Water-based acrylate emulsion for heavy ink flexible plate printing on BOPP (biaxially-oriented polypropylene) film and preparation method of water-based acrylate emulsion

Abstract

The invention provides a water-based acrylate emulsion with excellent heavy ink flexible plate printing performance on a BOPP (biaxially-oriented polypropylene) film and a preparation method of the water-based acrylate emulsion. In the preparation process, compounding of at least two hard monomers, compounding of at least two soft monomers and compounding of at least two emulsifiers are used, particularly, a polymerizable emulsifier is adopted, and a seed pre-emulsification process is adopted for preparation; the obtained water-based acrylate emulsion has excellent ice water resistance, excellent bar code printing performance and excellent heavy ink absorption performance when being used for flexible plate printing on a BOPP (biaxially-oriented polypropylene) film.

Description

Technical Field

[0001] The invention belongs to the technical field of water-based acrylic emulsion for flexographic printing, and particularly relates to a water-based acrylic emulsion for heavy-ink flexographic printing on a BOPP film and a preparation method thereof. Background Art

[0002] At present, the substrates used in the label industry are mainly films (BOPP, PVC, PET, PC, synthetic paper, PS, PE, etc.) and paper bases (glass cardboard, offset paper, coated paper, foil board paper, kraft paper, etc.); the inks used include UV ink, solvent ink, water-based ink, weak solvent ink, etc.; the resins used are mainly acrylates and polyurethanes.

[0003] Due to its excellent performance, BOPP film is widely used in beverage bottles, cosmetic bottles and other bottle labels. Beverage bottles are required to be placed in refrigerators, and the printed patterns, logos, barcodes, etc. must be clear and beautiful. Therefore, the label coating has excellent properties such as resistance to ice water, clear barcode printing, good color development, and heavy ink absorption.

[0004] The products that can meet all the above performance requirements on the market are mainly polyurethane, but polyurethane is expensive, and the price competition in the label market is becoming more and more fierce. Therefore, a low-priced and high-performance product is needed to replace polyurethane products. Summary of the invention

[0005] In view of the defects of the prior art, the object of the present invention is to provide an aqueous acrylic emulsion with excellent heavy ink flexographic printing performance on BOPP film and a preparation method thereof. The obtained aqueous acrylic emulsion is used for flexographic printing on BOPP film and has excellent ice water resistance, excellent barcode printing performance and excellent heavy ink absorption performance.

[0006] To achieve the above purpose, the solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing an aqueous acrylic emulsion for heavy ink flexographic printing on a BOPP film, comprising the following steps:

[0008] Step (1), preparation of a pre-emulsion: adding a hard monomer, a soft monomer, a carboxylic acid unsaturated monomer and a functional monomer to an aqueous solution containing a portion of an emulsifier to obtain a pre-emulsion;

[0009] Step (2), preparation of seed emulsion: a buffer, water and the remaining emulsifier are mixed, added to a reaction kettle, stirred and heated, and when the temperature reaches a set temperature, a portion of the pre-emulsified liquid in step (1) is added to the reaction kettle, and then a portion of the initiator is added, and the temperature is kept for a period of time to obtain a seed emulsion;

[0010] Step (3), preparation of the finished product: within a certain period of time, the remaining pre-emulsion is added dropwise to the seed emulsion, and then the pre-emulsion is added dropwise, and at the same time, the remaining initiator solution is added dropwise, after the addition is completed, the mixture is kept warm for a certain period of time, and then cooled to room temperature, the pH value is adjusted using a pH adjuster, and the material is filtered to obtain the finished product;

[0011] The raw materials used to prepare the aqueous acrylic emulsion include the following components in parts by weight: 10-50 parts by weight of hard monomer, 50-80 parts by weight of soft monomer, 0.1-10 parts by weight of carboxylic acid unsaturated monomer, 0.1-1 part by weight of functional monomer, 0.1-5 parts by weight of emulsifier, 0.1-2 parts by weight of initiator, and 0.1-1 part by weight of buffer.

