Blocked polyisocyanate as well as preparation method and application thereof

Abstract

The invention belongs to the field of isocyanate, and particularly relates to blocked polyisocyanate as well as a preparation method and application thereof. The preparation method comprises the following steps: firstly, adding polyisocyanate and other sealant components in the sealant composition into a reaction device, then respectively and continuously mixing a malonic acid diester compound and a basic catalyst in the sealant composition through a mixing device, and continuously adding the mixture into a reaction system; after the reaction is finished, the blocked polyisocyanate is obtained; the sealing agent composition is prepared from a malonic acid diester compound and other sealing agent components. The enclosed polyisocyanate prepared by the invention has the advantage of high transparency, and can improve the appearance of a paint film when being applied to downstream paint.

Description

Technical Field

[0001] The invention belongs to the field of isocyanates, and in particular relates to a blocked polyisocyanate and a preparation method and application thereof. Background Art

[0002] Blocked isocyanate is the product of the reaction between isocyanate and blocking agent. It is widely used in one-component polyurethane coatings, especially suitable for automotive coatings and coil coatings.

[0003] When commonly used oxime blocking agents, phenol blocking agents, alcohol blocking agents, and lactam blocking agents are used to prepare blocked polyisocyanates, the curing temperature usually needs to be above 140°C, which has high energy consumption costs and limits their use on plastic substrates with low heat resistance.

[0004] Malonic acid diester compounds, as isocyanate blocking agents, can effectively reduce the curing temperature and can even achieve low-temperature curing below 100°C. However, the resulting blocked isocyanate has the problem of low transparency, which in turn affects downstream coating applications, especially the appearance of the paint film.

[0005] In view of this, there is an urgent need in the art to develop a method for preparing a polyisocyanate composition blocked with a malonic acid diester compound with high transparency. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a blocked polyisocyanate in view of the problem of low transparency of a blocked polyisocyanate obtained by using a malonic acid diester compound as a blocking agent. By controlling the feeding method of part of the raw materials, the prepared blocked polyisocyanate has the advantage of high transparency, and can improve the appearance of the paint film when applied to downstream coatings.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] In a first aspect, a method for preparing a blocked polyisocyanate is provided, comprising the following steps:

[0009] Firstly, polyisocyanate and other blocking agent components in the blocking agent composition are added to the reaction device, and then the malonic acid diester compound and the alkaline catalyst in the blocking agent composition are continuously mixed through a mixing device (such as a pipeline mixer) and continuously added to the reaction system; after the reaction is completed, the blocked polyisocyanate is obtained; wherein,

[0010] The sealing agent composition comprises a malonic acid diester compound and other sealing agent components.

[0011] According to the preparation method provided by the present invention, in some embodiments, the polyisocyanate is selected from the self-polymerization product with diisocyanate as a monomer, and the isocyanate modified by the reaction of diisocyanate and polyol.

[0012] The diisocyanate is one or more aliphatic and / or alicyclic diisocyanates containing 4 to 30 carbon atoms in addition to the NCO group in the carbon skeleton. The diisocyanate can be 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(isocyanatomethyl)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, and the like.

[0014] In some embodiments, the polyisocyanate comprises one or more of isocyanurate, uretdione, biuret, carbamate, allophanate, iminooxadiazinedione and carbodiimide structures, preferably comprises isocyanurate and biuret structures.

[0015] The NCO functionality of the polyisocyanate is ≥2.5 (for example, 3, 4, 5, 6, 7, 8, 9, 10), usually the NCO functionality is less than or equal to 10, and the content of isocyanate groups is 5-40wt% (calculated without solvent), for example, 10wt%, 15wt%, 20wt%, 22wt%, 25wt%, 28wt%, 30wt%, 35wt%.

[0016] In some embodiments, the alkaline catalyst is a metal alkoxide, preferably one or more selected from the group consisting of sodium methoxide, sodium ethoxide, sodium phenolate and potassium methoxide, more preferably sodium methoxide.

