Bio-based self-repairing polyurethane hot melt adhesive and preparation method thereof

Abstract

The invention discloses a bio-based self-repairing polyurethane hot melt adhesive and a preparation method thereof. The preparation method comprises the following steps: uniformly mixing soybean oil-based polyol, PEG-400 and 1, 4-butanediol to obtain a mixture A, uniformly mixing the mixture A with MDI, reacting to obtain a prepolymer B, adding propyl gallate into the prepolymer B, heating until the propyl gallate is completely dissolved and is uniformly mixed with the prepolymer B, adding a catalyst, and reacting to obtain the bio-based self-repairing polyurethane hot melt adhesive. According to the invention, soybean oil-based polyol is used as a soft segment, MDI is used as a hard segment, 1, 4-butanediol is used as a chain extender, and propyl gallate is used as a cross-linking agent, so that the polyurethane resin for the bio-based hot melt adhesive is prepared; the contradictory problem of high strength and low softening point of polyurethane is solved through reversible reaction of phenolic hydroxyl group of propyl gallate and isocyanate, and the hot melt adhesive film with high bonding strength, low softening point, processability and repairability is provided.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane hot melt adhesive preparation, and specifically relates to a bio-based self-repairing polyurethane hot melt adhesive and a preparation method thereof. Background Art

[0002] In recent years, with the continuous upgrading of the industry, hot melt adhesives have gradually replaced traditional needles and glues due to their strong adhesion, easy operation, low cost and no pollution. Currently, the common hot melt adhesive films are PES, PA, EVA, and TPU. Among them, polyurethane has a wide variety of synthetic raw materials and a strong formula designability, which can meet the bonding and use conditions of different substrates. In particular, TPU also has excellent cold resistance, oil resistance, wear resistance, water washability, flexibility, etc. The fabric bonded by TPU hot melt adhesive film will be very comfortable to wear on the human body, without any plastic or foreign body feeling, and is very suitable for the compounding and bonding of textile fabrics in the clothing field.

[0003] However, the polyurethane resin for hot melt adhesive needs to take into account the bonding performance and processing performance of the material, so the contradiction between its high bonding strength and low melting point is a technical difficulty that needs to be solved urgently. The common polyester polyurethane on the market contains ester groups, the polarity of the bonds is strong, it is easy to crystallize, and has excellent heat resistance and bonding performance. The ether bonds in polyether polyurethanes are flexible, not easy to hydrolyze, and have excellent water resistance. In practical applications, the two are mixed to prepare polyurethane hot melt adhesives, and the high bonding performance and low melting point of the hot melt adhesive resin are balanced by changing the ratio of soft and hard segments. However, this method aims to make adjustments within a certain range, and it loses one thing while taking another into account. In order to find a balance between the two, it has certain limitations in the process of preparing high-strength and low-melting-point polyurethane resins for hot melt adhesives.

[0004] As one of the most commonly used renewable resources, vegetable oils have been used as a component of alkyd resins for wood coatings since the 1920s and have been used in printing inks for more than 500 years. In adhesive applications, the specific properties of vegetable oils can produce several different effects, the most important of which is the hydrophobic properties brought by the long alkyl chains of fatty acids. For example, in fiberboard bonding applications, the water absorption of samples added with soybean oil-based polyurethane adhesives was reduced from 50% to 26% in 2 hours, and the swelling thickness was reduced from 41% to 24%. In addition to inducing hydrophobicity through adhesives, the use of vegetable oils can also bring other advantages, such as improved compatibility with epoxy-based crosslinkers, secondary hydroxyl chain ends can act as plasticizers, and can be used as ionic segments in hydrolysis-resistant polyurethane dispersions. However, its higher molecular weight and side chain structure also affect the crystallization properties of polyurethanes, resulting in increased viscosity and decreased strength of adhesives. Summary of the invention

[0005] In order to effectively solve the above problems, the present invention provides a bio-based self-repairing polyurethane hot melt adhesive and a preparation method thereof.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A method for preparing a bio-based self-repairing polyurethane hot melt adhesive comprises the following steps:

[0008] (1) stirring soybean oil-based polyol, PEG-400, and 1,4-butylene glycol to obtain a mixture A;

[0009] (2) Mixing mixture A and diphenylmethane diisocyanate (MDI) uniformly, reacting at 60-85° C. for 15-30 min, and controlling the viscosity to be 4000-8000 cps to obtain prepolymer B;

[0010] (3) Add propyl gallate to prepolymer B, heat to 80-100° C. until propyl gallate is completely dissolved and mixed evenly with prepolymer B, add a catalyst, mix evenly, react at 90-120° C. for 2-6 hours, cool to 40° C., and discharge to obtain a bio-based self-healing polyurethane hot melt adhesive.

