A plasticizing external lubricating acrylate processing aid and its synthesis method

Abstract

This invention discloses a plasticizing-promoting external lubricating acrylate processing aid and its synthesis method. The aid has a four-layer structure from the inside out: a lubricating core layer formed by the polymerization of alkyl methacrylates; an anchoring layer containing reactive polar monomers; a plasticizing shell layer copolymerized from methyl methacrylate and alkyl acrylates; and an external lubricating brush layer grafted in situ onto the outermost surface. This invention utilizes the rheological spatiotemporal coupling between the core and shell to significantly shorten plasticizing time and increase equilibrium torque; it constructs a dual physical and chemical barrier through the anchoring layer, inhibiting core phase migration through physical isolation and chemical bonding; and, combined with surface tension driving the grafted external lubricating brush layer, it overcomes the technical bottleneck of traditional aids failing to simultaneously achieve high plasticizing efficiency and low precipitation, thus achieving efficient demolding.

Description

Technical Field

[0001] This invention belongs to the technical field of acrylate processing aids, specifically a plasticizing-promoting external lubricating acrylate processing aid and its synthesis method. Background Technology

[0002] In PVC processing, external lubricants are indispensable to prevent melt from adhering to equipment or degrading due to localized shear overheating. Traditional systems often rely on small-molecule substances such as stearic acid and polyethylene wax, but these have extremely poor compatibility with the rigid PVC matrix and are prone to freeing, migrating, and precipitating during high-shear processing or product storage. This not only degrades the appearance of the product but also severely delays the resin's polymerization and plasticizing process.

[0003] To overcome the defects caused by the release of small molecules, high-molecular-weight acrylate additives have emerged. However, most commercially available products physically separate the "plasticizing" and "external lubrication" functions, and the multi-component compounding significantly increases the sensitivity of processing and the risk of quality control failure. Therefore, the industry has attempted to develop integrated structural designs, but all have inherent limitations in microstructure construction. For example, Chinese patent publication CN112679669A proposes a dual-core-shell structured external lubricant with a low-molecular-weight polymer as the core and a high-molecular-weight polymethyl methacrylate as the shell. However, this approach only involves simple two-phase physical coating, lacking a chemical anchoring structure to inhibit the outward leakage of the low-molecular-weight lubricating core layer, and also failing to form a directional epitaxial lubrication network on the outermost layer of the particles. In a strong shear flow field, the internal lubricating phase is still easily released and precipitated, which slows down the overall plasticization.

[0004] For example, Chinese Patent Publication No. CN102532394B proposes a segmented emulsion polymerization aid that attempts to achieve early plasticization and late lubrication through the regulation of macroscopic components and molecular weight distribution. However, due to the lack of an interfacial anchoring layer constructed by non-polar reactive groups in the system, and the failure to fix the lubricating components on the outermost surface of the particles by covalent bonding, it still cannot get rid of its dependence on the free-migrating phase and is difficult to form a durable and stable boundary lubrication film.

[0005] In summary, existing polymer processing aids suffer from profound topological defects in their microscopic particle morphology design: they cannot effectively "lock" low-molecular-weight lubricating phases into the lubricating core layer using both chemical and physical barriers within a single polymer particle, while simultaneously achieving precise and covalently oriented grafting of low-surface-energy lubricating phases onto the outermost surface layer. Reconciling the intrinsic contradiction between "plasticization efficiency" and "long-lasting metal stripping (low precipitation)" at the underlying mechanism level constitutes a critical technical bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention proposes a plasticizing-promoting external lubricating acrylate processing aid and its synthesis method. This invention primarily addresses the technical problem that existing processing aids cannot simultaneously achieve high plasticizing efficiency and low free precipitation in a single microparticle.

[0007] According to one aspect of the present invention, a plasticizing-promoting external lubricating acrylate processing aid, wherein the processing aid is a powdered polymer particle obtained by emulsion polymerization followed by drying, and is polymerized from the following components based on 100 parts by weight of the total mass of monomers in each layer before polymerization: Lubricating core layer monomer: 30-40 parts, which is alkyl acrylate or alkyl methacrylate; its polymerization forms the lubricating core layer; Anchoring layer monomer: 5-10 parts, composed of a mixture of monomers including methyl methacrylate, butyl acrylate and reactive polar monomers, which are polymerized and coated on the outside of the lubricating core layer to form an anchoring layer; Plasticizing shell monomer: 45-60 parts, which is polymerized and coated on the outside of the anchoring layer. It is composed of methyl methacrylate and alkyl acrylate monomers containing 4 to 8 carbon atoms. After polymerization, it is coated on the outside of the anchoring layer to form a plasticizing shell. External lubricating brush layer monomer: 1-5 parts, which, after polymerization, is located on the outermost surface of the particles, and is selected from at least one of long-chain alkyl methacrylate monomers containing 12-22 carbon atoms and methacryloxypropyl-terminated polydimethylsiloxane monomers; its polymerization forms an external lubricating brush layer located on the outermost surface of the particles. The anchoring layer comprises structural units with active groups formed by the polymerization of reactive polar monomers; the chain segments formed by the monomers of the outer lubricating brush layer are grafted onto the particle surface through covalent anchor points formed by the active groups exposed in the plasticizing shell.

[0008] Unlike conventional physical blending or simple multilayer coating designs, this application constructs a multi-confined polymer heterogeneous topological architecture at the microscale. The rheological core of this architecture lies in the artificially created molecular weight difference and thermodynamic asymmetry. Under the intervention of the initial temperature field during processing, the lubricating core layer (C4-C8 alkyl acrylate lubricating core layer) with an extremely low fractional free volume is the first to cross the glass transition region, penetrating outwards in an in-situ rheologically excited state. This endogenous chain segment relaxation instantaneously compresses the plasticizing shell layer rich in methyl methacrylate, forcing the originally highly coiled skeletal chain system to complete topological disentanglement under extremely low shear work, thereby establishing a dense force-transferring network with the polyvinyl chloride. This synergistic mechanism fundamentally eliminates the inherent constraint that "external lubrication inevitably leads to delayed plasticization."

