Method for driving normal-temperature chemical copper plating to display oil latent fingerprint by primary battery

Abstract

The invention provides a method for displaying an oil latent fingerprint by driving normal-temperature chemical copper plating through a primary battery, which comprises the following steps: contacting an active metal with an object metal with the oil latent fingerprint, reacting with a chemical plating solution containing Ni < 2 + > and Cu < 2 + >, taking out the object metal after the reaction is completed, cleaning, and drying to display the oil latent fingerprint, the potential of the active metal is lower than the potential of the metal element in the guest metal. Compared with a traditional chemical copper plating technology, the method for realizing the development of the oil latent fingerprint through normal-temperature chemical copper plating on the basis of the primary battery principle has the advantages that the dependence on the concentration of a reducing agent is low, the reaction is more environment-friendly, a reaction system can be spontaneously carried out in a normal-temperature environment, an external heating device and a complex temperature control system are not needed, and the cost is low. Compared with the traditional chemical copper plating technology which has strict requirements on the temperature (generally 60-80 DEG C), the method has the advantages that the fingerprint with clear streaks can be quickly shown within 5 minutes, and the operation process is greatly simplified.

Description

Technical Field

[0001] This invention relates to the field of fingerprint development technology, specifically to a method for developing oil-based fingerprints using a galvanic cell driven at room temperature chemical copper plating. Background Technology

[0002] Fingerprints, due to their significant individual uniqueness and persistent stability, have established their core evidentiary status in crime scene investigation. However, in actual investigation scenarios, the inability to directly identify latent fingerprints left on object surfaces with the naked eye is a common challenge faced by investigators. Therefore, specific physical or chemical development techniques (such as powder method, fumigation method, ninhydrin method, etc.) must be used to effectively enhance these latent fingerprints in order to clearly and completely extract the detailed feature information contained within them. The microscopic material basis of these latent fingerprints mainly originates from the secretions of sweat glands and sebaceous glands (sebum) secreted by human skin. When the perpetrator's palm comes into contact with the surface of an object, according to the basic laws of material transfer, the aforementioned fingerprint residues on the skin surface may transfer and adhere to the contact surface, thus forming sweat latent fingerprints or oil latent fingerprints.

[0003] How to better reveal oil-embedded fingerprints has always been a hot topic. Traditional techniques such as powder application are easily affected by the amount of oil on the fingerprint surface, resulting in unsatisfactory fingerprint development. In recent years, some new techniques for revealing oil-embedded fingerprints have emerged, such as vacuum metal coating, electroplating, and chemical plating, to solve the problem of poor fingerprint development. However, various metal coating techniques still have technical shortcomings. Vacuum metal coating requires sophisticated equipment and is expensive, making it more suitable for laboratory fingerprint development and less widely used in field investigations. While electroplating offers faster development and does not require high reaction temperatures, it requires an external power supply, which is not conducive to fingerprint development in field investigations. Therefore, compared to vacuum metal coating and electroplating, chemical plating is a lower-cost, more convenient, and more suitable technique for fingerprint development in field investigations.

[0004] Chemical fingerprint plating utilizes the difference in electromagnetic shielding capabilities between the papillary ridges and furrows in sebum-covered fingerprints or oil-soaked fingerprints and metallic copper ions. The areas of the fingerprint without sebum are plated with metallic copper, while the areas of the oil-soaked fingerprint do not deposit copper, thus creating a clear "negative" image.

[0005] However, the technique of revealing potential fingerprints through electroless plating is limited by the following:

[0006] First, obtaining good fingerprint details requires a high reaction temperature. Copper has weak oxidizing properties, and copper ion deposition is difficult to form spontaneously at room temperature. Although better fingerprint details can be obtained at higher reaction temperatures, high temperatures can destroy potential fingerprints, accelerate the dissolution of fingerprint substances such as sweat and secretions in the electrolyte, and even destroy fingerprint biological evidence.

[0007] Secondly, traditional chemical copper plating requires a reaction time of more than 30 minutes at high temperatures to obtain a coating of a certain thickness. The reaction speed is slow, which is not conducive to the rapid appearance and extraction of fingerprints at the scene.

