Preparation method of polyisocyanate with adjustable viscosity

Abstract

The invention relates to a preparation method of polyisocyanate with adjustable viscosity. The preparation method comprises the following steps: reacting reaction raw materials containing diisocyanate; a step of recovering or supplementing diisocyanate so that the mass percentage of diisocyanate in the reaction system is 30%-80%; and heating the reaction system and further reacting. The polyisocyanate can be an isocyanurate tripolymer or polyisocyanate biuret, the raw material of the isocyanurate tripolymer is diisocyanate, and the raw material of the polyisocyanate biuret is diisocyanate and diamine. According to the preparation method, the viscosity range of the polyisocyanate product can be adjusted and expanded, meanwhile, it is guaranteed that the polyisocyanate product has enough crosslinking density, the production cost is low, and the requirement for equipment is low.

Description

Technical Field

[0001] The present invention specifically relates to a method for preparing polyisocyanate with adjustable viscosity. Background Art

[0002] Diisocyanate (including fat / alicyclic / aromatic, collectively referred to as DI) is a chemical substance containing two -NCO groups, -NCO is highly reactive and can react chemically with many substances. Therefore, isocyanate has a wide range of applications in many fields, such as coatings, adhesives, foam plastics, rubber, textiles, medicine, etc. It has been widely used in the above-mentioned fields, but its own toxicity and volatility also bring many restrictions to its direct use, so it is usually converted into polyisocyanates containing uretdione, carbamate, allophanate, isocyanurate ring, iminooxadiazinedione, and biuret structure before application. However, uretdione has a linear structure and a low cross-linking density, which is not conducive to the cross-linking of isocyanate during application. Therefore, the content of uretdione in polyisocyanate products should be controlled at a low level. In addition, in recent years, due to the increasingly perfect development of downstream application fields, polyisocyanates with different viscosities are usually required in different formulations. Therefore, how to obtain a polyisocyanate with a wide viscosity range and adjustable viscosity while ensuring sufficient cross-linking density of the polyisocyanate is a difficulty in polyisocyanate technology.

[0003] The two typical polyisocyanates are isocyanurate trimers containing an isocyanurate ring and polyisocyanates containing a biuret structure.

[0004] For isocyanurate trimers containing isocyanurate rings, in order to reduce their viscosity, there are currently two main preparation methods: 1. By introducing low-viscosity by-products such as uretdione to reduce the overall viscosity of the product, patents EP0166173B1, EP0481318B1, HK1117156A, CN1509301A, CN106604944B, CN110128624B, and CN114213625A respectively introduce uretdione by introducing specific catalysts and increasing the processing temperature, which greatly reduces the viscosity of the heavy component. However, uretdione with low crosslinking and low thermal stability often reduces the application performance of the product, and the content of uretdione in the polyisocyanate product should be controlled; in this method, since uretdione has a linear structure, introducing more uretdione into the polymer will result in low crosslinking strength and thermal stability after film formation, which has a negative impact on the quality of the paint film. At the same time, uretdione is easy to decompose during storage, resulting in an increase in monomers with low saturated vapor pressure, which is not conducive to the health of construction workers; ② Through the reasonable design of the catalyst, for example, patents CN114262302B and CN115246793B use steric hindrance to inhibit the formation of polymers and prepare low-viscosity isocyanurate trimers; patents EP0962455 A1, EP0339396 A1 and EP0315692 A1, CN114588939A use asymmetric catalysts containing fluorine and phosphorus catalysts to increase the proportion of asymmetric trimers (imidooxadiazinediones) during the reaction stage. Its asymmetric structure leads to a weakened molecular stacking, thereby weakening the intermolecular force and ultimately reducing the viscosity of the product. This method has high requirements for the route design of the catalyst and the production equipment, especially the catalysts used in the oxadiazinedione system are mostly made of hydrofluoric acid, which is dangerous and seriously corrosive to the equipment.

[0005] For polyisocyanates containing biuret structures, their preparation can generally be divided into two categories: amine method and water method. Currently, all patents reported to reduce the viscosity of such products use water method, such as CN 116444764 A and CN 108047428 B. Compared with the water method, amine method biuret has the advantages of high atomic utilization, economic and environmental protection, and small equipment footprint. At present, most of the industry uses amine method. However, there are other limitations when synthesizing biuret by amine method (diamine DA and diisocyanate DI react to generate biuret, and the flow rates of DA and DI raw materials are controlled separately). For example, when the flow rate of diamine DA is small, the requirements for the precision of the reactor nozzle are increased, otherwise the dispersion effect is poor and a large amount of polymers are easily generated, which may even cause equipment blockage in severe cases; when the flow rate of diamine DA is large, the flow rate of diisocyanate DI also needs to be increased accordingly, resulting in a large amount of energy consumption in the later stage of the reaction to evaporate the excess DI monomer, and the requirements for the equipment for conveying DI and DA are also increased. Therefore, the production cost of the product will be greatly increased. In addition, the viscosity range of the biuret prepared in the currently reported amine process is relatively narrow, which is not conducive to co-production; and no relevant patents for adjusting the viscosity of biuret using the amine process have been found. How to further expand the viscosity range of biuret while maintaining the advantages of amine-based biuret synthesis is a technical difficulty in this field. Summary of the invention

[0006] The object of the present invention is to provide a method for preparing polyisocyanates with adjustable viscosity, which can adjust and expand the viscosity range of the polyisocyanate products while ensuring that the polyisocyanate products have sufficient crosslinking density, and has low production costs and low equipment requirements.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A method for preparing polyisocyanate comprises the steps of reacting reaction raw materials containing diisocyanate; recovering or adding diisocyanate so that the mass percentage of diisocyanate in the reaction system is 30%-80%; and heating the reaction system and further reacting.

