Water-based self-crosslinking acrylic emulsion composition and preparation method thereof

Abstract

The invention provides a water-based self-crosslinking acrylic emulsion composition and a preparation method thereof. The acrylic emulsion composition comprises the following components: a styrene monomer, an acrylate monomer, a crosslinking monomer, a reactive emulsifier, alkali-soluble acrylic resin, an initiator, a chain transfer agent, a crosslinking aid and water. The water-based acrylic emulsion composition is prepared by adopting a pre-emulsification semi-continuous seed emulsion polymerization process. The preparation method has the beneficial effects of simple synthesis process and no need of complex structural design of latex particles, the conventional and easily available alkali-soluble acrylic resin and the reactive emulsifier are used for providing dual stable effects of steric hindrance and electrostatic repulsion, and the dissolution, migration and desorption of the emulsifier are reduced; the emulsion particles have high stability when ethanol is diluted and a high-concentration electrolyte solution is added, and water-based ink prepared from the emulsion has good ethanol dilutability and electrolyte tolerance during application, and cannot generate the problems of ink swelling, gelling, pigment flocculation and the like.

Description

[0001] The invention belongs to the technical field of water-based inks, and in particular relates to a water-based self-crosslinking acrylic emulsion composition and a preparation method thereof. Background Art

[0002] At present, expanding the application of green coatings or inks is one of the ways to reduce VOC emissions. Using source substitution with no or low VOCs raw materials can effectively reduce the emission of volatile organic compounds in the printing process and is also a relatively economical means of governance. Water-based inks with water as the main solvent have become the mainstream trend of source substitution solutions due to their low VOC content, no organic solvent residue, low environmental impact and high safety.

[0003] Water-based ink is mainly composed of pigments, additives, binders, water and other substances. Among the many materials that make up water-based ink, the binder plays a decisive role in the various properties of water-based ink, such as adhesion, water resistance, wear resistance, heat resistance, etc. It is also called the "heart of water-based ink". The binder used in water-based ink is water-based polymer or latex, among which water-based polyacrylate emulsion has been widely used due to its advantages of good film-forming properties, high gloss, good adhesion and low cost.

[0004] However, compared with solvent-based inks, water-based inks use water as a solvent, and at 25°C, the latent heat of evaporation of water is 44 kJ / mol, the highest among all known solvents. Therefore, during the printing process, the drying speed of water-based ink is slow, and it is easy to have serious problems such as sticking to the roller or back-sticking, which leads to product scrapping. In addition, the interaction between the printing substrate and the ink determines the adhesion of the ink layer to the substrate, and the strength of the interaction between the printing substrate and the ink is determined by the surface energy of the substrate and the surface tension of the ink. Since water is used as a solvent, the surface tension of the water-based ink is high, which cannot effectively wet some low surface energy films (such as polyethylene films or polypropylene films), resulting in low adhesion of the ink layer of the water-based ink and poor leveling.

[0005] Therefore, a solvent-ethanol with low toxicity and high volatility is usually added to water-based ink to improve its drying property, transfer leveling property and reduce surface tension. Therefore, improving the ethanol-resistant stability of water-based acrylic emulsion has important practical significance for improving the printing efficiency and printing quality of water-based ink and widening its application field. However, in actual production or application, when ethanol is added, even if there is mechanical stirring, the local concentration caused by uneven mixing is too high, and the problems of emulsion thickening, flocculation, and demulsification occur. Therefore, if the water-based acrylic emulsion can be diluted with ethanol in any proportion, the above problems will not occur.

[0006] As the main body of water-based ink, water-based polyacrylate emulsion acts as a binder in water-based ink, dispersing and stabilizing pigments, making the ink fluid, and providing adhesion to the substrate, so that the pattern printed by the ink maintains a stable color and the dry ink layer is water-resistant. However, compared with solvent-based inks, since water-based inks use water as a solvent, they dry slowly during the printing process, seriously affecting printing efficiency. Therefore, the application scope of water-based inks is greatly restricted, so that water-based inks cannot completely replace solvent-based inks.

