A low cyclic content polycarbonate resin and method of making

Abstract

The application provides a polycarbonate resin and a preparation method thereof, and the polycarbonate resin has the following characteristics: 1) the polycarbonate resin is extracted by a poor solvent, and the mass fraction of the solvent extractant in the total resin is not more than 2%; 2) the proportion of cyclic oligomers (the sum of D3-D10) in the solvent extractant is not more than 50 wt%; 3) the proportion of cyclic oligomers (hereinafter referred to as D3) corresponding to three monomer units in the solvent extractant is not more than 25 wt%; and 4) the polycarbonate resin has a structural unit as shown in formula II: The resin provided by the application has excellent optical properties and ultraviolet aging resistance and is mainly applied to light guide fields such as automobile components.

Description

Technical Field

[0001] This invention relates to a low-ring-content polycarbonate resin and its preparation method, belonging to the field of polymer materials technology. Background Technology

[0002] Polycarbonate is an engineering plastic with low yellowing and high light transmittance, widely used in light guides, lenses, optical instruments, and automotive light strips. However, when used in optical devices, the light transmittance of polycarbonate, one of the indicators of transparency, is still lower than that of polymethyl methacrylate (PMMA). Therefore, when using polycarbonate as a light guide or display panel light source, problems such as low light brightness and yellowing may occur. Preparing polycarbonate with good base color and high light transmittance remains an important cutting-edge research topic.

[0003] Patent CN104136489A provides a polycarbonate with high light transmittance and low yellowing, which is achieved by controlling the use of high-purity raw materials, such as controlling the purity of the bisphenol compound in the system, the metal ion content in the organic solvent, the conductivity of deionized water, and the free chlorine in phosgene.

[0004] Patents CN107614612B and CN108219431B provide a polycarbonate composition in which the YI of the injection-molded sample is below 1.21. This is mainly achieved by adding phosphite antioxidants and polyether polyols or polyester polyols with a molecular weight of 2000-5000 to the polycarbonate, and by controlling the potassium and sodium ion content in the polyether or polyester compound.

[0005] Taiwan patent TWI638003B provides a method for preparing a thin-walled polycarbonate resin with good light conductivity. By controlling the nitrogen atom content to be below 15 ppm and the hydroxyacetophenone content to be below 1 ppm, the resulting polycarbonate does not have a maximum absorption value in the wavelength range of 500-600 nm.

[0006] However, the aforementioned patents all focus on improving the YI sample by addressing impurity content or adding additives, lacking research on the polymer's own structure, and the performance of the cantilever beam impact test is essentially not improved. Summary of the Invention

[0007] The purpose of this invention is to provide a low-ring-content polycarbonate resin and its preparation method, aiming to obtain a product with less yellowing and good light transmittance that can be used in the field of light guide materials.

[0008] The inventors conducted extensive research on the polymer structure and optical properties, finding that a small amount of cyclic compounds in linear polycarbonate are unstable at high temperatures. Furthermore, the research revealed that the molecular weight of these cyclic compounds is mainly concentrated in the low molecular weight region (less than 5000). These factors contribute to the easier degradation of polycarbonate and negatively impact the optical properties of the product. Further analysis using liquid chromatography-mass spectrometry (LC-MS) revealed that the low molecular weight cyclic compounds are primarily composed of cyclic chains of bisphenol monomer units in the 3-10 (D3-D10) range. During the research, it was also found that high levels of D3-D10 cyclic chains undergo chain breakage under prolonged ultraviolet radiation, which affects the material's impact resistance.

[0009] Furthermore, during the preparation of polycarbonate using the interfacial phosgene method, the inventors discovered that the D3-D10 structure mainly forms before the polymer molecular weight reaches 3000 in the early stage of the reaction. In this early stage, the concentrations of bisphenol monomer and phosgene at the interface are very high, and the reaction rate is rapid. Because the concentration of reactive functional groups far exceeds the interfacial saturation concentration, the polymer chains with functional groups are compressed into a folded shape at the interface, giving them a chance to react end-to-end to form cyclic compounds, thus promoting the formation of cyclic oligomers. This invention avoids this process by using a homogeneous reaction method in the early stage and controlling the pH of the aqueous phase, which significantly reduces the proportion of cyclic oligomers.

