Treatment method for improving binding force of metal and lacquer

Abstract

The invention discloses a treatment method for improving binding force of metal and lacquer, which comprises the following steps: S1, coating primer on the surface of the metal, and curing to obtain a primer layer; the primer is prepared from the following components in parts by weight: 40 to 50 parts of Chinese lacquer, 10 to 15 parts of tung oil and 5 to 8 parts of lithopone; and S2, the primer layer is coated with lacquer, and a finish paint layer is obtained after curing. The invention further discloses the titanium metal / lacquer composite material obtained through the treatment method. According to the treatment method for improving the binding force of the metal and the lacquer, the stability after the metal and the lacquer are combined can be improved, and meanwhile the physical performance of the titanium metal and the attractiveness and protection performance of the lacquer are reserved.

Description

Technical Field

[0001] The present invention relates to the technical field of material surface treatment and process manufacturing, and particularly relates to a treatment method for improving the bonding strength between metal and Chinese lacquer. Background Art

[0002] Titanium metal has excellent properties such as high strength, light weight, and strong corrosion resistance, and is widely used in fields such as aerospace, medical devices, and high-end jewelry. Chinese lacquer, as a traditional natural paint in China, has a unique aesthetic texture and good weather resistance and wear resistance. However, the surface of titanium metal is extremely smooth and its chemical properties are relatively stable, making it difficult for Chinese lacquer to adhere to its surface. Existing bonding processes often have problems such as poor bonding strength and easy peeling of the paint layer, making it difficult to fully utilize the advantages of both and meet the requirements of high-quality products. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a process method that can firmly bond titanium metal and Chinese lacquer, improve the stability after their combination, and at the same time retain the physical properties of titanium metal and the aesthetic and protective properties of Chinese lacquer.

[0004] To solve the above technical problem, the present invention provides the following technical solutions:

[0005] The present invention provides a treatment method for improving the bonding strength between metal and Chinese lacquer, comprising the following steps:

[0006] S1. Coat a primer on the metal surface and obtain a primer layer after curing; the primer is composed of the following components by weight: 40-50 parts of Chinese lacquer, 10-15 parts of tung oil, and 5-8 parts of lithopone;

[0007] S2. Coat Chinese lacquer on the primer layer and obtain a topcoat layer after curing.

[0008] For titanium metal, its surface is extremely smooth and its chemical properties are relatively stable, making it difficult for Chinese lacquer to adhere to its surface. Existing bonding processes often have problems such as poor bonding strength and easy peeling of the paint layer.

[0009] In the present invention, through long-term experimental research, the inventor has proposed a treatment method for improving the bonding strength between metal and Chinese lacquer. Specifically, the inventor has proposed a special primer formulation, which is composed of 40-50 parts of Chinese lacquer, 10-15 parts of tung oil, and 5-8 parts of lithopone. A primer layer is first coated on the titanium metal surface before coating Chinese lacquer, and this primer layer is beneficial to improving the bonding strength between Chinese lacquer and titanium metal.

[0010] Traditional lacquer technology rarely considers adding extra ingredients for adapting to titanium metal. The primer of this technology scientifically compound lacquer, tung oil and lithopone. Tung oil improves the problems of slow drying and poor flexibility of lacquer, making the primer cure faster and fit well with titanium metal; lithopone enhances the covering power and initial adhesion force, enabling the subsequent lacquer layer to adhere more firmly, thus rewriting the inherent idea of traditional lacquer priming.

[0011] Furthermore, the treatment method of the present invention is not only applicable to titanium metal, but also applicable to other metals, and the present invention does not limit this.

[0012] Furthermore, the thickness of the primer layer coated on the metal surface is preferably 20 - 30μm, for example, it can be 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, etc.

