Isocyanate composition and preparation method thereof, optical material

Abstract

The present invention provides an isocyanate composition and a preparation method thereof, and an optical material. The isocyanate composition comprises isocyanate and dichlorobiphenyl, wherein the content of dichlorobiphenyl is greater than 0ppm and less than 1ppm, based on the mass of the isocyanate composition. In its preparation method, by strictly controlling the process conditions of the solvent refining tower, and arranging a circulating adsorption device at the bottom of the solvent refining tower to adsorb the tower bottom material, the iron content of the tower bottom material is controlled to the maximum extent, and then the circulating liquid phase logistics of the inert aromatic solvent and the content of dichlorobiphenyl in the isocyanate composition are controlled. The problem of the generation of harmful dichlorobiphenyl compounds in the diisocyanate solvent separation process is solved, the quality of isocyanate products and optical materials can be improved, the technical prejudice existing in the prior art is overcome, and unexpected effects are produced.

Description

Technical Field

[0001] The invention relates to the field of isocyanate, in particular to a process for preparing isocyanate, and also to the field of optical materials. Background Art

[0002] In the process of producing isocyanates by the liquid phase phosgene method, a large amount of organic solvents are often added to disperse the reaction and reduce the occurrence of side reactions. At the same time, in the process of recovering the solvent, the solvent, carbon tetrachloride, phosgene, hydrogen chloride and a small amount of isocyanate in the photochemical reaction process are removed. Different recovery conditions will cause the formation of by-products due to side reactions and incomplete separation. Therefore, the solvent must be continuously treated during the production process. While recovering phosgene, the adverse effects of impurities in the solvent on the photochemical reaction should be avoided to ensure the normal, continuous and stable operation of production.

[0003] Isocyanates are prepared in large quantities and are used primarily as starting materials for the preparation of polyurethanes. They are usually prepared by reacting appropriate amines with phosgene, allowing the reaction of the amine with phosgene to be carried out in the gas phase or in the liquid phase, generally using organic solvents of the benzene type. In these syntheses, small amounts of impurities remain in the solvent, and it is essential for the economical operation of the isocyanate synthesis to separate the impurities from the benzene solvent and to recycle the solvent into the reaction.

[0004] Various processes for preparing isocyanates by reacting amines with phosgene in the gas phase are known from the prior art. The present invention relates in particular to a process for recovering the solvent used in the preparation of isocyanates from amines and phosgene in the phosgenation and recycling the recovered solvent into the photochemical reactor.

[0005] A series of procedures are known from the prior art by which mixtures of hydrogen chloride and phosgene and possibly solvents can be fractionated in order to enable the phosgene to be recycled into the reaction. However, the prior art deals only with the economics of reusing phosgene and HCl on the one hand and with the fact that the burden of recycled inerts in the process leads to higher operating costs or, in one case, to corrosion of the equipment, which leads to side reactions on the other hand. The problems caused by side reactions of the benzene solvents recycled into the reactor are not described in the prior art.

[0006] Surprisingly, the solvent entering the purification process may lead to an increase in the formation of dichlorobiphenyl compounds. In particular, if the above-mentioned solvent is present as an impurity in the recycled solvent, dichlorobiphenyl will be contained in the final isocyanate product, which is an undesirable compound. This compound is very stable, not prone to oxidation and reduction reactions, and extremely difficult to be decomposed by microorganisms. It has the characteristics of bioaccumulation, difficulty in degradation, long-distance transmission, carcinogenicity, mutagenicity and endocrine disruption. At present, there is a lack of suitable treatment methods. When incinerated at high temperature, it not only cannot be burned and decomposed, but will instead increase the production of highly toxic dioxin compounds.

[0007] Patent CN201780062882. reports an isocyanate compound containing an ethylenically unsaturated bond, to which the addition of more than 1 ppm of a halogenated hydrocarbon substance can improve storage stability, but there is no description of the effect on polyurethane products.

