Low-voc flame-retardant double-faced adhesive tape for automotive interior and preparation method thereof

Abstract

The application relates to the technical field of adhesives, and discloses a low-VOC flame-retardant double-faced adhesive for automobile interiors and a preparation method thereof. In the application, tetramethyl ethylene (epoxy propyl ammonium chloride) and bis (4-aminophenyl) -phenyl phosphate are reacted to obtain a cationic flame retardant, which is then added into a water-based acrylic resin emulsion to obtain a flame-retardant water-based acrylic resin adhesive and a flame-retardant double-faced adhesive. The cationic groups in the cationic flame retardant and the sodium carboxylate anions in the water-based acrylic resin form electrostatic force, the crosslinking degree between acrylic resin molecular chains is improved, the cohesion is increased, and the bonding performance and tensile shear strength of the adhesive are improved. The cationic flame retardant contains a triphenyl phosphate flame-retardant structure, has condensed-phase flame-retardant effect, improves the limiting oxygen index and the flame-retardant performance of the adhesive, and has good practical application in adhesives for new energy vehicles, double-faced adhesives and the like.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, specifically to a low-VOC flame-retardant double-sided adhesive for automotive interiors and its preparation method. Background Technology

[0002] Double-sided tape mainly consists of adhesive, substrate, and release film. Water-based acrylic resin adhesives use water as a solvent, have low VOC content, and are environmentally friendly. They can be made into pressure-sensitive tapes, double-sided tapes, and other products, and are widely used in automobiles, furniture and building materials, and electronics. However, acrylic resin adhesives and their double-sided tape products have low shear strength and bonding performance, are easily flammable, and have poor flame retardancy, which is not conducive to their application in new energy vehicles and other products.

[0003] Flame retardants are typically added to acrylic resin adhesives to improve their flame retardant properties. Traditional phosphorus-containing flame retardants are hydrophobic and water-insoluble, exhibiting poor dispersibility in water-based acrylic resins and easily producing sediment, which affects the storage stability and bonding performance of the adhesive. Patent application CN118599452A discloses a water-based flame-retardant acrylic pressure-sensitive adhesive for carpet protective films, its preparation method, and its application. Using melamine, phytic acid, and acrylic monomers as raw materials, a water-based flame-retardant acrylic pressure-sensitive adhesive is prepared. Compared to that patent application, this invention utilizes cationic flame retardants to improve the flame retardant properties of the water-based acrylic resin adhesive and its double-sided tape, while also improving bonding performance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a low-VOC flame-retardant double-sided adhesive for automotive interiors and its preparation method, solving the problems of low shear strength and poor flame retardancy of acrylic resin adhesives.

[0005] The technical solution of this invention is: a method for preparing low-VOC flame-retardant double-sided adhesive for automotive interiors.

[0006] (1) Ethanol, tetramethylethylenedi(epoxypropylammonium chloride), and bis(4-aminophenyl)-phenyl phosphate were added to a flask. After stirring and reacting, the mixture was cooled in an ice-water bath, filtered, washed with ethanol, and dried to obtain a cationic flame retardant. The preparation reaction formula is as follows:

[0007]

[0008] (2) Add water-based acrylic resin emulsion, cationic flame retardant and defoamer to a container, stir and obtain flame-retardant water-based acrylic resin adhesive; finally, apply the adhesive to both sides of the substrate to obtain low VOC flame-retardant double-sided tape.

[0009] Furthermore, in (1), the ratio of tetramethylethylenedi(epoxypropylammonium chloride) to bis(4-aminophenyl)-phenyl phosphate is 1 mol:(1:1.1) mol.

[0010] Furthermore, the reaction in (1) is carried out at 45-70℃ for 6-10 hours.

[0011] Furthermore, the ratio of waterborne acrylic resin emulsion to cationic flame retardant is 1L:(15-50)g.