[0011] The invention uses propyl gallate as a cross-linking agent, soybean oil-based polyol as a soft segment, and MDI as a hard segment to prepare a polyurethane resin for hot melt adhesive with high strength and low melting point. Propyl gallate has three phenolic hydroxyl groups, which can form a highly cross-linked structure with an NCO group, improve the strength and bonding performance of the polyurethane, and effectively overcome the decrease in the strength of the polyurethane caused by the vegetable oil-based polyol. In addition, the phenolic carbamate formed by the phenolic hydroxyl group and the isocyanate is reversible. When heated to a certain temperature, the phenolic carbamate undergoes a reverse reaction and decomposes to regenerate -NCO and phenolic hydroxyl groups, thereby solving the contradiction between the high bonding performance and the low melting point required by the polyurethane hot melt adhesive.

[0012] Furthermore, the soybean oil-based polyol is prepared by the following method:

[0013] a) Methanol and isopropanol are mixed uniformly at a mass ratio of 1:2-3 to obtain a mixture, and 0.5-0.55% of HBF is added to the total mass of the mixture. 4 As a catalyst, stirring evenly obtains a hydroxylation reagent;

[0014] b) heating the epoxidized soybean oil to 50-55° C., adding the hydroxylation agent dropwise thereto, the mass ratio of the hydroxylation agent to the epoxidized soybean oil being 2-3:10, raising the temperature to 55-65° C. after the addition is complete, and continuing to stir and react for 1-2 hours;

[0015] c) distilling under reduced pressure at 115-125° C., cooling the material to obtain the soybean oil-based polyol, with a hydroxyl value of 70-120 mgKOH / g.

[0016] Furthermore, the mass ratio of the soybean oil-based polyol, PEG-400, and 1,4-butanediol is 100:5-15:25-50.

[0017] Furthermore, the R value of NCO / OH of the mixture A and diphenylmethane diisocyanate is 1.1 to 1.3.

[0018] Furthermore, the mass ratio of propyl gallate to prepolymer B is 0.08-0.1:1.

[0019] Furthermore, the catalyst is dibutyltin dilaurate, and the added amount of the dibutyltin dilaurate is 0.5-0.55% of the total mass of the reaction raw materials (soybean oil-based polyol, PEG-400, 1,4-butanediol, MDI, propyl gallate).

[0020] The present invention has the following beneficial effects:

[0021] 1. The rigid structure of gallic acid benzene ring can improve the mechanical properties of polyurethane resin; at the same time, the polyurethane resin prepared by its trivalent phenolic hydroxyl group has a cross-linked network structure, which can improve the mechanical properties of polyurethane resin. At the processing temperature, the cross-linked network can be depolymerized, the fluidity is improved, and the processability is strong.

[0022] 2. The electron-withdrawing group on the benzene ring of propyl gallate will reduce the electron cloud density of the phenolic hydroxyl group. The weaker the charge difference on the phenolic hydroxyl group, the weaker the strength of the phenolic urethane bond. At the same time, the steric effect of the substituent will also reduce the strength of the urethane bond in the polymer. Therefore, the urethane bond can be broken at about 120°C, solving the contradiction between high strength and low softening point of polyurethane.

[0023] 3. The present invention solves the problem of high viscosity and low strength of vegetable oil-based polyurethane adhesives. The raw materials are green and renewable. The product achieves the goal of environmental friendliness and low carbon while ensuring performance. DETAILED DESCRIPTION

[0024] The following examples can help those skilled in the art to better understand the present invention, but they are not intended to limit the present invention in any form.

[0025] Example 1

[0026] 1. Preparation of soybean oil-based polyols

[0027] (1) Methanol and isopropanol were mixed in a mass ratio of 1:2.7 to obtain a mixture, and 0.5% of the total mass of HBF was added to the mixture. 4 As a catalyst, stirring evenly obtains a hydroxylation reagent;

[0028] (2) heating the epoxidized soybean oil to 50° C., adding a hydroxylation agent dropwise thereto, the mass ratio of the hydroxylation agent to the epoxidized soybean oil being 2.8:10, raising the temperature to 60° C. after the addition is complete, stirring continuously, and reacting for 2 hours;

[0029] (3) Distill under reduced pressure at 120° C. and cool the product to obtain soybean oil-based polyol with a hydroxyl value of 90 mgKOH / g.

