CN103436111B - A kind of preparation method of the water-based ultraviolet shielded coating based on ZnO quantum dot - Google Patents

Abstract

The invention belongs to the field of fine chemicals and relates to a method for preparing water-based ultraviolet shielding coatings by using ZnO quantum dots. That is, ZnO quantum dots are prepared by sol-gel reaction of zinc salt and lithium hydroxide ethanol solution first, and then a layer of silicon dioxide is coated on the surface of ZnO quantum dots in situ using tetraethyl orthosilicate as raw material to obtain ZnO quantum dots@ _SiO2 core‑shell nanoparticles with effectively suppressed photocatalytic activity. Then the ZnO quantum dots@ _SiO2 nanoparticles were transferred into water, and then compounded with water-based film-forming resin and wetting agent to prepare water-based UV shielding coatings. The content of ZnO quantum dots @SiO ₂ in the dry coating film is 1-50%. By adjusting the thickness of the coating film and the content of ZnO quantum dots @SiO ₂ , full shielding of ultraviolet light below 340nm wavelength is achieved. The ultraviolet shielding paint of the present invention is water-based, environment-friendly and non-toxic, and can be used for outdoor bamboo, wood, plastic, etc., and can also be used to prepare transparent ultraviolet shielding glass.

Description

A kind of preparation method of waterborne ultraviolet shielding coating based on ZnO quantum dot

technical field

The invention belongs to the technical field of fine chemicals, and in particular relates to a preparation method of a water-based ultraviolet shielding coating based on ZnO quantum dots.

Background technique

Transparent UV shielding coatings are widely used in the protection of outdoor easily degradable materials (polymers, wood, bamboo, etc.), the preparation of UV shielding glass, and the UV isolation of indoor light sources. They are generally prepared by adding UV absorbers to varnishes. UV absorbers can generally be divided into two categories, one is organic UV absorbers, mainly including benzophenones, benzotriazoles, salicylates, oxalanilides, etc.; the other is inorganic nano UV absorbers mainly include titanium dioxide nanoparticles, ceria nanoparticles, zinc oxide nanoparticles, etc. Organic UV absorbers have the advantages of large UV absorption coefficient, high shielding efficiency, wide shielding band, and good transparency, but they have disadvantages such as poor light and thermal stability, easy volatility, and poor long-term stability. Moreover, organic UV absorbers decompose The product has certain toxicity. Although inorganic nano-ultraviolet absorbers have outstanding light and thermal stability, they are easy to agglomerate. While realizing ultraviolet shielding, it is easy to cause the transparency of the coating to decrease; at the same time, inorganic nanoparticles have strong photocatalytic activity. Under the action, it can accelerate the aging and degradation of the polymer coating, greatly reducing the service life of the coating. Chinese patent CN1412258A reports that titanium dioxide or zinc oxide nano-powders are ground and dispersed, and then added to polyacrylic resin to prepare an anti-ultraviolet coating. Since it is impossible for the nanopowder to completely reach the dispersion level of the primary particle size through grinding, the transparency of the coating is not good. Chinese patent CN101629033A prepared calcium-doped ceria nanoparticles by carboxymethyl cellulose ultrasonic-assisted method, and coated with an inert shell layer to reduce the photocatalytic activity of ceria nanoparticles, then modified with silane coupling agent, and then combined with Pure acrylic emulsion is compounded to prepare ultraviolet shielding paint. However, in this method, the ceria nanoparticles are sintered, the dispersion in the coating is not good, and the transparency of the coating is low. It can be seen that the preparation method of environmentally friendly UV shielding coatings with high weather resistance and high transparency still needs to be developed urgently.

