Modified starch styrene-butadiene latex and preparation method thereof

Abstract

The invention discloses modified starch styrene-butadiene latex and a preparation method thereof, and belongs to the technical field of preparation of modified starch styrene-butadiene latex. Comprising the following components in parts by weight: 15 to 25 parts of carboxymethylated hydroxypropyl modified starch, 50 to 70 parts of styrene-butadiene latex, 0.8 to 2 parts of nano zinc oxide, 3 to 5 parts of polyethylene glycol 400, 2 to 4 parts of an emulsifier, 50 to 70 parts of deionized water, 0.3 to 0.8 part of a defoaming agent, 0.15 to 0.3 part of a preservative and 0.1 to 0.5 part of a pH regulator. The carboxymethylated hydroxypropyl modified starch, the nano-zinc oxide and the polyethylene glycol 400 are synergic through intermolecular acting force, stable dispersion synergic and rheological film synergic, so that the comprehensive improvement of the leveling property, the stability and the mechanical property of the coating is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of modified starch styrene-butadiene latex preparation, and more particularly relates to a modified starch styrene-butadiene latex and a preparation method thereof. BACKGROUND

[0002] Styrene-butadiene latex, as an important synthetic polymer emulsion, is prepared from butadiene and styrene through emulsion polymerization reaction, and has been widely used in the coating industry due to its excellent film-forming property, adhesion, weather resistance and other characteristics, and is one of the commonly used film-forming substances in water-based coatings, which can impart good mechanical properties and decorative effects to coatings.

[0003] However, the styrene-butadiene latex in the prior art still has certain deficiencies in coating applications. In terms of leveling property, the coating prepared from ordinary styrene-butadiene latex is prone to brush marks, orange peel and other phenomena during the construction process due to the limitations of its molecular structure and rheological property, resulting in an uneven and rough coating surface, which affects the decorative property of the coating; in terms of stability, the ordinary styrene-butadiene latex coating is prone to delamination, flocculation and other problems during storage and use, which reduces the use property and shelf life of the coating, and further affects the protective property of the coating.

[0004] The present application aims to solve the problems of poor leveling property and stability of the existing styrene-butadiene latex in coating applications, and provides a modified starch styrene-butadiene latex, which improves the leveling property and stability of the coating through the synergistic effect of specific components, makes the coating more uniform and smooth, and thus improves the decorative property and protective property of the coating. SUMMARY

[0005] The present application provides a modified starch styrene-butadiene latex and a preparation method thereof, which overcomes the defects of poor leveling property and stability of the existing styrene-butadiene latex in coating applications.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] In one aspect, the present application provides a modified starch styrene-butadiene latex, which comprises the following components in the following amounts by weight: carboxymethylated hydroxypropyl modified starch 15-25 parts, styrene-butadiene latex 50-70 parts, nano-zinc oxide 0.8-2 parts, polyethylene glycol 400 3-5 parts, emulsifier 2-4 parts, deionized water 50-70 parts, defoaming agent 0.3-0.8 parts, preservative 0.15-0.3 parts, pH adjuster 0.1-0.5 parts.

[0008] In the prior art, in the preparation of styrene-butadiene latex, the modified starch is usually esterified modified starch or single etherified modified starch, and the content of the modified starch in the system is low, and its role in the system is mostly used as a thickening agent. The present application carries out carboxymethylation and hydroxypropylation double modification on starch. The inventors found that the carboxymethylated and hydroxypropylated modified starch can significantly improve the water solubility, paste stability, film forming property and compatibility with styrene-butadiene latex of the starch, and even if the dosage is increased, the water resistance, scrub resistance, hardness and gloss of the coating film will not be reduced.

[0009] Meanwhile, the inventors also found that when the carboxymethylated and hydroxypropylated modified starch is compounded with specific dispersant nano zinc oxide and specific rheological agent polyethylene glycol 400, a three-dimensional cross-linked network of "starch-nanoparticle-small molecule additive" is formed. This network structure not only utilizes the high molecular chain skeleton effect of starch, but also strengthens the network nodes through the interface effect of nano zinc oxide, and the flexible segment of polyethylene glycol 400 fills the network gap, reducing the intermolecular frictional resistance, realizing the synergy of rigid skeleton and flexible adjustment. The synergy of the three improves the dispersion stability of the system, so that the coating has good fluidity (flow leveling requirement) and thixotropy (anti-sagging requirement) during construction, and forms a dense and uniform coating after film forming. Moreover, the combination of the three effectively inhibits particle agglomeration and improves the stability of the system.

[0010] In summary, the carboxymethylated and hydroxypropylated modified starch, nano zinc oxide and polyethylene glycol 400 realize the synergy of intermolecular force, dispersion stability and rheological film forming, comprehensively improve the leveling property, stability and mechanical property of the coating, and have the advantages of environmental protection and cost, which are the core technical highlights of the modified starch styrene-butadiene latex.

[0011] Further, the emulsifier includes a complex of sodium dodecyl sulfate and OP-10 in a mass ratio of (1:1) to (1:2).

[0012] Further, the defoaming agent includes at least one of polyether modified polysiloxane and white mineral oil.

[0013] Further, the preservative includes at least one of octyl isothiazolinone, 5-chloro-2-methyl-4-isothiazolin-3-one and methyl isothiazolinone.

[0014] Further, the pH regulator includes 2-amino-2-methyl-1-propanol.

[0015] Compared with the prior art, when the emulsifier, defoaming agent, preservative and pH regulator are selected from the above components respectively, the compatibility of the components can be improved, the flocculation can be prevented, the bubbles generated during the preparation process can be eliminated, the reproduction of microorganisms can be prevented, and the stability of the latex and the modified starch can be maintained.

