Packing box PUR hot melt adhesive and preparation method thereof

Abstract

The invention relates to the field of adhesives, and particularly discloses a packaging box PUR hot melt adhesive and a preparation method thereof. The PUR hot melt adhesive for the packaging box is prepared from the following raw materials: polyether polyol, polyester polyol, isocyanate, sulfydryl silane modified kaolin, epoxy acrylate, a chain extender, an antioxidant and a catalyst. Wherein the preparation raw materials of the sulfydryl silane modified kaolin comprise sulfydryl silane and nano kaolin, and the sulfydryl silane is introduced to modify the kaolin, so that the compatibility of the kaolin and the hot melt adhesive is improved, the molecular structure of the hot melt adhesive is protected from being damaged, and the water resistance of the PUR hot melt adhesive is remarkably improved; and through the synergistic effect of epoxy acrylate and sulfydryl silane modified kaolin, the cross-linked structure of polyurethane is improved, so that the structure between molecules is more stable, and the water resistance and adhesive property of the hot melt adhesive are further improved.

Description

Technical Field

[0001] The invention relates to the field of adhesives, and in particular to a packaging box PUR hot melt adhesive and a preparation method thereof. Background Art

[0002] PUR hot melt adhesive is a polyurethane reactive hot melt adhesive, which belongs to the polyurethane glue system. Its curing process is mainly divided into two stages. The first stage is mainly the physical cross-linking stage. After the PUR hot melt adhesive is cooled and solidified in the molten state, a certain initial adhesive strength is formed; the second stage is the chemical cross-linking stage. After the moisture in the air and the substrate diffuses from the surrounding into the PUR hot melt adhesive, the highly active isocyanate group in the PUR hot melt adhesive undergoes a cross-linking reaction with the surrounding moisture or other substances containing active hydrogen, thereby increasing the bonding strength.

[0003] Although PUR hot melt adhesive has significant advantages in bonding performance, its poor water resistance has gradually emerged in practical applications, especially in high humidity environments. After long-term use, PUR hot melt adhesive is prone to debonding due to hydrolysis, which limits its application in specific environments. Summary of the invention

[0004] In order to improve the problem of insufficient water resistance of PUR hot melt adhesive, the present application provides a packaging box PUR hot melt adhesive and a preparation method thereof.

[0005] In the first aspect, the present application provides a packaging box PUR hot melt adhesive, which adopts the following technical solution: A packaging box PUR hot melt adhesive is prepared from the following raw materials in parts by weight: 40-50 parts of polyether polyol; 16-24 parts of polyester polyol; 30-40 parts of isocyanate; 12-18 parts of mercaptosilane modified kaolin; Epoxy acrylate 8-10 parts; 1-3 parts of chain extender; 0.3-0.5 parts of antioxidant; Catalyst 0.06-0.08 parts; The raw materials for preparing the mercaptosilane-modified kaolin include mercaptosilane and kaolin, and the weight ratio of the mercaptosilane to the kaolin is (0.7-0.9):12.

[0006] By adopting the above technical scheme and the reasonable ratio of polyether polyol and polyester polyol, the PUR hot melt adhesive of the present application exhibits excellent bonding performance in both the physical crosslinking stage and the chemical crosslinking stage. Among them, the introduction of mercaptosilane to modify kaolin improves the compatibility of kaolin and hot melt adhesive, thereby protecting the molecular structure of the hot melt adhesive from being destroyed and significantly improving the water resistance of the PUR hot melt adhesive. The combination of kaolin and mercaptosilane forms a stable nanoscale structure, enhances the barrier ability of the hot melt adhesive to moisture, effectively prevents the problem of debonding caused by hydrolysis, and extends the service life of the packaging box in a high humidity environment. Through the synergistic effect of epoxy acrylate, the crosslinking structure of polyurethane is improved, making the structure between molecules more stable, so that the water resistance and bonding performance of the hot melt adhesive are further improved.

[0007] Preferably, the mercaptosilane includes at least one of 3-octanoylthiopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane and 3-mercaptopropyltriethoxysilane.

[0008] By adopting the above technical scheme, the alkoxy groups in the mercaptosilane are hydrolyzed and combined with the hydroxyl groups on the surface of kaolin to form a strong Si-O-Si chemical bond, thereby achieving the combination and connection of inorganic materials to improve the compatibility of kaolin and hot melt adhesive. At the same time, the mercapto groups in the mercaptosilane chemically react with the polymer to form a strong chemical bond or form a stable three-dimensional network structure with the polymer through physical entanglement, effectively blocking the penetration of moisture and oxygen, thereby improving the water resistance and weather resistance of the adhesive, and ensuring that the bonding performance of the hot melt adhesive in a humid environment is not affected.

