Preparation method of acrylic resin hot-melt adhesive for paper-plastic film compounding

Abstract

The invention provides an acrylic resin hot-melt adhesive for paper-plastic film compounding and a preparation method thereof, and the acrylic resin hot-melt adhesive is mainly prepared from the following raw materials by weight: 55-152 parts of butyl acrylate, 26-123 parts of styrene, 3-10 parts of hydroxyethyl acrylate, 0-5 parts of acrylic acid, 2-10 parts of a long-chain flexible polyfunctional group cross-linking agent, and 2-5 parts of an emulsifier. 0.8 to 1.4 parts of initiator sodium persulfate and 120 to 280 parts of water; and the pH value of the acrylic resin hot-melt adhesive is 6-7.5. According to the method, a long-chain flexible polyfunctional group monomer containing double bonds and carboxyl groups at two ends of a molecular chain is taken as a cross-linking agent, an acrylic resin emulsion is prepared through a seed emulsion polymerization method, and the flexible cross-linked acrylic resin hot-melt adhesive can be used for a paper-plastic film pre-coating process and also can be used for a dry film coating process and has relatively good peel strength.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, specifically relating to an emulsion-type acrylic resin hot melt adhesive for paper-plastic film lamination, its preparation method and application. This adhesive can be used not only as a pre-coated film resin, but also as an adhesive resin for dry lamination processes. Background Technology

[0002] Paper-plastic composites are widely used in modern packaging. To protect the surface of printed materials, increase gloss, and improve waterproof and oil-proof properties, a layer of plastic film (such as BOPP, PET, PVC, etc.) is usually laminated with the printing paper; this process is called "lamination." The adhesive plays a crucial role in connecting the paper and plastic film, and its performance determines the quality of the paper-plastic composite product. Paper-plastic lamination generally uses pre-coating and dry lamination processes. The adhesive resin for pre-coating is mainly polyethylene-vinyl acetate resin, with the vinyl acetate content controlled at 18-20% and a melt index (MI) of 20g / 10min. Most of this type of resin on the market is imported.

[0003] To meet the quality requirements of paper-plastic laminated products, paper-plastic composite adhesives need to possess both high peel strength and excellent holding power. To balance peel strength and holding power, a common approach is to use a low glass transition temperature resin with a crosslinking agent. Crosslinking monomers are added during emulsion polymerization; commonly used crosslinking monomers include diallyl phthalate and ethylene glycol dimethacrylate, or a post-crosslinking method using diacetone acrylamide-adipate dihydrazide. These crosslinking systems share the characteristic of short crosslinking agent molecular chains, resulting in strong crosslinking rigidity. When the amount of crosslinking agent is small, the crosslinking density is low, leading to poor performance of the resulting paper-plastic composite material. The plastic film at embossed and creased areas is prone to springing and delamination, causing quality problems. However, increasing the amount of crosslinking agent increases the adhesive rigidity and decreases the peel strength. This situation makes truly high-peel-strength and embossed-resistant emulsion paper-plastic acrylic resin adhesives a scarce product.

[0004] Based on this, this application was developed. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide an emulsion-type acrylic resin hot melt adhesive for paper-plastic film lamination, which uses a new crosslinking agent and can effectively and significantly improve the performance of acrylic hot melt adhesive for paper-plastic lamination (coating).

[0006] This invention also provides a method for preparing and applying the above-mentioned emulsion-type acrylic resin hot melt adhesive for paper-plastic film lamination. The method uses a long-chain flexible multifunctional monomer with double bonds and carboxyl groups at both ends of its molecular chain as a crosslinking agent to prepare an acrylic resin emulsion via seed emulsion polymerization. The flexible crosslinked acrylic resin hot melt adhesive can be used in paper-plastic film pre-coating processes or in dry lamination processes.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: An acrylic resin hot melt adhesive for paper-plastic film lamination is mainly made of the following raw materials in the following weight ratios: 55-152 parts butyl acrylate, 26-123 parts styrene, 3-10 parts hydroxyethyl acrylate, 0-5 parts acrylic acid, 2-10 parts long-chain flexible multifunctional crosslinking agent (DMPG), 2-5 parts emulsifier, 0.8-1.4 parts sodium persulfate initiator, and 120-280 parts water; The pH of the acrylic resin hot melt adhesive is 6-7.5.

