A polyurethane casting adhesive - metal bonding gradient primer, its preparation method and application

Abstract

The present invention relates to the technical field of underwater acoustic transducers, and particularly relates to a polyurethane casting adhesive-metal bonding gradient primer, a preparation method and an application thereof. The primer of the primer is made of the following components in parts by mass: 95-105 parts of epoxy resin, 3-5 parts of 2-ethyl-4-methylimidazole, 18-22 parts of polysulfide rubber, 40-80 parts of xylene, and 280-350 parts of filler; the topcoat of the primer is made of the following components in parts by mass: 95-105 parts of epoxy resin, 3-5 parts of 2-ethyl-4-methylimidazole, 18-22 parts of polyurethane prepolymer, and 20-30 parts of xylene. The purpose of the present invention is to improve the stress distribution state on the bonding surface of the polyurethane casting adhesive and the metal, avoid reducing the watertight reliability of the underwater acoustic transducer due to stress concentration, and at the same time reduce the usage limitations. After applying the primer to the metal shell, it is not afraid of being contaminated and can be placed or operated for a long time without affecting the bonding effect.

Description

Technical Field

[0001] The present invention relates to the technical field of underwater acoustic transducers, and particularly relates to a polyurethane casting adhesive-metal bonding gradient primer, a preparation method and an application thereof. Background Art

[0002] Due to the characteristics that the acoustic impedance of polyurethane casting adhesive is relatively matched with water, it can be cast under normal pressure and cured at medium temperature, etc., it is widely used in the encapsulation of high-frequency underwater acoustic transducers. Metal materials such as 316 series stainless steel, titanium alloy, and aluminum alloy are widely used in the shells of underwater acoustic transducers due to their strength, specific strength, stiffness, electromagnetic shielding property, and easy machinability, etc. Therefore, the general structural form of current high-frequency underwater acoustic transducers is shown in Figure 1 . Such as Figure 1 shown. The bonding reliability between the polyurethane casting adhesive and the metal shell is one of the key factors affecting the watertight reliability of underwater acoustic transducers. Polyurethane casting adhesive and metal are extremely heterogeneous materials. The commonly used metal shell materials for underwater acoustic transducers are 316 series stainless steel, aluminum alloy and other materials. The linear expansion coefficient of 316 series stainless steel materials is about 16×10 -6 , the linear expansion coefficient of aluminum alloy materials is about 23.3×10 -6 , and the linear expansion coefficient of polyurethane casting adhesive materials is about 180×10 -6 . The linear expansion coefficient of polyurethane casting adhesive is about an order of magnitude larger than that of 316 series stainless steel, aluminum alloy and other metal materials. After encapsulating the transducer with a metal shell using polyurethane casting adhesive, due to the differences in properties such as linear expansion coefficient, hardness and stiffness, since the linear expansion coefficient of the metal is low and the structural stiffness is much greater than that of the polyurethane casting adhesive, when conditions such as temperature, force, and solvent change, concentrated stress is applied to the polyurethane casting adhesive-metal bonding surface, as shown in Figure 2 . The edge of the polyurethane casting adhesive when it is just cast is a solid line, and the dotted line is the edge after positive and negative changes. Under the action of alternating stress, the concentrated stress is easily released, causing the detachment and damage of the bonding surface, thereby reducing the watertight reliability of the underwater acoustic transducer.

