JP2020079362A - Sulfate sludge cleaning liquid and sulfate sludge cleaning method - Google Patents

Abstract

To provide a sulfate sludge cleaning liquid for removing sulfate sludge with an insoluble product generated when etching a glass substrate with an etching liquid containing sulfuric acid.SOLUTION: A sulfate sludge cleaning liquid according to the present invention is for removing sulfate sludge made of a sulfate ion and an alkaline earth metal ion. The sulfate sludge cleaning liquid contains a chelate agent having chelate stability of 7 or higher relative to the alkaline earth metal ion.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a cleaning liquid used for removing insoluble products generated when a glass substrate is etched with an etching liquid containing sulfuric acid, and a cleaning method using the cleaning liquid.

  In order to reduce the thickness of a liquid crystal panel, it is common to perform an etching process using an etching solution containing hydrofluoric acid. The etching solution used for the etching process contains hydrofluoric acid. In addition to hydrofluoric acid, an inorganic acid such as hydrochloric acid, sulfuric acid, or nitric acid may be used together with hydrofluoric acid for the purpose of improving the quality of the glass substrate after etching and improving the efficiency of etching treatment.

  On the other hand, in the etching process, there is a problem that an insoluble product (hereinafter, also referred to as sludge) is generated due to a reaction between the etching liquid and the glass substrate. Sludge is generated by the reaction between the etching solution and the metal ions contained in the glass substrate, but if it adheres to the glass substrate during the etching process, it may lead to etching failure. Therefore, it has been attempted to suppress the generation of sludge by adding an auxiliary agent or the like for suppressing the generation of sludge to the etching solution.

  However, it is difficult to prevent the generation of sludge when a large amount of glass substrates are etched. Further, the sludge not only adheres to the glass substrate but also adheres to the etching device to cause a problem. In particular, the clogging of the pipe and the damage of the driving unit due to the adherence of sludge make it costly and time consuming to repair the etching apparatus. Therefore, it is necessary to regularly clean the etching device and remove the sludge.

  As a method for removing the sludge generated by the etching treatment, there is a method of removing it using an electrolyte solution such as aluminum sulfate (see, for example, Patent Document 1). By using this electrolyte solution, sludge generated by the etching process can be dissolved, so that it is said that productivity can be improved by continuous operation of the etching apparatus.

Japanese Patent No. 5746578

  The electrolyte solution described in Patent Document 1 is effective only for removing sludge composed of fluorine and metal ions. As described above, when sulfuric acid is used in the etching process, it reacts with metal ions in the glass substrate to generate sulfuric acid sludge. The main component of the sulfuric acid sludge is composed of a sulfate ion and an alkaline earth metal ion, and calcium sulfate, strontium sulfate, barium sulfate or the like is a main component. Although these sulfuric acid sludges are also likely to cause a problem by sticking to the etching device, the electrolyte solution described in Patent Document 1 does not consider removal of the sulfuric acid sludges. Therefore, an effective method for removing sulfuric acid sludge has been demanded.

  An object of the present invention is to provide a cleaning solution for sulfuric acid sludge capable of dissolving and removing sulfuric acid sludge, and a cleaning method using the same.

  The sulfuric acid sludge cleaning liquid according to the present invention is for removing sulfuric acid sludge composed of sulfate ions and alkaline earth metal ions, and contains a chelating agent having a chelate stability constant of 7 or more for alkaline earth metal ions. There is. By using the cleaning solution for sulfuric acid sludge, the chelating agent contained in the cleaning solution for sulfuric acid sludge can form a complex with metal ions such as calcium ions, strontium ions, and barium ions that make up the sulfuric acid sludge, and dissolve the sulfuric acid sludge. It will be possible.

  The pH of the sulfuric acid sludge cleaning liquid is preferably 8 or more and 12 or less. If the pH of the chelating agent is acidic, the formation of the complex is hindered and it becomes difficult to wash the sulfuric acid sludge. Further, although the objects to be cleaned to which the sulfuric acid sludge is attached generally have acid resistance, many of them have low resistance to an alkaline chemical solution. Therefore, if the pH of the cleaning solution for sulfuric acid sludge exceeds 12, there is a risk that the object to be cleaned may deteriorate or corrode, so the pH is preferably 12 or less.

