Bimodal phenolic resin, its preparation method and application

Abstract

This invention discloses a bimodal styrene-acrylic resin, its preparation method, and its applications, belonging to the field of polymer materials. The method for preparing the bimodal styrene-acrylic resin provided by this invention first generates a prepolymer with a certain molecular weight (as a precursor for high molecular weight segments) through semi-continuous bulk polymerization; subsequently, a chain transfer agent is added during the suspension polymerization stage, and the growing polymer chains are quantitatively broken by chain transfer reaction to form low molecular weight segments and generate new active centers; by adjusting the concentration of the chain transfer agent, the short chain length can be controlled, and the bimodal molecular weight distribution of the styrene-acrylic resin can be precisely regulated. This allows for the simultaneous construction of high molecular weight and low molecular weight segments in the same resin system.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a bimodal styrene-acrylic resin, its preparation method, and its applications. Background Technology

[0002] Traditional toner resins (such as styrene-acrylic resin) exhibit a wide molecular weight distribution and are difficult to precisely control when using emulsion or solution polymerization processes. This is fundamentally due to the inherent characteristics of free radical polymerization and the randomness of chain initiation, propagation, and termination. However, in suspension polymerization, monomers are dispersed in the aqueous phase as millimeter- to micrometer-sized droplets under mechanical stirring and the action of dispersants. Each droplet acts as a miniature bulk polymerization reactor. The initiator dissolves within the monomer droplet, creating an environment very close to that of pure monomer bulk polymerization within each monomer droplet. The absence of the large number of emulsifier molecules and complex aqueous phase interfaces found in emulsion polymerization, along with the solvent chain transfer effect of solution polymerization, allows chain transfer reactions to primarily occur on the monomer or pre-added chain transfer agents. By precisely calculating and adding specific chain transfer agents (such as thiols), the average molecular weight can be controlled more directly and effectively, resulting in a more predictable and narrower molecular weight distribution than in emulsion polymerization (which involves complex systems and numerous side reactions).

[0003] While suspension polymerization helps improve the uniformity of product particle size, it still presents challenges in achieving the multi-peak molecular weight distribution required for low-temperature fixing while maintaining good mechanical strength. Common methods for preparing bimodal resins typically rely on multiple polymerizations or physical blending. Multiple polymerizations involve using single or multiple reactors in series with different polymerization conditions, such as varying hydrogen partial pressures, polymer temperatures and times, catalyst control, and changes in comonomer ratios, to obtain a bimodal polymer. Such synthetic processes are cumbersome. Physical blending includes melt blending and solution blending, but physical blending suffers from poor component compatibility. Summary of the Invention

[0004] The present invention aims to provide a method for preparing bimodal styrene-acrylic resin by stepwise coupling; another objective of the present invention is to provide a bimodal styrene-acrylic resin having high molecular weight segments and low molecular weight segments; yet another objective of the present invention is to provide an application of the bimodal styrene-acrylic resin.

[0005] This invention discloses a method for preparing bimodal styrene-acrylic resin, comprising the following steps: S1 Semi-continuous Bulk Polymerization: In an inert gas atmosphere, the first monomer, the first initiator, and the first chain transfer agent are mixed, heated to 60℃-90℃, the second monomer is added dropwise, and polymerization is carried out until the monomer conversion rate reaches 30%-50%. The mixture is then cooled and discharged to obtain the prepolymer. S2 Suspension Polymerization: The prepolymer is dispersed in an aqueous solution containing a dispersant and stirred at high speed to form a suspension dispersion; the third monomer, the second initiator, and the second chain transfer agent are added, and the temperature is controlled at 50℃-55℃, and the polymerization is stirred for 0.5h-1.5h; the temperature is raised to 60℃-80℃, and the polymerization is stirred until the monomer conversion rate is ≥99% to terminate the reaction. The product is then washed, dried, and styrene-acrylic resin is obtained.

[0006] In the semi-continuous bulk polymerization step, a prepolymer with high molecular weight polymer segments is generated. In the suspension polymerization step, the obtained prepolymer is dispersed in an aqueous phase containing a dispersant, and a third monomer, initiator, and chain transfer agent are added. The added initiator can decompose to generate free radicals, which attack the prepolymer molecular chains. The chain transfer agent adjusts the position of chain breaks. Suspension polymerization is carried out in a temperature range of 50℃-80℃, thereby generating low molecular weight polymer segments, forming the basis for the bimodal distribution.

