Blocked polyisocyanate composition and application thereof

Abstract

The present invention discloses a blocked polyisocyanate composition and uses thereof, the blocked polyisocyanate composition comprises at least one sealing agent, at least one polyisocyanate composition and at least one solvent, and the free water content of the blocked polyisocyanate composition is 50-2000 ppm. The closed polyisocyanate composition disclosed by the invention not only can improve the adhesive force of a paint film, but also can avoid the phenomenon of paint film pinholes and the phenomenon of system turbidity to a certain extent.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyisocyanates, and in particular relates to a blocked polyisocyanate composition and application thereof. Background Art

[0002] The reaction mechanism of blocked isocyanates has been widely reported, primarily resulting from the reaction of isocyanate groups with blocking agents, resulting in a system essentially devoid of free NCO groups. Because the chemical bond formed between the blocking agent and NCO is relatively weak, the blocking agent can dissociate under certain temperature conditions, releasing free NCO, which then undergoes a cross-linking reaction. Therefore, blocked isocyanates are often used as a single system in a wide range of applications, including adhesives, coatings, elastomers, and sealants. Commonly used isocyanate blocking agents include caprolactam, phenols, acetylacetone, sodium bisulfate, and butanone oxime. Caprolactam, due to its low cost and availability, is a common raw material for isocyanate blocking agents.

[0003] Patent US4302351 records that IPDI forms IPDI trimer under the action of trimerization catalyst, and the monomer is removed by thin film evaporation at 150-160°C to obtain IPDI trimer. Caprolactam is added at 150°C and reacted for 2 hours to obtain closed IPDI trimer.

[0004] Patent CN114276520A introduces a method for preparing a blocked isocyanate composition, which obtains a blocked IPDI trimer with color and thermal stability by adjusting the content of n-valeramide and caprolactam blocking compounds. Summary of the Invention

[0005] In products containing isocyanate groups, the water content is generally strictly controlled throughout the entire production process, and is even preferably required to be water-free. However, in actual applications, it was surprisingly discovered that when a certain water content is contained in the blocked isocyanate composition, the downstream application effect can be improved to a certain extent.

[0006] The present invention provides a blocked polyisocyanate composition with a specific water content, which can ensure good adhesion of the system and avoid the pinhole phenomenon of the paint film and the potential turbidity of the system, thereby completing the present invention.

[0007] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0008] A blocked polyisocyanate composition comprising the following components:

[0009] (a) at least one blocking agent;

[0010] (b) at least one polyisocyanate composition;

[0011] (c) at least one solvent;

[0012] Wherein, the free water content of the blocked polyisocyanate composition is 50-2000ppm, for example, 60ppm,

[0013] 70ppm, 80ppm, 90ppm, 100ppm, 200ppm, 300ppm, 400ppm, 500ppm,

[0014] 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1200ppm, 1500ppm,

[0015] 1600ppm, 1800ppm, 2000ppm, etc., preferably 80-500ppm.

[0016] In the present invention, there are no particular limitations on the method for controlling the free water content in the system. Various methods are available, such as adding water, or reacting the polyisocyanate composition with a blocking agent before dissolving the composition in solvents with varying water contents. Since the NCO groups react with the blocking agent, they are no longer able to consume water from the solvent system, inevitably leading to varying water contents in the system.

[0017] The blocking agent of the blocked polyisocyanate composition of the present invention includes one or more of caprolactam, methyl ethyl ketone oxime, acetone oxime, dimethylimidazole, etc., preferably caprolactam.

[0018] The blocked polyisocyanate composition of the present invention, the polyisocyanate composition of component (b) is based on the polymerization of hexamethylene diisocyanate or isophorone diisocyanate.

[0019] The blocked polyisocyanate composition of the present invention comprises an ester solvent, such as butyl acetate, ethyl acetate, propylene glycol methyl ether acetate, methyl acetate, etc.; a ketone, such as acetone, butanone, isophorone, etc.; an aromatic solvent oil, such as solvent oil S100, S150, S200, etc.; an aliphatic hydrocarbon, such as butane, pentane, cyclopentane, etc., preferably an aromatic solvent oil, more preferably solvent oil S100.

[0020] The blocked polyisocyanate composition of the present invention has a viscosity of 1000-3000 mPa·s at 25°C, for example, 1200 mPa·s, 1300 mPa·s, 1400 mPa·s, 1500 mPa·s, 1600 mPa·s, 1700 mPa·s,

[0021] 1800mPa·s, 1900mPa·s, 2000mPa·s, 2100mPa·s, 2200mPa·s, 2300mPa·s,

[0022] 2400mPa·s, 2500mPa·s, 2600mPa·s, 2700mPa·s, 2800mPa·s, 2900mPa·s,

[0023] 3000mPa·s, etc., preferably 1500-2500mPa·s.