[0008] Finally, although formaldehyde has strong reducing properties, enabling room-temperature chemical copper plating, it is volatile and toxic. Long-term exposure can harm the health of operators, and its emissions pollute the environment, failing to meet modern environmental protection requirements.

[0009] Therefore, further research is needed on how to improve the fingerprint development effect of chemical copper plating by optimizing the process in a green, environmentally friendly, low-cost, and easy-to-operate manner. Summary of the Invention

[0010] The purpose of this invention is to overcome at least one deficiency of the prior art and to provide a method for developing oil latent fingerprints by driving room temperature chemical copper plating using a galvanic cell.

[0011] The technical solution adopted in this invention is:

[0012] In a first aspect, the present invention provides a method for revealing oil-embedded fingerprints using a galvanic cell-driven room-temperature chemical copper plating process, the method comprising the following steps: contacting an object metal bearing an oil-embedded fingerprint with a reactive metal, and then contacting it with a metal containing Ni. 2+ and Cu 2+ The chemical plating solution reacts with the sample. After the reaction is complete, the sample metal is removed, cleaned, and dried to reveal the oil fingerprint. The potential of the active metal is lower than that of the metal element in the sample metal.

[0013] In some embodiments, the active metal is selected from any one of magnesium, aluminum, and zinc.

[0014] In some embodiments, the guest metal is selected from at least one of copper, copper alloys, manganese, silver, iron, and iron alloy metals.

[0015] In some embodiments, the composition of the electroless plating solution includes: 2.5-30 g / L copper salt, 10-20 g / L complexing agent, 0.5-5 g / L nickel salt, and 15-25 g / L boric acid.

[0016] In some embodiments, the composition of the electroless plating solution further includes: a reducing agent of 0-60 g / L.

[0017] In some embodiments, the reaction time is 0.5-8 min.

[0018] In some embodiments, the copper salt is selected from at least one of CuSO4, CuCl2, Cu(NO3)2, and Cu(CH3COO)2.

[0019] In some embodiments, the nickel salt includes at least one of NiSO4, NiCl2, Ni(NO3)2, and Ni(CH3COO)2.

[0020] In some embodiments, the reducing agent is selected from at least one of sodium hypophosphite, sodium thiosulfate, formaldehyde, hydrazine hydrate, ascorbic acid, sodium borohydride, ammonium borohydride, and formic acid.

[0021] In some embodiments, the complexing agent is selected from at least one of sodium citrate, lactic acid, and glycolic acid.

[0022] The beneficial effects of this invention are:

[0023] First, a method for revealing oil-based fingerprints in room-temperature chemical copper plating based on the principle of a galvanic cell is used. In this method, the galvanic cell is the primary electron source, and zinc anodizing provides electrons (Zn→Zn). 2+ +2e - Compared to traditional chemical copper plating technology, it has a lower dependence on the concentration of reducing agent, the reaction is more environmentally friendly, and it is more conducive to the appearance of fingerprints during on-site investigation;

[0024] Secondly, its reaction system can proceed spontaneously at room temperature without relying on external heating devices and complex temperature control systems. Compared with the strict temperature requirements (usually 60-80℃) of traditional chemical copper plating technology, it can quickly show clear fingerprints within 5 minutes, greatly simplifying the operation process.

[0025] Finally, this technology uses sodium hypophosphite, hydrazine hydride, or borohydride instead of formaldehyde as a reducing agent, making it green and environmentally friendly. Attached Figure Description

[0026] Figure 1 The image shows the result of chemical copper plating at room temperature to reveal a fingerprint, which is the blank group in Example 1.

[0027] Figure 2 The image shows the result of revealing a fingerprint after room temperature chemical copper plating in the experimental group of Example 1.

[0028] Figure 3 This is an image showing the effect of chemical copper plating at room temperature to reveal a fingerprint, performed under the reducing agent condition of 0 g / L in Example 2.