[0012] Furthermore, the preparation method of the waterborne acrylic resin emulsion is as follows: add acrylic monomer, acrylate monomer, and emulsifier to water to obtain a monomer solution; then introduce nitrogen gas into a flask, add the monomer solution and initiator solution dropwise, add a buffer, heat to 75-85℃, react for 30-40 minutes, add the monomer solution and initiator solution dropwise again, react for 3-4 hours, add a neutralizing agent to adjust the pH to 7-8, and obtain the waterborne acrylic resin emulsion.

[0013] Furthermore, the buffer includes sodium bicarbonate.

[0014] Furthermore, neutralizing agents include sodium hydroxide.

[0015] Furthermore, the ratio of acrylic monomer, acrylate monomer, initiator, and emulsifier is (6-10)g:(90-94)g:(0.4-0.7)g:(2-3)g.

[0016] Furthermore, acrylic monomers include acrylic acid and methacrylic acid.

[0017] Furthermore, acrylate monomers include methyl methacrylate and butyl acrylate.

[0018] Furthermore, initiators include potassium persulfate or ammonium persulfate.

[0019] Furthermore, the emulsifiers include sodium dodecyl sulfate and OP-10.

[0020] Furthermore, low-VOC flame-retardant double-sided adhesive is used in automotive interiors.

[0021] The beneficial technical effects of this invention are as follows: Tetramethylethylenedi(glycidyl chloride) and bis(4-aminophenyl)-phenyl phosphate undergo a ring-opening polymerization reaction to obtain a cationic flame retardant. This flame retardant is then added to an aqueous acrylic resin adhesive and finally coated onto a substrate surface to obtain a low-VOC flame-retardant double-sided adhesive. The polymer molecular chain of this cationic flame retardant contains hydrophilic cationic groups, hydroxyl groups, and imino groups, exhibiting excellent hydrophilicity and water solubility. It dissolves well in aqueous acrylic resin emulsions, resulting in good adhesive dispersibility, no precipitation, and, using water as a solvent, contains no organic solvents, has a very low VOC content, and is environmentally friendly.

[0022] In the cationic flame retardant of the present invention, the cationic groups form electrostatic forces with the sodium carboxylate anions in the waterborne acrylic resin, while the hydroxyl and imino groups form hydrogen bonds with the ester and carboxylic acid groups in the waterborne acrylic resin. This increases the degree of crosslinking between acrylic resin molecular chains, increases cohesion, and is beneficial to improving the adhesive performance of the adhesive, exhibiting higher tensile shear strength.

[0023] The cationic flame retardant of the present invention contains a triphenyl phosphate flame retardant structure, which has a condensed phase flame retardant effect, improves the limiting oxygen index and flame retardant performance of adhesives, and has good practical applications in adhesives for interior decoration of new energy vehicles, double-sided tape, etc. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] Tetramethylethylenedi(epoxypropylammonium chloride) was prepared according to the method described in the journal Molecules, 2023, 28, 4120; and the article "Influence of a Composite Polylysine-Polydopamine-Quaternary Ammonium Salt Coating on Titanium on Its Ostogenic and Antibacterial Performance".

[0026] The structural formula is

[0027] Bis(4-aminophenyl)-phenyl phosphate was prepared according to the method described in the article "Synthesis and Performance Study of Bis(4-aminophenyl)-phenyl phosphate" published in the April 2007 issue of the journal *Chinese Adhesives*, Vol. 16, No. 4. The structural formula is as follows:

[0028] Example 1:

[0029] (1) Add 150 mL of ethanol, 40 mmol of tetramethylethylenedi(epoxypropylammonium chloride) and 40 mmol of bis(4-aminophenyl)-phenyl phosphate to a flask, heat to 60 °C, stir and react for 10 h, cool in an ice-water bath, filter, wash with ethanol, and dry to obtain a cationic flame retardant.

