Emulsion polymerization method and application of emulsion polymerization method in preparation of water-based acrylic coating

Abstract

The invention provides an emulsion polymerization method and application of the emulsion polymerization method in preparation of a water-based acrylic coating. The polymerization method comprises the following steps: performing ionization treatment on a functional monomer acid, mixing with a reaction solution composed of an emulsifier, water and an acrylate monomer, and polymerizing under the action of an initiator to obtain the acrylic emulsion. According to the method, more molecules can be enriched in a shell layer of emulsion particles and form a hydrophilic protection layer, so that molecular chain segments are more efficiently enriched in the shell layer under the driving of hydrophilic group ions, and excellent performance is shown; especially, the waterborne acrylic emulsion prepared by the method can significantly improve the adhesive force of the resin to a biaxially oriented polypropylene (BOPP) base material.

Description

Technical Field

[0001] The invention relates to the field of water-based industrial coatings, and in particular to an emulsion polymerization method and application thereof in preparing water-based acrylic coatings. Background Art

[0002] BOPP is made by biaxial stretching of polypropylene. It has excellent mechanical properties, light weight and high strength. It is widely used in packaging and printing, such as packaging bags, labels, trademark substrates, etc. In practical applications, most coatings have poor adhesion to PP substrates due to their low polarity and difficulty in wetting. In addition, the surface roughness and surface energy of BOPP obtained after biaxial stretching are lower, making it more difficult to adhere. Therefore, BOPP substrates often require some surface treatment agents to pre-treat their surfaces before use, such as primer resins. Acrylic resin is a commonly used substrate primer, but acrylic resin will reduce the adhesion efficiency of molecular segments to the substrate surface due to the influence of the introduced emulsifier and metal ions such as sodium and potassium. In addition, the substrate can also be treated with corona, flame or ionization to increase the surface roughness of the substrate, increase the contact area with the coating, and make it easier to adhere. However, there is an obvious attenuation effect after the substrate is treated, causing the polar groups to migrate to the inside of the substrate and reduce the surface tension.

[0003] Improving the adhesion of acrylic primer resin to BOPP substrate can be designed based on the structure of the resin. For example, CN109852180A mentions the introduction of silane coupling agent to improve the adhesion of acrylic resin to PP substrate. This method is not effective for BOPP, which is more difficult to adhere to.

[0004] Therefore, developing an acrylic primer resin with low emulsifier content and excellent wetting and adhesion ability to BOPP substrate has important practical significance and practical value. Summary of the invention

[0005] To overcome the deficiencies in the prior art, one of the objectives of the present invention is to provide a novel emulsion polymerization method, by which the aqueous acrylic emulsion prepared can significantly improve the adhesion of the resin to a biaxially oriented polypropylene (BOPP) substrate.

[0006] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme:

[0007] A polymerization method for acrylic emulsion with low emulsifier dosage, wherein the functional monomer acid is first ionized, then mixed with a reaction solution consisting of an emulsifier, water, and an acrylate monomer, and polymerized under the action of an initiator to obtain an acrylic emulsion;

[0008] Wherein, the amount of emulsifier is 0.1% to 1.0% of the dry weight of the emulsion;

[0009] The amount of the functional monomer acid is 0.5% to 3.0% of the dry weight of the emulsion.

[0010] In the present invention, the functional monomer acid is first ionized and then evenly mixed with the pre-emulsion to ionize the hydrophilic groups in the pre-emulsion. During the reaction, the hydrophilic groups can be more enriched in the shell of the latex particles and form a hydrophilic protective layer. Compared with the traditional neutralization method, such as low-temperature post-addition neutralization, high-temperature neutralization, etc., this method can make the molecular segments more efficiently enriched in the shell under the drive of the hydrophilic group ions, thereby showing outstanding performance. On the one hand, the protective layer can replace the emulsifier to provide sufficient protection for the latex particles, reduce the amount of emulsifier, and greatly reduce the negative impact of the emulsifier in the acrylic emulsion on adhesion. At the same time, the amount of metal ions such as sodium and potassium introduced is limited, which can also effectively reduce its negative effect on the adhesion of the substrate. On the other hand, this polymerization method can also significantly improve the adhesion of the coating to the BOPP substrate by using a low amount of carboxyl groups, while ensuring the adhesion to the BOPP substrate, it can also maintain excellent chemical resistance and storage stability.

