Acrylic emulsion for paper glazing oil, and preparation method and application thereof

Abstract

The application discloses a kind of paper gloss oil acrylic emulsion and its preparation method and application, belong to acrylic emulsion technical field, it includes the following component by weight parts: acrylic resin mixture 639.9~700.1 parts, styrene 240~280 parts, deionized water 3~7 parts, first initiator solution 12.7~13.3 parts, second initiator solution 42.7~43.3 parts, third initiator solution 3.8~4.2 parts.Wherein, acrylic resin mixture is by the following component by weight parts: high viscosity acrylic resin liquid 155~175 parts, low viscosity acrylic resin liquid 375~395 parts, surfactant 4.9~5.1 parts, deionized water 105~125 parts.The paper gloss oil acrylic emulsion of the application can make paper gloss oil have the advantages of super high gloss, excellent transparency and extremely fast drying speed simultaneously.

Description

Technical Field

[0001] This invention relates to the field of water-based acrylic emulsion technology, specifically to an acrylic emulsion for paper varnishing, its preparation method, and its application. Background Technology

[0002] Ultra-high gloss, excellent transparency, and extremely fast drying speed are the three core indicators for evaluating the competitiveness of high-end paper varnishes. Water-based acrylic emulsions are currently the core film-forming substance in environmentally friendly paper varnishes.

[0003] To achieve high gloss and transparency, traditional water-based acrylic emulsions typically require a low glass transition temperature (Tg < 50°C) and the addition of film-forming aids. This allows the latex particles to fully deform and fuse at room temperature or lower to form a continuous, smooth film. However, a low Tg results in a softer film, and its drying process involves coagulation, fusion, and densification, gradually closing off moisture escape channels and leading to slow drying. To improve drying speed, the industry has attempted to increase the Tg of the emulsion. However, high-Tg, rigid latex particles are difficult to deform and fuse under conventional drying conditions. Their minimum film-forming temperature is far higher than the paper's tolerance temperature or incompatible with existing drying equipment, resulting in discontinuous film formation. The film appears powdery and rough, severely compromising gloss and transparency. In such cases, although the drying speed may be improved due to the presence of pores between particles, the most basic aesthetic effect is sacrificed, making it unsuitable for high-gloss applications.

[0004] Therefore, it is essential to develop an acrylic emulsion that can simultaneously achieve ultra-high gloss, excellent transparency, and extremely fast drying speed in paper varnishes, as well as its preparation method and applications. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide an acrylic emulsion for paper varnish, so as to solve the problem that traditional water-based acrylic emulsions cannot make paper varnish have ultra-high gloss, excellent transparency and extremely fast drying speed at the same time.

[0006] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0007] An acrylic emulsion for paper varnish comprises the following components in parts by weight: 639.9-700.1 parts of acrylic resin mixture, 240-280 parts of styrene, 3-7 parts of deionized water, 12.7-13.3 parts of a first initiator solution, 42.7-43.3 parts of a second initiator solution, and 3.8-4.2 parts of a third initiator solution;

[0008] The acrylic resin mixture comprises the following components in parts by weight: 155-175 parts of high-viscosity acrylic resin liquid, 375-395 parts of low-viscosity acrylic resin liquid, 4.9-5.1 parts of surfactant, and 105-125 parts of deionized water; the high-viscosity acrylic resin liquid has a viscosity of 2000-2500 mPa•s and a pH value of 8.0-9.0, and the low-viscosity acrylic resin liquid has a viscosity of 200-600 mPa•s and a pH value of 8.0-9.0.

[0009] In a preferred embodiment of the present invention, the solid content of the high-viscosity acrylic resin liquid is 30±1%; the solid content of the low-viscosity acrylic resin liquid is 30±1%.

[0010] As a preferred embodiment of the present invention, the acrylic emulsion of the present invention further includes the following components in parts by weight: 2.8 to 3.2 parts of propylene glycol and 1.9 to 2.1 parts of preservative solution.

