Low free radical reaction type polyurethane hot melt adhesive and preparation method thereof

Abstract

The application belongs to the field of adhesives, and relates to a low-free reactive polyurethane hot melt adhesive and a preparation method thereof. The low-free reactive polyurethane hot melt adhesive comprises a polyurethane body and tackifying resin, and the polyurethane body is prepared by the following method: S11, a first nucleophilic addition reaction is performed between a polyisocyanate monomer and an excess of a polyhydric alcohol polymer to obtain a hydroxyl double-terminated prepolymer; and S12, a second nucleophilic addition reaction is performed between the hydroxyl double-terminated prepolymer and a low-free polyurethane prepolymer. The reactive polyurethane hot melt adhesive prepared by the method has the characteristics of low melt viscosity, long open time, high bonding strength and low free isocyanate content (<0.1 wt%), and the comprehensive performance is better than that of the low-free reactive polyurethane hot melt adhesive prepared by the prior art.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of adhesives, and particularly relates to a low-free reactive polyurethane hot melt adhesive and a preparation method thereof. BACKGROUND

[0002] Traditional reactive polyurethane hot melt adhesive (PUR) is a polyurethane prepolymer prepared by the reaction of excess isocyanate and polyol. Due to the excess of isocyanate, the insufficient reaction of polyol with excess isocyanate, the reaction hindrance under high viscosity and other reasons, there are often unreacted free isocyanate monomers in the final product. Free isocyanate monomers will gasify to form irritating, allergenic or toxic substances at 85-200℃, thereby endangering the health of practitioners. The draft of the free isocyanate restriction prepared by the European Chemicals Agency (ECHA) shows that when the content of free isocyanate in the reactive polyurethane hot melt adhesive is >1wt%, there is a risk of carcinogenesis; if the content of free isocyanate is between 0.1-1wt%, there is a risk of inhalation or skin contact; products with free isocyanate content exceeding 0.1wt% will be restricted in use in the industry and certain professional fields unless the safety of users can be protected; and products with free isocyanate content <0.1wt% can be exempted from the restriction of this regulation. Therefore, it is urgent to develop a reactive polyurethane hot melt adhesive with excellent bonding performance and low free isocyanate content to meet the application needs of low-free reactive polyurethane hot melt adhesive in the fields of automobiles, new energy, consumer electronics, woodworking, textiles and the like.

[0003] In the existing solutions of low-free reactive polyurethane hot melt adhesive, there are physical methods such as reduced pressure distillation to remove free isocyanate monomers, but this method is only suitable for a small part of low-boiling-point isocyanate monomers and requires high-cost equipment and complicated process. In addition, there are also technologies that use low-free isocyanate oligomers with a free isocyanate content of less than 0.1% to replace isocyanate monomers to react with polyols to prepare low-free isocyanate reactive polyurethane hot melt adhesive, but the polyurethane hot melt adhesive obtained by using this method has the defects of high melt viscosity, short open time and low bonding strength. For example, US20170002239A uses Bayer's low-free MDI oligomer VPLS2397 to replace MDI monomers to react with polyols to prepare a reactive polyurethane hot melt adhesive, and the free MDI monomer in the final product is <0.1wt%, but the bulk strength decreases by about 50%. In addition, there are also technologies that use part of isocyanate monomers and part of low-free polyurethane oligomers (free isocyanate content less than 0.1wt%) to react with polyols. The bulk strength of the reactive polyurethane hot melt adhesive obtained by this method is improved, but the part of isocyanate monomers still remains, so that the final free isocyanate content is still higher than 0.1%, which is generally increased to 0.4-1%. SUMMARY

[0004] The present application aims to overcome the defects of high melt viscosity, short open time and low bonding strength of the existing low free reactive polyurethane hot melt adhesive, and to provide a low free reactive polyurethane hot melt adhesive with low melt viscosity, long open time, high bonding strength and free isocyanate content less than 0.1wt%, and a preparation method thereof.

[0005] The present application provides a low free reactive polyurethane hot melt adhesive, which comprises a polyurethane body and a tackifying resin, and the polyurethane body is prepared by the following method:

[0006] S11, a first nucleophilic addition reaction is carried out between a polyisocyanate monomer and an excess of a polyol polymer, the molar equivalent ratio of isocyanate groups in the polyisocyanate monomer to hydroxyl groups in the polyol polymer is 1:(2-2.2), to obtain a hydroxyl double-terminated prepolymer;

[0007] S12, a second nucleophilic addition reaction is carried out between the hydroxyl double-terminated prepolymer and a low free polyurethane prepolymer, the molar equivalent ratio of isocyanate groups in the low free polyurethane prepolymer to isocyanate groups in the polyisocyanate monomer is (3-6):1, to obtain a polyurethane body.

[0008] In the present application, the molar equivalent ratio of isocyanate groups in the polyisocyanate monomer, hydroxyl groups in the polyol polymer and isocyanate groups in the low free polyurethane prepolymer is 1:(2-2.2):(3-6). The amount of the polyisocyanate monomer is 1 mol based on isocyanate groups, and the amount of the polyol polymer is 2-2.2 mol based on hydroxyl groups, such as 2.0 mol, 2.1 mol, 2.2 mol and any value therebetween; the amount of the low free polyurethane prepolymer is 3-6 mol based on isocyanate groups, such as 3 mol, 3.5 mol, 4 mol, 4.5 mol, 5 mol, 5.5 mol, 6 mol and any value therebetween.

