Polyurethane binder as well as preparation method and application thereof

Abstract

The invention relates to the technical field of adhesives, and discloses a polyurethane adhesive as well as a preparation method and application thereof. The preparation method of the polyurethane binder comprises the following steps: mixing a component A and a component B to obtain the polyurethane binder, the component A comprises aliphatic isocyanate containing an aliphatic ring and an aliphatic isocyanate prepolymer; the component B is prepared from isocyanate modified polyester polyol and / or isocyanate modified polyether polyol; the preparation method of the aliphatic isocyanate prepolymer comprises the following steps: mixing aliphatic isocyanate and a compound containing trifunctional alcohol, and carrying out a first-stage heating reaction; and adding polyether polyol, and carrying out second-stage heating reaction to obtain the aliphatic isocyanate prepolymer. The polyurethane binder does not contain free aromatic isocyanate, and has excellent peel strength, heat resistance and water resistance.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, specifically to a polyurethane adhesive, its preparation method, and its application. Background Technology

[0002] Polyurethane laminating adhesives are commonly used for bonding flexible packaging composite films. Solvent-free polyurethane laminating adhesives, in particular, are widely used due to their outstanding environmental friendliness, safety, and economic efficiency, as they emit no VOCs (volatile organic compounds). However, solvent-free polyurethane laminating adhesives often use aromatic isocyanates in their preparation, resulting in a high content of free aromatic isocyanates in the product, which can generate primary aromatic amines upon hydrolysis. GB / T 4806.15-2024 clearly stipulates that the migration limit for primary aromatic amines (aromatic primary amines) is "not detectable" (detection limit = 0.01 mg / kg). This makes reducing the content of primary aromatic amines in solvent-free polyurethane laminating adhesives a pressing issue. While existing technologies include methods to reduce the content of free aromatic isocyanate monomers through molecular design and to rapidly react with small-molecule polyols to accelerate the decay of primary aromatic amines, these methods rely on strict process control during production and application, making large-scale production difficult. However, if non-aromatic isocyanates are used to prepare polyurethane laminating adhesives, although the content of free aromatic isocyanates is reduced, the resulting polyurethane laminating adhesives will have insufficient mechanical strength, especially poor peel strength, which will affect their specific use. Summary of the Invention

[0003] This invention provides a polyurethane adhesive, its preparation method, and its application, to solve problems such as excessive migration of primary aromatic amines in the prepared polyurethane adhesive and insufficient mechanical strength of polyurethane adhesives prepared from non-aromatic isocyanates.

[0004] In a first aspect, the present invention provides a method for preparing a polyurethane adhesive, comprising the following steps: Mixing components A and B yields a polyurethane adhesive; Component A includes aliphatic isocyanates containing aliphatic rings and aliphatic isocyanate prepolymers; Component B includes isocyanate-modified polyester polyols and / or isocyanate-modified polyether polyols; The preparation method of the aliphatic isocyanate prepolymer includes the following steps: Aliphatic isocyanate and a compound containing trifunctional alcohol are mixed and subjected to a first-stage heating reaction; then a polyether polyol is added and subjected to a second-stage heating reaction to obtain an aliphatic isocyanate prepolymer.

[0005] In one optional embodiment, the mass ratio of the aliphatic isocyanate containing aliphatic rings to the aliphatic isocyanate prepolymer is 10~40:100; optionally, it is 10~35:100.

[0006] In one optional embodiment, the molar ratio of the trifunctional alcohol-containing compound to the aliphatic isocyanate is 3 to 10:100.

[0007] In one optional embodiment, the molar ratio of the polyether polyol to the aliphatic isocyanate is 10~30:100.

[0008] In one optional embodiment, the polyether polyol has a weight-average molecular weight of 400 to 2000.

