Preparation method of UV-cured flame-retardant polyurethane adhesive for plastic-metal bonding and adhesive

Abstract

The invention relates to a preparation method of a UV (ultraviolet) curing flame-retardant polyurethane adhesive for plastic and metal bonding and an adhesive, the method comprises the following steps: S10: adding polyol and diisocyanate into a reaction container, mixing, heating to 45 + / -5 DEG C, adding a catalyst, controlling the temperature within 80 DEG C, reacting for several hours, and stopping the reaction to obtain a hydroxyl-terminated polyurethane prepolymer; s20, mixing the hydroxyl-terminated polyurethane prepolymer in the step S10 with phosphorus pentoxide in a reaction container, adding an antioxidant and a polymerization inhibitor, heating to 50 + / -5 DEG C, reacting for several hours, adding a hydroxyl end-capping reagent containing double bonds, and reacting for several hours to obtain UV urethane acrylate; and S30, kneading and mixing the UV polyurethane acrylate in the step S20, the reactive diluent and the photoinitiator in a reaction container, and obtaining the UV-cured flame-retardant polyurethane adhesive after the photoinitiator is completely dissolved.

Description

Technical Field

[0001] The invention belongs to the technical field of adhesives, and particularly relates to a preparation method of a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding and the adhesive. Background Art

[0002] Traditional UV phosphorus-based adhesion promoters contain reactive phosphate groups. The phosphorus-oxygen bond significantly enhances the interlayer adhesion of organic or inorganic materials. Common products on the market include PM-1, PM-2, and CD9051. These products have low molecular weights, strong polarity, and poor compatibility with resins, potentially causing turbidity or delamination in the finished product. Their strong acidity can lead to poor long-term storage stability and molecular chain breakage. Furthermore, these products function solely as adhesion promoters and lack the properties of resins or adhesives.

[0003] For a long time, UV-curable flame-retardant polyurethane acrylate adhesives have been almost blank in the market. Most technologies achieve flame-retardant effects by adding external flame retardants. However, the added flame retardants have poor compatibility with the system and will delaminate after being placed for a long time. In addition, if the added amount is too small, the flame-retardant effect cannot be achieved, and if the added amount is too large, the adhesive performance will be affected. For example, patent CN113930210A "A method for preparing a flame-retardant UV-curable polyurethane acrylate adhesive" mentions a polyurethane acrylate adhesive prepared by a graft copolymerization method. However, the raw materials are expensive and difficult to obtain, the steps are cumbersome and have certain production difficulties, and the reactants contain secondary amine groups that catalyze double bond reactions, deepen the product color, and greatly reduce storage stability.

[0004] Under this technical background, the market urgently needs a UV polyurethane acrylate adhesive with strong adhesion, stable storage and certain flame retardant effect. Summary of the Invention

[0005] In response to the above deficiencies in the prior art, the present invention provides a method for preparing a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding and an adhesive. The adhesive has good flame retardant effect, strong bonding strength, and a wide range of application scenarios.

[0006] The present invention is solved by the following technical solutions.

[0007] A method for preparing a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding comprises the following steps: S10: adding a polyol and a diisocyanate into a reaction container, mixing, heating to 45±5°C, adding a catalyst, controlling the temperature to below 80°C, reacting for several hours, and then stopping the reaction to obtain a hydroxyl-terminated polyurethane prepolymer; S20: mixing the hydroxyl-terminated polyurethane prepolymer in S10 with phosphorus pentoxide in a reaction container, adding an antioxidant and a polymerization inhibitor, heating to 50±5°C, reacting for several hours, adding a hydroxyl end-capping agent containing a double bond, and reacting for several hours to obtain UV polyurethane acrylate; S30: kneading and mixing the UV polyurethane acrylate in S20 with a reactive diluent and a photoinitiator in the reaction container, and obtaining a UV-curable flame-retardant polyurethane adhesive after the photoinitiator is completely dissolved.

[0008] Preferably, in step S10, the diisocyanate is one or more of 4,4-dicyclohexylmethane diisocyanate, 2,4-toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate; in step S10, the polyol is one or more of polyether polyol, polyester polyol, and polycarbonate polyol.

[0009] Preferably, in step S10, the catalyst is one of stannous octoate, dibutyltin dilaurate, stannous chloride, and bismuth isodecanoate.

[0010] Preferably, in step S20, the hydroxyl end-capping agent containing a double bond is one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxybutyl methacrylate, and hydroxybutyl acrylate.

[0011] Preferably, in step S20, the antioxidant is one or more of antioxidant 168, antioxidant 1076, antioxidant 1033, and triphenyl phosphite; and the polymerization inhibitor is one of p-hydroxyanisole, hydroquinone, p-benzoquinone, and tert-butylhydroquinone.

