Soft package hardening packaging hot melt adhesive for cigarettes and preparation method of soft package hardening packaging hot melt adhesive

Abstract

The invention provides a cigarette soft package hardened packaging hot melt adhesive and a preparation method thereof, the cigarette soft package hardened packaging hot melt adhesive is mainly prepared by reaction of hot melt adhesive base resin and polyurethane hot melt adhesive prepolymer, the melt viscosity of the hot melt adhesive at 150 DEG C is 500-1000 mPa.S, and the Tg is 60-80 DEG C; the hot melt adhesive is prepared from the following main raw materials in percentage by weight: 20-50% of base resin, 10-30% of polyurethane hot melt adhesive prepolymer, 30-60% of tackifying resin, 0-20% of viscosity modifier, 1-5% of compatilizer, antioxidant and base material wetting agent. The polyurethane hot melt adhesive prepolymer is mainly prepared from raw materials such as polyether polyol, polyester polyol and isocyanate according to the weight ratio of (20 to 40): (15 to 30): (15 to 30); the polyester polyol is not easy to crystallize and has low polarity. The hot melt adhesive can meet the requirements of the hot melt adhesive for hardening packaging of soft packages for cigarettes.

Description

Technical Field

[0001] The invention relates to the technical field of hot melt adhesive preparation, and in particular to a hot melt adhesive for hardening soft-pack packaging of cigarettes and a preparation method thereof. Technical Background

[0002] After satisfying their basic commodity needs, consumers are paying more and more attention to the exquisiteness and grade of packaging as the economy continues to develop and society progresses. In the field of tobacco, ordinary cigarette packages are mainly divided into two types: soft packaging and hard packaging. Because the soft packaging has a relatively thin packaging paper and a relatively low paper strength, it is very easy to cause insufficient protection of the cigarettes during transportation, resulting in deformation and even serious quality problems. Although the hard packaging provides sufficient protection for the internal cigarettes and will not cause serious quality problems, its packaging paper is thicker and heavier, which cannot be ignored for the increase in cost. At the same time, it is also a waste of resources from the perspective of environmental protection. Therefore, people are pursuing a packaging method that can reduce the thickness and weight of the paper as much as possible while better protecting the internal goods. Therefore, the concept of soft packaging hardening has been proposed and gradually put into practice in major cigarette factories. Because this packaging method is very novel, it can be packaged with a relatively low weight of packaging paper to produce the effect of a hard package, and the packaging grade and exquisiteness are greatly improved while perfectly protecting the internal goods.

[0003] However, since the density of paper used for hardening soft packs is relatively high, the indentation is large and there is a greater tendency to bounce off during machine packaging, the instantaneous bonding strength and stress creep resistance requirements of hot melt adhesives are higher than those of ordinary soft packs and hard packs. The existing ordinary cigarette packaging hot melt adhesives currently in use are difficult to meet the above technical requirements. For this reason, the applicant uses reactive polyurethane hot melt adhesives for soft pack hardening cigarette packaging, hoping to overcome the shortcomings of ordinary EVA and polyolefin hot melt adhesives for cigarette packaging, which have insufficient bonding strength and low creep resistance, thereby solving the industry pain points and difficulties of soft pack hardening cigarette packaging debonding during the shelf life. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention provides a hot melt adhesive for hardening soft packs of cigarettes and a preparation method thereof: first, a polyurethane hot melt adhesive prepolymer is designed, wherein a large amount of polyether polyol is selected to improve the wetting effect on the low polarity cigarette package substrate; at the same time, a relatively low polarity liquid polyester polyol is selected, which can not only improve the physical adsorption force and wetting effect on the surface of the low polarity cigarette package substrate, but also enhance the compatibility with the low polarity hot melt adhesive base resin; and the selected low crystallinity polyester polyol can improve the cohesive strength of the entire colloid. The developed polyurethane hot melt adhesive prepolymer can form a polymer network interpenetrating structure with the hot melt adhesive base resin, and the cohesive force is strengthened after NCO end-capping and curing, and the creep resistance is greatly improved, and it can also form a certain chemical bond with the surface of the low polarity cigarette package substrate. This low viscosity, low polarity, low tg polyurethane hot melt adhesive prepolymer can also play the role of viscosity regulator and tackifying resin. The prepared hot melt adhesive has good applicability on the machine, and can produce very excellent wetting, adsorption and bonding effects on the low-polarity surface of the substrate, and well balances the cohesive force and the interaction force between the hot melt adhesive and the substrate, thereby effectively solving the problem of packaging edge opening under the soft package hardening process.