[0029] Figure 4The images show the effects of chemical copper plating at room temperature to reveal fingerprints under different concentrations (20, 30, 40 g / L) of reducing agent in Example 2.

[0030] Figure 5 The images show the results of chemical copper plating at room temperature to reveal fingerprints under different concentrations (2.5, 10, 30 g / L) of copper salt in Example 3.

[0031] Figure 6 This is a comparison of the effects of different copper salt concentrations under different copper salt concentrations in Example 3.

[0032] Figure 7 The image shows the effect of chemical copper plating at room temperature to reveal fingerprints under different fingerprint composition conditions in Example 4.

[0033] Figure 8 This is a contrast diagram of fingerprints after being chemically plated at room temperature under different fingerprint composition conditions in Example 4.

[0034] Figure 9 The images show the results of chemical copper plating at room temperature to reveal fingerprints under different material conditions in Example 4.

[0035] Figure 10 The image shows a contrast diagram of fingerprints after being chemically plated with copper at room temperature under different material conditions in Example 4. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited thereto.

[0037] In this invention, the concentrations of copper salt and reducing agent in the chemical plating solution, as well as the reaction time, have a significant impact on the development effect.

[0038] When Cu 2+ When the concentration is too low, the deposition rate is slow, the development time is long, the hydrogen evolution reaction dominates, and the disturbance of a large number of hydrogen bubbles will cause the fingerprint material to detach from the object surface, destroying the fingerprint development; when Cu 2+ When the concentration is too high, the deposition rate is too fast, which will cover the papillary ridges of the fingerprint, resulting in low contrast and unclear ridges.

[0039] Ni provided by nickel salts 2+ The core function is as a "catalytic aid." Cu has low catalytic activity for the reduction of sodium hypophosphite; the reaction stops when the catalyzed surface is covered by copper. Adding a small amount of Ni to the plating bath... 2+ It preferentially reduces and forms nanoscale nickel nuclei at defects on inert metal surfaces (such as the oxide film on a stainless steel cathode), and these nickel nuclei are effective against Cu. 2+ The catalytic activity of reduction is much higher than that of stainless steel oxide film, and it can significantly reduce Cu2+ The activation energy of reduction allows Cu 2+ It rapidly gains electrons from the nickel nucleus and is reduced to metallic copper.

[0040] When NaH2PO2 is chosen as the reducing agent, because NaH2PO2·H2O has weak reducing power at room temperature, side reactions (H2PO2·H2O) will occur at lower temperatures. - + 2e - → HPO3 2- The addition of H2↑ competes for electrons, reducing copper deposition efficiency. Compared to plating solutions without the reducing agent NaH2PO2·H2O, the plating solution with added NaH2PO2·H2O has a slower reaction rate and better fingerprint texture rendering. When the concentration of the reducing agent was investigated as a variable, when the concentration of NaH2PO2·H2O was too low, the deposition rate was slow and the rendering time was long; when the concentration of NaH2PO2·H2O was high, the deposition rate was fast and the rendering time was short, but the stability of the plating solution was poor.

[0041] This invention employs a Cu plating process that differs from conventional chemical copper plating processes. 2+ And the concentration of NaH2PO2·H2O, specifically, when the mass concentration of sodium hypophosphite is 30 g / L, the mass concentration of sodium citrate is 15 g / L, and the time is 6 min, the suitable Cu 2+ The concentration is 5-30 g / L, preferably 5-10 g / L, and more preferably 10 g / L.

[0042] In this invention, suitable additives can also be added to the electroless plating solution to promote the forward shift of the electroless copper plating reaction. For example, adding an appropriate amount of 2,2'-bipyridine to the plating solution, when the volume fraction of 2,2'-bipyridine is low, is beneficial for hydrogen evolution and reduces the hydrogen embrittlement of the coating; further increasing its volume fraction accelerates the reaction rate, resulting in a looser and darker coating. Therefore, an appropriate amount of 2,2'-bipyridine is beneficial for promoting the forward shift of the electroless copper plating reaction. Simultaneously, 2,2'-bipyridine can also change the surface morphology of the coating. With the addition of 2,2'-bipyridine, the coating becomes denser, more uniform, and smoother, and the appearance color of the coating changes to pink; however, with the increase of the volume fraction of 2,2'-bipyridine, the reaction accelerates, and the porosity increases.

