Enclosed polyurethane hot melt adhesive as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of polyurethane, and discloses a closed polyurethane hot melt adhesive as well as a preparation method and application thereof, and the preparation method of the closed polyurethane hot melt adhesive comprises the following steps: (1) mixing dihydric alcohol and polyester dihydric alcohol, and adding isocyanate for reaction under the protection of inert gas to obtain a polyurethane prepolymer; (2) adding a sealing agent into the reactor, and carrying out a sealing reaction to obtain a sealed polyurethane prepolymer; and (3) continuously adding a catalyst and binary acid into the reactor, and uniformly stirring to obtain the closed polyurethane hot melt adhesive, the binary acid is selected from at least one of C5-C8 straight chain aliphatic binary acid. The closed polyurethane hot melt adhesive prepared by the invention is applied to bonding of nylon materials, and the problems that the bonding strength stability of cloth at high temperature is poor and the storage time of the glued cloth is short can be effectively solved.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane, and in particular relates to a closed polyurethane hot melt adhesive and a preparation method and application thereof. Background Art

[0002] Nylon (PA) fabrics are widely used in clothing, bags, car interiors and industrial fabrics, mainly due to its advantages of wear resistance, good elasticity, lightness and strong anti-pollution ability. In order to obtain better performance, nylon fabrics are often bonded and compounded with other substrates using adhesives so that they can be used in a wider range of fields; among them, copolyamide adhesives and solvent-free PUR adhesives are the most commonly used.

[0003] Copolyamide adhesives have high bonding strength to nylon fabrics, but in high-temperature environments, using high-temperature copolyamide adhesives will cause the nylon fabric to discolor. In low-temperature environments, using low-temperature copolyamide adhesives for bonding will cause debonding when exposed to temperatures of 80-100°C during long-term use. This is also the main problem of copolyamide adhesives.

[0004] PUR adhesive can prevent nylon fabric from changing color, and can be bonded at low temperatures. It can also be used at high temperatures of 130°C. However, the bonding strength is often poor at high temperatures, and after being coated on the surface of the fabric, it must be bonded to other substrates in a timely manner and cannot be stored for a long time. Blocked polyurethane hot melt adhesive uses a blocking agent to protect the terminal isocyanate group to prevent it from reacting with moisture or other compounds containing active hydrogen, thereby achieving the purpose of long-term stable storage. When in use, increasing the temperature can release the isocyanate group again, continue the cross-linking and curing reaction, and produce bonding strength. However, compared with unblocked PUR hot melt adhesive, the bonding strength is not significantly improved.

[0005] Therefore, the market is in urgent need of an adhesive for PA fabrics that has good bonding strength, resistance to high temperature environments, and stable long-term storage performance. Summary of the invention

[0006] In view of this, the object of the present invention is to provide a closed polyurethane hot melt adhesive and a preparation method and application thereof, so as to achieve excellent bonding strength and storage stability for nylon in a high temperature environment.

[0007] To achieve the above object, the technical solution provided by the present invention is as follows: A method for preparing a closed polyurethane hot melt adhesive comprises the following steps:

[0008] (1) adding the raw materials polyether diol and polyester diol into a reactor, stirring them sufficiently, and then adding isocyanate under the protection of an inert gas to react and obtain a polyurethane prepolymer;

[0009] (2) adding a blocking agent to the reactor until the NCO content in the product is ≤0.5%, the blocking reaction is completed, and a blocked polyurethane prepolymer is obtained;

[0010] (3) The catalyst and the dibasic acid are continuously added into the reactor and stirred evenly to obtain the closed polyurethane hot melt adhesive; wherein the dibasic acid is selected from at least one of C5 to C8 straight-chain aliphatic dibasic acids.

[0011] The present invention is further configured as follows: the preparation of the closed polyurethane hot melt adhesive comprises the following raw materials in parts by weight: polyether diol: 13-17 parts, polyester diol: 51-58 parts, isocyanate: 12-15 parts, catalyst: 0.02-0.05 parts; the ratio of the amount of -COOH group in the dibasic acid to the amount of -NCO group in the polyurethane prepolymer in step (1) is (0.9-1.1):1.

[0012] The present invention is further configured that the polyether diol is selected from polyethylene glycol and / or polypropylene glycol, and the number average molecular weight of the polyether diol is 1000-3000; the polyester diol is selected from crystalline polyester diol and / or non-crystalline polyester diol, and the number average molecular weight of the polyester diol is 1000-3500.

