CN102504612B - Novel modified nano silicon dioxide and composite coating prepared from same - Google Patents

Abstract

The invention discloses a modified nano-silica and a composite coating prepared therefrom. The modified nano-silica is composed of 4.0 generation polyamide-amine dendrimer and nano- _SiO2 powder according to Mixed in a weight ratio of 50:12, modified under the protection of inert gas, after magnetic stirring and ultrasonic oscillation. The composite coating is prepared by adding fillers such as the above-mentioned modified nano-silica, titanium dioxide, calcium carbonate, etc., adding various additives for grinding, and then adding emulsion. The present invention uses PAMAM as a template to dry-modify nano-silica, so that the surface of nano-silica is wrapped with a layer of carbon-nitrogen chain molecules, which increases the compatibility with the film-forming base material and has better dispersion. Wet modification saves a certain cost, the process is simple, and the modification effect is outstanding.

Description

Modified nano silica and composite coating prepared therefrom

technical field

The invention relates to the modification and application of nanometer powder, in particular to the preparation of water-based nanometer functional paint. the

Background technique

In recent years, a large number of foreign "high-end paint" products have poured into the Chinese market, which has severely impacted my country's paint industry. Through the detection of such imported "high-end paints", our scientific and technical personnel found that different types of nano-materials were added to them. The small size effect, quantum size effect and surface interface effect greatly improve the scratch resistance, anti-aging, water washing resistance, antistatic, smoothness, contrast ratio, surface hardness and self-cleaning ability of coating products. . For example: foreign countries have successfully developed scratch-resistant, UV-resistant and chemical-resistant transparent automotive topcoat organic/inorganic hybrid resin-based coatings (the size of the hybrid phase is nanoscale), and have been applied to Ford Taurus and other model of car. In addition, the Du Pont company of the United States also introduced antibacterial coatings added with nano-silver particles. German Nano Chem System company has developed coating materials that can be used on concrete, stone, ceramics, wood, glass and other surfaces. It is said that the coating applies nanotechnology and can reduce the surface tension (hydrophobic, oleophobic) of the coated surface. , so as to achieve the purpose of anti-fouling, anti-fog, and easy cleaning; the company has also introduced a self-cleaning exterior wall coating silicon nanostructure modified acrylate coating, the research found that: the resin is mixed with nano-scale TiO ₂ (white ), Cr ₂ O ₃ (green), Fe ₂ O ₃ (brown), ZnO and other powders with semiconducting properties will produce good electrostatic shielding performance. Based on this, the research institute of Matsushita Electric Co., Ltd. of Japan has successfully developed a The resin-based nano-oxide composite electrostatic shielding coating, compared with the traditional resin-based carbon black composite coating, the resin-based nano-oxide composite coating has more excellent electrostatic shielding performance, and the latter is also better in color selection In order to be flexible, the stealth coatings used in the military are also mostly in the form of adding nano-fillers. The principle of stealth is: the size of nanoparticles is much smaller than the wavelength of infrared and radar waves, that is, the nano-particle materials are sensitive to infrared and radar waves. The transmittance is higher than that of conventional materials; the specific surface area of nanoparticles is much larger than that of conventional powders, resulting in a high absorption rate of electromagnetic waves, which leads to a decrease in the reflectivity of nanoparticle materials to infrared and radar waves, making infrared detectors and radars The received signal becomes weaker, thereby playing a stealth role. For example, the American F117A aircraft is coated with a stealth material with broadband electromagnetic wave absorption capacity composed of a variety of ultrafine particles.

