A polyisocyanate composition and a method of preparation

Abstract

Disclosed are a polyisocyanate composition and a production method, the polyisocyanate composition being produced from raw materials including toluene diisocyanate and a polyol compound containing trimethylolpropane and optionally a di- to tetrahydric alcohol having a molecular weight of 62-200, the polyisocyanate composition containing urethane and allophanate, and simultaneously satisfying the following characteristics: a. the content of 2,4-toluene diisocyanate isomers forming the polyisocyanate composition is 85% or less, preferably 82% or less, more preferably 80% or less, of the total amount of toluene diisocyanate molar amount forming the polyisocyanate composition; and b. the polyisocyanate composition satisfies 33°C ≤ Tg ≤ 48°C, preferably 35°C ≤ Tg ≤ 42°C. The present application can obtain a polyisocyanate product having excellent normal-temperature and low-temperature storage stability without introducing impurity components.

Description

Technical Field

[0001] This invention relates to a polyisocyanate composition, and more particularly to a polyisocyanate composition and its preparation method. Background Technology

[0002] Polyurethane curing agents are widely used in high-performance coatings, paints, adhesives, decorative building materials, elastomers, and household goods. The flexible and versatile chemical reactions of polyurethane endow these products with excellent properties, such as compatibility with other components, outstanding thermal stability, and mechanical properties.

[0003] Compositions derived from organic polyhydroxy compounds, especially low-molecular-weight organic polyhydroxy compounds, and toluene diisocyanate-modified polyisocyanates are commonly used as polyisocyanate curing agents, finding wide application in coatings, adhesives, and inks. The preparation principle is based on the prepolymerization reaction of the diisocyanate component with the organic polyhydroxy compound to obtain a prepolymer reaction solution with NCO-terminated groups. Then, the diisocyanate monomer is removed, and the solution is diluted with solvent to obtain the final product.

[0004] Polyisocyanates with urethane groups synthesized from TDI are well known, such as those described in DE1090196(B) and DE953012(C). These polyisocyanates are very important in the fields of polyurethane coatings (also known as polyurethane paints) and polyurethane adhesives, particularly in wood coatings and adhesives. US3183112(A) describes the preparation of commercially available polyisocyanate products by reacting a polyhydroxy compound with 5 to 10 molar amounts of toluene diisocyanate, followed by separation and removal of excess starting diisocyanate in a thin-film evaporator, and then adding a suitable solvent.

[0005] However, in actual use of the above-mentioned polyisocyanate curing agents, some products sometimes develop flocculent matter after being stored at room temperature for a period of time. In severe cases, the flocculent matter may accumulate at the bottom of the product or cause stratification. Although the presence of flocculent matter or even stratification is a physical change, the product will become clear again after high-temperature heating treatment. The high-temperature treatment temperature is generally selected at 50-70℃. After heating and clarification, it does not affect the application performance of the product. However, the added heating treatment step affects the convenience of use of the product or increases customer inconvenience. In particular, when customers do not have the conditions for heating, it often leads to customer complaints. Therefore, how to solve such problems is a difficult problem currently faced by many TMP (trimethylolpropane) type polyisocyanate manufacturers.

[0006] CN112341595A discloses a polyisocyanate and its preparation method. A prepolymer reaction solution is obtained by reacting a system containing an organic polyhydroxy compound and an excess of toluene diisocyanate. The reaction temperature is controlled at 85℃-120℃, and the reaction time is 1 hour-24 hours. The ratio of the integrated area of ​​the component peak with a weight-average molecular weight of 800±50 to the integrated area of ​​the shoulder peak with a weight-average molecular weight of 950±50 is 2-14. Furthermore, the viscosity of the product is controlled to be less than or equal to 2500 mPa·s to improve its storage stability. However, the low-temperature storage stability of the product still does not adequately meet customer requirements.

