JPS5919989B2 - How to engrave metal plates - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal plate etching method, and more particularly to an etching method suitable for manufacturing a shadow mask for a color picture tube.

For example, a shadow mask for a color picture tube usually has a single metal plate with mask perforations formed in a predetermined arrangement, and the mask perforations have different diameters on both sides of the metal plate.

The mask perforations are generally etched by photolithography.

To explain the outline of this process, a photocurable resin (photoresist) is applied to both sides of a flat metal plate with a certain thickness.
After coating and drying to form a photoresist film, a negative master plate having a negative image of small diameter holes is placed on one side of this metal plate, and a negative master plate having a large diameter negative image on the other side are placed in close contact with each other.
Each negative image is printed onto a photosensitive film using an ultraviolet light source. Next, the uncured resin in the unexposed areas of the photoresist film is dissolved and removed using hot water to expose the parts of the metal plate where the mask perforations will be made, and then the water resistance and adhesion of the remaining photoresist film to the metal plate are tested. High-temperature heat treatment is applied to improve the quality and prevent decomposition and peeling caused by the etching solution. Next, the exposed portion of the metal plate is corroded by spraying an etching liquid, and a mask perforation portion is formed. There are chemical methods and electrochemical methods for etching the shadow mask, but chemical methods such as spraying an etching liquid or immersing a metal plate in an etching liquid are generally used.

The common problems of the spray method and dipping method are the shape of the perforation and the state of cutting around the perforation, which is mainly due to the adhesion strength between the photosensitive film and the metal plate, and the etching resistance and water resistance of the photosensitive film. be. These characteristics naturally depend on the characteristics of the photocurable resin forming the photoresist film, but they also vary depending on the photoresist film thickness and high-temperature heat treatment conditions. If the shape of the perforation is different from the desired shape and the cut is poor, the phosphor layer will be burned in a one-to-one manner by the light passing through the perforation, so the cut will not occur in striped color picture tubes. This is bad and tends to result in constricted phosphor stripes. As a result, the uniformity on the screen when producing a white image deteriorates, and there is a drawback that the electron beam's land ink margin decreases.
Compared to the spray method, immersion etching does not involve mechanical injection of etching liquid onto the metal plate, so consider factors that affect etching, such as spray pressure, overlapping spray patterns, and pooling of etching liquid. Although not necessary, variations in the shape of the perforations due to non-uniform stirring of the etching solution and variations in the diameter of the perforations due to side etching pose problems.

Furthermore, since the etching time is too long, this method may be used for small samples, but is not commonly used as a method for manufacturing shadow masks. Etching using the spray method described above has the advantage that the etching time is shorter than etching using the dipping method. However, due to uneven etching, the hole diameter is partially uneven.
There are variations in the hole shape and hole diameter due to side etching, and these are affected by the way the etching liquid hits the metal surface, the distribution of liquid pools on the metal surface, and the etching time and composition. . Particularly unevenness in the hole diameter,
Eliminating variations in perforation diameter due to side etching results in an ideal shadow mask with perforations that are one-to-one with the negative original. The unevenness of the perforation diameter mentioned above is greatly affected by the state of the etching liquid pooling on the surface of the metal plate, and the exchange rate with new etching liquid is faster in areas with a lot of liquid pooling compared to areas with less pooling. This is because the etching speed decreases. In particular, when the number of nozzles during spraying is increased and the amount of etching liquid supplied per hour is increased, the amount of liquid accumulated increases, the etching speed decreases, and the above-mentioned local unevenness becomes noticeable. This is because the etching liquid sprayed from above during etching first accumulates on the metal plate, and even after the hole is drilled, the diameter of the perforation is small, so the surface tension of the etching liquid prevents it from falling, and even after the hole is drilled, it does not fall down due to the surface tension of the metal plate. This is caused by being sprayed with etching liquid. Therefore, if the amount of liquid accumulated is small and the liquid is uniformly distributed, uniform etching without local unevenness can be performed. One way to counter this problem is to give the metal plate a curvature during etching so that the etching liquid always flows downward, but it is difficult to give the metal plate a certain curvature during the etching process, and the metal Although a constant tension is applied in the plate feeding direction, it is difficult to control liquid pooling due to deflection. Furthermore, variations in perforation diameter due to side etching can naturally occur from a corrosion chemical perspective, and the main cause of this is that the common area between the three layers of the metal plate, photosensitive film, and etching solution is This is because the plaster cast is more active against corrosion in terms of free energy than the common part of the two layers, and the corrosion rate is faster.

