A blocked isocyanate and its preparation method and application

Abstract

The present invention provides a blocked isocyanate and a preparation method and application thereof, wherein the preparation method comprises: mixing an oxime substance with an alkaline compound and treating it, purifying the product obtained by the treatment to obtain an oxime blocking agent; adding the oxime blocking agent to polyisocyanate in the form of droplets with a diameter of ≤500 μm and reacting to obtain the blocked isocyanate. The present invention is specially designed from two aspects: raw materials and reaction process / technique, and a specific treatment method is adopted to obtain an oxime blocking agent with a low acid value, which is then contacted with polyisocyanate in the form of fine droplets and reacted to obtain a blocked isocyanate. The blocked isocyanate has extremely low chroma and excellent storage stability, which fully meets the performance requirements of blocked isocyanates in products such as clear paints and light-colored paints.

Description

Technical Field

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

[0002] Blocked isocyanates are generated by the reaction of isocyanates with blocking agents. The chemical bond formed by the blocking agent and NCO can release free NCO under heating conditions. Therefore, blocked isocyanates are widely used in one-component polyurethane coatings and adhesives, especially for automotive coatings and coil coatings. There are many types of blocking agents that can be used for isocyanate groups. Currently, commonly used blocking agents include phenolic compounds, alcohol compounds, oxime compounds, β-dicarbonyl compounds, pyrazole compounds, amide compounds, etc.

[0003] Ketoximate compounds are widely used as isocyanate blocking agents because they have a low deblocking temperature and the raw materials are cheap and easily available. However, isocyanates blocked with ketoxime compounds are prone to yellowing during storage, and the coatings prepared with them will become more yellow during baking and curing, which seriously affects the application of the product in clear paint and light-colored paint.

[0004] In order to solve the discoloration problem of ketoxime blocked isocyanates, researchers have tried to introduce stabilizers into the system. For example, US5504178A discloses a single-component coating composition containing oxime or lactam blocked polyisocyanates, wherein the blocked polyisocyanates are the reaction products of polyisocyanates and i) 60-99.9 equivalent % of oxime or lactam blocking agents for isocyanate groups and ii) 0.1-40 equivalent % of hydrazine and / or compounds containing the group H(R)N-NR-CO- that are soluble in polyisocyanates, blocking agents, and solvents; hydrazine acyl compounds are used in the blocked polyisocyanates to improve the yellowing resistance of the product under heat, but hydrazine acyl compounds have poor solubility in the reaction system, and the reactive groups are sterically hindered and difficult to react completely with the NCO group. The presence of the hydrazine acyl compounds in the system in a free form will affect the transparency of the product. EP0829500A2 discloses a stable blocked isocyanate, using a compound combination as a blocked polyisocyanate stabilizer, wherein one compound is an amine (HALS) containing at least one 2,2,6,6-tetramethylpiperidin-4-yl, another compound containing a hydrazine acyl structure, and other optional stabilizers; the components in the stabilizer are not easy to obtain, and a part of the stabilizer contains two reactive groups, has a high viscosity, and needs to increase the amount of solvent during use, and even produces gel during use. US5631339A discloses an anti-yellowing isocyanate curing coating, which uses an anti-yellowing additive based on N-aminoalkyl carbamate for a heat-curable coating composition containing a polyisocyanate crosslinker blocked with ketoxime; although it can improve the color stability of blocked isocyanate products in baking and curing to a certain extent, it has the problem of difficult availability of raw materials and poor economy, and does not play an effective role in the color stability of blocked isocyanates during storage at room temperature.

[0005] Therefore, improving the chromaticity and storage chromaticity stability of blocked isocyanates is an urgent problem to be solved in the art. Summary of the invention

[0006] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a blocked isocyanate and a preparation method and application thereof. Through the design and coordination of raw materials and processes, the obtained blocked isocyanate has the characteristics of low chroma and stable storage chroma, which fully meets the performance requirements of blocked isocyanate in products such as clear paint and light-colored paint.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a blocked isocyanate, the method comprising: mixing an oxime substance with an alkaline compound and treating the mixture, purifying the product obtained by the treatment to obtain an oxime blocking agent; adding the oxime blocking agent in the form of droplets with a diameter of ≤500 μm to a polyisocyanate and reacting the mixture to obtain the blocked isocyanate.