[0012] Preferably, the hard monomer is selected from one or more of methyl methacrylate (MMA), styrene (SM), acrylonitrile (CAN) and vinyl acetate (PEVA); the soft monomer is selected from one or more of ethyl acrylate (EA), butyl acrylate (BA), isooctyl acrylate (2-EHA) and hydroxyethyl acrylate (HEA); the carboxylic acid unsaturated monomer is selected from one or more of acrylic acid (AA), methacrylic acid (MAA), itaconic acid (ITA) and maleic acid (MA).

[0013] Preferably, the hard monomer is selected from at least two combinations of methyl methacrylate (MMA), styrene (SM), acrylonitrile (CAN) and vinyl acetate (PEVA); the soft monomer is selected from at least two combinations of ethyl acrylate (EA), butyl acrylate (BA), isooctyl acrylate (2-EHA) and hydroxyethyl acrylate (HEA).

[0014] Preferably, the functional monomer includes a cross-linking monomer and / or a molecular weight regulator, the cross-linking monomer is selected from one or more of diacetone acrylamide (DAAM), adipic acid dihydrazide (ADH), organic zinc salts, organic aluminum salts, diallyl phthalate (DAP) and ethylene glycol dimethacrylate (EGDMA), and the molecular weight regulator is selected from one or more of mercaptoethanol (ME), mercaptopropionic acid (3-MPA), n-butyl mercaptopropionate, α-methylstyrene dimer (AMSD), n-dodecyl mercaptan and tert-dodecyl mercaptan.

[0015] Preferably, the emulsifier is selected from one or more of polymerizable emulsifiers, phosphate esters, sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate and sodium benzene sulfonate, preferably selected from at least two of polymerizable emulsifiers, phosphate esters, sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate and sodium benzene sulfonate, more preferably a combination of a polymerizable emulsifier and a phosphate ester; wherein the polymerizable emulsifier is selected from one or more of vinyl sulfonate sodium salt (SVS), allyl sulfonate sodium salt (SAS), allyloxy nonylphenol polyoxyethylene (10) ether (ANPEO10), allyloxy nonylphenol polyoxyethylene (10) ether monophosphate (ANPEO10-P1), allyloxy nonylphenol polyoxyethylene (10) ether ammonium sulfate (DNS-86), allyloxy hydroxypropane sulfonic acid sodium salt (HAPS), methacrylate hydroxypropane sulfonic acid sodium salt (HPMAS) and 2-acrylamido-2-methylpropane sulfonic acid sodium salt (AMPS-NA).

[0016] Preferably, the initiator is selected from one or more of ammonium persulfate (APS), potassium persulfate, sodium persulfate, tert-butyl hydroperoxide (TBHP), hydrogen peroxide, ascorbic acid (VC) and sodium sulfoxylate.

[0017] Preferably, the buffer is selected from one or more of sodium bicarbonate, ammonium bicarbonate, sodium carbonate and ammonium carbonate; and the pH adjuster is selected from one or more of ammonia water, sodium hydroxide and potassium hydroxide.

[0018] Preferably, in step (1), the amount of emulsifier added is 10 wt% to 90 wt% of the total amount of emulsifier used.

[0019] Preferably, in step (2), the set temperature is 70-90° C., the holding time is 15-30 min, and the amount of initiator added is 10wt%-50wt% of the total amount of initiator used; the amount of pre-emulsion added in step (2) is 5-20% of the total mass of the pre-emulsion prepared in step (1).

[0020] Preferably, in step (3), the remaining pre-emulsion is added to the seed emulsion for 120-240 min, the pre-emulsion and the remaining initiator solution are added for 120-240 min, and the insulation time after the addition is completed is 30-90 min; the pH value is adjusted to 7.5-8.5 using a pH adjuster.