[0030] 2. Preparation of bio-based self-healing polyurethane hot melt adhesive

[0031] (1) mixing soybean oil-based polyol, PEG-400, and 1,4-butanediol in a mass ratio of 100:15:40 to obtain a mixture A;

[0032] (2) Mixing mixture A and MDI uniformly, wherein the NCO / OH R value of the mixture A and MDI is 1.2, and then reacting at 85° C. for 20 minutes, controlling the viscosity to 4500 cps, to obtain prepolymer B;

[0033] (3) Propyl gallate is added to prepolymer B at a mass ratio of 0.1:1, and the mixture is heated to 90° C. until propyl gallate is completely dissolved and mixed evenly with prepolymer B, and 0.5% of the total mass of the reaction raw materials as a catalyst dibutyltin dilaurate is added, mixed evenly, reacted at 105° C. for 4 hours, and then cooled to 40° C. to obtain a bio-based self-healing polyurethane hot melt adhesive.

[0034] 3. Production of hot melt adhesive film

[0035] The bio-based self-healing polyurethane hot melt adhesive was extruded and cast into a film at a casting temperature of 195°C. After film formation, it was cooled to 120°C and cured for 10 hours. It was then cooled to room temperature to obtain a polyurethane hot melt adhesive film, and its softening point and mechanical properties were tested.

[0036] Example 2

[0037] 1. Soybean oil-based polyol was prepared according to the method of Example 1

[0038] 2. Preparation of bio-based self-healing polyurethane hot melt adhesive

[0039] (1) mixing soybean oil-based polyol, PEG-400, and 1,4-butanediol in a mass ratio of 100:10:40 to obtain a mixture A;

[0040] (2) Mixing mixture A and MDI uniformly, wherein the NCO / OH R value of the mixture A and MDI is 1.3, and then reacting at 80° C. for 30 minutes, controlling the viscosity to be 5500 cps, to obtain prepolymer B;

[0041] (3) Propyl gallate is added to prepolymer B at a mass ratio of 0.1:1, and the mixture is heated to 90° C. until propyl gallate is completely dissolved and mixed evenly with prepolymer B. A catalyst dibutyltin dilaurate is added at 0.5% of the total mass of the reaction raw materials, and the mixture is mixed evenly. The mixture is reacted at 10° C. for 4 hours, and the mixture is cooled to 40° C. to obtain a bio-based self-healing polyurethane hot melt adhesive.

[0042] 3. Production of hot melt adhesive film

[0043] The bio-based self-healing polyurethane hot melt adhesive was extruded and cast into a film at a casting temperature of 195°C. After film formation, it was cooled to 120°C and cured for 10 hours. It was then cooled to room temperature to obtain a polyurethane hot melt adhesive film, and its softening point and mechanical properties were tested.

[0044] Example 3

[0045] 1. Soybean oil-based polyol was prepared according to the method of Example 1

[0046] 2. Preparation of bio-based self-healing polyurethane hot melt adhesive

[0047] (1) mixing soybean oil-based polyol, PEG-400, and 1,4-butanediol in a mass ratio of 100:5:30 to obtain a mixture A;

[0048] (2) Mixing mixture A and MDI uniformly, wherein the NCO / OH R value of the mixture A and MDI is 1.1, and then reacting at 75° C. for 20 minutes, controlling the viscosity to be 6000-7000 cps, to obtain prepolymer B;

[0049] (3) Propyl gallate is added to prepolymer B at a mass ratio of 0.08:1, and the mixture is heated to 90° C. until propyl gallate is completely dissolved and mixed evenly with prepolymer B, and 0.5% of the total mass of the reaction raw materials as a catalyst dibutyltin dilaurate is added and mixed evenly, and the mixture is reacted at 105° C. for 4 hours, and the mixture is cooled to 40° C. to obtain a bio-based self-healing polyurethane hot melt adhesive.

[0050] 3. Production of hot melt adhesive film

[0051] The bio-based self-healing polyurethane hot melt adhesive was extruded and cast into a film at a casting temperature of 195°C. After film formation, it was cooled to 120°C and cured for 10 hours. It was then cooled to room temperature to obtain a polyurethane hot melt adhesive film, and its softening point and mechanical properties were tested.

[0052] Comparative Example 1

[0053] 1. Soybean oil-based polyol was prepared according to the method of Example 1.

[0054] 2. Preparation of soybean oil-based polyurethane hot melt adhesive

[0055] (1) mixing soybean oil-based polyol, PEG-400, and 1,4-butanediol in a mass ratio of 100:15:40 to obtain a mixture A;

[0056] (2) Mixing mixture A and MDI uniformly, wherein the NCO / OH R value of the mixture A and MDI is 0.9, adding 0.5% of the total mass of the reaction raw materials (soybean oil-based polyol, PEG-400, 1,4-butanediol, MDI) of the catalyst dibutyltin dilaurate, mixing uniformly, reacting at 75° C. for 30 minutes, cooling to 40° C., and discharging to obtain a soybean oil-based polyurethane hot melt adhesive, wherein the NCO / OH R value of the mixture A and MDI is 0.9;

[0057] 3. Production of hot melt adhesive film

[0058] The obtained soybean oil-based polyurethane hot melt adhesive was extruded and cast into a film at a casting temperature of 195°C. After film formation, it was cooled to 80°C and cured for 10 hours. It was then cooled to room temperature to obtain a polyurethane hot melt adhesive film, and its softening point and mechanical properties were tested.

