A magnetic positioning plate for a plastic-based embosser and a method of manufacturing the same

Abstract

The application discloses a plastic-based embossing machine magnetic positioning plate and a preparation method thereof, relates to the technical field of protective materials, and the raw material of the plastic-based embossing machine magnetic positioning plate comprises modified PA, modified PS, inorganic magnetic powder filler and other additives; the preparation method comprises the following steps: 1) blending and granulating; 2) injection molding; and 3) multi-pole magnetization process. The application is designed from the perspective of molecular chemistry, and through chemical reactions such as end capping, grafting and in-situ compatibilization, the core contradiction of poor interface combination of multi-component and multi-phase composite materials in the preparation process of the existing positioning plate is fundamentally solved, so that the mechanical properties, environmental stability and functional reliability of the material are synergistically improved, and finally, an innovative product meeting the requirements of extremely harsh industrial applications is successfully prepared.

Description

Technical Field

[0001] This invention relates to the field of modified nylon plastic preparation technology, and in particular to a magnetic positioning plate for a plastic-based embossing machine and its preparation method. Background Technology

[0002] As a key component in modern high-precision textile and leather processing equipment, the magnetic positioning plate of an embossing machine must simultaneously meet stringent mechanical and functional performance requirements. It not only needs high strength and rigidity to ensure dimensional stability over long-term use, but also requires a built-in precise multi-pole magnetic circuit to achieve rapid and accurate positioning and adsorption of the mold. Currently, the manufacturing of this type of product mainly faces the following technical bottlenecks:

[0003] First, the selection and compounding of the polymer matrix is ​​the core challenge. Nylon (PA) is considered one of the ideal matrix materials due to its excellent mechanical strength, wear resistance, and heat resistance. However, the amino groups at the ends of its molecular chains and the amide bonds in the chain are highly hygroscopic, causing the product to expand and shrink in humid environments, severely affecting positioning accuracy. Furthermore, its strength and modulus decrease significantly due to water absorption. Introducing polystyrene (PS) to improve dimensional stability introduces new problems: PA is a polar, semi-crystalline polymer, while PS is a non-polar, amorphous polymer, making them thermodynamically incompatible. Simple physical blending leads to severe phase separation, forming weak bonding zones at the interface between the two phases. These zones become stress defects within the material, ultimately deteriorating the mechanical properties of the composite material and making it prone to cracking and failure during use.

[0004] Secondly, the interfacial bonding between magnetic powder and the organic polymer matrix is ​​another major challenge. When directly blended, the interfacial energies of inorganic magnetic powder and organic polymer differ greatly, making it difficult to form an effective bond relying solely on weak van der Waals forces and mechanical bonding. Magnetic powder is prone to agglomeration and uneven dispersion, and is easily detached from the matrix under high stress or thermal cycling. This not only causes irreversible decay of magnetic properties but also leads to material wear and failure due to filler detachment.

[0005] Furthermore, to achieve complex multi-pole magnetic circuits, the magnetic powder during the magnetization process needs to be firmly fixed. Traditional magnetic materials, such as rubber magnets and sintered magnets, either lack sufficient processing precision and mechanical properties, or are difficult to use for complex multi-pole magnetization. Ordinary plastic matrices, due to insufficient strength and weak bonding with magnetic powder, cannot firmly lock the magnetic powder units after strong pulse magnetization, which may cause the magnetic pole pattern to shift or become blurred over time or under external force, failing to meet the stringent requirements of high-precision positioning for magnetic pole stability.

[0006] Therefore, there is an urgent need in this field for an innovative solution that can synergistically address the three core contradictions at the molecular level: polymer matrix compatibility, organic-inorganic interface bonding, and environmental resistance, thereby preparing a high-performance magnetic positioning plate that combines excellent mechanical properties, extremely high dimensional stability, strong magnetic function, and long-term durability. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by proposing a magnetic positioning plate for a plastic-based embossing machine and its preparation method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention first proposes a magnetic positioning plate for a plastic-based embossing machine, comprising the following raw materials in parts by weight:

[0010] Modified PA: 60 parts;

[0011] Modified PS: 10-20 parts;

[0012] Magnetic powder: 130-140 parts;

[0013] Antioxidant: 0.3-0.6 parts;

[0014] Lubricant: 0.5-1.0 parts;

[0015] Coupling agent: 0.5-1.5 parts;

[0016] Toughening agent: 5-10 parts;

[0017] Dehydrating agent: 0.2-0.5 parts;

[0018] The preparation process of the modified PA includes the following steps:

[0019] Under nitrogen protection, nylon was dissolved in xylene at 120°C, and a xylene solution of hexamethylene diisocyanate was slowly added dropwise. The reaction was carried out at 120°C for 2 hours. A xylene solution of butanone oxime was added dropwise, and the reaction was continued for 3 hours. After the reaction was completed, the mixture was cooled to room temperature, precipitated with ethanol, filtered and washed, and dried under vacuum to obtain modified PA.

[0020] The amino group at the end of the nylon molecular chain undergoes a nucleophilic addition reaction with the isocyanate group of hexamethylene diisocyanate (HDI) to form a urea bond;

[0021] Butanone oxime undergoes a blocking reaction with the remaining -NCO to generate a stable oxime-blocked isocyanate derivative, which avoids excessive cross-linking in subsequent reactions and protects the isocyanate groups.