[0009] To address the challenge of uncontrolled migration of easily free components, this solution innovatively incorporates a polar gradient anchoring layer at the core-shell interface. On one hand, this transition region, with its dense steric hindrance and cross-linking locking interface, effectively confines the aforementioned high-energy lubricating core layer components within the particle micro-region, forcibly blocking the path of phase-dissociated blooming during room-temperature static storage and later processing. On the other hand, the potentially reactive groups loaded within it construct cross-scale chemical junctions.

[0010] During the latex particle growth stage, the outer lubricating brush layer monomers (long-chain alkyl or organosiloxanes) with extremely low surface free energy are driven by the interfacial potential difference to spontaneously arrange themselves towards the outermost layer to complete the interfacial reconstruction. During the evolution, the lubricating segments not only extend into a high-density anti-adhesion conformation on the particle surface, but also, through the interphase penetration of the molecular backbone, form a steady-state covalent coupling with the hidden active sites in the anchoring layer. This "cross-layer penetration" topological anchoring provides the extremely thin boundary lubricating film with a rigid foundation to resist ultra-high tangential peel stress.

[0011] Thus, the system exhibits a highly adaptive phase response under macroscopic stress: maintaining zero-exudation interface passivation under low shear fields, and precisely releasing internal drag reduction and external metal release efficiency in high-temperature, high-shear melts. Ultimately, without degrading the surface morphology of the hard substrate, it achieves long-term isolation of the processing interface and a significant improvement in plasticization tolerance.

[0012] Preferably, the polymer segments obtained by polymerizing the lubricating core layer monomers have a weight-average molecular weight of 10,000 to 40,000. In the plasticizing shell monomers, methyl methacrylate accounts for 60%-95% of the total weight of the plasticizing shell monomers, and the weight-average molecular weight of the polymer segments obtained by polymerization is 800,000-2,000,000; the weight-average molecular weight is determined by gel permeation chromatography.

[0013] Traditional unimodal or homogeneous additives are often constrained by the intrinsic trade-off between "lubrication and melt tension": excessive emphasis on oligomers can induce melt tension collapse, which can easily lead to molding cracking or cell merging and collapse in complex flow fields; while relying solely on high molecular weight reinforcement will inevitably lead to dry friction heat in the early stages of plasticization, equipment overload, and localized thermo-oxidative degradation.

[0014] To address the aforementioned property antagonism, this application constructs a non-synchronous rheological phase transition gradient spanning tens of times within the microscopic phase region. The lubricating core layer is strictly confined within a specific molecular weight threshold of 10,000 to 40,000. This magnitude precisely anchors the critical balance between initial-state rheological wetting and mesoscopic thermal stability: below this lower limit, oligomers are prone to thermally induced vaporization desorption and free phase separation under thermal conditions, evolving into precipitates on the product surface or internal bubbles; above this upper limit, due to the surge in segment hydrodynamic volume and viscous flow temperature, they lose their leading interfacial slip and drag reduction capabilities on the hard matrix.

[0015] Meanwhile, the outer plasticizing shell is endowed with an ultra-long chain extension profile of 800,000 to 2,000,000. Combined with a methyl methacrylate unit content of 60% to 95%, this layer constructs polymer phase domains that highly coincide with the solubility parameters of PVC. This ultra-high molecular weight network skeleton can deeply topologically entangle the PVC matrix under stress, acting as a strong shear stress transfer hub that forces the resin to disintegrate rapidly; while the few flexible monomer blocks deliberately retained in the formulation effectively avoid the excessive vitrification of pure rigid segments, eliminating the hidden danger of plasticization lag at the source.

[0016] By employing extreme molecular weight differences, a spatiotemporally decoupled rheologically mediated mechanism is essentially established. During the low-enthalpy input phase of the extruder feeding section, the extremely low molecular weight lubricating core layer first transcends the viscous flow state, penetrating into the external high molecular weight hard shell and generating an in-situ solvation plasticizing effect, instantly and significantly reducing the activation energy required for the deentanglement of the ultra-long chain skeleton. This allows the originally rigid plasticizing shell layer to be activated in advance under extremely low temperature field and shear work, thereby rapidly grasping and encapsulating PVC particles.

[0017] As the material moves into the high-shear melting zone, the plasticizing shell has firmly established a high-strength melt support framework. Only then do the efficient sliding properties of the lubricating core layer directionally overflow along the phase interface. This temporal coupled evolution of "oligomeric micronucleus-led solvation activation—ultra-large molecular weight shell hysteretic strong entanglement" reshapes the melting process of polymer blends, exhibiting a comprehensive property tolerance that is difficult for conventional narrow-distribution additives to achieve.

[0018] Preferably, the reactive polar monomer is selected from at least one of glycidyl methacrylate, maleic anhydride, or methacrylic acid; the reactive polar monomer accounts for 8%-12% of the total weight of the anchoring layer monomer.

[0019] During operation, by introducing 8%-12% polar reactive monomers, a highly polar anchoring layer with a significant interfacial tension gradient is first constructed between the low-polarity alkyl acrylate lubricating core layer and the medium- and high-polarity polymethyl methacrylate shell layer. Based on the differences in solubility parameters of polymer chain segments and the steric hindrance effect, this anchoring layer can effectively inhibit the disordered migration and free diffusion of low molecular weight core phase components under thermal drive, blocking the extravasation pathway of low molecular weight substances from both physical and chemical dimensions. Secondly, it provides interfacial covalent anchoring and structural densification: the cross-linked active groups (such as epoxy or carboxyl groups) in the anchoring layer network act as covalent anchor points for interlayer branching reactions, further strengthening the interfacial chemical bonding between adjacent phase regions. This in-situ cross-linked network significantly improves the overall microstructural density, interlayer bonding force, and resistance to thermomechanical degradation under high temperature and high shear field conditions of the polymer multilayer composite particles.