  A method of cleaning sulfuric acid sludge according to the present invention comprises a first cleaning step for cleaning an object to be cleaned, and a sulfuric acid sludge containing a chelating agent having a chelate stability constant for alkaline earth metal ions of 7 or more after the first cleaning step. And a second cleaning step of removing the sulfuric acid sludge cleaning liquid from the object to be cleaned after the sludge cleaning step. In the method of cleaning sulfuric acid sludge, it is possible to suppress the deterioration of the cleaning power of the cleaning solution for sulfuric acid sludge by cleaning the cleaning object before cleaning the cleaning object with the cleaning solution for sulfuric acid sludge.

  According to the present invention, it is possible to provide a cleaning solution for sulfuric acid sludge capable of dissolving and removing sulfuric acid sludge, and a cleaning method using the same.

It is a figure which shows the outline of the etching apparatus of a glass substrate. It is a graph which shows the sludge dissolution performance of the cleaning solution for sulfuric acid sludge.

  From here, the cleaning solution for sulfuric acid sludge according to the present invention will be described. Sulfuric acid sludge is a complex of sulfate ion and metal ion. Examples of sludge sulfate include barium sulfate, strontium sulfate, barium sulfate and the like. Sulfuric acid sludge is generated, for example, when the etching liquid contains sulfuric acid during the etching process of the glass substrate. Sulfuric acid sludge is also generated in a pickling treatment of a metal with sulfuric acid, etc., and the sulfuric acid sludge cleaning liquid according to the present invention is applied as long as it is a sulfuric acid sludge in which a sulfate ion and an alkaline earth metal ion are combined. It is possible.

The cleaning solution for sulfuric acid sludge contains a chelating agent having a chelate stability constant of 7 or more for alkaline earth metal ions. When the chelate stability constant of the chelating agent is 7 or more, the solubility of sulfuric acid sludge is improved, and the sulfuric acid sludge can be sufficiently removed. The chelate stability constant in the present invention is an index showing the strength of the bond between the chelate compound and the metal, and is the logarithmic value of the stability constant K shown in Formula 1 below. Here, M is a metal ion, Z is a chelating agent, MZ is a complex salt, X is the number of Z bound to one M, [MZ _X ] is the concentration (mol/L) of MZ _X , and [M] is M Concentration (mol/L), [Z] represents the concentration of Z (mol/L).

  Examples of the chelating agent having a chelate stability constant of 7 or more include ethylenediaminetetraacetic acid (EDTA), triethylenetetraminehexaacetic acid (TTHA), glycol etherdiaminetetraacetic acid (EGTA), and the like. The chelating agent contained in the cleaning solution for sulfuric acid sludge may be one kind or two or more kinds. It may be appropriately adjusted depending on the properties of the sulfuric acid sludge and the properties of the chelating agent used.

  As an example of ethylenediaminetetraacetic acid (EDTA), CREST C, CREST 3D, CREST 2D, CREST 400 manufactured by CREST CORPORATION can be used. As an example of triethylenetetramine hexaacetic acid (TTHA), CREST 2QA, CREST QA, CREST Q manufactured by CREST CORPORATION can be used. As an example of glycol ether diamine tetraacetic acid (EGTA), CREST GEA manufactured by CREST Co., Ltd. can be used.

The pH of the cleaning solution for sulfuric acid sludge is adjusted to 8 or more and 12 or less. When the pH of the cleaning solution for sulfuric acid sludge is less than 8, dissolution of the sulfuric acid sludge is not promoted. In particular, in the acidic region, the ligand of the chelating agent is considered to bind to H ⁺ , which inhibits the dissolution of the sulfuric acid sludge. On the other hand, if the pH exceeds 12, there is a high possibility that the object to be cleaned will be soiled. The substance to which the sulfuric acid sludge adheres is generally composed of a substance having acid resistance, but it often has little resistance to alkalinity, and there is a risk that the object to be cleaned will be corroded. is there. Therefore, it is not preferable to exceed 12 of the cleaning solution for sulfuric acid sludge. The pH of the cleaning solution for sulfuric acid sludge may be adjusted using a pH adjusting agent according to the pH of the chelating agent.