Zinc oxide quantum dots (ZnO QDs) have strong ultraviolet absorption ability, high fluorescence emission intensity, and have the advantages of non-toxicity. They are often used in bioluminescence marking materials, and are also ideal for inorganic nano-ultraviolet absorbers for high-transparency ultraviolet shielding coatings. For example, Li et al. combined ZnO QDs with polymer resins to prepare transparent UV shielding coatings (S. Li, et al, Adv. Mater ., 2007, 19, 4347). However, the photocatalytic activity of ZnO QDs was not considered in this study, and the coating system was solvent-based. Coating of ZnO QDs by amphiphilic polymers and surfactants (NR Jana, et al, Chem. Commun ., 2007, 1406; HM Xiong, et al, J. Am. Chem. Soc ., 2008, 130 ,7522; X. Tang, et al, Langmuir , 2009, 25, 5271.), can improve the water solubility of ZnO QDs, but due to the photocatalytic activity of ZnO QDs, under the irradiation of ultraviolet light, these amphiphilic polymers And surfactants are easy to decompose, causing ZnO QDs to be unstable, and cannot be used for the preparation of high weather resistance and high transparency waterborne UV shielding coatings.

Contents of the invention

The object of the present invention is to provide a method for preparing a water-based UV shielding coating with high weather resistance and high transparency based on ZnO QDs. Specifically include the following steps:

Weigh the zinc salt and lithium hydroxide respectively, ultrasonically treat and fully dissolve them in absolute ethanol, then mix the ethanol solutions of the two, and react with stirring at 60-78°C for 3-10 h. , to obtain a dispersion of ZnO QDs in ethanol. Add tetraethyl orthosilicate and deionized water to the ethanol dispersion of ZnO QDs, mix thoroughly with ultrasonic waves, and stir at room temperature for 6 h to obtain a dispersion of SiO ₂ coated ZnO QDs (ZnO QDs@SiO ₂ ), which can be obtained by Centrifuge and wash, transfer and disperse ZnO QDs@SiO ₂ into water to obtain an aqueous dispersion of ZnO QDs@SiO ₂ , then mix with water-based film-forming resin and wetting agent in a certain proportion, and after fully stirring, the water-based UV Shielding paint. The coating can be coated on the surface of substrates such as bamboo, wood, plastic, glass, etc., and dried at low temperature to obtain a transparent ultraviolet shielding coating.

The water-based UV shielding coating based on ZnO QDs of the present invention is characterized in that the particle size of the ZnO QDs is 1-10 nm. If the particle size is too small, it is difficult to prepare, the crystallinity becomes poor, and the ultraviolet absorption ability is weakened; if the particle size is too large, the light scattering effect is enhanced, which is not conducive to the preparation of transparent UV shielding coatings.

The water-based UV shielding coating based on ZnO QDs of the present invention is characterized in that the molar ratio of zinc salt to lithium hydroxide is 1:4-2:3, and the reaction temperature is 60-78°C. The zinc salt is one of zinc nitrate, zinc sulfate, zinc chloride and zinc acetate, and has the advantages of low cost and non-toxicity.

The water-based UV shielding coating based on ZnO QDs of the present invention is characterized in that _SiO2 is used to coat ZnOQDs, which can effectively inhibit the photocatalytic activity of ZnO QDs, and can improve its dispersibility in water at the same time, which is beneficial to its application in water-based coatings. in the application. The SiO ₂ coating layer was prepared by the in situ sol-gel method of ethyl orthosilicate in ZnO QDs dispersion, in which ethyl orthosilicate was added within 24 h after ZnO QDs preparation at Si:Zn molar ratio of 1–3. If the amount of tetraethyl orthosilicate is too small, it will easily lead to incomplete coating of ZnO QDs, and the photocatalytic activity cannot be effectively isolated. If the amount is too large, it will easily lead to the agglomeration between ZnO QDs@SiO ₂ nanoparticles, and even the dispersion of the liquid system. gel. If the addition of tetraethyl orthosilicate is too late, the particle size of ZnO QDs will become larger due to Ostwald aging, which is not conducive to the preparation of transparent UV shielding coatings.

The water-based UV shielding coating based on ZnO QDs of the present invention is characterized in that the water-based film-forming resin used is styrene-acrylic emulsion, pure acrylic emulsion, silicon-acrylic emulsion, water-based polyurethane resin, water-based organic-inorganic hybrid resin One or a mixture of several.