[0021] In a second aspect, the present invention also provides an aqueous acrylic emulsion for heavy-ink flexographic printing on BOPP film prepared by the preparation method as described above, wherein the aqueous acrylic emulsion has a molecular weight of 50,000 to 500,000, a solid content of 30-50%, and an emulsion particle size of 50-500 nm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention provides an aqueous acrylic emulsion with excellent heavy-ink flexographic printing performance on a BOPP film and a preparation method thereof. In the preparation process, at least two hard monomers, at least two soft monomers and at least two emulsifiers are compounded, especially a polymerizable emulsifier is used, and the aqueous acrylic emulsion is prepared through a seed pre-emulsification process. The obtained aqueous acrylic emulsion is used for flexographic printing on a BOPP film and has excellent ice water resistance, excellent barcode printing performance and excellent heavy ink absorption performance. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with examples, the purpose of which is to better understand the content of the present invention and reflect the essential characteristics of the present invention, so the examples cited should not be regarded as limiting the scope of protection of the present invention. It is also particularly pointed out here that the specific experimental methods and equipment involved in the examples are conventional methods or implemented under the conditions recommended by the manufacturer's instructions unless otherwise specified, and the reagents involved are commercially available unless otherwise specified.

[0025] Embodiment 1:

[0026] This embodiment provides an aqueous acrylic emulsion for heavy-ink flexographic printing on a BOPP film, and the preparation method thereof comprises the following steps:

[0027] 1. Preparation of pre-emulsion: add 1 part of methacrylic acid (MAA, carboxylic acid unsaturated monomer), 16 parts of methyl methacrylate (MMA, hard monomer), 60 parts of butyl acrylate (BA, soft monomer), 1 part of hydroxyethyl acrylate (HEA, soft monomer), 22 parts of styrene (SM, hard monomer), 0.5 parts of mercaptopropionic acid (molecular weight regulator), 0.4 parts of phosphate emulsifier, 26 parts of water, and 0.1 parts of ammonium bicarbonate (buffer) into a premixing tank, stir and mix well at high speed to obtain a pre-emulsion;

[0028] 2. Preparation of seed emulsion: add 0.2 parts of phosphate emulsifier, 0.3 parts of sodium dodecyl sulfate emulsifier and 80 parts of water into the reactor, turn on the stirring at a speed of 120 rpm, and then raise the temperature of the reactor to 80°C. When the temperature of the reactor stabilizes, add 0.15 parts of ammonium persulfate solution, and then add 10% of the pre-emulsion, react for 15 minutes, and control the temperature between 70-90°C;

[0029] 3. Preparation of finished product: After the seed reaction is completed, the remaining pre-emulsion and the remaining 0.5 parts of ammonium persulfate solution are added dropwise for 3 hours. After the addition is completed, the mixture is kept warm for 1 hour. Then the temperature is lowered to 40°C, and ammonia water is added to neutralize the mixture to adjust the pH to between 7.5 and 8.5 to obtain an ink emulsion for high-performance heavy-ink flexographic printing.

[0030] Embodiment 2:

[0031] This embodiment provides an aqueous acrylic emulsion for heavy-ink flexographic printing on a BOPP film, and the preparation method thereof comprises the following steps:

[0032] 1. Preparation of pre-emulsion: add 1 part of methacrylic acid (MAA, carboxylic acid unsaturated monomer), 16 parts of methyl methacrylate (MMA, hard monomer), 60 parts of butyl acrylate (BA, soft monomer), 1 part of hydroxyethyl acrylate (HEA, soft monomer), 22 parts of styrene (SM, hard monomer), 0.5 parts of mercaptopropionic acid (molecular weight regulator), 0.4 parts of phosphate emulsifier, 26 parts of water, and 0.1 parts of ammonium bicarbonate (buffer) into a premixing tank, stir and mix well at high speed to obtain a pre-emulsion;

[0033] 2. Preparation of seed emulsion: 0.2 parts of phosphate emulsifier, 0.5 parts of sodium vinyl sulfonate (SVS, polymerizable emulsifier), and 80 parts of water were added to a reactor, stirring was started at a speed of 120 rpm, and then the reactor temperature was raised to 80°C. When the reactor temperature stabilized, 0.2 parts of ammonium persulfate solution was added, and then 10% of the pre-emulsion was added, and the reaction was carried out for 15 minutes, and the temperature was controlled between 70-90°C;

[0034] 3. Preparation of finished product: After the seed reaction is completed, the remaining pre-emulsion and the remaining 0.4 parts of ammonium persulfate solution are added dropwise for 3 hours. After the addition is completed, the mixture is kept warm for 1 hour. Then the temperature is lowered to 40°C, and ammonia water is added to neutralize the mixture to adjust the pH to between 7.5 and 8.5 to obtain an ink emulsion for high-performance heavy-ink flexographic printing.

