A method for improving the stability of modified isocyanate products

Abstract

The present application provides a method for improving the stability of modified isocyanate product, which is mainly achieved by controlling the sodium content in the catalyst triethyl phosphate. Through this method, the storage time of modified isocyanate can be improved, and the stability of modified isocyanate product can be improved.

Description

Technical Field

[0001] This invention relates to a method for improving the stability of modified isocyanate products, belonging to the field of isocyanate quality improvement applications. Background Technology

[0002] Diphenylmethane diisocyanate and polyphenylmethane polyisocyanate are important products in the field of isocyanates. With the increasing diversification of market demand for fine chemicals, the modification and production of these two important isocyanate products are of great significance for applications in different fields, market expansion, and the improvement of social living standards.

[0003] Currently, the most common method for modifying isocyanates is to achieve the production of pure MDI by adding catalysts and polymerization inhibitors. The application performance of modified isocyanates varies greatly depending on the catalytic effect of the catalyst. Isocyanates modified with inefficient phosphorus-containing catalysts are mainly used in the manufacture of high-performance microporous polyurethane elastomers and flexible self-skinning polyurethane foams, including shoe soles, solid tires, car bumpers, mudguards, shock absorbers, spoilers, steering wheels, seat headrests, armrests, and interior parts. They are also widely used in the manufacture of adhesives, coatings, prepolymers, and semi-prepolymers. Due to the wide range of applications, the storage stability of isocyanate products is of paramount importance.

[0004] Chinese Patent CN 108586706 A discloses a method for preparing a modified isocyanate mixture containing carbodiimide and / or urea-ketimide derivatives. The method includes a step of subjecting a reaction mixture containing isocyanate and a carbodiimide catalyst to a carbodiimide reaction. During the reaction, the volatilized components are stripped from the system by inert gas at a temperature of 180-210°C and a pressure of 1-20 kPa, and partially refluxed back into the system via condensation. After the reaction, when the temperature is 35-60°C, stabilizers A and B are added to the modified isocyanate mixture containing carbodiimide and / or urea-ketimide derivatives, thereby preparing a modified isocyanate mixture with improved storage stability, low stability, and stable stability.

[0005] Chinese patent CN110387031A discloses a method for preparing light-colored modified isocyanates. The method involves feeding a mixture of diphenylmethane diisocyanates containing different isomer contents into a distillation column for distillation. A high-purity isocyanate mixture with a 2,2'-MDI + 2,4'-MDI content of less than 0.1 wt% is obtained from the bottom vapor phase. Then, a triethyl phosphate catalyst with a diethyl phosphite impurity content of no more than 50 ppm is added to the mixture, and the reaction is carried out at a temperature of 180-210℃ and a pressure of 1-20 kPa. After the reaction, the temperature is lowered to 35-60℃ to obtain an intermediate product. A phosphite antioxidant is then added to the intermediate product to prepare a modified isocyanate product with low stability. The color of the product is improved by optimizing the impurity content in the catalyst.

[0006] Chinese patent CN112574068A discloses a method for preparing a low-color-number, high-stability carbodiimide-modified isocyanate. The method includes the following steps: S1: The isocyanate monomer undergoes a carbodiimide reaction to obtain a reaction solution containing carbodiimide (CDI) and / or urea-ketimide (UTI) groups; S2: A aging reaction reduces the CDI content in the reaction solution, controlling the CDI content to be between 0.5% and 4.0%; S3: A terminator is added to terminate the carbodiimide reaction. The modified isocyanate prepared by this method exhibits stability at room temperature and high-temperature storage, as well as low stability.

[0007] Analysis of the above patents shows that improvements in product stability are achieved by removing substances that affect product stability or adding stabilizers. However, the stability of modified isocyanate products produced using inefficient catalysts can generally be maintained for about 6 months. However, due to storage conditions and environmental factors, some manufacturers find it difficult to maintain stability for 6 months. Therefore, it is necessary to further improve the stability of modified isocyanate products and extend their storage time. Summary of the Invention

[0008] The purpose of this invention is to provide a method for improving the stability of modified isocyanate products. This method can improve the stability of modified isocyanates and extend the shelf life of the modified isocyanate products.

[0009] Currently, the production process of carbodiimide-modified isocyanate mainly involves reacting pure MDI with triethyl phosphate under certain conditions. The viscosity of the modified isocyanate produced by this process is generally maintained between 25-60 cp, while the dimer content is maintained between 0.8%-1.6%. The liquefied storage time can reach 6 months. After 6 months, the liquefied product will exhibit turbidity and increased viscosity. The applicant's research found that if the sodium content in triethyl phosphate is high, it will cause changes in the stability of the modified isocyanate product. By removing the sodium-containing substances from the triethyl phosphate through distillation and applying this to the synthesis experiments of modified isocyanate, the liquefaction stability can be increased from 6 months to 9 months, greatly enhancing the product's competitiveness.