[0011] In a preferred embodiment of the present invention, the first initiator solution is prepared by mixing initiator and deionized water at a weight ratio of 2.7 to 3.3:10; the second initiator solution is prepared by mixing initiator and deionized water at a weight ratio of 2.7 to 3.3:40; and the third initiator solution is prepared by mixing initiator and deionized water at a weight ratio of 0.8 to 1.2:3.

[0012] In a preferred embodiment of the present invention, the initiator is sodium persulfate and / or potassium persulfate.

[0013] In a preferred embodiment of the present invention, the surfactant is sodium dodecyl sulfate and / or sodium dodecylbenzenesulfonate.

[0014] In a preferred embodiment of the present invention, the preservative solution is prepared by mixing preservative and deionized water in a weight ratio of 0.9 to 1.1:1.

[0015] In a preferred embodiment of the present invention, the preservative is 1,2-benzisothiazolin-3-one and / or methylisothiazolinone.

[0016] The present invention also provides a method for preparing the above-mentioned acrylic emulsion for paper varnishing, which includes the following steps:

[0017] S1. Add the acrylic resin mixture to the reactor, stir and heat to 78~82℃ to obtain the first reactant;

[0018] S2. Add 4-6% of the total amount of styrene to the first reactant within 8-12 minutes. After the addition is complete, continue to add the first initiator solution. The addition is completed within 18-22 minutes to obtain the second reactant.

[0019] S3. Add the remaining styrene dropwise to the second reactant within 3.85~4.15h. After the addition is complete, continue to add the second initiator solution dropwise. The addition is completed within 4~4.3h to obtain the third reactant.

[0020] S4. Rinse the pipeline with deionized water to remove residual monomers, add the rinsed deionized water to the third reactant, add the third initiator solution dropwise, and keep warm at 86~88℃ for 55~65min to obtain the fourth reactant.

[0021] S5. Cool the fourth reactant to 73~77℃, evacuate for 25~35 minutes to completely remove trace amounts of styrene monomer, continue cooling to 36~40℃, discharge and filter to obtain the acrylic emulsion for paper varnish.

[0022] In a preferred embodiment of the present invention, step S5 further includes adding propylene glycol and preservative solution sequentially after vacuuming and stirring until homogeneous.

[0023] The present invention also provides the application of the above-mentioned acrylic emulsion for paper varnish in the preparation of inks or varnishes.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention first uses high-viscosity and low-viscosity acrylic resin solutions as reaction substrates. The high-molecular-weight segments of the high-viscosity acrylic resin solution provide a rigid framework for the final latex particles, while the low-viscosity acrylic resin solution, with its lower molecular weight and shorter segments, dissolves or swells better in water, acting as a solubilizer and adjusting the initial viscosity. The combination of the two effectively ensures the uniformity and stability of the reaction substrate, laying the foundation for the subsequent generation of latex particles with regular structure and uniform particle size. Then, a small amount of styrene and a first initiator solution are used to graft copolymerize styrene with the active sites on the resin chain. In the main polymerization stage, the remaining styrene and a second initiator solution are added to allow the hard monomer styrene to grow slowly and controllably on uniform monomers, further enhancing the particle rigidity (Tg of 110℃) and structural density, generating latex particles with highly uniform particle size and dense structure. Finally, by adding a third initiator solution and maintaining the temperature, small molecule migration of residual monomers during storage or film formation is prevented, which could lead to storage instability or haze or whitening of the paint film.

[0026] The emulsion of this invention possesses high Tg (110°C) and high MFFT (90°C) hardness properties. When the drying temperature is below the minimum film-forming temperature, the latex particles remain hard and undeformed, and moisture escapes rapidly through the microscopic pore network between the particles, achieving physical fast drying. When the drying temperature is above the minimum film-forming temperature, the latex particles in the emulsion soften and fuse instantly, forming a smooth and continuous paint film with a mirror-like finish. The gloss level can reach over 90 GU at 60°, and the paint film is clear and transparent, without obscuring the substrate pattern. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments.