[0016] Furthermore, the degree of substitution of the carboxymethylated hydroxypropyl modified starch is 0.5-0.8.

[0017] Furthermore, the solid content of the styrene-butadiene latex is 45%-55%.

[0018] Furthermore, the particle size of the nano zinc oxide is 20-50 nm.

[0019] A second aspect of the present invention provides a method for preparing modified starch styrene-butadiene latex, applicable to the preparation of the modified starch styrene-butadiene latex, comprising the following steps:

[0020] Carboxymethylated hydroxypropyl modified starch was prepared, and each component was weighed according to the modified starch styrene-butadiene latex.

[0021] Take 15 to 21 parts of deionized water and add the nano zinc oxide, stir, disperse at high speed and homogenize to obtain the first mixture;

[0022] The remaining deionized water is heated to 40℃~47℃, the emulsifier is added, and the mixture is stirred until transparent. Then, the modified starch is added, the temperature is raised to 80℃~87℃, and the mixture is kept at that temperature for 30 min. The temperature is then lowered to 40℃~50℃ to obtain the second mixture.

[0023] Mix the first mixture and the second mixture, stir until homogeneous, add styrene-butadiene latex preheated to 30°C~40°C, stir, add the polyethylene glycol, stir until homogeneous, and obtain the third mixture;

[0024] The defoamer was added to the third mixture in two batches, and after stirring evenly, the pH adjuster and the preservative were added, stirred evenly, and filtered to obtain the modified starch styrene-butadiene latex.

[0025] Compared with existing technologies, this invention, in preparing modified starch-styrene-butadiene latex, first mixes nano-zinc oxide with deionized water, followed by stirring, high-speed dispersion, and homogenization. This process controls the agglomeration size of the nano-zinc oxide to below 50 nm, achieving precise dispersion. This pretreatment avoids the agglomeration problem when nanoparticles are directly added to a high-viscosity system, ensuring uniform distribution within the latex during subsequent mixing. The remaining deionized water is heated to 40°C–47°C, and an emulsifier is added. After the emulsifier dissolves and becomes transparent, modified starch is added. The temperature is then raised to 80°C–87°C and held for 30 minutes, allowing the carboxymethylated hydroxypropyl modified starch to completely gelatinize and its molecular chains to fully extend. The gelatinized starch can more efficiently form hydrogen bonds and coordination bonds with styrene-butadiene latex particles and nano-zinc oxide, avoiding localized viscosity unevenness caused by incomplete starch dissolution. The first mixture (nano zinc oxide dispersion) and the second mixture (starch gelatinization liquid) are mixed first, and then styrene-butadiene latex preheated to 30℃~40℃ is added. Temperature matching promotes interfacial fusion between latex particles and starch molecules. After preheating, the surface activity of the styrene-butadiene latex particles increases, allowing them to bind more quickly to the polar groups of starch. Simultaneously, the nano zinc oxide is uniformly anchored around the latex particles through the bridging effect of starch molecules, forming a stable composite structure. This structure extends the storage stability of the latex (at room temperature) from 20 days using conventional methods to over 40 days. Polyethylene glycol 400 is added during stirring after the addition of the styrene-butadiene latex. It can be uniformly dispersed by utilizing the flow state of the system, fully utilizing its functions of reducing intermolecular friction and regulating rheology. The defoamer is added in two stages to avoid localized over- or under-addition of defoamer due to a single addition. The pH adjuster and preservative are added last to precisely control the pH value of the system and avoid the destruction of preservative activity by the initial high temperature.

[0026] Furthermore, the process for preparing carboxymethylated hydroxypropyl modified starch is as follows:

[0027] Hydroxypropylation reaction: Deionized water was added to corn starch at a ratio of 1g:40ml. After stirring evenly, the pH of the system was adjusted to 10-11 with 30% sodium hydroxide solution. The temperature was raised to 45℃-50℃, and propylene oxide was slowly added dropwise. The reaction was carried out under stirring for 3-4 hours. Then, the pH was adjusted to 6.5-7.0 with 10% hydrochloric acid to obtain crude hydroxypropyl starch.

[0028] The crude hydroxypropyl starch was redispersed in deionized water, sodium chloroacetate was added, and the mixture was stirred and dissolved. The pH was adjusted to 10-11 with 30% sodium hydroxide solution. The mixture was heated to 55-60℃ and reacted for 2-3 hours. The mixture was then neutralized with 10% hydrochloric acid. After precipitation with ethanol, washing, and drying, carboxymethylated hydroxypropyl starch was obtained.

[0029] Compared with existing technologies, the modified starch obtained by the above modification method contains carboxyl groups (-COOH), hydroxypropyl groups (-OCH2CH(OH)CH3), and hydroxyl groups (-OH). The carboxyl groups can form coordination bonds with the hydroxyl groups (-OH) on the surface of nano-zinc oxide, while the hydroxypropyl and hydroxyl groups can bind to the ether bonds (-O-) of polyethylene glycol 400 through hydrogen bonds, forming a three-dimensional cross-linked network of "starch-nanoparticles-small molecule additives". This network structure utilizes the polymer chain backbone of starch and strengthens the network nodes through the interfacial effect of nano-zinc oxide, reducing intermolecular frictional resistance. It achieves a synergy between a rigid framework and flexible adjustment, providing compatibility and film-forming properties between the modified starch and styrene-butadiene latex.

[0030] Further, 15 to 21 parts of deionized water were added to the nano zinc oxide and stirred at 800 to 1000 rpm for 10 minutes; then dispersed at 2500 to 3000 rpm for 20 minutes, and finally homogenized at 5000 rpm for 5 minutes.

[0031] Further, after adding the emulsifier, stir at 800 rpm for 10 min; after adding the modified starch, stir at 800~1000 rpm and heat to 85±2℃ at 2℃ / min.