[0013] Furthermore, the method of coating the primer is preferably by air spraying, and the spraying pressure is preferably 0.3 - 0.5Mpa, for example, it can be 0.3Mpa, 0.4Mpa, 0.5Mpa, etc. After spraying, it is left standing at room temperature for drying and curing to initially cure the primer and enhance the initial combination of lacquer and titanium metal. Among them, "room temperature" in the present invention refers to 10 - 30°C, and the standing time is 24 - 36 hours, for example, it can be 24 hours, 25 hours, 28 hours, 30 hours, 32 hours, 36 hours, etc.

[0014] Furthermore, in some preferred embodiments, in step S1, before coating the primer, there is also a step of surface pretreatment of the metal to further improve the grip force between the lacquer layer and the metal. The surface pretreatment includes soaking in the pretreatment liquid at room temperature for 10 - 15 minutes; among them, the pretreatment liquid is composed of the following components by weight: 5 - 10 parts of hydrofluoric acid, 3 - 6 parts of nitric acid, and 80 - 90 parts of water.

[0015] When the traditional technology deals with the combination of metal and lacquer, there is a lack of a pretreatment liquid specifically formulated for the chemical properties of titanium metal. This technology uses a pretreatment liquid prepared by mixing hydrofluoric acid, nitric acid and water in a specific ratio. Among them, hydrofluoric acid can precisely create a microscopic rough structure on the surface of titanium metal, and nitric acid can control the corrosion rate, avoiding excessive corrosion and creating ideal conditions for the subsequent adhesion of lacquer.

[0016] Furthermore, the surface pretreatment also includes: taking out the metal after soaking treatment with the pretreatment liquid, rinsing it with clean water, and then putting it into an alkaline degreasing liquid at 80 - 90°C for ultrasonic cleaning for 5 - 10 minutes, and drying it after cleaning. Among them, the alkaline degreasing liquid includes but is not limited to 5wt% sodium hydroxide.

[0017] In the present invention, in addition to soaking in the acid solution, ultrasonic cleaning is carried out with an alkaline degreasing solution at 80-90 °C, followed by drying. Compared with the traditional simple cleaning, this multi-step combination can deeply clean the surface of titanium metal, thoroughly remove oil and impurities, provide an ideal substrate with ultra-cleanliness and uniform micro-etching pits for the attachment of Chinese lacquer, and greatly enhance the grip between the lacquer layer and the metal.

[0018] Further, in step S2, the method of coating Chinese lacquer is preferably: scraping and coating 2-3 layers with a horn spatula, and the thickness of each layer is controlled at 0.1-0.2 mm.

[0019] Further, in the preferred embodiment, after each layer is coated, it is placed in a shady drying room with a humidity of 70-80% and a temperature of 25-30 °C for drying for 48-72 hours; after the last layer of Chinese lacquer is dried, it is heated in an oven at 60-80 °C for 2-3 hours for curing to obtain a topcoat layer.

[0020] In the past, most Chinese lacquer processes followed a fixed drying rhythm. The process of the present invention first dries in a shady drying room with specific humidity and temperature, using the natural environment to preliminarily crosslink the Chinese lacquer; then it is heated in an oven at 60-80 °C. Through the combination of high and low temperatures, it promotes the deep curing of the Chinese lacquer, forming a dense bond with the primer and titanium metal. This fine step-by-step curing process far exceeds the traditional single drying mode and ensures long-term stability.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. Through the special pretreatment liquid formula and treatment process of the present invention, the adhesion of Chinese lacquer on the surface of titanium metal is significantly improved. After testing, the adhesion is 2-3 times higher than that of the traditional process, overcoming the long-standing problem of poor bonding between the two, and achieving a qualitative leap in the durability of the product.

[0023] 2. The traditional Chinese lacquer process is limited by the poor bonding with metals and is difficult to apply in the fields of high-end cultural and creative products and art ornaments. The composite material prepared by the process provided by the present invention not only has the high strength and corrosion resistance of titanium metal, but also has the unique luster and texture of Chinese lacquer, broadening the application scenarios of the material in the fields of high-end cultural and creative products and art ornaments, and meeting the personalized and high-quality market demands. Specific Embodiments

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts belong to the scope of protection of the present invention.

