Surface-treatment-free water-based acrylate adhesive for PVC (polyvinyl chloride) floor and preparation method of surface-treatment-free water-based acrylate adhesive

Abstract

The invention discloses a surface-treatment-free water-based acrylate adhesive for a PVC (polyvinyl chloride) floor and a preparation method of the surface-treatment-free water-based acrylate adhesive, and belongs to the technical field of polymer adhesives. The adhesive comprises the following raw material components: 0.5-15% of ester-soluble chlorinated polypropylene and 26-32% of chlorine; 0.5-15% of acrylic acid; 1-5% of ethyl acrylate; 65 to 95% of butyl acrylate; 0.5 to 3 percent of nano ZnO emulsion; 0.5 to 2% of an aziridine cross-linking agent; 1-5% of a nonionic surfactant; 0.1-1% of a water-soluble initiator; wherein the ester-soluble chlorinated polypropylene is introduced by being dissolved in a mixed monomer of ethyl acrylate and butyl acrylate in advance. The obtained adhesive is good in stability and high in initial adhesion, surface treatment-free adhesion is realized, and the initial adhesion and cohesion are balanced; meanwhile, the coating has excellent heat resistance and creep resistance, is a full-water-based system, is extremely low in VOC content, is green and environment-friendly, and has important industrial application value.

Description

Technical Field

[0001] This invention relates to the field of polymer adhesives, and more particularly to a water-based acrylic adhesive for PVC flooring that requires no surface treatment and its preparation method. Background Technology

[0002] Polyvinyl chloride (PVC) flooring is widely used in medical, educational, and industrial fields due to its wear resistance, environmental friendliness, and ease of installation. However, the installation of PVC flooring places extremely high demands on adhesives. While traditional solvent-based adhesives have strong initial tack, they contain large amounts of volatile organic compounds (VOCs) such as toluene and ethyl acetate, which are strictly limited by environmental regulations.

[0003] Existing water-based acrylic adhesives have several problems in replacing solvent-based adhesives: 1) Difficult interface bonding: PVC is a material with low surface energy and weak surface polarity, and often contains plasticizers; ordinary acrylic emulsions have poor wettability with PVC surfaces, usually requiring sanding or corona treatment of the back of the PVC flooring, increasing construction costs. 2) Poor heat creep resistance: Traditional emulsion polymerized films, under high temperatures (such as underfloor heating environments or direct sunlight in summer, temperatures can reach 60~80℃), experience a significant decrease in cohesion due to the softening of thermoplastic resins, leading to blistering and edge warping of the flooring. 3) The contradiction between initial tack and holding power: To improve initial tack, the glass transition temperature (Tg) usually needs to be lowered, but this further sacrifices heat-resistant holding power.

[0004] Existing technologies (such as CN116769101A) attempt to improve performance by introducing special monomers, but they often fail to simultaneously solve the problems of polarity matching and heat-resistant crosslinking. For example, relying solely on aziridine crosslinking is prone to hydrolysis under high temperature and humidity conditions, leading to the failure of the crosslinking network. Therefore, developing a water-based adhesive that requires no surface treatment and possesses both high initial tack and excellent heat resistance is a pressing technical challenge for the industry. Summary of the Invention

[0005] The purpose of this invention is to provide a water-based acrylic adhesive for PVC flooring that requires no surface treatment and its preparation method. The resulting adhesive has good stability and high initial tack, achieving surface treatment-free bonding, and balancing initial tack and cohesive strength. It also has excellent heat resistance and creep resistance, and is a fully water-based system with extremely low VOC content, making it green and environmentally friendly.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: One objective of this invention is to provide a water-based acrylic adhesive for PVC flooring that requires no surface treatment. The raw material components, excluding the solvent, are as follows by mass percentage: Ester-soluble chlorinated polypropylene (CPP): 0.5~15%; Acrylic acid (AA): 0.5~15%; Ethyl acrylate (EA): 1~5%; Butyl acrylate (BA): 65~95%; Crosslinking agent A: 0.5-3% nano-ZnO emulsion; Crosslinking agent B: Aziridine crosslinking agent 0.5~2%; Nonionic surfactant: 1~5%; Water-soluble initiator: 0.1~1%; The total amount of the above components is 100%; of which: The chlorine content in the ester-soluble chlorinated polypropylene is 26-32%. The CPP is introduced by pre-dissolving a mixture of monomers of ethyl acrylate (EA) and butyl acrylate (BA).

