Biuret polyisocyanate composition with stable free monomer and preparation method thereof

Abstract

The invention provides a biuret polyisocyanate composition with stable free monomers. According to the method, at least one diisocyanate monomer is selected, vaporous water is used as a biuret reagent, a reaction solution is obtained by controlling the reaction process of the biuret reagent, after redundant diisocyanate monomers are separated and removed, heat treatment is carried out at a certain temperature, and the initial free monomer content of a final product is smaller than 0.50 wt%. And the growth is not more than 0.30 wt% after storage at room temperature for 12 months.

Description

Technical Field

[0001] This invention belongs to the field of isocyanates, specifically relating to a free monomer-stabilized biuret polyisocyanate composition. Background Technology

[0002] Polyurethane coatings, due to the special structure of urethane bonds in their molecules, possess excellent properties such as chemical resistance, impact and abrasion resistance, flexible curing, strong adhesion, and resistance to high and low temperatures. They are widely used in the automotive, shipbuilding, engineering machinery, rail transportation, furniture construction, aerospace and other fields.

[0003] Aliphatic or alicyclic polyisocyanates are the core raw materials for polyurethane coatings and must be used in combination with acrylic resins, polyester resins, alkyd resins, etc. During film formation, their NCO groups react with the resin's hydroxyl groups to form a polyurethane structure, giving the coating its unique properties. Among them, biuret polyisocyanates, due to their unique hydrogen bonds, offer superior coating adhesion and flexibility, playing a prominent role in the protection of bridges, ships, and construction machinery, and extending equipment lifespan.

[0004] With increasingly stringent environmental requirements in the coatings market, the limits on the free monomer content in polyisocyanate compositions are becoming stricter. However, during long-term storage, the free monomer content of biuret polyisocyanates gradually increases, affecting downstream applications. Therefore, improving the stability of free isocyanate monomers during biuret storage has become a key research focus for those skilled in the art.

[0005] US Patent 3358010 discloses a method for reacting polyisocyanates with tertiary alcohols. This method has significant advantages: the amount of white polyurea produced by the reaction is extremely small, and it can significantly improve the biuret yield; however, the reaction needs to be carried out at a high temperature of 200°C, the prepared biuret product has a high color number, and the content of volatile isocyanate monomers will further increase after long-term storage of its diluted product.

[0006] Patent CN1175965A discloses a method that uses tertiary alcohols or mixtures of water and tertiary alcohols as biureting agents to prepare biuret-containing polyisocyanates under conditions where urea, amines, biuret, urea derivatives, or amides are used as stabilizers. The products prepared by this method have relatively low viscosity and low content of volatile isocyanate monomers; however, the content of volatile isocyanate monomers increases during long-term storage.

[0007] Public patent CN106084182B proposes adding an N-heterocyclic carbene metal complex as a supplementary catalyst in the latter half of the reaction between polyisocyanates and water to improve the monomer content stability during product storage. However, the N-heterocyclic carbene metal complex catalyzes the reaction between isocyanates and water, and its presence is detrimental to the dilution stability of the product. Furthermore, it can interact with the catalyst in the formulation during downstream applications, causing adverse effects.

[0008] Public patent CN111217972B proposes a method to control the content of urea diketone groups in biuret polyisocyanate compositions by adding Brønsted protic acid as a co-catalyst during the reaction of polyisocyanates with water, thereby improving the stability of free monomers during long-term storage. The presence of Brønsted protic acid residues in the product can affect its reactivity in downstream applications.

[0009] Patent CN114249868A discloses a method that involves heat-treating the obtained polyisocyanate reaction solution and then separating the heat-treated polyisocyanate mixture. The resulting polyisocyanate composition, stored at 50°C for 30 days, shows an increase in isocyanate monomer content of less than or equal to 0.1 wt%, and a viscosity increase of no more than 15% of its initial viscosity. The main problem it addresses is the stability of viscosity and free monomer content in polyisocyanate curing agents during long-distance transportation. However, it offers no guidance for the stability of free HDI monomer content and viscosity in biuret polyisocyanate products during long-term storage.

[0010] The published patent CN118620179A proposes that by controlling the content of specific substances in tetraurea compounds in biuret, the monomer content can increase by less than 0.1% after 12 months of storage at room temperature, and the viscosity increase at 25°C can be less than 1000 cP. However, the reaction requires the use of a tertiary phosphine catalyst, which will affect the biuret reaction conversion rate, reduce production efficiency, and the process is relatively complex.

