CN111116831B - Preparation method of hydroxyl acrylic emulsion - Google Patents

Abstract

The invention belongs to the field of baking varnish, and discloses a preparation method of a hydroxy acrylic emulsion, which comprises the following steps: stirring and reacting an emulsifier, a buffer solution and water, heating to 84-86 ℃, adding an initiator solution a, dropwise adding a pre-emulsion A and a part of an initiator solution b, and carrying out heat preservation reaction to obtain a polymer A; dripping the pre-emulsion B into the polymer A, and carrying out heat preservation reaction to obtain a polymer B; dripping the pre-emulsion C and the rest initiator B solution into the polymer B, and carrying out heat preservation reaction; cooling, adding neutralizing agent to regulate pH value to 7.5-8, filtering and discharging to obtain the hydroxy acrylic emulsion. The preparation method of the invention uses water as a dispersion medium, does not contain any organic solvent, adopts a three-step dropwise reaction method, the monomer components dropwise added in each step are from weak to strong according to the hydrophilicity, and the Tg of the monomer in each step is from high to low, so that the special core-shell molecular structure of one-core double-shell composed of three polymers with different components is finally obtained.

Description

Preparation method of hydroxyl acrylic emulsion

Technical Field

The invention belongs to the field of baking varnish, and particularly relates to a preparation method of a hydroxy acrylic emulsion.

Background

Baking varnish is an important component in the whole industrial varnish field, and the application of the baking varnish relates to various fields of production, life and industrial application; the most common types of main baking varnish resins include hydroxy acrylic resins, alkyd resins, polyester resins, epoxy modified resins, and the like. The hydroxyl acrylic resin is the most common type in the market at present due to excellent light and color retention and good comprehensive performance and cost performance, and occupies a very important position in a resin system for baking finish.

Film forming materials of a traditional acrylic baking varnish system are all served by solvent type hydroxyl resin, and because the solvent contains more benzene, ketone and ether solvents and is harmful to human bodies and the environment, in recent years, due to national attention on environmental protection, the solvent type resin with high VOC tends to be gradually replaced by water-soluble resin and water-based dispersion resin, but even water-soluble acrylic resin and acrylic dispersion or acrylic modified dispersion are solvents with equivalent dosage.

CN 103467638 describes a preparation method of water-soluble hydroxy acrylic resin; alcohol and ether solvent are used as dispersion medium, methacrylic acid high-grade ester, methacrylic acid long carbon chain ester, acrylic acid multifunctional monomer, styrene and organosilicon monomer are initiated to carry out copolymerization reaction, and finally, organic amine is used for neutralization to achieve water solubility; although the product performance is excellent, the coating prepared by the traditional method generally contains 10-30% of alcohol ether solvents, and is not environment-friendly;

CN106957393A discloses a hydroxy acrylic acid water dispersion and a preparation method thereof, firstly polyethylene oxide is dissolved in an organic solvent, and the temperature is raised to fully dissolve the polyethylene oxide; and then dissolving an initiator and a chain transfer agent in the acrylate monomer mixture, dripping the monomer mixture added with the initiator and the chain transfer agent, gradually dripping amine for neutralization, finally adding water, and stirring at a high speed to uniformly mix a reaction system to obtain the modified hydroxyl acrylic acid aqueous dispersion. The synthesis method greatly reduces the addition of organic solvent, but still has the content of 5-10 wt% of organic solvent.

At present, the bottom baking finish coating of the commercially available electric kettle (metal material) mainly comprises water-soluble hydroxyl acrylic resin or oily acrylic resin, and the finish coating still mainly comprises the oily resin because the water-based resin can not meet the requirements of oily gloss and fullness. The average VOC content is generally 10-30 percent on the whole, and the VOC content in the baking varnish formula prepared by taking the VOC as a film forming matter reaches 20-40 percent; if the emulsion product is used for replacing water-soluble or oily resin as a base coat, the VOC of the baking varnish formula is obviously reduced compared with a water-soluble resin system.

