Hydroxyl acrylic emulsion with core-shell structure, rheology control agent containing hydroxyl acrylic emulsion as well as preparation method and application of hydroxyl acrylic emulsion

Abstract

The invention provides a hydroxy acrylic emulsion with a core-shell structure, a rheology control agent containing the hydroxy acrylic emulsion as well as a preparation method and application of the hydroxy acrylic emulsion. The hydroxy acrylic emulsion is prepared by carrying out reverse emulsion polymerization on a monomer composition A used for forming an emulsion particle shell layer and a monomer composition B used for forming an emulsion particle core layer under the action of an initiator and an emulsifier. The rheology control agent for the automobile refinishing paint is also prepared by utilizing the prepared hydroxyl acrylic emulsion, and the acrylic emulsion added with the polymerizable emulsifier is matched with the clay stabilizer to generate a synergistic interaction effect, so that more excellent rheology control capability can be provided for the rheology control agent; and the high heat storage stability is provided, and the 1-2-year room temperature stable storage requirement of the automobile refinishing paint is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of coatings, and specifically includes a hydroxyl acrylic emulsion with a core-shell structure, a rheology control agent containing the same, a preparation method and an application thereof. Background Art

[0002] With the continuous growth of the resident car ownership in recent years, the demand for automotive refinish coatings has gradually increased. Since there are a large number of plastic parts and electronic components in the cars to be repaired, there are many risks in directly using the high-temperature baking method adopted by OEM (original factory paint) for repair. Therefore, developing a waterborne automotive refinish coating that can dry at room temperature has broad prospects. In order to cope with the increasing variety of automotive colors, the automotive refinish industry usually adopts the method of mixing on demand to obtain automotive refinish coatings of different colors, that is, mixing the color paint containing colorants with the main paint containing film-forming resin, and then adding a diluent and a rheology control agent for mixing. The automotive refinish industry only needs to pre-store various series of color paints, main paints, diluents and rheology control agents. Different from the original factory automotive paint, due to the uncertainty of the repair business itself, these pre-stored raw materials usually need to have a shelf life of up to 1-2 years, which also poses challenges to the formulation design of the refinish coating.

[0003] Among the components of the refinish coating formulation, the rheology control agent has the most stringent requirements for stability. This is because in order to ensure the spraying construction effect during the repair of the automotive color paint layer, such as no sagging, uniform coating thickness, good aluminum powder orientation, etc., it is necessary to introduce a rheology control agent with excellent rheology control performance. Adding inorganic clay and / or organic wax emulsion to the rheology control agent has become an essential component for improving the rheological properties of automotive refinish coatings. However, both inorganic clay and organic wax emulsion will have an adverse impact on the long-term storage stability of the rheology control agent, causing problems such as an increase in fineness and viscosity thickening. Coupled with the relatively high cost of organic wax emulsion, there are still many problems in actual use. More critically, considering that the rheology control agent is only one component in the refinish coating, in order to ensure the content ratio of inorganic clay and organic wax emulsion in the refinish coating, the content of inorganic clay and organic wax emulsion in the rheology control agent is usually even higher, which will pose a greater challenge to the stability of the rheology control agent.

[0004] US 6,451,896E1 reported the composition of an aqueous automotive refinish paint, which is divided into three parts: Composition B containing colorants, Composition A containing film-forming substances, and rheology control agent C. The rheology control agent is an aqueous solution of plate-like silicate clay. By introducing a certain amount of polyurethane solution into the rheology control agent, its stability has been significantly improved, and the shelf life of the final product can reach about 6 months. However, in fact, the market's requirement for refinish paint is to have a shelf life of 1 - 2 years, so there is still a certain difference. Another common method is to reduce the introduction amount of inorganic clay and organic wax emulsion in the rheology control agent to reduce the adverse effects brought to the rheology control agent, and the rheology of the refinish paint is improved by introducing other components, but the effect is not ideal either. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the first object of the present invention is to provide a hydroxy acrylic emulsion with a core-shell structure. By developing a high-performance hydroxy acrylic emulsion that can be used in the rheology control agent, the rheology control performance and long-term storage stability of the rheology control agent can be improved.

[0006] The second object of the present invention is to provide a preparation method for the above-mentioned hydroxy acrylic emulsion.

[0007] The third object of the present invention is to provide a rheology control agent for automotive refinish paint containing the above-mentioned components.

[0008] The fourth object of the present invention is to provide a preparation method for the above-mentioned rheology control agent.

[0009] For the convenience of writing, in the technical solution of the present invention, the (meth)acrylate monomers containing hydroxyl groups represent acrylate monomers containing hydroxyl groups and / or methacrylate monomers containing hydroxyl groups, the (meth)acrylate monomers containing multiple unsaturated vinyl groups represent acrylate monomers containing multiple unsaturated vinyl groups and / or methacrylate monomers containing multiple unsaturated vinyl groups, and the (meth)acrylic monomers containing carboxyl groups represent acrylic monomers containing carboxyl groups and / or methacrylic monomers containing carboxyl groups.

[0010] To achieve the above first object, the technical solution adopted by the present invention includes:

[0011] The present invention discloses a hydroxy acrylic emulsion with a core-shell structure, which is obtained by inverse emulsion polymerization of the following monomer composition A for forming the shell layer of emulsion particles and monomer composition B for forming the core layer of emulsion particles under the action of an initiator and an emulsifier;

[0012] Among them, the monomer composition A is composed of the following raw materials as polymerization units:

[0013] 0.5 - 7 wt% of hydroxy group-containing (meth)acrylate monomers;

[0014] 0.5 - 5 wt% of (meth)acrylate monomers containing multiple unsaturated vinyl groups;

[0015] 0.2 - 7 wt% of carboxyl group-containing (meth)acrylic monomers;

[0016] 90 - 98 wt% of other polymerizable monomers;

[0017] The monomer composition B consists of the following raw materials as polymerization units:

[0018] 0 - 5 wt% of hydroxy group-containing (meth)acrylate monomers;

[0019] 1 - 5 wt% of (meth)acrylate monomers containing multiple unsaturated vinyl groups;

[0020] 0 - 5 wt% of carboxyl group-containing (meth)acrylic monomers;

[0021] 90 - 99 wt% of other polymerizable monomers;

[0022] The hydroxy acrylic emulsion contains 0.25 - 6 wt% of special monomers as polymerization units based on the total amount of monomers;

[0023] The structural general formula of the special monomer is shown as Formula I below:

[0024]

[0025] The R 1 and R 2 each independently selected from C1 - C6 alkyl groups, and the total number of carbon atoms of the R 1 and R 2 is 7;

[0026] The R 3 is selected from any one of H and C1 - C6 alkyl groups.

[0027] Furthermore, the emulsifier is selected from polymerizable emulsifiers, and the mass of the active ingredient in the emulsifier is 0.5 - 3 wt% of the total amount of monomers.