[0025] Next, the present invention will be further described in conjunction with specific embodiments and comparative examples.

[0026] Example 1

[0027] This example provides a treatment method for improving the bonding strength between metal and lacquer, including the following steps:

[0028] S1. Prepare a pretreatment solution by mixing 6 parts of hydrofluoric acid, 5 parts of nitric acid, and 80 parts of water. Then, place the titanium metal workpiece in the pretreatment solution and soak it at room temperature for 10 minutes. Subsequently, rinse it with a large amount of clean water, and then put it into a 5wt% sodium hydroxide solution at 90°C for ultrasonic cleaning for 10 minutes. After washing and drying, uniform micro-etching pits are formed on the surface of the titanium metal, and it is clean and free of oil and grease.

[0029] S2. Prepare a primer by mixing 40 parts of lacquer, 12 parts of tung oil, and 6 parts of lithopone. Then, stir the primer evenly and spray a layer of primer with a thickness of 30μm on the pretreated titanium metal surface by air spraying; the spraying pressure is 0.5MPa, and it is left standing at room temperature for 36 hours to preliminarily cure the primer and enhance the initial bonding between the lacquer and the titanium metal.

[0030] S3. Manually scrape and apply the lacquer evenly with a horn spatula for 3 layers, with the thickness of each layer controlled at 0.1mm. After each layer is applied, it is placed in a curing room with a humidity of 70 - 80% and a temperature of 25 - 30°C for drying for 48 hours; after the last layer of lacquer is dried, it is heated in an oven at 80°C for 3 hours for post-curing, so that the lacquer is fully crosslinked to form a stable whole with the primer and the titanium metal.

[0031] Example 2

[0032] This example provides a treatment method for improving the bonding strength between metal and lacquer, including the following steps:

[0033] S1. Prepare a pretreatment solution by mixing 8 parts of hydrofluoric acid, 4 parts of nitric acid, and 90 parts of water. Then, place the titanium metal workpiece in the pretreatment solution and soak it at room temperature for 10 minutes. Subsequently, rinse it with a large amount of clean water, and then put it into a 5wt% sodium hydroxide solution at 90°C for ultrasonic cleaning for 10 minutes. After washing and drying, uniform micro-etching pits are formed on the surface of the titanium metal, and it is clean and free of oil and grease.

[0034] S2. Prepare a primer by mixing 45 parts of lacquer, 15 parts of tung oil, and 8 parts of lithopone. Then, stir the primer evenly and spray a layer of primer with a thickness of 20μm on the pretreated titanium metal surface by air spraying; the spraying pressure is 0.4MPa, and it is left standing at room temperature for 30 hours to preliminarily cure the primer and enhance the initial bonding between the lacquer and the titanium metal.

[0035] S3. Manually and evenly scrape and coat the raw lacquer in 3 layers with a horn spatula, with the thickness of each layer controlled at 0.1 mm. After each coating, place it in a shaded drying room with a humidity of 70 - 80% and a temperature of 25 - 30°C for 64 hours of drying; after the last layer of raw lacquer is dried, heat it in an oven at 80°C for 3 hours for post-curing, so that the raw lacquer is fully cross-linked to form a stable whole with the primer and titanium metal.

[0036] Example 3

[0037] This example provides a treatment method for improving the bonding strength between metal and raw lacquer, including the following steps:

[0038] S1. Prepare a pretreatment solution by mixing 5 parts of hydrofluoric acid, 8 parts of nitric acid, and 90 parts of water. Then place the titanium metal workpiece in the pretreatment solution and soak it at room temperature for 10 minutes. Subsequently, rinse it thoroughly with a large amount of clear water, and then put it into a 5wt% sodium hydroxide solution at 90°C for ultrasonic cleaning for 10 minutes. After cleaning, dry it to form uniform micro-etching pits on the surface of the titanium metal, which is clean and free of oil.

