Polyurethane film-forming agent, preparation method thereof, and polyurethane primer

Abstract

The present invention provides a polyurethane film-forming agent and a preparation method thereof. The film-forming agent is primarily prepared by polymerization of the following raw materials in molar fractions: 50-80 parts of a small molecule triol, 20-50 parts of diethylenetriamine, 295-305 parts of a diisocyanate, and 5-40 parts of a diamine, with the total molar fraction of the small molecule triol and diethylenetriamine being 100 parts. The present invention also provides a polyurethane primer, comprising the following raw materials in parts by mass: 150 parts of the polyurethane film-forming agent, 20-70 parts of a triphenylisocyanate thiophosphate solution, 30-80 parts of an adhesion promoter, and 100-300 parts of a fourth solvent. During curing, the adhesion promoter and film-forming agent in the primer react with the isocyanate groups in the triphenylisocyanate thiophosphate to form a highly cross-linked, continuous entity. These interactions allow the primer to rapidly dry and cross-link, forming a high-strength paint film containing a large number of urea groups that facilitate adhesion to the substrate.

Description

Technical Field

[0001] The present invention relates to the technical field of primers for polyurethane adhesives, and in particular to a polyurethane film-forming agent and a preparation method thereof, and a polyurethane primer. Background Art

[0002] Polyurethane adhesives, with their high strength and excellent elasticity, are widely used in various fields, including automotive, rail transportation, electrical appliances, and construction. Although polyurethane adhesives contain a large number of reactive functional groups, which allow them to bond well to some substrates, they exhibit relatively high tensile strength, but their adhesion to substrates such as glass, steel, and plastic is poor, and their application performance is also limited, requiring the use of a primer.

[0003] To this end, people hope to improve the bonding effect and construction performance of polyurethane adhesives by developing suitable primers. For example, Chinese patent application CN 106752838A discloses a polyurethane sealant primer. This primer uses a self-made silane-terminated polyurethane polymer and a modified polyurethane as base materials. In particular, the use of polyacrylic polyol to introduce an acrylic component significantly improves the primer's environmental adaptability. The polyurethane sealant primer exhibits good fluidity and can quickly form a film on substrates such as glass, ceramics, and metals. It also exhibits strong adhesion to both these substrates and the polyurethane sealant. The isocyanate-modified acrylate prepolymer has excellent film-forming properties, facilitates rapid surface drying of the primer, and exhibits excellent adhesion to the substrate, promoting adhesion between the primer and the substrate. The primer disclosed in this patent application exhibits strong adaptability to substrates, good adhesion to various substrates such as fiberglass reinforced plastics, ceramics, and glass, and exhibits excellent water resistance, heat resistance, and humidity and heat resistance. It has a short dry-to-air time, a long open time, and a prolonged period for adhesive application after primer application.

[0004] However, the primer disclosed in the aforementioned patent application has a low film hardness after forming. This can easily cause the primer to crack after forming when subjected to external forces such as vibration or collision during construction. This not only affects product yield but also increases construction time. Furthermore, during the winter or in low-temperature environments when manufacturing vehicle windows or insulating glass, debonding often occurs during construction due to the polyurethane adhesive's poor initial adhesion and low initial bond strength, resulting in low product yield and high costs. Summary of the Invention

[0005] In view of this, an object of the present invention is to solve the problem that the paint film strength is low after the primer is formed and it is easily broken by external force; to this end, the present invention provides a polyurethane film-forming agent with higher strength and a preparation method thereof.

[0006] Another object of the present invention is to solve the problem of easy debonding of polyurethane adhesives when applied on substrates such as glass, anodized aluminum, and electrophoretic painted steel sheets in winter or at relatively low temperatures, thereby improving product yield and reducing costs. To this end, the present invention also provides a polyurethane primer having high film strength after film formation, which is beneficial for improving the low-temperature initial adhesion and bonding strength of the polyurethane adhesive.

