A blocked polyisocyanate composition and preparation method thereof

Abstract

The present invention discloses a blocked polyisocyanate composition and a preparation method thereof, the method comprising: reacting polyisocyanate with water, then adding a pyrazole compound as a blocking agent to react, and obtaining the blocked polyisocyanate composition. In the present invention, urea groups (I) are introduced by reacting polyisocyanate with water, and the proportion of urea groups (I) in the polyisocyanate can be adjusted, thereby effectively improving the appearance performance of the paint film when the blocked polyisocyanate composition is used.

Description

Technical Field

[0001] The invention relates to the technical field of isocyanate preparation, and in particular to a blocked polyisocyanate composition and a preparation method thereof. Background Art

[0002] Blocked isocyanate is produced by the reaction of isocyanate and blocking agent. The chemical bond formed by the blocking agent and the isocyanate group is relatively weak, and free isocyanate groups can be released under certain conditions. It is widely used in one-component polyurethane coatings, especially suitable for automotive coatings and coil coatings.

[0003] Patent US4976837 introduces pyrazole compounds as blocking agents, which can reduce the curing temperature of blocked isocyanates. However, sometimes the surface of the coating formed by using it as a curing agent will produce bumps and depressions that can be clearly distinguished by the naked eye, which significantly reduces the appearance of the coating. Patent EP222634 discloses a method for preparing a pyrazole-blocked isocyanate composition by modifying polyisocyanates with polyols, which can alleviate the appearance problem of the paint film to a certain extent, but there are problems such as large molecular weight and increased viscosity, and more dilution solvents need to be consumed during use. Summary of the invention

[0004] In view of this, the main purpose of the present invention is to provide a blocked polyisocyanate composition and a preparation method thereof which can significantly improve the appearance of the paint film.

[0005] To achieve the above-mentioned purpose, the first aspect of the present invention provides a method for preparing a blocked polyisocyanate composition, comprising the following steps: reacting a polyisocyanate with water, and then adding a pyrazole compound as a blocking agent to react to obtain the blocked polyisocyanate composition.

[0006] In a preferred embodiment, the polyisocyanate is obtained by polymerizing one or more diisocyanate monomers selected from aliphatic diisocyanate, alicyclic diisocyanate.

[0007] Preferably, the diisocyanate monomer is selected from one or more of 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-diisocyanatodicyclohexylmethane, methylcyclohexyl diisocyanate and di(isocyanatomethyl)cyclohexane, and hexamethylene diisocyanate is more preferred.

[0008] In a preferred embodiment, the method for preparing the polyisocyanate comprises: in the presence of an excess of diisocyanate monomers, an isocyanurate reaction to form an isocyanurate group derived from an isocyanate group, a uretdione reaction to form a uretdione group, and an allophanate reaction to form an allophanate group, and after the reaction is completed, removing the unreacted diisocyanate monomers.

[0009] Herein, the isocyanurate reaction, uretdione reaction and allophanate reaction can be carried out in the same reaction system to simultaneously obtain a polyisocyanate containing an isocyanurate group (II), a uretdione group (III) and an allophanate group (IV); the above three reactions can also be carried out separately in respective reaction systems to respectively obtain an isocyanurate group (II), a uretdione group (III) and an allophanate group (IV), and the polyisocyanate can be obtained by mixing them.

[0010] It is understood that when preparing polyisocyanates containing isocyanurate groups (II) from diisocyanate monomers, an isocyanurate reaction catalyst can be used, which is not particularly limited. Usually, a catalyst with alkalinity is selected, such as one or more of quaternary ammonium salts and quaternary phosphonium salts, and a preferred catalyst is one or more of tetrabutylammonium fluoride, benzyltrimethylammonium fluoride, tetramethylammonium acetate, and benzylammonium hydroxide. When the reaction reaches the desired polymerization degree, a catalyst poison is added to terminate the reaction, such as phosphoric acid, acid phosphate, etc.

[0011] It is understood that when preparing polyisocyanates containing uretdione groups (III) from diisocyanate monomers, a uretdione reaction catalyst may be used, which is not particularly limited, for example, one or more selected from trialkylphosphines such as tri-n-butylphosphine and tri-n-octylphosphine, or one or more selected from tri(dialkylamino)phosphines such as tri-(dimethylamino)phosphine, or one or more selected from cycloalkylphosphines such as cyclohexyl-di-n-hexylphosphine. When the reaction reaches the desired polymerization degree, a catalyst poison is added to terminate the reaction, for example, a deactivator of a uretdione reaction catalyst such as phosphoric acid or methyl p-toluenesulfonate is added to stop the uretdione reaction.

