RU2554608C2 - Method for producing anti-reflective coating - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method for producing a nanocomposite anti-reflective coating involves preparing a liquid composition containing a solution of carboxyl-containing acrylate copolymer mixed with solvents of various volatility and silver nanoparticles produced directly in the solution by reducing with solvent-borne aldehyde by UV radiation. The prepared nanocomposition covers a solid-state underlying surface; then it is dried.

EFFECT: simplifying technology, reducing the aggregating effect on a disperse phase of the suspension, increasing the coating adhesion.

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Description

The invention relates to the field of producing antireflection nanocomposite polymer coatings for various optical objects.

In the general case, when light falls on the interface between two materials, it is reflected. For example, when considering the interface between silicate glass and air with a glass refractive index n≈1.51, about 8.6% of the light incident at an angle of 0 ° is reflected from two glass-air interfaces, and pure polished silicon reflects more than 30%. Theoretically, in order to reduce to a minimum in the limit (0.0%) the reflection of light with a wavelength λ, it is necessary to cover the glass with a transparent film with a refractive index of n≈1.23 and an optical thickness of λ / 4. However, film-forming materials with such a low refractive index do not exist in nature.

Thin film interference coatings are used in the optical industry and in the commercial industry for the illumination of optical elements (display screens, photodetectors, fiber optical fibers, etc.). Known antireflection coatings made of MgF ₂ , ZnS, SiO, SiO ₂ (see M. M. Koltun. Optics and metrology of solar cells. M .: Nauka, 1985; Lique A. Solar cells and optics for photovoltaics. Bristol-Philadelphia , 1989; Wu WF, Chiou BS Appl. Sur. Sci. 1997, vol. 115, p. 96-102; Lemiti M., Boyeuaux JP, Vernay M. et. Al., Proc. 2 World Conf. And Exhib. Photovolt. Solar Energy Conversion. Vienna, 1998, p. 1471-1474), from TiO ₂ , Ta ₂ O ₅ , SnO ₂ , ZnO, ITO, SiN _x : H (see Lemiti M., Boyeuaux JP, Vernay M. et. al., Proc. 2 World Conf. and Exhib. Photovolt. Solar Energy Conversion. Vienna, 1998, p. 1471-1474; Vong MSW, Sermon PA, Thin Solid Films, 1997, vol. 293, p. 185- 195; Nishitani M., Ikeda M., Negami T., Solar Energy Mater & Solar Cells. 1994, vol. 35, p.203-208; Deng X., Miller G., Wang R., Proc. 2 World Conf . and Exhib. Photovolt. Solar Energy Conversion. Vienna, 1998, p. 700-712; Doshi P., Jellison JS, Rohatri A., J. Appl. Optics. 1997, vol. 36, p. 7826-7837; Ekai R., Verbeek M., Nagel H. Proc. 2 World Conf. and Exhib. Photovoltaic Solar Energy Conversion. Vienna, 1998, p. 1430-1433; H.I. Klyuy, V.G. Litovchenko, A.N. Lukyanov et al. Journal of Technical Physics, vol. 76, pp. 122-126 (2006)), based on diamond-like carbon films (N.I. Klyuy, V.G. Litovchenko, A.N. Lukyanov et al. Journal of Technical Physics, vol. 76, p. 122-126 (2006)). The main limitation of thin-film antireflection coatings is the impossibility of vacuum deposition on large optical parts (larger aperture optics based on optical elements from fused silica and optical glasses of various grades, nonlinear water-soluble crystals, etc.). In addition, when applying interference coatings, it is necessary to fulfill strict restrictions on the choice of refractive index of the coating material and coating thickness, since low reflection and high transmission is achieved only in a narrow wavelength range. To expand this range, it is necessary to use multilayer coatings, which leads to a significant increase in the cost of these coatings.

To obtain single-layer antireflection coatings with a low refractive index of 1.23-1.25 on products made of silicate glass in the visible spectral region, a method is proposed that includes a sol-gel process of silicon tetraalkoxide in the presence of low and high molecular weight, including surface-active organic compounds, using the technique of self-organization of nanostructures caused by solvent evaporation (EISA) when applying a sol to glass, heating a coated sample in an atmosphere of air at 500 ° C for 5-6 hours in order to destruction of the organic additive with the formation of a film of mesoporous silica (patents RU 2371399; RU 2466948).

The disadvantages of the coating technology used in these patents are the production of a silica sol by hydrolysis of silicon tetraalkoxide catalyzed by an acid, which is an aggressive substance, and the use of fire hazardous, toxic organic solvents as dispersion media, which are expensive substances that are irretrievably lost due to evaporation as well as the use of heat to destroy organic additives.