[0013] The present invention is further configured that the crystalline polyester diol is selected from polybutylene adipate diol and / or polyhexylene adipate diol, and the number average molecular weight of the crystalline polyester diol is 2000-3500;

[0014] The non-crystalline polyester diol is selected from one or more of polycaprolactone diol, polyoxalate neopentyl glycol diol, and polyadipate propylene glycol diol, and the number average molecular weight of the non-crystalline polyester diol is 1000-3500.

[0015] The present invention is further configured such that the isocyanate is selected from one or more of hexamethylene diisocyanate, diphenylmethane diisocyanate or toluene diisocyanate.

[0016] The present invention is further configured such that the blocking agent is selected from 3,5-dimethylpyrazole and / or phenol.

[0017] It should be noted that the amount of the blocking agent added is based on the molar amount of -NCO in the polyurethane prepolymer in step (1) to achieve blocking of -NCO; the molar ratio of the active hydrogen group -H in the blocking agent to the -NCO group in the polyurethane prepolymer is (1.0-1.2):1; preferably, the molar ratio of the active hydrogen group -H in the blocking agent to the -NCO group in the polyurethane prepolymer is 1.2:1 to fully block -NCO.

[0018] The present invention is further configured that the dibasic acid is selected from one or more of glutaric acid, adipic acid, pimelic acid or suberic acid.

[0019] The present invention is further configured that the catalyst is selected from one or more of triethylenediamine, bismorpholinyl diethyl ether, and tetrabutyl titanate.

[0020] The present invention also provides a closed polyurethane hot melt adhesive prepared according to the preparation method.

[0021] The present invention also provides an application of the closed polyurethane hot melt adhesive for bonding nylon fabrics.

[0022] The present invention is further configured such that the bonding temperature of the closed polyurethane hot melt adhesive is 120-160°C.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: the blocked polyurethane hot melt adhesive prepared by the present invention uses a blocking agent to protect the terminal isocyanate group, does not react before reaching the deblocking temperature, and can be stored for a long time; and by adding a dibasic acid to the system, it is achieved that when heated to the deblocking temperature when ready for use, the isocyanate is released and then undergoes a cross-linking reaction with the isocyanate, thereby introducing an amide structure, which significantly increases the bonding strength to nylon after curing, so that the prepared polyurethane hot melt adhesive still has excellent bonding strength under high-temperature bonding. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] It is worth noting that for those whose reaction conditions are not indicated, all reactions can be carried out under conventional conditions or conditions recommended by the manufacturer. For those whose manufacturers are not indicated, all the instruments or reagents used are commercially available products.

[0026] Example 1

[0027] A closed polyurethane hot melt adhesive, whose components and corresponding weight fractions are shown in Table 1, is prepared by the following steps:

[0028] Step 1: Weigh the corresponding mass fractions of polyether polyol and polyester polyol as shown in Table 1 and add them into the reactor. Under the vacuum condition of -0.1 MPa, heat it to 110-120°C, stir it thoroughly for 2-2.5 hours, and then cool it to 90-100°C.

[0029] Step 2: Under the protection of inert gas, add a selected mass fraction of hexamethylene diisocyanate into the reactor, stir and react for 1-2 hours at a vacuum of -0.1 MPa and 100-110° C., and cool to 80-90° C. after the reaction to obtain a polyurethane prepolymer.

[0030] Step 3: dissolving a selected mass fraction of the blocking agent 3,5-dimethylpyrazole in acetone to obtain a solution with a blocking agent content of 60%, and adding the selected mass fraction of the blocking agent solution to the reactor in batches under the conditions of -0.1MPa and 40-45°C; in this embodiment, the blocking agent is added according to the molar ratio of active hydrogen -H in the blocking agent to -NCO in the polyurethane prepolymer of 1.2:1; during the reaction, the NCO content in the blocked polyurethane hot melt adhesive is measured using the di-n-butylamine method until NCO% ≤0.5%, the temperature is raised to 80-90°C, and the acetone in the system is removed under vacuum conditions.

[0031] Step 4: Add selected mass fractions of catalyst and dibasic acid to the reactor under the conditions of -0.1MPa and 80-90°C, and stir for 0.5-1h to obtain the closed polyurethane hot melt adhesive; in this embodiment, the dibasic acid is adipic acid, and the amount of adipic acid added is based on the amount of -NCO in the polyurethane prepolymer obtained in step 2 to the amount of -COOH of the dibasic acid The ratio is 1:1.