[0007] Although there are many domestic patents on water-based acrylic emulsions for water-based inks, there are few patents on dilution with ethanol in any proportion. Patent CN 113527563 A of Wuhan University of Technology discloses a modified styrene-acrylic emulsion resistant to ethanol dilution and its preparation method and application. The silica-modified styrene-acrylic emulsion prepared in the invention has the characteristics of good ethanol dilution resistance, low monomer residue and stable emulsion. However, the ethanol dilution stability in the patent is determined by adding 10mL ethanol to 20g emulsion sample, shaking and shaking, and judging whether the emulsion is demulsified and flocculated. It does not achieve dilution in any proportion. Chinese patent CN102516436 A discloses a room temperature self-crosslinking styrene-acrylic emulsion resistant to ethanol dilution and its preparation method. The styrene-acrylic emulsion prepared in the invention has good compatibility with ethanol, improves the drying rate, and has significant improvements in water resistance, friction resistance, etc. However, the ethanol stability test method in the patent is to directly add ethanol to dilute it by one time, and the maximum ethanol dilution ratio is only 100%. Chinese patent CN 107298732 A discloses a core-shell structure styrene acrylic emulsion composition resistant to ethanol dilution and a preparation method thereof. The patent constructs a stable core-shell structure of latex particles, which greatly improves the ability of the emulsion to resist ethanol dilution from the latex particle structure. However, the synthesis method adopted in the patent is a segmented synthesis, and the monomers required for the core phase and the shell phase need to be pre-emulsified and added in sequence. The synthesis method of the core-shell structure of the latex particles is relatively cumbersome, and the requirements for the feeding reactor of the core-shell monomers are relatively high. In addition, the emulsifiers used in the above-mentioned patents are all traditional anionic non-ionic small molecule emulsifiers, but traditional small molecule emulsifiers often only emulsify and stabilize latex particles through adsorption. The emulsifier molecules will migrate to the interface between the film and the air and the film and the substrate during the latex film formation process, causing the migration of the emulsifier and causing environmental pollution or food and drug pollution and ink layer adhesion problems; In addition, in the process of preparing the ink, pigments, additives and salts and other additives will be added for use. These additives will form a certain amount of electrolytes in the water, and the counterions generated with different charges from the surface charges of the particles will compress the double layer, thereby reducing the repulsion between the particles. When the particles collide with each other, the gravitational force increases, causing the particles to condense and the emulsion to lose its stable dispersion state. Unfortunately, the above-mentioned invention patents only improve the tolerance of ethanol, and do not test its electrolyte stability. In actual applications, when encountering pigments or additives with high electrolyte strength, the problem of poor ink stability will also occur. Summary of the invention

[0008] The purpose of the present invention is to provide an aqueous self-crosslinking acrylic emulsion composition and a preparation method thereof in view of the above-mentioned key technical problems. The composition can be diluted with ethanol in any proportion, is stable to strong electrolytes and is suitable for aqueous inks, while improving the adhesion of the ink on different substrates and the printing safety.

[0009] In order to achieve the above object, the present invention adopts the following technical scheme: an aqueous self-crosslinking acrylic emulsion composition is prepared from the following components in parts by weight: Styrene monomer: 0-10 parts; Acrylate monomer: 15-30 parts; Cross-linking monomer: 1-5 parts; Reactive emulsifier: 1-5 parts; Alkali soluble acrylic resin: 10-30 parts; Chain transfer agent: 0-0.5 parts; Cross-linking aid: 0.5-1 part; Initiator: 0.5-1 part; Neutralizer: 0.5-2 parts; Water: 50-70 parts.

[0010] The styrene monomer may be one or both of styrene and methylstyrene, preferably styrene.

[0011] The above-mentioned acrylic acid ester monomers include, but are not limited to, one or more of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, isooctyl acrylate, hydroxyethyl acrylate, isobornyl acrylate, and isobornyl methacrylate, preferably one or more of methyl methacrylate, isooctyl acrylate, butyl acrylate, and isobornyl methacrylate.