[0008] Polyurethane resins are required to have excellent discoloration resistance depending on their purpose and use. However, in the process of obtaining polyurethane optical materials by polymerization of isocyanates and polythiol compounds, it has been found that polyurethane resins containing dichlorobiphenyls sometimes cannot ensure sufficient discoloration resistance, which has an adverse effect on the performance of the product material. Summary of the invention

[0009] In order to overcome the above technical problems, the purpose of the present invention is to provide an isocyanate composition and a preparation method thereof, which can effectively reduce the content of dichlorobiphenyl compounds in the isocyanate composition, reduce its influence on the change of key indicator color number, and control the content of dichlorobiphenyl to ensure the quality of optical resin.

[0010] To achieve the above purpose, the present invention adopts the following technical solutions.

[0011] An isocyanate composition comprises isocyanate and dichlorobiphenyl, wherein the content of the dichlorobiphenyl is greater than 0 ppm and less than 1 ppm based on the mass of the isocyanate composition.

[0012] As a preferred embodiment, the isocyanate composition contains dichlorobiphenyl greater than 0 and ≤ 0.9 ppm, preferably greater than 0 and ≤ 0.8 ppm, more preferably greater than 0 and ≤ 0.5 ppm, for example 0.1 ppm, 0.2 ppm, 0.3 ppm, 0.4 ppm, 0.5 ppm, 0.6 ppm or 0.7 ppm.

[0013] The dichlorobiphenyl, when present in isomers, may be any one isomer, or may be a mixture of these isomers. It should be noted that the content of the dichlorobiphenyl represents the total content of the isomers. The structural formula of the dichlorobiphenyl (DCBs) is shown in formula a:

[0014]

[0015] The isocyanate described in the present invention is an aliphatic, alicyclic or aromatic aliphatic polyisocyanate, and there is no special limitation. Specific examples of isocyanate compounds include but are not limited to toluene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, methylcyclohexyl diisocyanate, dimethylcyclohexyl diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, p-phenylene diisocyanate, norbornane diisocyanate, cyclohexyl dimethylene diisocyanate, xylylene diisocyanate, etc., preferably xylylene diisocyanate and cyclohexyl dimethylene diisocyanate.

[0016] It is an object of the present invention to provide a process which allows the reaction of aliphatic, cycloaliphatic or araliphatic diamines with phosgene to form the corresponding diisocyanates in such a way that the formation of dichlorobiphenyl compounds can be reduced.

[0017] A method for preparing the isocyanate composition of the present invention comprises the following steps:

[0018] a) photochemically reacting an organic primary amine with excess phosgene in a gas phase or liquid phase to obtain a liquid phase stream 10 containing isocyanate and a gas phase stream 1 containing phosgene and HCl; in step a), an inert aromatic solvent is used;

[0019] b) the liquid phase stream 10 containing isocyanate obtained in step a) is separated into a dephosgenated isocyanate crude stream 6 through a dephosgenating tower B, and the gas phase is passed through a condenser D to obtain a gas phase stream 2 containing phosgene and HCl and a liquid phase stream 3 containing an inert aromatic solvent;

[0020] c) removing HCl from the gas phase stream 2 containing phosgene and HCl obtained in step b) by condensing an inert aromatic solvent 9 to obtain a liquid phase stream 4 containing phosgene, and mixing it with the liquid phase stream 3 containing the inert aromatic solvent in step b) to obtain a mixed liquid phase stream 5;

[0021] d) separating the mixed liquid phase stream 5 of step c) through a solvent refining tower G to obtain a gas phase stream containing phosgene and a circulating liquid phase stream 8 containing an inert aromatic solvent, wherein the gas phase stream containing phosgene is directly or condensed into a liquid phase and recycled to step a) to participate in the photochemical reaction; the circulating liquid phase stream 8 containing an inert aromatic solvent contains less than 1 ppm, preferably less than 0.5 ppm of dichlorobiphenyl, and is recycled to step a) to participate in the photochemical reaction;

[0022] e) The crude product stream 6 of the dephosgenated isocyanate obtained in step b) is separated to obtain the isocyanate composition.

[0023] Specifically, as a preferred embodiment, the method for preparing the isocyanate composition of the present invention comprises the following steps:

[0024] Photochemical reaction (step a)

[0025] The step a) (photochemical reaction) of the present invention is carried out by reacting an organic primary amine with phosgene in a gas phase or a liquid phase, which is generally known from the prior art (eg US5599968, US004422976, US3470227, WO2008086922, US006930199).