[0011] In one embodiment of the present invention, the functional monomer acid is selected from monomers containing unsaturated double bonds and hydrophilic groups, preferably one or more of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, and maleic acid.

[0012] In one embodiment of the present invention, ionization treatment is performed using a base, preferably an organic amine and / or ammonia water, more preferably one or more of ammonia water, triethylamine, ethanolamine, diethanolamine, and N,N-dimethylethanolamine; preferably, the degree of acid ionization of the functional monomer after treatment is 15%-110%, preferably 20%-50%.

[0013] In one embodiment of the present invention, the emulsifier is an anionic nonionic emulsifier that does not contain sodium or potassium metal ions, preferably one or more of fatty alcohol polyoxyethylene ether or its ammonium salt, fatty alcohol ether phosphate or its ammonium salt.

[0014] In one embodiment of the present invention, the acrylate monomer is selected from monomers containing unsaturated double bonds, preferably one or more of methyl acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and isooctyl methacrylate; preferably, based on the dry weight of the emulsion, the proportion of the acrylate monomer is 50% to 99%, preferably 65% ​​to 88.5%.

[0015] In one embodiment of the present invention, the initiator is selected from initiators that do not contain sodium or potassium metal ions, preferably ammonium persulfate; preferably, the amount of the initiator is 0.1-1 wt % of the total weight of the acrylate monomer, functional monomer acid and emulsifier.

[0016] In one embodiment of the present invention, the polymerization process comprises the following steps:

[0017] S1: first ionize the functional monomer acid and then prepare the pre-emulsion;

[0018] S2: adding the pre-emulsion and the aqueous solution of the initiator to the polymerization system for reaction;

[0019] S3: After the emulsion polymerization is completed, a neutralizing agent is added for neutralization and the mixture is filtered to obtain the acrylic emulsion.

[0020] In one embodiment of the present invention, the reaction temperature of S2 is 70-100°C.

[0021] Another object of the present invention is to provide an acrylic emulsion with a low emulsifier dosage.

[0022] An acrylic emulsion with a low emulsifier dosage is prepared by the above-mentioned polymerization method. The total mass content of sodium and potassium ions in the emulsion is less than 500 ppm, and the solid content accounts for more than or equal to 50 wt%.

[0023] Another object of the present invention is to provide a use of acrylic emulsion with low emulsifier dosage.

[0024] A use of an acrylic emulsion with a low emulsifier dosage, wherein the emulsion is prepared by the above-mentioned polymerization method, and the emulsion is used for preparing acrylic emulsion or water-based acrylic paint, and more preferably for preparing water-based acrylic ink primer.

[0025] Another object of the present invention is to provide a water-based acrylic ink primer.

[0026] A water-based acrylic ink primer coating, the coating adopts the acrylic emulsion prepared by the above-mentioned polymerization method, or adopts the above-mentioned acrylic emulsion.

[0027] The water-based acrylic paint of the present invention may include any other commonly used components permitted in the art, including but not limited to neutralizers, film-forming aids, wetting agents, defoamers, thickeners, etc., in addition to acrylic emulsions. Those skilled in the art may specifically select and adjust other components and dosages of the water-based acrylic paint based on conventional technical means in the art. The preparation method of the water-based acrylic paint is also a commonly used method in the art, and can be prepared by those skilled in the art using conventional methods.

[0028] Compared with the prior art, the positive effects of the present invention are:

[0029] It can significantly improve the adhesion of acrylic resin to BOPP substrate while ensuring the resin has excellent chemical resistance and storage stability. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments.

[0031] The percentages used in the embodiments and comparative examples of the present invention are all mass percentages unless otherwise specified.