[0022] Taking Nylon 66 as an example, urea groups (-NH-CO-NH-) and oxime groups (-ON=C(CH3)2) are introduced at the end of the modified PA molecular chain, which enhances the polarity. It can improve the compatibility with inorganic magnetic powder fillers through hydrogen bonding or polar interaction. At the same time, the bond energy of urea bond is higher than that of amide bond, which improves the thermal stability of PA.

[0023]

[0024] The preparation process of the modified PS includes the following steps:

[0025] Polystyrene was dissolved in xylene at 60℃, and di[2-(methacryloyloxy)ethyl] phosphate and allyl alcohol were added. The mixture was stirred at 85℃ for 30 min, and then dicumyl peroxide was added. The temperature was raised to 110-115℃ and the reaction was carried out for 6-8 h. After the reaction was completed, the solution was poured into a large amount of methanol to precipitate the solid. The solid was filtered, washed with methanol, vacuum dried, and then pulverized to obtain modified PS powder, which was then sealed and stored.

[0026] Polystyrene (PS) backbone undergoes free radical graft copolymerization with di[2-(methacryloyloxy)ethyl]phosphate (DMEP) allyl alcohol under the initiation of dicumyl peroxide (DCP). The polar groups introduced through grafting, including phosphate esters and hydroxyl groups, solve the compatibility problem between pure PS (non-polar) and modified PA (polar) and inorganic magnetic powder fillers with surface polarity. At the same time, the phosphate ester groups impart flame retardancy to the material, and the hydroxyl groups can form hydrogen bonds with the hydroxyl groups on the surface of the magnetic powder, improving the interfacial bonding force.

[0027]

[0028] Preferably, in the preparation of the modified PA, the nylon can be nylon 6 or nylon 66;

[0029] The molar ratio of hexamethylene diisocyanate to the terminal amino group of nylon is 0.6-1.8:1;

[0030] The amount of methyl ethyl ketone oxime used was 1.05 times the molar amount of hexamethylene diisocyanate.

[0031] Preferably, in the preparation process of the modified PS, the mass ratio of polystyrene, di[2-(methacryloyloxy)ethyl]phosphate and allyl alcohol is 100:5-8:3-5;

[0032] The amount of dicumyl peroxide used is 0.5% of the total mass of polystyrene, di[2-(methacryloyloxy)ethyl]phosphate, and allyl alcohol.

[0033] Preferably, the antioxidant is obtained by compounding antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1; the lubricant is a stearate lubricant; the coupling agent is KH-550 silane coupling agent; the toughening agent is maleic anhydride-grafted polyolefin or maleic anhydride-grafted EPDM rubber; and the dehydrating agent is a carbodiimide dehydrating agent.

[0034] This invention also proposes a method for preparing a magnetic positioning plate for a plastic-based embossing machine, comprising the following steps:

[0035] S1, Blending Granulation

[0036] Modified PA, modified PS, antioxidant, lubricant, toughening agent, and dehydrating agent are added from the main feed port of the twin-screw extruder, and magnetic powder pretreated with coupling agent is added from the side feed port. Vacuum is opened at the end of the barrel to granulate and obtain plastic matrix masterbatch.

[0037] In the modified PA, methyl ethyl ketone oxime blocks the isocyanate group of HDI through an addition reaction. This blocked state is stable at low temperature, but a reversible deblocking reaction occurs at high temperature.

[0038] At the same time, the vacuum system at the end of the barrel will promptly remove the volatilized methyl ethyl ketone oxime, causing the equilibrium to shift towards the generation of free -NCO, ensuring that the deblocking reaction proceeds fully;

[0039]

[0040] High temperature accelerates the reaction, and the shearing action of the extruder ensures full contact between the modified PA and modified PS. The modified PS introduces hydroxyl groups derived from allyl alcohol into the main chain through the grafting reaction of S1.2. These hydroxyl groups undergo nucleophilic addition reactions with the free -NCO released by deblocking at high temperature to generate urethane bonds. The urethane bonds are strong polar covalent bonds, which connect the originally poorly compatible modified PA (polar) and modified PS (weakly polar) through chemical bonds to form a "molecular-level interpenetrating network".

[0041]

[0042] S2, Injection Molding

[0043] After vacuum drying, the plastic matrix masterbatch is added to an injection molding machine and injected at medium to high speed. It is then subjected to medium to low pressure and held for a relatively long time. After cooling, a plastic substrate is obtained.

[0044] S3, Multi-polar Magnetization Process

[0045] Place the positioning plate tightly into the magnetizing fixture, ensuring good contact between the plate surface and all poles. Start the magnetizer, and the magnetic field penetrates the plate, instantly saturating and magnetizing the magnetic powder at the corresponding position. The magnetization direction is consistent with the magnetic field direction of the poles, forming a series of alternating N and S poles on the plate surface. After multi-pole magnetization, a magnetic positioning plate for a plastic embossing machine is obtained.

[0046] Preferably, in step S1, the extruder inlet temperature is set to 175-185℃; the outlet temperature is set to 240-250℃; and the magnetic powder is neodymium iron boron magnetic powder, ferrite magnetic powder, or samarium cobalt magnetic powder.

[0047] Preferably, in step S2, the mold temperature is 100-120°C.

