A process for the preparation of and use of waterborne olefin polymer emulsions based on grafting of ethylene acrylic acid copolymers with unsaturated anhydrides

Abstract

The application discloses a preparation method and application of an unsaturated acid anhydride grafted ethylene acrylic acid copolymer water-based olefin polymer emulsion. The application modifies the ethylene acrylic acid copolymer with low carboxylic acid content (acrylic acid unit content < 15 wt%) by unsaturated acid anhydride grafting. Further, in a kneader, at a temperature lower than the melting point of the polymer, it is cooperated with an alkaline aqueous solution to realize self-emulsification, or emulsify the olefin polymer to form a stable water-based emulsion. The technology solves the problems of poor water resistance caused by traditional high-temperature shearing method relying on high carboxylic acid content of ethylene acrylic acid copolymer, environmental pollution of solvent viscosity reduction method, and difficult control of particle size of high-temperature emulsification method. The obtained emulsion has uniform particle size (D50 ≤ 0.99 μm), good water resistance (water absorption < 5%), strong adhesion (≥ 2 N / cm to olefin base, ≥ 5 N / cm to aluminum foil and other metals), and is suitable for water-based hot melt adhesive, water-based adhesive and other functional coating scenarios.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and more particularly to a method for preparing and using an aqueous olefin polymer emulsion based on an unsaturated anhydride-grafted ethylene-acrylic acid copolymer. More specifically, this invention relates to a self-emulsifying emulsion of an unsaturated anhydride-grafted ethylene-acrylic acid copolymer, the preparation of an aqueous emulsion by emulsifying an olefin polymer with an unsaturated anhydride-grafted ethylene-acrylic acid copolymer, and its use as an aqueous hot melt adhesive, functional coating, etc. Background Technology

[0002] Olefin polymers (such as polyethylene, polypropylene, and ethylene-propylene copolymers) have high melting points (typically 70-122℃) and high viscosity after melting, making it difficult to generate stable aqueous emulsions using conventional emulsification methods. Currently, there are two main known preparation methods: High-temperature shearing method: This involves adding an ethylene-acrylic acid copolymer with a high acrylic acid content (typically ≥15wt%) and performing high-speed shear emulsification at temperatures above the polymer's melting point (100-150℃). Ethylene-acrylic acid copolymers with low carboxylic acid content are generally difficult to emulsify; for example... Figure 1 , Figure 2 As shown.

[0003] Solvent viscosity reduction method: Organic solvents such as toluene and xylene are added to soften the olefin polymer, and then emulsified by high-speed shearing with an emulsifier. The solvent needs to be removed by distillation afterward.

[0004] Both methods have significant drawbacks that limit the industrial application of olefin polymer or copolymer emulsions: Poor water resistance: High-temperature shear solutions require high acrylic acid content EAA such as SK PRIMACOR™ 5980i (acid content 20.5wt%). Excessive carboxylic acid groups result in strong water absorption after the emulsion cures (water absorption rate is often >30%), making it prone to delamination and peeling in humid environments. Environmental pollution and complex process: The solvent viscosity reduction method requires the use of organic solvents accounting for 20%-50% of the system, and subsequent steps such as vacuum distillation and tail gas treatment are required, which not only increases the production cost, but also poses a risk of VOC emissions. Unstable emulsion properties: In high-temperature emulsification, the melting point of olefin polymers is close to or higher than the boiling point of water, which causes the aqueous phase to vaporize rapidly and form bubbles. The emulsion has a wide particle size distribution (D50>10μm), making it difficult to form a uniform and stable small particle size emulsion.

[0005] Therefore, there is an urgent need to develop an olefin polymer emulsion preparation technology that is low in acid dependence, free from solvent pollution, and has controllable particle size, in order to meet the multiple requirements of water-based materials for water resistance, stability, and environmental friendliness. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for preparing and using an aqueous olefin polymer emulsion based on an unsaturated anhydride-grafted ethylene-acrylic acid copolymer.

[0007] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing a self-emulsifying emulsion based on an unsaturated anhydride-grafted ethylene-acrylic acid copolymer, comprising the following steps: a) Add the unsaturated anhydride-grafted ethylene-acrylic acid copolymer to an electrically heated kneader, wherein the ethylene-acrylic acid copolymer has an acrylic acid unit content of 5-15 wt% and an unsaturated anhydride grafting amount of 0.05-3.5 wt%; b) Set the heating temperature and stirring speed of the electric heating kneader, start the kneader to knead and stir, add an alkaline aqueous solution during kneading and stirring, and after kneading and stirring is completed, cool the material to room temperature to obtain a self-emulsifying emulsion.

[0008] Secondly, the present invention provides a method for preparing an olefin polymer emulsion based on an unsaturated anhydride-grafted ethylene-acrylic acid copolymer, comprising the following steps: a) The unsaturated anhydride-grafted ethylene-acrylic acid copolymer and the olefin polymer are mixed and added to an electrically heated kneader, wherein the ethylene-acrylic acid copolymer has an acrylic acid unit content of 5-15 wt% and an unsaturated anhydride grafting amount of 0.05-3.5 wt%; b) Set the heating temperature and stirring speed of the electric heating kneader, start the kneader to knead and stir, add an alkaline aqueous solution during kneading and stirring, and after kneading and stirring is completed, cool the material to room temperature to obtain an olefin polymer emulsion.

[0009] Preferably, in step a) of the aforementioned two preparation methods, the unsaturated anhydride-grafted ethylene-acrylic acid copolymer is obtained by grafting a double-bonded anhydride onto the ethylene-acrylic acid copolymer, wherein the double-bonded anhydride is one or more of maleic anhydride, itaconic anhydride, citric acid anhydride, or other organic unsaturated anhydrides. Preferably, the amount of unsaturated anhydride grafted is 0.05-3.5 wt% (the percentage of the mass of the unsaturated anhydride grafted onto the polymer backbone to the total mass of the grafted product, the same below), more preferably, the amount of unsaturated anhydride grafted is 0.1-2.5 wt%.