[0003] Currently, in the underwater acoustic transducer industry, the bonding between polyurethane casting glue and metal shell mostly adopts the method of thermosulfurization bonding. That is, first, a series of surface treatments such as roughening, sandblasting, and cleaning are carried out on the metal, then primer adhesives such as Chemlok adhesive, Thixon adhesive, and Cilbond series adhesives are applied, and finally, polyurethane is vulcanized and poured. When it comes to small-sized transducers and short-term use, there are indeed no problems such as the separation and damage of the bonding surface. However, in the case of larger-scale transducers and after long-term use, the phenomenon of the separation and damage of the bonding surface significantly increases. From the statistical data on the failure of high-frequency underwater acoustic transducers currently available, the failure of transducers caused by the separation and damage of the bonding surface is the main factor. The disadvantages of the above adhesives are as follows: First, they are not suitable for larger-scale transducers and long-term use, while transducers must include larger-scale ones and need to be used in water for a long time. Although the above adhesives greatly increase the bonding force between polyurethane casting glue and metal, when performing a peel test immediately after the specimen is made, the internal damage of the polyurethane casting glue occurs in all cases. However, after being placed in a simulated actual use environment for a period of time and then performing a peel test again, the damage occurs between the polyurethane casting glue and the metal, indicating that although the bonding force between the polyurethane casting glue and the metal has increased, the stress concentration phenomenon as shown in Figure 2 has not been improved. With the extension of time and the attenuation of the bonding force, under the action of alternating stress, the concentrated stress is easily released, resulting in the separation and damage of the bonding surface. Second, the above adhesives have many usage restrictions, complex process requirements, and poor weather resistance. After the metal shell is coated with the metal shell, it must be in a clean and dry environment throughout the process, cannot be contaminated in any way, and the PU rubber vulcanization and pouring must be completed in a short time to complete the entire bonding process, otherwise the bonding effect will be seriously affected. Due to the relatively small overall size and single-element size of high-frequency underwater acoustic transducers, it is difficult to adopt a modular design. Therefore, after the surface treatment of the metal shell and the application of primer adhesives such as Chemlok adhesive, Thixon adhesive, and Cilbond series adhesives on the metal shell, multiple processes and a long time cycle are required. It is difficult to avoid contamination of the surface coated with the primer on the metal shell, and the entire cycle is also difficult to be compressed within the requirements of the above primers; at the same time, the functional part of the high-frequency underwater acoustic transducer is very delicate and fragile before encapsulation, and it is difficult to perform surface treatments such as roughening, sandblasting, and cleaning on the whole after being installed with the metal shell. Therefore, it is also impossible to pre-assemble and then operate to meet the applicable range of the primer. Therefore, researching and developing a polyurethane casting glue-metal bonding primer that can not only improve the stress distribution state on the bonding surface between polyurethane casting glue and metal, avoid the separation and damage of the bonding surface caused by stress concentration, thereby reducing the watertight reliability of underwater acoustic transducers, but also reduce the usage restrictions, and can not be afraid of contamination and can be placed or operated for a long time without affecting the bonding effect after applying the primer on the metal shell is of great significance for the field of high-frequency underwater acoustic transducers encapsulated with polyurethane casting glue. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, one of the purposes of the present invention is to provide a polyurethane casting adhesive-metal bonding primer material, which can not only improve the stress distribution state on the polyurethane casting adhesive-metal bonding surface, avoid reducing the watertight reliability of the underwater acoustic transducer due to stress concentration, but also reduce the usage limitations. After applying the primer to the metal shell, it is not afraid of being contaminated and can be placed or operated for a long time without affecting the bonding effect. Another purpose of the present invention is to provide a preparation method of a polyurethane casting adhesive-metal bonding primer. At the same time, the present invention also lies in providing an application of the polyurethane casting adhesive-metal bonding primer in high-frequency underwater acoustic transducers.

[0005] The present invention is achieved through the following technical solutions:

[0006] A polyurethane casting adhesive-metal bonding primer, which is divided into two formulations: the primer base glue and the primer top glue;

[0007] The primer base glue is made of the following components in parts by mass: 95-105 parts of epoxy resin, 3-5 parts of 2-ethyl-4-methylimidazole, 18-22 parts of polysulfide rubber, 40-80 parts of xylene, and 280-350 parts of filler;

[0008] The primer top glue is made of the following components in parts by mass: 95-105 parts of epoxy resin, 3-5 parts of 2-ethyl-4-methylimidazole, 18-22 parts of polyurethane prepolymer, and 20-30 parts of xylene.

[0009] Preferably, the epoxy resin is E-51 epoxy resin.