[0028] The acrylic emulsion for paper varnish provided by this invention comprises the following components by weight: 639.9-700.1 parts of acrylic resin mixture, 240-280 parts of styrene, 3-7 parts of deionized water, 12.7-13.3 parts of first initiator solution, 42.7-43.3 parts of second initiator solution, and 3.8-4.2 parts of third initiator solution;

[0029] The acrylic resin mixture comprises the following components by weight: 155-175 parts of high-viscosity acrylic resin liquid, 375-395 parts of low-viscosity acrylic resin liquid, 4.9-5.1 parts of surfactant, and 105-125 parts of deionized water. The high-viscosity acrylic resin liquid has a viscosity of 2000-2500 mPa•s, a pH value of 8.0-9.0, and a solid content of 30±1%, while the low-viscosity acrylic resin liquid has a viscosity of 200-600 mPa•s, a pH value of 8.0-9.0, and a solid content of 30±1%.

[0030] In the above formulation, the first initiator solution is prepared by mixing the initiator and deionized water at a weight ratio of 2.7~3.3:10. The second initiator solution is prepared by mixing the initiator and deionized water at a weight ratio of 2.7~3.3:40. The third initiator solution is prepared by mixing the initiator and deionized water at a weight ratio of 0.8~1.2:3. The initiator is sodium persulfate and / or potassium persulfate. The surfactant is sodium dodecyl sulfate and / or sodium dodecylbenzenesulfonate. The preservative solution is prepared by mixing the preservative and deionized water at a weight ratio of 0.9~1.1:1. The preservative is 1,2-benzisothiazolin-3-one and / or methylisothiazolinone.

[0031] The acrylic emulsion for paper varnish is prepared according to the following steps:

[0032] S1. Add the acrylic resin mixture to the reactor, stir and heat to 78~82℃ to obtain the first reactant.

[0033] In step S1, the acrylic resin mixture utilizes a high-viscosity, high-molecular-weight acrylic resin to provide a rigid framework, while the low-viscosity acrylic resin liquid acts as a solubilizer and adjusts the initial viscosity. The surfactant reduces surface tension in the initial stage, allowing the oil phase (resin) to disperse better in water, forming tiny micelles that provide sites for subsequent monomer polymerization and ensure the kinetic stability of the entire polymerization process, preventing demulsification and aggregation. Heating the system to 78-82°C allows for the effective decomposition of the subsequent initiator, providing the necessary activation energy for the polymerization reaction.

[0034] S2. Add 4-6% of the total amount of styrene to the first reactant within 8-12 minutes. After the addition is complete, continue to add the first initiator solution. The addition is completed within 18-22 minutes to obtain the second reactant.

[0035] In step S2, the small amount of styrene added first permeates and swells the acrylic resin, while the first initiator added later decomposes to generate free radicals, which in turn triggers graft copolymerization of styrene with the active sites on the resin chain. At the same time, homopolymerization of styrene itself also occurs, ensuring that a large number of uniform latex particles are generated instantaneously in the early stage of the reaction. This is beneficial to improve the high uniformity of the final emulsion particle size, laying the physical basis for achieving ultra-high gloss and high transparency. It effectively avoids the problems of wide particle size distribution and secondary nucleation caused by traditional one-time feeding or feeding in the opposite order.

[0036] S3. Add the remaining styrene dropwise to the second reactant within 3.85~4.15h. After the addition is complete, continue to add the second initiator solution dropwise. The addition is completed within 4~4.3h to obtain the third reactant.

[0037] Step S3 is the main polymerization stage. The remaining styrene and the second initiator solution continue to polymerize on the already formed seeds, allowing the latex particles to grow further and form the final structure. This effectively strengthens the rigidity of the latex particles, achieving a Tg of 110℃ and a minimum film-forming temperature of 90℃. This ensures the latex particles remain hard and undeformed until the drying temperature reaches 90℃, creating a microporous network that permeates the paint film, allowing moisture to escape quickly and achieving rapid physical drying. By controlling the dropping rate, the free monomer in the reactor is kept at a low concentration. When monomer molecules enter the system, they rapidly polymerize on the latex particles without nucleating themselves to form new particles, thus maintaining high particle size uniformity. Furthermore, slow dropping and constant temperature control avoid concentrated release of polymerization heat, ensuring a stable and controllable reaction.

