A water-based acrylic emulsion, its preparation method and application

Abstract

This invention relates to an aqueous acrylic emulsion, its preparation method, and its application. The aqueous acrylic emulsion has a core-shell structure. The raw materials for preparing the shell layer of the core-shell structure, by weight, include: 165-190 parts of shell layer reactive monomers and 400-550 parts of solvent A; the raw materials for preparing the core layer of the core-shell structure, by weight, include: 247-380 parts of core reactive monomers and 10-20 parts of solvent B; the glass transition temperature of the homopolymer of the core reactive monomers is greater than -30°C and less than -10°C. The aqueous acrylic emulsion provided by this invention has excellent heat-sealing and anti-tack properties, can impart strong heat-sealing capabilities to various substrates, and prevents coated paper from sticking together during stacking, winding, storage, and transportation, ensuring normal subsequent use.

Description

Technical Field

[0001] This invention relates to the field of coating technology, and in particular to an aqueous acrylic emulsion, its preparation method, and its application. Background Technology

[0002] Waterborne polymer materials, with their excellent film-forming properties and environmentally friendly characteristics, are widely used in food service, food packaging, and various paper product processing and manufacturing fields. They are currently the most sustainable green functional materials in the packaging industry. Waterborne polymer coatings with heat-sealing capabilities enable paper substrates to have heat-sealing capabilities, meeting the needs of rapid sealing, forming, and sealing protection in paper packaging. They have extremely high application value and development prospects in lightweight, plastic-free, and recyclable paper packaging systems.

[0003] Currently, functional barrier and heat-sealing coating materials used in paper products on the market are mainly divided into two categories. One category is fluorinated oil- and grease-resistant coating compositions. Although this type of coating can give paper substrates a certain barrier and protective effect, and some products can help achieve basic sealing performance, the fluorinated system has poor environmental friendliness and low biosafety. When applied to food packaging, it can easily cause food safety and human health risks, which does not meet the development requirements of green packaging and greatly limits its application scenarios. The other category is composite coating systems of polyethylene, polypropylene, and other polyolefin plastic films. This type of traditional coating can give cardboard a certain heat-sealing and barrier ability, but the presence of a large number of plastic components in this system will completely destroy the recyclability of paper products, greatly reducing the recyclability and reuse performance of coated paper products, making it impossible to achieve paper recycling, which contradicts the current development trend of green, low-carbon, and circular economy in the packaging industry. In addition, existing coating materials generally have insufficient anti-tack properties, making them difficult to adapt to the needs of industrial mass production and warehousing and transportation. After paper products are coated with functional coatings, they usually need to be stacked and rolled into tubes for bulk storage and transportation. If the coating surface is prone to stickiness or re-sticking, the stacked and rolled paper products will stick together and be difficult to peel off, which will seriously affect the normal operation of subsequent processing steps such as slitting, forming, and heat sealing, and greatly reduce the product production yield and industrial application adaptability.

[0004] Therefore, developing a waterborne polymer coating material that can impart excellent heat-sealing and anti-tack properties to the substrate, is environmentally friendly, safe, and recyclable is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an aqueous acrylic emulsion, its preparation method, and its application. This aqueous acrylic emulsion not only effectively imparts strong heat-sealing properties to various substrates, but also possesses good environmental friendliness and safety in use. Furthermore, it exhibits excellent anti-tack properties, preventing coated paper from sticking together during stacking, winding, storage, and transportation, thus ensuring normal subsequent use.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides an aqueous acrylic emulsion having a core-shell structure; The raw materials for preparing the shell layer in the core-shell structure include, by mass, 165-190 parts of shell layer reactive monomers and 400-550 parts of solvent A; The raw materials for preparing the core in the core-shell structure include, by mass, 247-380 parts of core reactive monomer and 10-20 parts of solvent B; The glass transition temperature of the homopolymer of the core reactive monomer is greater than -30°C and less than -10°C.

[0007] Among them, 165-190 portions can be, for example, 165 portions, 170 portions, 180 portions, 185 portions, or 190 portions; 400-550 portions can be, for example, 400 portions, 420 portions, 440 portions, 450 portions, 460 portions, 480 portions, 500 portions, 520 portions, 540 portions, or 550 portions; 247-380 portions can be, for example, 247 portions, 250 portions, 260 portions, 270 portions, 280 portions, 290 portions, 300 portions, 310 portions, 320 portions, or 330 portions. 0 parts, 340 parts, 350 parts, 360 parts, 370 parts, or 380 parts, etc.; 10-20 parts, for example, 10 parts, 12 parts, 14 parts, 15 parts, 16 parts, 18 parts, or 20 parts, etc.; glass transition temperature greater than -30℃ and less than -10℃, for example, -12℃, -13℃, -14℃, -15℃, -16℃, -17℃, -18℃, -20℃, -22℃, -24℃, -25℃, -26℃, -28℃, or -29℃, etc.

[0008] This invention provides an aqueous acrylic emulsion with a core-shell structure. Through emulsion formulation design, the polymerization process is driven by the hydrophilicity / hydrophobicity difference between the shell and core reactive monomers, resulting in a stable and orderly core-shell two-phase structure. This avoids the defects of core-shell miscibility and lack of clear stratification. The shell layer of this invention uses a high proportion of solvent compounded with soft monomer A, medium-soft monomer A, hard monomer A, and crosslinking monomer A, ensuring smooth and continuous film formation at room temperature (20-30℃). Simultaneously, the polar groups on the shell surface enhance the emulsion's storage stability and substrate adhesion, and the self-crosslinking of the shell after film formation further strengthens its water resistance. This invention controls the glass transition temperature of the homopolymer of the core reactive monomers within the range of -30℃ to -10℃. The relatively low glass transition temperature imparts good flexibility to the waterborne acrylic emulsion, effectively preventing coating brittleness and avoiding the problems of soft coatings and easy re-adhesion under heat and pressure caused by excessively low glass transition temperatures. It achieves short-time heat sealing of 1-2 seconds at a moderate temperature of 140-150℃. However, if the glass transition temperature is increased, the required heat-sealing activation temperature is higher; if the glass transition temperature is decreased, the coating tends to become softer and stickier. The core of this invention uses a blend of soft monomer B, medium-soft monomer B, hard monomer B, and crosslinking monomer B, which also improves the cohesive strength of the emulsion, suppresses high-temperature re-adhesion, and ensures the heat-sealing performance of the coating after the emulsion dries.

