Single-component moisture-curing reaction type PUR hot melt adhesive and preparation method thereof

Abstract

The invention belongs to the technical field of PUR hot melt adhesives, and relates to a single-component moisture-curing reaction type PUR hot melt adhesive and a preparation method thereof. The invention provides a preparation method of a single-component moisture-curing reaction type PUR hot melt adhesive, which comprises the following steps: heating acetic acid, adipic acid, citric acid and 1, 5-pentanediol to 60-80 DEG C to form a transparent liquid, then mixing the transparent liquid with a first catalyst, carrying out heating esterification reaction, and then carrying out condensation polymerization under a vacuum condition to prepare liquid polyester polyol; the preparation method comprises the following steps: mixing the liquid polyester polyol, the crystalline polyester polyol and the thermoplastic resin, heating, melting, stirring, carrying out vacuum dehydration, introducing nitrogen to eliminate vacuum, adding polyisocyanate, carrying out a stirring reaction, adding a second catalyst and pseudo-boehmite, continuously stirring, and carrying out vacuum pumping until a reaction system does not have bubbles. The single-component moisture-curing reaction type PUR hot melt adhesive provided by the invention is high in melt viscosity, high in initial adhesion strength and high in final adhesion strength.

Description

Technical Field

[0001] The invention belongs to the technical field of PUR hot melt adhesives and relates to a single-component moisture-curing reactive PUR hot melt adhesive and a preparation method thereof. Background Art

[0002] Reactive polyurethane (PUR) hot melt adhesives are divided into two types: closed hot melt adhesives and moisture-curing hot melt adhesives. Since the former has a high dissociation temperature of the sealant (generally above 100°C), it will cause bubbling of the adhesive layer, so it is only used for maintenance treatment; while moisture-curing PUR hot melt adhesives have the characteristics of both hot melt adhesives and reactive adhesives - the application temperature is lower than that of traditional hot melt adhesives, and after curing, the bonding strength is high, heat-resistant, and chemical-resistant. It can show excellent bonding properties to substrates containing active hydrogen such as wood, ceramics, and fabrics, and smooth substrates such as metals, glass, plastics, and rubber. At present, PUR hot melt adhesives are widely used in various industries and have become one of the fastest-growing adhesive varieties. At present, most researchers prepare PUR hot melt adhesives with different performances by screening different raw materials and ratios to solve problems such as slow curing speed, poor weather resistance, and low initial adhesion to meet the needs of different application scenarios. Summary of the invention

[0003] The object of the present invention is to provide a one-component moisture-curing reactive PUR hot melt adhesive with high melt viscosity, high initial adhesive strength and high final adhesive strength. To this end, the present invention provides a one-component moisture-curing reactive PUR hot melt adhesive and a preparation method thereof to meet this need in the art.

[0004] On the one hand, the present invention relates to a method for preparing a one-component moisture-curing reactive PUR hot melt adhesive, which comprises: heating acetic acid, adipic acid, citric acid, and 1,5-pentanediol to 60-80° C. to form a transparent liquid, then mixing the transparent liquid with a first catalyst, heating for esterification reaction, and then performing a polycondensation reaction under vacuum conditions to obtain a liquid polyester polyol;

[0005] The liquid polyester polyol, crystalline polyester polyol and thermoplastic resin are mixed, heated and melted, stirred and vacuum-dehydrated, and then filled with nitrogen to eliminate the vacuum. Then, polyisocyanate is added and stirred for reaction. Finally, the second catalyst and pseudo-boehmite are added and stirred continuously, and the reaction system is evacuated until no bubbles appear.

[0006] Furthermore, in the preparation method of the one-component moisture-curing reactive PUR hot melt adhesive provided by the present invention, the molar ratio of the acetic acid, adipic acid, citric acid, and 1,5-pentanediol is 1:2 to 3:1 to 2:3.

[0007] Furthermore, in the method for preparing the one-component moisture-curing reactive PUR hot melt adhesive provided by the present invention, the first catalyst is organic tin.

[0008] Furthermore, in the method for preparing the one-component moisture-curing reactive PUR hot melt adhesive provided by the present invention, the crystalline polyester polyol is poly(hexamethylene adipate) glycol.

[0009] Furthermore, in the method for preparing the one-component moisture-curing reactive PUR hot melt adhesive provided by the present invention, the mass ratio of the liquid polyester polyol to the crystalline polyester polyol is 1:1.5-2.

[0010] Furthermore, in the method for preparing the one-component moisture-curing reactive PUR hot melt adhesive provided by the present invention, the molecular weight of the liquid polyester polyol is 3000-4000.

