A method for preparing polycarbonate sheets

Abstract

The present application relates to the technical field of high polymer material preparation, in particular to a method for preparing polycarbonate sheet, which comprises the following steps: S1. surface pretreatment; S2. prepolymerization; S3. melt blending: the terminal hydroxyl prepolymer is added to the main feeding port of a double screw extruder, the cage type silsesquioxane, fluorinated epoxy compound and pretreated cerium oxide nanoparticles are synchronously added from the third zone side feeding port, and then the extrudate is obtained after melt blending and extrusion; S4. calendering. The cage type silsesquioxane, fluorinated epoxy compound and cerium oxide nanoparticles are scientifically compounded, so that the prepared polycarbonate sheet is greatly improved in terms of optics, mechanics and weather resistance. Meanwhile, the preparation method is simple and feasible, has low requirements on equipment and is easy to industrialize, and has obvious economic value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer material preparation, and particularly relates to a method for preparing polycarbonate sheet. BACKGROUND

[0002] Polycarbonate (PC) is widely used in the industrial fields of automotive parts, electronic and electrical products, optical lenses, mobile phone housings and other internal and external materials due to its excellent impact resistance, electrical properties, heat resistance and high light transmittance, and is particularly widely researched as the preferred substrate for mobile phone glass-imitating back covers. However, PC material has significant defects that restrict its application: its high melt viscosity leads to poor formability, and the impact resistance is thickness-dependent; the impact strength is low at low temperatures, and it is sensitive to notches, which easily causes stress cracking; yellowing, mechanical property degradation and surface deterioration easily occur during long-term outdoor use; and more importantly, the inherent hardness of PC is only 2B-3B, and the wear resistance is insufficient, which cannot meet the requirement of surface hardness of more than 2H for glass-imitating back covers.

[0003] To improve the weather resistance and toughness of polycarbonate, the existing technology often adds thermal stabilizers, toughening agents or hindered amine weathering agents in the composite material. However, such additives are prone to cause gelation and discoloration during processing, and still cannot effectively inhibit the mechanical property degradation and appearance deterioration in outdoor environments. For the hardness and wear resistance problems, the current mainstream solution is to coat the surface of the molded part with a high-hardness coating or add a scratch-resistant agent, but this leads to the complication of the process flow and the increase of the cost. At the same time, such modification often accompanies the decrease of the transparency of the material (color difference or fogging), and the hardening modification often sacrifices its core advantage-impact toughness.

[0004] Therefore, it is urgent to develop a new PC modification technology that can synergistically optimize the processing fluidity, low-temperature toughness, ultraviolet aging resistance and inherent hardness / wear resistance without relying on post-coating process, and break through the bottleneck that the transparency, mechanical properties and surface function are difficult to be considered in the existing technology. SUMMARY

[0005] OBJECTIVE

[0006] To overcome the shortcomings of existing technologies, the present invention aims to provide a method for preparing polycarbonate sheets. The method specifically includes the following steps: S1. Surface pretreatment; S2. Prepolymerization reaction; S3. Melt blending: The hydroxyl-terminated prepolymer is added to the main feed port of a twin-screw extruder, while cage-type silsesquioxane, fluorinated epoxy compound, and pretreated cerium oxide nanoparticles are simultaneously added from the third-zone side feed port. After melt blending, the mixture is extruded to obtain the extrudate; S4. Calendering. This invention, through the scientific compounding of cage-type silsesquioxane, fluorinated epoxy compound, and cerium oxide nanoparticles, achieves a breakthrough improvement in the optical, mechanical, and weather resistance properties of the prepared polycarbonate sheets. Furthermore, the preparation method provided by this invention is simple and feasible, requires minimal equipment, is easy to industrialize, and has significant economic value.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing polycarbonate sheets includes the following steps:

[0009] S1. Surface pretreatment: Mix 1-3 parts by weight of cerium oxide nanoparticles with 1-2 parts by weight of silane coupling agent in a sealed container and react at 60-70℃ for 10-15 min to allow silane hydrolysis to form a -Si-O-Ce- bonded layer on the surface of cerium oxide nanoparticles, thus obtaining pretreated cerium oxide nanoparticles.