[0011] Therefore, there is an urgent need in this field to develop a solution to address the stability of free isocyanate monomer content during long-term storage of biuret polyisocyanate products. Summary of the Invention

[0012] One of the objectives of this invention is to provide a free monomer-stabilized biuret polyisocyanate composition.

[0013] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0014] A free monomer-stabilized biuret polyisocyanate composition, wherein the molar content of the NH-urea component in the composition is less than 2% of the total NH content.

[0015] The biuret polyisocyanate composition has an initial free monomer content of less than 0.50%.

[0016] As is known to those skilled in the art, the -NH- in the biuret polyisocyanate composition mainly exists in the following forms:

[0017] Formula 1 (NH-urea):

[0018] Formula 2 (NH-biuret):

[0019] The molar content of NH-urea component in this invention as a percentage of the total NH content refers to the molar ratio of formula 1 to (formula 1 + formula 2).

[0020] The present invention also provides a method for preparing the aforementioned biuret polyisocyanate composition, the method comprising the following steps:

[0021] S1: After heating the diisocyanate monomer to temperature T1, add the catalyst and retain it for a certain time t1. Then raise the temperature to T2 and add the biuretizing agent in batches to react and obtain the reaction solution.

[0022] S2: Remove the diisocyanate monomer from the reaction solution to obtain the crude product;

[0023] S3: The above crude product is heat-treated at temperature T3 for time t2 to obtain the final product.

[0024] The initial free monomer content of this product is less than 0.50%, and the increase is no more than 0.30% after 12 months of storage at room temperature.

[0025] In this invention, the diisocyanate monomer described in S1 is a diisocyanate containing 4-18 carbon atoms in addition to the NCO group on the carbon chain. Preferably, it is one or more of the following: toluene diisocyanate, diphenylmethane diisocyanate, terephthalic diisocyanate, naphthalene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, trimethyl-1,6-hexamethylene diisocyanate, lysine diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexyl diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, norbornene diisocyanate, cyclohexane diisocyanate, phenyl diisocyanate, and tetramethyl-isophenyl diisocyanate. More preferably, it is one or more of the following: isophorone diisocyanate, 1,4-cyclohexane diisocyanate, pentamethylene diisocyanate, and hexamethylene diisocyanate. Most preferably, it is hexamethylene diisocyanate.

[0026] In this invention, the catalyst in S1 is one or more of monoalkyl phosphate, dialkyl phosphate, trialkyl phosphate, monoaryl phosphate, diaryl phosphate, monocarboxylic acid, and dicarboxylic acid, preferably diisooctyl phosphate, dibutyl phosphate, propionic acid, etc.; the amount added is 0.02-1.0% of the mass of the diisocyanate monomer, preferably 0.1-0.8%.

[0027] In this invention, the temperature T1 is 60-100℃, preferably 80-100℃. The time t1 is 0.2-3h, preferably 0.5-1h.

[0028] In this invention, the temperature T2 in S1 is 105-240℃, preferably 120-200℃.

[0029] In this invention, the biuretizing agent is water vapor; preferably, the molar ratio of the biuretizing agent to the diisocyanate monomer is 1:(3-20), more preferably 1:(5-10); preferably, the water vapor is added in 2-5 portions, with the amount added being evenly distributed; the interval between two additions is not less than 10 minutes, preferably 10-30 minutes.

[0030] In this invention, S2 removes the diisocyanate monomer from the reaction solution via an evaporator, preferably via a two-stage thin-film evaporator. The thin-film evaporator is either a roller-type or a scraped-plate type thin-film evaporator.

[0031] In this invention, the heat treatment temperature T3 in S3 is 40-80℃, preferably 50-70℃;

[0032] In this invention, the retention time t2 in S3 is 0.2-8h, preferably 0.5-5h.

[0033] The beneficial effects of this invention are as follows:

[0034] By controlling the molar content of the NH-urea component in the composition to be less than 2% of the total NH, the initial free monomer content of the final product is less than 0.5 wt%, and the growth is no more than 0.3 wt% after 12 months of storage at room temperature. Detailed Implementation

[0035] 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. Those skilled in the art will understand that, under the guidance of this specification, some modifications or adjustments can be made to the present invention. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

[0036] Information on the main raw materials used in this invention:

[0037] Hexamethylene diisocyanate, Wannate HDI, Wanhua Chemical, 99%

[0038] Isophorone diisocyanate, Wannate IPDI, Wanhua Chemical, 99%

[0039] Diisooctyl phosphate, TCI, 98.5%

[0040] Dibutyl phosphate, TCI, 98.5%

[0041] Propionic acid, TCI, 99.0%.