[0039] S2. Prepare a primer by mixing 50 parts of raw lacquer, 10 parts of tung oil, and 5 parts of lithopone. After stirring the primer evenly, use air spraying to spray a layer of primer with a thickness of 20 μm on the pretreated titanium metal surface; the spraying pressure is 0.3 MPa, and let it stand at room temperature for 24 hours to preliminarily cure the primer and enhance the preliminary bonding between the raw lacquer and the titanium metal.

[0040] S3. Manually and evenly scrape and coat the raw lacquer in 3 layers with a horn spatula, with the thickness of each layer controlled at 0.1 mm. After each coating, place it in a shaded drying room with a humidity of 70 - 80% and a temperature of 25 - 30°C for 72 hours of drying; after the last layer of raw lacquer is dried, heat it in an oven at 80°C for 3 hours for post-curing, so that the raw lacquer is fully cross-linked to form a stable whole with the primer and titanium metal.

[0041] Comparative Example 1

[0042] This comparative example provides a treatment method for improving the bonding strength between metal and raw lacquer, including the following steps:

[0043] S1. Put the titanium metal workpiece into a 5wt% sodium hydroxide solution at 90°C for ultrasonic cleaning for 10 minutes. After cleaning, dry it to make the surface of the titanium metal clean and free of oil.

[0044] S2. Prepare a primer by mixing 40 parts of raw lacquer, 12 parts of tung oil, and 6 parts of lithopone. After stirring the primer evenly, use air spraying to spray a layer of primer with a thickness of 30 μm on the pretreated titanium metal surface; the spraying pressure is 0.5 MPa, and let it stand at room temperature for 36 hours to preliminarily cure the primer and enhance the preliminary bonding between the raw lacquer and the titanium metal.

[0045] S3. Manually and evenly scrape and apply the raw lacquer in 3 layers with a thickness of 0.1 mm for each layer. After each application, place it in a shaded drying room with a humidity of 70 - 80% and a temperature of 25 - 30 °C for 48 hours of drying; after the last layer of raw lacquer is dried, heat it in an oven at 80 °C for 3 hours for post-curing, so that the raw lacquer is fully crosslinked to form a stable whole with the primer and titanium metal.

[0046] Comparative Example 2

[0047] This comparative example provides a treatment method for improving the bonding strength between metal and raw lacquer, including the following steps:

[0048] S1. Prepare a pretreatment solution by mixing 6 parts of hydrofluoric acid, 5 parts of nitric acid, and 80 parts of water. Then place the titanium metal workpiece in the pretreatment solution and soak it at room temperature for 10 minutes. Subsequently, wash it and dry it to form uniform micro-etching pits on the surface of the titanium metal.

[0049] S2. Prepare a primer by mixing 40 parts of raw lacquer, 12 parts of tung oil, and 6 parts of lithopone. Then, after stirring the primer evenly, use air spraying to spray a layer of primer with a thickness of 30 μm on the pretreated titanium metal surface; the spraying pressure is 0.5 MPa, and let it stand at room temperature for 36 hours to preliminarily cure the primer and enhance the initial bonding between the raw lacquer and the titanium metal.

[0050] S3. Manually and evenly scrape and apply the raw lacquer in 3 layers with a thickness of 0.1 mm for each layer. After each application, place it in a shaded drying room with a humidity of 70 - 80% and a temperature of 25 - 30 °C for 48 hours of drying; after the last layer of raw lacquer is dried, heat it in an oven at 80 °C for 3 hours for post-curing, so that the raw lacquer is fully crosslinked to form a stable whole with the primer and titanium metal.