[0032] The raw materials or reagents used in the examples and comparative examples of the present invention are shown in Table 1, and other raw materials or reagents are commercially available unless otherwise specified.

[0033] Table 1

[0034]

[0035] The degree of ionization is calculated by the formula (mass of the base / relative molecular mass of the base) / (mass of the functional monomer acid / relative molecular mass of the functional monomer acid).

[0036] Example 1

[0037] Preparation of acrylic emulsion

[0038] Step 1):

[0039] 1.1) First, 0.4 g of ammonia water and 2 g of AA (acrylic acid) were mixed evenly to obtain an ionized functional monomer acid; 90% of the total weight of AR-61 (polyoxyethyl tridecethoxy ammonium sulfate, 0.27 g) was dissolved in 30 g of deionized water, and then 47 g of MMA (methyl methacrylate), 40 g of BA (butyl acrylate) and the ionized functional monomer acid were added in sequence, and stirred in an emulsifier to form a pre-emulsion;

[0040] 1.2) Dissolve the remaining AR-61 (0.03 g) in 90 g of deionized water and add it to the reactor. Expel the air in the reactor by introducing nitrogen and maintain the reaction temperature at 85°C.

[0041] 4% (accounting for the total mass of the pre-emulsion) of the pre-emulsion from step 1.1) was put into the reactor as the seed emulsion of the core, and then 40% (accounting for the total mass of the initiator) of the initiator (2.0 g of 10% APS (ammonium persulfate) aqueous solution) was added;

[0042] 1.3) After the polymerization reaction has occurred for 30 minutes, the remaining pre-emulsion and the remaining initiator aqueous solution are added dropwise for a total of 4 hours, while maintaining the reaction temperature at 85°C; after the addition is completed, the temperature is kept at 85°C for 1 hour, and then the temperature is lowered to 40°C;

[0043] 1.4) Ammonia water was added to the obtained polymer emulsion to neutralize it to weak alkalinity (pH value was 8.0), and then the material was filtered out to obtain the final acrylic emulsion. After measurement, water was added to adjust its solid content to 50%.

[0044] Example 2-8, Comparative Example 1-2

[0045] The acrylic emulsions were prepared by the same preparation method as in Example 1, with the only difference being the type and amount of raw materials, as shown in Table 2; wherein, the difference between Comparative Examples 1 and 2 and Example 1 is the degree of ionization of the functional monomer acid.

[0046] Table 2 The amount of each raw material in Examples 2-8 and Comparative Examples 1-2 (unit: g)

[0047]

[0048]

[0049] The hydroxy acrylic emulsions prepared in Examples 2-8 and Comparative Examples 1-2 were used to prepare corresponding water-based acrylic coatings according to the water-based acrylic coating formula shown in Table 3-1.

[0050] Table 3 Water-based coating formula

[0051] name Mass% Lotion 50 Color paste 35 Wax emulsion Joncryl 8071 (BASF) 14 Brightener wax 28 (BASF) 0.3 Wear-resistant agent we 3227 (BASF) 0.3 Wetting agent DC 50 (Dow) 0.4 total 100

[0052] The preparation process of water-based acrylic paint is as follows:

[0053] According to the formulation in Table 3, first add 100 g of emulsion, 70 g of color paste, 28 g of wax emulsion, 0.6 g of brightener, 0.6 g of wear agent, and 0.8 g of wetting agent into a dispersion tank, and stir at 300 r / min for 30 min to obtain a water-based acrylic paint.

[0054] Emulsion performance evaluation

[0055] The film properties of water-based acrylic paints prepared from the commercially available product Wantipro 825 (Wanhua Chemical), the acrylic emulsions of Examples 1-8 and Comparative Examples 1-2 were evaluated. The specific results are shown in Table 4.

[0056] Table 4 Performance test results of water-based acrylic coatings

[0057]

[0058] Adhesion test refers to GB / T9286-1998; the adhesion level is 1-5, 1 is the best.

[0059] From the test results in Table 4, we can see that:

[0060] (1) As shown in Comparative Examples 1 and 2, the method without pre-emulsion neutralization resulted in poor resin adhesion.