[0028] Further, the emulsifier is selected from one or more of REASOAP SR-1025 (active ingredient content is 25 wt%), REASOAP SR-20 (active ingredient content is 100 wt%), REASOAP SR-30 (active ingredient content is 25 wt%), REASOAP ER-10 (active ingredient content is 100 wt%), REASOAP ER-20 (active ingredient content is 75 wt%), REASOAP ER-30 (active ingredient content is 65 wt%), REASOAP ER-40 (active ingredient content is 60 wt%), HITENOL AR-10 (active ingredient content is 97 wt%), HITENOL AR-20 (active ingredient content is 97 wt%), and REACTSURF 2490 (active ingredient content is 25 wt%).

[0029] Further, the special monomer is selected from one or more compounds having the following structures:

[0030]

[0031] The R 1 and R 2 each independently selected from C1-C6 alkyl groups, and the total number of carbon atoms of the R 1 and R 2 is 7.

[0032] Further, the (meth)acrylate monomer containing multiple unsaturated vinyl groups is selected from one or more of ethylene glycol diacrylate, ethylene glycol dimethacrylate, allyl methacrylate, polyethylene glycol acrylate, polyethylene glycol methacrylate, butanediol acrylate, butanediol methacrylate, 1,6-hexanediol acrylate, 1,6-hexanediol methacrylate, glycerol diacrylate, glycerol dimethacrylate, and trimethylolpropane methacrylate.

[0033] Further, the solid content of the hydroxyacrylate emulsion is 20 - 55%, the acid value is 5 - 50 mg KOH / g, the hydroxyl value is 1 - 30 mg KOH / g, the particle size is 120 - 180 nm, the pH value is 7.5 - 8.5, and the viscosity is 10 - 200 cp / 23°C.

[0034] To achieve the above second object, the technical solution adopted by the present invention includes:

[0035] The present invention discloses a preparation method of the hydroxyacrylate emulsion as described above, comprising the following steps:

[0036] Add water and an emulsifier into a first reactor, and then add monomer composition A to obtain a shell pre-emulsion;

[0037] Water and an emulsifier are added into the second reactor, and then monomer composition B is added to obtain a core layer pre-emulsion.

[0038] Water and an emulsifier are added into the third reactor, and the temperature is raised to 75 - 85 °C. 5 - 10 wt% of the shell layer pre-emulsion and an initiator solution are added successively. After stirring for 20 - 30 min, the remaining shell layer pre-emulsion is added. After addition, the mixture is kept warm for reaction for 0.5 - 2 h. After the heat preservation ends, the core layer pre-emulsion and the initiator solution are added successively. After addition, the mixture is kept warm for reaction for 0.5 - 2 h. After cooling, the pH is adjusted to the target value to obtain the product.

[0039] Furthermore, the time required for adding the remaining shell layer pre-emulsion is 1 - 6 h; the time required for adding the core layer pre-emulsion is 1 - 6 h.

[0040] To achieve the above third object, the technical solution adopted by the present invention includes:

[0041] The present invention discloses a rheology control agent for automotive refinish paints. By weight, the rheology control agent contains 10 - 45 parts of the hydroxy acrylic emulsion as described above;

[0042] The rheology control agent further contains

[0043] 0 - 30 parts of an aqueous polymer dispersion;

[0044] 0.2 - 3 parts of a rheology aid;

[0045] 0.05 - 0.3 parts of a clay stabilizer;

[0046] 0.1 - 3 parts of other additives;

[0047] 50 - 65 parts of water;

[0048] 0.5 - 8 parts of an organic solvent.

[0049] Furthermore, the clay stabilizer is selected from one or more of phosphate ester compounds, pyrophosphates, polyphosphates, metaphosphates, metal salt complexes, homopolymers of polyols, and copolymers of polyols.

[0050] Furthermore, the clay stabilizer is selected from pyrophosphates.

[0051] Furthermore, the rheology aid is selected from one or more of inorganic clays and / or organically modified clays.

[0052] Furthermore, the inorganic clay is selected from one or more of bentonite, montmorillonite, and silicates; the organically modified clay is selected from organically modified bentonite and / or organically modified silicates;

[0053] Furthermore, the rheology additive is selected from one or more of the BYK Laponite series, Optigel series, and Elementis BENTONE.

[0054] To achieve the above fourth object, the technical solution adopted by the present invention includes:

[0055] The present invention discloses a preparation method of the rheology control agent as described above, including the following steps:

[0056] Under high-speed stirring, the hydroxy acrylic emulsion, the aqueous polymer dispersion, and a part of water are mixed, then an organic solvent and other additives are added. After mixing evenly, a clay dispersion obtained by premixing with a rheology additive, a clay stabilizer, and the remaining part of water is added to obtain the product.

[0057] Advantages of the present invention:

[0058] First of all, the present invention prepares a hydroxy acrylic emulsion with a core-shell structure. By introducing special monomers into the hydroxy acrylic emulsion formulation, its film-forming property, water resistance, and salt spray resistance can be improved to a certain extent. At the same time, the polymerizable emulsifier plays an important role in the subsequent preparation of the rheology control agent.

[0059] Secondly, the present invention also prepares a rheology control agent using the self-made hydroxy acrylic emulsion as a raw material. By introducing rheology additives such as inorganic clay and / or organically modified clay into the formulation, its rheology control performance can be significantly improved. Then, a clay stabilizer such as pyrophosphate is added to improve the adverse effect of the rheology additive on the stability of the rheology control agent. It is found through experiments that the polymerizable emulsifier in the hydroxy acrylic emulsion and the clay stabilizer in the rheology control agent produce a synergistic effect, which can not only significantly improve the stability of the rheology control agent to meet the requirement of 1-2 years of room temperature stable storage for each raw material component of the automotive refinish paint, but also improve the rheology recovery ability of the rheology control agent to the main paint, thereby improving the sagging performance of the paint and enhancing the orientation of the effect pigment. Specific Embodiments

[0060] To illustrate the present invention more clearly, the present invention will be further described below in conjunction with preferred embodiments. It should be clear that the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0061] In the case of clarifying and explaining the object of the present invention through the following embodiments, the components of the composition are explained with weight parts as the general standard. Without special instructions, for the sake of simplicity, the "parts" described in the embodiments of the present invention have the same meaning as weight parts.