[0012] It is understood that when preparing polyisocyanates containing allophanate groups (IV) from diisocyanate monomers, an allophanate reaction catalyst can be used, which is not particularly limited, and can be selected from one or more of alkyl carboxylates of tin, lead, zinc, bismuth, zirconium, zirconium oxide, etc., or one or more of organic tin compounds such as 2-ethylhexanoic acid tin and dibutyltin dilaurate, or one or more of organic lead compounds such as 2-ethylhexanoic acid lead, or one or more of organic zinc compounds such as 2-ethylhexanoic acid zinc, or one or more of 2-ethylhexanoic acid bismuth, 2-ethylhexanoic acid zirconium, 2-ethylhexanoic acid zirconium oxide. When the polymerization reaches a certain degree, a catalyst poison is added to terminate the polymerization reaction, such as phosphoric acid, acid phosphate, etc.

[0013] As the alcohol that can be used to form the allophanate group (IV), preferably, a monohydric alcohol or a dihydric alcohol, for example, one or more of methanol, ethanol, propanol, butanol, ethylene glycol, 1,3-butanediol, neopentyl glycol and the like is used.

[0014] In a preferred embodiment, the polyisocyanate is reacted with water to form urea groups (I). By adjusting the amount of water, the content ratio of urea groups (I) in the polyisocyanate can be adjusted. For example, in a specific embodiment, the amount of water is controlled between 0.05-0.3% calculated based on the mass of the polyisocyanate.

[0015] Herein, the structural formulas of the urea group (I), the isocyanurate group (II), the uretdione group (III) and the allophanate group (IV) are as follows:

[0016]

[0017] Herein, A represents the content (mol %) of urea group (I), B represents the content (mol %) of isocyanurate group (II), C represents the content (mol %) of uretdione group (III), and D represents the content (mol %) of allophanate group (IV). Preferably, A / (A+B+C+D)=0.001-0.05. If this value is greater than 0.05, the viscosity of the composition increases significantly, and there is a possibility of solid precipitation. If this value is less than 0.001, there is no obvious improvement on the blocked isocyanate paint film.

[0018] Further preferably, (C+D) / (A+B+C+D)=0.005-0.1. If the value is higher than 0.1, the mechanical properties of the paint film will be affected. If the value is lower than 0.005, the appearance of the paint film will be affected.

[0019] In a preferred embodiment, the reaction temperature of polyisocyanate and water is 50-110°C. Below 50°C, water and isocyanate react slowly, while above 110°C, urea group (I) is easy to further react to form biuret group.

[0020] In a preferred embodiment, the pyrazole compound is selected from one or more of pyrazole, 3,5-dimethylpyrazole and 3-methylpyrazole.

[0021] In a preferred embodiment, the temperature of the blocking reaction of the pyrazole compound as a blocking agent is 30-120° C., preferably 50-80° C. Within this range, the color of the product can be lower.

[0022] It is understandable that the blocking reaction can be carried out with or without a solvent, which is mainly determined by the viscosity of the product. Generally, a solvent is added to adjust the viscosity of the product. The available solvents are common paint solvents that do not react with isocyanate, such as ethyl acetate, butyl acetate, 1-methoxy-2-propyl acetate, 3-methoxyacetic acid n-butyl ester, acetone, butanone, 4-methyl-2-pentanone, cyclohexanone, toluene, xylene, S100 solvent oil, etc. It can be a single solvent or a mixture of more than one solvent, preferably one or more of butyl acetate, 1-methoxy-2-propyl acetate, and S100 aromatic solvent oil.

[0023] In a preferred embodiment, the amount of 3,5-dimethylpyrazole used is 95-110 equivalents, preferably 99-105 equivalents, relative to the isocyanate groups of the polyisocyanate. Within this range, the free NCO group content can be less than 0.1%.

[0024] In a preferred embodiment, the method further comprises: removing free diisocyanate so that the free diisocyanate monomer content of the polyisocyanate is less than 0.5%, preferably less than 0.2%. For example, thin film evaporation treatment may be used.

[0025] It is understandable that antioxidants such as hindered phenols, hindered amines, phosphites, etc. may be added to the preparation method of the blocked polyisocyanate composition to improve the storage stability of the product.

[0026] The second aspect of the present invention provides a blocked polyisocyanate composition, which comprises a urea group (I), an isocyanurate group (II), a uretdione group (III) and an allophanate group (IV), and their molar percentages in the composition are: A / (A+B+C+D)=0.001-0.05;

[0027] Herein, A represents the content (mol %) of urea groups (I), B represents the content (mol %) of isocyanurate groups (II), C represents the content (mol %) of uretdione groups (III), and D represents the content (mol %) of allophanate groups (IV).