[0009] Preferably, the epoxy acrylate includes at least one of glycidyl acrylate, 3,4-epoxycyclohexyl methacrylate, and glycidyl linolenate.

[0010] By adopting the above technical solution, epoxy acrylate has good compatibility with polyester polyol and polyether polyol, and epoxy acrylate can be evenly dispersed in the hot melt adhesive through the synergistic effect of epoxy acrylate and mercaptosilane-modified kaolin. Among them, epoxy acrylate contains epoxy groups, which can react with the mercapto groups in mercaptosilane, thereby increasing the crosslinking density, giving full play to the role of epoxy acrylate, and improving the water resistance and bonding performance of the hot melt adhesive.

[0011] Preferably, the polyether polyol is polytetramethylene ether diol, and the polyester polyol includes at least one of polyhexane adipate diol, polyethylene adipate diol, polyethylene phthalate diol, polyphthalate-based glycol ester diol, and polybutylene adipate diol.

[0012] By adopting the above technical scheme, the above polyether polyol has good compatibility with polyester polyol, and the polyester polyol has a good combination effect with isocyanate, has strong cohesion and crystallization performance, and the prepared hot melt adhesive has excellent comprehensive performance.

[0013] Preferably, the isocyanate is at least one selected from 1,4-cyclohexanedimethyl diisocyanate, isophorone diisocyanate, dicyclohexylmethane 4,4'-diisocyanate, and xylylene diisocyanate.

[0014] By adopting the above technical solution, the molecular structure of aliphatic isocyanate does not contain benzene rings, has good hydrolysis resistance and storage stability, and the hot melt adhesive prepared by using the above aliphatic isocyanate has good yellowing resistance, reduces the oxidation reaction of the adhesive layer, and improves the bonding performance of the adhesive layer. Among them, although xylene diisocyanate has a benzene ring, there is a methylene gap between the benzene ring and the isocyanate group, which prevents the conjugation effect of the benzene ring macromolecule from affecting the isocyanate group, making the isocyanate group more stable and reducing the reaction activity, that is, the reaction activity is close to that of aliphatic isocyanate.

[0015] Preferably, the chain extender includes at least one of hexamethylenediamine, isophoronediamine, ethylenediamine, dimethylethylenediamine, dimethylpropylenediamine, and diisopropylethylenediamine.

[0016] By adopting the above technical solution, the above amine chain extender can react with isocyanate to increase the length and cross-linking degree of the polymer chain, thereby improving the comprehensive performance of the hot melt adhesive.

[0017] Preferably, the antioxidant includes at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanuric acid, and tris(2,4-di-tert-butyl)phosphite.

[0018] By adopting the above technical scheme, the above antioxidant has low volatility, good compatibility with the substrate, and has good thermal stability and antioxidant properties when added to the molten system, which is beneficial to reducing the thermal degradation problem of polyurethane, improving the structural stability of polyurethane, maintaining the bonding performance of the hot melt adhesive, and extending the service life of the hot melt adhesive.

[0019] Preferably, the catalyst includes at least one of dimorpholine diethyl ether, triethylamine, dimethylethanolamine, trimethyl-p-phenylenediamine, triethylenediamine, and N,N-dimethylcyclohexylamine.

[0020] By adopting the above technical solution, the above organic amine is used as a catalyst to significantly increase the reaction rate of isocyanate and polyol, thereby accelerating the curing process of PUR hot melt adhesive and improving production efficiency. At the same time, it can promote the cross-linking reaction of PUR hot melt adhesive, enhance the cohesion and adhesion of the adhesive, and thus improve the bonding strength and durability of the packaging box.

[0021] In the second aspect, the present application provides a method for preparing a packaging box PUR hot melt adhesive, which adopts the following technical solution: A method for preparing a packaging box PUR hot melt adhesive, comprising the following steps: Weigh the raw materials according to the component ratio, mix the polyether polyol and polyester polyol evenly at 110-120°C, and react for 55-65 minutes; cool to 60-70°C, add isocyanate and chain extender under nitrogen protection, mix evenly and react for 70-80 minutes; add mercaptosilane-modified kaolin, epoxy acrylate, antioxidant and catalyst, mix and react for 2-3 hours to obtain the packaging box PUR hot melt adhesive.

