Photo-degradable room temperature curing two-component polyurethane adhesive and preparation method thereof

Abstract

The invention relates to a photo-degradable room temperature curing double-component polyurethane adhesive and a preparation method thereof.The adhesive comprises a component A and a component B. The component A comprises a polyol modified polyurethane prepolymer with the end group being an isocyanate group, and the component B comprises a polyhydroxy composition; the component A and / or the component B further comprises a photodegradable oximido unit. After the two components in the adhesive are mixed, sized and cured, the oximido unit can be degraded through ultraviolet irradiation, so that the bonding strength is reduced, and a bonding base material can be naturally debonded along with the prolonging of the irradiation time. In the gluing process, curing can be completed at the room temperature after the two components are mixed, bonding of a heat-sensitive material can be achieved easily, then a bonding sample can be detached through ultraviolet irradiation, and good application prospects are achieved.

Description

Technical Field

[0001] The invention belongs to the field of polyurethane adhesives, and particularly relates to a photodegradable room temperature curing two-component polyurethane adhesive and a preparation method thereof. Background Art

[0002] Polyurethane adhesives are widely used in the fields of construction, automobiles, electronics, packaging, etc. due to their excellent bonding strength, chemical resistance and aging resistance. Traditional polyurethane adhesives may require an external heat source to accelerate the reaction during the curing process, which poses a great challenge to the bonding of heat-sensitive materials. Especially when bonding some plastic materials that are not resistant to high temperatures, high-temperature curing may cause degradation or deformation of material properties, thereby affecting the quality and service life of the bonded sample.

[0003] To overcome this problem, room temperature curing polyurethane adhesives have gradually attracted attention. This type of adhesive can be cured without heating, which greatly broadens its application range, especially in the application of heat-sensitive materials. However, existing room temperature curing polyurethane adhesives usually become permanently cross-linked structures after curing, making it extremely difficult to disassemble without destroying the material, which limits its flexibility and practicality in certain application scenarios. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a photodegradable room temperature curing two-component polyurethane adhesive and a preparation method thereof, wherein the adhesive can be cured at room temperature and can be conveniently debonded by ultraviolet degradation after curing, thereby protecting heat-sensitive materials from damage before and after bonding to the greatest extent. At the same time, there is no solvent involved in the curing process, and no complicated operation steps are required, and the adhesive can be used after being simply mixed according to the ratio.

[0005] The invention provides a photodegradable two-component polyurethane adhesive that cures at room temperature. The adhesive comprises a component A and a component B. The component A comprises a polyol-modified polyurethane prepolymer whose terminal group is an isocyanate group, and the component B comprises a polyhydroxy composition. The component A and / or the component B also comprise a photodegradable oxime unit.

[0006] Preferably, the polyol in the A component includes at least one of small molecule polyol, polyether polyol and polyester polyol; and the polyhydroxy composition in the B component includes at least one of small molecule polyol, polyether polyol and polyester polyol.

[0007] Preferably, the small molecule polyol is selected from at least one of ethylene glycol, propylene glycol, 1,2-propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,3-butanediol, 2-ethyl-1,3-hexanediol, 1,2-octanediol, glycerol, trimethylolpropane, tetraethylene glycol and castor oil; and the molecular weight of the small molecule polyol is 100-1000.

[0008] Preferably, the polyether polyol is selected from at least one of polyoxypropylene diol, polyoxypropylene triol, polyoxypropylene-ethylene oxide diol, polyoxypropylene-ethylene oxide triol, polytetrahydrofuran diol and polytetrahydrofuran triol; and the molecular weight of the polyether polyol is 200-4000.

[0009] Preferably, the polyester polyol is selected from at least one of polyethylene adipate diol, polybutylene adipate diol, polyhexane adipate diol, polycarbonate diol, polyphthalate diol, polyneopentyl adipate diol, polycaprolactone diol, polyethylene adipate monopropylene glycol ester diol, polyethylene adipate diacetate diol, and polyethylene adipate diacetate diol; and the molecular weight of the polyester polyol is 200-4000.

[0010] Preferably, the isocyanate group is derived from at least one of an aromatic polyisocyanate, an aliphatic polyisocyanate, and an aliphatic cyclopolyisocyanate. More preferably, the isocyanate group is derived from one or more of diphenylmethane diisocyanate, liquefied MDI, toluene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, hexamethylene diisocyanate trimer, isophorone diisocyanate trimer, diphenylmethane diisocyanate trimer, toluene diisocyanate trimer, and pentamethylene diisocyanate trimer.

[0011] Preferably, the isocyanate group content in the polyurethane prepolymer is 10-50%, including 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%; more preferably 20-30%, including 22.5%, 25%, 27.5%, 30%; most preferably 20-25%, including 21%, 22%, 23%, 24%, 25%. The isocyanate group content in the polyurethane prepolymer can be detected by conventional methods in the art, such as the commonly used titration method.

