RU2709558C1 - Method of selective etching of steel - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to chemical etching of metals, particularly to selective etching of steel in a solution based on oxalic acid and hydrogen peroxide, and can be used in making decorative articles with a relief image in the form of recesses and when making a printing plate for etching. In the method, steel sections not subject to etching are protected by deposition of copper, nickel, lead or their alloys with other metals, and selective etching is carried out at the following content of components in the solution, wt%: oxalic acid 4–22, hydrogen peroxide 1–6, water – balance.

EFFECT: invention provides higher rate of selective etching of steel with reduction of its lateral picking and reduced consumption of hydrogen peroxide per unit weight of etched metal, and consequently, and with reduced consumption of solution.

1 cl, 3 ex

Description

The invention relates to chemical etching of metals, in particular to a method for the selective etching of steel in a solution based on oxalic acid and hydrogen peroxide, and can be used to create decorative products with a relief image in the form of recesses and in the manufacture of a printing plate for etching.

Known solution for the etching of steel, containing oxalic acid, hydrogen peroxide and organic additives that improve the quality of the etching. [A.S. 1035093 USSR, IPC C23G 1/04. The solution for pickling steel. / G.A. Shapkin et al. (USSR) .- No. 3404504 / 22-02; declared 03/01/82; publ. 08/15/83 Bul. No. 30]. The solution provides a satisfactory speed of selective etching, a small amount of side etching, high surface finish, the safety of the photoresist film during prolonged contact with the solution. The disadvantage of the solution is the complexity of the composition and preparation, as well as the fact that all its advantages can be realized only by jet etching, which is applicable only for sheet-shaped products. During etching by immersion, the solution becomes similar in its properties to a solution without organic additives.

Closest to the proposed solution is a method of selective etching of sheet steel in a solution based on oxalic acid and hydrogen peroxide, which provides a high etching rate, high quality surface treatment and other advantages. The specified method is adopted as a prototype. [A.s. 239755 USSR, IPC C23G 1/02. The method of selective etching of sheet steel. / L.T. Dyakonova and others (USSR) .- No. 1149250 / 22-1; declared 04/15/67; publ. 03.03.70 Bull. No. 9].

However, it has a significant drawback associated with the requirement of special conditions and equipment for its implementation, which limits the application of the method. This is due to the fact that in peroxide solutions the etching process is accompanied by abundant gas formation due to the decomposition of hydrogen peroxide into water and oxygen. Due to the different catalytic activity of the open metal sites and the polymer-coated protective pattern, the degree of decomposition of hydrogen peroxide on them is not the same, as a result, bubbles are adsorbed at the metal-resist interface, creating a barrier to the etchant, which leads to uneven etching. To obtain a qualitative result, it is necessary to take measures for the forced removal of bubbles. To this end, etching is carried out during periodic impacts of the sheet blank with a protective layer on the surface of the etchant mirror. At the moment of separation of the workpiece from the surface of the etchant, the bubbles burst. You can also mechanically move the workpiece in the solution or mix the solution so that the etchant is in a state of intense turbulent motion and breaks down the gas barrier.

Another disadvantage of this method is the high consumption of reagents, which makes the method expensive. The pickling ability of a solution is based on the oxidizing effect of hydrogen peroxide on steel and the dissolution of oxides formed with oxalic acid. Since peroxide reacts not only with steel, but also with a polymer resist, part of it is consumed without benefit.

In addition, when etching reliefs in this way, side etching of image elements is observed all the more, the narrower the stroke. This is due to the separation of the polymer resist from the steel due to poor adhesion and intense gas formation from the etching sites.

The proposed method does not have these drawbacks and allows to simplify the etching process, reduce the consumption of reagents and the cost of manufacturing products, reduce side etching of image elements.

This object is achieved in that in the method of selective etching of steel in a solution based on oxalic acid and hydrogen peroxide, copper, nickel, lead, or their alloys with other metals are deposited to protect sections of steel not subject to etching, and etching is carried out at the following components in solution (wt.%): oxalic acid 4-22%, hydrogen peroxide 1-6%, the rest is water.

Using a metal resist significantly changes the etching process.

First, it was found that the reaction between hydrogen peroxide and metal resist proceeds much more slowly than the corresponding undesirable reaction with polymer resistors, and bubbles are not adsorbed at the steel-resist interface. This allows etching by immersion in an etching bath in a stationary mode, as well as minimizing the consumption of hydrogen peroxide per unit mass of the etched metal, since it is not lost in side reactions.

Secondly, the metal resist is in electrical contact with steel, forming an active galvanic pair in which steel is the anode. Therefore, electrochemical is added to the chemical dissolution and etching proceeds at a higher rate. This makes it possible, at the same etching rate, to carry out the process at a lower content of oxalic acid and hydrogen peroxide in comparison with the prototype.

Thirdly, the adhesion of the metal resist to the surface of the steel is higher and there is no violation of the adhesion of the protective pattern to the base due to gas formation from the etching sites. In this regard, when etching reliefs containing dashed elements of an image of small width (up to 300-500 microns), the etching factor can reach 2-3 or more, which allows etching to a greater depth and increase the yield of quality products by reducing lateral etching .

In addition, the advantage of the proposed method is the ability to use in the manufacture of various decorative products with a relief image metal resist (for example, from brass, bronze or nickel) simultaneously as a decorative coating and, thus, reduce their cost.