[0009] Preferably, the mass ratio of the shell reactive monomer to the core reactive monomer is 1:(1.5-2), for example, it can be 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2, etc.

[0010] This invention specifies a shell-layer reactive monomer to core reactive monomer mass ratio of 1:(1.5-2). This ratio lowers the film-forming temperature, forms a dense coating, and allows for rapid wetting of the substrate during heat sealing, achieving tight adhesion between substrates and effectively improving heat-sealing bond strength. If the proportion of shell-layer reactive monomer is too high, the overall glass transition temperature of the emulsion increases, the heat-sealing initiation temperature becomes higher, and the coating flexibility and film-forming properties decrease. Furthermore, if the proportion of core reactive monomer, which acts as a mechanical buffer structure during the heat sealing process, is insufficient, the molecular chains will lack mobility at the preset heat-sealing temperature, resulting in poor heat-sealing strength. If the proportion of core reactive monomer is too high (>1:2), the viscosity of the polymerization system will increase sharply, causing demulsification and preventing normal emulsion preparation.

[0011] Preferably, the glass transition temperature of the homopolymer of the shell reactive monomer is >80°C, for example, it can be 82°C, 85°C, 90°C, 95°C, 100°C or 105°C.

[0012] Preferably, the shell reactive monomer includes hard monomer A, soft monomer A, and crosslinking monomer A.

[0013] Preferably, the shell reactive monomer further includes a medium-soft monomer A.

[0014] Preferably, the core reactive monomers include hard monomer B, soft monomer B, and crosslinking monomer B.

[0015] Preferably, the core reactive monomer further includes the medium-soft monomer B.

[0016] This invention does not limit the amount of hard monomer A, medium-soft monomer A, soft monomer A, and crosslinking monomer A in the shell reactive monomer, or the amount of hard monomer B, soft monomer B, medium-soft monomer B, and crosslinking monomer B in the core reactive monomer. Depending on the monomer selection, the total amount of shell reactive monomer should be 165-190 parts by mass, and the glass transition temperature of the homopolymer should be >80°C; the total amount of core reactive monomer should be 247-380 parts by mass, and the glass transition temperature of the homopolymer should be greater than -30°C and less than -10°C.

[0017] Preferably, the glass transition temperatures of the homopolymers of hard monomer A and hard monomer B are each independently greater than 25°C, for example, they can be 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 120°C, 140°C, 150°C, 160°C, 180°C or 200°C.

[0018] Preferably, the hard monomer A and hard monomer B each independently comprise an aromatic olefinic unsaturated monomer and / or a first (meth)acrylate monomer.

[0019] Preferably, the hard monomer A and hard monomer B each independently comprise a combination of an aromatic olefinic unsaturated monomer and a first (meth)acrylate monomer.

[0020] Preferably, the aromatic olefinic unsaturated monomer includes any one or a combination of at least two of styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, or divinylbenzene, and more preferably styrene.

[0021] The present invention preferably uses styrene as a hard monomer, which can improve cohesion and strength while providing excellent hydrophobicity, thereby reducing the water absorption rate of the emulsion and giving the emulsion better water resistance.

[0022] Preferably, the first (meth)acrylate monomer includes any one or a combination of at least two of methyl methacrylate, tert-butyl methacrylate, or n-propyl methacrylate, and more preferably methyl methacrylate and / or n-butyl methacrylate.

[0023] The present invention preferably uses methyl methacrylate and / or n-butyl methacrylate as hard monomers, which can act as "skeleton builders" in the emulsion and improve the cohesive strength and surface hardness of the coating.

[0024] Preferably, the glass transition temperatures of the homopolymers of the medium-soft monomer A and the medium-soft monomer B are each independently greater than or equal to -25°C and less than or equal to 25°C.

[0025] Preferably, the intermediate soft monomer A and intermediate soft monomer B each independently comprise a second (meth)acrylate monomer.

[0026] Preferably, the second (meth)acrylate monomer includes any one or a combination of at least two of methyl acrylate, ethyl acrylate, ethyl methacrylate or isobutyl methacrylate.

[0027] Preferably, the glass transition temperatures of the homopolymers of the soft monomers A and B are each independently <-25°C.

[0028] Preferably, the soft monomer A and soft monomer B each independently comprise a third (meth)acrylate monomer.

[0029] Preferably, the third (meth)acrylate monomer includes any one or a combination of at least two of n-butyl acrylate, n-butyl methacrylate, isooctyl acrylate, tridecyl methacrylate, or octadecyl methacrylate, and more preferably n-butyl acrylate and / or isooctyl acrylate.

[0030] This invention preferably uses n-butyl methacrylate and / or isooctyl acrylate as soft monomers, as these choices combine hydrophobicity and internal plasticizing effects. Using n-butyl methacrylate allows the emulsion to achieve a certain degree of hardness while maintaining flexibility in the coating; isooctyl methacrylate is one of the (meth)acrylate monomers with the lowest glass transition temperature, exhibiting extreme flexibility and superior hydrophobicity, which significantly reduces the surface tension of the polymer, making it easier to wet the substrate.

[0031] Preferably, the crosslinking monomer A and crosslinking monomer B each independently comprise an acid-based olefinic unsaturated monomer.

[0032] Preferably, the acidic olefinic unsaturated monomer includes any one or a combination of at least two of acrylic acid, methacrylic acid, styrene sulfonic acid, vinyl sulfonic acid, 2-(meth)acryloylamino-2-methylpropanesulfonic acid and their salts or itaconic acid, preferably acrylic acid and / or methacrylic acid.

