A peelable polyurethane hot melt adhesive based on reactive extrusion and a synthesis method thereof

Abstract

The invention belongs to the technical field of polyurethane hot melt adhesives, and particularly relates to a strippable polyurethane hot melt adhesive based on reactive extrusion and a synthesis method thereof. The strippable polyurethane hot melt adhesive is synthesized from diisocyanate, polyester diol, polypropylene glycol, polypropylene glycol and pyrimidone derivatives through a reactive extrusion process, and a=n(-NCO) / n(-OH) is defined. When the a value is 1.1-1.3, the molar equivalent ratio of polyester diol: polypropylene glycol: polypropylene glycol: pyrimidone derivative is 1.0:1.0:0.5:(5.5a-5.5), and the strippable polyurethane hot melt adhesive is a thermoplastic polyurethane hot melt adhesive; when the a value is 1.8-2.0, the molar equivalent ratio of polyester diol: polypropylene glycol: polypropylene glycol: pyrimidone derivative is 1.0:1.0:0.5:(5.5a-5.5) / 2, and the strippable polyurethane hot melt adhesive is a reactive polyurethane hot melt adhesive. The present invention utilizes the reaction of pyrimidone derivatives with isocyanate to form a ureidopyrimidone UPy structure with self-complementary quadruple hydrogen bonds at the chain end, thereby increasing the number of hydrogen bonds, improving the bonding strength, and giving the hot melt adhesive a thermally responsive and peelable property, and can achieve large-scale continuous production.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane hot melt adhesives, and in particular relates to a peelable polyurethane hot melt adhesive based on reactive extrusion and a synthesis method thereof. Background Art

[0002] Strong adhesion between material interfaces often means that they are difficult to separate, and forced peeling may cause damage or even tearing of the base material. However, strong adhesion and peelability are contradictory. Traditional polyurethane adhesives have excellent adhesion to wood, fabric, paper, metal, rubber and other materials due to their significant performance advantages, and have been developed and applied in various fields. Electronic products or devices tend to be thinner and lighter, and the bonding requirements for precision parts are getting higher and higher. Although traditional polyurethane hot melt adhesives can meet the requirements of adhesion, strong adhesion is not conducive to disassembly.

[0003] Wang et al. [Materials Chemistry Frontiers, 2019, 3, 1833] used the reversibility of oxime carbamate groups to develop a hot melt adhesive that can be thermally responsive and peeled. However, this dynamic chemical bond will repeatedly produce isocyanate groups. Long-term exposure to heat will gradually consume isocyanate groups, and the number of oxime carbamate groups will gradually decrease, resulting in reduced bonding performance. Heinzmann et al. [ACS Applied Materials & Interfaces, 2014, 6, 4713] synthesized a supramolecular hot melt adhesive with self-complementary quadruple hydrogen bonds by combining ureidopyrimidone UPy with hydrogenated hydroxyl-terminated polybutadiene. The associated ureidopyrimidone UPy can dissociate under ultraviolet irradiation, thereby imparting peelability. However, the process for synthesizing ureidopyrimidone UPy monomers consumes excessive raw materials and a large amount of organic solvents, which is neither environmentally friendly nor can be produced on a large scale. It can be seen that the development of polyurethane hot melt adhesives with thermal responsive peelability urgently needs to explore new ways to ensure adhesion, peelability and large-scale production. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and to provide a peelable polyurethane hot melt adhesive based on reactive extrusion and a synthesis method thereof.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A peelable polyurethane hot melt adhesive based on reactive extrusion is synthesized from diisocyanate, polyester diol, polypropylene glycol, polypropylene glycol and pyrimidone derivatives through a reactive extrusion process, wherein a=n(-NCO) / n(-OH) is defined, and the value of a ranges from 1.1 to 1.3 or 1.8 to 2.0.

[0007] Preferably, the diisocyanate is one or more mixtures of isophorone diisocyanate IPDI, hydrogenated toluene diisocyanate HTDI, dicyclohexylmethane diisocyanate HMDI, 1,4-cyclohexane diisocyanate CHDI, and MDI-50.

[0008] Preferably, the polyester diol has a melting point of 50-70° C. and a number average molecular weight of 2000-7000 g / mol, the polypropylene glycol has a number average molecular weight of 1000-3000 g / mol, and the polyglycerol has a number average molecular weight of 300-1000 g / mol.

