Diisocyanate manufacturing method

Abstract

The present invention relates to a method for producing a diisocyanate which has high purity, excellent stability even during long-term storage, and little cloudiness.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0169321, dated November 30, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference. The present invention relates to a method for producing diisocyanates with high purity and improved stability. [Background technology]

[0002] Isocyanate compounds are highly valuable compounds that are used not only in the chemical and resin industries but also as fine chemical products, including optical materials. Demand for xylylene diisocyanate (XDI), a representative example of an isocyanate compound, is increasing as a high-value-added chemical material used as a raw material for high-end optical lenses.

[0003] Such isocyanates are highly reactive and easily denatured depending on the storage environment. When the isocyanates are denatured, not only the purity but also the transparency decreases, causing cloudiness, making them unsuitable for use in the optical field, where excellent appearance properties, particularly transparency, are required.

[0004] Therefore, a method of applying a stabilizer to the isocyanate has been used, but the stabilizer may cause coloration, and if the stability of the isocyanate itself is reduced, the effectiveness is limited.

[0005] Therefore, research is needed into the production of isocyanates that can suppress the occurrence of cloudiness even during long-term storage, maintain purity, and are free from the risk of denaturation. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for producing a diisocyanate which has high purity, is stable even during long-term storage, and is suitable for producing optical resins. [Means for solving the problem]

[0007] Therefore, according to one embodiment of the present invention, a reaction step in which the diamine or its salt is reacted with phosgene to obtain a reaction mixture; and a purification step of separating the diisocyanate from the reaction mixture; A method for producing diisocyanates is provided, wherein the purification step is carried out at a temperature of less than 170° C. for not more than 16 hours.

[0008] the diamine is at least one selected from the group consisting of 1,2-xylylenediamine, 1,3-xylylenediamine, 1,4-xylylenediamine, 1,2-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, and 1,4-bis(aminomethyl)cyclohexane; The diamine salt may be one or more selected from the group consisting of 1,2-xylylenediamine hydrochloride, 1,3-xylylenediamine hydrochloride, 1,4-xylylenediamine hydrochloride, 1,2-bis(aminomethyl)cyclohexane hydrochloride, 1,3-bis(aminomethyl)cyclohexane hydrochloride, 1,4-bis(aminomethyl)cyclohexane hydrochloride, 1,2-xylylenediamine carbonate, 1,3-xylylenediamine carbonate, and 1,4-xylylenediamine carbonate, 1,2-bis(aminomethyl)cyclohexane carbonate, 1,3-bis(aminomethyl)cyclohexane carbonate, and 1,4-bis(aminomethyl)cyclohexane carbonate.

[0009] In one embodiment, the reaction step is carried out at a temperature between 80°C and 180°C. In one embodiment, the purification step is carried out at a temperature of 100° C. to 150° C. for 5 hours to 15 hours. In one embodiment, the purification step is carried out by vacuum distillation and / or thin film distillation under a pressure of 0.001 to 50 kPa.

[0010] In one embodiment, the purification step may include the steps of: removing the solvent by vacuum distillation of the reaction mixture at a first temperature and a first pressure; removing low-boiling impurities by vacuum distillation at a second temperature and a second pressure; and removing oligomers by thin-film distillation at a third temperature and a third pressure, wherein the third temperature may be equal to or lower than the first temperature and / or the second temperature, and the third pressure may be equal to or lower than the first pressure and / or the second pressure. After the purification step, the purity of the diisocyanate may be 99% to 100%. [Effects of the Invention]

[0011] According to the method for producing a diisocyanate of the present invention, it is possible to produce a diisocyanate that is highly pure and has excellent stability even when stored for a long period of time. DETAILED DESCRIPTION OF THE INVENTION

[0012] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise. It should be understood that the terms "comprise," "comprise," or "have" used in this specification are intended to specify the presence of embodied features, steps, components, or combinations thereof, and do not preclude the possibility of the presence or addition of one or more other features, steps, components, or combinations thereof.