[0026] The photochemical reaction of the present invention is carried out in a photochemical reaction kettle A.

[0027] In step a) of the present invention, the isocyanate is an aliphatic, alicyclic or aromatic aliphatic polyisocyanate, and there is no particular limitation. Specific examples of isocyanate compounds include but are not limited to toluene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, methylcyclohexyl diisocyanate, dimethylcyclohexyl diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, p-phenylene diisocyanate, norbornane diisocyanate, cyclohexyl dimethylene diisocyanate, xylylene diisocyanate, etc., preferably xylylene diisocyanate and cyclohexyl dimethylene diisocyanate.

[0028] In step a) of the present invention, the organic primary amine is usually diluted with an inert aromatic solvent, or an inert aromatic solvent is used to absorb the photochemical reaction gas. The inert aromatic solvent comprises a fresh inert aromatic solvent and / or a circulating liquid phase stream 8 containing an inert aromatic solvent recycled from a post-treatment process; the inert aromatic solvent is preferably selected from benzene, chlorobenzene and dichlorobenzene or a mixture thereof, and the mass ratio of the inert aromatic solvent to the organic primary amine is preferably 2:1 to 20:1, more preferably 3:1 to 10:1, and further preferably 4:1 to 8:1.

[0029] HCl, phosgene, solvent separation (step b))

[0030] The concentration of the photochemical reaction liquid obtained in step a) is about 5 to 35 wt%. It is separated by a phosgene removal tower B, and a gas phase stream 2 mainly containing phosgene and hydrogen chloride and a liquid phase stream 3 containing an inert aromatic solvent are obtained at the top of the tower. A phosgene-removed crude isocyanate stream 6 with a concentration of 50 to 80 wt% is obtained at the bottom of the tower. The residual solvent is then removed by a solvent removal tower C, and a crude isocyanate stream 7 is obtained at the bottom of the tower.

[0031] The dephosgene tower B is a packed tower, which can be divided into bulk packing and structured packing, Raschig rings, ball rings, step rings, arc saddle packing, rectangular saddle packing, metal ring rectangular saddle packing, spherical packing and the like.

[0032] The bottom temperature of the phosgene removal tower B is required to be controlled at 90 to 130°C, and the top pressure is controlled at about -50 to -90 KPaG.

[0033] HCL removal (step c))

[0034] The gas phase flow 2 containing phosgene and HCl obtained in step b) is condensed and captured in a phosgene absorption tower E using a condensed inert aromatic solvent 9 to obtain a liquid phase flow 4 containing phosgene, which is mixed with the liquid phase flow 3 containing an inert aromatic solvent obtained in step b) in a buffer tank F to obtain a mixed liquid phase flow 5.

[0035] A portion of the material withdrawn from the bottom of the solvent refining tower G is condensed to obtain an inert aromatic solvent 9, and the condensation is carried out at a temperature of -40 to 0° C., preferably at a temperature of -25 to 0° C. The condensation is preferably carried out in a shell and tube heat exchanger, more preferably in a vertical shell and tube heat exchanger, and further preferably, the condensed inert aromatic solvent flows through the device from top to bottom.

[0036] The temperature of the condensed inert aromatic solvent 9 is preferably below 10°C, more preferably below 0°C.

[0037] The mixed liquid phase stream 5 contains more than 3000 ppm, preferably more than 2% phosgene.

[0038] Solvent refining (step d))

[0039] The mixed liquid phase stream 5 obtained in step c) is separated by a solvent refining tower G, and a gas phase stream containing phosgene is obtained at the top of the tower, which is then directly or condensed into a liquid phase and recycled to step a) to participate in the photochemical reaction. A circulating liquid phase stream 8 containing an inert aromatic solvent is obtained at the bottom of the tower, and the stream contains less than 1 ppm, preferably less than 0.5 ppm of dichlorobiphenyl.

