A preparation method of highly dispersible nano titanium dioxide and its application in coatings

Abstract

The invention relates to the technical field of titanium dioxide, and discloses a preparation method of highly dispersible nano titanium dioxide and its application in coatings. The nano titanium dioxide of the invention is modified by KH560, and then epoxy groups are introduced on the surface, and then a ring-opening reaction occurs with the active imino group of DOPO carboxyl phenolic resin, thereby introducing the hydrophilic carboxyl phenolic resin into the surface of the nano titanium dioxide, significantly improving its hydrophilicity, improving the dispersibility of the nano titanium dioxide in water, having good compatibility with acrylic resin, and improving the hardness and tensile properties of acrylic resin. The phenolic resin grafted on the surface of the nano titanium dioxide has high carbonization, and contains DOPO flame retardant groups, which can play a good condensed phase flame retardant role, so that the water-based coating has a good flame retardant effect.

Description

Technical Field

[0001] The invention relates to the technical field of titanium dioxide, in particular to a preparation method of highly dispersible nano titanium dioxide and application thereof in coatings. Background Art

[0002] Nano-titanium dioxide is a common inorganic nanomaterial with high specific surface area, high strength, strong antibacterial properties, and nano-small size effect. It can be used as a filler and added to polymer materials such as acrylic resin, polystyrene, and rubber to improve the antibacterial and mechanical properties of the materials. However, nano-titanium dioxide has poor dispersibility and is prone to agglomeration in media such as water-based coatings. It has poor compatibility with polymer matrix and cannot effectively improve the comprehensive performance of the material.

[0003] Water-based acrylic resin coating uses water as solvent, which is green, environmentally friendly and has little pollution. It is widely used in mechanical equipment, furniture, wood products, electronic instruments, etc. However, the strength of water-based acrylic resin coating is relatively low, and the limiting oxygen index of its paint film is only 17-18%, and the flame retardant performance is very poor, which limits the development and application of water-based acrylic resin coating. Adding nano titanium dioxide to water-based acrylic resin coating can improve mechanical, heat-resistant and other properties. The patent with publication number CN112029332B discloses a water-based antibacterial coating and a preparation method thereof, using silane-modified flower-shaped nano titanium dioxide as a core layer and an organosilicon-modified acrylic polymer as a shell layer. The obtained water-based antibacterial coating has excellent antibacterial properties and excellent thermal transfer properties, but the water-based antibacterial coating does not have flame retardancy. Summary of the invention

[0004] The invention solves the problem of poor dispersibility of nano titanium dioxide in water-based paint and simultaneously solves the problem of poor flame retardancy of acrylic resin paint.

[0005] Technical solution: A method for preparing highly dispersible nano titanium dioxide, comprising the following steps:

[0006] Step S1, add phenol and phenol-based DOPO to a reaction kettle, add an aqueous solution of formaldehyde component 1 and sodium hydroxide component 1 after heating and stirring, carry out a prepolymerization reaction, then add an aqueous solution of formaldehyde component 2 and sodium hydroxide component 2, carry out a polymerization reaction; finally, add water and sodium hydroxide component 3, carry out a hydrolysis reaction, cool, concentrate the solution, precipitate, filter, and dry to obtain DOPO carboxyl phenolic resin. The reaction formula is:

[0007] .

[0008] Step S2, using KH560 to perform surface modification on nano titanium dioxide to obtain KH560 modified titanium dioxide; then placing the KH560 modified titanium dioxide in ethanol, adding DOPO carboxyl phenolic resin, reacting, centrifuging, washing with ethanol, and drying to obtain highly dispersed nano titanium dioxide.

[0009] Furthermore, in step S1, the mass ratio of phenol, phenol-based DOPO, formaldehyde, sodium hydroxide component 1, sodium hydroxide component 2, and sodium hydroxide component 3 is (65-80): (20-35): (57-62): (3.1-3.3): (13-15): (1.2-1.3): (18-32).

[0010] Furthermore, in step S1, the temperature of the prepolymerization reaction is 70-75°C, and the time is 60-90 min; the temperature of the polymerization reaction is 90-95°C, and the time is 30-60 min; the temperature of the hydrolysis reaction is 80-90°C, and the time is 7-12 h.