[0011] Furthermore, in the method for preparing the one-component moisture-curing reactive PUR hot melt adhesive provided by the present invention, the thermoplastic resin is TPU.

[0012] Furthermore, in the method for preparing the one-component moisture-curing reactive PUR hot melt adhesive provided by the present invention, the second catalyst is at least one of triethylenediamine, dibutyltin dilaurate, and dimorpholinyl diethyl ether.

[0013] Furthermore, in the preparation method of the one-component moisture-curing reactive PUR hot melt adhesive provided by the present invention, the raw materials include, by mass: 50 parts of the liquid polyester polyol, 75-100 parts of the crystalline polyester polyol, 15-30 parts of the thermoplastic resin, 15-30 parts of the polyisocyanate, 1-2 parts of the second catalyst, and 5-8 parts of pseudo-boehmite.

[0014] On the other hand, the present invention relates to a one-component moisture-curing reactive PUR hot melt adhesive, which is prepared by the above-mentioned preparation method.

[0015] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0016] (1) The present invention significantly improves the melt viscosity of the PUR hot melt adhesive at 120°C through a specific raw material ratio and preparation process. As shown in Examples 1 to 3, the melt viscosity is above 9930 MPa·s, which is much higher than about 6780 MPa·s in the comparative example. The high melt viscosity helps the PUR hot melt adhesive maintain better stability and viscosity during the application process, thereby improving the bonding effect.

[0017] (2) The PUR hot melt adhesive of the present invention can still maintain good bonding performance under high temperature and high humidity and high and low temperature alternating environments. The test results show that after high temperature and high humidity treatment and high and low temperature alternating cycles, the bonding strength of the PUR hot melt adhesive does not show a significant decrease, indicating that it has good weather resistance and stability.

[0018] (3) The present invention improves the problem that adding pseudo-boehmite during the preparation process can effectively reduce the number of bubbles in the PUR hot melt adhesive, but will reduce the initial adhesive strength by means of a low melting point ionic liquid. The initial adhesive strength determines the bonding ability of the adhesive at the initial contact, while the final adhesive strength reflects the bonding strength of the adhesive after complete curing. The initial adhesive strength of the PUR hot melt adhesive in the examples is above 0.43 MPa, and the final adhesive strength is above 9.1 MPa, both of which are better than the performance in the comparative example. DETAILED DESCRIPTION

[0019] The technical scheme of the present invention is described below in conjunction with the embodiments, but the present invention is not limited to the following embodiments. The experimental methods and detection methods described in each embodiment are conventional methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0020] In the following examples, the TPU model is 9662DU, purchased from Dongguan Yichen Plastic Raw Materials Co., Ltd.

[0021] In the following examples, pseudo-boehmite, CAS No.: 21645-51-2, was purchased from Jinan Xiangfeng Weiye Chemical Co., Ltd.

[0022] In the following examples, the defoaming agent BYK-A535 was purchased from Shenzhen Liansheng Chemical Co., Ltd.

[0023] Preparation Example

[0024] This preparation example provides a preparation process of a one-component moisture-curing reactive PUR hot melt adhesive.

[0025] (1) Preparation of liquid polyester polyols

[0026] Weigh acetic acid, adipic acid, citric acid, and 1,5-pentanediol in a molar ratio of 1:2-3:1-2:3, mix them, add them to a round-bottom flask in turn, heat them in a water bath to 70°C, and stir them continuously for 0.5h to form a transparent liquid, which is an ionic solution. Combine the transparent liquid and tin dichloride, slowly heat them under nitrogen protection, start stirring after the materials are melted, and when the temperature reaches 150°C, water is distilled out. At this time, it can be considered that the esterification reaction has started. Control the water output rate and the temperature of the reaction system at about 180°C, keep the temperature until the water output reaches 60% of the theoretical water output, continue to heat to about 180°C and keep the temperature while increasing the stirring rate. When basically no water is discharged, start to reduce the pressure to evaporate the oligomers and excess alcohols generated by the reaction. When the distillate decreases or slows down, reduce the pressure to perform a high vacuum reaction, keep the system pressure below 80Pa, and monitor and control the polycondensation reaction to end the reaction when the molecular weight is 3500. Release the vacuum, cool, and discharge the material under nitrogen protection to obtain a liquid polyester polyol.

[0027] (2) Preparation of hot melt adhesive

[0028] Take 50 parts of liquid polyester polyol, 75-100 parts of polyhexanediol adipate, 15-30 parts of TPU, 15-30 parts of liquefied MDI, 1-2 parts of dibutyltin dilaurate and 5-8 parts of pseudo-boehmite by weight. Mix the liquid polyester polyol, polyhexanediol adipate and TPU, heat and melt, stir and vacuum dehydrate, fill with nitrogen to eliminate vacuum, then add liquefied MDI to stir and react, finally add dibutyltin dilaurate and pseudo-boehmite to continue stirring, and evacuate until no bubbles appear in the reaction system.

