CN110128855B

CN110128855B - Preparation method of anti-reflection coating composition containing silicon dioxide hollow particles

Info

Publication number: CN110128855B
Application number: CN201811460869.9A
Authority: CN
Inventors: 赵永亮; 朱晓敏
Original assignee: Ningbo Te Li Science And Technology Ltd
Current assignee: Ningbo Te Li Science and Technology Ltd.
Priority date: 2018-12-04
Filing date: 2018-12-04
Publication date: 2021-12-07
Anticipated expiration: 2038-12-04
Also published as: CN110128855A

Abstract

The invention relates to a preparation method of an anti-reflection coating composition containing silica hollow particles, which specifically comprises the following steps: 1) synthesizing an amphiphilic polyalkoxysiloxane precursor; 2) dispersing the precursor in an aqueous medium for self-assembly; 3) adding alkali to promote hydrolysis and condensation of the precursor; 4) purifying and concentrating the hollow particle water dispersion by centrifugation, ultrafiltration or dialysis, or drying by freezing, heating, spraying to obtain hollow particle powder; 5) modifying the surface of the hollow particles, and dispersing in different solvent systems. The method has the advantages that the cavity structure is directly obtained, a template does not need to be calcined or etched, the particle size, the cavity rate and the surface property are adjustable, different dispersion systems are met, and the addition of the adhesive and the auxiliary component into the hollow particle dispersion system is allowed. The invention also relates to a coating composition obtained by the preparation method, a method for coating a substrate by using the coating composition, and the obtained coated substrate.

Description

Preparation method of anti-reflection coating composition containing silicon dioxide hollow particles

Technical Field

The invention relates to a preparation method of an anti-reflection coating composition, which mainly comprises the following steps: synthesizing hollow silica particles, and optionally adding an organic polymer or a polymerizable compound or an inorganic oxide precursor or an inorganic compound as a binder. The invention also relates to an anti-reflective coating composition obtained by the preparation method, a method for coating an anti-reflective coating on a transparent substrate by using the coating composition, and the obtained coated substrate.

Background

When light enters the optically denser medium 2 from the optically thinner medium 1, because of the difference of refractive indexes between the two, a part of incident light is always reflected at the interface, and the proportion of the reflected light can be simply calculated according to the formula (1):

（1）

whereinR _fIn order to be the reflectivity,n ₁is the refractive index of the medium 1 and,n ₂is the refractive index of medium 2. For example, when the light is emitted from the air (n ₁= 1) on entry into the glass: (n ₂= 1.5), about 4.0% of the incident light is reflected at each interface, and 8% of the incident light is reflected at both interfaces. In the photovoltaic field, the fact that incident light is reflected means that the proportion of incident light participating in photoelectric conversion is reduced, and therefore the output power of the whole photovoltaic module is reduced. In the display field, reflection of light at the interface produces an image on the surface of the substrate, which can cause glare. The method effectively reduces the reflection of light at the interface of the air and the transparent substrate, and has very important significance in both industry and daily life.

It is now common to introduce one or more additional layers of coating between the air and the substrate, having a refractive index between that of the air and the substrate. According to the Fresnel equation:

wherein the content of the first and second substances,n _cis the refractive index of the coating. If the reflectance is to be made 0, then:

the optimal refractive index of the glass surface coating is then 1.22. When the thickness of the coating layer is smallhAt a wavelength λ of 1/4, i.e.:

when the optical film is used, the complete destructive interference of the reflected light of the upper surface and the lower surface of the coating can be met, and the reflection of the incident light is reduced to the maximum extent. Taking the wavelength of 550 nm as an example, to achieve zero reflection of incident light at this wavelength from the glass surface, the coating thickness ishIdeally 113 nm.

