PET engineering plastic and preparation method thereof

Abstract

The invention discloses PET engineering plastic and a preparation method thereof, and relates to the field of plastic preparation.The preparation method comprises the following steps that aluminum hydroxide powder is subjected to surface treatment and modification, and powder b with a high-resistance organic composite interface layer compatible with PET on the surface is obtained; then carrying out melt blending and granulation on the powder b, hollow silicon dioxide microspheres and PET resin a to obtain functional master batches; mixing the combined flame retardant with PET resin b to obtain a premix, and carrying out melt blending and granulation on the premix to obtain flame-retardant master batch; and mixing the functional master batch, the flame-retardant master batch and the PET resin c to obtain a dry blend, and carrying out melt blending and granulation on the dry blend to obtain the PET engineering plastic. According to the PET engineering plastic obtained by the invention, the anti-creepage tracking index of the PET engineering plastic can be remarkably improved while the UL94 V-0 high-flame-retardant grade is ensured, for example, the anti-creepage tracking index can reach 300V or above, so that the synergistic enhancement of the flame retardant property and the insulation safety is realized, and the bottleneck that the flame retardant property and the insulation safety are difficult to take into account in the traditional technology is broken through.

Description

Technical Field

[0001] This invention relates to the field of plastic preparation, and more particularly to a PET engineering plastic and its preparation method. Background Technology

[0002] PET engineering plastics refer to high-performance PET materials whose mechanical properties, heat resistance, and dimensional stability have been significantly improved through reinforcement, toughening, and flame retardancy modifications. They possess excellent overall performance, including high rigidity, good creep resistance, outstanding electrical insulation, and high heat resistance. These characteristics make them particularly suitable for the electronics and electrical fields where material requirements are stringent. For example, in connectors, PET ensures structural strength and dimensional accuracy during insertion and removal; in components such as circuit breakers, its stable insulation and flame-retardant properties are crucial for safe operation. Furthermore, its relatively low cost and excellent processing fluidity make it an ideal choice for the large-scale manufacturing of electronic and electrical structural components.

[0003] PET engineering plastics are widely used in electronic and electrical components such as connectors and circuit breakers. These components require materials to possess both high flame retardancy (typically meeting the UL94 V-0 rating) and high resistance to tracking (high CTI value, such as above 300V). In existing technologies, to meet these requirements, highly efficient flame retardants are added to PET, such as bromine-antimony synergistic systems or phosphorus-nitrogen intumescent flame retardants. When these flame retardants exert their flame-retardant effect, they promote the formation of a continuous, dense char layer on the burning or tracking surface of the material. This char layer itself is highly conductive. Simultaneously, the flame-retardant system may produce acidic substances such as hydrogen halides and phosphoric acid under thermal or electrical stress. These substances catalyze and accelerate the formation and corrosion of conductive carbonization pathways. As a result, while achieving the UL94 V-0 flame retardancy rating, the CTI value often drops significantly from above 250V of the base resin to 175V or even lower, thus failing to meet safety standards for high-voltage applications.

[0004] Therefore, this paper proposes a PET engineering plastic and its preparation method to address the issue of reduced tracking index when improving flame retardancy. Summary of the Invention

[0005] The purpose of this invention is to provide a PET engineering plastic and its preparation method, which solves the problem of decreased tracking index when flame retardancy is improved.

[0006] To achieve this objective, the present invention adopts the following technical solution: A method for preparing PET engineering plastic, the method comprising the following steps: Step S1: Surface treatment and modification of aluminum hydroxide powder to obtain powder b with a high-resistivity organic composite interface layer compatible with PET. Then, powder b, hollow silica microspheres and PET resin a are melt-blended and granulated to obtain functional masterbatch. Step S2: Mix the combined flame retardant with PET resin b to obtain a premix, and then melt-blend and granulate the premix to obtain flame retardant masterbatch. Step S3: Mix the functional masterbatch, flame retardant masterbatch and PET resin c to obtain a dry mixture, then melt-blend and granulate the dry mixture to obtain PET engineering plastic.

[0007] The powder b is obtained according to the following steps: Aluminum hydroxide powder was added to a reaction vessel along with a mixed solvent and stirred at 200-400 rpm to obtain a suspension. Then, a silane coupling agent was added to the suspension and stirring was continued for 8-12 minutes. Subsequently, polyphenylene ether oligomer was added to the system and stirred at 50-80°C for 1-3 hours. The system was then filtered, and the resulting filter cake was washed 2-3 times with ethanol. After washing, the filter cake was dried at 80-110°C for 6-12 hours. The dried filter cake was then pulverized and sieved through a 100-mesh sieve to obtain powder b.

[0008] The aluminum hydroxide powder has an average particle size D50 of 3-8 μm, the mixed solvent is a mixture of ethanol and water in a volume ratio of 1:1, the silane coupling agent is γ-aminopropyltriethoxysilane, and the number average molecular weight Mn of the polyphenylene ether oligomer is <2000. By weight, the aluminum hydroxide powder, mixed solvent, silane coupling agent and polyphenylene ether oligomer are 100 parts by weight, 300-500 parts by weight, 1-3 parts by weight and 5-15 parts by weight, respectively.

[0009] The functional masterbatch is obtained according to the following steps: Powder b, hollow silica microspheres, PET resin a, chain extender a, composite antioxidant, nucleating agent and lubricant a are mixed in a high-speed mixer for 3-5 minutes to obtain a mixture; then the mixture is fed into a twin-screw extruder a and melt-blended at 240-255℃ under a vacuum of (-0.03)-(-0.05MPa) and a screw speed of 150-250rpm. After cooling and granulation, functional masterbatch is obtained.

