JP2007161539A - Method for producing zinc oxide fine particle for ultraviolet shielding, and liquid dispersion for forming ultraviolet shielding agent using the fine particle and ultraviolet shielding agent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing zinc oxide fine particles excellent in dispersibility, ultraviolet shielding characteristics and productivity, and provide a liquid dispersion for forming an ultraviolet shielding agent using the fine particles, and provide the ultraviolet shielding agent. <P>SOLUTION: This zinc oxide fine particles for ultraviolet shielding are obtained by the steps of adding an alkali solution to a solution containing a zinc compound and stirring the mixture to obtain a precipitate, decanting the precipitate repeatedly until the electric conductivity of the washing liquid used for decantation becomes ≤1 mS/cm, drying the precipitate after conducting decantation to obtain a zinc oxide precursor, heat treating the zinc oxide precursor at 300-500°C under an atmosphere of a gas mixture of a reducing gas and an inert gas, where the concentration of the reducing gas is ≤5%. The liquid dispersion for forming the ultraviolet shielding agent is obtained by mixing the zinc oxide fine particle with a dispersant and a solvent. The ultraviolet shielding agent is obtained by dispersing a heat wave-shielding component dispersion obtained by removing a solvent from the dispersion for forming the ultraviolet shielding agent into a resin. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention can be applied to windows, telephone boxes, show windows, lighting lamps, transparent cases, etc., such as windows for vehicles, buildings, offices, ordinary houses, etc., for glass, plastics and other transparent base materials that require UV shielding function. In particular, the present invention relates to a method for producing ultraviolet shielding zinc oxide fine particles having desired ultraviolet shielding properties, a dispersion for forming an ultraviolet shielding material using the fine particles, and an ultraviolet shielding material. .

  The zinc oxide fine particles transmit visible light, the ultraviolet cut wavelength region is wider to the longer wavelength side than the titanium oxide fine particles, and the ultraviolet cut effect lasts for a long time. For this reason, zinc oxide fine particles are used as one of the materials for shielding ultraviolet rays. The fine particles are contained in a resin and used as resin molded products such as films, fibers and resin plates, or the fine particles are organically used. Alternatively, a transparent product having an ultraviolet shielding effect is produced by mixing with an inorganic binder and coating it on a substrate such as a film, fiber, resin plate, glass and paper.

  Here, as a method for producing zinc oxide having an ultraviolet shielding function, a dry method and a wet method are generally known. For example, in Patent Document 1, an aqueous solution containing a zinc salt is neutralized with an alkali, and a part or most of the zinc salt is once precipitated as a basic salt, then further neutralized as it is and finally 1 μm or less. A method for producing zinc oxide is disclosed.

  Patent Document 2 discloses a method in which an aqueous solution containing a zinc salt is neutralized with an alkali and zinc oxide is directly produced in the aqueous solution.

  Patent Document 3 discloses that a precipitate obtained by passing hydrogen sulfide through a mixed solution of zinc salt and ammonium acetate is dispersed in a non-aqueous solvent and heated at 250 to 400 ° C. with an autoclave. And the method of heat-processing the obtained dried powder at 500-800 degreeC is disclosed.

Furthermore, Patent Document 4 discloses that a zinc salt aqueous solution and an alkaline aqueous solution are separately and simultaneously charged into a reaction vessel continuously or semi-continuously and stirred at high speed, and the neutralized product is filtered. A method for producing ultrafine zinc oxide comprising washing, then drying and firing is proposed.
Japanese Patent Publication No. 56-18538 JP-A-53-116296 Japanese Patent Laid-Open No. 2-311314 JP-A-10-120418

  However, from the viewpoints of ultraviolet shielding performance and ease of manufacture, the present inventors have examined the prior art and have found that there are the following problems.

  First, the ultraviolet shielding property of the film formed using the zinc oxide powder produced by the methods disclosed in Patent Documents 1 and 2 was not satisfactory. Moreover, there existed a fault that the neutralization reaction time was long and production efficiency was bad.

  Further, in the method disclosed in Patent Document 3, it is necessary to further heat the dried powder after heating in a special pressure vessel such as an autoclave, and the productivity is low. Furthermore, since the final firing temperature has to be increased, there is a problem that the zinc oxide particles are coarsened and the dispersibility is deteriorated.

  Furthermore, the ultra-fine zinc oxide ultraviolet shielding properties presented in Patent Document 4 were not satisfactory.

  The inventor of the present invention has been made in the situation as described above, and the problem is that a method for producing zinc oxide fine particles for ultraviolet shielding excellent in dispersibility, ultraviolet shielding properties and productivity, and ultraviolet rays using the fine particles are used. The object is to provide a dispersion for forming a shielding body and an ultraviolet shielding body.

