A polyisocyanate composition, a method for producing the same, and use thereof

Abstract

The application discloses a polyisocyanate composition, a preparation method and application thereof. The polyisocyanate composition is prepared from aliphatic diisocyanate through a trimerization reaction; the content of allophanate in the composition is 1-4 wt%, and the mass ratio of allophanate to free metal ions is (200-4000):1, preferably (500-2000):1. The polyisocyanate composition provided by the application can beneficially improve the problem of surface defects of electrostatic spraying layers, meanwhile, excellent storage stability is ensured, the polyisocyanate composition has more competitiveness in the market similar products, and has typical application advantages.

Description

Technical Field

[0001] This invention relates to a polyisocyanate composition, and more particularly to a polyisocyanate composition, its preparation method, and its application. Background Technology

[0002] Carbamate-based coating compositions using polyisocyanates as curing agents are widely used in automotive, architectural interior and exterior trim, and home appliance coatings due to the excellent abrasion resistance, chemical resistance, and stain resistance of the resulting films. Among these, aliphatic / alicyclic diisocyanates and their derivatives are widely used due to their irreplaceable advantages in resistance to yellowing. Furthermore, for preferred spraying processes, electrostatic spraying is currently the cleanest and most environmentally friendly coating process. It utilizes the principle of corona discharge to negatively charge atomized coating material under a high-voltage DC electric field, causing it to adsorb onto a positively charged substrate surface and discharge. This spraying technology has developed rapidly in recent years, and providing a polyisocyanate suitable for electrostatic spraying is one of the key areas of ongoing research for the inventors.

[0003] Aliphatic / alicyclic diisocyanates have limited their application in the coatings industry due to their low vapor pressure. Currently, it is more common to convert them into isocyanurate-type polyisocyanate compositions through polymerization in the presence of quaternary ammonium salts or quaternary ammonium base trimerizing catalysts. This increases the tolerance of the processing process, improves the functionality and crosslinking degree, and further obtains products with excellent performance.

[0004] However, further in-depth research by the inventors revealed that traditional isocyanurate-type polyisocyanate compositions exhibit high surface defects when preparing coatings using electrostatic spraying. Improving the surface properties of the coating is a pressing technical problem that needs to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a polyisocyanate composition, its preparation method, and its applications. By introducing a small amount of urea-formate and controlling its ratio with free metal ions within a certain range, the polyisocyanate composition can effectively improve surface defects in electrostatic spray coatings while ensuring excellent storage stability. This makes it more competitive among similar products on the market and offers significant application advantages.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The present invention first provides a polyisocyanate composition, which is obtained by trimerization of aliphatic diisocyanate; the content of urea carbamate in the composition is 1-4 wt%, and the mass ratio of urea carbamate to free metal ions is (200-4000):1, preferably (500-2000):1.

[0008] In this invention, the content of urea-formaldehyde ester in the composition must be no less than 1 wt%, otherwise it will be detrimental to maintaining the storage stability of the product in the presence of metal ions. Furthermore, the content of urea-formaldehyde ester must be no more than 4 wt%, otherwise it will compromise the rigidity and solvent resistance of the prepared paint film. Simultaneously, the mass ratio of urea-formaldehyde ester to free metal ions in the composition must be no less than 200:1, otherwise the storage stability of the composition will be severely compromised. Moreover, the mass ratio of urea-formaldehyde ester to free metal ions in the composition must be no more than 4000:1, otherwise the improvement effect on surface defects of the electrostatic spray coating will be lost or the improvement effect will be insignificant.

[0009] In the polyisocyanate composition, urethane is a modified product of aliphatic diisocyanate in the presence of a monohydric alcohol. It is well known to those skilled in the art that diisocyanate and monohydric alcohol can generate urethane at a certain temperature, which can be largely converted to urethane by the action of metal carboxylate catalysts or trimerizing catalysts. The urethane contains the following structural groups:

[0010]

[0011] In the aforementioned polyisocyanate composition, isocyanurate, as the main trimer product, refers to a substance containing the following structural groups:

[0012]

[0013] In a preferred example of the composition described in this invention, the composition contains 85-99 wt% isocyanurate.