[0038] S4. Rinse the pipeline with deionized water to remove residual monomers, add the rinsed deionized water to the third reactant, add the third initiator solution dropwise, and keep warm at 86~88℃ for 55~65 min to obtain the fourth reactant.

[0039] Step S4 uses deionized water as flushing water to flush the residual monomers in the pipeline into the reactor. This reduces material waste and the subsequent cleaning burden. On the other hand, the reaction conversion rate is maximized under the action of the third initiator solvent and heat preservation. This avoids the migration of small molecules of residual monomers during storage or film formation, reduces the instability of later storage, and prevents the paint film from becoming cloudy or white.

[0040] S5. Cool the fourth reactant to 73~77℃, evacuate for 25~35 minutes to completely remove trace amounts of styrene monomer, continue cooling to 36~40℃, discharge and filter to obtain the acrylic emulsion for paper varnish.

[0041] In step S5, residual styrene monomer is removed by vacuuming to prevent it from acting as an internal plasticizer, lowering the Tg and minimum film-forming temperature, and consequently reducing the fast-drying performance. Filtering the discharged material removes any trace amounts of gel or impurities that may be generated during the reaction, preventing them from becoming defects on the paint film surface and causing a decrease in gloss.

[0042] When the acrylic emulsion also includes propylene glycol and a preservative solution, in step S5, after vacuuming, propylene glycol and the preservative solution are added sequentially and stirred until homogeneous. Propylene glycol, as a freeze-thaw stabilizer, prevents ice crystal formation and growth at low temperatures, disrupting the latex particle structure and thus protecting the emulsion's storage stability at low temperatures. The preservative prevents microbial contamination and damage to the emulsion during storage, further ensuring storage stability.

[0043] Example 1

[0044] An acrylic emulsion for paper varnish, the raw materials for which are prepared include the following components in parts by weight: 670 parts of acrylic resin mixture, 260 parts of styrene, 5 parts of deionized water, 13 parts of first initiator solution, 43 parts of second initiator solution, 4 parts of third initiator solution, 3 parts of propylene glycol, and 2 parts of preservative solution.

[0045] The acrylic resin mixture comprises the following components by weight: 165 parts of high-viscosity acrylic resin liquid 8066, 385 parts of low-viscosity acrylic resin liquid 8065, 5 parts of surfactant sodium dodecyl sulfate, and 115 parts of deionized water. The first initiator solution includes 3 parts of initiator sodium persulfate and 10 parts of deionized water. The second initiator solution includes 3 parts of initiator sodium persulfate and 40 parts of deionized water. The third initiator solution includes 1 part of initiator sodium persulfate and 3 parts of deionized water. The preservative solution includes 1 part of preservative 1,2-benzisothiazolin-3-one and 1 part of deionized water. The high-viscosity acrylic resin liquid has a solid content of 30.3%, a viscosity of 2280 mPa·s, and a pH of 8.4. The low-viscosity acrylic resin liquid has a solid content of 30.1%, a viscosity of 420 mPa·s, and a pH of 8.7.

[0046] The acrylic emulsion for paper varnish in this embodiment is prepared according to the following method:

[0047] S1. Add the acrylic resin mixture to the reactor, stir and heat to 80°C to obtain the first reactant;

[0048] S2. Add 5% styrene to the first reactant within 10 min. After the addition is complete, continue to add the first initiator solution. The addition is completed within 20 min to obtain the second reactant.

[0049] S3. Add the remaining 95% styrene dropwise to the second reactant within 4 hours. After the addition is complete, continue to add the second initiator solution dropwise. The addition is completed within 4.15 hours to obtain the third reactant.

[0050] S4. Rinse the pipeline with deionized water to remove residual monomers, add the rinsed deionized water to the third reactant, add the third initiator solution dropwise, and keep warm at 87°C for 60 min to obtain the fourth reactant.