The anti-reflective coating on the surface of the substrate can be generally realized by a dry method and a wet method. The dry process is a Chemical Vapor Deposition (CVD) or Physical Vapor Deposition (PVD) process for coating a layer of a low refractive index material, such as magnesium fluoride (MgF)₂) However, this method has high requirements for equipment and high price, and this method cannot be used for other polymer substrate films except for glass, and cannot meet the requirements of continuous production, thus greatly limiting its application; the wet method is to apply an antireflection coating to the surface of a substrate, and form a coating layer after drying and curing. It is generally desirable to introduce sufficient porosity into the coating to reduce the overall refractive index of the coating. There are two main methods for introducing pores, one is to introduce a large amount of nanoparticles into the binder, and the particles are piled up to generate more pores, for example, patent US6921578 describes a method for preparing an anti-reflective coating by adding a prepolymer generated by hydrolysis of tetraethyl silicate (TEOS) as a binder to a nanoparticle dispersion to crosslink the nanoparticles, thereby obtaining an anti-reflective coating. Although the method is effective, the accumulation of a large number of nano particles leads the surface of the coating to be rough, the wear resistance and the mechanical stability are reduced, meanwhile, the pores among the particles are easy to absorb water and adsorb dust after being exposed in the air for a long time, the weather resistance is deteriorated, and finally the anti-reflection performance is lost, so that the weather resistance requirement of the photovoltaic field in 25 years cannot be met. Another method is to introduce hollow particles directly into the binder, i.e. by placing voids inside the particles rather than between them, which results in better mechanical properties of the coating (see patents EP1674891, WO 2006033456). However, at present, there is no method for preparing hollow particles which is simple, effective, low-cost and industrially applicable. Currently, hollow particles are prepared mainly by a hard template method, i.e., a core which can be calcined at a high temperature or etched by a solvent at the later stage of synthesis is synthesized, then a layer of inorganic oxide is deposited on the surface of the core, and finally a template introduced before is removed.For example, in Chemistry of Materials 2009, 21, 3629-3637, a method for preparing hollow silica particles is described, in which Polystyrene (PS) microspheres are synthesized, TEOS is hydrolyzed and condensed in an alkaline environment to deposit on the PS surface to form a silica shell, and finally the PS template is removed by high temperature calcination or etching with toluene to obtain hollow silica particles. Although the literature on Macromolecules 2016, 49, 1552-1562 reports a one-step method for preparing PS/silica core-shell nanoparticles, the polymer removal process, whether the one-step method or the two-step method, inevitably causes the obtained hollow particles to agglomerate, and the surface of the hollow particles is difficult to modify and disperse in the required adhesive. In view of this, engineers have placed the calcination of the core-shell particles in the curing process of the final coating, effectively avoiding the agglomeration of the hollow particles. For example, patent CN101512387A discloses a method for preparing polymer/silica core-shell particles, then dispersing the core-shell particles in a dispersion system containing a binder to obtain an anti-reflective coating, and after drying the coating, subjecting the coating to high-temperature calcination to remove the polymer, thereby introducing pores in the coating, and also intra-particle pores, which has been highly successful on the glass surface. However, this method cannot be applied to a polymer substrate because high-temperature calcination sacrifices the polymer substrate, which greatly limits the application in this field. Although researchers have reported many methods for preparing hollow particles using soft templates, avoiding post-high temperature calcination, for example, in Journal of Materials Chemistry A2015, 3, 24428-^oAnd removing hexadecane under C to obtain the silicon dioxide hollow microsphere. Patent CN105745284A discloses a method for preparing hollow silica particles by using emulsion droplets as a template, which comprises preparing a block copolymer with interfacial activity, using it to stabilize a low boiling point solvent to obtain a stable oil-in-water emulsion, adding a silica precursor to form a silica shell by hydrolytic condensation on the surface of the emulsion droplets, adding the particles into a binder to prepare an anti-reflective coating, and coating the anti-reflective coating on the surface of a substrate. The problem with this method is that it requires the block copolymer to be synthesized beforehand, and that it requiresThe use of a large amount of volatile solvent as a template requires heating to remove the solvent from the interior of the particles during the drying and even curing of the coating, the drying time is long, and in addition, the polymer with interfacial activity is always present in the coating, which is a concern for the long-term stability of the coating. Other novel methods for directly preparing silica hollow particles mostly stay in experimental stages, and industrial scale production may have more problems, such as the size and the morphology of the particles cannot be effectively controlled, the surface properties of the hollow particles obtained in a specific system are difficult to match with other dispersion systems, and an anti-reflection coating which is relatively universal in the field cannot be obtained. With the heteromilitary projection in the field of flexible displays, the need in the industry for antireflective coatings that can be applied to polymer surfaces or that cannot be applied to high temperature calcination systems is still very strong.

Disclosure of Invention

In order to overcome the disadvantages of the prior art, it is an object of the present invention to provide an improved anti-reflective coating composition and a method for preparing the same, which achieves a solution to the above technical bottlenecks by providing the method as defined in the claims and described below.

Accordingly, the present invention provides a method for preparing an anti-reflective coating composition comprising silica hollow particles, comprising the steps of:

1) synthesis of amphiphilic polyalkoxysiloxane silica precursor: fully mixing silane A, a hydrophilic compound containing hydroxyl, a solvent and water with the aid of dispersing equipment, adding a catalyst solution, heating to react completely, and removing the solvent to obtain amphiphilic polyalkoxysiloxane;

2) self-assembly: adding the polyalkoxysiloxane obtained in the step 1) into an aqueous medium with the aid of a dispersing device for self-assembly to obtain a white or semitransparent dispersion liquid;

3) and (3) accelerated forming: adding alkali into the white or semitransparent dispersion liquid obtained in the step 2), adjusting the pH value to 8-12, and continuing to react until the reaction is finished to obtain a silicon dioxide hollow particle dispersion liquid;

4) washing and separating: separating, washing and concentrating the hollow particle dispersion liquid obtained in the step 3) by using a separation device to obtain a silica hollow particle dispersion liquid or obtaining hollow particle powder by using a drying method.