[0040] The bottom of the solvent refining tower G is provided with a circulating adsorption device I, which contains adsorption fillers. The adsorption fillers are one or more of sodium carbonate, potassium carbonate, ammonium carbonate, lithium carbonate, cesium carbonate, sodium bicarbonate, potassium bicarbonate, etc. The circulating solvent 11 at the bottom of the solvent refining tower can be circulated through the adsorption device for treatment.

[0041] The metal content of the circulating liquid phase stream 8 containing the inert aromatic solvent can be controlled by the flow rate of the circulating solvent at the bottom of the solvent refining tower flowing through the circulating adsorption device. The metal is preferably iron.

[0042] The solvent refining tower G has 1 to 50 theoretical plates, preferably 3 to 30 theoretical plates. Suitable plates or packings are known to those skilled in the art. Examples that can be mentioned but not limited to are structured metal sheets or woven fabric packings, or bubble caps, sieve plates or valve plates.

[0043] The bottom temperature of the solvent refining tower G and the iron content of the bottom material have a great influence on the formation of dichlorobiphenyl. The higher the bottom temperature and the higher the iron content of the bottom material, the more conducive to the formation of dichlorobiphenyl.

[0044] The present invention strictly controls the bottom temperature of the solvent refining tower G and designs a circulating adsorption device I at the bottom of the tower to control the generation of dichlorobiphenyl; further, by controlling the circulating solvent 11 at the bottom of the solvent refining tower to pass through the circulating adsorption device I at different space velocities, the iron content of the bottom material can be controlled, thereby controlling the circulating liquid phase logistics 8 containing the inert aromatic solvent and the content of dichlorobiphenyl in the isocyanate composition.

[0045] As a preferred solution, the operating conditions of the solvent refining tower G are: tower bottom temperature 150-170°C, tower bottom pressure 60-160 kPaG, and the iron content of the circulating liquid phase stream 8 containing the inert aromatic solvent is 0-20 ppm.

[0046] Further preferably, the mass space velocity of the circulating solvent 11 at the bottom of the solvent refining tower is 30-100h -1 .

[0047] Isocyanate separation (step e))

[0048] The heavy components in the crude isocyanate stream 7 obtained in step b) are separated, and the material after the heavy components are removed is further distilled and separated in a product distillation tower to obtain an isocyanate composition. The product distillation tower uses structured packing inside and steam heating outside. The top pressure of the product distillation tower is controlled at 0.1-10 kPa (absolute pressure) and the bottom temperature is 100-220°C.

[0049] The aliphatic, alicyclic or aromatic aliphatic isocyanate composition of the present invention significantly reduces the content of dichlorobiphenyl compounds compared with the prior art products.

[0050] The isocyanate composition according to the invention is understood to be essentially comprising preferably 99% by weight or more of the isocyanate, based on the total amount of the isocyanate composition. The isocyanate composition may contain other components, but preferably they are present in as low an amount as possible. However, the work required for complete removal should be balanced with their influence on the final product.

[0051] As a preferred embodiment, a meta-xylylene diisocyanate composition comprises meta-xylylene diisocyanate and dichlorobiphenyl, wherein the content of dichlorobiphenyl is greater than 0 ppm and less than 1 ppm, based on the mass of the meta-xylylene diisocyanate composition.

[0052] As a preferred embodiment, the meta-xylylene diisocyanate composition contains greater than 0 and ≤ 0.9 ppm, preferably greater than 0 and ≤ 0.8 ppm, more preferably greater than 0 and ≤ 0.5 ppm of dichlorobiphenyl, for example 0.1 ppm, 0.2 ppm, 0.3 ppm, 0.4 ppm, 0.5 ppm, 0.6 ppm or 0.7 ppm.

[0053] An optical material is prepared by polymerizing the above-mentioned meta-xylylene diisocyanate composition and a polythiol compound.

[0054] The polythiol compound is preferably selected from one or more of 1,2-bis[(2-mercaptoethyl)thio]-3-mercaptopropane, bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol, pentaerythritol tetrakis(3-mercaptopropionate), 1,1,3,3-tetrakis(mercaptomethylthio)propane and 2-mercaptoethanol.