[0014] In a preferred example of the composition described in this invention, the aliphatic diisocyanate is selected from one or more of tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate.

[0015] In a preferred example of the composition described in this invention, the free metal ion is selected from one or more of the following metals: potassium, calcium, sodium, aluminum, iron, magnesium, tin, bismuth, and zinc.

[0016] In a preferred embodiment of the composition described in this invention, the composition further comprises one or more of urea diketone, carbamate, iminooxadiazine diketone, biuret, and urea ketimine. The above substances correspond to the following structural groups:

[0017]

[0018]

[0019] In some embodiments of the polyisocyanate composition provided by the present invention, the color intensity of the polyisocyanate composition is less than 40 Hazen, preferably less than 30 Hazen.

[0020] According to the polyisocyanate composition provided by the present invention, in some embodiments, the viscosity of the polyisocyanate composition increases by no more than 20% of its initial viscosity when stored at room temperature for 12 months.

[0021] According to the polyisocyanate composition provided by the present invention, in some embodiments, when the polyisocyanate composition is used as a coating curing agent, the number of surface defects on the metal spray-painted panel prepared by electrostatic spraying process is small, preferably no more than 3 surface defects in a sample size of 40cm*40cm.

[0022] Based on a second aspect of the present invention, a method for preparing a polyisocyanate composition as described above includes the following steps:

[0023] Method 1

[0024] S1. Using aliphatic diisocyanate as raw material, esterification modification is carried out in the presence of monohydric alcohol and metal carboxylate catalysts. After the reaction, a trimerization catalyst is added to continue the reaction until the target conversion rate is reached and the reaction is terminated.

[0025] S2. Remove the free diisocyanate monomer from the reaction solution, optionally add a metal ion compound, mix well to obtain a polyisocyanate composition;

[0026] Method 2

[0027] S1. Using aliphatic diisocyanate as raw material, esterification modification is carried out in the presence of monohydric alcohol and optionally metal carboxylate catalyst. After the reaction, a trimerization catalyst is added to continue the reaction until the target conversion rate is reached and the reaction is terminated.

[0028] S2, Remove free diisocyanate monomers from the reaction solution;

[0029] S3. Add a metal ion compound and mix thoroughly to obtain the polyisocyanate composition.

[0030] In a preferred embodiment of the method described in this invention, the monohydric alcohol is a saturated fatty alcohol with 4-10 carbon atoms, preferably one or more of isooctyl alcohol, n-hexanol, n-butanol, and n-octanol;

[0031] Preferably, the amount of the monohydric alcohol added is 0.5-2% of the molar amount of the aliphatic diisocyanate;

[0032] Preferably, the metal carboxylate catalyst is selected from one or more of zinc isooctanoate, bismuth isooctanoate, and potassium acetate; the amount of the metal carboxylate catalyst added is preferably 50-300 ppm based on the mass of isocyanate;

[0033] Preferably, the reaction temperature for esterification modification is 80-140℃, and the reaction time is 0.5-4h.

[0034] In a preferred embodiment of the method described in this invention, the trimerizing catalyst is selected from one or more of quaternary ammonium salts and quaternary ammonium bases, preferably one or more of tetramethylammonium acetate, tetramethylammonium octanoate, and N,N,N-trimethylbenzylammonium hydroxide;

[0035] Preferably, the amount of the trimerizing catalyst is 20-500 ppm of the mass of the aliphatic diisocyanate;

[0036] Preferably, after the addition of the trimerizing catalyst, the reaction continues at 40-80°C until the target conversion rate is 20-50%, at which point the reaction is terminated.

[0037] In a preferred embodiment of the method described in this invention, the metal ion compound is selected from chlorides and / or carboxylates of at least one of potassium, calcium, sodium, aluminum, iron, magnesium, tin, bismuth, and zinc.

