CN109852326B - Polyurethane hot-melt adhesive containing oxime urethane dynamic bond and preparation method thereof - Google Patents
Polyurethane hot-melt adhesive containing oxime urethane dynamic bond and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a polyurethane hot melt adhesive containing oxime urethane dynamic bonds and a preparation method thereof, wherein a polymerization monomer comprises the following components: at least one polyisocyanate, at least one small molecule oxime, at least one polyol. The dynamic covalent bond is introduced into a cross-linked polyurethane hot melt adhesive system, the introduction of the dynamic bond enables the thermosetting material to have certain thermoplastic property, the hot melt adhesive with the advantages of the thermoplastic polyurethane and the reactive polyurethane hot melt adhesive is obtained, and the hot melt adhesive has great practical significance for the practical application of the polyurethane adhesive.
Description
Technical Field
The invention belongs to the field of hot-melt adhesives, and particularly relates to a polyurethane hot-melt adhesive containing oxime urethane dynamic bonds and a preparation method thereof.
Background
The hot melt adhesive is a solvent-free adhesive, is solid at normal temperature, does not have cohesiveness, can flow after being heated and melted, has a good wetting effect with the surface, and has excellent cohesiveness after being cooled. Compared with solvent-based adhesives, Hot Melt Adhesives (HMA) are expected to be the next generation of green adhesives because its solventless adhesive can avoid the emission of Volatile Organic Compounds (VOCs). The adjustability of the performance of polyurethane is very strong, and the polyurethane hot melt adhesive is an important hot melt adhesive. Existing hot melt polyurethane adhesives are mainly classified into two types, one being a Thermoplastic Polyurethane (TPU) adhesive, which is flowable when heated to a certain temperature and is fixed when cooled. The other is a reactive Polyurethane (PUR) which has a permanent cross-linked structure when it is fully cured. Reactive Polyurethane (PUR) generally means an isocyanate-terminated linear polyurethane having a low molecular weight, which can further react with moisture from the atmosphere and eventually form a permanently crosslinked structure. Compared with Thermoplastic Polyurethanes (TPU), reactive polyurethane PURs generally have higher adhesive strength, better heat resistance and excellent chemical resistance due to their permanently crosslinked structure. However, the initial adhesive strength of reactive Polyurethane (PUR) is generally low due to its low molecular weight and slow curing speed. Moreover, reactive Polyurethanes (PURs) hardly form a crosslinked network if the surrounding environment is relatively dry, and it always takes several days to react sufficiently with moisture even in a relatively humid atmosphere. In addition to this, the reactive Polyurethanes (PUR) have a relatively short pot life due to the large number of reactive isocyanate groups present in the reactive polyurethanes. Moreover, once the crosslinked structure is formed, it can hardly be removed from the substrate. Thermoplastic polyurethane adhesives, on the other hand, have some complementary properties such as relatively high initial adhesive strength, long shelf life and reversible adhesion.
The dynamic bond is a chemical bond formed by a series of reversible equilibrium chemical reversible reactions, and can generate reversible 'breaking' and 'combination' under the stimulation action of certain external conditions (such as heat, pH value, light, catalyst and the like), thereby realizing the dynamic separation and recombination between molecules. In recent years dynamic bonds have been widely introduced in cross-linked polymer systems to give the material some self-healing, reworking properties, such as CN 2017100311502. However, most of the previous materials prepared based on dynamic bonds only focus on the self-healing and reprocessing capabilities of the materials, and the reports on adhesives containing dynamic bonds are not many.
Disclosure of Invention
The invention aims to solve the technical problem of providing a polyurethane hot melt adhesive containing oxime urethane dynamic bonds and a preparation method thereof.
The invention provides a polyurethane hot-melt adhesive containing oxime urethane dynamic bonds, which comprises the following components in percentage by weight: the polymerized monomers include: at least one polyisocyanate, at least one small molecule oxime, at least one polyol.
Further, the polyisocyanate is at least one selected from the group consisting of toluene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, p-phenylene diisocyanate, dimethylbiphenyl diisocyanate, polymethylene polyphenyl isocyanate, 1, 6-hexamethylene diisocyanate, trimethyl-1, 6-hexamethylene diisocyanate, xylylene isocyanate, tetramethylm-xylylene diisocyanate, isophorone diisocyanate, 1, 4-cyclohexane diisocyanate, cyclohexanedimethylene diisocyanate, and norbornane diisocyanate.
Further, the small molecule oxime is selected from at least one of dimethylglyoxime (dimethyl acetaldoxime), methylglyoxaldoxime, 1, 4-benzoquinone dioxime, terephthalaldehyde dioxime, 1,3, 5-benzenetricarbaldehyde oxime, 4-aminobenzamidoxime, 2-propoxybenzaldehyde oxime, 2-aminobenzamidoxime, cyclopropane-1-methylaminoxime, furan-2-methylaminoxime, and 2, 3-dihydroxybenzaldehyde oxime.
