A process for the preparation of a polyisocyanate composition

Abstract

The application discloses a preparation method of the polyisocyanate composition, which comprises mixing isocyanate raw materials with a recycled diisocyanate stream, and performing partial self-polymerization in the presence of a catalyst to obtain a polyisocyanate composition containing isocyanurate, and the recycled diisocyanate stream contains 50-2000 ppm of phosphorus in mass. The polyisocyanate composition prepared by the method has excellent color stability.

Description

Technical Field

[0001] This invention belongs to the field of isocyanate technology and relates to a method for preparing a polyisocyanate composition. Background Technology

[0002] Aliphatic and alicyclic polyisocyanates and their derivatives have excellent weather resistance, chemical resistance and heat resistance, and are widely used in the coatings, adhesives and elastomers industries, especially in the paint industry, such as urethane-based coating compositions using polyisocyanates containing isocyanurate groups as curing agents.

[0003] Based on the application fields of aliphatic and alicyclic polyisocyanate compositions, good color stability is often required. Therefore, the preparation of polyisocyanate compositions with excellent color stability has become one of the research focuses of technicians in this field.

[0004] Patent CN101641387A discloses a curing agent composition for color stabilization of polyurethane paint. The polyisocyanate composition can directly react with components in polyurethane coatings that contain groups that are reactive with isocyanates, and has the characteristic of good color stability during storage. However, the composition is relatively complex. In addition to polyisocyanates, catalysts that can promote isocyanate reactions, phosphites, and hindered phenols, it also needs to contain at least one solvent and acid stabilizer. Color stability can only be achieved in a solvent-diluted system. The formulation components and realization conditions of the composition are relatively complex.

[0005] Patents CN110372846A, CN110790880A, and CN112225857A respectively obtained color-stable polyisocyanate compositions by controlling the content of secondary amines, secondary phosphines, and crackable amines in the catalyst. However, the color number of the compositions still increased during high-temperature storage, and the color thermal stability was still insufficient.

[0006] Patent DE102006043464A1 describes colorless polyisocyanates treated with peroxides or hydroperoxides. EP0630928A2 describes improved color number and storage stability of polyisocyanates prepared using ammonium or metal salts as catalysts, the latter obtained by adding organic peracids. The acid functionalization is also used to decompose the catalyst to stop the reaction. A disadvantage of these methods is that the added peroxides or hydroperoxides, as well as degradation products of the color-contributing components, remain in the product, which is detrimental to the color stability of the polyisocyanate composition.

[0007] Patent CN101646700A discloses a method for preparing a polyisocyanate composition containing isocyanurate groups with excellent color storage stability. The process includes the use of a catalyst poison with a special structure and a reaction process. However, there is still room for further improvement in the color stability of the polyisocyanate composition when stored at high temperatures.

[0008] As can be seen from the above-disclosed technical solutions, the polyisocyanate compositions with stable color during storage currently disclosed in the technology have shortcomings such as poor utilization, complex processes, and the need to improve color stability. Therefore, it is necessary to develop a polyisocyanate composition with better color stability and simpler preparation process. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing a polyisocyanate composition, wherein the polyisocyanate composition prepared by this method has low initial color and stable color during high-temperature storage.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing the polyisocyanate composition involves mixing isocyanate raw materials with a recycled diisocyanate stream and carrying out a partial self-polymerization reaction in the presence of a catalyst to obtain a polyisocyanate composition containing isocyanurate.

[0012] The recovered diisocyanate refers to unreacted diisocyanate recovered from the self-polymerization reaction of aliphatic and / or alicyclic polyisocyanates. The recovered diisocyanate stream contains 50-2000 ppm of phosphorus.

[0013] Preferably, the phosphorus content in the recovered diisocyanate stream is 500-1500 ppm.

[0014] In this invention, the recovered diisocyanate can come from unreacted diisocyanate generated by the reaction itself, or from unreacted diisocyanate recovered from the self-polymerization reaction of other aliphatic and / or alicyclic polyisocyanates.

[0015] Preferably, the preparation method includes the following steps:

[0016] S1: Fresh aliphatic and / or alicyclic diisocyanate and a recycled diisocyanate stream are subjected to partial self-polymerization in the presence of a catalyst. When the target NCO% is reached, a terminator is added to terminate the reaction and a reaction solution is obtained.

[0017] S2: The reaction solution is separated to remove unreacted diisocyanate, yielding a polyisocyanate composition containing isocyanurate.

[0018] Preferably, in step S3, the unreacted diisocyanate removed in step S2 is condensed and recycled as the diisocyanate stream recovered in step S1.