[0038] In step S1 of the above preparation method, the reaction is terminated, for example, by adding a terminator. Optional terminators are generally phosphoric acid, phosphate esters, or sulfate esters, preferably one or more of phosphoric acid, dibutyl phosphate, dimethyl sulfate, and p-toluenesulfonic acid. The amount of terminator added is generally 1-1.5 times the sum of the molar amounts of the trimerizing catalyst and the metal carboxylate catalyst.

[0039] In step S2 of the above preparation method, there are no particular limitations on the method for removing free monomers. For example, unreacted diisocyanate monomers can be removed by thin-film evaporation, vacuum distillation, etc. When thin-film evaporation is preferred, the evaporation temperature is controlled at 120-180℃ and the pressure is 5-100 Pa (absolute pressure). Step S2 is used to reduce the content of free diisocyanate monomers to below 0.5 wt%, preferably below 0.3 wt%.

[0040] In step S3 of the above preparation method, the content of free metal ions in the composition is adjusted by adding a metal ion compound to satisfy the mass ratio of urea ester to free metal ions as defined above as (200-4000):1, preferably (500-2000):1.

[0041] In the preparation method of the polyisocyanate composition of the present invention, a metal carboxylate catalyst can be added in the esterification modification stage to promote the formation of urethane ester, thereby introducing a certain amount of free metal ions. Alternatively, no catalyst can be added in the esterification modification stage, and the alcohol and diisocyanate can be directly reacted to generate urethane ester, which is then further generated in the trimerization process to generate urethane ester. Finally, a metal ion compound is added to introduce free metal ions. Alternatively, the designed amount of urethane ester can be obtained by combining the above two methods and the mass ratio of urethane ester to free metal ions can be controlled within a specific range to solve the above problems proposed by the present invention.

[0042] Therefore, the preparation method of the polyisocyanate composition provided by the present invention is only an example of a feasible implementation means and should not be construed as any limitation on the polyisocyanate composition of the present invention.

[0043] Based on a third aspect of the present invention, an application of a polyisocyanate composition as described above or a polyisocyanate composition prepared by the method described above as a curing agent in the preparation of a coating composition by an electrostatic spraying process.

[0044] The coating composition comprises the polyisocyanate composition described above or the polyisocyanate composition prepared by the method described above as a curing agent, and also comprises at least one acrylic polyol or polyester polyol as a base material; wherein the ratio of the two is (1.1-1.2):1 based on the molar ratio of isocyanate groups to hydroxyl groups.

[0045] The acrylic polyol is selected from polyols polymerized from at least one of the following monomers: 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, glycerol monoacrylate or methacrylate monoacrylate, trimethylolpropane monoacrylate or methacrylate monoacrylate; the polyester polyol is selected from polyester polyols obtained by condensation reaction of carboxylic acid / anhydride and polyol, wherein the carboxylic acid / anhydride is one or more of succinic acid, adipic acid, sebacic acid, maleic anhydride, phthalic anhydride, isophthalic acid, and terephthalic acid, and the polyol is one or more of ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, trimethylolpropane, and glycerol.

[0046] In addition, the coating composition may also contain optional conventional additives, such as cosolvents, defoamers, and colorants. Commonly used cosolvents include butyl acetate, No. 100 solvent oil, and ethyl acetate.

[0047] This invention, by modifying polyisocyanate compositions, not only ensures the viscosity and color stability of the product during storage, but also, when coating compositions prepared with polyisocyanate as curing agents are used to form a paint film using an electrostatic spraying process, exhibit improved solvent resistance and reduced surface defects. Detailed Implementation

[0048] 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.

[0049] The performance testing methods involved in the following embodiments of the present invention are as follows:

[0050] <Determination of Color of Polyisocyanate Compositions>

[0051] The colorimetry of the polyisocyanate composition was measured using a BYK-Gardner GmbH / USA colorimeter.