[0009] In a preferred embodiment, the content of the polyurethane body is 75-95%, such as 75%, 77%, 80%, 82%, 85%, 88%, 90%, 92%, 95% and any value therebetween, and the content of the tackifying resin is 5-25%, such as 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25% and any value therebetween, based on the total weight of the low free reactive polyurethane hot melt adhesive.

[0010] In a preferred embodiment, the polyisocyanate monomer is selected from at least one of isophorone diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, hydrogenated MDI, polymeric MDI, 1,5-naphthalene diisocyanate, 1,4-phenylene diisocyanate, xylylene diisocyanate, tetramethylxylene diisocyanate, and norbornane diisocyanate.

[0011] In a preferred embodiment, the polyol polymer is selected from at least one of polyester polyol, polyether polyol, polycarbonate polyol, and polyalkylene polyol.

[0012] In a preferred embodiment, the polyester polyol is at least one of a polyester polyol obtained by esterification of a polycarboxylic acid with a polyol, and a poly-ε-caprolactone polyol obtained by ring-opening polymerization of ε-caprolactone. Specific examples of the polycarboxylic acid include, but are not limited to, at least one of terephthalic acid, isophthalic acid, 1,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decamethylene dicarboxylic acid, dodecamethylene dicarboxylic acid. Specific examples of the polyol include, but are not limited to, at least one of ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, and cyclohexanediol.

[0013] In a preferred embodiment, the polyether polyol is selected from at least one of an open ring polymer of ethylene glycol, propylene glycol, tetrahydrofuran, 3-methyltetrahydrofuran, random copolymer, and block copolymer, and a bisphenol-type polyoxyalkylene modifier. The bisphenol-type polyoxyalkylene modifier is a polyether polyol obtained by addition reaction of an active hydrogen moiety of a bisphenol-type molecular skeleton with an alkylene oxide, and can be a random copolymer or a block copolymer. Specific examples of the alkylene oxide include, but are not limited to, at least one of ethylene oxide, propylene oxide, butylene oxide, and isobutylene oxide.

[0014] In a preferred embodiment, the polycarbonate polyol is selected from at least one of polycarbonate 1,6-hexanediol polyol, polycarbonate-1,4-butanediol-1,6-hexanediol diol, polycarbonate-1,5-pentanediol-1,6-hexanediol diol, polycarbonate caprolactone hexylene diol, polycarbonate-1,4-cyclohexanedimethanol-1,6-hexanediol diol, polycarbonate ethylene diol, polycarbonate propylene diol, polycarbonate butylene diol, and polycarbonate hexylene diol.

[0015] In a preferred embodiment, the polyalkylene polyol is selected from at least one of a polybutadiene polyol, a hydrogenated polybutadiene polyol, and a hydrogenated polyisoprene polyol.

[0016] In a preferred embodiment, the low free isocyanate polyurethane prepolymer is a low free polyether polyol-based polyurethane prepolymer and / or a low free polyester polyol-based polyurethane prepolymer, wherein the low free isocyanate polyurethane prepolymer contains less than 0.1 wt% of free isocyanate. In the present application, both ends of the low free polyether polyol-based polyurethane prepolymer and the low free polyester polyol-based polyurethane prepolymer are capped by isocyanate groups.

[0017] In a preferred embodiment, the low free isocyanate polyurethane prepolymer is a low free polyether polyol-based polyurethane prepolymer obtained by reacting a polyether polyol with a polyisocyanate monomer. Specific examples of the polyether polyol include, but are not limited to, at least one of an ethylene glycol, a propylene glycol, a ring-opening polymer of tetrahydrofuran and 3-methyltetrahydrofuran, a random copolymer, and a block copolymer. Specific examples of the polyisocyanate monomer include, but are not limited to, at least one of isophorone diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, hydrogenated MDI, polymeric MDI, 1,5-naphthalene diisocyanate, 1,4-phenylene diisocyanate, xylylene diisocyanate, tetramethyl xylene diisocyanate, and norbornane diisocyanate. The low free isocyanate polyurethane prepolymer can be obtained by commercial purchase, and examples include Adiprene LF TE 915, Adiprene LF TE 1050, Adiprene LF TE 980, Adiprene LF TE 330, Adiprene LF TE 365, Adiprene LF TE 440, Adiprene LFM G730, Adiprene LFM G750, Adiprene LFM G600, Adiprene LFMI G600, and Adiprene LFMI G1000 from Huntsman.

