CN104262531B - Unmodified Ludox/polyacrylate core-shell emulsion and preparation method thereof - Google Patents

Abstract

The invention discloses a preparation method of an unmodified silica sol/polyacrylate core-shell emulsion, which uses commercially available alkaline silica sol and acrylate monomers as main raw materials, and does not need to perform tedious surface modification treatment on nanoparticles , under the action of a reactive emulsifier, the monomer is polymerized in situ on the surface of unmodified SiO ₂ particles to obtain a seed emulsion with SiO ₂ as the core, and then acrylate shell polymerization is performed on the surface of the seed emulsion emulsion , synthesized unmodified silica sol/polyacrylate core-shell emulsion with excellent properties. The method of the present invention has simple production process and rapid synthesis, and the synthesized unmodified silica sol/polyacrylate core-shell emulsion film has high transparency, water resistance, high hardness, strong adhesion and other properties, and has good stain resistance Pollution, heat resistance, acid and alkali resistance, and environmental protection, flame retardant, is a high-performance, low-cost new environmentally friendly nano-core-shell water-based emulsion, which can be widely used in various coating fields.

Description

Unmodified silica sol/polyacrylate core-shell emulsion and preparation method thereof

technical field

The invention belongs to the field of environment-friendly nano-core-shell aqueous emulsion, and in particular relates to an unmodified silica sol/polyacrylate core-shell emulsion and a preparation method thereof.

Background technique

Inorganic/organic nanocomposite emulsion is a hot spot in the research of coating film-forming substances in recent years. Due to the introduction of rigid inorganic components, the hardness of the film is greatly improved, and it can overcome many problems such as "hot stickiness, cold brittleness" and poor UV aging resistance of simple polymers. However, the water resistance, acid and alkali resistance, stain resistance and scrub resistance of the coating film have also been greatly improved, and it has the characteristics of non-toxic environmental protection and mild reaction conditions.

In recent years, with the wide application of nanotechnology and the improvement of the polymerization process, the in-situ polymerization of polymer monomers on the surface of nano-inorganic particles and the formation of various coating structures can be used to obtain composite emulsions with excellent properties.

The high performance and various characteristics of silica sol/polyacrylate composite emulsion have demonstrated advantages in the field of emulsions, and have become a hot spot in the development of new composite emulsions. Research on the surface treatment of silica sol has also received great attention.

Chinese patent application "Nano silica modified elastic acrylate copolymer emulsion" (application number: 200810019036.9 publication date: 2008-07-09) discloses that the emulsion is made of nano- _SiO2 and It is prepared by in-situ polymerization of acrylate monomers, and the strength, water resistance, weather resistance and stain resistance of the coating film are all improved to a certain extent, but the powder needs to be subjected to complicated hydrophobic treatment during the preparation process, which requires high dispersion equipment. Some need to use organic solvents, and the stability needs to be further improved. The silicon content in the emulsion is generally not more than 5%, and the improvement of the performance of the emulsion is limited.

The composite emulsion of the Chinese patent "A Preparation Method of Nano-Silicon Dioxide/Polyacrylate Composite Emulsion" (Patent No.: 201010524511.5 Publication Date: 2011-04-27) is composed of tetraethyl orthosilicate, silane coupling agent and acrylate The emulsion is prepared by in-situ copolymerization of monomers. This emulsion effectively avoids the problem of "secondary agglomeration" of traditional nano-silica in the emulsion polymerization process. The stability is improved to a certain extent, and the heat resistance of the coating film is excellent. Tetraethyl orthosilicate needs to be hydrolyzed and coupled before polymerization, but there are still many shortcomings such as complex and cumbersome process and difficult control of reaction conditions, which cannot meet the actual production and application.

Chinese patent application "Nano silica sol/acrylate composite emulsion and its preparation method" (application number: 200910046420.2 publication date: 2009-08-05) uses alkyl alcohol solvent to inhibit the hydrolysis of silicon hydroxyl group, and polymerizes with acrylate monomer Composite emulsion, the composite latex particle is a nano-core-shell structure with silica particles as the core and acrylate as the shell, but there are still many shortcomings, such as the particle size of the composite latex particle is too large, the diameter is 150-200nm, the silicon content The maximum is no more than 10%, and the characteristics of nanomaterials and the effect of cost reduction cannot be brought into full play.

