Hydroxyl acrylic emulsion with high hardness and high wear resistance as well as preparation and application thereof

Abstract

The invention relates to a hydroxy acrylic emulsion with high hardness and high wear resistance as well as preparation and application thereof, the hydroxy acrylic emulsion is obtained by utilizing polymerization of a plurality of acrylate monomers, and a photopolymerization monomer is added, so that the obtained resin can be cured by being combined with an isocyanate curing agent and can also be photocured. No solvent is used in the synthesis process of the hydroxyl acrylic emulsion, the hydroxyl acrylic emulsion is green and environmentally friendly, and a coating film formed after curing has the characteristics of high hardness, good wear resistance, good water resistance and excellent comprehensive performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of waterborne coatings, and relates to a hydroxyl acrylic emulsion with high hardness and high wear resistance, and its preparation and application. Background Art

[0002] Waterborne (hydroxyl) acrylic resins have become one of the research hotspots in the field of waterborne industrial coatings due to their excellent weather resistance, decorative properties and mechanical properties, and are widely used in fields such as anti-corrosion and weather resistance. However, the market share of domestic waterborne (hydroxyl) acrylic resin coatings is still very low. For example, the film hardness, wear resistance, and aging resistance are relatively low, the drying time is relatively long, and the current production cost is relatively high, resulting in low market recognition.

[0003] For example, in the high wear-resistant hydroxyl acrylic resin and its preparation process disclosed in CN201910351033.3, by weight percentage, it contains 23-25.4 wt% of toluene, 23-26 wt% of butyl acetate, 8-10 wt% of hydroxyethyl methacrylate, 30-36 wt% of methyl methacrylate, 0.5-5.0 wt% of isobornyl methacrylate, 2.5-4.5 wt% of n-butyl methacrylate, 2.5-4.5 wt% of acrylic acid, and 1.1-1.54 wt% of benzoyl peroxide. This scheme is obtained by solution polymerization, is a secondary dispersion, has poor environmental protection, and there is still room for further improvement in the balance of film hardness, wear resistance and water resistance. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned existing technologies, and provide a hydroxyl acrylic emulsion with high hardness and high wear resistance, and its preparation and application. Its synthesis process does not use any solvents, is green and environmentally friendly, and the cured film has excellent comprehensive properties such as high hardness, good wear resistance and good water resistance.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] On the one hand, the present invention provides a preparation method of a hydroxyl acrylic emulsion with high hardness and high wear resistance, which is characterized by including the following steps:

[0007] S1. Add deionized water and a mixed emulsifier into a reaction kettle to obtain the bottom material in the kettle;

[0008] S2. Heat the reaction kettle to 77-82 °C, add the core layer pre-emulsion and the initiator aqueous solution, and keep the temperature for reaction;

[0009] S3. Continue to dropwise add the shell layer pre-emulsion and the initiator aqueous solution, and stir at a constant temperature;

[0010] S4. Then dropwise add the crosslinking monomer, and after the addition is completed, continue to stir at a constant temperature;

[0011] S5. Cool down to below 50°C, adjust the pH to 7 - 9, and filter to obtain a hydroxy acrylic emulsion;

[0012] S6. Add a photo - curing agent and a photo - initiator to the obtained hydroxy acrylic emulsion, and stir evenly to obtain a hydroxy acrylic emulsion with high hardness and high wear resistance.

[0013] Furthermore, in S1, the mass ratio of deionized water to the mixed emulsifier added is (14 - 40:1);

[0014] Furthermore, in S1, the mixed emulsifier is composed of an anionic emulsifier and a non - ionic emulsifier, and the mass ratio of the anionic emulsifier to the non - ionic emulsifier is 1:(1 - 5), where,

[0015] Preferably, the anionic emulsifier is selected from at least one of sodium dodecyl sulfonate (SLS), sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl diphenyl ether disulfonate (SLDED), sodium styrene sulfonate (SSS), or sodium stearate (SAS), more preferably sodium dodecyl benzene sulfonate or sodium dodecyl sulfate;

[0016] Preferably, the non - ionic emulsifier is isomeric alcohol polyoxyethylene ether, with the structural formula R - O-(CH2CH2O) n -H, where R is an alkyl group satisfying the m H 2m+1 general formula, m ranges from 8 to 13, exemplarily, it can be 8, 10, 11, 13, more preferably 10 and 13; where n ranges from 3 to 12, exemplarily, it can be 3, 5, 6, 7, 8, 10, 12, more preferably 6, 7, 8. Specifically, when m is 13 and n is 7, C 13 H 27 -O-(CH2CH2O)7 - H, abbreviated as 1307, and the abbreviation rules for other structures are the same.