[0010] Preferably, the polysulfide rubber is liquid polysulfide rubber LP-3.

[0011] Preferably, the filler is any one or several of silicon nitride, silica powder, and silicon carbide.

[0012] Preferably, the polyurethane prepolymer is JA-2S copolymer ether prepolymer produced by Shanxi Research Institute of Chemical Industry.

[0013] The present invention also provides a preparation method of the above-mentioned polyurethane casting adhesive-metal bonding primer, including:

[0014] (1) The preparation steps of the primer base glue are as follows:

[0015] Step 1: Weigh epoxy resin and 2-ethyl-4-methylimidazole in proportion, mix them evenly, then weigh polysulfide rubber in proportion, mix them evenly, then weigh xylene in proportion, mix them evenly, and finally weigh silicon nitride in proportion. After mixing evenly, the primer base glue of the polyurethane casting adhesive-metal bonding primer is obtained;

[0016] Step 2: After sealing, place it in a household refrigerator for later use. If it is not used for a long time, store it in the freezer. If it will be used soon, store it in the refrigerator compartment.

[0017] (2) The preparation steps of the primer and the surface adhesive are as follows:

[0018] Step 1: Weigh epoxy resin and 2-ethyl-4-methylimidazole in proportion and mix them evenly. Then weigh the polyurethane prepolymer in proportion and mix it evenly. Finally, weigh xylene in proportion. After mixing evenly, the primer and surface adhesive of the polyurethane casting adhesive - metal bonding primer are obtained.

[0019] Step 2: After sealing, place it in a household refrigerator for later use. If it is not used for a long time, store it in the freezer. If it will be used soon, store it in the refrigerator compartment.

[0020] The present invention also provides the application of the above-mentioned polyurethane casting adhesive - metal bonding primer in high-frequency underwater acoustic transducers. A series of surface treatments such as roughening, sandblasting, and cleaning are performed on the bonding surface between the metal shell of the high-frequency underwater acoustic transducer and the polyurethane casting adhesive. Then it is preheated in a heating and drying oven, and then the primer of this polyurethane casting adhesive - metal bonding primer is applied. It is put into the heating and drying oven for preliminary curing. After preliminary curing, the surface adhesive of this polyurethane casting adhesive - metal bonding primer is applied, and then it is put into the heating and drying oven for curing. After curing is completed, it is cooled to room temperature with the heating and drying oven. After taking it out, normal functional part assembly is carried out. After the assembly is completed, the surface of the metal shell coated with the primer is finally cleaned, and then the high-frequency underwater acoustic transducer is put into a sealed mold for polyurethane vulcanization perfusion.

[0021] Preferably, the temperatures for preheating, preliminary curing, and curing in the heating and drying oven are 110 °C. The preheating time is not less than 2 h, the preliminary curing time is 0.8 h, and the curing time is 1 h.

[0022] Preferably, the thickness of the primer is 0.1 - 1 mm and it can be coated repeatedly for multiple times; the thickness of the surface adhesive is 0.05 - 0.5 mm and it can be coated repeatedly for multiple times.

[0023] Preferably, the time period for completing the assembly is not limited. It can be several days or several months, as long as the surface of the metal shell coated with the primer is cleaned before vulcanization perfusion. The cleaning of the surface of the metal shell coated with the primer after the assembly is completed refers to degreasing treatment with acetone, No. 120 gasoline, etc.

[0024] The present invention has the following beneficial effects:

[0025] 1. The polyurethane casting adhesive - metal bonding primer of the present invention is composed of a primer base and a primer topcoat. The primer base is prepared from epoxy resin, 2 - ethyl - 4 - methylimidazole, polysulfide rubber, xylene, and fillers such as silicon nitride (silica powder, silicon carbide). It can be stored for a long time in years under freezing conditions and also for a long time in months under refrigeration conditions. 2 - ethyl - 4 - methylimidazole is a viscous liquid at room temperature, which is easier to formulate and disperse compared to imidazole that is a solid at room temperature. Polysulfide rubber is a toughening agent to increase the flexibility of the primer. Xylene is a non - reactive diluent that can adjust the fluidity to make it easy to coat and infiltrate the metal surface. The addition of fillers such as silicon nitride makes the stiffness, strength, coefficient of linear expansion, etc. of the primer material similar to those of the metal shell, thus reducing the internal stress between the primer and the metal; The primer topcoat is prepared from epoxy resin, 2 - ethyl - 4 - methylimidazole, polyurethane prepolymer, xylene, etc. It can also be stored for a long time in years under freezing conditions and for a long time in months under refrigeration conditions. The polyurethane prepolymer is a toughening agent that can not only increase the flexibility of the primer but also increase the adhesion to the polyurethane casting adhesive. The present invention specifically defines the mass fractions of each component to enable the synergistic effect of each component, achieving a gradient distribution of the material properties among the metal - primer base - primer topcoat - polyurethane casting adhesive, dispersing the stress on the polyurethane casting adhesive - metal bonding surface, such as Figure 3 , avoiding the peeling and damage of the polyurethane casting adhesive - metal bonding surface due to stress concentration, thereby improving the watertight reliability of the underwater acoustic transducer.

[0026] 2. The present invention can also reduce the usage restrictions. After the primer is coated on the metal shell, it can be placed for a long time, having sufficient operation time, expanding its application range, and meeting the environmental protection requirements. It can be used for batch - processing and warehousing of workpieces to be processed, etc. At the same time, since its coating surface is a fully cured toughened epoxy resin, it is not afraid of being contaminated during the operation process. As long as it is simply cleaned before bonding with the polyurethane casting adhesive, the bonding quality can be ensured. It effectively solves the problems that the existing primers are not suitable for transducers with larger scales, have many usage restrictions, complex process requirements, and poor weather resistance, etc., improving the operation space and watertight reliability of high - frequency underwater acoustic transducers, and having significant economic and social benefits.

[0027] 3. The preparation method of the polyurethane casting adhesive - metal bonding primer of the present invention is simple in operation, has low requirements for equipment, is easy to control the process, and is suitable for industrialized popularization and application.

[0028] 4. The polyurethane casting adhesive - metal bonding primer of the present invention is used for high - frequency underwater acoustic transducers, which not only greatly improves the watertight reliability of high - frequency underwater acoustic transducers but also simplifies the process flow and process control of high - frequency underwater acoustic transducers. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0030] Figure 1 This is the general structure diagram of the high-frequency underwater acoustic transducer of the present invention; in the figure: 101 - metal shell, 102 - transducer, 103 - polyurethane casting glue.

[0031] Figure 2 This is a schematic diagram of the concentrated stress on the polyurethane casting glue - metal bonding surface of the present invention; in the figure: 201 - metal shell, 202 - polyurethane casting glue, 203 - stress concentration point.

[0032] Figure 3 This is a schematic diagram of the material gradient distribution among the metal - primer glue base - primer glue top - polyurethane casting glue of the present invention; in the figure: 301 - metal shell, 302 - primer glue base, 303 - primer glue top, 304 - polyurethane casting glue. Detailed implementation manners

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0034] Embodiment 1

[0035] A polyurethane casting glue - metal bonding primer glue, which is divided into two formulations: primer glue base and primer glue top; the primer glue base is made of the following components in parts by mass: 95 parts of E - 51 epoxy resin, 3 parts of 2 - ethyl - 4 - methylimidazole, 22 parts of LP - 3 liquid polysulfide rubber, 40 parts of xylene, and 300 parts of silicon nitride; the primer glue top is made of the following components in parts by mass: 95 parts of E - 51 epoxy resin, 3 parts of 2 - ethyl - 4 - methylimidazole, 20 parts of JA - 2S copolymer ether prepolymer, and 25 parts of xylene.

[0036] This embodiment uses a 2 - mm - thick 316L stainless steel anti - peeling specimen, including the following steps:

[0037] Step S1: After the stainless steel bonding surface is cleaned with No. 120 gasoline and dried, it is sand - blasted on one side.