[0048] Preferably, in S3, the pulsed magnetic field strength is >3.5T.

[0049] Compared with the prior art, the beneficial effects of the present invention are:

[0050] 1. Simple physical blending methods are usually used, or unmodified PA, PS and magnetic powder are directly mixed. Since PA is a polar, semi-crystalline material and PS is a non-polar, amorphous material, they are thermodynamically incompatible systems, which will cause severe phase separation and form a fragile interface. At the same time, the interface energy difference between inorganic magnetic powder and organic polymer is huge, and the bonding force is extremely weak. This leads to a large number of defects in the composite material, poor mechanical properties, and easy cracking and damage at the interface during use.

[0051] This invention precisely modifies PA and PS through molecular design, introducing reactive functional groups, including the blocked isocyanate groups of PA and the hydroxyl groups of PS, onto their molecular chains. Under the high-temperature environment of blending, the blocked isocyanate groups at the PA chain ends unblock, releasing highly reactive -NCO groups, which react chemically with the -OH groups on the PS chain to form strong urethane bonds (-NH-COO-) in situ. This is equivalent to building countless molecular bridges between the PA and PS phase interfaces, forming interfacial chemical bonds in situ, thus achieving a chemical compatibilization effect. This transforms macroscopic physical blending into microscopic chemically reactive blending, greatly strengthening the phase interface and forming an organic "interpenetrating network" structure from two originally incompatible phases. The composite material exhibits extremely high cohesive strength, is not prone to phase separation and interfacial damage, and thus demonstrates excellent comprehensive mechanical properties and dimensional stability.

[0052] 2. Directly mixing magnetic powder with polymers can lead to agglomeration and uneven dispersion of the magnetic powder. The bonding between the magnetic powder and the polymer relies solely on weak van der Waals forces and mechanical anchoring, resulting in poor interfacial adhesion. Under high stress or thermal cycling, the magnetic powder is prone to detaching from the matrix, leading to magnetic performance degradation and material wear.

[0053] This invention introduces di[2-(methacryloyloxy)ethyl]phosphate into modified PS. Taking NdFeB magnetic powder as an example, the oxygen atom in its phosphate group (-P=O) has strong electronegativity, which can interact strongly with rare earth (Nd) and iron (Fe) atoms on the surface of the inorganic magnetic powder filler through Lewis acid-base coordination and dipole-dipole interactions. This interaction acts like an anchor, firmly locking the polymer molecular chain onto the surface of the magnetic powder particles. Simultaneously, this molecule is covalently grafted onto the PS chain, meaning that the magnetic powder is integrated into the polymer network through strong chemical forces. Even with a magnetic powder content of around 60%, good dispersibility and extremely strong interfacial bonding are achieved. The magnetic powder is not easily detached, its magnetic properties are stable over a long period, and the composite material itself exhibits higher strength and fatigue resistance due to the strong interfacial bonding.

[0054] 3. Ordinary nylon is highly hygroscopic due to its terminal amino and amide bonds. After absorbing water, the product will expand in size, plasticize, and its strength and modulus will be significantly reduced. This is a fatal flaw for positioning plates that require high-precision dimensional stability.

[0055] This invention utilizes the reaction of HDI with the terminal amino groups of nylon to transform the hydrophilic -NH2 group into a hydrophobic substituted urea structure, thereby eliminating the most important hygroscopic point at the molecular structure level. This fundamentally reduces the water absorption rate and speed of the material, resulting in a significant reduction in the hygroscopicity of the modified PA. This ensures that the dimensional accuracy of the magnetic positioning plate prepared from it remains extremely stable in humid environments, and its mechanical properties do not significantly decrease due to water absorption, overcoming the biggest application obstacle of ordinary nylon-based materials.

[0056] 4. Traditional magnetic materials, such as rubber magnets and sintered magnets, may suffer from insufficient processing precision, poor mechanical properties, or the inability to achieve complex multi-pole magnetization. Directly applying multi-pole magnetization to ordinary plastic matrices may result in poor magnetic pole stability due to insufficient matrix strength and weak bonding of magnetic powder.

[0057] This invention first creates a high-strength, high-rigidity composite material matrix. Through strong interfacial bonding, each magnetic powder particle is firmly fixed in a preset position. During powerful pulse magnetization, the magnetic powder is instantly magnetized, and its magnetization direction is frozen. Because the magnetic powder is firmly fixed, the resulting multi-pole magnetic circuit pattern is extremely precise and stable, and will not experience magnetic pole shift or attenuation due to external forces or the passage of time. This allows the product to simultaneously meet the dual requirements of "high-precision mechanical positioning" and "strong magnetic adsorption."

[0058] In summary, this invention, starting from molecular chemical design, fundamentally solves the core contradiction of the interface problem of multi-component and multi-phase composite materials through chemical reactions such as end-capping, grafting, and in-situ compatibilization. This synergistically improves the mechanical properties, environmental stability, and functional reliability of the materials, and ultimately successfully prepares innovative products that meet the requirements of extremely demanding industrial applications. Attached Figure Description

[0059] Figure 1 Infrared spectrum of the modified PS produced in this invention;

[0060] Figure 2 The infrared spectrum of the modified PA produced by this invention;

[0061] Figure 3 The infrared spectrum of the plastic matrix masterbatch obtained in Comparative Example 7 of this invention is shown. Detailed Implementation

[0062] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0063] The purity and manufacturers of the various drugs used in the experiment are shown in Table 1.

