 50 to 100 parts by weight, preferably 90 to 100 parts by weight of methyl methacrylate.
0 to 50 parts by weight, preferably 0 to 50 parts by weight of another copolymerizable monomer
To 10 parts by weight. When the amount of the other copolymerizable monomer exceeds 50 parts by weight, it is difficult to dissolve in the methyl methacrylate-based monomer. In particular, these monomers having two or more copolymerizable functional groups give a crosslinked body at the time of copolymerization, and the resulting polymer becomes insoluble in the methyl methacrylate-based monomer. It must be less than 1 part by weight per 1000 parts by weight.

The isotactic isotactic methyl methacrylate polymer can be produced by a conventionally known method, but is obtained by anionic polymerization using a Grignard reagent as a polymerization initiator. No. 61-179210).

The syndiotactic methyl methacrylate-based polymer in the present invention is a polymer having a methyl methacrylate unit as a main component and a syndiotacticity of a methyl methacrylate unit chain of 50% or more in triad display. And, if necessary, a copolymer with the other copolymerizable monomer.

The ratio of each monomer unit in the syndiotactic methyl methacrylate-based copolymer is 50 to 100 parts by weight, preferably 90 to 100 parts by weight of methyl methacrylate, and other copolymerizable monomers are used. 0 to 50 parts by weight, preferably 0 to 10 parts by weight. 5 other copolymerizable monomers
If it exceeds 0 parts by weight, it becomes difficult to dissolve in the methyl methacrylate monomer. In particular, these monomers having two or more copolymerizable functional groups give a crosslinked product at the time of copolymerization and the resulting polymer becomes insoluble in a solvent.
It must be less than 1 part by weight per 00 parts by weight.

The syndiotactic methyl methacrylate polymer can be produced by a conventionally known method. As the polymerization initiator, a known initiator for radical polymerization of a monomer containing methyl methacrylate as a main component may be used. For example, organic peroxide-based initiators such as benzoyl peroxide, di-t-butyl peroxide, t-butyl peroxy 2-ethylhexaate; 2,2′-azobisisobutyronitrile, 2,2 ′ -Azobis (2, 4
Azo initiators such as dimethylvaleronitrile); known redox initiators in which a peroxide initiator is combined with a reducing compound such as an amine or mercaptan as a main component; and benzoin, benzoin ether , A 1-hydrohexyl phenyl ketone, a benzyl dimethyl ketal, an acyl phosphenoxide, a benzophenone, a Michler's ketone, a thioxanthone, and the like, and a photopolymerization initiator system, if necessary. It can also be obtained by anionic polymerization using a complex compound of an organic aluminum compound and an organic phosphorus compound, or an organic lanthanide complex as an initiator (Japanese Patent Publication No. 6-89054, Japanese Patent Application Laid-Open No. 3-263412).

The monomer containing methyl methacrylate as a main component in the present invention is a monomer mixture containing 50% or more of methyl methacrylate and optionally containing the other copolymerizable monomer. is there.

The methyl methacrylate monomer solution referred to in the present invention means that an isotactic methyl methacrylate polymer and a syndiotactic methyl methacrylate polymer are dissolved in the methyl methacrylate monomer. Is obtained. It can also be obtained by dissolving an isotactic methyl methacrylate polymer in the methyl methacrylate monomer. The method of dissolving an isotactic methyl methacrylate polymer and a syndiotactic methyl methacrylate polymer in a methyl methacrylate monomer is as follows.
A conventionally known method can be used. For example, a method in which only an isotactic methyl methacrylate polymer is dissolved in a methyl methacrylate monomer. Alternatively, a method in which an isotactic methyl methacrylate polymer and a syndiotactic methyl methacrylate polymer are simultaneously dissolved, or one is dissolved first, and then the other is dissolved. Further, a part of the methyl methacrylate monomer is polymerized by pre-polymerization to obtain a methyl methacrylate monomer solution of a syndiotactic methyl methacrylate polymer, and then an isotactic methyl methacrylate monomer is obtained. A method in which a polymer is added and dissolved with stirring may be used. Furthermore, polystyrene and styrene-soluble in a methyl methacrylate-based monomer solution
Dissolve polymers, such as methyl methacrylate copolymer, release agents, plasticizers, various additives for polymers such as dyes, and disperse inorganic fillers such as calcium carbonate, organic pigments, inorganic pigments, and aluminum hydroxide It is also possible to make it. The viscosity of the methyl methacrylate-based monomer solution is greatly reduced by heating or stirring at a high speed. Therefore, it is very easy to dissolve or disperse the plate-like flakes and additives.