[0017] Furthermore, in S2, the core - layer pre - emulsion is formed by shear - dispersing core - layer monomers, water, and a mixed emulsifier, and the addition ratio of the core - layer monomers, water, and the mixed emulsifier is (32 - 86:15 - 50:1);

[0018] In S3, the shell - layer pre - emulsion is formed by shear - dispersing shell - layer monomers, water, and a mixed emulsifier, and the addition ratio of the shell - layer monomers, water, and the mixed emulsifier is (32 - 86:15 - 50:1);

[0019] The initiator in the initiator aqueous solution in S2 and S3 is ammonium persulfate, potassium persulfate, or ammonium persulfate, preferably ammonium persulfate.

[0020] The total amount of initiators used in S2 and S3 is 0.5%-3% of the total mass of all reaction monomers of the hydroxy acrylic emulsion, preferably 0.7%-2%, and most preferably 0.9%-1.5%.

[0021] Furthermore, the amount of initiator used in S2 is 50-70% of the total amount of initiators, and the amount of initiator used in S4 is 30-50% of the total amount of initiators.

[0022] Furthermore, in S2, the core layer monomers are obtained by mixing α,β-monoethylenically unsaturated monocarboxylic acids, esters of α,β-monoethylenically unsaturated monocarboxylic acids, vinyl aromatic compounds, and (meth)acrylic hydroxyalkyl esters in a mass ratio of (1-2):(17.2-27.2):(9-14):(5-30);

[0023] In S3, the shell layer monomers are obtained by mixing α,β-monoethylenically unsaturated monocarboxylic acids, esters of α,β-monoethylenically unsaturated monocarboxylic acids, vinyl aromatic compounds, and (meth)acrylic hydroxyalkyl esters in a mass ratio of (2.5-8):(40-75):(5-20):(5-30).

[0024] More preferably, the α,β-monoethylenically unsaturated monocarboxylic acid is selected from at least one of acrylic acid, methacrylic acid, ethylacrylic acid, acryloxypropionic acid, methacryloxypropionic acid, acryloxyacetic acid, and methacryloxyacetic acid;

[0025] The esters of α,β-monoethylenically unsaturated monocarboxylic acids are selected from at least one of methyl (meth)acrylate, methyl ethylacrylate, ethyl (meth)acrylate, ethyl ethylacrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, tert-butyl ethylacrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, and isooctyl (meth)acrylate;

[0026] The vinyl aromatic compounds are selected from at least one of styrene, 2-methylstyrene, 4-methylstyrene, 2-butylstyrene, 4-butylstyrene, and 4-decylstyrene;

[0027] The (meth)acrylic acid hydroxyalkyl ester is selected from at least one of hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate or 6-hydroxyhexyl acrylate. In addition, a neutralizing agent is added in the present invention to adjust the pH, and the neutralizing agent includes at least one of ammonia water, sodium hydroxide, N,N-dimethylethanolamine or triethylamine.

[0028] Furthermore, in S2, 8-15 wt% of the core layer pre-emulsion is first added and kept warm with the initiator aqueous solution for 20-40 min, and then the remaining core layer pre-emulsion is added dropwise within 2-4 h, and the temperature is kept constant for 0.5-1.5 h;

[0029] In S3, the shell layer pre-emulsion and the initiator aqueous solution are added dropwise within 3-4 h, and then the temperature is kept constant and stirred for 10-20 min;

[0030] In S4, the time for constant temperature stirring is 0.5-1.5 h.

[0031] Further, in S4, the chemical structural formula of the crosslinking monomer is:

[0032]

[0033] Among them, R1 is C, and R2 and R3 are each independently selected from H, CH3-, m is a natural number, and R4 and R5 are each independently selected from H, CH3-. Preferably, the crosslinking monomer is ethylene glycol dimethacrylate (EDGMA).

[0034] Further, in S6, the structure of the photocuring monomer is:

[0035]

[0036] Among them, R4 is hydrogen or methyl, and R5 and R6 are each independently selected from H, a straight-chain or branched-chain alkane with 1-8 carbon atoms substituted by a hydroxyl group, and R5 and R6 are not both hydrogen at the same time. Preferably, the photocuring monomer is N-hydroxymethylacrylamide;

[0037] The photoinitiator is selected from at least one of α,α-diethoxyacetophenone, sodium anthraquinone-2-sulfonate, 2-hydroxy-3-(2'-thioxanthonyloxy)-N,N,N-trimethyl-1-propanamine chloride, sodium 2-hydroxy-3-(4-benzoylphenoxy)propane sulfonate, 2-hydroxy-2-methylpropiophenone, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone.

[0038] Further, the addition amount of the photocuring monomer is 5-20% of the total mass of the monomers used in the shell layer (that is, the remaining substances participating in the reaction except water, emulsifier and initiator), preferably 10-18%, and most preferably 12-15%.

[0039] Furthermore, the amount of the photoinitiator added is 1.0-10% of the photocurable monomer, preferably 2-8%, and most preferably 4-7%.

[0040] In a second aspect, the present invention further provides a hydroxylated acrylic emulsion with high hardness and high wear resistance, which is prepared by the preparation method described in any one of the above items.