[0010] S2. Prepolymerization reaction: Mix 90-100 parts of polycarbonate, 5-10 parts of isosorbide and 3-5 parts of polyethylene glycol by mass, and carry out transesterification reaction at 200-220℃ for 30-40 min under nitrogen protection to generate hydroxyl-terminated prepolymer.

[0011] S3. Melt blending: The hydroxyl-terminated prepolymer is added to the main feed port of a twin-screw extruder, while cage-type silsesquioxane, fluorinated epoxy compound, and pretreated cerium oxide nanoparticles are simultaneously added from the third zone side feed port. After melt blending, the mixture is extruded to obtain the extrudate.

[0012] S4. Calendering: After the extrudate is water-cooled and pelletized, it is fed into a flat calender to calender into 0.2-1mm thin sheets, and pressure is maintained for 5-10 minutes to promote surface curing of the sheets, thus obtaining polycarbonate sheets.

[0013] Preferably, in step S1, the particle size range of the cerium oxide nanoparticles is 30-50 nm.

[0014] Preferably, in step S1, the silane coupling agent is selected from one or more of γ-aminopropyltriethoxysilane and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane.

[0015] Preferably, in step S2, the molecular weight of the polyethylene glycol is 2000-5000.

[0016] Preferably, in step S3, the mass ratio of the terminal hydroxyl prepolymer, cage-type silsesquioxane, fluorinated epoxy compound, and pretreated cerium oxide nanoparticles is 95-110:5-10:8-15:2-3.

[0017] Preferably, the cage-like silsesquioxane is a mixture of aminopropyl isobutyl cage-like silsesquioxane and octaglycidoxypropyl cage-like silsesquioxane in a mass ratio of 1-3:1-3.

[0018] Preferably, the fluorinated epoxy compound is selected from one or more of 1,1,1-trifluoromethyl-3,4-epoxycyclohexane and 3-(perfluorohexyl)-1,2-epoxypropane.

[0019] Preferably, in step S3, the temperatures of each zone of the twin-screw extruder are: zone 1 220-230℃, zone 230-240℃, zone 3 250-260℃, zone 4 260-270℃, zone 5 270-265℃, zone 6 265-255℃, and zone 7 245-235℃.

[0020] Preferably, in step S4, the process parameters of the flat calender are: temperature 190-200℃ and pressure 10-15MPa.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. This invention achieves a breakthrough improvement in the optical, mechanical, and weather resistance properties of the prepared polycarbonate sheet through the scientific compounding of cage-like silsesquioxane, fluorinated epoxy compound, and cerium oxide nanoparticles.

[0023] 2. The preparation method provided by the present invention is simple and feasible, has low equipment requirements, is easy to industrialize, and has significant economic value. Attached Figure Description

[0024] Figure 1 This is a flow chart of the production process of the polycarbonate sheet described in this invention. Detailed Implementation

[0025] The present invention will now be clearly and completely described in conjunction with embodiments thereof. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] Please see Figure 1The present invention provides a technical solution:

[0027] Example 1

[0028] A method for preparing polycarbonate sheets includes the following steps (where one part by weight is 200g):

[0029] S1. Surface Pretreatment: 1.45 parts by weight of cerium oxide nanoparticles and 1.2 parts by weight of silane coupling agent were mixed in a sealed container and reacted at 60°C for 10 min. This allowed silane hydrolysis to form a -Si-O-Ce- bonded layer on the surface of the cerium oxide nanoparticles, resulting in pretreated cerium oxide nanoparticles. The ethoxy groups of the silane coupling agent (KH-550) hydrolyzed to silanol (Si-OH), releasing ethanol. The silanol underwent dehydration condensation with the hydroxyl groups on the CeO2 surface to form Si-O-Ce covalent bonds. The amino group (-NH2) remained on the cerium oxide surface, providing active sites for subsequent reactions with epoxy groups. The reaction equation is shown below:

[0030] NH2(CH2)3Si(OC2H5)3+3H2O−>NH2(CH2)3Si(OH)3+3C2H5OH;

[0031] NH2(CH2)3Si(OH)3+HO−CeO2−>NH2(CH2)3Si−O−CeO2+2H2O;

[0032] S2. Prepolymerization reaction: 92 parts by weight of polycarbonate, 5.5 parts by weight of isosorbide and 3 parts by weight of polyethylene glycol are mixed and blended at 200°C for 30 min under nitrogen protection to carry out transesterification reaction and generate hydroxyl-terminated prepolymer.

[0033] The ester bonds (-OC(O)-O-) of bisphenol A polycarbonate undergo transesterification with the hydroxyl groups of isosorbide, breaking the polycarbonate chain and introducing a rigid furan ring at the end, thus improving heat resistance. PEG3000 acts as a plasticizer to reduce melt viscosity, and its terminal hydroxyl groups participate in the reaction to increase branching points. Nitrogen protection prevents oxidative degradation and inhibits yellowing. The reaction equation is shown below:

[0034] HO-[O-Ar-OC(O)] x -OC(O)-O-[O-Ar-OC(O)] y -OH+2HO-Isorbide-OH−>HO-[O-Ar-OC(O)] p -OC(O)-O-Isorbide-OC(O)-[O-Ar-OC(O)] q -OH+H2O;

[0035] Wherein, Ar: isopropylidene diphenyl;

[0036] Isorbide: 1,4:3,6-disohydrated sorbitol;

[0037] S3. Melt Blending: The hydroxyl-terminated prepolymer is added to the main feed port of a twin-screw extruder, while cage-type silsesquioxane, fluorinated epoxy compound, and pretreated cerium oxide nanoparticles are simultaneously added from the third-zone side feed port. After melt blending, the mixture is extruded to obtain the extrudate. This step constructs a high-performance network structure through a multi-component synergistic reaction, which is carried out through the following reaction:

[0038] 1. Amino-epoxy ring-opening crosslinking

[0039] The amino group (-NH2) nucleophilically attacks the methylene carbon of the epoxy ring, forming a β-hydroxy secondary amine structure through ring opening. This reaction constructs a three-dimensional cross-linked network, significantly increasing the rigidity of the molecular chain and raising the glass transition temperature. The simplified reaction equation is shown below:

[0040] R−NH2+R′−CH(O)CH−−>R−NH−CH2−CH(OH)−R′;

[0041] 2. Catalytic branching of silicon-oxygen framework

[0042] The silicon-oxygen framework (≡Si-O-Si≡) of cage-like silsesquioxanes (POSS) hydrolyzes in a high-temperature, aqueous environment to form a protic acid (≡Si-OH). This catalyzes the ring-opening reaction between the terminal hydroxyl group (-OH) and the epoxy group, forming a branched structure, broadening the molecular weight distribution, and improving the material's impact resistance. The simplified reaction equation is shown below:

[0043] HO−R′′+R′−CH(O)CH−−>[H + ]HO−CH2−CH(OH)−R′−R′′;

[0044] 3. CeO2-NH2 participates in cross-linking

[0045] Pretreated CeO2 participates in crosslinking via amino groups, anchoring the inorganic phase within the polymer network, wherein cerium oxide (CeO2) is crosslinked via Ce... 3+ / Ce 4+ The redox pair captures free radicals and repairs carbonate bonds damaged by UV radiation, inhibiting yellowing. The simplified reaction equation is shown below:

[0046] CeO2−NH2+CF3O−CH2−CH2O−>CeO2−NH−CH2−CH(OH)−CF3;

[0047] S4. Calendering: After the extrudate is water-cooled and pelletized, it is fed into a flat calender to be calendered into 1mm thin sheets and held under pressure for 10 minutes to promote surface curing of the sheets, thus obtaining polycarbonate sheets. The cross-linking structure of the sheets is improved by hot pressing, so that the unreacted epoxy groups and hydroxyl groups continue to react under pressure to form a dense surface layer, and further promote the rearrangement of the POSS network to improve the surface hardness. Fluorinated segments are enriched on the surface of the polycarbonate sheets to form a hydrophobic layer.