[0013] Although the present invention can be embodied in various forms through various modifications, specific embodiments are described in detail below by way of example, but it should be understood that this is not intended to limit the present invention to the specific disclosed embodiments, and that the present invention encompasses all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

[0014] The present invention will be described in detail below. The present inventors have been researching a method for producing a diisocyanate that can increase purity while improving stability so that denaturation such as cloudiness does not occur during long-term storage. As a result, they have found that the above effects can be achieved by controlling the maximum temperature and residence time in the purification step, and have completed the present invention.

[0015] Therefore, according to one embodiment of the present invention, a reaction step in which the diamine or its salt is reacted with phosgene to obtain a reaction mixture; and a purification step of separating the diisocyanate from the reaction mixture; A method for producing diisocyanates is provided, wherein the purification step is carried out at a temperature of less than 170° C. for not more than 16 hours.

[0016] The present invention will now be described step by step. First, a reaction step (phosgenation reaction step) is carried out in which a diamine or a salt thereof is reacted with phosgene to obtain a reaction mixture.

[0017] The diamine is an aromatic, alicyclic, or aliphatic amine containing two amine groups in the molecule. In one embodiment, the diamine is one or more selected from the group consisting of 1,2-xylylenediamine (o-xylylenediamine, o-XDA), 1,3-xylylenediamine (m-xylylenediamine, m-XDA), 1,4-xylylenediamine (p-xylylenediamine, p-XDA), 1,2-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, and 1,4-bis(aminomethyl)cyclohexane, and can be selected depending on the structure of the target diisocyanate.

[0018] The salt of the diamine refers to a salt produced by the reaction of the diamine with an acid, and may be, for example, a hydrochloride produced by the reaction of the diamine with anhydrous hydrochloric acid, a carbonate produced by the reaction of the diamine with carbonic acid, etc. Although the diamine reacts rapidly with phosgene, the reaction rate can be slowed when the diamine is converted into a solid salt and used.

[0019] Specifically, the diamine salt may be at least one selected from the group consisting of 1,2-xylylenediamine hydrochloride, 1,3-xylylenediamine hydrochloride, 1,4-xylylenediamine hydrochloride, 1,2-bis(aminomethyl)cyclohexane hydrochloride, 1,3-bis(aminomethyl)cyclohexane hydrochloride, 1,4-bis(aminomethyl)cyclohexane hydrochloride, 1,2-xylylenediamine carbonate, 1,3-xylylenediamine carbonate, and 1,4-xylylenediamine carbonate, 1,2-bis(aminomethyl)cyclohexane carbonate, 1,3-bis(aminomethyl)cyclohexane carbonate, and 1,4-bis(aminomethyl)cyclohexane carbonate.

[0020] The diamine salt is produced in a solvent, and examples of the solvent include aromatic hydrocarbon solvents such as benzene, toluene, xylene, and ethylbenzene; chlorinated aromatic hydrocarbon solvents such as monochlorobenzene, 1,2-dichlorobenzene, and 1,4-dichlorobenzene; and chlorinated hydrocarbon solvents such as dichloromethane, chloroform, and carbon tetrachloride, and a mixture of two or more of these can be used. These solvents can also be used as solvents for the phosgenation reaction, so that after the diamine salt is obtained by reacting the diamine with an acid in the solvent, phosgene can be added to carry out the phosgenation reaction without a separate purification process.

[0021] The diamine salt is preferably produced at a temperature of 60°C or less, preferably about 5 to 30°C. Although the temperature may temporarily rise due to the heat of reaction during the reaction, it is preferable that the maximum temperature in the reactor is maintained at 90°C or less, or 60°C or less.

[0022] Meanwhile, when reacting diamine with phosgene, phosgene may be added all at once at the beginning of the reaction, or a portion may be added at the beginning of the reaction and the remainder may be added in portions during the reaction. When adding phosgene, it is preferable that the temperature of the phosgene is −10° C. to 0° C., since this prevents the highly toxic phosgene from leaking and allows the temperature of the reactants to be smoothly increased.

[0023] During the phosgenation reaction, the temperature of the reactor can be adjusted to 80° C. to 180° C. Preferably, the temperature may be in the range of 100° C. or higher, or 120° C. or higher, and 150° C. or lower, or 140° C. or lower. Under such temperature conditions, the phosgenation reaction proceeds smoothly and thermal decomposition of the diisocyanate produced can be prevented.