[0011] Furthermore, in step S2, the mass ratio of KH560 modified titanium dioxide to DOPO carboxyl phenolic resin is 1:(0.3-2).

[0012] Furthermore, in step S2, the reaction temperature is 60-70° C., and the reaction time is 18-24 h.

[0013] Furthermore, the preparation method of phenol-based DOPO is to add ethanol, 3-aminopropionic acid methyl ester hydrochloride, triethylamine, and p-hydroxybenzaldehyde to a reaction bottle, react at 35-50°C for 3-6 hours, and then add DOPO, wherein the molar ratio of 3-aminopropionic acid methyl ester hydrochloride, triethylamine, p-hydroxybenzaldehyde, and DOPO is 1: (1-1.1): (0.9-1.1): (1-1.2); at 75-80°C, condense and reflux for 12-18 hours, concentrate the solution, wash the product with water and acetone in turn, and then purify it by recrystallization with ethanol to obtain phenol-based DOPO. The reaction formula is as follows:

[0014] .

[0015] Furthermore, the application of highly dispersible nano titanium dioxide in coatings is as follows: water, water-based acrylic resin, highly dispersible nano titanium dioxide, defoaming agent and leveling agent are added into a container, and the mixture is stirred and dispersed, wherein the mass ratio of the water-based acrylic resin to the highly dispersible nano titanium dioxide is 100:(0.5-10); a water-based acrylic resin coating is obtained.

[0016] The technical effect of the present invention is as follows: the present invention uses 3-aminopropionic acid methyl ester hydrochloride, p-hydroxybenzaldehyde and DOPO as reactants to prepare a novel phenol-based DOPO monomer, then uses sodium hydroxide as a catalyst to carry out a polymerization reaction with phenol and formaldehyde, and further adds an excess of sodium hydroxide to hydrolyze the ester group to generate a carboxyl group, thereby obtaining a DOPO carboxyl phenolic resin.

[0017] After the nano-titanium dioxide of the present invention is modified by KH560, epoxy groups are introduced on the surface, and then the epoxy groups undergo a ring-opening reaction with the active imino groups of the DOPO carboxyl phenolic resin, thereby introducing the hydrophilic carboxyl phenolic resin into the surface of the nano-titanium dioxide, significantly improving its hydrophilicity, improving the dispersibility of the nano-titanium dioxide in water, and expanding the practical application of the nano-titanium dioxide in water-based coatings.

[0018] The invention adds highly dispersible nano titanium dioxide into the water-based acrylic resin coating, the surface of the nano titanium dioxide is grafted with a hydrophilic carboxyl-containing phenolic resin, the nano titanium dioxide has good dispersibility in the water-based acrylic resin emulsion, reduces the agglomeration of nano silicon dioxide, and after the nano titanium dioxide is grafted and modified by the phenolic resin, the nano titanium dioxide has better compatibility with the acrylic resin, the nano titanium dioxide has a large specific surface area, high mechanical strength, and a nano small size effect, which is beneficial to improving the hardness and tensile properties of the acrylic resin.

[0019] The phenolic resin grafted on the surface of the nano-titanium dioxide of the present invention has a high carbon-forming property and contains a DOPO flame-retardant group. When combined with the phenolic resin, it can play a good condensed phase flame-retardant role. Combustion can promote the formation of a carbon layer structure in the acrylic resin matrix, and when combined with the nano-titanium dioxide, it forms a stable inorganic barrier layer, which can isolate oxygen and block heat transfer, thereby having a good flame-retardant effect. DETAILED DESCRIPTION

[0020] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] The water-based acrylic resin of the present invention is brand s70, from Shandong Lingchuang Biotechnology.

[0022] Nano-titanium dioxide, spherical, average particle size 40nm, Guangzhou Hongwu Material Technology.

[0023] Add 45 mL of water, 5 mL of ethanol, and 0.08 g of KH560 to the reaction bottle, stir, add 1 g of nano-titanium dioxide, disperse by ultrasound, condense and reflux at 80°C for 2 h, centrifuge, wash with ethanol, and dry to obtain KH560-modified titanium dioxide.