[0032] Furthermore, when mixing the first mixture and the second mixture, stir at 600 rpm for 10 min; after adding styrene-butadiene latex, stir at 800 rpm for 20 min; after adding polyethylene glycol 400, stir at 600 rpm for 5 min.

[0033] Further, the defoamer is added to the third mixture in two batches, each batch consisting of 1 / 2 of the total amount of defoamer, and the mixture is stirred at 1000 rpm for 10-15 min; after adding the pH adjuster and preservative, the mixture is stirred at 800 rpm for 10 min.

[0034] Compared with existing technologies, the above stirring speed can ensure that the mixing of each system is uniform and maintain the homogeneity and stability of the system.

[0035] A third aspect of the present invention provides the application of the modified starch styrene-butadiene latex in the preparation of water-based coatings.

[0036] Compared with the prior art, the present invention applies the prepared modified starch styrene-butadiene latex to water-based coatings, develops the uses of modified starch styrene-butadiene latex, and improves the film-forming properties, leveling properties and rheological properties of water-based coatings. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Existing styrene-butadiene latex technologies still have certain shortcomings in coating applications. Regarding leveling, coatings made from ordinary styrene-butadiene latex are prone to brush marks and orange peel effects during application due to limitations in their molecular structure and rheological properties, resulting in an uneven and rough coating surface that affects the coating's decorative properties. In terms of stability, ordinary styrene-butadiene latex coatings are prone to delamination and flocculation during storage and use, reducing their performance and shelf life, and consequently affecting the coating's protective properties.

[0039] To overcome the above-mentioned defects, in a first aspect, embodiments of the present invention provide a modified starch styrene-butadiene latex, comprising the following components in parts by weight: 15-25 parts of carboxymethylated hydroxypropyl modified starch, 50-70 parts of styrene-butadiene latex, 0.8-2 parts of nano zinc oxide, 3-5 parts of polyethylene glycol 400, 2-4 parts of emulsifier, 50-70 parts of deionized water, 0.3-0.8 parts of defoamer, 0.15-0.3 parts of preservative, and 0.1-0.5 parts of pH adjuster.

[0040] For example, a modified starch styrene-butadiene latex comprises the following components in parts by weight: 15 parts carboxymethylated hydroxypropyl modified starch, 50 parts styrene-butadiene latex, 0.8 parts nano zinc oxide, 3 parts polyethylene glycol 400, 2 parts emulsifier, 50 parts deionized water, 0.3 parts defoamer, 0.15 parts preservative, and 0.1 parts pH adjuster.

[0041] For example, a modified starch styrene-butadiene latex comprises the following components in parts by weight: 25 parts carboxymethylated hydroxypropyl modified starch, 70 parts styrene-butadiene latex, 2 parts nano zinc oxide, 5 parts polyethylene glycol 400, 4 parts emulsifier, 70 parts deionized water, 0.8 parts defoamer, 0.3 parts preservative, and 0.5 parts pH adjuster.

[0042] For example, a modified starch styrene-butadiene latex comprises the following components in parts by weight: 20 parts carboxymethylated hydroxypropyl modified starch, 60 parts styrene-butadiene latex, 1.2 parts nano zinc oxide, 4 parts polyethylene glycol 400, 3 parts emulsifier, 65 parts deionized water, 0.6 parts defoamer, 0.2 parts preservative, and 0.3 parts pH adjuster.

[0043] For example, a modified starch styrene-butadiene latex further includes a styrene-butadiene latex composed of components with any point value within the above range.

[0044] This invention involves dual modification of starch through carboxymethylation and hydroxypropylation, significantly improving its water solubility, gelatinization stability, film-forming properties, and compatibility with styrene-butadiene latex. Even with increased dosage, the water resistance, scrub resistance, hardness, and gloss of the coating film remain unaffected. When carboxymethylated hydroxypropylated modified starch is combined with a specific dispersant, nano-zinc oxide, and a specific rheology modifier, polyethylene glycol 400, a three-dimensional cross-linked network of "starch-nanoparticles-small molecule additives" is formed. This network structure utilizes the high molecular chain backbone of starch, strengthens network nodes through the interfacial effect of nano-zinc oxide, and simultaneously fills the network gaps with the flexible segments of polyethylene glycol 400, reducing intermolecular frictional resistance and achieving a synergistic effect between a rigid framework and flexible adjustment. The synergistic effect of these three components enhances the dispersion stability of the system, enabling the coating to exhibit both good flowability (for leveling) and thixotropy (for anti-sagging) during application, resulting in a dense and uniform coating after film formation. Furthermore, the combined use of these three components effectively inhibits particle aggregation and improves system stability. In some embodiments, the emulsifier comprises a compound of sodium dodecyl sulfate and OP-10 in a mass ratio of (1:1) to (1:2).

[0045] For example, the mass ratio of sodium dodecyl sulfate and OP-10 can be specifically selected as a range of values ​​consisting of 1:1, 1:2, 1:1.5, or any point values, preferably 1:1.

[0046] In some embodiments, the defoamer includes at least one of polyether-modified polysiloxane and white mineral oil; preferably polyether-modified polysiloxane, more preferably polyether-modified heptamethyltrisiloxane.

[0047] In some embodiments, the preservative includes at least one of octylisothiazolinone, 5-chloro-2-methyl-4-isothiazolin-3-one, and methylisothiazolinone.

[0048] In some of these embodiments, the pH adjuster includes 2-amino-2-methyl-1-propanol.

[0049] When the emulsifier, defoamer, preservative, and pH adjuster are selected from the above components, the compatibility of the components can be improved, flocculation can be prevented, bubbles generated during the preparation process can be eliminated, microbial growth can be prevented, and the stability of latex and modified starch can be maintained.