Further, the polyhydric alcohol is at least one selected from the group consisting of glycerin, trimethylolpropane, pentaerythritol, sorbitol, castor oil, polytetrahydrofuran diol, polyoxypropylene diol, tetrahydrofuran-oxypropylene copolyol, polyethylene adipate, polybutylene terephthalate, polyhexamethylene adipate, neopentyl glycol adipate, and poly-caprolactone
Preferably, the structural general formula of the polyurethane hot melt adhesive is as follows:
wherein m ranges from 2 to 150; n ranges from 2 to 600; r1Is composed of
R2Is composed of
R3Is composed of
The length of (a) is 50 to 700.
The invention also provides a preparation method of the polyurethane hot melt adhesive containing the oxime urethane dynamic bond, which comprises the following steps:
dissolving at least one polyol and at least one micromolecular oxime in an organic solvent, adding at least one polyisocyanate and a catalyst after the micromolecular dioxime is completely dissolved, reacting for 12-24 hours at 50-60 ℃, and heating to remove the organic solvent to obtain the catalyst.
Further, the organic solvent is one of acetone, tetrahydrofuran, dimethylformamide, dichloromethane and cyclohexanone.
Further, the catalyst is one of dibutyltin dilaurate, stannous octoate, triethylamine, N-dimethyl cyclohexylamine and triethanolamine
Advantageous effects
The invention introduces dynamic covalent bonds into a cross-linked polyurethane hot melt adhesive system, enables the thermosetting material to have certain thermoplastic property by utilizing the introduction of the dynamic bonds, obtains the hot melt adhesive with the advantages of thermoplastic polyurethane and reactive polyurethane hot melt adhesive, has higher initial bonding strength and final bonding strength, higher curing speed, good solvent resistance, removable adhesive and reusability, has longer storage period, and has great practical significance for the practical application of polyurethane adhesive.
Drawings
FIG. 1 is a scheme for synthesizing the product of example 1 (DMG-CPU);
FIG. 2 is a schematic diagram showing the structure of a product (DMG-CPU) of example 1 as a function of temperature;
FIG. 3 is a graph showing the infrared absorption spectrum of the product of example 1 (DMG-CPU) as a function of temperature;
FIG. 4 is a comparison of the lap shear strength of the product of example 1 (DMG-CPU), a commercially available thermoplastic polyurethane hot melt adhesive (TPU), and a commercially available reactive polyurethane hot melt adhesive (Hangolet 3542, 3M2665) bonded stainless steel over time;
FIG. 5 is a comparison of the initial bond strength of the product of example 1 (DMG-CPU), a commercially available thermoplastic polyurethane hot melt adhesive (TPU), bonded stainless steel, and the bond strength after 18 hours immersion in acetone solvent;
FIG. 6 is a comparison of the lap shear strengths of the product of example 1 (DMG-CPU), a commercially available thermoplastic polyurethane hot melt adhesive (TPU), and a commercially available reactive polyurethane hot melt adhesive (Hamoletai 3542, 3M2665) bonded stainless steel, aluminum, pine, phenolic resin, epoxy resin, and glass fiber reinforced epoxy resin;
FIG. 7 is a plot of tensile force versus displacement for the product of example 1 (DMG-CPU), initially bonded stainless steel and second bonded stainless steel
FIG. 8 shows a synthetic route of the product of the present invention.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
Example 1
(1) Experimental materials
Polytetrahydrofuran diol (PTMG, Mn ═ 1000g mol)-1Adadin), diphenylmethane diisocyanate (MDI, 99%, adadin) and dibutyltin dilaurate (DBTDL, 95%, adadin); dimethylglyoxime (DMG, 98%, national group) and glycerol (99%, national group). Acetone (99.8%, Yongcheng chemical).
