JP6602908B2 - Zirconia slurry for thin film formation and manufacturing method thereof - Google Patents

Description

  The present invention relates to a zirconia slurry for forming a thin film that is excellent in transparency and excellent in the formation of a thin film, and a method for producing the same.

  An optical thin film using zirconium oxide is excellent in mechanical strength and heat resistance, and can be a high refractive index material having a transmission wavelength region of 340 nm to 8 μm. Therefore, zirconium oxide and transparent resins and films have been conventionally used. Various technologies have been developed to combine the above.

  For example, there are a technique for using zirconium oxide as a sealing resin for covering a light emitting diode (LED), a technique for obtaining an LED sealing material in which surface-modified zirconia particles having a particle diameter of 1 to 20 nm are blended in a silicone resin, and the like. Are known.

  When obtaining such an optical thin film using zirconium oxide, it is necessary to make the particle diameter of zirconium oxide sufficiently smaller than the wavelength of transmitted light (in the case of visible light: 380 to 800 nm). Attempts have also been made to make the particles finer and homogenize the zirconium oxide dispersion.

  For example, Patent Document 1 discloses a zirconium oxide dispersion in which hydrochloric acid is added to a zirconium hydroxide slurry and heated, and Patent Document 2 adds an alkaline aqueous solution to an aqueous solution containing a carboxylic acid and a zirconium salt. Zirconium oxide dispersions obtained from zirconium hydroxide gel are disclosed. Further, in Patent Document 3, a zirconium oxide slurry obtained by reacting a zirconium salt with an alkali is filtered, washed, repulped, and then subjected to hydrothermal treatment by adding an organic acid to the resulting slurry, whereby zirconium oxide dispersed water is obtained. Have gained.

JP-A-5-24844 JP 2006-143535 A JP 2014-80361 A

  However, the zirconium oxide described in Patent Document 1 has an average particle diameter of 50 nm or more and is still insufficient in the form of fine particles, and the zirconia dispersion described in Patent Document 2 ensures a sufficient concentration. Have difficulty. Furthermore, in the zirconia dispersion described in Patent Document 3, the transmittance at a wavelength of 400 nm is as low as 50% or less, and even with the techniques described in any of these documents, it is still improved to obtain a thin film with high light transmittance. There is room for.

  Accordingly, an object of the present invention is to form a zirconia slurry for forming a thin film using zirconium oxide (hereinafter sometimes referred to as “zirconia”) capable of forming a thin film having excellent light transmittance and a method for producing the same. Is to provide.

  Therefore, the present inventors have made various studies, and using a cellulose nanofiber having a specific fiber diameter as a shaft or a base material, a plurality of zirconia fine particles having a specific particle diameter are supported linearly and continuously on this. It has been found that a zirconia slurry capable of forming a thin film having excellent light transmittance can be obtained by using a zirconia nanoparticle aggregate exhibiting a unique shape, and the present invention has been completed.

That is, the present invention includes the following components (X) to (Y):
(X) A zirconia nanoparticle aggregate in which a plurality of zirconia nanoparticles having an average particle diameter of 0.1 nm to 40 nm are linearly continuously supported on cellulose nanofibers having an average fiber diameter of 50 nm or less,
(Y) A zirconia slurry for forming a thin film containing a dispersion medium is provided.

Furthermore, the present invention provides the following steps (I) to (III):
(I) a step of preparing a slurry A using a zirconium raw material compound, cellulose nanofibers, and an alkaline solution;
(II) A slurry containing the zirconia nanoparticle aggregate (X) by subjecting the obtained slurry A to a hydrothermal reaction having a temperature of 100 ° C. or higher and a pressure of 0.3 MPa to 0.9 MPa. Obtaining B,
(III) The method for producing the zirconia slurry for forming a thin film is provided, which includes a step of filtering and washing the obtained slurry B and then repulping with a dispersion medium (Y).