[0005] In order to achieve the technical purpose of the invention, the technical solution of the present invention is implemented as follows:

[0006] The present invention provides a hot melt adhesive for hardening soft pack packaging of cigarettes, which is mainly prepared by reacting a hot melt adhesive base resin with a polyurethane hot melt adhesive prepolymer, wherein the hot melt adhesive for hardening soft pack packaging of cigarettes has a melt viscosity of 500 to 1000 mPa·S at 150°C, specifically, but not limited to, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 and 1000 mPa·S, and a Tg of 60 to 80°C, specifically, but not limited to, 60, 65 , 70, 75 and 80°C; and the main raw materials used in the hot melt adhesive for hardening the soft pack of cigarettes and their weight percentage ratio are: base resin 20-50% (specifically optional but not limited to 20, 25, 30, 35, 40, 45, 50%), polyurethane hot melt adhesive prepolymer 10-30% (specifically optional but not limited to 10, 15, 20, 25, 30%), tackifying resin 30-60% (specifically optional but not limited to 30, 35, 40, 45, 50, 55, 60%) , viscosity regulator 0-20% (specifically optional but not limited to 0, 5, 10, 15, 20%), compatibilizer 1-5% (specifically optional but not limited to 1, 2, 3, 4, 5%), antioxidant 0.25-1.5% (specifically optional but not limited to 0.25, 0.4, 0.75, 1.0, 1.25, 1.5%), substrate wetting agent 0.1-0.5% (specifically optional but not limited to 0.1, 0.2, 0.3, 0.4, 0.5%), the above raw materials by weight% The total is 100%; the polyurethane hot melt adhesive prepolymer is mainly prepared from polyether polyol, polyester polyol, isocyanate and other raw materials in a weight ratio of (20-40): (15-30): (15-30), and the specific weight ratio can be selected but not limited to (20, 25, 30, 35, 40): (15, 20, 25, 30): (15, 20, 25, 30); the polyester polyol used in the polyurethane hot melt adhesive prepolymer is a polyester polyol that is not easy to crystallize and has low polarity.

[0007] Preferably, the hot melt adhesive for hardening soft pack packaging of cigarettes provided by the present invention, wherein the base resin of the hot melt adhesive is selected from one or more of polyolefin, EVA, SBS, SEBS, and SIS.

[0008] Preferably, in the hot melt adhesive for hardening soft pack packaging of cigarettes provided by the present invention, the polyether polyol and polyester polyol used in the polyurethane hot melt adhesive prepolymer have a molecular weight of 1000-3000 (specifically, 1000, 2000, 3000 are optional but not limited to), a moisture content of ≤500ppm, and a functionality of 2.

[0009] Preferably, in the hot melt adhesive for hardening soft pack packaging of cigarettes provided by the present invention, the polyether polyol used in the polyurethane hot melt adhesive prepolymer is selected from one or more of polyoxypropylene polyol, polyoxyethylene polyol and polytetramethylene glycol.

[0010] Preferably, in the hot melt adhesive for hardening soft pack packaging of cigarettes provided by the present invention, the polyester polyol used in the polyurethane hot melt adhesive prepolymer is one or more of polyethylene adipate glycol ester diol, polybutylene adipate glycol 1,4-diol ester diol, dimer acid polyester diol and polyolefin polyol.

[0011] Preferably, in the hot melt adhesive for hardening soft pack packaging of cigarettes provided by the present invention, the isocyanate used in the polyurethane hot melt adhesive prepolymer is one or more of MDI-50, MDI-100, and liquefied MDI.