[0009] In one optional embodiment, the temperature of the first stage of heating reaction is 50~100°C, and the end point of the first stage of heating reaction is when the NCO content reaches 95%~105% of the theoretical value after the complete reaction of the hydroxyl groups in the compound containing the trifunctional alcohol. Typically, but not limited to, the theoretical value of the NCO content after the complete reaction of the hydroxyl groups in the compound containing the trifunctional alcohol is calculated as follows: Theoretical value of NCO content after the complete reaction of the hydroxyl groups in the compound containing the trifunctional alcohol = (molar amount of aliphatic isocyanate × functionality of isocyanate groups in aliphatic isocyanate - molar amount of compound containing trifunctional alcohol × 3) × 42 ÷ (mass of aliphatic isocyanate + mass of compound containing trifunctional alcohol).

[0010] In one optional embodiment, the temperature of the second stage heating reaction is 40~100℃, and the end point of the second stage heating reaction is when the NCO content reaches 95%~105% of the theoretical value after the complete reaction of the hydroxyl groups in the polyether polyol. Typically, but not limited to, the calculation method for the theoretical value of the NCO content after the complete reaction of the hydroxyl groups in the polyether polyol is as follows: Theoretical value of NCO content after the complete reaction of the hydroxyl groups in the polyether polyol = [(mass of aliphatic isocyanate + mass of compound containing trifunctional alcohol) × theoretical value of NCO content in the first stage heating reaction - mass of polyether polyol ÷ weight-average molecular weight of polyether polyol × 2 × 42] ÷ (mass of aliphatic isocyanate + mass of compound containing trifunctional alcohol + mass of polyether polyol).

[0011] In one optional embodiment, the aliphatic isocyanate containing an aliphatic ring has the general chemical formula Ca. X H YN₂O₂, where X and Y are both positive integers, 35≤X≤40, 60≤Y≤74. The aliphatic isocyanate used has a long carbon chain with isocyanate groups at the ends of the long chain segments, which gives it less steric hindrance and can improve the initial reaction rate. At the same time, the long carbon chain also means that it has a higher molecular weight, which can be combined with aliphatic isocyanate prepolymers to further increase the initial molecular weight of the binder, thereby improving the initial strength of the bond.

[0012] In one optional embodiment, the aliphatic isocyanate includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, dicyclohexylmethane diisocyanate, cyclohexyl diisocyanate, and dimethyl isocyanate cyclohexane.

[0013] In one alternative embodiment, the trifunctional alcohol-containing compound includes at least one of trimethylolpropane and glycerol.

[0014] In one optional embodiment, the aliphatic isocyanate containing aliphatic rings includes at least one of dimer diisocyanate, 2-octyl-3,4-bis(7-isocyanate heptyl)-1-hexylcyclohexane, and 8-[4,5-dihexyl-6-(10-isocyanate decyl)-2-cyclohexyl]octyl isocyanate; optionally, the aliphatic isocyanate containing aliphatic rings is dimer diisocyanate.

[0015] In one optional embodiment, the isocyanate-modified polyester polyol has a weight-average molecular weight of 2000-4000; typically, but not limited to, the isocyanate in the isocyanate-modified polyester polyol is an aromatic diisocyanate and / or an aliphatic diisocyanate, including at least one selected from diphenylmethane diisocyanate, liquefied MDI (diphenylmethane diisocyanate), dicyclohexylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, isophthalic acid diisocyanate, and 1,3-dimethylisocyanate cyclohexane; the polyester polyol is synthesized from a diacid and / or anhydride and a diol, wherein the diacid includes at least one selected from adipic acid, octanoic acid, glutaric acid, isophthalic acid, and terephthalic acid, the anhydride includes at least one selected from phthalic anhydride and sebacic acid, and the diol includes ethylene glycol, diethylene glycol, and 1,4-dimethylisocyanate. Butanediol, 1,3-Butanediol, 1,6 Hexanediol, neopentyl glycol, 2 methyl 1,3 Propylene glycol, 3 methyl 1,5 At least one of pentanediol.

[0016] The method for preparing the polyurethane adhesive provided by this invention includes the following steps: (1) Take the dicarboxylic acid and / or anhydride and diol, mix them in a molar ratio of 1:1.02~1.1, heat them to 100~150℃ to melt them, and after stirring evenly, add 50~200ppm of titanium-based catalyst and / or tin-based catalyst, heat them to 200~250℃, evacuate them at this temperature, and keep them at this temperature for 5~10h to obtain polyester polyol.