[0062] The first aspect of the present invention provides a hydroxyl acrylic emulsion with a core-shell structure, aiming to prepare a rheology control agent with good rheology control performance and good stability by using the self-made hydroxyl acrylic emulsion. The hydroxyl acrylic emulsion is obtained by inverse emulsion polymerization of the following monomer composition A for forming the shell layer of emulsion particles and monomer composition B for forming the core layer of emulsion particles under the action of an initiator and an emulsifier;

[0063] Wherein, the monomer composition A consists of the following raw materials as polymerization units:

[0064] Hydroxyl-containing (meth)acrylate monomer 0.5-7 wt%;

[0065] (Meth)acrylate monomer containing multiple unsaturated vinyl groups 0.5-5 wt%;

[0066] Carboxyl-containing (meth)acrylic monomer 0.2-7 wt%;

[0067] Other polymerization monomers 90-98 wt%;

[0068] The monomer composition B consists of the following raw materials as polymerization units:

[0069] Hydroxyl-containing (meth)acrylate monomer 0-5 wt%;

[0070] (Meth)acrylate monomer containing multiple unsaturated vinyl groups 1-5 wt%;

[0071] Carboxyl-containing (meth)acrylic monomer 0-5 wt%;

[0072] Other polymerization monomers 90-99 wt%.

[0073] Exemplarily, the hydroxyl-containing (meth)acrylate monomer at least includes a special monomer with the structure of formula I, and one or more of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, and hydroxybutyl methacrylate can also be added according to application needs.

[0074] Exemplarily, the general structural formula of the special monomer is shown as formula I below:

[0075]

[0076] The R 1 and R 2 each independently selected from C1-C6 alkyl groups, and the total number of carbon atoms of the R 1 and R 2 is 7;

[0077] The R3 Any one selected from H and C1-C6 alkyl.

[0078] Exemplarily, the special monomer is selected from one or more compounds having the following structures:

[0079]

[0080] The R 1 and R 2 are each independently selected from C1-C6 alkyl, and the total number of carbon atoms of the R 1 and R 2 is 7.

[0081] The two special monomers M1 and M2 provided by the present invention can be prepared by self-synthesis. The preparation process is to prepare by ring-opening of a carboxyl-containing monomer and glycidyl versatate. The carboxyl-containing monomer here is preferably methacrylic acid and acrylic acid.

[0082] In a specific embodiment, the preparation process of the special monomer is as follows:

[0083] Add 228.37 parts by mass of glycidyl versatate Hansencardura TM E10P (epoxy content 4100-4250 mmol / kg, viscosity at 25 °C is 7.13 mPa·s), 72.06 parts by mass of acrylic acid or 86.09 parts by mass of methacrylic acid, and 0.3 parts by mass of p-hydroxyanisole into the reaction vessel. After mixing evenly, carry out ring-opening reaction at 110 °C. When the acid value of the test sample < 2 mgKOH / g, the reaction is completed to obtain the special monomer. The acid value is tested according to GB / T 2895-2008.

[0084] From a structural point of view, a modified glycidyl versatate structure is introduced at one end of the special monomer. Since the versatic acid structure has extremely strong hydrophobicity and a low Tg, the polymer containing versatic acid improves the film-forming property, water resistance and salt spray resistance to a certain extent.

[0085] Furthermore, the hydroxy acrylic emulsion contains 0.25-6 wt% of the special monomer as a polymerization unit based on the total amount of monomers. This limitation is the content range of the special monomer contained in the monomer composition A and the monomer composition B in total.

[0086] Furthermore, the (meth)acrylate monomer containing multiple unsaturated vinyl groups is a crosslinking agent containing 2-6 unsaturated vinyl groups; exemplarily, it can be one or more of ethylene glycol diacrylate, ethylene glycol dimethacrylate, allyl methacrylate, polyethylene glycol acrylate, polyethylene glycol methacrylate, butanediol acrylate, butanediol methacrylate, 1,6-hexanediol acrylate, 1,6-hexanediol methacrylate, glycerol diacrylate, glycerol dimethacrylate, and trimethylolpropane trimethacrylate.

[0087] More preferably, the monomer composition A contains 0.7-3 wt% of the (meth)acrylate monomer containing multiple unsaturated vinyl groups; the monomer composition B contains 1-3 wt% of the (meth)acrylate monomer containing multiple unsaturated vinyl groups.

[0088] Exemplarily, the carboxyl group-containing (meth)acrylic monomer is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid, preferably acrylic acid and / or methacrylic acid.

[0089] Furthermore, the other polymerization monomers are selected from acrylate monomers and / or vinyl monomers other than those defined by the above groups. The acrylate monomers are selected from one or more of methyl acrylate, methyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, isooctyl acrylate, isooctyl methacrylate, dodecyl acrylate, dodecyl methacrylate, coconut oil acrylate, coconut oil methacrylate, octadecyl acrylate, octadecyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, dimethylaminopropyl acrylate, dimethylaminopropyl methacrylate, glycidyl acrylate, glycidyl methacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, propylene glycol diacrylate, propylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, polypropylene glycol dimethacrylate, trimethylolpropane triacrylate, and trimethylolpropane trimethacrylate; the vinyl monomers are selected from one or more of vinyl acetate, dichloroethylene, styrene, acrylonitrile, acrylamide, methacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, and divinylbenzene.

[0090] Further, the emulsifier is selected from polymerizable emulsifiers. Exemplarily, it can be REASOAP SR-1025 (active ingredient content is 25 wt%), REASOAP SR-20 (active ingredient content is 100 wt%), REASOAP SR-30 (active ingredient content is 25 wt%), REASOAP ER-10 (active ingredient content is 100 wt%), REASOAP ER-20 (active ingredient content is 75 wt%), REASOAP ER-30 (active ingredient content is 65 wt%), REASOAP ER-40 (active ingredient content is 60 wt%), HITENOL AR-10 (active ingredient content is 97 wt%), HITENOL AR-20 (active ingredient content is 97 wt%), REACTSURF 2490 (active ingredient content is 25 wt%), etc. Since the active ingredient contents in commercially available emulsifiers vary greatly, considering that the active ingredient in the emulsifier is responsible for the emulsifying function, it is advisable to control the mass of the active ingredient in the emulsifier to be 0.5 - 3 wt% of the total monomer amount.

[0091] Further, the initiator includes but is not limited to inorganic thermal initiators (such as sodium persulfate, ammonium persulfate, potassium persulfate), organic thermal initiators (such as peroxyacyl initiators like benzoyl peroxide, alkyl peroxides like tert-butyl hydroperoxide, cumene hydroperoxide, peroxyester initiators like tert-butyl peroxybenzoate); preferably, the addition amount of the initiator is 0.1 - 5 wt% of the total monomer amount.

[0092] Further, the solid content of the hydroxy acrylic emulsion is 20 - 55%, preferably 35 - 50%, the acid value is 5 - 50 mgKOH / g, the hydroxyl value is 1 - 30 mg KOH / g, the particle size is 120 - 180 nm, the pH value is 7.5 - 8.5, and the viscosity is 10 - 200 cp (rotary viscometer at 50 rpm / 23 °C).