[0043] In Examples 1-3 of this invention, the specific method for obtaining the object sample is as follows:

[0044] 1) Use your fingers to rub the oily residue on your forehead and nose.

[0045] 2) Wipe the object sample to be developed with an ethanol solution to reduce the interference of grease on the object, and then use a finger with grease to apply pressure of 1.5-3 N to form an oil fingerprint on the object sample.

[0046] The analysis method of this invention is as follows: To intuitively reflect the contrast effect of fingerprints, a computer vision analysis system is constructed using Python programming. Based on a grayscale gradient algorithm, the contrast of the fingerprint is quantitatively represented. The average grayscale value of the fingerprint area and the background area is calculated. Finally, the ratio of "light grayscale to dark grayscale" is used as the contrast index to achieve automated quantitative evaluation. A higher calculation result indicates a higher contrast and better display effect; conversely, a lower result indicates a lower contrast and worse display effect.

[0047] Example 1

[0048] This case study investigates the effect of adding reactive metals on electroless copper plating. The specific fingerprint development process is as follows:

[0049] (1) Under room temperature conditions, weigh out a certain amount of CuSO4·5H2O, NaH2PO2·H2O, C6H5Na3O7·2H2O, NiSO4·7H2O and boric acid respectively, and then add a certain amount of distilled water to them and stir to dissolve them, so as to prepare chemical plating solutions with the following concentrations: 5 g / L CuSO4·5H2O, 30 g / L NaH2PO2·H2O, 15 g / L C6H5Na3O7·2H2O, 2 g / L NiSO4·7H2O and 20 g / L boric acid.

[0050] (2) Stainless steel objects with latent fingerprints were set up as experimental groups with zinc metal sheets attached and blank groups without zinc metal sheets attached. The experimental groups and blank groups were then immersed in the chemical plating solution or the chemical plating solution was dripped onto the metal objects with latent fingerprints. After reacting for 1-2 minutes, the objects were removed, and excess chemical plating solution was rinsed off the surface of the objects with clean water and then dried. This process of chemically plating copper to reveal oil latent fingerprints was achieved.

[0051] like Figure 1 and Figure 2 As shown, Figure 1 The image shows the result of chemical copper plating at room temperature to reveal a fingerprint in the blank group. As can be seen from the image, a clear fingerprint image cannot be revealed under these conditions. Figure 2 The image shows the effect of fingerprint development after room temperature chemical copper plating in the experimental group. Figure 2 (a) It can be seen that the nipple pattern of this handprint is a whorl pattern. Figure 2 (b) The detailed features of the handprint are clearly visible, such as the joints, hooks, and bridges. From Figure 2 (c) The tertiary features of the handprint, such as sweat pores, are clearly visible. (Comparison) Figure 1 and Figure 2 The results show that the experimental group has similar color differences in the papillary lines and furrows, while the blank group has a larger color difference, indicating that the experimental group has a better effect in revealing fingerprints after chemical copper plating.

[0052] Example 2

[0053] This case study investigates the effect of different concentrations (0, 20, 30, 40 g / L) of the reducing agent NaH2PO2·H2O on electroless copper plating. The specific fingerprint development process is as follows:

[0054] (1) Under room temperature conditions, weigh out a certain amount of CuSO4·5H2O, C6H5Na3O7·2H2O, NiSO4·7H2O and boric acid respectively, and then add a certain amount of distilled water to them and stir to dissolve them, so as to prepare the chemical plating solution with the following concentration.

[0055] 5 g / L CuSO4·5H2O, 0-40 g / L NaH2PO2·H2O, 15 g / L C6H5Na3O7·2H2O, 2 g / L NiSO4·7H2O and 20 g / L boric acid.