In the preparation process of the Chinese patent application "a silica sol/acrylate nano-core-shell composite emulsion and its preparation method" (application number: 201310481166.5 publication date: 2014-03-26), the nano-silica sol was first chelated with titanium Treatment, under the action of the initiator, the environment-friendly reactive emulsifier and acrylate monomer polymerize in situ on the surface of nano-silica particles to form a nano-core-shell composite emulsion with SiO ₂ as the core, but there is still a need to first Sol modification and other cumbersome modification process problems.

Contents of the invention

The technical problem to be solved by the present invention is to provide an unmodified silica sol/polyacrylate core-shell emulsion with simple production process, high performance and low cost, and high coating rate and its preparation method.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical solutions: unmodified silica sol/polyacrylate core-shell emulsion, unmodified silica sol/polyacrylate core-shell structure with nano-silica particles as the core, acrylate copolymerization The substance is a shell layer; the solid content of the emulsion is 30-60%, and the mass content of _SiO2 in the emulsion is 10-25% in terms of silicon dioxide.

The above-mentioned unmodified silica sol/polyacrylate core-shell emulsion is mainly made of commercially available alkaline silica sol and acrylate monomers.

The preparation method of the above-mentioned unmodified silica sol/polyacrylate core-shell emulsion uses commercially available alkaline silica sol and acrylate monomers as main raw materials, and under the action of a reactive emulsifier, the monomers are unmodified In-situ polymerization occurs on the surface of the SiO ₂ particles to obtain a seed emulsion with SiO ₂ as the core, and then acrylate shell polymerization is performed on the surface of the seed emulsion emulsion to obtain the product.

The preparation method of above-mentioned unmodified silica sol/polyacrylate core-shell emulsion comprises the following steps:

<1> Preparation of silica sol/acrylate seed emulsion

Using commercially available alkaline silica sol and acrylate monomers as main raw materials, under the action of a reactive emulsifier, the monomers are polymerized in situ on the surface of unmodified _SiO2 particles to obtain a seed emulsion;

<2>Synthesis of unmodified silica sol/polyacrylate core-shell emulsion

Add a non-reactive emulsifier, sodium carbonate, and initiator into the seed emulsion, and start adding acrylate mixed monomers dropwise at a uniform speed to carry out shell layer polymerization to obtain an unmodified silica sol/polyacrylate core-shell emulsion.

Commercially available alkaline silica sol, calculated as silicon dioxide, has a silicon content of 30-50% by weight, an average particle size of 10-30nm, and a pH value of 9-10;

Acrylate monomers are two of methyl methacrylate, n-butyl acrylate, methacrylic acid, ethyl methacrylate, acrylic acid, hydroxyethyl acrylate, hydroxyethyl acrylate, and N-methylol acrylamide or more;

The reactive emulsifier is one or two of allyloxy nonylphenoxy propanol polyoxyethylene ether, allyloxy hydroxypropyl sulfonate, allyloxy fatty alcohol oxyethylene ether ammonium sulfate ;

Non-reactive emulsifiers are anionic or nonionic emulsifiers, and anionic emulsifiers are one or both of sodium lauryl sulfate, sodium dodecylsulfonate, and sodium dodecylbenzenesulfonate ;

The initiator is ammonium persulfate.

The preparation method of the above-mentioned unmodified silica sol/polyacrylate core-shell emulsion is carried out as follows:

<1> Seed emulsion polymerization: Place a four-neck flask equipped with a stirrer, reflux condenser, thermometer and titration funnel in a constant temperature water bath, stir at a constant speed of 300-400r/min, under the protection of _N2 , by weight In terms of parts, add 80-150 parts of deionized water, 2-6 parts of reactive emulsifier, add 120-320 parts of commercially available alkaline silica sol after 10 minutes, and disperse evenly; gradually raise the temperature to 75°C and keep it at a constant temperature , add 0.06 to 0.40 parts of initiator, start to titrate 5 to 20 parts of acrylate mixed monomer, drop it in 10 to 30 minutes, and keep it warm for 0.5 to 1 hour to obtain a seed emulsion;

<2>Polymerization of shell monomers: add 2-6 parts of non-reactive emulsifier, 0.6-2.5 parts of sodium carbonate, 0.3-0.8 parts of initiator to the seed emulsion, and start to add 80-150 parts of acrylates at a constant speed to mix The shell monomer is added dropwise in 2.5-3 hours; heat up to 80°C, keep warm for 1 hour, cool to room temperature, adjust the pH value to 8-8.5, filter and discharge the material, and you can get light white bluish unmodified silica sol/ Polyacrylate core-shell emulsion.