[0051] Comparative Example 3

[0052] This comparative example provides a treatment method for improving the bonding strength between metal and raw lacquer, including the following steps:

[0053] S1. Prepare a pretreatment solution by mixing 6 parts of hydrofluoric acid, 5 parts of nitric acid, and 80 parts of water. Then place the titanium metal workpiece in the pretreatment solution and soak it at room temperature for 10 minutes. Subsequently, rinse it with a large amount of clear water, then put it into a 5 wt% sodium hydroxide solution at 90 °C and ultrasonically clean it for 10 minutes. After washing and drying, form uniform micro-etching pits on the surface of the titanium metal, which is clean and free of oil.

[0054] S2. Prepare a primer by mixing 40 parts of raw lacquer and 12 parts of tung oil. Then, after stirring the primer evenly, use air spraying to spray a layer of primer with a thickness of 30 μm on the pretreated titanium metal surface; the spraying pressure is 0.5 MPa, and let it stand at room temperature for 36 hours to preliminarily cure the primer and enhance the initial bonding between the raw lacquer and the titanium metal.

[0055] S3. Manually and evenly scrape and apply the raw lacquer in 3 layers with a thickness of 0.1 mm for each layer. After applying each layer, place it in a curing room with a humidity of 70 - 80% and a temperature of 25 - 30°C for drying for 48 hours; after the last layer of raw lacquer is dried, heat it in an oven at 80°C for 3 hours for post-curing to fully crosslink the raw lacquer and form a stable whole with the primer and titanium metal.

[0056] Comparative Example 4

[0057] This comparative example provides a treatment method for improving the bonding strength between metal and raw lacquer, including the following steps:

[0058] S1. Prepare a pretreatment solution by mixing 6 parts of hydrofluoric acid, 5 parts of nitric acid, and 80 parts of water. Then place the titanium metal workpiece in the pretreatment solution and soak it at room temperature for 10 minutes. Subsequently, rinse it with a large amount of clear water, and then put it into a 5wt% sodium hydroxide solution at 90°C for ultrasonic cleaning for 10 minutes. After cleaning, dry it to form uniform micro-etching pits on the surface of the titanium metal, which is clean and free of oil.

[0059] S2. Prepare a primer by mixing 40 parts of raw lacquer and 6 parts of lithopone. After stirring the primer evenly, use air spraying to spray a layer of primer with a thickness of 30 μm on the surface of the pretreated titanium metal; the spraying pressure is 0.5 MPa, and let it stand at room temperature for 36 hours to preliminarily cure the primer and enhance the initial bonding between the raw lacquer and the titanium metal.

[0060] S3. Manually and evenly scrape and apply the raw lacquer in 3 layers with a thickness of 0.1 mm for each layer. After applying each layer, place it in a curing room with a humidity of 70 - 80% and a temperature of 25 - 30°C for drying for 48 hours; after the last layer of raw lacquer is dried, heat it in an oven at 80°C for 3 hours for post-curing to fully crosslink the raw lacquer and form a stable whole with the primer and titanium metal.

[0061] Comparative Example 5

[0062] This comparative example provides a treatment method for improving the bonding strength between metal and raw lacquer, including the following steps:

[0063] S1. Prepare a pretreatment solution by mixing 6 parts of hydrofluoric acid, 5 parts of nitric acid, and 80 parts of water. Then place the titanium metal workpiece in the pretreatment solution and soak it at room temperature for 10 minutes. Subsequently, rinse it with a large amount of clear water, and then put it into a 5wt% sodium hydroxide solution at 90°C for ultrasonic cleaning for 10 minutes. After cleaning, dry it to form uniform micro-etching pits on the surface of the titanium metal, which is clean and free of oil.

[0064] S2. Use raw lacquer as the primer and spray a layer of primer with a thickness of 30 μm on the surface of the pretreated titanium metal by air spraying; the spraying pressure is 0.5 MPa, and let it stand at room temperature for 36 hours to preliminarily cure the primer and enhance the initial bonding between the raw lacquer and the titanium metal.