  According to the zirconia slurry for forming a thin film of the present invention, it contains a zirconia nanoparticle aggregate exhibiting a unique shape in which a plurality of very fine zirconia nanoparticles are linearly and continuously supported on cellulose nanofibers. Therefore, there is no possibility that the zirconia nanoparticles aggregate to form secondary particles, and a highly homogeneous dispersion state can be maintained. Therefore, if such a zirconia slurry for forming a thin film is used, it is possible to easily produce a zirconia thin film that can sufficiently enhance light transmittance.

  Furthermore, by firing the obtained zirconia thin film, the cellulose nanofibers in the zirconia nanoparticle aggregate are carbonized, and the carbon chain axis having a periodic structure derived from the cellulose molecular chain that constitutes the carbon nanofibers remains. Therefore, excellent conductivity can be imparted.

FIG. 1 is a TEM photograph showing an aggregate of zirconia nanoparticles in the zirconia slurry for forming a thin film obtained in Example 1. 4 is a TEM photograph showing zirconia nanoparticles in a zirconia slurry for forming a thin film obtained in Comparative Example 1.

Hereinafter, the present invention will be described in detail.
The zirconia slurry for forming a thin film of the present invention has, as component (X), cellulose nanofibers (hereinafter also referred to as “CNF”) having an average fiber diameter of 50 nm or less and an average particle diameter of 0.1 nm to 40 nm. A good and homogeneously dispersed slurry containing a zirconia nanoparticle aggregate in which a plurality of zirconia nanoparticles are supported linearly and continuously, and containing a dispersion medium as a component (Y).
Here, the average particle diameter means an average value of measured values of the particle diameter (long axis length) of several tens of particles in observation with an electron microscope of SEM or TEM.

  In the zirconia slurry for forming a thin film of the present invention, since the contained zirconia nanoparticle aggregate (X) exhibits good dispersibility in the dispersion medium (Y), the surface modification is performed on the zirconia nanoparticles for the purpose of suppressing aggregation. There is no need to apply the zirconia nanoparticles, and since the zirconia nanoparticles maintain an appropriate dispersion state, it can be easily processed into a thin film.

  Cellulose nanofiber (CNF) constituting the zirconia nanoparticle aggregate of component (X) is a skeletal component that occupies about 50% of all plant cell walls. It is a lightweight high-strength fiber that can be obtained by fine fiber, etc., and also has good dispersibility of the component (Y) in the dispersion medium.

The average fiber diameter of CNF is 50 nm or less, preferably 20 nm or less, and more preferably 10 nm or less. Although there is no restriction | limiting in particular about a lower limit, Usually, it is 1 nm or more.
The average length of CNF is preferably 100 nm to 100 μm, more preferably 1 μm to 100 μm, and further preferably 5 μm to 100 μm, from the viewpoint of efficiently processing into a thin film.

  Furthermore, the CNF used in the present invention has a theoretical value of Fresnel reflection (surface reflection) at a refractive index of 1.4 to 1.6 and a refractive index of 1.58, and takes into account multiple Fresnel reflections. The theoretical value of the total light transmittance is 90.1%, and it is a transparent material with very high light transmittance.

  The zirconia nanoparticles constituting the zirconia nanoparticle aggregate of component (X) are fine particles composed of microcrystalline particles. Specifically, the average particle diameter of such zirconia nanoparticles is 40 nm or less, preferably 20 nm or less, and the lower limit is 0.1 nm or more.

Further, examples of the crystal habit (crystal outer shape) of the zirconia nanoparticles include a plate shape, a needle shape, a cube shape, a rectangular parallelepiped shape, a hexagonal column, and the like. Among these, hexahedral particles that are elongated in the axial length direction of CNF are preferable from the viewpoint of strong support with CNF.
In order to stabilize the optical properties, the zirconia nanoparticle aggregate is preferably an aggregate of zirconia nanoparticles having a uniform particle diameter and shape.