[0010] Based on the above research findings, in order to achieve the aforementioned objectives of this invention, the present invention provides the following technical solution:

[0011] A method for improving the stability of modified isocyanate products, comprising:

[0012] (1) Triethyl phosphate and antioxidant were added to pure MDI, and the resulting mixture was subjected to a heated reaction.

[0013] (2) The mixture obtained from the reaction is mixed with pure MDI and cooled to a certain temperature for aging treatment to obtain carbodiimide modified isocyanate;

[0014] In the triethyl phosphate, the sodium content (converted to inorganic sodium ions by ion chromatography) is controlled below 5 ppm, preferably below 2 ppm, and further preferably reduced to undetectable levels.

[0015] Sodium content can be controlled by methods such as distillation, for example, by distillation at an absolute pressure of 0-1 kPa and a temperature of 80-100 °C until the sodium content is reduced to within the range required by this application.

[0016] In the method of the present invention, in step (1), the amount of triethyl phosphate added is 1%-5% of the mass of pure MDI, preferably 2%-3%;

[0017] The antioxidant is selected from phosphite antioxidants, and the amount added is 0.8%-0.15% of the mass of pure MDI;

[0018] The reaction temperature was controlled at 190-210℃, and the reaction time was between 210 min and 280 min.

[0019] In step (2), the mixing mass ratio of the mixture to pure MDI is 1:0.5-0.8;

[0020] Cool down to 75-80℃ and allow to mature for 3-5 hours. After maturation, reduce the temperature to 40-50℃.

[0021] The inventors discovered that during the production of modified isocyanates, a high sodium content in the catalyst triethyl phosphate at high temperatures leads to a high viscosity in the modified isocyanate product. Consequently, the storage time of the modified isocyanate after the reaction can only be maintained for about 3 months. Therefore, analysis of trace impurities in triethyl phosphate revealed that the presence of sodium content significantly affects the stability of the modified isocyanate product. Sodium-containing substances in triethyl phosphate can be removed through distillation. When triethyl phosphate with sodium-containing components removed is reused in the production of modified isocyanates, its stability is found to be greatly improved.

[0022] The technical solution provided by this invention has the following beneficial effects:

[0023] The inventors unexpectedly discovered that the sodium content in the triethyl phosphate catalyst used in the production of modified isocyanates would have an adverse effect on product stability. By reducing the sodium content in triethyl phosphate, the storage stability of the product can be improved by about 3 months from the original process, reaching about 9 months, thereby enhancing the product competitiveness of modified isocyanates. Detailed Implementation

[0024] To better understand the technical solution of the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0025] All reagents used in the examples are conventional reagents in the art. Unless otherwise specified, the detection methods or experimental methods described below are conventional techniques known to those skilled in the art based on their existing knowledge.

[0026] Diphenylmethane diisocyanate (pure MDI), wherein the diphenylmethane diisocyanate contains 99% 4,4-isomer and 1% 2,4-isomer, and the NCO content is 33.6 wt%.

[0027] Antioxidant, which is provided by Lianlong.

[0028] The operating pressure mentioned below refers to absolute pressure.

[0029] In the following text, the percentage content "%" refers to "wt%".

[0030] The test methods involved in the following experiments are described below:

[0031] 1. Method for analyzing the content of diphenylmethane diisocyanate isomers:

[0032] The gas phase area normalization method was used, and dichloromethane was used as the solvent.

[0033] Temperature program: 150℃, hold for 0.5 min, increase to 300℃ at 10℃ / min, hold for 15 min;

[0034] Injection volume: 0.6 μL;

[0035] Inlet temperature: 280℃, split ratio: 10:1;

[0036] Chromatographic column: Agilent 19091J-413HP-5 30m x 320μm x 0.25μm;

[0037] Column flow rate: 1 mL / min;

[0038] The solvent is dichloromethane, HPLC grade.

[0039] Determining the peak position of isomers is a widely accepted method in the industry.

[0040] 2: Viscosity Analysis Method for Modified Isocyanates

[0041] Method: GB 2794—81

[0042] Operation procedure: Place 100g of sample into the viscometer, control the temperature of the outer jacket of the viscometer to 25℃, control the shear rate of the viscometer to 200r / min, and analyze the viscosity of the sample.

[0043] 3: Analytical methods for modified isocyanate dimers

[0044] Instrumentation: Fourier transform infrared spectrometer (Nicolet iS20), equipped with a light source, beam splitter, detector, and data processing system. Apparatus: Infrared liquid cell. Method: The internal standard method was used for determination; the dimer's peak position in the infrared spectrum was 1780 cm⁻¹.

[0045] 4: NCO Analysis Method for Modified Isocyanates

[0046] Method: GB 12009-4

[0047] 5: Color Analysis Method for Modified Isocyanates

[0048] Method: ISO A26 71.040.50

[0049] 6: Analytical methods for sodium content in triethyl phosphate

[0050] Model: Metrohm 883 Ion Chromatograph

[0051] Method: Cation analysis method

[0052] Pretreatment: The modified isocyanate was dissolved in dichloromethane at a mass ratio of 1:1, and then pure water of the same proportion was added for extraction for 3 minutes. The sodium ion content of the inorganic phase after extraction was analyzed.

