JPS6231441B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a reflective plate surface protective coating. It is well known that alkali metal silicate coatings are available as surface protective coatings for metal plates such as iron plates and aluminum plates. The alkali metal silicate coating is formed by dipping or coating a metal plate in an aqueous solution of an alkali metal oxide and a silica salt. The properties of an alkali metal silicate coating formed on a metal plate vary greatly depending on the amount of alkali metal remaining in the coating. Therefore, it is necessary to control the amount of residual alkali metal in the alkali metal silicate coating depending on the purpose of use. By the way, when a metal plate is used as a reflector for lighting and an alkali metal silicate coating is applied to the reflector,
It is known that it is possible to maintain the reflectance of the reflector plate without reducing it, and that it also has good corrosion resistance and weather resistance, and is currently being commercialized. In such applications, it is especially important to maintain a high reflectance of the reflector, and therefore it is necessary that the alkali metal silicate coating coated on the reflector does not become cloudy due to changes over time. be. When investigating the cause of cloudiness, it was discovered that the alkali metal contained in the alkali metal silicate film reacts with carbon dioxide gas in the air to produce carbonate, and that this carbonate is the cause of cloudiness. When potassium is used as the alkali metal, the reaction equation is estimated to be as follows. CO ₂ +H ₂ O→H ₂ CO ₃ K ₂ O+H ₂ O→2KOH 2KOH+H ₂ CO ₃ →K ₂ CO ₃ +2H ₂ O Therefore, in the above reaction formula, carbonate (K ₂ CO ₃ ), which causes cloudiness, alkali metals to suppress the formation of
In other words, it can be seen that it is sufficient to reduce the residual amount of potassium. From this point of view, Japanese Patent Application Laid-Open No. 49-24446 discloses that almost all alkali metal ions are removed from an alkali metal silicate coating. However, as a result of experiments, it has been found that when the alkali metal in the alkali metal silicate coating is removed and the remaining amount decreases, cracks occur in the coating. In fact, when an alkali metal silicate film was formed on an aluminum plate using the method disclosed in JP-A No. 49-24446 mentioned above, and the alkali metal was removed and measured, cracks were found in the film. There has occurred. The cause of cracks can be explained by referring to the same amorphous glass. Generally, glass is said to be an amorphous network structure having siloxane bonds with non-bridging oxygen atoms present here and there, and molecules are cut at these parts. By analogy from this, in the case of alkali metal silicate coatings, alkali metal ions are interposed between these non-bridging oxygen atoms, electrostatically bonding these oxygen atoms and interconnecting the disconnected molecules. It is thought that they are connected. Therefore, when these alkali metal ions are removed from the network structure, the molecules are cut off from each other, causing a cracking phenomenon to occur. For these reasons, if the residual amount of alkali metal in the alkali metal silicate coating is small, it is not preferable as a protective coating for the surface of a reflector. This is because the corrosion resistance of the coating decreases. Therefore, it is necessary to control the amount of alkali metal remaining in the coating. As mentioned above, cracks in the alkali metal silicate coating are mainly caused by the residual amount of alkali metal, but when a reflector coated with this coating is assembled as a lighting fixture and a lamp is lit, the coating cracks as the temperature of the reflector increases. Cracks may occur. This is due to the difference in thermal expansion between the reflector and the coating.
Since the differential thermal expansion is a function of temperature, temperature conditions must be taken into account. Generally, the temperature of the reflector plate used in lighting equipment reaches 200℃ when the lamp is turned on.
It is desirable to prevent the coating from cracking in an atmosphere of 150°C to 200°C. When considering the difference in thermal expansion between the reflector and the coating under such temperature conditions, it is found that the thickness of the alkali metal silicate coating and the amount of residual alkali metal are factors that affect the difference in thermal expansion. In general, the thicker the film, the more likely it is that cracks will occur, and the larger the amount of residual alkali metal, the higher the expansion coefficient.
Therefore, in order to provide a good reflective plate surface protective coating, it is necessary to establish a correlation between the thickness of the alkali metal silicate coating and the amount of residual alkali metal, and to appropriately control both. Therefore, the present invention provides good reflector surface protection by setting the residual amount of alkali metal in the alkali metal silicate coating on the reflector and its film thickness within an appropriate range that does not cause clouding or cracking. The purpose is to provide a coating. When forming an alkali metal silicate film, there is an initial problem as to which alkali metal to choose, but since potassium has a property that it is difficult to whiten during the treatment process, in the present invention, an alkali whose main component is potassium is used. An alkali metal silicate protective coating containing potassium is formed on the reflective plate by selecting a metal. However, it does not deviate from the present invention even if other alkali metals such as sodium and lithium are mixed as long as the same effects as the present invention are achieved. The invention will now be explained in conjunction with the drawings. FIG. 1 shows an embodiment of a projector in which a potassium silicate coating is applied to the reflector. The floodlight consists of a front light body 10 and a rear light body 11. Parts of the front light body and the rear light body constitute a reflecting plate, and the reflective inner surface is coated with a potassium silicate coating 20. .