  The present inventors have studied the problems of the prior art to solve the above-mentioned problems. As a result, in the methods disclosed in Patent Documents 1 and 2, the higher the neutralization reaction temperature, the easier the direct production of zinc oxide at a low pH. However, since the final temperature is low, the crystallinity of zinc oxide is complete. However, it was conceived that the film formed using this zinc oxide powder remained insufficient in ultraviolet shielding properties. In addition, this method has also been conceived that the production efficiency is low due to the long neutralization reaction time.

  On the other hand, in the method disclosed in Patent Document 3, it was conceived that a problem arises in dispersibility because the particles are coarsened because the final firing temperature is high.

  Furthermore, the ultrafine zinc oxide presented in Patent Document 4 has been conceived in that the trace impurities during the production of zinc oxide remain without being removed, and the ultraviolet shielding performance is lowered. In addition, the ultrafine zinc oxide was also considered to be inferior in ultraviolet shielding performance because it is crystalline and has no oxygen defects.

  As a result of continual research based on the above-described elucidation results, the present inventors have conceived a method for producing zinc oxide fine particles having an ultraviolet shielding function capable of solving the above-mentioned problems and completed the present invention.

That is, the first means for solving the above problems is
Adding an alkaline solution to a solution containing a zinc compound and stirring to obtain a precipitate;
The precipitate is decanted, and after the decantation is performed until the conductivity of the washing liquid after being used for the decantation is 1 mS / cm or less, the precipitate is dried to obtain zinc oxide. Obtaining a precursor of
The zinc oxide precursor is a heat treatment at 300 ° C. or more and 500 ° C. or less in a mixed gas atmosphere of a reducing gas and an inert gas in which the concentration of the reducing gas is 5% or less. And a process for producing zinc oxide fine particles for shielding ultraviolet rays.

The second means is
The method for producing ultraviolet shielding zinc oxide fine particles according to the first means, wherein the solution containing the zinc compound contains one or more selected from Si compounds and Ti compounds.

The third means is
The method for producing zinc oxide fine particles for ultraviolet shielding according to the first means, wherein the zinc compound is at least one selected from zinc nitrate, zinc chloride, zinc carbonate and zinc acetate zinc sulfate.

The fourth means is
The method for producing zinc oxide fine particles for ultraviolet shielding according to the first means, wherein the solution temperature of the zinc compound when the alkaline solution is added to the solution containing the zinc compound is 50 ° C. or less It is.

The fifth means is
The method for producing ultraviolet shielding zinc oxide fine particles according to the first means, wherein the addition time of the alkaline solution is 30 minutes or less.

The sixth means is
A dispersion for forming an ultraviolet shielding material, which comprises a solvent and fine particles for ultraviolet shielding dispersed in the solvent, and is applied to the formation of an ultraviolet shielding material,
The ultraviolet shielding fine particles are ultraviolet shielding zinc oxide fine particles obtained by the production method according to any one of the first to fifth means, and the ultraviolet shielding fine particles dispersed in the solvent. A dispersion liquid for forming an ultraviolet shielding material, wherein a dispersed particle diameter of zinc fine particles is 100 nm or less.

The seventh means is
As the ultraviolet shielding fine particles, in the powder color in the L * a * b * color system, L * is 70 or more and 95 or less, a * is −6 or more, −0.1 or less, and b * is 0.6. The dispersion for forming an ultraviolet shielding material according to claim 6, wherein the zinc oxide fine particles obtained by the production method according to any one of claims 1 to 5 in the range of 6 or less are used. It is a liquid.

The eighth means is
The dispersion for forming an ultraviolet shielding material according to the sixth or seventh means, which contains an inorganic binder or a resin binder.

The ninth means is
An ultraviolet shielding material, characterized by being formed using the ultraviolet shielding material-forming dispersion described in any one of the sixth to eighth means.

The tenth means is
The dry powder obtained by removing the solvent component from the dispersion liquid for forming an ultraviolet shielding material according to any one of the sixth to eighth means is kneaded into a thermoplastic resin. It is an ultraviolet shield.

  According to the method for producing ultraviolet shielding zinc oxide fine particles according to any one of the first to fifth means described above, the ultraviolet shielding zinc oxide fine particles having excellent dispersibility and ultraviolet shielding properties are obtained with high productivity. Obtainable. Moreover, according to the dispersion liquid for forming an ultraviolet shielding body according to any one of the sixth to eighth means, an ultraviolet shielding body having excellent ultraviolet shielding characteristics can be formed. Furthermore, since the ultraviolet shielding body according to the ninth or tenth means is excellent in transparency and ultraviolet shielding properties, it can be applied to uses where it is desired to transmit visible light and shield ultraviolet light.