(2) Preparation method
Firstly, taking the raw materials according to a proposed molar ratio, for example, taking polytetrahydrofuran diol (PTMG, 0.575g, 1 molar part), dimethylglyoxime (DMG, 0.200g, 3 molar parts) and glycerol (GLY, 0.026g, 0.5 molar part) to dissolve in 5ml of acetone; after the dimethylglyoxime was completely dissolved and a colorless transparent liquid was formed, diphenylmethane diisocyanate (MDI, 0.682g, 4.75 mole fraction) and dibutyltin dilaurate (DBTDL,0.015g,1 wt%) were added; after uniform mixing, transferring the liquid mixture into a tetrafluoro mold, putting the tetrafluoro mold filled with the liquid mixture into a 50 ℃ oven for 12 hours to enable the mixture to fully react, then heating to 70 ℃ to remove residual solvent, and finally taking out from the oven, thus obtaining a transparent polyurethane hot melt adhesive film in the tetrafluoro mold, which is recorded as DMG-CPU and has the structural formula:
(3) Demonstration of the dynamics of Oxime urethane linkages
The oxime urethane bond has stability at normal temperature, and can reversibly dissociate isocyanate groups and oxime groups at higher temperature. Due to the property of the oxime-urethane bond, oxime micromolecules are important blocking agents in the reactive polyurethane hot melt adhesive, and the stable oxime-urethane bond is formed at room temperature, so that the reaction of isocyanate groups and moisture in the air is avoided, and the service life of the reactive polyurethane hot melt adhesive is prolonged; at higher temperature, isocyanate group can be dissociated, thus achieving the purpose of curing with moisture and enhancing bonding property.
According to the invention, the micromolecule dioxime is introduced into a cross-linked polyurethane system, so that a molecular main chain contains reversible oxime urethane dynamic bonds, the stability is better at room temperature, a cross-linked structure is maintained, oxime urethane bonds can be reversibly dissociated to form isocyanate groups at high temperature, the cross-linked structure is destroyed, and the polyurethane has certain fluidity at higher temperature, so that the hot melt adhesive film can sufficiently wet the surface of a base material at high temperature, and the cross-linked structure can be formed again after the hot melt adhesive film is cooled to room temperature. By utilizing more hydrogen bond functions in the polyurethane system and the cross-linked chemical structure, the polyurethane can form better bonding performance with the base material.
In-situ heating infrared spectrum is used for analyzing reversible change of oxime ammonia ester bond in the process of changing along with temperature, and can be seen from an infrared spectrogram in the heating process (figure 3), wherein 2275cm is below 100 DEG C-1No obvious isocyanate absorption peak appears, and after the temperature exceeds 110 ℃, 2275cm-1The intensity of the isocyanate absorption peak is gradually increased, which shows that the rate of oxime urethane bond dissociation into isocyanate is gradually increased after the temperature exceeds 110 ℃. But 2275cm after the temperature is over 140 DEG C-1The absorption peak of the isocyanate becomes smaller due to the side reaction of the isocyanate group at a higher temperature.
(4) Adhesion property test of polyurethane hot melt adhesive
In order to prove the bonding performance of the polyurethane hot melt adhesive containing oxime urethane dynamic bonds, the lap shear strength of a commercial thermoplastic polyurethane hot melt adhesive (TPU), a commercial reactive polyurethane hot melt adhesive (Hamadolestai 3542 and 3M2665) and a polyurethane adhesive (DMG-CPU) containing oxime urethane dynamic bonds for bonding stainless steel were respectively tested. As shown in fig. 4, the polyurethane hot melt adhesive (DMG-CPU) containing the oxime urethane dynamic bond has a high initial adhesive strength, an adhesive strength of about 3MPa at 5min after sizing, and the adhesive can be substantially completely cured after 1 day of sizing, and has an adhesive strength of about 6 MPa. The initial bonding strength of the reactive polyurethane hot melt adhesive is lower, the bonding strength within 30min after glue application is below 0.5MPa, the reactive polyurethane hot melt adhesive is a polyurethane prepolymer blocked by isocyanate, the molecular weight is lower, a cross-linking structure is formed by the reaction of the isocyanate and moisture in the air, the test result shows that the curing speed is lower, the bonding strength after 14 days after glue application can reach about 6MPa, and the bonding strength is equivalent to the bonding strength after 1 day after glue application of the polyurethane hot melt adhesive containing an oxime urethane dynamic bond. The curing speed of the thermoplastic polyurethane adhesive is relatively high, the adhesive has the bonding strength of about 4MPa after one day of gluing, and the adhesive can reach the bonding strength of about 5MPa after 7 days of curing. The adhesive with the crosslinking structure has higher bonding strength than a thermoplastic adhesive, and the crosslinking structure can also enable the adhesive to have certain solvent resistance.
As shown in FIG. 5, after soaking stainless steel with a commercially available TPU hot melt adhesive and DMG-CPU in acetone for 18h, it was found that the two stainless steels bonded with the TPU hot melt adhesive fell off and did not have a bonding strength, while under the same conditions, the stainless steel bonded with DMG-CPU still had a bonding strength of approximately 3MPa after soaking in acetone for 18 h. The result shows that the polyurethane hot melt adhesive containing the oxime urethane dynamic bond has higher initial bonding strength, faster curing speed, stronger final bonding strength and certain chemical reagent resistance.