[0024] Example 1

[0025] (1) Add 15 mL of ethanol, 4 mmol of 3-aminopropionic acid methyl ester hydrochloride, 4 mmol of triethylamine, and 4.4 mmol of p-hydroxybenzaldehyde to a reaction flask, and react at 35°C for 5 h. Then add 4 mmol of DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) and react at 80°C under condensation reflux for 12 h. Concentrate the solution, wash the product with water and acetone in turn, and then purify it by recrystallization with ethanol to obtain phenol-based DOPO.

[0026] (2) Add 80 g of phenol and 20 g of phenol-based DOPO to a reactor, heat to 70°C, stir, add an aqueous solution containing 66 g of formaldehyde (mass fraction 37%) and 3.3 g of sodium hydroxide, carry out a prepolymerization reaction at 70°C for 60 min, then add an aqueous solution containing 15 g of formaldehyde (mass fraction 37%) and 1.3 g of sodium hydroxide, carry out a polymerization reaction at 95°C for 30 min; finally, add 30 mL of water and 18 g of sodium hydroxide, carry out a hydrolysis reaction at 85°C for 7 h, cool, concentrate the solution, precipitate, filter, and dry to obtain DOPO carboxyl phenolic resin.

[0027] (3) Place 5 g of KH560 modified titanium dioxide in ethanol, add 1.5 g of DOPO carboxyl phenolic resin, react at 60°C for 24 h, centrifuge, wash with ethanol, and dry to obtain highly dispersed nano titanium dioxide.

[0028] Example 2

[0029] (1) Add 20 mL of ethanol, 4 mmol of 3-aminopropionic acid methyl ester hydrochloride, 4.4 mmol of triethylamine, and 4.4 mmol of p-hydroxybenzaldehyde to a reaction flask, react at 50°C for 3 h, then add 4.8 mmol of DOPO, and react at 75°C under condensation reflux for 18 h. Concentrate the solution, wash the product with water and acetone in turn, and then purify it by recrystallization with ethanol to obtain phenol-based DOPO.

[0030] (2) Add 72 g of phenol and 28 g of phenol-based DOPO to a reactor, heat to 75°C, stir, add an aqueous solution containing 62 g of formaldehyde (mass fraction 37%) and 3.2 g of sodium hydroxide, carry out a prepolymerization reaction at 75°C for 60 min, then add an aqueous solution containing 14 g of formaldehyde (mass fraction 37%) and 1.3 g of sodium hydroxide, carry out a polymerization reaction at 90°C for 60 min; finally, add 40 mL of water and 26 g of sodium hydroxide, carry out a hydrolysis reaction at 80°C for 12 h, cool, concentrate the solution, precipitate, filter, and dry to obtain DOPO carboxyl phenolic resin.

[0031] (3) Place 5 g of KH560 modified titanium dioxide in ethanol, add 6 g of DOPO carboxyl phenolic resin, react at 70°C for 18 h, centrifuge, wash with ethanol, and dry to obtain highly dispersed nano titanium dioxide.

[0032] Example 3

[0033] (1) Add 15 mL of ethanol, 4 mmol of 3-aminopropionic acid methyl ester hydrochloride, 4 mmol of triethylamine, and 3.6 mmol of p-hydroxybenzaldehyde to a reaction flask, react at 40°C for 6 h, then add 4.4 mmol of DOPO, and react at 75°C under condensation reflux for 18 h. Concentrate the solution, wash the product with water and acetone in turn, and then purify it by recrystallization with ethanol to obtain phenol-based DOPO.

[0034] (2) Add 65 g of phenol and 35 g of phenol-based DOPO to a reactor, heat to 75°C, stir, add an aqueous solution containing 57 g of formaldehyde (mass fraction 37%) and 3.1 g of sodium hydroxide, and carry out a prepolymerization reaction at 75°C for 90 min. Then, add an aqueous solution containing 13 g of formaldehyde (mass fraction 37%) and 1.2 g of sodium hydroxide, and carry out a polymerization reaction at 95°C for 60 min. Finally, add 40 mL of water and 32 g of sodium hydroxide, and carry out a hydrolysis reaction at 90°C for 10 h. Cool, concentrate the solution, precipitate, filter, and dry to obtain DOPO carboxyl phenolic resin.