[0009] In the preparation method provided by the present invention, a special design is made from two aspects: raw materials and reaction process / process. First, an oxime substance is treated with an alkaline compound, and the treated product is purified to obtain an oxime blocking agent; then the oxime blocking agent is contacted with polyisocyanate in the form of fine droplets (diameter ≤ 500 μm) and reacted to obtain the blocked isocyanate. The present invention found in the research process that the product chromaticity storage stability of the prepared blocked isocyanate is significantly different when oxime substances with different acid values ​​are used as blocking agents. The higher the acid value of the oxime substance, the worse the product chromaticity storage stability of the blocked isocyanate; based on this, the present invention treats and purifies the oxime substance by an alkaline compound, so that the oxime blocking agent has a low acid value. In addition, the reaction of oxime substances with isocyanate groups is a strongly exothermic reaction. Conventionally, oxime substances are reacted with polyisocyanates in batches or dropwise, and there is a situation where the concentration of local oxime substances is too high and the temperature is too high, resulting in a significantly higher color of the product. Further studies have found that when the oxime substances are greatly excessive, the prepared blocked isocyanate products will also have obvious yellowing. Therefore, it is speculated that the excess oxime substances can react with the blocked isocyanate to form a certain colored group substance. Based on this, the present invention adds the specially treated oxime blocking agent in the form of fine droplets (diameter ≤500μm) to the polyisocyanate and reacts, which effectively suppresses the situation where the blocking agent is too high in local concentration and too high in local temperature, and also avoids the occurrence of excessive blocking agent, so that the obtained blocked isocyanate has extremely low color and excellent storage stability, and will not yellow during long-term storage.

[0010] Preferably, the oxime substance includes any one of butanone oxime, acetone oxime, cyclohexanone oxime, and acetaldehyde oxime, or a combination of at least two thereof.

[0011] Preferably, the alkaline compound includes any one of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, or a combination of at least two thereof.

[0012] Preferably, based on the mass of the oxime substance as 100%, the mass of the basic compound is 0.05-1%, for example, it can be 0.06%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or 0.9%, as well as specific point values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively enumerates the specific point values ​​included in the range, and 0.05-0.5% is further preferred.

[0013] Preferably, the treatment is carried out under stirring conditions.

[0014] In the present invention, the stirring speed is not particularly limited, and it only needs to be such that the oxime substances and the alkaline compounds in the system are fully mixed, dispersed and contacted.

[0015] Preferably, the treatment is carried out in an inert protective atmosphere.

[0016] Preferably, the inert protective atmosphere includes any one of CO2 atmosphere, CO atmosphere, N2 atmosphere, He atmosphere, and Ar atmosphere, or a combination of at least two of them. CO2 atmosphere and / or N2 atmosphere are further preferred, and N2 atmosphere is even more preferred.

[0017] Preferably, the treatment temperature is 30-100°C, for example, it can be 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or 95°C, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0018] Preferably, the treatment time is 30-90 min, for example, it can be 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min or 85 min, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0019] Preferably, the purification method comprises any one of filtration, distillation and rectification or a combination of at least two thereof, and a combination of filtration and distillation is further preferred.

[0020] Preferably, the purification method comprises: first filtering the product obtained by the treatment, distilling the obtained liquid phase, completing purification, and obtaining the oxime blocking agent.

[0021] Preferably, the distillation comprises distillation under reduced pressure.

[0022] Preferably, the distillation temperature is 70-100°C, for example, it can be 72°C, 75°C, 78°C, 80°C, 82°C, 85°C, 88°C, 90°C, 92°C, 95°C or 98°C, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0023] As a preferred technical solution of the present invention, after the oxime substances are treated and purified by alkaline compounds, the acidic substances therein can be effectively removed, so that the obtained oxime blocking agent has a lower acid value, thereby reducing the chromaticity of the blocked isocyanate and significantly improving the storage stability of the blocked isocyanate.