[0019] In this invention, since the recovered unreacted diisocyanate contains a certain amount of heavy components, which are impurities with a molecular weight greater than that of polyisocyanate, mainly including impurities containing urethane structure, impurities containing urea-formate structure, polymers such as dimers and trimers, as well as residual auxiliaries and coloring substances from the reaction preparation process, the recovered diisocyanate has a serious impact on the color and color stability of the prepared product when it is recycled again.

[0020] The inventors have discovered that by controlling the phosphorus content in the recovered unreacted diisocyanate to 50-2000 ppm, preferably 50-1500 ppm, and mixing it with fresh aliphatic and / or alicyclic diisocyanate raw materials, the color number of the polyisocyanate composition can be significantly reduced, and the color stability is excellent. When the phosphorus content in the unreacted diisocyanate is greater than 2000 ppm, its participation in recycling and repeated heating will cause the composition to have a high color; when the phosphorus content in the unreacted diisocyanate is less than 50 ppm, the color thermal stability of the composition is poor.

[0021] The method for controlling the phosphorus content in the recovered diisocyanate is existing technology and various methods exist; this invention does not impose any particular limitation. For example, phosphorus-containing compounds, such as phosphoric acid, tributyl phosphate, dibutyl phosphate, pyrophosphate, triethyl phosphate, phosphorus trichloride, and phosphorus pentachloride, can be added to the unreacted diisocyanate.

[0022] In this invention, the diisocyanate mentioned in step S1 is selected from aliphatic diisocyanates and / or alicyclic diisocyanates, preferably one or more of tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and lysine diisocyanate, more preferably hexamethylene diisocyanate and / or pentamethylene diisocyanate.

[0023] Preferably, the mass ratio of fresh aliphatic and / or alicyclic diisocyanate to recycled diisocyanate is (0.1-10):1.

[0024] In this invention, the catalyst in step S1 is selected from quaternary ammonium bases and / or quaternary ammonium salts, preferably any one or a combination of at least two of the following: choline hydroxide, trimethylhydroxyethylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, 1-adamantylammonium hydroxide, hexamethylbisammonium hydroxide, tetramethylammonium formate, tetramethylammonium decanoate, tetraethylammonium formate, tetraethylammonium acetate, tetraethylammonium decanoate, trimethylhydroxypropylammonium formate, trimethylhydroxypropylammonium acetate, trimethylhydroxypropyl octanoate, trimethylhydroxypropylammonium decanoate, trimethylhydroxyethylammonium formate, trimethylhydroxyethylammonium acetate, and trimethylhydroxyethylammonium decanoate, preferably benzyltrimethylammonium hydroxide and / or tetramethylammonium decanoate;

[0025] The amount of catalyst added is 10-1000 ppm of the mass of the mixture of fresh aliphatic and / or alicyclic diisocyanate and recycled diisocyanate.

[0026] The catalyst can be used as a pure substance or dissolved in an alcohol solvent at any concentration, preferably 0.1-50 wt%.

[0027] The alcohol solvent is selected from one or more monohydric alcohols and dihydric alcohols; the monohydric alcohol is selected from methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, and nonanol; the dihydric alcohol is selected from ethylene glycol, 1,3-butanediol, neopentyl glycol, and 2-ethylhexanediol; preferably a monohydric alcohol, more preferably a monohydric alcohol with a molecular weight of less than 200.

[0028] In this invention, the self-polymerization reaction described in step S1 is carried out at a reaction temperature of 30-120°C, preferably 50-100°C.

[0029] In this invention, the partial self-polymerization in step S1 refers to the polymerization reaction of diisocyanate with isocyanate ions (-NCO) in the presence of a catalyst. When the polymerization reaction reaches its endpoint, unreacted polyisocyanate is still present in the reaction solution. The reaction is terminated when the NCO content in the reaction system is 30-45%.

[0030] In this invention, the terminator is an acidic substance, and the amount added is 0.5-5 times the molar amount of the catalyst, preferably 1-3 times. Preferably, the acidic substance is one or more of hydrochloric acid, sulfuric acid, phosphoric acid, pyrophosphoric acid, phosphorous acid, di-n-butyl phosphate, diisooctyl phosphate, benzoic acid, and benzoyl chloride.

[0031] In this invention, step S2 purifies the reaction solution after the reaction in S1 to separate and obtain the polyisocyanate composition.