[0017] (2) Take the polyester polyol obtained in step (1), add diisocyanate, the molar ratio of polyester polyol to diisocyanate is 2~2.4:1, add it into the reaction vessel, heat to 50~100℃, keep warm for 3~5h to carry out the reaction.

[0018] In one optional embodiment, the isocyanate-modified polyether polyol has a weight-average molecular weight of 400-2000; typically, but not limited to, the isocyanate-modified polyester polyol contains an aromatic diisocyanate and / or an aliphatic diisocyanate, including at least one of diphenylmethane diisocyanate, liquefied MDI (diphenylmethane diisocyanate), dicyclohexylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, isophthalic diisocyanate, and 1,3-dimethylisocyanate cyclohexane.

[0019] In one optional embodiment, the molar ratio of isocyanate groups in component A to hydroxyl groups in component B is 1.3 to 2.0:1.

[0020] Secondly, the present invention provides a polyurethane adhesive prepared using the above-described preparation method.

[0021] Thirdly, the present invention provides an application of the above-mentioned polyurethane adhesive in flexible packaging laminating adhesive.

[0022] The technical solution of this invention has the following advantages: 1. The preparation method of the polyurethane adhesive provided by the present invention includes the following steps: mixing component A and component B to obtain a polyurethane adhesive; wherein component A includes an aliphatic isocyanate containing aliphatic rings and an aliphatic isocyanate prepolymer; wherein component B includes isocyanate-modified polyester polyol and / or isocyanate-modified polyether polyol; the preparation method of the aliphatic isocyanate prepolymer includes the following steps: mixing the aliphatic isocyanate and a compound containing a trifunctional alcohol, and carrying out a first-stage heating reaction; adding the polyether polyol, and carrying out a second-stage heating reaction to obtain the aliphatic isocyanate prepolymer. The polyurethane adhesive prepared by this method mainly uses aliphatic isocyanates in its raw materials, has no free aromatic isocyanates in its components, and has excellent peel strength, heat resistance, and water resistance.

[0023] Specifically, in this invention, component A of the polyurethane adhesive raw material includes aliphatic isocyanates containing aliphatic rings and aliphatic isocyanate prepolymers. The use of free aromatic isocyanates is avoided in the raw material composition, further preventing the generation of free primary aromatic amines after hydrolysis of free aromatic isocyanates. The aliphatic isocyanate prepolymers have a high molecular weight, which can increase the initial molecular weight of the adhesive and ensure the initial strength of the bond. In addition, the rigid cyclic structure in the aliphatic isocyanates containing aliphatic rings can increase the proportion of hard segments, and the trifunctional alcohol compounds in the aliphatic isocyanate prepolymers can provide a micro-crosslinking structure, making the cured adhesive structure more compact and less susceptible to external factors such as water and heat, thus improving the heat resistance and water resistance of the adhesive.

[0024] In the preparation of aliphatic isocyanate prepolymers, aliphatic isocyanate and trifunctional alcohol are reacted first, and then polyether polyol is added to continue the reaction. This two-stage reaction can achieve a small molecular weight of the system when a small amount of trifunctional alcohol reacts with NCO, making the reaction easier to control and less likely to cause gelation. This makes it easier to obtain a stable product, which is beneficial to the subsequent preparation steps. Detailed Implementation