[0012] Preferably, in step S30, the active diluent is one or more of acryloylmorpholine, isobornyl acrylate, isobornyl methacrylate, ethoxyethoxyethyl acrylate, and tetrahydrofuran acrylate; the photoinitiator is one or more of photoinitiator 184, photoinitiator TPO, photoinitiator 1173, photoinitiator ITX, and photoinitiator 907.

[0013] Preferably, in step S10, the molar ratio of isocyanate to polyol is 2:1 to 5:4, preferably 2:1 to 4:3; the molecular weight of the polyol is 650 to 2000; and the molecular weight of the hydroxyl-terminated polyurethane prepolymer is 1500 to 8600.

[0014] Preferably, in step S20, the molar ratio of the prepolymer to phosphorus pentoxide is 1:2 to 2:1; the molar number of the hydroxyl end-capping agent containing a double bond is (molar number of phosphorus pentoxide * 3 - molar number of prepolymer) * 1.05; the weight of the antioxidant is 0.03% to 0.08% of the total material; and the weight of the catalyst is 0.01% to 0.03% of the total material.

[0015] Preferably, in step S30, the weight ratio of polyurethane acrylate to diluent monomer is 1:9 to 8:2, and the weight of the photoinitiator is 3% to 7% of the total material; the viscosity of the obtained UV-curable flame-retardant polyurethane adhesive is 400 to 10,000 cps.

[0016] The present application also relates to a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding, which is prepared by the above method.

[0017] Compared with the prior art, the present invention has the following beneficial effects: providing a method for preparing a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding and the adhesive, which, after curing, exhibits strong bonding properties to a variety of substrates and good mechanical properties. Furthermore, by introducing the flame-retardant element P, the prepared adhesive exhibits strong storage and flame-retardant properties. During storage and use, the flame retardant does not migrate, precipitate, or delaminate, and is resistant to hydrolysis. Furthermore, the present invention does not use organic solvents during the preparation process, exhibiting outstanding green, environmentally friendly, healthy, and safe properties. It can be used for structural bonding between various plastics with flame-retardant requirements, such as ABS, PC, PMMA, and PET, and metallic glass. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a synthetic pathway diagram for step 1 of the present invention.

[0019] Figure 2 This is a synthetic pathway diagram for step 2 of the present invention.

[0020] Figure 3 This is the infrared image of the UV polyurethane acrylate prepared in Example 1.

[0021] Figure 4 A thermogravimetric analysis diagram of the adhesive of Example 1 is provided. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] In the following embodiments, the same or similar numbers throughout represent the same or similar components or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and are not to be construed as limiting the present invention.

[0024] The UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding in this application has a preparation method comprising: preparing a hydroxyl-terminated PUA prepolymer, preparing a phosphorus-branched P-PUA prepolymer, double-bond capping, and uniformly mixing the resin with an active diluent and a photoinitiator in a certain feeding ratio to finally obtain a UV-curable polyurethane acrylate adhesive.

[0025] The specific steps are as follows.

[0026] Step 1: After mixing the polyol and diisocyanate in a certain molar ratio, the temperature is raised to 45±5°C (temperature 1), a catalyst is added, the temperature is controlled within 80°C, and the NCO value is detected after the reaction for 4 hours until the NCO content is less than 0.05%. The reaction is stopped to obtain a hydroxyl-terminated polyurethane prepolymer.

[0027] Its synthesis route is as shown in the attached Figure 1 As shown, wherein: R1 is one or more of hexamethylene, isophorone, diphenylmethane, and tolyl; R2 is one or more of polyether, polyester, and polycarbonate.

[0028] Step 2: The hydroxyl-terminated polyurethane prepolymer and phosphorus pentoxide in step 1 are mixed in a certain molar ratio and put into a reactor, an antioxidant and an inhibitor are added, the temperature is raised to 50±5°C (temperature 2), the reaction is carried out for 3 hours, a hydroxyl-terminated agent containing a double bond is added, and the reaction is carried out for 2 hours to obtain UV polyurethane acrylate.

[0029] Its synthesis route is as shown in the attached Figure 2 As shown, wherein R1 and R2 are the same as above.

[0030] Step 3: Evenly mix the UV polyurethane acrylate, reactive diluent, and photoinitiator in step 2 in a certain proportion, and wait until the photoinitiator is completely dissolved to obtain a UV-curable flame-retardant polyurethane adhesive.

[0031] The following is step 1 of Examples 1 to 6 in this application.

[0032]

[0033] The following is step 2 of Examples 1 to 6 in this application.

[0034]

[0035] The following is step 3 of Examples 1 to 6 in this application.

[0036]

[0037]

[0038] In Examples 1 to 6 above, the molecular weight of the hydroxyl-terminated polyurethane prepolymer prepared in step 1 is between 1500 and 8600, the molar number of the double-bond-containing hydroxyl-terminated agent in step 2 is (moles of phosphorus pentoxide * moles of 3-hydroxyl-terminated polyurethane prepolymer) * 1.05, and the viscosity of the final adhesive prepared is 400 to 10,000 cps (25°C).