[0009] In the prior art, when synthesizing polyisocyanates such as isocyanurate trimer or polyisocyanate biuret, diisocyanate raw materials or diisocyanate and diamine raw materials are directly reacted, and after the reaction is completed, the reaction system is directly subjected to separation and purification such as distillation to obtain the target product of isocyanurate trimer or polyisocyanate biuret. During the reaction, the overall viscosity of the product is reduced by introducing low-viscosity byproducts such as uretdione, or by using a specific type of catalyst to increase the proportion of asymmetric trimers in the reaction stage to reduce the viscosity of the reaction product. The inventors of the present application have found through research that by controlling the mass percentage of diisocyanate in the reaction system during the reaction process within a specific range, and then further reacting the reaction system, the final polyisocyanate such as isocyanurate trimer or polyisocyanate biuret can have a suitable wide range of viscosity, and the quality of the polyisocyanate product is guaranteed, with sufficient crosslinking density, and does not affect subsequent utilization.

[0010] In some embodiments, the polyisocyanate includes an isocyanurate trimer, and the reaction raw material is a diisocyanate; the preparation method includes the following steps: 1) reacting the reaction raw material containing the diisocyanate, and terminating the reaction when the NCO mass percentage of the reaction system drops to 43.0%-49.5%; 2) recovering or adding the diisocyanate so that the mass percentage of the diisocyanate in the reaction system is 30%-80%; 3) heating the reaction system and further reacting, and when the NCO mass percentage of the reaction system drops to 30.0%-43.0%, cooling the reaction system; 4) separating and purifying the reaction system to obtain the polyisocyanate. This scheme targets isocyanurate trimer as the target product of polyisocyanate.

[0011] When the reaction in step 1) is terminated, if the content of diisocyanate in the reaction system is lower than the target content in step 2), the target content is met by additionally adding diisocyanate; when the reaction in step 1) is terminated, if the content of diisocyanate in the reaction system is higher than the target content in step 2), the target content is met by recovering diisocyanate.

[0012] In some embodiments, in step 2), the recovery is selected from a combination of one or more of rectification, distillation and flash evaporation.

[0013] In some embodiments, in step 3), when the NCO mass percentage of the reaction system drops to 33.0%-37.0%, the reaction system is cooled.

[0014] In some embodiments, in step 3), the temperature of the further reaction is 140-170°C.

[0015] In some embodiments, the further reaction time is 0.5-1.5 h.

[0016] In some embodiments, in step 3), the temperature of the reaction system is reduced to 20-100°C.

[0017] In some embodiments, in step 1), the reaction temperature is 50-260°C, preferably 55-230°C.

[0018] In some embodiments, the reaction in step 1) is carried out in the presence of a catalyst.

[0019] In some embodiments, the catalyst is selected from one or both of a quaternary ammonium salt and a quaternary ammonium base.

[0020] In some embodiments, the quaternary ammonium salt is selected from one or both of tetraalkyl quaternary ammonium salts and trialkyl aralkyl quaternary ammonium salts; the quaternary ammonium base is selected from one or both of tetraalkyl quaternary ammonium bases and trialkyl aralkyl quaternary ammonium bases; the number of carbon atoms of the alkyl group is 1-6, and the number of carbon atoms of the aralkyl group is 6-12.

[0021] Preferably, the catalyst is benzyltrimethylammonium hydroxide among trialkylaralkyl quaternary ammonium bases.

[0022] In some embodiments, in step 1), a terminator is added to the reaction system to terminate the reaction.

[0023] In some embodiments, the terminator is selected from a combination of one or more of phosphoric acid, dibutyl phosphate, benzoyl chloride, p-benzoic acid, and p-toluenesulfonic acid.

[0024] In some embodiments, the viscosity of the polyisocyanate at 25° C. is 350-650 mPa·s.

[0025] In some embodiments, the polyisocyanate further comprises uretdione dimer, and the mass percentage of the uretdione dimer in the polyisocyanate is 1%-5%. The viscosity of the uretdione dimer is relatively low, and the crosslinking density is also relatively low. By controlling the uretdione dimer within the above range, the isocyanurate trimer of the present invention can have a suitable and wide viscosity range, and the crosslinking density can also be guaranteed.

[0026] In some embodiments, the polyisocyanate further comprises a combination of one or more of isocyanurate tetramer, isocyanurate hexamer, isocyanurate octamer, isocyanurate decamer, and isocyanurate dodecamer or higher.

[0027] The aforementioned isocyanurate dodecamer refers to a polymer formed by the reaction of isocyanurate and twelve or more diisocyanate monomers.