[0033] The present invention preferably uses acrylic acid and / or methacrylic acid. The above selection not only enhances the stability of the emulsion, but also provides sites for subsequent crosslinking reactions, and can also regulate the hydrophilicity and hydrophobicity and rheological behavior of the polymer.

[0034] Preferably, the raw materials for preparing the shell layer in the core-shell structure further include, by weight, any one or a combination of at least two of the following: 0.05-1 parts emulsifier, 0.05-5 parts free radical initiator, or 0.1-2 parts neutralizer.

[0035] Preferably, the emulsifier comprises any one or at least two of substituted alkali metal sulfate, substituted ammonium sulfate, substituted alkali metal sulfonate, substituted ammonium sulfonate, substituted alkali metal phosphate, or substituted ammonium phosphate, wherein the substituted substituents comprise any one or at least two of alkyl, aryl, alkylaryl, or alkoxy groups.

[0036] Preferably, the free radical initiator comprises a peroxide.

[0037] Preferably, the peroxide comprises any one or a combination of at least two of potassium persulfate, ammonium persulfate, or sodium persulfate.

[0038] Preferably, the neutralizing agent comprises any one or a combination of at least two of organic amines, inorganic ammonia, or alkali metal hydroxides.

[0039] Preferably, solvent A comprises water.

[0040] Preferably, the raw materials for preparing the core in the core-shell structure further include, by mass, any one or a combination of at least two of the following: 0.001-0.005 parts of catalyst, 0.2-0.5 parts of oxidant, 0.001-0.005 parts of chelating agent, or 0.2-0.5 parts of reducing agent.

[0041] Among them, 0.001-0.005 parts can be, for example, 0.001 parts, 0.002 parts, 0.003 parts, 0.004 parts, or 0.005 parts; 0.2-0.5 parts can be, for example, 0.2 parts, 0.25 parts, 0.3 parts, 0.35 parts, 0.4 parts, 0.45 parts, or 0.5 parts.

[0042] Preferably, the catalyst comprises a metal catalyst.

[0043] Preferably, the metal catalyst includes any one or a combination of at least two of the following: iron-based catalyst, copper-based catalyst, manganese-based catalyst, silver-based catalyst, platinum-based catalyst, vanadium-based catalyst, nickel-based catalyst, or chromium-based catalyst.

[0044] Preferably, the metal catalyst comprises any one or a combination of at least two of ferrous sulfate, nickel sulfate, copper chloride, manganese acetate, or vanadium acetate.

[0045] Preferably, the oxidant includes any one or a combination of at least two of the following: tert-butyl peroxide, potassium permanganate, ammonium persulfate, or an alkali metal salt of persulfate.

[0046] Preferably, the chelating agent comprises disodium ethylenediaminetetraacetate dihydrate.

[0047] Preferably, the reducing agent comprises any one or a combination of at least two of the following: sodium formaldehyde sulfoxylate, ascorbic acid, isoascorbic acid, sodium sulfite, sodium bisulfite, sodium dithionite, formamidinium sulfinic acid, hydroxymethyl sulfonic acid, disodium hydroxysulfinate, or acetone bisulfite.

[0048] Preferably, solvent B comprises water.

[0049] In a second aspect, the present invention provides a method for preparing an aqueous acrylic emulsion as described in the first aspect, the preparation method comprising the following steps: (1) Mix and react the raw materials for the preparation of the shell to obtain a shell emulsion; (2) The core preparation raw materials are mixed and reacted with the shell emulsion to obtain the aqueous acrylic emulsion.

[0050] Preferably, step (1) specifically includes mixing the raw materials for shell preparation and reacting them, including a first stage of mixing, a second stage of mixing, a third stage of mixing and reacting, and a fourth stage of mixing.

[0051] Preferably, the first stage of mixing in step (1) includes mixing the components of the shell reactive monomer to obtain the shell reactive monomer.

[0052] Preferably, the second stage of mixing in step (1) includes mixing the emulsifier and solvent A accounting for 90-93 wt% of the total mass of solvent A (e.g., 90 wt%, 91 wt%, 92 wt%, or 93 wt%) and heating the mixture to 80-90°C (e.g., 80°C, 82°C, 84°C, 85°C, 86°C, 88°C, or 90°C), and then adding a portion of free radical initiator and mixing for 1-3 min (e.g., 1 min, 1.5 min, 2 min, 2.5 min, or 3 min).

[0053] Preferably, the portion of the free radical initiator accounts for 30-35 wt% of the total mass of the free radical initiator (e.g., it can be 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, or 35 wt%, etc.).

[0054] Preferably, a portion of the free radical initiator is dissolved in solvent A in an amount of 1-2 wt% (e.g., 1 wt%, 1.2 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, or 2 wt%) of the total mass of solvent A.

[0055] Preferably, the third stage of mixing and reaction in step (1) includes adding the mixed system of the shell reactant monomer and the remaining free radical initiator to the mixed system obtained in the second stage, and reacting at 80-90℃ (e.g., 80℃, 82℃, 84℃, 85℃, 86℃, 88℃ or 90℃, etc.) for 50-70 min (e.g., 50 min, 55 min, 60 min, 65 min or 70 min, etc.).

[0056] Preferably, the remaining free radical initiator is dissolved in solvent A in a concentration of 3-4 wt% (e.g., 3 wt%, 3.2 wt%, 3.4 wt%, 3.5 wt%, 3.6 wt%, 3.8 wt%, or 4 wt%) of the total mass of solvent A.

[0057] Preferably, the addition of the shell reaction monomer includes dropwise addition at a rate of 2.5-3.5 g / min, such as 2.5 g / min, 2.8 g / min, 3 g / min, 3.2 g / min, or 3.5 g / min.

[0058] Preferably, the addition of the remaining free radical initiator includes dropwise addition at a rate of 0.1-0.3 g / min, such as 0.1 g / min, 0.15 g / min, 0.2 g / min, 0.25 g / min, or 0.3 g / min.

