Preparation method of polyisocyanate composition

Abstract

The invention discloses a preparation method of the polyisocyanate composition, which comprises the following steps: mixing an isocyanate raw material with a recycled diisocyanate stream, and carrying out partial self-polymerization reaction in the presence of a catalyst to obtain the polyisocyanate composition containing isocyanurate, the mass content of the phosphorus element in the recycled diisocyanate stream is 50 to 2000 ppm. The polyisocyanate composition prepared by the preparation method disclosed by the invention is excellent in chroma stability.

Description

Technical Field

[0001] The invention belongs to the technical field of isocyanates and relates to a method for preparing a polyisocyanate composition. Background Art

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

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

[0004] Patent CN101641387A discloses a color-stable curing agent composition for polyurethane paint. The polyisocyanate composition can directly react with components in the polyurethane coating containing groups reactive to isocyanate, and has the characteristic of good color stability during storage. However, the composition components are relatively complex. In addition to polyisocyanate, a catalyst that can promote isocyanate reaction, phosphite, and hindered phenol, it must also contain at least one solvent and an acidic stabilizer. Chromatic stability can only be achieved in a solvent-diluted system. The formula components and implementation conditions of the composition are relatively complex.

[0005] Patents CN110372846A, CN110790880A and CN112225857A respectively obtain polyisocyanate compositions with stable color by controlling the contents of secondary amine, secondary phosphine and cleavable amine in the catalyst. However, the color number of the compositions still increases during high-temperature storage, and the color thermal stability is still insufficient.

[0006] Patent DE102006043464A1 describes colorless polyisocyanates treated with peroxides or hydroperoxides. EP0630928A2 describes improved color numbers and storage stability of polyisocyanates, which are prepared using ammonium salts or metal salts as catalysts, the latter being obtained by adding organic peracids. The acid function is simultaneously used to decompose the catalyst to stop the reaction. The disadvantage of these methods is that the added peroxide or hydroperoxide and degradation products of the color-imparting components remain in the product, which is disadvantageous for the stability of the color of the polyisocyanate composition.

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

[0008] It can be seen from the above-disclosed technical solutions that the polyisocyanate composition with stable chromaticity during storage in the current disclosed technology has the disadvantages of poor availability, complex process and the need to improve chromaticity stability. Therefore, it is necessary to develop a polyisocyanate composition with better chromaticity stability and simpler preparation process. Summary of the invention

[0009] The object of the present invention is to provide a method for preparing a polyisocyanate composition. The polyisocyanate composition prepared by the method has low initial chromaticity and stable chromaticity during high-temperature storage.

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

[0011] A method for preparing the polyisocyanate composition comprises mixing an isocyanate raw material with a recovered diisocyanate stream, and performing a partial self-polymerization reaction in the presence of a catalyst to obtain a polyisocyanate composition containing isocyanurate;

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

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

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

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

[0016] S1: subjecting fresh aliphatic and / or alicyclic diisocyanate to partial self-polymerization reaction with the recovered diisocyanate stream in the presence of a catalyst, and when the target NCO% is reached, adding a terminator to terminate the reaction to obtain a reaction solution;

[0017] S2: the reaction liquid is separated to remove unreacted diisocyanate to obtain a polyisocyanate composition containing isocyanurate;

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

[0019] In the present invention, since the recovered unreacted diisocyanate contains a certain amount of heavy components, the heavy components refer to impurities with a molecular weight greater than that of polyisocyanates, mainly including impurities containing carbamate structures, impurities containing allophanate structures, polymers such as dimers and trimers, and impurities such as residual additives and coloring substances in the preparation process of the reaction solution, the recovered diisocyanate has a serious impact on the chromaticity and chromaticity stability of the prepared product when it is recycled again.

[0020] The technicians of the present invention have found that by controlling the phosphorus content in the recovered unreacted diisocyanate to 50-2000ppm, preferably 50-1500ppm, 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 content of P element in the unreacted diisocyanate is greater than 2000ppm, it will cause the color of the composition to be high after being recycled and heated for many times; when the content of P element in the unreacted diisocyanate is less than 50ppm, the color thermal stability of the composition will be poor.

[0021] The method for controlling the phosphorus content in the recovered diisocyanate is a prior art method with various means, and the present invention does not specifically limit it. For example, phosphorus-containing compounds such as phosphoric acid, tributyl phosphate, dibutyl phosphate, pyrophosphoric acid, triethyl phosphate, phosphorus trichloride, phosphorus pentachloride, etc. can be added to the unreacted diisocyanate.

[0022] In the present invention, the diisocyanate 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 recovered diisocyanate is (0.1-10):1.

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

[0025] The catalyst is added in an amount of 10-1000 ppm of the mass of the mixture of fresh aliphatic and / or alicyclic diisocyanate and recovered diisocyanate;

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

[0027] The alcohol solvent is selected from one or more of 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, it is a monohydric alcohol, and more preferably, a monohydric alcohol with a molecular weight of less than 200.