[0039] Figure 3 The infrared image of the UV polyurethane acrylate prepared in Example 1 of the present application is shown, from which it can be seen that the 2280cm -1 The isocyanate peak at 1700 cm-1 disappeared, indicating that the isocyanate was completely reacted. -1 A carboxyl peak appears at 700 cm -1 The phosphorus-carbon peak appears at 3500 cm -1 The appearance of hydroxyl peaks at the bottom of the column indicated the successful synthesis of phosphorus-containing UV polyurethane acrylate.

[0040] The following is a description of the product testing and mechanism in Examples 1 to 6 of this application.

[0041] Adhesion tests were performed on different substrates for the adhesives of Examples 1 to 6. Adhesion tests on substrate surfaces were performed according to the ISO 2409:1992 cross-grid method. The results are shown in the following table:

[0042] Example Tinplate aluminum PET ABS PP PMMA PC PVC Glass 1 0 0 0 0 2 0 1 0 0 2 0 0 0 0 3 0 1 0 0 3 0 0 0 0 3 1 0 0 0 4 0 0 0 0 2 1 1 0 0 5 0 0 0 0 2 1 0 1 0 6 0 0 1 0 2 1 0 1 0

[0043] As can be seen from the above table, the products in Examples 1 to 6 can achieve adhesion level 0 on substrates such as tinplate, aluminum, and glass. This is because the phosphate groups in the adhesive and the metal surface active groups form a bond, which increases the adhesion. For other plastic substrates, except for the PP substrate with extremely low polarity, which is difficult to adhere to, most surfaces can achieve adhesion level 1 or above.

[0044] The peeling strength of the adhesives of Examples 1 to 6 on different substrates was tested. The peeling strength test of the substrates was carried out according to the peeling strength test method of standard GB / T 2790-1995. The length, width and thickness of the substrates were 100 mm*10 mm*0.6 mm, and the bonding area was 1 cm 2 The results are shown in the following table. The unit of tension value is Kgf.

[0045]

[0046] Note: B represents the substrate being broken.

[0047] As shown in the table above, with the exception of PP substrates with extremely low polarity, which have difficulty adhering, Examples 1-6 exhibit good adhesion to most plastics and metals. Examples 4 and 5 can even break through multiple substrates, demonstrating very high bond strength. Based on the structural design, Example 4 exhibits a higher molecular weight, and the phosphate groups in the adhesive form an anchoring effect with the substrate surface, significantly increasing the adhesive's cohesion and bond strength. Example 5 also exhibits a higher molecular weight, and the phosphate groups in the adhesive form an anchoring effect with the substrate surface. Furthermore, the polycarbonate structure in the chain segments possesses the best mechanical properties among polyols and is structurally similar to PC, thus enhancing adhesion to PC substrates.

[0048] After curing, the adhesives in Examples 1 to 6 were made into 130 mm * 13 mm * 10 mm strips, and their flame retardancy was tested using the UL94 standard. The results are shown in the following table:

[0049] Example Phosphorus content (%) flame retardancy 1 0.6 V2 2 1.7 V2 3 3.3 V1 4 4.4 V0 5 3.6 V1 6 2.9 V1 control group 0 flammable

[0050] As can be seen from the table, the flame retardancy of the adhesive is directly related to its phosphorus content. The flame retardant mechanism of the present invention is that when the adhesive decomposes under heat, it generates strong dehydrating agents such as phosphoric acid and metaphosphoric acid. These acidic substances can promote rapid dehydration and carbonization of the polymer surface, forming a dense carbonized layer. The carbonized layer effectively isolates oxygen and heat, preventing further combustion. During the combustion process, it decomposes to form a glassy or liquid protective layer that covers the polymer surface. This protective layer reduces heat and mass transfer between the gas and solid phases, inhibits the oxidation process of the carbon, interrupts the combustion chain reaction, and thus suppresses the spread of flames. The control group does not contain any flame retardant ingredients and can be ignited. The phosphorus content of Example 1 and Example 2 is less than 2%, and the flame retardancy is V2 level, which can be used in the bonding of toy shells with low flame retardancy requirements; the phosphorus content of Example 3, Example 5, and Example 6 is about 3%, and the flame retardancy reaches V1 level, which can be used in the bonding of small electrical appliances; the phosphorus content of Example 4 is greater than 4%, and the flame retardancy reaches the highest V0 level, which can be used in the bonding of electronic devices with more stringent flame retardancy requirements.