[0020] Preferably, the volume average particle size of the latex particles measured after the emulsion polymerization is 120-180 nm.

[0021] During operation, the monomer segments formed by the polymerization of the outer lubricating brush layer possess extremely low surface energy and spontaneously migrate towards the water-oil interface under the thermodynamic drive of the final stage of emulsion polymerization. At this time, some incompletely converted reactive polar groups (such as epoxy groups, carboxyl groups, etc.) in the anchoring layer or macromolecular free radicals that penetrate to the surface undergo in-situ graft copolymerization with the aforementioned low surface energy monomers. This reaction transforms the physical adsorption state of the outer lubricating segments, which originally depended on extremely weak van der Waals forces, into a covalently tethered state linked by primary valence bonds, constructing a highly stable polymer brush conformation on the particle surface. By limiting the volume average particle size of latex particles to 120-180 nm, the critical specific surface area threshold of the polymer particles in the dispersion system is established. This micro-nano-scale size arrangement not only determines the phase domain distribution state of the particles in the PVC melt but also precisely matches the spatial spreading requirements of 1-5 parts by weight of the outer lubricating brush layer monomers, ensuring that the lubricating segments can form a continuous molecular-level coverage on the particle surface.

[0022] At the optimal dispersion scale of 120-180 nm, covalent bonding forces the low surface energy brush layer segments to move synchronously with the particle skeleton, preventing them from independently diffusing into the melt. When these particles are transported to the metal mold interface with the material flow, the brush layer segments on their surface undergo interfacial adsorption and conformational rearrangement upon contact. With extremely small amounts of additives, a highly continuous and non-removable dynamic boundary lubricating film can be induced between the melt and the metal interface. This "point-to-surface, targeted response" coupling mechanism achieves long-lasting and stable demolding with extremely low lubricant addition. The volume average particle size was determined using the dynamic light scattering method.

[0023] Another aspect of the present invention provides a method for synthesizing a plasticizing external lubricating acrylate processing aid, comprising the following steps: Step 1: Raw material pretreatment and lubricating core layer synthesis. Deionized water and emulsifier are added to the reactor, and lubricating core layer monomer and chain transfer agent are added dropwise. Polymerization reaction is carried out under the action of initiator to obtain the first emulsion. During the nucleation and initial chain growth stages of emulsion polymerization, the quantitative intervention of chain transfer agents forces the chain transfer and termination processes of free radicals in both thermodynamic and kinetic dimensions. This operation precisely truncates the continuous growth of the polymer backbone, strictly limiting the weight-average molecular weight of the basic lubricating phase to an oligomer benchmark of 10,000-40,000. This microscopic conformation endows the layer with extremely high chain segment flexibility and free volume, laying the material basis for subsequent "leading gap slip." Furthermore, this stage establishes highly monodisperse polymer seed crystals with a large specific surface area, providing a uniform physical support substrate for subsequent heterogeneous topological growth.

[0024] Step 2: Anchoring layer synthesis. Once the monomer conversion rate in Step 1 (calculated based on the residual monomer content measured by sampling) reaches 90% or more, anchoring layer monomers are added dropwise to the system for a heat-preserving reaction to obtain the second emulsion. The monomer conversion rate can be determined by sampling and then measuring the residual monomer using gas chromatography or liquid chromatography; or by measuring the change in solid content plus theoretical calculation.

[0025] Step 3: Synthesis of plasticized shell layer. Plasticized shell layer monomers are added dropwise to the second emulsion obtained in Step 2 to carry out copolymerization reaction. During the dropwise addition process, the dropwise addition rate of the plasticized shell layer monomers is controlled to be less than or equal to the polymerization consumption rate of the monomers in the reaction system to maintain the starved feeding conditions and obtain the third emulsion. Step 4: In-situ grafting of the external lubricating brush layer. When the conversion rate of the plasticizing shell layer monomer in Step 3 reaches 85%-90%, the external lubricating brush layer monomer is added at once to carry out the in-situ grafting reaction and obtain the final emulsion. Step 5: Post-processing drying. The final emulsion obtained in Step 4 is spray-dried to obtain processing aid powder.

[0026] At the macroscopic level, this preparation method differs from the extensive approach of traditional batch or homogeneous droplet polymerization. It innovatively introduces a semi-continuous gradient seed emulsion polymerization process based on "spatiotemporal multidimensional decoupling." Its core synthesis mechanism lies in the evolution of the asymmetric hydrophilic-lipophilic balance and thermodynamic phase separation between deeply interwoven monomers. Utilizing kinetic starvation during feeding modulation, it induces the self-assembly and topological epitaxy of polymer domains at the interface. Through the temporal stepwise control of chain termination, interlayer crosslinking, and surface functionalization, it achieves the precise assembly of a highly compatible yet phase-independent "core-anchor-shell-brush layer" quaternary heterostructure within a single nanoscale particle. This inherently endows the composite microparticles with multiple rheological adaptability without the need for post-mixing physical additions.

[0027] Unlike traditional core-shell processes that focus solely on the resting ratio of copolymer monomers and are prone to getting trapped in disordered interpenetrating networks or fuzzy phase boundaries, the conversion rate time-series nodes in this method construct a highly original "kinetic and morphological spatiotemporal coupled response": Anti-permeability interface shaping: By setting a monomer conversion rate of ≥90%, a rigid repulsion boundary of the underlying microphase is forcibly established, which physically blocks the inward dissipation of highly polar monomers and ensures the efficient interface shaping of the polar anchoring layer.