The water-based UV shielding coating based on ZnO QDs of the present invention is characterized in that the wetting agent used is DISPERBYK-2010, DISPERBYK-2015, Hydropalat 875, WET265, WET500, DISPERBYK-346, DISPERBYK-349, BYK380N, BYK One or a mixture of water-based wetting agents such as -381, EFKA3030, EFKA3034, EFKA3500, EFKA3570, etc.

The ZnO QDs-based water-based UV shielding coating of the present invention is characterized in that the content of ZnO QDs in the dry coating film ranges from 1-50%, preferably 2-30%, and most preferably 5-20%. If the amount of ZnO QDs is too small, the UV shielding effect is not obvious; if the amount is too large, the transparency of the coating begins to decrease.

The coating obtained in the present invention can be coated on the surfaces of substrates such as bamboo, wood, plastic, glass, etc. After drying, the coating film has high-efficiency ultraviolet shielding performance below the wavelength of 340nm. transparency. Since the photocatalytic activity of ZnO QDs is effectively isolated, the photocatalytic effect on organic components is no longer generated in the coating film, and the weather resistance of the coating film is good, and the UV shielding performance is stable for a long time.

The water-based UV shielding coating based on ZnO QDs of the present invention has the advantages of:

(1) Water-based, environmentally friendly, ZnO QDs quantum dot UV absorber itself is non-toxic and stable; (2) The raw materials used are economical, the equipment used is simple, and the preparation method is easy to operate; (3) It can completely shield UV rays with wavelengths below 340 nm At the same time, the coating film can maintain high transparency similar to that of pure resin coating film; (4) The ZnO QDs@SiO ₂ obtained in the present invention can greatly weaken the photocatalytic activity of ZnO QDs, and the UV shielding performance of the coating film is Good long-term stability.

Test Methods:

(1) Photocatalytic activity test method: ZnO QDs and ZnO QDs@SiO ₂ were respectively dispersed in rhodamine B aqueous solution (10 mg/L), and irradiated with a 150 W high-pressure mercury lamp for different times under stirring , sampled, centrifuged, and tested for the UV-Vis absorption spectrum of the solution.

(2) UV shielding performance test method: Cover the pure polymer coating and UV shielding coating on the surface of the resin coating containing Rhodamine B respectively, place them in an accelerated aging instrument, and test the rhodamine-containing B coating after aging for different times. UV-Vis transmission spectrum of the resin coating of B.

(3) Weather resistance test method: put the UV-shielding coating in an accelerated aging instrument, and test its UV-visible transmission spectrum after aging for different times; test instrument: QUV/Se artificial accelerated aging instrument of Q-Panel Company in the United States ;Test conditions: wavelength 310 nm, radiation power 0.71 W/m ² ; Cycle program: UV irradiation for 4 h at 60°C, condensation for 4 h at 50°C.

Description of drawings

Figure 1 is the appearance of the aqueous dispersion of nanoparticles in Example 1 (a) and Comparative Example 1 (b) under the irradiation of a 365 nm ultraviolet lamp.

Figure 2 is the photocatalytic degradation curve of Rhodamine B by nanoparticles in Example 1 and Comparative Example 1 (absorbance (0), absorbance (t) represent the beginning and after degradation t min, respectively, the Rhodamine B aqueous solution at 552 nm absorbance).

Fig. 3 is the ultraviolet-visible transmission spectrum of the pure acrylic resin coating (Neat PA) and the coating in Example 1 (thickness: 350 μm).

Figure 4 shows the UV-Vis transmission spectra of the coatings (thickness: 65 μm) in Example 1(a) and Comparative Example 1(b) before and after accelerated aging.