The zirconia slurry for forming a thin film of the present invention contains a dispersion medium as the component (Y). As such a dispersion medium, water, an organic solvent, or a mixture thereof can be applied.
The organic solvent is not particularly limited, and examples thereof include aliphatic alcohols such as methanol, ethanol and 2-propanol, aliphatic carboxylic acid esters such as ethyl acetate and methyl formate, acetone, methyl ethyl ketone and methyl isobutyl. It is selected from aliphatic ketones such as ketones, polyhydric alcohols such as ethylene glycol and glycerin, or mixtures thereof. Among these, methanol, methyl ethyl ketone, methyl isobutyl ketone, or a mixture thereof is preferable.

  The content of the zirconia nanoparticle aggregate of component (X) in the zirconia slurry for thin film formation of the present invention is preferably 0.5 with respect to 100 parts by mass of the dispersion medium of component (Y) in the zirconia slurry for thin film formation. It is mass part-25 mass parts, More preferably, it is 1 mass part-18 mass parts, More preferably, it is 1.5 mass parts-14 mass parts. The content of the zirconia nanoparticle aggregate (X) in the zirconia slurry for thin film formation of the present invention is 100 masses from the viewpoint of sufficiently dispersing the zirconia nanoparticle aggregate (X) in the slurry. % Is preferably 0.5% by mass to 20% by mass, more preferably 1% by mass to 15% by mass, and still more preferably 1.5% by mass to 12% by mass.

The zirconia slurry for forming a thin film of the present invention includes the following steps (I) to (III):
(I) A step of preparing slurry A using a zirconium raw material compound, cellulose nanofibers, and an alkaline solution, and (II) the obtained slurry A has a temperature of 100 ° C. or higher and a pressure of 0.3 MPa to Step of obtaining slurry B containing zirconia nanoparticle aggregate by subjecting to hydrothermal reaction at 0.9 MPa (III) Step of filtering and washing the obtained slurry B with water and then repulping with dispersion medium (Y) It can obtain by a manufacturing method provided with.

Step (I) is a step of preparing slurry A using a zirconium raw material compound, cellulose nanofibers, and an alkaline solution.
In the step (I), first, it is preferable to obtain a slurry by mixing water together with a zirconium raw material compound and cellulose nanofibers.
As the zirconium raw material compound, zirconium sulfate, nitrate, carbonate, acetate, oxalate, oxide, hydroxide, halide and the like can be suitably used.

The amount of water used is preferably 10 mol to 300 mol with respect to 1 mol of zirconium in the raw material from the viewpoints of solubility or dispersibility of the zirconium raw material compound and CNF, easiness of stirring, and efficiency of hydrothermal reaction. Further, 50 to 200 mol is preferable.
Moreover, content of the cellulose nanofiber in the slurry A is 0.01 mass part-10 mass parts with respect to 100 mass parts of water in the slurry A, Preferably it is 0.01 mass part-10 mass parts, More preferably, it is 0.00. It is 05 mass parts-8 mass parts.

  In step (I), an alkali solution is added to a slurry obtained by mixing a zirconium raw material compound, CNF and water to form slurry A, and zirconium dissolved or dispersed in slurry A is neutralized by a neutralization reaction. Make hydroxide. The alkaline solution is preferably added dropwise in an amount sufficient to maintain the pH of the slurry A at 7-14. As such an alkaline solution, for example, an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia or the like can be used, but sodium hydroxide, sodium carbonate or a mixed solution thereof is preferably used.

  The slurry A is preferably stirred to advance the neutralization reaction from the viewpoint of satisfactorily producing zirconium hydroxide. The temperature of the slurry A during the neutralization reaction is preferably 5 ° C or higher, more preferably 10 ° C to 60 ° C. Further, the stirring time of the slurry A is preferably 5 minutes to 120 minutes, more preferably 30 minutes to 60 minutes.

In the step (II), the slurry A obtained in the step (I) is subjected to a hydrothermal reaction having a temperature of 100 ° C. or higher and a pressure of 0.3 MPa to 0.9 MPa to obtain a zirconia nanoparticle aggregate. In this step, a slurry B containing (X) is obtained.
The temperature of this hydrothermal reaction should just be 100 degreeC or more, and 130 to 180 degreeC is preferable. The hydrothermal reaction is preferably performed in a pressure vessel. When the reaction is performed at 130 ° C to 180 ° C, the pressure at this time is preferably 0.3 MPa to 0.9 MPa, and the reaction is performed at 140 ° C to 160 ° C. The pressure in carrying out is preferably 0.3 MPa to 0.6 MPa. The hydrothermal reaction time is preferably 0.5 hours to 24 hours, more preferably 0.5 hours to 15 hours.