[0030] (2) Add 35g acrylic acid, 190g methyl methacrylate, 275g butyl acrylate, 8g sodium dodecyl sulfate, and 4g OP-10 to 500mL of water to obtain a monomer solution; then introduce nitrogen gas into the flask, add 120mL of monomer solution, 3mL of 0.6g ammonium persulfate aqueous solution, and 0.23g sodium bicarbonate, heat to 75℃, react for 40min, then add the remaining monomer solution and 8mL of aqueous solution containing 2g ammonium persulfate, react for 4h, add sodium hydroxide to adjust the pH to 8, and obtain an aqueous acrylic resin emulsion.

[0031] (3) Add 1L of water-based acrylic resin emulsion, 15g of cationic flame retardant, and 6g of defoamer BYK-021 to a container, stir, and obtain flame-retardant water-based acrylic resin adhesive; finally, apply the adhesive to both sides of the polypropylene substrate to obtain low-VOC flame-retardant double-sided tape.

[0032] Example 2:

[0033] (1) Add 200 mL of ethanol, 40 mmol of tetramethylethylenedi(epoxypropylammonium chloride) and 44 mmol of bis(4-aminophenyl)-phenyl phosphate to a flask, heat to 45 °C, stir and react for 10 h, cool in an ice-water bath, filter, wash with ethanol, and dry to obtain a cationic flame retardant.

[0034] (2) Add 50g acrylic acid, 160g methyl methacrylate, 290g butyl acrylate, 10g sodium dodecyl sulfate, and 5g OP-10 to 500mL of water to obtain a monomer solution; then introduce nitrogen gas into the flask, add 150mL of monomer solution, 5mL of 0.9g potassium persulfate aqueous solution, and 0.28g sodium bicarbonate, heat to 85℃, react for 30min, then add the remaining monomer solution and 10mL of aqueous solution containing 2.6g potassium persulfate, react for 3h, add sodium hydroxide to adjust the pH to 7, and obtain an aqueous acrylic resin emulsion.

[0035] (3) Add 1L of water-based acrylic resin emulsion, 30g of cationic flame retardant, and 9g of defoamer BYK-021 to a container, stir, and obtain flame-retardant water-based acrylic resin adhesive; finally, apply the adhesive to both sides of the polypropylene substrate to obtain low-VOC flame-retardant double-sided tape.

[0036] Example 3:

[0037] (1) Add 200 mL of ethanol, 40 mmol of tetramethylethylenedi(epoxypropylammonium chloride) and 40 mmol of bis(4-aminophenyl)-phenyl phosphate to a flask, heat to 70 °C, stir for 6 h, cool in an ice-water bath, filter, wash with ethanol, and dry to obtain a cationic flame retardant.

[0038] (2) Add 30g methacrylic acid, 220g methyl methacrylate, 250g butyl acrylate, 6.5g sodium dodecyl sulfate, and 3.5g OP-10 to 600mL of water to obtain a monomer solution; then purge nitrogen gas into the flask, add 150mL of monomer solution, 3mL of aqueous solution of 0.5g ammonium persulfate, and 0.26g sodium bicarbonate, heat to 80℃, react for 40min, then add the remaining monomer solution and 10mL of aqueous solution containing 1.5g ammonium persulfate, react for 3h, add sodium hydroxide to adjust the pH to 8, and obtain an aqueous acrylic resin emulsion.

[0039] (3) Add 1L of water-based acrylic resin emulsion, 50g of cationic flame retardant, and 5g of defoamer BYK-021 to a container, stir, and obtain flame-retardant water-based acrylic resin adhesive; finally, apply the adhesive to both sides of the polypropylene substrate to obtain low-VOC flame-retardant double-sided tape.

[0040] Comparative Example 1 differs from Example 1 in that no cationic flame retardant is added.

[0041] (1) Add 1L of water-based acrylic resin emulsion and 6g of defoamer BYK-021 to a container, stir, and obtain water-based acrylic resin adhesive; finally, apply the adhesive to both sides of the polypropylene substrate to obtain double-sided tape.

