An ionic crosslinking agent and a preparation method thereof, a water-based acrylic pressure-sensitive adhesive for paper labels and a preparation method thereof

Abstract

The application discloses an ionic crosslinking agent and a preparation method thereof, a water-based acrylic pressure-sensitive adhesive with high initial adhesion and high holding adhesion for paper labels and a preparation method thereof, and the ionic crosslinking agent is a reaction product of an aminoguanidine salt and a polyglycidyl ether. The water-based acrylic pressure-sensitive adhesive with high initial adhesion and high holding adhesion comprises 70-90 parts of a water-based acrylic emulsion, 0.1-2 parts of the ionic crosslinking agent and 10-30 parts of a water-based tackifying resin. The ionic crosslinking agent forms an ionic bond with carboxyl in the water-based acrylic pressure-sensitive adhesive, and can improve the holding adhesion of the adhesive layer without affecting the initial adhesion and the peeling force of the adhesive layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cross-linking agents and adhesives, in particular to an ionic cross-linking agent and a water-based pressure-sensitive adhesive for paper labels. BACKGROUND

[0002] Paper labels are applied in all aspects of life, and the adhesive used for paper labels is a pressure-sensitive adhesive, which is a kind of adhesive that can be bonded with the adherend under external pressure. Currently, commonly used pressure-sensitive adhesives include solvent-based, water-based and hot-melt types. Solvent-based pressure-sensitive adhesives use toluene, benzene and other volatile organic compounds as solvents, which will produce a large amount of VOCs during use, polluting the environment and endangering the health of workers. In recent years, with the increasing environmental protection efforts, solvent-based pressure-sensitive adhesives are gradually changing to water-based and hot-melt pressure-sensitive adhesives.

[0003] The water-based pressure-sensitive adhesive on the market is mainly based on acrylic emulsion, which is increasingly favored by the market due to its simple preparation process, low cost, safety and non-toxicity. The main performance requirements of pressure-sensitive adhesives are three forces: initial adhesion, holding adhesion and peeling force. These three forces are related to the molecular weight of the pressure-sensitive adhesive. Generally, the initial adhesion and peeling force of the pressure-sensitive adhesive decrease with increasing molecular weight, and the holding adhesion increases with increasing molecular weight. Therefore, high initial adhesion pressure-sensitive adhesives need to sacrifice holding adhesion to achieve, and high holding adhesion pressure-sensitive adhesives need to sacrifice initial adhesion to achieve. Currently, patents CN102533174B and CN107699151A prepare a high initial adhesion pressure-sensitive adhesive by physical blending in water-based acrylic pressure-sensitive adhesive, but the holding adhesion and peeling strength are low; CN110527445A prepares a high holding adhesion pressure-sensitive adhesive by adding a large amount of cross-linking agent, but the initial adhesion is poor. How to better balance the initial adhesion and holding adhesion to prepare a high initial adhesion and high holding adhesion pressure-sensitive adhesive is the current technical difficulty. SUMMARY

[0004] The present application aims to solve the above-mentioned problems and provide an ionic cross-linking agent and a preparation method thereof, a high initial adhesion and high holding adhesion water-based acrylic pressure-sensitive adhesive for paper labels and a preparation method thereof.

[0005] To achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0006] An ionic cross-linking agent has the following structural formula:

[0007]

[0008]

[0009] X represents a chloride ion, a sulfate ion or a nitrate ion.

[0010] The preparation method of the ionic crosslinking agent of the present invention includes the following steps: dissolving 10-30 parts of aminoguanidine salt in 70-90 parts of deionized water, heating to 50-70°C, and adding polyglycidyl ether dropwise under stirring.

[0011] After adding the ingredients, continue the reaction for 30-60 minutes.

[0012] The polyglycidyl ethers described in this invention are one or both of diglycidyl ethers or glycerol triglycidyl ethers.

[0013] The aminoguanidine salt described in this invention is one or more of aminoguanidine hydrochloride, aminoguanidine nitrate, and aminoguanidine sulfate.

[0014] In the preparation method of the ionic crosslinking agent of the present invention, the molar amount of epoxy groups in the polyglycidyl ether is equal to the molar amount of primary amino groups in the aminoguanidine salt.