[0028] In some embodiments, the mass percentage of the isocyanurate tetramer in the polyisocyanate is 5%-15%.

[0029] In some embodiments, the mass percentage of isocyanurate pentamers (including the aforementioned isocyanurate hexamers, isocyanurate octamers, isocyanurate decamers, isocyanurate dodecamers and isocyanurate pentamers) in the polyisocyanate is 20%-25%.

[0030] In some embodiments, the polyisocyanate includes polyisocyanate biuret, and the reaction raw materials are diisocyanate and diamine; the preparation method includes the following steps: 1) reacting the reaction raw materials including diisocyanate and diamine, wherein the mass ratio of diisocyanate to diamine is 10 to 60:1; 2) recovering or adding the diisocyanate so that the mass percentage of diisocyanate in the reaction system is 30%-80%; 3) heating the reaction system and further reacting, and when the mass percentage of NCO in the reaction system drops to 30.0%-43.0%, cooling the reaction system; 4) separating and purifying the reaction system to obtain the polyisocyanate. This scheme targets polyisocyanate biuret as the target product of polyisocyanate.

[0031] In some embodiments, the mass ratio of the diisocyanate to the diamine is 15 to 50:1.

[0032] In some embodiments, the diamine is selected from one or more combinations of ethylenediamine, 1,3-propylenediamine, 1,3-butylenediamine, and hexamethylenediamine.

[0033] In some embodiments, in step 2), the recovery is selected from a combination of one or more of rectification, distillation and flash evaporation.

[0034] In some embodiments, in step 3), when the NCO mass percentage of the reaction system drops to 33%-37%, the reaction system is cooled.

[0035] In some embodiments, in step 3), the temperature of the further reaction is 140-170°C.

[0036] In some embodiments, in step 3), the further reaction time is 0.5-1.5 h.

[0037] In some embodiments, in step 1), the reaction temperature is 50-260°C, preferably 55-230°C.

[0038] In some embodiments, the viscosity of the polyisocyanate at 25° C. is 300-9000 mPa·s.

[0039] In some embodiments, the mass percentage of the polyisocyanate biuret to the polyisocyanate is 30%-70%.

[0040] In some embodiments, the polyisocyanate further comprises a combination of one or more of isocyanurate pentamer, isocyanurate heptamer, isocyanurate nonamer, and isocyanurate undecamer or higher.

[0041] In some embodiments, the mass percentage of the isocyanurate pentamer in the polyisocyanate is 13%-25%.

[0042] In some embodiments, the mass percentage of the isocyanurate heptamer in the polyisocyanate is 13%-20%.

[0043] In some embodiments, the mass percentage of the isocyanurate nonamer to the polyisocyanate is 1%-12%.

[0044] In some embodiments, the mass percentage of the isocyanurate undecamer or higher in the polyisocyanate is 0.5%-15%.

[0045] In some embodiments, the preparation method further comprises the step of preheating the diisocyanate and the diamine separately before the two are reacted.

[0046] In some embodiments, the step of reacting the reaction raw materials including diisocyanate and diamine comprises heating the diisocyanate and diamine in the diisocyanate pipe and diamine pipe of the heating furnace respectively, the diisocyanate pipe and the diamine pipe merge at the outlet of the heating furnace, and the steps of reacting and ejecting the diisocyanate and diamine at the outlet. Since the two react instantly at the outlet and the temperature of the reaction system is high, it is not convenient to sample and analyze the NCO content of the reaction system. However, by controlling the diisocyanate and diamine raw materials, the diisocyanate far exceeds the molar stoichiometric ratio, and the reaction system has a large amount of excess diisocyanate after the reaction. Therefore, the diisocyanate is recovered to meet the target content of 30%-80% required by the present invention, and the reaction system is further reacted.

[0047] In some embodiments, in step 4), the separation and purification is selected from rectification, distillation or flash evaporation.

[0048] In some embodiments, the diisocyanate is selected from aliphatic, alicyclic or aromatic diisocyanates.

[0049] Preferably, the diisocyanate is selected from methyl isocyanate, ethyl isocyanate, propyl isocyanate, phenyl isocyanate, cyclohexyl isocyanate, 1,4-butylene diisocyanate, 1,5-pentane diisocyanate, hexamethylene diisocyanate, cyclohexane dimethylene diisocyanate, 1,5-diisocyanate-2-methylpentane, 1,4-diisocyanate cyclohexane, isophorone diisocyanate, meta-xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, p-phenylene diisocyanate, 1,5-naphthalene diisocyanate, methylcyclohexane diisocyanate, trimethyl hexamethylene diisocyanate, tetramethyl meta-xylylene diisocyanate, dimethyl biphenyl diisocyanate esters, norbornane dimethylene isocyanate, 1,8-diisocyanato-4-isocyanatomethyloctane, nonane triisocyanate, 2-tetrahydrofuran isocyanate, polyphenyl polymethylene polyisocyanate, 1-isocyanato-1-methyl-4(3)-isocyanatomethylcyclohexane, triisocyanatocyclohexane, tri(isocyanatomethyl)cyclohexane, triisocyanatomethylcyclohexane, 1,8-diisocyanato-4-(isocyanatomethyl)octane, undecane 1,6,11-triisocyanate, 1,7-diisocyanato-4-(3-isocyanatopropyl)heptane, 1,6-diisocyanato-3-(isocyanatomethyl)hexane or 1,3,5-tri(isocyanatomethyl)cyclohexane.

