Core-shell structured polyurethane-acrylate emulsions, their preparation methods and applications

Abstract

This invention belongs to the field of polymer materials technology, specifically relating to a core-shell structured polyurethane-acrylate emulsion, its preparation method, and its applications. This invention introduces double bonds and ketone groups into polyurethane to form a core-shell structure with acrylate as the core and polyurethane as the shell, along with a ketone-hydrazine crosslinking system. The waterborne acrylate dispersion and the waterborne polyurethane dispersion form a double crosslinking through double bonds and ketone-hydrazine crosslinking, achieving a complementary effect and resulting in a waterborne wood coating resin with excellent comprehensive performance. Performance test results show that the core-shell structured polyurethane-acrylate emulsion coating film of this invention has excellent adhesion, gloss, hardness, abrasion resistance, and water resistance, making it suitable as a waterborne wood coating.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a core-shell structured polyurethane-acrylate emulsion, its preparation method, and its application. Background Technology

[0002] With increasing environmental awareness and stricter environmental regulations, water-based wood coatings are gaining more attention and popularity due to their advantages such as being non-toxic, non-flammable, and low-pollution. Water-based polyurethane wood coatings offer advantages such as high gloss, high abrasion resistance, good flexibility, and resistance to bubbles and pinholes. However, they suffer from poor self-thickening properties, low solid content, poor high-temperature resistance, poor water resistance, and higher cost. Acrylic wood coatings, on the other hand, offer advantages such as good weather resistance, resistance to yellowing, high hardness, good gloss, fast drying speed, and low cost. However, they have poor anti-blocking properties, are prone to hot-sticking and cold-brittle phenomena, and have poor film-forming properties with a higher minimum film-forming temperature. This necessitates the addition of film-forming aids, and sometimes plasticizers, to form a continuous and dense film, making it difficult to reduce the VOC content of the system.

[0003] Therefore, it is necessary to leverage the complementary advantages of the two polymers to prepare high-performance waterborne wood coatings. Summary of the Invention

[0004] The first objective of this invention is to provide a method for preparing a core-shell structured polyurethane-acrylate emulsion. The second objective of this invention is to provide the core-shell structured polyurethane-acrylate emulsion obtained by this method. The third objective of this invention is to provide the application of the core-shell structured polyurethane-acrylate emulsion.

[0005] According to a first aspect of the present invention, a method for preparing a core-shell structured polyurethane-acrylate emulsion is provided, comprising the following steps:

[0006] (1) Polycaprolactone diol and isophorone diisocyanate are reacted at 85-95℃ for 2-3h, then 2,2-dimethylolpropionic acid is added and reacted at 70-80℃ for 2-3h, then a catalyst is added and reacted at 75-80℃ for 1-2h, then a small molecule chain extender is added and reacted at 70-80℃ for 2-4h, then a capping agent is added and reacted at 70-80℃ for 3-5h to obtain a polyurethane prepolymer; then a first neutralizing agent is added to the polyurethane prepolymer at 30-50℃ for 10-20min, then an organic solvent and water are added and emulsified and dispersed for 1-2h, and the organic solvent is removed under reduced pressure to obtain a double-bond-capped polyurethane emulsion;

[0007] (2) Take emulsifier, soft monomer, hard monomer, crosslinking monomer, functional monomer containing ketone group and water and pre-emulsify for 10-20 min to obtain pre-emulsion;

[0008] (3) Mix water and buffer, then heat to 60-70℃, add 5wt% of the pre-emulsion prepared in step (2), then add the first initiator, react for 15-20 minutes until a faint blue light appears, and obtain seed emulsion;

[0009] (4) Add 95wt% of the pre-emulsion and the second initiator prepared in step (2) to the seed emulsion prepared in step (3) at 80-85℃ for 2-3 hours; then add the double-bond-terminated polyurethane emulsion and the third initiator prepared in step (1) at 78-88℃ for 1-2 hours. After the reaction is completed, keep warm for 1-2 hours, then cool down to 30-50℃, add the second neutralizing agent, stir evenly, add the auxiliary agent and stir for 10-20 minutes to discharge the material, and obtain the core-shell structure polyurethane-acrylate emulsion.

[0010] In some embodiments, in step (1), the catalyst is dibutyltin dilaurate and / or an organic bismuth catalyst.

[0011] In some embodiments, in step (1), the small molecule chain extender is dihydroxyacetone.

[0012] In some embodiments, in step (1), the capping agent is ethanol and / or 2-hydroxyethyl acrylate.

[0013] In some embodiments, in step (1), the first neutralizing agent is at least one of triethylamine, diethanolamine, and triethanolamine.

[0014] In some embodiments, in step (1), the organic solvent is acetone and / or N-methylpyrrolidone.

[0015] In some embodiments, in step (1), the amounts of each raw material, by mass parts, are as follows: 90-110 parts of polycaprolactone diol, 140-165 parts of isophorone diisocyanate, 10-30 parts of 2,2-dimethylolpropionic acid, 0.5-1.5 parts of catalyst, 2-6 parts of small molecule chain extender, 20-30 parts of end-capping agent, 10-30 parts of first neutralizing agent, 50-200 parts of organic solvent, and 400-500 parts of water.