[0012] Preferably, in the hot melt adhesive for hardening soft pack packaging of cigarettes provided by the present invention, the tackifying resin is one or more of rosin ester and its derivatives, terpene resin and modified resin, petroleum resin, monomer AMS resin, phenol-modified AMS resin, etc. The AMS resin refers to a-methylstyrene monomer polymer.

[0013] Preferably, in the hot melt adhesive for hardening soft pack packaging of cigarettes provided by the present invention, the viscosity regulator is one or more of paraffin wax, microcrystalline wax, Sasol wax, Fischer-Tropsch wax, PE wax, and cyclohexane oil.

[0014] Preferably, in the hot melt adhesive for hardening soft pack packaging of cigarettes provided by the present invention, the compatibilizer is a maleic anhydride grafted polymer, the antioxidant is 1010 (chemical name: pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate), and the substrate wetting agent is TEGO Wet 500, which is a silicon-free substrate wetting agent with low foaming tendency.

[0015] The present invention also provides a method for preparing the above-mentioned hot melt adhesive for hardening soft pack packaging of cigarettes, which specifically comprises the following steps:

[0016] Step 1: Heat the oil bath to 150°C, preheat the three-necked flask for 10-15 minutes, slowly add the viscosity regulator and tackifying resin into the three-necked flask, heat to 150°C while stirring, maintain 150°C at a speed of 200-300r / min until the tackifying resin is completely melted, then add the hot melt adhesive base resin, add part of the antioxidant after all the resins are melted and mixed evenly, and slowly turn on the vacuum pump at the same time, evacuate at 130°C-0.098Mpa for 2 hours, and seal and store for later use;

[0017] Step 2: dehydrate the polyether polyol and polyester polyol at 120°C and a vacuum of more than -0.098Mpa for 2 hours, then cool to 80°C, add isocyanate under nitrogen protection, gradually heat to 120°C and start timing, control the reaction temperature at 115-125°C for 2 hours, and obtain a polyurethane hot melt adhesive prepolymer;

[0018] Step 3: Heat and melt the hot melt adhesive prepared in step 1 and add it to the polyurethane hot melt adhesive prepolymer in step 2, add the remaining antioxidant, compatibilizer and substrate wetting agent, stir and disperse at high speed at 120-130°C for 1 hour to obtain a packaging hot melt adhesive suitable for soft package hardening process, and store the product under vacuum after cooling.

[0019] The present invention produces beneficial effects:

[0020] 1. The hot melt adhesive for hardening soft pack packaging of cigarettes provided by the present invention uses a polyurethane prepolymer that can partially act as a viscosity regulator and a tackifying resin, which can enhance the wetting and adsorption effect on low-polarity surfaces. At the same time, it is a non-crystalline high-molecular polymer with a low Tg, and can form a network interpenetrating configuration with the hot melt adhesive base resin, providing a strong holding force in a form similar to a pressure-sensitive adhesive, improving the cohesive force, balancing the surface adsorption force and bonding force, and achieving the improvement effect of cohesive failure or substrate failure rather than substrate surface failure;

[0021] 2. Polyurethane prepolymers are synthesized using polyester polyols that are not easy to crystallize and have low polarity. While maintaining the strong cohesive force of polyester polyols, the wetting, adsorption and bonding effects on the surface of low-polarity substrates can be enhanced;

[0022] 3. A large amount of tackifying resin is used as the main compatibilizer between the non-polar hot melt adhesive base resin and the polar polyurethane resin, and polar maleic anhydride grafted EVA is used as an auxiliary compatibilizer to effectively improve the compatibility between the non-polar base resin and the polar polyurethane resin, thereby producing the effect of balancing the cohesive force and the surface force of the substrate;

[0023] 4. Use polyurethane hot melt adhesive prepolymer for modification, so that ordinary non-reactive base hot melt adhesive also has the characteristics of reactive hot melt adhesive; after the polyurethane component is cured, the cohesive force is greatly improved, and a certain chemical bonding effect is formed on the surface of the substrate, and the temperature resistance is greatly improved. Therefore, there will be no edge splitting in high temperature places and during transportation;

[0024] 5. The hot melt adhesive for hardening the soft pack of cigarettes provided by the present invention has a relatively low and reasonable viscosity and a suitable softening point, and has a good gluing test effect: the peel strength value is high, and no edge opening will occur when stored for a long time at room temperature or at a high temperature of 60°C, thus meeting the requirements of hot melt adhesive for hardening the soft pack of cigarettes. DETAILED DESCRIPTION

[0025] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the protection scope of the present invention.