  Hereinafter, embodiments of the present invention will be specifically described.

  According to the present invention, there is provided a method for producing zinc oxide fine particles for shielding ultraviolet rays, the step of dropping an alkali solution into a raw material mixed solution containing a zinc compound and aging with continuous stirring to obtain a precipitate; After the product is washed by decantation, it is dried to obtain a zinc oxide precursor, and the precursor is mild at 300 ° C. to 500 ° C. in a mixed gas atmosphere of a reducing gas and an inert gas. And a reduction process. Therefore, the production of the ultraviolet shielding zinc oxide fine particles according to the present invention will be described for each step, and the ultraviolet shielding body forming dispersion and the ultraviolet shielding body will be described together.

1. Step of Obtaining Precipitate In the present invention, first, an alkaline solution is dropped into a raw material mixed solution containing a zinc compound, and the precipitate is obtained by aging with continuous stirring. Furthermore, in the present invention, if desired, a configuration may be adopted in which a Si compound is added in addition to the zinc compound prepared in the above-described step to suppress the catalytic activity of the zinc compound fine particles and to suppress the particle growth in the heat treatment. . Similarly, if desired, a configuration in which a Ti compound is added in addition to the zinc compound prepared in the above-described step to give an effect of shielding a wide range of ultraviolet rays from UVB to UVA may be adopted. Here, each content of the Si compound and the Ti compound with respect to the zinc compound may be appropriately selected so as to obtain desired characteristics.

  The zinc compound applied in the present invention is not particularly limited, and examples thereof include zinc nitrate, zinc chloride, zinc chloride, zinc acetate, and zinc sulfate. The solution of the zinc compound is preferably controlled to 30 ° C. or less in order to suppress the growth of particles and stably obtain a precipitate.

  Furthermore, when taking the structure which adds Si compound and Ti compound to a zinc compound, if this Si compound and Ti compound also become an oxide by baking, it will not specifically limit. Examples of the Si compound include water glass, alkoxysilane, and Ti compound such as titanium alkoxide, titanium chloride, and titanium sulfate. Further, the alkaline solution is not particularly limited, and examples thereof include aqueous solutions of ammonium hydrogen carbonate, ammonium hydroxide, sodium hydroxide, potassium hydroxide, and the like. The concentration of the alkali solution may be at least the chemical equivalent necessary for each salt to become a hydroxide as a precursor. However, from the viewpoint of shortening the washing time for removing the residual alkali and increasing the productivity, it is preferable to set the range from equivalent to 3 times equivalent.

  Moreover, it is preferable that the temperature of an alkaline solution shall be 50 degrees C or less. The lower limit of the temperature of the alkaline solution is not particularly limited from the characteristics of the obtained zinc oxide fine particles, but a cooling device or the like may be newly required to lower the solution temperature. Here, from the viewpoint of productivity, it is preferable that the temperature does not require such a cooling device. On the other hand, if the solution temperature is 50 ° C. or lower, it can be avoided that the zinc concentration in the system changes due to evaporation of water from the alkaline solution, and reproducibility such as the particle diameter of the obtained zinc hydroxide fine particles is obtained. This is because it can be avoided that the zinc oxide precursor particles grow excessively and the desired optical properties cannot be obtained.

  The dropping time of the alkaline solution is preferably 30 minutes or less from the viewpoint of productivity. More preferably, it should be 25 minutes or less.

  After completion of the dropwise addition of the alkaline solution, the pH of the solution is maintained at 7 or more and the precipitate is aged by continuously stirring the solution. The temperature is preferably the same as the settling temperature. The aging time is not particularly limited, but is 30 minutes or less, preferably 15 minutes or less from the viewpoint of productivity. By maintaining the pH of the solution at 7 or more, re-dissolution of the generated precipitate can be avoided and a good yield can be maintained.

2. A step of drying and obtaining a zinc oxide precursor after decantation The precipitate aged by continuously stirring the solution is washed by decantation, and the washing solution used for the decantation The decantation is repeated until the electrical conductivity of 1 mS / cm or less. That is, it is important that the precipitate generated from the solution is sufficiently washed and then dried. This is because impurities such as chloride ions, nitrate ions, sulfate ions, and acetate ions remaining in the precipitate fine particles adversely affect the dispersibility of the ultraviolet shielding zinc oxide fine particles according to the present invention, and a reducing gas described later. This is because mild reduction is hindered in the heat treatment step in a mixed atmosphere, and the ultraviolet shielding property of the zinc oxide fine particles for ultraviolet shielding according to the present invention cannot be obtained due to the inhibition of mild reduction.