[0022] By adopting the above technical solution, kaolin is modified by mercaptosilane, which effectively improves the poor compatibility of kaolin and hot melt adhesive, improves the stability of the internal molecular structure of the hot melt adhesive, and improves the water resistance of the hot melt adhesive.

[0023] Preferably, the preparation method of the mercaptosilane-modified kaolin is: Add kaolin to NaOH solution, stir and react at 60-70°C for 2-3h, filter and dry to obtain pretreated kaolin; add mercaptosilane to ethanol solution, adjust the pH to 6.0-7.0, hydrolyze for 2-3h to obtain a hydrolysis solution; adjust the temperature to 55-65°C, add the pretreated kaolin to the hydrolysis solution, ultrasonically disperse for 1-2h, filter and separate after the reaction is completed, and dry at 40-50°C for 2-3h to obtain mercaptosilane-modified kaolin.

[0024] By adopting the above technical scheme, under the action of NaOH, the surface activity and reactivity of kaolin are effectively improved, and the mercaptosilane is hydrolyzed by ethanol solution to ensure the uniform distribution of mercaptosilane on the surface of kaolin, so that mercaptosilane and kaolin are fully contacted and reacted to form chemical bonds, thereby improving the stability of the mercaptosilane-modified kaolin structure and forming a stable cross-linked structure, thereby improving the water resistance of the hot melt adhesive.

[0025] This application has the following beneficial effects: In the present application, through the reasonable ratio of polyether polyols and polyester polyols, the PUR hot melt adhesive of the present application exhibits excellent bonding performance in both the physical crosslinking stage and the chemical crosslinking stage. Among them, the introduction of mercaptosilane to modify kaolin improves the compatibility of kaolin and hot melt adhesive, thereby protecting the molecular structure of the hot melt adhesive from being destroyed and significantly improving the water resistance of the PUR hot melt adhesive. The combination of kaolin and mercaptosilane forms a stable nanoscale structure, enhances the water barrier ability of the hot melt adhesive, effectively prevents the debonding problem caused by hydrolysis, and extends the service life of the packaging box in a high humidity environment. Through the synergistic effect of epoxy acrylate, the crosslinking structure of polyurethane is improved, making the structure between molecules more stable, and further improving the water resistance and bonding performance of the hot melt adhesive. DETAILED DESCRIPTION

[0026] Preparation Example Preparation Example 1 The preparation method of mercaptosilane modified kaolin is: 12 kg of kaolin was added to NaOH solution, stirred and reacted at 60°C for 2 hours, filtered and dried to obtain pretreated kaolin; 0.7 kg of 3-octanoylthiopropyltriethoxysilane was added to ethanol solution, the pH was adjusted to 6.0, and hydrolyzed for 2 hours to obtain a hydrolysis solution; the temperature was adjusted to 55°C, the pretreated kaolin was added to the hydrolysis solution, ultrasonically dispersed for 1 hour, and after the reaction was completed, it was filtered and separated, and dried at 40°C for 2 hours to obtain mercaptosilane-modified kaolin.

[0027] Preparation Example 2 The preparation method of mercaptosilane modified kaolin is: 12 kg of kaolin was added to NaOH solution, stirred and reacted at 65°C for 2.5 hours, filtered and dried to obtain pretreated kaolin; 0.8 kg of 3-mercaptopropylmethyldimethoxysilane was added to ethanol solution, the pH was adjusted to 6.5, and hydrolyzed for 2.5 hours to obtain a hydrolysis solution; the temperature was adjusted to 60°C, the pretreated kaolin was added to the hydrolysis solution, ultrasonically dispersed for 1.5 hours, and after the reaction was completed, it was filtered and separated, and dried at 45°C for 2.5 hours to obtain mercaptosilane-modified kaolin.