[0007] The present invention achieves the above-mentioned object through the following technical solutions:

[0008] A polyurethane film-forming agent, mainly prepared by polymerization reaction of the following raw materials in molar fractions:

[0009] 50-80 parts of small molecule triol, 20-50 parts of diethylenetriamine, 295-305 parts of diisocyanate and 5-40 parts of diamine, wherein the sum of the molar parts of the small molecule triol and the diethylenetriamine is 100 parts, and the small molecule triol is trimethylolpropane, propylene glycol or any combination thereof.

[0010] The diisocyanate is HDI (1,6-hexamethylene diisocyanate), IPDI (isophorone diisocyanate) or TDI (toluene diisocyanate).

[0011] The diamine is preferably ethylenediamine, 1,2-propylenediamine, 1,3-propylenediamine or pentamethylenediamine.

[0012] A method for preparing the aforementioned polyurethane film-forming agent comprises first polymerizing a small molecule triol and a diisocyanate, followed by reaction with a mixture of diethylenetriamine and a diamine. Because the reaction of hydroxyl groups with isocyanate groups requires relatively high temperatures, and amino groups are highly reactive with isocyanate groups, the small molecule triol must be reacted with the diisocyanate first to avoid excessive viscosity during the subsequent reaction of the hydroxyl groups, necessitating the addition of a solvent, and resulting in incomplete reaction.

[0013] Based on the above, a small molecule triol and a diisocyanate are first polymerized in a nitrogen environment and diluted with a first solvent to form a first prepolymer mixture. A polyamine dilution is then added dropwise to the first prepolymer mixture for reaction, and a catalyst is added to continue the reaction to produce the polyurethane film-forming agent. The polyamine dilution comprises a uniform mixture of diethylenetriamine, a diamine, and a second solvent. The catalyst is added in this step to ensure complete reaction of all raw materials. The catalyst is added last because amino groups are highly reactive. If added earlier, the reaction will be more intense and difficult to control.

[0014] Among them, the step of forming the first prepolymer mixed liquid includes: dehydrating the small molecule triol at 80°C to 90°C and a vacuum degree lower than -0.095MPa for 2 to 3 hours, then lowering the temperature to 70°C to 75°C, adding diisocyanate under nitrogen protection conditions for reaction for 1 to 2 hours, then adding the first solvent for dilution for 15 to 45 minutes, and then lowering the temperature to 20°C to 30°C to obtain the first prepolymer mixed liquid.

[0015] The steps of preparing the polyurethane film-forming agent include: uniformly diluting a mixture of triamine and diamine with the second solvent to obtain the polyamine dilution liquid; slowly adding the polyamine dilution liquid dropwise to the first prepolymer mixture, continuing the reaction for 30 to 60 minutes after the addition is complete, then heating to 70 to 75° C., continuing the reaction for 30 to 60 minutes, and then adding a catalyst to continue the reaction for 1 to 2 hours.

[0016] In order to reduce the viscosity of the reaction system to an appropriate value, a first solvent is set. Preferably, the amount of the first solvent is 50% to 100% of the total mass of the small molecule triol and the diisocyanate, and the first solvent is one or a combination of two of ethyl acetate, butyl acetate, butanone, toluene, and xylene.

[0017] In order to reduce the concentration of the mixture of triamine and diamine and thereby control the reaction rate between amino groups and isocyanate groups, a second solvent is added to dilute the mixture of triamine and diamine. Preferably, the amount of the second solvent is 100% to 200% of the total mass of the triamine and diamine. The second solvent is one or a combination of ethyl acetate, butyl acetate, butanone, toluene, and xylene.

[0018] In order to make the reaction of the above system more complete, preferably, the amount of the catalyst used is 0.03% to 0.1% of the total mass of the small molecule triol and the diisocyanate. The catalyst is dibutyltin dilaurate or dibutyltin dichloride.

[0019] A polyurethane primer comprises the following raw materials, calculated by mass: 150 parts of the above-mentioned polyurethane film-forming agent, 20-70 parts of triphenylisocyanate thiophosphate solution (TPTI), 30-80 parts of an adhesive auxiliary agent, and 100-300 parts of a fourth solvent.

[0020] Preferably, the polyurethane primer comprises, by mass, 150 parts of a polyurethane film-forming agent, 30 to 60 parts of TPTI, 35 to 60 parts of an adhesion promoter, and 100 to 220 parts of a fourth solvent.