[0042] The test methods used for the samples obtained in the test examples of this invention are as follows:

[0043] NH-urea determination: using NMR. 1 H-spectral analysis showed that -NH-biuret... 1 The H spectrum shows a peak at 7.6 ppm, and the -NH-urea peak shows a peak at 5.0-5.1 ppm. The test conditions are as follows:

[0044] H-NMR equipment: AVANCE600 (Bruker)

[0045] BBO probe (Bruker)

[0046] Resonant frequency: 600MHz

[0047] Displacement reference: 7.28 ppm (CDCl3)

[0048] Pulse program: zg30

[0049] Spectral width: 20ppm

[0050] Spectral center: 6 ppm

[0051] Total number of sums: 64

[0052] Impulse delay: 3 seconds

[0053] Viscosity determination: The Brookfield RC / S rheometer was used for testing at 25°C.

[0054] Color number determination: The color number of biuret polyisocyanate was tested using a BYK LCS IV colorimeter and the Hazen color standard was used.

[0055] Unless otherwise specified, the reaction system is kept under the protection of a dry inert gas (nitrogen) throughout the entire reaction process.

[0056]

Example 1

[0057] 1) Add 4200.0g of hexamethylene diisocyanate to a jacketed reaction flask, turn on the stirrer and circulating oil bath, heat to 80℃, add 29g of diisooctyl phosphate, and stir for 30min. Continue heating until the temperature reaches 160℃, then add 75g of steam in three portions, 10min apart, at a uniform rate. The reaction is complete after the steam has been added.

[0058] 2) The biuret reaction solution obtained above is passed through a two-stage scraped film evaporator to remove the monomer, thereby obtaining the biuret polyisocyanate intermediate.

[0059] 3) Add the biuret intermediate obtained above into a three-necked flask, start stirring and circulating oil bath, heat to 60°C, and heat for 4 hours to obtain the final product.

[0060] The prepared polyisocyanate product was tested and found to have a viscosity of 8066 cP at 25°C, a color number of 16.3 Hazen, an NH-urea content of 0.4% of the total NH content, a free HDI monomer content of 0.28 wt%, and a free HDI monomer content of 0.41 wt% after 12 months of sealed storage under nitrogen at room temperature.

[0061]

Example 2

[0062] 1) Add 4200.0g of hexamethylene diisocyanate to a jacketed reaction flask, turn on the stirrer and circulating oil bath, heat to 60℃, add 17g of dibutyl phosphate, and stir for 180min. Continue to heat until the temperature reaches 120℃, then add 45g of steam in two portions, 10min apart, at a uniform rate. The reaction is complete after the steam has been added.

[0063] 2) The biuret reaction solution obtained above is passed through a two-stage scraped film evaporator to remove the monomer, thereby obtaining the biuret polyisocyanate intermediate.

[0064] 3) Add the biuret intermediate obtained above into a three-necked flask, turn on the stirring and circulating oil bath, raise the temperature to 50°C, and heat for 5 hours to obtain the final product.

[0065] The prepared polyisocyanate product was tested and found to have a viscosity of 8719 cP at 25°C, a color number of 10.2 Hazen, an NH-urea content of 0.6% of the total NH content, a free HDI monomer content of 0.26 wt%, and a free HDI monomer content of 0.42 wt% after 12 months of sealed storage under nitrogen at room temperature.

[0066]

Example 3

[0067] 1) Add 4200.0 g of hexamethylene diisocyanate to a jacketed reaction flask, turn on the stirrer and circulating oil bath, heat to 100°C, add 42 g of propionic acid, and stir for 12 min. Continue heating until the temperature reaches 200°C, then add 56.3 g of water vapor in four portions, 10 min apart, at a uniform rate. The reaction is complete after the water vapor has been added.

[0068] 2) The biuret reaction solution obtained above is passed through a two-stage scraped film evaporator to remove the monomer, thereby obtaining the biuret polyisocyanate intermediate.

[0069] 3) Add the biuret intermediate obtained above into a three-necked flask, turn on the stirring and circulating oil bath, raise the temperature to 70°C, and heat for 1.5 hours to obtain the final product.