[0032] Embodiments 2 to 7

[0033] A closed polyurethane hot melt adhesive, the preparation steps of which are different from those of Example 1 only in that the raw material components and their mass fractions are different. The raw material components and corresponding weight fractions of Examples 2 to 7 are shown in Table 1, wherein in Step 3, the blocking agent is 3,5-dimethylpyrazole, and the blocking agent is added according to the molar ratio of active hydrogen -H in the blocking agent to -NCO in the polyurethane prepolymer of 1.2:1; in Step 4, the dibasic acid is adipic acid, and the adipic acid is added according to the molar ratio of the amount of -NCO in the polyurethane prepolymer to the amount of -COOH of the dibasic acid of 1:1.

[0034] Table 1 Raw material components and their weight percentages in Examples 1-7

[0035]

[0036] Example 8

[0037] A closed polyurethane hot melt adhesive, the preparation steps of which are different from those of Example 1 only in that in step 4, the molar ratio of the amount of the substance of the -COOH group of adipic acid added to the amount of the substance of the -NCO group in the polyurethane prepolymer in step 2 is 0.9:1.

[0038] Example 9

[0039] A closed polyurethane hot melt adhesive, the preparation steps of which are different from those of Example 1 only in that in step 4, the molar ratio of the amount of the substance of the -COOH group of adipic acid added to the amount of the substance of the -NCO group in the polyurethane prepolymer in step 2 is 1.1:1.

[0040] Comparative Example 1

[0041] A closed polyurethane hot melt adhesive is different from Example 1 in that no dibasic acid is added in Comparative Example 1.

[0042] Comparative Example 2

[0043] A closed polyurethane hot melt adhesive, which is different from Example 1 only in that in step 4, the adipic acid is added according to the amount ratio of the amount of -NCO in the polyurethane prepolymer in step 2 to the amount of -COOH of the dibasic acid of 1:0.8.

[0044] Comparative Example 3

[0045] A closed polyurethane hot melt adhesive is different from Example 1 only in that in step 4, the molar ratio of the amount of -COOH of adipic acid added to the amount of -NCO group in the polyurethane prepolymer in step 2 is 1.2:1.

[0046] Comparative Example 4

[0047] A closed polyurethane hot melt adhesive, which is different from Example 1 only in that the dibasic acid added in Comparative Example 4 is azelaic acid.

[0048] Comparative Example 5

[0049] A closed polyurethane hot melt adhesive, which is different from Example 1 only in that the dibasic acid added in Comparative Example 5 is sebacic acid.

[0050] Comparative Example 6

[0051] A polyurethane hot melt adhesive, which is different from Example 1 in that Comparative Example 6 is a conventional polyurethane hot melt adhesive without adding a sealing agent and a dibasic acid.

[0052] Performance Testing

[0053] The closed polyurethane hot melt adhesives prepared in the above Examples 1 to 9 and Comparative Examples 1 to 5 and the conventional polyurethane hot melt adhesive prepared in Comparative Example 6 were glued to 210D nylon fabric using a hot melt adhesive laminating machine, and rolled up after gluing for subsequent performance testing.

[0054] Examples 1-9 and Comparative Examples 1-6 used glued nylon fabrics and un-glueized nylon fabrics to perform hot pressing at 130°C, with a hot pressing temperature of 130°C, a pressure of 0.1 MPa, and a time of 3 minutes. Comparative Example 6 used conventional polyurethane hot melt adhesive and did not require hot pressing.

[0055] Performance testing includes:

[0056] T peel strength test: refer to GB / T 2791-1995, "Adhesive T peel strength test method - Flexible material to flexible material";

[0057] T-peel strength (heat aging at 130℃ for 5 days): After hot pressing and pasting, the fabric is placed in a 130℃ oven, taken out after 5 days, and the T-peel strength is measured;

[0058] Shelf life test: The glued nylon fabric is rolled up and stored, and the bonding strength after hot pressing is tested every other day. The time from gluing to the beginning of the decrease in bonding strength is the shelf life.

[0059] The performance test results are shown in Table 2.