[0016] In some embodiments, in step (2), the emulsifier is allyloxyisomeric alcohol ether sulfate ammonium salt and / or sodium dodecylbenzene sulfonate. The emulsifier allows components that are immiscible with both monomers and water to be stably dispersed in water by forming latex particles.

[0017] In some embodiments, in step (2), the soft monomer is at least one of ethyl acrylate, n-butyl acrylate, and isooctyl acrylate. The soft monomer has a lower glass transition temperature, which can impart a certain degree of flexibility and elongation to the resin.

[0018] In some embodiments, in step (2), the hard monomer is at least one of methyl methacrylate, styrene, and acrylonitrile. Hard monomers have strong polarity and high glass transition temperature, which can impart high strength, hardness, and solvent resistance to the resin.

[0019] In some embodiments, in step (2), the crosslinking monomer is methacrylic acid. Methacrylic acid can add carboxyl groups to the polymer molecular chain, giving the resin high mechanical properties, stability, and alkali thickening properties.

[0020] In some embodiments, in step (2), the ketone-containing functional monomer is diacetone acrylamide and / or ethyl acetoacetate methacrylate.

[0021] In some embodiments, in step (2), the amounts of each raw material, by mass parts, are as follows: 2-8 parts of emulsifier, 30-80 parts of soft monomer, 150-200 parts of hard monomer, 5-10 parts of crosslinking monomer, 5-15 parts of functional monomer containing ketone group, and 80-100 parts of water.

[0022] In some embodiments, in step (3), the buffer is at least one of disodium hydrogen phosphate, sodium bicarbonate, or potassium hydroxide.

[0023] In some embodiments, in step (3), the first initiator is an aqueous solution of ammonium persulfate prepared by ammonium persulfate and water in a mass ratio of 0.8:10.

[0024] In some embodiments, in step (3), the amount of water is 150-200 parts by mass, the amount of buffer is 0.6-1 parts, the amount of pre-emulsion is 10-22 parts, and the amount of first initiator is 5-15 parts.

[0025] In some embodiments, in step (4), the second initiator is an aqueous solution of ammonium persulfate prepared by ammonium persulfate and water in a mass ratio of 0.9:10.

[0026] In some embodiments, in step (4), the third initiator is an aqueous solution of ammonium persulfate prepared by ammonium persulfate and water in a mass ratio of 0.9:10.

[0027] In some embodiments, in step (4), the second neutralizing agent is ammonia water with a concentration of 18-30 wt%.

[0028] In some embodiments, in step (4), the post-additional agent is at least one of oxalic acid dihydrazide, succinic acid dihydrazide, and hydrazine hydrate.

[0029] In some embodiments, in step (4), by mass parts, the amount of seed emulsion is 180-220 parts, the amount of pre-emulsion is 322-334 parts, the amount of second initiator is 5-15 parts, the amount of double bond-terminated polyurethane emulsion is 380-420 parts, the amount of third initiator is 5-15 parts, the amount of second neutralizer is 4-8 parts, and the amount of post-additional agent is 1-5 parts.

[0030] According to a second aspect of the present invention, a core-shell structured polyurethane-acrylate emulsion prepared by the above-described preparation method is provided.

[0031] According to a third aspect of the present invention, the application of the above-described core-shell structured polyurethane-acrylate emulsion in the preparation of waterborne wood coatings is provided.

[0032] The beneficial effects of this invention include:

[0033] (1) In this invention, double bonds and ketone groups are introduced into polyurethane to form a core-shell structure with acrylate as the core and polyurethane as the shell, and a ketone-hydrazine crosslinking double crosslinking system. The waterborne acrylate dispersion and the waterborne polyurethane dispersion form a double crosslinking through double bonds and ketone-hydrazine crosslinking, achieving a complementary effect, thereby obtaining a waterborne wood coating resin with excellent comprehensive performance.

[0034] (2) In this invention, a core layer polyacrylate emulsion is first synthesized by seed emulsion polymerization, and then a hydroxyl-terminated polyurethane emulsion containing ketone groups is added dropwise to form a core-shell structure with polyacrylate as the core and polyurethane as the shell. The advantage of this structure is that the polyacrylate in the core layer provides weather resistance, and the polyurethane in the shell layer provides high hardness and high gloss.

[0035] (3) In this invention, dihydroxyacetone is introduced into polyurethane as a chain extender, which introduces ketone groups into the polyurethane chain segments. At the same time, functional monomers containing ketone groups, such as diacetone acrylamide, are also added to polyacrylate to introduce ketone groups. After the reaction with the ketone groups of both by post-auxiliaries such as oxalic acid dihydrazide, a cross-linked structure is formed. At the same time, 2-hydroxyethyl acrylate is used to end the polyurethane to introduce double bonds and polymerize with polyacrylate. Thus, polyacrylate and polyurethane can be cross-linked through double bonds and ketone hydrazide. The two cross-linking methods make the structure more compact, thereby improving its toughness, stability and adhesion.

[0036] (4) Performance test results show that the core-shell structure polyurethane-acrylate emulsion coating of the present invention has good adhesion, gloss, hardness, wear resistance and water resistance, and is suitable as a water-based wood coating. Attached Figure Description

[0037] Figure 1 The transmission electron microscopy results are those of the core-shell structured polyurethane-acrylate emulsion in Example 4 of this invention.

