Polymethyl methacrylate for polaroid and preparation method thereof

Abstract

The invention relates to polymethyl methacrylate for a polaroid and a preparation method of the polymethyl methacrylate. The method comprises the following steps: (1) feeding raw material resin from a main feed port of an extruder, melting, mixing saturated fatty alcohol serving as an esterifying agent and an imidization agent, injecting into molten resin from a liquid spray gun, and mixing; (2) fully reacting the raw material resin, the saturated fatty alcohol and the imidization agent in the reaction area, and (3) further removing the unreacted modifier and monomers and oligomers in the raw material resin in the devolatilization area. The esterifying agent and the imidization agent are mixed and dissolved and are fed at one time, and the imidization reaction and esterification modification of the raw material resin are realized in one extruder. The polymer disclosed by the invention has excellent purity, optical transparency, high heat resistance and low water absorption, and can meet the requirements of polaroids in the fields of high-end optics and electronics.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, specifically to a polymethyl methacrylate for polarizing films. Background Technology

[0002] Polarizing film (POL) is one of the three key raw materials for LCD panels. With the advancement of display panels to higher generations and the rapid growth in demand for large-size TVs, traditional polarizing film protective film material TAC (cellulose triacetate) is gradually being replaced by PMMA material due to its susceptibility to water absorption and heat deformation. PMMA, with its high heat resistance, high water resistance, and excellent optical properties, is an ideal material to replace TAC for polarizing film protective films in large-size panels.

[0003] Heat-resistant PMMA resin for polarizing films is a high-end specialty PMMA product. To meet the heat resistance requirements of PMMA for polarizing films, researchers have developed various modification methods. Copolymerization with special monomers is one of the effective ways to improve the heat resistance of PMMA. CN101001910B synthesized a special monomer, methyl hydroxymethyl acrylate, and copolymerized it with methyl acrylate monomer to obtain a lactone-cyclic polymer molecule with a Tg ≥ 127℃; however, the introduction of a large amount of solvent and catalysts such as phosphate esters led to high component residues, and the long process also limited its further application. CN102317333B obtained a high heat-resistant polymer molecule with a Tg ≥ 130℃ by copolymerizing special monomers such as methyl methacrylate (MMA), N-phenylmaleimide monomer, and cyclopentyl methacrylate. At the same time, the birefringence parameter can be flexibly controlled by the type and ratio of monomers; however, the introduction of rigid structural units often reduces the light transmittance and processing performance of the material, and the introduction of multiple special monomers also limits its further application expansion from a cost perspective.

[0004] The mainstream production process for heat-resistant PMMA resin used in polarizing films is continuous reactive extrusion using a two-stage extruder. This involves imidization and esterification of the polymer side groups of ordinary PMMA particles. The entire process is relatively short, the modifier is easily removed, and the resulting product has high purity. The birefringence coefficient can also be adjusted later through process parameters such as the imide grafting rate of the particles. During the reaction, nucleophilic substitution of amino groups and hydrolysis of ester groups increase the carboxyl content in the polymer, leading to defects such as watermarks after film formation. Therefore, it is necessary to suppress the excess carboxyl groups through esterification. CN103380175B uses PMMA (Mw = 105,000) as the raw material resin and monomethylamine as the imidizing agent. Imidization modification is performed in the first extruder. Simultaneously, to meet the processability requirements such as moisture resistance after particle film formation, dimethyl carbonate is used as the esterifying agent, and a second-stage extruder is set up for esterification modification and volatile matter removal. The resulting resin has a Tg as high as 130℃ and an acid value of 0.4 mmol / g. However, the segmented modification process means additional investment in equipment. At the same time, the process of two-stage extruders in series places high demands on the design of the screws before and after the process, torque matching, and melt delivery, requiring a lot of experience exploration and process improvement.

