Self-repairing polyurethane hot melt adhesive and preparation method thereof

Abstract

The invention discloses a self-repairing polyurethane hot melt adhesive and a preparation method thereof. The preparation method comprises the following steps: uniformly stirring adipic acid polyester polyol, polypropylene glycol 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 stirring to obtain a mixture B; and reacting to obtain the self-repairing polyurethane hot melt adhesive. Polypropylene glycol and adipic acid series polyester glycol are adopted as soft segments, MDI is adopted as a hard segment, 1, 4-butanediol is adopted as a chain extender, propyl gallate is adopted as a cross-linking agent, the polyurethane resin for the hot melt adhesive is prepared, and the contradiction problem of high strength and low softening point of polyurethane is solved through the reversible reaction of phenolic hydroxyl groups of propyl gallate and isocyanate. Through reversibility of phenolic carbamate formed by gallic acid phenolic hydroxyl groups and isocyanate, 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 elastomer preparation, and specifically relates to a 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. Summary of the invention

[0004] The object of the present invention is to provide a self-repairing polyurethane hot melt adhesive with high bonding strength and low softening point and a preparation method thereof.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a self-repairing polyurethane hot melt adhesive comprises the following steps:

[0007] (1) stirring adipic acid polyester polyol, polypropylene glycol, and 1,4-butanediol to obtain a mixture A;

[0008] (2) Mixing mixture A and diphenylmethane diisocyanate (MDI) uniformly, reacting at 60-85° C. for 15-30 min, and controlling the viscosity to be 2000-5000 cps to obtain prepolymer B;

[0009] (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 and mix evenly, react at 90-120° C. for 2-6 hours, cool to about 40° C., and discharge to obtain a self-healing polyurethane hot melt adhesive.

[0010] The invention uses propyl gallate as a cross-linking agent 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, thereby improving the strength and bonding performance of the polyurethane. Moreover, 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.

[0011] Furthermore, the adipic acid polyester polyol is one or more of polyethylene adipate, polypropylene adipate, polybutylene adipate, and polyhexane adipate.

[0012] Furthermore, the polypropylene glycol is one or more of PPG-200, PPG-400, and PPG-1000.

[0013] Furthermore, the mass ratio of the adipic acid-based polyester polyol, polypropylene glycol, and 1,4-butanediol is 100:5-25:25-50.

[0014] Furthermore, the R value of NCO / OH of the mixture A and diphenylmethane diisocyanate is 1.1 to 1.3.

[0015] Furthermore, the mass ratio of propyl gallate to prepolymer B is 0.08-0.1:1.

[0016] 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 (adipic acid polyester polyol, polypropylene glycol, 1,4-butanediol, MDI, propyl gallate).

[0017] The present invention adopts polypropylene glycol and adipic acid polyester polyol as soft segment, MDI as hard segment, 1,4-butanediol as chain extender, propyl gallate as crosslinking agent to prepare polyurethane resin for hot melt adhesive, which has the following beneficial effects:

[0018] 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.

[0019] 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. DETAILED DESCRIPTION

[0020] 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.

[0021] Example 1

[0022] A method for preparing a self-repairing polyurethane hot melt adhesive comprises the following steps:

[0023] (1) polybutylene adipate, PPG-400 and 1,4-butanediol were mixed in a mass ratio of 100:15:40, and stirred to obtain a mixture A;

[0024] (2) Mixing mixture A and MDI uniformly, wherein the NCO / OH R value of the mixture A and MDI is 1.2, reacting at 75° C. for 30 minutes, and controlling the viscosity to be 3500 cps, to obtain prepolymer B;

[0025] (3) Propyl gallate was added to prepolymer B at a mass ratio of 0.08:1, and the mixture was heated to 80° C. until propyl gallate was completely dissolved and mixed evenly with prepolymer B. Dibutyltin dilaurate (0.5% by mass of the total reaction raw materials) was added, and the mixture was mixed evenly. The mixture was reacted at 95° C. for 4 hours, and the mixture was cooled to 40° C. to obtain a self-healing polyurethane hot melt adhesive.

[0026] The prepared self-healing polyurethane hot melt adhesive was extruded and cast into a film at a casting temperature of 200°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.

[0027] Example 2

[0028] A method for preparing a self-repairing polyurethane hot melt adhesive comprises the following steps:

[0029] (1) poly(hexanediol adipate), PPG-400, and 1,4-butanediol were mixed in a mass ratio of 100:25:50, and stirred to obtain a mixture A;

[0030] (2) Mixing mixture A and MDI uniformly, wherein the NCO / OH R value of the mixture A and MDI is 1.3, reacting at 85° C. for 15 min, and controlling the viscosity to be 2500 cps, to obtain prepolymer B;

[0031] (3) Propyl gallate is added to prepolymer B at a mass ratio of 0.1:1, and the mixture is heated to 100° C. until propyl gallate is completely dissolved and mixed evenly with prepolymer B. Dibutyltin dilaurate (0.5% by mass of the total reaction raw materials) is added, mixed evenly, reacted at 105° C. for 3 hours, cooled to 40° C., and discharged to obtain a self-healing polyurethane hot melt adhesive.

