A water-based acrylic pressure-sensitive adhesive, a self-adhesive layer, and splicing paper

Abstract

This invention discloses a water-based acrylic pressure-sensitive adhesive, a self-adhesive layer, and a tipping paper, belonging to the field of adhesive technology. The adhesive, by weight, comprises: 6075 parts of acrylate soft monomer, 1525 parts of 2-ethylhexyl acrylate, 36 parts of acrylic acid, 13 parts of hydroxyethyl acrylate, 0.52 parts of fluorinated acrylate monomer, 13 parts of nano-silica, and 515 parts of tackifying resin. This invention, through the synergistic effect of the fluorinated monomer and nano-silica, enables the adhesive to possess both low surface energy and high cohesive strength, successfully overcoming the technical bias in the field of tobacco materials regarding the storage and coating stability of heterogeneous systems. The self-adhesive layer formed by this adhesive and the tipping paper containing this layer exhibit extremely low silicon transfer, excellent heat resistance, and high peel strength, meeting the stringent requirements of high-speed cigarette production and demonstrating good environmental performance.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, specifically relating to a water-based acrylic pressure-sensitive adhesive, a self-adhesive layer, and a splicing paper. Background Technology

[0002] Tipping paper, commonly known as cork paper, is a core component in cigarette production. Its back side requires an adhesive coating to achieve stable bonding with the filter and cigarette itself. The performance of the adhesive directly determines the efficiency of cigarette production and the quality stability of the final product. With the continuous improvement of green production standards in the tobacco industry, water-based acrylic pressure-sensitive adhesives, with their advantages of being environmentally friendly and solvent-free, having good coating compatibility, and excellent bonding performance, are gradually replacing traditional hot melt adhesives and solvent-based adhesives, becoming the mainstream development direction in the cigarette tipping paper field.

[0003] Existing water-based acrylic pressure-sensitive adhesives for cigarette tipping papers all employ a homogeneous and symmetrical latex particle system. The overall chemical composition, surface energy, and viscoelasticity of the adhesive layer are completely uniform. However, the performance requirements of the two interfaces of the adhesive layer in tipping paper are fundamentally contradictory: the interface in contact with the release paper requires extremely low surface energy to inhibit silicone oil migration and avoid silicone transfer contamination during long-term storage, which could affect subsequent bonding effects; the interface in contact with the base paper of the tipping paper requires high polarity and wettability to ensure anchoring force and bonding strength to the porous paper base. At the same time, the high-temperature drying conditions in high-speed cigarette production require the adhesive layer to have extremely high cohesive strength and creep resistance, while room temperature bonding scenarios require the adhesive layer to have good pressure-sensitive properties and flexibility. This contradiction in performance requirements between the two interfaces under different operating conditions is a structural bottleneck that cannot be completely resolved thermodynamically from the perspective of homogeneous systems.

[0004] Existing technologies address these issues by employing multi-component additive modification: adding fluorinated monomers to reduce the overall surface energy of the adhesive layer and inhibit silicon transfer, but this significantly reduces the wettability and adhesion of the adhesive layer to the paper substrate; adding nanofillers to improve the cohesive strength and heat resistance of the adhesive layer, but this sacrifices the flexibility and initial tack of the adhesive layer; adding large amounts of tackifying resins to compensate for the loss of adhesive performance, but this leads to decreased heat resistance and easy glue overflow. All modification methods are limited by the homogeneity of the system, only able to balance various properties within a limited range, and ultimately failing to achieve synergistic balance of multiple core properties. This results in problems such as excessive silicon transfer during storage, glue overflow and debonding during high-speed production, and insufficient adhesive strength, making them unsuitable for the increasingly stringent production and quality requirements of the tobacco industry.

[0005] Meanwhile, a long-standing and widespread technical bias exists in this field: in the actual production of cigarette tipping paper, adhesives must meet extremely stringent industrial requirements. To ensure continuous production and supply chain stability, industry practice requires them to have a shelf life of no less than 6 months at room temperature, extremely high batch uniformity, and high-speed coating and leveling properties suitable for production lines with speeds of 8,000-10,000 pieces per minute. Based on classical colloid chemistry theory, those skilled in the art generally hold a technical perception and bias: they believe that only by using a latex particle system with uniform chemical composition and symmetrical morphology can the stability requirements of water-based adhesives for long-term storage and high-speed coating be ensured. Any design that might introduce microscopic phase separation or structural asymmetry, such as the addition of strongly hydrophobic monomers or inorganic nanoparticles, is considered to compromise emulsion stability and has therefore been avoided in this high-end application area for a long time. This widespread technical bias has constrained the technical path to resolve performance contradictions through structural design. Summary of the Invention

[0006] In view of this, the present invention proposes a water-based acrylic pressure-sensitive adhesive, a self-adhesive layer, and a tipping paper, aiming to break through the structural bottleneck of existing homogeneous adhesive systems, overcome long-standing technical biases in the field, and fundamentally solve the inherent contradiction between low silicone transfer and high adhesion, high heat resistance and high tack of pressure-sensitive adhesives for cigarette tipping paper, while meeting the requirements of the entire process of industrial production, storage and high-speed application.