[0015] A water-based acrylic pressure-sensitive adhesive for high initial tack and high holding power paper labels comprises the following components:

[0016] 70-90 parts of water-based acrylic emulsion;

[0017] 0.1-2 parts of ionic crosslinking agent;

[0018] 10-30 parts of water-based tackifying resin.

[0019] This invention uses an ionic crosslinking agent as an aid to balance the initial tack and holding power of waterborne acrylic pressure-sensitive adhesive. After the pressure-sensitive adhesive is coated and dried to form a film, the guanidine group in the ionic crosslinking agent is acidified, reducing its complexation ability with the carboxyl group. It will only form ionic bonds with the carboxyl group in the waterborne acrylic pressure-sensitive adhesive. The ionic bond energy is relatively weak, which can improve the holding power of the adhesive layer without affecting the initial tack and peel force. This better balances the initial tack and holding power of the waterborne acrylic pressure-sensitive adhesive, resulting in a waterborne acrylic pressure-sensitive adhesive with high initial tack and high holding power.

[0020] In this invention, the glass transition temperature of the aqueous acrylic emulsion is -46 to -25°C, preferably -40 to -30°C. Examples include Wanhua Chemical's Adwel 1370 and Wanhua Chemical's Adwel 1367A.

[0021] In this invention, the preparation method of the high initial tack and high holding power paper label using water-based acrylic pressure-sensitive adhesive includes the following steps:

[0022] S1: Add water and emulsifier to an emulsification tank and stir. Add a mixture of polymer monomers and functional monomers and stir to obtain a pre-emulsion.

[0023] S2: Add water and part of the pre-emulsion to the reactor, stir and heat, add initiator solution, heat and keep warm to obtain seed emulsion; add the remaining pre-emulsion and keep warm, add initiator solution, heat and keep warm to react after the addition is complete;

[0024] S3: After the reaction is complete, add a post-treatment agent to eliminate unreacted monomers;

[0025] S4: Cool down, add pH adjuster, add ionic crosslinking agent and stir for 5-10 minutes, add water-based thickening resin and stir for 5-10 minutes, then filter and discharge.

[0026] In S1 of the present invention, the emulsifier is selected from one or more of OP10, CM-30, and EPA-073.

[0027] Preferably, the amount of emulsifier is 0.5-1.5% of the total mass of the total monomer mixture.

[0028] In S1 of this invention, the polymer monomer is selected from (meth)acrylate monomers or a mixture of (meth)acrylate monomers and vinyl monomers; wherein, the (meth)acrylate monomer is selected from one or more of alkyl (meth)acrylates with alkyl chains containing 1-20 carbon atoms, preferably one or more of methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, isooctyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate, more preferably... The vinyl monomer is selected from one or more of methyl methacrylate, methyl acrylate, n-butyl acrylate, n-butyl methacrylate, and isooctyl acrylate; the vinyl monomer is selected from one or more of vinyl esters of carboxylic acids containing ≤20 carbon atoms and vinyl aromatic compounds containing ≤20 carbon atoms; the vinyl ester of carboxylic acids containing ≤20 carbon atoms is one or more of vinyl acetate, vinyl propionate, vinyl laurate, or vinyl stearate; the vinyl aromatic compound containing ≤20 carbon atoms is selected from one or more of styrene, α-methylstyrene, p-methylstyrene, and vinyltoluene.

[0029] Preferably, the polymer monomer accounts for 95%-99.5% of the total mass of the total monomer mixture.

[0030] In S1 of this invention, the functional monomer is selected from one or more olefinic unsaturated monomers containing carboxyl, sulfonic acid, hydroxyl, or amide functional groups; wherein, the carboxyl-containing olefinic unsaturated monomer is preferably one or more of acrylic acid, methacrylic acid, maleic acid, and itaconic acid; the sulfonic acid-containing olefinic unsaturated monomer is preferably one or more of sodium p-styrene sulfonate, sodium vinyl sulfonate, and sodium allyl ether hydroxypropyl sulfonate; the hydroxyl-containing olefinic unsaturated monomer is preferably one or more of hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, and hydroxypropyl acrylate; and the amide-containing olefinic unsaturated monomer is acrylamide.