[0017] In some embodiments, the amount of the alkaline catalyst used is 0.01wt%-5wt% (e.g., 0.02wt%, 0.04wt%, 0.05wt%, 0.1wt%, 0.2wt%, 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 4.0wt%, 4.5wt%) of the mass of the polyisocyanate.

[0018] In some embodiments, the malonic acid diester 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 types of blocking agents are selected from one or more of ethyl acetoacetate, methyl acetoacetate, butyl acetoacetate, diisopropylamine, 3,5-dimethylpyrazole, butanone oxime, caprolactam, methanol, ethanol, isobutanol and isopentanol, preferably selected from diisopropylamine and / or ethyl acetoacetate.

[0020] In some embodiments, in the sealing agent composition, the molar amount of the malonic acid diester compound is 30-90% (e.g., 32%, 35%, 40%, 45%, 50%, 60%, 70%, 80%, 85%) of the total molar amount of the sealing agent composition, and the molar amount of other types of sealing agents is 10-70% (e.g., 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%) of the total molar amount of the sealing agent composition.

[0021] In some embodiments, the blocking agent composition is used in an amount of 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, relative to the isocyanate groups of the polyisocyanate.

[0022] In some embodiments, the polyisocyanate and the blocking agent composition are subjected to blocking reaction in the presence of a solvent or without a solvent. Whether a solvent needs to be added is mainly determined by 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-methoxybutyl acetate, acetone, butanone, 4-methyl-2-pentanone and cyclohexanone.

[0024] In some embodiments, the amount of the solvent added is 10-70wt% (e.g., 12wt%, 15wt%, 20wt%, 25wt%, 30wt%, 40wt%, 50wt%, 55wt%, 60wt%, 65wt%, 68wt%) of the blocked isocyanate.

[0025] According to the preparation method provided by the present invention, in some embodiments, the reaction temperature of the reaction system is 30-120°C (for example, 50°C, 60°C, 70°C, 85°C, 100°C, 110°C), preferably 40-80°C.

[0026] In a second aspect, a closed polyisocyanate prepared by the preparation method described above is provided.

[0027] According to the closed polyisocyanate provided by the present invention, in some embodiments, the turbidity of the closed polyisocyanate is less than or equal to 0.8NTU, for example, ≤0.6NTU, ≤0.5NTU, ≤0.4NTU, ≤0.3NTU, ≤0.2NTU, ≤0.1NTU.

[0028] In the process of preparing the blocked polyisocyanate, an antioxidant may be added; or in the prepared blocked polyisocyanate, an antioxidant may be added. The amount of the antioxidant added may be a conventional choice in the art and will not be described in detail here.

[0029] In some embodiments, the antioxidant may include hindered phenol antioxidants, hindered amine antioxidants, and phosphite antioxidants.

[0030] In a third aspect, provided is the blocked polyisocyanate prepared by the preparation method described above or the use of the blocked polyisocyanate described above.

[0031] According to the application provided by the present invention, in some embodiments, the blocked polyisocyanate is used to prepare a one-component coating system.

[0032] In this article, the operation steps and specific formulations of the blocked polyisocyanate used in the one-component coating system may be conventional methods in the art and will not be described in detail here.

[0033] After conducting a systematic experimental study on the factors causing the transparency of the polyisocyanate composition blocked by the malonic acid diester compound, the inventor surprisingly found that during the preparation of the polyisocyanate composition blocked by the malonic acid diester compound, the addition method of the malonic acid diester compound and the alkaline catalyst will affect the transparency of the product. Further experiments found that the malonic acid diester compound and the alkaline catalyst were continuously added to a mixing device (such as a pipeline mixer) for mixing, and the mixture was immediately and continuously added to the reaction system. The transparency of the obtained blocked polyisocyanate product was significantly improved, and the turbidity of the product was significantly reduced.

[0034] Mixing the diester of malonate with the alkaline catalyst is a process of pre-activating the blocking agent, which can reduce the polymerization catalytic activity of the alkaline catalyst on the NCO group. The diester of malonate and the alkaline catalyst are continuously mixed and added to the reaction system to avoid turbidity or solid formation after mixing, and to avoid the problem of impurities generated by long-term mixing.