[0061] (2) As shown in Examples 2-8, after the pre-emulsion is neutralized, the adhesion of the resin to the substrate is significantly improved. When the degree of ionization of the functional monomer acid is 15%-110%, it is the adjustment range for improving the freeze-thaw stability of the acrylic emulsion by this method, and the preferred degree of ionization is 20%-50%.

[0062] The above results show that the acrylic emulsion prepared by the pre-emulsion neutralization method of the present invention has excellent adhesion and can significantly improve the adhesion of the BOPP substrate, and thus has industrial practical value.

[0063] Unless otherwise specified, the terms used in the present invention have the meanings commonly understood by those skilled in the art. The embodiments described in the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Those skilled in the art may make various other substitutions, changes and improvements within the scope of the present invention. Therefore, the present invention is not limited to the above embodiments, but is only limited by the claims.

Claims

1. A polymerization method for acrylic emulsion with low emulsifier dosage, characterized in that: The polymerization method first ionizes the functional monomer acid, then mixes it with a reaction solution consisting of an emulsifier, water, and an acrylate monomer, and polymerizes it under the action of an initiator to obtain an acrylic emulsion; Wherein, the amount of emulsifier is 0.1% to 1.0% of the dry weight of the emulsion; The amount of the functional monomer acid is 0.5% to 3.0% of the dry weight of the emulsion.

2. The polymerization method according to claim 1, characterized in that: The functional monomer acid is selected from monomers containing unsaturated double bonds and hydrophilic groups, preferably one or more of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, and maleic acid; and / or, using a base for ionization treatment, preferably the base is an organic amine and / or ammonia water, more preferably the base is one or more of ammonia water, triethylamine, ethanolamine, diethanolamine, N,N-dimethylethanolamine; Preferably, the degree of acid ionization of the treated functional monomer is 15%-110%, preferably 20%-50%.

3. The polymerization method according to claim 1 or 2, characterized in that The emulsifier is an anionic nonionic emulsifier that does not contain sodium or potassium metal ions, preferably one or more of fatty alcohol polyoxyethylene ether or its ammonium salt, fatty alcohol ether phosphate or its ammonium salt; And / or, the acrylate monomer is selected from monomers containing unsaturated double bonds, preferably one or more of methyl acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and isooctyl methacrylate; Preferably, the proportion of acrylate monomer is 50% to 99%, preferably 65% ​​to 88.5%, based on the dry weight of the emulsion; and / or, the initiator is selected from an initiator that does not contain sodium or potassium metal ions, preferably ammonium persulfate; Preferably, the amount of the initiator used is 0.1-1 wt % of the total weight of the acrylate monomer, the functional monomer acid and the emulsifier.

4. The polymerization method according to any one of claims 1 to 3, characterized in that The polymerization method comprises the following steps: S1: first ionize the functional monomer acid and then prepare the pre-emulsion; S2: adding the pre-emulsion and the aqueous solution of the initiator to the polymerization system for reaction; S3: After the emulsion polymerization is completed, a neutralizing agent is added for neutralization and the mixture is filtered to obtain the acrylic emulsion.

5. The preparation method according to claim 4, characterized in that: The reaction temperature of S2 is 70-100°C.

6. An acrylic emulsion with low emulsifier dosage, wherein the emulsion is prepared by the polymerization method according to any one of claims 1 to 5, characterized in that: The total mass content of sodium and potassium ions in the emulsion is less than 500 ppm, and the solid content accounts for more than or equal to 50 wt%.

7. Use of an acrylic emulsion with a low emulsifier dosage, wherein the emulsion is prepared by the polymerization method according to any one of claims 1 to 5, and the emulsion is used to prepare acrylic emulsion or water-based acrylic coating, more preferably used to prepare water-based acrylic ink primer.

8. A water-based acrylic ink primer, wherein the primer is an acrylic emulsion prepared by the polymerization method according to any one of claims 1 to 5, or an acrylic emulsion according to claim 6.

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