[0035] Embodiment 3:

[0036] This embodiment provides an aqueous acrylic emulsion for heavy-ink flexographic printing on a BOPP film, and the preparation method thereof comprises the following steps:

[0037] 1. Preparation of pre-emulsion: add 1 part of methacrylic acid (MAA, carboxylic acid unsaturated monomer), 6 parts of methyl methacrylate (MMA, hard monomer), 10 parts of acrylonitrile (CAN, hard monomer), 60 parts of butyl acrylate (BA, soft monomer), 1 part of hydroxyethyl acrylate (HEA, soft monomer), 22 parts of styrene (SM, hard monomer), 0.5 parts of mercaptopropionic acid (molecular weight regulator), 0.4 parts of phosphate emulsifier, 26 parts of water, and 0.1 parts of ammonium bicarbonate (buffer) into a premixing tank, stir and mix well at high speed to obtain a pre-emulsion;

[0038] 2. Preparation of seed emulsion: 0.2 parts of phosphate emulsifier, 0.5 parts of sodium vinyl sulfonate (SVS, polymerizable emulsifier), and 80 parts of water were added to a reactor, stirring was started at a speed of 120 rpm, and then the reactor temperature was raised to 80°C. When the reactor temperature stabilized, 0.15 parts of ammonium persulfate solution was added, and then 10% of the pre-emulsion was added, and the reaction was carried out for 15 minutes, and the temperature was controlled between 70-90°C;

[0039] 3. Preparation of finished product: After the seed reaction is completed, the remaining pre-emulsion and the remaining 0.5 parts of ammonium persulfate solution are added dropwise for 3 hours. After the addition is completed, the mixture is kept warm for 1 hour. Then the temperature is lowered to 40°C, and ammonia water is added to neutralize the mixture to adjust the pH to between 7.5 and 8.5 to obtain an ink emulsion for high-performance heavy-ink flexographic printing.

[0040] Embodiment 4:

[0041] This embodiment provides an aqueous acrylic emulsion for heavy-ink flexographic printing on a BOPP film, and the preparation method thereof comprises the following steps:

[0042] 1. Preparation of pre-emulsion: add 1 part of methacrylic acid (MAA, carboxylic acid unsaturated monomer), 6 parts of methyl methacrylate (MMA, hard monomer), 10 parts of acrylonitrile (CAN, hard monomer), 60 parts of butyl acrylate (BA, soft monomer), 1 part of hydroxyethyl acrylate (HEA, soft monomer), 22 parts of styrene (SM, hard monomer), 0.3 parts of mercaptopropionic acid (molecular weight regulator), 0.8 parts of sodium vinyl sulfonate (SVS, polymerizable emulsifier), 26 parts of water, and 0.1 parts of ammonium bicarbonate (buffer) into a premixing tank, stir and mix well at high speed to obtain a pre-emulsion;

[0043] 2. Preparation of seed emulsion: 0.2 parts of phosphate emulsifier, 0.5 parts of sodium vinyl sulfonate (SVS, polymerizable emulsifier), and 80 parts of water were added to a reactor, stirring was started at a speed of 120 rpm, and then the reactor temperature was raised to 80°C. When the reactor temperature stabilized, 0.15 parts of ammonium persulfate solution was added, and then 10% of the pre-emulsion was added, and the reaction was carried out for 15 minutes, and the temperature was controlled between 70-90°C;

[0044] 3. Preparation of finished product: After the seed reaction is completed, the remaining pre-emulsion and the remaining 0.4 parts of ammonium persulfate solution are added dropwise for 3 hours. After the addition is completed, the mixture is kept warm for 1 hour. Then the temperature is lowered to 40°C, and ammonia water is added to neutralize the mixture to adjust the pH to between 7.5 and 8.5 to obtain an ink emulsion for high-performance heavy-ink flexographic printing.