[0010] By weight, the powder b, hollow silica microspheres, PET resin a, chain extender a, composite antioxidant, nucleating agent and lubricant a are 4-5.5 parts by weight, 4-5.5 parts by weight, 25 parts by weight, 0.5-0.75 parts by weight, 0.5-0.8 parts by weight, 0.3-0.5 parts by weight and 0.25-0.4 parts by weight, respectively; the hollow silica microspheres have a particle size of 2-5 μm and are encapsulated with hydrocarbon phase change substances with a phase change temperature of 120-180℃; the nucleating agent is an organic carboxylate nucleating agent; the composite antioxidant includes 1010 antioxidant and 168 antioxidant in a mass ratio of 1:1.

[0011] Step S2 specifically includes the following steps: Step S21: Mix flame retardant a, flame retardant b, PET resin b, chain extender b, and lubricant b in a high-speed mixer for 3-5 minutes to obtain a premix. Step S22: The premixed material is fed into the twin-screw extruder b and melt-blended at 250-260°C under a vacuum of (-0.07)-(-0.08MPa) and a screw speed of 200-300rpm. After cooling and granulation, flame retardant masterbatch is obtained.

[0012] In step S21, flame retardant a is surface-coated ammonium polyphosphate, and flame retardant b is melamine polyphosphate. By weight, flame retardant a, flame retardant b, PET resin b, chain extender b, and lubricant b are 10-14 parts by weight, 6-8 parts by weight, 30 parts by weight, 0.5-0.75 parts by weight, and 0.25-0.4 parts by weight, respectively. In addition, the intrinsic viscosity of both PET resin a and PET resin b is 0.65-0.75 dL / g, both lubricant a and lubricant b are pentaerythritol stearate, and both chain extender a and chain extender b are styrene-acrylate-glycidyl methacrylate copolymer.

[0013] Step S3 specifically includes the following steps: Step S31: Mix PET resin c, flame retardant masterbatch and functional masterbatch in a drum mixer for 5-10 minutes to obtain dry mix; Step S32: The dry mixture is fed into the twin-screw extruder c and melt-blended at 245-260℃ under a vacuum of (-0.05)-(-0.07MPa) and a screw speed of 180-250rpm. After cooling and granulation, the granules are obtained. The granules are then dried at 120-130℃ for 4-6 hours. After drying, PET engineering plastic is obtained.

[0014] In step S31, by weight, the PET resin c, flame retardant masterbatch, and functional masterbatch are 40-50 parts by weight, 46.5-52.5 parts by weight, and 34.5-37.3 parts by weight, respectively; the intrinsic viscosity of the PET resin c is 0.70-0.80 dL / g. In step S32, the moisture content of the PET engineering plastic is <50ppm.

[0015] A PET engineering plastic, said PET engineering plastic being obtained according to the preparation method described above.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a PET engineering plastic and its preparation method. The method involves surface-treating and modifying aluminum hydroxide powder to construct a high-resistivity organic composite interface layer compatible with PET, thereby transforming it into powder b. Subsequently, powder b, along with hollow silica microspheres encapsulated with phase change materials, is melt-blended with PET resin a to prepare a functional masterbatch integrating stable insulation and thermal response disturbance functions. Simultaneously, a flame retardant is combined with PET resin b to prepare a flame-retardant masterbatch. Finally, the functional masterbatch, flame-retardant masterbatch, and PET resin c are melt-blended to successfully obtain the final product. The core of this method lies in the construction of numerous microscopic insulating structures within the matrix through the high-resistivity interface layer in powder b, persistently hindering the formation of conductive pathways. Furthermore, the physical response of the hollow microspheres during localized overheating of the electrical traces interferes with the continuous development of carbonization channels. The synergistic effect of these two methods fundamentally alters the material's failure behavior under an electric field. Therefore, the PET engineering plastic obtained by this method can significantly improve its tracking resistance index, for example, to more than 300V, while ensuring that it reaches the UL94 V-0 high flame retardant rating. This achieves a synergistic enhancement of flame retardant performance and insulation safety, breaking through the bottleneck of traditional technologies where both are difficult to achieve simultaneously. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] The structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0019] Figure 1 This is a flowchart of the method in this invention. Detailed Implementation

[0020] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] In the description of this invention, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be a component positioned centrally in the connection.

[0022] Please see Figure 1 This embodiment describes a method for preparing PET engineering plastic, the method comprising the following steps: Step S1: Surface treatment and modification of aluminum hydroxide powder to obtain powder b with a high-resistivity organic composite interface layer compatible with PET. Then, powder b, hollow silica microspheres and PET resin a are melt-blended and granulated to obtain functional masterbatch. Step S2: Mix the combined flame retardant with PET resin b to obtain a premix, and then melt-blend and granulate the premix to obtain flame retardant masterbatch. Step S3: Mix the functional masterbatch, flame retardant masterbatch and PET resin c to obtain a dry mixture, then melt-blend and granulate the dry mixture to obtain PET engineering plastic.

[0023] Specifically, in step S1, aluminum hydroxide powder is surface treated and modified to obtain powder b with a high-resistivity organic composite interface layer compatible with PET. Then, powder b, hollow silica microspheres and PET resin a are melt-blended and granulated to obtain functional masterbatch. The powder b is obtained according to the following steps: Aluminum hydroxide powder was added to a reaction vessel along with a mixed solvent and stirred at 200-400 rpm to obtain a suspension. Then, a silane coupling agent was added to the suspension and stirring was continued for 8-12 minutes. Subsequently, polyphenylene ether oligomer was added to the system and stirred at 50-80°C for 1-3 hours. The system was then filtered, and the resulting filter cake was washed 2-3 times with ethanol. After washing, the filter cake was dried at 80-110°C for 6-12 hours. The dried filter cake was then pulverized and sieved through a 100-mesh sieve to obtain powder b.