[0050] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0051] The present invention can adjust the collision probability of different molecules in the reaction system by adjusting the content of diisocyanate DI monomer in the crude product, and then flexibly adjust the composition and viscosity of the final polyisocyanate product, so that the final polyisocyanate product has a suitable viscosity for subsequent applications but in a wide range, and its performance such as crosslinking density can be guaranteed.

[0052] The present invention can realize the co-production of biuret with different viscosities, meet the needs of different customers, and the production process has low requirements on equipment.

[0053] The present invention does not require deliberate design and development of new catalysts, which reduces research and development costs while also improving process safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a schematic diagram of the reaction apparatus of Example 10;

[0055] Among them, 1-nitrogen cylinder, 2-first buffer bottle, 3-nitrogen spare pipeline, 4-diisocyanate pipeline, 5-diamine pipeline, 6-heating furnace, 7-export, 8-second buffer bottle, 9-flash evaporator, 10-heater, 11-oil bath pot, 12-diisocyanate storage tank, 13-diamine storage tank, 14-double plunger pump. DETAILED DESCRIPTION

[0056] In the prior art, when synthesizing polyisocyanates such as isocyanurate trimer or polyisocyanate biuret, diisocyanate raw materials or diisocyanate and diamine raw materials are directly reacted, and after the reaction is completed, the reaction system is directly subjected to separation and purification such as distillation to obtain the target product of isocyanurate trimer or polyisocyanate biuret. During the reaction, the overall viscosity of the product is reduced by introducing low-viscosity byproducts such as uretdione, or by using a specific type of catalyst to increase the proportion of asymmetric trimers in the reaction stage to reduce the viscosity of the reaction product. The inventors of the present application have found through research that the viscosity of the polyisocyanate product can be flexibly adjusted by adjusting the monomer content of diisocyanate in the crude product (pre-distillation or addition of diisocyanate monomers).

[0057] Among them, for the target product of isocyanurate trimer, its synthesis reaction principle is as follows, wherein AB represents the catalyst of the reaction, and step 1) of the present invention mainly performs the following reaction:

[0058]

[0059] Where R is C 3-16 Straight chain, branched chain or cyclic hydrocarbon group; preferably C 3-16 Straight chain, branched chain or cyclic alkyl, or C 6-16 Aromatic groups;

[0060] In the reaction process of step 1), in addition to the above-mentioned isocyanurate trimer, uretdione dimer is also generated. The reaction principle of uretdione dimer is as follows. It has a linear structure and a cross-linking functionality of 2. The cross-linking density of the final polyisocyanate product containing it is low:

[0061]

[0062] The NCO group on the side arm of the above-mentioned isocyanate trimer will react with two molecules of isocyanate monomers to form a pentamer, and the NCO group on the side arm of the pentamer will react with two molecules of isocyanate monomers to form a heptamer. This process can be repeated to form an isocyanurate nonamer / higher odd-numbered polymer.

[0063] During the reheating reaction in step 3), the isocyanurate trimer will combine with the diisocyanate monomer to form a tetramer, and the reaction principle is shown in the following formula; the isocyanurate pentamer / heptamer / nonamer / higher odd-numbered polymers generated above will also react with the monomers to generate isocyanurate hexamer / octamer / decamer / higher even-numbered polymers. The isocyanurate hexamer / octamer / decamer / higher even-numbered polymers are asymmetric structures, and their symmetry is significantly lower than that of the original isocyanurate pentamer / heptamer / nonamer / higher odd-numbered polymers, and the molecular stacking degree is reduced, resulting in a decrease in the viscosity of the product.

[0064]

[0065] In the reaction system for synthesizing isocyanurate trimer, a trace amount of asymmetric trimer containing iminooxadiazinedione structure is also generated. The reaction formula is as follows:

[0066]

[0067] For the target product of polyisocyanate biuret, taking the preparation of HDI biuret from hexamethylene diisocyanate (HDI) and hexamethylene diamine (HDA) as an example, the reaction principle is shown in the following formula:

[0068] The first step is to form the intermediate product "bisurea" by reaction:

[0069]

[0070] The second step is to generate the intermediate product biuret:

[0071] The third step is to generate HDI biuret:

[0072]

[0073] In the present invention, after further heating and reaction by setting step 3), the above-mentioned biuret undergoes a cracking-recombination reaction, and the mechanism and reaction formula are as follows, so that the final polyisocyanate product, in addition to the HDI biuret target product, also contains isocyanurate pentamer, isocyanurate heptamer, isocyanurate nonamer, isocyanurate undecamer or more, etc.:

[0074]

[0075] The reaction and combination mechanism of isocyanurate nonamers and isocyanurate undecamers is similar to the above formula.