[0041] In a third aspect, the present invention also provides a use of a hydroxylated acrylic emulsion with high hardness and high wear resistance in coatings.

[0042] Further, the application process of the emulsion in the coating is:

[0043] Weigh a certain amount of high-hardness and high-wear-resistant hydroxyl acrylic emulsion, apply it evenly on a clean PC board with a wire rod, bake it at about 60°C for about 3 minutes, and then place it on a conveyor-type UV curing machine to obtain a coating after UV curing.

[0044] The invention is based on semi-continuous seed emulsion polymerization. In the process of shell polymerization, α,β-monoethylenically unsaturated monocarboxylic acid and (meth) hydroxyalkyl acrylate containing polar groups are introduced into the shell of latex particles through free radical copolymerization, so that a large number of polar groups are enriched on the surface of the particles. By adding a cross-linking monomer with multiple double bonds, the cohesion of the polymer is increased, the end of the shell polymer has a carbon-carbon double bond, and the hardness and resistance of the paint film are improved. In the film-forming and curing process, NMA is introduced into the emulsion system as an external cross-linking functional monomer. Since NMA is a water-soluble monomer, it can be uniformly dispersed in the water continuous phase. After adding a photoinitiator, UV irradiation causes the photoinitiator to decompose to form primary free radicals, and the NMA in the water phase undergoes free radical polymerization, and the end of the shell polymer is connected to form a macromolecular chain. Since NMA has a hydrophilic hydroxymethyl group and a polar amide group, it can have good water solubility in the case of a large molecular weight. Since there are two hydrogen bond donors and two hydrogen bond acceptors in NMA, it can form a weak interaction with the carboxyl group and the hydroxyl group on the surface of the latex particles. Therefore, by modifying the surface of the latex particles with hydroxyl and carboxyl groups, and using the free radical polymerization reaction of NMA in the UV trigger system, a physical-chemical cross-linking network is constructed in the aqueous hydroxypropyl core-shell emulsion to achieve a comprehensive improvement in the performance of the paint film. The synthesis process of the hydroxyl acrylic emulsion in the present invention does not use any solvent, the synthesis process is simple, zero VOC can be achieved, green and environmentally friendly, the curing speed is fast, and the coating formed after curing has the characteristics of high hardness, good wear resistance, and excellent comprehensive performance.

[0045] Compared with the prior art, the present invention has the following advantages:

[0046] (1) The hydroxyl acrylic emulsion provided by the present invention can be cured by combining with a hydrophilic modified isocyanate curing agent or by photocuring through a photopolymerizable monomer N-hydroxymethyl acrylamide (NMA) and a photoinitiator. The prepared emulsion has a fast curing speed, a high hardness of the cured paint film, and excellent scratch resistance.

[0047] (2) No solvent is used in the synthesis process of the hydroxyl acrylic emulsion. The synthesis process is simple, achieving zero VOC, being green and environmentally friendly, having a fast curing speed, and the formed coating film after curing has the characteristics of high hardness, good wear resistance, and excellent comprehensive performance. Detailed implementation mode

[0048] The present invention will be described in detail below with reference to specific embodiments. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0049] In the following embodiments, the core layer pre-emulsion used is obtained by dispersing and mixing the following component ratios: 40 g of deionized water, a mixed emulsifier (0.38 g of sodium dodecylbenzenesulfonate, 1.2 g of DOWFAX X-405), 15.6 g of methyl methacrylate, 21.7 g of styrene, 13.9 g of butyl acrylate, 3.2 g of acrylic acid, 5.2 g of isooctyl acrylate, 15.2 g of 2-hydroxyethyl methacrylate.

[0050] The shell layer emulsion used is obtained by dispersing and mixing the following component ratios: 40 g of deionized water, (0.38 g of sodium dodecylbenzenesulfonate, 1.2 g of DOWFAX X-405), 15.6 g of methyl methacrylate, 17.7 g of styrene, 9.9 g of butyl acrylate, 3.2 g of acrylic acid, 5.2 g of isooctyl acrylate, 15.2 g of 2-hydroxyethyl methacrylate.

[0051] The photoinitiator monomer (i.e., photocuring monomer) used is N-hydroxymethyl acrylamide, and the crosslinking monomer used is ethylene glycol dimethacrylate (EDGMA).

[0052] For the rest of the raw materials or processing techniques without special instructions, it means that they are all conventional commercially available raw materials or conventional processing techniques in the art.