[0024] Preferably, the acid value of the oxime blocking agent is ≤0.03 mg KOH / g, for example, it can be 0.001 mg KOH / g, 0.003 mg KOH / g, 0.005 mg KOH / g, 0.008 mg KOH / g, 0.01 mg KOH / g, 0.012 mg KOH / g, 0.015 mg KOH / g, 0.018 mg KOH / g, 0.02 mg KOH / g, 0.022 mg KOH / g, 0.025 mg KOH / g or 0.028 mg KOH / g, as well as specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively enumerates the specific points included in the range, and is further preferably ≤0.01 mg KOH / g.

[0025] In the present invention, the oxime blocking agent is added to the polyisocyanate in the form of droplets of ≤500 μm, and the diameter of the droplets can be 10 μm, 30 μm, 50 μm, 70 μm, 90 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm or 480 μm, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range; the droplets are calculated based on the average particle size, and the droplet size of ≤100 μm is further preferred. The smaller the droplet diameter of the oxime blocking agent, the faster it can be mixed with the polyisocyanate, the faster the blocking reaction is completed, the local high concentration of the oxime blocking agent is avoided, and the situation of excessively high local temperature in the reaction system is effectively suppressed, and the chromaticity of the blocked isocyanate is effectively reduced.

[0026] Exemplarily, the droplet diameter of the oxime blocking agent can be controlled by an atomizing nozzle.

[0027] Preferably, the molar ratio of the oxime blocking agent to the NCO group in the polyisocyanate is (0.95-1.1):1, for example, it can be 0.96:1, 0.97:1, 0.98:1, 0.99:1, 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1 or 1.09:1, and more preferably (1-1.05):1

[0028] Preferably, the NCO functionality of the polyisocyanate is ≥ 2.5.

[0029] Preferably, the mass percentage of NCO groups in the polyisocyanate is 5-30%, for example, it can be 6%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25% or 28%, as well as specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific points included in the range, and 15-25% is further preferred.

[0030] In the present invention, the polyisocyanate is obtained by modification of isocyanate, and its NCO functionality is ≥2.5, and the mass percentage of NCO groups is 5-30%, and more preferably 15-25%.

[0031] Preferably, the polyisocyanate includes any one of isocyanurate, uretdione, biuret, carbamate, allophanate, and iminooxadiazinedione, or a combination of at least two thereof.

[0032] Preferably, the isocyanate comprises an aliphatic isocyanate and / or an alicyclic isocyanate, and more preferably a C4-C20 (e.g., C5, C6, C7, C8, C9, C10, C12, C14, C15, C16, C18, etc.) aliphatic diisocyanate and / or a C4-C20 (e.g., C5, C6, C7, C8, C9, C10, C12, C14, C15, C16, C18, etc.) alicyclic diisocyanate.

[0033] Preferably, the isocyanate comprises tetramethylene diisocyanate, pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, tetradecamethylene diisocyanate, derivatives of lysine diisocyanate, 4,4'-bis(isocyanatocyclohexyl)methane, 2,4'-bis(isocyanatocyclohexyl)methane, (H 12MDI), 3-isocyanate methylene-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate, IPDI), any one or a combination of at least two thereof, more preferably hexamethylene-1,6-diisocyanate (HDI), 4,4'-bis(isocyanatocyclohexyl)methane, 2,4'-bis(isocyanatocyclohexyl)methane (HDI), 12 Any one of MDI (MDI) and isophorone diisocyanate (IPDI) or a combination of at least two thereof.

[0034] Preferably, the reaction is carried out in an inert protective atmosphere.

[0035] Preferably, the inert protective atmosphere includes any one of CO2 atmosphere, CO atmosphere, N2 atmosphere, He atmosphere, and Ar atmosphere, or a combination of at least two of them. CO2 atmosphere and / or N2 atmosphere are further preferred, and N2 atmosphere is even more preferred.

[0036] Preferably, the reaction is carried out under stirring conditions.

[0037] In the present invention, the stirring speed is not particularly limited, and it only needs to be such that the oxime blocking agent and the polyisocyanate in the system are fully mixed, dispersed and contacted.

[0038] Preferably, the reaction temperature is 30-120°C, for example, it can be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C or 110°C, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and 40-80°C is further preferred.

[0039] Preferably, the reaction time is 0.5-10 h, for example, it can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h or 9 h, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively enumerates the specific point values ​​included in the range, and 2-5 h is further preferred.