[0005] Therefore, there is an urgent need to develop a new PMMA modification method that simplifies the process, reduces equipment investment, and maintains high transmittance, high heat resistance, low acid value, and good purity to meet the polarizer requirements of high-end optics and electronics. Summary of the Invention

[0006] To meet the application requirements of polarizers, simplify the production process of imidized heat-resistant polymethyl methacrylate, reduce equipment investment, and achieve the technical effects of high light transmittance, high heat resistance, low acid value and good purity, this invention provides a polymethyl methacrylate for polarizers and its preparation method.

[0007] To solve the above technical problems, the present invention adopts the following technical solution:

[0008] This invention provides a method for preparing polymethyl methacrylate for polarizing films, comprising the following steps:

[0009] (1) Input raw material resin into the main feed port of the extruder, melt it, and inject the mixture of saturated fatty alcohol and imidizing agent into the molten resin from the liquid spray gun for mixing;

[0010] (2) In the reaction zone, the raw material resin, saturated fatty alcohol and imidizing agent are fully reacted;

[0011] (3) In the devolatilization zone, two-stage dynamic devolatilization is used to remove volatiles.

[0012] The raw material resin of this invention is prepared by homopolymerization or copolymerization of the following raw material monomers:

[0013] (a) 80-100 parts by weight of methyl methacrylate monomer;

[0014] (b) 0-10 parts by weight of methyl acrylate monomer;

[0015] (c) 0-10 parts by mass of styrene-based monomers.

[0016] The raw material resin of the present invention has the following properties:

[0017] (1) Weight-average molecular weight is 100,000-130,000;

[0018] (2) The glass transition temperature is 105-115℃;

[0019] (3) The acid value is 0.01-0.05 mmol / g;

[0020] (4) Water absorption rate (soaked in pure water at 25℃ for 24 hours) is 0.10-0.30%;

[0021] (5) The content of residual small components is <1500 ppm;

[0022] (6) Total light transmittance is 92.0-95.0%.

[0023] The preparation method of the raw material resin of the present invention includes the following steps: methyl methacrylate, optionally methyl acrylate monomer, and optionally styrene monomer are polymerized in an inert gas atmosphere in the presence of an initiator and a chain transfer agent; after polymerization, volatile matter is removed, and the resin is extruded and granulated to obtain granular raw material resin. The introduction of styrene can improve the water resistance and solvent resistance of the resin, but it will impair its heat resistance; while the introduction of a small amount of methyl acrylate helps to improve the flowability of the resin during processing, and the resin still maintains high heat resistance. The preparation method of the raw material resin is well known to those skilled in the art and will not be described in detail here.

[0024] The saturated fatty alcohols described in this invention are used as esterifying agents with a molecular weight less than 200. Suitable examples include, but are not limited to, one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol, diethylene glycol, and propylene glycol. The conventional esterifying agent dimethyl carbonate (DMC) is not chosen because of its weak polarity, poor solubility of imidizing agents within it, and its tendency to undergo nucleophilic substitution reactions. This makes it unsuitable for one-step imidization for heat-resistant modification and acid value optimization. Methanol is the most preferred esterifying agent because the strong polarity of small-molecule alcohols allows for miscibility with imidizing agents, enabling single-feeding. Furthermore, methanol, as a byproduct of the reaction itself, does not introduce other unnecessary components and can esterify excess carboxyl groups in the polymer side chains to methoxy groups, ensuring the consistency of the polymer's side functional groups, maintaining the molecular structure, and guaranteeing product purity.

[0025] The amount of saturated fatty alcohol used in this invention is 1-9 parts by weight, based on 100 parts by weight of the raw material resin.

[0026] Suitable examples of the imidizing agents described in this invention include, but are not limited to, one or more of ammonia, ammonia water, monomethylamine, ethylamine, n-propylamine, aniline, cyclohexylamine, and urea. Monomethylamine is the most preferred imidizing agent due to its unique reactivity and low cost, and can undergo imidization and heat-resistant modification reactions with raw material resins.

[0027] The amount of the imidizing agent used in this invention is 1-5 parts by weight, based on 100 parts by weight of the raw material resin.

[0028] In this invention, the preferred extruder is a co-rotating twin-screw extruder, whose screw includes conveying elements, shearing elements, anti-threading elements and sealing elements, etc., which can realize a combination of multiple sections such as resin melting, mixing, conveying, reaction, homogenization, devolatilization and extrusion.