[0032] Preferably, the refining method is any one of thin-film evaporation, falling-film evaporation, short-path evaporation, and vacuum distillation, with two-stage thin-film evaporation being the most preferred. Specifically, when using a two-stage thin-film evaporator, the first-stage separation temperature is 120-200℃ and the pressure is 20-200Pa, while the second-stage separation temperature is 120-200℃ and the pressure is 0.1-100Pa.

[0033] In this invention, if phosphoric acid or phosphorus-containing compounds such as phosphates are added to the reaction system, the phosphorus content in the unreacted diisocyanate can be adjusted by controlling the distillation or evaporation reaction conditions in step S2, so that it can be directly recycled back to the self-polymerization reaction in step 1).

[0034] Preferably, a phosphorus-containing compound is added to the reaction system, wherein the phosphorus-containing compound includes one or more of phosphoric acid, phosphates, or phosphate esters, and more preferably one or more of phosphoric acid, tributyl phosphate, dibutyl phosphate, pyrophosphate, triethyl phosphate, phosphorus trichloride, and phosphorus pentachloride.

[0035] In this invention, the content of unreacted diisocyanate monomers in the polyisocyanate composition obtained in step S2 is less than 0.2 wt%.

[0036] In this invention, the color value of the polyisocyanate composition decreases by 0-10 Hazen, preferably by 0-5 Hazen, when stored at 100°C for 24 hours.

[0037] The polyisocyanate composition has a color value of less than 30 Hazen, preferably less than 25 Hazen, before storage at 100°C for 24 hours.

[0038] In this invention, the polyisocyanate composition containing isocyanurate with excellent color stability may contain, in addition to isocyanurate structure, one or more of iminooxadiazine dione structure, biuret structure, urea diketone group, urea carbamate group, carbamate group, and urea ketimino group.

[0039] The polyisocyanate composition contains an isocyanurate structure, which gives the polyisocyanate composition excellent chemical resistance and heat resistance.

[0040] In this invention, the isocyanurate ester has the following structure:

[0041]

[0042] The structure of iminooxadiazine dione is:

[0043]

[0044] The structure of biuret is:

[0045]

[0046] The specific structure of the urea diketone group is as follows:

[0047]

[0048] The specific structure of the urea-formate group is as follows:

[0049]

[0050] The specific structure of the urethane group is as follows:

[0051]

[0052] The specific structure of the urea-ketone imine group is as follows:

[0053]

[0054] The aforementioned isocyanurate, iminooxadiazine dione, and biuret structures can all be detected by carbon NMR spectroscopy.

[0055] In the context of this article, the meaning of "color code" can be found in the color code determination method in GB / T 3143-1982.

[0056] The beneficial effects of this invention are as follows:

[0057] By adjusting the phosphorus content in the recovered unreacted free diisocyanate and reusing it in the trimerization reaction at a certain mass ratio, a polyisocyanate composition with low initial color and excellent color stability during storage can be prepared. Detailed Implementation

[0058] 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.

[0059] <Main Raw Material Information>

[0060] HDI: Hexamethylene diisocyanate, Wanhua Chemical Group Co., Ltd.

[0061] PDI: Pentamethylene diisocyanate, Wanhua Chemical Group Co., Ltd.

[0062] N,N,N-Trimethylbenzylammonium hydroxide, Aladdin Reagent Platform

[0063] di-n-butyl phosphate, Aladdin Reagent Platform

[0064] Isooctyl alcohol, Aladdin Reagent Platform

[0065] Triethyl phosphate, Aladdin Reagent Platform

[0066] <NCO content (NCO%)>

[0067] The NCO% content test shall be performed in accordance with standard GB / T 12009.4.

[0068] <Determination of Phosphorus Content in Unreacted Diisocyanates>

[0069] The phosphorus content (mass standard) in unreacted diisocyanates was determined using X-ray fluorescence chromatography (XRF).

[0070] <Determination of Free Diisocyanate Monomer Content>

[0071] This invention is based on the method of GB / T18583-2008, and uses an Agilent GC-7890B gas chromatograph manufactured by Agilent to determine the content of residual monomers in the reaction system.

[0072] <Determination of Color and Color Stability of Polyisocyanate Compositions>

[0073] In the examples and comparative examples, the color of the polyisocyanate compositions was measured using the method of GB / T 3143-1982, with the color number measured in a 50mm disposable rectangular cuvette using a HACH Lange LICO 400. The initial color and the color of the product after cooling in a 100°C oven for 24 hours under nitrogen-sealed conditions were also measured.

[0074] The following examples and comparative examples are intended to illustrate the present invention, but the present invention is not limited to these examples.