In China, many research institutions of companies have also developed hydrophobic and pollution-resistant architectural coatings, antibacterial interior wall coatings, and latex paint anti-ultraviolet anti-aging nano-coatings and have certain photocatalytic activity (can catalyze the oxidation of harmful gases in the air) and sterilization and disinfection. Functional nano-coatings. In addition to improving the process formulation of the film-forming base material, these nano-scale coatings are also mostly prepared by adding nano-scale powders to prepare nano-composite coatings. For example: in the process of designing water-based architectural coating formulations, Adding nano-SiO ₂ with a mass fraction of about 3%, the modified coating is obtained through sufficient dispersion, and its technical performance indicators have been greatly improved: the drying time is shortened from the original 2h to less than 1h; the washing resistance Increased from 1000 times (external wall paint) and 100 times (interior wall paint) to more than 10,000 times; the artificial accelerated aging test increased from 240h primary discoloration and secondary pulverization to 450h without any change. However, due to nano-SiO ₂ It is an amorphous white powder (referring to its soft agglomerates). According to the transmission electron microscope test and analysis, this material obviously presents a flocculent and network quasi-granular structure, with small particle size (3-15nm) and large specific surface area (640 ±50m ² /g), there are a large number of unsaturated residual bonds and hydroxyl groups in different bonding states on the surface, which can easily cause agglomeration and affect dispersion, especially when the content is higher, the agglomeration is more prominent. Since the application efficacy of nanomaterials mainly depends on the surface molecular design of nanopowder materials (that is, how to solve the compatibility problem with the matrix material system) and its dispersion in the matrix material, when preparing nano coatings, The dispersion of nano-powders has become the key to the preparation of coatings with excellent performance, while improving the dispersion of nano-powders, ensuring the compatibility of fillers with film-forming base materials, and modifying the surface of nano-powders has become the key to preparing functional coatings. It is because the surface properties of the inorganic powder and the properties of the film-forming organic matrix are quite different, and the poor compatibility will affect the uniform dispersion of the inorganic nano-powder in the film-forming process.

sex. the

Currently, in the process of preparing nano coatings. For the dispersion of fillers, physical dispersion methods are often used, such as: grinding dispersion, sand mill dispersion, ball mill dispersion, high-speed stirring (above 1500r/min), etc. In addition, when nano powders are dispersed in liquids, ultrasonic dispersion, Colloid mill dispersion, high-energy particle treatment and other dispersion methods. However, the above-mentioned mechanical dispersion methods are not easy to "overheat" dispersion, because during the dispersion process, the powder particles will be subjected to strong shear force or impact force, and the nano-powder is likely to be cracked to produce more active bodies (such as: ≡ Si-O-Si≡→≡Si ⁺ +≡SiO ^-or ≡Si-O-Si≡→≡Si ^{+ ≡SiO} , ≡Si represents the silicon-oxygen bond connecting the surface of the powder), so the surface of the powder is easier A chemical reaction occurs, and with the increase of thermal and mechanical energy, the probability of particle collision also increases, which in turn leads to further agglomeration. This secondary "agglomeration" makes the storage stability of the slurry worse, and it is difficult to maintain stable suspension performance and construction performance. Therefore, on the one hand, the surface modification of the powder can reduce the surface energy of the powder, and on the other hand, it can improve the same Compatibility of the matrix, the main methods of powder modification are: ①Coupling agent method. The powder is modified by the coupling agent, which enhances the solubility of nanoparticles in the organic medium, so that they can be better dispersed In the organic matrix, the amount of powder filling is increased, thereby improving the overall performance of the product. ② Surfactant modification method. This method is to modify the surface of nano-powder by anionic, neutral or cationic surfactants. Modification. ③Surface grafting modification method. The surface groups of nanoparticles are used to chemically bond with reactive organic compounds to form nano-organic grafted compounds. Through the solubility of organic branched compounds in organic media, nanoparticles are enhanced. Dispersion in organic media. For example: the use of nano-SiO ₂ The active point on the surface is easy to generate the properties of active free radicals, Thmoas and Espiard have studied the graft polymerization of vinyl acetate on its surface and the grafting of ethyl acrylate Branch polymerization reaction, Tsubokawa N and Kaneko Y et al. used Michael addition reaction to study the process of grafting polyamidoamine (PAMAM) on the surface of nano-SiO ₂ respectively. No matter using coupling agent modification or surface graft modification, This modification effect of forming chemical adsorption (chemical bond) on the surface of the powder mainly depends on factors such as the number of powder surface active points, the concentration and molecular weight of the modifier, and the amount of powder surface active points is difficult to quantitatively measure, and It is closely related to particle size, powder crystal form, surface state, etc., so the control of powder particle size and distribution is more important.