[0038] Step S2: Place the 316L stainless steel plate into the mold and preheat it at 110°C for 2 h; apply the primer of the polyurethane casting adhesive - metal bonding primer, with a thickness of about 0.2 mm, and the initial curing time at 110°C is 0.8 h;

[0039] Step S3: Apply the topcoat of the polyurethane casting adhesive - metal bonding primer, with a thickness of about 0.1 mm, and the curing time at 110°C is 1 h;

[0040] Step S4: Pour the polyurethane casting adhesive and cure it at 110°C for 5 h.

[0041] Test results: After completion, for the cured 316L stainless steel peel - resistant specimens, after cooling to room temperature and standing for 24 h, the peel strength was tested, and all were greater than 12 kN / m, and the failure was cohesive failure of the polyurethane casting adhesive; when immersed in artificial seawater, during the working hours of weekdays, it was heated to 60°C, and at other times, it followed the room temperature. After 3 months of accelerated aging, the peel strength was tested, and all were greater than 9 kN / m, and the failure was cohesive failure of the polyurethane casting adhesive.

[0042] Example 2

[0043] A polyurethane casting adhesive - metal bonding primer, which is divided into two formulations: primer and topcoat; the primer is made of the following components in parts by mass: 100 parts of E - 51 epoxy resin, 4 parts of 2 - ethyl - 4 - methylimidazole, 18 parts of LP - 3 liquid polysulfide rubber, 60 parts of xylene, 320 parts of silicon nitride; the topcoat is made of the following components in parts by mass: 100 parts of E - 51 epoxy resin, 3.5 parts of 2 - ethyl - 4 - methylimidazole, 18 parts of JA - 2S copolymer polyether prepolymer, 20 parts of xylene.

[0044] In this example, a 2 - mm - thick 316L stainless steel peel - resistant specimen was used, and the following steps were included:

[0045] Step S1: After cleaning the stainless steel bonding surface with No. 120 gasoline and drying it, perform sandblasting on one side;

[0046] Step S2: Place the 316L stainless steel plate into the mold and preheat it at 110°C for 2 h; apply the primer of the polyurethane casting adhesive - metal bonding primer, with a thickness of about 0.2 mm, and the initial curing time at 110°C is 0.8 h;

[0047] Step S3: Apply the topcoat of the polyurethane casting adhesive - metal bonding primer, with a thickness of about 0.1 mm, and the curing time at 110°C is 1 h;

[0048] Step S4: Pour the polyurethane casting adhesive and cure it at 110°C for 5 h.

[0049] Test results: After the test, the cured 316L stainless steel anti-peeling specimen was cooled to room temperature and left standing for 24 hours before testing the anti-peeling strength. The strength was greater than 12 kN / m in all cases, and the failure mode was cohesive failure within the polyurethane casting adhesive. When immersed in artificial seawater, the temperature was raised to 60 °C during the working hours on weekdays, and the rest of the time followed the room temperature. After 3 months of accelerated aging, the anti-peeling strength was tested, and it was greater than 9 kN / m in all cases, and the failure mode was cohesive failure within the polyurethane casting adhesive.

[0050] Example 3

[0051] A polyurethane casting adhesive-metal bonding primer, which is divided into two formulations: the primer for the primer coating and the primer for the primer coating surface. The primer for the primer coating is made of the following components in parts by mass: 98 parts of E-51 epoxy resin, 5 parts of 2-ethyl-4-methylimidazole, 20 parts of LP-3 liquid polysulfide rubber, 80 parts of xylene, and 350 parts of silicon nitride; the primer for the primer coating surface is made of the following components in parts by mass: 102 parts of E-51 epoxy resin, 4.5 parts of 2-ethyl-4-methylimidazole, 19 parts of JA-2S copolymer polyether prepolymer, and 28 parts of xylene.