[0018] In a preferred embodiment, the low free polyester polyol based polyurethane prepolymer is obtained by reacting a polyester polyol with a polyisocyanate monomer. Specific examples of the polyester polyol include, but are not limited to, at least one of polyethylene adipate diol, polypropylene adipate diol, polybutylene adipate diol, poly-1,4-butylene adipate diol, polyneopentyl adipate diol, and poly-1,6-hexanediol adipate diol. Specific examples of the polyisocyanate monomer include, but are not limited to, at least one of isophorone diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, hydrogenated MDI, polymeric MDI, 1,5-naphthalene diisocyanate, 1,4-phenylene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, and norbornane diisocyanate. The low free polyester polyol based polyurethane prepolymer can be obtained commercially, such as Adiprene LFM S200, Adiprene LFM S300, Adiprene LFM S500, etc. from Lubrizol.

[0019] In a preferred embodiment, the conditions of the first nucleophilic addition reaction include a temperature of 70-90 °C, such as 70 °C, 72 °C, 75 °C, 78 °C, 80 °C, 82 °C, 85 °C, 88 °C, 90 °C, and any value therebetween; a rotation speed of 100-200 r / min, such as 100, 120, 150, 180, 200 r / min, and any value therebetween; and a time of 1-5 h, such as 1, 2, 3, 4, 5 h, and any value therebetween.

[0020] In a preferred embodiment, the conditions of the second nucleophilic addition reaction include a temperature of 70-90 °C, such as 70 °C, 72 °C, 75 °C, 78 °C, 80 °C, 82 °C, 85 °C, 88 °C, 90 °C, and any value therebetween; a rotation speed of 100-200 r / min, such as 100, 120, 150, 180, 200 r / min, and any value therebetween; and a time of 1-5 h, such as 1, 2, 3, 4, 5 h, and any value therebetween.

[0021] In a preferred embodiment, the first nucleophilic addition reaction and the second nucleophilic reaction are carried out in the presence of a catalyst. Specific examples of the catalyst include, but are not limited to, at least one of dibutyltin dilaurate, stannous octoate, triethylamine, diethylenetriamine, triethylenediamine, N-ethylmorpholine, and 2,2-dimorpholinyl diethyl ether.

[0022] In the present application, the nucleophilic addition reaction between the polyisocyanate monomer and the excess polyol polymer is referred to as the "first nucleophilic addition reaction", and the nucleophilic addition reaction between the hydroxyl double-terminated prepolymer and the low free polyurethane prepolymer is referred to as the "second nucleophilic addition reaction", and the terms "first" and "second" are merely for the convenience of distinguishing and describing, and have no special meaning.

[0023] In a preferred embodiment, the tackifying resin is selected from at least one of thermoplastic acrylic resin, polyurethane resin, amorphous polyalphaolefin resin, rosin resin, rosin pentaerythritol ester, petroleum resin, terpene resin, and EVA resin.

[0024] The present application provides a preparation method of the low free reactive polyurethane hot melt adhesive, which comprises the following steps:

[0025] S21, vacuum stirring and dehydrating the polyol polymer and the tackifying resin at 100-120℃ and at a rotation speed of 100-200r / min for 1-5h, and then cooling to 70-90℃ to obtain a pretreated product;

[0026] S22, stirring and reacting the pretreated product and the polyisocyanate monomer under vacuum at 70-90℃ and at a rotation speed of 100-200r / min for 1-5h to obtain a hydroxyl double-terminated prepolymer;

[0027] S23, stirring and reacting the hydroxyl double-terminated prepolymer, the low free polyurethane prepolymer and the catalyst under vacuum at 70-90℃ and at a rotation speed of 100-200r / min for 1-5h to obtain the low free reactive polyurethane hot melt adhesive.

[0028] Due to the great difference between the low free polyurethane prepolymer (free isocyanate content less than 0.1wt%) and the isocyanate monomer, simply replacing the low free polyurethane prepolymer with the isocyanate monomer to prepare the low free reactive polyurethane hot melt adhesive has the defects of high melt viscosity, short open time and low bonding strength. The reason is probably that the low free polyurethane prepolymer has more flexible chain components than the isocyanate monomer, and the molecular weight of the polyurethane prepolymer is larger, and the number of isocyanate groups in the polyurethane prepolymer is lower than that in the isocyanate monomer when the same mass fraction is used. When the polyurethane prepolymer is used to replace the isocyanate monomer to form the polyurethane hot melt adhesive, the hard segment component will be less and the soft segment component will be higher, and the isocyanate content of the final product will be lower and the molecular weight will be larger, resulting in the defects of high melt viscosity, short open time and low bonding strength of the final product.

[0029] In addition, the prior art adopts part of isocyanate monomers and part of low free polyurethane oligomers (free isocyanate content less than 0.1 wt%) to react with polyols to prepare low free reactive polyurethane hot melt adhesive by one-step method, that is, the isocyanate monomers and the low free polyurethane prepolymer are added together to react with the polyols in one step. Although the free isocyanate content in the low free polyurethane prepolymer is less than 0.1 wt%, the added isocyanate monomers still have the risk of insufficient reaction, which increases the free isocyanate content in the final product, so that the free isocyanate content in the final product is still higher than 0.1%.