[0024] The diamine may further include at least one additive selected from the group consisting of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (hereinafter referred to as 4-hydroxy TEMPO), 4-methoxy-2,2,6,6-tetramethyl-piperidine-1-oxyl (4-methoxy-TEMPO), 2,2,6,6-tetramethyl-4-benzyloxypiperidine-1-oxyl (4-benzyloxy-TEMPO), and 4-acetamido-2,2,6,6-tetramethylpiperidin-1-oxyl (hereinafter referred to as 4-acetamido TEMPO) to suppress the generation of by-products during the reaction of the diamine with phosgene. When the additive is used, the content of the additive may be 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight or 0.5 to 3 parts by weight, per 100 parts by weight of the diamine or diamine salt.

[0025] After the phosgenation reaction, a purification step is then carried out to separate the diisocyanate from the resulting reaction mixture.

[0026] Isocyanate groups are highly reactive and prone to side reactions. Impurities formed by side reactions can affect the purity and color of the isocyanate compound, making a purification step necessary. However, the inventors' research has revealed that if the purification step is performed under excessively high temperature conditions or if the purification step time is prolonged, the stability of the isocyanate compound is significantly reduced. Therefore, the present invention aims to improve the stability of diisocyanates by maintaining the temperature of the purification step at an appropriate level and controlling the total time (residence time) of the purification step.

[0027] Specifically, in the production method of the present invention, the purification step is carried out at a temperature of less than 170°C for 16 hours or less. If the maximum temperature of the purification step is 170°C or higher or the residence time of the purification step exceeds 16 hours, the diisocyanate produced may absorb excessive heat and become less stable. However, if the temperature of the purification step is controlled to less than 170°C and the residence time is controlled to 16 hours or less, the stability of the diisocyanate can be improved regardless of the amount of reaction mixture purified.

[0028] Preferably, the maximum temperature in the purification step is maintained at 160°C or less, or 150°C or less. Meanwhile, the minimum temperature in the purification step is not particularly limited since it does not significantly affect the stability of the diisocyanate, but may be 100°C or more, or 110°C or more, when the efficiency of the purification process is taken into consideration.

[0029] The residence time in the purification step may be 16 hours or less, or 15 hours or less. The shorter the residence time in the purification step, the more improved the stability of the diisocyanate. However, since a certain period of time is required for the purification process to achieve high purity, the purification time is preferably 5 hours or more, 8 hours or more, 10 hours or more, or 13 hours or more.

[0030] The purification step is carried out by a method generally used for purifying isocyanate compounds. In one embodiment, the purification step is carried out by vacuum distillation and / or thin film distillation using a distillation column. The vacuum distillation and / or thin film distillation is carried out under a pressure of 0.001 to 50 kPa, which satisfies the above-mentioned temperature and residence time conditions and enables high-purity purification.

[0031] The distillation column used for the vacuum distillation may be a plate tower or a packed tower without limitation. The number of theoretical plates of the distillation column may be, for example, 2 or more, 5 or more, or 10 or more, and 60 or less, or 40 or less.

[0032] The temperature during the vacuum distillation is maintained below 170°C, and specifically may be 100°C or higher, or 130°C or higher, and 160°C or lower, or 150°C or lower. The pressure during the vacuum distillation may be 0.001 kPa or higher, or 0.005 kPa or higher, or 0.01 kPa or higher, and 50 kPa or lower, or 30 kPa or lower, or 10 kPa or lower, or 1 kPa or lower. The temperature and pressure during the vacuum distillation refer to the column bottom temperature of the distillation column.

[0033] The temperature at the top of the column during the reduced pressure distillation may be 10°C or higher, or 20°C or higher, and 100°C or lower, or 80°C or lower, and the pressure may be the same as the column low pressure, 0.001 kPa or higher, or 0.005 kPa or higher, or 0.01 kPa or higher, and 50 kPa or lower, or 30 kPa or lower, or 10 kPa or lower, or 1 kPa or lower.