[0051] S5. Cool the fourth reactant to 75°C and evacuate for 30 minutes to completely remove trace amounts of styrene monomer. Continue cooling to 45°C, add propylene glycol and preservative solution in sequence and stir evenly. Cool to 38°C, discharge and filter to obtain acrylic emulsion for paper varnish.

[0052] Example 2

[0053] An acrylic emulsion for paper varnish, the raw materials for which are prepared include the following components in parts by weight: 639.9 parts of acrylic resin mixture, 240 parts of styrene, 3 parts of deionized water, 12.7 parts of first initiator solution, 42.7 parts of second initiator solution, 3.8 parts of third initiator solution, 2.8 parts of propylene glycol, and 1.9 parts of preservative solution.

[0054] The acrylic resin mixture comprises the following components by weight: 155 parts of high-viscosity acrylic resin liquid 8066, 375 parts of low-viscosity acrylic resin liquid 8065, 4.9 parts of surfactant sodium dodecyl sulfate, and 105 parts of deionized water. The first initiator solution includes 2.7 parts of initiator sodium persulfate and 10 parts of deionized water. The second initiator solution includes 2.7 parts of initiator sodium persulfate and 40 parts of deionized water. The third initiator solution includes 0.8 parts of initiator sodium persulfate and 3 parts of deionized water. The preservative solution includes 0.9 parts of preservative 1,2-benzisothiazolin-3-one and 1 part of deionized water. The high-viscosity acrylic resin liquid has a solid content of 29.7%, a viscosity of 2100 mPa·s, and a pH of 8.0. The low-viscosity acrylic resin liquid has a solid content of 29.1%, a viscosity of 230 mPa·s, and a pH of 8.2.

[0055] The acrylic emulsion for paper varnish in this embodiment is prepared according to the following method:

[0056] S1. Add the acrylic resin mixture to the reactor, stir and heat to 78°C to obtain the first reactant;

[0057] S2. Add 4% styrene to the first reactant within 8 minutes. After the addition is complete, continue to add the first initiator solution. The addition is completed within 18 minutes to obtain the second reactant.

[0058] S3. Add the remaining 96% styrene dropwise to the second reactant within 3.85 hours. After the addition is complete, continue to add the second initiator solution dropwise. The addition is completed within 4 hours to obtain the third reactant.

[0059] S4. Rinse the pipeline with deionized water to remove residual monomers, add the rinsed deionized water to the third reactant, add the third initiator solution dropwise, and keep warm at 86℃ for 55 min to obtain the fourth reactant.

[0060] S5. Cool the fourth reactant to 73°C and evacuate for 25 minutes to completely remove trace amounts of styrene monomer. Continue cooling to 45°C, add propylene glycol and preservative solution in sequence and stir evenly. Cool to 38°C, discharge and filter to obtain acrylic emulsion for paper varnish.

[0061] Example 3

[0062] An acrylic emulsion for paper varnish, the raw materials for which are prepared include the following components in parts by weight: 700.1 parts of acrylic resin mixture, 280 parts of styrene, 7 parts of deionized water, 13.3 parts of first initiator solution, 43.3 parts of second initiator solution, 4.2 parts of third initiator solution, 3.2 parts of propylene glycol, and 2.1 parts of preservative solution.

[0063] The acrylic resin mixture comprises the following components by weight: 175 parts of high-viscosity acrylic resin liquid 8066, 395 parts of low-viscosity acrylic resin liquid 8065, 5.1 parts of surfactant sodium dodecyl sulfate, and 125 parts of deionized water. The first initiator solution includes 3.3 parts of initiator sodium persulfate and 10 parts of deionized water. The second initiator solution includes 3.3 parts of initiator sodium persulfate and 40 parts of deionized water. The third initiator solution includes 1.2 parts of initiator sodium persulfate and 3 parts of deionized water. The preservative solution includes 1.1 parts of preservative 1,2-benzisothiazolin-3-one and 1 part of deionized water.

[0064] The acrylic emulsion for paper varnish in this embodiment is prepared according to the following method:

[0065] S1. Add the acrylic resin mixture to the reactor, stir and heat to 82°C to obtain the first reactant;

[0066] S2. Add 6% styrene to the first reactant within 12 minutes. After the addition is complete, continue to add the first initiator solution. The addition is completed within 22 minutes to obtain the second reactant.