[0030] The present application creatively adopts a two-step method to prepare low free reactive polyurethane hot melt adhesive. In the first step, polyisocyanate monomers are reacted with excess polyol polymers to prepare a hydroxyl double-terminated prepolymer. In the second step, the hydroxyl double-terminated prepolymer is reacted with excess low free polyurethane prepolymer to prepare low free reactive polyurethane hot melt adhesive. In the first step, the excess polyol polymer is added to react with the isocyanate monomers, which on the one hand ensures that there is no residual free isocyanate monomer in the reaction system, and on the other hand increases the proportion of rigid hard segments in the molecular chain through chain extension reaction of the polyol polymer and the isocyanate monomer, providing strength for the reactive polyurethane hot melt adhesive. In the second step, excess low free polyurethane prepolymer is added to adjust the melt viscosity, open time and bonding strength of the reaction system. The reactive polyurethane hot melt adhesive prepared by the method provided by the present application has the characteristics of low melt viscosity, long open time, high bonding strength and low free isocyanate content (<0.1 wt%), and the comprehensive performance is better than that of the low free reactive polyurethane hot melt adhesive prepared by the prior art. DETAILED DESCRIPTION

[0031] The present application will be described in detail below through examples.

[0032] Example 1

[0033] S21, 19.4 g (9.719 mmol) of polyethylene terephthalate diol with a number average molecular weight of 2000, 9.7 g (9.719 mmol) of polycarbonate-1,5-pentanediol-1,6-hexanediol diol with a number average molecular weight of 1000 and 10.0 g of thermoplastic polyurethane resin Pearlbond 523 were added to a reaction bottle, heated to 110°C, vacuum dehydrated at 150 r / min for 2 h, and then cooled to 80°C to obtain a pretreated product;

[0034] S22, 2.4 g (9.719 mmol) of 4,4'-diphenyl methane diisocyanate (MDI, the molar equivalent ratio of isocyanate groups in the polyisocyanate monomer to hydroxyl groups in the polyol polymer is 1:2) was added to the pretreated product, and after stirring at 150 r / min under vacuum for 2 h, a hydroxyl-terminated prepolymer was obtained;

[0035] S23, 31.1 g (38.88 mmol) of low-free polyurethane prepolymer Adiprene TE1050 based on polyether polyol, 27.2 g (9.719 mmol) of low-free polyurethane prepolymer Adiprene LFM S300 based on polyester polyol, and 0.1 g of 2,2-dimorpholinyl diethyl ether (the molar equivalent ratio of isocyanate groups in the low-free polyurethane prepolymer to isocyanate groups in the polyisocyanate monomer is 5:1) were added to the hydroxyl-terminated prepolymer, and after stirring at 150 r / min under vacuum for 2 h, the low-free reactive polyurethane hot melt adhesive was discharged and stored in a vacuum-sealed manner.

[0036] Example 2

[0037] S21, 14.4 g (7.213 mmol) of poly-caprolactone diol with a number average molecular weight of 2000, 14.4 g (7.213 mmol) of polyoxypropylene ether diol with a number average molecular weight of 2000, and 14.0 g of acrylic resin BR106 were added to a reaction bottle, heated to 110°C, and dehydrated under vacuum at 150 r / min for 2 h; then cooled to 80°C to obtain a pretreated product;

[0038] S22, 1.8 g (7.213 mmol) of 4,4'-diphenyl methane diisocyanate (MDI, the molar equivalent ratio of isocyanate groups in the polyisocyanate monomer to hydroxyl groups in the polyol polymer is 1:2) was added to the pretreated product, and after stirring at 150 r / min under vacuum for 2 h, a hydroxyl-terminated prepolymer was obtained;

[0039] S23, 24.8 g (28.85 mmol) of low-free polyurethane prepolymer Adiprene TE980 based on polyether polyol, 30.3 g (7.213 mmol) of low-free polyurethane prepolymer Adiprene LFM S200 based on polyester polyol, and 0.3 g of dibutyltin dilaurate (the molar equivalent ratio of isocyanate groups in the low-free polyurethane prepolymer to isocyanate groups in the polyisocyanate monomer is 5:1) were added to the hydroxyl-terminated prepolymer, and after stirring at 150 r / min under vacuum for 2 h, the low-free reactive polyurethane hot melt adhesive was discharged and stored in a vacuum-sealed manner.

[0040] Example 3

[0041] S21, 10.2 g (5.105 mmol) of polytetrahydrofuran ether diol with a number average molecular weight of 2000, 21.9 g (7.213 mmol) of polyterephthalate diethylene glycol with a number average molecular weight of 2000 and 20.0 g of polyalphaolefin resin VESTOPLAST 520 were added into a reaction bottle, heated to 110°C, vacuum dehydrated for 2 h under the condition of stirring at 150 r / min, and then cooled to 80°C to obtain a pretreated product;

[0042] S22, 1.9 g (7.293 mmol) of 4,4-diisocyanate dicyclohexyl methane (the molar equivalent ratio of isocyanate groups in the polyisocyanate monomer to hydroxyl groups in the polyol polymer was 1:2.2) was added into the pretreated product, and after stirring at 150 r / min for 2 h under vacuum, a hydroxyl double-terminated prepolymer was obtained;

[0043] S23, 33.5 g (29.17 mmol) of low-free polyurethane prepolymer Adiprene G730 based on polyether polyol, 12.3 g (7.293 mmol) of low-free polyurethane prepolymer Adiprene LFM S500 based on polyester polyol and 0.2 g of dibutyl tin dilaurate (the molar equivalent ratio of isocyanate groups in the low-free polyurethane prepolymer to isocyanate groups in the polyisocyanate monomer was 5:1) were added into the hydroxyl double-terminated prepolymer, and after stirring at 150 r / min for 2 h under vacuum, the reaction was discharged, and a low-free reactive polyurethane hot melt adhesive was obtained, which was vacuum sealed and stored.