[0025] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0026] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0027] Experimental materials: DL-400: Polyether polyol, produced by Shandong Lanxing Dongda; weight average molecular weight is 400, functionality is 2; DL-1000: Polyether polyol, produced by Shandong Lanxing Dongda; weight average molecular weight is 1000, functionality is 2; DL-2000: Polyether polyol, produced by Shandong Lanxing Dongda; weight average molecular weight is 2000, functionality is 2; MDI-100: Diphenylmethane diisocyanate, produced by Wanhua Chemical Group Co., Ltd. MDI-50: Diphenylmethane diisocyanate, produced by Wanhua Chemical Group Co., Ltd. IPDI: Isophorone diisocyanate, produced by Wanhua Chemical Group Co., Ltd. HMDI: Dicyclohexylmethane diisocyanate, produced by Wanhua Chemical Group Co., Ltd. H6XDI: Hydrogenated diphenylmethylene diisocyanate, produced by Wanhua Chemical Group Co., Ltd. DDI: Diisocyanate dimer, an aliphatic isocyanate containing aliphatic rings, produced by Liming Chemical Research Institute; Trimethylolpropane: a trifunctional alcohol, purchased from Sigma-Aldrich; Glycerin: a trifunctional alcohol, purchased from Sigma-Aldrich; Neopentyl glycol: Produced by Wanhua Chemical Group Co., Ltd.; Diethylene glycol, ethylene glycol, isophthalic acid, oxalic acid, and 2-methyl-1,3-propanediol were all purchased from Sigma-Aldrich.

[0028] The preparation method of component B used in this invention is as follows: (1) Take 650g of isophthalic acid, 63g of oxalic acid, 40g of 2-methyl-1,3-propanediol, 110g of neopentyl glycol, 265g of diethylene glycol, and 45g of ethylene glycol, add them to a reaction vessel, heat to 100℃ to melt them, and after stirring evenly, add 0.06g of tetrabutyl titanate catalyst. Gradually increase the temperature to 230℃ at a rate of 10℃ / h, evacuate at this temperature, and keep warm for 5h to obtain polyester polyol with a hydroxyl value of 115mg KOH / g and a molecular weight of approximately 1000. The hydroxyl value determination method refers to GB / T7383-2020, and the molecular weight is simply estimated by hydroxyl value × 1000 ÷ 56 ÷ 2.

[0029] (2) Take 1000g of the polyester polyol obtained in step (1) and 113g of MDI-100, add them to the reaction vessel, heat to 50℃, and keep warm for 3h to carry out the reaction; add 80g of diethylene glycol and 200g of DL-400 to the reaction vessel, and continue to keep warm at the above temperature for 2h to obtain component B with a hydroxyl value of 87 mgKOH / g.

[0030] Example 1 This embodiment provides a polyurethane adhesive and its preparation method, including the following steps: (1) Place 1000g of IPDI into a reactor. Under a nitrogen atmosphere, add 42g of trimethylolpropane dropwise. Heat to 80℃ for the first stage of heating reaction. When the NCO content reaches 100% of the theoretical value after the complete reaction of the hydroxyl groups in trimethylolpropane, add 900g of DL-1000 (polyether polyol). Continue the second stage of heating reaction at the above temperature until the NCO content reaches 100% of the theoretical value after the complete reaction of the hydroxyl groups in DL-1000. Then stop heating and allow to cool naturally to room temperature to obtain the aliphatic isocyanate prepolymer. The NCO content test method is the same as HG_T 2409-2023.

[0031] In the first stage of the heating reaction, the theoretical value of the NCO content after the complete reaction of the hydroxyl groups in the compound containing the trifunctional alcohol is: (molar amount of aliphatic isocyanate × functionality of isocyanate group in aliphatic isocyanate - molar amount of compound containing trifunctional alcohol × 3) × 42 ÷ (mass of aliphatic isocyanate + mass of compound containing trifunctional alcohol) = (1000 / 222.3 × 2 - 42 / 134 × 3) × 42 ÷ (1000 + 42) ≈ 32.5%; the subsequent calculation process is the same and will not be given one by one.

[0032] In the second stage of the heating reaction, the NCO content reaches the theoretical value after the complete reaction of the hydroxyl groups in the polyether polyol = [(mass of aliphatic isocyanate + mass of the compound containing trifunctional alcohol) × theoretical value of NCO content in the first stage of the heating reaction - mass of polyether polyol ÷ weight-average molecular weight of polyether polyol × 2 × 42] ÷ (mass of aliphatic isocyanate + mass of the compound containing trifunctional alcohol + mass of polyether polyol) = ((1000 + 42) × 32% - 900 / 1000 × 2 × 42) ÷ (1000 + 42 + 900) ≈ 13.5%; the subsequent calculation process is the same and will not be given one by one.