[0048] In the above preparation process, in step S1, the particle size range of the cerium oxide nanoparticles is 30-40 nm;

[0049] The silane coupling agent is γ-aminopropyltriethoxysilane, specifically model KH-550;

[0050] In step S2, the polyethylene glycol has a molecular weight of 3000; the polycarbonate is bisphenol A type polycarbonate, with the brand name Makrolon® 2805;

[0051] In step S3, the mass ratio of the terminal hydroxyl prepolymer, cage-like silsesquioxane, fluorinated epoxy compound, and pretreated cerium oxide nanoparticles is 92:5:8:2.

[0052] The cage-like silsesquioxane is a mixture of aminopropyl isobutyl cage-like silsesquioxane and octaglycidyl oxypropyl cage-like silsesquioxane in a mass ratio of 1.5:3; the aminopropyl isobutyl cage-like silsesquioxane is of type KH-540-POSS and was purchased from Tianjin Bodi Chemical; the octaglycidyl oxypropyl cage-like silsesquioxane is of type JH-P201 and was purchased from Shanghai Jiehua New Materials.

[0053] The fluorinated epoxy compound is 1,1,1-trifluoromethyl-3,4-epoxycyclohexane;

[0054] In step S3, the process parameters of the twin-screw extruder are as follows: zone temperatures are 230℃ for zone 1, 240℃ for zone 2, 250℃ for zone 3, 270℃ for zone 4, 265℃ for zone 5, 255℃ for zone 6, and 235℃ for zone 7 (L / D = 40); the screw speed is 300 rpm; and the extrusion pressure is 0.5 MPa.

[0055] In step S4, the process parameters of the flat calender are: temperature 190℃ and pressure 10MPa.

[0056] Example 2: Example 2 differs from Example 1 in that, in Example 2, the cage-like silsesquioxane is a mixture of aminopropyl isobutyl cage-like silsesquioxane and octaglycidoxypropyl cage-like silsesquioxane in a mass ratio of 3:1.5. The remaining steps are exactly the same as in Example 1 and Example 2.

[0057] Example 3: Example 3 differs from Example 1 in that, in Example 3, the cage-like silsesquioxane is a mixture of aminopropyl isobutyl cage-like silsesquioxane and octaglycidoxypropyl cage-like silsesquioxane in a mass ratio of 1:1. The remaining steps are exactly the same as in Example 1 and Example 3.

[0058] Example 4: Example 4 differs from Example 1 in that, in Example 4, the mass ratio of the terminal hydroxyl prepolymer, cage-like silsesquioxane, fluorinated epoxy compound, and pretreated cerium oxide nanoparticles in step S3 is 100:10:15:3. The remaining steps are exactly the same as in Example 1 and Example 4.

[0059] Comparative Example

[0060] Comparative Example 1: The only difference between Comparative Example 1 and Example 1 is that the cage-like silsesquioxane present in Example 1 was omitted in Comparative Example 1. The remaining steps are exactly the same in Comparative Example 1 and Example 1.

[0061] Comparative Example 2: Comparative Example 2 differs from Example 1 in that the cage-like silsesquioxane and fluorinated epoxy compound present in Example 1 are omitted in Comparative Example 2. The remaining steps are exactly the same in Comparative Example 2 and Example 1.