[0045] Comparative Example 1 (using one hard monomer and one soft monomer based on Example 2):

[0046] This embodiment provides an aqueous acrylic emulsion for heavy-ink flexographic printing on a BOPP film, and the preparation method thereof comprises the following steps:

[0047] 1. Preparation of pre-emulsion: add 1 part of methacrylic acid (MAA, carboxylic acid unsaturated monomer), 38 parts of methyl methacrylate (MMA, hard monomer), 61 parts of butyl acrylate (BA, soft monomer), 0.5 parts of mercaptopropionic acid (molecular weight regulator), 0.4 parts of phosphate emulsifier, 26 parts of water, and 0.1 parts of ammonium bicarbonate (buffer) into a premixing tank, stir and mix well at high speed to obtain a pre-emulsion;

[0048] 2. Preparation of seed emulsion: 0.2 parts of phosphate emulsifier, 0.5 parts of sodium vinyl sulfonate (SVS, polymerizable emulsifier), and 80 parts of water were added to a reactor, stirring was started at a speed of 120 rpm, and then the reactor temperature was raised to 80°C. When the reactor temperature stabilized, 0.15 parts of ammonium persulfate solution was added, and then 10% of the pre-emulsion was added, and the reaction was carried out for 15 minutes, and the temperature was controlled between 70-90°C;

[0049] 3. Preparation of finished product: After the seed reaction is completed, the remaining pre-emulsion and the remaining 0.5 parts of ammonium persulfate solution are added dropwise for 3 hours. After the addition is completed, the mixture is kept warm for 1 hour. Then the temperature is lowered to 40°C, and ammonia water is added to neutralize the mixture to adjust the pH to between 7.5 and 8.5 to obtain an ink emulsion for high-performance heavy-ink flexographic printing.

[0050] Comparative Example 2 (using a phosphate emulsifier based on Comparative Example 1):

[0051] This embodiment provides an aqueous acrylic emulsion for heavy-ink flexographic printing on a BOPP film, and the preparation method thereof comprises the following steps:

[0052] 1. Preparation of pre-emulsion: add 1 part of methacrylic acid (MAA, carboxylic acid unsaturated monomer), 38 parts of methyl methacrylate (MMA, hard monomer), 61 parts of butyl acrylate (BA, soft monomer), 0.5 parts of mercaptopropionic acid (molecular weight regulator), 0.4 parts of phosphate emulsifier, 26 parts of water, and 0.1 parts of ammonium bicarbonate (buffer) into a premixing tank, stir and mix well at high speed to obtain a pre-emulsion;

[0053] 2. Preparation of seed emulsion: add 0.7 parts of phosphate emulsifier and 80 parts of water into the reactor, turn on the stirring, the stirring speed is 120rpm, and then raise the temperature of the reactor to 80°C. When the temperature of the reactor stabilizes, add 0.15 parts of ammonium persulfate solution, and then add 10% of pre-emulsion, react for 15 minutes, and control the temperature between 70-90°C;

[0054] 3. Preparation of finished product: After the seed reaction is completed, the remaining pre-emulsion and the remaining 0.5 parts of ammonium persulfate solution are added dropwise for 3 hours. After the addition is completed, the mixture is kept warm for 1 hour. Then the temperature is lowered to 40°C, and ammonia water is added to neutralize the mixture to adjust the pH to between 7.5 and 8.5 to obtain an ink emulsion for high-performance heavy-ink flexographic printing.

[0055] Efficacy test:

[0056] 1. Barcode printing performance test: Tested in accordance with GB T18805-2002 standard;

[0057] 2. Heavy ink absorption test: Test according to GB12911-91 standard;

[0058] 3. Ice water resistance test: The test condition is 4 degrees Celsius ice water, the label size is 20*5cm, the immersion time is 12 hours, and the coating is tested to see if it falls off;

[0059] 4. Ink shedding test: Conduct standard testing in accordance with GB / T 15962-2008.