[0021] The bonding agent is a macromolecule containing an isocyanate group, a silicon-oxygen-carbon bond, and a urea group; for example, a diamine silane coupling agent, aminopropyltriethoxysilane, or bis-γ-trimethoxysilylpropylamine. Preferably, the bonding agent is mainly prepared by polymerization of HDI biuret and monoaminosilane coupling agent. The molar ratio of HDI biuret to monoaminosilane coupling agent is 10:23 to 27. This is so that the bonding agent contains as many silicon-oxygen-carbon structures as possible while also having some isocyanate groups, so that the isocyanate groups can subsequently form a whole with the film-forming agent and TPTI. Preferably, the molar ratio of HDI biuret to monoaminosilane coupling agent is 10:25 to 27.

[0022] Specifically, 100 parts by mass of HDI biuret and 50 to 100 parts by mass of the third solvent are mixed evenly and placed in a water bath at 20 to 30° C. Under nitrogen protection and stirring, the monoaminosilane coupling agent is added dropwise to the water bath. After the addition is complete, stirring is continued for 20 to 40 minutes, and then the temperature is raised to 60 to 70° C. and the reaction is continued for 1.0 to 2.0 hours to prepare the above-mentioned bonding agent.

[0023] The monoaminosilane coupling agent is one or both of aminopropyltrimethoxysilane and bis(3-trimethoxysilylpropyl)amine, preferably bis(3-trimethoxysilylpropyl)amine.

[0024] The third solvent and the fourth solvent are both one or a combination of two of ethyl acetate, butyl acetate, butanone, toluene and xylene.

[0025] Based on the above polyurethane primer, it also includes 3 to 15 parts by mass of glass microspheres. This increases the interfacial area of ​​the primer in contact with the air, which, on the one hand, accelerates the volatilization of the solvent in the primer and accelerates its surface drying. On the other hand, it increases the contact area of ​​the paint film with the air, thereby increasing the probability of its contact with moisture and improving the low-temperature initial adhesion performance of the primer. In addition, the polyurethane primer has a frosted feel after film formation. Preferably, the polyurethane primer includes 5 to 12 parts by mass of glass microspheres, and the glass microspheres have a true density of 0.15 g / cm 3 ~0.70g / cm 3 The hollow microspheres have a particle size D90 between 15 μm and 110 μm, preferably glass microspheres produced by Zhengzhou Shenglait Hollow Microsphere New Materials Co., Ltd.

[0026] The polyurethane primer described above further comprises 0 to 15 parts by weight of a pigment. The pigment is carbon black, titanium dioxide, or iron oxide red. When no pigment is added to the polyurethane primer, the primer has a relatively light film color after forming, making it suitable for use in special occasions. When a pigment is added, the amount of pigment added is preferably 3 to 10 parts by weight.

[0027] The polyurethane primer is mainly prepared by uniformly dispersing its raw materials in a fourth solvent in a nitrogen environment.

[0028] The polyurethane film-forming agent provided by the present invention is mainly a polymer having a high viscosity and containing a certain amount of urea groups, a certain amount of isocyanate groups, and a large amount of carbamate groups, prepared by the reaction of a small molecule triol, a diisocyanate, diethylenetriamine, and a diamine. The polymer comprises trimethylolpropane or propylene glycol and the isocyanate groups in the diisocyanate to form a first prepolymer molecule containing a large amount of isocyanate groups and a large amount of carbamate groups. A mixture of the triamine and the diamine is then added to react to further extend the chain of the first prepolymer molecule, thereby forming a polyurethane film-forming agent having a high viscosity and a substantially semi-solid body. The film-forming agent is a molecule containing a certain amount of isocyanate groups, a certain amount of urea groups, and a certain amount of carbamate groups. Since the polyurethane film-forming agent basically does not contain a soft segment and all functional groups are structures with relatively high strength, the polyurethane film-forming agent is beneficial to improving the strength of the polyurethane primer; due to its high degree of cross-linking and the very small molecular weight of the triol, triamine and diamine, the prepared product contains a certain amount of carbamate groups and a certain amount of urea groups, so its own bulk viscosity is relatively large.