[0033] (2) Mix 1000g of aliphatic isocyanate prepolymer obtained in step (1) with 200g of dimer diisocyanate to obtain component A, wherein the NCO content is 13.6%.

[0034] (3) Mix component A and component B at a mass ratio of 80:100 to obtain a polyurethane adhesive.

[0035] Example 2 This embodiment provides a polyurethane adhesive and its preparation method, including the following steps: (1) Place 1000g of IPDI into a reactor, add 12.5g of glycerol dropwise under nitrogen atmosphere protection, heat to 100℃ for the first stage of heating reaction, and when the NCO content reaches 105% of the theoretical value after the complete reaction of the hydroxyl groups in glycerol, add 900g of DL-1000, and continue the second stage of heating reaction at the above temperature until the NCO content reaches 95% of the theoretical value after the complete reaction of the hydroxyl groups in DL-1000, then stop heating and let it cool naturally to room temperature to obtain aliphatic isocyanate prepolymer.

[0036] In the first stage of the heating reaction, the NCO content reaches the theoretical value of 35.6% after the complete reaction of the hydroxyl groups in the compound containing trifunctional alcohols.

[0037] In the second stage of the heating reaction, the NCO content reaches the theoretical value of 14.9% after the complete reaction of the hydroxyl groups in the polyether polyol.

[0038] (2) Mix 1000g of aliphatic isocyanate prepolymer obtained in step (1) with 350g of dimer diisocyanate to obtain component A with an NCO content of 14.8%.

[0039] (3) Mix component A and component B at a mass ratio of 80:100 to obtain a polyurethane adhesive.

[0040] Example 3 This embodiment provides a polyurethane adhesive and its preparation method, including the following steps: (1) Place 1000g of IPDI into a reactor, add 60g of trimethylolpropane dropwise under nitrogen atmosphere protection, heat to 70℃ for the first stage of heating reaction, and when the NCO content reaches 100% of the theoretical value after the complete reaction of the hydroxyl groups in trimethylolpropane, add 900g of DL-2000, and continue the second stage of heating reaction at the above temperature until the NCO content reaches 100% of the theoretical value after the complete reaction of the hydroxyl groups in DL-2000, then stop heating and let it cool naturally to room temperature to obtain aliphatic isocyanate prepolymer.

[0041] In the first stage of the heating reaction, the NCO content reaches the theoretical value of 30.3% after the complete reaction of the hydroxyl groups in the compound containing trifunctional alcohols.

[0042] In the second stage of the heating reaction, the NCO content reaches the theoretical value of 14.5% after the complete reaction of the hydroxyl groups in the polyether polyol.

[0043] (2) Mix 1000g of aliphatic isocyanate prepolymer obtained in step (1) with 100g of dimer diisocyanate to obtain component A, with an NCO content of 14.3%.

[0044] (3) Mix component A and component B at a mass ratio of 80:100 to obtain a polyurethane adhesive.

[0045] Example 4 This embodiment provides a polyurethane adhesive and its preparation method, including the following steps: (1) Place 1000g HMDI into a reaction vessel, add 11.0g glycerol dropwise under nitrogen atmosphere protection, heat to 80℃ for the first stage of heating reaction, and when the NCO content reaches 100% of the theoretical value after the complete reaction of the hydroxyl groups in glycerol, add 458g DL-400, and continue the second stage of heating reaction at the above temperature until the NCO content reaches 100% of the theoretical value after the complete reaction of the hydroxyl groups in DL-400, then stop heating and let it cool naturally to room temperature to obtain aliphatic isocyanate prepolymer.

[0046] In the first stage of the heating reaction, the NCO content reaches the theoretical value of 30.2% after the complete reaction of the hydroxyl groups in the compound containing trifunctional alcohols.

[0047] In the second stage of the heating reaction, the NCO content reaches the theoretical value of 14.2% after the complete reaction of the hydroxyl groups in the polyether polyol.

[0048] (2) Mix 1000g of aliphatic isocyanate prepolymer obtained in step (1) with 200g of dimer diisocyanate to obtain component A with an NCO content of 14.2%.

[0049] (3) Mix component A and component B at a mass ratio of 60:100 to obtain polyurethane adhesive.

