Core-shell structure polyurethane-acrylate emulsion as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to a polyurethane-acrylate emulsion with a core-shell structure as well as a preparation method and application of the polyurethane-acrylate emulsion. Double bonds and keto groups are introduced into polyurethane to form a core-shell structure with acrylate as a core and polyurethane as a shell and a keto-hydrazine crosslinking double-crosslinking system with acrylate as a core and polyurethane as a shell, and a water-based acrylate dispersion and a water-based polyurethane dispersion form double crosslinking through double bonds and keto-hydrazine crosslinking, so that the effect of complementary advantages is achieved; therefore, the water-borne wood paint resin with excellent comprehensive performance is obtained. Performance test results show that the polyurethane-acrylate emulsion film with the core-shell structure has good adhesive force, glossiness, hardness, wear resistance and water resistance, and is suitable for being used as water-borne wood paint.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and in particular relates to a core-shell structure polyurethane-acrylate emulsion and a preparation method and application thereof. Background Art

[0002] With the increasing awareness of environmental protection and the increasingly stringent environmental regulations, water-based wood paint has attracted more and more attention and favor due to its advantages such as non-toxicity, non-flammability and low pollution. Water-based polyurethane wood paint has the advantages of high gloss, high wear resistance, good flexibility, and not easy to produce bubbles and shrinkage holes, but it has poor self-thickening, low solid content, poor high temperature resistance, poor water resistance and high cost; while acrylic wood paint has good weather resistance, not easy to yellow, high hardness, good gloss, fast drying speed and low cost, but its anti-adhesion is poor, it is easy to be hot and sticky, and its film-forming property is poor, and the minimum film-forming temperature is high. It is necessary to add a certain amount of film-forming aids, and sometimes plasticizers, to form a continuous and dense coating film, which makes it difficult to reduce the VOC of the system.

[0003] Therefore, it is necessary to complement the advantages of the above two polymers according to their characteristics in order to prepare water-based wood coatings with excellent performance. Summary of the invention

[0004] The first object of the present invention is to provide a method for preparing a core-shell structured polyurethane-acrylate emulsion, the second object of the present invention is to provide a core-shell structured polyurethane-acrylate emulsion prepared by the preparation method, and the third object of the present invention is to provide an application of the core-shell structured polyurethane-acrylate emulsion.

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

[0006] (1) reacting polycaprolactone diol and isophorone diisocyanate at 85-95° C. for 2-3 hours, then adding 2,2-dimethylol propionic acid and reacting at 70-80° C. for 2-3 hours, then adding a catalyst and reacting at 75-80° C. for 1-2 hours, then adding a small molecule chain extender and reacting at 70-80° C. for 2-4 hours, then adding a capping agent and reacting at 70-80° C. for 3-5 hours to obtain a polyurethane prepolymer; then adding a first neutralizing agent to the polyurethane prepolymer at 30-50° C. for neutralization for 10-20 minutes, then adding an organic solvent and water for emulsification and dispersion for 1-2 hours, and removing the organic solvent under reduced pressure to obtain a double-bond-terminated polyurethane emulsion;

[0007] (2) taking an emulsifier, a soft monomer, a hard monomer, a cross-linking monomer, a ketone-containing functional monomer and water and pre-emulsifying them for 10-20 minutes to obtain a pre-emulsion;

[0008] (3) mixing water and a buffer, and then heating the mixture to 60-70° C., adding 5 wt % of the pre-emulsion prepared in step (2), and then adding a first initiator, and reacting for 15-20 min until a faint blue light appears, thereby obtaining a seed emulsion;