Since Tomalia first synthesized polyamide-amine dendrimers (hereinafter referred to as PAMAM), because PAMAM has a high degree of geometric symmetry, precise molecular structure, a large number of functional groups, the presence of cavities in the molecule and the controllable molecular chain growth In recent years, the research work on PAMAM is very active. Researchers at home and abroad have prepared Cu, Ag, Pd, Pt, Au, ZnO, CdS, ZnS and other nano-materials by using PAMAM as a template, and obtained nanoparticles with uniform particle size and narrow distribution range. At present, the literature on the preparation and modification of inorganic nano-silica using PAMAM as a template has not been reported. According to the research, it has been found that PAMAM has more than 4 generations and almost becomes a spherical structure with a large volume of cavities inside. Contains more functional groups, such as carbonyl (C=O) and imide hydrogen (-NH), these active functional groups are the prerequisites for adsorbing and modifying nano-powder silica. the

Contents of the invention

The purpose of the present invention is to provide a modified nano-silica powder with controllable size distribution and uniform particle size, which can be modified by functional groups on the PAMAM molecular chain. the

The invention also provides a composite paint prepared from the modified nano silicon dioxide powder. the

The modified nano silicon dioxide powder of the present invention is to be by 4.0 generation polyamide-amine type dendrimers (substituting with PAMAM below) and nanometer _SiO Powder is mixed according to 50: 12 weight ratio, under inert gas protection, Modified after magnetic stirring and ultrasonic oscillation.

Modified nano silica powder of the present invention can be prepared by the following methods:

Synthesize PAMAM first, and then use it as a template to realize the purpose of dry modification of nano- _SiO2 powder. The detailed production process is as follows:

Step 1: Preparation of PAMAM

First, with ethylenediamine as the core element, a thorough Michael addition reaction was carried out with methyl acrylate in methanol to obtain the addition product of methyl triacrylate. Then use excess ethylenediamine to carry out the aminolysis reaction of the ester to obtain the amidated triamino product, and then repeat the addition reaction with methyl acrylate to prepare the 4.0th generation PAMAM. the

The second step: preparation of modified nano-silica

Add 50g of the prepared 4.0-generation PAMAM to 12g of nano-silica (with a particle size of about 10nm) and mix them. Under the protection of an inert gas, magnetic force stirs at a constant speed for 2 hours, and then ultrasonically oscillates for 30 minutes to obtain the modified nano-silica powder to be prepared. the

The above inert gas is preferably helium. the

The composite coating of the present invention is prepared by adding fillers such as the above-mentioned modified nano-silica, titanium dioxide, calcium carbonate, etc., adding various additives for grinding, and then adding emulsion. The above-mentioned additives include film-forming aids, dispersants, wetting Agent, antifungal agent and defoamer are all commercially available products for preparing coatings;

In order to greatly reduce the VOC content in the coating, the film-forming aids are selected: high boiling point film-forming aids DBE-IB (ester content ≥ 99%, acid value ≤ 1.0mgKOH/g, moisture ≤ 0.2%, boiling point: 253-283 ℃) and the non-VOC coalescent LOXANOL EFC300 produced by Corning Company (density (20℃): 0.85-0.95, viscosity: 20-30mPa·s, acidity: 0-5, VOC is 0). the

The modified nano-silica of the present invention can also be added to polymer composite materials such as rubber and plastics to improve the overall performance of the material. the

The advantages of the present invention are:

1. Using PAMAM as a template to dry-modify nano-silica, so that the surface of nano-silica is covered with a layer of carbon-nitrogen chain molecules, which increases the compatibility with the film-forming base material and has better dispersion. Wet modification saves a certain cost, the process is simple, and the modification effect is outstanding. It can be seen from Figure 3 that the dispersibility is improved after modification, and a denser coating can be formed when the prepared coating is formed into a film. It can be seen from Figure 4 that the fillers in the coating are evenly distributed, which improves the overall performance of the coating. the

2. This method uses high-boiling film-forming additives DBE-IB and LOXANOL EFC300, and calculates the amount of EFC300 and DBE-IB according to the minimum film-forming temperature (MFFT). According to the US EPA24 testing standard, the VOC of the coating is 0.1g/l . The invention improves the weather resistance and scrub resistance of the paint coating, and greatly reduces the VOC content, and the test results prove the feasibility of the above scheme. the

Description of drawings

Fig. 1 is nano-silica dry method modification schematic diagram of the present invention;

Fig. 2 is the SEM picture before nano-silica modification;

Fig. 3 is the SEM picture after nano-silica modification of the present invention;

Fig. 4 is the SEM picture of the composite paint coating prepared by utilizing the nano silicon dioxide of the present invention. the

In Figure 1: 91-silicon atom, 76-nitrogen atom (bonded with silicon with a single bond). the

Detailed ways

The technical solution of the present invention will be described in detail below through specific implementation steps. the

The preparation method of modified nano silicon dioxide of the present invention is as follows:

The first step: preparation of PAMAM template

(1) Preparation of 0.5 generation PAMAM: put 120g of methyl acrylate and 10g of methanol in a 400mL volumetric flask, stir magnetically at 5°C, pass He protection for 1h, add 10.5g of ethylenediamine and 27.5g of methanol dropwise with a dropping funnel The mixture of g was added dropwise for 1h and passed through He. After the dropwise addition was completed, the reaction was carried out at room temperature for 36h. Use a rotary evaporator to distill under reduced pressure (about 140 Pa, 40° C.) to remove unreacted methyl acrylate and methanol to obtain a slightly yellowish viscous liquid. the

(2) Preparation of 1.0-generation PAMAM: Put 84g of ethylenediamine and 11g of methanol in a 500mL volumetric flask, stir magnetically at 5°C, and pass He protection for 1 hour, then add 20g of 0.5-generation PAMAM and 64g of methanol dropwise with a dropping funnel. The mixture was added dropwise for 2h and passed through He. After the dropwise addition was completed, it was reacted at room temperature for 36h. Use a rotary evaporator to distill under reduced pressure (about 140Pa, 60°C) to remove unreacted ethylenediamine and methanol to obtain a light yellow viscous liquid. the

Preparation of half-generation 1.5, 2.5 and 3.5-generation PAMAM: same as preparation of 0.5-generation PAMAM. the

The preparation of the whole generation 2.0, 3.0 and 4.0 generation PAMAM: same as the preparation of the 1.0 generation PAMAM

The reaction principle is: (a): Methanol and methyl acrylate (MA) undergo a Michael addition reaction to generate a tetrabasic ester, which is called the 0.5 generation; (b): the tetrabasic ester reacts with excess EDA to generate a Quaternary amide compounds, known as generation 1.0. By repeating the reaction steps of (a), (b) Michael addition and ammonolysis, PAMAM-type macromolecular compounds of different generations (ie, different terminal groups and relative molecular masses) can be obtained. the

The second step: preparation of modified nano-powder silica

Add 50g of the 4.0-generation PAMAM prepared in the first step, add 12g of nano-silica (particle size about 10nm), and put it into a 500ml three-necked flask at the same time, and stir it magnetically at 3000r/min for 2h under the protection of inert gas helium (He) , take out the modified powder, and disperse with ultrasonic vibration for 30 minutes at 10°C for later use. the