[0008] Specifically, the long-chain flexible multifunctional crosslinking agent (DMPG) is obtained by reacting two molecules of maleic anhydride or itaconic anhydride with one molecule of polyoxyolefin ether at 60-120°C for 5-8 hours, followed by cooling. As a functional crosslinking monomer, the molecular chain contains a double bond and a carboxyl group at both ends, and the entire molecule has four active groups and multiple COC structural units that can provide hydrogen bond acceptors, enabling simultaneous chemical crosslinking and physical crosslinking by hydrogen bonds to form a network crosslinking system. Preferably, 0.1-0.5% by mass of p-toluenesulfonic acid of maleic anhydride or itaconic anhydride is added as a catalyst during the reaction to accelerate the reaction rate and increase the yield.

[0009] Alternatively, the long-chain flexible multifunctional crosslinking agent (DMPG) can also be obtained by reacting one molecule of maleic anhydride or itaconic anhydride with one molecule of alkenyl polyoxyethylene ether at 60-120℃ for 5-8 hours and then cooling. The molecule contains a double bond at one end and a double bond and a carboxyl group at the other end. The entire molecule has three active groups and multiple COC structural units that can provide hydrogen bond acceptors.

[0010] Specifically, the polyoxyolefin ether can be polyoxyethylene ether, polyoxypropylene ether, or polyoxyethylene-polyoxypropylene block polyether, etc.

[0011] Furthermore, the molecular weight of the polyoxyethylene ether is 200-5000, preferably 200-1000. When used as a crosslinking agent, the DMPG can be a mixture of two or more polyoxyethylene ethers with different molecular weights. Specifically, the alkenyl polyoxyethylene ethers include allyl polyoxyethylene ether, isopentenyl polyoxyethylene ether, or methyl allyl polyoxyethylene ether, etc.

[0012] Furthermore, the molecular weight of the alkenyl polyoxyethylene ether is 400-2000, preferably 400-800.

[0013] This invention also provides a method for preparing the above-mentioned acrylic resin hot melt adhesive for paper-plastic film lamination, wherein the resin is obtained by emulsion polymerization of butyl acrylate, styrene, hydroxyethyl acrylate and a long-chain flexible multifunctional crosslinking agent (DMPG); specifically, it includes the following steps: 1) Using the seed pre-emulsified emulsion polymerization method, 55-152 parts by weight of butyl acrylate, 26-123 parts by weight of styrene, 3-10 parts by weight of hydroxyethyl acrylate, 0-5 parts by weight of acrylic acid, and 2-10 parts by weight of long-chain flexible multifunctional crosslinking agent are mixed at room temperature, and then 60-100 parts by weight of water and 1-3 parts by weight of emulsifier are added for emulsification to obtain pre-emulsified monomer; 2) Take a portion of the pre-emulsified monomer (15-30 parts) as seed and add it to a reaction flask containing the remaining water (60-180 parts), 1-2 parts of emulsifier, and 0.3-0.6 parts of sodium persulfate initiator. React at 80-85℃ for 15-40 min. Then, add the remaining pre-emulsified monomer and 0.5-0.8 parts of sodium persulfate initiator (preferably added in the form of an aqueous solution) at 80-85℃. After the addition is complete, maintain the temperature for another 1.5-2 h, then cool to room temperature and adjust the pH to 6-7.5 to obtain an emulsion-type acrylic resin hot melt adhesive for paper-plastic coating, which is also a flexible cross-linked acrylic resin emulsion. The glass transition temperature (tg) of the flexible cross-linked acrylic resin emulsion is -35~30℃, preferably -25~15℃.

[0014] The present invention provides an acrylic resin hot melt adhesive for paper-plastic film lamination prepared by the above method.

[0015] The present invention also provides the application of the above-mentioned acrylic resin hot melt adhesive for paper-plastic film lamination as a pre-coating resin or as an adhesive resin in dry lamination processes.

[0016] Furthermore, in the above applications, the plastic film includes biaxially oriented polypropylene film (BOPP film), polyethylene terephthalate film (PET film), or polyvinyl chloride film (PVC film), etc.

[0017] The preparation of the hot-melt adhesive of this invention utilizes a long-chain flexible multifunctional monomer containing double bonds and carboxyl groups at both ends of the molecular chain as a crosslinking agent. One molecule of DMPG contains two double bonds, two carboxyl groups, and multiple COC structural units that can provide hydrogen bond acceptors, enabling simultaneous chemical crosslinking and physical crosslinking via hydrogen bonding. During emulsion polymerization, a flexible network crosslinking is formed. By adjusting the chain length of the polyoxyethylene ether in the DMPG molecule, the flexibility of the crosslinking agent and the distance between crosslinking points can be controlled. In paper-plastic lamination, through the coating-drying-thermal lamination process, the flexible crosslinking facilitates the bonding between the adhesive layer and the ink layer on the paper surface, improving adhesion and better meeting the quality requirements of paper-plastic laminated products. It can be used for dry lamination in the coating-drying-thermal lamination process, as well as for pre-coated film lamination.

