A method for electrolytic coloring of aluminum profiles

Abstract

The present invention relates to a method for electrolytic coloring of aluminum profiles, which sequentially includes the following processes: an anodic oxidation treatment process, in which an anodic oxidation film with a predetermined thickness is formed from an aluminum profile according to a current density having a varying current density value; an electrolytic coloring treatment process, in which the aluminum profile is immersed as a cathode in an electrolytic coloring solution, a pulsed current is applied, and electrolytic coloring is carried out according to a current density having a periodically varying current density value.

Description

Technical Field

[0001] The present invention relates to the field of surface treatment of aluminum profiles, and particularly to a method for electrolytic coloring of aluminum profiles. Background Art

[0002] Aluminum has excellent high-temperature processing properties (it is relatively easy to obtain profiles with various cross-sectional shapes through hot extrusion), light weight, easy processing, and good corrosion resistance. Therefore, aluminum and its alloys can be widely used in fields such as building materials, vehicle components, and furniture.

[0003] Anodic oxidation of aluminum / aluminum alloy refers to the process in which aluminum / aluminum alloy acts as an anode in an electrolytic bath and passes an electric current under an applied voltage to maintain an electrochemical oxidation reaction. During this process, the surface of the aluminum / aluminum alloy is transformed into an oxide film, which has protective, decorative, and some other functional characteristics.

[0004] For the purpose of forming an oxide film with a good appearance on the surface of aluminum / aluminum alloy, the existing technical solutions include performing electrolytic coloring treatment after anodic oxidation treatment on aluminum / aluminum alloy. Specifically: after anodic oxidation treatment on aluminum / aluminum alloy, an oxide film is formed. The surface layer of this oxide film is a porous structure (also known as a porous layer), and the bottom layer of the oxide film is a dense oxide film thin layer (also known as an active layer or a barrier layer). The bottom layer of the oxide film is in contact with the substrate; the aluminum / aluminum alloy after anodic oxidation treatment is immersed in an electrolyte containing metal salts and acts as a cathode (the anode can be graphite, a stainless steel plate, etc.), and a negative direct current or alternating current is provided to the aluminum / aluminum alloy for electrolytic coloring. As for alternating current, in addition to commercial alternating current, alternating current with waveforms such as sine wave, square wave, triangular wave, sawtooth wave, or waveforms similar to them can be used. The electrolytic coloring treatment can also be carried out by the constant voltage method, but from the perspective of reducing the deviation of the coating film thickness, it is preferably carried out by the constant current method; during the process of electrolytic coloring with a constant current, metal ions in the electrolyte form a strong ion concentration difference near the surface of the aluminum / aluminum alloy. The metal ions penetrate through the porous layer into the activation layer, and metal ions form metal particles or metal oxide particles on the active layer. These particles are usually in the shape of hair, spheres, or grains, and their diameters are usually Under the action of light, these particles will undergo diffraction, thereby endowing the oxide film with various color appearances.

[0005] However, the technical problems existing in the above-mentioned existing technical solutions are: the time required for electrolytic coloring is relatively long, and the production efficiency is relatively low. Therefore, the existing technology still needs to be improved.

[0006] Term Explanation

[0007] As used herein, the term anodization is an electrolytic passivation process for increasing the thickness of the natural oxide layer on the surface of a metal component, where the component to be treated forms the anode of an electric circuit, and anodization enhances corrosion resistance and wear resistance.

[0008] As used herein, the terms anodic film, anodic layer, anodized film, anodized oxide film, oxide layer, and oxide film are used interchangeably and may refer to any suitable metal oxide film. The anodic film is formed on the metal surface of a metal substrate. The metal substrate may include any of a variety of suitable metals.

[0009] As used herein, the term aluminum profile refers to aluminum materials composed of pure aluminum or aluminum alloys. In some embodiments, suitable aluminum alloys include 1000, 2000, 5000, 6000, and 7000 series aluminum alloys. Summary of the Invention

[0010] The object of the present invention is to solve the above problems and provide a method for forming a colored anodic film on an aluminum profile with good weather resistance, durability, and appearance.

[0011] The present invention provides a method for electrolytic coloring of an aluminum profile, characterized by sequentially including the following processes:

[0012] (A) An anodization treatment process for the aluminum profile, in which an anodic film with a predetermined thickness is formed from the aluminum profile according to a current density having a varying current density value.

[0013] (B) An electrolytic coloring treatment process in which the aluminum profile is immersed as a cathode in an aqueous solution or aqueous dispersion (i.e., an electrolytic coloring solution) containing at least one of water-soluble or water-dispersible oxygen-containing salts, a pulsed current is applied, and electrolysis is carried out according to a current density having a periodically varying current density value to precipitate a metal or metal oxide for coloring.