[0059] Preferably, the fourth stage mixing in step (1) includes adding a neutralizing agent to the reaction system after the third stage mixing and reaction, and mixing to obtain the shell emulsion.

[0060] Preferably, the neutralizing agent is dissolved in the remaining solvent A.

[0061] Preferably, the addition of the neutralizing agent includes dripping, and the dripping rate is 0.3-0.7 g / min, for example, 0.3 g / min, 0.4 g / min, 0.5 g / min, 0.6 g / min or 0.7 g / min, etc.

[0062] Preferably, the pH of the shell emulsion is 7.5-8, for example, it can be pH=7.5, pH=7.6, pH=7.7, pH=7.8, pH=7.9 or pH=8, etc.

[0063] Preferably, step (2) specifically includes a first stage of mixing, a second stage of mixing and reaction, and a third stage of mixing and reaction.

[0064] Preferably, the first stage of mixing in step (2) includes mixing the components of the core reactive monomer to obtain the core reactive monomer.

[0065] Preferably, the second stage of mixing and reaction in step (2) includes cooling the shell emulsion obtained in step (1) to 45-55°C (e.g., 45°C, 46°C, 48°C, 50°C, 52°C, 54°C, or 55°C), adding a portion of the core reactive monomer, mixing for 10-30 min, then adding a catalyst, chelating agent, a portion of oxidant and a portion of reducing agent, and then heating the mixed system to 80-90°C (e.g., 80°C, 82°C, 84°C, 85°C, 86°C, 88°C, or 90°C) and reacting for 15-25 min (e.g., 15 min, 16 min, 18 min, 20 min, 22 min, 24 min, or 25 min).

[0066] Preferably, the portion of the core reactive monomer accounts for 45-55 wt% of the total mass of the core reactive monomer, for example, it can be 45 wt%, 46 wt%, 48 wt%, 50 wt%, 52 wt%, 54 wt%, or 55 wt%, etc.

[0067] Preferably, the portion of the oxidant accounts for 45-55 wt% of the total mass of the oxidant, for example, it can be 45 wt%, 46 wt%, 48 wt%, 50 wt%, 52 wt%, 54 wt%, or 55 wt%, etc.

[0068] Preferably, a portion of the oxidant is dissolved in solvent B in an amount of 10-20 wt% (e.g., 10 wt%, 12 wt%, 14 wt%, 15 wt%, 16 wt%, 18 wt%, or 20 wt%) of the total mass of solvent B.

[0069] Preferably, the reducing agent accounts for 45-55 wt% of the total mass of the reducing agent, for example, it can be 45 wt%, 46 wt%, 48 wt%, 50 wt%, 52 wt%, 54 wt%, or 55 wt%.

[0070] Preferably, the reducing agent is dissolved in solvent B in a concentration of 30-40 wt% (e.g., 30 wt%, 32 wt%, 34 wt%, 35 wt%, 36 wt%, 38 wt%, or 40 wt%) of the total mass of solvent B.

[0071] Preferably, the third stage of mixing and reacting in step (2) includes cooling the reaction system obtained after mixing and reacting in the second stage of step (2) to 45-55℃ (e.g., 45℃, 46℃, 48℃, 50℃, 52℃, 54℃ or 55℃, etc.), adding the remaining core reactant monomers, mixing for 10-30 min, then adding the remaining oxidant and the remaining reducing agent, and heating to 80-90℃ (e.g., 80℃, 82℃, 84℃, 85℃, 86℃, 88℃ or 90℃, etc.) and reacting for 15-25 min (e.g., 15 min, 16 min, 18 min, 20 min, 22 min, 24 min or 25 min, etc.).

[0072] Preferably, the remaining oxidant is dissolved in solvent B in a concentration of 10-20 wt% (e.g., 10 wt%, 12 wt%, 14 wt%, 15 wt%, 16 wt%, 18 wt%, or 20 wt%) of the total mass of solvent B.

[0073] Preferably, the remaining reducing agent is dissolved in solvent B in a concentration of 30-40 wt% (e.g., 30 wt%, 32 wt%, 34 wt%, 35 wt%, 36 wt%, 38 wt%, or 40 wt%) of the total mass of solvent B.

[0074] Thirdly, the present invention provides an application of the aqueous acrylic emulsion as described in the first aspect in packaging materials.

[0075] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The water-based acrylic emulsion provided by the present invention can effectively impart excellent heat-sealing performance to various substrates, with high heat-sealing strength and good sealing effect. It can significantly improve the substrate packaging forming and sealing protection capabilities, effectively prevent packaging leakage and air leakage, and is suitable for various packaging sealing application scenarios. At the same time, the product itself is environmentally friendly and non-toxic, with high safety in use, and is widely used in food service, food packaging and various paper product manufacturing fields, which meets the development requirements of green production.

[0076] (2) The water-based acrylic emulsion provided by the present invention has excellent anti-tack properties, which are fully adapted to the actual production and storage and transportation conditions of paper coating. After the paper is coated with this emulsion, the coating is not easy to become sticky during stacking, winding into tubes and long-term storage and transportation. It can effectively avoid the problem of paper sticking together and being difficult to separate, ensure the integrity of the paper product, and ensure the smooth progress of subsequent cutting, processing and use processes. Detailed Implementation

[0077] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0078] The specific information of the materials used in the following specific embodiments of the present invention is as follows: Emulsifier, sodium fatty alcohol polyoxyethylene ether sulfate (Disponil FES32), purchased from BASF; Ammonium persulfate, a free radical initiator; Neutralizing agent: ammonia (25 wt%). Catalyst, ferrous sulfate heptahydrate; Oxidizing agent: tert-butyl hydrogen peroxide (70 wt%); Chelating agent: disodium ethylenediaminetetraacetic acid dihydrate; The reducing agent, disodium 2-hydroxy-2-sulfinylacetate (FF6M), was purchased from Brügmann.