[0024] The aluminum hydroxide powder has an average particle size D50 of 3-8 μm, the mixed solvent is a mixture of ethanol and water in a volume ratio of 1:1, the silane coupling agent is γ-aminopropyltriethoxysilane, and the number average molecular weight Mn of the polyphenylene ether oligomer is <2000. By weight, the aluminum hydroxide powder, mixed solvent, silane coupling agent and polyphenylene ether oligomer are 100 parts by weight, 300-500 parts by weight, 1-3 parts by weight and 5-15 parts by weight, respectively.

[0025] It should be noted that in the above steps, a stable organic coating layer is constructed on the surface of aluminum hydroxide particles through a stepwise process. First, a mixed solvent is used to uniformly disperse the aluminum hydroxide powder, exposing the active hydroxyl groups on its surface. Subsequently, the added silane coupling agent undergoes hydrolysis, and its silanol groups condense with the hydroxyl groups on the aluminum hydroxide surface to form Si-O-Al chemical bonds, thereby chemically anchoring the coupling agent to the surface of the aluminum hydroxide powder. This process transforms the surface properties of the aluminum hydroxide powder from hydrophilic inorganic to containing organic amino groups. Then, a poly(hydroxyl group) is added... The molecular chains of polyphenylene ether oligomers are enriched and attached to the surface of aluminum hydroxide powder through physical adsorption and interaction with the organic ends of the bonded silane coupling agent. Under heating and stirring at 50-80℃, this attachment becomes stronger and more uniform, thus forming a rich organic coating layer composed of silane coupling agent and polyphenylene ether oligomers around each aluminum hydroxide particle. Subsequently, after filtration, washing and drying, the obtained powder b has good flowability, enhanced hydrophobicity, reduced surface energy, and fundamentally improved compatibility with PET resin.

[0026] It is understood that this step, by constructing a high-resistivity organic composite interface layer on the surface of aluminum hydroxide powder, alters the surface properties of the aluminum hydroxide powder and enhances its interfacial performance in the polymer matrix. Under these effects, on the one hand, the interface layer exhibits better thermodynamic affinity with the PET molecular chains, improving the interfacial compatibility and bonding strength between the aluminum hydroxide powder and the PET matrix; on the other hand, the encapsulated polyphenylene ether oligomer itself is an excellent high-resistivity organic material, thus endowing the originally generally conductive aluminum hydroxide powder surface with extremely high resistivity. Simultaneously, the treated powder b is easier to disperse in subsequent melt processing, reducing performance defects caused by agglomeration. Through this step, aluminum hydroxide powder is transformed into a functionalized filler possessing good dispersibility, excellent interfacial bonding strength, and intrinsically high resistivity.

[0027] Understandably, when powder b is introduced into the PET matrix as a functional component, its high-resistivity organic interface layer makes each powder particle a microscopic insulating structure. When the material undergoes tracking tests, the conductive carbonization pathways that the electrolyte and discharge attempt to form encounter a large number of such randomly distributed insulating structures during expansion. Electrically, the high-resistivity interface of the insulating structure forces the current to detour, increasing the tortuosity and effective resistance of the conductive path, thus delaying local overheating and carbonization. Physically, good interfacial bonding avoids electric field concentration and preferential breakdown caused by interface defects. Therefore, even if the flame-retardant system promotes charring during combustion or tracking, the dispersed insulating structure constructed by powder b can effectively disrupt the continuity of the char layer and inhibit the penetration of low-resistivity pathways, thereby maintaining a high flame-retardant rating while ensuring or even improving the CTI value of the material.

[0028] It is worth noting that this step employs a wet surface treatment process to sequentially process the material, achieving a controllable and uniform surface modification effect. Specifically, a 1:1 volume ratio of ethanol to water is used as a solvent, providing the necessary aqueous environment for the hydrolysis of the silane coupling agent. Ethanol also reduces the surface tension of water and dissolves the polyphenylene ether oligomer, ensuring a uniform reaction. The aluminum hydroxide powder has an average particle size (D50) of 3-8 μm, balancing its dispersibility in the matrix, its improvement effect on CTI, and its impact on the material's mechanical properties. The silane coupling agent is used in an amount of 1-3 parts by weight, sufficient to form a monolayer of chemical anchoring points on the surface of the aluminum hydroxide powder; excessive amounts may result in multilayer formation. Adsorption affects the effect; the amount of polyphenylene ether oligomer is 5-15 parts by weight to ensure that a high-resistivity coating layer with sufficient thickness and integrity can be formed on the surface of aluminum hydroxide powder. If it is too thin, the effect will be poor, and if it is too thick, it may affect the processing and cost. During the reaction, 50-80℃ and 1-3h provide suitable kinetic conditions for the hydrolysis and condensation of silane and the adsorption of polyphenylene ether. If the temperature is too low or the time is too short, the reaction will be insufficient, and if it is too high or too long, it may lead to side reactions or energy waste. The subsequent washing, drying, pulverizing and sieving processes are aimed at removing free reactants and obtaining dry and uniformly sized powder b to ensure that it can be added stably and uniformly in the subsequent preparation of functional masterbatch.

[0029] The functional masterbatch is obtained according to the following steps: Powder b, hollow silica microspheres, PET resin a, chain extender a, composite antioxidant, nucleating agent and lubricant a are mixed in a high-speed mixer for 3-5 minutes to obtain a mixture; then the mixture is fed into a twin-screw extruder a and melt-blended at 240-255℃ under a vacuum of (-0.03)-(-0.05MPa) and a screw speed of 150-250rpm. After cooling and granulation, functional masterbatch is obtained.