[0038] Figure 2 The particle size test results are for the core-shell structured polyurethane-acrylate emulsions of Examples 1-6 of this invention.

[0039] Figure 3 The contact angle test results are for the core-shell structure polyurethane-acrylate emulsions of Examples 1-6 of this invention. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. The materials involved in the following embodiments are all commercially available.

[0041] Example 1

[0042] The preparation method of the core-shell structured polyurethane-acrylate emulsion in this embodiment includes the following steps:

[0043] (1) Under nitrogen protection, 100g of polycaprolactone diol and 161g of isophorone diisocyanate were added to the reactor and pre-reacted at 90℃ for 2h; then 12g of 2,2-dimethylolpropionic acid was added and reacted at 80℃ for 2h, then the temperature was lowered to 78℃, 1.2g of organic bismuth catalyst 2810 was added and reacted at 78℃ for 1h, then 4g of dihydroxyacetone was added and reacted at 75℃ for 2h, then 18g of 2-hydroxyethyl acrylate and 5g of ethanol were added and reacted at 75℃ for 4h to obtain polyurethane prepolymer; then 12g of triethylamine was added to the polyurethane prepolymer at 30℃ for 10min to neutralize, then 80g of acetone and 450g of deionized water were added to emulsify and disperse for 1h, and the acetone was removed under reduced pressure to obtain a polyurethane emulsion with double bond end capping.

[0044] (2) Take 4g of allyl oxyisomeric alcohol ether sulfate ammonium salt, 50g of n-butyl acrylate, 183g of methyl methacrylate, 8g of methacrylic acid, 9g of diacetone acrylamide and 90g of deionized water and pre-emulsify for 15min to obtain a pre-emulsion.

[0045] (3) Add 180g of deionized water and 0.8g of sodium bicarbonate to a three-necked flask, then heat to 70°C, add 5wt% of the pre-emulsion prepared in step (2) to the three-necked flask, and then add an aqueous solution of ammonium persulfate made of 0.8g of ammonium persulfate and 10g of deionized water. React for 15 minutes until a faint blue light appears to obtain the seed emulsion.

[0046] (4) Add 95wt% of the pre-emulsion prepared in step (2) and an aqueous solution of ammonium persulfate consisting of 0.9g ammonium persulfate and 10g deionized water to the seed emulsion prepared in step (3) at a constant rate at 80℃ for 2h. Then add 400g of the double-bond-terminated polyurethane emulsion prepared in step (1) and an aqueous solution of ammonium persulfate consisting of 0.9g ammonium persulfate and 10g deionized water at 86℃ for 1h. After the reaction is completed, keep warm for about 1.5h, then cool down to 50℃, add 4g of ammonia water with a concentration of 25wt%, stir evenly, add 3g of oxalic acid dihydrazide, stir for 10min and discharge to obtain the core-shell structure polyurethane-acrylate emulsion.

[0047] Example 2

[0048] The preparation method of the core-shell structured polyurethane-acrylate emulsion in this embodiment includes the following steps:

[0049] (1) Under nitrogen protection, 100g of polycaprolactone diol and 158g of isophorone diisocyanate were added to the reactor and pre-reacted at 90℃ for 2h; then 15g of 2,2-dimethylolpropionic acid was added and reacted at 80℃ for 2h, then the temperature was lowered to 78℃, 1.1g of organic bismuth catalyst 2810 was added and reacted at 78℃ for 1h, then 4g of dihydroxyacetone was added and reacted at 75℃ for 2h, then 18g of 2-hydroxyethyl acrylate and 5g of ethanol were added and reacted at 75℃ for 4h to obtain polyurethane prepolymer; then 15g of triethylamine was added to the polyurethane prepolymer at 30℃ for 10min to neutralize, then 100g of acetone and 450g of deionized water were added to emulsify and disperse for 1h, and the acetone was removed under reduced pressure to obtain a polyurethane emulsion with double bond end capping.

[0050] (2) Take 4g of allyl oxyisomeric alcohol ether sulfate ammonium salt, 50g of n-butyl acrylate, 183g of methyl methacrylate, 8g of methacrylic acid, 9g of diacetone acrylamide and 90g of deionized water and pre-emulsify for 15min to obtain a pre-emulsion.

[0051] (3) Add 180g of deionized water and 0.8g of sodium bicarbonate to a three-necked flask, then heat to 70°C, add 5wt% of the pre-emulsion prepared in step (2) to the three-necked flask, and then add an aqueous solution of ammonium persulfate made of 0.8g of ammonium persulfate and 10g of deionized water. React for 15 minutes until a faint blue light appears to obtain the seed emulsion.

[0052] (4) Add 95wt% of the pre-emulsion prepared in step (2) and an aqueous solution of ammonium persulfate consisting of 0.9g ammonium persulfate and 10g deionized water to the seed emulsion prepared in step (3) at a constant rate at 80℃ for 2h. Then add 400g of the double-bond-terminated polyurethane emulsion prepared in step (1) and an aqueous solution of ammonium persulfate consisting of 0.9g ammonium persulfate and 10g deionized water at 86℃ for 1h. After the reaction is completed, keep warm for about 1.5h, then cool down to 50℃, add 4g of ammonia water with a concentration of 27wt%, stir evenly, add 3g of oxalic acid dihydrazide, stir for 10min and discharge to obtain a core-shell structured polyurethane-acrylate emulsion.