[0079] Example 1 This embodiment provides an aqueous acrylic emulsion having a core-shell structure; The raw materials for preparing the shell layer in the core-shell structure include, by mass, 64.36 parts styrene, 84.02 parts methyl methacrylate, 15.02 parts butyl acrylate, 19.11 parts methacrylic acid, 0.5 parts Disponil FES32, 3 parts ammonium persulfate, 1 part ammonia, and 480 parts water. The raw materials for preparing the core in the core-shell structure, by mass, include: 60 parts styrene, 72 parts butyl acrylate, 85 parts isooctyl methacrylate, 60 parts methyl methacrylate, 0.003 parts ferrous sulfate heptahydrate, 0.3 parts tert-butyl hydroperoxide, 0.003 parts disodium ethylenediaminetetraacetate dihydrate, 0.3 parts disodium 2-hydroxy-2-sulfinylacetate, and 15 parts water; The preparation method includes: (1) Styrene, butyl acrylate, methyl methacrylate and methacrylic acid are mixed to obtain shell reaction monomers; Styrene, butyl acrylate, methyl methacrylate, and isooctyl methacrylate are mixed to obtain the core reaction monomer; (2) Mix Disponil FES32 and water (accounting for 92 wt% of the total water content in the raw materials for shell preparation) and heat to 85°C. Then add ammonium persulfate (accounting for 32 wt% of the total ammonium persulfate, dissolved in 1.5 wt% of the total water content in the raw materials for shell preparation) to the system and continue mixing for 2 min. (3) The shell reaction monomer was added dropwise at a rate of 3.04 g / min and the remaining ammonium persulfate (dissolved in 3.5 wt% of the total water content in the raw materials for the preparation of the shell) was added dropwise at a rate of 0.2 g / min to the mixed system obtained in step (2), and the mixture was reacted at 85°C for 60 min. (4) After the reaction described in step (3) is completed, ammonia water (dissolved in the remaining water in the raw materials for the preparation of the shell layer) is added dropwise to the reaction system obtained in step (2) at a rate of 0.5 g / min until the pH value of the reaction system is 7.5-8, and the shell layer emulsion is obtained. (5) Cool the shell emulsion obtained in step (4) to 50°C, add 50 wt% of the core reactant monomers, mix for 20 min, then add ferrous sulfate heptahydrate, disodium ethylenediaminetetraacetate dihydrate, tert-butyl hydroperoxide (dissolved in 15 wt% of the total water content of the core raw materials), and disodium 2-hydroxy-2-sulfinyl acetate (dissolved in 35 wt% of the total water content of the core raw materials) and react at 85°C for 20 min. (6) After the reaction described in step (5) is completed, the reaction system is cooled to 50°C, the remaining core reaction monomer is added, and the mixture is mixed for 20 min. Then, the remaining tert-butyl hydroperoxide (dissolved in 15 wt% of the total water content in the core preparation raw materials) and the remaining disodium 2-hydroxy-2-sulfinic acid (dissolved in 35 wt% of the total water content in the core preparation raw materials) are added and the mixture is reacted at 85°C for 20 min. (7) After the reaction in step (6) is completed, the reaction system is cooled to 40°C and then filtered through a 200-mesh filter cloth to obtain the aqueous acrylic emulsion.

[0080] Example 2 This embodiment provides an aqueous acrylic emulsion, which differs from Embodiment 1 in that the core-shell structure contains the following raw materials by mass: 75 parts styrene, 105 parts butyl acrylate, 105 parts isooctyl methacrylate, 75 parts methyl methacrylate, 0.001 parts ferrous sulfate heptahydrate, 0.2 parts tert-butyl hydroperoxide, 0.001 parts disodium ethylenediaminetetraacetate dihydrate, 0.2 parts disodium 2-hydroxy-2-sulfinylacetate, and 20 parts water.

[0081] Example 3 This embodiment provides an aqueous acrylic emulsion, which differs from Embodiment 1 in that the core-shell structure contains the following raw materials by mass: 70 parts styrene, 95 parts butyl acrylate, 95 parts isooctyl methacrylate, 70 parts methyl methacrylate, 0.005 parts ferrous sulfate heptahydrate, 0.5 parts tert-butyl hydroperoxide, 0.005 parts disodium ethylenediaminetetraacetate dihydrate, 0.5 parts disodium 2-hydroxy-2-sulfinylacetate, and 10 parts water.

[0082] Example 4 This embodiment provides an aqueous acrylic emulsion, which differs from Embodiment 1 in that: the raw materials for preparing the core in the core-shell 1 structure include, by mass, 59.4 parts styrene, 80.6 parts butyl acrylate, 80.6 parts isooctyl methacrylate, 59.4 parts methyl methacrylate, 0.003 parts ferrous sulfate heptahydrate, 0.3 parts tert-butyl hydroperoxide, 0.003 parts disodium ethylenediaminetetraacetate dihydrate, 0.3 parts disodium 2-hydroxy-2-sulfinylacetate, and 15 parts water.

[0083] Example 5 This embodiment provides an aqueous acrylic emulsion, which differs from Embodiment 1 in that the core-shell structure contains the following raw materials by mass: 76.4 parts styrene, 103.6 parts butyl acrylate, 103.6 parts isooctyl methacrylate, 76.4 parts methyl methacrylate, 0.003 parts ferrous sulfate heptahydrate, 0.3 parts tert-butyl hydroperoxide, 0.003 parts disodium ethylenediaminetetraacetate dihydrate, 0.3 parts disodium 2-hydroxy-2-sulfinylacetate, and 15 parts water.

[0084] Example 6 This embodiment provides an aqueous acrylic emulsion, which differs from Embodiment 1 in that the core-shell structure contains the following raw materials by mass: 50 parts styrene, 105 parts butyl acrylate, 105 parts isooctyl methacrylate, 50 parts methyl methacrylate, 0.003 parts ferrous sulfate heptahydrate, 0.3 parts tert-butyl hydroperoxide, 0.003 parts disodium ethylenediaminetetraacetate dihydrate, 0.3 parts disodium 2-hydroxy-2-sulfinylacetate, and 15 parts water.