The modification principle is: during the stirring process, the nano-silica powder is subjected to mechanical shear force, collision force and friction force, and undergoes heterolytic or homolytic cracking to obtain active silica powder. See the formulas (1) and (2) for the cracking process and results, and see the structural formula (3) for the simplified structure of the active body after cracking;

Then under the action of modifier PAMAM, the active silica powder reacts with PAMAM to obtain modified nano-silica powder. The modification principle is shown in Figure 1; in the figure, 1.0 generation PAMAM is used to modify silica Cationic groups are taken as an example to illustrate the combination of PAMAM and silicon ions. It can be seen from the figure that a chemical bond is formed between silicon ions and PAMAM. The dry modification fully utilizes the activity of the amide group in the PAMAM molecule. The N atom 76 presents a negative charge, while the silicon cation 91 presents a positive charge, and it is easier to form an N-Si bond. the

Finally, the activation value of the modified nano-silica was measured, and the method for determining the activation index was as follows: add 150 mL of distilled water to a 200 mL beaker, add 10 g of the modified filler powder into it, stir with a glass rod for 2 min and let it stand for 1 h Above, then filter, dry, and weigh the material settled at the bottom of the beaker, and subtract the mass of the settled material from the originally weighed mass (10 g) to obtain the mass of the floating part of the sample. The activation index can be obtained from the activation value = the mass of the floating part in the sample / the total mass of the sample. the

After inspection, the activation value of the modified silicon dioxide of the present invention reaches 0.94, and it can be seen from the comparison of Figure 2 and Figure 3 that the dispersion of the modified silicon dioxide of the present invention is greatly improved. the

The coating of the present invention is prepared by adding fillers such as the above-mentioned modified nano-silica, titanium dioxide, calcium carbonate, etc., adding various additives and film-forming base materials for grinding, and then adding emulsion. The composition of various pigments, fillers, additives, and emulsions Proportion, see Table 1 for the specific proportion, and the detailed preparation steps are as follows:

Step 1: Take high boiling point film-forming aid DBE-IB: 1.4g, LOXANOL EFC300: 2.8g, dispersant FS3204: 0.15g, dispersant CD50: 0.4g, wetting agent H885: 0.2g, wetting agent 188A : 0.10g, defoamer A10: 0.10g, defoamer F111: 0.15g, adhesion promoter 0.05: g and deionized water 20g, stir at low speed for 15min and mix evenly, then add modified silicon dioxide 20g and others 11g of pigments and fillers, thickener HEC: 0.4g, thickener DSX3116: 0.5g and supplementary part of deionized water are dispersed at high speed to make white pulp, and the dispersion time is not less than 1.5h. the

Step 2: Add the ground white pulp into 35g of styrene-acrylic emulsion PA237 in batches at a slow speed (slow speed in batches means that the white pulp added in the previous batch can be stirred evenly at a low speed before adding the white pulp in the next batch. slurry) and then continue to stir evenly at a low speed, and finally adjust the viscosity of the initial coating with a thickener, and adjust the pH value to 8.5 with a pH regulator to obtain the finished latex paint. the

In order to verify the performance of the composite paint of the present invention, the modified nano-silica of the present invention and the existing unmodified nano-silica are prepared into a composite paint for performance comparison. The comparison results are shown in Table 2, and the test method is based on GB/ T9755-2001. the

It can be seen from Table 2 that the performance indicators of the prepared composite coatings have been significantly improved. the

Table 1 formula ratio (unit: g)

Table 2 Comparison of conventional properties of coatings prepared before and after nano-silica modification

Claims (7)

1. a modified manometer silicon dioxide, is characterized in that, it is by 4.0 PAMAM type dendrimers and nanometer SiO ₂powder mixes according to 50: 12 part by weight, under protection of inert gas, through magnetic agitation and sonic oscillation post-modification, comes; Magnetic agitation speed is 3000r/min, churning time 2h.

2. modified manometer silicon dioxide as claimed in claim 1, is characterized in that, described rare gas element is helium.