Known antireflection coating based on fullerene-silicon (C ₆₀ / p-Si) heterostructures with strong absorption in the short-wave region of the solar spectrum (Light S., Khaselev O., Ramakrishna P.A. et. Al. Fullerene Photoelectromechanical Solar Cells. - Solar Energy Materials and Solar Cells, 51 (1998), p. 9-19). Polycrystalline fullerene 1 μm thick is deposited on a silicon substrate in high vacuum. The contacts are aluminum and a Ga _x In _y alloy on a gold-plated substrate.

The disadvantage of this coating is the low efficiency of photoelectric conversion in the visible and near infrared regions of the solar spectrum.

A transparent or translucent product is proposed, containing at least one layer of an antireflection coating, the thickness of which is chosen such that the perceived reflectance of the coated product, determined by the formula f _AR = 0.5F _o , where F _o is the perceived coefficient before coating, was minimal. A device for depositing an antireflection film contains a reactor chamber, a plasma generator, and an optical measuring instrument that contains a polarized radiation source for directing a light beam with a selected wavelength onto a substrate at a selected angle of incidence, a photodetector for measuring the intensity of the reflected part of the light beam, and a microprocessor connected with a photodetector, flow valve, discharge valve and power source and controlling them in accordance with the intensity of the reflected part tovogo beam (see. US patent №2204153).

The disadvantage of this method of deposition of an antireflection film is the complexity of the equipment used.

A method for producing an antireflective thin-film nanocomposite coating on a solid-state substrate (RF patent for invention No. 2323464, IPC B82B 3/00) is proposed, which involves introducing a solution of nanocomponents and a water-insoluble compound of an amphiphilic polyelectrolyte in a volatile non-polar solvent onto the surface of the aqueous phase with the formation of its nanocomposite monolayer and by the Langmuir-Blodgett method on a solid-state substrate with the formation of a nanocomposite coating on its surface. Moreover, in the process of formation, the nanocomposite monolayer is incubated at T = 16-58 ° C for a time sufficient for the formation of an ordered structure of nanocomponents in the plane of the monolayer.

However, this method is time-consuming, time-consuming and requires the use of a whole range of chemical components, many operations and a wide temperature regime.

The closest in technical essence to the claimed object is a method for producing a nanocomposite antireflection coating, including obtaining a liquid composition containing a polymer solution and 3 ± 0.5% by weight of a polymer of silver nanoparticles 1-10 nm in size, stabilization of the resulting composition through the formation of an adsorption-solvation layer on the surface of the particles, followed by applying the resulting nanocomposite on a solid-state underlying surface and drying (RF patent for the invention RU 2456710).

A method of manufacturing this antireflection coating has the following disadvantages:

1. The liquid composition is prepared by dissolving the nanocomposite obtained by the Caspol method, which consists in the following: the polymer base (polymethylmethacrylate (PMMA)) is dissolved in a high-boiling solvent (with a boiling point above the decomposition temperature of the silver precursor), the silver precursor is added and the nanosilver is synthesized by heating the resulting silver mixtures to a temperature above the decomposition temperature of silver. After that, the obtained nanocomposite is cooled and the high-boiling solvent is extracted with a low-boiling one, after which the latter is removed by drying.

2. The increased temperature increases the tendency of dispersed systems to aggregation, which may result in a decrease in the effectiveness of antireflection coatings in this case.

3. The need to use a high-boiling PMMA solvent during the thermolysis of a silver precursor makes it impossible to directly use the resulting composition to form a coating without heat supply due to the long duration of the process of removing the solvent from the film. To obtain a composition suitable for forming coatings, it is necessary to remove a volatile solvent and dissolve the composition in a more volatile solvent. This complicates the process due to the increase in staging, in addition, the double transition of the composition from a liquid to a solid state inevitably negatively affects the aggregative stability and, as a consequence, the dispersion of silver and the effectiveness of the antireflective effect of the coating.

4. In the process of obtaining a nanocomposite by the method of "caspol" in the system there is no component that has a stabilizing effect of silver nanoparticles in situ (at the time of formation) due to the presence of functional groups characterized by affinity for the surface of silver nanoparticles.

5. The choice of dichloroethane as a too volatile solvent to obtain a coating composition is unsuccessful. It is known that the high rate of solvent removal during the formation of polymer coatings causes incomplete relaxation processes in polymer chains. The consequence of this is the occurrence of internal stresses in the coating, which cause a violation of adhesion and reduce the life of the coatings due to their accelerated aging. Therefore, as a rule, when preparing compositions for the formation of polymer coatings, mixtures of solvents with different volatilities are used (see Drinberg S.A., Itsko E.F. Solvents for paints and varnishes: Reference guide - L .: Chemistry, 1986. - 208 p. .).

The objective of the invention is to simplify the technology, improve the economic characteristics of producing silver nanosuspension, reduce the aggregating effects on the dispersed phase of the suspension and create conditions for its stabilization, as well as increase the adhesion of coatings to the surface of the substrate.

The technical problem is solved in that in the method of producing antireflection coatings, a liquid composition is obtained by reducing silver acetate by reaction with an organosoluble aldehyde directly in a solution of a carboxyl-containing acrylate copolymer (5-30% by weight in the composition) in a mixture of organic solvents with different volatilities under the influence of ultraviolet radiation.