  As a result of the study by the present inventors, if the amount of impurities remaining in the precipitate after washing is 1.5% by weight or less, the dispersibility of the above-described zinc oxide fine particles for ultraviolet shielding is deteriorated or in the heat treatment step. It turned out that the situation of the inhibition of mild reduction could be avoided. As a result of examining the relationship between the amount of impurities remaining in the washed precipitate and the conductivity of the cleaning solution used for decantation, the decantation is performed until the conductivity of the cleaning solution becomes 1 mS / cm or less. It is conceived that the amount of impurities remaining in the precipitate can be reduced to 1.5% by weight or less by repeating the above.

  Next, the drying temperature and drying time after washing the precipitate are not particularly limited. What is necessary is just to select suitably by conditions, such as a sediment processing amount and a processing apparatus. Thus, a dried zinc oxide precursor is obtained.

3. Mild reduction treatment process From the viewpoint of improving the dispersibility and UV shielding properties of the dried zinc oxide precursor,
It is important to subject the zinc oxide precursor to a mild reduction treatment. In this reduction treatment method, it is preferable to use a mixed gas of an inert gas such as nitrogen, argon or helium and a reducing gas such as hydrogen, carbon monoxide or ammonia as a reducing agent. Further, the mild reduction treatment means that the reducing gas concentration in the mixed gas to be fed is in the range of 0.1% to 5%.

  By applying the mild reduction treatment to the dried zinc oxide precursor, oxygen defects are generated in the zinc oxide precursor, although the details are unknown. It is thought to do. Further, by setting the reducing gas concentration to 0.1% or more and 5% or less, excessive grain growth due to the balance with the reduction treatment temperature is avoided, and the production of zinc oxide particles having low ultraviolet shielding properties is suppressed. Here, the lower limit of the reduction treatment temperature is set to 300 ° C. from the viewpoint of controlling the reduction state of the zinc oxide fine particles obtained by the mild reduction treatment, exhibiting dispersibility, ultraviolet shielding properties, and productivity. It is essential. Further, from the viewpoint of reducing the dispersibility due to excessive grain growth and the formation of strong aggregates during the reduction treatment, thereby reducing the optical properties of the ultraviolet shielding zinc oxide fine particles according to the present invention, the upper limit of the reduction treatment temperature is set. It is preferable to set it as 500 degreeC. The reduction treatment time may be appropriately selected in consideration of the treatment amount and treatment temperature of the zinc oxide precursor, but generally it may be in the range of 10 minutes to 3 hours. As described above, the ultraviolet shielding zinc oxide fine particles according to the present invention can be obtained by subjecting the dried zinc oxide precursor to the mild reduction treatment.

  Powder color in the L * a * b * color system (JIS Z 8729) recommended by the International Commission on Illumination (CIE) of the zinc oxide fine particles for ultraviolet shielding according to the present invention obtained by the production method described above. It is preferable that L * is in the range of 70 or more and 95 or less, a * is −6 or more and −0.1 or less, and b * is 0.6 or more and 6 or less. This is because the powder color in the L * a * b * color system is considered to be a result of the reduced state of the zinc oxide fine particles. Therefore, when L * exceeds 95, when a * exceeds −0.1, and when b * is less than 0.6, the reduction is insufficient, and it is considered that this corresponds to the zinc oxide fine particles according to the prior art. . On the other hand, when L * is less than 70, when a * is less than −6, and when b * exceeds 6, it is considered that reduction is excessive and metal Zn is generated, which is not preferable. In addition, the zinc oxide fine particles in the above preferred color system range exhibited a slightly light gray color by visual observation.

4). Ultraviolet shielding body forming dispersion The ultraviolet shielding body forming dispersion according to the present invention contains the ultraviolet shielding zinc oxide fine particles according to the present invention, and is applied to the formation of an ultraviolet shielding body. The ultraviolet shielding fine particles are composed of the zinc oxide fine particles obtained by the above-described production method, and the dispersed particle diameter of the zinc oxide fine particles dispersed in the solvent is 100 nm or less. . Further, the solid content concentration of the ultraviolet shielding fine particles dispersed in the solvent is 30% by weight or less, preferably 20% by weight or less. Although the solid content concentration is proportional to the production cost, in general, since the improvement in the shielding property is not proportional to the rate of increase in the solid content concentration, in consideration of the desired ultraviolet shielding property, as described above, The solid content concentration of the ultraviolet shielding fine particles dispersed in the solvent is adjusted to be 30% by weight or less, preferably 20% by weight or less.