[0007] According to the above scheme, the mass ratio of the ester-soluble chlorinated polypropylene (CPP), acrylic acid (AA), ethyl acrylate (EA), and butyl acrylate (BA) is (5~10):(1~5):(1~5):(80~93).

[0008] According to the above scheme, the weight-average molecular weight (Mw) of the ester-soluble chlorinated polypropylene (CPP) is 50,000 to 120,000.

[0009] According to the above scheme, the average particle size of the nano-ZnO emulsion is 20~100nm.

[0010] According to the above scheme, the aziridine crosslinking agent is selected from at least one of trimethylolpropane tris(2-methylaziridine)propionate (CX-100), bis(2-methylaziridine)urea (XAMA-7), and 2-methylaziridine (XAMA-2).

[0011] According to the above scheme, the nonionic surfactant is selected from at least one or a combination of several of octylphenol polyoxyethylene ether (OP-10), fatty alcohol polyoxyethylene ether (AEO-9), sorbitan monooleate (Span-80), and polyoxyethylene sorbitan monolaurate (Tween-20).

[0012] According to the above scheme, the water-soluble initiator is selected from ammonium persulfate (APS), potassium persulfate (KPS), and azobisisobutyramidine hydrochloride (AIBA).

[0013] According to the above scheme, the solid content of the adhesive is 40~55%, and the viscosity is 1000~5000 mPa·s.

[0014] According to the above scheme, the solvent of the adhesive is water.

[0015] According to the above scheme, the peel strength of the adhesive is >1.9 N / mm, and the shear strength retention rate at 80℃ is >80%.

[0016] Another object of the present invention is to provide a method for preparing the above-mentioned adhesive, comprising the following steps: 1) Add ester-soluble chlorinated polypropylene (CPP) to a mixture of ethyl acrylate (EA) and butyl acrylate (BA) monomers and dissolve completely to obtain a homogeneous oil phase; 2) Dissolve the nonionic surfactant in water, add 20-40% of the total mass of acrylic acid (AA), and stir until homogeneous; then add 10-30% of the total amount of the oil phase obtained in step 1), and stir to pre-emulsify; then heat to 70-80℃, add some water-soluble initiator, and react to obtain seed emulsion; 3) The remaining oil phase, remaining acrylic acid and remaining initiator solution are simultaneously added dropwise to the seed emulsion obtained in step 2) under heat preservation conditions. After the addition is completed, the reaction is kept at heat to form a stable emulsion containing CPP grafted segments. 4) Cool the stable emulsion obtained in step 3) to 40~50℃, add nano ZnO emulsion and aziridine crosslinking agent in sequence, adjust the pH to 7.0~8.0, stir, and the adhesive is obtained.

[0017] According to the above scheme, in step 1), the mixture is stirred at 25~40℃ until the CPP is completely dissolved, ensuring that the CPP molecular chains are fully extended and dispersed in the acrylate monomer.

[0018] According to the above scheme, in step 2), the reaction time is 0.5 to 1 hour.

[0019] According to the above scheme, in step 2), the amount of water-soluble initiator added is 20-40% of the total amount.

[0020] According to the above scheme, in step 3), the dripping time is controlled to be 2-4 hours.

[0021] According to the above scheme, in step 3), after the addition is completed, the reaction is kept at a constant temperature for 1 to 2 hours.