[0009] (4) adding 95 wt % of the pre-emulsion and the second initiator obtained in step (2) to the seed emulsion obtained in step (3) at 80-85° C. for 2-3 h; then adding the double-bond terminated polyurethane emulsion and the third initiator obtained in step (1) at 78-88° C. for 1-2 h. After the reaction is completed, the mixture is kept warm for 1-2 h, then cooled to 30-50° C., and then the second neutralizer is added. After stirring evenly, a post-additive is added and stirred for 10-20 min to obtain a 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 end-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 the raw materials used, by weight, are: 90-110 parts of polycaprolactone diol, 140-165 parts of isophorone diisocyanate, 10-30 parts of 2,2-dihydroxymethylpropionic 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 allyloxy isomeric alcohol ether sulfate ammonium salt and / or sodium dodecylbenzene sulfonate. The emulsifier can stably disperse the immiscible components of monomer and water 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 and can give the resin a certain degree of flexibility and extensibility.

[0018] In some embodiments, in step (2), the hard monomer is at least one of methyl methacrylate, styrene, and acrylonitrile. The hard monomer has a strong polarity and a high glass transition temperature, and can give the resin high strength, hardness, and solvent resistance.

[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 group-containing functional monomer is diacetone acrylamide and / or ethyl acetoacetate methacrylate.

[0021] In some embodiments, in step (2), the amounts of the raw materials used, by weight, are: 2-8 parts of emulsifier, 30-80 parts of soft monomer, 150-200 parts of hard monomer, 5-10 parts of cross-linking monomer, 5-15 parts of ketone-containing functional monomer, 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 from ammonium persulfate and water in a mass ratio of 0.8:10.

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

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

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

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

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

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

[0032] The beneficial effects of the present invention include:

[0033] (1) The present 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, as well as a ketone-hydrazine crosslinking double crosslinking system. The water-based acrylate dispersion and the water-based polyurethane dispersion are double crosslinked through double bonds and ketone-hydrazine crosslinking to achieve the effect of complementary advantages, thereby obtaining a water-based wood paint resin with excellent comprehensive performance.

[0034] (2) The present invention first synthesizes a core-layer polyacrylate emulsion by seed emulsion polymerization, and then drops a prepared hydroxyl-terminated ketone-containing polyurethane emulsion 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 can provide weather resistance, and the polyurethane in the shell layer can provide high hardness and high gloss.

[0035] (3) The present invention introduces dihydroxyacetone as a chain extender into the polyurethane to introduce ketone groups into the polyurethane chain segments. At the same time, a ketone group-containing functional monomer such as diacetone acrylamide is added into the polyacrylate to introduce ketone groups. A post-additive such as oxalic acid dihydrazide reacts with the ketone groups of the two to form a cross-linked structure. At the same time, the polyurethane is capped with 2-hydroxyethyl acrylic acid to introduce double bonds to polymerize with the polyacrylate. In this way, the polyacrylate and the polyurethane can be cross-linked through the double bonds and ketone hydrazide. The two cross-linking methods make the structure more compact, thereby improving its tolerance, 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 paint. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the transmission electron microscopy test result of the core-shell structure polyurethane-acrylate emulsion of Example 4 of the present invention.

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

[0039] Figure 3 These are the contact angle test results of the core-shell structured polyurethane-acrylate emulsions of Examples 1-6 of the present invention. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below in conjunction with specific examples, but the embodiments of the present invention are not limited thereto. The materials involved in the following examples can all be obtained from commercial channels.

[0041] Example 1

[0042] The preparation method of the core-shell structure polyurethane-acrylate emulsion of this embodiment comprises the following steps:

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

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

[0045] (3) 180 g of deionized water and 0.8 g of sodium bicarbonate were added to a three-necked flask, and then the temperature was raised to 70° C., 5 wt % of the pre-emulsion prepared in step (2) was added to the three-necked flask, and then an ammonium persulfate aqueous solution prepared by 0.8 g of ammonium persulfate and 10 g of deionized water was added, and the mixture was reacted for 15 min until a faint blue light appeared, thereby obtaining a seed emulsion.