[0024] In the blocked polyisocyanate composition of the present invention, the content of free caprolactam accounts for 0.1-2wt% of the blocked isocyanate composition, for example, 0.1wt%, 0.3wt%, 0.5wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%, etc., preferably 0.5-1.5wt%.

[0025] In the blocking process of the blocked polyisocyanate composition of the present invention, the material feed ratio is calculated by molar amount as caprolactam / NCO=1-1.2:1, for example, 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1.

[0026] 1, 1.07:1, 1.08:1, 1.09:1, 1.1:1, 1.12:1, 1.15:1, 1.18:1, 1.2:1, etc., preferably 1-1.05:1.

[0027] The blocked polyisocyanate composition of the present invention is used in one-component polyurethane coatings or adhesives, preferably in coil or can coatings.

[0028] Regarding the preparation method of the blocked polyisocyanate composition, reference may be made to the prior art. Taking isophorone diisocyanate as a polymerization monomer as an example, the method generally includes the following steps:

[0029] Step 1: preparing a polyisocyanate composition: in the presence of a trimerization catalyst, isophorone diisocyanate is polymerized, and the polymerization reaction is terminated when the NCO content in the system reaches 20% to 26%;

[0030] removing unreacted isophorone diisocyanate monomers to reduce the content of unreacted isophorone diisocyanate monomers to less than 1 wt %, preferably less than 0.5 wt %, and more preferably less than 0.3 wt %, thereby preparing a polyisocyanate composition;

[0031] Step 2: The polyisocyanate composition may be first dissolved in a solvent and then further reacted with caprolactam, or the polyisocyanate composition may be first reacted with caprolactam and then dissolved in a solvent.

[0032] The general steps for preparing a polyisocyanate composition are as follows: first, isophorone diisocyanate (IPDI) is added to a round-bottom flask equipped with a reflux condenser, a stirrer, a thermometer, and a nitrogen inlet. The system is then heated to 50-140°C, and a catalyst is then added dropwise to initiate a polymerization reaction. As is well known to those skilled in the art, the specific polymerization reaction sequence is common knowledge in the art and will not be elaborated upon here.

[0033] In the above-mentioned polymerization reaction, the trimerization catalyst is selected from tetraalkylammonium hydroxides and organic acid salts thereof. More preferably, the amount of the trimerization catalyst used is 5-100 ppm, preferably 10-90 ppm, based on the mass of the diisocyanate monomer. Examples of the above-mentioned tetraalkylammonium hydroxides are tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, etc., and examples of the organic acid salts of tetraalkylammonium are acetates, butyrates, decanoates, etc. of tetramethylammonium and tetraethylammonium.

[0034] The trimerization catalyst used in the present invention can be used without a solvent or dissolved in a solvent. The solvent mainly includes a linear or branched monohydric alcohol or dihydric alcohol with 1 to 20 carbon atoms. Examples of solvents for dissolving the catalyst include methanol, ethanol, n-butanol, isobutanol, tert-butanol, n-octanol, isooctyl alcohol, and heptanol, with methanol, ethanol, n-butanol, and heptanol being preferred.

[0035] When the trimerization catalyst of the present invention is used in the form of a solution, the concentration of the trimerization catalyst is 5-50%, preferably 10-30%, based on the catalyst solution.

[0036] In some specific embodiments, when the polymerization reaction is carried out to an NCO value of 20%-26% in the system, a terminator can be used to terminate the reaction, and the amount of the terminator used is 0.8-1 times the molar amount of the catalyst. The terminator is an acid compound, preferably at least one of dimethyl phosphate, diethyl phosphate, dibutyl phosphate, dioctyl phosphate, 2-ethylhexyl phosphate, phosphoric acid, hydrochloric acid, benzenesulfonic acid, p-toluenesulfonic acid, benzoyl chloride, and acetyl chloride. In addition, the polymerization reaction can also be terminated by thermal deactivation. In a specific implementation process, the system can be heated to 110-140°C and left for 30-60 minutes.

[0037] For unreacted isophorone diisocyanate, thin film evaporation can be used to remove unreacted isophorone diisocyanate monomer in the polymerization reaction system; in some specific embodiments, a thin film evaporator can be used at 140~

[0038] Unreacted monomers are removed from the reaction system at 170°C (e.g., 150°C, 160°C) and a pressure of 10-200 Pa (e.g., 50 Pa, 100 Pa, 150 Pa) to obtain a polyisocyanate composition. This polyisocyanate composition can be dissolved in a solvent to form a solution or directly used in a subsequent reaction with a blocking agent.