[0018] This invention utilizes a long-chain flexible multifunctional group with double bonds and carboxyl groups at both ends of the molecular chain, along with multiple COC structural units that can provide hydrogen bond acceptors, as a crosslinking agent. An acrylic resin emulsion prepared via seed emulsion polymerization is used as a pre-coating adhesive for paper-plastic composites and as a dry-coating adhesive. The flexible long-chain crosslinking agent can also be used in combination with other crosslinking agents. Using an appropriate flexible crosslinking agent to prepare the acrylic resin emulsion as an adhesive resin effectively improves the peel strength of the paper-plastic composite material, and the composite product is resistant to embossing and less prone to paper-plastic film separation.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The paper-plastic composite emulsion acrylic resin adhesive prepared in this invention overcomes the drawback of low bonding strength in existing adhesives. By using a flexible multifunctional crosslinking agent, the formed film exhibits good flexibility. The crosslinked network deforms to a certain extent under stress without easily breaking, significantly improving peel strength. The resulting composite of printed packaging paper and plastic film possesses high peel strength and resistance to embossing. Furthermore, the long-chain flexible crosslinking agent used in this invention can also be used in conjunction with post-crosslinking systems such as diacetone acrylamide-adipate dihydrazide to achieve even better results. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0021] Unless otherwise specified, all raw materials used in the following embodiments are common commercially available raw materials that can be purchased directly, or are prepared using conventional techniques in the art. For example, the emulsifier used is the reactive emulsifier LRS-10, which is a common commercially available product.

[0022] In the examples, the polyoxyethylene ether dimaleic acid monoester used was prepared by the following steps: 200g of polyoxyethylene ether 200 was placed in a 500ml reaction flask, heated to 80°C, the water was removed under reduced pressure, and then the temperature was lowered to 60°C. 0.5g of p-toluenesulfonic acid was added, and after stirring evenly, 196g of maleic anhydride was slowly added. The reaction temperature was controlled at 70-75°C, and the reaction was continued for 5 hours. The mixture was then cooled to obtain the final product.

[0023] DMPGs with different segment lengths were prepared using the same method described above.

[0024] Room temperature refers to 25±5℃. Example 1

[0025] A method for preparing an acrylic resin hot melt adhesive for paper-plastic film lamination specifically includes the following steps: 1) 116.0 g of butyl acrylate, 59.0 g of styrene, 5.0 g of hydroxyethyl acrylate, 3.0 g of acrylic acid, and 3 g of polyoxyethylene ether dimaleate monoester (molecular weight of polyoxyethylene ether is 200) were mixed evenly at room temperature and then added to a container containing 70.0 g of water and 1.8 g of emulsifier for pre-emulsification. The mixture was stirred at room temperature for 30 min to obtain the pre-emulsified monomer. 2) Take 20.0 g of pre-emulsified monomer as seed and add it to a reaction flask containing 120.0 g of water, 1.5 g of emulsifier and 0.4 g of sodium persulfate initiator. React at 80-85℃ for 30 min. Then, add the remaining pre-emulsified monomer and 0.5 g of sodium persulfate initiator dropwise at 80-82℃ (add in solution form, dissolve 0.5 g of ammonium persulfate in 5 g of water). The addition is completed within 2 h. After keeping the reaction at this temperature for 2 h, cool to room temperature and add ammonia to adjust the pH to 6.5-7.0. This yields an emulsion-type acrylic resin hot melt adhesive that can be used for paper-plastic coating.