[0012] Preferably, the photodegradable oxime unit includes at least one of dimethylglyoxime, 1,4-benzoquinone dioxime, acetone aldehyde dioxime, terephthalaldehyde dioxime, 1,2-cyclohexanedione dioxime, furil dioxime, diphenylglyoxime, and diaminoglyoxime.

[0013] Preferably, the photodegradable oxime units account for 2-10% of the total mass of the polyurethane adhesive system, including 2%, 3%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%. The oxime units in the polyurethane adhesive system can be detected by a simple method, such as the commonly used infrared spectroscopy.

[0014] It will be appreciated by those skilled in the art that other additives, such as plasticizers, tackifiers, leveling agents, defoamers, dispersants, etc., may be added to the photodegradable room temperature curing two-component polyurethane adhesive of the present invention according to process requirements, which is a routine operation in the art.

[0015] On the other hand, the present invention also provides a method for preparing a photodegradable two-component polyurethane adhesive that cures at room temperature, comprising the following steps: mixing the component A and the component B in proportion to obtain a photodegradable two-component polyurethane adhesive that cures at room temperature.

[0016] Preferably, the component A and the component B are mixed in a mass ratio of component A: component B of 0.8-1:1, for example, 0.8:1, 0.9:1, 0.91:1, 0.92:1, 0.93:1, 0.94:1, 0.95:1, 0.96:1, 0.97:1, 0.98:1, 0.99:1, 1:1, etc.

[0017] The above mixing steps can refer to the existing technology, and the two materials can be mixed and stirred at the same time to make the two materials mixed evenly. There is no restriction on the specific stirring speed and duration, as long as the two components A and B are mixed evenly. Conventional equipment or stirring tools can also be used as the stirring equipment.

[0018] In another aspect, the present invention further provides a polyurethane product prepared from the aforementioned photodegradable room temperature curing two-component polyurethane adhesive or a composition of the polyurethane adhesive prepared by the aforementioned preparation method.

[0019] The adhesive of the present invention can be cured at room temperature and is applicable to many heat-sensitive plastic materials, thus avoiding material damage caused by high-temperature curing. At the same time, the adhesive of the present invention has unique photodegradation properties, and users can degrade the adhesive by ultraviolet light irradiation, thereby achieving on-demand fixed-point disassembly. This property enables the adhesive of the present invention to not only provide a stable bonding effect, but also to achieve convenient disassembly when needed, greatly improving flexibility and convenience during use.

[0020] In addition, the two-component system used in the present invention is solvent-free throughout the entire process, is environmentally friendly and easy to operate. Users only need to mix the components in proportion and then use them, eliminating the need for complex synthesis steps and additional equipment. Therefore, the polyurethane adhesive of the present invention not only has significantly improved performance, but also meets the requirements of today's society for environmental protection and sustainable development, and has broad market application prospects.

[0021] Beneficial Effects

[0022] (1) The photodegradable room temperature curing two-component polyurethane adhesive of the present invention can be cured at room temperature and does not require solvent participation during the entire gluing process, which is conducive to achieving the bonding of many heat-sensitive materials without causing damage to the materials themselves.

[0023] (2) The photodegradable room temperature curing two-component polyurethane adhesive of the present invention contains a photodegradable oxime unit in the component, which can be degraded by ultraviolet irradiation, thereby reducing the bonding strength. As the irradiation time increases, the bonded substrate can be naturally debonded. When applying the adhesive, the two components can be cured at room temperature after mixing, which is conducive to the bonding of heat-sensitive materials. After that, the bonded sample can be disassembled by ultraviolet irradiation, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the principle diagram of the adhesive of the present invention;

[0025] Figure 2 It is the photodegradation reaction diagram of the adhesive of the present invention;

[0026] Figure 3 This is a graph showing the changes of a polycarbonate bonding sample using the adhesive of Example 1 before and after illumination;

[0027] Figure 4 The graph is a graph showing the bonding strength variation of polycarbonate bonded samples using the adhesive of Example 1 after being subjected to different UV exposure times;

[0028] Figure 5 This is a graph showing the changes of a polyvinyl chloride bonding sample using the adhesive of Example 1 before and after illumination;

[0029] Figure 6 The graph is a graph showing the bonding strength variation of polyvinyl chloride bonding samples using the adhesive of Example 1 after being subjected to different UV exposure times;

[0030] Figure 7 This is a diagram showing changes in the infrared structure of the adhesive of Example 1 after being exposed to different ultraviolet light exposure times;

[0031] Figure 8The graph is a graph showing the change in bonding strength of polycarbonate samples bonded using the adhesive of Comparative Example 1 after being exposed to different UV light exposure times. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0033] The raw materials used in the embodiments and comparative examples are as follows:

[0034] Liquefied MDI (MDI-50) and hexamethylene diisocyanate trimer (HDI-trimer) were purchased from Wanhua Chemical Group Co., Ltd.; DMN1000 and polyoxypropylene triol were purchased from Zibo Dexin Federal Company; dimethylglyoxime (butanedione oxime) was purchased from Sinopharm Chemical Reagent Co., Ltd.; acetone aldehyde dioxime and castor oil were purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0035] The test characterization method involved in the embodiment is as follows:

[0036] Oxime structure characterization: Fourier transform infrared spectroscopy (FTIR) was used to characterize the structure of the adhesive before and after UV irradiation. The attenuated total reflectance (ATR) accessory was used for testing. The number of scans was set to 32 and the wavelength scanning range was 4000-400cm -1 , the spectral resolution is 4cm -1 .

[0037] Adhesive performance characterization: A micro-controlled electronic universal testing machine was used to test the adhesive performance of the photodegradable adhesive. The dimensions of the bonded substrate (length × width × thickness: 100 mm × 25 mm × 2 mm), the adhesive application area (12.5 mm × 25 mm), and the cooling and curing conditions (room temperature) were as follows. The adhesive was applied to the adhesive application area and fixed with a metal clip. It was placed at room temperature for 24 hours before the adhesive performance test was performed. The tensile rate was set to 5 mm min -1 During the test, the peak value of the tensile shear force is taken and calculated according to the formula (adhesion strength (MPa) = Fmax / (12.5×25)).

[0038] Characterization of photodegradation performance: UVATAUPP0404A ultraviolet irradiator (Yiwata (Shanghai) Precision Optoelectronics Co., Ltd.) was used for irradiation degradation, and the exposure time was continuously extended to 5 min. Then, the tensile shear strength of the bonding samples at different exposure times was measured respectively. At the same time, an infrared spectrometer was used to monitor the changes in the oxime structure in the adhesive in the bonding area.

[0039] Example 1

[0040] Castor oil, polyoxypropylene triol, dimethylglyoxime, MDI-50, HDI-trimer and castor oil are dried and stored separately before use. According to the mass fraction, component A is prepared: 60.9 parts of MDI-50, 3.3 parts of HDI-trimer and 35.8 parts of castor oil are mixed to form a prepolymer and then stored. The isocyanate content is measured by titration and is 21.6%; component B is prepared: 89.8 parts of castor oil, 10.2 parts of polyoxypropylene triol and 8 parts of dimethylglyoxime are mixed and then stored; when applying the glue, components A and B are directly stirred and mixed at a ratio of 1:1 and can be used.

[0041] Example 2

[0042] Castor oil, polyoxypropylene triol, methylglyoxime, MDI-50, HDI-trimer and castor oil are dried and stored separately before use. According to the mass fraction, component A is prepared: 60.9 parts of MDI-50, 3.3 parts of HDI-trimer and 35.8 parts of castor oil are mixed to form a prepolymer and then stored. The isocyanate content is measured by titration and is 21.6%; component B is prepared: 89.8 parts of castor oil, 10.2 parts of polyoxypropylene triol and 7 parts of methylglyoxime are mixed and then stored; when applying the glue, components A and B are directly stirred and mixed at a ratio of 1:1 and can be used.

[0043] Comparative Example 1

[0044] Castor oil, polyoxypropylene triol, 1,4-butanediol, MDI-50, HDI-trimer and castor oil were dried and stored separately before use. According to the mass percentage, component A was prepared: 60.9 parts of MDI-50, 3.3 parts of HDI-trimer and 35.8 parts of castor oil were mixed to form a prepolymer and then stored. The isocyanate content was measured by titration and was 21.6%; component B was prepared: 89.8 parts of castor oil, 10.2 parts of polyoxypropylene triol and 8 parts of 1,4-butanediol were mixed and then stored; when applying the glue, components A and B were directly stirred and mixed at a ratio of 1:1 and can be used.

[0045] Results

[0046] Photolysis reactions in adhesives such as Figure 2 As shown: after ultraviolet light irradiates the bonding area, the oxime amine ester structure in the molecular adhesive is cracked to generate free radicals. The free radicals can couple with each other or generate amine groups through hydrogen abstraction reactions, thereby destroying the cross-linking structure of the adhesive and reducing the bonding strength of the adhesive until it is completely debonded.