In order to illustrate the practicability of the polyurethane hot-melt adhesive containing oxime urethane dynamic bonds, the feasibility of bonding different base materials including metal, wood, plastic and composite materials by using DMG-CPU is also tested, and the commercially available thermoplastic polyurethane hot-melt adhesive is compared with a reactive hot-melt adhesive. As the curing speed of the reactive adhesive is lower, the bonding strength of the reactive polyurethane hot melt adhesive after being cured for 7 days is tested, and the bonding strength of TPU and DMG-CPU are both the bonding strength after being applied for one day. As shown in FIG. 6, the test results show that DMG-CPU has better adhesion to stainless steel, aluminum, pine, phenolic resin, epoxy resin and glass fiber reinforced epoxy resin. It can be speculated that the excellent bonding performance has a great relationship with a cross-linking structure in the polyurethane adhesive, an oxime-urethane bond can dissociate to form an isocyanate group at a higher temperature, and if the surface of the base material contains active hydrogen capable of reacting with the isocyanate group, covalent bond connection can be formed between the adhesive and the base material, so that the bonding strength is further enhanced.
The detachable adhesive is also an important adhesive, and can meet the requirements of disassembling and recycling bonded parts, and the disassembly of the parts bonded by the crosslinking adhesive requires large mechanical force, and the bonded parts can be damaged possibly, so that the recycling of the parts becomes difficult. Although the polyurethane adhesive containing the oxime urethane dynamic bond has a crosslinking structure, the oxime urethane bond can be dissociated at a higher temperature, so that the adhesive can also be used as a detachable adhesive, and for heat-resistant components, the bonded components can be easily detached by heating the heat-resistant components to a temperature higher than the dissociation temperature of the oxime urethane bond. The stainless steel bonded by the DMG-CPU can bear the weight of 300g at room temperature, the adhesive is damaged after the stainless steel is heated for 30s by a hot air gun, and the bonded stainless steel can be easily disassembled.
The hot melt adhesive containing dynamic bonds also has the ability to be repeatedly bonded, as shown in FIG. 7, after testing for a failure in the bond, and re-bonding the stainless steel according to the original sizing process, it was found that the primary bond strength was substantially maintained during the second bonding of the stainless steel. The property of being capable of being recycled has great significance for recycling materials.
Claims (4)
1. The polyurethane hot melt adhesive containing oxime urethane dynamic bonds is characterized in that: the polymerized monomers include: at least one polyisocyanate, at least one small molecule oxime, at least one polyol; the general structural formula is as follows:
wherein m ranges from 2 to 150; n ranges from 2 to 600; r1Is composed of
R2Is composed of
R3Is composed of
X is 50 to 700.
2. A method for preparing the polyurethane hot melt adhesive containing oxime urethane dynamic bonds as claimed in claim 1, comprising the following steps:
dissolving at least one polyol and at least one micromolecular oxime in an organic solvent, adding at least one polyisocyanate and a catalyst after the micromolecular oxime is completely dissolved, reacting for 12-24 hours at 50-60 ℃, and heating to remove the organic solvent to obtain the catalyst.
3. The method of claim 2, wherein: the organic solvent is one of acetone, tetrahydrofuran, dimethylformamide, dichloromethane and cyclohexanone.
4. The method of claim 2, wherein: the catalyst is one of dibutyltin dilaurate, stannous octoate, triethylamine, N-dimethyl cyclohexylamine and triethanolamine.
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| WO2023168077A1 (en) * | 2022-03-04 | 2023-09-07 | Conagen Inc. | Phenol-based hot melt adhesives for rework, repair and recycle |
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| CN110066414B (en) * | 2019-04-09 | 2021-09-21 | 东华大学 | Multifunctional multiple protection material and preparation method thereof |
| CN112126036A (en) * | 2020-09-11 | 2020-12-25 | 常州大学 | Disulfide bond-based biodegradable cross-linked self-repairing polyurethane and preparation method thereof |
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| CN112778489B (en) * | 2020-12-31 | 2022-03-18 | 东华大学 | Reconfigurable driver based on self-healing elastomer and preparation method thereof |
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| WO2023168066A1 (en) | 2022-03-04 | 2023-09-07 | Conagen Inc. | Oxime-based hot melt adhesives for rework, repair and recycle |
| WO2023168045A1 (en) | 2022-03-04 | 2023-09-07 | Conagen Inc. | Hydroxy/amino oxime-based hot melt adhesives for rework, repair and recycle |
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| CN101469259A (en) * | 2007-12-27 | 2009-07-01 | 上海轻工业研究所有限公司 | Polyurethane reactive hot melt structure adhensive |
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| WO2023168077A1 (en) * | 2022-03-04 | 2023-09-07 | Conagen Inc. | Phenol-based hot melt adhesives for rework, repair and recycle |
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