High-strength high-water-resistance polyacrylate resin emulsion and preparation method thereof

Abstract

The application discloses a kind of high-strength high water resistance polyacrylate resin emulsion and preparation method thereof, the method is as follows: (1) reaction raw material ratio is as follows: acrylate 15-30%, acrylonitrile 15-25%, styrene 2-10%, crosslinking monomer 1-3%, amphiphilic macromolecule RAFT reagent 0.15-2%, aqueous solution of alkali 0.5-2%, initiator 0.05-0.15%, deionized water 40-55%; (2) acrylate, part of acrylonitrile, part of crosslinking monomer are mixed to obtain oil phase, amphiphilic macromolecule RAFT reagent is dissolved in deionized water to obtain water phase, water phase is added dropwise into oil phase to prepare pre-emulsion; (3) pre-emulsion is reacted under the action of initiator to prepare core layer, then the remaining raw materials are added, and shell layer is polymerized to prepare polyacrylate resin emulsion with core-shell structure high acrylonitrile content, and mechanical properties and water resistance are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a high-strength, highly water-resistant polyacrylate emulsion and its preparation method. Background Technology

[0002] Polyacrylate emulsions are an important class of polymer materials, widely used in coatings, adhesives, textile coatings, and other fields. Their core performance requirements include high strength, good substrate adhesion, and water resistance. Traditional polyacrylate emulsions are usually prepared through conventional emulsion polymerization (such as emulsion free radical polymerization), but this method has the following limitations:

[0003] (1) Insufficient mechanical properties and adhesion: The proportion of polar monomers in conventional emulsion polymerization is low, and the molecular chain distribution is wide and poorly controllable. Although polar monomers, represented by acrylonitrile, can improve the cohesive energy between polymer chains and improve mechanical properties and water resistance, in emulsion free radical polymerization systems, when the acrylonitrile content is high, problems such as reduced polymerization rate, decreased monomer conversion rate, and non-uniform molecular structure are likely to occur, making it difficult to significantly improve emulsion performance while maintaining high conversion rate. Therefore, the amount of acrylonitrile used in existing polyacrylate emulsions usually has an upper limit (the conventional acrylonitrile usage range is below 15%), and further increasing the usage has limited room for performance improvement and may even lead to performance degradation.

[0004] (2) Poor water resistance: Conventional emulsion polymerization relies on emulsifiers to stabilize latex particles. Emulsifiers are difficult to completely remove after polymerization, and the residual hydrophilic components will reduce the water resistance and wet adhesion of the film after film formation. In water immersion or high humidity environment, the film is prone to water absorption, swelling or even interfacial peeling, which limits the application of polyacrylate emulsions in humid environments.

[0005] (3) Difficulty in structural control: Although there are reports in the existing technology of controlling the properties of emulsions through core / shell structure design, it is difficult to effectively control the spatial distribution of different monomers and crosslinking monomers in latex particles under conventional emulsion polymerization conditions. Crosslinking monomers are often randomly distributed inside and on the surface of latex particles, which can easily lead to insufficient internal crosslinking or excessive surface crosslinking, resulting in decreased flexibility or insufficient adhesion, thus affecting the overall performance.

[0006] In recent years, reversible addition-fragmentation chain transfer (RAFT) polymerization technology has become a potential direction for the preparation of high-performance polyacrylate emulsions due to its advantages such as "emulsifier-free" (or extremely low emulsifier dosage), controllable molecular weight, and broad comonomer compatibility. Existing RAFT emulsion polymerization technologies mainly focus on molecular weight control or the formation of self-stabilizing emulsions, and systematic studies on specific functional improvements such as softness and strength, high adhesion, and water resistance have not yet been reported.