[0047] Specifically, various heat-sensitive materials were bonded, and then the photodegradation and debonding effect of the adhesive prepared in Example 1 was evaluated by ultraviolet light irradiation. Figure 3 and Figure 4As shown in the figure, the bonding sample of polycarbonate is subjected to UV irradiation degradation. Under different exposure times, the bonding strength decreases continuously, but the degree of decrease is not large. It is not until 5 minutes that the bonding strength decreases to less than 50% of the original strength. This shows that because the polarity of polycarbonate is relatively close to that of polyurethane, the adhesive of the present invention has a good bonding effect on polycarbonate, so it has a certain resistance to light degradation after bonding. For heat-sensitive polyvinyl chloride, such as Figure 5 and Figure 6 As shown in the figure, the bonded samples of polyvinyl chloride were subjected to ultraviolet irradiation degradation. Under different exposure times, the bonding strength continued to decrease. After only 1 minute, the bonding strength could drop to less than 50% of the original strength. This shows that the bonding effect of the adhesive of the present invention on polyvinyl chloride is slightly weaker. Therefore, the photodegradation debonding effect is more obvious. After 5 minutes, some bonded samples were completely debonded, indicating that the bonded samples can be disassembled without damaging the material. The principle behind this was studied, and the changes in the oxime unit structure were explored through infrared spectroscopy, such as Figure 7 As shown, it can be seen that 920cm -1 The intensity of the characteristic absorption peak representing -C=N-OH continues to decrease, which indicates that the oxime unit is continuously being degraded, thereby realizing the photodegradation of the adhesive.

[0048] To demonstrate the practical effect of the present invention, the oxime unit was replaced with non-photodegradable 1,4-butanediol, and the resulting adhesive was used to bond polycarbonate, which was then exposed to ultraviolet light for different periods of time. The results are shown in FIG. Figure 8 As shown, it shows that under the same conditions, although the bonding strength decreases, the strength reduction is not obvious, which indirectly verifies the photodegradation effect of the photodegradable adhesive of the present invention.

Claims

1. A photodegradable room temperature curing two-component polyurethane adhesive, comprising component A and component B, characterized in that: The component A comprises a polyol-modified polyurethane prepolymer whose terminal group is an isocyanate group, and the component B comprises a polyhydroxy composition; the component A and / or the component B further comprises a photodegradable oxime unit.

2. The room temperature curing two-component polyurethane adhesive according to claim 1, characterized in that: The polyol in the A component includes at least one of small molecule polyol, polyether polyol and polyester polyol; the polyhydroxy composition in the B component includes at least one of small molecule polyol, polyether polyol and polyester polyol.

3. The room temperature curing two-component polyurethane adhesive according to claim 2, characterized in that: The small molecule polyol is selected from at least one of ethylene glycol, propylene glycol, 1,2-propylene glycol, 1,4-butylene glycol, 1,6-hexanediol, neopentyl glycol, 1,3-butylene glycol, 2-ethyl-1,3-hexanediol, 1,2-octanediol, glycerol, trimethylolpropane, tetraethylene glycol and castor oil; the molecular weight of the small molecule polyol is 100-1000.

4. The room temperature curing two-component polyurethane adhesive according to claim 2, characterized in that: The polyether polyol is selected from at least one of polyoxypropylene diol, polyoxypropylene triol, polyoxypropylene-ethylene oxide diol, polyoxypropylene-ethylene oxide triol, polytetrahydrofuran diol and polytetrahydrofuran triol; the molecular weight of the polyether polyol is 200-4000.

5. The room temperature curing two-component polyurethane adhesive according to claim 2, characterized in that: The polyester polyol is selected from at least one of polyethylene adipate glycol ester diol, polybutylene adipate glycol ester diol, polyhexane adipate glycol ester diol, polycarbonate diol, polyphthalate glycol ester diol, polyneopentyl adipate glycol ester diol, polycaprolactone diol, polyethylene adipate glycol monopropylene glycol ester diol, polyethylene adipate glycol ether diol, and polyethylene adipate glycol ether diethylene glycol ester diol; the molecular weight of the polyester polyol is 200-4000.

6. The room temperature curing two-component polyurethane adhesive according to claim 1, characterized in that: The isocyanate group is derived from at least one of aromatic polyisocyanate, aliphatic polyisocyanate and alicyclic polyisocyanate.

7. The room temperature curing two-component polyurethane adhesive according to claim 1, characterized in that: The isocyanate group content in the polyurethane prepolymer is 10-50%.

8. The room temperature curing two-component polyurethane adhesive according to claim 1, characterized in that: The photodegradable oxime unit includes at least one of dimethylglyoxime, 1,4-benzoquinone dioxime, acetone aldehyde dioxime, terephthalaldehyde dioxime, 1,2-cyclohexanedione dioxime, furil dioxime, diphenylglyoxime, and diaminoglyoxime.

9. The room temperature curing two-component polyurethane adhesive according to claim 1, characterized in that: The photodegradable oxime unit accounts for 2-10% of the total mass of the entire polyurethane adhesive system.

10. A method for preparing the photodegradable two-component polyurethane adhesive that cures at room temperature as claimed in any one of claims 1 to 9, comprising the following steps: mixing the component A and the component B in proportion to obtain the photodegradable two-component polyurethane adhesive that cures at room temperature.

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