[0009] Preferably, the pyrimidinone derivative is a mixture of one or more of 1-methylcytosine, 5-azacytosine, cytosine, isocytosine, 5-methylcytosine, 2-amino-4-hydroxy-6-methylpyrimidine, 2-amino-4-hydroxypyrimidine, 5,6-dimethyl-2-amino-4-hydroxypyrimidine, 2-amino-5-ethoxycarbonyl-4-hydroxypyrimidine, 2-amino-(6-benzyl)-4(3H)pyrimidinone, and 2-amino-4-hydroxy-6-phenylpyrimidine.

[0010] Preferably, when the a value is 1.1 to 1.3, the molar equivalent ratio of polyester diol: polypropylene glycol: polypropylene glycol: pyrimidone derivative is 1.0:1.0:0.5:(5.5a-5.5), and a thermoplastic polyurethane hot melt adhesive is obtained; when the a value is 1.8 to 2.0, the molar equivalent ratio of polyester diol: polypropylene glycol: polypropylene glycol: pyrimidone derivative is 1.0:1.0:0.5:(5.5a-5.5) / 2, and a reactive polyurethane hot melt adhesive is obtained.

[0011] The present invention also discloses a method for synthesizing the peelable polyurethane hot melt adhesive based on reactive extrusion, comprising the following steps:

[0012] (1) Put diisocyanate into a constant temperature storage tank A, the storage temperature is 50-70°C, and fill it with high-purity nitrogen;

[0013] (2) putting polyester diol, polypropylene glycol, polyglycerol and pyrimidone derivative into a mixer, and adding 5-10 ppm of an organic bismuth catalyst accounting for the total weight of the formula, removing water at -0.095 MPa and 120° C. for 1-2 hours, cooling to 90° C. and then putting into a constant temperature storage tank B, storing at 80-90° C., and filling with high-purity nitrogen;

[0014] (3) The materials in storage tank A and storage tank B are accurately metered by metering pumps and flow meters and input into a twin-screw premixer with a rotation speed of 300-600 rpm. The reaction time is controlled to be 1-2 min and the reaction temperature is 150°C. The obtained pre-reaction material is uniformly introduced into a co-rotating reaction type twin-screw extruder. The rotation speed is controlled at 50-200 rpm. The temperature of each section of the screw is controlled at 180-250°C. The product with a value of 1.1-1.3 is pelletized underwater to obtain thermoplastic polyurethane hot melt adhesive particles. The product with a value of 1.8-2.0 is directly collected at the extrusion die head and sealed and filled.

[0015] Preferably, the peelable polyurethane hot melt adhesive based on reactive extrusion has a viscosity-flow transition temperature of 80-90° C. as measured by a temperature sweep rheology test.

[0016] Preferably, the shear strength of thermoplastic polyurethane hot melt adhesive for bonding steel plates, aluminum plates and PET substrates is greater than 6.5 MPa, 4.5 MPa and 1.5 MPa, respectively; the shear strength of reactive polyurethane hot melt adhesive for bonding steel plates, aluminum plates and PET substrates is greater than 11.0 MPa, 8.0 MPa and 3.0 MPa, respectively.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1) The synthesis process does not require any organic solvent as a reaction medium, the preparation process is environmentally friendly, and the reaction extrusion equipment can achieve large-scale continuous production; 2) The pyrimidone derivative reacts with the isocyanate to form a ureidopyrimidone UPy structure with self-complementary quadruple hydrogen bonds at the end of the chain, which increases the number of hydrogen bonds, improves the bonding strength, and gives the hot melt adhesive a thermally responsive and removable property. The hot melt adhesive is used to bond soft materials such as fabrics and leather, and hard materials such as metals and plastics, and can be reused or solve the problem of difficult disassembly for aftermarket repairs. DETAILED DESCRIPTION

[0018] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0019] The raw materials used in the experiments in the embodiments and comparative examples of the present invention are as follows, but are not limited to the following raw materials. The present invention only uses the following raw materials as specific examples to further illustrate the effect of the peelable polyurethane hot melt adhesive based on reactive extrusion in the present invention:

[0020] Polyester diol: Dynacoll 7360, number average molecular weight 3500 g / mol, Evonik Degussa.

[0021] Polypropylene glycol: DL-2000, number average molecular weight 2000 g / mol, Shandong Bluestar Dongda.

[0022] Polypropylene glycol: C305, number average molecular weight 500 g / mol, Shandong Yinuowei.