[0028] Preparation Example 3 The preparation method of mercaptosilane modified kaolin is: 12 kg of kaolin was added to NaOH solution, stirred and reacted at 70°C for 3 hours, filtered and dried to obtain pretreated kaolin; 0.9 kg of 3-mercaptopropyltriethoxysilane was added to ethanol solution, the pH was adjusted to 7.0, and hydrolyzed for 3 hours to obtain a hydrolysis solution; the temperature was adjusted to 65°C, the pretreated kaolin was added to the hydrolysis solution, ultrasonically dispersed for 2 hours, and after the reaction was completed, it was filtered and separated, and dried at 50°C for 3 hours to obtain mercaptosilane-modified kaolin. Example

[0029] Example 1 A packaging box PUR hot melt adhesive comprises 40kg of polytetramethylene glycol (molecular weight 2000), 16kg of polyhexanediol adipate glycol (molecular weight 1800), 30kg of 1,4-cyclohexanedimethyl diisocyanate, 12kg of mercaptosilane-modified kaolin (prepared in Preparation Example 1), 8kg of glycidyl acrylate, 1kg of isophorone diamine, 0.2kg of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 0.1kg of tris(2,4-di-tert-butyl) phosphite, and 0.06kg of dimorpholine diethyl ether.

[0030] Among them, in this embodiment, the preparation method of the packaging box PUR hot melt adhesive includes the following steps: The raw materials were weighed according to the component ratio, polytetramethylene glycol ether diol and polyhexane adipate diol were mixed evenly at 110°C and reacted for 55 minutes; the temperature was lowered to 60°C, and 1,4-cyclohexanedimethyl diisocyanate and isophoronediamine were added under nitrogen protection, mixed evenly and reacted for 70 minutes; mercaptosilane-modified kaolin, glycidyl acrylate, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, tris(2,4-di-tert-butyl) phosphite and dimorpholine diethyl ether were added and mixed and reacted for 2 hours to obtain a packaging box PUR hot melt adhesive.

[0031] Example 2 A PUR hot melt adhesive for a packaging box comprises 45 kg of polytetramethylene ether glycol (molecular weight 2200), 20 kg of polyethylene phthalate glycol (molecular weight 2000), 35 kg of isophorone diisocyanate, 15 kg of mercaptosilane-modified kaolin (prepared in Preparation Example 2), 9 kg of 3,4-epoxycyclohexyl methacrylate, 2 kg of ethylenediamine, 0.3 kg of 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanuric acid, 0.1 kg of tris(2,4-di-tert-butyl) phosphite, and 0.07 kg of dimethylethanolamine.

[0032] Among them, in this embodiment, the preparation method of the packaging box PUR hot melt adhesive includes the following steps: The raw materials were weighed according to the group distribution ratio, polytetramethylene phthalate diol and poly(ethylene glycol phthalate) diol were mixed evenly at 110°C and reacted for 55 minutes; the temperature was lowered to 60°C, and isophorone diisocyanate and ethylenediamine were added under nitrogen protection, mixed evenly and reacted for 70 minutes; mercaptosilane-modified kaolin, 3,4-epoxycyclohexyl methacrylate, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanuric acid, tris(2,4-di-tert-butyl) phosphite and dimethylethanolamine were added and mixed for 2 hours to obtain a packaging box PUR hot melt adhesive.

[0033] Example 3 A packaging box PUR hot melt adhesive comprises 50kg of polytetramethylene glycol (molecular weight 2400), 24kg of polybutylene adipate glycol (molecular weight 2200), 40kg of dicyclohexylmethane 4,4'-diisocyanate, 18kg of mercaptosilane-modified kaolin (prepared in Preparation Example 3), 10kg of glycidyl linolenate, 3kg of hexamethylenediamine, 0.4kg of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 0.1kg of tris(2,4-di-tert-butyl) phosphite, and 0.08kg of trimethyl-p-phenylenediamine.

[0034] Among them, in this embodiment, the preparation method of the packaging box PUR hot melt adhesive includes the following steps: Mix polytetrahydrofuran ether diol and polybutylene adipate diol evenly at 120°C and react for 65 minutes; cool to 70°C, add dicyclohexylmethane 4,4'-diisocyanate and hexamethylenediamine under nitrogen protection, mix evenly and react for 80 minutes; add mercaptosilane-modified kaolin, linolenic acid glycidyl ester, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], tris(2,4-di-tert-butyl) phosphite and trimethyl-p-phenylenediamine and mix and react for 2-3 hours to obtain a packaging box PUR hot melt adhesive.

[0035] Example 4 A packaging box PUR hot melt adhesive, which is different from Example 2 in that isophorone diisocyanate is replaced by an equal amount of diphenylmethane diisocyanate.

[0036] Comparative Example Comparative Example 1 A PUR hot melt adhesive for packaging boxes, which differs from Example 2 in that the mercaptosilane-modified kaolin is replaced by an equal amount of nano-kaolin.