[0029] Example 1

[0030] This embodiment provides a one-component moisture-curing reactive PUR hot melt adhesive.

[0031] Referring to the preparation example, the dosage of each component is:

[0032] Weigh acetic acid, adipic acid, citric acid, and 1,5-pentanediol and mix them in a molar ratio of 1:2:1:3; take 50 parts of liquid polyester polyol, 75 parts of polyhexamethylene adipate diol, 15 parts of TPU, 15 parts of liquefied MDI, 1 part of dibutyltin dilaurate, and 5 parts of pseudoboehmite, in parts by mass.

[0033] Example 2

[0034] This embodiment provides a one-component moisture-curing reactive PUR hot melt adhesive.

[0035] Referring to the preparation example, the dosage of each component is:

[0036] Weigh acetic acid, adipic acid, citric acid, and 1,5-pentanediol and mix them in a molar ratio of 1:2:2:3; take 50 parts of liquid polyester polyol, 80 parts of polyhexamethylene adipate diol, 20 parts of TPU, 20 parts of liquefied MDI, 1 part of dibutyltin dilaurate, and 6 parts of pseudoboehmite, in parts by mass.

[0037] Example 3

[0038] This embodiment provides a one-component moisture-curing reactive PUR hot melt adhesive.

[0039] Referring to the preparation example, the dosage of each component is:

[0040] Weigh acetic acid, adipic acid, citric acid, and 1,5-pentanediol in a molar ratio of 1:3:2:3 and mix; in parts by mass, take 50 parts of liquid polyester polyol, 100 parts of polyhexamethylene adipate diol, 30 parts of TPU, 30 parts of liquefied MDI, 2 parts of dibutyltin dilaurate, and 8 parts of pseudoboehmite.

[0041] Comparative Example 1

[0042] This comparative example is intended to illustrate the effect of the ionic solution composition on the properties of PUR hot melt adhesive.

[0043] This comparative example is the same as Example 3, except that acetic acid is not added. Due to the lack of acetic acid, an ionic liquid cannot be formed. In the preparation of liquid polyester polyol, the following specific adjustments are made: adipic acid, citric acid, and 1,5-pentanediol are weighed and mixed in a molar ratio of 3:2:3, added to a round-bottom flask in sequence, heated in a water bath to 70°C and stirred continuously for 0.5h to form a mixed liquid. The mixed liquid is combined with tin dichloride for subsequent reaction.

[0044] Comparative Example 2

[0045] This comparative example is intended to illustrate the effect of pseudo-boehmite on the performance of PUR hot melt adhesive.

[0046] The pseudo-boehmite is replaced with a pretreated zeolite molecular sieve, which is obtained by drying the zeolite molecular sieve in a forced air drying oven at 90° C. for 5 hours, and the particle size screening is ≤10 μm.

[0047] Comparative Example 3

[0048] This comparative example is intended to illustrate the effect of pseudo-boehmite on the performance of PUR hot melt adhesive.

[0049] The pseudo-boehmite was replaced by the defoamer BYK-A535.

[0050] Test Case

[0051] This test example provides the performance of the PUR hot melt adhesives obtained in Examples 1 to 3 and Comparative Examples 1 to 3. The test items and reference standards are as follows.

[0052] Melt viscosity: refer to the standard "HG / T 3660-1999 Determination of melt viscosity of hot melt adhesives" to measure the melt viscosity at 120°C;

[0053] Open time: Determined in accordance with the standard "HG / T 3716-2003 Determination of open time of hot melt adhesives";

[0054] Initial bond strength: The bonded specimens were cured for 15 min at 25°C @ 50% RH;

[0055] Final bonding strength: The bonding specimens were cured at 25°C @ 50% RH for 7 days;

[0056] Bond strength after high temperature and high humidity: After the bonding sample is cured at 25℃ / 50%RH for 7 days, it is placed at 85℃ / 85%RH for another 7 days;

[0057] High and low temperature alternating tensile shear strength: The bonded sample is kept at -40℃ for 1 hour, heated to 85℃ within 3 minutes, kept for 1 hour, and then cooled to -40℃ within 3 minutes and kept for 1 hour. A total of 20 cycles are performed and placed under standard test conditions for 1 hour.

[0058] The initial adhesion strength, final adhesion strength, adhesion strength after high temperature and high humidity, and high and low temperature alternating tensile shear strength are measured with reference to the standard "GB / T 7124-2008 Determination of tensile shear strength of adhesives (rigid material to rigid material)".