[0007] CN1793194A describes an approach to improving the storage stability of a curing agent by adding high-molecular-weight polyethylene glycol 200 to a low-molecular-weight organic polyhydroxy compound. It is generally understood in the industry that high-molecular-weight polyethylene glycol 200 reacts with toluene diisocyanate to form a polymer component with an even higher molecular weight, potentially leading to increased viscosity and reduced isocyanate group content in the curing agent, which is detrimental to industrial applications. Furthermore, increasing the variety of raw material components also increases process complexity and raw material costs.

[0008] CN109824865A discloses a method for preparing a polyurethane curing agent with storage stability. The method involves reacting excess toluene diisocyanate with a hydroxyl compound, then adding an organic acid with a pKa value of 1-15 to the reaction solution, followed by high-temperature separation of the excess toluene diisocyanate monomer using a thin-film evaporator. The added organic acid is believed to reduce the activity of the isocyanate groups, inhibit product gelation, and thus improve the stability of the curing agent. However, the addition of organic acids (such as dibutyl phosphate) not only increases the complexity of the process and the cost of raw materials but also limits the application areas of the curing agent. Summary of the Invention

[0009] To address the above technical problems, this invention proposes a polyisocyanate composition and its preparation method. During the research on the influence of the structural composition of the polyisocyanate composition on its performance, the inventors unexpectedly discovered that when the content of the 2,4-toluene diisocyanate isomer in the polyisocyanate composition is adjusted to be less than 85%, preferably less than 82%, and more preferably less than 80% of the total molar amount of toluene diisocyanate in the polyisocyanate composition, and simultaneously the glass transition temperature (Tg) of the composition is adjusted to meet the following requirement: 33℃≤Tg≤48℃, preferably 35℃≤Tg≤42℃, a polyisocyanate product with superior room temperature and low-temperature storage stability can be obtained, thus completing this invention.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A polyisocyanate composition prepared from a raw material comprising toluene diisocyanate and a polyol compound, said polyol compound comprising trimethylolpropane and optionally a di- to tetraol with a molecular weight of 62-200, said polyisocyanate composition comprising a carbamate and a urethane, said polyisocyanate composition simultaneously satisfying the following characteristics:

[0012] a. The content of the 2,4-toluene diisocyanate isomer forming the polyisocyanate composition is 85% or less, preferably 82% or less, and more preferably 80% or less by mass of the toluene diisocyanate forming the polyisocyanate composition;

[0013] b. The polyisocyanate composition is 33℃≤Tg≤48℃, preferably 35℃≤Tg≤42℃.

[0014] Further, the di- to tetraol is one or more of the following polyols other than trimethylolpropane, having a functionality of 2-4 and a molecular weight of 62-200, preferably 62-146; preferably one or more of ethylene glycol, 1,2-propanediol, 2-methyl-1,3-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentanediol, 1,6-hexanediol, 2-ethylhexanediol, trimethylolethane, glycerol, and pentaerythritol.

[0015] Furthermore, in the polyol compound, the mass ratio of trimethylolpropane to di- to tetrahydric alcohol is (1-5):1, preferably (2-4):1.

[0016] Furthermore, the ratio of the amount of toluene diisocyanate to the polyol compound, based on the molar ratio of the reactive functional groups NCO:OH, is (3-6):1.

[0017] The 2,4-toluene diisocyanate isomer content in the polyisocyanate composition described in this invention does not refer to the 2,4-toluene diisocyanate isomer content in the raw toluene diisocyanate, but rather to the proportion of the 2,4-TDI isomer content in the polyisocyanate composition, as determined by 13C-NMR spectroscopy, relative to the total 2,4-TDI and 2,6-TDI isomer content. The inventors surprisingly discovered in their research that, due to differences in isomer reactivity, more 2,4-TDI isomers participate in the formation of the polyisocyanate composition, resulting in the 2,4-TDI isomer content in the product polyisocyanate composition often exceeding the proportion of 2,4-TDI isomers in the raw toluene diisocyanate.

[0018] This invention, by simultaneously controlling the content of the 2,4-toluene diisocyanate isomer in the polyisocyanate composition and the glass transition temperature of the polyisocyanate composition, can obtain polyisocyanate products with better room temperature and low temperature storage stability. This is quite remarkable, and it can avoid the introduction of impurities and components that adversely affect product performance into the system.