With the process of the present invention it was found that hollow silica particles for the preparation of antireflective coatings can be obtained, which particles have an average particle size of 20-500 nm and an average wall thickness of 3-100 nm, said particle size and wall thickness being characterized by Transmission Electron Microscopy (TEM). The size and wall thickness of the particles can be controlled by changing the molecular weight of the amphiphilic polyalkoxysiloxane and the proportion of the hydrophilic compound containing hydroxyl groups, and the method is simple and easy to operate. The method has the greatest advantage that the obtained silicon dioxide hollow particles can directly obtain dispersion liquid and powder without high-temperature calcination or solvent etching, so that surface functionalization can be carried out according to needs, the silicon dioxide hollow particles can be dispersed in different solvent systems, and the problems of particle agglomeration, difficult redispersion and the like caused by high-temperature calcination or solvent etching are effectively avoided. The coating composition obtained by the invention can be widely applied to different substrate surfaces, including the surface of an inorganic substrate which can resist high temperature or the surface of a polymer substrate which cannot resist high temperature, and the cavity structure in the particle exists from the beginning of the preparation of the coating, so that the requirements on the drying and curing conditions in the later period are not high, the coating composition can be cured at low temperature and can be photocured, and the application field of the coating composition obtained by the invention is greatly expanded.

Silane a used in step 1) is to be understood as meaning all silica precursors which are capable of forming oligomers by hydrolytic condensation, which are the main source of silicon for the formation of hollow silica particles. Preferably, silane A may have the formula R¹ _4-n-Si-(OR²)_nWherein n = 2-4, R¹The non-hydrolyzable group is a halogenated alkyl group such as an alkyl group, a vinyl alkyl group, an epoxy alkyl group, a styryl alkyl group, a methacryloxyalkyl group, an acryloxyalkyl group, an aminoalkyl group, a ureido alkyl group, a chloropropyl alkyl group, or a sulfanyl group, an isocyanate alkyl group, or a hydroxyalkyl group. OR (OR)²Is a hydrolyzable group, R²Is alkyl with 1-6 carbon atoms. With a plurality of R¹When each R is¹May be identical to each other orIn different, have a plurality of ORs²When each OR is²May be the same or different from each other. Meanwhile, the silane A can also be a commercially available polyalkoxysiloxane prepolymer with the silicon dioxide content of below 60 percent, and comprises one or more than two of silicon 40, silicon 48, silicon 53 and the like.

The hydroxyl-containing hydrophilic compounds described in step 1) are primarily used to increase the hydrophilicity of the resulting polyalkoxysiloxanes and to make them amphiphilic. Preferably one of polyethylene glycol, polyethylene glycol monoether, copolymer of ethylene glycol and propylene glycol, polyvinyl alcohol, polyglycerin, and the like, more preferably one of polyethylene glycol, polyethylene glycol monoether, and polyvinyl alcohol, and even more preferably polyethylene glycol or polyethylene glycol monoether;

preferably, the hydroxyl-containing hydrophilic compound used in step 1) has a molecular weight of 200-10000, more preferably 200-2000, even more preferably 200-1000.

Preferably, the weight ratio of hydroxyl-containing hydrophilic compound to silane a used in step 1) is (0.01-1): 1, more preferably (0.05-0.5): 1, even more preferably (0.1-0.25): 1.

the solvent in step 1) is understood to be any organic solvent which promotes the miscibility of silane A, the hydroxyl-containing hydrophilic compound and water. Preferably one or more of methanol, ethanol, isopropanol, butanol, propylene glycol methyl ether, acetone, butanone, etc., more preferably one or more of methanol, ethanol, isopropanol, and even more preferably one or more of methanol and ethanol.

Preferably, the weight ratio of solvent to silane a in step 1) is (0.05-10): 1, more preferably (0.2-5): 1, even more preferably (0.5-2): 1.

the water added in step 1) is intended to hydrolyze and condense silane A, preferably in a weight ratio of water to silane A of (0.01-1): 1, more preferably (0.05-0.5): 1, even more preferably (0.1-0.3): 1.

the catalyst is added in the step 1) to promote the hydrolysis and condensation of alkoxy, and improve the reaction efficiency. Preferably, but not limited to, one of protonic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, solid acids such as acidic cation exchange resins, or lewis acids such as aluminum trichloride, boron trifluoride, titanium alkoxide, and the like.

Preferably, the molar concentration of the catalyst in step 1) is from 0.01 to 10mol/L, and the weight ratio thereof to the silane a is (0.001 to 0.2): 1.

preferably, the temperature of the heating reaction in step 1) is from 30 to 100 ℃, more preferably from 50 to 90 ℃, even more preferably from 70 to 80 ℃.

