Blocked polyisocyanate composition as well as preparation method and application thereof

Abstract

The invention provides a blocked polyisocyanate composition as well as a preparation method and application thereof. The present invention relates to a blocked polyisocyanate containing a polyisocyanate and a blocking agent containing compounds represented by general formula (I) and general formula (II), and the molar ratio of the total structure obtained by bonding the sealant represented by general formula (I) and the isocyanate group to the total structure obtained by bonding the sealant represented by general formula (II) and the isocyanate group is 75 / 25 to 90 / 10 (inclusive). The composition has good low-temperature curing performance, and the storage stability of the composition is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of isocyanate, and particularly relates to a blocked polyisocyanate composition, a preparation method and application thereof. BACKGROUND

[0002] The blocked isocyanate is a kind of compound in which the terminal isocyanate group is blocked by using a substance containing active hydrogen as a blocking agent, and the blocking agent dissociates to regenerate the terminal isocyanate at a certain temperature. Unlike the 2K coating, the blocked isocyanate can be mixed and stored with a resin polyol, and has the characteristics of convenient transportation and simple use. Commonly used blocking agents include caprolactam, oxime, 3,5-dimethylpyrazole and malonate, etc. When malonate is used as a blocking agent, the unblocking temperature can be as low as within 100 DEG C, but such products often have a crystallization phenomenon during storage.

[0003] Patent US5350825A discloses a polyisocyanate blocked by mixing diisopropylamine, active methylene compound and 1,2,4-triazole, although the crystallization problem is improved to a certain extent, but the low-temperature curing effect is obviously not as good as that of the malonate blocked isocyanate.

[0004] Patent CN107922584B discloses a polyisocyanate blocked by diethyl malonate and ethyl acetoacetate, and the product has good low-temperature curing effect, but the crystallization problem still needs to be further improved.

[0005] In view of the deficiencies of the existing methods, there is an urgent need in the art to develop a solvent-based blocked polyisocyanate composition which has low curing temperature and is compatible with storage stability. SUMMARY

[0006] The present application provides a blocked polyisocyanate composition, a preparation method and application thereof. The curing temperature of the blocked polyisocyanate composition of the present application can be as low as about 90 DEG C; it can be applied to plastic substrates with low heat resistance; and no precipitates and crystallization precipitates are likely to occur during low-temperature storage or long-term storage.

[0007] To achieve the above-mentioned purposes, the following technical solutions are adopted in the present application:

[0008] A blocked polyisocyanate composition comprises a reaction product of a polyisocyanate and a compound represented by formula (I) and formula (II)

[0009]

[0010] In the formula (I) and (II), R1, R2 and R3 each independently represent an alkyl group, a cycloalkyl group, a phenyl group or a benzyl group with a carbon number of 1-8; preferably, the alkyl group is a methyl group, an ethyl group, a n-propyl group or an isopropyl group.

[0011] As a preferred aspect, the compound represented by formula (I) is diethyl malonate and / or diisopropyl malonate.

[0012] As a preferred aspect, the compound represented by formula (II) is methyl 2-piperidinecarboxylate and / or ethyl 2-piperidinecarboxylate.

[0013] As a preferred aspect, the molar ratio of the structure in which the compound represented by formula (I) is bonded to an isocyanate group to the structure in which the compound represented by formula (II) is bonded to an isocyanate group is 75 / 25 or more and 90 / 10 or less.

[0014] As a preferred aspect, the molar ratio of the structure in which the compound represented by formula (I) is bonded to an isocyanate group to the structure in which the compound represented by formula (II) is bonded to an isocyanate group is 80 / 20 or more and 90 / 10 or less.

[0015] As a further preferred aspect, the molar ratio of the structure in which the compound represented by formula (I) is bonded to an isocyanate group to the structure in which the compound represented by formula (II) is bonded to an isocyanate group is 83 / 17 or more and 90 / 10 or less.

[0016] In the present application, the molar ratio of the structure in which the compound represented by formula (I) is bonded to an isocyanate group to the structure in which the compound represented by formula (II) is bonded to an isocyanate group is 75 / 25 or more, and good low-temperature curing properties can be obtained. In addition, the above molar ratio is 90 / 10 or less, and good storage stability can be exhibited.

[0017] As a preferred aspect, the polyisocyanate according to the present application is selected from the group consisting of a self-polymerization product of a diisocyanate as a monomer, and an isocyanate obtained by modifying a diisocyanate with a polyol.

[0018] As a preferred aspect, the diisocyanate according to the present application is one or more of aliphatic and / or alicyclic diisocyanates having 4 to 30 carbon atoms in the carbon skeleton in addition to the NCO group. The diisocyanate may, for example, include but is not limited to one or more of 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, and is preferably 1,6-hexamethylene diisocyanate (HDI).