[0023] Diisocyanate: Isophorone diisocyanate IPDI, Covestro.

[0024] Cytosine, Wuhan Kanos, 2-amino-6-methylpyridine AMPy, Henan Evonik.

[0025] Organic bismuth catalyst: bismuth neodecanoate, Shanghai Xindian.

[0026] Adhesive performance evaluation: The polyurethane hot melt adhesive melted at 150°C was used to prepare samples, and the shear strength was tested according to the method specified in GB / T7124-2008.

[0027] The present invention sets Examples 1 to 6 and Comparative Examples 1 to 6, and the molar equivalents of the feed materials are shown in Table 1:

[0028] Table 1 Equivalent amounts of materials in Examples 1 to 6 and Comparative Examples 1 to 6

[0029]

[0030] The synthesis methods of Examples 1 to 6 and Comparative Examples 1 to 6 comprise the following steps:

[0031] (1) Put IPDI diisocyanate into a constant temperature storage tank A at a storage temperature of 60° C. and fill it with high-purity nitrogen;

[0032] (2) Polyester diol 7360, polypropylene glycol DL-2000, polyglycerol C305 and cytosine or 2-amino-6-methylpyridine AMPy are put into a mixer, and an organic bismuth catalyst bismuth neodecanoate is added at a total weight of 5 to 10 ppm, and water is removed at -0.095 MPa and 120° C. for 1 hour. After cooling to 90° C., the mixture is put into a constant temperature storage tank B, stored at a temperature of 90° C., and filled with high-purity nitrogen;

[0033] (3) The materials in storage tank A and storage tank B are accurately metered by metering pumps and flow meters and input into a twin-screw premixer with a rotation speed of 300 rpm. The reaction time is controlled to be 2 min and the reaction temperature is controlled to be 150°C. The obtained pre-reaction material is uniformly introduced into a co-rotating reaction type twin-screw extruder. The rotation speed is controlled at 100 rpm. The temperature of each section of the screw is controlled at 180-250°C. The product with a value of 1.1-1.3 is pelletized underwater to obtain thermoplastic polyurethane hot melt adhesive particles. The product with a value of 1.8-2.0 is directly collected at the extrusion die head and sealed and filled.

[0034] The performance of the hot melt adhesives obtained in Examples 1 to 6 and Comparative Examples 1 to 6 was evaluated, and the evaluation results are shown in Table 2:

[0035] Table 2 Properties of the hot melt adhesives obtained in Examples 1 to 6 and Comparative Examples 1 to 6

[0036]

[0037] The viscosity transition temperature of the thermoplastic polyurethane hot melt adhesive of Examples 1 to 3 is between 80 and 90°C, and the bonded substrates are easily peeled off when heated; the a value of Comparative Example 1 is lower than the lower limit, the molecular weight of the first step reaction product increases, the urea-pyrimidinone UPy unit that can be introduced decreases, the viscosity transition temperature increases, and the bonding ability is weakened; the a value of Comparative Example 2 is higher than the upper limit, although the viscosity transition temperature is close to that of Example 1, the bonding strength is significantly reduced, because the molecular weight of the first step reaction product is reduced too much and the bulk strength is reduced; Comparative Example 3 using 2-amino-6-methylpyridine AMPy has no urea-pyrimidinone UPy unit at the end of the chain. Compared with Example 2, the viscosity transition temperature is greatly increased, and the thermal response peelability is lost.