[0007] The technical solution of this invention is implemented as follows: This invention provides a water-based acrylic pressure-sensitive adhesive. The raw materials for preparing the water-based acrylic pressure-sensitive adhesive, by weight, include an A-phase hydrophobic preemulsion, a B-phase hydrophilic preemulsion, an aqueous base liquid, an emulsifier system, and an initiator system, wherein the mass ratio of the A-phase hydrophobic preemulsion to the B-phase hydrophilic preemulsion is 1:(4-9); the A-phase hydrophobic preemulsion contains 2-5 parts of fluorinated acrylate monomers and 8-15 parts of soft acrylate monomers; the B-phase hydrophilic preemulsion contains propylene... The mixture contains 60-75 parts of ester soft monomers and 5-10 parts of functional monomers; the emulsifier system is added to the A-phase hydrophobic preemulsion, the B-phase hydrophilic preemulsion, and the aqueous base liquid, respectively; the waterborne acrylate pressure-sensitive adhesive is prepared by a phase separation seed semi-continuous polymerization method, specifically: first, a hydrophilic seed emulsion is prepared with 10% of the B-phase hydrophilic preemulsion and part of the initiator system, and then the remaining B-phase hydrophilic preemulsion and all of the A-phase hydrophobic preemulsion are added dropwise at a uniform rate, controlling the endpoints of the two phases to be completely consistent, and then obtained after polymerization, post-curing, and pH adjustment.

[0008] The core inventive concept of this invention lies in abandoning the fixed approach of existing homogeneous systems and instead using a seed polymerization process with biphasic pre-emulsion partitioning design and simultaneous equal-endpoint addition to prepare asymmetric latex particles with fluorinated hydrophobic segments enriched on one side and polar hydrophilic segments enriched on the other. During film formation, the latex particles spontaneously orient themselves based on the principle of minimizing interfacial energy, resulting in a low surface energy hydrophobic layer at the interface between the adhesive layer and the release paper, and a high polar hydrophilic layer at the interface with the tipping paper. This fundamentally eliminates the conflicting performance requirements of the positive and negative interfaces, achieving a synergistic balance of multiple core properties without the need for adding multiple auxiliary modifying components. Simultaneously, through synergistic optimization of the formulation and process, the industry pain points of easy asymmetric latex particle aggregation and poor storage stability are solved, breaking through long-standing technical biases in this field.

[0009] In some embodiments, the fluorinated acrylate monomer is at least one of dodecafluoroheptyl methacrylate and hexafluorobutyl acrylate. This type of fluorinated monomer possesses strong hydrophobic and oleophobic properties and extremely low surface energy, forming a dense, low-surface-energy barrier on the hydrophobic side of the latex particles. Simultaneously, its carbon chain structure is highly compatible with the acrylate backbone, allowing it to stably integrate into the polymer molecular chain, preventing the migration and precipitation of fluorinated segments, thus balancing anti-silicone transfer effects with the long-term stability of the adhesive layer.

[0010] In some embodiments, the acrylate soft monomer is at least one of butyl acrylate and 2-ethylhexyl acrylate; the functional monomer is at least two of acrylic acid, hydroxyethyl acrylate, and hydroxyethyl methacrylate. This type of soft monomer can precisely control the glass transition temperature of the polymer, ensuring the pressure-sensitive properties and flexibility of the adhesive layer; the multifunctional functional monomer can provide sufficient polar groups and crosslinking sites, which can enhance the hydrogen bond anchoring effect on the polar bonding paper substrate and form a stable crosslinking network during film formation, improving the cohesive strength and heat resistance of the adhesive layer.

[0011] In some embodiments, the mass ratio of the hydrophobic preemulsion A to the hydrophilic preemulsion B is 1:(4-9). This mass ratio is the only effective range for achieving stable preparation of asymmetric latex particles, balance of interfacial properties, and long-term storage stability of the emulsion. When the proportion of phase A is too high, the overall surface energy of the latex particles will be too low, affecting the wettability to the paper substrate, and it is also prone to hydrophobic association and aggregation of latex particles, which will damage storage stability. When the proportion of phase A is too low, a continuous low surface energy hydrophobic layer cannot be formed on one side of the latex particles, and the anti-silicon transfer effect cannot meet the standard. By limiting this ratio, the controllable preparation of asymmetric latex particles, balance of interfacial properties, and long-term storage stability of the emulsion can be simultaneously achieved.

[0012] In some embodiments, during the synchronous uniform dropping step, the reaction temperature is controlled at 80-82℃, the dropping time is controlled at 2 hours, and the stirring speed is stabilized at 150 rpm. These process parameters are crucial for achieving precise matching between phase separation and polymerization rate. The reaction temperature and dropping time determine the polymerization rate of the monomer, and the stable stirring speed ensures uniform dispersion and unilateral enrichment of the biphase monomer in the reaction system. When the parameters exceed this range, phase separation will become uncontrolled, making it impossible to form stable asymmetric latex particles, resulting only in core-shell structures or random copolymers, thus failing to achieve the purpose of the invention.