[0053] Example 3

[0054] The preparation method of the core-shell structured polyurethane-acrylate emulsion in this embodiment includes the following steps:

[0055] (1) Under nitrogen protection, 100g of polycaprolactone diol and 155g of isophorone diisocyanate were added to the reactor and pre-reacted at 90℃ for 2h; then 18g of 2,2-dimethylolpropionic acid was added and reacted at 80℃ for 2h, then the temperature was lowered to 78℃, 1g of organic bismuth catalyst 2810 was added and reacted at 78℃ for 1h, then 4g of dihydroxyacetone was added and reacted at 75℃ for 2h, then 18g of 2-hydroxyethyl acrylate and 5g of ethanol were added and reacted at 75℃ for 4h to obtain polyurethane prepolymer; then 18g of triethylamine was added to the polyurethane prepolymer at 30℃ for 10min to neutralize, then 120g of acetone and 450g of deionized water were added to emulsify and disperse for 1h, and the acetone was removed under reduced pressure to obtain a polyurethane emulsion with double bond end capping.

[0056] (2) Take 4g of allyl oxyisomeric alcohol ether sulfate ammonium salt, 50g of n-butyl acrylate, 183g of methyl methacrylate, 8g of methacrylic acid, 9g of diacetone acrylamide and 90g of deionized water and pre-emulsify for 15min to obtain a pre-emulsion.

[0057] (3) Add 180g of deionized water and 0.8g of sodium bicarbonate to a three-necked flask, then heat to 70°C, add 5wt% of the pre-emulsion prepared in step (2) to the three-necked flask, and then add an aqueous solution of ammonium persulfate made of 0.8g of ammonium persulfate and 10g of deionized water. React for 15 minutes until a faint blue light appears to obtain the seed emulsion.

[0058] (4) Add 95wt% of the pre-emulsion prepared in step (2) and an aqueous solution of ammonium persulfate consisting of 0.9g ammonium persulfate and 10g deionized water to the seed emulsion prepared in step (3) at a constant rate at 80℃ for 2h. Then add 400g of the double-bond-terminated polyurethane emulsion prepared in step (1) and an aqueous solution of ammonium persulfate consisting of 0.9g ammonium persulfate and 10g deionized water at 86℃ for 1h. After the reaction is completed, keep warm for about 1.5h, then cool down to 50℃, add 4g of ammonia water with a concentration of 22wt%, stir evenly, add 3g of oxalic acid dihydrazide, stir for 10min and discharge to obtain a core-shell structured polyurethane-acrylate emulsion.

[0059] Example 4

[0060] The preparation method of the core-shell structured polyurethane-acrylate emulsion in this embodiment includes the following steps:

[0061] (1) Under nitrogen protection, 100g of polycaprolactone diol and 152g of isophorone diisocyanate were added to the reactor and pre-reacted at 90℃ for 2h; then 21g of 2,2-dimethylolpropionic acid was added and reacted at 80℃ for 2h, then the temperature was lowered to 78℃, 0.9g of organic bismuth catalyst 2810 was added and reacted at 78℃ for 1h, then 4g of dihydroxyacetone was added and reacted at 75℃ for 2h, then 18g of 2-hydroxyethyl acrylate and 5g of ethanol were added and reacted at 75℃ for 4h to obtain polyurethane prepolymer; then 21g of triethylamine was added to the polyurethane prepolymer at 30℃ for 10min to neutralize, then 140g of acetone and 450g of deionized water were added to emulsify and disperse for 1h, and the acetone was removed under reduced pressure to obtain a polyurethane emulsion with double bond end capping.

[0062] (2) Take 4g of allyl oxyisomeric alcohol ether sulfate ammonium salt, 50g of n-butyl acrylate, 183g of methyl methacrylate, 8g of methacrylic acid, 9g of diacetone acrylamide and 90g of deionized water and pre-emulsify for 15min to obtain a pre-emulsion.

[0063] (3) Add 180g of deionized water and 0.8g of sodium bicarbonate to a three-necked flask, then heat to 70°C, add 5wt% of the pre-emulsion prepared in step (2) to the three-necked flask, and then add an aqueous solution of ammonium persulfate made of 0.8g of ammonium persulfate and 10g of deionized water. React for 15 minutes until a faint blue light appears to obtain the seed emulsion.

[0064] (4) Add 95wt% of the pre-emulsion prepared in step (2) and an aqueous solution of ammonium persulfate consisting of 0.9g ammonium persulfate and 10g deionized water to the seed emulsion prepared in step (3) at a constant rate at 80℃ for 2h. Then add 400g of the double-bond-terminated polyurethane emulsion prepared in step (1) and an aqueous solution of ammonium persulfate consisting of 0.9g ammonium persulfate and 10g deionized water at 86℃ for 1h. After the reaction is completed, keep warm for about 1.5h, then cool down to 50℃, add 4g of ammonia water with a concentration of 20wt%, stir evenly, add 3g of oxalic acid dihydrazide, stir for 10min and discharge to obtain a core-shell structured polyurethane-acrylate emulsion.