[0028] Anti-embedding active traces: By deliberately retaining 10%-15% of the unconverted monomer residue at the end of the plasticizing shell growth, a "transient reactive active domain" in a viscous flow state is ingeniously constructed on the particle's extreme surface. If the introduction is delayed until the conversion rate reaches its peak (100%), the particle surface will lose its grafting anchor points due to free radical quenching and glassy freezing; conversely, if it is introduced prematurely (e.g., when the conversion rate is <80%), the extremely low surface energy lubricating precursor will inevitably be swallowed and embedded by the surging plasticizing shell monomer phase, resulting in the loss of the metal interface demolding function.

[0029] Preferably, the initiator in step one is a redox initiation system composed of hydrogen peroxide and ascorbic acid; the chain transfer agent is n-dodecyl mercaptan, and its addition amount is 0.5%-6% of the total weight of the lubricating core layer monomer; the polymerization temperature is controlled at 55-60℃.

[0030] The use of hydrogen peroxide and ascorbic acid redox initiation system combined with low temperature conditions of 55-60℃ can effectively reduce the reaction activation energy, avoid high-temperature explosive polymerization, and ensure the stability of primary micelle nucleation. The quantitative introduction of 0.5%-6% n-dodecyl mercaptan forcibly cuts off free radical growth from a kinetic perspective, strictly limiting the weight-average molecular weight of the lubricating core layer to the oligomer range of 10,000-40,000, thus establishing the compliance of the internal lubricating phase.

[0031] Preferably, the anchoring layer monomers are added dropwise in a polar gradient manner, that is, in the first half of the dropwise addition process, only a mixture of methyl methacrylate and butyl acrylate is added dropwise, and in the second half of the dropwise addition process, reactive polar monomers are added dropwise in parallel flow; the temperature of the heat preservation reaction is controlled at 65-70℃.

[0032] The incremental polarity gradient addition method forces reactive polar monomers to accumulate on the outermost surface of the anchoring layer. This process prevents polar groups from being trapped and embedded in the lubricating core layer, and provides the highest density of surface-active anchor points for subsequent capture of the outer lubricating brush layer; the holding temperature of 65-70℃ ensures extremely high conversion rates of crosslinking monomers, forming a dense anchoring layer.

[0033] Preferably, the plasticizing shell monomer is added over a period of 2-5 hours, and the copolymerization reaction temperature is controlled at 65-70℃; the in-situ grafting reaction is carried out at a temperature of 75-80℃ for 0.5-1 hour.

[0034] The slow dripping over 2-5 hours maintained the kinetic starvation state of the polymerization system, ensuring the ultra-high molecular weight and high coverage of the plasticized shell. During the grafting maturation period, the temperature was increased to 75-80℃, which utilized the increased interphase surface tension difference to thermodynamically drive the low surface energy brush layer monomers to rapidly migrate to the water-oil interface of the outermost layer of the particles and complete the covalent grafting.

[0035] Preferably, the inlet air temperature of the spray dryer is controlled at 185-205℃, and the outlet air temperature is controlled at 80-95℃.

[0036] Preferably, the emulsifier is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, or sodium alkyl diphenyl ether disulfonate; the total amount of emulsifier added is 1.0%-3.0% of the total mass of monomers before polymerization of each layer of processing aid.

[0037] By using three types of high-performance anionic surfactants in a specific ratio of 1.0%-3.0%, the polymerization system can be provided with the optimal initial micelle density and spatial electric double-layer repulsion, thereby precisely locking the volume average particle size of the final latex particles within the ideal range of 120-180nm. This is the core particle size indicator to ensure that the additives achieve nanoscale uniform dispersion and efficient plasticization in PVC substrates.

[0038] The beneficial effects of this invention are as follows: 1. This invention artificially creates a rheological time difference within polymer particles by constructing a molecular weight difference of tens of times (a low molecular weight lubricating core layer of 10,000-40,000 and an ultra-high molecular weight plasticizing shell layer of 800,000-2,000,000). In the initial processing stage, the low molecular weight lubricating core layer softens first, penetrating into the outer plasticizing shell layer and acting as an in-situ internal plasticizer, stimulating the movement and activity of the high molecular weight chain segments in the shell layer within a short time. This allows the previously difficult-to-untangle ultra-high molecular weight shell layer to rapidly expand, grasping and promoting the breakage and aggregation of PVC particles; subsequently, a melt network is established, significantly increasing the equilibrium torque. Through the rheological coupling of leading internal plasticizer activation and delayed strong entanglement, the system achieves extremely high melt strength exceeding that of conventional additives while shortening the plasticizing time.

[0039] 2. In this invention, a barrier network with a significant interfacial tension gradient is constructed between a low-polarity lubricating core layer and a high-polarity plasticizing shell layer. Under low-shear conditions during room temperature storage or preheating, this network acts as a barrier, effectively blocking the outward leakage of free substances. When entering the high-temperature, high-shear zone of the extruder, this structure is mechanically torn at specific points, allowing the lubricating efficacy of the core layer to be precisely released to the interface. This intelligent valve control mechanism of "static barrier and dynamic release" enables the product to achieve extremely excellent zero-precipitation stability even with a high proportion of lubricating phase.

[0040] 3. This invention utilizes surface tension to arrange long-chain alkyl or siloxane monomers containing 12-22 carbon atoms at the water-oil interface, and then grafts them in situ using active groups exposed through the anchoring layer. This "cross-layer chemical capture" covalently binds the extremely low surface energy lubricating phase to the outermost surface of the particles via primary valence bonds, forming an extremely stable boundary lubrication layer. Even under heavy-load, high-friction, high-shear extrusion conditions, this outer lubrication brush layer does not detach, significantly reducing the coefficient of friction between the melt and the metal equipment, extending the shutdown and mold-clearing restart cycle by several times, and imparting excellent surface gloss to the product.