[0053] Examples 1-3

[0054] In this embodiment, the relevant indicators of triethyl phosphate, diphenylmethane diisocyanate, and antioxidants were analyzed:

[0055] Sodium content / ppm 30 Not detected Not detected

[0056] The above-mentioned triethyl phosphate was subjected to vacuum distillation to obtain triethyl phosphates with different purities and sodium contents. The method for applying the low-sodium triethyl phosphate obtained by vacuum distillation to the production of modified isocyanates to improve product stability is as follows:

[0057] 1) Weigh out 9g of triethyl phosphate with a sodium content of 15ppm (purity 99%), a sodium content of 5ppm (purity 98.9%), and no sodium content (purity 99.1%) respectively.

[0058] 2) Add 300g of pure MDI to each of the three portions of triethyl phosphate of equal mass.

[0059] 3) Then add 0.384g of antioxidant and stir thoroughly.

[0060] 4) Heat the mixture after stirring to 200°C and react for 240 min.

[0061] 5) After the reaction is complete, add 240g of pure MDI and mix.

[0062] 6) Cool the mixed product with circulating water. When the temperature drops to 75°C, maintain this temperature for 3 hours for the ripening reaction.

[0063] 7) After the curing process is complete, the temperature is lowered to 45℃ for relevant index analysis.

[0064] 8) The sample was subjected to long-term storage experiments, and then routine indicators were analyzed.

[0065] The analysis indicators within one year are as follows:

[0066] Table 1: Analysis of relevant indicators before and after storage when sodium content is 15 ppm

[0067] initial 45 1.01 29.43 1 month 46 1.02 29.43 3 months 88 1.38 29.42 9 months 120 1.53 29.40 12 months 210 1.82 29.38

[0068] Note: Product I is a product obtained using triethyl phosphate with a sodium content of 15 ppm;

[0069] Table 2: Analysis of relevant indicators before and after storage when sodium content is 5 ppm

[0070] initial 34 0.95 29.26 1 month 41 1.01 29.26 6 months 45 1.05 29.25 9 months 59 1.28 29.23 12 months 110 1.45 29.21

[0071] Note: Product II is a product obtained using triethyl phosphate with a sodium content of 5 ppm;

[0072] Table 3: Analysis of relevant indicators before and after storage (sodium content not detected)

[0073] initial 26 0.87 29.16 1 month 28 0.91 29.16 6 months 35 0.99 29.15 9 months 38 1.08 29.15 12 months 70 1.25 29.14

[0074] Note: Product III is a product obtained using triethyl phosphate with undetectable sodium content;

[0075] A comparison of Examples 1 with Examples 2 and 3 clearly shows that the sodium content in triethyl phosphate has a significant impact on the storage stability of the modified isocyanate product. In Example 1, with a sodium content of 15 ppm, after 9 months of storage, the product viscosity increased from 45 cp to 120 cp (product specification 40-60 cp), while the dimer content increased from 1.01% to 1.53% (precipitation point 1.46%). In Example 2, with a sodium content of 5 ppm, after 9 months of storage, the product viscosity increased from 34 cp to 59 cp, while the dimer content increased from 0.95% to 1.28%. In Example 3, with a sodium content of 0%, after 9 months of storage, the product viscosity increased from 26 cp to 38 cp (product specification 40-60 cp), while the dimer content increased from 0.87% to 1.08%. Comparatively, controlling the sodium content below 5 ppm can improve product stability.

[0076] Therefore, effectively controlling the sodium content in triethyl phosphate will help improve the storage stability of modified isocyanate. At the same time, a lower sodium content will also help improve other product indicators of modified isocyanate. Thus, this invention can improve the product stability of modified isocyanate and enhance product competitiveness.

Claims

1. A method for improving the stability of modified isocyanate products, the method comprising the following steps: (1) Pure MDI was mixed with triethyl phosphate and phosphite antioxidants, and the resulting mixture was subjected to a heated reaction; wherein... In triethyl phosphate, the sodium content is controlled below 5 ppm, and the amount of triethyl phosphate added is 1%-5% of the mass of pure MDI. Sodium ions were not detected in the phosphite antioxidants, and the amount of antioxidants added is 0.15%-0.8% of the mass of pure MDI. (2) The mixture obtained from the reaction is mixed with pure MDI at a mass ratio of 1:0.5-0.8 and cooled to a certain temperature for aging treatment to obtain carbodiimide modified isocyanate; Sodium ions were not detected in pure MDI.

2. The method according to claim 1, wherein, In step (1), the reaction temperature is controlled at 190-210℃ and the reaction time is 210min-280min.

3. The method according to claim 1, wherein, In step (2), the temperature is lowered to 75-80℃ and a ripening reaction is carried out for 3-5 hours. After ripening, the temperature is lowered to 40-50℃.