[0065] Example 5

[0066] The preparation method of the core-shell structured polyurethane-acrylate emulsion in this embodiment includes the following steps:

[0067] (1) Under nitrogen protection, 100g of polycaprolactone diol and 149g of isophorone diisocyanate were added to the reactor and pre-reacted at 90℃ for 2h; then 24g of 2,2-dimethylolpropionic acid was added and reacted at 80℃ for 2h, then the temperature was lowered to 78℃, 0.8g of organic bismuth catalyst 2810 was added and reacted at 78℃ for 1h, then 4g of dihydroxyacetone was added and reacted at 70℃ for 2h, then 18g of 2-hydroxyethyl acrylate and 5g of ethanol were added and reacted at 70℃ for 4h to obtain polyurethane prepolymer; then 24g of triethylamine was added to the polyurethane prepolymer at 30℃ for 10min to neutralize, then 160g of acetone and 450g of deionized water were added to emulsify and disperse for 1h, and the acetone was removed under reduced pressure to obtain a polyurethane emulsion with double bond end capping.

[0068] (2) Take 4g of allyl oxyisomeric alcohol ether sulfate ammonium salt, 50g of n-butyl acrylate, 183g of methyl methacrylate, 8g of methacrylic acid, 9g of diacetone acrylamide and 90g of deionized water and pre-emulsify for 15min to obtain a pre-emulsion.

[0069] (3) Add 180g of deionized water and 0.8g of sodium bicarbonate to a three-necked flask, then heat to 70°C, add 5wt% of the pre-emulsion prepared in step (2) to the three-necked flask, and then add an aqueous solution of ammonium persulfate made of 0.8g of ammonium persulfate and 10g of deionized water. React for 15 minutes until a faint blue light appears to obtain the seed emulsion.

[0070] (4) Add 95wt% of the pre-emulsion prepared in step (2) and an aqueous solution of ammonium persulfate consisting of 0.9g ammonium persulfate and 10g deionized water to the seed emulsion prepared in step (3) at a constant rate at 80℃ for 2h. Then add 400g of the double-bond-terminated polyurethane emulsion prepared in step (1) and an aqueous solution of ammonium persulfate consisting of 0.9g ammonium persulfate and 10g deionized water at 86℃ for 1h. After the reaction is completed, keep warm for about 1.5h, then cool down to 50℃, add 4g of ammonia water with a concentration of 30wt%, stir evenly, add 3g of oxalic acid dihydrazide, stir for 10min and discharge to obtain a core-shell structured polyurethane-acrylate emulsion.

[0071] Example 6

[0072] The preparation method of the core-shell structured polyurethane-acrylate emulsion in this embodiment includes the following steps:

[0073] (1) Under nitrogen protection, 100g of polycaprolactone diol and 146g of isophorone diisocyanate were added to the reactor and pre-reacted at 90℃ for 2h; then 27g of 2,2-dimethylolpropionic acid was added and reacted at 80℃ for 2h, then the temperature was lowered to 78℃, 0.7g of organic bismuth catalyst 2810 was added and reacted at 78℃ for 1h, then 4g of dihydroxyacetone was added and reacted at 80℃ for 2h, then 18g of 2-hydroxyethyl acrylate and 5g of ethanol were added and reacted at 80℃ for 4h to obtain polyurethane prepolymer; then 27g of triethylamine was added to the polyurethane prepolymer at 30℃ for 10min to neutralize, then 180g of acetone and 450g of deionized water were added to emulsify and disperse for 1h, and the acetone was removed under reduced pressure to obtain a polyurethane emulsion with double bond end capping.

[0074] (2) Take 4g of allyl oxyisomeric alcohol ether sulfate ammonium salt, 50g of n-butyl acrylate, 183g of methyl methacrylate, 8g of methacrylic acid, 9g of diacetone acrylamide and 90g of deionized water and pre-emulsify for 15min to obtain a pre-emulsion.

[0075] (3) Add 180g of deionized water and 0.8g of sodium bicarbonate to a three-necked flask, then heat to 70°C, add 5wt% of the pre-emulsion prepared in step (2) to the three-necked flask, and then add an aqueous solution of ammonium persulfate made of 0.8g of ammonium persulfate and 10g of deionized water. React for 15 minutes until a faint blue light appears to obtain the seed emulsion.

[0076] (4) Add 95wt% of the pre-emulsion prepared in step (2) and an aqueous solution of ammonium persulfate consisting of 0.9g ammonium persulfate and 10g deionized water to the seed emulsion prepared in step (3) at a constant rate at 80℃ for 2h. Then add 400g of the double-bond-terminated polyurethane emulsion prepared in step (1) and an aqueous solution of ammonium persulfate consisting of 0.9g ammonium persulfate and 10g deionized water at 86℃ for 1h. After the reaction is completed, keep warm for about 1.5h, then cool down to 50℃, add 4g of ammonia water with a concentration of 18wt%, stir evenly, add 3g of oxalic acid dihydrazide, stir for 10min and discharge to obtain the core-shell structure polyurethane-acrylate emulsion.