[0056] (2) Immerse the stainless steel object with the latent fingerprint and zinc sheet attached into the chemical plating solution, react for 2 minutes, take out the object, rinse the surface of the object with clean water, remove the excess chemical plating solution and let it dry, so as to realize the chemical copper plating to reveal the latent fingerprint.

[0057] Figure 3 The image shows the effect of developing a fingerprint after electroless copper plating at room temperature under a reducing agent concentration of 0 g / L. Figure 3 (a) It can be seen that the nipple pattern of this handprint is a whorl pattern. Figure 3 (b) The detailed features of the handprint, such as the points of contact, divergence, and small eyes, are clearly visible. From Figure 3 (c) The tertiary features of the fingerprint, such as sweat pores, are clearly visible. It can be seen that the method provided by this invention has low dependence on the concentration of the reducing agent and can achieve a green and efficient chemical reaction.

[0058] When the reducing agent NaH2PO2·H2O is added, due to the weak reducing power of NaH2PO2·H2O at room temperature, the side reaction (H2PO2) will occur. - + 2e - → HPO3 2- The addition of H2↑ competes for electrons, reducing copper deposition efficiency and thus decreasing the reaction rate. However, compared to the reaction without NaH2PO2·H2O, it is easier to control the rate and effect of fingerprint development. Simultaneously, a comparison was made with the reaction without NaH2PO2·H2O. Figure 3 And the effects of adding different concentrations of NaH2PO2·H2O Figure 4It can be seen that without a reducing agent, copper deposition is less uniform, with similar color differences between the papillary ridges and the small pear grooves. After adding a reducing agent, the color difference is greater and the pore structure is more sparse. The color difference between the copper deposition area (handprint furrows) and the low deposition area (papillary ridges / base) is greater, and the handprint outline is clearer.

[0059] Example 3

[0060] This case study investigates the effect of different concentrations (2.5, 5, 10, 20, 30 g / L) of copper salt CuSO4 on electroless copper plating. The specific fingerprint development process is as follows:

[0061] (1) Under room temperature conditions, weigh out a certain amount of CuSO4·5H2O, C6H5Na3O7·2H2O, NiSO4·7H2O and boric acid respectively, and then add a certain amount of distilled water to them and stir to dissolve them, so as to prepare the chemical plating solution with the following concentration.

[0062] 2.5-30 g / L CuSO4·5H2O, 30 g / L NaH2PO2·H2O, 15 g / L C6H5Na3O7·2H2O, 2 g / L NiSO4·7H2O and 20 g / L boric acid.

[0063] (2) Immerse the stainless steel object with the latent fingerprint and zinc sheet attached into the chemical plating solution and react for 6 minutes. Remove the object, rinse the surface of the object with clean water, remove the excess chemical plating solution and let it dry to achieve chemical copper plating to reveal the latent fingerprint.

[0064] like Figure 5 As shown, with the increase of the main salt concentration, the deposition amount of metallic Cu continuously increases, improving the color difference in the small furrows and ridges, thus enhancing the visibility of the fingerprint. When Cu... 2+ When the concentration is below 2.5 g / L, although there is a significant color difference between the small furrows and the papillary lines, some substrate areas still exhibit the natural color of metallic copper, indicating insufficient reaction and uneven copper plating. When the CuSO4 concentration reaches 10 g / L, the latent fingerprint is fully revealed, with excellent development and clear details. When the concentration continues to rise to 30 g / L, the development effect does not improve significantly.

[0065] Figure 6 This represents the contrast of the display effect under different copper salt concentrations. A higher contrast indicates a greater color difference between the papillary ridges and the pear-shaped grooves, resulting in a better display effect. From... Figure 6 It can be seen that when the copper sulfate concentration is greater than or equal to 20 g / L, due to the large amount of copper deposition, the reaction rate is fast, the copper film has poor adhesion, and it peels off, covering the fingerprint papillary ridges, resulting in unclear ridges, low contrast, and poor fingerprint display effect.