[0030] By weight, the powder b, hollow silica microspheres, PET resin a, chain extender a, composite antioxidant, nucleating agent and lubricant a are 4-5.5 parts by weight, 4-5.5 parts by weight, 25 parts by weight, 0.5-0.75 parts by weight, 0.5-0.8 parts by weight, 0.3-0.5 parts by weight and 0.25-0.4 parts by weight, respectively; the hollow silica microspheres have a particle size of 2-5 μm and are encapsulated with hydrocarbon phase change substances with a phase change temperature of 120-180℃; the nucleating agent is an organic carboxylate nucleating agent; the composite antioxidant includes 1010 antioxidant and 168 antioxidant in a mass ratio of 1:1.

[0031] It should be noted that in this step, when the mixture enters the heating section a of the twin-screw extruder, PET resin a first melts into a viscous fluid. Under the conveying and shearing action of the screw, the agglomerates of powder b are gradually broken up. The high-resistivity organic composite interface layer on its surface is in close contact with the PET melt and mutually wetting, achieving uniform dispersion with single or a small number of particles as units. At the same time, under the action of low shear force, most of the hollow silica microspheres are able to maintain their complete spherical shell structure. The phase change material encapsulated inside is protected within the silica wall material. The chain extender a reacts with the end groups of PET, which helps to maintain the viscosity of the system. Antioxidants, nucleating agents and other small molecule additives dissolve or disperse throughout the melt. After the above process, the mixture is discharged from the extruder, transformed into a homogeneous, dense melt strip with a certain degree of toughness. After cooling and solidification, it becomes a functional masterbatch with uniform particles.

[0032] It is known that this step, by pre-dispersing and encapsulating powder b and hollow silica microspheres in PET resin a under a mild process, yields a functional masterbatch with high concentration, high dispersibility, and complete structure, possessing anti-tracking properties. This step achieves two key benefits: firstly, it pre-disperses powder b in PET resin a, laying a solid foundation for achieving uniform nano- and micron-level distribution in the overall material during final mixing, avoiding uneven dispersion and agglomeration caused by direct final mixing; secondly, it preserves the fine structure of the hollow silica microspheres. By controlling a lower processing temperature, limited shear force, and a micro-negative pressure environment, it minimizes microsphere breakage and the loss of internal phase change substances, thus ensuring the responsiveness of the hollow silica microspheres in the final material.

[0033] It should also be noted that the hollow silica microspheres act as thermal response disturbance units in the entire system, and their function is both auxiliary and conditional. The phase change material encapsulated inside the hollow silica microspheres has a phase change temperature of 120-180℃. Under certain specific conditions tested by the IEC60112 standard, when local instantaneous overheating occurs at the electrolyte bridging point due to current concentration and chemical reaction, and the temperature reaches the phase change threshold, the material inside the hollow silica microspheres will vaporize or expand, thereby causing deformation of the hollow silica microspheres themselves or stress disturbance at the interface between them and the surrounding PET matrix. This disturbance increases the randomness and instability of the extension of the electrical tracking front, interferes with the connection trend of carbonization points, and provides an additional, probabilistic auxiliary contribution to the improvement of CTI.

[0034] Understandably, the functional masterbatch prepared in this step is a highly integrated intermediate. In the functional masterbatch, powder b serves as an insulating structure, and its good pre-dispersion ensures the formation of a large number of effective resistance barriers in the final material. Hollow silica microspheres serve as thermal response perturbation units, and the integrity of their structure is a prerequisite for their physical changes and interference with the formation of conductive paths during local overheating in electrical tracking tests. By preparing the functional masterbatch, the issues of adding, dispersing, and protecting powder b and hollow silica microspheres are moved forward and simplified from the complex final mixing process. This allows the final composite process to focus only on ensuring the fusion of the masterbatch and the resin, reducing the process difficulty and improving the reliability and reproducibility of the final product performance. This is an important process guarantee for the synergistic improvement of CTI.

[0035] It is worth noting that in this step, powder b and hollow silica microspheres are each used at 4-5.5 parts by weight to ensure a sufficiently high concentration of both in the masterbatch, thereby improving the final blending efficiency while avoiding processing difficulties or insufficient carrier resin coating due to excessive filling. PET resin a with an intrinsic viscosity of 0.65-0.75 dL / g is selected as the carrier to ensure good flowability and coating capacity at a processing temperature of 240-255℃. The melt blending temperature is controlled within the lower range of 240-255℃, and is combined with... A medium-low screw speed of 150-250 rpm is key to achieving full melting and basic dispersion of PET while applying the gentlest possible shear force, thus protecting the hollow microsphere shell from mechanical damage. Meanwhile, the use of a micro-negative pressure venting of (-0.03) to (-0.05 MPa) avoids the pressure difference caused by a strong vacuum, which could lead to an imbalance between the internal and external pressures of the microsphere shell and cause it to rupture. The synergistic combination of these material ratios and process parameters ensures the successful preparation of the functional masterbatch as a stable and fully functional intermediate product.

[0036] Specifically, in step S2, the combined flame retardant is mixed with PET resin b to obtain a premix, and the premix is ​​melt-blended and granulated to obtain flame retardant masterbatch. Step S2 specifically includes the following steps: Step S21: Mix flame retardant a, flame retardant b, PET resin b, chain extender b, and lubricant b in a high-speed mixer for 3-5 minutes to obtain a premix. In step S21, flame retardant a is surface-coated ammonium polyphosphate, and flame retardant b is melamine polyphosphate. By weight, flame retardant a, flame retardant b, PET resin b, chain extender b, and lubricant b are 10-14 parts by weight, 6-8 parts by weight, 30 parts by weight, 0.5-0.75 parts by weight, and 0.25-0.4 parts by weight, respectively. In addition, the intrinsic viscosity of both PET resin a and PET resin b is 0.65-0.75 dL / g, both lubricant a and lubricant b are pentaerythritol stearate, and both chain extender a and chain extender b are styrene-acrylate-glycidyl methacrylate copolymer.