[0019] In some embodiments, the polyisocyanate comprises one or more of isocyanurate, uretdione, biuret, carbamate, allophanate, iminooxadiazinedione, and carbodiimide structures, preferably comprises isocyanurate structures.

[0020] In another aspect, the present application provides a method for preparing the blocked polyisocyanate composition as described above, comprising the steps of:

[0021] reacting the polyisocyanate with the compound of formula (I) in the presence of a basic catalyst at a temperature of 30-100°C, preferably 40-80°C, and when the NCO content of the system is 1-2.5 wt%, the temperature is set to 20-70°C, preferably 30-60°C, and then adding the compound of formula (II) and reacting until no free isocyanate groups are detected by infrared spectroscopy.

[0022] In some embodiments, the molar amount of the compound of formula (I) in the blocking agent composition is 75-90% (e.g., 70%, 75%, 80%, 85%, 90%) of the sum of the molar amounts of the compounds of formula (I) and formula (II); and the molar amount of the compound of formula (II) is 10-25% (e.g., 10%, 15%, 20%, 25%) of the sum of the molar amounts of the compounds of formula (I) and formula (II).

[0023] In some embodiments, the total amount of the compounds of formula (I) and formula (II) is 0.90-1.2 (e.g., 0.92, 0.94, 0.95, 0.96, 0.98, 1.0, 1.15, 1.2) molar equivalents, preferably 0.95-1.05 molar equivalents, relative to the isocyanate groups of the polyisocyanate.

[0024] In some embodiments, the method is carried out in the presence of a solvent or without a solvent. Whether a solvent is needed depends mainly on the viscosity of the product, and generally adding a solvent before the reaction can reduce the viscosity of the reaction system.

[0025] In some embodiments, the solvent is selected from one or more of aromatic hydrocarbon solvents (e.g., toluene, xylene, aromatic hydrocarbon solvent oil), ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, n-butyl 3-methoxyacetate, acetone, butanone, 4-methyl-2-pentanone, and cyclohexanone.

[0026] In some embodiments, the amount of the solvent added is 10-40 wt% (e.g., 12 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 40 wt%) of the blocked polyisocyanate composition.

[0027] In the present application, the blocked reaction of polyisocyanate is carried out in the presence of a basic catalyst. Examples of the basic catalyst include metal alkoxides such as sodium methoxide, sodium ethoxide, sodium phenoxide, and potassium methoxide; hydroxides, acetates, octanoates, myristates, and benzoates of tetraalkylammonium such as tetramethylammonium, tetraethylammonium, and tetrabutylammonium; alkali metal salts of alkyl carboxylic acids such as sodium acetate, sodium hexanoate, sodium octanoate, and sodium myristate; metal salts of alkyl carboxylic acids such as tin, zinc, and lead acetates, hexanoates, octanoates, and myristates; compounds containing aminosilyl group such as hexamethylenedisilazane; and hydroxides of alkali metals such as lithium hydroxide, sodium hydroxide, and potassium hydroxide. The alkali metal alkoxide is preferred, and sodium methoxide is further preferred.

[0028] In the present application, the basic catalyst is added in an amount of 0.005 to 5% by weight (for example, 0.008, 0.01, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, or 1.5% by weight) relative to the mass of the polyisocyanate, and preferably in an amount of 0.1 to 2% by weight.

[0029] The blocked polyisocyanate composition of the present application is particularly suitable for use in the preparation of one-component coating or adhesive systems.

[0030] The blocked polyisocyanate composition of the present application has the following technical effects: by controlling the molar ratio of the two blocking agents to the isocyanate groups in the polyisocyanate, the composition has good low-temperature curing performance, and the storage stability of the composition is improved. DETAILED DESCRIPTION

[0031] In order to enable a detailed understanding of the technical features and content of the present application, the preferred embodiments of the present application will be described in more detail below. Although the preferred embodiments of the present application are described in the examples, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. If no specific conditions are specified in the examples, the conditions are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The sources of some raw materials used in the following examples and comparative examples of the present application are as follows:

[0032] Sources of main raw materials:

[0033] Wannate HT-100 (HDI polymer), NCO content: 22.0%, Wanhua Chemical;

[0034] Diethyl malonate, Aldrich Reagent;

[0035] Diisopropyl malonate, Aldrich Reagent;

[0036] Ethyl 2-piperidinecarboxylate, Aldrich Reagent;

[0037] 2-Piperidincarboxylate, Aladdin reagent;