[0012] The cross-linking monomers include, but are not limited to, one or more of vinyl siloxane monomers, diacetone acrylamide, N-hydroxymethyl acrylamide, glycidyl methacrylate, allyl acetoacetate, ethyl acetoacetate methacrylate, and hydroxyethyl methacrylate, preferably one of diacetone acrylamide, glycidyl methacrylate, and allyl acetoacetate.

[0013] The above-mentioned reactive emulsifier includes one or more of anionic reactive emulsifiers, cationic reactive emulsifiers, nonionic reactive emulsifiers and amphiphilic reactive emulsifiers, preferably one or two of 1-allyloxy-3-(4-nonylphenol)-2-propanol polyoxyethylene (10) ether ammonium sulfate, allyloxy isoalcohol ether sulfate ammonium salt, polyoxyethylene allyl alkyl ether ammonium sulfate, 3-allyloxy-1-hydroxy-1-propane sulfonate among the anionic reactive emulsifiers and 1-allyloxy-3-(4-nonylphenol)-2-propanol polyoxyethylene (10) ether, allyloxy nonylphenoxy propanol polyoxyethylene ether among the nonionic reactive emulsifiers.

[0014] The weight average molecular weight of the alkali-soluble acrylic resin is in the range of 2000-16000Da, the acid value is in the range of 50-250mgKOH / g, and the neutralization degree of the alkali-soluble resin solution prepared therefrom is in the range of 90-110%. Preferably, the alkali-soluble acrylic resin has a weight average molecular weight of 6000Da, an acid value of 65mgKOH / g, and a neutralization degree of 95%; a weight average molecular weight of 8500Da, an acid value of 215mgKOH / g, and a neutralization degree of 100%; and a weight average molecular weight of 10000Da, an acid value of 215mgKOH / g, and a neutralization degree of 110%.

[0015] The above-mentioned chain transfer agent includes but is not limited to one or more of aliphatic mercaptans, mercaptopropionic acid, 2-hydroxyethyl mercaptopropionate, 2-ethylhexyl mercaptoacetate, α-methylstyrene dimer, trichloroethylene, and tetrachloromethane, preferably one of 2-hydroxyethyl mercaptopropionate, 2-ethylhexyl mercaptoacetate, and α-methylstyrene dimer.

[0016] The cross-linking aid includes but is not limited to one or more of adipic acid dihydrazide, 1,6-hexanediamine, polycarbodiimide, polyethyleneimine, and nano zinc oxide, preferably one or two of adipic acid dihydrazide, 1,6-hexanediamine, and nano zinc oxide.

[0017] The preparation method of the above-mentioned aqueous self-crosslinking acrylic emulsion composition comprises the following steps: (1) Preparation of alkali-soluble acrylic resin solution: The weighed alkali-soluble acrylic resin and water are added into a 500 mL four-necked flask equipped with a reflux condenser, a temperature probe, a feed inlet and a stirrer, and dissolved for 3 h at a water bath temperature of 60°C and a stirring speed of 300 rpm. The neutralizer is added in 6 portions, each with an interval of 30 min. After stirring, a uniform, transparent aqueous solution with a solid content of 30% is obtained. The mass percentage of the solid alkali-soluble acrylic resin to the total amount of the monomer and the solid alkali-soluble acrylic resin is 20-40%.

[0018] (2) Preparation of pre-emulsion: Add styrene monomer, acrylate monomer, cross-linking monomer, reactive emulsifier, chain transfer agent and water in a three-necked round-bottom flask according to a set ratio and stir vigorously at room temperature for 30 min to prepare a pre-emulsion.