[0028] In the present invention, the self-polymerization reaction in step S1 has a reaction temperature of 30-120°C, preferably 50-100°C.

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

[0030] In the present invention, the terminator is an acidic substance, and the amount added is 0.5-5 times, preferably 1-3 times, of the molar amount of the catalyst. 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 the present invention, step S2 is to purify the reaction liquid after the reaction in S1 is completed, and separate to obtain a polyisocyanate composition.

[0032] Preferably, the refining method is any one of thin film evaporation, falling film evaporation, short path evaporation and vacuum distillation, preferably two-stage thin film evaporation. Wherein, when a two-stage thin film evaporator is used, the first-stage separation temperature is 120-200°C and the pressure is 20-200Pa, and the second-stage separation temperature is 120-200°C and the pressure is 0.1-100Pa.

[0033] In the present invention, if phosphoric acid or phosphate-containing compounds are added to the reaction system, the phosphorus content in the removed unreacted diisocyanate can be adjusted by regulating 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 phosphine-containing compound is added to the reaction system, and the phosphorus-containing compound includes one or more of phosphoric acid, phosphate or phosphate ester, preferably one or more of phosphoric acid, tributyl phosphate, dibutyl phosphate, pyrophosphoric acid, triethyl phosphate, phosphorus trichloride, phosphorus pentachloride

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

[0036] In the present invention, the polyisocyanate composition is stored at 100° C. for 24 hours, and its chromaticity value is reduced by 0-10 Hazen, preferably by 0-5 Hazen.

[0037] The chromaticity value of the polyisocyanate composition before storage at 100° C. / 24 h is lower than 30 Hazen, preferably lower than 25 Hazen.

[0038] In the present invention, the isocyanurate-containing polyisocyanate composition with excellent chromatic stability may contain one or more of an iminooxadiazinedione structure, a biuret structure, a uretdione group, an allophanate group, a carbamate group, and a uretonimine group in addition to an isocyanurate structure.

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

[0040] In the present invention, the isocyanurate structure is:

[0041]

[0042] The structure of iminooxadiazinedione is:

[0043]

[0044] The biuret structure is:

[0045]

[0046] The specific structure of the uretdione group is:

[0047]

[0048] The specific structure of the allophanate group is:

[0049]

[0050] The specific structure of the carbamate group is:

[0051]

[0052] The specific structure of the uretonimine group is:

[0053]

[0054] The above-mentioned isocyanurate structure, iminooxadiazinedione, biuret structure, etc. can all be detected by nuclear magnetic resonance carbon spectrum.

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

[0056] The beneficial effects of the present invention are:

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

[0058] The present invention is further described below by means of specific examples. The examples described in the present invention are only used to illustrate the present invention and do not limit the scope of the present 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-Trimethylbenzyl ammonium 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] NCO% content test, refer to standard GB / T 12009.4.

[0068] <Determination of phosphorus content in unreacted diisocyanate>

[0069] The phosphorus content (based on mass) in the unreacted diisocyanate was measured using X-ray fluorescence spectrometry (XRF).

[0070] <Determination of free diisocyanate monomer content>

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

[0072] <Measurement of chromaticity and chromaticity stability of polyisocyanate composition>

[0073] The chromaticity of the polyisocyanate composition in the examples and comparative examples was measured based on the method of GB / T 3143-1982 using LICO 400 from HACH Lange in a 50 mm disposable rectangular cuvette to measure the initial chromaticity and the chromaticity of the product after cooling in a 100° C. oven under nitrogen sealing conditions for 24 hours.

[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, 2000g of fresh HDI monomer was added to a 2L four-necked flask, and then the system was heated to 70°C, and 1.0g of 20% mass concentration of N,N,N-trimethylbenzyl ammonium hydroxide isooctanol solution (1.2mmol) was added for trimerization. When the NCO content in the reaction solution reached 39.3%, 0.3g of di-n-butyl phosphate (1.44mmol) was added to terminate the reaction. Then, a thin film evaporator was used to perform two thin film evaporation purifications at 150°C and 30Pa to obtain 800g of a polyisocyanate composition and 1200g of unreacted HDI (M).

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

[0079] [Example and Comparative Example]

[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: adding a certain amount of triethyl phosphate to the unreacted diisocyanate M recovered in the synthesis example to adjust the phosphorus content therein to obtain the recovered diisocyanate N;

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

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

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

[0085]

[0086]

[0087] From the comparison results of parameters and material properties in Table 1, it can be seen that the phosphorus content in the unreacted diisocyanate that is recycled is effectively controlled to be between 50-2000ppm, and the obtained composition has low chromaticity and excellent chromaticity stability. When the phosphorus content in the unreacted diisocyanate is less than 50ppm, the chromaticity thermal stability of the obtained composition is poor; when the phosphorus content in the unreacted diisocyanate is higher than 2000ppm, the initial chromaticity of the obtained composition is higher.