[0037] Step S22: The premixed material is fed into the twin-screw extruder b and melt-blended at 250-260°C under a vacuum of (-0.07)-(-0.08MPa) and a screw speed of 200-300rpm. After cooling and granulation, flame retardant masterbatch is obtained.

[0038] It should be noted that in step S2, the material system undergoes a complete process from physical dry mixing to melt shear dispersion, and finally solidification into particles. Through melt blending, solid additives such as flame retardants are uniformly dispersed and coated into PET resin b. Specifically, in a high-speed mixer, surface-coated ammonium polyphosphate of flame retardant a, melamine polyphosphate of flame retardant b, and PET resin b particles are physically mixed, allowing the components to initially contact each other and form a premix. When the premix enters the twin-screw extruder b, as the temperature rises to 250-260℃, PET resin b melts into a continuous phase. Under the shearing and kneading action of the screw, the agglomerates of flame retardant a and flame retardant b are gradually opened and dispersed in the PET melt. Chain extender b reacts with the end groups of PET, which helps to compensate for the possible decrease in molecular weight caused by processing. After the above process, the premix is ​​discharged from the extruder, transformed into a uniform and dense melt. After extrusion, cooling, and pelletizing by the die head, flame retardant masterbatch with uniform color and regular particles is obtained.

[0039] It is known that step S2, by pre-dispersing heat-sensitive flame retardants a and b in PET resin b under controlled high temperature and vacuum and then granulating them, yields a high-concentration, thermally stable, and low-volatile flame retardant masterbatch. In step S2, effective protection and pre-dispersion of flame retardants a and b are achieved. By using PET resin b as a carrier for the first melt blending, the heating time and thermomechanical effects of flame retardants a and b in the subsequent final blending step are significantly shortened, reducing the risk of premature decomposition during final processing. At the same time, this step is carried out under a relatively high vacuum, which can effectively remove moisture that may be adsorbed by the flame retardants (especially ammonium polyphosphate) and small molecule volatiles generated during processing. This helps to avoid defects such as bubbles and silver streaks in the final product and reduces the possibility of PET hydrolysis and degradation due to moisture, thereby indirectly maintaining the insulation performance of the material and effectively preventing the hydrolysis and degradation of PET resin during processing, which helps to maintain the stability of the material's molecular weight and overall performance.

[0040] Understandably, step S2, by preparing flame-retardant masterbatch, ensures that the key flame-retardant system (an intumescent flame-retardant system composed of flame retardant a and flame retardant b) can be introduced into the final material in a highly dispersed state. This is a prerequisite for fully exerting its synergistic flame-retardant effect and achieving the UL94V-0 rating. At the same time, the protective and purification treatment of flame retardant a and flame retardant b in this step ensures the effective content and chemical stability of the flame retardants, avoiding negative impacts on the CTI performance of the material due to processing losses or decomposition acid production.

[0041] It is worth noting that step S2 employs a stepwise premixing and corresponding melt blending process based on the heat sensitivity and processing characteristics of the flame retardant. Regarding the material ratio, the total amount of flame retardant a and flame retardant b is at a relatively high concentration relative to 30 parts by weight of PET resin b, which can prepare a masterbatch with high functional content, thereby improving the proportioning efficiency and uniformity of the subsequent final blending. Since the selected surface-coated ammonium polyphosphate typically has a thermal stability higher than 270℃, the upper limit of the melt blending temperature of the twin-screw extruder b at 260℃ can ensure sufficient melt flow of PET while minimizing flame retardant degradation. Significant decomposition of the flame retardant occurred; a screw speed of 200-300 rpm provided sufficient shear force to ensure dispersion, while a relatively high vacuum of (-0.07)-(-0.08 MPa) specifically removed moisture and small volatile ammonia molecules from the flame retardant surface. This vacuum level was stronger than the micro-negative pressure during the preparation of functional masterbatches, reflecting a differentiated process response to different material characteristics (flame retardants are hygroscopic and hollow microspheres are easily broken). The combined effect of these parameters ensured that the flame retardant masterbatch had a stable chemical composition, good dispersion, and low defect risk.

[0042] Specifically, in step S3, the functional masterbatch, flame retardant masterbatch and PET resin c are mixed to obtain a dry mixture, and then the dry mixture is melt-blended and granulated to obtain PET engineering plastic.

[0043] Step S3 specifically includes the following steps: Step S31: Mix PET resin c, flame retardant masterbatch, and functional masterbatch in a drum mixer for 5-10 minutes to obtain a dry mix; in step S31, by weight, the PET resin c, flame retardant masterbatch, and functional masterbatch are 40-50 parts by weight, 46.5-52.5 parts by weight, and 34.5-37.3 parts by weight, respectively; the intrinsic viscosity of the PET resin c is 0.70-0.80 dL / g; Step S32: The dry mixture is fed into a twin-screw extruder c and melt-blended at 245-260°C under a vacuum of (-0.05)-(-0.07MPa) and a screw speed of 180-250rpm. After cooling and granulation, granules are obtained. The granules are then dried at 120-130°C for 4-6 hours. After drying, PET engineering plastic is obtained. In step S32, the moisture content of the PET engineering plastic is <50ppm.

[0044] It should be noted that in step S3, PET resin c particles, flame retardant masterbatch particles, and functional masterbatch particles are physically mixed to obtain a dry mixture. When this dry mixture enters the twin-screw extruder c, as the temperature gradually increases, all PET components (including PET resin a and PET resin b in the functional masterbatch and flame retardant masterbatch) melt and merge into a continuous matrix phase. Under the conveying and low-to-medium shear action of the screw, flame retardant particles from the flame retardant masterbatch, powder b from the functional masterbatch, and hollow silica microspheres are further released from their respective carriers and dispersed in the entire continuous melt phase, achieving the ultimate uniform distribution of each component, while chain extenders and other additives continue to play their role. As melt blending proceeds, the dry mixture transforms into a uniform and dense melt. After water cooling, pelletizing, and thorough drying, the final PET engineering plastic pellets with a moisture content of <50ppm and uniform particle size are obtained.