[0031] Preferably, the amount of the functional monomer is 0.5%-5% of the total mass of the total monomer mixture.

[0032] In this invention, the initiator in S2 is a thermal initiator and / or a redox initiator; wherein, the thermal initiator is preferably one or more of ammonium persulfate, potassium persulfate, sodium persulfate, tert-butyl hydroperoxide, hydrogen peroxide, BPO, and AIBN; the redox initiator is composed of an oxidant and a reducing agent, wherein the oxidant is preferably one or more of ammonium persulfate, potassium persulfate, sodium persulfate, tert-butyl hydroperoxide, hydrogen peroxide, BPO, and AIBN, and the reducing agent is preferably one or more of sodium sulfite, sodium bisulfite, sodium formaldehyde sulfoxylate, and ascorbic acid; preferably, the amount of the initiator accounts for 0.2-0.5% of the total mass of the monomer mixture, more preferably 0.3-0.4%.

[0033] In this invention, the portion of pre-emulsion added in S2 accounts for 5%-15% of the total mass of the emulsion, preferably 6-10%.

[0034] In this invention, after S2 is added to the initiator solution, the temperature is raised to 83-85°C. After the pre-emulsified monomer is added, the temperature is raised to 85-88°C and held for 20-40 minutes.

[0035] In this invention, the post-treatment agent in S3 is an oxidant and a reducing agent; preferably, the oxidant is one or more of hydrogen peroxide, tert-butyl hydrogen peroxide, sodium persulfate, potassium persulfate, and ammonium persulfate; the reducing agent is one or more of sodium sulfite, sodium bisulfite, sodium formaldehyde sulfoxylate, and ascorbic acid; preferably, the mass ratio of the oxidant to the reducing agent is 1:1 to 3:1; preferably, the amount of the post-treatment agent is 0.1-0.5% of the total mass of the monomer mixture.

[0036] In this invention, the pH adjuster in S4 is one or more of ammonia, ethanolamine, and triethylamine.

[0037] In this invention, the waterborne tackifying resin in S4 is one or more of waterborne rosin resin, waterborne terpene resin, and waterborne terpene phenolic resin, preferably waterborne rosin resin SE780g.

[0038] The guanidine salt ionic crosslinking agent of the present invention serves as an aid to balance the initial tack and holding power of waterborne acrylic pressure-sensitive adhesives. After the pressure-sensitive adhesive is coated and dried to form a film, the guanidine groups in the ionic crosslinking agent are acidified, reducing their complexation ability with carboxyl groups. They only form ionic bonds with carboxyl groups in the waterborne acrylic pressure-sensitive adhesive. The ionic bond energy is relatively weak, which can improve the holding power of the adhesive layer without affecting the initial tack and peel strength. This better balances the initial tack and holding power of the waterborne acrylic pressure-sensitive adhesive, resulting in a waterborne acrylic pressure-sensitive adhesive with high initial tack and high holding power.

[0039] Instruction manual illustrations

[0040] Figure 1 The infrared spectrum of the ionic crosslinking agent prepared in Example 1. Detailed Implementation

[0041] The technical solution of the present invention will be described in further detail below, but the scope of protection of the present invention is not limited to the following description.

[0042] Main raw material sources:

[0043] 99% Methyl Methacrylate, Shandong Weiming Chemical Co., Ltd.

[0044] Styrene 99% Henan Tianfu Chemical Co., Ltd.;

[0045] 99% n-Butyl Acrylate, Henan Tianfu Chemical Co., Ltd.

[0046] Isooctyl acrylate 99% Hubei Jusheng Technology Co., Ltd.

[0047] 99% Methacrylic Acid, Henan Tianfu Chemical Co., Ltd.

[0048] Hydroxyethyl methacrylate 99% Henan Tianfu Chemical Co., Ltd.

[0049] 99% Ammonium Persulfate, Tianjin Kemeo Chemical Reagent Co., Ltd.

[0050] 99% tert-butyl hydrogen peroxide (Wuhan Jiakailong Technology Development Co., Ltd.)