  From here, a method of cleaning sulfuric acid sludge using a cleaning solution for sulfuric acid sludge will be described. FIG. 1 is a diagram schematically showing an etching apparatus 10 for etching a glass substrate. The etching apparatus 10 includes a transport roller 12, an etching chamber 14, a post-cleaning chamber 16 and a spray nozzle 18. The transport roller 12 is configured to transport the glass substrate 20 introduced from one end of the etching apparatus 10 to the other end.

  The etching chamber 14 performs an etching process by spraying an etching liquid onto the glass substrate 20 being transported by the transport roller 12. The spray nozzles 18 are vertically arranged in the etching chamber 14 with a predetermined distance from the transport roller 12, and are configured to spray the etching liquid onto the glass substrate 20. A plurality of etching chambers 14 are provided along the transport direction of the glass substrate 20.

  The post-cleaning chamber 16 is provided in the subsequent stage of the etching chamber 14 in the transport direction of the glass substrate 20, and is configured to eject the cleaning liquid from the spray nozzle 18 to remove the etching liquid from the glass substrate 20. The glass substrate 20 that has undergone the cleaning process is recovered from the etching apparatus 10 and is appropriately processed in a post process.

  The etching solution used for the etching treatment generally contains hydrofluoric acid, but in addition to hydrofluoric acid, an inorganic acid such as hydrochloric acid, sulfuric acid, or nitric acid may be used. The etching liquid sprayed on the glass substrate 20 is discharged from the lower portion of the etching chamber 14, collected in a tank (not shown) or the like, and then sprayed again from the spray nozzle 18. As the number of processed glass substrates increases, metal ions contained in the glass substrates will dissolve in the etching solution. When the amount of dissolved metal ions exceeds a certain amount, it is deposited as sludge which is an insoluble product and adheres to the wall surface of the etching chamber 14, pipes and the like.

  In the present embodiment, after treating a predetermined number of glass substrates 20, the inside of the etching apparatus 10 is cleaned with a cleaning solution for sulfuric acid sludge to remove the adhered sulfuric acid sludge. As described above, the cleaning solution for sulfuric acid sludge used in the present embodiment has a low sludge removal performance in an environment of low pH. Therefore, the etching apparatus is cleaned before cleaning the sulfuric acid sludge, and remains in the apparatus. It is necessary to remove the etching solution used.

  FIG. 2 is a diagram showing the relationship between the dissolution performance of sulfuric acid sludge in a cleaning solution for sulfuric acid sludge and pH.

  In Reference Example 1, 10 ml of a sulfuric acid sludge cleaning liquid was added to 1 ml of water containing 0.5 g of sulfuric acid sludge, and the mixture was allowed to react for 1 hour, after which the amount of dissolved sulfuric acid sludge was measured.

  In Comparative Example 1, 10 ml of the sulfuric acid sludge cleaning liquid was added to 1 ml of the etching liquid containing 0.5 g of the sulfuric acid sludge, the mixture was reacted for 1 hour, and then the dissolved amount of the sulfuric acid sludge was measured. In Comparative Example 2, the experiment was performed under the same conditions as in Comparative Example 1 except that the etching solution was diluted 10 times with water, and the dissolved amount of sulfuric acid sludge was measured.

  Example 1 and Example 2 show the results of measuring the amount of sludge dissolved under the above conditions after diluting the etching solution 100 times and 1000 times with water, respectively. In Example 3, a 10-fold diluted etching solution was neutralized with sodium carbonate to a pH of 10, and the neutralized etching solution was treated under the above conditions to measure the amount of dissolved sulfuric acid sludge.

  FIG. 2 shows the amount of dissolved sulfuric acid sludge in Reference Example 1 as 100 and the amount of dissolved sulfuric acid sludge in Comparative Examples 1 and 2 and Examples 1 to 3 as a relative value. As shown in FIG. 2, the sulfuric acid sludge was not dissolved in Comparative Example 1, and the dissolved amount of the sulfuric acid sludge was less than half in Comparative Example 2. On the other hand, in Examples 1 to 3, even when compared with Reference Example 1, almost no decrease in the amount of dissolution was observed.