[0040] Preferably, since the blocked isocyanate has a relatively high viscosity, the reaction is carried out in the presence of a solvent; a solvent needs to be added during the reaction to adjust the viscosity.

[0041] Preferably, the solvent comprises a common paint solvent, including any one of an ester solvent, a ketone solvent, an aromatic hydrocarbon solvent, and an alkane solvent, or a combination of at least two thereof.

[0042] Preferably, the solvent includes any one of ethyl acetate, butyl acetate, 1-methoxy-2-propyl acetate, 3-methoxyacetic acid n-butyl ester, acetone, butanone, 4-methyl-2-pentanone, cyclohexanone, toluene, xylene, and S100 solvent oil, or a combination of at least two of them. More preferably, the solvent includes any one of butyl acetate, 1-methoxy-2-propyl acetate, and S100 solvent oil, or a combination of at least two of them.

[0043] Preferably, the reaction is carried out in the presence of a solvent, the solvent is mixed with a polyisocyanate to obtain a polyisocyanate solution; the oxime blocking agent is added to the polyisocyanate solution in the form of droplets with a diameter of ≤500 μm and reacted to obtain the blocked isocyanate.

[0044] In the present invention, the amount of the solvent is not particularly limited, and those skilled in the art can make routine adjustments according to the viscosity of the system.

[0045] Preferably, the mass ratio of the solvent to the polyisocyanate is (0.1-1):1, for example, it can be 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, etc.

[0046] Preferably, the preparation method comprises the following steps:

[0047] (1) mixing an oxime substance with an alkaline compound, treating the mixture at 30-100° C. with stirring for 30-90 min; purifying the product obtained by the treatment to obtain an oxime blocking agent, wherein the acid value of the oxime blocking agent is ≤0.03 mg KOH / g;

[0048] (2) adding the oxime blocking agent obtained in step (1) into the polyisocyanate in the form of droplets with a diameter of ≤500 μm, reacting at 30-120° C. for 0.5-10 h in an inert protective atmosphere to obtain the blocked isocyanate; the molar ratio of the oxime blocking agent to the NCO group in the polyisocyanate is (0.95-1.1):1.

[0049] In a second aspect, the present invention provides a blocked isocyanate, wherein the blocked isocyanate is prepared by the preparation method described in the first aspect.

[0050] Preferably, the chromaticity of the blocked isocyanate is ≤12 Hazen, for example, it may be 1 Hazen, 2 Hazen, 3 Hazen, 4 Hazen, 5 Hazen, 6 Hazen, 7 Hazen, 8 Hazen, 9 Hazen, 10 Hazen or 11 Hazen, and more preferably ≤10 Hazen.

[0051] Preferably, the blocked isocyanate has a chromaticity of ≤25 Hazen after being stored at 60° C. for 3 months, more preferably ≤20 Hazen, and even more preferably ≤15 Hazen, and may be 12-15 Hazen.

[0052] In a third aspect, the present invention provides a use of the blocked isocyanate as described in the second aspect in a polyurethane coating, a polyurethane adhesive or a polyurethane elastomer.

[0053] Preferably, the blocked isocyanate is applied to polyurethane coating, more preferably polyurethane one-component baking varnish.

[0054] Preferably, the blocked isocyanate is used as a curing agent in a polyurethane coating and is prepared with a polyol to form a polyurethane one-component baking varnish, which is particularly suitable for use as an automotive coating or a coil coating.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] In the preparation method provided by the present invention, special designs are made from two aspects: raw materials and reaction process / technique. A specific treatment method is adopted to obtain an oxime-type blocking agent with a low acid value, which is then contacted with polyisocyanate in the form of fine droplets and reacted to obtain a blocked isocyanate. Through the design and coordinated coordination of raw materials and processes, the blocked isocyanate has an extremely low chroma, which is ≤10 Hazen; and has excellent storage stability, with a chroma of ≤15 Hazen after storage at 60°C for 3 months, and the chroma is stable during long-term storage, which fully meets the performance requirements of blocked isocyanates in products such as clear paints and light-colored paints. DETAILED DESCRIPTION

[0057] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0058] As used herein, the terms "comprises," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0059] "Optional" or "any one" means that the subsequently described matter or event can or cannot occur, and that the description includes instances where the event occurs and instances where it does not.