Disclosure of Invention

The invention aims to provide a preparation method of hydroxyl acrylic emulsion; the method takes water as a dispersion medium, does not contain any organic solvent, and the hydroxyl acrylic emulsion prepared by three-step dropwise adding has a more regular molecular structure, a lower particle size, a better film-forming property and a good recoatability.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of hydroxyl acrylic emulsion comprises the following steps:

(1) stirring an emulsifier and water, adding an acrylic monomer and a vinyl monomer, and stirring to obtain a pre-emulsion A with Tg of 45-50 ℃;

(2) stirring an emulsifier and water, adding an acrylic monomer and a vinyl monomer, and stirring to obtain a pre-emulsion B with the Tg of 20-25 ℃;

(3) mixing an emulsifier with water, adding an acrylic monomer, and stirring to obtain a pre-emulsion C;

(4) preparing an initiator solution a from an initiator and water according to the mass ratio of 1 (13-15);

(5) preparing an initiator solution b from the initiator and water according to the mass ratio of 1 (40-50);

(6) stirring an emulsifier and water for reaction, introducing protective gas, heating to 84-86 ℃, adding an initiator a solution, dropwise adding a pre-emulsion A and a part of an initiator b solution, and carrying out heat preservation reaction to obtain a polymer A;

(7) dripping the pre-emulsion B into the polymer A, and carrying out heat preservation reaction to obtain a polymer B;

(8) dripping the pre-emulsion C and the rest initiator B solution into the polymer B, and carrying out heat preservation reaction;

(9) cooling, adding neutralizing agent to regulate pH value to 7.5-8, filtering and discharging to obtain the hydroxyl acrylic emulsion.

Preferably, the temperature of the incubation reaction in step (3), step (5) and step (7) is 84-86 ℃.

Preferably, the time of the heat preservation reaction in the step (3) is 20-30min, the time of the heat preservation reaction in the step (5) is 30-60min, and the time of the heat preservation reaction in the step (7) is 60-90 min.

Preferably, the shielding gas is nitrogen.

Preferably, the emulsifier is at least one of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, sodium allyl ether hydroxypropyl sulfonate, fatty alcohol polyoxyethylene ether, alkyl polyoxyethylene ether phosphate, alkyl polyoxyethylene ether, allyl polyoxyethylene ether, fatty alcohol ether sodium sulfate, heterogeneous alkyl polyether sodium sulfate or alkyl ether sulfosuccinate.

Preferably, the acrylic monomer is at least one of acrylic acid, methacrylic acid, butyl methacrylate, isobutyl methacrylate, ethyl acrylate, isooctyl methacrylate, methyl methacrylate, ethyl methacrylate, dodecyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, isobornyl acrylate, cyclohexyl acrylate, acrylamide or N-methylolacrylamide.

Preferably, the ethylenic monomer is styrene.

Preferably, the initiator is at least one of ammonia persulfate, potassium persulfate, or sodium persulfate.

Preferably, the neutralizing agent is at least one of Dimethylethanolamine (DMEA), ethylenetriamine, ethanolamine, diethanolamine, or triethanolamine.

Preferably, the pre-emulsion C of step (3) has a Tg of 0-10 ℃.

A hydroxyl acrylic emulsion is prepared by the preparation method.

The metal baking paint comprises the hydroxyl acrylic emulsion.

The invention has the beneficial effects that:

1) the preparation method of the invention uses water as a dispersion medium, does not contain any organic solvent, adopts a three-step dropwise reaction method, the monomer components dropwise added in each step are from weak to strong according to the hydrophilicity, and the Tg of the monomer in each step is from high to low, so that the special core-shell molecular structure of one-core double-shell composed of three polymers with different components is finally obtained.

2) Compared with the conventional core-shell polymerization, the hydroxyl acrylic emulsion prepared by the invention has a more regular molecular structure, smaller particle size, better film-forming property and good recoatability; the problems that the traditional hydroxyl acrylic emulsion is poor in solubility with amino resin and free of recoatability when being used for preparing amino baking varnish are solved, and meanwhile, in the process of preparing baking varnish, extremely low VOC is released, so that the preparation method has good environmental protection significance.

Drawings

Fig. 1 is a graph of the results of baking finish coating 1 and baking finish coating 3 tested for stability in a 50 degree oven.

Detailed Description

For a further understanding of the invention, preferred embodiments of the invention are described below with reference to the examples to further illustrate the features and advantages of the invention, and any changes or modifications that do not depart from the gist of the invention will be understood by those skilled in the art to which the invention pertains, the scope of which is defined by the scope of the appended claims.