[0050] In some of these embodiments, the solid content of the styrene-butadiene latex is 45% to 55%.

[0051] For example, the solid content of styrene-butadiene latex can be specifically selected as 45%, 55%, or 50%.

[0052] In some of these embodiments, the particle size of the nano-zinc oxide is 20-50 nm.

[0053] For example, the particle size of nano zinc oxide can be selected as a range of values ​​consisting of 20nm, 30nm, 50nm, or any point values, preferably 20nm~30nm.

[0054] Secondly, embodiments of the present invention provide a method for preparing modified starch styrene-butadiene latex, applicable to the preparation of modified starch styrene-butadiene latex, comprising the following steps:

[0055] Carboxymethylated hydroxypropyl modified starch was prepared, and each component was weighed according to the modified starch styrene-butadiene latex.

[0056] Take 15 to 21 parts of deionized water, add nano zinc oxide, stir, disperse at high speed, and homogenize to obtain the first mixture;

[0057] The remaining deionized water was heated to 40℃~47℃, emulsifier was added, and the mixture was stirred until transparent. Then, modified starch was added, the temperature was raised to 80℃~87℃, and the mixture was kept at that temperature for 30 min. The temperature was then lowered to 40℃~50℃ to obtain the second mixture.

[0058] Mix the first mixture and the second mixture, stir until homogeneous, add styrene-butadiene latex preheated to 30℃~40℃, stir, add polyethylene glycol, stir until homogeneous, and obtain the third mixture;

[0059] Add the defoamer to the third mixture in two batches, stir well, then add the pH adjuster and preservative, stir well, filter, and obtain the modified starch styrene-butadiene latex.

[0060] In preparing modified starch-styrene-butadiene latex, this invention first mixes nano-zinc oxide with deionized water. Through stirring, high-speed dispersion, and homogenization, the agglomeration particle size of the nano-zinc oxide can be controlled below 50 nm, achieving precise dispersion. This pretreatment avoids the agglomeration problem when nanoparticles are directly added to a high-viscosity system, ensuring uniform distribution within the latex during subsequent mixing. The remaining deionized water is heated to 40℃~47℃, and an emulsifier is added. After it dissolves and becomes transparent, modified starch is added. The temperature is then raised to 80℃~87℃ and held for 30 minutes, allowing the carboxymethylated hydroxypropyl modified starch to completely gelatinize and its molecular chains to fully extend. The gelatinized starch can more efficiently form hydrogen bonds and coordination bonds with styrene-butadiene latex particles and nano-zinc oxide, avoiding the problem of uneven viscosity in the system caused by incomplete starch dissolution. The first mixture (nano zinc oxide dispersion) and the second mixture (starch gelatinization liquid) are mixed first, and then styrene-butadiene latex preheated to 30℃~40℃ is added. Temperature matching promotes interfacial fusion between latex particles and starch molecules. After preheating, the surface activity of the styrene-butadiene latex particles increases, allowing them to bind more quickly to the polar groups of starch. Simultaneously, the nano zinc oxide is uniformly anchored around the latex particles through the bridging effect of starch molecules, forming a stable composite structure. This structure extends the storage stability of the latex (at room temperature) from 20 days using conventional methods to over 40 days. Polyethylene glycol 400 is added during stirring after the addition of the styrene-butadiene latex. It can be uniformly dispersed by utilizing the flow state of the system, fully utilizing its functions of reducing intermolecular friction and regulating rheology. The defoamer is added in two stages to avoid localized over- or under-addition of defoamer due to a single addition. The pH adjuster and preservative are added last to precisely control the pH value of the system and avoid the destruction of preservative activity by the initial high temperature.

[0061] In some embodiments, the process for preparing carboxymethylated hydroxypropyl modified starch is as follows:

[0062] Hydroxypropylation reaction: Deionized water was added to corn starch at a ratio of 1g:40ml. After stirring evenly, the pH of the system was adjusted to 10-11 with 30% sodium hydroxide solution. The temperature was raised to 45℃-50℃, and propylene oxide was slowly added dropwise. The reaction was carried out under stirring for 3-4 hours. Then, the pH was adjusted to 6.5-7.0 with 10% hydrochloric acid to obtain crude hydroxypropyl starch.

[0063] The crude hydroxypropyl starch was redispersed in deionized water, sodium chloroacetate was added, and the mixture was stirred and dissolved. The pH was adjusted to 10-11 with 30% sodium hydroxide solution. The mixture was heated to 55-60℃ and reacted for 2-3 hours. The mixture was then neutralized with 10% hydrochloric acid. After precipitation with ethanol, washing, and drying, carboxymethylated hydroxypropyl starch was obtained.

[0064] For example, the preparation process of the modified starch described above is as follows:

[0065] Hydroxypropylation reaction: 50g of corn starch was placed in a three-necked flask, and 200mL of deionized water was added. After stirring evenly, the pH of the system was adjusted to 10 using a 30% sodium hydroxide solution. The temperature was raised to 50℃, and 20mL of propylene oxide was slowly added dropwise. The reaction was carried out with stirring for 4 hours. After the reaction was completed, the pH was adjusted to 6.5 using 10% hydrochloric acid to obtain crude hydroxypropyl starch.

[0066] Carboxymethylation reaction: Crude hydroxypropyl starch was redispersed in 150 mL of deionized water, and 9 g of sodium chloroacetate was added. After stirring and dissolving, the pH was adjusted to 10 with 30% sodium hydroxide solution, and the mixture was heated to 60 °C for 2.5 h. After the reaction was completed, the mixture was neutralized to neutral with 10% hydrochloric acid solution. After precipitation with ethanol, washing, and drying, carboxymethylated hydroxypropyl starch with a degree of substitution of 0.6 was obtained.