[0044] Example 4

[0045] S21, 10.7 g (3.567 mmol) of polyneopentyl glycol adipate diol with a number average molecular weight of 3000, 17.1 g (7.213 mmol) of polyhexylene isophthalate diol with a number average molecular weight of 1600 and 17.0 g of acrylic resin BM751 were added into a reaction bottle, heated to 110°C, vacuum dehydrated for 2 h under the condition of stirring at 150 r / min, and then cooled to 80°C to obtain a pretreated product;

[0046] S22, 1.9 g (7.134 mmol) of 4,4-diisocyanate dicyclohexyl methane (the molar equivalent ratio of isocyanate groups in the polyisocyanate monomer to hydroxyl groups in the polyol polymer was 1:2) was added into the pretreated product, and after stirring at 150 r / min for 2 h under vacuum, a hydroxyl double-terminated prepolymer was obtained;

[0047] S23, 41.0 g (35.67 mmol) of low free polyether polyol-based polyurethane prepolymer Adiprene LFG963A, 12.0 g (7.134 mmol) of low free polyester polyol-based polyurethane prepolymer Adiprene LFM S200, and 0.3 g of 2,2-dimorpholinyl diethyl ether (the molar equivalent ratio of isocyanate groups in the low free polyurethane prepolymer to isocyanate groups in the polyisocyanate monomer is 6:1) are added to the hydroxyl double-terminated prepolymer, and after stirring at a rotation speed of 150 r / min under vacuum for 2 h, the low free reactive polyurethane hot melt adhesive is discharged, and vacuum sealed and stored.

[0048] Example 5

[0049] S21, 11.4 g (5.689 mmol) of polytetrahydrofuran ether diol with a number average molecular weight of 2000, 11.4 g (5.689 mmol) of polycaprolactone diol with a number average molecular weight of 2000, and 13.0 g of acrylic resin BR113 are added to a reaction bottle, heated to 110°C, and vacuum dehydrated at a stirring speed of 150 r / min for 2 h; then cooled to 80°C to obtain a pretreated product;

[0050] S22, 1.0 g (5.689 mmol) of hexamethylene diisocyanate (the molar equivalent ratio of isocyanate groups in the polyisocyanate monomer to hydroxyl groups in the polyol polymer is 1:2) is added to the pretreated product, and after stirring at a rotation speed of 150 r / min under vacuum for 2 h, a hydroxyl double-terminated prepolymer is obtained;

[0051] S23, 54.3 g (28.44 mmol) of low free polyether polyol-based polyurethane prepolymer Adiprene LF TE440, 8.0 g (2.844 mmol) of low free polyester polyol-based polyurethane prepolymer Adiprene LFM S300, and 1 g of dibutyltin dilaurate (the molar equivalent ratio of isocyanate groups in the low free polyurethane prepolymer to isocyanate groups in the polyisocyanate monomer is 5.5:1) are added to the hydroxyl double-terminated prepolymer, and after stirring at a rotation speed of 150 r / min under vacuum for 2 h, the low free reactive polyurethane hot melt adhesive is discharged, and vacuum sealed and stored.

[0052] Example 6

[0053] S21, 30.2 g (8.642 mmol) of polyhexanediol adipate diol with a number average molecular weight of 3500, 17.3 g (8.642 mmol) of polyoxypropylene ether diol with a number average molecular weight of 2000, and 12.0 g of thermoplastic polyurethane resin Pearl bond 539 were added into a reaction bottle, heated to 110°C, and vacuum dehydrated for 2 h under stirring at 150 r / min; then cooled to 80°C to obtain a pretreated product;

[0054] S22, 1.5 g (8.642 mmol) of hexamethylene diisocyanate (the molar equivalent ratio of isocyanate groups in the polyisocyanate monomer to hydroxyl groups in the polyol polymer was 1:2) was added into the pretreated product, and after stirring at 150 r / min for 2 h under vacuum, a hydroxyl double-terminated prepolymer was obtained;

[0055] S23, 23.8 g (25.93 mmol) of low-free polyether polyol-based polyurethane prepolymer Adiprene LF TE915, 14.5 g (8.642 mmol) of low-free polyester polyol-based polyurethane prepolymer Adiprene LFM S500, and 0.7 g of stannous octoate (the molar equivalent ratio of isocyanate groups in the low-free polyurethane prepolymer to isocyanate groups in the polyisocyanate monomer was 4:1) were added into the hydroxyl double-terminated prepolymer, and after stirring at 150 r / min for 2 h under vacuum, the low-free reactive polyurethane hot melt adhesive was discharged and vacuum sealed for storage.