[0085] Comparative Example 1 This comparative example provides an aqueous acrylic emulsion, which differs from Example 1 in that the core-shell structure contains the following raw materials by mass: 47.5 parts styrene, 62 parts butyl acrylate, 78 parts isooctyl methacrylate, 30 parts methyl methacrylate, 0.003 parts ferrous sulfate heptahydrate, 0.3 parts tert-butyl hydroperoxide, 0.003 parts disodium ethylenediaminetetraacetate dihydrate, 0.3 parts disodium 2-hydroxy-2-sulfinylacetate, and 15 parts water.

[0086] Comparative Example 2 This comparative example provides an aqueous acrylic emulsion, which differs from Example 1 in that the core-shell structure contains the following raw materials by mass: 87 parts styrene, 115 parts butyl acrylate, 115 parts isooctyl methacrylate, 87 parts cyclohexyl methacrylate, 0.003 parts ferrous sulfate heptahydrate, 0.3 parts tert-butyl hydroperoxide, 0.003 parts disodium ethylenediaminetetraacetate dihydrate, 0.3 parts disodium 2-hydroxy-2-sulfinylacetate, and 15 parts water.

[0087] Comparative Example 3 This comparative example provides an aqueous acrylic emulsion, which differs from Example 1 in that the core-shell structure contains the following raw materials by mass: 46.5 parts styrene, 63.5 parts butyl acrylate, 63.5 parts isooctyl methacrylate, 46.5 parts methyl methacrylate, 0.003 parts ferrous sulfate heptahydrate, 0.3 parts tert-butyl hydroperoxide, 0.003 parts disodium ethylenediaminetetraacetate dihydrate, 0.3 parts disodium 2-hydroxy-2-sulfinylacetate, and 15 parts water.

[0088] Comparative Example 4 This comparative example provides an aqueous acrylic emulsion, which differs from Example 1 in that the core-shell structure contains the following raw materials by mass: 25 parts styrene, 48.75 parts butyl acrylate, 62.5 parts isooctyl methacrylate, 41.25 parts methyl methacrylate, 0.003 parts ferrous sulfate heptahydrate, 0.3 parts tert-butyl hydroperoxide, 0.003 parts disodium ethylenediaminetetraacetate dihydrate, 0.3 parts disodium 2-hydroxy-2-sulfinylacetate, and 15 parts water.

[0089] Comparative Example 5 This comparative example provides an aqueous acrylic emulsion, which differs from Example 1 in that the core-shell structure contains the following raw materials by mass: 21 parts styrene, 55 parts butyl acrylate, 45 parts isooctyl methacrylate, 25 parts cyclohexyl methacrylate, 0.003 parts ferrous sulfate heptahydrate, 0.3 parts tert-butyl hydroperoxide, 0.003 parts disodium ethylenediaminetetraacetate dihydrate, 0.3 parts disodium 2-hydroxy-2-sulfinylacetate, and 15 parts water.

[0090] Comparative Example 6 This comparative example provides an aqueous acrylic emulsion, which differs from Example 1 in that the core-shell structure contains the following raw materials by mass: 40 parts styrene, 115 parts butyl acrylate, 115 parts isooctyl methacrylate, 40 parts methyl methacrylate, 0.003 parts ferrous sulfate heptahydrate, 0.3 parts tert-butyl hydroperoxide, 0.003 parts disodium ethylenediaminetetraacetate dihydrate, 0.3 parts disodium 2-hydroxy-2-sulfinylacetate, and 15 parts water.

[0091] Test methods The aqueous acrylic emulsions provided in the examples and comparative examples were subjected to the following performance tests: (1) Glass transition temperature (Tg, °C): Calculated with reference to the FOX formula; (2) Solid content (%): The solid content of acrylic resin was calculated by drying at 150℃ for 20 min under ventilation conditions to remove the solvent components in the emulsion. (3) pH value: Measured using a pH meter at 25℃; (4) Brinell viscosity (mPa.s): The test was conducted using a Brinell rotational viscometer (LV range model), with the test temperature kept constant at 20℃ and the rotation speed set at 60 r / min; The aqueous acrylic emulsions provided in the examples and comparative examples were coated onto a substrate with a basis weight of 400 g / m². 2 The coating amount on the kraft paper is 9 g / m 2 The coating sample was dried in an oven at 130℃ for 3 minutes and then subjected to the following tests: (1) Heat-sealing performance: Take the above sample and cut it into a strip with a width of 20 mm. Adjust the sealing temperature of the heat sealer to 200℃, the pressure to 0.2 MPa, and the time to 1s to perform heat sealing from coating surface to coating surface (face to face). After the sample cools down to 25℃, cut it into a strip with a width of 15 mm for heat sealing strength test. Complete tearing indicates excellent heat sealing strength; partial tearing indicates unqualified heat sealing strength; strength indicates no heat sealing performance. (2) Heat resistance to tackiness: The test was conducted according to GB / T 23982-2009 9.2 / 9.3, referring to the anti-tackiness evaluation standard; A-0: No adhesion marks, no coating migration; B-0: Slight adhesion marks, which disappear completely after wiping, with no coating peeling; C-0: Obvious sticky marks, with a small amount of coating migration and whitening; D-0: Severe adhesion, with large areas of coating peeling off and transferring to contaminate the substrate; Cut the above sample into 3 cm × 3 cm square samples, place them with the coated side facing the coated side (face to face) and the coated side facing the blank side (face to back), press them down with a 1 kg weight, and bake them in an 80℃ oven for 16 h before taking them out.