[0052] <Determination of product rheological viscosity>

[0053] The viscosity of the polyisocyanate composition was determined using a Brookfield RC / S rheometer with a CC-40 rotor, in a constant-temperature water bath at 25 ± 0.1 °C. The shear rate was 25 s⁻¹. -1 -250S -1 .

[0054] <Metal Ion Content Determination>

[0055] Take 10g of the polyisocyanate composition sample, 10g of dichloromethane, and 10g of deionized water. Shake the mixture for 10 minutes using a Hengao HVS-10M vertical shaker. After shaking, centrifuge the mixture at 10,000 rpm for 10 minutes using a Lu Xiangyi high-speed centrifuge. Remove the supernatant and analyze the metal element content X in the polyisocyanate composition sample using ICP.

[0056] <Determination of Urea Carbamate Content>

[0057] The determination was performed using 13C-NMR nuclear magnetic resonance. The instrument used was a Bruker 400MHz instrument, the sample concentration was 50% (CDCl3 solution), the test conditions were 100MHz, relaxation time: 4s, 2000 scans, and δ = 77.0ppm CDCl3 was used as the shift reference.

[0058] The absorption peak with a chemical shift of 154.4 ppm indicates urethane, the absorption peak near 148.4 ppm indicates isocyanurate, the absorption peak near 157.8 ppm indicates urea diketone, the absorption peaks near 148.3 ppm / 144.9 ppm / 135.6 ppm indicate iminooxadiazine diketone, and the absorption peak near 156.2 ppm indicates carbamate. The ratio of the area of ​​the urethane absorption peak to the sum of the areas of all peaks with chemical shifts between 135 and 160 ppm is the urethane content Y.

[0059] Ultimately, the ratio of urethane ester to free metal ion content is Z = Y / X.

[0060] <NCO content (NCO%)>

[0061] The NCO content (%) is determined by neutralizing the isocyanate groups in the sample with an excess of 1 mol / L di-n-butylamine, followed by back titration with 1 mol / L hydrochloric acid.

[0062] <Determination of Free Isocyanate Monomer Content>

[0063] Place a 20 mL sample vial on a digital balance, accurately weigh 1 g of the sample, and add it to the vial. Next, accurately weigh 0.04 g of nitrobenzene (internal standard solution) and add it to the vial. Finally, add 9 mL of ethyl acetate to the vial, cap it, and stir thoroughly to prepare the test sample. Perform colorimetric analysis on the test sample under the following conditions to quantify the amount of HDI monomer:

[0064] Device: Shimadzu Corporation, "GC-8A"

[0065] Pillar: Made by Shin-Ho Chemical Co., Ltd., "Silicone OV-17"

[0066] Column oven temperature: 120℃

[0067] Injection / detector temperature: 160℃

[0068] <Coating Surface Defect Performance Testing>

[0069] The coating composition was prepared into a film using an electrostatic spraying process to obtain a paint film sample. The number of defects in a 40*40cm paint film sample was counted.

[0070] <Coating Solvent Resistance Test>

[0071] The polyisocyanate composition was mixed with Tongde ACR6780 resin at NCO / OH = 1.2:1, and then the mixture was diluted with butyl acetate to a solid content of 50% to obtain the paint.

[0072] The paint was evenly applied to a sanded tinplate (100μm). The freshly made sample was placed at room temperature for 15 minutes, then baked at 75℃ for 2 hours. The sample was then removed and placed at room temperature. The number of times the paint film could withstand 1kg of methyl ethyl ketone (MEK) was tested using a solvent resistance wiping instrument with a load (1kg weight).

[0073]

Example 1

[0074] S1. Place 1000g (5.95mol) of hexamethylene diisocyanate in a 2L four-necked flask, heat to 90℃ under nitrogen protection, add 6g (0.046mol) of isooctanol to the system, and add 0.1g of zinc isooctanoate catalyst dropwise. React for 2h. Then lower the system temperature to 65℃, add 1g of a 10wt% isooctol solution of 2-hydroxy-N,N,N-trimethyl-1-propylcarbamate, and control the reaction temperature at 60℃. When the reaction conversion rate is 40%, add 0.01g of phosphoric acid to terminate the reaction.

