Encapsulated polyisocyanates, process for their preparation and use thereof
By continuously mixing malonate diesters and alkaline catalysts in a mixing device and continuously adding them to the reaction system, the problem of low transparency of blocked polyisocyanates was solved, and the preparation of high-transparency blocked polyisocyanates was achieved, thus improving the appearance of the coating film.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WANHUA CHEM GRP CO LTD
- Filing Date
- 2024-12-18
- Publication Date
- 2026-05-19
AI Technical Summary
Malonate-based compounds that block polyisocyanates have low transmittance, which affects the appearance of the coating film in downstream coatings.
By continuously mixing malondiester compounds and an alkaline catalyst in a mixing device and continuously adding them to the reaction system, a blocked polyisocyanate is prepared, avoiding the formation of turbidity and impurities and improving transparency.
The prepared closed-type polyisocyanate product has low turbidity and high transparency, which improves the appearance of the paint film when applied to single-component coatings.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of isocyanates, specifically relating to a blocked polyisocyanate, its preparation method, and its application. Background Technology
[0002] Blocked isocyanates are products formed by the reaction of isocyanates with blocking agents. They are widely used in one-component polyurethane coatings, especially suitable for automotive coatings and coil coatings.
[0003] Commonly used oxime blockers, phenolic blockers, alcohol blockers, and lactam blockers typically require a curing temperature above 140°C when preparing blocked polyisocyanates, resulting in high energy consumption and costs, and limiting their use on plastic substrates with low heat resistance.
[0004] Malonate diesters, as isocyanate sealants, can effectively lower the curing temperature, even achieving low-temperature curing below 100°C. However, the resulting sealed isocyanates suffer from low transparency, which in turn affects downstream coating applications, particularly the appearance of the paint film.
[0005] Therefore, there is an urgent need in the field to develop a method for preparing a polyisocyanate composition blocked by a high-transmittance malondiester compound. Summary of the Invention
[0006] The purpose of this invention is to address the problem of low transparency in blocked polyisocyanates obtained by using malondiacrylate compounds as blocking agents, and to provide a method for preparing blocked polyisocyanates. By controlling the feeding method of some raw materials, the resulting blocked polyisocyanates have the advantage of high transparency, which can improve the appearance of the paint film when applied to downstream coatings.
[0007] To achieve the above objectives, the present invention provides the following technical solution:
[0008] In the first aspect, a method for preparing a blocked polyisocyanate is provided, comprising the following steps:
[0009] In a reaction apparatus, polyisocyanate and other blocking agent components from the blocking agent composition are first added. Then, malondiacrylate compounds and a basic catalyst from the blocking agent composition are continuously mixed through a mixing device (e.g., a pipe mixer) and continuously added to the reaction system. After the reaction is complete, the blocked polyisocyanate is obtained.
[0010] The sealing agent composition includes malonate compounds and other sealing agent components.
[0011] According to the preparation method provided by the present invention, in some embodiments, the polyisocyanate is selected from self-polymerized products with diisocyanate as monomer, and isocyanates modified by reaction of diisocyanate and polyol.
[0012] The diisocyanate is one or more aliphatic and / or alicyclic diisocyanates containing 4-30 carbon atoms in addition to the NCO group in its carbon skeleton. The diisocyanate may be selected, for example, but not limited to, one or more selected from, but not limited to, 1,4-butane diisocyanate, 1,5-pentane diisocyanate, 2,2,4-trimethyl-hexamethylene-1,6-diisocyanate, lysine diisocyanate, isophorone diisocyanate, 1,6-hexamethylene diisocyanate (HDI), 1,3-bis(isocyanate methyl)cyclohexane, and 4,4'-dicyclohexylmethane diisocyanate, preferably 1,6-hexamethylene diisocyanate (HDI).
[0013] The polyol may be glycerol, trimethylolpropane, pentaerythritol, polyester polyols, polyether polyols, acrylic polyols, polyolefin polyols, etc.
[0014] In some embodiments, the polyisocyanate comprises one or more of the following structures: isocyanurate, urea diketone, biuret, carbamate, urethane, iminooxadiazine diketone, and carbodiimide, preferably isocyanurate and biuret structures.
[0015] The polyisocyanate has an NCO functionality ≥ 2.5 (e.g., 3, 4, 5, 6, 7, 8, 9, 10), typically with an NCO functionality ≤ 10, and the isocyanate group content is 5-40 wt% (calculated without solvent), for example, 10 wt%, 15 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, 30 wt%, 35 wt%.