[0066] Example 4

[0067] This case study investigates the influence of different object materials containing latent fingerprints on electroless copper plating. The specific method for obtaining the object samples is as follows:

[0068] 1) A certain amount of exogenous oils (foundation, engine oil, peanut oil, sunscreen) adhere to the fingers;

[0069] 2) Wipe the object sample to be developed (bottom of stainless steel cup, kitchen knife, door lock, five-cent coin, one-cent coin, one-yuan coin) with ethanol solution to reduce the interference of grease on the object. Then, use your grease-covered fingers to apply pressure of 1.5-3 N to form an oil fingerprint on the object sample.

[0070] The specific process for revealing handprints is as follows:

[0071] (1) Under room temperature conditions, weigh out a certain amount of CuSO4·5H2O, NaH2PO2·H2O, C6H5Na3O7·2H2O, NiSO4·7H2O and boric acid respectively, and then add a certain amount of distilled water to them and stir to dissolve them, so as to prepare chemical plating solutions with the following concentrations: 5 g / L CuSO4·5H2O, 30 g / L NaH2PO2·H2O, 15 g / L C6H5Na3O7·2H2O, 2 g / L NiSO4·7H2O and 20 g / L boric acid.

[0072] (2) The object sample with the latent fingerprint is attached with a zinc metal sheet. Depending on the material of the object sample, it is immersed in a chemical plating solution or the chemical plating solution is dripped onto the metal object with the latent fingerprint.

[0073] 3) After reacting for 1-2 minutes, remove the object, rinse the surface of the object with clean water to remove excess chemical plating solution, and then air dry. This achieves the discovery of oil-based fingerprints in chemical copper plating.

[0074] like Figure 7 and Figure 8 As shown, the visibility of fingerprints is related to the oil content and type of the main components of the dirt, with significant differences in visibility. Peanut oil has the highest oil content. The third ingredient in sunscreen is glycerin, while the fifth ingredient in foundation is trimethylsiloxysilicate. Therefore, sunscreen has a higher oil content than foundation, resulting in a higher gray value for sunscreen fingerprints and better visibility of sunscreen fingerprints.

[0075] The visibility of motor oil is worse than that of sunscreen, which may be related to its oil content. Motor oil is a mineral oil with a complex composition containing different types of additives and chemicals, most of which are volatile. Glycerin and peanut oil, on the other hand, are glycerides, which are usually not volatile. Therefore, motor oil and foundation are less visible than sunscreen.

[0076] like Figure 9 and Figure 10 As shown, among different object materials, the bottom of the cup showed the worst display effect. It is speculated that the height difference between the bottom of the cup, which is convex in the middle and concave around the edges, causes the reaction at the center of the fingerprint to be weaker than that at the edge of the fingerprint, resulting in poor fingerprint display effect.

[0077] The gray values ​​of the three coins were significantly higher than those of the other three object materials. It is speculated that this is because the three coins were produced using an immersion plating method, while the other three objects were produced using a drop plating method. The difference in the display method is one of the reasons for the difference in gray values. The immersion plating method results in better contact between the reactants than the drop plating method. Therefore, the fingerprint effect produced by the immersion plating method is better than that produced by the drop plating method.

[0078] Based on the examples 1-4 above, the conclusions are as follows:

[0079] 1) This invention solves the problem that chemical copper plating technology relies on high temperatures:

[0080] Based on the principle of a galvanic cell, a galvanic cell system is constructed by introducing the active metal Zn into direct contact with the fingerprint substrate. Utilizing the potential difference between the two metal electrodes in the electrolyte, the directional reduction and deposition of copper ions on the latent fingerprint substrate is driven, eliminating the need for an external power source or high-temperature conditions, thus overcoming the dependence of traditional chemical plating on the catalytic activity of the substrate.

[0081] Chemical copper plating is essentially a process involving metal ions (Cu). 2+ The autocatalytic redox reaction between Cu and the reducing agent (sodium hypophosphite) 2+ →Cu 0 This technology utilizes the potential difference of a Zn-Cu galvanic cell to generate an electrochemical driving force, enabling the spontaneous reduction of copper ions on non-catalytic substrates (such as palladium and nickel), while simultaneously accelerating the electron transfer rate and significantly shortening the deposition time.