[0067] S3. Add the remaining 94% styrene dropwise to the second reactant within 4.15 hours. After the addition is complete, continue to add the second initiator solution dropwise. The addition is completed within 4.3 hours to obtain the third reactant.

[0068] S4. Rinse the pipeline with deionized water to remove residual monomers, add the rinsed deionized water to the third reactant, add the third initiator solution dropwise, and keep warm at 88°C for 65 min to obtain the fourth reactant.

[0069] S5. Cool the fourth reactant to 77°C and evacuate under vacuum for 35 minutes to completely remove trace amounts of styrene monomer. Continue cooling to 45°C, then add propylene glycol and preservative solution sequentially and stir until homogeneous. Cool to 38°C, discharge, and filter to obtain an acrylic emulsion for paper varnishing. The high-viscosity acrylic resin solution has a solid content of 30.8%, a viscosity of 2480 mPa·s, and a pH of 8.8. The low-viscosity acrylic resin solution has a solid content of 31%, a viscosity of 590 mPa·s, and a pH of 9.0.

[0070] Comparative Example 1

[0071] The difference between this comparative example and Example 1 is that step S2 is omitted, and in step S3, all the styrene is added dropwise to the first reactant within 4 hours. After the addition is complete, a fourth initiator solution is added dropwise. The fourth initiator solution is a mixture of the first and second initiator solutions from Example 1. The addition is completed within 4.15 hours to obtain the second reactant. The amounts of other components and the preparation steps are exactly the same as in Example 1.

[0072] Comparative Example 2

[0073] The difference between this comparative example and Example 1 is that in step S3, the remaining 95% styrene is added dropwise to the second reactant within 3 hours. After the addition is complete, the second initiator solution is added dropwise, and the addition is completed within 3.15 hours to obtain the third reactant. The amounts of other components and the preparation steps are exactly the same as in Example 1.

[0074] Comparative Example 3

[0075] The difference between this comparative example and Example 1 is that the acrylic resin mixture consists of the following components by weight: 365 parts of high-viscosity acrylic resin liquid 8066, 185 parts of low-viscosity acrylic resin liquid 8065, 5 parts of surfactant sodium dodecyl sulfate, and 115 parts of deionized water. The amounts of other components and the preparation steps are exactly the same as in Example 1.

[0076] Comparative Example 4

[0077] The difference between this comparative example and Example 1 is that the acrylic resin mixture consists of the following components by weight: 65 parts of high-viscosity acrylic resin liquid 8066, 485 parts of low-viscosity acrylic resin liquid 8065, 5 parts of surfactant sodium dodecyl sulfate, and 115 parts of deionized water. The amounts of other components and the preparation steps are exactly the same as in Example 1.

[0078] I. Acrylic Emulsion Performance Testing

[0079] The acrylic emulsions prepared in Examples 1-3 and Comparative Examples 1-4 were tested for solid content, acid value, glass transition temperature, minimum film-forming temperature, particle size, film gloss, haze, and initial drying properties. The specific test methods are as follows:

[0080] 1. Solid content: determined according to GB / T 2793-1995;

[0081] 2. The acid value test method refers to the standard GB / T 6743-2008. The acid value is defined as the number of milligrams of potassium hydroxide (KOH) required to neutralize 1g of resin under specified experimental conditions.

[0082] 3. Glass transition temperature (Tg) test method: Measured by differential scanning calorimetry under a nitrogen atmosphere at a heating rate of 10℃ / min. The glass transition temperature (Tg) is the characteristic temperature at which an amorphous polymer transitions from a glassy state to a rubbery state.

[0083] 4. Minimum film-forming temperature (MFFT): Measured according to GB / T 9267;

[0084] 5. Particle size: Determined according to section 6.9 of GB / T 11175-2021. The spectrophotometer method was used. Two parallel measurements were performed on the same sample, and the average value was taken as the final result. The value was retained to one decimal place.