[0007] Furthermore, the first portion of monomers includes hard monomers and soft monomers; the hard monomers are selected from at least one of styrene, α-methylstyrene, acrylic acid, methyl methacrylate, methacrylic acid, maleic anhydride, and dimethylstyrene; the soft monomers are selected from at least one of butyl acrylate, isooctyl acrylate, butyl methacrylate, and lauryl acrylate.

[0008] Furthermore, in the first portion of monomers, the mass ratio of the hard monomer to the soft monomer is (2.9-10):1; the second portion of monomers is selected from all or part of the types of monomers in the first portion; the mass ratio of the second portion of monomers to the first portion of monomers is (0.25-0.85):1.

[0009] Furthermore, the third monomer component includes hard monomers and soft monomers; the types of hard monomers in the third monomer component are the same as or a subset of the types of hard monomers in the first monomer component, and the types of soft monomers in the third monomer component are the same as or a subset of the types of soft monomers in the first monomer component.

[0010] Furthermore, the mass of the hard monomer accounts for 70%-95% of the total mass of the first, second, and third monomer portions; the mass of the soft monomer accounts for 2%-25% of the total mass of the first, second, and third monomer portions; and the ratio of the mass of the third monomer portion to the total mass of the first and second monomer portions is (0.03-0.05):1.

[0011] The relative content of the bimodal components can be adjusted by changing the ratio of the mass of the third monomer to the sum of the masses of the first and second monomers.

[0012] Hard monomers are mainly used to enhance the mechanical properties and thermal stability of resins. After polymerization, they form rigid segments, which, when used in toner systems, help improve the hardness and heat resistance of toners.

[0013] Soft monomers are used to improve the flexibility and flowability of resins, improve the fixing effect of toners at low temperatures, and enhance their applicability in the processing.

[0014] Furthermore, the first initiator includes benzoyl peroxide or azobisisobutyronitrile; the added mass of the first initiator is 0.5%-2% of the sum of the masses of the first monomer and the second monomer; the second initiator is a water-soluble persulfate; the added mass of the second initiator is 0.02%-0.4% of the sum of the masses of the first monomer, the second monomer, and the third monomer.

[0015] In semi-continuous bulk polymerization, oil-soluble initiators, such as benzoyl peroxide (BPO) or azobisisobutyronitrile (AIBN), are used to initiate the polymerization reaction and promote molecular chain growth. In suspension polymerization, water-soluble persulfate initiators are usually used to achieve precise control of the reaction process and regulation of the molecular weight distribution of the product.

[0016] Furthermore, the first or second chain transfer agent comprises dodecyl mercaptan or mercaptoacetic acid; the mass ratio of the first to the second chain transfer agent is (0.6-2):1; the ratio of the total mass of the first and second chain transfer agents to the total mass of the first, second, and third monomers is (0.0015-0.005):1.

[0017] The introduction of chain transfer agents is used to regulate the molecular weight and distribution morphology of polymers. By controlling the timing and amount of their addition, a multi-peak molecular weight distribution of the synthesized resin can be achieved. By using chain transfer agents to synergistically regulate the molecular weight distribution of the two-stage polymerization products, a styrene-acrylic resin with bimodal molecular weight characteristics is ultimately obtained.

[0018] Furthermore, the aqueous solution containing the dispersant comprises water and a dispersant, wherein the dispersant comprises polyvinyl alcohol or hydroxypropyl methylcellulose; the concentration of the dispersant is 0.015%-0.5%; and the D50 of the suspension dispersion is 30 μm-65 μm.

[0019] Dispersants stabilize the suspension and effectively inhibit the aggregation of prepolymer particles in the aqueous phase, ensuring uniform dispersion of the reaction system and thus obtaining polymer particles with a concentrated particle size distribution.

[0020] This invention allows for the control of fixing temperature within a certain range by adjusting the ratio of high molecular weight to low molecular weight molecules, thus adapting to the needs of different fixing equipment.