[0034] The thin-film distillation is carried out using a thin-film distillation apparatus equipped with an evaporator, a condenser, and a pressure reducing means. The rotor speed of the thin-film distillation apparatus may be 50 rpm or more, or 120 rpm or more, or 200 rpm or more, and 500 rpm or less, 400 rpm or less, or 350 rpm or less. The temperature during thin-film distillation is also maintained below 170°C, and may be, for example, 100°C or more, or 110°C or more, and 160°C or less, or 130°C or less. The pressure may be 0.001 kPa or more, or 0.005 kPa or more, or 0.01 kPa or more, and 50 kPa or less, 30 kPa or less, 10 kPa or less, or 1 kPa or less.

[0035] Under such reduced pressure distillation conditions and / or thin film distillation conditions, the residence time in the purification step can be reduced while improving the purification efficiency, thereby making it possible to obtain a highly pure diisocyanate compound.

[0036] In one embodiment, the purification step is carried out in multiple stages while varying the temperature and / or pressure conditions. For example, the purification step may be carried out by sequentially removing the solvent, removing low-boiling impurities, and removing oligomers.

[0037] Specifically, the purification step can be carried out at a temperature of less than 170°C and a pressure of 0.001 to 50 kPa; or at a temperature of 130 to 150°C and a pressure of 0.01 to 1 kPa, and by carrying out reduced pressure distillation to remove the solvent at a first temperature and a first pressure, followed by removing low-boiling impurities at a second temperature and a second pressure, and then removing oligomers at a third temperature and a third pressure using a thin-film distillation apparatus.

[0038] In this case, the first to third temperatures may be the same or different, and the first to third pressures may be the same or different. For example, the third temperature may be equal to or lower than the first temperature and / or the second temperature, and the third pressure may be equal to or lower than the first pressure and / or the second pressure.

[0039] Meanwhile, before the vacuum distillation step, a nitrogen bubbling step may be further carried out in order to remove unreacted phosgene and hydrogen chloride gas from the reactor after the phosgenation reaction is completed.

[0040] The diisocyanate can be produced by the above-described production method. Depending on the diamine used, the diisocyanate may be one or more selected from the group consisting of 1,2-xylylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, 1,2-bis(isocyanatomethyl)cyclohexane, 1,3-bis(isocyanatomethyl)cyclohexane, and 1,4-bis(isocyanatomethyl)cyclohexane.

[0041] The diisocyanate produced by the production method of the present invention may have a purity of 99% to 100% after purification, preferably 99.2% or more, or 99.4% or more, and more preferably 100%.

[0042] Meanwhile, the diisocyanate is produced through a purification step in which the temperature and residence time are controlled as described above, and therefore has the advantages of excellent stability even during long-term storage, little denaturation, and excellent color and transparency.

[0043] Specifically, the difference between the purity of the diisocyanate after storage under refrigerated (4°C) conditions for 6 months after production and the initial purity immediately after production may be 1.5% or less, or 1% or less.

[0044] For example, the purity of the diisocyanate may be 98% or more, 98.4% or more, or 98.6% or more, as measured after storage under refrigerated (4°C) conditions for 6 months after production. The higher the purity after storage, the better, and the purity may be theoretically 100%, or, for example, 99.5% or less, or 99% or less.

[0045] Furthermore, the diisocyanate may have a content of cloudy substances generated after storage under refrigerated (4°C) conditions for 6 months after production of less than 0.8% by weight, 0.5% by weight or less, 0.3% by weight or less, or 0.1% by weight or less, and preferably 0% by weight.

[0046] The methods for measuring the purity of the diisocyanate, the purity after refrigerated storage, and the content of cloudy substances will be embodied in the examples described below.

[0047] The diisocyanate produced by the above-described production method of the present invention has excellent stability and high transparency, and can be suitably used in polymerizable compositions for producing optical elements. The polymerizable composition may contain, for example, the diisocyanate of the present invention and a polyol and / or polythiol component.

[0048] Such a polymerizable composition has excellent transparency and little yellowing, and can be suitably used as an optical material for producing eyeglass lenses, camera lenses, etc.