[0035] (3) Place 5 g of KH560 modified titanium dioxide in ethanol, add 10 g of DOPO carboxyl phenolic resin, react at 65°C for 24 h, centrifuge, wash with ethanol, and dry to obtain highly dispersed nano titanium dioxide.

[0036] Comparative Example 1

[0037] (1) Add 80g phenol and 20g phenol-based DOPO to the reactor, heat to 70°C, stir, add 66g formaldehyde aqueous solution (mass fraction 37%) and 3.3g sodium hydroxide, carry out prepolymerization at 70°C for 60min, then add 15g formaldehyde aqueous solution (mass fraction 37%) and 1.3g sodium hydroxide, carry out polymerization at 95°C for 30min; cool, concentrate the solution, dry, and obtain water-soluble phenolic resin. Brown liquid.

[0038] (2) Place 5 g of KH560 modified titanium dioxide in ethanol, add 1.5 g of water-soluble phenolic resin, react at 60° C. for 24 h, centrifuge, wash with ethanol, and dry to obtain modified nano titanium dioxide.

[0039] Weigh 1g of highly dispersible nano titanium dioxide, nano titanium dioxide, and KH560 modified titanium dioxide respectively, add them to 100mL of water, disperse them by ultrasonication for 2h, transfer 20mL of the solution into a cuvette, let it stand at 25℃, and observe the time when obvious precipitation appears in the solution. The results are shown in Table 1.

[0040] Table 1 Dispersibility test of aqueous solution of nano-titanium dioxide

[0041] Time for precipitation to appear (h) Example 1 64 Example 2 57 Example 3 89 Comparative Example 1 2 Nano Titanium Dioxide 2 KH560 modified titanium dioxide 1.5

[0042] After testing, the unmodified nano-titanium dioxide has poor dispersibility in water, and obvious precipitation appears in the solution after 2 hours. However, the KH560 modified titanium dioxide solution has obvious precipitation after 1.5 hours. This is because KH560 is oil-soluble and has no hydrophilic groups. The modified nano-titanium dioxide has poor hydrophilicity and poor dispersibility in water, which easily produces precipitation.

[0043] After the nano-titanium dioxide of Examples 1-3 was modified with KH560, epoxy groups were introduced on the surface, and then the epoxy groups underwent a ring-opening reaction with the active imino groups of the DOPO carboxyl phenolic resin, thereby introducing the hydrophilic carboxyl phenolic resin into the surface of the nano-titanium dioxide, significantly improving its hydrophilicity and the dispersibility of the nano-titanium dioxide in water. The time for the precipitate to appear reached 64-89 hours.

[0044] In Comparative Example 1, ordinary water-soluble phenolic resin was used to react with KH560 modified titanium dioxide. Since the phenolic resin only contains hydroxyl groups, when no catalyst is added, the reaction activity of hydroxyl groups and epoxy groups of KH560 is low, and it is difficult to effectively graft the water-soluble phenolic resin molecular chains to the surface of nano-titanium dioxide. The time for precipitate to appear in the modified nano-titanium dioxide aqueous solution of Comparative Example 1 is 2 hours, and the dispersibility is poor.

[0045] Example 4

[0046] 120 mL of water, 100 g of water-based acrylic resin, 0.5 g of highly dispersible nano titanium dioxide (prepared in the same manner as in Example 3), 0.8 g of defoamer TEGO810, and 0.5 g of leveling agent BYK-333 were added to a container, and the mixture was stirred and dispersed to obtain a water-based acrylic resin coating.

[0047] Example 5

[0048] 120 mL of water, 100 g of water-based acrylic resin, 2 g of highly dispersible nano titanium dioxide (prepared in the same manner as in Example 3), 0.8 g of defoamer TEGO810, and 0.5 g of leveling agent BYK-333 were added to a container, and the mixture was stirred and dispersed to obtain a water-based acrylic resin coating.