[0059] Number of bubbles: Heat the hot melt adhesive at 130℃ and evenly coat it on the aluminum sheet that has been pretreated with 99% alcohol. The thickness of the adhesive film should be controlled at 2mm. After the adhesive film is completely cured, count the number of bubbles per unit area. The width of the aluminum sheet is 25mm and the length is 200mm. Cut off the 10mm×10mm adhesive film in the middle and count the number of bubbles. The bubbles are small and dense, so they can be counted with a magnifying glass and a counter.

[0060] The test results of PUR hot melt adhesive performance are as follows:

[0061]

[0062] It can be seen from the above test results that the PUR hot melt adhesive provided by the present invention has the advantages of high melt viscosity, high initial adhesive strength and high final adhesive strength. Based on Comparative Document 1, it can be seen that only adding pseudo-boehmite to the PUR hot melt adhesive can reduce the number of bubbles, improve the final adhesive strength, improve the bonding strength after high temperature and high humidity, and improve the high and low temperature alternating tensile shear strength, but there is little improvement in the two properties of melt viscosity and open time, and the initial adhesive strength has decreased. This may be due to the poor interfacial compatibility between the pseudo-boehmite and PUR hot melt adhesive system, which affects the initial adhesive strength. Based on Comparative Document 2, it can be seen that although zeolite molecular sieves can reduce the number of bubbles, they have no improvement effect on other properties, and have the problem of decreased high and low temperature alternating tensile shear strength. Based on Comparative Document 3, it can be seen that general defoamers do not have much improvement effect on the performance of PUR hot melt adhesives.

[0063] The embodiments described above are part of the embodiments of the present invention, but not all of them. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but only represents selected embodiments of the present invention. All other embodiments obtained without creative work and related deductions and substitutions made by ordinary technicians in the field under the conditions of the concept of the present invention belong to the scope of protection of the present invention.

Claims

1. A method for preparing a one-component moisture-curing reactive PUR hot melt adhesive, characterized in that: include: Acetic acid, adipic acid, citric acid and 1,5-pentanediol are heated to 60-80° C. to form a transparent liquid, and then the transparent liquid is mixed with a first catalyst, heated for esterification reaction, and then subjected to polycondensation reaction under vacuum conditions to obtain a liquid polyester polyol; The liquid polyester polyol, crystalline polyester polyol and thermoplastic resin are mixed, heated and melted, stirred and vacuum-dehydrated, and then filled with nitrogen to eliminate the vacuum. Then, polyisocyanate is added and stirred for reaction. Finally, the second catalyst and pseudo-boehmite are added and stirred continuously, and the reaction system is evacuated until no bubbles appear.

2. The method for preparing a one-component moisture-curing reactive PUR hot melt adhesive according to claim 1, characterized in that: The molar ratio of the acetic acid, adipic acid, citric acid and 1,5-pentanediol is 1:2-3:1-2:

3.

3. The method for preparing a one-component moisture-curing reactive PUR hot melt adhesive according to claim 1, characterized in that: The first catalyst is organic tin.

4. The method for preparing a one-component moisture-curing reactive PUR hot melt adhesive according to claim 1, characterized in that: The crystalline polyester polyol is polyhexamethylene adipate diol.

5. The method for preparing a one-component moisture-curing reactive PUR hot melt adhesive according to claim 1, characterized in that: The mass ratio of the liquid polyester polyol to the crystalline polyester polyol is 1:1.5-2.

6. The method for preparing a one-component moisture-curing reactive PUR hot melt adhesive according to claim 1, characterized in that: The molecular weight of the liquid polyester polyol is 3000-4000.

7. The method for preparing a one-component moisture-curing reactive PUR hot melt adhesive according to claim 1, characterized in that: The thermoplastic resin is TPU.

8. The method for preparing a one-component moisture-curing reactive PUR hot melt adhesive according to claim 1, characterized in that: The second catalyst is at least one of triethylenediamine, dibutyltin dilaurate, and dimorpholinyl diethyl ether.

9. The method for preparing a one-component moisture-curing reactive PUR hot melt adhesive according to claim 1, characterized in that: The raw materials include, by mass, 50 parts of the liquid polyester polyol, 75-100 parts of the crystalline polyester polyol, 15-30 parts of the thermoplastic resin, 15-30 parts of polyisocyanate, 1-2 parts of the second catalyst, and 5-8 parts of pseudo-boehmite.

10. A one-component moisture-curing reactive PUR hot melt adhesive, characterized in that: The method is prepared according to any one of claims 1 to 9.

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