[0062] Comparative Example 3: Comparative Example 3 differs from Example 1 in that the use of cerium oxide nanoparticles, which were present in Example 1, is omitted in Comparative Example 3. The remaining steps are exactly the same in Comparative Example 3 and Example 1.

[0063] Performance testing:

[0064] The tensile strength of polycarbonate sheets prepared according to GB / T 1040.1-2018 standard; the notched impact strength of polycarbonate sheets prepared according to GB / T 1843-2008 standard; the pencil hardness of polycarbonate sheets prepared according to GB / T 6739-2006 standard; the light transmittance of polycarbonate sheets prepared according to GB / T 2410-2008 standard; and the yellowing index of polycarbonate sheets prepared according to GB / T 2409-2014 standard are tested. The test results are shown below:

[0065]

[0066] Referring to the performance test data of Examples 1-4 and Comparative Examples 1-3, it can be seen that in the performance test of the polycarbonate sheet prepared in Example 1, when amino POSS (KH-540) and epoxy POSS (JH-P201) are mixed at a mass ratio of 1.5:3, the molar ratio of primary amino (-NH2) to epoxy (-CH(O)CH-) in the system approaches 1:2. Following the stoichiometric law of epoxy-amine addition reaction, a chain addition is initiated in the high-temperature shear field of the third zone of the twin-screw extruder, constructing a three-dimensional network of [POSS-(PC)n] with uniform crosslinking density. The Si-O-Si rigid skeleton of this network is anchored to the polycarbonate main chain through covalent bonds, which greatly improves the tensile strength. However, Comparative Example 1 lacks POSS crosslinking points and relies solely on physical entanglement to resist deformation. The lack of crosslinking network leads to a decrease in stress transfer efficiency, premature cracking in the yield stage, and a sharp drop in strength to 68.4 MPa.

[0067] The difference in notched impact strength between Examples 1 and 4 is presumably due to the fact that when the mass ratio of aminopropyl to glycidyl ether in POSS is 1.5:3, the resulting β-hydroxyamine structure (R-NH-CH2-CH(OH)-R') possesses both rigidity and flexibility, inducing multiple shear yielding under impact loads and absorbing energy through plastic deformation. However, in Example 4, the total filler content increased to 28% of the prepolymer, and the excess aminopropyl POSS preferentially reacted with fluorinated epoxy to form microgel domains, becoming stress concentration points. When impact energy is transferred to these regions, cracks propagate along the POSS / PC interface, leading to a sharp drop in impact strength.

[0068] The difference in pencil hardness between Example 4 and Comparative Example 2 is mainly due to the fact that during the 190℃ / 10MPa holding pressure stage of the calendering process, the unreacted epoxy and hydroxyl groups in the melt blending stage continue to react under pressure to form a dense surface layer. At the same time, the compressive stress field forces the POSS cage skeleton to arrange itself in an orderly manner along the shear direction, and its Si-O-Si inorganic network forms a ceramic-like structure on the surface, which increases the surface hardness. Meanwhile, fluorinated segments are enriched on the surface of the polycarbonate sheet to form a fluorinated layer. This dual mechanism of reducing surface energy and strengthening the POSS network causes the surface hardness of Example 4 to jump to 3H pencil hardness, while Comparative Example 2, due to the lack of POSS skeleton and fluorinated chain migration, relies only on the physical entanglement of molecular chains on the surface, and its hardness drops to HB level.

[0069] In the weather resistance test of polycarbonate sheets, the excellent yellowing index of the examples originates from the dual-channel photon management mechanism of cerium oxide (CeO2). Firstly, Ce... 3+ The absorption of ultraviolet photons via fd electron transitions generates photogenerated electrons that efficiently reduce broken carbonate radicals, thus blocking the chain oxidation of free radicals. Secondly, the hydroxyl groups on the CeO2 surface trap holes, inhibiting the formation of quinone yellowing groups. The corresponding simplified chemical equations are shown below:

[0070] eCe 3+ +hν---->Ce 4+ +e − ;

[0071] RO∙+e − ->RO − ;

[0072] Ce 4+ -O∙+H + ->Ce 3+ -OH;

[0073] In Comparative Example 3, the absence of cerium oxide nanoparticles caused ultraviolet light to continuously attack the carbonate bonds under the quenching effect of the absence of cerium oxide nanoparticles, leading to the breakage of carbonate bonds and exacerbating yellowing.