[0021] The present invention also discloses a bimodal styrene-acrylic resin, which is prepared by the preparation method described above, with a high molecular weight peak weight average molecular weight of 200,000-300,000 and a low molecular weight peak weight average molecular weight of 4,000-20,000; the ratio of the high molecular weight peak weight average molecular weight to the low molecular weight peak weight average molecular weight is 15:1 to 70:1.

[0022] The prepared bimodal styrene-acrylic resin exhibits a synergistic effect between high molecular weight segments and low molecular weight segments. The former imparts mechanical strength to the material, while the latter improves its flowability, resulting in a material with both good mechanical strength and flowability.

[0023] The present invention also discloses a toner comprising the bimodal styrene-acrylic resin described above.

[0024] This invention provides a method for preparing bimodal styrene-acrylic resin. First, a prepolymer with a certain molecular weight is generated through semi-continuous bulk polymerization (serving as a precursor for high molecular weight segments). Then, a chain transfer agent is added during suspension polymerization. Through chain transfer reaction, the growing polymer chains are quantitatively broken, forming low molecular weight segments and generating new active centers. By adjusting the concentration of the chain transfer agent, the short chain length can be controlled, precisely regulating the bimodal molecular weight distribution of the styrene-acrylic resin. This allows for the simultaneous construction of high molecular weight segments (ensuring mechanical strength) and low molecular weight segments (improving melt flowability) within the same resin system. This preparation method simultaneously solves problems such as molecular weight distribution control, compatibility between high and low molecular weight segments, and monomer residue in a single reaction system. The resulting styrene-acrylic resin effectively overcomes the traditional contradiction between low-temperature fixing performance and mechanical strength. Attached Figure Description

[0025] Figure 1 This is a GPC test curve of the styrene-acrylic resin prepared in Example 1. Detailed Implementation

[0026] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] The reagents, methods, and equipment used in the embodiments of this application are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used are commercially available.

[0028] Example 1 Preparation of bimodal styrene-acrylic resin: (1) Semi-continuous bulk polymerization was carried out in a 5 L four-necked glass reactor (equipped with an anchor-type stirrer, a nitrogen inlet pipe, and a ±1℃ temperature control system): 660.0±0.5 g of styrene (with polymerization inhibitor removed using an alkaline alumina column), 30.0±0.1 g of methacrylic acid (vacuum dehydration treatment), 70.0±0.5 g of butyl acrylate, 9.60±0.05 g of recrystallized and purified benzoyl peroxide (BPO), and 1.60±0.01 g of dodecyl mercaptan (DDM) were added sequentially. The mixture was stirred at 150±5 rpm for 30 minutes until homogeneous. A nitrogen inlet pipe was inserted below the liquid surface. Nitrogen gas was first introduced at a flow rate of 200 mL / min for 30 minutes to remove air. Subsequently, the nitrogen flow rate was adjusted to 50 mL / min to maintain the system under positive pressure. Under continuous nitrogen purging, 200 g of styrene was added dropwise at a constant rate of 1.5 mL / min. By controlling the dropping rate, the reaction temperature fluctuations were limited to ±2 °C, while the temperature was increased to 85 ± 0.5 °C at a rate of 2 °C / min. Every 15 minutes during the reaction, 0.5 g of sample was collected, and monomer conversion was monitored by gas chromatography (using an HP-INNOWax column and an FID detector, with a programmed temperature range of 50 °C to 250 °C). After 90 minutes, when the monomer conversion reached 38 ± 1%, the mixture was immediately placed in an ice-water bath to cool to 30 °C, ultimately yielding a viscous prepolymer.