[0070] The prepared polyisocyanate product was tested and found to have a viscosity of 8420 cP at 25°C, a color number of 18.1 Hazen, an NH-urea content of 0.3% of the total NH content, a free HDI monomer content of 0.32 wt%, and a free HDI monomer content of 0.48 wt% after 12 months of sealed storage under nitrogen at room temperature.

[0071]

Example 4

[0072] 1) Add 4466.0 g of isophorone diisocyanate to a jacketed reaction flask, turn on the stirrer and circulating oil bath, heat to 80°C, add 22 g of diisooctyl phosphate, and stir for 60 min. Continue to heat until the temperature reaches 110°C, then add 20.0 g of water vapor in three portions, 10 min apart, at a uniform rate. The reaction is complete after the water vapor has been added.

[0073] 2) The biuret reaction solution obtained above is passed through a two-stage scraped film evaporator to remove the monomer, thereby obtaining the biuret polyisocyanate intermediate.

[0074] 3) Add the biuret intermediate obtained above into a three-necked flask, turn on the stirring and circulating oil bath, raise the temperature to 80°C, heat for 1 hour, and obtain the final product.

[0075] The prepared polyisocyanate product was tested and found to have a viscosity of 10240 cP at 25°C, a color number of 8.6 Hazen, an NH-urea content of 1.8% of the total NH content, a free IPDI monomer content of 0.33 wt%, and a free IPDI monomer content of 0.55 wt% after 12 months of sealed storage under nitrogen at room temperature.

[0076]

Example 5

[0077] 1) Add 4466.0 g of isophorone diisocyanate to a jacketed reaction flask, turn on the stirrer and circulating oil bath, heat to 100°C, add 22 g of diisooctyl phosphate, and stir for 36 min. Continue heating until the temperature reaches 220°C, then add 90.0 g of water vapor in two portions, 10 min apart, at a uniform rate. The reaction is complete after the water vapor has been added.

[0078] 2) The biuret reaction solution obtained above is passed through a two-stage scraped film evaporator to remove the monomer, thereby obtaining the biuret polyisocyanate intermediate.

[0079] 3) Add the biuret intermediate obtained above into a three-necked flask, start stirring and circulating oil bath, heat to 40°C, heat for 7 hours to obtain the final product.

[0080] The prepared polyisocyanate product had a viscosity of 7150 cP at 25°C, a color number of 22.7 Hazen, an NH-urea content of 1.2% of the total NH content, a free IPDI monomer content of 0.27 wt%, and a free IPDI monomer content of 0.53 wt% after 12 months of sealed storage under nitrogen at room temperature.

[0081] Comparative Example 1

[0082] 1) Add 4200.0g of hexamethylene diisocyanate to a jacketed reaction flask, turn on the stirring and circulating oil bath, add 29g of diisooctyl phosphate, heat to 160℃, add 75g of water vapor in three portions, 10min apart, at a uniform rate, and wait until the water vapor is added before the reaction is complete.

[0083] 2) The biuret reaction solution obtained above is passed through a two-stage scraped film evaporator to remove the monomer, thereby obtaining the biuret polyisocyanate intermediate.

[0084] 3) Add the biuret intermediate obtained above into a three-necked flask, start stirring and circulating oil bath, heat to 60°C, and heat for 4 hours to obtain the final product.

[0085] The prepared polyisocyanate product was tested and found to have a viscosity of 7920 cP at 25°C, a color number of 15.2 Hazen, an NH-urea content of 2.3% of the total NH content, a free HDI monomer content of 0.28 wt%, and a free HDI monomer content of 0.66 wt% after 12 months of sealed storage under nitrogen at room temperature.

[0086] Comparative Example 2

[0087] 1) Add 4200.0g of hexamethylene diisocyanate to a jacketed reaction flask, turn on the stirrer and circulating oil bath, heat to 80℃, add 29g of diisooctyl phosphate, and stir for 30min. Continue to heat until the temperature reaches 160℃, then add 75g of water vapor at a uniform rate all at once. The reaction is complete after the water vapor has been added.

[0088] 2) The biuret reaction solution obtained above is passed through a two-stage scraped film evaporator to remove the monomer, thereby obtaining the biuret polyisocyanate intermediate.

[0089] 3) Add the biuret intermediate obtained above into a three-necked flask, start stirring and circulating oil bath, heat to 60°C, and heat for 4 hours to obtain the final product.