  The dispersion for forming an ultraviolet shielding material is obtained by dispersing ultraviolet shielding fine particles in a solvent. The solvent will be described here.

  The solvent is not particularly limited, and may be appropriately selected according to the coating conditions and coating environment. Further, when an inorganic binder or a resin binder is added to the dispersion for forming an ultraviolet shielding material, They can be selected as appropriate. For example, alcohols such as water, ethanol, propanol, butanol, isopropyl alcohol, isobutyl alcohol, diacetone alcohol, methyl ether, ethyl ether, propyl ether, etc. Various organic solvents such as ethers, esters, acetone, methyl ethyl ketone, diethyl ketone, cyclohexanone, isobutyl ketone, etc. can be used, and if necessary, pH can be adjusted by adding acid or alkali. May be. Furthermore, it is preferable to add various surfactants, coupling agents and the like as a dispersant for further improving the dispersion stability of the fine particles in the coating solution.

  Here, the dispersion particle diameter of the zinc oxide fine particles which are the fine particles for ultraviolet shielding in the dispersion for forming the ultraviolet shielding material will be briefly described. First, the dispersed particle diameter of the zinc oxide fine particles means the diameter of the aggregated particles formed by aggregation of the zinc oxide fine particles dispersed in the solvent. Can be measured. For example, a sample containing zinc oxide fine particles alone or aggregates is collected from the zinc oxide fine particle dispersion, and the sample is applied to ELS-8000 manufactured by Otsuka Electronics Co., Ltd. based on the principle of dynamic light scattering. It can be obtained by measuring.

  The dispersed particle diameter of the zinc oxide fine particles is desirably 100 nm or less. This is because if the dispersed particle diameter is 100 nm or less, it can be avoided that the zinc oxide fine particles serve as a light scattering source to cause haze and cause a decrease in visible light transmittance.

  Moreover, the kind of the inorganic binder and the resin binder to be blended in the ultraviolet shielding body-forming dispersion liquid as necessary is not particularly limited. For example, as the inorganic binder, a metal alkoxide of silicon, zirconium, titanium, or aluminum, a partially hydrolyzed polycondensation product thereof, or an organosilazane can be used. As the resin binder, thermoplastic resins such as acrylic resins, thermosetting resins such as epoxy resins, and the like can be used.

  The method for dispersing the zinc oxide fine particles, which are the ultraviolet shielding fine particles, in the dispersion for forming the ultraviolet shielding material is not particularly limited as long as the zinc oxide fine particles are uniformly dispersed. -Lumil, sand mill, paint shaker, ultrasonic homogenizer and the like.

5. Ultraviolet shielding body One of the forms of the ultraviolet shielding body according to the present invention is, for example, by applying the above-described dispersion for forming an ultraviolet shielding body according to the present invention on a transparent substrate, and fine zinc oxide particles that are ultraviolet shielding fine particles. Are deposited at high density to form a film. Here, when a resin binder or an inorganic binder is included in the dispersion liquid for forming an ultraviolet shielding body, the binder provides adhesion of the zinc oxide fine particles to the substrate after the dispersion liquid for forming an ultraviolet shielding body is cured. This has the effect of improving the hardness of the film.

  Further, a film made of a metal alkoxide of silicon, zirconium, titanium, or aluminum, or a partially hydrolyzed polycondensation product thereof on the first layer film formed on the transparent substrate or the like obtained as described above. As a second layer, an oxide film of silicon, zirconium, titanium, or aluminum is formed, so that the binding force of the first layer film containing zinc oxide fine particles as a main component to the base material or ultraviolet light The hardness and weather resistance of the shielding film can be further improved.

  Further, the method for applying the ultraviolet shielding composition-forming dispersion of the present invention onto a transparent substrate is not particularly limited, and examples thereof include spin coating, bar coating, spray coating, dip coating, screen printing, Any method may be used as long as the treatment liquid can be applied flatly, thinly and uniformly, such as roll coating and flow coating.

  Further, the different form of the ultraviolet shield according to the present invention is that the above-described dispersion for forming an ultraviolet shield is heated to remove the solvent to obtain a dry powder, and then the dry powder is further converted into a thermoplastic resin or fiber. There are things that are used by kneading. In this form, a dispersant, an antioxidant, or the like may be appropriately introduced when kneading the dry powder, and it is added to a thermoplastic resin or fiber via a compound or masterbatch for adjusting the dilution ratio. It can be kneaded. In the case where a polycarbonate resin or the like is used as the ultraviolet shielding body, it is possible to disperse the ultraviolet shielding zinc oxide fine particles only in the outermost surface layer number of 10 μm by performing a coextrusion operation. .