[0077] The following performance tests were performed on the core-shell structured polyurethane-acrylate emulsions prepared in Examples 1-6.

[0078] 1. Transmission electron microscopy examination

[0079] The core-shell polyurethane-acrylate emulsion prepared in Example 4 was examined using a transmission electron microscope (model: TECNAI12, manufacturer: FEI, Netherlands). The test conditions were as follows: 10 μL of the sample emulsion was added to a copper grid and precipitated for 1 min. After staining with phosphotungstic acid and drying at room temperature of 25°C, it was observed using a transmission electron microscope with a working voltage of 80–120 kV.

[0080] Transmission electron microscopy results are as follows Figure 1 As shown in the figure, the dark part is polyurethane and the light part is polyacrylate. The two are cross-linked through double bonds and ketone hydrazine to form a relatively clear core-shell structure.

[0081] 2. Particle size detection

[0082] The core-shell polyurethane-acrylate emulsions prepared in Examples 1-6 were analyzed by laser diffraction particle size analyzer, and the results are as follows: Figure 2 As shown.

[0083] from Figure 2 It can be seen that the amount of 2,2-dimethylolpropionic acid used in Examples 1-6 gradually increases, while the particle size of the latex particles in the resulting emulsions gradually decreases and the particle size distribution gradually narrows. This is because when the content of 2,2-dimethylolpropionic acid is low, the content of hydrophilic groups in the system is insufficient, which prevents the polyurethane prepolymer from self-dispersing into a stable emulsion. As the content of 2,2-dimethylolpropionic acid increases, the content of hydrophilic groups in the polyurethane molecular chain increases, which can form a stable double-layer structure in the system, thereby reducing the aggregation effect between particles. The polymer backbone can be uniformly dispersed in water, and the number of latex particles increases while the particle size decreases.

[0084] 3. Contact Angle Test

[0085] The contact angle was measured using a DCA20 contact angle measuring instrument. 5 μL of the core-shell polyurethane-acrylate emulsion prepared in Examples 1-6 was drawn off by the sampling knob and dropped onto the paper surface to form droplets. The contact angle of the solid-liquid-gas interface formed by the droplets on the paper surface was measured.

[0086] Figure 3 This refers to the contact angle of the core-shell structured polyurethane-acrylate emulsions prepared in Examples 1-6 on the paper surface. From... Figure 3 As can be seen, the amount of 2,2-dimethylolpropionic acid used in Examples 1-6 gradually increased, while the water contact angle of the resulting emulsion decreased from 98.32° to 80.12°. This is because 2,2-dimethylolpropionic acid is distributed on the periphery of the polyurethane, making it easier for the hydrophilic groups on the polyurethane molecular chain to bind water molecules, resulting in a decrease in the water contact angle.

[0087] Then, the core-shell structured polyurethane-acrylate emulsions obtained in Examples 1-6 were used to prepare wood coatings.

[0088] In the following application examples, the defoamer used is: silicone defoamer BYK028 (BYK);

[0089] The leveling agent used was: Acrysol SCT-275 (Rohm & Hass);

[0090] The wetting agent used is: WET500 (Tego);

[0091] The film-forming aids used are DPM and DPnB (Dow Chemical), which are mixed at a mass ratio of 1:1.

[0092] The thickener used is a polyurethane associative thickener (King Industry).

[0093] The neutralizing agent used was AMP-95 (Dow Chemical).

[0094] The preservative used is BIT 20 (Clariant).

[0095] Application Example 1

[0096] A water-based wood coating is prepared from the following components: 85g of the core-shell structure polyurethane-acrylate emulsion of Example 1, 1g of defoamer, 0.2g of leveling agent, 0.2g of wetting agent, 6g of film-forming aid, 0.4g of thickener, 0.2g of neutralizer, 0.1g of preservative, and 6.9g of water.

[0097] Its preparation method includes the following steps:

[0098] Neutralizer, defoamer, wetting agent, and leveling agent were added sequentially to a core-shell polyurethane-acrylate emulsion at room temperature and stirred for 30 minutes. Then, film-forming aid and water were mixed evenly and added, and stirred for 10 minutes. Finally, thickener and preservative were added sequentially and stirred for 30 minutes to obtain water-based wood coating.

[0099] Application Example 2

[0100] A water-based wood coating is prepared from the following components: 85g of the core-shell structure polyurethane-acrylate emulsion of Example 2, 1g of defoamer, 0.2g of leveling agent, 0.2g of wetting agent, 6g of film-forming aid, 0.4g of thickener, 0.2g of neutralizer, 0.1g of preservative, and 6.9g of water.

[0101] Its preparation method is the same as that of Application Example 1.

[0102] Application Example 3

[0103] A water-based wood coating is prepared from the following components: 85g of the core-shell structure polyurethane-acrylate emulsion of Example 3, 1g of defoamer, 0.2g of leveling agent, 0.2g of wetting agent, 6g of film-forming aid, 0.4g of thickener, 0.2g of neutralizer, 0.1g of preservative, and 6.9g of water.

[0104] Its preparation method is the same as that of Application Example 1.