[0049] Preferred examples are presented below to aid in understanding the present invention. However, the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical idea of ​​the present invention. It goes without saying that such changes and modifications fall within the scope of the appended claims.

[0050] [Example] Example 1 (1) Reaction step 471 g of 1,2-dichlorobenzene, 32.5 g of meta-xylylenediamine (m-XDA) with a purity of 99.4%, and 0.24 g of 4-hydroxy TEMPO were placed in a reactor, and anhydrous hydrochloric acid was added at a rate of 20 g / hr at room temperature (23±5°C) and stirred. During the addition of the anhydrous hydrochloric acid, the temperature rose to 50°C.

[0051] After injecting anhydrous hydrochloric acid for 4 hours, the salt formed was cooled to room temperature, and 43 g of phosgene was added to the reactor, which was then heated to a temperature of 130° C. During this time, a dry ice-acetone cooler was used from the time of adding phosgene until the end of the reaction to prevent phosgene from leaking out. After the temperature of the reactor reached 130°C, the temperature of the reactor was maintained at 125 to 135°C for 2 hours so that the reaction solution became transparent. The completion of the reaction was confirmed when the solution became transparent.

[0052] (2) Refining stage After completion of step (1), nitrogen was blown into the reactor and cooled to room temperature. The reaction mixture from which phosgene had been removed was distilled under reduced pressure using a 20-plate column at a pressure of 10.0 kPa, a column bottom temperature of 150°C, and a column top temperature of 60°C to remove the solvent, followed by distillation under reduced pressure at a pressure of 1.0 kPa, a column bottom temperature of 150°C, and a column top temperature of 60°C to remove low-boiling impurities. The resulting mixture was then distilled under reduced pressure using a thin-film distillation apparatus with a rotor rotating at 200 rpm at 130°C and 0.5 kPa to remove oligomers, yielding meta-xylylene diisocyanate (m-XDI). The maximum temperature in the purification step was 150°C, which is the temperature during vacuum distillation, and the purification step took a total of 15 hours.

[0053] Example 2 The phosgenation reaction of m-XDA was carried out in the same manner as in step (1) of Example 1. The reactor was then cooled to room temperature by blowing nitrogen into it. The reaction mixture from which the phosgene had been removed was distilled under reduced pressure using a 20-plate column at a pressure of 5.0 kPa, a column bottom temperature of 140°C, and a column top temperature of 50°C to remove the solvent, followed by distillation under reduced pressure at a pressure of 0.5 kPa, a column bottom temperature of 140°C, and a column top temperature of 50°C to remove low-boiling impurities. The resulting mixture was then distilled using a thin-film distillation apparatus with a rotor rotating at 200 rpm at 130°C and 0.5 kPa to remove oligomers, yielding m-XDI. The maximum temperature in the purification step was 140°C, which is the temperature during vacuum distillation, and the purification step took a total of 16 hours.

[0054] Comparative Example 1 The phosgenation reaction of m-XDA was carried out in the same manner as in step (1) of Example 1. The reactor was then cooled to room temperature by blowing nitrogen into it. The reaction mixture from which the phosgene had been removed was distilled under reduced pressure using a 20-plate column at a pressure of 5.0 kPa, a column bottom temperature of 140°C, and a column top temperature of 50°C to remove the solvent, followed by distillation under reduced pressure at a pressure of 0.5 kPa, a column bottom temperature of 140°C, and a column top temperature of 50°C to remove low-boiling impurities. The resulting mixture was then distilled using a thin-film distillation apparatus with a rotor rotating at 200 rpm at 130°C and 0.5 kPa to remove oligomers, yielding m-XDI. The maximum temperature in the purification step was 140°C, which is the temperature during vacuum distillation, and the purification step took a total of 32 hours.