[0053] Comparative example 1

[0054] In a reaction kettle equipped with a stirrer, a condenser and a thermometer, 105 g of deionized water and a mixed emulsifier (1.2 g of sodium dodecylbenzenesulfonate, 3.6 g of DOWFAX X-405) are added to prepare the bottom material of the kettle. When the temperature in the reaction kettle reaches about 80 °C, 10% of the core layer pre-emulsion (40 g of deionized water, 0.75 g of sodium dodecylbenzenesulfonate, 2.3 g of DOWFAX X-405, 15.6 g of methyl methacrylate, 21.7 g of styrene, 13.9 g of butyl acrylate, 3.2 g of acrylic acid, 5.2 g of isooctyl acrylate, 15.2 g of 2-hydroxyethyl methacrylate) and an aqueous initiator solution (0.89 g of ammonium persulfate, 10 g of deionized water) are added to the bottom material of the kettle, and the temperature is kept for 30 min. Then the remaining core pre-emulsion is added dropwise over 3 h. After the addition is completed, the temperature is kept for 1 h. Then the shell layer pre-emulsion (40 g of deionized water, 0.75 g of sodium dodecylbenzenesulfonate, 2.3 g of DOWFAX X-405, 15.6 g of methyl methacrylate, 17.7 g of styrene, 9.9 g of butyl acrylate, 3.2 g of acrylic acid, 5.2 g of isooctyl acrylate, 15.2 g of 2-hydroxyethyl methacrylate) and an aqueous initiator solution (0.6 g of ammonium persulfate, 25 g of deionized water) are added dropwise. The shell layer pre-emulsion and the aqueous initiator solution are added dropwise simultaneously and completed after 3 - 4 h of dropping. Then continue to stir at a constant temperature for 0.5 - 1.5 h. After the above operations are completed, the emulsion is cooled to below 50 °C, and the pH is adjusted to 7.0 - 9.0 with a neutralizing agent, and then filtered through a 200-mesh filter to obtain a hydroxy acrylic emulsion.

[0055] Comparative Example 2

[0056] In a reaction kettle equipped with a stirrer, a condenser and a thermometer, 105 g of deionized water and a mixed emulsifier (1.2 g of sodium dodecylbenzenesulfonate, 3.6 g of DOWFAX X-405) are added to prepare the bottom material of the kettle. When the temperature in the reaction kettle reaches about 80 °C, 10% of the core layer pre-emulsion (40 g of deionized water, 0.75 g of sodium dodecylbenzenesulfonate, 2.3 g of DOWFAX X-405, 15.6 g of methyl methacrylate, 21.7 g of styrene, 13.9 g of butyl acrylate, 3.2 g of acrylic acid, 5.2 g of isooctyl acrylate, 15.2 g of 2-hydroxyethyl methacrylate) and an aqueous initiator solution (0.89 g of ammonium persulfate, 10 g of deionized water) are added to the bottom material of the kettle, and the temperature is kept for 30 min. Then the remaining core pre-emulsion is added dropwise over 3 h. After the dropwise addition is completed, the temperature is kept for 1 h. Then the shell layer pre-emulsion (40 g of deionized water, 0.75 g of sodium dodecylbenzenesulfonate, 2.3 g of DOWFAX X-405, 15.6 g of methyl methacrylate, 17.7 g of styrene, 9.9 g of butyl acrylate, 3.2 g of acrylic acid, 5.2 g of isooctyl acrylate, 15.2 g of 2-hydroxyethyl methacrylate) and an aqueous initiator solution (0.6 g of ammonium persulfate, 25 g of deionized water) are added dropwise. The shell layer pre-emulsion and the aqueous initiator solution are added dropwise simultaneously and completed after 3 - 4 h of dropwise addition. Then, stirring is continued at a constant temperature for 15 min. Then, 4 g of EDGMA is slowly added dropwise to the reaction kettle over 10 min. After the dropwise addition is completed, stirring is continued at a constant temperature for 0.5 - 1.5 h. After the above operations are completed, the emulsion is cooled to below 50 °C, and the pH is adjusted to 7.0 - 9.0 with a neutralizing agent, and then filtered through a 200-mesh filter to obtain a hydroxy acrylic emulsion.

[0057] Comparative Example 3

[0058] In a reaction kettle equipped with a stirrer, a condenser and a thermometer, 105 g of deionized water and a mixed emulsifier (1.2 g of sodium dodecylbenzenesulfonate, 3.6 g of DOWFAX X-405) were added to prepare the bottom material of the kettle. When the temperature in the reaction kettle reached about 80 °C, 10% of the core layer pre-emulsion (40 g of deionized water, 0.75 g of sodium dodecylbenzenesulfonate, 2.3 g of DOWFAX X-405, 15.6 g of methyl methacrylate, 21.7 g of styrene, 13.9 g of butyl acrylate, 3.2 g of acrylic acid, 5.2 g of isooctyl acrylate, 15.2 g of 2-hydroxyethyl methacrylate) and an aqueous initiator solution (0.89 g of ammonium persulfate, 10 g of deionized water) were added to the bottom material of the kettle, and the temperature was kept for 30 min. Then the remaining core pre-emulsion was added dropwise over 3 h. After the dropwise addition was completed, the temperature was kept for 1 h. Then the shell layer pre-emulsion (40 g of deionized water, 0.75 g of sodium dodecylbenzenesulfonate, 2.3 g of DOWFAX X-405, 15.6 g of methyl methacrylate, 17.7 g of styrene, 9.9 g of butyl acrylate, 3.2 g of acrylic acid, 5.2 g of isooctyl acrylate, 15.2 g of 2-hydroxyethyl methacrylate) and an aqueous initiator solution (0.6 g of ammonium persulfate, 25 g of deionized water) were added dropwise. The shell layer pre-emulsion and the aqueous initiator solution were added dropwise simultaneously and completed after 3 - 4 h of dropwise addition. Then, stirring was continued at a constant temperature for 15 min. Then, 8 g of EDGMA was slowly added dropwise to the reaction kettle over 10 min. After the dropwise addition was completed, stirring was continued at a constant temperature for 0.5 - 1.5 h. After the above operations were completed, the emulsion was cooled to below 50 °C, and the pH was adjusted to 7.0 - 9.0 with a neutralizing agent and filtered through a 200-mesh filter to obtain a hydroxy acrylic emulsion.