[0056] Comparative Example 1

[0057] S21, 23.1 g (7.709 mmol) of polyneopentyl glycol adipate diol with a number average molecular weight of 3000, 15.4 g (7.709 mmol) of polyoxypropylene ether diol with a number average molecular weight of 2000, and 15.0 g of acrylic resin BM751 were added into a reaction bottle, heated to 110°C, and vacuum dehydrated for 2 h under stirring at 150 r / min; then cooled to 80°C to obtain a pretreated product;

[0058] S22, 15.4 g (61.67 mmol) of 4,4'-diphenylmethane diisocyanate (MDI) (the molar equivalent ratio of isocyanate groups in the polyisocyanate monomer to hydroxyl groups in the polyol polymer was 1:0.5) was added into the pretreated product, and after stirring at 150 r / min for 2 h under vacuum, the traditional reactive polyurethane hot melt adhesive was discharged and vacuum sealed for storage.

[0059] Comparative Example 2

[0060] S21, 21.9 g (10.96 mmol) of polytetramethylene terephthalate diol with a number average molecular weight of 2000, 11.0 g (10.96 mmol) of polycarbonate-1,5-pentanediol-1,6 hexanediol diol with a number average molecular weight of 1000, and 10.0 g of thermoplastic polyurethane resin Pearlbond 523 were added into a reaction bottle, heated to 110°C, vacuum dehydrated for 2 h under the condition of stirring at 150 r / min, and then cooled to 80°C to obtain a pretreated product;

[0061] S22, 26.3 g (32.89 mmol) of low-free polyurethane prepolymer Adiprene TE1050 based on a low-free polyether polyol, 30.7 g (10.96 mmol) of low-free polyurethane prepolymer Adiprene LFMS300 based on a low-free polyester polyol, and 0.1 g of 2,2-dimorpholinyl diethyl ether (the molar equivalent ratio of isocyanate groups in the low-free polyurethane prepolymer to hydroxyl groups in the polyol polymer is 1:0.5) were added into the pretreated product, and after stirring at a rotation speed of 150 r / min for 2 h under vacuum, the product was discharged to obtain a low-free reactive polyurethane hot melt adhesive in which the low-free prepolymer completely replaced the isocyanate monomer, and the product was vacuum sealed and stored.

[0062] Comparative Example 3

[0063] The low-free reactive polyurethane hot melt adhesive was prepared by the method of Example 1, except that the two-step method was replaced by a one-step method, and the specific steps were as follows:

[0064] By weight, 19.4 g (9.719 mmol) of polytetramethylene terephthalate diol with a number average molecular weight of 2000, 9.7 g (9.719 mmol) of polycarbonate-1,5-pentanediol-1,6 hexanediol diol with a number average molecular weight of 1000, and 10.0 g of thermoplastic polyurethane resin Pearlbond 523 were added into a reaction bottle, heated to 110°C, vacuum dehydrated for 2 h under the condition of stirring at 150 r / min, and then cooled to 80°C to obtain a pretreated product, 2.4 g (9.719 mmol) of 4,4'-diphenyl methane diisocyanate (MDI), 31.1 g (38.88 mmol) of low-free polyurethane prepolymer Adiprene TE1050 based on a low-free polyether polyol, 27.2 g (9.719 mmol) of low-free polyurethane prepolymer Adiprene LFMS300 based on a low-free polyester polyol, and 0.1 g of 2,2-dimorpholinyl diethyl ether were added under vacuum at a rotation speed of 150 r / min for 2 h, and then the product was discharged to obtain a low-free reactive polyurethane hot melt adhesive prepared by a one-step process, and the product was vacuum sealed and stored.

[0065] Comparative Example 4

[0066] The process of Example 1 was used to prepare a low free reactive polyurethane hot melt adhesive, except that in step S23, the amount of low free polyether polyol based polyurethane prepolymer Adiprene TE1050 was adjusted to 6.22 g (7.78 mmol) and the amount of low free polyester polyol based polyurethane prepolymer Adiprene LFM S300 was adjusted to 5.44 g (1.944 mmol), i.e. the molar equivalent ratio of isocyanate groups in the low free polyurethane prepolymer to isocyanate groups in the polyisocyanate monomer was 1:1, and the remaining conditions were the same as in Example 1, to obtain a low free reactive polyurethane hot melt adhesive, which was vacuum sealed and stored.

[0067] Test Example

[0068] The samples of the examples and comparative examples were tested by the following methods:

[0069] (1) Melt viscosity: The sealed reactive polyurethane hot melt adhesive was placed in a needle cylinder heater at 110 °C for 10 min, at which time the hot melt adhesive was already a molten fluid, which was quickly poured into a sleeve in a Brookfield-DV2T viscometer, the heater temperature was set to 110 °C and maintained for 10 min to make the internal temperature of the hot melt adhesive uniform and deaerated. The constant temperature melt viscosity of the hot melt adhesive was measured at a temperature of 110 °C. The results are shown in Table 1.

[0070] (2) Open time: The reactive polyurethane hot melt adhesive obtained in the examples and comparative examples was coated on a polycarbonate substrate using a dispensing machine at a width of about 2 mm, timing started after dispensing was completed, the adhesive line was gently touched with a finger, and when the adhesive line was not sticky, timing was stopped, and the time was recorded as the open time of the reactive polyurethane hot melt adhesive. The results are shown in Table 1.

