A pigment printing adhesive for aramid fabric and a preparation method thereof

Abstract

The application discloses a pigment printing adhesive for aramid fabric and a preparation method thereof, and belongs to the technical field of high molecular polymers. The adhesive is an emulsion polymer with a core-shell structure. The core layer polymer contains a dynamic covalent disulfide bond crosslinking structure derived from a disulfide bond functional monomer and a permanent chemical crosslinking structure derived from a crosslinking monomer. The shell layer polymer contains phosphate groups derived from a phosphate functional monomer and silane groups derived from a silane functional monomer. The application simultaneously introduces a disulfide bond dynamic covalent crosslinking and a permanent chemical crosslinking into the core layer, so that the coating has high cohesive strength and self-repairing capability, and micro-crack propagation and interface peeling are avoided. The shell layer simultaneously introduces phosphate groups and silane groups, and the strong hydrogen bond / coordination effect of the phosphate and aramid and the covalent bonding of the silane with the fiber after hydrolysis are utilized to synergistically enhance the wet adhesion. The core-shell functional design cooperates with each other, and the water washing fastness, rubbing fastness and coating flexibility of the adhesive are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of polymer technology, and in particular to a coating printing adhesive for aramid fabrics and its preparation method. Background Technology

[0002] Aramid fiber, also known as aromatic polyamide fiber, contains a large number of benzene rings and amide bonds in its molecular chain. Due to its unique chemical structure, aramid fabrics have characteristics such as low surface energy, strong chemical inertness, and few polar groups, making it difficult for conventional pigment printing adhesives to effectively wet, spread, and adhere firmly to their surface. Therefore, how to improve the fastness of pigment printing on aramid fabrics, especially its wash fastness, is a technical problem that the industry urgently needs to solve.

[0003] In existing technologies, adhesives used for textile coating printing are mainly polyacrylates, polyurethanes, and copolymers or mixtures of the two. Among them, polyacrylate adhesives are widely used due to their good film-forming properties, light and weather resistance, and low cost. However, when conventional polyacrylate adhesives are directly applied to aramid fabrics, the following drawbacks exist: poor adhesion, the printed layer is prone to peeling and fading after washing; and insufficient wash fastness, with color fastness typically only lasting for 10-20 washes before significantly decreasing, making it difficult to meet the 50+ wash fastness standards required in fields such as protective clothing. Summary of the Invention

[0004] This invention provides a coating printing adhesive for aramid fabrics and its preparation method, which can solve the defects of poor adhesion and insufficient wash fastness of existing coating printing adhesives when applied to aramid fabrics.

[0005] To solve the above-mentioned technical problems, the present invention provides a coating printing adhesive for aramid fabrics, wherein the adhesive is a core-shell structured emulsion polymer having a core polymer and a shell polymer; The core polymer contains a dynamic covalent disulfide crosslinking structure derived from disulfide functional monomers and a permanent chemical crosslinking structure derived from crosslinking monomers. The shell polymer contains phosphate groups derived from phosphate ester functional monomers and silane groups derived from silane functional monomers.

[0006] In a preferred embodiment of the present invention, the disulfide functional monomer is a bis(methacryloyloxyalkyl) disulfide compound; the crosslinking monomer is a polyvinylbenzene compound.

[0007] In a preferred embodiment of the present invention, the disulfide functional monomer is bis(methacryloyloxyethyl) disulfide; and the crosslinking monomer is divinylbenzene.

[0008] In a preferred embodiment of the present invention, the core polymer is obtained by copolymerization of methyl methacrylate, butyl acrylate, divinylbenzene and bis(methacryloyloxyethyl) disulfide.

[0009] In a preferred embodiment of the present invention, the phosphate ester functional monomer is (meth)acryloyloxyalkyl phosphate; and the silane functional monomer is vinyltrialkoxysilane.

[0010] In a preferred embodiment of the present invention, the phosphate ester functional monomer is methacryloyloxyethyl phosphate; and the silane functional monomer is vinyltriethoxysilane.

[0011] In a preferred embodiment of the present invention, the shell polymer is obtained by copolymerization of butyl acrylate, ethyl acrylate, hydroxyethyl methacrylate, methacryloyloxyethyl phosphate and vinyltriethoxysilane.