[0029] In this invention, the imidization and esterification modification reactions of the raw material resin are carried out in one extruder; and all modifiers are fed in one go by dissolving and mixing them at the spray gun position.

[0030] The beneficial effects of the present invention are: (1) By selecting saturated fatty alcohol as esterifying agent, the imidizing agent and esterifying agent can be fed at one time, and the heat resistance modification reaction and acid value optimization modification reaction of the resin can be completed simultaneously in one extruder, which simplifies the process and greatly reduces the investment in equipment.

[0031] (2) The glass transition temperature of the heat-resistant polymethyl methacrylate material for polarizers prepared by the present invention is not lower than 125℃, which significantly improves the thermal stability compared with traditional PMMA materials.

[0032] (3) Through the two-stage dynamic devolatilization design, the purity of the product obtained by this invention is very high. The total content of residual unreacted modifiers, monomers and oligomers from the raw material resin in the sample is <1500ppm; at the same time, the total light transmittance is not less than 92%.

[0033] (4) The PMMA resin prepared by this invention has an acid value of less than 0.40 mmol / g and a water absorption rate (soaked in pure water at 25°C for 24 hours) of less than 0.50%. It has excellent water resistance and greatly improves the defects such as water marks and bubbles in the film forming process of heat-resistant PMMA materials. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the extruder apparatus for resin preparation according to an embodiment of the present invention; 1 metering particle feeder; 2 liquid spray gun injection port; 3 first exhaust port; 4 second exhaust port; 5 die head discharge port. Detailed Implementation

[0035] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. 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.

[0036] The raw material information involved in the examples is shown in Table 1:

[0037] Table 1. Information on Main Raw Materials

[0038] Raw material name level supplier Methyl methacrylate Industrial grade Wanhua Chemical Methyl acrylate Industrial grade Wanhua Chemical styrene Industrial grade Wanhua Chemical tert-butyl peroxide-3,5,5-trimethylhexanoate Industrial grade Liaoning Zhongmao New Materials Co., Ltd. n-Octamethrin reagent grade Aladdin Methylamine Industrial grade Dalian Date Gas Co., Ltd. Amphetamine reagent grade Inokai Cyclohexylamine reagent grade Inokai methanol reagent grade Aladdin ethanol reagent grade Aladdin n-Propanol reagent grade Aladdin dimethyl carbonate reagent grade Inokai

[0039] The physical property testing methods involved in the embodiments are as follows:

[0040] Relative molecular mass (Mw): Molecular weight was determined by liquid gel chromatography (GPC) using a Water 996 instrument, with tetrahydrofuran as the mobile phase and a test temperature of 40℃. Monodisperse polystyrene was used as the standard, and the unit is g / mol.

[0041] Total light transmittance: A haze meter (Suga Test Instruments, HZ-V3) was used, and the test standard of ISO13486 was adopted. The thickness of the test film was 3 mm.

[0042] Glass transition temperature (Tg): Tested using a Swiss METTLER instrument under a nitrogen atmosphere at a heating rate of 10℃ / min, with a test range of 10-180℃. The glass transition temperature was determined by the midpoint method, and the unit is ℃.

[0043] PMMA water resistance test: Sheet samples with dimensions of 60mm×60mm×2mm were prepared by injection molding and immersed in deionized water at a constant temperature of 25℃. After immersion for 24 hours, the samples were removed, and the surface moisture was absorbed with filter paper. The weight change before and after immersion was measured.

[0044] Acid value: Dissolve 0.3g of heat-resistant PMMA resin sample in a mixed solvent of 37.5ml dichloromethane and 37.5ml methanol. Using a Chemtron CAT2-16 fully automated potentiometric titrator, add 5ml of 0.1mol / L NaOH aqueous solution, then titrate the excess alkali with 0.1mol / L hydrochloric acid. Calculate the acid value (mmol / g) using the difference between the volume of alkali added and the volume of hydrochloric acid used to achieve neutralization.