[0067] The modified starch obtained through the above modification method contains carboxyl groups (-COOH), hydroxypropyl groups (-OCH2CH(OH) CH3), and hydroxyl groups (-OH). The carboxyl groups can form coordination bonds with the hydroxyl groups (-OH) on the surface of nano-zinc oxide, while the hydroxypropyl and hydroxyl groups can bind to the ether bonds (-O-) of polyethylene glycol 400 through hydrogen bonds, forming a three-dimensional cross-linked network of "starch-nanoparticles-small molecule additives". This network structure utilizes the polymer chain backbone of starch and strengthens the network nodes through the interfacial effect of nano-zinc oxide, reducing intermolecular frictional resistance. It achieves a synergy between a rigid framework and flexible adjustment, providing compatibility and film-forming properties between the modified starch and styrene-butadiene latex.

[0068] In some embodiments, 15 to 21 parts of deionized water are added to the nano zinc oxide and stirred at 800 to 1000 rpm for 10 min; then dispersed at 2500 to 3000 rpm for 20 min, and finally homogenized at 5000 rpm for 5 min.

[0069] In some embodiments, after adding the emulsifier, the mixture is stirred at 800 rpm for 10 min; after adding the modified starch, the mixture is stirred at 800~1000 rpm and heated to 85±2℃ at 2℃ / min.

[0070] In some embodiments, when mixing the first mixture and the second mixture, the mixture is stirred at 600 rpm for 10 min; after adding styrene-butadiene latex, the mixture is stirred at 800 rpm for 20 min; and after adding polyethylene glycol 400, the mixture is stirred at 600 rpm for 5 min.

[0071] In some embodiments, the defoamer is added to the third mixture in two portions, each time in an amount equal to half the total amount of defoamer, and the mixture is stirred at 1000 rpm for 10-15 min; after adding the pH adjuster and preservative, the mixture is stirred at 800 rpm for 10 min.

[0072] At the above stirring speed, it is possible to ensure that the mixtures in each system are homogeneous and maintain the uniformity and stability of the system.

[0073] Thirdly, embodiments of the present invention provide the application of the modified starch styrene-butadiene latex in the preparation of water-based coatings.

[0074] This invention applies the prepared modified starch styrene-butadiene latex to water-based coatings, explores the uses of modified starch styrene-butadiene latex, and improves the film-forming properties, leveling properties, and rheological properties of water-based coatings.

[0075] To better illustrate the technical solution of the present invention, the following embodiments are provided. It should be understood that, unless otherwise stated, the components in the embodiments are all commercially available.

[0076] Example 1

[0077] A modified starch styrene-butadiene latex comprises the following components in parts by weight: 15 parts carboxymethylated hydroxypropyl modified starch, 50 parts styrene-butadiene latex, 0.8 parts nano zinc oxide, 3 parts polyethylene glycol 400, 2 parts emulsifier, 50 parts deionized water, 0.3 parts polyether-modified heptamethyltrisiloxane, 0.15 parts octylisothiazolinone, and 0.1 parts 2-amino-2-methyl-1-propanol.

[0078] The emulsifier includes a compound of sodium dodecyl sulfate and OP-10 in a mass ratio of 1:1, the styrene-butadiene rubber latex solid content is 50%, and the nano zinc oxide particles have a diameter of 20nm~30nm.

[0079] The preparation process of the above modified starch styrene-butadiene latex is as follows:

[0080] To prepare carboxymethylated hydroxypropyl modified starch, 15 parts of deionized water were added to nano zinc oxide, stirred at 800 rpm for 10 min, then dispersed at 2500 rpm for 20 min, and finally homogenized at 5000 rpm for 5 min to obtain the first mixture.

[0081] The remaining deionized water was heated to 40°C, emulsifier was added, and the mixture was stirred at 800 rpm for 10 min until it became transparent. Modified starch was added and stirred at 800 rpm. The temperature was increased to 80°C at 2°C / min, kept at that temperature for 30 min, and then cooled to 40°C to obtain the second mixture.

[0082] Mix the first and second mixtures together and stir at 600 rpm for 10 min. After stirring evenly, add styrene-butadiene latex preheated to 30°C and stir at 800 rpm for 20 min. Add polyethylene glycol 400 and stir at 600 rpm for 5 min to obtain the third mixture.

[0083] Polyether-modified heptamethyltrisiloxane was added to the third mixture in two portions, each time by half the total amount of polyether-modified heptamethyltrisiloxane, and the mixture was stirred at 1000 rpm for 12 min. Octylisothiazolinone and 2-amino-2-methyl-1-propanol were added, and the mixture was stirred at 800 rpm for 10 min. The mixture was then filtered through a 200-mesh sieve to obtain modified starch styrene-butadiene latex.

[0084] The process for preparing carboxymethylated hydroxypropyl modified starch is as follows:

[0085] Hydroxypropylation reaction: 50g of corn starch was placed in a three-necked flask, and 200mL of deionized water was added. After stirring evenly, the pH of the system was adjusted to 10 using a 30% sodium hydroxide solution. The temperature was raised to 50℃, and 20mL of propylene oxide was slowly added dropwise. The reaction was carried out with stirring for 4 hours. After the reaction was completed, the pH was adjusted to 6.5 using 10% hydrochloric acid to obtain crude hydroxypropyl starch.

[0086] Carboxymethylation reaction: Crude hydroxypropyl starch was redispersed in 150 mL of deionized water, and 9 g of sodium chloroacetate was added. After stirring and dissolving, the pH was adjusted to 10 with 30% sodium hydroxide solution, and the mixture was heated to 60 °C for 2.5 h. After the reaction was completed, the mixture was neutralized to neutral with 10% hydrochloric acid solution. After precipitation with ethanol, washing, and drying, carboxymethylated hydroxypropyl starch with a degree of substitution of 0.6 was obtained.