[0105] Application Example 4

[0106] A water-based wood coating is prepared from the following components: 85g of the core-shell structure polyurethane-acrylate emulsion of Example 4, 1g of defoamer, 0.2g of leveling agent, 0.2g of wetting agent, 6g of film-forming aid, 0.4g of thickener, 0.2g of neutralizer, 0.1g of preservative, and 6.9g of water.

[0107] Its preparation method is the same as that of Application Example 1.

[0108] Application Example 5

[0109] A water-based wood coating is prepared from the following components: 85g of the core-shell structure polyurethane-acrylate emulsion of Example 5, 1g of defoamer, 0.2g of leveling agent, 0.2g of wetting agent, 6g of film-forming aid, 0.4g of thickener, 0.2g of neutralizer, 0.1g of preservative, and 6.9g of water.

[0110] Its preparation method is the same as that of Application Example 1.

[0111] Application Example 6

[0112] A water-based wood coating is prepared from the following components: 85g of the core-shell structure polyurethane-acrylate emulsion of Example 6, 1g of defoamer, 0.2g of leveling agent, 0.2g of wetting agent, 6g of film-forming aid, 0.4g of thickener, 0.2g of neutralizer, 0.1g of preservative, and 6.9g of water.

[0113] Its preparation method is the same as that of Application Example 1.

[0114] To verify the performance of the water-based wood coating of the present invention, the water-based wood coatings prepared in Application Examples 1-6 were subjected to comprehensive tests on adhesion, gloss, hardness, abrasion resistance, and water resistance.

[0115] 1. Testing Method

[0116] (1) Coating adhesion test: The adhesion was determined according to GB / T 9286-1998 "Cross-cut test for paint and varnish film". Grade 0: The cut edges are completely smooth, with no cells peeling off; Grade 1: A small amount of coating peels off at the intersection of the cuts, but the cross-cut area is not more than 5% affected; Grade 2: Coating peels off at the intersection of the cuts and / or along the cut edges, with the affected cross-cut area significantly greater than 5%, but not significantly greater than 15%; Grade 3: The coating peels off in large fragments along the cut edges, and / or partially or completely peels off at different parts of the cells, with the affected cross-cut area significantly greater than 15%, but not significantly greater than 35%; Grade 4: The coating peels off in large fragments along the cut edges, and / or some cells partially or completely peel off, with the affected cross-cut area significantly greater than 35%, but not significantly greater than 65%; Grade 5: The degree of peeling is significantly greater than 65%.

[0117] (2) Gloss test: The gloss was measured according to GB / T23999-2009 "Water-based Wood Coatings for Interior Decoration and Renovation". High gloss paint: gloss level above 75. Matte paint: gloss level between 50 and 75. Semi-gloss paint: gloss level between 10 and 50. Matte paint: gloss level below 10.

[0118] (3) Coating hardness test: The hardness of the coating film was determined according to GB / T 6739-2006 "Determination of Hardness of Paint and Varnish Film by Pencil Method". The hardness of the pencil from low to high is: 6B, 5B, 4B, 3B, 2B, B, HB, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, 9H.

[0119] (4) Coating abrasion resistance test: determined according to QB / T 2309-2010 "Eraser".

[0120] (5) Water immersion resistance test of coating: Immerse 1 / 2 of the coated wood block in water and leave the other half for comparison. After a certain period of time, take out the coating sample and observe the tested paint film with the naked eye to see if bubbling, whitening or peeling occurs.

[0121] 2. Test Results

[0122] The performance test results of water-based wood coatings are shown in Table 1.

[0123] Table 1 Performance test results of water-based wood coatings

[0124]

[0125]

[0126] As can be seen from Table 1, the amount of 2,2-dimethylolpropionic acid used in Examples 1-6 gradually increased. With the increase of the hydrophilic chain extender 2,2-dimethylolpropionic acid, the molecular weight of polyurethane increased, and the adhesion of the resulting wood coating also gradually increased. At the same time, due to the interaction between the -COOH on 2,2-dimethylolpropionic acid and the -OH contained in the wood, the adhesion was further improved. The increase of 2,2-dimethylolpropionic acid reduced the particle size, thereby improving the gloss of the wood coating. However, as the molecular weight further increased, the molecular chains became entangled, resulting in insufficient molecular arrangement after drying, causing the gloss to first increase and then decrease. 2,2-Dimethylolpropionic acid (2,2-DMA) is a component of the hard segment in polyurethane. The more 2,2-DMA added, the more hard segments there are, resulting in greater hardness of the wood coating. Simultaneously, as the amount of 2,2-DMA increases, the molecular weight increases, leading to increased abrasion resistance in the wood coating. Initially, due to the low amount of 2,2-DMA added and its small molecular weight, the adhesion of the wood coating decreased after soaking in water, resulting in slight bubbling on the surface. As the amount of 2,2-DMA added increased, the bubbling disappeared. However, further increasing the amount of 2,2-DMA led to increased hydrophilic groups (-COOH), causing the coating to easily absorb water and swell after soaking, resulting in surface whitening.