[0052] In this example, a 2-mm-thick 316L stainless steel anti-peeling specimen was used, and the following steps were included:

[0053] Step S1: After the stainless steel bonding surface was cleaned with No. 120 gasoline and dried, it was treated with sandblasting on one side.

[0054] Step S2: The 316L stainless steel plate was preheated at 110 °C for 2 hours; the primer for the primer coating of the polyurethane casting adhesive-metal bonding primer was applied, with a thickness of about 0.2 mm, and the initial curing time at 110 °C was 0.8 h.

[0055] Step S3: The primer for the primer coating surface of the polyurethane casting adhesive-metal bonding primer was applied, with a thickness of about 0.1 mm, and the curing time at 110 °C was 1 h.

[0056] Step S4: After cooling to room temperature with the drying oven, it was placed in the workshop, and the process of transducer assembly was simulated for repeated grasping and moving, and some oil stains were intentionally contacted.

[0057] Step S5: After ten days, the primer-coated part of the 316L stainless steel plate was cleaned with acetone.

[0058] Step S6: The 316L stainless steel plate was installed in the mold, and at the same time, it was preheated at 110 °C for 2 hours; the polyurethane casting adhesive was poured, and it was cured at 110 °C for 5 hours.

[0059] Test results: After the test, the cured 316L stainless steel anti-peeling sample was cooled to room temperature and left standing for 24 hours before testing the anti-peeling strength. All values were greater than 12 kN / m, and the failure mode was cohesive failure within the polyurethane casting adhesive. When immersed in artificial seawater, the temperature was raised to 60 °C during the working hours of weekdays and left at room temperature for the rest of the time. After 3 months of accelerated aging, the anti-peeling strength was tested, and all values were greater than 9 kN / m, and the failure mode was cohesive failure within the polyurethane casting adhesive.

[0060] Example 4

[0061] A polyurethane casting adhesive - metal bonding primer, which is divided into two formulations: the primer base and the primer topcoat. The primer base is made of the following components in parts by mass: 105 parts of E-51 epoxy resin, 3.5 parts of 2-ethyl-4-methylimidazole, 21 parts of LP-3 liquid polysulfide rubber, 70 parts of xylene, and 280 parts of silicon nitride. The primer topcoat is made of the following components in parts by mass: 103 parts of E-51 epoxy resin, 5 parts of 2-ethyl-4-methylimidazole, 22 parts of JA-2S copolymer polyether prepolymer, and 30 parts of xylene.

[0062] In this example, a 2-mm-thick 316L stainless steel anti-peeling sample was used, and the following steps were included:

[0063] Step S1: After cleaning the stainless steel bonding surface with No. 120 gasoline and drying it, one side was treated with sandblasting.

[0064] Step S2: Preheat the 316L stainless steel plate at 110 °C for 2 hours; apply the primer base of the polyurethane casting adhesive - metal bonding primer, with a thickness of about 0.2 mm, and the initial curing time at 110 °C is 0.8 h.

[0065] Step S3: Apply the primer topcoat of the polyurethane casting adhesive - metal bonding primer, with a thickness of about 0.1 mm, and the curing time at 110 °C is 1 h.

[0066] Step S4: After cooling to room temperature with the drying oven, place it in the workshop, simulate the process of transducer assembly, and perform repeated grasping and moving, and intentionally come into contact with some oil stains.

[0067] Step S5: After ten days, clean the primer-coated part of the 316L stainless steel plate with No. 120 gasoline.

[0068] Step S6: Place the 316L stainless steel plate in the mold, and at the same time preheat it at 110 °C for 2 hours; pour the polyurethane casting adhesive, and cure it at 110 °C for 5 hours.

[0069] Test results: After the test, the cured 316L stainless steel anti-peeling specimen was cooled to room temperature and left to stand for 24 hours before testing the anti-peeling strength. All values were greater than 12 kN / m, and the failure mode was cohesive failure of the polyurethane casting adhesive. When immersed in artificial seawater, it was heated to 60 °C during working hours on weekdays and at room temperature for the rest of the time. After 3 months of accelerated aging, the anti-peeling strength was tested, and all values were greater than 9 kN / m, and the failure mode was cohesive failure of the polyurethane casting adhesive.