Preferably, the heating reaction of step 1) is carried out for a period of time ranging from 1 to 24 hours, more preferably from 5 to 15 hours, even more preferably from 8 to 10 hours.

Preferably, the method for removing the solvent in step 1) is one of atmospheric distillation, reduced pressure distillation, thin film evaporation or rotary evaporation, and more preferably one of reduced pressure distillation or thin film evaporation.

Preferably, the aqueous medium of step 2) refers to a liquid comprising water, which may contain, in addition to water, at least one organic solvent capable of being dissolved in or miscible with water, such as an alcohol, a ketone, an ether or an ester.

Preferably, the polyalkoxysiloxane added in step 2) is present in a percentage by weight with respect to the aqueous medium of between 1 and 50%, more preferably between 5 and 30%, even more preferably between 10 and 20%.

Preferably, the dispersing device in step 2) can be understood as any device or technical means in the field that can disperse the precursor in the aqueous medium in the form of smaller droplets, including but not limited to mechanical stirring, magnetic stirring, ultrasound, a homogenizer, a colloid mill, and the like.

Preferably, the alkali in step 3) is sodium hydroxide, potassium hydroxide, ammonia water, etc.

The purpose of washing and separation in step 4) is to remove impurities including minute solid particles of silica, hydrophilic compounds containing hydroxyl groups, and an excess amount of alkali from the dispersion of hollow silica particles obtained in step 3). The separation apparatus is well known to those skilled in the art and includes, but is not limited to, centrifuges, ultrafiltration devices, dialysis devices.

Preferably, the mass concentration of the hollow particles obtained in step 4) is between 1 and 40%, more preferably between 5 and 30%, even more preferably between 10 and 20%.

The hollow silica particles obtained in any of the above steps have an average particle size of 20 to 500 nm and an average wall thickness of 3 to 100 nm, and can be detected by Transmission Electron Microscopy (TEM). In view of the use of the hollow particles obtained according to the present invention for the preparation of an anti-reflective coating, the variables of the process described hereinabove are selected such that the hollow particles have more preferably a size of 30 to 200 nm and a wall thickness of 3 to 20 nm, even more preferably a hollow particle size of 50 to 100 nm and a wall thickness of 5 to 10 nm.

The method according to the invention comprises the further steps of:

5) modification: adding silane B into the hollow particle dispersion liquid or the powder redispersion system obtained in the step 4), heating for reaction, and obtaining modified hollow particle powder after complete reaction or dispersing into a required solvent or drying;

6) the solid content of the resulting coating composition is adjusted by adding 0.1 to 10 times the weight of the binder and other known auxiliaries relative to the weight of the hollow particles, and adding a solvent.

The term "solids" as used herein refers to the weight percentage after removal of the solvent (including water).

The purpose of the modification in step 5) is to enable the hollow silica particles obtained by the invention to meet the requirements of different dispersion systems, have good compatibility with other coating compositions, and do not undergo phase separation after the coating is cured. Preferably, silane B has the formula R³ _4-m-Si-R⁴ _mWherein m = 1-3, R³The non-hydrolyzable group is a halogenated alkyl group such as an alkyl group, a vinyl alkyl group, an epoxy alkyl group, a styryl alkyl group, a methacryloxyalkyl group, an acryloxyalkyl group, an aminoalkyl group, a ureido alkyl group, a chloropropyl alkyl group, or a sulfanyl group, an isocyanate alkyl group, or a hydroxyalkyl group. R⁴The hydrolyzable group includes alkoxy (with carbon number of 1-6) and halogen (such as chlorine, bromine, and iodine). With a plurality of R³When each R is³May be the same or different from each other, and has a plurality of R⁴When each R is⁴May be the same or different from each other.

Preferably, the mass fraction of silane B used in step 5) is 1 to 60%, more preferably 5 to 40%, even more preferably 10 to 30% relative to the hollow particles.

The binder added in step 6) is understood to be a compound capable of chemically or physically crosslinking the silica hollow particles to form a continuous, integral coating while improving the bonding of the hollow particles to the coated substrate, preferably at least one inorganic or organic polymeric or polymerizable compound.

Preferably, suitable inorganic binders in step 6) include those precursor compounds known to those skilled in the art that are capable of forming the corresponding inorganic oxides by hydrolysis, condensation reactions, such as metal alkoxides, metal salts, siloxanes, silicates and mixtures thereof, which may comprise two or more precursor compounds simultaneously or both precursor compounds and the corresponding inorganic oxides in order to enhance certain properties of the resulting coating.