[0012] To address the aforementioned technical problems, this invention also discloses a method for preparing a coating printing adhesive for aramid fabrics, comprising the following steps: (1) Pre-emulsification of the core monomer: Methyl methacrylate, butyl acrylate, divinylbenzene, bis(methacryloyloxyethyl) disulfide, emulsifier and deionized water are mixed, dispersed and emulsified to obtain a core pre-emulsion; (2) Seed nuclear emulsion preparation: Take a portion of the nuclear pre-emulsion, add an initiator, and carry out seed emulsion polymerization to obtain seed nuclear emulsion; (3) Core layer polymerization: The remaining portion of the nuclear pre-emulsion is added dropwise to the seed nuclear emulsion, and the initiator is added to carry out core layer polymerization to obtain a nuclear emulsion; (4) Shell monomer pre-emulsification: Butyl acrylate, ethyl acrylate, hydroxyethyl methacrylate, methacryloyloxyethyl phosphate, vinyltriethoxysilane, the emulsifier and deionized water are mixed, dispersed and emulsified to obtain shell pre-emulsion; (5) Shell polymerization: The shell pre-emulsion is added dropwise to the core emulsion, and the initiator is added to carry out shell polymerization; (6) Post-treatment: Adjust the pH value, filter, and obtain the adhesive.

[0013] In a preferred embodiment of the present invention, the reaction temperature of seed emulsion polymerization in step (2) is 75-85°C, the reaction temperature of core layer polymerization in step (3) is 75-85°C, and the reaction temperature of shell layer polymerization in step (5) is 80-90°C.

[0014] In a preferred embodiment of the present invention, after adjusting the pH value in step (6), a post-crosslinking agent is also added.

[0015] The beneficial effects of this invention are as follows: This invention provides a coating printing adhesive for aramid fabrics and its preparation method. By simultaneously introducing disulfide bonds for dynamic covalent crosslinking and permanent chemical crosslinking in the core layer, the coating possesses both high cohesive strength and self-healing ability, effectively preventing microcrack propagation and interfacial peeling. By simultaneously introducing phosphate ester groups and silane groups in the shell layer, the strong hydrogen bonding / coordination between phosphate esters and the aramid surface, as well as the covalent bonding between silane and the fiber after hydrolysis, synergistically enhance wet adhesion. Through the functional design of the core and shell layers, the adhesive's wash fastness, rubbing fastness, and coating flexibility are significantly improved. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the process for preparing a coating printing adhesive for aramid fabrics according to the present invention. Figure 2 This is a schematic diagram of the core-shell structure shown. The components in the attached diagram are labeled as follows: 10. Core polymer; 20. Shell polymer. Detailed Implementation

[0017] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0018] This invention addresses the problem of high surface inertness and difficulty in wetting and adhering to aramid fabrics by providing a coating printing adhesive for aramid fabrics. The adhesive is a core-shell structured emulsion polymer, having a core polymer 10 and a shell polymer 20, such as... Figure 2 As shown.

[0019] Core layer design The core polymer contains a dynamic covalent disulfide crosslinking structure derived from a disulfide functional monomer and a permanent chemical crosslinking structure derived from a crosslinking monomer. The disulfide functional monomer is bis(methacryloyloxyethyl) disulfide; the crosslinking monomer is divinylbenzene. Specifically, the core polymer is obtained by copolymerizing methyl methacrylate, butyl acrylate, divinylbenzene, and bis(methacryloyloxyethyl) disulfide.

[0020] By introducing disulfide-bonded bifunctional monomers into the core layer, reversible covalent crosslinks are formed after polymerization, creating a dynamically exchangeable crosslinked network during film formation. This design offers the following advantages: First, while disulfide bonds are stable at room temperature, they can be dynamically exchanged and repaired after breakage under external force, thus repairing microcracks caused by mechanical friction or stretching and significantly improving the integrity of the coating during repeated washing and abrasion resistance. Second, the dynamic exchange of disulfide bonds can relax internal stress, preventing the coating from peeling due to shrinkage, thereby improving wash fastness. Third, permanent chemical crosslinking provides the basic network framework, ensuring the basic dimensional stability and solvent resistance of the coating.

[0021] Shell design The shell polymer contains phosphate groups derived from phosphate ester functional monomers and silane groups derived from silane functional monomers. Specifically, the phosphate ester functional monomer is methacryloyloxyethyl phosphate; and the silane functional monomer is vinyltriethoxysilane. More specifically, the shell polymer is obtained by copolymerizing butyl acrylate, ethyl acrylate, hydroxyethyl methacrylate, methacryloyloxyethyl phosphate, and vinyltriethoxysilane.