[0087] Example 2

[0088] A modified starch styrene-butadiene latex comprises the following components in parts by weight: 25 parts carboxymethylated hydroxypropyl modified starch, 70 parts styrene-butadiene latex, 2 parts nano zinc oxide, 5 parts polyethylene glycol 400, 4 parts emulsifier, 70 parts deionized water, 0.8 parts white mineral oil, 0.3 parts 5-chloro-2-methyl-4-isothiazolin-3-one, and 0.5 parts 2-amino-2-methyl-1-propanol.

[0089] The emulsifier includes a compound of sodium dodecyl sulfate and OP-10 in a mass ratio of 1:1.5, the styrene-butadiene rubber latex solid content is 55%, and the nano zinc oxide particles have a size of 30nm~40nm.

[0090] The preparation process of the above modified starch styrene-butadiene latex is as follows:

[0091] To prepare carboxymethylated hydroxypropyl modified starch, 15 parts of deionized water were added to nano zinc oxide, stirred at 1000 rpm for 10 min, then dispersed at 3000 rpm for 20 min, and finally homogenized at 5000 rpm for 5 min to obtain the first mixture.

[0092] The remaining deionized water was heated to 47°C, emulsifier was added, and the mixture was stirred at 800 rpm for 10 min until transparent. Modified starch was added and stirred at 1000 rpm. The temperature was increased to 87°C at 2°C / min, kept at that temperature for 30 min, and then cooled to 50°C to obtain the second mixture.

[0093] Mix the first and second mixtures and stir at 600 rpm for 10 min; after stirring evenly, add styrene-butadiene latex preheated to 40℃ and stir at 800 rpm for 20 min; add polyethylene glycol 400 and stir at 600 rpm for 5 min; to obtain the third mixture.

[0094] Add white mineral oil to the third mixture in two portions, each time adding half of the total amount of white mineral oil, and stir at 1000 rpm for 10 min. After adding 5-chloro-2-methyl-4-isothiazolin-3-one and 2-amino-2-methyl-1-propanol, stir at 800 rpm for 10 min, filter through a 200-mesh sieve to obtain modified starch styrene-butadiene latex.

[0095] The process for preparing carboxymethylated hydroxypropyl modified starch is as follows:

[0096] Hydroxypropylation reaction: 50g of corn starch was placed in a three-necked flask, and 200mL of deionized water was added. After stirring evenly, the pH of the system was adjusted to 10 using a 30% sodium hydroxide solution. The temperature was raised to 50℃, and 20mL of propylene oxide was slowly added dropwise. The reaction was carried out with stirring for 4 hours. After the reaction was completed, the pH was adjusted to 6.5 using 10% hydrochloric acid to obtain crude hydroxypropyl starch.

[0097] Carboxymethylation reaction: Crude hydroxypropyl starch was redispersed in 150 mL of deionized water, and 9 g of sodium chloroacetate was added. After stirring and dissolving, the pH was adjusted to 10 with 30% sodium hydroxide solution, and the mixture was heated to 60 °C for 2.5 h. After the reaction was completed, the mixture was neutralized to neutral with 10% hydrochloric acid solution. After precipitation with ethanol, washing, and drying, carboxymethylated hydroxypropyl starch with a degree of substitution of 0.6 was obtained.

[0098] Example 3

[0099] A modified starch styrene-butadiene latex comprises the following components in parts by weight: 20 parts carboxymethylated hydroxypropyl modified starch, 60 parts styrene-butadiene latex, 1.2 parts nano zinc oxide, 4 parts polyethylene glycol 400, 3 parts emulsifier, 65 parts deionized water, 0.6 parts white mineral oil, 0.2 parts methylisothiazolinone, and 0.3 parts 2-amino-2-methyl-1-propanol.

[0100] The emulsifier includes a compound of sodium dodecyl sulfate and OP-10 in a mass ratio of 1:2, the styrene-butadiene rubber latex solid content is 45%, and the nano zinc oxide particles have a size of 40nm~50nm.

[0101] The preparation process of the above modified starch styrene-butadiene latex is as follows:

[0102] To prepare carboxymethylated hydroxypropyl modified starch, 15 parts of deionized water were added to nano zinc oxide, stirred at 900 rpm for 10 min, then dispersed at 2600 rpm for 20 min, and finally homogenized at 5000 rpm for 5 min to obtain the first mixture.

[0103] The remaining deionized water was heated to 43°C, emulsifier was added, and the mixture was stirred at 800 rpm for 10 min until it became transparent. Modified starch was added and stirred at 900 rpm. The temperature was increased to 85°C at 2°C / min, kept at that temperature for 30 min, and then cooled to 45°C to obtain the second mixture.

[0104] Mix the first and second mixtures together and stir at 600 rpm for 10 min. After stirring evenly, add styrene-butadiene latex preheated to 35°C and stir at 800 rpm for 20 min. Add polyethylene glycol 400 and stir at 600 rpm for 5 min to obtain the third mixture.

[0105] Add white mineral oil to the third mixture in two batches, each batch consisting of 1 / 2 of the total amount of white mineral oil, and stir at 1000 rpm for 15 min. After adding methylisothiazolinone and 2-amino-2-methyl-1-propanol, stir at 800 rpm for 10 min, and filter through a 200-mesh sieve to obtain modified starch styrene-butadiene latex.

[0106] The process for preparing carboxymethylated hydroxypropyl modified starch is as follows:

[0107] Hydroxypropylation reaction: 50g of corn starch was placed in a three-necked flask, and 200mL of deionized water was added. After stirring evenly, the pH of the system was adjusted to 10 using a 30% sodium hydroxide solution. The temperature was raised to 50℃, and 20mL of propylene oxide was slowly added dropwise. The reaction was carried out with stirring for 4 hours. After the reaction was completed, the pH was adjusted to 6.5 using 10% hydrochloric acid to obtain crude hydroxypropyl starch.