[0010] Based on the above research, in order to obtain polycarbonate with less yellowing and good optical and aging resistance properties, the technical solution adopted in this invention is as follows:

[0011] A polycarbonate resin suitable for light guide applications has the following characteristics:

[0012] 1) Polycarbonate resin is extracted with a poor solvent, and the solvent extract accounts for no more than 2% of the total resin mass.

[0013] 2) The proportion of cyclic oligomers (the sum of D3-D10) in its solvent extract does not exceed 50 wt%;

[0014] 3) The proportion of the cyclic oligomers corresponding to the three monomer units (hereinafter referred to as D3) in its solvent extract does not exceed 25 wt%;

[0015] The structures of D3 and D4 in cyclic oligomers are as shown in formulas I-1 and I-2;

[0016]

[0017] 4) Polycarbonate resin has structural units as shown in Formula II:

[0018]

[0019] In Formula II, R1 and R2 independently represent hydrogen, halogen, alkyl with 1-6 carbon atoms, cycloalkyl with 5-20 carbon atoms and their derivatives, and aryl with 6-20 carbon atoms and their derivatives, respectively; a and b independently represent integers from 0 to 4; X is present or absent, and when present, it represents carbonyl, ether, thioether, sulfone, sulfone, alkylene with 1-6 carbon atoms, cycloalkyl with 5-20 carbon atoms and their derivatives, and aryl with 6-20 carbon atoms and their derivatives, etc.

[0020] Furthermore, the solvent extract is obtained by extracting polycarbonate with a poor solvent (such as acetone, n-hexane, cyclohexane, and methanol). Only the low molecular weight region of polycarbonate can be dissolved by the poor solvent. Therefore, a poor solvent such as pure acetone can be used to continuously extract the oligomers of polycarbonate until all the oligomers are extracted. A Soxhlet extractor can usually be used, and the extraction time can last for 5-15 hours.

[0021] Furthermore, the solvent extract can be tested using liquid chromatography-mass spectrometry (LC-MS). First, HPLC can be used to separate oligomers with different degrees of polymerization. Then, mass spectrometry can be used to determine the type of oligomer corresponding to each peak in the LC spectrum, and the positions of the LC peaks corresponding to D3-D10 can be sequentially identified. The ratio of the LC peak area of ​​D3 to D10 to the total LC spectrum area should not exceed 50%, and the ratio of the D3 LC peak area to the total LC spectrum area should not exceed 25%, as indicators to control the content of D3 and D3-D10, thus ensuring the optical properties of polycarbonate.

[0022] Furthermore, the polycarbonate resin structural unit II is mainly derived from bisphenol compounds and phosgene, wherein the bisphenol compound can be one or more of 2,2-bis(4-hydroxyphenyl)propane (i.e., bisphenol A), bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, bis(4-hydroxyphenyl)sulfide, 4,4'-dihydroxybiphenyl, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxyphenyl)octane, bis(4-hydroxyphenyl)phenylmethane, bis(4-hydroxyphenyl)diphenylmethane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, bis(4-hydroxyphenyl)oxide, bis(4-hydroxyphenyl)sulfone, etc., with bisphenol A being preferred.

[0023] Furthermore, the polycarbonate structural unit may incorporate branched monomers, which may be 1,1,1-tris(4-hydroxyphenyl)ethane, α,α',α”-tris(4-hydroxyphenyl)-1,3,5-triisopropylbenzene, phloroglucinol, trimellitic acid, and 1,3-bis(o-cresol), etc.

[0024] Furthermore, the YI of the polycarbonate sample after injection molding is below 1.20, preferably below 1.15.

[0025] Furthermore, the polycarbonate resin injection molded specimen has a transmittance of over 80% in the range of 360nm-800nm, preferably over 85%.

[0026] Furthermore, the polycarbonate, after undergoing UV aging tests under specific conditions, exhibits a cantilever beam impact strength of over 850 J / m.

[0027] Furthermore, the polycarbonate has a weight-average molecular weight between 10,000 and 40,000, preferably between 13,000 and 25,000.

[0028] A method for preparing polycarbonate as described above includes the following synthetic steps:

[0029] 1) Preparation of prepolymer reaction solution: After 1 part by mass of deionized water, 0.06-0.10 parts by mass of alkali (preferably sodium hydroxide) and 0.20-0.25 parts by mass of bisphenol compound (preferably bisphenol A) are fully dissolved in the reaction vessel, 0.06-0.07 parts by mass of phosgene are added to the reaction vessel and mixed and stirred for 30-50 min.