[0026] Example 2 A method for preparing an acrylic resin hot melt adhesive for paper-plastic film lamination specifically includes the following steps: 1) 120.0 g of butyl acrylate, 55.0 g of styrene, 5.0 g of hydroxyethyl acrylate, 3.0 g of acrylic acid, and 4 g of polyoxyethylene ether dimaleate monoester (molecular weight of polyoxyethylene ether is 400) as a long-chain flexible multifunctional crosslinking agent were mixed evenly at room temperature and then added to a container containing 70.0 g of water and 1.8 g of emulsifier for pre-emulsification. The mixture was stirred at room temperature for 30 min to obtain a pre-emulsified monomer. 2) Take 20.0 g of pre-emulsified monomer as seed and add it to a reaction flask containing 120.0 g of water, 1.5 g of emulsifier and 0.4 g of sodium persulfate initiator. React at 80-85℃ for 30 min. Then, add the remaining pre-emulsified monomer and 0.5 g of sodium persulfate initiator dropwise at 80-85℃ (add in solution form, dissolve 0.5 g of ammonium persulfate in 5 g of water). The addition is completed within 2 h. After keeping the reaction at this temperature for 2 h, cool to room temperature and add ammonia to adjust the pH to 6.5-7.0. This is the emulsion-type acrylic resin hot melt adhesive that can be used for paper-plastic coating. Example 3

[0027] A method for preparing an acrylic resin hot melt adhesive for paper-plastic film lamination specifically includes the following steps: 1) 126.0 g of butyl acrylate, 50.0 g of styrene, 5.0 g of hydroxyethyl acrylate, 3.0 g of acrylic acid, and 5 g of polyoxyethylene ether dimaleate monoester (molecular weight of polyoxyethylene ether is 600) as a long-chain flexible multifunctional crosslinking agent were mixed evenly at room temperature and then added to a container containing 70.0 g of water and 1.8 g of emulsifier for pre-emulsification. The mixture was stirred at room temperature for 30 min to obtain a pre-emulsified monomer. 2) Take 20.0 g of pre-emulsified monomer as seed and add it to a reaction flask containing 130.0 g of water, 1.5 g of emulsifier and 0.4 g of sodium persulfate initiator. React at 80-85℃ for 30 min. Then, add the remaining pre-emulsified monomer and 0.5 g of sodium persulfate (added in solution form, dissolving 0.5 g of ammonium persulfate in 5 g of water) dropwise at 80-82℃. The addition is completed within 2 h. After keeping the reaction at this temperature for 2 h, cool to room temperature and adjust the pH to 6.5-7.0 with ammonia water to obtain an emulsion-type acrylic resin hot melt adhesive that can be used for paper-plastic coating. Example 4

[0028] A method for preparing an acrylic resin hot melt adhesive for paper-plastic film lamination specifically includes the following steps: 1) 131.0 g of butyl acrylate, 45.0 g of styrene, 5.0 g of hydroxyethyl acrylate, 2.0 g of acrylic acid, and 7 g of polyoxyethylene ether dimaleate monoester (molecular weight of polyoxyethylene ether is 1000) as a long-chain flexible multifunctional crosslinking agent were mixed evenly at room temperature and then added to a container containing 70.0 g of water and 1.8 g of emulsifier for pre-emulsification. The mixture was stirred at room temperature for 30 min to obtain a pre-emulsified monomer. 2) Take 20.0 g of pre-emulsified monomer as seed and add it to a reaction flask containing 130.0 g of water, 1.5 g of emulsifier and 0.4 g of sodium persulfate initiator. React at 80-85℃ for 30 min. Then, add the remaining pre-emulsified monomer and 0.5 g of sodium persulfate (added in solution form, dissolving 0.5 g of ammonium persulfate in 5 g of water) dropwise at 80-82℃. The addition is completed within 3 h. After keeping the reaction at this temperature for 2 h, cool to room temperature and add ammonia to adjust the pH to 6.5-7.0. This yields an emulsion-type acrylic resin hot melt adhesive that can be used for paper-plastic coating.

[0029] Comparative Example 1

[0030] A method for preparing an emulsion-type acrylic resin hot melt adhesive for paper-plastic coating specifically includes the following steps: 1) Mix 126.0 g of butyl acrylate, 50.0 g of styrene, 5.0 g of hydroxyethyl acrylate and 3.0 g of acrylic acid at room temperature until homogeneous, then add the mixture to a container containing 70.0 g of water and 1.8 g of emulsifier for pre-emulsification to obtain a pre-emulsified monomer. 2) Take 20.0 g of pre-emulsified monomer as seed and add it to a reaction flask containing 120.0 g of water, 1.5 g of emulsifier and 0.4 g of sodium persulfate initiator. React at 80-85℃ for 30 min. Then, add the remaining pre-emulsified monomer and 0.5 g of sodium persulfate (added in solution form, dissolving 0.5 g of ammonium persulfate in 5 g of water) dropwise at 80-82℃. The addition is completed within 2 h. After keeping the reaction at this temperature for 2 h, cool to room temperature and add ammonia to adjust the pH to 6.5-7.0 to obtain the emulsion-type acrylic resin hot melt adhesive for paper-plastic coating.