[0038] The a values ​​of the reactive polyurethane hot melt adhesives in Examples 4 to 6 are relatively high, and the molecular weight of the first step reaction product is relatively low, but the final product contains -NCO at some chain ends, and a chemical cross-linking network will be formed after moisture curing, and the bulk strength will be higher than that of Examples 1 to 3. Some chain ends contain urea-pyrimidone UPy moieties, which on the one hand improve the bonding strength, and on the other hand give the hot melt adhesive a lower viscosity transition temperature. The a values ​​of Comparative Examples 4 to 5 exceed the specified range, and their viscosity transition temperatures increase, and the bonding strength decreases. Although the viscosity transition temperature of Comparative Example 5 is close to 90°C, the a value is higher than 2.0, which makes the system contain free -NCO, and the environmental protection is poor, which limits its application field. Comparative Example 6 using 2-amino-6-methylpyridine AMPy does not have urea-pyrimidone UPy moieties at the chain ends. Compared with Example 5, the viscosity transition temperature is greatly increased, and the ability to be thermally responsive and peelable is lost.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A peelable polyurethane hot melt adhesive based on reactive extrusion, characterized in that: It is synthesized from diisocyanate, polyester diol, polypropylene glycol, polypropylene glycol, and pyrimidone derivatives through a reactive extrusion process, and a=n(-NCO) / n(-OH) is defined, and the a value ranges from 1.1 to 1.3 or 1.8 to 2.0; The synthesis method of the strippable polyurethane hot melt adhesive based on reactive extrusion comprises the following steps: (1) Place diisocyanate into a constant temperature storage tank A at a storage temperature of 50-70°C and fill it with high-purity nitrogen; (2) Put polyester diol, polypropylene glycol, polypropylene glycol and pyrimidone derivative into a mixer, add 5-10 ppm of organic bismuth catalyst accounting for the total weight of the formula, remove water at -0.095 MPa and 120°C for 1-2 hours, cool to 90°C and put into constant temperature storage tank B, store at 80-90°C, and fill with high-purity nitrogen; (3) The materials in storage tank A and storage tank B are accurately metered by metering pumps and flow meters and input into a twin-screw premixer with a rotation speed of 300-600 rpm. The reaction time is controlled to be 1-2 min and the reaction temperature is 150°C. The obtained pre-reaction material is uniformly introduced into a co-rotating reaction type twin-screw extruder. The rotation speed is controlled at 50-200 rpm and the temperature of each section of the screw is controlled at 180-250°C. The product with a value of 1.1-1.3 is pelletized underwater to obtain thermoplastic polyurethane hot melt adhesive particles. The product with a value of 1.8-2.0 is directly collected at the extrusion die head and sealed and filled. When the a value is 1.1-1.3, the molar equivalent ratio of polyester diol: polypropylene glycol: polypropylene glycol: pyrimidone derivative is 1.0:1.0:0.5:(5.5a-5.5), the peelable polyurethane hot melt adhesive based on reactive extrusion is a thermoplastic polyurethane hot melt adhesive, and the shear strength of the thermoplastic polyurethane hot melt adhesive for bonding steel plates, aluminum plates and PET substrates is greater than 6.5 MPa, 4.5 MPa and 1.5 MPa, respectively; When the a value is 1.8~2.0, the molar equivalent ratio of polyester diol: polypropylene glycol: polypropylene glycol: pyrimidone derivative is 1.0:1.0:0.5:(5.5a-5.5) / 2, and the strippable polyurethane hot melt adhesive based on reactive extrusion is a reactive polyurethane hot melt adhesive. The shear strengths of the reactive polyurethane hot melt adhesive for bonding steel plates, aluminum plates and PET substrates are greater than 11.0 MPa, 8.0 MPa and 3.0 MPa, respectively.

2. The peelable polyurethane hot melt adhesive based on reactive extrusion according to claim 1, characterized in that: The diisocyanate is one or more mixtures of isophorone diisocyanate IPDI, hydrogenated toluene diisocyanate HTDI, dicyclohexylmethane diisocyanate HMDI, 1,4-cyclohexane diisocyanate CHDI, and MDI-50; The pyrimidinone derivative is a mixture of one or more of 1-methylcytosine, 5-azacytosine, cytosine, isocytosine, 5-methylcytosine, 2-amino-4-hydroxy-6-methylpyrimidine, 2-amino-4-hydroxypyrimidine, 5,6-dimethyl-2-amino-4-hydroxypyrimidine, 2-amino-5-ethoxycarbonyl-4-hydroxypyrimidine, 2-amino-(6-benzyl)-4(3H)pyrimidinone, and 2-amino-4-hydroxy-6-phenylpyrimidine.

3. The peelable polyurethane hot melt adhesive based on reactive extrusion according to claim 1, characterized in that: The polyester diol has a melting point of 50-70° C. and a number average molecular weight of 2000-7000 g / mol, the polypropylene glycol has a number average molecular weight of 1000-3000 g / mol, and the polypropylene glycol has a number average molecular weight of 300-1000 g / mol.

4. The peelable polyurethane hot melt adhesive based on reactive extrusion according to any one of claims 1 to 3, characterized in that: The peelable polyurethane hot melt adhesive based on reactive extrusion has a viscosity-flow transition temperature of 80-90° C. as measured by a temperature sweep rheological test.

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