Further, the zinc oxide fine particles for ultraviolet shielding according to the present invention are further added with lanthanum boride, ATO, ITO, AZO, Cs _0.3 WO ₃ , W ₁₈ O ₄₉ , Si-added tungsten oxide, or Si-added Cs oxide. It is also preferable to add a material that shields near infrared rays, such as tungsten, and use them in combination.

  As described above, according to the method for producing ultraviolet shielding zinc oxide fine particles according to the present invention, the ultraviolet shielding zinc oxide fine particles having excellent dispersibility and ultraviolet shielding properties can be produced with high productivity. And according to the dispersion liquid for forming an ultraviolet shielding body according to the present invention containing the produced zinc oxide fine particles for ultraviolet shielding excellent in dispersibility and ultraviolet shielding characteristics, the present invention having an excellent effect in ultraviolet shielding characteristics is provided. Such an ultraviolet shield can be manufactured efficiently.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples. The powder color of the obtained zinc oxide fine particles, the visible light transmittance of the zinc oxide fine particle dispersion, and the ultraviolet transmittance were measured using a spectrophotometer U-4000 manufactured by Hitachi, Ltd. The powder color is based on a 10 ° field of view using the light source D65.

[Example 1]
25582.7 g of 10% Zn (NO ₃ ) ₂ 6H ₂ O aqueous solution was controlled at 30 ° C. and stirred. Then, 15% NH ₄ HCO ₃ aqueous solution was dropped into the Zn (NO ₃ ) ₂ 6H ₂ O aqueous solution over 20 minutes to form a precipitate at pH 7.6, and then stirring was continued for another 10 minutes. Aged.

  Next, the produced precipitate was collected and washed by decantation. The decantation cleaning was repeated until the conductivity in the cleaning liquid after the cleaning operation was 1 mS / cm or less. After the washing, the washed precipitate was dried at 105 ° C.

Next, the dried precipitate is placed in an atmospheric furnace and baked at a temperature of 400 ° C. for 1 hour while supplying 2% H ₂ gas with N ₂ gas as a carrier to perform mild reduction treatment. As a result, zinc oxide fine particles were obtained. As a result of performing X-ray diffraction measurement (hereinafter sometimes referred to as XRD measurement) on the zinc oxide fine particles, it was found to be a single phase of ZnO.

  Table 1 shows the color system of the zinc oxide fine particles.

Here, a paint containing 10% by weight of the obtained zinc oxide fine particles, 10% by weight of a polymeric dispersant as a dispersant, 80% by weight of toluene, and 0.3 mmφ zirconia beads corresponding to a filling rate of 63%. The mixture was loaded into a shaker and dispersed for 8 hours to obtain dispersion A. At this time, the dispersed particle diameter of the zinc oxide fine particles in the dispersion A was 85 nm, and it was found that the zinc oxide fine particles were easy to disperse.
Next, the dispersion was appropriately diluted with toluene, and the relationship between the visible light transmittance and the ultraviolet transmittance of the diluted solution and the relationship between the ultraviolet transmittance of the diluted solution and the zinc oxide fine particle concentration were determined. The results are shown in Table 1 and FIGS.

[Example 2 to Example 3, Comparative Example 1 to Comparative Example 2]
Zinc oxide fine particles according to Example 2 were produced in the same manner as in Example 1 except that the firing temperature at the time of mild reduction treatment was set to 300 ° C., and the zinc oxide fine particles were used in the same manner as in Example 1. Thus, Dispersion B according to Example 2 was produced.

  Next, zinc oxide fine particles according to Example 3 were produced in the same manner as in Example 1 except that the firing temperature was changed to 500 ° C., and in the same manner as in Example 1 using these zinc oxide fine particles, Such dispersion C was prepared.

  Next, the zinc oxide fine particles according to Comparative Example 1 were produced in the same manner as in Example 1 except that the firing temperature was set to 200 ° C., and in the same manner as in Example 1 using the zinc oxide fine particles, Such a dispersion D was produced.

  Furthermore, the zinc oxide fine particles according to Comparative Example 2 were produced in the same manner as in Example 1 except that the firing temperature was set to 700 ° C., and according to Comparative Example 2 in the same manner as in Example 1 using these zinc oxide fine particles. Dispersion E was produced.

  As a result of measuring the structure of each manufactured zinc oxide fine particle by XRD, it was found that the zinc oxide fine particles according to Example 2, Example 3 and Comparative Example 2 were a single phase of ZnO. It was found that zinc carbonate fine particles were mixed with basic carbonate.