The non-reactive emulsifier is dissolved in 10 parts of distilled water to make a solution and added, the sodium carbonate is dissolved in 10 parts of distilled water to make a solution and added, and the initiator is dissolved in 10 parts of distilled water to make a solution and added.

Aiming at the current environment-friendly nano-core-shell water-based emulsion and the problems in its preparation, the inventor established a method for preparing an unmodified silica sol/polyacrylate core-shell emulsion, that is: commercially available alkaline silica sol, acrylate Monomer is the main raw material, and there is no need for tedious surface modification of nanoparticles. Under the action of reactive emulsifier, based on multiple mechanisms such as interface media and electrostatic adsorption, a special seed polymerization process is adopted to make the monomer unmodified. In-situ polymerization occurs on the surface of the permanent SiO ₂ particles to obtain a seed emulsion with SiO ₂ as the core, and then acrylate shell polymerization is performed on the surface of the seed emulsion emulsion to obtain nano-silica particles as the core and acrylate copolymer as the core The composite latex particles of the shell layer are used to synthesize an unmodified silica sol/polyacrylate core-shell emulsion with excellent performance.

The method of the invention has simple production technology and rapid synthesis, and the composite latex particle has an obvious nano core-shell composite structure, small particle size and narrow distribution (60-80nm). The synthesized unmodified silica sol/polyacrylate core-shell emulsion has the characteristics of small particle size, high silicon content (accounting for 40-50% of the total dry film mass), good core-shell coating, and good stability. The coating film has high transparency, water resistance, high hardness, strong adhesion and other properties, and also has good stain resistance, heat resistance, acid and alkali resistance, and is environmentally friendly and flame retardant. It is a high-performance, A low-cost new environmentally friendly nano-core-shell aqueous emulsion. Therefore, the emulsion is widely used as a film-forming substance in various coating fields such as high-grade architectural coatings, metal protective coatings, and ship anti-corrosion coatings. Based on this, the performance of the new nano-composite water-based exterior wall coating product meets the technical requirements of the national standard GB/T9755-2001 for water-based exterior wall coatings, especially water resistance, acid and alkali resistance, stain resistance, and artificial resistance. Excellent aging resistance. Due to the use of high-content silica sol, the present invention greatly saves petroleum resources and is low in cost, which not only meets the requirements of performance but also meets the needs of modern environmental protection development.

Description of drawings

Fig. 1 is a transmission electron microscope image of the unmodified silica sol/polyacrylate core-shell composite latex particle of the present invention.

detailed description

Example 1

<1> Seed emulsion polymerization: Place a four-neck flask equipped with a stirrer, reflux condenser, thermometer and titration funnel in a constant temperature water bath, stir at a constant speed of 300-400r/min, under the protection of _N2 , by weight In terms of parts, add 80g deionized water, 2g reactive emulsifier allyloxynonylphenoxypropanol polyoxyethylene ether, and add 120g of commercially available alkaline silica sol (calculated as silicon dioxide, The weight content of silicon is 30%, the average particle diameter is 10nm, and the pH value is 9), uniformly dispersed; gradually warming up to 75°C, and keeping a constant temperature, add 0.10g ammonium persulfate (dissolved in 10 parts of distilled water to make a solution and add) , start to titrate 5g of acrylate mixed monomer (MMA/n-BA/MAA=46/50/4, mass ratio), drop it in 10 minutes, and keep it warm for 1 hour to obtain the seed emulsion;

<2> Polymerization of shell monomers: Add 2g of non-reactive emulsifier sodium lauryl sulfate (dissolved in 10 parts of distilled water to make a solution), 0.6g of sodium carbonate (dissolved in 10 parts of distilled water to make solution), 0.3g ammonium persulfate (dissolved in 10g distilled water to make a solution to add), began to drop 80g acrylate mixed shell monomer (MMA/n-BA/MAA=46/50/4, mass ratio ), the dropwise addition was completed in 2.5 hours; the temperature was raised to 80°C, kept for 1 hour, then cooled to room temperature, the pH value was adjusted to 8, and the material was filtered to obtain a light white bluish unmodified silica sol/polyacrylate core-shell emulsion.