[0035] Compared with the prior art, the beneficial effect of the technical solution of the present invention is at least that: by optimizing the addition method of the malonic acid diester compound and the alkaline catalyst, the obtained 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 easily available, and it is easy to realize industrialization. DETAILED DESCRIPTION

[0036] In order to understand the technical features and content of the present invention in detail, the preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described in the embodiments, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. For those who do not specify specific conditions in the embodiments, they are carried out according to normal conditions or the conditions recommended by the manufacturer.

[0037] Main raw material sources:

[0038] Wannate HT-100 (HDI trimer, NCO content 22.0wt%), 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 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 polyisocyanate is as follows:

[0049] A nitrogen environment is formed in a four-necked flask equipped with a stirrer, a thermometer, a reflux cooling tube, and a nitrogen blowing tube; 200 g of polyisocyanate Wannate HT-100 and 148 g of propylene glycol methyl ether acetate are added to the four-necked flask, mixed evenly, heated to 40° C., 53 g of diisopropylamine is added, and the temperature is controlled at 40-50° C. After the addition is completed, the system is heated to 60° C.; then 92 g of diethyl malonate is pumped into a pipeline mixer at a flow rate of 1.5 g / min through a peristaltic pump, and at the same time, 1.2 g of a methanol solution containing 30 wt% of sodium methoxide is pumped into the pipeline mixer at a flow rate of 0.02 g / min through a peristaltic pump, the two streams of materials are mixed through a pipeline mixer and immediately added to the reaction system continuously to start a blocking reaction of diethyl malonate; after the materials are added, the temperature is continued to be maintained at 60° C., the reaction is carried out for 24 hours, the NCO content in the detection system is less than 0.2 wt%, the reaction is completed, and a blocked polyisocyanate is obtained.

[0050] Example 2

[0051] The preparation process of blocked polyisocyanate is as follows:

[0052] A nitrogen environment is formed in a four-necked flask equipped with a stirrer, a thermometer, a reflux cooling tube, and a nitrogen blowing tube; 200 g of polyisocyanate Wannate HT-100, 249 g of butyl acetate, and 27 g of ethyl acetoacetate are added to the four-necked flask and mixed evenly. After the addition is completed, the system is heated to 60° C.; then 147 g of diethyl malonate is pumped into a pipeline mixer through a peristaltic pump at a flow rate of 1.3 g / min, and at the same time, 2.2 g of a methanol solution containing 30 wt% of sodium methoxide is pumped into the pipeline mixer through a peristaltic pump at a flow rate of 0.02 g / min. The two streams of materials are mixed through the pipeline mixer and immediately added to the reaction system continuously to start the diethyl malonate blocking reaction; after the materials are added, the temperature is continued to be maintained at 60° C. for 24 hours, and the NCO content in the detection system is less than 0.2 wt%, and the reaction is completed to obtain a blocked polyisocyanate.

[0053] Example 3

[0054] The preparation process of blocked polyisocyanate is as follows:

[0055] A nitrogen environment is formed in a four-necked flask equipped with a stirrer, a thermometer, a reflux cooling tube, and a nitrogen blowing tube; 200 g of polyisocyanate Wannate HB-100, 275 g of butyl acetate, and 39 g of ethyl acetoacetate are added to the four-necked flask and mixed evenly. After the addition is completed, the system is heated to 60° C.; then 173 g of diisopropyl malonate is pumped into a pipeline mixer through a peristaltic pump at a flow rate of 1.3 g / min, and at the same time, 2.2 g of a methanol solution containing 30 wt% of sodium methoxide is pumped into the pipeline mixer through a peristaltic pump at a flow rate of 0.02 g / min. The two streams of materials are mixed through the pipeline mixer and immediately added to the reaction system continuously to start the diisopropyl malonate blocking reaction; after the materials are added, the temperature is continued to be maintained at 60° C. for 24 hours, and the NCO content in the detection system is less than 0.2 wt%, and the reaction is completed to obtain a blocked polyisocyanate.