[0022] The shell copolymer contains phosphate ester groups and silane groups, which can strongly interact with amide groups and hydroxyl groups on the aramid surface to form strong hydrogen bonds and coordination bonds, significantly improving wet adhesion. The phosphate ester groups can form strong hydrogen bonds with the amide groups in the aramid molecular chain, and residual metal ions (such as Ca²⁺) on the aramid surface can form coordination bonds with phosphate groups, providing water and solvent resistance. During baking, the silane groups hydrolyze to generate silanol (Si–OH), which undergoes a condensation reaction with –OH and –NH– groups on the aramid surface to form covalent Si–O–C or Si–N bonds, achieving irreversible chemical bonding. The synergistic effect of these two components allows the adhesive to maintain extremely high peel strength even in a wet state, significantly increasing the number of washes.

[0023] Multiple cross-linking system This invention may also include a post-crosslinking agent, which is a blocked isocyanate crosslinking agent. This post-crosslinking agent, together with the divinylbenzene (permanent crosslinking) and disulfide bonds (dynamic crosslinking) in the core layer, constitutes a multi-crosslinking system. The permanent crosslinking ensures the basic dimensional stability and solvent resistance of the coating; the dynamic crosslinking provides self-healing functionality; the blocked isocyanate crosslinking agent is unblocked during the high-temperature baking stage, releasing isocyanate groups (-NCO) that react with the hydroxyl groups of hydroxyethyl methacrylate (HEMA) in the shell layer to form stable carbamate crosslinks, thereby introducing additional chemical crosslinking points in the shell layer, further increasing the overall crosslinking density, and effectively preventing water molecules from penetrating the coating-fiber interface. The synergistic effect of this multi-crosslinking system allows the coating to maintain high density and adhesion even after multiple washes.

[0024] It should be noted that even without the addition of a post-crosslinking agent, the permanent and dynamic crosslinking of the core layer and the dual anchoring groups of the shell layer alone can achieve a wash fastness far superior to that of conventional adhesives; the addition of a post-crosslinking agent can further increase the crosslinking density, thereby achieving an even higher level of wash fastness.

[0025] This invention employs core-shell emulsion polymerization technology. The resulting core layer is a highly cross-linked, hard polymer with a glass transition temperature (Tg) of 50-85℃, which improves the coating's abrasion and wash resistance, and provides excellent water permeability resistance and cohesive strength, resisting water molecule swelling. The shell layer is a soft polymer with a lower glass transition temperature of -20-20℃, rich in reactive groups (phosphate esters, silanes, hydroxyl groups), making it soft and deformable, giving the printed coating a good hand feel and good adhesion to the aramid surface. Simultaneously, the functional groups on the shell layer are concentrated on the particle surface (the outer surface in contact with the fiber), maximizing interfacial bonding efficiency. The core-shell morphology is achieved through seed emulsion polymerization, preventing the functional groups from being encapsulated inside the particles and becoming ineffective.

[0026] like Figure 1 As shown, the preparation method of the above adhesive includes the following specific steps: (1) Pre-emulsification of the core monomer: Methyl methacrylate, butyl acrylate, divinylbenzene, bis(methacryloyloxyethyl) disulfide, emulsifier and deionized water are mixed, dispersed and emulsified to obtain a core pre-emulsion; (2) Seed nuclear emulsion preparation: Take a portion of the nuclear pre-emulsion, add an initiator, and carry out seed emulsion polymerization at a reaction temperature of 75-85℃ to obtain seed nuclear emulsion; (3) Core layer polymerization: The remaining portion of the pre-emulsion of the core is added dropwise to the seed core emulsion, and the initiator is added. Core layer polymerization is carried out at 75-85°C to obtain a core emulsion. (4) Shell monomer pre-emulsification: Butyl acrylate, ethyl acrylate, hydroxyethyl methacrylate, methacryloyloxyethyl phosphate and vinyltriethoxysilane, the emulsifier and the deionized water are mixed, dispersed and emulsified to obtain shell pre-emulsion; (5) Shell polymerization: The shell pre-emulsion is added dropwise to the core emulsion and the initiator is added. Shell polymerization is carried out at 80-90°C. (6) Post-treatment: Adjust the pH value, filter, and obtain the adhesive.