[0041] 4. In this invention, by controlling the critical particle size of 120-180 nm, the extremely low content of the lubricating phase is ensured to achieve full coverage from both geometric and specific surface area perspectives. Through the covalent bonding of the anchoring layer, the free degree of freedom of the lubricating phase is confined from an interfacial chemical perspective. This rigid locking of mesoscopic size and microscopic covalent topology allows the polymeric plasticizing shell to deeply participate in the friction and physical entanglement of the PVC matrix, thereby ensuring high plasticizing efficiency. Simultaneously, it confines low surface energy segments to the outer surface of the particles to provide interfacial slip, thus ensuring excellent demolding properties and zero precipitation. Thus, this invention reconciles the intrinsic thermodynamic contradiction between plasticizing and lubrication at a single microscopic particle scale, achieving a substantial technological breakthrough. Detailed Implementation

[0042] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0043] Example 1: Step 1: Raw Material Pretreatment and Synthesis of Lubricating Core Layer: In a reactor, 200g of deionized water and 2.0g of sodium dodecylbenzenesulfonate were added. Nitrogen gas was purged for 30 minutes to remove oxygen, and the temperature was raised to 58°C. The lubricating core layer monomer (containing 25.0g butyl acrylate and 10.0g 2-ethylhexyl acrylate) was mixed thoroughly with 0.875g of n-dodecyl mercaptan. A dropping funnel was opened, and the mixture was added dropwise to the reactor at a uniform rate over 1.5 hours. Simultaneously, the first-stage initiator solution (prepared by dissolving 0.15g hydrogen peroxide and 0.15g ascorbic acid in 20g deionized water) was added dropwise at the same uniform rate over the same 1.5 hours. After the addition was complete, the polymerization reaction was carried out at a constant temperature for 1 hour to obtain the first emulsion. A sample was taken, and the weight-average molecular weight of the polymer segments in this layer was measured to be 28,000.

[0044] Step 2, Anchoring Layer Synthesis: When the monomer conversion rate in Step 1 reaches 92%, a total of 8.0 g of anchoring layer monomers is added dropwise to the system in an increasing polarity gradient manner, with a total dropwise addition time of 1.0 hour. Specifically, for the first 30 minutes, only a mixture of 3.6 g of methyl methacrylate and 3.6 g of butyl acrylate is added dropwise at a uniform rate; for the following 30 minutes, 0.8 g of glycidyl methacrylate (a reactive polar monomer) is added dropwise simultaneously and at a uniform rate in parallel flow. After the addition is complete, the reaction is maintained at 68°C for 1 hour to obtain the second emulsion; in which the reactive polar monomer accounts for 0.8 / 8.0 = 10% of the anchoring layer monomers.

[0045] Step 3: Synthesis of the Plasticizing Shell: Maintaining the system temperature at 68℃, the plasticizing shell monomer (containing 47.0g methyl methacrylate and 8.0g butyl acrylate) was continuously added dropwise to the second emulsion at a constant rate of approximately 15.7g / h, with the total addition time strictly controlled to 3.5 hours. During this addition process, sampling and measurement showed that the mass fraction of free monomer in the reaction system remained below 2.0%, thus ensuring that the monomer addition rate was strictly less than the polymerization consumption rate, achieving starved feeding conditions throughout the process. At this stage, the second-stage initiator solution (prepared by dissolving 0.05g hydrogen peroxide and 0.05g ascorbic acid in 10g deionized water) was added simultaneously and uniformly to maintain reaction activity. After the copolymerization reaction was completed, the mixture was allowed to mature at the specified temperature for 1 hour to obtain the third emulsion. Sampling and measurement revealed that the weight-average molecular weight of the plasticizing shell polymer segments was 1,450,000.

[0046] Step 4: In-situ grafting of the external lubricating brush layer: The system from Step 3 was monitored in real time. When the conversion rate of the plasticizing shell monomer reached 88%, 2.0 g of octadecyl methacrylate was added at once as the external lubricating brush layer monomer. The temperature of the in-situ grafting reaction was then increased and maintained at 78°C for 0.8 hours to obtain the final emulsion. Dynamic light scattering analysis showed that the volume average particle size of the latex particles at this point was 145 nm.

[0047] Step 5, Post-treatment Drying: Cool the final emulsion to below 40°C, add ammonia (alkaline regulator) dropwise to adjust its pH to 7.5, and add an appropriate amount of deionized water to adjust the solid content of the emulsion to 38%. Then send the emulsion into a spray drying tower, control the inlet air temperature to 195°C and the outlet air temperature to 85°C, and collect the dried powder to obtain the processing aid.

[0048] Example 2: Step 1: Raw Material Pretreatment and Synthesis of Lubricating Core Layer: In a reactor, 220g of deionized water and 2.5g of sodium dodecyl sulfate were added. Nitrogen gas was purged for 30 minutes to remove oxygen, and the temperature was raised to 55°C. The lubricating core layer monomer (30.0g butyl acrylate) and 1.2g of n-dodecyl mercaptan were mixed thoroughly. A dropping funnel was opened, and the mixture was added dropwise over 1.5 hours at a uniform rate. Simultaneously, the first-stage initiator solution (prepared by dissolving 0.1g hydrogen peroxide and 0.1g ascorbic acid in 20g deionized water) was added dropwise over the same 1.5 hours. After the addition was complete, the polymerization reaction was carried out at a constant temperature for 1 hour to obtain the first emulsion. A sample was taken, and the weight-average molecular weight of the polymer segments in this layer was measured to be 18,000.

[0049] Step 2, Anchoring Layer Synthesis: When the monomer conversion rate in Step 1 reaches 91%, a total of 6.0 g of anchoring layer monomers is added dropwise to the system in an increasing polarity gradient manner, with a total addition time of 1.0 hour. Specifically, for the first 30 minutes, only a mixture of 2.7 g of methyl methacrylate and 2.7 g of butyl acrylate is added dropwise at a uniform rate; then, for the next 30 minutes, 0.6 g of methacrylic acid (a reactive polar monomer) is added dropwise simultaneously and at a uniform rate in parallel flow. After the addition is complete, the reaction is maintained at 65°C for 1 hour to obtain the second emulsion.