[0031] Performance testing

[0032] The emulsion-type acrylic resin hot melt adhesives prepared in Examples 1-4 and Comparative Example 1, which can be used for paper-plastic coating, were uniformly coated onto BOPP film (8-10 μm) using a coating rod. After being dried with hot air, the film was laminated with full-page black printed paper, passed through a hot roller at 100°C, and left for 24 hours. The peel strength was then measured. The results are shown in the table below.

[0033]

[0034] As can be seen from the data in the table above, compared with Comparative Example 1, the emulsion-type acrylic resin hot melt adhesives prepared in Examples 1 to 4 all have higher peel strength when used for paper-plastic coating. The 180-degree peel strength is between 4.8 and 5.5 N / 25 mm, which is significantly higher than the peel strength of Comparative Example 1 (3.5 N / 25 mm) without the addition of a long-chain flexible multifunctional crosslinking agent.

[0035] In summary, by selecting a long-chain flexible multifunctional crosslinking agent, the present invention enables the formed film to have good flexibility. The crosslinking network undergoes a certain degree of deformation under stress and is not easily broken, resulting in significantly improved peel strength. After the color-printed packaging paper-plastic film is laminated, it has high peel strength and embossing resistance.

Claims

1. An acrylic resin hot melt adhesive for paper-plastic film lamination, characterized in that, It is mainly made of the following raw materials in the following weight ratio: 55-152 parts butyl acrylate, 26-123 parts styrene, 3-10 parts hydroxyethyl acrylate, 0-5 parts acrylic acid, 2-10 parts long-chain flexible multifunctional crosslinking agent, 2-5 parts emulsifier, 0.8-1.4 parts sodium persulfate initiator, and 120-280 parts water. The pH of the acrylic resin hot melt adhesive is 6-7.

5.

2. The acrylic resin hot melt adhesive for paper-plastic film lamination as described in claim 1, characterized in that, The long-chain flexible multifunctional crosslinking agent is obtained by reacting two molecules of maleic anhydride or itaconic anhydride with one molecule of polyoxyolefin ether at 60-120℃ for 5-8 hours and then cooling, or by reacting one molecule of maleic anhydride or itaconic anhydride with one molecule of alkenyl polyoxyethylene ether at 60-120℃ for 5-8 hours and then cooling.

3. The acrylic resin hot melt adhesive for paper-plastic film lamination as described in claim 2, characterized in that, The polyoxyolefin ether is a polyoxyethylene ether, a polyoxypropylene ether, or a polyoxyethylene-polyoxypropylene block polyether.

4. The acrylic resin hot melt adhesive for paper-plastic film lamination as described in claim 2, characterized in that, The molecular weight of the polyoxyolefin ether is 200-5000.

5. The acrylic resin hot melt adhesive for paper-plastic film lamination as described in claim 2, characterized in that, The alkenyl polyoxyethylene ethers include allyl polyoxyethylene ether, isopentenyl polyoxyethylene ether, or methyl allyl polyoxyethylene ether.

6. The acrylic resin hot melt adhesive for paper-plastic film lamination as described in claim 2, characterized in that, The molecular weight of the alkenyl polyoxyethylene ether is 400-2000.

7. The method for preparing the acrylic resin hot melt adhesive for paper-plastic film lamination according to any one of claims 1 to 6, characterized in that, Includes the following steps: 1) After mixing butyl acrylate, styrene, hydroxyethyl acrylate, acrylic acid, and a long-chain flexible multifunctional crosslinking agent at room temperature, a portion of water and a portion of emulsifier are added for emulsification to obtain a pre-emulsified monomer. 2) Take a portion of the pre-emulsified monomer as seed and add it to a reaction flask containing the remaining water, emulsifier and part of the initiator sodium persulfate. React at 80-85℃ for 15-40 min. Then add the remaining pre-emulsified monomer and initiator sodium persulfate at 80-85℃. After the addition is complete, keep the reaction at 80-85℃ for 1.5-2 h. Then cool to room temperature and adjust the pH to 6-7.5 to obtain the final product.

8. An acrylic resin hot melt adhesive for paper-plastic film lamination prepared by the method of claim 7.

9. The application of the acrylic resin hot melt adhesive of claim 8 for paper-plastic film lamination as a pre-coating resin or as an adhesive resin in a dry lamination process.

10. The application as described in claim 9, characterized in that, The plastic film includes BOPP film, PET film or PVC film.

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