[0059] Table 1 Hot melt adhesive film performance test

[0060]

[0061] As can be seen from Examples 1 to 3 in the table, the addition of propyl gallate significantly improves the Shore A hardness, tensile strength, and right-angle tear of the bio-based hot melt adhesive film, and the elongation at break is significantly improved. The ring softening point is about 120°C, which is equivalent to the depolymerization temperature of the phenolic carbamate bond; compared with Comparative Example 1, the mechanical strength and toughness of the embodiment are significantly improved. This is because the phenolic carbamate formed by cross-linking propyl gallate and NCO groups in the embodiment forms a cross-linked network structure in the hot melt adhesive, which improves the crystallinity of the bio-based polyurethane, which is beneficial to improving the mechanical strength and bonding properties of the bio-based polyurethane hot melt adhesive, and the improvement of the elongation at break may be that the cross-linking structure reduces the influence of the soybean oil-based side chain on the crystallization of the polyurethane hard segment to a certain extent, improves the structure of the separation of the soft and hard segments of the polyurethane, and improves the toughness of the film. In general, the bio-based polyurethane hot melt adhesive with propyl gallate as a cross-linking agent provided by the present invention solves the problem of high viscosity and low strength of the vegetable oil-based polyurethane adhesive, has high bonding strength, and has a high softening point.

[0062] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art should understand that the above specific descriptions are illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

Claims

1. A method for preparing a bio-based self-repairing polyurethane hot melt adhesive, characterized in that: The following steps are involved: (1) Mix soybean oil-based polyol, PEG-400, and 1,4-butylene glycol to obtain a mixture A; (2) Mix the mixture A and diphenylmethane diisocyanate evenly, react at 60-85°C for 15-30 minutes, and control the viscosity to 4000-8000 cps to obtain prepolymer B; (3) Add propyl gallate to prepolymer B, heat to 80-100°C until propyl gallate is completely dissolved and mixed evenly with prepolymer B, add a catalyst, mix evenly, react at 90-120°C for 2-6 hours, cool and discharge the material to obtain a bio-based self-healing polyurethane hot melt adhesive.

2. The method for preparing a bio-based self-repairing polyurethane hot melt adhesive according to claim 1, characterized in that: The soybean oil-based polyol is prepared by the following method: a) Methanol and isopropanol are mixed uniformly in a mass ratio of 1:2-3 to obtain a mixture, 0.5-0.55% of the total mass of the mixture is added with HBF4 as a catalyst, and the mixture is stirred uniformly to obtain a hydroxylation reagent; b) heating the epoxidized soybean oil to 50-55°C, adding the hydroxylation reagent dropwise thereto, raising the temperature to 55-65°C after the addition is complete, and stirring the reaction for 1-2 hours; c) distilling under reduced pressure at 115-125° C. and cooling the discharged material to obtain the soybean oil-based polyol.

3. The method for preparing a bio-based self-repairing polyurethane hot melt adhesive according to claim 2, characterized in that: The mass ratio of the hydroxylation agent to the epoxidized soybean oil is 2-3:

10.

4. The method for preparing a bio-based self-repairing polyurethane hot melt adhesive according to claim 2, characterized in that: The hydroxyl value of the prepared soybean oil-based polyol is 70-120 mgKOH / g.

5. The method for preparing a bio-based self-repairing polyurethane hot melt adhesive according to claim 1, characterized in that: The mass ratio of the soybean oil-based polyol, PEG-400, and 1,4-butylene glycol is 100:5-15:25-50.

6. The method for preparing a bio-based self-repairing polyurethane hot melt adhesive according to claim 1, characterized in that: The R value of NCO / OH of the mixture A and diphenylmethane diisocyanate is 1.1-1.

3.

7. The method for preparing a bio-based self-repairing polyurethane hot melt adhesive according to claim 1, characterized in that: The mass ratio of propyl gallate to prepolymer B is 0.08-0.1:

1.

8. The method for preparing a bio-based self-repairing polyurethane hot melt adhesive according to claim 1, characterized in that: The catalyst is dibutyltin dilaurate.

9. The method for preparing a bio-based self-repairing polyurethane hot melt adhesive according to claim 1, characterized in that: The added amount of dibutyltin dilaurate is 0.5-0.55% of the total mass of the reaction raw materials.

10. A bio-based self-repairing polyurethane hot melt adhesive obtained according to the preparation method according to any one of claims 1 to 9.

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