Example 1

A preparation method of a hydroxyl acrylic emulsion comprises the following steps:

(1) preparing a pre-emulsion A: in an emulsion bottle, 155 g of deionized water, 5 g of allyl polyoxyethylene ether, 1.2 g of sodium allyl ether hydroxypropyl sulfonate and water are mixed and stirred uniformly, then a stirrer is started, 20 g of hydroxypropyl acrylate, 103 g of styrene, 223 g of methyl methacrylate and 90 g of butyl acrylate are added at the rotating speed of 1000rpm and stirred for 30 minutes until a stable pre-emulsion A is formed;

(2) preparing an initiator solution a and an initiator solution b: stirring and dissolving 25 g of deionized water and 1.8 g of ammonium persulfate to obtain an initiator solution a, and stirring and dissolving 200 g of deionized water and 4.5 g of ammonium persulfate to obtain an initiator solution b;

(3) putting 1200 g of deionized water and 10 g of sodium dodecyl sulfate into a reaction bottle, starting stirring, introducing nitrogen for inerting, and heating to 85 ℃;

(4) when the temperature reaches 85 ℃, adding an initiator solution a, beginning to simultaneously dropwise add a pre-emulsion A and an initiator solution b within 3 minutes, wherein the dropwise adding time of the pre-emulsion A is 90 minutes, the dropwise adding time of the initiator solution b is 420 minutes, the dropwise adding does not need to be stopped until the pre-emulsion C is dropwise added, and after the pre-emulsion A is dropwise added, keeping the temperature at 85 ℃ for 20 minutes to obtain a polymer A;

(5) preparing a pre-emulsion B: mixing 136 g of deionized water, 5.8 g of sodium dodecyl benzene sulfonate and water in an emulsion bottle, starting a stirrer, adding 35 g of hydroxypropyl acrylate, 70 g of styrene, 160 g of methyl methacrylate and 120 g of butyl acrylate at the rotating speed of 1000rpm, and stirring for 30 minutes until a stable pre-emulsion B is formed;

(6) dropwise adding the pre-emulsion B into the polymer A for 120 minutes, and preserving heat for 30 minutes after dropwise adding to obtain a polymer B;

(7) preparing a monomer pre-emulsion C: mixing 128 g of deionized water, 1.2 g of allyl polyoxyethylene ether, 2 g of sodium dodecyl benzene sulfonate and water in an emulsion bottle, starting a stirrer, adding 15 g of acrylic acid, 55 g of hydroxypropyl acrylate, 40 g of isooctyl acrylate, 130 g of methyl methacrylate and 110 g of butyl acrylate at the rotating speed of 1000rpm, and stirring for 30 minutes until a stable pre-emulsion C is formed;

(8) dripping the pre-emulsion C into the polymer B for 150 minutes, and preserving the heat for 60 minutes after dripping;

(9) cooling to normal temperature, adding dimethylethanolamine to regulate the pH value to 7.5-8, filtering and discharging to obtain the hydroxyl acrylic emulsion.

The physical properties of the obtained hydroxyacrylic emulsion are shown in Table 1:

TABLE 1

pH	7.6
		Solids content/%)	45.1
Particle size/nm	78
		Tg/℃	23.8
Hydroxyl number/KOH mg	41.5

Example 2

A preparation method of hydroxyl acrylic emulsion comprises the following steps:

(1) preparing a pre-emulsion A: 160 g of deionized water, 2 g of sodium dodecylbenzenesulfonate and 4 g of sodium allyl ether hydroxypropylsulfonate are mixed with water in an emulsion bottle, and then a stirrer is started, 20 g of hydroxyethyl methacrylate, 103 g of styrene, 205 g of methyl methacrylate and 105 g of butyl acrylate are added at the rotation speed of 1000rpm and stirred for 30 minutes until a stable pre-emulsion A is formed;

(2) initiator solution a and initiator solution b: stirring and dissolving 25 g of deionized water and 1.8 g of ammonium persulfate to obtain an initiator solution a;

(3) stirring and dissolving 200 g of deionized water and 4.5 g of ammonium persulfate to obtain an initiator solution b;

(4) putting 1180 g of deionized water, 5 g of sodium dodecyl sulfate and 5 g of sodium dodecyl sulfate into a reaction bottle, starting stirring, introducing nitrogen for inerting, heating to 84 ℃, adding an initiator solution a, starting dropwise adding a pre-emulsion A and an initiator solution b simultaneously within 3 minutes, wherein the dropwise adding time of the pre-emulsion A is 90 minutes, dropwise adding the initiator solution b for 420 minutes until the pre-emulsion C is dropwise added, and keeping the temperature at 84 ℃ for 20 minutes after the pre-emulsion A is dropwise added to obtain a polymer A;

(5) preparing a pre-emulsion B: mixing 130 g of deionized water, 5.2 g of sodium dodecyl sulfate and water in an emulsion bottle, then starting a stirrer, adding 35 g of hydroxyethyl methacrylate, 3 g of acrylic acid, 70 g of styrene, 145 g of methyl methacrylate and 135 g of isooctyl acrylate at 1000rpm, and stirring for 30 minutes until a stable pre-emulsion B is formed;