[0064] Table 1. Raw Material Drug Information

[0065]

[0066] Preparation Example 1:

[0067] The preparation process of modified PA includes the following steps:

[0068] Under nitrogen protection, nylon was dissolved in xylene at 120°C, and a xylene solution of hexamethylene diisocyanate was slowly added dropwise. The reaction was carried out at 120°C for 2 hours. A xylene solution of butanone oxime was added dropwise, and the reaction was continued for 3 hours. After the reaction was completed, the mixture was cooled to room temperature, precipitated with ethanol, filtered and washed, and dried under vacuum to obtain modified PA.

[0069] The nylon is nylon 66; the molar ratio of hexamethylene diisocyanate to the terminal amino group of nylon is 1.8:1;

[0070] The amount of methyl ethyl ketone oxime used was 1.05 times the molar amount of hexamethylene diisocyanate.

[0071] A portion of the modified PA was dissolved in dimethyl sulfoxide, and after separation and purification, infrared spectroscopy was performed. The results are as follows: Figure 1 As shown;

[0072] Spectral analysis shows that the characteristic absorption peak of -NCO is located at approximately 2250 cm⁻¹. -1 At this point, as can be seen from the spectrum, 2250cm -1 The absence of a strong peak indicates that the -NCO group in HDI has completely reacted; Nylon 66 itself contains amide bonds, and its characteristic absorption is the C=O stretching vibration, located at 1690 cm⁻¹. -1The superposition of NH bending vibration and CN stretching vibration is located at 1530-1570 cm. -1 During the modification process, the -NCO group of HDI reacts with the terminal amino group of nylon to form a urea bond. The urea bond also contains C=O and NH functional groups, and its vibrational peak overlaps with that of the amide bond. In the spectrum, the peaks are at 1600-1700 cm⁻¹. -1 and 1500-1600cm -1 The presence of a strong absorption peak indicates that the amide structure of nylon 66 is retained, and the reaction produces a modified structure containing an imide / urea bond, proving the successful reaction of HDI with the terminal amino group. Butanone oxime is used to cap the remaining -NCO group; its oxime bond (C=N) stretching vibration peak is located at 1650-1690 cm⁻¹. -1 Meanwhile, the vibrations of the methyl and hydroxyoxime groups in methyl ethyl ketone oxime will occur in the fingerprint area, specifically at 1000-1500 cm⁻¹. -1 The complex peak shape and multiple peaks in the fingerprint region of the spectrum indicate that the butanone oxime has successfully reacted with the remaining -NCO, introducing end-capping groups, which further proves the completion of the modification reaction.

[0073] The preparation process of modified PS includes the following steps:

[0074] Polystyrene was dissolved in xylene at 60℃, and di[2-(methacryloyloxy)ethyl] phosphate and allyl alcohol were added. The mixture was stirred at 85℃ for 30 min, and dicumyl peroxide was added. The temperature was raised to 110-115℃ and the reaction was carried out for 7 h. After the reaction was completed, the solution was poured into a large amount of methanol to precipitate the solid. The solid was filtered, washed with methanol, vacuum dried, and then pulverized to obtain modified PS powder, which was then sealed and stored.

[0075] The mass ratio of polystyrene, di[2-(methacryloyloxy)ethyl]phosphate, and allyl alcohol is 100:5:3;

[0076] The amount of dicumyl peroxide used is 0.5% of the total mass of polystyrene, di[2-(methacryloyloxy)ethyl]phosphate, and allyl alcohol.

[0077] A portion of modified PS was dissolved in dimethyl sulfoxide, and after separation and purification, infrared spectroscopy was performed. The results are as follows: Figure 2 As shown;

[0078] 3200-3600cm -1 The weakening of the hydroxyl peak in the region indicates that the -OH group of allyl alcohol participates in the reaction; 1620-1680 cm⁻¹ -1 The weakening of the C=C peak in the region indicates that double bond polymerization has occurred; 1700-1750 cm⁻¹ -1 A strong peak appears at the C=O group of the ester group, 1000-1300 cm⁻¹. -1The presence of phosphate ester characteristic peaks proves that the phosphate ester monomer was successfully grafted; the retention of benzene ring characteristic peaks indicates that the PS backbone structure is intact; infrared spectroscopy proves that the preparation reaction of modified PS proceeded as expected: di[2-(methacryloyloxy)ethyl]phosphate and allyl alcohol were grafted onto the PS chain via free radical polymerization, and the PS backbone was not destroyed.

[0079] Preparation Example 2:

[0080] The formulation and preparation method are the same as those in Preparation Example 1, but the molar ratio of hexamethylene diisocyanate to the terminal amino group of nylon is 1.2:1; the mass ratio of polystyrene, di[2-(methacryloyloxy)ethyl]phosphate and allyl alcohol is 100:6.5:4.

[0081] Preparation Example 3:

[0082] The formulation and preparation method are the same as those in Preparation Example 1, but the molar ratio of hexamethylene diisocyanate to the terminal amino group of nylon is 0.6:1; the mass ratio of polystyrene, di[2-(methacryloyloxy)ethyl]phosphate and allyl alcohol is 100:8:5.