[0076] From the above reaction formula and reaction mechanism, it can be known that the biuret generated by the reaction of diisocyanate and diamine can be cleaved to produce urea diisocyanate, which can be recombined with diisocyanate DI mono / tri(biuret) / penta / hepta / nona / polymer to produce corresponding polymers. Theoretically, before the cleavage-recombination process reaches dynamic equilibrium, the more DI content, the higher the content of trimer (biuret), the lower the content of polymer, and the lower the viscosity of the polyisocyanate product; if before reaching dynamic equilibrium, the less DI content, the lower the content of trimer (biuret), the higher the content of polymer, the higher the viscosity of the polyisocyanate product.

[0077] The present invention converts linear uretdione dimers into more stable asymmetric isocyanurate-uretdione tetra / hexa / octa / deca / polymers, and the packing density between asymmetric molecules is less than that between symmetric molecules. Therefore, the present invention can reduce the viscosity of polyisocyanate, effectively reduce the uretdione content in the product, and improve product performance.

[0078] The present invention can flexibly select the ratio of diisocyanate DI monomer to biuret reagent according to the equipment capacity, thereby reducing the requirements of amine-based biuret on equipment.

[0079] In the present invention, the ratio of diisocyanate / diamine (DI / DA) in the amine-based biuret synthesis stage does not need to be too extreme, which can reduce the process difficulty (ensuring continuous and efficient operation of the equipment) and post-processing energy consumption.

[0080] The method for detecting the mass percentage of NCO in the present invention adopts the commonly used hydrochloric acid-di-n-butylamine chemical titration method.

[0081] The technical solution of the present invention is described in detail below in conjunction with specific embodiments so that those skilled in the art can better understand and implement the technical solution of the present invention, but the present invention is not limited to the scope of the examples.

[0082] Among them, Examples 1-9 and Comparative Examples 1-6 involve the synthesis of isocyanurate trimers; the others involve the synthesis of polyisocyanate biuret.

[0083] Example 1

[0084] This embodiment provides a method for preparing an isocyanurate trimer, and the specific steps are as follows:

[0085] 1) Add 1500g of hexamethylene diisocyanate (HDI) to a 2L four-necked bottle, check the air tightness and use a vacuum pump to remove dissolved air for 1h while stirring. After heating to 60°C, slowly drop a 3% ethanol solution of a catalyst, the catalyst being benzyltrimethylammonium hydroxide. Monitor the change of NCO in the reaction system while the reaction is carried out. When the mass percentage of NCO drops to 46.3%, add a terminator, dibutyl phosphate, to terminate the reaction and obtain a trimer reaction solution, in which the mass percentage of HDI is 83%.

[0086] 2) recovering part of HDI from the terminated reaction solution by continuous distillation, so that the HDI mass content in the reaction solution is 60%, and the NCO mass percentage is 38%;

[0087] 3) The reaction solution after recovering part of the HDI was heated to 155°C and kept warm for 1 hour, at which time the NCO mass percentage of the reaction system dropped to 35%, and the temperature was rapidly lowered to 90°C;

[0088] 4) Rectification to remove HDI and obtain a low-viscosity HDI polyisocyanate product.

[0089] Example 2

[0090] This embodiment provides a method for preparing an isocyanurate trimer. The specific steps are basically the same as those in Embodiment 1, except that after recovering part of HDI in step 2), the HDI mass content in the reaction solution is set to 70%.

[0091] Example 3

[0092] This embodiment provides a method for preparing an isocyanurate trimer. The specific steps are basically the same as those in Embodiment 1, except that after recovering part of HDI in step 2), the HDI mass content in the reaction solution is set to 65%.

[0093] Example 4

[0094] This embodiment provides a method for preparing an isocyanurate trimer. The specific steps are basically the same as those in Embodiment 1, except that after recovering part of HDI in step 2), the HDI mass content in the reaction solution is adjusted to 50%.

[0095] Example 5

[0096] This embodiment provides a method for preparing an isocyanurate trimer. The specific steps are basically the same as those in Embodiment 1, except that after recovering part of HDI in step 2), the HDI mass content in the reaction solution is set to 40%.

[0097] Example 6

[0098] This embodiment provides a method for preparing an isocyanurate trimer. The specific steps are basically the same as those in Embodiment 1, except that the insulation temperature in step 3) is replaced with 145° C., at which time the NCO mass percentage of the reaction system drops to 35.5%.

[0099] Example 7

[0100] This embodiment provides a method for preparing an isocyanurate trimer. The specific steps are basically the same as those in Embodiment 1, except that the insulation temperature in step 3) is replaced with 165° C., at which time the NCO mass percentage of the reaction system drops to 34.5%.

[0101] Example 8

[0102] This embodiment provides a method for preparing an isocyanurate trimer. The specific steps are basically the same as those in Embodiment 1, except that the holding time in step 3) is replaced with 0.5 h, at which time the NCO mass percentage of the reaction system drops to 35.7%.

[0103] Example 9

[0104] This embodiment provides a method for preparing an isocyanurate trimer. The specific steps are basically the same as those in Embodiment 1, except that the holding time in step 3) is replaced with 1.5 h, at which time the NCO mass percentage of the reaction system drops to 34.8%.

[0105] Comparative Example 1

[0106] This comparative example provides a method for preparing an isocyanurate trimer. The specific steps are basically the same as those in Example 1, except that step 2) is not performed, and the reaction solution obtained in step 1) is directly subjected to the temperature-raising reaction in step 3).