It was experimentally found that when using copper or its alloy with zinc as a resist (copper content is 65-70%) and when the surface area of the resist is greater than the surface area of open sections of steel, etching does not start or begins and immediately stops or has a cyclic nature, which noticeable by the change in the intensity of gas formation from the etching sites. Apparently, the passive state of steel is caused by a displacement of the electrode potentials of the metals forming a galvanic pair. The assumption is supported by the fact that when etching workpieces with the same resistivity topology, but made of lead or nickel, this phenomenon is not observed. The ratio of the surface area of the resist and the open areas of steel at which this effect is manifested depends on the concentration and temperature of the solution and is usually greater than or equal to 1. In this case, the workpiece must be etched in contact with a piece of steel, and its surface area should be chosen such so that the steel is in a state of active dissolution.

The use of an etching solution in which the concentrations of the components do not fall within the limits is impractical, since with a lower content of oxalic acid and hydrogen peroxide the quality of the etched surface deteriorates. An increase in the content of hydrogen peroxide of more than 6% is accompanied by spontaneous decomposition in solution. An increase in oxalic acid concentration of more than 22% does not increase the etching rate. The etching process is recommended to be carried out in the temperature range of 18-35 ° C. This range is primarily determined by the solubility of oxalic acid. Oxalic acid is sparingly soluble, at 20 ° C a saturated solution is obtained with its content of 8.7%, an increase in temperature allows the use of more concentrated solutions.

The present invention is illustrated by examples that clearly demonstrate the ability to achieve the above set of features of the desired technical result.

The samples were made of cold rolled steel sheet 08KP. Preparation of the sample surface includes grinding, polishing, degreasing, forming by means of photolithography a protective pattern containing line elements of the image with a width of 300-500 microns from photoresist FN11 and galvanic copper or brass (copper content 65-70%) with a thickness of 5-8 microns deposited in windows photoresist. In each example, the topology of the protective pattern and the dimensions of the samples are the same.

The effectiveness of the invented method was judged by the speed and etching factor (the ratio of the etching depth to the value of lateral etching) and appearance.

The etching depth and the deviation of the sizes of the elements of the pattern were measured by the metallographic method. The appearance of the sample was evaluated visually by the condition of the etched surface, the roughness of the edge of the elements of the pattern, and the presence of etching with an increase of 50-80 ^X.

Example 1. Samples with resist from FN11 and copper were simultaneously immersed in a solution containing, wt.%: Hydrogen peroxide 1.5, oxalic acid 6, the rest was water. The process was conducted in a stationary mode at 20-22 ° C. The etching rate was 1.5-1.6 μm / min and 0.9-1.0 μm / min for the sample with resist from copper and FN11, respectively, the etching factor is 2.5-3 and 1.5-2. Samples with a copper resist are etched evenly, the surface is fine-grained, uniform, the edge of the contour is even, the etching process is not accompanied by bubble adsorption. Samples with a resistor from ФН11 are not etched uniformly, the surface is not uniform in texture, the edge of the contour is not even, during etching the surface of the sample is covered with bubbles.

Example 2. Samples with resist from FN11 and brass were simultaneously immersed in a solution containing, wt.%: Hydrogen peroxide 5, oxalic acid 20, the rest water. The process was conducted in a stationary mode at 33-35 ° С. The etching rate was 11–12 μm / min and 7–8 μm / min for the sample with brass and FN11 resist, respectively, the etching factor was 2–2.5 and 1.5–2. Samples with a metal resist are etched evenly, the surface is fine-grained, homogeneous, the edge of the contour is even, the etching process is not accompanied by bubble adsorption. Samples with a resistor from ФН11 are not etched uniformly, the surface is not uniform in texture, the edge of the contour is not even, during etching the surface of the sample is covered with bubbles.

Example 3. Pre-weighed samples with resist from FN11 and copper were simultaneously immersed in separate containers with equal portions of the solution, cast from the total volume of the solution containing, wt.%: Hydrogen peroxide 2%, oxalic acid 8%, water the rest. The process was conducted in a stationary mode at 18-22 ° C until the solution was completely developed (24 hours). After etching, the samples were weighed and the efficiency of the solution was evaluated by the decrease in the mass of the samples. The flow rate of the solution per unit mass of the etched steel for samples with a protective pattern of copper (depending on the topology of the protective pattern) is 15–25% less compared to samples with a protective pattern of FN11.

It can be seen from the above examples that obtaining a qualitative result during etching by immersion in a stationary mode in a solution with a concentration of the starting components in the selected intervals without the use of a metal resist to protect the etched sections is impossible, since there are no conditions preventing the surface of the workpiece from blocking by bubbles. The obtained data also show that the proposed method of selective etching increases the etching efficiency by increasing the etching rate, reducing side etching and consumption of the solution per unit mass of the etched metal and, therefore, provides economic advantages compared with the known technical solutions to the same problem.

The analysis of known methods of selective etching shows that most of the essential features used in the inventive method of selective etching separately are known, however, the non-obviousness and, therefore, the inventive step of the claimed technical solution follows from the fact that their combined use gives a new positive result, not directly derived from these methods, for example, the possibility of etching by immersion in a stationary mode and reducing the consumption of etching solution.

Claims (1)

The method of selective etching of steel in a solution based on oxalic acid and hydrogen peroxide, characterized in that copper, nickel, lead or their alloys with other metals are deposited to protect sections of steel not subject to etching, and etching is carried out at the following components in the solution ( wt.%): oxalic acid 4-22, hydrogen peroxide 1-6, water - the rest.