[0029] Therefore, the polyurethane primer provided by the present invention has the following advantages:

[0030] First, the polyurethane primer has a film-forming agent that is a molecule with an extremely high functional group density and a very high viscosity. The added triphenyl isocyanate thiophosphate is a solid and highly active trifunctional isocyanate molecule. The adhesion promoter contains a certain amount of isocyanate groups and has a relatively high viscosity. During curing, the isocyanate groups can react with the isocyanate groups in the film-forming agent and triphenyl isocyanate thiophosphate to form a highly cross-linked continuous whole. The combined effect of the above-mentioned agents can quickly dry and cross-link during use. The resulting paint film has high strength, and the large amount of urea groups contained in the formed film facilitates adhesion to the substrate.

[0031] Second, since the prepared bonding aid contains a large amount of silicon-oxygen-carbon structures, a large number of urea groups, and a certain amount of isocyanate groups, and its functional group density is also very large, during curing, its isocyanate groups can react with the isocyanate groups in the film-forming agent and triphenyl isocyanate thiophosphate to form a highly cross-linked continuous whole, while also introducing a large number of silicon-oxygen-carbon bonds into it. A large number of silicon-oxygen-carbon bonds mainly react with the inorganic interface, and by adding glass microbeads, the surface area of ​​the primer is increased during the drying process, thereby increasing the probability of contact with moisture, increasing the surface drying speed of the primer and the hydrolysis of the silicon-oxygen-carbon bonds. Therefore, the polyurethane primer can improve the low-temperature initial adhesion performance and bonding strength of the polyurethane adhesive to substrates such as glass, stainless steel, and anodized aluminum, which is beneficial to improving the product yield and construction quality of vehicle window manufacturing, insulating glass manufacturing, etc. in low-temperature environments, and the cost is low.

[0032] Third, during the use of the primer, the polyurethane film-forming agent used has a high viscosity and is basically in a semi-solid state. On the one hand, it can quickly dry the primer surface, and on the other hand, it can form a continuous film with high strength, making the primer strong after film formation.

[0033] Fourth, since the urea and carbamate groups contained in the polyurethane film-forming agent are conducive to adhesion to the substrate, some of the amino groups formed by the reaction of isocyanate groups and water in the primer during the cross-linking process do not participate in the film-forming reaction and can react with the polyurethane adhesive, allowing the primer to form adhesion with the polyurethane adhesive. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further described in detail below through specific implementation methods.

[0035] Examples 1 to 5 Polyurethane film-forming agents

[0036] The raw materials of the polyurethane film-forming agents provided in Examples 1 to 5 of the present invention are mainly shown in Table 1 below.

[0037] Table 1 Molar ratio of raw materials of polyurethane film-forming agent

[0038] sample Trimethylolpropane Diamine diisocyanates diethylenetriamine Example 1 50 Ethylenediamine 20 IPDI Isocyanate 295 50 Example 2 80 1,2-Propylenediamine 23 HDI Isocyanate 300 20 Example 3 70 1,3-Propanediamine 40 TDI Isocyanate 305 30 Example 4 60 Pentamethylenediamine 10 IPDI Isocyanate 300 40 Example 5 80 Ethylenediamine 5 IPDI Isocyanate 300 20

[0039] The preparation methods of the polyurethane film-forming agents provided in Examples 1 to 5 are as follows:

[0040] Trimethylolpropane was dehydrated at 85° C. and a vacuum degree of less than -0.095 MPa for 2.5 hours, then the temperature was lowered to 70° C., and the isocyanate shown in Table 1 was added under nitrogen protection for 1.5 hours. Then, a first solvent was added for dilution for 0.5 hours, and the temperature was lowered to about 25° C. to form a first prepolymer mixed solution; wherein the amount of the first solvent was 75% of the total mass of the trimethylolpropane and the corresponding isocyanate. The first solvent used in Examples 1 to 3 was ethyl acetate, the first solvent used in Example 4 was butanone, and the first solvent used in Example 5 was toluene.