[0107] Comparative Example 2

[0108] This comparative example provides a method for preparing an isocyanurate trimer. The specific steps are basically the same as those in Example 1, except that after recovering part of HDI in step 2), the HDI mass content in the reaction solution is set to 25%.

[0109] Comparative Example 3

[0110] This comparative example provides a method for preparing an isocyanurate trimer. The specific steps are basically the same as those in Example 1, except that the insulation temperature in step 3) is replaced with 135°C.

[0111] Comparative Example 4

[0112] This comparative example provides a method for preparing an isocyanurate trimer. The specific steps are basically the same as those in Example 1, except that the insulation temperature in step 3) is replaced with 175°C.

[0113] Comparative Example 5

[0114] This comparative example provides a method for preparing an isocyanurate trimer. The specific steps are basically the same as those in Example 1, except that step 3) is not performed, and the reaction liquid obtained in step 1) is directly subjected to continuous distillation to remove all HDI to obtain an HDI polyisocyanate product.

[0115] Comparative Example 6

[0116] This comparative example provides a method for preparing an isocyanurate trimer. The specific steps are basically the same as those in Example 1, except that the holding time in step 3) is replaced with 2 hours.

[0117] The polyisocyanate products of the above-mentioned embodiments and comparative examples were subjected to composition detection and viscosity detection. Among them, the composition detection uses liquid chromatography, the chromatographic column is a gel chromatographic column, the sample is diluted and detected using ethyl acetate, the mobile phase is tetrahydrofuran, the detection wavelength is 210nm, and the area normalization method is used to process the spectrum. The viscosity detection is detected using a BROOKFIELD-RSX model rheometer, and the detection temperature is 25°C. The results are shown in Table 1 below, and the process parameters are also listed in Table 1. Among them, "-" means not involved, trimer refers to isocyanurate trimer and asymmetric trimer containing trace amounts of imino oxadiazinedione structure, tetramer refers to isocyanurate tetramer, pentamer or more refers to isocyanurate pentamer, cyanurate hexamer, cyanurate heptamer, isocyanurate octamer, cyanurate nonamer, isocyanurate decamer, cyanurate elevenmer, isocyanurate twelve or more polymers, etc., and uretdione refers to uretdione dimer.

[0118] Table 1

[0119]

[0120] In Table 1, in Comparative Example 1, the HDI monomer content in the reaction solution is too much, the probability of monomer-monomer reaction increases, and the content of uretdione generated is too much; in Comparative Example 2, the HDI monomer content is too little, the probability of polymer-polymer reaction increases, a product with a higher degree of polymerization is generated, and the product viscosity is too large; in Comparative Example 3, the insulation reaction temperature is too low, which is not enough to trigger the formation of uretdione structure, and the product viscosity cannot be reduced, and the product viscosity is too high; in Comparative Example 4, the insulation reaction temperature is too high, a large amount of uretdione is generated, the content is too high, the product quality is poor, and the cross-linking density is low; in Comparative Example 5, without further heating and reaction, tetra / hexa / octa / decamers containing uretdione structure cannot be generated, the molecular symmetry is not reduced, and the product viscosity cannot be reduced; in Comparative Example 6, the heating time for further reaction is too long, a large amount of uretdione is generated, the content is too high, the product quality is poor, and the cross-linking density is low.

[0121] Example 10

[0122] This embodiment provides a method for preparing polyisocyanate biuret, which adopts Figure 1 The device shown in the figure, the specific steps of the method are as follows:

[0123] First, the nitrogen in the nitrogen cylinder 1 is used, and then the nitrogen is transported from the nitrogen standby pipeline 3 to the diisocyanate pipeline 4 and the diamine pipeline 5 through the first buffer bottle 2. The nitrogen passes through the heating furnace 6, the outlet 7 of the heating furnace, the second buffer bottle 8, the flash evaporation device, and the heating device in turn, and the entire device system is replaced with nitrogen. The diisocyanate pipeline 4 and the diamine pipeline 5 inside the heating furnace 6 are respectively in the shape of coils, and the diisocyanate and diamine are heated in their corresponding pipelines. At the outlet 7 of the heating furnace, the diisocyanate pipeline 4 and the diamine pipeline 5 are merged, and the diisocyanate and diamine raw materials are mixed and reacted instantly. The second buffer bottle 8 is used to buffer the initially unstable crude product. When the crude product accumulates to a certain amount, the crude product is discharged into the flash evaporation device.

[0124] The flash evaporation device is an oil bath arrangement, including an oil bath pot 11 and a flash evaporator 9, and the flash evaporator can be a four-necked flask. The heating device can also be an oil bath arrangement, including an oil bath pot 11 and a heater 10, and the heater can be a four-necked flask.

[0125] After nitrogen replacement is completed, the nitrogen is directly introduced into the diisocyanate pipeline 4 and the diamine pipeline 5, and respectively passes through the diisocyanate storage tank 12 and the diamine storage tank 13, as well as the double plunger pump 14, the heating furnace 6 and the subsequent system. Among them, the diisocyanate is hexamethylene diisocyanate (HDI) and the diamine is hexamethylene diamine (HDA).