[0045] It is known that step S3 achieves high dispersion, structural integrity, and synergistic integration of functional components in the final product by finally fusing and homogenizing the functional masterbatch, flame retardant masterbatch, and PET resin c under controlled and mild processes. Under the action of step S3, the process from functional unit prefabrication to overall material synthesis is completed, so that the flame retardant function and anti-tracking function are locked in a unified PET matrix and produce synergy. At the same time, the specific process conditions adopted in this step are designed to balance the relationship between thorough mixing and homogenization, elimination of volatiles, and protection of sensitive structures. The appropriate vacuum degree helps to remove residual moisture and small molecules, ensuring the material density and electrical stability. The controlled temperature and shear force are the key to prevent the protected hollow silica microspheres in the functional masterbatch from being damaged, ensuring their structural integrity and functional potential.

[0046] Understandably, the preceding steps prepared functional masterbatches to enhance CTI and flame-retardant masterbatches to ensure flame retardancy, respectively. Step S3 is responsible for combining and maximizing the effectiveness of these two with the base resin. Through this step, the insulating structure constructed by powder b is widely distributed in the overall material, interfering with the conductive path both electrically and physically. The structure of the hollow silica microspheres as thermal response perturbation units is preserved, ensuring that they generate perturbations when the electrical tracking is locally overheated. The flame retardant system is uniformly distributed in the matrix, ensuring its flame retardant efficiency. Powder b provides a solid foundation for high tracking voltage, while the hollow silica microspheres apply random interference in the early dynamic process when the electrical tracking attempts to break through this foundation. The two complement each other in time and space, jointly managing the development process of the electrical tracking, thereby realizing the transformation from a zero-sum game to a synergistic improvement in flame retardancy and anti-tracking properties.

[0047] It is worth noting that in step S3, the ratio of PET resin c, functional masterbatch, and flame retardant masterbatch determines the final concentration and synergistic relationship of the matrix resin, anti-tracking functional component, and flame retardant functional component in the final material. PET resin c, as the main matrix phase, provides the necessary continuity and basic mechanical property framework for the entire composite material at a dosage of 40-50 parts by weight, ensuring the material's processability and the structural integrity of the final product. Meanwhile, the dosage of 46.5-52.5 parts by weight of flame retardant masterbatch and 34.5-37.3 parts by weight of functional masterbatch ensures the content of the combined flame retardant, powder b, and hollow silica microspheres. The melt blending temperature of the twin-screw extruder c, 245-260℃, provides sufficient and uniform heat to blend all the P... The ET components are completely melted and well mixed, while avoiding localized overheating that could lead to degradation. A medium vacuum of (-0.05) to (-0.07 MPa) is used to achieve a balance between removing volatiles and protecting the hollow microspheres. The screw speed is 180-250 rpm to provide the necessary mixing shear force without damaging the hollow silica microspheres, thus protecting them. Drying at 120-130℃ for 4-6 hours until the moisture content is <50 ppm is a crucial post-treatment to remove adsorbed moisture from the surface and interior of the granules, ensuring the stability of the PET engineering plastic in subsequent injection molding and the electrical insulation properties of the final product. The synergy of these proportions and parameters ensures the reliability and reproducibility of the final PET engineering plastic's performance.

[0048] The present invention also proposes a PET engineering plastic, which is obtained by the above-described PET engineering plastic preparation method, as detailed in Examples 1, 2, and 3.

[0049] Example 1: Step S1: 100 parts by weight of aluminum hydroxide powder with an average particle size D50 of 5.5 μm and 400 parts by weight of a 1:1 volume ratio of ethanol and water mixed solvent were added to a reactor and stirred at 300 rpm to form a suspension. 2 parts by weight of γ-aminopropyltriethoxysilane were added to the suspension, and stirring was continued for 10 min. Subsequently, 10 parts by weight of polyphenylene ether oligomer with a number average molecular weight Mn of approximately 1500 were added, and the system was heated to 65°C and stirred continuously at this temperature for 2 h. After the reaction was completed, the system was filtered, and the resulting filter cake was washed twice with ethanol. The filter cake was then dried in an oven at 95°C for 9 h. Finally, the dried material was pulverized and passed through a 100-mesh sieve to obtain powder b with a high-resistivity organic composite interface layer on its surface.

[0050] 4.75 parts by weight of powder b, 4.75 parts by weight of hollow silica microspheres with a particle size of 3.5 μm and internally encapsulated with paraffin wax at a phase change temperature of 150℃, 25 parts by weight of PET resin a with an intrinsic viscosity of 0.70 dL / g, 0.625 parts by weight of chain extender a, 0.65 parts by weight of composite antioxidant, 0.4 parts by weight of organic carboxylate nucleating agent, and 0.325 parts by weight of lubricant a were added to a high-speed mixer and mixed for 4 minutes. Subsequently, this mixture was fed into a twin-screw extruder a and melt-blended, extruded, cooled, and pelletized under conditions of a set temperature range of 245-255℃, a vacuum degree of -0.04 MPa, and a screw speed of 200 rpm to obtain the functional masterbatch.

[0051] Step S2: 12 parts by weight of surface-coated ammonium polyphosphate, 7 parts by weight of melamine polyphosphate, 30 parts by weight of PET resin b with an intrinsic viscosity of 0.70 dL / g, 0.625 parts by weight of chain extender b and 0.325 parts by weight of lubricant b are premixed and fed into a twin-screw extruder b. The mixture is melt-blended and granulated under the conditions of 250-260℃, vacuum degree -0.075MPa and screw speed 250rpm to obtain flame retardant masterbatch.