Example 2

<1> Seed emulsion polymerization: Place a four-neck flask equipped with a stirrer, reflux condenser, thermometer and titration funnel in a constant temperature water bath, stir at a constant speed of 300-400r/min, under the protection of _N2 , by weight In parts, add 150g deionized water, 6g reactive emulsifier allyloxy hydroxypropyl sodium sulfonate, add 320g of commercially available alkaline silica sol after 10 minutes (in terms of silicon dioxide, the weight content of silicon is 50%, the average particle size is 30nm, and the pH value is 10), uniformly dispersed; gradually warming up to 75°C, and keeping a constant temperature, add 0.40g ammonium persulfate (dissolved in 10g distilled water to make a solution and add), start to titrate 20g acrylate Mixed monomers (ethyl methacrylate/n-butyl acrylate/N-methylolacrylamide/acrylic acid=46/25/25/4, mass ratio), dripped in 20 minutes, and incubated for 1 hour to obtain seeds lotion;

<2> shell monomer polymerization: add 6g non-reactive emulsifier sodium dodecylbenzene sulfonate (dissolved in 10g distilled water to make a solution), 2.5g sodium carbonate (dissolved in 10g distilled water to make solution), 0.8g ammonium persulfate (dissolved in 10g distilled water to make a solution), began to drop 150g acrylate mixed shell monomer (ethyl methacrylate/n-butyl acrylate/N-methylol Acrylamide/acrylic acid = 46/25/25/4, mass ratio), and the dropwise addition is completed in 3 hours; the temperature is raised to 80°C, kept for 1 hour, cooled to room temperature, adjusted to pH 8, and filtered to obtain light white Bluish unmodified silica sol/polyacrylate core-shell emulsion.

Example 3

<1> Seed emulsion polymerization: Place a four-neck flask equipped with a stirrer, reflux condenser, thermometer and titration funnel in a constant temperature water bath, stir at a constant speed of 300-400r/min, under the protection of _N2 , by weight In parts, add 120g deionized water, 4g reactive emulsifier allyloxy fatty alcohol oxyethylene ether ammonium sulfate, add 200g of commercially available alkaline silica sol after 10 minutes (calculated as silicon dioxide, the weight content of silicon 40%, the average particle size is 20nm, the pH value is 9), and the dispersion is uniform; gradually warming up to 75 ° C, and maintaining a constant temperature, add 0.30 g of ammonium persulfate (dissolved in 10 g of distilled water to make a solution and add), and start to titrate 10 g of acrylic acid Ester mixed monomers (ethyl methacrylate/n-butyl acrylate/hydroxyethyl acrylate/acrylic acid = 46/30/20/4, mass ratio), dripped in 30 minutes, and kept warm for 1 hour to obtain a seed emulsion;

<2> Shell monomer polymerization: Add 4g non-reactive emulsifier sodium dodecylsulfonate and sodium dodecylbenzenesulfonate mixture (1:1, mass ratio, dissolved in 10g distilled water) to the seed emulsion Make a solution and add), 1.5g sodium carbonate (dissolved in 10g distilled water to make a solution and add), 0.6g ammonium persulfate (dissolved in 10g distilled water to make a solution and add), start to add 120g acrylate mixed shell monomer dropwise at a constant speed (ethyl methacrylate/n-butyl acrylate/hydroxyethyl acrylate/acrylic acid=47/30/20/3, mass ratio), the dropwise addition was completed in 2.5 hours; the temperature was raised to 80°C, kept for 1h, then cooled to room temperature, adjusted The pH value reaches 8, and the material is filtered to obtain a light white bluish unmodified silica sol/polyacrylate core-shell emulsion.

Example 4

It is basically the same as Example 1, except that the reactive emulsifier in the seed emulsion polymerization of step <1> is changed to allyloxynonylphenoxypropanol polyoxyethylene ether ammonium sulfate.

Example 5

It is basically the same as in Example 1, except that the non-reactive emulsifier in the polymerization of the shell monomer in step <2> is changed to sodium dodecylbenzenesulfonate.

Example 6

It is basically the same as in Example 1, except that the non-reactive emulsifier in the polymerization of the shell monomer in step <2> is changed to a mixture of sodium lauryl sulfate and sodium dodecyl sulfate (mass ratio 1:1).

The basic properties of the unmodified silica sol/polyacrylate core-shell emulsion products obtained in Examples 1-6 were tested, and the results are shown in Table 1 and Figure 1.

Table 1 Basic performance indicators of emulsion

Fig. 1 shows, the particle size of latex particle in the emulsion of the present invention is 60～80nm, is to take nano-silica particle as core (inner layer dark black), polymer (outer layer light gray) is the coated structure of shell.