[0059] Example 1

[0060] In a reaction kettle equipped with a stirrer, a condenser and a thermometer, 105 g of deionized water and a mixed emulsifier (1.2 g of sodium dodecylbenzenesulfonate, 3.6 g of DOWFAX X-405) were added to prepare the bottom material of the kettle. When the temperature in the reaction kettle reached about 80 °C, 10% of the core layer pre-emulsion (40 g of deionized water, 0.75 g of sodium dodecylbenzenesulfonate, 2.3 g of DOWFAX X-405, 15.6 g of methyl methacrylate, 21.7 g of styrene, 13.9 g of butyl acrylate, 3.2 g of acrylic acid, 5.2 g of isooctyl acrylate, 15.2 g of 2-hydroxyethyl methacrylate) and an aqueous initiator solution (0.89 g of ammonium persulfate, 10 g of deionized water) were added to the bottom material of the kettle, and it was kept warm for 30 min. Then the remaining core pre-emulsion was added dropwise over 3 h. After the addition was completed, it was kept warm for 1 h. Then the shell layer pre-emulsion (40 g of deionized water, 0.75 g of sodium dodecylbenzenesulfonate, 2.3 g of DOWFAX X-405, 15.6 g of methyl methacrylate, 17.7 g of styrene, 9.9 g of butyl acrylate, 3.2 g of acrylic acid, 5.2 g of isooctyl acrylate, 15.2 g of 2-hydroxyethyl methacrylate) and an aqueous initiator solution (0.6 g of ammonium persulfate, 25 g of deionized water) were added dropwise. The shell layer pre-emulsion and the aqueous initiator solution were added dropwise simultaneously and completed after 3 - 4 h of dropping. Then it was continuously stirred at a constant temperature for 15 min. Then 8 g of EDGMA was slowly added dropwise to the reaction kettle over 10 min. After the addition was completed, it was continuously stirred at a constant temperature for about 1 h. After the above operations were completed, the emulsion was cooled to below 50 °C, and the pH was adjusted to 7.0 - 9.0 with a neutralizing agent and filtered through a 200-mesh filter to obtain a hydroxy acrylic emulsion. 4 g of NMA, a photocuring monomer, and 0.2 g of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, a photoinitiator, were added to the obtained hydroxy acrylic emulsion and stirred evenly to obtain a hydroxy acrylic emulsion with high hardness and high wear resistance.

[0061] Example 2

[0062] In a reaction kettle equipped with a stirrer, a condenser and a thermometer, 105 g of deionized water and a mixed emulsifier (1.2 g of sodium dodecylbenzenesulfonate, 3.6 g of DOWFAX X-405) were added to prepare the bottom material of the kettle. When the temperature in the reaction kettle reached about 80 °C, 10% of the core layer pre-emulsion (40 g of deionized water, 0.75 g of sodium dodecylbenzenesulfonate, 2.3 g of DOWFAX X-405, 15.6 g of methyl methacrylate, 21.7 g of styrene, 13.9 g of butyl acrylate, 3.2 g of acrylic acid, 5.2 g of isooctyl acrylate, 15.2 g of 2-hydroxyethyl methacrylate) and an aqueous initiator solution (0.89 g of ammonium persulfate, 10 g of deionized water) were added to the bottom material of the kettle, and it was kept warm for 30 min. Then the remaining core pre-emulsion was added dropwise over 3 h. After the dropwise addition was completed, it was kept warm for 1 h. Then the shell layer pre-emulsion (40 g of deionized water, 0.75 g of sodium dodecylbenzenesulfonate, 2.3 g of DOWFAX X-405, 15.6 g of methyl methacrylate, 17.7 g of styrene, 9.9 g of butyl acrylate, 3.2 g of acrylic acid, 5.2 g of isooctyl acrylate, 15.2 g of 2-hydroxyethyl methacrylate) and an aqueous initiator solution (0.6 g of ammonium persulfate, 25 g of deionized water) were added dropwise. The shell layer pre-emulsion and the aqueous initiator solution were added dropwise at the same time. After the dropwise addition was completed over 3 - 4 h, stirring was continued at a constant temperature for 15 min. Then 8 g of EDGMA was slowly added dropwise to the reaction kettle over 10 min. After the dropwise addition was completed, stirring was continued at a constant temperature for 0.5 - 1.5 h. After the above operations were completed, the emulsion was cooled to below 50 °C, and the pH was adjusted to 7.0 - 9.0 with a neutralizing agent, and then filtered through a 200-mesh filter to obtain a hydroxy acrylic emulsion. 8.4 g of NMA, a photo-curing monomer, and 0.42 g of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, a photo-initiator, were added to the obtained hydroxy acrylic emulsion and stirred evenly to obtain a hydroxy acrylic emulsion with high hardness and high wear resistance.