[0093] The second aspect of the present invention provides a preparation method for the hydroxy acrylic emulsion as described above, comprising the following steps:

[0094] Add part of the water and the emulsifier into the first reactor, and then add the monomer composition A to obtain a shell layer pre-emulsion;

[0095] Add part of the water and the emulsifier into the second reactor, and then add the monomer composition B to obtain a core layer pre-emulsion;

[0096] Water and an emulsifier are added into the third reactor, and the temperature is raised to 75 - 85°C under nitrogen protection. 5 - 10 wt% of the shell pre - emulsion and the initiator solution are added in sequence. After stirring for 20 - 30 min, the remaining shell pre - emulsion is added, and after addition, the mixture is kept warm for reaction for 0.5 - 2 h; after the heat preservation ends, the pH of the system is adjusted to 5.5 - 7, then the core pre - emulsion and the initiator solution are added in sequence, and after addition, the mixture is kept warm for reaction for 0.5 - 2 h; after cooling, a neutralizing agent is added to adjust the pH to the target value, and a bactericide is added to obtain the product.

[0097] Furthermore, the time required for adding the remaining shell pre - emulsion is 1 - 6 h, preferably 2 - 4 h; the time required for adding the core pre - emulsion is 1 - 6 h, preferably 2 - 4 h.

[0098] Furthermore, the target value of the pH is 7.5 - 8.5.

[0099] Furthermore, the neutralizing agent is selected from one or more of ammonia water, triethylamine, triethanolamine, dimethylethanolamine, 2 - methyl - 2 - aminopropanol, dimethylisopropanolamine, methyldiethanolamine, ethyldiisopropylamine, diethylethanolamine.

[0100] Furthermore, the bactericide is selected from ACTICIDE MBS, ACTICIDE B20, NIPACIDE B20, NIPACIDE CI15, VINKOCIDE CMI, VINKOCIDE KT, etc.

[0101] The third aspect of the present invention provides a rheology control agent for automotive refinish paints. Through a large number of experiments, it is found that using a self - made hydroxy - acrylic emulsion as the raw material, in combination with rheology aids such as inorganic clay and / or organically modified clay, and clay stabilizers such as pyrophosphates, the obtained rheology control agent can not only have more excellent rheology control ability but also have high thermal storage stability (equivalent to stable storage at room temperature for more than 1 year), thus meeting the application requirements.

[0102] By weight, the rheology control agent contains

[0103] 10 - 45 parts of hydroxy - acrylic emulsion;

[0104] 0 - 30 parts of aqueous polymer dispersion;

[0105] 0.2 - 3 parts of rheology aid;

[0106] 0.05 - 0.3 parts of clay stabilizer;

[0107] 0.1 - 3 parts of other aids;

[0108] 50 - 65 parts of water;

[0109] 0.5 - 8 parts of organic solvent.

[0110] Furthermore, the hydroxy acrylic emulsion required for preparing the rheology control agent is prepared by a reverse emulsion polymerization technique based on the formulation of the first aspect of the present invention; preferably, the rheology control agent contains 15-35 parts of hydroxy acrylic emulsion.

[0111] Furthermore, the aqueous polymer dispersion is selected from one or more of a polyurethane dispersion, a polyester dispersion, and an acrylic dispersion; the polyurethane dispersion has a molecular weight of 1000-50000 g / mol, an acid value of 10-100 mg KOH / g, and a hydroxyl value of 0-400 mg KOH / g, and can be Bayhydrol UH2110, Bayhydrol U 2757, Bayhydrol UH240, etc.; preferably, the rheology control agent contains 0-20 parts of the aqueous polymer dispersion.

[0112] Furthermore, the rheology aid is selected from one or more inorganic clays and / or organically modified clays, which are mainly used to provide the rheology control ability of the rheology control agent. The inorganic clays include, but are not limited to, one or more of natural bentonite, montmorillonite, natural flaky silicate, and synthetic flaky silicate, and the organically modified clays include, but are not limited to, organically modified bentonite and / or organically modified silicate, all of which are directly purchased from suppliers, such as BYK Laponite series products (BYK Laponite RD, etc.), Optigel series products (Optigel CG, etc.), Heiminshi BENTONE (BENTONE EW-NA, etc.), etc. When in use, the rheology aid can be pre-mixed in water and then added to the raw material mixture of the rheology control agent, or the rheology aid powder and water can be added to the raw material mixture of the rheology control agent simultaneously. In the embodiments of the present invention, the dosage of the rheology aid is the dosage of the pure rheology aid powder. Preferably, the rheology control agent contains 0.5-2 parts of the rheology aid.

[0113] Furthermore, in order to reduce problems such as the decline in storage stability, the increase in fineness, and the thickening of viscosity caused by rheology aids such as inorganic clay in the system, the present invention uses a clay stabilizer in combination therewith. Through experiments, it has been found that when the clay stabilizer is selected from one or more of phosphate ester compounds, pyrophosphates, polyphosphates, metaphosphates, metal salt complexes, homopolymers of polyols, and copolymers of polyols, the adverse effects brought by the rheology aid can be eliminated to a certain extent; Exemplarily, the phosphate ester compounds are selected from alkyl phosphate esters, phosphodiesters, etc.; the pyrophosphates are selected from sodium pyrophosphate, potassium pyrophosphate, etc.; the polyphosphates are selected from sodium tripolyphosphate, sodium diphosphate, etc.; the metaphosphates are selected from sodium metaphosphate, sodium trimetaphosphate, sodium hexametaphosphate, etc.; the metal salt complexes are selected from sodium ferric ethylenediaminetetraacetate, zinc amine solution, etc.; the copolymers of polyols are selected from polyethylene glycol, polypropylene glycol, polytetrahydrofuran, etc.; Preferably, when the clay stabilizer is selected from pyrophosphates such as sodium pyrophosphate, the effect of eliminating the adverse effects brought by the rheology aid is the best; Preferably, the rheology control agent contains 0.1-0.3 parts of the clay stabilizer.

[0114] Furthermore, the other aids are selected from commonly used functional aids in the art, including but not limited to defoamers, leveling agents, thickeners, dispersants, wetting agents, adhesion promoters, pH adjusters, etc. Since clay substances usually require the pH of the mixture to be not lower than 8.5, the rheology control agent of the present invention contains 0.1-1 part of a pH adjuster, and the pH adjuster includes but not limited to one or more of ammonia water, triethylamine, triethanolamine, dimethylethanolamine, 2-methyl-2-aminopropanol, dimethylisopropanolamine, methyldiethanolamine, AMP-95, ethyldiisopropylamine, diethylethanolamine.

[0115] Furthermore, the water and the organic solvent play a role in adjusting the solid content of the formulation and diluting and dissolving the formulation components; Exemplarily, the organic solvent includes but not limited to one or more of ethanol, isopropanol, n-pentanol, isopentanol, n-octanol, isooctanol, acetone, butanone, ethyl acetate, butyl acetate, propylene glycol methyl ether, ethylene glycol butyl ether, dipropylene glycol butyl ether, dipropylene glycol methyl ether, alkyl solvents, etc.; Preferably, the rheology control agent contains 2-6 parts of the organic solvent.