[0026] Example 1

[0027] A hot melt adhesive for hardening soft pack packaging of cigarettes, the raw materials of which are composed of the following materials in the following mass ratios, specifically 25% of hot melt adhesive base resin, 18% of polyurethane hot melt adhesive prepolymer, 55% of tackifying resin, 0% of viscosity regulator, 1.5% of compatibilizer, 0.4% of antioxidant, and 0.1% of wetting agent. The base resin of the hot melt adhesive is EVA (VA content 28%, melt index 800); the tackifying resin is rosin resin: C5 petroleum resin: monomer AMS resin: phenol-modified monomer AMS resin = 19%: 9%: 36%: 36%; the polyurethane hot melt adhesive prepolymer is PPG (molecular weight 2000): polyethylene glycol adipate diol (molecular weight 3000): dimer acid polyester diol (molecular weight 2000): terminal hydroxyl polybutadiene (molecular weight 2000): MDI-50 = 35%: 5%: 20%: 20%: 20% synthesized in proportion; the compatibilizer is maleic anhydride grafted EVA; the antioxidant is 1010; and the wetting agent is TEGO Wet 500.

[0028] Example 2

[0029] A hot melt adhesive for hardening soft pack packaging of cigarettes, the raw materials of which are composed of the following materials in mass ratio, specifically 30% hot melt adhesive base resin, 20.5% polyurethane hot melt adhesive prepolymer, 45% tackifier resin, 0 viscosity modifier, 4% compatibilizer, 0.4% antioxidant, and 0.1% wetting agent. The hot melt adhesive base resin is SBS; the tackifier resin is rosin glycerol ester: C9 petroleum resin: monomer AMS resin: phenol modified monomer AMS resin = 25%: 15%: 30%: 30%; the polyurethane hot melt adhesive prepolymer is PTMEG (molecular weight 2000): dimer acid polyester diol (molecular weight 2000): terminal hydroxyl polybutadiene (molecular weight 2000): MDI-50 = 40%: 20%: 15%: 25% synthesized in proportion; the compatibilizer is maleic anhydride grafted EVA; the antioxidant is 1010; and the wetting agent is TEGO Wet 500.

[0030] Example 3

[0031] A hot melt adhesive for hardening soft pack packaging of cigarettes, the raw materials of which are composed of the following materials in the following mass ratios, specifically 20% of hot melt adhesive base resin, 24.5% of polyurethane hot melt adhesive prepolymer, 50% of tackifying resin, 0% of viscosity regulator, 5% of auxiliary compatibilizer, 0.4% of antioxidant, and 0.1% of wetting agent. The hot melt adhesive base resin is SIS; the tackifying resin is styrene terpene resin: rosin ester: monomer AMS resin: phenol modified monomer AMS resin = 30%: 20%: 25%: 25%; the polyurethane hot melt adhesive prepolymer is PTMEG (molecular weight 2000): polyethylene glycol adipate diol (molecular weight 3000): dimer acid polyester diol (molecular weight 2000): terminal hydroxyl polybutadiene (molecular weight 2000): MDI-50 = 20%: 10%: 15%: 30%: 25% synthesized in proportion; the compatibilizer is maleic anhydride grafted EVA; the antioxidant is 1010; and the wetting agent is TEGO Wet 500.