[0085] 6. Gloss: Prepare a sample of the acrylic emulsion according to the wire rod scraping method in GB / T 13217.1-2020 6.1.3. After drying for 24 hours, test the gloss (60°) at three points (top, middle and bottom) on the sample according to GB / T 13217.2-2024. Take the average value of the result.

[0086] 7. Haze: Using a quartz glass plate as the substrate, the acrylic emulsion was prepared into a sample according to the wire rod scraping method in GB / T 13217.1-2020, 6.1.3, and allowed to air dry for 24 hours. The haze was measured according to the haze meter method in GB / T 2410-2008, and calculated using the following formula:

[0087]

[0088] In the formula: T4 is the scattered light flux of the instrument and the sample; T3 is the total scattered light flux through the sample; T2 is the scattered light flux of the instrument; and T1 is the incident light flux.

[0089] Perform two parallel measurements on the same sample and take the average value as the final result, accurate to 0.1%.

[0090] 8. Initial dryness: Determined according to the method in part 5.2 of GB / T 13217.5-2023.

[0091] The results are shown in Table 1.

[0092] Table 1. Performance test results of acrylic emulsions in Examples 1-3 and Comparative Examples 1-4

[0093]

[0094] As shown in Table 1, the acrylic emulsions prepared in Examples 1-3 have high Tg and high MFFT. At the same time, the high solids content of 45±2% reduces the total evaporation water, achieving physical fast drying. The particle size is between 200-300nm, which makes the film surface extremely smooth. The measured 60° gloss is ≥90 GU, and the haze is only ≤3%, achieving high gloss and high transparency. The acid value of 65±2mgKOH / g ensures the haze after film formation. If the acid value is too low, the compatibility of the emulsion will be poor, and micro-phase separation will occur in the wet film. This non-uniform structure will freeze in the dry film and become a permanent scattering center, resulting in increased haze.

[0095] The acrylic emulsion in Comparative Example 1 exhibited increased particle size. This was due to the uncontrollable nucleation after the elimination of seed formation and initiation step S2, resulting in secondary nucleation and ultimately larger particle size, leading to a decrease in MFFT. Decreased molecular chain regularity also caused a slight decrease in Tg. Particle size unevenness further resulted in a rough paint film surface, reduced gloss, and increased haze due to scattering from large internal particles. Simultaneously, the reduced MFFT caused premature particle adhesion, blocking moisture channels and leading to decreased initial drying properties.

[0096] In Comparative Example 2, the acrylic emulsion underwent rapid dropwise addition of styrene monomer during the main polymerization stage. This resulted in an excessively high instantaneous monomer concentration in the reaction system, leading to localized burst polymerization and gelation. This caused the formation of large particles and, moreover, the rapid polymerization embedded some carboxyl groups, lowering the acid value. The molecular chain defects significantly reduced Tg and MFFT. Consequently, the paint film exhibited severely rough surface, extremely low gloss, strong internal scattering, and extremely high haze. Furthermore, the reduced MFFT caused early particle adhesion, blocking moisture channels and resulting in extremely poor initial drying properties.

[0097] In Comparative Example 3, the proportion of high-viscosity resin in the acrylic emulsion was significantly increased. High-viscosity resin molecules have strong rigidity and large molecular weight; excessive use leads to uneven dispersion in the substrate. During subsequent styrene polymerization, rigid steric hindrance restricts uniform monomer diffusion, resulting in a significant increase in latex particle size. The increased proportion of rigid segments further increases Tg and MFFT. Increased particle size causes microscopic undulations on the film surface, decreased gloss, enhanced internal scattering, and increased haze. While increased MFFT helps maintain the drying channel, excessively high MFFT may exceed the drying tunnel's capacity, and the increased particle size itself impairs optical properties, ultimately leading to a decrease in gloss and transparency.

[0098] In Comparative Example 4, the proportion of low-viscosity resin in the acrylic emulsion increased significantly. Low-viscosity resin molecules are flexible, have low molecular weight, and lack sufficient rigid framework support. During polymerization, latex particles easily aggregate and grow, resulting in a significant increase in particle size. The increase in flexible segments significantly reduces Tg and MFFT. Larger particle size leads to a rougher paint film surface, decreased gloss, strong light scattering, and increased haze; simultaneously, the reduced MFFT causes particles to adhere and block moisture channels in the early drying stage, resulting in decreased initial drying properties.