[0070] Example 5

[0071] A polyurethane casting adhesive - metal bonding primer, which is divided into two formulations: primer base and primer topcoat. The primer base is made of the following components in parts by mass: 102 parts of E-51 epoxy resin, 4.5 parts of 2-ethyl-4-methylimidazole, 19 parts of LP-3 liquid polysulfide rubber, 50 parts of xylene, and 290 parts of silicon nitride. The primer topcoat is made of the following components in parts by mass: 105 parts of E-51 epoxy resin, 4 parts of 2-ethyl-4-methylimidazole, 21 parts of JA-2S copolymer polyether prepolymer, and 23 parts of xylene.

[0072] In this example, a 2-mm-thick 316L stainless steel anti-peeling specimen was used, and the following steps were included:

[0073] Step S1: After cleaning the stainless steel bonding surface with No. 120 gasoline and drying it, it was sandblasted on one side.

[0074] Step S2: The 316L stainless steel plate was preheated at 110 °C for 2 hours; the primer base of the polyurethane casting adhesive - metal bonding primer was applied, with a thickness of about 0.2 mm, and the initial curing time at 110 °C was 0.8 h.

[0075] Step S3: The primer topcoat of the polyurethane casting adhesive - metal bonding primer was applied, with a thickness of about 0.1 mm, and the curing time at 110 °C was 1 h.

[0076] Step S4: After cooling to room temperature with the drying oven, it was placed in the workshop, and the process of transducer assembly was simulated for repeated grasping and moving, and it was intentionally contacted with some oil stains.

[0077] Step S5: After ten days, the primer-coated part of the 316L stainless steel plate was cleaned with No. 120 gasoline.

[0078] Step S6: The 316L stainless steel plate was installed in the mold and preheated at 110 °C for 2 hours at the same time; the polyurethane casting adhesive was poured and cured at 110 °C for 5 hours.

[0079] Test results: After the test, for the cured 316L stainless steel anti-peeling specimens, after cooling to room temperature and standing for 24 hours, the anti-peeling strength was tested, and all were greater than 12 kN / m. The failure was all cohesive failure of the polyurethane casting adhesive. When immersed in artificial seawater, the temperature was heated to 60 °C during the working hours on weekdays, and the rest was at room temperature. After accelerating aging for 3 months, the anti-peeling strength was tested, and all were greater than 9 kN / m. The failure was all cohesive failure of the polyurethane casting adhesive.

[0080] Comparative Example 1:

[0081] This embodiment uses a 2-mm-thick 316L stainless steel anti-peeling specimen, and includes the following steps:

[0082] Step S1: After cleaning the stainless steel bonding surface with No. 120 gasoline and drying it, perform sandblasting treatment on one side.

[0083] Step S2: Apply Chemlok218 adhesive according to the usage instructions.

[0084] Step S3: Install the 316L stainless steel plate in the mold and preheat it at 110 °C at the same time.

[0085] Step S4: Pour the polyurethane casting adhesive and cure it at 110 °C for 5 hours.

[0086] Test results: After the test, for the cured 316L stainless steel anti-peeling specimens, after cooling to room temperature and standing for 24 hours, the anti-peeling strength was tested, and all were greater than 12 kN / m. The failure was all cohesive failure of the polyurethane casting adhesive. When immersed in artificial seawater, the temperature was heated to 60 °C during the working hours on weekdays, and the rest was at room temperature. After accelerating aging for 3 months, the anti-peeling strength was basically zero, and it peeled off with a slight tear by hand. The failure was all the bonding interface failure between the polyurethane casting adhesive and the 316L stainless steel.