[0010] According to a preferred embodiment of the present invention, in step a) of the aforementioned two preparation methods, the acrylic acid unit content of the ethylene acrylic acid copolymer is 7.5-14.5 wt%.

[0011] According to a preferred embodiment of the present invention, in step b) of the two aforementioned preparation methods, the alkaline aqueous solution is one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, 2-amino-2-methyl-1-propanol or other inorganic alkaline compound solutions or organic amine solutions, and the molar ratio of the alkaline substance in the alkaline aqueous solution to the carboxylic acid in the unsaturated anhydride-grafted ethylene-acrylic acid copolymer is (0.5-1.5):1.

[0012] According to a preferred embodiment of the present invention, in step b) of the two aforementioned preparation methods, the heating temperature of the electrically heated kneader is set to be 5-10°C lower than the higher melting point of the ethylene-acrylic acid copolymer or olefin polymer. Preferably, the temperature is set to 80-99°C, while satisfying the aforementioned temperature requirements.

[0013] According to a preferred embodiment of the present invention, in step b) of the two aforementioned preparation methods, the total duration of electric heating kneading is 3-5 hours, wherein the alkaline aqueous solution can be added in the early to mid-stage of the kneading process. Preferably, the kneading duration after the addition of the alkaline aqueous solution can be set to about 3 hours, for example, 2-4 hours.

[0014] According to a preferred embodiment of the present invention, the particle size of the self-emulsifying emulsion satisfies D50≤0.99 micrometers and D90≤3 micrometers.

[0015] According to a preferred embodiment of the present invention, in the method for preparing the olefin polymer emulsion, the mass ratio of the olefin polymer to the unsaturated anhydride-grafted ethylene-acrylic acid copolymer is (0-9):(1-10).

[0016] Furthermore, the olefin polymer is one or more of the following: polyethylene, maleic anhydride-grafted polyethylene, polypropylene, maleic anhydride-grafted polypropylene, ethylene-propylene copolymer, maleic anhydride-grafted ethylene-propylene copolymer, ethylene-butene copolymer, maleic anhydride-grafted ethylene-butene copolymer, ethylene-octene copolymer, maleic anhydride-grafted ethylene-octene copolymer, ethylene-vinyl acetate copolymer, maleic anhydride-grafted ethylene-vinyl acetate copolymer, hydrogenated styrene-butadiene block copolymer, maleic anhydride-grafted hydrogenated styrene-butadiene block copolymer, ethylene-isooctyl acrylate copolymer, ethylene-ethyl acrylate copolymer, diisobutylene-methyl methacrylate copolymer, acrylate-acrylic acid copolymer, styrene-butadiene rubber, hydrogenated nitrile rubber, ethylene propylene diene monomer (EPDM) rubber, polymerized rosin, hydrogenated rosin, hydrogenated terpene resin, hydrogenated C5 petroleum resin, or other olefin copolymers.

[0017] According to a preferred embodiment of the present invention, the particle size of the olefin polymer emulsion satisfies D50≤0.99 micrometers and D90≤3 micrometers.

[0018] Thirdly, the present invention provides the use of the aforementioned self-emulsifying emulsion or the aforementioned olefin polymer emulsion in the preparation of waterborne hot melt adhesives or functional coatings.

[0019] According to a preferred embodiment of the present invention, the adhesive layer formed by the functional coating or water-based hot melt adhesive has a water absorption rate of < 5%, an adhesion force of ≥ 2 N / cm to olefin polymer substrates, and an adhesion force of ≥ 5 N / cm to metal substrates, thus meeting the multiple requirements of the material for water resistance, stability, etc.

[0020] Compared with existing technologies, the beneficial effects of this invention include: 1) This invention selects ethylene-acrylic acid copolymers with a carboxylic acid content of 5-15 wt% (such as Mobil Escor™ 5020, with an acid content of 7.5 wt%; SK PRIMACOR™ 3004, with an acid content of 9.7 wt%), and introduces highly polar anhydride groups onto the ethylene-acrylic acid copolymer molecular chain by grafting unsaturated anhydrides (such as maleic anhydride). The resulting unsaturated anhydride-grafted ethylene-acrylic acid copolymer combines hydrophilicity and hydrophobicity. After grafting with unsaturated anhydrides such as maleic anhydride, the ethylene-acrylic acid copolymer molecular chain simultaneously contains a high content of hydrophobic olefin segments (compatible with olefin polymers) and a low content of polar hydrophilic carboxylic acid / anhydride groups (compatible with water). In particular, the highly polar, large-volume anhydride groups greatly enhance the interaction with water. This ethylene-acrylic acid copolymer containing unsaturated anhydride structures such as maleic anhydride can effectively reduce interfacial tension, thereby forming small-particle-size self-emulsifying emulsions or olefin polymer emulsions.

[0021] 2) This invention involves adding unsaturated anhydride-grafted ethylene-acrylic acid copolymer to an alkaline aqueous solution (lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, 2-amino-2-methyl-1-propanol or other inorganic alkaline compound solutions or organic amine solutions, etc.) in an electrically heated kneader, or blending the unsaturated anhydride-grafted ethylene-acrylic acid copolymer with an olefin polymer and then adding it to an alkaline aqueous solution in an electrically heated kneader. The mixture is then vigorously kneaded at 80-99°C to ensure that the polar hydrophilic groups in the polymer are fully in contact with water. The uniform dispersion is achieved through the squeezing and shearing action of the paddles, preventing the aqueous phase from vaporizing, resulting in a self-emulsifying emulsion or an olefin polymer emulsion. Since the viscosity of unsaturated anhydride-grafted ethylene-acrylic acid copolymer, such as maleic anhydride, is similar to that of the olefin polymer, it can penetrate into the softened olefin polymer after kneading, thus achieving uniform emulsification and dispersion to obtain an emulsion. This solves the problem that small molecule emulsifiers are difficult to uniformly disperse within high-viscosity olefin polymers.