[0022] According to the above scheme, in step 3), the remaining oil phase, the remaining acrylic acid and the remaining initiator solution are added dropwise simultaneously, or the remaining oil phase and the remaining acrylic acid are mixed and then added dropwise simultaneously with the remaining initiator solution.

[0023] According to the above scheme, in step 4), the stirring time is 0.5 to 1 hour.

[0024] This invention provides a surface-treatment-free water-based acrylic adhesive for PVC flooring, comprising ester-soluble chlorinated polypropylene (CPP), acrylic acid, ethyl acrylate (EA), butyl acrylate (BA), nano-ZnO emulsion, aziridine crosslinking agent, nonionic surfactant, and water-soluble initiator; CPP is pre-dissolved in a mixture of ethyl acrylate (EA) and butyl acrylate (BA) monomers using an "oil-phase pre-dissolution" method. Wherein: First, selecting ester-soluble CPP with a specific chlorine content (20~35%) is beneficial for its full dissolution in the EA / BA mixed oil phase while also matching the polarity of PVC. By pre-dissolving CPP in acrylate monomers, the CPP molecular chains are grafted onto the acrylic acid backbone during polymerization. The chlorine atoms of its side chains generate strong dispersion forces and dipole interactions with the chlorine atoms in the PVC substrate, achieving a "like dissolves like" molecular anchoring effect, which acts as a "molecular glue". High-strength adhesion (peel strength > 1.9 N / mm) can be achieved without physical polishing or corona treatment of the PVC surface.

[0025] Secondly, within the film, a dual crosslinking synergistic network was constructed, consisting of room-temperature covalent crosslinking of "aziridine-carboxyl groups" and high-temperature coordination crosslinking of "nano-ZnO-chloride ions / carboxyl groups." Specifically, on one hand, the aziridine crosslinking agent undergoes a ring-opening reaction with the carboxyl groups (-COOH) of acrylic acid during film formation and drying, forming a dense network structure through room-temperature covalent crosslinking, providing fundamental cohesion. On the other hand, nano-ZnO and Zn... 2+ Not only can it form ionic bonds with carboxyl groups, but more importantly, Zn at high temperatures... 2+ It can form coordinate bonds with unstable chlorine atoms in PVC and CPP (Lewis acid-base interaction) and act as an acid absorber to inhibit the dehydrochlorination reaction. This coordinate bond is thermally reversible, and at high temperatures, it enhances the stability of the interface, effectively inhibits polymer chain slippage, and significantly improves the shear strength at 80℃, solving the problem of high-temperature failure of traditional water-based adhesives.

[0026] Finally, the high-density carboxyl groups provided by the acrylic monomer can form ionic bonds with calcium ions in the cement floor and hydrogen bonds with the hydroxyl groups on the surface of the PVC filler (calcium carbonate), enhancing the adhesion to the substrate. At the same time, the soft monomer (BA) provides initial tack, while the hard segments (CPP) and the dual crosslinking network provide cohesion, overcoming the contradiction of traditional adhesives that are difficult to balance initial tack and holding power.

[0027] The beneficial effects of this invention are as follows: 1. This invention provides a water-based acrylic adhesive for PVC flooring that requires no surface treatment. It employs an "oil-phase pre-dissolution" process, where ester-soluble CPP is pre-dissolved in acrylate monomers to form a graft copolymer precursor. Utilizing the polarity matching between CPP and the PVC substrate, the hydrogen bonding of acrylic acid, and the synergistic crosslinking mechanism of ZnO / aziridine, the resulting adhesive exhibits good stability and high initial tack, achieving surface-treatment-free bonding while maintaining a balance between initial tack and cohesive strength. Furthermore, it possesses excellent heat resistance and creep resistance, with a shear strength retention rate >80% at 80℃. Moreover, this invention is a fully water-based system with extremely low VOC content, making it environmentally friendly and possessing significant industrial application value.