[0029] (2) Suspension polymerization: The prepolymer was transferred to a 10 L stainless steel suspension reactor (three-blade swept-back stirrer), and 4000±10 g of pre-nitrogen-purified deionized water and polyvinyl alcohol aqueous solution were added (the polyvinyl alcohol dry agent was PVA-1788 with a degree of alcoholysis of 88±2%. In order to disperse more evenly in deionized water, 8.00±0.05 g of the dry agent was dissolved in 160 g of pre-nitrogen-purified deionized water to prepare an aqueous solution). The mixture was stirred at a stirring rate of 320±10 rpm for 30 minutes to form a suspension dispersion with a D50 of 50±5 μm (measured by a Malvern Mastersizer 3000 instrument). 20.0±0.1 g of styrene, 20.0±0.1 g of butyl acrylate, freshly prepared ammonium persulfate (APS) aqueous solution (0.20±0.01 g of ammonium persulfate dissolved in 4 g of deionized water) and 2.40±0.01 g of dodecyl mercaptan (DDM) were added. The first stage involved heating to 50±0.5 ℃ and reacting for 30 minutes (stirring at 270 rpm). The second stage involved heating to 65 ℃ at a rate of 0.5 ℃ / min and reacting for 180 minutes (stirring at 220 rpm). The reaction was terminated when the monomer conversion was ≥99% (monitored by gas chromatography). The product was then passed through a 200-mesh stainless steel sieve while still hot, washed three times with 80 ℃ hot water (2 L of hot water added each time), and vacuum dried at 60±2 ℃ for 12 hours to constant weight, yielding a white powder product.

[0030] The obtained white powder was subjected to gel permeation chromatography (GPC) testing, and the test results are as follows: Figure 1 As shown. By Figure 1 It can be seen that the molecular weight of the styrene-acrylic resin prepared in Example 1 exhibits a bimodal distribution: the high molecular weight peak weight average molecular weight Mw1 = 250,000, and the low molecular weight peak weight average molecular weight Mw2 = 16,700, with a ratio of Mw1 / Mw2 = 15:1. The high molecular weight fraction provides mechanical strength to the styrene-acrylic resin, while the low molecular weight fraction is beneficial for improving the flowability of the styrene-acrylic resin and its miscibility with fillers, charge agents, etc., which is advantageous for processing into toner.

[0031] Example 2 Preparation of bimodal styrene-acrylic resin: (1) Semi-continuous bulk polymerization was carried out in a 5 L four-necked glass reactor: 367.5±0.3 g of styrene (treated with an alkaline alumina column), 15.0±0.1 g of maleic anhydride (vacuum dehydrated at 40 ℃ for 4 h), 50.0±0.5 g of butyl methacrylate, 4.50±0.01 g of recrystallized azobisisobutyronitrile (AIBN), and 0.90±0.01 g of mercaptoacetic acid were added sequentially. The mixture was stirred at a stirring rate of 150±5 rpm for 10 minutes until homogeneous. Then, a constant pressure dropping funnel was installed and 367.5±0.3 g of styrene was added. Nitrogen gas was introduced below the liquid surface (nitrogen flow rate of 200 mL / min, for 30 minutes) to replace the air. After that, the nitrogen flow rate was maintained at 50 mL / min to obtain a positive nitrogen pressure. The temperature was increased to 75±0.5 ℃ at a heating rate of 3 ℃ / min, and the remaining styrene was added dropwise at a constant rate of 3.68±0.05 g / min. 0.5 g of sample was taken every 20 minutes, and the monomer conversion rate was monitored by gas chromatography. After the monomer conversion rate reached 40±1% at 100 minutes, the mixture was rapidly cooled to 30 ℃ in an ice-water bath to obtain the prepolymer.

[0032] (2) Suspension polymerization: The prepolymer was transferred to a 10 L stainless steel suspension reactor (three-blade swept-back stirrer), and 4200±10 g of deionized water pre-purged with nitrogen and deoxygenated was added, along with an aqueous solution of hydroxypropyl methylcellulose (HPMC viscosity is 4000 cps; 6.70±0.05 g of dry agent was dissolved in 200 g of pre-purged deionized water to prepare an aqueous solution). The mixture was dispersed at a stirring rate of 380±10 rpm for 35 minutes to form a suspension dispersion with a D50 of 35±5 μm (measured using a Malvern Mastersizer 3000). 15.0±0.1 g of styrene, 10.0±0.1 g of butyl methacrylate, an aqueous solution of potassium persulfate (0.30±0.01 g of potassium persulfate dissolved in 6 g of deionized water), and 0.70±0.01 g of mercaptoacetic acid were then added. The first stage involved heating to 55±0.5 ℃ and reacting for 40 minutes (stirring at 300 rpm). The second stage involved heating to 70 ℃ at a rate of 0.4 ℃ / min and reacting for 200 minutes (stirring at 250 rpm). The reaction was terminated when the monomer conversion was ≥99% (monitored by gas chromatography). The product was washed three times with 80 ℃ hot water (2 L each time) and dried under vacuum at 60±2 ℃ for 12 hours to obtain a white powder product.