[0007] It is necessary to develop a high-performance polyacrylate emulsion that relies on RAFT emulsion polymerization technology to edit the molecular structure and regulate the core-shell structure of latex particles, thereby preparing a polyacrylate emulsion with excellent mechanical properties, adhesion, and water resistance. Summary of the Invention

[0008] The purpose of this invention is to provide a polyacrylate emulsion with high polar monomer content and core / shell structure, which improves the strength, water resistance and adhesion of the film.

[0009] The technical solution adopted in this invention is: A method for preparing a high-strength, high-water-resistant polyacrylate resin emulsion, the method comprising the following steps: (1) Weigh the reaction raw materials according to the ratio. The mass fraction of each component in the reaction raw materials is: Acrylic ester 15-30%, acrylonitrile 15-25%, styrene 2-10%, crosslinking monomer 1-3%, amphiphilic macromolecular RAFT reagent 0.15-2%, alkaline aqueous solution 0.5-2%, initiator 0.05-0.15%, deionized water 40-55%; (2) Mix and dissolve the acrylate and the first crosslinking monomer to obtain the oil phase. Dissolve the amphiphilic macromolecular RAFT reagent in deionized water to obtain the aqueous phase. Add the oil phase to the aqueous phase and emulsify by shearing and stirring to obtain the pre-emulsion. (3) After nitrogen deoxygenation, the pre-emulsion is heated to 65-75 ℃, an initiator is added, and a core-layer polymerization reaction is carried out. The temperature is raised to 80-85 ℃ and the reaction is maintained for 3-4 hours. Acrylonitrile, the second part of the crosslinking monomer, and styrene are then added to carry out a shell-layer polymerization reaction. An aqueous solution of alkali is added dropwise at the same time. After the addition is complete, the temperature is maintained at 80-85 ℃ and the reaction is continued for 3-4 hours. After cooling to 40-60 ℃, post-treatment is carried out to obtain the high-strength and high-water-resistant polyacrylate resin emulsion.

[0010] Furthermore, the post-processing step is as follows: the reaction solution is cooled to 40-60℃, an aqueous solution of oxidant is added, and then an aqueous solution of reducing agent is slowly added dropwise. After the addition is complete, the polymerization reaction is carried out for 30-60 minutes to obtain the high-strength, high-water-resistant polyacrylate resin emulsion.

[0011] The acrylate is one or two of the following: methyl acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate, hexadecyl acrylate, octadecyl acrylate, hexadecyl methacrylate, and octadecyl methacrylate.

[0012] Preferably, the acrylate is a mixture of long-chain acrylate and short-chain acrylate, wherein the long-chain acrylate is hexadecyl acrylate, octadecyl acrylate, hexadecyl methacrylate or octadecyl methacrylate; the short-chain acrylate is one of methyl acrylate, ethyl acrylate, butyl acrylate and isooctyl acrylate; the mass fraction of the long-chain acrylate is 2 to 5% of the total mass of all monomers.

[0013] The total mass of all monomers refers to the total mass of acrylate, acrylonitrile, styrene, and crosslinking monomers.

[0014] The crosslinking monomer is one of N-hydroxymethylacrylamide, N-(isobutoxymethyl)acrylamide, and N-n-butoxymethylacrylamide.

[0015] The initiator is one of potassium persulfate, ammonium persulfate, and hydrogen peroxide.

[0016] The aqueous solution of the alkali is preferably ammonia, or an aqueous solution of any one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, potassium carbonate, diethanolamine, or triethanolamine. The mass fraction of ammonia is preferably 25%, and the mass fraction of the alkali in the aqueous solution of any one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, potassium carbonate, diethanolamine, or triethanolamine is 0.4% to 1%.

[0017] The addition time of the aqueous solution of alkali is controlled at 10-20 minutes.

[0018] The first part of the crosslinking monomer is used in an amount of 10-20% of the total mass of the crosslinking monomer, and the remainder is used in the second part of the crosslinking monomer.