[0028] In a preferred embodiment, (C+D) / (A+B+C+D)=0.005-0.1.

[0029] The third aspect of the present invention provides a blocked polyisocyanate composition prepared by the above method.

[0030] The fourth aspect of the present invention provides the use of the blocked polyisocyanate composition or the blocked polyisocyanate composition prepared by the preparation method in a one-component polyurethane coating or adhesive.

[0031] Preferably, the one-component polyurethane coating is an automotive coating or a coil coating.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] When a blocked polyisocyanate composition is mixed with an active hydrogen component to form a one-component coating, if the coating is uneven along the depth direction during curing, the appearance of the coating film may be reduced; especially when some solid substances are used as sealants, the cured sealants with medium and high boiling points cannot completely escape from the paint film, which can easily cause unevenness of the paint film. The inventors of the present application found during the experiment that designing a blocked polyisocyanate containing a specific structure and a preferred content has a significant effect on the appearance performance of the paint film; the polyisocyanate of the present invention comprises an isocyanurate group (II), a uretdione group (III) and an allophanate group (IV). The present invention introduces a urea group (I) into the above-mentioned polyisocyanate by reacting with water, and then reacts with a blocking agent to prepare a blocked polyisocyanate. By controlling the amount of water, the content ratio of the urea group (I) in the polyisocyanate can be adjusted, for example, the molar content of the urea group (I) accounts for 0.001-0.05 of the total molar content of the urea group (I), isocyanurate group (II), uretdione group (III) and allophanate group (IV), thereby effectively improving the appearance performance of the paint film formed by the blocked polyisocyanate composition.

[0034] Other features and advantages of the present invention will be described in detail through the following detailed description. DETAILED DESCRIPTION

[0035] The present application is further described below in conjunction with embodiments, but the present application is not limited to the listed embodiments, but also includes equivalent improvements and modifications of the technical solutions defined in the claims attached to the present application.

[0036] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0037] Certain specific steps involved in the experimental methods used in the following examples are routine operations unless otherwise specified.

[0038] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0039] Main raw material sources:

[0040] Wannate HT-100 (mainly contains isocyanurate, NCO content 22.0%), Wanhua Chemical;

[0041] Wannate HT-300 (mainly contains allophanate, NCO content 20.0%), Wanhua Chemical;

[0042] Wannate HT-400 (mainly containing uretdione, NCO content 22.0%), Wanhua Chemical;

[0043] No. 100 aromatic solvent oil, Mobil Petroleum;

[0044] 3,5-Dimethylpyrazole, Wacker Chemicals;

[0045] Propylene glycol methyl ether acetate, Jiangsu Hualun Chemical Co., Ltd.

[0046] Butyl acetate, Jin Yimeng

[0047] The following test method is used in the embodiments of the present invention:

[0048] (1) Calculation of group molar ratio

[0049] The test was conducted by 13C-NMR nuclear magnetic resonance method. The instrument used was a Bruker 400MHz instrument, the sample concentration was 50% by mass (CDCl3 solution), and the test condition was 100MHz. The integral value of the following signal was divided by the measured carbon number, and each molar ratio was calculated from this value.

[0050] Urea group molar amount (mol%, represented by "A"): around 155.6 ppm: integrated value ÷ 1

[0051] Molar amount of isocyanurate group (mol%, represented by "B"): around 148.6 ppm: integrated value ÷ 3

[0052] Molar amount of uretdione group (mol%, represented by "C"): around 157.5 ppm: integrated value ÷ 2

[0053] Molar amount of allophanate group (mol%, represented by "D"): around 154 ppm: integrated value ÷ 1

[0054] (2) Appearance of paint film: The cured coating film was tested using Zigo's Newview 7300 to measure the difference between the maximum peak and the minimum peak.

[0055] Example 1

[0056] In a four-necked flask equipped with a stirrer and a thermometer, add 100g Wannate HT-100, 3g Wannate HT-300, 3g Wannate HT-400, and 54g No. 100 aromatic solvent oil, protect with nitrogen, mix evenly, heat to 90°C, add 0.2g water, stir and react for 3 hours, then cool to 50°C, add 54g 3,5-dimethylpyrazole, and react until the characteristic absorption peak of NCO is no longer detected by infrared spectrum.