[0028] 2. This invention provides a method for preparing the above-mentioned adhesive. The "oil-phase pre-dissolution" process, which completely dissolves CPP in EA / BA monomers, solves the dispersion problem of hydrophobic CPP in aqueous systems, ensuring that the CPP molecular chains are fully extended before polymerization. During polymerization, the free radicals generated by the initiator not only initiate monomer polymerization but also undergo chain transfer reactions on the CPP chains, allowing acrylate branches to be directly grafted onto the CPP backbone, ultimately resulting in a molecular-level interpenetrating network (IPN) structure. This eliminates macroscopic phase separation and greatly enhances cohesion and interfacial adhesion. The unique polymerization process of this invention ensures the long-term storage stability of hydrophobic CPP in the aqueous phase, without delamination or emulsification. Furthermore, the process is simple, the conditions are mild, and it has promising prospects for industrial application. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the microstructure and triple action mechanism of the adhesive of the present invention.

[0030] Figure 2 This is a flowchart of the preparation process. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] Example 1 A method for preparing a surface-treatment-free water-based acrylic adhesive for PVC flooring is provided, the process flow is as follows: Figure 2 As shown, it includes the following steps: 1) Preparation of oil phase: Weigh 10g of ester-soluble CPP (chlorine content 30%, Mw 80,000) and add it to a mixed monomer consisting of 5g of ethyl acrylate (EA) and 80g of butyl acrylate (BA). Stir at 35°C for 30 minutes. The solution is clear and transparent, and a homogeneous oil phase is obtained.

[0033] 2) Seed emulsion preparation: Add 100g of deionized water and 3g of OP-10 to the reaction vessel and stir to dissolve. Add 1.5g of acrylic acid (AA) (30% of the total AA content) and stir until homogeneous. Then, add 28.5g of the oil phase prepared in step 1) (30% of the total oil phase content) to the vessel and pre-emulsify by high-speed stirring for 30 minutes. Raise the temperature to 75℃, add 0.15g of ammonium persulfate (30% of the total initiator content, dissolved in a small amount of water), and react for 45 minutes. When the emulsion shows a bluish tint and no obvious particles, the seed emulsion is obtained.

[0034] 3) Polymerization: Maintaining the temperature at 75°C, mix the remaining 66.5g of oil phase and the remaining 3.5g of acrylic acid (AA) thoroughly and place the mixture into dropping funnel A. Dissolve the remaining 0.35g of ammonium persulfate in water and place the mixture into dropping funnel B. Simultaneously add solutions A and B, controlling the adding time to 3 hours. After the addition is complete, raise the temperature to 80°C and maintain this temperature for 1.5 hours. The conversion rate is >98%.

[0035] 4) Synergistic crosslinking modification: Cool to 45℃, add 1.5g of nano ZnO emulsion (solid content 40%) and 1.0g of CX-100, adjust the pH to 7.5 with ammonia, stir for 45 minutes, discharge and filter to obtain water-based acrylic adhesive for PVC flooring without surface treatment.

[0036] Example 2-3 The specific preparation is the same as in Example 1, and the specific formula is shown in Table 1.

[0037] Comparative Example 1 (blank control, no CPP) Without adding CPP, replace the CPP mass fraction with BA, and follow the same steps as in Example 1. See Table 1 for the specific formulation. This is used to verify the contribution of CPP to PVC adhesion.

[0038] Comparative Example 2 (single crosslinking agent, no ZnO) Without adding nano-ZnO emulsion, only CX-100 was used, and the rest was the same as in Example 1. The specific formulation is shown in Table 1. This was used to verify the synergistic effect of ZnO on heat resistance.

[0039] Comparative Example 3 (single crosslinking agent, aziridine-free) Without adding aziridine, only nano ZnO was used, and the rest was the same as in Example 1. The specific formulation is shown in Table 1.

[0040] Comparative Example 4 (Process Comparison, CPP Physical Blending) The raw material formulation of Comparative Example 4 is exactly the same as that of Example 1, except that the preparation process is physical blending.