[0051] Sodium bisulfite 99% Henan Tianfu Chemical Co., Ltd.;

[0052] Diglycidyl ether and glycerol triglycidyl ether 99% Wuhan Beileye Biomedical Technology Co., Ltd.;

[0053] 780g tackifying resin 55% Shanghai Sangjing Chemical Co., Ltd.;

[0054] Aminoguanidine hydrochloride 98% Aladdin;

[0055] Aminoguanidine nitrate 99% Aladdin;

[0056] Aminoguanidine sulfate 98% Aladdin.

[0057] All water mentioned is deionized water; all other raw materials or reagents are purchased from the market unless otherwise specified.

[0058] Test method:

[0059] FINAT Technical Manual, 7th Edition;

[0060] FTM2 90° peel force test (peel speed 300mm / min);

[0061] FTM9 ring initial tack test;

[0062] FINAT FTM-8 holding power test.

[0063] Example 1

[0064] Synthesis of ionic crosslinking agents

[0065] Dissolve 200g of aminoguanidine hydrochloride in 800g of deionized water, heat to 60℃, and add an equal molar amount of diglycidyl ether under stirring. After the addition is complete, continue stirring for 45 minutes, cool to room temperature, and discharge for later use.

[0066] like Figure 1 As shown, 1640cm -1 The absorption peak for the guanidine group is at 2960 cm⁻¹. -1 and 2870cm -1 The absorption peaks at 910 cm⁻¹ are for methyl and methylene groups, and also at 910 cm⁻¹. -1 No peaks of epoxy groups were found at the location, indicating that the polyglycidyl ether has reacted with the aminoguanidine salt to form an ionic crosslinking agent.

[0067] Synthesis of acrylic emulsion

[0068] S1: Preparation of pre-emulsion: Add 300g of deionized water and 1g of CM-30 to the emulsification kettle and stir at 400rpm for 30min until CM-30 is completely dissolved. Then add a mixture of 140g of methyl methacrylate monomer, 860g of n-butyl acrylate monomer and 10g of acrylic acid monomer to the kettle and stir at 500rpm for 50min to obtain a uniform and stable pre-emulsion for later use.

[0069] S2: Emulsion polymerization reaction: Add 450g of deionized water and 80g of pre-emulsion to the reactor, stir at 300rpm and heat to 80℃, add 3.2g of 5.7% ammonium persulfate aqueous solution, then heat to 85℃ and keep warm for one hour to obtain seed emulsion. After the heat preservation is completed, slowly add the remaining pre-emulsion, keep the temperature at 83℃, and at the same time add 49.8g of 5.7% ammonium persulfate aqueous solution at a uniform rate for 5 hours. After the pre-emulsion monomer is added, raise the temperature to 88℃ and keep warm for 30 minutes.

[0070] S3: Add 4g of tert-butyl hydroperoxide and 2g of sodium bisulfite to eliminate unreacted monomers;

[0071] S4: Cool to 35℃, add ammonia to adjust the pH of the emulsion to 8, add 12.5g of ionic crosslinking agent, filter and discharge, stir for 5 minutes, add 500g of tackifying resin and 780g of tackifying resin, stir for 5 minutes, filter and discharge.

[0072] Example 2

[0073] Except for the addition of 25g of ionic crosslinking agent, the rest is the same as in Example 1.

[0074] Example 3

[0075] Synthesis of ionic crosslinking agents

[0076] Dissolve 300g of aminoguanidine hydrochloride in 700g of deionized water, heat to 60℃, and add an equal molar amount of glycerol triglycidyl ether under stirring. After the addition is complete, continue stirring for 45 minutes, cool to room temperature, and discharge for later use.

[0077] Synthesis of acrylic emulsion

[0078] S1: Preparation of pre-emulsion: Add 300g deionized water, 10g CM-30, and 5g OP-10 to the emulsification kettle and stir at 400rpm for 20min until CM-30 and OP-10 are completely dissolved. Then add a mixture of 190g methyl methacrylate monomer, 800g n-butyl acrylate monomer, and 10g acrylic acid monomer to the kettle and stir at 500rpm for 120min to obtain a uniform and stable pre-emulsion for later use.