[0057] Example 2

[0058] In a four-necked flask equipped with a stirrer and a thermometer, add 100g Wannate HT-100, 3g Wannate HT-300, 3g Wannate HT-400, and 54g No. 100 aromatic solvent oil, protect with nitrogen, mix evenly, heat to 110°C, add 0.25g water, stir and react for 3 hours, then cool to 60°C, add 46.5g 3-methylpyrazole, and react until the characteristic absorption peak of NCO is no longer detected by infrared spectrum.

[0059] Example 3

[0060] In a four-necked flask equipped with a stirrer and a thermometer, add 100 g of Wannate HT-100, 2 g of Wannate HT-300, 1 g of Wannate HT-400, and 47 g of No. 100 aromatic solvent oil, protect with nitrogen, mix evenly, heat to 50°C, add 0.1 g of water, stir and react for 3 hours, then raise the temperature to 80°C, add 38.5 g of pyrazole, and react until the characteristic absorption peak of NCO is no longer detected by infrared spectrum.

[0061] Example 4

[0062] In a four-necked flask equipped with a stirrer and a thermometer, 100 g of Wannate HT-100, 34 g of No. 100 aromatic solvent oil and 16 g of propylene glycol methyl ether acetate were added. The mixture was uniformly mixed under nitrogen protection, and heated to 90°C. 0.05 g of water was added, and the mixture was stirred for reaction for 3 hours. The temperature was then lowered to 60°C, and 51 g of 3,5-dimethylpyrazole was added. The mixture was reacted until no characteristic absorption peak of NCO was detected by infrared spectrum.

[0063] Example 5

[0064] In a four-necked flask equipped with a stirrer and a thermometer, add 100g Wannate HT-100, 2g Wannate HT-300, 1g Wannate HT-400, and 52g No. 100 aromatic solvent oil, protect with nitrogen, mix evenly, heat to 60°C, add 0.3g water, stir and react for 3 hours, then add 52.5g 3,5-dimethylpyrazole, and react until the characteristic absorption peak of NCO is no longer detected by infrared spectrum.

[0065] Example 6

[0066] In a four-necked flask equipped with a stirrer and a thermometer, add 100g Wannate HT-100, 1g Wannate HT-300, and 51g No. 100 aromatic solvent oil, protect with nitrogen, mix evenly, heat to 90°C, add 0.2g water, stir and react for 3 hours, cool to 60°C, then add 51.5g 3,5-dimethylpyrazole, and react until the characteristic absorption peak of NCO is no longer detected by infrared spectrum.

[0067] Example 7

[0068] In a four-necked flask equipped with a stirrer and a thermometer, add 100g Wannate HT-100, 6g Wannate HT-300, 6g Wannate HT-400, and 51g No. 100 aromatic solvent oil, protect with nitrogen, mix evenly, heat to 90°C, add 0.2g water, stir and react for 3 hours, cool to 60°C, then add 57g 3,5-dimethylpyrazole, and react until the characteristic absorption peak of NCO is no longer detected by infrared spectrum.

[0069] Comparative Example 1

[0070] In a four-necked flask equipped with a stirrer and a thermometer, add 100g Wannate HT-100, 3g Wannate HT-300, 3g Wannate HT-400, and 54g No. 100 aromatic solvent oil, protect with nitrogen, mix evenly, heat to 60°C, stir and react for 3 hours, then add 54g 3,5-dimethylpyrazole, and react until the characteristic absorption peak of NCO is no longer detected by infrared spectrum.

[0071] Comparative Example 2

[0072] In a four-necked flask equipped with a stirrer and a thermometer, add 100 g of Wannate HT-100, 1 g of Wannate HT-300, and 51 g of No. 100 aromatic solvent oil, protect with nitrogen, mix evenly, heat to 90°C, stir and react for 3 hours, then cool to 60°C, add 51.5 g of 3,5-dimethylpyrazole, and react until the characteristic absorption peak of NCO is no longer detected by infrared spectrum.

[0073] Comparative Example 3

[0074] In a four-necked flask equipped with a stirrer and a thermometer, add 100g Wannate HT-100, 1g Wannate HT-300, 1g Wannate HT-400, and 52g of No. 100 aromatic solvent oil, protect with nitrogen, mix evenly, heat to 90°C, then add 0.02g of water, stir and react for 3 hours, then cool to 60°C, add 52.5g of 3,5-dimethylpyrazole, and react until the characteristic absorption peak of NCO is no longer detected by infrared spectrum.

[0075] Comparative Example 4

[0076] In a four-necked flask equipped with a stirrer and a thermometer, add 100g Wannate HT-100, 1g Wannate HT-300, 1g Wannate HT-400, and 52g of No. 100 aromatic solvent oil, protect with nitrogen, mix evenly, heat to 90°C, then add 0.4g water, stir and react for 3 hours, then cool to 60°C, add 52.5g of 3,5-dimethylpyrazole, and react until the characteristic absorption peak of NCO is no longer detected by infrared spectrum.