[0060] In the following specific embodiments of the present invention, the testing methods of components and performances are as follows:

[0061] (1) Acid value

[0062] Acid-base potentiometric titration was performed using 0.05 mol / L KOH ethanol solution to obtain the acid values ​​of oxime substances and oxime blocking agents.

[0063] (2) Chroma

[0064] The test was carried out using a BYK digital colorimeter.

[0065] In the following specific embodiments of the present invention, the sources of the raw materials used are as follows:

[0066] (1) Polyisocyanate: Wanhua Chemical WANNATE HT-100, NCO content 21.9%, color 15 Hazen;

[0067] (2) Oxime substances: butanone oxime, acid value of 0.05 mg KOH / g, purchased from Sheng'an Chemical; acetone oxime, acid value of 0.06 mg KOH / g, purchased from Sheng'an Chemical; acetaldehyde oxime, acid value of 0.04 mg KOH / g, purchased from Aladdin Reagent; cyclohexanone oxime, acid value of 0.05 mg KOH / g, purchased from Aladdin Reagent.

[0068] (3) Solvent: S100 solvent oil, purchased from Hualun Chemical.

[0069] Example 1

[0070] A blocked isocyanate and a preparation method thereof, wherein the steps of the preparation method are as follows:

[0071] (1) 600 g of butanone oxime was added to a flask, and 1 g of sodium hydroxide was added under nitrogen atmosphere, and the mixture was stirred at 40° C. for 60 min, and filtered; then, the mixture was heated to 90° C. and distilled under reduced pressure to obtain the treated butanone oxime, i.e., an oxime-based blocking agent, whose acid value was 0.01 mgKOH / g;

[0072] (2) 1000 g of polyisocyanate and 487 g of S100 solvent oil were stirred in a reactor, protected by nitrogen, condensed and refluxed, and the temperature was raised to 50° C.; 463 g of the treated butanone oxime (acid value: 0.01 mg KOH / g) obtained in step (1) was added to the reactor at a rate of 3 g / min by spraying so that the average diameter of the droplets was 200 μm, and reacted with the polyisocyanate. After the butanone oxime was added, the reaction was continued to be stirred until there was no NCO characteristic absorption peak in infrared detection, thereby obtaining the blocked isocyanate, and the test chromaticity was 9 Hazen.

[0073] Example 2

[0074] A blocked isocyanate and a preparation method thereof, wherein the steps of the preparation method are as follows:

[0075] (1) 600 g of butanone oxime was added to a flask, and 1 g of sodium carbonate was added under nitrogen atmosphere, and the mixture was stirred at 40° C. for 60 min, and filtered; then, the mixture was heated to 90° C. and distilled under reduced pressure to obtain the treated butanone oxime, i.e., an oxime blocking agent, whose acid value was 0.02 mg KOH / g;

[0076] (2) 1000 g of polyisocyanate and 487 g of S100 solvent oil were stirred in a reactor, protected by nitrogen, condensed and refluxed, and the temperature was raised to 50° C.; 463 g of the treated butanone oxime (acid value: 0.02 mg KOH / g) obtained in step (1) was added to the reactor at a rate of 5 g / min by spraying so that the average diameter of the droplets was 450 μm, and reacted with the polyisocyanate. After the butanone oxime was added, the reaction was continued to be stirred until there was no NCO characteristic absorption peak in infrared detection, thereby obtaining the blocked isocyanate, and the test chromaticity was 10 Hazen.

[0077] Example 3

[0078] A blocked isocyanate and a preparation method thereof, wherein the steps of the preparation method are as follows:

[0079] (1) 600 g of acetone oxime was added to a flask, heated to 65° C. in a nitrogen atmosphere, 1 g of sodium carbonate was added, stirred at 65° C. for 60 min, and filtered; then heated to 90° C. and distilled under reduced pressure to obtain the treated acetone oxime, i.e., an oxime blocking agent, whose acid value was 0.03 mg KOH / g;

[0080] (2) 1000 g of polyisocyanate and 460 g of S100 solvent oil were stirred in a reactor, protected by nitrogen, condensed and refluxed, and the temperature was raised to 50° C.; 380 g of the treated acetone oxime (acid value: 0.03 mg KOH / g) obtained in step (1) was added to the reactor at a rate of 3 g / min by spraying so that the average diameter of the droplets was 400 μm to react with the polyisocyanate. After the addition of acetone oxime, the reaction was continued by stirring until there was no NCO characteristic absorption peak in infrared detection, thereby obtaining the blocked isocyanate, and the test chromaticity was 10 Hazen.