[0045] Residual component content: The residual small molecules in the resin were separated, qualitatively and quantitatively analyzed using an Agilent GC-MS system, with units of ppm.

[0046] Example

[0047] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0048]

Example 1

[0049] In this embodiment, the following steps and conditions are used to prepare heat-resistant polymethyl methacrylate (PMMA) for polarizing films:

[0050] Ingredients preparation: 100 parts by weight of methyl methacrylate (MMA), 0 parts by weight of methyl acrylate and 0 parts by weight of styrene, 0.2 parts by weight of n-octyl mercaptan, and 0.1 parts by weight of initiator tert-butyl peroxide-3,5,5-trimethylhexanoate.

[0051] Polymerization reaction: To ensure a safe reaction environment, nitrogen gas is introduced until the oxygen concentration drops below 1 ppm. The above materials are continuously fed into a fully mixed-flow polymerization reactor, with the reactor temperature controlled at 140°C and the average residence time of the materials ensured to be 4 hours. Subsequently, the resulting slurry is sequentially fed into a two-stage static devolatilizer and a dynamic extruder for devolatilization treatment at a temperature of 200°C. After extrusion granulation, granular raw material resin is obtained, which has the following properties:

[0052] (1) The weight-average molecular weight is 122,000;

[0053] (2) The glass transition temperature is 115℃;

[0054] (3) The acid value is 0.03 mmol / g;

[0055] (4) The water absorption rate (soaked in pure water at 25℃ for 24 hours) is 0.14%;

[0056] (5) The residual component content was 1398 ppm;

[0057] (6) Total light transmittance is 93.6%.

[0058] Methylamine and methanol were selected as imidizing agent and esterifying agent, respectively, and were fully dissolved in a mass ratio of 3:5 to prepare a mixed solution.

[0059] Reactive extrusion process: Raw material resin particles are continuously fed into the extruder through the metering feed port. The barrel temperature of the extruder reaction zone is set at 250℃. The residence time of the resin in the reaction zone is controlled at 60s under the process conditions of a feed rate of 5kg / h and a screw speed of 150rpm, and the resin pressure in the reaction zone is controlled at approximately 4MPa. Based on the raw material resin (100 parts by mass / min), a mixed solution of methylamine and methanol is delivered at a constant flow rate (8 parts by mass / min) using a horizontal flow pump to ensure stable and controllable feeding. An imidizing agent and an esterifying agent are prepared in a ratio of 3 parts by mass and 5 parts by mass to complete the imidization and esterification modification reactions in one step. Heat-resistant polymethyl methacrylate resin is obtained in the reaction zone. In the devolatilization section, effective flash evaporation and dynamic devolatilization are achieved through two-stage devolatilization. The two vacuum levels are controlled at -0.090MPa and -0.095MPa, respectively, to efficiently devolatilize the molten resin and remove residual volatile substances. Finally, after being discharged from the die head, the material undergoes a strip-forming granulation process to obtain granular heat-resistant PMMA finished products.

[0060] The heat-resistant polymethyl methacrylate for polarizing films prepared in this embodiment has the following properties:

[0061] (1) The weight-average molecular weight is 124,000;

[0062] (2) The glass transition temperature is 131℃;

[0063] (3) The acid value is 0.24 mmol / g;

[0064] (4) The water absorption rate (after soaking in pure water at 25℃ for 24 hours) is 0.32%;

[0065] (5) The residual component content was 1368 ppm.

[0066] (6) Total light transmittance is 94.5%.

[0067] The heat-resistant polymethyl methacrylate for polarizing films prepared in this embodiment has higher heat resistance while retaining the excellent transparency, purity, moisture resistance and mechanical strength of the raw material resin, making it more suitable for processing and molding in the field of polarizing film protective films.

[0068]

Examples 2-4

[0069] Using raw material resins with different monomer compositions as shown in Table 2, and referring to the preparation method in Example 1, heat-resistant PMMA products were prepared by reactive extrusion to achieve imidization and esterification modification. The product analysis and performance test results are shown in Table 2.