[0038] A methanol solution containing 30 wt% sodium methoxide, Aladdin's reagent;

[0039] Toluene, Yantai Far East Fine Chemical Company;

[0040] Propylene glycol methyl ether acetate, Jiangsu Hualun Chemical Co., Ltd.;

[0041] The relevant test methods in the following embodiments and comparative examples of this invention are as follows:

[0042] (1) The NCO content test shall be performed in accordance with standard GB / T 12009.4;

[0043] (2) The ratio of the total number of moles of the structure obtained by bonding the blocking agent to the isocyanate group as shown in general formula (I) to the total number of moles of the structure obtained by both the blocking agent and the isocyanate group as shown in general formula (II) is a / b, and the determination method is as follows:

[0044] Using an AVANCE 600 prepared by Bruker FT-NMR, with deuterated chloroform (CDCl3) as solvent, and with a sample mass concentration of 5%, 600 MHz, 256 cycles, and a chemical shift reference of 0 ppm tetramethylsilane, the following parameters were determined. 1 Qualitative analysis was performed using H NMR spectroscopy. The integral value of the signal was divided by the number of hydrogen atoms measured, and a / b was calculated from this value.

[0045] (a): The number of isocyanate and malonic acid ester compounds bonded by the number of amino groups adjacent to the amide body formed by the isocyanate group and malonic acid ester bond (=peak area near 7.3 ppm + peak area near 8.0 ppm / 2 + peak area near 9.8 ppm: the peak near 8.0 ppm (diamid diester body) has a structure with 2 amino groups in 1 bonded structure, so 1 / 2 of the peak area is taken as the number of bonded structures).

[0046] (b): The number of isocyanate groups and 2-piperidine carboxylate bonds (in moles) determined by the number of amino groups adjacent to the amide body formed by the bonding of isocyanate and 2-piperidine carboxylate (peak area around 7.5 ppm).

[0047] (Evaluation 1) Low-temperature curing properties

[0048] A mixture of "Setalux 1152" (acrylic polyol, trade name manufactured by Nuplex Resins, hydroxyl value 138 mg KOH / g resin, solid content concentration 51% by mass) and a blocked polyisocyanate was prepared with NCO / OH = 1.0. The mixture was adjusted to 20 seconds / 23°C with butyl acetate using a Ford cup No. 4 to obtain an α-coating solution. The obtained α-coating solution was applied to PP boards using an air spray gun to achieve a dry film thickness of 40 μm. After drying at 23°C for 30 minutes, it was sintered at 90°C for 20 minutes to obtain a cured coating film.

[0049] After the obtained cured coating is sintered, it is placed at 20°C for 1 hour, peeled off from the PP board, and impregnated in acetone at 20°C for 24 hours. The value of the undissolved mass relative to the mass before impregnation (gel fraction) is calculated and evaluated according to the following criteria.

[0050] ①: Gel fraction of 90% or higher

[0051] ②: Gel fraction is above 80% but less than 90%

[0052] ③: Gel fraction is 70% or higher but less than 80%

[0053] ④: Gel fraction less than 70%

[0054] (Evaluation 2) Storage stability

[0055] The test sample was placed in a 125mL glass bottle under air atmosphere and stored in a -20℃ refrigerator for 3 weeks. Then it was taken out and brought back to room temperature, and the appearance of the product was observed.

[0056] Preparation of blocked polyisocyanate compositions:

[0057] Example 1

[0058] A nitrogen atmosphere was created in a four-necked flask equipped with a stirrer, thermometer, reflux cooling pipe, and nitrogen inlet pipe. 500g of Wannate HT-100 polyisocyanate, 404g of diisopropyl malonate, and 419g of toluene were added to the flask. The mixture was heated to 60°C. Under a nitrogen atmosphere, 5.0g of 30% sodium methoxide solution (0.05g / min) was added to the reaction flask. When the NCO content in the system reached 1.52wt%, the reaction temperature was set to 45°C, and 74.1g of ethyl 2-piperidinecarboxylate (1.8g / min) was added. After all materials were added, the reaction was continued at 45°C until no free NCO groups were detected by infrared spectroscopy, thus obtaining a blocked polyisocyanate composition.

[0059] Example 2

[0060] A nitrogen atmosphere was created in a four-necked flask equipped with a stirrer, thermometer, reflux cooling pipe, and nitrogen inlet pipe. 500g of Wannate HT-100 polyisocyanate, 378g of diethyl malonate, and 392g of propylene glycol methyl ether acetate were added to the flask. The mixture was heated to 60°C. Under a nitrogen atmosphere, 5.0g of 30% sodium methoxide solution (0.05g / min) was added to the reaction flask. When the NCO content in the system reached 1.41wt%, the reaction temperature was set to 50°C, and 37.5g of methyl 2-piperidinecarboxylate (0.9g / min) was added. After all materials were added, the reaction was continued at 50°C until no free NCO groups were detected by infrared spectroscopy, yielding a blocked polyisocyanate composition.