[0016] In some embodiments, the alkaline catalyst is a metal alkoxide, preferably selected from one or more of sodium methoxide, sodium ethoxide, sodium phenolate and potassium methoxide, more preferably sodium methoxide.
[0017] In some embodiments, the amount of the alkaline catalyst is 0.01 wt% to 5 wt% of the mass of the polyisocyanate (e.g., 0.02 wt%, 0.04 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 4.0 wt%, 4.5 wt%).
[0018] In some embodiments, the malondiester compound is selected from one or more of dimethyl malonate, diethyl malonate, di-n-propyl malonate, diisopropyl malonate, di-n-butyl malonate, diisobutyl malonate, and di-tert-butyl malonate, preferably diethyl malonate.
[0019] In some embodiments, the other type of blocking agent is selected from one or more of ethyl acetoacetate, methyl acetoacetate, butyl acetoacetate, diisopropylamine, 3,5-dimethylpyrazole, butanone oxime, caprolactam, methanol, ethanol, isobutanol, and isoamyl alcohol, preferably selected from diisopropylamine and / or ethyl acetoacetate.
[0020] In some embodiments, the molar amount of malondiester compounds in the blocking composition is 30-90% of the total molar amount of the blocking composition (e.g., 32%, 35%, 40%, 45%, 50%, 60%, 70%, 80%, 85%), and the molar amount of other types of blocking agents is 10-70% of the total molar amount of the blocking composition (e.g., 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%).
[0021] In some embodiments, the amount of the blocking agent composition relative to the isocyanate group of the polyisocyanate is 0.90-1.3 (e.g., 0.92, 0.94, 0.95, 0.96, 0.98, 1.0, 1.15, 1.2) molar equivalents, preferably 0.95-1.1 molar equivalents.
[0022] In some implementations, the polyisocyanate reacts with the blocking agent composition under solvent or solvent-free conditions. Whether a solvent needs to be added depends primarily on the viscosity of the product; generally, adding a solvent before the reaction can reduce the viscosity of the reaction system.
[0023] In some embodiments, the solvent is selected from one or more of aromatic solvents (such as toluene, xylene, aromatic solvent oil), ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, 3-methoxyethyl acetate, acetone, butanone, 4-methyl-2-pentanone, and cyclohexanone.
[0024] In some embodiments, the amount of solvent added is 10-70 wt% of the mass of the blocked isocyanate (e.g., 12 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 40 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 68 wt%).
[0025] According to the preparation method provided by the present invention, in some embodiments, the reaction temperature of the reaction system is 30-120℃ (e.g., 50℃, 60℃, 70℃, 85℃, 100℃, 110℃), preferably 40-80℃.
[0026] In a second aspect, a closed-type polyisocyanate prepared by the preparation method described above is provided.
[0027] In some embodiments of the closed-cell polyisocyanate provided by the present invention, the turbidity of the closed-cell polyisocyanate is less than or equal to 0.8 NTU, for example, ≤0.6 NTU, ≤0.5 NTU, ≤0.4 NTU, ≤0.3 NTU, ≤0.2 NTU, ≤0.1 NTU.
[0028] Antioxidants may be added during the preparation of the blocked polyisocyanate; or antioxidants may be added to the obtained blocked polyisocyanate. The amount of antioxidant added can be a conventional choice in the art, and will not be elaborated here.
[0029] In some embodiments, the antioxidant may include hindered phenolic antioxidants, hindered amine antioxidants, and phosphite antioxidants.
[0030] In a third aspect, an application is provided of the blocked polyisocyanate prepared by the method described above, or the blocked polyisocyanate as described above.
[0031] In some embodiments of the application provided by the present invention, the blocked polyisocyanate is used to prepare a one-component coating system.
[0032] In this paper, the operational steps and specific formulations for applying the blocked polyisocyanates to single-component coating systems are conventional methods in the field and will not be elaborated here.
[0033] After conducting systematic experimental research on the factors affecting the transparency of polyisocyanate compositions blocked by malondialdehyde (MDA), the inventors surprisingly discovered that the method of adding MDA and alkaline catalyst during the preparation of MDA compositions affects the product's transparency. Further experiments revealed that continuously adding MDA and alkaline catalyst into a mixing device (such as a pipeline mixer) and immediately and continuously adding this mixture to the reaction system significantly improved the transparency of the resulting blocked MDA product and significantly reduced its turbidity.
[0034] Mixing malonate with a basic catalyst is a pre-activation process for the blocking agent, which reduces the catalytic activity of the basic catalyst for the polymerization of NCO groups. Adding malonate and the basic catalyst to the reaction system continuously while mixing them avoids turbidity or the formation of solids after mixing, and also avoids the problem of impurities arising from prolonged mixing.