[0030] 2) Polymerization reaction: Add 1.5-2.0 parts by weight of solvent to the prepolymer reaction solution and stir thoroughly. Then add 0.04-0.08 parts by weight of phosgene and 0.005-0.050 parts by weight of end-capping agent, while continuously adding alkaline solution to maintain the pH of the aqueous phase between 11 and 13. After stirring the reaction for 30-50 minutes, add 0.001-0.005 parts by weight of catalyst and continue the reaction until it is complete.

[0031] The solvent is one or more of dichloromethane, trichloromethane, monochlorobenzene, and o-dichlorobenzene;

[0032] The terminator is one or more of p-tert-butylphenol, phenol, p-cumylphenol, cresol, p-phenylphenol, p-chlorophenol, tribromocresol, and pentabromophenol;

[0033] The catalyst is one or more selected from triethylamine, tripropylamine, pyridine, and n-butylammonium bromide;

[0034] 3) Post-processing: After the reaction is completed, the reaction solution is separated into oil and water. The lower oil phase is washed with dilute acid and deionized water in sequence, and the solvent in the oil phase is removed to obtain polycarbonate powder.

[0035] The advantages of this invention are:

[0036] This invention utilizes a special polymerization process to control the content of cyclic oligomers in polycarbonate, thereby obtaining resins with excellent YI values ​​in the test pieces. These resins exhibit less yellowing even under harsh environments and also have good resistance to UV aging. Detailed Implementation

[0037] The present invention is illustrated by the following embodiments, but the scope of the present invention is not limited to these embodiments.

[0038] The analytical and evaluation methods involved in the embodiments or comparative examples of this invention are as follows:

[0039] The molecular weight of polycarbonate was obtained by Agilent Technologies 1260 Infinity test, using an RI detector, dichloromethane as the mobile phase, a flow rate of 1 mL / min, and column and chamber temperatures of 30 °C.

[0040] Using a Haitian MA900II 1260 injection molding machine at 320℃, the powder was injection molded into 100mm×100mm×3mm test pieces for YI testing; and sample strips of 63.5mm×12.7mm×3.2mm were injection molded for UV aging resistance testing.

[0041] The YI value of the polycarbonate sample was obtained by testing with an UltraScan PRO colorimeter, and the transmittance was obtained by testing with a BYK HAZE-GARD PLUS, with the wavelength range selected between 360nm and 800nm.

[0042] UV aging resistance test of polycarbonate: The sample was placed in a UV weathering chamber and subjected to accelerated UV aging test under UV irradiation. The aging temperature was 60℃, the irradiation wavelength was 340nm, and the irradiation intensity was 0.68W / m². 2 The irradiation time was 28 days, and the distance between the sample and the light source was 5 cm.

[0043] The notched impact strength of the cantilever beam was tested according to ASTM D256 standard.

[0044] The polycarbonate resin solvent extract was obtained by Agilent Technologies 1260infinity II (HPLC) analysis using a ZORBAX SB-C18 column with acetonitrile, water, and isopropanol as solvents.

[0045] Example 1

[0046] (1) Preparation of prepolymerization reaction solution

[0047] Add 6154g of deionized water, 493g of sodium hydroxide, and 1399g of bisphenol A to a glass reactor. Purge the reactor with nitrogen and start mechanical stirring. After mixing evenly, slowly introduce 430.8g of phosgene into the reactor. After the raw materials are added, mix and stir for 30 minutes.

[0048] (2) Polymerization reaction

[0049] Add 10142g of dichloromethane to the glass reactor and stir thoroughly. Then, continue to introduce 285.2g of phosgene. Add 36.3g of p-tert-butylphenol to the oil phase. After reacting at room temperature for 30 minutes, add 18.1g of triethylamine and continue the reaction until it is complete. During the reaction, maintain the pH of the aqueous phase at around 11.5.

[0050] (3) Post-processing:

[0051] After the reaction was completed, the oil phase was first washed with 1 L of 0.4 M dilute acid solution, and then washed repeatedly with deionized water until the conductivity of the aqueous phase was below 50 μS / cm. After the solvent in the oil phase was removed, it was pulverized and dried at 130℃ for 8 h to obtain polycarbonate powder. The powder was then subjected to conventional weight-average molecular weight test.