[0082] Compared to traditional high-temperature immersion processes, this solution can achieve clear visualization of latent fingerprints at room temperature in a short time, significantly improving the timeliness and operational feasibility of on-site investigations.

[0083] 2) The electrolyte used in this invention is green and environmentally friendly:

[0084] This invention changes the type of reducing agent in common room-temperature chemical copper plating by using sodium hypophosphite instead of formaldehyde, and explores a fingerprint development plating solution technology with weak reducing power, which is green and environmentally friendly.

[0085] By adjusting the type of reducing agent and using sodium hypophosphite instead of formaldehyde, sodium hypophosphite is more environmentally friendly than formaldehyde due to its toxicity, thus meeting the requirement of protecting the health of staff involved in fingerprint extraction.

[0086] This invention addresses the shortcomings of common room-temperature copper plating methods, such as high toxicity affecting workers' health and damaging the environment. It also overcomes the drawbacks of sodium hypophosphite systems with weak reducing power at room temperature. This invention can reveal fingerprints on common materials other than copper and its alloys, such as stainless steel, silver, and high-strength iron alloys, and produces fingerprints with good contrast and high effect.

[0087] 3) Optimization of process parameters for developing fingerprints using chemical copper plating

[0088] This invention develops a latent fingerprint development scheme based on chemical copper plating, the key of which lies in the synergistic optimization of core process parameters such as main salt concentration, reducing agent concentration and development time.

[0089] By precisely adjusting the concentration of the main salt, the concentration of the reducing agent, and the reaction time in the plating bath, the reduction deposition rate and deposition amount of copper ions were effectively controlled. This control ensured the formation of a sufficiently differentiated and uniform copper plating layer in the furrows of the fingerprint and the substrate area, thereby achieving a clear display effect.

[0090] The optimized combination of process parameters (especially the matching of the concentration of the main salt and reducing agent with the reaction time) maximizes the visual contrast of the deposition area and significantly enhances the recognizability of fingerprint details.

[0091] The above is a further detailed description of the present invention and should not be considered as a limitation on the specific implementation of the present invention. For those skilled in the art, simple deductions or substitutions without departing from the concept of the present invention are all within the protection scope of the present invention.

Claims

1. A method for developing latent oil handprints by normal temperature chemical copper plating driven by a primary cell, characterized in that, The method comprises the following steps: contacting a live metal with an object metal with oil latent fingerprints, and then reacting with a chemical plating solution containing Ni 2+ and Cu 2+ , and taking out the object metal after the reaction is completed, cleaning and drying to show the oil latent fingerprints; the potential of the live metal is lower than the potential of the metal elements in the object metal.

2. The method of claim 1, wherein, The active metal is selected from any one of magnesium, aluminum, zinc.

3. The method of claim 1, wherein, The guest metal is selected from at least one of copper, copper alloy, manganese, silver, iron, and iron alloy.

4. The method of claim 1, wherein, The composition of the electroless plating solution comprises 2.5-30 g / L of copper salt, 10-20 g / L of complexing agent, 0.5-5 g / L of nickel salt, and 15-25 g / L of boric acid.

5. The method of claim 4, wherein, The composition of the electroless plating solution further comprises 0-60 g / L of reducing agent.

6. The method of claim 1, wherein, The reaction time is 0.5-8 min.

7. The method of claim 4, wherein, The copper salt is selected from at least one of CuSO4, CuCl2, Cu(NO3)2, and Cu(CH3COO)2.

8. The method of claim 4, wherein, The nickel salt comprises at least one of NiSO4, NiCl2, Ni(NO3)2, and Ni(CH3COO)2.

9. The method of claim 4, wherein, The reducing agent is selected from at least one of sodium hypophosphite, sodium thiosulfate, formaldehyde, hydrazine hydrate, ascorbic acid, sodium borohydride, ammonium borohydride, and formic acid.

10. The method of claim 4, wherein, The complexing agent is selected from at least one of sodium citrate, lactic acid, and glycolic acid.

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