[0019] (3) Synthesis of emulsion: The above-mentioned aqueous self-crosslinking acrylic emulsion composition with arbitrary dilution ratio of ethanol and strong electrolyte resistance is prepared by pre-emulsification semi-continuous seed polymerization process. The dissolved alkali-soluble acrylic resin solution is placed in a flask, heated and stirred in a water bath. When the material temperature reaches 80°C, 10-15% of the pre-emulsion and 20-30% of the initiator solution are respectively added to the four-necked flask through a constant pressure dropping funnel. After the pre-emulsion is added, it is kept at 80°C for 30 minutes to obtain a blue phase seed emulsion. Subsequently, the remaining pre-emulsion and initiator solution are added to the reaction system, and the addition time is controlled to be 3-4 hours. After the pre-emulsion and initiator are added, the system temperature is raised to 90°C and kept for 1.5-2 hours to complete the post-polymerization. After the system is cooled to 40°C, the pH value of the latex is adjusted to between 8.0 and 8.5 with a neutralizer, and a cross-linking aid is added. After stirring for 30 minutes, the material is filtered through a 200-mesh filter and discharged.

[0020] The aqueous self-crosslinking acrylic emulsion group prepared above has the appearance of a translucent liquid; the particle size of the latex particles is 60-110nm; the glass transition temperature is 0-40°C; and the solid content is 40-50%. The synthetic emulsion can be directly added with ethanol or diluted in ethanol in any proportion without flocculation, demulsification, etc.; in addition, adding a 2% CaCl2 solution at a mass ratio of 40% of the emulsion into the emulsion will not cause the emulsion to demulsify or gel.

[0021] Compared with the prior art, the present invention has the following advantages: 1. The present invention has the beneficial effects of simple synthesis process and no need for complex latex particle structure design, so that the alkali-soluble acrylic resin and the reactive emulsifier provide dual stabilizing effects of steric hindrance and electrostatic repulsion, so that the synthetic emulsion can be diluted with ethanol in any proportion without any flocculation, demulsification and other unstable phenomena.

[0022] 2. The reactive emulsifier used in the present invention has the dual functions of a surfactant and a polymer monomer. The emulsifier forms a covalent bond by reacting with the polymer monomer and is tightly bound to the periphery of the latex particles, making it have excellent stability for high-concentration electrolyte solutions. The counterions in the electrolyte solution compress the double layer, and the flocculation and gelation of the emulsion are greatly reduced.

[0023] 3. Compared with traditional non-reactive small molecule emulsifiers, the use of large molecular alkali-soluble acrylic resins and small molecule reactive emulsifiers reduces the environmental pollution and safety problems caused by the dissolution, desorption and migration of emulsifiers during the application of the emulsion and after film formation. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with embodiments. The examples are only used to explain the present invention and are not used to limit the scope of the present invention. Example

[0025] (1) Preparation of alkali-soluble acrylic resin solution: The weighed alkali-soluble acrylic resin and water are added into a 500 mL four-necked flask equipped with a reflux condenser, a temperature probe, a feed inlet and a stirrer. The flask is dissolved for 3 h at a water bath temperature of 60 ° C and a stirring speed of 300 rpm. The neutralizer is added in 6 times, each time with an interval of 30 minutes. After stirring, a uniform and transparent aqueous solution is obtained. Among them, the weight average molecular weight of the alkali-soluble acrylic resin is 6000 Da, the acid value is 65 mgKOH / g, the neutralization degree of the alkali-soluble acrylic resin solution is 95%, and the neutralizer is ammonia water. Among them, the mass percentage of solid alkali-soluble acrylic resin to the total amount of monomers and solid alkali-soluble acrylic resin is 25%.

[0026] (2) Preparation of pre-emulsion: Add styrene monomer, acrylate monomer, cross-linking monomer, reactive emulsifier, chain transfer agent and water in a three-necked round-bottom flask according to the set ratio, and stir vigorously at room temperature for 30 minutes to prepare a pre-emulsion. Among them, styrene is selected as the styrene monomer, with a weight of 5.7 parts; butyl acrylate, methyl methacrylate and isooctyl acrylate are selected as the acrylate monomers, with a weight of 5.7 parts, 11.2 parts and 11.2 parts respectively; diacetone acrylamide is selected as the cross-linking monomer, with a weight of 1.1 parts; 1-allyloxy-3-(4-nonylphenol)-2-propanol polyoxyethylene (10) ether ammonium sulfate is selected as the reactive emulsifier, with a weight of 1.3 parts; and α-methylstyrene dimer is selected as the chain transfer agent, with a weight of 0.1 parts.