[0055] The preparation of the optical material can be carried out in the presence of a polymerization catalyst, and the polymerization catalyst is preferably an organic tin compound, which includes dialkyl tin halides such as dibutyltin dichloride and dimethyltin dichloride; dialkyl tin dicarboxylates such as dimethyltin diacetate, dibutyltin dioctoate, and dibutyltin dilaurate.

[0056] The optical material substrate of the present invention has a transmittance greater than 90% at a visible light wavelength (380-780nm) and a yellowness index less than 1.60 without any treatment.

[0057] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following aspects: the isocyanate composition and the preparation method thereof of the present invention solve the problem of the generation of harmful dichlorobiphenyl compounds in the process of separating diisocyanate solvents, can improve the quality of isocyanate products and optical materials, overcome the technical prejudice existing in the prior art, and produce unexpected effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 The process flow diagram of the present invention is shown in Figure 1, wherein 1 is a gas phase logistics containing phosgene and HCl, 2 is a gas phase logistics containing phosgene and hydrogen chloride, 3 is a liquid phase logistics containing chlorobenzene solvent, 4 is a liquid phase logistics containing phosgene, 5 is a mixed liquid phase logistics, 6 is a dephosgene isocyanate crude product logistics, 7 is an isocyanate crude product logistics, 8 is a chlorobenzene circulating liquid phase logistics, 9 is a condensed chlorobenzene solvent, 10 is an isocyanate containing liquid phase logistics, and 11 is a solvent refining tower bottom circulating solvent. A is a photochemical reactor, B is a dephosgene tower, C is a solvent removal tower, D is a heat exchanger, E is a phosgene absorption tower, F is a buffer tank, G is a solvent refining tower, H is a heat exchanger, and I is a circulating adsorption device. DETAILED DESCRIPTION

[0059] In order to better understand the technical solutions and advantages of the present invention, the content of the present invention is further described below in conjunction with the accompanying drawings and embodiments, but the content of the present invention is not limited to the following embodiments.

[0060] The compound dichlorobiphenyl is denoted as DCBs below.

[0061] The dichlorobiphenyl analysis method described in the article is gas chromatography, and the chromatographic conditions are as follows.

[0062] Chromatographic column: DB-5 (30m×0.32mm×0.25μm); Column temperature: starting temperature 60℃, heating to 300℃ at 10℃ / min, maintaining for 8min, a total of 32min; Inlet temperature: 260℃

[0063] Septum purge gas flow rate: 2.0mL / min; column flow: 2mL / min; split injection 0.3uL, split ratio 20:1; FID: 300℃.

[0064] Turn on the gas chromatograph, and after the instrument is stable according to the above conditions, put the prepared standard sample and sample into the automatic sampler for injection, and collect data after injection. Use the instrument software to process the data and obtain the chromatogram data. The concentration of dichlorobiphenyl is determined by gas chromatography relative to the internal standard test organic layer, thereby determining the amount of each of these components present in the gas sample.

[0065] Analysis method for the total content of phosgene and hydrogen chloride in the chlorobenzene circulating liquid phase logistics: After the hydrogen chloride and phosgene in the sample are heated and reacted in methanol and sodium hydroxide solution, they are potentiometrically titrated with a standard silver nitrate solution to calculate the total content of hydrogen chloride and phosgene (in terms of phosgene) from the total chlorine content.

[0066] The iron content was analyzed by atomic absorption method. Atomic absorption spectrometer (instrument type: flame; wavelength 100-900nm; instrument mode: absorption method; calibration mode: standard addition method; wavelength: 248.3nm; slit: 1.8mm (width) / 1.35mm (height); lamp current: 30mA; background subtraction: on; flame type: air / acetylene; air flow: 15.0L / min; acetylene flow: 2.50L / min). The sample was reacted with a mixed reagent of acetone and ethanol, analyzed by atomic absorption spectrophotometer, and the iron content was quantitatively determined by standard addition method.

[0067] The product evaluation uses a Hunterlab USVIS 1839 colorimeter to test the yellowness index and transmittance (light transmittance) of solid polymers. The test uses a fixed mold to prepare the samples.