[0046] (4) adding 95 wt % of the pre-emulsion prepared in step (2) and an aqueous solution of ammonium persulfate consisting of 0.9 g of ammonium persulfate and 10 g of deionized water to the seed emulsion prepared in step (3) at a constant rate at 80° C. for reaction, and the adding time is 2 h; then adding 400 g of the double-bond terminated polyurethane emulsion prepared in step (1) and an aqueous solution of ammonium persulfate consisting of 0.9 g of ammonium persulfate and 10 g of deionized water at 86° C. for reaction time of 1 h, keeping the temperature for about 1.5 h after the reaction is completed, then cooling to 50° C., adding 4 g of 25 wt % ammonia water, stirring evenly, and then adding 3 g of oxalic acid dihydrazide and stirring for 10 min to obtain a core-shell structure polyurethane-acrylate emulsion.

[0047] Example 2

[0048] The preparation method of the core-shell structure polyurethane-acrylate emulsion of this embodiment comprises the following steps:

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

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

[0051] (3) 180 g of deionized water and 0.8 g of sodium bicarbonate were added to a three-necked flask, and then the temperature was raised to 70° C., 5 wt % of the pre-emulsion prepared in step (2) was added to the three-necked flask, and then an ammonium persulfate aqueous solution prepared by 0.8 g of ammonium persulfate and 10 g of deionized water was added, and the mixture was reacted for 15 min until a faint blue light appeared, thereby obtaining a seed emulsion.

[0052] (4) adding 95 wt % of the pre-emulsion prepared in step (2) and an aqueous solution of ammonium persulfate consisting of 0.9 g of ammonium persulfate and 10 g of deionized water to the seed emulsion prepared in step (3) at a constant rate at 80° C. for reaction, and the adding time is 2 h; then adding 400 g of the double-bond terminated polyurethane emulsion prepared in step (1) and an aqueous solution of ammonium persulfate consisting of 0.9 g of ammonium persulfate and 10 g of deionized water at 86° C. for reaction time of 1 h. After the reaction is completed, the mixture is kept warm for about 1.5 h, then cooled to 50° C., 4 g of 27 wt % ammonia water is added, stirred evenly, and then 3 g of oxalic acid dihydrazide is added and stirred for 10 min to obtain a core-shell structure polyurethane-acrylate emulsion.

[0053] Example 3

[0054] The preparation method of the core-shell structure polyurethane-acrylate emulsion of this embodiment comprises the following steps:

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

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

[0057] (3) 180 g of deionized water and 0.8 g of sodium bicarbonate were added to a three-necked flask, and then the temperature was raised to 70° C., 5 wt % of the pre-emulsion prepared in step (2) was added to the three-necked flask, and then an ammonium persulfate aqueous solution prepared by 0.8 g of ammonium persulfate and 10 g of deionized water was added, and the mixture was reacted for 15 min until a faint blue light appeared, thereby obtaining a seed emulsion.

[0058] (4) adding 95 wt % of the pre-emulsion prepared in step (2) and an aqueous solution of ammonium persulfate consisting of 0.9 g of ammonium persulfate and 10 g of deionized water to the seed emulsion prepared in step (3) at 80° C. at a constant rate for 2 h; then adding 400 g of the double-bond terminated polyurethane emulsion prepared in step (1) and an aqueous solution of ammonium persulfate consisting of 0.9 g of ammonium persulfate and 10 g of deionized water at 86° C. for 1 h. After the reaction is completed, the mixture is kept warm for about 1.5 h, then cooled to 50° C., 4 g of 22 wt % ammonia water is added, stirred evenly, and then 3 g of oxalic acid dihydrazide is added and stirred for 10 min to obtain a core-shell structure polyurethane-acrylate emulsion.

[0059] Example 4

[0060] The preparation method of the core-shell structure polyurethane-acrylate emulsion of this embodiment comprises the following steps:

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

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

[0063] (3) 180 g of deionized water and 0.8 g of sodium bicarbonate were added to a three-necked flask, and then the temperature was raised to 70° C., 5 wt % of the pre-emulsion prepared in step (2) was added to the three-necked flask, and then an ammonium persulfate aqueous solution prepared by 0.8 g of ammonium persulfate and 10 g of deionized water was added, and the mixture was reacted for 15 min until a faint blue light appeared, thereby obtaining a seed emulsion.