[0083] Example 1:

[0084] A method for preparing a magnetic positioning plate for a plastic-based embossing machine includes the following steps:

[0085] Modified PA: 60kg;

[0086] Modified PS: 10kg;

[0087] The example used 130 kg of NdFeB magnetic powder;

[0088] Antioxidant: 0.6 kg;

[0089] Lubricant: 1.0 kg;

[0090] Coupling agent: 0.5 kg;

[0091] Toughening agent: 5kg;

[0092] Dehydrating agent: 0.2 kg;

[0093] S1, Blending Granulation

[0094] Using the modified PA and modified PS prepared in Preparation Example 3, the modified PA, modified PS, antioxidant, lubricant, toughening agent and dehydrating agent were added from the main feed port of the twin-screw extruder, and NdFeB magnetic powder pretreated with coupling agent was added from the side feed port. The end of the barrel was vacuumed to granulate and obtain plastic matrix masterbatch.

[0095] S2, Injection Molding

[0096] After vacuum drying, the plastic matrix masterbatch is added to an injection molding machine and injected at medium to high speed. It is then subjected to medium to low pressure and held for a relatively long time. After cooling, a plastic substrate is obtained.

[0097] S3, Multi-polar Magnetization Process

[0098] The positioning plate is placed tightly into the magnetizing fixture, ensuring good contact between the plate surface and all poles. The magnetizer is started, and the magnetic field penetrates the plate, instantly saturating the neodymium iron boron magnetic powder at the corresponding position. The magnetization direction is consistent with the magnetic field direction of the poles, forming a series of alternating N poles and S poles on the plate surface. After multi-pole magnetization is completed, a magnetic positioning plate for a plastic embossing machine is obtained.

[0099] In S1, the extruder inlet temperature is set to 175°C, and the outlet temperature is set to 250°C.

[0100] In S2, the mold temperature is 100°C.

[0101] In S3, the pulsed magnetic field strength is 4.5T.

[0102] Example 2:

[0103] The experimental scheme was the same as in Preparation Example 1, but modified PA and modified PS prepared in Preparation Example 2 were used. In S1, the extruder inlet temperature was set to 180°C and the outlet temperature was set to 245°C.

[0104] In S2, the mold temperature is 110°C.

[0105] In S3, the pulsed magnetic field strength is 4T.

[0106] Modified PA: 60kg;

[0107] Modified PS: 15kg;

[0108] NdFeB magnetic powder: 135kg;

[0109] Antioxidant: 0.45 kg;

[0110] Lubricant: 0.75 kg;

[0111] Coupling agent: 1 kg;

[0112] Toughening agent: 7.5 kg;

[0113] Dehydrating agent: 0.35 kg;

[0114] Example 3:

[0115] The experimental scheme was the same as in Preparation Example 1, but the modified PA and modified PS prepared in Preparation Example 1 were used. In S1, the extruder inlet temperature was set to 185°C and the outlet temperature was set to 240°C.

[0116] In S2, the mold temperature is 120°C.

[0117] In S3, the pulsed magnetic field strength is 3.6T.

[0118] Modified PA: 60kg;

[0119] Modified PS: 20kg;

[0120] NdFeB magnetic powder: 140kg;

[0121] Antioxidant: 0.3 kg;

[0122] Lubricant: 0.5 kg;

[0123] Coupling agent: 1.5;

[0124] Toughening agent: 10kg;

[0125] Dehydrating agent: 0.5 kg;

[0126] Based on this, the following design was also created:

[0127] Comparative Example 1: The formulation and experimental method were the same as those in Preparation Example 2, but the molar ratio of hexamethylene diisocyanate to the terminal amino group of nylon was 0.4:1;

[0128] Comparative Example 2: The formulation and experimental method were the same as those in Preparation Example 2, but the molar ratio of hexamethylene diisocyanate to the terminal amino group of nylon was 3:1;

[0129] Comparative Example 3: The formulation and experimental method were the same as those in Preparation Example 2, but the mass ratio of polystyrene, di[2-(methacryloyloxy)ethyl]phosphate and allyl alcohol was 100:2:4;

[0130] Comparative Example 4: The formulation and experimental method were the same as those in Preparation Example 2, but the mass ratio of polystyrene, di[2-(methacryloyloxy)ethyl]phosphate and allyl alcohol was 100:15:4;

[0131] Comparative Example 5: The formulation and experimental methods were the same as in Example 2, but the mass ratio of polystyrene, di[2-(methacryloyloxy)ethyl]phosphate, and allyl alcohol was 100:6.5:1;

[0132] Comparative Example 6: The formulation and experimental methods were the same as in Example 2, but the mass ratio of polystyrene, di[2-(methacryloyloxy)ethyl]phosphate, and allyl alcohol was 100:6.5:10;

[0133] Comparative Example 7: The formulation and experimental method were the same as in Example 2, but no other additives were added.