[0019] The amphiphilic macromolecular RAFT reagent comprises hydrophilic segments, hydrophobic segments, and RAFT functional groups, and the molecular formula of the amphiphilic macromolecular RAFT reagent is shown below:

[0020] Wherein, X group is a C1-C15 alkyl group; A segment is a lipophilic segment, preferably one or more copolymers of styrene, acrylonitrile, acrylates, methacrylates, etc.; B segment is a hydrophilic segment, preferably one or more copolymers of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, acrylic acid, methacrylic acid, etc.; wherein m and n are the number of monomers in A segment and B segment, respectively, and the ratio of m to n is 1:3-7; R group is 1-methylbenzyl, 1,1-dimethylbenzyl, isopropionic acid, 2-diisobutyric acid, 2-isobutyronitrile, cyanopentaic acid, 3-benzoic acid, 2-hydroxyisobutyric acid, or isopropylamino.

[0021] A common example is the polyacrylic acid-polystyrene RAFT reagent (PAAn-PStm-RAFT), in which the degrees of polymerization m and n of polystyrene and polyacrylic acid can be adjusted adaptively.

[0022] This invention also provides a high-strength, high-water-resistant polyacrylate resin emulsion prepared by the above method, and its application as an adhesive or special coating.

[0023] The present invention improves the mechanical properties, adhesion, and water resistance of the adhesive film. Its technical principle lies in: 1. Adding a high proportion of acrylonitrile to enhance polarity: The cyano group (-CN) of acrylonitrile has strong polarity and can form dipole-dipole interactions or hydrogen bonds with the -CN of adjacent polymer chains or polar groups (such as -OH) on the substrate surface, which significantly improves the inter-chain cohesive energy (theoretical calculations show that the molar cohesive energy of AN is about 38.6 kJ / mol, which is higher than that of BA, which is 26.5 kJ / mol), thereby enhancing the mechanical properties (tensile strength) and water resistance (reducing water molecule penetration) of the film.

[0024] 2. The RAFT system improves acrylonitrile conversion: RAFT polymerization controls the free radical concentration through a reversible chain transfer reaction, avoiding the chain termination competition caused by high AN content in conventional emulsion polymerization (AN has a low polymerization rate in conventional polymerization and is easily terminated after combining with free radicals). At the same time, it optimizes the polymerization process (increasing the reaction temperature and extending the reaction time), further improving the AN conversion rate. Therefore, even if the AN content is ≥15%, the conversion rate can still be maintained at ≥99%. 3. Improved water resistance: The RAFT system does not require emulsifiers, and the hydrophobicity of the long-chain hydrophobic monomers further reduces the hydrophilicity of the film. The two work together to significantly reduce the water absorption rate of the film.

[0025] 4. Core / shell structure: The core layer is mainly composed of acrylate to provide flexibility, while the shell layer is mainly composed of acrylonitrile and styrene to provide rigidity and polarity. The crosslinking monomers are enriched at a high concentration in the shell layer, which forms a dense network on the surface of the film. On the one hand, this enhances the degree of reaction with the active groups on the substrate surface, and on the other hand, it enhances the surface hydrophobicity, further improving adhesion and water resistance.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Improved mechanical properties and adhesion: The high proportion of acrylonitrile enhances the inter-chain interactions (such as dipole-dipole interactions) and cohesive energy of polymers through strong polar cyano groups (-CN). Combined with the precise control of RAFT polymerization, the tensile strength and abrasion resistance of the film are significantly better than those of conventional emulsions, while the adhesion to the substrate (fibers, plastics) is greatly improved.

[0027] 2. Enhanced water resistance: The long-chain hydrophobic monomers have excellent hydrophobicity, and the RAFT system has no emulsifier residue, which also improves water resistance. Furthermore, the core-shell structure of soft core and hard shell particles further enhances the integrity of film formation, making the water absorption rate of the film of this invention much lower than that of conventional emulsions. After soaking at 25°C for 24 hours, it still has good adhesion and mechanical properties, that is, the water absorption rate decreases and the wet strength retention rate is significantly improved.