[0049] Example 6

[0050] 120 mL of water, 100 g of water-based acrylic resin, 6 g of highly dispersible nano titanium dioxide (prepared in the same manner as in Example 3), 0.8 g of defoamer TEGO810, and 0.5 g of leveling agent BYK-333 were added to a container, and the mixture was stirred and dispersed to obtain a water-based acrylic resin coating.

[0051] Example 7

[0052] 120 mL of water, 100 g of water-based acrylic resin, 10 g of highly dispersible nano titanium dioxide (prepared in the same manner as in Example 3), 0.8 g of defoamer TEGO810, and 0.5 g of leveling agent BYK-333 were added to a container, and the mixture was stirred and dispersed to obtain a water-based acrylic resin coating.

[0053] Comparative Example 2

[0054] 120 mL of water, 100 g of water-based acrylic resin, 0.8 g of defoamer TEGO810, and 0.5 g of leveling agent BYK-333 were added to a container, and the mixture was stirred and dispersed to obtain a water-based acrylic resin coating.

[0055] Comparative Example 3

[0056] 120 mL of water, 100 g of water-based acrylic resin, 0.5 g of nano titanium dioxide, 0.8 g of defoamer TEGO810, and 0.5 g of leveling agent BYK-333 were added to a container, and the mixture was stirred and dispersed to obtain a water-based acrylic resin coating.

[0057] Comparative Example 4

[0058] 120 mL of water, 100 g of water-based acrylic resin, 0.5 g of KH560 modified titanium dioxide, 0.8 g of defoamer TEGO810, and 0.5 g of leveling agent BYK-333 were added to a container, and the mixture was stirred and dispersed to obtain a water-based acrylic resin coating.

[0059] Comparative Example 5

[0060] 120 mL of water, 100 g of water-based acrylic resin, 0.5 g of DOPO, 0.8 g of defoamer TEGO810, and 0.5 g of leveling agent BYK-333 were added to a container, and the mixture was stirred and dispersed to obtain a water-based acrylic resin coating.

[0061] The hardness of acrylic resin paint film was tested according to the method of GB / T 6739-2022. The curing conditions of the paint were 90℃×8h.

[0062] The water-based acrylic resin coating was heat-cured to make a standard specimen, and the tensile properties were tested according to the GB / T 1040.1-2018 method. The limiting oxygen index and vertical burning performance of the coating film were tested according to the GB / T 2406.1-2008 and UL94 standards.

[0063] Table 2 Water-based acrylic resin coating performance test

[0064]

[0065] After testing, the water-based acrylic resin coatings of Examples 4-7 were added with highly dispersible nano titanium dioxide, and the hardness of the coating film reached 3-5H, the tensile strength of the cured sample reached 19.4-24.5MPa, and the elongation at break reached 210.2-265.1%, showing good mechanical properties, much higher than the acrylic resin coating of Comparative Example 2; and the limiting oxygen index reached 25.9-30.6%, UL94 was V1 and V0 grades, and the flame retardant properties were very good. This is because the surface of the highly dispersible nano titanium dioxide was grafted with a hydrophilic carboxyl-containing phenolic resin, which had good dispersibility in the water-based acrylic resin emulsion, reduced the agglomeration of nano silicon dioxide, and after the nano titanium dioxide was grafted with phenolic resin, it had better compatibility with acrylic resin, thereby improving the hardness and tensile properties of acrylic resin. At the same time, the phenolic resin grafted on the surface of nano-titanium dioxide has a high carbon-forming property and contains DOPO flame-retardant groups. When combined with phenolic resin, it can play a good condensed phase flame-retardant role. Combustion can promote the formation of a carbon layer structure in the acrylic resin matrix, and form a stable inorganic barrier layer in combination with nano-titanium dioxide, which can isolate oxygen and block heat transfer, thus having a good flame-retardant effect.

[0066] The acrylic resin coating of Comparative Example 3 added unmodified nano titanium dioxide, which has poor hydrophilicity, poor dispersibility in water-based coatings, poor interfacial compatibility with acrylic resin, and low improvement in the hardness and tensile properties of the coating film. In addition, the limiting oxygen index of acrylic resin is 18.4%, UL94 has no grade, and the flame retardant performance is very poor.