[0077] A varnish was prepared based on the blocked polyisocyanate and polyacrylic polyol (Desmophen A870) prepared in Examples 1-7 and Comparative Examples 1-4, with NCO / OH=1.05 and a solid content of 50% (the dilution solvent was butyl acetate), and 0.5% (calculated based on the solid content of the varnish) of dibutyltin dilaurate was added to the coating.

[0078] The prepared varnish was sprayed on clean tinplate and baked at 140°C for 30 minutes to obtain a 30-40 μm paint film, and then a white interferometer was used to test the maximum peak and minimum peak difference of the paint film. The test results are shown in the following table.

[0079]

[0080]

[0081] As can be seen from the table above, the paint films prepared using the blocked isocyanates prepared in Examples 1 to 7 as raw materials have significantly better appearance smoothness than the paint films prepared using the blocked isocyanates prepared in Comparative Examples 1 to 4. The blocked polyisocyanates prepared in the present invention have better paint film appearance.

[0082] Obviously, the above embodiments of the present invention are merely examples for clearly explaining the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are within the spirit scope of the present invention.

Claims

1. A method for preparing a blocked polyisocyanate composition, characterized in that: The method comprises the following steps: reacting polyisocyanate with water, and then adding a pyrazole compound as a blocking agent to react to obtain the blocked polyisocyanate composition; The polyisocyanate comprises an isocyanurate group (II), a uretdione group (III) and an allophanate group (IV), and the amount of water used accounts for 0.05-0.3% of the mass of the polyisocyanate; the pyrazole compound is selected from one or more of pyrazole, 3,5-dimethylpyrazole and 3-methylpyrazole.

2. The method for preparing a blocked polyisocyanate composition according to claim 1, characterized in that: The polyisocyanate is obtained by polymerizing one or more diisocyanate monomers selected from aliphatic diisocyanate, alicyclic diisocyanate; The diisocyanate monomer is selected from one or more of 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-diisocyanatodicyclohexylmethane, methylcyclohexyl diisocyanate and di(isocyanatomethyl)cyclohexane.

3. The method for preparing a blocked polyisocyanate composition according to claim 2, characterized in that: The diisocyanate monomer is hexamethylene diisocyanate.

4. The method for preparing a blocked polyisocyanate composition according to claim 1 or 2, characterized in that: The preparation method of the polyisocyanate comprises: in the presence of an excess of diisocyanate monomers, an isocyanurate reaction to form isocyanurate groups derived from isocyanate groups, a uretdione reaction to form uretdione groups, and an allophanate reaction to form allophanate groups, and after the reaction is completed, removing unreacted diisocyanate monomers.

5. The method for preparing the blocked polyisocyanate composition according to claim 1, characterized in that: The reaction temperature of the polyisocyanate and water is 50-110°C.

6. The method for preparing the blocked polyisocyanate composition according to claim 1, characterized in that: The temperature for the blocking reaction of the pyrazole compound as a blocking agent is 30-120°C.

7. The method for preparing the blocked polyisocyanate composition according to claim 6, characterized in that: The temperature for the blocking reaction of the pyrazole compound as a blocking agent is 50-80°C.

8. The method for preparing the blocked polyisocyanate composition according to claim 4, characterized in that: Unreacted diisocyanate monomers are removed so that the free diisocyanate content in the polyisocyanate is less than 0.5%.

9. The method for preparing the blocked polyisocyanate composition according to claim 8, characterized in that: Unreacted diisocyanate monomers are removed so that the free diisocyanate content in the polyisocyanate is less than 0.2%.

10. A blocked polyisocyanate composition, characterized in that: The composition comprises urea groups (I), isocyanurate groups (II), uretdione groups (III) and allophanate groups (IV), and their molar percentages in the composition are: A / (A+B+C+D)=0.001-0.05; Wherein, A represents the molar percentage of urea group (I), B represents the molar percentage of isocyanurate group (II), C represents the molar percentage of uretdione group (III), and D represents the molar percentage of allophanate group (IV).

11. The blocked polyisocyanate composition according to claim 10, characterized in that: (C+D) / (A+B+C+D)=0.005-0.

1.

12. A blocked polyisocyanate composition prepared by the method of any one of claims 1 to 9.

13. Use of the blocked polyisocyanate composition prepared by the method according to any one of claims 1 to 9 or the blocked polyisocyanate composition according to claims 10 to 11 in a one-component polyurethane coating or adhesive.

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