[0075] S2. The reaction solution was separated twice using a thin-film evaporator to remove unreacted monomers; the separation temperature was 150℃ and the separation pressure was 10 Pa (absolute pressure) to obtain polyisocyanate composition A1. The color of polyisocyanate composition A1 was tested to be 18 Hazen, the free monomer content was 0.20%, the viscosity was 2498 mPa·s (25℃), the content of urea carbamate was 1.91 wt%, the content of isocyanurate was 97.2 wt%, and the mass ratio of urea carbamate to free metal ions was 424:1.

[0076]

Example 2

[0077] S1. Place 1000g (5.95mol) of hexamethylene diisocyanate in a 2L four-necked flask, heat to 90℃ under nitrogen protection, add 8g (0.062mol) of isooctanol to the system, and react for 2h. Then lower the system temperature to 65℃, add 1g of a 10wt% isooctanol solution of 2-hydroxy-N,N,N-trimethyl-1-propylcarbamate, and control the reaction temperature at 60℃; when the reaction conversion rate is 40%, add 0.01g of phosphoric acid to terminate the reaction.

[0078] S2. The reaction solution is separated twice using a thin-film evaporator at a separation temperature of 150℃ and a separation pressure of 10Pa to remove unreacted monomers.

[0079] S3. Add 25 mg of sodium chloride and mix thoroughly to obtain polyisocyanate composition A2. The color of polyisocyanate composition A2 was tested to be 19 Hazen, the free monomer content was 0.21%, the viscosity was 2508 mPa·s (25℃), the content of urea carbamate was 2.55 wt%, the content of isocyanurate was 96.4 wt%, and the mass ratio of urea carbamate to free metal ions was 1050:1.

[0080]

Example 3

[0081] S1. Place 1000g (6.49mol) of pentamethylene diisocyanate in a 2L four-necked flask, heat to 90℃ under nitrogen protection, add 4.4g (0.034mol) of isooctanol to the system, and react for 2h. Then lower the system temperature to 65℃, add 1g of a 10wt% isooctanol solution of 2-hydroxy-N,N,N-trimethyl-1-propylcarbamate, and control the reaction temperature at 70℃; when the reaction conversion rate is 40%, add 0.01g of phosphoric acid to terminate the reaction.

[0082] S2. The reaction solution is separated twice using a thin-film evaporator at a separation temperature of 150℃ and a separation pressure of 10Pa to remove unreacted monomers.

[0083] S3. Add 6 mg of potassium acetate and mix thoroughly to obtain polyisocyanate composition A3. The color of polyisocyanate composition A3 was tested to be 22 Hazen, the free monomer content was 0.19%, the viscosity was 7658 mPa·s (25℃), the content of urea carbamate was 1.19 wt%, the content of isocyanurate was 97.1 wt%, and the mass ratio of urea carbamate to free metal ions was 2035:1.

[0084]

Example 4

[0085] S1. Place 1000g (5.95mol) of hexamethylene diisocyanate in a 2L four-necked flask, heat to 90℃ under nitrogen protection, add 11.0g (0.085mol) of isooctanol to the system, and react for 2h. Then lower the system temperature to 65℃, add 1g of a 10wt% isooctanol solution of 2-hydroxy-N,N,N-trimethyl-1-propylcarbamate, and control the reaction temperature at 60℃; when the reaction conversion rate is 40%, add 0.01g of phosphoric acid to terminate the reaction.

[0086] S2. The reaction solution is separated twice using a thin-film evaporator at a separation temperature of 150℃ and a separation pressure of 10Pa to remove unreacted monomers.