In the step (III), the slurry B obtained in the step (II) is filtered and washed with water, and then repulped with the dispersion medium (Y). Through this step, a zirconia slurry for forming a thin film is obtained. be able to.
The hydrothermal reaction product in the slurry B obtained in the step (II) is a zirconia nanoparticle aggregate (X) composed of cellulose nanofibers and zirconia nanoparticles, and the slurry B is filtered and washed with water. This can be isolated.
As the filtration means, vacuum filtration, pressure filtration, centrifugal filtration, or the like can be used, but pressure filtration such as a filter press is preferable from the viewpoint of simplicity of operation. Moreover, when wash | cleaning the zirconia nanoparticle aggregate | assembly (X) after filtration with water, it is preferable to use 5 mass parts-100 mass parts with respect to 1 mass part of zirconia nanoparticle aggregates (X).

  Before replacing the water in the zirconia nanoparticle aggregate (X) after washing with water with an organic solvent before repulping with the dispersion medium (Y), the zirconia nanoparticle aggregate (X) containing the washing water is once dried. Then, a new organic solvent may be added. Examples of the drying method at this time include constant temperature drying, warm air drying, spray drying, freeze drying, and vacuum drying. Among these, freeze drying or spray drying is preferable from the viewpoint of effectively controlling aggregation of the obtained zirconia nanoparticle aggregate (X).

  Further, for example, the zirconia nanoparticle aggregate (X) is immersed in a predetermined organic solvent, the water in the zirconia nanoparticle aggregate is replaced with the organic solvent, and the zirconia for forming a thin film using the organic solvent as a dispersion medium. A slurry can also be obtained. The solvent replacement operation may be completed by performing a plurality of operations while changing the concentration of the organic solvent.

  Next, the zirconia nanoparticle aggregate (X) is repulped (resuspended) with the dispersion medium (Y) to obtain the zirconia slurry for forming a thin film of the present invention. There is no restriction | limiting in particular as a means to repulp, What is necessary is just to repulp using the dispersion medium (Y) of the quantity that content of a zirconia nanoparticle aggregate | assembly (X) becomes the said range.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

[Example 1: Aggregation of zirconia nanoparticles]
_{Zr (NO 3) 4 · 5H} 2 O1.81g, CNF19.29g ( Sugino Machine Ltd. TMa-10002, water content 98 wt%), and water 55mL were mixed for 60 minutes to prepare a slurry A1. To the resulting slurry A1, 20 mL of a 10% strength by weight aqueous NaOH solution was added and mixed for 5 minutes to produce slurry B1. Slurry B1 was put into an autoclave and subjected to a hydrothermal reaction at 140 ° C. for 1 hour. The resulting hydrothermal reaction product is allowed to cool, then filtered, washed with water, then repulped with ethanol, and 1 part by mass of the zirconia nanoparticle aggregate (X) with respect to 100 parts by mass of the dispersion medium (Y). A zirconia slurry for forming a thin film was obtained. In addition, the BET specific surface area of the zirconia nanoparticle aggregate | assembly in the zirconia slurry for thin film formation was 150 m < ² > / g, and the average particle diameter of the zirconia nanoparticle was 10 nm.
A TEM observation image of the zirconia nanoparticle aggregate contained in the obtained zirconia slurry for forming a thin film is shown in FIG. The TEM used was JEM-ARM200F manufactured by JEOL Ltd.