The front lamp body 10 and the rear lamp body 11 are connected by an opening/closing mechanism 12 so as to be openable and closable. A front glass 13 is airtightly attached to the front opening of the front lamp body 10, and a support frame 14 is attached to the periphery of the rear opening, which is pivotally supported by support legs 15. The rear light body 11 houses a socket 16 inside, and a lamp 17 is inserted into it.
is installed, and feeder 18 is connected from the socket.
is being drawn out. As is well known, it is necessary for a lighting reflector to have a high reflectance on its reflecting surface, be able to maintain this high reflectance for a long period of time, and have excellent corrosion resistance and weather resistance. For this reason, reflective plates are usually coated with a protective coating, but if the coating itself becomes cloudy or cracks, the intended purpose cannot be achieved. According to experiments, the reflectance of aluminum reflectors coated with a good potassium silicate coating is 80 to 82%, but if the coating becomes cloudy over time, the reflectance drops to 70% or less. is known. In the present invention, such clouding does not occur in the potassium silicate film coated on the reflective plate, but on the other hand,
In order to provide a good protective film that does not cause cracks, the amount of residual potassium in the film and the film thickness are controlled within appropriate ranges. First, a machined and shaped reflector, for example 10 in FIG. 1, is prepared. The reflecting plate may be a metal plate made of a desired material such as an iron plate or an aluminum plate, but an aluminum plate is used in the embodiment of the present invention to improve reflectance. The reflector plate made of aluminum is degreased in a conventional manner, washed with water, electrically or chemically polished, and washed again with water. Next, a potassium silicate solution is applied to the inner surface of the reflector. In one embodiment, the potassium silicate solution consists of the following components: Potassium oxide (K ₂ O) 1.6% Silica (SiO ₂ ) 4.1% Water 94.3% The aqueous solution is applied to the reflector by a spray method, but of course a dipping method may also be used. According to the dipping method, the outer surface of the reflector is also coated with a film, which is useful from the viewpoint of corrosion resistance, weather resistance, and aesthetics of the outer surface of the reflector. The potassium silicate solution may be applied at once or multiple times. In any case, it is necessary to apply the solution so that the film has a predetermined thickness. If the coating is applied all at once, pinholes may be formed in the coating due to dust in the air or impurities mixed in the solution. Therefore, the corrosion resistance will be improved if the coating is applied two or more times to obtain a coating of the same thickness. The potassium silicate coating formed by applying and baking a potassium silicate solution one or more times contains a large amount of ionized potassium therein. Therefore, depotassium treatment is performed to prevent clouding of the film. Depotassium treatment is carried out by immersing in dilute nitric acid or warm water for a predetermined period of time. In the former case, the amount of potassium removed in the potassium removal treatment is related to the concentration and temperature of the nitric acid solution, but also to the immersion time. Therefore, when the concentration and temperature of the solution are kept constant, the amount of potassium removed and therefore also the amount of potassium remaining in the coating can be controlled by varying the soaking time. According to experiments, when a 3% nitric acid aqueous solution was kept at 70 DEG C. and immersed in the solution for 3 minutes, the amount of potassium remaining in a 2 micron thick potassium silicate coating was about 2 to 3 ppm. As will become clear later from FIG. 2, if the amount of residual potassium is to be reduced, the immersion time may be lengthened, and if it is to be increased, the immersion time may be shortened, and the amount of residual potassium can be freely controlled by the immersion time. Note that the potassium removal treatment can be performed each time after baking the film, but care must be taken to control the amount of residual potassium. As mentioned above, if the amount of potassium remaining in the potassium silicate coating is small, cracks will occur, whereas if the amount of residual potassium is large, the coating will become cloudy. Therefore, the amount of residual potassium must be controlled to an appropriate value. However, there is a correlation between the amount of residual potassium and the thickness of the film, and the amount of residual potassium is determined within an appropriate range in relation to the film thickness. Table 1 below shows the measured values of the film thickness and amount of residual potassium for each sample of the potassium silicate film formed on the reflector by the method described above, and the values for each sample corresponding to the measured values. Indicates the appearance (cloudiness, presence or absence of cracks).