[0032] The preparation methods of the soft package hardening packaging hot melt adhesive of Examples 1 to 3 all include the following steps:

[0033] Step 1: Heat the oil bath to 150°C, preheat the three-necked flask for 10 to 15 minutes, slowly add the viscosity regulator and tackifying resin into the three-necked flask, heat to 150°C while stirring, maintain 150°C at a speed of 200 to 300 r / min to completely melt the tackifying resin, then add the hot melt adhesive base resin, after all the resins are melted and mixed evenly, add a portion of the antioxidant, and slowly open the vacuum pump at the same time, evacuate at a vacuum of 130°C-0.098Mpa for 2 hours, and seal and store for later use.

[0034] Step 2: dehydrate the polyether polyol and polyester polyol at 120°C and a vacuum of more than -0.098Mpa for 2 hours, then cool to 80°C, add isocyanate under nitrogen protection, gradually heat to 120°C and start timing, control the reaction temperature at 115-125°C for 2 hours, and obtain a polyurethane hot melt adhesive prepolymer;

[0035] Step 3: Melt the hot melt adhesive prepared in step 1 and add it to the polyurethane hot melt adhesive prepolymer in step 2, add the remaining antioxidant, compatibilizer and substrate wetting agent, stir and disperse at high speed at 120-130°C for 1h, evenly compound to obtain a packaging hot melt adhesive suitable for soft package hardening process, and store it in vacuum directly after cooling.

[0036] Comparative Example 1

[0037] In contrast to Example 1, the polyurethane hot melt adhesive prepolymer modified raw material is not used in the hot melt adhesive product, and its 18% component ratio is completely replaced by viscosity modifier paraffin, and the remaining preparation steps, ratios, dosages and process conditions are the same as those in Example 1.

[0038] A hot melt adhesive for hardening soft pack packaging of cigarettes, the raw materials of which are composed of the following materials in mass ratio, specifically 25% hot melt adhesive base resin, 55% tackifying resin, 18% liquid paraffin, 0% viscosity modifier, 1.5% compatibilizer, 0.4% antioxidant, and 0.1% wetting agent. The hot melt adhesive base resin is EVA (VA content 28%, melt index 800); the tackifying resin is rosin resin: C5 petroleum resin: monomer AMS resin: phenol modified monomer AMS resin = 19%: 9%: 36%: 36%; the compatibilizer is maleic anhydride grafted EVA; the antioxidant is 1010; and the wetting agent is TEGO Wet 500.

[0039] Comparative Example 2

[0040] In contrast to Example 2, the polyurethane hot melt adhesive prepolymer modified raw material is not used in the product hot melt adhesive, 12.5% ​​of the viscosity modifier naphthenic oil is used to replace 12.5% ​​of the polyurethane hot melt adhesive prepolymer, and 8% of the tackifying resin is added to replace 8% of the polyurethane hot melt adhesive prepolymer. The remaining steps, proportions, dosages and process conditions are the same as those in Example 2.

[0041] A hot melt adhesive for hardening soft pack packaging of cigarettes, the raw materials of which are composed of the following materials in mass ratio, specifically 30% hot melt adhesive base resin, 53% tackifying resin, 12.5% ​​viscosity modifier naphthenic oil, 4% compatibilizer, 0.4% antioxidant, and 0.1% wetting agent. The hot melt adhesive base resin is SBS; the tackifying resin is rosin glycerol ester: C9 petroleum resin: monomer AMS resin: phenol modified monomer AMS resin = 25%: 15%: 30%: 30%; the compatibilizer is maleic anhydride grafted EVA; the antioxidant is 1010; and the wetting agent is TEGO Wet 500.

[0042] Comparative Example 3

[0043] In contrast to Example 3, the polyurethane hot melt adhesive prepolymer modified raw material is not used in the product hot melt adhesive, 4.5% of the viscosity modifier naphthenic oil is used to replace 4.5% of the polyurethane hot melt adhesive prepolymer, 10% of the hot melt adhesive base resin is used to replace 10% of the polyurethane hot melt adhesive prepolymer, and 10% of the tackifying resin is used to replace 10% of the polyurethane hot melt adhesive prepolymer. The remaining steps, proportions, dosages and process conditions are the same as those in Example 3.