Preferably, suitable organic binders in step 6) include various polymers and monomers and oligomers that are thermally or radiation (e.g., UV) curable, as are well known to those skilled in the art, including acrylate monomers, methacrylate monomers, and various oligomers derived therefrom, such as (meth) acrylate oligomers, urethane (meth) acrylate oligomers, epoxy (meth) acrylate oligomers, polyester (meth) acrylate oligomers, fluoro (meth) acrylate oligomers, and unsaturated polyesters or polyurethanes that are free radically curable in acrylates, methacrylates. One advantage of the invention is that the added hollow silica particles have a hollow structure and do not need to be subjected to higher-temperature treatment on the coating, so that low-temperature curing or radiation curing after low-temperature drying can be satisfied for some polymer substrates which do not resist high temperature.

Preferably, the suitable binder in step 6) may also be a combination of inorganic and organic binders, to further improve various properties of the coating, such as adhesion, oil stain resistance, mechanical properties or toughness.

Preferably, the auxiliaries added in step 6) are various auxiliaries well known to those skilled in the art of coatings, including buffers, initiators, catalysts, surfactants, defoamers, thickeners and leveling agents.

Preferably, the binder added in step 6) is 0.1 to 10 times, more preferably 0.2 to 5 times, even more preferably 0.5 to 2 times the weight of the silica hollow particles.

Preferably, the solvent added in step 6) comprises water, an organic solvent or a combination of both, with the aim of adjusting the solids content and viscosity of the resulting coating composition in order to expect a desired coating. The amount of the solvent added is 5 to 100 times of the total weight of the silica hollow particles and the binder.

Preferably, the coating composition obtained according to the invention has a solids content of from 0.5 to 20%, more preferably from 1 to 10%, even more preferably from 2 to 5%.

The present invention also relates to a method for preparing an antireflective coating on a substrate comprising the steps of:

a) coating the coating composition obtained by the method on a substrate;

b) the resulting coating is dried and cured.

Preferably, the substrate in step a) is a transparent substrate with a light transmittance of 80-100%, and may be high temperature resistant ceramic, cermet, glass, quartz and a combination thereof, or may be organic plastic which is not high temperature resistant, such as polyethylene terephthalate (PET), Triacetylcellulose (TAC), Polycarbonate (PC), Polyethylene (PE), polypropylene (PP), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), Polystyrene (PS), or may be a composite material derived from the above materials.

Preferably, the coating composition obtained in step a) can be directly coated on the surface of a bare substrate, can be coated on the surface of a substrate already containing various coating layers (such as a high-refractive-index layer, a hardening layer, an anti-dazzle layer and the like), and can be coated among other coating layers.

Preferably, the coating method used in step a) comprises all possible coating methods known to the person skilled in the art, such as meniscus (knife) coating, spin coating, spray coating, dip coating, roll coating, slot die coating. The wet film thickness of the coating layer depends on the solids content of the coating composition obtained according to the invention and on the dry film thickness after drying and curing.

The drying in step b) is aimed at removing the volatile part of the coating obtained in step a), mainly the solvent used to adjust the coating solids in step 6). One advantage of the present invention is that the added hollow silica particles do not contain any component to be removed by heat drying, and thus the drying temperature and time can be flexibly selected according to the heat-resistant temperature of the base material.

Preferably, the curing means used in step b) comprises thermal curing and radiation curing. For inorganic glasses, curing can be carried out at higher temperatures, for plastics, at lower temperatures or by radiation.

Preferably, the thickness of the coating obtained after curing in step b) is between 50 and 200 nm, more preferably between 80 and 150 nm.

Preferably, in the coating obtained after curing in step b), the hollow silica particles obtained in the present invention may be uniformly distributed in the bulk phase of the coating or may be concentrated at the interface, and at the same time, the hollow particles may be distributed in a single layer or multiple layers (two or more layers) in the coating.

The coating obtained in the step b) contains the silicon dioxide hollow particles obtained by the invention, so that the refractive index is lower and the coating has an anti-reflection function. Preferably, the coating has a reflectance of 2% or less, more preferably 1.5% or less, even more preferably 1% or less, for visible light in the wavelength 380-.

The coating obtained in the step b) contains inorganic silica hollow particles, so that the coating has better mechanical properties, including scratch resistance, wear resistance and good adhesion with a base material.

Drawings

FIG. 1 is a Transmission Electron Microscope (TEM) photograph of hollow silica particles obtained in example 1;

FIG. 2 is a graph showing Dynamic Light Scattering (DLS) of the silica hollow particles obtained in example 1 in water;

FIG. 3 is a Transmission Electron Microscope (TEM) photograph of the hollow silica particles obtained in example 2;

FIG. 4 is a graph showing Dynamic Light Scattering (DLS) in water of the hollow silica particles obtained in example 2;

FIG. 5 is a Transmission Electron Microscope (TEM) photograph of the hollow silica particles obtained in example 3;

FIG. 6 is a graph of Dynamic Light Scattering (DLS) in water of the hollow silica particles obtained in example 3;

FIG. 7 is a Transmission Electron Microscope (TEM) photograph of the hollow silica particles obtained in example 4;

FIG. 8 is a photograph of a dispersion of hollow silica particles obtained in example 5 in water, isopropanol and ethyl acetate;

FIG. 9 is a Transmission Electron Microscope (TEM) photograph of a cross-section of an anti-reflection coated polyethylene terephthalate (PET) film obtained in example 6;

FIG. 10 shows the reflectance of a PET film containing an antireflection coating obtained in example 6 with respect to light of different wavelengths.