[0064] (4) adding 95 wt % of the pre-emulsion prepared in step (2) and an aqueous solution of ammonium persulfate consisting of 0.9 g of ammonium persulfate and 10 g of deionized water to the seed emulsion prepared in step (3) at a constant rate at 80° C. for reaction, and the adding time is 2 h; then adding 400 g of the double-bond terminated polyurethane emulsion prepared in step (1) and an aqueous solution of ammonium persulfate consisting of 0.9 g of ammonium persulfate and 10 g of deionized water at 86° C. for reaction time of 1 h. After the reaction is completed, the mixture is kept warm for about 1.5 h, then cooled to 50° C., 4 g of 20 wt % ammonia water is added, stirred evenly, and then 3 g of oxalic acid dihydrazide is added and stirred for 10 min to obtain a core-shell structure polyurethane-acrylate emulsion.

[0065] Example 5

[0066] The preparation method of the core-shell structure polyurethane-acrylate emulsion of this embodiment comprises the following steps:

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

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

[0069] (3) 180 g of deionized water and 0.8 g of sodium bicarbonate were added to a three-necked flask, and then the temperature was raised to 70° C., 5 wt % of the pre-emulsion prepared in step (2) was added to the three-necked flask, and then an ammonium persulfate aqueous solution prepared by 0.8 g of ammonium persulfate and 10 g of deionized water was added, and the mixture was reacted for 15 min until a faint blue light appeared, thereby obtaining a seed emulsion.

[0070] (4) adding 95 wt % of the pre-emulsion prepared in step (2) and an aqueous solution of ammonium persulfate consisting of 0.9 g of ammonium persulfate and 10 g of deionized water to the seed emulsion prepared in step (3) at a constant rate at 80° C. for reaction, and the adding time is 2 h; then adding 400 g of the double-bond terminated polyurethane emulsion prepared in step (1) and an aqueous solution of ammonium persulfate consisting of 0.9 g of ammonium persulfate and 10 g of deionized water at 86° C. for reaction time of 1 h. After the reaction is completed, the mixture is kept warm for about 1.5 h, then cooled to 50° C., 4 g of 30 wt % ammonia water is added, stirred evenly, and then 3 g of oxalic acid dihydrazide is added and stirred for 10 min to obtain a core-shell structure polyurethane-acrylate emulsion.

[0071] Example 6

[0072] The preparation method of the core-shell structure polyurethane-acrylate emulsion of this embodiment comprises the following steps:

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

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

[0075] (3) 180 g of deionized water and 0.8 g of sodium bicarbonate were added to a three-necked flask, and then the temperature was raised to 70° C., 5 wt % of the pre-emulsion prepared in step (2) was added to the three-necked flask, and then an ammonium persulfate aqueous solution prepared by 0.8 g of ammonium persulfate and 10 g of deionized water was added, and the mixture was reacted for 15 min until a faint blue light appeared, thereby obtaining a seed emulsion.

[0076] (4) adding 95 wt % of the pre-emulsion prepared in step (2) and an aqueous solution of ammonium persulfate consisting of 0.9 g of ammonium persulfate and 10 g of deionized water to the seed emulsion prepared in step (3) at 80° C. at a constant rate for 2 h; then adding 400 g of the double-bond terminated polyurethane emulsion prepared in step (1) and an aqueous solution of ammonium persulfate consisting of 0.9 g of ammonium persulfate and 10 g of deionized water at 86° C. for 1 h. After the reaction is completed, the mixture is kept warm for about 1.5 h, then cooled to 50° C., 4 g of 18 wt % ammonia water is added, stirred evenly, and then 3 g of oxalic acid dihydrazide is added and stirred for 10 min to obtain a core-shell structure polyurethane-acrylate emulsion.