[0050] Step 3: Synthesis of the plasticized shell layer: Maintaining the system temperature at 65℃, the plasticized shell layer monomer (containing 54.0 g methyl methacrylate and 6.0 g butyl acrylate) was continuously added dropwise to the second emulsion at a constant rate of approximately 13.3 g / h. The total addition time was strictly controlled to 4.5 hours to maintain the system in an extremely kinetically starved state, ensuring that the plasticized shell layer polymer obtained ultra-high molecular weight. During this stage, the second-stage initiator solution (prepared by dissolving 0.05 g hydrogen peroxide and 0.05 g ascorbic acid in 10 g deionized water) was added dropwise at a uniform rate to maintain reaction activity. After the copolymerization reaction was completed, the mixture was allowed to mature at this temperature for 1 hour to obtain the third emulsion. The weight-average molecular weight of the shell layer polymer segments was measured to be 1,850,000.

[0051] Step 4: In-situ grafting of the external lubricating brush layer: The system from Step 3 was monitored in real time. When the conversion rate of the plasticized shell monomer reached 86%, 4.0 g of methacryloyloxypropyl-terminated polydimethylsiloxane monomer was added at once as the external lubricating brush layer monomer. The temperature of the in-situ grafting reaction was then increased and maintained at 75°C for 1 hour to obtain the final emulsion. Dynamic light scattering analysis showed that the volume average particle size of the latex particles at this point was 165 nm.

[0052] Step 5, Post-treatment Drying: Cool the final emulsion to below 40°C, add ammonia water dropwise to adjust its pH to 7.5, and add approximately 120g of deionized water to adjust the solid content of the emulsion to 28%. Then, send the emulsion into a spray drying tower, control the inlet air temperature at 185°C and the outlet air temperature at 80°C, and collect the dried powder to obtain the processing aid.

[0053] Example 3: Step 1: Raw Material Pretreatment and Synthesis of Lubricating Core Layer: In a reactor, 180g of deionized water and 1.5g of sodium alkyl diphenyl ether disulfonate were added. Nitrogen gas was purged for 30 minutes to remove oxygen, and the temperature was raised to 60°C. The lubricating core layer monomer (containing 20.0g butyl methacrylate and 20.0g butyl acrylate) was mixed thoroughly with 0.4g of n-dodecyl mercaptan. A dropping funnel was opened, and the mixture was added dropwise over 2.0 hours at a uniform rate. Simultaneously, the first-stage initiator solution (prepared by dissolving 0.2g hydrogen peroxide and 0.2g ascorbic acid in 25g deionized water) was added dropwise over the same 2.0 hours. After the addition was complete, the polymerization reaction was carried out at a constant temperature for 1.5 hours to obtain the first emulsion. A sample was taken, and the weight-average molecular weight of the polymer segments in this layer was measured to be 35,000.

[0054] Step 2, Anchoring Layer Synthesis: When the monomer conversion rate in Step 1 reaches 95%, a total of 10.0 g of anchoring layer monomers is added dropwise to the system in an increasing polarity gradient manner, with a total dropwise addition time of 1.0 hour. Specifically, for the first 30 minutes, only a mixture of 4.6 g of methyl methacrylate and 4.6 g of butyl acrylate is added dropwise at a uniform rate; then, for the next 30 minutes, 0.8 g of maleic anhydride (a reactive polar monomer) is added dropwise simultaneously and at a uniform rate in parallel flow. After the addition is complete, the reaction is maintained at 70°C for 1.5 hours to obtain the second emulsion.

[0055] Step 3: Synthesis of the plasticized shell layer: Maintaining the system temperature at 70℃, the plasticized shell layer monomer (containing 27.0 g methyl methacrylate and 18.0 g butyl acrylate) was continuously added dropwise to the second emulsion at a constant rate of 18.0 g / h, with the total addition time strictly controlled to 2.5 hours to maintain the system in a kinetically starved state. During this stage, the second-stage initiator solution (prepared by dissolving 0.05 g hydrogen peroxide and 0.05 g ascorbic acid in 10 g deionized water) was added dropwise at a uniform rate to maintain reaction activity. After the copolymerization reaction was completed, the mixture was allowed to mature at this temperature for 1 hour to obtain the third emulsion. The weight-average molecular weight of the shell layer polymer segments was measured to be 850,000.

[0056] Step 4: In-situ grafting of the external lubricating brush layer: The system from Step 3 was monitored in real time. When the conversion rate of the plasticizing shell monomer reached 90%, 5.0 g of docosahexamethacrylate was added at once as the external lubricating brush layer monomer. The temperature of the in-situ grafting reaction was then increased and maintained at 80°C for 0.5 hours to obtain the final emulsion. Dynamic light scattering analysis showed that the volume average particle size of the latex particles at this point was 125 nm.

[0057] Step 5, Post-treatment Drying: Cool the final emulsion to below 40°C, add ammonia water dropwise to adjust its pH to 7.2, and add approximately 15g of deionized water to adjust the solid content of the emulsion to 36%. Then, send the emulsion into a spray drying tower, control the inlet air temperature at 205°C and the outlet air temperature at 95°C, and collect the dried powder to obtain the processing aid.

[0058] Comparative Example 1: The difference from Example 1 is that in the second synthesis step, the reactive polar monomer (glycidyl methacrylate) in the anchoring layer monomer formulation is removed and replaced by an equal mass of ordinary methyl methacrylate monomer, while the other raw materials and steps remain unchanged.

[0059] Comparative Example 2 The difference from Example 1 is that in synthesis step four, the feeding and grafting reaction of the external lubricating brush layer monomer (octadecyl methacrylate) are completely eliminated. That is, in step three, after the copolymerization reaction of the plasticizing shell monomer is completely completed, the external lubricating brush layer monomer is not added, and no temperature jump is performed. The process proceeds directly to step five for post-treatment drying, resulting in a conventional polymer powder without the external lubricating brush layer. As a form of compensation, in the final PVC processing performance test, an additional 2.0g of traditional free small molecule polyethylene wax is added via physical blending.