[0013] In some embodiments, the raw materials for preparing the waterborne acrylate pressure-sensitive adhesive also include an anionic nonionic composite emulsifier, which is a compound of sodium dodecyl sulfate and fatty alcohol polyoxyethylene ether in a mass ratio of 1:2. This compound emulsifier can form a dense hydration layer on the surface of latex particles, providing strong electrostatic repulsion and steric hindrance effects, effectively inhibiting the hydrophobic association and aggregation of asymmetric latex particles, which is key to ensuring the long-term storage stability of the emulsion. At the same time, this emulsifier system has good compatibility with acrylate monomers, which can ensure the stability of the pre-emulsion and polymerization process and avoid demulsification and flocculation problems.

[0014] In some embodiments, the total solids content of the waterborne acrylic pressure-sensitive adhesive is 50%-55%, and the pH value of the finished product is 6.5-7.5. This solids content range ensures that the adhesive has suitable viscosity and leveling properties, making it suitable for high-speed gravure / microgravure coating processes and avoiding problems such as excessive drying energy consumption due to too low solids content and poor coating leveling due to too high solids content. The pH value range of 6.5-7.5 ensures the storage stability of the acrylic emulsion and avoids problems such as polymer hydrolysis and sudden viscosity changes caused by excessive acidity or alkalinity.

[0015] A second aspect of the present invention also provides a pressure-sensitive self-adhesive layer, wherein the pressure-sensitive self-adhesive layer is formed by coating and curing the above-described water-based acrylic pressure-sensitive adhesive.

[0016] A third aspect of the present invention also provides a tipping paper, comprising a tipping paper base paper and a pressure-sensitive self-adhesive layer laminated on the back side of the tipping paper base paper, wherein the pressure-sensitive self-adhesive layer is formed by coating and curing the above-described water-based acrylic pressure-sensitive adhesive.

[0017] In some embodiments, the dry coating weight of the pressure-sensitive self-adhesive layer is 5-15 g / m². 2This coating amount range can adapt to the high-speed coating process and bonding requirements of cigarette tipping paper. If the coating amount is too low, a continuous and complete adhesive layer cannot be formed, which can easily lead to poor bonding. If the coating amount is too high, glue overflow and seepage can easily occur during high-speed drying, while increasing production costs. By limiting this range, the bonding performance can be guaranteed while adapting to the process requirements of high-speed industrial production.

[0018] In some embodiments, the tipping paper base paper is cigarette tipping paper base paper with a basis weight of 30-50 g / m³. 2 The base paper within this basis weight range is a common substrate in the tobacco processing field. It has suitable porosity and strength, which can ensure that the adhesive can penetrate and anchor the paper base appropriately, thereby improving the bonding strength. It can also adapt to the operating requirements of high-speed cigarette machines, avoiding problems such as paper breakage and wrinkles, and ensuring the complete compatibility of the product of this invention with existing tobacco processing technology.

[0019] In some embodiments, the post-curing step specifically involves: after the biphasic pre-emulsion is added, the temperature is raised to 85-88°C, the remaining initiator solution is added, and the reaction is maintained at this temperature for 1.5 hours, resulting in a monomer conversion rate ≥99.5%. This post-curing process ensures complete monomer reaction, reduces the residual monomer content in the emulsion, meets the food contact safety requirements of the tobacco industry, and simultaneously improves the uniformity of polymer molecular weight, further optimizing the adhesive properties and heat resistance of the adhesive layer.

[0020] The present invention has the following advantages over the prior art:

[0021] This invention utilizes a biphasic pre-emulsion partitioning design and a seed polymerization process with simultaneous equal-endpoint addition to prepare latex particles with an asymmetric structure of one side hydrophobic and the other side hydrophilic. This overcomes the long-standing technical bias in the field of relying on homogeneous and symmetrical latex particle systems, fundamentally resolving the inherent structural contradiction in existing cigarette tipping paper pressure-sensitive adhesives: the inability to simultaneously achieve low silica transfer, high adhesion, high heat resistance, and high viscosity. Compared to existing technologies, this invention eliminates the need for additional nanofillers, tackifying resins, or other auxiliary modifying components. The innovative polymerization process alone achieves a synergistic balance of multiple core properties, resulting in stable adhesive layer performance and an emulsion storage period of ≥6 months at room temperature. It is fully compatible with existing high-speed coating and cigarette production processes for cigarette tipping paper, significantly improving the storage stability and application reliability of pressure-sensitive self-adhesive tipping paper while ensuring environmental friendliness. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] General experimental specifications 1. Standardized specifications for experimental materials: Butyl acrylate (BA) and 2-ethylhexyl acrylate (2-EHA) were industrial grade, purified by distillation to remove polymerization inhibitors; acrylic acid (AA), hydroxyethyl acrylate (HEA), and hydroxyethyl methacrylate (HEMA) were analytical grade; dodecyl fluoroheptyl methacrylate (DFMA) and hexafluorobutyl acrylate (HFBA) were industrial grade with a purity ≥98%; sodium dodecyl sulfate (SDS) and fatty alcohol polyoxyethylene ether (AEO-9) were analytical grade; ammonium persulfate (APS) was analytical grade; 25% ammonia water was analytical grade; the basis weight of cigarette tipping paper was 40 g / m2; the basis weight of glassine silicone oil release paper was 75 g / m2; and the conductivity of deionized water was ≤5 μS / cm.