[0050] Example 5 This embodiment provides a polyurethane adhesive and its preparation method, including the following steps: (1) Place 1000g H6XDI into a reactor, add 33g trimethylolpropane dropwise under nitrogen atmosphere protection, heat to 50℃ for the first stage of heating reaction, and when the NCO content reaches 100% of the theoretical value after the complete reaction of the hydroxyl groups in trimethylolpropane, add 1030g DL-1000, and continue the second stage of heating reaction at the above temperature until the NCO content reaches 100% of the theoretical value after the complete reaction of the hydroxyl groups in DL-1000, then stop heating and let it cool naturally to room temperature to obtain aliphatic isocyanate prepolymer.

[0051] In the first stage of the heating reaction, the NCO content reaches the theoretical value of 38.9% after the complete reaction of the hydroxyl groups in the compound containing trifunctional alcohols.

[0052] In the second stage of the heating reaction, the NCO content reaches the theoretical value of 15.3% after the complete reaction of the hydroxyl groups in the polyether polyol.

[0053] (2) Mix 1000g of aliphatic isocyanate prepolymer obtained in step (1) with 200g of dimer diisocyanate to obtain component A with an NCO content of 14.8%.

[0054] (3) Mix component A and component B at a mass ratio of 85:100 to obtain a polyurethane adhesive.

[0055] Example 6 This embodiment provides a polyurethane adhesive and its preparation method. The only difference from Embodiment 2 is that 400g of dimer diisocyanate is used in step (2).

[0056] Comparative Example 1 This comparative example provides a polyurethane adhesive and its preparation method, including the following steps: (1) 1000g MDI-50 was placed in a reactor and heated to 60°C under nitrogen atmosphere protection. 100g DL-1000 and 400g DL-400 were added. At the above temperature, the reaction was continued until the NCO content reached 95% of the theoretical value (hereinafter referred to as the target value) after the hydroxyl groups in DL-1000 and DL-400 were completely reacted. Heating was then stopped and the mixture was allowed to cool naturally to room temperature to obtain component 1, in which the NCO content was 15.4%.

[0057] Target value = [Molecular weight of MDI-50 × 2 - Molecular weight of DL-1000 × 2 - Molecular weight of DL-400 × 2] × 42 ÷ Total weight = (1000 / 250 × 2 - 100 / 1000 × 2 - 400 / 400 × 2) × 42 ÷ (1000 + 100 + 500) ≈ 16.2%.

[0058] (2) Mix component 1 and component B at a mass ratio of 80:100 to obtain a polyurethane adhesive.

[0059] Comparative Example 2 This comparative example provides a polyurethane adhesive and its preparation method. Compared with Example 1, the only difference is that step (2) is not performed. In step (3), the aliphatic isocyanate prepolymer obtained in step (1) of equal mass is used to replace component A.

[0060] Comparative Example 3 This comparative example provides a polyurethane adhesive and its preparation method. Compared with Example 1, the only difference is that in step (1), an equimolar amount of trimethylolpropane is used to replace DL-1000, and only the first stage of heating reaction is carried out; the resulting aliphatic isocyanate prepolymer exhibits gelation, the actual NCO value is not detected, and no subsequent preparation steps are carried out.

[0061] Comparative Example 4 This comparative example provides a polyurethane adhesive and its preparation method. Compared with Example 1, the only difference is that in step (1), an equimolar amount of DL-1000 is used to replace trimethylolpropane, and only one heating reaction is carried out; in step (2), the NCO content of component A is 12.9%.

[0062] Comparative Example 5 This comparative example provides a polyurethane adhesive and its preparation method. Compared with Example 1, the only difference is that in step (1), diethylene glycol is used instead of trimethylolpropane in an equimolar amount; and in step (2), the NCO content of component A is 13.6%.

[0063] Experimental Example 1 The polyurethane adhesives prepared in the examples and comparative examples were used to prepare CPP (chlorinated polypropylene) / PET (polyethylene terephthalate) composite films. The peel strength, peel strength after boiling, and migration of primary aromatic amines were then tested. The test results are shown in Table 1.