[0068] The photochemical reaction kettle, phosgene absorption tower, phosgene removal tower, solvent removal tower and solvent refining tower described in the present invention may be equipment known in the art.

[0069] Example 1

[0070] A chlorobenzene circulating liquid phase stream 8 is used as a solvent and mixed with meta-xylylenediamine (XDA) to enter a photochemical reactor A, wherein the XDA concentration is 11.6 wt %, and the equivalent ratio of hydrogen chloride gas to XDA is 2.1:1. After a salt-forming reaction is carried out in chlorobenzene, the liquid phase stream 8 reacts with phosgene at an absolute pressure of 0.5 MPa and 160° C. for 3 h, and the equivalent ratio of phosgene to XDA is 5:1. Finally, a liquid phase stream 10 containing meta-xylylenediamine with a concentration of 16% and a gas phase stream 1 containing phosgene and HCl are obtained in the photochemical reactor A.

[0071] The liquid phase stream 10 containing XDI is passed through a dephosgenating tower B to remove phosgene, wherein the operating pressure is -50 KPaG and the bottom temperature is 130° C. The top material of the dephosgenating tower is condensed by a heat exchanger D to obtain a gas phase stream 2 mainly containing phosgene and hydrogen chloride and a liquid phase stream 3 (35° C.) containing a chlorobenzene solvent, and a dephosgenated crude isocyanate stream 6 with a concentration of 80 wt% is obtained at the bottom of the dephosgenating tower. The dephosgenated isocyanate crude product stream 6 is separated through a solvent removal tower C (rectangular saddle ring packing tower, operating pressure 30 kPaA, tower bottom temperature 120°C) to obtain a crude meta-xylylene diisocyanate stream 7, which is then purified through a short-path evaporator (operating pressure 0.2 kPa (absolute pressure), separation temperature 160°C) to remove high-boiling point impurities and low-boiling point impurities, and then separated in a plate tower with 20 plates, the separation pressure is controlled at 0.2 kPa (absolute pressure), the product extraction temperature is 138°C, and the meta-xylylene diisocyanate composition product is obtained. The results are shown in Table 1.

[0072] The gas phase stream 2 containing phosgene and HCl is absorbed by the condensed chlorobenzene stream 9 through the phosgene absorption tower E, and the liquid phase stream 4 containing phosgene and the liquid phase stream 3 containing the chlorobenzene solvent obtained at the bottom of the tower are mixed in the buffer tank F to obtain a mixed liquid phase stream 5. The operating pressure of the phosgene absorption tower E is -50 KPaG, and the temperature of the condensed chlorobenzene solvent 9 is -20°C.

[0073] The obtained mixed liquid phase logistics 5 is pumped to the solvent refining tower G for phosgene gas separation. The solvent refining tower G is made of 316 stainless steel, with a top pressure of 36.73 kpa, a bottom pressure of 60.56 kpa, a bottom temperature of 150.6 ° C, and a circulating adsorption device 11 at the bottom of the tower, wherein there is an adsorption filler sodium carbonate. The iron content of the bottom solvent is controlled by controlling the flow rate of the circulating solvent 11 at the bottom of the solvent refining tower. The mixed liquid phase logistics 5 is fed between the rectifying section and the stripping section of the solvent refining tower G. A gas stream containing about 98% by weight of phosgene and 2% by weight of HCl is taken out from the top of the tower, and the stream is mixed with fresh phosgene and transported to the photochemical reactor to participate in the photochemical reaction. The chlorobenzene circulating liquid phase logistics 8 is extracted from the bottom of the tower, circulated to the photochemical reactor to participate in the photochemical reaction, and the dichlorobiphenyl and iron content in the chlorobenzene circulating liquid phase logistics 8 are analyzed. A part of the material at the bottom of the solvent refining tower is condensed by the heat exchanger H to obtain the condensed chlorobenzene solvent 9.

[0074] Examples 2 to 20 and Comparative Examples 1 to 5:

[0075] The same process as in Example 1 was adopted, except that the operating conditions of the solvent refining tower G were different. The tower top pressure, tower bottom pressure, and tower bottom temperature were adjusted to investigate the formation of dichlorobiphenyl in the chlorobenzene circulating liquid phase stream 8, and meta-xylylene diisocyanate compositions containing different amounts of dichlorobiphenyl were obtained. The results are shown in Table 1.