[0027] (3) Synthesis of emulsion: Put the dissolved alkali-soluble acrylic resin solution into a flask, heat it in a water bath and stir it. When the material temperature reaches 80°C, add 10-15% of the pre-emulsion and 20-30% of the initiator solution into the four-necked flask through a constant pressure dropping funnel. After the pre-emulsion is added, keep it at 80°C for 30 minutes to obtain a blue phase seed emulsion. Then, add the remaining pre-emulsion and initiator solution to the reaction system, and the addition time is controlled to be 3-4 hours. After the pre-emulsion and initiator are added, the system temperature is raised to 90°C and kept for 1.5-2 hours to complete the post-polymerization. After the system is cooled to 40°C, adjust the pH value of the latex to between 8.0 and 8.5 with a neutralizer, add a cross-linking aid, stir for 30 minutes, and filter with a 200-mesh filter to obtain an aqueous self-cross-linking acrylic emulsion that can be diluted in any proportion of ethanol and is resistant to strong electrolytes. Among them, the initiator is ammonium persulfate, 0.4 parts by weight, which is prepared into an initiator solution with 10.6 parts of water; the neutralizer for adjusting the pH of the emulsion is ammonia water, 1 part by weight; the cross-linking auxiliary agent is adipic acid dihydrazide, 0.5 parts by weight. Example

[0028] (1) Preparation of alkali-soluble acrylic resin solution: The weighed alkali-soluble acrylic resin and water are added into a 500 mL four-necked flask equipped with a reflux condenser, a temperature probe, a feed inlet and a stirrer. The flask is dissolved for 3 h at a water bath temperature of 60 ° C and a stirring speed of 300 rpm. The neutralizer is added in 6 times, each time with an interval of 30 minutes. After stirring, a uniform and transparent solution is obtained. Among them, the weight average molecular weight of the alkali-soluble acrylic resin is 8500 Da, the acid value is 215 mgKOH / g, the neutralization degree of the alkali-soluble acrylic resin solution is 100%, and the neutralizer is ammonia water. Among them, the mass percentage of solid alkali-soluble acrylic resin to the total amount of monomers and solid alkali-soluble acrylic resin is 30%.

[0029] (2) Preparation of pre-emulsion: Add styrene monomer, acrylate monomer, cross-linking monomer, reactive emulsifier, chain transfer agent and water in a three-necked round-bottom flask according to the set ratio, and stir vigorously at room temperature for 30 minutes to prepare a pre-emulsion. Among them, the styrene monomer is styrene, with a weight of 5 parts; the acrylate monomers are butyl methacrylate, methyl methacrylate, and isooctyl acrylate, with a weight of 5 parts, 12 parts, and 12 parts respectively; the cross-linking monomer is allyl acetoacetate, with a weight of 1.1 parts; the reactive emulsifier is allyloxy isomeric alcohol ether sulfate ammonium salt, with a weight of 1.3 parts; the chain transfer agent is 2-ethylhexyl thioglycolate, with a weight of 0.1 parts.

[0030] (3) Synthesis of emulsion: Put the dissolved alkali-soluble acrylic resin solution into a flask, heat it in a water bath and stir it. When the material temperature reaches 80°C, add 10-15% of the pre-emulsion and 20-30% of the initiator solution into the four-necked flask through a constant pressure dropping funnel. After the pre-emulsion is added, keep it at 80°C for 30 minutes to obtain a blue phase seed emulsion. Then, add the remaining pre-emulsion and initiator solution to the reaction system, and the addition time is controlled to be 3-4 hours. After the pre-emulsion and initiator are added, the system temperature is raised to 90°C and kept for 1.5-2 hours to complete the post-polymerization. After the system is cooled to 40°C, adjust the pH value of the latex to between 8.0 and 8.5 with a neutralizer, add a cross-linking aid, stir for 30 minutes, and filter with a 200-mesh filter to obtain an aqueous self-cross-linking acrylic emulsion that can be diluted in any proportion of ethanol and is resistant to strong electrolytes. Among them, the initiator is ammonium persulfate, 0.4 parts by weight, which is prepared into an initiator solution with 10.6 parts of water; the neutralizer for adjusting the pH of the emulsion is ammonia water, 1 part by weight; the cross-linking auxiliary agent is 1,6-hexanediamine, 0.5 parts by weight. Example