[0088] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing the polyisocyanate composition, characterized in that: The isocyanate raw material is mixed with the recovered diisocyanate stream, and a partial self-polymerization reaction is carried out in the presence of a catalyst to obtain a polyisocyanate composition containing isocyanurate; The recovered diisocyanate refers to the unreacted diisocyanate recovered from the self-polymerization reaction of aliphatic and / or alicyclic polyisocyanate, and the mass content of phosphorus in the recovered diisocyanate stream is 50-2000ppm; Preferably, the mass content of phosphorus in the recovered diisocyanate stream is 50-1500 ppm.

2. The preparation method according to claim 1, characterized in that: The recovered diisocyanate may come from the unreacted diisocyanate generated by the reaction itself, or may come from the unreacted diisocyanate recovered from the polymerization reaction of other aliphatic and / or alicyclic polyisocyanates.

3. The preparation method according to claim 1, characterized in that: The preparation method comprises the following steps: S1: subjecting fresh aliphatic and / or alicyclic diisocyanate to partial self-polymerization reaction with the recovered diisocyanate stream in the presence of a catalyst, and when the target NCO% is reached, adding a terminator to terminate the reaction to obtain a reaction solution; S2: the reaction liquid is separated to remove unreacted diisocyanate to obtain a polyisocyanate composition containing isocyanurate; Preferably, S3: the unreacted diisocyanate removed in step S2 is condensed and recycled as the diisocyanate stream recovered in S1.

4. The preparation method according to any one of claims 1 to 3, characterized in that The diisocyanate 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; Preferably, the mass ratio of fresh aliphatic and / or alicyclic diisocyanate to recovered diisocyanate is (0.1-10):1; Preferably, the catalyst in step S1 is selected from quaternary ammonium bases and / or quaternary ammonium salt compounds, preferably choline hydroxide, trimethylhydroxyethylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, 1-adamantylammonium hydroxide, hexamethylammonium hydroxide, tetramethylammonium formate, tetramethylammonium decanoate, tetraethylammonium formate, tetraethylammonium acetate, tetraethylammonium decanoate, trimethylhydroxypropylammonium formate, trimethylhydroxypropylammonium acetate, trimethylhydroxypropylammonium octanoate, trimethylhydroxypropylammonium decanoate, trimethylhydroxyethylammonium formate, trimethylhydroxyethylammonium acetate and trimethylhydroxyethylammonium decanoate, any one or a combination of at least two thereof, preferably benzyltrimethylammonium hydroxide and / or tetramethylammonium decanoate; Preferably, the catalyst is added in an amount of 10-1000 ppm based on the mass of the mixture of fresh aliphatic and / or alicyclic diisocyanate and recycled diisocyanate; Preferably, the alcohol solvent is selected from one or more of monohydric alcohols and dihydric alcohols; Preferably, 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, it is a monohydric alcohol, and more preferably, a monohydric alcohol with a molecular weight of less than 200.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The self-polymerization reaction in step S1 has a reaction temperature of 30-120°C, preferably 50-100°C; Preferably, the partial self-polymerization in step S1 refers to the polymerization reaction of isocyanate groups (-NCO) of diisocyanate in the presence of a catalyst. When the polymerization reaction reaches the end point, unreacted polyisocyanate still exists in the reaction solution, and the reaction is terminated when the NCO content in the reaction system is 30-45%; Preferably, 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, di-isooctyl phosphate, benzoic acid, and benzoyl chloride.

6. The preparation method according to any one of claims 1 to 5, characterized in that: Step S2: purifying the reaction liquid after the reaction in S1 to separate and obtain a polyisocyanate composition; Preferably, the refining method is any one of thin film evaporation, falling film evaporation, short path evaporation, and vacuum distillation, preferably two-stage thin film evaporation; Wherein, when a two-stage thin film evaporator is used, the first-stage separation temperature is 120-200°C and the pressure is 20-200Pa, and the second-stage separation temperature is 120-200°C and the pressure is 0.1-100Pa.

7. The preparation method according to any one of claims 1 to 4, characterized in that: A phosphine-containing compound is added to the reaction system, and the phosphorus-containing compound includes one or more of phosphoric acid, phosphate or phosphate ester, preferably one or more of phosphoric acid, tributyl phosphate, dibutyl phosphate, pyrophosphoric acid, triethyl phosphate, phosphorus trichloride and phosphorus pentachloride.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The content of unreacted diisocyanate monomers in the polyisocyanate composition separated in step S2 is less than 0.2 wt %; Preferably, the polyisocyanate composition is stored at 100° C. for 24 hours, and its chromaticity value decreases by 0-10 Hazen, preferably by 0-5 Hazen; Preferably, the chromaticity value of the polyisocyanate composition before storage at 100° C. / 24 h is lower than 30 Hazen, preferably lower than 25 Hazen.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The polyisocyanate composition further contains one or more of an iminooxadiazinedione structure, a biuret structure, a uretdione group, an allophanate group, a carbamate group, and a uretonimine group.

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