[0092] The test results are shown in Tables 1 and 2: Table 1 Table 2 The test results show that: (1) As can be seen from Examples 1-5, the present invention, through the formulation design of waterborne acrylic emulsion and the control of the glass transition temperature of the homopolymer of the core reactive monomers to be greater than -30℃ and less than -10℃, produces waterborne acrylic emulsions with a uniform and stable emulsion solid content of 42.17-42.78%, with minimal fluctuations, and excellent batch consistency in industrial production; the pH of the system is maintained stably at 7.59-7.89, and the emulsion has good storage stability; the Brookfield viscosity is 67-86 mPa·s, with a moderate viscosity range, smooth coating construction, and no problems of clogging or sagging. At the same time, this series of emulsions has excellent heat-sealing performance. After heat-sealing tests, the coating can be completely torn, and the heat-sealing adhesion strength is sufficient; whether the coating is face-to-face or face-to-back stacked, the heat resistance tack level can reach B-0 or above after long-term aging at 80℃, with no coating adhesion or stickiness, making it suitable for paper stacking, winding, and warehousing and transportation conditions.

[0093] (2) As can be seen from Examples 3 and 4-5 and Comparative Examples 2-3, the present invention further limits the mass ratio of the shell reactive monomer to the core reactive monomer to 1:(1.5-2). If the mass ratio is greater than 1:2, the emulsion will break during the polymerization process, the reaction will terminate, and the emulsion cannot be formed. If the mass ratio is less than 1:1.5, that is, the proportion of shell monomer is too high, the coating is too rigid and not flexible enough, the heat sealing toughness of the coating is worse, the heat sealing bonding strength is reduced, and the overall viscosity of the emulsion increases, the smoothness of coating construction decreases, which is not conducive to on-site coating operations.

[0094] (3) As can be seen from Example 1, Comparative Example 1 and Comparative Example 4-5, the proportion of core reactive monomers in Comparative Example 1 and Comparative Example 4-5 is too low, resulting in film formation defects. When the heat resistance and tack test is carried out, it will absorb moisture from the environment, and the shell layer will also soften, resulting in the coating surface becoming sticky.

[0095] (4) As can be seen from Examples 1, 3, 6 and Comparative Example 6, when the core reactive monomer and the shell reactive monomer are in the range of 1: (1.5-2) and the glass transition temperature is between -10 and -30°C, the coating has strong heat sealing performance. However, when the glass transition temperature is less than -30°C, the overall flexibility of the core is too large, which will cause the coating surface to become sticky and the heat resistance to re-adhesion will decrease.

[0096] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. An aqueous acrylic emulsion, characterized in that, The aqueous acrylic emulsion has a core-shell structure; The raw materials for preparing the shell layer in the core-shell structure include, by mass, 165-190 parts of shell layer reactive monomers and 400-550 parts of solvent A; The raw materials for preparing the core in the core-shell structure include, by mass, 247-380 parts of core reactive monomer and 10-20 parts of solvent B; The glass transition temperature of the homopolymer of the core reactive monomer is greater than -30°C and less than -10°C.

2. The aqueous acrylic emulsion according to claim 1, characterized in that, The mass ratio of the shell reactive monomer to the core reactive monomer is 1:(1.5-2); Preferably, the glass transition temperature of the homopolymer of the shell reactive monomer is >80°C.

3. The aqueous acrylic emulsion according to claim 1 or 2, characterized in that, The shell reactive monomers include hard monomer A, soft monomer A, and crosslinking monomer A; Preferably, the shell reactive monomer further includes a medium-soft monomer A; Preferably, the core reactive monomer includes hard monomer B, soft monomer B, and crosslinking monomer B; Preferably, the core reactive monomer further includes the medium-soft monomer B.

4. The aqueous acrylic emulsion according to claim 3, characterized in that, The glass transition temperatures of the homopolymers of hard monomer A and hard monomer B are each independently greater than 25°C. Preferably, the hard monomer A and hard monomer B each independently comprise an aromatic olefinic unsaturated monomer and / or a first (meth)acrylate monomer; Preferably, the hard monomer A and hard monomer B each independently comprise a combination of an aromatic olefinic unsaturated monomer and a first (meth)acrylate monomer; Preferably, the aromatic olefinic unsaturated monomer includes any one or a combination of at least two of styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, α-butylstyrene, 4-n-butylstyrene or divinylbenzene, and more preferably styrene; Preferably, the first (meth)acrylate monomer includes any one or a combination of at least two of methyl methacrylate, tert-butyl methacrylate or n-propyl methacrylate, and more preferably methyl methacrylate and / or n-butyl methacrylate; Preferably, the glass transition temperatures of the homopolymers of the medium-soft monomer A and the medium-soft monomer B are each independently greater than or equal to -25°C and less than or equal to 25°C. Preferably, the intermediate soft monomer A and the intermediate soft monomer B each independently comprise a second (meth)acrylate monomer; Preferably, the second (meth)acrylate monomer includes any one or a combination of at least two of methyl acrylate, ethyl acrylate, ethyl methacrylate or isobutyl methacrylate; Preferably, the glass transition temperatures of the homopolymers of the soft monomer A and the soft monomer B are each independently < -25°C; Preferably, the soft monomer A and soft monomer B each independently comprise a third (meth)acrylate monomer; Preferably, the third (meth)acrylate monomer includes any one or a combination of at least two of n-butyl acrylate, n-butyl methacrylate, isooctyl acrylate, tridecyl methacrylate, or octadecyl methacrylate, and more preferably n-butyl acrylate and / or isooctyl acrylate.

5. The aqueous acrylic emulsion according to any one of claims 1-4, characterized in that, The crosslinking monomer A and crosslinking monomer B each independently comprise an acid-based olefinic unsaturated monomer; Preferably, the acidic olefinic unsaturated monomer includes any one or a combination of at least two of acrylic acid, methacrylic acid, styrene sulfonic acid, vinyl sulfonic acid, 2-(meth)acryloylamino-2-methylpropanesulfonic acid and their salts or itaconic acid, preferably acrylic acid and / or methacrylic acid.