[0019] A method for preparing the polyisocyanate composition as described above includes the following steps:

[0020] 1) React toluene diisocyanate and polyol compounds to generate NCO-terminated prepolymers, and obtain a reaction solution;

[0021] 2) Separate and remove unreacted toluene diisocyanate from the reaction solution; heat-cook the separated product at 150-180℃, preferably 155-175℃, more preferably 160-170℃ for 3-20 minutes, preferably 4-15 minutes, more preferably 6-10 minutes.

[0022] 3) Add solvent to dilute the product to obtain a polyisocyanate composition.

[0023] Further, in step 1), the toluene diisocyanate comprises 2,4-toluene diisocyanate isomer and 2,6-toluene diisocyanate isomer, and the mass ratio of the two is (0-65):(35-100), preferably (25-58):(42-75).

[0024] In step 1) of this invention, the polyol compound can be added separately to the reaction vessel and mixed with toluene diisocyanate for reaction, or it can be premixed before reacting with toluene diisocyanate. The premixing method includes using a pipeline mixer or mixing in a premixing tank in advance. The reaction is carried out at 50-80°C and the reaction time is generally 4-24 hours to prepare a prepolymer reaction solution.

[0025] Furthermore, the ratio of the amount of toluene diisocyanate to the polyol compound, based on the molar ratio of the reactive functional groups NCO:OH, is (3-6):1.

[0026] In step 2) of this invention, the obtained prepolymer reaction liquid is separated to remove unreacted toluene diisocyanate monomers by a separation device. In some examples, the separation treatment method for removing unreacted isocyanate monomers is a conventional operation in the art and is not particularly limited thereto. The separation device used may be, for example, a rotary evaporator, a short-path evaporator or a thin-film evaporator or a combination thereof, to remove residual unreacted isocyanate monomers until the isocyanate monomer content in the product is low.

[0027] In the separated product obtained in step 2) of the present invention, the content of residual toluene diisocyanate monomer is 0.1-5%, preferably 0.3-5%, more preferably 0.5-3%. According to one aspect of the present invention, the separation device can be multi-stage in series, optionally using two-stage thin-film evaporators in series, two-stage short-path evaporators in series, or a short-path evaporator and a thin-film evaporator in series to separate the reaction liquid. The separated residue can be divided into primary residue and secondary residue, wherein the monomer content of the primary residue is preferably 1-10%, and the monomer content of the secondary residue is preferably 0.1-5%, more preferably 0.3-5%, and even more preferably 0.5-3%. In another embodiment of the present invention, a single-stage thin-film evaporator or a short-path evaporator can also be used, and the monomer content of the residue is most preferably 0.5-1%. The product obtained in step 2) does not specifically refer to primary residue or secondary residue.

[0028] In step 2) of this invention, the separated product is heat-cured at 150-180℃, preferably 155-175℃, more preferably 160-170℃, for 3-20 minutes, preferably 4-15 minutes, more preferably 6-10 minutes. After separating and removing unreacted toluene diisocyanate monomers, further heat curing of the polyisocyanate can promote more cross-linking reactions of the 2,4-TDI isomers and the transformation of the product's Tg, thereby improving the polyisocyanate's resistance to crystallization and flocculation, and obtaining a polyisocyanate product with excellent stability at room temperature and low temperature storage.

[0029] In step 3) of this invention, the diluent is one or more of toluene, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, and propylene glycol methyl ether acetate, preferably ethyl acetate. The solid content of the diluted polyisocyanate composition solution is 30-80%, preferably 50-80%.

[0030] Preferably, the solvent for dilution is preheated to 30-90°C, more preferably 50-80°C.

[0031] The polyisocyanate composition of the present invention can be used to prepare polyurethane coatings, polyurethane adhesives, inks and other related products.

[0032] In addition, the polyisocyanate composition prepared by the polyisocyanate composition or the preparation method of the present invention can be used to prepare polyurethane coatings, polyurethane adhesives, inks and other related products after being sealed with a sealing agent.