[0035] Compared with the prior art, the beneficial effects of the technical solution of the present invention are at least as follows: by optimizing the addition method of malondiester compounds and alkaline catalysts, the resulting blocked polyisocyanate product can have low turbidity and high transparency; in addition, the improved process of the present invention is simple to operate, the raw materials are readily available, and it is easy to industrialize. Detailed Implementation
[0036] To provide a detailed understanding of the technical features and content of this invention, preferred embodiments will be described in more detail below. While preferred embodiments are described in the examples, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply.
[0037] Main raw material sources:
[0038] Wannate HT-100 (HDI trimer, NCO content 22.0 wt%), Wanhua Chemical;
[0039] Wannate HB-100 (HDI biuret, NCO content 22.0wt%), Wanhua Chemical;
[0040] Diethyl malonate, Aladdin reagent;
[0041] Diisopropyl malonate, Aladdin reagent;
[0042] Ethyl acetoacetate, Aladdin reagent;
[0043] Diisopropylamine, Zhejiang Xinhua Chemical Co., Ltd.;
[0044] A methanol solution containing 30 wt% sodium methoxide, Aladdin's reagent;
[0045] Propylene glycol methyl ether acetate, Jiangsu Hualun Chemical Co., Ltd.;
[0046] Butyl acetate, Jin Yimeng Group.
[0047] Example 1
[0048] The preparation process of blocked polyisocyanates is as follows:
[0049] A nitrogen atmosphere was created in a four-necked flask equipped with a stirrer, thermometer, reflux cooling pipe, and nitrogen inlet pipe. 200g of Wannate HT-100 polyisocyanate and 148g of propylene glycol methyl ether acetate were added to the flask and mixed thoroughly. The mixture was heated to 40°C, and 53g of diisopropylamine was added, maintaining the temperature between 40-50°C. After the addition was complete, the system temperature was raised to 60°C. Then, 92g of diethyl malonate was pumped into a tubular mixer at a flow rate of 1.5g / min using a peristaltic pump. Simultaneously, 1.2g of a methanol solution containing 30wt% sodium methoxide was pumped into the tubular mixer at a flow rate of 0.02g / min using a peristaltic pump. These two streams were mixed in the tubular mixer and immediately and continuously added to the reaction system to begin the closed reaction of diethyl malonate. After the materials were completely added, the temperature was maintained at 60°C, and the reaction was allowed to proceed for 24 hours. The NCO content in the system was measured to be below 0.2wt%, indicating the reaction was complete, yielding a closed polyisocyanate.
[0050] Example 2
[0051] The preparation process of blocked polyisocyanates is as follows:
[0052] A nitrogen atmosphere was created in a four-necked flask equipped with a stirrer, thermometer, reflux cooling pipe, and nitrogen inlet pipe. 200g of Wannate HT-100 polyisocyanate, 249g of butyl acetate, and 27g of ethyl acetoacetate were added to the flask and mixed thoroughly. After the addition was complete, the system was heated to 60°C. Then, 147g of diethyl malonate was pumped into a tubular mixer at a flow rate of 1.3g / min using a peristaltic pump, and simultaneously, 2.2g of a methanol solution containing 30wt% sodium methoxide was pumped into the tubular mixer at a flow rate of 0.02g / min using a peristaltic pump. These two streams were mixed in the tubular mixer and immediately and continuously added to the reaction system to begin the closed reaction of diethyl malonate. After the materials were completely added, the temperature was maintained at 60°C, and the reaction was carried out for 24 hours. The NCO content in the system was detected to be below 0.2wt%, indicating the reaction was complete, yielding a closed polyisocyanate.
[0053] Example 3
[0054] The preparation process of blocked polyisocyanates is as follows:
[0055] A nitrogen atmosphere was created in a four-necked flask equipped with a stirrer, thermometer, reflux cooling pipe, and nitrogen inlet pipe. 200g of Wannate HB-100 polyisocyanate, 275g of butyl acetate, and 39g of ethyl acetoacetate were added to the flask and mixed thoroughly. After the addition was complete, the system was heated to 60°C. Then, 173g of diisopropyl malonate was pumped into a tubular mixer at a flow rate of 1.3g / min using a peristaltic pump. Simultaneously, 2.2g of a methanol solution containing 30wt% sodium methoxide was pumped into the tubular mixer at a flow rate of 0.02g / min using a peristaltic pump. These two streams were mixed in the tubular mixer and immediately and continuously added to the reaction system to begin the closed reaction of diisopropyl malonate. After the materials were completely added, the temperature was maintained at 60°C, and the reaction was carried out for 24 hours. The NCO content in the system was measured to be below 0.2wt%, indicating the reaction was complete, yielding a closed polyisocyanate.