[0022] 3) The carboxylic acid groups and grafted anhydride groups in the ethylene-acrylic acid copolymer neutralize in alkaline aqueous solution to form carboxylate salts. The large size and strong polarity of the anhydride groups effectively enhance the hydrophilicity of the latex particle surface, forming a stable negatively charged double layer on the latex particle surface. This inhibits particle aggregation through charge repulsion, ensuring emulsion stability. Figure 3 As shown. At the same time, the ethylene-acrylic acid copolymer with low carboxylic acid content contains a high content of hydrocarbon hydrophobic segments, as well as a small amount of polar carboxylic acids and strongly polar anhydrides. This structure is beneficial to enhancing the hydrophilic and lipophilic surface activity, thereby enabling the formation of small-particle-size self-emulsifying emulsions or olefin polymer emulsions.

[0023] 4) The alkaline aqueous solution used in the preparation of the emulsion in this invention is not only used to neutralize carboxyl / anhydride groups, but also the pH of the emulsion can be adjusted by adjusting the alkalinity (3-14) to adapt to different olefin polymers and broaden the applicability of the process. Attached Figure Description

[0024] Figure 1 It is an emulsion formed from ethylene-acrylic acid copolymer with high carboxylic acid content; it has sufficient carboxylic acid functional groups located on the surface of the particles to stabilize the emulsion.

[0025] Figure 2 It is an emulsion formed by ethylene-acrylic acid copolymer with low carboxylic acid content; a small number of carboxylic acid functional groups are located on the surface of the particles, which makes it difficult to stabilize the emulsion and leads to particle aggregation.

[0026] Figure 3 This is an emulsion formed by grafting anhydride molecules onto an ethylene-acrylic acid copolymer with low carboxylic acid content. The anhydride forms two carboxylic acid groups, which increase in volume and interact with water to form a stable emulsion. Detailed Implementation

[0027] The present invention will be further described and illustrated below with reference to specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly, provided that there is no mutual conflict.

[0028] I. Experimental Materials and Equipment 1. Experimental Materials Table 1 shows the main raw materials and their specifications used in the embodiments of the present invention. The acid content recorded in the present invention refers to the mass percentage of acrylic acid units in ethylene acrylic acid copolymer (EAA).

[0029] Table 1

[0030] 2. Experimental Equipment Wankai Machinery Electric Heating Vacuum Kneader (5L, Temperature Control Accuracy ±1℃, Rotation Speed ​​0-100 rpm). Dandong Better Laser Particle Size Analyzer (BT-9300ST, testing range 0.1-3000μm, accuracy ±2%). Instron universal tensile testing machine (5969, testing range 0-500N, accuracy ±0.5%).

[0031] II. Testing Methods 1. Determination of maleic anhydride grafting rate Sample pretreatment: The ethylene-acrylic acid copolymer before and after grafting was dissolved in tetrahydrofuran under reflux (80℃, 2h). After acetone precipitation, it was extracted with acetone for 12h using a Soxhlet extractor (to remove ungrafted maleic anhydride and other unsaturated anhydrides). It was then dried in a vacuum oven (80℃, -0.09MPa) for 5h to constant weight. Titration procedure: Take 2.0 ± 0.1 g of dried sample, add 50 mL of tetrahydrofuran and dissolve under reflux, add 2 drops of 1% phenolphthalein-ethanol solution, and titrate with 0.1 mol / L potassium hydroxide-methanol solution until pink (the color does not fade in 30 s), and record the volume V0; add 10 mL of 0.1 mol / L hydrochloric acid-isopropanol solution, stir for 10 min, and titrate again until pink, and record the volume V. KOH ; Grafting rate calculation: Grafting rate (wt%) = (V KOH - V0)×C×98.06) / (m×1000)×100%, where C is the concentration of potassium hydroxide-methanol solution (0.1mol / L), m is the sample mass (g), and 98.06 is the molecular weight of maleic anhydride (g / mol).

[0032] 2. Emulsion stability evaluation Particle size distribution: D50 (median particle size) and D90 (90% of particles have a diameter smaller than this value) were measured using a laser particle size analyzer. Centrifugation stability: Centrifuge at 3000 rpm for 30 minutes; no stratification is acceptable. 3. Adhesion test (GB / T 2792-2014) Substrate preparation: polyethylene (PE) film (200μm thickness, surface tension 32mN / m), aluminum foil (20μm thickness, clean and oxidation-free surface); Coating preparation: The emulsion was uniformly coated on the substrate surface and dried at 80℃ for 2 hours, with a coating thickness of 20±2μm; Test procedure: The 180° peeling method was used, the peeling speed was 300 mm / min, the peeling force was recorded, and the average value of 5 parallel tests was taken.

[0033] 4. Water absorption rate test (GB / T 9273-2008) Sample preparation: Coated strips (150mm×150mm×20μm) were dried at 80℃ to constant weight, and their mass m was measured. 干 ; Soaking treatment: Soak in deionized water at 23±2℃ for 48 hours, then remove and blot dry with filter paper. Weigh the sample (m). 湿 ; Calculate: Water absorption rate = m 湿 - m 干 ) / m 干 ×100%.

[0034] III. Detailed Description of Comparative Examples (Note: The total weight of all comparative example samples was 2.5 kg. The amount of alkaline substance used was designed according to the molar ratio of pure alkaline substance to total acid (2 times the amount of carboxylic acid converted from carboxylic acid and anhydride). The weights of each substance are as follows.) Comparative Example 1: Self-emulsification of ethylene-acrylic acid copolymer with low carboxylic acid content Composition (total weight 2.5kg): EAA (Escor™ 5020, acid content 7.5wt%) 0.625kg, deionized water 1.510kg, 10 wt% KOH aqueous solution 0.365kg; Preparation process: Add the ethylene-acrylic acid copolymer to a kneader, heat it to 80°C to soften it (60 rpm), add KOH and water, and continue kneading for 30 minutes; Phenomena and results: The system exhibited "blocky agglomeration" and could not form a uniform emulsion; after diluting a portion of the sample with water, laser particle size analyzer tests showed D50=45.60μm and D90=135.70μm; it separated into layers without centrifugation and has no practical application value. Cause analysis: The 7.5 wt% carboxylic acid content of the ethylene-acrylic acid copolymer is not hydrophilic enough to form a stable double layer in the aqueous phase. There is no charge repulsion between particles, which leads to agglomeration.