[0061] Example 3

[0062] A nitrogen atmosphere was created in a four-necked flask equipped with a stirrer, thermometer, reflux cooling pipe, and nitrogen inlet pipe. 500g of Wannate HT-100 polyisocyanate, 357g of diethyl malonate, and 394g of toluene were added to the flask. The mixture was heated to 60°C. Under a nitrogen atmosphere, 5.0g of 30% sodium methoxide solution (0.05g / min) was added to the reaction flask. When the NCO content in the system reached 1.34wt%, the reaction temperature was set to 45°C, and 61.8g of ethyl 2-piperidinecarboxylate (1.5g / min) was added. After all materials were added, the reaction continued at 45°C until no free NCO groups were detected by infrared spectroscopy, yielding a blocked polyisocyanate composition.

[0063] Example 4

[0064] A nitrogen atmosphere was created in a four-necked flask equipped with a stirrer, thermometer, reflux cooling pipe, and nitrogen inlet pipe. 500g of Wannate HT-100 polyisocyanate, 323g of diethyl malonate, and 393g of propylene glycol methyl ether acetate were added to the flask. The mixture was heated to 60°C. Under a nitrogen atmosphere, 5.0g of 30% sodium methoxide solution (0.05g / min) was added to the reaction flask. When the NCO content in the system reached 2.12wt%, the reaction temperature was set to 40°C, and 94.7g of ethyl 2-piperidinecarboxylate (2.4g / min) was added. After all materials were added, the reaction was continued at 40°C until no free NCO groups were detected by infrared spectroscopy, yielding a blocked polyisocyanate composition.

[0065] Comparative Example 1

[0066] A nitrogen atmosphere was created in a four-necked flask equipped with a stirrer, thermometer, reflux cooling pipe, and nitrogen inlet pipe. 500g of Wannate HT-100 polyisocyanate, 365g of diisopropyl malonate, and 417 toluene were added to the flask. The mixture was heated to 60°C. Under a nitrogen atmosphere, 5.0g of 30% sodium methoxide solution (0.05g / min) was added to the reaction flask. When the NCO content in the system reached 1.87wt%, the reaction temperature was set to 45°C, and 107g of ethyl 2-piperidinecarboxylate (2.7g / min) was added. After all materials were added, the reaction continued at 45°C until no free NCO groups were detected by infrared spectroscopy, yielding a blocked polyisocyanate composition.

[0067] Comparative Example 2

[0068] A nitrogen atmosphere was created in a four-necked flask equipped with a stirrer, thermometer, reflux cooling pipe, and nitrogen inlet pipe. 500g of Wannate HT-100 polyisocyanate, 390g of diethyl malonate, and 393g of propylene glycol methyl ether acetate were added to the flask. The mixture was heated to 60°C. Under a nitrogen atmosphere, 5.0g of 30% sodium methoxide solution (0.05g / min) was added to the reaction flask. When the NCO content in the system reached 1.14wt%, the reaction temperature was set to 50°C, and 26.2g of methyl 2-piperidinecarboxylate (0.7g / min) was added. After all materials were added, the reaction was continued at 50°C until no free NCO groups were detected by infrared spectroscopy, thus obtaining a blocked polyisocyanate composition.

[0069] Comparative Example 3

[0070] A nitrogen atmosphere was created in a four-necked flask equipped with a stirrer, thermometer, reflux cooling pipe, and nitrogen inlet pipe. 500g of Wannate HT-100 polyisocyanate, 399g of diethyl malonate, and 394g of toluene were added to the flask. The mixture was heated to 60°C. Under a nitrogen atmosphere, 5.0g of 30% sodium methoxide solution (0.05g / min) was added to the reaction flask. When the NCO content in the system reached 1.08wt%, the reaction temperature was set to 45°C, and 20.6g of ethyl 2-piperidinecarboxylate (0.5g / min) was added. After all materials were added, the reaction continued at 45°C until no free NCO groups were detected by infrared spectroscopy, yielding a blocked polyisocyanate composition.

[0071] Examples of applications of blocked polyisocyanate compositions:

[0072] The storage stability and low-temperature curing properties of the blocked polyisocyanate compositions prepared in the above examples and comparative examples were tested. The test results are shown in Table 1.

