A chromium-free aqueous preservative for plating all-tin products

Abstract

The application discloses a chromium-free water-based protective agent for full-tin plating products, which has excellent performance, and contains a urethane prepolymer A, wherein the urethane prepolymer A is obtained by reacting a trimer of diisocyanate with 2-hydroxyphosphonoacetic acid, and the molar ratio of the trimer of diisocyanate to 2-hydroxyphosphonoacetic acid is 1:3. When the chromium-free water-based protective agent is used to treat a full-tin plating layer, the following performance requirements can be achieved: excellent corrosion resistance, meeting the performance requirement of 72 hours of salt spray; excellent conduction performance, with extremely low surface contact impedance of the metal tin itself; excellent stability, with the protective film being able to stably exist for a long time and resisting various storage environments; and excellent welding performance, with the tin plating area of the immersed pure tin being more than 98% after high-temperature and high-humidity aging test.

Description

Technical Field

[0001] This invention belongs to the field of metal coating protection, specifically relating to a chromium-free water-based protective agent that can improve the salt spray corrosion resistance, high temperature resistance and weldability of all-tin coatings and its application. Background Technology

[0002] With the rapid development of electric vehicles, the number and functional requirements of electronic components in electric vehicles are increasing. Currently, connectors for electric vehicles are mainly silver-plated and gold-plated. However, with the development of electric vehicles, the number of electronic devices is increasing, and the demand for electronic connectors is also increasing. Traditional silver-plated and gold-plated connectors are costly and wasteful of gold and silver resources. Therefore, a new type of plating is needed to replace gold- and silver-plated connectors. The main functional requirements of connectors are conductivity and solderability. Conductivity mainly relies on the connector base (copper) to transmit electrical signals. While gold and silver offer long-term solderability, tin has become an excellent alternative plating material. Therefore, fully tin-plated automotive connectors can completely replace gold- and silver-plated automotive connectors in terms of functionality. However, tin... Tin is an amphoteric metal, meaning it is highly reactive and therefore easily oxidized and corroded during use. To address this corrosion issue, two approaches can be taken: one is to replace the full tin plating of automotive connectors with tin alloy plating. This involves adding one or more metallic elements to tin to alter its reactivity, resulting in tin-bismuth alloys, tin-cobalt alloys, tin-nickel alloys, and tin-lead alloys. However, none of these tin alloy plating connectors can completely replace gold- or silver-plated connectors. Tin-bismuth alloy plating only increases hardness but reduces corrosion resistance; tin-cobalt plating only improves corrosion resistance but reduces solderability; tin-nickel alloy plating only increases hardness but significantly reduces corrosion resistance; and while tin-lead plating meets performance requirements, it fails to meet environmental regulations. Therefore, using tin alloy plating to replace pure tin plating has inherent drawbacks, and research in this area still has some way to go. Secondly, we need to develop a high-performance all-tin protective agent. This agent should have excellent protective and soldering properties for all-tin plating. Currently, there is a lot of research on this type of protective agent by industry researchers. However, most of the research focuses on phosphorus-containing and sulfur-containing organic and inorganic substances. However, phosphorus-containing substances are very harmful to the environment. Phosphorus is difficult to degrade in the environmental purification process and can cause red tides in water bodies. The use of sulfur-containing substances will result in the release of sulfide ions or sulfates. After sulfide ions combine with tin atoms, they will accelerate the sulfidation or corrosion of tin. The presence of sulfates will lead to increased ionic contamination of connectors, resulting in ionic short circuits in connectors, and even failure of automotive electronic performance.

[0003] Chinese Patent ZL 2012103627538 discloses a chromium-free water-based protective agent and its application, which can improve the overall performance of tin and its alloy plating. The chromium-free water-based protective agent contains an organophosphonic acid compound with a conjugated structure formed by styrene and phosphonic acid groups. It can form a high-density, high-adhesion protective film on the surface of tin or its alloy plating. For full tin plating, it fully meets the requirement of 48 hours of salt spray corrosion resistance; for half-gold tin plating, it enables it to meet the requirement of 24 hours of salt spray corrosion resistance. The chromium-free water-based protective agent has excellent high-temperature resistance; tin and its alloy plating treated with the chromium-free water-based protective agent of this invention can remain unchanged at 260°C for 5 minutes. After high-temperature and high-humidity aging tests, the tin-covered area of ​​the tin plating treated with the chromium-free water-based protective agent can still reach over 95%. Although the above-mentioned water-based protective agent has a relatively excellent protective effect, it still cannot meet the needs of long-term storage under various storage environments.