[0063] Example 3

[0064] In a reaction kettle equipped with a stirrer, a condenser, and a thermometer, 105 g of deionized water and a mixed emulsifier (1.2 g of sodium dodecylbenzenesulfonate, 3.6 g of DOWFAX X-405) were added to prepare the bottom material of the kettle. When the temperature in the reaction kettle reached about 80 °C, 10% of the core layer pre-emulsion (40 g of deionized water, 0.75 g of sodium dodecylbenzenesulfonate, 2.3 g of DOWFAX X-405, 15.6 g of methyl methacrylate, 21.7 g of styrene, 13.9 g of butyl acrylate, 3.2 g of acrylic acid, 5.2 g of isooctyl acrylate, 15.2 g of 2-hydroxyethyl methacrylate) and an aqueous initiator solution (0.89 g of ammonium persulfate, 10 g of deionized water) were added to the bottom material of the kettle, and it was kept warm for 30 min. Then the remaining core pre-emulsion was added dropwise over 3 h. After the dropwise addition was completed, it was kept warm for 1 h. Then the shell layer pre-emulsion (40 g of deionized water, 0.75 g of sodium dodecylbenzenesulfonate, 2.3 g of DOWFAX X-405, 15.6 g of methyl methacrylate, 17.7 g of styrene, 9.9 g of butyl acrylate, 3.2 g of acrylic acid, 5.2 g of isooctyl acrylate, 15.2 g of 2-hydroxyethyl methacrylate) and an aqueous initiator solution (0.6 g of ammonium persulfate, 25 g of deionized water) were added dropwise. The shell layer pre-emulsion and the aqueous initiator solution were added dropwise simultaneously and completed after 3 - 4 h of dropwise addition. Then it was continuously stirred at a constant temperature for 15 min. Then 8 g of EDGMA was slowly added dropwise to the reaction kettle over 10 min. After the dropwise addition was completed, it was continuously stirred at a constant temperature for 0.5 - 1.5 h. After the above operations were completed, the emulsion was cooled to below 50 °C, and the pH was adjusted to 7.0 - 9.0 with a neutralizing agent and filtered through a 200-mesh filter to obtain a hydroxy acrylic emulsion. 13.2 g of NMA, a photocuring monomer, and 0.66 g of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, a photoinitiator, were added to the obtained hydroxy acrylic emulsion and stirred evenly to obtain a hydroxy acrylic emulsion with high hardness and high wear resistance.

[0065] Table 1

[0066] Comparative Example Addition percentage of NMA based on the total amount of shell monomers Addition amount of EDGMA / g 1 0 0 2 0 4 3 0 8 Example Addition percentage of NMA based on the total amount of shell monomers Addition amount of EDGMA / g 1 5 8 2 10 8 3 15 8

[0067] The shell layer monomers here refer to the reactive monomers used in the shell layer, that is, those substances remaining in the shell layer pre-emulsion except for water and emulsifier (including EDGMA).

[0068] Among them, in Comparative Examples 1 - 3, OH% was 1.5% (based on the monomer mass), and the solid content was 40%.

[0069] Film curing: Comparative Examples 1 - 3 and Examples 1 - 3 were formulated into paints according to Table 2, diluted with water to an appropriate viscosity, and sprayed on clean tinplates. After surface drying at room temperature, they were placed in an 80 °C oven and baked for 2 h to obtain coatings (corresponding to Examples 1 - 3 and Comparative Examples 1 - 3 respectively), and their properties were tested.

[0070] Examples 1 - 3 were evenly coated on clean tinplate using a 30 - μm wire bar, baked at 80 °C for 3 min, and then placed on a conveyor - type UV curing machine. After UV curing with 800 mJ of ultraviolet light, a coating was obtained, and its performance was tested as Examples 4, 5, and 6.

[0071] That is, Examples 1 - 3 and Comparative Examples 1 - 3 used conventional isocyanate curing, and then Examples 4 - 6 were the results of UV curing based on the emulsions in Examples 1 - 3.

[0072] Table 2

[0073]

[0074] The performance of the obtained coating film was tested. The testing methods and standards of the coating film are shown in Table 3, and the measured coating film properties are shown in Table 4.