[0134] A portion of the plastic matrix masterbatch obtained in Comparative Example 7 was dissolved in dimethyl sulfoxide, separated and purified, and then subjected to infrared spectroscopy. The results are as follows: Figure 3 As shown;

[0135] Modified PA contains amide bonds CO-NH, and its NH stretching vibration peak is located at 3300-3400 cm⁻¹. -1 Nearby; if modified PS retains a small amount of hydroxyl groups, it may also show a weak peak in this region; the presence of an absorption peak in this region in the spectrum indicates that the amide structure of modified PA is preserved, and the NH functional group is not destroyed due to blending. The amide I band (Amide bond C=O stretching vibration) of modified PA is located at 1650 cm⁻¹. -1 Nearby; the carbonyl group (C=O stretching vibration) of the phosphate ester in modified PS: located at 1720 cm⁻¹ -1 Nearby. A strong absorption peak appears in this region of the spectrum, proving the presence of both the amide carbonyl group in the modified PA and the ester carbonyl group in the modified PS, indicating that the characteristic functional groups of the two modified polymers have not disappeared due to blending. The amide II band of the modified PA: a superposition peak of the NH bending vibration and CN stretching vibration, located at 1530 cm⁻¹. -1 Nearby; phosphate ester groups of modified PS: P=O stretching vibration (1250-1300 cm⁻¹) -1 ), POC stretching vibration (1000-1200cm) -1 Complex peak shapes are observed in this region of the spectrum. The complex peak shapes and characteristic absorptions in this region indicate that the phosphate ester groups of the modified PS and the amide structure of the modified PA are retained, and the blending process did not disrupt the integrity of the polymer's functional groups. The modified PS matrix contains benzene rings, and its characteristic peak is: benzene ring skeletal vibration: 1450 cm⁻¹. -1 1500cm -1 1600cm -1 Nearby; out-of-plane bending vibration of the benzene ring CH: 700-900 cm -1 Monosubstituted benzene rings are typically around 700 cm². -1 and 750cm -1 There are peaks nearby. The peaks in the relevant region of the spectrum correspond to benzene ring vibrations, proving that the main chain structure of the modified PS is intact and that the blending did not destroy the characteristic functional groups of the benzene ring.

[0136] For each embodiment and comparative example, the following standards were followed: IEC 60404-14:2018 Magnetic materials – Part 14: Measurement of surface magnetic field distribution; JB / T 10194-2019 Permanent magnet chucks; IEC 60404-8-1:2020 Magnetic materials – Part 8-1: Tests for long-term stability of magnetic properties; GB / T 1040.1-2006 Plastics – Determination of tensile properties – Part 1: General principles; GB / T 9286-1998 Paints and varnishes – Cross-cut test; GB / T 1634.1-2021 Plastics – Determination of heat deflection temperature and Vicat softening temperature – Part 1: Heat deflection temperature; GB / T 26572-2011 Limits of restricted substances in electrical and electronic products; GB / T 15255-2019 The "Test on Heat Resistance and Water Resistance of Vulcanized Rubber or Thermoplastic Rubber Bonded to Metal" includes specific tests on surface magnetic field strength, uniformity of magnetic pole distribution, magnetic stability, tensile strength, interfacial bond strength, heat distortion temperature, restriction of hazardous substances, and resistance to damp heat aging. The corresponding results are shown in the table below.

[0137] Table 2. Performance test data of the magnetic positioning plate for plastic embossing machines

[0138]

[0139] Data Analysis:

[0140] As can be seen from Example 2, Comparative Example 1, and Comparative Example 2:

[0141] The HDI content in Comparative Example 1 was severely insufficient, meaning that at most only 80% of the nylon terminal amino groups were reacted, leaving a large number of hydrophilic terminal amino groups uncapped and exposed in the polymer system. -NH2 readily forms hydrogen bonds with water molecules, making the material highly hygroscopic. After absorbing water, the water molecules act as plasticizers, weakening intermolecular forces and leading to a significant decrease in glass transition temperature (Tg) and strength. Furthermore, the number of closed isocyanate functional groups available for reacting with -OH groups on PS to form chemical bonds was insufficient, resulting in poor adhesion between the PA and PS phases. The in-situ compatibilization reaction is incomplete, and the interface lacks a strong chemical bridge, relying mainly on weak physical forces for bonding. Therefore, under external forces, the interface is very easy to become the starting point of fracture, resulting in poor interfacial bonding and low tensile strength. The strong hygroscopicity and poor interfacial bonding together lead to poor magnetic property stability. The intruding moisture will cause oxidation and corrosion on the surface of NdFeB magnetic powder, directly leading to the decay of magnetic properties. The weak interfacial bonding force cannot firmly "lock" the magnetic powder. Under thermal stress or service stress, the magnetic powder is more likely to loosen or fall off, causing magnetic loss.

[0142] In Comparative Example 2, the amount of HDI used far exceeded the theoretical requirement. After all the terminal amino groups were capped, a large amount of excess HDI existed in the system. This excess HDI reacted with the amide bonds on the nylon backbone, leading to molecular chain branching or cross-linking. Two HDI molecules may react with one amino group or react with themselves, resulting in mild cross-linking of the nylon molecular chains. Cross-linking restricts the movement and orderly arrangement of molecular chains, making the material brittle and negatively impacting toughness and strength. At the same time, complex by-reaction products may disrupt the regularity of the polymer, which is not conducive to the formation of a strong and tough interface. Excessive isocyanate groups may also cause problems during processing. Because its terminal amino groups are capped, its hygroscopicity is controlled, so its resistance to damp heat, HDT, and other properties are far superior to Comparative Example 1. It also provides sufficient potential reaction sites for reaction with PS, and the interfacial bonding is stronger than that of Comparative Example 1. However, the excess capping agent will produce more small molecule volatiles when decapping, which has an adverse effect on processing stability and product odor.