[0039] The subsequent reaction of the blocking agent with the isocyanate composition can be carried out in a solvent or without a solvent. Preferably, the temperature is raised to 80-140°C, and caprolactam is added dropwise. The free NCO content is monitored during the reaction. When the free NCO content is less than 0.2 wt%, the reaction is stopped. The reaction is generally allowed to proceed for 3-24 hours to obtain a blocked polyisocyanate composition.

[0040] In the present invention, in the reaction between the blocking agent and the polyisocyanate composition, the material feeding ratio is calculated by molar amount as caprolactam / NCO=1-1.2:1, preferably 1-1.05:1.

[0041] The blocked polyisocyanate composition of the present invention is mainly used in one-component polyurethane coatings or adhesives, and is preferably used in coil and can coatings.

[0042] The present invention adopts the above technical solution and has the following technical effects:

[0043] The blocked polyisocyanate composition of the present invention has a free water content of 50-2000 ppm, which can not only improve the adhesion of the paint film, but also avoid the occurrence of paint film pinholes and system turbidity to a certain extent. DETAILED DESCRIPTION

[0044] The method provided by the present invention will be further illustrated by the following examples, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention.

[0045] Main raw material sources:

[0046] Wannate IPDI, 99.5% purity, Wanhua Chemical;

[0047] Aromatic solvent oil S100, purity 99.5%, Jiangsu Hualun Chemical Co., Ltd.;

[0048] Molten caprolactam, Sinopec Shijiazhuang Refining and Chemical Company;

[0049] Tetrabutylammonium hydroxide, Sigma-Aldrich, 95%;

[0050] Dibutyl phosphate, Sigma-Aldrich, 97%;

[0051] Dioctyl phosphate, Sigma-Aldrich, 96%;

[0052] Diethyl phosphate, Sigma-Aldrich, 98%.

[0053] The following examples are tested using the following methods:

[0054] (1) Test method for monomer content in polyisocyanate composition: GB / T18446-2009;

[0055] (2) Viscosity test: Brookfield CAP2000+ rotational viscometer, test temperature 25°C, speed set to 50 rpm;

[0056] (3) Determination of NCO content: The isocyanate groups in the test sample were neutralized with an excess of 2 mol / L di-n-butylamine and then back-titrated with 1 mol / L hydrochloric acid.

[0057] (4) Testing method for free water content in the system: Karl Fischer standard method is used for testing.

[0058] ⑸ For the test method of adhesion of polyisocyanate application products, refer to: GB / T 9286-2021 Paint and varnish cross-cut test.

[0059] (6) Based on ISO2409 standard, coating pinholes are divided into 4 grades according to their diameter, namely grade 0, grade 1, grade 2 and grade 3. The paint film standard is required to be grade 1 or above.

[0060] The specific definitions are as follows:

[0061] Level 0 pinhole: There must be no pinholes on the coating surface.

[0062] Level 1 pinhole: diameter ≤ 20 μm, number ≤ 5 pinholes / m 2 , spacing ≥5mm, uneven distribution.

[0063] Level 2 pinholes: diameter ≤ 50 μm, number ≤ 50 pinholes / m 2 , spacing ≥ 2mm, and the distribution is relatively uniform.

[0064] Level 3 pinholes: diameter ≤ 100 μm, unlimited number, independent of distance, and evenly distributed.

[0065] Example 1

[0066] 20,000 g of IPDI was placed in a round-bottom flask equipped with a reflux condenser, a stirrer, a thermometer, and a nitrogen inlet. The reaction system was heated to 80° C., and then 2.66 g of a 5 wt % butanol solution of tetrabutylammonium hydroxide was added dropwise to the reaction system with stirring. The polymerization reaction was carried out at a temperature between 80° C. and 120° C. When the NCO content of the reaction solution reached 25.5%, dibutyl phosphate in an amount equimolar to the tetrabutylammonium hydroxide was added to terminate the reaction to obtain a polymerization reaction solution.

[0067] Unreacted isophorone diisocyanate monomer was evaporated from the polymerization reaction solution using a thin film evaporator at 190°C and 50 Pa absolute pressure to a content of 0.3 wt%, yielding a polyisocyanate composition. This was then reacted with caprolactam until the NCO content fell below 0.2%, and the mixture was dissolved in solvent oil S100 to a solids content of 60%, yielding blocked polyisocyanate composition 1. The water content was measured to be 150 ppm.

[0068] Examples 2-4

[0069] Water was added based on Example 1 to control the water content of the system to 400 ppm, 1000 ppm, and 2000 ppm, respectively.