[0077] Next, the core-shell structure polyurethane-acrylate emulsions prepared in Examples 1-6 were subjected to the following performance tests.

[0078] 1. Transmission electron microscopy

[0079] The core-shell polyurethane-acrylate emulsion prepared in Example 4 was tested using a transmission electron microscope (model: TECNAI12, manufacturer: FEI, the Netherlands). The test conditions were: 10 μL of the sample emulsion was dropped onto a copper mesh and precipitated for 1 min, stained with phosphotungstic acid, dried at room temperature of 25°C, and observed using a transmission electron microscope with an operating voltage of 80 to 120 kV.

[0080] The 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, and 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 emulsion prepared in Examples 1-6 was tested by a laser diffraction particle size analyzer. The test results are as follows: Figure 2 shown.

[0083] from Figure 2 It can be seen that the amount of 2,2-dimethylolpropionic acid used in Examples 1-6 is gradually increased, while the particle size of the latex particles of the obtained emulsion is gradually reduced, and the particle size distribution is gradually narrowed. This is because when the content of 2,2-dimethylolpropionic acid is small, the content of hydrophilic groups in the system is insufficient, so that the polyurethane prepolymer cannot be self-dispersed into a stable emulsion; as the content of 2,2-dimethylolpropionic acid increases, the content of hydrophilic groups in the polyurethane molecular chain increases, and a stable double electric layer structure can be formed in the system, resulting in a reduction in the agglomeration effect between particles, the main chain of the polymer can be evenly dispersed in water, and the number of latex particles increases and the particle size becomes smaller.

[0084] 3. Contact angle test

[0085] The contact angle was measured by using a DCA20 contact angle meter, where 5 μL of the core-shell polyurethane-acrylate emulsion prepared in Examples 1-6 were extracted through a sampling knob and dropped onto the surface of paper to form liquid drops, and the contact angle of the solid-liquid-gas triple interface formed by the liquid drops on the surface of paper was measured.

[0086] Figure 3 is the contact angle of the core-shell polyurethane-acrylate emulsion prepared in Examples 1-6 on the paper surface. Figure 3 It can be seen that the amount of 2,2-dimethylolpropionic acid used in Examples 1-6 is gradually increased, and the water contact angle of the resulting emulsion decreases from 98.32° to 80.12°. This is because 2,2-dimethylolpropionic acid is distributed on the periphery of the polyurethane, making it easy 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 polyurethane-acrylate emulsions prepared in Examples 1-6 were used to prepare wood coatings.

[0088] In the following application examples, the defoaming agents used are: silicone defoaming agent BYK028 (BYK);

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

[0090] The wetting agents used are: WET500 (Tego);

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

[0092] The thickeners used were: polyurethane associative thickener (King Industry);

[0093] The neutralizing agents used were: AMP-95 (Dow Chemical);

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

[0095] Application Example 1

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

[0097] The preparation method thereof comprises the following steps:

[0098] At room temperature, add neutralizer, defoamer, wetting agent and leveling agent to core-shell polyurethane-acrylate emulsion in sequence and stir for 30 minutes; then mix film-forming aid and water evenly and add and stir for 10 minutes; finally, add thickener and preservative in sequence and stir for 30 minutes to prepare water-based wood paint.

[0099] Application Example 2

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

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

[0102] Application Example 3

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

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

[0105] Application Example 4

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

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

[0108] Application Example 5

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

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

[0111] Application Example 6

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

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

[0114] In order to verify the performance of the water-based wood paint of the present invention, comprehensive tests such as adhesion, glossiness, hardness, wear resistance, and water resistance were performed on the water-based wood paints prepared in Application Examples 1-6.