[0075] Table 3

[0076] Test item Test method Pencil hardness GB / T 6739—2022 Adhesion / level GB / T 9286—2021 Impact resistance (front and back impacts) / (kg·cm) GB / T 1732—2020 Flexibility / mm GB / T 1731—2020 Water resistance / h GB / T 1733—1993 <![CDATA[Acid resistance (10% H2SO4)]]> GB / T 1763-1979 Alkali resistance (10% NaOH) GB / T 1763-1979

[0077] Table 4

[0078]

[0079]

[0080] Based on Comparative Example 1, in Comparative Examples 2 and 3 and Examples 1 - 3, EDGMA was added during the shell polymerization process to modify the polymer shell layer. On the basis of Comparative Example 2, Comparative Example 3 increased the amount of EDGMA in the shell layer. On the basis of Comparative Example 3, Examples 1 - 3 added the photocurable monomer NMA and the photoinitiator 2 - hydroxy - 4'-(2 - hydroxyethoxy)-2 - methylpropiophenone. Examples 4 - 6 were cured by UV curing the emulsions obtained in Examples 1 - 3.

[0081] As can be seen from Table 4, at the same solid content and hydroxyl content, the hardness and water resistance of the paint films prepared from the aqueous hydroxyl acrylate microsphere emulsions in Comparative Examples 2 and 3 as raw materials are higher than those of the paint films prepared from the aqueous hydroxyl acrylate microsphere emulsion in Comparative Example 1. It can be seen that modifying the polymer microsphere shell layer by adding the crosslinking monomer EDGMA is beneficial to improving the hardness and resistance of the paint film, and the hardness and resistance of the paint film corresponding to Comparative Example 3 are higher than those of the paint corresponding to Comparative Example 2, indicating that the increase in the amount of the crosslinking monomer can effectively improve the hardness and resistance of the polymer paint film. Since the photo-curing monomer NMA itself also contains hydroxyl functional groups, the hardness of the corresponding paint films after adding NMA in Examples 1-3 is also slightly improved compared with the paint films in Comparative Examples 2 and 3. However, NMA itself has strong hydrophilicity. Therefore, when the amount of NMA increases significantly and there is no UV curing, the resistance of the paint film decreases slightly. After UV curing, compared with Examples 1-3, the paint film properties in Examples 4-6 are significantly improved in terms of hardness and resistance. It can be seen that adding the photo-curing monomer NMA and the photo-initiator and performing UV curing can further improve the hardness and resistance of the paint film.

[0082] In summary, the present invention synthesizes hydroxyl acrylate emulsion microsphere particles with a core-shell structure by emulsion polymerization. In the shell polymerization, α,β-monoethylenically unsaturated monocarboxylic acids and (meth)acrylic acid hydroxyalkyl esters containing polar groups are introduced, so that a large number of polar groups are enriched on the particle surface. By adding a crosslinking monomer with multiple double bonds, the internal cohesion of the polymer is increased, the end of the shell polymer is provided with carbon-carbon double bonds, and the hardness and resistance of the paint film are improved. During the film-forming curing process, NMA is introduced into the emulsion system as an external crosslinking functional monomer, and a photo-initiator is added. Through UV irradiation, NMA undergoes free radical polymerization to connect the end links of the shell polymer to form a macromolecular chain, and weak interactions are formed with the carboxyl and hydroxyl groups on the surface of the latex particles. By modifying the surface of the latex particles with hydroxyl and carboxyl groups, and simultaneously using UV to trigger the free radical polymerization reaction of NMA in the system, a physical-chemical crosslinking network is constructed in the aqueous hydroxypropyl core-shell emulsion to comprehensively improve the properties of the paint film.

[0083] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a hydroxylated acrylic emulsion with high hardness and high wear resistance, characterized in that: The following steps are involved: S1, adding deionized water and mixed emulsifier into the reaction kettle to obtain kettle bottom material; S2, heating the reactor to 77-82°C, adding the core layer pre-emulsion and the initiator aqueous solution, and keeping the temperature for reaction; S3, continue to drop the shell pre-emulsion and the initiator aqueous solution, and stir at a constant temperature; S4, then add the cross-linking monomer dropwise, and after the addition is complete, continue stirring at a constant temperature; S5, cooling to below 50°C, adjusting the pH to 7-9, filtering, and obtaining a hydroxy acrylic emulsion; S6. Add photocurable monomer and photoinitiator to the obtained hydroxy acrylic emulsion, stir evenly, and obtain a hydroxy acrylic emulsion with high hardness and high wear resistance, which is the target product.

2. The method for preparing a high-hardness and high-wear-resistant hydroxy acrylic emulsion according to claim 1, characterized in that: In S1, the added mass ratio of deionized water and mixed emulsifier is (14-40:1); The mixed emulsifier is composed of an anionic emulsifier and a nonionic emulsifier, and the mass ratio of the anionic emulsifier to the nonionic emulsifier is 1:(1-5), wherein: The anionic emulsifier is selected from at least one of sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium dodecyl diphenyl ether disulfonate, sodium styrene sulfonate or sodium stearate; The nonionic emulsifier is an isomeric alcohol polyoxyethylene ether, and the structural formula is RO-(CH2CH2O) n -H, where R satisfies C m H 2m+1 In the alkyl group of the general formula, m is in the range of 8 to 13, and n is in the range of 3 to 12.