[0033] Example 3 Preparation of bimodal styrene-acrylic resin: (1) Semi-continuous bulk polymerization was carried out in a 5 L four-necked glass reactor: 52.5±0.3 g of acrylic acid (hard monomer, vacuum dehydrated), 22.5±0.1 g of methacrylic acid (hard monomer), 25.0±0.3 g of isooctyl acrylate (soft monomer), 3.60±0.01 g of recrystallized azobisisobutyronitrile (AIBN), and 0.80±0.01 g of dodecyl mercaptan (DDM) were added. The mixture was stirred at 160±5 rpm for 10 minutes. A constant pressure dropping funnel was installed and filled with 52.5±0.3 g of acrylic acid, 22.5±0.1 g of methacrylic acid, and 25.0±0.3 g of isooctyl acrylate. Nitrogen gas was introduced below the liquid surface (at a flow rate of 200 mL / min for 30 minutes), and then the flow rate of nitrogen was adjusted to 40 mL / min to maintain positive nitrogen pressure. The temperature was increased to 60±0.5 ℃ at a heating rate of 1.5 ℃ / min, and the remaining monomer was added dropwise at a constant rate of 1.33±0.02 g / min. 0.4 g samples were taken every 25 minutes, and the monomer conversion rate was monitored by gas chromatography. The monomer conversion rate was 33±1% at 138 minutes. The mixture was cooled to 25 ℃ in an ice-water bath to obtain the prepolymer.

[0034] (2) Suspension polymerization: The prepolymer was transferred to a 10 L suspension reactor, and 4500 g of deionized water (mass deviation controlled within ±10 g) and hydroxypropyl methylcellulose (HPMC viscosity 6000 cps, 19.80±0.05 g dry agent, the dry agent was first dissolved in 4500 g of deionized water) were added. Then, it was dispersed at a stirring rate of 360±10 rpm for 40 minutes to form a suspension system with a particle size D50 of 48±3 μm. Then, 15.0±0.1 g of acrylic acid, 10.0±0.1 g of isooctyl acrylate, ammonium persulfate aqueous solution (containing 0.45±0.01 g of ammonium persulfate and 10.5 g of water) and 0.40±0.01 g of dodecyl mercaptan (DDM) were added in sequence. The reaction was carried out in two stages: In the first stage, the temperature was raised to 52±0.5 ℃, and the reaction was stirred at 300 rpm for 44 minutes. In the second stage, the temperature was raised to 80±0.5 ℃ at 0.6 ℃ / min, the stirring rate was adjusted to 220 rpm, and the reaction was continued for 186 minutes until the monomer conversion rate was not less than 99%. After the reaction, the product was washed four times with 2.4 L of hot water at 87 ℃ each time, and then vacuum dried at 60±2 ℃ for 14 h to constant weight. The resulting pale yellow powder was the target styrene-acrylic resin.

[0035] Example 4 Preparation of bimodal styrene-acrylic resin: (1) Semi-continuous bulk polymerization was carried out in a 5 L four-necked glass reactor: 340.0±0.3 g of dimethylstyrene (hard monomer) (dehydrated by 4 Å molecular sieve for 48 hours), 35.0±0.1 g of acrylic acid (hard monomer), 85.0±0.5 g of lauryl acrylate (soft monomer), 4.00±0.01 g of recrystallized benzoyl peroxide (BPO), and 1.20±0.005 g of dodecyl mercaptan (DDM) were added. The mixture was stirred at 160±5 rpm for 10 minutes. A constant pressure dropping funnel was installed and 340.0±0.3 g of dimethylstyrene was added. Nitrogen gas was continuously introduced below the liquid surface (200 mL / min, 40 minutes), and then the nitrogen flow rate was adjusted to 60 mL / min to maintain positive pressure in the system. The mixture was then slowly heated to 90±0.5 °C at a rate of 1 °C per minute, while the remaining monomers were added dropwise at a constant rate of 2.27±0.03 g / min. During the reaction, 0.5 g samples were taken every 30 minutes, and the monomer conversion was monitored using gas chromatography (DB-WAXetr column, dimethylstyrene retention time 14.2 minutes). When the reaction proceeded to 150 minutes and the monomer conversion rate reached 42±1%, the system was immediately cooled to 25 °C in an ice-water bath to finally obtain the prepolymer.