【table】

【table】

[Table] Fifty samples were used in the experiment, as indicated by sample numbers 1 to 50 in the leftmost column of Table 1.Excluding untreated samples, the depotassium treatment conditions were changed one by one to determine the film thickness and residual potassium. As a result of the measurement, the measured values shown in Table 1 were obtained. As the depotassium treatment conditions, nitric acid or water at 70°C to 90°C was used as the treatment liquid, and the treatment was carried out individually within the range of 30 seconds to 30 minutes. What should be kept in mind here is that clouding and cracking of the alkali metal silicate film formed on the reflector depends on the thickness of the film and the amount of residual potassium, and treatment must be carried out so that both are within an appropriate range. This means that all you have to do is control the conditions. FIG. 2 is a semi-logarithm graph plotting the above-mentioned Table 1. As mentioned above, Figure 2 shows that in order to form an alkali metal silicate film on a reflector that does not cause clouding or cracking, it is necessary to appropriately control the film thickness and the amount of residual potassium. Recognize. The horizontal axis shows the film thickness in μ, and the vertical axis shows the amount of residual alkali in ppm, which is shown on a logarithmic scale. The amount of residual potassium is measured under the following conditions. That is, a potassium silicate coating sample with a surface area of 3000 mm ² was divided into several pieces, and all of them were immersed in 50 ml of a 5% by weight solution of hydrofluoric acid for about 10 minutes or more to remove the potassium silicate coating on the aluminum reflector. Dissolve completely. After dissolution, remove the reflector from the solution and measure the amount of potassium in 50 ml of this hydrofluoric acid solution. On this occasion,
The amount of potassium contained as an impurity in the hydrofluoric acid solution used and the amount of potassium eluted from the aluminum reflector are excluded, and only the amount of potassium in the potassium silicate film is measured. The measurement method is based on atomic absorption spectrometry or flame spectroscopy. The amount of residual potassium in the potassium silicate coating described in this specification and shown in the drawings was measured under the above measurement conditions, but the measured value indicates that the coating covers only the reflective surface of the aluminum reflector plate. This is the case when the
In addition, when preparing the sample, rather than applying an alkali silicate coating to a reflector sample with a size of 3000 mm ² , it is necessary to apply a 3000 mm ² coating to a larger reflector sample.
It should be noted that stable measurement data with no variation in measurement values can be obtained by cutting out the size. As is clear from the graph of FIG. 2, there is a correlation between the thickness of the potassium silicate coating and the amount of residual alkali, and the allowable amount of residual potassium changes depending on the film thickness. For example, if the film thickness of the film is 1μ, the appropriate amount of residual potassium is in the range of 0.03ppm to 5.8ppm, and if the film thickness of the film is 3μ, the appropriate amount of residual potassium is in the range of 8.8ppm to 53ppm. amount.
When the amount of residual potassium relative to the film thickness of the coating is within the shaded range in FIG. 2, a good potassium silicate coating without cracking or clouding can be obtained.
However, in practice, it is desirable that the film thickness be 1 μm or more from the viewpoint of wear resistance and corrosion resistance, even if it falls within the appropriate range indicated by diagonal lines in FIG. On the other hand, in order to increase the film thickness, it is necessary to repeat the treatment process multiple times, so from the viewpoint of manufacturing cost, it is desirable that the film thickness is about 4 μm or less. There are various methods for measuring the film thickness, but it can be measured non-destructively by observing the interference waveform of light based on the spectral reflectance of the film on the reflector. If the film thickness of the coating is 3 μm or more, it can also be measured by measuring changes in eddy current due to high frequency waves. The measured values of film thickness in this specification are those measured by the above method. As described above, by controlling the amount of residual potassium in the thickness of the potassium silicate film according to the present invention so that it falls within the appropriate range indicated by the diagonal lines in Figure 2, it is possible to achieve a good result with no cracking and no clouding. A protective film is obtained.