[0033] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0034] Without introducing impurities, polyisocyanate products with excellent stability at room temperature and low temperature storage can be obtained. Detailed Implementation

[0035] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0036] <Testing Methods>

[0037] (1) Determination of the content of free isocyanate monomers:

[0038] Polyisocyanates were quantified using gel permeation chromatography (LC-20AD / RID-10A, columns: MZ-Gel SD plus10E3A, 5μm (8.0*300mm), MZ-Gel SDplus 500A, 5μm (8.0*300mm), MZ-Gel SDplus100A, 5μm (8.0*300mm) in series, Shimadzu; mobile phase: tetrahydrofuran; flow rate: 1.0 mL / min; analysis time: 40 min; column temperature: 35℃). The area of ​​polymers and monomers in the test system was determined by the area normalization method. The isocyanate monomer content (%) was calculated as S(isocyanate monomer peak area) / S(sum of peak areas of all components) * 100%.

[0039] (2) Nuclear magnetic resonance (NMR) testing method

[0040] The nuclear magnetic resonance (NMR) spectrometer used was a Bruker AVANCE NEO 600 MHz. The spectrum type was C13IG, the pulse sequence was ZGIG30, the number of scans was 4096, the D1 time was 2 seconds, the solvent was CDCl3, the spectral width was 220 ppm, the center spectral value was 100 ppm, and the sampling time was 0.9 seconds. The 2,6-TDI isomer and the 2,4-TDI isomer were distinguished based on their carbon chemical shifts. The chemical shift of the 2,6-TDI isomer was 13 ppm, and that of the 2,4-TDI isomer was 17 ppm.

[0041] (3) Solid content (also known as non-volatile content)

[0042] Weigh 2g (1mg accurate) of polyisocyanate product and place it in an aluminum foil dish with a diameter of 75mm. Spread the product evenly on the bottom of the dish and bake it in a forced-air oven at 120±2℃ for 1 hour. Remove the product and weigh it. The ratio of the remaining weight of the product to the weight of the product (excluding the weight of the aluminum foil) is the solid content.

[0043] (4) Tg test method

[0044] Differential scanning calorimetry (DSC) was used: a thermal flow differential scanning calorimeter equipped with liquid nitrogen cooling accessories and an autosampler. Instrument brand and model: METTLER TOLEDO DSC3+. Crucible: 40 μL standard aluminum crucible with a perforated lid; purge gas: nitrogen; carrier gas flow rate: 50 mL / min; temperature program: -100℃~150℃, 20℃ / min; 150℃, hold for 1 min; 150℃~100℃, 20℃ / min; -100℃, hold for 2 min; -100℃~150℃, 20℃ / min.

[0045] (5) Stability test at room temperature

[0046] Polyisocyanate samples were sealed and stored in a 25°C incubator for one year. The samples were then irradiated with a cold light source to observe for any flocculent or suspended matter. If the sample became clear after one year, it was considered to have good storage stability; if the sample became turbid, it was considered to have poor storage stability. The time at which the sample began to precipitate was also recorded.

[0047] (6) Low-temperature storage stability test

[0048] The polyisocyanate samples were sealed and stored in a freezer at -18°C for 30 days. The samples were then irradiated with a cold light source to observe for crystallization or turbidity. If the sample became clear after 30 days, it was considered to have good storage stability; if the sample became turbid, it was considered to have poor storage stability. The time at which the sample began to precipitate was also recorded.

[0049] <Chemical Raw Material Information>

[0050] Toluene diisocyanate, Wanhua Chemical;

[0051] 2,6-Toluene diisocyanate, Wanhua Chemical;

[0052] Trimethylolpropane, purity ≥99%, Jiangxi Gaoxin Organic Chemical Co., Ltd.;

[0053] Ethyl acetate, purity ≥99%, Linyi Jinyimeng Co., Ltd.