[0065] S3. Manually and evenly scrape and apply the raw lacquer in 3 layers with a thickness of 0.1 mm for each layer. After each application, place it in a curing room with a humidity of 70 - 80% and a temperature of 25 - 30°C for 48 hours of drying; after the last layer of raw lacquer is dried, heat it in an oven at 80°C for 3 hours for post-curing, so that the raw lacquer is fully crosslinked to form a stable whole with the primer and titanium metal.

[0066] Comparative Example 6

[0067] This comparative example provides a treatment method for improving the bonding strength between metal and raw lacquer, including the following steps:

[0068] S1. Prepare a pretreatment solution by mixing 6 parts of hydrofluoric acid, 5 parts of nitric acid, and 80 parts of water. Then place the titanium metal workpiece in the pretreatment solution and soak it at room temperature for 10 minutes. Subsequently, rinse it with a large amount of clear water, and then put it into a 5wt% sodium hydroxide solution at 90°C for ultrasonic cleaning for 10 minutes. After cleaning, dry it to form uniform micro-etching pits on the surface of the titanium metal, which is clean and free of oil.

[0069] S2. Prepare a primer by mixing 40 parts of raw lacquer, 12 parts of tung oil, and 6 parts of lithopone. Then, after stirring the primer evenly, use the air spraying method to spray a layer of primer with a thickness of 30 μm on the surface of the pretreated titanium metal; the spraying pressure is 0.5 MPa, and let it stand at room temperature for 36 hours to preliminarily cure the primer and enhance the preliminary bonding between the raw lacquer and the titanium metal.

[0070] S3. Manually and evenly scrape and apply the raw lacquer in 3 layers with a thickness of 0.1 mm for each layer. After coating, heat it in an oven at 80°C for 3 hours for post-curing, so that the raw lacquer is fully crosslinked to form a stable whole with the primer and titanium metal.

[0071] Performance testing

[0072] Take the samples prepared in Examples 1 - 3 and Comparative Examples 1 - 6, and test the hardness and adhesion of the paint surface. The obtained results are shown in Table 1. Among them, the hardness test is carried out according to Method B in GB / T6739 - 1996 "Determination of Film Hardness by Pencil Method", that is, the manual method; the adhesion test is carried out according to GB / T9286 - 1998 "Cross-Cut Test for Coatings and Varnishes".

[0073] Table 1

[0074] Hardness Adhesion Example 1 1H Grade 0 Example 2 1H Grade 0 Example 3 1H Grade 0 Comparative Example 1 1H Grade 2 Comparative Example 2 1H Grade 2 Comparative Example 3 1H Grade 1 Comparative Example 4 1H Grade 1 Comparative Example 5 HB Grade 2 Comparative Example 6 HB Grade 1

[0075] Please refer to Table 1. For the samples in Examples 1 - 3, the pencil hardness of the paint surface has reached 1H, and the adhesion between the paint surface and the titanium metal surface is relatively high, all reaching level 0.

[0076] In Comparative Example 1, since pretreatment with a pretreatment liquid was not carried out, a microscopically rough surface would not be formed on the titanium metal surface, which would affect the adhesion of the subsequent paint film, resulting in a relatively low adhesion of the paint film, only reaching Level 2.

[0077] In Comparative Example 2, since degreasing treatment with an alkaline degreaser was not carried out, the oil and impurity on the titanium metal surface could not be completely removed, thus unable to provide a clean base for the attachment of the lacquer. Therefore, the adhesion of the paint film in Comparative Example 2 decreased significantly compared with that in Example 1, only reaching Level 2.

[0078] It can be seen from Comparative Examples 3 - 5 that the components in the primer have an obvious influence on the adhesion of the paint film. In the primer of Comparative Example 3, lithopone was not added, resulting in a relatively low initial adhesion between the primer and the titanium metal; in the primer of Comparative Example 4, tung oil was not added, resulting in slow drying and poor flexibility of the lacquer; these factors ultimately led to a significant decrease in the adhesion of the paint film compared with that in Example 1, only reaching Level 1. In the primer of Comparative Example 5, neither tung oil nor lithopone was added, resulting in the lowest hardness and adhesion of its paint film.