[0090] The prepared polyisocyanate product had a viscosity of 8367 cP at 25°C, a color number of 14.9 Hazen, an NH-urea content of 2.6% of the total NH content, a free HDI monomer content of 0.28 wt%, and a free HDI monomer content of 0.7 wt% after 12 months of sealed storage under nitrogen at room temperature.

[0091] Comparative Example 3

[0092] 1) Add 4200.0g of hexamethylene diisocyanate to a jacketed reaction flask, turn on the stirrer and circulating oil bath, heat to 80℃, add 29g of diisooctyl phosphate, and stir for 30min. Continue heating until the temperature reaches 160℃, then add 75g of steam in three portions, 10min apart, at a uniform rate. The reaction is complete after the steam has been added.

[0093] 2) The biuret reaction solution obtained above is passed through a two-stage scraped film evaporator to remove the monomers, and the final product is obtained.

[0094] The prepared polyisocyanate product was tested and found to have a viscosity of 7688 cP at 25°C, a color number of 13.1 Hazen, an NH-urea content of 2.4% of the total NH content, a free HDI monomer content of 0.26 wt%, and a free HDI monomer content of 0.65 wt% after 12 months of sealed storage under nitrogen at room temperature.

Claims

1. A biuret polyisocyanate composition characterized in that, The molar content of the NH-urea component in the composition is less than 2% of the total NH content.

2. Biuret polyisocyanate composition according to claim 1, characterized in that The initial free monomer content is less than 0.50 wt%.

3. The process for the preparation of a biuret polyisocyanate composition according to claim 1 or 2, characterized in that The method comprises the following steps: S1: after heating the diisocyanate monomer to a temperature T1, a catalyst is added and retained for a certain time t1, then heated to a temperature T2, and a biuretizing agent is added in batches to react, to obtain a reaction liquid; S2: removing the diisocyanate monomer in the reaction liquid to obtain a crude product; S3: heat treating the crude product at a temperature T3 for a heat treatment time t2 to obtain a final product.

4. The production method according to claim 3, characterized by, The diisocyanate monomer in S1 is one or more of diisocyanates containing 4-18 carbon atoms in the carbon chain in addition to the NCO group, preferably toluene diisocyanate, diphenylmethane diisocyanate, p-phenylene diisocyanate, naphthalene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, trimethyl-1,6-hexamethylene diisocyanate, lysine diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexyl diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, norbornane diisocyanate, cyclohexane dimethylene diisocyanate, benzene dimethylene diisocyanate, tetramethyl m-xylylene diisocyanate.

5. The preparation method according to claim 3, characterized in that, The catalyst in S1 is one or more of monoalkyl phosphate, dialkyl phosphate, trialkyl phosphate, monoaryl phosphate, diaryl phosphate, monocarboxylic acid, and dicarboxylic acid, preferably diisooctyl phosphate, dibutyl phosphate, and propionic acid. Preferably, the catalyst is added in an amount of 0.02-1.0% of the mass of the diisocyanate monomer, preferably 0.1-0.8%.

6. The preparation method according to claim 3, characterized in that, The biuretizing agent in S1 is water vapor. Preferably, the molar ratio of the biuretizing agent to the diisocyanate monomer is 1:(3-20), preferably 1:(5-10). The biuretizing agent needs to be added in batches, preferably in 2-5 batches; the mass of the biuretizing agent added each time is the same; the interval between the two times of addition is not less than 10 min, preferably 10-30 min.

7. The production method according to claim 3 or 6, characterized by, The temperature T1 in S1 is 60-100°C, preferably 80-100°C. And / or, the time t1 is 0.2-3h, preferably 0.5-1h. And / or, the temperature T2 in S1 is 105-240°C, preferably 120-200°C.

8. The preparation method according to claim 3, characterized in that, S2 removes the diisocyanate monomer in the reaction liquid by an evaporator, preferably a secondary thin film evaporator.

9. The preparation method according to claim 3, characterized in that, The heat treatment temperature T3 in S3 is 40-80°C, preferably 50-70°C. And / or, the retention time t2 is 0.2-8h, preferably 0.5-5h.

10. A biuret polyisocyanate composition stabilized against free monomer, obtainable by the process according to any one of claims 3 to 9, characterized in that The initial free monomer content of the composition is less than 0.50 wt%, and the increase after 12 months of room temperature storage is not more than 0.30 wt%.