Claims (6)

1. An unmodified silica sol/polyacrylate core-shell emulsion, characterized in that: the unmodified silica sol/polyacrylate core-shell structure takes nano-silica particles as the core and acrylate copolymer as the shell layer; the solid content of the emulsion is 30 to 60%, and the mass content of SiO in the emulsion is ₁₀ to 25% in terms of silicon dioxide; the emulsion is made of alkaline silica sol and acrylate monomers, Under the action of a reactive emulsifier, the monomer is polymerized in situ on the surface of the unmodified _SiO2 particles to obtain a seed emulsion with _SiO2 as the core, and then the acrylate shell polymerization is carried out on the surface of the seed emulsion emulsion, that is have to. 2. the preparation method of the described unmodified silica sol/polyacrylate core-shell emulsion of claim 1 is characterized in that: with alkaline silica sol, acrylate monomer as raw material, under the action of reactive emulsifier, make The monomer is in-situ polymerized on the surface of unmodified _SiO2 particles to obtain a seed emulsion with _SiO2 as the core, and then the acrylate shell layer is polymerized on the surface of the seed emulsion emulsion to obtain the product. 3. the preparation method of unmodified silica sol/polyacrylate core-shell emulsion according to claim 2, is characterized in that comprising the following steps: <1> Preparation of silica sol/acrylate seed emulsion Using alkaline silica sol and acrylate monomers as raw materials, under the action of a reactive emulsifier, the monomers are polymerized in situ on the surface of unmodified _SiO2 particles to obtain a seed emulsion; <2>Synthesis of unmodified silica sol/polyacrylate core-shell emulsion Add a non-reactive emulsifier, sodium carbonate, and initiator into the seed emulsion, and start adding acrylate mixed monomers dropwise at a uniform speed to carry out shell layer polymerization to obtain an unmodified silica sol/polyacrylate core-shell emulsion. 4. The preparation method of unmodified silica sol/polyacrylate core-shell emulsion according to claim 3, characterized in that: the alkaline silica sol, calculated as silica, has a silicon weight content of 30 to 50 %, the average particle size is 10-30nm, and the pH value is 9-10; The acrylic monomer is methyl methacrylate, n-butyl acrylate, methacrylic acid, ethyl methacrylate, acrylic acid, hydroxyethyl acrylate, hydroxyethyl acrylate, N-methylolacrylamide two or more; The reactive emulsifier is one of allyloxy nonylphenoxy propanol polyoxyethylene ether, allyloxy hydroxypropyl sulfonate, allyloxy fatty alcohol oxyethylene ether ammonium sulfate or two kinds; Described non-reactive emulsifier is anionic or nonionic emulsifier, and anionic emulsifier is one of sodium lauryl sulfate, sodium dodecylsulfonate, sodium dodecylbenzenesulfonate or two kinds; The initiator is ammonium persulfate. 5. the preparation method of unmodified silica sol/polyacrylate core-shell emulsion according to claim 4 is characterized in that carrying out as follows: <1> Place the four-necked flask equipped with a stirrer, reflux condenser, thermometer and titration funnel in a constant temperature water bath, stir at a constant speed of 300 to _400r /min, under N protection, by weight parts, Add 80-150 parts of deionized water, 2-6 parts of reactive emulsifier, 10 minutes later, add 120-320 parts of alkaline silica sol, and disperse evenly; gradually raise the temperature to 75°C, and keep constant temperature, add 0.06-0.40 parts Initiator, start to titrate 5 to 20 parts of acrylate mixed monomer, drop it in 10 to 30 minutes, and keep it warm for 0.5 to 1 hour to obtain a seed emulsion; <2> Add 2 to 6 parts of non-reactive emulsifier, 0.6 to 2.5 parts of sodium carbonate, 0.3 to 0.8 parts of initiator to the seed emulsion, and start to add 80 to 150 parts of acrylate mixed shell monomers at a constant speed, 2.5 The dropwise addition is completed in ~3 hours; heat up to 80°C, keep warm for 1 hour, then cool to room temperature, adjust the pH value to 8-8.5, filter and discharge the material, and you can get a light white bluish unmodified silica sol/polyacrylate core-shell emulsion . 6. the preparation method of unmodified silica sol/polyacrylate core-shell emulsion according to claim 5 is characterized in that: described non-reactive emulsifier is dissolved in 10 parts of distilled water and makes solution and adds, and described sodium carbonate Dissolved in 10 parts of distilled water to make a solution and added, and the initiator was dissolved in 10 parts of distilled water to make a solution and added.