[0035] Comparative Example 2: Self-emulsification of ethylene-acrylic acid copolymer with low carboxylic acid content Composition (total weight 2.5kg): 1.25kg ethylene acrylic acid copolymer (Escor™ 5200, carboxylic acid content 15 wt%), 0.417kg deionized water, 0.833kg 10 wt% NaOH aqueous solution; Preparation process: Kneader temperature 90℃ (EAA melting point 90℃), add EAA to soften, then add NaOH aqueous solution, knead for 20 min; Phenomena and Results: The system was a "high-viscosity suspension", and some of the ethylene-acrylic acid copolymer was not dispersed and emulsified; D50=4.41μm, D90=30.99μm; centrifugation test showed stratification, and water absorption test was not performed because uniform coating could not be achieved. Cause analysis: Although the 15 wt% carboxylic acid content of the ethylene-acrylic acid copolymer improves hydrophilicity, the carboxylic acid at the interface cannot effectively prevent particle aggregation during emulsification.

[0036] Comparative Example 3: Self-emulsification of ethylene-acrylic acid copolymer with low carboxylic acid content Composition (total weight 2.5kg): EAA (Escor™ 5050, acid content 9 wt%) 1.25kg, deionized water 1.122kg, 25 wt% ammonia water 0.128kg; Preparation process: Kneader temperature 95℃ (2℃ below the melting point of EAA), kneading time 25min; Phenomena and results: The system exhibited a "coarse-particle emulsion" structure with D50 = 12.93 μm and D90 = 39.22 μm; it separated into layers after centrifugation. Cause analysis: The hydrophilicity and hydrophobicity of 9 wt% acid content EAA are unbalanced, making it impossible to form a uniform emulsion and resulting in uneven particle dispersion.

[0037] Comparative Example 4: Self-emulsification of ethylene-acrylic acid copolymer with low carboxylic acid content Composition (total weight 2.5kg): EAA (Escor™ 5050, acid content 9 wt%) 0.75kg, deionized water 0.916kg, 10 wt% AMP aqueous solution 0.834kg; Preparation process: Kneader temperature 95℃, kneading time 30min; Phenomena and results: The system was a "dilute suspension" with D50 = 12.41 μm and D90 = 43.48 μm; it separated into layers after centrifugation. Cause analysis: When the content of ethylene-acrylic acid copolymer is reduced, the emulsification capacity of the system is insufficient, and it cannot completely cover the particle surface, causing the particles to agglomerate through van der Waals forces.

[0038] Comparative Example 5: Self-emulsification of high-acid-content ethylene-acrylic acid copolymer (conventional method) Composition (total weight 2.5kg): EAA (PRIMACOR™ 5980i, acid content 20.5 wt%) 1.0kg, deionized water 0.065kg, 10 wt% KOH aqueous solution 1.435kg; Preparation process: Kneader temperature 80℃ (3℃ lower than the melting point of ethylene-acrylic acid copolymer), knead for 15 min; Phenomena and Results: A uniform milky white emulsion was formed with D50=0.34μm and D90=0.57μm; no stratification occurred after centrifugation; the coating showed adhesion of only 0.76N / cm to PE substrate and 5.3N / cm to aluminum foil; the coating had a water absorption rate as high as 39%, and blistered and peeled off after immersion in water for 24 hours. Cause analysis: The high carboxylic acid content of 20.5 wt% provides sufficient hydrophilicity, which can form a stable electric double layer to stabilize the emulsion. However, after a large number of carboxylic acid groups absorb water, the coating cohesion decreases, and the water resistance and adhesion deteriorate.

[0039] Comparative Example 6: Emulsified polyethylene with high carboxylic acid content ethylene-acrylic acid copolymer Composition (total weight 2.5kg): LDPE 1I50A 1.125kg, EAA (PRIMACOR™ 5980i, acid content 20.5 wt%) 0.125kg, deionized water 1.122kg, 10 wt% NaOH aqueous solution 0.128kg; Preparation process: Kneader temperature 99℃ (2℃ higher than the melting point of polyethylene), add polyethylene and ethylene-acrylic acid copolymer to soften, then add NaOH aqueous solution, knead for 20 min; Phenomena and Results: The system was a "high-viscosity, non-uniform white liquid" that separated into layers without centrifugation; the particle size of the sample was tested, with D50=43.48μm and D90=107.20μm; it was impossible to form a uniform coating for performance testing. Cause analysis: The high carboxylic acid content ethylene-acrylic acid copolymer has poor compatibility with polyethylene, and cannot effectively reduce interfacial tension for emulsification.

[0040] Tables 2 and 3 show the raw material addition amounts and product performance test results for each comparative example.

[0041] Table 2

[0042] Table 3

[0043] IV. Detailed Description of Invention Embodiments (Note: The total weight of samples in Examples 1-10 is 2.5 kg, and that in Examples 11-15 is 3 kg. The amount of alkaline substance used is designed according to the molar ratio of alkaline pure substance to total acid (carboxylic acid + twice the amount of carboxylic acid converted from acid anhydride). The weights of each substance are as follows.) Invention Example 1: Low carboxylic acid content ethylene-acrylic acid copolymer grafted with maleic anhydride self-emulsifying (grafting rate 2.5wt%) Composition (total weight 2.5kg): 1.25kg of maleic anhydride-grafted ethylene-acrylic acid copolymer (PRIMACOR™ 3004, acid content 9.0wt%, grafting rate 2.5wt%), 0.039kg of deionized water, and 1.211kg of 10wt% KOH aqueous solution; Preparation process: Synthesis of maleic anhydride-grafted ethylene-acrylic acid copolymer: 136g MAH, 4g DCP, and 20g liquid paraffin were mixed into a paste, then mixed with 2000g EAA. The mixture was extruded using a twin-screw extruder at 140-190℃, followed by crushing and drying. The synthesis reaction formula is as follows:

[0044] Self-emulsification: Kneader temperature 83℃ (5℃ lower than the melting point of ethylene-acrylic acid copolymer), add maleic anhydride-grafted ethylene-acrylic acid copolymer, soften and then add KOH aqueous solution, knead for 10 min. Phenomena and Results: A uniform milky white emulsion was formed with D50 = 0.287 μm and D90 = 0.490 μm; no stratification was observed after centrifugation at 3000 rpm for 30 min; the water absorption rate of the resulting coating was 3.70% (<5%); the adhesion to polyethylene substrate was 2.8 N / cm (≥2 N / cm), and the adhesion to aluminum foil was 11.2 N / cm (≥5 N / cm). Advantages Analysis: After grafting with maleic anhydride, anhydride groups are introduced, and a stable double electric layer can still be formed even with a low acid content (9wt%). The low acid content ensures the water resistance of the coating, while the MAH groups enhance the bonding with low surface energy materials (such as polyethylene) or metal substrates, resulting in significantly better adhesion than Comparative Example 5.

[0045] Example 2 of the invention: Self-emulsification of maleic anhydride grafted onto ethylene-acrylic acid copolymer with low carboxylic acid content (grafting rate 0.1%) Composition (total weight 2.5kg): 1.25kg of maleic anhydride-grafted ethylene-acrylic acid copolymer (PRIMACOR™ 4810, acid content 14.5 wt%, grafting rate 0.1 wt%), 0.336kg of deionized water, and 0.914kg of 10 wt% NaOH aqueous solution; Preparation process: The grafting rate was reduced, and the rest was the same as in Example 1; Phenomena and results: Emulsion D50=0.902μm, D90=1.682μm; Water absorption rate of the coating is 4.70% (<5%); Adhesion to polyethylene substrate is 2.3N / cm (≥2N / cm), and adhesion to aluminum foil is 7.8N / cm (≥5N / cm). Advantages Analysis: Even with a grafting rate of only 0.1 wt%, it can still compensate for the interfacial tension defects of the 14.5 wt% carboxylic acid content ethylene-acrylic acid copolymer, forming a stable emulsion; and the carboxylic acid content is lower than that of Comparative Example 5 (20.5 wt%), resulting in significantly improved water resistance (water absorption rate 4.70% vs 39%). This embodiment of the invention exhibits superior adhesion.

[0046] Invention Example 3: Self-emulsification of maleic anhydride grafted onto ethylene-acrylic acid copolymer with low carboxylic acid content (adjusting grafting ratio) Composition (total weight 2.5kg): maleic anhydride-grafted ethylene-acrylic acid copolymer (Escor™ 5020, acid content 7.5 wt%, grafting rate 1.27 wt%) 0.75kg, deionized water 1.678kg, 25 wt% ammonia water 0.072kg; Preparation process: Grafting rate 1.27 wt% (maleic anhydride dosage 80g), the rest is the same as in Comparative Example 1; Phenomena and results: The emulsion has a D50 of 0.990 μm and a D90 of 1.695 μm; it does not separate into layers after centrifugation; the water absorption rate of the resulting coating is 2.00% (<5%); the adhesion to polyethylene substrate is 2.5 N / cm (≥2 N / cm), and the adhesion to aluminum foil is 8.9 N / cm (≥5 N / cm). Advantages Analysis: The 7.5 wt% low carboxylic acid content ethylene-acrylic acid copolymer grafted with 1.27 wt% MAH not only solved the aggregation problem of Comparative Example 1, but also reduced the water absorption rate to 2.00% due to its low acid content and numerous hydrophobic groups. Furthermore, this invention embodiment exhibits superior adhesion.

[0047] Invention Example 4: Emulsified polyethylene with maleic anhydride-grafted ethylene-acrylic acid copolymer Composition (total weight 2.5kg): LDPE polyethylene 0.75kg, maleic anhydride grafted ethylene acrylic acid copolymer (product of Example 1 of the invention, acid content 9.0 wt%, grafting rate 2.5 wt%) 0.5kg, deionized water 0.766kg, 10 wt% KOH aqueous solution 0.484kg; Preparation process: Kneader temperature 85℃ (18℃ lower than LDPE melting point), add polyethylene and maleic anhydride grafted ethylene acrylic acid copolymer to mix and soften (5 min), add KOH aqueous solution and knead for 10 min; Phenomena and results: The emulsion has a D50 of 0.886 μm and a D90 of 1.483 μm; it does not separate into layers after centrifugation; the water absorption rate of the resulting coating is 1.60% (<5%); the adhesion to polyethylene substrate is 2.7 N / cm (≥2 N / cm), and the adhesion to aluminum foil is 10.1 N / cm (≥5 N / cm). Advantages Analysis: The low temperature of 85℃ avoids vaporization of the aqueous phase; the maleic anhydride-grafted ethylene-acrylic acid copolymer has good compatibility with polyethylene; the emulsion has uniform particle size and excellent water resistance and adhesion.

[0048] Invention Example 5: Emulsified maleic anhydride-grafted polyethylene with maleic anhydride-grafted acrylic acid copolymer Composition (total weight 2.5kg): maleic anhydride grafted polyethylene 0.875kg, maleic anhydride grafted ethylene acrylic acid copolymer (acid content 14.5 wt%, grafting rate 0.1 wt%) 0.375kg, deionized water 0.776kg, 10 wt% AMP aqueous solution 0.474kg; Preparation process: Kneader temperature 90℃ (lower than the melting point of maleic anhydride-grafted polyethylene 32℃), the rest is the same as in Example 4; Phenomena and results: Emulsion D50=0.926μm, D90=1.651μm; no stratification after centrifugation; water absorption rate 2.90% (<5%); adhesion to polyethylene substrate 4.5N / cm (≥2N / cm), adhesion to aluminum foil 6.6N / cm (≥5N / cm); Advantages Analysis: The groups between maleic anhydride-grafted polyethylene and maleic anhydride-grafted ethylene-acrylic acid copolymer have a synergistic effect, which improves the interfacial bonding force and the adhesion to the polyethylene substrate reaches 4.5 N / cm (5.9 times that of Comparative Example 5).