[0079] S2: Emulsion polymerization reaction: 650g of deionized water and 200g of pre-emulsion were added to the reactor, stirred at 300rpm and heated to 80℃. 9g of 9% ammonium persulfate aqueous solution was added, and then the temperature was raised to 85℃ and kept at that temperature for one hour to obtain the seed emulsion. After the temperature was kept at that temperature, the remaining pre-emulsion was slowly added dropwise while the temperature was maintained at 83℃. At the same time, 46g of 9% ammonium persulfate aqueous solution was added dropwise at a uniform rate for 5 hours. After the pre-emulsion monomer was added, the temperature was raised to 88℃ and kept at that temperature for 20 minutes.

[0080] S3: Add 4g of tert-butyl hydroperoxide and 2g of sodium bisulfite to eliminate unreacted monomers;

[0081] S4: Cool to 35℃, add ammonia to adjust the pH of the emulsion to 8, add 8.6g of ionic crosslinking agent, stir for 5 minutes, add 857g of tackifying resin and 780g of tackifying resin, stir for 5 minutes, and filter out the material.

[0082] Example 4

[0083] Synthesis of ionic crosslinking agents

[0084] Dissolve 150g of aminoguanidine sulfate in 850g of deionized water, heat to 70℃, and add an equal molar amount of diglycidyl ether with functionality dropwise while stirring. After the addition is complete, continue stirring for 30 minutes, cool to room temperature, and discharge for later use.

[0085] Synthesis of acrylic emulsion

[0086] S1: Preparation of pre-emulsion: Add 300g deionized water, 0.5g EPA-073, and 0.3g OP-10 to the emulsification tank and stir at 400rpm for 20min until EPA-073 and OP-10 are completely dissolved. Then add a mixture of 120g methyl methacrylate monomer, 865g n-butyl acrylate monomer, 10g methacrylate monomer, and 5g acrylic acid monomer to the tank and stir at 500rpm for 50min to obtain a uniform and stable pre-emulsion for later use.

[0087] S2: Emulsion polymerization reaction: Add 450g of deionized water and 80g of pre-emulsion to the reactor, stir at 300rpm and heat to 80℃, add 3.2g of 5.7% ammonium persulfate aqueous solution, then heat to 85℃ and keep warm for one hour to obtain seed emulsion. After the heat preservation is completed, slowly add the remaining pre-emulsion, keep the temperature at 83℃, and at the same time add 49.8g of 5.7% ammonium persulfate aqueous solution at a uniform rate for 5 hours. After the pre-emulsion monomer is added, raise the temperature to 85℃ and keep warm for 40 minutes.

[0088] S3: Add 4g of tert-butyl hydroperoxide and 2g of sodium bisulfite to eliminate unreacted monomers;

[0089] S4: Cool to 35℃, add ammonia to adjust the pH of the emulsion to 8, add 17.5g of ionic crosslinking agent, stir for 5 minutes, add 500g of tackifying resin and 780g of tackifying resin, stir for 5 minutes, and filter out the material.

[0090] Example 5

[0091] Synthesis of ionic crosslinking agents

[0092] Dissolve 100g of aminoguanidine sulfate in 900g of deionized water, heat to 70℃, and add an equal molar amount of triglycidyl ether under stirring. After the addition is complete, continue stirring for 30 minutes, cool to room temperature, and discharge for later use.

[0093] Synthesis of acrylic emulsion

[0094] S1: Preparation of pre-emulsion: Add 300g deionized water, 0.5g EPA-073, and 0.3g OP-10 to the emulsification tank and stir at 400rpm for 20min until EPA-073 and OP-10 are completely dissolved. Then add 100g methyl methacrylate monomer, 860g n-butyl acrylate monomer, 20g methacrylate monomer, and 20g hydroxyethyl methacrylate mixture to the tank and stir at 500rpm for 50min to obtain a uniform and stable pre-emulsion for later use.

[0095] S2: Emulsion polymerization reaction: 650g of deionized water and 8g of pre-emulsion were added to the reactor, stirred and heated. When the temperature reached 80℃, 3.2g of 5.7% ammonium persulfate aqueous solution was added. Then the temperature was raised to 85℃ and kept for one hour to obtain seed emulsion. After the temperature was kept, the remaining pre-emulsion was slowly added dropwise while the temperature was maintained at 83℃. At the same time, 49.7g of 5.7% ammonium persulfate aqueous solution was added dropwise at a uniform rate for 5 hours. After the pre-emulsion monomer was added, the temperature was raised to 88℃ and kept for 20 minutes.