[0070] Table 2. Composition of raw material resin monomers and product test results in Examples 1-4

[0071]

[0072]

Examples 5-6

[0073] Using the same raw material resin as in Example 1, and referring to the preparation method of Example 1, heat-resistant PMMA products were prepared according to the different types of imidizing agents in Table 3. The product analysis and performance test results are shown in Table 3.

[0074] Table 3. Types of imidizing agents and product test results in Examples 5-6

[0075]

[0076]

[0077] Methylamine, due to its unique reactivity and small molecular structure, yields the product with the highest heat resistance when used as an imidizing agent. Propylamine's reactivity is slightly weaker than methylamine, which is determined by the difference in alkyl groups. Cyclohexylamine, due to its unique cyclic structure and steric hindrance, has relatively lower reactivity, and the resulting product shows less significant improvement in heat resistance compared to methylamine and propylamine. Considering the degree of heat resistance modification of the raw resin and the cost, methylamine is the preferred imidizing agent.

[0078]

Examples 7-10

[0079] Using the same raw material resin as in Example 1, and referring to the preparation method of Example 1, heat-resistant PMMA products were prepared according to different contents of methylamine as imide agents as shown in Table 4. The product analysis and performance test results are shown in Table 4.

[0080] Table 4. Imidinizing agent content and product test results in Examples 7-10

[0081] Performance parameters Example 7 Example 8 Example 9 Example 10 Types of imidizing agents Methylamine Methylamine Methylamine Methylamine imidizing agent content 1％ 2％ 4％ 5％ Mw 12.4w 12.2w 11.9w 11.8w Product Tg (°C) 125 127 131 132 Acid value (mmol / g) 0.15 0.18 0.29 0.36 Water absorption rate 0.22％ 0.26％ 0.36％ 0.48％ Residual (ppm) 1310 1296 1411 1498 Light transmittance 94.6％ 94.2％ 93.6％ 92.4％

[0082]

Examples 11-12

[0083] Using the same raw material resin as in Example 1, and referring to the preparation method of Example 1, heat-resistant PMMA products were prepared according to the different types of saturated fatty alcohol esterifying agents in Table 5. The product analysis and performance test results are shown in Table 5.

[0084] Table 5. Esterifying agent types and product test results in Examples 11-12

[0085] Performance parameters Example 11 Example 12 Types of imidizing agents ethanol n-Propanol Mw 12.2w 12.5w Product Tg (°C) 128 125 Acid value (mmol / g) 0.25 0.27 Water absorption rate 0.34％ 0.37％ Residual (ppm) 1384 1332 Light transmittance 94.2％ 92.7％

[0086] Saturated fatty alcohols with a molecular weight less than 200 were chosen as esterifying agents because the strong polarity of small-molecule alcohols allows for miscibility and formulation with imide esterifying agents, enabling the one-time addition of all modifiers. Methanol, due to its unique reactivity and small molecular structure, yields products with the highest heat resistance and acid value when used as an esterifying agent. Ethanol's reactivity is slightly weaker than methanol's, while n-propanol, due to its larger alkyl group structure, does not significantly improve heat resistance or optimize acid value as much as methanol and ethanol. This is because methanol, as a byproduct of the reaction itself, does not introduce other unnecessary components and can esterify excess carboxyl groups in the polymer side chains to methoxy groups, ensuring the consistency of the polymer's side functional groups and not altering the molecular structure. Ethanol and n-propanol, on the other hand, esterify carboxyl groups to longer-branched ethoxy and propoxy groups, thereby reducing the polymer's thermal stability. Considering the degree of heat resistance and acid value modification of the raw material resin, methanol is the preferred esterifying agent.

[0087]

Examples 13-16

[0088] Using the same raw material resin as in Example 1, and referring to the preparation method of Example 1, heat-resistant PMMA products were prepared using methanol with different contents as esterifying agents as shown in Table 6. The product analysis and performance test results are shown in Table 6.