[0041] This comparative example does not involve "oil phase pre-dissolution". First, a pure acrylic emulsion is prepared, and then commercially available water-based CPP is added during the physical mixing stage at the same solids content ratio; the specific steps are as follows: 1) Preparation of pure acrylic emulsion: The formulation of Example 1 was followed, but without the addition of CPP. 5g of EA and 80g of BA were mixed as the oil phase. Pure acrylic emulsion was prepared using the same seed emulsion polymerization process as in Example 1.

[0042] 2) Preparation of aqueous CPP solution: Take another 10g of water-soluble CPP, dissolve it in 10g of water, and force emulsify it through a high-shear emulsifier to obtain a CPP solution.

[0043] 3) Physical blending: The pure acrylic emulsion from step 1) and the CPP solution from step 2) are mechanically mixed and stirred at room temperature for 30 minutes.

[0044] 4) Post-treatment: Add 1.5g of nano ZnO emulsion and 1.0g of CX-100 to the mixed emulsion, adjust the pH to 7.5, and obtain a physically blended adhesive.

[0045] Table 1. Raw material formulations for Examples 1-3 and Comparative Examples 1-3 (unit: g)

[0046] Performance test results: Test standards: GB / T 2794-2011 (adhesive viscosity), GB / T 2790-1995 (180° peel strength, PVC-cement board), heat resistance shear strength (tested in an 80°C constant temperature chamber). Specific results are shown in Table 2.

[0047] Table 2. Performance test comparison of Examples 1-3 and Comparative Examples 1-4

[0048] From Table 1 and Table 2, we can see that: Compared with Comparative Example 1, Example 1 shows that in the absence of CPP, ordinary acrylate has extremely low peel strength to PVC (0.85 N / mm) and extremely poor heat resistance, which illustrates the importance of polarity matching.

[0049] Compared with Comparative Example 2, it can be seen that although the strength of aziridine alone (Comparative Example 2) is acceptable at room temperature, the strength is greatly reduced at 80°C (the retention rate is only 58.5%). After adding ZnO (Example 1), the retention rate is increased to 92.6% by utilizing its heat-resistant coordination bonds, indicating that the double crosslinking has a synergistic effect.

[0050] Comparing Example 1 and Comparative Example 4, it can be seen that in Comparative Example 4, the film obtained by physical blending suffers from stress concentration due to the difference in solubility parameters between CPP and acrylate polymers, and the fact that they are formed in separate latex particles. During drying and film formation, physical stacking is the primary method, resulting in a clear phase interface between the CPP and acrylate phases. In contrast, in the "oil phase pre-dissolution" process of this invention, the acrylate monomers (EA / BA) act as a good solvent for CPP, allowing the CPP molecular chains to fully extend before polymerization. During polymerization, the free radicals generated by the initiator not only initiate monomer polymerization but also undergo chain transfer reactions on the CPP chains, causing acrylate branches to be directly grafted onto the CPP backbone. The latex particles formed by this in-situ polymerization have an internal molecular-level interpenetrating network (IPN) structure, eliminating macroscopic phase separation and greatly enhancing cohesiveness and interfacial adhesion. Therefore, even with the same formulation, the peel strength and heat resistance of Example 1 are significantly better than those of Comparative Example 4.

[0051] in: Figure 1 This is a schematic diagram of the microstructure and triple action mechanism of the adhesive of the present invention. The diagram shows: First, at the PVC interface, ester-soluble CPP segments grafted onto the acrylate backbone are oriented, utilizing their abundant chlorine atoms to generate strong dispersion forces and dipole interactions with chlorine atoms in the PVC substrate, forming a "like dissolves like" molecular anchoring effect, thus achieving high-strength adhesion without surface treatment. Second, within the adhesive film, a dual synergistic network is constructed, consisting of room-temperature covalent crosslinking of "aziridine-carboxyl groups" and high-temperature coordination crosslinking of "nano-ZnO-chloride ions / carboxyl groups." The ZnO coordination bonds act as heat-resistant anchors, effectively limiting the slippage of polymer segments at high temperatures, solving the problem of poor heat resistance in traditional adhesives. Finally, at the cement substrate interface, the high-density carboxyl groups on the acrylate segments form strong ionic and hydrogen bonds with calcium ions and hydroxyl groups on the substrate surface, ultimately forming a stable sandwich structure that "grips onto PVC at the top, resists high-temperature creep in the middle, and anchors the substrate at the bottom."