[0071] (3) Adhesion strength (30 min, 24 h): The reactive polyurethane hot melt adhesive obtained in the examples and comparative examples was dispensed at 110 °C using a dispensing machine, and a 25 mm * 25 mm rectangular adhesive frame was coated on a polycarbonate substrate at a width of about 1 mm, then another polycarbonate substrate was attached to the polycarbonate substrate, after the dispensing and pressing were completed, the sample was cured in an environment of 25 °C, 50% RH for 30 min, 24 h, then the adhesive sample was run to adhesive failure along the pulling direction at a speed of 10 mm / min using a universal material testing machine, and the maximum force value displayed by the instrument was recorded, and the adhesion strength of the hot melt adhesive to the polycarbonate substrate was calculated based on the adhesive area. The results are shown in Table 1.

[0072] (4) Free isocyanate content: determined using a high performance liquid chromatograph (HPLC), specifically, using a liquid as a mobile phase, using a high-pressure infusion system, pumping the mobile phase into a chromatographic column containing a stationary phase, after the components in the column are separated, entering the detector for detection to obtain the chromatogram of the detected substance. The content of free isocyanate monomer in the reactive polyurethane hot melt adhesive is quantitatively calculated using an external standard method, and the chromatograms of the sample to be tested and the standard are recorded respectively, and the content of free isocyanate in the sample to be tested is calculated according to the integral area of the specific peak on the chromatogram. The results obtained are shown in Table 1.

[0073] Table 1

[0074]

[0075] As can be seen from the comparison of Examples 1-6 and Comparative Example 1, the reactive polyurethane hot melt adhesive prepared by the two-step process of the present application has a similar melt viscosity, open time and bonding strength to the traditional reactive polyurethane hot melt adhesive, and the present application has a lower free isocyanate content than the traditional reactive polyurethane hot melt adhesive. The free isocyanate content of the reactive polyurethane hot melt adhesive prepared by the two-step process is below 0.1 wt%, the free isocyanate content is significantly reduced, which meets the performance requirements of general applications, and greatly increases the safety of using reactive polyurethane hot melt adhesive, avoiding harm to the health of practitioners. As can be seen from the comparison of Examples 1-6 and Comparative Example 2, the present application has lower melt viscosity, longer open time and higher bonding strength than the method of simply replacing the isocyanate monomer reaction with low free polyurethane prepolymer to prepare low free reactive polyurethane hot melt adhesive. The reactive polyurethane hot melt adhesive prepared by the present application is more in line with the performance requirements of actual applications. As can be seen from the comparison of Examples 1-6 and Comparative Example 3, the reactive polyurethane hot melt adhesive prepared by the one-step reaction process has the risk of insufficient isocyanate monomer reaction, and the final free isocyanate content is still higher than 0.1 wt%. As can be seen from the comparison of Examples 1-6 and Comparative Example 4, the present application has lower melt viscosity, longer open time and higher bonding strength than the system with low free polyurethane prepolymer without excess. In summary, the reactive polyurethane hot melt adhesive prepared by the two-step process of the present application has a low isocyanate content, and at the same time has lower melt viscosity, longer open time and higher bonding strength.

[0076] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments without departing from the principles and spirit of the present application within the scope of the present application.

Claims

1. A low free reactive polyurethane hot-melt adhesive, characterized in that, The low free reactive polyurethane hot melt adhesive comprises a polyurethane body and a tackifying resin, wherein the polyurethane body is prepared by the following method: S11, a first nucleophilic addition reaction is performed between a polyisocyanate monomer and an excess of a polyol polymer, the molar equivalent ratio of isocyanate groups in the polyisocyanate monomer to hydroxyl groups in the polyol polymer is 1:(2-2.2), and a hydroxyl double-terminated prepolymer is obtained; S12, a second nucleophilic addition reaction is performed between the hydroxyl double-terminated prepolymer and a low free polyurethane prepolymer, the molar equivalent ratio of isocyanate groups in the low free polyurethane prepolymer to isocyanate groups in the polyisocyanate monomer is (3-6):1, and a polyurethane body is obtained; The content of free isocyanate contained in the low free polyurethane prepolymer is less than 0.1wt%.

2. The low free reactive, polyurethane hot-melt glue according to claim 1, characterized in that, The content of the polyurethane body is 75-95% and the content of the tackifying resin is 5-25% based on the total weight of the low free reactive polyurethane hot melt adhesive.

3. The low free reactive, polyurethane hot-melt glue according to claim 1, characterized in that, The polyisocyanate monomer is at least one selected from isophorone diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, hydrogenated MDI, polymeric MDI, 1,5-naphthalene diisocyanate, 1,4-phenylene diisocyanate, xylylene diisocyanate, tetramethyl xylene diisocyanate, and norbornane diisocyanate.

4. The low free reactive, polyurethane hot-melt glue according to claim 1, characterized in that, The polyol polymer is at least one selected from polyester polyol, polyether polyol, polycarbonate polyol, and polyalkylene polyol.