[0116] The fourth aspect of the present invention provides a preparation method of the rheology control agent as described above, comprising the following steps:

[0117] Under high-speed stirring, mix the hydroxyacrylic emulsion, the aqueous polymer dispersion, and a part of the water, then add the organic solvent and other aids, and after mixing evenly, add the clay dispersion obtained by premixing the rheology aid, the clay stabilizer, and the remaining part of the water to obtain the product.

[0118] Furthermore, the rotation speed of the high-speed stirring is 200-800 rpm.

[0119] The technical solution of the present invention will be further described below by taking specific embodiments as examples.

[0120] Example 1 Synthesis of Acrylic Emulsion

[0121] This example provides an acrylic emulsion, and its specific formulation is shown in Table 1.

[0122] Table 1

[0123]

[0124]

[0125] Among them, the preparation process of the special monomer is as follows:

[0126] Add 228.37 parts by mass of glycidyl versatate Hansen Cardura TM E10P (epoxy content 4100 - 4250 mmol / kg, viscosity at 25 °C is 7.13 mPa·s), 86.09 parts by mass of methacrylic acid, and 0.3 parts by mass of p-hydroxyanisole into the reaction vessel. After mixing evenly, carry out ring-opening reaction at 110 °C. When the acid value of the test sample < 2 mgKOH / g, the reaction is completed to obtain the special monomer, and the acid value is tested according to GB / T 2895 - 2008.

[0127] This example also provides a method for preparing an acrylic emulsion, and its specific steps are as follows:

[0128] Under the condition of high-speed stirring, add 300 g of methyl methacrylate, 200 g of n-butyl acrylate, 20 g of special monomer, 20 g of acrylic acid, and 5 g of ethylene glycol dimethacrylate into 315 g of deionized water and 9 g of REASOAP SR-20 to obtain the shell pre-emulsion.

[0129] Under the condition of high-speed stirring, add 20 g of ethylene glycol dimethacrylate, 220 g of methyl methacrylate, and 330 g of n-butyl acrylate into 200 g of deionized water and 11 g of REASOAP SR-20 to obtain the core pre-emulsion.

[0130] 680 g of deionized water and 3 g of REASOAP SR-20 emulsifier were added to a reactor, heated to 80 °C under nitrogen protection, 8 wt% of the shell pre-emulsion was added, and after holding for 5 min, an ammonium persulfate solution (containing 2 g of ammonium persulfate and 35 g of deionized water) was added. After 20 min, the remaining shell pre-emulsion was slowly added dropwise over 150 min, and after the addition was completed, it was held for 1.5 h. After the holding was completed, 20 g of deionized water and 6 g of dimethylethanolamine were added, and it was held again for 20 min. After the holding was completed, the core pre-emulsion was slowly added dropwise over 150 min, and at the same time, an ammonium persulfate solution (containing 2 g of ammonium persulfate and 180 g of deionized water) was added. After the addition was completed, it was held for 1.5 h. After the holding was completed, the temperature was lowered to room temperature, 6 g of dimethylethanolamine, 2.7 g of ACTICIDE MBS and 35 g of deionized water were added, and it was filtered to obtain a hydroxyacrylic emulsion with a particle size of 134 nm, a pH of 8.1, and a viscosity of 35 cp (rotary viscometer, 50 rpm / 23 °C).

[0131] Example 2 Synthesis of Acrylic Emulsion

[0132] This example provides an acrylic emulsion, and its specific formulation is shown in Table 2.

[0133] Table 2

[0134]

[0135]

[0136] Among them, the preparation process of the special monomer is the same as that in Example 1.

[0137] This example also provides a method for preparing a hydroxyacrylic emulsion, and its specific steps are as follows:

[0138] Under the condition of high-speed stirring, 250 g of methyl methacrylate, 250 g of n-butyl acrylate, 15 g of special monomer, 15 g of acrylic acid and 10 g of 1,6-hexanediol dimethacrylate were added to 315 g of deionized water and 30 g of Reactsurf 2490 to obtain a shell pre-emulsion.

[0139] Under the condition of high-speed stirring, 20 g of 1,6-hexanediol dimethacrylate, 200 g of methyl methacrylate and 250 g of n-butyl acrylate were added to 200 g of deionized water and 34 g of Reactsurf 2490 to obtain a core pre-emulsion.

[0140] 680 g of deionized water and 11 g of Reactsurf 2490 emulsifier were added to a reactor, heated to 80 °C under nitrogen protection, 5 wt% of the shell pre-emulsion was added, after keeping warm for 5 min, ammonium persulfate solution (containing 35 g of deionized water and 1.25 g of ammonium persulfate) was added, after 20 min, the remaining shell pre-emulsion was slowly added dropwise, the dropping time was 180 min, and after the dropping was completed, it was kept warm for 1 h. After the heat preservation was completed, 20 g of deionized water and 6 g of triethanolamine were added, and then kept warm for 20 min again. After the heat preservation was completed, the core pre-emulsion was slowly added dropwise, the dropping time was 180 min, and at the same time, ammonium persulfate solution (containing 180 g of deionized water and 1.25 g of ammonium persulfate) was added dropwise. After the dropping was completed, it was kept warm for 1 h. After the heat preservation was completed, the temperature was lowered to room temperature, 6 g of triethanolamine, 2.7 g of Vinkocide CMI and 35 g of deionized water were added, and then filtered to obtain a hydroxyacrylic emulsion with a particle size of 145 nm, a pH of 8.3, and a viscosity of 20 cp (rotary viscometer, 50 rpm / 23 °C).

[0141] Synthesis of Rheology Control Agent in Example 3

[0142] This example provides a rheology control agent for automotive refinish paints. The specific formulation is shown in Table 3, in which the acrylic emulsion is the acrylic emulsion prepared in Example 1.

[0143] Table 3

[0144] Number Material Name Dosage / part 1 Acrylic Emulsion 35 2 BYK Laponite RD 1 3 Isopropanol 5 4 Sodium Pyrophosphate 0.15 5 Deionized Water 58.4 6 Triethanolamine 0.5

[0145] This example also provides a preparation method for the rheology control agent. The specific steps are as follows:

[0146] Under high-speed stirring, 35 parts of acrylic emulsion and 9.4 parts of deionized water were added to a stirring tank, then 5 parts of isopropanol and 0.5 part of triethanolamine were added, and stirred evenly to obtain an emulsion solvent mixture;

[0147] 1 part of BYK Laponite RD, 0.15 part of sodium pyrophosphate and 49 parts of deionized water were premixed to obtain a clay dispersion;

[0148] The clay dispersion was slowly added to the emulsion solvent mixture to obtain a rheology control agent.