[0024] 2. General preparation operation specifications: The high-speed shearing speed in the pre-emulsification process is uniformly 3000 rpm, and the shearing time is uniformly 30 min; the polymerization reaction is protected by high-purity nitrogen gas for deoxygenation throughout, and the nitrogen flow rate is uniformly 50 mL / min; the post-curing and blending process is to allow the temperature to drop naturally to below 40℃ after the heat preservation, adjust the pH to 6.5-7.5 with ammonia water, and filter the material through a 200-mesh stainless steel filter screen; the coating and curing process is uniformly coated using a wire bar coater, dried with hot air at 100℃ for 60 s, and after laminating with release paper, cured at room temperature (25℃, 50% relative humidity) for 24 h before basic performance testing.

[0025] 3. Testing standards: 180° peel strength test according to GB / T2792-2014; holding power test according to GB / T4851-2014; silicone transfer test according to the test principle and method in the appendix of YC / T207-2014; storage stability test according to GB / T11175-2021; double-sided contact angle test of adhesive layer according to GB / T30693-2014, used to verify the asymmetry of the front and back interfaces of the adhesive layer.

[0026] 4. Performance Testing and Characterization: The adhesives obtained from the examples and comparative examples were coated to form standard test strips. After being conditioned for 24 hours in a standard environment with a temperature of (23±2)℃ and a relative humidity of (50±5)%, the following tests were conducted: 180° peel strength test: Press the tipping paper strip coated with adhesive (width 25 mm, length 200 mm) against the standard stainless steel plate at a roller speed of 2.0 m / min. After placing for 20 minutes, conduct peeling on a universal material testing machine at a peeling speed of 300 mm / min and a peeling angle of 180°, and record the stable average force value in N / 25 mm.

[0027] Adhesive holding power test: Paste a strip of the same specification on the standard stainless steel plate with an effective contact area of 25 mm × 25 mm, and reciprocally roll it three times with a 2 kg standard pressure roller. After the test plate is vertically suspended, hang a 1 kg weight at the lower end of the strip. Record the time when the strip completely falls off the test plate in hours (h). If it does not fall off after more than 48 hours, record it as >48 h.

[0028] Silicone transfer amount test: After tightly contacting and storing the adhesive strip with the corresponding release paper at (40 ± 2) °C for 7 days, take a certain area of the release paper contact surface, and refer to the general pretreatment and analysis principle of "Determination of solvent residues in tobacco paper - Headspace-gas chromatography / mass spectrometry", and determine the content of characteristic siloxane substances migrated to the surface of the release paper by a gas chromatography-mass spectrometry (GC-MS). The result is expressed in micrograms per square centimeter (μg / cm 2 )

[0029] Storage stability test: Seal the emulsion adhesive in a plastic can and place it in a constant temperature environment of (25 ± 2) °C. Observe and record its appearance state before storage, and after 1 month, 3 months, and 6 months of storage, and measure its viscosity change using a rotational viscometer. If there is no obvious stratification, caking, or mildew, and the viscosity change rate is within ±20% of the initial value, it is judged to be qualified.

[0030] Contact angle test: Using a video optical contact angle measuring instrument, drop 2 μL of ultrapure water on the front (air contact surface) and back (substrate contact surface) of the adhesive dry film respectively. Collect images and calculate the static contact angle 5 seconds after the liquid droplet contacts the surface. Test at least 5 points for each sample and take the average value to characterize the wettability difference between the two interfaces.

[0031] Example 1 1. Formula (by mass parts): A-phase hydrophobic pre-emulsion: 3 parts of dodecafluoroheptyl methacrylate, 10 parts of butyl acrylate, 0.2 parts of SDS, 0.4 parts of AEO-9, 12 parts of deionized water; Phase B hydrophilic preemulsion: 55 parts butyl acrylate, 12 parts 2-ethylhexyl acrylate, 4 parts acrylic acid, 3 parts hydroxyethyl acrylate, 0.5 parts SDS, 1.0 parts AEO-9, and 25 parts deionized water; Aqueous base solution: 0.1 parts SDS, 0.2 parts AEO-9, 20 parts deionized water; Initiator system: 0.5 parts ammonium persulfate, 8 parts deionized water; The mass ratio of the hydrophobic preemulsion A to the hydrophilic preemulsion B is 1:5.5, and the total solid content of the system is 52%.

[0032] 2. Preparation steps: Step 1: Pre-emulsion preparation: Weigh all components of phase A and phase B according to the formula, add them to two separate pre-emulsification tanks, turn on the high-speed shearing machine, shear at 3000 rpm for 30 min, and obtain stable hydrophobic pre-emulsion of phase A and hydrophilic pre-emulsion of phase B respectively; Weigh ammonium persulfate and dissolve it in deionized water, stir until completely dissolved, divide it into 3 equal portions to prepare initiator solutions I, II and III, and seal them for later use.