[0041] The diamine and diethylenetriamine described in Table 1 were evenly diluted with a second solvent and slowly added dropwise to the first prepolymer mixture. After the addition was complete, the reaction was continued for about 45 minutes, then the temperature was raised to 70° C., the reaction was continued for 45 minutes, and then the catalyst was added and the reaction was continued for 1.5 hours. The amount of the second solvent was 150% of the total mass of the diamine and diethylenetriamine. The second solvent used in Examples 1 to 3 was ethyl acetate, the second solvent used in Example 4 was butanone, and the second solvent used in Example 5 was toluene. The amount of the catalyst used was 0.05% of the total mass of trimethylolpropane and isocyanate. The catalyst used in Examples 1 to 3 was dibutyltin dilaurate, and the catalyst used in Example 4 was dibutyltin dichloride.

[0042] Polyurethane primers of Examples 6 to 10

[0043] The polyurethane primer provided in Examples 6 to 10 of the present invention is mainly obtained by uniformly dispersing the raw materials shown in Table 2 in a fourth solvent in a nitrogen atmosphere.

[0044] Table 2. Ratio of raw materials of adhesive additives by mass

[0045]

[0046] The raw material composition of the bonding agent used in each embodiment in Table 2 is shown in Table 3.

[0047] Table 3 Main raw materials of adhesive additives

[0048]

[0049] The "ratio of the two" in Table 3 refers to the molar ratio of HDI biuret to monoaminosilane coupling agent.

[0050] The bonding agent used in Examples 6 to 10 was prepared by the following method: 100 parts by mass of HDI biuret and 70 parts by mass of the third solvent were mixed evenly and placed in a water bath at about 25° C. Under nitrogen protection, the monoaminosilane coupling agent was added dropwise to the water bath according to the ratio shown in Table 3. After the addition, stirring was continued for about 25 minutes, and then the temperature was raised to about 65° C. and the reaction was continued for 1.5 hours.

[0051] Comparative Example 1

[0052] This comparative example provides a polyurethane primer, which differs from the polyurethane primer provided in Example 7 mainly in that the film-forming agent in this comparative example is a polyurethane sealant prepolymer having the same solid content as the film-forming agent provided in Example 2. Specifically, the polyurethane sealant prepolymer is prepared by dehydrating 100 parts by mass of a 5000 molecular weight trifunctional polyether polyol 330n and 50 parts by mass of a 2000 molecular weight difunctional polyether polyol 2000D at 120° C. and a pressure below −0.095 MPa for 2 h, then cooling the temperature to 70° C., adding 40 parts by mass of MDI and reacting for 2 h, and then adding 0.1 parts by mass of dibutyltin diisocyanate and continuing the reaction for 2 h.

[0053] Comparative Example 2

[0054] This comparative example provides a polyurethane primer, which is mainly different from the polyurethane primer provided in Example 7 in that the bonding aid in this comparative example is r-glycidyloxypropyltrimethoxysilane, which has the same solid content as the bonding aid provided in Example 7.

[0055] Comparative Example 3

[0056] This comparative example provides a polyurethane primer, which is mainly different from the polyurethane primer provided in Example 9 in that the bonding aid in this comparative example is vinyltriethoxysilane, which has the same solid content as the bonding aid provided in Example 9.

[0057] Performance Testing

[0058] The polyurethane primers provided in Examples 6-10 and Comparative Examples 1-3 were applied to clean, dry 50 mm × 40 mm × 6 mm glass and 100 mm × 25 mm × 2 mm anodized aluminum surfaces, respectively, to form polyurethane primer films. The dry-to-air time of the polyurethane primer films, as well as the standard shear strength, low-temperature shear strength, and shear performance of the corresponding polyurethane adhesives, were then tested. The results are shown in Table 4.

[0059] 1) Surface drying time: Apply the primer on a 50mm×40mm×6mm glass surface. Under standard conditions, use gauze to stick to the primer surface. The time required for no obvious marks on the paint film surface is the surface drying time.

[0060] 2) Shear test: A polyurethane adhesive (commercially available Huitian 8960H) was applied to a 50mm×40mm×6mm glass surface coated with primer to a thickness of 3mm and a bonding area of ​​25mm×12.5mm. The adhesive was then attached to a 100mm×25mm×2mm anodized aluminum surface coated with the same primer. The surfaces were cured at standard conditions of 23°C*50%RH and a low temperature of -5°C for 7 days. The shear strength was tested and the failure mode was observed.