[0027] The technical solution of the present invention will be described in detail below through specific embodiments. The composition and mass ratio of the raw materials used in the embodiments are listed in Table 1. In actual preparation, the scale can be increased or decreased accordingly, and the specific amounts used in each embodiment are described in the corresponding descriptions.

[0028] Table 1. Raw material composition and mass distribution ratio Example 1 Scaled up to approximately 100g of total monomers by mass, magnification 2.24. (1) Pre-emulsification of nuclear monomers In a pre-emulsification vessel equipped with a stirrer, add 135g of deionized water, 1.8g of sodium dodecylbenzenesulfonate, 0.9g of OP-10, and 0.45g of sodium bicarbonate, and stir to dissolve. Slowly add the core monomers: 26.9g of MMA, 17.9g of BA, 1.12g of DVB, and 2.69g of bis(methacryloyloxyethyl) disulfide. Disperse at a high speed of 3000 rpm for 30 min to obtain the core pre-emulsion.

[0029] (2) Preparation of seed nuclear emulsion Add 225g of deionized water and 1.1g of SDBS to the reactor and heat to 80℃. Take 1 / 3 of the total amount of the nuclear pre-emulsion from step (1) and add it to the reactor, followed by 0.3g of initiator KPS (dissolved in 10g of water). Keep the reaction at this temperature for 30min to obtain the seed nuclear emulsion.

[0030] (3) Core layer aggregation At 80℃, the remaining nuclear pre-emulsion was added dropwise at a uniform rate to the seed nuclear emulsion, while 0.3 g of KPS (dissolved in 10 g of water) was added simultaneously. The addition time was 1.5 h, and the mixture was kept warm for 0.5 h after the addition was complete to obtain the nuclear emulsion.

[0031] (4) Shell monomer pre-emulsification In another pre-emulsification vessel, add 90g of deionized water and 1.1g of SDBS, and stir to dissolve. Add shell monomers: 22.4g BA, 13.4g EA, 5.6g HEMA, 6.7g MEP, and 3.36g VTES. Disperse at a high speed of 3000 rpm for 20 minutes to obtain a shell pre-emulsion.

[0032] (5) Shell aggregation The nucleus emulsion was heated to 85°C, and simultaneously, the shell pre-emulsion and 0.3 g of KPS (dissolved in 8 g of water) were added dropwise over a period of 2 hours. After the addition was complete, the temperature was raised to 88°C and the reaction was maintained at this temperature for 1 hour (ensuring a conversion rate >99%). The temperature was then lowered to 50°C, and the pH of the solution was adjusted to 7.5 with 25% ammonia.

[0033] (6) Post-processing Add 2.2g of a blocked isocyanate crosslinking agent (such as Bayhydur® 3100) to the emulsion obtained in step (5), stir for 30min, filter with a 200-mesh filter and discharge to obtain a core-shell structured emulsion polymer adhesive.

[0034] The adhesive prepared in this embodiment was used for coating printing on aramid fabrics. The printing paste formulation and process are as follows: Adhesive dosage: 25-30% of the paint pigment mass; Thickener: Polyacrylic acid synthetic thickener, appropriate amount, to adjust the viscosity to 2000-3000 mPa·s; Baking conditions: 160℃×4min (to ensure silane condensation and isocyanate deblocking and crosslinking), or two-step baking: 110℃×2min (pre-drying) + 160℃×3min (curing).

[0035] The printing process follows the steps of paste preparation, printing, pre-drying (if a two-step method is used), baking, and final product printing. Since the phosphate monomer MEP is acidic, the system pH must be ensured to be greater than 6 during polymerization; otherwise, gelation may easily occur. The pH can be adjusted online by adding phosphate buffer or using ammonia.

[0036] Performance test results: Solid content: 43.5%; Viscosity at 25℃: 850 mPa·s; Core polymer Tg (DSC test): 76℃; Shell polymer Tg (DSC test): -8℃; Dry rubbing fastness grade 4-5; Wet rubbing fastness grade 4; Wash fastness to soap is grade 4; It has a soft feel.

[0037] Example 2 The difference from Example 1 is that in the post-processing step (6), no post-crosslinking agent is added, and the pH is adjusted to 7.5 with ammonia water before direct filtration and discharge.