[Brief explanation of the drawing]

Fig. 1 is a side view showing an embodiment of a projector having a reflector coated with a potassium silicate film according to the present invention, and Fig. 2 is a side view showing the thickness of the potassium silicate film and the measured values of residual potassium. It is a logarithmic graph. [Explanation of symbols of main parts], Reflector plate...10,
Potassium silicate coating...20.

Claims (1)

[Claims] 1. In an alkali metal silicate reflective surface protective coating containing potassium, the film thickness of the film and the amount of residual potassium are 0.05 ppm at a film thickness of 0.3 microns (6); Point (8) of 0.02 ppm when the film thickness of the film is 0.5 microns, Point (20) of 0.066 ppm when the film thickness of the film is 1.3 microns, Point (21) of 0.61 ppm when the film thickness of the film is 1.5 microns, 1.2 ppm point (17) when the film thickness is 1.1 microns, 6.5 ppm point (29) when the film thickness is 2.5 microns, 14.0 ppm point (32) when the film thickness is 2.7 microns, the film thickness of the film 21.0 ppm point (39) at 4.0 micron, 49.0 ppm point (43) at 5.2 micron film thickness, 71.0 ppm point (47) at 7.0 micron film thickness, 5.5 micron film thickness 68.0 ppm point (44) when the coating thickness is 4.0 microns, 53.0 ppm point (40) when the coating thickness is 2.9 microns, 32.0 ppm point (33) when the coating thickness is 1.5 microns, 10.0 when the coating thickness is 1.5 microns. ppm point (22), 3.4 ppm point (19) when the coating thickness is 1.2 microns, 0.5 ppm point when the coating thickness is 0.5 microns.
(10), a point (6) of 0.05 ppm when the thickness of the film is 0.3 microns, and a range surrounded by a path sequentially connected with a straight line, and a point (17) of 1.2 ppm when the thickness of the film is 1.1 microns; 0.61 ppm point (21) when the film thickness is 1.5 microns, 9.0 ppm point (26) when the film thickness is 2.0 microns, 6.5 ppm point (29) when the film thickness is 2.5 microns, the film 21.0 ppm point (36) when the film thickness is 3.5 microns, 71.0 ppm point (47) when the film thickness is 7.0 microns, 68.0 ppm point (44) when the film thickness is 5.5 microns, the film of the film. 21.0 ppm point (36) at 3.5 micron thickness, 9.0 ppm point (26) at 2.0 micron thickness, 3.4 ppm point (19) at 1.2 micron thickness, 1.1 point at film thickness A point (17) of 1.2 ppm in microns, an area surrounded by a path connecting with a straight line in sequence, and a point (19) of 3.4 ppm in a film thickness of 1.2 microns, and 21.0 ppm in a film thickness of 4.0 microns. point (39), point (27) of 1.5 ppm when the thickness of the coating is 2.3 microns, point (19) of 3.4 ppm when the thickness of the coating is 1.2 microns, and are surrounded by a path sequentially connecting with a straight line. A reflective plate surface protective coating characterized by being defined by a range consisting of a range and a union thereof.