[0056] Comparative Example 1

[0057] The preparation process of blocked polyisocyanate is as follows:

[0058] A nitrogen environment is formed in a four-necked flask equipped with a stirrer, a thermometer, a reflux cooling tube, and a nitrogen blowing tube; 200 g of polyisocyanate Wannate HT-100 and 148 g of propylene glycol methyl ether acetate are added to the four-necked flask, mixed evenly, heated to 40° C., 53 g of diisopropylamine is added, and the temperature is controlled at 40-50° C. After the raw materials are added, the system is heated to 60° C.; then 92 g of diethyl malonate and 1.2 g of a methanol solution containing 30 wt % of sodium methoxide are mixed evenly, and then the mixed material flow is pumped into the reaction system at a flow rate of 1.5 g / min by a peristaltic pump; after the raw materials are added, the temperature is continued to be maintained at 60° C., the reaction is carried out for 24 hours, the NCO content in the detection system is less than 0.2 wt %, the reaction is completed, and a blocked polyisocyanate is obtained.

[0059] Comparative Example 2

[0060] The preparation process of blocked polyisocyanate is as follows:

[0061] A nitrogen environment is formed in a four-necked flask equipped with a stirrer, a thermometer, a reflux cooling tube, and a nitrogen blowing tube; 200 g of polyisocyanate Wannate HT-100, 249 g of butyl acetate, 27 g of ethyl acetoacetate, and 147 g of diethyl malonate are added to the four-necked flask and mixed evenly. After the raw materials are added, the system is heated to 60° C. to start the reaction; then 2.2 g of a methanol solution containing 30 wt % of sodium methoxide is added to the system by a peristaltic pump at a flow rate of 0.02 g / min. After the addition is completed, the temperature is continued to be maintained at 60° C., the reaction is carried out for 24 hours, the NCO content in the detection system is less than 0.2 wt %, the reaction is completed, and a blocked polyisocyanate is obtained.

[0062] Comparative Example 3

[0063] The preparation process of blocked polyisocyanate is as follows:

[0064] A nitrogen environment is formed in a four-necked flask equipped with a stirrer, a thermometer, a reflux cooling tube, and a nitrogen blowing tube; 200 g of polyisocyanate Wannate HB-100, 275 g of butyl acetate, and 39 g of ethyl acetoacetate are added to the four-necked flask and mixed evenly. After the addition is completed, the system is heated to 60° C.; then 173 g of diisopropyl malonate and 2.2 g of a methanol solution containing 30 wt % of sodium methoxide are mixed evenly, and then the mixture is pumped into the reaction system at a flow rate of 1.3 g / min through a peristaltic pump. After the addition is completed, the temperature is continued to be maintained at 60° C., the reaction is carried out for 24 hours, the NCO content in the detection system is less than 0.2 wt %, the reaction is completed, and a blocked polyisocyanate is obtained.

[0065] The products obtained in each embodiment and comparative example were subjected to turbidity test using a Hach 2100N turbidity meter, and the data are shown in Table 1. The transparency of the blocked polyisocyanate in the present invention is characterized by turbidity, and the lower the turbidity, the higher the transparency of the product.

[0066] Table 1 Turbidity test results of blocked polyisocyanate

[0067]

[0068]

[0069] As can be seen from 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. It can be explained that in the preparation process, the polyisocyanate is first contacted with other types of blocking agents, and then the malonic acid diester compound and the alkaline catalyst are continuously mixed and continuously added to the reaction system (i.e., mixed and added to the reaction system) for blocking reaction, which can improve the transparency of the blocked polyisocyanate.

[0070] In the preparation process of Comparative Example 2, the malonic acid diester compound and the alkaline catalyst were not mixed, and the two were added to the reaction system separately, which would affect the improvement of the transparency of the blocked polyisocyanate. In Comparative Examples 1 and 3, although the malonic acid diester compound and the alkaline catalyst were mixed, the two were not continuously mixed and continuously added to the reaction system, and the transparency of the blocked polyisocyanate could not be effectively improved.