[0033] Step 2, Seed emulsion preparation: Add all components of the aqueous base liquid to a reactor equipped with a stirrer, condenser, and nitrogen inlet device. Turn on the stirrer and stabilize the speed at 150 rpm. After purging with nitrogen for 30 min to remove oxygen, raise the temperature to 78-80℃. Add 10% of phase B hydrophilic pre-emulsion and 30% of initiator solution I to the reactor and keep the reaction at this temperature for 30 min to obtain a hydrophilic seed emulsion.

[0034] Step 3, Asymmetric latex particle polymerization: Keep the reactor temperature stable at 80-82℃, turn on the dual constant flow drip pump, and add the remaining 90% of the B phase hydrophilic pre-emulsion and 40% of the initiator solution II to the reactor at a uniform rate over 2 hours; while adding the B phase pre-emulsion, simultaneously add all the A phase hydrophobic pre-emulsion at a uniform rate, strictly control the drip flow rate of the two phases, and ensure that the drip endpoint is completely consistent.

[0035] Step 4, Post-maturation: After the biphase pre-emulsion is added, heat the reactor to 85-88℃, add the remaining 30% of initiator solution III, and keep the reaction at this temperature for 1.5 hours to ensure that the monomer conversion rate is ≥99.5%.

[0036] Step 5, Cooling and Mixing: Turn off the heating device and allow it to cool naturally to below 40°C. Add 25% ammonia to adjust the pH of the system to 7.0. Filter the mixture through a 200-mesh stainless steel filter to obtain the target water-based acrylic pressure-sensitive adhesive.

[0037] 3. Coating and Sample Preparation: The prepared water-based acrylic pressure-sensitive adhesive was coated onto a 40g / m² plate using a wire bar coater. 2 The back of the cigarette tipping paper base paper has a dry basis coating of 10 g / m².2 Dry with hot air at 100℃ for 60 seconds, and with 75g / m 2 Glassine release paper composites were cured at room temperature for 24 hours before testing.

[0038] 4. Asymmetric structure verification: The cured adhesive layer was completely peeled off, and the contact angles of pure water on both sides were tested. The contact angle of the release paper contact surface was 108°, and the contact angle of the splice paper contact surface was 72°. The difference between the two sides was 36°, which proved that the adhesive layer has significant asymmetry of the front and back interfaces, and the corresponding latex particles have an asymmetric structure of unilateral hydrophobicity and unilateral hydrophilicity.

[0039] Example 2 1. Formulation: Only the mass ratio of hydrophobic preemulsion A to hydrophilic preemulsion B was adjusted to 1:4. The other components and dosages were completely consistent with those in Example 1. The total solid content of the system was 52%.

[0040] 2. Preparation steps, coating and sample preparation, and verification of asymmetric structure: completely consistent with Example 1, the contact angle difference between the two sides of the adhesive layer is 39°, which shows significant interfacial asymmetry.

[0041] Example 3 1. Formulation: Only the mass ratio of hydrophobic preemulsion A to hydrophilic preemulsion B was adjusted to 1:9. The other components and dosages were completely consistent with those in Example 1. The total solid content of the system was 52%.

[0042] 2. Preparation steps, coating and sample preparation, and verification of asymmetric structure: completely consistent with Example 1, the contact angle difference between the two sides of the adhesive layer is 32°, which shows significant interfacial asymmetry.

[0043] Example 4 1. Formulation: The mass ratio of hydrophobic preemulsion A to hydrophilic preemulsion B was adjusted to 1:6. The other components and dosages were completely consistent with those in Example 1. The total solid content of the system was 52%.

[0044] 2. Preparation steps, coating and sample preparation, and verification of asymmetric structure: completely consistent with Example 1, the contact angle difference between the two sides of the adhesive layer is 35°, which shows significant interfacial asymmetry.

[0045] Example 5 1. Formulation: The mass ratio of hydrophobic preemulsion A to hydrophilic preemulsion B was adjusted to 1:7. The other components and dosages were completely consistent with those in Example 1. The total solid content of the system was 52%.

[0046] 2. Preparation steps, coating and sample preparation, and verification of asymmetric structure: completely consistent with Example 1, the contact angle difference between the two sides of the adhesive layer is 34°, which shows significant interfacial asymmetry.

[0047] Example 6 1. Formulation: Only the mass ratio of hydrophobic preemulsion A to hydrophilic preemulsion B was adjusted to 1:8. The other components and dosages were completely consistent with those in Example 1. The total solid content of the system was 52%.

[0048] 2. Preparation steps, coating and sample preparation, and verification of asymmetric structure: completely consistent with Example 1, the contact angle difference between the two sides of the adhesive layer is 33°, which shows significant interfacial asymmetry.

[0049] Example 7 1. Formulation: The only difference is that the mass of dodecafluoroheptyl methacrylate in the hydrophobic preemulsion of phase A is replaced with hexafluorobutyl acrylate. The other components, dosages, and the mass ratio of phase A / B are completely consistent with those in Example 1. The total solid content of the system is 52%.