[0032] The prepared self-healing polyurethane hot melt adhesive was extruded and cast into a film at a casting temperature of 200°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.

[0033] Example 3

[0034] A method for preparing a self-repairing polyurethane hot melt adhesive comprises the following steps:

[0035] (1) polyethylene adipate, PPG-400 and 1,4-butanediol were mixed in a mass ratio of 100:20:45 and stirred to obtain a mixture A;

[0036] (2) Mixing mixture A and MDI uniformly, wherein the NCO / OH R value of the mixture A and MDI is 1.25, reacting at 75° C. for 25 minutes, and controlling the viscosity to be 2500 cps, to obtain prepolymer B;

[0037] (3) Propyl gallate was added to prepolymer B at a mass ratio of 0.09:1, and the mixture was heated to 85° C. until propyl gallate was completely dissolved and mixed evenly with prepolymer B. Dibutyltin dilaurate (0.5% by weight of the total weight of the reaction raw materials) was added, and the mixture was mixed evenly. The mixture was reacted at 95° C. for 4 hours, and the mixture was cooled to 40° C. to obtain a self-healing polyurethane hot melt adhesive.

[0038] The self-repairing polyurethane hot melt adhesive was extruded and cast into a film at a casting temperature of 200° C. After film formation, it was cooled to 120° C. and cured for 10 hours, and then cooled to room temperature to obtain a polyurethane hot melt adhesive film, and its softening point and mechanical properties were tested.

[0039] Comparative Example 1:

[0040] (1) mixing polybutylene adipate, polypropylene glycol, and 1,4-butanediol in a mass ratio of 100:15:38 and stirring to obtain a mixture A;

[0041] (2) Mixing mixture A with MDI, wherein the NCO / OH R value of the mixture A and MDI is 0.95, adding 0.5% of the total weight of the catalyst dibutyltin dilaurate to the reaction raw materials (polybutylene adipate, polypropylene glycol, 1,4-butanediol, MDI) and mixing evenly, reacting at 75° C. for 30 min, cooling to 40° C. and discharging to obtain a polyurethane hot melt adhesive;

[0042] The polyurethane hot melt adhesive was extruded and cast into a film at a casting temperature of 200° C., and then cooled to room temperature to obtain a polyurethane hot melt adhesive film, and its softening point and mechanical properties were tested. The polyurethane hot melt adhesive film was obtained, and its softening point and mechanical properties were tested.

[0043] Table 1 Hot melt adhesive film performance test

[0044]

[0045] As can be seen from Table 1, the Shore A hardness, tensile strength, and right-angle tear of the repairable polyurethane hot melt adhesive film of Examples 1 to 3 gradually increase with the increase in the amount of propyl gallate, and the elongation at break decreases. The ball and ring softening point is around 120°C, which is equivalent to the depolymerization temperature of the phenolic carbamate bond; compared with Comparative Example 1, the mechanical strength is significantly improved, indicating that the phenolic carbamate cross-linked network structure formed by the cross-linking of propyl gallate and NCO groups in the embodiment is beneficial to improving the mechanical strength and bonding properties of the hot melt adhesive, but with the increase in the degree of cross-linking, its elongation at break decreases. At the same time, the ball and ring softening point of the embodiment is also significantly higher than that of Comparative Example 1, which solves the contradiction between the high strength and low softening point of the polyurethane hot melt adhesive. In general, the comprehensive performance of the polyurethane hot melt adhesive with propyl gallate as a cross-linking agent provided by the present invention is better than that of ordinary polyurethane hot melt adhesive.

[0046] 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 self-repairing polyurethane hot melt adhesive, characterized in that: The following steps are involved: (1) Adipic acid polyester polyol, polypropylene glycol, and 1,4-butanediol are uniformly stirred 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 2000-5000 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 and mix evenly, react at 90-120°C for 2-6 hours, cool and discharge to obtain a self-healing polyurethane hot melt adhesive.

2. The method for preparing a self-repairing polyurethane hot melt adhesive according to claim 1, characterized in that: The adipic acid polyester polyol is one or more of polyethylene adipate, polypropylene adipate, polybutylene adipate and polyhexane adipate.

3. The method for preparing a self-repairing polyurethane hot melt adhesive according to claim 1, characterized in that: The polypropylene glycol is one or more of PPG-200, PPG-400 and PPG-1000.

4. The method for preparing a self-repairing polyurethane hot melt adhesive according to claim 1, characterized in that: The mass ratio of the adipic acid polyester polyol, polypropylene glycol and 1,4-butanediol is 100:5-25:25-50.

5. The method for preparing a 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.

6. The method for preparing a 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.

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

8. The method for preparing a self-repairing polyurethane hot melt adhesive according to claim 7, characterized in that: The added amount of dibutyltin dilaurate is 0.5-0.55% of the total mass of the reaction raw materials.

9. A self-repairing polyurethane hot melt adhesive obtained according to the preparation method according to any one of claims 1 to 8.

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