3. The method for preparing a hydroxy acrylic emulsion with high hardness and high wear resistance according to claim 1, characterized in that: In S2, the core layer pre-emulsion is formed by shearing and dispersing the core layer monomer, water, mixed emulsifier, and chain transfer agent, and the added mass ratio of the core layer monomer to water and mixed emulsifier is 32-86:15-50:1; Further, the amount of initiator used in S2 is 50-70% of the total amount of initiators used, and the amount of initiator used in S4 is 30-50% of the total amount of initiators used; In S3, the shell pre-emulsion is formed by shearing and dispersing the shell monomer, water and mixed emulsifier, and the added mass ratio of the core monomer to water and mixed emulsifier is 32-86:15-50:1; The initiator in the initiator aqueous solution in S2 and S3 is sodium persulfate, potassium persulfate or ammonium persulfate.

4. The method for preparing a hydroxy acrylic emulsion with high hardness and high wear resistance according to claim 3, characterized in that: In S2, the core layer monomer is obtained by mixing α,β-monoethylenically unsaturated monocarboxylic acid, ester of α,β-monoethylenically unsaturated monocarboxylic acid, vinyl aromatic compound, and hydroxyalkyl (meth)acrylate in a mass ratio of (1-2): (17.2-27.2): (9-14): (5-30); In S3, the shell monomer is obtained by mixing α,β-monoethylenically unsaturated monocarboxylic acid, ester of α,β-monoethylenically unsaturated monocarboxylic acid, vinyl aromatic compound, and hydroxyalkyl (meth)acrylate in a mass ratio of (2.5-8):(40-75):(5-20):(5-30).

5. The method for preparing a hydroxy acrylic emulsion with high hardness and high wear resistance according to claim 4, characterized in that: The α,β-monoethylenically unsaturated monocarboxylic acid is selected from at least one of acrylic acid, methacrylic acid, ethacrylic acid, acryloxypropionic acid, methacryloyloxypropionic acid, acryloxyacetic acid, and methacryloyloxyacetic acid; The ester of the α,β-monoethylenically unsaturated monocarboxylic acid is selected from at least one of methyl (meth)acrylate, methyl ethylacrylate, ethyl (meth)acrylate, ethyl ethylacrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, tert-butyl ethylacrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, and isooctyl (meth)acrylate; The vinyl aromatic compound is selected from at least one of styrene, 2-methylstyrene, 4-methylstyrene, 2-butylstyrene, 4-butylstyrene or 4-decylstyrene; The (meth) hydroxyalkyl acrylate is selected from at least one of hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate or 6-hydroxyhexyl acrylate; In S2, 8-15 wt% of the core layer pre-emulsion is first added and kept warm together with the initiator aqueous solution for 20-40 minutes, and then the remaining core layer pre-emulsion is added dropwise within 2-4 hours, and the temperature is kept warm for 0.5-1.5 hours; In S3, the shell pre-emulsion and the initiator aqueous solution are added dropwise within 3-4 hours, and then the stirring is continued at a constant temperature for 10-20 minutes; In S4, the constant temperature stirring time is 0.5-1.5h.

6. The method for preparing a hydroxy acrylic emulsion with high hardness and high wear resistance according to claim 1, characterized in that: In S4, the chemical structural formula of the cross-linking monomer is: Wherein, R1 is C, R2, R3, R4, and R5 are independently selected from H, CH3-, m is a natural number.

7. The method for preparing a hydroxy acrylic emulsion with high hardness and high wear resistance according to claim 1, characterized in that: In S6, the structure of the photocurable monomer is: Wherein, R4 is hydrogen or methyl, R5 and R6 are independently selected from 1-8 straight-chain or branched alkanes substituted with H or hydroxyl groups, and R5 and R6 are not hydrogen at the same time; The photoinitiator is selected from at least one of α,α-diethoxyacetophenone, sodium anthraquinone-2-sulfonate, 2-hydroxy-3-(2'-thioxanthoneoxy)-N,N,N-trimethyl-1-propylamine chloride, sodium 2-hydroxy-3-(4-benzoylphenoxy)propanesulfonate, 2-hydroxy-2-methylpropiophenone, and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone.

8. The method for preparing a hydroxy acrylic emulsion with high hardness and high wear resistance according to claim 1, characterized in that: The amount of the photocurable monomer added is 5-20% of the total mass of the hydroxylated acrylic emulsion; The amount of the photoinitiator added is 1.0-10% of the photocurable monomer.

9. A hydroxy acrylic emulsion with high hardness and high wear resistance, which is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the high-hardness and high-wear-resistant hydroxyl acrylic emulsion according to claim 9 in coatings.

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