  Moreover, when the dispersed particle diameter in each dispersion liquid was measured, the dispersion liquid B (Example 2) was 79 nm, the dispersion liquid C (Example 3) was 96 nm, the dispersion liquid D (Comparative Example 1) was 81 nm, and the dispersion liquid. E (Comparative Example 2) was 230 nm, and particles other than Dispersion E according to Comparative Example 2 were easily dispersed fine particles having a dispersed particle diameter of 100 nm or less.

[Examples 4 to 5]
A zinc oxide fine particle according to Example 4 was produced in the same manner as in Example 1 except that the solution temperature was controlled at 50 ° C., and the dispersion according to Example 4 was performed in the same manner as in Example 1 using the zinc oxide fine particle. Liquid F was produced.

  A zinc oxide fine particle according to Example 5 was produced in the same manner as in Example 1 except that the dropping time of the alkaline solution was changed to 30 minutes, and the zinc oxide fine particle was used in the same manner as in Example 1 in Example 5. Such a dispersion G was produced.

  As a result of measuring the structure of each manufactured zinc oxide fine particle by XRD, it was found that the zinc oxide fine particles according to Example 4 and Example 5 were ZnO single phase.

  Further, when the dispersed particle size in each dispersion was measured, the dispersion F (Example 4) was 86 nm and the dispersion G (Example 5) was 83 nm, both of which were dispersed with a dispersed particle size of 100 nm or less. It was a fine particle.

[Comparative Examples 3 to 4]
In the cleaning of the zinc oxide fine particles, the zinc oxide fine particles according to Comparative Example 3 were obtained in the same manner as in Example 2 except that the cleaning by decantation was stopped when the conductivity of the cleaning liquid reached 20 mS / cm. A dispersion H according to Comparative Example 3 was produced in the same manner as Example 1 using the zinc oxide fine particles.

Zinc oxide fine particles according to Comparative Example 4 were produced in the same manner as in Example 1 except that 6% H ₂ gas using N ₂ gas as a carrier was supplied during firing during the reduction treatment, and the zinc oxide fine particles were produced. A dispersion I according to Comparative Example 4 was produced in the same manner as in Example 1.

  As a result of measuring the structure of each manufactured zinc oxide fine particle by XRD, the zinc oxide fine particle according to Comparative Example 3 has an unidentified peak in addition to the relatively broad ZnO peak, and the zinc oxide according to Comparative Example 4 is observed. The fine particles were found to be a ZnO single phase.

  Further, when the dispersed particle size in each dispersion liquid was measured, the dispersion liquid H (Comparative Example 3) was 130 nm, and the dispersion liquid I (Comparative Example 4) was 160 nm, both of which were dispersed when the dispersed particle diameter was 130 nm or more. It was a difficult fine particle.

[Summary of Examples 1 to 5 and Comparative Examples 1 to 4]
As in Example 1, Table 1 shows the color system of zinc oxide fine particles according to Examples 2 to 5 and Comparative Examples 1 to 4.

  Next, in the same manner as in Example 1, each dispersion according to Examples 2 to 5 and Comparative Examples 1 to 4 is appropriately diluted with toluene to obtain a diluted solution, and the visible light transmittance of each diluted solution And the relationship between UV transmittance and UV transmittance. The results are shown in Table 1 and FIG. Further, the relationship between the ultraviolet transmittance of each diluted solution and the zinc oxide fine particle concentration was determined. The results are shown in Table 1 and FIG.

  FIG. 1 shows the relationship between the ultraviolet transmittance and the visible light transmittance in each of the diluted liquid samples of Examples 1 to 5 and Comparative Examples 1 to 4 with the ultraviolet transmittance on the vertical axis and the visible light transmittance on the horizontal axis. This is a plotted graph.

  From the results shown in Table 1 and FIG. 1, the dispersions prepared using the dispersions according to Examples 1 to 5 and the dispersions prepared using the dispersions according to Comparative Examples 1 to 4. When compared with the liquid diluent, the dispersion liquid prepared using the dispersion liquids according to Examples 1 to 5 has a higher ultraviolet transmittance if the liquid dispersion liquid exhibits the same visible light transmittance. Clearly low.

  FIG. 2 shows the relationship between the ultraviolet transmittance and the zinc oxide concentration in each of the diluted liquid samples of Examples 1 and 2 and Comparative Example 1, with the vertical axis representing the ultraviolet transmittance and the horizontal axis representing the zinc oxide concentration in the dispersion. This is a plotted graph.