3. a method for preparing modified manometer silicon dioxide as claimed in claim 1 or 2, is characterized in that, first synthesizes PAMAM, then realize dry method modification nanometer SiO as template ₂the purpose of powder, manufacture craft is as follows in detail:

The first step: preparation PAMAM

At first, take quadrol as the core primitive, in methyl alcohol, with methyl acrylate, carry out Michael addition reaction thoroughly, obtain the adduct of tetrapropylene acid methyl esters; Then carry out the aminolysis reaction of ester with excessive quadrol, obtain amidation tetramino product, then the addition reaction of repetition and methyl acrylate, prepare the PAMAM in 4.0 generations;

Second step: prepare modified manometer silicon dioxide

By 4.0 generation PAMAM50g of preparation, add the nano silicon 12g of particle diameter 10nm to mix, at the uniform velocity stir 2h at the protection of inert gas lower magnetic force, then sonic oscillation 30min, obtain needing the modified manometer silicon dioxide powder prepared.

4. the method for preparing modified manometer silicon dioxide as claimed in claim 3, is characterized in that, detailed step is as follows:

The first step: the preparation of PAMAM template

The preparation of (1) 0.5 generation PAMAM: methyl acrylate 120g and methyl alcohol 10g are placed in to the 400mL volumetric flask, and 5 ℃ of lower magnetic forces stir, after logical He protection 1h, drip the mixture of quadrol 10.5g and methyl alcohol 27.5g with dropping funnel, drip 1h logical He, after dropwising, under room temperature, react 36h; With Rotary Evaporators underpressure distillation under 140Pa, 40 ℃ of conditions, remove unreacted methyl acrylate and methyl alcohol, obtain micro-yellow slightly thick liquid;

The preparation of (2) 1.0 generation PAMAM: quadrol 84g and methyl alcohol 11g are placed in to the 500mL volumetric flask, and 5 ℃ of lower magnetic forces stir, after logical He protects after 1h, drip the mixture of 0.5 generation PAMAM20g and methyl alcohol 64g with dropping funnel, drip 2h logical He, after dropwising, under room temperature, react 36h; With Rotary Evaporators underpressure distillation under 140Pa, 60 ℃ of conditions, remove unreacted quadrol and methyl alcohol, obtain micro-yellow thick liquid;

The preparation of half generation 1.5,2.5 and 3.5 generation PAMAM: with the preparation of 0.5 generation PAMAM;

The preparation of whole generation 2.0,3.0 and 4.0 generation PAMAM: with the preparation of 1.0 generation PAMAM;

Second step: the preparation of modified nano powder silicon-dioxide

The 4.0 generation PAMAM50g that the first step is prepared, add particle diameter 10nm nano silicon 12g, inserts in the 500ml there-necked flask simultaneously; under rare gas element helium He protection; with 3000r/min magnetic agitation 2h, take out modified powder, with sonic oscillation, disperse 30min standby again under 10 ℃.

5. the composite coating prepared by the described modified manometer silicon dioxide of claim 1 or 2, it is characterized in that, it is by above-mentioned modified manometer silicon dioxide, titanium dioxide and pearl filler, add various auxiliary agents to be ground, then add the emulsion allotment to form, above-mentioned auxiliary agent comprises commercially available film coalescence aid, dispersion agent, wetting agent, mould inhibitor and defoamer.

6. composite coating as claimed in claim 5, it is characterized in that, described film coalescence aid selects the film coalescence aid that the high boiling point film coalescence aid of ester content >=99%, acid number≤1.0mKgKOH/Kg, moisture content≤0.2%, boiling point: 253-283 ℃ and 20 ℃ of density 0.85g/ml～0.95g/ml, viscosity 20～30mPas, pH values are 0～5, VOC is 0 to mix.

7. the application of modified manometer silicon dioxide as claimed in claim 1 or 2 in preparing emulsion paint composite coating, rubber and plastics polymer composite.

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