[0149] Synthesis of Rheology Control Agent in Example 4

[0150] This example provides a rheology control agent for automotive refinish paints. The specific formulation is shown in Table 4, in which the acrylic emulsion is the acrylic emulsion prepared in Example 1.

[0151] Table 4

[0152] Number Material Name Dosage / part 1 Acrylic Emulsion 35 2 BYK Laponite RD 1 3 Isopropanol 5 4 Sodium Pyrophosphate 0.05 5 Deionized Water 58.4 6 Triethanolamine 0.5

[0153] This embodiment also provides a preparation method of a rheology control agent, and the specific steps are as follows:

[0154] Under high-speed stirring, add 35 parts of acrylic emulsion and 9.4 parts of deionized water into a stirring tank, then add 5 parts of isopropanol and 0.5 part of triethanolamine, and stir evenly to obtain an emulsion solvent mixture;

[0155] Pre-mix 1 part of BYK Laponite RD, 0.05 part of sodium pyrophosphate and 49 parts of deionized water to obtain a clay dispersion;

[0156] Slowly add the clay dispersion into the emulsion solvent mixture to obtain a rheology control agent.

[0157] Synthesis of rheology control agent in Comparative Example 1

[0158] This comparative example provides a rheology control agent for automotive refinish paint, and the specific formulation is shown in Table 5. Among them, the acrylic emulsion is the acrylic emulsion prepared in Example 1.

[0159] Table 5

[0160] Number Material Name Dosage / part 1 Acrylic Emulsion 20 2 Bayhydrol UH2110 20 3 BYK Laponite RD 1 4 Isopropanol 5 5 Sodium Pyrophosphate 0.02 6 Deionized Water 53.5 7 Triethanolamine 0.5

[0161] This comparative example also provides a preparation method of a rheology control agent, and the specific steps are as follows:

[0162] Under high-speed stirring, add 20 parts of acrylic emulsion, 20 parts of Bayhydrol UH2110 and 4.5 parts of deionized water into a stirring tank, then add 5 parts of isopropanol and 0.5 part of triethanolamine, and stir evenly to obtain an emulsion solvent mixture;

[0163] Pre-mix 1 part of BYK Laponite RD, 0.02 part of sodium pyrophosphate and 49 parts of deionized water to obtain a clay dispersion;

[0164] Slowly add the clay dispersion into the emulsion solvent mixture to obtain a rheology control agent.

[0165] Synthesis of rheology control agent in Comparative Example 2

[0166] This embodiment provides a rheology control agent for automotive refinish paint, and the specific formulation is shown in Table 6. Among them, the acrylic emulsion is the acrylic emulsion prepared in Example 1.

[0167] Table 6

[0168] Number Material Name Dosage / part 1 Acrylic Emulsion 20 2 Bayhydrol UH2110 20 3 BYK Laponite RD 1 4 Isopropanol 5 5 Sodium Pyrophosphate 0.35 6 Deionized Water 53.2 7 Triethanolamine 0.5

[0169] This comparative example also provides a preparation method of a rheology control agent, and the specific steps are as follows:

[0170] Under high-speed stirring, 20 parts of acrylic emulsion, 20 parts of Bayhydrol UH2110 and 4.2 parts of deionized water are added to a stirring tank, then 5 parts of isopropanol and 0.5 part of triethanolamine are added, and they are stirred evenly to obtain an emulsion solvent mixture;

[0171] 1 part of BYK Laponite RD, 0.35 part of sodium pyrophosphate and 49 parts of deionized water are premixed to obtain a clay dispersion;

[0172] The clay dispersion is slowly added to the emulsion solvent mixture to obtain a rheology control agent.

[0173] Synthesis of rheology control agent in Example 5

[0174] This example provides a rheology control agent for automotive refinish paint. The specific formulation is shown in Table 7. Among them, the acrylic emulsion is the acrylic emulsion prepared in Example 2.

[0175] Table 7

[0176] Number Material Name Dosage / part 1 Acrylic Emulsion 35 2 BYK Laponite RD 1 3 Isopropanol 5 4 Sodium Pyrophosphate 0.15 5 Deionized Water 58.4 6 Triethanolamine 0.5

[0177] This example also provides a preparation method for the rheology control agent. The specific steps are as follows:

[0178] Under high-speed stirring, 35 parts of acrylic emulsion and 9.4 parts of deionized water are added to a stirring tank, then 5 parts of isopropanol and 0.5 part of triethanolamine are added, and they are stirred evenly to obtain an emulsion solvent mixture;

[0179] 1 part of BYK Laponite RD, 0.15 part of sodium pyrophosphate and 49 parts of deionized water are premixed to obtain a clay dispersion;

[0180] The clay dispersion is slowly added to the emulsion solvent mixture to obtain a rheology control agent.

[0181] Synthesis of rheology control agent in Comparative Example 3

[0182] This comparative example provides a rheology control agent for automotive refinish paint. The specific formulation is shown in Table 8. Among them, the acrylic emulsion is the acrylic emulsion prepared in Example 1.

[0183] Table 8

[0184] Number Material Name Dosage / part 1 Acrylic Emulsion 35 2 BYK Laponite RD 1 3 Isopropanol 5 4 Sodium Pyrophosphate - 5 Deionized Water 55.5 6 Triethanolamine 0.5

[0185] This comparative example also provides a preparation method for the rheology control agent. The specific steps are as follows:

[0186] Under high-speed stirring, 35 parts of acrylic emulsion and 6.5 parts of deionized water were added to a stirring tank, then 5 parts of isopropanol and 0.5 part of triethanolamine were added, and the mixture was stirred evenly to obtain an emulsion solvent mixture;

[0187] 1 part of BYK Laponite RD and 49 parts of deionized water were premixed to obtain a clay dispersion;

[0188] The clay dispersion was slowly added to the emulsion solvent mixture to obtain a rheology control agent.

[0189] Synthesis of rheology control agent in Comparative Example 4

[0190] This comparative example provides a rheology control agent for automotive refinish paints. The specific formulation is shown in Table 9. Among them, the acrylic emulsion was prepared from the acrylic emulsion obtained in Example 1.

[0191] Table 9

[0192] Number Material Name Dosage / part 1 Acrylic Emulsion 20 2 Bayhydrol UH2110 20 3 BYK Laponite RD 1 4 Isopropanol 5 5 Sodium Pyrophosphate - 6 Deionized Water 53.5 7 Triethanolamine 0.5

[0193] This comparative example also provides a method for preparing a rheology control agent. The specific steps are as follows:

[0194] Under high-speed stirring, 20 parts of acrylic emulsion, 20 parts of Bayhydrol UH2110 and 4.5 parts of deionized water were added to a stirring tank, then 5 parts of isopropanol and 0.5 part of triethanolamine were added, and the mixture was stirred evenly to obtain an emulsion solvent mixture;

[0195] 1 part of BYK Laponite RD and 49 parts of deionized water were premixed to obtain a clay dispersion;

[0196] The clay dispersion was slowly added to the emulsion solvent mixture to obtain a rheology control agent.