[0081] Example 4

[0082] A blocked isocyanate and a preparation method thereof, wherein the steps of the preparation method are as follows:

[0083] (1) Add 600 g of acetaldehyde oxime into a flask, heat to 40° C. in a nitrogen atmosphere, add 1 g of sodium carbonate, stir at 40° C. for 60 min, and filter; perform vacuum distillation to obtain the treated acetaldehyde oxime, i.e., an oxime blocking agent, whose acid value is 0.02 mg KOH / g;

[0084] (2) 1000 g of polyisocyanate and 438 g of S100 solvent oil were stirred in a reactor, protected by nitrogen, condensed and refluxed, and the temperature was raised to 50° C.; 313 g of the treated acetaldehyde oxime (acid value: 0.02 mg KOH / g) obtained in step (1) was added into the reactor at a rate of 5 g / min by spraying so that the average diameter of the droplets was 300 μm to react with the polyisocyanate. After the addition of acetaldehyde oxime, the reaction was continued by stirring until there was no NCO characteristic absorption peak in infrared detection, thereby obtaining the blocked isocyanate, and the tested chromaticity was 10 Hazen.

[0085] Example 5

[0086] A blocked isocyanate and a preparation method thereof, wherein the steps of the preparation method are as follows:

[0087] (1) 600 g of cyclohexanone oxime was added to a flask, heated to 100° C. in a nitrogen atmosphere, 1 g of sodium carbonate was added, stirred at 100° C. for 60 min, and filtered; and vacuum distilled to obtain the treated cyclohexanone oxime, i.e., an oxime blocking agent, whose acid value was 0.01 mgKOH / g;

[0088] (2) 500 g of polyisocyanate and 534 g of S100 solvent oil were stirred in a reactor, protected by nitrogen, condensed and refluxed, and the temperature was raised to 50° C.; 300 g of the treated cyclohexanone oxime (acid value: 0.01 mg KOH / g) obtained in step (1) was added into the reactor at a rate of 3 g / min by spraying so that the average diameter of the droplets was 400 μm to react with the polyisocyanate. After the addition of cyclohexanone oxime, the reaction was continued by stirring until there was no NCO characteristic absorption peak in infrared detection, thereby obtaining the blocked isocyanate, and the tested chromaticity was 10 Hazen.

[0089] Comparative Example 1

[0090] A blocked isocyanate and a preparation method thereof, wherein the steps of the preparation method are as follows:

[0091] 1000g of polyisocyanate and 487g of S100 solvent oil were stirred in a reactor, protected by nitrogen, condensed and refluxed, and the temperature was raised to 50°C; 463g of butanone oxime (untreated, acid value of 0.05mg KOH / g) was added to the reactor at a uniform rate of 3g / min by dropwise addition to react with the polyisocyanate, and after the butanone oxime was added, the stirring reaction was continued until there was no NCO characteristic absorption peak in infrared detection, to obtain the blocked isocyanate, and the test chromaticity was 14Hazen.

[0092] Comparative Example 2

[0093] A blocked isocyanate and a preparation method thereof, wherein the steps of the preparation method are as follows:

[0094] (1) 600 g of butanone oxime was added to a flask, and 1 g of sodium hydroxide was added under nitrogen atmosphere, and the mixture was stirred at 40° C. for 60 min, and filtered; then, the mixture was heated to 90° C. and distilled under reduced pressure to obtain the treated butanone oxime, i.e., an oxime-based blocking agent, whose acid value was 0.01 mgKOH / g;

[0095] (2) 1000 g of polyisocyanate and 487 g of S100 solvent oil were stirred in a reactor, protected by nitrogen, condensed and refluxed, and the temperature was raised to 50° C.; 463 g of the treated butanone oxime (acid value: 0.01 mg KOH / g) obtained in step (1) was added to the reactor at a uniform rate of 3 g / min to react with the polyisocyanate. After the butanone oxime was added, the reaction was continued to be stirred until there was no NCO characteristic absorption peak in infrared detection, thereby obtaining the blocked isocyanate, and the tested chromaticity was 12 Hazen.