[0143] By comparing Example 2, Comparative Example 4, and Comparative Example 3, it can be seen that:

[0144] The core variable in these three sets of experiments is the amount of bis[2-(methacryloyloxy)ethyl]phosphate functional monomer. The amount of phosphate monomer directly determines the density of "anchor points" on the modified PS molecular chain that can be used to bond with NdFeB magnetic powder, which is the core factor affecting the magnetic powder dispersibility, interfacial bonding force and final magnetic stability.

[0145] In Comparative Example 3, the amount of phosphate ester was severely insufficient, resulting in an extremely low density of phosphate ester groups (-P=O) grafted onto the PS chain, which could not provide enough binding sites for the large amount of NdFeB magnetic powder. Due to the lack of sufficient "anchor points," the bonding between the magnetic powder and the polymer mainly relied on weak van der Waals forces. Under high stress, such as magnetizing shock, vibration, and thermal cycling, the magnetic powder was easily detached from the matrix, leading to an irreversible and rapid decay of magnetic flux. At the same time, the magnetic powder was unevenly dispersed and prone to agglomeration during processing, resulting in uneven magnetic pole distribution and extremely poor magnetic stability. The fragility of the magnetic powder-polymer interface directly led to the loss of macroscopic interfacial bonding. The detached magnetic powder left voids in the matrix, becoming stress concentration points, which greatly reduced the mechanical strength of the material. The interfacial bonding was extremely poor, resulting in the lowest tensile strength. The phosphate ester monomer itself has a certain plasticizing effect, but due to its extremely small amount, this effect was not obvious. In this case, the main reason for the low HDT was more likely due to the extremely poor interfacial bonding and the magnetic powder agglomerates disrupting the continuity of the matrix, making the material more prone to deformation under load.

[0146] In Comparative Example 4, the amount of phosphate ester used far exceeded the optimized value. Excessive phosphate ester monomers were grafted onto the PS chain, which produced two main side effects: First, the excessive phosphate ester groups had a significant "plasticizing" effect on the PS matrix, softening the polymer; second, the excessively high functional group density may lead to excessive adsorption of local magnetic powder, which in turn affected the dispersion uniformity. Thanks to the huge number of phosphate ester "anchor points," the magnetic powder and polymer were very firmly bonded, and the filling amount was guaranteed. Therefore, the surface magnetic field strength after magnetization was very high. However, although the magnetic powder was firmly bonded, the PS matrix itself was softened due to the large number of grafted phosphate ester branches, resulting in a decrease in overall tensile strength and a drop in the interfacial bonding level to level 2. This may also be because the excessive phosphate ester layer formed a relatively weak boundary layer at the interface. Excessive, highly polar phosphate ester groups may have caused local agglomeration of magnetic powder to some extent, rather than ideal single-particle dispersion, thus affecting the uniformity of magnetic pole distribution and preventing it from achieving the "excellent" level of magnetic pole distribution uniformity.

[0147] By comparing Example 2, Comparative Example 6, and Comparative Example 5, it can be seen that:

[0148] The amount of allyl alcohol directly determines the density of hydroxyl groups (-OH) on the modified PS molecular chain. These hydroxyl groups are the functional groups that react with the isocyanate groups (-NCO) generated after the modified PA is deblocked, thus achieving in-situ compatibilization of PA-PS. Therefore, its amount is crucial.

[0149] In Comparative Example 5, the amount of allyl alcohol was severely insufficient, resulting in a far too few hydroxyl groups grafted onto the PS chain. During blending, the large number of highly reactive -NCO groups released from the deblocking of modified PA could not find enough -OH groups to react with. Due to the lack of sufficient chemical reaction sites, a sufficient number of urethane bonds (-NH-COO-) could not be formed between the PA and PS phases for chemical bridging. The interface between the two phases mainly relied on physical interpenetration and weak van der Waals forces, becoming the weakest link in the material. Under external forces, cracks easily propagate along this fragile interface, leading to adhesion... The test results showed a decrease in grade and macroscopic tensile strength, poor interfacial bonding, and low tensile strength. Although the amount of phosphate ester was sufficient and the bonding between the magnetic powder and the PS phase was strong, the overall bonding force between the PS and PA phases was weak. Under external stress or thermal cycling, the fragile PA-PS interface may break first, causing the entire composite material structure to loosen, which indirectly affected the stability of the magnetic powder fixation and thus aggravated the decay of magnetic properties. The fragile two-phase interface could not effectively transfer and disperse stress, and was more prone to creep and deformation under heat load, resulting in a decrease in HDT value.

[0150] The amount of allyl alcohol used in Comparative Example 6 far exceeded the optimized value. Excess allyl alcohol grafted onto the PS chain generated a large number of short-chain hydroxyl branches. This could potentially disrupt the regularity of the PS molecular chain and have a certain plasticizing effect on the matrix; however, overly dense hydroxyl groups might form hydrogen bonds or polar microdomains around them, which could interfere with the effective and orderly reaction with the PA-NCO groups to some extent. Despite a sufficient number of hydroxyl groups, the interfacial and mechanical properties decreased compared to Example 2, indicating that more hydroxyl groups are not necessarily better. Excessive short-chain hydroxyl branches may result in a less regular and robust cross-linked network formed by the interfacial reaction compared to Example 2. Simultaneously, the slight plasticizing effect on the PS matrix also contributed to the overall decrease in strength, with interfacial bonding and tensile strength not reaching optimal levels. Because it provided sufficient functional groups, ensuring a considerable degree of chemical compatibilization, its performance was far superior to Comparative Example 5, which lacked sufficient hydroxyl groups. This demonstrates that chemical compatibilization, even if not optimal, is far superior to physical blending.