When the content of the copolymer in the composition is less than 5% of the mass. there is a danger of aggregation of silver nanoparticles as a result of insufficient stabilization, when the content of the copolymer in the composition is above 30% of the mass. defects on the surface of the coating result from an increase in the viscosity of the composition.

The solution of the technical problem allows us to simplify the technology for producing silver nanosuspension and improve its economic characteristics, to reduce the aggregating effect on the dispersed phase of the suspension by eliminating the effects of elevated temperature by using ultraviolet radiation to stimulate the recovery of nanosilver from a silver precursor and to obtain nanosilver as a result of a homogeneous reduction reaction environment, create conditions for stabilization of nanosuspension due to the formation of organic acid as a result of the reduction of an organically soluble aldehyde, which forms an adsorption layer on the surface of silver nanoparticles at the time of their formation, and due to the adsorption stabilization of the used film-forming polymer containing carboxyl groups with high affinity for the silver surface, and also to increase the adhesion of coatings due to reduction of internal stresses due to the use of a mixture of solvents with different volatilities in the preparation of the composition and as a result of application film former containing carboxyl groups interacting with the active sites of the substrate surface.

The following examples illustrate the subject matter of the invention.

Example 1. The calculated amount of a mixture of butyl acetate (C ₆ H ₁₂ O ₂ ), toluene (C ₆ H ₅ CH ₃ ) and butanol (C ₄ H ₉ OH) and ethanol (C ₂ H ₅ OH) (in ratio,% mass .: 50: 20: 10: 20) and stirred on a magnetic stirrer. An equimolar amount of a reducing agent and an estimated amount of a polymer acting as a film former and a stabilizer of the resulting nanosilver corresponding to its content in the composition of 5% by weight are added to the resulting solution.

As a reducing agent, a compound from the class of organosoluble aldehydes forming acid (benzaldehyde) during oxidation is used, and a copolymer of acrylic acid (BMK-5B) is used as a carboxyl-containing acrylate polymer.

After uniform distribution of all components, the resulting mixture is exposed to UV radiation with a wavelength of 365 nm using an FC100 UV lamp. In the process of irradiation spectrophotometrically, using a Proscan MC122 spectrophotometer, the magnitude and position of the peak due to the occurrence of the plasmon effect are monitored. The absence of changes in these parameters over time is used as a criterion for completing the recovery process with the formation of stable silver nanosuspension.

Silicate glasses with a refractive index of 1.51 and a thickness of 2.0 mm are used as a substrate for applying the resulting composition. The glass surface is cleaned of contaminants by immersion in a solution of alkali with hydrogen peroxide, the glass was washed with water, distilled water and dried in an oven at 150 ° C for 1 hour. The composition is applied using a spray gun (HVLP) in a spray booth and the solvent is removed without applying heat.

Example 2

A composition containing 10% of the mass. film-forming polymer, receive and applied to the glass surface, as in example 1

Example 3

A composition containing 20% of the mass. film-forming polymer, receive and applied to the glass surface, as in example 1

Example 4

A composition containing 30% of the mass. film-forming polymer, receive and apply to the surface of the glass, as in example 1.

In parallel, they were made and applied to the surface of the glass coating according to the technology described in the prototype.

The thickness of the coatings and adhesion by the normal peeling method (see table) were measured using a TT210 thickness gauge and an NK-10 adhesive meter, respectively. Evaluation of the optical characteristics of the coatings obtained according to the prototype and patent, showed their practical coincidence, taking into account the error of the experiment. The results are shown in table 1.

Table 1 Coating Characteristics №№ p.p. The concentration of polymer in the composition,% mass. According to patent According to the prototype Thickness, microns Adhesion, MPa Thickness, microns Adhesion, MPa one 5 33 ± 2 923.2 31 ± 2 723.2 2 10 52 ± 2 876.4 48 ± 2 676.4 3 twenty 64 ± 3 846.1 65 ± 3 624.3 four thirty 71 ± 3 782.7 73 ± 3 585.5

A comparison of the results given in the table allows us to conclude that the coatings obtained by the proposed method are characterized by higher adhesion.

Claims (1)

A method for producing a nanocomposite antireflection coating, comprising obtaining a liquid composition containing a polymer solution and 3 ± 0.5% by weight of a polymer of silver nanoparticles 1-10 nm in size, stabilizing the resulting composition by forming an adsorption-solvate layer on the surface of the particles, followed by applying the resulting nanocomposite on solid-state underlying surface and drying, characterized in that the liquid composition is obtained by reduction of silver acetate by reaction with organosoluble aldehyde directly GOVERNMENTAL a carboxyl-acrylate copolymer solution (5-30 wt.% in the composition) in a mixture of organic solvents with different volatilities under the action of ultraviolet radiation.