[0108] Carboxymethylation reaction: Crude hydroxypropyl starch was redispersed in 150 mL of deionized water, and 9 g of sodium chloroacetate was added. After stirring and dissolving, the pH was adjusted to 10 with 30% sodium hydroxide solution, and the mixture was heated to 60 °C for 2.5 h. After the reaction was completed, the mixture was neutralized to neutral with 10% hydrochloric acid solution. After precipitation with ethanol, washing, and drying, carboxymethylated hydroxypropyl starch with a degree of substitution of 0.6 was obtained.

[0109] Comparative Example 1

[0110] Taking Example 1 as an example, the difference from Example 1 is that nano zinc oxide is removed, the amount of carboxymethylated hydroxypropyl modified starch is increased to 15.4 parts and polyethylene glycol 400 to 3.4 parts, while the other components and preparation process remain unchanged.

[0111] Comparative Example 2

[0112] Taking Example 1 as an example, the difference from Example 1 is that polyethylene glycol 400 is removed, the amount of carboxymethylated hydroxypropyl modified starch is increased to 17 parts, and the amount of nano zinc oxide is increased to 1.8 parts, while the other components and preparation process remain unchanged.

[0113] Comparative Example 3

[0114] The carboxymethylated hydroxypropyl modified starch was replaced with an equal amount of acetate starch, while the remaining components and preparation process remained unchanged.

[0115] Comparative Example 4

[0116] The carboxymethylated hydroxypropyl modified starch was replaced with an equal amount of hydroxyethyl starch, while the remaining components and preparation process remained unchanged.

[0117] Comparative Example 5

[0118] The carboxymethylated hydroxypropyl modified starch was replaced in equal amounts with styrene-grafted copolymerized starch, while the remaining components and preparation process remained unchanged.

[0119] Using the styrene-butadiene latex from Examples (1-3) and Comparative Examples (1-5) as film-forming base materials, water-based coatings were prepared according to the following formulation: styrene-butadiene latex (40 parts, based on solid content), titanium dioxide (20 parts), heavy calcium carbonate (15 parts), dispersant (0.5 parts, sodium polycarboxylate), and deionized water (appropriate amount, adjusted to viscosity 60-80 KU). The coatings were dispersed for 30 minutes using a high-speed disperser (2000 rpm) to obtain the water-based coating to be tested.

[0120] Testing indicators and process

[0121] 1. Rheological and thixotropic testing

[0122] Indicators: viscosity-shear rate curve, pseudoplasticity index (η) 10 / η100 ), thixotropic ring area (hysteresis ring area).

[0123] Testing process:

[0124] The coating was measured at a shear rate of 10 s using a Brookfield R / S-Plus rotational viscometer (cone-plate rotor, 25°C). -1 30s -1 50s -1 100s -1 Apparent viscosity (η) at time;

[0125] Calculate the pseudoplasticity index: η 10 / η 100 (The higher the value, the stronger the pseudoplasticity, and the easier it is to level and prevent sagging during construction.)

[0126] Thixotropic ring test: shear rate from 0 to 100 s -1 (Linear increase within 3 min) → 0 (linear decrease within 3 min), record the viscosity-shear rate curve, and calculate the hysteresis loop area (the larger the area, the stronger the thixotropy and the better the anti-sagging property when stationary).

[0127] 2. Film-forming property testing

[0128] Indicators: Minimum film-forming temperature (MFT), film appearance, flexibility, adhesion, and water absorption.

[0129] Testing process:

[0130] MFT: Using a film-forming temperature meter (QFM-III), the coating is applied to a gradient temperature control plate, and the lowest film-forming temperature (the lowest temperature of a crack-free, continuous film) is observed.

[0131] Membrane appearance: The coating was applied to a glass plate (wet film thickness 100μm), dried at 25℃ and 50% RH for 24h, and visually inspected to see if it was smooth, without cracks or bubbles;

[0132] Flexibility: According to GB / T 1731-2020, the dry film (50μm thick) is attached to the tinplate and bent 180° with cylindrical shafts of 2mm, 4mm and 6mm in diameter, and observed for cracking.

[0133] Adhesion: According to GB / T 9286-2021 cross-cut test (1mm×1mm grid, 3M tape application), rating (0: no peeling; 5: complete peeling);

[0134] Water absorption rate: Weigh the dry film (m1), soak it in distilled water for 24 hours, wipe off the surface moisture and weigh it (m2), calculate the water absorption rate = (m2-m1) / m1×100%.

[0135] 3. Stability Detection

[0136] Indicators: Storage stability, mechanical stability, freeze-thaw stability.

[0137] Detection process:

[0138] Storage stability: After the samples are sealed, they are placed under the conditions of 25°C (for 30 days), 50°C (hot storage, for 15 days), and -5°C (cold storage, for 7 days) respectively. Observe whether there is stratification, precipitation, or gelation, and measure the viscosity change rate (Δη = |ηfinal - ηinitial| / ηinitial × 100%, ≤10% is qualified);

[0139] Mechanical stability: Stir at a high speed of 3000 rpm for 30 min, pass through a 200-mesh sieve, and calculate the mass fraction of the residue on the sieve (≤0.1% is qualified);

[0140] Freeze-thaw stability: Freeze at -20°C for 24 h → thaw at room temperature for 6 h, repeat 5 times, and observe whether there is stratification or gelation (no obvious change is qualified).