[0075]

Synthesis example

[0076] Preparation of unreacted free diisocyanate M:

[0077] Under nitrogen protection, 2000 g of fresh HDI monomer was added to a 2 L four-necked flask. The system was then heated to 70 °C, and 1.0 g (1.2 mmol) of a 20% (w / w) isooctyl alcohol solution of N,N,N-trimethylbenzylammonium hydroxide was added to initiate a trimerization reaction. When the NCO content in the reaction solution reached 39.3%, 0.3 g (1.44 mmol) of di-n-butyl phosphate was added to terminate the reaction. Subsequently, the mixture was purified by two thin-film evaporations at 150 °C and 30 Pa using a thin-film evaporator to obtain 800 g of the polyisocyanate composition and 1200 g of unreacted HDI(M).

[0078] The phosphorus content of unreacted free diisocyanate M was determined to be 18 ppm.

[0079] [Examples and Comparative Examples]

[0080] Different polyisocyanate compositions were prepared according to the following methods and the distinguishing parameters in Table 1. The process parameters and physical properties of the products are shown in Table 1.

[0081] Step S1: Add a certain amount of triethyl phosphate to the unreacted diisocyanate M recovered in the synthesis example to adjust the phosphorus content and obtain the recovered diisocyanate N.

[0082] Step S2: Under nitrogen protection, 700g of fresh HDI monomer and 700g of unreacted diisocyanate N recovered in step S1 were added to a 2L four-necked flask. The system was then heated to 70°C, and 4.2g of a 5% (w / w) isooctyl alcohol solution of N,N,N-trimethylbenzylammonium hydroxide (1.25 mmol) was added to initiate a trimerization reaction. When the NCO content in the reaction solution reached 39.0%, 0.27g of di-n-butyl phosphate (1.3 mmol) was added to terminate the reaction, yielding reaction solution A.

[0083] Step S3: Purify twice using a thin-film evaporator at 150°C and 30Pa to obtain 450g of polyisocyanate composition B and 550g of unreacted free HDI.

[0084] Table 1. Process parameters and physical property data of examples / comparative examples

[0085]

[0086]

[0087] The comparison of parameters and material properties in Table 1 shows that effectively controlling the phosphorus content in the recycled unreacted diisocyanate between 50-2000 ppm results in compositions with low color and excellent color stability. When the phosphorus content in the unreacted diisocyanate is below 50 ppm, the resulting composition exhibits poor color thermal stability; when the phosphorus content in the unreacted diisocyanate is above 2000 ppm, the resulting composition has a higher initial color.

[0088] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a polyisocyanate composition, characterized in that, Step S1: Fresh aliphatic and / or alicyclic diisocyanate and the recovered diisocyanate stream undergo a partial self-polymerization reaction in the presence of a catalyst. When the NCO content in the reaction system is 30-45%, a terminator is added to terminate the reaction and obtain a reaction solution. Step S2: The reaction solution is separated to remove unreacted diisocyanate, yielding a polyisocyanate composition containing isocyanurate. The recovered diisocyanate refers to unreacted diisocyanate recovered from the self-polymerization reaction of aliphatic and / or alicyclic polyisocyanates, and the phosphorus content in the recovered diisocyanate stream is 50-2000 ppm by mass. The mass ratio of fresh aliphatic and / or alicyclic diisocyanate to recycled diisocyanate is (0.1-10):

1.

2. The preparation method according to claim 1, characterized in that, The recovered diisocyanate stream contains 50-1500 ppm of phosphorus.

3. The preparation method according to claim 1, characterized in that, The recovered diisocyanates are derived from unreacted diisocyanates produced by the reaction itself, or from unreacted diisocyanates recovered from the self-polymerization of other aliphatic and / or alicyclic polyisocyanates.

4. The preparation method according to claim 1, characterized in that, It also includes step S3: the unreacted diisocyanate removed in step S2 is condensed and recycled as the diisocyanate stream recovered in S1.

5. The preparation method according to claim 1, characterized in that, The diisocyanate mentioned in step S1 is selected from one or more of tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and lysine diisocyanate.

6. The preparation method according to claim 5, characterized in that, The diisocyanate mentioned in step S1 is selected from hexamethylene diisocyanate and / or pentamethylene diisocyanate.

7. The preparation method according to claim 1, characterized in that, The catalyst in step S1 is selected from quaternary ammonium bases and / or quaternary ammonium salt compounds.