[Comparative Example 1: Zirconia nanoparticles (sol-gel method)]
_{Zr (NO 3) 4 · 5H} 2 O20g dehydrated ethanol - were mixed le 60 mL, was obtained was heated to _{40 ℃ Zr (NO 3) 4} · 5H 2 O was dissolved solution A2. The obtained slurry solution A2 was heated at 90 ° C. to volatilize ethanol to obtain a porous zirconia gel. The obtained gel was dried for 2 hours and then calcined in the atmosphere at 600 ° C. for 2 hours to obtain zirconia nanoparticles. The zirconia nanoparticles had a BET specific surface area of 130 m ² / g and an average particle size of 7 nm. The obtained zirconia nanoparticles are crushed in a mortar, mixed with ethanol, and prepared so that the zirconia nanoparticles are 1 part by mass with respect to 100 parts by mass of ethanol, and then dispersed with an ultrasonic disperser. Thus, a zirconia slurry for forming a thin film was obtained.
A TEM photograph of the zirconia nanoparticles contained in the obtained zirconia slurry for forming a thin film is shown in FIG.

≪Evaluation of light transmittance of zirconia thin film≫
The zirconia slurry for thin film formation obtained in Example 1 and Comparative Example 1 was dip coated on a glass substrate to prepare a zirconia thin film. Specifically, after immersing the glass substrate in each zirconia slurry for forming a thin film, the glass substrate was pulled up at a speed of 5 μm / second. The obtained glass substrate was dried at 80 ° C. for 12 hours and then baked in the air at 500 ° C. for 3 hours.
The prepared zirconia thin film is irradiated with light having a wavelength of 440 nm, and the intensity of transmitted light is measured using an ultraviolet-visible-near infrared spectrophotometer (manufactured by Shimadzu Corporation, UV3600 Plus). Calculated. The results are shown in Table 1.
Light transmittance (%) =
(Intensity of light transmitted through zirconia thin film) / (Intensity of blank light) × 100 (I)
Blank light intensity: transmission intensity in air

As is clear from Table 1, the zirconia thin film using the zirconia nanoparticle aggregate obtained in Example 1 is superior in light transmittance to the zirconia thin film using the zirconia nanoparticle obtained in Comparative Example 1. ing.
This is because the aggregate of zirconia nanoparticles obtained in Example 1 has a unique shape in which fine zirconia nanoparticles are linearly continuously supported on cellulose nanofibers, thereby interposing cellulose nanofibers. This is considered to be because the zirconia nanoparticles themselves did not aggregate unnecessarily and were well dispersed in the slurry. On the other hand, although the zirconia nanoparticles of Comparative Example 1 are fine, they are not supported on cellulose nanofibers as in Example 1, and thus it is determined that a strong aggregation state has occurred.

Claims (3)

Next components (X) to (Y):
(X) A zirconia nanoparticle aggregate in which a plurality of zirconia nanoparticles having an average particle diameter of 0.1 nm to 40 nm are linearly continuously supported on cellulose nanofibers having an average fiber diameter of 50 nm or less,
(Y) A zirconia slurry for forming a thin film containing a dispersion medium selected from aliphatic alcohols, aliphatic carboxylic acid esters, aliphatic ketones, polyhydric alcohols, and mixtures thereof . The content of the component (X) is the component (Y) is 0.5 parts by weight to 25 parts by weight per 100 parts by weight, film-forming zirconia slurry according to claim 1. Next components (X) to (Y):
(X) A zirconia nanoparticle aggregate in which a plurality of zirconia nanoparticles having an average particle diameter of 0.1 nm to 40 nm are linearly continuously supported on cellulose nanofibers having an average fiber diameter of 50 nm or less,
(Y) Dispersion medium
A method for producing a zirconia slurry for forming a thin film containing the following steps (I) to (III):
(I) a step of preparing a slurry A using a zirconium raw material compound, cellulose nanofiber, and an alkaline solution;
(II) A slurry containing the zirconia nanoparticle aggregate (X) by subjecting the obtained slurry A to a hydrothermal reaction having a temperature of 100 ° C. or higher and a pressure of 0.3 MPa to 0.9 MPa. Obtaining B,
(III) A method for producing a zirconia slurry for forming a thin film, comprising a step of filtering and washing the obtained slurry B with water and then repulping with a dispersion medium (Y).