[0054] Diethylene glycol monohydrate, purity ≥99%, Wanhua Chemical;

[0055] 2-Methyl-1,3-propanediol, purity ≥99%, Aladdin.

[0056] Unless otherwise specified, in all the following examples and comparative examples, the aging reaction solution was kept under a dry nitrogen atmosphere before the reaction and throughout the entire reaction and solvent dilution process. Unless otherwise stated, all percentages are by mass. The different 2,4-toluene diisocyanate contents in the various examples can be obtained by... It is blended with 2,6-toluene diisocyanate.

[0057] Example 1:

[0058] Under a nitrogen atmosphere, 18,000 g of toluene diisocyanate (55 wt% of 2,4-toluene diisocyanate) was added to a 25 L reactor equipped with a reflux condenser and heated to 70 °C. 1,500 g of trimethylolpropane and 1,000 g of diethylene glycol were added, and the mixture was reacted at 80 °C for 8 hours to obtain a reaction solution. The resulting reaction solution was subjected to two-stage vacuum thin-film distillation (separation temperatures of 160 °C and 170 °C, separation pressure ≤0.5 mbar) to remove unreacted toluene diisocyanate monomers. The residue was maintained at 150 °C for 15 minutes, and then ethyl acetate preheated to 70 °C was added. After thorough mixing, the mixture was cooled to 30 °C, resulting in a solid content of 75.4%.

[0059] Example 2:

[0060] Under a nitrogen atmosphere, 21,000 g of toluene diisocyanate (2,4-toluene diisocyanate accounting for 27 wt%) was added to a 25 L reactor equipped with a reflux condenser and heated to 70 °C. 1,500 g of trimethylolpropane and 1,000 g of diethylene glycol were added, and the reaction was carried out at 80 °C for 8 hours to obtain a reaction solution. The resulting reaction solution was subjected to two-stage vacuum thin-film distillation (separation temperatures of 160 °C and 170 °C, separation pressure ≤0.5 mbar) to remove unreacted toluene diisocyanate monomers. The resulting distillate residue was maintained at 160 °C for 10 minutes, and then ethyl acetate preheated to 70 °C was added. After thorough mixing, the mixture was cooled to 30 °C, resulting in a solid content of 75.2%.

[0061] Example 3:

[0062] Under a nitrogen atmosphere, 15,000 g of toluene diisocyanate (40 wt% of 2,4-toluene diisocyanate) was added to a 20 L reactor equipped with a reflux condenser and heated to 70 °C. 1,300 g of trimethylolpropane and 690 g of diethylene glycol were added, and the mixture was reacted at 80 °C for 8 hours to obtain a reaction solution. The resulting reaction solution was subjected to two-stage vacuum thin-film distillation (separation temperatures of 160 °C and 170 °C, separation pressure ≤0.5 mbar) to remove unreacted toluene diisocyanate monomers. The resulting distillate residue was maintained at 160 °C for 6 minutes, and then ethyl acetate preheated to 70 °C was added. After thorough mixing, the mixture was cooled to 30 °C, resulting in a solid content of 74.9%.

[0063] Example 4:

[0064] Under a nitrogen atmosphere, 13,000 g of toluene diisocyanate (58 wt% of 2,4-toluene diisocyanate) was added to a 20 L reactor equipped with a reflux condenser and heated to 70 °C. Then, 1,300 g of trimethylolpropane and 685 g of 2-methyl-1,3-propanediol were added, and the mixture was reacted at 80 °C for 8 hours to obtain a reaction solution. The resulting reaction solution was subjected to two-stage vacuum thin-film distillation (separation temperatures of 160 °C and 170 °C, and separation pressure ≤0.5 mbar) to remove unreacted toluene diisocyanate monomers. The resulting distillate residue was maintained at 170 °C for 5 minutes, and then ethyl acetate preheated to 75 °C was added. After thorough mixing, the mixture was cooled to 30 °C, resulting in a solid content of 75.3%.