The plate-like flake referred to in the present invention is not particularly limited as long as it is insoluble in a conventionally known methyl methacrylate monomer and does not inhibit its polymerization and curing. For example, titanium oxide-coated mica, titanium oxide flakes, basic lead carbonate flakes and the like can be mentioned. In addition, two or more of these plate-shaped flakes can be used in combination. The particle size of the plate-like flake to be added is not particularly limited, but preferably has an average particle size of 0.1 to 600 μm, and more preferably has an average particle size of 0.1 to 200 μm. In addition, the aspect ratio of the plate-like flake is preferably large from the viewpoint of the pigment orientation, and is preferably 3%.
The number is more preferably 5 or more. The thickness is 5 μm or less, preferably 3 μm or less, and the width and length are 5 to 150.
μm, preferably 5 to 100 μm.

The polymerization initiator in the present invention may be any of the known ones described above for radical polymerization of methyl methacrylate-based monomers.

A method for obtaining a syrup containing an isotactic methyl methacrylate polymer, a syndiotactic methyl methacrylate polymer, a methyl methacrylate monomer, a plate-like flake and a polymerization initiator is known in the art. And there is no particular limitation. For example, the dispersion of the plate-like flakes and the dissolution of the polymerization initiator may be simultaneously performed in the methyl methacrylate-based monomer solution. After dispersing the inorganic filler in the methyl methacrylate-based monomer solution, the polymerization initiator may be dissolved. When small flakes having a particle size of several microns or less are added, the viscosity of the syrup may increase significantly. Therefore, the initiator may be dissolved first, and then the flakes may be dispersed. In addition to the syrup, a polymer insoluble in the methyl methacrylate monomer solution,
It is also possible to add and disperse crosslinked polymer particles.

Depending on the amount of the isotactic methyl methacrylate-based polymer and the amount of the syndiotactic methyl methacrylate-based polymer, the liquid quality of the methyl methacrylate-based monomer solution and syrup is changed. Within the range, it must be in a high-viscosity gel state under low stirring and a low-viscosity sol state under high stirring. Such solutions, JIS K-7117 to measure the viscosity by a method according to the viscosity eta ₂ of the viscosity eta ₁ and 60min ^-1 at 6min ^-1
Is a methyl methacrylate-based monomer solution having a ratio (η ₁ / η ₂ ) of 1.3 or more. The amounts of the isotactic methyl methacrylate polymer, the syndiotactic methyl methacrylate polymer and the methyl methacrylate monomer in the syrup depend on the viscosity characteristics of the obtained methyl methacrylate monomer solution. For example, with respect to a total of 100 parts by weight of the isotactic methyl methacrylate-based polymer, the syndiotactic methyl methacrylate-based polymer and the methyl methacrylate-based monomer in the syrup, the isotactic methyl methacrylate-based polymer is used. Amount of 0.01 to 40
0 to 50 parts by weight of a syndiotactic methyl methacrylate-based polymer in parts by weight, and methyl methacrylate-based monomer 4
9.99 to 99.99 parts by weight, whereby the viscosity under high shear becomes lower than the viscosity under low shear in the range of 0 to 60 ° C., that is, the stirring speed becomes high. It also has a thixotropic property in which the viscosity decreases.