[0089] Table 6. Esterifying agent content and product test results in Examples 13-16

[0090] Performance parameters Example 13 Example 14 Example 15 Example 16 Esterifying agent type methanol methanol methanol methanol imidizing agent content 1％ 3％ 7％ 9％ Mw 12.2w 12.1w 12.0w 11.9w Product Tg (°C) 132 131 127 125 Acid value (mmol / g) 0.38 0.30 0.15 0.12 Water absorption rate 0.49％ 0.39％ 0.22％ 0.18％ Residual (ppm) 1296 1397 1310 1336 Light transmittance 94.1％ 93.8％ 93.4％ 93.6％

[0091] Comparative Example 1

[0092] Using the same raw material resin as in Example 1, PMMA resin was prepared according to essentially the same process as in Example 1, except that the mixed modification solution of methylamine and methanol was not added. The polymethyl methacrylate prepared in this comparative example has the following properties:

[0093] (1) The weight-average molecular weight is 122,000;

[0094] (2) The glass transition temperature is 115℃;

[0095] (3) The acid value is 0.02 mmol / g;

[0096] (4) The water absorption rate (after soaking in pure water at 25℃ for 24 hours) is 0.12%;

[0097] (5) The residual component content was 1362 ppm;

[0098] (6) Total light transmittance is 94.3%.

[0099] Compared with Comparative Example 1, Example 1 significantly improves the heat resistance properties of the raw material resin.

[0100] Comparative Example 2

[0101] Using the same raw material resin as in Example 1, PMMA resin was prepared according to essentially the same process as in Example 1, except that the esterifying agent methanol was not added. The polymethyl methacrylate prepared in this comparative example has the following properties:

[0102] (1) The weight-average molecular weight is 121,000;

[0103] (2) The glass transition temperature is 133℃;

[0104] (3) The acid value is 0.46 mmol / g;

[0105] (4) The water absorption rate (after soaking in pure water at 25℃ for 24 hours) is 0.61%;

[0106] (5) The residual component content was 1425 ppm;

[0107] (6) Total light transmittance is 93.4%.

[0108] Compared with Comparative Example 2, Example 1 significantly reduced the acid value of the PMMA resin after imidization and heat-resistant modification, thus optimizing its water-blocking properties.

[0109] Comparative Example 3

[0110] Using the same raw material resin as in Example 1, PMMA resin was prepared according to essentially the same process as in Example 1, except that the imidizing agent methylamine was not added. The polymethyl methacrylate prepared in this comparative example has the following properties:

[0111] (1) The weight-average molecular weight is 121,000;

[0112] (2) The glass transition temperature is 113℃;

[0113] (3) The acid value is 0.02 mmol / g;

[0114] (4) The water absorption rate (soaked in pure water at 25℃ for 24 hours) is 0.13%;

[0115] (5) The residual component content was 1387 ppm;

[0116] (6) Total light transmittance is 92.6%.

[0117] Compared with Comparative Example 3, Example 1 significantly improves the heat resistance properties of the raw material resin.

[0118] Comparative Example 4

[0119] Using the same raw material resin as in Example 1, PMMA resin was prepared according to essentially the same process as in Example 1, except that the reaction process was divided into two stages of reactive extrusion modification. Methylamine was added during the first stage of reactive extrusion, and methanol was added during the second stage. The imidizing agent and esterifying agent were not mixed. The polymethyl methacrylate prepared in this comparative example has the following properties:

[0120] (1) The weight-average molecular weight is 123,000;

[0121] (2) The glass transition temperature is 123℃;

[0122] (3) The acid value is 0.23 mmol / g;

[0123] (4) The water absorption rate (soaked in pure water at 25℃ for 24 hours) is 0.30%;

[0124] (5) The residual component content was 1416 ppm;

[0125] (6) Total light transmittance is 91.6%.

[0126] Compared with Comparative Example 4, Example 1 can significantly simplify the process, shorten the reaction process, reduce equipment investment, and obtain a heat-resistant PMMA resin product with performance as excellent as that of the two-stage continuous reactive extrusion method.