[0049] Invention Example 6: Maleic anhydride-grafted ethylene-acrylic acid copolymer emulsified ethylene-propylene copolymer Composition (total weight 2.5kg): 1.0kg ethylene-propylene copolymer, 0.25kg maleic anhydride-grafted ethylene-acrylic acid copolymer (PRIMACOR™ 4810, acid content 14.5 wt%, grafting rate 0.1 wt%), 1.086kg deionized water, 0.162kg 10wt% NaOH aqueous solution; Preparation process: Kneader temperature 85℃ (12℃ lower than the melting point of ethylene-propylene copolymer), otherwise the same as in Example 4 of the invention; Phenomena and results: The emulsion has a D50 of 0.643 μm and a D90 of 2.046 μm; it does not separate into layers after centrifugation; the water absorption rate of the resulting coating is 3.70% (<5%); the adhesion to PE substrate is 3.2 N / cm (≥2 N / cm), and the adhesion to aluminum foil is 6.2 N / cm (≥5 N / cm). Advantages: Only 10% maleic anhydride-grafted ethylene-acrylic acid copolymer can emulsify 40% ethylene-propylene copolymer, resulting in high emulsification efficiency.

[0050] Example 7 of the invention: Emulsified maleic anhydride-grafted ethylene-acrylic acid copolymer Composition (total weight 2.5kg): maleic anhydride-grafted ethylene-propylene copolymer 0.5kg, maleic anhydride-grafted ethylene-acrylic acid copolymer (product of Example 1 of the Invention, acid content 9.0 wt%, grafting rate 2.5 wt%) 0.75kg, deionized water 0.523kg, 10 wt% KOH aqueous solution 0.727kg; Preparation process: Kneader temperature 88℃ (6℃ lower than the melting point of maleic anhydride-grafted ethylene-propylene copolymer), the rest is the same as in Example 4 of the invention; Phenomena and results: The emulsion has a D50 of 0.839 μm and a D90 of 1.479 μm; it does not separate into layers after centrifugation; the water absorption rate of the resulting coating is 2.90% (<5%); the adhesion to polyethylene substrate is 5.9 N / cm (≥2 N / cm), and the adhesion to aluminum foil is 10.9 N / cm (≥5 N / cm). Advantages Analysis: The double-grafted structure of maleic anhydride-grafted ethylene-propylene copolymer and maleic anhydride-grafted ethylene-acrylic acid copolymer significantly improves the physical entanglement and chemical bonding with the polyethylene substrate, with an adhesion force of 5.9 N / cm (one of the highest values ​​in the embodiments of the invention).

[0051] Example 8 of the Invention: Maleic anhydride-grafted ethylene-acrylic acid copolymer emulsified ethylene-vinyl acetate copolymer Composition (total weight 2.5kg): ethylene vinyl acetate EVA 0.875kg, maleic anhydride grafted ethylene acrylic acid copolymer (Escor™ 5020, carboxylic acid content 7.5 wt%, grafting rate 1.27 wt%) 0.375kg, deionized water 1.217kg, 25 wt% ammonia water 0.033kg; Preparation process: Kneader temperature 75℃ (5℃ lower than EVA melting point), otherwise the same as in Example 4 of the invention; Phenomena and results: The emulsion has a D50 of 0.942 μm and a D90 of 1.862 μm; it does not separate into layers after centrifugation; the water absorption rate of the resulting coating is 4.10% (<5%); the adhesion to polyethylene substrate is 4.7 N / cm (≥2 N / cm), and the adhesion to aluminum foil is 7.5 N / cm (≥5 N / cm). Advantages Analysis: The vinyl acetate groups and the anhydride groups of the maleic anhydride-grafted ethylene-acrylic acid copolymer have hydrogen bonding, so the emulsification process does not require high temperature, and uniform dispersion can be achieved at 75℃, and the adhesion is excellent.

[0052] Invention Example 9: Emulsified maleic anhydride-grafted ethylene-acrylic acid copolymer (different anhydrides) Composition (total weight 2.5 kg): itaconic anhydride-grafted ethylene-propylene copolymer 0.857 kg, maleic anhydride-grafted ethylene-acrylic acid copolymer (product of Example 1) 0.5 kg, deionized water 0.814 kg, 10 wt% KOH aqueous solution 0.436 kg; Preparation process: Same as in Example 7 of the invention; Phenomena and results: The emulsion has a D50 of 0.512 μm and a D90 of 1.014 μm; it does not separate into layers after centrifugation; the water absorption rate of the resulting coating is 3.70% (<5%); the adhesion to polyethylene substrate is 5.3 N / cm (≥2 N / cm), and the adhesion to aluminum foil is 10.4 N / cm (≥5 N / cm). Advantages Analysis: Experiments verified the stability of maleic anhydride-grafted ethylene-propylene copolymers emulsified with different anhydride-grafted ethylene-propylene copolymers, while also demonstrating excellent adhesion to different substrates.