[0036] (2) Suspension polymerization: The prepolymer was transferred to a 10 L suspension reactor, and 5000±10 g of deionized water (pre-purified with nitrogen) and polyvinyl alcohol (PVA-1788, degree of alcoholysis 88%, 3.00±0.03 g of dry agent was first dissolved in 5000 g of pre-purified with nitrogen) were added. The mixture was dispersed at a stirring rate of 340±10 rpm for 50 minutes to form a suspension dispersion with a D50 of 60±5 μm. 40.0±0.1 g of dimethylstyrene, 15.0±0.1 g of lauryl acrylate, potassium persulfate solution (0.22±0.01 g of potassium persulfate dissolved in 4.4 g of water) and 2.80±0.005 g of DDM were added. The first stage involved heating to 50±0.5 ℃ and reacting for 60 minutes (stirring rate 260 rpm). The second stage involved heating to 80±0.5 ℃ at a rate of 0.3 ℃ / min and reacting for 240 minutes (stirring rate 170 rpm). The reaction was terminated when the monomer conversion was ≥99% (monitored by gas chromatography). The sample was washed five times with 90 ℃ hot water (2 L of hot water each time) and then vacuum dried at 65±2 ℃ for 16 hours to constant weight, yielding a off-white powder.

[0037] Example 5 Preparation of bimodal styrene-acrylic resin: (1) Semi-continuous bulk polymerization was carried out in a 5 L four-necked glass reactor: 312.0±0.3 g of styrene (hard monomer) (treated with alkaline alumina), 80.0±0.1 g of methacrylic acid (hard monomer), 96.0±0.5 g of butyl acrylate (soft monomer), 10.67±0.02 g of recrystallized azobisisobutyronitrile (AIBN), and 2.40±0.02 g of mercaptoacetic acid were added. The mixture was stirred at a stirring rate of 170±5 rpm for 10 minutes until homogeneous. A constant pressure dropping funnel was installed and 312.0±0.3 g of styrene was added. Nitrogen gas was introduced below the liquid surface at a flow rate of 250 mL / min for 35 minutes. The flow rate of nitrogen was then adjusted to 70 mL / min to maintain positive pressure. The temperature was increased to 70±0.5 ℃ at a heating rate of 2.5 ℃ / min, and the remaining styrene was added dropwise at a constant rate of 3.47±0.05 g / min. 0.5 g samples were taken every 10 minutes, and the monomer conversion rate was monitored by gas chromatography (DB-1701 column, styrene retention time 7.9 min). The monomer conversion rate was 35±1% at 70 minutes. The mixture was then cooled to 20 ℃ in an ice-water bath to obtain the prepolymer.

[0038] (2) Suspension polymerization: The prepolymer was transferred to a 10 L suspension reactor, and then approximately 4800 g of deionized water (controlled to an accuracy of ±10 g) and polyvinyl alcohol (PVA-1788, degree of alcoholysis 88%, first dissolved 19.20±0.10 g of dried polyvinyl alcohol in deionized water) were added. The mixture was then dispersed at a stirring rate of 400±10 rpm for 30 minutes to obtain a suspension with a particle size D50 of 40±3 μm (measured using a Malvern Mastersizer 3000, opacity 15%). Subsequently, 20.0±0.1 g of styrene, 4.0±0.1 g of butyl acrylate, an aqueous solution of ammonium persulfate (prepared from 2.88±0.02 g of ammonium persulfate and 57.6 g of deionized water), and 1.60±0.02 g of mercaptoacetic acid were added to the reaction system. The first stage reaction was carried out at 50±0.3 ℃ for 50 minutes (stirring at 320 rpm). The second stage reaction was carried out at a rate of 0.8 ℃ / min, increasing the temperature to 75±0.5 ℃ and reacting for 150 minutes (stirring at 220 rpm). The reaction was terminated when the monomer conversion reached ≥99% (monitored by gas chromatography). The sample was washed four times with 75 ℃ hot water (2.2 L each time) and then vacuum dried at 60±2 ℃ for 18 hours to constant weight (mass change <0.05%), yielding a milky white powder.