[0096] Comparative Example 3

[0097] A blocked isocyanate and a preparation method thereof, wherein the steps of the preparation method are as follows:

[0098] 1000g of polyisocyanate and 487g of S100 solvent oil were stirred in a reactor, protected by nitrogen, condensed and refluxed, and the temperature was raised to 50°C; 463g of butanone oxime (untreated, acid value of 0.05mg KOH / g) was added to the reactor at a speed of 3g / min by spraying so that the average diameter of the droplets was 200μm, and reacted with the polyisocyanate. After the butanone oxime was added, the reaction was continued to be stirred until there was no NCO characteristic absorption peak in infrared detection, to obtain the blocked isocyanate, and the test chromaticity was 13Hazen.

[0099] Comparative Example 4

[0100] A blocked isocyanate and a preparation method thereof, wherein the steps of the preparation method are as follows:

[0101] (1) After filtering butanone oxime, heating to 90° C. and distilling under reduced pressure to obtain treated butanone oxime, i.e., an oxime blocking agent, the acid value of which is 0.05 mg KOH / g;

[0102] (2) 1000 g of polyisocyanate and 487 g of S100 solvent oil were stirred in a reactor, protected by nitrogen, condensed and refluxed, and the temperature was raised to 50° C.; 463 g of the treated butanone oxime (acid value: 0.05 mg KOH / g) obtained in step (1) was added to the reactor at a rate of 3 g / min by spraying so that the average diameter of the droplets was 200 μm, and reacted with the polyisocyanate. After the butanone oxime was added, the reaction was continued to be stirred until there was no NCO characteristic absorption peak in infrared detection, thereby obtaining the blocked isocyanate, and the test chromaticity was 14 Hazen.

[0103] Comparative Example 5

[0104] A blocked isocyanate and a preparation method thereof, wherein the steps of the preparation method are as follows:

[0105] (1) purifying butanone oxime by distillation, wherein the theoretical plate number of the packed tower is 20, the butanone oxime is purified by continuous distillation, the tower top pressure is 5 kPa, the tower bottom temperature is 95° C., and the purified butanone oxime is extracted from the side line, and the acid value thereof is 0.05 mg KOH / g;

[0106] (2) 1000 g of polyisocyanate and 487 g of S100 solvent oil were stirred in a reactor, protected by nitrogen, condensed and refluxed, and the temperature was raised to 50° C.; 463 g of the purified butanone oxime (acid value: 0.05 mg KOH / g) obtained in step (1) was added to the reactor at a rate of 3 g / min by spraying so that the average diameter of the droplets was 200 μm to react with the polyisocyanate. After the butanone oxime was added, the reaction was continued to be stirred until there was no NCO characteristic absorption peak in infrared detection, thereby obtaining the blocked isocyanate, and the test chromaticity was 13 Hazen.

[0107] The blocked isocyanates obtained in Examples 1-3 and Comparative Examples 1-5 were stored in a constant temperature environment at 60° C. for 3 months, and then the chromaticity thereof was tested using a BYK digital colorimeter and compared with the chromaticity before storage. The results are shown in Table 1:

[0108] Table 1

[0109]

[0110]

[0111] Combined with the test data in Table 1, it can be seen that compared with the conventional preparation method of Comparative Example 1, in the preparation method provided by the present invention, an oxime blocking agent is obtained by a specific alkali treatment method, and the droplet diameter of the oxime blocking agent is controlled. Through the design of raw materials and processes and their synergistic effect, the chromaticity of the blocked isocyanate can be effectively reduced, and the storage stability of the blocked isocyanate can be significantly improved. The chromaticity is ≤10 Hazen, and the chromaticity after storage at 60°C for 3 months is 12-15 Hazen.