[0050] 2. Preparation steps, coating and sample preparation, and verification of asymmetric structure: completely consistent with Example 1, the contact angle difference between the two sides of the adhesive layer is 35°, which shows significant interfacial asymmetry.

[0051] Example 8 1. Formulation: The hydroxyethyl acrylate in the hydrophilic preemulsion of phase B was replaced with hydroxyethyl methacrylate by mass, while the other components, dosages, and A / B phase mass ratios were completely consistent with those in Example 1. The total solid content of the system was 52%.

[0052] 2. Preparation steps, coating and sample preparation, and verification of asymmetric structure: completely consistent with Example 1, the contact angle difference between the two sides of the adhesive layer is 36°, which shows significant interfacial asymmetry.

[0053] Example 9 1. Formulation and preparation steps: The same as in Example 1 were used to prepare the same water-based acrylic pressure-sensitive adhesive.

[0054] 2. Coating and Sample Preparation: Two parallel experiments were conducted, with the dry coating amount adjusted to 5 g / m². 2 15g / m 2 The remaining drying, compounding, and aging conditions were completely consistent with those in Example 1, and both groups of samples were verified to have significant interfacial asymmetry.

[0055] Comparative Example 1 Formulation (by weight, the total monomer types, total amount, emulsifier, initiator, and solid content are completely consistent with Example 1, except that the two-phase pre-emulsion partition design is omitted): Basic monomers: 3 parts dodecafluoroheptyl methacrylate, 65 parts butyl acrylate, 12 parts 2-ethylhexyl acrylate, 4 parts acrylic acid, and 3 parts hydroxyethyl acrylate; Emulsifiers: 0.8 parts SDS, 1.6 parts AEO-9; Initiator: 0.5 parts ammonium persulfate; Deionized water: 65 parts; The total solids content of the system was 52%, which was completely consistent with Example 1.

[0056] Preparation steps (using conventional homogeneous semi-continuous emulsion polymerization in the field of pressure-sensitive adhesives for cigarettes, without simultaneous drop-feeding of biphase pre-emulsion process): Step 1, Pre-emulsion preparation: Add all monomers, all emulsifiers, and 50 parts of deionized water to the pre-emulsion tank according to the formula, and shear at 3000 rpm for 30 min to obtain a homogeneous pre-emulsion; dissolve ammonium persulfate in the remaining 15 parts of deionized water, stir until completely dissolved, and divide into 3 equal parts to prepare initiator solutions I, II, and III, and seal for later use.

[0057] Step 2, Preparation of base solution: Add 10 parts of deionized water to the reaction vessel, purge with nitrogen to remove oxygen for 30 min, raise the temperature to 78-80℃, add 10% homogeneous pre-emulsion and 30% initiator solution I, keep the temperature and react for 30 min to obtain seed emulsion.

[0058] Step 3, homogeneous polymerization: Maintain the reaction temperature at 80-82℃, and add the remaining 90% of the homogeneous pre-emulsion and 40% of the initiator solution II to the reactor at a uniform rate over 2 hours. After the addition is complete, keep the temperature for 30 minutes.

[0059] Step 4, Post-curing: Heat to 85-88℃, add the remaining 30% of initiator solution III, keep the reaction at this temperature for 1.5h, and ensure that the monomer conversion rate is ≥99.5%.

[0060] Step 5, Cooling and Adjustment: Allow the mixture to cool naturally to below 40°C, add 25% ammonia to adjust the pH of the system to 7.0, filter through a 200-mesh stainless steel filter, and the homogeneous water-based acrylic pressure-sensitive adhesive is obtained.

[0061] Coating and sample preparation and performance testing methods are completely consistent with those in Example 1. The contact angle difference between the two sides of the adhesive layer is 3°, and there is no interface asymmetry.

[0062] Comparative Example 2 The formulation is completely consistent with Example 1, except that the dropping process is adjusted. The remaining 90% of the B phase pre-emulsion is added dropwise at a uniform rate within 2 hours, and then all the A phase pre-emulsion is added dropwise. The remaining seed polymerization, post-ripening, and blending steps are completely consistent with Example 1. The coating and sample preparation are completely consistent with Example 1. The contact angle difference between the two sides of the adhesive layer is 7°, with no significant interface asymmetry. The product is a core-shell structured latex particle.

[0063] Comparative Example 3 The formulation is completely consistent with Example 1, except that the dropping process is adjusted. All of the A-phase pre-emulsion is added at a uniform rate within 1 hour, and then the remaining 90% of the B-phase pre-emulsion is added. The remaining seed polymerization, post-ripening, and blending steps are completely consistent with Example 1. The coating and sample preparation are completely consistent with Example 1. The contact angle difference between the two sides of the adhesive layer is 5°, with no significant interfacial asymmetry. The product is an anti-core-shell structure latex particle.

[0064] Comparative Example 4 The formulation is completely consistent with Example 1, except that the dropping process is adjusted. Phase B pre-emulsion is added at a uniform rate over 2 hours, and Phase A pre-emulsion is added at a uniform rate over 1 hour. The remaining seed polymerization, post-ripening, and blending steps are completely consistent with Example 1. The coating and sample preparation are completely consistent with Example 1. The contact angle difference between the two sides of the adhesive layer is 8°, with no significant interfacial asymmetry. The product is a gradient core-shell structure latex particle.