[0039] Comparative Example 1 BASF JONCRYL® 67 styrene-acrylic resin: Appearance: Transparent granular solid; Solid content: 98.6%; Molecular weight: 13000; Acid value: 213; Tg: 73 ℃; Softening point: 143 ℃.

[0040] Performance testing: The performance of the styrene-acrylic resins obtained in the examples and comparative examples was tested. First, differential scanning calorimetry (DSC) was used to analyze their glass transition temperature (Tg); the ring and ball method was used to determine the softening point (Tm); and the molecular weight data was characterized by gel permeation chromatography (GPC). Dynamic thermomechanical analysis (DMA) was used at a temperature range of 30–150 °C and a frequency of 1 Hz to evaluate the resin's rigidity (strength) and damping characteristics (toughness). Resin powder was hot-pressed into specimens conforming to ASTM D256 standard dimensions (typically rectangular strips with specified notches), and after conditioning in a standard laboratory environment for at least 24 hours, cantilever beam notched impact strength tests were performed. The solubility and viscosity of the resin in toluene (non-polar) and ethyl acetate (polar) were determined to indirectly evaluate its compatibility with carbon black and charge modifiers of different polarities.

[0041] Subsequently, the styrene-acrylic resins obtained in the examples and comparative examples were compounded with carbon black and charge control agents according to conventional processes to obtain toner samples. Using a fixing tester, the toner was uniformly coated onto the surface of standard paper, and the temperature of the fixing roller was gradually reduced until the image fastness was ≥95%, thus determining the minimum fixing temperature for the toner sample. Using a microforce tester, 50 resin particles with similar particle sizes (D50≈12μm) were randomly selected, and the force they experienced when crushed was measured, and the average value was calculated. This method directly simulates the ability of toner particles to withstand mechanical stress during transport and development. The prepared toner samples were placed in sealed glass bottles and stored in a 50°C oven for 21 days (accelerated aging). Before and after storage, their charge (Q / M) was measured, the charge decay rate was calculated, and the retention rate of working performance after long-term storage was evaluated. The results are summarized in Table 1.

[0042] Table 1 Performance Test Results

[0043] As shown in Table 1, compared with the commercially available typical product JONCRYL® 67, the bimodal styrene-acrylic resins provided in the five embodiments of the present invention exhibit fundamental performance differences and significant advantages, and the performance of each embodiment is controllable by adjusting the formulation parameters.

[0044] First, the molecular structure and performance design philosophies differ. JONCRYL® 67 is a single low molecular weight, high acid value resin that relies on high polarity to provide adhesion, but suffers from poor mechanical strength and contradictory thermal stability. All embodiments of this invention utilize a bimodal molecular weight design, resulting in high strength and high heat resistance (high storage modulus).

[0045] Furthermore, the low-temperature fixing performance offers significant advantages and adjustability. By adjusting the ratio of high and low molecular weight segments (such as the Mw1 / Mw2 ratio), the minimum fixing temperature (MFT from 112℃ to 150℃) can be effectively controlled to meet the needs of different fixing conditions.

[0046] Superior mechanical strength and charge stability. The mechanical properties (storage modulus, impact strength) of all embodiments of the present invention are several times that of JONCRYL® 67. Lower acid values ​​reduce polar end groups, resulting in significantly better charge stability of the prepared toner (charge decay rate ≤12%, far lower than the 35% of the comparative example).

[0047] Finally, considering both balance and designability, this invention successfully resolves the contradictions inherent in traditional resins: "high flowability inevitably sacrifices strength" and "high acid value inevitably leads to hygroscopic and electrically unstable properties." Five embodiments demonstrate that by adjusting parameters such as monomer composition and molecular weight ratio, precise balance and customized design can be achieved among multiple key performance indicators, including low-temperature fixing, mechanical strength, softening point, and charge stability, thereby meeting the stringent requirements of various application scenarios, from ultra-low temperature fixing to high mechanical strength.

[0048] The method for preparing bimodal styrene-acrylic resin disclosed in this invention combines semi-continuous bulk polymerization with suspension polymerization to prepare styrene-acrylic resin with a bimodal molecular weight distribution. This material exhibits excellent low-temperature fixing properties, mechanical strength, and storage stability in toner applications.