As a result, the syrup becomes a fluid having an appropriate viscosity, is easy to handle and can be easily poured even in a mold having a small clearance, and prevents sedimentation of plate-like flakes during polymerization. The heat ray shielding plate is obtained in which the flakes are uniformly dispersed and the plate surface is oriented parallel to the surface of the molded product. When the amount of the isotactic methyl methacrylate-based polymer and the syndiotactic methyl methacrylate-based polymer in the syrup is less than the above-mentioned amounts, the viscosity under low shear becomes low, and sedimentation of the plate-like flakes cannot be prevented. If the amount is more than the above, it becomes difficult to inject the liquid into the mold under high shear.

The amount of the plate-like flakes is determined by the properties required for the acrylic polymer to be obtained and is not particularly limited, but is preferably an isotactic methyl methacrylate-based polymer in a syrup. , Syndiotactic methyl methacrylate-based polymer, 0.01 to 100 parts by weight of the total of methyl methacrylate-based monomer
10 parts by weight.

If necessary, an antioxidant, an ultraviolet absorber, a chain transfer agent, a dye, a light diffusing agent, an organic pigment, an inorganic pigment, a filler and the like can be added to the syrup.

The syrup can be polymerized and cured by a conventionally known casting polymerization method. For example, there is a method in which a radical polymerization initiator is added to a syrup and polymerization is performed by heating. The amount of the radical polymerization initiator used is 0.001 to 100 parts by weight of the total of the syrup polymer and the monomer.
About 4 parts by weight. Preferably 0.001-0.4
It is about parts by weight.

In the casting polymerization, the mold may be, for example,
A batch type cell casting method using a cell composed of two glass plates or a metal plate, a soft sealing material and a clamp, and a continuous cell using two stainless steel continuous belts can also be used. In addition, it is also possible to inject into a mold having an arbitrary shape made of metal or the like and polymerize.

As a heating method in the polymerization, heating is performed by a known method, for example, a hot air, hot water, or a heat source such as an infrared heater. When the polymerization is performed by light irradiation, the light irradiation method includes a high-pressure mercury lamp, a metal halide lamp, a low-wavelength UV lamp, a xenon lamp, a krypton arc lamp, a xenon flash lamp, a flash UV lamp, and the like. Irradiation may be performed. These methods are not particularly limited.

The polymerization conditions are appropriately selected according to the type and amount of the polymerization initiator used or the composition of the monomer mixture. Generally, the polymerization is carried out at 0 to 80 ° C. for 1 to several tens of hours.

During or before the polymerization, the cells can be vibrated or the cells can be slid to increase the degree of orientation of the plate-like flakes.

After completion of the casting polymerization, the glass or metal constituting the mold is removed to obtain an acrylic polymer.

[0033]

According to the present invention, a heat shielding plate in which plate-like flakes are uniformly dispersed can be easily obtained. Since the syrup of the present invention has an appropriate viscosity, it has good handleability, can prevent sedimentation during polymerization of the plate-like flakes, and can be easily poured into a mold having a small clearance, and has a good appearance and a good appearance. Can be manufactured.

[0034]

Hereinafter, the present invention will be described with reference to Examples.
The present invention is not limited to this. In addition, the physical property evaluation and the test method performed in the Example are as follows. (1) Evaluation of molecular weight: It was measured using gel permeation chromatography (Waters, 150-CV) using THF as a solvent. The molecular weight was determined using a polymethyl methacrylate standard calibration curve. (2) Evaluation of stereoregularity of polymer: Measured using a proton nuclear magnetic resonance spectrometer (XL-200, manufactured by Varian) using nitrobenzene-d5 as a solvent. Isotacticity and syndiotacticity are shown in triad. (3) Viscosity measurement: B-type viscometer (manufactured by Tokimec Co., Ltd.)
DVM-B2) in accordance with JIS K-7117. Viscosity eta ₁ at 6min ^-1, showed a viscosity eta ₂ at 60min ^-1. (4) Visual appearance evaluation: The surface and cross section of the acrylic polymer were observed, and the uniformity of the titanium oxide-coated mica was visually observed. (5) visible light transmittance (T _1), the solar transmittance (T _2): fitted with an integrating sphere Hitachi Co., Ltd., in conformity with JIS R-3106 using a 330-inch next partial photometer It was measured. Further, the heat ray shielding rate (P) was obtained from the following equation. P = (1−T ₂ / T ₁ ) × 100