[0028] 3. Core / shell structure optimization performance: The core layer (BA + a small amount of long-chain acrylate monomers + crosslinking monomers) moderately crosslinks to inhibit phase inversion and ensure emulsion stability; the shell layer (AN + St + a large number of crosslinking monomers) enriches crosslinking sites, enhances the reactivity between the surface and the substrate active groups (such as -OH, -COOH), and further strengthens adhesion.

[0029] The acrylic emulsion of the present invention produces a film with tensile properties ≥10MPa, modulus ≤2.5MPa, wet strength retention ≥60%, and water absorption ≤2.0%. Compared with the peel strength of the substrate, the film has a comparative improvement of more than 20%, exhibiting excellent comprehensive performance and possessing significant industrialization value. Detailed Implementation

[0030] The technical solution of the present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0031] The amphiphilic macromolecular RAFT reagent used in the embodiments of this invention has the following structural formula:

[0032] Examples 1-3, Comparative Examples 1-3 Peel strength of PP / PET / fiberboard (1) Weigh the reaction raw materials according to the proportions in Table 1. In the examples, the initiator is potassium persulfate, the crosslinking monomer is N-hydroxymethylacrylamide, and the aqueous solution of the alkali is 25% ammonia. Table 1

[0033] (2) Mix and dissolve butyl acrylate, hexadecyl acrylate, and the first crosslinking monomer to obtain an oil phase. Dissolve 0.1 g of potassium persulfate in 4 g of water as an initiator solution. Dissolve the amphiphilic macromolecular RAFT reagent in the remaining deionized water to obtain an aqueous phase. Add the oil phase to the aqueous phase and emulsify by shearing and stirring to obtain a pre-emulsion. (3) Under nitrogen protection, the pre-emulsion was heated to 75 °C, and an initiator solution was added to carry out the core layer polymerization reaction. The temperature was raised to 85 °C and the reaction was kept at this temperature for 4 hours. Acrylonitrile, the second part of the crosslinking monomer, and styrene were then added to carry out the shell layer polymerization reaction. Ammonia water was added dropwise at the same time. After the addition was completed, the temperature was kept at 85 °C and the reaction was continued for 4 hours. After the temperature was lowered to 45 °C, post-treatment was carried out. 1 g of 5% tert-butyl hydrogen peroxide aqueous solution was added, and then 1 g of 5% ascorbic acid was added. After the addition was completed, the polymerization reaction was carried out for 30 minutes to obtain the high-strength and high-water-resistant polyacrylate resin emulsion.

[0034] The prepared polyacrylate resin emulsion was used to make a film, and its mechanical properties and water resistance were tested. The results are shown in Table 2 below: Table 2

[0035] Peel strength testing was conducted according to GB / T2790-1995 standard to test the 180° peel strength of the film with different substrates.

[0036] The wet strength retention rate is the tensile strength of the film after soaking at 25°C for 24 hours / the original tensile strength.

[0037] The results showed that the polyacrylate emulsions prepared in Examples 1-3 of this application had tensile properties ≥10MPa, modulus ≤2.5MPa, wet strength retention ≥60%, water absorption ≤2.0%, and high peel strength with PP, PET, and fiberboard, and had good adhesion.

[0038] In Comparative Example 1, where no long-chain hexadecyl acrylate was added, the water resistance of the film was significantly reduced due to the lack of hydrophobic effect of the long-chain acrylate during film formation.

[0039] Comparative Example 2 shows that no crosslinking monomer was added during the core layer polymerization stage, which makes the core layer structure prone to inversion, leading to a decrease in the product's water resistance and adhesion.

[0040] In Comparative Example 3, the amount of acrylonitrile was reduced to 10%. Due to the small amount of acrylonitrile, the improvement in mechanical properties and water resistance was limited, and it was not as good as Examples 1-3.