[0052] Step S3: 45 parts by weight of PET resin c with an intrinsic viscosity of 0.75 dL / g, 49.95 parts by weight of the flame-retardant masterbatch prepared above, and 35.925 parts by weight of functional masterbatch are added to a drum mixer and mixed for 8 minutes to obtain a uniform dry mixture. This dry mixture is then fed into a twin-screw extruder c, and subjected to final melt blending, extrusion, cooling, and pelletizing under the conditions of a set temperature range of 245-260℃, a vacuum degree of -0.06MPa, and a screw speed of 220rpm. Finally, the resulting pellets are dried at 125℃ for 5 hours to achieve a moisture content of <50ppm, yielding PET engineering plastic.

[0053] Example 2: The basic content is the same as in Example 1, except that: In step S1, by weight, powder b is 5.5 parts by weight, hollow silica microspheres are 5.5 parts by weight, and PET resin a is 25 parts by weight.

[0054] In step S2, by weight, flame retardant a is 11 parts by weight, flame retardant b is 6.5 parts by weight, and PET resin b is 30 parts by weight.

[0055] In step S3, by weight, PET resin c is 46 parts by weight, flame retardant masterbatch is 46.6 parts by weight, and functional masterbatch is 37.4 parts by weight.

[0056] Example 3: The basic content is the same as in Example 1, except that: In step S1, by weight, powder b is 4.0 parts by weight, hollow silica microspheres are 4.0 parts by weight, and PET resin a is 25 parts by weight.

[0057] In step S2, by weight, flame retardant a is 14 parts by weight, flame retardant b is 8 parts by weight, and PET resin b is 30 parts by weight.

[0058] In step S3, by weight, PET resin c is 43 parts by weight, flame retardant masterbatch is 52.4 parts by weight, and functional masterbatch is 34.1 parts by weight.

[0059] Comparative Example 1: The comparative example is a method for preparing PET engineering plastics in the prior art, specifically as follows: First, 100 parts by weight of PET resin with an intrinsic viscosity of 0.75 dL / g, 15 parts by weight of surface-coated ammonium polyphosphate, 9 parts by weight of melamine polyphosphate, 0.7 parts by weight of a composite antioxidant composed of antioxidants 1010 and 168 in a 1:1 mass ratio, 0.4 parts by weight of an organic carboxylate nucleating agent, 0.7 parts by weight of pentaerythritol stearate lubricant, 1.0 part by weight of an epoxy chain extender, and 9.5 parts by weight of untreated aluminum hydroxide powder with an average particle size D50 of 5.5 μm are all added to a high-speed mixer and mixed for 5 minutes to obtain a premix. Subsequently, the premix is ​​fed into a twin-screw extruder and subjected to a one-time melt blending, extrusion, water cooling, and pelletizing process at a temperature range of 250-265℃, a vacuum degree of -0.08 MPa, and a screw speed of 300 rpm. Finally, the obtained granules were dried at 125°C for 5 hours to obtain the PET engineering plastic of Comparative Example 1.

[0060] The following table shows the corresponding data for Examples 1, 2, and 3 and Comparative Example 1. See Table 1 for details: Table 1

[0061] In Table 1 above, the flame retardant performance is tested using UL 94 as the test standard and the vertical burning method; the tracking resistance index is tested using IEC 60112 as the test standard and the solution dripping method; the tensile strength is tested using ASTM D638 as the test standard, using a Type I standard dumbbell-shaped specimen, and is tested on a universal testing machine at a constant tensile rate until the specimen breaks; the impact strength is tested using ASTM D256 as the test standard, using a rectangular specimen with a specified V-notch, which is placed horizontally on a simply supported beam impact testing machine, and the energy consumed by the pendulum to break the specimen in one strike is measured and converted into the energy consumed per unit notch thickness.

[0062] As shown in Table 1, although Comparative Example 1, which used a traditional direct blending method with flame retardants, achieved a UL94V-0 flame retardant rating for the PET material, its tracking index (CTI) was only 175V, and its impact strength was only 3.0 kJ / m². 2 This confirms the common problem pointed out in the background section: existing technical solutions, when improving flame retardant performance, lead to a significant decrease in CTI and damage to material toughness. In contrast, Embodiment 1 of the present invention, while achieving the same V-0 flame retardant rating, significantly increases the CTI value to 325V, while the tensile strength and impact strength reach 58MPa and 4.5kJ / m, respectively. 2 This demonstrates that the invention significantly improves the material's resistance to tracking and overall mechanical properties without sacrificing flame retardancy. Example 2, by moderately increasing the proportion of functional components, further enhances the CTI value to 350V. This reflects the effectiveness and adjustment potential of the present invention in overcoming the traditional CTI bottleneck. Although its flame retardancy time and mechanical properties are slightly adjusted, it is still comprehensively superior to Comparative Example 1. Example 3, by focusing on the flame retardant components, maintains the V-0 rating and shorter burning time while keeping the CTI at a relatively high level of 300V. Its mechanical properties are also superior to the comparative example. This further demonstrates that the method of the present invention can achieve a synergistic improvement in flame retardancy and CTI performance, rather than a trade-off. In summary, the three embodiments of the present invention construct dispersed insulating barriers in the matrix by using surface-modified aluminum hydroxide powder to hinder the formation of conductive pathways, and utilize the potential disturbance effect of hollow microspheres in the early stage of electrical tracking to interfere with the continuity of carbonization channels. Combined with a stepwise masterbatch process, the effective dispersion and structural preservation of each functional unit are ensured, thereby successfully solving the technical problems of low CTI value and poor toughness of high flame retardant PET materials, and obtaining a material with more balanced and excellent comprehensive performance.