[0038] The adhesive prepared in Example 2 was used for printing on aramid fabrics using the same process. The test results were: dry rubbing fastness grade 4-5, wet rubbing fastness grade 4, soap washing fastness grade 4 (slightly lower than Example 1 after 50 washes, but still >4), and soft hand feel.

[0039] Comparative Example 1 The difference from Example 1 is that bis(methacryloyloxyethyl) disulfide is not added to the core monomer; its amount is made up by MMA. Everything else is the same as in Example 1.

[0040] Performance testing: Dry rubbing fastness grade 4, wet rubbing fastness grade 3, slight cracking of the coating after bending, and a slightly hard feel.

[0041] Comparative Example 2 The difference from Example 1 is that methacryloyloxyethyl phosphate and vinyltriethoxysilane are not added to the shell monomer; their amounts are supplemented by BA and EA. The rest is the same as in Example 1.

[0042] Performance testing: Dry rubbing fastness grade 3-4, wet rubbing fastness grade 3, washability significantly decreased.

[0043] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A coating printing adhesive for aramid fabrics, characterized in that, The adhesive is a core-shell structured emulsion polymer, having a core polymer and a shell polymer; The core polymer contains a dynamic covalent disulfide crosslinking structure derived from disulfide functional monomers and a permanent chemical crosslinking structure derived from crosslinking monomers. The shell polymer contains phosphate groups derived from phosphate ester functional monomers and silane groups derived from silane functional monomers.

2. The adhesive according to claim 1, characterized in that, The disulfide functional monomer is a bis(methacryloyloxyalkyl) disulfide compound; the crosslinking monomer is a polyvinylbenzene compound.

3. The adhesive according to claim 2, characterized in that, The disulfide functional monomer is bis(methacryloyloxyethyl) disulfide; the crosslinking monomer is divinylbenzene.

4. The adhesive according to claim 3, characterized in that, The core polymer is obtained by copolymerization of methyl methacrylate, butyl acrylate, divinylbenzene and bis(methacryloyloxyethyl) disulfide.

5. The adhesive according to claim 1, characterized in that, The phosphate ester functional monomer is (meth)acryloyloxyalkyl phosphate; the silane functional monomer is vinyltrialkoxysilane.

6. The adhesive according to claim 5, characterized in that, The phosphate ester functional monomer is methacryloyloxyethyl phosphate; the silane functional monomer is vinyltriethoxysilane.

7. The adhesive according to claim 6, characterized in that, The shell polymer is obtained by copolymerization of butyl acrylate, ethyl acrylate, hydroxyethyl methacrylate, methacryloyloxyethyl phosphate, and vinyltriethoxysilane.

8. A method for preparing a coating printing adhesive for aramid fabrics, characterized in that, Includes the following steps: (1) Pre-emulsification of the core monomer: Methyl methacrylate, butyl acrylate, divinylbenzene, bis(methacryloyloxyethyl) disulfide, emulsifier and deionized water are mixed, dispersed and emulsified to obtain a core pre-emulsion; (2) Seed nuclear emulsion preparation: Take a portion of the nuclear pre-emulsion, add an initiator, and carry out seed emulsion polymerization to obtain seed nuclear emulsion; (3) Core layer polymerization: The remaining portion of the nuclear pre-emulsion is added dropwise to the seed nuclear emulsion, and the initiator is added to carry out core layer polymerization to obtain a nuclear emulsion; (4) Shell monomer pre-emulsification: Butyl acrylate, ethyl acrylate, hydroxyethyl methacrylate, methacryloyloxyethyl phosphate, vinyltriethoxysilane, the emulsifier and deionized water are mixed, dispersed and emulsified to obtain shell pre-emulsion; (5) Shell polymerization: The shell pre-emulsion is added dropwise to the core emulsion, and the initiator is added to carry out shell polymerization; (6) Post-treatment: Adjust the pH value, filter, and obtain the adhesive.

9. The method according to claim 8, characterized in that, The reaction temperature for seed emulsion polymerization in step (2) is 75-85℃, the reaction temperature for core polymerization in step (3) is 75-85℃, and the reaction temperature for shell polymerization in step (5) is 80-90℃.

10. The method according to claim 8, characterized in that, After adjusting the pH value in step (6), a post-crosslinking agent is also added.

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