[0087] S3. Add 300 mg of magnesium nitrate and mix thoroughly to obtain polyisocyanate composition A4. The color of polyisocyanate composition A4 was tested to be 20 Hazen, the free monomer content was 0.21%, the viscosity was 2554 mPa·s (25℃), the content of urea carbamate was 3.44 wt%, the content of isocyanurate was 95.2 wt%, and the mass ratio of urea carbamate to free metal ions was 286:1.

[0088]

Example 5

[0089] Polyisocyanate composition A5 was prepared using essentially the same method as in Example 2, except that the sodium chloride added in step S3 was replaced with 9 mg of zinc sulfate. The polyisocyanate composition A5 was tested and found to have a color of 19 Hazen, a free monomer content of 0.21%, a viscosity of 2508 mPa·s (25°C), a urethane content of 2.48 wt%, an isocyanurate content of 96.2 wt%, and a urethane to free metal ion mass ratio of 2754:1.

[0090]

Example 6

[0091] Polyisocyanate composition A6 was prepared using essentially the same method as in Example 2, except that the sodium chloride added in step S3 was replaced with 7.5 mg of zinc sulfate. The polyisocyanate composition A6 was tested and found to have a color of 19 Hazen, a free monomer content of 0.21%, a viscosity of 2508 mPa·s (25°C), a urethane content of 2.51 wt%, an isocyanurate content of 96.3 wt%, and a urethane to free metal ion mass ratio of 3400:1.

[0092]

Example 7

[0093] Polyisocyanate composition A7 was prepared using essentially the same method as in Example 3, except that the sodium chloride added in step S3 was replaced with 14 mg of calcium acetate. The polyisocyanate composition A7 was tested and found to have a color of 22 Hazen, a free monomer content of 0.21%, a viscosity of 7658 mPa·s (25°C), a urethane content of 1.12 wt%, an isocyanurate content of 97.3 wt%, and a urethane to free metal ion mass ratio of 1222:1.

[0094] Comparative Example 1

[0095] Polyisocyanate composition D1 was prepared using essentially the same method as in Example 2, except that the amount of sodium chloride added in step S3 was changed to 170 mg. The polyisocyanate composition D1 was tested and found to have a color of 19 Hazen, a free monomer content of 0.21%, a viscosity of 2511 mPa·s (25°C), a urethane content of 2.52%, an isocyanurate content of 96.4 wt%, and a urethane to free metal ion mass ratio of 153:1.

[0096] Comparative Example 2

[0097] Polyisocyanate composition D2 was prepared using essentially the same method as in Example 1, except that the amount of zinc isooctanoate catalyst added in step S1 was modified to 0.01 g. The polyisocyanate composition D2 was tested and found to have a color of 18 Hazen, a free monomer content of 0.20%, a viscosity of 2498 mPa·s (25°C), a urethane content of 1.92 wt%, an isocyanurate content of 97.3 wt%, and a urethane to free metal ion mass ratio of 4328:1.

[0098] Comparative Example 3

[0099] Polyisocyanate composition D3 was prepared according to the following method:

[0100] S1. Place 1000g (6.49mol) of pentamethylene diisocyanate in a 2L four-necked flask, heat to 90℃ under nitrogen protection, add 2g (0.015mol) of isooctanol to the system, and react for 2h. Then lower the system temperature to 65℃, add 1g of a 10wt% isooctanol solution of 2-hydroxy-N,N,N-trimethyl-1-propylcarbamate, and control the reaction temperature at 70℃; when the reaction conversion rate is 40%, add 0.01g of phosphoric acid to terminate the reaction.

[0101] S2. The reaction solution is separated twice using a thin-film evaporator at a separation temperature of 150℃ and a separation pressure of 10Pa.

[0102] S3. Add 2.9 mg of sodium chloride to obtain polyisocyanate composition D3. The color of polyisocyanate composition D3 was tested to be 22 Hazen, the free monomer content was 0.21%, the viscosity was 7711 mPa·s (25℃), the urethane content was 0.55%, the isocyanurate content was 98.2 wt%, and the mass ratio of urethane to free metal ions was 1990:1.