[0115] 1. Test methods

[0116] (1) Coating adhesion test: Determined in accordance with GB / T 9286-1998 "Cross-cut test for paint and varnish". Grade 0: The cut edge is completely smooth, and no square falls off; Grade 1: A small amount of coating falls off at the intersection of the cuts, but the affected cross-cut area is no more than 5%; Grade 2: The coating falls off at the intersection of the cuts and / or along the cut edges, and the affected cross-cut area is significantly greater than 5%, but not significantly greater than 15%; Grade 3: The coating falls off partially or completely in large pieces along the cut edge, and / or partially or completely peels off at different parts of the grid, and the affected cross-cut area is significantly greater than 15%, but not significantly greater than 35%; Grade 4: The coating falls off in large pieces along the cut edge, and / or some squares fall off partially or completely, and the affected cross-cut area is 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: Tested in accordance with GB_T23999-2009 "Water-based Wood Coatings for Interior Decoration and Renovation". High gloss paint: gloss above 75. Flat paint: gloss between 50-75. Semi-gloss paint: gloss between 10-50. Matt paint: gloss below 10.

[0118] (3) Film hardness test: The test is carried out in accordance with GB / T 6739-2006 "Determination of film hardness of paints and varnishes by pencil method". The hardness of the pencils from low to high is: 6B, 5B, 4B, 3B, 2B, B, HB, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, 9H.

[0119] (4) Coating wear resistance test: measured in accordance with QB / T 2309-2010 "Eraser".

[0120] (5) Test of coating resistance to water immersion: immerse 1 / 2 of the coated wood block in water and keep the other half for comparison. After a certain period of time, take out the coated sample and observe the tested paint film with the naked eye to see if there is bubbling, whitening or falling off.

[0121] 2. Test results

[0122] The performance test results of water-based wood paint 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 is gradually increased. With the increase of the hydrophilic chain extender 2,2-dimethylolpropionic acid, the molecular weight of the polyurethane increases, and the adhesion of the obtained wood coating gradually increases. At the same time, due to the interaction between the -COOH on the 2,2-dimethylolpropionic acid and the -OH contained in the wood, the adhesion is further improved; the increase of 2,2-dimethylolpropionic acid reduces the particle size and improves the gloss of the wood coating, but as the molecular weight further increases, the molecular chains are entangled with each other, resulting in the molecules after drying. The arrangement is not tight enough, causing the gloss to rise first and then fall; 2,2-Dimethylolpropionic acid belongs to the hard segment part of polyurethane. The more 2,2-dimethylolpropionic acid there is, the more hard segments there are and the harder the resulting wood paint is. At the same time, as the amount of 2,2-dimethylolpropionic acid increases, the molecular weight increases and the wear resistance of the resulting wood paint increases. Initially, due to the small amount of 2,2-dimethylolpropionic acid added and the small molecular weight, the adhesion of the resulting wood paint decreased after soaking in water and slight bubbling on the surface. As the amount of 2,2-dimethylolpropionic acid added increased, the bubbling phenomenon disappeared. However, after further increasing the amount of 2,2-dimethylolpropionic acid, due to the increase in the hydrophilic group -COOH, it is easy to absorb water and swell after soaking in water, so the surface becomes white.