[0127] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. Process for the preparation of core-shell polyurethane-acrylate emulsions, characterized in that, The method comprises the following steps: (1) reacting polycaprolactone diol and isophorone diisocyanate at 85-95 DEG C for 2-3 h, then adding 2,2-dimethylol propionic acid and reacting at 70-80 DEG C for 2-3 h, then adding a catalyst and reacting at 75-80 DEG C for 1-2 h, then adding a small molecule chain extender and reacting at 70-80 DEG C for 2-4 h, then adding an end-capping agent and reacting at 70-80 DEG C for 3-5 h to obtain a polyurethane prepolymer; then adding a first neutralizing agent to the polyurethane prepolymer at 30-50 DEG C for 10-20 min, then adding an organic solvent and water and emulsifying and dispersing for 1-2 h, and then removing the organic solvent under reduced pressure to obtain a double bond end-capped polyurethane emulsion; the amounts of the raw materials are as follows: polycaprolactone diol 90-110 parts, isophorone diisocyanate 140-165 parts, 2,2-dimethylol propionic acid 18-21 parts, catalyst 0.5-1.5 parts, small molecule chain extender 2-6 parts, end-capping agent 20-30 parts, first neutralizing agent 10-30 parts, organic solvent 50-200 parts, and water 400-500 parts, all by mass fraction; the small molecule chain extender is dihydroxyacetone; and the first neutralizing agent is triethylamine; (2) pre-emulsifying an emulsifier, a soft monomer, a hard monomer, a crosslinking monomer, a functional monomer containing a ketone group, and water for 10-20 min to obtain a pre-emulsion; the amounts of the raw materials are as follows: emulsifier 2-8 parts, soft monomer 30-80 parts, hard monomer 150-200 parts, crosslinking monomer 5-10 parts, functional monomer containing a ketone group 5-15 parts, and water 80-100 parts, all by mass fraction; (3) mixing water and a buffer agent, then heating to 60-70 DEG C, then adding 5 wt% of the pre-emulsion prepared in step (2), then adding a first initiator, and then reacting for 15-20 min until a weak blue light appears to obtain a seed emulsion; the amounts of the raw materials are as follows: water 150-200 parts, buffer agent 0.6-1 part, pre-emulsion 10-22 parts, and first initiator 5-15 parts, all by mass fraction; (4) adding 95 wt% of the pre-emulsion prepared in step (2) and a second initiator to the seed emulsion prepared in step (3) at 80-85 DEG C and reacting for 2-3 h, then adding the double bond end-capped polyurethane emulsion prepared in step (1) and a third initiator at 78-88 DEG C and reacting for 1-2 h, then keeping warm for 1-2 h after the reaction, then cooling to 30-50 DEG C, then adding a second neutralizing agent, then stirring uniformly, then adding a post-addition agent and stirring for 10-20 min to discharge to obtain a core-shell structure polyurethane-acrylate emulsion; the amounts of the raw materials are as follows: seed emulsion 180-220 parts, pre-emulsion 322-334 parts, second initiator 5-15 parts, double bond end-capped polyurethane emulsion 380-420 parts, third initiator 5-15 parts, second neutralizing agent 4-8 parts, and post-addition agent 1-5 parts, all by mass fraction.

2. The process for preparing core-shell structured polyurethane-acrylate emulsion according to claim 1, characterized in that, In step (1), the catalyst is dibutyltin dilaurate and / or an organic bismuth catalyst. The end-capping agent is ethanol and / or 2-hydroxyethyl acrylate; The organic solvent is acetone and / or N-methyl pyrrolidone.

3. The process for the preparation of core-shell polyurethane-acrylate emulsions according to claim 1 or 2, characterized in that, In step (2), the emulsifier is allyloxy isomeric alcohol ether sulfate amine salt and / or sodium dodecyl benzene sulfonate; The soft monomer is at least one of ethyl acrylate, n-butyl acrylate, and isooctyl acrylate; The hard monomer is at least one of methyl methacrylate, styrene, and acrylonitrile; The crosslinking monomer is methacrylic acid; The functional monomer containing ketone group is diketone acrylamide and / or acetyl acetic acid methyl methacrylate.

4. The method for preparing a core-shell structured polyurethane-acrylate emulsion according to claim 1 or 2, characterized in that, In step (3), the buffer is at least one of disodium hydrogen phosphate, sodium bicarbonate, or potassium hydroxide; The first initiator is an aqueous solution of ammonium persulfate prepared by ammonium persulfate and water in a mass ratio of 0.8:

10.

5. The method for preparing a core-shell structured polyurethane-acrylate emulsion according to claim 1 or 2, characterized in that, In step (4), the second initiator is an aqueous solution of ammonium persulfate prepared by ammonium persulfate and water in a mass ratio of 0.9:10; The third initiator is an aqueous solution of ammonium persulfate prepared by ammonium persulfate and water in a mass ratio of 0.9:10; The second neutralizing agent is ammonia water with a concentration of 18-30 wt%; The post-aiding agent is at least one of oxalic acid dihydrazide, oxalic acid dihydrazide, succinic acid dihydrazide, and hydrazine hydrate.

6. The core-shell structured polyurethane-acrylate emulsion prepared by the preparation method of any one of claims 1-5.

7. The use of the core-shell structured polyurethane-acrylate emulsion of claim 6 in the preparation of water-based wood paint.

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