[0067] The acrylic resin coating of Comparative Example 4 added KH560 modified nano titanium dioxide, which has poor hydrophilicity and poor dispersibility in water-based coatings. However, after being organically modified by KH560, nano titanium dioxide has good interfacial compatibility with acrylic resin, which is beneficial to improving the hardness and tensile properties of the paint film. However, the flame retardant performance is very poor.

[0068] The acrylic resin coating of Comparative Example 5 contains DOPO but no nano titanium dioxide. Although DOPO can improve the flame retardant properties of acrylic resin, its compatibility with acrylic resin is poor. When added to the coating, it affects the mechanical properties of the coating and reduces the hardness, tensile strength and elongation at break.

[0069] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for preparing highly dispersible nano titanium dioxide, characterized in that: The preparation method comprises the following steps: step S1, adding phenol and phenol-based DOPO into a reaction kettle, heating and stirring, adding an aqueous solution of formaldehyde component 1 and sodium hydroxide component 1, performing a prepolymerization reaction, and then adding an aqueous solution of formaldehyde component 2 and sodium hydroxide component 2 to perform a polymerization reaction; finally, adding water and sodium hydroxide component 3 to perform a hydrolysis reaction, cooling, concentrating the solution, precipitating a precipitate, filtering, and drying to obtain a DOPO carboxyl phenolic resin; The phenol-based DOPO has the following structural formula (I): Formula (I); Step S2, using KH560 to perform surface modification on nano-titanium dioxide to obtain KH560-modified titanium dioxide; Then, the KH560 modified titanium dioxide is placed in ethanol, DOPO carboxyl phenolic resin is added, reacted, centrifuged, washed, and dried to obtain highly dispersed nano titanium dioxide; The preparation method of the phenol-based DOPO is as follows: adding ethanol, 3-aminopropionic acid methyl ester hydrochloride, triethylamine, and p-hydroxybenzaldehyde into a reaction bottle, reacting at 35-50° C. for 3-6 hours, then adding DOPO, reacting at 75-80° C. under condensation reflux for 12-18 hours, concentrating the solution, washing the product, and then recrystallizing and purifying it to obtain the phenol-based DOPO; The molar ratio of 3-aminopropionic acid methyl ester hydrochloride, triethylamine, p-hydroxybenzaldehyde and DOPO is 1:(1-1.1):(0.9-1.1):(1-1.2).

2. The method for preparing highly dispersible nano titanium dioxide according to claim 1, characterized in that: In the step S1, the mass ratio of phenol, phenol-based DOPO, formaldehyde component 1, sodium hydroxide component 1, formaldehyde component 2, sodium hydroxide component 2, and sodium hydroxide component 3 is (65-80): (20-35): (57-62): (3.1-3.3): (13-15): (1.2-1.3): (18-32).

3. The method for preparing highly dispersible nano titanium dioxide according to claim 1, characterized in that: In step S1, the temperature of the prepolymerization reaction is 70-75°C, and the time is 60-90 min; the temperature of the polymerization reaction is 90-95°C, and the time is 30-60 min; the temperature of the hydrolysis reaction is 80-90°C, and the time is 7-12 h.

4. The method for preparing highly dispersible nano titanium dioxide according to claim 1, characterized in that: In the step S2, the mass ratio of KH560 modified titanium dioxide to DOPO carboxyl phenolic resin is 1:(0.3-2).

5. The method for preparing highly dispersible nano titanium dioxide according to claim 1, characterized in that: In step S2, the reaction temperature is 60-70° C., and the reaction time is 18-24 hours.

6. Use of highly dispersible nano titanium dioxide obtained by the preparation method according to any one of claims 1 to 5 in coatings, characterized in that: Add water, water-based acrylic resin, highly dispersible nano titanium dioxide, a defoamer and a leveling agent into a container, stir and disperse, and obtain a water-based acrylic resin coating.

7. The use of highly dispersible nano titanium dioxide in coatings according to claim 6, characterized in that: The mass ratio of the water-based acrylic resin to the highly dispersed nano titanium dioxide is 100:(0.5-10).

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