[0031] (1) Preparation of alkali-soluble acrylic resin solution: The weighed alkali-soluble acrylic resin and water are added into a 500 mL four-necked flask equipped with a reflux condenser, a temperature probe, a feed inlet and a stirrer. The flask is dissolved for 3 h at a water bath temperature of 60 ° C and a stirring speed of 300 rpm. The neutralizer is added in 6 times, each time with an interval of 30 minutes. After stirring, a uniform and transparent aqueous solution is obtained. Among them, the weight average molecular weight of the alkali-soluble acrylic resin is 10000 Da, the acid value is 215 mgKOH / g, the neutralization degree of the alkali-soluble acrylic resin solution is 110%, and the neutralizer is ammonia water. Among them, the mass percentage of solid alkali-soluble acrylic resin to the total amount of monomers and solid alkali-soluble acrylic resin is 20%.

[0032] (2) Preparation of pre-emulsion: Add styrene monomer, acrylate monomer, cross-linking monomer, reactive emulsifier, chain transfer agent and water in a three-necked round-bottom flask according to the set ratio, and stir vigorously at room temperature for 30 minutes to prepare a pre-emulsion. Among them, the acrylate monomers are butyl acrylate, methyl methacrylate, and isooctyl acrylate, with weight parts of 10, 10, and 10 respectively; the cross-linking monomer is diacetone acrylamide, with weight parts of 1.1; the reactive emulsifier is 1-allyloxy-3-(4-nonylphenol)-2-propanol polyoxyethylene (10) ether ammonium sulfate and 1-allyloxy-3-(4-nonylphenol)-2-propanol polyoxyethylene (10) ether, with weight parts of 2, and the ratio of the two is 1:1; the chain transfer agent is α-methylstyrene dimer, with weight parts of 0.1.

[0033] (3) Put the dissolved alkali-soluble acrylic resin solution into a flask, heat it in a water bath and stir it. When the material temperature reaches 80°C, add 10-15% of the pre-emulsion and 20-30% of the initiator solution into the four-necked flask through a constant pressure dropping funnel. After the pre-emulsion is added, keep it at 80°C for 30 minutes to obtain a blue phase seed emulsion. Then, add the remaining pre-emulsion and initiator solution to the reaction system, and the addition time is controlled to be 3-4 hours. After the pre-emulsion and initiator are added, the system temperature is raised to 90°C and kept for 1.5-2 hours to complete the post-polymerization. After the system is cooled to 40°C, adjust the pH value of the latex to between 8.0 and 8.5 with a neutralizer, add a cross-linking aid, stir for 30 minutes, and filter with a 200-mesh filter to obtain an aqueous self-cross-linking acrylic emulsion that can be diluted in any proportion of ethanol and is resistant to strong electrolytes. Among them, the initiator is ammonium persulfate, 0.4 parts by weight, which is prepared into an initiator solution with 10.6 parts of water; the neutralizer for adjusting the pH of the emulsion is ammonia water, 1 part by weight; the cross-linking auxiliary agent is adipic acid dihydrazide, 0.5 parts by weight.

[0034] The comparative example emulsion was synthesized according to the following experimental steps, which belongs to the conventional preparation method of water-based polyacrylic acid emulsion in the prior art. No alkali-soluble acrylic resin and reactive emulsifier were used in the synthesis. The synthesis process is as follows: (1) Preparation of pre-emulsion: Add styrene monomer, acrylate monomer, cross-linking monomer, traditional anionic and nonionic emulsifier, chain transfer agent and water in a three-necked round-bottom flask according to the set ratio, and stir vigorously at room temperature for 30 minutes to prepare a pre-emulsion. Among them, styrene is used as the styrene monomer, with a weight of 5.7 parts; butyl acrylate, methyl methacrylate and isooctyl acrylate are used as the acrylate monomers, with a weight of 5.7 parts, 11.2 parts and 11.2 parts respectively; diacetone acrylamide is used as the cross-linking monomer, with a weight of 1.1 parts; sodium dodecyl sulfate and octylphenol polyoxyethylene (10) ether are used as emulsifiers, with a weight of 2 parts, and the ratio of the two is 1:1; α-methylstyrene dimer is used as the chain transfer agent, with a weight of 0.1 parts.