6. The aqueous acrylic emulsion according to any one of claims 1-5, characterized in that, The raw materials for preparing the shell layer in the core-shell structure also include, by weight, any one or a combination of at least two of the following: 0.05-1 parts emulsifier, 0.05-5 parts free radical initiator, or 0.1-2 parts neutralizer; Preferably, the emulsifier comprises any one or at least two of substituted alkali metal sulfate, substituted ammonium sulfate, substituted alkali metal sulfonate, substituted ammonium sulfonate, substituted alkali metal phosphate, or substituted ammonium phosphate, and the substituted substituents comprise any one or at least two of alkyl, aryl, alkylaryl, or alkoxy groups. Preferably, the free radical initiator comprises a peroxide; Preferably, the peroxide comprises any one or a combination of at least two of potassium persulfate, ammonium persulfate, or sodium persulfate; Preferably, the neutralizing agent includes any one or a combination of at least two of organic amines, inorganic ammonia neutralizing agents, or alkali metal hydroxides; Preferably, solvent A comprises water.

7. The aqueous acrylic emulsion according to any one of claims 1-6, characterized in that, The raw materials for preparing the core in the core-shell structure also include, by mass, any one or a combination of at least two of the following: 0.001-0.005 parts of catalyst, 0.2-0.5 parts of oxidant, 0.001-0.005 parts of chelating agent, or 0.2-0.5 parts of reducing agent; Preferably, the catalyst comprises a metal catalyst; Preferably, the metal catalyst includes any one or a combination of at least two of the following: iron-based catalyst, copper-based catalyst, manganese-based catalyst, silver-based catalyst, platinum-based catalyst, vanadium-based catalyst, nickel-based catalyst, or chromium-based catalyst. Preferably, the metal catalyst comprises any one or a combination of at least two of the following: ferrous sulfate, ferrous sulfate hydrate, nickel sulfate, nickel sulfate hydrate, copper chloride, copper chloride hydrate, manganese acetate, manganese acetate hydrate, vanadium acetate, or vanadium acetate hydrate. Preferably, the oxidant includes any one or a combination of at least two of the following: tert-butyl peroxide, potassium permanganate, ammonium persulfate, or an alkali metal salt of persulfate; Preferably, the chelating agent comprises disodium ethylenediaminetetraacetate dihydrate; Preferably, the reducing agent includes any one or a combination of at least two of the following: sodium formaldehyde sulfoxylate, ascorbic acid, isoascorbic acid, sodium sulfite, sodium bisulfite, sodium dithionite, formamidinium sulfinic acid, hydroxymethyl sulfonic acid, disodium hydroxysulfinate acetate, or acetone bisulfite. Preferably, solvent B comprises water.

8. A method for preparing an aqueous acrylic emulsion as described in any one of claims 1-7, characterized in that, The preparation method includes the following steps: (1) Mix and react the raw materials for the preparation of the shell to obtain a shell emulsion; (2) The core preparation raw materials are mixed and reacted with the shell emulsion to obtain the aqueous acrylic emulsion.

9. The method for preparing the aqueous acrylic emulsion according to claim 8, characterized in that, Step (1) specifically includes mixing the raw materials for shell preparation and reacting them, including the first stage mixing, the second stage mixing, the third stage mixing and reaction, and the fourth stage mixing; Preferably, the first stage of mixing in step (1) includes mixing the components of the shell reactive monomer to obtain the shell reactive monomer; Preferably, the second stage of mixing in step (1) includes mixing the emulsifier and solvent A accounting for 90-93 wt% of the total mass of solvent A, heating the mixture to 80-90°C, and then adding a portion of free radical initiator and mixing for 1-3 min; Preferably, the portion of the free radical initiator accounts for 30-35 wt% of the total mass of the free radical initiator; Preferably, a portion of the free radical initiator is dissolved in solvent A in an amount of 1-2 wt% of the total mass of solvent A; Preferably, the third stage of mixing and reaction in step (1) includes adding the mixed system of the shell reaction monomer and the remaining free radical initiator to the mixed system obtained in the second stage, and heating to 80-90℃ for 50-70 min; Preferably, the remaining free radical initiator is dissolved in solvent A in an amount of 3-4 wt% of the total mass of solvent A; Preferably, the fourth stage mixing in step (1) includes adding a neutralizing agent to the reaction system after the third stage mixing and reaction, and mixing to obtain the shell emulsion; Preferably, the neutralizing agent is dissolved in the remaining solvent A; Preferably, the pH of the shell emulsion is 7.5-8; Preferably, step (2) specifically includes a first stage of mixing, a second stage of mixing and reaction, and a third stage of mixing and reaction; Preferably, the first stage of mixing in step (2) includes mixing the components of the core reactive monomer to obtain the core reactive monomer; Preferably, the second stage of mixing and reaction in step (2) includes cooling the shell emulsion obtained in step (1) to 45-55°C, adding a portion of the core reaction monomer, mixing for 10-30 min, then adding a catalyst, chelating agent, a portion of oxidant and a portion of reducing agent, and then heating the mixed system to 80-90°C and reacting for 15-25 min. Preferably, the portion of the core reactive monomer accounts for 45-55 wt% of the total mass of the core reactive monomer. Preferably, the portion of the oxidant accounts for 45-55 wt% of the total mass of the oxidant. Preferably, a portion of the oxidant is dissolved in solvent B in an amount of 10-20 wt% of the total mass of solvent B; Preferably, the reducing agent accounts for 45-55 wt% of the total mass of the reducing agent. Preferably, a portion of the reducing agent is dissolved in solvent B, which accounts for 30-40 wt% of the total mass of solvent B; Preferably, the third stage of mixing and reaction in step (2) includes cooling the reaction system obtained after mixing and reaction in the second stage of step (2) to 45-55°C, adding the remaining core reaction monomers, mixing for 10-30 min, adding the remaining oxidant and the remaining reducing agent, and heating to 80-90°C for 15-25 min. Preferably, the remaining oxidant is dissolved in solvent B in an amount of 10-20 wt% of the total mass of solvent B; Preferably, the remaining reducing agent is dissolved in solvent B, which accounts for 30-40 wt% of the total mass of solvent B.

10. The use of an aqueous acrylic emulsion as described in any one of claims 1-7 in packaging materials.

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