[0053] Example 10 of the Invention: Emulsified Maleic Anhydride-Grafted Ethylene Acrylic Acid Copolymer with Maleic Anhydride-Grafted Ethylene Vinyl Acrylate Copolymer Composition (total weight 2.5kg): maleic anhydride-grafted ethylene vinyl acetate copolymer 0.125kg, maleic anhydride-grafted ethylene acrylic acid copolymer (acid content 7.5 wt%, maleic anhydride grafting rate 1.27 wt%) 0.5kg, deionized water 1.188kg, 10 wt% AMP aqueous solution 0.687kg; Preparation process: Kneader temperature 78℃ (5℃ lower than the melting point of maleic anhydride-grafted vinyl acetate copolymer), the rest is the same as in Example 4 of the invention; Phenomena and results: The emulsion has a D50 of 0.856 μm and a D90 of 1.435 μm; it does not separate into layers after centrifugation; the water absorption rate of the resulting coating is 1.30% (the lowest value in the invention embodiments); the adhesion to polyethylene substrate is 6.4 N / cm (the highest value in the invention embodiments), and the adhesion to aluminum foil is 9.1 N / cm (≥5 N / cm). Advantages Analysis: Maleic anhydride-grafted ethylene-acrylic acid copolymer is fully compatible with maleic anhydride-grafted ethylene-vinyl acetate copolymer to emulsify and form a dense double electric layer, resulting in a coating with a water absorption rate reduced to 1.30%. Furthermore, both polymers are grafted with maleic anhydride, exhibiting good compatibility with the substrate and excellent adhesion.

[0054] Invention Example 11: Boundary Verification of High Carboxylic Acid Content and High Maleic Anhydride Grafting Rate Composition (total weight 3kg): maleic anhydride-grafted ethylene-acrylic acid copolymer (acid content 20.5 wt%, maleic anhydride grafting rate 3.05 wt%) 0.6kg, deionized water 1.268kg, 10 wt% KOH aqueous solution 1.132kg; Preparation process: Kneader temperature 72℃ (5℃ lower than EAA melting point), add maleic anhydride-grafted ethylene-acrylic acid copolymer to soften, then add KOH aqueous solution, knead for 10 min; Phenomenon and results: D50 = 19.24 μm, unable to form a stable emulsion; Conclusion: The excessively high content of carboxylic acid and the excessively high grafting rate of maleic anhydride resulted in poor emulsification due to excessive hydrophilicity.

[0055] Invention Example 12: Boundary Verification of Low Carboxylic Acid Content and High Maleic Anhydride Grafting Rate Composition (total weight 3kg): 1.5kg maleic anhydride-grafted ethylene-acrylic acid copolymer (Escor™ 5200, acid content 15wt%, maleic anhydride grafting rate 3.12 wt%), 1.485kg deionized water, 1.545kg 10 wt% NaOH aqueous solution; Preparation process: Kneader temperature 85℃ (5℃ lower than the melting point of ethylene-acrylic acid copolymer), otherwise the same as in Example 11 of the invention; Phenomena and results: D50 = 1.697 μm, and the particles separated after centrifugation; Conclusion: The grafting rate of maleic anhydride is too high, resulting in excessive interfacial tension, making it difficult to emulsify and disperse to form a uniform emulsion.

[0056] Invention Example 13: Boundary Verification of Low Carboxylic Acid Content and Low Maleic Anhydride Grafting Rate Composition (total weight 3kg): 1.5kg maleic anhydride-grafted ethylene-acrylic acid copolymer (Escor™ 5000, acid content 6wt%, MAH grafting rate 0.08 wt%), 1.491kg deionized water, 0.052kg 25 wt% ammonia; Preparation process: Kneader temperature 95℃ (5℃ lower than EAA melting point), otherwise the same as in Example 11 of the invention; Phenomena and results: D50 = 4.333 μm, centrifugation resulted in layer separation; Conclusion: The carboxylic acid content is too low, the maleic anhydride grafting rate is too low, and the hydrophilicity is insufficient, making emulsification difficult.

[0057] Invention Example 14: Boundary Verification of Emulsified LDPE with Low Carboxylic Acid Content and Low Maleic Anhydride Grafting Rate Composition (total weight 3kg): LDPE 0.9kg, maleic anhydride-grafted ethylene-acrylic acid copolymer (Escor™5000, acid content 6 wt%, MAH grafting rate 0.08 wt%) 0.6kg, deionized water 1.092kg, 10 wt% AMP aqueous solution 0.408kg; Preparation process: Kneader temperature 95℃ (8℃ lower than the melting point of polyethylene), otherwise the same as in Example 4 of the invention; Phenomena and results: D50 = 17.50 μm, centrifugation resulted in layer separation; Conclusion: The emulsifier lacks sufficient hydrophilicity, making it difficult to emulsify polyethylene.

[0058] Invention Example 15: Boundary Verification of Emulsified Maleic Anhydride-Grafted Ethylene Vinyl Acetate with High Maleic Anhydride Grafting Rate Ethylene Acrylic Acid Copolymer Composition (total weight 3kg): 1.11kg maleic anhydride-grafted vinyl acetate copolymer, 0.09kg maleic anhydride-grafted ethylene acrylic acid copolymer (carboxylic acid content 15 wt%, maleic anhydride grafting rate 3.12 wt%), 1.717kg deionized water, 0.083kg 10 wt% NaOH aqueous solution; Preparation process: Kneader temperature 77℃ (5℃ lower than the melting point of MAH-g-EVA), otherwise the same as in Example 4 of the invention; Phenomenon and results: D50 = 43.48 μm, emulsion failed to form; Conclusion: The maleic anhydride grafting rate in ethylene-acrylic acid is too high (>3%) and the content of maleic anhydride-grafted ethylene-acrylic acid copolymer is too low. The combination of the two makes it difficult to form an emulsion.

[0059] Tables 4 and 5 show the raw material addition amounts and product performance test results for each embodiment.

[0060] Table 4

[0061] Table 5

[0062] As can be seen from the results in Tables 2-5 above, the ethylene-acrylic acid copolymers with low carboxylic acid content (7.5 wt%, 9 wt%, 15 wt%) without maleic anhydride grafting cannot form stable emulsions (Comparative Examples 1-4); while the ethylene-acrylic acid copolymers with high carboxylic acid content (20.5 wt%) without maleic anhydride grafting, although capable of self-emulsification, have extremely poor water resistance (water absorption rate 39%, Comparative Example 5), and still cannot form emulsions when emulsifying olefin polymers (Comparative Example 6). Its adhesion to low surface energy polyethylene substrates is only 0.76 N / cm, which is far from meeting the application requirements.