[0052] The polycarbonate was subjected to Soxhlet extraction with acetone, and the mass of the extract was weighed and analyzed by HPLC.

[0053] Polycarbonate powder was transferred to a Haitian MA900II 1260 injection molding machine. Under the conditions of screw temperature of 320℃ and mold temperature of 80℃, it was injection molded into a square sheet of 100mm×100mm×3mm for YI and light transmittance testing. Sample strips of 63.5mm×12.7mm×3.2mm were first used to test the notched impact strength of cantilever beams, and then used for UV aging resistance test and cantilever beam notched impact strength test.

[0054] The test data is shown in Table 1 below.

[0055] Example 2-3

[0056] Polycarbonate was prepared using essentially the same method as in Example 1, except that the conditions for the preparation of the prepolymer reaction solution in step (1) were: 369.2 g of phosgene added and 40 min of mixing and stirring (Example 2), and 400.0 g of phosgene added and 50 min of mixing and stirring (Example 3), to control the degree of reaction in this stage. The conditions for the polymerization reaction in step (2) were: 346.8 g of phosgene added (Example 2) and 316 g (Example 3).

[0057] Perform performance testing using the same method.

[0058] The test data is shown in Table 1 below.

[0059] Comparative Example 1

[0060] Polycarbonate is prepared using a typical one-step batch process, as follows.

[0061] (1) Preparation of prepolymerization reaction solution

[0062] Add 6154g of deionized water, 493g of sodium hydroxide, and 1399g of bisphenol A to a glass reactor. Purge the reactor with nitrogen and start mechanical stirring until homogeneous. Add 10142g of dichloromethane, 36.3g of p-tert-butylphenol, and 18.1g of triethylamine to the reactor, then slowly introduce 716.0g of phosgene. Continuously add alkali solution throughout the process to maintain the pH of the aqueous phase between 11 and 12, and stir for 30 minutes.

[0063] (2) Post-processing:

[0064] After the above reaction was completed, the oil phase was first washed with 1 L of 0.4 M dilute acid solution, and then washed repeatedly with deionized water until the conductivity of the aqueous phase was below 50 μS / cm. After the solvent in the oil phase was removed, the polycarbonate powder was obtained by pulverizing and drying at 130℃ for 8 h. The powder was then subjected to conventional weight-average molecular weight testing.

[0065] Comparative Example 2

[0066] The method for preparing polycarbonate using a continuous process, as described in patent CN100349954C, was replicated in the laboratory with a reduced production volume. The resulting powder was then subjected to routine testing.

[0067] The preparation method is as follows:

[0068] Pre-prepared BPA solution ensured a BPA concentration of 160 g / L and an alkali content of 5.8 wt%; a dichloromethane solution of N-ethylpyridine with an N-ethylpyridine content of 3 wt%; and a dichloromethane solution of p-tert-butylphenol with a p-tert-butylphenol content of 10.9 wt%.

[0069] BPA solution was pumped into a 3L glass reactor at a flow rate of 150 g / min, while phosgene was fed into the reactor at a rate of 11.2 g / min and dichloromethane at a rate of 198 g / min. The dichloromethane and phosgene were mixed and then fed into the reactor together. An external circulation system was introduced outside the reactor, and the circulating liquid exchanged heat through a heat exchanger.

[0070] Connect another pipeline to the glass reactor and draw out the buffer solution at a rate of 300 g / min. Simultaneously, add N-ethylpyridine solution at a rate of 1.3 g / min and p-tert-butylphenol solution at a rate of 5.6 g / min to the pipeline, while also adding a certain amount of alkali solution to ensure the pH of the solution is between 11 and 12. Pour the reaction solution into the polymerization reactor until the reaction is complete.

[0071] The obtained polymerization reaction solution is separated by centrifugation, then the electrolyte in the oil phase is washed away with deionized water, and the dichloromethane solution in the oil phase is removed. After pulverization and drying, polycarbonate powder can be obtained.

[0072] The test data is shown in Table 1 below.

[0073] Comparative Example 3

[0074] Referring to the method for preparing polycarbonate provided in patent CN101434695B, the prepared powder was also subjected to relevant tests.