[0063] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing PET engineering plastic, characterized in that, The preparation method includes the following steps: Step S1: Surface treatment and modification of aluminum hydroxide powder to obtain powder b with a high-resistivity organic composite interface layer compatible with PET. Then, powder b, hollow silica microspheres and PET resin a are melt-blended and granulated to obtain functional masterbatch. Step S2: Mix the combined flame retardant with PET resin b to obtain a premix, and then melt-blend and granulate the premix to obtain flame retardant masterbatch. Step S3: Mix the functional masterbatch, flame retardant masterbatch and PET resin c to obtain a dry mixture, then melt-blend and granulate the dry mixture to obtain PET engineering plastic.

2. The method for preparing PET engineering plastic according to claim 1, characterized in that, The powder b is obtained according to the following steps: Aluminum hydroxide powder was added to a reaction vessel along with a mixed solvent and stirred at 200-400 rpm to obtain a suspension. Then, a silane coupling agent was added to the suspension and stirring was continued for 8-12 minutes. Subsequently, polyphenylene ether oligomer was added to the system and stirred at 50-80°C for 1-3 hours. The system was then filtered, and the resulting filter cake was washed 2-3 times with ethanol. After washing, the filter cake was dried at 80-110°C for 6-12 hours. The dried filter cake was then pulverized and sieved through a 100-mesh sieve to obtain powder b.

3. The method for preparing PET engineering plastic according to claim 2, characterized in that, The aluminum hydroxide powder has an average particle size D50 of 3-8 μm, the mixed solvent is a mixture of ethanol and water in a volume ratio of 1:1, the silane coupling agent is γ-aminopropyltriethoxysilane, and the number average molecular weight Mn of the polyphenylene ether oligomer is <2000. By weight, the aluminum hydroxide powder, mixed solvent, silane coupling agent and polyphenylene ether oligomer are 100 parts by weight, 300-500 parts by weight, 1-3 parts by weight and 5-15 parts by weight, respectively.

4. The method for preparing PET engineering plastic according to claim 1, characterized in that, The functional masterbatch is obtained according to the following steps: Powder b, hollow silica microspheres, PET resin a, chain extender a, composite antioxidant, nucleating agent and lubricant a are mixed in a high-speed mixer for 3-5 minutes to obtain a mixture; then the mixture is fed into a twin-screw extruder a and melt-blended at 240-255℃ under a vacuum of (-0.03)-(-0.05MPa) and a screw speed of 150-250rpm. After cooling and granulation, functional masterbatch is obtained.

5. The method for preparing PET engineering plastic according to claim 4, characterized in that, By weight, the powder b, hollow silica microspheres, PET resin a, chain extender a, composite antioxidant, nucleating agent and lubricant a are 4-5.5 parts by weight, 4-5.5 parts by weight, 25 parts by weight, 0.5-0.75 parts by weight, 0.5-0.8 parts by weight, 0.3-0.5 parts by weight and 0.25-0.4 parts by weight, respectively; the hollow silica microspheres have a particle size of 2-5 μm and are encapsulated with hydrocarbon phase change substances with a phase change temperature of 120-180℃; the nucleating agent is an organic carboxylate nucleating agent; the composite antioxidant includes 1010 antioxidant and 168 antioxidant in a mass ratio of 1:

1.

6. The method for preparing PET engineering plastic according to claim 5, characterized in that, Step S2 specifically includes the following steps: Step S21: Mix flame retardant a, flame retardant b, PET resin b, chain extender b, and lubricant b in a high-speed mixer for 3-5 minutes to obtain a premix. Step S22: The premixed material is fed into the twin-screw extruder b and melt-blended at 250-260°C under a vacuum of (-0.07)-(-0.08MPa) and a screw speed of 200-300rpm. After cooling and granulation, flame retardant masterbatch is obtained.

7. The method for preparing PET engineering plastic according to claim 6, characterized in that, In step S21, flame retardant a is surface-coated ammonium polyphosphate, and flame retardant b is melamine polyphosphate. By weight, flame retardant a, flame retardant b, PET resin b, chain extender b, and lubricant b are 10-14 parts by weight, 6-8 parts by weight, 30 parts by weight, 0.5-0.75 parts by weight, and 0.25-0.4 parts by weight, respectively. In addition, the intrinsic viscosity of both PET resin a and PET resin b is 0.65-0.75 dL / g, both lubricant a and lubricant b are pentaerythritol stearate, and both chain extender a and chain extender b are styrene-acrylate-glycidyl methacrylate copolymer.

8. The method for preparing PET engineering plastic according to claim 1, characterized in that, Step S3 specifically includes the following steps: Step S31: Mix PET resin c, flame retardant masterbatch and functional masterbatch in a drum mixer for 5-10 minutes to obtain dry mix; Step S32: The dry mixture is fed into the twin-screw extruder c and melt-blended at 245-260℃ under a vacuum of (-0.05)-(-0.07MPa) and a screw speed of 180-250rpm. After cooling and granulation, the granules are obtained. The granules are then dried at 120-130℃ for 4-6 hours. After drying, PET engineering plastic is obtained.

9. The method for preparing PET engineering plastic according to claim 8, characterized in that, In step S31, by weight, the PET resin c, flame retardant masterbatch, and functional masterbatch are 40-50 parts by weight, 46.5-52.5 parts by weight, and 34.5-37.3 parts by weight, respectively; the intrinsic viscosity of the PET resin c is 0.70-0.80 dL / g. In step S32, the moisture content of the PET engineering plastic is <50ppm.

10. A PET engineering plastic, characterized in that, The PET engineering plastic is obtained by the preparation method according to any one of claims 1-9.

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