[0065] Comparative Example 5 The mass ratio of the hydrophobic preemulsion A to the hydrophilic preemulsion B was adjusted to 1:3, while the other components and dosages were completely consistent with those in Example 1. The preparation steps and coating were also completely consistent with those in Example 1. The emulsion showed stratification and flocculation after one month of storage.

[0066] Comparative Example 6 Only the mass ratio of the hydrophobic preemulsion A to the hydrophilic preemulsion B was adjusted to 1:10. The other components and amounts were completely consistent with those in Example 1. The preparation steps and coating sample preparation were completely consistent with those in Example 1. The contact angle difference between the two sides of the adhesive layer was 10°, with no significant interface asymmetry. The amount of silicon transferred was seriously exceeded.

[0067] Comparative Example 7 The total types and amounts of monomers are completely consistent with those in Example 1. The biphase pre-emulsion design is cancelled. All monomers are random copolymerized using conventional homogeneous emulsion polymerization. The amounts of other emulsifiers, initiators, and deionized water are completely consistent with those in Example 1. The preparation steps and coating sample preparation are completely consistent with those in Example 1. The contact angle difference between the two sides of the adhesive layer is 4°, and there is no interfacial asymmetry.

[0068] Comparative Example 8 The total types and amounts of monomers were completely consistent with those in Example 1. A core-shell structure design was adopted, with fluorinated monomers and butyl acrylate as the shell layer and acrylate soft monomers and functional monomers as the core layer. The amounts of other emulsifiers, initiators and deionized water were completely consistent with those in Example 1. The sample was prepared by conventional core-shell emulsion polymerization. The coating and sample preparation were completely consistent with those in Example 1. The contact angle difference between the two sides of the adhesive layer was 6°, with no significant interfacial asymmetry.

[0069] Comparative Example 9 Formulation (by weight, the total monomer types, total solids content, and emulsifier system are consistent with Example 1, only using the existing conventional asymmetric emulsion phase ratios and preparation processes, without any adaptation or optimization for tobacco use scenarios): Oil phase preemulsion: 3 parts dodecafluoroheptyl methacrylate, 20 parts butyl acrylate, 0.3 parts SDS, 0.6 parts AEO-9, and 15 parts deionized water; Aqueous preemulsion: 45 parts butyl acrylate, 12 parts 2-ethylhexyl acrylate, 4 parts acrylic acid, 3 parts hydroxyethyl acrylate, 0.4 parts SDS, 0.8 parts AEO-9, and 22 parts deionized water; Aqueous base solution: 0.1 parts SDS, 0.2 parts AEO-9, 20 parts deionized water; Initiator system: 0.5 parts ammonium persulfate, 8 parts deionized water; The total solids content of the system was 52%, which was completely consistent with Example 1.

[0070] Preparation steps (using conventional asymmetric emulsion semi-continuous polymerization method, without the synchronous equal endpoint dropping process of this invention): Step 1: Pre-emulsion preparation: Weigh all components of the oil phase and aqueous phase according to the formula, add them to two separate pre-emulsion tanks, and shear at 3000 rpm for 30 min to obtain stable oil phase pre-emulsion and aqueous phase pre-emulsion respectively; Dissolve ammonium persulfate in deionized water, stir until completely dissolved, divide into 3 equal portions to prepare initiator solutions I, II and III, and seal for later use.

[0071] Step 2, Seed emulsion preparation: Add all components of the aqueous base liquid to the reaction vessel, purge with nitrogen to remove oxygen for 30 min, stir at 150 rpm, heat to 78-80℃, add 10% aqueous pre-emulsion and 30% initiator solution I, keep warm and react for 30 min to obtain hydrophilic seed emulsion.

[0072] Step 3, Asymmetric Emulsion Polymerization: Maintain the reaction temperature at 80-82℃. First, add all the oil phase pre-emulsion to the reactor at a uniform rate over 1 hour. After the addition is complete, add the remaining 90% of the aqueous phase pre-emulsion and 40% of the initiator solution II to the reactor at a uniform rate over 1 hour. After the addition is complete, keep the temperature for 30 minutes.

[0073] Step 4, Post-curing: Heat to 85-88℃, add the remaining 30% of initiator solution III, keep the reaction at this temperature for 1.5h, and ensure that the monomer conversion rate is ≥99.5%.

[0074] Step 5, Cooling and Blending: Allow the mixture to cool naturally to below 40°C, add 25% ammonia to adjust the pH of the system to 7.0, filter the mixture through a 200-mesh stainless steel filter, and you will obtain the conventional asymmetric structure acrylate pressure-sensitive adhesive.

[0075] Coating sample preparation and performance testing methods: completely consistent with Example 1. The emulsion showed obvious stratification and flocculation after being stored at room temperature for 1 month, which completely failed to meet the industrial storage requirements of cigarette tipping paper.