[0049] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. 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 modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing bimodal styrene-acrylic resin, characterized in that, Includes the following steps: S1 Semi-continuous Bulk Polymerization: In an inert gas atmosphere, the first monomer, the first initiator, and the first chain transfer agent are mixed, heated to 60℃-90℃, the second monomer is added dropwise, and polymerization is carried out until the monomer conversion rate reaches 30%-50%. The mixture is then cooled and discharged to obtain the prepolymer. S2 Suspension Polymerization: The prepolymer is dispersed in an aqueous solution containing a dispersant and stirred at high speed to form a suspension dispersion; the third monomer, the second initiator, and the second chain transfer agent are added, and the temperature is controlled at 50℃-55℃, and the polymerization is stirred for 0.5h-1.5h; the temperature is raised to 60℃-80℃, and the polymerization is stirred until the monomer conversion rate is ≥99% to terminate the reaction. The product is then washed, dried, and styrene-acrylic resin is obtained.

2. The method for preparing a bimodal styrene-acrylic resin according to claim 1, characterized in that, The first portion of monomers includes hard monomers and soft monomers; the hard monomers are selected from at least one of styrene, α-methylstyrene, acrylic acid, methyl methacrylate, methacrylic acid, maleic anhydride, and dimethylstyrene; the soft monomers are selected from at least one of butyl acrylate, isooctyl acrylate, butyl methacrylate, and lauryl acrylate.

3. The method for preparing a bimodal styrene-acrylic resin according to claim 2, characterized in that, In the first part of the monomers, the mass ratio of the hard monomers to the soft monomers is 2.9-10:1; the second part of the monomers is selected from all or part of the types of monomers in the first part; the mass ratio of the second part of the monomers to the first part of the monomers is 0.25-0.85:

1.

4. The method for preparing a bimodal styrene-acrylic resin according to claim 2, characterized in that, The third part of the monomer includes hard monomers and soft monomers; the types of hard monomers in the third part of the monomer are the same as or a subset of the types of hard monomers in the first part of the monomer, and the types of soft monomers in the third part of the monomer are the same as or a subset of the types of soft monomers in the first part of the monomer.

5. The method for preparing a bimodal styrene-acrylic resin according to claim 4, characterized in that, The mass of the hard monomer accounts for 70%-95% of the total mass of the first, second, and third monomer portions; the mass of the soft monomer accounts for 2%-25% of the total mass of the first, second, and third monomer portions; and the ratio of the mass of the third monomer portion to the total mass of the first and second monomer portions is 0.03-0.05:

1.

6. The method for preparing a bimodal styrene-acrylic resin according to claim 1, characterized in that, The first initiator includes benzoyl peroxide or azobisisobutyronitrile; the added mass of the first initiator is 0.5%-2% of the sum of the masses of the first monomer and the second monomer; the second initiator is a water-soluble persulfate; the added mass of the second initiator is 0.02%-0.4% of the sum of the masses of the first monomer, the second monomer and the third monomer.

7. The method for preparing a bimodal styrene-acrylic resin according to claim 1, characterized in that, The first or second chain transfer agent comprises dodecyl mercaptan or mercaptoacetic acid; the mass ratio of the first chain transfer agent to the second chain transfer agent is 0.6-2:1; the ratio of the total mass of the first and second chain transfer agents to the total mass of the first monomer, the second monomer, and the third monomer is 0.0015-0.005:

1.

8. The method for preparing a bimodal styrene-acrylic resin according to claim 1, characterized in that, The aqueous solution containing a dispersant comprises water and a dispersant, wherein the dispersant comprises polyvinyl alcohol or hydroxypropyl methylcellulose; the concentration of the dispersant is 0.015%-0.5%; and the D50 of the suspension dispersion is 30 μm-65 μm.

9. A bimodal styrene-acrylic resin, characterized in that, Prepared by the preparation method according to any one of claims 1-8, the high molecular weight peak weight average molecular weight is 200,000-300,000, and the low molecular weight peak weight average molecular weight is 4,000-20,000; the ratio of the high molecular weight peak weight average molecular weight to the low molecular weight peak weight average molecular weight is 15:1 to 70:

1.

10. A type of toner, characterized in that, Includes the bimodal styrene-acrylic resin as described in claim 9.

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