[0087] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polyurethane casting adhesive - metal bonding primer, characterized in that, The primer is divided into two formulations: primer base glue and primer top glue; The primer base glue is made of the following components in parts by mass: 95 - 105 parts of epoxy resin, 3 - 5 parts of 2 - ethyl - 4 - methylimidazole, 18 - 22 parts of polysulfide rubber, 40 - 80 parts of xylene, and 280 - 350 parts of filler; The primer top glue is made of the following components in parts by mass: 95 - 105 parts of epoxy resin, 3 - 5 parts of 2 - ethyl - 4 - methylimidazole, 18 - 22 parts of polyurethane prepolymer, and 20 - 30 parts of xylene; The epoxy resin is E - 51 epoxy resin; the polysulfide rubber is liquid polysulfide rubber LP - 3; the filler is any one or several of silicon nitride, silica powder, and silicon carbide; the polyurethane prepolymer is JA - 2S copolymer ether prepolymer.

2. The preparation method of a polyurethane casting adhesive - metal bonding primer according to claim 1, characterized in that, Including: (1) The preparation steps of the primer base glue are as follows: Step 1: Weigh epoxy resin and 2 - ethyl - 4 - methylimidazole according to the ratio, mix them evenly, then weigh polysulfide rubber according to the ratio, mix them evenly, then weigh xylene according to the ratio, mix them evenly, and finally weigh silicon nitride according to the ratio. After mixing evenly, the primer base glue of the polyurethane casting adhesive - metal bonding primer is obtained; Step 2: Seal it and place it in a household refrigerator for standby. If it is not used for a long time, put it in the freezer for storage. If it will be used soon, put it in the refrigerator for storage; (2) The preparation steps of the primer top glue are as follows: Step 1: Weigh epoxy resin and 2 - ethyl - 4 - methylimidazole according to the ratio, mix them evenly, then weigh polyurethane prepolymer according to the ratio, mix them evenly, and finally weigh xylene according to the ratio. After mixing evenly, the primer top glue of the polyurethane casting adhesive - metal bonding primer is obtained; Step 2: Seal it and place it in a household refrigerator for standby. If it is not used for a long time, put it in the freezer for storage. If it will be used soon, put it in the refrigerator for storage.

3. The application of a polyurethane casting adhesive-metal bonding primer as described in claim 1 in high-frequency underwater acoustic transducers, characterized in that, Roughen, sandblast, and clean the bonding surface of the metal shell of the high - frequency underwater acoustic transducer and the polyurethane casting adhesive. Preheat it in a heating and drying oven, then apply the primer base glue of this polyurethane casting adhesive - metal bonding primer, and put it in the heating and drying oven for preliminary curing. After preliminary curing, apply the primer top glue of this polyurethane casting adhesive - metal bonding primer, and then put it in the heating and drying oven for curing; after curing is completed, cool it to room temperature with the heating and drying oven, take it out and perform normal functional part assembly. After assembly is completed, finally clean the surface of the metal shell where the primer is applied, and then put the high - frequency underwater acoustic transducer into the encapsulated mold for polyurethane vulcanization perfusion.

4. The application of a polyurethane casting adhesive - metal bonding primer as described in claim 3 in high - frequency underwater acoustic transducers, characterized in that, The temperatures for preheating, preliminary curing, and curing in the heating and drying oven are 110 °C. The preheating time is not less than 2 h, the preliminary curing time is 0.8 h, and the curing time is 1 h.

5. The application of a polyurethane casting adhesive - metal bonding primer as described in claim 3 in high - frequency underwater acoustic transducers, characterized in that, The thickness of the primer base glue is 0.1 - 1 mm, and multiple repeated coatings are selected during coating; the thickness of the primer top glue is 0.05 - 0.5 mm, and multiple repeated coatings are selected during coating.

6. The application of a polyurethane casting adhesive - metal bonding primer as described in claim 3 in high-frequency underwater acoustic transducers, characterized in that, The time period for completing the assembly is not limited, as long as the surface of the metal shell where the primer is applied is cleaned before vulcanization perfusion; the cleaning of the surface of the metal shell where the primer is applied after assembly is completed refers to degreasing treatment with acetone and No. 120 gasoline.

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