[0051] Thermogravimetric analysis was performed on the adhesive of Example 1 with the lowest phosphorus content. The results are shown in the attached figure. Figure 4 As shown. Figure 4 It can be seen that the thermal decomposition temperature of Example 1 with a phosphorus content of 0.6% is around 250°C. The slight weight loss before 250°C may be due to the slight precipitation of water and small molecular substances. The decomposition peak temperature is around 320°C, while adhesives with poor flame retardancy generally have a thermal decomposition temperature of around 200°C. This proves that the patented product has good thermal stability and heat resistance.

[0052] As can be seen from the above description, the present invention provides a method for preparing a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding and the adhesive. After curing, the adhesive has strong bonding properties to various substrates and good mechanical properties. In addition, by introducing the flame retardant element P, the prepared adhesive has strong storage performance and flame retardant properties. It can be used for structural bonding between various plastics with flame retardant requirements, such as ABS, PC, PMMA, PET, and metal glass.

[0053] The protection scope of the present invention includes but is not limited to the above embodiments. The protection scope of the present invention is based on the claims. Any replacement, deformation, and improvement of the technology that can be easily thought of by those skilled in the art fall within the protection scope of the present invention.

Claims

1. A method for preparing a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding, characterized in that: The following steps are involved: S10: adding polyol and diisocyanate to a reaction vessel, mixing, heating to 45±5°C, adding a catalyst, controlling the temperature below 80°C, reacting for several hours, and then stopping the reaction to obtain a hydroxyl-terminated polyurethane prepolymer; S20: In a reaction vessel, the hydroxyl-terminated polyurethane prepolymer in S10 and phosphorus pentoxide are mixed, an antioxidant and a polymerization inhibitor are added, the temperature is raised to 50±5° C., the reaction is carried out for several hours, a hydroxyl-terminated agent containing a double bond is added, and the reaction is carried out for several hours to obtain UV polyurethane acrylate; S30: In a reaction container, the UV polyurethane acrylate, reactive diluent, and photoinitiator in S20 are kneaded and mixed, and after the photoinitiator is completely dissolved, a UV-curable flame-retardant polyurethane adhesive is obtained.

2. The method for preparing a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding according to claim 1, characterized in that: In step S10, the diisocyanate is one or more of 4,4-dicyclohexylmethane diisocyanate, 2,4-toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate; In step S10, the polyol is one or more of polyether polyol, polyester polyol, and polycarbonate polyol.

3. The method for preparing a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding according to claim 2, characterized in that: In step S10, the catalyst is one of stannous octoate, dibutyltin dilaurate, stannous chloride, and bismuth isodecanoate.

4. The method for preparing a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding according to claim 3, characterized in that: In step S20, the hydroxyl end-capping agent containing a double bond is one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxybutyl methacrylate, and hydroxybutyl acrylate.

5. The method for preparing a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding according to claim 4, characterized in that: In step S20, the antioxidant is one or more of antioxidant 168, antioxidant 1076, antioxidant 1033, and triphenyl phosphite; the polymerization inhibitor is one of p-hydroxyanisole, hydroquinone, p-benzoquinone, and tert-butylhydroquinone.

6. The method for preparing a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding according to claim 5, characterized in that: In step S30, the active diluent is one or more of acryloylmorpholine, isobornyl acrylate, isobornyl methacrylate, ethoxyethoxyethyl acrylate, and tetrahydrofuran acrylate; the photoinitiator is one or more of photoinitiator 184, photoinitiator TPO, photoinitiator 1173, photoinitiator ITX, and photoinitiator 907.

7. The method for preparing a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding according to claim 1, characterized in that: In step S10, the molar ratio of isocyanate to polyol is 2:1 to 5:4; the molecular weight of the polyol is 650 to 2000; and the molecular weight of the hydroxyl-terminated polyurethane prepolymer is 1500 to 11000.

8. The method for preparing a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding according to claim 1, characterized in that: In step S20, the molar ratio of the prepolymer to phosphorus pentoxide is 1:2 to 2:1; the molar number of the hydroxyl end-capping agent containing a double bond is (molar number of phosphorus pentoxide * 3 - molar number of prepolymer) * 1.05; the weight of the antioxidant is 0.03% to 0.08% of the total material; and the weight of the catalyst is 0.01% to 0.03% of the total material.

9. The method for preparing a UV-curable flame-retardant polyurethane adhesive for plastic-metal bonding according to claim 1, characterized in that: In step S30 , the weight ratio of polyurethane acrylate to diluent monomer is 1:9 to 8:2, and the weight of the photoinitiator is 3% to 7% of the total material; the viscosity of the obtained UV-curable flame-retardant polyurethane adhesive is 400 to 10,000 cps.

10. A UV curable flame retardant polyurethane adhesive for plastic-metal bonding, characterized in that: The adhesive is a UV-curable flame-retardant polyurethane adhesive prepared by the method according to any one of claims 1 to 9.

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