[0035] (2) Synthesis of emulsion: 5% of sodium dodecyl sulfate and octylphenol polyoxyethylene (10) ether and the remaining water are added to a flask, heated in a water bath and stirred. When the material temperature reaches 80°C, 10-15% of the pre-emulsion and 20-30% of the initiator solution are added to the four-necked flask through a constant pressure dropping funnel. After the pre-emulsion is added, keep it warm at 80°C for 30 minutes to obtain a blue phase seed emulsion. Then, the remaining pre-emulsion and initiator solution are added to the reaction system, and the addition time is controlled to be 3-4 hours. After the pre-emulsion and initiator are added, the system temperature is raised to 90°C and kept warm for 1.5-2 hours to complete the post-polymerization. After the system is cooled to 40°C, the pH value of the latex is adjusted to between 8.0 and 8.5 with a neutralizer, and a crosslinking aid is added. After stirring for 30 minutes, the material is filtered with a 200-mesh filter to obtain an aqueous self-crosslinking acrylic emulsion that can be diluted with any proportion of ethanol and is resistant to strong electrolytes. Among them, the initiator is ammonium persulfate, which is 0.4 parts by weight and is prepared with 10.6 parts of water to form an initiator solution; the neutralizer for adjusting the pH of the emulsion is ammonia water, which is 1 part by weight; and the crosslinking aid is adipic acid dihydrazide, which is 0.5 parts by weight.

[0036] In order to verify the implementation effect of the emulsions prepared in Examples 1-3 and the emulsions prepared in the comparative example, the product performance indexes were tested, and the test method was as follows: Ethanol dilution stability test: Take 10g, 30g, 50g, 70g, and 100g of the emulsion and mix them with 100g of ethanol respectively, shake them and observe whether the emulsion breaks and flocculates.

[0037] Strong electrolyte stability test: Take a 2% CaCl2 solution by mass and add it to the emulsion at a mass ratio of 40% of the emulsion and shake it evenly to observe whether the emulsion breaks and flocculates.

[0038] Table 1 Comparison of ethanol dilution stability test of emulsions prepared in Example and Comparative Example Table 2 Comparison of stability test of emulsion strong electrolyte prepared in Example and Comparative Example Example 1 Example 2 Example 3 Comparative Example <![CDATA[2% CaCl2 test]]> Translucent emulsion Translucent emulsion Translucent emulsion Complete flocculation, precipitation, demulsification From Table 1 and Table 2, it can be seen that the aqueous self-crosslinking acrylic emulsion prepared by adding alkali-soluble acrylic resin and reactive emulsifier in the present invention has better dilution stability with ethanol, and also has good stability for high-concentration CaCl2 solution when the added amount reaches 40% of the emulsion mass ratio. The dilution stability of the synthetic emulsion with ethanol in any proportion and the stability to strong electrolytes are of great practical significance for improving the drying efficiency of water-based inks, and can expand the application of water-based inks in occasions with high hygiene requirements.

[0039] The above description is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this field, without departing from the creative concept of the present invention, several improvements and changes can be made, which all fall within the protection scope of the present invention.

Claims

1. An aqueous self-crosslinking acrylic emulsion composition, characterized in that: It includes the following components by weight: Styrene monomer: 0-10 parts; Acrylate monomer: 15-30 parts; Cross-linking monomer: 1-5 parts; Reactive emulsifier: 1-5 parts; Alkali soluble acrylic resin: 10-30 parts; Chain transfer agent: 0-0.5 parts; Cross-linking aid: 0.5-1 part; Initiator: 0.5-1 part; Neutralizer: 0.5-2 parts; Water: 50-70 parts.