[0096] S3: Add 4g of hydrogen peroxide and 2g of sodium bisulfite to eliminate unreacted monomers;

[0097] S4: Cool to 35℃, add ammonia to adjust the pH of the emulsion to 8, add 20g of ionic crosslinking agent, stir for 5 minutes, add 500g of tackifying resin and 780g of tackifying resin, stir for 5 minutes, and filter out the material.

[0098] Example 6

[0099] Synthesis of ionic crosslinking agents

[0100] Dissolve 250g of aminoguanidine nitrate in 750g of deionized water, heat to 50℃, and add an equal molar amount of diglycidyl ether with functionality dropwise while stirring. After the addition is complete, continue stirring for 60 minutes, cool to room temperature, and discharge for later use.

[0101] Synthesis of acrylic emulsion

[0102] S1: Preparation of pre-emulsion: Add 300g deionized water, 0.5g EPA-073, and 0.3g OP-10 to the emulsification tank and stir at 400rpm for 20min until EPA-073 and OP-10 are completely dissolved. Then add 60g methyl methacrylate monomer, 890g n-butyl acrylate monomer, 30g acrylic acid monomer, and 20g hydroxyethyl methacrylate mixture to the tank and stir at 500rpm for 50min to obtain a uniform and stable pre-emulsion for later use.

[0103] S2: Emulsion polymerization reaction: 650g of deionized water and 8g of pre-emulsion were added to the reactor, stirred and heated. When the temperature reached 80℃, 3.2g of 5.7% ammonium persulfate aqueous solution was added. Then the temperature was raised to 85℃ and kept for one hour to obtain seed emulsion. After the temperature was kept for one hour, the remaining pre-emulsion was slowly added dropwise while the temperature was maintained at 83℃. At the same time, 49.7g of 5.7% ammonium persulfate aqueous solution was added dropwise at a uniform rate for 5 hours. After the pre-emulsion monomer was added, the temperature was raised to 88℃ and kept for 30 minutes.

[0104] S3: Add 4g of tert-butyl hydroperoxide and 2g of sodium bisulfite to eliminate unreacted monomers;

[0105] S4: Cool to 35℃, add ammonia to adjust the pH of the emulsion to 8, add 44g of ionic crosslinking agent, stir for 5 minutes, add 222g of tackifying resin and 780g of tackifying resin, stir for 5 minutes, and filter out the material.

[0106] Comparative Example 1

[0107] Except for the absence of an ionic crosslinking agent, the process is the same as in Example 1.

[0108] Comparative Example 2

[0109] Except for the monomers being changed to 200g of methyl methacrylate monomer, 790g of n-butyl acrylate monomer, and 10g of acrylic acid monomer, the rest are the same as in comparative example 1.

[0110] Comparative Example 3

[0111] Except for replacing aminoguanidine hydrochloride in the ion crosslinking agent synthesis process with aminoguanidine, the rest is the same as in Example 1.

[0112] The data for the relevant embodiments and comparative examples are shown in Table 1:

[0113] Table 1. Test data results for Examples 1-6 and Comparative Example 1

[0114] Sample Loop tack N / 25 mm Peel force N / 25 mm Holding power h Comparative Example 1 18.5 12.1 3 Comparative Example 2 14.2 8.4 45 Comparative Example 3 14.9 9.2 52 Example 1 18.6 12.5 60 Example 2 19.2 12.3 ＞200 Example 3 18.7 13.5 ＞200 Example 4 18.2 12.9 ＞200 Example 5 17.9 14.0 ＞200 Example 6 19.8 13.2 ＞200