[0061] Table 4 Primer performance test table

[0062]

[0063] It can be seen from Table 4 that compared with Comparative Example 1, the surface drying time of the polyurethane primer provided in Example 7 is significantly accelerated, which shows that the film-forming agent provided in the embodiment of the present invention is conducive to accelerating the drying time of the primer.

[0064] Compared with Comparative Examples 2 and 3, the drying time of the polyurethane primer provided by Examples 7 and 9 is faster, and the corresponding standard shear strength and low-temperature shear strength of the polyurethane adhesive are relatively large. This shows that the combination of the bonding aid provided by the embodiments of the present invention and the polyurethane film-forming agent is beneficial to enhancing the bonding strength and low-temperature initial adhesion strength of the polyurethane adhesive, increasing the construction performance in a low-temperature environment, and helping to shorten the construction period.

[0065] From the shear test on the substrate, it can be seen that the polyurethane primer provided by the embodiment of the present invention is beneficial to enhancing the bonding strength of the polyurethane adhesive to substrates such as glass and anodized aluminum.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solutions of the present invention. They should all be included in the scope of the technical solutions claimed for protection by the present invention.

Claims

1. A polyurethane film-forming agent for a polyurethane primer, characterized in that: Prepared by polymerization reaction of the following raw materials in molar proportions: 50-80 parts of a small molecule triol, 20-50 parts of diethylenetriamine, 295-305 parts of a diisocyanate, and 5-40 parts of a diamine, wherein the sum of the molar proportions of the small molecule triol and the diethylenetriamine is 100 parts, the small molecule triol is trimethylolpropane, glycerol, or any combination thereof, and the diamine is ethylenediamine, 1,2-propylenediamine, 1,3-propylenediamine, or pentamethylenediamine; The polyurethane film-forming agent is prepared by the following method: firstly, the small molecule triol and diisocyanate undergo polymerization reaction, and then the reaction is carried out with diethylenetriamine and the diamine.

2. The polyurethane film-forming agent according to claim 1, characterized in that: The diisocyanate is HDI, IPDI or TDI.

3. A method for preparing the polyurethane film-forming agent according to claim 1 or 2, comprising firstly polymerizing a small molecule triol and a diisocyanate, and then reacting the mixture with diethylenetriamine and the diamine.

4. The preparation method according to claim 3, wherein: In a nitrogen environment, the small molecule triol and diisocyanate are first polymerized, and a first solvent is added for dilution to form a first prepolymer mixture; a polyamine dilution liquid is then added dropwise to the first prepolymer mixture for reaction, and then a catalyst is added to continue the reaction to obtain the polyurethane film-forming agent; wherein the polyamine dilution liquid is composed of a uniform mixture of diethylenetriamine, the diamine and a second solvent.

5. The preparation method according to claim 4, characterized in that: The amount of the first solvent used is 50% to 100% of the total mass of the small molecule triol and the diisocyanate; the amount of the second solvent used is 100% to 200% of the total mass of diethylenetriamine and the diamine; and the amount of the catalyst used is 0.03% to 0.1% of the total mass of the small molecule triol and the diisocyanate.

6. A polyurethane primer, characterized in that: The invention comprises the following raw materials in parts by weight: 150 parts of the polyurethane film-forming agent according to claim 1 or 2, 20 to 70 parts of triphenyl isocyanate thiophosphate solution, 30 to 80 parts of an adhesive auxiliary agent, and 100 to 300 parts of a fourth solvent.

7. The polyurethane primer according to claim 6, wherein: The bonding agent is mainly prepared by polymerizing HDI biuret and monoaminosilane coupling agent, and the molar ratio of HDI biuret to monoaminosilane coupling agent is 10:23-27.

8. The polyurethane primer according to claim 6 or 7, characterized in that: The invention also comprises 3 to 15 parts by weight of glass microspheres.

9. The polyurethane primer according to claim 8, characterized in that: It also contains 0 to 15 parts by weight of pigment.

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