[0014] Generally, before the method of the present invention, as a pretreatment, the aluminum profile is sequentially subjected to surface treatments of degreasing, etching, and neutralization using conventional methods.

[0015] In the anodization treatment process, the electrolytic bath solution composition includes 190 - 200 g / L of sulfuric acid and 12 - 16 g / L of Al 3+ , the Al 3+ comes from an inorganic salt containing Al. Preferably, the Al 3+It comes from aluminum sulfate. The temperature of the electrolytic bath liquid is 20 - 25 °C. By controlling the change of the current density during the anodizing process, the microporous structure of the anodic oxidation film is modified. A layer of anodic oxidation film formed on the surface of the aluminum profile is a porous structure. This porous structure has multiple self-organized pores. The pores are slender nano-scale pores and are highly ordered. They are each arranged in a vertical orientation relative to the surface of the anodic oxidation film and are equidistant and parallel to each other. These pores include a wide part and a narrow part, and the narrow part of the pore is close to the surface of the anodic oxidation film.

[0016] The aluminum profile obtained from process (A) must be immersed in an aqueous solution or aqueous dispersion containing one or more oxygen-containing salts selected from water-soluble or water-dispersible sulfates, silicates, borates, phosphates, chromates, molybdates, vanadates, permanganates, tungstates, and stannates for electrolytic coloring treatment. The above-mentioned oxygen-containing salts also contain at least one of nickel, cobalt, copper, and tin.

[0017] In the electrolytic coloring treatment process, by applying a pulsed current to the aluminum profile in an electrolytic coloring solution containing a metal salt, metal or metal oxide is precipitated for coloring. The temperature range of the electrolytic coloring solution is 10 - 40 °C. The pulsed current is a square wave with a frequency of 4 - 8 MHz. The pulsed current includes a time t1 of applying a high current density to the load and a time t2 of applying a low current density to the load within one cycle T, satisfying: T = t1 + t2, 0.7 ≤ t1 / T ≤ 0.9.

[0018] Beneficial effects: The method for electrolytic coloring of aluminum profiles provided by the present invention controls the current density used during the anodizing treatment of the aluminum profile, making the pore diameter of the part of the oxide film close to the bottom layer of the oxide film larger. Then, by controlling the pulsed current during the electrolytic coloring treatment, the metal deposition rate in the oxide film during the electrolytic coloring process is increased, thereby shortening the electrolytic coloring time of the aluminum profile and achieving the purpose of improving the production efficiency of electrolytic coloring of aluminum profiles. Description of the Drawings

[0019] The drawings further illustrate the present invention, but the embodiments in the drawings do not constitute any limitation to the present invention.

[0020] Figure 1 It is a cross-sectional view of an aluminum profile with an anodized film formed using a varying current density;

[0021] Figure 2 It is a graph of the current density varying with time during the anodizing process;

[0022] Figure 3 It is a graph of the current density varying with time during the electrolytic coloring process. Detailed Embodiments

[0023] It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0024] Representative applications of the method according to the present application are described below. The purpose of providing these examples is only to add context and facilitate understanding of the embodiments. Thus, it will be apparent to those skilled in the art that the embodiments may be practiced without some or all of these specific details. In other instances, well-known procedures have not been described in detail in order to avoid unnecessarily obscuring the embodiments. Other applications are possible, such that the following examples should not be considered restrictive.

[0025] In this embodiment, before electrolytic coloring, the aluminum profile needs to be anodized in a sulfuric acid solution. The electrolytic bath solution used for anodizing can be the electrolytic bath solution used in the existing sulfuric acid anodizing process. From the perspective of improving the efficiency of anodizing treatment (i.e., forming an anodic oxide film with a target thickness on the aluminum profile surface in a shorter time), preferably, the electrolytic bath solution composition includes 190 - 200 g / L of sulfuric acid and 12 - 16 g / L of Al 3+ , the Al 3+ comes from aluminum sulfate, and the temperature of the electrolytic bath solution is controlled at 20 - 25 °C.

[0026] Figure 2 Shows a graph of the current density (A / dm 2 ) varying with time (min) during an anodizing process with a varying current density. During the anodizing process, the aluminum profile is placed in the electrolytic bath solution and acts as the anode when a voltage is applied. As the anodizing process converts a part of the aluminum profile into metal oxide, the voltage is increased to a high current density B and decreased to a low current density A at different intervals.