[0041] Comparative Example 4 Synthesis experiments were conducted using conventional emulsion polymerization processes according to the formulation in Example 1: (1) Mix and dissolve butyl acrylate, hexadecyl acrylate, and the first part of the crosslinking monomer to obtain the oil phase. Dissolve 0.1g of potassium persulfate in 4g of water as an initiator solution. Dissolve the anionic emulsifier in the remaining deionized water to obtain the aqueous phase. Mix half of the aqueous phase with the oil phase, and emulsify by shearing and stirring to obtain a pre-emulsion; (2) The pre-emulsion is heated to 75 °C, an initiator solution is added, and the core layer polymerization reaction is carried out. The temperature is raised to 85 °C and the reaction is carried out for 4 hours. Then acrylonitrile, the second part of crosslinking monomer, styrene and the other half of the aqueous phase are mixed and emulsified by high-speed stirring. The mixture is then slowly added dropwise to the core layer emulsion to carry out the shell layer polymerization reaction. The dropwise addition time is controlled to be 1.5-2 hours. After the dropwise addition is completed, the reaction is continued for 3 hours. After the temperature is lowered to 45 °C, the post-treatment is carried out. 1 g of 5% tert-butyl hydrogen peroxide aqueous solution is added, and then 1 g of 5% ascorbic acid is added. After the dropwise addition is completed, the polymerization reaction is carried out for 30 minutes to obtain the high-strength and high-water-resistant polyacrylate resin emulsion.

[0042] The conversion rate of acrylonitrile was tested, and the results showed that the conversion rate of Example 1 was 99.3%, while the conversion rate of Comparative Example 4 was only 75%.

[0043] The comparison results show that the acrylonitrile conversion rate is low when using anionic emulsifiers and conventional emulsion polymerization processes.

[0044] Comparative Example 5 The experiment was conducted according to the formulation of Example 1, wherein step (3) was changed to: (3) Under nitrogen protection, the pre-emulsion was heated to 75 °C, and an initiator solution was added to carry out the core layer polymerization reaction. The reaction was carried out at 75 °C for 4 hours. Then acrylonitrile, the second part of the crosslinking monomer, and styrene were added to carry out the shell layer polymerization reaction. Ammonia water was added dropwise at the same time. After the addition was completed, the temperature was kept at 75 °C and the reaction was continued for 2 hours. After cooling to 45 °C, post-treatment was carried out. 1g of 5% tert-butyl hydrogen peroxide aqueous solution was added, and then 1g of 5% ascorbic acid was added. After the addition was completed, the polymerization reaction was carried out for 30 minutes to obtain the high-strength and high-water-resistant polyacrylate resin emulsion.

[0045] The conversion rate of acrylonitrile was tested, and the results showed that the conversion rate of Example 5 was only 82%.

[0046] The comparative results show that increasing the reaction temperature and time helps to improve the conversion rate of acrylonitrile, thereby increasing the acrylonitrile content in the polymer product.

[0047] The performance test results of comparative examples 4 and 5 are shown in Table 3 below: Table 3

[0048] Table 3 shows that Comparative Example 4, using a conventional emulsion polymerization process, exhibited significantly lower tensile strength, poorer peel strength, and significantly worse water resistance. Comparative Example 5, due to its lower reaction temperature and lower acrylonitrile conversion rate, showed a significant decrease in mechanical properties and water resistance compared to Comparative Example 1.