[0074] The above performance test data strongly demonstrates that the present invention achieves a breakthrough improvement in the optical, mechanical, and weather resistance of the polycarbonate sheet prepared by the scientific compounding of cage-type silsesquioxane, fluorinated epoxy compound, and cerium oxide nanoparticles. At the same time, the preparation method provided by the present invention is simple and feasible, has low equipment requirements, is easy to industrialize, and has significant economic value.

[0075] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing polycarbonate sheets, characterized in that, Includes the following steps: S1. Surface pretreatment: Mix 1-3 parts by weight of cerium oxide nanoparticles with 1-2 parts by weight of silane coupling agent in a sealed container and react at 60-70℃ for 10-15 min to allow silane hydrolysis to form a -Si-O-Ce- bonded layer on the surface of cerium oxide nanoparticles, thus obtaining pretreated cerium oxide nanoparticles. S2. Prepolymerization reaction: Mix 90-100 parts of polycarbonate, 5-10 parts of isosorbide and 3-5 parts of polyethylene glycol by mass, and carry out transesterification reaction at 200-220℃ for 30-40 min under nitrogen protection to generate hydroxyl-terminated prepolymer. S3. Melt blending: The hydroxyl-terminated prepolymer is added to the main feed port of a twin-screw extruder, while cage-type silsesquioxane, fluorinated epoxy compound, and pretreated cerium oxide nanoparticles are simultaneously added from the third zone side feed port. After melt blending, the mixture is extruded to obtain the extrudate. S4. Calendering: After the extrudate is water-cooled and pelletized, it is fed into a flat calender to calender into 0.2-1mm thin sheets, and the pressure is held for 5-10 minutes to promote surface curing of the sheets, thus obtaining polycarbonate sheets. In step S3, the mass ratio of the terminal hydroxyl prepolymer, cage-type silsesquioxane, fluorinated epoxy compound, and pretreated cerium oxide nanoparticles is 95-110:5-10:8-15:2-3.

2. The method for preparing polycarbonate sheets according to claim 1, characterized in that, In step S1, the particle size range of the cerium oxide nanoparticles is 30-50 nm.

3. The method for preparing polycarbonate sheets according to claim 1, characterized in that, In step S1, the silane coupling agent is selected from one or more of γ-aminopropyltriethoxysilane and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane.

4. The method for preparing polycarbonate sheets according to claim 1, characterized in that, In step S2, the molecular weight of the polyethylene glycol is 2000-5000.

5. The method for preparing polycarbonate sheets according to claim 1, characterized in that, The cage-like silsesquioxane is a mixture of aminopropyl isobutyl cage-like silsesquioxane and octaglycidoxypropyl cage-like silsesquioxane in a mass ratio of 1-3:1-3.

6. The method for preparing polycarbonate sheets according to claim 1, characterized in that, The fluorinated epoxy compound is selected from one or more of 1,1,1-trifluoromethyl-3,4-epoxycyclohexane and 3-(perfluorohexyl)-1,2-epoxypropane.

7. The method for preparing polycarbonate sheets according to claim 1, characterized in that, In step S3, the temperatures of each zone of the twin-screw extruder are: zone 1 220-230℃, zone 2 230-240℃, zone 3 250-260℃, zone 4 260-270℃, zone 5 270-265℃, zone 6 265-255℃, and zone 7 245-235℃.

8. The method for preparing polycarbonate sheets according to claim 1, characterized in that, In step S4, the process parameters of the flat calender are: temperature 190-200℃ and pressure 10-15MPa.

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