[0037] Comparative Example 2 A PUR hot melt adhesive for a packaging box, which differs from Example 2 in that the mercaptosilane-modified kaolin is replaced by an equal amount of 3-aminopropylmethyldimethoxysilane-modified kaolin, that is, 3-aminopropylmethyldimethoxysilane is used to modify the kaolin.

[0038] Comparative Example 3 A PUR hot melt adhesive for packaging boxes, which differs from Example 2 in that the mercaptosilane-modified kaolin is replaced by an equal amount of 3-glycidyloxypropyltriethoxysilane-modified kaolin, that is, 3-glycidyloxypropyltriethoxysilane is used to modify kaolin.

[0039] Comparative Example 4 A packaging box PUR hot melt adhesive, which is different from Example 2 in that mercaptosilane-modified kaolin is not added.

[0040] Comparative Example 5 A packaging box PUR hot melt adhesive, which is different from Example 2 in that epoxy acrylate is not added.

[0041] Performance testing 1. Viscosity test: Prepare samples and test according to HG / T3660-1999 standard to test the melt viscosity of hot melt adhesive.

[0042] 2. Initial adhesion test: Prepare and test the sample according to GB / T 7124-2008 standard to test the initial adhesion of hot melt adhesive. The tensile shear strength of the sample is tested after curing for 3 minutes at 25℃ / 50%RH.

[0043] 3. Final bonding strength test: Prepare and test the hot melt adhesive final bonding strength according to GB / T 7124-2008. The tensile shear strength of the sample is tested after curing for 7 days at 25℃ / 50%RH.

[0044] 4. Water resistance test: After the substrates bonded with the sample hot melt adhesive are aged in air, hot water (80°C) and cold water (30°C) for 7 days, they are dried for 1 day in an environment of 25°C and 50% relative humidity, and then a shear strength test is performed, which intuitively reflects the hydrolysis resistance of the hot melt adhesive.

[0045] 5. Water absorption test: The samples bonded with the hot melt adhesive prepared in Examples 1-4 and Comparative Examples 1-5 were placed in an oven at 70°C and fully dried to constant weight, and their initial mass was recorded as m0. The samples were then immersed in deionized water at room temperature for 24 hours. After being taken out, the surface moisture was quickly absorbed with a paper towel and weighed. The mass was recorded as m1. The water absorption (η) of the samples after immersion for 24 hours was calculated according to formula (1): Water absorption rate can characterize the ability of water molecules to enter the adhesive. The greater the water absorption rate, the easier it is for water to erode the adhesive layer.

[0046] Table 1 According to the comparison between Example 2 and Comparative Example 1 and the data in Table 1, when kaolin is added directly to the raw material without modification, the cross-linked structure formed is not stable enough due to the poor compatibility of nano-kaolin with the molten system, making the hot melt adhesive prone to hydrolysis. On the contrary, by modifying kaolin with mercaptosilane, the compatibility of kaolin with the sol is improved, and under the action of mercaptosilane, the nano-kaolin is evenly dispersed in the molten system to form a stable cross-linked structure, thereby improving the hydrolysis stability of the hot melt adhesive.

[0047] According to the comparison between Example 2 and Comparative Examples 2-3 and the data in Table 1, it can be seen that the reactivity of the mercapto group is greater than that of the amino group and the epoxy group. The mercapto group in the mercaptosilane chemically reacts with the high molecular polymer to form a more solid three-dimensional network structure, which has faster curing efficiency and better bonding performance, so that the adhesive layer can effectively block the penetration of moisture and oxygen, thereby improving the water resistance of the adhesive and ensuring that the bonding performance of the hot melt adhesive in a humid environment is not affected.

[0048] According to the comparison between Example 2 and Comparative Example 4 and the data in Table 1, it can be seen that when mercaptosilane-modified kaolin is not added, the water resistance of the hot melt adhesive is poor. On the contrary, after adding mercaptosilane-modified kaolin, the hydrolysis resistance of the hot melt adhesive can be improved. The combination of kaolin and mercaptosilane forms a stable nanostructure, which enhances the water barrier ability of the hot melt adhesive.