[0052] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A water-based acrylic adhesive for surface-treatment-free PVC flooring, characterized in that, The raw material components, excluding the solvent, are as follows by mass percentage: Ester-soluble chlorinated polypropylene: 0.5~15%; Acrylic acid: 0.5~15%; Ethyl acrylate: 1~5%; Butyl acrylate: 65~95%; Crosslinking agent A: 0.5-3% nano-ZnO emulsion; Crosslinking agent B: Aziridine crosslinking agent 0.5~2%; Nonionic surfactant: 1~5%; Water-soluble initiator: 0.1~1%; wherein: The chlorine content in the ester-soluble chlorinated polypropylene is 26-32%. The ester-soluble chlorinated polypropylene is introduced by pre-dissolving a mixture of monomers of ethyl acrylate and butyl acrylate.

2. The water-based acrylic adhesive according to claim 1, characterized in that, The mass ratio of the ester-soluble chlorinated polypropylene, acrylic acid, ethyl acrylate, and butyl acrylate is (5~10):(1~5):(1~5):(80~93).

3. The water-based acrylic adhesive according to claim 1, characterized in that, The ester-soluble chlorinated polypropylene has a weight-average molecular weight of 50,000 to 120,000; the nano-ZnO emulsion has an average particle size of 20 to 100 nm.

4. The water-based acrylic adhesive according to claim 1, characterized in that, The aziridine crosslinking agent is selected from at least one of trimethylolpropane tris(2-methylaziridine)propionate, bis(2-methylaziridine)urea, and 2-methylaziridine.

5. The water-based acrylic adhesive according to claim 1, characterized in that, The nonionic surfactant is selected from at least one or a compound of several of octylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, sorbitan monooleate, and polyoxyethylene sorbitan monolaurate; the water-soluble initiator is selected from ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride.

6. The water-based acrylic adhesive according to claim 1, characterized in that, The adhesive has a peel strength >1.9 N / mm and a shear strength retention rate >80% at 80°C.

7. A method for preparing the water-based acrylic adhesive according to any one of claims 1-6, characterized in that, Includes the following steps: 1) Add ester-soluble chlorinated polypropylene to a mixture of ethyl acrylate and butyl acrylate monomers and dissolve completely to obtain a homogeneous oil phase; 2) Dissolve the nonionic surfactant in water, add 20-40% of the total mass of acrylic acid, and stir until homogeneous; then add 10-30% of the total oil phase obtained in step 1), and stir to pre-emulsify; then heat to 70-80℃, add some water-soluble initiator, and react to obtain seed emulsion; 3) The remaining oil phase, remaining acrylic acid and remaining initiator solution are simultaneously added dropwise to the seed emulsion obtained in step 2) under heat preservation conditions. After the addition is completed, the reaction is kept at heat to obtain a stable emulsion. 4) Cool the stable emulsion obtained in step 3) to 40~50℃, add nano ZnO emulsion and aziridine crosslinking agent in sequence, adjust the pH to 7.0~8.0, stir, and the water-based acrylic adhesive is obtained.

8. The preparation method according to claim 7, characterized in that, In step 2), the reaction time is 0.5 to 1 hour; the amount of water-soluble initiator added is 20 to 40% of the total amount.

9. The preparation method according to claim 7, characterized in that, In step 3), the dropping time is controlled to be 2-4 hours; after the dropping is completed, the reaction is kept at a constant temperature for 1-2 hours.

10. The preparation method according to claim 7, characterized in that, In step 4), the stirring time is 0.5 to 1 hour.

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