[0115] Comparative Examples 1 and 2 are samples without ionic crosslinking agents. Table 1 shows that Comparative Example 1 has a higher initial tack (18.5 N / 25 mm) but poor holding power (only 3 hours). However, by adjusting the monomer to increase the holding power to 45 hours (Comparative Example 2), the initial tack decreased to 14 N / 25 mm. Examples 1 and 2 are samples of Comparative Example 1 with different amounts of ionic crosslinking agents added. Table 1 shows that with the same base emulsion, the sample without ionic crosslinking agents has a higher ring-shaped initial tack, but a very low holding power (only 3 hours). After adding ionic crosslinking agents… With the increase of ionic crosslinking agent content, the initial ring tack remained unchanged, but the holding power gradually increased to 40h and >200h, indicating that the prepared ionic crosslinking agent can better balance the initial tack and holding power. In addition, in Comparative Example 3, we replaced the aminoguanidine hydrochloride in the ionic crosslinking agent with aminoguanidine. The acidification of the acid radical ions was lost, and the guanidine group formed a complex bond with the carboxyl group in the pressure-sensitive adhesive, affecting the initial tack, resulting in a decrease in initial tack and an increase in holding power. Examples 3-6 show that the emulsions with this polyguanidine salt ionic crosslinking all exhibited good initial ring tack and holding power.

[0116] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended patent claims.

Claims

1. A water-based acrylic pressure-sensitive adhesive for paper labels, comprising the following components: 70-90 parts of water-based acrylic emulsion; 0.1-2 parts of ionic crosslinking agent; 10-30 parts of water-based tackifying resin; The ionic crosslinking agent has the following structural formula: or ; in, X represents chloride ion, sulfate ion, or nitrate ion; The preparation method of the aqueous acrylic emulsion includes the following steps: S1: Add water and emulsifier to an emulsification tank and stir. Add a mixture of polymer monomers and functional monomers and stir to obtain a pre-emulsion. S2: Add water and part of the pre-emulsion to the reactor, stir and heat, add initiator solution, heat and keep warm to obtain seed emulsion; add the remaining pre-emulsion and keep warm, add initiator solution, heat and keep warm to react after the addition is complete; S3: After the reaction is complete, add a post-treatment agent to eliminate unreacted monomers; In S1, the polymer monomer is selected from (meth)acrylate monomers; the (meth)acrylate monomer is selected from one or more alkyl (meth)acrylates whose alkyl chain contains 1-20 carbon atoms. In step S1, the functional monomer is selected from one or more olefinic unsaturated monomers containing carboxyl or hydroxyl groups; the olefinic unsaturated monomer containing carboxyl groups is one or more of acrylic acid and methacrylic acid; the olefinic unsaturated monomer containing hydroxyl groups is one or more of hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, and hydroxypropyl acrylate.

2. The pressure-sensitive adhesive according to claim 1, characterized in that, The preparation method of the ionic crosslinking agent includes the following steps: dissolving 10-30 parts of aminoguanidine salt in 70-90 parts of deionized water, heating to 50-70°C, adding polyglycidyl ether dropwise under stirring, and continuing the reaction for 30-60 minutes after the addition is complete.

3. The pressure-sensitive adhesive according to claim 2, characterized in that, The polyglycidyl ether is one or both of diglycidyl ether or glycerol triglycidyl ether.

4. The pressure-sensitive adhesive according to claim 2, characterized in that, The aminoguanidine salt is one or more of aminoguanidine hydrochloride, aminoguanidine nitrate, and aminoguanidine sulfate.

5. The pressure-sensitive adhesive according to claim 2, characterized in that, The molar amount of epoxy groups in the polyglycidyl ether is equal to the molar amount of primary amino groups in the aminoguanidine salt.

6. The pressure-sensitive adhesive according to claim 1, characterized in that, The preparation method of the paper label using water-based acrylic pressure-sensitive adhesive includes the following steps: Steps S1-S3 as described in claim 1, and, S4: Cool down, add pH adjuster, add ionic crosslinking agent and stir for 5-10 minutes, add water-based thickening resin and stir for 5-10 minutes, then filter and discharge.

7. The pressure-sensitive adhesive according to claim 1, characterized in that, The (meth)acrylate monomer is selected from one or more of methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, isooctyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate.

8. The pressure-sensitive adhesive according to claim 1, characterized in that, The glass transition temperature of the aqueous acrylic emulsion is -46 to -25°C; the aqueous tackifying resin is one or more of the following: aqueous rosin resin, aqueous terpene resin, and aqueous terpene phenolic resin.

9. The pressure-sensitive adhesive according to claim 8, characterized in that, The glass transition temperature of the aqueous acrylic emulsion is -40 to -30°C.

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