Figure 5 is the accelerated aging degradation curve of Rhodamine B in the resin coating (absorbance (0), absorbance (t ) represent the absorbance at 552 nm of the rhodamine B-containing coating at the initial stage and after accelerated aging t min, respectively).

detailed description

Example 1:

(1) Add 1 mmol LiOH ^. H ₂ O into 50 mL of ethanol, sonicate for 30 min to fully dissolve it. Add 0.25 mmol Zn(Ac) ₂ .2H ₂ O and sonicate for 5 min to obtain a clear and transparent solution. Then, the transparent solution was heated to 70 °C and stirred for 3 h to obtain the ZnO QDs dispersion. 120 μL tetraethyl orthosilicate and 400 μL distilled water were sequentially added to the dispersion, and immediately ultrasonically oscillated for 20 min, followed by stirring at room temperature for 6 h to obtain a dispersion of ZnO QDs@SiO ₂ nanoparticles. Add 200 mL of n-hexane to the dispersion, centrifuge, wash twice with 15 mL of ethanol, and disperse into water. The aqueous dispersion of the nanoparticles can remain transparent and stable for a long time (see Figure 1a); while in Comparative Example 1, the ZnO QDs dispersed in water for 10 min and agglomerated and precipitated (see Figure 1b), indicating that ZnO QDs@SiO ₂ Nanoparticles have excellent water dispersibility. At the same time, the ZnO QDs@SiO ₂ nanoparticles were dispersed into the rhodamine B aqueous solution, and after stirring for 2 h in the dark, the rhodamine was degraded by 20% after being irradiated with ultraviolet light for 80 min (see Figure 2); In Comparative Example 1, 93% of Rhodamine B was degraded after UV irradiation for 80 min, which indicated that the SiO ₂ shell could effectively isolate the photocatalytic activity of ZnO QDs.

(2) The nanoparticle aqueous dispersion obtained in step (1) was mixed with 2 g of pure acrylic emulsion and 5 mg of Hydropalat875, and ultrasonicated for 20 min to obtain a water-based UV shielding coating. Then it was coated on the surface of quartz glass and dried at 30°C for 48 h to prepare two kinds of UV shielding coatings with thicknesses of 350 μm and 65 μm respectively (see Figure 3 and Figure 4 for UV-Vis spectra, respectively). The coating with a film thickness of 65 μm has no change in transparency after 200 h of artificial accelerated aging (see Figure 4a), indicating that the UV shielding coating has good weather resistance; while the UV shielding coating in Comparative Example 1 was artificially accelerated After aging for 200 h, the transparency decreased greatly (see Figure 4b), indicating that part of the polymer coating had been degraded.

Example 2:

Add 0.4 mmol LiOH ^. H ₂ O into 50 mL of ethanol, and sonicate for 30 min to fully dissolve it. Add 0.25mmol Zn(Ac) ₂ .2H ₂ O and sonicate for 5 min to obtain a clear and transparent solution. Then, the transparent solution was heated to 60 °C and stirred for 10 h to obtain the ZnO QDs dispersion. 120 μL tetraethyl orthosilicate and 300 μL distilled water were sequentially added to the dispersion, and immediately ultrasonically oscillated for 20 min, followed by stirring at room temperature for 6 h to obtain a dispersion of ZnO QDs@SiO ₂ nanoparticles. Add 200 mL of n-hexane to the dispersion, centrifuge, wash twice with 15 mL of ethanol, and disperse into water. The obtained nanoparticle aqueous dispersion was mixed with 2 g of pure acrylic emulsion and 5 mg of DISPERBYK-346, and ultrasonicated for 20 min to obtain a water-based UV shielding coating. Then it was coated on the surface of quartz glass and dried at 30°C for 48 h to obtain a UV shielding coating. The thickness of the coating is 350 μm, the light transmittance at 300 nm is 4%, and the light transmittance at 550 nm is 88%, which is close to the transparency (91%) of pure acrylic resin coating, indicating that the coating has High transparency and UV shielding effect.