[0126] After nitrogen replacement is completed, HDI and HDA are preheated to 100°C in the diisocyanate storage tank 12 and the diamine storage tank 13, respectively, and then pumped into the heating furnace 6 at a flow rate of 460 mL / min and 20 mL / min (the flow ratio of HDI and HDA is 23:1, the relative density of HDI is 1.047, the relative density of HAD is 0.883, and the mass ratio of the two is about 27.27:1) through two double plunger pumps 14, and heated to 180°C in the heating furnace 6. , reacts instantly at the outlet 7, and is immediately ejected, flows into the flash evaporation device through the second buffer bottle 8, and flashes out a portion of HDI at 135°C, so that the mass percentage of HDI in the crude product is 50%, and the mass percentage of NCO is 37.2% at this time; the crude product after flash evaporation is transferred to a heating device, heated at 180°C for 1h, at which time the mass percentage of NCO is 36.5%, and then cooled to 90°C; finally, the HDI monomer is removed by molecular distillation to obtain an HDI biuret product.

[0127] Examples 11-14

[0128] This embodiment provides a method for preparing polyisocyanate biuret, and the specific steps are basically the same as those of Embodiment 10, except that the mass content of HDI in the crude product after flash evaporation is adjusted, as shown in Table 2 below.

[0129] Comparative Examples 7-9

[0130] This comparative example provides a method for preparing polyisocyanate biuret, and the specific steps are basically the same as those in Example 10, except that the mass content of HDI in the crude product after flash evaporation is adjusted, as shown in Table 2 below.

[0131] Embodiment 15

[0132] This embodiment provides a method for preparing polyisocyanate biuret, and the specific steps are basically the same as those in Example 10, except that the flow rates of HDI and HDA are adjusted to 800 mL / min and 20 mL / min, respectively, and the mass content of HDI in the crude product after flash evaporation is adjusted, as shown in Table 2 below.

[0133] Example 16

[0134] This embodiment provides a method for preparing polyisocyanate biuret, and the specific steps are basically the same as those in Example 10, except that the flow rates of HDI and HDA are adjusted to 300 mL / min and 20 mL / min, respectively, and the mass content of HDI in the crude product after flash evaporation is adjusted, as shown in Table 2 below.

[0135] The polyisocyanate biuret products of the above-mentioned embodiments 10-16 and comparative examples 7-9 were subjected to composition detection and viscosity detection. Among them, the composition detection uses liquid chromatography, the chromatographic column is a gel chromatographic column, the sample is diluted and detected using ethyl acetate, the mobile phase is tetrahydrofuran, the detection wavelength is 210nm, and the area normalization method is used to process the spectrum. The viscosity detection is detected using a BROOKFIELD-RSX model rheometer, and the detection temperature is 25°C. The results are shown in Table 2 below. Among them, biuret refers to polyisocyanate biuret, pentamer refers to isocyanurate pentamer, heptamer refers to isocyanurate heptamer, nonamer refers to isocyanurate nonamer, and polymer refers to isocyanurate eleven or more polymers (expressed as polymers in Table 2), etc.

[0136] Table 2

[0137]

[0138] It can be seen from Examples 10 to 14 that by adjusting the mass proportion of HDI in the crude product kettle after flash evaporation, HDI biuret products with different compositions and viscosities can be obtained. And the final product composition is only related to the HDI content after flash evaporation, so that the ratio of HDI / EA can be adjusted according to actual needs during the biuret synthesis process.

[0139] It can be seen from Comparative Examples 7-9 that when the mass proportion of HDI in the crude product kettle after flash evaporation is not within the scope of the present application, the viscosity of the obtained HDI biuret product is too large or too small.

[0140] It can be seen from Examples 15-16 that when synthesizing biuret in the present invention, the ratio of HDI to HDA ​​can be adjusted according to the equipment, rather than selecting the equipment according to a fixed ratio, thereby reducing equipment investment.

[0141] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a polyisocyanate, characterized in that: The preparation method comprises the steps of reacting reaction raw materials containing diisocyanate; recovering or adding diisocyanate so that the mass percentage of diisocyanate in the reaction system is 30%-80%; and heating the reaction system and further reacting.

2. The method for preparing polyisocyanate according to claim 1, characterized in that: The polyisocyanate includes isocyanurate trimer, and the reaction raw material is diisocyanate; the preparation method includes the following steps: 1) reacting the reaction raw material containing diisocyanate, and terminating the reaction when the NCO mass percentage of the reaction system drops to 43.0%-49.5%; 2) recovering or adding the diisocyanate so that the mass percentage of the diisocyanate in the reaction system is 30%-80%; 3) heating the reaction system and further reacting, and when the NCO mass percentage of the reaction system drops to 30.0%-43.0%, cooling the reaction system; 4) separating and purifying the reaction system to obtain the polyisocyanate.

3. The method for preparing polyisocyanate according to claim 2, characterized in that: In step 2), the recovery is selected from a combination of one or more of rectification, distillation and flash evaporation; and / or, in step 3), when the NCO mass percentage of the reaction system drops to 33.0%-37.0%, the reaction system is cooled; and / or, in step 3), the temperature of the further reaction is 140-170°C; and / or, the time of the further reaction is 0.5-1.5h.