Detailed Description

The present invention will be further illustrated with reference to the accompanying drawings and specific examples, which are not intended to limit the scope of the invention in any way and, unless otherwise indicated, the reagents used in the specific examples may be obtained by commercially available means or by routine experimentation.

Example 1

The method of the invention is utilized to prepare the silicon dioxide hollow particles. 1) Uniformly mixing 208 g of tetraethyl orthosilicate, 50 g of ethanol and 15 g of polyethylene glycol (average molecular weight 750) until the mixture is transparent, then respectively adding 15 g of concentrated hydrochloric acid (mass fraction is 37%) and 10 g of deionized water, uniformly mixing, stirring for 5 minutes, heating to 80 ℃, continuing to react for 2 hours, decompressing, rapidly and rotationally distilling off a solvent and a low molecular weight compound in a system, and obtaining a flowable transparent polyalkoxysiloxane precursor with certain viscosity; 2) adding 100 g of polyalkoxysiloxane precursor into 350 g of deionized water, and rapidly stirring to obtain white dispersion liquid; 3) adding 25 g of strong ammonia water (the mass fraction is 25%) into the white dispersion liquid, and continuously stirring for 5 hours to obtain a semitransparent dispersion liquid; 4) centrifuging the dispersion to remove supernatant, washing the lower colloidal solid with water until the pH is less than 10, and adjusting the solid content of the dispersion to 15%.

The transmission electron micrograph of the obtained silica hollow particles is shown in FIG. 1, and the dynamic light scattering pattern of the dispersion is shown in FIG. 2. It can be seen that the hollow particles have uniform size distribution, average size of 40 nm, wall thickness of 5-6 nm, complete spherical structure, obvious cavity structure, uniform wall thickness, and no agglomeration after drying.

Example 2

Example 2 differs from example 1 in that 208 grams of tetraethyl orthosilicate in step 1) was replaced with 146 grams of silicon 40 commonly used in the silicone industry, polyethylene glycol (average molecular weight 750) was replaced with polyvinyl alcohol (average molecular weight 500), the amounts of concentrated hydrochloric acid and deionized water were reduced to 7.5 grams and 5 grams, respectively, the centrifugation-water wash operation in step 4) was replaced with dialysis, and the selected dialysis bag had a molecular weight cutoff of 14000.

The transmission electron micrograph of the obtained silica hollow particles is shown in FIG. 3, and the dynamic light scattering pattern of the dispersion is shown in FIG. 4. It can be seen that the hollow particles have uniform size distribution, average size of 70-80 nm, wall thickness of 7-8 nm, complete spherical structure, obvious cavity structure, uniform wall thickness, and no agglomeration after drying.

Example 3

Example 3 differs from example 1 in that 208 grams of tetraethyl orthosilicate in step 1) was replaced with 152 grams of tetramethyl orthosilicate, ethanol was replaced with isopropanol, polyethylene glycol was replaced with polyethylene glycol monomethyl ether (average molecular weight 500), 15 grams of concentrated hydrochloric acid (mass fraction 37%) was replaced with 14 grams of concentrated nitric acid (mass fraction 68%), 350 grams of deionized water in step 2) was replaced with a mixed solvent of 300 grams of deionized water and 50 grams of ethanol, and 25 grams of concentrated aqueous ammonia in step 3) was replaced with 25 grams of aqueous sodium hydroxide (0.1M).

The transmission electron micrograph of the obtained silica hollow particles is shown in FIG. 5, and the dynamic light scattering pattern of the dispersion is shown in FIG. 6. The hollow particles are uniform in size distribution, the average size is about 100 nanometers, the wall thickness is 15 nanometers, the spherical structure is complete, the cavity structure is obvious, the wall thickness is uniform, and no agglomeration phenomenon occurs after drying.

Example 4

Example 4 differs from example 1 in that 15 g of polyethylene glycol (average molecular weight 1000) in step 1) was replaced by 30 g of polyethylene glycol monoethyl ether (average molecular weight 500), 15 g of concentrated hydrochloric acid (mass fraction 37%) and 10 g of deionized water were replaced by 9 g of concentrated hydrochloric acid (mass fraction 37%) and 14 g of deionized water, respectively, the mass of the polyalkoxysiloxane precursor in step 2) was reduced to 50 g, and the centrifugation-water washing operation in step 4) was replaced by ultrafiltration.