[0112] Combining Example 1 with Comparative Examples 2-3, it can be seen that in the present invention, the specific alkali treatment method of the oxime substance and the droplet control of the oxime blocking agent have a synergistic effect, and both are indispensable. If only butanone oxime is subjected to alkali treatment (Comparative Example 2) or only the droplet diameter of butanone oxime is controlled (Comparative Example 3), the chromaticity of the blocked isocyanate cannot be effectively reduced and its storage stability cannot be improved. In addition, if the specific alkali treatment method in the present invention is not adopted, even if butanone oxime is purified by distillation or rectification (Comparative Examples 4-5), low chromaticity and good storage stability cannot be obtained.

[0113] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate the blocked isocyanate and its preparation method and application, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a blocked isocyanate, characterized in that: The preparation method comprises: mixing an oxime substance with an alkaline compound and treating the mixture, purifying the product obtained by the treatment, and obtaining an oxime blocking agent; The oxime blocking agent is added to the polyisocyanate in the form of droplets with a diameter of ≤500 μm and reacted to obtain the blocked isocyanate; The acid value of the oxime blocking agent is ≤0.03 mg KOH / g; The molar ratio of the oxime blocking agent to the NCO group in the polyisocyanate is (0.95-1.1):

1.

2. The preparation method according to claim 1, characterized in that: The oxime substances include any one of butanone oxime, acetone oxime, cyclohexanone oxime and acetaldehyde oxime, or a combination of at least two of them.

3. The preparation method according to claim 1, characterized in that: The alkaline compound includes any one of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate, or a combination of at least two thereof.

4. The preparation method according to claim 1, characterized in that: Based on the mass of the oxime substance being 100%, the mass of the basic compound is 0.05-1%.

5. The preparation method according to claim 1, characterized in that: The treatment is carried out under stirring conditions.

6. The preparation method according to claim 1, characterized in that: The treatment is carried out in an inert protective atmosphere.

7. The preparation method according to claim 1, characterized in that: The treatment temperature is 30-100°C.

8. The preparation method according to claim 1, characterized in that: The treatment time is 30-90 min.

9. The preparation method according to claim 1, characterized in that: The purification method includes any one of filtration, distillation, and rectification, or a combination of at least two of them.

10. The preparation method according to claim 9, characterized in that: The purification method includes a combination of filtration and distillation.

11. The preparation method according to claim 9, characterized in that: The distillation includes reduced pressure distillation.

12. The preparation method according to claim 9, characterized in that: The distillation temperature is 70-100°C.

13. The preparation method according to claim 1, characterized in that: The acid value of the oxime sealing agent is ≤0.01 mgKOH / g.

14. The preparation method according to claim 1, characterized in that: The NCO functionality of the polyisocyanate is ≥2.

5.

15. The preparation method according to claim 1, characterized in that: The mass percentage of NCO groups in the polyisocyanate is 5-30%.

16. The preparation method according to claim 1, characterized in that: The reaction is carried out in an inert protective atmosphere.

17. The preparation method according to claim 1, characterized in that: The reaction temperature is 30-120°C.

18. The preparation method according to claim 17, characterized in that: The reaction temperature is 40-80°C.

19. The preparation method according to claim 1, characterized in that: The reaction time is 0.5-10h.

20. The preparation method according to claim 19, characterized in that: The reaction time is 2-5h.

21. The preparation method according to claim 1, characterized in that: The preparation method comprises the following steps: (1) mixing an oxime substance with an alkaline compound, treating the mixture at 30-100° C. with stirring for 30-90 min; purifying the product obtained by the treatment to obtain an oxime blocking agent, wherein the acid value of the oxime blocking agent is ≤0.03 mg KOH / g; (2) adding the oxime blocking agent obtained in step (1) to the polyisocyanate in the form of droplets with a diameter of ≤500 μm, and reacting at 30-120° C. for 0.5-10 h in an inert protective atmosphere to obtain the blocked isocyanate; The molar ratio of the oxime blocking agent to the NCO group in the polyisocyanate is (0.95-1.1):

1.

22. A blocked isocyanate, characterized in that: The blocked isocyanate is prepared by the preparation method according to any one of claims 1 to 21.

23. The blocked isocyanate according to claim 22, characterized in that The chromaticity of the blocked isocyanate is ≤12 Hazen.

24. Use of the blocked isocyanate according to claim 22 or 23 in polyurethane coatings, polyurethane adhesives or polyurethane elastomers.

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