(6) dropwise adding the pre-emulsion B into the polymer A for 120 minutes, and keeping the temperature for 30 minutes after the dropping to obtain a polymer B;

(7) preparing a pre-emulsion C: mixing 128 g of deionized water, 6.4 g of sodium dodecyl sulfate, 3 g of sodium allyl ether hydroxypropyl sulfonate and water in an emulsion bottle, starting a stirrer, adding 12 g of acrylic acid, 55 g of hydroxyethyl methacrylate, 40 g of isooctyl acrylate, 120 g of methyl methacrylate and 123 g of butyl acrylate at the rotating speed of 1000rpm, and stirring for 30 minutes until a stable pre-emulsion C is formed;

(8) dropwise adding the pre-emulsion C into the polymer B, wherein the dropwise adding time is 150 minutes, and keeping the temperature for 60 minutes after the dropwise adding is finished;

(9) cooling to normal temperature, adding triethanolamine to adjust the pH value to 7.5-8, filtering and discharging to obtain the hydroxyl acrylic emulsion.

The physical properties of the obtained hydroxyacrylic emulsion are shown in Table 2:

TABLE 2

pH	7.8
		Solids content/%)	45.7
Particle size/nm	82
		Tg/℃	25.6
Hydroxyl number/KOH mg	39.5

The preparation of a baking varnish coating comprises the following steps:

the hydroxy acrylic emulsion prepared in the embodiment 1 and the embodiment 2 and the hydroxy acrylic emulsion on the market are stirred and added with curing agent amino resin at the rotating speed of 200rpm, then water, film forming auxiliary agent, wetting agent, flatting agent and thickening agent are added to adjust to proper viscosity, after being dispersed uniformly, the mixture is filtered and packaged (the fineness is less than 30um as a standard) when the fineness test is qualified, and baking varnish coatings 1-3 are obtained in sequence.

TABLE 3 composition of baking finish coatings

Application of metal baking varnish coating

Preparing a tinplate, polishing and cleaning the tinplate, coating the prepared paint to a proper thickness by using a spray gun, baking a paint film at 150 ℃ for 20 minutes, standing the paint film at normal temperature for 1 hour, and testing the performance of the paint baking paint 1-3.

The performance test results are shown in table 4:

TABLE 4

The water-based paint film is baked for 20 minutes at 150 ℃, then is placed for 1 hour at normal temperature, has the hardness of 2H, the gloss of 85 degrees, the adhesive force of 0 grade, the impact resistance of 50, the ethanol wiping resistance of more than 100 times, the water resistance of more than 120 hours and the salt spray resistance of more than 96 hours, and meets the requirements of the conventional water-based metal baking paint. And the repairability is good, and the primer can be applied to the primer of the electric kettle.

The stability of both baking varnish coating 1 and baking varnish coating 3 was tested in a 50 degree oven and judged as a change in viscosity, with the results shown in table 5 and fig. 1:

TABLE 5

As is apparent from table 5 and fig. 1, the heat storage stability of the baking varnish coating 1 is significantly superior to that of the baking varnish coating 3.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and they are included in the scope of the present invention.

Claims (3)

1. The preparation method of the hydroxyl acrylic emulsion is characterized by comprising the following steps:

(1) preparing a pre-emulsion A: in an emulsion bottle, 155 g of deionized water, 5 g of allyl polyoxyethylene ether, 1.2 g of sodium allyl ether hydroxypropyl sulfonate and water are mixed and stirred uniformly, then a stirrer is started, 20 g of hydroxypropyl acrylate, 103 g of styrene, 223 g of methyl methacrylate and 90 g of butyl acrylate are added at the rotating speed of 1000rpm and stirred for 30 minutes until a stable pre-emulsion A is formed;

(2) preparing an initiator solution a and an initiator solution b: stirring and dissolving 25 g of deionized water and 1.8 g of ammonium persulfate to obtain an initiator solution a, and stirring and dissolving 200 g of deionized water and 4.5 g of ammonium persulfate to obtain an initiator solution b;

(3) putting 1200 g of deionized water and 10 g of sodium dodecyl sulfate into a reaction bottle, starting stirring, introducing nitrogen for inerting, and heating to 85 ℃;

(4) when the temperature reaches 85 ℃, adding the initiator solution a, starting to simultaneously dropwise add the pre-emulsion A and the initiator solution b within 3 minutes, wherein the dropwise adding time of the pre-emulsion A is 90 minutes, the dropwise adding time of the initiator solution b is 420 minutes, stopping dropwise adding until the dropwise adding of the pre-emulsion C is finished, and preserving heat at 85 ℃ for 20 minutes after the dropwise adding of the pre-emulsion A is finished to obtain a polymer A;