[0197] Synthesis of acrylic emulsion in Comparative Example 5

[0198] This comparative example provides an acrylic emulsion. The specific formulation is shown in Table 10.

[0199] Table 10

[0200]

[0201]

[0202] Note: The active ingredient content of DOWFAX2A1 is 45 wt%.

[0203] Among them, the preparation process of the special monomer was the same as that in Example 1.

[0204] This comparative example also provides a method for preparing an acrylic emulsion. The specific steps are as follows:

[0205] Under the condition of high-speed stirring, 300 g of methyl methacrylate, 200 g of n-butyl acrylate, 20 g of special monomer, 20 g of acrylic acid and 5 g of ethylene glycol dimethacrylate were added to 315 g of deionized water and 5.6 g of DOWFAX 2A1 to obtain a shell pre-emulsion.

[0206] Under the condition of high-speed stirring, 20 g of ethylene glycol dimethacrylate, 220 g of methyl methacrylate and 330 g of n-butyl acrylate were added to 200 g of deionized water and 6 g of DOWFAX 2A1 to obtain a core pre-emulsion.

[0207] 680 g of deionized water and 2.9 g of DOWFAX 2A1 emulsifier were added to the reactor, heated to 80 °C under nitrogen protection, 8 wt% of the shell pre-emulsion was added, after holding for 5 min, an ammonium persulfate solution (containing 35 g of deionized water and 2 g of ammonium persulfate) was added. After 20 min, the remaining shell pre-emulsion was slowly added dropwise over 150 min, and after the addition was completed, it was held for 1.5 h. After the holding was completed, 20 g of deionized water and 6 g of dimethylethanolamine were added, and it was held again for 20 min. After the holding was completed, the core pre-emulsion was slowly added dropwise over 150 min, and at the same time an ammonium persulfate solution (containing 180 g of deionized water and 2 g of ammonium persulfate) was added dropwise. After the addition was completed, it was held for 1.5 h. After the holding was completed, the temperature was lowered to room temperature, 6 g of dimethylethanolamine, 2.7 g of ACTICIDE MBS and 35 g of deionized water were added, and then it was filtered and discharged to obtain a hydroxy acrylic emulsion with a particle size of 120 nm, a pH of 7.8 and a viscosity of 43 cp / 23 °C. In addition, considering the particle size requirements of the hydroxy acrylic emulsion, when DOWFAX 2A1 was used as the emulsifier, the appropriate active ingredient content was 6.5 g.

[0208] Synthesis of rheology control agent in Comparative Example 6

[0209] This comparative example provides a rheology control agent for automotive refinish paints, and its specific formulation is shown in Table 11, wherein the acrylic emulsion was prepared from the acrylic emulsion obtained in Comparative Example 5.

[0210] Table 11

[0211] Number Material Name Dosage / part 1 Acrylic Emulsion 20 2 Bayhydrol UH2110 20 3 BYK Laponite RD 1 4 Isopropanol 5 5 Sodium Pyrophosphate 0.15 6 Deionized Water 55.5 7 Triethanolamine 0.5

[0212] This comparative example also provides a preparation method for preparing a rheology control agent, and its specific steps are as follows:

[0213] Under high-speed stirring, 20 parts of acrylic emulsion, 20 parts of Bayhydrol UH2110 and 6.5 parts of deionized water were added to the stirring tank, then 5 parts of isopropanol and 0.5 part of triethanolamine were added, and stirred evenly to obtain an emulsion solvent mixture;

[0214] Pre-mix 1 part of BYK Laponite RD, 0.15 part of sodium pyrophosphate and 49 parts of deionized water to obtain a clay dispersion;

[0215] Slowly add the clay dispersion to the emulsion solvent mixture to obtain a rheology control agent.

[0216] Performance test

[0217] Since the rheology control agent needs to be mixed with the main paint and then sprayed to detect the influence of the rheology control agent on the construction performance of the main paint, the rheology control agents prepared in Examples 3-5, Comparative Examples 1-4, and Comparative Example 6 are respectively formulated with the main paint according to a mass ratio of 2:1 into coatings for performance evaluation. Among them, the formulation of the main paint is shown in Table 12.

[0218] Table 12

[0219] Type Material Name Dosage / part Acrylic Emulsion Self - made in Example 1 35 Polyurethane Dispersion WLS - 210 42 Water Deionized Water 20 Organic Solvent n - Pentanol 2 Organic Solvent Propylene Glycol Methyl Ether 3 Wetting Agent TEGO wet - 280 0.2 Thickener Rheovis PU1191 1 pH Regulator Triethanolamine 0.05

[0220] Add 35 parts of the acrylic emulsion prepared in Example 1, 42 parts of DIC WLS-210, and 20 parts of deionized water to a stirring tank. After mixing evenly, add 2 parts of n-pentanol and 3 parts of propylene glycol methyl ether. After mixing evenly, add 0.2 part of TEGO wet-280. After mixing evenly, add 1 part of Rheovis PU1191 and 0.05 part of triethanolamine, and adjust the viscosity to 1000 cp / 23 °C to obtain.

[0221] 1) Rheology test

[0222] Perform a rheology test on the coatings obtained by mixing the main paint with each rheology control agent. The test instrument is Anton Paar MCR702. The test method is as follows: Apply a shear force of 10000 s to the sample to be tested, and then apply a shear force of 1 s to allow the sample to be tested to fully recover. Monitor the viscosity change of the sample to be tested during the process. When the viscosity ratio of the sample to be tested after 60 s of recovery under a shear force of 1 s to the viscosity under a shear force of 10000 s is greater than 100, it is qualified; otherwise, it is unqualified. The test results are shown in Table 13. -1 of shear force and then apply a shear force of 1 s -1 to allow the sample to be tested to fully recover. Monitor the viscosity change of the sample to be tested during the process. When the viscosity after 60 s of recovery under a shear force of 1 s -1 is greater than 100 times the viscosity under a shear force of 10000 s -1 it is qualified; otherwise, it is unqualified. The test results are shown in Table 13.

[0223] Table 13

[0224]

[0225]

[0226] 2) Heat storage test

[0227] The coating obtained by mixing the main paint with each rheology control agent was placed in an oven at 50 °C for 4 weeks for heat storage test. After the test, the fineness of the sample to be tested was measured. If the fineness ≤ 10 μm, it was considered qualified. Generally, heat storage in an oven at 50 °C for 4 weeks is considered equivalent to storage at room temperature for one year. The test results are shown in Table 14.