[0049] According to the comparison between Example 2 and Comparative Example 5 and the data in Table 1, it can be seen that when epoxy acrylate is not added, the water resistance and bonding performance of the hot melt adhesive are poor. On the contrary, by adding epoxy acrylate, epoxy acrylate and mercaptosilane-modified kaolin can synergistically improve the cross-linking structure of polyurethane, making the structure between molecules more stable, so that the water resistance and bonding performance of the hot melt adhesive are further improved.

[0050] According to the comparison between Example 2 and Example 4 and the data in Table 1, compared with aliphatic isocyanates, the isocyanate group is directly connected to the benzene ring and is easily oxidized to generate quinone substances. Aromatic isocyanates have poor hydrolysis resistance and are prone to cause oxidation and yellowing of the product, reducing the firmness of the hot melt adhesive, especially in a humid environment. However, aliphatic isocyanates do not contain a benzene ring structure and show better chemical stability, and the prepared hot melt adhesive has better performance.

[0051] This specific implementation manner is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the specific implementation manner as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A packaging box PUR hot melt adhesive, characterized in that: The invention is prepared from the following raw materials by weight: 40-50 parts of polyether polyol; 16-24 parts of polyester polyol; 30-40 parts of isocyanate; 12-18 parts of mercaptosilane modified kaolin; Epoxy acrylate 8-10 parts; 1-3 parts of chain extender; 0.3-0.5 parts of antioxidant; Catalyst 0.06-0.08 parts; The raw materials for preparing the mercaptosilane-modified kaolin include mercaptosilane and nano-kaolin, and the weight ratio of the mercaptosilane to the nano-kaolin is (0.7-0.9):

12.

2. A packaging box PUR hot melt adhesive according to claim 1, characterized in that: The mercaptosilane includes at least one of 3-octanoylthiopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane and 3-mercaptopropyltriethoxysilane.

3. A packaging box PUR hot melt adhesive according to claim 1, characterized in that: The epoxy acrylate includes at least one of glycidyl acrylate, 3,4-epoxycyclohexyl methacrylate, and glycidyl linolenate.

4. The PUR hot melt adhesive for packaging box according to claim 1, characterized in that: The polyether polyol is polytetramethylene ether diol, and the polyester polyol includes at least one of polyhexane adipate diol, polyethylene adipate diol, polydiethylene phthalate diol, polyphthalate-based glycol ester diol, and polybutylene adipate diol.

5. The PUR hot melt adhesive for packaging box according to claim 1, characterized in that: The isocyanate is selected from at least one of 1,4-cyclohexanedimethyl diisocyanate, isophorone diisocyanate, dicyclohexylmethane 4,4'-diisocyanate and xylylene diisocyanate.

6. A packaging box PUR hot melt adhesive according to claim 1, characterized in that: The chain extender includes at least one of hexamethylenediamine, isophoronediamine, ethylenediamine, dimethylethylenediamine, dimethylpropylenediamine, and diisopropylethylenediamine.

7. The PUR hot melt adhesive for packaging box according to claim 1, characterized in that: The antioxidant includes at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanuric acid, and tris(2,4-di-tert-butyl) phosphite.

8. The PUR hot melt adhesive for packaging box according to claim 1, characterized in that: The catalyst comprises at least one of dimorpholine diethyl ether, triethylamine, dimethylethanolamine and trimethyl-p-phenylenediamine.

9. A method for preparing a packaging box PUR hot melt adhesive according to any one of claims 1 to 8, characterized in that: The following steps are involved: Mix the polyether polyol and polyester polyol evenly at 110-120°C and react for 55-65 minutes; cool to 60-70°C, add isocyanate and chain extender under nitrogen protection, mix evenly and react for 70-80 minutes; add mercaptosilane-modified kaolin, epoxy acrylate, antioxidant and catalyst and mix and react for 2-3 hours to obtain PUR hot melt adhesive for packaging boxes.

10. A method for preparing a packaging box PUR hot melt adhesive according to claim 9, characterized in that: The preparation method of the mercaptosilane-modified kaolin is: Add nano-kaolin to NaOH solution, stir and react at 60-70°C for 2-3h, filter and dry to obtain pretreated kaolin; add mercaptosilane to ethanol solution, adjust the pH to 6.0-7.0, hydrolyze for 2-3h to obtain a hydrolysis solution; adjust the temperature to 55-65°C, add the pretreated kaolin to the hydrolysis solution, ultrasonically disperse for 1-2h, filter and separate after the reaction is completed, and dry at 40-50°C for 2-3h to obtain mercaptosilane-modified kaolin.

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