[0103] Comparative Example 4

[0104] Polyisocyanate composition D4 was prepared according to the following method:

[0105] S1. Place 1000g (6.49mol) of pentamethylene diisocyanate in a 2L four-necked flask, heat to 90℃ under nitrogen protection, add 30g (0.231mol) of isooctanol to the system, and react for 2h. Then lower the system temperature to 65℃, add 1g of a 10wt% isooctanol solution of 2-hydroxy-N,N,N-trimethyl-1-propylcarbamate, and control the reaction temperature at 70℃; when the reaction conversion rate is 40%, add 0.01g of phosphoric acid to terminate the reaction.

[0106] S2. The reaction solution is separated twice using a thin-film evaporator at a separation temperature of 150℃ and a separation pressure of 10Pa.

[0107] S3. Add 45 mg of sodium chloride to obtain polyisocyanate composition D4. The color of polyisocyanate composition D4 was tested to be 20 Hazen, the free monomer content was 0.20%, the viscosity was 6721 mPa·s (25℃), the content of urea carbamate was 8.90 wt%, the content of isocyanurate was 87.9 wt%, and the mass ratio of urea carbamate to free metal ions was 2077:1.

[0108] Comparative Example 5

[0109] Polyisocyanate composition D5 was prepared according to the following method:

[0110] S1. Place 1000g (6.49mol) of pentamethylene diisocyanate in a 2L four-necked flask, heat to 65℃ under nitrogen protection, add 0.1g of a 10wt% butyl acetate solution of 2-hydroxy-N,N,N-trimethyl-1-propylcarbamate to the system, and control the reaction temperature at 70℃; when the reaction conversion rate is 40%, add 0.01g of phosphoric acid to terminate the reaction;

[0111] S2. The reaction solution is separated twice using a thin-film evaporator at a separation temperature of 150℃ and a separation pressure of 10Pa.

[0112] S3. Add 2.9 mg of sodium chloride to obtain polyisocyanate composition D5. The color of polyisocyanate composition D5 was tested to be 22 Hazen, the free monomer content was 0.21%, the viscosity was 7723 mPa·s (25℃), and no urethane was detected. The content of isocyanurate was 98.2 wt%.

[0113] Storage stability tests were conducted on the polyisocyanate compositions provided in each embodiment and comparative example, and the results are shown in Table 1.

[0114] Table 1. Storage stability test results

[0115]

[0116]

Application Example

[0117] An acrylic polyol (manufactured by Nuplex Resin, "SETALUX1753" (trade name), resin concentration 70 wt%, hydroxyl value 138.6 mg KOH / g) was compounded with a polyisocyanate composition at a molar ratio of isocyanate group to hydroxyl group of 1.10. The mixture was then adjusted with butyl acetate to achieve a solids content of 50 wt%, resulting in a coating composition.

[0118] The coating is applied to a clean tinplate using an electrostatic spray gun, and then heat-treated at 80°C for 60 minutes to cure the coating composition and obtain the coating film.

[0119] Surface defect tests and solvent resistance tests were performed on the coatings prepared by the polyisocyanate compositions in each embodiment and comparative example. The results are shown in Table 2.

[0120] Table 2. Performance Evaluation Results of the Coating Film

[0121] Surface defects / number Solvent resistance / number of times Example 1 0 99 Example 2 0 95 Example 3 2 100 Example 4 0 95 Example 5 2 97 Example 6 1 98 Example 7 2 102 Comparative Example 1 0 95 Comparative Example 2 6 97 Comparative Example 3 7 105 Comparative Example 4 2 35 Comparative Example 5 9 110

[0122] 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 polyisocyanate composition, characterized in that, It is prepared by trimerization of aliphatic diisocyanate; the content of urethane in the composition is 1-4 wt%, and the mass ratio of urethane to free metal ions is (200-4000):1; The composition contains 85-99 wt% isocyanurate.

2. The polyisocyanate composition according to claim 1, characterized in that, The mass ratio of urea ester to free metal ions is (500-2000):

1.