[0027] As Figure 2 shown, during time interval a, the current density is ramped up from 0 to the high current density B; during time interval b, the current density is maintained at the high current density B. During time interval b, the width of the pores formed in the anodic oxide film is relatively wide; during time interval c, the current density is decreased to the low current density A; during time interval d, the current density is maintained at the low current density A. During time interval d, pores continue to form but have a narrower width compared to the pores formed during time interval b. The total time of the entire anodizing treatment is (a + b + c + d), at which point the anodic oxide film reaches the target thickness and the anodizing process is completed. In this way, the width of the pores can vary as they are formed, and the way of increasing and decreasing the current density can affect the pore structure shape in the resulting anodic oxide film. The resulting pore structure is such as Figure 1 shown.

[0028] Figure 1 FIG. 1 shows a cross-sectional view of an aluminum profile having an anodized film 1 formed using an anodization technique. During the anodization process, the top portion of the substrate 2 of the aluminum profile is converted into a metal oxide layer or anodized film 1, thereby forming a plurality of self-organized pores 3 within the anodized film 1. The pores 3 are elongated nano-scale pores, and the pores 3 include a wide portion 31 and a narrow portion 30. The pores 3 open at the top surface 10 of the anodized film 1 and are defined by the pore walls of the narrow portion 30. The pores 3 are highly ordered, each being arranged in a vertical orientation with respect to the top surface 10 and being equidistant and parallel to each other.

[0029] Appear in Figure 2 The relative time periods of the intervals a, b, c, and d shown are merely illustrative of a particular embodiment and do not necessarily prescribe the relative time periods of other embodiments. For example, in other embodiments, the time intervals a, b, c, and d are the same.

[0030] Refer to Figure 2 The described low current density value and high current density value can vary according to the desired pore shape and specific application requirements. In some embodiments, the high current density B varies in the range of between about 2.0 - 4.0 A / dm 2 and the low current density A varies in the range of between about 0.5 - 1.0 A / dm 2 . Since the applied current density is related to the voltage, the process can also vary with respect to high voltage values and low voltage values. The target thickness of the anodized film can also vary partly according to specific application requirements. In some embodiments, the anodization process is carried out until a target thickness of about 30 - 50 μm is achieved. In some embodiments, the total time (a + b + c + d) of the entire anodization process is between 40 - 90 min to achieve the target thickness.

[0031] In addition to controlling the pore shape and structure by varying the current density, the pore density can also be controlled during the anodization process by adjusting the electrolyte temperature. Generally speaking, the higher the electrolyte temperature, the thinner the metal oxide material formed between the pores and the higher the pore density. The lower the electrolyte temperature, the thicker the metal oxide material formed between the pores and the lower the pore density. The higher the pore density, the greater the amount of pores. Therefore, a higher electrolyte temperature is beneficial for shortening the subsequent electrolytic coloring time of the aluminum profile. However, when selecting the electrolyte temperature, other factors such as the durability of the anodized film should also be considered. In some embodiments, it is suitable to use an anodization bath temperature of 20 - 25 °C.

[0032] By controlling the change of current density and the temperature of the electrolytic bath during the anodizing process, the pore structure of the obtained anodic film needs to meet the following requirements: the maximum width of the narrow part of the pore is 40-50% of the maximum width of the wide part of the pore. In this range, the electrolytic coloring time of the subsequent aluminum profiles can be significantly shortened.

[0033] It should be noted that before the anodizing treatment of the aluminum profiles, one or more of any suitable pre- and post-anodizing processes can be implemented. For example, before anodizing, the aluminum profiles can undergo one or more cleaning, polishing, and sandblasting operations.

[0034] Form an anodic film on the surface of the aluminum profiles; place the aluminum profiles in an electrolytic coloring solution for electrolytic coloring treatment. The anodic film formed on the surface of the aluminum profiles is a porous structure. The depth of the color that the aluminum profiles can present mainly depends on the amount of metal deposited in the pores of the oxide film. If more metal is deposited in the pores of the oxide film during the same electrolytic coloring time, the color will be deeper; otherwise, it will be shallower.

[0035] Compared with the existing electrolytic coloring process for aluminum profiles, the method for electrolytic coloring of aluminum profiles provided by the present invention can achieve the preparation of aluminum profiles with the same film thickness and the same color in a shorter time. The principle of its realization is as follows:

[0036] 1. Due to the special structure of the pore structure of the anodic film, when the aluminum profiles after anodizing treatment are placed in the electrolytic coloring solution, capillary action can be formed in the narrow part of the pores, guiding the electrolytic coloring solution to the wide part of the pores. The larger pore diameter of the wide part of the pores can deposit more metal during the same electrolytic coloring time;