[0044] A hot melt adhesive for hardening soft pack packaging of cigarettes, the raw materials of which are composed of the following materials in mass ratio, specifically 30% hot melt adhesive base resin, 60% tackifying resin, 4.5% viscosity modifier naphthenic oil, 5% auxiliary compatibilizer, 0.4% antioxidant, and 0.1% wetting agent. The hot melt adhesive base resin is SIS; the tackifying resin is styrene terpene resin: rosin ester: monomer AMS resin: phenol modified monomer AMS resin = 30%: 20%: 25%: 25%; the compatibilizer is maleic anhydride grafted EVA; the antioxidant is 1010; and the wetting agent is TEGO Wet 500.

[0045] Comparative Example 4

[0046] Comparative Example 1, wherein the dimer acid polyester diol (molecular weight 2000) and the terminal hydroxyl polybutadiene (molecular weight 2000) in the polyurethane hot melt adhesive prepolymer raw material are all replaced by poly (1,6-hexanediol adipate) (molecular weight 2000), and the remaining steps, proportions, dosages and process conditions are the same as those in Example 1.

[0047] A hot melt adhesive for hardening soft pack packaging of cigarettes, the raw materials of which are composed of the following materials in the following mass ratios, specifically 25% of hot melt adhesive base resin, 18% of polyurethane hot melt adhesive prepolymer, 55% of tackifying resin, 0% of viscosity regulator, 1.5% of compatibilizer, 0.4% of antioxidant, and 0.1% of wetting agent. The base resin of the hot melt adhesive is EVA (VA content 28%, melt index 800); the tackifying resin is rosin resin: C5 petroleum resin: monomer AMS resin: phenol-modified monomer AMS resin = 19%: 9%: 36%: 36%; the polyurethane hot melt adhesive prepolymer is PPG (molecular weight 2000): polyethylene glycol adipate (molecular weight 3000): polyethylene glycol adipate (molecular weight 2000): MDI-50 = 35%: 5%: 40%: 20% synthesized in proportion; the compatibilizer is maleic anhydride grafted EVA; the antioxidant is 1010; and the wetting agent is TEGOWet500.

[0048] Performance Testing

[0049] The hot melt adhesive products obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were tested for melt viscosity at 150° C. using a Brookfield viscometer according to HG / 3660-1999 standard method; and for softening point using the ring and ball method according to GB / T15332-1994 standard method.

[0050] The hot melt adhesive products obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were subjected to gluing tests: the hot melt adhesive products were melted at 120°C for 20 minutes, and the glue dispenser was operated to dispense glue (the glue area was 10mm*10mm) on the soft package hardened packaging box or the packaging paper strip at a glue dispensing speed of 1g / 20s, and then a 1kg weight was placed to press the test sample for 30 seconds. The obtained glued samples were placed at room temperature (25°C) for 48h and at a high temperature of 60°C for 48h, and then the edge opening on the packaging box was observed and the peel strength value of the packaging paper strip in the glued samples was tested. The test results are shown in the following table:

[0051]

[0052] It can be seen from the data in the above table that the hot melt adhesive for hardening soft pack packaging of cigarettes provided by the present invention has a relatively low and suitable viscosity and a suitable softening point, the peel strength value of the gluing test is ideal, and the edge will not open when stored for a long time either at room temperature or at a high temperature of 60°C, which can meet the requirements of hot melt adhesive for hardening soft pack packaging of cigarettes.

[0053] The above contents are merely examples and explanations of the concept of the present invention. Personnel in the technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A hot melt adhesive for hardening soft pack packaging of cigarettes, mainly prepared by reacting a hot melt adhesive base resin with a polyurethane hot melt adhesive prepolymer, characterized in that: The hot melt adhesive for hardening the packaging of soft cigarette packs has a melt viscosity of 500-1000 mPa·S at 150° C. and a Tg of 60-80° C. The main raw materials used in the hot melt adhesive for hardening the packaging of soft cigarette packs and their weight percentage ratios are: 20-50% base resin, 10-30% polyurethane hot melt adhesive prepolymer, 30-60% tackifying resin, 0-20% viscosity regulator, 1-5% compatibilizer, 0.25-1.5% antioxidant, and 0.1-0.5% substrate wetting agent; the polyurethane hot melt adhesive prepolymer is mainly prepared from raw materials such as polyether polyol, polyester polyol, and isocyanate in a weight ratio of (20-40): (15-30): (15-30); the polyester polyol used in the polyurethane hot melt adhesive prepolymer is a polyester polyol that is not easy to crystallize and has low polarity.