[0228] Table 14

[0229]

[0230] When formulating a rheology control agent using an acrylic emulsion containing an anionic emulsifier, with the basic formula being the same, it can be seen that its rheological properties and heat storage properties significantly decline. However, an acrylic emulsion synthesized using a polymerizable emulsifier can meet the high requirements of this rheology control agent, and has good compatibility with other film-forming resins of different types (such as polyurethane dispersions, etc.) and additives.

[0231] It can be seen that, compared with the comparative example, after adding the clay stabilizer, the stability of the rheology control agent is greatly improved, and it can meet the requirement of stable storage at room temperature for 1 - 2 years for automotive refinish paints. At the same time, the rheology control agent of the present invention can effectively improve the rheological recovery ability of the main paint, thereby improving the sagging performance of the paint and enhancing the orientation of the effect pigments. When adding an acrylic emulsion using a polymerizable emulsifier and the clay stabilizer to the formula of the rheology control agent, the rheology control agent can obtain excellent rheology control ability while having high storage stability, showing a synergistic effect.

[0232] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, based on the above description, other different forms of changes or modifications can be made. It is impossible to list all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A hydroxyl acrylic emulsion with a core-shell structure, characterized in that, the hydroxyl acrylic emulsion is obtained by inverse emulsion polymerization of the following monomer composition A for forming the shell layer of emulsion particles and monomer composition B for forming the core layer of emulsion particles under the action of an initiator and an emulsifier; wherein, the monomer composition A uses the following raw materials as polymerization units: Hydroxy (meth) acrylate monomers 0.5 - 7 wt%; (Meth) acrylate monomers containing multiple unsaturated vinyl groups 0.5 - 5 wt%; (Meth) acrylic monomers containing carboxyl groups 0.2 - 7 wt%; Other polymerization monomers 90 - 98 wt%; The monomer composition B uses the following raw materials as polymerization units: Hydroxy (meth) acrylate monomers 0 - 5 wt%; (Meth) acrylate monomers containing multiple unsaturated vinyl groups 1 - 5 wt%; (Meth) acrylic monomers containing carboxyl groups 0 - 5 wt%; Other polymerization monomers 90 - 99 wt%; The hydroxyl acrylic emulsion contains a special monomer accounting for 0.25 - 6 wt% of the total monomers as a polymerization unit; The structural general formula of the special monomer is shown as the following formula I: The R 1 and R 2 are each independently selected from C1-C6 alkyl groups, and the total number of carbon atoms of the R 1 and R 2 is 7; The R 3 is selected from any one of H and C1-C6 alkyl groups.

2. The hydroxyl acrylic emulsion according to claim 1, characterized in that, the emulsifier is selected from polymerizable emulsifiers, and the mass of the active ingredient in the emulsifier is 0.5 - 3 wt% of the total monomers; Preferably, the emulsifier is selected from one or more of REASOAP SR - 1025, REASOAP SR - 20, REASOAP SR - 30, REASOAP ER - 10, REASOAP ER - 20, REASOAP ER - 30, REASOAP ER - 40, HITENOL AR - 10, HITENOL AR - 20 and REACTSURF 2490.

3. The hydroxyl acrylic emulsion according to claim 1, characterized in that, the special monomer is selected from one or more compounds with the following structures: The R 1 and R 2 are each independently selected from C1-C6 alkyl groups, and the total number of carbon atoms of the R 1 and R 2 is 7.

4. The hydroxyl acrylic emulsion according to claim 1, characterized in that, the (meth) acrylate monomers containing multiple unsaturated vinyl groups are selected from one or more of ethylene glycol diacrylate, ethylene glycol dimethacrylate, allyl methacrylate, polyethylene glycol acrylate, polyethylene glycol methacrylate, butanediol acrylate, butanediol methacrylate, 1,6 - hexanediol acrylate, 1,6 - hexanediol methacrylate, glycerol diacrylate, glycerol dimethacrylate and trimethylolpropane methacrylate.

5. The hydroxyl acrylic emulsion according to claim 1, characterized in that, the solid content of the hydroxyl acrylic emulsion is 20 - 55%, the acid value is 5 - 50 mg KOH / g, the hydroxyl value is 1 - 30 mg KOH / g, the particle size is 120 - 180 nm, the pH value is 7.5 - 8.5, and the viscosity is 10 - 200 cp / 23 °C.

6. The preparation method of the hydroxyl acrylic emulsion according to any one of claims 1 - 5, characterized in that, it includes the following steps: Water and an emulsifier are added into the first reactor, and then monomer composition A is added to obtain a shell pre-emulsion; Water and an emulsifier are added into the second reactor, and then monomer composition B is added to obtain a core pre-emulsion; Water and an emulsifier are added into the third reactor, and the temperature is raised to 75 - 85 °C. 5 - 10 wt% of the shell pre-emulsion and an initiator solution are added in sequence. After stirring for 20 - 30 min, the remaining shell pre-emulsion is added. After addition, keep the temperature for reaction for 0.5 - 2 h; after the heat preservation ends, the core pre-emulsion and the initiator solution are added in sequence. After addition, keep the temperature for reaction for 0.5 - 2 h; after cooling, adjust the pH to the target value to obtain the product; Preferably, the time required for adding the remaining shell pre-emulsion is 1 - 6 h; the time required for adding the core pre-emulsion is 1 - 6 h.

7. A rheology control agent for automotive refinish paint, characterized in that by weight, the rheology control agent comprises 10 - 45 parts of the hydroxyl acrylic emulsion according to any one of claims 1 - 5; the rheology control agent further comprises 0 - 30 parts of an aqueous polymer dispersion; 0.2 - 3 parts of a rheology aid; 0.05 - 0.3 parts of a clay stabilizer; 0.1 - 3 parts of other additives; 50 - 65 parts of water; 0.5 - 8 parts of an organic solvent.

8. The rheology control agent according to claim 7, characterized in that the clay stabilizer is selected from one or more of phosphate ester compounds, pyrophosphates, polyphosphates, metaphosphates, metal salt complexes, homopolymers of polyols, and copolymers of polyols; Preferably, the clay stabilizer is selected from pyrophosphates.

9. The rheology control agent according to claim 7, characterized in that the rheology aid is selected from one or more of inorganic clays and / or organically modified clays; Preferably, the inorganic clay is selected from one or more of bentonite, montmorillonite, and silicates; the organically modified clay is selected from organically modified bentonite and / or organically modified silicates; Preferably, the rheology aid is selected from one or more of BYK Laponite series, Optigel series, and Elementis BENTONE.

10. The preparation method of the rheology control agent according to any one of claims 7 - 9, characterized in that comprises the following steps: Under high-speed stirring, the hydroxyl acrylic emulsion, the aqueous polymer dispersion, and a part of water are mixed, then the organic solvent and other additives are added. After mixing evenly, a clay dispersion obtained by pre-mixing with a rheology aid, a clay stabilizer, and the remaining part of water is added to obtain the product.

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