[0004] Therefore, developing a chromium-free water-based protective agent with superior performance is of great significance. Summary of the Invention

[0005] To overcome the aforementioned shortcomings in the existing technology, the primary objective of this invention is to provide a high-performance, chromium-free, water-based protective agent for tin-plated products, which achieves the following performance requirements: excellent corrosion resistance, meeting the 72-hour salt spray performance requirement; excellent conductivity, with extremely low surface contact resistance, reducing the surface contact resistance of the tin metal itself; excellent stability, ensuring the protective film remains stable during long-term storage and resisting various storage environments; and excellent solderability, achieving a tinning area of ​​over 98% after high-temperature and high-humidity aging tests.

[0006] The second objective of this invention is to provide a method for preparing the above-mentioned chromium-free water-based protective agent.

[0007] A third objective of this invention is to provide the use of the aforementioned chromium-free water-based protective agent.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0009] In a first aspect, a chromium-free water-based protective agent for tin-plated products, wherein the chromium-free water-based protective agent contains urethane prepolymer A, wherein urethane prepolymer A is obtained by reacting a trimer of diisocyanate with 2-hydroxyphosphonoacetic acid, wherein the molar ratio of the trimer of diisocyanate to 2-hydroxyphosphonoacetic acid is 1:3.

[0010] Preferably, the diisocyanate trimer is selected from one or more of TDI trimer, MDI trimer, IPDI trimer, and HDI trimer.

[0011] Preferably, the diisocyanate trimer is selected from TDI trimer or MDI trimer.

[0012] Preferably, the trimer of the diisocyanate is selected from 2,6-TDI trimer.

[0013] Preferably, the chromium-free water-based protective agent further comprises a surfactant, a corrosion inhibitor, and deionized water.

[0014] Preferably, the weight parts of each raw material in the chromium-free water-based protective agent for tin-plated products are as follows:

[0015] urethane prepolymer A 25-60

[0016] Surfactant 5-15

[0017] Corrosion inhibitor 5-10

[0018] Deionized water 10-20.

[0019] Preferably, the weight parts of each raw material in the chromium-free water-based protective agent for tin-plated products are as follows:

[0020] Carbamate prepolymer A 35-50

[0021] Surfactant 8-12

[0022] Corrosion inhibitor 7-8

[0023] Deionized water 14-16.

[0024] Preferably, the weight parts of each raw material in the chromium-free water-based protective agent for tin-plated products are as follows:

[0025] Carbamate prepolymer A 45

[0026] Surfactant 10

[0027] Corrosion inhibitor 8

[0028] 15g of deionized water.

[0029] The present invention also provides a method for preparing a chromium-free water-based protective agent for tin-plated products. The method involves adding a surfactant and a corrosion inhibitor to deionized water and stirring for 10 minutes, then adding urethane prepolymer A and stirring for another 20 minutes to obtain the chromium-free water-based protective agent.

[0030] This invention also provides the application of the aforementioned chromium-free water-based protective agent in the protection of fully tin-plated products.

[0031] Furthermore, the surfactant contains one or more hydrocarbon surfactants, one or more fluorinated surfactants and / or biosurfactants;

[0032] The hydrocarbon surfactants mentioned include nonionic and anionic types;

[0033] The fluorosurfactants mentioned include nonionic and anionic types;

[0034] The biosurfactant is one or more of rhamnolipin, sophorolipid, or polysaccharide, preferably rhamnolipin.

[0035] The corrosion inhibitor is one or more of the following: nitrazole compounds, imidazole compounds, mercapto compounds, thiazole compounds, long-chain aromatic hydrocarbon sulfonic acids, or their salts.

[0036] When using this solution, you can use Method 1 to dilute the above-mentioned chromium-free water-based protective agent with deionized water to make a working solution with a volume ratio of 5%. Then, immerse the workpiece to be treated in the working solution for 5 to 10 seconds. The working solution temperature should be room temperature. After removing the workpiece, dry it with hot air at 50±10℃.

[0037] Method 2 can also be used: Dilute the above-mentioned chromium-free water-based protective agent with deionized water to make a working solution with a volume ratio of 5%, heat the working solution to 60±5℃, then immerse the workpiece to be treated in the working solution for 5 to 10 seconds, then take out the workpiece, rinse it with room temperature pure water for 2 to 3 seconds, and finally blow it dry with hot air.