[0070] Example 5

[0071] On the basis of Example 1, a dehydrating agent Ti was added in an amount of 0.1% by mass of the blocked polyisocyanate composition 1 of Example 1, and the water content was controlled to be 50 ppm.

[0072] Comparative Example 1

[0073] 20,000 g of IPDI was placed in a round-bottom flask equipped with a reflux condenser, a stirrer, a thermometer, and a nitrogen inlet. The reaction system was heated to 80° C., and then 2.66 g of a 5 wt % butanol solution of tetrabutylammonium hydroxide was added dropwise to the reaction system with stirring. The polymerization reaction was carried out at a temperature between 80° C. and 120° C. When the NCO content of the reaction solution reached 25.5%, dibutyl phosphate in an amount equimolar to the tetrabutylammonium hydroxide was added to terminate the reaction to obtain a polymerization reaction solution.

[0074] Unreacted isophorone diisocyanate monomer was evaporated from the polymerization reaction solution using a thin film evaporator at 190° C. and an absolute pressure of 50 Pa to a content of 0.3 wt % to obtain a polyisocyanate composition. This composition was dissolved in S100 and further reacted with caprolactam. The reaction was stopped when the NCO content was less than 0.2%. The solid content was 60%, resulting in a blocked polyisocyanate composition a. The water content was tested to be 40 ppm.

[0075] Comparative Example 2

[0076] On the basis of Comparative Example 1, a dehydrating agent Ti was added in an amount equal to 1 wt % of the mass of the blocked polyisocyanate composition a in Comparative Example 1. The tested water content was 0.

[0077] Comparative Examples 3-4

[0078] Water was added based on the results of Example 1 to control the free water content of the system to 2200 ppm and 2700 ppm.

[0079] Example 6

[0080] A varnish was prepared based on the blocked polyisocyanate composition prepared above and a polyester resin (Evonik resin DYNAPOL 915) with an NCO / OH ratio of 1.02 and a solids content of 50% (the diluent was butyl acetate). 0.5 wt% (calculated based on the solids content of the varnish) of the catalyst dibutyltin dilaurate was added to the coating to promote the crosslinking reaction.

[0081] The prepared varnish was sprayed onto clean tinplate and baked at 190°C for 15 minutes to obtain a 100 μm film. The adhesion of the film was then tested using the 100-grid method. The evaluation was performed according to the grading method in Table 1. The test results are shown in Table 2.

[0082] Table 1 Classification method

[0083]

[0084]

[0085] Table 2 Test results

[0086]

[0087] It will be readily understood that the above embodiments are merely examples for clarity of description and are not intended to limit the present invention to these examples. Those skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. It is not necessary and impossible to provide an exhaustive list of all possible implementations. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A blocked polyisocyanate composition, characterized in that Contains the following ingredients: (a) at least one blocking agent; (b) at least one polyisocyanate composition; (c) at least one solvent; Wherein, the free water content of the blocked polyisocyanate composition is 50-2000 ppm, preferably 80-500 ppm.

2. The blocked polyisocyanate composition according to claim 1, wherein The blocking agent includes one or more of caprolactam, methyl ethyl ketone oxime, acetone oxime, and dimethylimidazole, preferably caprolactam.

3. The blocked polyisocyanate composition according to claim 2, wherein The polyisocyanate composition of component (b) is based on the polymerization of hexamethylene diisocyanate or the polymerization of isophorone diisocyanate.

4. The blocked polyisocyanate composition according to claim 1, wherein The solvent comprises one or more of esters, ketones, aromatic solvent oils, and aliphatic hydrocarbons, preferably aromatic solvent oils.

5. The blocked polyisocyanate composition according to claim 1, wherein The blocked polyisocyanate composition has a viscosity of 1000-3000 mPa·s at 25° C., preferably 1500-2500 mPa·s.

6. The blocked polyisocyanate composition according to claim 2, wherein The content of free caprolactam accounts for 0.1-2 wt %, preferably 0.5-1.5 wt % of the blocked polyisocyanate composition.

7. The blocked polyisocyanate composition according to claim 3 or 6, characterized in that During the end-capping process, the material feed ratio is calculated by molar amount, caprolactam / NCO=1-1.2:

1.

8. The blocked polyisocyanate composition according to claim 7, wherein During the end-capping process, the material feed ratio is calculated by molar amount, caprolactam / NCO=1-1.05:

1.

9. Use of the blocked polyisocyanate composition according to any one of claims 1 to 8, characterized in that: For use in one-component polyurethane coatings or adhesives.

10. The use of the blocked polyisocyanate composition according to claim 9, characterized in that: For coil or can coatings.

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