A transmission electron micrograph of the obtained silica hollow particles is shown in FIG. 7. The hollow particles are uniform in size distribution, the average size is about 50 nanometers, the wall thickness is 6-7 nanometers and is close to a spherical structure, the cavity structure is obvious, the wall thickness is uniform, and no agglomeration phenomenon occurs after drying.

Example 5

The surface modification is carried out on the hollow silica particles obtained by the invention. To 100 g of the aqueous dispersion of hollow particles obtained in example 2 (see FIG. 8), 100 g of ethanol was added, 3 g of gamma-methacryloxypropyltrimethoxysilane was added with stirring, the mixture was heated to 75 ℃ and reacted for 16 hours, and the resulting modified hollow particles were separated by centrifugation and redispersed in ethyl acetate, and the resulting dispersion was as shown in FIG. 8. Thus, the modified silicon dioxide hollow particles have very good dispersion stability in ethyl acetate and no agglomeration phenomenon.

Example 6

Example 6 differs from example 5 in that 100 grams of ethanol was replaced with 200 grams of propylene glycol methyl ether, gamma-methacryloxypropyltrimethoxysilane was replaced with gamma-glycidoxypropyltrimethoxysilane, and ethyl acetate was replaced with isopropanol, and the resulting dispersion is shown in fig. 8. Therefore, the modified silicon dioxide hollow particles have very good dispersion stability in isopropanol and no agglomeration phenomenon.

Example 7

The method is suitable for preparing the glass surface anti-reflection coating and the surface anti-reflection coating thereof: 1) mixing 17.5 g of tetraethyl orthosilicate, 35 g of ethanol and 17.5 g of 0.1mol/L hydrochloric acid, and stirring at room temperature for 24 hours to fully hydrolyze the tetraethyl orthosilicate, thereby finally obtaining the inorganic adhesive with the solid content of 7%; 2) diluting the solid content of the adhesive to 4.2% by using isopropanol; 3) the hollow particle dispersion obtained in example 6 was diluted with isopropyl alcohol to a solid content of 2.8%; 4) mixing the adhesive obtained in the step 2) with the hollow particle dispersion liquid obtained in the step 3) in the same mass ratio to obtain the desired antireflection coating, the solid content of which is 3.5%.

The glass surface was coated with the obtained coating by using the obtained coating under constant temperature (25 ℃) and constant humidity (50%) in a clean room. The glass surface was first ultrasonically cleaned with isopropyl alcohol and rinsed with deionized water, and after drying, the glass was immersed in a container containing the coating composition, pulled at a rate of 2.7mm/s, and dried at room temperature for 10 minutes. The glass plate was then cured in a muffle furnace at 600 ℃ for 5 minutes. The obtained glass containing the anti-reflection coating has an average reflectivity of 2.0% and a haze of less than 0.8% in a wavelength range of 380-760 nm.

Example 8

The method is suitable for preparing the transparent polymer surface anti-reflection coating and the surface anti-reflection coating thereof: 1) the dispersion of hollow particles from example 5 in ethyl acetate was further diluted to a solids content of 4%; 2) adjusting solid content of an organic adhesive (Changxing chemical, product name 5105A) to 4% by using ethyl acetate, and adding a required photoinitiator, a flatting agent and other auxiliary agents; 3) mixing the hollow particle dispersion liquid in the step 1) and the adhesive in the step 2) in equal mass ratio to obtain the anti-reflection coating with the solid content of 4%.

Polyethylene terephthalate (PET) film was selected as a base material, and coated with a wire bar (BYK, # 5) in a clean room at a constant temperature (25 ℃) and a constant humidity (50%). And after drying for two minutes at ambient temperature, sending the PET film into a blast oven, continuously drying for two minutes at 80 ℃, and then carrying out UV curing by using a UV curing machine to obtain the PET surface antireflection coating.

By slicing the PET having the anti-reflection coating and observing through a Transmission Electron Microscope (TEM), it was observed in the surface coating of the PET that the silica hollow particles are uniformly distributed in the coating on the surface of the PET in a single layer or multiple layers, the porous structure given to the coating by the hollow particles is clearly visible, and the structure of the hollow particles is complete, as shown in fig. 9. The PET film has a reflectivity of less than 1% at a wavelength of 550 nm, an average reflectivity of less than 1.5% and a haze of less than 0.5% in a wavelength range of 300-800 nm, as shown in FIG. 10.