[0060] Comparative Example 3 The difference from Example 1 is that in the first synthesis step (raw material pretreatment and lubricating core layer synthesis), the addition of chain transfer agent (n-dodecyl mercaptan) is completely eliminated, and the free radical chains of the core layer are not forcibly terminated, so that the low molecular weight polymer component of the core layer grows freely into a high molecular weight polymer.

[0061] Comparative Example 4 The difference from Example 1 is that the timing and thermodynamic conditions for adding the outer lubricating brush layer monomer were changed, and the independent delayed grafting operation in step four was eliminated. Specifically, 2g of the outer lubricating brush layer monomer (octadecyl methacrylate) was directly mixed with 55g of the plasticizing shell layer monomer, and then simultaneously and continuously added dropwise at 68°C in step three. After the addition was completed, no new monomer was added, and no temperature jump was performed; the mixture was then kept at 68°C for 0.8 hours to directly obtain the final emulsion.

[0062] Test example: The processing aids obtained in Examples 1-3 and Comparative Examples 1-4 were added to the standard rigid polyvinyl chloride test base formulation at a ratio of 2.0 per 100 parts of resin (based on 100 parts by weight of PVC resin). The base formulation composition (by weight) was: 100 parts of PVC resin (SG-5 type), 4.5 parts of calcium-zinc composite heat stabilizer, 10 parts of calcium carbonate filler, and 4 parts of titanium dioxide.

[0063] The specific steps are as follows: 100 parts of weighed PVC resin and 4.5 parts of calcium-zinc composite heat stabilizer are added to a high-speed mixer. Low-speed mixing is started for 1-2 minutes, then switched to high-speed mixing to utilize frictional heat to raise the material temperature. When the material temperature in the high-speed mixer reaches 80℃-85℃, 10 parts of the weighed calcium carbonate, 4 parts of titanium dioxide, and 2.0 parts of the processing aid to be tested are added sequentially. High-speed mixing continues until the material temperature reaches 115℃-120℃ (i.e., the PVC resin absorbs the aid and reaches the gelation critical point). High-speed mixing is then stopped, and the material is quickly discharged. The discharged high-temperature material is directly introduced into a low-speed cooling mixer with a water-cooled jacket for low-speed cold mixing. The material is discharged when the temperature drops to 40℃-45℃, yielding a dry-mix powder with good flowability. The resulting dry mixtures are allowed to stand at room temperature for 24 hours to eliminate static electricity and balance internal stress, and then used for subsequent rheological and dynamic calendering tests.

[0064] The following standardized performance tests were performed on the mixtures of the above formulations: 1. Torque rheology and plasticizing properties testing (refer to ASTM D2538); The test was conducted using a torque rheometer, with the chamber temperature set at 185℃, the rotor speed at 40 rpm, and the feed amount at 60g.

[0065] Plasticizing time: The time from the initial feeding peak to the plasticizing peak (maximum torque) indicates the speed at which the material melts and coalesces.

[0066] Equilibrium torque: The torque value after plasticization is completed and the system enters the constant shear stage, which directly characterizes the melt strength and viscoelasticity of the system.

[0067] 2. Dynamic thermal stability and metal peeling performance test (demolding time); Dynamic calendering tests were conducted using a two-roll open mill with the roll temperature set at 195℃ and the speed ratio of the front roll to the rear roll at 1:1.2. The time required from when the material was completely plasticized over the rolls until it began to adhere to the surface of the metal rolls and could not be easily peeled off by the scraper was recorded.

[0068] Demolding time: The longer this time, the more stable the boundary lubricating film of the additive at the metal-melt interface, and the better the shear peel resistance and metal demolding performance.

[0069] 3. Accelerate precipitation and blooming assessment; The PVC samples rolled out by the open mill were cut into 5cm×5cm standard blocks and placed in a constant temperature oven at 70℃ for continuous heat aging for 7 days. The surface condition was observed and rated.

[0070] Surface precipitation rating criteria: Grade 0: Perfect surface, without any oil mist or white bloom; Level 1: Very slight fogging, no obvious residue after wiping; Level 3: Visible oil spots or white frost, affecting luster and giving a slippery feel; Level 5: Severe precipitation, with a thick layer of waxy substance forming on the surface or obvious precipitation and dripping.

[0071] The test results for the above test items are shown in the table below. The table below shows the performance test results of the processing aids prepared in Examples 1-3 and Comparative Examples 1-4;

[0072] By comparing and analyzing the data in the table, it can be seen that when the polar reactive monomers in the anchoring layer are removed (Comparative Example 1), although the additive can promote plasticization in the early stage, the lack of a high-polarity barrier network causes the internal low-molecular-weight core phase to become free, resulting in severe grade 3 oil spot precipitation in the aging test. Simultaneously, the outermost brush layer, having lost its covalent anchor points, is rapidly peeled off under the high-shear flow field of the open mill, causing the demolding time to plummet from 48 minutes in Example 1 to 22 minutes. This data confirms the dual core role of the polar anchoring layer in both "confining the core layer" and "tethering the brush layer."

[0073] When the core layer grows to a high molecular weight without the control of a chain transfer agent, it loses its rheological advantages of high fluidity and low glass transition temperature. Because there is no low-molecular-weight lubricating core layer to act as an "in-situ plasticizer" for the plasticizing shell in the early stages of processing, the ultra-high molecular weight plasticizing shell is extremely difficult to disentangle, resulting in a significant delay in plasticizing time to 168 seconds. This data precisely confirms that the "10,000-40,000" low molecular weight limitation in the claims is not arbitrary, but a necessary thermodynamic prerequisite for activating the plasticizing shell and shortening the plasticizing time.