[0038] Diisocyanate trimers are obtained by the trimerization of diisocyanates under suitable conditions. The main polymerization methods include bulk polymerization and solution polymerization. Catalysts can be used to increase the reaction rate. Suitable catalysts include alkali metal catalysts, organometallic compound catalysts, rare earth metal salt catalysts, amine catalysts, and organophosphorus catalysts. Typical diisocyanate trimers contain an isocyanuric acid ring and an active isocyanate group. For example, toluene diisocyanate trimer (i.e., TDI trimer) has the following structure:

[0039]

[0040] The prepolymer of diisocyanate is reacted with 2-hydroxyphosphonoacetic acid to obtain urethane prepolymer A. The specific preparation method is to dissolve the prepolymer of diisocyanate in butyl acetate, heat it to 75°C, and then add 2-hydroxyphosphonoacetic acid to react. When there are no free NCO groups, the reaction is stopped, and the solvent butyl acetate is removed to obtain the prepolymer.

[0041] The structure of 2-hydroxyphosphonoacetic acid is as follows:

[0042]

[0043] The present invention has the following advantages over the prior art:

[0044] (1) The chromium-free water-based protective agent for tin-plated products of the present invention has excellent corrosion resistance for tin-plated coatings and meets the salt spray 72-hour performance requirements.

[0045] (2) The chromium-free water-based protective agent of the present invention for tin-plated products provides good solderability assurance. After high temperature and high humidity aging test, the tin plating area of ​​the tin-plated layer treated with the chromium-free water-based protective agent of the present invention can still reach more than 98%. Detailed Implementation

[0046] To make the technical problem to be solved, the technical solution, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0047] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are all conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or through existing methods; unless otherwise specified, the amounts of experimental reagents used are the amounts used in conventional experimental operations; unless otherwise specified, the experimental methods are all conventional methods.

[0048] The prepolymer of diisocyanate is reacted with 2-hydroxyphosphonoacetic acid to obtain urethane prepolymer A. The specific preparation method is to dissolve the prepolymer of diisocyanate in butyl acetate, heat it to 75°C, and then add 2-hydroxyphosphonoacetic acid to react. When there are no free NCO groups, the reaction is stopped, and the solvent butyl acetate is removed to obtain the prepolymer.

[0049] The urethane prepolymer A obtained using 2,6-toluene diisocyanate via the above method is denoted as A1.

[0050] The urethane prepolymer A obtained using the above method with 4,4'-diphenylmethane diisocyanate is denoted as A2.

[0051] The urethane prepolymer A obtained using hexamethylene diisocyanate via the above method is denoted as A3.

[0052] The urethane prepolymer A obtained using isophorone diisocyanate via the above method is denoted as A4.

[0053] The chromium-free water-based protective agent for tin-plated products was prepared using the following method: A surfactant and corrosion inhibitor were added to deionized water and stirred for 10 minutes, then urethane prepolymer A was added and stirring continued for 20 minutes to obtain the chromium-free water-based protective agent. The raw material composition and dosage for each embodiment are shown in Table 1.

[0054] Table 1. Raw material composition and dosage in Examples 1-7

[0055]

[0056] Comparative Example 1 was obtained by replacing urethane prepolymer A with 2-styrenephosphonic acid, and Comparative Example 2 was obtained by omitting urethane prepolymer A. The raw material composition and dosage of each comparative example are shown in Table 2.

[0057] Table 2. Raw material composition and dosage of Comparative Examples 1-2

[0058]

[0059]

[0060] Chinese Patent ZL 2012103627538, Formula 1, serves as Comparative Example 3.

[0061] Examples 1-7 and Comparative Examples 1-3 were used as follows: The chromium-free water-based protective agent was diluted with deionized water to prepare a working solution with a volume ratio of 5%. The working solution was heated to 60±5°C. The workpiece to be treated was then immersed in the working solution for 5-10 seconds. After that, the workpiece was removed, rinsed with room temperature pure water for 2-3 seconds, and finally dried with hot air. The workpiece to be treated was a fully tin-plated workpiece.

[0062] Salt spray resistance tests were conducted on the treated tin-plated workpieces according to GB / T10125-1997, with a test duration of 72 hours. A blank control group was also included. The test results were evaluated according to the national standard GB / T6461-2002, where the degree of corrosion on the workpiece plating appearance was expressed as a numerical rating. The more severe the corrosion, the lower the appearance rating; the less severe the corrosion, the higher the appearance rating. If no corrosion was observed, the appearance rating was 10. The test results are shown in Table 3.