3. The polyisocyanate composition according to claim 1, characterized in that, The aliphatic diisocyanate is selected from one or more of tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate.

4. The polyisocyanate composition according to any one of claims 1-3, characterized in that, The free metal ions are selected from one or more of the following metals: potassium, calcium, sodium, aluminum, iron, magnesium, tin, bismuth, and zinc.

5. The polyisocyanate composition according to any one of claims 1-3, characterized in that, The composition also contains one or more of urea diketone, carbamate, iminooxadiazine diketone, biuret, and urea ketimine.

6. A method for preparing the polyisocyanate composition according to any one of claims 1-5, characterized in that, Includes the following steps: Method 1 S1. Using aliphatic diisocyanate as raw material, esterification modification is carried out in the presence of monohydric alcohol and metal carboxylate catalysts. After the reaction, a trimerization catalyst is added to continue the reaction until the target conversion rate is reached and the reaction is terminated. S2. Remove the free diisocyanate monomer from the reaction solution, optionally add a metal ion compound, mix well to obtain a polyisocyanate composition; Method 2 S1. Using aliphatic diisocyanate as raw material, esterification modification is carried out in the presence of monohydric alcohol and optionally metal carboxylate catalyst. After the reaction, a trimerization catalyst is added to continue the reaction until the target conversion rate is reached and the reaction is terminated. S2, Remove free diisocyanate monomers from the reaction solution; S3. Add a metal ion compound and mix thoroughly to obtain the polyisocyanate composition.

7. The method for preparing the polyisocyanate composition according to claim 6, characterized in that, The monohydric alcohol is a saturated fatty alcohol with 4-10 carbon atoms.

8. The method for preparing the polyisocyanate composition according to claim 7, characterized in that, The monohydric alcohol is one or more of isooctyl alcohol, n-hexanol, n-butanol, and n-octanol.

9. The method for preparing the polyisocyanate composition according to claim 7, characterized in that, The amount of the monohydric alcohol added is 0.5-2% of the molar amount of the aliphatic diisocyanate.

10. The method for preparing the polyisocyanate composition according to claim 7, characterized in that, The metal carboxylate catalyst is selected from one or more of zinc isooctanoate, bismuth isooctanoate, and potassium acetate.

11. The method for preparing the polyisocyanate composition according to claim 10, characterized in that, The amount of the metal carboxylate catalyst added is based on 50-300 ppm of isocyanate mass.

12. The method for preparing the polyisocyanate composition according to claim 7, characterized in that, The reaction temperature for esterification modification is 80-140℃, and the reaction time is 0.5-4h.

13. The method for preparing the polyisocyanate composition according to claim 7, characterized in that, The trimerizing catalyst is selected from one or more of quaternary ammonium salts and quaternary ammonium bases.

14. The method for preparing the polyisocyanate composition according to claim 13, characterized in that, The trimer catalyst is selected from one or more of tetramethylammonium acetate, tetramethylammonium octanoate, and N,N,N-trimethylbenzylammonium hydroxide.

15. The method for preparing the polyisocyanate composition according to claim 13, characterized in that, The trimerizing catalyst is selected from those used in amounts ranging from 20 to 500 ppm of the mass of the aliphatic diisocyanate.

16. The method for preparing the polyisocyanate composition according to claim 13, characterized in that, The trimerizing catalyst is selected from the reaction that continues at 40-80°C after the addition of the trimerizing catalyst until the target conversion rate is 20-50%, at which point the reaction is terminated.

17. The method for preparing the polyisocyanate composition according to any one of claims 6-16, characterized in that, The metal ion compound is selected from the chlorides and / or carboxylates of at least one of the following metals: potassium, calcium, sodium, aluminum, iron, magnesium, tin, bismuth, and zinc.

18. The use of a polyisocyanate composition as described in any one of claims 1-5 or a polyisocyanate composition prepared by the method described in any one of claims 6-17 as a curing agent to prepare a coating composition by an electrostatic spraying process.

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