[0065] Example 5:

[0066] Under a nitrogen atmosphere, 13,000 g of toluene diisocyanate (50 wt% of 2,4-toluene diisocyanate) was added to a 20 L reactor equipped with a reflux condenser and heated to 70 °C. 1,300 g of trimethylolpropane and 690 g of diethylene glycol were then added, and the mixture was reacted at 80 °C for 8 hours to obtain a reaction solution. The resulting reaction solution was subjected to two-stage vacuum thin-film distillation (separation temperatures of 160 °C and 170 °C, separation pressure ≤0.5 mbar) to remove unreacted toluene diisocyanate monomers. The resulting distillate residue was maintained at 150 °C for 10 minutes, and then ethyl acetate preheated to 70 °C was added. After thorough mixing, the mixture was cooled to 30 °C, resulting in a solid content of 75.2%.

[0067] Example 6:

[0068] Under a nitrogen atmosphere, 13,000 g of toluene diisocyanate (57 wt% of 2,4-toluene diisocyanate) was added to a 20 L reactor equipped with a reflux condenser and heated to 70 °C. Then, 1,300 g of trimethylolpropane, 345 g of diethylene glycol, and 345 parts by weight of 2-methyl-1,3-propanediol were added, and the mixture was reacted at 80 °C for 8 hours to obtain a reaction solution. The resulting reaction solution was subjected to two-stage vacuum thin-film distillation (separation temperatures of 160 °C and 170 °C, and separation pressure ≤0.5 mbar) to remove unreacted toluene diisocyanate monomers. The resulting distillate residue was maintained at 150 °C for 10 minutes, and then ethyl acetate preheated to 70 °C was added. After thorough mixing, the mixture was cooled to 30 °C, resulting in a solid content of 75.1%.

[0069] Comparative Example 1:

[0070] Under a nitrogen atmosphere, 18,000 g of toluene diisocyanate (80 wt% of 2,4-toluene diisocyanate) was added to a 25 L reactor equipped with a reflux condenser and heated to 70 °C. 1,500 g of trimethylolpropane and 1,000 g of diethylene glycol were added, and the mixture was reacted at 80 °C for 8 hours to obtain a reaction solution. The resulting reaction solution was subjected to two-stage vacuum thin-film distillation (separation temperatures of 160 °C and 170 °C, separation pressure ≤0.5 mbar) to remove unreacted toluene diisocyanate monomers. The residue was maintained at 150 °C for 15 minutes, and then ethyl acetate preheated to 70 °C was added. After thorough mixing, the mixture was cooled to 30 °C, resulting in a solid content of 75.3%.

[0071] Comparative Example 2:

[0072] Under a nitrogen atmosphere, 18,000 g of toluene diisocyanate (55 wt% of 2,4-toluene diisocyanate) was added to a 25 L reactor equipped with a reflux condenser and heated to 70 °C. 1,500 g of trimethylolpropane and 1,000 g of diethylene glycol were then added, and the mixture was reacted at 80 °C for 8 hours to obtain a reaction solution. The resulting reaction solution was subjected to two-stage vacuum thin-film distillation (separation temperatures of 160 °C and 170 °C, separation pressure ≤0.5 mbar) to remove unreacted toluene diisocyanate monomers. Ethyl acetate preheated to 70 °C was then added, and after thorough mixing, the mixture was cooled to 30 °C, resulting in a solid content of 75.4%.

[0073] The polyisocyanate compositions prepared in each example and comparative example were analyzed and their storage stability was tested. The results are shown in Table 1.

[0074] Table 1. Analysis and Storage Stability Test Results of Polyisocyanate Compositions

[0075]

[0076] Note: The isomer ratio indicates the mass ratio of 2,4-toluene diisocyanate to 2,6-toluene diisocyanate in the polyisocyanate composition.

[0077] The test results above show that the polyisocyanate composition provided by the present invention does not precipitate after one year of storage at room temperature and does not precipitate after 30 days of storage at -18℃. The low-temperature storage stability and room-temperature storage stability of the product meet the requirements of downstream applications.