[0055] Comparative Example 2 The phosgenation reaction of m-XDA was carried out in the same manner as in step (1) of Example 1. The reactor was then cooled to room temperature by blowing nitrogen into it. The reaction mixture from which the phosgene had been removed was distilled under reduced pressure using a 20-plate column at a pressure of 10.0 kPa, a column bottom temperature of 150°C, and a column top temperature of 60°C to remove the solvent, followed by distillation under reduced pressure at a pressure of 1.0 kPa, a column bottom temperature of 150°C, and a column top temperature of 60°C to remove low-boiling impurities. The resulting mixture was then distilled using a thin-film distillation apparatus with a rotor rotating at 200 rpm at 130°C and 0.5 kPa to remove oligomers, yielding m-XDI. The maximum temperature in the purification step was 150°C, which is the temperature during vacuum distillation, and the purification step took a total of 24 hours.

[0056] Comparative Example 3 The phosgenation reaction of m-XDA was carried out in the same manner as in step (1) of Example 1. The reactor was then cooled to room temperature by blowing nitrogen into it. The reaction mixture from which the phosgene had been removed was subjected to vacuum distillation using a 20-plate column at a pressure of 10.0 kPa, a column bottom temperature of 150°C, and a column top temperature of 60°C to remove the solvent, followed by vacuum distillation at a pressure of 1.0 kPa, a column bottom temperature of 150°C, and a column top temperature of 60°C to remove low-boiling impurities, and then distillation using a thin-film distillation apparatus with a rotor rotating at 200 rpm at 0.5 kPa to remove oligomers, yielding m-XDI. The maximum temperature in the purification step was 150°C, which is the temperature during vacuum distillation, and the purification step took a total of 32 hours.

[0057] Comparative Example 4 The phosgenation reaction of m-XDA was carried out in the same manner as in step (1) of Example 1. The reactor was then cooled to room temperature by blowing nitrogen into it. The reaction mixture from which the phosgene had been removed was distilled under reduced pressure using a 20-plate column at a pressure of 50.0 kPa, a column bottom temperature of 170°C, and a column top temperature of 80°C to remove the solvent, followed by distillation under reduced pressure at a pressure of 10.0 kPa, a column bottom temperature of 170°C, and a column top temperature of 80°C to remove low-boiling impurities. The resulting mixture was then distilled under 0.5 kPa at a thin-film distillation apparatus with a rotor rotating at 200 rpm to remove oligomers, yielding m-XDI. The maximum temperature in the purification step was 170°C, which is the temperature during vacuum distillation, and the purification step took a total of 16 hours.

[0058] Experimental example (1) Purity measurement of XDI The purity of the m-XDI in the Examples and Comparative Examples was analyzed using GC. First, GC analysis was performed on the m-XDI composition immediately after purification, and then GC analysis was performed on the m-XDI after storing it under refrigerated conditions (4°C) for 6 months. For m-XDI that had become cloudy after 6 months, the insoluble cloudy material was filtered, and the filtrate was then analyzed by GC.

[0059] The GC used for the analysis was an HP-6890, and detection was performed with an FID. The column used was a DB-17 (30 m x 0.25 mm x 0.5 μm), the carrier gas was nitrogen (1.0 mL / min), and the oven temperature was 80 °C → 5 °C / min → 160 °C (8 min) → 20 °C / min → 280 °C (18 min).

[0060] (2) Evaluation of turbidity and measurement of content of turbid substances After storing m-XDI under refrigerated conditions (4°C) for 6 months, the presence or absence of cloudiness was visually inspected. For m-XDI that was cloudy to the naked eye, 300g was weighed and filtered, and the weight of the filtered solids (cloudy matter) was measured, from which the content of the cloudy matter (wt%) was calculated.

[0061] (3) Manufacturing of optical materials and evaluation of transparency Using each of the m-XDIs obtained in the above Examples and Comparative Examples, polymerizable compositions and optical elements (plastic lenses) were produced by the following methods.

[0062] 20.8 g of m-XDI, 0.04 g of zelec UN (a release agent, acidic phosphate ester, manufactured by Stepan), and 0.04 g of biosorb583 (an ultraviolet absorber, 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole, manufactured by Sakai Chemical Industry Co., Ltd.) were stirred in a flask at room temperature for approximately 20 minutes.

[0063] After visually confirming that all components were thoroughly mixed, 0.002 g of dibutyltin chloride was added and stirred for 10 minutes to form a mixture. 19.2 g of 2,3-bis(2-sulfanyl ethyl sulfanyl)propane-1-thiol was added to the mixture, which was then degassed at 5 mbar and stirred for 1 hour to prepare a polymerizable composition.