  From the results shown in Table 1 and FIG. 2, a dispersion dilution prepared using the dispersion according to Example 1 and Example 2, and a dispersion dilution prepared using the dispersion according to Comparative Example 1, In comparison, the dispersion diluted with the dispersions according to Example 1 and Example 2 is less oxidized than the dispersion diluted with the dispersion obtained in Comparative Example 1. It can be seen that ultraviolet rays can be shielded by the concentration of zinc fine particles.

[Example 6]
To 500 g of the zinc oxide fine particle dispersion A obtained in Example 1, 375 g of a dispersing agent was added, and the solvent was completely removed under reduced pressure at 60 ° C. while stirring to obtain a heat ray shielding component dispersion (zinc oxide concentration: (10.5% by weight) was obtained (heat ray shielding component dispersion A). The mixing ratio of the dispersant was 8.5 parts by weight with respect to 1 part by weight of LaB ₆ . Next, the obtained heat ray shielding component dispersion A is added to a polycarbonate resin powder, which is a thermoplastic resin, so that the zinc oxide concentration becomes 2.0% by weight, and the mixture is uniformly mixed with a blender. did. Next, the mixture was melt-kneaded with a twin-screw extruder and extruded to a thickness of 2.0 mm using a T-die to obtain a heat ray shielding transparent resin molded product in which zinc oxide fine particles were uniformly dispersed throughout the resin. . As a result of evaluating the optical characteristics of the transparent resin molding with a spectrophotometer, the visible light transmittance was 94.5%, and the ultraviolet transmittance was 1.24%.

It is the graph which showed the relationship between the visible light transmittance | permeability and the ultraviolet-ray transmittance in the dilution liquid of the zinc oxide fine particle dispersion liquid for ultraviolet shielding which concerns on this invention. It is the graph which showed the relationship between the ultraviolet-ray transmittance in the dilution liquid of the zinc oxide fine particle dispersion for ultraviolet shielding which concerns on this invention, and the zinc oxide fine particle density | concentration.

Claims (10)

Adding an alkaline solution to a solution containing a zinc compound and stirring to obtain a precipitate;
The precipitate is decanted, and after the decantation is performed until the conductivity of the washing liquid after being used for the decantation is 1 mS / cm or less, the precipitate is dried to obtain zinc oxide. Obtaining a precursor of
The zinc oxide precursor is a heat treatment at 300 ° C. or more and 500 ° C. or less in a mixed gas atmosphere of a reducing gas and an inert gas in which the concentration of the reducing gas is 5% or less. And a process for producing zinc oxide fine particles for shielding ultraviolet rays.   The method for producing zinc oxide fine particles for ultraviolet shielding according to claim 1, wherein the solution containing the zinc compound contains one or more selected from Si compounds and Ti compounds.   2. The method for producing ultraviolet shielding zinc oxide fine particles according to claim 1, wherein the zinc compound is at least one selected from zinc nitrate, zinc chloride, zinc carbonate, and zinc acetate zinc sulfate.   The method for producing zinc oxide fine particles for ultraviolet shielding according to claim 1, wherein the solution temperature of the zinc compound when the alkaline solution is added to the solution containing the zinc compound is 50 ° C or lower.   2. The method for producing zinc oxide fine particles for ultraviolet shielding according to claim 1, wherein the addition time of the alkaline solution is 30 minutes or less. A dispersion for forming an ultraviolet shielding material, which comprises a solvent and fine particles for ultraviolet shielding dispersed in the solvent, and is applied to the formation of an ultraviolet shielding material,
The ultraviolet shielding zinc oxide dispersed in the solvent, wherein the ultraviolet shielding fine particles are the ultraviolet shielding zinc oxide fine particles obtained by the production method according to any one of claims 1 to 5. A dispersion for forming an ultraviolet shielding material, wherein the dispersed particle diameter of the fine particles is 100 nm or less.   As the ultraviolet shielding fine particles, in the powder color in the L * a * b * color system, L * is 70 or more and 95 or less, a * is −6 or more, −0.1 or less, and b * is 0.6. The dispersion for forming an ultraviolet shielding material according to claim 6, wherein the zinc oxide fine particles obtained by the production method according to any one of claims 1 to 5 in the range of 6 or less are used. liquid.   The dispersion liquid for forming an ultraviolet shielding body according to claim 6 or 7, comprising an inorganic binder or a resin binder.   An ultraviolet shielding body formed using the ultraviolet shielding body-forming dispersion liquid according to any one of claims 6 to 8.   An ultraviolet ray obtained by kneading a dry powder obtained by removing the solvent component from the dispersion for forming an ultraviolet shielding body according to any one of claims 6 to 8, into a thermoplastic resin. Shield.

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