(5) preparing a pre-emulsion B: mixing 136 g of deionized water, 5.8 g of sodium dodecyl benzene sulfonate and water in an emulsion bottle, starting a stirrer, adding 35 g of hydroxypropyl acrylate, 70 g of styrene, 160 g of methyl methacrylate and 120 g of butyl acrylate at the rotating speed of 1000rpm, and stirring for 30 minutes until a stable pre-emulsion B is formed;

(6) dropwise adding the pre-emulsion B into the polymer A for 120 minutes, and keeping the temperature for 30 minutes after the dropping to obtain a polymer B;

(7) preparing a monomer pre-emulsion C: mixing 128 g of deionized water, 1.2 g of allyl polyoxyethylene ether, 2 g of sodium dodecyl benzene sulfonate and water in an emulsion bottle, starting a stirrer, adding 15 g of acrylic acid, 55 g of hydroxypropyl acrylate, 40 g of isooctyl acrylate, 130 g of methyl methacrylate and 110 g of butyl acrylate at the rotating speed of 1000rpm, and stirring for 30 minutes until a stable pre-emulsion C is formed;

(8) dropwise adding the pre-emulsion C into the polymer B for 150 minutes, and keeping the temperature for 60 minutes after dropwise adding;

(9) cooling to normal temperature, adding dimethylethanolamine to adjust the pH value to 7.5-8, filtering and discharging to obtain the hydroxyl acrylic emulsion.

2. A hydroxy acrylic emulsion, characterized in that the preparation method comprises the following steps:

(1) preparing a pre-emulsion A: 160 g of deionized water, 2 g of sodium dodecyl benzene sulfonate and 4 g of sodium allyl ether hydroxypropyl sulfonate are mixed with water in an emulsion bottle, then a stirrer is started, 20 g of hydroxyethyl methacrylate, 103 g of styrene, 205 g of methyl methacrylate and 105 g of butyl acrylate are added at the rotating speed of 1000rpm and stirred for 30 minutes until a stable pre-emulsion A is formed;

(2) initiator solution a and initiator solution b: stirring and dissolving 25 g of deionized water and 1.8 g of ammonium persulfate to obtain an initiator solution a;

(3) stirring and dissolving 200 g of deionized water and 4.5 g of ammonium persulfate to obtain an initiator solution b;

(4) putting 1180 g of deionized water, 5 g of sodium dodecyl sulfate and 5 g of sodium dodecyl sulfate into a reaction bottle, starting stirring, introducing nitrogen for inerting, heating to 84 ℃, adding the initiator solution a, starting dropwise adding the pre-emulsion A and the initiator solution b simultaneously within 3 minutes, wherein the dropwise adding time of the pre-emulsion A is 90 minutes, the dropwise adding of the initiator solution b is 420 minutes until the dropwise adding of the pre-emulsion C is finished, and keeping the temperature at 84 ℃ for 20 minutes after the dropwise adding of the pre-emulsion A is finished to obtain a polymer A;

(5) preparing a pre-emulsion B: mixing 130 g of deionized water, 5.2 g of sodium dodecyl sulfate and water in an emulsion bottle, then starting a stirrer, adding 35 g of hydroxyethyl methacrylate, 3 g of acrylic acid, 70 g of styrene, 145 g of methyl methacrylate and 135 g of isooctyl acrylate at 1000rpm, and stirring for 30 minutes until a stable pre-emulsion B is formed;

(6) dropwise adding the pre-emulsion B into the polymer A for 120 minutes, and keeping the temperature for 30 minutes after the dropping to obtain a polymer B;

(7) preparing a pre-emulsion C: mixing 128 g of deionized water, 6.4 g of sodium dodecyl sulfate, 3 g of sodium allyl ether hydroxypropyl sulfonate and water in an emulsion bottle, starting a stirrer, adding 12 g of acrylic acid, 55 g of hydroxyethyl methacrylate, 40 g of isooctyl acrylate, 120 g of methyl methacrylate and 123 g of butyl acrylate at the rotating speed of 1000rpm, and stirring for 30 minutes until a stable pre-emulsion C is formed;

(8) dropwise adding the pre-emulsion C into the polymer B, wherein the dropwise adding time is 150 minutes, and keeping the temperature for 60 minutes after the dropwise adding is finished;

(9) cooling to normal temperature, adding triethanolamine to adjust the pH value to 7.5-8, filtering and discharging to obtain the hydroxyl acrylic emulsion.

3. A metal baking varnish comprising the hydroxyacrylic emulsion of claim 1 or 2.

Images