Example 3:

Add 1 mmol LiOH ^. H ₂ O into 50 mL of ethanol, and sonicate for 30 min to fully dissolve it. Add 0.25mmol Zn(Ac) ₂ .2H ₂ O and sonicate for 5 min to obtain a clear and transparent solution. Then, the transparent solution was heated to 70 °C and stirred for 3 h to obtain a ZnO QDs dispersion. 120 μL tetraethyl orthosilicate and 300 μL distilled water were sequentially added to the dispersion, and immediately ultrasonically oscillated for 20 min, followed by stirring at room temperature for 6 h to obtain a dispersion of ZnO QDs@SiO ₂ nanoparticles. Add 200 mL of n-hexane to the dispersion, centrifuge, wash twice with 15 mL of ethanol, and disperse into water. The obtained aqueous dispersion of nanoparticles was mixed with 2 g of water-based polyurethane and 5 mg of DISPERBYK-346, and ultrasonicated for 20 min to obtain a water-based UV shielding coating. Then it was coated on the surface of quartz glass and dried at 30°C for 48 h to obtain a UV shielding coating. The coating has a thickness of 300 μm and a transmittance of 5% at 300 nm and 89% at 500 nm.

Comparative example 1:

Add 1 mmol LiOH ^. H ₂ O into 50 mL of ethanol, and sonicate for 30 min to fully dissolve it. Add 0.25mmol Zn(Ac) ₂ .2H ₂ O and sonicate for 5 min to obtain a clear and transparent solution. Then, the transparent solution was heated to 70 °C and stirred for 3 h to obtain a ZnO QDs dispersion. Add 200 mL of n-hexane to the dispersion, centrifuge, wash twice with 15 mL of ethanol, and disperse into water. The dispersion was mixed with 2 g of pure acrylic emulsion and 5 mg of Hydropalat875, ultrasonicated for 20 min, coated on the surface of quartz glass, and dried at 30 °C for 48 h to obtain a UV shielding coating with a thickness of 65 μm. The ultraviolet-visible spectrum and artificial accelerated aging results are shown in Figure 4b.

Claims (4)

1. A method for preparing a water-based ultraviolet shielding paint based on ZnO quantum dots, characterized in that it comprises the following steps: first utilize zinc salt and lithium hydroxide to produce ZnO quantum dots in ethanol solution by sol-gel reaction, then add orthosilicon ethyl orthosilicate and water, using the hydrolysis-polycondensation reaction of tetraethyl orthosilicate to coat a layer of silica on the surface of ZnO quantum dots in situ to prepare ZnO QDs@SiO ₂ nanoparticles; ZnO QDs@SiO ₂ nanoparticles Transfer and disperse into water, and then fully stir and mix with water-based film-forming resin and wetting agent to obtain a water-based UV shielding coating based on ZnO quantum dots; in, The particle size of ZnO quantum dots is 1-10 nm; _The SiO coating on the surface of ZnO QDs was carried out within 24 h after the ZnO QDs were prepared; According to Si: Zn molar ratio is 1-3 metering adds ethyl orthosilicate to carry out hydrolysis-polycondensation reaction; The water-based film-forming resin is one or a mixture of styrene-acrylic emulsion, pure acrylic emulsion, silicon-acrylic emulsion, water-based polyurethane resin and water-based organic-inorganic hybrid resin; The wetting agent is DISPERBYK-2010, DISPERBYK-2015, Hydropalat875, WET265, WET500, DISPERBYK-346, DISPERBYK-349, BYK380N, BYK-381, EFKA3030, EFKA3034, EFKA3500, EFKA3570 water-based wetting agent or one of several mixture. 2. by the preparation method of the water-based ultraviolet shielding coating based on ZnO quantum dot described in claim 1, it is characterized in that the molar ratio of the substance of zinc salt and lithium hydroxide is 1:4-2:3, and temperature of reaction is 60-78 ℃, the reaction time is 3-10 h. 3. according to the preparation method of the water-based ultraviolet shielding paint based on ZnO quantum dots claimed in claim 1, it is characterized in that zinc salt is the one in zinc nitrate, zinc sulfate, zinc chloride or zinc acetate. 4. according to the preparation method of the water-based ultraviolet shielding paint based on ZnO quantum dots claimed in claim 1, it is characterized in that the percentage composition of ZnOQDs in coating film is 1-50%, by adjusting coating film thickness or ZnO QDs nanoparticle The content realizes the full shielding of ultraviolet rays with a wavelength of <340 nm.