[0151] By comparing Example 2 and Comparative Example 7, it can be seen that:

[0152] Additives are not "optional" but "essential." In such a complex multiphase composite system, the optimized bulk formulation solves the problems of thermodynamic compatibility and major interfacial bonding, while the additive system solves the kinetic and stability problems in the processing and long-term use environment. Polymer modification and additive addition are complementary and indispensable. The former builds a robust "molecular skeleton," while the latter ensures that the skeleton is not damaged during construction and use. Omitting additives may slightly reduce raw material costs, but at the cost of a significant reduction in product life, reliability, and performance consistency, which is fatal for industrial applications.

[0153] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A magnetic positioning plate for a plastic-based embossing machine, characterized in that, Including the following parts by weight of raw materials: Modified PA: 60 parts; Modified PS: 10-20 parts; Magnetic powder: 130-140 parts; Antioxidant: 0.3-0.6 parts; Lubricant: 0.5-1.0 parts; Coupling agent: 0.5-1.5 parts; Toughening agent: 5-10 parts; Dehydrating agent: 0.2-0.5 parts; The preparation process of the modified PA includes the following steps: Under nitrogen protection, nylon was dissolved in xylene at 120°C, and a xylene solution of hexamethylene diisocyanate was slowly added dropwise. The reaction was carried out at 120°C for 2 hours. A xylene solution of butanone oxime was added dropwise, and the reaction was continued for 3 hours. After the reaction was completed, the mixture was cooled to room temperature, precipitated with ethanol, filtered and washed, and dried under vacuum to obtain modified PA. Among them, nylon can be nylon 6 or nylon 66; The molar ratio of hexamethylene diisocyanate to the terminal amino group of nylon is 0.6-1.8:1; The amount of methyl ethyl ketone oxime used was 1.05 times the molar amount of hexamethylene diisocyanate; The preparation process of the modified PS includes the following steps: Polystyrene was dissolved in xylene at 60℃, and di[2-(methacryloyloxy)ethyl] phosphate and allyl alcohol were added. The mixture was stirred at 85℃ for 30 min, and then dicumyl peroxide was added. The temperature was raised to 110-115℃ and the reaction was carried out for 6-8 h. After the reaction was completed, the solution was poured into a large amount of methanol to precipitate the solid. The solid was filtered, washed with methanol, vacuum dried, and then pulverized to obtain modified PS powder, which was then sealed and stored. The mass ratio of polystyrene, di[2-(methacryloyloxy)ethyl]phosphate, and allyl alcohol is 100:5-8:3-5; The amount of dicumyl peroxide used is 0.5% of the total mass of polystyrene, di[2-(methacryloyloxy)ethyl]phosphate, and allyl alcohol.

2. The magnetic positioning plate for a plastic-based embossing machine according to claim 1, characterized in that: The antioxidant is obtained by compounding antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1; the lubricant is a stearate lubricant; the coupling agent is KH-550 silane coupling agent; the toughening agent is maleic anhydride-grafted polyolefin or maleic anhydride-grafted EPDM rubber; and the dehydrating agent is a carbodiimide dehydrating agent.

3. The method for preparing a magnetic positioning plate for a plastic-based embossing machine according to claim 1, characterized in that: Includes the following steps: S1, Blending Granulation Modified PA, modified PS, antioxidant, lubricant, toughening agent, and dehydrating agent are added from the main feed port of the twin-screw extruder, and magnetic powder pretreated with coupling agent is added from the side feed port. Vacuum is opened at the end of the barrel to granulate and obtain plastic matrix masterbatch. S2, Injection Molding After vacuum drying, the plastic matrix masterbatch is added to an injection molding machine and injected at medium to high speed. It is then subjected to medium to low pressure and held for a relatively long time. After cooling, a plastic substrate is obtained. S3, Multi-polar Magnetization Process Place the positioning plate tightly into the magnetizing fixture, ensuring good contact between the plate surface and all poles. Start the magnetizer, and the magnetic field penetrates the plate, instantly saturating and magnetizing the magnetic powder at the corresponding position. The magnetization direction is consistent with the magnetic field direction of the poles, forming a series of alternating N and S poles on the plate surface. After multi-pole magnetization, a magnetic positioning plate for a plastic embossing machine is obtained.

4. The method for preparing a magnetic positioning plate for a plastic-based embossing machine according to claim 3, characterized in that: In S1, the extruder inlet temperature is set to 175-185℃; the outlet temperature is set to 240-250℃; and the magnetic powder is neodymium iron boron magnetic powder, ferrite magnetic powder, or samarium cobalt magnetic powder.

5. The method for preparing a magnetic positioning plate for a plastic-based embossing machine according to claim 3, characterized in that: In S2, the mold temperature is 100-120℃.

6. The method for preparing a magnetic positioning plate for a plastic-based embossing machine according to claim 3, characterized in that: In S3, the pulsed magnetic field strength is >3.5T.

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