[0063] By grafting maleic anhydride onto ethylene-acrylic acid copolymers (7.5 wt%, 9.0 wt%, 14.5 wt%) with low carboxylic acid content using the method of this invention, both self-emulsification and stable emulsification of olefin polymers such as polyethylene and ethylene-propylene copolymers are achieved (Examples 1-10 of the invention). Furthermore, regardless of whether it is self-emulsification or emulsification of other olefin polymers, the resulting emulsion particle size is controlled as follows: D50 ≤ 0.99 μm, D90 ≤ 3 μm, and the particle size distribution is uniform. Table 5 shows that the water absorption rate is <5% (minimum 1.30%), indicating good water resistance and solving the high water absorption defect of traditional high carboxylic acid content systems. In addition, the adhesion of the obtained emulsion to polyethylene substrate is ≥2.3 N / cm (maximum 6.4 N / cm), and the adhesion to aluminum foil is ≥6.2 N / cm (maximum 11.2 N / cm), which is several times that of traditional methods.

[0064] In summary, this invention addresses the pain points of traditional olefin emulsions, namely "high dependence on carboxylic acid content, poor water resistance, and weak adhesion to low surface energy substrates." It achieves this by grafting unsaturated anhydrides onto ethylene-acrylic acid copolymers with low carboxylic acid content, combined with a low-temperature kneading emulsification method. This allows for the formation of a stable emulsion from ethylene-acrylic acid copolymers with low carboxylic acid content (7.5wt%-14.5wt%), avoiding the high water absorption problem associated with high carboxylic acid content. Furthermore, it achieves precise control of emulsion particle size and significantly enhances adhesion to low surface energy olefin substrates and metals, thus broadening the application scenarios of waterborne olefin emulsions.

[0065] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for preparing an aqueous olefin polymer emulsion based on an unsaturated anhydride-grafted ethylene-acrylic acid copolymer, characterized in that, Includes the following steps: a) The unsaturated anhydride-grafted ethylene-acrylic acid copolymer is added alone or mixed with an olefin polymer into an electrically heated kneader, wherein the acrylic acid unit content of the ethylene-acrylic acid copolymer is 5-15 wt%, and the amount of unsaturated anhydride grafting is 0.05-3.5 wt%; b) Set the heating temperature and stirring speed of the electric heating kneader, start the kneader to knead and stir, add an alkaline aqueous solution during the kneading and stirring process, and after the kneading and stirring is completed, cool the material to room temperature to obtain a self-emulsifying emulsion or olefin polymer emulsion.

2. The preparation method according to claim 1, characterized in that, The unsaturated anhydride-grafted ethylene-acrylic acid copolymer is obtained from an anhydride-grafted ethylene-acrylic acid copolymer with double bonds, wherein the anhydride with double bonds is one or more of maleic anhydride, itaconic anhydride, citric acid anhydride, or other organic unsaturated anhydrides.

3. The preparation method according to claim 1, characterized in that, In the unsaturated anhydride-grafted ethylene-acrylic acid copolymer, the acrylic acid unit content is 7.5-14.5 wt%, and the unsaturated anhydride grafting amount is 0.1-2.5 wt%.

4. The preparation method according to claim 1, characterized in that, The olefin polymer is polyethylene, maleic anhydride-grafted polyethylene, polypropylene, maleic anhydride-grafted polypropylene, ethylene-propylene copolymer, maleic anhydride-grafted ethylene-propylene copolymer, ethylene-butene copolymer, maleic anhydride-grafted ethylene-butene copolymer, ethylene-octene copolymer, maleic anhydride-grafted ethylene-octene copolymer, ethylene-vinyl acetate copolymer, maleic anhydride-grafted ethylene-vinyl acetate copolymer, hydrogenated styrene-butadiene block copolymer, maleic anhydride-grafted hydrogenated styrene-butadiene block copolymer, ethylene-isooctyl acrylate copolymer, ethylene-ethyl acrylate copolymer, diisobutylene-methyl methacrylate copolymer, diisobutylene-methyl methacrylate copolymer, diisobutylene-ethyl acrylate-methyl methacrylate copolymer, diisobutylene-butyl acrylate-methyl methacrylate copolymer, diisobutylene-isooctyl acrylate-methyl methacrylate copolymer, acrylate-acrylic acid copolymer, styrene-butadiene rubber, hydrogenated nitrile rubber, ethylene propylene diene monomer (EPDM) rubber, polymerized rosin, hydrogenated rosin, hydrogenated terpene resin, hydrogenated C5 petroleum resin, hydrogenated C9 petroleum resin, or other olefin copolymers, or one or more combinations thereof.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the olefin polymer to the unsaturated anhydride-grafted ethylene-acrylic acid copolymer is (0-9):(1-10).

6. The preparation method according to claim 1, characterized in that, The heating temperature of the electrically heated kneader is set to be 5-10°C lower than the higher melting point of the ethylene-acrylic acid copolymer or olefin polymer.

7. The preparation method according to claim 1, characterized in that, The alkaline aqueous solution is one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, 2-amino-2-methyl-1-propanol or other inorganic alkaline compound solutions or organic amine solutions, and the molar ratio of the alkaline substance in the alkaline aqueous solution to the carboxylic acid in the unsaturated anhydride-grafted ethylene-acrylic acid copolymer is (0.5-1.5):

1.

8. The preparation method according to claim 1, characterized in that, The particle size of the self-emulsifying emulsion or olefin polymer emulsion satisfies D50≤0.99 micrometers and D90≤3 micrometers.

9. Use of the self-emulsifying emulsion or olefin polymer emulsion prepared by the method of any one of claims 1-8 in the preparation of waterborne hot melt adhesives or functional coatings.

10. The use according to claim 9, characterized in that, The functional coating or water-based hot melt adhesive layer has a water absorption rate of < 5%, an adhesion force of ≥ 2 N / cm to olefin polymer substrates, and an adhesion force of ≥ 5 N / cm to metal substrates.

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