[0056] Comparative Example 1
[0057] The preparation process of blocked polyisocyanates is as follows:
[0058] A nitrogen atmosphere was created in a four-necked flask equipped with a stirrer, thermometer, reflux cooling pipe, and nitrogen purge pipe. 200g of Wannate HT-100 polyisocyanate and 148g of propylene glycol methyl ether acetate were added to the flask and mixed thoroughly. The mixture was heated to 40°C, and 53g of diisopropylamine was added, maintaining the temperature between 40-50°C. After the raw materials were added, the system temperature was raised to 60°C. Then, 92g of diethyl malonate and 1.2g of a methanol solution containing 30wt% sodium methoxide were mixed thoroughly, and the mixture was pumped into the reaction system at a flow rate of 1.5g / min using a peristaltic pump. After the raw materials were added, the temperature was maintained at 60°C, and the reaction was carried out for 24 hours. The NCO content in the system was measured to be below 0.2wt%, indicating the reaction was complete, yielding a blocked polyisocyanate.
[0059] Comparative Example 2
[0060] The preparation process of blocked polyisocyanates is as follows:
[0061] A nitrogen atmosphere was created in a four-necked flask equipped with a stirrer, thermometer, reflux cooling pipe, and nitrogen inlet pipe. 200g of Wannate HT-100 polyisocyanate, 249g of butyl acetate, 27g of ethyl acetoacetate, and 147g of diethyl malonate were added to the flask and mixed thoroughly. After the raw materials were added, the system was heated to 60°C to initiate the reaction. Then, 2.2g of a methanol solution containing 30wt% sodium methoxide was added to the system at a flow rate of 0.02g / min using a peristaltic pump. After the addition was complete, the temperature was maintained at 60°C, and the reaction was allowed to proceed for 24 hours. The NCO content in the system was measured to be below 0.2wt%, indicating the reaction was complete, yielding a blocked polyisocyanate.
[0062] Comparative Example 3
[0063] The preparation process of blocked polyisocyanates is as follows:
[0064] A nitrogen atmosphere was created in a four-necked flask equipped with a stirrer, thermometer, reflux cooling pipe, and nitrogen inlet pipe. 200g of Wannate HB-100 polyisocyanate, 275g of butyl acetate, and 39g of ethyl acetoacetate were added to the flask and mixed thoroughly. After the addition was complete, the system was heated to 60°C. Then, 173g of diisopropyl malonate and 2.2g of a methanol solution containing 30wt% sodium methoxide were mixed thoroughly, and the mixture was then pumped into the reaction system at a flow rate of 1.3g / min using a peristaltic pump. After the addition was complete, the temperature was maintained at 60°C, and the reaction was carried out for 24 hours. The NCO content in the system was detected to be below 0.2wt%, indicating the reaction was complete, yielding a blocked polyisocyanate.
[0065] Turbidity tests were performed on the products obtained in each embodiment and comparative example using a Hach 2100N turbidimeter. The data are shown in Table 1 below. The transmittance of the blocked polyisocyanate in this invention is characterized by turbidity; lower turbidity indicates higher product transmittance.
[0066] Table 1. Turbidity test results of closed-type polyisocyanates
[0067]
[0068]
[0069] As shown in Table 1 above, the blocked polyisocyanate products prepared in Examples 1-3 have lower turbidity and higher transparency; while the blocked polyisocyanate products prepared in Comparative Examples 1-3 have higher turbidity and lower transparency. This indicates that in the preparation process, first contacting the polyisocyanate with other types of blocking agents, and then continuously mixing and adding the malondiester compound and alkaline catalyst to the reaction system (i.e., adding to the reaction system while mixing) can improve the transparency of the blocked polyisocyanate.
[0070] In Comparative Example 2, the malondialdehyde ester compound and the alkaline catalyst were not mixed in the preparation process; instead, they were added to the reaction system separately, which affected the improvement of the transparency of the blocked polyisocyanate. In Comparative Examples 1 and 3, although the malondialdehyde ester compound and the alkaline catalyst were mixed, they were not continuously mixed and added to the reaction system, which also failed to effectively improve the transparency of the blocked polyisocyanate.