[0049] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-strength, high-water-resistant polyacrylate resin emulsion, characterized in that... The method includes the following steps: (1) Weigh the reaction raw materials according to the ratio. The mass fraction of each component in the reaction raw materials is: Acrylic ester 15-30%, acrylonitrile 15-25%, styrene 2-10%, crosslinking monomer 1-3%, amphiphilic macromolecular RAFT reagent 0.15-2%, alkaline aqueous solution 0.5-2%, initiator 0.05-0.15%, deionized water 40-55%; (2) Mix and dissolve the acrylate and the first crosslinking monomer to obtain the oil phase. Dissolve the amphiphilic macromolecular RAFT reagent in deionized water to obtain the aqueous phase. Add the oil phase to the aqueous phase and emulsify by shearing and stirring to obtain the pre-emulsion. (3) After nitrogen deoxygenation, the pre-emulsion is heated to 65-75 ℃, an initiator is added, and a core-layer polymerization reaction is carried out. The temperature is raised to 80-85 ℃ and the reaction is maintained for 3-4 hours. Acrylonitrile, the second part of the crosslinking monomer, and styrene are then added to carry out a shell-layer polymerization reaction. An aqueous solution of alkali is added dropwise at the same time. After the addition is complete, the temperature is maintained at 80-85 ℃ and the reaction is continued for 3-4 hours. After cooling to 40-60 ℃, post-treatment is carried out to obtain the high-strength and high-water-resistant polyacrylate resin emulsion.

2. The method as described in claim 1, characterized in that... The acrylate is one or two of the following: methyl acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate, hexadecyl acrylate, octadecyl acrylate, hexadecyl methacrylate, and octadecyl methacrylate. The crosslinking monomer is one of N-hydroxymethylacrylamide, N-(isobutoxymethyl)acrylamide, and N-n-butoxymethylacrylamide; The initiator is one of potassium persulfate, ammonium persulfate, and hydrogen peroxide.

3. The method as described in claim 1, characterized in that... The post-processing steps are as follows: the reaction solution is cooled to 40-60℃, an aqueous solution of oxidant is added, and then an aqueous solution of reducing agent is slowly added dropwise. After the addition is complete, the polymerization reaction is carried out for 30-60 minutes to obtain the high-strength, high-water-resistant polyacrylate resin emulsion.

4. The method as described in claim 1, characterized in that... The aqueous solution of the alkali is ammonia, or an aqueous solution of any one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, potassium carbonate, diethanolamine, or triethanolamine.

5. The method as described in claim 3, characterized in that... The first part of the crosslinking monomer is used in an amount of 10-20% of the total mass of the crosslinking monomer, and the remainder is used in the second part of the crosslinking monomer. The acrylate is a mixture of long-chain acrylate and short-chain acrylate, wherein the long-chain acrylate is hexadecyl acrylate, octadecyl acrylate, hexadecyl methacrylate or octadecyl methacrylate; the short-chain acrylate is one of methyl acrylate, ethyl acrylate, butyl acrylate or isooctyl acrylate; the mass fraction of the long-chain acrylate is 2 to 5% of the total mass of all monomers.

6. The method as described in claim 1, characterized in that... The amphiphilic macromolecular RAFT reagent includes hydrophilic segments, hydrophobic segments, and RAFT functional groups.

7. The method as described in claim 6, characterized in that... The molecular formula of the amphiphilic macromolecular RAFT reagent is shown below: Wherein, X group is a C1~C15 alkyl group; A segment is a lipophilic segment, which is one or more copolymers of styrene, acrylonitrile, acrylates, methacrylates, etc.; B segment is a hydrophilic segment, which is one or more copolymers of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, acrylic acid, methacrylic acid, etc.; where m and n are the number of monomers in A segment and B segment, respectively, and the ratio of m to n is 1:3 to 7; R group is 1-methylbenzyl, 1,1-dimethylbenzyl, isopropionic acid, 2-diisobutyric acid, 2-isobutyronitrile, cyanopentaic acid, 3-benzoic acid, 2-hydroxyisobutyric acid, or isopropylamino.

8. The method as described in claim 7, characterized in that The amphiphilic macromolecular RAFT reagent is a polyacrylate-polystyrene RAFT reagent.

9. The high-strength, high-water-resistant polyacrylate resin emulsion prepared according to any one of claims 1 to 8.

10. The application of the high-strength, high-water-resistant polyacrylate resin emulsion as described in claim 9 as an adhesive.

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