[0060] The test results of various properties of the aqueous acrylic emulsion for heavy-ink flexographic printing on BOPP film obtained in Examples 1 to 4 and Comparative Examples 1 to 2 are shown in Table 1.

[0061] Table 1

[0062]

[0063] From Table 1 we can see that:

[0064] (1) Comparison between Example 1 and Example 2: Example 1 uses two hard monomers, two soft monomers and two emulsifiers. Compared with Example 1, the two emulsifiers used in Example 2 are a compound of phosphate ester and polymerizable emulsifier. The molecular weight and particle size of the aqueous acrylate emulsion obtained in Example 2 are smaller, but the barcode printing performance is improved, indicating that the use of polymerizable emulsifiers can improve the barcode printing performance;

[0065] (2) Comparison between Example 2 and Example 3: Example 2 uses a compound of two hard monomers, a compound of two soft monomers, and a compound of a phosphate emulsifier and a polymerizable emulsifier. Compared with Example 2, Example 3 uses a compound of three hard monomers, a compound of two soft monomers, and a compound of a phosphate emulsifier and a polymerizable emulsifier. The molecular weight and particle size of the aqueous acrylic emulsion obtained in Example 3 are larger, but the barcode printing performance, heavy ink absorption, ice water resistance, and oil film shedding performance are not significantly improved;

[0066] (3) Comparison between Example 3 and Example 4: Example 3 uses a compound of three hard monomers, a compound of two soft monomers, and a compound of a phosphate emulsifier and a polymerizable emulsifier. Compared with Example 3, Example 4 uses relatively less molecular weight regulator and relatively more polymerizable emulsifier. The aqueous acrylic emulsion obtained in Example 4 has a larger molecular weight and a smaller emulsion particle size, and the barcode printing performance, heavy ink absorption, and oil film shedding performance are significantly improved.

[0067] (4) Comparative Examples 1 and 2 both use a single hard monomer and a single soft monomer. Compared with Examples 1 to 4, the obtained aqueous acrylic emulsions have a larger molecular weight and a smaller emulsion particle size. The barcode printing performance, heavy ink absorption, ice water resistance and oil film shedding performance cannot meet the requirements.

[0068] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing an aqueous acrylic emulsion for heavy ink flexographic printing on BOPP film, characterized in that: The steps include: Step (1), preparation of a pre-emulsion: adding a hard monomer, a soft monomer, a carboxylic acid unsaturated monomer and a functional monomer to an aqueous solution containing a portion of an emulsifier to obtain a pre-emulsion; Step (2), preparation of seed emulsion: a buffer, water and the remaining emulsifier are mixed, added to a reaction kettle, stirred and heated, and when the temperature reaches a set temperature, a portion of the pre-emulsified liquid in step (1) is added to the reaction kettle, and then a portion of the initiator is added, and the temperature is kept for a period of time to obtain a seed emulsion; Step (3), preparation of the finished product: within a certain period of time, the remaining pre-emulsion is added dropwise to the seed emulsion, and then the pre-emulsion is added dropwise, and at the same time, the remaining initiator solution is added dropwise, after the addition is completed, the mixture is kept warm for a certain period of time, and then cooled to room temperature, the pH value is adjusted using a pH adjuster, and the material is filtered to obtain the finished product; The raw materials used to prepare the aqueous acrylic emulsion include the following components in parts by weight: 10-50 parts by weight of hard monomer, 50-80 parts by weight of soft monomer, 0.1-10 parts by weight of carboxylic acid unsaturated monomer, 0.1-1 part by weight of functional monomer, 0.1-5 parts by weight of emulsifier, 0.1-2 parts by weight of initiator and 0.1-1 part by weight of buffer.