4. The method for preparing polyisocyanate according to claim 2, characterized in that: In step 1), the reaction temperature is 50-260° C.; and / or, the reaction in step 1) is carried out in the presence of a catalyst; and / or, in step 1), a terminator is added to the reaction system to terminate the reaction.

5. The method for preparing polyisocyanate according to claim 4, characterized in that: The catalyst is selected from one or two of quaternary ammonium salts and quaternary ammonium bases; and / or the terminator is selected from one or more combinations of phosphoric acid, dibutyl phosphate, benzoyl chloride, p-benzoic acid, and p-toluenesulfonic acid.

6. The method for preparing polyisocyanate according to claim 2, characterized in that: The viscosity of the polyisocyanate at 25° C. is 350-650 mPa·s; and / or, the polyisocyanate further includes a uretdione dimer, and the mass percentage of the uretdione dimer in the polyisocyanate is 1%-5%; and / or, the polyisocyanate further includes a combination of one or more of an isocyanurate tetramer, an isocyanurate hexamer, an isocyanurate octamer, an isocyanurate decamer, and an isocyanurate dodecamer or more.

7. The method for preparing polyisocyanate according to claim 1, characterized in that: The polyisocyanate includes polyisocyanate biuret, and the reaction raw materials are diisocyanate and diamine; the preparation method includes the following steps: 1) reacting the reaction raw materials including diisocyanate and diamine, wherein the mass ratio of the diisocyanate to the diamine is 10 to 60:1; 2) recovering or adding the diisocyanate so that the mass percentage of the diisocyanate in the reaction system is 30%-80%; 3) heating the reaction system and further reacting, and when the mass percentage of NCO in the reaction system drops to 30.0%-43.0%, cooling the reaction system; 4) separating and purifying the reaction system to obtain the polyisocyanate.

8. The method for preparing polyisocyanate according to claim 7, characterized in that: The diamine is selected from a combination of one or more of ethylenediamine, 1,3-propylenediamine, 1,3-butylenediamine, and hexamethylenediamine; and / or, in step 2), the recovery is selected from a combination of one or more of rectification, distillation, and flash evaporation; and / or, in step 3), when the NCO mass percentage of the reaction system drops to 33.0%-37.0%, the reaction system is cooled; and / or, in step 3), the temperature of the further reaction is 120-200°C; and / or, in step 3), the time of the further reaction is 0.5-1.5h.

9. The method for preparing polyisocyanate according to claim 7, characterized in that: In step 1), the reaction temperature is 50-260° C.; and / or the viscosity of the polyisocyanate at 25° C. is 300-9000 mPa·s; and / or the mass percentage of the polyisocyanate biuret in the polyisocyanate is 30%-70%; and / or the polyisocyanate further comprises a combination of one or more of isocyanurate pentamer, isocyanurate heptamer, isocyanurate nonamer, and isocyanurate undecamer or above.

10. The method for preparing polyisocyanate according to claim 7, characterized in that: The preparation method further includes the step of preheating the diisocyanate and the diamine separately before the two are reacted: and / or, the step of reacting the reaction raw materials containing diisocyanate and diamine includes heating the diisocyanate and the diamine in the diisocyanate pipe and the diamine pipe of the heating furnace respectively, the diisocyanate pipe and the diamine pipe merge at the outlet of the heating furnace, and the diisocyanate and the diamine react and spray out at the outlet.

11. The method for preparing a polyisocyanate according to claim 2 or 7, characterized in that: In step 4), the separation and purification is selected from rectification, distillation or flash evaporation.

12. The method for preparing polyisocyanate according to claim 1, characterized in that: The diisocyanate is selected from aliphatic, alicyclic or aromatic diisocyanates; preferably, the diisocyanate is selected from methyl isocyanate, ethyl isocyanate, propyl isocyanate, phenyl isocyanate, cyclohexyl isocyanate, 1,4-butanediisocyanate, 1,5-pentanediisocyanate, hexamethylene diisocyanate, cyclohexane dimethylene diisocyanate, 1,5-diisocyanate-2-methylpentane, 1,4-diisocyanate cyclohexane, isophorone diisocyanate, meta-xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, p-phenylene diisocyanate, 1,5-naphthalene diisocyanate, methylcyclohexane diisocyanate, trimethyl hexane diisocyanate, tetramethyl meta-xylylene diisocyanate isocyanate, dimethylbiphenyl diisocyanate, norbornane dimethylene isocyanate, 1,8-diisocyanato-4-isocyanatomethyloctane, nonane triisocyanate, 2-tetrahydrofuran isocyanate, polyphenyl polymethylene polyisocyanate, 1-isocyanato-1-methyl-4(3)-isocyanatomethylcyclohexane, triisocyanatocyclohexane, tris(isocyanatomethyl)cyclohexane, triisocyanatomethylcyclohexane, 1,8-diisocyanato-4-(isocyanatomethyl)octane, undecane 1,6,11-triisocyanate, 1,7-diisocyanato-4-(3-isocyanatopropyl)heptane, 1,6-diisocyanato-3-(isocyanatomethyl)hexane or 1,3,5-tris(isocyanatomethyl)cyclohexane.

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