2. The hot melt adhesive for hardening soft pack packaging of cigarettes according to claim 1, characterized in that: The hot melt adhesive base resin is selected from one or more of polyolefin, EVA, SBS, SEBS and SIS.

3. A hot melt adhesive for hardening soft pack packaging of cigarettes according to claim 1 or 2, characterized in that: The polyether polyol and polyester polyol used in the polyurethane hot melt adhesive prepolymer have a molecular weight of 1000-3000, a moisture content of ≤500ppm, and a functionality of 2.

4. The hot melt adhesive for hardening soft pack packaging of cigarettes according to claim 3, characterized in that: The polyether polyol used in the polyurethane hot melt adhesive prepolymer is selected from one or more of polyoxypropylene polyol, polyoxyethylene polyol and polytetramethylene glycol.

5. The hot melt adhesive for hardening soft pack packaging of cigarettes according to claim 3, characterized in that: The polyester polyol used in the polyurethane hot melt adhesive prepolymer is one or more of polyethylene adipate glycol ester diol, polybutylene adipate glycol 1,4-diol ester diol, dimer acid polyester diol and polyolefin polyol.

6. A hot melt adhesive for hardening soft pack packaging of cigarettes according to claim 1 or 2, characterized in that: The isocyanate used in the polyurethane hot melt adhesive prepolymer is one or more of MDI-50, MDI-100 and liquefied MDI.

7. A hot melt adhesive for hardening soft pack packaging of cigarettes according to claim 1 or 2, characterized in that: The tackifying resin is one or more of rosin ester and its derivatives, terpene resin and modified resin, petroleum resin, monomer AMS resin, phenol-modified AMS resin and the like.

8. The hot melt adhesive for hardening soft pack packaging of cigarettes according to claim 1 or 2, characterized in that: The viscosity modifier is one or more of paraffin wax, microcrystalline wax, Sasol wax, Fischer-Tropsch wax, PE wax and naphthenic oil.

9. The hot melt adhesive for hardening soft pack packaging of cigarettes according to claim 1 or 2, characterized in that: The compatibilizer is maleic anhydride grafted polymer, the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate), and the substrate wetting agent is TEGO Wet 500.

10. A method for preparing the hot melt adhesive for hardening soft pack packaging of cigarettes according to claims 1 to 9, characterized in that: The specific steps include: Step 1: Heat the oil bath to 150°C, preheat the three-necked flask for 10-15 minutes, slowly add the viscosity regulator and tackifying resin into the three-necked flask, heat to 150°C while stirring, maintain 150°C at a speed of 200-300r / min until the tackifying resin is completely melted, then add the hot melt adhesive base resin, add part of the antioxidant after all the resins are melted and mixed evenly, and slowly turn on the vacuum pump at the same time, evacuate at 130°C-0.098Mpa for 2 hours, and seal and store for later use; Step 2: dehydrate the polyether polyol and polyester polyol at 120°C and a vacuum of more than -0.098Mpa for 2 hours, then cool to 80°C, add isocyanate under nitrogen protection, gradually heat to 120°C and start timing, control the reaction temperature at 115-125°C for 2 hours, and obtain a polyurethane hot melt adhesive prepolymer; Step 3: Heat and melt the hot melt adhesive prepared in step 1 and add it to the polyurethane hot melt adhesive prepolymer in step 2, add the remaining antioxidant, compatibilizer and substrate wetting agent, stir and disperse at high speed at 120-130°C for 1 hour to obtain a packaging hot melt adhesive suitable for soft package hardening process, and store the product under vacuum after cooling.

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