[0127] Comparative Example 5

[0128] Using the same raw material resin as in Example 1, PMMA resin was prepared according to essentially the same process as in Example 1, except that the reaction process was divided into two stages of reactive extrusion modification. Methylamine was added during the first stage of reactive extrusion, and dimethyl carbonate was added during the second stage. The imidizing agent and esterifying agent were not mixed. The polymethyl methacrylate prepared in this comparative example has the following properties:

[0129] (1) The weight-average molecular weight is 124,000;

[0130] (2) The glass transition temperature is 124℃;

[0131] (3) The acid value is 0.24 mmol / g;

[0132] (4) The water absorption rate (soaked in pure water at 25℃ for 24 hours) is 0.31%;

[0133] (5) The residual component content was 1398 ppm;

[0134] (6) Total light transmittance is 91.5%.

[0135] Dimethyl carbonate (DMC), a conventional esterifying agent, has poor polarity, resulting in poor solubility of imidizing agents within it. Monomethylamine is a strong nucleophile, while the carbonyl carbon of dimethyl carbonate is a potentiophilic site; both readily undergo nucleophilic substitution reactions, producing N-methylcarbamate and methanol. This creates a competitive reaction for esterification modification, exhibiting high reactivity. This not only reduces the selectivity of the esterification reaction but also significantly consumes the content of both monomethylamine and dimethyl carbonate, leading to reaction control failure and the introduction of new impurities. Therefore, dimethyl carbonate is not suitable as an esterifying agent for one-step imidization for heat-resistant modification and acid value optimization. Compared to Comparative Example 5, Example 1 significantly simplifies the process, shortens the reaction time, reduces equipment investment, and yields a resin product with performance comparable to the mainstream production process of heat-resistant PMMA for polarizers.

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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; and these 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 polymethyl methacrylate for polarizing films, comprising the following steps: (1) Input raw material resin into the main feed port of the extruder, melt it, and inject the mixture of saturated fatty alcohol and imidizing agent into the molten resin from the liquid spray gun for mixing; (2) In the reaction zone, the raw material resin, saturated fatty alcohol and imidizing agent are fully reacted; (3) In the devolatilization zone, two-stage dynamic devolatilization is used to remove volatiles.

2. The method according to claim 1, characterized in that, The raw material resin is prepared by homopolymerization or copolymerization of the following raw material monomers: (a) 80-100 parts by weight of methyl methacrylate monomer; (b) 0-10 parts by weight of methyl acrylate monomer; (c) 0-10 parts by mass of styrene-based monomers.

3. The method according to claim 1 or 2, characterized in that, The raw material resin has the following properties: (1) Weight-average molecular weight is 100,000-130,000; (2) The glass transition temperature is 105-115℃; (3) The acid value is 0.01-0.05 mmol / g; (4) Water absorption rate (soaked in pure water at 25℃ for 24 hours) is 0.10-0.30%; (5) The content of residual small components is <1500 ppm; (6) Total light transmittance is 92.0-95.0%.

4. The method according to any one of claims 1-3, characterized in that, The molecular weight of the saturated fatty alcohol is less than 200.

5. The method according to any one of claims 1-4, characterized in that, The saturated fatty alcohol is selected from one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol, diethylene glycol, and propylene glycol.

6. The method according to any one of claims 1-5, characterized in that, The amount of saturated fatty alcohol used is 1-9 parts by weight, based on 100 parts by weight of the raw material resin.

7. The method according to any one of claims 1-6, characterized in that, The imidizing agent includes one or more of ammonia, ammonia water, monomethylamine, ethylamine, n-propylamine, aniline, cyclohexylamine, and urea.

8. The method according to any one of claims 1-7, characterized in that, The amount of the primary amine used is 1-5 parts by weight, based on 100 parts by weight of the raw material resin.

9. The heat-resistant polymethyl methacrylate resin for polarizing films prepared by the method according to any one of claims 1-8, characterized in that: (1) Glass transition temperature ≥125℃; (2) Acid value < 0.40 mmol / g; (3) Water absorption rate (soaked in pure water at 25℃ for 24 hours) < 0.50%; (4) The content of residual small components in the resin is <1500ppm; (5) Total light transmittance ≥ 92%.

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