[0099] In summary, the acrylic emulsion for paper varnish of the present invention enables paper varnish to simultaneously possess ultra-high gloss, excellent transparency, and extremely fast drying speed.

[0100] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. An acrylic emulsion for paper varnishing, characterized in that: It includes the following components by weight: 639.9~700.1 parts of acrylic resin mixture, 240~280 parts of styrene, 3~7 parts of deionized water, 12.7~13.3 parts of first initiator solution, 42.7~43.3 parts of second initiator solution, and 3.8~4.2 parts of third initiator solution; The acrylic resin mixture comprises the following components in parts by weight: 155-175 parts of high-viscosity acrylic resin liquid, 375-395 parts of low-viscosity acrylic resin liquid, 4.9-5.1 parts of surfactant, and 105-125 parts of deionized water; the high-viscosity acrylic resin liquid has a viscosity of 2000-2500 mPa•s and a pH value of 8.0-9.0, and the low-viscosity acrylic resin liquid has a viscosity of 200-600 mPa•s and a pH value of 8.0-9.

0.

2. The acrylic emulsion for paper varnishing according to claim 1, characterized in that: It also includes the following components by weight: 2.8 to 3.2 parts of propylene glycol and 1.9 to 2.1 parts of preservative solution.

3. The acrylic emulsion for paper varnishing according to claim 1 or 2, characterized in that: The first initiator solution is prepared by mixing initiator and deionized water at a weight ratio of 2.7~3.3:10; the second initiator solution is prepared by mixing initiator and deionized water at a weight ratio of 2.7~3.3:40; and the third initiator solution is prepared by mixing initiator and deionized water at a weight ratio of 0.8~1.2:

3.

4. The acrylic emulsion for paper varnishing according to claim 3, characterized in that: The initiator is sodium persulfate and / or potassium persulfate.

5. The acrylic emulsion for paper varnishing according to claim 1 or 2, characterized in that: The surfactant is sodium dodecyl sulfate and / or sodium dodecylbenzenesulfonate.

6. The acrylic emulsion for paper varnishing according to claim 2, characterized in that: The preservative solution is prepared by mixing preservative and deionized water in a weight ratio of 0.9 to 1.1:

1.

7. The acrylic emulsion for paper varnishing according to claim 2, characterized in that: The preservative is 1,2-benzisothiazolin-3-one and / or methylisothiazolinone.

8. A method for preparing an acrylic emulsion for paper varnish as described in any one of claims 1 to 7, characterized in that: Includes the following steps: S1. Add the acrylic resin mixture to the reactor, stir and heat to 78~82℃ to obtain the first reactant; S2. Add 4-6% of the total amount of styrene to the first reactant within 8-12 minutes. After the addition is complete, continue to add the first initiator solution. The addition is completed within 18-22 minutes to obtain the second reactant. S3. Add the remaining styrene dropwise to the second reactant within 3.85~4.15h. After the addition is complete, continue to add the second initiator solution dropwise. The addition is completed within 4~4.3h to obtain the third reactant. S4. Rinse the pipeline with deionized water to remove residual monomers, add the rinsed deionized water to the third reactant, add the third initiator solution dropwise, and keep warm at 86~88℃ for 55~65min to obtain the fourth reactant. S5. Cool the fourth reactant to 73~77℃, evacuate for 25~35 minutes to completely remove trace amounts of styrene monomer, continue cooling to 36~40℃, discharge and filter to obtain the acrylic emulsion for paper varnish.

9. The method for preparing the acrylic emulsion for paper varnish according to claim 8, characterized in that: Step S5 also includes adding propylene glycol and preservative solution sequentially after vacuuming and stirring until homogeneous.

10. The use of the acrylic emulsion for paper varnish as described in any one of claims 1 to 7 in the preparation of inks or varnishes.

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