[0063] Table 3. Comparison Results of Neutral Salt Spray Tests on All-Tin Coatings

[0064] Test group Appearance rating The workpiece was treated with the working fluid prepared in Example 1. 10 The workpiece was treated with the working fluid prepared in Example 2. 10 The workpiece was treated with the working fluid prepared in Example 3. 10 The workpiece was treated with the working fluid prepared in Example 4. 10 The workpiece was treated with the working fluid prepared in Example 5. 10 The workpiece was treated with the working fluid prepared in Example 6. 10 The workpiece was treated with the working fluid prepared in Example 7. 10 The workpiece was treated with the working fluid prepared in Comparative Example 1. 5-6 The workpiece was treated with the working fluid prepared in Comparative Example 2. 2-3 The workpiece was treated with the working fluid prepared in Comparative Example 3. 6-7 The blank control group consisted of workpieces that were not processed. 1-2

[0065] Using the same testing methods and evaluation rules, with the testing time set at 100 hours, only the workpieces treated with the working fluids prepared in Examples 1, 2, and 5 were rated as level 10 in appearance.

[0066] The treated tin-plated workpieces underwent immersion tin testing. The treatment method using a water-based protective agent was identical to that used in the salt spray resistance test. The test method involved subjecting the treated workpieces to a high-temperature and high-humidity aging test for 8 hours at 85% humidity and 85℃. Immersion tin tests were performed before and after the high-temperature and high-humidity aging test, with a blank control group included. The immersion tin test conditions were immersion in pure tin at 255±5℃ for 5±0.5s. The solderability of the tin plating was evaluated based on the tin-covered area of ​​each workpiece; a larger tin-covered area indicated better solderability. The test results are shown in Table 4.

[0067] Table 4. Aging resistance test results of tin-plated workpieces

[0068] Test group Tinning area The workpiece was treated with the working fluid prepared in Example 1. >98％ The workpiece was treated with the working fluid prepared in Example 2. >98％ The workpiece was treated with the working fluid prepared in Example 3. >98％ The workpiece was treated with the working fluid prepared in Example 4. >98％ The workpiece was treated with the working fluid prepared in Example 5. >98％ The workpiece was treated with the working fluid prepared in Example 6. >98％ The workpiece was treated with the working fluid prepared in Example 7. >98％ The workpiece was treated with the working fluid prepared in Comparative Example 1. 40％-60％ The workpiece was treated with the working fluid prepared in Comparative Example 2. 10％-20％ The workpiece was treated with the working fluid prepared in Comparative Example 3. 95％-97％ The blank control group consisted of workpieces that were not processed. 1％-2％

[0069] Using the same testing method and evaluation rules, with the test time set to 20 hours, only the workpieces treated with the working solution prepared in Examples 1-7 could achieve a tinning area of ​​over 90%, while the workpieces treated with the working solution prepared in Comparative Example 3 had a tinning area of ​​less than 80%.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A chromium-free aqueous preservative for plating all-tin products, characterized in that, The weight parts of each raw material are: urethane prepolymer A 25-60 surfactant 5-15 corrosion inhibitor 5-10 deionized water 10-20. The urethane prepolymer A is obtained by reacting a trimer of diisocyanate with 2-hydroxyphosphonoacetic acid, and the molar ratio of the trimer of diisocyanate to 2-hydroxyphosphonoacetic acid is 1:

3. The trimer of diisocyanate is selected from one or more of TDI trimer, MDI trimer, IPDI trimer, and HDI trimer.

2. The chromium-free aqueous preservative for plating a full-tin product according to claim 1, characterized by, The trimer of diisocyanate is selected from TDI trimer or MDI trimer.

3. The chromium-free aqueous preservative for plating a full-tin product according to claim 2, characterized by, The trimer of diisocyanate is selected from 2,6-TDI trimer.

4. The chromium-free aqueous preservative for plating a full-tin product according to claim 1, characterized by, The weight parts of each raw material are: urethane prepolymer A 25-60 surfactant 5-15 corrosion inhibitor 5-10 deionized water 10-20.

5. The chromium-free aqueous preservative for plating a full-tin product according to claim 4, characterized by, The weight parts of each raw material are: urethane prepolymer A 45 surfactant 10 corrosion inhibitor 8 deionized water 15 6. The process for the preparation of a chromium-free aqueous preservative for the plating of full-tin products according to any one of claims 1-5, characterized in that, The surfactant and the corrosion inhibitor are added to the deionized water and stirred for 10 minutes, then the urethane prepolymer A is added and stirred for 20 minutes to obtain the chromium-free water-based protective agent.

7. The use of the chromium-free water-based protective agent of any one of claims 1-5 in the protection of tin-plated products.

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