[0073] Table 1. Experimental results of storage stability and low-temperature curing performance tests

[0074] No. a / b Low temperature curability Storage stability Example 1 80:20 ② clear and transparent Example 2 89:11 ① clear and transparent Example 3 84:16 ① clear and transparent Example 4 76:24 ③ clear and transparent Comparative Example 1 73:27 ④ clear and transparent Comparative Example 2 91:9 ① a small amount of white flocculation appeared Comparative Example 3 94:6 ① a large amount of white flocculation appeared

[0075] As can be seen from the table above, the low-temperature curing performance of the blocked polyisocyanate compositions prepared in Examples 1-4 is significantly better than that of Comparative Example 1, and the storage stability of Examples 1-4 is better than that of Comparative Examples 2 and 3. Therefore, the blocked polyisocyanate compositions prepared in this invention have good low-temperature curing performance and good storage stability.

Claims

1. A blocked polyisocyanate composition comprising a reaction product of a polyisocyanate and a compound represented by formula (I) and formula (II) ###0001### (I) (II) wherein R1, R2, R3 each independently represents an alkyl group having a carbon number of 1 to 8, a cycloalkyl group, a phenyl group, a benzyl group; preferably a methyl group, an ethyl group, a n-propyl group, an iso-propyl group. The compound represented by formula (I) is diethyl malonate and / or diisopropyl malonate; and / or the compound represented by formula (II) is methyl 2-piperidinecarboxylate and / or ethyl 2-piperidinecarboxylate.

2. The blocked polyisocyanate composition according to claim 1, characterized in that, The molar ratio of the structure obtained by bonding the compound represented by formula (I) to an isocyanate group to the structure obtained by bonding the compound represented by formula (II) to an isocyanate group is 75 / 25 or more and 90 / 10 or less.

3. The blocked polyisocyanate composition according to claim 1 or 2, characterized in that The molar ratio of the structure obtained by bonding the compound represented by formula (I) to an isocyanate group to the structure obtained by bonding the compound represented by formula (II) to an isocyanate group is 80 / 20 or more and 90 / 10 or less.

4. The blocked polyisocyanate composition according to claim 1, characterized in that, The molar ratio of the structure obtained by bonding the compound represented by formula (I) to an isocyanate group to the structure obtained by bonding the compound represented by formula (II) to an isocyanate group is 83 / 17 or more and 90 / 10 or less.

5. The blocked polyisocyanate composition according to claim 1, characterized in that, The polyisocyanate is selected from the group consisting of a self-polymerization product of a diisocyanate as a monomer, an isocyanate modified by reacting a diisocyanate with a polyol; preferably, the diisocyanate comprises one or more of 1,4-butane diisocyanate, 1,5-pentane diisocyanate, 2,2,4-trimethyl-hexamethylene-1,6-diisocyanate, lysine diisocyanate, isophorone diisocyanate, 1,6-hexamethylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and 4,4'-dicyclohexylmethane diisocyanate; and / or one or more of a polyisocyanate comprising an isocyanurate, a uretdione, a biuret, a urethane, a uretonimine, an iminooxadiazinedione, a carbodiimide structure.

6. The blocked polyisocyanate composition according to claim 1, characterized in that, 7. A method for producing the blocked polyisocyanate composition according to any one of claims 1 to 6, comprising the steps of: reacting a polyisocyanate with a compound represented by formula (I) in the presence of a basic catalyst, at a reaction temperature of 30 to 100°C, preferably 40 to 80°C, and when the NCO content of the system is 1 to 2.5 wt%, setting the reaction temperature to 20 to 70°C, preferably 30 to 60°C, and further adding a compound represented by formula (II) and reacting until no free isocyanate group is detected by infrared spectroscopy. The amount of the compound represented by formula (I) and formula (II) is 0.90 to 1.2 molar equivalents, preferably 0.95 to 1.05 molar equivalents, relative to the isocyanate groups of the polyisocyanate.

8. The method of claim 7, wherein, The basic catalyst is selected from one or more of a metal alkoxide, a hydroxide, an acetate, an octoate, a myristate, or a benzoate of a tetraalkylammonium, an alkali metal salt of an alkylcarboxylic acid, a tin, zinc, or lead metal salt of an alkylcarboxylic acid, an aminosilyl-containing compound, and a hydroxide of an alkali metal; preferably an alkali metal alkoxide, more preferably sodium methoxide.

9. The preparation method according to claim 6, characterized in that, ​ 10. Use of the blocked polyisocyanate composition according to any one of claims 1 to 6 or of the blocked polyisocyanate composition prepared according to the process of any one of claims 7 to 10 for the production of one-component coatings or adhesives.

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