  Further, in Comparative Examples 1 and 2, the pH of the post-reaction solution was 5 or less, whereas in Examples 1 to 3, the pH was 8 or more. From this, it is considered that the complex formation of the sulfuric acid sludge cleaning liquid is inhibited in the acidic region. For this reason, when using the cleaning solution for sulfuric acid sludge in the etching apparatus 10, it is necessary to wash the etching apparatus 10 in advance and remove the etching solution.

  The etching apparatus 10 is cleaned by discharging the etching liquid from the etching chamber 14 and then spraying water from the spray nozzle 18 for a predetermined time to clean the etching chamber 14. At this time, by swinging the spray nozzle 18, the etching liquid scattered in the etching chamber 14 is washed away. By this cleaning step, the etching liquid is cleaned from the inside of the etching chamber 14 and the piping of the etching apparatus 10, and the deterioration of the cleaning power of the cleaning liquid for sulfuric acid sludge can be suppressed.

  Further, in cleaning the etching apparatus 10, it is possible to use an alkaline cleaning liquid instead of water. Sodium carbonate can be used as the alkaline cleaning liquid. The etching apparatus 10 is made of a resin material having acid resistance, but since it often has low resistance to alkaline chemicals, it is preferable to wash it with a chemical solution having a pH of less than 12.

  After cleaning the etching apparatus 10 for a predetermined time, a cleaning solution for sulfuric acid sludge is introduced into the etching apparatus 10. The cleaning solution for sulfuric acid sludge is contained in a tank (not shown) and is ejected from the spray nozzle 18 by being sent by a pump or the like. The sulfuric acid sludge cleaning liquid reacts with the sulfuric acid sludge adhering to the etching chamber 14, the transport roller 12, the pipe, and the like. By injecting the cleaning solution for sulfuric acid sludge for a predetermined time, the sulfuric acid sludge is dissolved and the sulfuric acid sludge is removed. The cleaning time with the cleaning solution for sulfuric acid sludge is adjusted depending on the composition of the etching solution and the number of processed glass substrates, but the sulfuric acid sludge is removed by cleaning for about 1 to 4 hours.

  When the etching device 10 with the sulfuric acid sludge cleaning liquid is completed, the sulfuric acid sludge cleaning liquid is discharged from the etching device 10 to clean the etching device 10. In this cleaning step, in order to inject the etching solution into the etching apparatus 10 again, water is sprayed from the spray nozzle 18 to wash away the sulfuric acid sludge cleaning solution.

  The etching apparatus 10 is washed for a predetermined time to remove the sulfuric acid sludge cleaning solution, and then the etching solution is injected into the etching apparatus 10 again to perform the etching process. In the etching apparatus 10 after cleaning the sludge, the pipe clogging and the like are eliminated, and the etching process can be preferably continued.

  The description of the above embodiments is to be considered as illustrative in all points and not restrictive. The scope of the invention is indicated by the claims rather than the embodiments described above. Further, the scope of the present invention is intended to include meanings equivalent to the scope of the claims and all modifications within the scope.

10-Etching device 12-Conveying roller 14-Etching chamber 16-Post cleaning chamber 18-Spray nozzle 20-Glass substrate

Claims (4)

A cleaning solution for sulfuric acid sludge for removing sulfuric acid sludge composed of sulfate ions and alkaline earth metal ions,
A cleaning solution for sulfuric acid sludge, which contains a chelating agent having a chelate stability constant of 7 or more for alkaline earth metal ions. The cleaning solution for sulfuric acid sludge according to claim 1, wherein the alkaline earth metal ion is at least one of Ba ²⁺ ion, Ca ²⁺ ion, and Sr ²⁺ ion.   The cleaning solution for sulfuric acid sludge according to claim 1 or 2, wherein the cleaning solution for sulfuric acid sludge has a pH of 8 or more and 12 or less. A first cleaning step for cleaning the object to be cleaned,
A sludge cleaning step of cleaning with a cleaning solution for sulfuric acid sludge containing a chelating agent having a chelate stability constant for alkaline earth metal ions of 7 or more after the first cleaning step;
A second cleaning step of removing the cleaning solution for sulfuric acid sludge from the object to be cleaned after the sludge cleaning step,
A method for cleaning sulfuric acid sludge, which comprises:

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