[0076] Table 1 DCBs data corresponding to different operating parameters

[0077]

[0078] From the above examples and comparative examples, it can be seen that the content of dichlorobiphenyl is detected in the chlorobenzene circulating liquid phase stream 8 at the bottom of the solvent refining tower under different working conditions, and the content of the isocyanate composition after synthesis and separation changes according to the working conditions. In combination with the examples, controlling certain conditions can reduce or avoid the content of dichlorobiphenyl in the isocyanate composition.

[0079] In addition, the influence of different dichlorobiphenyl contents on the stability of isocyanate compositions was studied. According to the results of gas chromatography analysis, the color change of XDI samples with different DCBS contents at 40°C was investigated.

[0080] The experimental results are shown in Table 2 below.

[0081] Table 2 Color change of XDI at 40℃ with different DCBs contents

[0082]

[0083] It can be seen that the dichlorobiphenyl content has a significant effect on the XDI color number.

[0084] Application Examples

[0085] Into a stirred reactor, 52 parts by mass of the meta-xylylene diisocyanate composition prepared in the examples and comparative examples were added, and 0.015 parts by mass of dibutyltin dichloride as a catalyst, 0.10 parts by mass of acidic phosphate (Stepan, trade name Zelec UN), and 0.05 parts by mass of ultraviolet absorber (Rianlon, trade name RIASORB UV531) were added at 25°C to mix and dissolve. Furthermore, 48 parts by mass of 1,2-bis[(2-mercaptoethyl)thio]-3-mercaptopropane was added as a polythiol compound, and the mixture was mixed to form a polymerizable raw material composition. After cooling to 20°C, degassing was performed at 2kPa and 25°C for 1 hour, filtered with a polytetrafluoroethylene membrane filter with a pore size of 1μmm, and injected into a lens mold. The mixture was heated from 20°C to 120°C in an oven for 24 hours to polymerize and cure, demolded, and then subjected to secondary curing at 130°C for 2 hours to obtain an optical material.

[0086] The synthesis of the polymerizable raw material composition and the manufacturing of the plastic optical material were carried out in the same manner as above using m-xylylene diisocyanate compositions with different DCBs contents. The test results of the products are shown in Table 3.

[0087] Table 3 Evaluation results of synthetic optical materials with different dichlorobiphenyl contents

[0088] Application Examples XDI Transmittance / % Yellowness Index 1 Example 1 91.25 1.58 2 Example 6 90.10 1.59 3 Comparative Example 1 85.01 1.68 4 Comparative Example 3 84.25 1.77 5 Comparative Example 4 83.09 1.92 6 Comparative Example 7 83.20 2.20 7 Comparative Example 5 82.15 2.93

[0089] According to the results of the application examples, it can be seen that the content of dichlorobiphenyl in the raw material of the isocyanate composition has an important influence on the quality of the material. As the amount of dichlorobiphenyl in the raw material of the isocyanate composition increases, the material indicators of the product gradually deteriorate. Special attention should be paid to controlling the content of dichlorobiphenyl in the raw material of the isocyanate composition.

[0090] According to the analysis results of Table 2 and Table 3, by controlling the content of dichlorobiphenyl in the isocyanate composition raw material used in the preparation of the polyurethane optical resin, its influence on the change of the key indicator color number can be reduced, and controlling the content of dichlorobiphenyl can ensure the quality of the resin.

[0091] Those skilled in the art will appreciate that, based on the teachings of this specification, some modifications or adjustments may be made to the present invention, and these modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. An isocyanate composition comprising isocyanate and dichlorobiphenyl, wherein: The content of dichlorobiphenyl is greater than 0 ppm and less than 1 ppm based on the mass of the isocyanate composition.

2. The isocyanate composition according to claim 1, characterized in that The isocyanate composition contains more than 0 and ≤ 0.9 ppm of dichlorobiphenyl.

3. The isocyanate composition according to claim 2, characterized in that The isocyanate composition contains more than 0 and ≤ 0.8 ppm of dichlorobiphenyl.