[0064] The amount of adhesive applied to prepare the composite membrane was 2.5 g / m³. 2 Peel strength conforms to standard GB / T 8808. In 1988, tests were conducted to assess the peel strength after 24 hours and 48 hours of storage. The peel strength after boiling was determined by first boiling the composite film at 121℃ for 40 minutes, followed by further testing according to standard GB / T 8808. The test was conducted in 1988; the migration of primary aromatic amines was tested according to standard GB / T 31604.52-2021.

[0065] Table 1

[0066] As can be seen from Table 1, the polyurethane adhesive prepared by the preparation method provided by the present invention in the examples mainly uses aliphatic isocyanate as raw material. No primary aromatic amine migration was detected when tested according to GB / T 31604.52-2021. In addition, it has good peel strength and peel strength after cooking, and has excellent comprehensive performance.

[0067] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a polyurethane adhesive, characterized in that, Includes the following steps: Mixing components A and B yields a polyurethane adhesive; Component A includes aliphatic isocyanates containing aliphatic rings and aliphatic isocyanate prepolymers; Component B includes isocyanate-modified polyester polyols and / or isocyanate-modified polyether polyols; The preparation method of the aliphatic isocyanate prepolymer includes the following steps: Aliphatic isocyanate and a compound containing trifunctional alcohol are mixed and subjected to a first-stage heating reaction; then a polyether polyol is added and subjected to a second-stage heating reaction to obtain an aliphatic isocyanate prepolymer.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the aliphatic isocyanate containing aliphatic rings to the aliphatic isocyanate prepolymer is 10~40:100; optionally, it is 10~35:

100. And / or, the molar ratio of the trifunctional alcohol-containing compound to the aliphatic isocyanate is 3~10:100; And / or, the molar ratio of the polyether polyol to the aliphatic isocyanate is 10~30:

100.

3. The preparation method according to claim 1 or 2, characterized in that, The weight-average molecular weight of the polyether polyol is 400-2000.

4. The preparation method according to claim 1, characterized in that, The temperature of the first stage of heating reaction is 50~100℃, and the end point of the first stage of heating reaction is when the NCO content reaches 95%~105% of the theoretical value after the complete reaction of the hydroxyl groups in the compound containing trifunctional alcohol; And / or, the temperature of the second stage heating reaction is 40~100℃, and the end point of the second stage heating reaction is when the NCO content reaches 95%~105% of the theoretical value after the complete reaction of the hydroxyl groups in the polyether polyol.

5. The preparation method according to claim 1, characterized in that, The general chemical formula of the aliphatic isocyanate containing aliphatic rings is Ca. X H Y N2O2, where X and Y are both positive integers, 35≤X≤40, 60≤Y≤74; And / or, the aliphatic isocyanate includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, dicyclohexylmethane diisocyanate, cyclohexyl diisocyanate, and dimethyl isocyanate cyclohexane. And / or, the trifunctional alcohol-containing compound includes at least one of trimethylolpropane and glycerol.

6. The preparation method according to claim 5, characterized in that, The aliphatic isocyanate containing aliphatic rings includes at least one of dimer acid diisocyanate, 2-octyl-3,4-bis(7-isocyanate heptyl)-1-hexylcyclohexane, and 8-[4,5-dihexyl-6-(10-isocyanate decyl)-2-cyclohexyl]octyl isocyanate; optionally, the aliphatic isocyanate containing aliphatic rings is dimer acid diisocyanate.

7. The preparation method according to claim 1, characterized in that, The isocyanate-modified polyester polyol has a weight-average molecular weight of 2000-4000. And / or, in the isocyanate-modified polyether polyol, the weight-average molecular weight of the polyether polyol is 400~2000.

8. The preparation method according to any one of claims 1 to 7, characterized in that, The molar ratio of isocyanate groups in component A to hydroxyl groups in component B is 1.3~2.0:

1.

9. A polyurethane adhesive, characterized in that, It was prepared using the preparation method described in any one of claims 1 to 8.

10. The application of the polyurethane adhesive as described in claim 9 in flexible packaging laminating adhesive.

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