8. The preparation method according to claim 7, characterized in that, The catalyst in step S1 is selected from any one or a combination of at least two of the following: choline hydroxide, trimethylhydroxyethylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, 1-adamantylammonium hydroxide, hexamethylbisammonium hydroxide, tetramethylammonium formate, tetramethylammonium decanoate, tetraethylammonium acetate, tetraethylammonium decanoate, trimethylhydroxypropylammonium formate, trimethylhydroxypropylammonium acetate, trimethylhydroxypropyl octanoate, trimethylhydroxypropylammonium decanoate, trimethylhydroxyethylammonium formate, trimethylhydroxyethylammonium acetate, and trimethylhydroxyethylammonium decanoate.

9. The preparation method according to claim 8, characterized in that, The catalyst in step S1 is selected from benzyltrimethylammonium hydroxide and / or tetramethylammonium decanoate.

10. The preparation method according to claim 1, characterized in that, The catalyst is added in an amount of 10-1000 ppm by mass of a mixture of fresh aliphatic and / or alicyclic diisocyanate and recycled diisocyanate.

11. The preparation method according to claim 1, characterized in that, The catalyst is used either as a pure substance or dissolved in an alcohol solvent at any concentration, wherein the alcohol solvent is selected from one or more monohydric alcohols and dihydric alcohols.

12. The preparation method according to claim 11, characterized in that, The monohydric alcohol is selected from methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, and nonanol; the dihydric alcohol is selected from ethylene glycol, 1,3-butanediol, neopentyl glycol, and 2-ethylhexanediol.

13. The preparation method according to claim 11, characterized in that, The alcohol solvent is selected from monohydric alcohols with a molecular weight of less than 200.

14. The preparation method according to claim 1, characterized in that, The self-polymerization reaction described in step S1 is carried out at a temperature of 30-120℃.

15. The preparation method according to claim 14, characterized in that, The self-polymerization reaction described in step S1 is carried out at a temperature of 50-100℃.

16. The preparation method according to claim 1, characterized in that, The terminator is an acidic substance, and the amount added is 0.5-5 times the molar amount of the catalyst.

17. The preparation method according to claim 16, characterized in that, The terminator is an acidic substance, and the amount added is 1-3 times the molar amount of the catalyst.

18. The preparation method according to claim 16, characterized in that, The acidic substance is one or more of the following: hydrochloric acid, sulfuric acid, phosphoric acid, pyrophosphoric acid, phosphorous acid, di-n-butyl phosphate, diisooctyl phosphate, benzoic acid, and benzoyl chloride.

19. The preparation method according to claim 1, characterized in that, Step S2 purifies the reaction solution after the reaction in S1 is completed, and separates the polyisocyanate composition.

20. The preparation method according to claim 19, characterized in that, The refining method is any one of thin-film evaporation, short-path evaporation, or vacuum distillation.

21. The preparation method according to claim 19, characterized in that, The refining method is a two-stage thin-film evaporation process.

22. The preparation method according to claim 21, characterized in that, When using a two-stage thin-film evaporator, the first-stage separation temperature is 120-200℃ and the pressure is 20-200Pa, while the second-stage separation temperature is 120-200℃ and the pressure is 0.1-100Pa.

23. The preparation method according to claim 1, characterized in that, A phosphorus-containing compound is added to the reaction system, wherein the phosphorus-containing compound includes one or more of phosphoric acid, phosphate, or phosphate ester.

24. The preparation method according to claim 23, characterized in that, The phosphorus-containing compound is selected from one or more of phosphoric acid, tributyl phosphate, dibutyl phosphate, pyrophosphate, triethyl phosphate, phosphorus trichloride, and phosphorus pentachloride.

25. The preparation method according to claim 1, characterized in that, The content of unreacted diisocyanate monomers in the polyisocyanate composition obtained in step S2 is less than 0.2 wt%.

26. The preparation method according to claim 1, characterized in that, The color value of the polyisocyanate composition decreased by 0-10 Hazen when stored at 100°C for 24 hours.

27. The preparation method according to claim 26, characterized in that, The color value of the polyisocyanate composition decreased by 0-5 Hazen when stored at 100°C for 24 hours.

28. The preparation method according to claim 1, characterized in that, The color value of the polyisocyanate composition is less than 30 Hazen before storage at 100°C for 24 hours.

29. The preparation method according to claim 28, characterized in that, The color value of the polyisocyanate composition is less than 25 Hazen before storage at 100°C for 24 hours.

30. The preparation method according to any one of claims 1-29, characterized in that, The polyisocyanate composition further contains one or more of the following: iminooxadiazine dione structure, biuret structure, urea dione group, urea carbamate group, carbamate group, and urea ketimino group.

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