5. The low free reactive, polyurethane hot-melt glue according to claim 4, characterized in that, The polyester polyol is at least one selected from polyester polyol obtained by esterification reaction of polycarboxylic acid and polyol, and poly-ε-caprolactone polyol obtained by ring-opening polymerization of ε-caprolactone; the polycarboxylic acid is at least one selected from terephthalic acid, isophthalic acid, 1,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid; and the polyol is at least one selected from ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, and cyclohexanediol; The polyether polyol is at least one selected from ring-opening polymers of ethylene glycol, propylene glycol, tetrahydrofuran, 3-methyltetrahydrofuran, random copolymers and block copolymers, and bisphenol-type polyoxyalkylene modified products; the bisphenol-type polyoxyalkylene modified product is a polyether polyol obtained by addition reaction of active hydrogen moieties of a bisphenol-type molecular skeleton with an alkylene oxide, and the alkylene oxide is at least one selected from ethylene oxide, propylene oxide, butylene oxide, and isobutylene oxide; The polycarbonate polyol is selected from at least one of polycarbonate 1,6-hexanediol polyol, polycarbonate-1,4-butanediol-1,6 hexanediol diol, polycarbonate-1,5-pentanediol-1,6 hexanediol diol, polycarbonate caprolactone hexylene diol, polycarbonate-1,4-cyclohexanedimethanol-1,6 hexanediol diol, polyethylene carbonate diol, polypropylene carbonate diol, polybutylene carbonate diol, and polyhexylene carbonate diol. The polyalkylene polyol is selected from at least one of polybutadiene polyol, hydrogenated polybutadiene polyol, and hydrogenated polyisoprene polyol.

6. The low free reactive, polyurethane hot-melt glue according to claim 1, wherein, The low-free polyurethane prepolymer is a low-free polyether polyol-based polyurethane prepolymer and / or a low-free polyester polyol-based polyurethane prepolymer.

7. The low free reactive, polyurethane hot-melt glue according to claim 6, characterized in that, The low-free polyether polyol-based polyurethane prepolymer is obtained by reacting a polyether polyol with a polyisocyanate monomer; the polyether polyol is selected from at least one of an open ring polymer of ethylene glycol, propylene glycol, tetrahydrofuran, and 3-methyltetrahydrofuran, a random copolymer, and a block copolymer; and the polyisocyanate monomer is selected from at least one of isophorone diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, hydrogenated MDI, polymeric MDI, 1,5-naphthalene diisocyanate, 1,4-phenylene diisocyanate, xylylene diisocyanate, tetramethyl xylene diisocyanate, and norbornane diisocyanate. The low-free polyester polyol-based polyurethane prepolymer is obtained by reacting a polyester polyol with a polyisocyanate monomer; the polyester polyol is selected from at least one of polyethylene adipate diol, polypropylene adipate diol, polybutylene adipate diol, poly-1,4-butanediol adipate diol, polyneopentyl glycol adipate diol, and poly-1,6-hexanediol adipate diol; and the polyisocyanate monomer is selected from at least one of isophorone diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, hydrogenated MDI, polymeric MDI, 1,5-naphthalene diisocyanate, 1,4-phenylene diisocyanate, xylylene diisocyanate, tetramethyl xylene diisocyanate, and norbornane diisocyanate.

8. The low free reactive, polyurethane hot-melt glue according to claim 1, wherein, The conditions of the first nucleophilic addition reaction include a temperature of 70-90°C, a rotation speed of 100-200 r / min, and a time of 1-5 h; and the conditions of the second nucleophilic addition reaction include a temperature of 70-90°C, a rotation speed of 100-200 r / min, and a time of 1-5 h.

9. The low free reactive, polyurethane hot-melt glue according to claim 1, wherein, The first nucleophilic addition reaction and the second nucleophilic reaction are carried out in the presence of a catalyst; and the catalyst is selected from at least one of dibutyltin dilaurate, stannous octoate, triethylamine, diethylenetriamine, triethylenediamine, N-ethylmorpholine, and 2,2-dimorpholinyl diethyl ether.

10. The low free reactive, polyurethane hot-melt glue according to claim 1, wherein, The tackifying resin is selected from at least one of thermoplastic acrylic resin, polyurethane resin, amorphous poly-alpha olefin resin, rosin resin, petroleum resin, terpene resin, and EVA resin.

11. The process for preparing the low free reactive polyurethane hot-melt adhesive according to any one of claims 1 to 10, characterized in that, The method comprises the following steps: S21, vacuum stirring and dewatering the polyol polymer and the tackifying resin at 100-120 DEG C and a rotating speed of 100-200 r / min for 1-5 h, and then cooling to 70-90 DEG C to obtain a pretreated product; S22, stirring and reacting the pretreated product and the polyisocyanate monomer under vacuum at 70-90 DEG C and a rotating speed of 100-200 r / min for 1-5 h to obtain a hydroxyl double-terminated prepolymer; S23, stirring and reacting the low-free polyurethane prepolymer and the catalyst in the hydroxyl double-terminated prepolymer under vacuum at 70-90 DEG C and a rotating speed of 100-200 r / min for 1-5 h to obtain a low-free reactive polyurethane hot melt adhesive.

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