[0127] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for preparing a core-shell structured polyurethane-acrylate emulsion, characterized in that: The following steps are involved: (1) reacting polycaprolactone diol and isophorone diisocyanate at 85° C.-95° C. for 2-3 hours, then adding 2,2-dimethylol propionic acid and reacting at 70-80° C. for 2-3 hours, then adding a catalyst and reacting at 75-80° C. for 1-2 hours, then adding a small molecule chain extender and reacting at 70-80° C. for 2-4 hours, then adding a capping agent and reacting at 70-80° C. for 3-5 hours to obtain a polyurethane prepolymer; then adding a first neutralizing agent to the polyurethane prepolymer at 30-50° C. for neutralization for 10-20 minutes, then adding an organic solvent and water for emulsification and dispersion for 1-2 hours, and removing the organic solvent under reduced pressure to obtain a double-bond-terminated polyurethane emulsion; (2) taking an emulsifier, a soft monomer, a hard monomer, a cross-linking monomer, a ketone-containing functional monomer and water and pre-emulsifying them for 10-20 minutes to obtain a pre-emulsion; (3) mixing water and a buffer, and then heating the mixture to 60-70° C., adding 5 wt % of the pre-emulsion prepared in step (2), and then adding a first initiator, and reacting for 15-20 min until a faint blue light appears, thereby obtaining a seed emulsion; (4) adding 95 wt % of the pre-emulsion and the second initiator obtained in step (2) to the seed emulsion obtained in step (3) at 80-85° C. for 2-3 h; then adding the double-bond terminated polyurethane emulsion and the third initiator obtained in step (1) at 78-88° C. for 1-2 h. After the reaction is completed, the mixture is kept warm for 1-2 h, then cooled to 30-50° C., and then the second neutralizer is added. After stirring evenly, a post-additive is added and stirred for 10-20 min to obtain a core-shell structure polyurethane-acrylate emulsion.

2. The method for preparing the core-shell structure 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 small molecule chain extender is dihydroxyacetone; The end-capping agent is ethanol and / or 2-hydroxyethyl acrylate; The first neutralizing agent is at least one of triethylamine, diethanolamine, and triethanolamine; The organic solvent is acetone and / or N-methylpyrrolidone.

3. The method for preparing the core-shell structure polyurethane-acrylate emulsion according to claim 1 or 2, characterized in that: In step (1), the amounts of the raw materials used are, by weight, 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 a catalyst, 2-6 parts of a small molecule chain extender, 20-30 parts of a capping agent, 10-30 parts of a first neutralizing agent, 50-200 parts of an organic solvent, and 400-500 parts of water.

4. The method for preparing the core-shell structure polyurethane-acrylate emulsion according to claim 1 or 2, characterized in that: In step (2), the emulsifier is allyloxy isomeric alcohol ether sulfate ammonium salt and / or sodium dodecylbenzene 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 cross-linking monomer is methacrylic acid; The ketone group-containing functional monomer is diacetone acrylamide and / or ethyl acetoacetate methacrylate.

5. The method for preparing the core-shell structure polyurethane-acrylate emulsion according to claim 1 or 2, characterized in that: In step (2), the amounts of the raw materials used are, by weight, 2-8 parts of emulsifier, 30-80 parts of soft monomer, 150-200 parts of hard monomer, 5-10 parts of cross-linking monomer, 5-15 parts of ketone-containing functional monomer, and 80-100 parts of water.

6. The method for preparing the core-shell structure 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 from ammonium persulfate and water in a mass ratio of 0.8:10; In parts by mass, the amount of water used is 150-200 parts, the amount of buffer used is 0.6-1 part, the amount of pre-emulsion used is 10-22 parts, and the amount of the first initiator used is 5-15 parts.

7. The method for preparing the core-shell structure 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 from ammonium persulfate and water in a mass ratio of 0.9:10; The third initiator is an aqueous solution of ammonium persulfate prepared from ammonium persulfate and water in a mass ratio of 0.9:10; The second neutralizing agent is aqueous ammonia with a concentration of 18-30wt%; The post-additive is at least one of oxalic acid dihydrazide, oxalic acid dihydrazide, succinic acid dihydrazide and hydrazine hydrate.

8. The method for preparing the core-shell structure polyurethane-acrylate emulsion according to claim 1 or 2, characterized in that: In step (4), by weight, the amount of seed emulsion is 180-220 parts, the amount of pre-emulsion is 322-334 parts, the amount of the second initiator is 5-15 parts, the amount of double-bond terminated polyurethane emulsion is 380-420 parts, the amount of the third initiator is 5-15 parts, the amount of the second neutralizer is 4-8 parts, and the amount of the post-additive is 1-5 parts.

9. The core-shell structure polyurethane-acrylate emulsion prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the core-shell structure polyurethane-acrylate emulsion according to claim 9 in the preparation of water-based wood paint.

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