[0064] The polymerizable composition was filtered through a 1 μm PTFE filter and then poured into a mold consisting of a glass mold and tape. The mold was placed in an oven, and the temperature was gradually increased from 10°C to 120°C, allowing polymerization to occur for 20 hours. After polymerization was complete, the mold was removed from the oven and released, followed by annealing at 120°C for 6 hours to produce a plastic lens.

[0065] The degree of clouding of the lenses was evaluated with the naked eye using a general fluorescent lamp and a zirconium lamp (Y-100G).

[0066] <Evaluation criteria> C (Clear): Transparent under fluorescent and zirconium lamps SH (Slightly lamp Haze): Transparent under fluorescent lamps, but partially cloudy under zirconium lamps LH (Lamp Haze): Transparent under fluorescent lamps, but appears cloudy under zirconium lamps VH (Visual Haze): All surfaces are observed to be cloudy under fluorescent and zirconium lamps.

[0067] [Table 1]

[0068] Referring to Table 1, it can be seen that the XDIs of Examples 1 and 2, which were prepared by adjusting the maximum temperature in the purification step to less than 170°C and the residence time in the purification step to 16 hours or less, maintained excellent purity and had excellent long-term storage stability without cloudiness. In addition, it was confirmed that the optical elements prepared using the XDIs of Examples 1 and 2 exhibited excellent transparency.

[0069] However, as in Comparative Examples 1 to 4, when the temperature in the purification step during the production of XDI is excessively high, or when the temperature is appropriate but the residence time in the purification step is excessively long, the purity immediately after purification is excellent, but the stability of the XDI decreases, such as the occurrence of cloudiness or a significant decrease in purity during long-term storage, and ultimately this also affects the quality of optical elements manufactured using this.

Claims

1. a reacting step of reacting a diamine or a salt thereof with phosgene to obtain a reaction mixture; and a purification step of separating the diisocyanate from the reaction mixture; The purification step is carried out at a temperature of less than 170°C for a period of not more than 16 hours; The purification step comprises: vacuum distilling the reaction mixture at a first temperature and a first pressure to remove the solvent; vacuum distillation at a second temperature and a second pressure to remove low-boiling impurities; and thin film distillation at a third temperature and a third pressure to remove oligomers; the third temperature is equal to or lower than the first temperature and / or the second temperature; the third pressure is equal to or lower than the first pressure and / or the second pressure; Method for producing diisocyanates.

2. the diamine is at least one selected from the group consisting of 1,2-xylylenediamine, 1,3-xylylenediamine, 1,4-xylylenediamine, 1,2-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, and 1,4-bis(aminomethyl)cyclohexane; The method for producing a diisocyanate according to claim 1, wherein the diamine salt is at least one selected from the group consisting of 1,2-xylylenediamine hydrochloride, 1,3-xylylenediamine hydrochloride, 1,4-xylylenediamine hydrochloride, 1,2-bis(aminomethyl)cyclohexane hydrochloride, 1,3-bis(aminomethyl)cyclohexane hydrochloride, 1,4-bis(aminomethyl)cyclohexane hydrochloride, 1,2-xylylenediamine carbonate, 1,3-xylylenediamine carbonate, and 1,4-xylylenediamine carbonate, 1,2-bis(aminomethyl)cyclohexane carbonate, 1,3-bis(aminomethyl)cyclohexane carbonate, and 1,4-bis(aminomethyl)cyclohexane carbonate.

3. The method for producing diisocyanates according to claim 1, wherein the reaction step is carried out at 80°C to 180°C.

4. 2. The method for producing diisocyanates according to claim 1, wherein the purification step is carried out at a temperature of 100 to 150° C. for 5 to 15 hours.

5. The method for producing a diisocyanate according to claim 1, wherein the purification step is carried out by vacuum distillation under a pressure of 0.001 to 50 kPa and / or thin-film distillation.

6. 2. The method for producing a diisocyanate according to claim 1, wherein after the purification step, the purity of the diisocyanate is 99% to 100%.

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