2. The aqueous self-crosslinking acrylic emulsion composition according to claim 1, characterized in that: The styrene monomer is one or both of styrene and methyl styrene.

3. The aqueous self-crosslinking acrylic emulsion composition according to claim 1, It is characterized in that The acrylic acid ester monomers include, but are not limited to, one or more of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, isooctyl acrylate, hydroxyethyl acrylate, isobornyl acrylate, and isobornyl methacrylate.

4. The aqueous self-crosslinking acrylic emulsion composition according to claim 1, It is characterized in that The cross-linking monomers include, but are not limited to, one or more of vinyl siloxane monomers, diacetone acrylamide, N-hydroxymethyl acrylamide, glycidyl methacrylate, allyl acetoacetate, acetoacetoxyethyl methacrylate, and hydroxyethyl methacrylate.

5. The aqueous self-crosslinking acrylic emulsion composition according to claim 1, It is characterized in that The reactive emulsifier includes one or more of anionic reactive emulsifiers, cationic reactive emulsifiers, nonionic reactive emulsifiers and amphiphilic reactive emulsifiers.

6. The aqueous self-crosslinking acrylic emulsion composition according to claim 1, It is characterized in that The molecular weight of the alkali-soluble acrylic resin is in the range of 2000-16000, the acid value is in the range of 50-250 mgKOH / g, and the neutralization degree of the alkali-soluble resin solution prepared therefrom is in the range of 90-110%.

7. The aqueous self-crosslinking acrylic emulsion composition according to claim 1, It is characterized in that The chain transfer agent includes, but is not limited to, one or more of aliphatic mercaptans, mercaptopropionic acid, 2-hydroxyethyl mercaptopropionate, 2-ethylhexylthioacetate, α-methylstyrene dimer, trichloroethylene, and tetrachloromethane.

8. The aqueous self-crosslinking acrylic emulsion composition according to claim 1, It is characterized in that The cross-linking aid includes, but is not limited to, one or more of adipic acid dihydrazide, 1,6-hexamethylenediamine, polycarbodiimide, polyethyleneimine, and nano zinc oxide.

9. The method for preparing the aqueous self-crosslinking acrylic emulsion composition diluted with ethanol in any proportion and resistant to strong electrolytes according to claims 1-8, characterized in that: The following steps are involved: First, the weighed alkali-soluble acrylic resin and water are added to a 500 mL four-necked flask equipped with a reflux condenser, a temperature probe, a feed inlet and a stirrer, and dissolved for 3 hours at a water bath temperature of 60°C and a stirring speed of 300 rpm. The neutralizer is added in 6 times, each time with an interval of 30 minutes. After the stirring is completed, a uniform and transparent aqueous solution is obtained. Secondly, styrene monomers, acrylate monomers, cross-linking monomers, reactive emulsifiers, chain transfer agents and water are added to a three-necked round-bottom flask according to a set ratio, and vigorously stirred at room temperature for 30 minutes to prepare a pre-emulsion. Finally, the aqueous self-crosslinking acrylic emulsion composition described in claims 1-8 is prepared by a pre-emulsification semi-continuous seed polymerization process. The dissolved alkali-soluble acrylic resin solution is placed in a flask, heated and stirred in a water bath, and when the material temperature reaches 80°C, 10-15% of the pre-emulsion and 20-30% of the ammonium persulfate initiator solution are respectively added to the four-necked flask through a constant pressure dropping funnel. After the pre-emulsion is added, keep it warm at 80°C for 30 minutes to obtain a blue seed emulsion. Then, add the remaining pre-emulsion and initiator solution to the reaction system, and the addition time is controlled at 3-4 hours. After the pre-emulsion and initiator are added, the system temperature is raised to 90°C and kept warm for 1.5-2 hours to complete the post-polymerization. After the system is cooled to 40°C, adjust the pH value of the latex to between 8.0 and 8.5 with ammonia water, add the cross-linking agent, stir for 30 minutes, and filter with a 200-mesh filter before discharging.