[0078] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A polyisocyanate composition prepared from a raw material comprising toluene diisocyanate and a polyol compound, said polyol compound comprising trimethylolpropane and optionally other di- to tetraols with a molecular weight of 62-200, said polyisocyanate composition comprising urethane and urethane, characterized in that, The polyisocyanate composition simultaneously satisfies the following characteristics: a. The content of the 2,4-toluene diisocyanate isomer forming the polyisocyanate composition is less than 85% and greater than or equal to 48% of the total mass of toluene diisocyanate forming the polyisocyanate composition; b. Polyisocyanate composition 33℃≤Tg≤48℃; The method for preparing the polyisocyanate composition includes the following steps: 1) React toluene diisocyanate and polyol compounds to generate NCO-terminated prepolymers, and obtain a reaction solution; 2) Separate and remove unreacted toluene diisocyanate from the reaction solution; heat-cook the separated product at 150-180℃ for 3-20 minutes; 3) Add solvent to dilute the product to obtain a polyisocyanate composition.

2. The polyisocyanate composition according to claim 1, characterized in that, The content of the 2,4-toluene diisocyanate isomer forming the polyisocyanate composition is less than 82% and greater than or equal to 48% of the total mass of toluene diisocyanate forming the polyisocyanate composition.

3. The polyisocyanate composition according to claim 1, characterized in that, The content of the 2,4-toluene diisocyanate isomer forming the polyisocyanate composition is less than 80% and greater than or equal to 48% of the total mass of toluene diisocyanate forming the polyisocyanate composition.

4. The polyisocyanate composition according to claim 1, characterized in that, The polyisocyanate composition has a temperature range of 35℃ ≤ Tg ≤ 42℃.

5. The polyisocyanate composition according to claim 1, characterized in that, The other di- to tetrahydric alcohols are one or more of polyols with a functionality of 2-4 and a molecular weight of 62-146.

6. The polyisocyanate composition according to claim 1, characterized in that, The other di- to tetrahydric alcohols are one or more selected from ethylene glycol, 1,2-propanediol, 2-methyl-1,3-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentanediol, 1,6-hexanediol, 2-ethylhexanediol, trimethylolethane, glycerol, and pentaerythritol.

7. The polyisocyanate composition according to any one of claims 1-6, characterized in that, In the polyol compound, the mass ratio of trimethylolpropane to other di- to tetrahydric alcohols is (1-5):

1.

8. The polyisocyanate composition according to claim 7, characterized in that, In the polyol compound, the mass ratio of trimethylolpropane to other di- to tetrahydric alcohols is (2-4):

1.

9. The polyisocyanate composition according to claim 7, characterized in that, The ratio of the amount of toluene diisocyanate to the polyol compound, expressed as the molar ratio of the reactive functional groups NCO:OH, is (3-6):

1.

10. The polyisocyanate composition according to claim 1, characterized in that, In step 2), the separated product is heat-cooked at 155-175℃ for 4-15 minutes.

11. The polyisocyanate composition according to claim 1, characterized in that, In step 2), the separated product is heat-cooked at 160-170℃ for 6-10 minutes.

12. The polyisocyanate composition according to any one of claims 1-6, characterized in that, In step 1), the toluene diisocyanate comprises 2,4-toluene diisocyanate isomer and 2,6-toluene diisocyanate isomer, and the mass ratio of 2,4-toluene diisocyanate isomer to 2,6-toluene diisocyanate is (25-58):(42-75).

13. The polyisocyanate composition according to any one of claims 1-6, characterized in that, The ratio of the amount of toluene diisocyanate to the polyol compound, expressed as the molar ratio of the reactive functional groups NCO:OH, is (3-6):

1.

14. The polyisocyanate composition according to any one of claims 1-6, characterized in that, The residual toluene diisocyanate content in the polyisocyanate composition is 0.1-5%.

15. The polyisocyanate composition according to claim 14, characterized in that, The residual toluene diisocyanate content in the polyisocyanate composition is 0.3-5%.

16. The polyisocyanate composition according to claim 15, characterized in that, The residual toluene diisocyanate content in the polyisocyanate composition is 0.5-3%.

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