[0075] The preparation method is as follows:

[0076] Dissolve 2.5 kg of water, 12 kg of bisphenol A (as a diphenol), and 0.06 kg of bisulfite in 60 kg of 9% sodium hydroxide aqueous solution. Add 60 L of dichloromethane and stir, then add 0.31 kg of p-tert-butylphenol. Next, slowly add 6 kg of liquid phosgene over 60 min while stirring. After adding phosgene, add 14 g of triethylamine under vigorous stirring and stir for approximately 1 hour to initiate polymerization.

[0077] The emulsion resin solution is separated into oil and water by a metal filter. After the oil phase is washed, the solvent is removed by evaporation. Then, it is pulverized and dried to finally obtain powder.

[0078] The test data is shown in Table 1 below.

[0079] Table 1. Experimental Test Data

[0080]

[0081] The data comparison above shows that the polycarbonate preparation method and the product of this invention have good optical properties. The notched impact strength of the cantilever beam decreases only slightly before and after UV aging, and it also has good transmittance across the entire spectrum. Furthermore, according to the results in Table 1, increasing the content of D3 and D3-D10 significantly increases the YI value of the sample.

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A polycarbonate resin having the following characteristics: 1) the polycarbonate resin is extracted with a poor solvent, and the mass fraction of the solvent extract in the total resin is not more than 2%; 2) the proportion of D3-D10 cyclic oligomers in the solvent extract is not more than 50 wt%; the D3-D10 cyclic oligomers refer to cyclic chains composed of bisphenol monomer units in the range of 3-10; 3) the proportion of cyclic oligomer D3 in the solvent extract is not more than 25 wt%; 4) the polycarbonate resin has a structural unit as shown in Formula II: Formula II wherein R1 and R2 independently represent hydrogen, halogen, alkyl with carbon number 1-6, cycloalkyl with carbon number 5-20, aryl with carbon number 6-20; a and b independently represent an integer of 0-4; X is present or absent, and when present, represents a carbonyl group, an ether group, a sulfide group, a sulfoxide group, a sulfone group, an alkylene group with carbon number 1-6, a cycloalkyl group with carbon number 5-20, an aryl group with carbon number 6-20.

2. The polycarbonate resin according to claim 1, having a weight average molecular weight of between 10,000 and 40,000.

3. A method for preparing the polycarbonate resin as claimed in claim 1 or 2, comprising the following steps: 1) preparation of a prepolymerization solution: after the deionized water, base and bisphenol compound are fully dissolved in a reaction vessel, phosgene is added to the reaction vessel and mixed and stirred; 2) polymerization reaction: after the prepolymerization solution is added with a solvent and fully stirred, phosgene and a capping agent are added, while continuously adding a lye to maintain the pH of the aqueous phase between 11 and 13, a catalyst is added after stirring for a period of time, and the reaction is continued until the reaction is complete; 3) post-treatment: after the reaction is completed, the reaction liquid is separated into oil and water, the lower oil phase is washed, and after the solvent in the oil phase is removed, the polycarbonate resin is obtained. In step 1), the amounts of the components are: 1 part by mass of deionized water, 0.06-0.10 parts by mass of base, 0.20-0.25 parts by mass of bisphenol compound, and 0.06-0.07 parts by mass of phosgene. In step 1), the mixture is stirred for 30-50 minutes. In step 2), the amounts of the components are: 1.5-2.0 parts by mass of solvent, 0.04-0.08 parts by mass of phosgene, 0.005-0.050 parts by mass of capping agent, and 0.001-0.005 parts by mass of catalyst. In step 2), the solvent is one or more of dichloromethane, trichloromethane, monochlorobenzene and o-dichlorobenzene. In step 2), the capping agent is one or more of p-t-butylphenol, phenol, p-cumylphenol, cresol, p-phenylphenol, p-chlorophenol, tribromocresol and pentabromophenol. In step 2), the catalyst is one or more of triethylamine, tripropylamine, pyridine and n-butylammonium bromide. ​ ​ 4. The method of claim 3, wherein, ​ 5. The method of claim 3 or 4, wherein, ​ 6. The method according to any one of claims 3-4, wherein, ​ 7. The method of claim 3, wherein, ​ 8. The method of claim 3, wherein, ​ 9. The method of claim 3, wherein, ​

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