4. The isocyanate composition according to claim 2, characterized in that The isocyanate composition contains more than 0 and ≤ 0.5 ppm of dichlorobiphenyl.

5. The isocyanate composition according to any one of claims 1 to 4, characterized in that The isocyanate is an aliphatic, alicyclic or aromatic aliphatic polyisocyanate.

6. The isocyanate composition according to claim 5, characterized in that The isocyanate is one or more of toluene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, methylcyclohexyl diisocyanate, dimethylcyclohexyl diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, p-phenylene diisocyanate, norbornane diisocyanate, cyclohexyl dimethylene diisocyanate, and xylylene diisocyanate.

7. A method for preparing the isocyanate composition according to any one of claims 1 to 6, comprising the following steps: a) photochemically reacting an organic primary amine with an excess of phosgene in a gas phase or a liquid phase to obtain a liquid stream (10) containing an isocyanate and a gas stream (1) containing phosgene and HCl; in step a), an inert aromatic solvent is used; b) the liquid phase stream (10) containing isocyanate obtained in step a) is separated into a dephosgenated isocyanate crude stream (6) through a dephosgenating tower B, and the gas phase is passed through a condenser D to obtain a gas phase stream (2) containing phosgene and HCl and a liquid phase stream (3) containing an inert aromatic solvent; c) removing HCl from the gas phase stream (2) containing phosgene and HCl obtained in step b) by absorbing with a condensed inert aromatic solvent (9) to obtain a liquid phase stream (4) containing phosgene, and mixing the liquid phase stream (3) containing the inert aromatic solvent in step b) to obtain a mixed liquid phase stream (5); d) the mixed liquid phase stream (5) of step c) is separated into a gas phase stream containing phosgene and a circulating liquid phase stream (8) containing an inert aromatic solvent by passing it through a solvent refining tower G, wherein the gas phase stream containing phosgene is directly or condensed into a liquid phase and is recycled to step a) to participate in the photochemical reaction; the circulating liquid phase stream (8) containing an inert aromatic solvent contains less than 1 ppm of dichlorobiphenyl and is recycled to step a) to participate in the photochemical reaction; e) The dephosgenated isocyanate crude product stream (6) obtained in step b) is separated to obtain the isocyanate composition; the inert aromatic solvent is dichlorobenzene.

8. The method according to claim 7, characterized in that The inert aromatic solvent in step a) comprises fresh inert aromatic solvent and / or a circulating liquid phase stream (8) containing an inert aromatic solvent.

9. The method according to claim 8, characterized in that The mass ratio of the inert aromatic solvent to the organic primary amine is 2:1 to 20:

1.

10. The method according to any one of claims 7 to 9, characterized in that: A circulating adsorption device I is provided at the bottom of the solvent refining tower G, wherein there is an adsorption filler; the adsorption filler is one or more of sodium carbonate, potassium carbonate, ammonium carbonate, lithium carbonate, cesium carbonate, sodium bicarbonate, and potassium bicarbonate.

11. The method according to any one of claims 7 to 9, characterized in that: The solvent refining tower bottom has a solvent refining tower bottom circulating solvent (11) which is treated by a circulating adsorption device I.

12. The method according to any one of claims 7 to 9, characterized in that: The operating conditions of the solvent refining tower G are: tower bottom temperature 150-170°C, tower bottom pressure 60-160 kPaG, and the iron content of the circulating liquid phase stream (8) containing the inert aromatic solvent is 0-20 ppm.

13. The method according to any one of claims 7 to 9, characterized in that: The mass space velocity of the solvent (11) circulating at the bottom of the solvent refining tower is 30-100h -1 .

14. An optical material, characterized in that: The optical material is formed by polymerizing the isocyanate composition described in any one of claims 1 to 6 with a polythiol compound; the polythiol compound is selected from one or more of 1,2-bis[(2-mercaptoethyl)thio]-3-mercaptopropane, bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol, pentaerythritol tetrakis(3-mercaptopropionate), 1,1,3,3-tetrakis(mercaptomethylthio)propane and 2-mercaptoethanol.

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