[0037] 2. Pulse current is used during the electrolytic coloring process, Figure 3 Show a graph of the current density (A / dm 2 ) varying with time (ns) during the electrolytic coloring process with a varying current density. As shown in Figure 3, within a cycle T, during the time interval t1, the current density is maintained at the high current density B2. During this time, the electrolytic coloring solution in the pores of the anodic film, especially in the wide part of the pores, undergoes a strong reduction reaction to rapidly produce metal deposition, and at the same time, the metal ions in this part of the electrolytic coloring solution are rapidly consumed, causing the metal ion concentration to decrease rapidly; during the time interval t2, the current density is maintained at the low current density A2. During this time, the consumption rate of metal ions in the wide part of the pores decreases. Through the concentration difference of metal ions inside and outside the pores and the synergistic effect of the narrow part of the pores similar to a capillary, the metal ions in the pores of the anodic film, especially in the wide part of the pores, are rapidly replenished. By pulse-changing the current density during the electrolytic coloring process, the electrolytic coloring time of the aluminum profiles can be significantly shortened.

[0038] For further shortening the electrolytic coloring time of aluminum profiles, the pulsed current is a square wave with a frequency of 4 - 8 MHz. The pulsed current includes a time t1 of applying a high current density to the load and a time t2 of applying a current density to the load within one period T, satisfying: T = t1 + t2, 0.7 ≤ t1 / T ≤ 0.9. The high current density B2 varies within a range between approximately 1.5 - 5.0 A / dm 2 and the low current density A2 varies within a range between approximately 0.15 - 0.5 A / dm 2 between them.

[0039] In one embodiment, the anodized aluminum profiles are electrolytically colored black. The electrolytic coloring solution contains 10 - 15 g / L of stannous sulfate, 25 - 30 g / L of nickel sulfate, and 25 - 30 g / L of nickel sulfate salt. The pH value of the electrolytic coloring solution is 0.6 - 1.0, and the temperature of the electrolytic coloring solution is 15 - 20 °C. Using the existing electrolytic coloring process for aluminum profiles, after the aluminum profiles are sulfuric acid anodized (current density is 1.50 A / dm 2 , the anodizing time is 40 min, and the thickness of the anodized film is 20 μm), they are put into the above electrolytic coloring solution for electrolytic coloring. The time required to electrolytically color them to black is approximately 20 min. Under the same other conditions, using the method for electrolytic coloring of aluminum profiles provided by the present invention, the time required to electrolytically color them to black is approximately 10 min. The method for electrolytic coloring of aluminum profiles provided by the present invention can greatly reduce the electrolytic coloring time, accelerate the production of electrolytically colored aluminum profiles, and improve their production efficiency.

[0040] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0041] The above-described embodiments merely represent several implementation manners of the present invention. Their descriptions are relatively specific and detailed, but they should not be construed as limitations on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims.

Claims

1. A method for electrolytic coloring of aluminum profiles, characterized in that the method successively includes the following processes: An anodizing treatment process, in which an anodic oxidation film with a predetermined thickness is formed from the aluminum profile according to a current density having a varying current density value. A plurality of self-organized pores are formed in the anodic film, and the pores include a wide portion and a narrow portion. The pores open at the top surface of the anodic film and are defined by the pore walls of the narrow portion. The maximum width of the narrow portion of the pore is 40-50% of the maximum width of the wide portion of the pore; An electrolytic coloring treatment process, in which the aluminum profile is immersed as a cathode in an electrolytic coloring solution, and a pulsed current is applied for electrolytic coloring according to a current density having a periodically varying current density value; In the anodizing treatment process, the composition of the electrolytic bath solution includes 190-200 g / L of sulfuric acid and 12-16 g / L of trivalent aluminum ions, and the trivalent aluminum ions are from aluminum sulfate. The temperature of the electrolytic bath solution is 20-25 °C; In the anodizing treatment process, the anodic oxidation film is formed through the following steps: During a time interval a, the current density is ramped up from 0 to a high current density B; During a time interval b, the current density is maintained at the high current density B; During a time interval c, the current density is decreased to a low current density A; During a time interval d, the current density is maintained at the low current density A; The high current density B varies within a range between 2.0 - 4.0 A / dm 2 and the low current density A varies within a range between 0.5 - 1.0 A / dm 2 ; In the electrolytic coloring treatment process, electrolytic coloring is carried out through the following steps: (a) The current density is maintained at a high current density B2 during a time period t1; (b) The current density is maintained at a low current density A2 during a time period t2; The time period t1 and the time period t2 constitute a cycle T, and (a) to (b) are repeated until the aluminum profile can present a target color; The frequency of the pulsed current is 4-8 MHz, and the pulsed current satisfies: T = t1 + t2, 0.7 ≤ t1 / T ≤ 0.9; The high current density B2 varies within a range between 1.5 - 5.0 A / dm 2 and the low current density A2 varies within a range between 0.15 - 0.5 A / dm 2 and.

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