Further, since the desired perforation is a very thin hole of several hundred microns, as it corrodes, the flow of the etching liquid within the perforation deteriorates. As a result, pitting corrosion (
The pH of the etching liquid in the perforated portion is lower than that on the metal surface, accelerating the corrosion rate, which is also a major cause of side etching. Therefore, at the end of drilling, a hole with a larger diameter than desired is obtained, so when producing a negative master plate, the amount of increase in the hole diameter due to side etching must be taken into account, and the etching time, etching liquid composition, and metal Since the progress of side etching varies depending on the material and thickness of the plate, it is extremely difficult to obtain a shadow mask with consistent hole diameters. As a method to prevent this side etching, conventionally, giraffe blood is applied to the etched side surface during the etching process, and the etching is performed again.By repeating this several times, the amount of side etching can be minimized. In the Kirinke method, a surfactant, fatty acids, and certain aromatic and aliphatic hydrocarbons are added to the etching solution to create an adsorption layer that acts as a corrosion-preventing film on the metal surface to be corroded. Powderless etching methods have been considered to minimize the amount of side etching. However, the former method has the drawbacks of poor accuracy and poor shape of the perforation, and is too time-consuming, making mass production impossible. In the latter case, the amount of side etching can be suppressed to some extent, but there are problems in that it takes a long etching time to form an adsorption layer that serves as an anti-etching film, and the effect of additives on the etching solution. The present invention provides a shadow mask for color picture tubes, etc., which uses an etching method that combines the advantages of both the spray etching method and the immersion etching method from the viewpoint of corrosion chemistry as described above, to prevent unevenness and variation in the perforation diameter. A method of etching a metal plate is provided.

That is, the present invention applies ultrasonic waves continuously or intermittently to the metal plate corroded during spray etching in order to make the etching liquid pool on the metal plate uniform and to improve the flow of the etching liquid in the perforated portion. It is characterized by constantly giving high-frequency vibrations.

As a result, the fluidity of the etching liquid on the metal plate and in the perforation is promoted, and the corroded surface is constantly replaced with new etching liquid, which shortens the etching time and reduces the amount of side etching, resulting in uniform etching. It becomes possible to engrave. Examples of methods for applying ultrasonic waves include, for example, when a metal plate after high-temperature heat treatment enters the etching process, electrodes for emitting ultrasonic waves are brought into contact with both sides of the metal plate; It is also possible to use an electrode with a groove to prevent non-contact with the electrode, and perform spray etching while holding and sliding the metal plate through the groove.

Although good results are obtained with the frequency of the ultrasonic waves emitted from the electrodes in the range of 10 to 30 KHz, it is desirable to select an appropriate frequency depending on the width, thickness, etc. of the metal plate. Furthermore, if the amplitude of the electrode is too large, the sprayed etching liquid will be blown off the surface of the metal plate, so it is desirable to determine the optimum amplitude experimentally. Further, by making the frequency of the ultrasonic wave variable, the etching state can be further adjusted. The metal plate etching method of the present invention is applicable not only to the production of shadow masks for color picture tubes, but also to similar products.
Of course.

Claims (1)

[Scope of Claims] 1. A method for etching a metal plate, characterized in that spray etching is performed by directly applying ultrasonic waves to the metal plate via an electrode for emitting ultrasonic waves. 2. The method of etching a metal plate according to claim 1, wherein the metal plate is used for a shadow mask. 3. The method of etching a metal plate according to claim 1, wherein ultrasonic waves are applied to the metal plate continuously or intermittently during spray etching. 4. The method of etching a metal plate according to claim 1, wherein the ultrasonic emission electrode has a groove, and the metal plate is held between the grooves.