[0074] With identical chemical composition, only the timing of material addition was changed (Comparative Example 4: brush layer monomer and plasticizing shell layer monomer were added simultaneously without delay). The results showed that the demolding time was only 16.8 minutes. This kinetics demonstrates that without specific delayed addition and temperature surge, the low surface energy lubricating monomer would be "buried" inside the particles by a massive amount of shell layer monomer, making it impossible to form an effective polymer brush conformation at the water-oil interface, thus causing the failure of the patent's most critical tribological characteristic.

[0075] The embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A plasticizing external lubricating acrylate processing aid, characterized in that: The processing aid is a powdered polymer particle obtained by drying after emulsion polymerization. It is polymerized from the following components, based on a total mass of 100 parts by weight of monomers in each layer before polymerization: Lubricating core layer monomer: 30-40 parts, which is alkyl acrylate or alkyl methacrylate; Their polymerization forms a lubricating core layer; Anchoring layer monomer: 5-10 parts, composed of a mixture of monomers including methyl methacrylate, butyl acrylate and reactive polar monomers, which are polymerized and coated on the outside of the lubricating core layer to form an anchoring layer; Plasticizing shell monomer: 45-60 parts, composed of methyl methacrylate and alkyl acrylate monomers containing 4 to 8 carbon atoms; after polymerization, it is coated on the outside of the anchoring layer to form a plasticizing shell; External lubricating brush layer monomer: 1-5 parts, which, after polymerization, is located on the outermost surface of the particles, and is selected from at least one of long-chain alkyl methacrylate monomers containing 12-22 carbon atoms and methacryloxypropyl-terminated polydimethylsiloxane monomers; its polymerization forms an external lubricating brush layer located on the outermost surface of the particles. The anchoring layer comprises structural units with active groups formed by the polymerization of the reactive polar monomers; the chain segments formed by the monomers of the outer lubricating brush layer are grafted onto the particle surface through covalent anchor points formed by the active groups exposed in the plasticizing shell.

2. A plasticization-promoted external lubricating acrylate processing aid according to claim 1, characterized in that: The polymer segments obtained by polymerizing the lubricating core layer monomers have a weight-average molecular weight of 10,000 to 40,000. In the plasticizing shell monomer, methyl methacrylate accounts for 60%-95% of the total weight of the plasticizing shell monomer, and the polymer chain segment weight average molecular weight obtained by polymerization is 800,000-2,000,000. The weight-average molecular weight was determined by gel permeation chromatography.

3. A plasticization-promoted external lubricating acrylate processing aid according to claim 2, characterized in that: The reactive polar monomer is selected from at least one of glycidyl methacrylate, maleic anhydride, or methacrylic acid; the reactive polar monomer accounts for 8%-12% of the total weight of the anchoring layer monomer.

4. A plasticization-promoted external lubricating acrylate processing aid according to claim 3, characterized in that: The processing aid, after emulsion polymerization, yielded latex particles with a volume average size of 120-180 nm.

5. A process for the synthesis of a plasticizing external lubricating acrylate processing aid for the preparation of a plasticizing external lubricating acrylate processing aid according to any one of claims 1 to 4, characterized in that: Includes the following steps: Step 1: Raw material pretreatment and lubricating core layer synthesis. Deionized water and emulsifier are added to the reaction vessel, and the lubricating core layer monomer and chain transfer agent are added dropwise. Polymerization reaction is carried out under the action of an initiator to obtain the first emulsion. Step 2: Anchoring layer synthesis. When the monomer conversion rate in Step 1 reaches more than 90%, the anchoring layer monomer is added dropwise to the system for a heat preservation reaction to obtain the second emulsion. Step 3: Synthesis of plasticized shell layer. The plasticized shell layer monomer is added dropwise to the second emulsion obtained in Step 2 to carry out a copolymerization reaction. During the dropwise addition process, the dropwise addition rate of the plasticized shell layer monomer is controlled to be less than or equal to the polymerization consumption rate of the monomer in the reaction system to maintain the starved feeding condition and obtain the third emulsion. Step 4: In-situ grafting of the external lubricating brush layer. When the conversion rate of the plasticizing shell layer monomer mentioned in Step 3 reaches 85%-90%, the external lubricating brush layer monomer is added at once to carry out the in-situ grafting reaction and obtain the final emulsion. Step 5: Post-processing drying. The final emulsion obtained in Step 4 is subjected to spray drying to obtain the processing aid powder.

6. The method for synthesizing a plasticizing external lubricating acrylate processing aid according to claim 5, characterized in that: The initiator in step one is a redox initiation system composed of hydrogen peroxide and ascorbic acid; the chain transfer agent is n-dodecyl mercaptan, and its addition amount is 0.5%-6% of the total weight of the lubricating core layer monomer; the polymerization temperature is controlled at 55-60℃.

7. The method for synthesizing a plasticizing external lubricating acrylate processing aid according to claim 6, characterized in that: The anchoring layer monomer is added dropwise in a polar gradient manner, that is, in the first half of the dropwise addition process, only a mixture of methyl methacrylate and butyl acrylate is added dropwise, and in the second half of the dropwise addition process, the reactive polar monomer is added dropwise in parallel flow; the temperature of the heat preservation reaction is controlled at 65-70℃.

8. The method for synthesizing a plasticizing external lubricating acrylate processing aid according to claim 7, characterized in that: The plasticizing shell monomer is added over a period of 2-5 hours, and the copolymerization temperature is controlled at 65-70℃. The in-situ grafting reaction is carried out at a temperature of 75-80℃ for 0.5-1 hour.

9. The method for synthesizing a plasticizing external lubricating acrylate processing aid according to claim 8, characterized in that: The inlet air temperature of the spray dryer is controlled at 185-205℃, and the outlet air temperature is controlled at 80-95℃.

10. The method for synthesizing a plasticizing external lubricating acrylate processing aid according to claim 5, characterized in that: The emulsifier is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, or sodium alkyl diphenyl ether disulfonate; the total amount of the emulsifier added is 1.0%-3.0% of the total mass of monomers before polymerization of each layer of the processing aid.

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