[0076] Performance Test Results Summary Table

[0077] Results of long-term storage stability retest after 6 months

[0078] In summary, the above embodiments have stably implemented the technical solution of the present invention, fully covering the formulation and process parameter range within the scope of the claims, and verifying that pressure-sensitive adhesives with significant interfacial asymmetry can be prepared within the A / B phase mass ratio range of 1:(4-9). This simultaneously achieves a synergistic balance between low silicon transfer, high heat resistance, high adhesion performance, and long-term storage stability, fully achieving the intended purpose of the present invention. Comparative Example 1 demonstrates that existing homogeneous pressure-sensitive adhesives cannot resolve the core performance contradictions in this field; Comparative Examples 2-4 demonstrate that only the synchronous equal-endpoint dripping process of the present invention can prepare latex particles with significant interfacial asymmetry, while asynchronous dripping processes can only obtain core-shell structures or random copolymers, failing to achieve the purpose of the invention; Comparative Examples 5-8 demonstrate that exceeding the parameter range defined by the present invention and using conventional modification methods cannot achieve a synergistic balance of multiple properties; Comparative Example 9 demonstrates that existing general-purpose asymmetric emulsions cannot meet the industrial storage requirements of tobacco applications. The present invention overcomes long-standing technical biases in this field and achieves unexpected technical effects.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A water-based acrylic pressure-sensitive adhesive, characterized in that, The waterborne acrylic pressure-sensitive adhesive, by weight, comprises the following raw materials: an A-phase hydrophobic preemulsion, a B-phase hydrophilic preemulsion, an aqueous base liquid, an emulsifier system, and an initiator system, wherein the mass ratio of the A-phase hydrophobic preemulsion to the B-phase hydrophilic preemulsion is 1:(4-9); the A-phase hydrophobic preemulsion contains 2-5 parts of fluorinated acrylate monomers and 8-15 parts of soft acrylate monomers; the B-phase hydrophilic preemulsion contains 60-75 parts of soft acrylate monomers and 5-10 parts of functional monomers; the emulsifier... The system is an anionic nonionic composite emulsifier, which is added to the A-phase hydrophobic pre-emulsion, the B-phase hydrophilic pre-emulsion, and the aqueous base liquid, respectively. The waterborne acrylate pressure-sensitive adhesive is prepared by a phase separation seed semi-continuous polymerization method. Specifically, a hydrophilic seed emulsion is first prepared by using 10% of the B-phase hydrophilic pre-emulsion and part of the initiator system. Then, the remaining B-phase hydrophilic pre-emulsion and all of the A-phase hydrophobic pre-emulsion are added dropwise at the same rate, and the dropwise endpoints of the two phases are controlled to be completely consistent. After polymerization, post-curing, and pH adjustment, the final product is obtained.

2. The water-based acrylic pressure-sensitive adhesive according to claim 1, characterized in that, The fluorinated acrylate monomer is at least one of dodecafluoroheptyl methacrylate and hexafluorobutyl acrylate; the acrylate soft monomer is at least one of butyl acrylate and 2-ethylhexyl acrylate; and the functional monomer is at least two of acrylic acid, hydroxyethyl acrylate, and hydroxyethyl methacrylate.

3. The water-based acrylic pressure-sensitive adhesive according to claim 1, characterized in that, In the synchronous and uniform dripping step, the reaction temperature is controlled at 80-82℃, the dripping time is controlled at 2h, and the stirring speed is stabilized at 150rpm.

4. The water-based acrylic pressure-sensitive adhesive according to claim 1, characterized in that, The raw materials for preparing the water-based acrylate pressure-sensitive adhesive also include an anionic nonionic composite emulsifier, which is a compound of sodium dodecyl sulfate and fatty alcohol polyoxyethylene ether, with a compounding mass ratio of 1:

2.

5. The water-based acrylic pressure-sensitive adhesive according to claim 1, characterized in that, The total solids content of the water-based acrylic pressure-sensitive adhesive is 50%-55%, and the pH value of the finished product is 6.5-7.

5.

6. The water-based acrylic pressure-sensitive adhesive according to claim 1, characterized in that, The post-maturation step is as follows: after the biphase preemulsion is added, the temperature is raised to 85-88℃, the remaining part of the initiator system is added, the reaction is kept at this temperature for 1.5 hours, and the monomer conversion rate is controlled to be ≥99.5%.

7. A pressure-sensitive self-adhesive layer, characterized in that, The pressure-sensitive adhesive layer is formed by coating and curing the water-based acrylic pressure-sensitive adhesive according to any one of claims 1-6.

8. The pressure-sensitive self-adhesive layer according to claim 7, characterized in that, The cured pressure-sensitive adhesive layer has a silicone transfer amount ≤0.2μg / cm³. 2 The holding time at 80℃ is >72h, and the peel strength at 180° is 12-18N / 25mm.

9. A type of tipping paper, characterized in that, It includes a tipping paper base and a pressure-sensitive self-adhesive layer as described in claim 7 or 8, laminated on the back of the tipping paper base.

10. The tipping paper according to claim 9, characterized in that, The dry coating weight of the pressure-sensitive self-adhesive layer is 5-15 g / m². 2 The tipping paper base paper is cigarette tipping paper base paper with a basis weight of 30-50 g / m³. 2 .

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