[0071] Application examples of blocked polyisocyanates in the preparation of coatings

[0072] Based on the blocked polyisocyanate and acrylic polyol (Tongde Resin AC1100B) prepared in Examples 1-3 and Comparative Examples 1-3 as the basic raw materials, 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 50wt% with butyl acetate, and 0.1wt% of dibutyltin dilaurate was added (based on the total amount of the basic raw materials).

[0073] The prepared one-component varnish was sprayed onto a clean glass plate and cured at 100°C for 60 minutes. The appearance and transparency of the paint film obtained after curing were compared and observed, as shown in Table 2.

[0074] Table 2 Performance test of paint films prepared by blocked polyisocyanates

[0075]

[0076]

[0077] It can be seen from the test results in Table 2 that the blocked polyisocyanates obtained in Examples 1-3 have very low turbidity, and when applied to a one-component polyurethane varnish, the resulting paint film has a smooth and translucent appearance. However, the blocked polyisocyanates prepared in Comparative Examples 1-3 have a relatively high turbidity, and when applied to a one-component polyurethane varnish, the resulting paint film has a poor appearance and poor translucency.

[0078] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the spirit of the present invention.

Claims

1. A method for preparing a blocked polyisocyanate, characterized in that: The steps include: Firstly, polyisocyanate and other blocking agent components in the blocking agent composition are added to the reaction device, and then the malonic acid diester compound and the alkaline catalyst in the blocking agent composition are continuously mixed through a mixing device and continuously added to the reaction system; after the reaction is completed, the blocked polyisocyanate is obtained; wherein, The sealing agent composition comprises a malonic acid diester compound and other sealing agent components.

2. The preparation method according to claim 1, characterized in that: The polyisocyanate is selected from the self-polymerization product with diisocyanate as a monomer and the isocyanate modified by the reaction of diisocyanate and polyol.

3. The preparation method according to claim 1 or 2, characterized in that: The alkaline catalyst is a metal alkoxide, preferably one or more selected from sodium methoxide, sodium ethoxide, sodium phenolate and potassium methoxide, more preferably sodium methoxide; The amount of the alkaline catalyst used is 0.01wt%-5wt% of the mass of the polyisocyanate.

4. The preparation method according to any one of claims 1 to 3, characterized in that The malonic acid diester 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.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The other types of blocking agents are selected from one or more of ethyl acetoacetate, methyl acetoacetate, butyl acetoacetate, diisopropylamine, 3,5-dimethylpyrazole, butanone oxime, caprolactam, methanol, ethanol, isobutanol and isopentanol, preferably diisopropylamine and / or ethyl acetoacetate.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In the blocking agent composition, the molar amount of the malonic acid diester compound is 30-90% of the total molar amount of the blocking agent composition, and the molar amount of other types of blocking agents is 10-70% of the total molar amount of the blocking agent composition; Preferably, the amount of the blocking agent composition used is 0.90-1.3 molar equivalents, preferably 0.95-1.1 molar equivalents, relative to the isocyanate groups of the polyisocyanate.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The polyisocyanate and the blocking agent composition undergo a blocking reaction in the presence of a solvent or without a solvent; Preferably, the solvent is selected from one or more of aromatic hydrocarbon solvents, ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, 3-methoxybutyl acetate, acetone, butanone, 4-methyl-2-pentanone and cyclohexanone.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The reaction temperature of the reaction system is 30-120°C, preferably 40-80°C.

9. The closed polyisocyanate obtained by the preparation method according to any one of claims 1 to 8; Preferably, the blocked polyisocyanate has a turbidity of less than or equal to 0.8 NTU.

10. Use of the blocked polyisocyanate prepared by the preparation method according to any one of claims 1 to 8 or the blocked polyisocyanate according to claim 9; Preferably, the blocked polyisocyanate is used to prepare a one-component coating system.

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