2. The preparation method according to claim 1, characterized in that: The hard monomer is selected from one or more of methyl methacrylate (MMA), styrene (SM), acrylonitrile (CAN) and vinyl acetate (PEVA); the soft monomer is selected from one or more of ethyl acrylate (EA), butyl acrylate (BA), isooctyl acrylate (2-EHA) and hydroxyethyl acrylate (HEA); the carboxylic acid unsaturated monomer is selected from one or more of acrylic acid (AA), methacrylic acid (MAA), itaconic acid (ITA) and maleic acid (MA).

3. The preparation method according to claim 2, characterized in that: The hard monomer is selected from at least two combinations of methyl methacrylate (MMA), styrene (SM), acrylonitrile (CAN) and vinyl acetate (PEVA); the soft monomer is selected from at least two combinations of ethyl acrylate (EA), butyl acrylate (BA), isooctyl acrylate (2-EHA) and hydroxyethyl acrylate (HEA).

4. The preparation method according to claim 1, characterized in that: The functional monomers include cross-linking monomers and / or molecular weight regulators, wherein the cross-linking monomers are selected from one or more of diacetone acrylamide (DAAM), adipic acid dihydrazide (ADH), organic zinc salts, organic aluminum salts, diallyl phthalate (DAP) and ethylene glycol dimethacrylate (EGDMA), and the molecular weight regulator is selected from one or more of mercaptoethanol (ME), mercaptopropionic acid (3-MPA), n-butyl mercaptopropionate, α-methylstyrene dimer (AMSD), n-dodecyl mercaptan and tert-dodecyl mercaptan.

5. The preparation method according to claim 1, characterized in that: The emulsifier is selected from one or more of polymerizable emulsifiers, phosphate esters, sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate and sodium benzene sulfonate, preferably selected from at least two of polymerizable emulsifiers, phosphate esters, sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate and sodium benzene sulfonate, and more preferably a combination of a polymerizable emulsifier and a phosphate ester; wherein the polymerizable emulsifier is selected from one or more of sodium vinyl sulfonate (SVS), sodium allyl sulfonate (SAS), allyloxy nonylphenol polyoxyethylene (10) ether (ANPEO10), allyloxy nonylphenol polyoxyethylene (10) ether monophosphate (ANPEO10-P1), allyloxy nonylphenol polyoxyethylene (10) ether ammonium sulfate (DNS-86), allyloxy hydroxypropane sulfonic acid sodium salt (HAPS), methacrylate hydroxypropane sulfonic acid sodium salt (HPMAS) and 2-acrylamido-2-methylpropane sulfonic acid sodium salt (AMPS-NA).

6. The preparation method according to claim 1, characterized in that: The initiator is selected from one or more of ammonium persulfate (APS), potassium persulfate, sodium persulfate, tert-butyl hydroperoxide (TBHP), hydrogen peroxide, ascorbic acid (VC) and sodium sulfoxylate; the buffer is selected from one or more of sodium bicarbonate, ammonium bicarbonate, sodium carbonate and ammonium carbonate; The pH regulator is selected from one or more of ammonia water, sodium hydroxide and potassium hydroxide.

7. The preparation method according to claim 1, characterized in that: In step (1), the amount of emulsifier added is 10wt%-90wt% of the total amount of emulsifier used.

8. The preparation method according to claim 1, characterized in that: In step (2), the temperature is set at 70-90° C., the insulation time is 15-30 min, and the amount of initiator added is 10wt%-50wt% of the total amount of initiator used; the amount of pre-emulsion added in step (2) is 5-20% of the total mass of the pre-emulsion prepared in step (1).

9. The preparation method according to claim 1, characterized in that: In step (3), the remaining pre-emulsion is added to the seed emulsion for 120-240 minutes, the pre-emulsion and the remaining initiator solution are added for 120-240 minutes, and the insulation time after the addition is completed is 30-90 minutes; the pH value is adjusted to 7.5-8.5 using a pH adjuster.

10. An aqueous acrylic emulsion for heavy ink flexographic printing on BOPP film prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The molecular weight of the water-based acrylic emulsion is 50,000-500,000, the solid content is 30-50%, and the emulsion particle size is 50-500 nm.

Images