[0071] Application examples of coatings prepared by blocked polyisocyanates
[0072] Based on the blocked polyisocyanates and acrylic polyols (Tongde Resin AC1100B) prepared in Examples 1-3 and Comparative Examples 1-3, a one-component polyurethane varnish was prepared. The ingredients were formulated according to NCO / OH = 1. The solid content of the varnish was adjusted to 50 wt% using butyl acetate, and 0.1 wt% of dibutyltin dilaurate (based on the total amount of the base ingredients) was added.
[0073] The prepared single-component varnish was sprayed onto a clean glass plate and cured at 100℃ for 60 minutes. The appearance and gloss of the cured varnish film were compared and observed, as shown in Table 2.
[0074] Table 2. Performance tests of coatings prepared from blocked polyisocyanates
[0075]
[0076]
[0077] As can be seen from the test results in Table 2, the blocked polyisocyanates obtained in Examples 1-3 have very low turbidity, and the resulting paint films are smooth and transparent when applied to single-component polyurethane clear varnishes. In contrast, the blocked polyisocyanates prepared in Comparative Examples 1-3 have higher turbidity, and the resulting paint films have poor appearance and low transparency when applied to single-component polyurethane clear varnishes.
[0078] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the spirit of the invention.
Claims
1. A method for preparing a blocked polyisocyanate, characterized in that, Includes the following steps: In the reaction apparatus, the polyisocyanate and other blocking agent components of the blocking agent composition are first added. Then, the malondialdehyde ester compound and the basic catalyst in the blocking agent composition are continuously mixed through a pipe mixer and immediately added to the reaction system. After the reaction is completed, the blocked polyisocyanate is obtained. The alkaline catalyst is a metal alkoxide; the amount of the alkaline catalyst is 0.01 wt%-5 wt% of the mass of the polyisocyanate. The sealing agent composition includes malonate compounds and other sealing agent components; The other types of blocking agents are selected from one or more of ethyl acetoacetate, methyl acetoacetate, butyl acetoacetate, and diisopropylamine; In the sealing agent composition, the molar amount of malondialdehyde compounds is 30-90% of the total molar amount of the sealing agent composition, and the molar amount of other types of sealing agents is 10-70% of the total molar amount of the sealing agent composition.
2. The preparation method according to claim 1, characterized in that, The polyisocyanate is selected from self-polymerized products with diisocyanate as monomer, and isocyanates modified by reaction of diisocyanate and polyol.
3. The preparation method according to claim 1, characterized in that, The alkaline catalyst is selected from one or more of sodium methoxide, sodium ethoxide, sodium phenolate, and potassium methoxide.
4. The preparation method according to claim 3, characterized in that, The alkaline catalyst is sodium methoxide.
5. The preparation method according to claim 1, characterized in that, The malonate diesters are selected from one or more of dimethyl malonate, diethyl malonate, di-n-propyl malonate, diisopropyl malonate, di-n-butyl malonate, diisobutyl malonate, and di-tert-butyl malonate.
6. The preparation method according to claim 5, characterized in that, The malonic acid diester compound is diethyl malonate.
7. The preparation method according to claim 1, characterized in that, The other types of blocking agents are selected from diisopropylamine and / or ethyl acetoacetate.
8. The preparation method according to claim 1, characterized in that, The amount of the blocking agent composition relative to the isocyanate group of the polyisocyanate is 0.90-1.3 molar equivalents.
9. The preparation method according to claim 8, characterized in that, The amount of the blocking agent composition relative to the isocyanate group of the polyisocyanate is 0.95-1.1 molar equivalents.
10. The preparation method according to any one of claims 1-9, characterized in that, Polyisocyanates undergo a blocking reaction with the blocking agent composition under solvent or solvent-free conditions.
11. The preparation method according to claim 10, characterized in that, The solvent is selected from one or more of the following: aromatic solvents, ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, 3-methoxyacetic acid n-butyl ester, acetone, butanone, 4-methyl-2-pentanone, and cyclohexanone.
12. The preparation method according to any one of claims 1-9 and 11, characterized in that, The reaction temperature of the reaction system is 30-120℃.
13. The preparation method according to claim 12, characterized in that, The reaction temperature of the reaction system is 40-80℃.
14. The blocked polyisocyanate prepared by any one of claims 1-13; The turbidity of the blocked polyisocyanate is less than or equal to 0.8 NTU.
15. The application of the blocked polyisocyanate prepared by any one of claims 1-13 or the blocked polyisocyanate as described in claim 14; The closed-type polyisocyanate is used to prepare a single-component coating system.