[0079] It can be seen from Comparative Example 6 that the stepwise drying method also has a significant influence on the adhesion of the paint film. In Example 1, when applying the lacquer, each time a layer was applied, it was first dried in a drying room with specific humidity and temperature to allow the lacquer to crosslink preliminarily using the natural environment; then it was heated and cured in an 80°C oven. Through the combination of high and low temperatures, deep curing of the lacquer was promoted, forming a dense bond with the primer and the titanium metal, so it was beneficial to improve the hardness and adhesion of the paint film. While in Comparative Example 6, only one-step drying was adopted, resulting in a curing effect worse than that in Example 1, so both the hardness and adhesion of the paint film decreased.

[0080] In summary, the present invention provides a treatment method for improving the bonding force between metal and lacquer. This method significantly improves the adhesion of the lacquer on the titanium metal surface. After testing, the adhesion is 2 - 3 times higher than that of the traditional process, overcoming the long-standing problem of poor bonding between the two, and achieving a qualitative leap in the durability of the product. At the same time, the composite material not only has the high strength and corrosion resistance of titanium metal, but also has the unique luster and texture of the lacquer, broadening the application scenarios of the material in the fields of high-end cultural and creative products and art ornaments, and meeting the individual and high-quality market demands.

[0081] The above-described embodiments are only preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A method for improving the bonding strength between metal and lacquer, characterized in that: The following steps are involved: S1. Applying a primer on the metal surface to obtain a primer layer after curing; the primer is composed of the following components in parts by weight: 40-50 parts of lacquer, 10-15 parts of tung oil, 5-8 parts of lithopone; S2. applying lacquer on the primer layer, and obtaining a topcoat layer after curing.

2. A method for improving the bonding strength between metal and lacquer according to claim 1, characterized in that: In step S1, the metal is titanium metal.

3. The method for improving the bonding strength between metal and lacquer according to claim 1, characterized in that: The thickness of the primer layer is 20 to 30 μm; and / or, The method of applying the primer is: using air spraying with a spraying pressure of 0.3 to 0.5 MPa; after spraying, standing at room temperature for 24 to 36 hours for drying and curing.

4. The method for improving the bonding strength between metal and lacquer according to claim 1, characterized in that: In step S1, before applying the primer, the step of pre-treating the metal surface is also included; Wherein, the surface pretreatment includes soaking in a pretreatment liquid at room temperature for 10 to 15 minutes; the pretreatment liquid is composed of the following components by weight: 5 to 10 parts of hydrofluoric acid, 3 to 6 parts of nitric acid, and 80 to 90 parts of water.

5. A method for improving the bonding strength between metal and lacquer according to claim 4, characterized in that: The surface pretreatment also includes: taking out the metal after soaking in the pretreatment liquid, rinsing it with clean water, and then putting it into an alkaline degreasing liquid at 80-90° C. for ultrasonic cleaning for 5-10 minutes, and drying it after cleaning.

6. A method for improving the bonding strength between metal and lacquer according to claim 5, characterized in that: The alkaline degreasing solution includes 5 wt % of sodium hydroxide.

7. The method for improving the bonding strength between metal and lacquer according to claim 1, characterized in that: In step S2, the method of applying lacquer is: using a horn scraper to apply 2 to 3 layers, and the thickness of each layer is controlled at 0.1 to 0.2 mm.

8. A method for improving the bonding strength between metal and lacquer according to claim 7, characterized in that: After each layer is applied, it is placed in a shade room with a humidity of 70-80% and a temperature of 25-30°C to dry for 48-72 hours; after the last layer of lacquer is dried, it is heated in an oven at 60-80°C for 2-3 hours for curing to obtain a topcoat layer.

9. A titanium metal / lacquer composite material, characterized in that: The titanium metal / lacquer composite material is obtained by treating titanium metal using the treatment method described in any one of claims 1 to 8.