[0060] Table 2 Performance test results of polyurethane hot melt adhesive

[0061]

[0062]

[0063] According to the test results in Table 2, it can be seen that the closed polyurethane hot melt adhesive provided by the present invention has excellent stability and can be stored for a long time; at the same time, it has excellent bonding strength to nylon materials under high temperature environment. The method provided by the present invention selects a suitable dibasic acid-modified closed polyurethane hot melt adhesive, which shows excellent peel strength compared with Comparative Example 1 and Comparative Example 6, and the degree of strength reduction after 5 days of heat aging at 130°C is small. By comparing Example 1 with Comparative Examples 4 to 5, it can be seen that when the carbon chain of the dibasic acid used is too long, the bonding strength to the nylon material is significantly reduced.

[0064] In summary, the blocked polyurethane hot melt adhesive of the present invention has excellent stability when not in use and can be stored for a long time; when used for bonding, the blocked polyurethane hot melt adhesive is first deblocked at high temperature to release isocyanate, and the isocyanate undergoes a cross-linking reaction with the dibasic acid in the hot melt adhesive to introduce an amide structure, thereby significantly increasing the bonding strength to nylon after curing, so that the prepared polyurethane hot melt adhesive still has excellent bonding strength under high-temperature bonding.

[0065] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, various changes can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The changes derived or inspired by them are still within the protection scope of the invention.

Claims

1. A method for preparing a closed polyurethane hot melt adhesive, characterized in that: The steps include: (1) adding the raw materials polyether diol and polyester diol into a reactor, stirring them sufficiently, and then adding isocyanate under the protection of an inert gas to react and obtain a polyurethane prepolymer; (2) adding a blocking agent to the reactor until the NCO content in the product is ≤0.5%, the blocking reaction is completed, and a blocked polyurethane prepolymer is obtained; (3) The catalyst and the dibasic acid are continuously added into the reactor and stirred evenly to obtain the closed polyurethane hot melt adhesive; wherein the dibasic acid is selected from at least one of C5 to C8 straight-chain aliphatic dibasic acids.

2. The method for preparing a closed polyurethane hot melt adhesive according to claim 1, characterized in that: The method comprises the following raw materials in parts by weight: 13-17 parts of polyether diol, 51-58 parts of polyester diol, 12-15 parts of isocyanate and 0.02-0.05 parts of catalyst; the ratio of the amount of -COOH group in the dibasic acid to the amount of -NCO group in the polyurethane prepolymer in step (1) is (0.9-1.1):

1.

3. The method for preparing a closed polyurethane hot melt adhesive according to claim 1, characterized in that: The polyether diol is selected from polyethylene glycol and / or polypropylene glycol, and the number average molecular weight of the polyether diol is 1000-3000; the polyester diol is selected from crystalline polyester diol and / or non-crystalline polyester diol, and the number average molecular weight of the polyester diol is 1000-3500.

4. The method for preparing a closed polyurethane hot melt adhesive according to claim 3, characterized in that: The crystalline polyester diol is selected from polybutylene adipate diol and / or polyhexylene adipate diol, and the number average molecular weight of the crystalline polyester diol is 2000-3500; The non-crystalline polyester diol is selected from one or more of polycaprolactone diol, polyoxalate neopentyl glycol diol, and polyadipate propylene glycol diol, and the number average molecular weight of the non-crystalline polyester diol is 1000-3500.

5. The method for preparing a closed polyurethane hot melt adhesive according to claim 1, characterized in that: The isocyanate is selected from one or more of hexamethylene diisocyanate, diphenylmethane diisocyanate or toluene diisocyanate.

6. The method for preparing a closed polyurethane hot melt adhesive according to claim 1, characterized in that: The blocking agent is selected from 3,5-dimethylpyrazole and / or phenol.

7. The method for preparing a closed polyurethane hot melt adhesive according to claim 1, characterized in that: The dibasic acid is selected from one or more of glutaric acid, adipic acid, pimelic acid or suberic acid.

8. The method for preparing a closed polyurethane hot melt adhesive according to claim 1, characterized in that: The catalyst is selected from one or more of triethylenediamine, bismorpholinyl diethyl ether, and tetrabutyl titanate.

9. A blocked polyurethane hot melt adhesive prepared according to the preparation method according to any one of claims 1 to 8.

10. An application of the closed polyurethane hot melt adhesive as claimed in claim 9, characterized in that: Used for bonding nylon fabrics.

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