[0141] The results are shown in Table 1;

[0142] Table 1

[0143] As can be seen from Table 1, for the waterborne coatings prepared from the modified starch styrene-butadiene latex of Examples 1 to 3, due to the synergistic effects of carboxymethylated hydroxypropyl modified starch (bifunctional group, excellent compatibility), nano-zinc oxide (enhancing dispersion and crosslinking), and polyethylene glycol 400 (plasticizing and film-forming), they exhibit excellent rheology, thixotropy, film-forming property (MFT ≤ 10°C, the film is complete and has excellent mechanical properties), and stability (qualified in storage, mechanical, and freeze-thaw). For Comparative Examples 1 to 2, due to the removal of a certain component, the rheology and film-forming property become poor, further verifying the synergistic effects of carboxymethylated hydroxypropyl modified starch, nano-zinc oxide, and polyethylene glycol 400. For Comparative Examples 3 to 5, the type of modified starch is changed, and the rheology, film-forming property, and stability become poor, indicating that only the addition of carboxymethylated hydroxypropyl modified starch can meet the film-forming property and rheology.

[0144] The various embodiments described in this specification are presented in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A modified starch-styrene-butadiene latex, characterized in that, The product comprises the following components in parts by weight: 15-25 parts carboxymethylated hydroxypropyl modified starch, 50-70 parts styrene-butadiene latex, 0.8-2 parts nano zinc oxide, 3-5 parts polyethylene glycol 400, 2-4 parts emulsifier, 50-70 parts deionized water, 0.3-0.8 parts defoamer, 0.15-0.3 parts preservative, and 0.1-0.5 parts pH adjuster.

2. The modified starch-styrene-butadiene latex according to claim 1, characterized in that, The emulsifier comprises a compound of sodium dodecyl sulfate and OP-10 in a mass ratio of (1:1) to (1:2).

3. The modified starch-styrene-butadiene latex according to claim 1, characterized in that, The defoamer includes at least one of polyether-modified polysiloxane and white mineral oil; and / or, The preservative includes at least one of octylisothiazolinone, 5-chloro-2-methyl-4-isothiazolin-3-one, and methylisothiazolinone; and / or The pH adjuster includes 2-amino-2-methyl-1-propanol.

4. A modified starch-styrene-butadiene latex according to any one of claims 1 to 3, characterized in that, The degree of substitution of the carboxymethylated hydroxypropyl modified starch is 0.5~0.8; and / or, The solid content of the styrene-butadiene latex is 45%~55%; and / or, The particle size of the nano zinc oxide is 20~50nm.

5. A method for preparing modified starch styrene-butadiene latex, applied to the preparation of the modified starch styrene-butadiene latex according to any one of claims 1 to 4, characterized in that, The process includes the following: Prepare carboxymethylated hydroxypropyl modified starch, and weigh each component according to the modified starch styrene-butadiene latex as described in any one of claims 1 to 4; Take 15 to 21 parts of deionized water and add the nano zinc oxide, stir, disperse at high speed and homogenize to obtain the first mixture; The remaining deionized water is heated to 40℃~47℃, the emulsifier is added, and the mixture is stirred until transparent. Then, the modified starch is added, the temperature is raised to 80℃~87℃, and the mixture is kept at that temperature for 30 min. The temperature is then lowered to 40℃~50℃ to obtain the second mixture. Mix the first mixture and the second mixture, stir until homogeneous, add styrene-butadiene latex preheated to 30°C~40°C, stir, add the polyethylene glycol, stir until homogeneous, and obtain the third mixture; The defoamer was added to the third mixture in two batches, and after stirring evenly, the pH adjuster and the preservative were added, stirred evenly, and filtered to obtain the modified starch styrene-butadiene latex.

6. The method for preparing a modified starch styrene-butadiene latex according to claim 5, characterized in that, The process for preparing carboxymethylated hydroxypropyl modified starch is as follows: Hydroxypropylation reaction: Deionized water was added to corn starch at a ratio of 1g:40ml. After stirring evenly, the pH of the system was adjusted to 10-11 with 30% sodium hydroxide solution. The temperature was raised to 45℃-50℃, and propylene oxide was slowly added dropwise. The reaction was carried out under stirring for 3-4 hours. Then, the pH was adjusted to 6.5-7.0 with 10% hydrochloric acid to obtain crude hydroxypropyl starch. The crude hydroxypropyl starch was redispersed in deionized water, sodium chloroacetate was added, and the mixture was stirred and dissolved. The pH was adjusted to 10-11 with 30% sodium hydroxide solution. The mixture was heated to 55-60℃ and reacted for 2-3 hours. The mixture was then neutralized with 10% hydrochloric acid. After precipitation with ethanol, washing, and drying, carboxymethylated hydroxypropyl starch was obtained.

7. The method for preparing a modified starch styrene-butadiene latex according to claim 5, characterized in that, Add 15-21 parts of deionized water to the nano-zinc oxide and stir at 800-1000 rpm for 10 min; then disperse at 2500-3000 rpm for 20 min, and finally homogenize at 5000 rpm for 5 min; and / or, After adding the emulsifier, stir at 800 rpm for 10 min; after adding the modified starch, stir at 800~1000 rpm and heat at 2℃ / min to 85±2℃.

8. The method for preparing a modified starch styrene-butadiene latex according to claim 5, characterized in that, When mixing the first mixture and the second mixture, stir at 600 rpm for 10 min; after adding styrene-butadiene latex, stir at 800 rpm for 20 min; after adding polyethylene glycol 400, stir at 600 rpm for 5 min.

9. The method for preparing a modified starch styrene-butadiene latex according to claim 5, characterized in that, Add the defoamer to the third mixture in two portions, each time adding half of the total amount of defoamer, and stir at 1000 rpm for 10-15 min; after adding the pH adjuster and preservative, stir at 800 rpm for 10 min.

10. The use of the modified starch styrene-butadiene latex according to any one of claims 1 to 4 in the preparation of water-based coatings.

Images