[0042] Comparative Example 2 differs from Example 1 in that bis(4-aminophenyl)-phenyl phosphate is used instead of the cationic flame retardant.

[0043] (1) Add 1L of water-based acrylic resin emulsion, 15g of bis(4-aminophenyl)-phenyl phosphate, and 6g of defoamer BYK-021 to a container and stir to obtain water-based acrylic resin adhesive; finally, apply the adhesive to both sides of the polypropylene substrate to obtain double-sided tape.

[0044] Comparative Example 3 differs from Example 1 in that ethylene glycol diglycidyl ether is used instead of tetramethylethylenedi(epoxypropylammonium chloride).

[0045] (1) Add 150 mL of ethanol, 40 mmol of ethylene glycol diglycidyl ether, and 40 mmol of bis(4-aminophenyl)-phenyl phosphate to a flask, heat to 60 °C, stir and react for 10 h, cool in an ice-water bath, filter, wash with ethanol, and dry to obtain a polymer flame retardant.

[0046] (2) Add 1L of water-based acrylic resin emulsion, 15g of polymer flame retardant, and 6g of defoamer BYK-021 to a container, stir, and obtain water-based acrylic resin adhesive; finally, apply the adhesive to both sides of the polypropylene substrate to obtain double-sided tape.

[0047] Comparative Example 4 differs from Example 1 in that it uses benzidine instead of bis(4-aminophenyl)-phenyl phosphate.

[0048] (1) Add 150 mL of ethanol, 40 mmol of tetramethylethylenedi(epoxypropylammonium chloride) and 40 mmol of benzidine to a flask, heat to 60 °C, stir and react for 10 h, cool in an ice-water bath, filter, wash with ethanol, and dry to obtain a cationic polymer.

[0049] (2) Add 1L of water-based acrylic resin emulsion, 15g of cationic polymer and 6g of defoamer BYK-021 to a container and stir to obtain water-based acrylic resin adhesive; finally, apply the adhesive to both sides of the polypropylene substrate to obtain double-sided tape.

[0050] The water-based acrylic resin adhesive was left at room temperature for 3 months, and the dispersion state of the adhesive was observed.

[0051] Water-based acrylic resin adhesive is poured into a mold and then baked and cured at 60°C for 6 hours to form an adhesive film. The flame retardant properties are in accordance with GB / T 2406.1-2008 standard.

[0052] Two pieces of tinplate were bonded together with double-sided tape, then baked and cured at 60°C for 8 hours, and finally left to stand at room temperature for 12 hours. The tensile shear strength was tested according to GB / T 7124-2008 standard.

[0053] Table 1 Performance Tests

[0054]

[0055] The limiting oxygen index of the waterborne acrylic resin adhesive in Comparative Example 1 was only 18.3%, and the tensile shear strength was only 16.8 MPa, indicating poor flame retardancy and adhesion. In each example, a cationic flame retardant was added. Its polymer molecular chain contains hydrophilic cationic groups, hydroxyl groups, and imino groups, exhibiting excellent hydrophilicity and water solubility. It can dissolve well in the waterborne acrylic resin emulsion, resulting in good adhesive dispersibility and no precipitation. Furthermore, the cationic groups in the cationic flame retardant form electrostatic interactions with the sodium carboxylate anions in the waterborne acrylic resin, while the hydroxyl and imino groups form hydrogen bonds with the ester and carboxylic acid groups in the waterborne acrylic resin. This increases the crosslinking degree between the acrylic resin molecular chains, enhances cohesion, and improves the adhesive's adhesion performance, resulting in higher tensile shear strength. Additionally, the cationic flame retardant contains a triphenyl phosphate flame-retardant structure, exhibiting a condensed-phase flame-retardant effect, further improving the limiting oxygen index and flame retardant properties of the adhesive.

[0056] In Comparative Example 2, bis(4-aminophenyl)-phenyl phosphate was added to the water-based acrylic resin adhesive. Its water solubility is very poor, resulting in obvious precipitates in the adhesive emulsion, which affects the adhesive performance and leads to low tensile shear strength.