Claims

1. A method for preparing an antireflective coating composition comprising hollow silica particles, comprising the steps of:

1) synthesis of amphiphilic polyalkoxysiloxane silica precursor: fully mixing silane A, a hydrophilic compound containing hydroxyl, a solvent and water with the aid of dispersing equipment, adding a catalyst solution, heating for complete reaction, and removing the solvent to obtain amphiphilic polyalkoxysiloxane, wherein the molecular weight of the hydrophilic compound containing hydroxyl is 200-10000;

4) washing and separating: separating, washing and concentrating the hollow particle dispersion liquid obtained in the step 3) by using a separation device to obtain a silicon dioxide hollow particle dispersion liquid or obtaining hollow particle powder by using a drying method;

5) adding silane B into the hollow particle dispersion liquid or the powder redispersion system obtained in the step 4), heating for reaction, and obtaining modified hollow particle powder after complete reaction or dispersing into a required solvent or drying;

6) adding 0.1-10 times of binder and other known adjuvants, and adding solvent to adjust solid content of the obtained coating composition,

the weight ratio of the water added in the step 1) to the silane A is (0.05-0.5) to 1,

the weight ratio of the hydroxyl-containing hydrophilic compound added in the step 1) to the silane A is 0.1-0.25: 1;

the heating reaction temperature in the step 1) is 70-80 ℃;

the silane B in the step 5) has the following chemical formula,

R³ _4-m-Si-R⁴ _m，

wherein m is 1-3; r³Is a non-hydrolyzable group which is an alkyl group, a vinyl alkyl group, an epoxyalkyl group, a styrylalkyl group, a methacryloxyalkyl group, an acryloxyalkyl group, an aminoalkyl group, a ureidoalkyl group, a chloropropylalkyl group, a sulfanyl group, an isocyanatoalkyl group or a hydroxyalkyl group, and has a plurality of R³When each R is³May be the same or different from each other; r⁴Is a hydrolyzable group, is an alkoxy group having 1-6 carbon atoms or a halogen, and has a plurality of R⁴When each R is⁴May be the same as or different from each other,

the mass fraction of the silane B relative to the hollow particles is 1-60%.

2. The method of claim 1, wherein silane A in step 1) is a monomer having the following formula or a polyalkoxysiloxane prepolymer having a silica content of 60% or less,

R¹ _4-n-Si-(OR²)_n，

wherein n is 2-4; r¹Is a non-hydrolyzable group selected from the group consisting of an alkyl group, a vinyl alkyl group, an epoxy alkyl group, a styryl alkyl group, a,Methacryloxyalkyl, acryloxyalkyl, aminoalkyl, ureidoalkyl, chloropropylalkyl, sulfanyl, isocyanatoalkyl or hydroxyalkyl radicals, having a plurality of R¹When each R is¹May be the same or different from each other; OR (OR)²Is a hydrolyzable group, R²Is alkyl of 1-6 carbon atoms, with multiple OR²When each OR is²May be the same or different from each other.

3. The method as claimed in claim 1, wherein the solvent in step 1) is one or more selected from methanol, ethanol, isopropanol, butanol, ethylene glycol, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether, acetone, methyl ethyl ketone, etc., and the weight ratio of the solvent to the silane A is (0.1-10): 1.

4. The method as claimed in claim 1, wherein the catalyst in step 1) is a protonic acid, a solid acid or a Lewis acid, the molar concentration of the catalyst is 0.01-10mol/L, and the weight ratio of the catalyst to the silane A is (0.001-0.2) to 1.

5. The method according to claim 4, wherein the protic acid is hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid; the solid acid is acidic cation exchange resin; the Lewis acid is aluminum trichloride, boron trifluoride or alkoxy titanium.

6. The method of claim 1, wherein the reaction time in step 1) is 1-24 hours, and the solvent is removed by one or a combination of atmospheric distillation, vacuum distillation, thin film evaporation and rotary evaporation.

7. The method according to claim 1, wherein the aqueous medium in step 2) is water or a mixed solution of water and other water-soluble solvents, and the weight percentage of the polyalkoxysiloxane obtained in step 1) relative to the aqueous medium is 1-50%.

8. The method according to claim 1, wherein the base in step 3) is sodium hydroxide, potassium hydroxide or ammonia water.

9. The method according to claim 1, wherein the separation equipment in step 4) is a centrifuge, an ultrafiltration device or a dialysis equipment, and the drying method is oven drying, freeze drying or spray drying.

10. The method of claim 1, wherein the resulting hollow silica particles have an average particle size of 20-500 nanometers and an average wall thickness of 3-100 nanometers, the hollow particles being spherical or irregularly spherical, wherein the particle size and wall thickness are determined by transmission electron microscopy.

11. The method according to claim 1, wherein the binder in step 6) is at least one polymer or polymerizable compound or at least one inorganic oxide precursor.

12. An antireflective coating composition having a solids content of 0.5 to 20% obtained by the process according to any one of claims 1 to 11.

13. A method for forming an anti-reflective coating on a transparent substrate comprising the steps of: applying a coating composition obtained according to the method of any one of claims 1 to 11 on the transparent substrate; and allowing the applied coating to dry and cure.

14. The method of claim 13, wherein the transparent substrate is a transparent polymer film, sheet, ceramic, glass, quartz, or a combination thereof having a light transmittance of 80-100%.