EXAMPLE 1 0.6 parts by weight of an isotactic methyl methacrylate polymer (number average molecular weight: 31800, isotacticity: 85%) obtained by anionic polymerization was mixed with 91.4 parts by weight of methyl methacrylate monomer. 8 parts by weight of a syndiotactic methyl methacrylate-based polymer (98% by weight of methyl methacrylate units, 2% by weight of methyl acrylate units, a number average molecular weight of 64,400, and 59% of syndiotacticity) obtained by radical polymerization are added at 60 ° And dissolved with stirring. The viscosity of the obtained solution was measured with a B-type viscometer. Table 2 shows the results. To 100 parts by weight of the obtained solution, 0.3 part by weight of titanium oxide-coated mica (Iriodin 215, particle size distribution: 10 to 60 μm: manufactured by A. Merck) was added and stirred and dispersed uniformly to obtain a syrup. . 0.1 parts by weight of 2,2′-azobisisobutyronitrile was added to 100 parts by weight of this syrup and degassing was performed. The mixture was poured into a cell configured as described above, placed in a hot air drying oven, and polymerized at 60 ° C. for 6 hours. Further, heat treatment was performed at 120 ° C. for 2 hours, and after cooling, the glass cell was removed to obtain a heat ray shielding plate having a thickness of 3 mm. Table 2 shows the evaluation results.

Examples 2 and 3 The same procedures as in Example 1 were carried out except that a syrup having the composition shown in Table 1 was used.

Example 4 Iriodin 215 (particle size distribution: 10-60 μm: manufactured by A. Merck) was used as titanium oxide-coated mica.
(A particle size distribution of 10 to 60 μm: manufactured by A. Merck) was carried out in the same manner as in Example 1. The results are shown in Table 2.

Examples 5 and 6 The same procedures as in Example 4 were carried out except that a syrup having the composition shown in Table 1 was used. The results are shown in Table 2.

Comparative Examples 1 and 2 The same procedure as in Example 1 was carried out except that a solution having the composition shown in Table 1 was used. The results are shown in Table 2.

[0040]

[Table 1] it-PMMA: isotactic methyl methacrylate polymer st-PMMA: syndiotactic methyl methacrylate polymer MMA: methyl methacrylate monomer

[0041]

[Table 2] Unit of η ₁ and η ₂ : mPa · s *: η ₁ / η ₂

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // C08F 20/14 C08F 20/14 C08L 33/12 C08L 33/12

Claims (5)

[Claims] 1. A measured viscosity by the method based on JIS K-7117, viscosity eta ₂ of the ratio of the viscosity eta ₁ and 60min ^-1 at ^{_{6min -1 (η 1 / η 2}} ) is 1.3 or more Plate-shaped flakes in a methyl methacrylate monomer solution
A heat ray shielding plate obtained by injecting a syrup containing parts by weight and a polymerization initiator into a mold and polymerizing and curing the syrup. 2. The methyl methacrylate monomer solution is a solution comprising an isotactic methyl methacrylate polymer, a syndiotactic methyl methacrylate polymer, and a methyl methacrylate monomer. The heat ray shielding plate as described. 3. The method according to claim 1, wherein the methyl methacrylate monomer solution is an isotactic methyl methacrylate polymer of 0.01 to 4%.
0 parts by weight, 0 to 50 parts by weight of syndiotactic methyl methacrylate-based polymer, methyl methacrylate-based monomer 4
The heat ray shielding plate according to claim 1, which is a solution comprising 9.99 to 99.99 parts by weight. 4. The heat ray shielding factor P calculated by the formula 1 from the visible light transmittance T ₁ and the solar transmittance T ₂ measured according to JIS R-3106 is 20% or more. Item 2. The heat ray shielding plate according to Item 1. P = (1−T ₂ / T ₁ ) × 100 5. The heat ray shielding plate according to claim 1, wherein the plate-like flake is titanium oxide-coated mica or titanium oxide flake.