[0057] Comparative Example 3 involved polymerizing ethylene glycol diglycidyl ether and bis(4-aminophenyl)-phenyl phosphate. The resulting flame retardant lacked cationic groups, leading to poor water solubility and dispersion in water-based acrylic resin adhesives, resulting in significant precipitation. This negatively impacted the adhesive's bonding performance. Furthermore, the absence of cationic groups hindered the formation of electrostatic forces with sodium carboxylate anions in water-based acrylic resins, failing to effectively improve the cross-linking degree between acrylic resin molecular chains. Consequently, the adhesive's bonding performance and tensile shear strength were lower.

[0058] Comparative Example 4 involved polymerizing benzidine with tetramethylethylenedi(epoxypropylammonium chloride). The resulting cationic polymer did not contain the triphenyl phosphate flame-retardant structure, resulting in a low limiting oxygen index and poor flame retardancy of the flame retardant.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for producing a flame-retardant double-sided tape, characterized by, The preparation method comprises: (1) adding ethanol, tetramethyl ethylene (epoxy propyl ammonium chloride), bis (4-aminophenyl)-phenyl phosphate into a flask, stirring and reacting, cooling in an ice water bath, filtering, washing, drying, and obtaining a cationic flame retardant; (2) adding an aqueous acrylic resin emulsion, a cationic flame retardant, and a defoaming agent into a container, stirring, and obtaining a flame-retardant aqueous acrylic resin adhesive; finally, coating the adhesive on both sides of a substrate to obtain a low-VOC flame-retardant double-sided adhesive tape; The ratio of tetramethyl ethylene (epoxy propyl ammonium chloride) and bis (4-aminophenyl)-phenyl phosphate in (1) is 1 mol: (1-1.1) mol.

2. The preparation method of the low-VOC flame-retardant double-sided adhesive according to claim 1, characterized in that, The reaction in (1) is carried out at 45-70℃ for 6-10h.

3. The method of claim 1, wherein the low VOC flame-retardant double-sided tape is prepared by the steps of: The ratio of the aqueous acrylic resin emulsion and the cationic flame retardant is 1L: (15-50) g.

4. The method of claim 1, wherein the low VOC flame-retardant double-sided tape is prepared by the steps of: The preparation method of the aqueous acrylic resin emulsion comprises: adding an acrylic monomer, an acrylate monomer, and an emulsifier into water to obtain a monomer solution; then, introducing nitrogen into a flask, dropping the monomer solution and a solution of an initiator, adding a buffer, heating to 75-85℃, reacting for 30-40min, dropping the monomer solution and the solution of the initiator again, reacting for 3-4h, adding a neutralizing agent to adjust the pH to 7-8, and obtaining the aqueous acrylic resin emulsion.

5. The method of claim 4, wherein the low VOC flame-retardant double-sided tape is prepared by the steps of: The buffer comprises sodium bicarbonate, and the neutralizing agent comprises sodium hydroxide.

6. The method of claim 4, wherein the low VOC flame-retardant double-sided tape is prepared by the steps of: The ratio of the acrylic monomer, the acrylate monomer, the initiator, and the emulsifier is (6-10) g: (90-94) g: (0.4-0.7) g: (2-3) g.

7. The method of claim 6, wherein the low VOC flame-retardant double-sided tape is prepared by the steps of: The acrylic monomer comprises acrylic acid and methacrylic acid; the acrylate monomer comprises methyl methacrylate and butyl acrylate; the initiator comprises potassium persulfate or ammonium persulfate; and the emulsifier comprises sodium dodecyl sulfate and OP-10.

8. A low-VOC flame-retardant double-sided adhesive tape obtained by the preparation method according to any one of claims 1-7.

9. Use of the low-VOC flame-retardant double-sided adhesive tape according to claim 8 in automotive interiors.

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